Improved Subtraction by Adiabatic FAIR Perfusion Imaging

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Feb, 2002  |  Pubmed ID: 11810677

For pulsed arterial spin labeling techniques (e.g., FAIR), mismatches between the imaging and inversion slice profile result in a nonperfusion-related offset. Several methods have been proposed to reduce subtraction errors in FAIR imaging. Here an acquisition method for FAIR experiments based on adiabatic principles is proposed. It is shown that with adiabatic pulses the same pulse can be used for labeling and echo refocusing, thereby reducing the mismatch between imaging and labeling slice. A twofold reduction in subtraction errors compared to 5-lobe sinc excitation was shown both experimentally and by simulation.

The Quantitation of ADP Diffusion Gradients Across the Outer Membrane of Heart Mitochondria in the Presence of Macromolecules

Biochimica Et Biophysica Acta. Apr, 2002  |  Pubmed ID: 12034470

We have previously provided evidence that diffusion of metabolites across the porin pores of mitochondrial outer membrane is hindered. A functional consequence of this diffusion limitation is the dynamic compartmentation of ADP in the intermembrane space. These earlier studies were done on isolated mitochondria suspended in isotonic media without macromolecules, in which intermembrane space of mitochondria is enlarged. The present study was undertaken to assess the diffusion limitation of outer membrane in the presence of 10% (w/v) dextran M20, in order to mimic the action of cytosolic macromolecules on mitochondria. Under these conditions, mitochondria have a more native, condensed configuration.Flux-dependent concentration gradients of ADP were estimated by measuring the ADP diffusion fluxes across the porin pores of isolated rat heart mitochondria incubated together with pyruvate kinase (PK), both of which compete for ADP regenerated by mitochondrial creatine kinase (mtCK) within the intermembrane space or by yeast hexokinase (HK) extramitochondrially. From diffusion fluxes and bulk phase concentrations of ADP, its concentrations in the intermembrane space were calculated using Fick's law of diffusion. Flux-dependent gradients up to 23 microM ADP (for a diffusion rate of J(Dif)=1.9 micromol ADP/min/mg mitochondrial protein) were observed. These gradients are about twice those estimated in the absence of dextran and in the same order of magnitude as the cytosolic ADP concentration (30 microM), but they are negligibly low for cytosolic ATP (5 mM). Therefore, it is concluded that the dynamic ADP compartmentation is of biological importance for intact heart cells. If mtCK generates ADP within the intermembrane space, the local ADP concentration can be clearly higher than in the cytosol resulting in higher extramitochondrial phosphorylation potentials. In this way, mtCK contributes to ensure optimal kinetic conditions for ATP-splitting reactions in the extramitochondrial compartment.

Diffuse Signal Abnormalities in the Spinal Cord in Multiple Sclerosis: Direct Postmortem in Situ Magnetic Resonance Imaging Correlated with in Vitro High-resolution Magnetic Resonance Imaging and Histopathology

Annals of Neurology. May, 2002  |  Pubmed ID: 12112117

In this study, we compared direct postmortem in situ (whole-corpse) sagittal spinal cord magnetic resonance imaging (1.5T) of 7 multiple sclerosis cases with targeted high-resolution in vitro axial magnetic resonance imaging (4.7T) and histopathology. On sagittal in situ magnetic resonance imaging, 1 case had a normal spinal cord, 2 had only focal lesions, 3 had a combination of focal and diffuse abnormalities, and 1 had only diffuse abnormalities. All spinal cords showed abnormalities on high-resolution magnetic resonance imaging and histopathology, confirming the existence of diffuse cord changes as genuine multiple sclerosis-related abnormalities while highlighting the limited resolution of in vivo magnetic resonance imaging.

Role of Magnesium in the Reduction of Ischemic Depolarization and Lesion Volume After Experimental Subarachnoid Hemorrhage

Journal of Neurosurgery. Aug, 2002  |  Pubmed ID: 12186471

Ischemia-induced tissue depolarizations probably play an important role in the pathophysiology of cerebral ischemia caused by parent vessel occlusion. Their role in ischemia caused by subarachnoid hemorrhage (SAH) remains to be investigated. The authors determined whether ischemic depolarizations (IDs) or cortical spreading depressions (CSDs) occur after SAH, and how these relate to the extent of tissue injury measured on magnetic resonance (MR) images. In addition, they assessed whether administration of MgSO4 reduces depolarization time and lesion volume.

Reduction of Cerebral Injury in Stroke-prone Spontaneously Hypertensive Rats by Amlodipine

European Journal of Pharmacology. May, 2002  |  Pubmed ID: 12191585

Dihydropyridine Ca(2+) channel antagonists, initiated together with high salt intake, prevent the development of hypertension and subsequent cerebral damage in stroke-prone spontaneously hypertensive rats (SHRSP). We hypothesized that the dihydropyridine Ca(2+) channel antagonist amlodipine (approximately 15 mg/kg/day) could also reverse established hypertension and cerebral damage. SHRSP drank 1% NaCl from 8 weeks of age. Cerebral damage (cerebral edema and blood-brain barrier integrity) was investigated with magnetic resonance imaging twice a week. Systolic blood pressure was measured weekly. All rats developed severe hypertension and subsequent cerebral damage (defined as day 0). Untreated controls (n=7) died at day 12 (range: 7-28). Oral treatment with amlodipine (n=7), initiated at day 0, reduced systolic blood pressure, reversed cerebral edema and restored blood-brain barrier integrity. Systolic blood pressure remained low and eventually rats died after 450 days (range: 350-580) showing nephrosis but no recurrence of cerebral damage. In conclusion, established hypertension and cerebral damage are reversed by amlodipine in SHRSP.

Neuroprotection by Selective Nitric Oxide Synthase Inhibition at 24 Hours After Perinatal Hypoxia-ischemia

Stroke; a Journal of Cerebral Circulation. Sep, 2002  |  Pubmed ID: 12215603

Perinatal hypoxia-ischemia is a major cause of neonatal morbidity and mortality. Until now no established neuroprotective intervention after perinatal hypoxia-ischemia has been available. The delay in cell death after perinatal hypoxia-ischemia creates possibilities for therapeutic intervention after the initial insult. Excessive nitric oxide and reactive oxygen species generated on hypoxia-ischemia and reperfusion play a key role in the neurotoxic cascade. The present study examines the neuroprotective properties of neuronal and inducible but not endothelial nitric oxide synthase inhibition by 2-iminobiotin in a piglet model of perinatal hypoxia-ischemia.

On the Role of Mi-cK and VDAC in Mitochondrial Function of Heart Muscle Cells

Molecular Biology Reports. , 2002  |  Pubmed ID: 12241054

A two-compartment kinetic model was used to describe reconstituted systems in which mitochondria compete with pyruvate kinase for kinase-generated ADP. The modelling suggests that cytosolic CK deficiency results in a 50% increase in outer mitochondrial membrane permeability.

Pharmacological Interventions in the Newborn Piglet in the First 24 H After Hypoxia-ischemia. A Hemodynamic and Electrophysiological Perspective

Experimental Brain Research. Experimentelle Hirnforschung. Expérimentation Cérébrale. Nov, 2002  |  Pubmed ID: 12410335

The purpose of this study was to investigate whether combined inhibition of neuronal and inducible nitric oxide synthase (NOS) by 2-iminobiotin, free radical scavenging by allopurinol, and non-protein-bound iron chelation with deferoxamine improved cerebral oxygenation, electrocortical brain activity, and brain energy status during the first 24 h after hypoxia-ischemia (HI) in the newborn piglet. Forty-three newborn piglets were subjected to 1 h of severe HI by occluding both carotid arteries and phosphorous magnetic resonance spectroscopy ((31)P-MRS)-guided hypoxia, whereas five served as sham-operated controls. Upon reperfusion, piglets received vehicle (n=12), 2-iminobiotin (n=11), allopurinol (n=10), or deferoxamine (n=10). Cerebral oxygenation was recorded with near-infrared spectrophotometry (NIRS), electrocortical brain activity was assessed with amplitude-integrated EEG (aEEG), and cerebral energy status with (31)P-MRS. The oxygenated hemoglobin (HbO(2)) and total hemoglobin (tHb) were significantly increased in vehicle-treated piglets compared with 2-iminobiotin-treated and deferoxamine-treated piglets. No change in deoxygenated Hb (HHb) was demonstrated over time. The aEEG was significantly preserved in 2-iminobiotin- and deferoxamine-treated piglets compared with vehicle-treated piglets. Allopurinol treatment was not as effective as 2-iminobiotin treatment after HI. Phosphocreatine/inorganic phosphate ratios (PCr/P(i)) were significantly decreased for vehicle-treated piglets at 24 h post-HI, whereas 2-iminobiotin, allopurinol, and deferoxamine prevented the development of secondary energy failure. We speculate that the beneficial effects, especially of 2-iminobiotin, but also of deferoxamine, are due to reduced peroxynitrite-mediated oxidation.

Acute Neuronal Injury, Excitotoxicity, and the Endocannabinoid System

Molecular Neurobiology. Oct-Dec, 2002  |  Pubmed ID: 12428763

The endocannabinoid system is a valuable target for drug discovery, because it is involved in the regulation of many cellular and physiological functions. The endocannabinoid system constitutes the endogenous lipids anandamide, 2-arachidonoylglycerol and noladin ether, and the cannabinoid CB1 and CB2 receptors as well as the proteins for their inactivation. It is thought that (endo)cannabinoid-based drugs may potentially be useful to reduce the effects of neurodegeneration. This paper reviews recent developments in the endocannabinoid system and its involvement in neuroprotection. Exogenous (endo)cannabinoids have been shown to exert neuroprotection in a variety of in vitro and in vivo models of neuronal injury via different mechanisms, such as prevention of excitotoxicity by CB1-mediated inhibition of glutamatergic transmission, reduction of calcium influx, and subsequent inhibition of deleterious cascades, TNF-alpha formation, and anti-oxidant activity. It has been suggested that the release of endogenous endocannabinoids during neuronal injury might be a protective response. However, several observations indicate that the role of the endocannabinoid system as a general endogenous protection system is questionable. The data are critically reviewed and possible explanations are given.

In Vivo Excitotoxicity Induced by Ouabain, a Na+/K+-ATPase Inhibitor

Journal of Cerebral Blood Flow and Metabolism : Official Journal of the International Society of Cerebral Blood Flow and Metabolism. Jan, 2003  |  Pubmed ID: 12500092

The susceptibility of immature rat brain to neurotoxicity of N-methyl-D-aspartate (NMDA) has provided a widely used paradigm to study excitotoxicity relevant to acute neurodegenerative diseases such as cerebral ischemia. In this study, excitotoxicity was induced via injection of ouabain (1 mM/0.5 microL), a Na+/K+ -ATPase-inhibitor, into neonatal rat brain and compared with NMDA injection. The aim of the study was to induce excitotoxicity secondary to cellular membrane depolarization, thereby more closely mimicking the pathophysiologic processes of ischemia-induced brain injury where NMDA-receptor overstimulation by glutamate follows, not precedes, membrane depolarization. Na+/K+ -ATPase-inhibition caused an acute, 40% +/- 8% decrease of the apparent diffusion coefficient (ADC) of water, as measured using diffusion-weighted magnetic resonance imaging (MRI), and resulted in infarctlike lesions as measured using T2-weighted MRI and histology up to 2 weeks later. Localized one- and two-dimensional 1H-magnetic resonance spectroscopy (MRS) demonstrated that the early excitotoxic diffusion changes were not accompanied by an overall metabolic disturbance. Furthermore, 31P-MRS demonstrated that energy depletion is not a prerequisite for ADC decrease or excitotoxic cell death. Treatment with the NMDA-antagonist MK-801 (1 mg/kg) attenuated the volume of tissue exhibiting a decreased ADC (P < 0.005), demonstrating that the ouabain-induced injury is indeed excitotoxic in nature. The authors argue that, compared with NMDA-injection, ouabain-induced excitotoxicity elicits more appropriate glutamate-receptor overstimulation and is better suited to detect relevant neuroprotection in that it is more sensitive to attenuation of synaptic glutamate levels.

Effects of Allopurinol and Deferoxamine on Reperfusion Injury of the Brain in Newborn Piglets After Neonatal Hypoxia-ischemia

Pediatric Research. Oct, 2003  |  Pubmed ID: 12815112

The hypothesis was tested that treatment with allopurinol, a xanthine oxidase inhibitor, or deferoxamine, a chelator of nonprotein-bound iron, preserved cerebral energy metabolism, attenuated development of edema, and improved histologic outcome in the newborn piglet at 24 h after hypoxia-ischemia. Thirty-two newborn piglets were subjected to 1 h of hypoxia-ischemia by occluding both carotid arteries and reducing the fraction of inspired oxygen; five newborn piglets served as sham-operated controls. The depth of hypoxia-ischemia was controlled by phosphorous magnetic resonance spectroscopy. Upon reperfusion and reoxygenation, piglets received vehicle (n= 12), allopurinol (30 mg/kg/d, n = 10), or deferoxamine (12.5 mg/kg/d, n = 10). The cerebral energy status was determined with phosphorous magnetic resonance spectroscopy. The presence of vasogenic edema was assessed by T2-weighted magnetic resonance imaging. Brain cell injury was assessed with caspase-3 activity, histology, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end (TUNEL)-labeling. At 24 h after hypoxia-ischemia, the phosphocreatine/inorganic phosphate ratios were significantly decreased in vehicle-treated, but not in allopurinol- or deferoxamine-treated piglets. Water T2 values were significantly increased at 24 h after hypoxia-ischemia in cerebral cortex, thalamus, and striatum of vehicle-treated piglets, but not in allopurinol- and deferoxamine-treated piglets. No differences in caspase-3 activity, histologic outcome, or TUNEL-labeling were demonstrated between the three treatment groups. We suggest that allopurinol and deferoxamine may have an additional value in the treatment of perinatal hypoxia-ischemia with other neuroprotective agents or in combination with hypothermia.

Biosynthesis of Endocannabinoids and Their Modes of Action in Neurodegenerative Diseases

Neurotoxicity Research. , 2003  |  Pubmed ID: 12835123

Endocannabinoids are thought to function as retrograde messengers, which modulate neurotransmitter release by activating presynaptic cannabinoid receptors. Anandamide and 2-arachidonoylglycerol (2-AG) are the two best studied endogenous lipids which can act as endocannabinoids. Together with the proteins responsible for their biosynthesis, inactivation and the cannabinoid receptors, these lipids constitute the endocannabinoid system. This system is proposed to be involved in various neurodegenerative diseases such as Parkinson's and Huntington's diseases as well as Multiple Sclerosis. It has been demonstrated that the endocannabinoid system can protect neurons against glutamate excitotoxicity and acute neuronal damage in both in vitro and in vivo models. In this paper we review the data concerning the involvement of the endocannabinoid system in neurodegenerative diseases in which neuronal cell death may be elicited by excitotoxicity. We focus on the biosynthesis of endocannabinoids and on their modes of action in animal models of these neurodegenerative diseases.

Effect of Vascular Crushing on FAIR Perfusion Kinetics, Using a BIR-4 Pulse in a Magnetization Prepared FLASH Sequence

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Sep, 2003  |  Pubmed ID: 12939769

Flow-sensitive alternating inversion recovery (FAIR) perfusion imaging suffers from high vascular signal, resulting in artifacts and overestimation of perfusion. With TurboFLASH acquisition, crushing of vascular signal by bipolar gradients after each excitation is difficult due to the requirement of an ultrashort repetition time. Therefore, insertion of a preparation phase in the FAIR sequence, after labeling and prior to TurboFLASH acquisition, is proposed. A segmented adiabatic BIR-4 pulse, interleaved with crusher gradients, was used for flow crushing. The effect of the crusher preparation is shown as a function of crusher strength for a flow phantom and in rat brain. Influence of crusher strength on the time-dependent FAIR signal from rat brain was also measured. Signal from flowing spins in a flow phantom and from arterial spins in rat brain was significantly suppressed. Image quality was improved and the overestimation of perfusion at short inflow times was eliminated.

Interferon-beta Blocks Infiltration of Inflammatory Cells and Reduces Infarct Volume After Ischemic Stroke in the Rat

Journal of Cerebral Blood Flow and Metabolism : Official Journal of the International Society of Cerebral Blood Flow and Metabolism. Sep, 2003  |  Pubmed ID: 12973019

The inflammatory response that exacerbates cerebral injury after ischemia is an attractive therapeutic target: it progresses over days and strongly contributes to worsening of the neurologic outcome. The authors show that, after transient ischemic injury to the rat brain, systemic application of interferon-beta (IFN-beta), a cytokine with antiinflammatory properties, attenuated the development of brain infarction. Serial magnetic resonance imaging (MRI) showed that IFN-beta treatment reduced lesion volume on diffusion-weighted MRI by 70% (P < 0.01) at 1 day after stroke. IFN-beta attenuated the leakage of contrast agent through the blood-brain barrier (P < 0.005), indicating a better-preserved blood-brain barrier integrity. Both control and IFN-beta-treated animals showed a similar degree of relative hyperperfusion of the lesioned hemisphere, indicating that neuroprotection by IFN-beta was not mediated by improved cerebral perfusion as assessed 24 hours after stroke onset. IFN-beta treatment resulted in an 85% reduction (P < 0.0001) in infarct volume 3 weeks later, as determined from T2-weighted MRI and confirmed by histology. This effect was achieved even when treatment was started 6 hours after stroke onset. Quantitative immunohistochemistry at 24 hours after stroke onset showed that IFN-beta almost completely prevented the infiltration of neutrophils and monocytes into the brain. Gelatinase zymography showed that this effect was associated with a decrease in matrix metalloproteinase-9 expression. In conclusion, treatment with the antiinflammatory cytokine IFN-beta affords significant neuroprotection against ischemia/reperfusion injury, and within a relatively long treatment window. Because IFN-beta has been approved for clinical use, it may be rapidly tested in a clinical trial for its efficacy against human stroke.

Interferon-beta Prevents Cytokine-induced Neutrophil Infiltration and Attenuates Blood-brain Barrier Disruption

Journal of Cerebral Blood Flow and Metabolism : Official Journal of the International Society of Cerebral Blood Flow and Metabolism. Sep, 2003  |  Pubmed ID: 12973022

Inflammation can contribute to brain injury, such as that resulting from ischemia or trauma. The authors have previously shown that the cytokine interferon-beta (IFN-beta) affords protection against ischemic brain injury, which was associated with a diminished infiltration of neutrophils and a reduction in blood-brain barrier (BBB) disruption. The goal of the current study was to directly assess the effects of IFN-beta on neutrophil infiltration, with the use of an in vivo assay of neutrophil infiltration with relevance to ischemic brain injury. Intrastriatal injection of recombinant rat cytokine-induced neutrophil chemoattractant-1, a member of the interleukin-8 family (1 microg in 1 microl), triggered massive infiltration of neutrophils and extensive BBB disruption 6 hours later, as measured using immunofluorescence microscopy and magnetic resonance imaging in the rat, respectively. Depleting the animals of neutrophils before interleukin-8 injection prevented BBB disruption. Treatment with IFN-beta (5 x 106 U/kg) almost completely prevented neutrophil infiltration and attenuated BBB damage. Gelatinase zymography showed matrix metalloproteinase-9 expression in the ipsilateral striatum after interleukin-8 injection. Both neutrophil depletion and IFN-beta treatment downregulated matrix metalloproteinase-9. IFN-beta has already been approved for human use as a treatment for the chronic inflammatory disorder multiple sclerosis. The potential value of IFN-beta as a treatment that can attenuate acute brain inflammation is considered.

An MR-compatible Device for the in Situ Assessment of Isometric Contractile Performance of Mouse Hind-limb Ankle Flexors

Pflügers Archiv : European Journal of Physiology. Dec, 2003  |  Pubmed ID: 14530976

The goal of the present study was to develop and evaluate an isometric dynamometer for measuring mouse ankle flexor torque after electric stimulation of the nerve. The dynamometer was to be used within an magnetic resonance (MR) apparatus and should require minimal surgical intervention. To quantify the effect of the magnetic field on contractile parameters, measurements were performed both outside and inside the MR apparatus. The effect of magnetic field gradient switching that accompanies rapid MR scanning was tested also. The set-up required no surgical intervention except for chronic implantation of an electrode. The dynamometer has a high mechanical frequency response (270 Hz). Measured muscle strengths were identical outside and inside the MR scanner. However, during fast magnetic field gradient switching, the variability increased and the measured strength decreased slightly (7%). The noise level of the dynamometer (0.02-0.03 N.mm) was low compared with the strength of the dorsal flexors (2 N.mm). Fast gradient switching increased the noise level (0.07 N.mm). The dynamometer had no observable adverse effects on the quality of the MR images of the mouse hind limb. We conclude that the dynamometer enables accurate measurements of mechanical muscle performance during exercise protocols within an MR apparatus under physiological conditions.

Magnetic Resonance Imaging in Experimental Models of Brain Disorders

Journal of Cerebral Blood Flow and Metabolism : Official Journal of the International Society of Cerebral Blood Flow and Metabolism. Dec, 2003  |  Pubmed ID: 14663334

This review gives an overview of the application of magnetic resonance imaging (MRI) in experimental models of brain disorders. MRI is a noninvasive and versatile imaging modality that allows longitudinal and three-dimensional assessment of tissue morphology, metabolism, physiology, and function. MRI can be sensitized to proton density, T1, T2, susceptibility contrast, magnetization transfer, diffusion, perfusion, and flow. The combination of different MRI approaches (e.g., diffusion-weighted MRI, perfusion MRI, functional MRI, cell-specific MRI, and molecular MRI) allows in vivo multiparametric assessment of the pathophysiology, recovery mechanisms, and treatment strategies in experimental models of stroke, brain tumors, multiple sclerosis, neurodegenerative diseases, traumatic brain injury, epilepsy, and other brain disorders. This report reviews established MRI methods as well as promising developments in MRI research that have advanced and continue to improve our understanding of neurologic diseases and that are believed to contribute to the development of recovery improving strategies.

The Mitochondrial Outer Membrane is Not a Major Diffusion Barrier for ADP in Mouse Heart Skinned Fibre Bundles

Pflügers Archiv : European Journal of Physiology. Mar, 2004  |  Pubmed ID: 14722773

The response of mitochondrial oxygen consumption to ADP in saponin-skinned cardiac fibre bundles has an apparent Km an order of magnitude higher than that in isolated mitochondria. Here we report that incubating skinned cardiac fibre bundles from wild-type mice or double-knockout mice lacking both cytosolic and mitochondrial creatine kinase (CK) with CK and creatine or with yeast hexokinase and glucose as extramitochondrial ADP-producing systems decreases the apparent Km of the bundles for ADP severalfold. We conclude that the affinity of mitochondria for ADP in mouse heart is of the same order of magnitude as that of isolated mitochondria, while the high apparent Km of the bundles is caused by diffusion gradients outside the mitochondria.

Comparison of FAIR Perfusion Kinetics with DSC-MRI and Functional Histology in a Model of Transient Ischemia

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Feb, 2004  |  Pubmed ID: 14755657

Flow-sensitive alternating inversion recovery (FAIR) is a noninvasive method for perfusion imaging. It has been shown that the FAIR signal may depend on hemodynamic parameters other than perfusion, the most important one being transit delays of labeled spins to the observed tissue. These parameters are expected to change with ischemia. The goal of this study was to assess the effect of these changes on the interpretation of FAIR results in the case of altered perfusion. This was investigated in a rat model of transient cerebral ischemia. It was shown that the ratio of FAIR signal in the infarct compared to the contralateral side was lower at short inflow times, which suggests that transit times affected the effective FAIR signal. The FAIR results were compared with those from functional histology and dynamic susceptibility contrast MRI, and the findings indicated that the altered kinetics of the FAIR signal were related to reduced and delayed inflow in the infarct region--not to a decrease in the number of functional vessels.

The Use of High-resolution Magnetic Resonance Imaging for Monitoring Interbody Fusion and Bioabsorbable Cages: an Ex Vivo Pilot Study

Neurosurgical Focus. Mar, 2004  |  Pubmed ID: 15198491

Interbody fusion is a gradual process of graft resorption and tissue formation, ideally resulting in a bone bridge between two adjacent vertebral bodies. Initially, fibrous tissue and cartilage are formed, which subsequently are replaced by bone through the process of endochondral ossification. When cages and/or their contents are made of resorbable polymers like lactic or glycolic acids, there is a simultaneous process of implant degradation, which is eventually accompanied by reactions in the surrounding tissues. The purpose of this study was to explore the use of highresolution magnetic resonance (MR) imaging for monitoring tissue differentiation, spinal fusion, cage degradation, and eventually tissue reactions as a function of time.

MR Imaging of Mouse Leptomeningeal Metastases

Journal of Neuro-oncology. Jun, 2004  |  Pubmed ID: 15218948

To develop new treatment strategies for patients with leptomeningeal metastases (LM), potential therapeutic agents have to be tested in murine models first. In vivo magnetic resonance imaging has an additive value in non-invasive monitoring of the effects of therapeutic agents on LM. Previously, we described a reproducible mouse model for B16F-10 melanoma LM. In this paper, we visualize leptomeningeal melanoma metastases in mice on both T2 weighted MR images and gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) enhanced T1 weighted MR images, using a 4.7T MR spectrometer. We conclude that both MR sequences can be used to detect and monitor LM of melanoma cells in mice. Our data further suggest that LM are more clearly visualized using T1 weighted Gd-DTPA enhanced subtraction imaging than T2 weighted imaging.

A Liposomal System for Contrast-enhanced Magnetic Resonance Imaging of Molecular Targets

Bioconjugate Chemistry. Jul-Aug, 2004  |  Pubmed ID: 15264867

Pegylated paramagnetic and fluorescent immunoliposomes were designed to enable the parallel detection of the induced expression of molecular markers on endothelial cells with magnetic resonance imaging (MRI) and fluorescence microscopy. MRI is capable of three-dimensional noninvasive imaging of opaque tissues at near cellular resolution, while fluorescence microscopy can be used to investigate processes at the subcellular level. As a model for the expression of a molecular marker, human umbilical vein endothelial cells (HUVEC) were treated with the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha) to upregulate the expression of the adhesion molecule E-selectin/CD62E. E-selectin-expressing HUVEC were incubated with pegylated paramagnetic fluorescently labeled liposomes carrying anti-E-selectin monoclonal antibody as a targeting ligand. Both MRI and fluorescence microscopy revealed the specific association of the liposomal MR contrast agent with stimulated HUVEC. This study suggests that this newly developed system may serve as a useful diagnostic tool to investigate pathological processes in vivo with MRI.

In Vivo 1H Magnetic Resonance Spectroscopy, T2-weighted and Diffusion-weighted MRI During Lithium-pilocarpine-induced Status Epilepticus in the Rat

Brain Research. Dec, 2004  |  Pubmed ID: 15567333

Temporal lobe epilepsy (TLE) is associated with febrile convulsions and childhood status epilepticus (SE). Since the initial precipitating injury, triggering epileptogenesis, occurs during this SE, we aimed to examine the metabolic and morphological cerebral changes during the acute phase of experimental SE noninvasively. In the rat lithium-pilocarpine model of SE, we performed quantified T(2)- and isotropic-diffusion-weighted (DW) magnetic resonance imaging (MRI) at 3 and 5 h of SE and acquired single-voxel (1)H MR spectra at 2, 4 and 6 h of SE. T(2) was globally decreased, most pronounced in the amygdala (Am) and piriformic cortex (Pi), in which also a significant decrease in apparent diffusion coefficient (ADC) was found. In contrast, ADC values increased transiently in the hippocampus (HC) and thalamus (Th). MR spectra showed a decrease in N-acetylaspartate (NAA) and choline (Cho) and an increase of lactate in a hippocampal voxel. The T(2) decrease, attributed to raised deoxyhemoglobin, and the presence of lactate both indicate a mismatch between oxygen demand and delivery. The ADC decrease, indicative of excitotoxicity, confirms that the amygdala and piriformic cortex are particularly vulnerable to lithium-pilocarpine-induced seizures. The transient ADC increase in the thalamus may reflect the breakdown of the blood-brain barrier (BBB), which is shown to occur in this region at these time points. Neuronal damage and failure of energy-dependent formation of NAA are likely causes of an observed decrease in NAA, while the decrease in Cho is possibly due to depletion of the cholinergic system. This study illustrates that relative hypoxia, excitotoxicity and concomitant neuronal damage associated with SE can be probed noninvasively with MR. These pathological phenomena are the first to contribute to the pathophysiology of spontaneous recurrent seizures in a later stage in this animal model.

Mitochondrial Affinity for ADP is Twofold Lower in Creatine Kinase Knock-out Muscles. Possible Role in Rescuing Cellular Energy Homeostasis

The FEBS Journal. Feb, 2005  |  Pubmed ID: 15691329

Adaptations of the kinetic properties of mitochondria in striated muscle lacking cytosolic (M) and/or mitochondrial (Mi) creatine kinase (CK) isoforms in comparison to wild-type (WT) were investigated in vitro. Intact mitochondria were isolated from heart and gastrocnemius muscle of WT and single- and double CK-knock-out mice strains (cytosolic (M-CK-/-), mitochondrial (Mi-CK-/-) and double knock-out (MiM-CK-/-), respectively). Maximal ADP-stimulated oxygen consumption flux (State3 Vmax; nmol O2 x mg mitochondrial protein(-1) x min(-1)) and ADP affinity (K50ADP; microM) were determined by respirometry. State 3 Vmax and of M-CK-/- and MiM-CK-/- gastrocnemius mitochondria were twofold higher than those of WT, but were unchanged for Mi-CK-/-. For mutant cardiac mitochondria, only the of mitochondria isolated from the MiM-CK-/- phenotype was different (i.e. twofold higher) than that of WT. The implications of these adaptations for striated muscle function were explored by constructing force-flow relations of skeletal muscle respiration. It was found that the identified shift in affinity towards higher ADP concentrations in MiM-CK-/- muscle genotypes may contribute to linear mitochondrial control of the reduced cytosolic ATP free energy potentials in these phenotypes.

Determination of Mouse Skeletal Muscle Architecture Using Three-dimensional Diffusion Tensor Imaging

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Jun, 2005  |  Pubmed ID: 15906281

Muscle architecture is the main determinant of the mechanical behavior of skeletal muscles. This study explored the feasibility of diffusion tensor imaging (DTI) and fiber tracking to noninvasively determine the in vivo three-dimensional (3D) architecture of skeletal muscle in mouse hind leg. In six mice, the hindlimb was imaged with a diffusion-weighted (DW) 3D fast spin-echo (FSE) sequence followed by the acquisition of an exercise-induced, T(2)-enhanced data set. The data showed the expected fiber organization, from which the physiological cross-sectional area (PCSA), fiber length, and pennation angle for the tibialis anterior (TA) were obtained. The values of these parameters ranged from 5.4-9.1 mm(2), 5.8-7.8 mm, and 21-24 degrees , respectively, which is in agreement with values obtained previously with the use of invasive methods. This study shows that 3D DT acquisition and fiber tracking is feasible for the skeletal muscle of mice, and thus enables the quantitative determination of muscle architecture.

The Effect of B1 Field Inhomogeneity and the Nonselective Inversion Profile on the Kinetics of FAIR-based Perfusion MRI

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Jun, 2005  |  Pubmed ID: 15906290

Perfusion imaging with pulsed arterial spin labeling techniques, like flow-sensitive alternating inversion recovery (FAIR), may suffer from inflow of fresh, i.e., unlabeled, spins. Inflow of fresh spins is caused by the arrival of unlabeled spins in the image slice and can lead to underestimation of the perfusion if not taken into account. In this study it was shown that a decrease in B(1) field strength toward the edge of the transmit coil and the consequent reduction in the inversion efficiency leads to a narrowing of the arterial delivery function and a reduction in FAIR signal. Increasing the B(1) amplitude of the adiabatic inversion pulse from 2.3 to 5.7 times its minimum amplitude requirement resulted in an observed increase of 40 to 80% in the rat brain FAIR signal at inflow times longer than 0.65 s. For coils with limited dimensions and significant B(1) inhomogeneity over the perfusion labeling slab, the application of an excessively large B(1) amplitude in combination with adiabatic inversion is recommended to optimize the FAIR perfusion contrast.

MR Molecular Imaging and Fluorescence Microscopy for Identification of Activated Tumor Endothelium Using a Bimodal Lipidic Nanoparticle

FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology. Dec, 2005  |  Pubmed ID: 16204353

In oncological research, there is a great need for imaging techniques that specifically identify angiogenic blood vessels in tumors on the basis of differences in the expression level of biomolecular markers. In the angiogenic cascade, different cell surface receptors, including the alphavbeta3-integrin, are strongly expressed on activated endothelial cells. In the present study, we aimed to image angiogenesis by detecting the expression of alphavbeta3 in tumor bearing mice with a combination of magnetic resonance imaging (MRI) and fluorescence microscopy. To that end, we prepared MR-detectable and fluorescent liposomes, which carry approximately 700 alphavbeta3-specific RGD peptides per liposome. RGD competition experiments and RAD-conjugated liposomes were used as controls for specificity. In vivo, both RAD liposomes and RGD liposomes gave rise to signal increase on T1-weighted MR images. It was established by the use of ex vivo fluorescence microscopy that RGD liposomes and RAD liposomes accumulated in the tumor by different mechanisms. RGD liposomes were specifically associated with activated tumor endothelium, while RAD liposomes were located in the extravascular compartment. This study demonstrates that MR molecular imaging of angiogenesis is feasible by using a targeted contrast agent specific for the alphavbeta3-integrin, and that the multimodality imaging approach gave insight into the exact mechanism of accumulation in the tumor.

Intramyocellular Lipid Content and Molecular Adaptations in Response to a 1-week High-fat Diet

Obesity Research. Dec, 2005  |  Pubmed ID: 16421342

To investigate molecular adaptations that accompany the elevation of intramyocellular lipid (IMCL) content on a high-fat (HF) diet for 1 week.

Monitoring of Moisture Redistribution in Multicomponent Food Systems by Use of Magnetic Resonance Imaging

Journal of Agricultural and Food Chemistry. Feb, 2006  |  Pubmed ID: 16448166

Differences in water activity within multicomponent food systems inevitably lead to moisture (re)distribution phenomena, hence deteriorating textural quality during shelf life. Noninvasive assessment of moisture transport in such systems would promote mechanistic understanding and enable rational development of strategies to control migration. Magnetic resonance imaging (MRI) is an ideal candidate for such a measurement technique, but its use in systems with low-moisture components (e.g., cereal materials) is seriously hampered because of reduced transverse relaxation times. In this work, we report two MRI protocols for the noninvasive and quantitative assessment of moisture transport in multicomponent food products. The first protocol is suitable to study relatively slow (days/weeks) processes, whereas the second one is designed to study fast (hours) moisture transport. We have successfully applied this methodology to quantify moisture transport within multicomponent food systems, with adequate temporal and spatial resolution.

Lipid-based Nanoparticles for Contrast-enhanced MRI and Molecular Imaging

NMR in Biomedicine. Feb, 2006  |  Pubmed ID: 16450332

In the field of MR imaging and especially in the emerging field of cellular and molecular MR imaging, flexible strategies to synthesize contrast agents that can be manipulated in terms of size and composition and that can be easily conjugated with targeting ligands are required. Furthermore, the relaxivity of the contrast agents, especially for molecular imaging applications, should be very high to deal with the low sensitivity of MRI. Lipid-based nanoparticles, such as liposomes or micelles, have been used extensively in recent decades as drug carrier vehicles. A relatively new and promising application of lipidic nanoparticles is their use as multimodal MR contrast agents. Lipids are amphiphilic molecules with both a hydrophobic and a hydrophilic part, which spontaneously assemble into aggregates in an aqueous environment. In these aggregates, the amphiphiles are arranged such that the hydrophobic parts cluster together and the hydrophilic parts face the water. In the low concentration regime, a wide variety of structures can be formed, ranging from spherical micelles to disks or liposomes. Furthermore, a monolayer of lipids can serve as a shell to enclose a hydrophobic core. Hydrophobic iron oxide particles, quantum dots or perfluorocarbon emulsions can be solubilized using this approach. MR-detectable and fluorescent amphiphilic molecules can easily be incorporated in lipidic nanoparticles. Furthermore, targeting ligands can be conjugated to lipidic particles by incorporating lipids with a functional moiety to allow a specific interaction with molecular markers and to achieve accumulation of the particles at disease sites. In this review, an overview of different lipidic nanoparticles for use in MRI is given, with the main emphasis on Gd-based contrast agents. The mechanisms of particle formation, conjugation strategies and applications in the field of contrast-enhanced, cellular and molecular MRI are discussed.

Increased Resistance to Fatigue in Creatine Kinase Deficient Muscle is Not Due to Improved Contractile Economy

Pflügers Archiv : European Journal of Physiology. Jun, 2006  |  Pubmed ID: 16491397

There has been speculation on the origin of the increased endurance of skeletal muscles in creatine kinase (CK)-deficient mice. Important factors that have been raised include the documented increased mitochondrial capacity and alterations in myosin heavy chain (MyHC) isoform composition in CK-deficient muscle. More recently, the absence of inorganic phosphate release from phosphocreatine hydrolysis in exercising CK-deficient muscle has been postulated to contribute to the lower fatigueability in skeletal muscle. In this study, we tested the hypothesis that the reported shift in MyHC composition to slower isoforms in CK-deficient muscle leads to a decrease in oxygen cost of twitch performance. To that aim, extensor digitorum longus (EDL) and soleus (SOL) muscles were isolated from wild-type (WT) and knock-out mice deficient in the cytoplasmic muscle-type and sarcomeric mitochondrial isoenzymes of CK, and oxygen consumption per twitch time-tension-integral (TTI) was measured. The results show that the adaptive response to loss of CK function does not involve any major change to contractile economy of skeletal muscle.

Liposome-enhanced MRI of Neointimal Lesions in the ApoE-KO Mouse

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. May, 2006  |  Pubmed ID: 16598732

Conventional high-resolution MRI is capable of detecting lipid-rich atherosclerotic plaques in both human atherosclerosis and animal models of atherosclerosis. In this study we induced neointimal lesions in ApoE-KO mice by placing a constrictive collar around the right carotid artery. The model was imaged with conventional multispectral MRI, and the thickened wall could not be distinguished from surrounding tissue. We then tested paramagnetic liposomes (mean size=90 nm) for their ability to improve MRI visualization of induced thickening, using Gd-DTPA as a control. T1-weighted (T1-w), black-blood MRI of the neck area of the mice was performed before and 15 min, 45 min, and 24 hr after intravenous injection of either paramagnetic liposomes or Gd-DTPA. The collared vessel wall of mice that were injected with liposomes showed a pronounced signal enhancement of approximately 100% immediately after injection, which was sustained largely until 24 hr postinjection. In contrast, the vessel wall of all controls (left carotid artery and animals injected with Gd-DTPA) did not show significant contrast enhancement at those time points. This study demonstrates that intimal thickening in ApoE-KO mice can be effectively detected by contrast-enhanced (CE)-MRI upon injection of paramagnetic liposomes.

Annexin A5-functionalized Bimodal Lipid-based Contrast Agents for the Detection of Apoptosis

Bioconjugate Chemistry. May-Jun, 2006  |  Pubmed ID: 16704213

Apoptosis, or programmed cell death, plays an important role in the etiology of a variety of diseases, including cancer and myocardial infarction. Visualization of apoptosis would allow both early detection of therapy efficiency and evaluation of disease progression. To that aim, we synthesized two types of lipid-based bimodal contrast agents that enable the detection of apoptotic cells with both MRI and optical techniques. MR contrast was provided either by entrapment of iron oxide particles within pegylated micelles or by incorporation of Gd-DTPA-bis(stearylamide) (Gd-DTPA-BSA) lipids within the lipid bilayer of pegylated liposomes. The resulting contrast agents were approximately 10 and 100 nm in diameter, respectively. Additional fluorescent lipids were incorporated in the lipid (bi)layer of the contrast agents to allow parallel detection with optical methods. Multiple human recombinant annexin A5 molecules were covalently coupled to introduce specificity for apoptotic cells. Both annexin A5-conjugated contrast agents were shown to significantly increase the relaxation rates of apoptotic cell pellets compared to untreated control cells and apoptotic cells that were treated with nonfunctionalized nanoparticles. Increased relaxation rates were confirmed to originate from association of the contrast agents to apoptotic cells by confocal microscopy. The targeted nanoparticles presented in this study, which differ both in size and in magnetic properties, may have applications for the in vivo detection of apoptosis.

Regional Variations in Intramyocellular Lipid Concentration Correlate with Muscle Fiber Type Distribution in Rat Tibialis Anterior Muscle

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Jul, 2006  |  Pubmed ID: 16767761

1H MR spectroscopy (MRS) has proved to be a valuable noninvasive tool to measure intramyocellular lipids (IMCL) in research focused on insulin resistance and type II diabetes in both humans and rodents. An important determinant of IMCL is the muscle fiber type, since oxidative type I fibers can contain up to three times more IMCL than glycolytic type II muscle fibers. Because these different muscle fiber types are inhomogeneously distributed in rodent muscle, in the present study we investigated the distribution of IMCL within the rat tibialis anterior muscle (TA) in vivo using single-voxel 1H MRS along with the muscle fiber distribution in the TA ex vivo determined from immunohistological assays. IMCL levels in the TA differed by up to a factor of 3 depending on the position of the voxel. The distribution of IMCL over the TA cross section was not random, but emerged in a pattern similar to the distribution of the predominantly oxidative muscle fiber types. Dietary interventions, such as high-fat feeding and 15 hr of fasting, did not significantly change this typical fiber type-dependent pattern of IMCL content. These results stress the importance of voxel positioning when single-voxel 1H MRS is used to study IMCL in rodent muscle.

Functional MRI Reveals Declined Prefrontal Cortex Activation in Patients with Epilepsy on Topiramate Therapy

Epilepsy & Behavior : E&B. Aug, 2006  |  Pubmed ID: 16793345

Functional magnetic resonance imaging of covert word generation was used to examine brain activation abnormalities associated with topiramate-induced cognitive language impairment in patients with epilepsy. Compared with a control epilepsy group, in the topiramate-treated group, there was significantly less activation in the language-mediating regions of the prefrontal cortex; the topiramate group also had significantly lower neuropsychological language scores. These findings suggest that topiramate has a critical effect on the cerebral neural systems that mediate expressive language.

DTI-based Assessment of Ischemia-reperfusion in Mouse Skeletal Muscle

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Aug, 2006  |  Pubmed ID: 16826605

Diffusion tensor imaging (DTI) is frequently applied to characterize the microscopic geometrical properties of tissue. To establish whether and how diffusion MRI responds to transient ischemia of skeletal muscle, we studied the effects of ischemia and reperfusion using DTI and T2-weighted MRI before and during ischemia and up to 24 hr after reperfusion. Ischemia was induced by 50 min of hindlimb occlusion with or without dorsal flexor stimulation. During ischemia the apparent diffusion coefficient (ADC) tended to decrease (up to 15%), whereas the fractional anisotropy (FA) and T2 showed a varied response depending on the protocol and muscle type. During reperfusion the ADC and T2 initially increased and subsequently renormalized for the occlusion protocol. For the occlusion plus stimulation (OS) protocol, the FA was decreased by 13% and the ADC and T2 were increased by 20% and 57%, respectively, after 24 hr in the stimulated muscle complex. In the latter tissue the three DTI eigenvalues gradually increased upon reperfusion. The smallest eigenvalue (lambda3) showed the largest relative increase. Changes in DTI indices in the reperfusion phases followed a similar time course as the changes in T2. The changes in MR indices after 24 hr correlated with the tissue damage quantified with histology. The highest correlation was observed for lambda3 (R2 = 0.81). This study shows that DTI can be used to assess ischemia-induced damage to skeletal muscle.

Annexin A5-conjugated Quantum Dots with a Paramagnetic Lipidic Coating for the Multimodal Detection of Apoptotic Cells

Bioconjugate Chemistry. Jul-Aug, 2006  |  Pubmed ID: 16848390

Apoptosis, or programmed cell death, plays an important role in the etiology of a variety of diseases, including cancer. Visualization of apoptosis would allow both early detection of therapy efficiency and evaluation of disease progression. To that aim we developed a novel annexin A5-conjugated bimodal nanoparticle. The nanoparticle is composed of a quantum dot that is encapsulated in a paramagnetic micelle to enable its use both for optical imaging and MRI. Multiple recombinant human annexin A5 protein molecules were covalently coupled to the nanoparticle for targeting. In this study the specificity of the annexin A5-conjugated nanoparticles for apoptotic cells was demonstrated both with fluorescence microscopy and MRI, which confirms its potential for the detection of apoptosis with both imaging modalities in vivo.

1H MR Spectroscopy of the Brain: Absolute Quantification of Metabolites

Radiology. Aug, 2006  |  Pubmed ID: 16864664

Hydrogen 1 (1H) magnetic resonance (MR) spectroscopy enables noninvasive in vivo quantification of metabolite concentrations in the brain. Currently, metabolite concentrations are most often presented as ratios (eg, relative to creatine) rather than as absolute concentrations. Despite the success of this approach, it has recently been suggested that relative quantification may introduce substantial errors and can lead to misinterpretation of spectral data and to erroneous metabolite values. The present review discusses relevant methods to obtain absolute metabolite concentrations with a clinical MR system by using single-voxel spectroscopy or chemical shift imaging. Important methodological aspects in an absolute quantification strategy are addressed, including radiofrequency coil properties, calibration procedures, spectral fitting methods, cerebrospinal fluid content correction, macromolecule suppression, and spectral editing. Techniques to obtain absolute concentrations are now available and can be successfully applied in clinical practice. Although the present review is focused on 1H MR spectroscopy of the brain, a large part of the methodology described can be applied to other tissues as well.

Quantum Dots with a Paramagnetic Coating As a Bimodal Molecular Imaging Probe

Nano Letters. Jan, 2006  |  Pubmed ID: 16402777

MRI detectable and targeted quantum dots were developed. To that aim, quantum dots were coated with paramagnetic and pegylated lipids, which resulted in a relaxivity, r(1), of nearly 2000 mM(-1)s(-1) per quantum dot. The quantum dots were functionalized by covalently linking alphavbeta3-specific RGD peptides, and the specificity was assessed and confirmed on cultured endothelial cells. The bimodal character, the high relaxivity, and the specificity of this nanoparticulate probe make it an excellent contrast agent for molecular imaging purposes.

Dynamic MRS and MRI of Skeletal Muscle Function and Biomechanics

NMR in Biomedicine. Nov, 2006  |  Pubmed ID: 17075956

MR is a powerful technique for studying the biomechanical and functional properties of skeletal muscle in vivo in health and disease. This review focuses on 31P, 1H and 13C MR spectroscopy for assessment of the dynamics of muscle metabolism and on dynamic 1H MRI methods for non-invasive measurement of the biomechanical and functional properties of skeletal muscle. The information thus obtained ranges from the microscopic level of the metabolism of the myocyte to the macroscopic level of the contractile function of muscle complexes. The MR technology presented plays a vital role in achieving a better understanding of many basic aspects of muscle function, including the regulation of mitochondrial activity and the intricate interplay between muscle fiber organization and contractile function. In addition, these tools are increasingly being employed to establish novel diagnostic procedures as well as to monitor the effects of therapeutic and lifestyle interventions for muscle disorders that have an increasing impact in modern society.

Comparison Between Prospective and Retrospective Triggering for Mouse Cardiac MRI

NMR in Biomedicine. Jun, 2007  |  Pubmed ID: 17120296

High-resolution magnetic resonance imaging (MRI) has evolved into one of the major non-invasive tools to study the healthy and diseased mouse heart. This study presents a Cartesian CINE MRI protocol based on a fast low-angle shot sequence with a navigator echo to generate cardiac triggering and respiratory gating signals retrospectively, making the use of ECG leads and respiratory motion sensors obsolete. MRI of the in vivo mouse heart using this sequence resulted in CINE images with no detectable cardiac and respiratory motion artefacts. The retrospective method allows for steady-state imaging of the mouse heart, which is essential for quantitative contrast-enhanced MRI studies. A comparison was made between prospective and retrospective methods in terms of the signal-to-noise ratio and the contrast-to-noise ratio between blood and myocardial wall, as well as global cardiac functional indices: end-diastolic volume, end-systolic volume, stroke volume and ejection fraction. The retrospective method resulted in almost constant left-ventricle wall signal intensity throughout the cardiac cycle, at the expense of a decrease in the signal-to-noise ratio and the contrast-to-noise ratio between blood and myocardial wall as compared with the prospective method. Prospective and retrospective sequences yielded comparable global cardiac functional indices. The largest mean relative difference found was 8% for the end-systolic volume.

Early in Vivo Assessment of Angiostatic Therapy Efficacy by Molecular MRI

FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology. Feb, 2007  |  Pubmed ID: 17202248

Noninvasive diagnostic imaging methods to establish the efficacy of angiostatic therapies are becoming increasingly important with the first Food and Drug Administration approvals of such agents. Magnetic resonance molecular imaging is an imaging technique that allows the visualization of pathological processes in vivo with a better spatial resolution as compared with nuclear methods, such as photon emission tomography and single photon emission computed tomography. In this study, we used alpha(v)beta3 targeted bimodal liposomes to quantitate angiogenesis in a tumor mouse model with magnetic resonance imaging (MRI) and to evaluate the therapeutic efficacy of the angiogenesis inhibitors anginex and endostatin. The MRI findings were validated with fluorescence microscopy and showed a very good correlation with the microvessel density. In conclusion, this study provides evidence that molecular MRI can be used to noninvasively measure the efficacy of angiogenesis inhibitors during the course of therapy.

Role of Ischemia and Deformation in the Onset of Compression-induced Deep Tissue Injury: MRI-based Studies in a Rat Model

Journal of Applied Physiology (Bethesda, Md. : 1985). May, 2007  |  Pubmed ID: 17255369

A rat model was used to distinguish between the different factors that contribute to muscle tissue damage related to deep pressure ulcers that develop after compressive loading. The separate and combined effects of ischemia and deformation were studied. Loading was applied to the hindlimb of rats for 2 h. Muscle tissue was examined using MR imaging (MRI) and histology. An MR-compatible loading device allowed simultaneous loading and measurement of tissue status. Two separate loading protocols incorporated uniaxial loading, resulting in tissue compression and ischemic loading. Uniaxial loading was applied to the tibialis anterior by means of an indenter, and ischemic loading was accomplished with an inflatable tourniquet. Deformation of the muscle tissue during uniaxial loading was measured using MR tagging. Compression of the tissues for 2 h led to increased T2 values, which were correlated to necrotic regions in the tibialis anterior. Perfusion measurements, by means of contrast-enhanced MRI, indicated a large ischemic region during indentation. Pure ischemic loading for 2 h led to reversible tissue changes. From the MR-tagging experiments, local strain fields were calculated. A 4.5-mm deformation, corresponding to a surface pressure of 150 kPa, resulted in maximum shear strain up to 1.0. There was a good correlation between the location of damage and the location of high shear strain. It was concluded that the large deformations, in conjunction with ischemia, provided the main trigger for irreversible muscle damage.

Anginex-conjugated Liposomes for Targeting of Angiogenic Endothelial Cells

Bioconjugate Chemistry. May-Jun, 2007  |  Pubmed ID: 17378601

Identification of a tumor angiogenesis specific ligand would allow targeting of tumor vasculature. Lipidic vehicles can be used to deliver therapeutic agents for treatment of disease or contrast agents for molecular imaging. A targeting ligand would allow specific delivery of such formulations to angiogenic sites, thereby reducing side effects and gaining efficiency. Anginex, a synthetic 33-mer angiostatic peptide, has been described to home angiogenically activated endothelium, suggesting an ideal candidate as targeting ligand. To investigate this application of anginex, fluorescently labeled paramagnetic liposomes were conjugated with anginex. Using phase contrast and fluorescence microscopy as well as magnetic resonance imaging (MRI), we demonstrate that anginex-conjugated liposomes bind specifically to activated endothelial cells, suggesting application as an angiogenesis targeting agent for molecular targeting and molecular imaging of angiogenesis-dependent disease.

Skeletal Muscle Degeneration and Regeneration After Femoral Artery Ligation in Mice: Monitoring with Diffusion MR Imaging

Radiology. May, 2007  |  Pubmed ID: 17384238

To prospectively evaluate quantitative diffusion magnetic resonance (MR) imaging for monitoring skeletal muscle injury and repair after femoral artery ligation in mice.

Intersubject Differences in the Effect of Acidosis on Phosphocreatine Recovery Kinetics in Muscle After Exercise Are Due to Differences in Proton Efflux Rates

American Journal of Physiology. Cell Physiology. Jul, 2007  |  Pubmed ID: 17392383

(31)P magnetic resonance spectroscopy provides the possibility of obtaining bioenergetic data during skeletal muscle exercise and recovery. The time constant of phosphocreatine (PCr) recovery (tau(PCr)) has been used as a measure of mitochondrial function. However, cytosolic pH has a strong influence on the kinetics of PCr recovery, and it has been suggested that tau(PCr) should be normalized for end-exercise pH. A general correction can only be applied if there are no intersubject differences in the pH dependence of tau(PCr). We investigated the pH dependence of tau(PCr) on a subject-by-subject basis. Furthermore, we determined the kinetics of proton efflux at the start of recovery. Intracellular acidosis slowed PCr recovery, and the pH dependence of tau(PCr) differed among subjects, ranging from -33.0 to -75.3 s/pH unit. The slope of the relation between tau(PCr) and end-exercise pH was positively correlated with both the proton efflux rate and the apparent proton efflux rate constant, indicating that subjects with a smaller pH dependence of tau(PCr) have a higher proton efflux rate. Our study implies that simply correcting tau(PCr) for end-exercise pH is not adequate, in particular when comparing patients and control subjects, because certain disorders are characterized by altered proton efflux from muscle fibers.

MRI Contrast Agents: Current Status and Future Perspectives

Anti-cancer Agents in Medicinal Chemistry. May, 2007  |  Pubmed ID: 17504156

Magnetic Resonance Imaging (MRI) is increasingly used in clinical diagnostics, for a rapidly growing number of indications. The MRI technique is non-invasive and can provide information on the anatomy, function and metabolism of tissues in vivo. MRI scans of tissue anatomy and function make use of the two hydrogen atoms in water to generate the image. Apart from differences in the local water content, the basic contrast in the MR image mainly results from regional differences in the intrinsic relaxation times T(1) and T(2), each of which can be independently chosen to dominate image contrast. However, the intrinsic contrast provided by the water T(1) and T(2) and changes in their values brought about by tissue pathology are often too limited to enable a sensitive and specific diagnosis. For that reason increasing use is made of MRI contrast agents that alter the image contrast following intravenous injection. The degree and location of the contrast changes provide substantial diagnostic information. Certain contrast agents are predominantly used to shorten the T(1) relaxation time and these are mainly based on low-molecular weight chelates of the gadolinium ion (Gd(3+)). The most widely used T(2) shortening agents are based on iron oxide (FeO) particles. Depending on their chemical composition, molecular structure and overall size, the in vivo distribution volume and pharmacokinetic properties vary widely between different contrast agents and these largely determine their use in specific diagnostic tests. This review describes the current status, as well as recent and future developments of MRI contrast agents with focus on applications in oncology. First the basis of MR image contrast and how it is altered by contrast agents will be discussed. After some considerations on bioavailability and pharmacokinetics, specific applications of contrast agents will be presented according to their specific purposes, starting with non-specific contrast agents used in classical contrast enhanced magnetic resonance angiography (MRA) and dynamic contrast enhanced MRI. Next targeted contrast agents, which are actively directed towards a specific molecular target using an appropriate ligand, functional contrast agents, mainly used for functional brain and heart imaging, smart contrast agents, which generate contrast as a response to a change in their physical environment as a consequence of some biological process, and finally cell labeling agents will be presented. To conclude some future perspectives are discussed.

Reproducibility of Quantitative Cerebral T2 Relaxometry, Diffusion Tensor Imaging, and 1H Magnetic Resonance Spectroscopy at 3.0 Tesla

Investigative Radiology. Jun, 2007  |  Pubmed ID: 17507802

The reproducibility of quantitative cerebral T2 relaxometry, diffusion tensor imaging, and H magnetic resonance (MR) spectroscopic imaging was assessed on a clinical 3.0 T MR system.

Exercise Training Improves Glycemic Control in Long-standing Insulin-treated Type 2 Diabetic Patients

Diabetes Care. Oct, 2007  |  Pubmed ID: 17626892

Magnetic and Fluorescent Nanoparticles for Multimodality Imaging

Nanomedicine (London, England). Jun, 2007  |  Pubmed ID: 17716176

The development of nanoparticulate contrast agents is providing an increasing contribution to the field of diagnostic and molecular imaging. Such agents provide several advantages over traditional compounds. First, they may contain a high payload of the contrast-generating material, which greatly improves their detectability. Second, multiple properties may be easily integrated within one nanoparticle to allow its detection with several imaging techniques or to include therapeutic qualities. Finally, the surface of such nanoparticles may be modified to improve circulation half-lives or to attach targeting groups. Magnetic resonance imaging and optical techniques are highly complementary imaging methods. Combining these techniques would therefore have significant advantages and may be realized through the use of nanoparticulate contrast agents. This review gives a survey of the different types of fluorescent and magnetic nanoparticles that have been employed for both magnetic resonance and optical imaging studies.

Magnetic Resonance Molecular Imaging Contrast Agents and Their Application in Atherosclerosis

Topics in Magnetic Resonance Imaging : TMRI. Oct, 2007  |  Pubmed ID: 18025995

Heart disease is the most prevalent cause of mortality in the Western world and is most frequently caused by rupture of lesions in the arteries, which are formed by atherosclerosis. Atherosclerosis is a progressive disease, and therefore, there is a strong motivation to be able to image the stages of this disease in vivo. The pathogenesis of this disease is now well established, and a number of markers such as macrophages, vascular adhesion molecules, fibrin, and the alphanubeta3-integrin have been identified that are of particular interest for imaging. Furthermore, the differentiation between the stable and unstable plaque with imaging is a central goal of the field. Contrast can be generated in magnetic resonance imaging through the application of several types of agents such as T1, T2, chemical exchange saturation transfer or 19F-based imaging agents. Subsequent to the discussion of the above topics, we will describe some examples of molecular imaging agents that successfully detect specific markers in atherosclerotic plaques that are of interest in several stages of this disease.

Molecular Imaging of Macrophages in Atherosclerotic Plaques Using Bimodal PEG-micelles

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Dec, 2007  |  Pubmed ID: 18046703

Pegylated, fluorescent, and paramagnetic micelles were developed. The micelles were conjugated with macrophage scavenger receptor (MSR)-specific antibodies. The abdominal aortas of atherosclerotic apoE-KO mice were imaged with T(1)-weighted high-resolution MRI before and 24 h after intravenous administration of the contrast agent (CA). Pronounced signal enhancement (SE) (up to 200%) was observed for apolipoprotein E knockout (apoE-KO) mice that were injected with MSR-targeted micelles, while the aortic vessel wall of mice injected with nontargeted micelles showed little SE. To allow fluorescence microscopy and optical imaging of the excised aorta, the micelles were made fluorescent by incorporating either a quantum dot (QD) in the micelle corona or rhodamine lipids in the micelle. Ultraviolet (UV) illumination of the aorta allowed the identification of regions with high macrophage content, while MSR-targeted rhodamine micelles could be detected with fluorescence microscopy and were found to be associated with macrophages. In conclusion, this study demonstrates that macrophages in apoE-KO mice can be effectively and specifically detected by molecular MRI and optical methods upon administration of a pegylated micellar CA.

Quantitative MRI-pathology Correlations of Brain White Matter Lesions Developing in a Non-human Primate Model of Multiple Sclerosis

NMR in Biomedicine. Apr, 2007  |  Pubmed ID: 16948176

Experimental autoimmune encephalomyelitis (EAE) induced with recombinant human myelin/oligodendrocyte glycoprotein in the common marmoset is a useful preclinical model of multiple sclerosis in which white matter lesions can be well visualized with MRI. In this study we characterized lesion progression with quantitative in vivo MRI (4.7 T; T(1) relaxation time +/- Gd-DTPA; T(2) relaxation time; magnetization transfer ratio, MTR, imaging) and correlated end stage MRI presentation with quantitative ex vivo MRI (formaldehyde fixed brains; T(1) and T(2) relaxation times; MTR) and histology. The histopathological characterization included axonal density measurements and the numeric quantification of infiltrated macrophages expressing markers for early active [luxol fast blue (LFB) or migration inhibition factor-related protein-14 positive] or late active/inactive [periodic acid Schiff (PAS) positive] demyelinating lesion. MRI experiments were done every two weeks until the monkeys were sacrificed with severe EAE-related motor deficits. Compared with the normal appearing white matter, lesions showed an initial increase in T(1) relaxation times, leakage of Gd-DTPA and decrease in MTR values. The progressive enlargement of lesions was associated with stabilized T(1) values, while T(2) initially increased and stabilized thereafter and MTR remained decreased. Gd-DTPA leakage was highly variable throughout the experiment. MRI characteristics of the cortex and (normal appearing) white matter did not change during the experiment. We observed that in vivo MTR values correlated positively with the number of early active (LFB+) and negatively with late active (PAS+) macrophages. Ex vivo MTR and relaxation times correlated positively with the number of PAS-positive macrophages. None of the investigated MRI parameters correlated with axonal density.

Kinetics of Avidin-induced Clearance of Biotinylated Bimodal Liposomes for Improved MR Molecular Imaging

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Dec, 2008  |  Pubmed ID: 19025910

Dual labeled liposomes, carrying both paramagnetic and fluorescent lipids, were recently proposed as potent contrast agents for MR molecular imaging. These nanoparticles are coated with poly(ethylene glycol) (PEG) to increase their blood circulation half-life, which should allow extensive accumulation at the targeted site. To eliminate nonspecific blood pool signal from the MR images, the circulating liposomes should ideally be cleared from the circulation when sufficient target-specific contrast enhancement is obtained. To that aim, we designed an avidin chase that allowed controlled and rapid clearance of paramagnetic biotinylated liposomes from the blood circulation in C57BL/6 mice. Avidin-induced alterations in blood clearance kinetics and tissue distribution were studied quantitatively by determination of the Gd content in blood and tissue samples ex vivo. Intrinsic liposomal blood clearance showed bi-exponential behavior with half-lives t(1/2alpha) = 2.1 +/- 1.1 and t(1/2beta) = 15.1 +/- 5.4 hours, respectively. In contrast, the contrast agent was cleared from the blood by the avidin infusion to <1% of the initial dose within 4 hours. Avidin-induced liposomal blood clearance was also demonstrated in vivo by dynamic T(1)-weighted MRI. The ability to rapidly clear circulating contrast agents opens up exciting possibilities to study targeting kinetics, to increase the specificity of molecular MRI and to optimize nanoparticulate contrast agent formulations.

Paramagnetic Lipid-coated Silica Nanoparticles with a Fluorescent Quantum Dot Core: a New Contrast Agent Platform for Multimodality Imaging

Bioconjugate Chemistry. Dec, 2008  |  Pubmed ID: 19035793

Silica particles as a nanoparticulate carrier material for contrast agents have received considerable attention the past few years, since the material holds great promise for biomedical applications. A key feature for successful application of this material in vivo is biocompatibility, which may be significantly improved by appropriate surface modification. In this study, we report a novel strategy to coat silica particles with a dense monolayer of paramagnetic and PEGylated lipids. The silica nanoparticles carry a quantum dot in their center and are made target-specific by the conjugation of multiple alphavbeta3-integrin-specific RGD-peptides. We demonstrate their specific uptake by endothelial cells in vitro using fluorescence microscopy, quantitative fluorescence imaging, and magnetic resonance imaging. The lipid-coated silica particles introduced here represent a new platform for nanoparticulate multimodality contrast agents.

Improved Magnetic Resonance Molecular Imaging of Tumor Angiogenesis by Avidin-induced Clearance of Nonbound Bimodal Liposomes

Neoplasia (New York, N.Y.). Dec, 2008  |  Pubmed ID: 19048124

Angiogenic, that is, newly formed, blood vessels play an important role in tumor growth and metastasis and are a potential target for tumor treatment. In previous studies, the alpha(v)beta(3) integrin, which is strongly expressed in angiogenic vessels, has been used as a target for Arg-Gly-Asp (RGD)-functionalized nanoparticulate contrast agents for magnetic resonance imaging-based visualization of angiogenesis. In the present study, the target-to-background ratio was increased by diminishing the nonspecific contrast enhancement originating from contrast material present in the blood pool. This was accomplished by the use of a so-called avidin chase, which allowed rapid clearance of non-bound paramagnetic RGD-biotin-liposomes from the blood circulation. C57BL/6 mice, bearing a B16F10 mouse melanoma, received RGD-functionalized or untargeted biotin-liposomes, which was followed by avidin infusion or no infusion. Precontrast, postcontrast, and postavidin T(1)-weighted magnetic resonance images were acquired at 6.3 T. Postcontrast images showed similar percentages of contrast-enhanced pixels in the tumors of mice that received RGD-biotin-liposomes and biotin-liposomes. Post avidin infusion this percentage rapidly decreased to precontrast levels for biotin-liposomes, whereas a significant amount of contrast-enhanced pixels remained present for RGD-biotin-liposomes. These results showed that besides target-associated contrast agent, the circulating contrast agent contributed significantly to the contrast enhancement as well. Ex vivo fluorescence microscopy confirmed association of the RGD-biotin-liposomes to tumor endothelial cells both with and without avidin infusion, whereas biotin-liposomes were predominantly found within the vessel lumen. The clearance methodology presented in this study successfully enhanced the specificity of molecular magnetic resonance imaging and opens exciting possibilities for studying detection limits and targeting kinetics of site-directed contrast agents in vivo.

Evaluation of Manual and Automatic Segmentation of the Mouse Heart from CINE MR Images

Journal of Magnetic Resonance Imaging : JMRI. Jan, 2008  |  Pubmed ID: 18050352

To compare global functional parameters determined from a stack of cinematographic MR images of mouse heart by a manual segmentation and an automatic segmentation algorithm.

Improved Biocompatibility and Pharmacokinetics of Silica Nanoparticles by Means of a Lipid Coating: a Multimodality Investigation

Nano Letters. Aug, 2008  |  Pubmed ID: 18624389

Silica is a promising carrier material for nanoparticle-facilitated drug delivery, gene therapy, and molecular imaging. Understanding of their pharmacokinetics is important to resolve bioapplicability issues. Here we report an extensive study on bare and lipid-coated silica nanoparticles in mice. Results obtained by use of a wide variety of techniques (fluorescence imaging, inductively coupled plasma mass spectrometry, magnetic resonance imaging, confocal laser scanning microscopy, and transmission electron microscopy) showed that the lipid coating, which enables straightforward functionalization and introduction of multiple properties, increases bioapplicability and improves pharmacokinetics.

Increased Intramyocellular Lipid Content but Normal Skeletal Muscle Mitochondrial Oxidative Capacity Throughout the Pathogenesis of Type 2 Diabetes

FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology. Nov, 2008  |  Pubmed ID: 18653763

Currently inherited or acquired skeletal muscle mitochondrial dysfunction is linked to dysregulated fatty acid metabolism, resulting in increased levels of intramyocellular lipids (IMCLs) and lipid intermediates, inducing insulin resistance. The present study aimed to clarify the order of changes in IMCL levels and skeletal muscle mitochondrial function during the development of type 2 diabetes in Zucker diabetic fatty (ZDF) rats. IMCL levels and skeletal muscle oxidative capacity were determined in vivo, using localized (1)H magnetic resonance spectroscopy (MRS) and dynamic (31)P MRS, respectively. In parallel, in vitro activities were measured from enzymes involved in fatty acid oxidation, the tricarboxylic acid cycle and the electron transport chain. Fa/fa ZDF rats were studied at 3 different ages corresponding to different stages of type 2 diabetes, whereas fa/+ rats served as controls. Fa/fa ZDF rats had higher IMCL contents than controls throughout the duration of the study. In vivo muscle oxidative capacity was not different in fa/fa animals compared to controls, and in vitro enzyme activity data suggested improved functionality of enzymes involved in fat oxidation in type 2 diabetic animals. Accordingly, we can conclude that in the ZDF rat model, type 2 diabetes develops in the absence of skeletal muscle mitochondrial dysfunction.

Short- and Long-term Limbic Abnormalities After Experimental Febrile Seizures

Neurobiology of Disease. Nov, 2008  |  Pubmed ID: 18707002

Experimental febrile seizures (FS) are known to promote hyperexcitability of the limbic system and increase the risk for eventual temporal lobe epilepsy (TLE). Early markers of accompanying microstructural and metabolic changes may be provided by in vivo serial MRI. FS were induced in 9-day old rats by hyperthermia. Quantitative multimodal MRI was applied 24 h and 8 weeks later, in rats with FS and age-matched controls, and comprised hippocampal volumetry and proton spectroscopy, and cerebral T2 relaxometry and diffusion tensor imaging (DTI). At 9 weeks histology was performed. Hippocampal T2 relaxation time elevations appeared to be transient. DTI abnormalities detected in the amygdala persisted up to 8 weeks. Hippocampal volumes were not affected. Histology showed increased fiber density and anisotropy in the hippocampus, and reduced neuronal surface area in the amygdala. Quantitative serial MRI is able to detect transient, and most importantly, long-term FS-induced changes that reflect microstructural alterations.

Diffusion Tensor Imaging of Left Ventricular Remodeling in Response to Myocardial Infarction in the Mouse

NMR in Biomedicine. Feb, 2009  |  Pubmed ID: 18780284

The cardiac muscle architecture lies at the basis of the mechanical and electrical properties of the heart, and dynamic alterations in fiber structure are known to be of prime importance in healing and remodeling after myocardial infarction. In this study, left ventricular remodeling was characterized using diffusion tensor imaging (DTI) in a mouse model of myocardial infarction. Myocardial infarction was induced in mice by permanent ligation of the left anterior descending coronary artery. Serial ex vivo DTI measurements were performed 7, 14, 28, and 60 days after ligation. Apparent diffusion coefficient, fractional anisotropy, the three eigenvalues of the diffusion tensor, and the myofiber disarray served as readout parameters. After myocardial infarction, the mouse hearts displayed extreme wall thinning in the infarcted area, which covered large parts of the apex and extended into the free wall up to the equator. Average heart mass increased by 70% 7-60 days after infarction. Histological analysis showed that the infarct at 7 days consisted of unstructured tissue with residual necrosis and infiltration of macrophages and myofibroblasts. At 14 days after infarction, the necrotic tissue had disappeared and collagen fibers were starting to appear. From 28 to 60 days, the infarct had fully developed into a mature scar. DTI parameters showed dynamic changes as a function of time after infarction. The apparent diffusion coefficient in the infarcted region was lower than in remote regions and increased as a function of time after infarction. The fractional anisotropy was higher in the infarcted region and was maximum at 28 days, which was attributed to the development of structured collagen fibers. Myofiber disarray, which was analyzed by considering the alignment of fibers in neighboring voxels, was significantly higher in infarcted regions. DTI provides a valuable non-destructive tool for characterizing structural remodeling in diseased myocardium.

A High Relaxivity Gd(III)DOTA-DSPE-based Liposomal Contrast Agent for Magnetic Resonance Imaging

European Journal of Pharmaceutics and Biopharmaceutics : Official Journal of Arbeitsgemeinschaft Für Pharmazeutische Verfahrenstechnik E.V. Jun, 2009  |  Pubmed ID: 18940253

The field of molecular imaging aims to visualize and quantify (patho)physiological processes at the cellular and molecular level. Sensitive and site-targeted contrast agents are employed to visualize molecular constituents of processes of interest. The principal aim of this study was to develop a magnetic resonance imaging (MRI) detectable liposome with high relaxivity and stability. To this end, Gd(III)DOTA-DSPE was synthesized and incorporated in a liposomal formulation. The resulting liposomes were extensively characterized in vitro in terms of contrast agent efficiency and structural properties. The liposomes were shown to have a high longitudinal relaxivity, which is crucial for the detection of low concentration molecular markers in molecular imaging studies. We also demonstrated that Gd(III)DOTA-DSPE exhibits no detectable transmetallation upon incubation with Zn(II). This is important as it significantly contributes to the biocompatibility of the contrast agent. The present liposome preparation will serve as versatile and well characterized platform for molecular imaging and targeted drug delivery studies.

Molecular Imaging of Tumor Angiogenesis Using Alphavbeta3-integrin Targeted Multimodal Quantum Dots

Angiogenesis. , 2009  |  Pubmed ID: 19067197

Molecular imaging of angiogenesis is urgently needed for diagnostic purposes such as early detection, monitoring of (angiostatic) therapy and individualized therapy. Multimodality molecular imaging is a promising and refined technique to study tumor angiogenesis, which has so far been largely unexplored due to the lack of suitable multimodal contrast agents. Here, we report on the application of a novel alphavbeta3-specific quantum dot-based nanoparticle, which has been optimized for both optical and magnetic resonance detection of tumor angiogenesis. Upon intravenous injection of RGD-pQDs in tumor-bearing mice, intravital microscopy allowed the detection of angiogenically activated endothelium at cellular resolution with a small scanning window and limited penetration depth, while magnetic resonance imaging was used to visualize angiogenesis at anatomical resolution throughout the entire tumor. Fluorescence imaging allowed whole-body investigation of angiogenic activity. Using these quantum dots and the aforementioned imaging modalities, the angiogenic tumor vasculature was readily detected with the highest angiogenic activity occurring in the periphery of the tumor. This nanoparticle may be employed for multimodality imaging of a variety of diseases that are accompanied by activation of endothelial cells. Furthermore, the current technology might be developed for molecular imaging of other pathophysiological processes.

Quantification of Left Ventricular Volumes and Ejection Fraction in Mice Using PET, Compared with MRI

Journal of Nuclear Medicine : Official Publication, Society of Nuclear Medicine. Jan, 2009  |  Pubmed ID: 19091898

PET has become an important noninvasive imaging technique in cardiovascular research for the characterization of mouse models in vivo. This modality offers unique insight into biochemical changes on a molecular level, with excellent sensitivity. However, morphologic and functional changes may be of equal importance for a thorough assessment of left ventricular (LV) pathophysiology. Although echocardiography and MRI are widely considered the imaging techniques of choice for the assessment of these parameters, their use with PET considerably increases study complexity and decreases cost- and time-efficiency. In this study, a novel method for the additional quantification of LV volumes and ejection fraction (EF) from PET was evaluated using cardiac MRI as the reference method.

Well-defined, Multifunctional Nanostructures of a Paramagnetic Lipid and a Lipopeptide for Macrophage Imaging

Journal of the American Chemical Society. Jan, 2009  |  Pubmed ID: 19105654

In the field of nanomedicine there is a great demand for technologies that allow the creation of self-assembled structures of which the size and morphology can be accurately controlled. In the current study, we report a nanoparticle platform that is composed of a paramagnetic lipid and a fluorescently labeled lipopeptide. By judiciously controlling the ratio of the aforementioned amphiphilic molecules, a variety of well-defined nanosized supramolecular structures with different sizes and morphologies could be created. The hydrodynamic radii of the different structures were determined by dynamic light scattering. Cryo-TEM revealed the aggregate morphology to vary from small micellar structures to plate-like and even full grown ribbons of which the aspect ratios varied from a diameter of 5-8 nm to structures with a width of up to 25 nm and infinite length. Interestingly, nuclear magnetic resonance dispersion profiling revealed excellent properties for MRI and also showed that the relaxivity of the structures was tunable and morphology dependent. Finally, macrophage cells were treated with two selected nanoparticles and were shown to be avidly taken up. In conclusion we demonstrate a methodology to create structures that (1) are paramagnetic to enable their detection with MRI, (2) exhibit fluorescent properties, (3) can be tuned to defined sizes and shapes, and (4) are efficiently taken up by macrophage cells in vitro.

Internalization of Annexin A5-functionalized Iron Oxide Particles by Apoptotic Jurkat Cells

Contrast Media & Molecular Imaging. Jan-Feb, 2009  |  Pubmed ID: 19137542

Apoptosis plays an important role in the etiology of various diseases. Several studies have reported on the use of annexin A5-functionalized iron oxide particles for the detection of apoptosis with MRI, both in vitro and in vivo. The protein annexin A5 binds with high affinity to the phospholipid phosphatidylserine, which is exposed in the outer leaflet of the apoptotic cell membrane. When co-exposed to apoptotic stimuli, this protein was shown to internalize into endocytic vesicles. Therefore in the present study we investigated the possible internalization of commercially available annexin A5-functionalized iron oxide particles (r1 = 34.0 +/- 2.1 and r2 = 205.0 +/- 10.4 mm(-1) s(-1) at 20 MHz), and the effects of their spatial distribution on relaxation rates R2*, R2 and R1. Two different incubation procedures were performed, where (1) Jurkat cells were either incubated with the contrast agent after induction of apoptosis or (2) Jurkat cells were simultaneously incubated with the apoptotic stimulus and the contrast agent. Transmission electron microscopy images and relaxation rates showed that the first incubation strategy mainly resulted in binding of the annexin A5-iron oxide particles to the cell membrane, whereas the second procedure allowed extensive membrane-association as well as a small amount of internalization. Owing to the small extent of internalization, only minor differences were observed between the DeltaR2*/DeltaR2 and DeltaR2/DeltaR1 ratios of cell pellets with membrane-associated or internalized annexin A5 particles. Only the increase in R1 (DeltaR1) appeared to be diminished by the internalization. Internalization of annexin A5-iron oxide particles is also expected to occur in vivo, where the apoptotic stimulus and the contrast agent are simultaneously present. Where the extent of internalization in vivo is similar to that observed in the present study, both T2- and T2*-weighted MR sequences are considered suitable for the detection of these particles in vivo.

Three-compartment T1 Relaxation Model for Intracellular Paramagnetic Contrast Agents

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. May, 2009  |  Pubmed ID: 19215042

The goal of this work was to elaborate a model describing the effective longitudinal relaxation rate constant R(1) for (1)H(2)O in three cellular compartments experiencing possible equilibrium water exchange, and to apply this model to explain the effective R(1) dependence on the overall concentration of a cell-internalized Gd(3+)-based contrast agent (CA). The model voxel comprises three compartments representing extracellular, cytoplasmic, and vesicular (e.g., endosomal, lysosomal) subcellular spaces. Relaxation parameters were simulated using a modified Bloch-McConnell equation including magnetization exchange between the three compartments. With the model, several possible scenarios for internalized CA distribution were evaluated. Relaxation parameters were calculated for contrast agent restricted to the cytoplasmic or vesicular compartments. The size or the number of CA-loaded vesicles was varied. The simulated data were then separately fitted with empirical mono- and biexponential inversion recovery expressions. The voxel CA-concentration dependencies of R(1) can be used to qualitatively and quantitatively understand a number of different experimental observations reported in the literature. Most important, the simulations reproduced the relaxivity "quenching" for cell-internalized contrast agent that has been observed.

Cellular Compartmentalization of Internalized Paramagnetic Liposomes Strongly Influences Both T1 and T2 Relaxivity

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. May, 2009  |  Pubmed ID: 19235908

In recent years, numerous Gd(3+)-based contrast agents have been developed to enable target-specific MR imaging of in vivo processes at the molecular level. The combination of powerful contrast agents and amplification strategies, aimed at increasing the contrast agent dose at the target site, is an often-used strategy to improve the sensitivity of biomarker detection. One such amplification mechanism is to target a disease-specific cell membrane receptor that can undergo multiple rounds of internalization following ligand binding and thus shuttle a sizeable amount of contrast agent into the target cell. An example of such a membrane receptor is the alpha(nu)beta(3) integrin. The goal of this study was to investigate the consequences of this amplification approach for the T(1)- and T(2)-shortening efficacy of a paramagnetic contrast agent. Cultured endothelial cells were incubated with paramagnetic liposomes that were conjugated with a cyclic RGD-peptide to enable internalization by means of the alpha(nu)beta(3) integrin receptor. Non-targeted liposomes served as a control. This study showed that alpha(nu)beta(3) targeting dramatically increased the uptake of paramagnetic liposomes. This targeting strategy, however, strongly influenced both the longitudinal and transverse relaxivity of the internalized paramagnetic liposomes.

On the Use of Steady-state Signal Equations for 2D TrueFISP Imaging

Magnetic Resonance Imaging. Jul, 2009  |  Pubmed ID: 19249169

To explain the signal behavior in 2D-TrueFISP imaging, a slice excitation profile should be considered that describes a variation of effective flip angles and magnetization phases after excitation. These parameters can be incorporated into steady-state equations to predict the final signal within a pixel. The use of steady-state equations assumes that excitation occurs instantaneously, although in reality this is a nonlinear process. In addition, often the flip angle variation within the slice excitation profile is solely considered when using steady-state equations, while TrueFISP is especially known for its sensitivity to phase variations. The purpose of this study was therefore to evaluate the precision of steady-state equations in calculating signal intensities in 2D TrueFISP imaging. To that end, steady-state slice profiles and corresponding signal intensities were calculated as function of flip angle, RF phase advance and pulse shape. More complex Bloch simulations were considered as a gold standard, which described every excitation within the sequence until steady state was reached. They were used to analyze two different methods based on steady-state equations. In addition, measurements on phantoms were done with corresponding imaging parameters. Although the Bloch simulations described the steady-state slice profile formation better than methods based on steady-state equations, the latter performed well in predicting the steady-state signal resulting from it. In certain cases the phase variation within the slice excitation profile did not even have to be taken into account.

Synergy Between Anti-CCL2 and Docetaxel As Determined by DW-MRI in a Metastatic Bone Cancer Model

Journal of Cellular Biochemistry. May, 2009  |  Pubmed ID: 19259948

Metastatic prostate cancer continues to be the second leading cause of cancer death in American men with an estimated 28,660 deaths in 2008. Recently, monocyte chemoattractant protein-1 (MCP-1, CCL2) has been identified as an important factor in the regulation of prostate metastasis. CCL2, shown to attract macrophages to the tumor site, has a direct promotional effect on tumor cell proliferation, migration, and survival. Previous studies have shown that anti-CCL2 antibodies given in combination with docetaxel were able to induce tumor regression in a pre-clinical prostate cancer model. A limitation for evaluating new treatments for metastatic prostate cancer to bone is the inability of imaging to objectively assess response to treatment. Diffusion-weighted MRI (DW-MRI) assesses response to anticancer therapies by quantifying the random (i.e., Brownian) motion of water molecules within the tumor mass, thus identifying cells undergoing apoptosis. We sought to measure the treatment response of prostate cancer in an osseous site to docetaxel, an anti-CCL2 agent, and combination treatments using DW-MRI. Measurements of tumor apparent diffusion coefficient (ADC) values were accomplished over time during a 14-day treatment period and compared to response as measured by bioluminescence imaging and survival studies. The diffusion data provided early predictive evidence of the most effective therapy, with survival data results correlating with the DW-MRI findings. DW-MRI is under active investigation in the pre-clinical and clinical settings to provide a sensitive and quantifiable means for early assessment of cancer treatment outcome.

Nanoparticulate Assemblies of Amphiphiles and Diagnostically Active Materials for Multimodality Imaging

Accounts of Chemical Research. Jul, 2009  |  Pubmed ID: 19435319

Modern medicine has greatly benefited from recent dramatic improvements in imaging techniques. The observation of physiological events through interactions manipulated at the molecular level offers unique insight into the function (and dysfunction) of the living organism. The tremendous advances in the development of nanoparticulate molecular imaging agents over the past decade have made it possible to noninvasively image the specificity, pharmacokinetic profiles, biodistribution, and therapeutic efficacy of many novel compounds. Several types of nanoparticles have demonstrated utility for biomedical purposes, including inorganic nanocrystals, such as iron oxide, gold, and quantum dots. Moreover, natural nanoparticles, such as viruses, lipoproteins, or apoferritin, as well as hybrid nanostructures composed of inorganic and natural nanoparticles, have been applied broadly. However, among the most investigated nanoparticle platforms for biomedical purposes are lipidic aggregates, such as liposomal nanoparticles, micelles, and microemulsions. Their relative ease of preparation and functionalization, as well as the ready synthetic ability to combine multiple amphiphilic moieties, are the most important reasons for their popularity. Lipid-based nanoparticle platforms allow the inclusion of a variety of imaging agents, ranging from fluorescent molecules to chelated metals and nanocrystals. In recent years, we have created a variety of multifunctional lipid-based nanoparticles for molecular imaging; many are capable of being used with more than one imaging technique (that is, with multimodal imaging ability). These nanoparticles differ in size, morphology, and specificity for biological markers. In this Account, we discuss the development and characterization of five different particles: liposomes, micelles, nanocrystal micelles, lipid-coated silica, and nanocrystal high-density lipoprotein (HDL). We also demonstrate their application for multimodal molecular imaging, with the main focus on magnetic resonance imaging (MRI), optical techniques, and transmission electron microscopy (TEM). The functionalization of the nanoparticles and the modulation of their pharmacokinetics are discussed. Their application for molecular imaging of key processes in cancer and cardiovascular disease are shown. Finally, we discuss a recent development in which the endogenous nanoparticle HDL was modified to carry different diagnostically active nanocrystal cores to enable multimodal imaging of macrophages in experimental atherosclerosis. The multimodal characteristics of the different contrast agent platforms have proven to be extremely valuable for validation purposes and for understanding mechanisms of particle-target interaction at different levels, ranging from the entire organism down to cellular organelles.

Magnitude and Control of Mitochondrial Sensitivity to ADP

American Journal of Physiology. Endocrinology and Metabolism. Sep, 2009  |  Pubmed ID: 19622784

The transduction function for ADP stimulation of mitochondrial ATP synthesis in skeletal muscle was reconstructed in vivo and in silico to investigate the magnitude and origin of mitochondrial sensitivity to cytoplasmic ADP concentration changes. Dynamic in vivo measurements of human leg muscle phosphocreatine (PCr) content during metabolic recovery from contractions were performed by (31)P-NMR spectroscopy. The cytoplasmic ADP concentration ([ADP]) and rate of oxidative ATP synthesis (Jp) at each time point were calculated from creatine kinase equilibrium and the derivative of a monoexponential fit to the PCr recovery data, respectively. Reconstructed [ADP]-Jp relations for individual muscles containing more than 100 data points were kinetically characterized by nonlinear curve fitting yielding an apparent kinetic order and ADP affinity of 1.9 +/- 0.2 and 0.022 +/- 0.003 mM, respectively (means +/- SD; n = 6). Next, in silico [ADP]-Jp relations for skeletal muscle were generated using a computational model of muscle oxidative ATP metabolism whereby model parameters corresponding to mitochondrial enzymes were randomly changed by 50-150% to determine control of mitochondrial ADP sensitivity. The multiparametric sensitivity analysis showed that mitochondrial ADP ultrasensitivity is an emergent property of the integrated mitochondrial enzyme network controlled primarily by kinetic properties of the adenine nucleotide translocator.

Magnetic Quantum Dots for Multimodal Imaging

Wiley Interdisciplinary Reviews. Nanomedicine and Nanobiotechnology. Sep-Oct, 2009  |  Pubmed ID: 20049812

Multimodal contrast agents based on highly luminescent quantum dots (QDs) combined with magnetic nanoparticles (MNPs) or ions form an exciting class of new materials for bioimaging. With two functionalities integrated in a single nanoparticle, a sensitive contrast agent for two very powerful and highly complementary imaging techniques [fluorescence imaging and magnetic resonance imaging (MRI)] is obtained. In this review, the state of the art in this rapidly developing field is given. This is done by describing the developments for four different approaches to integrate the fluorescence and magnetic properties in a single nanoparticle. The first type of particles is created by the growth of heterostructures in which a QD is either overgrown with a layer of a magnetic material or linked to a (superpara, or ferro) MNP. The second approach involves doping of paramagnetic ions into QDs. A third option is to use silica or polymer nanoparticles as a matrix for the incorporation of both QDs and MNPs. Finally, it is possible to introduce chelating molecules with paramagnetic ions (e.g., Gd-DTPA) into the coordination shell of the QDs. All different approaches have resulted in recent breakthroughs and the demonstration of the capability of bioimaging using both functionalities. In addition to giving an overview of the most exciting recent developments, the pros and cons of the four different classes of bimodal contrast agents are discussed, ending with an outlook on the future of this emerging new field.

Current Applications of Nanotechnology for Magnetic Resonance Imaging of Apoptosis

Methods in Molecular Biology (Clifton, N.J.). , 2010  |  Pubmed ID: 20217606

Apoptosis, or programmed cell death, is a morphologically and biochemically distinct form of cell death, which together with proliferation plays an important role in tissue development and homeostasis. Insufficient apoptosis is important in the pathology of various disorders such as cancer and autoimmune diseases, whereas a high apoptotic activity is associated with myocardial infarction, neurodegenerative diseases, and advanced atherosclerotic lesions. Consequently, apoptosis is recognized as an important therapeutic target, which should be either suppressed, e.g., during an ischemic cardiac infarction, or promoted, e.g., in the treatment of cancerous lesions. Imaging tools to address location, amount, and time course of apoptotic activity non-invasively in vivo are therefore of great clinical use in the evaluation of such therapies. This chapter reviews current literature and new developments in the application of nanoparticles for non-invasive apoptosis imaging. Focus is on functionalized nanoparticle contrast agents for MR imaging and bimodal nanoparticle agents that combine magnetic and fluorescent properties.

MRI-determined Carotid Artery Flow Velocities and Wall Shear Stress in a Mouse Model of Vulnerable and Stable Atherosclerotic Plaque

Magma (New York, N.Y.). Apr, 2010  |  Pubmed ID: 20229088

We report here on the pre-clinical MRI characterization of an apoE-/- mouse model of stable and vulnerable carotid artery atherosclerotic plaques, which were induced by a tapered restriction (cast) around the artery. Specific focus was on the quantification of the wall shear stress, which is considered a key player in the development of the plaque phenotype.

Silencing of Glycolysis in Muscle: Experimental Observation and Numerical Analysis

Experimental Physiology. Feb, 2010  |  Pubmed ID: 19801387

The longstanding problem of rapid inactivation of the glycolytic pathway in skeletal muscle after contraction was investigated using (31)P NMR spectroscopy and computational modelling. Accumulation of phosphorylated glycolytic intermediates (hexose monophosphates) during cyclic contraction and subsequent turnover during metabolic recovery was measured in vivo in human quadriceps muscle using dynamic (31)P NMR spectroscopy. The concentration of hexose monophosphates in muscle peaked 40 s into metabolic recovery from maximal contractile work at 6.9 +/- 1.3 mm (mean +/- s.d.; n = 8) and subsequently declined at a rate of 0.009 +/- 0.001 mm s(1). It was next tested whether the current knowledge of the kinetic controls in the glycolytic pathway in muscle integrated in the Lambeth and Kushmerick computational model of skeletal muscle glycolysis explained the experimental data. It was found that the model underestimated the magnitude of deactivation of the glycolytic pathway in resting muscle, resulting in depletion of glycolytic intermediates and substrate for oxidative ATP synthesis. Numerical analysis of the model identified phosphofructokinase and pyruvate kinase as the kinetic control sites involved in deactivation of the glycolytic pathway. Ancillary 100-fold inhibition of both phosphofructokinase and pyruvate kinase was found necessary to predict glycolytic intermediate and ADP concentrations correctly in resting human muscle. Incorporation of this information into the model resulted in highly improved agreement between predicted and measured in vivo dynamics of hexose monophosphates in muscle following contraction. We concluded that silencing of the glycolytic pathway in muscle following contraction is most likely to be mediated by phosphofructokinase and pyruvate kinase inactivation on a time scale of seconds and minutes, respectively, and is necessary to prevent depletion of vital cellular substrates.

Chitosan-based Systems for Molecular Imaging

Advanced Drug Delivery Reviews. Jan, 2010  |  Pubmed ID: 19861142

Molecular imaging enables the non-invasive assessment of biological and biochemical processes in living subjects. Such technologies therefore have the potential to enhance our understanding of disease and drug activity during preclinical and clinical drug development. Molecular imaging allows a repetitive and non-invasive study of the same living subject using identical or alternative biological imaging assays at different time points, thus harnessing the statistical power of longitudinal studies, and reducing the number of animals required and cost. Chitosan is a hydrophilic and non-antigenic biopolymer and has a low toxicity toward mammalian cells. Hence, it has great potential as a biomaterial because of its excellent biocompatibility. Conjugated to additional materials, chitosan composites result in a new class of biomaterials that possess mechanical, physicochemical and functional properties, which have potential for use in advanced biomedical imaging applications. The present review will discuss the strengths, limitations and challenges of molecular imaging as well as applications of chitosan nanoparticles in the field of molecular imaging.

Adaptations in Mitochondrial Function Parallel, but Fail to Rescue, the Transition to Severe Hyperglycemia and Hyperinsulinemia: a Study in Zucker Diabetic Fatty Rats

Obesity (Silver Spring, Md.). Jun, 2010  |  Pubmed ID: 19875988

Cross-sectional human studies have associated mitochondrial dysfunction to type 2 diabetes. We chose Zucker diabetic fatty (ZDF) rats as a model of progressive insulin resistance to examine whether intrinsic mitochondrial defects are required for development of type 2 diabetes. Muscle mitochondrial function was examined in 6-, 12-, and 19-week-old ZDF (fa/fa) and fa/+ control rats (n = 8-10 per group) using respirometry with pyruvate, glutamate, and palmitoyl-CoA as substrates. Six-week-old normoglycemic-hyperinsulinemic fa/fa rats had reduced mitochondrial fat oxidative capacity. Adenosine diphosphate (ADP)-driven state 3 and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP)-stimulated state uncoupled (state u) respiration on palmitoyl-CoA were lower compared to controls (62.3 +/- 9.5 vs. 119.1 +/- 13.8 and 87.8 +/- 13.3 vs. 141.9 +/- 14.3 nmol O(2)/mg/min.). Pyruvate oxidation in 6-week-old fa/fa rats was similar to controls. Remarkably, reduced fat oxidative capacity in 6-week-old fa/fa rats was compensated for by an adaptive increase in intrinsic mitochondrial function at week 12, which could not be maintained toward week 19 (140.9 +/- 11.2 and 57.7 +/- 9.8 nmol O(2)/mg/min, weeks 12 and 19, respectively), whereas hyperglycemia had developed (13.5 +/- 0.6 and 16.1 +/- 0.3 mmol/l, weeks 12 and 19, respectively). This mitochondrial adaptation failed to rescue the progressive development of insulin resistance in fa/fa rats. The transition of prediabetes state toward advanced hyperglycemia and hyperinsulinemia was accompanied by a blunted increase in uncoupling protein-3 (UCP3). Thus, in ZDF rats insulin resistance develops progressively in the absence of mitochondrial dysfunction. In fact, improved mitochondrial capacity in hyperinsulinemic hyperglycemic rats does not rescue the progression toward advanced stages of insulin resistance.

Diffusion of Water in Skeletal Muscle Tissue is Not Influenced by Compression in a Rat Model of Deep Tissue Injury

Journal of Biomechanics. Feb, 2010  |  Pubmed ID: 19897200

Sustained mechanical loading of skeletal muscle may result in the development of a severe type of pressure ulcer, referred to as deep tissue injury. Recently it was shown that the diffusion of large molecules (10-150kDa) is impaired during deformation of tissue-engineered skeletal muscle, suggesting a role for impaired diffusion in the aetiology of deep tissue injury. However, the influence of deformation on diffusion of smaller molecules on its aetiology is less clear. This motivated the present study designed to investigate the influence of deformation of skeletal muscle on the diffusion of water, which can be measured with diffusion tensor magnetic resonance imaging (MRI). It could be predicted that this approach will provide valuable information on the diffusion of small molecules. Additionally the relationship between muscle temperature and diffusion was investigated. During deformation of the tibialis anterior a decrease of the apparent diffusion coefficient (ADC) was observed (7.2+/-3.9%). The use of a finite element model showed that no correlation existed between the maximum shear strain and the decrease of the ADC. The ADC in the uncompressed gastrocnemius muscle decreased with 5.9+/-3.7%. In an additional experiment a clear correlation was obtained between the decrease of the ADC and the relative temperature change of skeletal muscle tissue as measured by MRI. Taken together, it was concluded that (1) the decreased diffusion of water was not a direct effect of tissue deformation and (2) that it is likely that the observed decreased ADC during deformation was a result of a decreased muscle temperature. The present study therefore provides evidence that diffusion of small molecules, particularly oxygen and carbon dioxide, is not impaired during deformation of skeletal muscle tissue.

An MR-compatible Bicycle Ergometer for In-magnet Whole-body Human Exercise Testing

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Jan, 2010  |  Pubmed ID: 19918886

An MR-compatible ergometer was developed for in-magnet whole-body human exercise testing. Designed on the basis of conventional mechanically braked bicycle ergometers and constructed from nonferrous materials, the ergometer was implemented on a 1.5-T whole-body MR scanner. A spectrometer interface was constructed using standard scanner hardware, complemented with custom-built parts and software to enable gated data acquisition during exercise. High-quality 31P NMR spectra were reproducibly obtained from the medial head of the quadriceps muscle of the right leg of eight healthy subjects during two-legged high-frequency pedaling (80 revolutions per minute) at three incremental workloads, including maximal. Muscle phosphocreatine content dropped 82%, from 32.2+/-1.0 mM at rest to 5.7+/-1.1 mM at maximal workload (mean+/-standard error; n=8), indicating that the majority of quadriceps motor units were recruited. The cardiovascular load of the exercise was likewise significant, as evidenced by heart rates of 150 (+/-10%) beats per minute, measured immediately afterward. As such, the newly developed MR bicycling exercise equipment offers a powerful new tool for clinical musculoskeletal and cardiovascular MR investigation. The basic design of the ergometer is highly generic and adaptable for application on a wide selection of whole-body MR scanners.

Synergistic Targeting of Alphavbeta3 Integrin and Galectin-1 with Heteromultivalent Paramagnetic Liposomes for Combined MR Imaging and Treatment of Angiogenesis

Nano Letters. Jan, 2010  |  Pubmed ID: 19968235

Effective and specific targeting of nanoparticles is of paramount importance in the fields of targeted therapeutics and diagnostics. In the current study, we investigated the targeting efficacy of nanoparticles that were functionalized with two angiogenesis-specific targeting ligands, an alpha(v)beta(3) integrin-specific and a galectin-1-specific peptide. We show in vitro, using optical techniques and MRI, that the dual-targeting approach produces synergistic targeting effects, causing a dramatically elevated uptake of nanoparticles as compared to single ligand targeting.

Mouse Myocardial First-pass Perfusion MR Imaging

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Dec, 2010  |  Pubmed ID: 20928892

A first-pass myocardial perfusion sequence for mouse cardiac MRI is presented. A segmented ECG-triggered acquisition combined with parallel imaging acceleration was used to capture the first pass of a Gd-DTPA bolus through the mouse heart with a temporal resolution of 300-400 msec. The method was applied in healthy mice (N = 5) and in mice with permanent occlusion of the left coronary artery (N = 6). Baseline semiquantitative perfusion values of healthy myocardium showed excellent reproducibility. Infarct regions revealed a significant decrease in the semiquantitative myocardial perfusion values (0.05 ± 0.02) compared to remote myocardium (0.20 ± 0.04). Myocardial areas of decreased perfusion correlated well to infarct areas identified on the delayed-enhancement scans. This protocol is a valuable addition to the mouse cardiac MRI toolbox for preclinical studies of ischemic heart disease.

Multimodal Clinical Imaging to Longitudinally Assess a Nanomedical Anti-inflammatory Treatment in Experimental Atherosclerosis

Molecular Pharmaceutics. Dec, 2010  |  Pubmed ID: 21028895

Atherosclerosis is an inflammatory disease causing great morbidity and mortality in the Western world. To increase the anti-inflammatory action and decrease adverse effects of glucocorticoids (PLP), a nanomedicinal liposomal formulation of this drug (L-PLP) was developed and intravenously applied at a dose of 15 mg/kg PLP to a rabbit model of atherosclerosis. Since atherosclerosis is a systemic disease, emerging imaging modalities for assessing atherosclerotic plaque are being developed. (18)F-Fluoro-deoxy-glucose positron emission tomography and dynamic contrast enhanced magnetic resonance imaging, methods commonly used in oncology, were applied to longitudinally assess therapeutic efficacy. Significant anti-inflammatory effects were observed as early as 2 days that lasted up to at least 7 days after administration of a single dose of L-PLP. No significant changes were found for the free PLP treated animals. These findings were corroborated by immunohistochemical analysis of macrophage density in the vessel wall. In conclusion, this study evaluates a powerful two-pronged strategy for efficient treatment of atherosclerosis that includes nanomedical therapy of atherosclerotic plaques and the application of noninvasive and clinically approved imaging techniques to monitor delivery and therapeutic responses. Importantly, we demonstrate unprecedented rapid anti-inflammatory effects in atherosclerotic lesions after the nanomedical therapy.

Surface Modification of PLGA Nanospheres with Gd-DTPA and Gd-DOTA for High-relaxivity MRI Contrast Agents

Biomaterials. Nov, 2010  |  Pubmed ID: 20797782

The preparation of particulate contrast agents for magnetic resonance imaging (MRI) based on biodegradable poly(D,L-lactide-co-glycolide) (PLGA) nanocarriers is reported. By spacer-aided covalent surface-grafting of the prominent chelating ligands diethylenetriaminepentaacetic acid (DTPA) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), respectively, up to 236 μg gadolinium per mg PLGA can be immobilized in a stable manner. Due to the localisation at the particle surface, water protons may effectively interact with the gadolinium chelates and the modified particles exhibit high proton relaxivities as confirmed by T1 relaxivities of up to 17.5 mm(-1)s(-1) (25 °C, 1.41 T) in case of Gd-DOTA-functionalized carriers and also supported by NMRD profiles. The obtained values compare favorably with marketed low-molecular weight contrast agents and thus suggest suitability for in vivo use.

Annexin A5-functionalized Bimodal Nanoparticles for MRI and Fluorescence Imaging of Atherosclerotic Plaques

Bioconjugate Chemistry. Oct, 2010  |  Pubmed ID: 20804153

Apoptosis and macrophage burden are believed to correlate with atherosclerotic plaque vulnerability and are therefore considered important diagnostic and therapeutic targets for atherosclerosis. These cell types are characterized by the exposure of phosphatidylserine (PS) at their surface. In the present study, we developed and applied a small micellar fluorescent annexin A5-functionalized nanoparticle for noninvasive magnetic resonance imaging (MRI) of PS exposing cells in atherosclerotic lesions. Annexin A5-mediated target-specificity was confirmed with ellipsometry and in vitro binding to apoptotic Jurkat cells. In vivo T(1)-weighted MRI of the abdominal aorta in atherosclerotic ApoE(-/-) mice revealed enhanced uptake of the annexin A5-micelles as compared to control-micelles, which was corroborated with ex vivo near-infrared fluorescence images of excised whole aortas. Confocal laser scanning microscopy (CLSM) demonstrated that the targeted agent was associated with macrophages and apoptotic cells, whereas the nonspecific control agent showed no clear uptake by such cells. In conclusion, the annexin A5-conjugated bimodal micelles displayed potential for noninvasive assessment of cell types that are considered to significantly contribute to plaque instability and therefore may be of great value in the assessment of atherosclerotic lesion phenotype.

Block-copolymer-stabilized Iodinated Emulsions for Use As CT Contrast Agents

Biomaterials. Sep, 2010  |  Pubmed ID: 20541800

The objective of this study was to develop radiopaque iodinated emulsions for use as CT blood pool contrast agents. Three hydrophobic iodinated oils were synthesized based on the 2,3,5-triiodobenzoate moiety and formulated into emulsions using either phospholipids or amphiphilic polymers, i.e. Pluronic F68 and poly(butadiene)-b-poly(ethylene glycol) (PBD-PEO), as emulsifiers. The size, stability and cell viability was investigated for all stabilized emulsions. Three emulsions stabilized with either lipids or PBD-PEO were subsequently tested in vivo as a CT blood pool contrast agent in mice. While the lipid-stabilized emulsions turned out unstable in vivo, polymer-stabilized emulsions performed well in vivo. In blood, a contrast enhancement of 220 Hounsfield Units (HU) was measured directly after intravenous administration of 520 mg I/kg. The blood circulation half-life of a PBD-PEO stabilized emulsion was approximately 3 h and no noticeable in vivo toxicity was observed. These results show the potential of above emulsions for use as blood pool agents in contrast enhanced CT imaging.

Quantum Dots for Multimodal Molecular Imaging of Angiogenesis

Angiogenesis. Jun, 2010  |  Pubmed ID: 20552267

Quantum dots exhibit unique optical properties for bioimaging purposes. We have previously developed quantum dots with a paramagnetic and functionalized coating and have shown their potential for molecular imaging purposes. In the current mini-review we summarize the synthesis procedure, the in vitro testing and, importantly, the in vivo application for multimodal molecular imaging of tumor angiogenesis.

Reproducibility of Diffusion Tensor Imaging in Human Forearm Muscles at 3.0 T in a Clinical Setting

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Oct, 2010  |  Pubmed ID: 20725932

The aim of the present study was to evaluate a fast clinical protocol to enable diffusion tensor imaging of the human forearm and assess the reproducibility of six diffusion tensor imaging parameters, i.e., the tensor eigenvalues (λ(1), λ(2), and λ(3)), mean diffusivity, fractional anisotropy, and ellipsoid eccentricity. The right forearms of 10 healthy volunteers were scanned twice, with a 1-week interval. Reproducibility of the diffusion tensor imaging parameters was interpreted using Bland-Altman plots, coefficient of repeatability, repeatability index, and the intraclass correlation coefficient. Analysis was done for three regions of interest: the whole muscle volume, flexor digitorum profundus, and extensor digitorum. The Bland-Altman analysis showed that there is good agreement between the two measurements. Based on the intraclass correlation coefficients, agreement was substantial (0.59 < intraclass correlation coefficient < 0.92) for all six parameters of the whole muscle volume and flexor digitorum profundus but only fair (0.18 < intraclass correlation coefficient < 0.64) for the extensor digitorum. Using a 7 min 40 sec scan protocol, which was well tolerated by the volunteers, the reproducibility of diffusion tensor imaging parameters was demonstrated. However, repeatability varies, depending on the region of interest and diffusion tensor imaging parameters. This should be taken into account when a longitudinal study is designed.

Paramagnetic and Fluorescent Liposomes for Target-specific Imaging and Therapy of Tumor Angiogenesis

Angiogenesis. Jun, 2010  |  Pubmed ID: 20390447

Angiogenesis is essential for tumor growth and metastatic potential and for that reason considered an important target for tumor treatment. Noninvasive imaging technologies, capable of visualizing tumor angiogenesis and evaluating the efficacy of angiostatic therapies, are therefore becoming increasingly important. Among the various imaging modalities, magnetic resonance imaging (MRI) is characterized by a superb spatial resolution and anatomical soft-tissue contrast. Revolutionary advances in contrast agent chemistry have delivered versatile angiogenesis-specific molecular MRI contrast agents. In this paper, we review recent advances in the preclinical application of paramagnetic and fluorescent liposomes for noninvasive visualization of the molecular processes involved in tumor angiogenesis. This liposomal contrast agent platform can be prepared with a high payload of contrast generating material, thereby facilitating its detection, and is equipped with one or more types of targeting ligands for binding to specific molecules expressed at the angiogenic site. Multimodal liposomes endowed with contrast material for complementary imaging technologies, e.g., MRI and optical, can be exploited to gain important preclinical insights into the mechanisms of binding and accumulation at angiogenic vascular endothelium and to corroborate the in vivo findings. Interestingly, liposomes can be designed to contain angiostatic therapeutics, allowing for image-supervised drug delivery and subsequent monitoring of therapeutic efficacy.

Skeletal Muscle Metabolic Recovery Following Submaximal Exercise in Chronic Heart Failure is Limited More by O(2) Delivery Than O(2) Utilization

Clinical Science (London, England : 1979). Feb, 2010  |  Pubmed ID: 20310084

CHF (chronic heart failure) is associated with a prolonged recovery of skeletal muscle energy stores following submaximal exercise, limiting the ability to perform repetitive daily activities.However, the pathophysiological background of this impairment is not well established. The aim of the present study was to investigate whether muscle metabolic recovery following submaximal exercise in patients with CHF is limited by O2 delivery or O2 utilization. A total of 13 stable CHF patients (New York Heart Association classes II-III) and eight healthy subjects, matched for age and BMI (body mass index), were included. All subjects performed repetitive submaximal dynamic single leg extensions in the supine position. Post-exercise PCr (phosphocreatine) resynthesis was assessed by 31P-MRS (magnetic resonance spectroscopy). NIRS (near-IR spectroscopy) was applied simultaneously, using the rate of decrease in HHb (deoxygenated haemoglobin) as an index of post-exercise muscle re-oxygenation. As expected, PCr recovery was slower in CHF patients than in control subjects (time constant, 47+/-10 compared with 35+/-12 s respectively; P=0.04). HHb recovery kinetics were also prolonged in CHF patients (mean response time, 74+/-41 compared with 44+/-17 s respectively; P=0.04). In the patient group, HHb recovery kinetics were slower than PCr recovery kinetics (P=0.02), whereas no difference existed in the control group(P=0.32). In conclusion, prolonged metabolic recovery in CHF patients is associated with an even slower muscle tissue re-oxygenation, indicating a lower O(2) delivery relative to metabolic demands. Therefore we postulate that the impaired ability to perform repetitive daily activities in these patients depends more on a reduced muscle blood flow than on limitations in O(2) utilization.

Quantitative (1)H MRI, (19)F MRI, and (19)F MRS of Cell-internalized Perfluorocarbon Paramagnetic Nanoparticles

Contrast Media & Molecular Imaging. Jan-Feb, 2011  |  Pubmed ID: 20648660

In vivo molecular imaging with targeted MRI contrast agents will require sensitive methods to quantify local concentrations of contrast agent, enabling not only imaging-based recognition of pathological biomarkers but also detection of changes in expression levels as a consequence of disease development, therapeutic interventions or recurrence of disease. In recent years, targeted paramagnetic perfluorocarbon emulsions have been frequently applied in this context, permitting high-resolution (1)H MRI combined with quantitative (19)F MR imaging or spectroscopy, under the assumption that the fluorine signal is not altered by the local tissue and cellular environment. In this in vitro study we have investigated the (19)F MR-based quantification potential of a paramagnetic perfluorocarbon emulsion conjugated with RGD-peptide to target the cell-internalizing α(ν)β(3)-integrin expressed on endothelial cells, using a combination of (1)H MRI, (19)F MRI and (19)F MRS. The cells took up the targeted emulsion to a greater extent than nontargeted emulsion. The targeted emulsion was internalized into large 1-7 µm diameter vesicles in the perinuclear region, whereas nontargeted emulsion ended up in 1-4 µm diameter vesicles, which were more evenly distributed in the cytoplasm. Association of the targeted emulsion with the cells resulted in different proton longitudinal relaxivity values, r(1), for targeted and control nanoparticles, prohibiting unambiguous quantification of local contrast agent concentration. Upon cellular association, the fluorine R(1) was constant with concentration, while the fluorine R(2) increased nonlinearly with concentration. Even though the fluorine relaxation rate was not constant, the (19)F MRI and (19)F MRS signals for both targeted nanoparticles and controls were linear and quantifiable as function of nanoparticle concentration.

Contrast Enhancement by Differently Sized Paramagnetic MRI Contrast Agents in Mice with Two Phenotypes of Atherosclerotic Plaque

Contrast Media & Molecular Imaging. Jan-Feb, 2011  |  Pubmed ID: 20882509

Interest in the use of contrast-enhanced MRI to enable in vivo specific characterization of atherosclerotic plaques is increasing. In this study the intrinsic ability of three differently sized gadolinium-based contrast agents to permeate different mouse plaque phenotypes was evaluated with MRI. A tapered cast was implanted around the right carotid artery of apoE(-/-) mice to induce two different plaque phenotypes: a thin cap fibroatheroma (TCFA) and a non-TCFA lesion. Both plaques were allowed to develop over 6 and 9 weeks, leading to an intermediate and advanced lesion, respectively. Signal enhancement in the carotid artery wall, following intravenous injection of Gd-HP-DO3A as well as paramagnetic micelles and liposomes was evaluated. In vivo T(1) -weighted MRI plaque enhancement characteristics were complemented by fluorescence microscopy and correlated to lesion phenotype. The two smallest contrast agents, i.e. Gd-HP-DO3A and micelles, were found to enhance contrast in T(1) -weighted MR images of all investigated plaque phenotypes. Maximum contrast enhancement ranged between 53 and 70% at 6 min after injection of Gd-HP-DO3A with highest enhancement and longest retention in the non-TCFA lesion. Twenty-four hours after injection of micelles maximum contrast enhancement ranged between 24 and 35% in all plaque phenotypes. Administration of the larger liposomes did not cause significant contrast enhancement in the atherosclerotic plaques. Confocal fluorescence microscopy confirmed the MRI-based differences in plaque permeation between micelles and liposomes. Plaque permeation of contrast agents was strongly dependent on size. Our results implicate that, when equipped with targeting ligands, liposomes are most suitable for the imaging of plaque-associated endothelial markers due to low background enhancement, whereas micelles, which accumulate extravascularly on a long timescale, are suited for imaging of less abundant markers inside plaques. Low molecular weight compounds may be employed for target-specific imaging of highly abundant extravascular plaque-associated targets.

Photochemical Activation of Endosomal Escape of MRI-Gd-agents in Tumor Cells

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Jan, 2011  |  Pubmed ID: 21053327

Endocytosis is a common internalization pathway for cellular labeling with MRI contrast agents. However, the entrapment of the Gd(III) complexes into endosomes results in a "quenching" of the attainable relaxivity when the number of Gd(III) complexes reaches the number of ca. 1 × 10(9)/cell. Herein we show that the use of the newly developed photochemical internalization technique provides an efficient method for attaining the endosomal escape of GdHPDO3A molecules entrapped by pinocytosis into different kind of cells. Furthermore, it has been found that a new "quenching" limit is observed when the number of Gd-HPDO3A complexes is ca. five times higher than the value observed for the endosome entrapped conditions. The observed behavior is explained in terms of the attainment of the conditions in which the difference in proton relaxation rates between the cytoplasmic and the extracellular compartment is higher than the exchange rate of water molecules across the cellular membrane. The experimental data points have been reproduced by using a properly designed theoretical compartment T(1)-relaxation model.

The Binding of CNA35 Contrast Agents to Collagen Fibrils

Chemical Communications (Cambridge, England). Feb, 2011  |  Pubmed ID: 21088778

CryoTEM demonstrates that a CNA35-bearing liposomal MRI contrast agent selectively binds to poorly assembled collagen type I as opposed to well-assembled collagen fibrils, whereas monomeric CNA35 binds to all forms of collagen. It is shown that upon conjugation to liposomes and micelles CNA35 loses its ability to dissociate ordered collagen fibrils and thereby to create its own binding sites.

Anti-tumor Activity of Liposomal Glucocorticoids: The Relevance of Liposome-mediated Drug Delivery, Intratumoral Localization and Systemic Activity

Journal of Controlled Release : Official Journal of the Controlled Release Society. Apr, 2011  |  Pubmed ID: 21130819

Tumor-associated inflammation has been recognized as an important tumor growth propagator and, therefore, represents an attractive target for anti-cancer therapy. In the current study, inspired by recent findings on the anti-tumor activity of liposomal glucocorticoids, we introduce paramagnetic and fluorescent liposomes, encapsulating prednisolone phosphate (PLP), to evaluate the local delivery of liposomal glucocorticoids to the tumor and its importance for the therapeutic response. The new multifunctional liposomes (Gd-PLP-L) (120nm diameter, 5.8mg PLP/60μmol lipid, bioexponential blood-clearance kinetics (T(1/2α)=2.4±0.5h, T(1/2β)=42.0±12.4h), drug leakage of 15%/72h (in vitro)), containing 25mol% Gd-DTPA-lipid and 0.1mol% of rhodamine-lipid, were tested in B16F10 melanoma subcutaneously inoculated in C57BL/6 mice, and compared to the original PLP formulation (PLP-L). A single dose of Gd-PLP-L (20mgPLP/kg/week, i.v.) was found to significantly inhibit tumor growth compared to non-treated mice (P<0.05), similarly to PLP-L. The accumulation efficacy of the liposomal agent in the tumor was assessed with MRI, using the increase in the longitudinal relaxation rate (ΔR(1)) as a marker. Interestingly, large inter-tumor differences in ΔR(1) (0.009-0.063s(-1), 24h post-administration), corresponding to highly variable intratumoral Gd-PLP-L levels, did not correlate to the effectiveness of tumor growth inhibition. Uptake of liposomes by tumor-associated macrophages (TAM), determined by ex-vivo fluorescence microscopy, was limited to only 5% of the TAM population. Furthermore, the therapy did not lead to TAM depletion. Importantly, a 90% drop in white blood cell count both after Gd-PLP-L and PLP-L administration was observed. This depletion may reduce tumor infiltration of monocytes, which stimulate angiogenesis, and, thus, possibly co-contributes to the anti-tumor effects. In conclusion, MRI provides a powerful instrument to monitor the delivery of liposomal therapeutics to tumors and guided us to reveal that the activity of liposomal glucocorticoids is not limited to the tumor site only.

Multi-parametric Assessment of the Anti-angiogenic Effects of Liposomal Glucocorticoids

Angiogenesis. May, 2011  |  Pubmed ID: 21225337

Inflammation plays a prominent role in tumor growth. Anti-inflammatory drugs have therefore been proposed as anti-cancer therapeutics. In this study, we determined the anti-angiogenic activity of a single dose of liposomal prednisolone phosphate (PLP-L), by monitoring tumor vascular function and viability over a period of one week. C57BL/6 mice were inoculated subcutaneously with B16F10 melanoma cells. Six animals were PLP-L-treated and six served as control. Tumor tissue and vascular function were probed using MRI before and at three timepoints after treatment. DCE-MRI was used to determine K(trans), v(e), time-to-peak, initial slope and the fraction of non-enhancing pixels, complemented with immunohistochemistry. The apparent diffusion coefficient (ADC), T(2) and tumor size were assessed with MRI as well. PLP-L treatment resulted in smaller tumors and caused a significant drop in K(trans) 48 h post-treatment, which was maintained until one week after drug administration. However, this effect was not sufficient to significantly distinguish treated from non-treated animals. The therapy did not affect tumor tissue viability but did prevent the ADC decrease observed in the control group. No evidence for PLP-L-induced tumor vessel normalization was found on histology. Treatment with PLP-L altered tumor vascular function. This effect did not fully explain the tumor growth inhibition, suggesting a broader spectrum of PLP-L activities.

Dynamic Changes in 1H-MR Relaxometric Properties of Cell-internalized Paramagnetic Liposomes, As Studied over a Five-day Period

Contrast Media & Molecular Imaging. Mar-Apr, 2011  |  Pubmed ID: 20936712

Molecular imaging based on MRI requires the use of amplification strategies in order to achieve sufficient sensitivity for the detection of low-level molecular markers. Recently, we described a combination of two amplification methods: (i) the use of paramagnetic liposomes that can be prepared with a high payload of Gd(3+)-containing lipid; and (ii) targeting to a cell-surface receptor that can undergo multiple rounds of nanoparticle delivery in the cell, followed by recycling to the cell membrane. Liposome uptake was monitored over a period of 24 h and was found to lead to massive delivery in subcellular compartments. The present study aimed to monitor the longer-term fate of the cell-internalized contrast material by studying its relaxometric properties over 5 days, following an initial 24 h loading period. Circa 25% of the Gd(3+)-content delivered to the cells via integrin-targeted liposomes was lost in the first 24 h, which led to 65 and 77% reductions in R(1) and R(2), respectively, as compared with the original R(1) and R(2) enhancements. This implies that the remaining cell-associated gadolinium had relatively low effective r(1) and r(2) relaxivities. It is proposed that this is due to gradual release of Gd(3+) from the chelate in the cell, followed by sequestration in an MR silent state. Most of the gadolinium internalized by cells following incubation with non-targeted liposomes was released in the 5-day follow-up period.

Three-dimensional T1 Mapping of the Mouse Heart Using Variable Flip Angle Steady-state MR Imaging

NMR in Biomedicine. Feb, 2011  |  Pubmed ID: 20960583

Cardiac MR T(1) mapping is a promising quantitative imaging tool for the diagnosis and evaluation of cardiomyopathy. Here, we present a new preclinical cardiac MRI method enabling three-dimensional T(1) mapping of the mouse heart. The method is based on a variable flip angle analysis of steady-state MR imaging data. A retrospectively triggered three-dimensional FLASH (fast low-angle shot) sequence (3D IntraGate) enables a constant repetition time and maintains steady-state conditions. 3D T(1) mapping of the complete mouse heart could be achieved in 20 min. High-quality, bright-blood T(1) maps were obtained with homogeneous T(1) values (1764 ± 172 ms) throughout the myocardium. The repeatability coefficient of R(1) (1/T(1) ) in a specific region of the mouse heart was between 0.14 and 0.20 s(-1) , depending on the number of flip angles. The feasibility for detecting regional differences in ΔR(1) was shown with pre- and post-contrast T(1) mapping in mice with surgically induced myocardial infarction, for which ΔR(1) values up to 0.83 s(-1) were found in the infarct zone. The sequence was also investigated in black-blood mode, which, interestingly, showed a strong decrease in the apparent mean T(1) of healthy myocardium (905 ± 110 ms). This study shows that 3D T(1) mapping in the mouse heart is feasible and can be used to monitor regional changes in myocardial T(1), particularly in relation to pathology and in contrast-enhanced experiments to estimate local concentrations of (targeted) contrast agent.

Dual-targeting of α(v)β(3) and Galectin-1 Improves the Specificity of Paramagnetic/fluorescent Liposomes to Tumor Endothelium in Vivo

Journal of Controlled Release : Official Journal of the Controlled Release Society. Oct, 2011  |  Pubmed ID: 22079810

Molecular imaging of angiogenesis requires a highly specific and efficient contrast agent for targeting activated endothelium. We have previously demonstrated that paramagnetic and fluorescent liposomes functionalized with two angiogenesis-specific ligands, the galectin-1-specific anginex (Anx) and the α(v)β(3) integrin-specific RGD, produce synergistic targeting effect in vitro. In the current study, we applied Anx and RGD dual-conjugated liposomes (Anx/RGD-L) for angiogenesis-specific MRI in vivo, focusing on the specificity and efficacy of liposome association with tumor endothelium. The targeting properties, clearance kinetics and biodistribution of Anx/RGD-L were investigated in B16F10 melanoma-bearing mice, and compared to liposomes functionalized with either Anx (Anx-L) or RGD (RGD-L). The contrast enhancement produced by dual- and single-targeted nanoparticles in the tumor was measured using in vivo T(1)-weighted MRI, complemented by ex vivo immunohistochemical evaluation of tumor tissues. Blood clearance kinetics of Anx/RGD-L was three-fold more rapid than for RGD-L, but comparable to Anx-L. Both dual- and single-targeted liposomes produced similar changes in MRI contrast parameters in tumors with high inter-tumor variability (ΔR(1)=0.04±0.03s(-1), 24h post-contrast). Importantly, however, the specificity of Anx/RGD-L association with tumor endothelium of 53±6%, assessed by fluorescence microscopy, was significantly higher compared to 43±9% (P=0.043) and 28±8% (P=0.0001) of Anx-L and RGD-L, respectively. In contrast, long-circulating RGD-L were on average 16% more efficient in targeting tumor endothelium compared to Anx/RGD-L. Significant differences were also found in the biodistribution of investigated contrast agents. In conclusion, synergistic targeting of α(v)β(3) and galectin-1 improved the specificity of the association of the liposomal contrast agent to tumor endothelium in vivo, providing therefore a more reliable MRI readout of the angiogenic activity.

Tumor Targeting of MMP-2/9 Activatable Cell-penetrating Imaging Probes is Caused by Tumor-independent Activation

Journal of Nuclear Medicine : Official Publication, Society of Nuclear Medicine. Feb, 2011  |  Pubmed ID: 21233187

Activatable cell-penetrating peptides (ACPPs) are a new class of promising molecular imaging probes for the visualization of enzymes in vivo. The cell-penetrating function of a polycationic peptide is efficiently blocked by intramolecular electrostatic interactions with a polyanionic peptide. Proteolysis of a cleavable linker present between the polycationic cell-penetrating peptide and polyanionic peptide affords dissociation of both domains and enables the activated cell-penetrating peptide to enter cells. Here, we aimed to develop an ACPP sensitive to matrix metalloproteinase-2 and -9 (MMP-2/9) for nuclear imaging purposes.

Fasting-induced Myocardial Lipid Accumulation in Long-chain Acyl-CoA Dehydrogenase Knockout Mice is Accompanied by Impaired Left Ventricular Function

Circulation. Cardiovascular Imaging. Sep, 2011  |  Pubmed ID: 21737602

Lipotoxicity may be a key contributor to the pathogenesis of cardiac abnormalities in mitochondrial long-chain fatty acid β-oxidation (FAO) disorders. Few data are available on myocardial lipid levels and cardiac performance in FAO deficiencies. The purpose of this animal study is to assess fasting-induced changes in cardiac morphology, function, and triglyceride (TG) storage as a consequence of FAO deficiency in a noninvasive fashion.

The Effects of Deformation, Ischemia, and Reperfusion on the Development of Muscle Damage During Prolonged Loading

Journal of Applied Physiology (Bethesda, Md. : 1985). Jul, 2011  |  Pubmed ID: 21757578

Deep tissue injury (DTI) is a severe form of pressure ulcer where tissue damage starts in deep tissues underneath intact skin. In the present study, the contributions of deformation, ischemia, and reperfusion to skeletal muscle damage development were examined in a rat model during a 6 h period. Magnetic resonance imaging (MRI) was used to study perfusion (contrast-enhanced MRI) and tissue integrity (T(2)-weighted MRI). The levels of tissue deformation were estimated using finite element models. Complete ischemia caused a gradual homogeneous increase in T(2) (∼20 % during the 6 h period). The effect of reperfusion on T(2) was highly variable, depending on the anatomical location. In experiments involving deformation, inevitably associated with partial ischemia, a variable T(2) increase (17-66 % during the 6 h period) was observed reflecting the significant variation in deformation (with 2D strain energies of 0.60-1.51 J/mm) and ischemia (50.8-99.8 % of the leg) between experiments. These results imply that deformation, ischemia, and reperfusion all contribute to the damage process during prolonged loading, although their importance varies with time. The critical deformation threshold and period of ischemia that cause muscle damage will certainly vary between individuals. These variations are related to intrinsic factors, such as pathological state, which partly explain the individual susceptibility to the development of DTI and highlight the need for regular assessments of individual subjects.

Similar Mitochondrial Activation Kinetics in Wild-type and Creatine Kinase-deficient Fast-twitch Muscle Indicate Significant Pi Control of Respiration

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology. Jun, 2011  |  Pubmed ID: 21451138

Past simulations of oxidative ATP metabolism in skeletal muscle have predicted that elimination of the creatine kinase (CK) reaction should result in dramatically faster oxygen consumption dynamics during transitions in ATP turnover rate. This hypothesis was investigated. Oxygen consumption of fast-twitch (FT) muscle isolated from wild-type (WT) and transgenic mice deficient in the myoplasmic (M) and mitochondrial (Mi) CK isoforms (MiM CK(-/-)) were measured at 20°C at rest and during electrical stimulation. MiM CK(-/-) muscle oxygen consumption activation kinetics during a step change in contraction rate were 30% faster than WT (time constant 53 ± 3 vs. 69 ± 4 s, respectively; mean ± SE, n = 8 and 6, respectively). MiM CK(-/-) muscle oxygen consumption deactivation kinetics were 380% faster than WT (time constant 74 ± 4 s vs. 264 ± 4 s, respectively). Next, the experiments were simulated using a computational model of the oxidative ATP metabolic network in FT muscle featuring ADP and Pi feedback control of mitochondrial respiration (J. A. L. Jeneson, J. P. Schmitz, N. A. van den Broek, N. A. van Riel, P. A. Hilbers, K. Nicolay, J. J. Prompers. Am J Physiol Endocrinol Metab 297: E774-E784, 2009) that was reparameterized for 20°C. Elimination of Pi control via clamping of the mitochondrial Pi concentration at 10 mM reproduced past simulation results of dramatically faster kinetics in CK(-/-) muscle, while inclusion of Pi control qualitatively explained the experimental observations. On this basis, it was concluded that previous studies of the CK-deficient FT muscle phenotype underestimated the contribution of Pi to mitochondrial respiratory control.

Differential Effects of Short- and Long-term High-fat Diet Feeding on Hepatic Fatty Acid Metabolism in Rats

Biochimica Et Biophysica Acta. Jul-Aug, 2011  |  Pubmed ID: 21621638

Imbalance in the supply and utilization of fatty acids (FA) is thought to contribute to intrahepatic lipid (IHL) accumulation in obesity. The aim of this study was to determine the time course of changes in the liver capacity to oxidize and store FA in response to high-fat diet (HFD). Adult male Wistar rats were fed either normal chow or HFD for 2.5weeks (short-term) and 25weeks (long-term). Short-term HFD feeding led to a 10% higher palmitoyl-l-carnitine-driven ADP-stimulated (state 3) oxygen consumption rate in isolated liver mitochondria indicating up-regulation of β-oxidation. This adaptation was insufficient to cope with the dietary FA overload, as indicated by accumulation of long-chain acylcarnitines, depletion of free carnitine and increase in FA content in the liver, reflecting IHL accumulation. The latter was confirmed by in vivo((1))H magnetic resonance spectroscopy and Oil Red O staining. Long-term HFD feeding caused further up-regulation of mitochondrial β-oxidation (24% higher oxygen consumption rate in state 3 with palmitoyl-l-carnitine as substrate) and stimulation of mitochondrial biogenesis as indicated by 62% higher mitochondrial DNA copy number compared to controls. These adaptations were paralleled by a partial restoration of free carnitine levels and a decrease in long-chain acylcarnitine content. Nevertheless, there was a further increase in IHL content, accompanied by accumulation of lipid peroxidation and protein oxidation products. In conclusion, partially effective adaption of hepatic FA metabolism to long-term HFD feeding came at a price of increased oxidative stress, caused by a combination of higher FA oxidation capacity and oversupply of FA.

Pioglitazone Modulates Vascular Inflammation in Atherosclerotic Rabbits Noninvasive Assessment with FDG-PET-CT and Dynamic Contrast-enhanced MR Imaging

JACC. Cardiovascular Imaging. Oct, 2011  |  Pubmed ID: 21999870

We sought to determine the antiatherosclerotic properties of pioglitazone using multimethod noninvasive imaging techniques.

Target-specific Paramagnetic and Superparamagnetic Micelles for Molecular MR Imaging

Methods in Molecular Biology (Clifton, N.J.). , 2011  |  Pubmed ID: 21874503

Treatment of disease can only be effective when timely and accurate diagnosis of the pathology is achieved. More precise diagnosis can be accomplished if the underlying molecular processes involved in the pathology can be imaged in vivo. This is the field of molecular imaging, which aims to visualize cellular function and molecular processes in living organisms in a non-invasive way. With that aim, molecular markers are specifically targeted by imaging contrast agents. Molecular MRI needs powerful targeted contrast agents. For that purpose, target-specific gadolinium-containing paramagnetic and superparamagnetic, iron oxide-based micelles have been developed. Micelles are lipid-based nanoparticles which are biocompatible and carry a high payload of MR contrast-generating agent. The coupling of high-affinity ligands makes the micelles target-specific. Additionally, this lipid-based micelle platform allows for incorporation of contrast generating molecules for other imaging modalities, e.g., fluorescence or nuclear imaging. This permits applications for multiple imaging modalities, making micelles a highly versatile contrast agent.

Regional Contrast Agent Quantification in a Mouse Model of Myocardial Infarction Using 3D Cardiac T1 Mapping

Journal of Cardiovascular Magnetic Resonance : Official Journal of the Society for Cardiovascular Magnetic Resonance. , 2011  |  Pubmed ID: 21974927

Quantitative relaxation time measurements by cardiovascular magnetic resonance (CMR) are of paramount importance in contrast-enhanced studies of experimental myocardial infarction. First, compared to qualitative measurements based on signal intensity changes, they are less sensitive to specific parameter choices, thereby allowing for better comparison between different studies or during longitudinal studies. Secondly, T1 measurements may allow for quantification of local contrast agent concentrations. In this study, a recently developed 3D T1 mapping technique was applied in a mouse model of myocardial infarction to measure differences in myocardial T1 before and after injection of a liposomal contrast agent. This was then used to assess the concentration of accumulated contrast agent.

In Vivo Characterization of a New Abdominal Aortic Aneurysm Mouse Model with Conventional and Molecular Magnetic Resonance Imaging

Journal of the American College of Cardiology. Dec, 2011  |  Pubmed ID: 22133853

The goal of this study was to use noninvasive conventional and molecular magnetic resonance imaging (MRI) to detect and characterize abdominal aortic aneurysms (AAAs) in vivo.

Multitissue Assessment of in Vivo Postprandial Intracellular Lipid Partitioning in Rats Using Localized (1) H-[(13) C] Magnetic Resonance Spectroscopy

Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. Dec, 2011  |  Pubmed ID: 22213012

Excess accumulation of lipids in nonadipose tissues such as skeletal muscle and liver has been implicated in the development of obesity-related disorders, but the cause of this ectopic lipid overload remains unknown. The aim of this study was to determine in vivo postprandial lipid partitioning in rat skeletal muscle and liver, using localized (1) H-[(13) C] magnetic resonance spectroscopy in combination with the oral administration of (13) C-labeled lipids. Six rats were measured at baseline and 5 and 24 h after administration of 400 mg [U-(13) C]-labeled algal lipids. Five hours after administration, fractional (13) C enrichments of the lipid pools in muscle and liver were increased 3.9-fold and 4.6-fold (P < 0.05), respectively, indicating that part of the ingested lipids had been taken up by muscle and liver tissue. At 24 h, fractional (13) C enrichments of muscle and liver lipids were decreased 1.6-fold and 2.2-fold (P < 0.05), respectively, compared with the 5 h values. This can be interpreted as a depletion of (13) C-labeled lipids from the intracellular lipid pools as a consequence of lipid turnover. In conclusion, the novel application of (1) H-[(13) C] magnetic resonance spectroscopy in combination with the oral administration of (13) C-labeled lipids is applicable for the longitudinal assessment of in vivo lipid partitioning between multiple tissues. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

Contrast-enhanced MRI of Murine Myocardial Infarction - Part I

NMR in Biomedicine. Feb, 2012  |  Pubmed ID: 22308108

The use of contrast agents has added considerable value to the existing cardiac MRI toolbox that can be used to study murine myocardial infarction, as it enables detailed in vivo visualization of the molecular and cellular processes that occur in the infarcted and remote tissue. A variety of non-targeted and targeted contrast agents to study myocardial infarction are available and under development. Manganese, which acts as a calcium analogue, can be used to assess cell viability. Traditionally, low-molecular-weight Gd-containing contrast agents are employed to measure infarct size in a late gadolinium enhancement experiment. Gd-based blood-pool agents are used to study the vascular status of the myocardium. The use of targeted contrast agents facilitates more detailed imaging of pathophysiological processes in the acute and chronic infarct. Cell death was visualized by contrast agents functionalized with annexin A5 that binds specifically to phosphatidylserine accessible on dying cells and with an agent that binds to the exposed DNA of dead cells. Inflammation in the myocardium was depicted by contrast agents that target cell adhesion molecules expressed on activated endothelium, by contrast agents that are phagocytosed by inflammatory cells, and by using a probe that targets enzymes excreted by inflammatory cells. Cardiac remodeling processes were visualized with a contrast agent that binds to angiogenic vasculature and with an MR probe that specifically binds to collagen in the fibrotic myocardium. These recent advances in murine contrast-enhanced cardiac MRI have made a substantial contribution to the visualization of the pathophysiology of myocardial infarction, cardiac remodeling processes and the progression to heart failure, which helps to design new treatments. This review discusses the advances and challenges in the development and application of MRI contrast agents to study murine myocardial infarction. Copyright © 2012 John Wiley & Sons, Ltd.

Myofibrillar Distribution of Succinate Dehydrogenase Activity and Lipid Stores Differs in Skeletal Muscle Tissue of Paraplegic Subjects

American Journal of Physiology. Endocrinology and Metabolism. Feb, 2012  |  Pubmed ID: 22068603

Lack of physical activity has been related to an increased risk of developing insulin resistance. This study aimed to assess the impact of chronic muscle deconditioning on whole body insulin sensitivity, muscle oxidative capacity, and intramyocellular lipid (IMCL) content in subjects with paraplegia. Nine subjects with paraplegia and nine able-bodied, lean controls were recruited. An oral glucose tolerance test was performed to assess whole body insulin sensitivity. IMCL content was determined both in vivo and in vitro using (1)H-magnetic resonance spectroscopy and fluorescence microscopy, respectively. Muscle biopsy samples were stained for succinate dehydrogenase (SDH) activity to measure muscle fiber oxidative capacity. Subcellular distributions of IMCL and SDH activity were determined by defining subsarcolemmal and intermyofibrillar areas on histological samples. SDH activity was 57 ± 14% lower in muscle fibers derived from subjects with paraplegia when compared with controls (P < 0.05), but IMCL content and whole body insulin sensitivity did not differ between groups. In muscle fibers taken from controls, both SDH activity and IMCL content were higher in the subsarcolemmal region than in the intermyofibrillar area. This typical subcellular SDH and IMCL distribution pattern was lost in muscle fibers collected from subjects with paraplegia and had changed toward a more uniform distribution. In conclusion, the lower metabolic demand in deconditioned muscle of subjects with paraplegia results in a significant decline in muscle fiber oxidative capacity and is accompanied by changes in the subcellular distribution patterns of SDH activity and IMCL. However, loss of muscle activity due to paraplegia is not associated with substantial lipid accumulation in skeletal muscle tissue.

Molecular MRI of Inflammation in Atherosclerosis

Current Cardiovascular Imaging Reports. Feb, 2012  |  Pubmed ID: 22308200

Inflammatory activity in atherosclerotic plaque is a risk factor for plaque rupture and atherothrombosis and may direct interventional therapy. Inflammatory activity can be evaluated at the (sub)cellular level using in vivo molecular MRI. This paper reviews recent progress in contrast-enhanced molecular MRI to visualize atherosclerotic plaque inflammation. Various MRI contrast agents, among others ultra-small particles of iron oxide, low-molecular-weight Gd-chelates, micelles, liposomes, and perfluorocarbon emulsions, have been used for in vivo visualization of various inflammation-related targets, such as macrophages, oxidized LDL, endothelial cell expression, plaque neovasculature, MMPs, apoptosis, and activated platelets/thrombus. An enzyme-activatable magnetic resonance contrast agent has been developed to study myeloperoxidase activity in inflamed plaques. Agents creating contrast based on the chemical exchange saturation transfer mechanism were used for thrombus imaging. Transfer of these molecular MRI techniques to the clinic will critically depend on the safety profiles of these newly developed magnetic resonance contrast agents.

Contrast-enhanced MRI of Murine Myocardial Infarction - Part II

NMR in Biomedicine. Feb, 2012  |  Pubmed ID: 22311260

Mouse models are increasingly used to study the pathophysiology of myocardial infarction in vivo. In this area, MRI has become the gold standard imaging modality, because it combines high spatial and temporal resolution functional imaging with a large variety of methods to generate soft tissue contrast. In addition, (target-specific) MRI contrast agents can be employed to visualize different processes in the cascade of events following myocardial infarction. Here, the MRI sequence has a decisive role in the detection sensitivity of a contrast agent. However, a straightforward translation of clinically available protocols for human cardiac imaging to mice is not feasible, because of the small size of the mouse heart and its extremely high heart rate. This has stimulated intense research in the development of cardiac MRI protocols specifically tuned to the mouse with regard to timing parameters, acquisition strategies, and ECG- and respiratory-triggering methods to find an optimal trade-off between sensitivity, scan time, and image quality. In this review, a detailed analysis is given of the pros and cons of different mouse cardiac MR imaging methodologies and their application in contrast-enhanced MRI of myocardial infarction. Copyright © 2012 John Wiley & Sons, Ltd.

Diffusion-tensor MRI Reveals the Complex Muscle Architecture of the Human Forearm

Journal of Magnetic Resonance Imaging : JMRI. Feb, 2012  |  Pubmed ID: 22334539

PURPOSE: To design a time-efficient patient-friendly clinical diffusion tensor MRI protocol and postprocessing tool to study the complex muscle architecture of the human forearm. MATERIALS AND METHODS: The 15-minute examination was done using a 3 T system and consisted of: T(1) -weighted imaging, dual echo gradient echo imaging, single-shot spin-echo echo-planar imaging (EPI) diffusion tensor MRI. Postprocessing comprised of signal-to-noise improvement by a Rician noise suppression algorithm, image registration to correct for motion and eddy currents, and correction of susceptibility-induced deformations using magnetic field inhomogeneity maps. Per muscle one to five regions of interest were used for fiber tractography seeding. To validate our approach, the reconstructions of individual muscles from the in vivo scans were compared to photographs of those dissected from a human cadaver forearm. RESULTS: Postprocessing proved essential to allow muscle segmentation based on combined T(1) -weighted and diffusion tensor data. The protocol can be applied more generally to study human muscle architecture in other parts of the body. CONCLUSION: The proposed protocol was able to visualize the muscle architecture of the human forearm in great detail and showed excellent agreement with the dissected cadaver muscles. J. Magn. Reson. Imaging 2012;. © 2012 Wiley Periodicals, Inc.