The molecular mechanism(s) regulating hypoxia-induced vascular fibrosis are unresolved. Hyperaldosteronism correlates positively with vascular remodeling in pulmonary arterial hypertension, suggesting that aldosterone may contribute to the pulmonary vasculopathy of hypoxia. The hypoxia-sensitive transcription factors c-Fos/c-Jun regulate steroidogenic acute regulatory protein (StAR), which facilitates the rate-limiting step of aldosterone steroidogenesis. We hypothesized that c-Fos/c-Jun upregulation by hypoxia activates StAR-dependent aldosterone synthesis in human pulmonary artery endothelial cells (HPAECs) to promote vascular fibrosis in pulmonary arterial hypertension.
Pulmonary arterial hypertension (PAH) is associated with aberrant pulmonary vascular remodeling that leads to increased pulmonary artery pressure, pulmonary vascular resistance, and right ventricular dysfunction. There is now accumulating evidence that the renin-angiotensin-aldosterone system is activated and contributes to cardiopulmonary remodeling that occurs in PAH. Increased plasma and lung tissue levels of angiotensin and aldosterone have been detected in experimental models of PAH and shown to correlate with cardiopulmonary hemodynamics and pulmonary vascular remodeling. These processes are abrogated by treatment with angiotensin receptor or mineralocorticoid receptor antagonists. At a cellular level, angiotensin and aldosterone activate oxidant stress signaling pathways that decrease levels of bioavailable nitric oxide, increase inflammation, and promote cell proliferation, migration, extracellular matrix remodeling, and fibrosis. Clinically, enhanced renin-angiotensin activity and elevated levels of aldosterone have been detected in patients with PAH, which suggests a role for angiotensin and mineralocorticoid receptor antagonists in the treatment of PAH. This review will examine the current evidence linking renin-angiotensin-aldosterone system activation to PAH with an emphasis on the cellular and molecular mechanisms that are modulated by aldosterone and may be of importance for the pathobiology of PAH.
To establish a homing signal in the lung to recruit circulating stem cells for tissue repair, we formulated a nanoparticle, SDF-1? NP, by complexing SDF-1? with dextran sulfate and chitosan. The data show that SDF-1? was barely released from the nanoparticles over an extended period of time in vitro (3% in 7 days at 37 °C); however, incorporated SDF-1? exhibited full chemotactic activity and receptor activation compared to its free form. The nanoparticles were not endocytosed after incubation with Jurkat cells. When aerosolized into the lungs of rats, SDF-1? NP displayed a greater retention time compared to free SDF-1? (64 vs 2% remaining at 16 h). In a rat model of monocrotaline-induced lung injury, SDF-1? NP, but not free form SDF-1?, was found to reduce pulmonary hypertension. These data suggest that the nanoparticle formulation protected SDF-1? from rapid clearance in the lung and sustained its biological function in vivo.
Pulmonary hypertension (PH) is characterized by pathological changes to cell signaling pathways within the alveolar-pulmonary arteriole-right ventricular axis that results in increases in pulmonary vascular resistance and, ultimately, the development of right ventricular (RV) dysfunction. Cornerstone histopathological features of the PH vasculopathy include intimal thickening, concentric hypertrophy, and perivascular fibrosis of distal pulmonary arterioles. The presence of plexogenic lesions is pathognomonic of pulmonary arterial hypertension (PAH); when present, this severe form of remodeling is associated with subtotal obliteration of the blood vessel lumen. The extent of RV remodeling in PH correlates with clinical symptom severity and portends a poor outcome. Currently available PH-specific pharmacotherapies that aim to improve symptom burden by targeting pulmonary vasodilatory/vasoconstrictor cell signaling pathways do not fully reverse pulmonary vascular remodeling and, thus, are largely unsuccessful at maintaining normal cardiopulmonary hemodynamics long term. Thus, determining the molecular mechanisms that are responsible for pulmonary vascular remodeling in PH is of great potential therapeutic value, particularly pathways that promote apoptosis-resistant cellular proliferation, disrupt normal cellular bioenergetics to alter cell function, and/or modulate severely abnormal responses to pulmonary vascular injury. This chapter reviews current insights into PH pathophysiology and disease mechanisms, and discusses novel cell signaling pathways that implicate microRNAs and mitochondrial dysfunction in the development of the PH phenotype.
Pulmonary arterial hypertension (PAH) is characterized by dysregulated proliferation of pulmonary artery smooth muscle cells leading to (mal)adaptive vascular remodeling. In the systemic circulation, vascular injury is associated with downregulation of sarcoplasmic reticulum Ca(2+)-ATPase 2a (SERCA2a) and alterations in Ca(2+) homeostasis in vascular smooth muscle cells that stimulate proliferation. We, therefore, hypothesized that downregulation of SERCA2a is permissive for pulmonary vascular remodeling and the development of PAH.
In translational models of pulmonary arterial hypertension (PAH), spironolactone improves cardiopulmonary hemodynamics by attenuating the adverse effects of hyperaldosteronism on endothelin type-B receptor function in pulmonary endothelial cells. This observation suggests that coupling spironolactone with inhibition of endothelin type-A receptor-mediated pulmonary vasoconstriction may be a useful treatment strategy for patients with PAH. We examined clinical data from patients randomized to placebo or the selective endothelin type-A receptor antagonist ambrisentan (10 mg/day) and in whom spironolactone use was reported during ARIES-1 and -2, which were randomized, double-blind, placebo-controlled trials assessing the effect of ambrisentan for 12 weeks on clinical outcome in PAH. From patients randomized to placebo (n = 132) or ambrisentan (n = 67), we identified concurrent spironolactone use in 21 (15.9%) and 10 (14.9%) patients, respectively. Compared with patients treated with ambrisentan alone (n = 57), therapy with ambrisentan + spironolactone improved change in 6-minute walk distance by 94% at week 12 (mean ± SE, +38.2 ± 8.1 vs +74.2 ± 27.4 m, p = 0.11), improved plasma B-type natriuretic peptide concentration by 1.7-fold (p = 0.08), and resulted in a 90% relative increase in the number of patients improving ?1 World Health Organization functional class (p = 0.08). Progressive illness, PAH-associated hospitalizations, or death occurred as an end point for 5.3% of ambrisentan-treated patients; however, no patient treated with ambrisentan + spironolactone reached any of these end points. In conclusion, these pilot data suggest that coupling spironolactone and endothelin type-A receptor antagonism may be clinically beneficial in PAH. Prospective clinical trials are required to further characterize our findings.
Pulmonary hypertension includes heterogeneous diagnoses with distinct hemodynamic pathophysiologic features. Identifying elevated pulmonary vascular resistance (PVR) is critical for appropriate treatment. We reviewed data from patients seen at referral pulmonary hypertension clinics who had undergone echocardiography and right-side cardiac catheterization within 1 year. We derived equations to estimate PVR using the ratio of estimated pulmonary artery (PA) systolic pressure (PASPDoppler) to right ventricular outflow tract velocity time integral (VTI). We validated these equations in a separate sample and compared them with a published model based on the ratio of the transtricuspid flow velocity to right ventricular outflow tract VTI (model 1, Abbas et al 2003). The derived models were as follows: PVR = 1.2 × (PASP/right ventricular outflow tract VTI) (model 2) and PVR = (PASP/right ventricular outflow tract VTI) + 3 if notch present (model 3). The cohort included 217 patients with mean PA pressure of 45.3 ± 11.9 mm Hg, PVR of 7.3 ± 5.0 WU, and PA wedge pressure of 14.8 ± 8.1 mm Hg. Just >1/3 had a PA wedge pressure >15 mm Hg (35.5%) and 82.0% had PVR >3 WU. Model 1 systematically underestimated catheterization estimated PVR, especially for those with high PVR. The derived models demonstrated no systematic bias. Model 3 correlated best with PVR (r = 0.80 vs r = 0.73 and r = 0.77 for models 1 and 2, respectively). Model 3 had superior discriminatory power for PVR >3 WU (area under the curve 0.946) and PVR >5 WU (area under the curve 0.924), although all models discriminated well. Model 3-estimated PVR >3 was 98.3% sensitive and 61.1% specific for PVR >3 WU (positive predictive value 93%; negative predictive value 88%). In conclusion, we present an equation to estimate the PVR, using the ratio of PASPDoppler to right ventricular outflow tract VTI and a constant designating presence of right ventricular outflow tract VTI midsystolic notching, which provides superior agreement with catheterization estimates of PVR across a wide range of values.
The unique biochemical profile of homocysteine is characterized by chemical reactivity supporting a wide range of molecular effects and by a tendency to promote oxidant stress-induced cellular toxicity. Numerous epidemiological reports have established hyperhomocysteinemia as an independent risk factor for cardiovascular disease, cerebrovascular disease, dementia-type disorders, and osteoporosis-associated fractures. Although combined folic acid and B-vitamin therapy substantially reduces homocysteine levels, results from randomized placebo-controlled clinical trials testing the effect of vitamin therapy on outcome in these diseases have generally fallen short of expectations. These results have led some to abandon homocysteine monitoring in the management of patients with cardiovascular or cognitive disorders. These trials, however, have generally included patients with only mildly elevated homocysteine levels and have not addressed several clinical scenarios in which homocysteine reduction may be effective, including the primary prevention of atherothrombotic disease in individuals at low or intermediate risk, or those with severe hyperhomocysteinemia.
We present the case of a 57-year-old woman with no previous cardiovascular history in whom fatal right ventricular wall rupture was diagnosed by bedside echocardiography early in the management of an inferior wall acute myocardial infarction.
Hyperaldosteronism is associated with impaired endothelium-dependent vascular reactivity owing to increased reactive oxygen species and decreased bioavailable nitric oxide (NO(.)); however, the effects of aldosterone on vasodilatory signaling pathways in vascular smooth muscle cells (VSMC) remain unknown. Soluble guanylyl cyclase (GC) is a heterodimer that is activated by NO(.) to convert cytosolic GTP to cGMP, a second messenger required for normal VSMC relaxation. Here, we show that aldosterone (10(-9)-10(-7) mol/liter) diminishes GC activity by activating NADPH oxidase in bovine aortic VSMC to increase reactive oxygen species levels and induce oxidative posttranslational modification(s) of Cys-122, a beta(1)-subunit cysteinyl residue demonstrated previously to modulate NO(.) sensing by GC. In VSMC treated with aldosterone, Western immunoblotting detected evidence of GC beta(1)-subunit disulfide bonding, whereas mass spectrometry analysis of a homologous peptide containing the Cys-122-bearing sequence exposed to conditions of increased oxidant stress confirmed cysteinyl sulfinic acid (m/z 435), sulfonic acid (m/z 443), and disulfide (m/z 836) bond formation. The functional effect of these modifications was examined by transfecting COS-7 cells with wild-type GC or mutant GC containing an alanine substitution at Cys-122 (C122A). Exposure to aldosterone or hydrogen peroxide (H(2)O(2)) significantly decreased cGMP levels in cells expressing wild-type GC. In contrast, aldosterone or H(2)O(2) did not influence cGMP levels in cells expressing the mutant C122A GC, confirming that oxidative modification of Cys-122 specifically impairs GC activity. These findings demonstrate that pathophysiologically relevant concentrations of aldosterone increase oxidant stress to convert GC to an NO(.)-insensitive state, resulting in disruption of normal vasodilatory signaling pathways in VSMC.
Elevated levels of the mineralocorticoid hormone aldosterone are recognized as a modifiable contributor to the pathophysiology of select cardiovascular diseases due to left heart failure. In pulmonary arterial hypertension (PAH), pulmonary vascular remodelling induces right ventricular dysfunction and heart failure in the absence of left ventricular (LV) dysfunction. Hyperaldosteronism has emerged as a promoter of pulmonary vascular disease in experimental animal models of PAH; however, the extent to which hyperaldosteronism is associated with PAH in patients is unknown. Thus, the central aim of the current study is to determine if hyperaldosteronism is an unrecognized component of the PAH clinical syndrome.
Reactive oxygen species (ROS) have long been viewed as deleterious chemicals that lead to oxidative stress. More recently, ROS, especially the stable ROS hydrogen peroxide (H(2)O(2)), have been shown to have roles in normal physiological responses in vascular cells. Endothelial nitric oxide synthase (eNOS) is dynamically targeted to plasmalemmal caveolae, and represents the principal enzymatic source of nitric oxide (NO(•)) in the vascular wall. eNOS maintains normal vascular tone and inhibits the clinical expression of many cardiovascular diseases. Increases in oxidative stress are associated with eNOS dysfunction. In a paradigm shift in the conceptual framework linking redox biochemistry and vascular function, H(2)O(2) has been established as a physiological mediator in signaling pathways, yet the intracellular sources of H(2)O(2) and their regulation remain incompletely understood. The subcellular distributions of ROS and of ROS-modified proteins critically influence the redox-sensitive regulation of eNOS-dependent pathways. ROS localization in specific subcellular compartments can lead to selective oxidative modifications of eNOS and eNOS-associated proteins. Likewise, the dynamic targeting of eNOS and other signaling proteins influences their interactions with reactive nitrogen species and ROS that are also differentially distributed within the cell. Thus, the subcellular distribution both of eNOS and redox-active biomolecules serves as a critical basis for the control of the "redox switch" that influences NO(•)- and oxidant-regulated signaling pathways. Here we discuss the biochemical factors, cellular determinants, and molecular mechanisms that modulate redox-sensitive regulation of eNOS and NO(•) signaling under normal and pathological conditions.
Pulmonary arterial hypertension (PAH) is characterized, in part, by decreased endothelial nitric oxide (NO(·)) production and elevated levels of endothelin-1. Endothelin-1 is known to stimulate endothelial nitric oxide synthase (eNOS) via the endothelin-B receptor (ET(B)), suggesting that this signaling pathway is perturbed in PAH. Endothelin-1 also stimulates adrenal aldosterone synthesis; in systemic blood vessels, hyperaldosteronism induces vascular dysfunction by increasing endothelial reactive oxygen species generation and decreasing NO(·) levels. We hypothesized that aldosterone modulates PAH by disrupting ET(B)-eNOS signaling through a mechanism involving increased pulmonary endothelial oxidant stress.
Since their discovery in the early 1990s, S-nitrosylated proteins have been increasingly recognized as important determinants of many biochemical processes. Specifically, S-nitrosothiols in the cardiovascular system exert many actions, including promoting vasodilation, inhibiting platelet aggregation, and regulating Ca(2+) channel function that influences myocyte contractility and electrophysiologic stability.
Pulmonary hypertension (PH) is driven by diverse pathogenic etiologies. Owing to their pleiotropic actions, microRNA molecules are potential candidates for coordinated regulation of these disease stimuli.
Vascular remodeling of distal pulmonary arterioles that promotes abnormal pulmonary vascular reactivity is a central mechanism in the pathogenesis of pulmonary arterial hypertension (PAH). In selected patients, invasive pulmonary vasoreactivity testing performed in the cardiac catheterization laboratory with inhaled nitric oxide, epoprostenol, or adenosine is useful for PAH diagnosis, risk stratification, and assessing patient appropriateness for PAH-specific treatment(s). Limited accessibility to inhaled nitric oxide and a suboptimal test sensitivity profile reported for adenosine has contributed to the selection of epoprostenol for pulmonary vasoreactivity testing in some pulmonary hypertension referral centers. However, standardized procedural protocols for administrating epoprostenol for this purpose are largely unavailable to the practicing clinical community. The current work aims to bridge this gap by providing a stepwise procedure for the safe administration of clinically indicated intravenous epoprostenol during pulmonary vasoreactivity testing.
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