Circulating concentrations of vitamin D, 25(OH)D, and 1,25(OH)2D are lower in obese than lean individuals, but little is known about the adipose tissue content of these molecules. The aim of this study was to explore the possibility to use time-of-flight secondary ion mass spectrometry (TOF-SIMS) to measure vitamin D and its metabolites in fat tissue in obese and lean subjects. Abdominal subcutaneous adipose tissue (SAT) biopsies were obtained from three lean and three obese women, and paired biopsies SAT and visceral adipose tissue (VAT) were obtained from three obese subjects during gastric bypass surgery. TOF-SIMS was used to measure vitamin D3, 25(OH)D3, and 1,25(OH)2D3 in adipose tissue. We found that vitamin D3, 25(OH)D3, and 1,25(OH)2D3 in adipose tissue can be measured with TOF-SIMS. In adipose tissue, vitamin D3 and its metabolites were located in adipocyte lipid droplets. The content of vitamin D3 (P=0.006) and 25(OH)D3 (P=0.018) were lower in SAT in obese compared with lean women. TOF-SIMS has the potential to semi-quantitatively measure vitamin D metabolites in adipose tissue, and offers a possibility to compare vitamin D levels in different depots and groups of individuals. It also gives the opportunity to explore the localization of vitamin D metabolites at a cellular level.
Adipose tissue (AT) contributes to metabolic dysfunction through imbalanced production of adipokines, including cytokines. Visceral AT in particular is associated with metabolic disorders, indicating a specific secretory status. The relative significance of different human AT depots in adipokine release is not fully known. Further, previous in vitro systems usually included medium containing bovine serum albumin (BSA), which may induce cytokine release. Our aim was to compare release of a number of adipokines/cytokines - all implicated in insulin resistance - from human subcutaneous and visceral AT in a short-term incubation system minimizing cytokine induction and including repeated measurements during 24 h. A prerequisite was to evaluate a potential alternative to BSA in the incubation medium.
In rats with dihydrotestosterone (DHT)-induced polycystic ovary syndrome (PCOS), repeated low-frequency electrical stimulation of acupuncture needles restores whole-body insulin sensitivity measured by euglycemic hyperinsulinemic clamp. We hypothesized that electrical stimulation causing muscle contractions and manual stimulation causing needle sensation have different effects on insulin sensitivity and related signaling pathways in skeletal muscle and adipose tissue, with electrical stimulation being more effective in DHT-induced PCOS rats. From age 70 days, rats received manual or low-frequency electrical stimulation of needles in abdominal and hind limb muscle five times/wk for 4-5 wks; controls were handled but untreated rats. Low-frequency electrical stimulation modified gene expression (decreased Tbc1d1 in soleus, increased Nr4a3 in mesenteric fat) and protein expression (increased pAS160/AS160, Nr4a3 and decreased GLUT4) by western blot and increased GLUT4 expression by immunohistochemistry in soleus muscle; glucose clearance during oral glucose tolerance tests was unaffected. Manual stimulation led to faster glucose clearance and modified mainly gene expression in mesenteric adipose tissue (increased Nr4a3, Mapk3/Erk, Adcy3, Gsk3b), but not protein expression to the same extent; however, Nr4a3 was reduced in soleus muscle. The novel finding is that electrical and manual muscle stimulation affect glucose homeostasis in DHT-induced PCOS rats through different mechanisms. Repeated electrical stimulation regulated key functional molecular pathways important for insulin sensitivity in soleus muscle and mesenteric adipose tissue to a larger extent than manual stimulation. Manual stimulation improved whole-body glucose tolerance, an effect not observed after electrical stimulation, but did not affect molecular signaling pathways to the same extent as electrical stimulation. Although more functional signaling pathways related to insulin sensitivity were affected by electrical stimulation, our findings suggest that manual stimulation of acupuncture needles has a greater effect on glucose tolerance. The underlying mechanism of the differential effects of the intermittent manual and the continuous electrical stimulation remains to be elucidated.
Diet is a significant modifiable risk factor for cardiovascular disease and high fish intake has been associated with vascular health in population studies. However, intervention studies have been inconclusive. In this study, male low-density lipoprotein receptor-deficient mice were given 16-week high fat/high sucrose diets, supplemented with either minced herring fillets or minced beef. The diets were matched in total fat and cholesterol content; taurine content and fatty acid composition was analysed. Body weights were recorded throughout the study; plasma lipids were analysed at week 8 and 16. Body composition and adipocyte size were evaluated at study end. Atherosclerosis was evaluated at week 12 (ultrasound) and at termination (en face histology). Herring-fed mice had a higher proportion of long-chain n-3 polyunsaturated fatty acids in the hepatic triacylglycerides (TAG) and phospholipid fractions. The herring-fed mice had increased body weight (P=0.007), and reduced epididymal adipocyte size (P=0.009), despite similar food intake and body composition as the beef-fed mice. The herring-fed mice had lower plasma TAG and very-low-density lipoprotein (VLDL)-cholesterol concentrations throughout the study (TAG; P=0.0012 and 0.004, VLDL-cholesterol; P=0.006 and 0.041, week 8 and 16, respectively). At week 16, the herring-fed had higher plasma concentrations of HDL-cholesterol (P=0.004) and less atherosclerotic lesions in the aortic arch (P=0.007) compared with the beef-fed mice. In conclusion, dietary herring in comparison to beef markedly improved vascular health in this mouse model, suggesting that herring provides an added value beyond its content of macronutrients.
To investigate the possible effects of low-frequency electroacupuncture (EA) and physical exercise on markers of coagulation and fibrinolysis, insulin sensitivity, and adipose tissue characteristics in women with polycystic ovary syndrome (PCOS).
The perinatal environment appears important in establishing metabolic phenotypes in adulthood. Mice deficient in IL-6 (IL-6(-/-)) tend to develop mature-onset obesity, but it is unknown whether perinatal exposure to IL-6 produced by the dam influences the metabolism of adult offspring. To address this issue, we monitored IL-6(-/-) offspring of IL-6(-/-) or IL-6(+/-) dams, as well as wild-type (WT) mice. At adult age, IL-6(-/-) mice weighed significantly more and had more body fat than WT mice, regardless of maternal genotype, and had lower insulin sensitivity. This phenotype was more pronounced in IL-6(-/-) offspring of IL-6(-/-) dams, because they gained weight significantly faster than IL-6(-/-) offspring of IL-6(+/-) dams and had more body fat and higher serum leptin levels at an earlier age. The leptin content was 2-fold higher in milk from IL-6(-/-) than WT dams. However, cross-fostering IL-6(-/-) mice with WT dams did not alter body weight, body composition, or adipocyte size at adult age compared with IL-6(-/-) mice fostered by IL-6(-/-) dams. Conversely, WT mice fostered by IL-6(-/-) dams weighed significantly more than those fostered by WT dams and had more body fat, larger adipocytes, and altered hypothalamic gene expression. We conclude that body fat of adult mice can be increased by perinatal exposure to factors affected by lack of maternal IL-6.
Comprehensive characterization of the adipose tissue in women with polycystic ovary syndrome (PCOS), over a wide range of body mass indices (BMIs), is lacking. Mechanisms behind insulin resistance in PCOS are unclear.
Polycystic ovary syndrome (PCOS) is associated with hyperandrogenism and insulin resistance, possibly reflecting defects in skeletal muscle and adipocyte insulin signaling. Low-frequency (2 Hz) electroacupuncture (EA) increases insulin sensitivity in female rats with dihydrotestosterone (DHT)-induced PCOS, but the mechanism is unclear. We hypothesized that low-frequency EA regulates mediators involved in skeletal muscle glucose uptake and metabolism and alters the lipid profile in rats with DHT-induced PCOS. To test this hypothesis, we implanted in prepubescent female rats 90-day continuous-release pellets containing DHT (PCOS). At 70 days of age, the rats were randomly subdivided into two groups: one received low-frequency EA (evoking muscle twitches) for 20-25 min five times/wk for 4-5 wk; the other did not. Controls were implanted with pellets containing vehicle only. All three groups were otherwise handled similarly. Lipid profile was measured in fasting blood samples. Insulin sensitivity was determined by euglycemic hyperinsulinemic clamp, soleus muscle protein expression of glucose transporter 4 (GLUT4), and phosphorylated and nonphosphorylated Akt, and Akt substrate of 160 kDa was determined by Western blot analysis and GLUT4 location by immunofluorescence staining. PCOS EA rats had normalized insulin sensitivity, lower levels of total high-density lipoprotein and low-density lipoprotein cholesterol, and increased expression of GLUT4 in different compartments of skeletal muscle compared with PCOS rats. Total weight and body composition did not differ in the groups. Thus, in rats with DHT-induced PCOS, low-frequency EA has systemic and local effects involving intracellular signaling pathways in muscle that may, at least in part, account for the marked improved insulin sensitivity.
Enlarged subcutaneous abdominal adipocytes have been shown to predict incidence of type 2 diabetes (T2D) in the Pima population of Arizona (USA). We investigated the role of subcutaneous abdominal adipocyte size (AAS), as well as femoral adipocyte size (FAS), as predictors of T2D in a population-based Swedish cohort. In 1974-1975, a sample of 1302 middle-aged women underwent a health examination, including anthropometry and evaluation of parental medical history. In addition, body composition (total body potassium and total body water), AAS and FAS (adipose tissue needle biopsy) were assessed in a subsample of 245 women. Incidence of T2D was followed until 2001, with 36 cases eligible for inclusion in this analysis. Women developing T2D had larger AAS at baseline vs. women remaining healthy (age/heredity-adjusted hazard ratio for increase of AAS by 1 sd [AAS-HR] 1.91; P<0.001). Further adjustment for both body fat percentage and waist-to-height ratio (WHtR) indicated a robust association. For FAS, the corresponding associations were consistently weaker. WHtR retained a strong predictive association independent of AAS and FAS (WHtR-HR 2.6 and 2.7, respectively; P<0.001). To conclude, in addition to the amount and distribution of body fat in women, subcutaneous adipocyte size, particularly in the abdominal region, predicts incidence of T2D in later life.
Events during early life can affect reproductive and metabolic functions in adulthood. We evaluated the programming effects of a single early postnatal estradiol injection (within 3h after birth) in female rats. We assessed ovarian and parametrial adipose tissue morphology, evaluated gene expression related to follicular development and adipose tissue metabolism, and developed a non-invasive volumetric estimation of parametrial adipose tissue by magnetic resonance imaging. Estradiol reduced ovarian weight, increased antral follicle size and number of atretic antral follicles, and decreased theca interna thickness in atretic antral follicles. Adult estradiol-injected rats also had malformed vaginal openings and lacked corpora lutea, confirming anovulation. Estradiol markedly reduced parametrial adipose tissue mass. Adipocyte size was unchanged, suggesting reduced adipocyte number. Parametrial adipose tissue lipoprotein lipase activity was increased. In ovaries, estradiol increased mRNA expression of adiponectin, complement component 3, estrogen receptor ?, and glucose transporter 3 and 4; in parametrial adipose tissue, expression of complement component 3 was increased, expression of estrogen receptor ? was decreased, and expression of leptin, lipoprotein lipase, and hormone-sensitive lipase was unaffected. These findings suggest that early postnatal estradiol exposure of female rats result in long-lasting effects on the ovary and parametrial adipose tissue at adult age.
Early postnatal events can predispose to metabolic and endocrine disease in adulthood. In this study, we evaluated the programming effects of a single early postnatal oestradiol injection on insulin sensitivity in adult female rats. We also assessed the expression of genes involved in inflammation and glucose metabolism in skeletal muscle and adipose tissue and analysed circulating inflammation markers as possible mediators of insulin resistance. Neonatal oestradiol exposure reduced insulin sensitivity and increased plasma levels of monocyte chemoattractant protein-1 (MCP-1) and soluble intercellular adhesion molecule-1. In skeletal muscle, oestradiol increased the expression of genes encoding complement component 3 (C3), Mcp-1, retinol binding protein-4 (Rbp4) and transforming growth factor beta1 (Tgfbeta1). C3 and MCP-1 are both related to insulin resistance, and C3, MCP-1 and TGFbeta1 are also involved in inflammation. Expression of genes encoding glucose transporter-4 (Glut 4), carnitine-palmitoyl transferase 1b (Cpt1b), peroxisome proliferator-activated receptor delta (Ppard) and uncoupling protein 3 (Ucp3), which are connected to glucose uptake, lipid oxidation, and energy uncoupling, was down regulated. Expression of several inflammatory genes in skeletal muscle correlated negatively with whole-body insulin sensitivity. In s.c. inguinal adipose tissue, expression of Tgfbeta1, Ppard and C3 was decreased, while expression of Rbp4 and Cpt1b was increased. Inguinal adipose tissue weight was increased but adipocyte size was unaltered, suggesting an increased number of adipocytes. We suggest that early neonatal oestrogen exposure may reduce insulin sensitivity by inducing chronic, low-grade systemic and skeletal muscle inflammation and disturbances of glucose and lipid metabolism in skeletal muscle in adulthood.
Altered activity of the sympathetic nervous system, which innervates adipose and ovarian tissue, may play a role in polycystic ovary syndrome (PCOS). We hypothesize that electro-acupuncture (EA) and physical exercise reduce sympathetic activity by stimulating ergoreceptors and somatic afferent pathways in muscles. Here we investigated the effects of low-frequency EA and physical exercise on mRNA expression of sympathetic markers in adipose tissue and on ovarian morphology in female rats that received dihydrotestosterone (DHT) continuously, starting before puberty, to induce PCOS. At age 11 wk, rats with DHT-induced PCOS were randomly divided into three groups: PCOS, PCOS plus EA, and PCOS plus exercise. The latter two groups received 2-Hz EA (evoking muscle twitches) three times/week or had free access to a running wheel for 4-5 wk. In mesenteric adipose tissue, expression of beta(3)-adrenergic receptor (ADRB3), nerve growth factor (NGF), and neuropeptide Y (NPY) mRNA was higher in untreated PCOS rats than in controls. Low-frequency EA and exercise downregulated mRNA expression of NGF and NPY, and EA also downregulated expression of ADRB3, compared with untreated rats with DHT-induced PCOS. EA and exercise improved ovarian morphology, as reflected in a higher proportion of healthy antral follicles and a thinner theca interna cell layer than in untreated PCOS rats. These findings support the theory that increased sympathetic activity contributes to the development and maintenance of PCOS and that the effects of EA and exercise may be mediated by modulation of sympathetic outflow to the adipose tissue and ovaries.
Studying the mechanisms for the complex pathogenesis of polycystic ovary syndrome (PCOS) requires animal models with endocrine, reproductive, and metabolic features of the syndrome. Hyperandrogenism seems to be a central factor in PCOS, leading to anovulation and insulin resistance. In female rats, continuous administration of letrozole, a nonsteroidal inhibitor of P450 aromatase, at 400 ?g/d starting before puberty induces hyperandrogenemia and reproductive abnormalities similar to those in women with PCOS. However, despite high circulating testosterone levels, these rats do not develop metabolic abnormalities, perhaps because of their supraphysiological testosterone concentrations or because estrogen synthesis is completely blocked in insulin-sensitive tissues. To test the hypothesis that continuous administration of lower doses of letrozole starting before puberty would result in both metabolic and reproductive phenotypes of PCOS, we performed a 12-wk dose-response study. At 21 d of age, 46 female Wistar rats were divided into two letrozole groups (100 or 200 ?g/d) and a control group (placebo). Both letrozole doses resulted in increased body weight, inguinal fat accumulation, anovulation, larger ovaries with follicular atresia and multiples cysts, endogenous hyperandrogemia, and lower estrogen levels. Moreover, rats that received 200 ?g/d had insulin resistance and enlarged adipocytes in inguinal and mesenteric fat depots, increased circulating levels of LH, decreased levels of FSH, and increased ovarian expression of Cyp17a1 mRNA. Thus, continuous administration of letrozole, 200 ?g/d, to female rats for 90 d starting before puberty results in a PCOS model with reproductive and metabolic features of the syndrome.
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