Atrial natriuretic peptide inhibits the production of adipokines and cytokines linked to inflammation and insulin resistance in human subcutaneous adipose tissue

Aims/hypothesis Increased adipose tissue secretion of adipokines and cytokines has been implicated in the chronic low-grade inflammation state and insulin resistance associated with obesity. We tested here whether the cardiovascular and metabolic hormone atrial natriuretic peptide (ANP) was able to modulate adipose tissue secretion of several adipokines (derived from adipocytes) and cytokines (derived from adipose tissue macrophages). Subjects and methods We used protein array to measure the secretion of adipokines and cytokines after a 24-h culture of human subcutaneous adipose tissue pieces treated or not with a physiological concentration of ANP. The effect of ANP on protein secretion was also directly studied on isolated adipocytes and macrophages. Gene expression was measured by real-time RT-quantitative PCR. Results ANP decreased the secretion of the pro-inflammatory cytokines IL-6 and TNF-α, of several chemokines, and of the adipokines leptin and retinol-binding protein-4 (RBP-4). The secretion of the anti-inflammatory molecules IL-10 and adiponectin remained unaffected. The cytokines were mainly expressed in macrophages that expressed all components of the ANP-dependent signalling pathway. The adipokines, leptin, adiponectin and RBP-4 were specifically expressed in mature adipocytes. ANP directly inhibited the secretion of IL-6 and monocyte chemoattractant protein-1 by macrophages. The inhibitory effects of ANP on leptin and growth-related oncogene-α secretions were not seen under selective hormone-sensitive lipase inhibition. Conclusions/interpretation We suggest that ANP, either by direct action on adipocytes and macrophages or through activation of adipocyte hormone-sensitive lipase, inhibits the secretion of factors involved in inflammation and insulin resistance.     

Hypoadiponectinemia as a marker of adipocyte dysfunction--part II: the functional significance of low adiponectin secretion

Low adiponectin expression is common in obesity and is tightly linked to insulin resistance and fat mass expansion. Whereas normal adipocytes offer effective metabolic buffering through well-controlled release and uptake of free fatty acids on demand, adipocyte expansion induced by caloric excess and modulated by genetic, regional, and systemic factors elicits major unfavorable changes in fat cell phenotypes. Large, dysfunctional adipocytes show increased lipolysis and enhanced expression and secretion of proinflammatory and pro-oxidative cytokines. Low adiponectin secretion is a hallmark of impaired adipocyte function; its secretion is inhibited by cytokines such as tumor necrosis factor alpha, interleukin 6 and plasminogen activator inhibitor 1 and by high oxidative stress induced by increased fatty acids that activate nicotinamide adenine dinucleotide phosphate-oxidase. The ensuing hypoadiponectinemia may aggravate insulin resistance and facilitate the evolution of type 2 diabetes. Only massive weight loss allows true and sustained recovery of normal fat cell function as reflected by adiponectin secretion.     

Relationship between adipocyte size and adipokine expression and secretion

CONTEXT: Adipocytes are known to release a variety of factors that may contribute to the proinflammatory state characteristic for obesity. This secretory function is considered to provide the basis for obesity-related complications such as type 2 diabetes and atherosclerosis. OBJECTIVE: To get a better insight into possible underlying mechanisms, we investigated the effect of adipocyte size on adipokine production and secretion. DESIGN, PATIENTS, AND MAIN OUTCOME MEASURES: Protein secretion and mRNA expression in cultured adipocytes separated according to cell size from 30 individuals undergoing elective plastic surgery were investigated. RESULTS: The mean adipocyte volume of the four fractions ranged from 205 +/- 146 to 1.077 +/- 471 pl. There were strong linear correlations for the secretion of adipokines over time. Secretion of leptin, IL-6, IL-8, TNF-alpha, monocyte chemoattractant protein-1, interferon-gamma-inducible protein 10, macrophage inflammatory protein-1beta, granulocyte colony stimulating factor, IL-1ra, and adiponectin was positively correlated with cell size. After correction for cell surface, there was still a significant difference between fraction IV (very large) and fraction I (small cells), for leptin, IL-6, IL-8, monocyte chemoattractant protein-1, and granulocyte colony-stimulating factor. In contrast, antiinflammatory factors such as IL-1ra and adiponectin lost their association after correction for cell surface area comparing fraction I and IV. In addition, there was a decrease of IL-10 secretion with increasing cell size. CONCLUSIONS: The results clearly suggest that adipocyte size is an important determinant of adipokine secretion. There seems to be a differential expression of pro- and antiinflammatory factors with increasing adipocyte size resulting in a shift toward dominance of proinflammatory adipokines largely as a result of a dysregulation of hypertrophic, very large cells.     

Adipocytokine changes caused by low-carbohydrate compared to conventional diets in obesity

Modest weight loss causing a decrease in insulin resistance has been linked to favorable changes in the adipocyte cytokines leptin, adiponectin, and tumor necrosis factor-alpha (TNF-alpha), three emerging risk factors of cardiovascular disease. We previously observed a significant reduction in insulin resistance with weight loss in obese subjects on a low-carbohydrate diet. Based on these previous findings, we hypothesize that a low-carbohydrate diet would be more beneficial in changing leptin, TNF-alpha, and adiponectin than a conventional diet. A total of 75 severely obese (body mass index >/=35 kg/m(2)) subjects were randomized to instruction of 6 months of a low-carbohydrate diet or a conventional calorie-restricted diet. Serum levels of leptin, TNF-alpha, TNF-alpha-soluble receptor 1 (TNF-alpha SR1), and adiponectin were measured at baseline and after 6 months of dietary intervention. Subjects on low-carbohydrate diets experienced a greater decrease in leptin when compared to conventional dieters (p < 0.001). TNF-alpha increased significantly in nondiabetic subjects on conventional vs. low-carbohydrate diets (p = 0.003). Adiponectin and TNF-alpha SR1 change were not significantly different between diets. This is the first study to report the effects of dietary macronutrient alterations on serum adipocytokines in a randomized controlled trial. The greater reduction in insulin resistance and weight on a low-carbohydrate diet, in the short term, translates into greater improvement in leptin but with no significant improvements in TNF-alpha or adiponectin in patients with moderate to severe obesity after 6 months of dietary intervention.     

Hormonal regulation of interleukin-6 production in human adipocytes

OBJECTIVE: To elucidate the hormonal regulation of interleukin-6 (IL-6) production by human adipose tissue and its relation to leptin. DESIGN: In vitro study. Human adipocytes were incubated with dexamethasone (with or without RU486), norepinephrine and epinephrine (with or without propranolol), or insulin. MEASUREMENTS: IL-6 and leptin secretion by human adipocytes. RESULTS: A gradual increase in IL-6 secretion by adipocytes during differentiation was observed. A positive correlation was found between basal IL-6 release and both glycerol 3-phosphate dehydrogenase activity--a marker of adipocyte differentiation-and leptin release. Dexamethasone decreased IL-6 secretion and increased leptin secretion in a dose-dependent manner. Both catecholamines increased IL-6 and leptin secretion. The effects of dexamethasone and catecholamines on IL-6 and leptin were abrogated by RU486 and propranolol, respectively. Incubation with insulin resulted in a dose-dependent stimulation of IL-6 and leptin secretion. CONCLUSIONS: IL-6 is produced by human adipocytes and is a potential marker of adipocyte differentiation. Furthermore it is a hormonally regulated cytokine, suppressed by glucocorticoids, and stimulated by catecholamines and insulin in physiological concentrations.     

Synergistic effects of ascorbic acid and thiazolidinedione on secretion of high molecular weight adiponectin from human adipocytes

Aim: To test the hypothesis that ascorbic acid (AA) and thiazolidinedione (TZD) would have additive effects on HMW adiponectin secretion by virtue of different modes of action. Methods: We determined the effects of supplementation of AA and/or TZD on expression and secretion of total and HMW adiponectin from human Simpson–Golabi–Behmel syndrome (SGBS) adipocytes in the absence or presence of the proinflammatory cytokine TNFα. Results: AA supplementation significantly increased secretion of HMW adiponectin (1.7‐fold) without altering adiponectin expression or total adiponectin secretion. TZD significantly increased expression (3‐fold) and secretion of total (1.4‐fold) but not HMW adiponectin. Combined supplementation resulted in a significant increase in expression (3‐fold) and secretion of total (1.8‐fold) and HMW (5‐fold) adiponectin. Similar results were seen in cells co‐treated with TNFα. Conclusions: These data show that AA and TZD have synergistic rather than simple additive effects on secretion of HMW adiponectin from human adipocytes and raise the possibility that differences in AA levels may contribute to the variability in adiponectin multimer profiles and efficacy of TZD in humans. Our results also provide a rationale for longitudinal clinical trials investigating the effects of AA supplementation with or without TZD on adiponectin and metabolic profiles.     

性激素对脂肪细胞瘦素和脂联素分泌的影响

目的 观察性激素对前脂肪细胞增殖与分化及脂肪细胞瘦素脂联素分泌的影响.方法 原代培养人大网膜前脂肪细胞,观察其增殖、分化过程.性激素作用前脂肪细胞增殖和分化过程,检测瘦素、脂联素分泌及mRNA水平.结果 成功地培养出人大网膜前脂肪细胞.雌二醇促进前脂肪细胞增殖(0.823±0.059对0.276±0.032,P＜0.05)、抑制分化(P＜0.05);睾酮对前脂肪细胞增殖无明显作用,但抑制分化(P＜0.05).前脂肪细胞增殖及分化期均分泌瘦素.雌二醇促进瘦素分泌,而睾酮抑制(均P＜0.05).脂联素仅在分化期分泌,且性激素抑制其分泌.雌二醇促进瘦素mRNA表达但抑制脂联素mRNA表达;睾酮抑制瘦素、脂联素mRNA表达(均P＜0.05).结论 雌二醇促进脂肪细胞瘦素分泌及mRNA表达,抑制脂联素分泌及mRNA表达;睾酮抑制二者分泌及mRNA表达.     

脂联素在非酒精性脂肪肝中的作用及机制

脂联素是由脂肪细胞分泌的胰岛素敏感性脂肪因子,其对非酒精性脂肪肝病(NAFLD)有多种有益作用.在循环中脂联素有3种低聚亚型,包括三聚体、六聚体及高分子量低聚复合物.脂联素通过与靶器官上脂联素受体结合来发挥效应,其保肝作用已经在临床和实验室研究中证明.脂联素的下降是NAFLD及肝脏功能损害的独立危险因素.在动物实验中,通过药物或基因疗法使循环中的脂联素增高可导致肝肿大、脂肪变、坏死炎症及其相关肝脏疾病.脂联素敲除的小鼠,会发生肝脂肪变和线粒体功能损害,这致使小鼠易于遭受脂肪肝病的二次打击.本文旨在综述近年来对于脂联素在NAFLD中的保肝作用及机制的研究成果.     

Effects of tumor necrosis factor alpha on leptin secretion and gene expression: relationship to changes of glucose metabolism in isolated rat adipocytes.

OBJECTIVE: Our objective was to determine the effects of prolonged exposure to tumor necrosis factor-alpha (TNF-alpha) on leptin secretion from and leptin (OB) gene expression in isolated adipocytes. Because glucose uptake and the metabolism of glucose beyond lactate are important determinants of leptin production in adipocytes, we examined the effects of TNF-alpha on glucose uptake and lactate production and their relationship to leptin secretion. DESIGN AND METHODS: Isolated rat adipocytes were anchored in a defined matrix of basement membrane components and cultured with media containing 5 mM glucose, 0.16 nM insulin and several concentrations of TNF-alpha. Leptin secretion, steady-state levels of leptin mRNA levels, glucose uptake, and lactate production were assessed over 96 h. RESULTS: TNF-alpha at concentrations of 0.024, 0.24, 2.4 and 24 ng/ml did not affect leptin secretion over 24 h. TNF-alpha at concentrations of 0.24 to 24 ng/ml significantly inhibited leptin secretion over 96 h by 19-60%. TNF-alpha at concentrations of 0.024 to 24 ng/ml significantly decreased steady-state levels of leptin mRNA after 96 h by 32-95%. In addition, TNF-alpha at concentrations of 2.4 and 24 ng/ml significantly increased glucose uptake and lactate production over 96 h by 30-57%. TNF-alpha at a concentration of 0.024 ng/ml did not affect leptin secretion, glucose uptake or lactate production. Overall, for the TNF-alpha concentrations tested, leptin secretion was inversely related to the percent of glucose carbon released as lactate; however, TNF-alpha did not induce a proportional increase of lactate production from glucose. CONCLUSION: Short-term (24 h) exposure of isolated adipocytes to TNF-alpha does not affect leptin secretion. Prolonged exposure to TNF-alpha produces a concentration-dependent inhibition of leptin secretion and gene expression. This suggests that the acute effect of TNF-alpha to increase circulating leptin levels in vivo may be indirect. TNF-alpha at higher concentrations increases glucose uptake, but does not increase the conversion of glucose to lactate. Therefore, TNF-alpha appears to induce a dissociation between adipocyte glucose metabolism and leptin production.     

Association of the leptin to high-molecular-weight adiponectin ratio with metabolic syndrome

Recent studies have reported that leptin and adiponectin are associated with metabolic syndrome. The leptin/adiponectin ratio has been suggested as an atherosclerotic index. The objective of this study was to compare the degree of association of metabolic syndrome with adiponectin levels, leptin levels, leptin/adiponectin ratio, and leptin/high-molecular-weight (HMW) adiponectin ratio. The study population included 3272 Koreans (men: 1915, women: 1357; age, 30-84 years), who had visited the Health Examination Center. Adipokines were divided into quartiles, and metabolic syndrome was defined by the National Cholesterol Education Program Adult Treatment Panel-III (NCEP ATP III). A logistic regression model was fitted to establish the association between adipokines and metabolic syndrome. Adipokines, such as adiponectin, HMW adiponectin, and leptin, were found to be statistically related to metabolic syndrome. Compared to the lowest quartile, the leptin/HMW adiponectin ratio in the highest quartile was associated with a 5-fold increase in the probability of prevalent metabolic syndrome, which was independent of age, smoking status, exercise, low-density lipoprotein (LDL) cholesterol, and body mass index. There was a linear increase in the leptin/HMW adiponectin ratio as the number of metabolic syndrome components increased. The leptin/HMW adiponectin ratio had the highest odds ratio in women. In addition, compared to adiponectin or leptin alone, the AUC of the leptin/adiponectin ratio and leptin/HMW adiponectin ratio was higher for metabolic syndrome. We may suggest that the leptin/HMW adiponectin ratio is not superior to other adipokine markers, but is as effective as the leptin/total adiponectin ratio.     

Effect of weight loss induced by gastric bypass on proinflammatory interleukin-18, soluble tumour necrosis factor-alpha receptors, C-reactive protein and adiponectin in morbidly obese patients

OBJECTIVE: Interleukin-18 (IL-18) is a potent proinflammatory cytokine whose role in human obesity has recently been suggested. The aim of our study was to analyse in morbidly obese patients undergoing gastric bypass, the relationship of IL-18 with insulin resistance and with proinflammatory cytokines (tumour necrosis factor-alpha receptors, sTNFR), C-reactive protein (CRP) and with adiponectin. DESIGN: Observational and prospective study. PATIENTS: Sixty-five morbidly obese patients, aged 45 +/- 8.9 years, were studied before and 12 months after gastric bypass. MEASUREMENTS: We analysed plasma concentrations of IL-18, sTNFR, CRP and adiponectin. RESULTS: Plasma concentrations of sTNFR2, IL-18 and CRP were decreased and adiponectin significantly increased after bypass surgery. In the multiple regression analysis, preoperative values of IL-18 remained significantly associated with preoperative triglycerides (beta = 0.47, P = 0.005) and TNFR2 (beta = 0.47, P = 0.004). R(2) for the model = 0.38. Postoperative IL-18 concentrations in the multiple regression analysis were significantly associated with postoperative homeostasis model assessment of insulin resistance (HOMA-IR) (beta = 0.092, P = 0.019) and triglycerides (beta = 0.40, P = 0.036). R(2) for the model = 0.46. IL-18 did not correlate with body mass index, fat mass, fat-free mass or body fat. No relationship was either found between adiponectin and IL-18, TNFR1 and -2 and CRP. CONCLUSIONS: Massive weight loss induced by gastric bypass reduces IL-18, TNFR2 and CRP. IL-18 might be a marker of the chronic inflammatory process underlying insulin resistance but its lack of association with anthropometric and body composition parameters does not support a major secretion by human adipocytes. IL-18 and sTNFR1 and -2 do not play a main role in the inhibition of the secretion of adiponectin.     

Fenofibrate increases high molecular weight adiponectin in subjects with hypertriglyceridemia

Beneficial effects of peroxisome proliferator-activated receptor alpha (PPAR alpha) agonists have been reported in improving insulin sensitivity and raising serum total adiponectin. High molecular weight (HMW) adiponectin, which is secreted from adipocytes, and visfatin, which is also expressed in adipose tissue, is related to glucose metabolism. In view of the additive effects of PPAR alpha agonists on these adipocytokines and glucose metabolism, we investigated male hypertriglyceridemic subjects who were treated with fenofibrate. Eleven male subjects with hypertriglyceridemia were treated with fenofibrate and serum total cholesterol (T-cho), triglyceride, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), fasting glucose, fasting insulin, total and HMW adiponectin, and serum visfatin levels were determined before and 3 months after treatment. Fenofibrate treatment significantly lowered T-cho, triglyceride, and LDL-C levels. There was a statistically significant increase of HDL-C. No differences in insulin sensitivity indices (G/I ratio and HOMA-IR) were observed between before and after treatment with fenofibrate. The treatment did not alter the levels of serum total adiponectin and visfatin in the hypertriglyceridemic patients, while serum HMW adiponectin increased significantly. This study demonstrates that fenofibrate increases serum HMW adiponectin levels, whereas visfatin is not regulated by fenofibrate in hypertriglyceridemic subjects. Further investigations are warranted to determine whether the elevation of HMW adiponectin caused by fenofibrate might improve insulin sensitivity.     

Growth arrest-specific 6 modulates adiponectin expression and insulin resistance in adipose tissue

Aims/IntroductionObesity is characterized by disturbed adipocytokine expression and insulin resistance in adipocytes. Growth arrest‐specific 6 (GAS6) is a gene encoding the Gas6 protein, which is expressed in fibroblasts, and its related signaling might be associated with adipose tissue inflammation, glucose intolerance and insulin resistance. The aim of this study was to investigate the associations among Gas6, adipocytokines and insulin resistance in adipocytes.Materials and MethodsMature Simpson Golabi Behmel Syndrome adipocytes were treated with high levels of insulin to mimic insulin resistance, and were examined for the expressions of Gas6, cytokines and adipocytokines from preadipocytes in differentiation. In an animal study, high‐fat diet‐induced obese mice were used to verify the Gas6 expression in vitro.ResultsDuring the differentiation of adipocytes, the expression of Gas6 gradually decreased, and was obviously downregulated with adipocyte inflammation and insulin resistance. Gas6 levels were found to be in proportion to the expression of adiponectin, which has been regarded as closely relevant to improved insulin sensitivity after metformin treatment. Similar results were also confirmed in the animal study.ConclusionsOur results suggest that Gas6 might modulate the expression of adiponectin, and might therefore be associated with insulin resistance in adipose tissues.     

Extended-release niacin raises adiponectin and leptin

BACKGROUND: The lipid-lowering drug niacin has attracted renewed interest because it raises HDL-cholesterol and because it has recently been found to slow down the progression of intima media thickness in patients with coronary heart disease. Since niacin acts on adipocytes, we investigated its impact on adipokines and on some functions attributed to adipokines. METHODS AND RESULTS: In a randomized, placebo-controlled, double-blind study 30 men with the metabolic syndrome were treated for 6 weeks with 1500 mg extended-release niacin (n=20) or a placebo (n=10). Adiponectin increased by 56% (p<0.001) and leptin by 26.8% (p<0.012). Resistin, TNF-alpha, IL-6, and high sensitive CRP remained unchanged. In spite of the increase in adiponectin there was no improvement in endothelial function. The HOMA index actually deteriorated by 42% (p<0.014). CONCLUSION: Short-term treatment with extended-release niacin causes a pronounced increase in adiponectin but fails to improve atheroprotective functions attributed to adiponectin, such as insulin sensitivity, anti-inflammation and endothelial function.     

Hyperinsulinemia induces insulin resistance on glucose and lipid metabolism in a human adipocytic cell line: paracrine interaction with myocytes

CONTEXT: Adipocytes release a variety of factors which deregulation could provide the basis for complications such as insulin resistance, an early defect on the onset of type 2 diabetes. Such insulin resistance can initially be overcome by compensatory hyperinsulinemia, but the prolonged presence of the hormone can be detrimental for insulin sensitivity. OBJECTIVE: The objective of the study was to dissect the molecular mechanisms that may regulate hyperinsulinemia-induced insulin resistance in a human liposarcoma cell line and its paracrine interactions with a human rhabdomyosarcoma cell line. DESIGNS: We studied glucose uptake, lipolysis, insulin signaling, and secretion pattern at different days of adipocyte differentiation in the presence of insulin. RESULTS: Adipocytes differentiated for 14 d gain insulin sensitivity on glucose uptake and inhibition of lipolysis, but prolonged cultures develop an insulin-resistant state characterized by an increase in phosphatase and tensin homolog-deleted on chromosome 10 expression and defects in insulin signaling at the insulin receptor substrate-1/AKT level. The secretion pattern of nonesterified fatty acids, IL-6, adiponectin, leptin, and monocyte chemotactic protein-1 was in keeping with the changes in insulin sensitivity during differentiation. An inverse biphasic response was also observed in human myocytes when they were cultured with various adipocyte-conditioned media, although insulin resistance was detected earlier than in adipocytes. This behavior mimics hyperinsulinemia because insulin action was restored when adipocytes were cultured in the absence of the hormone. Pharmacological treatment of adipocytes with a liver X receptor agonist reestablishes insulin-stimulated glucose uptake, whereas treatment with a peroxisome proliferator-activated receptor-gamma agonist restored the antilipolytic action of insulin. CONCLUSIONS: Hyperinsulinemia deregulates adipocyte secretion pattern, producing insulin resistance in adipocytes and myocytes, a situation that can be ameliorated with nuclear receptor agonists.     

Effects of lactogen resistance and GH deficiency on mouse metabolism: pancreatic hormones, adipocytokines, and expression of adiponectin and insulin receptors

We recently described a novel mouse model that combines resistance to lactogenic hormones with GH deficiency (GHD). The GHD/lactogen-resistant males develop obesity and insulin resistance with age. We hypothesized that altered production of pancreatic hormones and dysregulation of adipocytokine secretion and action contribute to the pathogenesis of their insulin resistance. Double-mutant males (age 12–16 months) had fasting hyperinsulinemia, hyperamylinemia, hyperleptinemia, and a decreased ratio of adiponectin to leptin. Adiponectin receptor 1 and 2 (AdipoR1 and R2) mRNA levels in liver and skeletal muscle were normal but hepatic insulin receptor mRNA was increased. Relative to double-mutant males, GHD males had lower levels of insulin, amylin, and leptin, higher levels of adiponectin, and higher expression of hepatic AdipoR1 and insulin receptor mRNAs. Lactogen-resistant mice had reduced hepatic adipoR2 mRNA. In response to stress the plasma concentrations of MCP-1 and IL-6 increased in double-mutant males but not GHD or lactogen-resistant males. Our findings suggest that the insulin resistance of GHD/lactogen-resistant males is accompanied by dysregulation of pancreatic hormone and adipocytokine secretion and receptor expression. Phenotypic differences between double-mutant and GHD males suggest that lactogens and GH exert differential but overlapping effects on fat deposition and adipocytokine secretion and action.     

T cell-mediated hepatic inflammation modulates adiponectin levels in mice: role of tumor necrosis factor alpha

Experimental T cell-mediated hepatitis induced by concanavalin A (ConA) results in the initiation of an inflammatory response and the production of cytokines. Adiponectin is an adipocytokine produced by adipose tissue that is involved in the reciprocal regulation of other cytokines, including tumor necrosis factor alpha (TNF-alpha). Concanavalin A administration to C57BL/6J mice reduced circulating levels of adiponectin, whereas leptin was markedly increased. Adiponectin messenger RNA expression in adipose tissue was also decreased; however, the expression of both the adiponectin receptors remained unchanged. Neutralization of TNF-alpha reduced ConA-induced liver damage, and this was associated with restored circulating levels of adiponectin. These findings indicate that inflammation-induced TNF-alpha is a critical mediator of adipose-tissue-derived adiponectin in vivo.