Development of obesity in Zucker rats. Early insulin resistance in muscles but normal sensitivity in white adipose tissue

Euglycemic-hyperinsulinemic clamps were performed on 4- and 12-wk-old anesthetized lean and obese Zucker rats. During the clamp studies, total glucose production and utilization were assessed with a 3-[3H]glucose perfusion, whereas local glucose utilization was determined by measuring 2-deoxy-1-[3H]glucose 6-phosphate accumulation in various tissues. In the basal state, 4 wk-old obese rats were hyperinsulinemic (159 +/- 8 vs. 82 +/- 9 microU/ml), whereas glucose turnover rate was similar to that observed in lean rats (14.9 +/- 1.9 vs. 12.5 +/- 1.9 mg X min-1 X kg-1). Glucose utilization was identical in skeletal muscles, whereas it was increased in white adipose tissue of obese rats (22 +/- 4 vs. 8 +/- 2 ng X min-1 X mg-1). At plasma insulin level of 500 microU/ml, glucose production was totally suppressed in both groups, whereas overall glucose utilization was slightly less in 4-wk-old obese than in lean rats. This was due to a reduced stimulation of glucose utilization in skeletal muscles and brown adipose tissue. In contrast, glucose utilization in periovarian white adipose tissue was similarly increased in lean and obese rats. For a maximal insulin concentration (1500 microU/ml), all the differences were abolished between lean and obese young Zucker rats. In older (12-wk-old) obese rats, glucose utilization in various tissues was markedly reduced at maximal insulin level compared with that observed in age-matched lean animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Review article: The role of adipose tissue in uraemia-related insulin resistance

Adipose tissue is no longer considered to be an inert tissue of which function is to store fat. It actively secretes a number of biologic active compounds that are involved in the regulation of many processes like food intake, energy expenditure, metabolism homeostasis, immunity and blood pressure homeostasis. General metabolism alteration in patients with chronic kidney disease has a profound impact on biology of adipocytes. Chronic renal failure is a pathological condition, of which two major hallmarks are chronic inflammation and insulin resistance. In uraemic patients, adipose tissue became an important source of molecules that are responsible, at least in part, for the metabolic disturbances seen in these patients. Some of these molecules act as pro-inflammatory agents contributing to the maintenance and enhancement of the chronic inflammatory response. These pro-inflammatory molecules, along with other molecules secreted by the adipose tissue, have a central position in the aetiology of uraemia-associated insulin resistance. In this review, we intend to summarize some aspects of the biology of adipokines in uraemia, with emphasis on the link between these molecules and insulin resistance.     

Angiotensin receptor blockers improve insulin resistance in type 2 diabetic rats by modulating adipose tissue

Adipose tissue is recognized as a pivotal organ in the development of insulin resistance. This study seeks to determine the effect of angiotensin receptor blockade (ARB) on insulin resistance of adipocytes in culture and in a rat model of type 2 diabetes. Treatment of Otsuka Long-Evans Tokushima Fatty rats with the ARB L158809 for six months significantly lowered fasting plasma glucose, cholesterol and triglyceride levels but led to higher plasma adiponectin levels. Insulin resistance, measured by an intraperitoneal glucose tolerance test, of the treated rats was significantly improved along with an increase in the number of small differentiated adipocytes; however, epididymal fat mass decreased. Treatment significantly lowered lipid peroxidation and MCP-1 expression while increasing adiponectin production by the adipose tissue. ARB treatment significantly improved insulin sensitivity and markedly suppressed AT2-induced oxidative stress, PAI-1 and MCP-1 levels and NF-kappaB activation of adipocytes in culture. Treatment increased adiponectin and PPARgamma expression along with intracellular triglyceride levels reflecting differentiation of the cultured adipocytes. Our study suggests that ARB treatment improves insulin resistance by modification of adipose tissue thereby blunting the development of diabetes.     

Glucocorticoids and insulin promote plasminogen activator inhibitor 1 production by human adipose tissue

Plasminogen activator inhibitor 1 (PAI-1) is likely to play a role in vascular disease, primarily in subjects with android obesity. It has been demonstrated that PAI-1 is overexpressed in adipose tissue from obese subjects and that visceral adipose tissue produced more PAI-1 than subcutaneous fat. In the present study, the effect of insulin and glucocorticoids, which are key mediators of adipose tissue metabolism, was examined in relation to PAI-1 synthesis by human adipose tissue explants (HAT), collagenase isolated human adipocytes (IHA), cultured human stromal cells (cSC), and differentiated adipocytes from the murine clonal cell line 3T3-F442A. A significant increase in PAI-1 antigen release (1.5-fold) from HAT was detectable after 16 h of treatment with insulin concentrations of at least 10(-8) mol/l. This was associated with a PAI-1 mRNA increase. Concomitant addition of insulin (10(-8) mol/l) to forskolin (5 x 10(-5) mol/l) reversed the decrease in PAI-1 antigen caused by forskolin alone. No effect on PAI-1 antigen was observed when insulin was incubated with IHA or cSC. 3T3 F442A cells were sensitive to insulin with a four- and twofold increase in PAI-1 antigen and mRNA levels, respectively, after 16 h of stimulation with 10(-8) mol/l. Dexamethasone (DXM) significantly enhanced PAI-1 antigen and mRNA expression by HAT (1.5- and 2.5-fold increase, respectively) at concentrations of at least 10(-8) mol/l. A higher stimulation was observed with IHA (sevenfold increase) and with the differentiated 3T3 F442 cell line. Cortisol was found to be less potent than DXM. No effect was observed when glucocorticoids were incubated with cSC. Coincubation of HAT with insulin (10(-7) mol/l) and DXM (10(-7) mol/l) led to an additive effect on PAI-1 synthesis. These results support the hypothesis that PAI-1 expression in human adipose tissue is controlled by insulin and glucocorticoids and may help to explain the increase in plasma PAI-1 levels observed in patients with android obesity.     

Increased fatty acid re-esterification by PEPCK overexpression in adipose tissue leads to obesity without insulin resistance

Adipose tissue glyceroneogenesis generates glycerol 3-phosphate, which could be used for fatty acid esterification during starvation. To determine whether increased glyceroneogenesis leads to increased fat mass and to explore the role of obesity in the development of insulin resistance, we overexpressed PEPCK, a regulatory enzyme of glyceroneogenesis in adipose tissue. Transgenic mice showed a chronic increase in PEPCK activity, which led to increased glyceroneogenesis, re-esterification of free fatty acids (FFAs), increased adipocyte size and fat mass, and higher body weight. In spite of increased fat mass, transgenic mice showed decreased circulating FFAs and normal leptin levels. Moreover, glucose tolerance and whole-body insulin sensitivity were preserved. Skeletal muscle basal and insulin-stimulated glucose uptake and glycogen content were not affected, suggesting that skeletal muscle insulin sensitivity is normal in transgenic obese mice. Our results indicate the key role of PEPCK in the control of FFA re-esterification in adipose tissue and, thus, the contribution of glyceroneogenesis to fat accumulation. Moreover, they suggest that higher fat mass without increased circulating FFAs does not lead to insulin resistance or type 2 diabetes in these mice.     

CCNG2 and CDK4 is associated with insulin resistance in adipose tissue

BackgroundThe involvement of cyclin G2 (CCNG2) and cyclin-dependent kinase-4 (CDK4), cell cycle regulatory proteins, in adipose tissue metabolism and insulin resistance is still unknown. The objective of this study was to analyze CCNG2 and CDK4 levels in visceral (VAT) and subcutaneous adipose tissue (SAT) from nonobese and morbidly obese patients and their relationship with insulin resistance.MethodsWe studied the mRNA and protein levels of CCNG2 and CDK4 in VAT and SAT from 12 nonobese and 23 morbidly obese patients (11 with low [MO-L-IR] and 12 with high insulin resistance [MO-H-IR]).ResultsThe nonobese patients had a significantly greater CCNG2 expression in VAT (P = .004) and SAT (P<.001) than the MO-L-IR and MO-H-IR patients. The MO-H-IR patients had a significantly lower CDK4 expression in VAT than the MO-L-IR (P = .026), but similar to the nonobese patients. CDK4 and CCNG2 expression correlated significantly in VAT (r = 0.511, P<.001) and SAT (r = .535, P = .001). In different multiple regression analysis models, CCNG2 and CDK4 expression in VAT was mainly predicted by glucose (P = .047 and P = .008, respectively), and CCNG2 expression in SAT was mainly predicted by body mass index (P = .041). No significant associations were found with CDK4 expression in SAT. Moreover, VAT CCNG2 expression was the main determinant of the improvement in the homeostasis model assessment of insulin resistance index at 3 months after bariatric surgery (B = -271.7, P = .026).ConclusionOur data show for the first time that the human CCNG2 and CDK4 expression of VAT are inversely associated with glucose and insulin resistance.     

Influence of thyroid hormone level on insulin action in human adipose tissue

The relationship between the levels of circulating thyroid hormones and the action of insulin on adipose tissue was investigated in 6 hypothyroid patients and 6 hyperthyroid patients, all untreated, and 8 healthy control subjects. All were matched for age, body weight, and fat cell size. Gluteal s.c. adipose tissue was used. The insulin receptor number in isolated adipocytes was increased by 70% in hypothyroidism and decreased by 40% in hyperthyroidism. The sensitivities of the effects of insulin on lipolysis and glucose oxidation were increased fourfold in hypothyroidism and decreased fivefold in hyperthyroidism. The maximum insulin-induced glucose oxidation (insulin responsiveness) was inhibited by 60% in hypothyroidism and enhanced by 180% in hyperthyroidism. The thyroid hormone concentration was significantly correlated with insulin receptor number (r = -0.72), insulin responsiveness (r = 0.71), and insulin sensitivity (r = -0.75). It is suggested that thyroid hormones regulate the effect of insulin on adipose tissue, which occurs at the receptor and postreceptor levels of insulin action.     

Concomitant dysregulation of androgen secretion and dysfunction of adipose tissue induced insulin resistance

Hyperandrogenism and hyperinsulinemia have resulted from dysfunction of the theca cell of the ovary and adipose tissue and each one potentiates the other in patients with androgen excess disorders e.g., polycystic ovary disease and idiopathic hirsutism. Possible external and/or internal triggers can produce such cellular dysfunction. There is evidence that sodium valproate acts as a trigger of cellular dysfunction and produces both hyperinsulinemia and hyperandrogenism. Therefore, the elimination of these triggers can help the patients to recover from hyperinsulinemia, insulin resistance and hyperandrogenism.     

Heat shock protein 60 as a mediator of adipose tissue inflammation and insulin resistance

The stress protein heat shock protein 60 (Hsp60) induces secretion of proinflammatory mediators from murine adipocytes. This study aimed to study Hsp60 as a mediator of adipose tissue inflammation and skeletal muscle cell (SkMC) insulin sensitivity and to quantify plasma Hsp60 concentrations in lean and obese individuals. Regulation of Hsp60 release and Hsp60-induced cytokine secretion and signaling was measured in human adipocytes and SkMCs. Adipocytes exhibited higher Hsp60 release than preadipocytes and SkMCs, which was further stimulated by cytokines and Toll-like receptor (TLR)-4 activation. Hsp60 activated extracellular signal-related kinase (ERK)-1/2, Jun NH(2)-terminal kinase (JNK), p38, nuclear factor (NF)-κB, and impaired insulin-stimulated Akt phosphorylation in adipocytes. Furthermore, Hsp60 stimulated adipocytes to secrete tumor necrosis factor-α, interleukin (IL)-6, and IL-8. In SkMCs, Hsp60 activated ERK1/2, JNK, and NF-κB and inhibits insulin signaling and insulin-stimulated glucose uptake. SkMCs released IL-6, IL-8, and monocyte chemoattractant protein-1 on Hsp60 stimulation. Plasma Hsp60 was higher in obese males than in lean males and correlated positively with BMI, blood pressure, leptin, and homeostasis model assessment-insulin resistance. In summary, Hsp60 is released by human adipocytes, increased in plasma of obese humans, and induces insulin resistance. This is accompanied by activation of proinflammatory signaling in human adipocytes and SkMCs. Thus, Hsp60 might be a factor underlying adipose tissue inflammation and obesity-associated metabolic disorders.     

Influence of aging on insulin receptor binding and metabolic effects of insulin on human adipose tissue

The influence of aging on the peripheral action of insulin was studied using subcutaneous adipose tissue from eight young (range 22-30 yr) and seven middle-aged (40-59 yr), healthy, normal-weight subjects. Insulin binding per cell was 50% lower in the older than in the younger group (P less than 0.01), essentially owing to a decrease in the insulin receptor number. Concomitantly, insulin sensitivity, as reflected in the degree of antilipolysis and stimulation of glucose oxidation, was 10-20 times smaller in the older subjects (P less than 0.01). Basal lipolysis and the maximum antilipolytic effect of insulin were similar in the two groups. The basal rate of glucose oxidation in the older subjects was less than one-half that for the younger group (P less than 0.025), and the maximum level of insulin-induced glucose oxidation was lower by about 75% (P less than 0.012). Age was significantly and negatively correlated with insulin receptor number (r = -0.81), basal production of 14CO2 (r = -0.73) and maximum level of insulin-induced glucose oxidation (r =- -0.68). The decreases in the receptor number and insulin sensitivity were larger in early adulthood than in the elderly, while the decrease in insulin responsiveness was more uniform. It is concluded that aging is accompanied by impairment of the action of insulin on target cells, owing to alterations at both the receptor and the postreceptor levels. These mechanisms, and especially the postreceptor defect, may be essential factors in the development of relative glucose intolerance in the aged.     

人脂肪源细胞外囊泡联合脱细胞脂肪组织支架构建组织工程脂肪

目的探讨人脂肪源细胞外囊泡(human adipose tissue derived extracellular vesicle,hAT-EV)联合脱细胞脂肪组织支架(decellularized adipose tissues,DAT)构建组织工程脂肪的可能性,为临床上软组织缺损修复提供新方案。方法将吸脂手术患者自愿捐赠的脂肪组织分为2份,1份脂肪组织进行脱细胞处理,并采用组织学(HE、Masson染色)、扫描电镜观察,Ⅰ、Ⅳ型胶原及层粘连蛋白免疫组织化学染色和Western blot检测进行表征。另1份脂肪组织使用去外泌体的完全培养基孵化48 h,离心收集培养基上清并使用超高速离心法获取hATEV。使用透射电镜观察其形态,纳米颗粒跟踪分析仪NanoSight分析hAT-EV粒径分布范围,Western blot检测分析hAT-EV膜表面蛋白。将PKH26荧光标记的hAT-EV与脂肪干细胞(adipose derived stem cells,ADSCs)共培养后,共聚焦荧光显微镜观察hAT-EV能否进入ADSCs;将hAT-EV与ADSCs共培养15 d,油红O染色评估其成脂效果。将DAT组织剪碎并注射至8只6周龄雌性C57小鼠背部两侧,左侧每周注射0.2 mL hAT-EV作为实验组,右侧每周注射0.2 mL PBS作为对照组。12周后处死小鼠,取两侧DAT新生物进行湿重称量,并通过HE染色和围脂滴蛋白免疫荧光染色评估hAT-EV在体内诱导脂肪新生的能力。结果脂肪组织经脱细胞后,HE、Masson染色示DAT主要由排列松散的胶原构成,未见细胞核;扫描电镜示DAT中未发现细胞和细胞碎片,同时可见到粗大的胶原纤维束;免疫组织化学染色及Western blot检测示,DAT中保留了Ⅰ、Ⅳ型胶原和层粘连蛋白。经鉴定,hAT-EV呈双层包膜的球形,高表达CD63、凋亡诱导因子6相互作用蛋白抗体、肿瘤易感基因101,97.9%粒径分布范围为32.67~220.20 nm,峰值为91.28 nm。共聚焦荧光显微镜和油红O染色示,hAT-EV被ADSCs摄取并诱导其成脂分化。大鼠体内实验显示,实验组新生脂肪组织湿重显著高于对照组(t=2.278,P=0.048);HE染色示,实验组脂滴结构较对照组多,对照组胶原含量高于实验组;围脂滴蛋白免疫荧光染色示,实验组DAT新生物中脂肪组织比例高于对照组(t=4.648,P=0.017)。结论DAT搭载hAT-EV可作为一种诱导脂肪组织新生的新方法,在软组织缺损修复中具有潜在应用前景。     

Adiponectin expression from human adipose tissue: relation to obesity,insulin resistance,and tumor necrosis factor-alpha expression

Adiponectin is a 29-kDa adipocyte protein that has been linked to the insulin resistance of obesity and lipodystrophy. To better understand the regulation of adiponectin expression, we measured plasma adiponectin and adipose tissue adiponectin mRNA levels in nondiabetic subjects with varying degrees of obesity and insulin resistance. Plasma adiponectin and adiponectin mRNA levels were highly correlated with each other (r = 0.80, P < 0.001), and obese subjects expressed significantly lower levels of adiponectin. However, a significant sex difference in adiponectin expression was observed, especially in relatively lean subjects. When men and women with a BMI <30 kg/m(2) were compared, women had a twofold higher percent body fat, yet their plasma adiponectin levels were 65% higher (8.6 +/- 1.1 and 14.2 +/- 1.6 micro g/ml in men and women, respectively; P < 0.02). Plasma adiponectin had a strong association with insulin sensitivity index (S(I)) (r = 0.67, P < 0.0001, n = 51) that was not affected by sex, but no relation with insulin secretion. To separate the effects of obesity (BMI) from S(I), subjects who were discordant for S(I) were matched for BMI, age, and sex. Using this approach, insulin-sensitive subjects demonstrated a twofold higher plasma level of adiponectin (5.6 +/- 0.6 and 11.2 +/- 1.1 micro g/ml in insulin-resistant and insulin-sensitive subjects, respectively; P < 0.0005). Adiponectin expression was not related to plasma levels of leptin or interleukin-6. However, there was a significant inverse correlation between plasma adiponectin and tumor necrosis factor (TNF)-alpha mRNA expression (r = -0.47, P < 0.005), and subjects with the highest levels of adiponectin mRNA expression secreted the lowest levels of TNF-alpha from their adipose tissue in vitro. Thus, adiponectin expression from adipose tissue is higher in lean subjects and women, and is associated with higher degrees of insulin sensitivity and lower TNF-alpha expression.     

Effects of pioglitazone on adipose tissue remodeling within the setting of obesity and insulin resistance

Obesity and dysfunctional energy partitioning can lead to the development of insulin resistance and type 2 diabetes. The antidiabetic thiazolidinediones shift the energy balance toward storage, leading to an increase in whole-body adiposity. These studies examine the effects of pioglitazone (Pio) on adipose tissue physiology, accumulation, and distribution in female Zucker (fa/fa) rats. Pio treatment (up to 28 days) decreased the insulin-resistant and hyperlipidemic states and increased food consumption and whole-body adiposity. Magnetic resonance imaging (MRI) analysis and weights of fat pads demonstrated that the increase in adiposity was not only limited to the major fat depots but also to fat deposition throughout the body. Adipocyte sizing profiles, fat pad histology, and DNA content show that Pio treatment increased the number of small adipocytes because of both the appearance of new adipocytes and the shrinkage and/or disappearance of existing mature adipocytes. The remodeling was time dependent, with new small adipocytes appearing in clusters throughout the fat pad, and accompanied by a three- to fourfold increase in citrate synthase and fatty acid synthase activity. The appearance of new fat cells and the increase in fat mass were depot specific, with a rank order of responsiveness of ovarian > retroperitoneal > subcutaneous. This differential depot effect resulted in a redistribution of the fat mass in the abdominal region such that there was an increase in the visceral:subcutaneous ratio, as confirmed by MRI analysis. Although the increased adiposity is paradoxical to an improvement in insulin sensitivity, the quantitative increase of adipose mass should be viewed in context of the qualitative changes in adipose tissue, including the remodeling of adipocytes to a smaller size with higher lipid storage potential. This shift in energy balance is likely to result in lower circulating free fatty acid levels, ultimately improving insulin sensitivity and the metabolic state.     

Attenuated adiposopathy in perivascular adipose tissue compared with subcutaneous human adipose tissue

Background

We hypothesized that human perivascular and subcutaneous adipose tissues hold distinct phenotypic signatures. We also evaluated the impact of clinical parameters on the adipose phenotype. Our overall goal is to understand the determinants of adipose biology so that this tissue can be manipulated therapeutically to lessen peripheral vascular disease.

Methods

Perivascular and subcutaneous adipose tissues were collected from patients undergoing lower-extremity amputation (n = 27) and protein assayed for proinflammatory mediators (ie, interleukin 6, interleukin 8, leptin, tumor necrosis factor α, monocyte chemoattractant protein-1, and resistin), atheroprotective adiponectin, and the fibrinolysis inhibitor plasminogen activator inhibitor-1.

Results

Leptin (2.7-fold, P = .015), TNF-α (2.2-fold, P = .013), MCP-1 (1.5-fold, P = .047), and adiponectin (1.8-fold, P = .004) were more abundant in subcutaneous vs perivascular adipose tissue. Age positively correlated with perivascular adipose tissue PAI-1 expression (β = .64, P = .042), and hyperlipidemia negatively correlated with perivascular adiponectin (β = −1.18, P = .039).

Conclusions

Human perivascular and subcutaneous adipose tissues hold distinct phenotypic signatures. In amputation patients, the subcutaneous adipose tissue proinflammatory phenotype was relatively attenuated in perivascular adipose tissue.     

Nutrition,insulin resistance and dysfunctional adipose tissue determine the different components of metabolic syndrome

Obesity is an excessive accumulation of body fat that may be harmful to health. Today, obesity is a major public health problem, affecting in greater or lesser proportion all demographic groups. Obesity is estimated by body mass index(BMI) in a clinical setting, but BMI reports neither body composition nor the location of excess body fat. Deaths from cardiovascular diseases, cancer and diabetes accounted for approximately 65% of all deaths, and adiposity and mainly abdominal adiposity are associated with all these disorders. Adipose tissue could expand to inflexibility levels. Then, adiposity is associated with a state of low-grade chronic inflammation, with increased tumor necrosis factor-α and interleukin-6 release, which interfere with adipose cell differentiation, and the action pattern of adiponectin and leptin until the adipose tissue begins to be dysfunctional. In this state the subject presents insulin resistance and hyperinsulinemia, probably the first step of a dysfunctional metabolic system. Subsequent to central obesity, insulin resistance, hyperglycemia, hypertriglyceridemia, hypoalphalipoproteinemia, hypertension and fatty liver are grouped in the so-called metabolic syndrome(MetS). In subjects with MetS an energy balance is critical to maintain a healthy body weight, mainly limiting the intake of high energy density foods(fat). However, high-carbohydrate rich(CHO) diets increase postprandial peaks of insulin and glucose. Triglyceride-rich lipoproteins are also increased, which interferes with reverse cholesterol transport lowering highdensity lipoprotein cholesterol. In addition, CHO-rich diets could move fat from peripheral to central deposits and reduce adiponectin activity in peripheral adipose tissue. All these are improved with monounsaturated fatty acid-rich diets. Lastly, increased portions of ω-3 and ω-6 fatty acids also decrease triglyceride levels, and complement the healthy diet that is recommended in patients with MetS.