Cytochrome P-450 CYP2E1 knockout mice are protected against high-fat diet-induced obesity and insulin resistance

Conventional (whole body) CYP2E1 knockout mice displayed protection against high-fat diet-induced weight gain, obesity, and hyperlipidemia with increased energy expenditure despite normal food intake and spontaneous locomotor activity. In addition, the CYP2E1 knockout mice displayed a marked improvement in glucose tolerance on both normal chow and high-fat diets. Euglycemic-hyperinsulinemic clamps demonstrated a marked protection against high-fat diet-induced insulin resistance in CYP2E1 knockout mice, with enhanced adipose tissue glucose uptake and insulin suppression of hepatic glucose output. In parallel, adipose tissue was protected against high-fat diet-induced proinflammatory cytokine production. Taken together, these data demonstrate that the CYP2E1 deletion protects mice against high-fat diet-induced insulin resistance with improved glucose homeostasis in vivo.     

Childhood obesity and insulin resistance

Insulin resistance (IR) in childhood has importance to the understanding and prevention of the growing epidemic of insulin resistance syndrome (IRS) in adults with attendant obesity, type 2 diabetes (T2DM), atherosclerotic diseases, hypertension, gout, non-alcoholic, steato-hepatitis (NASH), gall bladder disease, nephropathy, polycystic ovarian disease (PCOS), infertility and premature senility. The severity of IR and its’ complications in children unfortunately and usually progresses in their pubertal transition to adulthood; affected young children are more likely than adults to have underlying causal monogenic disorders; the sequence of natural history and events give insights into disease pathogeneses, and optimal life style choices that last are best made during the early formative years. Some features of IR in children discussed herein are: a strong tendency to low birth weight for gestational age, adverse effects of adrenarche and therapeutic steroid therapy, predisposition to premature pubarche, acanthosis nigricans, tall stature despite pituitary GH suppression, allergic diathesis, hyperandrogenism and PCOS, dyslipidemia and fatty liver disease, and diagnosis by clinical and biochemical markers of IR including insulin regulated hepatic hormonal binding proteins such as IGFBP-1. The national preoccupation with the “metabolic syndrome” T2DM and obesity, should be appropriately directed to an improved understanding of IR in children and their management, if the looming health crisis in affected adults is to be seriously addressed. The nation is facing its’ first generation of children who will be less healthy and die younger than the previous generation (Marks (2005) Presentation to the American Association of Diabetes Educators 32nd Annual Meeting and Exhibition, August 10–13, Washington, DC).     

A PPAR agonist improves TNF-alpha-induced insulin resistance of adipose tissue in mice

Thiazolidinediones (TZDs), agonists for PPARs, have been shown to block the inhibitory effects of TNF-alpha on insulin action using cultured cells. In order to clarify the in vivo effects of TZDs on the inhibition of insulin sensitivity by TNF-alpha, insulin action in muscles and adipose tissues was assessed in the TNF-alpha-overexpression mice model using transplantation of cells secreting the TNF-alpha protein. After the pioglitazone treatment for 4 weeks, glucose uptake, insulin-induced IRS-1 phosphorylation, and lipoprotein lipase mRNA levels were analyzed. Pioglitazone did not ameliorate TNF-alpha-induced hyperinsulinemia in this model, as assessed by the OGTT. Glucose uptake and lipoprotein lipase mRNA levels were decreased by TNF-alpha in adipose tissues from the TNF-alpha-overexpressing mice, and pioglitazone blocked these inhibitions by TNF-alpha. On the other hand, in muscles, pioglitazone did not reverse the effects of TNF-alpha on insulin-induced phosphorylation of IRS-1, glucose uptake, and lipoprotein lipase mRNA levels. Present study revealed the different sensitivities of pioglitazone for the recovery of decreased insulin action in a TNF-alpha-overexpressing model using cell transplantation. These results suggest that the effect of TZDs is dependent on the fat distribution and accumulation in humans.     

钙结合蛋白S100A16对胰岛素抵抗的作用研究

目的探究钙结合蛋白S100A16在胰岛素抵抗中的作用。方法用S100A16抗体进行免疫沉淀,然后用蛋白质谱分析寻找与S100A16相互作用的蛋白。实验1转染Vector质粒的HepG2细胞作为对照,用转染shRNA质粒、S100A16过表达质粒干预作为处理组。实验2以慢性胰岛素刺激细胞构建胰岛素抵抗模型,采用转染shRNA质粒的细胞作为对照,用未转染和转染Vector质粒干预作为处理组。实验3以不做任何处理的细胞作为对照,在胰岛素抵抗模型中用吡格列酮干预作为处理组。Western blot检测相关蛋白的表达水平。组间比较采用成组t检验。结果与转染Vector质粒比较,转染S100A16过表达质粒中胎球蛋白A表达(1.39±0.54比2.85±0.25)水平上调(P<0.05);与转染Vector质粒比较,转染shRNA质粒胎球蛋白A蛋白表达(0.36±0.03比0.20±0.03)水平降低(P<0.01)。在胰岛素抵抗条件下,与转染shRNA质粒的细胞比较,未转染和转染Vector质粒的IRS-2蛋白表达(0.11±0.04比1.65±0.48)水平上调(P<0.01);与不做任何处理的细胞比较,用吡格列酮处理的细胞IRS-2表达(0.26±0.11比0.52±0.05)水平上升(P<0.01)。结论S100A16在HepG2细胞中通过胎球蛋白A促进胰岛素抵抗。     

Protein-tyrosine phosphatases are involved in interferon resistance associated with insulin resistance in HepG2 cells and obese mice

Insulin resistance is a risk factor for non-response to interferon/ribavirin therapy in patients with chronic hepatitis C. The aim of this study was to determine the role played by protein-tyrosine phosphatases (PTPs) in the absence of interferon-α (IFNα) response associated with insulin resistance. We induced insulin resistance by silencing IRS-2 or by treating HepG2 cells with tumor necrosis factor-α (TNFα) and analyzed insulin response by evaluating Akt phosphorylation and IFNα response by measuring Stat-1 tyrosine phosphorylation and 2',5'-oligoadenylate synthase and myxovirus resistance gene expression. The response to IFNα was also measured in insulin-resistant obese mice (high fat diet and ob/ob mice) untreated and treated with metformin. Silencing IRS-2 mRNA induces insulin resistance and inhibits IFNα response. Likewise, TNFα suppresses insulin and IFNα response. Treatment of cells with pervanadate and knocking down PTP-1B restores insulin and IFNα response. Both silencing IRS-2 and TNFα treatment increase PTP and PTP-1B activity. Metformin inhibits PTP and improves IFNα response in insulin-resistant cells. Insulin-resistant ob/ob mice have increased PTP-1B gene expression and activity in the liver and do not respond to IFNα administration. Treatment with metformin improves this response. In HepG2 cells, insulin resistance provokes IFNα resistance, which is associated with an increased PTP-1B activity in the liver. Inhibition of PTP-1B activity with pervanadate and metformin or knocking down PTP-1B reestablishes IFNα response. Likewise, metformin decreases PTP-1B activity and improves response to IFNα in insulin-resistant obese mice. The use of PTP-1B inhibitors may improve the response to IFNα/ribavirin therapy.     

IRS-1 transgenic mice show increased epididymal fat mass and insulin resistance

Insulin receptor substrate-1 (IRS-1) is the major substrate of both the insulin receptor and the IGF-1 receptor. In this study, we created IRS-1 transgenic (IRS-1-Tg) mice which express human IRS-1 cDNA under control of the mouse IRS-1 gene promoter. In the IRS-1-Tg mice, IRS-1 mRNA expression was significantly increased in almost all tissues, but its protein expression was increased in very limited tissues (epididymal fat and skeletal muscle). IRS-1-Tg mice showed glucose intolerance and significantly enlarged epididymal fat mass, as well as elevated serum TNF-α concentrations. Importantly insulin signaling was significantly attenuated in the liver of IRS-1-Tg mice, which may contribute to the glucose intolerance. Our results suggest that excess IRS-1 expression may not provide a beneficial impact on glucose homeostasis in vivo.     

A polyphenol rescues lipid induced insulin resistance in skeletal muscle cells and adipocytes

Skeletal muscle and adipose tissues are known to be two important insulin target sites. Therefore, lipid induced insulin resistance in these tissues greatly contributes in the development of type 2 diabetes (T2D). Ferulic acid (FRL) purified from the leaves of Hibiscus mutabilis, showed impressive effects in preventing saturated fatty acid (SFA) induced defects in skeletal muscle cells. Impairment of insulin signaling molecules by SFA was significantly waived by FRL. SFA markedly reduced insulin receptor β (IRβ) in skeletal muscle cells, this was affected due to the defects in high mobility group A1 (HMGA1) protein obtruded by phospho-PKCε and that adversely affects IRβ mRNA expression. FRL blocked PKCε activation and thereby permitted HMGA1 to activate IRβ promoter which improved IR expression deficiency. In high fat diet (HFD) fed diabetic rats, FRL reduced blood glucose level and enhanced lipid uptake activity of adipocytes isolated from adipose tissue. Importantly, FRL suppressed fetuin-A (FetA) gene expression, that reduced circulatory FetA level and since FetA is involved in adipose tissue inflammation, a significant attenuation of proinflammatory cytokines occurred. Collectively, FRL exhibited certain unique features for preventing lipid induced insulin resistance and therefore promises a better therapeutic choice for T2D.     

Immunity as a link between obesity and insulin resistance

Obesity is a major public health problem in the United States and worldwide. Further, obesity is causally linked to the pathogenesis of insulin resistance, metabolic syndrome and type-2 diabetes (T2D). A chronic low-grade inflammation occurring in adipose tissue is at least in part responsible for the obesity-induced insulin resistance. This adipose tissue inflammation is characterized by changes in immune cell populations giving rise to altered adipo/cytokine profiles, which in turn induces skeletal muscle and hepatic insulin resistance. Detailed molecular mechanisms of insulin resistance, adipose tissue inflammation and the implications of these findings on therapeutic strategies are discussed in this review.     

Cafeteria diet induces obesity and insulin resistance associated with oxidative stress but not with inflammation: improvement by dietary supplementation with a melon superoxide dismutase

Oxidative stress is involved in obesity. However, dietary antioxidants could prevent oxidative stress-induced damage. We have previously shown the preventive effects of a melon superoxide dismutase (SODB) on oxidative stress. However, the mechanism of action of SODB is still unknown. Here, we evaluated the effects of a 1-month curative supplementation with SODB on the liver of obese hamsters. Golden Syrian hamsters received either a standard diet or a cafeteria diet composed of high-fat, high-sugar, and high-salt supermarket products, for 15 weeks. This diet resulted in insulin resistance and in increased oxidative stress in the liver. However, inflammatory markers (IL-6, TNF-α, and NF-κB) were not enhanced and no liver steatosis was detected, although these are usually described in obesity-induced insulin resistance models. After the 1-month supplementation with SODB, body weight and insulin resistance induced by the cafeteria diet were reduced and hepatic oxidative stress was corrected. This could be due to the increased expression of the liver antioxidant defense proteins (manganese and copper/zinc superoxide dismutase, catalase, and glutathione peroxidase). Even though no inflammation was detected in the obese hamsters, inflammatory markers were decreased after SODB supplementation, probably through the reduction of oxidative stress. These findings suggest for the first time that SODB could exert its antioxidant properties by inducing the endogenous antioxidant defense. The mechanisms underlying this induction need to be further investigated.     

Lecithin cholesterol acyltransferase null mice are protected from diet-induced obesity and insulin resistance in a gender-specific manner through multiple pathways

Complete lecithin cholesterol acyltransferase (LCAT) deficiency uniformly results in a profound HDL deficiency. We recently reported unexpected enhanced insulin sensitivity in LCAT knock-out mice in the LDL receptor knock-out background (Ldlr(-/-)×Lcat(-/-); double knock-out (DKO)), when compared with their Ldlr(-/-)×Lcat(+/+) (single knock-out (SKO)) controls. Here, we report that LCAT-deficient mice (DKO and Lcat(-/-)) are protected against high fat high sucrose (HFHS) diet-induced obesity without hypophagia in a gender-specific manner compared with their respective (SKO and WT) controls. The metabolic phenotypes are more pronounced in the females. Changes in endoplasmic reticulum stress were examined as a possible mechanism for the metabolic protection. The female DKO mice developed attenuated HFHS-induced endoplasmic reticulum stress as evidenced by a lack of increase in mRNA levels of the hepatic unfolded protein response (UPR) markers Grp78 and CHOP compared with SKO controls. The DKO female mice were also protected against diet-induced insulin resistance. In white adipose tissue of chow-fed DKO mice, we also observed a reduction in UPR, gene markers for adipogenesis, and markers for activation of Wnt signaling. In skeletal muscles of female DKO mice, we observed an unexpected increase in UCP1 in association with increase in phospho-AMPKα, PGC1α, and UCP3 expressions. This increase in UCP1 was associated with ectopic islands of brown adipocytes between skeletal muscle fibers. Our findings suggest that LCAT deficiency confers gender-specific protection against diet-induced obesity and insulin resistance at least in part through regulation in UPR, white adipose tissue adipogenesis, and brown adipocyte partitioning.     

Increased dosage of Ink4/Arf protects against glucose intolerance and insulin resistance associated with aging

Recent genome‐wide association studies have linked type‐2 diabetes mellitus to a genomic region in chromosome 9p21 near the Ink4/Arf locus, which encodes tumor suppressors that are up‐regulated in a variety of mammalian organs during aging. However, it is unclear whether the susceptibility to type‐2 diabetes is associated with altered expression of the Ink4/Arf locus. In the present study, we investigated the role of Ink4/Arf in age‐dependent alterations of insulin and glucose homeostasis using Super‐Ink4/Arf mice which bear an extra copy of the entire Ink4/Arf locus. We find that, in contrast to age‐matched wild‐type controls, Super‐Ink4/Arf mice do not develop glucose intolerance with aging. Insulin tolerance tests demonstrated increased insulin sensitivity in Super‐Ink4/Arf compared with wild‐type mice, which was accompanied by higher activation of the insulin receptor substrate (IRS)‐PI3K‐AKT pathway in liver, skeletal muscle and heart. Glucose uptake studies in Super‐Ink4/Arf mice showed a tendency toward increased ¹⁸F‐fluorodeoxyglucose uptake in skeletal muscle compared with wild‐type mice (P = 0.079). Furthermore, a positive correlation between glucose uptake and baseline glucose levels was observed in Super‐Ink4/Arf mice (P < 0.008) but not in wild‐type mice. Our studies reveal a protective role of the Ink4/Arf locus against the development of age‐dependent insulin resistance and glucose intolerance.     

Exercise-induced enhancement of insulin sensitivity is associated with accumulation of M2-polarized macrophages in mouse skeletal muscle

Exercise enhances insulin sensitivity in skeletal muscle, but the underlying mechanism remains obscure. Recent data suggest that alternatively activated M2 macrophages enhance insulin sensitivity in insulin target organs such as adipose tissue and liver. Therefore, the aim of this study was to determine the role of anti-inflammatory M2 macrophages in exercise-induced enhancement of insulin sensitivity in skeletal muscle. C57BL6J mice underwent a single bout of treadmill running (20 m/min, 90 min). Twenty-four hours later, ex vivo insulin-stimulated 2-deoxy glucose uptake was found to be increased in plantaris muscle. This change was associated with increased number of CD163-expressing macrophages (i.e. M2-polarized macrophages) in skeletal muscle. Systemic depletion of macrophages by pretreatment of mice with clodronate-containing liposome abrogated both CD163-positive macrophage accumulation in skeletal muscle as well as the enhancement of insulin sensitivity after exercise, without affecting insulin-induced phosphorylation of Akt and AS160 or exercise-induced GLUT4 expression. These results suggest that accumulation of M2-polarized macrophages is involved in exercise-induced enhancement of insulin sensitivity in mouse skeletal muscle, independently of the phosphorylation of Akt and AS160 and expression of GLUT4.     

Effect of resistance exercise on dehydroepiandrosterone sulfate concentrations during a 72-h recovery: relation to glucose tolerance and insulin response

Serum dehydroepiandrosterone sulfate (DHEA-S) concentration is known to be associated with the whole-body insulin sensitivity. The main purpose of the study was to investigate the effect of resistance exercise on DHEA-S concentration during a 72 h post-exercise recovery, and its relation to glucose tolerance and insulin sensitivity. Morning fasted serum samples was obtained from 19 male volunteers (aged 21.1+/-0.4 years) 24 h before the onset of exercise and 24 h, 48 h, and 72 h following exercise for measurements of DHEA-S, cortisol, and TNF-alpha. Oral glucose tolerance test (OGTT) and insulin response were determined 24 h before and 48 h after exercise. We found that resistance exercise causes a delayed suppression in serum DHEA-S levels during recovery (48 h and 72 h). This exercise challenge did not affect glucose tolerance, but insulin response during OGTT was significantly elevated. The increased insulin level was not associated with serum levels of cortisol and TNF-alpha. In conclusion, the present study found that resistance exercise has a DHEA-S lowering effect that persisted for 72 h. This change could be related to the elevated insulin concentrations during OGTT.     

Common STAT3 variants are not associated with obesity or insulin resistance in female twins

In animal models, STAT3 action in the hypothalamus and liver appears essential for normal body weight and glucose homeostasis in response to insulin. We hypothesized that variation in the STAT3 gene may be associated with body fat and/or insulin resistance in the general population. Five tagging SNPs spanning the STAT3 gene, rs8074524, rs2293152, rs2306580, rs6503695, and rs7211777 were genotyped in 2776 white female twins (mean age, 47.4+/-12.5 yrs) from the St Thomas' United Kingdom Adult Twin Registry (Twins UK). Minor allele frequencies were as follows: rs8074524 (0.19), rs2293152 (0.37), rs2306580 (0.06), rs6503695 (0.35), and rs7211777 (0.34). The minor allele of rs2293152 was associated with higher homeostasis model assessment index of insulin resistance (p=0.013) in the full cohort and confirmed in sib-transmission/disequilibrium test (TDT): (p=0.015; n=60). However, there were no associations with fasting serum insulin or glucose or with obesity variables. Although defective STAT3 action results in obesity and insulin resistance in animal models, we failed to establish any indicative associations with common SNPs in this human study.     

Abdominal obesity in BTBR male mice is associated with peripheral but not hepatic insulin resistance

Insulin resistance is a common feature of obesity. BTBR mice have more fat mass than most other inbred mouse strains. On a chow diet, BTBR mice have elevated insulin levels relative to the C57BL/6J (B6) strain. Male F1 progeny of a B6 x BTBR cross are insulin resistant. Previously, we reported insulin resistance in isolated muscle and in isolated adipocytes in this strain. Whereas the muscle insulin resistance was observed only in male F1 mice, adipocyte insulin resistance was also present in male BTBR mice. We examined in vivo mechanisms of insulin resistance with the hyperinsulinemic euglycemic clamp technique. At 10 wk of age, BTBR and F1 mice had a >30% reduction in whole body glucose disposal primarily due to insulin resistance in heart, soleus muscle, and adipose tissue. The increased adipose tissue mass and decreased muscle mass in BTBR and F1 mice were negatively and positively correlated with whole body glucose disposal, respectively. Genes involved in focal adhesion, actin cytoskeleton, and inflammation were more highly expressed in BTBR and F1 than in B6 adipose tissue. The BTBR and F1 mice have higher levels of testosterone, which may be related to the pathological changes in adipose tissue that lead to systemic insulin resistance. Despite profound peripheral insulin resistance, BTBR and F1 mice retained hepatic insulin sensitivity. These studies reveal a genetic difference in body composition that correlates with large differences in peripheral insulin sensitivity.     

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many “distal” causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity—those that directly regulate energy metabolism or caloric intake—seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.     

Reduced biliverdin reductase-A levels are associated with early alterations of insulin signaling in obesity

Biliverdin reductase-A (BVR-A) is a serine/threonine/tyrosine kinase involved in the regulation of insulin signaling. In vitro studies have demonstrated that BVR-A is a substrate of the insulin receptor and regulates IRS1 by avoiding its aberrant activation, and in animal model of obesity the loss of hepatic BVR-A has been associated with glucose/insulin alterations and fatty liver disease. However, no studies exist in humans. Here, we evaluated BVR-A expression levels and activation in peripheral blood mononuclear cells (PBMC) from obese subjects and matched lean controls and we investigated the related molecular alterations of the insulin along with clinical correlates. We showed that BVR-A levels are significantly reduced in obese subjects and associated with a hyper-activation of the IR/IRS1/Akt/GSK-3β/AS160/GLUT4 pathway. Low BVR-A levels also associate with the presence of obesity, metabolic syndrome, NASH and visceral adipose tissue inflammation. These data suggest that the reduction of BVR-A may be responsible for early alterations of the insulin signaling pathway in obesity and in this context may represent a novel molecular target to be investigated for the comprehension of the process of insulin resistance development in obesity.