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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The adipose tissue has become a central focus in the pathogenesis of obesity-mediated cardiovascular and metabolic disease. Here we demonstrate that adipose sphingolipid metabolism is altered in genetically obese (ob/ob) mice. Expression of enzymes involved in ceramide generation (neutral sphingomyelinase [NSMase], acid sphingomyelinase [ASMase], and serine-palmitoyl-transferase [SPT]) and ceramide hydrolysis (ceramidase) are elevated in obese adipose tissues. Our data also suggest that hyperinsulinemia and elevated tumor necrosis factor (TNF)-alpha associated with obesity may contribute to the observed increase in adipose NSMase, ASMase, and SPT mRNA in this murine model of obesity. Liquid chromatography/mass spectroscopy revealed a decrease in total adipose sphingomyelin and ceramide levels but an increase in sphingosine in ob/ob mice compared with lean mice. In contrast to the adipose tissue, plasma levels of total sphingomyelin, ceramide, sphingosine, and sphingosine 1-phosphate (S1P) were elevated in ob/ob mice. In cultured adipocytes, ceramide, sphingosine, and S1P induced gene expression of plasminogen activator inhibitor-1, TNF-alpha, monocyte chemoattractant protein-1, interleukin-6, and keratinocyte-derived chemokine. Collectively, our results identify a novel role for sphingolipids in contributing to the prothrombotic and proinflammatory phenotype of the obese adipose tissue currently believed to play a major role in the pathogenesis of obesity-mediated cardiovascular and metabolic disease.
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PMID:Altered adipose and plasma sphingolipid metabolism in obesity: a potential mechanism for cardiovascular and metabolic risk. 1693 7

Lifestyle interventions including exercise programmes are cornerstones in the prevention of obesity-related diabetes. In this study, we demonstrate that a single bout of exercise inhibits high-fat diet-induced insulin resistance. Diet-induced obesity (DIO) increased the expression and activity of the protein tyrosine phosphatase 1B (PTP1B) and attenuated insulin signalling in gastrocnemius muscle of rats, a phenomenon which was reversed by a single session of exercise. In addition, DIO was observed to lead to serine phosphorylation of insulin receptor substrate 1 (IRS-1), which was also reversed by exercise in muscle in parallel with a reduction in c-Jun N-terminal kinase (JNK) activity. Thus, acute exercise increased the insulin sensitivity during high-fat feeding in obese rats. Overall, these results provide new insights into the mechanism by which exercise restores insulin sensitivity.
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PMID:Reversal of diet-induced insulin resistance with a single bout of exercise in the rat: the role of PTP1B and IRS-1 serine phosphorylation. 1700 71

The role of inflammation as a mediator of insulin resistance in type 2 diabetes and obesity has been a major focus of studies over the past ten years. In mouse models of obesity and type 2 diabetes, the development of insulin resistance correlates with elevated levels of endoplasmic reticulum stress and induction of the unfolded protein response. Activation of N-terminal C-Jun kinase is known to be associated with unfolded protein response activation, and has been shown to participate in the inhibition of insulin action by stimulating serine phosphorylation of the insulin receptor substrate 1, an event that attenuates insulin signaling. 'Chemical chaperones' are small molecules that have been shown to attenuate unfolded protein response activation. The exciting new findings of Ozcan et al. indicate that chemical chaperones improve glucose tolerance and insulin action in a mouse model of type 2 diabetes. These findings offer a potential new target for therapeutic strategies designed to improve insulin action and glucose tolerance in diabetic individuals.
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PMID:Chemically chaperoning the actions of insulin. 1711 1

Obesity is often associated with diabetes and insulin resistance. This review summarizes evidence obtained in our lab on the role of the serine phosphorylation of the insulin receptor substrate 1 in the down regulation of insulin signalling. The role of the ERK1 isoform in the development of adipose tissue and insulin sensitivity is also presented.
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PMID:[Obesity, diabetes and insulin resistance. Alterations of insulin signalling]. 1714 67

Insulin resistance is a feature of a number of clinical disorders, including type 2 diabetes/glucose intolerance, obesity, dyslipidaemia and hypertension clustering in the so-called metabolic syndrome. Insulin resistance in skeletal muscle manifests itself primarily as a reduction in insulin-stimulated glycogen synthesis due to reduced glucose transport. Ectopic lipid accumulation plays an important role in inducing insulin resistance. Multiple defects in insulin signalling are responsible for impaired glucose metabolism in target tissues of subjects with features of insulin resistance. Inflammatory molecules and lipid metabolites inhibit insulin signalling by stimulating a number of different serine kinases which are responsible for serine phosphorylation of Insulin Receptor Substrate-1 (IRS-1).
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PMID:Pathophysiology of insulin resistance. 1716 38

Adipose tissue secretes different adipokines, including interleukin-6 (IL-6), that have been implicated in the insulin resistance and inflammatory state characterizing obesity. We examined the putative cross-talk between insulin and IL-6 in adipose cells and found that insulin exerts an inhibitory effect on the IL-6 signaling pathway by altering the post-translational modifications of the signal transducer and activator of transcription 3 (STAT3). Insulin reduces the tyrosine phosphorylation and increases the serine phosphorylation of STAT3, thereby reducing its nuclear localization and transcriptional activity. Signaling through the MEK/MAPK pathway plays an important role as treatment with the MEK inhibitor PD98059 reduces the effects of insulin on IL-6 signaling. We also show that the protein tyrosine phosphatase SHP2 is activated upon insulin signaling and is required for the dephosphorylation of STAT3 and that insulin exerts a synergistic effect with IL-6 on suppressor of cytokine signaling 3 expression. As a consequence, the IL-6-induced expression of the inflammatory markers serum amyloid A 3 and haptoglobin are significantly decreased in cells incubated with both IL-6 and insulin. Thus, insulin exerts an important anti-inflammatory effect in adipose cells by impairing the IL-6 signal at several levels.
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PMID:Insulin antagonizes interleukin-6 signaling and is anti-inflammatory in 3T3-L1 adipocytes. 1726 1

Insulin resistance is a pathophysiological link of obesity to type 2 diabetes. The initial cause of insulin resistance is critical for prevention and treatment of type 2 diabetes. Lipotoxicity is a well-known concept in the explanation of initiation of insulin resistance. Although there are several prevailing hypotheses about the cellular/molecular mechanisms of lipotoxicity, such as inflammation, oxidative stress, hyperinsulinemia, and ER stress, the relative importance of these hypothesized events remains to be determined. The role of hyperinsulinemia is relatively under documented in the literature for the initiation of insulin resistance. In this review, an interaction of fatty acid and beta-cells, and a synergy between free fatty acids (FFAs) and insulin are emphasized for the role of hyperinsulinemia. This article presents the evidence about FFA-induced insulin secretion in vitro and in vivo, recent advances in the molecular mechanism of FFA action in beta-cells, a role of GPR40 in the development of insulin resistance, and the negative feedback loop of the insulin receptor signal pathway. The negative feedback loop is discussed in detail with a focus on IRS-1 serine kinases. This article provides a substantial support for the role of insulin in the early stages of FFA-associated insulin resistance. The hypothesis of insulin's role in lipotoxicity is referred to as the "insulin hypothesis" in this review. According to this hypothesis, prevention of increased beta-cell response to glucose may be a potential approach for early intervention of metabolic syndrome.
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PMID:Role of insulin in the pathogenesis of free fatty acid-induced insulin resistance in skeletal muscle. 1734 4

Free fatty acid (FFA) is believed to be a major environmental factor linking obesity to Type II diabetes. We have recently reported that FFA can induce gluconeogenesis in hepatocytes through p38 mitogen-activated protein kinase (p38). In this study, we have investigated the role of p38 in oleate-induced hepatic insulin resistance. Our results show that a prolonged treatment of primary hepatocytes with oleate blunted insulin suppression of hepatic gluconeogenesis, and decreased insulin-induced phosphorylation of Akt in a p38-dependent manner. Reduction of the insulin-induced Akt phosphorylation by oleate correlated with activation of p38. In the presence of p38 inhibition, prolonged exposure of hepatocytes to oleate failed to reduce insulin-stimulated phosphorylation of Akt. An siRNA against p38alpha prevented oleate suppression of the insulin-induced phosphorylation of Akt. Furthermore, a prolonged exposure of hepatocytes to oleate decreased insulin-induced tyrosine phosphorylation of IRS1/2, while slightly increasing serine phosphorylation of IRS. The decrease of insulin-stimulated tyrosine phosphorylation of IRS1/2 in hepatocytes by oleate was reversed by the inhibition of p38. We further show that a prolonged exposure of primary hepatocytes to oleate elevated the protein level of the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene in a p38-dependent manner, but had no effect on the mRNA level of PTEN. Knocking down the PTEN gene prevented oleate to inhibit insulin activation of Akt and insulin suppression of gluconeogenesis. Together, results from this study demonstrate a critical role for p38 in oleate-induced hepatic insulin resistance.
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PMID:Prolonged treatment of primary hepatocytes with oleate induces insulin resistance through p38 mitogen-activated protein kinase. 1738 40

NO plays critical roles in vascular function. We show that modulation of the eNOS serine 1179 (S1179) phosphorylation site affects vascular reactivity and determines stroke size in vivo. Transgenic mice expressing only a phosphomimetic (S1179D) form of eNOS show greater vascular reactivity, develop less severe strokes, and have improved cerebral blood flow in a middle cerebral artery occlusion model than mice expressing an unphosphorylatable (S1179A) form. These results provide a molecular mechanism by which multiple diverse cardiovascular risks, such as diabetes and obesity, may be centrally integrated by eNOS phosphorylation in vivo to influence blood flow and cardiovascular disease. They also demonstrate the in vivo relevance of posttranslational modification of eNOS in vascular function.
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PMID:The phosphorylation state of eNOS modulates vascular reactivity and outcome of cerebral ischemia in vivo. 1755 22

Genetic deletion of inducible nitric oxide synthase (NOS) in mice has been shown to improve high-fat diet (HFD)-induced insulin resistance. However, a pathophysiological role of endogenous nitric oxide (NO) in obesity-related insulin resistance remains controversial. To address this issue, we examined the metabolic phenotypes in HFD-induced obese mice with chronic blockade of NO synthesis by a NOS inhibitor, N(G)-nitro-l-arginine methyl ester (L-NAME). Six-week-old male C57BL/6j mice were provided free access to either a standard diet (SD) or a HFD and tap water with or without L-NAME (100 mg/kg.d) for 12 wk. L-NAME treatment significantly attenuated body weight gain of mice fed either SD or HFD without affecting calorie intake. L-NAME treatment in HFD-fed mice improved glucose tolerance and insulin sensitivity. HFD feeding induced inducible NOS mRNA expression, but not the other two NOS isoforms, in white adipose tissue (WAT) and skeletal muscle. L-NAME treatment up-regulated uncoupling protein-1 in brown adipose tissue of HFD-fed mice but down-regulated monocyte chemoattractant protein-1 and CD68 mRNAs levels in WAT. HFD feeding up-regulated leptin mRNA levels but conversely down-regulated adiponectin mRNA levels in WAT, but these effects were unaffected by L-NAME treatment. Moreover, L-NAME treatment also increased peroxisome proliferator-uncoupling protein-3 mRNA levels in skeletal muscles of HFD-fed mice. Increased urinary excretion of norepinephrine after HFD feeding was augmented in L-NAME-treated mice. Insulin-stimulated tyrosine phosphorylation of insulin receptor substrate-1 and serine phosphorylation of Akt/Akt2 in soleus muscle was markedly impaired in HFD-fed mice but reversed by L-NAME treatment. In conclusion, chronic NOS blockade by L-NAME in mice ameliorates HFD-induced adiposity and glucose intolerance, accompanied by reduced adipose inflammation and improved insulin signaling in skeletal muscle, suggesting that endogenous NO plays a modulatory role in the development of obesity-related insulin resistance.
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PMID:Chronic blockade of nitric oxide synthesis reduces adiposity and improves insulin resistance in high fat-induced obese mice. 1787 34


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