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

Evidence is presented that shows that free fatty acids (FFA) are one important link between obesity, insulin resistance, and type 2 diabetes. Plasma FFA levels are elevated in most obese subjects, and physiological elevations of plasma FFA inhibit insulin-stimulated glucose uptake into muscle. This peripheral insulin resistance is caused by an FFA-induced defect, which develops 3-4 hr after raising plasma FFA, in insulin-stimulated glucose transport or phosphorylation, or both. This resistance is also caused by a second defect, which develops after 4-6 hr, consisting of inhibition of glycogen synthase activity. Whether elevated plasma FFA levels inhibit insulin action on endogenous glucose production (EGP), that is, cause central insulin resistance, is more difficult to demonstrate. On the one hand, FFA increase gluconeogenesis, which enhances EGP; on the other hand, FFA increase insulin secretion, which decreases EGP. Basal plasma FFA support approximately one third of basal insulin secretion in diabetic and nondiabetic subjects and, hence, are responsible for some of the hyperinsulinemia in obese, normoglycemic patients. In addition, elevated plasma FFA levels potentiate glucose-stimulated insulin secretion acutely and during prolonged exposure (48 hr). It is hypothesized that obese subjects who are genetically predisposed to develop type 2 diabetes will become partially "lipid blind," that is, unable to compensate for their FFA-induced insulin resistance with FFA-induced insulin oversecretion. The resulting insulin resistance/secretion deficit will then have to be compensated for with glucose-induced insulin secretion, which, because of their partial "glucose blindness," will result in hyperglycemia and eventually in type 2 diabetes.
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PMID:Free fatty acids, insulin resistance, and type 2 diabetes mellitus. 1035 64

The development of late onset non-insulin dependent diabetes mellitus (NIDDM) is due to a complicated interplay between genes and environment on one side, and the interaction between metabolic defects in various tissues including the pancreatic beta cell (decreased insulin secretion), skeletal muscle (insulin resistance), liver (increased gluconeogenesis), adipose tissue (increased lipolysis) and possibly gut incretin hormones (defective glucagon like peptide 1 (GLP1) secretion) on the other side. Evidence for a genetic component includes the finding of a variety of metabolic defects in various tissues in non-diabetic subjects with a genetic predisposition to NIDDM, higher concordance rates for abnormal glucose tolerance including NIDDM in monozygotic compared with dizygotic twins, and the more recent demonstration of different NIDDM susceptibility genes at the sites of Insulin Receptor Substrate 1 (IRS1), the beta-3 adrenergic receptor, and the sulfonylurea receptor. However, the latter susceptibility genes only explain a minor proportion of NIDDM in the general population, and the quantitative extent to which genetic versus non-genetic factors contribute to NIDDM is presently unsolved. Environmental components include both an early intrauterine component associated with low birth weight, and later postnatal components including low physical activity, high fat diet, and the subsequent development of obesity and elevated plasma and tissue free fatty acid levels. Our finding of lower birth weights in monozygotic twins compared with their non-diabetic genetically identical co-twins excludes the possibility that the association between NIDDM and low birth weight as demonstrated in several studies may solely be explained by a coincidence between a certain gene causing both a low birth weight and an increased risk of NIDDM. Young first degree relatives of patients with NIDDM are characterized by hyperinsulinaemia and peripheral insulin resistance, which in turn may be explained by a decreased insulin activation of the enzyme glycogen synthase in skeletal muscle. Therefore, a defective skeletal muscle glycogen synthase activation may represent an early phenotypic expression of a genetic defect contributing to an increased risk of later development of NIDDM. However, elderly insulin resistant non-diabetic co-twins (64 years old) of twins with overt NIDDM does not--in contrast to their NIDDM co-twins--have a significantly decreased insulin activation of glycogen synthase in skeletal muscle. This demonstrates that the defective muscle glycogen synthase insulin activation has an apparent non-genetic component, and that this key defect of metabolism can be escaped or postponed even in non-diabetic subjects with a presumably 100% genetic predisposition to NIDDM. The insulin activation of glycogen synthase in skeletal muscle is compensated or apparently normalised in NIDDM patients when studied during their ambient fasting hyperglycaemia and a subsequent isoglycaemic (hyperglycaemic) physiologic insulin infusion. This indicates that the prevailing hyperglycaemia in NIDDM subjects compensates for the defective insulin activation of glycogen synthase present in those subjects when studied during eulycaemia. Our data and those of others also indicates that hyperglycaemia in NIDDM compensates for the defects in insulin secretion, the disproportionately elevated hepatic glucose production, and to some extent for the increased lipid oxidation and the decreased glucose oxidation present in NIDDM patients. Accordingly, NIDDM subjects exhibit all of those defects of metabolism when studied during "experimental decompensation" when the ambient hyperglycaemia is normalized by a prior and later withdrawn intravenous insulin infusion. However, shortly after the withdrawal of the intravenous insulin infusion, the plasma glucose concentration increased spontaneously in the NIDDM patients. (ABSTRACT TRUNCATED)
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PMID:On the pathophysiology of late onset non-insulin dependent diabetes mellitus. Current controversies and new insights. 1042 79

Growth hormone (GH) deficiency in adults is characterized by central obesity, dyslipidemia, coagulopathy and glucose intolerance, all features of the "metabolic syndrome", explaining the increased cardiovascular morbidity and mortality associated with GH deficiency in adults. Employing the 2-step euglycemic-hyperinsulinemic clamp, we have demonstrated severe insulin resistance in GH-deficient adults, with a reduction in insulin-mediated glucose utilization of -50%. Basal glucose turnover and partitioning of whole body glucose utilization into glycolytic flux (GF) and glycogen synthesis/glucose storage (GS) pathways are normal, but insulin activation of these 2 pathways is reduced, predominantly in the GS pathway. Activation of muscle glycogen synthase by insulin is markedly decreased, as is glycogen content of muscle. Insulin-induced muscle hexokinase activity appears also to be attenuated in GH-deficient adults with raised intramuscular cellular glucose and normal-reduced concentrations of glucose-6-phosphate. Beta-cell function is not excessive in GH-deficient adults and is inappropriately low for the insulin resistance. Following treatment of GH-deficient adults with recombinant GH (rhGH), the insulin resistance is either unchanged or more pronounced by 3, 6 or 24 months of treatment, despite the significant reduction in general and central obesity. The GF and GS pathways and muscle glycogen synthase and hexokinase activities remain severely impaired. Abnormalities in free fatty acid (FFA) metabolism are present in rhGH-treated GH-deficient adults and correlate significantly with the degree of insulin resistance as do the concentrations of rhGH-induced insulin-like growth factor (IGF)-I, the post-basal insulinemia and the duration of the GHD, but is independent of obesity. In conclusion, long-term rhGH treatment in GH-deficient adults results in persistent insulin resistance and abnormalities in the GF and GS pathways due to reduced glycogen synthase and hexokinase activities, in the presence of an ongoing reduction of central obesity. We postulate that the insulin resistance is due to chronic rhGH-induced alterations in FFA metabolism, non-physiological levels of IGF-I and chronic basal hyperinsulinemia.
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PMID:Insulin sensitivity in growth hormone (GH)-deficient adults and effect of GH replacement therapy. 1044 67

Insulin resistance seems to be a metabolic aberration associated with obesity. Impaired insulin action is also central to a cluster of diseases including non-insulin dependent diabetes, hypertension, dyslipidemias and atherosclerosis. Body fat distribution, especially upper body segment obesity is related to insulin-resistance. Glucose uptake is insulin dependent in skeletal muscle and adipose tissue. From a quantitative standpoint, skeletal muscle has the greater impact on whole body glucose economy, therefore the cause of altered insulin sensitivity has been looked for in this tissue. The skeletal muscle is composed of different types of fibers with specific metabolic and circulatory characteristics; type IIB fibers are less insulin-sensitive and their proportion has been related to obesity and insulin resistance. The different factors that may impair insulin action and alter glucose uptake in skeletal muscle are: lower blood flow to muscle, produced by either decreased vasodilation or by increased sympathetic nerve activity; augmented diffusion distance from capillaries to muscle due to a decrease in capillary number or to enlarged muscle cells; decrease of insulin receptors; change in the fatty acid profile of major membrane structural phospholipids; decrease in glucose transporters (GLUT 4) and/or hexokinase; impairment in metabolic routes of glucose in muscle as reduction in glycogen synthase. Also, the high rate of lipolysis present in obesity and in insulin resistance could lead to an impaired glucose oxidation in muscle.
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PMID:[Obesity, insulin resistance and skeletal muscle characteristics]. 1051 36

In Western countries 25-35% of the population have insulin resistance syndrome characteristics. The defects most likely to explain the insulin resistance of the insulin resistance syndrome include: 1) the glucose transport system of skeletal muscle (GLUT-4) and its different signalling proteins and enzymes; 2) glucose phosphorylation by hexokinase; 3) glycogen synthase activity and 4) competition between glucose and fatty acid oxidation (glucose-fatty acid cycle). High carbohydrate/low fat diets deteriorate insulin sensitivity on the short term. However, on the long term, high fat/low carbohydrate diets have a lower satiating power, induce low leptin levels and eventually lead to higher energy consumption, obesity and more insulin resistance. Moderately high-carbohydrate (45-55% of the daily calories)/low-fat diets seem to be a good choice with regard to the prevention of diabetes and cardiovascular risk factors as far as the carbohydrates are rich in fibers. Long-term interventions with regular exercise programs show a 1/3 decrease in the appearance of overt diabetes in glucose intolerant subjects. Furthermore, diet and exercise interventions "normalise" the mortality rate of patients with impared glucose tolerance. Therefore, moderately high carbohydrate/low fat diets are most likely to prevent obesity and type 2 diabetes. Triglycerides should be monitored and, in some cases, a part of the carbohydrates could be replaced by fat rich in monounsaturated fatty acids. However, total caloric intake is of utmost importance, as weight gain is the major determinant for the onset of insulin resistance and glucose intolerance. Regular (when possible daily) exercise, decreases cardiovascular risk. With regard to insulin resistance, resistance training seems to offer some advantages over aerobic endurance activities.
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PMID:Interaction of physical activity and diet: implications for insulin-glucose dynamics. 1061 74

Long term chronic calorie restriction (CR) of adult nonhuman primates significantly reduces morbidity and increases median age of death. The present review is focused upon an ongoing study of sustained adult-onset calorie restriction, which has been underway for 15 years. Monkeys, initially calorie restricted at about 10 years of age, are now approximately 25 years old. The median life span of these restricted monkeys is increasing, now exceeding that of ad libitum (AL)-fed monkeys. In our laboratory, maximum life span for AL-fed monkeys appears to be about 40 years. Thus, whether CR can also increase maximal life span, as it does in rodents, cannot be determined for at least another 15 years. The earliest detectable positive benefit on morbidity in these monkeys was previously reported as the prevention of obesity. Current evidence, as reviewed here, suggests that much obesity-associated morbidity is also mitigated by sustained calorie restraint in nonhuman primates. Furthermore, probably because of the prevention of obesity, diabetes has also been prevented. Recent findings include the identification of extraordinary changes in the glycogen synthesis pathway, and on the phosphorylation of glycogen synthase in response to insulin. This calorie restriction-induced prevention of morbidity does not require excessive leanness, but is clearly present when body fat is within the normal range of 10 to 22%, and this is likely to be true in humans as well.
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PMID:Calorie restriction in nonhuman primates: mechanisms of reduced morbidity and mortality. 1063 May 91

Insulin resistance is followed by several prevalent diseases. The most common condition with insulin resistance is obesity, particularly when localized to abdominal, visceral regions. A summary of recent reviews on the pathogenesis of systemic insulin resistance indicates that major factors are decreased insulin effects on muscular glycogen synthase or preceding steps in the insulin signalling cascade, on endogenous glucose production and on circulating free fatty acids (FFA) from adipose tissue lipolysis. Contributions of morphologic changes in muscle and other factors are considered more uncertain. Newly developed methodology has made it possible to determine more precisely the neuroendocrine abnormalities in abdominal obesity including increased cortisol and adrenal androgen secretions. This is probably due to a hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, amplified by inefficient feedback inhibition by central glucocorticoid receptors, associated with molecular genetic defects. Secondly, secretion of gender-specific sex steroid hormones becomes inhibited and the sympathetic nervous system activated. At this stage the HPA axis shows signs of a 'burned-out' condition, and cortisol secretion is no longer elevated. Cortisol counteracts the insulin activation of glycogen synthase in muscle, the insulin inhibition of hepatic glucose production and the insulin inhibition of lipolysis in adipose tissue, leading to the well-established systemic insulin resistance caused by excess cortisol. This is exaggerated by increased free fatty acid mobilization, particularly with a concomitant elevation of the activity of the sympathetic nervous system. Furthermore, capillarization and fiber composition in muscle are changed. These are the identical perturbations responsible for insulin resistance in recent reviews. The diminished sex steroid secretion in abdominal obesity has the same consequences. It is thus clear that insulin resistance may be induced by neuroendocrine abnormalities, such as those seen in abdominal obesity. These endocrine perturbations also direct excess fat to visceral fat depots via mechanisms that are largely known, indicating why abdominal obesity is commonly associated with insulin resistance. This possible background to the most prevalent condition of insulin resistance has been revealed by development of methodology that allows sufficiently sensitive measurements of HPA axis activity. These findings demonstrate the power of neuroendocrine regulations for somatic health.
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PMID:Neuroendocrine perturbations as a cause of insulin resistance. 1063 68

To examine the effect of increased hexosamine flux in liver, the rate-limiting enzyme in hexosamine biosynthesis (glutamine:fructose-6-phosphate amidotransferase [GFA]) was overexpressed in transgenic mice using the PEPCK promoter. Liver from random-fed transgenic mice had 1.6-fold higher GFA activity compared with nontransgenic control littermates (276 +/- 24 pmol x mg(-1) x min(-1) in transgenic mice vs. 176 +/- 18 pmol x mg(-1) x min(-1) in controls, P < 0.05) and higher levels of the hexosamine end product UDP-N-acetyl glucosamine (288 +/- 11 pmol/g in transgenic mice vs. 233 +/- 10 pmol/g in controls, P < 0.001). Younger transgenic mice compared with control mice had lower fasting serum glucose (4.8 +/- 0.5 mmol/l in transgenic mice vs. 6.5 +/- 0.8 mmol/l in controls, P < 0.05) without higher insulin levels (48.0 +/- 7.8 pmol/l in transgenic mice vs. 56.4 +/- 5.4 pmol/l in controls, P = NS); insulin levels were significantly lower in transgenic males (P < 0.05). At 6 months of age, transgenic animals had normal insulin sensitivity by the hyperinsulinemic clamp technique. Hepatic glycogen content was higher in the transgenic mice (108.6 +/- 5.2 pmol/g in transgenic mice vs. 32.8 +/- 1.3 micromol/g in controls, P < 0.01), associated with an inappropriate activation of glycogen synthase. Serum levels of free fatty acids (FFAs) and triglycerides were also elevated (FFAs, 0.67 +/- 0.03 mmol/l in transgenic mice vs. 0.14 +/- 0.01 in controls; triglycerides, 1.34 +/- 0.15 mmol/l in transgenic mice vs. 0.38 +/- 0.01 in controls, P < 0.01). Older transgenic mice became heavier than control mice and exhibited relative glucose intolerance and insulin resistance. The glucose disposal rate at 8 months of age was 154 +/- 5 mg x kg(-1) x min(-1) in transgenic mice vs. 191 +/- 6 mg x kg(-1) x min(-1) in controls (P < 0.05). We conclude that hexosamines are mediators of glucose sensing for the regulation of hepatic glycogen and lipid metabolism. Increased hexosamine flux in the liver signals a shift toward fuel storage, resulting ultimately in obesity and insulin resistance.
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PMID:Overexpression of glutamine: fructose-6-phosphate amidotransferase in the liver of transgenic mice results in enhanced glycogen storage, hyperlipidemia, obesity, and impaired glucose tolerance. 1111 9

Our aim was to investigate the effects of one year recombinant human growth hormone (rhGH) therapy on the regulation by insulin of gene expression in muscle and adipose tissue in adults with secondary GH deficiency (GHD). Six GHD subjects without upper-body obesity were submitted to a 3-h euglycemic hyperinsulinemic clamp before and after one year of rhGH therapy. Muscle and abdominal subcutaneous adipose tissue biopsies were taken before and at the end of each clamp. The mRNA levels of insulin receptor, p85 alpha-phosphatidylinositol-3 kinase (p85 alpha PI-3K), insulin dependent glucose transporter (Glut4), hexokinase II, glycogen synthase, lipoprotein lipase (LPL) in muscle and in adipose tissue, hormone sensitive lipase and peroxisome proliferator-activated receptor gamma (PPAR gamma) in adipose tissue were quantified by RT-competitive PCR. One year treatment with rhGH (1.25 IU/day) increased plasma IGF-I concentrations (54+/-7 vs 154+/-11 ng/ml, P<0.01) but did not affect insulin-stimulated glucose disposal rate measured during the hyperinsulinemic clamp (74+/-9 vs 85+/-5 micromol/kg free fat mass/min). Insulin significantly increased p85 alpha PI-3K, hexokinase II and Glut4 mRNA levels in muscle both before and after rhGH treatment. One year of GH therapy increased LPL mRNA levels in muscle (38+/-2 vs 70+/-7 amol/microg total RNA, P<0.05) and in adipose tissue (2490+/-260 vs 4860+/-880 amol/microg total RNA, P<0.05), but did not change the expression of the other mRNAs. We conclude from this study that GH therapy did not alter whole body insulin sensitivity and the response of gene expression to insulin in skeletal muscle of adult GHD patients, but it did increase LPL expression in muscle and adipose tissue. This result could be related to the documented beneficial effect of GH therapy on lipid metabolism.
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PMID:Expression of insulin target genes in skeletal muscle and adipose tissue in adult patients with growth hormone deficiency: effect of one year recombinant human growth hormone therapy. 1169 48

Type 2 diabetes is characterised by both impaired insulin secretion and insulin resistance but their relative contribution to the development of hyperglycaemia may differ due to heterogeneity of the disease. Under most circumstances, insulin resistance is the earliest detectable defect in pre-diabetic individuals but it is not known whether this is the primary defect or secondary to other abnormalities such as abdominal obesity with excessive free fatty acid turnover and increased lipid deposits in muscle. Initially, enhanced insulin secretion can compensate for the insulin resistance but early phase insulin secretion is impaired. In the transition from normal to impaired and diabetic glucose tolerance, insulin sensitivity deteriorates about 40% whereas insulin secretion deteriorates 3-4 fold. In addition to insulin resistance, the metabolic syndrome includes hypertension, dyslipidaemia, obesity and microalbuminuria. In patients with manifest diabetes, chronic hyperglycaemia can result in further deterioration of insulin sensitivity and secretion (glucotoxicity), which is aggravated by elevated free fatty acids (lipotoxicity). Abdominal obesity and insulin resistance are strongly correlated and studies have aimed at understanding the genetic basis. Candidate genes for the metabolic syndrome include those for the beta 3-adrenergic receptor, lipoprotein lipase, hormone sensitive lipase, peroxisome proliferator-activated receptor-gamma, insulin receptor substrate-1 and glycogen synthase. Therefore, type 2 diabetes is multigenic and appears to represent a collision between thrifty genes and an affluent society. Successful management will require treatments targeted at defects of both insulin secretion and insulin resistance.
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PMID:Pathogenesis of type 2 diabetes: the relative contribution of insulin resistance and impaired insulin secretion. 1196 29


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