Showing papers on "Insulin resistance published in 2003"
TL;DR: It is proposed that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue, and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced insulin resistance.
Abstract: Insulin resistance arises from the inability of insulin to act normally in regulating nutrient metabolism in peripheral tissues Increasing evidence from human population studies and animal research has established correlative as well as causative links between chronic inflammation and insulin resistance However, the underlying molecular pathways are largely unknown In this report, we show that many inflammation and macrophage-specific genes are dramatically upregulated in white adipose tissue (WAT) in mouse models of genetic and high-fat diet-induced obesity (DIO) The upregulation is progressively increased in WAT of mice with DIO and precedes a dramatic increase in circulating-insulin level Upon treatment with rosiglitazone, an insulin-sensitizing drug, these macrophage-originated genes are downregulated Histologically, there is evidence of significant infiltration of macrophages, but not neutrophils and lymphocytes, into WAT of obese mice, with signs of adipocyte lipolysis and formation of multinucleate giant cells These data suggest that macrophages in WAT play an active role in morbid obesity and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced insulin resistance We propose that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue
6,165 citations
TL;DR: The cloning of complementary DNAs encoding adiponectin receptors 1 and 2 by expression cloning supports the conclusion that they serve as receptors for globular and full-length adiponECTin, and that they mediate increased AMP kinase and PPAR-α ligand activities, as well as fatty-acid oxidation and glucose uptake by adiponectionin.
Abstract: Adiponectin (also known as 30-kDa adipocyte complement-related protein; Acrp30) is a hormone secreted by adipocytes that acts as an antidiabetic and anti-atherogenic adipokine. Levels of adiponectin in the blood are decreased under conditions of obesity, insulin resistance and type 2 diabetes. Administration of adiponectin causes glucose-lowering effects and ameliorates insulin resistance in mice. Conversely, adiponectin-deficient mice exhibit insulin resistance and diabetes. This insulin-sensitizing effect of adiponectin seems to be mediated by an increase in fatty-acid oxidation through activation of AMP kinase and PPAR-alpha. Here we report the cloning of complementary DNAs encoding adiponectin receptors 1 and 2 (AdipoR1 and AdipoR2) by expression cloning. AdipoR1 is abundantly expressed in skeletal muscle, whereas AdipoR2 is predominantly expressed in the liver. These two adiponectin receptors are predicted to contain seven transmembrane domains, but to be structurally and functionally distinct from G-protein-coupled receptors. Expression of AdipoR1/R2 or suppression of AdipoR1/R2 expression by small-interfering RNA supports our conclusion that they serve as receptors for globular and full-length adiponectin, and that they mediate increased AMP kinase and PPAR-alpha ligand activities, as well as fatty-acid oxidation and glucose uptake by adiponectin.
3,013 citations
TL;DR: There is a need to continue to explore the relationship between free radicals, diabetes, and its complications, and to elucidate the mechanisms by which increased oxidative stress accelerates the development of diabetic complications, in an effort to expand treatment options.
Abstract: Increasing evidence in both experimental and clinical studies suggests that oxidative stress plays a major role in the pathogenesis of both types of diabetes mellitus. Free radicals are formed disproportionately in diabetes by glucose oxidation, nonenzymatic glycation of proteins, and the subsequent oxidative degradation of glycated proteins. Abnormally high levels of free radicals and the simultaneous decline of antioxidant defense mechanisms can lead to damage of cellular organelles and enzymes, increased lipid peroxidation, and development of insulin resistance. These consequences of oxidative stress can promote the development of complications of diabetes mellitus. Changes in oxidative stress biomarkers, including superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, glutathione levels, vitamins, lipid peroxidation, nitrite concentration, nonenzymatic glycosylated proteins, and hyperglycemia in diabetes, and their consequences, are discussed in this review. In vivo studies of the effects of various conventional and alternative drugs on these biomarkers are surveyed. There is a need to continue to explore the relationship between free radicals, diabetes, and its complications, and to elucidate the mechanisms by which increased oxidative stress accelerates the development of diabetic complications, in an effort to expand treatment options.
2,930 citations
TL;DR: The presence of multiple metabolic disorders is associated with a potentially progressive, severe liver disease and the increasing prevalence of obesity, coupled with diabetes, dyslipidemia, hypertension, and ultimately the metabolic syndrome puts a very large population at risk of forthcoming liver failure in the next decades.
2,538 citations
TL;DR: The research agenda for the future includes establishing the role of insulin resistance and abnormal lipoprotein metabolism in NASH, determining the pathogenesis of cellular injury, defining predisposing genetic abnormalities, identifying better noninvasive predictors of disease, and defining effective therapy.
2,134 citations
TL;DR: Greater understanding of the relative roles of insulin resistance and beta-cell dysfunction in Type 2 diabetes can anticipate advances in the identification of genes contributing to the development of the disease as well as approaches to the treatment and prevention of Type 1 diabetes.
Abstract: The relative contributions of insulin resistance and beta-cell dysfunction to the pathophysiology of Type 2 diabetes have been debated extensively. The concept that a feedback loop governs the interaction of the insulin-sensitive tissues and the beta cell as well as the elucidation of the hyperbolic relationship between insulin sensitivity and insulin secretion explains why insulin-resistant subjects exhibit markedly increased insulin responses while those who are insulin-sensitive have low responses. Consideration of this hyperbolic relationship has helped identify the critical role of beta-cell dysfunction in the development of Type 2 diabetes and the demonstration of reduced beta-cell function in high risk subjects. Furthermore, assessments in a number of ethnic groups emphasise that beta-cell function is a major determinant of oral glucose tolerance in subjects with normal and reduced glucose tolerance and that in all populations the progression from normal to impaired glucose tolerance and subsequently to Type 2 diabetes is associated with declining insulin sensitivity and beta-cell function. The genetic and molecular basis for these reductions in insulin sensitivity and beta-cell function are not fully understood but it does seem that body-fat distribution and especially intra-abdominal fat are major determinants of insulin resistance while reductions in beta-cell mass contribute to beta-cell dysfunction. Based on our greater understanding of the relative roles of insulin resistance and beta-cell dysfunction in Type 2 diabetes, we can anticipate advances in the identification of genes contributing to the development of the disease as well as approaches to the treatment and prevention of Type 2 diabetes.
2,028 citations
TL;DR: Elderly study participants were markedly insulin-resistant as compared with young controls, and this resistance was attributable to reduced insulin-stimulated muscle glucose metabolism, which supports the hypothesis that an age-associated decline in mitochondrial function contributes to insulin resistance in the elderly.
Abstract: Insulin resistance is a major factor in the pathogenesis of type 2 diabetes in the elderly. To investigate how insulin resistance arises, we studied healthy, lean, elderly and young participants matched for lean body mass and fat mass. Elderly study participants were markedly insulin-resistant as compared with young controls, and this resistance was attributable to reduced insulin-stimulated muscle glucose metabolism. These changes were associated with increased fat accumulation in muscle and liver tissue assessed by 1H nuclear magnetic resonance (NMR) spectroscopy, and with a approximately 40% reduction in mitochondrial oxidative and phosphorylation activity, as assessed by in vivo 13C/31P NMR spectroscopy. These data support the hypothesis that an age-associated decline in mitochondrial function contributes to insulin resistance in the elderly.
1,984 citations
TL;DR: Older age, postmenopausal status, Mexican American ethnicity, higher body mass index, current smoking, low household income, high carbohydrate intake, no alcohol consumption, and physical inactivity were associated with increased odds of the metabolic syndrome.
Abstract: Coronary heart disease (CHD) is the leading cause of death in the United States.1 Factors associated with an increased risk of developing CHD that tend to cluster in individuals include older age, high blood pressure, a low level of high-density lipoprotein (HDL) cholesterol, a high triglyceride level, a high plasma glucose concentration, and obesity.2 These associated risk factors have been called syndrome X,3 the insulin resistance syndrome,4 or the metabolic syndrome.5
The mechanisms underlying the metabolic syndrome are not fully known; however, resistance to insulin-stimulated glucose uptake seems to modify biochemical responses in a way that predisposes to metabolic risk factors.3,6,7 Insulin resistance is thought to be primarily due to obesity or an inherited genetic defect.8 As the prevalence of obesity increases in the United States, the prevalence of the metabolic syndrome may be expected to increase markedly. Estimates of the prevalence of the metabolic syndrome have varied substantially in part because of the variability of evaluated populations and of diagnostic criteria.9
The recent Third Report of the National Cholesterol Education Program Adult Treatment Panel (ATP III) included clinical diagnosis guidelines for the metabolic syndrome.10 Compared with findings from earlier studies3-5 and World Health Organization guidelines, the new ATP III defines criteria readily measured in clinical practice. These consensus-generated guidelines provide the opportunity to assess the overall prevalence of the metabolic syndrome in the US population according to an accepted standard definition. In an initial study, Ford et al11 reported un-adjusted and age-adjusted metabolic syndrome prevalences of 21.8% and 23.7%, respectively, for the US population. The objectives of this study are to examine the prevalence of the metabolic syndrome by ethnicity, age, body mass index (BMI) (calculated as weight in kilograms divided by the square of height in meters), socioeconomic status, and lifestyle factors.
1,950 citations
TL;DR: It is demonstrated that insulin resistance and DM associate with reduced expression of multiple nuclear respiratory factor-1 (NRF-1)-dependent genes encoding key enzymes in oxidative metabolism and mitochondrial function.
Abstract: Type 2 diabetes mellitus (DM) is characterized by insulin resistance and pancreatic beta cell dysfunction. In high-risk subjects, the earliest detectable abnormality is insulin resistance in skeletal muscle. Impaired insulin-mediated signaling, gene expression, glycogen synthesis, and accumulation of intramyocellular triglycerides have all been linked with insulin resistance, but no specific defect responsible for insulin resistance and DM has been identified in humans. To identify genes potentially important in the pathogenesis of DM, we analyzed gene expression in skeletal muscle from healthy metabolically characterized nondiabetic (family history negative and positive for DM) and diabetic Mexican-American subjects. We demonstrate that insulin resistance and DM associate with reduced expression of multiple nuclear respiratory factor-1 (NRF-1)-dependent genes encoding key enzymes in oxidative metabolism and mitochondrial function. Although NRF-1 expression is decreased only in diabetic subjects, expression of both PPAR gamma coactivator 1-alpha and-beta (PGC1-alpha/PPARGC1 and PGC1-beta/PERC), coactivators of NRF-1 and PPAR gamma-dependent transcription, is decreased in both diabetic subjects and family history-positive nondiabetic subjects. Decreased PGC1 expression may be responsible for decreased expression of NRF-dependent genes, leading to the metabolic disturbances characteristic of insulin resistance and DM.
1,915 citations
TL;DR: This is the first of two articles describing a symposium on insulin action, insulin resistance, inflammation, and Atherosclerosis in Niagara Falls, New York, 20–21 September 2002, which will cover topics related to atherosclerosis pathobiology and the cell biology of insulin resistance.
Abstract: This Is the second of two articles describing a symposium on the relationship between inflammation and insulin resistance that was held in Niagra Falls, NY, 20–21 September 2002.
Antonio Ceriello (Udine, Italy) discussed the role of glucose intake and postprandial hyperglycemia in the development of diabetes complications, as well as the relationship of hyperglycemia to oxidative stress. The DECODE (Diabetes Epidemiology: Collaborative analysis Of Diagnostic criteria in Europe) study showed high 2-h postload glucose to be associated with increased mortality independent of fasting glucose (1), and the Pacific and Indian Ocean Study showed isolated 2-h hyperglycemia to double the risk of mortality (2). The Funagata Diabetes Study showed that impaired glucose tolerance (IGT) but not impaired fasting glucose was a risk factor for cardiovascular disease (CVD) (3). There is evidence that lowering postprandial glucose improves outcome. Post hoc analysis of the STOP-type 2 diabetes study showed that myocardial infarction and hypertension decrease with use of the prandial glucose-lowering agent acarbose (4). In the Kumamoto study, postprandial hyperglycemia strongly predicted retinopathy and nephropathy (5).
Endothelial dysfunction (ED) is a potential mediator of the effect of prandial glycemia, with altered vasodilation and procoagulant abnormalities. ED can be induced by hyperglycemia following a 75-g oral glucose load in persons with normal or IGT or with diabetes, with reduction of flow-mediated brachial artery dilation proportional to the degree of hyperglycemia (6). In a study of 225 persons with hypertension followed for 32 months, forearm ED was a marker of future CVD events (7), with a 4.5-year follow-up of 281 persons showing both ED and measures of oxidative stress to predict CVD events (8). Acute hyperglycemia may suppress vasodilation, which may involve oxidant stress, as it is reversed with antioxidant or l-arginine treatment (9).
Glucose increases endothelial cell free radical production leading …
1,773 citations
TL;DR: A multidisciplinary program aimed to reduce body weight in obese women through lifestyle changes was associated with a reduction in markers of vascular inflammation and insulin resistance.
Abstract: ContextObesity is an independent risk factor for cardiovascular disease, which
may be mediated by increased secretion of proinflammatory cytokines by adipose
tissue.ObjectiveTo determine the effect of a program of changes in lifestyle designed
to obtain a sustained reduction of body weight on markers of systemic vascular
inflammation and insulin resistance.Design and SettingRandomized single-blind trial conducted from February 1999 to February
2002 at a university hospital in Italy.PatientsOne hundred twenty premenopausal obese women (body mass index ≥30)
aged 20 to 46 years without diabetes, hypertension, or hyperlipidemia.InterventionsThe 60 women randomly assigned to the intervention group received detailed
advice about how to achieve a reduction of weight of 10% or more through a
low-energy Mediterranean-style diet and increased physical activity. The control
group (n = 60) was given general information about healthy food choices and
exercise.Main Outcome MeasuresLipid and glucose intake; blood pressure; homeostatic model assessment
of insulin sensitivity; and circulating levels of interleukin 6 (IL-6), interleukin
18 (IL-18), C-reactive protein (CRP), and adiponectin.ResultsAfter 2 years, women in the intervention group consumed more foods rich
in complex carbohydrates (9% corrected difference; P<.001),
monounsaturated fat (2%; P = .009), and fiber (7
g/d; P<.001); had a lower ratio of omega-6 to
omega-3 fatty acids (−5; P<.001); and had
lower energy (−310 kcal/d; P<.001), saturated
fat (−3.5%; P = .007), and cholesterol intake
(−92 mg/d; P<.001) than controls. Body mass
index decreased more in the intervention group than in controls (−4.2; P<.001), as did serum concentrations of IL-6 (−1.1
pg/mL; P = .009), IL-18 (−57 pg/mL; P = .02), and CRP (−1.6 mg/L; P = .008),
while adiponectin levels increased significantly (2.2 µg/mL; P = .01). In multivariate analyses, changes in free fatty acids (P = .008), IL-6 (P = .02), and
adiponectin (P = .007) levels were independently
associated with changes in insulin sensitivity.ConclusionIn this study, a multidisciplinary program aimed to reduce body weight
in obese women through lifestyle changes was associated with a reduction in
markers of vascular inflammation and insulin resistance.
TL;DR: It is proposed here that the hyperglycemia- induced, and possibly FFA-induced, activation of stress pathways plays a key role in the development of not only the late complications in type 1 and type 1 diabetes, but also the insulin resistance and impaired insulin secretion seen in type 2 diabetes.
Abstract: In both type 1 and type 2 diabetes, diabetic complications in target organs arise from chronic elevations of glucose. The pathogenic effect of high glucose, possibly in concert with fatty acids, is mediated to a significant extent via increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and subsequent oxidative stress. ROS and RNS directly oxidize and damage DNA, proteins, and lipids. In addition to their ability to directly inflict damage on macromolecules, ROS and RNS indirectly induce damage to tissues by activating a number of cellular stress-sensitive pathways. These pathways include nuclear factor-kappaB, p38 mitogen-activated protein kinase, NH(2)-terminal Jun kinases/stress-activated protein kinases, hexosamines, and others. In addition, there is evidence that in type 2 diabetes, the activation of these same pathways by elevations in glucose and free fatty acid (FFA) levels leads to both insulin resistance and impaired insulin secretion. Therefore, we propose here that the hyperglycemia-induced, and possibly FFA-induced, activation of stress pathways plays a key role in the development of not only the late complications in type 1 and type 2 diabetes, but also the insulin resistance and impaired insulin secretion seen in type 2 diabetes.
TL;DR: It is suggested that adiponectin concentrations are determined by intra-abdominal fat mass, with additional independent effects of age and sex, and could link intra- abdominalFat with insulin resistance and an atherogenic lipoprotein profile.
Abstract: Aims/hypothesis
Increased intra-abdominal fat is associated with insulin resistance and an atherogenic lipoprotein profile. Circulating concentrations of adiponectin, an adipocyte-derived protein, are decreased with insulin resistance. We investigated the relationships between adiponectin and leptin, body fat distribution, insulin sensitivity and lipoproteins.
TL;DR: The features of the metabolic syndrome that emerge with estrogen deficiency are reviewed to aid in the recognition and treatment of women at risk for future CVD, leading to appropriate interventions.
Abstract: Women with the metabolic syndrome (central obesity, insulin resistance, and dyslipidemia) are known to be at especially high risk for cardiovascular disease (CVD). The prevalence of the metabolic syndrome increases with menopause and may partially explain the apparent acceleration in CVD after menopause. The transition from pre- to postmenopause is associated with the emergence of many features of the metabolic syndrome, including 1) increased central (intraabdominal) body fat; 2) a shift toward a more atherogenic lipid profile, with increased low density lipoprotein and triglycerides levels, reduced high density lipoprotein, and small, dense low density lipoprotein particles; 3) and increased glucose and insulin levels. The emergence of these risk factors may be a direct result of ovarian failure or, alternatively, an indirect result of the metabolic consequences of central fat redistribution with estrogen deficiency. It is unclear whether the transition to menopause increases CVD risk in all women or only those who develop features of the metabolic syndrome. This article will review the features of the metabolic syndrome that emerge with estrogen deficiency. A better understanding of these metabolic changes with menopause will aid in the recognition and treatment of women at risk for future CVD, leading to appropriate interventions. (J Clin Endocrinol Metab 88: 2404 –2411, 2003)
TL;DR: Severely obese subjects with a high prevalence of diabetes or the metabolic syndrome lost more weight during six months on a carbohydrate- restricted diet than on a calorie- and fat-restricted diet, with a relative improvement in insulin sensitivity and triglyceride levels, even after adjustment for the amount of weight lost.
Abstract: Background The effects of a carbohydrate-restricted diet on weight loss and risk factors for atherosclerosis have been incompletely assessed. Methods We randomly assigned 132 severely obese subjects (including 77 blacks and 23 women) with a mean body-mass index of 43 and a high prevalence of diabetes (39 percent) or the metabolic syndrome (43 percent) to a carbohydrate-restricted (low-carbohydrate) diet or a calorie- and fat-restricted (low-fat) diet. Results Seventy-nine subjects completed the six-month study. An analysis including all subjects, with the last observation carried forward for those who dropped out, showed that subjects on the low-carbohydrate diet lost more weight than those on the low-fat diet (mean [±SD], –5.8±8.6 kg vs. –1.9±4.2 kg; P=0.002) and had greater decreases in triglyceride levels (mean, –20±43 percent vs. –4±31 percent; P=0.001), irrespective of the use or nonuse of hypoglycemic or lipid-lowering medications. Insulin sensitivity, measured only in subjects without diabetes, als...
TL;DR: Adiponectin was effective in ameliorating hepatomegaly, steatosis, and alanine aminotransferase abnormality associated with nonalcoholic obese, ob/ob mice and could suppress the hepatic production of TNF-alpha and plasma concentrations of this proinflammatory cytokine.
Abstract: Adiponectin has recently been shown to be a promising candidate for the treatment of obesity-associated metabolic syndromes. Replenishment of recombinant adiponectin in mice can decrease hyperglycemia, reverse insulin resistance, and cause sustained weight loss without affecting food intake. Here we report its potential roles in alcoholic and nonalcoholic fatty liver diseases in mice. Circulating concentrations of adiponectin decreased significantly following chronic consumption of high-fat ethanol-containing food. Delivery of recombinant adiponectin into these mice dramatically alleviated hepatomegaly and steatosis (fatty liver) and also significantly attenuated inflammation and the elevated levels of serum alanine aminotransferase. These therapeutic effects resulted partly from the ability of adiponectin to increase carnitine palmitoyltransferase I activity and enhance hepatic fatty acid oxidation, while it decreased the activities of two key enzymes involved in fatty acid synthesis, including acetyl-CoA carboxylase and fatty acid synthase. Furthermore, adiponectin treatment could suppress the hepatic production of TNF-alpha and plasma concentrations of this proinflammatory cytokine. Adiponectin was also effective in ameliorating hepatomegaly, steatosis, and alanine aminotransferase abnormality associated with nonalcoholic obese, ob/ob mice. These results demonstrate a novel mechanism of adiponectin action and suggest a potential clinical application of adiponectin and its agonists in the treatment of liver diseases.
TL;DR: The results suggest that elevated MCP-1 may induce adipocyte dedifferentiation and contribute to pathologies associated with hyperinsulinemia and obesity, including type II diabetes.
Abstract: This study identifies monocyte chemoattractant protein 1 (MCP-1) as an insulin-responsive gene. It also shows that insulin induces substantial expression and secretion of MCP-1 both in vitro in insulin-resistant (IR) 3T3-L1 adipocytes and in vivo in IR obese mice (ob/ob). Thus, MCP-1 resembles other previously described genes (e.g., PAI-1 and SREBP-1c) that remain sensitive to insulin in IR states. The hyperinsulinemia that frequently accompanies obesity and insulin resistance may therefore contribute to the altered expression of these and other genes in insulin target tissues. In vivo studies also demonstrate that MCP-1 is overexpressed in obese mice compared with their lean controls, and that white adipose tissue is a major source of MCP-1. The elevated MCP-1 may alter adipocyte function because addition of MCP-1 to differentiated adipocytes in vitro decreases insulin-stimulated glucose uptake and the expression of several adipogenic genes (LpL, adipsin, GLUT-4, aP2, beta3-adrenergic receptor, and peroxisome proliferator-activated receptor gamma). These results suggest that elevated MCP-1 may induce adipocyte dedifferentiation and contribute to pathologies associated with hyperinsulinemia and obesity, including type II diabetes.
TL;DR: The ability of adiponectin to increase insulin sensitivity in conjunction with its anti-inflammatory and anti-atherogenic properties have made this novel adipocytokine a promising therapeutic tool for the future, with potential applications in states associated with low plasma adiponECTin levels.
Abstract: Adiponectin, also called GBP-28, apM1, AdipoQ and Acrp30, is a novel adipose tIssue-specific protein that has structural homology to collagen VIII and X and complement factor C1q, and that circulates in human plasma at high levels. It is one of the physiologically active polypeptides secreted by adipose tIssue, whose multiple functions have started to be understood in the last few Years.A reduction in adiponectin expression is associated with insulin resistance in some animal models. Administration of adiponectin has been accompanied by a reduction in plasma glucose and an increase in insulin sensitivity. In addition, thiazolidinediones, drugs that enhance insulin sensitivity through stimulation of the peroxisome proliferator-activated receptor-gamma, increase plasma adiponectin and mRNA levels in mice. On the other hand, this adipocyte protein seems to play a protective role in experimental models of vascular injury. In humans, adiponectin levels are inversely related to the degree of adiposity and positively associated with insulin sensitivity both in healthy subjects and in diabetic patients. Plasma adiponectin levels have been reported to be decreased in some insulin-resistant states, such as obesity and type 2 diabetes mellitus, and also in patients with coronary artery disease. On the contrary, chronic renal failure, type 1 diabetes and anorexia nervosa are associated with increased plasma adiponectin levels. Concentrations of plasma adiponectin have been shown to correlate negatively with glucose, insulin, triglyceride levels and body mass index, and positively with high-density lipoprotein-cholesterol levels and insulin-stimulated glucose disposal. Weight loss and therapy with thiazolidinediones increased endogenous adiponectin production in humans. Adiponectin increases insulin sensitivity by increasing tIssue fat oxidation, resulting in reduced circulating fatty acid levels and reduced intracellular triglyceride contents in liver and muscle. This protein also suppresses the expression of adhesion molecules in vascular endothelial cells and cytokine production from macrophages, thus inhibiting the inflammatory processes that occur during the early phases of atherosclerosis. In view of these data, it is possible that hypoadiponectinemia may play a role in the development of atherosclerotic vascular disease. In summary, the ability of adiponectin to increase insulin sensitivity in conjunction with its anti-inflammatory and anti-atherogenic properties have made this novel adipocytokine a promising therapeutic tool for the future, with potential applications in states associated with low plasma adiponectin levels.
TL;DR: It is shown that human subcutaneous adipose cells, like 3T3-L1 cells, are target cells for IL-6 and that it may act in concert with other cytokines that also are up-regulated in adipose Cells in insulin resistance.
TL;DR: It is shown that replenishment of globular adiponectin may provide a novel treatment modality for both type 2 diabetes and atherosclerosis, and this is the first demonstration that globular leptin can protect against Atherosclerosis in vivo.
TL;DR: Surprisingly, TZD treatment effectively reversed liver IR, whereas it failed to lower plasma free fatty acids, suggesting that syndrome X may be comprised of separable PPARγ-dependent components whose origins and therapeutic sites may reside in distinct tissues.
Abstract: Syndrome X, typified by obesity, insulin resistance (IR), dyslipidemia, and other metabolic abnormalities, is responsive to antidiabetic thiazolidinediones (TZDs). Peroxisome proliferator-activated receptor (PPAR) γ, a target of TZDs, is expressed abundantly in adipocytes, suggesting an important role for this tissue in the etiology and treatment of IR. Targeted deletion of PPARγ in adipose tissue resulted in marked adipocyte hypocellularity and hypertrophy, elevated levels of plasma free fatty acids and triglyceride, and decreased levels of plasma leptin and ACRP30. In addition, increased hepatic glucogenesis and IR were observed. Despite these defects, blood glucose, glucose and insulin tolerance, and insulin-stimulated muscle glucose uptake were all comparable to those of control mice. However, targeted mice were significantly more susceptible to high-fat diet-induced steatosis, hyperinsulinemia, and IR. Surprisingly, TZD treatment effectively reversed liver IR, whereas it failed to lower plasma free fatty acids. These results suggest that syndrome X may be comprised of separable PPARγ-dependent components whose origins and therapeutic sites may reside in distinct tissues.
TL;DR: 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, as measured in nondiabetic subjects with varying degrees of obesity and insulin resistance.
Abstract: 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.
TL;DR: The prevalence of insulin resistance is increased in patients with type 2 diabetes mellitus, essential hypertension, and CVD and that insulin resistance and compensatory hyperinsulinemia have been shown to be independent predictors of all 3 clinical syndromes.
Abstract: Background Insulin resistance is more common in overweight individuals and is associated with increased risk for type 2 diabetes mellitus and cardiovascular disease. Given the current epidemic of obesity and the fact that lifestyle interventions, such as weight loss and exercise, decrease insulin resistance, a relatively simple means to identify overweight individuals who are insulin resistant would be clinically useful. Objective To evaluate the ability of metabolic markers associated with insulin resistance and increased risk for cardiovascular disease to identify the subset of overweight individuals who are insulin resistant. Design Cross-sectional study. Setting General clinical research center. Patients 258 nondiabetic, overweight volunteers. Measurements Body mass index; fasting glucose, insulin, lipid and lipoprotein concentrations; and insulin-mediated glucose disposal as quantified by the steady-state plasma glucose concentration during the insulin suppression test. Overweight was defined as body mass index of 25 kg/m2 or greater, and insulin resistance was defined as being in the top tertile of steady-state plasma glucose concentrations. Receiver-operating characteristic curve analysis was used to identify the best markers of insulin resistance; optimal cut-points were identified and analyzed for predictive power. Results Plasma triglyceride concentration, ratio of triglyceride to high-density lipoprotein cholesterol concentrations, and insulin concentration were the most useful metabolic markers in identifying insulin-resistant individuals. The optimal cut-points were 1.47 mmol/L (130 mg/dL) for triglyceride, 1.8 in SI units (3.0 in traditional units) for the triglyceride-high-density lipoprotein cholesterol ratio, and 109 pmol/L for insulin. Respective sensitivity and specificity for these cut-points were 67%, 64%, and 57% and 71%, 68%, and 85%. Their ability to identify insulin-resistant individuals was similar to the ability of the criteria proposed by the Adult Treatment Panel III to diagnose the metabolic syndrome (sensitivity, 52%, and specificity, 85%). Conclusions Three relatively simple metabolic markers can help identify overweight individuals who are sufficiently insulin resistant to be at increased risk for various adverse outcomes. In the absence of a standardized insulin assay, we suggest that the most practical approach to identify overweight individuals who are insulin resistant is to use the cut-points for either triglyceride concentration or the triglyceride-high-density lipoprotein cholesterol concentration ratio.
TL;DR: The concept that intestinal bacteria induce endogenous signals that play a pathogenic role in hepatic insulin resistance and NAFLD are supported and novel therapies for these common conditions are suggested.
TL;DR: The recommendations contained herein are consistent with the American Diabetes Association’s Clinical Practice Recommendations and recent research has found that left ventricular hypertrophy is related to other risk factors, including obesity and insulin resistance in children and adolescents.
Abstract: This statement was reviewed by the American Diabetes Association. The recommendations contained herein are consistent with the American Diabetes Association’s Clinical Practice Recommendations.
Atherosclerotic cardiovascular disease is the No. 1 killer in the adult population of Western societies,1 but the pathological processes and risk factors associated with its development have been shown to begin during childhood.2 Obesity plays a central role in the insulin resistance syndrome, which includes hyperinsulinemia, hypertension, hyperlipidemia, type 2 diabetes mellitus, and an increased risk of atherosclerotic cardiovascular disease. The incidence of type 2 diabetes reported in children has increased alarmingly.3,4
Resistance of the body to the actions of insulin results in increased production of this hormone by the pancreas and ensuing hyperinsulinemia. Obesity beginning in childhood often precedes the hyperinsulinemic state. Other components of the insulin resistance syndrome are also present in children and adolescents.5,6 An association between obesity and insulin resistance has been reported in the young, as has the link between insulin resistance, hypertension, and abnormal lipid profile. There is an increasing amount of data showing that being overweight during childhood and adolescence is significantly associated with insulin resistance, dyslipidemia, and elevated blood pressure in young adulthood. Weight loss by obese youngsters results in a decrease in insulin concentration and improvement in insulin sensitivity. Moreover, it has been determined that increased left ventricular mass, which is an independent risk factor for cardiovascular disease in adults, is present in childhood. Recent research has found that left ventricular hypertrophy is related to other risk factors, including obesity and insulin resistance in children and adolescents.7 The specifics of the transition from risk factors in childhood to diabetes and cardiovascular disease are not clear, but compelling evidence points to their association with overt disease in adults. On the basis of current knowledge …
TL;DR: The effective administration of antiinflammatory agents in the treatment of insulin resistance and atherosclerosis is only the beginning of a promising approach in the management of these syndromes.
Abstract: Insulin resistance is increasingly recognized as a chronic, low-level, inflammatory state. Hyperinsulinemia and insulin action were initially proposed as the common preceding factors of hypertension, low high-density lipoprotein cholesterol, hypertriglyceridemia, abdominal obesity, and altered glucose tolerance, linking all these abnormalities to the development of coronary heart disease. The similarities of insulin resistance with another inflammatory state, atherosclerosis, have been described only in the last few decades. Atherosclerosis and insulin resistance share similar pathophysiological mechanisms, mainly due to the actions of the two major proinflammatory cytokines, TNF-alpha and IL-6. Genetic predisposition to increased transcription rates of these cytokines is associated with metabolic derangement and simultaneously with coronary heart disease. Dysregulation of the inflammatory axis predicts the development of insulin resistance and type 2 diabetes mellitus. The knowledge of how interactions between metabolic and inflammatory pathways occur will be useful in future therapeutic strategies. The effective administration of antiinflammatory agents in the treatment of insulin resistance and atherosclerosis is only the beginning of a promising approach in the management of these syndromes.
TL;DR: It is shown that TRB3, a mammalian homolog of Drosophila tribbles, functions as a negative modulator of Akt, which contributes to insulin resistance in individuals with susceptibility to type II diabetes.
Abstract: Insulin resistance is a major hallmark in the development of type II diabetes, which is characterized by the failure of insulin to promote glucose uptake in muscle and to suppress glucose production in liver. The serine-threonine kinase Akt (PKB) is a principal target of insulin signaling that inhibits hepatic glucose output when glucose is available from food. Here we show that TRB3, a mammalian homolog of Drosophila tribbles, functions as a negative modulator of Akt. TRB3 expression is induced in liver under fasting conditions, and TRB3 disrupts insulin signaling by binding directly to Akt and blocking activation of the kinase. Amounts of TRB3 RNA and protein were increased in livers of db/db diabetic mice compared with those in wild-type mice. Hepatic overexpression of TRB3 in amounts comparable to those in db/db mice promoted hyperglycemia and glucose intolerance. Our results suggest that, by interfering with Akt activation, TRB3 contributes to insulin resistance in individuals with susceptibility to type II diabetes.
TL;DR: Lowering the fasting glucose cutoff to 5.4 mmol/l improves the prediction of diabetes by the metabolic syndrome, and the NCEP definition performs better than the modified 1999 WHO definition.
Abstract: OBJECTIVE —The oral glucose tolerance test identifies high-risk subjects for diabetes, but it is costly and inconvenient. To find better predictors of type 2 diabetes, we evaluated two different definitions of the metabolic syndrome because insulin resistance, which is commonly associated with this clustering of metabolic factors, frequently precedes the onset of type 2 diabetes. RESEARCH DESIGN AND METHODS —We compared the ability of the National Cholesterol Education Program (NCEP) definition, a modified version of the 1999 World Health Organization (WHO) definition that excludes the 2-h glucose requirement, and impaired glucose tolerance (IGT) to predict incident type 2 diabetes. In the San Antonio Heart Study, 1,734 participants completed a 7- to 8-year follow-up examination. RESULTS —IGT and the NCEP definition had higher sensitivity than the modified WHO definition (51.9, 52.8, and 42.8%, respectively). IGT had a higher positive predictive value than the NCEP and modified WHO definitions (43.0, 30.8, and 30.4%, respectively). The combination of the IGT and NCEP definitions increased the sensitivity to 70.8% with an acceptable positive predictive value of 29.7%. Risk for incidence of type 2 diabetes using the NCEP definition was independent of other risk factors, including IGT and fasting insulin (odds ratio 3.30, 95% CI 2.27-4.80). The NCEP definition performed better with fasting glucose ≥5.4 mmol/l (sensitivity 62.0% and positive predictive value 30.9%). CONCLUSIONS —The metabolic syndrome predicts diabetes independently of other factors. However, the NCEP definition performs better than the modified 1999 WHO definition. Lowering the fasting glucose cutoff to 5.4 mmol/l improves the prediction of diabetes by the metabolic syndrome.
TL;DR: Analysis of rat L6 myotubes treated with the PPARδ subtype-selective agonist, GW501516, by the Affymetrix oligonucleotide microarrays revealed that PPAR Δ is pivotal to control the program for fatty acid oxidation in the skeletal muscle, thereby ameliorating obesity and insulin resistance through its activation in obese animals.
Abstract: In this study, we defined the role of peroxisome proliferator-activated receptor beta/delta (PPARdelta) in metabolic homeostasis by using subtype selective agonists. Analysis of rat L6 myotubes treated with the PPARdelta subtype-selective agonist, GW501516, by the Affymetrix oligonucleotide microarrays revealed that PPARdelta controls fatty acid oxidation by regulating genes involved in fatty acid transport, beta-oxidation, and mitochondrial respiration. Similar PPARdelta-mediated gene activation was observed in the skeletal muscle of GW501516-treated mice. Accordingly, GW501516 treatment induced fatty acid beta-oxidation in L6 myotubes as well as in mouse skeletal muscles. Administration of GW501516 to mice fed a high-fat diet ameliorated diet-induced obesity and insulin resistance, an effect accompanied by enhanced metabolic rate and fatty acid beta-oxidation, proliferation of mitochondria, and a marked reduction of lipid droplets in skeletal muscles. Despite a modest body weight change relative to vehicle-treated mice, GW501516 treatment also markedly improved diabetes as revealed by the decrease in plasma glucose and blood insulin levels in genetically obese ob/ob mice. These data suggest that PPARdelta is pivotal to control the program for fatty acid oxidation in the skeletal muscle, thereby ameliorating obesity and insulin resistance through its activation in obese animals.