Showing papers on "Insulin resistance published in 1997"
TL;DR: Since PCOS usually has a menarchal age of onset, this makes it a particularly appropriate disorder in which to examine the ontogeny of defects in carbohydrate metabolism and for ascertaining large three-generation kindreds for positional cloning studies to identify NIDDM genes.
Abstract: It is now clear that PCOS is often associated with profound insulin resistance as well as with defects in insulin secretion. These abnormalities, together with obesity, explain the substantially increased prevalence of glucose intolerance in PCOS. Moreover, since PCOS is an extremely common disorder, PCOS-related insulin resistance is an important cause of NIDDM in women (Table 3). The insulin resistance in at least 50% of PCOS women appears to be related to excessive serine phosphorylation of the insulin receptor. A factor extrinsic to the insulin receptor, presumably a serine/threonine kinase, causes this abnormality and is an example of an important new mechanism for human insulin resistance related to factors controlling insulin receptor signaling. Serine phosphorylation appears to modulate the activity of the key regulatory enzyme of androgen biosynthesis, P450c17. It is thus possible that a single defect produces both the insulin resistance and the hyperandrogenism in some PCOS women (Fig. 19). Recent studies strongly suggest that insulin is acting through its own receptor (rather than the IGF-I receptor) in PCOS to augment not only ovarian and adrenal steroidogenesis but also pituitary LH release. Indeed, the defect in insulin action appears to be selective, affecting glucose metabolism but not cell growth. Since PCOS usually has a menarchal age of onset, this makes it a particularly appropriate disorder in which to examine the ontogeny of defects in carbohydrate metabolism and for ascertaining large three-generation kindreds for positional cloning studies to identify NIDDM genes. Although the presence of lipid abnormalities, dysfibrinolysis, and insulin resistance would be predicted to place PCOS women at high risk for cardiovascular disease, appropriate prospective studies are necessary to directly assess this.
2,571 citations
TL;DR: Results indicate that TNF-α is an important mediator of insulin resistance in obesity through its effects on several important sites of insulin action.
Abstract: Obesity is highly associated with insulin resistance and is the biggest risk factor for non-insulin-dependent diabetes mellitus. The molecular basis of this common syndrome, however, is poorly understood. It has been suggested that tumour necrosis factor (TNF)-alpha is a candidate mediator of insulin resistance in obesity, as it is overexpressed in the adipose tissues of rodents and humans and it blocks the action of insulin in cultured cells and whole animals. To investigate the role of TNF-alpha in obesity and insulin resistance, we have generated obese mice with a targeted null mutation in the gene encoding TNF-alpha and those encoding the two receptors for TNF-alpha. The absence of TNF-alpha resulted in significantly improved insulin sensitivity in both diet-induced obesity and that resulting for the ob/ob model of obesity. The TNFalpha-deficient obese mice had lower levels of circulating free fatty acids, and were protected from the obesity-related reduction in the insulin receptor signalling in muscle and fat tissues. These results indicate that TNF-alpha is an important mediator of insulin resistance in obesity through its effects on several important sites of insulin action.
2,161 citations
TL;DR: Continuously elevated levels of plasma FFAs may play a key role in the pathogenesis of NIDDM in predisposed individuals by impairing peripheral glucose utilization and by promoting hepatic glucose overproduction.
Abstract: Evidence is reviewed that free fatty acids (FFAs) are one important link between obesity and insulin resistance and NIDDM. First, plasma FFA levels are elevated in most obese subjects. Second, physiological elevations in plasma FFA concentrations inhibit insulin stimulated peripheral glucose uptake in a dose-dependent manner in normal controls and in patients with NIDDM. Two possible mechanisms are identified: 1) a fat-related inhibition of glucose transport or phosphorylation, which appears after 3-4 h of fat infusion, and 2) a decrease in muscle glycogen synthase activity, which appears after 4-6 h of fat infusion. Third, FFAs stimulate insulin secretion in nondiabetic individuals. Some of this insulin is transmitted in the peripheral circulation and is able to compensate for FFA-mediated peripheral insulin resistance. FFA-mediated portal hyperinsulinemia counteracts the stimulation of FFAs on hepatic glucose production (HGP) and thus prevents hepatic glucose overproduction. We speculate that, in obese individuals who are genetically predisposed to develop NIDDM, FFAs will eventually fail to promote insulin secretion. The stimulatory effect of FFAs on HGP would then become unchecked, resulting in hyperglycemia. Hence, continuously elevated levels of plasma FFAs may play a key role in the pathogenesis of NIDDM in predisposed individuals by impairing peripheral glucose utilization and by promoting hepatic glucose overproduction.
1,726 citations
TL;DR: NIDDM is associated with an elevated acute-phase response, particularly in those with features of syndrome X, and abnormalities of the innate immune system may be a contributor to the hypertriglyceridaemia, low HDL cholesterol, hypertension, glucose intolerance, insulin resistance and accelerated atherosclerosis of NIDDM.
Abstract: Non-insulin-dependent diabetes mellitus (NIDDM) is commonly associated with hypertrigly-ceridaemia, low serum HDL-cholesterol concentrations, hypertension, obesity and accelerated atherosclerosis (metabolic syndrome X). Since a similar dyslipidaemia occurs with the acute-phase response, we investigated whether elevated acute-phase/stress reactants (the innate immune system’s response to environmental stress) and their major cytokine mediator (interleukin-6, IL-6) are associated with NIDDM and syndrome X, and may thus provide a unifying pathophysiological mechanism for these conditions. Two groups of Caucasian subjects with NIDDM were studied. Those with any 4 or 5 features of syndrome X (n = 19) were compared with a group with 0 or 1 feature of syndrome X (n = 25) but similar age, sex distribution, diabetes duration, glycaemic control and diabetes treatment. Healthy non-diabetic subjects of comparable age and sex acted as controls. Overnight urinary albumin excretion rate, a risk factor for cardiovascular disease, was also assayed in subjects to assess its relationship to the acute-phase response. Serum sialic acid was confirmed as a marker of the acute-phase response since serum concentrations were significantly related to established acute-phase proteins such as α-1 acid glycoprotein (r = 0.82, p < 0.0001). There was a significant graded increase of serum sialic acid, α-1 acid glycoprotein, IL-6 and urinary albumin excretion rate amongst the three groups, with the lowest levels in non-diabetic subjects, intermediate levels in NIDDM patients without syndrome X and highest levels in NIDDM patients with syndrome X. C-reactive protein and cortisol levels were also higher in syndrome X-positive compared to -negative patients and serum amyloid A was higher in both diabetic groups than in the control group. We conclude that NIDDM is associated with an elevated acute-phase response, particularly in those with features of syndrome X. Abnormalities of the innate immune system may be a contributor to the hypertriglyceridaemia, low HDL cholesterol, hypertension, glucose intolerance, insulin resistance and accelerated atherosclerosis of NIDDM. Microalbuminuria may be a component of the acutephase response.
1,208 citations
TL;DR: The results suggest that in this human population, as in animal models, skeletal muscle insulin sensitivity is strongly influenced by local supplies of triglycerides, as well as by remote depots and circulating lipids.
Abstract: In animal studies, increased amounts of triglyceride associated with skeletal muscle (mTG) correlate with reduced skeletal muscle and whole body insulin action. The aim of this study was to test this relationship in humans. Subjects were 38 nondiabetic male Pima Indians (mean age 28 ± 1 years). Insulin sensitivity at physiological ( M ) and supraphysiological ( MZ ) insulin levels was assessed by the euglycemic clamp. Lipid and carbohydrate oxidation were determined by indirect calorimetry before and during insulin administration. mTG was determined in vastus lateralis muscles obtained by percutaneous biopsy. Percentage of body fat (mean 29 ± 1%, range 14–44%) was measured by underwater weighing. In simple regressions, negative relationships were found between mTG (mean 5.4 ± 0.3 μmol/g, range 1.3–1.9 μmol/g) and log10 M ( r = −0.53, P ≤ 0.001), MZ ( r = −0.44, P = 0.006), and nonoxidative glucose disposal ( r = −0.48 and −0.47 at physiological and supraphysiological insulin levels, respectively, both P = 0.005) but not glucose or lipid oxidation. mTG was not related to any measure of adiposity. In multiple regressions, measures of insulin resistance (log10 M , MZ , log10[fasting insulin]) were significantly related to mTG independent of all measures of obesity (percentage of body fat, BMI, waist-to-thigh ratio). In turn, all measures of obesity were related to the insulin resistance measures independent of mTG. The obesity measures and mTG accounted for similar proportions of the variance in insulin resistance in these relationships. The results suggest that in this human population, as in animal models, skeletal muscle insulin sensitivity is strongly influenced by local supplies of triglycerides, as well as by remote depots and circulating lipids. The mechanism(s) underlying the relationship between mTG and insulin action on skeletal muscle glycogen synthesis may be central to an understanding of insulin resistance.
1,180 citations
TL;DR: As a component of central adiposity, subcutaneous abdominal fat has as strong an association with insulin resistance as visceral fat, and altered muscle composition, suggestive of increased fat content, is an important independent marker of insulin resistance in obesity.
Abstract: Whether visceral adipose tissue has a uniquely powerful association with insulin resistance or whether subcutaneous abdominal fat shares this link has generated controversy in the area of body composition and insulin sensitivity. An additional issue is the potential role of fat deposition within skeletal muscle and the relationship with insulin resistance. To address these matters, the current study was undertaken to measure body composition, aerobic fitness, and insulin sensitivity within a cohort of sedentary healthy men ( n = 26) and women ( n = 28). The subjects, who ranged from lean to obese (BMI 19.6-41.0 kg/m2), underwent dual energy X-ray absorptiometry (DEXA) to measure fat-free mass (FFM) and fat mass (FM), computed tomography to measure cross-sectional abdominal subcutaneous and visceral adipose tissue, and computed tomography (CT) of mid-thigh to measure muscle cross-sectional area, muscle attenuation, and subcutaneous fat. Insulin sensitivity was measured using the glucose clamp technique (40 mU · m∼2 · min−1), in conjunction with [3-3H]glucose isotope dilution. Maximal aerobic power (Vo2max) was determined using an incremental cycling test. Insulin-stimulated glucose disposal ( R d) ranged from 3.03 to 16.83 mg · min−1· kg−1 FFM. R d was negatively correlated with FM ( r = -0.58), visceral fat ( r = -0.52), subcutaneous abdominal fat ( r = -0.61), and thigh fat ( r = -0.38) and positively correlated with muscle attenuation ( r = 0.48) and Vo2max ( r = 0.26, P < 0.05). In addition to manifesting the strongest simple correlation with insulin sensitivity, in stepwise multiple regression, subcutaneous abdominal fat retained significance after adjusting for visceral fat, while the converse was not found. Muscle attenuation contributed independent significance to multiple regression models of body composition and insulin sensitivity, and in analysis of obese subjects, muscle attenuation was the strongest single correlate of insulin resistance. In summary, as a component of central adiposity, subcutaneous abdominal fat has as strong an association with insulin resistance as visceral fat, and altered muscle composition, suggestive of increased fat content, is an important independent marker of insulin resistance in obesity.
972 citations
TL;DR: In nondiabetic, normotensive obese subjects, the prevalence of insulin resistance is relatively low, and is exceeded by the prevalenceOf insulin hypersecretion, particularly in women with central obesity, in the obese with preserved insulin sensitivity.
Abstract: Insulin resistance and insulin hypersecretion are established features of obesity. Their prevalence, however, has only been inferred from plasma insulin concentrations. We measured insulin sensitivity (as the whole-body insulin-mediated glucose uptake) and fasting posthepatic insulin delivery rate (IDR) with the use of the euglycemic insulin clamp technique in a large group of obese subjects in the database of the European Group for the Study of Insulin Resistance (1,146 nondiabetic, normotensive Caucasian men and women aged 18-85 yr, with a body mass index (BMI) ranging from 15 to 55 kg.m-2). Insulin resistance, defined as the lowest decile of insulin sensitivity in the lean subgroup (608 subjects with a mean BMI of 29 kg.m-2). Insulin sensitivity declined linearly with BMI at an age- and sex-adjusted rate of 1.2 micromol.min-1.kg FFM-1 per BMI unit (95% confidence intervals = 1.0-1.4). Insulin hypersecretion, defined as the upper decile of IDR, was significantly (P<0.0001) more prevalent (38%) than insulin resistance in the obese group. In the whole dataset, IDR rose as a function of both BMI and insulin resistance in a nonlinear fashion. Neither the waist circumference nor the waist-to-hip ratio, indices of body fat distribution, was related to insulin sensitivity after adjustment for age, gender, and BMI; both, however, were positively associated (P<0.001) with insulin hypersecretion, particularly in women. In nondiabetic, normotensive obese subjects, the prevalence of insulin resistance is relatively low, and is exceeded by the prevalence of insulin hypersecretion, particularly in women with central obesity. In the obese with preserved insulin sensitivity, risk for diabetes, cardiovascular risk, and response to treatment may be different than in insulin resistant obesity.
855 citations
TL;DR: HOMA provides a useful model to assess insulin resistance and β-cell function in epidemiological studies in which only fasting samples are available and that, further, it is critical to take into account the degree of insulin resistance in assessing insulin secretion by the HOMA model.
Abstract: OBJECTIVE Both insulin resistance and decreased insulin secretion have been shown to predict the development of NIDDM. However, methods to assess insulin sensitivity and secretion are complicated and expensive to apply in epidemiological studies. The homeostasis model assessment (HOMA) has been suggested as a method to assess insulin resistance and secretion from the fasting glucose and insulin concentrations. However, this method has not been extensively evaluated, particularly in different ethnic groups. RESEARCH DESIGN AND METHODS We applied the HOMA model to cross-sectional analyses of the San Antonio Heart Study ( n = 2,465). RESULTS HOMA insulin resistance (IR) was very strongly correlated with fasting insulin ( r = 0.98) and HOMA β-cell function (β-cell) was moderately correlated with the 30-min increment in insulin concentration over the 30-min increment in glucose concentration (Δ I 30 /Δ G 30 ) in an oral glucose tolerance test (OGTT) ( r = 0.44). NIDDM was characterized by both high HOMA IR and low HOMA β-cell function. In Mexican-Americans, HOMA IR in NIDDM subjects was 9.5 compared with 2.7 in normal glucose tolerance (NGT) subjects. In contrast, HOMA β-cell function showed only small differences in Mexican-Americans (176 NIDDM; 257 NGT). However, the ΔI 30 /ΔG 30 (pmol/mmol) showed much larger differences (75 NIDDM; 268 NGT). When modeled separately, impaired glucose tolerance (IGT) was characterized by high HOMA IR and high HOMA β-cell function. However, when analyzed in the same regression model, high HOMA IR and low HOMA β-cell function characterized subjects with IGT. These results were similar in both ethnic groups. Mexican-Americans had increased insulin resistance (as judged by both HOMA IR and fasting insulin) and insulin secretion (by HOMA β-cell and ΔI 30 /ΔG 30 ) relative to non-Hispanic whites. CONCLUSIONS We conclude that HOMA provides a useful model to assess insulin resistance and β-cell function in epidemiological studies in which only fasting samples are available and that, further, it is critical to take into account the degree of insulin resistance in assessing insulin secretion by the HOMA model.
771 citations
TL;DR: It is suggested that insulin resistance is associated with enhanced Ser/Thr phosphorylation of IRS-1 and IRS-2, which impairs their interaction with the JM region of IR, which abolishes their ability to undergo insulin-induced Tyrosphorylation and propagate the insulin receptor signal.
545 citations
TL;DR: This NIDDM mouse model in which diabetes arises in an age-dependent manner from the interaction between two genetically determined, subclinical defects in the insulin signaling cascade demonstrates the role of epistatic interactions in the pathogenesis of common diseases with non-Mendelian genetics.
535 citations
TL;DR: The insulin resistance of glucose transport in 3T3-L1 adipocytes exposed to TNF-α for 72-96 h results from a reduced amount in requisite proteins involved in insulin action, consistent with earlier studies indicating that T NF-α reduces the transcriptional activity of the GLUT4 gene in murine adipocytes, and reduced mRNA transcription of a number of relevant genes.
TL;DR: These results were consistent with more than one independent physiological process underlying risk variable clustering: a central metabolic syndrome (characterized by hyperinsulinemia, dyslipidemia, and obesity), glucose intolerance, and hypertension.
Abstract: Insulin resistance has been hypothesized to unify the clustering of hypertension, glucose intolerance, hyperinsulinemia, increased levels of triglyceride and decreased HDL cholesterol, and central and overall obesity. We tested this hypothesis with factor analysis, a statistical technique that should identify one factor if a single process underlies the clustering of these risk variables. From 2,458 nondiabetic subjects of the Framingham Offspring Study, we collected clinical data, fasting and 2-h postchallenge glucose and insulin levels, and fasting lipid levels. We performed factor analyses separately for men and women in the entire population and among subgroups with features of the insulin resistance syndrome. Subjects ranged in age from 26 to 82 years (mean age 54); 53% were women, 13.4% had impaired glucose tolerance, 27.6% had hypertension, 40% were obese, and 11.6% were hyperinsulinemic, defined by elevated fasting insulin levels. Underlying the clustering of these risk variables were three factors. Fasting and 2-h postchallenge insulin levels, fasting triglyceride and HDL cholesterol levels, BMI, and waist-to-hip ratio were associated with one factor. Fasting and 2-h levels of glucose and insulin were associated with a second factor. Systolic blood pressure, diastolic blood pressure, and BMI were associated with a third factor. Results were similar for men and women and for all subgroups. These results were consistent with more than one independent physiological process underlying risk variable clustering: a central metabolic syndrome (characterized by hyperinsulinemia, dyslipidemia, and obesity), glucose intolerance, and hypertension. Glucose intolerance and hypertension were linked to the central syndrome through shared correlations with insulin levels and obesity. Insulin resistance (reflected by hyperinsulinemia) alone did not appear to underlie all features of the insulin resistance syndrome.
TL;DR: Similarities between the hlGFBP-1 and phosphoenolpyruvate kinase (PEPCK) promoters, including regions conferring insulin, glucocorticoid, and cyclic adenosine-monophosphate responses, are consistent with the previous hypothesis that IGF BP-1 is involved in regulation of glucose metabolism.
Abstract: In 1988, insulin-like growth factor-binding protein-1 (IGFBP-1) became the first characterized member of a group of structurally related soluble proteins which specifically bind and modulate the actions of the IGFs. Since then, a wealth of information has accumulated regarding the physiology of this dynamic serum protein. In this review, we update our 1993 summary (Lee PDK et al. Proc Soc Exp Biol Med 204:4-29) of the status of IGFBP-1 research. The IGFBP-1 protein sequence contains 12 N-terminal and 6 C-terminal cysteine residues which are conserved in other mammalian IGFBP-1 sequences and amongst other IGFBPs; both of the cysteine-rich regions are required for optimal IGF binding. The nonconserved IGFBP-1 midregion may act as both a hinge which defines ligand binding characteristics and as a specific target for protease activity. Integrin-binding and phosphorylation sites within the IGFBP-1 sequence have functional significance in vitro, but their physiologic relevance in vivo have not been defined. The human IGFBP-1 and IGFBP-3 genes are contiguous and located in close proximity to the homeobox A (HOXA) gene cluster on chromosome 7. The other IGFBP genes, located on chromosomes 2, 12, and 17, are also associated with HOX clusters, suggesting evolutionary linkage of the IGFBP and HOX gene families. Similarities between the hIGFBP-1 and phosphoenolpyruvate kinase (PEPCK) promoters, including regions conferring insulin, glucocorticoid, and cyclic adenosine-monophosphate responses, are consistent with our previous hypothesis that IGFBP-1 is involved in regulation of glucose metabolism. The tissue-specific patterns of IGFBP-1 gene expression in liver, kidney, decidua, and ovary may be due to stimulation of IGFBP-1 transcription by hepatic nuclear factor 1 (HNF1) proteins. Clinical and basic studies of IGFBP-1 physiology have been aided by several recently developed assay methods. Numerous investigations have confirmed that insulin, via inhibition of IGFBP-1 transcription, is the primary determinant of IGFBP-1 expression both in vitro and in vivo. IGF-I and IGF-II also have specific inhibitory effects on IGFBP-1 expression. Glucocorticoids and cAMP stimulate IGFBP-1 transcription, but these effects are observed only in conditions of low or absent insulin effect. Other stimulants of IGFBP-1 expression include thyroid hormones and epidermal growth factor. Phorbol ester stimulation of IGFBP-1 expression can supersede the effects of insulin in vitro;however, the mechanism and in vivo correlates of this effect have not been determined. Cytokines and, perhaps, growth hormones may affect IGFBP-1 expression, perhaps by altering the regulatory actions of insulin; this effect may have important clinical relevance. IGFBP-1 expression is upregulated in liver and (nonhuman) kidney during postinjury regeneration. The IGF-inhibitory actions of IGFBP-1 has been confirmed by numerous in vitro studies and several in vivo animal investigations, including administration of recombinant IGFBP-1 and IGFBP-1 transgenic models. IGFBP-1 has been shown to inhibit somatic linear growth, weight gain, tissue growth, and glucose metabolism. Moreover, IGFBP-1 appears to be a primary determinant of free IGF-I levels in serum. Excess levels of IGFBP-1 may contribute to growth failure in intrauterine growth restriction and in pediatric chronic renal failure, while low IGFBP-1 levels are associated with obesity and with cardiovascular risk factors in insulin resistance syndromes. Serum IGFBP-1 measurements may be useful biochemical marker in these pathologic conditions. IGFBP-1 is expressed in decidualized stromal cells of the uterine endometrium and in ovarian granulosa cells. IGFBP-1, together with IGFs, insulin, ovarian steroids, cytokines, and other factors, is involved in a complex system which regulates menstrual cycles, ovulation, decidualization, blastocyst implantation, and fetal growth. (ABSTRACT TRUNCATED)
TL;DR: CHF is associated with marked insulin resistance, characterized by both fasting and stimulated hyperinsulinemia, but this is not directly mediated through ventricular dysfunction or increased catecholamine levels.
TL;DR: Somatotropin is almost certainly a predominant homeorhetic influence during lactation because its exogenous administration causes specific changes in glucose metabolism (and many other functions) of various nonmammary tissues which faithfully mimic normal adaptations to early lactation.
Abstract: Increased glucose requirements of the gravid uterus during late pregnancy and even greater requirements of the lactating mammary glands necessitate major adjustments in glucose production and utilization in maternal liver, adipose tissue, skeletal muscle, and other tissues In ruminants, which at all times rely principally on hepatic gluconeogenesis for their glucose supply, hepatic glucose synthesis during late pregnancy and early lactation is increased to accommodate uterine or mammary demands even when the supply of dietary substrate is inadequate At the same time, glucose utilization by adipose tissue and muscle is reduced In pregnant animals, these responses are exaggerated by moderate undernutrition and are mediated by reduced tissue sensitivity and responsiveness to insulin, associated with decreased tissue expression of the insulin-responsive facilitative glucose transporter, GLUT4 Peripheral tissue responses to insulin remain severely attenuated during early lactation but recover as the animal progresses through mid lactation Specific homeorhetic effectors of decreased insulin-mediated glucose metabolism during late pregnancy have yet to be conclusively identified In contrast, somatotropin is almost certainly a predominant homeorhetic influence during lactation because its exogenous administration causes specific changes in glucose metabolism (and many other functions) of various nonmammary tissues which faithfully mimic normal adaptations to early lactation
TL;DR: The observation that serum leptin is not related to energy expenditure rates suggests that leptin regulates body fat predominantly by altering eating behavior rather than calorigenesis, and there are important gender-based differences in the regulation and action of leptin in humans.
Abstract: Leptin is an adipocyte-derived hormone that interacts with a putative receptor(s) in the hypothalamus to regulate body weight. The relationship of leptin to metabolic abnormalities associated with obesity together with hormonal and substrate regulation of leptin have not been extensively studied. Therefore, 116 subjects (62 men and 54 women) with a wide range of body weight [body mass index (BMI), 17-54 kg/m2] were characterized on a metabolic ward with regard to body composition, glucose intolerance, insulin sensitivity, energy expenditure, substrate utilization, and blood pressure. Eighty-five of the subjects had normal glucose tolerance (50 men and 35 women), and 31 had noninsulin-dependent diabetes mellitus (12 men and 19 women). In both men and women, fasting leptin levels were highly correlated with BMI (r = 0.87 and r = 0.88, respectively) and percent body fat (r = 0.82 and r = 0.88, respectively; all P < 0.0001). However, men exhibited lower leptin levels at any given measure of obesity. Compared with those in men, leptin levels rose 3.4-fold more rapidly as a function of BMI in women [leptin = 1.815 (BMI)-31.103 in women; leptin = 0.534 (BMI)-8.437 in men] and 3.2 times more rapidly as a function of body fat [leptin = 1.293 (% body fat)-24.817 in women; leptin = 0.402 (% body fat)-3.087 in men]. Hyperleptinemia was associated with insulin resistance (r = -0.57; P < 0.0001) and high waist to hip ratio (r = 0.75; P < 0.0001) only in men. On the other hand, during the hyperinsulinemic euglycemic clamp studies, hyperinsulinemia acutely increased leptin concentrations (20%) only in women. There was no correlation noted between fasting leptin levels and either resting energy expenditure or insulin-induced thermogenesis in men or women (P = NS). In stepwise and multiple regression models with leptin as the dependent variable, noninsulin-dependent diabetes mellitus did not enter the equations at a statistically significant level. The data indicate that there are important gender-based differences in the regulation and action of leptin in humans. Serum leptin levels increase with progressive obesity in both men and women. However, for any given measure of obesity, leptin levels are higher in women than in men, consistent with a state of relative leptin resistance. These findings have important implications regarding differences in body composition in men and women. The observation that serum leptin is not related to energy expenditure rates suggests that leptin regulates body fat predominantly by altering eating behavior rather than calorigenesis.
TL;DR: These findings strongly support the interpretation that a stress reaction activating the HPA axis is involved also in the human syndrome, suggesting that the pathogenesis of abdominal preponderance of body fat and its endocrine, anthropometric and metabolic abnormalities are indeed consequences of the endocrine abnormalities identified.
TL;DR: Short prepubertal IUGR children have a specific impairment in insulin sensitivity compared to their normal birth weight peers, a potential marker for the early identification and intervention in the development of late adult-onset noninsulin-dependent diabetes mellitus.
Abstract: Epidemiological studies have demonstrated an association between intrauterine growth retardation and an increased risk of adult diseases that include essential hypertension, noninsulin-dependent diabetes mellitus, and ischemic heart disease. A common feature of these diseases is insulin resistance. To investigate whether abnormal insulin sensitivity was a characteristic of subjects with intrauterine growth retardation (IUGR), we compared two groups of short prepubertal children: a group with IUGR (birth weight less than the tenth percentile; n = 15) and a normal birth weight group (n = 12). Subjects underwent a modified frequently sampled iv glucose tolerance test that permitted calculation of the acute insulin response, insulin sensitivity index, and glucose effectiveness. A marked difference in the insulin sensitivity index was noted between groups, with the IUGR group being less insulin sensitive [6.9 vs. 16.9 10(-4)min-1.(microU/mL); P = 0.0048]. The acute insulin response was also significantly different between groups, with IUGR subjects having higher insulin levels (445 vs. 174 microU/mL; P = 0.005). There was no difference in glucose effectiveness between groups. Short prepubertal IUGR children have a specific impairment in insulin sensitivity compared to their normal birth weight peers. In short IUGR children, impaired insulin sensitivity is a potential marker for the early identification and intervention in the development of late adult-onset noninsulin-dependent diabetes mellitus.
TL;DR: Specific and potent impairment of insulin action by leptin in the physiological concentration range of both leptin and insulin is shown, which may be related to the pathophysiology of insulin resistance in both non-insulin-dependent diabetes mellitus and obesity.
TL;DR: The altered ratio between glycolytic and oxidative enzyme activities found in skeletal muscle of individuals with NIDDM suggests that a dysregulation between mitochondrial oxidative capacity and capacity for gly colysis is an important component of the expression of insulin resistance.
Abstract: The insulin resistance of skeletal muscle in glucose-tolerant obese individuals is associated with reduced activity of oxidative enzymes and a disproportionate increase in activity of glycolytic enzymes. Because non-insulin-dependent diabetes mellitus (NIDDM) is a disorder characterized by even more severe insulin resistance of skeletal muscle and because many individuals with NIDDM are obese, the present study was undertaken to examine whether decreased oxidative and increased glycolytic enzyme activities are also present in NIDDM. Percutaneous biopsy of vatus lateralis muscle was obtained in eight lean (L) and eight obese (O) nondiabetic subjects and in eight obese NIDDM subjects and was assayed for marker enzymes of the glycolytic [phosphofructokinase, glyceraldehyde phosphate dehydrogenase, hexokinase (HK)] and oxidative pathways [citrate synthase (CS), cytochrome-c oxidase], as well as for a glycogenolytic enzyme (glycogen phosphorylase) and a marker of anaerobic ATP resynthesis (creatine kinase). Insulin sensitivity was measured by using the euglycemic clamp technique. Activity for glycolytic enzymes (phosphofructokinase, glyceraldehye phosphate dehydrogenase, HK) was highest in subjects with subjects with NIDDM, following the order of NIDDM > O > L, whereas maximum velocity for oxidative enzymes (CS, cytochrome-c oxidase) was lowest in subjects with NIDDM. The ratio between glycolytic and oxidative enzyme activities within skeletal muscle correlated negatively with insulin sensitivity. The HK/CS ratio had the strongest correlation (r = -0.60, P < 0.01) with insulin sensitivity. In summary, an imbalance between glycolytic and oxidative enzyme capacities is present in NIDDM subjects and is more severe than in obese or lean glucose-tolerant subjects. The altered ratio between glycolytic and oxidative enzyme activities found in skeletal muscle of individuals with NIDDM suggests that a dysregulation between mitochondrial oxidative capacity and capacity for glycolysis is an important component of the expression of insulin resistance.
TL;DR: Hyperinsulinaemia and other features of the insulin resistance syndrome were associated with Alzheimer's disease Insulin resistance is affected by modifications in lifestyle, so the risk of Alzheimer’s disease might be reducible by the same measures.
Abstract: OBJECTIVE: To determine the association between features of the insulin resistance syndrome and Alzheimer's disease. DESIGN: Cross sectional population based study. SUBJECTS: 980 people aged 69 to 78 (349 men, 631 women). SETTING: Population of Kuopio, eastern Finland. MAIN OUTCOME MEASURES: Presence of features of the insulin resistance syndrome and diagnosis of Alzheimer's disease by detailed neurological and neuropsychological evaluation. RESULTS: 46 (4.7%) subjects were classified as having probable or possible Alzheimer's disease. In univariate analyses, apolipoprotein E4 phenotype (odds ratio; 95% confidence interval 3.24: 1.77 to 5.92), age (1.16; 1.05 to 1.29), low level of education (0.82; 0.72 to 0.93), low total cholesterol concentration (0.77; 0.59 to 1.00), high systolic blood pressure (1.01; 1.00 to 1.03), high fasting and 2 hour plasma glucose concentrations (1.11; 1.01 to 1.23 and 1.08; 1.03 to 1.13, respectively), high fasting and 2 hour insulin concentrations (1.05; 1.02 to 1.08 and 1.003; 1.00 to 1.01, respectively), and abnormal glucose tolerance (1.86; 1.23 to 2.80) were significantly associated with Alzheimer's disease. In multivariate analysis including apolipoprotein E4 phenotype, age, education, systolic blood pressure, total cholesterol concentration, fasting glucose concentration, and insulin concentration, apolipoprotein E4 phenotype, age, education, total cholesterol, and insulin were significantly associated with Alzheimer's disease. In 532 non-diabetic subjects without the e4 allele hyperinsulinaemia was associated with an increased risk for Alzheimer's disease (prevalence of disease 7.5% v 1.4% in normoinsulinaemic subjects, P = 0.0004). In contrast, in the 228 with the e4 allele hyperinsulinaemia had no effect on the risk of disease (7.0% v 7.1%, respectively). CONCLUSION: Features of the insulin resistance syndrome are associated with Alzheimer's disease independently of apolipoprotein E4 phenotype.
TL;DR: In the insulin-resistant HFF rat, acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, and evidence is provided for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.
Abstract: To elucidate cellular mechanisms of insulin resistance induced by excess dietary fat, we studied conscious chronically high-fat-fed (HFF) and control chow diet-fed rats during euglycemic-hyperinsulinemic (560 pmol/l plasma insulin) clamps. Compared with chow diet feeding, fat feeding significantly impaired insulin action (reduced whole body glucose disposal rate, reduced skeletal muscle glucose metabolism, and decreased insulin suppressibility of hepatic glucose production [HGP]). In HFF rats, hyperinsulinemia significantly suppressed circulating free fatty acids but not the intracellular availability of fatty acid in skeletal muscle (long chain fatty acyl-CoA esters remained at 230% above control levels). In HFF animals, acute blockade of beta-oxidation using etomoxir increased insulin-stimulated muscle glucose uptake, via a selective increase in the component directed to glycolysis, but did not reverse the defect in net glycogen synthesis or glycogen synthase. In clamp HFF animals, etomoxir did not significantly alter the reduced ability of insulin to suppress HGP, but induced substantial depletion of hepatic glycogen content. This implied that gluconeogenesis was reduced by inhibition of hepatic fatty acid oxidation and that an alternative mechanism was involved in the elevated HGP in HFF rats. Evidence was then obtained suggesting that this involves a reduction in hepatic glucokinase (GK) activity and an inability of insulin to acutely lower glucose-6-phosphatase (G-6-Pase) activity. Overall, a 76% increase in the activity ratio G-6-Pase/GK was observed, which would favor net hepatic glucose release and elevated HGP in HFF rats. Thus in the insulin-resistant HFF rat 1) acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, 2) elevated lipid oxidation opposes insulin stimulation of muscle glucose oxidation (perhaps via the glucose-fatty acid cycle) and suppression of hepatic gluconeogenesis, and 3) mechanisms of impaired insulin-stimulated glucose storage and HGP suppressibility are not dependent on concomitant lipid oxidation; in the case of HGP we provide evidence for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.
TL;DR: It is demonstrated that GH can favorably affect some of the multiple perturbations associated with abdominal/visceral obesity, an improved insulin sensitivity, and favorable effects on lipoprotein metabolism and diastolic blood pressure.
Abstract: The most central findings in both GH deficiency in adults and the metabolic syndrome are abdominal/visceral obesity and insulin resistance. Abdominal obesity is associated with blunted GH secretion and low serum insulin-like growth factor-I concentrations. GH treatment in GH-deficient adults has demonstrated favorable effects on most of the features of GH deficiency in adults, but it is not known whether GH can improve some of the metabolic aberrations observed in abdominal/visceral obesity. Thirty men, 48-66 yr old, with abdominal/visceral obesity were treated with recombinant human GH (rhGH) in a 9-month randomized, double-blind, placebo-controlled trial. The daily dose of rhGH was 9.5 micrograms/kg. Body fat was assessed from total body potassium, and abdominal sc and visceral adipose tissue was measured using computed tomography. The glucose disposal rate (GDR) was measured during an euglycemic, hyperinsulinemic glucose clamp. In response to the rhGH treatment, total body fat and abdominal sc and visceral adipose tissue decreased by 9.2 +/- 2.4%, 6.1 +/- 3.2%, and 18.1 +/- 7.6%, respectively. After an initial decrease in the GDR at 6 weeks, the GDR increased in the rhGH-treated group as compared with the placebo-treated one (P < 0.05). The mean serum concentrations of total cholesterol (P < 0.01) and triglyceride (P < 0.05) decreased, whereas blood glucose and serum insulin concentrations were unaffected by the rhGH treatment. Furthermore, diastolic blood pressure decreased and systolic blood pressure was unchanged in response to rhGH treatment. This trial has demonstrated that GH can favorably affect some of the multiple perturbations associated with abdominal/visceral obesity. This includes a reduction in abdominal/visceral obesity, an improved insulin sensitivity, and favorable effects on lipoprotein metabolism and diastolic blood pressure.
TL;DR: An important physiological role for leptin as an inhibitor of insulin secretion is indicated and the failure of leptin to inhibit insulin secretion from the β-Cells of ob/ob and db/db mice may explain, in part, the development of hyperinsulinemia, insulin resistance, and the progression to NIDDM.
Abstract: In the genetic mutant mouse models ob/ob or db/db , leptin deficiency or resistance, respectively, results in severe obesity and the development of a syndrome resembling NIDDM. One of the earliest manifestations in these mutant mice is hyperinsulinemia, suggesting that leptin may normally directly suppress the secretion of insulin. Here, we show that pancreatic islets express a long (signal-transducing) form of leptin-receptor mRNA and that β-cells bind a fluorescent derivative of leptin (Cy3-leptin). The expression of leptin receptors on insulin-secreting β-cells was also visualized utilizing antisera generated against an extracellular epitope of the receptor. A functional role for the β-cell leptin receptor is indicated by our observation that leptin (100 ng/ml) suppressed the secretion of insulin from islets isolated from ob/ob mice. Furthermore, leptin produced a marked lowering of ]Ca 2+ ] i in ob/ob β-cells, which was accompanied by cellular hyperpolarization and increased membrane conductance. Cell-attached patch measurements of ob/ob β-Cells demonstrated that leptin activated ATP-sensitive potassium channels (K ATP ) by increasing the open channel probability, while exerting no effect on mean open time. These effects were reversed by the sulfonylurea tolbutamide, a specific inhibitor of K ATP . Taken together, these observations indicate an important physiological role for leptin as an inhibitor of insulin secretion and lead us to propose that the failure of leptin to inhibit insulin secretion from the β-Cells of ob/ob and db/db mice may explain, in part, the development of hyperinsulinemia, insulin resistance, and the progression to NIDDM.
TL;DR: The notion that PAI-1 can be a link between obesity, insulin resistance and cardiovascular disease is supported.
Abstract: Circulating (PAI-1) levels are elevated in patients with coronary heart disease and may play an important role in the development of atherothrombosis. Many clinical studies have indicated that the insulin resistance syndrome, which is a situation predisposing to diabetes and ischemic heart disease, may be a major regulator of PAI-1 expression, especially in determining plasma PAI-1 levels. Central obesity is a characteristic of insulin resistance and is a well recognized risk factor for coronary heart disease. Recently the production of PAI-1 by adipose tissue, in particular by tissue from omentum, has been demonstrated and could be an important contributor to the elevated plasma PAI-1 levels observed in insulin resistant patients. Besides the effect of the metabolic status on plasma PAI-1 levels, the role of a genetic control has been emphasized, but according to recent results obtained in a family segregation study, its participation seems limited. Prospective cohort studies of patients with previous myocardial infarction or angina pectoris have underlined the association between increased plasma PAI-1 levels and the risk of coronary events, but the predictive capacity of PAI-1 disappears after insulin resistance marker adjustments. Taken together these results support the notion that PAI-1 can be a link between obesity, insulin resistance and cardiovascular disease.
TL;DR: Reduced final height and raised serum insulin and proinsulin concentrations during oral glucose tolerance testing were found in young adults born small for gestational age compared with young adults with an appropriate birth weight for Gestational age.
Abstract: OBJECTIVE: To investigate whether the association between low birth weight and increased risk of developing impaired glucose tolerance, insulin resistance, hypertriglyceridaemia, and hypertension in middle age is apparent by the age of 20 in people born small for gestational age. DESIGN: Regional cohort study. SETTING: Maternity registry, Haguenau, France. SUBJECTS: 236 full term singleton babies born small for gestational age (birth weight or length, or both, below third centile) during 1971-8 and 281 with normal birth weight (between 25th and 75th centile). All subjects were contacted and evaluated at a mean (SD) age of 20.6 (2.1) years. MAIN OUTCOME MEASURES: Adult height; concentrations of glucose, insulin, and proinsulin during an oral glucose tolerance test; lipid and fibrinogen concentrations; and blood pressure. RESULTS: After sex and target height were adjusted for, subjects who had been born small for gestational age were significantly shorter at age 20 than those with a normal birth weight (men 4.5 cm shorter (95% confidence interval 6.0 to 3.0 cm); women 3.94 cm shorter (5.2 to 2.7 cm)). After sex and body mass index were adjusted for, mean plasma glucose concentration 30 minutes after a glucose load, fasting insulin concentration (in women), and insulin and proinsulin concentrations 30 and 120 minutes after a glucose load were significantly higher in subjects who had been born small for gestational age than in those with a normal birth weight. Mean lipid and fibrinogen concentrations and blood pressure were not different between the two groups. CONCLUSIONS: Intrauterine growth retardation has long term consequences such as reduced final height Raised insulin and proinsulin concentrations are present in young adults born small for gestational age and could be markers of early changes in insulin sensitivity.
TL;DR: Exercise training has been found to help alleviate the problem of insulin resistance, and substantially improve the control of insulin over blood glucose, and to help prevent muscle atrophy and stimulate muscle development.
Abstract: Recent epidemiological studies indicate that individuals who maintain a physically active lifestyle are much less likely to develop impaired glucose tolerance and non-insulin-dependent diabetes mellitus (NIDDM). Moreover, it was found that the protective effect of physical activity was strongest for individuals at highest risk of developing NIDDM. Reducing the risk of insulin resistance and NIDDM by regularly performed exercise is also supported by several aging studies. It has been found that older individuals who vigorously train on a regular basis exhibit a greater glucose tolerance and a lower insulin response to a glucose challenge than sedentary individuals of similar age and weight.
TL;DR: It is argued that dysfunction of peripheral vascular endothelium, at arteriolar and capillary level, plays the primary role in the pathogenesis of both insulin resistance and the associated features of the insulin resistance syndrome.
Abstract: Insulin resistance has been proposed as the metabolic basis of atherogenesis. This hypothesis is based on the concept of the "insulin resistance syndrome," according to which insulin resistance is viewed as the primary abnormality that gives rise to dyslipidemia, essential hypertension, impaired glucose tolerance, and NIDDM. However, this hypothesis takes no account of the well-established and central role of vascular endothelium in the atherogenic process. Although endothelial injury is an early and prominent feature of atherogenesis, relatively little attention has been given to its metabolic consequences. In subjects with NIDDM, we have shown that endothelial dysfunction is associated with insulin resistance, raising the question of whether this relationship could be causal. In this article, we review the factors that are considered to be responsible for the development of endothelial dysfunction during atherogenesis, together with the metabolic consequences of endothelial dysfunction. While dysfunction of the endothelium in large and medium-sized arteries plays a central role in atherogenesis, we argue that dysfunction of peripheral vascular endothelium, at arteriolar and capillary level, plays the primary role in the pathogenesis of both insulin resistance and the associated features of the insulin resistance syndrome. We propose that the insulin resistance syndrome, together with many aspects of atherogenesis, can be viewed as the diverse consequences of endothelial dysfunction in different vascular beds. This new and testable hypothesis accounts for both the endothelial and metabolic abnormalities associated with atherogenesis.
TL;DR: This contribution reviews the convincing evidence from glucose-clamp studies that all of these conditions are characterised by the presence of combined insulin resistance and hyperinsulinaemia and examines the relationships of the components of this syndrome to coronary artery disease and to the rational choice of antihypertensive therapy.
Abstract: Insulin resistance syndrome (IRS) has the potential to explain a large group of common metabolic and cardiovascular disorders [e.g., obesity, non-insulin-dependent diabetes mellitus (NIDDM), hypertension, hyperlipidaemia, hypercoagulability] which are all in themselves cardiovascular risk factors. This contribution firstly reviews the convincing evidence from glucose-clamp studies that all of these conditions are characterised by the presence of combined insulin resistance and hyperinsulinaemia, and secondly examines the relationships of the components of this syndrome to coronary artery disease and to the rational choice of antihypertensive therapy.
TL;DR: This review summarizes the current understanding and gaps in knowledge on cardiovascular actions of insulin in humans and pathophysiological consequences of derangements of such actions.
Abstract: The past several years have witnessed a major surge of interest in the cardiovascular actions of insulin. This interest has stemmed on the one hand from epidemiological studies that demonstrated an association between obesity, insulin resistance, and hypertension, leading to the so-called insulin hypothesis of hypertension. On the other hand, this interest has been stimulated by experimental evidence suggesting that the vascular actions of insulin may play a role in its main action, namely the promotion of glucose uptake in skeletal muscle tissue. Two tenets have emerged about how insulin may exert its cardiovascular actions. First, it is now firmly established that acute insulin administration stimulates sympathetic nerve activity in both animals and humans. Second, there is increasing evidence that insulin stimulates muscle blood flow, an effect that appears to be mediated at least in part by an endothelium-dependent mechanism. This review summarizes the current understanding and gaps in knowle...