Adiponutrin: A new gene regulated by energy balance in human adipose tissue

Adiponutrin is a newly identified nonsecreted adipocyte protein regulated by changes in energy balance in rodents. We documented the influence of energy balance modification on adiponutrin gene expression in humans. We investigated the mRNA expression in sc adipose tissue of nonobese women and in obese women during 2-d very low-calorie diet (VLCD) and subsequent refeeding as well as before and after a VLCD of 3 wk (21-d VLCD). The adiponutrin mRNA levels of the nonobese and obese women were not different (P > 0.05). Two-day VLCD reduced the average level of adiponutrin mRNA expression by 36% (P = 0.0016), whereas refeeding elevated the mRNA level by 31% (P = 0.004). The 3-wk VLCD caused a dramatic 58% fall of the adiponutrin mRNA expression level (P = 0.001). The mRNA level was negatively correlated with fasting glucose (Rho = -0.62; P < 0.0001), and subjects with high adiponutrin mRNA level had an increased insulin sensitivity. Compared with other adipocyte proteins such as leptin and adiponectin, adiponutrin mRNA did not show correlation with either adiposity indexes or with leptin or adiponectin mRNAs. These results indicate that adiponutrin gene expression in humans is highly regulated by changes in energy balance.     

Insulin regulation of gene expression and concentrations of white adipose tissue-derived proteins in vivo in healthy men: relation to adiponutrin

Adiponutrin is a newly described white adipose tissue (WAT)-derived protein whose function and regulation remain widely unclear in humans though it is suggested to be related to insulin sensitivity. Recently, we found that adiponutrin expression is reduced in type 2 diabetic subjects in basal and insulin-stimulated states. To examine adiponutrin regulation by the insulin pathway in relation to other WAT-related proteins with well-known relation to insulin signaling and action, we examined in healthy young men (1) the association of adiponutrin with p85alpha PI3K and HKII, leptin, adiponectin, and acylation-stimulating protein (ASP) and (2) the regulation of adiponutrin and WAT-derived proteins by 3-h hyperinsulinemic euglycemic clamp (HIEG). At baseline (N = 20), adiponutrin expressions were positively correlated with those of p85alpha PI3K (R = 0.54, P = 0.017), HKII (R = 0.58, P = 0.010), and serum leptin (R = 0.51, P = 0.036), but not with any other parameter measured including insulin sensitivity. Hyperinsulinemia (N = 10, +2365% above baseline) significantly increased the expression of adiponutrin (+770%, P = 0.002), p85alpha PI3K (+150%, P = 0.033), HKII (+147%, P = 0.007), and serum leptin (+11%, P = 0.031), while it decreased serum adiponectin (-15%, P = 0.001). In the insulin-stimulated state, adiponutrin mRNA expression levels correlated with basal p85alpha PI3K (R = 0.76, P = 0.018) and HKII (R = 0.86, P = 0.003) expression levels, with percentage increase in insulin (R = 0.73, P = 0.040), and with insulin-stimulated state HKII (R = 0.82, P = 0.007), leptin (R = 0.84, P = 0.005), and adiponectin (R = 0.85, P = 0.004) mRNA levels. In healthy young men, adiponutrin expression is upregulated [corrected] by hyperinsulinemia and is related to basal and/or insulin-stimulated p85alpha PI3K, HKII, adiponectin, and leptin expression levels. We hypothesize that insulin-mediated regulation of adiponutrin expression is under the PI3K pathway. The relevance of the present findings to reduced adiponutrin expression in type 2 diabetes is discussed.     

Obesity and insulin resistance in humans: a dose-response study

Insulin-mediated glucose metabolism (euglycemic insulin clamp at plasma insulin concentration of 100 microU/mL) and glucose-stimulated insulin secretion (hyperglycemic clamp) were examined in 42 obese subjects (ideal body weight [IBW], 158 +/- 4%) with normal glucose tolerance and in 36 normal weight (IBW, 102% +/- 1%) age-matched controls. In 10 obese and eight control subjects, insulin was infused at six rates to increase plasma insulin concentration by approximately 10, 20, 40, 80, 2,000, and 20,000 microU/mL. Throughout the physiologic range of plasma insulin concentrations, both the increase in total body glucose uptake and the suppression of hepatic glucose production (HGP) were significantly impaired in the obese group (P less than .001 to .01). At the two highest plasma insulin concentrations, inhibition of HGP and the stimulation of glucose disposal were similar in both the obese and control groups. Insulin secretion during the hyperglycemic (+/- 125 mg/dL) clamp was twofold greater in obese subjects than in controls (P less than .01) and was inversely related to the rate of glucose uptake during the insulin clamp (r = -.438, P less than .05), but was still unable to normalize glucose disposal (P less than .05). In conclusion, our results indicate that insulin resistance is a common accompaniment of obesity and can be overcome at supraphysiological insulin concentrations. Both in the basal state and following a hyperglycemic stimulus obese people display hyperinsulinemia, which correlates with the degree of insulin resistance. However, endogenous hyperinsulinemia fails to fully compensate for the insulin resistance.     

Increased insulin clearance in peroxisome proliferator-activated receptor gamma2 Pro12Ala

The Pro12Ala polymorphism of the peroxisome proliferator-activated receptor (PPARgamma(2)) is associated with reduced risk for type 2 diabetes. Although increased insulin sensitivity of glucose disposal and lipolysis has been reported, the exact mechanism by which the risk reduction is conferred is not clear. Because the conclusion of greater insulin sensitivity hinged upon lower insulin levels in some studies, it is possible that more efficient insulin clearance is involved. We therefore estimated insulin clearance during a euglycemic hyperinsulinemic clamp (insulin infusion rate divided by steady-state insulin concentration, 229 normal glucose tolerant [NGT] subjects), an oral glucose tolerance test (OGTT) (mean C-peptide divided by mean insulin concentrations, 406 NGT, 54 impaired glucose tolerant or mildly diabetic subjects), and a hyperglycemic clamp (120 minutes, 10 mmol/L, C-peptide divided by insulin in the steady-state, 56 NGT subjects). In the carriers of the Ala allele (prevalence approximately 24%), insulin clearance in all 3 protocols was significantly greater ( approximately 10%), than in controls. While the results from the euglycemic clamp reflect both hepatic and peripheral insulin clearance, those from the OGTT and the hyperglycemic clamp reflect mainly hepatic insulin extraction. Free fatty acids (FFA) during the steady state of the euglycemic hyperinsulinemic clamp were significantly lower in carriers of the Ala allele (26 +/- 5 micromol/L) than in controls (46 +/- 3 micromol/L, P =.02). In conclusion, the Pro12Ala polymorphism is associated with increased insulin clearance. This could be the result of reduced FFA delivery, which has been shown to improve hepatic insulin removal and sensitivity. Because PPARgamma(2) is mainly expressed in adipose tissue, one of the main regulatory effects of the polymorphism may well be the more efficient suppression of (possibly intra-abdominal) lipolysis.     

女性肥胖和2型糖尿病患者高葡萄糖钳夹过程中胰岛素原的分泌和释放

目的 探讨女性肥胖和2型糖尿病患者在持续高糖情况下胰岛素原分泌和释放的变化.方法 12例肥胖、7例2型糖尿病和9例正常对照组,行150分钟高葡萄糖钳夹试验,用酶联免疫法测定各时点胰岛素原.结果 肥胖组和2型糖尿病组空腹胰岛素原(PI)水平高于对照组.2型糖尿病组在10～150分钟期间胰岛素原/胰岛素比值高于肥胖组和对照组.Spearman相关分析显示,PI与胰岛素原分泌第一时相(FPPR)(r=0.464,P=0.026)和内脏脂肪(VA)(r=0.447,P=0.033)呈正相关;与葡萄糖代谢清除率(GDR)(r=-0.533,P=0.009)呈负相关.结论 胰岛素原分泌与胰岛素抵抗密切相关.持续高糖情况下肥胖患者由于胰岛素抵抗代偿性高分泌胰岛素原,2型糖尿病患者存在胰岛功能损害,胰岛素原分泌降低,而且胰岛素原转换胰岛素过程中存在缺陷.     

Epicardial adipose tissue and insulin resistance in obese subjects

CONTEXT: Epicardial adipose tissue has been recently recognized as a source of bioactive molecules as well as free fatty acids, adiponectin, and inflammatory cytokines. Epicardial fat reflects intraabdominal visceral fat, and the echocardiographic assessment of this tissue is an easy and reliable marker of visceral adiposity. OBJECTIVE: In this study we evaluated whether epicardial adipose tissue is related to insulin sensitivity and glucose metabolism in obese subjects. PATIENTS: Thirty obese subjects (20 women and 10 men; mean age, 40.8 +/- 11.5 yr; body mass index, 43 +/- 9.1 kg/m2) were included in this study. No subject was taking drugs or had a history or evidence of metabolic, cardiovascular, respiratory, or hepatic disease. MAIN OUTCOME MEASURES: Each subject underwent a transthoracic echocardiogram to evaluate epicardial adipose tissue thickness, a euglycemic hyperinsulinemic clamp to estimate insulin sensitivity, and an oral glucose tolerance test to evaluate glucose tolerance. RESULTS: The thickness of the epicardial adipose tissue on the right ventricle varied between 4 and 17.4 mm. Echocardiographic epicardial adipose tissue was significantly correlated with whole-body glucose uptake index from the clamp and with all indices of insulin resistance and glucose intolerance measured, except the 120-min plasma glucose level after an oral glucose tolerance test. CONCLUSIONS: Our study showed that the epicardial fat is significantly related to obesity-related insulin resistance. This finding could be of potential interest in clinical practice and research of obesity-related risk stratification.     

Effects of hyperinsulinemia on lipoprotein lipase, angiopoietin-like protein 4, and glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 in subjects with and without type 2 diabetes mellitus

Our aims were to compare the systemic effects of insulin on lipoprotein lipase (LPL) in tissues from subjects with different degrees of insulin sensitivity. The effects of insulin on LPL during a 4-hour hyperinsulinemic, euglycemic clamp were studied in skeletal muscle, adipose tissue, and postheparin plasma from young healthy subjects (YS), older subjects with type 2 diabetes mellitus (DS), and older control subjects (CS). In addition, we studied the effects of insulin on the expression of 2 recently recognized candidate genes for control of LPL activity: angiopoietin-like protein 4 (ANGPTL4) and glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1. As an effect of insulin, LPL activity decreased by 20% to 25% in postheparin plasma and increased by 20% to 30% in adipose tissue in all groups. In YS, the levels of ANGPTL4 messenger RNA in adipose tissue decreased 3-fold during the clamp. In contrast, there was no significant change in DS or CS. Regression analysis showed that the ability of insulin to reduce the expression of ANGPTL4 was positively correlated with M-values and inversely correlated with factors linked to the metabolic syndrome. Expression of glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 tended to be higher in YS than in DS or CS, but the expression was not affected by insulin in any of the groups. Our data imply that the insulin-mediated regulation of LPL is not directly linked to the control of glucose turnover by insulin or to ANGPTL4 expression in adipose tissue or plasma. Interestingly, the response of ANGPTL4 expression in adipose tissue to insulin was severely blunted in both DS and CS.     

Enhanced metabolic cycling in subjects after colonic resection for ulcerative colitis

Colonic resection leads to insulin resistance, but the mechanisms are unknown. We used an integrated approach to examine adipose tissue and skeletal muscle metabolism in patients lacking a colon. Ten healthy colectomized patients having undergone surgery for ulcerative colitis and 10 matched control subjects were studied with a hyperinsulinemic-euglycemic clamp to measure insulin sensitivity, an arteriovenous sampling meal tolerance study to measure postprandial substrate flux across adipose tissue and skeletal muscle, and adipose tissue and skeletal muscle biopsies to quantify the expression of genes involved in glucose and lipid metabolism. Colectomized subjects exhibited lower insulin sensitivity (homeostatic model assessment model, 33% reduction, P = 0.03; minimal model, 29% reduction, P = 0.05), elevated aldosterone (9-fold, P = 0.003), leptin (2.2-fold, P = 0.03), and an increased rate of nonesterified fatty acid and glycerol release from adipose tissue (P = 0.02) especially in the late postprandial period. The uptake of fatty acids into muscle was also significantly increased (P = 0.007), as were muscle CD36 and LPL mRNA expression compared with controls. In adipose tissue, hormone-sensitive lipase mRNA expression was increased (P = 0.015), whereas peroxisome proliferator-activated receptor-gamma expression was decreased (P = 0.02), as was that of CD36 (P = 0.001). In this study, alterations in fatty acid metabolism after colonic resection altered may have contributed to the impairment of insulin sensitivity.     

What are the physical characteristics associated with a normal metabolic profile despite a high level of obesity in postmenopausal women?

Although obesity is often associated with insulin resistance and a cluster of metabolic disturbances, the existence of a subgroup of healthy but obese individuals has been postulated. It is unclear why some obese individuals fail to show traditional risk factors associated with the insulin resistance syndrome despite having a very high accumulation of body fat. To address this issue, we identified and studied a subgroup of metabolically normal but obese (MNO) postmenopausal women to gain insight into potential physiological factors that may protect them against the development of obesity-related comorbidities. We carefully examined the metabolic characteristics of 43 obese, sedentary postmenopausal women (mean +/- SD, 58.0 +/- 6.0 yr). Subjects were classified as MNO or as metabolically abnormal obese (MAO) based on an accepted cut-point for insulin sensitivity (measured by the hyperinsulinemic/euglycemic clamp technique). Thereafter, we determined 1) body composition (fat mass and lean body mass), 2) body fat distribution (abdominal visceral and sc adipose tissue areas, midthigh sc adipose tissue and muscle attenuation), 3) plasma lipid-lipoprotein levels, 4) plasma glucose and insulin concentrations, 5) resting blood pressure, 6) peak oxygen consumption, 7) physical activity energy expenditure, and 8) age-related onset of obesity with a questionnaire as potential modulators of differences in the risk profile. We identified 17 MNO subjects who displayed high insulin sensitivity (11.2 +/- 2.6 mg/min.kg lean body mass) and 26 MAO subjects with lower insulin sensitivity (5.7 +/- 1.1 mg/min.kg lean body mass). Despite comparable total body fatness between groups (45.2 +/- 5.3% vs. 44.8 +/- 6.6%; P: = NS), MNO individuals had 49% less visceral adipose tissue than MAO subjects (141 +/- 53 vs. 211 +/- 85 cm(2); P: < 0.01). No difference was noted between groups for abdominal sc adipose tissue (453 +/- 126 vs. 442 +/- 144 cm(2); P: = NS), total fat mass (38.1 +/- 10.6 vs. 40.0 +/- 11.8 kg), muscle attenuation (42.2 +/- 2.6 vs. 43.6 +/- 4.8 Houndsfield units), and physical activity energy expenditure (1060 +/- 323 vs. 1045 +/- 331 Cal/day). MNO subjects had lower fasting plasma glucose and insulin concentrations and lower insulin levels during the oral glucose tolerance test (P: values ranging between 0.01-0.001). No difference was observed between groups for 2-h glucose levels and glucose area during the oral glucose tolerance test. MNO subjects showed lower plasma triglycerides and higher high density lipoprotein cholesterol concentrations than MAO individuals (P: < 0.01 in both cases). Results from the questionnaire indicated that 48% of the MNO women presented an early onset of obesity (<20 yr old) compared with 29% of the MAO subjects (P: = 0.09). Stepwise regression analysis showed that visceral adipose tissue and the age-related onset of obesity explained 22% and 13%, respectively, of the variance observed in insulin sensitivity (total r(2) = 0.35; P: < 0.05 in both cases). Our results support the existence of a subgroup of obese but metabolically normal postmenopausal women who display high levels of insulin sensitivity despite having a high accumulation of body fat. This metabolically normal profile is associated with a lower accumulation of visceral adipose tissue and an earlier age-related onset of obesity.     

Ghrelin enhances glucose-induced insulin secretion in scheduled meal-fed sheep

The purpose of this study was to investigate the effects of physiologic levels of ghrelin on insulin secretion and insulin sensitivity (glucose disposal) in scheduled fed-sheep, using the hyperglycemic clamp and hyperinsulinemic euglycemic clamp respectively. Twelve castrated Suffolk rams (69.8 +/- 0.6 kg) were conditioned to be fed alfalfa hay cubes (2% of body weight) once a day. Three hours after the feeding, synthetic ovine ghrelin was intravenously administered to the animals at a rate of 0.025 and 0.05 mug/kg body weight (BW) per min for 3 h. Concomitantly, the hyperglycemic clamp or the hyperinsulinemic euglycemic clamp was carried out. In the hyperglycemic clamp, a target glucose concentration was clamped at 100 mg/100 ml above the initial level. In the hyperinsulinemic euglycemic clamp, insulin was intravenously administered to the animals for 3 h at a rate of 2 mU/kg BW per min. Basal glucose concentrations (44+/- 1 mg/dl) were maintained by variably infusing 100 mg/dl glucose solution. In both clamps, plasma ghrelin concentrations were dose-dependently elevated and maintained at a constant level within the physiologic range. Ghrelin infusions induced a significant (ANOVA; P < 0.01) increase in plasma GH concentrations. In the hyperglycemic clamp, plasma insulin levels were increased by glucose infusion and were significantly (P < 0.05) greater in ghrelin-infused animals. In the hyperinsulinemic euglycemic clamp, glucose infusion rate, an index of insulin sensitivity, was not affected by ghrelin infusion. In conclusion, the present study has demonstrated for the first time that ghrelin enhances glucose-induced insulin secretion in the ruminant animal.     

Insulin secretion and insulin sensitivity in diabetic and non-diabetic subjects with hepatic nuclear factor-1alpha (maturity-onset diabetes of the young-3) mutations

OBJECTIVE: To evaluate insulin secretion and sensitivity in affected (diabetes mellitus or impaired glucose tolerance; n=7) and in unaffected (normal glucose tolerance; n=3) carriers of hepatocyte nuclear factor-1alpha (maturity-onset diabetes of the young-3 (MODY3)) gene mutations. METHODS: Insulin secretion was assessed by an i.v. glucose tolerance test (IVGTT), hyperglycemic clamp and arginine test, and insulin sensitivity by an euglycemic hyperinsulinemic clamp. Results were compared with those of diabetic MODY2 (glucokinase-deficient) and control subjects. RESULTS: The amount of insulin secreted during an IVGTT was decreased in affected MODY3 subjects (46+/-24 (s.d.) pmol/kg body weight (BW)) as compared with values in MODY2 (120+/-49pmol/kg BW) and control (173+/-37pmol/kg BW; P=0.0004) subjects. The amount of insulin secreted during a 10mmol/l glucose clamp was decreased in affected MODY3 subjects (171+/-78pmol/kg BW) and MODY2 subjects (302+/-104pmol/kg BW) as compared with control subjects (770+/-199pmol/kg BW; P=0.0001). Insulin secretion in response to arginine was decreased in affected MODY3 subjects. Milder and heterogeneous defects were observed in the unaffected MODY3 subjects; the amount of insulin secreted during the hyperglycemic clamp was 40-79% of that of controls. The response to arginine was abnormally delayed. Insulin sensitivity was decreased in diabetic but not in non-diabetic MODY3 subjects. CONCLUSIONS: Beta-cell dysfunction in response to glucose and arginine is observed in affected and unaffected MODY3 subjects. The MODY3 and MODY2 subtypes present different insulin secretion profiles. Secondary insulin resistance might contribute to the chronic hyperglycemia of MODY3 patients and modulate their glucose tolerance.     

Insulin resistance early in adulthood in subjects born with intrauterine growth retardation

In a case-control study that investigated the effect of intrauterine growth retardation (IUGR) on glucose homeostasis, 20-yr-old adults born with IUGR were shown to be hyperinsulinemic in an oral glucose tolerance test, suggestive of insulin resistance. The aim of this study was to ascertain the decreased insulin sensitivity in young IUGR-born adults compared to that in controls. We studied 26 IUGR-born subjects and 25 controls, aged 25 yr. Insulin sensitivity was assessed by peripheral glucose uptake and monitoring free fatty acid (FFA) concentrations under euglycemic hyperinsulinemic clamp. The percent body fat was significantly higher in the IUGR group (27.2 +/- 7.6% vs. 22.0 +/- 7.3%; P = 0.02), contrasting with comparable body mass index in both groups. Insulin-stimulated glucose uptake was significantly lower in IUGR-born subjects than in controls (6.7 +/- 2.9 vs. 8.0 +/- 1.9 mg/kg fat-free mass x min; P = 0.05), and the difference remained significant after adjustment for body mass index, total body fat, or waist to hip ratio. In IUGR-born subjects, insulin-stimulated FFA suppression correlated significantly with peripheral glucose uptake (r2 = 0.23; P = 0.02). First phase insulin release in the iv glucose tolerance test, adjusted for insulin sensitivity, did not significantly differ between IUGR and control groups (442 +/- 284 vs. 391 +/- 209 pmol/L; P = 0.86). In conclusion, IUGR subjects have decreased insulin-stimulated glucose uptake as early as 25 yr of age without major impairment of insulin secretion. Low glucose uptake is associated with a lesser degree of FFA suppression in adipose tissue, which suggests a role of adipose tissue at an early stage of insulin resistance in these subjects.     

Expression of insulin target genes in skeletal muscle and adipose tissue in adult patients with growth hormone deficiency: effect of one year recombinant human growth hormone therapy.

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

Polycystic ovary syndrome is associated with tissue-specific differences in insulin resistance

OBJECTIVE: The potential differential contributions of skeletal muscle and adipose tissue to whole body insulin resistance were evaluated in subjects with polycystic ovary syndrome (PCOS). Research Design and METHODS: Forty-two PCOS subjects and 15 body mass index-matched control subjects were studied. Insulin action was evaluated by the hyperinsulinemic/euglycemic clamp procedure. Isolated adipocytes and cultured muscle cells were analyzed for glucose transport activity; adipocytes, muscle tissue, and myotubes were analyzed for the expression and phosphorylation of insulin-signaling proteins. RESULTS: Fifty-seven per cent of the PCOS subjects had impaired glucose tolerance and the lowest rate of maximal insulin-stimulated whole body glucose disposal compared to controls (P < 0.01). PCOS subjects with normal glucose tolerance had intermediate reduction in glucose disposal rate (P < 0.05 vs. both control and impaired glucose tolerance subjects). However, rates of maximal insulin-stimulated glucose transport (insulin responsiveness) into isolated adipocytes were comparable between all three groups, whereas PCOS subjects displayed impaired insulin sensitivity. In contrast, myotubes from PCOS subjects displayed reduced insulin responsiveness for glucose uptake and normal sensitivity. There were no differences between groups in the expression of glucose transporter 4 or insulin-signaling proteins or maximal insulin stimulation of phosphorylation of Akt in skeletal muscle, myotubes, or adipocytes. CONCLUSIONS: Individuals with PCOS display impaired insulin responsiveness in skeletal muscle and myotubes, whereas isolated adipocytes display impaired insulin sensitivity but normal responsiveness. Skeletal muscle and adipose tissue contribute differently to insulin resistance in PCOS. Insulin resistance in PCOS cannot be accounted for by differences in the expression of selected signaling molecules or maximal phosphorylation of Akt.     

Insulin sensitivity assessment in uncomplicated obese women: comparison of indices from fasting and oral glucose load with euglycemic hyperinsulinemic clamp

BACKGROUND AND AIM: Obesity is associated with a great variability to insulin sensitivity degree. Several formulae developed from measurements in the fasting state and during the oral glucose tolerance test (OGTT) have been proposed to assess insulin sensitivity. AIM: In this work we sought to compare the published insulin sensitivity indices with the metabolized glucose index obtained by hyperinsulinemic euglycemic clamp in uncomplicated obese subjects. Uncomplicated obesity provides a good model in order to study insulin sensitivity per se. METHODS AND RESULTS: In this protocol, 65 obese women affected by uncomplicated obesity (without impaired glucose tolerance, diabetes, hypertension and dyslipidemia) underwent 2 h OGTT and euglycemic hyperinsulinemic clamp. Common formulae obtained in the fasting state and from a 2h OGTT were calculated. Simple linear regression analysis showed that ISI (r=0.592, p=0.01), 2 h OGIS (r=0.576, p=0.02), MCRest (r=0.507, p=0.02), 120 insulin (r=-0.494, p=0.03) and fasting insulin (r=-0.382, p =0.02) are significantly correlated to the M index obtained from the hyperinsulinemic euglycemic clamp. The Bland-Altman plot confirmed the good agreement between indices from OGTT and the clamp. CONCLUSION: OGTT-derived indices provide a good assessment of insulin sensitivity in obesity. OGTT could easily be applied in a large number of obese patients in order to obtain information on both glucose tolerance and insulin sensitivity.     

Estimates of in vivo insulin action in man: comparison of insulin tolerance tests with euglycemic and hyperglycemic glucose clamp studies

We compared estimates of in vivo insulin action derived from insulin tolerance tests (ITT) and euglycemic and hyperglycemic glucose clamp studies in 17 normal subjects and 19 patients with various diseases characterized by insulin resistance. Fifteen subjects underwent an ITT and a euglycemic clamp study, 17 subjects underwent an ITT and a hyperglycemic clamp study, and 4 subjects underwent all 3 tests. The ITT consisted of a bolus iv injection of regular insulin (0.1 U/kg BW). The plasma glucose disappearance rate during the 3- to 15-min period following the insulin injection was taken as a measure of insulin action. In both euglycemic and hyperglycemic clamp studies, which were carried out with standard techniques, the ratio between the amount of glucose infused to maintain glycemia at the desired level and the mean plasma insulin concentration from 60-120 min (M) (euglycemic clamp studies) or 20-120 min (I) (hyperglycemic clamp studies) was used as a measure of insulin action. A close correlation was found between plasma glucose disappearance rate and the M/I ratio during either the euglycemic (r = 0.811; P less than 0.001) or the hyperglycemic (r = 0.826; P less than 0.001) clamp studies. These results suggest that the 15-min ITT is suitable as a simple and rapid estimation of in vivo insulin action when glucose clamp studies are not feasible, as in large series of subjects or serial studies.     

Stimulation in vivo of expression of intra-abdominal adipose tissue plasminogen activator inhibitor Type I by proinsulin

Aims/hypothesis: Impaired fibrinolytic system capacity secondary to increased plasminogen activator inhibitor type-1 expression has been suggested as a pathogenetic link between insulin resistance and increased cardiovascular risk in patients with Type II (non-insulin-dependent) diabetes mellitus, obesity, or both. In patients with syndromes of insulin resistance including those with Type II diabetes, precursors of insulin such as proinsulin can constitute more than 50 % of insulin-like molecules in blood. The aim of this study was to determine whether proinsulin can increase plasminogen activator inhibitor type-1 expression in intra-abdominal adipose tissue in vivo, potentially contributing to the increased PAI-1 seen with insulin resistance. Methods: Lightly sedated normal rabbits were given intravenous proinsulin, insulin, or vehicle alone under euglycaemic clamp conditions with serial sampling of blood and assessment of PAI-1 expression in visceral fat. Results: Both proinsulin and insulin increased expression of plasminogen activator inhibitor type-1 in intra-abdominal adipose tissue, 5.3-fold (p = 0.006 vs control) and 2.5-fold (p = 0.031 vs control) respectively. PAI-1 inhibitor activity in blood peaked 3 h after administration of each, 5.1-fold, p = 0.020, and 3.4-fold, p = 0.004, respectively but did not change under control conditions. Conclusion/interpretation: Hyperproinsulinaemia can contribute to increased expression of plasminogen activator inhibitor type-1 in intra-abdominal adipose tissue implicated in increasing PAI-1 activity in blood, impaired fibrinolysis, and accelerated atherogenesis typical of Type II diabetes. [Diabetologia (2001) 44: 1121–1124] Received: 21 March 2001 and in revised form: 21 May 2001     

Adipose tissue IL-6 content correlates with resistance to insulin activation of glucose uptake both in vivo and in vitro

Obesity and type 2 diabetes are associated with insulin resistance, the mechanisms of which remain poorly understood. A significant correlation between circulating IL-6 level and insulin sensitivity has recently been found in humans. Because adipose tissue could be a significant source of IL-6, we analyzed the relationship between the levels of adipose tissue IL-6 and insulin action in vivo, during a hyperinsulinemic normoglycemic clamp, and in vitro by measuring glucose transport in adipocytes from 12 obese subjects with (n = 7) or without (n = 5) diabetes. We observed an inverse correlation between adipose tissue IL-6 content and maximal insulin-responsiveness measured in vivo (P < 0.02) and in vitro (P < 0.02). Conversely, there was no significant correlation between these two later parameters and adipose tissue leptin or tumor necrosis factor-alpha protein contents. Furthermore, we showed, for the first time, the presence of immunoreactive IL-6 receptors in the plasma membrane of human abdominal sc adipocytes. This suggests that locally secreted IL-6 could act on adipocytes by an autocrine/paracrine mechanism. In conclusion, increased IL-6 production by sc adipose cells might participate to the insulin-resistant state observed in human obesity.     

Relationship between serum resistin concentrations and insulin resistance in nonobese, obese, and obese diabetic subjects

Early reports suggested that resistin is associated with obesity and insulin resistance in rodents. However, subsequent studies have not supported these findings. To our knowledge, the present study is the first assessment in human subjects of serum resistin and insulin sensitivity by the insulin clamp technique. Thirty-eight nonobese subjects [age, 23 +/- 4 yr; body mass index (BMI), 25.4 +/- 4.3 kg/m(2)], 12 obese subjects (age, 54 +/- 8 yr; BMI, 33.0 +/- 2.5 kg/m(2)), and 22 obese subjects with type 2 diabetes (age, 59 +/- 7 yr; BMI, 34.0 +/- 2.4 kg/m(2)) were studied. Serum resistin concentrations were not different among nonobese (4.1 +/- 1.7 ng/ml), obese (4.2 +/- 1.6 ng/ml), and obese diabetic subjects (3.7 +/- 1.2 ng/ml), and were not significantly correlated to glucose disposal rate during a hyperinsulinemic glucose clamp across groups. Serum resistin was, however, inversely related to insulin sensitivity in nonobese subjects only (r = -0.35; P = 0.05), although this association was lost after adjusting for percent body fat. Serum resistin was not related to percent fat, BMI, or fat cell size. A strong correlation was observed between serum resistin and resistin mRNA expression from abdominal sc adipose tissue in a separate group of obese subjects (r = 0.62; P < 0.01; n = 56). Although the exact function of resistin is unknown, we demonstrated only a weak relationship between resistin and insulin sensitivity in nonobese subjects, indicating that resistin is unlikely to be a major link between obesity and insulin resistance in humans.     

Possible novel index determined by the glucose clamp test for selection of a suitable therapy for each type 2 diabetic patient

The hallmark of type 2 diabetes is insulin resistance and insufficient insulin secretion, and appropriate therapy should be selected for each patient. In this study, to establish some index to select suitable therapy for each patient, we evaluated insulin sensitivity and insulin secretion with euglycemic hyperinsulinemic clamp and hyperglycemic clamp tests, respectively, and found that specific GIR index (GIRxIRI (90)) could be a useful marker to select suitable therapy for each type 2 diabetic patient (GIR: glucose infusion rate in euglycemic hyperinsulinemic clamp test; IRI (90): plasma insulin level 90 min after starting the hyperglycemic clamp test).