Insulin resistance does not influence gene expression in skeletal muscle.

Insulin resistance is commonly observed in patients prior to the development of type 2 diabetes and may predict the onset of the disease. We tested the hypothesis that impairment in insulin stimulated glucose-disposal in insulin resistant patients would be reflected in the gene expression profile of skeletal muscle. We performed gene expression profiling on skeletal muscle of insulin resistant and insulin sensitive subjects using microarrays. Microarray analysis of 19,000 genes in skeletal muscle did not display a significant difference between insulin resistant and insulin sensitive muscle. This was confirmed with real-time PCR. Our results suggest that insulin resistance is not reflected by changes in the gene expression profile in skeletal muscle.

Serum adiponectin levels in normal and hypertensive pregnancy.

OBJECTIVE: The aim of this study was to quantify adiponectin levels in women with normal and hypertensive pregnancies to determine whether there is an independent association, while controlling for body fat and insulin sensitivity. METHODS: A cross-sectional study was conducted in the following categories: 12 normotensive non-pregnant women, 10 normotensive, 12 gestational hypertensive, 13 essential hypertensive, and 12 preeclamptic women. All subjects underwent measurements of body fat by bio-impedance analysis and blood sampling. RESULTS: Percentage of body fat and insulin resistance were greater in all pregnant groups compared with non-pregnant women. Adiponectin concentrations were significantly lower in women with normal pregnancies (18.6 +/- 1.4 microg/mL, p = 0.02) compared with non-pregnant women (24.0 +/- 1.5 microg/mL). However, adiponectin levels were not significantly different among normal pregnancy, gestational hypertension (19.0 +/- 3.1 microg/mL), essential hypertension (24.0 +/- 3.7 microg/mL) and pre-eclampsia (22.4 +/- 2.5 microg/mL) groups. Adiponectin levels were inversely related to percent body fat and insulin resistance. When adiponectin levels were corrected for percent body fat and insulin resistance, no significant differences were seen among the study groups. CONCLUSIONS: Adiponectin levels are decreased in normal pregnancy, however this difference disappears when adiponectin levels are corrected for the pregnancy-related increases in body fat and insulin resistance. Adiponectin levels are not altered significantly in states of hypertension in pregnancy compared with normal pregnancy.

The metabolism of isoforms of human adiponectin: studies in human subjects and in experimental animals.

OBJECTIVE: Little is known of the metabolism of different isoforms of adiponectin. We therefore (a) characterised the size distribution of human adiponectin in relation to gender, body composition and following a challenge with a fat meal or oral glucose in humans, and (b) studied the metabolism of isoforms of human adiponectin in rabbits. METHOD: Electrophoresis, blotting and chromatography were used to characterise human adiponectin in 36 healthy subjects, including 15 with at least two first-degree relatives with type 2 diabetes, before and after consumption of a fatty meal or glucose. The metabolism of column-fractionated human adiponectin was studied in rabbits, some of which were coinjected with insulin. RESULTS: Females had a higher proportion of high molecular weight (HMW) and hexameric adiponectin (P = 0.002 and 0.004 respectively), and a lower proportion of trimers (P < 0.0001) than males. Females also showed a strong negative relationship between body fat measures and the proportion of HMW adiponectin. There were no differences in isoforms between insulin-resistant and -sensitive subjects, or following oral glucose or a fat meal. Adiponectin in rabbits had an extravascular/intravascular ratio of 0.71, and a half-life (T1/2) of 14.3 h. Metabolism was not influenced by insulin or reduction of sulphydryl bonds. HMW and trimeric isoforms had a significantly different T1/2 of 13.0 and 17.5 h respectively (P < 0.05), and these isoforms did not interconvert in vivo. CONCLUSIONS: Human adiponectin is present as trimers, hexamers and HMW forms. Females had a higher proportion and absolute amount of HMW species compared with males, and female, but not male, subjects showed a strong negative relationship between measures of body fat, and the proportion of HMW species. These isoforms did not respond to challenge in man with a fatty meal or oral glucose, and in the rabbit, to injected insulin. HMW adiponectin was more rapidly metabolised than the trimeric form, but both were stable in vivo, and did not interconvert. We conclude that human adiponectin is much longer-lived than is the case with other hormones, a finding with positive implications for the potential to supplement levels of adiponectin in man.

Insulin resistance and postprandial triglyceride levels in primary renal disease.

BACKGROUND: Renal failure is associated with a range of metabolic abnormalities including insulin resistance and dyslipidemia. We examined the role of creatinine clearance (CrCl) and body composition in the development of insulin resistance in patients with primary renal disease and a variable degree of renal failure. We also determined the effect of a high-fat meal on postprandial triglyceride levels in a subgroup of these patients. METHODS: Forty-four patients with primary renal disease (men, 25; women, 19; age, 21-75 years) were compared to 44 controls matched for age, sex, and body composition. Renal biochemistry, plasma glucose, insulin, lipids, and nonesterified fatty acids were measured in the fasting state. Insulin sensitivity was calculated using the Homeostasis Model Assessment for Insulin Resistance (HOMA-R), and pancreatic beta-cell secretory capacity by HOMA- beta . Fourteen normotriglyceridemic subjects from each group consumed an 80-g fat meal to examine their postprandial metabolic response. RESULTS: Although there was no significant difference between HOMA-R for the controls and the entire patient group ( P = .06), HOMA-R was significantly higher in patients with CrCl less than 60 mL/min than those with CrCl greater than 60 mL/min or control subjects ( P < .01 for each pair). Exponential analysis of the relationship between CrCl and HOMA-R and - beta showed a line of best fit that was superior to that obtained by linear regression analysis ( P < .01 and P < .005, respectively). HOMA-R in renal patients was correlated with several parameters of body composition, including central fat (kilogram) ( P < .005). There was no difference in body fat parameters or HOMA-R for the patient and control subgroups undergoing a fat meal challenge. However, the patient subgroup showed a greater postprandial incremental rise in plasma triglycerides compared to controls ( P < .02). CONCLUSION: Patients with renal disease exhibit metabolic features typically associated with the metabolic syndrome. Insulin resistance increased with decline in renal function and was significantly higher in patients with CrCl less than 60 mL/min compared to subjects with CrCl greater than 60 mL/min or carefully matched controls. Renal patients also showed significant postprandial hypertriglyceridemia.

Inflammation, insulin resistance, and adiposity: a study of first-degree relatives of type 2 diabetic subjects.

OBJECTIVE: Inflammatory markers such as C-reactive protein (CRP) are associated with insulin resistance, adiposity, and type 2 diabetes. Whether inflammation causes insulin resistance or is an epiphenomenon of obesity remains unresolved. We aimed to determine whether first-degree relatives of type 2 diabetic subjects differ in insulin sensitivity from control subjects without a family history of diabetes, whether first-degree relatives of type 2 diabetic subjects and control subjects differ in CRP, adiponectin, and complement levels, and whether CRP is related to insulin sensitivity independently of adiposity. RESEARCH DESIGN AND METHODS: We studied 19 young normoglycemic nonobese first-degree relatives of type 2 diabetic subjects and 22 control subjects who were similar for age, sex, and BMI. Insulin sensitivity (glucose infusion rate [GIR]) was measured by the euglycemic-hyperinsulinemic clamp. Dual-energy X-ray absorptiometry determined total and abdominal adiposity. Magnetic resonance imaging measured abdominal adipose tissue volumes. RESULTS: First-degree relatives of type 2 diabetic subjects had a 20% lower GIR than the control group (51.8 +/- 3.9 vs. 64.9 +/- 4.6 micromol x min(-1) x kg fat-free mass(-1), P = 0.04). However, first-degree relatives of subjects with type 2 diabetes and those without a family history of diabetes had normal and comparable levels of CRP, adiponectin, and complement proteins. When the cohort was examined as a whole, CRP was inversely related to GIR (r = -0.33, P = 0.04) and adiponectin (r = -0.34, P = 0.03) and positively related to adiposity (P < 0.04). However, CRP was not related to GIR independently of fat mass. In contrast to C3 (r = 0.41, P = 0.009) and factor B (r = 0.43, P = 0.005), CRP was unrelated to factor D. CONCLUSIONS: The insulin-resistant state is not associated with changes in inflammatory markers or complement proteins in subjects at high risk of type 2 diabetes. Our study confirms a strong relationship between CRP and fat mass. Increasing adiposity and insulin resistance may interact to raise CRP levels.

Changes in aerobic capacity and visceral fat but not myocyte lipid levels predict increased insulin action after exercise in overweight and obese men.

OBJECTIVE: To examine the effect of moderate intensity physical activity on the interactions between central abdominal adiposity, myocyte lipid content, and insulin action in overweight and obese, sedentary men. RESEARCH DESIGN AND METHODS: Myocyte lipid (biochemical triglyceride and long-chain acyl CoA [LCAC] from vastus lateralis biopsy and soleus and tibialis anterior intramyocellular lipid by (1)H-magnetic resonance spectroscopy), regional body and abdominal fat (dual-energy X-ray absorptiometry and magnetic resonance imaging), serum lipids, insulin action (hyperinsulinemic-euglycemic clamp), and substrate oxidation were measured in 18 nondiabetic, sedentary, and overweight to obese men (aged 37.4 +/- 1.3 years and BMI 30.9 +/- 0.7 kg/m(2), range 26.4-37.6) at baseline, after the first two to four bouts of aerobic exercise (55-70% of VO(2max) for 40 min/session), and at completion of 4.1 +/- 0.2 exercise sessions/week for 9.7 +/- 0.5 weeks (postexercise measurements performed 24-36 h after the last exercise bout). RESULTS: Mean whole body insulin-stimulated glucose uptake and basal fat oxidation rate increased 16 and 41%, respectively, after two to four bouts of exercise, without further increase at program end. Mean aerobic capacity increased 11%, and central abdominal fat decreased 5% at program end, but myocyte lipid levels were not significantly changed. Posttraining increases in insulin-stimulated glucose uptake were predicted by increase in aerobic capacity (r = 0.726, P = 0.001) and magnitude of reduction in visceral fat (r = -0.544, P = 0.02) and not by changes in myocyte lipid or LCAC levels. CONCLUSIONS: These results suggest that in overweight and obese sedentary men, increase in insulin sensitivity with moderate intensity exercise is predicted by improvement in aerobic capacity and reduction in visceral fat but is independent of myocyte triglyceride or LCAC levels.

Multiple indexes of lipid availability are independently related to whole body insulin action in healthy humans.

An increase in muscle lipid content has been postulated to relate closely to the evolution of insulin resistance. We aimed to test whether the multiple indexes of lipid supply within man [namely, circulating triglycerides, skeletal muscle triglycerides (SMT), total and central fat mass, and circulating leptin] were independent predictors of insulin resistance, or whether triglycerides from different sources are additive in their influence on whole body insulin sensitivity. Whole body insulin sensitivity, body composition, and SMT content were determined in 49 sedentary, nondiabetic males (age, 20-74 yr; body mass index, 20-38 kg/m(2)). Insulin sensitivity was inversely associated with central abdominal fat (r(2) = 0.38; P < 0.0001), total body fat (r(2) = 0.21; P = 0.0003), SMT content (r(2) = 0.16; P = 0.005), and fasting triglycerides (r(2) = 0.24; P = 0.0003), nonesterified free fatty acid (r(2) = 0.19; P = 0.002), and leptin (r(2) = 0.35; P < 0.0001) levels. However, only central abdominal fat was significantly related to SMT content (r(2) = 0.10; P = 0.03). SMT content, circulating triglycerides, and measurements of total or central adiposity were independent predictors of whole body insulin sensitivity.

Muscle oxidative capacity is a better predictor of insulin sensitivity than lipid status.

We determined whole-body insulin sensitivity, long-chain fatty acyl coenzyme A (LCACoA) content, skeletal muscle triglyceride (TG(m)) concentration, fatty acid transporter protein content, and oxidative enzyme activity in eight patients with type 2 diabetes (TYPE 2); six healthy control subjects matched for age (OLD), body mass index, percentage of body fat, and maximum pulmonary O(2) uptake; nine well-trained athletes (TRAINED); and four age-matched controls (YOUNG). Muscle biopsies from the vastus lateralis were taken before and after a 2-h euglycemic-hyperinsulinemic clamp. Oxidative enzyme activities, fatty acid transporters (FAT/CD36 and FABPpm), and TG(m) were measured from basal muscle samples, and total LCACoA content was determined before and after insulin stimulation. Whole-body insulin-stimulated glucose uptake was lower in TYPE 2 (P < 0.05) than in OLD, YOUNG, and TRAINED. TG(m) was elevated in TYPE 2 compared with all other groups (P < 0.05). However, both basal and insulin-stimulated skeletal muscle LCACoA content were similar. Basal citrate synthase activity was higher in TRAINED (P < 0.01), whereas beta-hydroxyacyl CoA dehydrogenase activity was higher in TRAINED compared with TYPE 2 and OLD. There was a significant relationship between the oxidative capacity of skeletal muscle and insulin sensitivity (citrate synthase, r = 0.71, P < 0.001; beta-hydroxyacyl CoA dehydrogenase, r = 0.61, P = 0.001). No differences were found in FAT/CD36 protein content between groups. In contrast, FABPpm protein was lower in OLD compared with TYPE 2 and YOUNG (P < 0.05). In conclusion, despite markedly elevated skeletal muscle TG(m) in type 2 diabetic patients and strikingly different levels of whole-body glucose disposal, both basal and insulin-stimulated LCACoA content were similar across groups. Furthermore, skeletal muscle oxidative capacity was a better predictor of insulin sensitivity than either TG(m) concentration or long-chain fatty acyl CoA content.

Nicotinic acid-induced insulin resistance is related to increased circulating fatty acids and fat oxidation but not muscle lipid content.

Insulin resistance is associated with increased circulating lipids and skeletal muscle lipid content. Chronic nicotinic acid (NA) treatment reduces insulin sensitivity and provides a model of insulin resistance. We hypothesized that the reduction in insulin sensitivity occurs via elevation of circulating nonesterified fatty acids (NEFAs) and an increase in intramyocellular lipid (IMCL). A total of 15 nondiabetic males (mean age 27.4 +/- 1.6 years) were treated with NA (500 mg daily for 1 week, 1 g daily for 1 week). Insulin sensitivity (glucose infusion rate [GIR]) was determined pre- and post-NA by euglycemic-hyperinsulinemic clamp. Substrate oxidation was determined by indirect calorimetry. Skeletal muscle lipid was assessed by estimation of long-chain acyl-CoA (LCACoA) and triglyceride (TG) content and by (1)H-magnetic resonance spectroscopy quantification of IMCL (n = 11). NA reduced GIR (P =.03) and nonoxidative glucose disposal (P <.01) and increased fasting NEFAs (P =.01). The decrease in GIR related significantly to the increase in fasting NEFAs (r(2) =.30, P =.03). The intrasubject increase in basal and clamp fat oxidation correlated with the decrease in GIR (r(2) =.45, P <.01 and r(2) =.63, P <.01). There were no significant changes in muscle LCACoA, TG, or IMCL content. Therefore, induction of insulin resistance by NA occurs with increased availability of circulating fatty acids to muscle rather than with increased muscle lipid content.

Islet-1: a potentially important role for an islet cell gene in visceral fat.

OBJECTIVE: To examine differences in gene expression between visceral (VF) and subcutaneous fat (SF) to identity genes of potential importance in regulation of VF. METHODS AND PROCEDURES: We compared gene expression (by DNA array and quantitative PCR (qPCR)) in paired VF and SF adipose biopsies from 36 subjects (age 54 +/- 15 years, 15 men/21 women) with varying degrees of adiposity and insulin resistance, in chow and fat fed mice (+/- rosiglitazone treatment) and in c-Cbl(-/-) mice. Gene expression was also examined in 3T3-L1 preadipocytes during differentiation. RESULTS: A twofold difference or more was found between VF and SF in 1,343 probe sets, especially for genes related to development, cell differentiation, signal transduction, and receptor activity. Islet-1 (ISL1), a LIM-homeobox gene with important developmental and regulatory function in islet, neural, and cardiac tissue, not previously recognized in adipose tissue was virtually absent in SF but substantially expressed in VF. ISL1 expression correlated negatively with BMI (r = -0.37, P = 0.03), abdominal fat (by dual energy X-ray absorptiometry, r = -0.44, P = 0.02), and positively with circulating adiponectin (r = 0.33, P = 0.04). In diet-induced obese mice, expression was reduced in the presence or absence of rosiglitazone. Correspondingly, expression was increased in the c-Cbl(-/-) mouse, which is lean and insulin sensitive (IS). ISL1 expression was increased sevenfold in 3T3-L1 preadipocytes during early (day 1) differentiation and was reduced by day 2 differentiation. DISCUSSION: An important developmental and regulatory gene ISL1 is uniquely expressed in VF, probably in the preadipocyte. Our data suggest that ISL1 may be regulated by adiposity and its role in metabolic regulation merits further study.

Relationship of adiponectin with insulin sensitivity in humans, independent of lipid availability.

OBJECTIVE: To test in humans the hypothesis that part of the association of adiponectin with insulin sensitivity is independent of lipid availability. RESEARCH METHODS AND PROCEDURES: We studied relationships among plasma adiponectin, insulin sensitivity (by hyperinsulinemic-euglycemic clamp), total adiposity (by DXA), visceral adiposity (VAT; by magnetic resonance imaging), and indices of lipid available to muscle, including circulating and intramyocellular lipid (IMCL; by 1H-magnetic resonance spectroscopy). Our cohort included normal weight to obese men (n = 36). RESULTS: Plasma adiponectin was directly associated with insulin sensitivity and high-density lipoprotein-cholesterol and inversely with plasma triglycerides but not IMCL. These findings are consistent with adiponectin promoting lipid uptake and subsequent oxidation in muscle and inhibiting TG synthesis in the liver. In multiple regression models that also included visceral and total fat, free fatty acids, TGs, and IMCL, either alone or in combination, adiponectin independently predicted insulin sensitivity, consistent with some of its insulin-sensitizing effects being mediated through mechanisms other than modulation of lipid metabolism. Because VAT directly correlated with total fat and all three indices of local lipid availability, free fatty acids, and IMCL, an efficient regression model of insulin sensitivity (R2 = 0.69, p < 0.0001) contained only VAT (part R2 = 0.12, p < 0.002) and adiponectin (part R2 = 0.41, p < 0.0001) as independent variables. DISCUSSION: Given the broad range of total adiposity and body fat distribution in our cohort, we suggest that insulin sensitivity is robustly associated with adiponectin and VAT.

Body fatness, insulin sensitivity and muscle oxygen supply in adolescents.

Muscle blood flow can be reduced in insulin-resistant states. The present study examined the importance of body fatness and insulin sensitivity as variables that may be associated with muscle oxygen supply. We studied 38 adolescents (22 males, 16 females; age 15.3-18.6 years; body mass index 17.7-34.7 kg/m(2)) and used near-IR spectroscopy to measure the muscle re-oxygenation rate after ischaemic finger flexion exercise. Total body fat content was estimated by bioelectrical impedance analysis, and insulin sensitivity was assessed by homoeostasis model assessment. Regional lipid compartments were also assessed for potential associations with muscle oxygen supply. Abdominal adiposity (visceral and subcutaneous) was assessed by magnetic resonance imaging, and soleus intramyocellular lipid levels were determined by magnetic resonance spectroscopy. Total body fat content ( r =0.67, P <0.001), abdominal subcutaneous fat area ( r =0.78, P <0.001), abdominal visceral fat area ( r =0.54, P <0.001) and intramyocellular lipid levels ( r =0.68, P <0.001) were significantly related to forearm re-oxygenation half-time. After adjusting for insulin sensitivity, both total body fat content ( r =0.395, P =0.02) and abdominal subcutaneous fat area ( r =0.543, P =0.001) remained positively associated with relatively reduced muscle oxygen supply in adolescent subjects. After adjusting for body fat content, abdominal subcutaneous fat area ( r =0. 511, P =0.002) was significantly associated with muscle oxygen supply. Thus muscle oxygen supply is associated with body fat content, and certain fat compartments may be more influential than others.

Insulin action, regional fat, and myocyte lipid: altered relationships with increased adiposity.

OBJECTIVE: Abdominal fat and myocyte triglyceride levels relate negatively to insulin sensitivity, but their interrelationships are inadequately characterized in the overweight. Using recent methods for measuring intramyocyte triglyceride, these relationships were studied in men with a broad range of adiposity. RESEARCH METHODS AND PROCEDURES: Myocyte triglyceride content ((1)H-magnetic resonance spectroscopy of soleus and tibialis anterior muscles and biochemical assessment of vastus lateralis biopsies), regional fat distribution (DXA and abdominal magnetic resonance imaging), serum lipids, insulin action (euglycemic hyperinsulinemic clamp), and substrate oxidation rates (indirect calorimetry) were measured in 39 nondiabetic men (35.1 +/- 7.8 years) with a broad range of adiposity (BMI 28.6 +/- 4.1 kg/m(2), range 20.1 to 37.6 kg/m(2)). RESULTS: Relationships between insulin-stimulated glucose disposal and regional body fat depots appeared more appropriately described by nonlinear than linear models. When the group was subdivided using median total body fat as the cut-point, insulin-stimulated glucose disposal correlated negatively to all regional body fat measures (all p < or = 0.004), serum triglycerides and free fatty acids (p < 0.02), and both soleus intramyocellular lipid (p = 0.003) and vastus lateralis triglyceride (p = 0.04) in the normal/less overweight group. In contrast, only visceral abdominal fat showed significant negative correlation with insulin-stimulated glucose disposal in more overweight men (r = -0.576, p = 0.01), some of whom surprisingly had lower than expected myocyte lipid levels. These findings persisted when the group was subdivided using different cut-points or measures of adiposity. DISCUSSION: Interrelationships among body fat depots, myocyte triglyceride, serum lipids, and insulin action are generally absent with increased adiposity. However, visceral abdominal fat, which corresponds less closely to total adiposity, remains an important predictor of insulin resistance in men with both normal and increased adiposity.