Nonoxidative Glucose Disposal Research Articles

Soluble urokinase plasminogen activator receptor is a marker of dysmetabolism in HIV‐infected patients receiving highly active antiretroviral therapy

Circulating soluble urokinase plasminogen activator receptor (suPAR) reflects the immune and pro-inflammatory status of the HIV-infected patient. Highly active antiretroviral therapy (HAART) suppresses suPAR. Independent of the immune response to HAART, suPAR remains elevated in some HIV-infected patients, reflecting possibly a low-grade pro-inflammatory state. Low-grade inflammation has been implicated in insulin resistance and other features of dysmetabolism. Accordingly it is hypothesized that circulating suPAR is associated with the metabolic status of HIV-infected patients on HAART. Fasting plasma suPAR was determined in 36 normoglycaemic HIV-infected patients on HAART (n = 18 lipodystrophic, and n = 18 non-lipodystrophic) who had estimated insulin sensitivity (Rd) and non-oxidative glucose disposal (NOGM) by euglycaemic hyperinsulinaemic clamps, indirect calorimetry, and glucose tracer infusion. Five patients had circadian suPAR concentrations measured (24 hr, 20 min-intervals). suPAR and non-HDL-cholesterol were higher and Rd, NOGM, and limb fat were lower in lipodystrophic patients than in non-lipodystrophic patients (P < 0.05). suPAR correlated positively with non-HDL-cholesterol and inversely with Rd, NOGM and limb fat (P < 0.005, n = 36). suPAR also correlated positively with leukocyte count and TNF-alpha (P < 0.01, n = 36) but not with IL-6. In multiple regression analyses suPAR was a stronger predictor of dysmetabolism than TNF-alpha and IL-6. Circadian suPAR did not systematically fluctuate. In conclusion, suPAR may reflect the metabolic status of the HIV-infected patient on HAART, thus linking low-grade inflammation, immune constitution, lipid and glucose metabolism, and fat redistribution. Circadian suPAR concentration appeared stable, suggesting that sampling schedule does not affect measurement. Further studies addressing whether suPAR predicts lipodystrophy and dysmetabolism in HIV-infected patients are warranted.

Impaired Insulin-Stimulated Phosphorylation of Akt and AS160 in Skeletal Muscle of Women With Polycystic Ovary Syndrome Is Reversed by Pioglitazone Treatment

Insulin resistance in skeletal muscle is a major risk factor for type 2 diabetes in women with polycystic ovary syndrome (PCOS). However, the molecular mechanisms underlying skeletal muscle insulin resistance and the insulin-sensitizing effect of thiazolidinediones in PCOS in vivo are less well characterized. We determined molecular mediators of insulin signaling to glucose transport in skeletal muscle biopsies of 24 PCOS patients and 14 matched control subjects metabolically characterized by euglycemic-hyperinsulinemic clamps and indirect calorimetry, and we examined the effect of 16 weeks of treatment with pioglitazone in PCOS patients. Impaired insulin-mediated total (R(d)) oxidative and nonoxidative glucose disposal (NOGD) was paralleled by reduced insulin-stimulated Akt phosphorylation at Ser473 and Thr308 and AS160 phosphorylation in muscle of PCOS patients. Akt phosphorylation at Ser473 and Thr308 correlated positively with R(d) and NOGD in the insulin-stimulated state. Serum free testosterone was inversely related to insulin-stimulated R(d) and NOGD in PCOS. Importantly, the pioglitazone-mediated improvement in insulin-stimulated glucose metabolism, which did not fully reach normal levels, was accompanied by normalization of insulin-mediated Akt phosphorylation at Ser473 and Thr308 and AS160 phosphorylation. AMPK activity and phosphorylation were similar in the two groups and did not respond to pioglitazone in PCOS patients. Impaired insulin signaling through Akt and AS160 in part explains insulin resistance at the molecular level in skeletal muscle in PCOS, and the ability of pioglitazone to enhance insulin sensitivity involves improved signaling through Akt and AS160. Moreover, our data provide correlative evidence that hyperandrogenism in PCOS may contribute to insulin resistance.

Reduced Expression of Nuclear-Encoded Genes Involved in Mitochondrial Oxidative Metabolism in Skeletal Muscle of Insulin-Resistant Women With Polycystic Ovary Syndrome

Insulin resistance in skeletal muscle is a major risk factor for the development of type 2 diabetes in women with polycystic ovary syndrome (PCOS). In patients with type 2 diabetes, insulin resistance in skeletal muscle is associated with abnormalities in insulin signaling, fatty acid metabolism, and mitochondrial oxidative phosphorylation (OXPHOS). In PCOS patients, the molecular mechanisms of insulin resistance are, however, less well characterized. To identify biological pathways of importance for the pathogenesis of insulin resistance in PCOS, we compared gene expression in skeletal muscle of metabolically characterized PCOS patients (n = 16) and healthy control subjects (n = 13) using two different approaches for global pathway analysis: gene set enrichment analysis (GSEA 1.0) and gene map annotator and pathway profiler (GenMAPP 2.0). We demonstrate that impaired insulin-stimulated total, oxidative and nonoxidative glucose disposal in PCOS patients are associated with a consistent downregulation of OXPHOS gene expression using GSEA and GenMAPP analysis. Quantitative real-time PCR analysis validated these findings and showed that reduced levels of peroxisome proliferator-activated receptor gamma coactivator alpha (PGC-1alpha) could play a role in the downregulation of OXPHOS genes in PCOS. In these women with PCOS, the decrease in OXPHOS gene expression in skeletal muscle cannot be ascribed to obesity and diabetes. This supports the hypothesis of an early association between insulin resistance and impaired mitochondrial oxidative metabolism, which is, in part, mediated by reduced PGC-1alpha levels. These abnormalities may contribute to the increased risk of type 2 diabetes observed in women with PCOS.

Ovarian suppression with a gonadotropin-releasing hormone agonist does not alter insulin-stimulated glucose disposal

Aging is associated with reduced tissue sensitivity to insulin. In women, these age-related changes may be accelerated by menopause. The effect of ovarian hormone deficiency on tissue insulin sensitivity in humans, however, has not been defined clearly. Thus, the goal of this study was to evaluate the effect of suppression of endogenous ovarian hormone production on insulin-stimulated glucose disposal. Randomized, single-blind, placebo-controlled trial. General clinical research center. Thirteen healthy, nonobese premenopausal women. Insulin-stimulated glucose disposal was determined by hyperinsulinemic (40 mU/m(2)/min) clamp during the early to midfollicular and midluteal phase of the menstrual cycle. Volunteers then received 2 months of treatment with the GnRH agonist (GnRHa) leuprolide acetate (n = 6) or placebo (n = 7) and were retested. Total, oxidative, and nonoxidative insulin-stimulated glucose disposal. Because no effect of cycle phase was found on total, oxidative, or nonoxidative glucose disposal, pretreatment follicular and luteal phase values were averaged. Treatment with GnRHa had no effect on total glucose disposal (GnRHa: 10.6 +/- 0.9 to 10.8 +/- 0.9 vs. placebo: 10.2 +/- 0.7 to 10.4 +/- 1.0 mg/kg fat-free mass/min, P = .99). Similarly, there was no effect of GnRHa administration on oxidative (GnRHa: 2.77 +/- 0.58 to 3.89 +/- 0.58 vs. placebo: 2.74 +/- 0.42 to 3.33 +/- 0.62 mg/kg fat-free mass/min, P = .52; n = 6 and 6, respectively) or nonoxidative (GnRHa: 7.82 +/- 0.68 to 6.91 +/- 0.66 vs. placebo: 7.94 +/- 0.72 to 7.79 +/- 0.99 mg/kg fat-free mass/min, P = .59; n = 6 and 6, respectively) components of glucose disposal. Our results suggest that endogenous ovarian hormones do not regulate tissue responsiveness to insulin or intracellular pathways of glucose disposal.

Non‐oxidative glucose disposal is reduced in type 2 diabetes, but can be restored by aerobic exercise

Whole-body glucose utilization consists of mitochondrial glucose oxidation and non-oxidative glycogen synthesis. We examined whether reduction of both non-oxidative glucose disposal and glucose oxidation contributes to insulin resistance in type 2 diabetes. We also examined the effects of exercise on these two components. Whole-body glucose disposal rate (GDR, mg/kg/min) was evaluated in 37 type 2 diabetic (T2DM) and 17 non-diabetic (non-DM) subjects as the mean of glucose infusion rate during steady state in the euglycaemic-hyperinsulinaemic clamp study. Glucose oxidation rates were assessed by indirect calorimetry, and non-oxidative GDR was calculated by subtracting glucose oxidation rate from GDR. Intramyocellular lipid (IMCL) content of the soleus muscle was measured using (1)H-magnetic resonance spectroscopy. In 10 T2DM subjects, the changes in oxidative and non-oxidative glucose disposal during clamp were examined after 3-month exercise intervention. GDR (2.93 +/- 1.55 vs. 4.55 +/- 1.83, p = 0.001) and non-oxidative GDR (1.45 +/- 1.52 vs. 3.01 +/- 1.87, p = 0.002) were significantly lower in T2DM than in non-DM subjects. Glucose oxidation rate was comparable in the two groups, and inversely correlated with IMCL (n = 15, r =-0.565, p = 0.028). GDR (2.28 +/- 1.67 to 4.63 +/- 2.42, p = 0.021) and non-oxidative GDR (0.72 +/- 1.27 to 2.26 +/- 1.91, p = 0.047) were increased after exercise intervention, although the change in glucose oxidation rate was not significant. In summary, reduction of non-oxidative glucose disposal may contribute to decreased whole-body glucose utilization. In addition, exercise improves insulin resistance mainly by increasing non-oxidative glucose disposal in type 2 diabetes.

Dose-Response Effects of Free Fatty Acids on Glucose and Lipid Metabolism during Somatostatin Blockade of Growth Hormone and Insulin in Humans

GH and other stress hormones stimulate lipolysis, which may result in free fatty acid (FFA)-mediated insulin resistance. However, there are also indications that FFAs in the very low physiological range have the same effect. The objective of the study was to address systematically the dose-response relations between FFAs and insulin sensitivity. We therefore examined eight healthy men for 8 h (6 h basal and 2 h glucose clamp) on four occasions. Intralipid was infused at varying rates (0, 3, 6, 12 microl.kg(-1).min(-1)); lipolysis was blocked by acipimox; and endogenous GH, insulin, and glucagon secretion was blocked by somatostatin and subsequently replaced at fixed rates. This resulted in four different FFA levels between 50 and 2000 micromol/liter, with comparable levels of insulin and counterregulatory hormones. Both in the basal state and during insulin stimulation, we saw progressively decreased glucose disposal, nonoxidative glucose disposal, and forearm muscle glucose uptake at FFA levels above 500 micromol/liter. Apart from forearm glucose uptake, the very same parameters were decreased at low FFA levels (approximately 50 micromol/liter). FFA rate of disposal was linearly related to the level of FFAs, whereas lipid oxidation reached a maximum at FFA levels approximately 1000 micromol/liter. In the presence of comparable levels of all major metabolic hormones, insulin sensitivity peaks at physiological levels of FFAs with a gradual decrease at elevated as well as suppressed FFA concentrations. These data constitute comprehensive dose-response curves for FFAs in the full physiological range from close to zero to above 2000 micromol/liter.

High-Fat/Low-Carbohydrate Diet Reduces Insulin-Stimulated Carbohydrate Oxidation but Stimulates Nonoxidative Glucose Disposal in Humans: An Important Role for Skeletal Muscle Pyruvate Dehydrogenase Kinase 4

The aim of this report was to study the effect of high-fat (HF)/low-carbohydrate (CHO) diet on regulation of substrate metabolism in humans. Ten healthy men consumed either a HF (75% energy as fat) or control (35%) diet for 6 d in random order. On d 7, blood glucose disappearance rate (Rd) was determined before and during a hyperinsulinemic euglycemic clamp. Substrate oxidation was determined by indirect calorimetry. Muscle biopsies were obtained prediet, postdiet, and postclamps. Rd was similar under basal conditions but slightly elevated (approximately 10%, P < 0.05) during the last 30 min of the clamp after the HF diet. HF diet reduced CHO oxidation under basal (by approximately 40%, P < 0.05) and clamp conditions (by approximately 20%, P < 0.05), increased insulin-mediated whole-body nonoxidative glucose disposal (by 30%, P < 0.05) and muscle glycogen storage (by approximately 25%, P < 0.05). Muscle pyruvate dehydrogenase complex activity was blunted under basal and clamp conditions after HF compared with control (P < 0.05) and was accompanied by an approximately 2-fold increase (P < 0.05) in pyruvate dehydrogenase kinase 4 (PDK4) mRNA and protein expression. Short-term HF/low-CHO dietary intake did not induce whole-body insulin resistance, but caused a shift in im glucose metabolism from oxidation to glycogen storage. Insulin-stimulated CHO oxidation and muscle pyruvate dehydrogenase complex activity were blunted after the HF diet. Up-regulation of muscle PDK4 expression was an early molecular adaptation to these changes, and we showed for the first time in healthy humans, unlike insulin-resistant individuals, that insulin can suppress PDK4 but not PDK2 gene expression in skeletal muscle.

Plasma Adiponectin is not Altered by Moderate or Heavy Aerobic Exercise Training in Elderly, Overweight Individuals

PURPOSE: To examine the influence of moderate-intensity (50% of VO2 peak) exercise training (MI) versus high-intensity (75% of VO2 peak) exercise training (HI) on plasma adiponectin in elderly, overweight individuals. METHODS: Following complete medical and physical exams, 18 overweight (BMI=29±1 kg/m2) elderly (74±1 y) subjects were randomized to 1) HI, 2) MI, or a non-exercising control group (CON). Subjects enrolled in HI or MI completed a 12 week exercise training protocol designed to expend 1000 kcal/week. Body composition testing was completed prior to and immediately following the exercise training intervention using dual energy x-ray absorptiometry. Plasma adiponectin was measured by ELISA, and the enzyme activity was determined spectrophotometrically by increased absorbance at 450 nm – 590nm. RESULTS: As expected, there was no change in VO2peak in CON, while VO2peak was significantly improved in HI and MI. There was no significant change in body weight or BMI, and % fat did not change from pre- to post-intervention in MI, HI or CON. In terms of plasma adiponectin, there was no change in MI (A of 1.1±2.1 ng/ml), HI (A of 0.9±2.1 ng/ml) or CON (A of 1.2±1.3 ng/ml). CONCLUSION: We have previously shown that exercise training-induced improvements in glucose metabolism that occur without weight loss are completely reliant on changes in non-oxidative glucose disposal. In addition, we have now demonstrated that aerobic exercise training intensity independent of weight loss does not influence plasma adiponectin levels, and therefore does not play a plausible role in the improvement of glucose metabolism under such conditions. Supported by NIH grants KO1 DK 64716–01 (RHC), F32AG21374 (NPH), and RO1 AG 19346–01 (WJE) and AHA grant SDA 0335172N (rHC).

Exercise-Induced Changes in Insulin Action and Glycogen Metabolism in Elderly Adults

Although data suggest that physical activity is associated with decreased insulin resistance, recommendations for exercise training are not specific for age or level of obesity. Therefore, we examined the influence of moderate-intensity (50% of VO2max) exercise training (MI) versus high-intensity (75% of VO2max) exercise training (HI) on insulin-stimulated glucose disposal (ISGD) in elderly individuals. Following medical examinations, 21 overweight (body mass index = 29 +/- 1 kg x m(-2)) elderly (74 +/- 1 yr) subjects were randomized to 1) HI, 2) MI, or a 3) nonexercising control group. Subjects enrolled in HI or MI completed a 12-wk exercise training regimen designed to expend 1000 kcal x wk. ISGD was assessed using a hyperinsulinemic, euglycemic clamp pre- and postintervention. ISGD was corrected for hepatic glucose production (glucose Ra) using a constant rate infusion of [6,6-H2]glucose and determined during the last 30 min of the clamp by subtracting glucose Ra from the exogenous glucose infusion rate. Nonoxidative glucose disposal was calculated using indirect calorimetry. Body composition testing was completed using dual energy x-ray absorptiometry. ISGD increased by approximately 20% with HI (Delta of 1.4 +/- 0.5 mg x kg(-1) FFM.min(-1)). However, ISGD did not change (Delta of -0.4 +/- 0.1 mg x kg(-1) FFM.min(-1)) with MI and was not different (Delta of -0.2 +/- 0.1 mg x kg(-1) FFM.min(-1)) in the control group. Nonoxidative glucose disposal increased with HI (Delta of 1.4 +/- 0.5 mg x kg(-1) FFM.min(-1)), but there was no change in nonoxidative glucose disposal with MI or in the control group. No change in body weight or percentage of body fat was observed in any group. In weight-stable subjects, MI resulted in no change in ISGD, and the improvement in ISGD with HI was completely reliant on improvements in nonoxidative glucose disposal.

Effects of hyperglycemia on glucose metabolism before and after oral glucose ingestion in normal men

The plasma glucose excursion may influence the metabolic responses after oral glucose ingestion. Although previous studies addressed the effects of hyperglycemia in conditions of hyperinsulinemia, it has not been evaluated whether the route of glucose administration (oral vs. intravenous) plays a role. Our aim was to determine the effects of moderately controlled hyperglycemia on glucose metabolism before and after oral glucose ingestion. Eight normal men underwent two oral glucose clamps at 6 and 10 mmol/l plasma glucose. Glucose turnover and cycling rates were measured by infusion of [2H7]glucose. The oral glucose load was labeled by D-[6,6-2H2]glucose to monitor exogenous glucose appearance, and respiratory exchanges were measured by indirect calorimetry. Sixty percent of the oral glucose load appeared in the systemic circulation during both the 6 and 10 mmol/l plasma glucose tests, although less endogenous glucose appeared during the 10 mmol/l tests before glucose ingestion (P < 0.05). This inhibitory effect of hyperglycemia was not detectable after oral glucose ingestion, although glucose utilization was increased (+28%, P < 0.05) due to increased nonoxidative glucose disposal [10 vs. 6 mmol/l: +20%, not significant (NS) before oral glucose ingestion; +40%, P < 0.05 after oral glucose ingestion]. Glucose cycling rates were increased by hyperglycemia (+13% before oral glucose ingestion, P < 0.001; +31% after oral glucose ingestion, P < 0.05) and oral glucose ingestion during both the 6 (+10%, P < 0.05) and 10 mmol/l (+26%, P < 0.005) tests. A moderate hyperglycemia inhibits endogenous glucose production and contributes to glucose tolerance by enhancing nonoxidative glucose disposal. Hyperglycemia and oral glucose ingestion both stimulate glucose cycling.

Thiazolidinediones: The case for early use

Editor’s note: This commentary was originally solicited as part of a Point-Counterpoint feature, but the author of the Counterpoint failed to provide the promised manuscript. Thiazolidinediones (TZDs), or “glitazones,” were first introduced for the treatment of type 2 diabetes in 1996, when troglitazone (Rezulin; Parke-Davis/Warner-Lambert) was approved by the Food and Drug Administration. Since the introduction of this unique class of compounds, many clinicians have embraced their use, whereas others have debated the role of insulin-sensitizing therapy for the management of type 2 diabetes. While troglitazone was withdrawn from the market in 2000 due to idiosyncratic hepatoxicity, two other glitazones, pioglitazone (Actos; Takeda Chemical Industries) and rosiglitazone (Avandia; GlaxoSmithKline), continue to be widely used by clinicians. Before the introduction of glitazones, conventional management of type 2 diabetes involved stepwise addition of medical nutrition therapy, sulfonylureas, and metformin. Despite broader use of early drug therapy, many patients do not achieve adequate blood glucose control (1). Even in those who do achieve treatment targets, a gradual deterioration in blood glucose control is often seen (2). These observations have prompted clinicians to use newer therapies, such as the glitazones, and have increased the use of early combination therapy to achieve glycemic targets Glitazones uniquely target insulin resistance—a core physiologic defect in those with type 2 diabetes—and by so doing significantly improve glucose control. Glitazones improve insulin action in muscle, adipose, and hepatic tissue by acting as agonists of peroxisome proliferator–activated receptor-γ (PPAR-γ) nuclear receptors. Activation of PPAR-γ results in a myriad of both metabolic and vascular effects by upregulating and downregulating expression of numerous genes, including genes known to regulate lipid and glucose metabolism, vascular function, thrombotic function, and the inflammatory response. Glitazones increase nonoxidative glucose disposal, increase triglyceride synthesis, and improve free fatty acid (FFA) metabolism (3). Glitazones also lower blood pressure, …

Thiazolidinediones

Editor’s note: This commentary was originally solicited as part of a Point-Counterpoint feature, but the author of the Counterpoint failed to provide the promised manuscript. Thiazolidinediones (TZDs), or “glitazones,” were first introduced for the treatment of type 2 diabetes in 1996, when troglitazone (Rezulin; Parke-Davis/Warner-Lambert) was approved by the Food and Drug Administration. Since the introduction of this unique class of compounds, many clinicians have embraced their use, whereas others have debated the role of insulin-sensitizing therapy for the management of type 2 diabetes. While troglitazone was withdrawn from the market in 2000 due to idiosyncratic hepatoxicity, two other glitazones, pioglitazone (Actos; Takeda Chemical Industries) and rosiglitazone (Avandia; GlaxoSmithKline), continue to be widely used by clinicians. Before the introduction of glitazones, conventional management of type 2 diabetes involved stepwise addition of medical nutrition therapy, sulfonylureas, and metformin. Despite broader use of early drug therapy, many patients do not achieve adequate blood glucose control (1). Even in those who do achieve treatment targets, a gradual deterioration in blood glucose control is often seen (2). These observations have prompted clinicians to use newer therapies, such as the glitazones, and have increased the use of early combination therapy to achieve glycemic targets Glitazones uniquely target insulin resistance—a core physiologic defect in those with type 2 diabetes—and by so doing significantly improve glucose control. Glitazones improve insulin action in muscle, adipose, and hepatic tissue by acting as agonists of peroxisome proliferator–activated receptor-γ (PPAR-γ) nuclear receptors. Activation of PPAR-γ results in a myriad of both metabolic and vascular effects by upregulating and downregulating expression of numerous genes, including genes known to regulate lipid and glucose metabolism, vascular function, thrombotic function, and the inflammatory response. Glitazones increase nonoxidative glucose disposal, increase triglyceride synthesis, and improve free fatty acid (FFA) metabolism (3). Glitazones also lower blood pressure, …

Plasma Adiponectin Level Is Associated with Insulin-Stimulated Nonoxidative Glucose Disposal

Impaired nonoxidative glucose disposal and decrease in mitochondrial glucose oxidation both contribute to insulin resistance in diabetic subjects. In the present study, we investigated whether plasma adiponectin is associated with glucose oxidation and nonoxidative glucose disposal in subjects with and without type 2 diabetes. Euglycemic-hyperinsulinemic clamp was performed in 42 type 2 diabetic (T2DM) and 13 nondiabetic (non-DM) subjects. The whole-body glucose disposal rate (GDR) was evaluated as the mean of the glucose infusion rate during steady state of the clamp. Glucose and fat oxidation rates were assessed by indirect calorimetry, and nonoxidative glucose disposal rate was calculated by subtracting glucose oxidation rate from GDR. Plasma adiponectin level was significantly lower in T2DM than non-DM (2.87 +/- 1.40 vs. 3.96 +/- 2.39 microg/ml, P = 0.045). GDR (3.39 +/- 1.53 vs. 4.83 +/- 1.70 mg/kg x min, P = 0.006) and nonoxidative glucose disposal rate (1.89 +/- 1.39 vs. 3.11 +/- 1.76 mg/kg x min, P = 0.012) were significantly lower in T2DM, compared with non-DM, although no difference was found in glucose oxidation rate between the two groups. In all subjects, plasma adiponectin level was positively correlated with GDR (r = 0.351, P = 0.009) and nonoxidative glucose disposal rate (r = 0.324, P = 0.016) but not glucose oxidation rate. There was no significant correlation between plasma adiponectin level and fat oxidation, either before or during the clamp. In conclusion, plasma adiponectin level is associated with nonoxidative glucose disposal, which is reduced in type 2 diabetic subjects. Our results suggest that adiponectin controls insulin sensitivity by modulating the glycogen synthetic process in human skeletal muscle.

High amount of visceral fat mass is associated with multiple metabolic changes in offspring of type 2 diabetic patients

To investigate the relative contribution of total body fat mass (TFM) and intra-abdominal fat mass (IAFM) to metabolic consequences of obesity in offspring of type 2 diabetic parents. Cross-sectional study of 129 nondiabetic offspring of diabetic parents (59 men, 70 women, age 35.7 +/- 6.3 y, body mass index 26.2 +/- 4.6 kg/m2). Study subjects were grouped according to TFM (assessed with bioelectrical impedance) and IAFM (assessed with CT). Insulin sensitivity was assessed with the euglycemic hyperinsulinemic clamp, insulin secretion with the intravenous glucose tolerance test and energy expenditure with indirect calorimetry. Furthermore, C-reactive protein (CRP) and adiponectin levels were measured. Insulin resistance, low rates of oxidative and nonoxidative glucose disposal, high rates of lipid oxidation and reduced energy expenditure during hyperinsulinemia were associated with high IAFM, independently of TFM. Adiponectin level was reduced and CRP level increased in subjects with high IAFM. The metabolic changes relating to obesity are largely attributable to high IAFM, and are present even in normal weight subjects with high IAFM.

Oxidative and nonoxidative glucose disposal in elderly vs younger men with similar and smaller body mass indices and waist circumferences

Defects in oxidative and nonoxidative glucose metabolism may be involved in the insulin resistance of aging, possibly linked to a central redistribution of body fat. By hyperinsulinemic-euglycemic clamps with whole-body indirect calorimetry, we assessed the contributions of oxidative and nonoxidative glucose disposal to insulin action in 12 elderly persons and 2 groups of younger subjects (14 in each) who had participated in a large population study. Subjects from Young-1 were individually matched to the elderly persons by body mass index and had similar waist circumferences, whereas subjects from Young-2 had a body mass index typical of their age group in the population study and smaller waist measurements. In the combined sample, we also considered possible determinants, related to age and central fat, of flux through these metabolic pathways. The elderly persons had lower nonoxidative glucose disposal compared with the men in Young-2 ( P = .0450 by analysis of variance), whereas glucose oxidation did not differ between the groups. Glucose oxidation correlated negatively with waist circumferences, triglycerides, and alanine aminotransferase and positively with total testosterone and sex hormone–binding globulin. Nonoxidative glucose metabolism correlated inversely with waist circumferences, triglycerides, and free fatty acids and positively with maximum O 2 consumption and total testosterone. In the best regression models, alanine aminotransferase and triglycerides were negatively associated with glucose oxidation (model R 2 = 39%), whereas lower baseline free fatty acids and higher maximum O 2 consumption and sex hormone–binding globulin predicted enhanced nonoxidative glucose metabolism (model R 2 = 47%). These results substantiate that measures to avert abdominal adiposity may prevent insulin resistance and its related metabolic derangements in elderly persons.

Association of Adiponectin Level and Variants in the Adiponectin Gene with Glucose Metabolism, Energy Expenditure, and Cytokines in Offspring of Type 2 Diabetic Patients

Adiponectin is an adipose-specific secretory protein abundantly present in the circulation. The role of adiponectin in the control of energy expenditure and substrate utilization has not yet been established. We performed detailed metabolic studies in a large cohort (n = 158) of offspring of patients with type 2 diabetes (T2DM) to determine the association of adiponectin level with glucose and lipid oxidation, energy expenditure, insulin sensitivity, and visceral obesity by applying the euglycemic clamp technique and indirect calorimetry. The adiponectin level was lower in offspring of T2DM patients than in control subjects. When the data were analyzed by adiponectin tertiles, an elevated adiponectin level was associated with high total, oxidative, and nonoxidative glucose disposal and high energy expenditure during hyperinsulinemia; low levels of free fatty acids and low rates of lipid oxidation during hyperinsulinemia; as well as low levels of inflammatory cytokines; and a low amount of intraabdominal fat evaluated by computed tomography. No association of single nucleotide polymorphism 45 or single nucleotide polymorphism 276 with adiponectin level was found. We conclude that adiponectin has multiple effects on glucose, lipid and free fatty acid metabolism, and cytokines in offspring of T2DM subjects.

Alterations in carbohydrate metabolism in response to short-term dietary carbohydrate restriction

Dietary carbohydrate restriction (CR) presents a challenge to glucose homeostasis. Despite the popularity of CR diets, little is known regarding the metabolic effects of CR. The purpose of this study was to examine changes in whole body carbohydrate oxidation, glucose availability, endogenous glucose production, and peripheral glucose uptake after dietary CR, without the confounding influence of a negative energy balance. Postabsorptive rates of glucose appearance in plasma (R(a); i.e., endogenous glucose production) and disappearance from plasma (R(d); i.e., glucose uptake) were measured using isotope dilution methods after a conventional diet [60% carbohydrate (CHO), 30% fat, and 10% protein; kcals = 1.3 x resting energy expenditure (REE)] and after 2 days and 7 days of CR (5% CHO, 60% fat, and 35% protein; kcals = 1.3 x REE) in eight subjects (means +/- SE; 29 +/- 4 yr; BMI 24 +/- 1 kg/m(2)) during a 9-day hospital visit. Postabsorptive plasma glucose concentration was reduced (P = 0.01) after 2 days but returned to prediet levels the next day and remained at euglycemic levels throughout the diet (5.1 +/- 0.2, 4.3 +/- 0.3, and 4.8 +/- 0.4 mmol/l for prediet, 2 days and 7 days, respectively). Glucose R(a) and glucose R(d) were reduced to below prediet levels (9.8 +/- 0.6 micromol x kg(-1) x min(-1)) after 2 days of CR (7.9 +/- 0.3 micromol x kg(-1) x min(-1)) and remained suppressed after 7 days (8.3 +/- 0.4 micromol x kg(-1) x min(-1); both P < 0.001). A greater suppression in carbohydrate oxidation, compared with the reduction in glucose R(d), led to an increased (all P </= 0.05) rate of nonoxidative glucose disposal at 7 days (5.2 +/- 0.5 micromol x kg(-1) x min(-1)), compared with 2 days (2.7 +/- 0.5 micromol x kg(-1) x min(-1)) and prediet (1.6 +/- 0.8 micromol x kg(-1) x min(-1)). In response to eucaloric CR, a marked increase in nonoxidative glucose disposal may help maintain systemic glucose availability.

Multiple Abnormalities in Glucose and Energy Metabolism and Coordinated Changes in Levels of Adiponectin, Cytokines, and Adhesion Molecules in Subjects With Metabolic Syndrome

Detailed metabolic defects in glucose and energy metabolism and abnormalities in a variety of cardiovascular risk factors are largely unknown in subjects with the metabolic syndrome. We characterized the metabolic syndrome in 119 nondiabetic offspring of diabetic probands. Cardiovascular risk factors, including cytokines and adhesion molecules, were measured. Insulin sensitivity was assessed by the euglycemic hyperinsulinemic clamp and indirect calorimetry; intra-abdominal fat and subcutaneous fat were assessed by CT; and maximal oxygen consumption was measured with a bicycle ergometer test. By applying factor analysis, we identified a single factor, the metabolic syndrome factor, from the following variables: 2-hour glucose, fasting insulin, body mass index, waist, HDL cholesterol, triglycerides, and mean blood pressure. Subjects with the highest factor score were defined as having the metabolic syndrome. During hyperinsulinemia, the highest factor score was associated with decreased rates of glucose oxidation and nonoxidative glucose disposal, high rates of lipid oxidation, low energy expenditure, and impaired suppression of free fatty acids during hyperinsulinemia. Furthermore, the metabolic syndrome was associated with a high amount of visceral fat, hypoadiponectinemia, a low maximum oxygen uptake, and high levels of C-reactive protein, proinflammatory cytokines, and adhesion molecules. The metabolic syndrome is characterized by an excess of intra-abdominal fat, hypoadiponectinemia, insulin resistance in skeletal muscle and adipose tissue, multiple defects in glucose and energy metabolism, and elevated levels of cytokines and adhesion molecules.

Carnitine in Type 2 Diabetes

Carnitine, the L-beta-hydroxy-gamma-N-trimethylaminobutyric acid, is synthesized primarily in the liver and kidneys from lysine and methionine. Carnitine covers an important role in lipid metabolism, acting as an obligatory cofactor for beta-oxidation of fatty acids by facilitating the transport of long-chain fatty acids across the mitochondrial membrane as acylcarnitine esters. Furthermore, since carnitine behaves as a shuttle for acetyl groups from inside to outside the mitochondrial membrane, it covers also a key role in glucose metabolism and assists in fuel-sensing. A reduction of the fatty acid transport inside the mitochondria results in the cytosolic accumulation of triglycerides, which is implicated in the pathogenesis of insulin resistance. Acute hypercarnitinemia stimulates nonoxidative glucose disposal during euglycemic hyperinsulinemic clamp in healthy volunteers. Similar results were obtained in type 2 diabetic patients. The above findings were confirmed in healthy volunteers using the minimal modeling of glucose kinetics. The total end-clamp glucose tissue uptake was significantly increased by the administration of doses of acetyl-L-carnitine (ALC) from 3.8 to 5.2 mg/kg/min, without a significant dose-response effect. In conclusion, both L-carnitine and ALC are effective in improving insulin-mediated glucose disposal either in healthy subjects or in type 2 diabetic patients. Two possible mechanisms might be invoked in the metabolic effect of carnitine and its derivative: the first is a regulation of acetyl and acyl cellular trafficking for correctly meeting the energy demand; the second is a control action in the synthesis of key glycolytic and gluconeogenic enzymes.

Sustained reduction in plasma free fatty acid concentration improves insulin action without altering plasma adipocytokine levels in subjects with strong family history of type 2 diabetes.

To investigate the effect of a sustained (7-d) decrease in plasma free fatty acid (FFA) concentration in individuals genetically predisposed to develop type 2 diabetes mellitus (T2DM), we studied the effect of acipimox, a potent inhibitor of lipolysis, on insulin action and adipocytokine concentrations in eight normal glucose-tolerant subjects (aged 40 +/- 4 yr, body mass index 26.5 +/- 0.8 kg/m(2)) with at least two first-degree relatives with T2DM. Subjects received an oral glucose tolerance test (OGTT) and 120 min euglycemic insulin clamp (80 mU/m(2).min) with 3-[(3)H] glucose to quantitate rates of insulin-mediated whole-body glucose disposal (Rd) and endogenous (primarily hepatic) glucose production (EGP) before and after acipimox, 250 mg every 6 h for 7 d. Acipimox significantly reduced fasting plasma FFA (515 +/- 64 to 285 +/- 58 microm, P < 0.05) and mean plasma FFA during the OGTT (263 +/- 32 to 151 +/- 25 microm, P < 0.05); insulin-mediated suppression of plasma FFA concentration during the insulin clamp also was enhanced (162 +/- 18 to 120 +/- 15 microm, P < 0.10). Following acipimox, fasting plasma glucose (5.1 +/- 0.1 vs. 5.2 +/- 0.1 mm) did not change, whereas mean plasma glucose during the OGTT decreased (7.6 +/- 0.5 to 6.9 +/- 0.5 mm, P < 0.01) without change in mean plasma insulin concentration (402 +/- 90 to 444 +/- 102 pmol/liter). After acipimox Rd increased from 5.6 +/- 0.5 to 6.8 +/- 0.5 mg/kg.min (P < 0.01) due to an increase in insulin-stimulated nonoxidative glucose disposal (2.5 +/- 0.4 to 3.5 +/- 0.4 mg/kg.min, P < 0.05). The increment in Rd correlated closely with the decrement in fasting plasma FFA concentration (r = -0.80, P < 0.02). Basal EGP did not change after acipimox (1.9 +/- 0.1 vs. 2.0 +/- 0.1 mg/kg.min), but insulin-mediated suppression of EGP improved (0.22 +/- 0.09 to 0.01 +/- 0.01 mg/kg.min, P < 0.05). EGP during the insulin clamp correlated positively with the fasting plasma FFA concentration (r = 0.49, P = 0.06) and the mean plasma FFA concentration during the insulin clamp (r = 0.52, P < 0.05). Plasma adiponectin (7.1 +/- 1.0 to 7.2 +/- 1.1 microg/ml), resistin (4.0 +/- 0.3 to 3.8 +/- 0.3 ng/ml), IL-6 (1.4 +/- 0.3 to 1.6 +/- 0.4 pg/ml), and TNFalpha (2.3 +/- 0.3 to 2.4 +/- 0.3 pg/ml) did not change after acipimox treatment. We concluded that sustained reduction in plasma FFA concentration in subjects with a strong family history of T2DM increases peripheral (muscle) and hepatic insulin sensitivity without increasing adiponectin levels or altering the secretion of other adipocytokines by the adipocyte. These results suggest that lipotoxicity already is well established in individuals who are genetically predisposed to develop T2DM and that drugs that cause a sustained reduction in the elevated plasma FFA concentration may represent an effective modality for the prevention of T2DM in high-risk, genetically predisposed, normal glucose-tolerant individuals despite the lack of an effect on adipocytokine concentrations.