Body Glucose Disposal Research Articles

A Thr94Ala mutation in human liver fatty acid-binding protein contributes to reduced hepatic glycogenolysis and blunted elevation of plasma glucose levels in lipid-exposed subjects

Liver fatty acid-binding protein (L-FABP) is a highly conserved key factor in lipid metabolism. Amino acid replacements in L-FABP might alter its function and thereby affect glucose metabolism in lipid-exposed subjects, as indicated by studies in L-FABP knockout mice. Amino acid replacements in L-FABP were investigated in a cohort of 1,453 Caucasian subjects. Endogenous glucose production (EGP), gluconeogenesis, and glycogenolysis were measured in healthy carriers of the only common Thr(94)-to-Ala amino acid replacement (Ala/Ala(94)) vs. age-, sex-, and BMI-matched wild-type (Thr/Thr(94)) controls at baseline and after 320-min lipid/heparin-somatostatin-insulin-glucagon clamps (n = 18). Whole body glucose disposal was further investigated (subset; n = 13) using euglycemic-hyperinsulinemic clamps without and with lipid/heparin infusion. In the entire cohort, the only common Ala/Ala(94) mutation was significantly associated with reduced body weight, which is in agreement with a previous report. In lipid-exposed, individually matched subjects there was a genotype vs. lipid-treatment interaction for EGP (P = 0.009) driven mainly by reduced glycogenolysis in Ala/Ala(94) carriers (0.46 +/- 0.05 vs. 0.59 +/- 0.05 mgxkg(-1)xmin(-1), P = 0.013). The lipid-induced elevation of plasma glucose levels was smaller in Ala/Ala(94) carriers compared with wild types (P < 0.0001). Whole body glucose disposal was not different between lipid-exposed L-FABP genotypes. In summary, the Ala/Ala(94)-mutation contributed significantly to reduced glycogenolysis and less severe hyperglycemia in lipid-exposed humans and was further associated with reduced body weight in a large cohort. Data clearly show that investigation of L-FABP phenotypes in the basal overnight-fasted state yielded incomplete information, and a challenge test was essential to detect phenotypical differences in glucose metabolism between L-FABP genotypes.

Abdominal obesity in BTBR male mice is associated with peripheral but not hepatic insulin resistance

Insulin resistance is a common feature of obesity. BTBR mice have more fat mass than most other inbred mouse strains. On a chow diet, BTBR mice have elevated insulin levels relative to the C57BL/6J (B6) strain. Male F1 progeny of a B6 × BTBR cross are insulin resistant. Previously, we reported insulin resistance in isolated muscle and in isolated adipocytes in this strain. Whereas the muscle insulin resistance was observed only in male F1 mice, adipocyte insulin resistance was also present in male BTBR mice. We examined in vivo mechanisms of insulin resistance with the hyperinsulinemic euglycemic clamp technique. At 10 wk of age, BTBR and F1 mice had a &gt;30% reduction in whole body glucose disposal primarily due to insulin resistance in heart, soleus muscle, and adipose tissue. The increased adipose tissue mass and decreased muscle mass in BTBR and F1 mice were negatively and positively correlated with whole body glucose disposal, respectively. Genes involved in focal adhesion, actin cytoskeleton, and inflammation were more highly expressed in BTBR and F1 than in B6 adipose tissue. The BTBR and F1 mice have higher levels of testosterone, which may be related to the pathological changes in adipose tissue that lead to systemic insulin resistance. Despite profound peripheral insulin resistance, BTBR and F1 mice retained hepatic insulin sensitivity. These studies reveal a genetic difference in body composition that correlates with large differences in peripheral insulin sensitivity.

Antisense oligonucleotides against the lipid phosphatase SHIP2 improve muscle insulin sensitivity in a dietary rat model of the metabolic syndrome

The lipid phosphatase SH2 domain-containing lipid phosphatase (SHIP2) has been implicated in the regulation of insulin sensitivity, but its role in the therapy of insulin-resistant states remains to be defined. Here, we examined the effects of an antisense oligonucleotide (AS) therapy directed against SHIP2 on whole body insulin sensitivity and insulin action in liver and muscle tissue in a dietary rodent model of the metabolic syndrome, the high-fat-fed (HF) rat. Whole body insulin sensitivity was examined in vivo by insulin tolerance tests before and after the intraperitoneal application of an AS directed against SHIP2 (HF-SHIP2-AS) or a control AS (HF-Con-AS) in HF rats. Insulin action in liver and muscle was assayed by measuring the activation of protein kinase B (Akt) and insulin receptor substrate (IRS)-1/2 after a portal venous insulin bolus. SHIP2 mRNA and protein content were quantified in these tissues by real-time PCR and immunoblotting, respectively. In HF-SHIP2-AS, whole body glucose disposal after an insulin bolus was markedly elevated compared with HF-Con-AS. In liver, insulin activated Akt similarly in both groups. In muscle, insulin did not clearly activate Akt in HF-Con-AS animals, whereas insulin-induced Akt phosphorylation was sustained in SHIP2-AS-treated rats. IRS-1/2 activation did not differ between the experimental groups. SHIP2 mRNA and protein content were markedly reduced only in muscle. In standard diet-fed controls, SHIP2-AS reduced SHIP2 protein levels in liver and muscle, but it had no significant effect on insulin sensitivity. We conclude that treatment with SHIP2-AS can rapidly improve muscle insulin sensitivity in dietary insulin resistance. The long-term feasibility of such a strategy should be examined further.

Thiazolidinediones improve β-cell function in type 2 diabetic patients

Thiazolidinediones (TZDs) improve glycemic control and insulin sensitivity in patients with type 2 diabetes mellitus (T2DM). There is growing evidence from in vivo and in vitro studies that TZDs improve pancreatic β-cell function. The aim of this study was to determine whether TZD-induced improvement in glycemic control is associated with improved β-cell function. We studied 11 normal glucose-tolerant and 53 T2DM subjects [age 53 ± 2 yr; BMI 29.4 ± 0.8 kg/m2; fasting plasma glucose (FPG) 10.3 ± 0.4 mM; Hb A1c8.2 ± 0.3%]. Diabetic patients were randomized to receive placebo or TZD for 4 mo. Subjects received 1) 2-h OGTT with determination of plasma glucose, insulin, and C-peptide concentrations and 2) two-step euglycemic insulin (40 and 160 mUm−2min−1) clamp with [3-3H]glucose. T2DM patients were then randomized to receive 4 mo of treatment with pioglitazone (45 mg/day), rosiglitazone (8 mg/day), or placebo. Pioglitazone and rosiglitazone similarly improved FPG, mean plasma glucose during OGTT, Hb A1c, and insulin-mediated total body glucose disposal (Rd) and decreased mean plasma FFA during OGTT (all P &lt; 0.01, ANOVA). The insulin secretion/insulin resistance (disposition) index [ΔISR(AUC)/Δglucose(AUC) ÷ IR] was significantly improved in all TZD-treated groups: +1.8 ± 0.7 (PIO + drug-naïve diabetics), +0.7 ± 0.3 (PIO + sulfonylurea-treated diabetics), and 0.7 ± 0.2 (ROSI + sulfonylurea-withdrawn diabetics) vs. −0.2 ± 0.3 in the two placebo groups ( P &lt; 0.01, all TZDs vs. placebo, ANOVA). Improved insulin secretion correlated positively with increased body weight, fat mass, and Rdand inversely with decreased plasma glucose and FFA during the OGTT. In T2DM patients, TZD treatment leads to improved β-cell function, which correlates strongly with improved glycemic control.

Chronic PYY3–36 treatment promotes fat oxidation and ameliorates insulin resistance in C57BL6 mice

PYY(3-36) is a gut-derived hormone acting on hypothalamic nuclei to inhibit food intake. We recently showed that PYY(3-36) acutely reinforces insulin action on glucose disposal in mice. We aimed to evaluate effects of PYY(3-36) on energy metabolism and the impact of chronic PYY(3-36) treatment on insulin sensitivity. Mice received a single injection of PYY(3-36) or were injected once daily for 7 days, and energy metabolism was subsequently measured in a metabolic cage. Furthermore, the effects of chronic PYY(3-36) administration (continuous and intermittent) on glucose turnover were determined during a hyperinsulinemic-euglycemic clamp. PYY(3-36) inhibited cumulative food intake for 30 min of refeeding after an overnight fast (0.29 +/- 0.04 vs. 0.56 +/- 0.12 g, P = 0.036) in an acute setting, but not after 7 days of daily dosing. Body weight, total energy expenditure, and physical activity were not affected by PYY(3-36). However, it significantly decreased the respiratory quotient. Both continuous and intermittent PYY(3-36) treatment significantly enhanced insulin-mediated whole body glucose disposal compared with vehicle treatment (81.2 +/- 6.2 vs. 77.1 +/- 5.2 vs. 63.4 +/- 5.5 micromol.min(-1).kg(-1), respectively). In particular, PYY(3-36) treatment increased glucose uptake in adipose tissue, whereas its impact on glucose disposal in muscle did not attain statistical significance. PYY(3-36) treatment shifts the balance of fuel use in favor of fatty acids and enhances insulin sensitivity in mice, where it particularly promotes insulin-mediated glucose disposal. Notably, these metabolic effects of PYY(3-36) remain unabated after chronic administration, in contrast to its anorexic effects.

Exercise and dexamethasone oppositely modulate β-cell function and survival via independent pathways in 90% pancreatectomized rats

Long-term dexamethasone (DEX) treatment is well known for its ability to increase insulin resistance in liver and adipose tissues leading to hyperinsulinemia. On the other hand, exercise enhances peripheral insulin sensitivity. However, it is not clear whether DEX and/or exercise affect beta-cell mass and function in diabetic rats, and whether their effects can be associated with the modulation of the insulin/IGF-I signaling cascade in pancreatic beta-cells. After an 8-week study, whole body glucose disposal rates in 90% pancreatectomized (Px) and sham-operated male rats decreased with a high dose treatment of DEX (0.1mg DEX/kg body weight/day)(HDEX) treatment, while disposal rates increased with exercise. First-phase insulin secretion was decreased and delayed by DEX via the impairment of the glucose-sensing mechanism in beta-cells, while exercise reversed the impairment of first-phase insulin secretion caused by DEX, suggesting ameliorated beta-cell functions. However, exercise and DEX did not alter second-phase insulin secretion except for the fact that HDEX decreased insulin secretion at 120 min during hyperglycemic clamp in Px rats. Unlike beta-cell functions, DEX and exercise exhibited increased pancreatic beta-cell mass in two different pathways. Only exercise, through increased proliferation and decreased apoptosis, increased beta-cell mass via hyperplasia, which resulted from an enhanced insulin/IGF-I signaling cascade by insulin receptor substrate 2 induction. By contrast, DEX expanded beta-cell mass via hypertrophy and neogenesis from precursor cells, rather than increasing proliferation and decreasing apoptosis. In conclusion, the improvement of beta-cell function and survival via the activation of an insulin/IGF-I signaling cascade due to exercise has a crucial role in preventing the development and progression of type 2 diabetes.

Tissue-specific expression and regulation of GSK-3 in human skeletal muscle and adipose tissue

Glycogen synthase kinase-3 (GSK-3) is a ubiquitous kinase implicated in both insulin action and adipogenesis. To determine how these multiple roles may relate to insulin resistance, we studied the regulation of GSK-3 protein expression and phosphorylation in skeletal muscle and isolated adipocytes from nonobese healthy control (HC), obese control (OC), and obese type 2 diabetic (OT2D) subjects. At baseline there were no differences in the GSK-3 protein expression in adipocytes. OC subjects underwent a 6-mo caloric restriction resulting in a 7% decrease in body mass index (BMI) and a 21% improvement in insulin-stimulated whole body glucose disposal rate (GDR). GSK-3alpha and GSK-3beta expression decreased in adipocytes (P < 0.05), whereas GSK-3alpha protein expression increased in skeletal muscle (P < 0.05). OT2D subjects were treated with troglitazone or metformin for 3-4 mo. After troglitazone treatment GDR improved (P < 0.05) despite an increase in BMI (P < 0.05), whereas metformin had no significant effect on GDR. There was no significant change in GSK-3 expression in adipocytes following troglitazone, whereas both GSK-3alpha and -beta were decreased in skeletal muscle (P < 0.05). Metformin treatment had no significant impact on GSK-3 protein expression in either adipocytes or skeletal muscle. Neither treatment influenced GSK-3 serine phosphorylation in skeletal muscle or adipocytes. These results suggest that there is tissue specificity for the regulation of GSK-3 in humans. In skeletal muscle GSK-3 plays a role in control of metabolism and insulin action, whereas the function in adipose tissue is less clear.

Repletion of Atypical Protein Kinase C following RNA Interference-mediated Depletion Restores Insulin-stimulated Glucose Transport

The role of atypical protein kinase C (aPKC) in insulin-stimulated glucose transport in myocytes and adipocytes is controversial. Whereas studies involving the use of adenovirally mediated expression of kinase-inactive aPKC in L6 myocytes and 3T3/L1 and human adipocytes, and data from knock-out of aPKC in adipocytes derived from mouse embryonic stem cells and subsequently derived adipocytes, suggest that aPKCs are required for insulin-stimulated glucose transport, recent findings in studies of aPKC knockdown by small interfering RNA (RNAi) in 3T3/L1 adipocytes are conflicting. Moreover, there are no reports of aPKC knockdown in myocytes, wherein insulin effects on glucose transport are particularly relevant for understanding whole body glucose disposal. Presently, we exploited the fact that L6 myotubes and 3T3/L1 adipocytes have substantially different (30% nonhomology) major aPKCs, viz. PKC-zeta in L6 myotubes and PKC-lambda in 3T3/L1 adipocytes, that nevertheless can function interchangeably for glucose transport. Accordingly, in L6 myotubes, RNAi-targeting PKC-zeta, but not PKC-lambda, markedly depleted aPKC and concomitantly inhibited insulin-stimulated glucose transport; more importantly, these depleting/inhibitory effects were rescued by adenovirally mediated expression of PKC-lambda. Conversely, in 3T3/L1 adipocytes, RNAi constructs targeting PKC-lambda, but not PKC-zeta, markedly depleted aPKC and concomitantly inhibited insulin-stimulated glucose transport; here again, these depleting/inhibitory effects were rescued by adenovirally mediated expression of PKC-zeta. These findings in knockdown and, more convincingly, rescue studies, strongly support the hypothesis that aPKCs are required for insulin-stimulated glucose transport in myocytes and adipocytes.

Depot-specific regulation of glucose uptake and insulin sensitivity in HIV-lipodystrophy

Altered fat distribution is associated with insulin resistance in HIV, but little is known about regional glucose metabolism in fat and muscle depots in this patient population. The aim of the present study was to quantify regional fat, muscle, and whole body glucose disposal in HIV-infected men with lipoatrophy. Whole body glucose disposal was determined by hyperinsulinemic clamp technique (80 mU x m(-2) x min(-1)) in 6 HIV-infected men and 5 age/weight-matched healthy volunteers. Regional glucose uptake in muscle and subcutaneous (SAT) and visceral adipose tissue (VAT) was quantified in fasting and insulin-stimulated states using 2-deoxy-[18F]fluoro-D-glucose positron emission tomography. HIV-infected subjects with lipoatrophy had significantly increased glucose uptake into SAT (3.8 +/- 0.4 vs. 2.3 +/- 0.5 micromol x kg tissue(-1) x min(-1), P < 0.05) in the fasted state. Glucose uptake into VAT did not differ between groups. VAT area was inversely related with whole body glucose disposal, insulin sensitivity, and muscle glucose uptake during insulin stimulation. VAT area was highly predictive of whole body glucose disposal (r2 = 0.94, P < 0.0001). This may be mediated by adiponectin, which was significantly associated with VAT area (r = -0.75, P = 0.008), and whole body glucose disposal (r = 0.80, P = 0.003). This is the first study to directly demonstrate increased glucose uptake in subcutaneous fat of lipoatrophic patients, which may partially compensate for loss of SAT. Furthermore, we demonstrate a clear relationship between VAT and glucose metabolism in multiple fat and muscle depots, suggesting the critical importance of this depot in the regulation of glucose and highlighting the significant potential role of adiponectin in this process.

Chronic estradiol and progesterone treatment in conscious dogs: effects on insulin sensitivity and response to hypoglycemia

We evaluated the effect of chronic (3 wk) subcutaneous treatment with progesterone and estradiol (PE; producing serum levels observed in the 3rd trimester of pregnancy) or placebo (C) on hepatic and whole body insulin sensitivity and response to hypoglycemia in conscious, overnight-fasted nonpregnant female dogs, using tracer and arteriovenous difference techniques. Insulin was infused peripherally for 3 h at 1.8 mU x kg(-1) x min(-1). Glucose was allowed to fall to 3 mM (Hypo) or maintained at 6 mM (Eugly) by peripheral glucose infusion. Insulin concentrations were significantly higher in Eugly-PE (n = 7) and Hypo-PE (n = 7) than in Eugly-C (n = 6) and Hypo-C groups (n = 7), but there were no significant differences in hepatic insulin extraction. Concentrations of glucagon, cortisol, epinephrine, and norepinephrine did not differ significantly between Eugly groups or between Hypo groups. Whole body glucose disposal, adjusted for the differences in insulin between groups, was 35% higher in Eugly-C vs. Eugly-PE groups (P < 0.05). Eugly-C and Eugly-PE groups exhibited similar rates of net hepatic glucose uptake, but the rate of glucose appearance was greater in Eugly-PE in the last hour (P < 0.05). Net hepatic glucose output was greater (P < 0.05) in Hypo-PE than in Hypo-C groups, and the glucose infusion rate required to maintain equivalent hypoglycemia was less (P < 0.05). The rate of gluconeogenic flux did not differ between Hypo groups. Chronic progesterone and estradiol exposure caused whole body (primarily skeletal muscle) insulin resistance and enhanced the liver's response to hypoglycemia without altering counterregulatory hormone concentrations.

Two days of a very low calorie diet reduces endogenous glucose production in obese type 2 diabetic patients despite the withdrawal of blood glucose–lowering therapies including insulin

The mechanism of the blood glucose–lowering effect of a 2-day very low calorie diet (VLCD; 1890 kJ/d) in combination with the cessation of all blood glucose–lowering agents was studied in 12 (7 women, 5 men) obese (body mass index, 36.3 ± 1.0 kg/m 2 [mean ± SEM]) type 2 diabetic patients (age, 55 ± 4 years; HbA 1c, 7.3% ± 0.4%) undergoing insulin therapy. Endogenous glucose production (EGP) and whole body glucose disposal (6,6 2H 2-glucose), lipolysis ( 2H 5-glycerol), and substrate oxidation (indirect calorimetry) rates were measured before and after the intervention in basal and hyperinsulinemic conditions. After 2 days of a VLCD and discontinuation of all blood glucose–lowering therapies, fasting plasma glucose levels did not increase (11.3 ± 1.3 vs 10.3 ± 1.0 mmol/L). Basal EGP significantly declined (14.2 ± 1.0 to 11.9 ± 0.7 μmol/kg per minute; P = .009). Basal metabolic clearance rate of glucose and rate of basal lipolysis did not change. During hyperinsulinemia, EGP (5.5 ± 0.8 to 5.2 ± 0.5 μmol/kg per minute), whole body glucose disposal (12.1 ± 0.7 to 11.3 ± 1.0 μmol/kg per minute), the metabolic clearance rate of glucose, and the rate of lipolysis did not change after the 2-day intervention. Cessation of blood glucose–lowering therapy in combination with a 2-day VLCD does not lead to hyperglycemia and is associated with a reduction in basal EGP. Insulin-stimulated whole body glucose disposal did not improve, nor did insulin suppressibility of EGP and lipolysis.

Red wine consumption improves insulin resistance but not endothelial function in type 2 diabetic patients

Epidemiological studies have shown that red wine consumption is associated with less cardiovascular mortality in the general population and in the diabetic patients. To determine whether red wine improves insulin resistance in diabetic patients and to explore the relation between insulin sensitivity and endothelial function, we studied vascular reactivity and insulin-mediated glucose uptake in 9 type 2 diabetic patients before and after 2 weeks of red wine consumption (360 mL/d, wine-treated diabetics) and 8 type 2 diabetic patients who did not consume wine (control diabetics). Vascular reactivity was evaluated by plethysmography during intraarterial infusion of acetylcholine (Ach), sodium nitroprusside, and l- N-monomethylarginine. Forearm nitrite balance was measured during Ach infusion. Insulin sensitivity was measured by euglycemic hyperinsulinemic clamp at 1 mU/kg per minute. The basal forearm blood flow and the response to Ach, to sodium nitroprusside, and to l- N-monomethylarginine were unchanged both in the wine-treated and in the control diabetics. In contrast, insulin-mediated whole body glucose disposal improved by 43% after red wine consumption (from 2.79 ± 0.4 to 4.02 ± 0.5 mg/kg of lean body mass per minute, P = .02), but did not change in the control group. In conclusion, red wine consumption for 2 weeks markedly attenuates insulin-resistance in type 2 diabetic patients, without affecting vascular reactivity and nitric oxide production.

Changes in Insulin Secretion and Glucose Metabolism Induced by Dexamethasone in Lean and Obese Females

In healthy lean individuals, changes in insulin sensitivity occurring as a consequence of a 2-day dexamethasone administration are compensated for by changes in insulin secretion, allowing glucose homeostasis to be maintained. This study evaluated the changes in glucose metabolism and insulin secretion induced by short-term dexamethasone administration in obese women. Eleven obese women with normal glucose tolerance were studied on two occasions, without and after 2 days of low-dose dexamethasone administration. A two-step hyperglycemic clamp (7.5 and 10 mM glucose) with 6,6 (2)H(2) glucose was used to assess insulin secretion and whole body glucose metabolism. Results were compared with those obtained in a group of eight lean women. Without dexamethasone, obese women had higher plasma insulin concentrations in the fasting state, during the first phase of insulin secretion, and at the two hyperglycemic plateaus. However, they had normal whole body glucose metabolism compared with lean women, indicating adequate compensation. After dexamethasone, obese women had a 66% to 92% increase in plasma insulin concentrations but a 15.4% decrease in whole body glucose disposal. This contrasted with lean women, who had a 91% to 113% increase in plasma insulin concentrations, with no change in whole body glucose disposal. Dexamethasone administration led to a significant reduction in whole body glucose disposal at fixed glycemia in obese but not lean women. This indicates that obese women are unable to increase their insulin secretion appropriately.

Calorie restriction improves whole-body glucose disposal and insulin resistance in association with the increased adipocyte-specific GLUT4 expression in Otsuka Long–Evans Tokushima Fatty rats

Calorie restriction (CR) has been shown to improve peripheral insulin resistance and type 2 diabetes in animal models. However, the exact mechanism of CR on GLUT4 expression and translocation in insulin-sensitive tissues has not been well elucidated. In the present study, we examine the effect of CR on the expression of glucose transporter 4 (GLUT4), GLUT4 translocation, and glucose transport activity in adipose tissue from Otsuka Long–Evans Tokushima Fatty (OLETF) rat and control (LETO) rats. CR (70% of satiated group) ameliorated hyperglycemia and improved impaired glucose tolerance (IGT) in OLETF rats. In skeletal muscle, the expression levels of GLUT4 and GLUT1 were not significantly different between LETO and OLETF rats, and were not affected by CR. By contrast, the expression level of GLUT4 was markedly decreased in the adipose tissue of OLETF rats, but was dramatically increased by CR. The GLUT4 recruitment stimulated by insulin was also improved in OLETF rat adipocytes by CR. The insulin-stimulated 2-deoxyglucose (2DG) uptake was significantly increased in adipocytes from the CR OLETF rats, as compared with the satiated OLETF rats. Taken together, these results suggest that CR improves whole body glucose disposal and insulin resistance in OLETF rats, and that these effects may associate with the increased adipocyte-specific GLUT4 expression.

Whole Body Protein Breakdown Is Less Inhibited by Insulin, But Still Responsive to Amino Acid, in Nondiabetic Elderly Subjects

Responses of whole body glucose disposal (GDR) and protein breakdown (PB) to physiological insulin levels are altered in nondiabetic elderly subjects. Amino acids enhance inhibition of PB by insulin in young subjects. We hypothesized that addition of amino acid to insulin may improve the defect in PB regulation by insulin in elderly people. Therefore, we investigated the effect of hyperinsulinemia combined to either euaminoacidemia (EuAA) or hyperaminoacidemia (HyperAA) on GDR and PB, using isotopic dilution of D-[6,6-2H2]glucose and L-[1-13C]leucine, in young (mean +/- SEM, 24.4 +/- 0.8 yr) and elderly (70.2 +/- 0.7 yr) subjects. GDR was lower in elderly than in young subjects in all situations (P < 0.05). Despite a greater inhibition with HyperAA, PB was less inhibited in elderly than in young subjects during both clamps (ratio between change over basal PB and change over basal insulinemia, -0.014 +/- 0.002 vs. -0.024 +/- 0.003 in EuAA and -0.022 +/- 0.002 vs. -0.036 +/- 0.003 micromol/ml.microU/kg fat-free mass.min in HyperAA; elderly vs. young, P < 0.05). In conclusion, in nondiabetic elderly subjects, PB is less inhibited by insulin with either basal or high amino acid concentrations. Addition of amino acid potentiates insulin-induced suppression of PB in both groups to the same extent, suggesting a specific dysregulation of PB by insulin with age.

Transgenic Overexpression of Protein-tyrosine Phosphatase 1B in Muscle Causes Insulin Resistance, but Overexpression with Leukocyte Antigen-related Phosphatase Does Not Additively Impair Insulin Action

Previous studies implicate protein-tyrosine phosphatase 1B (PTP1B) and leukocyte antigen-related phosphatase (LAR) as negative regulators of insulin signaling. The expression and/or activity of PTP1B and LAR are increased in muscle of insulin-resistant rodents and humans. Overexpression of LAR selectively in muscle of transgenic mice causes whole body insulin resistance. To determine whether overexpression of PTP1B also causes insulin resistance, we generated transgenic mice overexpressing human PTP1B selectively in muscle at levels similar to those observed in insulin-resistant humans. Insulin-stimulated insulin receptor (IR) tyrosyl phosphorylation and phosphatidylinositol 3'-kinase activity were impaired by 35% and 40-60% in muscle of PTP1B-overexpressing mice compared with controls. Insulin stimulation of protein kinase C (PKC)lambda/zeta activity, which is required for glucose transport, was impaired in muscle of PTP1B-overexpressing mice compared with controls, showing that PTP1B overexpression impairs activation of these PKC isoforms. Furthermore, hyperinsulinemic-euglycemic clamp studies revealed that whole body glucose disposal and muscle glucose uptake were decreased by 40-50% in PTP1B-overexpressing mice. Overexpression of PTP1B or LAR alone in muscle caused similar impairments in insulin action; however, compound overexpression achieved by crossing PTP1B- and LAR-overexpressing mice was not additive. Antibodies against specific IR phosphotyrosines indicated overlapping sites of action of PTP1B and LAR. Thus, overexpression of PTP1B in vivo impairs insulin sensitivity, suggesting that overexpression of PTP1B in muscle of obese humans and rodents may contribute to their insulin resistance. Lack of additive impairment of insulin signaling by PTP1B and LAR suggests that these PTPs have overlapping actions in causing insulin resistance in vivo.

Plasma resistin concentration, hepatic fat content, and hepatic and peripheral insulin resistance in pioglitazone-treated type II diabetic patients.

To study the effect of pioglitazone (PIO) on plasma resistin concentration, endogenous glucose production (EGP), and hepatic fat content (HFC) in patients with type II diabetes (T2DM). A total of 13 T2DM patients (age=51+/-2 y, BMI=29.7+/-1.1 kg/m(2), HbA(1c)=8.0+/-0.5%). HFC (magnetic resonance spectroscopy) and basal plasma resistin concentration were quantitated before and after PIO treatment (45 mg/day) for 16 weeks. Subjects received a 3 h euglycemic insulin (100 mU/m(2)/min) clamp with 3-[(3)H] glucose to determine rates of EGP and tissue glucose disappearance (Rd) before and after PIO. PIO reduced fasting plasma glucose (10.3+/-0.7 to 7.6+/-0.6 mmol/l, P<0.001) and HbA(1c) (8.0+/-0.4 to 6.8+/-0.3%, P<0.001) despite increased body weight (83.2+/-3.4 to 86.3+/-3.4 kg, P<0.001). PIO improved Rd (4.9+/-0.4 to 6.6+/-0.5 mg/kg/min, P<0.005) and reduced EGP (0.22+/-0.04 to 0.06+/-0.02 mg/kg/min, P<0.01) during the insulin clamp. Following PIO, HFC decreased from 21.1+/-3.5 to 11.2+/-2.1% (P<0.005), and plasma resistin decreased from 5.3+/-0.6 to 3.5+/-0.3 ng/ml (P<0.01). Plasma resistin concentration correlated positively with HFC before (r=0.58, P<0.05) and after (r=0.55, P<0.05) PIO treatment. Taken collectively, plasma resistin concentration, before and after PIO treatment, correlated positively with hepatic fat content (r=0.66, P<0.001) and EGP during the insulin clamp (r=0.41, P<0.05). However, the plasma resistin concentration did not correlate with whole body glucose disposal (Rd) during the insulin clamp either before (r=-0.18, P=NS) or after (r=-0.13, P=NS) PIO treatment. PIO treatment in T2DM causes a significant decrease in plasma resistin concentration. The decrease in plasma resistin is positively correlated with the decrease in hepatic fat content and improvement in hepatic insulin sensitivity.

Improvement of Insulin Resistance and Insulin Secretion by Water Extracts ofCordyceps militaris,Phellinus linteus, andPaecilomyces tenuipesin 90% Pancreatectomized Rats

The effect of supplementation with Phellinus linteus (P. linteus), Paecilomyces tenuipes (P. tenuipes), and Cordyceps militaris (C. militaris) mushroom water extracts on the insulin secretion and insulin resistance of 90% pancreatectomized (Px) male Sprague Dawley rats was investigated. Px rats were daily administered 0.5 g of P. linteus, P. tenuipes, and C. militaris aqueous extracts or a placebo per 1 kg body weight with a 40% fat diet for 8 weeks. Fasting serum glucose levels were lower in rats receiving C. militaris than in the control group. Insulin secretion at the elevated serum glucose levels was lowest in rats that consumed P. tenuipes in hyperglycemic clamp. Whole body glucose disposal rates increased in C. militaris but decreased in P. tenuipes compared to those in the control group in euglycemic hyperinsulinemic clamp. The GLUT4 content and fraction velocity of glycogen synthase in the soleus and quadriceps muscles increased in the rats treated with C. militaris, but P. tenuipes decreased both. In sum, a water extract of C. militaris ameliorates insulin resistance by enhancing glucose utilization in skeletal muscles.

Short- and long-term beneficial effects of trimetazidine in patients with diabetes and ischemic cardiomyopathy

Background Trimetazidine (TMZ) has been shown to partially inhibit free fatty acid oxidation by shifting substrate utilization from fatty acid to glucose. The aim of this study was to assess the effects of TMZ in patients with diabetes and ischemic cardiomyopathy. Methods Sixteen patients with diabetes and ischemic hypokinetic cardiomyopathy (all males) on conventional therapy were randomized to receive either placebo or TMZ (20 mg 3 times per day), each arm lasting 15 days, and then again to receive either placebo or TMZ for 2 additional 6-month periods, according to a double-blind, crossover design. At the end of each period, all patients underwent exercise testing, 2-dimensional echocardiography, and hyperinsulinemic/euglycemic clamp. Among the others, New York Heart Association class, ejection fraction, exercise time, fasting blood glucose, end-clamp M value (index of total body glucose disposal) and endothelin-1 levels were evaluated. Results Both in the short and long term (completed by 13 patients), on TMZ compared to placebo, ejection fraction (47 ± 7 vs 41 ± 9 and 45 ± 8 vs 36 ± 8%, P < .001 for both) and M value (4.0 ± 1.8 vs 3.3 ± 1.6, P = .003, and 3.5 ± 1.5 vs 2.7 ± 1.6 mg/kg body weight/min, P < .01) increased, while fasting blood glucose (121 ± 30 vs 136 ± 40, P = .02 and 125 ± 36 vs 140 ± 43, P = .19) and endothelin-1 (8.8 ± 3.8 vs 10.9 ± 3.8, P < .001 and 6.2 ± 2.4 vs 9.2 ± 4.3 pg/mL, P = .03) decreased. In the short term, 10 patients decreased 1 class on the NYHA scale during treatment with TMZ ( P = .019 vs placebo). Eight patients decreased 1 NYHA class while on long-term TMZ treatment, while on placebo 1 patient increased 1 NYHA class and none improved ( P = .018 vs placebo). Conclusions In a short series of patients with diabetes and ischemic cardiomyopathy, TMZ improved left ventricular function, symptoms, glucose metabolism, and endothelial function. Shifting energy substrate preference away from fatty acid metabolism and toward glucose metabolism by TMZ appears an effective adjunctive treatment in patients with diabetes with postischemic cardiomyopathy.

Microarray Profiling of Human Skeletal Muscle Reveals That Insulin Regulates ∼800 Genes during a Hyperinsulinemic Clamp

Insulin action in target tissues involved precise regulation of gene expression. To define the set of insulin-regulated genes in human skeletal muscle, we analyzed the global changes in mRNA levels during a 3-h hyperinsulinemic euglycemic clamp in vastus lateralis muscle of six healthy subjects. Using 29,308 cDNA element microarrays, we found that the mRNA expression of 762 genes, including 353 expressed sequence tags, was significantly modified during insulin infusion. 478 were up-regulated and 284 down-regulated. Most of the genes with known function are novel targets of insulin. They are involved in the transcriptional and translational regulation (29%), intermediary and energy metabolisms (14%), intracellular signaling (12%), and cytoskeleton and vesicle traffic (9%). Other categories consisted of genes coding for receptors, carriers, and transporters (8%), components of the ubiquitin/proteasome pathways (7%) and elements of the immune response (5.5%). These results thus define a transcriptional signature of insulin action in human skeletal muscle. They will help to better define the mechanisms involved in the reduction of insulin effectiveness in pathologies such as type 2 diabetes mellitus, a disease characterized by defective regulation of gene expression in response to insulin.