Insulin-stimulated Glucose Disposal Research Articles

Association between hemoglobin glycation index with insulin resistance and carotid atherosclerosis in non-diabetic individuals.

Hemoglobin glycation index (HGI), defined as the difference between the observed HbA1c value and the value of HbA1c predicted from plasma glucose levels, represents a measure of the degree of non-enzymatic glycation of hemoglobin and it has been found to be positively associated with micro- and macro-vascular complications in subjects with type 2 diabetes. To investigate the pathophysiological abnormalities responsible for the increased cardiovascular risk of patients with higher HGI, we evaluated the association of HGI with cardio-metabolic characteristics in nondiabetic offspring of type 2 diabetic individuals. Insulin sensitivity, measured by a hyperinsulinemic-euglycemic clamp, cardio-metabolic risk factors including lipid profile, uric acid and inflammatory factors, and ultrasound measurement of carotid intima–media thickness (IMT) were assessed in 387 nondiabetic individuals. Participants were stratified in tertiles according to HGI (high, moderate and low). As compared with subjects with low HGI, those with high HGI displayed an unfavorable cardio-metabolic risk profile having significantly higher values of BMI, waist circumference, triglycerides, uric acid, fasting insulin, inflammatory markers, such as high sensitivity C reactive protein, erythrocytes sedimentation rate, complement C3, fibrinogen, and white blood cell count, and carotid IMT, and lower HDL and insulin-stimulated glucose disposal. In a linear regression analysis model including several atherosclerotic risk factors such as gender, age, BMI, inflammatory factors, lipid profile, insulin-stimulated glucose disposal, fasting insulin, uric acid, and blood pressure, HGI was the major predictor of IMT (β = 0.35; P = 0.001). In a logistic regression analysis adjusted for confounders, individuals with high HGI showed a 2.7-fold increased risk of vascular atherosclerosis (OR 2.72, 95%CI 1.01–7.37) as compared with subjects with low HGI. The present findings support the notion that HGI may be a useful tool to identify a subset of nondiabetic individuals conceivably harboring a higher risk of cardiovascular disease.

The heterozygous N291S mutation in the lipoprotein lipase gene impairs whole-body insulin sensitivity and affects a distinct set of plasma metabolites in humans

Mutations in the lipoprotein lipase gene causing decreased lipoprotein lipase activity are associated with surrogate markers of insulin resistance and the metabolic syndrome in humans. We investigated the hypothesis that a heterozygous lipoprotein lipase mutation (N291S) induces whole-body insulin resistance and alterations in the plasma metabolome. In 6 carriers of a heterozygous lipoprotein lipase mutation (N291S) and 11 age-matched and weight-matched healthy controls, we examined insulin sensitivity and substrate metabolism by euglycemic-hyperinsulinemic clamps combined with indirect calorimetry. Plasma samples were taken before and after the clamp (4hours of physiological hyperinsulinemia), and metabolites were measured enzymatically or by gas chromatography-mass spectrometry. Compared with healthy controls, heterozygous carriers of a defective lipoprotein lipase allele had elevated fasting plasma levels triglycerides (P<.006), and markedly impaired insulin-stimulated glucose disposal rates (P<.024) and nonoxidative glucose metabolism (P<.015). Plasma metabolite profiling demonstrated lower circulating levels of pyruvic acid and α-tocopherol in the N291S carriers than in controls both before and after stimulation with insulin (all >1.5-fold change and P<.05). Heterozygous carriers with a defective lipoprotein lipase allele are less insulin sensitive and have increased plasma levels of nonesterified fatty acids and triglycerides. The heterozygous N291S carriers also have a distinct plasma metabolomic signature, which may serve as a diagnostic tool for deficient lipoprotein lipase activity and as a marker of lipid-induced insulin resistance.

Lipid droplet dynamics and insulin sensitivity upon a 5-day high-fat diet in Caucasians and South Asians

A 5-day High-Fat High-Calorie diet (HFHC-diet) reduces insulin-stimulated glucose disposal (Rd) in South Asian, but not Caucasian healthy lean males. We aimed to investigate if differences in myocellular lipid handling are underlying this differential response. A two-step hyperinsulinemic-euglycemic clamp and muscle biopsies were performed in 12 healthy lean Caucasian and South Asian males (BMI < 25 kg/m2, 19–25 years) before and after a 5-day HFHC-diet (regular diet + 375 mL cream/day; 1275 kcal/day; 94% fat). Triglyceride extractions and Western Blots for lipid droplet and mitochondrial proteins were performed. Intramyocellular lipid content and HFHC-diet response were similar between ethnicities (group effect: P = 0.094; diet effect: +~30%, P = 0.044). PLIN5 protein content increased upon the HFHC-diet (P = 0.031) and tended to be higher in South Asians (0.87 ± 0.42 AU vs. 1.35 ± 0.58 AU, P = 0.07). 4-HNE tended to increase in South Asians upon the HFHC-diet (interaction effect: P = 0.057). In Caucasians ΔPLIN5 content correlated with ΔRd (Caucasians: r = 0.756, P = 0.011; South Asians: r = −0.085, P = 0.816), while in South Asians Δ4-HNE associated with ΔPLIN5 content (Caucasians: r = 0.312, P = 0.380; South Asians: r = 0.771, P = 0.003). These data indicate that in Caucasians, PLIN5 may be protective against HFHC-diet induced insulin resistance, which for reasons not yet understood is not observed in South Asians, who possess increased lipid peroxidation levels.

Skeletal muscle inflammation and insulin resistance in obesity.

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.

The Phospholipid Linoleoylglycerophosphocholine as a Biomarker of Directly Measured Insulin Resistance.

BackgroundPlasma concentrations of some lysophospholipids correlate with metabolic alterations in humans, but their potential as biomarkers of insulin resistance (IR) is insufficiently known. We aimed to explore the association between plasma linoleoylglycerophosphocholine (LGPC) and objective measures of IR in adults with different metabolic profiles.MethodsWe studied 62 men and women, ages 30 to 69 years, (29% normal weight, 59% overweight, 12% obese). Participants underwent a 5-point oral glucose tolerance test (5p-OGTT) from which we calculated multiple indices of IR and insulin secretion. Fifteen participants additionally underwent a hyperinsulinemic-euglycemic clamp for estimation of insulin-stimulated glucose disposal. Plasma LGPC was determined using high performance liquid chromatography/time-of-flight mass spectrometry. Plasma LGPC was compared across quartiles defined by the IR indices.ResultsMean LGPC was 15.4±7.6 ng/mL in women and 14.1±7.3 ng/mL in men. LGPC did not correlate with body mass in-dex, percent body fat, waist circumference, blood pressure, glycosylated hemoglobin, log-triglycerides, or high density lipoprotein cholesterol. Plasma LGPC concentrations was not systematically associated with any of the studied 5p-OGTT-derived IR indices. However, LGPC exhibited a significant negative correlation with glucose disposal in the clamp (Spearman r=−0.56, P=0.029). Despite not being diabetic, participants with higher plasma LGPC exhibited significantly higher post-challenge plasma glucose excursions in the 5p-OGTT (P trend=0.021 for the increase in glucose area under the curve across quartiles of plasma LGPC).ConclusionIn our sample of Latino adults without known diabetes, LGPC showed potential as a biomarker of IR and impaired glucose metabolism.

Liver-specific G0 /G1 switch gene 2 (G0s2) expression promotes hepatic insulin resistance by exacerbating hepatic steatosis in male Wistar rats.

Hepatic steatosis is strongly associated with insulin resistance. It has been reported that G0 /G1 switch gene 2 (G0s2) inhibits the lipolytic activity of adipose triglyceride lipase, which is a major lipase in the liver as well as in adipocytes. Moreover, G0s2 protein content is increased in the livers of high-fat diet (HFD)-fed rats. In the present study, we investigated the effect of hepatic G0s2 on insulin sensitivity in male Wistar rats. Male Wistar rats were fed a 60% HFD for 4 weeks. After 3 weeks of feeding, rats were injected with adenovirus-expressing green fluorescent protein (Ad-GFP; control) or adenovirus-expressing mouse G0s2 (Ad-G0s2). On Day 7 after injection, a euglycemic-hyperinsulinemic clamp study was performed in rats fasted for 8 h. Body weight and fasting glucose levels were not significantly different between the Ad-GFP and Ad-G0s2 groups. During the clamp study, the glucose infusion rate required for euglycemia decreased significantly by 16% in the Ad-G0s2 compared with Ad-GFP group. The insulin-suppressed hepatic glucose output increased significantly in the Ad-G0s2 group, but the insulin-stimulated glucose disposal rate was not significantly different between the two groups. Consistent with the clamp data, insulin-stimulated phosphorylation of Akt decreased significantly in livers of rats injected with Ad-G0s2. Furthermore, Oil Red O-staining indicated that overexpression of G0s2 protein in the liver promoted hepatic steatosis by 2.5-fold in HFD-fed rats. The results of the present study indicate that hepatic G0s2 protein may promote hepatic insulin resistance by exacerbating hepatic steatosis.

Mechanisms Underlying the Pathogenesis of Isolated Impaired Glucose Tolerance in Humans

Prediabetes is a heterogeneous disorder classified on the basis of fasting glucose concentrations and 2-hour glucose tolerance. We sought to determine the relative contributions of insulin secretion and action to the pathogenesis of isolated impaired glucose tolerance (IGT). The study consisted of an oral glucose tolerance test and a euglycemic clamp performed in two cohorts matched for anthropometric characteristics and fasting glucose but discordant for glucose tolerance. An inpatient clinical research unit at an academic medical center. Twenty-five subjects who had normal fasting glucose (NFG) and normal glucose tolerance (NGT) and 19 NFG/IGT subjects participated in this study. Subjects underwent a seven-sample oral glucose tolerance test and a 4-hour euglycemic, hyperinsulinemic clamp on separate occasions. Glucose turnover during the clamp was measured using tracers, and endogenous hormone secretion was inhibited by somatostatin. We sought to determine whether hepatic glucose metabolism, specifically the contribution of gluconeogenesis to endogenous glucose production, differed between subjects with NFG/NGT and those with NFG/IGT. Endogenous glucose production did not differ between groups before or during the clamp. Insulin-stimulated glucose disappearance was lower in NFG/IGT (24.6 ± 2.2 vs 35.0 ± 3.6 μmol/kg/min; P = .03). The disposition index was decreased in NFG/IGT (681 ± 102 vs 2231 ± 413 × 10-14 dL/kg/min2 per pmol/L; P < .001). We conclude that innate defects in the regulation of glycogenolysis and gluconeogenesis do not contribute to NFG/IGT. However, insulin-stimulated glucose disposal is impaired, exacerbating defects in β-cell function.

Short-term Effects of Laparoscopic Adjustable Gastric Banding Versus Roux-en-Y Gastric Bypass

Bariatric surgery has been shown to have important long-term metabolic effects resulting in enhanced insulin sensitivity and improved glucose tolerance in patients with type 2 diabetes. The contribution of reduced caloric intake to these beneficial effects of surgery remains unclear. The aim of this study was to compare the short-term effects (1 week) of bariatric surgical procedures with a very low caloric intake (VLCI) on insulin sensitivity (IS) and insulin secretion (ISR) in nondiabetic obese subjects. Twenty obese patients without diabetes (BMI 44.2 ± 0.7 kg/m2) were admitted to the clinic for 1 week. At baseline and 1 week after VLCI (600 kcal/day), subjects received a hyperinsulinemic-euglycemic clamp with tracer infusion to quantify endogenous glucose production (EGP), lipolysis (rate of appearance of glycerol [RaGlycerol]), peripheral insulin sensitivity (insulin-stimulated glucose disposal [M value] divided by the steady-state plasma insulin concentration [M/I]), hepatic insulin sensitivity (Hep-IS [= 1/(EGP ⋅ insulin)]), and adipose insulin sensitivity (Adipo-IS [= 1/(RaGlycerol ⋅ insulin)]). An intravenous glucose bolus was administered at the end of the insulin clamp to measure ISR and β-cell function (disposition index [DI]). Approximately 3 months later, patients were admitted for laparoscopic adjustable gastric banding (LAGB) (n = 10) or Roux-en-Y gastric bypass (RYGB) (n = 10), and were restudied 1 week after surgery under the same caloric regimen (600 kcal/day). After 1 week of VLCI, patients lost 2.1 kg without significant changes in Hep-IS, Adipo-IS, M/I, or DI. RYGB and LAGB led to greater weight loss (5.5 and 5.2 kg, respectively) and to significant improvement in Hep-IS, EGP, and lipolysis. Only RYGB improved Adipo-IS and M/I. No change in ISR or DI was observed in either surgical group. Bariatric surgery improves IS within 1 week. These metabolic effects were independent of caloric intake and more pronounced after RYGB compared with LAGB.

One-hour post-load hyperglycemia combined with HbA1c identifies pre-diabetic individuals with a higher cardio-metabolic risk burden

Background and aimsEvidence suggests that combining 1-hour plasma glucose ≥155 mg/dl during an oral glucose tolerance test (OGTT) with glycosylated hemoglobin (HbA1c) significantly increases their predictive power for incident diabetes, while their individual and joint associations with cardio-metabolic risk factors remain undefined. Herein, we evaluated whether 1-hour post-load plasma glucose ≥155 mg/dl combined with HbA1c may identify pre-diabetic individuals with a higher cardio-metabolic risk. MethodsAnthropometric and metabolic characteristics, insulin sensitivity and insulin secretion assessed by OGTT-derived indexes, carotid intima-media thickness (IMT), pulse pressure, and rate pressure product were evaluated in 1495 individuals. ResultsAs compared with subjects with 1-hour post-load glucose <155 mg/dl, individuals with 1-hour post-load glucose ≥155 mg/dl exhibited a significantly worse cardio metabolic profile, both in the group with HbA1c <5.7%, and in the group with prediabetes (HbA1c 5.7–6.4%). Specifically, in both groups, subjects with 1-hour post-load glucose ≥155 mg/dl had higher fasting and 2-h post-load glucose (p < 0.0001 for all in both groups), higher HOMA-IR (p < 0.0001 in both groups), and carotid IMT (p = 0.05 in the group with HbA1c <5.7% and p = 0.03 in the group HbA1c 5.7–6.4%), as well as lower Matsuda index, insulinogenic index and disposition index (p < 0.0001 in both groups), and lower insulin-stimulated glucose disposal (p < 0.0001 in the group with HbA1c <5.7% and p = 0.03 in the group HbA1c 5.7–6.4%). ConclusionsHyperglycemia at 1-hour during an OGTT may be a useful tool to identify a subset of individuals within HbA1c-defined glycemic categories at higher risk of developing type 2 diabetes and cardiovascular disease.

Dapagliflozin Enhances Fat Oxidation and Ketone Production in Patients With Type 2 Diabetes.

Insulin resistance is associated with mitochondrial dysfunction and decreased ATP synthesis. Treatment of individuals with type 2 diabetes mellitus (T2DM) with sodium-glucose transporter 2 inhibitors (SGLT2i) improves insulin sensitivity. However, recent reports have demonstrated development of ketoacidosis in subjects with T2DM treated with SGLT2i. The current study examined the effect of improved insulin sensitivity with dapagliflozin on 1) mitochondrial ATP synthesis and 2) substrate oxidation rates and ketone production. The study randomized 18 individuals with T2DM to dapagliflozin (n = 9) or placebo (n = 9). Before and after 2 weeks, subjects received an insulin clamp with tritiated glucose, indirect calorimetry, and muscle biopsies. Dapagliflozin reduced fasting plasma glucose (167 ± 13 to 128 ± 6 mg/dL) and increased insulin-stimulated glucose disposal by 36% (P < 0.01). Glucose oxidation decreased (1.06 to 0.80 mg/kg ⋅ min, P < 0.05), whereas nonoxidative glucose disposal (glycogen synthesis) increased (2.74 to 4.74 mg/kg ⋅ min, P = 0.03). Dapagliflozin decreased basal glucose oxidation and increased lipid oxidation and plasma ketone concentration (0.05 to 0.19 mmol/L, P < 0.01) in association with an increase in fasting plasma glucagon (77 ± 8 to 94 ± 13, P < 0.01). Dapagliflozin reduced the ATP synthesis rate, which correlated with an increase in plasma ketone concentration. Dapagliflozin improved insulin sensitivity and caused a shift from glucose to lipid oxidation, which, together with an increase in glucagon-to-insulin ratio, provide the metabolic basis for increased ketone production.

Lipid-Induced Insulin Resistance in Skeletal Muscle: The Chase for the Culprit Goes from Total Intramuscular Fat to Lipid Intermediates, and Finally to Species of Lipid Intermediates.

The skeletal muscle is the largest organ in the body. It plays a particularly pivotal role in glucose homeostasis, as it can account for up to 40% of the body and for up to 80%–90% of insulin-stimulated glucose disposal. Hence, insulin resistance (IR) in skeletal muscle has been a focus of much research and review. The fact that skeletal muscle IR precedes β-cell dysfunction makes it an ideal target for countering the diabetes epidemic. It is generally accepted that the accumulation of lipids in the skeletal muscle, due to dietary lipid oversupply, is closely linked with IR. Our understanding of this link between intramyocellular lipids (IMCL) and glycemic control has changed over the years. Initially, skeletal muscle IR was related to total IMCL. The inconsistencies in this explanation led to the discovery that particular lipid intermediates are more important than total IMCL. The two most commonly cited lipid intermediates for causing skeletal muscle IR are ceramides and diacylglycerol (DAG) in IMCL. Still, not all cases of IR and dysfunction in glycemic control have shown an increase in either or both of these lipids. In this review, we will summarise the latest research results that, using the lipidomics approach, have elucidated DAG and ceramide species that are involved in skeletal muscle IR in animal models and human subjects.

Liraglutide prevents microvascular insulin resistance and preserves muscle capillary density in high-fat diet-fed rats.

Muscle microvasculature critically regulates endothelial exchange surface area to facilitate transendothelial delivery of insulin, nutrients, and oxygen to myocytes. Insulin resistance blunts insulin-mediated microvascular recruitment and decreases muscle capillary density; both contribute to lower microvascular blood volume. Glucagon-like peptide 1 (GLP-1) and its analogs are able to dilate blood vessels and stimulate endothelial cell proliferation. In this study, we aim to determine the effects of sustained stimulation of the GLP-1 receptors on insulin-mediated capillary recruitment and metabolic insulin responses, small arterial endothelial function, and muscle capillary density. Rats were fed a high-fat diet (HFD) for 4 wk with or without simultaneous administration of liraglutide and subjected to a euglycemic hyperinsulinemic clamp for 120 min after an overnight fast. Insulin-mediated muscle microvascular recruitment and muscle oxygenation were determined before and during insulin infusion. Muscle capillary density was determined and distal saphenous artery used for determination of endothelial function and insulin-mediated vasodilation. HFD induced muscle microvascular insulin resistance and small arterial vessel endothelial dysfunction and decreased muscle capillary density. Simultaneous treatment of HFD-fed rats with liraglutide prevented all of these changes and improved insulin-stimulated glucose disposal. These were associated with a significantly increased AMPK phosphorylation and the expressions of VEGF and its receptors. We conclude that GLP-1 receptor agonists may exert their salutary glycemic effect via improving microvascular insulin sensitivity and muscle capillary density during the development of insulin resistance, and early use of GLP-1 receptor agonists may attenuate metabolic insulin resistance as well as prevent cardiovascular complications of diabetes.

Effect of testosterone on insulin sensitivity, oxidative metabolism and body composition in aging men with type 2 diabetes on metformin monotherapy.

To evaluate the effect of testosterone replacement therapy (TRT) on body composition, insulin sensitivity, oxidative metabolism and glycaemic control in aging men with lowered bioavailable testosterone (BioT) levels and type 2 diabetes mellitus (T2D) controlled on metformin monotherapy. We conducted a randomized, double-blind, placebo-controlled study in 39 men aged 50-70 years with BioT levels <7.3 nmol/L and T2D treated with metformin monotherapy. Patients were randomized to testosterone gel (TRT, n = 20) or placebo (n = 19) for 24 weeks. Lean body mass (LBM), total and regional fat mass were measured using whole-body dual-energy X-ray absorptiometry scans. Whole-body peripheral insulin sensitivity, endogenous glucose production (EGP) and substrate oxidation were assessed by euglycaemic-hyperinsulinaemic clamp with glucose tracer and combined with indirect calorimetry. Coefficients (β) represent the placebo-controlled mean effect of intervention. LBM (β = 1.9 kg, p = 0.001) increased after TRT, while total fat mass (β = -1.3 kg, p = 0.009), fat mass trunk (β = -0.7 kg, p = 0.043), fat mass legs (β = -0.7 kg, p = 0.025), fat mass arms (β = -0.3 kg, p = 0.001), and HDL cholesterol (β = -0.11 mmol/L, p = 0.009) decreased after TRT compared with placebo. Insulin-stimulated glucose disposal rates did not change in response to TRT compared with placebo (p = 0.18). Moreover, glycated haemoglobin, and basal and insulin-stimulated rates of EGP, lipid- and glucose-oxidation were unaltered after TRT. TRT in aging men with lowered BioT levels and T2D controlled on metformin monotherapy improved body composition; however, glycaemic control, peripheral insulin sensitivity, EGP and substrate metabolism were unchanged.

Combined epigallocatechin-3-gallate and resveratrol supplementation for 12 wk increases mitochondrial capacity and fat oxidation, but not insulin sensitivity, in obese humans: a randomized controlled trial

The obese insulin-resistant state is characterized by impairments in lipid metabolism. We previously showed that 3-d supplementation of combined epigallocatechin-3-gallate and resveratrol (EGCG+RES) increased energy expenditure and improved the capacity to switch from fat toward carbohydrate oxidation with a high-fat mixed meal (HFMM) test in men. The present study aimed to investigate the longer-term effect of EGCG+RES supplementation on metabolic profile, mitochondrial capacity, fat oxidation, lipolysis, and tissue-specific insulin sensitivity. In this randomized double-blind study, 38 overweight and obese subjects [18 men; aged 38 ± 2 y; body mass index (kg/m(2)): 29.7 ± 0.5] received either EGCG+RES (282 and 80 mg/d, respectively) or placebo for 12 wk. Before and after the intervention, oxidative capacity and gene expression were assessed in skeletal muscle. Fasting and postprandial (HFMM) lipid metabolism was assessed by using indirect calorimetry, blood sampling, and microdialysis. Tissue-specific insulin sensitivity was assessed by a hyperinsulinemic-euglycemic clamp with [6,6-(2)H2]-glucose infusion. EGCG+RES supplementation did not affect the fasting plasma metabolic profile. Although whole-body fat mass was not affected, visceral adipose tissue mass tended to decrease after the intervention compared with placebo (P-time × treatment = 0.09). EGCG+RES supplementation significantly increased oxidative capacity in permeabilized muscle fibers (P-time × treatment < 0.05, P-EGCG+RES < 0.05). Moreover, EGCG+RES reduced fasting (P-time × treatment = 0.03) and postprandial respiratory quotient (P-time × treatment = 0.01) compared with placebo. Fasting and postprandial fat oxidation was not significantly affected by EGCG+RES (P-EGCG+RES = 0.46 and 0.38, respectively) but declined after placebo (P-placebo = 0.05 and 0.03, respectively). Energy expenditure was not altered (P-time × treatment = 0.96). Furthermore, EGCG+RES supplementation attenuated the increase in plasma triacylglycerol concentrations during the HFMM test that was observed after placebo (P-time × treatment = 0.04, P-placebo = 0.01). Finally, EGCG+RES had no effect on insulin-stimulated glucose disposal, suppression of endogenous glucose production, or lipolysis. Twelve weeks of EGCG+RES supplementation increased mitochondrial capacity and stimulated fat oxidation compared with placebo, but this did not translate into increased tissue-specific insulin sensitivity in overweight and obese subjects. This trial was registered at clinicaltrials.gov as NCT02381145.

A novel protein tyrosine phosphatase 1B inhibitor with therapeutic potential for insulin resistance.

Insulin-sensitizing drugs are currently limited, and identifying new candidates is a challenge. Protein tyrosine phosphatase 1B (PTP1B) negatively regulates insulin signalling, and its inhibition is anticipated to improve insulin resistance. Here, the pharmacological properties of CX08005, a novel PTP1B inhibitor, were investigated. Recombinant hPTP1B protein was used to study enzyme activity and mode of inhibition. Docking simulation explored the interactions between CX08005 and PTP1B. Insulin sensitivity was evaluated by glucose tolerance test (GTT) in diet-induced obese (DIO) and KKAy mice; glucose-stimulated insulin secretion (GSIS), homeostasis model assessment of insulin resistance index (HOMA-IR) and whole-body insulin sensitivity (ISWB ) were also determined. A hyperinsulinaemic-euglycaemic clamp was performed to evaluate insulin-stimulated glucose disposal in both whole-body and insulin-sensitive tissues. Furthermore, CX08005's effects on muscle, fat and liver cells were determined in vitro. CX08005 competitively inhibited PTP1B by binding to the catalytic P-loop through hydrogen bonds. In DIO mice, CX08005 ameliorated glucose intolerance dose-dependently (50-200mg·kg(-1) ·day(-1) ) and decreased the HOMA-IR. In KKAy mice, CX08005 (50mg·kg(-1) ·day(-1) ) improved glucose intolerance, GSIS, ISWB and hyperglycaemia. CX08005 also enhanced insulin-stimulated glucose disposal, increased glucose infusion rate and glucose uptake in muscle and fat in DIO mice (hyperinsulinaemic-euglycaemic clamp test). CX08005 enhanced insulin-induced glucose uptake in 3T3-L1 adipocytes and C2C12 myotubes, and increased phosphorylation of IRβ/IRS1 and downstream molecules in hepatocytes in a dose- and insulin-dependent manner respectively. Our results strongly suggest that CX08005 directly enhances insulin action in vitro and in vivo through competitive inhibition of PTP1B.

Rehabilitative Exercise Training Increases Skeletal Muscle Contractile and Metabolic Function in Severely Burned Children

Wasting and deconditioning of skeletal muscle contributes to the prolonged morbidity observed in burn victims. PURPOSE: To study the impact of rehabilitative exercise training (RET) on skeletal muscle contractile and metabolic function in children recovering from major burns. METHODS: Twenty-one children (7-18 years) with burns covering ≥30% of their total body surface area were studied at approximately three and six months post-injury. Body composition, muscle strength (peak torque) and endurance (total work), insulin sensitivity (euglycemic-hyperinsulinemic clamp), and mitochondrial function (muscle biopsies) measurements were performed at each study. In the twelve intervening weeks, n=8 patients received standard rehabilitative care including occupational and physical therapy (standard of care, SoC), while n=13 patients performed a 12-week supervised outpatient RET program in addition to receiving standard care. RET consisted of progressive resistive and aerobic exercise performed at least 5-times weekly. RESULTS: Total and fat-free body mass significantly increased in the RET group only (P<0.05). Peak torque significantly increased with RET (+51%, P<0.001) but not in SoC (+35%, P=0.08). Total work significantly increased with RET (+66%, P<0.001) but not in SoC (+44%, P=0.23). Insulin stimulated glucose disposal tended to decrease in the SoC group (1.87±0.31 vs. 1.35±0.24 mg/min/kg; P=0.07) but significantly increased in the RET group (1.12±0.11 vs. 1.59±0.10 mg/min/kg; P=0.004). ADP-dependent mitochondrial respiration increased with RET (25.0±4.3 vs. 52.8±4.1 pmol/s/mg; P<0.001) but not SoC (37.6±4.7 vs. 41.7±6.4 pmol/s/mg). The mitochondrial respiratory control ratio for ADP increased with RET (1.54±0.12 vs. 2.27±0.12 pmol/s/mg; P=0.01) but not SoC (1.72±0.12 vs. 1.45±0.07). CONCLUSIONS: In agreement with previous studies, RET increases muscle strength and endurance in burn survivors. Here, we show that this is accompanied by increased peripheral insulin stimulated glucose disposal and skeletal muscle mitochondrial respiratory capacity and coupling control. These data demonstrate that in addition to contractile function, RET improves skeletal muscle metabolic function in burn survivors.

Impaired insulin action in the liver, but not in adipose tissue or muscle, is a distinct metabolic feature of impaired fasting glucose in obese humans

AimElevated basal endogenous glucose production (EGP), impaired suppression of EGP by insulin and reduced insulin-stimulated glucose disposal are cornerstones of the pathogenesis of hyperglycemia in patients with type 2 diabetes. We aimed to determine the contribution of these processes to impaired fasting glucose (IFG) levels in obese non-diabetic adults. MethodsWe included 131 obese non-diabetic adults with normal fasting glucose levels (NFG; fasting glucose <5.6mmol/L; 62 men, 25 women; mean±SEM age 49±1years; median (IQR) BMI 36 (34–41) kg/m2) or IFG (fasting glucose 5.6–6.9mmol/L; 35 men, 9 women; age 53±1years; BMI 36 (34–42) kg/m2) and studied basal EGP and hepatic, adipose tissue and peripheral insulin sensitivity by two-step euglycemic hyperinsulinemic clamp studies with [6,6-2H2]glucose infusion. ResultsCompared to equally obese adults with NFG, individuals with IFG did not differ in basal EGP (9.1±0.2 vs 9.8±0.3μmolkg−1min−1, p=0.082), insulin-mediated suppression of circulating free fatty acid levels (75±1 vs 72±3%, p=0.240) and insulin-stimulated glucose disposal (26.6±1.0 vs 25.2±1.5μmolkg−1min−1, p=0.441). Insulin-mediated suppression of EGP (68±2 vs 55±3%, p<0.001) was markedly reduced in obese subjects with IFG. ConclusionsHepatic insulin resistance is a distinct metabolic feature of IFG in obesity. Insulin sensitivity of free fatty acid suppression and skeletal muscle does not differ between obese people with NFG and IFG. Hepatic insulin resistance may contribute to the onset of prediabetes in obese adults.

Proteomics of Skeletal Muscle: Focus on Insulin Resistance and Exercise Biology.

Skeletal muscle is the largest tissue in the human body and plays an important role in locomotion and whole body metabolism. It accounts for ~80% of insulin stimulated glucose disposal. Skeletal muscle insulin resistance, a primary feature of Type 2 diabetes, is caused by a decreased ability of muscle to respond to circulating insulin. Physical exercise improves insulin sensitivity and whole body metabolism and remains one of the most promising interventions for the prevention of Type 2 diabetes. Insulin resistance and exercise adaptations in skeletal muscle might be a cause, or consequence, of altered protein expressions profiles and/or their posttranslational modifications (PTMs). Mass spectrometry (MS)-based proteomics offer enormous promise for investigating the molecular mechanisms underlying skeletal muscle insulin resistance and exercise-induced adaptation; however, skeletal muscle proteomics are challenging. This review describes the technical limitations of skeletal muscle proteomics as well as emerging developments in proteomics workflow with respect to samples preparation, liquid chromatography (LC), MS and computational analysis. These technologies have not yet been fully exploited in the field of skeletal muscle proteomics. Future studies that involve state-of-the-art proteomics technology will broaden our understanding of exercise-induced adaptations as well as molecular pathogenesis of insulin resistance. This could lead to the identification of new therapeutic targets.

Predictors of Whole-Body Insulin Sensitivity Across Ages and Adiposity in Adult Humans

Numerous factors are purported to influence insulin sensitivity including age, adiposity, mitochondrial function, and physical fitness. Univariate associations cannot address the complexity of insulin resistance or the interrelationship among potential determinants. The objective of the study was to identify significant independent predictors of insulin sensitivity across a range of age and adiposity in humans. Peripheral and hepatic insulin sensitivity were measured by two stage hyperinsulinemic-euglycemic clamps in 116 men and women (aged 19-78 y). Insulin-stimulated glucose disposal, the suppression of endogenous glucose production during hyperinsulinemia, and homeostatic model assessment of insulin resistance were tested for associations with 11 potential predictors. Abdominal subcutaneous fat, visceral fat (AFVISC), intrahepatic lipid, and intramyocellular lipid (IMCL) were quantified by magnetic resonance imaging and spectroscopy. Skeletal muscle mitochondrial respiratory capacity (state 3), coupling efficiency, and reactive oxygen species production were evaluated from muscle biopsies. Aerobic fitness was measured from whole-body maximum oxygen uptake (VO2 peak), and metabolic flexibility was determined using indirect calorimetry. Multiple regression analysis revealed that AFVISC (P < .0001) and intrahepatic lipid (P = .002) were independent negative predictors of peripheral insulin sensitivity, whereas VO2 peak (P = .0007) and IMCL (P = .023) were positive predictors. Mitochondrial capacity and efficiency were not independent determinants of peripheral insulin sensitivity. The suppression of endogenous glucose production during hyperinsulinemia model of hepatic insulin sensitivity revealed percentage fat (P < .0001) and AFVISC (P = .001) as significant negative predictors. Modeling homeostatic model assessment of insulin resistance identified AFVISC (P < .0001), VO2 peak (P = .001), and IMCL (P = .01) as independent predictors. The reduction in insulin sensitivity observed with aging is driven primarily by age-related changes in the content and distribution of adipose tissue and is independent of muscle mitochondrial function or chronological age.

Cognitively impaired elderly exhibit insulin resistance and no memory improvement with infused insulin

Insulin resistance is a risk factor for Alzheimer's disease (AD), although its role in AD etiology is unclear. We assessed insulin resistance using fasting and insulin-stimulated measures in 51 elderly subjects with no dementia (ND; n = 37) and with cognitive impairment (CI; n = 14). CI subjects exhibited either mild CI or AD. Fasting insulin resistance was measured using the homeostatic model assessment of insulin resistance (HOMA-IR). Insulin-stimulated glucose disposal was assessed using the hyperinsulinemic-euglycemic clamp to calculate glucose disposal rate into lean mass, the primary site of insulin-stimulated glucose disposal. Because insulin crosses the blood-brain barrier, we also assessed whether insulin infusion would improve verbal episodic memory compared to baseline. Different but equivalent versions of cognitive tests were administered in counterbalanced order in the basal and insulin-stimulated state. Groups did not differ in age or body mass index. Cognitively impaired subjects exhibited greater insulin resistance as measured at fasting (HOMA-IR; ND: 1.09 [1.1] vs. CI: 2.01 [2.3], p = 0.028) and during the hyperinsulinemic clamp (glucose disposal rate into lean mass; ND: 9.9 (4.5) vs. AD 7.2 (3.2), p = 0.040). Cognitively impaired subjects also exhibited higher fasting insulin compared to ND subjects, (CI: 8.7 [7.8] vs. ND: 4.2 [3.8] μU/mL; p = 0.023) and higher fasting amylin (CI: 24.1 [39.1] vs. 8.37 [14.2]; p = 0.050) with no difference in fasting glucose. Insulin infusion elicited a detrimental effect on one test of verbal episodic memory (Free and Cued Selective Reminding Test) in both groups (p < 0.0001) and no change in performance on an additional task (delayed logical memory). In this study, although insulin resistance was observed in cognitively impaired subjects compared to ND controls, insulin infusion did not improve memory. Furthermore, a significant correlation between HOMA-IR and glucose disposal rate was present only in ND (p = 0.0002) but not in cognitively impaired (p = 0.884) subjects, indicating potentially important physiological differences between these cohorts.