Total Glucose Disposal Research Articles

Development of a New Model of Insulin Sensitivity in Patients With Type 2 Diabetes and Association With Mortality.

Despite being one of the major drivers of diabetes incidence, the degree of insulin resistance in patients with type 2 diabetes (T2D) is not usually evaluated in clinical practice or in large epidemiologic studies. To identify a model of insulin sensitivity using widely available clinical and laboratory parameters in patients with T2D and evaluate its association with all-cause and cardiovascular mortality. One hundred forty patients with T2D underwent a euglycemic hyperinsulinemic clamp to measure total body glucose disposal rate (mg kg-1 minute-1). We used demographic, clinical, and common laboratory parameters to estimate insulin sensitivity (IS) via stepwise linear regression on 85 patients (training cohort) and validated it in the remaining 55 (validation cohort). The identified equation was then applied to 3553 patients with T2D from the 1999-2010 cycles of the National Health and Nutrition Examination Survey (NHANES) to evaluate its association with all-cause and cardiovascular mortality up to December 2015. The best model included triglycerides, gamma glutamyl transpeptidase, albumin excretion rate, and body mass index. The identified IS score correlated well with the clamp-derived glucose disposal rate in both the training (r = 0.77, P < .001) and the validation (r = 0.74, P < .001) cohorts. In the NHANES cohort, after a median follow-up of 8.3 years, 1054 patients died, 265 of cardiovascular causes. In a multivariable Cox proportional hazard model adjusted for age, sex, race-ethnicity, education, cigarette smoke, total cholesterol, chronic kidney disease, blood pressure, prevalent cardiovascular disease, and alcohol consumption, a higher estimated IS was associated with a lower risk of both all-cause and cardiovascular mortality. We propose a new model of IS in patients with T2D based on readily available clinical and laboratory data. Its potential applications are in both diagnosis as well as prognostication.

NSAID-Induced Enteropathy Affects Regulation of Hepatic Glucose Production by Decreasing GLP-1 Secretion.

Background/Aim: Given their widespread use and their notorious effects on the lining of gut cells, including the enteroendocrine cells, we explored if chronic exposure to non-steroidal anti-inflammatory drugs (NSAIDs) affects metabolic balance in a mouse model of NSAID-induced enteropathy. Method: We administered variable NSAIDs to C57Blk/6J mice through intragastric gavage and measured their energy balance, glucose hemostasis, and GLP-1 levels. We treated them with Exendin-9 and Exendin-4 and ran a euglycemic-hyperinsulinemic clamp. Results: Chronic administration of multiple NSAIDs to C57Blk/6J mice induces ileal ulcerations and weight loss in animals consuming a high-fat diet. Despite losing weight, NSAID-treated mice exhibit no improvement in their glucose tolerance. Furthermore, glucose-stimulated (glucagon-like peptide -1) GLP-1 is significantly attenuated in the NSAID-treated groups. In addition, Exendin-9—a GLP-1 receptor antagonist—worsens glucose tolerance in the control group but not in the NSAID-treated group. Finally, the hyper-insulinemic euglycemic clamp study shows that endogenous glucose production, total glucose disposal, and their associated insulin levels were similar among an ibuprofen-treated group and its control. Exendin-4, a GLP-1 receptor agonist, reduces insulin levels in the ibuprofen group compared to their controls for the same glucose exchange rates. Conclusions: Chronic NSAID use can induce small intestinal ulcerations, which can affect intestinal GLP-1 production, hepatic insulin sensitivity, and consequently, hepatic glucose production.

Skeletal Muscle Proteomic Profile Revealed Gender-Related Metabolic Responses in a Diet-Induced Obesity Animal Model.

Obesity is a chronic, complex pathology associated with a risk of developing secondary pathologies, including cardiovascular diseases, cancer, type 2 diabetes (T2DM) and musculoskeletal disorders. Since skeletal muscle accounts for more than 70% of total glucose disposal, metabolic alterations are strictly associated with the onset of insulin resistance and T2DM. The present study relies on the proteomic analysis of gastrocnemius muscle from 15 male and 15 female C56BL/J mice fed for 14 weeks with standard, 45% or 60% high-fat diets (HFD) adopting a label-free LC–MS/MS approach followed by bioinformatic pathway analysis. Results indicate changes in males due to HFD, with increased muscular stiffness (Col1a1, Col1a2, Actb), fiber-type switch from slow/oxidative to fast/glycolytic (decreased Myh7, Myl2, Myl3 and increased Myh2, Mylpf, Mybpc2, Myl1), increased oxidative stress and mitochondrial dysfunction (decreased respiratory chain complex I and V and increased complex III subunits). At variance, females show few alterations and activation of compensatory mechanisms to counteract the increase of fatty acids. Bioinformatics analysis allows identifying upstream molecules involved in regulating pathways identified at variance in our analysis (Ppargc1a, Pparg, Cpt1b, Clpp, Tp53, Kdm5a, Hif1a). These findings underline the presence of a gender-specific response to be considered when approaching obesity and related comorbidities.

An Analysis of Glucose Effectiveness in Subjects With or Without Type 2 Diabetes via Hierarchical Modeling.

Glucose effectiveness, defined as the ability of glucose itself to increase glucose utilization and inhibit hepatic glucose production, is an important mechanism maintaining normoglycemia. We conducted a minimal modeling analysis of glucose effectiveness at zero insulin (GEZI) using intravenous glucose tolerance test data from subjects with type 2 diabetes (T2D, n=154) and non-diabetic (ND) subjects (n=343). A hierarchical statistical analysis was performed, which provided a formal mechanism for pooling the data from all study subjects, to yield a single composite population model that quantifies the role of subject specific characteristics such as weight, height, age, sex, and glucose tolerance. Based on the resulting composite population model, GEZI was reduced from 0.021 min–1 (standard error – 0.00078 min–1) in the ND population to 0.011 min–1 (standard error – 0.00045 min–1) in T2D. The resulting model was also employed to calculate the proportion of the non–insulin-dependent net glucose uptake in each subject receiving an intravenous glucose load. Based on individual parameter estimates, the fraction of total glucose disposal independent of insulin was 72.8% ± 12.0% in the 238 ND subjects over the course of the experiment, indicating the major contribution to the whole-body glucose clearance under non-diabetic conditions. This fraction was significantly reduced to 48.8% ± 16.9% in the 30 T2D subjects, although still accounting for approximately half of the total in the T2D population based on our modeling analysis. Given the potential application of glucose effectiveness as a predictor of glucose intolerance and as a potential therapeutic target for treating diabetes, more investigations of glucose effectiveness in other disease conditions can be conducted using the hierarchical modeling framework reported herein.

MG53 is not a critical regulator of insulin signaling pathway in skeletal muscle

In type 2 diabetes (T2D), both muscle and liver are severely resistant to insulin action. Muscle insulin resistance accounts for more than 80% of the impairment in total body glucose disposal in T2D patients and is often characterized by an impaired insulin signaling. Mitsugumin 53 (MG53), a muscle-specific TRIM family protein initially identified as a key regulator of cell membrane repair machinery has been suggested to be a critical regulator of muscle insulin signaling pathway by acting as ubiquitin E3 ligase targeting both the insulin receptor and insulin receptor substrate 1 (IRS1). Here, we show using in vitro and in vivo approaches that MG53 is not a critical regulator of insulin signaling and glucose homeostasis. First, MG53 expression is not consistently regulated in skeletal muscle from various preclinical models of insulin resistance. Second, MG53 gene knock-down in muscle cells does not lead to impaired insulin response as measured by Akt phosphorylation on Serine 473 and glucose uptake. Third, recombinant human MG53 does not alter insulin response in both differentiated C2C12 and human skeletal muscle cells. Fourth, ectopic expression of MG53 in HEK293 cells lacking endogenous MG53 expression fails to alter insulin response as measured by Akt phosphorylation. Finally, both male and female mg53 -/- mice were not resistant to high fat induced obesity and glucose intolerance compared to wild-type mice. Taken together, these results strongly suggest that MG53 is not a critical regulator of insulin signaling pathway in skeletal muscle.

AKT2 regulates development and metabolic homeostasis via AMPK-depedent pathway in skeletal muscle.

Skeletal muscle is responsible for the majority of glucose disposal in the body. Insulin resistance in the skeletal muscle accounts for 85-90% of the impairment of total glucose disposal in patients with type 2 diabetes (T2D). However, the mechanism remains controversial. The present study aims to investigate whether AKT2 deficiency causes deficits in skeletal muscle development and metabolism, we analyzed the expression of molecules related to skeletal muscle development, glucose uptake and metabolism in mice of 3- and 8-months old. We found that AMP-activated protein kinase (AMPK) phosphorylation and myocyte enhancer factor 2 (MEF2) A (MEF2A) expression were down-regulated in AKT2 knockout (KO) mice, which can be inverted by AMPK activation. We also observed reduced mitochondrial DNA (mtDNA) abundance and reduced expression of genes involved in mitochondrial biogenesis in the skeletal muscle of AKT2 KO mice, which was prevented by AMPK activation. Moreover, AKT2 KO mice exhibited impaired AMPK signaling in response to insulin stimulation compared with WT mice. Our study establishes a new and important function of AKT2 in regulating skeletal muscle development and glucose metabolism via AMPK-dependent signaling.

2031-P: Obesity and Insulin Resistance Alter the Biodistribution of Whole Body Insulin-Stimulated Glucose Disposal

Insulin-stimulated whole-body (WB) glucose disposal (GD) is thought to occur predominately in skeletal muscle (SM). Studies in animals suggest adipose tissue (AT) could also be an important site of GD, especially in people with obesity and insulin resistance. The interrelationship between adiposity, insulin sensitivity, and organ-specific insulin-stimulated GD is not known. We evaluated WB, SM, and AT insulin-stimulated GD by using the hyperinsulinemic-euglycemic clamp procedure together with [6,6-2H2]glucose infusion and 18F-deoxyglucose positron emission tomography in healthy lean people (n=13, age: 39±12 yrs, BMI: 23±2 kg/m2; body fat: 31±7%, mean±SD) and 27 people with obesity, who were then characterized as insulin sensitive (OIS, n=9, age: 48±10 yrs, body fat: 45±10%) or insulin resistant (OIR, n=9, age: 40±10 yrs, body fat: 48±4%) based on the top and bottom tertile values for WB insulin-stimulated GD. WB insulin-stimulated GD was 60% lower in the OIR (1,636±283 µmol/min) than both the OIS and Lean groups (P&amp;lt;0.01), without a difference between the OIS and Lean groups (4,188±758 and 3,855±1115 µmol/min). Total GD in subcutaneous AT was lower in the OIR than the OIS group (392±134 vs. 663±224 µmol/min) and greater in the OIS than the Lean (305±97 µmol/min, P&amp;lt;0.01) group. However, the contribution of AT to WB GD was greater in the OIR than the OIS and Lean groups (24±6%, 16±5%, and 9±4% of WB GD, P&amp;lt;0.01). GD rate in four major muscle groups (erector spinae, obliques, hamstrings, quadriceps) was 75% lower in the OIR (median [IQR]: 29 [23-35] µmol/kg muscle/min) than the OIS and the Lean groups (P&amp;lt;0.01), without a difference between the OIS and Lean groups (115 [89-139] and 102 [90-127] µmol/kg muscle/min). We conclude that: 1) a decrease in insulin-stimulated SM GD is responsible for the decrease in WB insulin-stimulated GD in the OIR group and 2) AT is a more important site of insulin-stimulated GD in people with obesity, particularly those with insulin resistance, than lean people. Disclosure H. Koh: None. S. van Vliet: None. R. Laforest: None. R. Gropler: None. S. Klein: Advisory Panel; Self; Danone Nutricia, Merck &amp; Co., Inc. Research Support; Self; Johnson &amp; Johnson, Pfizer Inc. Stock/Shareholder; Self; Aspire Bariatrics. B. Mittendorfer: None. Funding American Diabetes Association (1-18-ICTS-119 to B.M.); National Institutes of Health (DK115400, DK56341, DK020579, UL1TR000448)

MON-613 The Expression of TBC1 Domain Family, Member 4 (TBC1D4) in Skeletal Muscles of Insulin-Resistant Mice in Response to Sulforaphane

The Expression of TBC1 Domain Family, member 4 (TBC1D4) in Skeletal Muscles of Insulin-Resistant Mice in Response to Sulforaphane. Background: Obesity is commonly accompanied by impaired glucose homeostasis. Decreased glucose transport to the peripheral tissues, mainly skeletal muscle, leads to reduced total glucose disposal and hyperglycemia. TBC1D4 gene is involved in the trafficking of GLUT4 to the outer cell membrane in skeletal muscle. Sulforaphane (SFN) has been suggested as a new potential anti-diabetic compound acting by reducing blood glucose levels through mechanisms not fully understood (1). The aim of this study is to investigate the effects SFN on TBC1D4 and GLUT4 gene expression in skeletal muscles of DIO mice, in order to elucidate the mechanism(s) through which SFN improves glucose homeostasis. Methodology: C57BL/6 mice (n=20) were fed with a high fat diet (60%) for 16 weeks to generate diet induced obese (DIO) mice with body weights between 45–50 gm. Thereafter, DIO mice received either SFN (5mg/kg BW) (n=10) or vehicle (n=10) as controls daily by intraperitoneal injections for four weeks. Glucose tolerance test (1g/kg BW, IP) and insulin sensitivity test (ITT) were conducted (1 IU insulin/ g BW, IP route) at the beginning and end of the third week of the injection.At the end of 4 weeks of the injection, samples of blood and skeletal muscles of both hindlimbs were collected. The expression levels of GLUT4 and TBC1D4 genes were analyzed by qRT-PCR. Blood was also used for glucose, adiponectin and insulin measurements. Results: SFN-treated DIO mice had significantly lower non-fasting blood glucose levels than vehicle-treated mice (194.16 ± 14.12 vs. 147.44 ± 20.31 mg/dL, vehicle vs. SFN, p value=0.0003). Furthermore, GTT results indicate that the blood glucose levels at 120 minutes after glucose infusion in was (199.83±34.53 mg/dl vs. 138.55±221.78 mg/dl) for vehicle vs. SFN with p=0.0011 respectively. ITT showed that SFN treatment did not enhance insulin sensitivity in DIO mice. Additionally, SFN treatment did not significantly change the expression of TBC1D4, and GLUT4 genes in skeletal muscles compared to vehicle treatment (p values >0.05).Furthermore, SFN treatment did not significantly affect the systemic insulin (1.84±0.74 vs 1.54±0.55 ng/ml, p=0.436), or adiponectin (11.96 ±2.29 vs 14.4±3.33 ug/ml, p=0.551) levels in SFN vs. vehicle-treated DIO mice, respectively. Conclusion: SFN treatment improves glucose disposal in DIO mice, which is not linked to the gene expression of GLUT4 and TBC1D4 and its mechanism of glucose disposal in skeletal muscles. Furthermore, SFN treatment did not improve insulin level, and the insulin sensitizer hormone adiponectin as potential players for enhancing insulin sensitivity.1.Axelsson AS, Tubbs E, Mecham B, Chacko S, Nenonen HA, Tang Y, et al. Sci Transl Med. 2017;9(394).

Substantial inter-individual variations in insulin secretion and sensitivity across the glucometabolic spectrum

Impaired insulin secretion and action are important for development of type 2 diabetes (T2D) and metabolic syndrome (MetS). Despite recognized heterogeneity of these glucometabolic disorders, few data are available of biological variation in insulin secretion and action among individuals with T2D and MetS. The aim of this study was to explore the inter-individual variations using gold standard methods in a cross-sectional study of two independent cohorts of phenotypically well-characterized subjects. Cohort I included 486 subjects with MetS, and cohort II 62 subjects with established T2D. First phase insulin secretion was defined as the incremental area under the curve 0–8 min (iAUC0–8 min) during an intravenous glucose tolerance test (IVGTT). Insulin sensitivity was measured as the insulin sensitivity index (SI) modelled from IVGTT in cohort I, and in II as total glucose disposal (TGD) estimated from a euglycaemic-hyperinsulinaemic clamp. Variation is given as total range and, fold-variation between 5%- and 95%-percentile. The iAUC0–8 min ranged from −60 to 3397 mUL−1min−1 among subjects with MetS and from −263 to 1194 mUL−1min−1 in subjects with T2D, representing a more than 10-fold variation. Insulin sensitivity ranged from SI 0.19 to 15.29 (mU/L)−1min−1 among subjects with MetS and TGD 12.9–101.6 μmolkgFFM−1min−1 in subjects with T2D, representing a 6.8 and 5.5-fold variation, respectively. The other components of MetS; BMI, waist-hip ratio, HDL-cholesterol, triglycerides and blood pressure (BP), showed a 1.4–4.7-fold variation. In conclusion, our data demonstrated extensive inter-individual variations in insulin secretion and sensitivity. These variations may be essential to take into account when planning clinical research and treatment in subjects with T2D and MetS.

Effect of Chronic Hyperglycemia on Glucose Metabolism in Subjects With Normal Glucose Tolerance.

Chronic hyperglycemia causes insulin resistance, but the inheritability of glucotoxicity and the underlying mechanisms are unclear. We examined the effect of 3 days of hyperglycemia on glucose disposal, enzyme activities, insulin signaling, and protein O-GlcNAcylation in skeletal muscle of individuals without (FH−) or with (FH+) family history of type 2 diabetes. Twenty-five subjects with normal glucose tolerance received a [3-3H]glucose euglycemic insulin clamp, indirect calorimetry, and vastus-lateralis biopsies before and after 3 days of saline (n = 5) or glucose (n = 10 FH− and 10 FH+) infusion to raise plasma glucose by ∼45 mg/dL. At baseline, FH+ had lower insulin-stimulated glucose oxidation and total glucose disposal (TGD) but similar nonoxidative glucose disposal and basal endogenous glucose production (bEGP) compared with FH−. After 3 days of glucose infusion, bEGP and glucose oxidation were markedly increased, whereas nonoxidative glucose disposal and TGD were lower versus baseline, with no differences between FH− and FH+ subjects. Hyperglycemia doubled skeletal muscle glycogen content and impaired activation of glycogen synthase (GS), pyruvate dehydrogenase, and Akt, but protein O-GlcNAcylation was unchanged. Insulin resistance develops to a similar extent in FH− and FH+ subjects after chronic hyperglycemia, without increased protein O-GlcNAcylation. Decreased nonoxidative glucose disposal due to impaired GS activation appears to be the primary deficit in skeletal muscle glucotoxicity.

Effects of Hyperglycemia on Skeletal Muscle Glucose Metabolism in Healthy Subjects

Background: Physiological hyperglycemia can induce skeletal muscle insulin resistance and alterations in metabolic glucose partitioning. We investigated the mechanisms driving this muscle glucotoxicity in response to a three day elevation of plasma glucose concentrations. Methods: Twenty-five lean, glucose tolerant subjects (mean ± SD age 46 ± 4 years; BMI 25 ± 1 kg/m2) underwent a euglycemic insulin clamp (80 mU/m2·min) at baseline and following three days of saline (n=5) or glucose (n=20) infusion to raise plasma glucose by 45 mg/dL. Oxidative (GOX), non-oxidative (NOGD) and total (TGD) glucose disposal were calculated from indirect calorimetry and glucose infusion rate. Skeletal muscle biopsies were obtained prior to and after each clamp for the determination of metabolite concentrations, protein phosphorylation and pyruvate dehydrogenase (PDH) activation status (PDHa). Data are presented as mean ± SE and were analyzed using two-way ANOVA. Results: Three days of glucose infusion increased basal (1.2 ± 0.1 vs. 4.3 ± 0.3) and insulin-stimulated (2.3 ± 0.2 vs. 4.8 ± 0.3 mg/kg/min) GOX by 3.5 and 2.2-fold, respectively (P&amp;lt;0.001), whereas NOGD was 51% lower (9.2 ± 2.6 vs. 4.5 ± 2.1 mg/kg/min; P&amp;lt;0.001), resulting in a 16% reduction in TGD (10.3 ± 2.4 vs. 8.7 ± 2.1 mg/kg/min; P&amp;lt;0.01). Muscle glycogen content was doubled (343 ± 18 vs. 759 ± 47 mmol/kg dry weight; P&amp;lt;0.001) and glycogen synthase phosphorylation (Ser641) was increased by 46% (P=0.03), whilst GSK3β phosphorylation (Ser9) tended to be reduced (P=0.07). Glucose infusion also reduced insulin-stimulated PDHa by 20% (P=0.02) and Akt phosphorylation (Ser473) by 27% (P=0.03). No changes were observed in the saline group. Conclusion: Hyperglycemia caused a robust increase in basal GOX, such that further insulin-stimulated activation of GOX (distal insulin signaling and PDH) was impaired. Deficits in NOGD, and subsequently, TGD likely occur as a consequence of perturbed glycogen synthase activation in the face of augmented muscle glycogen concentrations. Disclosure C. Shannon: None. A. Merovci: None. D. Tripathy: None. M. Abdul-Ghani: None. L. Norton: None. R.A. DeFronzo: Speaker's Bureau; Self; AstraZeneca, Novo Nordisk Inc.. Advisory Panel; Self; AstraZeneca, Novo Nordisk Inc., Janssen Pharmaceuticals, Inc., Boehringer Ingelheim Pharmaceuticals, Inc., Elcelyx Therapeutics, Inc., Intarcia Therapeutics, Inc.. Research Support; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Takeda Pharmaceuticals U.S.A., Inc..

Increased lipid availability for three days reduces whole body glucose uptake, impairs muscle mitochondrial function and initiates opposing effects on PGC-1α promoter methylation in healthy subjects.

AimsFFA and FFA metabolites cause insulin resistance and impair beta cell function. The goal of our research was to examine whether elevation of plasma FFA impairs mitochondrial function and alters PGC-1α promoter methylation.MethodsIn this uncontrolled, change from baseline study design, insulin sensitivity and glucose-stimulated insulin secretion were measured in 9 normal glucose tolerant subjects before and after 3 day lipid infusion to elevate plasma FFA concentration. Vastus lateralis muscle biopsies were obtained and mitochondrial function, PGC-1α expression, and PGC-1α promoter methylation were quantitated.ResultsIncreased plasma FFA (440±93 μmol/Lto 997±242 μM, p<0.001) decreased insulin-stimulated total glucose disposal (TGD) by 25% (p = 0.008), impaired suppression of endogenous glucose production (p = 0.01), and reduced mitochondrial ATP synthesis with complex 1 (34%, p<0.05) and complex 2 (30%, p<0.05) substrates. Lipid infusion had no effect on muscle PGC-1α RNA expression, total methylation or non-CpG methylation, but methylation of the alternative PGC-1α promoter decreased (1.30±0.30 to 0.84±0.15% methylated residues/patient•strand, p = 0.055). Within PGC-1α promoter there was demethylation of CpT residues (0.72±0.16 vs. 0.28±0.10 methylated residues/patient•strand) (p = 0.002), which was inversely correlated with PGC-1α mRNA expression (r = -0.94, p<0.0001) and ATP synthesis with complex 1 (r = -0.80, p<0.01) and complex 2 (r = -0.69, p<0.05) substrates. Lipid infusion increased DNMT-3B (methyltransferase associated with PGC-1α promoter non-CpG methylation) mRNA expression (0.87 ± 0.09 to 1.62 ± 0.22 arbitrary units, p = 0.005), which correlated inversely with CpT demethylation (r = 0.67, p<0.05).Conclusion/InterpretationPhysiologic plasma FFA elevation in NGT individuals has opposing effects on PGC-1α non-CpG residue methylation (CpT demethylation and increased DNMT-3B expression), which is correlated with changes in PGC-1α expression and skeletal muscle mitochondrial function.

Effects of the BET-inhibitor, RVX-208 on the HDL lipidome and glucose metabolism in individuals with prediabetes: A randomized controlled trial

AimsHigh-density lipoprotein (HDL) and apolipoprotein A-I (apoA-I) can modulate glucose metabolism through multiple mechanisms. This study determined the effects of a novel bromodomain and extra-terminal (BET) inhibitor (RVX-208) and putative apoA-I inducer on lipid species contained within HDL (HDL lipidome) and glucose metabolism. Materials and methodsTwenty unmedicated males with prediabetes received 100mg b.i.d. RVX-208 and placebo for 29–33days separated by a wash-out period in a randomized, cross-over design trial. Plasma HDL-cholesterol and apoA-I were assessed as well as lipoprotein particle size and distribution using NMR spectroscopy. An oral glucose tolerance test (OGTT) protocol with oral and infused stable isotope tracers was employed to assess postprandial plasma glucose, indices of insulin secretion and insulin sensitivity, glucose kinetics and lipolysis. Whole plasma and HDL lipid profiles were measured using mass spectrometry. ResultsRVX-208 treatment for 4weeks increased 6 sphingolipid and 4 phospholipid classes in the HDL lipidome (p≤0.05 versus placebo), but did not change conventional clinical lipid measures. The concentration of medium-sized HDL particles increased by 11% (P=0.01) and small-sized HDL particles decreased by 10% (P=0.04) after RVX-208 treatment. In response to a glucose load, after RVX-208 treatment, plasma glucose peaked at a similar level to placebo, but 30min later with a more sustained elevation (treatment effect, P=0.003). There was a reduction and delay in total (P=0.001) and oral (P=0.003) glucose rates of appearance in plasma and suppression of endogenous glucose production (P=0.014) after RVX-208 treatment. The rate of glucose disappearance was also lower following RVX-208 (P=0.016), with no effect on glucose oxidation or total glucose disposal. ConclusionsRVX-208 increased 10 lipid classes in the plasma HDL fraction, without altering the concentrations of either apoA-I or HDL-cholesterol (HDL-C). RVX-208 delayed and reduced oral glucose absorption and endogenous glucose production, with plasma glucose maintained via reduced peripheral glucose disposal. If sustained, these effects may protect against the development of type 2 diabetes.

Fish oil supplemented for 9 months does not improve glycaemic control or insulin sensitivity in subjects with impaired glucose regulation: a parallel randomised controlled trial.

The effects of fish oil (FO) supplementation on glycaemic control are unclear, and positive effects may occur only when the phospholipid content of tissue membranes exceeds 14% as n-3 PUFA. Subjects (n 36, thirty-three completed) were paired based on metabolic parameters and allocated into a parallel double-blind randomised trial with one of each pair offered daily either 6 g of FO (3·9 g n-3 PUFA) or 6 g of maize oil (MO) for 9 months. Hyperinsulinaemic-euglycaemic-euaminoacidaemic (HIEGEAA) clamps (with [6,6 2H2 glucose]) were performed at the start and end of the intervention. Endogenous glucose production (EGP) and whole-body protein turnover (WBPT) were each measured after an overnight fast. The primary outcome involved the effect of oil type on insulin sensitivity related to glycaemic control. The secondary outcome involved the effect of oil type on WBPT. Subjects on FO (n 16) had increased erythrocyte n-3 PUFA concentrations >14%, whereas subjects on MO (n 17) had unaltered n-3 PUFA concentrations at 9%. Type of oil had no effect on fasting EGP, insulin sensitivity or total glucose disposal during the HIEGEAA clamp. In contrast, under insulin-stimulated conditions, total protein disposal (P=0·007) and endogenous WBPT (P=0·001) were both increased with FO. In an associated pilot study (n 4, three completed), although n-3 PUFA in erythrocyte membranes increased to >14% with the FO supplement, the enrichment in muscle membranes remained lower (8%; P<0·001). In conclusion, long-term supplementation with FO, at amounts near the safety limits set by regulatory authorities in Europe and the USA, did not alter glycaemic control but did have an impact on WBPT.

Body Mass Index below Obesity Threshold Implies Similar Cardiovascular Risk among Various Polycystic Ovary Syndrome Phenotypes

Objective: The aim of this study was to determine the cardiometabolic risk factors in different polycystic ovary syndrome (PCOS) phenotypes. Subjects and Methods: This cross-sectional study was performed between 2010 and 2011. Eighty-nine patients with PCOS and 25 age- and weight-matched healthy controls were included in the study. Patients were grouped using the Rotterdam 2003 criteria as: group 1, oligomenorrhea and/or anovulation (ANOV) and hyperandrogenemia (HA) and/or hyperandrogenism (n = 23); group 2, ANOV and polycystic ovaries (PCO; n = 22); group 3, HA and PCO (n = 22); group 4, ANOV, HA and PCO (n = 22); group 5, controls (n = 25). Laboratory blood tests for diagnosis and cardiometabolic risk assessments were performed. Insulin resistance (IR) was calculated in all patients with the homeostasis model assessment of IR (HOMA-IR) formula. An euglycemic hyperinsulinemic clamp test was performed on 5 randomly selected cases in each subgroup, making 25 cases in total, and indicated as the ‘M' value (mg/kg/min), which is the total body glucose disposal rate. Results: The mean BMl values of the groups were: group 1, 26.1 ± 5.3; group 2, 27.9 ± 5.2; group 3, 24.3 ± 4.2; group 4, 27.9 ± 7.5; group 5, 24.7 ± 5.2 (p > 0.05). There were no differences in the lipid profile, plasma glucose, HOMA-IR, insulin and M values between the groups (p > 0.05). Phenotypes with oligomenorrhea/anovulation (groups 1, 2 and 4) were more obese than group 3 (p = 0.039). Conclusions: The cardiometabolic risk profile was similar among the PCOS subgroups. This finding could be attributed to the mean BMl values, which, being below 30, were not within the obesity range. Obesity appeared to be an important determinant of high cardiovascular risk in PCOS.

Sclerostin and Insulin Resistance in Prediabetes: Evidence of a Cross Talk Between Bone and Glucose Metabolism.

A gene mutation of the Wnt/β-catenin signaling cascade is present in rare patients with the insulin resistance syndrome. Sclerostin is a circulating peptide inhibiting Wnt/β-catenin signaling. Our aims were to evaluate serum sclerostin in subjects with prediabetes and to analyze its relationship with insulin resistance and β-cell function. We performed a cross-sectional study including 43 healthy normal glucose-tolerant (NGT) individuals and 79 individuals with impaired glucose regulation (IGR), which included subjects with impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and combined IFG-IGT, undergoing oral glucose tolerance test (OGTT) and dual-energy X-ray absorptiometry. A subgroup of 18 with NGT and 30 with IGR also underwent a euglycemic-hyperinsulinemic clamp with tracer. Sclerostin levels were higher in IGR compared with NGT (50.8 ± 2.4 vs. 38.7 ± 2.3 pmol/L; P = 0.01), positively correlated with HOMA-insulin resistance (IR) (r = 0.62; P < 0.001), and negatively correlated with insulin-mediated total body glucose disposal (r = -0.40; P < 0.001). Fasting endogenous glucose production (EGP) and hepatic and adipose tissue insulin resistance indexes were positively correlated with sclerostin levels (r = 0.48, r = 0.62, and r = 0.61, respectively; P < 0.001). Fasting and OGTT insulin clearance were inversely correlated with sclerostin serum levels (r = -0.52 and r = -0.44, respectively; both P < 0.001). Sclerostin levels were not correlated with β-cell function parameters. In multiple linear regression analysis, the addition of sclerostin levels to the traditional risk factors for insulin resistance improved the r(2) associated with HOMA-IR (r(2) change: 0.055; F change: 28.893; P = 0.001) and insulin-mediated total body glucose disposal (r(2) change: 0.059; F change: 4.938; P = 0.033). Sclerostin levels are increased in individuals with prediabetes and correlated with insulin resistance in skeletal muscle, liver, and adipose tissue. The correlation between sclerostin and insulin clearance at fasting state and during OGTT is novel; thus, studies are needed to explore the potential causal relationship.

Brown adipose tissue--not as hot as we thought.

The article by Blondin et al. (2015) in the current issue of The Journal of Physiology brings together and expands upon three adipose/muscle-related concepts that emphasize the importance of understanding physiology before jumping to conclusions when new findings are reported. First, the excitement following the reports of brown adipose tissue (BAT) in 2009 (Cypess et al. 2009; van Marken Lichtenbelt et al. 2009; Virtanen et al. 2009) has spawned a number of additional, enthusiastic reports of human BAT activity (Orava et al. 2011). Some authors suggest that BAT accounts for up to 20% of the cold-stimulated increase in energy expenditure in humans (Cypess et al. 2009). In the rush to characterize BAT as the next frontier in obesity treatment investigators have largely ignored the obligate relationship between energy expenditure and oxygen delivery, which in turn is dependent upon blood flow and tissue mass. Adipose tissue blood flow is notoriously low relative to metabolically active tissues (Summers et al. 1996; Karpe et al. 2002), and it turns out that BAT is not an exception. Even during cold exposure BAT blood flow averages only 13 ml (100 g tissue)−1 min−1 (Muzik et al. 2012, 2013). Under conditions of normal oxygen saturation and 16 g dl−1 of haemoglobin, 100 ml of arterial blood contains only 21.3 ml of O2. With an average total body BAT volume of 57 ml, the amount of oxygen delivered to total body BAT would be only ∼1.6 ml min−1. Furthermore, BAT oxygen extraction is reported to be ∼56% (Muzik et al. 2012). Thus, under steady-state, cold-stimulated conditions, average whole-body BAT oxygen consumption should be ∼1 ml min−1, very similar to that measured using oxygen isotopes and PET approaches (Muzik et al. 2012). This is underwhelming considering the cold-induced increase in oxygen uptake of ∼270 ml min−1 that was observed by Blondin et al. (2015). The BAT oxygen uptake data (Muzik et al. 2012, 2013) are consistent with the limited total body BAT glucose uptake relative to the increase in total glucose disposal in response to cold (Blondin et al. 2015). Even individuals at the high end of BAT blood flow (25 ml (100 g tissue)−1 min−1; Orava et al. 2011) and with 100 g of total body BAT, actual BAT thermogenesis would account for only ∼1% of the increase in energy expenditure above basal induced by cold exposure. The second important observation is the contribution of subclinical muscle shivering to cold-induced increases in muscle glucose uptake and presumably energy expenditure. Blondin et al.’s careful and extensive use of surface electromyography showed that muscle contraction (shivering) is the major component of the increase in whole-body glucose uptake. This suggests that investigations directed at the role of muscle, rather than BAT, will be more promising. Finally, the observation by Blondin et al. (2015) that the cold-induced increase in non-esterified fatty acid release from adipose tissue lipolysis relates to the activation of BAT is important. It is consistent with animal data indicating that the sympathetic innervation of BAT and white adipose tissue (WAT) is similar (reviewed in Vaughan et al. 2014). This implies that variations in sympathetic activation or the sensitivity to such activation is similar in human BAT and WAT. If the former, then variations in observed BAT activation during cold exposure could reflect more of a central nervous system sympathetic response to cold rather than a peripheral, e.g. BAT, difference. In summary, the findings of Musik (Muzik et al. 2012, 2013) and Blondin et al. (2015) suggest to me that BAT is most likely a vestigial and largely irrelevant tissue when it comes to adult human energy expenditure. They also provide some renewed excitement about the role of muscle in resting energy expenditure. None declared.

Acute and Short-term Chronic Testosterone Fluctuation Effects on Glucose Homeostasis, Insulin Sensitivity, and Adiponectin: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study

Low levels of adiponectin and T in men have been shown to predict development of the metabolic syndrome, but the effects of T on glucose metabolism are incompletely understood and may be influenced either directly or indirectly through changes in body composition or in levels of adiponectin. The aim of the study was to test whether T exerts its effects on glucose metabolism directly or indirectly. In a randomized, double-blind, placebo-controlled, crossover study, 12 healthy young males were studied on four separate occasions. They received GnRH agonist treatment 1 month before 3 of 4 trial days to induce castrate levels of T. On trial days, T gel containing either high or low physiological T dose or placebo was applied to the body. On a fourth trial day, participants constituted their own eugonadal controls. Each study comprised a 5-hour basal period and a 3-hour hyperinsulinemic euglycemic clamp. We measured the effect of acute T on peripheral glucose disposal, total adiponectin and subforms, and other indices of glucose metabolism. Short-term hypogonadism was associated with increased high molecular weight adiponectin levels (P < .03) and increased oxidative glucose disposal (P = .03) but not total glucose disposal (P = .07). Acute T treatment was an independent suppressor of high molecular weight adiponectin levels (P = .04) but did not affect total glucose disposal (P = .17). These data show that T can act through putative fast nongenomic pathways to affect adiponectin levels in humans. The early hypogonadal state is characterized by a marked shift in fuel oxidation from lipids toward glucose, which may rely partly on buffering capabilities of adiponectin.

Characteristics of Glucose Metabolism in Nordic and South Asian Subjects with Type 2 Diabetes

BackgroundInsulin resistance and type 2 diabetes are more prevalent in people of South Asian ethnicity than in people of Western European origin. To investigate the source of these differences, we compared insulin sensitivity, insulin secretion, glucose and lipid metabolism in South Asian and Nordic subjects with type 2 diabetes.MethodsForty-three Nordic and 19 South Asian subjects with type 2 diabetes were examined with intra-venous glucose tolerance test, euglycemic clamp including measurement of endogenous glucose production, indirect calorimetry measuring glucose and lipid oxidation, and dual x-ray absorptiometry measuring body composition.ResultsDespite younger mean ± SD age (49.7±9.4 vs 58.3±8.3 years, p = 0.001), subjects of South Asian ethnicity had the same diabetes duration (9.3±5.5 vs 9.6±7.0 years, p = 0.86), significantly higher median [inter-quartile range] HbA1c (8.5 [1.6] vs 7.3 [1.6] %, p = 0.024) and lower BMI (28.7±4.0 vs 33.2±4.7 kg/m2, p<0.001). The South Asian group exhibited significantly higher basal endogenous glucose production (19.1 [9.1] vs 14.4 [6.8] µmol/kgFFM⋅min, p = 0.003). There were no significant differences between the groups in total glucose disposal (39.1±20.4 vs 39.2±17.6 µmol/kgFFM⋅min, p = 0.99) or first phase insulin secretion (AUC0–8 min: 220 [302] vs 124 [275] pM, p = 0.35). In South Asian subjects there was a tendency towards positive correlations between endogenous glucose production and resting and clamp energy expenditure.ConclusionsSubjects of South Asian ethnicity with type 2 diabetes, despite being younger and leaner, had higher basal endogenous glucose production, indicating higher hepatic insulin resistance, and a trend towards higher use of carbohydrates as fasting energy substrate compared to Nordic subjects. These findings may contribute to the understanding of the observed differences in prevalence of type 2 diabetes between the ethnic groups.

Canagliflozin lowers postprandial glucose and insulin by delaying intestinal glucose absorption in addition to increasing urinary glucose excretion: results of a randomized, placebo-controlled study.

OBJECTIVECanagliflozin, a sodium glucose cotransporter (SGLT) 2 inhibitor, is also a low-potency SGLT1 inhibitor. This study tested the hypothesis that intestinal canagliflozin levels postdose are sufficiently high to transiently inhibit intestinal SGLT1, thereby delaying intestinal glucose absorption.RESEARCH DESIGN AND METHODSThis two-period, crossover study evaluated effects of canagliflozin on intestinal glucose absorption in 20 healthy subjects using a dual-tracer method. Placebo or canagliflozin 300 mg was given 20 min before a 600-kcal mixed-meal tolerance test. Plasma glucose, 3H-glucose, 14C-glucose, and insulin were measured frequently for 6 h to calculate rates of appearance of oral glucose (RaO) in plasma, endogenous glucose production, and glucose disposal.RESULTSCompared with placebo, canagliflozin treatment reduced postprandial plasma glucose and insulin excursions (incremental 0- to 2-h area under the curve [AUC0–2h] reductions of 35% and 43%, respectively; P < 0.001 for both), increased 0- to 6-h urinary glucose excretion (UGE0–6h, 18.2 ± 5.6 vs. <0.2 g; P < 0.001), and delayed RaO. Canagliflozin reduced AUC RaO by 31% over 0 to 1 h (geometric means, 264 vs. 381 mg/kg; P < 0.001) and by 20% over 0 to 2 h (576 vs. 723 mg/kg; P = 0.002). Over 2 to 6 h, canagliflozin increased RaO such that total AUC RaO over 0 to 6 h was <6% lower versus placebo (960 vs. 1,018 mg/kg; P = 0.003). A modest (∼10%) reduction in acetaminophen absorption was observed over the first 2 h, but this difference was not sufficient to explain the reduction in RaO. Total glucose disposal over 0 to 6 h was similar across groups.CONCLUSIONSCanagliflozin reduces postprandial plasma glucose and insulin by increasing UGE (via renal SGLT2 inhibition) and delaying RaO, likely due to intestinal SGLT1 inhibition.