Whole-body Insulin Sensitivity Research Articles

Impaired Suppression of Glucagon in Obese Subjects Parallels Decline in Insulin Sensitivity and Beta-Cell Function.

To examine the relationship between plasma glucagon levels and insulin sensitivity and insulin secretion in obese subjects. Suppression of plasma glucagon was examined in 275 obese Hispanic Americans with varying glucose tolerance. All subjects received a 2-hour oral glucose tolerance test (OGTT) and a subset (n = 90) had euglycemic hyperinsulinemic clamp. During OGTT, we quantitated suppression of plasma glucagon concentration, Matsuda index of insulin sensitivity, and insulin secretion/insulin resistance (disposition) index. Plasma glucagon suppression was compared between quartiles of insulin sensitivity and beta-cell function. Fasting plasma glucagon levels were similar in obese subjects with normal glucose tolerance (NGT), prediabetes, and type 2 diabetes (T2D), but the fasting glucagon/insulin ratio decreased progressively from NGT to prediabetes to T2D (9.28 ± 0.66 vs 6.84 ± 0.44 vs 5.84 ± 0.43; P < 0.001). Fasting and 2-hour plasma glucagon levels during OGTT progressively increased and correlated positively with severity of insulin resistance (both Matsuda index and euglycemic hyperinsulinemic clamp). The fasting glucagon/insulin ratio declined with worsening insulin sensitivity and beta-cell function, and correlated with whole-body insulin sensitivity (Matsuda index, r = 0.81; P < 0.001) and beta-cell function (r = 0.35; P < 0.001). The glucagon/insulin ratio also correlated and with beta-cell function during OGTT at 60 and 120 minutes (r = -0.47; P < 0.001 and r = -0.32; P < 0.001). Insulin-mediated suppression of glucagon secretion in obese subjects is impaired with increasing severity of glucose intolerance and parallels the severity of insulin resistance and beta-cell dysfunction.

Prevalence and Features of Impaired Glucose Tolerance in Young Underweight Japanese Women.

In Japan, while it is known that underweight women over the age of 40 years have a high risk for type 2 diabetes, there is a lack of clarity on the association between glucose tolerance and underweight in younger women. Accordingly, we investigate the prevalence and features of impaired glucose tolerance (IGT) in young underweight Japanese women. In this cross-sectional study, we recruited 56 normal weight and 98 underweight young Japanese women and evaluated their glucose tolerance levels using an oral glucose tolerance test. Then, we compared the clinical characteristics associated with normal glucose tolerance (NGT) and IGT in the underweight women. Insulin secretion, whole-body insulin sensitivity, and adipose tissue insulin resistance values were measured using the insulinogenic index, whole-body insulin sensitivity index (Matsuda index), and adipose insulin resistance index (Adipo-IR), respectively. Fitness level (peak VO2) was measured using an ergometer. The prevalence of IGT was higher in the underweight women than the normal weight women (13.3% vs 1.8%). The underweight women with IGT showed a lower insulinogenic index, lower peak VO2, and Matsuda index and a higher fasting free fatty acid level and Adipo-IR than those with NGT. The whole-body composition was comparable between the NGT and IGT groups. The prevalence of IGT was higher in young Japanese women with underweight than those with a normal weight. The underweight women with IGT showed impaired early-phase insulin secretion, low fitness levels, and reduced whole-body and adipose tissue insulin sensitivity levels.

Time-restricted feeding normalizes hyperinsulinemia to inhibit breast cancer in obese postmenopausal mouse models

Accumulating evidence indicates that obesity with its associated metabolic dysregulation, including hyperinsulinemia and aberrant circadian rhythms, increases the risk for a variety of cancers including postmenopausal breast cancer. Caloric restriction can ameliorate the harmful metabolic effects of obesity and inhibit cancer progression but is difficult to implement and maintain outside of the clinic. In this study, we aim to test a time-restricted feeding (TRF) approach on mouse models of obesity-driven postmenopausal breast cancer. We show that TRF abrogates the obesity-enhanced mammary tumor growth in two orthotopic models in the absence of calorie restriction or weight loss. TRF also reduces breast cancer metastasis to the lung. Furthermore, TRF delays tumor initiation in a transgenic model of mammary tumorigenesis prior to the onset of obesity. Notably, TRF increases whole-body insulin sensitivity, reduces hyperinsulinemia, restores diurnal gene expression rhythms in the tumor, and attenuates tumor growth and insulin signaling. Importantly, inhibition of insulin secretion with diazoxide mimics TRF whereas artificial elevation of insulin through insulin pumps implantation reverses the effect of TRF, suggesting that TRF acts through modulating hyperinsulinemia. Our data suggest that TRF is likely to be effective in breast cancer prevention and therapy.

Sensory neurons expressing calcitonin gene-related peptide α regulate adaptive thermogenesis and diet-induced obesity

ObjectivesHeat-sensory neurons from the dorsal root ganglia (DRG) play a pivotal role in detecting the cutaneous temperature and transmission of external signals to the brain, ensuring the maintenance of thermoregulation. However, whether these thermoreceptor neurons contribute to adaptive thermogenesis remains elusive. It is also unknown whether these neurons play a role in obesity and energy metabolism. MethodsWe used genetic ablation of heat-sensing neurons expressing calcitonin gene-related peptide α (CGRPα) to assess whole-body energy expenditure, weight gain, glucose tolerance, and insulin sensitivity in normal chow and high-fat diet-fed mice. Exvivo lipolysis and transcriptional characterization were combined with adipose tissue-clearing methods to visualize and probe the role of sensory nerves in adipose tissue. Adaptive thermogenesis was explored using infrared imaging of intrascapular brown adipose tissue (iBAT), tail, and core temperature upon various stimuli including diet, external temperature, and the cooling agent icilin. ResultsIn this report, we show that genetic ablation of heat-sensing CGRPα neurons promotes resistance to weight gain upon high-fat diet (HFD) feeding and increases energy expenditure in mice. Mechanistically, we found that loss of CGRPα-expressing sensory neurons was associated with reduced lipid deposition in adipose tissue, enhanced expression of fatty acid oxidation genes, higher exvivo lipolysis in primary white adipocytes, and increased mitochondrial respiration from iBAT. Remarkably, mice lacking CGRPα sensory neurons manifested increased tail cutaneous vasoconstriction at room temperature. This exacerbated cold perception was not associated with reduced core temperature, suggesting that heat production and heat conservation mechanisms were engaged. Specific denervation of CGRPα neurons in intrascapular BAT did not contribute to the increased metabolic rate observed upon global sensory denervation. ConclusionsTaken together, these findings highlight an important role of cutaneous thermoreceptors in regulating energy metabolism by triggering counter-regulatory responses involving energy dissipation processes including lipid fuel utilization and cutaneous vasodilation.

Maternal Overweight vs. Polycystic Ovary Syndrome: Disentangling Their Impact on Insulin Action in Pregnancy-A Prospective Study.

Background: To investigate insulin sensitivity and glucose metabolism in pregnant lean and overweight polycystic ovary syndrome (PCOS) patients vs. lean and overweight controls without PCOS. Methods: Prospective cohort study on 67 pregnant women (31 with PCOS and 36 controls, subdivided into overweight or obese and normal weight). All women underwent a 2h-OGTT including glucose, insulin, and C-peptide in early- and mid-gestation and were followed-up until delivery. Results: Insulin sensitivity and glucometabolic parameters were comparable between PCOS patients and controls, whereas marked differences were observed between overweight/obese and lean mothers. Impaired whole-body insulin sensitivity at early pregnancy is mainly a consequence of higher BMI (body mass index; p < 0.001) compared to PCOS (p = 0.216), whereby no interaction between overweight/obesity and PCOS was observed (p = 0.194). Moreover, overweight was significantly associated with gestational diabetes (p = 0.0003), whereas there were no differences between women with and without PCOS (p = 0.51). Birth weight was inversely related to whole-body insulin sensitivity (rho = −0.33, p = 0.014) and positively associated with higher pregestational BMI (rho = 0.33, p = 0.012), whereas there was no association with PCOS. Conclusions: Impaired insulin action was mainly a consequence of overweight rather than PCOS. Our data suggest that overweight is more relevant than PCOS for the effects on insulin sensitivity and impaired glucose metabolism.

Stimulation of endogenous pulsatile growth hormone secretion by activation of growth hormone secretagogue receptor reduces the fat accumulation and improves the insulin sensitivity in obese mice.

Obese individuals often show low growth hormone (GH) secretion, which leads to reduced lipid mobilization and further fat accumulation. Pharmacological approaches to increase GH levels in obese individuals by GH injection or GH-releasing hormone receptor agonist showed promising effects on fat reduction. However, side effects on glucose metabolism and the heavy costs on making large peptides hindered their clinical application. Here, we tested whether stimulation of endogenous GH secretion by a synthetic GH secretagogue receptor (GHSR) agonist, hexarelin, improved the metabolism in a hyperphagic obese mouse model. Male melanocortin 4 receptor knockout mice (MC4RKO) were pair-fed and received continuous hexarelin (10.56μg/day) or vehicle infusion by an osmotic pump for 3-4weeks. Hexarelin treatment significantly increased the pulsatile GH secretion without detectable alteration on basal GH secretion in MC4RKO mice. The treated mice showed increased lipolysis and lipid oxidation in the adipose tissue, and reduced de novo lipogenesis in the liver, leading to reduced visceral fat mass, reduced triglyceride content in liver, and unchanged circulating free fatty acid levels. Importantly, hexarelin treatment improved the whole-body insulin sensitivity but did not alter glucose tolerance, insulin levels, or insulin-like growth factor 1 (IGF-1) levels. The metabolic effects of hexarelin were likely through the direct action of GH, as indicated by the increased expression level of genes involved in GH signaling pathways in visceral adipose tissues and liver. In conclusion, hexarelin treatment stimulated the pulsatile GH secretion and reduced the fat accumulation in visceral depots and liver in obese MC4RKO mice with improved insulin sensitivity without altered levels of insulin or IGF-1. It provides evidence for managing obesity by enhancing pulsatile GH secretion through activation of GHSR in the pituitary gland.

Ca2+/calmodulin-dependent protein kinase IV attenuates inflammation and mitochondrial dysfunction under insulin resistance in C2C12 cells

CaMKIV has been reported involved in the improvement of whole-body insulin sensitivity and mitochondrial biogenesis of skeletal muscle. Here, we first investigate the effects of CaMKIV on glucose metabolism, cell viability, inflammatory function, and mitochondrial function in palmitate-induced C2C12 cells of insulin resistance. Then we explored the potential mechanism of these effects. Differentiated C2C12 cells were treated with or without 100 ng/ml of CaMKIV under palmitate-induced insulin resistance. The results suggest palmitate induced insulin sensitivity, reduced glucose uptake, decreased cell viability, increased inflammatory factors, and caused mitochondrial dysfunction in C2C12 cells. Of note, CaMKIV reversed palmitate-induced insulin resistance, increased the reduction of glucose uptake, inhibited inflammatory response, and mitochondrial dysfunction, despite of no change in cells viabilities. However, these beneficial effects of CaMKIV were blocked by the downregulation of CREB1. Taken together, our data demonstrated CaMKIV prevents palmitate-induced insulin resistance, inflammatory response, and mitochondrial dysfunction through phosphorylated CREB1 in differentiated C2C12 cells.

Molecular mechanism of down-regulating adipogenic transcription factors in 3T3-L1 adipocyte cells by bioactive anti-adipogenic compounds.

Obesity is growing at an alarming rate, which is characterized by increased adipose tissue. It increases the probability of many health complications, such as diabetes, arthritis, cardiac disease, and cancer. In modern society, with a growing population of obese patients, several individuals have increased insulin resistance. Herbal medicines are known as the oldest method of health care treatment for obesity-related secondary health issues. Several traditional medicinal plants and their effective phytoconstituents have shown anti-diabetic and anti-adipogenic activity. Adipose tissue is a major site for lipid accumulation as well as the whole-body insulin sensitivity region. 3T3-L1 cell line model can achieve adipogenesis. Adipocyte characteristics features such as expression of adipocyte markers and aggregation of lipids are chemically induced in the 3T3-L1 fibroblast cell line. Differentiation of 3T3-L1 is an efficient and convenient way to obtain adipocyte like cells in experimental studies. Peroxisome proliferation activated receptor γ (PPARγ) and Cytosine-Cytosine-Adenosine-Adenosine-Thymidine/Enhancer-binding protein α(CCAAT/Enhancer-binding protein αor C/EBPα) are considered to be regulating adipogenesis at the early stage, while adiponectin and fatty acid synthase (FAS) is responsible for the mature adipocyte formation. Excess accumulation of these adipose tissues and lipids leads to obesity. Thus, investigating adipose tissue development and the underlying molecular mechanism is important in the therapeutical approach. This review describes the cellular mechanism of 3T3-L1 fibroblast cells on potential anti-adipogenic herbal bioactive compounds.

PSVIII-40 Late-Breaking Abstract: Variability in body composition is associated with insulin sensitivity in growing-finishing pigs

Abstract Growing pigs’ body composition variation can be associated with differences in insulin sensitivity given the insulin anabolic effect on protein and lipid synthesis. The objective of this study was to elucidate this association by relating the individual insulin response to the oral glucose tolerance test (OGTT) with the body composition of growing pigs. Thirty 95 kg jugular vein catheterized pigs received an oral dose of 1.75 g of glucose/kg of BW after 18 hours of fasting. Blood samples were collected at -20, -10, 5, 10, 15, 20, 25, 30, 45, 60, 90, 120, 150, 180, 210, 240, 300 and 360 min following glucose ingestion. Insulin sensitivity indexes were calculated and analyzed. Body lipids (LB, %) and protein (PB, %) composition were estimated by dual X-ray densitometry. Association between body composition and insulin sensitivity were studied by using partial least squares and correlations. Average LB and PB were 19.7% (CV = 7.6 %) and 16.2% (CV = 2.2%), respectively. Basal insulin blood concentration and area-under-the-curve (AUC) CV (51.9 % and 26.9 %, respectively) were larger than those for basal glucose and AUC (5.52 and 5.48 %, respectively). Additionally, insulin sensitivity (%S), steady-state beta cell function (%B), and insulin resistance (HOMA-IR) estimated with the Homeostasis Model Assessment (HOMA 2) and whole-body insulin sensitivity index (ISI) were highly variable between pigs which CV ranged from 30.1 % to 54.5 %. These results can indicate an early stage of insulin resistance in an important part of the studied pig population. LB and PB were affected by insulin sensitivity indexes (P &amp;lt; 0.05) which accounted, respectively, for 48% and 44% of the observed variation. In conclusion, lower insulin sensitivity was associated with higher body fat in growing pigs raised under similar conditions.

Hepatocyte-specific PKCβ deficiency protects against high-fat diet-induced nonalcoholic hepatic steatosis

ObjectiveNonalcoholic hepatic steatosis, also known as fatty liver, is a uniform response of the liver to hyperlipidic-hypercaloric diet intake. However, the post-ingestive signals and mechanistic processes driving hepatic steatosis are not well understood. Emerging data demonstrate that protein kinase C beta (PKCβ), a lipid-sensitive kinase, plays a critical role in energy metabolism and adaptation to environmental and nutritional stimuli. Despite its powerful effect on glucose and lipid metabolism, knowledge of the physiological roles of hepatic PKCβ in energy homeostasis is limited. MethodsThe floxed-PKCβ and hepatocyte-specific PKCβ-deficient mouse models were generated to study the in vivo role of hepatocyte PKCβ on diet-induced hepatic steatosis, lipid metabolism, and mitochondrial function. ResultsWe report that hepatocyte-specific PKCβ deficiency protects mice from development of hepatic steatosis induced by high-fat diet, without affecting body weight gain. This protection is associated with attenuation of SREBP-1c transactivation and improved hepatic mitochondrial respiratory chain. Lipidomic analysis identified significant increases in the critical mitochondrial inner membrane lipid, cardiolipin, in PKCβ-deficient livers compared to control. Moreover, hepatocyte PKCβ deficiency had no significant effect on either hepatic or whole-body insulin sensitivity supporting dissociation between hepatic steatosis and insulin resistance. ConclusionsThe above data indicate that hepatocyte PKCβ is a key focus of dietary lipid perception and is essential for efficient storage of dietary lipids in liver largely through coordinating energy utilization and lipogenesis during post-prandial period. These results highlight the importance of hepatic PKCβ as a drug target for obesity-associated nonalcoholic hepatic steatosis.

Early changes in hepatic energy metabolism and lipid content in recent-onset type 1 and 2 diabetes mellitus

Non-alcoholic fatty liver disease (NAFLD) is associated with abnormal mitochondrial capacity. While oxidative capacity can be increased in steatosis, hepatic ATP decreases in long-standing diabetes. However, longitudinal studies on diabetes-related NAFLD and its relationship to hepatic energy metabolism are lacking. This prospective study comprised volunteers with type 1 (T1DM, n= 30) and type 2 (T2DM, n= 37) diabetes. At diagnosis and 5 years later, we used 1H/31P magnetic resonance spectroscopy to measure hepatocellular lipid (HCL), γATP and inorganic phosphate (Pi) concentrations, and to assess adipose tissue volumes. Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamps. At diagnosis, individuals with T2DM had higher HCL and adipose tissue volumes, but lower whole-body insulin sensitivity than those with T1DM, despite comparable glycemic control. NAFLD was present in 38% of individuals with T2DM and 7% with T1DM. After 5 years, visceral adipose tissue only increased in individuals with T2DM, while HCL almost doubled in this group (p <0.001), resulting in a 70% prevalence of NAFLD (independent of diabetes treatment). Changes in HCL correlated with adipose tissue volume and insulin resistance (r= 0.50 and r= 0.44, both p <0.05). Pi decreased by 17% and 10% in individuals with T2DM and T1DM (p <0.05), respectively. In T1DM, HCL did not change, whereas γATP decreased by 10% and correlated negatively with glycated hemoglobin (r= -0.56, p <0.05). The rapid increase in HCL during the early course of T2DM likely results from enlarging adipose tissue volume and insulin resistance in response to impaired hepatic mitochondrial adaptation. The decrease of phosphorus metabolites in T1DM may be due to pharmacological insulin supply. Previous studies suggested that the impaired function of mitochondria, the power plants of cells, can promote fatty liver and type 2 diabetes mellitus. This study now shows that during the first 5 years of type 2 diabetes the increase in body fat content rapidly leads to a doubling of liver fat content, whereas the energy metabolism of the patients' livers progressively declines. These data suggest that fat tissue mass and liver mitochondria have an important role in the development of fatty liver disease in humans with diabetes. NCT01055093.

PPARγ S273 Phosphorylation Modifies the Dynamics of Coregulator Proteins Recruitment.

The nuclear receptor PPARγ is essential to maintain whole-body glucose homeostasis and insulin sensitivity, acting as a master regulator of adipogenesis, lipid, and glucose metabolism. Its activation through natural or synthetic ligands induces the recruitment of coactivators, leading to transcription of target genes such as cytokines and hormones. More recently, post translational modifications, such as PPARγ phosphorylation at Ser273 by CDK5 in adipose tissue, have been linked to insulin resistance trough the dysregulation of expression of a specific subset of genes. Here, we investigate how this phosphorylation may disturb the interaction between PPARγ and some coregulator proteins as a new mechanism that may leads to insulin resistance. Through cellular and in vitro assays, we show that PPARγ phosphorylation inhibition increased the activation of the receptor, therefore the increased recruitment of PGC1-α and TIF2 coactivators, whilst decreases the interaction with SMRT and NCoR corepressors. Moreover, our results show a shift in the coregulators interaction domains preferences, suggesting additional interaction interfaces formed between the phosphorylated PPARγ and some coregulator proteins. Also, we observed that the CDK5 presence disturb the PPARγ-coregulator’s synergy, decreasing interaction with PGC1-α, TIF2, and NCoR, but increasing coupling of SMRT. Finally, we conclude that the insulin resistance provoked by PPARγ phosphorylation is linked to a differential coregulators recruitment, which may promote dysregulation in gene expression.

Small Amounts of Dietary Medium-Chain Fatty Acids Protect Against Insulin Resistance During Caloric Excess in Humans.

Medium-chain fatty acids (MCFAs) have in rodents been shown to have protective effects on glucose homeostasis during high-fat overfeeding. In this study, we investigated whether dietary MCFAs protect against insulin resistance induced by a hypercaloric high-fat diet in humans. Healthy, lean men ingested a eucaloric control diet and a 3-day hypercaloric high-fat diet (increase of 75% in energy, 81-83% energy [E%] from fat) in randomized order. For one group (n = 8), the high-fat diet was enriched with saturated long-chain FAs (LCSFA-HFD), while the other group (n = 9) ingested a matched diet, but with ∼30 g (5E%) saturated MCFAs (MCSFA-HFD) in substitution for a corresponding fraction of the saturated long-chain fatty acids (LCFAs). A hyperinsulinemic-euglycemic clamp with femoral arteriovenous balance and glucose tracer was applied after the control and hypercaloric diets. In LCSFA-HFD, whole-body insulin sensitivity and peripheral insulin-stimulated glucose disposal were reduced. These impairments were prevented in MCSFA-HFD, accompanied by increased basal fatty acid oxidation, maintained glucose metabolic flexibility, increased nonoxidative glucose disposal related to lower starting glycogen content, and increased glycogen synthase activity, together with increased muscle lactate production. In conclusion, substitution of a small amount of dietary LCFAs with MCFAs rescues insulin action in conditions of lipid-induced energy excess.

Ethinyl estradiol vs estradiol valerate in combined oral contraceptives – Effect on glucose tolerance: A randomized, controlled clinical trial

ObjectiveTo compare the effects of two formulations of combined oral contraceptives (COCs), estradiol valerate (EV) and ethinyl estradiol (EE) combined with dienogest (DNG), and DNG-only, on glucose tolerance. Study DesignWe performed a randomized, controlled 9-week clinical trial. Inclusion criteria were: age 18–35 years, regular menstrual cycle (28 ± 7 days), no polycystic ovaries, non-smoking, no contraindications for COC use and a 2-month wash-out from hormonal contraceptive use. The women were randomized to EV + DNG (n = 20), EE + DNG (n = 20), and DNG-only (n = 19), and evaluated at baseline, at 4–5 weeks and 8–9 weeks of treatment. Study medications were used continuously for 63 days. Primary outcome measure was change in the whole-body insulin sensitivity index (Matsuda index) derived from the oral glucose tolerance test (OGTT) over the treatment period. Secondary outcome measures were area under curves (AUC) of glucose and insulin, homeostatic model assessment – insulin resistance (HOMA-IR) and Insulin Sensitivity Index (ISI). ResultsFifty-nine women enrolled, and 56 women completed the study. The Matsuda index changed from baseline as follows (mean percentage change, mean change [95%CI]): DNG-only −12%, −1.45 [95%CI −3.22–0.325] P = 0.10; EV + DNG + 2.7%, −0.10 [−1.34 to 1.14] P = 0.86; EE + DNG −5.5%, −1.02 [−2.51 to 0.46] P = 0.16, comparing the groups P = 0.27. There were no clinically significant differences in glucose tolerance between the COC groups, but the DNG-only group showed an improvement in the 2-h glucose levels (5.5 [95%CI 5.0–6.0] to 4.7 mmol/l [4.2–5.2], P = 0.001). ConclusionWe found no clinically significant differences between EV and EE combined with DNG and DNG-only on glucose tolerance in healthy, young, normal-weight women, indicating that these preparations appear close to neutral regarding glucose metabolism when used continuously for nine weeks. ImplicationsCombinations of both ethinyl estradiol and natural estradiol (estradiol valerate) with dienogest (DNG), as well as DNG-only, seem metabolically safe in young and healthy women in short-term continuous use.

Uric acid, impaired fasting glucose and impaired glucose tolerance in youth with overweight and obesity

Background and aimThe relationships between uric acid (UA) and prediabetes is poorly explored in youth. We investigated the association between UA, impaired fasting glucose (IFG), impaired glucose tolerance (IGT), insulin resistance (IR) and low insulin sensitivity (IS) in youth with overweight/obesity (OW/OB). Methods and resultsA cross-sectional study was performed in 2248 youths with OW/OB (age 5–17 years). The sample was stratified in sex-specific quintiles (Q1 to Q5) of UA and the associations with fasting (FG), 2-h post-load glucose (2H-PG), IR and low IS were investigated. IR and low IS were estimated by assessment model of insulin resistance (HOMA-IR) and whole-body IS index (WBISI), respectively. IFG was defined as FG ≥ 100 < 126 mg/dL, IGT as 2H-PG ≥140 < 200 mg/dL, IR as HOMA-IR ≥75th percentile and low IS as WBISI ≤25th percentile by sex. Age, body mass index z-score, 2H-PG, HOMA-IR and WBISI, increased across sex-quintiles of UA while FG did not. The prevalence of IFG and IR were significantly increased in Q5 vs Q1 (reference quartile, P < 0.025). The prevalence of IGT increased from Q3 to Q5 vs Q1 (P < 0.025–0.0001) and that of low IS from Q2 to Q5 vs Q1 (P < 0.005–0.0001). ConclusionsIn youth with OW/OB, rates of IGT and low IS increased progressively across quintiles of UA. On the contrary, IFG and IR were associated only with the highest quintile of UA. Our data suggest that UA is a biomarker of impaired glucose metabolism prevalently in post–challenge condition rather than in fasting state.

Putting the muscle back in microcirculation: From firefighters to near-infrared spectroscopy.

Putting the muscle back in microcirculation: From firefighters to near-infrared spectroscopy.

β-catenin regulates muscle glucose transport via actin remodelling and M-cadherin binding

ObjectiveSkeletal muscle glucose disposal following a meal is mediated through insulin-stimulated movement of the GLUT4-containing vesicles to the cell surface. The highly conserved scaffold-protein β-catenin is an emerging regulator of vesicle trafficking in other tissues. Here, we investigated the involvement of β-catenin in skeletal muscle insulin-stimulated glucose transport. MethodsGlucose homeostasis and transport was investigated in inducible muscle specific β-catenin knockout (BCAT-mKO) mice. The effect of β-catenin deletion and mutation of β-catenin serine 552 on signal transduction, glucose uptake and protein–protein interactions were determined in L6-G4-myc cells, and β-catenin insulin-responsive binding partners were identified via immunoprecipitation coupled to label-free proteomics. ResultsSkeletal muscle specific deletion of β-catenin impaired whole-body insulin sensitivity and insulin-stimulated glucose uptake into muscle independent of canonical Wnt signalling. In response to insulin, β-catenin was phosphorylated at serine 552 in an Akt-dependent manner, and in L6-G4-myc cells, mutation of β-cateninS552 impaired insulin-induced actin-polymerisation, resulting in attenuated insulin-induced glucose transport and GLUT4 translocation. β-catenin was found to interact with M-cadherin in an insulin-dependent β-cateninS552-phosphorylation dependent manner, and loss of M-cadherin in L6-G4-myc cells attenuated insulin-induced actin-polymerisation and glucose transport. ConclusionsOur data suggest that β-catenin is a novel mediator of glucose transport in skeletal muscle and may contribute to insulin-induced actin-cytoskeleton remodelling to support GLUT4 translocation.

Two weeks of early time-restricted feeding (eTRF) improves skeletal muscle insulin and anabolic sensitivity in healthy men

ABSTRACTBackgroundAltering the temporal distribution of energy intake (EI) and introducing periods of intermittent fasting (IF) exert important metabolic effects. Restricting EI to earlier in the day [early time-restricted feeding (eTRF)] is a novel type of IF.ObjectivesWe assessed the chronic effects of eTRF compared with an energy-matched control on whole-body and skeletal muscle insulin and anabolic sensitivity.MethodsSixteen healthy males (aged 23 ± 1 y; BMI 24.0 ± 0.6 kg·m−2) were assigned to 2 groups that underwent either 2 wk of eTRF (n = 8) or control/caloric restriction (CON:CR; n = 8) diet. The eTRF diet was consumed ad libitum and the intervention was conducted before the CON:CR, in which the diet was provided to match the reduction in EI and body weight observed in eTRF. During eTRF, daily EI was restricted to between 08:00 and 16:00, which prolonged the overnight fast by ∼5 h. The metabolic responses to a carbohydrate/protein drink were assessed pre- and post-interventions following a 12-h overnight fast.ResultsWhen compared with CON:CR, eTRF improved whole-body insulin sensitivity [between-group difference (95% CI): 1.89 (0.18, 3.60); P = 0.03; η2p = 0.29] and skeletal muscle uptake of glucose [between-group difference (95% CI): 4266 (261, 8270) μmol·min−1·kg−1·180 min; P = 0.04; η2p = 0.31] and branched-chain amino acids (BCAAs) [between-group difference (95% CI): 266 (77, 455) nmol·min−1·kg−1·180 min; P = 0.01; η2p = 0.44]. eTRF caused a reduction in EI (∼400 kcal·d−1) and weight loss (−1.04 ± 0.25 kg; P = 0.01) that was matched in CON:CR (−1.24 ± 0.35 kg; P = 0.01).ConclusionsUnder free-living conditions, eTRF improves whole-body insulin sensitivity and increases skeletal muscle glucose and BCAA uptake. The metabolic benefits of eTRF are independent of its effects on weight loss and represent chronic adaptations rather than the effect of the last bout of overnight fast. This trial was registered at clinicaltrials.gov as NCT03969745.

Effects of short-term physical training on the interleukin-15 signalling pathway and glucose tolerance in aged rats

PurposeInterleukin-15 (IL-15) is a myokine that has been proposed to modulate skeletal muscle and adipose tissue mass, as well as insulin sensitivity. However, the evidence suggesting a role for IL-15 in improving whole-body insulin sensitivity and decreasing adiposity comes mainly from studies using supraphysiological levels of this cytokine. This study examined the effect of a short-term exercise training protocol on the protein content of IL-15, it's signaling pathway, and glucose tolerance in aged rats. MethodsFourteen Wistar rats were divided into Young Sedentary (Young, n = 4); Old Sedentary (Old, n = 5); Old Exercise (Old.Exe, n = 5) groups. The animals from the exercised group were submitted to a short-term physical exercise protocol for five days. At the end of physical training and after 16 h of the last exercise session, the animals were euthanized, and tissue collection was done. ResultsPhysical exercise decreased epididymal and mesenteric fat mass and promoted positive effects on glucose tolerance and insulin sensitivity. Muscle IL-15 protein levels were not changed following the short-term physical exercise training with no alterations in the post-exercise IL-15–JAK/STAT signaling pathway. We found a tendency to increased HIF1α and a significant increase in its regulator, PHD2, in the skeletal muscle after exercise. ConclusionThe elderly rats submitted to short-term aerobic physical training did not present skeletal muscle alteration in the protein content of the IL-15 and IL-15-JAK/STAT signaling pathway. However, short-term aerobic physical training was able to modulate the expression of HIF1α and its regulator PHD2, suggesting an essential role of these proteins in improving post-exercise glucose tolerance and insulin sensitivity in elderly rats.

STAT1 Dissociates Adipose Tissue Inflammation From Insulin Sensitivity in Obesity.

Obesity fosters low-grade inflammation in white adipose tissue (WAT) that may contribute to the insulin resistance that characterizes type 2 diabetes. However, the causal relationship of these events remains unclear. The established dominance of STAT1 function in the immune response suggests an obligate link between inflammation and the comorbidities of obesity. To this end, we sought to determine how STAT1 activity in white adipocytes affects insulin sensitivity. STAT1 expression in WAT inversely correlated with fasting plasma glucose in both obese mice and humans. Metabolomic and gene expression profiling established STAT1 deletion in adipocytes (STAT1 a-KO ) enhanced mitochondrial function and accelerated tricarboxylic acid cycle flux coupled with reduced fat cell size in subcutaneous WAT depots. STAT1 a-KO reduced WAT inflammation, but insulin resistance persisted in obese mice. Rather, elimination of type I cytokine interferon-γ activity enhanced insulin sensitivity in diet-induced obesity. Our findings reveal a permissive mechanism that bridges WAT inflammation to whole-body insulin sensitivity.