Glucose Disposal In Skeletal Muscle Research Articles

Hepatic sialic acid synthesis modulates glucose homeostasis in both liver and skeletal muscle

ObjectiveSialic acid is a terminal monosaccharide of glycans in glycoproteins and glycolipids, and its derivation from glucose is regulated by the rate-limiting enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE). Although the glycans on key endogenous hepatic proteins governing glucose metabolism are sialylated, how sialic acid synthesis and sialylation in the liver influence glucose homeostasis is unknown. Studies were designed to fill this knowledge gap. MethodsTo decrease the production of sialic acid and sialylation in hepatocytes, a hepatocyte-specific GNE knockdown mouse model was generated, and systemic glucose metabolism, hepatic insulin signaling and glucagon signaling were evaluated in vivo or in primary hepatocytes. Peripheral insulin sensitivity was also assessed. Furthermore, the mechanisms by which sialylation in the liver influences hepatic insulin signaling and glucagon signaling and peripheral insulin sensitivity were identified. ResultsLiver GNE deletion in mice caused an impairment of insulin suppression of hepatic glucose production. This was due to a decrease in the sialylation of hepatic insulin receptors (IR) and a decline in IR abundance due to exaggerated degradation through the Eph receptor B4. Hepatic GNE deficiency also caused a blunting of hepatic glucagon receptor (GCGR) function which was related to a decline in its sialylation and affinity for glucagon. An accompanying upregulation of hepatic FGF21 production caused an enhancement of skeletal muscle glucose disposal that led to an overall increase in glucose tolerance and insulin sensitivity. ConclusionThese collective observations reveal that hepatic sialic acid synthesis and sialylation modulate glucose homeostasis in both the liver and skeletal muscle. By interrogating how hepatic sialic acid synthesis influences glucose control mechanisms in the liver, a new metabolic cycle has been identified in which a key constituent of glycans generated from glucose modulates the systemic control of its precursor.

Pancreastatin inhibitor PSTi8 ameliorates insulin resistance by decreasing fat accumulation and oxidative stress in high-fat diet-fed mice.

Abnormal fat accumulation, enhanced free fatty acids (FFA) release, and their metabolites cause insulin resistance (IR) in major glucose-lipid metabolic organs such as skeletal muscle and adipose tissue. However, excessive lipolysis and FFA release from adipose tissue elevate plasma FFA levels leading to oxidative stress and skeletal muscle IR. Indeed, in obese individuals, there is enhanced pro-inflammatory secretion from adipose tissue influencing insulin signaling in skeletal muscles. Here, we investigated the effect of PSTi8 on FFA-induced IR in both in vitro and in vivo models. Palmitate (Pal)-treated 3T3-L1 cells increased lipid accumulation as well as lipolysis, which reduced the insulin-stimulated glucose uptake. PSTi8 treatment significantly prevented Pal-induced lipid accumulation, and release and enhanced insulin-stimulated glucose uptake. It further reduced the release of pro-inflammatory cytokines from Pal-treated 3T3-L1 cells as well as from adipose tissue explants. In addition, PSTi8 treatment decreases M1 surface markers in Pal-treated bone marrow-derived monocytes (BMDM). PSTi8 treatment also significantly enhanced the Pal-mediated reduced skeletal muscle glucose disposal and reduced intracellular oxidative stress. In vitro effect of PSTi8 was consistent with in vivo HFD-fed mice IR model. PSTi8 treatment in HFD-fed mice significantly improved glucose metabolism and enhanced skeletal muscle insulin sensitivity with reduced adiposity and pro-inflammatory cytokines. Taken together, our results support that PSTi8 treatment can protect both adipose and skeletal muscles from FFA-induced IR.

Endothelial ERα promotes glucose tolerance by enhancing endothelial insulin transport to skeletal muscle

The estrogen receptor (ER) designated ERα has actions in many cell and tissue types that impact glucose homeostasis. It is unknown if these include mechanisms in endothelial cells, which have the potential to influence relative obesity, and processes in adipose tissue and skeletal muscle that impact glucose control. Here we show that independent of impact on events in adipose tissue, endothelial ERα promotes glucose tolerance by enhancing endothelial insulin transport to skeletal muscle. Endothelial ERα-deficient male mice are glucose intolerant and insulin resistant, and in females the antidiabetogenic actions of estradiol (E2) are absent. The glucose dysregulation is due to impaired skeletal muscle glucose disposal that results from attenuated muscle insulin delivery. Endothelial ERα activation stimulates insulin transcytosis by skeletal muscle microvascular endothelial cells. Mechanistically this involves nuclear ERα-dependent upregulation of vesicular trafficking regulator sorting nexin 5 (SNX5) expression, and PI3 kinase activation that drives plasma membrane recruitment of SNX5. Thus, coupled nuclear and non-nuclear actions of ERα promote endothelial insulin transport to skeletal muscle to foster normal glucose homeostasis.

Pancreastatin inhibitor PSTi8 ameliorates streptozotocin-induced diabetes by suppressing hepatic glucose production

Elevated plasma glucose concentration, as a consequence of excessive hepatic glucose production, plays a pivotal role in the development of diabetes. A chromogranin A-derived diabetogenic peptide Pancreastatin (PST) enhances hepatic glucose output leading to diabetes. Therefore, here we probed the role of PSTi8, a PST inhibitor in ameliorating diabetes by investigating the effect of high glucose (HG) or PST on glucose metabolism. Further, we also explored the action mechanism of the underlying anti-hyperglycemic effect of PSTi8. PSTi8 treatment rescue cultured L6 and HepG2 cells from HG and PST-induced insulin resistance, respectively. It also enhances insulin receptor kinase activity by interacting with the insulin receptor and enhancing GLUT4 translocation and glucose uptake. Thus, our in-silico and in-vitro data support the PST-dependent and independent activity of PSTi8. Additionally, PSTi8 treatment in streptozotocin-induced diabetic rats improved glucose tolerance by lowering blood glucose and plasma PST levels. Concomitantly, the treated animals exhibited reduced hepatic glucose production accompanied by downregulation of hepatic gluconeogenic genes PEPCK and G6Pase. PSTi8-treated rats also exhibited enhanced hepatic glycogen in line with reduced plasma glucagon concentrations. Consistently, improved plasma insulin levels in PSTi8-treated rats enhanced skeletal muscle glucose disposal via enhanced P-Akt expression. In summary, these findings suggest PSTi8 has anti-hyperglycemic properties with enhanced skeletal muscle glucose disposal and reduced hepatic gluconeogenesis both PST dependent as well as independent.

Whipple's triad with high and low insulin levels

A69-year-old female patient and a70-year-old male patient were admitted to hospital with recurrent, severe hypoglycemic episodes and atypical manifestation of Whipple's triad. In the female, elevated levels of insulin, C‑peptide and pro-insulin together with pathological findings during afasting test proved the presence of an insulinoma, which could be detected by Ga-68-DOTATOC-PET-CT in the pancreas. There was avery rare co-existence of aneuroendocrine Merkel cell carcinoma. In the male, levels of insulin and C‑peptide were suppressed and adiagnosis of paraneoplastic hypoglycemia by IGF‑2 secretion was made with increased glucose disposal in skeletal muscle proven by 18F‑FDG-PET-CT.

1118-P: Prediction of Clamp-Derived Insulin Sensitivity in African Americans from Clinical Risk Factors

Surrogate indices of insulin sensitivity based on fasting glucose and insulin values fail to adequately predict insulin sensitivity in African-Americans (AA) , a group with high risk for type 2 diabetes. The objective of this study was to evaluate the individual and combined utility of clinically accessible risk factors (demographic, anthropometric, and metabolic traits) to predict clamp-derived insulin sensitivity in 53 AA adults without diabetes. Insulin sensitivity was measured with the euglycemic clamp (SI-clamp) at an insulin dose of 120 µU/m2/min/kg lean body mass to assess primarily skeletal muscle glucose disposal. Concentrations of lipid/lipoproteins, adipokines, glucose, insulin, C-peptide, proinsulin, and inflammatory markers were obtained from fasting sera. Individual associations between SI-clamp and predictors were evaluated with linear regression, adjusting for age and sex. Multiple regression analyses with backward stepwise selection of all candidate predictors were used to derive prediction models. Body mass, triglycerides (TAG) , glucose, insulin, C-peptide, proinsulin, and TNF-α were inversely associated with SI-clamp, whereas female sex, HDL-cholesterol, adiponectin, and IFN-γ were positively associated (P< 0.05) . For the prediction models, HDL-cholesterol, TAG, C-peptide, adiponectin, leptin, and IL-6 explained the highest proportion of variance in SI-clamp (AIC = 15.8 and adjusted R2 = 54.27%) . A second, more clinically applicable model was also derived using HDL-cholesterol, TAG, C-peptide, and adiponectin (AIC = 18.136 and adjusted R2 = 50.63%) . These results suggest that in AA, fasting levels of lipid/lipoproteins, C-peptide, and adiponectin are stronger predictors of insulin sensitivity than fasting glucose and insulin. Development of a surrogate index for insulin sensitivity with these predictors may aid in accurately identifying AA at increased risk for type 2 diabetes in clinical settings and epidemiological studies. Disclosure L.A.Fowler: None. V.Parcha: None. C.Couch: None. W.Garvey: Other Relationship; Boehringer Ingelheim International GmbH, Eli Lilly and Company, Epitomee, JAZZ Pharmaceuticals, Novo Nordisk, Novo Nordisk, Pfizer Inc., Pfizer Inc. B.Gower: None. Funding NIH/NIDDK (R01DK096288) NIH/NIDDK (P30DK056336) NIH/NIDDK (P60DK079626) NIH/NIDDK (T32DK062710) NIH/NCATS CTSA (U54TR001368-01)

Muscle hypertrophic effect of inhaled beta2 -agonist is associated with augmented insulin-stimulated whole-body glucose disposal in young men.

Rodent studies highlight enhancement of glucose tolerance and insulin sensitivity as potential clinically relevant effects of chronic beta2‐agonist treatment. However, the doses administered to rodents are not comparable with the therapeutic doses used for humans. Thus, we investigated the physiological effects of prolonged beta2‐agonist treatment at inhaled doses resembling those used in respiratory diseases on insulin‐stimulated whole‐body glucose disposal and putative mechanisms in skeletal muscle and adipose tissue of healthy men. Utilizing a randomized placebo‐controlled parallel‐group design, we assigned 21 healthy men to 4 weeks daily inhalation of terbutaline (TER; 4 mg × day−1, n = 13) or placebo (PLA, n = 8). Before and after treatments, we assessed subjects’ whole‐body insulin‐stimulated glucose disposal and body composition, and collected vastus lateralis muscle and abdominal adipose tissue biopsies. Glucose infusion rate increased by 27% (95% CI: 80 to 238 mg × min−1, P = 0.001) in TER, whereas no significant changes occurred in PLA (95% CI: −37 to 195 mg × min−1, P = 0.154). GLUT4 content in muscle or adipose tissue did not change, nor did hexokinase II content or markers of mitochondrial volume in muscle. Change in lean mass was associated with change in glucose infusion rate in TER (r = 0.59, P = 0.03). Beta2‐agonist treatment in close‐to‐therapeutic doses may augment whole‐body insulin‐stimulated glucose disposal in healthy young men and part of the change is likely to be explained by muscle hypertrophy. These findings highlight the therapeutic potential of beta2‐agonists for improving insulin sensitivity.Key points While studies in rodents have highlighted beta2‐agonists as a means to augment insulin sensitivity, these studies utilized beta2‐agonists at doses inapplicable to humans.Herein we show that a 4‐week treatment period with daily therapeutic inhalation of beta2‐agonist increases insulin‐stimulated whole‐body glucose disposal in young healthy lean men.This effect was associated with an increase of lean mass but not with changes in GLUT4 and hexokinase II or basal glycogen content in skeletal muscle nor GLUT4 content in abdominal adipose tissue.These findings suggest that the enhanced insulin‐stimulated whole‐body glucose disposal induced by a period of beta2‐agonist treatment in humans, at least in part, is attributed to muscle hypertrophy.Our observations extend findings in rodents and highlight the therapeutic potential of beta2‐agonists to enhance the capacity for glucose disposal and whole‐body insulin sensitivity, providing important knowledge with potential application in insulin resistance.

Gastric inhibitory polypeptide as the new candidate for the interaction of skeletal muscle blood flow and glucose disposal.

Gastric inhibitory polypeptide as the new candidate for the interaction of skeletal muscle blood flow and glucose disposal.

Abstract 102: Apolipoprotein E Receptor 2 In Endothelium Affords Protection From Both Atherosclerosis And Insulin Resistance

Introduction: Apolipoprotein E Receptor 2 (ApoER2) is an LDL receptor family member that mediates the actions of apolipoprotein E (apoE) and other ligands. The LRP8 gene that encodes ApoER2 is a major gene locus for premature atherosclerosis and myocardial infarction. Studies were designed to determine how ApoER2 in endothelial cells impacts cardiovascular and metabolic health. Hypothesis: Based on prior cell culture studies, the hypothesis was that endothelial ApoER2 is atheroprotective. How endothelial ApoER2 impacts adiposity or glucose homeostasis is more difficult to predict. Methods: In vivo studies were done in control ApoER2 floxed mice (ApoER2 fl/fl ) and mice deficient in ApoER2 in endothelial cells (ApoER2 ΔEC ). Studies of endothelial cell insulin uptake and transcytosis were performed in human aortic and skeletal muscle endothelial cells (HAEC and HSMEC). Results: Atherosclerotic lesion severity on LDLR -/- background was increased in ApoER2 ΔEC mice compared to ApoER2 fl/fl , and this was not related to differences in circulating lipids. Intravital microscopy revealed that leukocyte-endothelial cell adhesion is increased in ApoER2 ΔEC , and vascular TNFα and IL-1β expression was exaggerated. There was no impact of endothelial ApoER2 silencing on adiposity. However, standard chow-fed ApoER2 ΔEC mice displayed marked glucose intolerance and insulin resistance. Both pancreatic insulin secretion and hepatic insulin sensitivity were normal. Alternatively, in ApoER2 ΔEC mice skeletal muscle glucose disposal was decreased by 41%, and this was due to a 55% fall in insulin delivery to muscle. Using human apoE3 ex vivo, apoE stimulated a 279% increase in insulin uptake in HAEC, and the finding was confirmed in HSMEC. Insulin transcytosis rose 209% with apoE, and apoE enhancement of insulin transport was fully ApoER2-dependent. Conclusions: Endothelial ApoER2 affords atheroprotection by decreasing leukocyte-endothelial cell adhesion and inflammatory gene expression in the vessel wall. Endothelial ApoER2 also has antidiabetic action, and this is due to the promotion of endothelial insulin transport to skeletal muscle. Targeting of the related mechanisms may provide protection from both cardiovascular and metabolic disease.

Hyperpolarized NMR study of the impact of pyruvate dehydrogenase kinase inhibition on the pyruvate dehydrogenase and TCA flux in type 2 diabetic rat muscle.

The role of pyruvate dehydrogenase in mediating lipid-induced insulin resistance stands as a central question in the pathogenesis of type 2 diabetes mellitus. Many researchers have invoked the Randle hypothesis to explain the reduced glucose disposal in skeletal muscle by envisioning an elevated acetyl CoA pool arising from increased oxidation of fatty acids. Over the years, in vivo NMR studies have challenged that monolithic view. The advent of the dissolution dynamic nuclear polarization NMR technique and a unique type 2 diabetic rat model provides an opportunity to clarify. Dynamic nuclear polarization enhances dramatically the NMR signal sensitivity and allows the measurement of metabolic kinetics in vivo. Diabetic muscle has much lower pyruvate dehydrogenase activity than control muscle, as evidenced in the conversion of [1-13C]lactate and [2-13C]pyruvate to HCO3- and acetyl carnitine. The pyruvate dehydrogenase kinase inhibitor, dichloroacetate, restores rapidly the diabetic pyruvate dehydrogenase activity to control level. However, diabetic muscle has a much larger dynamic change in pyruvate dehydrogenase flux than control. The dichloroacetate-induced surge in pyruvate dehydrogenase activity produces a differential amount of acetyl carnitine but does not affect the tricarboxylic acid flux. Further studies can now proceed with the dynamic nuclear polarization approach and a unique rat model to interrogate closely the biochemical mechanism interfacing oxidative metabolism with insulin resistance and metabolic inflexibility.

DHA/EPA Improves GLUT4 Translocation, Glycogen Synthesis and Aerobic Glycolysis in Skeletal Muscle of db/db Mice

Abstract Objectives The aim of this study was to investigate the effects of DHA and EPA on glucose metabolism including glucose uptake and disposal in skeletal muscle and C2C12 myotubes. Methods Four-week-old db/db diabetic mice were fed with control diet enriched with DHA/EPA (purity > 99%, 1% wt/wt) for 10 weeks. To further explore the underlying mechanism, C2C12 myotubes were induced insulin resistance by palmitate and treated with 25 and 50 μM DHA/EPA for 24 h after differentiation. Results The untargeted metabolome of skeletal muscle showed BCAAs and other metabolites associated with glycolysis and TCA cycle were altered by DHA/EPA treatment. Further detections revealed DHA/EPA treatment promoted the translocation of GLUT4 via increasing Rab8a and SNAP23 expression, and enhanced the activity of GS and PDH. In vitro, the glucose consumption was improved coupled with promoted Rab8a or SNAP23, and GS and PDH were also activated under DHA/EPA intervention increased glucose consumption via promoted Rab8a and SNAP23. The GS and PDH were also activated, which were in line with the results in vivo. Conclusions Long-term intake of DHA and EPA may have a protective effect on diabetes through promoted GLUT4 translocation, glycogen synthesis and aerobic glycolysis in skeletal muscle. Funding Sources This work was supported by the National Natural Science Foundation of China (grant number 81773419 and 81300309), Chinese Institute of Nutrition DSM Research Fund (grant number CNS-DSM-2017–035), China National Program for Support of Top-notch Young Professionals and China Postdoctoral Science Foundation (grant number 2020M681869).

The effects of hydroxychloroquine on insulin sensitivity, insulin clearance and inflammation in insulin-resistant adults: A randomized trial.

To determine the effect of hydroxychloroquine (HCQ) on skeletal muscle and liver insulin sensitivity, insulin clearance, inflammation and adipokines. Insulin-resistant adults without rheumatic disease were randomized to 13 weeks of HCQ (400 mg/day) versus placebo (double-blinded). Primary outcomes were changes in skeletal muscle and liver insulin sensitivity assessed by hyperinsulinaemic-euglycaemic clamp and stable-isotope tracer methods. Secondary outcomes included insulin clearance, inflammation biomarkers and adipokines. Compared with placebo, HCQ significantly improved skeletal muscle insulin sensitivity by 26% (p = .019) and enhanced systemic glucose clearance (p = .025). By contrast, HCQ had no effect on hepatic insulin sensitivity. HCQ did not affect insulin clearance but decreased circulating IL-6 (p = .01) and increased adiponectin (p = .045). There were no effects on leptin, RBP-4, FGF-21 or C-reactive protein. HCQ selectively enhances insulin sensitivity and glucose disposal in skeletal muscle, without affecting hepatic insulin sensitivity or insulin clearance. These findings offer a mechanistic explanation for the antidiabetic properties of HCQ and suggest that this medication might be useful in conditions linked to insulin resistance such as type 2 diabetes.

Increasing skeletal muscle carnitine content in older individuals increases whole-body fat oxidation during moderate-intensity exercise.

Intramyocellular lipid (IMCL) utilization is impaired in older individuals, and IMCL accumulation is associated with insulin resistance. We hypothesized that increasing muscle total carnitine content in older men would increase fat oxidation and IMCL utilization during exercise, and improve insulin sensitivity. Fourteen healthy older men (69 ± 1 year, BMI 26.5 ± 0.8 kg/m2) performed 1 h of cycling at 50% VO2max and, on a separate occasion, underwent a 60 mU/m2/min euglycaemic hyperinsulinaemic clamp before and after 25 weeks of daily ingestion of a 220 ml insulinogenic beverage (44.4 g carbohydrate, 13.8 g protein) containing 4.5 g placebo (n = 7) or L‐carnitine L‐tartrate (n = 7). During supplementation, participants performed twice‐weekly cycling for 1 h at 50% VO2max. Placebo ingestion had no effect on muscle carnitine content or total fat oxidation during exercise at 50% VO2max. L‐carnitine supplementation resulted in a 20% increase in muscle total carnitine content (20.1 ± 1.2 to 23.9 ± 1.7 mmol/kg/dm; p < 0.01) and a 20% increase in total fat oxidation (181.1 ± 15.0 to 220.4 ± 19.6 J/kg lbm/min; p < 0.01), predominantly due to increased IMCL utilization. These changes were associated with increased expression of genes involved in fat metabolism (ACAT1, DGKD & PLIN2; p < 0.05). There was no change in resting insulin‐stimulated whole‐body or skeletal muscle glucose disposal after supplementation. This is the first study to demonstrate that a carnitine‐mediated increase in fat oxidation is achievable in older individuals. This warrants further investigation given reduced lipid turnover is associated with poor metabolic health in older adults.

Metabolic and Energy Imbalance in Dysglycemia-Based Chronic Disease.

Metabolic flexibility is the ability to efficiently adapt metabolism based on nutrient availability and requirement that is essential to maintain homeostasis in times of either caloric excess or restriction and during the energy-demanding state. This regulation is orchestrated in multiple organ systems by the alliance of numerous metabolic pathways under the master control of the insulin-glucagon-sympathetic neuro-endocrine axis. This, in turn, regulates key metabolic enzymes and transcription factors, many of which interact closely with and culminate in the mitochondrial energy generation machinery. Metabolic flexibility is compromised due to the continuous mismatch between availability and intake of calorie-dense foods and reduced metabolic demand due to sedentary lifestyle and age-related metabolic slowdown. The resultant nutrient overload leads to mitochondrial trafficking of substrates manifesting as mitochondrial dysfunction characterized by ineffective substrate switching and incomplete substrate utilization. At the systemic level, the manifestation of metabolic inflexibility comprises reduced skeletal muscle glucose disposal rate, impaired suppression of hepatic gluconeogenesis and adipose tissue lipolysis manifesting as insulin resistance. This is compounded by impaired β-cell function and progressively reduced β-cell mass. A consequence of insulin resistance is the upregulation of the mitogen-activated protein kinase pathway leading to a pro-hypertensive, atherogenic, and thrombogenic environment. This is further aggravated by oxidative stress, advanced glycation end products, and inflammation, which potentiates the risk of micro- and macro-vascular complications. This review aims to elucidate underlying mechanisms mediating the onset of metabolic inflexibility operating at the main target organs and to understand the progression of metabolic diseases. This could potentially translate into a pharmacological tool that can manage multiple interlinked conditions of dysglycemia, hypertension, and dyslipidemia by restoring metabolic flexibility. We discuss the breadth and depth of metabolic flexibility and its impact on health and disease.

Metformin May Contribute to Inter-individual Variability for Glycemic Responses to Exercise.

Metformin and exercise independently improve glycemic control. Metformin traditionally is considered to reduce hepatic glucose production, while exercise training is thought to stimulate skeletal muscle glucose disposal. Collectively, combining treatments would lead to the anticipation for additive glucose regulatory effects. Herein, we discuss recent literature suggesting that metformin may inhibit, enhance or have no effect on exercise mediated benefits toward glucose regulation, with particular emphasis on insulin sensitivity. Importantly, we address issues surrounding the impact of metformin on exercise induced glycemic benefit across multiple insulin sensitive tissues (e.g., skeletal muscle, liver, adipose, vasculature, and the brain) in effort to illuminate potential sources of inter-individual glycemic variation. Therefore, the review identifies gaps in knowledge that require attention in order to optimize medical approaches that improve care of people with elevated blood glucose levels and are at risk of cardiovascular disease.

Multiscale and morphological analysis of microvascular patterns depicted in contrast-enhanced ultrasound images.

Purpose: Impaired insulin-induced microvascular recruitment in skeletal muscle contributes to insulin resistance in type 2 diabetic disease. Previously, quantification of microvascular recruitment at the capillary level has been performed with either the full image or manually selected region-of-interests. These subjective approaches are imprecise, time-consuming, and unsuitable for automated processes. Here, an automated multiscale image processing approach was performed by defining a vessel diameter threshold for an objective and reproducible analysis at the microvascular level. Approach: A population of C57BL/6J male mice fed standard chow and studied at age 13 to 16 weeks comprised the lean group and 24- to 31-week-old mice who received a high-fat diet were designated the obese group. A clinical ultrasound scanner (Acuson Sequoia 512) equipped with an 15L8-S linear array transducer was used in a nonlinear imaging mode for sensitive detection of an intravascular microbubble contrast agent. Results: By eliminating large vessels from the dynamic contrast-enhanced ultrasound (DCE-US) images (above in diameter), obesity-related changes in perfusion and morphology parameters were readily detected in the smaller vessels, which are known to have a greater impact on skeletal muscle glucose disposal. The results from the DCE-US images including all of the vessels were compared for three different-sized vessel groups, namely, vessels smaller than 300, 200, and in diameter. Conclusions: Our automated image processing provides objective and reproducible results by focusing on a particular size of vessel, thereby allowing for a selective evaluation of longitudinal changes in microvascular recruitment for a specific-sized vessel group between diseased and healthy microvascular networks.

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)

Local myostatin inhibition improves skeletal muscle glucose uptake in insulin-resistant high-fat diet-fed mice.

Myostatin inhibition is thought to improve whole body insulin sensitivity and mitigate the development of insulin resistance in models of obesity. However, although myostatin is known to be a major regulator of skeletal muscle mass, the direct effects of myostatin inhibition in muscle on glucose uptake and the mechanisms that may underlie this are still unclear. We investigated the effect of local myostatin inhibition by adeno-associated virus-mediated overexpression of the myostatin propeptide on insulin-stimulated skeletal muscle glucose disposal in chow-fed or high fat diet-fed mice and evaluated the molecular pathways that might mediate this. We found that myostatin inhibition improved glucose disposal in obese high fat diet-fed mice alongside the induction of muscle hypertrophy but did not have an impact in chow-fed mice. This improvement was not associated with greater glucose transporter or peroxisome proliferator-activated receptor-γ coactivator-1α expression or 5' AMP-activated protein kinase activation as previously suggested. Instead, transcriptomic analysis suggested that the improvement in glucose disposal was associated with significant enrichment in genes involved in fatty acid metabolism and translation of mitochondrial genes. Thus, myostatin inhibition improves muscle insulin-stimulated glucose disposal in obese high fat diet-fed mice independent of muscle hypertrophy, potentially involving previously unidentified pathways.

Pancreastatin inhibitor PSTi8 protects the obesity associated skeletal muscle insulin resistance in diet induced streptozotocin-treated diabetic mice

Pancreastatin (PST), a chromogranin A (CHGA) derived peptide connects obesity with insulin resistance by inducing inflammation. Previously, we have evaluated potential activity of PST inhibitor (PSTi8) in liver and adipose tissue in type 2 diabetic mice model. In this study we further explore the therapeutic effect of PSTi8 on glucose metabolism in skeletal muscle cells/tissue and its effect on energy homeostasis in diet induced diabetic mice model. In in-vitro studies, we found that PSTi8 increases glucose uptake via enhanced GLUT4 translocation in L6 cells. This positive effect of PSTi8 led us to proceed with in-vivo studies in diabetic mice. C57BL/6 mice were fed HFD or HFrD diet for 12 weeks along with single STZ induction at 4th week followed by PSTi8 treatment. We found that HFD and HFrD model showed increased fat mass, caused glucose intolerance and insulin resistance, with accompanying proinflammatory effect on epididymal white adipose tissue (eWAT) together leading to skeletal muscle insulin resistance. Administration of PSTi8 protects from diet induced inflammatory response and enhances glucose tolerance and insulin sensitivity. PSTi8 improves circulating adipokine and lipid parameters, along with switch in macrophage polarisation from M1 to M2 in stromal vascular fraction of adipose tissue. In addition, treatment of PSTi8 also improves energy homeostasis, decreases circulatory non-esterified fatty acids level and inhibits ceramide deposition in muscle tissue. Overall this increased muscle insulin sensitivity is mediated via AKT/AS160/GLUT4 pathway activation. Our results reveal that PSTi8 inhibits the obesity mediated inflammation which enhances glucose disposal in skeletal muscle.

Insulin-independent stimulation of skeletal muscle glucose uptake by low-dose abscisic acid via AMPK activation

Abscisic acid (ABA) is a plant hormone active also in mammals where it regulates, at nanomolar concentrations, blood glucose homeostasis. Here we investigated the mechanism through which low-dose ABA controls glycemia and glucose fate. ABA stimulated uptake of the fluorescent glucose analog 2-NBDG by L6, and of [18F]-deoxy-glucose (FDG) by mouse skeletal muscle, in the absence of insulin, and both effects were abrogated by the specific AMPK inhibitor dorsomorphin. In L6, incubation with ABA increased phosphorylation of AMPK and upregulated PGC-1α expression. LANCL2 silencing reduced all these ABA-induced effects. In vivo, low-dose oral ABA stimulated glucose uptake and storage in the skeletal muscle of rats undergoing an oral glucose load, as detected by micro-PET. Chronic treatment with ABA significantly improved the AUC of glycemia and muscle glycogen content in CD1 mice exposed to a high-glucose diet. Finally, both acute and chronic ABA treatment of hypoinsulinemic TRPM2-/- mice ameliorated the glycemia profile and increased muscle glycogen storage. Altogether, these results suggest that low-dose oral ABA might be beneficial for pre-diabetic and diabetic subjects by increasing insulin-independent skeletal muscle glucose disposal through an AMPK-mediated mechanism.