Increased Muscle Glucose Uptake Research Articles

Coconut (Cocos nucifera (L.)) Water Improves Glucose Uptake with Concomitant Modulation of Antioxidant and Purinergic Activities in Isolated Rat Psoas Muscles.

The present study investigated the effect of coconut water on glucose uptake and utilization, and metabolic activities linked to hyperglycemia in isolated rat psoas muscles. Coconut water was subjected to in vitro antioxidant and antidiabetic assays, which cover 2,2'-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, ferric reducing antioxidant power (FRAP), and inhibition of α-glucosidase and α-amylase activities. Psoas muscles were isolated from male Sprague Dawley rats and incubated with coconut water in the presence of glucose. Control consisted of muscles incubated with glucose only, while normal control consisted of muscles not incubated in coconut water and/or glucose. The standard antidiabetic drug was metformin. Incubation with coconut water led to a significant increase in muscle glucose uptake, with concomitant exacerbation of glutathione level, and SOD and catalase activities, while suppressing malondialdehyde level, and ATPase and E-NTDase activities. Coconut water showed significant scavenging activity against DPPH, and significantly inhibited α-glucosidase and α-amylase activities. LC-MS analysis of coconut water revealed the presence of ellagic acid, butin, quercetin, protocatechuic acid, baicalin, and silibinin. Molecular docking analysis revealed potent molecular interactions between the LC-MS-identified compounds, and AKT-2 serine and PI-3 kinase. These results indicate the potential of coconut water to enhance glucose uptake, while concomitantly improving antioxidative and purinergic activities. They also indicate the potential of coconut water to suppress postprandial hyperglycemia. These activities may be attributed to the synergistic effects of the LC-MS-identified compounds.

Arginine and Lysine Supplementation Potentiates the Beneficial β-Hydroxy ß-Methyl Butyrate (HMB) Effects on Skeletal Muscle in a Rat Model of Diabetes.

Skeletal muscle is the key tissue for maintaining protein and glucose homeostasis, having a profound impact on the development of diabetes. Diabetes causes deleterious changes in terms of loss of muscle mass, which will contribute to reduced glucose uptake and therefore progression of the disease. Nutritional approaches in diabetes have been directed to increase muscle glucose uptake, and improving protein turnover has been at least partially an oversight. In muscle, β-hydroxy β-methyl butyrate (HMB) promotes net protein synthesis, while arginine and lysine increase glucose uptake, albeit their effects on promoting protein synthesis are limited. This study evaluates if the combination of HMB, lysine, and arginine could prevent the loss of muscle mass and function, reducing the progression of diabetes. Therefore, the combination of these ingredients was tested in vitro and in vivo. In muscle cell cultures, the supplementation enhances glucose uptake and net protein synthesis due to an increase in the amount of GLUT4 transporter and stimulation of the insulin-dependent signaling pathway involving IRS-1 and Akt. In vivo, using a rat model of diabetes, the supplementation increases lean body mass and insulin sensitivity and decreases blood glucose and serum glycosylated hemoglobin. In treated animals, an increase in GLUT4, creatine kinase, and Akt phosphorylation was detected, demonstrating the synergic effects of the three ingredients. Our findings showed that nutritional formulations based on the combination of HMB, lysine, and arginine are effective, not only to control blood glucose levels but also to prevent skeletal muscle atrophy associated with the progression of diabetes.

Acadesine supplementation in a soybean oil-based diet remodels hepatic lipid and glucose metabolism in juvenile large yellow croaker (Larimichthys crocea)

Dietary high soybean oil (SO) inclusion leads to excessive hepatic lipid accumulation and metabolism disorder in fish species. This study was conducted to investigate the effects of adenosine 5’-monophosphate-activated protein kinase (AMPK) pathway activation by acadesine (AICAR) on hepatic histology and metabolism-related gene expression of juvenile large yellow croakers (Larimichthys crocea) fed with SO-based diet. In this study, fish (initial body weight 3.89 ± 0.02 g) were fed fish oil (FO)-based, SO, or SOA (SO diet supplemented with 100 mg kg−1 AICAR) diets with three replicates of each treatment for 70 days. In general, the replacement of dietary FO with SO led to excessive hepatic lipid accumulation and a glucose metabolism disorder. Histological sections and biochemical analysis of hepatic tissue consistently revealed that AICAR supplementation could partly ameliorate SO-induced excessive hepatic lipid accumulation, probably by suppressing the expression of genes related to fatty acid uptake and lipogenesis while enhancing the expression of lipolysis-related genes. Nevertheless, AICAR regulated lipid metabolism in muscle tissue in an inverse pattern to that in hepatic tissue, indicating that muscle tissue could attempt to mitigate lipid accumulation by improving lipolysis in response to the dietary inclusion of SO. Dietary AICAR partly improved glucose metabolism by reducing the expression of genes related to gluconeogenesis in hepatic tissue while increasing the expression of genes related to glucose uptake and glycolysis in muscle tissue. Collectively, dietary AICAR mitigated excessive hepatic lipid accumulation and glucose metabolism disorder. The amelioration of hepatic lipid accumulation by AICAR is likely caused by increasing lipid catabolism and decreasing lipid anabolism. The improved glucose metabolism by AICAR may be ascribed to decreased hepatic gluconeogenesis, as well as increased muscle glucose uptake and utilization.

BPA exposure in L6 myotubes increased basal glucose metabolism in an estrogen receptor-dependent manner but induced insulin resistance

Exposure to bisphenol A (BPA) is associated with insulin resistance and type 2 diabetes (T2D). Since muscle insulin resistance is the primary defect in T2D, we aimed to determine whether BPA alters glucose metabolism in L6 muscle cells. L6 or L6-GLUT4-myc cells were exposed to 1-104 nM BPA or the vehicle (0.1% DMSO) for 7 days. BPA at 103-104 nM significantly decreased the levels of the muscle differentiation markers troponin- T and myosin heavy chain 3. Insulin-stimulated phosphorylation of Akt and GSK3, insulin-stimulated glucose uptake, and insulin-stimulated GLUT4 translocation were significantly decreased with 103-104 nM BPA. Basal glucose uptake and glycolysis (extracellular acidification rates measured by Seahorse XFe96) were increased with 103-104 nM BPA. Levels of ROS detoxifying enzymes were increased with BPA >10nM, while catalase activity was increased with 103-104 nM BPA. However, BPA did not induce oxidative stress (measured by protein carbonylation and lipid peroxidation) nor mitochondrial dysfunction. The effects of BPA on basal glucose uptake and catalase activity, but not on insulin sensitivity, were restored when estrogen receptors (ERs) were inhibited with ICI. These findings suggest that high concentrations of BPA increase muscle glucose uptake through the ERs but induce insulin resistance through another pathway.

Eugenol improves high-fat diet/streptomycin-induced type 2 diabetes mellitus (T2DM) mice muscle dysfunction by alleviating inflammation and increasing muscle glucose uptake.

Eugenol has been used in dietary interventions for metabolic diseases such as diabetes and obesity. However, the protective effect of eugenol on muscle function in diabetes is unclear. In this study, a high-fat diet (HFD) with a streptozocin (STZ) injection induced type II diabetes mellitus in a mouse model. Oral eugenol lowered blood glucose and insulin resistance of HFD/STZ-treated mice. Eugenol reduced HFD/STZ-induced muscle inflammation and prevented muscle weakness and atrophy. Eugenol administration significantly increased GLUT4 translocation and AMPK phosphorylation in skeletal muscle, thereby enhancing glucose uptake. By silencing the transient receptor potential vanilloid channel 1 (TRPV1) gene in C2C12 myotube cells, eugenol was found to increase intracellular Ca2+ levels through TRPV1, which then activated calmodulin-dependent protein kinase-2 (CaMKK2) and affected AMPK protein phosphorylation. In conclusion, eugenol is a potential nutraceutical for preventing high-glucose-induced muscle impairments, which could be explained by its mediating effects on glucose absorption and inflammatory responses in the muscle.

Caloric restriction alters galanin and its receptor in hypothalamus of wistar rats

Caloric restriction (CR) reverses obesity and insulin resistance, yet the detailed mechanism underlying its beneficial effects is poorly understood. The galanin system is closely associated with energy metabolism. It is yet unclear whether this effect of CR is operating through the regulation of the galanin system. To test this effect, we subjected rats to either 60% or 40% calorie restriction for one week. After the one-week's experiment, galanin and many genes associated with the function of metabolism were examined. The present findings showed that 7 days of 60% or 40% calorie restriction lowered body weight and plasma glucose concentration in rats, suggesting that rats under CR have improved weight loss and systemic glucose metabolism. Besides, the lower plasma glucose was associated with an increase in muscle glucose uptake resulting from elevations of both glucose transporter 4 (GLUT4) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression in skeletal muscles. Moreover, the levels of galanin and its receptors (GALR1-3) mRNA markedly increased in the hypothalamus of CR rats. Taken together, these results supported that non-pharmacological activation of the galanin/GALR signaling with CR regimen led to activation of the PGC-1α/GLUT4 axis in skeletal muscles which can enhance energy metabolism. The current findings provide additional evidence that galanin is a critical factor for CR-induced weight loss and metabolic changes. CR regimen may be recognized as a non-pharmacological intervention that could prevent obesity and its associated metabolic disorders.

Chronic Elevation of Skeletal Muscle [Ca2+]i Impairs Glucose Uptake. An in Vivo and in Vitro Study.

Skeletal muscle is the primary site of insulin-mediated glucose uptake through the body and, therefore, an essential contributor to glucose homeostasis maintenance. We have recently provided evidence that chronic elevated intracellular Ca2+ concentration at rest [(Ca2+)i] compromises glucose homeostasis in malignant hyperthermia muscle cells. To further investigate how chronic elevated muscle [Ca2+]i modifies insulin-mediated glucose homeostasis, we measured [Ca2+]i and glucose uptake in vivo and in vitro in intact polarized muscle cells from glucose-intolerant RYR1-p.R163C and db/db mice. Glucose-intolerant RYR1-p.R163C and db/db mice have significantly elevated muscle [Ca2+]i and reduced muscle glucose uptake compared to WT muscle cells. Dantrolene treatment (1.5 mg/kg IP injection for 2 weeks) caused a significant reduction in fasting blood glucose levels and muscle [Ca2+]i and increased muscle glucose uptake compared to untreated RYR1-p.R163C and db/db mice. Furthermore, RYR1-p.R163C and db/db mice had abnormal basal insulin levels and response to glucose-stimulated insulin secretion. In vitro experiments conducted on single muscle fibers, dantrolene improved insulin-mediated glucose uptake in RYR1-p.R163C and db/db muscle fibers without affecting WT muscle fibers. In muscle cells with chronic elevated [Ca2+]i, GLUT4 expression was significantly lower, and the subcellular fraction (plasma membrane/cytoplasmic) was abnormal compared to WT. The results of this study suggest that i) Chronic elevated muscle [Ca2+]i decreases insulin-stimulated glucose uptake and consequently causes hyperglycemia; ii) Reduced muscle [Ca2+]i by dantrolene improves muscle glucose uptake and subsequent hyperglycemia; iii) The mechanism by which chronic high levels of [Ca2+]i interfere with insulin action appears to involve the expression of GLUT4 and its subcellular fractionation.

Transcriptome Analysis of Liver Cancer Cell Huh-7 Treated With Metformin.

Metformin is a kind of widely used antidiabetic drug that regulates glucose homeostasis by inhibiting liver glucose production and increasing muscle glucose uptake. Recently, some studies showed that metformin exhibits anticancer properties in a variety of cancers. Although several antitumor mechanisms have been proposed for metformin action, its mode of action in human liver cancer remains not elucidated. In our study, we investigated the underlying molecular mechanisms of metformin's antitumor effect on Huh-7 cells of hepatocellular carcinoma (HCC) in vitro. RNA sequencing was performed to explore the effect of metformin on the transcriptome of Huh-7 cells. The results revealed that 4,518 genes (with log2 fold change > 1 or < −1, adjusted p-value < 0.05) were differentially expressed in Huh-7 cells with treatment of 25-mM metformin compared with 0-mM metformin, including 1,812 upregulated and 2,706 downregulated genes. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses identified 54 classical pathways that were significantly enriched, and 16 pathways are closely associated with cancer, such as cell cycle, DNA replication, extracellular matrix–receptor interaction, and so on. We selected 11 differentially expressed genes, which are closely associated with HCC, to validate their differential expressions through a quantitative real-time reverse transcription-polymerase chain reaction. The result exhibited that the genes of fatty acid synthase, mini-chromosome maintenance complex components 6 and 5, myristoylated alanine-rich C-kinase substrate, fatty acid desaturase 2, C-X-C motif chemokine ligand 1, bone morphogenetic protein 4, S-phase kinase-associated protein 2, kininogen 1, and proliferating cell nuclear antigen were downregulated, and Dual-specificity phosphatase-1 is significantly upregulated in Huh-7 cells with treatment of 25-mM metformin. These differentially expressed genes and pathways might play a crucial part in the antitumor effect of metformin and might be potential targets of metformin treating HCC. Further investigations are required to evaluate the metformin mechanisms of anticancer action in vivo.

Vanillin modulates activities linked to dysmetabolism in psoas muscle of diabetic rats

Skeletal muscles are important in glucose metabolism and are affected in type 2 diabetes (T2D) and its complications. This study investigated the effect of vanillin on redox imbalance, cholinergic and purinergic dysfunction, and glucose-lipid dysmetabolism in muscles of rats with T2D. Male albino rats (Sprague–Dawley strain) were fed 10% fructose ad libitum for 2 weeks before intraperitoneally injecting them with 40 mg/kg streptozotocin to induce T2D. Low (150 mg/kg bodyweight (BW)) and high (300 mg/kg BW) doses of vanillin were orally administered to diabetic rats. Untreated diabetic rats and normal rats made up the diabetic control (DC) and normal control (NC) groups, respectively. The standard antidiabetic drug was metformin. The rats were humanely put to sleep after 5 weeks of treatment and their psoas muscles were harvested. There was suppression in the levels of glutathione, activities of SOD, catalase, ENTPDase, 5′Nucleotidase and glycogen levels on T2D induction. This was accompanied by concomitantly elevated levels of malondialdehyde, serum creatine kinase-MB, nitric oxide, acetylcholinesterase, ATPase, amylase, lipase, glucose-6-phosphatase (G6Pase), fructose-1,6-biphophastase (FBPase) and glycogen phosphorylase activities. T2D induction further resulted in the inactivation of fatty acid biosynthesis, glycerolipid metabolism, fatty acid elongation in mitochondria and fatty acid metabolism pathways. There were close to normal and significant reversals in these activities and levels, with concomitant reactivation of the deactivated pathways following treatment with vanillin, which compared favorably with the standard drug (metformin). Vanillin also significantly increased muscle glucose uptake ex vivo. The results suggest the therapeutic effect of vanillin against muscle dysmetabolism in T2D as portrayed by its ability to mitigate redox imbalance, inflammation, cholinergic and purinergic dysfunctions, while modulating glucose-lipid metabolic switch and maintaining muscle histology.

Synthesis of a novel glibenclamide-pioglitazone hybrid compound and its effects on glucose homeostasis in normal and insulin-resistant rats

A new library of hybrid compounds that combine the functional parts of glibenclamide and pioglitazone was designed and developed. Compounds were screened for their antihyperglycemic effects on the glucose tolerance curve. This approach provided a single molecule that optimizes the pharmacological activities of two drugs used for the treatment of diabetes mellitus type 2 (DM2) and that have distinct biological activities, potentially minimizing the adverse effects of the original drugs. From a total of 15 compounds, 7 were evaluated in vivo; the compound 2; 4- [2- (2-phenyl-4-oxo-1,3-thiazolidin-3-yl) ethyl] benzene-1-sulfonamide (PTEBS) was selected to study its mechanism of action on glucose and lipid homeostasis in acute and chronic animal models related to DM2. PTEBS reduced glycemia and increased serum insulin in hyperglycemic rats, and elevated in vitro insulin production from isolated pancreatic islets. This compound increased the glycogen content in hepatic and muscular tissue. Moreover, PTEBS stimulated the uptake of glucose in soleus muscle through a signaling pathway similar to that of insulin, stimulating translocation and protein synthesis of glucose transporter 4 (GLUT4). PTEBS was effective in increasing insulin sensitivity in resistance rats by stimulating increased muscle glucose uptake, among other mechanisms. In addition, this compound reduced total triglycerides in a tolerance test to lipids and reduced advanced glycation end products (AGES), without altering lactate dehydrogenase (LDH) activity. Thus, we suggest that PTEBS may have similar effects to the respective prototypes, which may improve the therapeutic efficacy of these molecules and decrease adverse effects in the long-term.

L-leucine stimulation of glucose uptake and utilization involves modulation of glucose - lipid metabolic switch and improved bioenergetic homeostasis in isolated rat psoas muscle ex vivo.

The antidiabetic effect of l-leucine has been attributed to its modulatory effect on glucose uptake and lipid metabolism in muscles. However, there is a dearth on its effect on glucose metabolism in muscles. Thus, the present study investigated the effect of l-leucine - stimulated glucose uptake on glucose metabolism, dysregulated lipid metabolic pathways, redox and bioenergetic homeostasis, and proteolysis in isolated psoas muscle from Sprague Dawley male rats. Isolated psoas muscles were incubated with l-leucine (30-240μg/mL) in the presence of 11.1 mMol glucose at 37 ˚C for 2h. Muscles incubated in only glucose served as the control, while muscles not incubated in l-leucine and/or glucose served as the normal control. Metformin (6.04mM) was used as the standard antidiabetic drug. Incubation with l-leucine caused a significant increase in muscle glucose uptake, with an elevation of glutathione levels, superoxide dismutase, catalase, E-NTPDase and 5'nucleotidase activities. It also led to the depletion of malondialdehyde and nitric oxide levels, ATPase, chymotrypsin, acetylcholinesterase, glycogen phosphorylase, glucose-6-phosphatase, fructose-1,6-bisphosphatase and lipase activities. There was an alteration in lipid metabolites, with concomitant activation of glycerolipid metabolism, fatty acid metabolism, and fatty acid elongation in mitochondria in the glucose-incubated muscle (negative control). Incubation with l-leucine reversed these alterations, and concomitantly deactivated the pathways. These results indicate that l-leucine-enhanced muscle glucose uptake involves improved redox and bioenergetic homeostasis, with concomitant suppressed proteolytic, glycogenolytic and gluconeogenetic activities, while modulating glucose - lipid metabolic switch.

Measurement of Insulin- and Contraction-Stimulated Glucose Uptake in Isolated and Incubated Mature Skeletal Muscle from Mice.

Skeletal muscle is an insulin-responsive tissue and typically takes up most of the glucose that enters the blood after a meal. Moreover, it has been reported that skeletal muscle may increase the extraction of glucose from the blood by up to 50-fold during exercise compared to resting conditions. The increase in muscle glucose uptake during exercise and insulin stimulation is dependent on the translocation of glucose transporter 4 (GLUT4) from intracellular compartments to the muscle cell surface membrane, as well as phosphorylation of glucose to glucose-6-phosphate by hexokinase II. Isolation and incubation of mouse muscles such as m. soleus and m. extensor digitorum longus (EDL) is an appropriate ex vivo model to study the effects of insulin and electrically-induced contraction (a model for exercise) on glucose uptake in mature skeletal muscle. Thus, the ex vivo model permits evaluation of muscle insulin sensitivity and makes it possible to match muscle force production during contraction ensuring uniform recruitment of muscle fibers during measurements of muscle glucose uptake. Moreover, the described model is suitable for pharmacological compound testing that may have an impact on muscle insulin sensitivity or may be of help when trying to delineate the regulatory complexity of skeletal muscle glucose uptake. Here we describe and provide a detailed protocol on how to measure insulin- and contraction-stimulated glucose uptake in isolated and incubated soleus and EDL muscle preparations from mice using radiolabeled [3H]2-deoxy-D-glucose and [14C]mannitol as an extracellular marker. This allows accurate assessment of glucose uptake in mature skeletal muscle in the absence of confounding factors that may interfere in the intact animal model. In addition, we provide information on metabolic viability of incubated mouse skeletal muscle suggesting that the methodapplied possesses some caveats under certain conditions when studying muscle energy metabolism.

Imeglimin: Current Development and Future Potential in Type 2 Diabetes.

Imeglimin is the first of the "glimins," a new class of drugs developed for the treatment of type 2 diabetes mellitus (T2DM). This review highlights its mechanism of action and its context in the field of T2DM treatment. Preclinical data in multiple rodent models have detailed significant effects on mitochondria, particularly improved mitochondrial bioenergetics. This includes changes favoring complex II and complex III metabolism, a mechanism potentially promoting increased fatty acid oxidation, leading to the decrease in hepatic lipid accumulation observed in these mice. Imeglimin was also shown to increase muscle glucose uptake and decrease hepatic glucose production, both in vitro and in vivo. Though studies have also shown imeglimin to significantly improve insulin secretion and decrease β-cell death, whether its physiologic effects are purely insulin dependent remains unclear. Early preclinical studies have shown evidence for improvements in cardiac and renal function in rats with metabolic syndrome, effects not conferred by most currently available T2DM drugs. Clinical studies of imeglimin in humans have shown increased insulin secretion, along with decreased fasting plasma glucose and glycated hemoglobin. Its observed efficacy was comparable to that of currently available agents metformin and sitagliptin and was increased when given in combination with either agent. When considered alongside its benign safety profile reported in patients with chronic kidney disease, imeglimin shows true promise to provide a novel mechanism for T2DM treatment, with potential application in a larger, more comprehensive patient population.

Is GLUT4 translocation the answer to exercise-stimulated muscle glucose uptake?

Exercise in humans increases muscle glucose uptake up to 100-fold compared with rest. The magnitude of increase depends on exercise intensity and duration. Although knockout of glucose transporter type 4 (GLUT4) convincingly has shown that GLUT4 is necessary for exercise to increase muscle glucose uptake, studies only show an approximate twofold increase in GLUT4 translocation to the muscle cell membrane when transitioning from rest to exercise. Therefore, there is a big discrepancy between the increase in glucose uptake and GLUT4 translocation. It is suggested that either the methods for measurements of GLUT4 translocation in muscle grossly underestimate the real translocation of GLUT4 or, alternatively, GLUT4 intrinsic activity increases in muscle during exercise, perhaps due to increased muscle temperature and/or mechanical effects during contraction/relaxation cycles.

Does Acute Exercise Increase Insulin‐Stimulated Skeletal Muscle Glucose Uptake, Blood Flow And Insulin Signalling In Response To A Meal?

A single bout of exercise increases skeletal muscle insulin sensitivity measured by euglycemic, hyperinsulinemic clamp (EHC) through coordinated increases in skeletal muscle insulin‐stimulated microvascular perfusion and molecular signalling at the level of TBC1D4 (2, 3). Surpringly, however, skeletal muscle interstitial glucose concentration decreases substantially during a EHC, especially after one‐legged exercise, reaching 2–3 mM (1). This result may, however, be a artifact of the EHC because, unlike after a meal, blood glucose does not rise during a EHC but is “clamped” at around 5 mM while plasma insulin is elevated. Therefore, the aim of this project was to determine the effect on leg blood flow and skeletal muscle glucose metabolism of meals begun 4 hours after one‐legged exercise. We hypothesized that hyperglycemia after the meal would prevent a drop in muscle interstitial glucose concentrations and result in large increases in leg glucose uptake. Four healthy young males performed 60 min of 1‐legged knee extensor exercise involving at 80% of 1‐legged peak work load (PWL) with three 5 min intervals at 100% 1‐legged PWL. Participants then rested for 4 hours and catheters were inserted into the femoral artery of one leg and the femoral vein of both legs and two microdialysis catheters for measurement of interstitial glucose concentration were inserted into the vastus lateral muscle of both legs. A solid meal was ingested (40 kJ.kg BW−1) 4 hrs after the 1‐legged exercise with smaller liquid meals (20 kJ.kg BW−1) ingested 4.5 and 5 hrs after the exercise. Four hours after exercise there was no significant difference between the exercised and rested leg for leg blood flow, leg arteriovenous glucose difference, leg glucose uptake, vastus lateralis interstitial glucose concentration or apparent muscle membrane glucose permeability. Meal ingestion increased arterial blood glucose concentration and increased leg blood flow, leg arteriovenous glucose difference and leg glucose uptake more in the exercised leg than the rested leg. Meals increased vastus lateralis interstitial glucose concentration, especially in the rested leg. Vastus lateralis apparent muscle membrane glucose permeability increased with the meals in both legs and moreso in the previously exercised leg. Ingestion of meals several hours after 1‐legged exercise results in hyperglycemia, increased skeletal muscle interstitial glucose concentration and increased muscle membrane permeability to glucose. This results in larger increases in muscle glucose uptake in the previously exercised than the rested leg. Real life feeding after exercise confirms and extends findings from clamp studies.

Glucocorticoids affect metabolic but not muscle microvascular insulin sensitivity following high versus low salt intake.

BACKGROUNDSalt-sensitive hypertension is often accompanied by insulin resistance in obese individuals, but the underlying mechanisms are obscure. Microvascular function is known to affect both salt sensitivity of blood pressure and metabolic insulin sensitivity. We hypothesized that excessive salt intake increases blood pressure and decreases insulin-mediated glucose disposal, at least in part by impairing insulin-mediated muscle microvascular recruitment (IMMR).METHODSIn 20 lean and 20 abdominally obese individuals, we assessed mean arterial pressure (MAP; 24-hour ambulatory blood pressure measurements), insulin-mediated whole-body glucose disposal (M/I value; hyperinsulinemic-euglycemic clamp technique), IMMR (contrast-enhanced ultrasound), osmolyte and water balance, and excretion of mineralocorticoids, glucocorticoids, and amino and organic acids after a low- and high-salt diet during 7 days in a randomized, double-blind, crossover design.RESULTSOn a low-, as compared with a high-salt, intake, MAP was lower, M/I value was lower, and IMMR was greater in both lean and abdominally obese individuals. In addition, natural logarithm IMMR was inversely associated with MAP in lean participants on a low-salt diet only. On a high-salt diet, free water clearance decreased, and excretion of glucocorticoids and of amino acids involved in the urea cycle increased.CONCLUSIONOur findings imply that hemodynamic and metabolic changes resulting from alterations in salt intake are not necessarily associated. Moreover, they are consistent with the concept that a high-salt intake increases muscle glucose uptake as a response to high salt-induced, glucocorticoid-driven muscle catabolism to stimulate urea production and thereby renal water conservation.TRIAL REGISTRATIONClinicalTrials.gov, NCT02068781.

Impaired skeletal muscle mitochondrial pyruvate uptake rewires glucose metabolism to drive whole-body leanness.

Metabolic cycles are a fundamental element of cellular and organismal function. Among the most critical in higher organisms is the Cori Cycle, the systemic cycling between lactate and glucose. Here, skeletal muscle-specific Mitochondrial Pyruvate Carrier (MPC) deletion in mice diverted pyruvate into circulating lactate. This switch disinhibited muscle fatty acid oxidation and drove Cori Cycling that contributed to increased energy expenditure. Loss of muscle MPC activity led to strikingly decreased adiposity with complete muscle mass and strength retention. Notably, despite decreasing muscle glucose oxidation, muscle MPC disruption increased muscle glucose uptake and whole-body insulin sensitivity. Furthermore, chronic and acute muscle MPC deletion accelerated fat mass loss on a normal diet after high fat diet-induced obesity. Our results illuminate the role of the skeletal muscle MPC as a whole-body carbon flux control point. They highlight the potential utility of modulating muscle pyruvate utilization to ameliorate obesity and type 2 diabetes.

2173-P: Effects of AMP-Activated Protein Kinase Activation on Insulin Secretion in Mice

AMP-activated protein kinase (AMPK) is an important cellular energy sensor in regulation of metabolic activity. AMPK activation improves glucose homeostasis by increasing muscle glucose uptake and reducing hepatic glucose production. Although the effects on glucose-stimulated insulin secretion in the pancreatic β cells are still controversial. Our aim was to investigate the regulation of insulin secretion in pancreatic β cells using specific pharmacological AMPK activators and in mouse models of constitutive activation. We used a chronic global AMPK (γ1D316A) and a pancreatic β cell specific (β-D316A) activation mouse model that express the AMPK γamma1 isoform with a D316A mutation under the control of β-actin and ins1 promoter respectively. We tested how chronic AMPK activation impacted insulin secretion on C57BL6 mouse isolated islets using direct activators PF-06409577 (β1 isoform-selective) and RA089 (binds both β1 and β2 isoforms). Global activation of AMPK reduced insulin secretion from islets isolated from γ1D316A mice on chow and high-fat diet (2.4-fold, p&amp;lt;0.05 and 1.9-fold p&amp;lt;0.01, respectively). Dual AMPK activation of β1 and β2 (RA089) on control mouse islets enhanced in a dose-response manner insulin secretion in response to high glucose (17mM) and KCl after 30 minutes of incubation (1.7-fold p&amp;lt;0.005 and 1.7-fold p&amp;lt;0.005, respectively). The same effects were observed by activating AMPK β1 isoform with PF-06409577, increasing insulin release in response to high glucose and KCl (2-fold, p&amp;lt;0.005 and 1.7-fold, p&amp;lt;0.05). These findings suggest that the effects of AMPK on insulin secretion depends on its mode of activation. Acute pharmacological activation targetting β1 and/or β2 subunit increased insulin secretion whereas chronic global activation in mice reduced insulin release. Investigating our second model of chronic activation β-D316A and further studies of our models will help us decipher the role of AMPK in the pancreas. Disclosure M. Nguyen-Tu: None. J.P. Harris: None. A. Martinez-Sanchez: None. I. Leclerc: None. G.A. Rutter: Consultant; Self; Sun Pharma.

Raffia palm (Raphia hookeri) wine: Qualitative sugar profile, functional chemistry, and antidiabetic properties

The effects of short-term fermentation on the sugar quality, functional chemistry, antioxidant and antidiabetic properties of Raffia palm (Raphia hookeri) wine were investigated. Palm wine samples were subjected to open air fermentation for 24 and 48 h. The samples showed significant (p < 0.05) antioxidant activities with little or no differences between the unfermented and fermented samples. There was a dose-dependent inhibitory effect on α-glucosidase, α-amylase and intestinal glucose absorption with increasing fermentation time. Both non-fermented and 24 h fermentation led to increased muscle glucose uptake in a dose-dependent manner. 1H NMR spectroscopy showed the presence of allose, cellobiose, d-tagatose, fructose, galactitol, gluconic acid, rhamnose, sucrose, xylose and β-N-acetylglucosamine in the samples. FTIR spectroscopy showed the presence of alcohols, phenols, 1° and 2° amines and aromatics functional groups in all samples. Fermentation led to the addition of the functional group, bend alkenes. These results suggested that un-fermented and fermented Raffia palm wine may have antioxidant and antidiabetic properties.

D-mannitol modulates glucose uptake ex vivo; suppresses intestinal glucose absorption in normal and type 2 diabetic rats

Mannitol is a widely used reduced-calorie sweetener with limited studies on its anti-hyperglycemic potential. The anti-hyperglycemic potential of mannitol was investigated using different experimental models. Mannitol inhibited α-glucosidase (IC50 = 180 ± 20% w/v) and α-amylase (IC50 = 75 ± 20% w/v) activities in a dose dependent (2.5–20% w/v) manner, in vitro, although the effective doses are not gastrointestinally tolerable. Mannitol inhibited glucose absorption (IC50 = 19 ± 3% w/v) in isolated rat jejunum in a dose dependent (2.5–20% w/v) manner, perhaps by entrapment of glucose molecules. Acute administration of 0.3 g/kg bw reduced small intestinal glucose absorption in type 2 diabetic rats, which was accompanied by reduced blood glucose. The reduced intestinal glucose absorption may be influenced by the concomitant delayed gastric emptying observed in the mannitol-treated diabetic animals. On the other hand, mannitol increased glucose uptake in a yeast cell suspension (GU50 = 4.7 ± 1.2% w/v), 3T3-L1 adipocytes (GU50 = 1.2 ± 0.4% w/v) and isolated rat muscle (GU50 = 25 ± 3% w/v) in a dose dependent manner. In silico docking suggested that GLUT-4 (binding energy = −15.5 kcal/mol) is a possible molecular target of mannitol. Data from this study suggest that mannitol may be used as a dietary supplement in controlling postprandial blood glucose increase by reducing intestinal glucose absorption and increasing muscle glucose uptake, which needs further study.