Increased 2-deoxyglucose Uptake Research Articles

Genetically determined exercise capacity affects systemic glucose response to insulin in rats.

Aerobic exercise capacity is inversely related to morbidity and mortality as well as to insulin resistance. However, exercising in patients has led to conflicting results, presumably because aerobic exercise capacity consists of intrinsic (genetically determined) and extrinsic (environmentally determined) parts. The contribution of both parts to insulin sensitivity is also not clear. We investigated sedentary and exercised (aerobic interval training) high-capacity runners (HCR) and low-capacity runners (LCR) differing in their genetically determined aerobic exercise capacity to determine the contribution of both parts to insulin sensitivity. LCR and HCR differed in their untrained exercise capacity and body weight. Sedentary LCR displayed a diabetic phenotype with higher random glucose, lower glucose infusion rate during hyperinsulinemic euglycemic clamping than HCR. Echocardiography showed equal morphological and functional parameters and no change with exercise. Four week of exercise caused significant improvements in aerobic exercise capacity, which was more pronounced in LCR. However, with respect to glucose use, exercise affected HCR only. In these animals, exercise increased 2-deoxyglucose uptake in gastrocnemius (+58.5%, P = 0.1) and in epididymal fat (+106%; P < 0.05). Citrate synthase activity also increased in these tissues (gastrocnemius 69% epididymal fat 63%). In our model of HCR and LCR, genetic predisposition for low exercise capacity is associated with impaired insulin sensitivity and impedes exercise-induced improvements in insulin response. Our results suggest that genetic predisposition for low aerobic exercise capacity impairs insulin response, which may not be overcome by exercise.

Insulin acutely increases glucose transporter 1 on plasma membranes and glucose uptake in an AKT-dependent manner in chicken adipocytes

Avian glucose transporters (GLUT) responsible for insulin-responsive glucose uptake into adipocytes remain poorly characterized. We aimed to identify the insulin-responsive GLUT using primary culture of chicken adipocytes. Acute stimulation with 1 μM insulin for 20 min increased 2-deoxyglucose uptake, AKT protein phosphorylation, and GLUT1 protein levels on the plasma membrane of the chicken adipocytes, whereas pretreatment with 10 μM triciribine, an AKT inhibitor, canceled these effects. Furthermore, the insulin stimulation did not affect GLUT12 protein levels on the plasma membrane of the chicken adipocytes. Our results suggest that GLUT1 is an insulin-responsive GLUT in chicken adipocytes.

OR31-4 Neonatal Vitamin D Deficiency and Insulin Resistance

Background: Vitamin D deficiency is prevalent in pregnant women and their offspring. Maternal vitamin D deficiency is associated with insulin resistance in children and can induce a proinflammatory macrophage phenotype [1, 2]. Purpose: We hypothesized that maternal vitamin D deficiency induces immune cell reprogramming that promotes adipose insulin resistance in the offspring and is detectable in the newborn period. Methods: We enrolled 32 normal pregnant women prior to delivery of AGA, term infants. Cord blood was obtained and used to determine vitamin D [25(OH)D] levels and qPCR of microRNA levels. Cord blood monocytes were co-cultured with 3T3L1 adipocytes for insulin-stimulated 2-deoxyglucose uptake studies, and the monocyte media and co-cultured adipocytes were analyzed for microRNA expression. 3T3L1 adipocytes were transfected with miR106b mimic and antagonist to confirm the effect of the 2-deoxyglucose results. Results: 83% of the newborn’s venous cord blood showed vitamin D deficiency with 25(OH)D <20 ng/mL (n=24, total n=29). Adipocytes co-cultured with cord blood monocytes showed an inverse correlation between insulin stimulated 2-deoxyglucose uptake and cord blood 25(OH)D levels (n=29, Spearman r=0.43, p=0.02). Adipocytes exposed to monocytes or to monocyte media elevated miR106b by 7 to 12-fold (n=8, p<0.01). Interestingly, cord blood plasma miR106b levels were found to inversely correlate with 25(OH)D levels (n=27, Spearman r=-0.41, p<0.04). Transfection of adipocytes with miR106b mimic reduced the 2-deoxyglucose uptake after insulin stimulation, whereas transfection with anti-miR-106b increased 2-deoxyglucose uptake after insulin stimulation, suggesting that monocyte secretion of miR106b induced adipose insulin resistance (n=8, p<0.05). Conclusions: This study provides evidence of a novel intercellular miRNA communication mechanism enabling monocytes programmed in utero by vitamin D deficiency to induce adipose insulin resistance. Identification of circulating miR106b as a mechanism of insulin resistance in offspring born with vitamin D deficiency is a potential advance toward precision medicine as it allows for optimal targeting of those at risk for diabetes later in life within a heterogeneous population. These findings serve as background for interventional studies evaluating the effect of maternal vitamin D supplementation on offspring insulin resistance later in life.

Characterization of Macrophage Polarization States Using Combined Measurement of 2-Deoxyglucose and Glutamine Accumulation: Implications for Imaging of Atherosclerosis.

Despite the early promising results of 18F-fluorodeoxyglucose positron emission tomography for assessment of vessel wall inflammation, its accuracy in prospective identification of vulnerable plaques has remained limited. Additionally, previous studies have indicated that 18F-fluorodeoxyglucose uptake alone may not allow for accurate identification of specific macrophage activation states. We aimed to determine whether combined measurement of glucose and glutamine accumulation-the 2 most important bioenergetic substrates for macrophages-improves the distinction of macrophage inflammatory states and can be utilized to image atherosclerosis. Murine peritoneal macrophages (MΦ) were activated ex vivo into proinflammatory states with either lipopolysaccharide (MΦLPS) or interferon-γ+tumor necrosis factor-α (MΦIFN-γ+TNF-α). An alternative polarization phenotype was induced with interleukin-4 (MΦIL-4). The pronounced increase in 2-deoxyglucose uptake distinguishes MΦLPS from MΦIFN-γ+TNF-α, MΦIL-4, and unstimulated macrophages (MΦ0). Despite having comparable levels of 2-deoxyglucose accumulation, MΦIL-4 can be distinguished from both MΦIFN-γ+TNF-α and MΦ0 based on the enhanced glutamine accumulation, which was associated with increased expression of a glutamine transporter, Slc1a5. Ex vivo autoradiography experiments demonstrated distinct and heterogenous patterns of 18F-fluorodeoxyglucose and 14C-glutamine accumulation in atherosclerotic lesions of low-density lipoprotein receptor-null mice fed a high-fat diet. Combined assessment of glutamine and 2-deoxyglucose accumulation improves the ex vivo identification of macrophage activation states. Combined ex vivo metabolic imaging demonstrates heterogenous and distinct patterns of substrate accumulation in atherosclerotic lesions. Further studies are required to define the in vivo significance of glutamine uptake in atherosclerosis and its potential application in identification of vulnerable plaques.

Differential Regulation of Macrophage Glucose Metabolism by Macrophage Colony-stimulating Factor and Granulocyte-Macrophage Colony-stimulating Factor: Implications for 18F FDG PET Imaging of Vessel Wall Inflammation.

Purpose To determine the divergence of immunometabolic phenotypes of macrophages stimulated with macrophage colony-stimulating factor (M-CSF) and granulocyte-M-CSF (GM-CSF) and its implications for fluorine 18 (18F) fluorodeoxyglucose (FDG) imaging of atherosclerosis. Materials and Methods This study was approved by the animal care committee. Uptake of 2-deoxyglucose and various indexes of oxidative and glycolytic metabolism were evaluated in nonactivated murine peritoneal macrophages (MΦ0) and macrophages stimulated with M-CSF (MΦM-CSF) or GM-CSF (MΦGM-CSF). Intracellular glucose flux was measured by using stable isotope tracing of glycolytic and tricyclic acid intermediary metabolites. 18F-FDG uptake was evaluated in murine atherosclerotic aortas after stimulation with M-CSF or GM-CSF by using quantitative autoradiography. Results Despite inducing distinct activation states, GM-CSF and M-CSF stimulated progressive but similar levels of increased 2-deoxyglucose uptake in macrophages that reached up to sixfold compared with MΦ0. The expression of glucose transporters, oxidative metabolism, and mitochondrial biogenesis were induced to similar levels in MΦM-CSF and MΦGM-CSF. Unexpectedly, there was a 1.7-fold increase in extracellular acidification rate, a 1.4-fold increase in lactate production, and overexpression of several critical glycolytic enzymes in MΦM-CSF compared with MΦGM-CSF with associated increased glucose flux through glycolytic pathway. Quantitative autoradiography demonstrated a 1.6-fold induction of 18F-FDG uptake in murine atherosclerotic plaques by both M-CSF and GM-CSF. Conclusion The proinflammatory and inflammation-resolving activation states of macrophages induced by GM-CSF and M-CSF in either cell culture or atherosclerotic plaques may not be distinguishable by the assessment of glucose uptake. © RSNA, 2016 Online supplemental material is available for this article.

GM-CSF Enhances Macrophage Glycolytic Activity In Vitro and Improves Detection of Inflammation In Vivo.

(18)F-FDG accumulates in glycolytically active tissues and is known to concentrate in tissues that are rich in activated macrophages. In this study, we tested the hypotheses that human granulocyte-macrophage colony-stimulating factor (GM-CSF), a clinically used cytokine, increases macrophage glycolysis and deoxyglucose uptake in vitro and acutely enhances (18)F-FDG uptake within inflamed tissues such as atherosclerotic plaques in vivo. In vitro experiments were conducted on human macrophages whereby inflammatory activation and uptake of radiolabeled 2-deoxyglucose was assessed before and after GM-CSF exposure. In vivo studies were performed on mice and New Zealand White rabbits to assess the effect of GM-CSF on (18)F-FDG uptake in normal versus inflamed arteries, using PET. Incubation of human macrophages with GM-CSF resulted in increased glycolysis and increased 2-deoxyglucose uptake (P < 0.05). This effect was attenuated by neutralizing antibodies against tumor necrosis factor-α or after silencing or inhibition of 6-phosphofructo-2-kinase. In vivo, in mice and in rabbits, intravenous GM-CSF administration resulted in a 70% and 73% increase (P < 0.01 for both), respectively, in arterial (18)F-FDG uptake in atherosclerotic animals but not in nonatherosclerotic controls. Histopathologic analysis demonstrated a significant correlation between in vivo (18)F-FDG uptake and macrophage staining (R = 0.75, P < 0.01). GM-CSF substantially augments glycolytic flux in vitro (via a mechanism dependent on ubiquitous type 6-phosphofructo-2-kinase and tumor necrosis factor-α) and increases (18)F-FDG uptake within inflamed atheroma in vivo. These findings demonstrate that GM-CSF can be used to enhance detection of inflammation. Further studies should explore the role of GM-CSF stimulation to enhance the detection of inflammatory foci in other disease states.

Glycolipids: isolated from Oplismenus burmannii induce glucose uptake in L6-GLUT4myc myotube cells.

Bioactivity guided separation of combined n-hexane and chloroform extracts of Oplismenus burmannii resulted in the isolation and characterization of five new glycoglycerolipids, (2S)-1,2,6'-tri- O-hexadecanoyl-3-O-β-D-galactopyranosyl glycerol (1a), (2S)-1,2,6'-tri-O-[(9Z,12Z)-octadeca-9,12- dienoyl]-3-O-β-D-galactopyranosyl glycerol (1b), (2S)-1,6'-di-O-[(9Z,12Z)-octadeca-9,12-dienoyl]-3- O-β-D-galactopyranosyl glycerol (2b), (2S)-1,6'-di-O-[(9Z,12Z,15Z)-octadeca-9,12,15-trienoyl]-3-O-β-D-galactopyranosyl glycerol (2c), and (2S)-1,2-di-O-[(9Z,12Z)-octadeca-9,12-dienoyl]-3-O-(6- sulpho-α-D)-quinovopyranosyl glycerol (3b) along with five known glycoglycerolipids (1c, 2a, 3a, 3c and 4), a cerebroside (5), three monoacylglycerols (6a-c) and α-linoleic acid (7). The isolated compounds, 1-5 were in-vitro tested for their antihyperglycemic potential in terms of increase in 2-deoxyglucose uptake in L6-GLUT4myc myotube cells. The results showed that compounds, 1-5 were showing 1.52 (P<0.05), 1.50 (P<0.05), 1.28, 1.49 (P<0.05) and 1.50 (P<0.05) fold increase in the glucose uptake at concentration of 10 μg/mL and 1.71 (P<0.001), 1.74 (P<0.001), 1.50 (P<0.05), 1.76 (P<0.001) and 1.74 (P<0.001) fold increase in the glucose uptake at concentration of 25 μg/mL respectively. However, standard drug Rosiglitazone increases the glucose uptake by 1.59 fold at the concentration of 10μM. Further work on optimization of the anti-diabetic lead is under progress.

Mechanisms of increased in vivo insulin sensitivity by dietary methionine restriction in mice.

To understand the physiological significance of the reduction in fasting insulin produced by dietary methionine restriction (MR), hyperinsulinemic-euglycemic clamps were used to examine the effect of the diet on overall and tissue-specific insulin sensitivity in mice. The steady-state glucose infusion rate was threefold higher in the MR group and consistent with the 2.5- to threefold increase in 2-deoxyglucose uptake in skeletal muscle, heart, and white adipose tissue. Dietary MR enhanced suppression of hepatic glucose production by insulin, enhanced insulin-dependent Akt phosphorylation in the liver, and increased hepatic expression and circulating fibroblast growth factor 21 (FGF-21) by fourfold. Limitation of media methionine recapitulated amplification of Akt phosphorylation by insulin in HepG2 cells but not in 3T3-L1 adipocytes or C2C12 myotubes. Amplification of insulin signaling in HepG2 cells by MR was associated with reduced glutathione, where it functions as a cofactor for phosphatase and tensin homolog. In contrast, FGF-21, but not restricting media methionine, enhanced insulin-dependent Akt phosphorylation in 3T3-L1 adipocytes. These findings provide a potential mechanism for the diet-induced increase in insulin sensitivity among tissues that involves a direct effect of methionine in liver and an indirect effect in adipose tissue through MR-dependent increases in hepatic transcription and release of FGF-21.

Discovery of biaryl-4-carbonitriles as antihyperglycemic agents that may act through AMPK-p38 MAPK pathway

A series of functionalized biaryl-4-carbonitriles was synthesized in three steps and evaluated for PTP-1B inhibitory activity. Among the synthesized compounds, four biaryls 6a–d showed inhibition (IC50 58–75μM) against in vitro PTP-1B assay possibly due to interaction with amino acid residues Lys120, Tyr46 through hydrogen bonding and aromatic–aromatic interactions, respectively. Two biaryl-4-carbonitriles 6b and 6c showed improved glucose tolerance, fasting as well as postprandial blood glucose, serum total triglycerides, and increased high-density lipoprotein-cholesterol in SLM, STZ, STZ-S and C57BL/KsJ-db/db animal models. The bioanalysis of 4′-bromo-2,3-dimethyl-5-(piperidin-1-yl)biphenyl-4-carbonitrile (6b) revealed that like insulin, it increased 2-deoxyglucose uptake in skeletal muscle cells (L6 and C2C12 myotubes). The compound 6b significantly up-regulated the genes related to the insulin signaling pathways like AMPK, MAPK including glucose transporter-4 (GLUT-4) gene in muscle tissue of C57BL/KsJ-db/db mice. Furthermore, it was observed that the compound 6b up-regulated PPARα, UCP2 and HNF4α, which are key regulator of glucose, lipid, and fatty acid metabolism. Western blot analysis of the compound 6b showed that it significantly increased the phosphorylation of AMPK and p38 MAPK and ameliorated glucose uptake in C57BL/KsJ-db/db mice through the AMPK-p38 MAPK pathway.

Abstract P3-01-06: TIGAR induces two compartment metabolic coupling and tamoxifen resistance

Abstract We have previously demonstrated that metabolic coupling occurs in a subgroup of human breast cancers between fibroblasts and carcinoma cells. In metabolically coupled tumors, cancer associated fibroblasts (CAFs) have low Cav-1 protein expression, are highly glycolytic and generate large amounts of lactate which is then released to the extracellular space via increased expression of monocarboxylate transporter 4 (MCT4) compared to normal fibroblasts (NFs). Conversely, in metabolically coupled tumors, carcinoma cells have low glycolysis with high uptake of lactate via monocarboxylate transporter 1 (MCT1) and high mitochondrial oxidative phosphorylation (OXPHOS) using lactate as a substrate compared to non-carcinoma epithelial cells. We have identified two fibroblast markers of metabolically coupled breast cancer: low caveolin-1 (Cav-1) protein expression and high MCT4 protein expression. Low Cav-1 expression and high MCT4 expression in breast cancer fibroblasts are prognostic biomarkers associated with poor outcomes. However, the mechanisms by which carcinoma cells reprogram CAFs to induce loss of fibroblast Cav-1 or increased expression of MCT4 protein are unknown. TP53 inducible glycolysis and apoptosis regulator (TIGAR) is a p53 regulated protein that inhibits glycolysis and induces OXPHOS. We investigated the role of TIGAR on expression of the fibroblast prognostic biomarkers Cav-1 and MCT4. We immunohistochemically stained 10 human ER+ breast cancer samples for TIGAR. TIGAR protein expression was highest in the carcinoma cells compared to fibroblasts and non-carcinoma epithelial cells in all 10 samples. We then cocultured T47D ER+ breast cancer cells with human fibroblasts (BJ-1) and discovered that the presence of fibroblasts was sufficient to increase TIGAR protein expression in carcinoma cells (1.5 fold, p&amp;lt;0.05). This coculture system was also sufficient to downregulate Cav-1 protein expression in fibroblasts (2.3 fold, p&amp;lt;0.01). We generated fibroblasts with Cav-1 shRNA knockdown and discovered that TIGAR protein expression decreased. We generated TIGAR overexpressing T47D cells and found that they had higher OXPHOS activity. Coculture of TIGAR overexpressing T47D cells with fibroblasts induced further downregulation of Cav-1 protein in fibroblasts (3.2 fold, p&amp;lt;0.05) and increased MCT4 protein in fibroblasts (2 fold, p&amp;lt;0.05) compared to coculture with control T47D cells. Overexpression of TIGAR in T47D cells was sufficient to increase 2-deoxyglucose uptake in fibroblasts by 1.2 fold (p&amp;lt;0.01) and decrease 2-deoxyglucose uptake in T47D cells by 1.3 fold (p&amp;lt;0.05). 2-deoxyglycose uptake is a marker of glycolysis. Finally, resistance to baseline apoptosis (1.6 fold,p&amp;lt;0.001) and with tamoxifen (1.2 fold, p&amp;lt;0.01) was induced by TIGAR overexpression. In summary, TIGAR expression in carcinoma cells is sufficient to induce carcinoma cell resistance to apoptosis, decrease Cav-1 and increase MCT4 protein expression in fibroblasts. TIGAR should be studied as a prognostic and predictive biomarker in breast cancer and a potential drug target. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-01-06.

A new, highly selective murine peroxisome proliferator-activated receptor δ agonist increases responsiveness to thermogenic stimuli and glucose uptake in skeletal muscle in obese mice

We investigated how GW800644, the first pharmacologically selective murine peroxisome proliferator-activated receptor δ (PPARδ) agonist, affects energy balance, glucose homeostasis and fuel utilization by muscle in obese mice. Potencies were determined in transactivation assays. Oral glucose tolerance was determined after 14 and 22 days' administration (10 mg/kg body weight, twice daily) to Lep(ob)/Lep(ob) mice. Food intake and energy expenditure were measured during a 26-day experiment, and plasma metabolites and 2-deoxyglucose uptake in vivo at termination. Palmitate oxidation and 2-deoxyglucose uptake by isolated soleus muscles were measured after 14 (in lean and obese mice) and 26 days. GW800644 activated murine PPARδ (EC(50) 2 nM), but caused little to no activation of PPARα or PPARγ up to 10 µM. It did not increase liver weight. GW800644 reduced food intake and body weight in obese mice after 8 days. It did not affect resting energy expenditure, but, compared to pair-fed mice, it increased the response to a β(3)-adrenoceptor agonist. It improved glucose tolerance. GW800644, but not pair-feeding, reduced plasma glucose, insulin and triglyceride concentrations. It increased 2-deoxyglucose uptake in vivo in adipose tissue, soleus muscle, heart, brain and liver, and doubled 2-deoxyglucose uptake and palmitate oxidation in isolated soleus muscle from obese but not lean mice. PPARδ agonism reduced food intake and independently elicited metabolic effects that included increased responsiveness to β(3)-adrenoceptor stimulation, increased glucose utilization and fat oxidation in soleus muscle of Lep(ob)/Lep(ob) but not lean mice and increased glucose utilization in vivo in Lep(ob)/Lep(ob) mice.

Biphasic effects of chronic ethanol exposure on insulin‐stimulated glucose uptake in primary cultured rat skeletal muscle cells: role of the Akt pathway and GLUT4

mild or moderate chronic alcohol intake has been shown to be associated with increased insulin sensitivity, while chronic alcohol abuse demonstrates a contrary effect. The mechanism underlying this biphasic effect has not yet been clarified. We investigated whether chronic ethanol exposure mediates biphasic changes on insulin sensitivity and whether the phosphatidylinositol 3-kinase/Akt pathway is involved in vitro. primary cultured rat skeletal muscle cells were exposed to ethanol (0-400 mM) for 24 h. Insulin sensitivity was assessed by the (3) H-labelled 2-deoxyglucose uptake assay. Phosphatidylinositol 3-kinase, cytosol and cell membrane glucose transporter-4 (GLUT4), as well as the Akt phosphorylated form, were analyzed by Western blots. biphasic effects of ethanol on insulin sensitivity were observed in primary cultured skeletal muscle cells in a dose-dependent manner. Compared with the untreated group, 50 and 100 mM concentrations of ethanol resulted in a significant increase in 2-deoxyglucose uptake by 29 and 28%, respectively, while higher concentrations of ethanol (200, 400 mM) showed a significant decrease in 2-deoxyglucose uptake by 28 and 47%, respectively. The changes in glucose transport activity were in line with the changes in Akt Ser473 phosphorylation and GLUT4 expression in an ethanol dose-dependent biphasic manner. The phosphorylation of Akt and GLUT4 protein contents were up-regulated after treatment with low concentrations of ethanol (50, 100 mM) and down-regulated with high concentrations of ethanol (200, 400 mM) for 24 h. ethanol mediates biphasic changes on insulin sensitivity at least in part via the Akt pathway and GLUT4 expression.

The Cannabinoid CB1 Receptor Antagonist Rimonabant Stimulates 2-Deoxyglucose Uptake in Skeletal Muscle Cells by Regulating the Expression of Phosphatidylinositol-3-kinase

The endocannabinoid system regulates food intake, energy, and glucose metabolism at both central and peripheral levels. We have investigated the mechanism by which it may control glucose uptake in skeletal muscle cells. Detectable levels of the cannabinoid receptor type 1 (CB1) were revealed in L6 cells. Exposure of differentiated L6 myotubes to the CB1 antagonist rimonabant (SR141716) selectively increased 2-deoxyglucose uptake (2-DG) in a time- and dose-dependent manner. A similar effect was induced by genetic silencing of CB1 by small interfering RNA. Protein expression profiling revealed that both the regulatory p85 and the catalytic p110 subunits of the phosphatidylinositol-3-kinase (PI3K) were increased by SR141716. No significant change in the cellular content of other known molecules regulating PI3K was observed. However, phosphoinositide-dependent kinase-1, Akt/protein kinase B, and protein kinase Czeta activities were rapidly induced after SR141716 treatment of L6 cells in a PI3K-dependent manner. The stimulatory effect of SR141716 on PI3K expression and activity was largely prevented by N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H-89), an inhibitor of the cAMP-dependent protein kinase. Moreover, SR141716-stimulated 2-DG uptake was blunted by the coincubation either with H-89 or with the PI3K inhibitor 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002), both in L6 cells and in mouse primary myocytes. Thus, modulation of CB1 regulates glucose uptake at the level of the PI3K signaling system in skeletal muscle cells. Interfering with CB1 signaling may therefore ameliorate glucoregulatory functions in peripheral tissues.

Galectin-1 upregulates glucose transporter-1 expression level via protein kinase C, phosphoinositol-3 kinase, and mammalian target of rapamycin pathways in mouse embryonic stem cells

Although galectin-1 is expressed in various stem cells, our understanding of the functional roles of galectin-1 in embryonic stem (ES) cells is still fragmentary and incomplete. Thus, this study investigated the effect of galectin-1 on the 2-deoxyglucose (2-DG) uptake and its related signal cascades. Galectin-1 significantly increased 2-deoxyglucose uptake time- and dose-dependently. In addition, galectin-1-induced 2-deoxyglucose uptake was inhibited by glucose transporter-1 siRNA. Moreover, galectin-1 increased glucose transporter-1 mRNA and protein expression levels, which were inhibited by a disruption in transcription by actinomycin D and translation by the cycloheximide. Subsequently, the galectin-1-induced 2-deoxyglucose uptake was attenuated by these inhibitors. In investigation of signal transduction involved in this process, galectin-1 increased intracellular Ca 2+ concentration and the protein kinase C activation, which induced extracellular signal regulated kinase1/2 phosphorylation. On the other hand, phosphoinositol-3-kinase/Akt activated by galectin-1 was not involved in extracellular signal regulated kinase1/2 pathway. Moreover, mammalian target of rapamycin signal pathway was stimulated in response to galectin-1. Finally, galectin-1-induced increase of glucose transporter-1 expression and 2-deoxyglucose uptake were inhibited by blocking of Ca 2+/protein kinase C/extracellular signal regulated kinase1/2, phosphoinositol-3-kinase/Akt, and mammalian target of rapamycin pathways. In conclusion, galectin-1 upregulates glucose uptake through Ca 2+/protein kinase C/extracellular signal regulated kinase1/2, phosphoinositol-3-kinase/Akt, and mammalian target of rapamycin pathways in mouse ES cells.

Vascular and metabolic effects of methacholine in relation to insulin action in muscle

Methacholine (MC) is a nitric oxide vasodilator, but unlike other vasodilators, it potentiates insulin-mediated glucose uptake by muscle. The present study aimed to resolve whether this action was the result of a vascular effect of MC leading to increased muscle perfusion or a direct effect of MC on the myocytes. We hypothesise that vascular-mediated insulin-stimulated glucose uptake responses to MC occur at lower doses than direct myocyte MC-mediated increases in glucose uptake. The vascular and metabolic effects of this vasodilator were examined in rats in vivo using a novel local infusion technique, and in the pump-perfused rat hindlimb under conditions of constant flow. Local infusion of low-dose MC (0.3 micromol/l) into the epigastric artery of one leg (test) in vivo markedly increased femoral blood flow and decreased vascular resistance, without effects in the contra-lateral leg. Capillary recruitment, but not glucose uptake, was increased in the test leg. All increases caused by MC were confined to the test leg and blocked by local infusion into the test leg of N-nitro-L-arginine methyl ester (L-NAME), but not by infusion of N-nitro-D-arginine methyl ester (D-NAME). In the constant-flow pump-perfused rat hindlimb, infusion of 0.6 micromol/l MC vasodilated the pre-constriction effected by 70 nmol/l noradrenaline or 300 nmol/l serotonin, and this was blocked by 10 micromol/l L-NAME. 2-Deoxyglucose in muscle was increased by 30 micromol/l MC (p<0.05), but was unaffected by 3 micromol/l MC. All increases in 2-deoxyglucose uptake by 30 micromol/l MC were blocked by 10 micromol/l L-NAME. MC has dose-dependent effects both on the vasculature and on muscle metabolism. At low dose (0.3-3 micromol/l), MC is a potent vasodilator in muscle, both in vivo and in vitro, without metabolic effects; at higher doses (> or =30 micromol/l) MC has a direct metabolic effect leading to increased glucose uptake. Both the vascular and metabolic effects are sensitive to L-NAME. The low-dose enhancement of insulin action in vivo by MC, which has been reported previously, thus seems to be attributable to vascular effects.

Improving glycogenesis in Streptozocin (STZ) diabetic mice after administration of green algae Chlorella

Chlorella, a type of unicellular fresh water algae, has been a popular foodstuff in Japan and Taiwan. Studies have shown the hypoglycemic effects of Chlorella in alloxan-induced and Streptozocin (STZ)-induced diabetic animals. However, the mechanisms by which Chlorella treatment affects blood glucose homeostasis have not been studied. Diabetes in ICR mice was induced by injection of STZ. Lipogenesis in vivo was measured by incorporating 3H–H 2O into lipids in brown and white adipose tissues. Glucose uptake in the liver and soleus muscles was measured by assaying 2-deoxy- d-[1,2- 3H] glucose levels. The effects of Chlorella on serum non-esterified fatty acids (NEFA) were measured with commercial assay kits. Insulin-stimulated lipogenic rates in brown and white adipose tissues were unaffected by Chlorella. However, Chlorella increased 2-deoxyglucose uptake in the livers and soleus muscles in normal and STZ mice compared to that in their respective controls ( p < 0.01). In addition, fasting NEFA levels were lower in Chlorella-treated STZ mice compared to H 2O-treated STZ mice ( p < 0.005). The current results suggest that the hypoglycemic effects of Chlorella are due to an enhancement of glucose uptake in the liver and in soleus muscles. The improved insulin sensitivity after Chlorella treatment could be also due to lower NEFA levels, since insulin sensitivity is usually blunted by elevated NEFA in diabetes.

β‐endorphin decreases fatigue and increases glucose uptake independently in normal and dystrophic mice

beta-Endorphin and a C-terminal analogue have been shown to decrease muscle fatigue and increase glucose uptake in muscles of normal mice. In order to provide evidence whether these peptides might be useful in muscle-wasting conditions and whether the two actions of the peptides are interdependent, the effect of beta-endorphin on muscle fatigue and glucose uptake was studied using isolated hemidiaphragm preparations of dystrophic mice as well as normal mice. Muscle contractions were elicited by high-frequency stimulation of the phrenic nerve. Glucose uptake was measured using (nonmetabolizable) 2-deoxy-D-[1-(3)H]glucose. beta-Endorphin and the C-terminal analogue reduced fatigue in normal muscles of males but not females. Insulin had no effect in either sex. The peptides increased 2-deoxyglucose uptake in contracting and noncontracting muscles of normal males and females. beta-Endorphin reduced fatigue and increased deoxyglucose uptake in dystrophic muscles. The effect on fatigue was not due to increased glucose uptake, as the energy substrate present was pyruvate. Nerve stimulation released beta-endorphin immunoreactivity from intramuscular nerves of dystrophic mice. It is hypothesized that beta-endorphin released from motor nerves as well as from the pituitary could be responsible for improving muscle function during exercise. beta-Endorphin or analogues could have therapeutic use in muscle-wasting disease.

Local methacholine but not bradykinin potentiates insulin-mediated glucose uptake in muscle in vivo by augmenting capillary recruitment

Insulin has nitric-oxide-dependent vasodilatory effects in muscle, including capillary recruitment, that enhance access for itself and glucose. However, nitric-oxide-dependent vasodilators other than methacholine do not enhance insulin action. Our hypothesis is that methacholine, unlike bradykinin, enhances insulin-mediated glucose uptake in muscle by augmenting capillary recruitment. Local infusion of either methacholine or bradykinin into one leg of the anaesthetised rat was made during physiological insulin (3 mU.kg(-1).min(-1)) infusion under euglycaemic conditions and without affecting systemic blood pressure. Whole-body glucose infusion was determined, as was femoral blood flow, 2-deoxyglucose uptake into calf muscles and the metabolism of infused 1-methylxanthine, a measure of capillary recruitment for each leg. Methacholine alone (0.3 micromol.l(-1)) increased femoral arterial blood flow, increased capillary recruitment but had no effect on 2-deoxyglucose uptake of the test leg relative to the contra-lateral control leg. Insulin alone (systemically) required a glucose infusion rate of 8.7 mg.kg(-1).min(-1) to maintain euglycaemia, increased 2-deoxyglucose uptake and capillary recruitment, but was without effect on femoral blood flow in either leg. Local methacholine with systemic insulin infusion increased femoral blood flow, 2-deoxyglucose uptake and capillary recruitment in the test leg only. Bradykinin (0.07 micromol.l(-1)), alone or with insulin, administered in a manner that increased femoral blood flow similarly to methacholine, did not affect 2-deoxyglucose uptake or capillary recruitment. Methacholine but not bradykinin enhances insulin-mediated muscle glucose uptake in vivo. We conclude that methacholine acts at specific sites in the vasculature of muscle to stimulate capillary recruitment and thereby enhance insulin access.

Intracellular Delivery of Phosphatidylinositol (3,4,5)-Trisphosphate Causes Incorporation of Glucose Transporter 4 into the Plasma Membrane of Muscle and Fat Cells without Increasing Glucose Uptake

Insulin stimulates glucose uptake into muscle and fat cells by translocating glucose transporter 4 (GLUT4) to the cell surface, with input from phosphatidylinositol (PI) 3-kinase and its downstream effector Akt/protein kinase B. Whether PI 3,4,5-trisphosphate (PI(3,4,5)P(3)) suffices to produce GLUT4 translocation is unknown. We used two strategies to deliver PI(3,4,5)P(3) intracellularly and two insulin-sensitive cell lines to examine Akt activation and GLUT4 translocation. In 3T3-L1 adipocytes, the acetoxymethyl ester of PI(3,4,5)P(3) caused GLUT4 migration to the cell periphery and increased the amount of plasma membrane-associated phospho-Akt and GLUT4. Intracellular delivery of PI(3,4,5)P(3) using polyamine carriers also induced translocation of myc-tagged GLUT4 to the surface of intact L6 myoblasts, demonstrating membrane insertion of the transporter. GLUT4 translocation caused by carrier-delivered PI(3,4,5)P(3) was not reproduced by carrier-PI 4,5-bisphosphate or carrier alone. Like insulin, carrier-mediated delivery of PI(3,4,5)P(3) elicited redistribution of perinuclear GLUT4 and Akt phosphorylation at the cell periphery. In contrast to its effect on GLUT4 mobilization, delivered PI(3,4,5)P(3) did not increase 2-deoxyglucose uptake in either L6GLUT4myc myoblasts or 3T3-L1 adipocytes. The ability of exogenously delivered PI(3,4,5)P(3) to augment plasma membrane GLUT4 content without increasing glucose uptake suggests that input at the level of PI 3-kinase suffices for GLUT4 translocation but is insufficient to stimulate glucose transport.

Creatine supplementation increases glucose oxidation and AMPK phosphorylation and reduces lactate production in L6 rat skeletal muscle cells.

Recent observations have suggested that creatine supplementation might have a beneficial effect on glucoregulation in skeletal muscle. However, conclusive studies on the direct effects of creatine on glucose uptake and metabolism are lacking. The objective of this study was to investigate the effects of creatine supplementation on basal and insulin-stimulated glucose transporter (GLUT4) translocation, glucose uptake, glycogen content, glycogen synthesis, lactate production, glucose oxidation and AMP-activated protein kinase (AMPK) phosphorylation in L6 rat skeletal muscle cells. Four treatment groups were studied: control, insulin (100 nM), creatine (0.5 mM) and creatine + insulin. After 48 h of creatine supplementation the creatine and phosphocreatine contents of L6 myoblasts increased by approximately 9.3- and approximately 5.1-fold, respectively, but the ATP content of the cells was not affected. Insulin significantly increased 2-deoxyglucose uptake ( approximately 1.9-fold), GLUT4 translocation ( approximately 1.8-fold), the incorporation of D-[U-(14)C]glucose into glycogen ( approximately 2.3-fold), lactate production ( approximately 1.5-fold) and (14)CO(2) production ( approximately 1.5-fold). Creatine neither altered the glycogen and GLUT4 contents of the cells nor the insulin-stimulated rates of 2-DG uptake, GLUT4 translocation, glycogen synthesis and glucose oxidation. However, creatine significantly reduced by approximately 42% the basal rate of lactate production and increased by approximately 40% the basal rate of (14)CO(2) production. This is in agreement with the approximately 35% increase in citrate synthase activity and also with the approximately 2-fold increase in the phosphorylation of both alpha-1 and alpha-2 isoforms of AMPK after creatine supplementation. We conclude that 48 h of creatine supplementation does not alter insulin-stimulated glucose uptake and glucose metabolism; however, it activates AMPK, shifts basal glucose metabolism towards oxidation and reduces lactate production in L6 rat skeletal muscle cells.