Glucose Transport In Adipose Tissue Research Articles

Conjugated Linoleic Acid Ameliorates High Fat-Induced Insulin Resistance via Regulating Gut Microbiota-Host Metabolic and Immunomodulatory Interactions.

Interaction between gut microbiota, host immunity and metabolism has been suggested to crucially affect the development of insulin resistance (IR). This study aims to investigate how gut microbiota, inflammatory responses and metabolism in individuals with IR are affected by the supplementation of conjugated linoleic acid (CLA) and how this subsequently affects the pathophysiology of IR by using a high-fat diet-induced IR mouse model. Serum biochemical indices showed that 400 mg/kg body weight of CLA effectively attenuated hyperglycemia, hyperlipidemia, glucose intolerance and IR, while also promoting antioxidant capacities. Histomorphology, gene and protein expression analysis revealed that CLA reduced fat deposition and inflammation, and enhanced fatty acid oxidation, insulin signaling and glucose transport in adipose tissue or liver. Hepatic transcriptome analysis confirmed that CLA inhibited inflammatory signaling pathways and promoted insulin, PI3K-Akt and AMPK signaling pathways, as well as linoleic acid, arachidonic acid, arginine and proline metabolism. Gut microbiome analysis further revealed that these effects were highly associated with the enriched bacteria that showed positive correlation with the production of short-chain fatty acids (SCFAs), as well as the improved SCFAs production simultaneously. This study highlights the therapeutic actions of CLA on ameliorating IR via regulating microbiota-host metabolic and immunomodulatory interactions, which have important implications for IR control.

Forkhead box C2 is associated with insulin resistance in gestational diabetes mellitus

Objective This study aimed to investigate serum levels of adiponectin, and the mRNA expression of forkhead box C2 (FOXC2) and glucose transporter-4 (GLUT4) in visceral adipose tissue obtained from patients with gestational diabetes mellitus (GDM) and healthy pregnant women. Methods Venous blood samples were obtained from 60 pregnant women with gestational normal glucose tolerance (GNGT) and 21 patients with GDM. Visceral adipose tissues were obtained from 11 women with GDM and 30 with GNGT. Serum adiponectin levels were detected by enzyme-linked immunosorbent assay, and FOXC2 and GLUT4 mRNA expression were detected by quantitative polymerase chain reaction. Results Serum adiponectin concentrations were lower in the women with GDM than in the controls (p < .05). FOXC2 and GLUT4 mRNA expression were decreased in visceral adipose tissue of GDM women than in the controls (p < .05). Correlation analyses showed that FOXC2 tended to have a positive correlation with GLUT4 in GDM patients' visceral adipose tissue (p =.0564). Conclusion Our results revealed that decreased adiponectin, FOXC2, and GLUT4 expression were associated with increased risk of GDM and the regulation mechanism of GLUT4 mediated by FOXC2 would be the focus of further studies.

Lack of serum albumin improves insulin sensitivity in both male and female mice

Insulin resistance is a global health problem. It has been shown that free fatty acids (FFA) play a major role in insulin resistance. Albumin acts as main fatty acid binding protein in blood. To improve understanding of the role of FFA in insulin resistance, we aimed to determine whether lack of serum albumin and the associated suppression of plasma FFA concentration would improve insulin sensitivity in albumin knockout mice compared to wild type mice. Male and female homozygous albumin knockout mice and C57BL/6J wild‐type controls, each fed a chow diet, were studied at 6‐8 weeks of age. Glucose tolerance test, insulin tolerance test, tissue analyses, and plasma proteomics were performed. In both sexes of albumin knockout mice compared to wild‐type mice, we observed lower levels of hepatic diacylglycerol content, as well as lower blood glucose during glucose tolerance test and insulin tolerance test (P &lt; 0.05). The level of mRNA measurement showed higher expression of adiponectin, lipoprotein lipase, diacylglycerol acyltransferase‐1 and ‐2, and glucose transporter‐4 in adipose tissue, as well as lower hepatic perilipin‐2 expression (P&lt;0.05). In agreement with adipose mRNA level analysis, plasma proteomics indicated that circulating adiponectin concentration was higher in albumin knockout compared to wild‐type mice (P&lt;0.05). The results indicate an important role of albumin and plasma FFA concentration in lipid and glucose metabolism. We suggest that the lower plasma FFA concentration in albumin knockout mice compared to wild‐type mice leads to less hepatic diacylglycerol accumulation, and the lower level of this lipotoxic compound may contribute to the enhanced insulin sensitivity.

Simultaneous Effects of Metformin and Sitagliptin on the Contents of Insulin Resistance Proteins Glucose Transporter 4 and Protein Kinase B in Diabetic Patients' Adipose Tissue

Objective: Obesity is a factor in the development of insulin resistance and type 2 diabetes. Obesity contributes a wide variety of metabolic changes such as insulin resistance. The insulin signal mechanism to intra-cells occurs in insulin resistance, primarily in adipose tissue cells, which can be appropriate targets for therapeutic approaches by recognizing the proteins in this pathway. The study aimed to evaluate the simultaneous impact of metformin and sitagliptin on the expression of protein levels involved in insulin resistance Protein Kinase B (Akt) and Glucose Transporter 4 (GLUT4) in diabetic adipose tissue.&#x0D; Materials and Methods: In order to evaluate the content of proteins involved in insulin resistance Akt and GLUT4 in adipose tissue of diabetic patients with the use of SDS-PAGE and western blot analyses, we studied 6 persons of type 2 diabetic patients who obtained 3 months of care with simultaneous metformin and sitagliptin, 4 persons returned from them after treatment and 8 persons as a stable case (control group).&#x0D; Results: There was an increase in glucose intake and a decrease in serum glucose levels (P-value= 0.025) and no decrease in insulin resistance (P-value= 0.6) following simultaneous metformin and sitagliptin therapy, but no improvement in serum insulin levels (Pvalue=1.01). Increases in the content of Akt protein (P-value= 0.682) and GLUT4 protein (P-value= 0.851) involved in insulin resistance in diabetic patients' adipose tissue, were not observed.&#x0D; Conclusion: Simultaneous treatment with metformin and sitagliptin had no effect on insulin resistance proteins Akt and GLUT4 in type 2 diabetic adipose tissue.

Effect of Quercetin and Metformin on Glucose Transporter-4 Expression, Oxidative Stress, Inflammation Markers and Insulin Resistance in Type 2 Diabetes Mellitus

Background: Defects in glucose transporter-4 (GLUT-4) expression and function in the skeletal muscles and adipose tissue can be considered as the main cause of insulin resistance (IR) in type 2 diabetes mellitus (T2DM). Also, Oxidative stress and inflammation play a very important role in the development of IR and T2DM. Aim: Studying the effect of quercetin and metformin on GLUT-4 expression, oxidative stress, inflammation markers and IR in T2DM. Method: This study was carried out on 50 male Wistar rats which were divided into five groups; control, untreated diabetic rats, diabetic rats treated with metformin, diabetic rats treated with quercetin and diabetic rats treated with metformin and quercetin. Results: The use of metformin and quercetin separately produced significant decrease in plasma glucose, insulin, IL-6, TNF-α levels, HOMA-IR and TBARS level in skeletal muscle. Also, they caused significant elevation in the antioxidant enzyme activities in skeletal muscles with increased expression of GLUT-4 in the skeletal muscles and adipose tissue compared to the diabetic rats. Evidently, the quercetin effects were more significant than that of metformin on all the parameters except on HOMA-IR (similar significant improvement). Moreover, the combined use of quercetin and metformin produced highly significant improvement approaching control level in all the parameters than that observed by using either of them. Conclusion: The combined use of QC and MF improved hyperglycemia and IR by increasing the expression of GLUT-4 in skeletal muscles and adipose tissue together with the reversal of the oxidative stress and inflammatory states.

Gastric Sleeve Surgery Alleviates Obesity-Associated Insulin Resistance and Suppresses Endoplasmic Reticulum Stress in Adipose Tissue of db/db Mice.

The aims of this study were to evaluate the effects of gastric sleeve surgery on diabetes remission in db/db mice as well as to determine the underlying mechanisms. Thirty spontaneously obese, diabetic mice (C57BL/Ksj-db/db) were randomly divided into three groups: sleeve gastrectomy group, sham-operated group, and control db/db group. Ten db/m lean mice were used as nondiabetic littermate controls. All mice were sacrificed on day 28. The fasting plasma glucose, serum insulin, lipid profile, and oral glucose tolerance were measured pre- and postoperatively. Inflammatory cytokines (TNF-α and IL-6), endoplasmic reticulum (ER) stress-related markers (GRP78, PERK, IRE-1, and ATF6), and glucose transporter 4 (GLUT4) in the adipose tissue were assayed. Sleeve gastrectomy significantly reduced the body weight and food intake in the db/db mice. This surgery improved glucose and lipid metabolism, as manifested by the decrease in the fasting plasma glucose level and partial restoration of lipid abnormalities. Also, the surgery improved glucose tolerance and alleviated insulin resistance in db/db mice. Sleeve gastrectomy surgery induced downregulation of the inflammatory adipocytokines TNF-α and IL-6; suppressed expression of the ER stress-related markers GRP78, PERK, IRE-1, and ATF-6; and increased the expression and distribution of GLUT4 in adipose tissue of db/db mice. The improvement in glucose tolerance following sleeve gastrectomy is associated with alleviation of insulin resistance, reduction of inflammatory adipocytokine levels, and suppression of ER stress. Further studies are needed to assess whether these effects have a causal role.

De novo Lipogenesis in Adipocytes Results in the Production of Structurally Novel Signaling Lipids with Beneficial Metabolic and Anti‐inflammatory Effects

Increased de novo lipogenesis in adipose tissue is associated with enhanced insulin sensitivity in humans and rodents. Mice overexpressing the Glut4 glucose transporter in adipose tissue have elevated adipose tissue lipogenesis and increased glucose tolerance in spite of obesity and elevated circulating fatty acids. Untargeted lipidomic analysis of adipose tissue from these mice revealed marked elevation of a structurally novel class of lipids, branched Fatty Acid esters of Hydroxy Fatty Acids (FAHFAs). More than 25 FAHFA family members, which are distinguished by different acyl chain composition, have been identified in mammalian tissues and plants. Levels of some family members such as Palmitic Acid esters of Hydroxy Stearic Acids (PAHSAs) are highly regulated in altered nutritional and metabolic states. PAHSA levels are reduced in serum and subcutaneous adipose tissue of insulin‐resistant humans and serum PAHSA levels correlate very strongly with insulin sensitivity in humans. Chronic PAHSA treatment improves glucose tolerance and insulin sensitivity in insulin‐resistant mice. PAHSAs also have anti‐inflammatory effects in states such as obesity, colitis and auto‐immune Type 1 diabetes in mice. Many effects of PAHSA are mediated through G‐protein coupled receptors. Thus, PAHSAs exert multiple beneficial metabolic and anti‐inflammatory effects in diabetes and immune‐mediated diseases. The pathways that regulate these lipids provide new opportunities for disease prevention and treatment.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

RalA controls glucose homeostasis by regulating glucose uptake in brown fat

Insulin increases glucose uptake into adipose tissue and muscle by increasing trafficking of the glucose transporter Glut4. In cultured adipocytes, the exocytosis of Glut4 relies on activation of the small G protein RalA by insulin, via inhibition of its GTPase activating complex RalGAP. Here, we evaluate the role of RalA in glucose uptake in vivo with specific chemical inhibitors and by generation of mice with adipocyte-specific knockout of RalGAPB. RalA was profoundly activated in brown adipose tissue after feeding, and its inhibition prevented Glut4 exocytosis. RalGAPB knockout mice with diet-induced obesity were protected from the development of metabolic disease due to increased glucose uptake into brown fat. Thus, RalA plays a crucial role in glucose transport in adipose tissue in vivo.

Curculigoside and polyphenol-rich ethyl acetate fraction of Molineria latifolia rhizome improved glucose uptake via potential mTOR/AKT activated GLUT4 translocation

Adipose tissue is one of the major organs responsible for rapid restoration of postprandial glucose fluxes. Being the major isoform of glucose transporter in adipose tissue, regulations of insulin-dependent GLUT4 trafficking have always been of research interest. The present study aimed to examine the molecular mechanisms underlying the efficacy of curculigoside and polyphenol-rich ethyl acetate fraction (EAF) of Molineria latifolia rhizome in triggering glucose uptake. We assessed the adipogenic potential and glucose uptake stimulatory activity of curculigoside and EAF by employing a murine 3T3-L1 adipocyte model. The transcriptional and translational expressions of selected intermediates in the insulin signalling pathway were evaluated. While curculigoside neither promoted adipogenesis nor activated peroxisome proliferator activated receptor gamma, treatment with polyphenol-rich EAF resulted otherwise. However, both treatments enhanced insulin-stimulated uptake of glucose. This was coupled with increased availability of GLUT4 at the plasma membrane of the differentiated adipocytes although the total GLUT4 protein level was unaffected. In addition, the treatment increased the phosphorylation of both AKT and mTOR, which have been reported to be associated with GLUT4 translocation. The present findings proposed that curculigoside and EAF increased glucose transport activity of 3T3-L1 adipocytes via GLUT4 translocation as a result of potential mTOR/AKT activation. The more potent efficacy observed with EAF suggested potential synergistic and multi-targeted action.

Absence of Carbohydrate Response Element Binding Protein in Adipocytes Causes Systemic Insulin Resistance and Impairs Glucose Transport

Lower adipose-ChREBP and de novo lipogenesis (DNL) are associated with insulin resistance in humans. Here, we generated adipose-specific ChREBP knockout (AdChREBP KO) mice with negligible sucrose-induced DNL in adipose tissue (AT). Chow-fed AdChREBP KO mice are insulin resistant with impaired insulin action in the liver, muscle, andAT and increased AT inflammation. HFD-fed AdChREBP KO mice are also more insulin resistantthan controls. Surprisingly, adipocytes lacking ChREBP display a cell-autonomous reduction in insulin-stimulated glucose transport that is mediated by impaired Glut4 translocation and exocytosis, not lower Glut4 levels. AdChREBP KO mice have lower levels of palmitic acid esters of hydroxy stearic acids (PAHSAs) in serum, and AT. 9-PAHSA supplementation completely rescues their insulin resistance and AT inflammation. 9-PAHSA also normalizes impaired glucose transport and Glut4 exocytosis in ChREBP KO adipocytes. Thus, lossof adipose-ChREBP is sufficient to cause insulin resistance, potentially by regulating AT glucose transport and flux through specific lipogenic pathways.

Fucoidan from sea cucumber Cucumaria frondosa exhibits anti-hyperglycemic effects in insulin resistant mice via activating the PI3K/PKB pathway and GLUT4

The present study investigated the anti-hyperglycemic properties and mechanisms of fucoidan, isolated from Cucumaria frondosa (Cf-FUC), in insulin resistant mice. Male C57BL/6J mice were fed regular diet or high-fat/high-sucrose diet for 19 weeks. Model animals were dietary administrated either rosiglitazone (RSG, 1mg/kg·bw), fucoidan (Cf-FUC, 80mg/kg·bw) or their combinations. Results showed that Cf-FUC significantly reduced fasting blood glucose and insulin levels, and enhanced glucose tolerance and insulin tolerance in insulin-resistant mice. Quantitative real-time PCR analysis showed that Cf-FUC increased the mRNA expressions of insulin receptors (IR), insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3 kinase (PI3K), protein kinase B (PKB), and glucose transporter 4 (GLUT4). Western blot assays demonstrated that Cf-FUC showed no effect on total protein expression but nevertheless enhanced the phosphorylation of proteins listed above and increased translocation of GLUT4 to the cell membrane. Furthermore, Cf-FUC enhanced the effects of RSG. These results indicated that Cf-FUC exhibited significant anti-hyperglycemic effects via activating PI3K/PKB pathway and GLUT4 in skeletal muscle and adipose tissue.

In vivo and in vitro antidiabetic effects of citrus flavonoids; a study on the mechanism of action

Type 2 diabetes mellitus is a result of hyperglycemia caused by overproduction of glucose at the hepatic level or because of abnormal β cell function or insulin resistance at target cells. The purpose of this study was to investigate the hypoglycemic effect of hesperidin and naringin and to suggest their probable mechanisms of action in high fat-fed/streptozotocin (STZ)-induced type 2 diabetic rats. Male albino rats were divided into four groups. Group 1 was normal control, and others were induced with diabetes by feeding a high-fat diet for 2 weeks followed by an intraperitoneal injection of streptozotocin (35 mg/kg b.wt.). Group 2 was kept as diabetic control, and groups 3 and 4 were further treated with an oral dose of 50 mg/kg hesperidin and naringin. In the diabetic control group, levels of glucose and glycosylated hemoglobin were significantly increased, while serum insulin level and hepatic and muscle glycogen were decreased. Both hesperidin and naringin supplementation significantly reversed these parameters. The activity of the hepatic key enzyme hexokinase was significantly increased whereas, glucose-6-phosphatase, glycogen phosphorylase, and fructose-1,6-bisphosphatase activities were significantly decreased as a result of treatment. Furthermore, both compounds were found to decrease intestinal glucose absorption in situ and to increase insulin release from isolated islets, peripheral glucose uptake in vitro, and adipose tissue glucose transporter type 4 (GLUT4) messenger RNA (mRNA) and protein expressions. These results showed that hesperidin and naringin have potent antihyperglycemic activity in high fat-fed/STZ-induced diabetic rats.

Gallic acid attenuates high-fat diet fed-streptozotocin-induced insulin resistance via partial agonism of PPARγ in experimental type 2 diabetic rats and enhances glucose uptake through translocation and activation of GLUT4 in PI3K/p-Akt signaling pathway

In this study, the therapeutic efficacy of gallic acid from Cyamopsis tetragonoloba (L.) Taub. (Fabaceae) beans was examined against high-fat diet fed-streptozotocin-induced experimental type 2 diabetic rats. Molecular-dockings were done to determine the putative binding modes of gallic acid into the active sites of key insulin-signaling markers. Gallic acid (20mg/kg) given to high-fat diet fed-streptozotocin-induced rats lowered body weight gain, fasting blood glucose and plasma insulin in diabetic rats. It further restored the alterations of biochemical parameters to near normal levels in diabetic treated rats along with cytoprotective action on pancreatic β-cell. Histology of liver and adipose tissues supported the biochemical findings. Gallic acid significantly enhanced the level of peroxisome proliferator-activated receptor γ (PPARγ) expression in the adipose tissue of treated rat compared to untreated diabetic rat; it also slightly activated PPARγ expressions in the liver and skeletal muscle. Consequently, it improved insulin-dependent glucose transport in adipose tissue through translocation and activation of glucose transporter protein 4 (GLUT4) in phosphatidylinositol 3-kinase (PI3K)/phosphorylated protein kinase B (p-Akt) dependent pathway. Gallic acid docked with PPARγ; it exhibited promising interactions with the GLUT4, glucose transporter protein 1 (GLUT1), PI3K and p-Akt. These findings provided evidence to show that gallic acid could improve adipose tissue insulin sensitivity, modulate adipogenesis, increase adipose glucose uptake and protect β-cells from impairment. Hence it can be used in the management of obesity-associated type 2 diabetes mellitus.

Rab5 activity regulates GLUT4 sorting into insulin-responsive and non-insulin-responsive endosomal compartments: a potential mechanism for development of insulin resistance.

Glucose transporter isoform 4 (GLUT4) is the insulin-responsive glucose transporter mediating glucose uptake in adipose and skeletal muscle. Reduced GLUT4 translocation from intracellular storage compartments to the plasma membrane is a cause of peripheral insulin resistance. Using a chronic hyperinsulinemia (CHI)-induced cell model of insulin resistance and Rab5 mutant overexpression, we determined these manipulations altered endosomal sorting of GLUT4, thus contributing to the development of insulin resistance. We found that CHI induced insulin resistance in 3T3-L1 adipocytes by retaining GLUT4 in a Rab5-activity-dependent compartment that is unable to equilibrate with the cell surface in response to insulin. Furthermore, CHI-mediated retention of GLUT4 in this non-insulin-responsive compartment impaired filling of the transferrin receptor (TfR)-positive and TfR-negative insulin-responsive storage compartments. Our data suggest that hyperinsulinemia may inhibit GLUT4 by chronically maintaining GLUT4 in the Rab5 activity-dependent endosomal pathway and impairing formation of the TfR-negative and TfR-positive insulin-responsive GLUT4 pools. This model suggests that an early event in the development of insulin-resistant glucose transport in adipose tissue is to alter the intracellular localization of GLUT4 to a compartment that does not efficiently equilibrate with the cell surface when insulin levels are elevated for prolonged periods of time.

Gastric bypass surgery alters the mechanisms of insulin resistance in the adipose tissue of GK rats

Roux-en-Y gastric bypass (RYGB) has become an effective treatment for type 2 diabetes mellitus (T2DM). However, the blood glucose mechanism involved remains unclear. In this study, 60 male Goto-Kakizaki (GK) rats were randomly divided into 6 groups (each with 10 rats): the GB1/2 group (treated with gastric bypass surgery), the SO1/2 group (treated with sham operation) and the CO1/2 group (with normal water consumption only). We tested expression levels of tumor necrosis factor α (TNFα) mRNA, glucose transporter4 (GLUT4), peroxisome proliferator-activated receptorγ2 (PPARγ2) and phosphatidylinositol-3-kinase subunit p85α (PI3Kp85α) in the adipose tissues. We found that the weight, fasting blood glucose and postprandial blood glucose decreased in the GB group compared with the CO group. A total of 20 and 30 days after surgery, PPARγ2, PI3Kp85α and GLUT4 increased in the fat tissue in the GB group compared with the CO group. However, 20 days after surgery, TNFα mRNA decreased in fat tissue by 0.51 times in the GB group compared with the CO group, and serum TNFα levels showed no statistically significant difference. Fasting blood glucose and GLUT4 membrane protein were negatively correlated. In conclusion, RYGB may improve insulin resistance and treat T2DM through upregulation of the PPARγ2 protein, downregulation of TNFα mRNA transcription, through the autocrine pathway, upregulation of PI3Kp85α expression, upregulation of GLUT4 mRNA transcripts and by inducing translocation of GLUT4 in adipose tissue.

Glucose metabolism in insulin-sensitive tissue: from health to disease and Glucose Transport in Adipose Tissue: Novel Insights into the Pathogenesis of Insulin Resistance

Glucose metabolism in insulin-sensitive tissue: from health to disease and Glucose Transport in Adipose Tissue: Novel Insights into the Pathogenesis of Insulin Resistance

Treatment with a melanocortin agonist improves abnormal lipid metabolism in streptozotocin-induced diabetic mice

Impairments in leptin-melanocortin signaling are associated with insulin-deficient diabetes and leptin treatment has been shown to be effective in reversing hyperglycemia in animal models of type 1 diabetes. Therefore, we hypothesized that enhanced central melanocortin signaling reverses the metabolic impairments associated with type 1 diabetes. To address this hypothesis, streptozotocin (STZ)-induced diabetic mice were treated with daily intracerebroventricular injection of MTII, a melanocortin agonist, for 11days. STZ-induced hyperglycemia and glucose intolerance were not improved by MTII treatment. MTII treatment did not alter expression levels of genes encoding gluconeogenic enzymes including glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), in the liver of diabetic mice. Skeletal muscle and white adipose tissue glucose transporter 4 (GLUT4) mRNA levels were not altered by MTII treatment in diabetic mice. In contrast, serum nonesterified fatty acid (NEFA) levels were significantly increased in STZ-induced diabetic mice compared to non-diabetic control mice and MTII treatment significantly reduced serum NEFA levels in diabetic mice. MTII treatment also significantly reduced expression levels of hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) mRNA in white adipose tissue of diabetic mice without a significant change in serum insulin levels. Expression levels of lipoprotein lipase (LPL) and fatty acid translocase (FAT/CD36) mRNA in white adipose tissue and skeletal muscle were not changed by MTII treatment. These data suggest that central melanocortin signaling regulates lipid metabolism and that enhancing central melanocortin signaling is effective in reversing abnormal lipid metabolism, but not carbohydrate metabolism, at least partly by reducing lipolysis in type 1 diabetes.

Human Cytomegalovirus Activates Glucose Transporter 4 Expression To Increase Glucose Uptake during Infection

Glucose transport into mammalian cells is mediated by a group of glucose transporters (GLUTs) on the plasma membrane. Human cytomegalovirus (HCMV)-infected human fibroblasts (HFs) demonstrate significantly increased glucose consumption compared to mock-infected cells, suggesting a possible alteration in glucose transport during infection. Inhibition of GLUTs by using cytochalasin B indicated that infected cells utilize GLUT4, whereas normal HFs use GLUT1. Quantitative reverse transcription-PCR and Western analysis confirmed that GLUT4 levels are greatly increased in infected cells. In contrast, GLUT1 was eliminated by a mechanism involving the HCMV major immediate-early protein IE72. The HCMV-mediated induction of GLUT4 circumvents characterized controls of GLUT4 expression that involve serum stimulation, glucose concentration, and nuclear functions of ATP-citrate lyase (ACL). In infected cells the well-characterized Akt-mediated translocation of GLUT4 to the cell surface is also circumvented; GLUT4 localized on the surface of infected cells that were serum starved and had Akt activity inhibited. The significance of GLUT4 induction for the success of HCMV infection was indicated using indinavir, a drug that specifically inhibits glucose uptake by GLUT4. The addition of the drug inhibited glucose uptake in infected cells as well as viral production. Our data show that HCMV-specific mechanisms are used to replace GLUT1, the normal HF GLUT, with GLUT4, the major glucose transporter in adipose tissue, which has a 3-fold-higher glucose transport capacity.

Effects of the HIV Protease Inhibitor Ritonavir on GLUT4 Knock-out Mice

HIV protease inhibitors acutely block glucose transporters (GLUTs) in vitro, and this may contribute to altered glucose homeostasis in vivo. However, several GLUT-independent mechanisms have been postulated. To determine the contribution of GLUT blockade to protease inhibitor-mediated glucose dysregulation, the effects of ritonavir were investigated in mice lacking the insulin-sensitive glucose transporter GLUT4 (G4KO). G4KO and control C57BL/6J mice were administered ritonavir or vehicle at the start of an intraperitoneal glucose tolerance test and during hyperinsulinemic-euglycemic clamps. G4KO mice exhibited elevated fasting blood glucose compared with C57BL/6J mice. Ritonavir impaired glucose tolerance in control mice but did not exacerbate glucose intolerance in G4KO mice. Similarly, ritonavir reduced peripheral insulin sensitivity in control mice but not in G4KO mice. Serum insulin levels were reduced in vivo in ritonavir-treated mice. Ritonavir reduced serum leptin levels in C57BL/6J mice but had no effect on serum adiponectin. No change in these adipokines was observed following ritonavir treatment of G4KO mice. These data confirm that a primary effect of ritonavir on peripheral glucose disposal is mediated through direct inhibition of GLUT4 activity in vivo. The ability of GLUT4 blockade to contribute to derangements in the other molecular pathways that influence insulin sensitivity remains to be determined.

Pioglitazone Treatment Enlarges Subcutaneous Adipocytes in Insulin-Resistant Patients

Obesity-related insulin resistance is associated with an increase in adipocyte size. In rodent models, treatment with the insulin-sensitizers thiazolidinediones (TZDs) leads to the appearance of small, insulin-sensitive adipocytes. Whether such TZD-dependent morphological changes occur in adipose tissue of insulin-resistant patients is unclear. The objective of the study was to study the effects of treatment with the TZD pioglitazone on sc adipose tissue morphology and function in insulin-resistant subjects. This was a placebo-controlled, randomized crossover study. The study was conducted at a university medical center. Twelve adult patients with congenital adrenal hyperplasia (CAH) characterized by insulin resistance were included in this study. After a 4-wk run-in phase, patients were treated with pioglitazone (45 mg/d) followed by placebo, each for 16 wk or vice versa. After both placebo and pioglitazone treatment, insulin sensitivity was determined by hyperinsulinemic euglycemic clamp and abdominal sc adipose tissue was obtained to measure adipocyte cell surface and expression of genes involved in glucose uptake and inflammation. Pioglitazone treatment significantly improved the insulin sensitivity index (placebo: 0.35 +/- 0.16 micromol/kg . min per milliunit per liter; pioglitazone 0.53 +/- 0.16 micromol/kg . min per milliunit per liter, P < 0.001) and increased mRNA expression levels of adiponectin and glucose transporter-4 in adipose tissue. The increase in insulin sensitivity was accompanied by a significant enlargement of the sc adipocyte cell surface (placebo: 2323 +/- 725 microm(2); pioglitazone 2821 +/- 885 microm(2), P = 0.03). In the human situation, treatment of insulin-resistant subjects with pioglitazone improves insulin sensitivity, whereas at the same time, sc adipocyte cell surface increases.