Differential regulation of adipose tissue glucose transporters in genetic obesity (fatty rat). Selective increase in the adipose cell/muscle glucose transporter (GLUT 4) expression.

Adipocytes from young obese Zucker rats exhibit a hyperresponsive insulin-mediated glucose transport, together with a marked increase in cytochalasin B binding as compared with lean rat adipocytes. Here, we examined in these cells the expression of two isoforms of glucose transporter, the erythroid (GLUT 1) and the adipose cell/muscle (GLUT 4) types, in rats aged 16 or 30 d, i.e., before and after the emergence of hyperinsulinemia. GLUT 1 protein and mRNA levels were identical in the two genotypes at both ages. In contrast, the levels of GLUT 4 protein in obese rat adipocytes were 2.4- and 4.5-fold those of lean littermates at 16 and 30 d of age, respectively, in perfect agreement with the genotype effect on insulin-stimulated glucose transport activity. The levels of GLUT 4 mRNA per fat pad were increased 2.3- and 6.2-fold in obese vs. lean rats 16- and 30-d-old, indicating a pretranslational level of regulation. The obese phenotype was not associated with overexpression of GLUT 4 mRNA in gastrocnemius muscle. This work indicates that the fa gene exerts a differential control on the expression of GLUT 1 and GLUT 4 in adipose tissue and provides evidence that independent of hyperinsulinemia, genotype is a major regulatory factor of GLUT 4 expression in this tissue.     

Glycemic improvement in diabetic db/db mice by overexpression of the human insulin-regulatable glucose transporter (GLUT4).

The effects of increased GLUT4 (insulin-regulatable muscle/fat glucose transporter) expression on glucose homeostasis in a genetic model of non-insulin-dependent diabetes mellitus were determined by expressing a human GLUT4 transgene (hGLUT4) in diabetic C57BL/KsJ-db/db mice. A genomic hGLUT4 construct was microinjected directly into pronuclear murine embryos of db/+ matings to maintain the inbred background. Four lines of hGLUT4 transgenic mice were bred to homozygosity at the db locus and all showed a marked reduction of both fasted and fed plasma glucose levels (to approximately 50 and 360 mg/dl, respectively) compared with age-matched nontransgenic db/db mice (approximately 215 and 550 mg/dl, respectively), as well as an enhanced disposal of an oral glucose challenge. In situ immunocytochemical localization of GLUT4 protein in muscle from hGLUT4 db/db mice showed elevated plasma membrane-associated GLUT4 protein in the basal state, which markedly increased after an insulin/glucose injection. In contrast, nontransgenic db/db mice had low levels of plasma membrane-associated GLUT4 protein in the basal state with a relatively small increase after an insulin/glucose challenge. Since the intracellular GLUT4 levels in db/db mice were similar to nontransgenic db/+ mice, the glucose transport defect in db/db mice is at the level of glucose transporter translocation. Together, these data demonstrate that GLUT4 upregulation overcomes the glucose transporter translocation defect and alleviates insulin resistance in genetically diabetic mice, thus resulting in markedly improved glycemic control.     

Glycerol production in subcutaneous adipose tissue in lean and obese humans.

To estimate the regional subcutaneous glycerol production rate in normal and obese humans, the venous arterialized plasma glycerol, interstitial glycerol in the subcutaneous adipose tissue together with adipose tissue blood flow (ATBF, ml/100 g.min) were measured in the postabsorptive state and for 2 h after ingestion of 100 g of oral glucose. Eight lean and eight obese men with normal oral glucose tolerance tests were investigated with the subcutaneous microdialysis technique and 133Xe clearance. In the postabsorptive state, the interstitial glycerol concentrations in lean and obese subjects were 170 +/- 21 vs. 282 +/- 28 microM (P less than 0.01) and 156 +/- 23 vs. 225 +/- 12 microM (P less than 0.05) in the abdominal and femoral subcutaneous adipose tissue, respectively. The corresponding arterial glycerol levels were 54 +/- 4 vs. 75 +/- 14 microM (NS). Abdominal ATBF was greater in lean subjects (3.2 +/- 0.6 vs. 1.6 +/- 0.3; P less than 0.05), whereas femoral ATBF was similar in both groups (2.7 +/- 0.4 vs. 2.4 +/- 0.7). Estimated mean local glycerol release (mumol/100 g.min) was similar in the lean and obese group (0.16 +/- 0.03 vs. 0.20 +/- 0.05 and 0.18 +/- 0.02 vs. 0.17 +/- 0.04) in the abdominal and femoral site, respectively. We conclude that glycerol production from the subcutaneous tissue is increased in obesity, irrespective of adipose tissue distribution. This enhancement is due to the increased adipose tissue mass.     

Lactate release from the subcutaneous tissue in lean and obese men.

Lactate concentration in the subcutaneous interstitial fluid and adipose tissue blood flow (ATBF, ml/100 g.min) were simultaneously measured with the microdialysis technique combined with 133Xe clearance in the abdominal and femoral subcutaneous adipose tissue in nine lean and nine obese men. The studies were performed both in the postabsorptive state and 2 h after an oral glucose load and the results compared to the lactate levels in arterialized venous plasma. After an overnight's fast, arterial lactate was 738 +/- 49 and 894 +/- 69 microM (mean +/- SE) (P < 0.05) in the lean and obese subjects, respectively. The interstitial lactate levels were significantly higher than blood lactate in both subject groups without any regional differences. Abdominal and femoral ATBF was 3.2 +/- 0.6 vs. 2.8 +/- 0.4 and 1.7 +/- 0.3 vs. 2.4 +/- 0.4 ml/100 g.min (P < 0.05) in lean and obese subjects, respectively. Mean apparent lactate release from the abdominal vs. femoral adipose tissue in the fasting state was 10.5 +/- 3.1 vs. 8.6 +/- 2.3 and 6.0 +/- 2.3 vs. 8.5 +/- 2.3 mumol/kg.min (NS) in lean and obese subjects, respectively. Both plasma and interstitial lactate levels increased significantly after an oral glucose load in both subject groups. However, apparent lactate release increased significantly only in the lean group. It is concluded that subcutaneous adipose tissue is a significant source of whole-body lactate release in the postabsorptive state and that this is further enhanced in obese subjects due to their large adipose mass.     

Lipocalin-2 is an inflammatory marker closely associated with obesity, insulin resistance, and hyperglycemia in humans

BACKGROUND: Lipocalin-2, a 25-kDa secreted glycoprotein, is a useful biomarker for early detection of various renal injuries. Because lipocalin-2 is abundantly expressed in adipose tissue and liver, we investigated its relevance to obesity-related pathologies. METHODS: We used real-time PCR and in-house immunoassays to quantify the mRNA and serum concentrations of lipocalin-2 in C57BL/KsJ db/db obese mice and their age- and sex-matched lean littermates. We analyzed the association between serum lipocalin-2 concentrations and various metabolic and inflammatory variables in 229 persons (121 men and 108 women) recruited from a previous cross-sectional study, and we evaluated the effect of the insulin-sensitizing drug rosiglitazone on serum lipocalin-2 concentrations in 32 diabetic patients (21 men and 11 women). RESULTS: Compared with the lean littermates, lipocalin-2 mRNA expression in adipose tissue and liver and its circulating concentrations were significantly increased in db/db diabetic/obese mice (P <0.001). These changes were normalized after rosiglitazone treatment. In humans, circulating lipocalin-2 concentrations were positively correlated (P <0.005) with adiposity, hypertriglyceridemia, hyperglycemia, and the insulin resistance index, but negatively correlated (P = 0.002) with HDL cholesterol. There was also a strong positive association between lipocalin-2 concentrations and high sensitivity C-reactive protein (hs-CRP), independent of age, sex, and adiposity (P = 0.007). Furthermore, rosiglitazone-mediated decreases in lipocalin-2 concentrations correlated significantly with increases in insulin sensitivity (r = 0.527; P = 0.002) and decreases in hs-CRP concentrations (r = 0.509; P = 0.003). CONCLUSIONS: Lipocalin-2 is an inflammatory marker closely related to obesity and its metabolic complications. Measurement of serum lipocalin-2 might be useful for evaluating the outcomes of various clinical interventions for obesity-related metabolic and cardiovascular diseases.     

Is 11beta-hydroxysteroid dehydrogenase type 1 a therapeutic target? Effects of carbenoxolone in lean and obese Zucker rats

In liver and adipose tissue, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) regenerates glucocorticoids from inactive 11-keto metabolites. Pharmacological inhibition or transgenic disruption of 11beta-HSD1 attenuates glucocorticoid action and increases insulin sensitivity. Increased adipose 11beta-HSD1 may also contribute to the metabolic complications of obesity. Here, we examine the effects of inhibition of 11beta-HSDs with carbenoxolone in obese insulin-resistant Zucker rats, a strain in which tissue-specific dysregulation of 11beta-HSD1 (increased in adipose, decreased in liver) mirrors changes in human obesity. Six-week-old male rats were treated orally with carbenoxolone (50 mg/kg/day) or water (1 ml/kg/day) for 3 weeks. Carbenoxolone inhibited 11beta-HSD1 activity in liver (25 +/- 3 versus 52 +/- 2% conversion in lean; 18 +/- 3 versus 35 +/- 3% in obese; p < 0.01) but not in adipose tissue or skeletal muscle. Carbenoxolone had no effect on weight gain or food intake, did not affect plasma glucose during an oral glucose tolerance test, and increased the plasma insulin response to glucose. However, high-density lipoprotein cholesterol was increased by carbenoxolone in obese animals (1.52 +/- 0.24 versus 1.21 +/- 0.26 mM; p < 0.03). Carbenoxolone did not inhibit hepatic inactivation of glucocorticoid by 5beta-reductase and had no significant effect on plasma corticosterone levels. In conclusion, carbenoxolone provides a model for liver-specific inhibition of 11beta-HSD1, which results in improved lipid profile, in Zucker obese rats. Failure to inhibit 11beta-HSD1 in adipose tissue and/or skeletal muscle may explain the lack of effect on glucose tolerance and obesity. Inhibition of adipose 11beta-HSD1 is probably necessary to gain the maximum benefit of an 11beta-HSD1 inhibitor.     

A nonthiazolidinedione peroxisome proliferator-activated receptor gamma agonist reverses endothelial dysfunction in diabetic (db/db-/-) mice

We have previously reported that endothelium-dependent relaxation to acetylcholine is impaired in small mesenteric arteries from spontaneously diabetic (db/db) mice. The objective of the present study was to examine the effects of treatment of the db/db and the insulin-resistant ob/ob mice with the PPARgamma agonist 2-(2-(4-phenoxy-2-propylphenoxy)ethyl)indole-5-acetic acid (COOH). In the db/db model, an 8-week treatment with COOH (30 mg/kg/day) reduced plasma glucose from 48.0 +/- 2.5 (untreated) to 12.6 +/- 1.1 mM. In contrast, plasma glucose was not elevated in untreated ob/ob mice. Relaxation of small mesenteric arteries mediated by acetylcholine was impaired in the untreated db/db diabetic mice (51.7 +/- 7.4% maximal relaxation, n = 6) but not in the ob/ob mice (70.8 +/- 8.6% maximal relaxation, n = 3). This impairment was reversed with COOH treatment (86.9 +/- 0.4% maximal relaxation, n = 5). Malondialdehyde was elevated in plasma from diabetic db/db mice (13.9 +/- 1.1 versus 12.0 +/- 0.7 micromol/ml); however, when normalized to total cholesterol, no significant differences in the ratio of lipid peroxidation in plasma were identified. Western blot analysis and quantitative polymerase chain reaction for eNOS was performed on the isolated mesenteric vessels and revealed no differences in the relative levels of eNOS expression in diabetic and control animals; in addition, treatment with COOH had no significant effect on eNOS levels in either group. In summary, endothelial dysfunction and hyperglycemia were completely normalized in COOH-treated db/db mice. In contrast, nonhyperglycemic ob/ob mice exhibited normal vasodilatory responses to acetylcholine and, consequently, COOH treatment had no effect on endothelial function.     

Glucagon-like peptide 1 receptor agonist ZP10A increases insulin mRNA expression and prevents diabetic progression in db/db mice

We characterized the novel, rationally designed peptide glucagon-like peptide 1 (GLP-1) receptor agonist H-HGEGTFTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPSK KKKKK-NH2 (ZP10A). Receptor binding studies demonstrated that the affinity of ZP10A for the human GLP-1 receptor was 4-fold greater than the affinity of GLP-1 (7-36) amide. ZP10A demonstrated dose-dependent improvement of glucose tolerance with an ED50 value of 0.02 nmol/kg i.p. in an oral glucose tolerance test (OGTT) in diabetic db/db mice. After 42 days of treatment, ZP10A dose-dependently (0, 1, 10, or 100 nmol/kg b.i.d.; n = 10/group), decreased glycosylated hemoglobin (HbA1C) from 8.4 +/- 0.4% (vehicle) to a minimum of 6.2 +/- 0.3% (100 nmol/kg b.i.d.; p < 0.05 versus vehicle) in db/db mice. Fasting blood glucose (FBG), glucose tolerance after an OGTT, and HbA1C levels were significantly improved in mice treated with ZP10A for 90 days compared with vehicle-treated controls. Interestingly, these effects were preserved 40 days after drug cessation in db/db mice treated with ZP10A only during the first 50 days of the study. Real-time polymerase chain reaction measurements demonstrated that the antidiabetic effect of early therapy with ZP10A was associated with an increased pancreatic insulin mRNA expression relative to vehicle-treated mice. In conclusion, long-term treatment of diabetic db/db mice with ZP10A resulted in a dose-dependent improvement of FBG, glucose tolerance, and blood glucose control. Our data suggest that ZP10A preserves beta-cell function. ZP10A is considered one of the most promising new drug candidates for preventive and therapeutic intervention in type 2 diabetes.     

Antihyperglycemic and antioxidant properties of caffeic acid in db/db mice

This study investigated the blood glucose-lowering effect and antioxidant capacity of caffeic acid in C57BL/KsJ-db/db mice. Caffeic acid induced a significant reduction of the blood glucose and glycosylated hemoglobin levels than the control group. The plasma insulin, C-peptide, and leptin levels in caffeic acid group were significantly higher than those of the control group, whereas the plasma glucagon level was lower. Increased plasma insulin by caffeic acid was attributable to an antidegenerative effect on the islets. Caffeic acid also markedly increased glucokinase activity and its mRNA expression and glycogen content and simultaneously lowered glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities and their respective mRNA expressions, accompanied by a reduction in the glucose transporter 2 expression in the liver. In contrast to the hepatic glucose transporter 2, adipocyte glucose transporter 4 expression was greater than the control group. In addition, caffeic acid significantly increased superoxide dismutase, catalase, and glutathione peroxidase activities and their respective mRNA levels, while lowering the hydrogen peroxide and thiobarbituric acid reactive substances levels in the erythrocyte and liver of db/db mice. These results indicate that caffeic acid exhibits a significant potential as an antidiabetic agent by suppressing a progression of type 2 diabetic states that is suggested by an attenuation of hepatic glucose output and enhancement of adipocyte glucose uptake, insulin secretion, and antioxidant capacity.     

Overexpression of glutamine:fructose-6-phosphate amidotransferase in transgenic mice leads to insulin resistance.

The hexosamine biosynthetic pathway has been hypothesized to be involved in mediating some of the toxic effects of hyperglycemia. Glutamine:fructose-6-phosphate amidotransferase (GFA), the first and rate limiting enzyme of the hexosamine biosynthetic pathway, was overexpressed in skeletal muscle and adipose tissue of transgenic mice. A 2.4-fold increase of GFA activity in muscle of the transgenic mice led to weight-dependent hyperinsulinemia in random-fed mice. The hyperinsulinemic-euglycemic clamp technique confirmed that transgenic mice develop insulin resistance, with a glucose disposal rate of 68.5 +/- 3.5 compared with 129.4 +/- 9.4 mg/kg per min (P < 0.001) for littermate controls. The decrease in the glucose disposal rate of the transgenic mice is accompanied by decreased protein but not mRNA levels of the insulin-stimulated glucose transporter (GLUT4). These data support the hypothesis that excessive flux through the hexosamine biosynthesis pathway mediates adverse regulatory and metabolic effects of hyperglycemia, specifically insulin resistance of glucose disposal. These mice can serve as a model system to study the mechanism for the regulation of glucose homeostasis by hexosamines.     

Evidence that insulin resistance is responsible for the decreased thermic effect of glucose in human obesity.

The thermic effect of glucose was investigated in nine obese and six lean subjects in whom the same rate of glucose uptake was imposed. Continuous indirect calorimetry was performed for 240 min on the supine subject. After 45 min, 20% glucose was infused (609 mg/min) for 195 min and normoglycemia was maintained by adjusting the insulin infusion rate. At 2 h, propranolol was infused (bolus 100 micrograms/kg; 1 microgram/kg X min) for the remaining 75 min. To maintain the same glucose uptake (0.624 g/min), it was necessary to infuse insulin at 3.0 +/- 0.6 (leans) and 6.6 +/- 1.2 mU/kg X min (obese) (P less than 0.02). At this time, glucose oxidation was 0.248 +/- 0.019 (leans) and 0.253 +/- 0.022 g/min (obese) (NS), and nonoxidative glucose disposal was 0.375 +/- 0.011 and 0.372 +/- 0.029 g/min, respectively. Resting metabolic rate (RMR) rose significantly by 0.13 +/- 0.02 kcal/min in both groups, resulting in similar thermic effects, i.e., 5.5 +/- 0.7% (leans) 5.4 +/- 0.9% (obese) (NS) and energy costs of glucose storage 0.35 +/- 0.06 and 0.39 +/- 0.09 kcal/g (NS), respectively. With propranolol, glucose uptake and storage remained the same, while RMR fell significantly in both groups, with corresponding decreases (P less than 0.05) in the thermic effects of glucose to 3.7 +/- 0.6% and 2.9 +/- 0.8% (NS) and the energy costs of glucose storage 0.23 +/- 0.04 and 0.17 +/- 0.05 kcal/g (NS) in the lean and obese subjects, respectively. These results suggest that the defect in the thermic effect of glucose observed in obese subjects is due to their insulin resistance, which is responsible for a lower rate of glucose uptake and hence decreased rate of glucose storage, which is an energy-requiring process.     

Lactobacillus rhamnosus GG improves glucose tolerance through alleviating ER stress and suppressing macrophage activation in db/db mice

Although recent studies have reported that Lactobacillus rhamnosus GG (LGG), the most extensively studied probiotic strain, exerts an anti-hyperglycemic effect on several rodent models, the underlying mechanism remains unclear. In this study, twenty male C57BL/KsJ-db/db (db/db) mice were divided into 2 groups, LGG-treated and control group, which received a daily dose of LGG (1 × 10⁸ CFU per mouse) and PBS orally for 4 weeks, respectively. We observed that glucose tolerance was significantly improved in LGG-treated db/db mice. Insulin-stimulated Akt phosphorylation and GLUT4 translocation were higher in skeletal muscle of LGG-treated mice relative to their controls. It was also observed that LGG treatment caused significant reductions in endoplasmic reticulum (ER) stress in skeletal muscle and M1-like macrophage activation in white adipose tissues. Our results indicate that the anti-diabetic effect of LGG in db/db mice is associated with alleviated ER stress and suppressed macrophage activation, resulting in enhanced insulin sensitivity. These findings suggest a therapeutic potential of probiotics for prevention and treatment of type 2 diabetes.     

Effect of denervation on the expression of two glucose transporter isoforms in rat hindlimb muscle.

Denervation rapidly (within 24 h) induces insulin resistance of several insulin-responsive pathways in skeletal muscle, including glucose transport; resistance is usually maximal by 3 d. We examined the effect of denervation on the expression of two glucose transporter isoforms (GLUT-1 and GLUT-4) in rat hindlimb muscle; GLUT-4 is the predominant species in muscle. 1 d postdenervation, GLUT-1 and GLUT-4 mRNA and protein concentrations were unchanged. 3 and 7 d postdenervation, GLUT-4 mRNA and protein (per microgram DNA) were decreased by 50%. The minor isoform, GLUT-1 mRNA increased by approximately 500 and approximately 100%, respectively, on days 3 and 7 while GLUT-1 protein increased by approximately 60 and approximately 100%. The data suggest that the insulin resistance of glucose transport early after denervation does not reflect a decrease in total glucose transporter number; however, decreased GLUT-4 expression may contribute to its increased severity after 3 d. Parallel decreases in GLUT-4 mRNA and GLUT-4 protein postdenervation are consistent with pretranslational regulation; GLUT-1 expression may be regulated pre- and posttranslationally. The cell type(s) which overexpress GLUT-1 postdenervation need to be identified. Nervous stimuli and/or contractile activity may modulate the expression of GLUT-1 and GLUT-4 in skeletal muscle tissue.     

Recombinant basic fibroblast growth factor stimulates wound healing in healing-impaired db/db mice

The stimulatory effect of recombinant basic fibroblast growth factor (bFGF) on wound healing was assessed using healing-impaired (db/db) mice. Full-thickness wounds were made in female diabetic C57BL/KsJ db/db mice, and their normal (db/+) littermates with a punch biopsy instrument. Recombinant bFGF was applied locally to the open wound once a day. The mice were later killed and histological sections of the wounds were prepared. The degree of wound healing was evaluated using several histological parameters such as degree of reepithelialization, granulation tissue thickness, matrix density, number of infiltrated cells, and number of capillaries. Wounds from normal mice displayed good reepithelialization rates and granulation tissue formation, while wounds from db/db mice had poor responses, especially in the dermal parameters. Although the application of bFGF to wounds in the normal (db/+) mice had little effect, application of bFGF to wounds in db/db mice induced significant responses in all of the dermal parameters compared with nontreated db/db mice (p less than 0.001). In the presence of bFGF, these parameters approximated those observed in nontreated littermates. A minimum of 0.5 microgram bFGF in either single or multiple applications was required for a significant effect. bFGF that was either boiled or pretreated with neutralizing antibody had little stimulatory effect. Time-course experiments indicated that the granulation response in bFGF-treated mice peaked between 8 and 12 d, and decreased after 12 d, while matrix density continued to increase until the 18th day (p less than 0.05). The breaking strength of healed linear wounds in db/db mice was also decreased when compared with heterozygous littermates. This parameter was also improved by the administration of bFGF to the wounds (p less than 0.05).     

富含半胱氨酸的酸性分泌蛋白在db/db鼠肝脏组织中的表达及意义

目的 观察富含半胱氨酸的酸性分泌蛋白(secreted protein acidic rich in cysteine,SPARC)在具有2型糖尿病表型的db/db鼠(10周龄)肝脏组织中的表达情况.方法 选择10周龄的db/db鼠(C57BL/KSJ)与其同窝野生对照型各6只,采用反转录-聚合酶链反应(RT-PCR)方法检测肝脏组织中SPARC mRNA的表达水平,免疫荧光染色方法检测肝脏组织中SPARC蛋白的表达水平.结果 SPARC在db/db鼠肝脏组织中呈现高表达(36.91±1.91vs 15.31±0.31)(P＜0.01).结论 SPARC在db/db鼠肝脏组织中呈现高表达,其可能与糖尿病有关的脂肪肝病变有关.     

Prevention of diabetic nephropathy in db/db mice with glycated albumin antagonists. A novel treatment strategy.

Accelerated protein glycation in diabetes has been mechanistically linked to the pathogenesis of diabetic nephropathy. Because glycated albumin induces abnormalities in cultured mesangial cells that resemble those characterizing the glomerular mesangium in diabetes, and monoclonal antibodies (A717) specific for Amadori-modified glycated albumin prevent these abnormalities, we postulated that in vivo administration of A717 could retard the progression of diabetic nephropathy. To test this hypothesis, diabetic db/db mice and their nondiabetic db/m littermates were treated with eight consecutive weekly injections of 150 micrograms of A717 (Fab fragments) to reduce the elevated plasma glycated albumin concentration, or with irrelevant murine IgG (MIg). Relative to nondiabetics, diabetic mice (MIg treated) manifested proteinuria (3.35 +/- 0.15 vs 0.87 +/- 0.1 mg albumin/mg creatinine), 3.8-fold increase in mesangial matrix fraction, and renal cortical overexpression of mRNAs encoding alpha 1(IV) collagen (2.6-fold increase) and fibronectin (3.8-fold increase). Treatment of db/db mice with A717 significantly reduced the proteinuria (1.52 +/- 0.3 mg/mg creatinine), inhibited mesangial matrix expansion, and attenuated overexpression of matrix mRNAs. The nephropathic protective effects of A717 were independent of any change in blood glucose concentrations. Antibodies unreactive with glycated albumin did not duplicate the beneficial effects of A717. Thus, abrogating the biologic effects of increased glycated albumin with A717 has a salutary influence on the pathogenesis of diabetic nephropathy and has novel therapeutic potential in its management.     

Restoration of insulin responsiveness in skeletal muscle of morbidly obese patients after weight loss. Effect on muscle glucose transport and glucose transporter GLUT4.

A major defect contributing to impaired insulin action in human obesity is reduced glucose transport activity in skeletal muscle. This study was designed to determine whether the improvement in whole body glucose disposal associated with weight reduction is related to a change in skeletal muscle glucose transport activity and levels of the glucose transporter protein GLUT4. Seven morbidly obese (body mass index = 45.8 +/- 2.5, mean +/- SE) patients, including four with non-insulin-dependent diabetes mellitus (NIDDM), underwent gastric bypass surgery for treatment of their obesity. In vivo glucose disposal during a euglycemic clamp at an insulin infusion rate of 40 mU/m2 per min was reduced to 27% of nonobese controls (P less than 0.01) and improved to 78% of normal after weight loss of 43.1 +/- 3.1 kg (P less than 0.01). Maximal insulin-stimulated glucose transport activity in incubated muscle fibers was reduced by approximately 50% in obese patients at the time of gastric bypass surgery but increased twofold (P less than 0.01) to 88% of normal in five separate patients after similar weight reduction. Muscle biopsies obtained from vastus lateralis before and after weight loss revealed no significant change in levels of GLUT4 glucose transporter protein. These data demonstrate conclusively that insulin resistance in skeletal muscle of mobidly obese patients with and without NIDDM cannot be causally related to the cellular content of GLUT4 protein. The results further suggest that morbid obesity contributes to whole body insulin resistance through a reversible defect in skeletal muscle glucose transport activity. The mechanism for this improvement may involve enhanced transporter translocation and/or activation.     

Reduced capacity and affinity of skeletal muscle for insulin-mediated glucose uptake in noninsulin-dependent diabetic subjects. Effects of insulin therapy.

We have estimated the capacity and affinity of insulin-mediated glucose uptake (IMGU) in whole body and in leg muscle of obese non-insulin-dependent diabetics (NIDDM, n = 6) with severe hyperglycemia, glycohemoglobin (GHb 14.4 +/- 1.2%), lean controls (ln, n = 7) and obese nondiabetic controls (ob, n = 7). Mean +/- SEM weight (kg) was 67 +/- 2 (ln), 100 +/- 7 (ob), and 114 +/- 11 (NIDDM), P = NS between obese groups. NIDDM were also studied after 3 wk of intensive insulin therapy, GHb post therapy was 10.1 +/- 0.9, P less than 0.01 vs. pretherapy. Insulin (120 mu/m2 per min) was infused and the arterial blood glucose (G) sequentially maintained at approximately 4, 7, 12, and 21 mmol/liter utilizing the G clamp technique. Leg glucose uptake (LGU) was calculated as the product of the femoral arteriovenous glucose difference (FAVGd) and leg blood flow measured by thermodilution. Compared to ln, ob and NIDDM had significantly lower rates of whole body IMGU and LGU at all G levels. Compared to ob, the NIDDM exhibited approximately 50% and approximately 40% lower rates of whole body IMGU over the first two G levels (P less than 0.02) but did not differ at the highest G, P = NS. LGU was 83% lower in NIDDM vs. ob, P less than 0.05 at the first G level only. After insulin therapy NIDDM were indistinguishable from ob with respect to whole body IMGU or LGU at all G levels. A significant correlation was noted between the percent GHb and the EG50 (G at which 1/2 maximal FAVGd occurs) r = 0.73, P less than 0.05. Thus, (a) insulin resistance in NIDDM and obese subjects are characterized by similar decreases in capacity for skeletal muscle IMGU, but differs in that poorly controlled NIDDM display a decrease in affinity for skeletal muscle IMGU, and (b) this affinity defect is related to the degree of antecedent glycemic control and is reversible with insulin therapy, suggesting that it is an acquired defect.     

The loss of GLUT2 expression by glucose-unresponsive beta cells of db/db mice is reversible and is induced by the diabetic environment.

Glucose-induced insulin secretion by beta cells of diabetic db/db mice was studied by a pancreas perfusion technique, and the levels of GLUT2 protein in pancreatic islets were assessed by immunofluorescence microscopy and protein blot analysis. Beta cells from diabetic mice had a high basal rate of insulin secretion; they did not respond to glucose stimulation but displayed a normal secretory response to arginine. At the same time, GLUT2 expression by db/db islets was lost whereas beta cells from nondiabetic db/+ mice expressed high levels of this transporter. GLUT2 levels in liver or kidney of diabetic mice were, however, mostly unaltered. Transplanting islets from db/db mice under the kidney capsule of db/+ mice restored normal GLUT2 levels. Conversely, transplantation of db/+ islets into db/db mice induced the disappearance of GLUT2 expression. When islets from db/+ mice were transplanted under the kidney capsule of streptozocin-diabetic mice, the immunodetection of GLUT2 also disappeared. We conclude that: (a) GLUT2 expression is decreased in glucose-unresponsive beta cells from db/db mice; (b) the decreased expression of GLUT2 is reversible; (c) the loss of GLUT2 expression is induced by the diabetic environment of db/db and streptozocin-induced diabetic mice. These observations together with previously published data suggest that a factor different from glucose or insulin regulates the beta cell expression of GLUT2.