bluuebunny/crossref_metadata_2025 huggingface dataset:
A Cluster of Three Single Nucleotide Polymorphisms in the 3′-Untranslated Region of Human Glycoprotein PC-1 Gene Stabilizes PC-1 mRNA and Is Associated With Increased PC-1 Protein Content and Insulin Resistance–Related Abnormalities
Authors: Frittitta Lucia , Ercolino Tonino , Bozzali Maura , Argiolas Alessandra , Graci Salvo , Santagati Maria G. , Spampinato Daniela , Di Paola Rosa , Cisternino Carmela , Tassi Vittorio , Vigneri Riccardo , Pizzuti Antonio , Trischitta Vincenzo
Published: March 2007

Glycoprotein PC-1 inhibits insulin signaling and, when overexpressed, plays a role in human insulin resistance. Mechanisms of PC-1 overexpression are unknown. We have identified a haplotype in the 3′-untranslated region of the PC-1 gene that may modulate PC-1 expression and confer an increased risk for insulin resistance. Individuals from Sicily, Italy, carrying the “P” haplotype (i.e., a cluster of three single nucleotide polymorphisms: G2897A, G2906C, and C2948T) were at higher risk (P < 0.01) for insulin resistance and had higher (P < 0.05) levels of plasma glucose and insulin during an oral glucose tolerance test and higher levels of cholesterol, HDL cholesterol, and systolic blood pressure. They also had higher (P < 0.05–0.01) PC-1 protein content in both skeletal muscle and cultured skin fibroblasts. In CHO cells transfected with either P or wild-type cDNA, specific PC-1 mRNA half-life was increased for those transfected with P (t/2 = 3.73 ± 1.0 vs. 1.57 ± 0.2 h; P < 0.01). In a population of different ethnicity (Gargano, East Coast Italy), patients with type 2 diabetes (the most likely clinical outcome of insulin resistance) had a higher P haplotype frequency than healthy control subjects (7.8 vs. 1.5%, P < 0.01), thus replicating the association between the P allele and the insulin resistance–related abnormalities observed among Sicilians. In conclusion, we have identified a possible molecular mechanism for PC-1 overexpression that confers an increased risk for insulin resistance–related abnormalities.
Interactions of Impaired Glucose Transport and Phosphorylation in Skeletal Muscle Insulin Resistance
Authors: Williams Katherine V. , Price Julie C. , Kelley David E.
Published: March 2007

It has been postulated that glucose transport is the principal site of skeletal muscle insulin resistance in obesity and type 2 diabetes, though a distribution of control between glucose transport and phosphorylation has also been proposed. The current study examined whether the respective contributions of transport and phosphorylation to insulin resistance are modulated across a dose range of insulin stimulation. Rate constants for transport and phosphorylation in skeletal muscle were estimated using dynamic positron emission tomography (PET) imaging of 2-deoxy-2[18F]fluoro-d-glucose ([18F]FDG) during insulin infusions at three rates (0, 40, and 120 mU/m2 per min) in lean glucose-tolerant, obese glucose-tolerant, and obese type 2 diabetic subjects. Parallel studies of arteriovenous fractional extraction across the leg of [18F]FDG and [2-3H] glucose were performed to measure the “lumped constant” (LC) (i.e., the analog effect) for [18F]FDG to determine whether this value is affected by insulin dose or insulin resistance. The value of the LC was similar across insulin doses and groups. Leg glucose uptake (LGU) also provided a measure of skeletal muscle glucose metabolism independent of PET. [18F]FDG uptake determined by PET imaging strongly correlated with LGU across groups and across insulin doses (r = 0.81, P < 0.001). Likewise, LGU correlated with PET parameters of glucose transport (r = 0.67, P < 0.001) and glucose phosphorylation (r = 0.86, P < 0.001). Glucose transport increased in response to insulin in the lean and obese groups (P < 0.05), but did not increase significantly in the type 2 diabetic group. A dose-responsive pattern of stimulation of glucose phosphorylation was observed in all groups of subjects (P < 0.05); however, glucose phosphorylation was lower in both the obese and type 2 diabetic groups compared with the lean group at the moderate insulin dose (P < 0.05). These findings indicate an important interaction between transport and phosphorylation in the insulin resistance of obesity and type 2 diabetes.
The Effect of Dimethylbiguanide on Thrombin Activity, FXIII Activation, Fibrin Polymerization, and Fibrin Clot Formation
Authors: Standeven Kristina F. , Ariëns Robert A.S. , Whitaker Paul , Ashcroft Alison E. , Weisel John W. , Grant Peter J.
Published: March 2007

The antihyperglycemic drug dimethylbiguanide (DMB, also known as metformin) reduces the risk of cardiovascular complications in type 2 diabetes, although the mechanism(s) involved are unclear. DMB reduces glycosylation-related protein cross-linking, a process similar to fibrin cross-linking catalyzed by activated factor XIII (FXIII). To investigate whether the cardioprotective effect of DMB could be related to effects on clot stabilization, we studied the effects of DMB on FXIII, thrombin activity, and cleavage of fibrin(ogen). Activity of purified and plasma FXIII was inhibited by DMB. Analysis by mass spectrometry and FXIII-coupled magnetic particles excluded binding of DMB to FXIII. Thrombin-induced cleavage of the activation peptide from FXIII was inhibited in a dose-dependent manner, as was fibrinopeptide cleavage from fibrinogen. Ancrod-induced cleavage of fibrinopeptide A was not affected. DMB prolonged clotting time of normal plasma. Fiber thickness and pore size of fibrin clots, measured by permeation experiments and visualized by scanning electron microscopy, decreased significantly with DMB. No interactions between DMB and the active site of thrombin were found. Turbidity experiments demonstrated that DMB changed polymerization and lateral aggregation of protofibrils. These results suggest that DMB interferes with FXIII activation and fibrin polymerization, but not only by binding to thrombin on a different location than the active site. In patients on DMB therapy, FXIII antigen and activity levels in vivo were reduced over a 12-week period. These findings indicate that part of the cardioprotective effect of DMB in patients with type 2 diabetes may be attributed to alterations in fibrin structure/function.
SNP43 of CAPN10 and the Risk of Type 2 Diabetes in African-Americans
Authors: Garant Michael J. , Kao W.H. Linda , Brancati Frederick , Coresh Josef , Rami Tejal M. , Hanis Craig L. , Boerwinkle Eric , Shuldiner Alan R.
Published: March 2007

Recently, an A-to-G variant in intron 3 (SNP43) of the calcium-activated neutral protease 10 gene (CAPN10) was identified as a possible type 2 diabetes susceptibility gene through positional cloning in Mexican-Americans. We conducted cross-sectional and prospective studies to evaluate the relation between SNP43 and type 2 diabetes and related traits in middle-aged African-American participants of the Atherosclerosis Risk in Communities Study, a population-based longitudinal study. At baseline, 269 prevalent diabetes cases and 1,159 nondiabetic control subjects were studied. Those with the G/G genotype were more likely to have diabetes than those with the A/G or A/A genotype (odds ratio [OR] 1.41, 95% CI 1.00–1.99, P = 0.05). In the prospective study, 166 of the control subjects developed incident diabetes over 9 years of follow-up. The incidence of diabetes for individuals with the G/G genotype did not differ significantly from those with at least one copy of the A allele (23.3 vs. 19.5 per 1,000 person years, P = 0.29). Pooling prevalent and incident diabetic cases together, individuals with the G/G genotype were ∼40% more likely to have diabetes than those without (OR 1.38, 95% CI 1.04–1.83, P = 0.03). Because of the high frequency of the G allele (0.88), ∼25% of the susceptibility to type 2 diabetes in African-Americans may be attributed to the G/G genotype at SNP43 of CAPN10, although most of the subjects with the G/G genotype did not develop diabetes over the 9 years of follow-up. We conclude from this large prospective study that the G allele of SNP43 of CAPN10 or another allele or gene that is in linkage disequilibrium with it increases susceptibility to type 2 diabetes in African-Americans.
Hepatic Glycogen Metabolism in Type 1 Diabetes After Long-Term Near Normoglycemia
Authors: Bischof Martin G. , Bernroider Elisabeth , Krssak Martin , Krebs Michael , Stingl Harald , Nowotny Peter , Yu Chunlin , Shulman Gerald I. , Waldhäusl Werner , Roden Michael
Published: March 2007

We tested the impact of long-term near normoglycemia (HbA1c <7% for >1 year) on glycogen metabolism in seven type 1 diabetic and seven matched nondiabetic subjects after a mixed meal. Glycemic profiles (6.2 ± 0.10 vs. 5.9 ± 0.07 mmol/l; P < 0.05) of diabetic patients were approximated to that of nondiabetic subjects by variable insulin infusion. Rates of hepatic glycogen synthesis and breakdown were calculated from the glycogen concentration time curves between 7:30 p.m. and 8:00 a.m. using in vivo 13C nuclear magnetic resonance spectroscopy. Glucose production was determined with d-[6,6-2H2]glucose, and the hepatic uridine-diphosphate glucose pool was sampled with acetaminophen. Glycogen synthesis and breakdown as well as glucose production were identical in diabetic and healthy subjects: 7.3 ± 0.9 vs. 7.1 ± 0.7, 4.2 ± 0.5 vs. 3.8 ± 0.3, and 8.7 ± 0.5 vs. 8.4 ± 0.7 μmol · kg−1 · min−1, respectively. Although portal vein insulin concentrations were doubled, the flux through the indirect pathway of glycogen synthesis remained higher in type 1 diabetic subjects: ∼70 vs. ∼50%; P < 0.05. In conclusion, combined long- and short-term intensified insulin substitution normalizes rates of hepatic glycogen synthesis but not the contribution of gluconeogenesis to glycogen synthesis in type 1 diabetes.
β-Cell Death and Mass in Syngeneically Transplanted Islets Exposed to Short- and Long-Term Hyperglycemia
Authors: Biarnés Montserrat , Montolio Marta , Nacher Victor , Raurell Mercè , Soler Joan , Montanya Eduard
Published: March 2007

We studied the effects of hyperglycemia on β-cell death and mass in syngeneically transplanted islets. Six groups of STZ-induced diabetic C57BL/6 mice were transplanted with 100 syngeneic islets, an insufficient β-cell mass to restore normoglycemia. Groups 1, 2, and 3 remained hyperglycemic throughout the study. Groups 4, 5, and 6 were treated with insulin from day 7 before transplantation to day 10 after transplantation. After insulin discontinuation, group 6 mice achieved definitive normoglycemia. Grafts were harvested at 3 (groups 1 and 4), 10 (groups 2 and 5), and 30 (groups 3 and 6) days after transplantation. On day 3, the initially transplanted β-cell mass (0.13 ± 0.01 mg) was dramatically and similarly reduced in the hyperglycemic and insulin-treated groups (group 1: 0.048 ± 0.002 mg; group 4: 0.046 ± 0.007 mg; P < 0.001). Extensive islet necrosis (group 1: 30.7%; group 4: 26.8%) and increased β-cell apoptosis (group 1: 0.30 ± 0.05%; group 4: 0.42 ± 0.07%) were found. On day 10, apoptosis remained increased in both hyperglycemic and insulin-treated mice (group 2: 0.44 ± 0.09%; group 5: 0.48 ± 0.08%) compared with normal pancreas (0.04 ± 0.03%; P < 0.001). In contrast, on day 30, β-cell apoptosis was increased in grafts exposed to sustained hyperglycemia (group 3: 0.37 ± 0.03%) but not in normoglycemic mice (group 6: 0.12 ± 0.02%); β-cell mass was selectively reduced in islets exposed to hyperglycemia (group 3: 0.046 ± 0.02 mg; group 6: 0.102 ± 0.009 mg; P < 0.01). In summary, even in optimal conditions, ∼60% of transplanted islet tissue was lost 3 days after syngeneic transplantation, and both apoptosis and necrosis contributed to β-cell death. Increased apoptosis and reduced β-cell mass were also found in islets exposed to chronic hyperglycemia, suggesting that sustained hyperglycemia increased apoptosis in transplanted β-cells.
Oral Exposure to Diabetes-Promoting Food or Immunomodulators in Neonates Alters Gut Cytokines and Diabetes
Authors: Scott Fraser W. , Rowsell Paul , Wang Gen-Sheng , Burghardt Karolina , Kolb Hubert , Flohé Stefanie
Published: March 2007

Disease development in diabetes-prone BB rats is modified by the type of diet fed after weaning. The aim of this investigation was to determine whether exposure during the first week of life to antigens from a known diabetes-promoting diet (NIH-07) could modify diabetes incidence and, if so, to what extent this occurs via alterations in systemic T-cell reactivity, gut cytokines, or islet infiltration. Diabetes-prone BB (BBdp) rats were hand-fed twice daily between age 4 and 7 days with vehicle, a hydrolyzed casein (HC)–based infant formula, Pregestimil (PG), PG + cereal-based NIH-07 diet, PG + lipopolysaccharides (LPS) or PG + LPS + silica. After weaning, they were fed either an NIH-07 diet or a semipurified HC (diabetes-retardant) diet until 150 days. In separate studies, 5-day-old BBdp rat pups were administered the aforementioned treatments, and expression of intestinal mRNA for γ-interferon (IFN-γ) or transforming growth factor-β (TGF-β) was quantified using reverse transcriptase–polymerase chain reaction. The effect of early oral treatment with NIH-07 or PG on systemic T-cell reactivity was evaluated using footpad swelling delayed-type hypersensitivity (DTH) and the popliteal lymph node assay. Oral exposure of neonates to a complex mixture of antigens from the diabetes-promoting diet delayed onset of diabetes (79 vs. 88 days) and prevented disease in approximately one-third of animals. A similar protective effect was seen for neonatal exposure to wheat gluten in animals subsequently weaned onto a semipurified wheat gluten diet. By contrast, LPS-treated neonates displayed more severe insulitis and developed diabetes at an increased rate, which was significantly suppressed by co-administration of silica particles. The protective effect of early exposure to diabetogenic diets was not associated with significant reduction of islet infiltration, and there was no impact on the DTH response to food antigens. However, whereas diabetes-resistant BBc rats developed systemic tolerance to NIH-07 antigens fed chronically, BBdp rats did not. The lack of effect of the early oral antigen regimen on the DTH reaction in the footpad, a classic Th1-mediated reaction, suggests little effect on systemic T-cell reactivity. However, local effects were observed in the small intestine. Oral exposure to diabetes-promoting food antigens or LPS downregulated the Th1 cytokine IFN-γ and decreased the IFN-γ/TGF-β ratio. Thus, oral exposure to diabetes-promoting food antigens and immune modulators in neonates can modify diabetes expression in association with changes in local cytokine balance in the gut.
Phosphatidylinositol 3-Kinase Suppresses Glucose-Stimulated Insulin Secretion by Affecting Post-Cytosolic [Ca2+] Elevation Signals
Authors: Eto Kazuhiro , Yamashita Tokuyuki , Tsubamoto Yoshiharu , Terauchi Yasuo , Hirose Kenzo , Kubota Naoto , Yamashita Shigeo , Taka Junko , Satoh Shinobu , Sekihara Hisahiko , Tobe Kazuyuki , Iino Masamitsu , Noda Mitsuhiko , Kimura Satoshi , Kadowaki Takashi
Published: March 2007

The role of phosphatidylinositol (PI) 3-kinase in the regulation of pancreatic β-cell function was investigated. PI 3-kinase activity in p85α regulatory subunit–deficient (p85α−/−) islets was decreased to ∼20% of that in wild-type controls. Insulin content and mass of rough endoplasmic reticula were decreased in β-cells from p85α−/− mice with increased insulin sensitivity. However, p85α−/− β-cells exhibited a marked increase in the insulin secretory response to higher concentrations of glucose. When PI 3-kinase in wild-type islets was suppressed by wortmannin or LY294002, the secretion was also substantially potentiated. Wortmannin’s potentiating effect was not due to augmentation in glucose metabolism or cytosolic [Ca2+] elevation. Results of p85α−/− islets and wortmannin-treated wild-type islets stimulated with diazoxide and KCl showed that inhibition of PI 3-kinase activity exerted its effect on secretion, at least in part, distal to a cytosolic [Ca2+] elevation. These results suggest that PI 3-kinase activity normally plays a crucial role in the suppression of glucose-stimulated insulin secretion.
Low Plasma Adiponectin Concentrations Do Not Predict Weight Gain in Humans
Authors: Vozarova Barbora , Stefan Norbert , Lindsay Robert S. , Krakoff Jonathan , Knowler William C. , Funahashi Tohru , Matsuzawa Yuji , Stumvoll Michael , Weyer Christian , Tataranni P. Antonio
Published: March 2007

Low concentrations of plasma adiponectin, the most abundant adipose-specific protein, are observed in obese individuals and predict the development of type 2 diabetes. Administration of adiponectin to rodents prevented diet-induced weight gain, suggesting a potential etiologic role of hypoadiponectinemia in the development of obesity. Our aim was to prospectively examine whether low plasma adiponectin concentrations predict future weight gain in Pima Indians, explaining the predictive effect of adiponectin on the development of type 2 diabetes. We measured plasma adiponectin concentrations in 219 nondiabetic Pima Indians (112 M/107 F, age 31 ± 9 years, body weight 96 ± 20 kg [mean ± SD]) in whom body weight and height were measured and BMI calculated at baseline and follow-up. Cross-sectionally, plasma adiponectin concentrations were negatively associated with body weight (r = −0.28, P = 0.0001). Prospectively, plasma adiponectin concentrations at baseline were not associated with change in weight or BMI before or after adjustment for time of follow-up or after additional adjustment for age at follow-up and sex (all P > 0.3). Our data suggest that low plasma adiponectin concentrations do not play an etiologic role in development of obesity in Pima Indians. Therefore, the predictive effect of low plasma adiponectin concentrations on the development of type 2 diabetes seems to be mediated by factors other than increased adiposity.
Role of NADH Shuttles in Glucose-Induced Insulin Secretion From Fetal β-Cells
Authors: Tan Cynthia , Tuch Bernard E. , Tu Jian , Brown Shane A.
Published: March 2007

The NADH shuttle system, which transports the substrate for oxidative metabolism directly from the cytosol to the mitochondrial electron transport chain, has been shown to be essential for glucose-induced activation of mitochondrial metabolism and insulin secretion in adult β-cells. We examined the role of these shuttles in the fetal β-cell, which is immature in being unable to secrete insulin in response to glucose. The activity and concentration of the two key enzymes of the NADH shuttles, mitochondrial glycerol phosphate dehydrogenase (mGPDH) and mitochondrial malate dehydrogenase (mMDH), were eight- and threefold lower, respectively, in fetal compared with adult rat islets. Likewise, mGPDH and mMDH activity was fivefold lower in islet-like cell clusters (ICCs) and sevenfold lower in purified β-cells compared with adult islets in the pig. The low level of enzyme activity was a result of low gene expression of the mitochondrial enzymes in the fetal β-cells. Increasing NADH shuttle activity by transduction of fetal rat islets with mGPDH cDNA enabled the fetal islets to secrete insulin when stimulated with glucose. We concluded that the immaturity of the NADH shuttles contributes to the inability of fetal β-cells to secrete insulin in response to glucose.
Overexpression of Parathyroid Hormone-Related Protein Inhibits Pancreatic β-Cell Death In Vivo and In Vitro
Authors: Cebrian Ana , García-Ocaña Adolfo , Takane Karen K. , Sipula Darinka , Stewart Andrew F. , Vasavada Rupangi C.
Published: March 2007

Pancreatic β-cell survival is critical in the setting of diabetes as well as in islet transplantation. Transgenic mice overexpressing parathyroid hormone-related protein (PTHrP) targeted to β-cells using the rat insulin II promoter (RIP) display hyperinsulinemia, hypoglycemia, and islet hyperplasia, without a concomitant increase in β-cell proliferation rate or enlargement of individual β-cell size. Thus, the mechanism for increased β-cell mass is unknown. In this study, we demonstrated that β-cells of transgenic mice are resistant to the cytotoxic effects of streptozotocin (STZ) in vivo, as documented by a sixfold reduction in the rate of STZ-induced β-cell death in RIP-PTHrP mice relative to their normal siblings. The reduced cell death in transgenic mice is due neither to their increased islet mass nor to a decrease in their sensing of STZ, but rather results from PTHrP-induced resistance to β-cell death. This is also demonstrated in vitro by markedly reduced cell death rates observed in β-cells of transgenic mice compared with normal mice when cultured in the absence of serum and glucose or in the presence of STZ. Finally, we demonstrated that NH2-terminal PTHrP inhibits β-cell death. These findings support the concept that PTHrP overexpression increases islet mass in transgenic mice through inhibition of β-cell death.
Risk Factor Groupings Related to Insulin Resistance and Their Synergistic Effects on Subclinical Atherosclerosis
Authors: Golden Sherita Hill , Folsom Aaron R. , Coresh Josef , Sharrett A. Richey , Szklo Moyses , Brancati Frederick
Published: March 2007

The extent to which groupings of insulin resistance-related cardiovascular risk factors synergize to produce atherosclerosis beyond what is expected from their additive effects is uncertain. The objective of this study was to measure interactions among groupings of the features of the insulin resistance syndrome (IRS) on carotid intimal-medial thickness (IMT). This cross-sectional study used baseline data from the Atherosclerosis Risk in Communities Study on 11,790 adults aged 45–64 years without diagnosed diabetes, treated dyslipidemia, or coronary heart disease. The main outcome was carotid IMT, assessed using B-mode ultrasound. The excess carotid IMT attributable to each IRS grouping was determined using multiple linear regression models. There were 57 possible combinations of six IRS components (hypertension, hyperinsulinemia, obesity, hypertriglyceridemia, low HDL cholesterol, and hyperglycemia). In multivariate analysis, 29 of the 57 groupings were associated with excess carotid IMT. Individuals with all six IRS components had the greatest excess IMT compared with those without this grouping (71 μm; 95% CI 40–102 μm). The groupings most strongly associated with excess carotid IMT included hypertension and hypertriglyceridemia. Interventions aimed at ameliorating the IRS may produce reductions in atherosclerotic risk beyond that predicted by treatment of individual IRS-related risk factors.
Pericytes and the Pathogenesis of Diabetic Retinopathy
Authors: Hammes Hans-Peter , Lin Jihong , Renner Oliver , Shani Moshe , Lundqvist Andrea , Betsholtz Christer , Brownlee Michael , Deutsch Urban
Published: March 2007

Pericytes provide vascular stability and control endothelial proliferation. Pericyte loss, microaneurysms, and acellular capillaries are characteristic for the diabetic retina. Platelet-derived growth factor (PDGF)-B is involved in pericyte recruitment, and brain capillaries of mice with a genetic ablation of PDGF-B show pericyte loss and microaneurysms. We investigated the role of capillary coverage with pericytes in early diabetic retinopathy and the contribution to proliferative retinopathy using mice with a single functional allele of PDGF-B (PDGF-B+/− mice). As assessed by quantitative morphometry of retinal digest preparations, pericyte numbers in nondiabetic PDGF-B+/− mice were reduced by 30% compared with wild-type mice, together with a small but significant increase in acellular capillaries. Pericyte numbers were reduced by 40% in diabetic wild-type mice compared with nondiabetic wild-type controls. Pericyte numbers were decreased by 50% in diabetic PDGF-B+/− mice compared with nondiabetic wild-type littermates, and the incidence of acellular capillaries was increased 3.5-fold when compared with nondiabetic PDGF-B+/− mice. To investigate the effect of pericyte loss in the context of ongoing angiogenesis, we subjected mice to hypoxia-induced proliferative retinopathy. As a result, PDGF-B+/− mice developed twice as many new blood vessels as their wild-type littermates. We conclude that retinal capillary coverage with pericytes is crucial for the survival of endothelial cells, particularly under stress conditions such as diabetes. At high vascular endothelial growth factor levels, such as those in the retinopathy of prematurity model, pericyte deficiency leads to reduced inhibition of endothelial proliferation in vivo.
Profiling Gene Transcription In Vivo Reveals Adipose Tissue as an Immediate Target of Tumor Necrosis Factor-α
Authors: Ruan Hong , Miles Philip D. G. , Ladd Christine M. , Ross Kenneth , Golub Todd R. , Olefsky Jerrold M. , Lodish Harvey F.
Published: March 2007

Despite extensive studies implicating tumor necrosis factor (TNF)-α as a contributing cause of insulin resistance, the mechanism(s) by which TNF-α alters energy metabolism in vivo and the tissue specificity of TNF-α action are unclear. Here, we investigated the effects of TNF-α infusion on gene expression and energy metabolism in adult rats. A 1-day TNF-α treatment decreased overall insulin sensitivity and caused a 70% increase (P = 0.005) in plasma levels of free fatty acids (FFAs) and a 46% decrease (P = 0.01) in ACRP30. A 4-day TNF-α infusion caused insulin resistance and significant elevation of plasma levels of FFAs and triglycerides and reduction of ACRP30. Plasma glucose concentration was not altered following TNF-α infusion for up to 4 days. As revealed by oligonucleotide microarrays, TNF-α evoked major and rapid changes in adipocyte gene expression, favoring FFA release and cytokine production, and fewer changes in liver gene expression, but favoring FFA and cholesterol synthesis and VLDL production. There was only a moderate repressive effect on skeletal muscle gene expression. We demonstrate that TNF-α antagonizes the actions of insulin, at least in part, through regulation of adipocyte gene expression including reduction in ACRP30 mRNA and induction of lipolysis resulting in increased plasma FFAs. TNF-α later alters systemic energy homeostasis that closely resembles the insulin resistance phenotype. Our data suggest that blockade of TNF-α action in adipose tissue may prevent TNF-α-induced insulin resistance in vivo.
Reduction of the Accumulation of Advanced Glycation End Products by ACE Inhibition in Experimental Diabetic Nephropathy
Authors: Forbes Josephine M. , Cooper Mark E. , Thallas Vicki , Burns Wendy C. , Thomas Merlin C. , Brammar Gail C. , Lee Fiona , Grant Sharon L. , Burrell Louise M. , Jerums George , Osicka Tanya M.
Published: March 2007

The effect of ACE inhibition on the formation of advanced glycation end products (AGEs) and oxidative stress was explored. Streptozocin-induced diabetic animals were randomized to no treatment, the ACE inhibitor ramipril (3 mg/l), or the AGE formation inhibitor aminoguanidine (1 g/l) and followed for 12 weeks. Control groups were followed concurrently. Renal AGE accumulation, as determined by immunohistochemistry and both serum and renal fluorescence, were increased in diabetic animals. This was attenuated by both ramipril and aminoguanidine to a similar degree. Nitrotyrosine, a marker of protein oxidation, also followed a similar pattern. The receptor for AGEs, gene expression of the membrane-bound NADPH oxidase subunit gp91phox, and nuclear transcription factor-κB were all increased by diabetes but remained unaffected by either treatment regimen. Two other AGE receptors, AGE R2 and AGE R3, remained unchanged for the duration of the study. The present study has identified a relationship between the renin-angiotensin system and the accumulation of AGEs in experimental diabetic nephropathy that may be linked through oxidative stress
Miniglucagon (Glucagon 19-29)
Authors: Dalle Stéphane , Fontés Ghislaine , Lajoix Anne-Dominique , LeBrigand Laurence , Gross René , Ribes Gérard , Dufour Michel , Barry Léo , LeNguyen Dung , Bataille Dominique
Published: March 2007

Miniglucagon, the COOH-terminal (19-29) fragment processed from glucagon, is a potent and efficient inhibitor of insulin secretion from the MIN 6 β-cell line. Using the rat isolated-perfused pancreas, we investigated the inhibitory effect of miniglucagon on insulin secretion and evaluated the existence of an inhibitory tone exerted by this peptide inside the islet. Miniglucagon dose-dependently inhibited insulin secretion stimulated by 8.3 mol/l glucose, with no change in the perfusion flow rate. A concentration of 1 nmol/l miniglucagon had a significant inhibitory effect on a 1 nmol/l glucagon-like peptide 1 (7-36) amide-potentiated insulin secretion. A decrease in extracellular glucose concentration simultaneously stimulated glucagon and miniglucagon secretion from pancreatic α-cells. Using confocal and electron microscopy analysis, we observed that miniglucagon is colocalized with glucagon in mature secretory granules of α-cells. Perfusion of an anti-miniglucagon antiserum directed against the biologically active moiety of the peptide resulted in a more pronounced effect of a glucose challenge on insulin secretion, indicating that miniglucagon exerts a local inhibitory tone on β-cells. We concluded that miniglucagon is a novel local regulator of the pancreatic islet physiology and that any abnormal inhibitory tone exerted by this peptide on the β-cell would result in an impaired insulin secretion, as observed in type 2 diabetes.
Synaptic Adaptation to Repeated Hypoglycemia Depends on the Utilization of Monocarboxylates in Guinea Pig Hippocampal Slices
Authors: Sakurai Takashi , Yang Bo , Takata Toshihiro , Yokono Koichi
Published: March 2007

This report provides in vitro evidence that synaptic activity becomes resistant to repeated hypoglycemia, i.e., hypoglycemic synaptic adaptation occurs. Synaptic function was estimated by the amplitude of the postsynaptic population spike (PS) recorded in the granule cell layer of guinea pig hippocampal slices. ATP, phosphocreatine (PCr), glycogen, and glucose concentrations were measured to investigate energy metabolism homeostasis. Glucose deprivation produced a complete elimination of the PS amplitude, with a 50% inhibition by 10.6 min, and a ∼15% reduction in ATP and PCr concentrations. Low-glucose (0.5–1 mmol/l) medium gradually depressed the PS. After recovery from glucose depletion, repeated glucose deprivation produced a slowly developing depression of PS, with a 50% inhibition by 36.5 min. However, ATP and PCr concentrations were maintained. Incubation in secondary low-glucose medium maintained PS amplitude. Hippocampal glycogen and glucose concentrations promptly decreased during repeated glucose deprivation, indicating that glycogenolysis does not fuel synaptic adaptation to repeated hypoglycemia. Synaptic function during repeated glucose depletion was reversibly depressed by addition of α-cyano-4-hydroxycinnamic acid or 3-isobutyl-1-methylxanthine, inhibitors of the monocarboxylate transporter. Replacement of extracellular glucose with Na-lactate or Na-pyruvate sustained synaptic transmission after transient glucose depletion. These results indicate that synaptic utilization of monocarboxylates sustains hypoglycemic synaptic adaptation.
The Concept of Selective Leptin Resistance
Authors: Correia Marcelo L.G. , Haynes William G. , Rahmouni Kamal , Morgan Donald A. , Sivitz William I. , Mark Allyn L.
Published: March 2007

Leptin, a hormone secreted by adipose tissue, acts to inhibit appetite and promote metabolism, thereby reducing body weight. Leptin also increases sympathetic activity and arterial pressure. Several murine models of obesity, including agouti obese mice, exhibit resistance to the anorexic and weight-reducing effects of leptin. Hypertension in agouti mice has been attributed to hyperleptinemia. These observations pose a seeming paradox. If these mice are leptin-resistant, then how can leptin contribute to hypertension? We tested the novel hypothesis that these mice have selective leptin resistance, with preservation of the sympathoexcitatory action despite resistance to the weight-reducing actions. Leptin-induced decreases in food intake and body weight were less in agouti obese mice than in lean littermates. In contrast, leptin-induced increases in sympathetic nerve activity did not differ in obese and lean mice. These findings support the concept of selective leptin resistance, with resistance to the metabolic actions of leptin but preservation of the sympathoexcitatory actions. This finding may have potential implications for human obesity, which is associated with elevated plasma leptin and is thought to be a leptin-resistant state. If leptin resistance is selective in obese humans, then leptin could contribute to sympathetic overactivity and its adverse consequences in human obesity.
Insulin Signaling After Exercise in Insulin Receptor Substrate-2-Deficient Mice
Authors: Howlett Kirsten F. , Sakamoto Kei , Hirshman Michael F. , Aschenbach William G. , Dow Matthew , White Morris F. , Goodyear Laurie J.
Published: March 2007

The period immediately after exercise is characterized by enhanced insulin action in skeletal muscle, and on the molecular level, by a marked increase in insulin-stimulated, phosphotyrosine-associated phosphatidylinositol (PI) 3-kinase activity. Because the increase in PI 3-kinase activity cannot be explained by increased insulin receptor substrate (IRS)-1 signaling, the present study examined whether this effect is mediated by enhanced IRS-2 signaling. In wild-type (WT) mice, insulin increased IRS-2 tyrosine phosphorylation (∼2.5-fold) and IRS-2−associated PI 3-kinase activity (∼3-fold). Treadmill exercise, per se, had no effect on IRS-2 signaling, but in the period immediately after exercise, there was a further increase in insulin-stimulated IRS-2 tyrosine phosphorylation (∼3.5-fold) and IRS-2−associated PI 3-kinase activity (∼5-fold). In IRS-2−deficient (IRS-2−/−) mice, the increase in insulin-stimulated, phosphotyrosine-associated PI 3-kinase activity was attenuated as compared with WT mice. However, in IRS-2−/− mice, the insulin-stimulated, phosphotyrosine-associated PI 3-kinase response after exercise was slightly higher than the insulin-stimulated response alone. In conclusion, IRS-2 tyrosine phosphorylation and associated PI 3-kinase activity are markedly enhanced by insulin in the immediate period after exercise. IRS-2 signaling can partially account for the increase in insulin-stimulated phosphotyrosine-associated PI 3-kinase activity after exercise.
Clinical Characterization of Insulin Secretion as the Basis for Genetic Analyses
Authors: Stumvoll Michael , Fritsche Andreas , Häring Hans-Ulrich
Published: March 2007

A strong genetic component of the β-cell defect of type 2 diabetes is undisputed. We recently developed a modification of the classic hyperglycemic clamp to assess β-cell function in response to various stimuli (10 mmol/l glucose, additional glucagon-like peptide [GLP]-1, and arginine). Subjects at risk for developing type 2 diabetes (impaired glucose-tolerant individuals, women with gestational diabetes, and individuals with a family history of type 2 diabetes) clearly showed a significantly decreased mean secretory response to all secretagogues compared with controls. We also showed that normal glucose-tolerant carriers of the Gly972Arg polymorphism in the insulin receptor substrate 1 have significantly reduced insulin secretion in response to glucose and arginine but not to GLP-1. More remarkably, however, the relative impairment of the different secretory phases varied greatly in the same individual, indicating a substantial heterogeneity of β-cell dysfunction. Specific prominence of this heterogeneity may reflect a specific cellular defect of the β-cell. In subjects sharing this pattern of heterogeneity, any underlying genetic variant may be enriched and thus more likely not only to be identified but also to be related to a pathophysiological mechanism. In conclusion, we believe that careful clinical characterization of β-cell function (and dysfunction) is one way of identifying and understanding the genetic factors leading to the insulin secretory failure of type 2 diabetes.
Role of Oscillations in Membrane Potential, Cytoplasmic Ca2+, and Metabolism for Plasma Insulin Oscillations
Authors: Bergsten Peter
Published: March 2007

A model for the relationship between ionic and metabolic oscillations and plasma insulin oscillations is presented. It is argued that the pancreatic β-cell in vivo displays two intrinsic frequencies that are important for the regulation of plasma insulin oscillations. The rapid oscillatory activity (2–7 oscillations [osc] per minute), which is evident in both ionic and metabolic events, causes the required elevation in cytoplasmic Ca2+ concentration ([Ca2+]i) for the exocytosis of insulin granules. This activity is important for regulation of the amplitude of plasma insulin oscillations. The frequency of the rapid oscillatory ionic activities is regulated by glucose and allows the β-cell to respond in an analogous way, with gradual changes in [Ca2+]i and insulin release in response to the alterations in glucose concentration. The slower oscillatory activity (0.2–0.4 osc/min), which is evident in the metabolism of the β-cell, has a frequency corresponding to the frequency observed in plasma insulin oscillations. The frequency is not affected by changes in the glucose concentration. This activity is suggested to generate energy in a pulsatile fashion, which sets the frequency of the plasma insulin oscillations. It is proposed that the slow oscillations in [Ca2+]i observed in vitro are a manifestation of the metabolic oscillations and do not represent an in vivo phenomenon.
Molecular Determinants of Regulated Exocytosis
Authors: Gerber Stefan H. , Südhof Thomas C.
Published: March 2007

Regulated exocytosis forms the basis for many intercellular signaling processes, for example, in hormone secretion or neurotransmitter release. During regulated exocytosis, the membrane of a secretory vesicle fuses with the plasma membrane in a tightly controlled reaction that is most often triggered by calcium. Recent advances have allowed major insights into the molecular mechanisms that mediate regulated exocytosis. In the present review, we will briefly discuss two key features of regulated exocytosis that have been particularly well studied recently. First, we will examine the current understanding of the membrane fusion reaction that underlies regulated exocytosis and that is effected by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) and munc18-like proteins similar to other membrane fusion reactions. Second, we will describe the role of the major candidates for the calcium sensors that trigger exocytosis, a protein family called synaptotagmins. Although our understanding of regulated exocytosis is as yet incomplete, the results from the studies of SNAREs, munc18s, and synaptotagmins have provided a molecular anchor for a more complete future description.
Malonyl-CoA Signaling, Lipid Partitioning, and Glucolipotoxicity
Authors: Prentki Marc , Joly Erik , El-Assaad Wissal , Roduit Raphaël
Published: March 2007

β-Cells possess inherent mechanisms to adapt to overnutrition and the prevailing concentrations of glucose, fatty acids, and other fuels to maintain glucose homeostasis. However, this is balanced by potentially harmful actions of the same nutrients. Both glucose and fatty acids may cause good/adaptive or evil/toxic actions on the β-cell, depending on their concentrations and the time during which they are elevated. Chronic high glucose dramatically influences β-cell lipid metabolism via substrate availability, changes in the activity and expression of enzymes of glucose and lipid metabolism, and modifications in the expression level of key transcription factors. We discuss here the emerging view that β-cell “glucotoxicity” is in part indirectly caused by “lipotoxicity,” and that β-cell abnormalities will become particularly apparent when both glucose and circulating fatty acids are high. We support the concept that elevated glucose and fatty acids synergize in causing toxicity in islets and other organs, a process that may be instrumental in the pleiotropic defects associated with the metabolic syndrome and type 1 and type 2 diabetes. The mechanisms by which hyperglycemia and hyperlipidemia alter insulin secretion are discussed and a model of β-cell “glucolipotoxicity” that implicates alterations in β-cell malonyl-CoA concentrations; peroxisome proliferator-activated receptor-α and -γ and sterol regulatory element binding protein-1c expression; and lipid partitioning is proposed.
A Subset of 50 Secretory Granules in Close Contact With l-Type Ca2+ Channels Accounts for First-Phase Insulin Secretion in Mouse β-Cells
Authors: Barg Sebastian , Eliasson Lena , Renström Erik , Rorsman Patrik
Published: March 2007

Capacitance measurements were applied to mouse pancreatic β-cells to elucidate the cellular mechanisms underlying biphasic insulin secretion. We report here that only <50 of the β-cell’s >10,000 granules are immediately available for release. The releasable granules tightly associate with the voltage-gated α1C Ca2+ channels, and it is proposed that the release of these granules accounts for first-phase insulin secretion. Subsequent replenishment of the releasable pool by priming of previously nonreleasable granules is required for second-phase insulin secretion. The latter reaction depends on intragranular acidification due to the concerted action of granular bafilomycin-sensitive v-type H+-ATPase and 4,4-diisothiocyanostilbene-2,2-disulfonate–blockable ClC-3 Cl− channels. Lowering the cytoplasmic ATP/ADP ratio prevents granule acidification, granule priming, and refilling of the releasable pool. The latter finding provides an explanation to the transient nature of insulin secretion elicited by, for example, high extracellular K+ in the absence of metabolizable fuels.
Implication of Glutamate in the Kinetics of Insulin Secretion in Rat and Mouse Perfused Pancreas
Authors: Maechler Pierre , Gjinovci Asllan , Wollheim Claes B.
Published: March 2007

It is intriguing that the kinetics of glucose-stimulated insulin secretion from the in situ perfused pancreas differ between the rat and the mouse. Here we confirm that insulin release in the rat is clearly biphasic, whereas in the mouse glucose essentially elicits a transient monophasic insulin release. Glucose-derived glutamate has been suggested to participate in the full development of the secretory response. The present report shows that the expression of glutamate dehydrogenase is lower in mouse than in rat or human islets, paralleling the insulin secretion profile. Addition of glutamic acid dimethyl ester mainly enhances insulin release at an intermediate glucose concentration in the rat pancreas. In the mouse preparation, glutamic acid dimethyl ester induces a sustained secretory response, both at 7.0 and 16.7 mmol/l glucose. These results are compatible with a role for glucose-derived glutamate principally in the sustained phase of nutrient-stimulated insulin secretion.
Unregulated Elevation of Glutamate Dehydrogenase Activity Induces Glutamine-Stimulated Insulin Secretion
Authors: Tanizawa Yukio , Nakai Kazuaki , Sasaki Terumasa , Anno Takatoshi , Ohta Yasuharu , Inoue Hiroshi , Matsuo Kiyosato , Koga Mayumi , Furukawa Susumu , Oka Yoshitomo
Published: March 2007

Glutamate dehydrogenase (GDH) is important in normal glucose homeostasis. Mutations of GDH result in hyperinsulinism/hyperammonemia syndrome. Using PCR/single-strand conformation polymorphism analysis of the gene encoding GDH in 12 Japanese patients with persistent hyperinsulinemic hypoglycemia of infancy (PHHI), we found a mutation (Y266C) in one PHHI patient. This mutation was not found in any of the control or type 2 diabetic subjects. The activity of the mutant GDH (GDH266C), expressed in COS-7 cells, was constitutively elevated, and allosteric regulations by ADP and GTP were severely impaired. The effect of the unregulated increase in GDH activity on insulin secretion was examined by overexpressing GDH266C in an insulinoma cell line, MIN6. Although glutamine alone did not stimulate insulin secretion from control MIN6-lacZ, it remarkably stimulated insulin secretion from MIN6-GDH266C. This finding suggests that constitutively activated GDH enhances oxidation of glutamate, which is intracellularly converted from glutamine to α-ketoglutarate, a tricarboxylic acid cycle substrate, which thereby stimulates insulin secretion. Interestingly, insulin secretion is also exaggerated significantly at low glucose concentrations (2 and 5 mmol/l) but not at higher glucose concentrations (8–25 mmol/l). Our results directly illustrate the importance of GDH in the regulation of insulin secretion from pancreatic β-cells.
Increased Insulin Sensitivity in IGF-I Receptor–Deficient Brown Adipocytes
Authors: Mur Cecilia , Valverde Angela M. , Kahn C. Ronald , Benito Manuel
Published: March 2007

Immortalized brown adipocyte cell lines have been generated from fetuses of mice deficient in the insulin-like growth factor I receptor gene (IGF-IR−/−), as well as from fetuses of wild-type mice (IGF-IR+/+). These cell lines maintained the expression of adipogenic- and thermogenic-differentiation markers and show a multilocular fat droplets phenotype. IGF-IR−/− brown adipocytes lacked IGF-IR protein expression; insulin receptor (IR) expression remained unchanged as compared with wild-type cells. Insulin-induced tyrosine autophosphorylation of the IR β-chain was augmented in IGF-IR–deficient cells. Upon insulin stimulation, tyrosine phosphorylation of (insulin receptor substrate-1) IRS-1 was much higher in IGF-IR−/− brown adipocytes, although IRS-1 protein content was reduced. In contrast, tyrosine phosphorylation of IRS-2 decreased in IGF-IR–deficient cells; its protein content was unchanged as compared with wild-type cells. Downstream, the association IRS-1/growth factor receptor binding protein-2 (Grb-2) was augmented in the IGF-IR−/− brown adipocyte cell line. However, SHC expression and SHC tyrosine phosphorylation and its association with Grb-2 were unaltered in response to insulin in IGF-IR–deficient brown adipocytes. These cells also showed an enhanced activation of mitogen-activated protein kinase (MAPK) kinase (MEK1/2) and p42/p44 mitogen-activated protein kinase (MAPK) upon insulin stimulation. In addition, the lack of IGF-IR in brown adipocytes resulted in a higher mitogenic response (DNA synthesis, cell number, and proliferating cell nuclear antigen expression) to insulin than wild-type cells. Finally, cells lacking IGF-IR showed a much lower association between IR or IRS-1 and phosphotyrosine phosphatase 1B (PTP1B) and also a decreased PTP1B activity upon insulin stimulation. However, PTP1B/Grb-2 association remained unchanged in both cell types, regardless of insulin stimulation. Data presented here provide strong evidence that IGF-IR–deficient brown adipocytes show an increased insulin sensitivity via IRS-1/Grb-2/MAPK, resulting in an increased mitogenesis in response to insulin.