bluuebunny/crossref_metadata_2025 huggingface dataset:
Adipocyte-Specific Overexpression of FOXC2 Prevents Diet-Induced Increases in Intramuscular Fatty Acyl CoA and Insulin Resistance
Authors: Kim Jason K. , Kim Hyo-Jeong , Park So-Young , Cederberg Anna , Westergren Rickard , Nilsson Daniel , Higashimori Takamasa , Cho You-Ree , Liu Zhen-Xiang , Dong Jianying , Cline Gary W. , Enerback Sven , Shulman Gerald I.
Published: March 2007

Insulin resistance plays a major role in the development of type 2 diabetes and may be causally associated with increased intracellular fat content. Transgenic mice with adipocyte-specific overexpression of FOXC2 (forkhead transcription factor) have been generated and shown to be protected against diet-induced obesity and glucose intolerance. To understand the underlying mechanism, we examined the effects of chronic high-fat feeding on tissue-specific insulin action and glucose metabolism in the FOXC2 transgenic (Tg) mice. Whole-body fat mass were significantly reduced in the FOXC2 Tg mice fed normal diet or high-fat diet compared with the wild-type mice. Diet-induced insulin resistance in skeletal muscle of the wild-type mice was associated with defects in insulin signaling and significant increases in intramuscular fatty acyl CoA levels. In contrast, FOXC2 Tg mice were completely protected from diet-induced insulin resistance and intramuscular accumulation of fatty acyl CoA. High-fat feeding also blunted insulin-mediated suppression of hepatic glucose production in the wild-type mice, whereas FOXC2 Tg mice were protected from diet-induced hepatic insulin resistance. These findings demonstrate an important role of adipocyte-expressed FOXC2 on whole-body glucose metabolism and further suggest FOXC2 as a novel therapeutic target for the treatment of insulin resistance and type 2 diabetes.
Insulin-Stimulated Phosphorylation of the Akt Substrate AS160 Is Impaired in Skeletal Muscle of Type 2 Diabetic Subjects
Authors: Karlsson Håkan K.R. , Zierath Juleen R. , Kane Susan , Krook Anna , Lienhard Gustav E. , Wallberg-Henriksson Harriet
Published: March 2007

AS160 is a newly described substrate for the protein kinase Akt that links insulin signaling and GLUT4 trafficking. In this study, we determined the expression of and in vivo insulin action on AS160 in human skeletal muscle. In addition, we compared the effect of physiological hyperinsulinemia on AS160 phosphorylation in 10 lean−to−moderately obese type 2 diabetic and 9 healthy subjects. Insulin infusion increased the phosphorylation of several proteins reacting with a phospho-Akt substrate antibody. We focused on AS160, as this Akt substrate has been linked to glucose transport. A 160-kDa phosphorylated protein was identified as AS160 by immunoblot analysis with an AS160-specific antibody. Physiological hyperinsulinemia increased AS160 phosphorylation 2.9-fold in skeletal muscle of control subjects (P < 0.001). Insulin-stimulated AS160 phosphorylation was reduced 39% (P < 0.05) in type 2 diabetic patients. AS160 protein expression was similar in type 2 diabetic and control subjects. Impaired AS160 phosphorylation was related to aberrant Akt signaling; insulin action on Akt Ser473 phosphorylation was not significantly reduced in type 2 diabetic compared with control subjects, whereas Thr308 phosphorylation was impaired 51% (P < 0.05). In conclusion, physiological hyperinsulinemia increases AS160 phosphorylation in human skeletal muscle. Moreover, defects in insulin action on AS160 may impair GLUT4 trafficking in type 2 diabetes.
The Link Between Nutritional Status and Insulin Sensitivity Is Dependent on the Adipocyte-Specific Peroxisome Proliferator–Activated Receptor-γ2 Isoform
Authors: Medina-Gomez Gema , Virtue Sam , Lelliott Christopher , Boiani Romina , Campbell Mark , Christodoulides Constantinos , Perrin Christophe , Jimenez-Linan Mercedes , Blount Margaret , Dixon John , Zahn Dirk , Thresher Rosemary R. , Aparicio Sam , Carlton Mark , Colledge William H. , Kettunen Mikko I. , Seppänen-Laakso Tuulikki , Sethi Jaswinder K. , O’Rahilly Stephen , Brindle Kevin , Cinti Saverio , Orešič Matej , Burcelin Remy , Vidal-Puig Antonio
Published: March 2007

The nuclear receptor peroxisome proliferator–activated receptor-γ (PPARγ) is critically required for adipogenesis. PPARγ exists as two isoforms, γ1 and γ2. PPARγ2 is the more potent adipogenic isoform in vitro and is normally restricted to adipose tissues, where it is regulated more by nutritional state than PPARγ1. To elucidate the relevance of the PPARγ2 in vivo, we generated a mouse model in which the PPARγ2 isoform was specifically disrupted. Despite similar weight, body composition, food intake, energy expenditure, and adipose tissue morphology, male mice lacking the γ2 isoform were more insulin resistant than wild-type animals when fed a regular diet. These results indicate that insulin resistance associated with ablation of PPARγ2 is not the result of lipodystrophy and suggests a specific role for PPARγ2 in maintaining insulin sensitivity independently of its effects on adipogenesis. Furthermore, PPARγ2 knockout mice fed a high-fat diet did not become more insulin resistant than those on a normal diet, despite a marked increase in their mean adipocyte cell size. These findings suggest that PPARγ2 is required for the maintenance of normal insulin sensitivity in mice but also raises the intriguing notion that PPARγ2 may be necessary for the adverse effects of a high-fat diet on carbohydrate metabolism.
β-Cell Function Across the Spectrum of Glucose Tolerance in Obese Youth
Authors: Weiss Ram , Caprio Sonia , Trombetta Maddalena , Taksali Sara E. , Tamborlane William V. , Bonadonna Riccardo
Published: March 2007

The profile of insulin secretion and the role of proinsulin processing across the spectrum of glucose tolerance in obese youth have not been studied. The aims of this study were to define the role of insulin secretion and proinsulin processing in glucose regulation in obese youth. We performed hyperglycemic clamps to assess insulin secretion, applying a model of glucose-stimulated insulin secretion to the glucose and C-peptide concentration data. Thirty obese youth with normal glucose tolerance (NGT), 22 with impaired glucose tolerance (IGT), and 10 with type 2 diabetes were studied. The three groups had comparable anthropometric measures and insulin sensitivity. The glucose sensitivity of first-phase secretion showed a significant stepwise decline from NGT to IGT and from IGT to type 2 diabetes. The glucose sensitivity of second-phase secretion was similar in NGT and IGT subjects yet was significantly lower in subjects with type 2 diabetes. Proinsulin-to-insulin ratios were comparable during first- and second-phase secretion between subjects with NGT and IGT and were significantly increased in type 2 diabetes. Obese youth with IGT have a significant defect in first-phase insulin secretion, while a defect in second-phase secretion and proinsulin processing is specific for type 2 diabetes in this age-group.
C/EBPα Regulates Human Adiponectin Gene Transcription Through an Intronic Enhancer
Authors: Qiao Liping , MacLean Paul S. , Schaack Jerome , Orlicky David J. , Darimont Christian , Pagliassotti Michael , Friedman Jacob E. , Shao Jianhua
Published: March 2007

Adiponectin is an adipose-derived hormone that enhances insulin sensitivity and plays an important role in regulating energy homeostasis. Here, we demonstrate that the DNA encoding the first intron of the human adiponectin gene contains an intronic enhancer that regulates adiponectin gene expression in an adipose tissue–specific manner. Insertion of the DNA encoding the first intron into reporter constructs containing the proximal adiponectin promoter (Pro-Int1-Luc) resulted in a 20-fold increase in activity relative to the promoter alone in 3T3-L1 adipocytes. Coexpression of CCAAT/enhancer-binding protein (C/EBP)α increased luciferase activity of the Pro-Int1-Luc construct ∼75-fold but had no effect on the constructs containing the proximal adiponectin promoter alone. At least eight potential C/EBPα response elements are located between +3000 to +10000 nucleotides within the DNA encoding the first intron, including a 34-bp core sequence for the intronic enhancer that contains three tandem C/EBPα response elements. However, the intronic enhancer is not conserved between human and mouse. Overexpression or siRNA-mediated knockdown of endogenous C/EBPα significantly increased or decreased, respectively, adiponectin mRNA levels in differentiated human Chub-S7 adipocytes, while neither C/EBPβ nor C/EBPδ significantly affected adiponectin expression in mature adipocytes. Thus, C/EBPα is a key transcription factor for full activation of human adiponectin gene transcription in mature adipocytes through interaction with response elements in the intronic enhancer.
Inhibition of Superoxide Generation and Associated Nitrosative Damage Is Involved in Metallothionein Prevention of Diabetic Cardiomyopathy
Authors: Cai Lu , Wang Jianxun , Li Yan , Sun Xuihua , Wang Lipeng , Zhou Zhanxiang , Kang Y. James
Published: March 2007

The mechanisms of metallothionein prevention of diabetic cardiomyopathy are largely unknown. The present study was performed to test whether inhibition of nitrosative damage is involved in metallothionein prevention of diabetic cardiomyopathy. Cardiac-specific metallothionein-overexpressing transgenic (MT-TG) mice and wild-type littermate controls were treated with streptozotocin (STZ) by a single intraperitoneal injection, and both developed diabetes. However, the development of diabetic cardiomyopathy, revealed by histopathological and ultrastructural examination, serum creatine phosphokinase, and cardiac hemodynamic analysis, was significantly observed only in the wild-type, but not in MT-TG, diabetic mice 2 weeks and 6 months after STZ treatment. Formations of superoxide and 3-nitrotyrosine (3-NT), a marker for peroxynitrite-induced protein damage, were detected only in the heart of wild-type diabetic mice. Furthermore, primary cultures of cardiomyocytes from wild-type and MT-TG mice were exposed to lipopolysaccharide/tumor necrosis factor-α for generating intracellular peroxynitrite. Increases in 3-NT formation and cytotoxicity were observed in wild-type, but not in MT-TG, cardiomyocytes. Either urate, a peroxynitrite-specific scavenger, or Mn(111) tetrakis 1-methyl 4-pyridyl porphyrin pentachloride (MnTMPyP), a superoxide dismutase mimic, significantly inhibited the formation of 3-NT along with a significant prevention of cytotoxicity. These results thus suggest that metallothionein prevention of diabetic cardiomyopathy is mediated, at least in part, by suppression of superoxide generation and associated nitrosative damage.
Pharmacogenetic Analysis of Rosiglitazone-Induced Hepatosteatosis in New Mouse Models of Type 2 Diabetes
Authors: Pan Huei-Ju , Reifsnyder Peter , Vance Dennis E. , Xiao Qiang , Leiter Edward H.
Published: March 2007

Although thiazolidinediones suppress hyperglycemia in diabetic (NON × NZO)F1 males, these mice exhibit unusual sensitivity to drug-induced exacerbation of an underlying hepatosteatosis only rarely experienced in human patients. To establish the pharmacogenetic basis for this sensitivity, a panel of recombinant congenic strains (RCSs) with varying degrees of obesity and diabetes was generated by fixing selected NZO HlLt alleles on the diabetes- and hepatosteatosis-resistant NON/Lt background. Four new strains in this panel were exposed to chronic rosiglitazone treatment. Only one, NONcNZO8 (designated RCS8), exhibited an F1-like hepatosteatotic response. In both the F1 and RCS8 males, this adverse effect correlated with rosiglitazone suppression of already impaired hepatic phosphatidylcholine biosynthetic enzymes in both arms of the biosynthetic pathway, the phosphatidylethanolamine methyl- transferase pathway, and the CDP-choline pathway, including choline kinase and CTP-cholinephosphate cytidylyltransferase. This adverse response was not reproduced by CL316,243, a β3-adrenergic receptor agonist with potent antihyperlipemic effects. Genome comparison showed that RCS8 differed from the other strains in carrying NZO-derived genome on virtually all of chromosome 16 and in smaller segments on chromosomes 6, 14, and 17. Thus, these RCSs present a panel of new mouse models exhibiting differential levels of obesity and diabetes as well as different drug responses. This panel can be used to screen for treatments for type 2 diabetes and its complications.
Evidence that the Mitochondrial Leucyl tRNA Synthetase (LARS2) Gene Represents a Novel Type 2 Diabetes Susceptibility Gene
Authors: ‘t Hart Leen M. , Hansen Torben , Rietveld Ingrid , Dekker Jacqueline M. , Nijpels Giel , Janssen George M.C. , Arp Pascal A. , Uitterlinden André G. , Jørgensen Torben , Borch-Johnsen Knut , Pols Huibert A.P. , Pedersen Oluf , van Duijn Cornelia M. , Heine Robert J. , Maassen J. Antonie
Published: March 2007

Previously, we have shown that a mutation in the mitochondrial DNA–encoded tRNALeu(UUR) gene is associated with type 2 diabetes. One of the consequences of this mutation is a reduced aminoacylation of tRNALeu(UUR). In this study, we have examined whether variants in the leucyl tRNA synthetase gene (LARS2), involved in aminoacylation of tRNALeu(UUR), associate with type 2 diabetes. Direct sequencing of LARS2 cDNA from 25 type 2 diabetic subjects revealed eight single nucleotide polymorphisms. Two of the variants were examined in 7,836 subjects from four independent populations in the Netherlands and Denmark. A −109 g/a variant was not associated with type 2 diabetes. Allele frequencies for the other variant, H324Q, were 3.5% in type 2 diabetic and 2.7% in control subjects, respectively. The common odds ratio across all four studies was 1.40 (95% CI 1.12–1.76), P = 0.004. There were no significant differences in clinical variables between carriers and noncarriers. In this study, we provide evidence that the LARS2 gene may represent a novel type 2 diabetes susceptibility gene. The mechanism by which the H324Q variant enhances type 2 diabetes risk needs to be further established. This is the first report of association between an aminoacyl tRNA synthetase gene and disease. Our results further highlight the important role of mitochondria in glucose homeostasis.
The Influence of the Major Histocompatibility Complex on Development of Autoimmune Diabetes in RIP-B7.1 Mice
Authors: Wong F. Susan , Du Wei , Thomas Ian J. , Wen Li
Published: March 2007

The most important genetic susceptibility factor for type 1 diabetes is encoded in the major histocompatibility complex (MHC). The nonobese diabetic (NOD) mouse, which develops spontaneous diabetes, expresses H-2g7 comprising the MHC class I molecules Kd and Db and the MHC class II molecule I-Ag7. However, neither B6.H-2g7 mice, in which H-2g7 is expressed on the C57BL/6 genetic background, nor the nonobese resistant (NOR) mouse, in which H-2g7 is expressed on a genetic background that is 88% similar to NOD mice, develop diabetes. Immune tolerance can be broken in these diabetes-resistant mice expressing H-2g7 if the costimulatory molecule B7.1 is present on the islet β cells. This does not occur if only single MHC class I components of the H-2g7 haplotype are present, such as Kd in BALB/c mice or Db in C57BL/6 mice, both of which develop only a low level of diabetes when B7.1 is expressed. The presence of I-Ag7 leads to the development of an autoimmune T-cell repertoire, and local costimulation of CD8 T-cells precipitates aggressive diabetes. This implies that a major role of the MHC class II molecules in diabetes is the development of an autoreactive T-cell repertoire.
Immune Cell Infiltration, Cytokine Expression, and β-Cell Apoptosis During the Development of Type 1 Diabetes in the Spontaneously Diabetic LEW.1AR1/Ztm-iddmRat
Authors: Jörns Anne , Günther Armin , Hedrich Hans-Jürgen , Wedekind Dirk , Tiedge Markus , Lenzen Sigurd
Published: March 2007

The IDDM (LEW.1AR1/Ztm-iddm) rat is a type 1 diabetic animal model characterized by a rapid apoptotic pancreatic β-cell destruction. Here we have analyzed the time course of islet infiltration, changes in the cytokine expression pattern, and β-cell apoptosis in the transition from the pre-diabetic to the diabetic state. Transition from normoglycemia to hyperglycemia occurred when β-cell loss exceeded 60–70%. At the early stages of islet infiltration, macrophages were the predominant immune cell type in the peripherally infiltrated islets. Progression of β-cell loss was closely linked to a severe infiltration of the whole islet by CD8+ T-cells. With progressive islet infiltration, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) were expressed in immune cells but not in β-cells. This proinflammatory cytokine expression pattern coincided with the expression of inducible nitric oxide synthase (iNOS) and procaspase 3 in β-cells and a peak apoptosis rate of 6.7%. Islet infiltration declined after manifestation of clinical diabetes, yielding end-stage islets devoid of β-cells and immune cells without any sign of cytokine expression. The observed coincidence of IL-1β and TNF-α expression in the immune cells and the induction of iNOS and procaspase 3 mRNA expression in the β-cells depicts a sequence of pathological changes leading to apoptotic β-cell death in the IDDM rat. This chain of events provides a mechanistic explanation for the development of the diabetic syndrome in this animal model of human type 1 diabetes.
Saturated and cis/trans Unsaturated Acyl CoA Esters Differentially Regulate Wild-Type and Polymorphic β-Cell ATP-Sensitive K+ Channels
Authors: Riedel Michael J. , Light Peter E.
Published: March 2007

Metabolic regulation of pancreatic β-cell ATP-sensitive K+ channel (KATP channel) function plays a key role in the process of glucose-stimulated insulin secretion (GSIS). Modulation of KATP channel activity by long-chain acyl CoAs represents an important endogenous regulatory mechanism. Elevated acyl CoA levels have been reported in obese and type 2 diabetic individuals and may contribute to reduced β-cell excitability and impaired GSIS. Recent studies suggest that the composition of dietary fat may influence the effects of high-fat feeding on impaired GSIS. Therefore, we examined the effects of side-chain length and the degree of saturation of various acyl CoAs on KATP channel activity. Macroscopic currents from either wild-type or polymorphic (Kir6.2[E23K/I337V]) recombinant β-cell KATP channels were measured in inside-out patches by exposing the inner surface of the membrane to acyl CoAs at physiological nanomolar concentrations. Acyl CoAs increased both wild-type and polymorphic KATP channel activity with the following rank order of efficacy: C18:0, C18:1trans ∼ C18:1cis, C20:4 = C16:0, C16:1, and C18:2. A significant correlation exists between activation and acyl CoA hydrophobicity, suggesting that both side-chain length and degree of saturation are critical determinants of KATP channel activation. Our observations reveal a plausible mechanism behind the disparate effects of acyl CoA saturation on KATP channel activation and suggest that dietary fat composition may determine the severity of impaired GSIS via differential activation of β-cell KATP channels.
Impaired Arachidonic Acid–Mediated Activation of Large-Conductance Ca2+-Activated K+ Channels in Coronary Arterial Smooth Muscle Cells in Zucker Diabetic Fatty Rats
Authors: Lu Tong , Wang Xiao-Li , He Tongrong , Zhou Wei , Kaduce Terry L. , Katusic Zvonimir S. , Spector Arthur A. , Lee Hon-Chi
Published: March 2007

We studied the arachidonic acid (AA)-mediated modulation of large-conductance Ca2+-activated K+ (BK) channels in coronary arterial smooth myocytes from lean control and Zucker Diabetic Fatty (ZDF) rats. A total of 1 μmol/l AA enhanced BK current by 274% in lean and by 98% in ZDF rats. After incubation with 10 μmol/l indomethacin, 1 μmol/l AA increased BK currents by 80% in lean and by 70% in ZDF rats. Vasoreactivity studies showed that the dilation of small coronary arteries produced by 1 μmol/l AA was reduced by 44% in ZDF rats. [3H]6-keto-prostagladin F1α ([3H]6-keto-PGF1α,), the stable metabolite of prostacyclin (PGI2), was the major [3H]AA metabolite produced by coronary arteries of lean vessels, but ZDF vessels produced only 15% as much [3H]6-keto-PGF1α. BK channel activation and vasorelaxation by iloprost were similar in lean and ZDF rats. Immunoblots showed a 73% reduction in PGI2 synthase (PGIS) expression in ZDF vessels compared with lean vessels, and there was no change in cyclooxygenase (COX) and BK channel expressions. Real-time PCR studies showed that mRNA levels of PGIS, COX-1, and COX-2 were similar between lean and ZDF vessels. We conclude that PGI2 is the major AA metabolite in lean coronaries, and AA-mediated BK channel activation is impaired in ZDF coronaries due to reduced PGIS activity.
Advanced Glycation End Product Precursors Impair ABCA1-Dependent Cholesterol Removal From Cells
Authors: Passarelli Marisa , Tang Chongren , McDonald Thomas O. , O’Brien Kevin D. , Gerrity Ross G. , Heinecke Jay W. , Oram John F.
Published: March 2007

Abnormal HDL metabolism may contribute to the increased atherosclerosis associated with diabetes. The ATP-binding cassette transporter A1 (ABCA1) is an atheroprotective cell protein that mediates cholesterol transport from cells to apolipoprotein (apo) A-I, the major protein in HDL. Because formation of advanced glycation end products (AGEs) is associated with diabetic vascular complications, we examined the effects of carbonyls implicated in AGE formation on the ABCA1 pathway in cultured fibroblasts and macrophages. Treating cells with glycolaldehyde (GA) and glyoxal (GO) strongly inhibited ABCA1-dependent transport of cholesterol from cells to apoA-I, while methylglyoxal had little effect. This occurred under conditions where other lipoprotein receptors or lipid metabolic pathways were little affected, indicating that ABCA1 was uniquely sensitive to these carbonyls. GA and GO destabilized ABCA1 and nearly abolished its binding of apoA-I, indicating that these carbonyls directly modified ABCA1. Immunohistology of coronary arteries from hyperlipidemic swine revealed that inducing diabetes with streptozotocin increased atherosclerotic lesion area and dramatically reduced the fraction of macrophages that expressed detectable ABCA1. These results raise the possibility that reactive carbonyl-mediated damage to ABCA1 promotes accumulation of cholesterol in arterial macrophages and thus contribute to the increased cardiovascular disease associated with diabetes, insulin resistance, and other inflammatory conditions.
Erythromycin Antagonizes the Deceleration of Gastric Emptying by Glucagon-Like Peptide 1 and Unmasks Its Insulinotropic Effect in Healthy Subjects
Authors: Meier Juris J. , Kemmeries Guido , Holst Jens J. , Nauck Michael A.
Published: March 2007

Glucagon-like peptide 1 (GLP-1) has been proposed to act as an incretin hormone due to its ability to enhance glucose-stimulated insulin secretion. Because GLP-1 also decelerates gastric emptying, it physiologically reduces rather than augments postprandial insulin secretory responses. Therefore, we aimed to antagonize the deceleration of gastric emptying by GLP-1 to study its effects on insulin secretion after a meal. Nine healthy male volunteers (age 25 ± 4 years, BMI 25.0 ± 4.9 kg/m2) were studied with an infusion of GLP-1 (0.8 pmol · kg−1 · min−1 from −30 to 240 min) or placebo. On separate occasions, the prokinetic drugs metoclopramide (10 mg), domperidone (10 mg), cisapride (10 mg, all at −30 min per oral), or erythromycin (200 mg intravenously from −30 to −15 min) were administered in addition to GLP-1. A liquid test meal (50 g sucrose and 8% mixed amino acids in 400 ml) was administered at 0 min. Capillary and venous blood samples were drawn for the determination of glucose (glucose oxidase), insulin, C-peptide, GLP-1, glucagon, gastric inhibitory polypeptide (GIP), and pancreatic polypeptide (specific immunoassays). Gastric emptying was assessed by the phenol red dilution technique. Statistical analyses were performed using repeated-measures ANOVA and Duncan’s post hoc test. GLP-1 significantly decelerated the velocity of gastric emptying (P < 0.001). This was completely counterbalanced by erythromycin, whereas the other prokinetic drugs used had no effect. Postprandial glucose concentrations were lowered by GLP-1 (P < 0.001 vs. placebo), but this effect was partially reversed by erythromycin (P < 0.05). Insulin secretory responses to the meal were lower during GLP-1 administration (P < 0.05 vs. placebo). However, when erythromycin was added to GLP-1, insulin concentrations were similar to those in placebo experiments. The suppression of meal-related increments in glucagon secretion by GLP-1 was reversed by erythromycin (P < 0.001). The time course of GIP secretion was delayed during GLP-1 administration (P < 0.05), but when erythromycin was added, the pattern was similar to placebo experiments. GLP-1 administration led to a reduction in pancreatic polypeptide plasma concentrations (P < 0.05). In contrast, pancreatic polypeptide levels were markedly increased by erythromycin (P < 0.001). Intravenous erythromycin counteracts the deceleration of gastric emptying caused by GLP-1, probably by interacting with the parasympathetic nervous system (pancreatic polypeptide responses). Despite augmented rises in insulin secretion, the glucose-lowering effect of GLP-1 is markedly reduced when the deceleration of gastric emptying is antagonized, illustrating the importance of this facet of the multiple antidiabetic actions of GLP-1.
Tempol Reduces Oxidative Stress, Improves Insulin Sensitivity, Decreases Renal Dopamine D1 Receptor Hyperphosphorylation, and Restores D1 Receptor–G-Protein Coupling and Function in Obese Zucker Rats
Authors: Banday Anees Ahmad , Marwaha Aditi , Tallam Lakshmi S. , Lokhandwala Mustafa F.
Published: March 2007

Oxidative stress plays a pathogenic role in hypertension, particularly the one associated with diabetes and obesity. Here, we test the hypothesis that renal dopamine D1 receptor dysfunction in obese Zucker rats is caused by oxidative stress. One group each from lean and obese Zucker rats received tempol, a superoxide dismutase mimetic in drinking water for 2 weeks. Obese animals were hypertensive, hyperglycemic, and hyperinsulinemic, exhibited renal oxidative stress, and increased protein kinase C activity. Also, there was hyperphosphorylation of D1 receptor, defective receptor–G-protein coupling, blunted dopamine-induced Na+-K+-ATPase inhibition, and diminished natriuretic response to D1 receptor agonist, SKF-38393. However, obese animals had elevated levels of plasma nitric oxide and urinary cGMP. In addition, l-N-nitroarginine and sodium nitroprusside showed similar effect on blood pressure in lean and obese rats. In obese animals, tempol reduced blood pressure, blood glucose, insulin, renal oxidative stress, and protein kinase C activity. Tempol also decreased D1 receptor phosphorylation and restored receptor G-protein coupling. Dopamine inhibited Na+-K+-ATPase activity, and SKF-38393 elicited a natriuretic response in tempol-treated obese rats. Thus in obese Zucker rats, tempol ameliorates oxidative stress and improves insulin sensitivity. Consequently, hyperphosphorylation of D1 receptor is reduced, leading to restoration of receptor–G-protein coupling and the natriuretic response to SKF-38393.
Signaling Pathways Involved in Human Vascular Smooth Muscle Cell Proliferation and Matrix Metalloproteinase-2 Expression Induced by Leptin
Authors: Li Ling , Mamputu Jean-Claude , Wiernsperger Nicolas , Renier Geneviève
Published: March 2007

Accumulating evidence suggests that high concentrations of leptin observed in obesity and diabetes may contribute to their adverse effects on cardiovascular health. Metformin monotherapy is associated with reduced macrovascular complications in overweight patients with type 2 diabetes. It is uncertain whether such improvement in the cardiovascular outcome is related to specific vasculoprotective effects of this drug. In the present study, we determined the effect of leptin on human aortic smooth muscle cell (HASMC) proliferation and matrix metalloproteinase (MMP)-2 expression, the signaling pathways mediating these effects, and the modulatory effect of metformin on these parameters. Incubation of HASMCs with leptin enhanced the proliferation and MMP-2 expression in these cells and increased the generation of intracellular reactive oxygen species (ROS). These effects were abolished by vitamin E. Inhibition of NAD(P)H oxidase and protein kinase C (PKC) suppressed the effect of leptin on ROS production. In HASMCs, leptin induced PKC, extracellular signal–regulated kinase (ERK)1/2, and nuclear factor-κB (NF-κB) activation and inhibition of these signaling pathways abrogated HASMC proliferation and MMP-2 expression induced by this hormone. Treatment of HASMCs with metformin decreased leptin-induced ROS production and activation of PKC, ERK1/2, and NF-κB. Metformin also inhibited the effect of leptin on HASMC proliferation and MMP-2 expression. Overall, these results demonstrate that leptin induced HASMC proliferation and MMP-2 expression through a PKC-dependent activation of NAD(P)H oxidase with subsequent activation of the ERK1/2/NF-κB pathways and that therapeutic metformin concentrations effectively inhibit these biological effects. These results suggest a new mechanism by which metformin may improve cardiovascular outcome in patients with diabetes.
Long-Term Treatment With Rosiglitazone and Metformin Reduces the Extent of, but Does Not Prevent, Islet Amyloid Deposition in Mice Expressing the Gene for Human Islet Amyloid Polypeptide
Authors: Hull Rebecca L. , Shen Zhen-Ping , Watts Melissah R. , Kodama Keiichi , Carr Darcy B. , Utzschneider Kristina M. , Zraika Sakeneh , Wang Feng , Kahn Steven E.
Published: March 2007

Islet amyloid deposition in type 2 diabetes is associated with reduced β-cell mass. Therefore, interventions aimed at reducing islet amyloid formation may help preserve β-cell mass in type 2 diabetes. Rosiglitazone and metformin act by different mechanisms to improve insulin sensitivity and thereby reduce β-cell secretory demand, resulting in decreased release of insulin and islet amyloid polypeptide (IAPP), the unique constituent of islet amyloid deposits. We hypothesized that this reduced β-cell secretory demand would lead to reduced islet amyloid formation. Human IAPP (hIAPP) transgenic mice, a model of islet amyloid, were treated for 12 months with rosiglitazone (1.5 mg · kg−1 · day−1, n = 19), metformin (1 g · kg−1 · day−1, n = 18), or control (n = 17). At the end of the study, islet amyloid prevalence (percent islets containing amyloid) and severity (percent islet area occupied by amyloid), islet mass, β-cell mass, and insulin release were determined. Islet amyloid prevalence (44 ± 8, 13 ± 4, and 11 ± 3% for control, metformin-, and rosiglitazone-treated mice, respectively) and severity (9.2 ± 3.0, 0.22 ± 0.11, and 0.10 ± 0.05% for control, metformin-, and rosiglitazone-treated mice, respectively) were markedly reduced with both rosiglitazone (P < 0.001 for both measures) and metformin treatment (P < 0.001 for both measures). Both treatments were associated with reduced insulin release assessed as the acute insulin response to intravenous glucose (2,189 ± 857, 621 ± 256, and 14 ± 158 pmol/l for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin vs. control and P < 0.005 for rosiglitazone vs. control), consistent with reduced secretory demand. Similarly, islet mass (33.4 ± 7.0, 16.6 ± 3.6, and 12.2 ± 2.1 mg for control, metformin-, and rosiglitazone-treated mice, respectively) was not different with metformin treatment (P = 0.06 vs. control) but was significantly lower with rosiglitazone treatment (P < 0.05 vs. control). When the decreased islet mass was accounted for, the islet amyloid–related decrease in β-cell mass (percent β-cell mass/islet mass) was ameliorated in both rosiglitazone- and metformin-treated animals (57.9 ± 3.1, 64.7 ± 1.4, and 66.1 ± 1.6% for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin or rosiglitazone vs. control). In summary, rosiglitazone and metformin protect β-cells from the deleterious effects of islet amyloid, and this effect may contribute to the ability of these treatments to alleviate the progressive loss of β-cell mass and function in type 2 diabetes.
Evidence of an Association Between the Arg72 Allele of the Peptide YY and Increased Risk of Type 2 Diabetes
Authors: Torekov Signe S. , Larsen Lesli H. , Glümer Charlotte , Borch-Johnsen Knut , Jørgensen Torben , Holst Jens J. , Madsen Ole D. , Hansen Torben , Pedersen Oluf
Published: March 2007

We tested the hypothesis that variants in the gene encoding the prepropeptide YY (PYY) associate with type 2 diabetes and/or obesity. Mutation analyses of DNA from 84 patients with obesity and familial type 2 diabetes identified two polymorphisms, IVS3 + 68C>T and Arg72Thr, and one rare variant, +151C>A of PYY. The common allele of the Arg72Thr variant associated with type 2 diabetes with an allele frequency of the Arg allele of 0.667 (95% CI 0.658–0.677) among 4,639 glucose-tolerant subjects and 0.692 (0.674–0.710) among 1,326 patients with type 2 diabetes (P = 0.005, odds ratio 1.19 [95% CI 1.05–1.35]). The same polymorphism associated with overweight (25 ≤ BMI < 30 kg/m2) (P = 0.018, 1.15 [1.02–1.28]). In quantitative trait analyses of a population-based sample of 6,022 subjects, the Arg allele was associated with an increased plasma glucose level 2 h after an oral glucose tolerance test (OGTT) (P = 0.03), an increased area under the curve for the post-OGTT plasma glucose level (P = 0.03), and a lower insulinogenic index (P = 0.01). In conclusion, the common Arg allele of the PYY Arg72Thr variant modestly associates with type 2 diabetes and with type 2 diabetes–related quantitative traits.
Reduction of Macrophage Infiltration and Chemoattractant Gene Expression Changes in White Adipose Tissue of Morbidly Obese Subjects After Surgery-Induced Weight Loss
Authors: Cancello Raffaella , Henegar Corneliu , Viguerie Nathalie , Taleb Soraya , Poitou Christine , Rouault Christine , Coupaye Muriel , Pelloux Veronique , Hugol Danielle , Bouillot Jean-Luc , Bouloumié Anne , Barbatelli Giorgio , Cinti Saverio , Svensson Per-Arne , Barsh Gregory S. , Zucker Jean-Daniel , Basdevant Arnaud , Langin Dominique , Clément Karine
Published: March 2007

In human obesity, the stroma vascular fraction (SVF) of white adipose tissue (WAT) is enriched in macrophages. These cells may contribute to low-grade inflammation and to its metabolic complications. Little is known about the effect of weight loss on macrophages and genes involved in macrophage attraction. We examined subcutaneous WAT (scWAT) of 7 lean and 17 morbidly obese subjects before and 3 months after bypass surgery. Immunomorphological changes of the number of scWAT-infiltrating macrophages were evaluated, along with concomitant changes in expression of SVF-overexpressed genes. The number of scWAT-infiltrating macrophages before surgery was higher in obese than in lean subjects (HAM56+/CD68+; 22.6 ± 4.3 vs. 1.4 ± 0.6%, P < 0.001). Typical “crowns” of macrophages were observed around adipocytes. Drastic weight loss resulted in a significant decrease in macrophage number (−11.63 ± 2.3%, P < 0.001), and remaining macrophages stained positive for the anti-inflammatory protein interleukin 10. Genes involved in macrophage attraction (monocyte chemotactic protein [MCP]-1, plasminogen activator urokinase receptor [PLAUR], and colony-stimulating factor [CSF]-3) and hypoxia (hypoxia-inducible factor-1α [HIF-1α]), expression of which increases in obesity and decreases after surgery, were predominantly expressed in the SVF. We show that improvement of the inflammatory profile after weight loss is related to a reduced number of macrophages in scWAT. MCP-1, PLAUR, CSF-3, and HIF-1α may play roles in the attraction of macrophages in scWAT.
Insulin Resistance and Type 2 Diabetes in High-Fat–Fed Mice Are Linked to High Glycotoxin Intake
Authors: Sandu Oana , Song Keying , Cai Weijing , Zheng Feng , Uribarri Jaime , Vlassara Helen
Published: March 2007

Dietary advanced glycosylation end products (AGEs) have been linked to insulin resistance in db/db(++) mice. To test whether dietary AGEs play a role in the progression of insulin resistance in normal mice fed high-fat diets, normal C57/BL6 mice were randomly assigned to high-fat diets (35% g fat), either high (HAGE-HF group; 995.4 units/mg AGE) or low (by 2.4-fold LAGE-HF group; 329.6 units/mg AGE) in AGE content for 6 months. Age-matched C57/BL6 and db/db(++) mice fed regular diet (5% g fat, 117.4 units/mg AGE) served as controls. After 6 months, 75% of HAGE-HF mice were diabetic and exhibited higher body weight (P < 0.001), fasting glucose (P < 0.001), insulin (P < 0.001), and serum AGEs (P < 0.01) than control mice, while none of the LAGE-HF mice were diabetic despite a similar rise in body weight and plasma lipids. The HAGE-HF group displayed markedly impaired glucose and insulin responses during glucose tolerance tests and euglycemic and hyperglycemic clamps and altered pancreatic islet structure and function compared with those of LAGE-HF mice, in which findings resembled those of control mice. The HAGE-HF group had more visceral fat (by two- and fourfold) and more AGE-modified fat (by two- and fivefold) than LAGE-HF and control mice, respectively. In the HAGE-HF group, plasma 8-isoprostane was higher (P < 0.01) and adiponectin lower (P < 0.001) than control mice, while in the LAGE-HF group, these were more modestly affected (P < 0.05). These results demonstrate that the development of insulin resistance and type 2 diabetes during prolonged high-fat feeding are linked to the excess AGEs/advanced lipoxidation end products inherent in fatty diets.
Differentiation of Human Liver-Derived, Insulin-Producing Cells Toward the β-Cell Phenotype
Authors: Zalzman Michal , Anker-Kitai Leeat , Efrat Shimon
Published: March 2007

β-Cell transplantation is viewed as a cure for type 1 diabetes; however, it is limited by the number of pancreas donors. Human stem cells offer the promise of an abundant source of insulin-producing cells, given the existence of methods for manipulating their differentiation. We have previously demonstrated that the expression of the β-cell transcription factor pancreatic duodenal homeobox 1 (PDX-1) in human fetal liver cells activates multiple aspects of the β-cell phenotype. These cells, termed FH-B-TPN cells, produce insulin, release insulin in response to physiological glucose levels, and replace β-cell function in diabetic immunodeficient mice. However, they deviate from the normal β-cell phenotype by the lack of expression of a number of β-cell genes, the expression of non−β-cell genes, and a lower insulin content. Here we aimed to promote differentiation of FH-B-TPN cells toward the β-cell phenotype using soluble factors. Cells cultured with activin A in serum-free medium upregulated expression of NeuroD and Nkx2.2 and downregulated paired box homeotic gene 6 (PAX-6). Glucokinase and prohormone convertase 1/3 were also upregulated, whereas pancreatic polypeptide and glucagon as well as liver markers were downregulated. Insulin content was increased by up to 33-fold, to ∼60% of the insulin content of normal β-cells. The cells were shown to contain human C-peptide and release insulin in response to physiological glucose levels. Cell transplantation into immunodeficient diabetic mice resulted in the restoration of stable euglycemia. The cells continued to express insulin in vivo, and no cell replication was detected. Thus, the manipulation of culture conditions induced a significant and stable differentiation of FH-B-TPN cells toward the β-cell phenotype, making them excellent candidates for β-cell replacement in type 1 diabetes.
Marked Increase in White Adipose Tissue Blood Perfusion in the Type 2 Diabetic GK Rat
Authors: Kampf Caroline , Bodin Birgitta , Källskog Örjan , Carlsson Carina , Jansson Leif
Published: March 2007

The aim of the present study was to evaluate and cor-relate islet to brown and white adipose tissue (WAT) blood perfusion in one obese rat and one nonobese rat with type 2 diabetes (obese Zucker [OZ] and GK rats, respectively). We measured blood perfusion with a microsphere technique in anesthetized animals and subsequently estimated the blood flow to seven different WAT depots and brown adipose tissue, in addition to the whole pancreas and pancreatic islets. Both GK and OZ rats had higher islet blood perfusion than their respective control strains. Adipose tissue blood flow (ATBF) was similar to or lower than that of controls in the normoglycemic OZ rats. GK rats, however, had 5–10 times higher blood perfusion than control Wistar rats in most WAT depots. Vascular density and macrophage numbers in WAT did not differ between the different strains. The discrepancy in ATBF between the obese-normoglycemic and type 2 diabetic rats opens the intriguing possibility that changes in this blood perfusion may influence and/or modulate the β-cell dysfunction in type 2 diabetes.
Genome-Wide Linkage Analyses of Type 2 Diabetes in Mexican Americans
Authors: Hunt Kelly J. , Lehman Donna M. , Arya Rector , Fowler Sharon , Leach Robin J. , Göring Harald H.H. , Almasy Laura , Blangero John , Dyer Tom D. , Duggirala Ravindranath , Stern Michael P.
Published: March 2007

The San Antonio Family Diabetes/Gallbladder Study was initiated to identify susceptibility genes for type 2 diabetes. Evidence was previously reported of linkage to diabetes on 10q with suggestive evidence on 3p and 9p in a genome-wide scan of 440 individuals from 27 pedigrees ascertained through a single diabetic proband. Subsequently, the study was expanded to include 906 individuals from 39 extended Mexican-American pedigrees, two additional examination cycles ∼5.3 and 7.6 years after baseline, and genotypes for a new set of genome-wide markers. Therefore, we completed a second genome-wide linkage scan. Using information from a participant’s most recent exam, the prevalence of diabetes in nonprobands was 21.8%. We performed genome-wide variance components-based genetic analysis on the discrete trait diabetes using a liability model and on the quantitative Martingale residual obtained from modeling age of diabetes diagnosis using Cox proportional hazard models. Controlling for age and age2, our strongest evidence for linkage to the trait diabetes and the quantitative Martingale residual was on chromosome 3p at marker D3S2406 with multipoint empirical logarithm of odds scores of 1.87 and 3.76, respectively. In summary, we report evidence for linkage to diabetes on chromosome 3p in a region previously identified in at least three independent populations.
Increased Fat Mass Compensates for Insulin Resistance in Abdominal Obesity and Type 2 Diabetes
Authors: Virtanen Kirsi A. , Iozzo Patricia , Hällsten Kirsti , Huupponen Risto , Parkkola Riitta , Janatuinen Tuula , Lönnqvist Fredrik , Viljanen Tapio , Rönnemaa Tapani , Lönnroth Peter , Knuuti Juhani , Ferrannini Ele , Nuutila Pirjo
Published: March 2007

To evaluate the relative impact of abdominal obesity and newly diagnosed type 2 diabetes on insulin action in skeletal muscle and fat tissue, we studied 61 men with (n = 31) or without (n = 30) diabetes, subgrouped into abdominally obese or nonobese according to the waist circumference. Adipose tissue depots were quantified by magnetic resonance imaging, and regional glucose uptake was measured using 2-[18F]fluoro-2-deoxyglucose/positron emission tomography during euglycemic hyperinsulinemia. Across groups, glucose uptake per unit tissue weight was higher in visceral (20.5 ± 1.4 μmol · min−1 · kg−1) than in abdominal (9.8 ± 0.9 μmol min−1 · kg−1, P < 0.001) or femoral (12.3 ± 0.6 μmol · min−1 · kg−1, P < 0.001) subcutaneous tissue and ∼40% lower than in skeletal muscle (33.1 ± 2.5 μmol · min−1 · kg−1, P < 0.0001). Abdominal obesity was associated with a marked reduction in glucose uptake per unit tissue weight in all fat depots and in skeletal muscle (P < 0.001 for all regions). Recent type 2 diabetes per se had little additional effect. In both intra-abdominal adipose (r = −0.73, P < 0.0001) and skeletal muscle (r = −0.53, P < 0.0001) tissue, glucose uptake was reciprocally related to intra-abdominal fat mass in a curvilinear fashion. When regional glucose uptake was multiplied by tissue mass, total glucose uptake per fat depot was similar irrespective of abdominal obesity or type 2 diabetes, and its contribution to whole-body glucose uptake increased by ∼40% in obese nondiabetic and nonobese diabetic men and was doubled in obese diabetic subjects. We conclude that 1) in abdominal obesity, insulin-stimulated glucose uptake rate is markedly reduced in skeletal muscle and in all fat depots; 2) in target tissues, this reduction is reciprocally (and nonlinearly) related to the amount of intra-abdominal fat; 3) mild, recent diabetes adds little insulin resistance to that caused by abdominal obesity; and 4) despite fat insulin resistance, an expanded fat mass (especially subcutaneous) provides a sink for glucose, resulting in a compensatory attenuation of insulin resistance at the whole-body level in men.
LEW.1WR1 Rats Develop Autoimmune Diabetes Spontaneously and in Response to Environmental Perturbation
Authors: Mordes John P. , Guberski Dennis L. , Leif Jean H. , Woda Bruce A. , Flanagan Joan F. , Greiner Dale L. , Kislauskis Edward H. , Tirabassi Rebecca S.
Published: March 2007

We describe a new rat model of autoimmune diabetes that arose in a major histocompatibility complex congenic LEW rat. Spontaneous diabetes in LEW.1WR1 rats (RT1u/u/a) occurs with a cumulative frequency of ∼2% at a median age of 59 days. The disease is characterized by hyperglycemia, glycosuria, ketonuria, and polyuria. Both sexes are affected, and islets of acutely diabetic rats are devoid of β-cells, whereas α- and δ-cell populations are spared. The peripheral lymphoid phenotype is normal, including the fraction of ART2+ regulatory T-cells. We tested the hypothesis that the expression of diabetes would be increased by immunological perturbation of innate or adaptive immunity. Treatment of young rats with depleting anti-ART2.1 monoclonal antibody increased the frequency of diabetes to 50%. Treatment with the toll-like receptor 3 ligand polyinosinic:polycytidylic acid increased the frequency of diabetes to 100%. All diabetic rats exhibited end-stage islets. The LEW.1WR1 rat is also susceptible to collagen-induced arthritis but is free of spontaneous thyroiditis. The LEW.1WR1 rat provides a new model for studying autoimmune diabetes and arthritis in an animal with a genetic predisposition to both disorders that can be amplified by environmental perturbation.