bluuebunny/crossref_metadata_2025 huggingface dataset:
Overexpression of Metallothionein Reduces Diabetic Cardiomyopathy
Authors: Liang Qiangrong , Carlson Edward C. , Donthi Rajakumar V. , Kralik Patrica M. , Shen Xia , Epstein Paul N.
Published: March 2007

Many diabetic patients suffer from cardiomyopathy, even in the absence of vascular disease. This diabetic cardiomyopathy predisposes patients to heart failure and mortality from myocardial infarction. Evidence from animal models suggests that reactive oxygen species play an important role in the development of diabetic cardiomyopathy. Our laboratory previously developed a transgenic mouse model with targeted overexpression of the antioxidant protein metallothionein (MT) in the heart. In this study we used MT-transgenic mice to test whether an antioxidant protein can reduce cardiomyopathy in the OVE26 transgenic model of diabetes. OVE26 diabetic mice exhibited cardiomyopathy characterized by significantly altered mRNA expression, clear morphological abnormalities, and reduced contractility under ischemic conditions. Diabetic hearts appeared to be under oxidative stress because they had significantly elevated oxidized glutathione (GSSG). Diabetic mice with elevated cardiac MT (called OVE26MT mice) were obtained by crossing OVE26 transgenic mice with MT transgenic mice. Hyperglycemia in OVE26MT mice was indistinguishable from hyperglycemia in OVE26 mice. Despite this, the MT transgene significantly reduced cardiomyopathy in diabetic mice: OVE26MT hearts showed more normal levels of mRNA and GSSG. Typically, OVE26MT hearts were found to be morphologically normal, and elevated MT improved the impaired ischemic contractility seen in diabetic hearts. These results demonstrate that cardiomyocyte-specific expression of an antioxidant protein reduces damage to the diabetic heart.
Autocrine Activation of the IGF-I Signaling Pathway in Mesangial Cells Isolated From Diabetic NOD Mice
Authors: Tack Ivan , Elliot Sharon J. , Potier Mylene , Rivera Ana , Striker Gary E. , Striker Liliane J.
Published: March 2007

Mesangial cells isolated from NOD mice after the onset of diabetes have undergone a stable phenotypic change. This phenotype is characterized by increased expression of IGF-I and downregulation of collagen degradation, which is associated with decreased MMP-2 activity. Here, we investigated the IGF-I signaling pathway in mesangial cells isolated from NOD mice before (nondiabetic NOD mice [ND-NOD]) and after (diabetic NOD mice [D-NOD]) the onset of diabetes. We found that the IGF-I signaling pathway in D-NOD cells was activated by autocrine IGF-I. They had phosphorylation of the IGF-I receptor β-subunit, phosphorylation of insulin receptor substrate (IRS)-1, and association of the p85 subunit (phosphatidylinositol 3-kinase [PI3K]) with the IGF-I receptor and IRS-1 in D-NOD cells in the basal state. This was also associated with increased phosphorylation of ERK2 in D-NOD mesangial cells. Inhibiting autocrine IGF-I from binding to its receptor using an IGF-I–neutralizing antibody or inhibiting IGF-I signaling pathways using a specific PI3K inhibitor or a specific mitogen-activated protein kinase/extracellular response kinase kinase inhibitor decreased phosphorylated ERKs in D-NOD cells. Importantly, this was associated with increased MMP-2 activity. The addition of exogenous IGF-I to ND-NOD activated signal transduction. Therefore, we conclude that the IGF-I signaling pathway is intact in both D-NOD and ND-NOD cells. However, the phenotypic change in D-NOD cells is associated with constitutive activation of the IGF-I signaling pathways, which may participate in the development and progression of diabetic glomerulosclerosis.
High Familial Risk and Genetic Susceptibility in Early Onset Childhood Diabetes
Authors: Gillespie Kathleen M. , Gale Edwin A.M. , Bingley Polly J.
Published: March 2007

Early onset type 1 diabetes is associated with rapid β-cell failure and high levels of HLA-mediated genetic susceptibility. We examined familial risk of disease in relation to age at onset in 1,299 families participating in the Bart’s Oxford population-based family study of type 1 diabetes. Risk of diabetes was estimated by survival analysis in 1,430 siblings and 2,419 parents and related to age at onset in the proband. Unaffected relatives at high risk were identified by measurement of islet autoantibodies, and HLA class II genotyping was performed in probands where DNA was available (573 children). The cumulative risk of diabetes by age 20 years was 11.7% in siblings of probands diagnosed before age 5 years, compared with 3.6% for ages 5–9 years and 2.3% for ages 10–14 years (P < 0.0001). In parents, the cumulative risk by age 40 years was 5.9% if the proband was diagnosed before age 5 years, compared with 3.7% for ages 5–9 years and 3.7% for ages 10–14 years (P = 0.04). Of 1,169 unaffected siblings tested at study entry, 7.3% had two or more autoantibody markers if the proband was diagnosed before age 5 years, compared with 2.2 and 2.4%, respectively, for ages 5–9 and 10–14 years (P = 0.002). The frequency of the highest risk genotype decreased with increasing age at onset. Of children diagnosed before age 5 years, 52% were heterozygous for HLA DRB1*03-DQA1*0501-DQB1*02/DRB1*04-DQA1*0301-DQB1*0302 compared with 32% and 33%, respectively, for children diagnosed at ages 5–9 and 10–14 years (P < 0.001). Diabetes with onset before age 5 years is therefore a marker of high familial risk.
Metabolic and Autocrine Regulation of the Mammalian Target of Rapamycin by Pancreatic β-Cells
Authors: McDaniel Michael L. , Marshall Connie A. , Pappan Kirk L. , Kwon Guim
Published: March 2007

Mammalian target of rapamycin (mTOR) is a serine and threonine protein kinase that regulates numerous cellular functions, in particular, the initiation of protein translation. mTOR-mediated phosphorylation of both the translational repressor eukaryotic initiation factor 4E binding protein-1 and p70 S6 kinase are early events that control the translation initiation process. Rapamycin, an inhibitor of mTOR, is a potent immunosuppressant due, in part, to its ability to interfere with T-cell activation at the level of translation, and it has gained a prominent role in preventing the development and progression of rejection in pancreatic islet transplant recipients. The characterization of the insulin signaling cascade that modulates mTOR in insulin-sensitive tissues has been a major focus of investigation. Recently, the ability of nutrients, in particular the branched-chain amino acid leucine, to activate mTOR independent of insulin by a process designated as nutrient signaling has been identified. The β-cell expresses components of the insulin signaling cascade and utilizes the metabolism of nutrients to affect insulin secretion. These combined transduction processes make the β-cell an unique cell to study metabolic and autocrine regulation of mTOR signaling. Our studies have described the ability of insulin and IGFs in concert with the nutrients leucine, glutamine, and glucose to modulate protein translation through mTOR in β-cells. These findings suggest that mitochondria-derived factors, ATP in particular, may be responsible for nutrient signaling. The significance of these findings is that the optimization of mitochondrial function is not only important for insulin secretion but may significantly impact the growth and proliferation of β-cells through these mTOR signaling pathways.
AICAR Administration Causes an Apparent Enhancement of Muscle and Liver Insulin Action in Insulin-Resistant High-Fat-Fed Rats
Authors: Iglesias Miguel A. , Ye Ji-Ming , Frangioudakis Georgia , Saha Asish K. , Tomas Eva , Ruderman Neil B. , Cooney Gregory J. , Kraegen Edward W.
Published: March 2007

Exercise improves insulin sensitivity. As AMP-activated protein kinase (AMPK) plays an important role in muscle metabolism during exercise, we investigated the effects of the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) on insulin action in insulin-resistant high-fat-fed (HF) rats. Rats received a subcutaneous injection of 250 mg/kg AICAR (HF-AIC) or saline (HF-Con). The next day, euglycemic-hyperinsulinemic clamp studies were performed. Glucose infusion rate during the clamp was enhanced (50%) in HF-AIC compared with HF-Con rats. Insulin-stimulated glucose uptake was improved in white but not in red quadriceps, whereas glycogen synthesis was improved in both red and white quadriceps of HF-AIC rats. HF-AIC rats also showed increased insulin suppressibility of hepatic glucose output (HGO). AICAR-induced responses in both liver and muscle were accompanied by reduced malonyl-CoA content. Clamp HGO correlated closely with hepatic triglyceride content (r = 0.67, P < 0.01). Thus, a single dose of AICAR leads to an apparent enhancement in whole-body, muscle, and liver insulin action in HF rats that extends beyond the expected time of AMPK activation. Whether altered tissue lipid metabolism mediates AICAR effects on insulin action remains to be determined. Follow-up studies suggest that at least some of the post-AICAR insulin-enhancing effects also occur in normal rats. Independent of this, the results suggest that pharmacological activation of AMPK may have potential in treating insulin-resistant states and type 2 diabetes.
Effects of a Novel Glycogen Synthase Kinase-3 Inhibitor on Insulin-Stimulated Glucose Metabolism in Zucker Diabetic Fatty (fa/fa) Rats
Authors: Cline Gary W. , Johnson Kirk , Regittnig Werner , Perret Pascale , Tozzo Effie , Xiao Linda , Damico Christine , Shulman Gerald I.
Published: March 2007

Defects in liver and muscle glycogen synthesis are major factors contributing to postprandrial hyperglycemia in patients with type 2 diabetes. Therefore, activation of glycogen synthase through inhibition of glycogen synthase kinase (GSK)-3 represents a potential new therapeutic target. To examine this possibility, we performed oral glucose tolerance tests (OGTTs) and euglycemic-insulinemic clamp studies in Zucker diabetic fatty (fa/fa) rats before and after treatment with novel GSK-3 inhibitors. GSK-3 inhibition caused a 41 ± 2% (P < 0.001) and 26 ± 4% (P < 0.05) reduction in the area under the glucose and insulin concentration curves, respectively, during the OGTT. This improvement in glucose disposal could mostly be attributed to an approximate twofold increase in liver glycogen synthesis. In contrast, there was no significant increase in muscle glycogen synthesis despite an approximate threefold activation of muscle glycogen synthase activity. GSK-3 inhibitor treatment increased liver glycogen synthesis about threefold independent of insulin concentration during the clamp studies. In contrast, muscle glucose uptake and muscle glycogen synthesis were independent of drug treatment. GSK-3 inhibitor treatment lowered fasting hyperglycemia in diabetic rats by 6.0 ± 1.3 mmol/l but had no significant effect on glucose disposal during the clamp. In conclusion, GSK-3 inhibition significantly improved oral glucose disposal, mostly by increasing liver glycogen synthesis. These studies suggest that GSK-3 inhibition may represent an important new therapeutic target for treatment of patients with type 2 diabetes.
Dysfunction of Mitochondria in Human Skeletal Muscle in Type 2 Diabetes
Authors: Kelley David E. , He Jing , Menshikova Elizabeth V. , Ritov Vladimir B.
Published: March 2007

Skeletal muscle is strongly dependent on oxidative phosphorylation for energy production. Because the insulin resistance of skeletal muscle in type 2 diabetes and obesity entails dysregulation of the oxidation of both carbohydrate and lipid fuels, the current study was undertaken to examine the potential contribution of perturbation of mitochondrial function. Vastus lateralis muscle was obtained by percutaneous biopsy during fasting conditions from lean (n = 10) and obese (n = 10) nondiabetic volunteers and from volunteers with type 2 diabetes (n = 10). The activity of rotenone-sensitive NADH:O2 oxidoreductase, reflecting the overall activity of the respiratory chain, was measured in a mitochondrial fraction by a novel method based on providing access for NADH to intact mitochondria via alamethicin, a channel-forming antibiotic. Creatine kinase and citrate synthase activities were measured as markers of myocyte and mitochondria content, respectively. Activity of rotenone-sensitive NADH:O2 oxidoreductase was normalized to creatine kinase activity, as was citrate synthase activity. NADH:O2 oxidoreductase activity was lowest in type 2 diabetic subjects and highest in the lean volunteers (lean 0.95 ± 0.17, obese 0.76 ± 0.30, type 2 diabetes 0.56 ± 0.14 units/mU creatine kinase; P < 0.005). Also, citrate synthase activity was reduced in type 2 diabetic patients (lean 3.10 ± 0.74, obese 3.24 ± 0.82, type 2 diabetes 2.48 ± 0.47 units/mU creatine kinase; P < 0.005). As measured by electron microscopy, skeletal muscle mitochondria were smaller in type 2 diabetic and obese subjects than in muscle from lean volunteers (P < 0.01). We conclude that there is an impaired bioenergetic capacity of skeletal muscle mitochondria in type 2 diabetes, with some impairment also present in obesity.
Removal of Visceral Fat Prevents Insulin Resistance and Glucose Intolerance of Aging
Authors: Gabriely Ilan , Ma Xiao Hui , Yang Xiao Man , Atzmon Gil , Rajala Michael W. , Berg Anders H. , Scherer Phillip , Rossetti Luciano , Barzilai Nir
Published: March 2007

Age-dependent changes in insulin action and body fat distribution are risk factors for the development of type 2 diabetes. To examine whether the accumulation of visceral fat (VF) could play a direct role in the pathophysiology of insulin resistance and type 2 diabetes, we monitored insulin action, glucose tolerance, and the expression of adipo-derived peptides after surgical removal of VF in aging (20-month-old) F344/Brown Norway (FBN) and in Zucker Diabetic Fatty (ZDF) rats. As expected, peripheral and hepatic insulin action were markedly impaired in aging FBN rats, and extraction of VF (accounting for ∼18% of their total body fat) was sufficient to restore peripheral and hepatic insulin action to the levels of young rats. When examined at the mechanistic level, removal of VF in ZDF rats prevented the progressive decrease in insulin action and delayed the onset of diabetes, but VF extraction did not alter plasma free fatty acid levels. However, the expression of tumor necrosis factor-α and leptin in subcutaneous (SC) adipose tissue were markedly decreased after VF removal (by approximately three- and twofold, respectively). Finally, extracted VF retained ∼15-fold higher resistin mRNA compared with SC fat. Our data suggest that insulin resistance and the development of diabetes can be significantly reduced in aging rats by preventing the age-dependent accumulation of VF. This study documents a cause-and-effect relationship between VF and major components of the metabolic syndrome.
Independent Association of Type 2 Diabetes and Coronary Artery Disease With Myocardial Insulin Resistance
Authors: Iozzo Patricia , Chareonthaitawee Panithaya , Dutka David , Betteridge D. John , Ferrannini Ele , Camici Paolo G.
Published: March 2007

Clustering of classical cardiovascular risk factors is insufficient to account for the excess coronary artery disease (CAD) of patients with diabetes, and chronic hyperglycemia and insulin resistance (IR) are obvious culprits. Whole-body and skeletal muscle IR is characteristic of patients with type 2 diabetes, but whether it extends to the normally contracting cardiac muscle is controversial. We investigated whether type 2 diabetes is associated with myocardial IR independent of CAD in a case-control series (n = 55) of male nondiabetic and diabetic (type 2 and type 1) patients with or without angiographically documented CAD. Baseline blood flow (15O-water) and insulin-stimulated glucose uptake (18F-fluoro-deoxyglucose) during euglycemic (5.6 mmol/l), physiological hyperinsulinemia (40 mU · min−1 · m−2 insulin clamp) were measured by positron emission tomography in skeletal muscle and normally contracting myocardium. Skeletal muscle glucose uptake was reduced in association with both CAD and type 2 diabetes. In regions with normal baseline perfusion, insulin-mediated myocardial glucose uptake was reduced in non-CAD type 2 diabetic (0.36 ± 0.14 μ mol · min−1 · g−1) and nondiabetic CAD patients (0.44 ± 0.15 μmol · min− 1 · g−1) in comparison with healthy control subjects (0.61 ± 0.08) or with non-CAD type 1 diabetic patients (0.80 ± 0.13; P < 0.001 for both CAD and diabetes). Neither basal skeletal muscle nor basal myocardial blood flow differed across groups; both skeletal muscle and myocardial IR were directly related to whole-body IR. We conclude that type 2 diabetes is specifically associated with myocardial IR that is independent of and nonadditive with angiographic CAD and proportional to skeletal muscle and whole-body IR.
Free Fatty Acids Reduce Splanchnic and Peripheral Glucose Uptake in Patients With Type 2 Diabetes
Authors: Bajaj Mandeep , Pratipanawatr Thongchai , Berria Rachele , Pratipanawatr Wilailak , Kashyap Sangeeta , Cusi Kenneth , Mandarino Lawrence , DeFronzo Ralph A.
Published: March 2007

Splanchnic glucose uptake (SGU) plays a major role in the disposal of an oral glucose load (OGL). To investigate the effect of an elevated plasma free fatty acid (FFA) concentration on SGU in patients with type 2 diabetes, we measured SGU in eight diabetic patients (mean age 51 ± 4 years, BMI 29.3 ± 1.4 kg/m2, fasting plasma glucose 9.3 ± 0.7 mmol/l) during an intravenous Intralipid/heparin infusion and 7–10 days later during a saline infusion. SGU was estimated by the OGL insulin clamp method: subjects received a 7-h euglycemic-hyperinsulinemic clamp (insulin infusion rate = 100 mU · m−2 · min−1), and a 75-g OGL was ingested 3 h after starting the insulin clamp. After glucose ingestion, the steady-state glucose infusion rate during the insulin clamp was decreased appropriately to maintain euglycemia. SGU was calculated by subtracting the integrated decrease in glucose infusion rate during the 4-h period after glucose ingestion from the ingested glucose load (75 g). 3-[3H]glucose was infused during the 3-h insulin clamp before glucose ingestion to determine the rates of endogenous glucose production and glucose disappearance (Rd). Intralipid/heparin or saline infusion was initiated 2 h before the start of the OGL clamp. Plasma FFA concentrations were significantly higher during the OGL clamp with the intralipid/heparin infusion than with the saline infusion (2.5 ± 0.3 vs. 0.11 ± 0.02 mmol/l, P < 0.001). During the 3-h insulin clamp period before glucose ingestion, Intralipid/heparin infusion reduced Rd (4.4 ± 0.3 vs. 5.3 ± 0.3 mg · kg−1 · min−1, P < 0.01). During the 4-h period after glucose ingestion, SGU was significantly decreased during the intralipid/heparin versus saline infusion (30 ± 2 vs. 37 ± 2%, P < 0.01). In conclusion, an elevation in plasma FFA concentration impairs both peripheral and SGU in patients with type 2 diabetes.
α-Tocopherol Decreases Superoxide Anion Release in Human Monocytes Under Hyperglycemic Conditions Via Inhibition of Protein Kinase C-α
Authors: Venugopal Senthil Kumar , Devaraj Sridevi , Yang Teddy , Jialal Ishwarlal
Published: March 2007

Diabetes is a major risk factor for premature atherosclerosis, and oxidative stress appears to be an important mechanism. Previously, we showed that diabetic monocytes produce increased superoxide anion (O2−), and α-tocopherol (AT) supplementation decreases this. The aim of this study was to elucidate the mechanism(s) of O2− release and inhibition by AT under hyperglycemic (HG) conditions in monocytes. O2− release, protein kinase C (PKC) activity, and translocation of PKC-α and -βII and p47phox were increased in THP-1 cells (human monocytic cell line) under HG (15 mmol/l glucose) conditions, whereas AT supplementation inhibited these changes. AT, NADPH oxidase inhibitors (apocynin and diphenyleneiodonium chloride [DPI]), and an inhibitor to PKC-α and other isoforms (2,2′,3,3′,4,4′-hexahydroxy-1,1′-biphenyl-6,6′-dimethanol dimethyl ether [HBDDE]) but not PKC-β II (LY379196) decreased O2− release and p47phox translocation. Antisense oligodeoxynucleotides to PKC-α and p47phox but not to PKC-βII inhibited HG-induced O2− release and p47phox translocation in THP-1 cells. Under HG conditions, reactive oxygen species release from monocytes was not inhibited by agents affecting mitochondrial metabolism but was inhibited in human endothelial cells. We conclude that under HG conditions, monocytic O2− release is dependent on NADPH oxidase activity but not the mitochondrial respiratory chain; HG-induced O2− release is triggered by PKC-α, and AT inhibits O2− release via inhibition of PKC-α.
Podocyte Number in Normotensive Type 1 Diabetic Patients With Albuminuria
Authors: White Kathryn E. , Bilous Rudolf W. , Marshall Sally M. , El Nahas Meguid , Remuzzi Giuseppe , Piras Giampiero , De Cosmo Salvatore , Viberti GianCarlo ,   on behalf of the European Study for the Prevention of Renal Disease in Type 1 Diabetes (ESPRIT)
Published: March 2007

We estimated glomerular cell number in 50 normotensive type 1 diabetic patients with raised albumin excretion rate (AER) and investigated any change after 3 years in a subgroup of 16 placebo-treated patients. Biopsies from 10 normal kidney donors were used as controls. Mesangial and endothelial cell number was increased in the 50 diabetic patients at the start of the study compared with control subjects. There was no difference in podocyte number. Glomerular volume was increased in diabetic patients, but surface area of glomerular basement membrane (GBM) underlying the podocytes did not differ between groups. AER correlated positively with mesangial cell number in microalbuminuric patients (r = 0.44, P = 0.012) and negatively with podocyte number in proteinuric patients (r = −0.48, P = 0.040). In the 16 placebo-treated patients, glomerular volume increased after 3 years owing to matrix accumulation and increased GBM surface area. Although overall cell number did not differ significantly from baseline, the decrease in podocyte number during follow-up correlated with AER at follow-up (r = −0.72, P = 0.002). In conclusion, cross-sectional analysis of podocyte number in type 1 diabetic patients with raised AER but normal blood pressure shows no significant reduction compared with nondiabetic control subjects. Longitudinal data provide evidence for an association between podocyte loss and AER, but whether cellular changes are a response to, a cause of, or concomitant with the progression of nephropathy remains uncertain.
Nitric Oxide Prevents Aldose Reductase Activation and Sorbitol Accumulation During Diabetes
Authors: Chandra Deepak , Jackson Elias B. , Ramana Kota V. , Kelley Rocky , Srivastava Satish K. , Bhatnagar Aruni
Published: March 2007

Increased glucose utilization by aldose reductase (AR) has been implicated in the development of diabetes complications. However, the mechanisms that regulate AR during diabetes remain unknown. Herein we report that several nitric oxide (NO) donors prevent ex vivo synthesis of sorbitol in erythrocytes obtained from diabetic or nondiabetic rats. Compared with erythrocytes of nondiabetic rats, the AR activity in the erythrocytes of diabetic rats was less sensitive to inhibition by NO donors or by AR inhibitors—sorbinil or tolrestat. Treatment with NG-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NO synthesis, enhanced AR activity and sorbitol accumulation in tissues of nondiabetic rats. Application of transdermal nitroglycerin patches or treatment with l-arginine did not inhibit AR activity or sorbitol accumulation in the tissues of nondiabetic animals. Treatment with l-NAME increased, whereas treatment with l-arginine or nitroglycerine patches decreased AR activity and sorbitol content in tissues of diabetic rats. These observations suggest that NO maintains AR in an inactive state and that this repression is relieved in diabetic tissues. Thus, increasing NO availability may be a useful strategy for inhibiting the polyol pathway and preventing the development of diabetes complications.
Insulin Stimulates Long-Chain Fatty Acid Utilization by Rat Cardiac Myocytes Through Cellular Redistribution of FAT/CD36
Authors: Luiken Joost J.F.P. , Koonen Debby P.Y. , Willems Jodil , Zorzano Antonio , Becker Christoph , Fischer Yvan , Tandon Narendra N. , van der Vusse Ger J. , Bonen Arend , Glatz Jan F.C.
Published: March 2007

The existence of an intracellular pool of fatty acid translocase (FAT/CD36), an 88-kDa membrane transporter for long-chain fatty acids (FAs), and the ability of insulin to induce translocation events prompted us to investigate the direct effects of insulin on cellular uptake of FA by the heart. Insulin (0.1 nmol/l and higher) increased FA uptake by isolated rat cardiac myocytes by 1.5-fold. This insulin-induced increase in FA uptake was completely blocked by phloretin, sulfo-N-succinimidylpalmitate (SSP), and wortmannin, indicating the involvement of FAT/CD36 and the dependence on phosphatidylinositol-3 (PI-3) kinase activation. Subcellular fractionation of insulin-stimulated cardiac myocytes demonstrated a 1.5-fold increase in sarcolemmal FAT/CD36 and a 62% decrease in intracellular FAT/CD36 with parallel changes in subcellular distribution of GLUT4. Induction of cellular contractions upon electrostimulation at 4 Hz enhanced cellular FA uptake 1.6-fold, independent of PI-3 kinase. The addition of insulin to 4 Hz-stimulated cells further stimulated FA uptake to 2.3-fold, indicating that there are at least two functionally independent intracellular FAT/CD36 pools, one recruited by insulin and the other mobilized by contractions. In conclusion, we have demonstrated a novel role of insulin in cardiac FA utilization. Malfunctioning of insulin-induced FAT/CD36 translocation may be involved in the development of type 2 diabetic cardiomyopathies.
A Polymorphism in the Glucocorticoid Receptor Gene, Which Decreases Sensitivity to Glucocorticoids In Vivo, Is Associated With Low Insulin and Cholesterol Levels
Authors: van Rossum Elisabeth F.C. , Koper Jan W. , Huizenga Nannette A.T.M. , Uitterlinden André G. , Janssen Joop A.M.J.L. , Brinkmann Albert O. , Grobbee Diederick E. , de Jong Frank H. , van Duyn Cornelia M. , Pols Huibert A.P. , Lamberts Steven W.J.
Published: March 2007

We investigated whether a polymorphism in codons 22 and 23 of the glucocorticoid (GC) receptor gene [GAGAGG(GluArg) → GAAAAG(GluLys)] is associated with altered GC sensitivity, anthropometric parameters, cardiovascular risk factors, and sex steroid hormones. In a subgroup of 202 healthy elderly subjects of the Rotterdam Study, we identified 18 heterozygotes (8.9%) for the 22/23EK allele (ER22/23EK carriers). In the highest age group, the number of ER22/23EK carriers was higher (67–82 years, 12.9%) than in the youngest age group (53–67 years, 4.9%; P < 0.05). Two dexamethasone (DEX) suppression tests with 1 and 0.25 mg DEX were performed, and serum cortisol and insulin concentrations were compared between ER22/23EK carriers and noncarriers. After administration of 1 mg DEX, the ER22/23EK group had higher serum cortisol concentrations (54.8 ± 18.3 vs. 26.4 ± 1.4 nmol/l, P < 0.0001), as well as a smaller decrease in cortisol (467.0 ± 31.7 vs. 484.5 ± 10.3 nmol/l, P < 0.0001). ER22/23EK carriers had lower fasting insulin concentrations (P < 0.001), homeostasis model assessment- insulin resistance (IR) (index of IR, P < 0.05), and total (P < 0.02) and LDL cholesterol concentrations (P < 0.01). Our data suggest that carriers of the 22/23EK allele are relatively more resistant to the effects of GCs with respect to the sensitivity of the adrenal feedback mechanism than noncarriers, resulting in a better metabolic health profile.
Comparison of Central and Peripheral Administration of C75 on Food Intake, Body Weight, and Conditioned Taste Aversion
Authors: Clegg Deborah J. , Wortman Matt D. , Benoit Stephen C. , McOsker Charles C. , Seeley Randy J.
Published: March 2007

Mice respond to fatty acid synthase (FAS) inhibitors by profoundly reducing their food intake and body weight. Evidence indicates that the central nervous system (CNS) may be the critical site of action; however, a peripheral contribution cannot be ruled out. We compared doses of the FAS inhibitor C75 in the CNS (third ventricle [i3vt]) and periphery (intraperitoneal [IP]) to reduce food intake and body weight in rats. Centrally, the threshold dose was 3 μg, whereas a dose of 10 mg/kg was required peripherally. Such data argue for FAS activity in the CNS as a potent target for the actions of C75. To control for nonspecific effects of FAS inhibition, we compared C75 administration in two models of illness, conditioned taste aversion and need-induced sodium appetite. Our results suggest the anorexia produced by IP C75 is accompanied by visceral illness, whereas the anorexia produced by i3vt is not. In addition, we placed animals in an indirect calorimeter after an IP injection of C75. We found that consistent with behavioral measures of visceral illness, peripheral C75 reduced heat expenditure and resulted in animals losing less weight than fasted control animals, suggesting that peripherally administered C75 has aversive properties. Understanding the mechanisms by which FAS inhibition in the CNS reduces food intake could lead to specific targets for the manipulation of energy balance and the treatment of obesity.
Decreased Myocardial Perfusion Reserve in Diabetic Autonomic Neuropathy
Authors: Taskiran Mustafa , Fritz-Hansen Thomas , Rasmussen Verner , Larsson Henrik B.W. , Hilsted Jannik
Published: March 2007

The pathophysiological mechanisms responsible for increased cardiovascular mortality in diabetic autonomic neuropathy are unknown. To investigate the effect of autonomic neuropathy on myocardial function, we performed dynamic contrast-enhanced magnetic resonance perfusion imaging during baseline conditions and after Dipyridamole-induced vasodilatation in nine type 1 diabetic patients with autonomic neuropathy (AN+), defined by cardiovascular tests, as well as in 10 type 1 diabetic patients without autonomic neuropathy (AN−) and 10 healthy control subjects. Baseline myocardial perfusion index (Ki) was similar in the three groups (AN+ 88.6 ± 8.7 ml · 100 g−1 · min−1, AN− 82.6 ± 7.2, control subjects 93.7 ± 9.0) (means ± SE). Ki during Dipyridamole vasodilatation was significantly lower in the patients with autonomic neuropathy (P < 0.001) than in the other groups (AN+ 131.1 ± 13.0 ml · 100 g−1 · min−1, AN− 177.3 ± 8.6, control subjects 197.2 ± 8.9). Mean blood pressure was unchanged during Dipyridamole infusion in AN− and control subjects, whereas a significant blood pressure decrease was found in AN+ (15.6 ± 2.6 mmHg, P < 0.025). There was a significant correlation between blood pressure response to Dipyridamole and myocardial perfusion reserve index. We conclude that type 1 diabetic patients with autonomic neuropathy have a decreased myocardial perfusion reserve capacity when challenged with a vasodilatator, a finding that may in part be the pathophysiological substrate for the increase in mortality in these patients. The underlying mechanism may be defective myocardial sympathetic vasodilatation, a lack of ability to maintain blood pressure during vasodilatation, or both.
A Functional Polymorphism in the Promoter of UCP2 Enhances Obesity Risk but Reduces Type 2 Diabetes Risk in Obese Middle-Aged Humans
Authors: Krempler Franz , Esterbauer Harald , Weitgasser Raimund , Ebenbichler Christoph , Patsch Josef R. , Miller Karl , Xie Mingqiang , Linnemayr Veronika , Oberkofler Hannes , Patsch Wolfgang
Published: March 2007

Obesity is frequently associated with type 2 diabetes. We previously observed an association of a functional G/A polymorphism in the uncoupling protein 2 (UCP2) promoter with obesity. The wild-type G allele was associated with reduced adipose tissue mRNA expression in vivo, reduced transcriptional activity in vitro, and increased risk of obesity. On the other hand, studies in animal and cell culture models identified pancreatic β-cell UCP2 expression as a main determinant of the insulin secretory response to glucose. We therefore ascertained associations of the −866G/A polymorphism with β-cell function and diabetes risk in obesity. We show here that the pancreatic transcription factor PAX6 preferentially binds to and more effectively trans activates the variant than the wild-type UCP2 promoter allele in the β-cell line INS1-E. By studying 39 obese nondiabetic humans, we observed genotype differences in β-cell function; wild-type subjects displayed a greater disposition index (the product of insulin sensitivity and acute insulin response to glucose) than subjects with the variant allele (P < 0.03). By comparing obese subjects with and without type 2 diabetes, we observed genotype-associated differences in diabetes prevalence that translated into a twofold age-adjusted risk reduction in wild-type subjects. Thus, the more common UCP2 promoter G allele, while being conducive for obesity, affords relative protection against type 2 diabetes.
Interleukin-18 Promoter Polymorphisms in Type 1 Diabetes
Authors: Kretowski Adam , Mironczuk Katarzyna , Karpinska Anna , Bojaryn Urszula , Kinalski Maciej , Puchalski Zbigniew , Kinalska Ida
Published: March 2007

Type 1 diabetes is believed to be a Th1 lymphocyte–mediated disease, and both environmental and genetic factors play a role in its pathogenesis. It was recently found that interleukin (IL)-18 acts as a proinflammatory cytokine and, in synergy with IL-12, promotes development of Th1 lymphocyte response by induction of γ-interferon production. The aim of our study was to evaluate the frequency of known polymorphisms in the IL-18 promoter in patients with type 1 diabetes in comparison with healthy control subjects, since higher levels of IL-18 were recently reported in the subclinical stage of type 1 diabetes. We studied two recently described single-nucleotide polymorphisms of the promoter of IL-18 gene at the position −137 and −607, which have been suggested to cause differences in transcription factor binding and have an impact on IL-18 gene activity. The genotype distribution differed significantly between patients with type 1 diabetes and control subjects. The difference reflected an increase in the GC genotypes and a decrease in GG genotypes at position −137 in the promoter of IL-18 gene. AA genotype at position −607 was found only in the control group. The results also demonstrated that the contribution of −137GC genotypes to genetic susceptibility to type 1 diabetes differs depending on the combination of IL-18 promotor gene haplotypes. Our study suggests the first evidence of an association between type 1 diabetes and polymorphisms in the promoter of IL-18 gene.
Lipolysis in the Absence of Hormone-Sensitive Lipase
Authors: Okazaki Hiroaki , Osuga Jun-ichi , Tamura Yoshiaki , Yahagi Naoya , Tomita Sachiko , Shionoiri Futoshi , Iizuka Yoko , Ohashi Ken , Harada Kenji , Kimura Satoshi , Gotoda Takanari , Shimano Hitoshi , Yamada Nobuhiro , Ishibashi Shun
Published: March 2007

Hormone-sensitive lipase (HSL) is presumed to be essential for lipolysis, which is defined as the mobilization of free fatty acids from adipocytes. In the present study, we investigated the effects of various lipolytic hormones on the lipolysis in adipocytes derived from mouse embryonic fibroblasts (MEF adipocytes) prepared from HSL-deficient mice (HSL−/−). HSL−/− MEF differentiated into mature adipocytes in a manner indistinguishable from that of wild-type mice. Both isoproterenol (ISO) and tumor necrosis factor (TNF)-α stimulated the rate of lipolysis in HSL−/− MEF adipocytes, although to a lesser extent than in wild-type cells, and these lipolytic activities were inhibited by H-89, a cAMP-dependent protein kinase inhibitor, and troglitazone, respectively. Thus, the responses of the residual lipolytic activity to lipolytic hormones and TNF-α were well conserved in the absence of HSL. Extracts from HSL−/− MEF adipocytes hydrolyzed triacylglycerol (TG) but not cholesterol ester, indicating that the residual lipolytic activity was mediated by another TG-specific lipase. The TG lipase activity, which was decreased in cytosolic fraction in response to ISO, was increased in fat cake fraction. Therefore, translocation of the TG lipase may explain, at least partially, the ISO-stimulated lipolysis in HSL−/− adipocytes. In conclusion, lipolysis is mediated not only by HSL but also by the non-HSL TG lipase, whose responses to lipolytic hormones are similar to those of HSL. We propose that both lipases are regulated by common mechanism of lipolysis.
The Role of Insulin in Human Brain Glucose Metabolism
Authors: Bingham Emma M. , Hopkins David , Smith Diarmuid , Pernet Andrew , Hallett William , Reed Laurence , Marsden Paul K. , Amiel Stephanie A.
Published: March 2007

The effect of basal insulin on global and regional brain glucose uptake and metabolism in humans was studied using 18-fluorodeoxyglucose and positron emission tomography (FDG-PET). Eight healthy male volunteers aged 49.3 ± 5.1 years were studied twice in random order. On each occasion, they received an infusion of 0.1 mg · kg−1 · min−1 somatostatin to suppress endogenous insulin production. In one study 0.3 mU · kg−1 · min−1 insulin was infused to replace basal circulating insulin levels, and in the other study a saline infusion was used as control. We sought stimulatory effects of basal insulin on brain glucose metabolism particularly in regions with deficiencies in the blood-brain barrier and high density of insulin receptors. Insulin levels were 27.07 ± 1.3 mU/l with insulin replacement and 3.51 ± 0.4 mU/l without (P = 0.001). Mean global rate of brain glucose utilization was 0.215 ± 0.030 mmol · kg−1 · min−1 without insulin and 0.245 ± 0.021 mmol · kg−1 · min−1 with insulin (P = 0.008, an average difference of 15.3 ± 12.5%). Regional analysis using statistical parametric mapping showed that the effect of basal insulin was significantly less in the cerebellum (Z = 5.53, corrected P = 0.031). We conclude that basal insulin has a role in regulating global brain glucose uptake in humans, mostly marked in cortical areas.
Fasting Plasma Ghrelin Levels Are Negatively Correlated With Insulin Resistance and PAI-1, but Not With Leptin, in Obese Children and Adolescents
Authors: Ikezaki Ayako , Hosoda Hiroshi , Ito Keiko , Iwama Saika , Miura Naoko , Matsuoka Hisafumi , Kondo Chisato , Kojima Masayasu , Kangawa Kenji , Sugihara Shigetaka
Published: March 2007

Ghrelin is a novel growth hormone−releasing peptide isolated from human and rat stomach that induces weight gain by increasing food intake and reducing fat utilization. Although recent data indicate that ghrelin is downregulated in human adult obesity, the characteristics of human obesity are heterogeneous, especially in children and adolescents, and depend on the distribution of subcutaneous and visceral fat tissue. We measured fasting plasma ghrelin concentrations by radioimmunoassay in 49 obese Japanese children and adolescents (38 boys and 11 girls; mean age 10.2 ± 2.8 years; BMI 28.0 ± 4.5 kg/m2, percent overweight 56.0 ± 20.7%), and analyzed associations of their ghrelin concentrations with their body composition, insulin resistance, and adipocytokine concentrations. Fasting plasma ghrelin levels were negatively correlated with BMI and waist circumference, but not with percent overweight or percent body fat, whereas fasting leptin levels were positively correlated with all of the following parameters: BMI, waist circumference, percent overweight, and percent body fat. Plasma ghrelin levels were negatively correlated with fasting immunoreactive insulin, homeostasis model assessment insulin resistance index, and quantitative insulin sensitivity check index values. There was no correlation between plasma ghrelin and leptin, but ghrelin was negatively correlated with the PAI-1 concentrations. The results suggest that the downregulation of ghrelin secretion may be a consequence of higher insulin resistance associated with visceral fat accumulation and elevated PAI-1 concentrations, and not a consequence of total body fat accumulation associated with elevated leptin concentrations.
Endothelin Contributes to Basal Vascular Tone and Endothelial Dysfunction in Human Obesity and Type 2 Diabetes
Authors: Mather Kieren J. , Mirzamohammadi Bahram , Lteif Amale , Steinberg Helmut O. , Baron Alain D.
Published: March 2007

Endothelium-dependent vasodilation is impaired in clinical states of insulin resistance such as obesity and type 2 diabetes. Individuals who have hyperinsulinemic insulin resistance have relatively elevated circulating levels of endothelin (ET)-1, suggesting that ET-1 may be important in the endothelial dysfunction and alterations of vascular tone in these conditions. In 8 lean subjects, 12 nondiabetic obese subjects, and 8 subjects with type 2 diabetes, we measured basal and methacholine-stimulated rates of leg blood flow (LBF) and total serum nitrates (NOx) before and after the intrafemoral arterial administration of BQ123, a specific blocker of ETA receptors. BQ123 produced significant vasodilation in the obese and type 2 diabetic subjects (leg vascular resistance = mean arterial pressure/LBF fell by 34 and 36%; P < 0.005) but not in the lean subjects (13%; P = NS, P = 0.018 comparing all groups). ETA blockade did not change basal NOx flux (NOx*LBF). This suggests increased basal ET-1 constrictor tone among obese and type 2 diabetic subjects. BQ123 corrected the baseline defect in endothelium-dependent vasodilation seen in obese and type 2 diabetic subjects, suggesting an important contribution of ET-1 to endothelial dysfunction in these subjects. In contrast to basal conditions, stimulated NOx flux was augmented by BQ123 in obese and type 2 diabetic subjects but not in L subjects (P = 0.04), suggesting a combined effect of ETA blockade to reduce constrictor tone and augment dilator tone. Endothelin seems to contribute to endothelial dysfunction and the regulation of vascular tone in human obesity and type 2 diabetes.
Local Sympathetic Denervation in Painful Diabetic Neuropathy
Authors: Tack Cees J. , van Gurp Petra J. , Holmes Courtney , Goldstein David S.
Published: March 2007

This study assessed whether painful diabetic neuropathy is associated with abnormal sympathetic nervous function in the affected limbs. Nine patients with diabetes (four men, five women; age 61 ± 7 years) and painful peripheral neuropathy of the feet, but without evidence of generalized autonomic neuropathy, underwent intravenous infusion of tritiated norepinephrine (NE) and sampling of arterial and venous blood in both feet and in one arm to quantify the rate of entry of NE into the local venous plasma (NE spillover). In the same patients, positron emission tomography (PET) scanning after intravenous injection of the sympathoneural imaging agent 6-[18F]fluorodopamine was used to visualize sympathetic innervation and after intravenous [13N]ammonia to visualize local perfusion. The results were compared with those in the feet of normal volunteers and in an unaffected foot of patients with unilateral complex regional pain syndrome (CRPS). In addition, neurochemical results obtained in painful diabetic neuropathy were compared with those obtained in diabetic control patients with painless neuropathy and diabetic control patients without neuropathy. Local arteriovenous difference in plasma NE levels (ΔNEAV) and NE spillover in the arms did not differ across the groups. However, ΔNEAV in the feet was significantly less in the group with painful diabetic neuropathy than in the control groups. Also NE spillover in the feet tended to be lower in painful neuropathy. ΔNEAV of diabetic control patients without neuropathy (n = 6) resembled values in the control groups without diabetes, whereas patients with painless diabetic neuropathy (n = 6) had evidence suggesting partial loss of sympathetic innervation. PET scanning revealed decreased flow-corrected 6-[18F]fluorodopamine-derived radioactivity in patients with painful diabetic neuropathy, compared with values in normal volunteers and patients with CRPS. The results provide neurochemical and neuroimaging evidence for regionally selective sympathetic denervation in the painful feet of patients with diabetic neuropathy.
Indoleamine 2,3-Dioxygenase Expression in Transplanted NOD Islets Prolongs Graft Survival After Adoptive Transfer of Diabetogenic Splenocytes
Authors: Alexander Angela M. , Crawford Megan , Bertera Suzanne , Rudert William A. , Takikawa Osamu , Robbins Paul D. , Trucco Massimo
Published: March 2007

Indoleamine 2,3-dioxygenase (IDO) catalyzes the breakdown of the amino acid tryptophan into kyneurenine. It has been shown that IDO production by placental trophoblasts prevents the attack of maternal T-cells activated in response to the paternal HLA alleles expressed by the tissues of the fetus. In this article, we show that adenoviral gene transfer of IDO to pancreatic islets can sufficiently deplete culture media of tryptophan and consequently inhibit the proliferation of T-cells in vitro. Experiments in vivo have also demonstrated that transplantation of IDO-expressing islets from prediabetic NOD mouse donors into NODscid recipient mice is associated with a prolongation in islet graft survival after adoptive transfer of NOD diabetogenic T-cells. This protection is attributed to the depletion of tryptophan at the transplantation site beneath the kidney capsule. These results suggest that local modulation of tryptophan catabolism may be a means of facilitating islet transplantation as a therapy for type 1 diabetes.
Acyl-CoA Binding Protein Expression Is Fiber Type- Specific and Elevated in Muscles From the Obese Insulin-Resistant Zucker Rat
Authors: Franch Jesper , Knudsen Jens , Ellis Bronwyn A. , Pedersen Preben K. , Cooney Gregory J. , Jensen Jørgen
Published: March 2007

Accumulation of acyl-CoA is hypothesized to be involved in development of insulin resistance. Acyl-CoA binds to acyl-CoA binding protein (ACBP) with high affinity, and therefore knowledge about ACBP concentration is important for interpreting acyl-CoA data. In the present study, we used a sandwich enzyme-linked immunosorbent assay to quantify ACBP concentration in different muscle fiber types. Furthermore, ACBP concentration was compared in muscles from lean and obese Zucker rats. Expression of ACBP was highest in the slow-twitch oxidative soleus muscle and lowest in the fast-twitch glycolytic white gastrocnemius (0.46 ± 0.02 and 0.16 ± 0.005 μg/mg protein, respectively). Expression of ACBP was soleus > red gastrocnemius > extensor digitorum longus > white gastrocnemius. Similar fiber type differences were found for carnitine palmitoyl transferase (CPT)-1, and a correlation was observed between ACBP and CPT-1. Muscles from obese Zucker rats had twice the triglyceride content, had approximately twice the long-chain acyl CoA content, and were severely insulin resistant. ACBP concentration was ∼30% higher in all muscles from obese rats. Activities of CPT-1 and 3-hydroxy-acyl-CoA dehydrogenase were increased in muscles from obese rats, whereas citrate synthase activity was similar. In conclusion, ACBP expression is fiber type-specific with the highest concentration in oxidative muscles and the lowest in glycolytic muscles. The 90% increase in the concentration of acyl-CoA in obese Zucker muscle compared with only a 30% increase in the concentration of ACBP supports the hypothesis that an increased concentration of free acyl-CoA is involved in the development of insulin resistance.