bluuebunny/crossref_metadata_2025 huggingface dataset:
Liver Markers and Development of the Metabolic Syndrome
Authors: Hanley Anthony J.G. , Williams Ken , Festa Andreas , Wagenknecht Lynne E. , D’Agostino Ralph B. , Haffner Steven M.
Published: March 2007

Nonalcoholic fatty liver disease (NAFLD) is emerging as a component of the metabolic syndrome, although it is not known whether markers of NAFLD, including elevated concentrations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALK), predict the development of metabolic syndrome. Our objective was to investigate the associations of elevated AST, ALT, and other liver markers, including C-reactive protein (CRP), with incident National Cholesterol Education Program–defined metabolic syndrome among 633 subjects in the Insulin Resistance Atherosclerosis Study who were free of metabolic syndrome at baseline. Insulin sensitivity (Si) and acute insulin response (AIR) were directly measured from the frequently sampled intravenous glucose tolerance test among African-American, Hispanic, and non-Hispanic white subjects aged 40–69 years. After 5.2 years, 127 individuals had developed metabolic syndrome. In separate logistic regression models adjusting for age, sex, ethnicity, clinic, and alcohol consumption, subjects in the upper quartiles of ALT, ALK, and CRP were at significantly increased risk of incident metabolic syndrome compared with those in the lowest quartile: ALT, odds ratio 2.50 (95% CI 1.38–4.51); ALK, 2.28 (1.24–4.20); and CRP, 1.33 (1.09–1.63). Subjects in the upper quartile of the AST-to-ALT ratio were at significantly reduced metabolic syndrome risk (0.40 [0.22–0.74]). After further adjustment for waist circumference, Si, AIR, and impaired glucose tolerance, the associations of ALT and the AST-to-ALT ratio with incident metabolic syndrome remained significant (ALT, 2.12 [1.10–4.09]; the AST-to-ALT ratio, 0.48 [0.25–0.95]). These associations were not modified by ethnicity or sex, and they remained significant after exclusion of former and heavy drinkers. In conclusion, NAFLD markers ALT and the AST-to-ALT ratio predict metabolic syndrome independently of potential confounding variables, including directly measured Si and AIR.
Apoptotic Stress Is Counterbalanced by Survival Elements Preventing Programmed Cell Death of Dorsal Root Ganglions in Subacute Type 1 Diabetic BB/Wor Rats
Authors: Kamiya Hideki , Zhangm Weixian , Sima Anders A.F.
Published: March 2007

Several groups have reported apoptosis of dorsal root ganglion (DRG) cells as a prominent feature of diabetic polyneuropathy (DPN), although this has been controversial. Here, we examined subacute (4-month) type 1 diabetic BB/Wor rats with respect to sensory nerve functions, DRG and sural nerve morphometry, pro- and antiapoptotic proteins, and the expression of neurotrophic factors and their receptors. Sensory nerve conduction velocity was reduced by 13% and was accompanied by significant hyperalgesia. The numbers of DRG neurons including substance P–and calcitonin gene–related peptide–positive neurons were not altered, although they showed significant atrophy. Sural nerve morphometry showed decreased numbers of myelinated and unmyelinated fibers. Active caspase-3 and Bax expressions were increased, whereas antiapoptotic Bcl-xl and heat shock protein (HSP) 27 expressions in DRGs were increased. Nerve growth factor (NGF) contents in sciatic nerves and the expression of NGF receptor TrkA in DRGs were decreased. Immunohistochemistry showed increased numbers of active caspase-3–, HSP70-, and HSP27-positive neurons. Examinations of DRGs revealed no structural evidence of apoptosis but rather progressive hydropic degenerative changes. We conclude that apoptotic stress is induced in DRGs but is counterbalanced by survival elements in subacute type 1 diabetic BB/Wor rats and that distal nerve fiber loss reflects a dying-back phenomenon caused by impaired neurotrophic support.
Assessment of 115 Candidate Genes for Diabetic Nephropathy by Transmission/Disequilibrium Test
Authors: Ewens Kathryn Gogolin , George Roberta Ann , Sharma Kumar , Ziyadeh Fuad N. , Spielman Richard S.
Published: March 2007

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.
Expression of Inducible 6-Phosphofructo-2-Kinase/Fructose-2,6-Bisphosphatase/PFKFB3 Isoforms in Adipocytes and Their Potential Role in Glycolytic Regulation
Authors: Atsumi Toshiya , Nishio Taro , Niwa Hirokatsu , Takeuchi Jun , Bando Hidenori , Shimizu Chikara , Yoshioka Narihito , Bucala Richard , Koike Takao
Published: March 2007

6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase) catalyzes the synthesis and degradation of fructose 2,6-bisphosphate (F2,6BP), which is a powerful activator of 6-phosphofructo-1-kinase, the rate-limiting enzyme of glycolysis. Four genes encode PFK-2/FBPase (PFKFB1–4), and an inducible isoform (iPFK-2/PFKFB3) has been found to mediate F2,6BP production in proliferating cells. We have investigated the role of iPFK-2/PFKFB3 and related isoforms in the regulation of glycolysis in adipocytes. Human visceral fat cells express PFKFB3 mRNA, and three alternatively spliced isoforms of iPFK-2/PFKFB3 are expressed in the epididymal fat pad of the mouse. Forced expression of the iPFK-2/PFKFB3 in COS-7 cells resulted in increased glucose uptake and cellular F2,6BP content. Prolonged insulin treatment of 3T3-L1 adipocytes led to reduced PFKFB3 mRNA expression, and epididymal fat pads from db/db mice also showed decreased expression of PFKFB3 mRNA. Finally, anti–phospho-iPFK-2(Ser461) Western blotting revealed strong reactivity in insulin-treated 3T3-L1 adipocyte, suggesting that insulin induces the phosphorylation of PFKFB3 protein. These data expand the role of these structurally unique iPFK-2/PFKFB3 isoforms in the metabolic regulation of adipocytes.
Whole-body Insulin Resistance in the Absence of Obesity in FVB Mice With Overexpression of Dgat1 in Adipose Tissue
Authors: Chen Nancy , Liu Li , Zhang Yiying , Ginsberg Henry N. , Yu Yi-Hao
Published: March 2007

Insulin resistance is often associated with obesity. We tested whether augmentation of triglyceride synthesis in adipose tissue by transgenic overexpression of the diacylglycerol aclytransferase-1 (Dgat1) gene causes obesity and/or alters insulin sensitivity. Male FVB mice expressing the aP2-Dgat1 had threefold more Dgat1 mRNA and twofold greater DGAT activity levels in adipose tissue. After 30 weeks of age, these mice had hyperglycemia, hyperinsulinemia, and glucose intolerance on a high-fat diet but were not more obese than wild-type littermates. Compared with control littermates, Dgat1 transgenic mice were both insulin and leptin resistant and had markedly elevated plasma free fatty acid levels. Adipocytes from Dgat1 transgenic mice displayed increased basal and isoproterenol-stimulated lipolysis rates and decreased gene expression for fatty acid uptake. Muscle triglyceride content was unaffected, but liver mass and triglyceride content were increased by 20 and 300%, respectively. Hepatic insulin signaling was suppressed, as evidenced by decreased phosphorylation of insulin receptor-β (Tyr1,131/Tyr1,146) and protein kinase B (Ser473). Gene expression data suggest that the gluconeogenic enzymes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, were upregulated. Thus, adipose overexpression of Dgat1 gene in FVB mice leads to diet-inducible insulin resistance, which is secondary to redistribution of fat from adipose tissue to the liver in the absence of obesity.
Aspirin at Low-Intermediate Concentrations Protects Retinal Vessels in Experimental Diabetic Retinopathy Through Non–Platelet-Mediated Effects
Authors: Sun Wei , Gerhardinger Chiara , Dagher Zeina , Hoehn Todd , Lorenzi Mara
Published: March 2007

The prevention of diabetic retinopathy requires drugs that leverage the benefits of glycemic control without adding the burden of side effects. Aspirin at dosages of 1–1.5 g/day has prevented manifestations of diabetic retinal microangiopathy in a clinical trial as well as in studies with dogs. Because lower and safer doses of aspirin could be used if its beneficial effects on retinopathy were due to antithrombotic effects, we compared the effects of a selective antiplatelet drug (clopidogrel) to those of aspirin in streptozotocin-induced diabetic rats. Clopidogrel did not prevent neuronal apoptosis, glial reactivity, capillary cell apoptosis, or acellular capillaries in the retina of diabetic rats. Aspirin, at doses yielding serum levels (<0.6 mmol/l) well below the anti-inflammatory range for humans, prevented apoptosis of capillary cells and the development of acellular capillaries but did not prevent neuroglial abnormalities. The aldose reductase inhibitor sorbinil, used as the benchmark for the effect of the other drugs, prevented all abnormalities. The diabetic rat retina showed increased expression of the transcription factor CCAAT/enhancer-binding protein-β, one of the known targets of low-intermediate concentrations of aspirin. Thus we found a spectrum of drug efficacy on the prevention of experimental diabetic retinopathy, ranging from the absent effect of a selective antiplatelet drug to the prevention of all abnormalities by an aldose reductase inhibitor. Aspirin at low-intermediate concentrations selectively prevented microangiopathy. The minimal effective dose of aspirin should now be sought.
Localization ofIdd11Is Not Associated With Thymus and NKT Cell Abnormalities in NOD Mice
Authors: Brodnicki Thomas C. , Fletcher Anne L. , Pellicci Daniel G. , Berzins Stuart P. , McClive Peter , Quirk Fiona , Webster Kylie E. , Scott Hamish S. , Boyd Richard L. , Godfrey Dale I. , Morahan Grant
Published: March 2007

Congenic mouse strains provide a unique resource for genetic dissection and biological characterization of chromosomal regions associated with diabetes progression in the nonobese diabetic (NOD) mouse. Idd11, a mouse diabetes susceptibility locus, was previously localized to a region on chromosome 4. Comparison of a panel of subcongenic NOD mouse strains with different intervals derived from the nondiabetic C57BL/6 (B6) strain now maps Idd11 to an ∼8-Mb interval. B6-derived intervals protected congenic NOD mice from diabetes onset, even though lymphocytic infiltration of pancreatic islets was similar to that found in NOD mice. In addition, neither thymic structural irregularities nor NKT cell deficiencies were ameliorated in diabetes-resistant congenic NOD mice, indicating that Idd11 does not contribute to these abnormalities, which do not need to be corrected to prevent disease.
A Reduced-Fat Diet and Aerobic Exercise in Japanese Americans With Impaired Glucose Tolerance Decreases Intra-Abdominal Fat and Improves Insulin Sensitivity but not β-Cell Function
Authors: Carr Darcy B. , Utzschneider Kristina M. , Boyko Edward J. , Asberry Pamela J. , Hull Rebecca L. , Kodama Keiichi , Callahan Holly S. , Matthys Colleen C. , Leonetti Donna L. , Schwartz Robert S. , Kahn Steven E. , Fujimoto Wilfred Y.
Published: March 2007

Lifestyle modification reduces the risk of developing type 2 diabetes and may have its effect through improving insulin sensitivity, β-cell function, or both. To determine whether diet and exercise improve insulin sensitivity and/or β-cell function and to evaluate these effects over time, we quantified insulin sensitivity and the acute insulin response to glucose (AIRg) in 62 Japanese Americans (age 56.5 ± 1.3 years; mean ± SE) with impaired glucose tolerance (IGT) who were randomized to the American Heart Association (AHA) Step 2 diet plus endurance exercise (n = 30) versus the AHA Step 1 diet plus stretching (n = 32) for 24 months. β-Cell function (disposition index [DI]) was calculated as Si × AIRg, where Si is the insulin sensitivity index. The incremental area under the curve for glucose (incAUCg) was calculated from a 75-g oral glucose tolerance test. Intra-abdominal fat (IAF) and subcutaneous fat (SCF) areas were measured by computed tomography. At 24 months, the Step 2/endurance group had lower weight (63.1 ± 2.4 vs. 71.3 ± 2.9 kg; P = 0.004) and IAF (75.0 ± 7.9 vs. 112.7 ± 10.4 cm2; P = 0.03) and SCF (196.5 ± 18.0 vs. 227.7 ± 19.9 cm2; P < 0.001) areas, greater Si (4.7 ± 0.5 vs. 3.3 ± 0.3 × 10−5 min · pmol−1 · l−1; P = 0.01), and a trend toward lower AIRg (294.9 ± 50.0 vs. 305.4 ± 30.0 pmol/l; P = 0.06) and incAUCg (8,217.3 ± 350.7 vs. 8,902.0 ± 367.2 mg · dl−1 · 2 h−1; P = 0.08) compared with the Step 1/stretching group after adjusting for baseline values. There was no difference in the DI (P = 0.7) between the groups. Si was associated with changes in weight (r = −0.426, P = 0.001) and IAF (r = −0.395, P = 0.003) and SCF (r = −0.341, P = 0.01) areas. Thus, the lifestyle modifications decreased weight and central adiposity and improved insulin sensitivity in Japanese Americans with IGT. However, such changes did not improve β-cell function, suggesting that this degree of lifestyle modifications may be limited in preventing type 2 diabetes over the long term.
Portal Venous 5-Aminoimidazole-4-Carboxamide-1-β-d-Ribofuranoside Infusion Overcomes Hyperinsulinemic Suppression of Endogenous Glucose Output
Authors: Camacho Raul C. , Pencek R. Richard , Lacy D. Brooks , James Freyja D. , Donahue E. Patrick , Wasserman David H.
Published: March 2007

AMP-activated protein kinase (AMPK) plays a key role in regulating metabolism, serving as a metabolic master switch. The aim of this study was to assess whether increased concentrations of the AMP analog, 5-aminoimidazole-4-carboxamide-1-β-d-ribosyl-5-monophosphate, in the liver would create a metabolic response consistent with an increase in whole-body metabolic need. Dogs had sampling (artery, portal vein, hepatic vein) and infusion (vena cava, portal vein) catheters and flow probes (hepatic artery, portal vein) implanted >16 days before a study. Protocols consisted of equilibration (−130 to −30 min), basal (−30 to 0 min), and hyperinsulinemic-euglycemic or -hypoglycemic clamp periods (0–150 min). At t = 0 min, somatostatin was infused and glucagon was replaced in the portal vein at basal rates. An intraportal hyperinsulinemic (2 mU · kg−1 · min−1) infusion was also initiated at this time. Glucose was clamped at hypoglycemic or euglycemic levels in the presence (H-AIC, n = 6; E-AIC, n = 6) or absence (H-SAL, n = 6; E-SAL, n = 6) of a portal venous 5-aminoimidazole-4-carboxamide-ribofuranoside (AICAR) infusion (1 mg · kg−1 · min−1) initiated at t = 60 min. In the presence of intraportal saline, glucose was infused into the vena cava to match glucose levels seen with intraportal AICAR. Glucagon remained fixed at basal levels, whereas insulin rose similarly in all groups. Glucose fell to 50 ± 2 mg/dl by t = 60 min in hypoglycemic groups and remained at 105 ± 3 mg/dl in euglycemic groups. Endogenous glucose production (Ra) was similarly suppressed among groups in the presence of euglycemia or hypoglycemia before t = 60 min and remained suppressed in the H-SAL and E-SAL groups. However, intraportal AICAR infusion stimulated Ra to increase by 2.5 ± 1.0 and 3.4 ± 0.4 mg · kg−1 · min−1 in the E-AIC and H-AIC groups, respectively. Arteriovenous measurement of net hepatic glucose output showed similar results. AICAR stimulated hepatic glycogen to decrease by 5 ± 3 and 19 ± 5 mg/g tissue (P < 0.05) in the presence of euglycemia and hypoglycemia, respectively. AICAR significantly increased net hepatic lactate output in the presence of hypoglycemia. Thus, intraportal AICAR infusion caused marked stimulation of both hepatic glucose output and net hepatic glycogenolysis, even in the presence of high levels of physiological insulin. This stimulation of glucose output by AICAR was equally marked in the presence of both euglycemia and hypoglycemia. However, hypoglycemia amplified the net hepatic glycogenolytic response to AICAR by approximately fourfold.
Hyperglycemia ActivatesJAK2 Signaling Pathway in Human Failing Myocytes via AngiotensinII–Mediated Oxidative Stress
Authors: Modesti Alessandra , Bertolozzi Iacopo , Gamberi Tania , Marchetta Matilde , Lumachi Camilla , Coppo Mirella , Moroni Federico , Toscano Thomas , Lucchese Gianluca , Gensini Gian F. , Modesti Pietro A.
Published: March 2007

Hyperglycemia was reported to enhance angiotensin (Ang) II generation in rat cardiomyocytes, and Ang II inhibition reduces cardiovascular morbidity and mortality in diabetic patients. In diabetic patients, the enhanced activation of intracellular pathways related with myocyte hypertrophy and gene expression might enhance the progression of cardiac damage. Therefore, we investigated the effects of glucose on Ang II–mediated activation of Janus-activated kinase (JAK)-2, a tyrosine kinase related with myocyte hypertrophy and cytokine and fibrogenetic growth factor overexpression, in ventricular myocytes isolated from nonfailing human hearts (n = 5) and failing human hearts (n = 8). In nonfailing myocytes, JAK2 phosphorylation was enhanced by Ang II only in the presence of high glucose (25 mmol/l) via Ang II type I (AT1) receptors (+79% vs. normal glucose, P < 0.05). JAK2 activation was prevented by inhibitors of reactive oxygen species (ROS) generation (diphenyleneiodonium [DPI], tiron, and apocynin). In myocytes isolated from failing hearts, JAK2 phosphorylation was enhanced by high glucose alone (+107%, P < 0.05). High glucose–induced JAK2 activation was blunted by both ACE inhibition (100 nmol/l ramipril) and AT1 antagonism (1 μmol/l valsartan), thus revealing that the effects are mediated by autocrine Ang II production. Inhibition of ROS generation also prevented high glucose–induced JAK2 phosphorylation. In conclusion, in human nonfailing myocytes, high glucose allows Ang II to activate JAK2 signaling, whereas in failing myocytes, hyperglycemia alone is able to induce Ang II generation, which in turn activates JAK2 via enhanced oxidative stress.
Folic Acid Supplementation Diminishes Diabetes- and Glucose-Induced Dysmorphogenesis in Rat Embryos In Vivo and In Vitro
Authors: Wentzel Parri , Gäreskog Mattias , Eriksson Ulf J.
Published: March 2007

Maternal administration of folic acid diminishes the risk of neural tube defects (NTDs) in offspring, but whether folic acid exerts a similar effect in diabetic pregnancy is unknown. The aim was to investigate whether maldevelopment in rat embryos caused by exposure to diabetes in vivo or high-glucose concentrations in vitro is affected by subcutaneous administration of folic acid to the pregnant mother or by adding the compound to the culture medium, respectively. Exposure of embryos to maternal diabetes in vivo or 30 mmol/l glucose in vitro yielded an increased malformation rate (71 and 88% NTD, respectively) and lowered somite number and crown-rump length compared with control embryos. When we injected folic acid into the diabetic pregnant rat, or added 2 mmol/l folic acid to the culture medium with high glucose, the embryonic parameters improved (3 and 5% NTD, respectively). The present work shows that administration of folic acid can diminish diabetes-induced maldevelopment. This suggests that folic acid supplementation may have a role in the prevention of malformations in diabetic pregnancy.
Rosiglitazone Treatment in Zucker Diabetic Fatty Rats Is Associated With Ameliorated Cardiac Insulin Resistance and Protection From Ischemia/Reperfusion-Induced Myocardial Injury
Authors: Yue Tian-Li , Bao Weike , Gu Juan-Li , Cui Jianqi , Tao Ling , Ma Xin-Liang , Ohlstein Eliot H. , Jucker Beat M.
Published: March 2007

The mechanism responsible for the enhanced myocardial susceptibility to ischemic insult in patients with type 2 diabetes is not clear. The present study examines the effect of rosiglitazone treatment on cardiac insulin sensitization and its association with cardioprotection from ischemia/reperfusion injury in an animal model of diabetes. Male Zucker diabetic fatty (ZDF) rats were treated with rosiglitazone (3 mg · kg−1 · day−1 orally) or vehicle for 8 days before undergoing 30 min of coronary artery ligation, followed by reperfusion for 4 h (apoptosis) or 24 h (infarction). Rosiglitazone reduced the blood levels of glucose, triglycerides, and free fatty acids; enhanced cardiac glucose oxidation; and increased Akt phosphorylation (Akt-pS473) 2.1-fold and Akt kinase activity 1.8-fold in the ischemic myocardium. The phosphorylation of two downstream targets of Akt, glycogen synthase kinase-3β and FKHR (forkhead transcription factor), was also enhanced by 2- and 2.9-fold, respectively. In rosiglitazone-treated rats, the number of apoptotic cardiomyocytes and the myocardial infarct size were decreased by 58 and 46%, respectively, and the myocardial contractile dysfunction was improved. Blockade of the insulin-Akt signaling pathway by wortmannin in the 8-day rosiglitazone-treated ZDF rats resulted in a markedly diminished cardioprotective effect of rosiglitazone. In addition, 8-day rosiglitazone treatment in Zucker lean rats or 2-day rosiglitazone treatment in ZDF rats, both of which showed no change in whole-body insulin sensitivity, resulted in a significant reduction in cardiac infarct size, but to a lesser degree when compared with that observed in 8-day rosiglitazone–treated ZDF rats. These results suggest that chronic treatment with rosiglitazone protects the heart against ischemia/reperfusion injury in ZDF rats, and that the enhanced cardiac protection observed after rosiglitazone treatment might be attributable in part to an improvement in cardiac insulin sensitivity.
Matrix Metalloproteinases 2 and 9 Are Dispensable for Pancreatic Islet Formation and Function In Vivo
Authors: Perez Sabina E. , Cano David A. , Dao-Pick Trang , Rougier Jean-Phillipe , Werb Zena , Hebrok Matthias
Published: March 2007

Pancreatic islet formation is a highly regulated process that is initiated at the end of gestation in rodents. Endocrine precursor cells first form within the epithelium of duct-like structures and then delaminate from the epithelium, migrate, and cluster during the early stages of islet formation. The molecular mechanisms that regulate endocrine cell migration and islet formation are not well understood. Cell culture studies suggest that matrix metalloproteinases (MMPs) 2 and 9 are required for islet formation. To address whether MMP2 and MMP9 function are essential for endocrine cell migration and islet formation in vivo, we analyzed pancreas development in MMP2/MMP9 double-deficient mice. Our results show that islet architecture and function are unperturbed in these knockout mice, demonstrating that both MMP2 and MMP9 functions are dispensable for islet formation and endocrine cell differentiation. Our studies also show that a number of other MMPs are expressed at the time islet formation is initiated. This observation suggests that other MMPs may substitute for MMP2 and MMP9 loss in pancreatic tissue. However, islet formation is unaffected in transgenic mice with modified tissue inhibitor of metalloproteinase-1 (TIMP1) levels, suggesting that MMP activity may contribute little to islet morphogenesis in vivo.
Regulated Exocytosis and Kiss-and-Run of Synaptic-Like Microvesicles in INS-1 and Primary Rat β-Cells
Authors: MacDonald Patrick E. , Obermüller Stefanie , Vikman Jenny , Galvanovskis Juris , Rorsman Patrik , Eliasson Lena
Published: March 2007

We have applied cell-attached capacitance measurements to investigate whether synaptic-like microvesicles (SLMVs) undergo regulated exocytosis in insulinoma and primary pancreatic β-cells. SLMV and large dense-core vesicle (LDCV) exocytosis was increased 1.6- and 2.4-fold upon stimulation with 10 mmol/l glucose in INS-1 cells. Exocytosis of both types of vesicles was coupled to Ca2+ entry through l-type channels. Thirty percent of SLMV exocytosis in INS-1 and rat β-cells was associated with transient capacitance increases consistent with kiss-and-run. Elevation of intracellular cAMP (5 μmol/l forskolin) increased SLMV exocytosis 1.6-fold and lengthened the duration of kiss-and-run events in rat β-cells. Experiments using isolated inside-out patches of INS-1 cells revealed that the readily releasable pool (RRP) of SLMVs preferentially undergoes kiss-and-run exocytosis (67%), is proportionally larger than the LDCV RRP, and is depleted more quickly upon Ca2+ stimulation. We conclude that SLMVs undergo glucose-regulated exocytosis and are capable of high turnover. Following kiss-and-run exocytosis, the SLMV RRP may be reloaded with γ-aminobutyric acid and undergo several cycles of exo- and endocytosis. Our observations support a role for β-cell SLMVs in a synaptic-like function of rapid intra-islet signaling.
Effects of Sustained Insulin-Induced Hypoglycemia on Cardiovascular Autonomic Regulation in Type 1 Diabetes
Authors: Koivikko Minna L. , Salmela Pasi I. , Airaksinen K.E. Juhani , Tapanainen Juha S. , Ruokonen Aimo , Mäkikallio Timo H. , Huikuri Heikki V.
Published: March 2007

Effects of hypoglycemia on cardiac autonomic regulation may contribute to the occurrence of adverse cardiac events. This study assessed the effects of sustained hyperinsulinemic hypoglycemia on cardiovascular autonomic regulation in type 1 diabetic patients and their nondiabetic counterparts. The study consisted of 16 type 1 diabetic patients and 8 age-matched healthy control subjects who underwent euglycemic and hypoglycemic clamp procedures in a random order. Heart rate variability was measured from continuous electrocardiogram recordings by time and frequency domain methods, along with Poincaré plot analysis during both a hyperinsulinemic-euglycemic and hypoglycemic clamp at three different glucose levels (4.5–5.5, 3.0–3.5, and 2.0–2.5 mmol/l). Controlled hypoglycemia resulted in an increase of supine heart rate in both the diabetic patients (from 72 ± 9 to 80 ± 11 bpm, P < 0.01) and the control subjects (from 59 ± 5 to 65 ± 5 bpm, P < 0.05) and progressive reductions of the high-frequency spectral component and beat-to-beat heart rate variability (SD1; P < 0.05 in the diabetic patients and P < 0.01 in control subjects). No significant changes in heart rate variability occurred during the euglycemic clamp. We conclude that hypoglycemia results in a reduction of cardiac vagal outflow in both diabetic and nondiabetic subjects. Altered autonomic regulation may contribute to the occurrence of cardiac events during hypoglycemia.
Thiazolidinediones Upregulate Fatty Acid Uptake and Oxidation in Adipose Tissue of Diabetic Patients
Authors: Boden Guenther , Homko Carol , Mozzoli Maria , Showe Louise C. , Nichols Calen , Cheung Peter
Published: March 2007

Thiazolidinediones (TZDs) are a new class of insulin-sensitizing drugs. To explore how and in which tissues they improve insulin action, we obtained fat and muscle biopsies from eight patients with type 2 diabetes before and 2 months after treatment with rosiglitazone (n = 5) or troglitazone (n = 3). TZD treatment was associated with a coordinated upregulation in the expression of genes and synthesis of proteins involved in fatty acid uptake, binding, β-oxidation and electron transport, and oxidative phosphorylation in subcutaneous fat but not in skeletal muscle. These changes were accompanied by a 13% increase in total body fat oxidation, a 20% decrease in plasma free fatty acid levels, and a 46% increase in insulin-stimulated glucose uptake. We conclude that TZDs induced a coordinated stimulation of fatty acid uptake, oxidation, and oxidative phosphorylation in fat of diabetic patients and thus may have corrected, at least partially, a recently recognized defect in patients with type 2 diabetes consisting of reduced expression of genes related to oxidative metabolism and mitochondrial function.
The Common Polymorphisms (Single Nucleotide Polymorphism [SNP] +45 and SNP +276) of the Adiponectin Gene Predict the Conversion From Impaired Glucose Tolerance to Type 2 Diabetes
Authors: Zacharova Jelena , Chiasson Jean-Louis , Laakso Markku ,   the STOP-NIDDM Study Group
Published: March 2007

Adiponectin is an adipose tissue-specific protein with insulin-sensitizing and antiatherogenic properties. Therefore, the adiponectin gene is a promising candidate gene for type 2 diabetes. We investigated the single nucleotide polymorphisms (SNPs) +45T/G and +276G/T of the adiponectin gene as predictors for the conversion from impaired glucose tolerance to type 2 diabetes in the STOP-NIDDM trial, which aimed to investigate the effect of acarbose compared with placebo on the prevention of type 2 diabetes. Compared with the TT genotype, the G-allele of SNP +45 was associated with a 1.8-fold risk for type 2 diabetes (95% CI 1.12–3.00, P = 0.015) in the placebo group. Subjects treated with placebo and simultaneously having the G-allele of SNP +45 and the T-allele of SNP +276 (the risk genotype combination) had a 4.5-fold (1.78–11.3, P = 0.001) higher risk of developing type 2 diabetes compared with subjects carrying neither of these alleles. Women carrying the risk genotype combination had an especially high risk of conversion to diabetes (odds ratio 22.2, 95% CI 2.7–183.3, P = 0.004). In conclusion, the G-allele of SNP +45 is a predictor for the conversion to type 2 diabetes. Furthermore, the combined effect of SNP +45 and SNP +276 on the development of type 2 diabetes was stronger than that of each SNP alone.
The Role of Amylin and Glucagon in the Dampening of Glycemic Excursions in Children With Type 1 Diabetes
Authors: Heptulla Rubina A. , Rodriguez Luisa M. , Bomgaars Lisa , Haymond Morey W.
Published: March 2007

Postprandial hyperglycemia and preprandial hypoglycemia contribute to poor glycemic control in type 1 diabetes. We hypothesized that postprandial glycemic excursions could be normalized in type 1 diabetes by suppressing glucagon with pramlintide acetate in the immediate postprandial period and supplementing glucagon in the late postprandial period. A total of 11 control subjects were compared with 8 type 1 diabetic subjects on insulin pump therapy, using the usual insulin bolus–to–carbohydrate ratio during a standard liquid meal. Type 1 diabetic subjects were then randomized to two open-labeled studies. On one occasion, type 1 diabetic subjects received a 60% increase in the insulin bolus–to–carbohydrate ratio with minidose glucagon rescue injections, and on the other occasion type 1 diabetic subjects received 30–45 μg pramlintide with their usual insulin bolus–to–carbohydrate ratio. Glucose, glucagon, amylin (pramlintide), and insulin concentrations were measured for 420 min. The plasma glucose area under the curve (AUC) for 0–420 min was lower in control versus type 1 diabetic subjects (316 ± 5 vs. 929 ± 18 mg · h−1 · dl−1, P < 0.0001). Pramlintide, but not an increase in insulin, reduced immediate postprandial hyperglycemia (AUC0–180 min 470 ± 43 vs. 434 ± 48 mg · h−1 · dl−1, P < 0.01). Pramlintide administration suppressed glucagon (P < 0.02), and glucagon injections prevented late hypoglycemia with increased insulin. In summary, in type 1 diabetes, glucagon modulation with pramlintide as an adjunct to insulin therapy may prove beneficial in controlling postmeal glycemic swings.
Skeletal Muscle Lipid Accumulation in Type 2 Diabetes May Involve the Liver X Receptor Pathway
Authors: Kase Eili T. , Wensaas Andreas J. , Aas Vigdis , Højlund Kurt , Levin Klaus , Thoresen G. Hege , Beck-Nielsen Henning , Rustan Arild C. , Gaster Michael
Published: March 2007

Liver X receptors (LXRs) are important regulators of cholesterol and lipid metabolism and are also involved in glucose metabolism. However, the functional role of LXRs in human skeletal muscle is at present unknown. This study demonstrates that chronic ligand activation of LXRs by a synthetic LXR agonist increases the uptake, distribution into complex cellular lipids, and oxidation of palmitate as well as the uptake and oxidation of glucose in cultured human skeletal muscle cells. Furthermore, the effect of the LXR agonist was additive to acute effects of insulin on palmitate uptake and metabolism. Consistently, activation of LXRs induced the expression of relevant genes: fatty acid translocase (CD36/FAT), glucose transporters (GLUT1 and -4), sterol regulatory element–binding protein-1c, peroxisome proliferator–activated receptor-γ, carnitine palmitoyltransferase-1, and uncoupling protein 2 and 3. Interestingly, in response to activation of LXRs, myotubes from patients with type 2 diabetes showed an elevated uptake and incorporation of palmitate into complex lipids but an absence of palmitate oxidation to CO2. These results provide evidence for a functional role of LXRs in both lipid and glucose metabolism and energy uncoupling in human myotubes. Furthermore, these data suggest that increased intramyocellular lipid content in type 2 diabetic patients may involve an altered response to activation of components in the LXR pathway.
Loss of Heparan N-Sulfotransferase in Diabetic Liver
Authors: Williams Kevin Jon , Liu Ming-Lin , Zhu Yanqing , Xu Xiangsheng , Davidson William R. , McCue Peter , Sharma Kumar
Published: March 2007

The basis for accelerated atherosclerosis in diabetes is unclear. Diabetes is associated with loss of heparan sulfate (HS) from the liver, which may impede lipoprotein clearance and thereby worsen atherosclerosis. To study hepatic HS loss in diabetes, we examined regulation of HS N-deacetylase/N-sulfotransferase-1 (NDST), a key enzyme in hepatic HS biosynthesis. Hepatic NDST mRNA, protein, and enzymatic activity were suppressed by >50% 2 weeks after induction of type 1 diabetes in rats. Treatment of diabetic rats with enalapril, an ACE inhibitor, had no effect on hyperglycemia or hepatic NDST mRNA levels, yet increased hepatic NDST protein and enzymatic activity. Similar results were obtained in diabetic animals treated with losartan, which blocks the type 1 receptor for angiotensin II (AngII). Consistent with these findings, diabetic livers exhibited increased ACE expression, and addition of AngII to cultured hepatoma cells reduced NDST activity and protein. We conclude that diabetes substantially suppresses hepatic NDST mRNA, protein, and enzymatic activity. AngII contributes to suppression of NDST protein and enzymatic activity, whereas mRNA suppression occurs independently. Suppression of hepatic NDST may contribute to diabetic dyslipidemia, and stimulation of NDST activity by AngII inhibitors may provide cardiovascular protection.
ENPP1/PC-1 K121Q Polymorphism and Genetic Susceptibility to Type 2 Diabetes
Authors: Abate Nicola , Chandalia Manisha , Satija Pankaj , Adams-Huet Beverley , Grundy Scott M. , Sandeep Sreedharan , Radha Venkatesan , Deepa Raj , Mohan Viswanathan
Published: March 2007

Genetic susceptibility modulates the impact of obesity on risk for type 2 diabetes. The present study evaluates the role of ENPP1 K121Q polymorphism in prediction of type 2 diabetes in three populations that differ in susceptibility to diabetes and environmental exposure. The three cohorts included 679 nonmigrant South Asians living in Chennai, India (223 with type 2 diabetes); 1,083 migrant South Asians living in Dallas, Texas (121 with type 2 diabetes); and 858 nonmigrant Caucasians living in Dallas, Texas (141 with type 2 diabetes). Patients with type 2 diabetes were included in these cohorts if they had diabetes onset before the age of 60 years. The prevalence of subjects carrying the polymorphic ENPP1 121Q allele was 25% in the nondiabetic group and 34% in the diabetic group of South Asians living in Chennai (P = 0.01). The prevalence in the nondiabetic and diabetic groups were 33 and 45% (P = 0.01) for the South Asians living in Dallas and 26 and 39% (P = 0.003) for the Caucasians. Although further replication studies are necessary to test the validity of the described genotype-phenotype relationship, our study supports the hypothesis that ENPP1 121Q predicts genetic susceptibility to type 2 diabetes in both South Asians and Caucasians.
The Rat Diabetes Susceptibility LocusIddm4and at Least One Additional Gene Are Required for Autoimmune Diabetes Induced by Viral Infection
Authors: Blankenhorn Elizabeth P. , Rodemich Lucy , Martin-Fernandez Cristina , Leif Jean , Greiner Dale L. , Mordes John P.
Published: March 2007

BBDR rats develop autoimmune diabetes only after challenge with environmental perturbants. These perturbants include polyinosinic:polycytidylic acid (poly I:C, a ligand of toll-like receptor 3), agents that deplete regulatory T-cell (Treg) populations, and a non–β-cell cytopathic parvovirus (Kilham rat virus [KRV]). The dominant diabetes susceptibility locus Iddm4 is required for diabetes induced by treatment with poly I:C plus Treg depletion. Iddm4 is penetrant in congenic heterozygous rats on the resistant WF background and is 79% sensitive and 80% specific as a predictor of induced diabetes. Surprisingly, an analysis of 190 (BBDR × WF)F2 rats treated with KRV after brief exposure to poly I:C revealed that the BBDR-origin allele of Iddm4 is necessary but not entirely sufficient for diabetes expression. A genome scan identified a locus on chromosome 17, designated Iddm20, that is also required for susceptibility to diabetes after exposure to KRV and poly I:C (logarithm of odds score 3.7). These data suggest that the expression of autoimmune diabetes is a complex process that requires both major histocompatibility complex genes that confer susceptibility and additional genes such as Iddm4 and Iddm20 that operate only in the context of specific environmental perturbants, amplifying the immune response and the rate of disease progression.
Long-Term AICAR Administration and Exercise Prevents Diabetes in ZDF Rats
Authors: Pold Rasmus , Jensen Lasse S. , Jessen Niels , Buhl Esben S. , Schmitz Ole , Flyvbjerg Allan , Fujii Nobuharu , Goodyear Laurie J. , Gotfredsen Carsten F. , Brand Christian L. , Lund Sten
Published: March 2007

Lifestyle interventions including exercise programs are cornerstones in the prevention of obesity-related diabetes. The AMP-activated protein kinase (AMPK) has been proposed to be responsible for many of the beneficial effects of exercise on glucose and lipid metabolism. The effects of long-term exercise training or 5-aminoimidazole-4-carboxamide-1-β-d-riboruranoside (AICAR) treatment, both known AMPK activators, on the development of diabetes in male Zucker diabetic fatty (ZDF) rats were examined. Five-week-old, pre-diabetic ZDF rats underwent daily treadmill running or AICAR treatment over an 8-week period and were compared with an untreated group. In contrast to the untreated, both the exercised and AICAR-treated rats did not develop hyperglycemia during the intervention period. Whole-body insulin sensitivity, as assessed by a hyperinsulinemic-euglycemic clamp at the end of the intervention period, was markedly increased in the exercised and AICAR-treated animals compared with the untreated ZDF rats (P < 0.01). In addition, pancreatic β-cell morphology was almost normal in the exercised and AICAR-treated animals, indicating that chronic AMPK activation in vivo might preserve β-cell function. Our results suggest that activation of AMPK may represent a therapeutic approach to improve insulin action and prevent a decrease in β-cell function associated with type 2 diabetes.
Endoplasmic Reticulum Stress–Induced Apoptosis Is Partly Mediated by Reduced Insulin Signaling Through Phosphatidylinositol 3-Kinase/Akt and Increased Glycogen Synthase Kinase-3β in Mouse Insulinoma Cells
Authors: Srinivasan Shanthi , Ohsugi Mitsuru , Liu Zhonghao , Fatrai Szabolcs , Bernal-Mizrachi Ernesto , Permutt M. Alan
Published: March 2007

An imbalance between the rate of protein synthesis and folding capacity of the endoplasmic reticulum (ER) results in stress that has been increasingly implicated in pancreatic islet β-cell apoptosis and diabetes. Because insulin/IGF/Akt signaling has been implicated in β-cell survival, we sought to determine whether this pathway is involved in ER stress–induced apoptosis. Mouse insulinoma cells treated with pharmacological agents commonly used to induce ER stress exhibited apoptosis within 48 h. ER stress–induced apoptosis was inhibited by cotreatment of the cells with IGF-1. Stable cell lines were created by small-interfering RNA (siRNA) with graded reduction of insulin receptor expression, and these cells had enhanced susceptibility to ER stress–induced apoptosis and reduced levels of phospho–glycogen synthase kinase 3β (GSK3β). In control cells, ER stress–induced apoptosis was associated with a reduction in phospho-Akt and phospho-GSK3β. To further assess the role of GSK3β in ER stress–induced apoptosis, stable cell lines were created by siRNA with up to 80% reduction in GSK3β expression. These cells were found to resist ER stress–induced apoptosis. These results illustrate that ER stress–induced apoptosis is mediated at least in part by signaling through the phosphatidylinositol 3-kinase/Akt/GSK3β pathway and that GSK3β represents a novel target for agents to promote β-cell survival.
Chronic Hyperglycemia Enhances PEPCK Gene Expression and Hepatocellular Glucose Production Via Elevated Liver Activating Protein/Liver Inhibitory Protein Ratio
Authors: Shao Jianhua , Qiao Liping , Janssen Rachel C. , Pagliassotti Michael , Friedman Jacob E.
Published: March 2007

Acute hyperglycemia normally suppresses hepatic glucose production (HGP) and gluconeogenic gene expression. Conversely, chronic hyperglycemia is accompanied by progressive increases in basal HGP and is a major contributor to hyperglycemia in both type 1 and type 2 diabetes by mechanisms that are poorly understood. The aim of this study was to investigate the molecular mechanisms whereby hyperglycemia contributes to excessive gluconeogenesis in Fao hepatoma cells. Increasing glucose from 5 to 20 mmol/l resulted in loss of glucose inhibition of PEPCK gene expression after 12 h. Furthermore, 24 h of incubation with 20 mmol/l glucose increased cAMP-stimulated PEPCK mRNA by ∼40% (P < 0.05) and similarly increased glucose production. Although total CCAAT/enhancer-binding protein β (C/EBPβ) protein levels were suppressed, 20 mmol/l glucose increased the liver activating protein (LAP; an active isoform of C/EBPβ)/liver inhibitory protein (LIP; an inhibitory isoform of C/EBPβ) ratio significantly. Chromatin immunoprecipitation studies of the endogenous PEPCK gene demonstrated an increased association of LAP with the cAMP response element of the promoter. Using transient transfection to manipulate the LAP/LIP ratio, we also demonstrate a direct relationship between this ratio and PEPCK promoter activity. An increased LAP/LIP ratio not only enhanced cAMP- and dexamethasone-induced PEPCK gene expression but also impaired the repressive effect of insulin. These results demonstrate that sustained hyperglycemia diminishes the inhibitory effect of glucose and insulin on PEPCK expression and enhances hormone-stimulated PEPCK gene expression and hepatocellular glucose production. Because prolonged hyperglycemia increases the LAP/LIP ratio and can potentiate hormone induction of PEPCK transcription, our results suggest that a hyperglycemia-driven increased LAP/LIP ratio may be a critical molecular event in the pathogenesis of increased HGP in diabetes.
Glycogen Synthesis in Human Gastrocnemius Muscle Is Not Representative of Whole-Body Muscle Glycogen Synthesis
Authors: Serlie Mireille J.M. , de Haan Jacco H. , Tack Cees J. , Verberne Hein J. , Ackermans Mariette T. , Heerschap Arend , Sauerwein Hans P.
Published: March 2007

The introduction of 13C magnetic resonance spectroscopy (MRS) has enabled noninvasive measurement of muscle glycogen synthesis in humans. Conclusions based on measurements by the MRS technique assume that glucose metabolism in gastrocnemius muscle is representative for all skeletal muscles and thus can be extrapolated to whole-body muscle glucose metabolism. An alternative method to assess whole-body muscle glycogen synthesis is the use of [3-3H]glucose. In the present study, we compared this method to the MRS technique, which is a well-validated technique for measuring muscle glycogen synthesis. Muscle glycogen synthesis was measured in the gastrocnemius muscle of six lean healthy subjects by MRS and by the isotope method during a hyperinsulinemic-euglycemic clamp. Mean muscle glycogen synthesis as measured by the isotope method was 115 ± 26 μmol · kg−1 muscle · min−1 vs. 178 ± 72 μmol · kg−1 muscle · min−1 (P = 0.03) measured by MRS. Glycogen synthesis rates measured by MRS exceeded 100% of glucose uptake in three of the six subjects. We conclude that glycogen synthesis rates measured in gastrocnemius muscle cannot be extrapolated to whole-body muscle glycogen synthesis.
Rosiglitazone Increases Indexes of Stearoyl-CoA Desaturase Activity in Humans
Authors: Risérus Ulf , Tan Garry D. , Fielding Barbara A. , Neville Matt J. , Currie Jenny , Savage David B. , Chatterjee V. Krishna , Frayn Keith N. , O’Rahilly Stephen , Karpe Fredrik
Published: March 2007

Fatty acid desaturases such as steaoryl-CoA desaturase (SCD) convert saturated to unsaturated fatty acids and are involved in lipogenesis. Observational and animal data suggest that SCD-1 activity is related to insulin sensitivity. However, the effects of insulin-sensitizing drugs on SCD gene expression and desaturase activities are unknown in humans. In a randomized, placebo-controlled, double-blind, crossover study, 24 subjects with type 2 diabetes and one subject with partial lipodystrophy and diabetes due to dominant-negative mutation in the peroxisome proliferator-activated receptor-γ (PPARγ) gene (P467L) received placebo and rosiglitazone for 3 months. SCD gene expression in adipose tissue was determined in 23 subjects, and in a representative subgroup (n = 10) we assessed fatty acid composition in fasting plasma triglycerides to estimate SCD and Δ6- and Δ5-desaturase activity, using product-to-precursor indexes. SCD mRNA expression increased by 48% after rosiglitazone (P < 0.01). SCD and Δ5-desaturase but not Δ6-desaturase activity indexes were increased after rosiglitazone versus placebo (P < 0.01 and P < 0.05, respectively). The change in activity index but not the expression of SCD was associated with improved insulin sensitivity (r = 0.73, P < 0.05). In the P467L PPARγ carrier, SCD and Δ5-desaturase activity indexes were exceptionally low but were restored (52- and 15-fold increases, respectively) after rosiglitazone treatment. This study shows for the first time that rosiglitazone increases SCD activity indexes and gene expression in humans. An increased SCD activity index may reflect increased lipogenesis and might contribute to insulin sensitization by rosiglitazone. The restored SCD activity index after rosiglitazone in PPARγ mutation supports a pivotal role of PPARγ function in SCD regulation.