bluuebunny/crossref_metadata_2025 huggingface dataset:
The Lack of β-Adrenoceptors Results in Enhanced Insulin Sensitivity in Mice Exhibiting Increased Adiposity and Glucose Intolerance
Authors: Asensio Cédric , Jimenez Maria , Kühne Françoise , Rohner-Jeanrenaud Françoise , Muzzin Patrick
Published: March 2007

We and others have previously shown that triple knockout mice lacking the β1/β2/β3-adrenoceptors (β-less mice) developed a progressive obesity at adulthood. Here, we studied the glucose homeostasis in β-less mice before the onset of obesity. We show that β-less mice have increased fat mass and are glucose intolerant. In addition, we observed that β-less mice have impaired glucose-induced insulin secretion and exhibit an increase in liver PEPCK gene expression in the fed state, suggesting that they have increased gluconeogenesis. Although these characteristics are usually associated with insulin resistance, β-less mice exhibit enhanced insulin sensitivity during insulin tolerance tests. This is keeping with the results obtained during euglycemic-hyperinsulinemic clamps showing that β-less mice display increased insulin responsiveness with normal suppression of hepatic glucose production. Altogether, our results suggest that an intact β-adrenergic system is required to regulate overall glucose homeostasis and, in particular, insulin-mediated glucose uptake, most likely at the level of muscles and adipose tissue.
Resistance to Diet-Induced Obesity in μ-Opioid Receptor–Deficient Mice
Authors: Tabarin Antoine , Diz-Chaves Yolanda , Carmona Maria del Carmen , Catargi Bogdan , Zorrilla Eric P. , Roberts Amanda J. , Coscina Donald V. , Rousset Sophie , Redonnet Anabelle , Parker Graham C. , Inoue Koki , Ricquier Daniel , Pénicaud Luc , Kieffer Brigitte L. , Koob Georges F.
Published: March 2007

Using pharmacological tools, a role for opioid receptors in the regulation of food intake has been documented. However, the involvement of specific receptor subtypes remains questionable, and little information is available regarding a role for opioid receptors in energy metabolism. Using adult male mice lacking the μ-opioid receptor (MOR) gene (MOR−/−), we show that the MOR is not essential for the maintenance of normal levels of ad libitum food intake but does modulate the efficiency of energy storage during high-fat diets through the regulation of energy partitioning. When fed a regular diet, MOR−/− mice displayed only subtle alterations in energy homeostasis, suggesting a relative overuse of fat as a fuel source in the fed state. When fed a high-fat diet, MOR−/− mice were resistant to obesity and impaired glucose tolerance, despite having similar energy intake to wild-type mice. This resistance to obesity was associated with a strong induction of the expression of key mitochondrial enzymes involved in fatty acid oxidation within skeletal muscle. This metabolic role of the MOR, which is consistent with the properties of a “thrifty gene,” suggests that the MOR pathway is a potential target for pharmacological intervention in the treatment of obesity associated with the intake of fatty diets.
Individual Mice Can Be Distinguished by the Period of Their Islet Calcium Oscillations
Authors: Nunemaker Craig S. , Zhang Min , Wasserman David H. , McGuinness Owen P. , Powers Alvin C. , Bertram Richard , Sherman Arthur , Satin Leslie S.
Published: March 2007

Pulsatile insulin secretion in vivo is believed to be derived, in part, from the intrinsic glucose-dependent intracellular calcium concentration ([Ca2+]i) pulsatility of individual islets. In isolation, islets display fast, slow, or mixtures of fast and slow [Ca2+]i oscillations. We show that the period of islet [Ca2+]i oscillations is unique to each mouse, with the islets from an individual mouse demonstrating similar rhythms to one another. Based on their rhythmic period, mice were broadly classified as being either fast (0.65 ± 0.1 min; n = 6 mice) or slow (4.7 ± 0.2 min; n = 15 mice). To ensure this phenomenon was not an artifact of islet-to-islet communication, we confirmed that islets cultured in isolation (period: 2.9 ± 0.1 min) were not statistically different from islets cultured together from the same mouse (3.1 ± 0.1 min, P > 0.52, n = 5 mice). We also compared pulsatile insulin patterns measured in vivo with islet [Ca2+]i patterns measured in vitro from six mice. Mice with faster insulin pulse periods corresponded to faster islet [Ca2+]i patterns, whereas slower insulin patterns corresponded to slower [Ca2+]i patterns, suggesting that the insulin rhythm of each mouse is preserved to some degree by its islets in vitro. We propose that individual mice have characteristic oscillatory [Ca2+]i patterns, which are imprinted in vivo through an unknown mechanism.
Rho Guanosine Diphosphate–Dissociation Inhibitor Plays a Negative Modulatory Role in Glucose-Stimulated Insulin Secretion
Authors: Kowluru Anjaneyulu , Veluthakal Rajakrishnan
Published: March 2007

Extant studies have implicated the Rho subfamily of guanosine triphosphate–binding proteins (G-proteins; e.g., Rac1) in physiological insulin secretion from isolated β-cells. However, very little is known with regard to potential regulation by G-protein regulatory factors (e.g., the guanosine diphosphate–dissociation inhibitor [GDI]) of insulin secretion from the islet β-cell. To this end, using Triton X-114 phase partition, co-immunoprecipitation, and sucrose density gradient centrifugation approaches, we report coexistence of GDI with Rac1 in insulin-secreting β-cells (INS cells). Overexpression of wild-type GDI significantly inhibited glucose-induced, but not KCl- or mastoparan-induced, insulin secretion from INS cells. Furthermore, glucose-stimulated insulin secretion (GSIS) was significantly increased in INS cells in which expression of GDI was inhibited via the small interfering RNA–mediated knockdown approach. Together, these data appear to suggest an inhibitory role for GDI in the glucose metabolic signaling cascade, which may be relevant for GSIS.
Nonalcoholic Fatty Liver Disease and Risk of Future Cardiovascular Events Among Type 2 Diabetic Patients
Authors: Targher Giovanni , Bertolini Lorenzo , Poli Felice , Rodella Stefano , Scala Luca , Tessari Roberto , Zenari Luciano , Falezza Giancarlo
Published: March 2007

Nonalcoholic fatty liver disease (NAFLD) is closely correlated to several metabolic syndrome features. We assessed prospectively whether NAFLD predicts future cardiovascular disease (CVD) events among type 2 diabetic individuals, independent of metabolic syndrome features and other classical risk factors. We carried out a prospective nested case-control study in 2,103 type 2 diabetic patients who were free of diagnosed CVD at baseline. During 5 years of follow-up, 248 participants (case subjects) subsequently developed nonfatal coronary heart disease (myocardial infarction and coronary revascularization procedures), ischemic stroke, or cardiovascular death. Using risk-set sampling, 496 patients (control subjects) among those who remained free of diagnosed CVD during follow-up were randomly selected in a 2:1 ratio, matched for age and sex to the case subjects. After adjustment for age, sex, smoking history, diabetes duration, HbA1c, LDL cholesterol, liver enzymes, and use of medications, the presence of NAFLD was significantly associated with an increased CVD risk (odds ratio 1.84, 95% CI 1.4–2.1, P < 0.001). Additional adjustment for the metabolic syndrome (as defined by National Cholesterol Education Program Adult Treatment Panel III criteria) appreciably attenuated, but did not abolish, this association (1.53, 1.1–1.7, P = 0.02). In conclusion, NAFLD is significantly associated with a moderately increased CVD risk among type 2 diabetic individuals. This relationship is independent of classical risk factors and is only partly explained by occurrence of metabolic syndrome.
Patterns of Linkage Disequilibrium in the Type 2 Diabetes Gene Calpain-10
Authors: Hayes M. Geoffrey , del Bosque-Plata Laura , Tsuchiya Takafumi , Hanis Craig L. , Bell Graeme I. , Cox Nancy J.
Published: March 2007

We investigated the patterns and extent of linkage disequilibrium (LD) in the vicinity of the type 2 diabetes gene calapin-10 (CAPN10) in Mexican Americans, European Americans, African Americans, and Chinese Americans. We found that CAPN10 occurs within a single block of high LD and that LD decays rapidly outside of the gene. This reduces the likelihood that associations between CAPN10 polymorphisms and type 2 diabetes could be attributed to variation at some distance from CAPN10. We also consistently observed that cases have more extensive LD than control subjects and that cases from families with evidence for linkage have more extensive LD than cases from families without evidence for linkage. These observations further suggest that there are one or more relatively common alleles increasing risk of type 2 diabetes in this local region.
Dissipating Excess Energy Stored in the Liver Is a Potential Treatment Strategy for Diabetes Associated With Obesity
Authors: Ishigaki Yasushi , Katagiri Hideki , Yamada Tetsuya , Ogihara Takehide , Imai Junta , Uno Kenji , Hasegawa Yutaka , Gao Junhong , Ishihara Hisamitsu , Shimosegawa Tooru , Sakoda Hideyuki , Asano Tomoichiro , Oka Yoshitomo
Published: March 2007

For examining whether dissipating excess energy in the liver is a possible therapeutic approach to high-fat diet–induced metabolic disorders, uncoupling protein-1 (UCP1) was expressed in murine liver using adenoviral vectors in mice with high-fat diet–induced diabetes and obesity, and in standard diet–fed lean mice. Once diabetes with obesity developed, hepatic UCP1 expression increased energy expenditure, decreased body weight, and reduced fat in the liver and adipose tissues, resulting in markedly improved insulin resistance and, thus, diabetes and dyslipidemia. Decreased expressions of enzymes for lipid synthesis and glucose production and activation of AMP-activated kinase in the liver seem to contribute to these improvements. Hepatic UCP1 expression also reversed high-fat diet–induced hyperphagia and hypothalamic leptin resistance, as well as insulin resistance in muscle. In contrast, intriguingly, in standard diet–fed lean mice, hepatic UCP1 expression did not significantly affect energy expenditure or hepatic ATP contents. Furthermore, no alterations in blood glucose levels, body weight, or adiposity were observed. These findings suggest that ectopic UCP1 in the liver dissipates surplus energy without affecting required energy and exerts minimal metabolic effects in lean mice. Thus, enhanced UCP expression in the liver is a new potential therapeutic target for the metabolic syndrome.
Identification of Individuals With Insulin Resistance Using Routine Clinical Measurements
Authors: Stern Steven E. , Williams Ken , Ferrannini Eleuterio , DeFronzo Ralph A. , Bogardus Clifton , Stern Michael P.
Published: March 2007

Insulin resistance is a treatable precursor of diabetes and potentially of cardiovascular disease as well. To identify insulin-resistant patients, we developed decision rules from measurements of obesity, fasting glucose, insulin, lipids, and blood pressure and family history in 2,321 (2,138 nondiabetic) individuals studied with the euglycemic insulin clamp technique at 17 European sites; San Antonio, Texas; and the Pima Indian reservation. The distribution of whole-body glucose disposal appeared to be bimodal, with an optimal insulin resistance cutoff of <28 μmol/min · kg lean body mass. Using recursive partitioning, we developed three types of classification tree models: the first, based on clinical measurements and all available laboratory determinations, had an area under the receiver operator characteristic curve (aROC) of 90.0% and generated a simple decision rule: diagnose insulin resistance if any of the following conditions are met: BMI >28.9 kg/m2, homeostasis model assessment of insulin resistance (HOMA-IR) >4.65, or BMI >27.5 kg/m2 and HOMA-IR >3.60. The fasting serum insulin concentrations corresponding to these HOMA-IR cut points were 20.7 and 16.3 μU/ml, respectively. This rule had a sensitivity and specificity of 84.9 and 78.7%, respectively. The second model, which included clinical measurements but no laboratory determinations, had an aROC of 85.0% and generated a decision rule that had a sensitivity and specificity of 78.7 and 79.6%, respectively. The third model, which included clinical measurements and lipid measurements but not insulin (and thus excluded HOMA-IR as well), had a similar aROC (85.1%), sensitivity (81.3%), and specificity (76.3%). Thus, insulin-resistant individuals can be identified using simple decision rules that can be tailored to specific needs.
Luminal Leptin Induces Rapid Inhibition of Active Intestinal Absorption of Glucose Mediated by Sodium-Glucose Cotransporter 1
Authors: Ducroc Robert , Guilmeau Sandra , Akasbi Khalil , Devaud Hélène , Buyse Marion , Bado André
Published: March 2007

The effect of leptin on glucose transport was studied in rat jejunal mucosa in Ussing chambers. Leptin was added in the luminal or the serosal compartment before the tissues were challenged with 1, 10, or 50 mmol/l glucose. In response to 10 mmol/l glucose, the increase in short-circuit current (ΔIsc) reached 26.8 ± 2.1 μA/cm2. Luminal addition of leptin dramatically decreased glucose-induced Isc (90.5% for 10 nmol/l leptin). Inhibition was maximal after 5 min and dose dependent (IC50 = 0.13 nM). Western blot analysis showed that rapid inhibition of glucose-induced Isc by leptin was associated with a parallel decrease in the abundance of sodium-glucose transporter-1 in brush border membranes. Inhibition by luminal leptin of ΔIsc was prevented by inhibitor of conventional protein kinase C isoforms. Serosal addition of leptin did not decrease glucose-induced Isc within 5 min and reached maximum after 10 min. The effect of leptin from serosal side was blocked by cholecystokinin (CCK) receptor-2 receptor antagonist YM022. Altogether, these data demonstrate that luminal leptin induces rapid inhibition of glucose entry into enterocyte. The slower action of leptin on the serosal side of mucosa seems indirect and is likely mediated by endogenous CCK. They demonstrate that gut leptin is a major regulator of rapid intestinal glucose transport.
High Glucose Regulates the Activity of Cardiac Sarcolemmal ATP-Sensitive K+ Channels via 1,3-Bisphosphoglycerate
Authors: Jovanović Sofija , Jovanović Aleksandar
Published: March 2007

Because we were interested in assessing glucose-mediated regulation of the activity of sarcolemmal ATP-sensitive K+ channels (KATP channels) (which are closed by physiological levels of intracellular ATP and serve to couple intracellular metabolism with the membrane excitability in the heart) during ischemia, we performed experiments designed to test whether high extracellular glucose would have effects on sarcolemmal KATP channels per se. Surprisingly, we found that high extracellular glucose (50 mmol/l) activates sarcolemmal KATP channels in isolated guinea pig cardiomyocytes. To activate KATP channels, glucose had to be transported into cardiomyocytes and subjected to glycolysis. The activation of these channels was independent of ATP production and intracellular ATP levels. The effect of glucose on sarcolemmal KATP channels was mediated by the catalytic activity of glyceraldehyde-3-phosphate dehydrogenase and consequent generation of 1,3-bisphosphoglycerate. The 1,3-bisphosphoglycerate (20 mmol/l), an intermediate product of glycolysis, directly targeted and activated KATP channels, despite physiological levels of intracellular ATP (5 mmol/l). We conclude that glucose, so far exclusively viewed as a metabolic fuel in the heart important only during ischemia/hypoxia, may serve a signaling role in the nonstressed myocardium by producing an agent that regulates cardiac membrane excitability independently of high-energy phosphates.
Adenovirus-Mediated XIAP Gene Transfer Reverses the Negative Effects of Immunosuppressive Drugs on Insulin Secretion and Cell Viability of Isolated Human Islets
Authors: Hui Hongxiang , Khoury Nasif , Zhao Xiaoning , Balkir Levent , D’Amico Eugenio , Bullotta Angela , Nguyen Elizabeth D. , Gambotto Andrea , Perfetti Riccardo
Published: March 2007

Immunosuppressive drugs are routinely used to provide tolerance after whole pancreas and islet cell transplantations. While they are essential in inhibiting graft rejection, little is known about their effect on islet function and β-cell viability. In this study, we report that tacrolimus, sirolimus, and mycophenolic acid, when added to cultures of freshly isolated human islets, induce a downregulation of the synthesis and secretion of insulin. These functional changes are associated with decreased islet cell viability. All three agents induce a decrease of intracellular levels of Bcl-2 and Bcl-xL, with an increased level of Smac, indicating that they are capable of promoting a downregulation of anti-apoptotic factors and an accumulation of pro-apoptotic mediators. Transduction of islet cells with the anti-apoptotic gene XIAP prevents the negative effects of these drugs on the function and viability of islets. XIAP-infected cells show a higher expression of phospho-CREB (cAMP-responsive element binding protein) and a reduced level of Smac, resulting in a significant reduction of apoptotic cells and a preservation of the glucose-dependent secretion of insulin. In conclusion, the present study demonstrates that genetically modified human islets expressing XIAP are resistant to the negative effects of immunosuppressive drugs on insulin secretion and cell viability.
β-Cell Pdx1 Expression Is Essential for the Glucoregulatory, Proliferative, and Cytoprotective Actions of Glucagon-Like Peptide-1
Authors: Li Yazhou , Cao Xiemin , Li Li-Xin , Brubaker Patricia L. , Edlund Helena , Drucker Daniel J.
Published: March 2007

Glucagon-like peptide-1 (GLP-1) regulates energy intake, gastrointestinal motility, and nutrient disposal. The relative importance of the islet β-cell for GLP-1 actions remains unclear. We determined the role of the islet β-cell and the pancreatic duodenal homeobox-1 (Pdx1) transcription factor for GLP-1 receptor (GLP-1R)-dependent actions through analysis of mice with β-cell–specific inactivation of the Pdx1 gene (β-cellPdx1−/− mice). The GLP-1R agonist exendin-4 (Ex-4) reduced glycemic excursion following intraperitoneal (i.p.) glucose challenge in control littermates (β-cellPdx1+/+ mice) but not in β-cellPdx1−/− mice. Similarly, Ex-4 failed to increase levels of plasma insulin, pancreatic insulin content, and pancreatic insulin mRNA transcripts in β-cellPdx1−/− mice. Furthermore, Ex-4 significantly increased β-cell proliferation and reduced β-cell apoptosis in β-cellPdx1+/+ mice but not in β-cellPdx1−/− mice. Moreover, Ex-4 increased the levels of insulin and amylin mRNA transcripts and augmented glucose-stimulated insulin secretion in islets from β-cellPdx1+/+ mice but not in β-cellPdx1−/− islets. Surprisingly, Ex-4 failed to reduce levels of plasma glucagon in β-cellPdx1−/− mice. These findings demonstrate that Pdx1 expression is essential for integrating GLP-1R–dependent signals regulating α-cell glucagon secretion and for the growth, differentiated function, and survival of islet β-cells.
Transgenic Mice Overexpressing Nuclear SREBP-1c in Pancreatic β-Cells
Authors: Takahashi Akimitsu , Motomura Kaori , Kato Toyonori , Yoshikawa Tomohiro , Nakagawa Yoshimi , Yahagi Naoya , Sone Hirohito , Suzuki Hiroaki , Toyoshima Hideo , Yamada Nobuhiro , Shimano Hitoshi
Published: March 2007

Influx of excess fatty acids and the resultant accumulation of intracellular triglycerides are linked to impaired insulin secretion and action in the pathogenesis of type 2 diabetes. Sterol regulatory element-binding protein (SREBP)-1c is a transcription factor that controls cellular synthesis of fatty acids and triglycerides. SREBP-1c is highly expressed in high-energy and insulin-resistant states. To investigate effects of this synthetic lipid regulator on insulin secretion, we generated transgenic mice overexpressing nuclear SREBP-1c under the insulin promoter. β-Cell-specific expression of SREBP-1c caused reduction in islet mass and impaired glucose-stimulated insulin secretion and was associated with accumulation of triglycerides, suppression of pancreas duodenal homeobox-1, and upregulation of uncoupling protein 2 gene expression. The mice presented with impaired glucose tolerance that was exacerbated by a high-energy diet. Taken together with enhanced insulin secretion from SREBP-1-null islets, these data suggest that SREBP-1c and endogenous lipogenesis could be involved in β-cell dysfunction and diabetes.
The Relationship of Diabetic Retinopathy to Preclinical Diabetic Glomerulopathy Lesions in Type 1 Diabetic Patients
Authors: Klein Ronald , Zinman Bernard , Gardiner Robert , Suissa Samy , Donnelly Sandra M. , Sinaiko Alan R. , Kramer Michael S. , Goodyer Paul , Moss Scot E. , Strand Trudy , Mauer Michael
Published: March 2007

Few epidemiological data exist regarding the correlation of anatomic measures of diabetic retinopathy and nephropathy, especially early in the disease processes. The aim of this study was to examine the association of severity of diabetic retinopathy with histological measures of diabetic nephropathy in normoalbuminuric patients with type 1 diabetes. The study included participants (n = 285) in the Renin-Angiotensin System Study (RASS; a multicenter diabetic nephropathy primary prevention trial) who were aged ≥16 years and had 2–20 years of type 1 diabetes with normal baseline renal function measures. Albumin excretion rate (AER), blood pressure, serum creatinine, and glomerular filtration rate (GFR) were measured using standardized protocols. Diabetic retinopathy was determined by masked grading of 30° color stereoscopic fundus photographs of seven standard fields using the Early Treatment Diabetic Retinopathy Study (ETDRS) severity scale. Baseline renal structural parameters, e.g., fraction of the glomerulus occupied by the mesangium or mesangial fractional volume [Vv(Mes/glom)] and glomerular basement membrane width, were assessed by masked electron microscopic morphometric analyses of research percutaneous renal biopsies. No retinopathy was present in 36%, mild nonproliferative diabetic retinopathy in 53%, moderate to severe nonproliferative diabetic retinopathy in 9%, and proliferative diabetic retinopathy in 2% of the cohort. Retinopathy was not related to AER, blood pressure, serum creatinine, or GFR. All renal anatomical end points were associated with increasing severity of diabetic retinopathy, while controlling for other risk factors. These data demonstrate a significant association between diabetic retinopathy and preclinical morphologic changes of diabetic nephropathy in type 1 diabetic patients.
Differential Responses of Visceral and Subcutaneous Fat Depots to Nutrients
Authors: Einstein Francine H. , Atzmon Gil , Yang Xiao-man , Ma Xiao-Hui , Rincon Marielisa , Rudin Eric , Muzumdar Radhika , Barzilai Nir
Published: March 2007

Increased visceral adiposity is a pivotal component of the metabolic syndrome. Differential gene expression patterns of fat-derived peptides (FDPs) in visceral fat and subcutaneous fat have been characterized in the fasting state. Here we examined whether delivery of nutrients differentially affects the expression of FDPs in visceral fat versus subcutaneous fat (in the fed state). We increased the rate of glucose flux into adipose tissue of normal rats (n = 16) by hyperglycemia or hyperinsulinemia using the clamp technique. Glucose uptake was associated with increased expression of FDPs, including resistin (∼5-fold), adiponectin (∼2-fold), leptin (∼15-fold), plasminogen activating inhibitor-1 (∼10-fold), and angiotensinogen (∼4-fold) in visceral fat, but markedly less in subcutaneous fat. Cytokine expression de-rived mainly from vascular/stromal/macrophage components of adipose tissue was less dramatically increased. Infusion of glucosamine amplified the results obtained by increasing glucose uptake into adipose tissue, suggesting that flux through the hexosamine biosynthetic pathway may serve as a mechanism for “nutrient sensing.” Nutrient-dependent expression of FDPs in visceral fat was also associated with increased plasma levels of several FDPs. Because a biologic sensing pathway can dynamically couple daily food intake to abnormal plasma levels of important FDPs, we challenge the practice of obtaining plasma levels after fasting to assess risk factors for metabolic syndrome.
Loss of the Decrement in Intraislet Insulin Plausibly Explains Loss of the Glucagon Response to Hypoglycemia in Insulin-Deficient Diabetes
Authors: Raju Bharathi , Cryer Philip E.
Published: March 2007

The intraislet insulin hypothesis for the signaling of the glucagon secretory response to hypoglycemia states that a decrease in arterial glucose → a decrease in β-cell insulin secretion → a decrease in tonic α-cell inhibition by insulin → an increase in α-cell glucagon secretion. To test this hypothesis in humans, a hyperinsulinemic- euglycemic (∼5.0 mmol/l [90 mg/dl] × 2 h) and then a hypoglycemic (∼3.0 mmol/l [55 mg/dl] × 2 h) clamp was performed in 14 healthy young adults on two occasions, once with oral administration of the ATP-sensitive potassium channel agonist diazoxide to selectively suppress baseline insulin secretion and once with the administration of a placebo. The decrement in plasma C-peptide during the induction of hypoglycemia was reduced by ∼50% in the diazoxide clamps (from 0.3 ± 0.0 to 0.1 ± 0.0 nmol/l [0.8 ± 0.1 to 0.4 ± 0.1 ng/ml]) compared with the placebo clamps (from 0.4 ± 0.0 to 0.1 ± 0.0 nmol/l [1.2 ± 0.1 to 0.4 ± 0.1 ng/ml]) (P = 0.0015). This reduction of the decrement in intraislet insulin during induction of hypoglycemia caused an ∼50% reduction (P = 0.0010) of the increase in plasma glucagon in the diazoxide clamps (from 29 ± 3 to 35 ± 2 pmol/l [102 ± 9 to 123 ± 8 pg/ml]) compared with the placebo clamps (from 28 ± 2 to 43 ± 5 pmol/l [98 ± 7 to 151 ± 16 pg/ml]). Baseline glucagon levels, the glucagon response to intravenous arginine, and the autonomic (adrenomedullary, sympathetic neural, and parasympathetic neural) responses to hypoglycemia were not altered by diazoxide. These data indicate that a decrease in intraislet insulin is a signal for the glucagon secretory response to hypoglycemia in healthy humans. The absence of that signal plausibly explains the loss of the glucagon response to falling plasma glucose concentrations, a key feature of the pathogenesis of iatrogenic hypoglycemia, in insulin-deficient (type 1 and advanced type 2) diabetes.
Absence of Heme Oxygenase-1 Exacerbates Myocardial Ischemia/Reperfusion Injury in Diabetic Mice
Authors: Liu Xiaoli , Wei Jiao , Peng David H. , Layne Matthew D. , Yet Shaw-Fang
Published: March 2007

Increased production of reactive oxygen species contributes to the etiology of diabetes complications. Pathophysiological stimuli that increase oxidative stress upregulate heme oxygenase (HO)-1, a cytoprotective heme–degrading enzyme. We hypothesized that HO-1 may be important in myocardial injury that is exacerbated by diabetes. To test this hypothesis, the left anterior descending coronary arteries of nondiabetic and diabetic wild-type (HO-1+/+) and HO-1 null (HO-1–/–) mice were ligated for 1 h followed by 24 h reperfusion. The absence of HO-1 significantly increased myocardial infarct size (36.4 ± 2.0 vs. 21.4 ± 1.8% in HO-1+/+ mice), while cardiac-specific overexpression of HO-1 protected against myocardial ischemic injury in diabetic mice. Despite similar high blood glucose levels, diabetic HO-1–/– mice had fourfold higher oxidative stress and larger infarcts (56.0 ± 2.8%) than diabetic HO-1+/+ mice (30.8 ± 6.1%). Moreover, hyperglycemia increased the mortality of HO-1–/– mice (31.3%) after ischemia/reperfusion injury, and 55% of diabetic HO-1–/– mice had mural thrombi in the left ventricles. The increased mortality of diabetic HO-1–/– mice may be in part due to formation of left ventricular mural thrombi. Our data demonstrate that the absence of HO-1 renders animals more susceptible to myocardial ischemia/reperfusion damage and diabetes worsens the injury.
Adipocytokines and VLDL Metabolism
Authors: Ng Theodore W.K. , Watts Gerald F. , Farvid Maryam S. , Chan Dick C. , Barrett P. Hugh R.
Published: March 2007

We investigated the relationship of plasma adipocytokine concentrations with VLDL apolipoprotein B (apoB)-100 kinetics in men. Plasma adiponectin, leptin, resistin, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) concentrations were measured using enzyme immunoassays and insulin resistance by homeostasis model assessment (HOMA) score in 41 men with BMI of 22–35 kg/m2. VLDL apoB kinetics were determined using an intravenous infusion of 1-[13C]leucine, gas chromatography–mass spectrometry, and compartmental modeling. Visceral and subcutaneous adipose tissue mass (ATM) were determined using magnetic resonance imaging, and total ATM was measured by bioelectrical impedance. In univariate regression, plasma adiponectin and leptin concentrations were inversely and directly associated, respectively, with plasma triglyceride; HOMA score; and visceral, subcutaneous, and total ATMs. Conversely, adiponectin and leptin were directly and inversely correlated, respectively, with VLDL apoB catabolism and HDL cholesterol concentration (P < 0.05). Resistin, IL-6, and TNF-α were not significantly associated with any of these variables. In multivariate regression, adiponectin was the most significant predictor of plasma VLDL apoB concentration (P = 0.001) and, together with total or subcutaneous ATM, was an independent predictor of VLDL apoB catabolism (P < 0.001); HOMA score was the most significant predictor of VLDL apoB hepatic secretion (P < 0.05). Leptin was not an independent predictor of VLDL apoB kinetics. In conclusion, plasma VLDL apoB kinetics may be differentially controlled by adiponectin and insulin resistance, with adiponectin regulating catabolism and insulin resistance regulating hepatic secretion in men. Total body fat may also independently determine the rate of VLDL catabolism, but leptin, resistin, IL-6, and TNF-α do not have a significant effect in regulating apoB kinetics.
Pioglitazone Induces Vascular Smooth Muscle Cell Apoptosis Through a Peroxisome Proliferator-Activated Receptor-γ, Transforming Growth Factor-β1, and a Smad2-Dependent Mechanism
Authors: Redondo Santiago , Ruiz Emilio , Santos-Gallego Carlos G. , Padilla Eugenia , Tejerina Teresa
Published: March 2007

Thiazolidinediones, such as pioglitazone, seem to exert direct antiatherosclerotic and antirestenotic effects on type 2 diabetes, in part due to an induction of vascular smooth muscle cell (VSMC) apoptosis. We aimed to study the role of transforming growth factor (TGF)-β in rat aortic VSMC. Pioglitazone at 100 μmol/l increased apoptosis without affecting DNA synthesis, and this effect was reversed by an anti-TGF-β1 antibody. Extracellular TGF-β1 levels were rapidly increased after treatment with pioglitazone in a peroxisome proliferator-activated receptor (PPAR)-γ-dependent mechanism because this secretion was blocked by the PPAR-γ inhibitor GW9662. Pioglitazone subsequently increased the nuclear recruitment of phospho-Smad2, without any effect on protein expression. According to our results, we propose that the apoptotic effect of pioglitazone on VSMC depends on the following sequence: PPAR-γ activation, TGF-β1 release, and selective phospho-Smad2 nuclear recruitment. Management of Smad signaling on VSMC might provide future clinical benefits in vascular diseases.
Topical Pretreatment of Diabetic Rats With All-trans Retinoic Acid Improves Healing of Subsequently Induced Abrasion Wounds
Authors: Lateef Humaira , Abatan Omorodola I. , Aslam Muhammad Nadeem , Stevens Martin J. , Varani James
Published: March 2007

In the current study, rats were made diabetic with streptozotocin (STZ) and maintained for 8 weeks, during which time they were treated topically on alternative days with a solution of 0.1% all-trans retinoic acid in a vehicle of 70:30% ethanol/propylene glycol. STZ-induced diabetic rats treated with vehicle served as controls. Additional nondiabetic rats were treated with all-trans retinoic acid or vehicle in parallel. At the end of the 8-week period, rats from all four treatment groups were subjected to abrasion wound formation. Wounds healed more rapidly in vehicle-treated nondiabetic skin than in vehicle-treated diabetic skin (96% of the wound surface area closed in nondiabetic rats within 6 days vs. 41% closed in diabetic rats). Wounds in all-trans retinoic acid-treated diabetic skin healed more rapidly than wounds in vehicle-treated diabetic skin (85% of the wound surface area closed in all-trans retinoic acid-treated diabetic rats vs. 41% closed in vehicle-treated diabetic rats). At the histological level, recently healed skin from vehicle-treated diabetic rats was shown to contain a thin, wispy provisional matrix in which many of the embedded cells were rounded and some were pycnotic. In contrast, a much denser provisional matrix with large numbers of embedded spindle-shaped cells was observed in healed wounds from diabetic skin that had been pretreated with all-trans retinoic acid. The all-trans retinoic acid-treated diabetic skin was histologically similar to vehicle-treated (or all-trans retinoic acid-treated) skin from nondiabetic animals. In light of these findings, we suggest that prophylactic use of retinoid-containing preparations might be useful in preventing the development of nonhealing skin ulcers resultant from minor traumas in at-risk skin.
Retrovirus-Like Long-Terminal Repeat DQ-LTR13 and Genetic Susceptibility to Type 1 Diabetes and Autoimmune Addison’s Disease
Authors: Gambelunghe Giovanni , Kockum Ingrid , Bini Vittorio , Giorgi Giovanni De , Celi Federica , Betterle Corrado , Giordano Roberta , Libè Rossella , Falorni Alberto ,   on behalf of the Umbria Type 1 Diabetes Registry and the Italian Addison Network
Published: March 2007

Controversial data are available on the association between the retrovirus-like long-terminal repeat (LTR) DQ-LTR13 and genetic susceptibility to type 1 diabetes and other autoimmune diseases. We analyzed DNA samples from 315 type 1 diabetic patients, 166 autoimmune Addison’s disease (AAD) patients, 1,054 healthy subjects, and 144 families of type 1 diabetic offspring. DQ-LTR13 was more frequent among patients than healthy subjects (Pc < 0.0006), and a preferential transmission of DQB1*0302-LTR13+ from parents to type 1 diabetic offspring was observed. DQ-LTR13 was in linkage disequilibrium (LD) with DQB1*0302 but not DQB1*0201. The presence of DQ-LTR13 increased the odds ratio of DQB1*0302 2.9- to 3.2-fold for type 1 diabetes and AAD. DRB1*0403 was absent in all of the 169 DRB1*04-positive patients but present in 27% (34 of 127) DRB1*04-positive healthy subjects (Pc < 0.001). DQ-LTR13 was detected in 1 of 34 (3%) DRB1*0403-positive healthy subjects and 36 of 93 (39%) individuals carrying another DRB1*04 allele (Pc = 0.002). Multivariate logistic regression analysis revealed that DQ-LTR13 is not independently associated with type 1 diabetes and AAD after correction for DQB1*0302 and DRB1*0403. Conversely, DQB1*0201, DQB1*0302, DRB1*0401, and DRB1*0403 were all significantly associated with disease risk also after correction for DQ-LTR13. We provide conclusive evidence that the genetic association of DQ-LTR13 with type 1 diabetes and AAD is primarily due to a LD with DQB1*0302 and DRB1*0403.
Genome-wide Linkage Scans for Fasting Glucose, Insulin, and Insulin Resistance in the National Heart, Lung, and Blood Institute Family Blood Pressure Program
Authors: An Ping , Freedman Barry I. , Hanis Craig L. , Chen Yii-Der I. , Weder Alan B. , Schork Nicholas J. , Boerwinkle Eric , Province Michael A. , Hsiung Chao Agnes , Wu Xiaodong , Quertermous Thomas , Rao D.C.
Published: March 2007

Genome-wide linkage analyses were performed using a multipoint variance components method in eight study groups from four multicenter networks (whites and blacks in GenNet; whites, blacks, and Mexican Americans in GENOA; whites and blacks in HyperGEN; and Asians in SAPPHIRe) that comprise the National Heart, Lung, and Blood Institute Family Blood Pressure Program (FBPP), in order to identify quantitative trait loci (QTLs) influencing fasting glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR). These study populations were enriched with subjects who had elevated blood pressure. Participants fasting <8 h, those with a history of type 2 diabetes, or those on antidiabetic medications were excluded from the current investigation. These three phenotypes were suitably transformed to approximate normal distributions. Each phenotype was adjusted for the effects of age, BMI, and field center separately by sex within each of the eight network ethnicity groups before genetic analysis. A total of 8,664 subjects comprising 5,923 sibpairs from 4,043 families with 365 markers were available for conducting a meta-analysis using a modified Fisher’s method of combining the P values from each of the eight scans. Evidence of linkages was found on chromosome 7q36 at 163 cM, with a logarithm of odds (LOD) score of 3.21 for HOMA-IR, and on chromosome 19q13 at 88 cM, with a LOD score of 3.33 for fasting glucose. We also found suggestive linkages (LOD score ≥2.2) on chromosome 7q36 at 163 cM, with LOD scores of 2.31 for fasting glucose and 2.26 for fasting insulin (versus the LOD score of 3.21 for HOMA-IR at this locus). In conclusion, QTLs were identified on chromosomes 7q36 and 19q13 for fasting glucose, insulin, and insulin resistance in large and multiple-ethnicity populations in the FBPP with good replications across several other independent studies for relevant traits. Follow-up dense mapping and association studies are warranted.
Androgen Receptor Null Male Mice Develop Late-Onset Obesity Caused by Decreased Energy Expenditure and Lipolytic Activity but Show Normal Insulin Sensitivity With High Adiponectin Secretion
Authors: Fan WuQiang , Yanase Toshihiko , Nomura Masatoshi , Okabe Taijiro , Goto Kiminobu , Sato Takashi , Kawano Hirotaka , Kato Shigeaki , Nawata Hajime
Published: March 2007

Androgen receptor (AR) null male mice (ARL−/Y) revealed late-onset obesity, which was confirmed by computed tomography–based body composition analysis. ARL−/Y mice were euphagic compared with the wild-type male (ARX/Y) controls, but they were also less dynamic and consumed less oxygen. Transcript profiling indicated that ARL−/Y mice had lower transcripts for the thermogenetic uncoupling protein 1, which was subsequently found to be ligand-dependently activated by AR. We also found enhanced secretion of adiponectin, which is insulin sensitizing, from adipose tissue and a relatively lower expression of peroxisome proliferator–activated receptor-γ in white adipose tissue in comparison to ARX/Y mice. Both factors might explain why the overall insulin sensitivity of ARL−/Y mice remained intact, despite their apparent obesity. The results revealed that AR plays important roles in male metabolism by affecting the energy balance, and it is negative to both adiposity and insulin sensitivity.
Reversal of Diabetes in Pancreatectomized Pigs After Transplantation of Neonatal Porcine Islets
Authors: Kin Tatsuya , Korbutt Gregory S. , Kobayashi Tsunehiro , Dufour Jannette M. , Rajotte Ray V.
Published: March 2007

Neonatal porcine islets (NPIs) are able to grow and to reverse hyperglycemia after transplantation in immunoincompetent mice. The aim of this study was to demonstrate the feasibility of allogeneic NPI grafts to achieve normoglycemia in a pancreatectomized diabetic pig. NPIs were isolated from pancreases of 1- to 3-day-old pigs, cultured, and then transplanted via the portal vein into the liver of totally pancreatectomized pigs (mean body weight, 20.8 kg). Each pig received NPIs consisting of 3.1 ± 0.3 × 106 β-cells/kg (12,476 ± 1,146 islet equivalent/kg). The six pigs that were given cyclosporine and sirolimus achieved normoglycemia by day 14 without insulin therapy. Three pigs died of surgical complications shortly after transplantation, whereas the other three remained insulin independent up to day 69. Of seven nonimmunosuppressed recipients, four pigs became normoglycemic by day 14 without insulin treatment, with two of the animals remaining normoglycemic long term. Well-preserved insulin-positive cells were found in the graft at the end of follow-up with a significant increase in insulin content in long-term survivors of both groups. This study demonstrates for the first time that allogeneic NPIs can reverse hyperglycemia in totally pancreatectomized diabetic pigs.
Nonhuman Primate Models for Diabetic Ocular Neovascularization Using AAV2-Mediated Overexpression of Vascular Endothelial Growth Factor
Authors: Lebherz Corinna , Maguire Albert M. , Auricchio Alberto , Tang Waixing , Aleman Tomas S. , Wei Zhangyong , Grant Rebecca , Cideciyan Artur V. , Jacobson Samuel G. , Wilson James M. , Bennett Jean
Published: March 2007

Neovascularization leads to blindness in numerous ocular diseases, including diabetic retinopathy, age-related macular degeneration, retinopathy of prematurity, and sickle cell disease. More effective and stable treatments for ocular neovascularization are needed, yet there are major limitations in the present animal models. To develop primate models of diabetic retinopathy and choroidal neovascularization, rhesus monkeys were injected subretinally or intravitreally with an adeno-associated virus (AAV)-2 vector carrying the cDNA encoding human vascular endothelial growth factor (VEGF). Overexpression of VEGF was measured by intraocular fluid sampling over time. Neovascularization was evaluated by ophthalmoscopy through angiography, optical coherence tomography, and ultimately histopathology. Overexpression of VEGF through AAV2 results in rapid development of features of diabetic retinopathy or macular edema, depending on the targeted cell type/mode of production of VEGF and diffusion of VEGF. Nonhuman primate models will be useful in testing long-term safety and efficacy of novel therapeutic agents for blinding neovascular diseases.
Genetic Variations in the Gene Encoding ELMO1 Are Associated With Susceptibility to Diabetic Nephropathy
Authors: Shimazaki Atsuyuki , Kawamura Yoshihiro , Kanazawa Akio , Sekine Akihiro , Saito Susumu , Tsunoda Tatsuhiko , Koya Daisuke , Babazono Tetsuya , Tanaka Yasushi , Matsuda Masafumi , Kawai Koichi , Iiizumi Tomohiro , Imanishi Masahito , Shinosaki Toshihiro , Yanagimoto Toru , Ikeda Minoru , Omachi Shigeki , Kashiwagi Atsunori , Kaku Kohei , Iwamoto Yasuhiko , Kawamori Ryuzou , Kikkawa Ryuichi , Nakajima Masatoshi , Nakamura Yusuke , Maeda Shiro
Published: March 2007

To search for a gene(s) conferring susceptibility to diabetic nephropathy (DN), we genotyped over 80,000 gene-based single nucleotide polymorphisms (SNPs) in Japanese patients and identified that the engulfment and cell motility 1 gene (ELMO1) was a likely candidate for conferring susceptibility to DN, in view of the significant association of an SNP in this gene with the disease (intron 18+9170, GG vs. GA+AA, χ2 = 19.9, P = 0.000008; odds ratio 2.67, 95% CI 1.71–4.16). In situ hybridization (ISH) using the kidney of normal and diabetic mice revealed that ELMO1 expression was weakly detectable mainly in tubular and glomerular epithelial cells in normal mouse kidney and was clearly elevated in the kidney of diabetic mice. Subsequent in vitro analysis revealed that ELMO1 expression was elevated in cells cultured under high glucose conditions (25 mmol/l) compared with cells cultured under normal glucose conditions (5.5 mmol/l). Furthermore, we identified that the expression of extracellular matrix protein genes, such as type 1 collagen and fibronectin, were increased in cells that overexpress ELMO1, whereas the expression of matrix metalloproteinases was decreased. These results indicate that ELMO1 is a novel candidate gene that both confers susceptibility to DN and plays an important role in the development and progression of this disease.
Ultrafine Mapping of SNPs From Mouse Strains C57BL/6J, DBA/2J, and C57BLKS/J for Loci Contributing to Diabetes and Atherosclerosis Susceptibility
Authors: Davis Richard C. , Schadt Eric E. , Cervino Alessandra C.L. , Péterfy Miklós , Lusis Aldons J.
Published: March 2007

The inbred mouse strain C57BLKS/J (BKS) carrying a mutation of the leptin receptor lepr−/− (BKS-db) is a classic mouse model of type 2 diabetes. While BKS was originally presumed to be a substrain of C57BL/6J (B6), it has become apparent that its genome contains introgressed regions from a DBA/2 (DBA)-like strain and perhaps other unidentified sources. It has been hypothesized that the strikingly enhanced diabetes susceptibility of BKS-db compared with B6-db is conferred by this introgressed DNA. Using high-density single nucleotide polymorphisms, we have mapped the DBA and other contaminating DNA regions present in BKS. Thus, ∼70% of its genome appears to derive from B6, with ∼20% from DBA and another 9% from an unidentified donor. Comparison with 56 diverse inbred strains suggests that this donor may be a less common inbred strain or an outbred or wild strain. Using expression data from a B6 × DBA cross, we identified differentially regulated genes between these two strains. Those cis-regulated genes located on DBA-like blocks in BKS constitute primary candidates for genes contributing to diabetes susceptibility in the BKS-db strain. To further prioritize these candidates, we identified those cis-acting expression quantitative trait loci whose expression significantly correlates with diabetes-related phenotypes.
Acute Induction of Gene Expression in Brain and Liver by Insulin-Induced Hypoglycemia
Authors: Mastaitis Jason W. , Wurmbach Elisa , Cheng Hui , Sealfon Stuart C. , Mobbs Charles V.
Published: March 2007

The robust neuroendocrine counterregulatory responses induced by hypoglycemia protect the brain by restoring plasma glucose, but little is known about molecular responses to hypoglycemia that may also be neuroprotective. To clarify these mechanisms, we examined gene expression in hypothalamus, cortex, and liver 3 h after induction of mild hypoglycemia by a single injection of insulin, using cDNA microarray analysis and quantitative real-time PCR. Real-time PCR corroborated the induction of six genes (angiotensinogen, GLUT-1, inhibitor of κB, inhibitor of DNA binding 1 [ID-1], Ubp41, and mitogen-activated protein kinase phosphatase-1 [MKP-1]) by insulin-induced hypoglycemia in the hypothalamus: five of these six genes in cortex and three (GLUT-1, angiotensinogen, and MKP-1) in liver. The induction was due to hypoglycemia and not hyperinsulinemia, since fasting (characterized by low insulin and glucose) also induced these genes. Four of these genes (angiotensinogen, GLUT-1, ID-1, and MKP-1) have been implicated in enhancement of glucose availability, which could plausibly serve a neuroprotective role during acute hypoglycemia but, if persistent, could also cause glucose-sensing mechanisms to overestimate plasma glucose levels, potentially causing hypoglycemia-induced counterregulatory failure. Although using cDNA microarrays with more genes, or microdissection, would presumably reveal further responses to hypoglycemia, these hypoglycemia-induced genes represent useful markers to assess molecular mechanisms mediating cellular responses to hypoglycemia.