bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased In Vivo Regeneration of Cortisol in Adipose Tissue in Human Obesity and Effects of the 11β-Hydroxysteroid Dehydrogenase Type 1 Inhibitor Carbenoxolone
Authors: Sandeep Thekkepat C. , Andrew Ruth , Homer Natalie Z.M. , Andrews Robert C. , Smith Ken , Walker Brian R.
Published: March 2007

11β-Hydroxysteroid dehydrogenase type 1 (11HSD1) regenerates cortisol from cortisone within adipose tissue and liver. 11HSD1 inhibitors may enhance insulin sensitivity in type 2 diabetes and be most efficacious in obesity when 11HSD1 is increased in subcutaneous adipose biopsies. We examined the regeneration of cortisol in vivo in obesity, and the effects of the 11HSD1 inhibitor carbenoxolone. We compared six lean and six obese men and performed a randomized, placebo-controlled crossover study of carbenoxolone in obese men. The obese men had no difference in their whole-body rate of regenerating cortisol (measured with 9,11,12,12-[2H4]cortisol tracer), but had more rapid conversion of [3H]cortisone to [3H]cortisol in abdominal subcutaneous adipose tissue (measured with microdialysis). During insulin infusion, adipose 11HSD1 activity fell markedly in lean but not in obese men. Carbenoxolone inhibited whole-body cortisol regeneration, but did not significantly inhibit adipose 11HSD1 and had no effects on insulin sensitivity (measured by [2H2]glucose infusion with or without hyperinsulinemia). Thus, in vivo cortisol generation is increased selectively within adipose tissue in obesity, perhaps reflecting resistance to insulin-mediated downregulation of 11HSD1. However, obese men are less susceptible than lean men to the insulin-sensitizing effects of carbenoxolone. To be useful in obese patients, 11HSD1 inhibitors will need to inhibit the enzyme more effectively in adipose tissue.
In Vivo Control of Diabetogenic T-Cells by Regulatory CD4+CD25+ T-Cells ExpressingFoxp3
Authors: Lundsgaard Dorthe , Holm Thomas Lindebo , Hornum Lars , Markholst Helle
Published: March 2007

To understand the ability of regulatory T-cells to control diabetes development in clinically relevant situations, we established a new model of accelerated diabetes in young DP-BB rats by transferring purified T-cells from DR-BB rats made acutely diabetic. Transfer of 3, 5, 10, or 23 million pure in vitro−activated T-cells accelerated diabetes onset in >90% of the recipients, with the degree of acceleration being dosage dependent. Cotransfer of unfractionated leukocytes from healthy donors prevented diabetes. Full protection was achieved when protective cells were transferred 3–4 days before diabetogenic cells, whereas transfer 2 days before conferred only partial protection. Protection resided in the CD4+ fraction, as purified CD4+ T-cells prevented the accelerated diabetes. When CD25+ cells were depleted from these cells before they were transferred, their ability to prevent diabetes was impaired. In contrast, two million CD4+CD25+ cells (expressing Foxp3) prevented the accelerated diabetes when transferred both before and simultaneously with the diabetogenic T-cells. In addition, 2 million CD4+CD25+ T-cells prevented spontaneous diabetes, even when given to rats age 42 days, whereas 20 million CD4+CD25− cells (with low Foxp3 expression) were far less effective. We thus demonstrated that CD4+CD25+ cells exhibit powerful regulatory potential in rat diabetes.
Distinct Effects of Glucose-Dependent Insulinotropic Polypeptide and Glucagon-Like Peptide-1 on Insulin Secretion and Gut Motility
Authors: Miki Takashi , Minami Kohtaro , Shinozaki Hidehiro , Matsumura Kimio , Saraya Atsunori , Ikeda Hiroki , Yamada Yuichiro , Holst Jens Juul , Seino Susumu
Published: March 2007

Glucose-induced insulin secretion from pancreatic β-cells depends critically on ATP-sensitive K+ channel (KATP channel) activity, but it is not known whether KATP channels are involved in the potentiation of insulin secretion by glucose-dependent insulinotropic polypeptide (GIP). In mice lacking KATP channels (Kir6.2−/− mice), we found that pretreatment with GIP in vivo failed to blunt the rise in blood glucose levels after oral glucose load. In Kir6.2−/− mice, potentiation of insulin secretion by GIP in vivo was markedly attenuated, indicating that KATP channels are essential in the insulinotropic effect of GIP. In contrast, pretreatment with glucagon-like peptide-1 (GLP-1) in Kir6.2−/− mice potentiated insulin secretion and blunted the rise in blood glucose levels. We also found that GLP-1 inhibited gut motility whereas GIP did not. Perfusion experiments of Kir6.2−/− mice revealed severely impaired potentiation of insulin secretion by 1 nmol/l GIP and substantial potentiation by 1 nmol/l GLP-1. Although both GIP and GLP-1 increase the intracellular cAMP concentration and potentiate insulin secretion, these results demonstrate that the GLP-1 and GIP signaling pathways involve the KATP channel differently.
Neuronatin, a Downstream Target of BETA2/NeuroD1 in the Pancreas, Is Involved in Glucose-Mediated Insulin Secretion
Authors: Chu Khoi , Tsai Ming-Jer
Published: March 2007

BETA2 (NeuroD1) is a member of the basic helix-loop-helix transcription factor family. BETA2 plays an important role in the development of the pancreas and the nervous system. Using microarray technology, we identified neuronatin (Nnat) as differentially expressed between wild-type (WT) and knockout (KO) pancreatic RNA from embryonic day 14 (e14.5). NNAT is a member of the proteolipid family of amphipathic polypeptides and is believed to be involved in ion channel transport or channel modulation. Northern blot and in situ hybridization analysis of WT and KO samples confirmed the downregulation of Nnat in pancreas of mutant BETA2 embryos. Chromatin immunoprecipitation and gel shift assays were performed and demonstrated the presence of BETA2 on the Nnat promoter, thus confirming the direct transcriptional regulation of Nnat by BETA2. To assess NNAT potential function, we performed knockdown studies by siRNA in NIT cells and observed a reduction in the ability of the NIT cells to respond to glucose. These results suggest for the first time an important role for NNAT in insulin secretion and for proper β-cell function.
Pancreatic β-Cell Failure and Diabetes in Mice With a Deletion Mutation of the Endoplasmic Reticulum Molecular Chaperone Gene P58IPK
Authors: Ladiges Warren C. , Knoblaugh Sue E. , Morton John F. , Korth Marcus J. , Sopher Bryce L. , Baskin Carole R. , MacAuley Alasdair , Goodman Alan G. , LeBoeuf Renee C. , Katze Michael G.
Published: March 2007

The endoplasmic reticulum (ER) transmits apoptotic signals in the pancreas during ER stress, implicating ER stress–mediated apoptosis in the development of diabetes. P58IPK (DNAJC3) is induced during ER stress and functions as a negative feedback component to inhibit eIF-2α signaling and attenuate the later phases of the ER stress response. To gain insight into a more comprehensive role of P58IPK function, we generated deletion mutant mice that showed a gradual onset of glucosuria and hyperglycemia associated with increasing apoptosis of pancreatic islet cells. Lack of P58IPK had no apparent effect on the functional integrity of viable β-cells. A set of genes associated with apoptosis showed altered expression in pancreatic islets from P58IPK-null mice, further substantiating the apoptosis phenotype. The data provide in vivo evidence to support the concept that P58IPK functions as a signal for the downregulation of ER-associated proteins involved in the initial ER stress response, thus preventing excessive cell loss by degradation pathways. Insulin deficiency associated with the absence of P58IPK mimics β-cell failure associated with type 1 and late-stage type 2 diabetes. P58IPK function and activity may therefore provide a novel area of investigation into ER-mediated mechanistic and therapeutic approaches for diabetes.
Inducible Nitric Oxide Synthase Has Divergent Effects on Vascular and Metabolic Function in Obesity
Authors: Noronha Brian T. , Li Jian-Mei , Wheatcroft Stephen B. , Shah Ajay M. , Kearney Mark T.
Published: March 2007

Previous studies have suggested an involvement of inducible nitric oxide synthase (iNOS) in obesity, but the relation, if any, between this and mechanisms underlying endothelial dysfunction in obesity is unknown. We studied mice fed an obesogenic high-fat or standard diet for up to 8 weeks. Obesity was associated with elevated blood pressure; resistance to the glucoregulatory actions of insulin; resistance to the vascular actions of insulin, assessed as the reduction in phenylephrine constrictor response of aortic rings after insulin preincubation (lean −21.7 ± 11.5 vs. obese 18.2 ± 15.5%; P < 0.05); and evidence of reactive oxygen species (ROS)-dependent vasodilatation in response to acetylcholine in aortic rings (change in maximal relaxation to acetylcholine after exposure to catalase: lean −2.1 ± 6.0 vs. obese −15.0 ± 3.8%; P = 0.04). Obese mice had increased expression of iNOS in aorta, with evidence of increased vascular NO production, assessed as the increase in maximal constriction to phenylephrine after iNOS inhibition with 1400W (lean −3.5 ± 9.1 vs. obese 42.1 ± 11.2%; P < 0.001). To further address the role of iNOS in obesity-induced vascular and metabolic dysfunction, we studied the effect of a high-fat diet in iNOS knockout mice (iNOS KO). Obese iNOS KO mice were protected against the development of resistance to insulin’s glucoregulatory and vascular effects (insulin-dependent reduction in maximal phenylephrine response: obese wild-type 11.2 ± 15.0 vs. obese iNOS KO −20.0 ± 7.7%; P = 0.02). However, obese iNOS KO mice remained hypertensive (124.0 ± 0.7 vs. 114.9 ± 0.5 mmHg; P < 0.01) and had evidence of increased vascular ROS production. Although these data support iNOS as a target to protect against the adverse effects of obesity on glucoregulation and vascular insulin resistance, iNOS inhibition does not prevent the development of raised blood pressure or oxidative stress.
The Calcium-Dependent Protease Calpain Causes Endothelial Dysfunction in Type 2 Diabetes
Authors: Stalker Timothy J. , Gong Yulan , Scalia Rosario
Published: March 2007

Cardiovascular complications are the leading cause of morbidity and mortality in diabetic patients. Endothelial dysfunction with impaired endothelial nitric oxide (NO) synthase (eNOS) activity is a widely accepted cause of diabetic vasculopathy. The mechanisms of endothelial dysfunction in diabetes remain elusive, thus limiting effective therapeutic interventions. We report novel evidence demonstrating that the calcium-dependent protease calpain causes endothelial dysfunction and vascular inflammation in the microcirculation of the ZDF (Zucker diabetic fatty) rat, a genetic rat model of type 2 diabetes. We found evidence of increased calpain activity and leukocyte trafficking in the microcirculation of ZDF rats. Inhibition of calpain activity significantly attenuated leukocyte-endothelium interactions in the vasculature of ZDF rats. Expression of cell adhesion molecules in the vascular endothelium of ZDF rats was consistently increased, and it was suppressed by calpain inhibition. In vivo measurement of endothelial NO availability demonstrated a 60% decrease in NO levels in the microcirculation of diabetic rats, which was also prevented by calpain inhibition. Immunoprecipitation studies revealed calpain-dependent loss of association between eNOS and the regulatory protein heat shock protein 90. Collectively, these data provide evidence for a novel mechanism of endothelial dysfunction and vascular inflammation in diabetes. Calpains may represent a new molecular target for the prevention and treatment of diabetic vascular complications.
Inhalation of Insulin (Exubera) Is Associated With Augmented Disposal of Portally Infused Glucose in Dogs
Authors: Edgerton Dale S. , Neal Doss W. , Scott Melanie , Bowen Larry , Wilson Warren , Hobbs Charles H. , Leach Chet , Sivakumaran Shantha , Strack Thomas R. , Cherrington Alan D.
Published: March 2007

The results of the present study, using the conscious beagle dog, demonstrate that inhaled insulin (INH; Exubera) provides better glycemic control during an intraportal glucose load than identical insulin levels induced by insulin (Humulin) infusion into the inferior vena cava (IVC). In the INH group (n = 13), portal glucose infusion caused arterial plasma glucose to rise transiently (152 ± 9 mg/dl), before it returned to baseline (65 min) for the next 2 h. Net hepatic glucose uptake was minimal, whereas nonhepatic uptake rose to 12.5 ± 0.5 mg · kg−1 · min−1 (65 min). In the IVC group (n = 9), arterial glucose rose rapidly (172 ± 6 mg/dl) and transiently fell to 135 ± 13 mg/dl (65 min) before returning to 165 ± 15 mg/dl (125 min). Plasma glucose excursions and hepatic glucose uptake were much greater in the IVC group, whereas nonhepatic uptake was markedly less (8.6 ± 0.9 mg · kg−1 · min−1; 65 min). Insulin kinetics and areas under the curve were identical in both groups. These data suggest that inhalation of Exubera results in a unique action on nonhepatic glucose clearance.
An Autosomal Genome-wide Scan for Loci Linked to Pre-Diabetic Phenotypes in Nondiabetic Chinese Subjects From the Stanford Asia-Pacific Program of Hypertension and Insulin Resistance Family Study
Authors: Chiu Yen-Feng , Chuang Lee-Ming , Hsiao Chin-Fu , Hung Yi-Jen , Lin Ming-Wei , Chen Ying-Tsung , Grove John , Jorgenson Eric , Quertermous Thomas , Risch Neil , Hsiung Chao A.
Published: March 2007

Type 2 diabetes is a complex disease involving both genetic and environmental components. Abnormalities in insulin secretion and insulin action usually precede the development of type 2 diabetes and can serve as good quantitative measures for genetic mapping. We therefore undertook an autosomal genomic search to locate the quantitative trait locus (QTL) linked to these traits in 1,365 nondiabetic Chinese subjects from 411 nuclear families. Residuals of these log-transformed quantitative traits were analyzed in multipoint linkage analysis using a variance-components approach. The most significant QTL for fasting insulin, which coincides with the QTL for homeostasis model assessment of insulin resistance, was located at 37 cM on chromosome 20, with a maximum empirical logarithm of odds (LOD) score of 3.01 (empirical P = 0.00006) when adjusted for age, sex, BMI, antihypertensive medications, recruitment centers, and environmental factors. In the same region, a QTL for fasting glucose was identified at 51 cM, with an empirical LOD score of 2.03 (empirical P = 0.0012). There were other loci with maximum empirical LOD scores ≥1.29 located on chromosomes 1q, 2p, 5q, 7p, 9q, 10p, 14q, 18q, and 19q for different diabetes-related traits. These loci may harbor genes that regulate glucose homeostasis either independently or via interactions of the genes within these regions.
Variation in the Gene for Muscle-Specific AMP Deaminase Is Associated With Insulin Clearance, a Highly Heritable Trait
Authors: Goodarzi Mark O. , Taylor Kent D. , Guo Xiuqing , Quiñones Manuel J. , Cui Jinrui , Li Xiaohui , Hang Tieu , Yang Huiying , Holmes Edward , Hsueh Willa A. , Olefsky Jerrold , Rotter Jerome I.
Published: March 2007

The rising prevalence of the insulin resistance syndrome in our society necessitates a better understanding of the genetic determinants of all aspects of insulin action and metabolism. We evaluated the heritability of insulin sensitivity and the metabolic clearance rate of insulin (MCRI) as quantified by the euglycemic-hyperinsulinemic clamp in 403 Mexican Americans. We tested the candidate gene AMP deaminase 1 (AMPD1) for association with insulin-related traits because it codes for an enzyme that has the potential to influence multiple aspects of insulin pharmacodynamics. By converting AMP to inosine monophosphate, AMPD1 plays a major role in regulating cellular AMP levels; AMP activates AMP kinase, an enzyme that modulates cellular energy and insulin action. We determined that nine AMPD1 single nucleotide polymorphisms (SNPs) defined two haplotype blocks. Insulin clearance was found to have a higher heritability (h2 = 0.58) than fasting insulin (h2 = 0.38) or insulin sensitivity (h2 = 0.44). The MCRI was associated with AMPD1 SNPs and haplotypes. Insulin clearance is a highly heritable trait, and specific haplotypes within the AMPD1 gene, which encodes a skeletal muscle−specific protein, are associated with variation in insulin clearance. We postulated that the processes of insulin action and insulin clearance in skeletal muscle are highly regulated and that AMPD1 function may play an important role in these phenomena.
Altered Hepatic and Muscle Substrate Utilization Provoked by GLUT4 Ablation
Authors: Ranalletta Mollie , Jiang Hua , Li Jing , Tsao T.S. , Stenbit Antine E. , Yokoyama Masayoshi , Katz Ellen B. , Charron Maureen J.
Published: March 2007

Studies were conducted to explore altered substrate utilization and metabolism in GLUT4 null mice. Liver fatty acid synthase mRNA and fatty acid synthesis rates were dramatically increased in GLUT4 null mice compared with control mice and were supported by increased rates of the pentose phosphate pathway oxidative phase and sterol regulatory binding protein mRNA expression. Increased GLUT2 protein content, glucokinase mRNA, and glucose-6-phosphate in GLUT4 null mice may provide substrate for the enhanced fatty acid synthesis. Increased fatty acid synthesis, however, did not lead to hepatic triglyceride accumulation in GLUT4 null mice because of increased hepatic triglyceride secretion rates. GLUT4 null mice rapidly cleared orally administered olive oil, had reduced serum triglyceride concentrations in the fed and the fasted state, and increased skeletal muscle lipoprotein lipase when compared with controls. Oleate oxidation rates were increased in GLUT4 null skeletal muscle in association with mitochondrial hyperplasia/hypertrophy. This study demonstrated that GLUT4 null mice had increased hepatic glucose uptake and conversion into triglyceride for subsequent use by muscle. The ability of GLUT4 null mice to alter hepatic carbohydrate and lipid metabolism to provide proper nutrients for peripheral tissues may explain (in part) their ability to resist diabetes when fed a normal diet.
Insulin Signaling in the Central Nervous System
Authors: Porte Daniel , Baskin Denis G. , Schwartz Michael W.
Published: March 2007

Insulin and its signaling systems are implicated in both central and peripheral mechanisms governing the ingestion, distribution, metabolism, and storage of nutrients in organisms ranging from worms to humans. Input from the environment regarding the availability and type of nutrients is sensed and integrated with humoral information (provided in part by insulin) regarding the sufficiency of body fat stores. In response to these afferent inputs, neuronal pathways are activated that influence energy flux and nutrient metabolism in the body and ensure reproductive competency. Growing evidence supports the hypothesis that reduced central nervous system insulin signaling from either defective secretion or action contributes to the pathogenesis of common metabolic disorders, including diabetes and obesity, and may therefore help to explain the close association between these two disorders. These considerations implicate insulin action in the brain, an organ previously considered to be insulin independent, as a key determinant of both glucose and energy homeostasis.
Proteome Analysis of Skeletal Muscle From Obese and Morbidly Obese Women
Authors: Hittel Dustin S. , Hathout Yetrib , Hoffman Eric P. , Houmard Joseph A.
Published: March 2007

Obesity-related diseases such as the metabolic syndrome and type 2 diabetes originate, in part, from the progressive metabolic deterioration of skeletal muscle. A preliminary proteomic survey of rectus abdominus muscle detected a statistically significant increase in adenylate kinase (AK)1, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and aldolase A in obese/overweight and morbidly obese women relative to lean control subjects. AK1 is essential for the maintenance of cellular energy charge, and GAPDH and aldolase A are well known glycolytic enzymes. We found that muscle AK1 protein and enzymatic activity increased 2.9 and 90%, respectively, in obese women and 9.25 and 100%, respectively, in morbidly obese women. The total enzymatic activity of creatine kinase, which also regulates energy metabolism in muscle, was shown to increase 30% in obese/overweight women only. We propose that increased protein and enzymatic activity of AK1 is representative of a compensatory glycolytic drift to counteract reduced muscle mitochondrial function with the progression of obesity. This hypothesis is supported by increased abundance of the glycolytic enzymes GAPDH and aldolase A in obese and morbidly obese muscle. In summary, proteome analysis of muscle has helped us better describe the molecular etiology of obesity-related disease.
Adenovirus-Mediated Adiponectin Expression Augments Skeletal Muscle Insulin Sensitivity in Male Wistar Rats
Authors: Satoh Hiroaki , Nguyen M.T. Audrey , Trujillo Maria , Imamura Takeshi , Usui Isao , Scherer Philipp E. , Olefsky Jerrold M.
Published: March 2007

In this study, we investigated the chronic in vivo effect of adiponectin on insulin sensitivity and glucose metabolism by overexpressing the adiponectin protein in male Wistar rats using intravenous administration of an adenovirus (Adv-Adipo). Virally infected liver secreted adiponectin as high and low molecular weight complexes. After 7 days of physiological or supraphysiological hyperadiponectinemia, the animals displayed enhanced insulin sensitivity during the glucose tolerance and insulin tolerance tests. Glucose clamp studies performed at submaximal and maximal insulin infusion rates (4 and 25 mU · kg−1 · min−1, respectively) also demonstrated increased insulin sensitivity in Adv-Adipo animals, with the insulin-stimulated glucose disposal rate being increased by 20–67%. In contrast, insulin’s effect on the suppression of hepatic glucose output and plasma free fatty acid levels was not enhanced in Adv-Adipo rats compared with controls, suggesting that high levels of adiponectin expression in the liver may lead to a local desensitization. Consistent with the clamp data, the activation of AMP-activated protein kinase was significantly enhanced in skeletal muscle (by 50%) but not in liver. One interesting finding was that in male Wistar rats, both AdipoR1 and AdipoR2 expression levels were higher in skeletal muscle than in liver, as it is the case in humans. These results indicate that chronic adiponectin treatment enhances insulin sensitivity and could serve as a therapy for human insulin resistance.
Pioglitazone Induces Mitochondrial Biogenesis in Human Subcutaneous Adipose Tissue In Vivo
Authors: Bogacka Iwona , Xie Hui , Bray George A. , Smith Steven R.
Published: March 2007

Thiazolidenediones such as pioglitazone improve insulin sensitivity in diabetic patients by several mechanisms, including increased uptake and metabolism of free fatty acids in adipose tissue. The purpose of the present study was to determine the effect of pioglitazone on mitochondrial biogenesis and expression of genes involved in fatty acid oxidation in subcutaneous fat. Patients with type 2 diabetes were randomly divided into two groups and treated with placebo or pioglitazone (45 mg/day) for 12 weeks. Mitochodrial DNA copy number and expression of genes involved in mitochondrial biogenesis were quantified by real-time PCR. Pioglitazone treatment significantly increased mitochondrial copy number and expression of factors involved in mitochondrial biogenesis, including peroxisome proliferator–activated receptor (PPAR)-γ coactivator-1α and mitochondrial transcription factor A. Treatment with pioglitazone stimulated the expression of genes in the fatty acid oxidation pathway, including carnitine palmitoyltransferase-1, malonyl-CoA decarboxylase, and medium-chain acyl-CoA dehydrogenase. The expression of PPAR-α, a transcriptional regulator of genes encoding mitochondrial enzymes involved in fatty acid oxidation, was higher after pioglitazone treatment. Finally, the increased mitochondrial copy number and the higher expression of genes involved in fatty acid oxidation in human adipocytes may contribute to the hypolipidemic effects of pioglitazone.
Donor Treatment With Carbon Monoxide Can Yield Islet Allograft Survival and Tolerance
Authors: Wang Hongjun , Lee Soo Sun , Gao Wenda , Czismadia Eva , McDaid James , Öllinger Robert , Soares Miguel P. , Yamashita Kenichiro , Bach Fritz H.
Published: March 2007

Treatment of animals or certain cells with carbon monoxide (CO), a product of heme degradation by heme oxygenase-1 (HO-1), has potent anti-inflammatory and antiapoptotic effects that contribute to the survival of transplanted organs. We report here that inducing HO-1 in, or administering CO to, only the donor can be used in a therapeutic manner to sustain the survival of transplanted allogeneic islets. Similar treatments of only the islets or only the recipient are also salutary. Administering CO only to the donor frequently leads to long-term survival of those islets in untreated allogeneic recipients, which are then antigen-specifically tolerant. Several proinflammatory and proapoptotic genes that are strongly induced in islets after transplantation in the untreated situation were significantly suppressed after administering CO to the donor without further treatment. These included tumor necrosis factor-α, inducible nitric oxide synthase, monocyte chemoattractant protein-1, granzyme B, and Fas/Fas ligand, all of which contribute to the pathogenesis of the rejection of transplanted islets. This correlated with a lesser infiltration of recipient macrophages into the transplanted islets. Our present findings show that induction of HO-1 in, or administration of CO to, only the donor, islets, or the recipient or combinations of such treatments improve allogeneic islet survival.
Nonproteinuric Diabetes-Associated Nephropathy in the Cohen Rat Model of Type 2 Diabetes
Authors: Yagil Chana , Barak Adiel , Ben-Dor David , Rosenmann Eliezer , Bernheim Joel , Rosner Mordechai , Segev Yael , Weksler-Zangen Sarah , Raz Itamar , Yagil Yoram
Published: March 2007

The Cohen diabetic rat is an experimental model reminiscent of human type 2 diabetes. The aim of this study was to characterize the development of end-organ damage in this model. Cohen diabetic sensitive (CDs) and Cohen diabetic resistant (CDr) rats were fed regular diet or a diabetogenic diet. Glucose tolerance, renal function, and renal and retinal histology were studied at set intervals. CDs fed diabetogenic diet were the only strain that expressed the diabetic metabolic phenotype. In this strain, urinary protein excretion did not increase with the development of diabetes, but plasma urea and creatinine levels increased and creatinine clearance decreased. Light microscopy revealed in CDs enlarged glomeruli with increased mesangial matrix and thickening of the glomerular capillary wall; electron microscopy demonstrated thickened basement membrane and mesangial abundance. There was increased staining for type IV collagen in glomeruli and interstitium of CDs. The retinas of diabetic CDs demonstrated pathology consistent with nonproliferative diabetic retinopathy. The histological findings in the kidneys, the absence of proteinuria, the impairment in glomerular filtration, and the development of retinopathy in CDs are consistent with diabetes-associated nephropathy that is similar to a nonalbuminuric type of nephropathy associated with type 2 diabetes in humans.
Kallikrein Gene Delivery Improves Serum Glucose and Lipid Profiles and Cardiac Function in Streptozotocin-Induced Diabetic Rats
Authors: Montanari David , Yin Hang , Dobrzynski Eric , Agata Jun , Yoshida Hideaki , Chao Julie , Chao Lee
Published: March 2007

We investigated the role of the kallikrein-kinin system in cardiac function and glucose utilization in the streptozotocin (STZ)-induced diabetic rat model using a gene transfer approach. Adenovirus harboring the human tissue kallikrein gene was administered to rats by intravenous injection at 1 week after STZ treatment. Human kallikrein transgene expression was detected in the serum and urine of STZ-induced diabetic rats after gene transfer. Kallikrein gene delivery significantly reduced blood glucose levels and cardiac glycogen accumulation in STZ-induced diabetic rats. Kallikrein gene transfer also significantly attenuated elevated plasma triglyceride and cholesterol levels, food and water intake, and loss of body weight gain, epididymal fat pad, and gastrocnemius muscle weight in STZ-induced diabetic rats. However, these effects were blocked by icatibant, a kinin B2 receptor antagonist. Cardiac function was significantly improved after kallikrein gene transfer as evidenced by increased cardiac output and ±ΔP/Δt (maximum speed of contraction/relaxation), along with elevated cardiac sarco(endo)plasmic reticulum (Ca2+ + Mg2+)-ATPase (SERCA)-2a, phosphorylated phospholamban, NOx and cAMP levels, and GLUT4 translocation into plasma membranes of cardiac and skeletal muscle. Kallikrein gene delivery also increased Akt and glycogen synthase kinase (GSK)-3β phosphorylation, resulting in decreased GSK-3β activity in the heart. These results indicate that kallikrein through kinin formation protects against diabetic cardiomyopathy by improving cardiac function and promoting glucose utilization and lipid metabolism.
The +276 Polymorphism of the APM1 Gene, Plasma Adiponectin Concentration, and Cardiovascular Risk in Diabetic Men
Authors: Qi Lu , Li Tricia , Rimm Eric , Zhang Cuilin , Rifai Nader , Hunter David , Doria Alessandro , Hu Frank B.
Published: March 2007

Recently, the genetic variability at adiponectin locus (APM1) was associated with cardiovascular risk in patients with type 2 diabetes. We sought to examine the associations of five variants of APM1 gene (C-11365G, A-4034C, A-3964G, T45G, and G276T) with the risk of cardiovascular diseases (CVDs) in a larger cohort of diabetic patients. Of 879 diabetic men from the Health Professionals Follow-up Study, 239 participants developed coronary heart disease or stroke during 14 years of follow-up and 640 CVD-negative subjects were used as control subjects. The risk of CVD was significantly lower in TT homozygotes at locus +276 than in other genotypes under a recessive inheritance model after adjusting for age, BMI, smoking, alcohol consumption, physical activity, aspirin use, HbA1c, and history of hypertension or hypercholesterolemia (odds ratio 0.38 [95% CI 0.18–0.79]; P = 0.009). In the CVD-negative control subjects, the allele 276T was associated with significantly higher plasma adiponectin levels in a dose-dependent pattern (GG 14.8, GT 16.2, and TT 18.8 μg/ml) after adjusting for age, BMI, and other variables (P for trend = 0.0019). In conclusion, our study showed significant associations between APM1 G276T and decreased CVD risk and increased plasma adiponectin levels in diabetic men.
Continuous Glucose Monitoring in Interstitial Subcutaneous Adipose Tissue and Skeletal Muscle Reflects Excursions in Cerebral Cortex
Authors: Nielsen Jannik Kruse , Djurhuus Christian Born , Gravholt Claus Højbjerg , Carus Andreas Christiansen , Granild-Jensen Jacob , Ørskov Hans , Christiansen Jens Sandahl
Published: March 2007

Continuous glucose monitoring (CGM) is being explored using several types of glucose sensors. Some are designed for subcutaneous adipose tissue. It is important to determine to which extent these glucose fluctuations in different tissues reflect changes taking place in the central nervous system, where glucose sensing is thought to occur. We studied the ability of subcutaneous adipose interstitial fluid measurements to parallel glucose propagations in blood, muscle, and central nervous system (CNS) during hyper- and hypoglycemia. A subcutaneous CGM system was applied in the CNS, subcutaneous adipose tissue, and skeletal muscle of nine Vietnamese potbellied pigs, and data were compared with frequent sampling in blood. Alterations in glucose levels were induced with intravenous glucose and insulin. During hyperglycemia, no difference was detected in delay between blood and interstitial glucose levels in subcutaneous adipose tissue (18.0 ± 0.8 min), muscle (18.0 ± 0.9 min), and CNS (20.3 ± 1.2 min), respectively. During hypoglycemia, we found no time difference between interstitial parameters in the three tissues. However, the amplitude of glucose changes varied considerably, with a smaller magnitude of glucose change taking place in the brain. The timing of glucose excursions in subcutaneous adipose tissue and muscle reflect excursions in CNS. The reduced magnitude of glucose excursions in the brain suggests that different mechanisms of glucose transport are operative in CNS compared with subcutaneous adipose tissue and muscle.
Inhibition of Microsomal Triglyceride Transfer Protein Expression and Apolipoprotein B100 Secretion by the Citrus Flavonoid Naringenin and by Insulin Involves Activation of the Mitogen-Activated Protein Kinase Pathway in Hepatocytes
Authors: Allister Emma M. , Borradaile Nica M. , Edwards Jane Y. , Huff Murray W.
Published: March 2007

Microsomal triglyceride transfer protein (MTP) is necessary for hepatocyte assembly and secretion of apolipoprotein (apo)B100-containing lipoproteins. The citrus flavonoid naringenin, like insulin, decreased MTP expression in HepG2 cells, resulting in inhibition of apoB100 secretion; however, the mechanism for naringenin is independent of insulin receptor substrate-1/2. Recently, it was reported that insulin decreased MTP expression in HepG2 cells via the mitogen-activated protein kinase (MAPK)/extracellular signal–regulated kinase (ERK) (MAPKerk) pathway. We hypothesized that naringenin acts via a similar mechanism. Inhibition of MAPK kinase (MEK) 1/2 in HepG2 cells significantly attenuated the naringenin- and insulin-induced reduction in MTP expression. Both naringenin and insulin increased ERK1/2 phosphorylation, which was completely inhibited by MEK1/2 inhibition and enhanced by inhibition of MAPKp38, a negative regulator of MAPKerk activity. Inhibition of MEK1/2 significantly attenuated both the naringenin- and insulin-induced decrease in apoB100 secretion demonstrating a direct link between MAPKerk activation and apoB100 secretion. Furthermore, both compounds increased MAPKp38 activation, and therefore inhibition of MAPKp38 amplified thenaringenin- and insulin-induced decrease in apoB100 secretion. We conclude that MAPKerk signaling in hepatocytes is critical for inhibition of apoB100 secretion by naringenin and insulin. Therefore, naringenin may prove useful for activating insulin-signaling pathways important for regulation of hepatocyte lipid homeostasis.
Insulin and Leptin Resistance With Hyperleptinemia in Mice Lacking Androgen Receptor
Authors: Lin Hung-Yun , Xu Qingquan , Yeh Shuyuan , Wang Ruey-Sheng , Sparks Janet D. , Chang Chawnshang
Published: March 2007

Epidemiological evidence suggests that sex differences exist in type 2 diabetes. Men seem to be more susceptible than women to the consequences of obesity and sedentary lifestyle, possibly because of differences in insulin sensitivity and regional body fat deposition. Thus, lacking androgen receptor (AR) in male individuals may promote insulin resistance. To determine whether lacking AR in male individuals contributes to in vivo insulin resistance, an AR knockout model (AR−/y) was used to study the correlation between AR and insulin resistance. Progressive reduced insulin sensitivity and impaired glucose tolerance were seen in AR−/y mice with advancing age. Aging AR−/y mice displayed accelerated weight gain, hyperinsulinemia, and hyperglycemia, and loss of AR contributes to increased triglyceride content in skeletal muscle and liver. Leptin is higher in serum of AR−/y mice. Treatment with exogenous leptin fails to stimulate weight loss in AR−/y mice in advanced age, suggesting leptin resistance in the AR−/y/ mice. Exogenous dihydrotestosterone replacement fails to reverse the metabolic abnormalities and insulin resistance in AR−/y mice. Our in vivo studies demonstrate that androgen-AR plays key roles in the development of insulin and leptin resistance, which may contribute to the development of type 2 diabetes and cardiovascular disease.
A Human-Specific Role of Cell Death-Inducing DFFA (DNA Fragmentation Factor-α)-Like Effector A (CIDEA) in Adipocyte Lipolysis and Obesity
Authors: Nordström Elisabet Arvidsson , Rydén Mikael , Backlund Emma C. , Dahlman Ingrid , Kaaman Maria , Blomqvist Lennart , Cannon Barbara , Nedergaard Jan , Arner Peter
Published: March 2007

Elevated circulating fatty acid concentration is a hallmark of insulin resistance and is at least in part attributed to the action of adipose tissue-derived tumor necrosis factor-α (TNF-α) on lipolysis. Cell death-inducing DFFA (DNA fragmentation factor-α)-like effector A (CIDEA) belongs to a family of proapoptotic proteins that has five known members in humans and mice. The action of CIDEA is unknown, but CIDEA-null mice are resistant to obesity and diabetes. We investigated CIDEA in adipose tissue of obese and lean humans and mice. The mRNA was expressed in white human fat cells and in brown mouse adipocytes. The adipose mRNA expression of CIDEA in mice was not influenced by obesity. However, CIDEA expression was decreased twofold in obese humans and normalized after weight reduction. Low adipose CIDEA expression was associated with several features of the metabolic syndrome. Human adipocyte depletion of CIDEA by RNA interference stimulated lipolysis and increased TNF-α secretion by a posttranscriptional effect. Conversely, TNF-α treatment decreased adipocyte CIDEA expression via the mitogen-activated protein kinase c-Jun NH2-terminal kinase. We propose an important and human-specific role for CIDEA in lipolysis regulation and metabolic complications of obesity, which is at least in part mediated by cross-talk between CIDEA and TNF-α.
Therapeutic Neovascularization Using Cord Blood–Derived Endothelial Progenitor Cells for Diabetic Neuropathy
Authors: Naruse Keiko , Hamada Yoji , Nakashima Eitaro , Kato Koichi , Mizubayashi Ryuichi , Kamiya Hideki , Yuzawa Yukio , Matsuo Seiichi , Murohara Toyoaki , Matsubara Tatsuaki , Oiso Yutaka , Nakamura Jiro
Published: March 2007

Diabetic neuropathy is based on the impairment of nerve blood flow and the metabolic disorder. Although the vasodilating agents and anticoagulants improve nerve function and symptoms in diabetic neuropathy, more effective treatments are needed. Because endothelial progenitor cells (EPCs) have been identified in adult human peripheral blood, many studies have shown that transplantation of EPCs improves circulation to ischemic tissues. In this study, we have demonstrated that therapeutic neovascularization using human umbilical cord blood–derived EPCs reversed diabetic neuropathy. EPCs were isolated and expanded on day 7 of culture from cord blood mononuclear cells. Unilateral intramuscular injection of EPCs into hindlimb skeletal muscles significantly ameliorated impaired sciatic motor nerve conduction velocity and sciatic nerve blood flow in the EPC-injected side of streptozotocin-induced diabetic nude rats compared with the saline-injected side of diabetic nude rats. Histological study revealed an increased number of microvessels in hindlimb skeletal muscles in the EPC-injected side of diabetic rats. These findings suggest that transplantation of EPCs from cord blood may be a useful treatment for diabetic neuropathy.
Palmitate-Induced Apoptosis in Cultured Bovine Retinal Pericytes
Authors: Cacicedo Jose M. , Benjachareowong Sunun , Chou Eva , Ruderman Neil B. , Ido Yasuo
Published: March 2007

Apoptosis of pericytes (PCs) is an early event in diabetic retinopathy. It is generally thought to be a consequence of sustained hyperglycemia. In keeping with this, long-term (>7 days) incubation of cultured PCs in a high-glucose media has been shown to increase apoptosis. We examine here whether the saturated free fatty acid palmitate, the concentration of which is often elevated in diabetes, has similar effects on cultured PCs. Incubation with 0.4 mmol/l palmitate for 24 h induced both oxidant stress and apoptosis, as evidenced by a sixfold increase in DCF fluorescence and a twofold increase in caspase-3 activation, respectively. NAD(P)H oxidase appeared to be involved in these responses, since overexpression of dominant-negative subunits of NAD(P)H oxidase, such as phox47(DN), diminished oxidant stress, and phox67(DN) and N-17 RAC1(DN) prevented the increase in caspase-3 activity. Likewise, overexpression of vRAC, a constitutively active RAC1, increased caspase-3 activity to the same extent as palmitate alone. The effects of vRAC and palmitate were not additive. In parallel with the increases in oxidative stress, the redox-sensitive transcription factor nuclear factor-κB (NF-κB) was activated in cells incubated with 0.4 mmol/l palmitate. Furthermore, inhibition of NF-κB activation by various means inhibited caspase-3 activation. Finally, incubation with palmitate increased the cellular content of ceramide, a molecule linked to apoptosis and increases in oxidative stress and NF-κB activation in other cells. In keeping with such a role, in PCs both coincubation with fumonisin B1 (a ceramide synthase inhibitor) and overexpression of ceramidase I reversed the proapoptotic effect of palmitate. On the other hand, they increased rather than decreased DCF fluorescence. In conclusion, the results suggest that palmitate-induced apoptosis in PCs is associated with activation of NAD(P)H oxidase and NF-κB and an increase in ceramide. The precise interactions between these molecules in causing apoptosis and the importance of oxidant stress as a contributory factor remain to be determined.
Association Testing of the Protein Tyrosine Phosphatase 1B Gene (PTPN1) With Type 2 Diabetes in 7,883 People
Authors: Florez Jose C. , Agapakis Christina M. , Burtt Noël P. , Sun Maria , Almgren Peter , Råstam Lennart , Tuomi Tiinamaija , Gaudet Daniel , Hudson Thomas J. , Daly Mark J. , Ardlie Kristin G. , Hirschhorn Joel N. , Groop Leif , Altshuler David
Published: March 2007

Protein tyrosine phosphatase (PTP)-1B, encoded by the PTPN1 gene, inactivates the insulin signal transduction cascade by dephosphorylating phosphotyrosine residues in insulin signaling molecules. Due to its chromosomal location under a chromosome 20 linkage peak and the metabolic effects of its absence in knockout mice, it is a candidate gene for type 2 diabetes. Recent studies have associated common sequence variants in PTPN1 with type 2 diabetes and diabetes-related phenotypes. We sought to replicate the association of common single nucleotide polymorphisms (SNPs) and haplotypes in PTPN1 with type 2 diabetes, fasting plasma glucose, and insulin sensitivity in a large collection of subjects. We assessed linkage disequilibrium, selected tag SNPs, and typed these markers in 3,347 cases of type 2 diabetes and 3,347 control subjects as well as 1,189 siblings discordant for type 2 diabetes. Despite power estimated at >95% to replicate the previously reported associations, no statistically significant evidence of association was observed between PTPN1 SNPs or common haplotypes with type 2 diabetes or with diabetic phenotypes.
Effect of Fructose Overfeeding and Fish Oil Administration on Hepatic De Novo Lipogenesis and Insulin Sensitivity in Healthy Men
Authors: Faeh David , Minehira Kaori , Schwarz Jean-Marc , Periasamy Raj , Park Seongsoo , Tappy Luc
Published: March 2007

High-fructose diet stimulates hepatic de novo lipogenesis (DNL) and causes hypertriglyceridemia and insulin resistance in rodents. Fructose-induced insulin resistance may be secondary to alterations of lipid metabolism. In contrast, fish oil supplementation decreases triglycerides and may improve insulin resistance. Therefore, we studied the effect of high-fructose diet and fish oil on DNL and VLDL triglycerides and their impact on insulin resistance. Seven normal men were studied on four occasions: after fish oil (7.2 g/day) for 28 days; a 6-day high-fructose diet (corresponding to an extra 25% of total calories); fish oil plus high-fructose diet; and control conditions. Following each condition, fasting fractional DNL and endogenous glucose production (EGP) were evaluated using [1-13C]sodium acetate and 6,6-2H2 glucose and a two-step hyperinsulinemic-euglycemic clamp was performed to assess insulin sensitivity. High-fructose diet significantly increased fasting glycemia (7 ± 2%), triglycerides (79 ± 22%), fractional DNL (sixfold), and EGP (14 ± 3%, all P < 0.05). It also impaired insulin-induced suppression of adipose tissue lipolysis and EGP (P < 0.05) but had no effect on whole- body insulin-mediated glucose disposal. Fish oil significantly decreased triglycerides (37%, P < 0.05) after high-fructose diet compared with high-fructose diet without fish oil and tended to reduce DNL but had no other significant effect. In conclusion, high-fructose diet induced dyslipidemia and hepatic and adipose tissue insulin resistance. Fish oil reversed dyslipidemia but not insulin resistance.
A High-Fat Diet Coordinately Downregulates Genes Required for Mitochondrial Oxidative Phosphorylation in Skeletal Muscle
Authors: Sparks Lauren M. , Xie Hui , Koza Robert A. , Mynatt Randall , Hulver Matthew W. , Bray George A. , Smith Steven R.
Published: March 2007

Obesity and type 2 diabetes have been associated with a high-fat diet (HFD) and reduced mitochondrial mass and function. We hypothesized a HFD may affect expression of genes involved in mitochondrial function and biogenesis. To test this hypothesis, we fed 10 insulin-sensitive males an isoenergetic HFD for 3 days with muscle biopsies before and after intervention. Oligonucleotide microarray analysis revealed 297 genes were differentially regulated by the HFD (Bonferonni adjusted P < 0.001). Six genes involved in oxidative phosphorylation (OXPHOS) decreased. Four were members of mitochondrial complex I: NDUFB3, NDUFB5, NDUFS1, and NDUFV1; one was SDHB in complex II and a mitochondrial carrier protein SLC25A12. Peroxisome proliferator–activated receptor γ coactivator-1 (PGC1) α and PGC1β mRNA were decreased by −20%, P < 0.01, and −25%, P < 0.01, respectively. In a separate experiment, we fed C57Bl/6J mice a HFD for 3 weeks and found that the same OXPHOS and PGC1 mRNAs were downregulated by ∼90%, cytochrome C and PGC1α protein by ∼40%. Combined, these results suggest a mechanism whereby HFD downregulates genes necessary for OXPHOS and mitochondrial biogenesis. These changes mimic those observed in diabetes and insulin resistance and, if sustained, may result in mitochondrial dysfunction in the prediabetic/insulin-resistant state.