bluuebunny/crossref_metadata_2025 huggingface dataset:
A Genome-Wide Scan for Type 2 Diabetes in African-American Families Reveals Evidence for a Locus on Chromosome 6q
Authors: Sale Michèle M. , Freedman Barry I. , Langefeld Carl D. , Williams Adrienne H. , Hicks Pamela J. , Colicigno Carla J. , Beck Stephanie R. , Brown W. Mark , Rich Stephen S. , Bowden Donald W.
Published: March 2007

African Americans are at increased risk of type 2 diabetes and many diabetes complications. We have carried out a genome-wide scan for African American type 2 diabetes using 638 affected sibling pairs (ASPs) from 247 families ascertained through impaired renal function to identify type 2 diabetes loci in this high-risk population. Of the 638 ASPs, 210 were concordant for diabetes with impaired renal function. A total of 390 markers, at an average spacing of 9 cM, were genotyped by the Center for Inherited Disease Research (CIDR) as part of the International Type 2 Diabetes Linkage Analysis Consortium. Nonparametric linkage (NPL) analyses conducted using the exponential model implemented in Genehunter Plus provided suggestive evidence for linkage at 6q24-q27 (163.5 cM, logarithm of odds [LOD] 2.26). Multilocus NPL regression analysis identified the 6q locus (D6S1035, LOD 2.67) and two additional regions: 7p (LOD 1.06) and 18q (LOD 0.87) as important in this model. NPL regression-based interaction analyses and ordered subset analyses (OSAs) supported the presence of a locus at chromosome 7p (29–34 cM) in the pedigrees with the earliest mean age of diagnosis of type 2 diabetes (P = 0.009 for interaction, ΔP = 0.0034 for OSA) and lower mean BMI (P = 0.009 for interaction, ΔP = 0.070 for OSA). These results provide evidence that genes predisposing African-American individuals to type 2 diabetes are located in the 6q and 7p regions of the genome.
Association of Human Endogenous Retrovirus K-18 Polymorphisms With Type 1 Diabetes
Authors: Marguerat Samuel , Wang William Y.S. , Todd John A. , Conrad Bernard
Published: March 2007

Several lines of evidence suggest the involvement of the human endogenous retrovirus (HERV)-K18 in the etiology of type 1 diabetes. HERV-K18 encodes for a T-cell superantigen (SAg). T-cells with T-cell receptor Vβ7 chains reactive to the SAg and HERV-K18 mRNA were enriched in the tissues at the onset of the disease. HERV-K18 transcription and SAg function in cells capable of efficient presentation are induced by proinflammatory stimuli such as viruses and interferon-α and may trigger progression of disease to insulitis or from insulitis to overt diabetes. Allelic variation of HERV-K18 or the DNA flanking it, the CD48 gene, could modulate genetic susceptibility. Analysis of 14 polymorphisms in the locus using 754 diabetic families provided positive evidence of association of three variants belonging to a single haplotype (P = 0.0026), present at 21.8% frequency in the population. Genotype analysis suggested a dominantly protective effect of this haplotype (P = 0.0061). Further genetic and functional analyses are required to confirm these findings.
Scrutiny of the Glutamine-Fructose-6-Phosphate Transaminase 1 (GFPT1) Locus Reveals Conserved Haplotype Block Structure not Associated With Diabetic Nephropathy
Authors: Ng Daniel P.K. , Walker William H. , Chia Kee-Seng , Choo Serena , Warram James H. , Krolewski Andrzej S.
Published: March 2007

Glutamine-fructose-6-phosphate transaminase 1 (GFAT) is the rate-limiting enzyme of the hexosamine pathway that has been implicated in the pathogenesis of diabetic nephropathy. As such, we hypothesized that GFPT1, which encodes for GFAT, may confer genetic susceptibility to this complication among Caucasians. Screening of all known functional regions of GFPT1 revealed six single nucleotide polymorphisms (SNPs) that were located in the promoter, introns, and 3′ untranslated region. The ∼60 kb GFPT1 locus was encompassed in a single conserved haplotype block, and two tagging SNPs were sufficient to capture >90% of the haplotype diversity. Analysis of these SNPs in a case-control study made up of type 1 diabetic subjects (324 case subjects with diabetic nephropathy and 289 control subjects with normoalbuminuria despite >15 years of diabetes) revealed no significant association even after stratification by sex, diabetes duration, glucose control, and blood pressure. Similar results were obtained among type 2 diabetic subjects (202 case and 114 control subjects). Genetic variation in GFPT1 is thus unlikely to have a major impact on susceptibility to diabetic nephropathy.
Analysis of the Type 2 Diabetes-Associated Single Nucleotide Polymorphisms in the Genes IRS1, KCNJ11, and PPARG2 in Type 1 Diabetes
Authors: Eftychi Christina , Howson Joanna M.M. , Barratt Bryan J. , Vella Adrian , Payne Felicity , Smyth Deborah J. , Twells Rebecca C.J. , Walker Neil M. , Rance Helen E. , Tuomilehto-Wolf Eva , Tuomilehto Jaakko , Undlien Dag E. , Rønningen Kjersti S. , Guja Cristian , Ionescu-Tı̂irgovişte Constantin , Savage David A. , Todd John A.
Published: March 2007

It has been proposed that type 1 and 2 diabetes might share common pathophysiological pathways and, to some extent, genetic background. However, to date there has been no convincing data to establish a molecular genetic link between them. We have genotyped three single nucleotide polymorphisms associated with type 2 diabetes in a large type 1 diabetic family collection of European descent: Gly972Arg in the insulin receptor substrate 1 (IRS1) gene, Glu23Lys in the potassium inwardly-rectifying channel gene (KCNJ11), and Pro12Ala in the peroxisome proliferative-activated receptor γ2 gene (PPARG2). We were unable to confirm a recently published association of the IRS1 Gly972Arg variant with type 1 diabetes. Moreover, KCNJ11 Glu23Lys showed no association with type 1 diabetes (P > 0.05). However, the PPARG2 Pro12Ala variant showed evidence of association (RR 1.15, 95% CI 1.04–1.28, P = 0.008). Additional studies need to be conducted to confirm this result.
A Role for the Malonyl-CoA/Long-Chain Acyl-CoA Pathway of Lipid Signaling in the Regulation of Insulin Secretion in Response to Both Fuel and Nonfuel Stimuli
Authors: Roduit Raphaël , Nolan Christopher , Alarcon Cristina , Moore Patrick , Barbeau Annie , Delghingaro-Augusto Viviane , Przybykowski Ewa , Morin Johane , Massé Frédéric , Massie Bernard , Ruderman Neil , Rhodes Christopher , Poitout Vincent , Prentki Marc
Published: March 2007

The malonyl-CoA/long-chain acyl-CoA (LC-CoA) model of glucose-induced insulin secretion (GIIS) predicts that malonyl-CoA derived from glucose metabolism inhibits fatty acid oxidation, thereby increasing the availability of LC-CoA for lipid signaling to cellular processes involved in exocytosis. For directly testing the model, INSr3 cell clones overexpressing malonyl-CoA decarboxylase in the cytosol (MCDc) in a tetracycline regulatable manner were generated, and INS(832/13) and rat islets were infected with MCDc-expressing adenoviruses. MCD activity was increased more than fivefold, and the malonyl-CoA content was markedly diminished. This was associated with enhanced fat oxidation at high glucose, a suppression of the glucose-induced increase in cellular free fatty acid (FFA) content, and reduced partitioning at elevated glucose of exogenous palmitate into lipid esterification products. MCDc overexpression, in the presence of exogenous FFAs but not in their absence, reduced GIIS in all β-cell lines and in rat islets. It also markedly curtailed the stimulation of insulin secretion by other fuel and nonfuel secretagogues. In the absence of MCDc overexpression, the secretory responses to all types of secretagogues were amplified by the provision of exogenous fatty acids. In the presence of exogenous FFAs, the fatty acyl-CoA synthetase inhibitor triacsin C reduced secretion in response to glucose and nonfuel stimuli. The data show the existence of important links between the metabolic coupling factor malonyl-CoA, the partitioning of fatty acids, and the stimulation of insulin secretion to both fuel and nonfuel stimuli.
Glucose Inhibition of Glucagon Secretion From Rat α-Cells Is Mediated by GABA Released From Neighboring β-Cells
Authors: Wendt Anna , Birnir Bryndis , Buschard Karsten , Gromada Jesper , Salehi Albert , Sewing Sabine , Rorsman Patrik , Braun Matthias
Published: March 2007

γ-Aminobutyric acid (GABA) has been proposed to function as a paracrine signaling molecule in islets of Langerhans. We have shown that rat β-cells release GABA by Ca2+-dependent exocytosis of synaptic-like microvesicles. Here we demonstrate that GABA thus released can diffuse over sufficient distances within the islet interstitium to activate GABAA receptors in neighboring cells. Confocal immunocytochemistry revealed the presence of GABAA receptors in glucagon-secreting α-cells but not in β- and δ-cells. RT-PCR analysis detected transcripts of α1 and α4 as well as β1–3 GABAA receptor subunits in purified α-cells but not in β-cells. In whole-cell voltage-clamp recordings, exogenous application of GABA activated Cl− currents in α-cells. The GABAA receptor antagonist SR95531 was used to investigate the effects of endogenous GABA (released from β-cells) on pancreatic islet hormone secretion. The antagonist increased glucagon secretion at 1 mmol/l glucose twofold and completely abolished the inhibitory action of 20 mmol/l glucose on glucagon release. Basal and glucose-stimulated secretion of insulin and somatostatin were unaffected by SR95531. The L-type Ca2+ channel blocker isradipine evoked a paradoxical stimulation of glucagon secretion. This effect was not observed in the presence of SR95531, and we therefore conclude that isradipine stimulates glucagon secretion by inhibition of GABA release.
Differential Effects of Interleukin-6 and -10 on Skeletal Muscle and Liver Insulin Action In Vivo
Authors: Kim Hyo-Jeong , Higashimori Takamasa , Park So-Young , Choi Hyejeong , Dong Jianying , Kim Yoon-Jung , Noh Hye-Lim , Cho You-Ree , Cline Gary , Kim Young-Bum , Kim Jason K.
Published: March 2007

The circulating level of the inflammatory cytokine interleukin (IL)-6 is elevated in various insulin-resistant states including type 2 diabetes, obesity, cancer, and HIV-associated lipodystrophy. To determine the role of IL-6 in the development of insulin resistance, we examined the effects of IL-6 treatment on whole-body insulin action and glucose metabolism in vivo during hyperinsulinemic-euglycemic clamps in awake mice. Pretreatment of IL-6 blunted insulin’s ability to suppress hepatic glucose production and insulin-stimulated insulin receptor substrate (IRS)-2–associated phosphatidylinositol (PI) 3-kinase activity in liver. Acute IL-6 treatment also reduced insulin-stimulated glucose uptake in skeletal muscle, and this was associated with defects in insulin-stimulated IRS-1–associated PI 3-kinase activity and increases in fatty acyl-CoA levels in skeletal muscle. In contrast, we found that co-treatment of IL-10, a predominantly anti-inflammatory cytokine, prevented IL-6–induced defects in hepatic insulin action and signaling activity. Additionally, IL-10 co-treatment protected skeletal muscle from IL-6 and lipid-induced defects in insulin action and signaling activity, and these effects were associated with decreases in intramuscular fatty acyl-CoA levels. This is the first study to demonstrate that inflammatory cytokines IL-6 and IL-10 alter hepatic and skeletal muscle insulin action in vivo, and the mechanism may involve cytokine-induced alteration in intracellular fat contents. These findings implicate an important role of inflammatory cytokines in the pathogenesis of insulin resistance.
A Common Polymorphism in the Upstream Promoter Region of the Hepatocyte Nuclear Factor-4α Gene on Chromosome 20q Is Associated With Type 2 Diabetes and Appears to Contribute to the Evidence for Linkage in an Ashkenazi Jewish Population
Authors: Love-Gregory Latisha D. , Wasson Jonathon , Ma Jiyan , Jin Carol H. , Glaser Benjamin , Suarez Brian K. , Permutt M. Alan
Published: March 2007

Variants in hepatocyte nuclear factor-4α (HNF4α), a transcription factor that influences the expression of glucose metabolic genes, have been correlated with maturity-onset diabetes of the young, a monogenic form of diabetes. Previously, in a genome scan of Ashkenazi Jewish type 2 diabetic families, we observed linkage to the chromosome 20q region encompassing HNF4α. Here, haplotype-tag single nucleotide polymorphisms (htSNPs) were identified across a 78-kb region around HNF4α and evaluated in an association analysis of Ashkenazi Jewish type 2 diabetic (n = 275) and control (n = 342) subjects. We found that two of nine htSNPs were associated with type 2 diabetes: a 3′ intronic SNP, rs3818247 (29.2% case subjects vs. 21.7% control subjects; P = 0.0028, odds ratio [OR] 1.49) and a 5′ htSNP located ∼3.9 kb upstream of P2, rs1884614 (26.9% case subjects vs. 20.3% control subjects; P = 0.0078, OR 1.45). Testing of additional SNPs 5′ of rs1884614 revealed a >10-kb haplotype block that was associated with type 2 diabetes. Conditioning on the probands’ rs1884614 genotype suggested that the chromosomal region identified by the htSNP accounted for the linkage signal on chromosome 20q in families in which the proband carried at least one risk allele. Notably, the associations and the partitioned linkage profiles near P2 were independently observed in a Finnish sample, suggesting the presence of potential regulatory element(s) that may contribute to the risk for type 2 diabetes.
Genetic Variation Near the Hepatocyte Nuclear Factor-4α Gene Predicts Susceptibility to Type 2 Diabetes
Authors: Silander Kaisa , Mohlke Karen L. , Scott Laura J. , Peck Erin C. , Hollstein Pablo , Skol Andrew D. , Jackson Anne U. , Deloukas Panagiotis , Hunt Sarah , Stavrides George , Chines Peter S. , Erdos Michael R. , Narisu Narisu , Conneely Karen N. , Li Chun , Fingerlin Tasha E. , Dhanjal Sharanjeet K. , Valle Timo T. , Bergman Richard N. , Tuomilehto Jaakko , Watanabe Richard M. , Boehnke Michael , Collins Francis S.
Published: March 2007

The Finland-United States Investigation Of NIDDM Genetics (FUSION) study aims to identify genetic variants that predispose to type 2 diabetes by studying affected sibling pair families from Finland. Chromosome 20 showed our strongest initial evidence for linkage. It currently has a maximum logarithm of odds (LOD) score of 2.48 at 70 cM in a set of 495 families. In this study, we searched for diabetes susceptibility variant(s) at 20q13 by genotyping single nucleotide polymorphism (SNP) markers in case and control DNA pools. Of 291 SNPs successfully typed in a 7.5-Mb interval, the strongest association confirmed by individual genotyping was with SNP rs2144908, located 1.3 kb downstream of the primary β-cell promoter P2 of hepatocyte nuclear factor-4α (HNF4A). This SNP showed association with diabetes disease status (odds ratio [OR] 1.33, 95% CI 1.06–1.65, P = 0.011) and with several diabetes-related traits. Most of the evidence for linkage at 20q13 could be attributed to the families carrying the risk allele. We subsequently found nine additional associated SNPs spanning a 64-kb region, including the P2 and P1 promoters and exons 1–3. Our results and the independent observation of association of SNPs near the P2 promoter with diabetes in a separate study population of Ashkenazi Jewish origin suggests that variant(s) located near or within HNF4A increases susceptibility to type 2 diabetes.
Inhalation of Insulin in Dogs
Authors: Cherrington Alan D. , Neal Doss W. , Edgerton Dale S. , Glass Dana , Bowen Larry , Hobbs Charles H. , Leach Chet , Rosskamp Ralf , Strack Thomas R.
Published: March 2007

Pulmonary insulin delivery is being developed as a more acceptable alternative to conventional subcutaneous administration. In 15 healthy Beagle dogs (average weight 9.3 kg), we compared insulin distribution in arterial, deep venous, and hepatic portal circulation. Dogs received 0.36 units/kg s.c. regular human insulin (n = 6) or 1 mg (2.8 units/kg) or 2 mg (5.6 units/kg) dry-powder human inhaled insulin (n = 3 and 6, respectively). Postinhalation of inhaled insulin (1 or 2 mg), arterial insulin levels quickly rose to a maximum of 55 ± 6 or 92 ± 9 μU/ml, respectively, declining to typical fasting levels by 3 h. Portal levels were lower than arterial levels at both doses, while deep venous levels were intermediate to arterial and portal levels. In contrast, subcutaneous insulin was associated with a delayed and lower peak arterial concentration (55 ± 8 μU/ml at 64 min), requiring 6 h to return to baseline. Peak portal levels for subcutaneous insulin were comparable to those for 1 mg and significantly less than those for 2 mg inhaled insulin, although portal area under the curve (AUC) was comparable for the subcutaneous and 2-mg groups. The highest insulin levels with subcutaneous administration were seen in the deep venous circulation. Interestingly, the amount of glucose required for maintaining euglycemia was highest with 2 mg inhaled insulin. We conclude that plasma insulin AUC for the arterial insulin level (muscle) and hepatic sinusoidal insulin level (liver) is comparable for 2 mg inhaled insulin and 0.36 units/kg subcutaneous insulin. In addition, arterial peak concentration following insulin inhalation is two times greater than subcutaneous injection; however, the insulin is present in the circulation for half the time.
One Week’s Treatment With the Long-Acting Glucagon-Like Peptide 1 Derivative Liraglutide (NN2211) Markedly Improves 24-h Glycemia and α- and β-Cell Function and Reduces Endogenous Glucose Release in Patients with Type 2 Diabetes
Authors: Degn Kristine B. , Juhl Claus B. , Sturis Jeppe , Jakobsen Grethe , Brock Birgitte , Chandramouli Visvanathan , Rungby Joergen , Landau Bernard R. , Schmitz Ole
Published: March 2007

Glucagon-like peptide 1 (GLP-1) is potentially a very attractive agent for treating type 2 diabetes. We explored the effect of short-term (1 week) treatment with a GLP-1 derivative, liraglutide (NN2211), on 24-h dynamics in glycemia and circulating free fatty acids, islet cell hormone profiles, and gastric emptying during meals using acetaminophen. Furthermore, fasting endogenous glucose release and gluconeogenesis (3-3H-glucose infusion and 2H2O ingestion, respectively) were determined, and aspects of pancreatic islet cell function were elucidated on the subsequent day using homeostasis model assessment and first- and second-phase insulin response during a hyperglycemic clamp (plasma glucose ∼16 mmol/l), and, finally, on top of hyperglycemia, an arginine stimulation test was performed. For accomplishing this, 13 patients with type 2 diabetes were examined in a double-blind, placebo-controlled crossover design. Liraglutide (6 μg/kg) was administered subcutaneously once daily. Liraglutide significantly reduced the 24-h area under the curve for glucose (P = 0.01) and glucagon (P = 0.04), whereas the area under the curve for circulating free fatty acids was unaltered. Twenty-four-hour insulin secretion rates as assessed by deconvolution of serum C-peptide concentrations were unchanged, indicating a relative increase. Gastric emptying was not influenced at the dose of liraglutide used. Fasting endogenous glucose release was decreased (P = 0.04) as a result of a reduced glycogenolysis (P = 0.01), whereas gluconeogenesis was unaltered. First-phase insulin response and the insulin response to an arginine stimulation test with the presence of hyperglycemia were markedly increased (P < 0.001), whereas the proinsulin/insulin ratio fell (P = 0.001). The disposition index (peak insulin concentration after intravenous bolus of glucose multiplied by insulin sensitivity as assessed by homeostasis model assessment) almost doubled during liraglutide treatment (P < 0.01). Both during hyperglycemia per se and after arginine exposure, the glucagon responses were reduced during liraglutide administration (P < 0.01 and P = 0.01). Thus, 1 week’s treatment with a single daily dose of the GLP-1 derivative liraglutide, operating through several different mechanisms including an ameliorated pancreatic islet cell function in individuals with type 2 diabetes, improves glycemic control throughout 24 h of daily living, i.e., prandial and nocturnal periods. This study further emphasizes GLP-1 and its derivatives as a promising novel concept for treatment of type 2 diabetes.
High Serum Resistin Is Associated With an Increase in Adiposity But Not a Worsening of Insulin Resistance in Pima Indians
Authors: Vozarova de Courten Barbora , Degawa-Yamauchi Mikako , Considine Robert V. , Tataranni P. Antonio
Published: March 2007

Resistin is an adipokine with putative prodiabetogenic properties. Like other hormones secreted by adipose tissue, resistin is being investigated as a possible etiologic link between excessive adiposity and insulin resistance. Although there is growing evidence that circulating levels of this adipokine are proportional to the degree of adiposity, an effect on insulin resistance in humans remains unproven. To evaluate the relations among resistin, obesity, and insulin resistance, we measured fasting serum resistin levels in 113 nondiabetic (75-g oral glucose tolerance test) Pima Indians (ages 29 ± 7 years, body fat 31 ± 8%, resistin 3.7 ± 1.1 ng/ml [means ± SD]), who were characterized for body composition (assessed by hydrodensitometry or dual-energy X-ray absorptiometry), whole-body insulin sensitivity (M; assessed by hyperinsulinemic clamp), basal hepatic glucose output (BHGO) and hepatic glucose output during low-dosage insulin infusion of a hyperinsulinemic clamp (HGO; a measure of hepatic insulin resistance), and acute insulin secretory response (AIR; assessed by 25-g intravenous glucose tolerance test). Follow-up measurements of M, BHGO, HGO, and AIR were available for 34 subjects who had normal glucose tolerance at baseline and remained nondiabetic at follow-up. The average time to follow-up was 4.5 ± 2.7 years. In cross-sectional analyses, serum resistin levels were positively associated with percent body fat (r = 0.37, P = 0.0001) and 2-h glucose (r = 0.19, P = 0.04), respectively. Serum resistin levels were not associated with fasting glucose and insulin levels, M, BHGO, HGO, or AIR (r = 0.17, 0.12, −0.13, −0.06, −0.03, and −0.04, respectively; all P > 0.05). After adjusting for percent body fat, there was no association between serum resistin levels and 2-h glucose (r = 0.06, P = 0.6). In prospective analyses, high serum resistin levels at baseline were not associated with a decline in M (r = −0.1, P > 0.5). Resistin levels were, however, associated with increases in percent body fat, fasting plasma insulin, and HGO (r = 0.34, 0.36, and 0.37; all P < 0.05) after adjusting for sex, age, and time to follow-up. After additional adjustment for the change in percent body fat, there was no association between baseline serum resistin levels and changes in plasma insulin or HGO (r = 0.26 and 0.23; both P > 0.1). We conclude that in Pima Indians, like other human populations, circulating resistin levels are proportional to the degree of adiposity, but not the degree of insulin resistance. We unexpectedly found that high serum resistin levels do predict future increases in percent body fat. Our data suggest that resistin promotes obesity but not obesity-associated insulin resistance in humans.
Intraislet Endothelial Cells Contribute to Revascularization of Transplanted Pancreatic Islets
Authors: Brissova Marcela , Fowler Michael , Wiebe Peter , Shostak Alena , Shiota Masakazu , Radhika Aramandla , Lin P. Charles , Gannon Maureen , Powers Alvin C.
Published: March 2007

Pancreatic islet transplantation is an emerging therapy for type 1 diabetes. To survive and function, transplanted islets must revascularize because islet isolation severs arterial and venous connections; the current paradigm is that islet revascularization originates from the transplant recipient. Because isolated islets retain intraislet endothelial cells, we determined whether these endothelial cells contribute to the revascularization using a murine model with tagged endothelial cells (lacZ knock-in to Flk-1/VEGFR2 gene) and using transplanted human islets. At 3–5 weeks after transplantation beneath the renal capsule, we found that islets were revascularized and that the transplant recipient vasculature indeed contributed to the revascularization process. Using the lacZ-tagged endothelial cell model, we found that intraislet endothelial cells not only survived after transplantation but became a functional part of revascularized islet graft. A similar contribution of intraislet endothelial cells was also seen with human islets transplanted into an immunodeficient mouse model. In the murine model, individual blood vessels within the islet graft consisted of donor or recipient endothelial cells or were a chimera of donor and recipient endothelial cells, indicating that both sources of endothelial cells contribute to the new vasculature. These observations suggest that interventions to activate, amplify, or sustain intraislet endothelial cells before and after transplantation may facilitate islet revascularization, enhance islet survival, and improve islet transplantation.
Cerebrovascular Dysfunction in Zucker Obese Rats Is Mediated by Oxidative Stress and Protein Kinase C
Authors: Erdös Benedek , Snipes James A. , Miller Allison W. , Busija David W.
Published: March 2007

Insulin resistance (IR) impairs vascular function in the peripheral and coronary circulations, but its effects on cerebral arteries are virtually unexplored. We examined the vascular responses of the basilar artery (BA) and its side branches through a cranial window in Zucker lean (ZL) and IR Zucker obese (ZO) rats. Nitric oxide (NO) and K+ channel-mediated dilator responses, elicited by acetylcholine, iloprost, cromakalim, and elevated [K+], were greatly diminished in the ZO rats compared with ZL rats. In contrast, sodium nitroprusside induced similar relaxations in the two experimental groups. Expressions of the K+ channel pore-forming subunits were not affected by IR, while endothelial NO synthase was upregulated in the ZO arteries compared with ZL arteries. Protein kinase C (PKC) activity and production of superoxide anion were increased in the cerebral arteries of ZO rats, and pretreatment with superoxide dismutase restored all examined dilator responses. In contrast, application of PKC inhibitors improved only receptor-linked NO-mediated relaxation, but not K+ channel-dependent responses. Thus, IR induces in ZO rats cerebrovascular dysfunction, which is mediated by oxidative stress and partly by PKC activation. The revealed impairment of NO and K+ channel-dependent dilator responses may be responsible for the increased risk of cerebrovascular events and neurodegenerative disorders in IR.
Microvascular Recruitment Is an Early Insulin Effect That Regulates Skeletal Muscle Glucose Uptake In Vivo
Authors: Vincent Michelle A. , Clerk Lucy H. , Lindner Jonathan R. , Klibanov Alexander L. , Clark Michael G. , Rattigan Stephen , Barrett Eugene J.
Published: March 2007

Insulin increases glucose disposal into muscle. In addition, in vivo insulin elicits distinct nitric oxide synthase-dependent vascular responses to increase total skeletal muscle blood flow and to recruit muscle capillaries (by relaxing resistance and terminal arterioles, respectively). In the current study, we compared the temporal sequence of vascular and metabolic responses to a 30-min physiological infusion of insulin (3 mU · min−1 · kg−1, euglycemic clamp) or saline in rat skeletal muscle in vivo. We used contrast-enhanced ultrasound to continuously quantify microvascular volume. Insulin recruited microvasculature within 5–10 min (P < 0.05), and this preceded both activation of insulin-signaling pathways and increases in glucose disposal in muscle, as well as changes in total leg blood flow. Moreover, l-NAME (Nω-nitro-l-arginine-methyl ester), a specific inhibitor of nitric oxide synthase, blocked this early microvascular recruitment (P < 0.05) and at least partially inhibited early increases in muscle glucose uptake (P < 0.05). We conclude that insulin rapidly recruits skeletal muscle capillaries in vivo by a nitric oxide-dependent action, and the increase in capillary recruitment may contribute to the subsequent glucose uptake.
Relationship Between Serum Amyloid A Level andTanis/SelSmRNA Expression in Skeletal Muscle and Adipose Tissue From Healthy and Type 2 Diabetic Subjects
Authors: Karlsson Håkan K.R. , Tsuchida Hiroki , Lake Staffan , Koistinen Heikki A. , Krook Anna
Published: March 2007

Tanis is a recently described protein reported to be a putative receptor for serum amyloid A and found to be dysregulated with diabetes in the Israeli sand rat Psamommys obesus. Tanis has also been identified as a selenoprotein, one of the first two identified membrane selenoproteins. We determined mRNA expression of the human homologue of Tanis, SelS/AD-015, in skeletal muscle and adipose tissue biopsies obtained from 10 type 2 diabetic patients and 11 age- and weight-matched healthy subjects. Expression of Tanis/SelS mRNA in skeletal muscle and adipose tissue biopsies was similar between diabetic and control subjects. A subset of subjects underwent a euglycemic-hyperinsulinemic clamp, and adipose tissue expression of Tanis/SelS was determined after in vivo insulin stimulation. Adipose tissue Tanis/SelS mRNA expression was unchanged after insulin infusion in control subjects, whereas Tanis/SelS mRNA increased in seven of eight subjects following insulin stimulation in diabetic subjects. Skeletal muscle and adipose tissue Tanis/SelS mRNA expression were positively correlated with plasma serum amyloid A. In conclusion, there is a strong trend toward upregulation of Tanis/SelS following insulin infusion in adipose tissue from type 2 diabetic subjects. Moreover, the positive relationship between Tanis mRNA and the acute-phase protein serum amyloid A suggests an interaction between innate immune system responses and Tanis expression in muscle and adipose tissue.
Role of Adipocyte-Derived Factors in Enhancing Insulin Signaling in Skeletal Muscle and White Adipose Tissue of Mice Lacking Acyl CoA:Diacylglycerol Acyltransferase 1
Authors: Chen Hubert C. , Rao Meghana , Sajan Mini P. , Standaert Mary , Kanoh Yoshinori , Miura Atsushi , Farese Robert V. , Farese Robert V.
Published: March 2007

Mice that lack acyl CoA:diacylglycerol acyltransferase 1 (DGAT1), a key enzyme in mammalian triglyceride synthesis, have decreased adiposity and increased insulin sensitivity. Here we show that insulin-stimulated glucose transport is increased in the skeletal muscle and white adipose tissue (WAT) of chow-fed DGAT1-deficient mice. This increase in glucose transport correlated with enhanced insulin-stimulated activities of phosphatidylinositol 3-kinase, protein kinase B (or Akt), and protein kinase Cλ (PKC-λ), three key molecules in the insulin-signaling pathway, and was associated with decreased levels of serine-phosphorylated insulin receptor substrate 1 (IRS-1), a molecule implicated in insulin resistance. Similar findings in insulin signaling were also observed in DGAT1-deficient mice fed a high-fat diet. Interestingly, the increased PKC-λ activity and decreased serine phosphorylation of IRS-1 were observed in chow-fed wild-type mice transplanted with DGAT1-deficient WAT, consistent with our previous finding that transplantation of DGAT1-deficient WAT enhances glucose disposal in wild-type recipient mice. Our findings demonstrate that DGAT1 deficiency enhances insulin signaling in the skeletal muscle and WAT, in part through altered expression of adipocyte-derived factors that modulate insulin signaling in peripheral tissues.
Regulation of α-Cell Function by the β-Cell During Hypoglycemia in Wistar Rats: the “Switch-off” Hypothesis
Authors: Zhou Huarong , Tran Phuong Oanh T. , Yang Shilin , Zhang Tao , LeRoy Eric , Oseid Elizabeth , Robertson R. Paul
Published: March 2007

The glucagon response is the first line of defense against hypoglycemia and is lost in insulin-dependent diabetes. The β-cell “switch-off” hypothesis proposes that a sudden cessation of insulin secretion from β-cells into the portal circulation of the islet during hypoglycemia is a necessary signal for the glucagon response from downstream α-cells. Although indirect evidence exists to support this hypothesis, it has not been directly tested in vivo by provision and then discontinuation of regional reinsulinization of α-cells at the time of a hypoglycemic challenge. We studied streptozotocin (STZ)-induced diabetic Wistar rats that had no glucagon response to a hypoglycemic challenge. We reestablished insulin regulation of the α-cell by regionally infusing insulin (0.025 μU/min) directly into the superior pancreaticoduodenal artery (SPDa) of STZ-administered rats at an infusion rate that did not alter systemic venous glucose levels. SPDa insulin infusion was switched off simultaneously when blood glucose fell to <60 mg/dl after a jugular venous insulin injection. This maneuver restored the glucagon response to hypoglycemia (peak change within 5–10 min = 326 ± 98 pg/ml, P < 0.05; and peak change within 15–20 min = 564 ± 148 pg/ml, P < 0.01). No response was observed when the SPDa insulin infusion was not turned off (peak change within 5–10 min = 44 ± 85 pg/ml, P = NS; and peak change within 15–20 min = 67 ± 97 pg/ml, P = NS) or when saline instead of insulin was infused and then switched off (peak change within 5–10 min = −44 ± 108 pg/ml, P = NS; and peak change within 15–20 min = −13 ± 43 pg/ml, P = NS). No responses were observed during euglycemia (peak change within 5–10 min = 48 ± 35 pg/ml, P = NS; and peak change within 15–20 min = 259 ± 129 pg/ml, P = NS) or hyperglycemia (peak change within 5–10 min = 49 ± 62 pg/ml, P = NS; and peak change within 15–20 min = 138 ± 87 pg/ml, P = NS). Thus, the glucagon response to hypoglycemia that was absent in rats made diabetic by STZ was restored by regional infusion and then discontinuation of insulin. These data provide direct in vivo support for the β-cell “switch-off” hypothesis and indicate that the α-cell is not intrinsically abnormal in insulin-dependent diabetes because of STZ-induced destruction of β-cells.
Islet Secretory Defect in Insulin Receptor Substrate 1 Null Mice Is Linked With Reduced Calcium Signaling and Expression of Sarco(endo)plasmic Reticulum Ca2+-ATPase (SERCA)-2b and -3
Authors: Kulkarni Rohit N. , Roper Michael G. , Dahlgren Gabriella , Shih David Q. , Kauri Lisa M. , Peters Jennifer L. , Stoffel Markus , Kennedy Robert T.
Published: March 2007

Mice with deletion of insulin receptor substrate (IRS)-1 (IRS-1 knockout [KO] mice) show mild insulin resistance and defective glucose-stimulated insulin secretion and reduced insulin synthesis. To further define the role of IRS-1 in islet function, we examined the insulin secretory defect in the knockouts using freshly isolated islets and primary β-cells. IRS-1 KO β-cells exhibited a significantly shorter increase in intracellular free Ca2+ concentration ([Ca2+]i) than controls when briefly stimulated with glucose or glyceraldehyde and when l-arginine was used to potentiate the stimulatory effect of glucose. These changes were paralleled by a lower number of exocytotic events in the KO β-cells in response to the same secretagogues, indicating reduced insulin secretion. Furthermore, the normal oscillations in intracellular Ca2+ and O2 consumption after glucose stimulation were dampened in freshly isolated KO islets. Semiquantitative RT-PCR showed a dramatically reduced islet expression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)-2b and -3 in the mutants. These data provide evidence that IRS-1 modulation of insulin secretion is associated with Ca2+ signaling and expression of SERCA-2b and -3 genes in pancreatic islets and provides a direct link between insulin resistance and defective insulin secretion.
Early Endothelial Dysfunction Severely Impairs Skin Blood Flow Response to Local Pressure Application in Streptozotocin-Induced Diabetic Mice
Authors: Sigaudo-Roussel Dominique , Demiot Claire , Fromy Bérengère , Koïtka Audrey , Lefthériotis Georges , Abraham Pierre , Saumet Jean Louis
Published: March 2007

Pressure-induced vasodilation (PIV) is a mechanism whereby skin blood flow increases in response to progressive locally applied pressure. Skin blood flow in response to applied pressure decreased early in diabetic patients as a result of vascular and/or neural impairment. This study was designed to determine the effect of vascular changes on PIV in 1-week streptozotocin-induced diabetic mice. We assessed cutaneous microvascular response to local increasing pressure application measured by laser Doppler flowmetry (LDF) and endothelium-dependent and -independent vasodilation by iontophoretic delivery of acetylcholine and sodium nitroprusside and sciatic motor nerve conduction velocity and morphometry. In control mice, LDF increased 34% from baseline to 0.2 kPa external pressure, showing PIV response. In contrast, diabetic mice had no LDF increase in response to progressive external pressure. Moreover, after iontophoretic delivery of acetylcholine, endothelium-dependent vasodilation was largely attenuated in diabetic mice (25%) compared with control mice (81%), whereas vasodilation to sodium nitroprusside was not different between groups. Nerve function as assessed by sciatic nerve conduction velocity and morphometry did not differ between groups. These findings suggest that endothelial impairment is sufficient to severely alter PIV response, which seems to be highly sensitive to endothelial nitric oxide levels. PIV suppression could favor diabetes complications such as diabetic foot ulcers.
AMP-Activated Protein Kinase Activation by AICAR Increases Both Muscle Fatty Acid and Glucose Uptake in White Muscle of Insulin-Resistant Rats In Vivo
Authors: Iglesias Miguel A. , Furler Stuart M. , Cooney Gregory J. , Kraegen Edward W. , Ye Ji-Ming
Published: March 2007

Insulin-stimulated glucose uptake is increased in white but not red muscle of insulin-resistant high-fat–fed (HF) rats after administration of the AMP-activated protein kinase (AMPK) activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR). To investigate whether a lesser AICAR effect on glucose uptake in red muscle was offset by a greater effect on fatty acid (FA) uptake, we examined acute effects of AICAR on muscle glucose and FA fluxes in HF rats. HF rats received AICAR (250 mg/kg) subcutaneously. At 30 min, a mixture of either 3H-(R)-2-bromopalmitate/14C-palmitate or 3H-2-deoxyglucose/14C-glucose was administered intravenously to assess muscle FA and glucose uptake. AICAR decreased plasma levels of glucose (∼25%), insulin (∼ 60%), and FAs (∼30%) at various times over the next 46 min (P < 0.05 vs. controls). In white muscle, AICAR increased both FA (2.4-fold) and glucose uptake (4.9-fold), associated with increased glycogen synthesis (6-fold). These effects were not observed in red muscle. We conclude that both glucose and FA fluxes are enhanced by AICAR more in white versus red muscle, consistent with the relative degree of activation of AMPK. Therefore, a lesser effect of AICAR to alleviate muscle insulin resistance in red versus white muscle is not explained by a relatively greater effect on FA uptake in the red muscle.
C-Peptide Induces Chemotaxis of Human CD4-Positive Cells
Authors: Walcher Daniel , Aleksic Milos , Jerg Verena , Hombach Vinzenz , Zieske Arthur , Homma Satoki , Strong Jack , Marx Nikolaus
Published: March 2007

Increased levels of C-peptide, a cleavage product of proinsulin, circulate in patients with insulin resistance and early type 2 diabetes, a high-risk population for the development of a diffuse and extensive pattern of arteriosclerosis. The present study examined the effect of C-peptide on CD4+ lymphocyte migration, an important process in early atherogenesis. C-peptide stimulated CD4+ cell chemotaxis in a concentration-dependent manner. This process involves pertussis toxin–sensitive G-proteins as well as activation of phosphoinositide 3-kinase (PI 3-K). Biochemical analysis showed that C-peptide induced recruitment of PI 3-K to the cell membrane as well as PI 3-K activation in human CD4+ cells. In addition, antidiabetic peroxisome proliferator–activated receptor γ–activating thiazolidinediones inhibited C-peptide–induced CD4+ cell chemotaxis as well as PI 3-Kγ activation. Finally, immunofluorescence staining of thoracic artery specimen of diabetic patients showed intimal CD4+ cells in areas with C-peptide deposition. Thus, C-peptide might deposit in the arterial intima in diabetic patients during early atherogenesis and subsequently attract CD4+ cells to migrate into the vessel wall.
Cure of Overt Diabetes in NOD Mice by Transient Treatment With Anti-Lymphocyte Serum and Exendin-4
Authors: Ogawa Norihiko , List James F. , Habener Joel F. , Maki Takashi
Published: March 2007

Treatment of overtly diabetic NOD mice with anti-lymphocyte serum (ALS), a polyclonal anti–T-cell antibody, abrogates autoimmunity and achieves partial clinical remission. Here we investigated whether the addition of exendin-4, a hormone that stimulates insulin secretion and β-cell replication and differentiation, improves induction of remission by ALS. Transient treatment of overtly diabetic NOD mice with ALS and exendin-4 achieved complete remission in 23 of 26 mice (88%) within 75 days, accompanied by progressive normalization of glucose tolerance, improved islet histology, increased insulin content in the pancreas, and insulin release in response to a glucose challenge. Syngeneic islets transplanted into mice cured by treatment with ALS plus exendin-4 remained intact, and cotransfer of lymphocytes from cured mice delayed diabetes induction by adoptive transfer, suggesting the long-lasting presence of autoimmune regulatory cells. Although ALS alone also achieved reversal of diabetes, the frequency of remission was low (40%). No treatment or exendin-4 alone failed to produce remission. These results show that exendin-4 synergistically augments the remission-inducing effect of ALS. The addition of β-cell growth factors, such as exendin-4, to immunotherapy protocols with anti–T-cell antibodies presents a potential novel approach to the cure of patients with new-onset type 1 diabetes.
Regulation of Inducible Nitric Oxide Synthase Expression in Advanced Glycation End Product–Stimulated RAW 264.7 Cells
Authors: Sumi Daigo , Ignarro Louis J.
Published: March 2007

Advanced glycation end products (AGEs) are closely linked to the development of diabetic atherosclerosis. The current study examines the induction of inducible nitric oxide (NO) synthase (iNOS) and heme oxygenase (HO)-1 expression by AGEs, as well as the signaling pathways involved and the interplay between these two enzymes. The stimulation of RAW 264.7 cells with 6.64 or 33.2 μg/ml AGEs leads to HO-1 protein expression, iNOS protein expression, and nitrite accumulation. AGEs lead to the phosphorylation of p42/44 and p38 mitogen-activated protein kinase (MAPK). The inhibition of p42/44 MAPK and protein kinase C prevented, whereas inhibition of p38 MAPK augmented, AGE-induced nitrite release and iNOS expression. In contrast, HO-1 expression was downregulated by inhibition of p38 MAPK. Furthermore, the expression of both proteins was prevented by coincubation with acetovanillone (NADPH oxidase inhibitor). AGE-induced iNOS expression was negatively regulated by stimulation of HO-1 expression with cadmium chloride or endogenous NO. Tin-protoporphyrin IX (HO-1 inhibitor) partially reversed the cadmium chloride–mediated downregulation of iNOS expression. The current study demonstrates that multiple signaling molecules are involved in AGE-stimulated iNOS and HO-1 expression. There also exists a downregulation of iNOS by its own product as well as the products of HO-1.
Mitogen-Activated Protein Kinase p38 Mediates Reduced Nerve Conduction Velocity in Experimental Diabetic Neuropathy
Authors: Price Sally A. , Agthong Sithiporn , Middlemas Alicia B. , Tomlinson David R.
Published: March 2007

This study examined the role of p38 mitogen-activated protein (MAP) kinase in transducing high glucose into deficits in nerve conduction velocity (NCV) that are characteristic of diabetic neuropathy. p38 activation and NCV were measured in streptozocin-induced diabetic rats treated with a p38 inhibitor, an aldose reductase inhibitor, and insulin. Dorsal root ganglia (DRG) from diabetic animals showed marked activation of p38 at 12 weeks of diabetes. Insulin treatment for the last 4 of 12 weeks of diabetes normalized p38 activation. Furthermore, activation was completely prevented by 12 weeks’ treatment with the aldose reductase inhibitor, fidarestat. Immunocytochemistry localized activation of p38 to the nuclei of virtually all sensory neuronal phenotypes in the DRG, and activation was clear in diabetes, as was inhibition by fidarestat and by the p38 inhibitor SB 239063. In the ventral horn of the spinal cord, p38 was present in motoneuron cell bodies; and again, activation in diabetes and fidarestat inhibition was clear. Treatment of diabetic animals with a specific inhibitor of p38 (SB 239063), fidarestat, or insulin also prevented reductions in both motor and sensory NCV. These findings suggest that increased polyol pathway flux in diabetic animals leads to the activation of p38. This activation can mediate changes in gene transcription and cellular phenotype that are likely to underlie the NCV deficits. Insulin and aldose reductase inhibitors can prevent excess polyol pathway flux, and hence these agents may prevent NCV deficits by preventing p38 MAP kinase activation.
Identification of Quantitative Trait Loci for Glucose Homeostasis
Authors: Rich Stephen S. , Bowden Donald W. , Haffner Steven M. , Norris Jill M. , Saad Mohammed F. , Mitchell Braxton D. , Rotter Jerome I. , Langefeld Carl D. , Wagenknecht Lynne E. , Bergman Richard N.
Published: March 2007

Genetic and environmental determinants play critical roles in insulin resistance and β-cell function. A model of the complex feedback system for maintenance of glucose tolerance has been developed that reflects the constraint of glycemia within narrow physiologic limits. The “glucose homeostasis” model is described by insulin sensitivity (SI), glucose disposition (SG), acute insulin response to glucose (AIRG), and disposition index (DI). Relatively little is known about the genetic basis of glucose homeostasis phenotypes or their relationship to risk of diabetes and atherosclerotic cardiovascular disease. A genome scan for glucose homeostasis phenotypes in nondiabetic subjects has been carried out in African-American (n = 21) and Hispanic (n = 45) extended families as part of the IRAS Family Study. In African-American families, there was significant evidence for linkage of DI between D11S2371 and D11S2002 (logarithm of odds [LOD] = 3.21) at 81 cM, and in the combined sample of African-American and Hispanic families, there was evidence at GATA117D01 (140 cM) on chromosome 11 (LOD = 2.21). Evidence of linkage was also observed for SI in Hispanic (LOD = 2.28, between D15S822 and GTTTT001) and AIRG in African-American families (LOD = 2.73, between D4S1625 and D4S1629; and LOD = 2.56 at PAH (phenylalanine hydroxylase) on chromosome 12). These results provide impetus for future positional cloning of quantitative trait loci (QTLs). Identifying genes in these regions should provide insight into the nature of the metabolic syndrome and diabetes, and facilitate the development of more effective therapies for prevention and treatment of diabetes and other diseases associated with disordered glucose metabolism.