bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of Growth Hormone Signal Transduction in Kidneys of Streptozotocin-Induced Diabetic Animals
Authors: Thirone Ana C.P. , Scarlett John A. , Gasparetti Alessandra L. , Araujo Eliana P. , Lima Maria H.L. , Carvalho Carla R.O. , Velloso Lício A. , Saad Mario J.A.
Published: March 2007

Growth hormone (GH) and IGFs have a long distinguished history in diabetes, with possible participation in the development of renal complications. The implicated effect of GH in diabetic end-stage organ damage may be mediated by growth hormone receptor (GHR) or postreceptor events in GH signal transduction. The present study investigates the effects of diabetes induced by streptozotocin (STZ) on renal GH signaling. Our results demonstrate that JAK2, insulin receptor substrate (IRS)-1, Shc, ERKs, and Akt are widely distributed in the kidney, and after GH treatment, there is a significant increase in phosphorylation of these proteins in STZ-induced diabetic rats compared with controls. Moreover, the GH-induced association of IRS-1/phosphatidylinositol 3-kinase, IRS-1/growth factor receptor bound 2 (Grb2), and Shc/Grb2 are increased in diabetic rats as well. Immunohistochemical studies show that GH-induced p-Akt and p-ERK activation is apparently more pronounced in the kidneys of diabetic rats. Administration of G120K-PEG, a GH antagonist, in diabetic mice shows inhibitory effects on diabetic renal enlargement and reverses the alterations in GH signal transduction observed in diabetic animals. The present study demonstrates a role for GH signaling in the pathogenesis of early diabetic renal changes and suggests that specific GHR blockade may present a new concept in the treatment of diabetic kidney disease.
Endothelial Dysfunction Relates to Folate Status in Children and Adolescents With Type 1 Diabetes
Authors: Wiltshire Esko J. , Gent Roger , Hirte Craig , Pena Alexia , Thomas David W. , Couper Jennifer J.
Published: March 2007

Endothelial dysfunction occurs early in the development of vascular disease in diabetes. Total plasma homocyst(e)ine (tHcy) is associated with endothelial dysfunction. We therefore aimed to assess endothelial function in children with type 1 diabetes in relation to tHcy and its determinants. Endothelial function was assessed in 36 children with type 1 diabetes aged 13.7 ± 2.2 years and 20 age- and sex-matched control subjects using ultrasound assessment of flow-mediated dilatation (FMD) and glyceryl trinitrate (GTN)-dependent brachial artery responses. von Willebrand factor (vWF) and thrombomodulin, markers of endothelial activation, were measured in 64 children with type 1 diabetes and 52 control subjects. Fasting glucose, tHcy, serum and red cell folate, vitamin B12, HbA1c, creatinine, and lipids were also measured. FMD (5.2 ± 4.7 vs. 9.1 ± 4.0%, P = 0.002) and the ratio of FMD:GTN-induced dilatation (0.22 ± 0.39 vs. 0.41 ± 0.29%, P = 0.008) were significantly lower in diabetic subjects, indicating endothelial dysfunction. In diabetic subjects, red cell folate correlated independently with FMD (β = 0.42, P = 0.028) and the ratio of FMD:GTN-induced dilatation (β = 0.59, P < 0.001). Resting vessel diameter correlated independently with tHcy (β = −0.51, P < 0.001) and height (β = 0.65, P < 0.001). vWF correlated independently with HbA1c (β = 0.38, P = 0.003), and thrombomodulin correlated independently with red cell folate (β = −0.38, P = 0.005), tHcy (β = −0.37, P = 0.004), diastolic blood pressure (β = −0.28, P = 0.025), and creatinine clearance (β = 0.26, P = 0.033). Children with type 1 diabetes have early endothelial dysfunction. Better folate status is associated with better endothelial function, as measured by higher FMD, higher FMD:GTN ratio, and lower thrombomodulin. Folate may therefore protect against endothelial dysfunction in children with diabetes.
Defining the Importance of Mitochondrial Gene Defects in Maternally Inherited Diabetes by Sequencing the Entire Mitochondrial Genome
Authors: Choo-Kang Alan T.W. , Lynn Stephen , Taylor Geoffrey A. , Daly Mark E. , Sihota Sarbpreet S. , Wardell Teressa M. , Chinnery Patrick F. , Turnbull Douglass M. , Walker Mark
Published: March 2007

For any mitochondrial DNA (mtDNA) mutation, the ratio of mutant to wild-type mtDNA (% heteroplasmy) varies across tissues, with low levels in leukocytes and high levels in postmitotic tissues (e.g., skeletal muscle). Direct sequencing is the gold-standard method used to detect novel mutations, but can only reliably detect % heteroplasmy >25%, which is rare in leukocytes. Therefore, we investigated the role of mtDNA defects in maternally inherited diabetes by first screening for the A3243G tRNALeu(UUR) mutation by restriction assay, followed by sequencing of the entire mitochondrial genome using skeletal muscle derived mtDNA. A total of 28 patients had maternally inherited diabetes either alone (group 1, n = 17) or with one or more additional features of mitochondrial disease, including bilateral sensori-neural deafness and neuromuscular disease (group 2, n = 11). Three patients (all from group 2) carried the A3243G mutation. Skeletal muscle mtDNA from eight group 1 patients and six more group 2 patients was sequenced. No pathogenic mutations were found in the group 1 patients, while two patients from group 2 had mutations at positions 12258 and 14709 in the tRNA serine and glutamic acid genes, respectively. We conclude, therefore, that screening for mtDNA mutations should be considered in patients with maternally inherited diabetes, but only when additional features of mitochondrial disease are present.
A Genetic Switch in Pancreatic β-Cells
Authors: Ferrer Jorge
Published: March 2007

Heterozygous mutations in the genes encoding transcriptional regulators hepatocyte nuclear factor (HNF)-1α and HNF-4α cause a form of diabetes known as maturity-onset diabetes of the young (MODY). Haploinsufficiency of HNF-1α or HNF-4α results in MODY because of defective function of pancreatic islet cells. In contrast, homozygous null mutations in mouse models lead to widespread and profound gene expression defects in multiple cell types. Thus, it is not surprising that HNF-1α function is now known to have distinct properties in pancreatic β-cells. It controls a complex tissue-selective genetic network that is activated when pancreatic cells differentiate, and allows these cells to maintain critical specialized functions. The network contains an indispensable core component formed by a positive cross-regulatory feedback circuit between HNF-1α and HNF-4α. This type of circuit configuration can exhibit a switch-like behavior with two stable states. In the default active state, it can serve to perpetuate network activity in differentiated β-cells. However, the loss of one HNF-1α or HNF-4α allele can increase the probability that the feedback circuit is permanently switched off, resulting in decreased expression of all four alleles selectively in β-cells. Such a model can serve to rationalize key aspects of the pathogenic mechanism in MODY.
Potentiation of Insulin Signaling in Tissues of Zucker Obese Rats After Acute and Long-Term Treatment With PPARγ Agonists
Authors: Jiang Guoqiang , Dallas-Yang Qing , Li Zhihua , Szalkowski Deborah , Liu Franklin , Shen Xiaolan , Wu Margaret , Zhou Gaochao , Doebber Thomas , Berger Joel , Moller David E. , Zhang Bei B.
Published: March 2007

Thiazolidinediones (TZDs), agonists of peroxisome proliferator-activated receptor-γ (PPARγ), improve insulin sensitivity in vivo, and the mechanism remains largely unknown. In this study, we showed that, in Zucker obese (fa/fa) rats, acute (1-day) treatment with both rosiglitazone (a TZD) and a non-TZD PPARγ agonist (nTZD) reduced plasma free fatty acid and insulin levels and, concomitantly, potentiated insulin-stimulated Akt phosphorylation at threonine 308 (Akt-pT308) in adipose and muscle tissues. A similar effect on Akt was observed in liver after a 7-day treatment. The increase in Akt-pT308 was correlated with an increase in Akt phosphorylation at serine 473 (Akt-pS473), tyrosine phosphorylation of insulin receptor β subunit and insulin receptor substrate-1, and serine phosphorylation of glycogen synthase kinase-3α/β. The agonists appeared to potentiate Akt1 phosphorylation in muscle and liver and both Akt1 and Akt2 in adipose. Finally, potentiation of insulin signaling was also observed in isolated adipose tissue ex vivo and differentiated 3T3 L1 adipocytes in vitro, but not in rat primary hepatocytes in vitro. These results suggest that 1) PPARγ agonists acutely potentiate insulin signaling in adipose and muscle tissues and such regulation may be physiologically relevant to insulin sensitization in vivo; 2) the agonists directly target adipose tissues; and 3) the metabolic and signaling effects of the agonists are mediated by structurally distinct PPARγ agonists.
Liver X Receptors Downregulate 11β-Hydroxysteroid Dehydrogenase Type 1 Expression and Activity
Authors: Stulnig Thomas M. , Oppermann Udo , Steffensen Knut R. , Schuster Gertrud U. , Gustafsson Jan-Åke
Published: March 2007

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1) converts inactive corticosteroids into biologically active corticosteroids, thereby regulating the local concentration of active glucocorticoids, such as cortisol. 11β-HSD-1 is particularly expressed in adipocytes and liver and appears to be causally linked to the development of type 2 diabetes and the metabolic syndrome. Liver X receptor (LXR)-α and -β are nuclear oxysterol receptors whose key role in lipid metabolic regulation has recently been established. In this study, we show that treatment of adipocytes derived from 3T3-L1 cells and mouse embryonic fibroblasts in vitro with synthetic or natural LXR agonists decreases mRNA expression of 11β-HSD-1 by ∼50%, paralleled by a significant decline in 11β-HSD-1 enzyme activity. Downregulation of 11β-HSD-1 mRNA by LXRs started after a lag period of 8 h and required ongoing protein synthesis. Moreover, long-term per os treatment with a synthetic LXR agonist downregulated 11β-HSD-1 mRNA levels by ∼50% in brown adipose tissue and liver of wild-type but not of LXRα−/−β−/− mice and was paralleled by downregulation of hepatic PEPCK expression. In conclusion, LXR ligands could mediate beneficial metabolic effects in insulin resistance syndromes including type 2 diabetes by interfering with peripheral glucocorticoid activation.
Leptin Potentiates Thermogenic Sympathetic Responses to Hypothermia
Authors: Hausberg Martin , Morgan Donald A. , Mitchell Jennifer L. , Sivitz William I. , Mark Allyn L. , Haynes William G.
Published: March 2007

Leptin contributes to the regulation of thermogenesis. In rodents, sympathetic nerve activity efferent to interscapular brown adipose tissue (IBAT-SNA) is involved. On the basis of the hypotheses that 1) leptin acutely potentiates hypothermia-induced increases in IBAT-SNA; 2) this action of leptin is specific to IBAT-SNA, i.e., it does not occur with renal sympathetic nerve activity (R-SNA); and 3) this effect of leptin depends on intact and functional leptin receptors, we measured IBAT-SNA and R-SNA in anesthetized lean and diet-induced obese Sprague-Dawley and in obese Zucker rats, randomly assigned to low-dose leptin or vehicle. Before the start of leptin or vehicle and 5 min, 90 min, and 180 min after, hypothermia (30° C) was induced. Compared with vehicle, leptin did not significantly alter baseline R-SNA or IBAT-SNA. In lean Sprague-Dawley rats, hypothermia-induced increases in IBAT-SNA were significantly augmented by leptin but not by vehicle. In obese Sprague-Dawley rats, leptin did not potentiate hypothermia-induced increases in IBAT-SNA. In Zucker rats, IBAT-SNA did not increase with hypothermia and leptin was not able to induce sympathoactivation with cooling. Changes in R-SNA during hypothermia were not significantly modified by leptin in either group. Thus, low-dose leptin, although not altering baseline SNA, acutely enhances hypothermia-induced sympathetic outflow to IBAT in lean rats. This effect is specific for thermogenic SNA because leptin does not significantly alter the response of R-SNA to hypothermia. The effect depends on intact and functional leptin receptors because it occurs neither in rats with a leptin receptor defect nor in rats with acquired leptin resistance.
Islet Hyperperfusion During Prediabetic Phase in OLETF Rats, a Model of Type 2 Diabetes
Authors: Iwase Masanori , Uchizono Yuji , Tashiro Kenji , Goto Daisuke , Iida Mitsuo
Published: March 2007

Although it has been hypothesized that initial hyperperfusion followed by late hypoperfusion in islet circulation occurs in rodent models of type 2 diabetes, islet blood flow has not been measured during prediabetic phase. We studied islet blood flow in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of slowly progressive obese type 2 diabetes. Islet blood flow was measured by the two-color microsphere method under anesthesia at different ages. Islet blood flow was significantly higher in young OLETF rats compared with control Long-Evans Tokushima Otsuka (LETO) rats when the former were not obese or diabetic and had normal insulin secretion at 5 weeks of age (LETO 4.6 ± 1.1, OLETF 8.8 ± 1.2 ml · min−1 · mg− 1, P < 0.01). At 6 months of age, islet hyperperfusion was observed in OLETF rats, and >40% of whole pancreatic blood flow was diverted into islets in OLETF rats. Prevention of obesity by food restriction increased basal islet blood flow. On the other hand, long-term hyperglycemia induced by sucrose feeding decreased fractional islet blood flow as well as glucose-stimulated islet blood flow. Our results indicate that hyperperfusion is present during the preobese and prediabetic phase in our type 2 diabetes rats.
Impaired Long-Chain Fatty Acid Oxidation and Contractile Dysfunction in the Obese Zucker Rat Heart
Authors: Young Martin E. , Guthrie Patrick H. , Razeghi Peter , Leighton Brendan , Abbasi Shahrzad , Patil Sarita , Youker Keith A. , Taegtmeyer Heinrich
Published: March 2007

We investigated whether decreased responsiveness of the heart to physiological increases in fatty acid availability results in lipid accumulation and lipotoxic heart disease. Lean and obese Zucker rats were either fed ad libitum or fasted overnight. Fasting increased plasma nonesterified fatty acid levels in both lean and obese rats, although levels were greatest in obese rats regardless of nutritional status. Despite increased fatty acid availability, the mRNA transcript levels of peroxisome proliferator-activated receptor (PPAR)-α-regulated genes were similar in fed lean and fed obese rat hearts. Fasting increased expression of all PPAR-α -regulated genes in lean Zucker rat hearts, whereas, in obese Zucker rat hearts, muscle carnitine palmitoyltransferase and medium-chain acyl-CoA dehydrogenase were unaltered with fasting. Rates of oleate oxidation were similar for hearts from fed rats. However, fasting increased rates of oleate oxidation only in hearts from lean rats. Dramatic lipid deposition occurred within cardiomyocytes of obese, but not lean, Zucker rats upon fasting. Cardiac output was significantly depressed in hearts isolated from obese rats compared with lean rats, regardless of nutritional status. Fasting increased cardiac output in hearts of lean rats only. Thus, the heart’s inability to increase fatty acid oxidation in proportion to increased fatty acid availability is associated with lipid accumulation and contractile dysfunction of the obese Zucker rat.
Factor Analysis of Metabolic Syndrome Using Directly Measured Insulin Sensitivity
Authors: Hanley Anthony J.G. , Karter Andrew J. , Festa Andreas , D’Agostino Ralph , Wagenknecht Lynne E. , Savage Peter , Tracy Russell P. , Saad Mohammed F. , Haffner Steven
Published: March 2007

Factor analysis, a multivariate correlation technique, has been used to provide insight into the underlying structure of metabolic syndrome, which is characterized by physiological complexity and strong statistical intercorrelation among its key variables. The majority of previous factor analyses, however, have used only surrogate measures of insulin sensitivity. In addition, few have included members of multiple ethnic groups, and only one has presented results separately for subjects with impaired glucose tolerance. The objective of this study was to investigate, using factor analysis, the clustering of physiologic variables using data from 1,087 nondiabetic participants in the Insulin Resistance Atherosclerosis Study (IRAS). This study includes information on the directly measured insulin sensitivity index (SI) from intravenous glucose tolerance testing among African-American, Hispanic, and non-Hispanic white subjects aged 40–69 years at various stages of glucose tolerance. Principal factor analysis identified two factors that explained 28 and 9% of the variance in the dataset, respectively. These factors were interpreted as 1) a “ metabolic” factor, with positive loadings of BMI, waist, fasting and 2-h glucose, and triglyceride and inverse loadings of log(SI+1) and HDL; and 2) a “blood pressure” factor, with positive loadings of systolic and diastolic blood pressure. The results were unchanged when surrogate measures of insulin resistance were used in place of log(SI+1). In addition, the results were similar within strata of sex, glucose tolerance status, and ethnicity. In conclusion, factor analysis identified two underlying factors among a group of metabolic syndrome variables in this dataset. Analyses using surrogate measures of insulin resistance suggested that these variables provide adequate information to explore the underlying intercorrelational structure of metabolic syndrome. Additional clarification of the physiologic characteristics of metabolic syndrome is required as individuals with this condition are increasingly being considered candidates for behavioral and pharmacologic intervention.
Peroxisome Proliferator-Activated Receptor-γ2 Polymorphism Pro12Ala Is Associated With Nephropathy in Type 2 Diabetes
Authors: Herrmann Stefan-Martin , Ringel Jens , Wang Ji-Guang , Staessen Jan A. , Brand Eva
Published: March 2007

The Pro12Ala polymorphism of the gene encoding the peroxisome proliferator-activated receptor (PPAR)-γ2 has recently been shown to be associated with type 2 diabetes. In the present analysis, we investigated whether PPAR-γ2 Pro12Ala was associated with microvascular complications of type 2 diabetes, such as albuminuria, end-stage renal failure (ESRF), or retinopathy. A total of 445 patients with type 2 diabetes who were enrolled in the Berlin Diabetes Mellitus Study and in whom we determined albuminuria and the presence of ESRF and retinopathy were genotyped for the PPAR-γ2 Pro12Ala polymorphism. We also measured potentially important covariables, such as blood pressure, BMI, duration of diabetes, glycosylated hemoglobin, serum creatinine, and serum lipids. Among 445 patients with type 2 diabetes (mean age 59.3 years), the Pro12Ala genotype distribution was in Hardy-Weinberg equilibrium (P = 0.42). The Ala12 allele frequency was 0.14. With adjustment for covariables, the 118 Ala12 allele carriers had significantly lower urinary albumin excretion (UAE) than the 327 noncarriers (17.1 vs. 25.8 mg/d; P = 0.01). The percentage decrease in UAE observed in PPAR-γ Ala12 allele carriers relative to noncarriers (P = 0.003) rose from 0.2% (P = 0.99) to 54% (P = 0.008) and to 70% (P = 0.01) when the duration of diabetes increased from <10 years to 10–19 years and to ≥20 years, respectively. Similarly, the odds ratios of having albuminuria decreased from 1.22 (P = 0.54) to 0.61 (P = 0.23) and to 0.11 (P = 0.007), respectively. Among patients with type 2 diabetes, PPAR-γ2 Ala12 allele carriers had significantly lower UAE and tended to develop overt proteinuria less frequently. These observations suggest a protective effect of the Ala12 allele in relation to diabetic nephropathy.
The Succinate Mechanism of Insulin Release
Authors: Fahien Leonard A. , MacDonald Michael J.
Published: March 2007

Nutrient secretagogues can increase the production of succinyl-CoA in rat pancreatic islets. When succinate esters are the secretagogue, succinyl-CoA can be generated via the succinate thiokinase reaction. Other secretagogues can increase production of succinyl-CoA secondary to increasing α-ketoglutarate production by glutamate dehydrogenase or mitochondrial aspartate aminotransferase followed by the α-ketoglutarate dehydrogenase reaction. Although secretagogues can increase the production of succinyl-CoA, they do not increase the level of this metabolite until after they decrease the level of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). This suggests that the generated succinyl-CoA initially reacts with acetoacetate to yield acetoacetyl-CoA plus succinate in the succinyl-CoA-acetoacetate transferase reaction. This would be followed by acetoacetyl-CoA reacting with acetyl-CoA to generate HMG-CoA in the HMG-CoA synthetase reaction. HMG-CoA will then be reduced by NADPH to mevalonate in the HMG-CoA reductase reaction and/or cleaved to acetoacetate plus acetyl-CoA by HMG cleavage enzyme. Succinate derived from either exogenous succinate esters or generated by succinyl-CoA-acetoacetate transferase is metabolized to malate followed by the malic enzyme reaction. Increased production of NADPH by the latter reaction then increases reduction of HMG-CoA and accounts for the decrease in the level of HMG-CoA produced by secretagogues. Pyruvate carboxylation catalyzed by pyruvate carboxylase will supply oxaloacetate to mitochondrial aspartate aminotransferase. This would enable this aminotransferase to supply α-ketoglutarate to the α-ketoglutarate dehydrogenase complex and would, in part, account for secretagogues increasing the islet level of succinyl-CoA after they decrease the level of HMG-CoA. Mevalonate could be a trigger of insulin release as a result of its ability to alter membrane proteins and/or cytosolic Ca2+. This is consistent with the fact that insulin secretagogues decrease the level of the mevalonate precursor HMG-CoA. In addition, inhibitors of HMG-CoA reductase interfere with insulin release and this inhibition can be reversed by mevalonate.
Role of ATP Production and Uncoupling Protein-2 in the Insulin Secretory Defect Induced by Chronic Exposure to High Glucose or Free Fatty Acids and Effects of Peroxisome Proliferator-Activated Receptor-γ Inhibition
Authors: Patanè Giovanni , Anello Marcello , Piro Salvatore , Vigneri Riccardo , Purrello Francesco , Rabuazzo Agata Maria
Published: March 2007

In rat pancreatic islets chronically exposed to high glucose or high free fatty acid (FFA) levels, glucose-induced insulin release and mitochondrial glucose oxidation are impaired. These abnormalities are associated with high basal ATP levels but a decreased glucose-induced ATP production (Δ of increment over baseline 0.7 ± 0.5 or 0.5 ± 0.3 pmol/islet in islets exposed to glucose or FFA vs. 12.0 ± 0.6 in control islets, n = 3; P < 0.01) and, as a consequence, with an altered ATP/ADP ratio. To investigate further the mechanism of the impaired ATP formation, we measured in rat pancreatic islets glucose-stimulated pyruvate dehydrogenase (PDH) activity, a key enzyme for pyruvate metabolism and for the subsequent glucose oxidation through the Krebs cycle, and also the uncoupling protein-2 (UCP-2) content by Western blot. In islets exposed to high glucose or FFA, glucose-stimulated PDH activity was impaired and UCP-2 was overexpressed. Because UCP-2 expression is modulated by a peroxisome proliferator- activated receptor (PPAR)-dependent pathway, we measured PPAR-γ contents by Western blot and the effects of a PPAR-γ antagonist. PPAR-γ levels were overexpressed in islets cultured with high FFA levels but unaffected in islets exposed to high glucose. In islets exposed to high FFA concentration, a PPAR-γ antagonist was able to prevent UCP-2 overexpression and to restore insulin secretion and the ATP/ADP ratio. These data indicate that in rat pancreatic islets chronically exposed to high glucose or FFA, glucose-induced impairment of insulin secretion is associated with (and might be due to) altered mitochondrial function, which results in impaired glucose oxidation, overexpression of the UCP-2 protein, and a consequent decrease of ATP production. This alteration in FFA cultured islets is mediated by the PPAR-γ pathway.
Plasma Ghrelin Concentrations Are Not Regulated by Glucose or Insulin
Authors: Schaller Georg , Schmidt Adele , Pleiner Johannes , Woloszczuk Wolfgang , Wolzt Michael , Luger Anton
Published: March 2007

Ghrelin plasma concentrations increase during fasting and fall rapidly after nutrient ingestion. We hypothesized that insulin or glucose could regulate ghrelin secretion by a feedback mechanism. In this randomized, double-blind, placebo-controlled crossover study, three different study days were carried out in nine healthy volunteers (age 26 ± 6 years). On each day, stepwise increasing systemic glucose concentrations of 5.0, 8.3, and 11.1 mmol/l were attained by intravenous infusion of glucose, representing fasting and postprandial conditions. Ghrelin plasma concentration was studied during concomitant exogenous hyperinsulinemia, inhibition of endogenous insulin production by somatostatin infusion, and placebo time control, respectively. Elevated glucose concentrations increased circulating insulin to 612 ± 85 pmol/l (P < 0.01), but they did not affect ghrelin concentrations. Prolonged hyperinsulinemia by exogenous infusion resulted in circulating insulin of 1,602 ± 261 pmol/l (P < 0.01) and suppressed plasma ghrelin to 49.6% of baseline (P < 0.01). During administration of somatostatin, insulin concentration remained constant, but an even greater decrease in ghrelin to 39.5% of baseline was noted (P < 0.01). Hyperglycemia does not decrease ghrelin, and a reduction in ghrelin is only seen at supraphysiological insulin concentrations. In contrast, systemic ghrelin concentrations are decreased by somatostatin. The meal-related suppression of ghrelin appears not directly regulated by glucose or insulin.
The Insulin Gene Variable Number Tandem Repeat Class I/III Polymorphism Is in Linkage Disequilibrium With Birth Weight but Not Type 2 Diabetes in the Pima Population
Authors: Lindsay Robert S. , Hanson Robert L. , Wiedrich Chris , Knowler William C. , Bennett Peter H. , Baier Leslie J.
Published: March 2007

The insulin gene variable number tandem repeat (INS-VNTR) is proposed to exert pleiotropic genetic effects on birth weight and diabetes susceptibility. In our study, we examined the influence of a polymorphism in tight linkage disequilibrium with INS-VNTR (−23Hph1) on birth weight and type 2 diabetes in the Pima population. A parent-offspring “trio” design was used to assess parent-of-origin effects and population stratification. The presence of the −23Hph1 T-allele was associated with lower birth weight (n = 192; −140 g per copy of the T-allele; P = 0.04), even after adjustment for effects of population stratification (P = 0.03). The effects of paternally transmitted T-alleles were greater than those of maternally transmitted alleles (paternally transmitted: −250 g, P = 0.05; maternally transmitted: −111 g, P = 0.43), but this difference was not statistically significant (P = 0.50). The −23Hph1 T-allele was associated with an increased prevalence of type 2 diabetes (P = 0.009), which family-based association analysis suggested was attributable to population structure (P = 0.04) without significant evidence of linkage disequilibrium between diabetes prevalence and genotype (P = 0.86). Thus allelic variation of the INS gene is associated with lower birth weight and increased prevalence of type 2 diabetes. Significant linkage disequilibrium was found between −23Hph1 and birth weight but not type 2 diabetes, an observation that supports a potential functional role of INS polymorphisms in the regulation of birth weight.
Mapping Genes Influencing Type 2 Diabetes Risk and BMI in Japanese Subjects
Authors: Iwasaki Naoko , Cox Nancy J. , Wang Yan-Qing , Schwarz Peter E.H. , Bell Graeme I. , Honda Masashi , Imura Mitsuo , Ogata Makiko , Saito Masayuki , Kamatani Naoyuki , Iwamoto Yasuhiko
Published: March 2007

We have carried out an autosomal genome scan for genes contributing to the development of type 2 diabetes and affecting BMI in the Japanese population (164 families, 256 affected sib-pairs). We found 12 regions that showed nominally significant multipoint evidence of linkage with type 2 diabetes (i.e. logarithm of odds [LOD] score >0.59, P < 0.05): chromosome 1 29.9 cM; chromosome 2 169.6 and 236.8 cM; chromosome 4 104.9 cM; chromosome 5 114.8 cM; chromosome 6 42.3 cM; chromosome 8 15.3 and 93.3 cM; chromosome 9 140.0 cM; chromosome 11 131.6 cM; chromosome 17 36.1 cM; and chromosome 21 48.0 cM. Twelve regions showed nominal multipoint evidence for linkage with log-transformed BMI (lnBMI): chromosome 2 167.9 and 210.5 cM; chromosome 3 185.7 cM; chromosome 4 118.9 and 145.6 cM; chromosome 5 131.9 cM; chromosome 7 7.4 cM; chromosome 10 70.0 cM; chromosome 15 12.8 cM; chromosome 16 30.0 cM; and chromosome 17 47.8 and 100.2 cM. Although none of the regions achieved genome-wide levels of significance, simulation studies showed that we observed more linkage signals than expected if there were no loci contributing to type 2 diabetes or BMI. Eight of the regions showing nominal evidence for linkage with type 2 diabetes have been reported in other genome scans, and seven of the regions showing linkage with lnBMI have shown linkage with BMI and BMI-related traits in other studies. Thus, our results may replicate findings in other studies. They may also indicate new regions of the genome that are involved in the regulation of blood glucose levels or body weight.
Reduction of Protein Tyrosine Phosphatase 1B Increases Insulin-Dependent Signaling in ob/ob Mice
Authors: Gum Rebecca J. , Gaede Lori L. , Koterski Sandra L. , Heindel Matthew , Clampit Jill E. , Zinker Bradley A. , Trevillyan James M. , Ulrich Roger G. , Jirousek Michael R. , Rondinone Cristina M.
Published: March 2007

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin receptor (IR) signal transduction and a drug target for treatment of type 2 diabetes. Using PTP1B antisense oligonucleotides (ASOs), effects of decreased PTP1B levels on insulin signaling in diabetic ob/ob mice were examined. Insulin stimulation, prior to sacrifice, resulted in no significant activation of insulin signaling pathways in livers from ob/ob mice. However, in PTP1B ASO-treated mice, in which PTP1B protein was decreased by 60% in liver, similar stimulation with insulin resulted in increased tyrosine phosphorylation of the IR and IR substrate (IRS)-1 and -2 by threefold, fourfold, and threefold, respectively. IRS-2-associated phosphatidylinositol 3-kinase activity was also increased threefold. Protein kinase B (PKB) serine phosphorylation was increased sevenfold in liver of PTP1B ASO-treated mice upon insulin stimulation, while phosphorylation of PKB substrates, glycogen synthase kinase (GSK)-3α and -3β, was increased more than twofold. Peripheral insulin signaling was increased by PTP1B ASO, as evidenced by increased phosphorylation of PKB in muscle of insulin-stimulated PTP1B ASO-treated animals despite the lack of measurable effects on muscle PTP1B protein. These results indicate that reduction of PTP1B is sufficient to increase insulin-dependent metabolic signaling and improve insulin sensitivity in a diabetic animal model.
All-Trans Retinoic Acid Induces Differentiation of Ducts and Endocrine Cells by Mesenchymal/Epithelial Interactions in Embryonic Pancreas
Authors: Tulachan Sidhartha Singh , Doi Ryuichiro , Kawaguchi Yoshiya , Tsuji Shoichiro , Nakajima Sanae , Masui Toshihiko , Koizumi Masayuki , Toyoda Eiji , Mori Tomohiko , Ito Daisuke , Kami Kazuhiro , Fujimoto Koji , Imamura Masayuki
Published: March 2007

Retinoids during the embryonic period act as a mesenchymal inducer in many organs, including kidney, lung, central nervous system, and gut. Retinoic acid (RA) demonstrates insulinotropic effects in adult pancreas, but only a limited study has elucidated its role in pancreatic organogenesis. In this study, we have analyzed the existence of RA-signaling machinery in embryonic pancreas and evaluated its role using in vitro tissue culture experiments. Here we show the presence of endogenous retinaldehyde dehydrogenase 2 (RALDH2), the most effective RA-synthesizing enzyme, RA-binding proteins, and RA receptors (RARs) in embryonic pancreatic tissue. RALDH2 is expressed exclusively in the mesenchyme. Exogenously added all-trans-retinoic acid (atRA) in tissue culture experiments stimulated differentiation of endocrine and duct cells and promoted apoptotic cell death of acinar tissue. Furthermore, we demonstrate that atRA upregulates the PDX-1 expression. Taken together, our data suggest that atRA-mediated mesenchymal/epithelial interactions play an important role in determining the cell fate of epithelial cells via regulation of the PDX-1 gene, leading to the proper formation of the endocrine versus exocrine component during pancreatic organogenesis.
A Sustained Increase in Plasma Free Fatty Acids Impairs Insulin Secretion in Nondiabetic Subjects Genetically Predisposed to Develop Type 2 Diabetes
Authors: Kashyap Sangeeta , Belfort Renata , Gastaldelli Amalia , Pratipanawatr Thongchai , Berria Rachele , Pratipanawatr Wilailak , Bajaj Mandeep , Mandarino Lawrence , DeFronzo Ralph , Cusi Kenneth
Published: March 2007

Acute elevations in free fatty acids (FFAs) stimulate insulin secretion, but prolonged lipid exposure impairs β-cell function in both in vitro studies and in vivo animal studies. In humans data are limited to short-term (≤48 h) lipid infusion studies and have led to conflicting results. We examined insulin secretion and action during a 4-day lipid infusion in healthy normal glucose tolerant subjects with (FH+ group, n = 13) and without (control subjects, n = 8) a family history of type 2 diabetes. Volunteers were admitted twice to the clinical research center and received, in random order, a lipid or saline infusion. On days 1 and 2, insulin and C-peptide concentration were measured as part of a metabolic profile after standardized mixed meals. Insulin secretion in response to glucose was assessed with a +125 mg/dl hyperglycemic clamp on day 3. On day 4, glucose turnover was measured with a euglycemic insulin clamp with [3-3H]glucose. Day-long plasma FFA concentrations with lipid infusion were increased within the physiological range, to levels seen in type 2 diabetes (∼500–800 μmol/l). Lipid infusion had strikingly opposite effects on insulin secretion in the two groups. After mixed meals, day-long plasma C-peptide levels increased with lipid infusion in control subjects but decreased in the FH+ group (+28 vs. −30%, respectively, P < 0.01). During the hyperglycemic clamp, lipid infusion enhanced the insulin secretion rate (ISR) in control subjects but decreased it in the FH+ group (first phase: +75 vs. −60%, P < 0.001; second phase: +25 vs. −35%, P < 0.04). When the ISR was adjusted for insulin resistance (ISRRd = ISR ÷ [1/Rd], where Rd is the rate of insulin-stimulated glucose disposal), the inadequate β-cell response in the FH+ group was even more evident. Although ISRRd was not different between the two groups before lipid infusion, in the FH+ group, lipid infusion reduced first- and second-phase ISRRd to 25 and 42% of that in control subjects, respectively (both P < 0.001 vs. control subjects). Lipid infusion in the FH+ group (but not in control subjects) also caused severe hepatic insulin resistance with an increase in basal endogenous glucose production (EGP), despite an elevation in fasting insulin levels, and impaired suppression of EGP to insulin. In summary, in individuals who are genetically predisposed to type 2 diabetes, a sustained physiological increase in plasma FFA impairs insulin secretion in response to mixed meals and to intravenous glucose, suggesting that in subjects at high risk of developing type 2 diabetes, β-cell lipotoxicity may play an important role in the progression from normal glucose tolerance to overt hyperglycemia.
NN414, a SUR1/Kir6.2-Selective Potassium Channel Opener, Reduces Blood Glucose and Improves Glucose Tolerance in the VDF Zucker Rat
Authors: Carr Richard D. , Brand Christian L. , Bodvarsdottir Thora B. , Hansen John B. , Sturis Jeppe
Published: March 2007

A novel potassium channel opener compound, NN414, selective for the SUR1/Kir6.2 subtype of the ATP-sensitive potassium channel, was used to examine the effect of reducing β-cell workload in the male Vancouver diabetic fatty (VDF) Zucker rat model of mild type 2 diabetes. Two chronic dosing protocols of NN414 of 3 weeks’ duration were compared with appropriate vehicle-treated controls. In the first group, rats received NN414 (continued group; 1.5 mg/kg p.o. twice daily), during which an oral glucose tolerance test (OGTT) (on day 19 of dosing) was performed and insulin secretion from an in situ perfused pancreas preparation (on day 21) was measured. The second group received NN414 (discontinued group; same dose), but active treatment was replaced by vehicle treatment 2 days before the OGTT and for a further 2 days before the perfused pancreas study. Basal glucose was significantly reduced by NN414, with the fall averaging 0.64 mmol/l after 3 weeks of treatment (P < 0.0001). The glucose excursion and hyperinsulinemia during the OGTT were significantly different between the continued, discontinued, and vehicle groups (glucose area under the curve [AUC]: 640 ± 29, 740 ± 27, and 954 ± 82 mmol · l−1 · min−1, respectively, P < 0.0001; insulin AUC: 38.9 ± 4.2, 44.2 ± 4.2, and 55.1 ± 2.6 nmol · l−1 · min−1, respectively, P < 0.0001). Hyperinsulinemia during the pancreas perfusion with 4.4 mmol/l glucose was significantly reduced in both treatment groups versus vehicle (P < 0.0005). Insulin secretory responsiveness to a step increase in glucose from 4.4 to 16.6 mmol/l, calculated relative to basal, was significantly improved in the continued group versus vehicle (P < 0.01). In conclusion, administration of NN414 for 3 weeks in VDF rats reduces basal hyperglycemia, improves glucose tolerance, and reduces hyperinsulinemia during an OGTT and improves insulin secretory responsiveness ex vivo. NN414 may therefore represent a novel approach to the prevention and treatment of impaired glucose tolerance and type 2 diabetes.
Learned Meal Initiation Attenuates the Anorexic Effects of the Melanocortin Agonist MTII
Authors: Benoit Stephen C. , Clegg Deborah J. , Barrera Jason G. , Seeley Randy J. , Woods Stephen C.
Published: March 2007

The central melanocortin system is critically involved in the control of food intake and body weight. Administration of melanocortin agonists reduces food intake and adiposity, and the central melanocortin system is demonstrated to mediate the anorexic effects of both leptin and insulin. An important unanswered question has been whether melanocortin agonists would also reduce food intake that is driven by factors other than homeostatic mechanisms (e.g., conditioned eating). In the first experiment, we identified that long-term maintenance on a meal-feeding schedule attenuated rats’ sensitivity to central administration of the melanocortin agonist MTII. The results from a second experiment demonstrate that the attenuation of the MTII-induced anorexia was due to learned schedules of food intake rather than food deprivation per se. Results from the final experiment suggest that this attenuation of MTII-induced anorexia may be independent of the decreased sensitivity caused by a high-fat diet. These results support the hypothesis that meal-feeding schedules can lead to anticipatory physiological responses that attenuate the anorexic effects of exogenous melanocortin agonists.
Prevalence and Clinicopathological Characteristics of Islet Amyloid in Chinese Patients With Type 2 Diabetes
Authors: Zhao Hai-Lu , Lai Fernand M.M. , Tong Peter C.Y. , Zhong Ding-Rong , Yang Di , Tomlinson Brian , Chan Juliana C.N.
Published: March 2007

Islet amyloid has been suggested to be an important link between insulin resistance and β-cell dysfunction in type 2 diabetes. To investigate the prevalence and clinicopathological characteristics of islet amyloid, we examined consecutive autopsies of 235 Chinese patients with type 2 diabetes and 533 nondiabetic subjects. Islet amyloid deposits were identified using Congo red staining and quantitated by image analysis. We found that 3.0% of the nondiabetic subjects versus 39.6% of the diabetic patients displayed islet amyloid (P < 0.001). In diabetic patients, the amyloid deposits occupied a mean islet area of 36.2%, which was positively associated with BMI, blood pressure, and glycemic control. Pancreatic fibrosis and fat infiltration were more frequently found in diabetic patients with islet amyloid than those without islet amyloid, whereas pancreatic arteriosclerosis was identified in all diabetic patients. These findings suggest that islet amyloid deposits reflect greater insulin resistance and islet failure in a subgroup of type 2 diabetic patients. Islet failure may also have been exacerbated by fat infiltration, fibrosis, and arteriosclerosis. Optimal blood pressure and metabolic control may reduce these pathological changes and help preserve islet cell mass.
Timing of Changes in Interstitial and Venous Blood Glucose Measured With a Continuous Subcutaneous Glucose Sensor
Authors: Boyne Michael S. , Silver David M. , Kaplan Joy , Saudek Christopher D.
Published: March 2007

The objective of this study was to use a subcutaneous continuous glucose sensor to determine time differences in the dynamics of blood glucose and interstitial glucose. A total of 14 patients with type 1 diabetes each had two sensors (Medtronic/MiniMed CGMS) placed subcutaneously in the abdomen, acquiring data every 5 min. Blood glucose was sampled every 5 min for 8 h, and two liquid meals were given. A smoothing algorithm was applied to the blood glucose and interstitial glucose curves. The first derivatives of the glucose traces defined and quantified the timing of rises, peaks, falls, and nadirs. Altogether, 24 datasets were used for the analysis of time differences between interstitial and blood glucose and between sensors in each patient. Time differences between blood and interstitial glucose ranged from 4 to 10 min, with the interstitial glucose lagging behind blood glucose in 81% of cases (95% CIs 72.5 and 89.5%). The mean (±SD) difference between the two sensors in each patient was 6.7 ± 5.1 min, representing random variation in sensor response. In conclusion, there is a time lag of interstitial glucose behind blood glucose, regardless of whether glycemia is rising or falling, but intersensor variability is considerable in this sensor system. Comparisons of interstitial and blood glucose kinetics must take statistical account of variability between sensors.
Permanent Neonatal Diabetes Caused by Glucokinase Deficiency
Authors: Njølstad Pål R. , Sagen Jørn V. , Bjørkhaug Lise , Odili Stella , Shehadeh Naim , Bakry Doua , Sarici S. Umit , Alpay Faruk , Molnes Janne , Molven Anders , Søvik Oddmund , Matschinsky Franz M.
Published: March 2007

Neonatal diabetes can be either permanent or transient. We have recently shown that permanent neonatal diabetes can result from complete deficiency of glucokinase activity. Here we report three new cases of glucokinase-related permanent neonatal diabetes. The probands had intrauterine growth retardation (birth weight <1,900 g) and insulin-treated diabetes from birth (diagnosis within the first week of life). One of the subjects was homozygous for the missense mutation Ala378Val (A378V), which is an inactivating mutation with an activity index of only 0.2% of wild-type glucokinase activity. The second subject was homozygous for a mutation in the splice donor site of exon 8 (intervening sequence 8 [IVS8] + 2T→G), which is predicted to lead to the synthesis of an inactive protein. The third subject (second cousin of subject 2) was a compound heterozygote with one allele having the splice-site mutation IVS8 + 2T→G and the other the missense mutation Gly264Ser (G264S), a mutation with an activity index of 86% of normal activity. The five subjects with permanent neonatal diabetes due to glucokinase deficiency identified to date are characterized by intrauterine growth retardation, permanent insulin-requiring diabetes from the first day of life, and hyperglycemia in both parents. Autosomal recessive inheritance and enzyme deficiency are features typical for an inborn error of metabolism, which occurred in the glucose-insulin signaling pathway in these subjects.
Microvascular Complications of Impaired Glucose Tolerance
Authors: Singleton J. Robinson , Smith A. Gordon , Russell James W. , Feldman Eva L.
Published: March 2007

Impaired glucose tolerance (IGT) serves as a marker for the state of insulin resistance and predicts both large- and small-vessel vascular complications, independent of a patient’s progression to diabetes. Patients with IGT are at significantly increased risk for death and morbidity due to myocardial infarction, stroke, and large-vessel occlusive disease. IGT is more predictive of cardiovascular morbidity than impaired fasting glucose, probably because it is a better surrogate for the state of insulin resistance. IGT is also independently associated with traditional microvascular complications of diabetes, including retinopathy, renal disease, and polyneuropathy, which are the topics of this review. Inhibition of nitric oxide-mediated vasodilation, endothelial injury due to increased release of free fatty acids and adipocytokines from adipocytes, and direct metabolic injury of endothelial and end-organ cells contribute to vascular complications. Early detection of IGT allows intensive diet and exercise modification, which has proven significantly more effective than drug therapy in normalizing postprandial glucose and inhibiting progression to diabetes. To what degree intervention will limit recognized complications is not known.
Brain Death Significantly Reduces Isolated Pancreatic Islet Yields and Functionality In Vitro and In Vivo After Transplantation in Rats
Authors: Contreras Juan L. , Eckstein Christopher , Smyth Cheryl A. , Sellers Marty T. , Vilatoba Mario , Bilbao Guadalupe , Rahemtulla Firoz G. , Young Carlton J. , Thompson J. Anthony , Chaudry Irshad H. , Eckhoff Devin E.
Published: March 2007

Although ∼1 million islets exist in the adult human pancreas, current pancreas preservation and islet isolation techniques recover <50%. Presently, cadaveric donors remain the sole source of pancreatic tissue for transplantation. Brain death is characterized by activation of proinflammatory cytokines and organ injury during preservation and reperfusion. In this study, we assessed the effects of brain death on islet isolation yields and functionality. Brain death was induced in male 250- to 350-g Lewis rats by inflation of a Fogarty catheter placed intracranially. The rats were mechanically ventilated for 2, 4, and 6 h before removal of the pancreas (n = 6). In controls, the catheter was not inflated (n = 6). Shortly after brain death induction, a significant increase in serum tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 was demonstrated in a time-dependent manner. Upregulation of TNF-α, IL-1β, and IL-6 mRNA was noted in the pancreas. Brain death donors presented lower insulin release after glucose stimulation assessed by in situ perfusion of the pancreas. Islet recovery was reduced in brain death donors compared with controls (at 6 h 602.3 ± 233.4 vs. 1,792.5 ± 325.4 islet equivalents, respectively; P < 0.05). Islet viability assessed in dissociated islet cells and in intact cultured islets was reduced in islets recovered from brain death donors, an effect associated with higher nuclear activities of NF-κB p50, c-Jun, and ATF-2. Islet functionality evaluated in vitro by static incubation and in vivo after intraportal transplantation in syngeneic streptozotocin-induced diabetic rats was significantly reduced in preparations obtained from brain death donors. In conclusion, brain death significantly reduced islet yields and functionality. These observations may lead to strategies to reduce the effects of brain death on pancreatic islets and improve the results in clinical transplantation.