bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Insulin on In Vivo Cerebral Glucose Concentrations and Rates of Glucose Transport/Metabolism in Humans
Authors: Seaquist Elizabeth R. , Damberg Gregory S. , Tkac Ivan , Gruetter Rolf
Published: March 2007

The continuous delivery of glucose to the brain is critically important to the maintenance of normal metabolic function. However, elucidation of the hormonal regulation of in vivo cerebral glucose metabolism in humans has been limited by the lack of direct, noninvasive methods with which to measure brain glucose. In this study, we sought to directly examine the effect of insulin on glucose concentrations and rates of glucose transport/metabolism in human brain using 1H-magnetic resonance spectroscopy at 4 Tesla. Seven subjects participated in paired hyperglycemic (16.3 ± 0.3 mmol/l) clamp studies performed with and without insulin. Brain glucose remained constant throughout (5.3 ± 0.3 μmol/g wet wt when serum insulin = 16 ± 7 pmol/l vs. 5.5 ± 0.3 μmol/g wet wt when serum insulin = 668 ± 81 pmol/l, P = NS). Glucose concentrations in gray matter–rich occipital cortex and white matter–rich periventricular tissue were then simultaneously measured in clamps, where plasma glucose ranged from 4.4 to 24.5 mmol/l and insulin was infused at 0.5 mU · kg–1 · min–1. The relationship between plasma and brain glucose was linear in both regions. Reversible Michaelis-Menten kinetics fit these data best, and no differences were found in the kinetic constants calculated for each region. These data support the hypothesis that the majority of cerebral glucose uptake/metabolism is an insulin-independent process in humans.
Structural Basis for the Interference Between Nicorandil and Sulfonylurea Action
Authors: Reimann Frank , Ashcroft Frances M. , Gribble Fiona M.
Published: March 2007

Nicorandil is a new antianginal agent that potentially may be used to treat the cardiovascular side effects of diabetes. It is both a nitric oxide donor and an opener of ATP-sensitive K+ (KATP) channels in muscle and thereby causes vasodilation of the coronary vasculature. The aim of this study was to investigate the domains of the KATP channel involved in nicorandil activity and to determine whether nicorandil interacts with hypoglycemic sulfonylureas that target KATP channels in pancreatic β-cells. KATP channels in muscle and β-cells share a common pore-forming subunit, Kir6.2, but possess alternative sulfonylurea receptors (SURs; SUR1 in β-cells, SUR2A in cardiac muscle, and SUR2B in smooth muscle). We expressed recombinant KATP channels in Xenopus oocytes and measured the effects of drugs and nucleotides by recording macroscopic currents in excised membrane patches. Nicorandil activated Kir6.2/SUR2A and Kir6.2/SUR2B but not Kir6.2/SUR1 currents, consistent with its specificity for cardiac and smooth muscle KATP channels. Drug activity depended on the presence of intracellular nucleotides and was impaired when the Walker A lysine residues were mutated in either nucleotide-binding domain of SUR2. Chimeric studies showed that the COOH-terminal group of transmembrane helices (TMs), especially TM 17, is responsible for the specificity of nicorandil for channels containing SUR2. The splice variation between SUR2A and SUR2B altered the off-rate of the nicorandil response. Finally, we showed that nicorandil activity was unaffected by gliclazide, which specifically blocks SUR1-type KATP channels, but was severely impaired by glibenclamide and glimepiride, which target both SUR1 and SUR2-type KATP channels.
Small Molecule Insulin Receptor Activators Potentiate Insulin Action in Insulin-Resistant Cells
Authors: Li Ming , Youngren Jack F. , Manchem Vara Prasad , Kozlowski Michael , Zhang Bei B. , Maddux Betty A. , Goldfine Ira D.
Published: March 2007

In type 2 diabetes, impaired insulin signaling leads to hyperglycemia and other metabolic abnormalities. To study a new class of antidiabetic agents, we compared two small, nonpeptide molecules that activate insulin receptor (IR) β-subunit tyrosine kinase activity: Merck L7, a direct IR agonist, and Telik’s TLK16998, an IR sensitizer. In rat hepatoma cells (HTCs) that overexpress the IR (HTC-IR), IR autophosphorylation was directly activated by L7 in the absence of insulin. TLK16998 did not directly activate IR autophosphorylation, but it enhanced IR autophosphorylation in the presence of insulin. Tyrosine phosphorylation of an endogenous 185-kDa IR substrate was also significantly enhanced by both Merck L7 alone and TLK16998 plus insulin. Adding TLK16998 to L7 produced synergistic effects, further indicating that these two compounds act on the IR through separate mechanisms. We next studied HTC-IRΔ485–599 cells, which overexpress a mutant IR with a deletion in the α-subunit connecting domain that does not undergo autophosphorylation in response to insulin binding. L7 was able to directly activate autophosphorylation of the deletion mutant IR in these cells, whereas TLK16998 had no effect. Compounds were then tested in three other cell models of impaired IR function. Both TLK16998 and Merck L7 improved IR autophosphorylation in cells with diminished IR signaling due to either treatment with tumor necrosis factor-α or overexpression of membrane glycoprotein PC-1. However, in TPA (tetradecanoylphorbol acetate)-treated cells, TLK16998 but not Merck L7 was able to significantly reverse the impaired insulin-stimulated IR autophosphorylation. In summary, these two classes of IR activators selectively increased IR function in a variety of insulin-resistant cell lines.
Intramyocellular Lipid Is Associated With Resistance to In Vivo Insulin Actions on Glucose Uptake, Antilipolysis, and Early Insulin Signaling Pathways in Human Skeletal Muscle
Authors: Virkamäki Antti , Korsheninnikova Elena , Seppälä-Lindroos Anneli , Vehkavaara Satu , Goto Takashi , Halavaara Juha , Häkkinen Anna-Maija , Yki-Järvinen Hannele
Published: March 2007

To examine whether and how intramyocellular lipid (IMCL) content contributes to interindividual variation in insulin action, we studied 20 healthy men with no family history of type 2 diabetes. IMCL was measured as the resonance of intramyocellular CH2 protons in lipids/resonance of CH3 protons of total creatine (IMCL/CrT), using proton magnetic resonance spectroscopy in vastus lateralis muscle. Whole-body insulin sensitivity was measured using a 120-min euglycemic-hyperinsulinemic (insulin infusion rate 40 mU/m2 · min) clamp. Muscle biopsies of the vastus lateralis muscle were taken before and 30 min after initiation of the insulin infusion to assess insulin signaling. The subjects were divided into groups with high IMCL (HiIMCL; 9.5 ± 0.9 IMCL/CrT, n = 10) and low IMCL (LoIMCL; 3.0 ± 0.5 IMCL/CrT, n = 10), the cut point being median IMCL (6.1 IMCL/CrT). The groups were comparable with respect to age (43 ± 3 vs. 40 ± 3 years, NS, HiIMCL versus LoIMCL), BMI (26 ± 1 vs. 26 ± 1 kg/m2, NS), and maximal oxygen consumption (33 ± 2 vs. 36 ± 3 ml · kg−1 · min−1, NS). Whole-body insulin-stimulated glucose uptake was lower in the HiIMCL group (3.0 ± 0.4 mg · kg−1 · min−1) than the LoIMCL group (5.1 ± 0.5 mg · kg−1 · min−1, P < 0.05). Serum free fatty acid concentrations were comparable basally, but during hyperinsulinemia, they were 35% higher in the HiIMCL group than the LoIMCL group (P < 0.01). Study of insulin signaling indicated that insulin-induced tyrosine phosphorylation of the insulin receptor (IR) was blunted in HiIMCL compared with LoIMCL (57 vs. 142% above basal, P < 0.05), while protein expression of the IR was unaltered. IR substrate-1–associated phosphatidylinositol (PI) 3-kinase activation by insulin was also lower in the HiIMCL group than in the LoIMCL group (49 ± 23 vs. 84 ± 27% above basal, P < 0.05 between HiIMCL and LoIMCL). In conclusion, IMCL accumulation is associated with whole-body insulin resistance and with defective insulin signaling in skeletal muscle independent of body weight and physical fitness.
Increased Lactate Release per Fat Cell in Normoglycemic First-Degree Relatives of Individuals With Type 2 Diabetes
Authors: Sandqvist Madeléne M. , Eriksson Jan W. , Jansson Per-Anders E.
Published: March 2007

The aim of this study was to examine subcutaneous lactate production in the relatives of individuals with type 2 diabetes. Therefore, we recruited seven healthy first-degree relatives of type 2 diabetic patients and seven pairwise, matched, healthy control subjects without any heredity for diabetes. All subjects were studied with a euglycemic insulin clamp at ∼600 pmol/l, abdominal subcutaneous microdialysis, and 133Xe clearance. Furthermore, a subcutaneous needle biopsy was performed to determine fat cell size. In the fasting state, interstitial lactate was 40% higher in relatives than in control subjects (P = 0.043), but net lactate production was similar in both groups. However, during the insulin clamp, interstitial lactate (2.50 ± 0.29 vs. 1.98 ± 0.26 mmol/l, P = 0.018), interstitial-arterial lactate concentration difference (1.08 ± 0.30 vs. 0.53 ± 0.24 mmol/l, P = 0.028), and net lactate release per fat cell (10.9 ± 3.7 vs. 2.8 ± 1.3 fmol · cell–1 · min–1, P = 0.018) were increased in the relatives. We conclude that first-degree relatives of type 2 diabetic patients may have an enhanced net lactate release per fat cell in abdominal subcutaneous tissue. This could suggest a pathological regulation in adipose tissue that is of importance for the metabolic defects known in type 2 diabetic relatives.
The Relation of Markers of Inflammation to the Development of Glucose Disorders in the Elderly
Authors: Barzilay Joshua I. , Abraham Linn , Heckbert Susan R. , Cushman Mary , Kuller Lewis H. , Resnick Helaine E. , Tracy Russell P.
Published: March 2007

Several studies suggest that inflammation plays a role in the pathogenesis of some glucose disorders in adults. We tested this hypothesis in a longitudinal cohort study of older individuals who had normal fasting glucose (FG) values at baseline. We compared the baseline levels of six inflammatory markers in participants who had developed glucose disorders at follow-up with those of participants whose FG remained normal at follow-up. Participants were members of the Cardiovascular Health Study, a prospective study of risk factors for cardiovascular disease in adults ≥65 years. All 5,888 participants had baseline testing, including FG and markers of inflammation: white blood cell and platelet counts and albumin, fibrinogen, C-reactive protein (CRP), and factor VIIIc levels. At 3–4 years of follow-up, 4,481 (84.5%) of those who were alive had FG levels retested. Participants who developed diabetes (n = 45) had higher median levels of CRP at baseline than those who remained normoglycemic. On multivariate analysis, those with elevated CRP levels (75th percentile [2.86 mg/l] vs. 25th percentile [0.82 mg/l]) were 2.03 times (95% confidence intervals, 1.44–2.86) more likely to have diabetes on follow-up. Adjustment for confounders and other inflammatory markers did not appreciably change this finding. There was no relationship between the development of diabetes and other markers of inflammation. Inflammation, as measured by CRP levels, is associated with the development of diabetes in the elderly. Understanding the role of inflammation in the pathogenesis of glucose disorders in this age-group may lead to better classification and treatment of glucose disorders among them.
Adenovirus-Mediated Overexpression of Sterol Regulatory Element Binding Protein-1c Mimics Insulin Effects on Hepatic Gene Expression and Glucose Homeostasis in Diabetic Mice
Authors: Bécard Dominique , Hainault Isabelle , Azzout-Marniche Dalila , Bertry-Coussot Lydia , Ferré Pascal , Foufelle Fabienne
Published: March 2007

In vitro, the transcription factor sterol regulatory element binding protein-1c (SREBP-1c) mimics the positive effects of insulin on hepatic genes involved in glucose utilization, such as glucokinase (GK) and enzymes of the lipogenic pathway, suggesting that it is a key factor in the control of hepatic glucose metabolism. Decreased glucose utilization and increased glucose production by the liver play an important role in the development of the hyperglycemia in diabetic states. We thus reasoned that if SREBP-1c is indeed a mediator of hepatic insulin action, a hepatic targeted overexpression of SREBP-1c should greatly improve glucose homeostasis in diabetic mice. This was achieved by injecting streptozotocin-induced diabetic mice with a recombinant adenovirus containing the cDNA of the mature, transcriptionally active form of SREBP-1c. We show here that overexpressing SREBP-1c specifically in the liver of diabetic mice induces GK and lipogenic enzyme gene expression and represses the expression of phosphoenolpyruvate carboxykinase, a key enzyme of the gluconeogenic pathway. This in turn increases glycogen and triglyceride hepatic content and leads to a marked decrease in hyperglycemia in diabetic mice. We conclude that SREBP-1c has a major role in vivo in the long-term control of glucose homeostasis by insulin.
Chronic Central Infusion of Ghrelin Increases Hypothalamic Neuropeptide Y and Agouti-Related Protein mRNA Levels and Body Weight in Rats
Authors: Kamegai Jun , Tamura Hideki , Shimizu Takako , Ishii Shinya , Sugihara Hitoshi , Wakabayashi Ichiji
Published: March 2007

Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor (GHS-R), was originally purified from the rat stomach. Like the synthetic growth hormone secretagogues (GHSs), ghrelin specifically releases growth hormone (GH) after intravenous administration. Also consistent with the central actions of GHSs, ghrelin-immunoreactive cells were shown to be located in the hypothalamic arcuate nucleus as well as the stomach. Recently, we showed that a single central administration of ghrelin increased food intake and hypothalamic agouti-related protein (AGRP) gene expression in rodents, and the orexigenic effect of this peptide seems to be independent of its GH-releasing activity. However, the effect of chronic infusion of ghrelin on food consumption and body weight and their possible mechanisms have not been elucidated. In this study, we determined the effects of chronic intracerebroventricular treatment with ghrelin on metabolic factors and on neuropeptide genes that are expressed in hypothalamic neurons that have been previously shown to express the GHS-R and to regulate food consumption. Chronic central administration of rat ghrelin (1 μg/rat every 12 h for 72 h) significantly increased food intake and body weight. However, it did not affect plasma insulin, glucose, leptin, or GH concentrations. We also found that chronic central administration of ghrelin increased both neuropeptide Y (NPY) mRNA levels (151.0 ± 10.1% of saline-treated controls; P < 0.05) and AGRP mRNA levels (160.0 ± 22.5% of saline-treated controls; P < 0.05) in the arcuate nucleus. Thus, the primary hypothalamic targets of ghrelin are NPY/AGRP-containing neurons, and ghrelin is a newly discovered orexigenic peptide in the brain and stomach.
Loss of HNF-1α Function in Mice Leads to Abnormal Expression of Genes Involved in Pancreatic Islet Development and Metabolism
Authors: Shih David Q. , Screenan Seamus , Munoz Karla N. , Philipson Lou , Pontoglio Marco , Yaniv Moshe , Polonsky Kenneth S. , Stoffel Markus
Published: March 2007

Mutations in hepatocyte nuclear factor 1α (HNF-1α) lead to maturity-onset diabetes of the young type 3 as a result of impaired insulin secretory response in pancreatic β-cells. The expression of 50 genes essential for normal β-cell function was studied to better define the molecular mechanism underlying the insulin secretion defect in Hnf-1α−/− mice. We found decreased steady-state mRNA levels of genes encoding glucose transporter 2 (Glut2), neutral and basic amino acid transporter, liver pyruvate kinase (L-Pk), and insulin in Hnf-1α−/− mice. In addition, we determined that the expression of several islet-enriched transcription factors, including Pdx-1, Hnf-4α, and Neuro-D1/Beta-2, was reduced in Hnf-1α−/− mice. These changes in pancreatic islet mRNA levels were already apparent in newborn animals, suggesting that loss of Hnf-1α function rather than chronic hyperglycemia is the primary cause of the altered gene expression. This expression profile was pancreatic islet–specific and distinct from hepatocytes, where we found normal expression of Glut2, L-Pk, and Hnf-4α in the liver of Hnf-1α−/− mice. The expression of small heterodimer partner (Shp-1), an orphan receptor that can heterodimerize with Hnf-4α and inhibit its transcriptional activity, was also reduced in Hnf-1α−/− islets. We characterized a 0.58-kb Shp-1 promoter and determined that the decreased expression of Shp-1 may be indirectly mediated by a downregulation of Hnf-4α. We further showed that Shp-1 can repress its own transcriptional activation by inhibiting Hnf-4α function, thereby establishing a feedback autoregulatory loop. Our results indicate that loss of Hnf-1α function leads to altered expression of genes involved in glucose-stimulated insulin secretion, insulin synthesis, and β-cell differentiation.
Acute Inhibition of Glucose-6-Phosphate Translocator Activity Leads to Increased De Novo Lipogenesis and Development of Hepatic Steatosis Without Affecting VLDL Production in Rats
Authors: Bandsma Robert H.J. , Wiegman Coen H. , Herling Andreas W. , Burger Hans-Joerg , ter Harmsel Anke , Meijer Alfred J. , Romijn Johannes A. , Reijngoud Dirk-Jan , Kuipers Folkert
Published: March 2007

Glucose-6-phosphatase (G6Pase) is a key enzyme in hepatic glucose metabolism. Altered G6Pase activity in glycogen storage disease and diabetic states is associated with disturbances in lipid metabolism. We studied the effects of acute inhibition of G6Pase activity on hepatic lipid metabolism in nonanesthetized rats. Rats were infused with an inhibitor of the glucose-6-phosphate (G6P) translocator (S4048, 30 mg · kg–1 · h–1) for 8 h. Simultaneously, [1-13C]acetate was administered for determination of de novo lipogenesis and fractional cholesterol synthesis rates by mass isotopomer distribution analysis. In a separate group of rats, Triton WR 1339 was injected for determination of hepatic VLDL-triglyceride production. S4048 infusion significantly decreased plasma glucose (−11%) and insulin (−48%) levels and increased hepatic G6P (201%) and glycogen (182%) contents. Hepatic triglyceride contents increased from 5.8 ± 1.4 μmol/g liver in controls to 20.6 ± 5.5 μmol/g liver in S4048-treated animals. De novo lipogenesis was increased >10-fold in S4048-treated rats, without changes in cholesterol synthesis rates. Hepatic mRNA levels of acetyl-CoA carboxylase and fatty acid synthase were markedly induced. Plasma triglyceride levels increased fourfold, but no differences in plasma cholesterol levels were seen. Surprisingly, hepatic VLDL-triglyceride secretion was not increased in S4048-treated rats. These studies demonstrate that inhibition of the G6Pase system leads to acute stimulation of fat synthesis and development of hepatic steatosis, without affecting hepatic cholesterol synthesis and VLDL secretion. The results emphasize the strong interactions that exist between hepatic carbohydrate and fat metabolism.
Insulin Therapy Improves Insulin-Stimulated Endothelial Function in Patients With Type 2 Diabetes and Ischemic Heart Disease
Authors: Rask-Madsen Christian , Ihlemann Nikolaj , Krarup Thure , Christiansen Erik , Kober Lars , Nervil Kistorp Caroline , Torp-Pedersen Christian
Published: March 2007

Blunted insulin-stimulated endothelial function may be a mechanism for the development of atherothrombotic disease in type 2 diabetes, but it is unknown whether hypoglycemic drug therapy can modulate this abnormality. We studied patients with type 2 diabetes and stable ischemic heart disease (n = 28) and lean, healthy control subjects (n = 31). Forearm blood flow was measured by venous occlusion plethysmography during dose-response studies of acetylcholine (ACh) and sodium nitroprusside (SNP) infused into the brachial artery. In the patients and 10 healthy control subjects, ACh was repeated after intrabrachial infusion of insulin. Patients were restudied after 2 months of insulin therapy with four daily subcutaneous injections (treatment group, n = 19) or without hypoglycemic drug therapy (time control group, n = 9). Insulin infusion raised venous serum insulin in the forearm to high physiological levels (133 ± 14.6 mU/l in patients) with a minor increase in systemic venous serum insulin. This increased the ACh response by 149 ± 47, 110 ± 33, 100 ± 45, and 106 ± 44% during the four ACh doses in healthy control subjects (P < 0.0001) but had no effect in patients (P = 0.3). After 2 months, HbA1c in the treatment group had decreased from 10.0 ± 0.4 to 7.5 ± 0.2%. Although neither the ACh response (P = 0.09) nor the SNP response (P = 0.4) had changed significantly, insulin stimulation had a significant effect, as the ACh response increased by 58 ± 25, 84 ± 66, 120 ± 93, and 69 ± 36% (P = 0.0002). In the time control group, insulin stimulation remained without effect after 8 weeks (P = 0.7). In conclusion, insulin therapy partly restores insulin-stimulated endothelial function in patients with type 2 diabetes and ischemic heart disease.
Interplay Between Galanin and Leptin in the Hypothalamic Control of Feeding via Corticotropin-Releasing Hormone and Neuropeptide Y
Authors: Bergonzelli Gabriela E. , Pralong François P. , Glauser Micheline , Cavadas Claudia , Grouzmann Eric , Gaillard Rolf C.
Published: March 2007

Over long periods, feeding and metabolism are tightly regulated at the central level. The total amount of nutrients ingested is thought to result from a delicate balance between orexigenic and anorexigenic factors expressed and secreted by specialized hypothalamic neuronal populations. We have developed a system of perifused hypothalamic neurons to characterize the relationships existing between the orexigenic peptide galanin and two other physiological modulators of feeding: neuropeptide Y (NPY) and corticotropin-releasing hormone (CRH). We demonstrated that galanin stimulates CRH and NPY secretion from hypothalamic neurons in a dose-dependent manner. Exposure to leptin for 24 h before galanin stimulation decreased NPY secretion by 30%, leaving the responsiveness of CRH neurons intact. These results suggest that CRH and NPY neurons participate to the intrahypothalamic signaling pathway of galanin, an observation that can explain the lower potency of galanin to stimulate food intake in vivo compared with NPY. The differential effects exerted by leptin on CRH and NPY suggest that there exists a subset of NPY neurons that are exquisitely sensitive to marked variations in leptin levels, and that the CRH neurons are less responsive to increases in leptin concentrations.
Selective Modification of Pyruvate Dehydrogenase Kinase Isoform Expression in Rat Pancreatic Islets Elicited by Starvation and Activation of Peroxisome Proliferator–Activated Receptor-α
Authors: Sugden Mary C. , Bulmer Karen , Augustine Daniel , Holness Mark J.
Published: March 2007

The pyruvate dehydrogenase complex (PDC) has a pivotal role in islet metabolism. The pyruvate dehydrogenase kinases (PDK1–4) regulate glucose oxidation through inhibitory phosphorylation of PDC. Starvation increases islet PDK activity (Am J Physiol Endocrinol Metab 270:E988–E994, 1996). In this study, using antibodies against PDK1, PDK2, and PDK4 (no sufficiently specific antibodies are as yet available for PDK3), we identified the PDK isoform profile of the pancreatic islet and delineated the effects of starvation (48 h) on protein expression of individual PDK isoforms. Rat islets were demonstrated to contain all three PDK isoforms, PDK1, PDK2, and PDK4. Using immunoblot analysis with antibodies raised against the individual recombinant PDK isoforms, we demonstrated increased islet protein expression of PDK4 in response to starvation (2.3-fold; P < 0.01). Protein expression of PDK1 and PDK2 was suppressed in response to starvation (by 27% [P < 0.01] and 10% [NS], respectively). We demonstrated that activation of peroxisome proliferator–activated receptor-α (PPAR-α) by the selective agonist WY14,643 for 24 h in vivo leads to specific upregulation of islet PDK4 protein expression by 1.8-fold (P < 0.01), in the absence of change in islet PDK1 and PDK2 protein expression but in conjunction with a 2.2-fold increase (P < 0.01) in islet PPAR-α protein expression. Thus, although no changes in islet PPAR-α expression were observed after the starvation protocol, activation of PPAR-α in vivo may be a potential mechanism underlying upregulation of islet PDK4 protein expression in starvation. We evaluated the effects of antecedent changes in PDK profile and/or PPAR-α activation induced by starvation or PPAR-α activation in vivo on glucose-stimulated insulin secretion (GSIS) in isolated islets. GSIS at 20 mmol/l glucose was modestly impaired on incubation with exogenous triglyceride (1 mmol/l triolein) (∼20% inhibition; P < 0.05) in islets from fed rats. Starvation (48 h) impaired GSIS in the absence of triolein (by 57%; P < 0.001), but GSIS after the further addition of triolein did not differ significantly between islets from fed or starved rats. GSIS by islets prepared from WY14,643-treated fed rats did not differ significantly from that seen with islets from control fed rats, and the response to triolein addition resembled that of islets prepared from fed rather than starved rats. PPAR-α activation in vivo led to increased insulin secretion at low glucose concentrations. Our results are discussed in relation to the potential impact of changes in islet PDK profile on the insulin secretory response to lipid and of PPAR-α activation in the cause of fasting hyperinsulinemia.
γ-Interferon Signaling in Pancreatic β-Cells Is Persistent but Can Be Terminated by Overexpression of Suppressor of Cytokine Signaling-1
Authors: Chong Mark M.W. , Thomas Helen E. , Kay Thomas W.H.
Published: March 2007

Proinflammatory cytokines, including γ-interferon (IFN-γ), have been implicated in the destruction of β-cells in autoimmune diabetes. IFN-γ signaling is transient in some cell types, but there is indirect evidence that it may be prolonged in β-cells. In this study, we have shown that IFN-γ signaling, measured by signal transducer and activator of transcription-1 (STAT1) activation and the expression of IFN-γ–responsive genes, is persistent in β-cells for as long as the cytokine is present. Because members of the suppressor of cytokine signaling (SOCS) family may regulate the duration of IFN-γ signaling, their expression was investigated in β-cells. We found that cytokine-inducible SH2-containing protein, SOCS-1, and SOCS-2 are expressed in primary islets and NIT-1 insulinoma cells, both at the mRNA and protein levels, after treatment with IFN-γ and other proinflammatory cytokines. Transfected SOCS-1 was found to inhibit responses to IFN-γ in NIT-1 insulinoma cells, including STAT1 activation, class I major histocompatibility complex upregulation, and IFN-γ–induced cell death, but only when expressed at levels higher than those found in untransfected cells. Consistent with this, IFN-γ signaling was not affected in SOCS-1–deficient β-cells. Therefore, persistent IFN-γ signaling in β-cells is associated with SOCS-1 expression that is not sufficient to terminate signaling. Because overexpression of SOCS-1 can suppress responses to IFN-γ, this may be a useful strategy for protecting β-cells from cytotoxicity mediated by IFN-γ and possibly other proinflammatory cytokines.
A Nonlinear Effect of Hyperglycemia and Current Cigarette Smoking Are Major Determinants of the Onset of Microalbuminuria in Type 1 Diabetes
Authors: Scott Laura J. , Warram James H. , Hanna Linda S. , Laffel Lori M. B. , Ryan Louise , Krolewski Andrzej S.
Published: March 2007

Cigarette smoking and poor glycemic control are risk factors for diabetic nephropathy in type 1 diabetes. However, the specifics of the relation of these risk factors to the onset of this complication have not been elucidated. To investigate these issues, we followed for 4 years 943 Joslin Clinic patients aged 15–44 years with type 1 diabetes who had normoalbuminuria during the 2-year baseline period. Microalbuminuria developed in 109 of the 943 individuals, giving an incidence rate of 3.3/100 person-years. The risk of onset of microalbuminuria was predicted somewhat more precisely by the measurements during the 1st and 2nd years preceding onset than by all the measurements during the longer (4-year) interval, suggesting attenuation of the impact of past hyperglycemia over time. Point estimates of the incidence rate (per 100 person-years) according to quartiles of HbA1c during the 1st and 2nd years preceding the outcome were 1.3 in the 1st, 1.5 in the 2nd, 3.1 in the 3rd, and 6.9 in the 4th (P = 1.3 × 10−9). Point estimates of the incidence rate (per 100 person-years) according to smoking status were 7.9 for current smokers, 1.8 for past smokers, and 2.2 for those who had never smoked (P = 2.0 × 10−7). In a multiple logistic model, the independent effects of HbA1c level and cigarette smoking remained highly significant, but their magnitudes were reduced. Using the same covariates in a generalized additive model, we examined the shape of the relationship between HbA1c and onset of microalbuminuria and found significant nonlinearity in the logarithm of odds scale (P = 0.04). The slope was steeper with HbA1c >8% than <8%. Furthermore, the change in the slope was magnified among current smokers. In conclusion, patients with type 1 diabetes who smoke and have an HbA1c >8% have the highest risk of onset of microalbuminuria.
HbA1c Levels Are Genetically Determined Even in Type 1 Diabetes
Authors: Snieder Harold , Sawtell Pamela A. , Ross Lesley , Walker James , Spector Tim D. , Leslie R. David Graham
Published: March 2007

HbA1c, a measure of blood glucose regulation, reflects glucose levels in the preceding months. In diabetes, HbA1c levels predict the risk of microvascular complications. The aim of this study was to determine whether genetic factors could influence HbA1c levels in normal subjects and type 1 diabetic patients. We performed a classical twin study of HbA1c in healthy nondiabetic female twins and 42 monozygotic (MZ) and 47 dizygotic (DZ) pairs. Interclass correlations (r) were higher in MZ (r = 0.77) compared with DZ (r = 0.53) twin pairs, suggesting a substantial genetic effect; this was confirmed by quantitative genetic model fitting. Additive genetic effects (heritability) explained 62% (95% CI 47–75) of population variance in HbA1c; the remainder was attributable to the influence of unique environment (23% [15–36]) and age (14% [5–28]). Multivariate modeling showed that genetic factors also have a substantial influence on fasting glucose levels (51%). However, HbA1c heritability could not be explained by genes in common with fasting glucose. In the patients with type 1 diabetes, HbA1c levels were correlated in 33 MZ twins concordant for diabetes (r = 0.68; P < 0.001) but also in 45 MZ twins discordant for the disease (r = 0.52; P < 0.001). These significant correlations for HbA1c in both concordant and discordant pairs indicate a diabetes-independent familial effect. Thus, HbA1c levels are largely genetically determined and independent of the genes influencing fasting glucose. Even in type 1 diabetes, familial (i.e., diabetes-independent) factors influence protein glycation, implying that familial factors may explain, in part, the risk for microvascular complications, as indicated by high HbA1c levels.
Ghrelin, an Endogenous Growth Hormone Secretagogue, Is a Novel Orexigenic Peptide That Antagonizes Leptin Action Through the Activation of Hypothalamic Neuropeptide Y/Y1 Receptor Pathway
Authors: Shintani Mitsuyo , Ogawa Yoshihiro , Ebihara Ken , Aizawa-Abe Megumi , Miyanaga Fumiko , Takaya Kazuhiko , Hayashi Tatsuya , Inoue Gen , Hosoda Kiminori , Kojima Masayasu , Kangawa Kenji , Nakao Kazuwa
Published: March 2007

Ghrelin, an endogenous ligand for growth hormone secretagogue (GHS)receptor originally isolated from the stomach, occurs in the hypothalamic arcuate nucleus and may play a role in energy homeostasis. Synthetic GHSs have activated the hypothalamic arcuate neurons containing neuropeptide Y (NPY),suggesting the involvement of NPY in some of ghrelin actions. This study was designed to elucidate the role of ghrelin in the regulation of food intake. A single intracerebroventricular (ICV) injection of ghrelin (5-5,000 ng/rat)caused a significant and dose-related increase in cumulative food intake in rats. Ghrelin (500 ng/rat) was also effective in growth hormone-deficient spontaneous dwarf rats. Hypothalamic NPY mRNA expression was increased in rats that received a single ICV injection of ghrelin (500 ng/rat) (∼ 160% of that in vehicle-treated groups, P < 0.05). The ghrelin's orexigenic effect was abolished dose-dependently by ICV co-injection of NPY Y1 receptor antagonist (10-30 μg/rat). The leptin-induced inhibition of food intake was reversed by ICV co-injection of ghrelin in a dose-dependent manner(5-500 ng/rat). Leptin reduced hypothalamic NPY mRNA expression by 35%(P < 0.05), which was abolished by ICV co-injection of ghrelin(500 ng/rat). This study provides evidence that ghrelin is an orexigenic peptide that antagonizes leptin action through the activation of hypothalamic NPY/Y1 receptor pathway.
Nitric Oxide Increases Glucose Uptake Through a Mechanism That Is Distinct From the Insulin and Contraction Pathways in Rat Skeletal Muscle
Authors: Higaki Yasuki , Hirshman Michael F. , Fujii Nobuharu , Goodyear Laurie J.
Published: March 2007

Insulin, contraction, and the nitric oxide (NO) donor, sodium nitroprusside(SNP), all increase glucose transport in skeletal muscle. Some reports suggest that NO is a critical mediator of insulin- and/or contraction-stimulated transport. To determine if the mechanism leading to NO-stimulated glucose uptake is similar to the insulin- or contraction-dependent signaling pathways,isolated soleus and extensor digitorum longus (EDL) muscles from rats were treated with various combinations of SNP (maximum 10 mmol/l), insulin (maximum 50 mU/ml), electrical stimulation to produce contractions (maximum 10 min),wortmannin (100 nmol/l), and/or the NO synthase (NOS) inhibitor NG-monomethyl-L-arginine (L-NMMA) (0.1 mmol/l). The combinations of SNP plus insulin and SNP plus contraction both had fully additive effects on 2-deoxyglucose uptake. Wortmannin completely inhibited insulinstimulated glucose transport and only slightly inhibited SNP-stimulated 2-deoxyglucose uptake, whereas L-NMMA did not inhibit contraction-stimulated 2-deoxyglucose uptake. SNP significantly increased the activity of theα1 catalytic subunit of 5′ AMP-activated protein kinase (AMPK), a signaling molecule that has been implicated in mediating glucose transport in fuel-depleted cells. Addition of the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (1 mg/ml) to the drinking water of rats for 2 days failed to affect the increase in muscle 2-deoxyglucose uptake in response to treadmill exercise. These data suggest that NO stimulates glucose uptake through a mechanism that is distinct from both the insulin and contraction signaling pathways.
Characterization of a KATP Channel—Independent Pathway Involved in Potentiation of Insulin Secretion by Efaroxan
Authors: Chan Sue L.F. , Mourtada Mirna , Morgan Noel G.
Published: March 2007

Efaroxan, like several other imidazoline reagents, elicits a glucose-dependent increase in insulin secretion from pancreatic β-cells. This response has been attributed to efaroxan-mediated blockade of KATP channels, with the subsequent gating of voltage-sensitive calcium channels. However, increasing evidence suggests that, at best, this mechanism can account for only part of the secretory response to the imidazoline. In support of this, we now show that efaroxan can induce functional changes in the secretory pathway of pancreatic β-cells that are independent of KATP channel blockade. In particular, efaroxan was found to promote a sustained sensitization of glucose-induced insulin release that persisted after removal of the drug and to potentiate Ca2+-induced insulin secretion from electropermeabilized islets. To investigate the mechanisms involved, we studied the effects of the efaroxan antagonist KU14R. This agent is known to selectively inhibit insulin secretion induced by efaroxan, without altering the secretory response to glucose or KCl. Surprisingly, however, KU14R markedly impaired the potentiation of insulin secretion mediated by agents that raise cAMP, including the adenylate cyclase activator, forskolin, and the phosphodiesterase inhibitor isobutylmethyl xanthine (IBMX). These effects were not accompanied by any reduction in cAMP levels, suggesting an antagonistic action of KU14R at a more distal point in the pathway of potentiation. In accord with our previous work,islets that were exposed to efaroxan for 24 h became selectively desensitized to this agent, but they still responded normally to glucose. Unexpectedly,however, the ability of either forskolin or IBMX to potentiate glucose-induced insulin secretion was severely impaired in these islets. By contrast, the elevation of cAMP was unaffected by culture of islets with efaroxan. Taken together, the data suggest that, in addition to effects on the KATPchannel, imidazolines also interact with a more distal component that is crucial to the potentiation of insulin secretion. This component is not required for Ca2+-dependent secretion per se but is essential to the mechanism by which cAMP potentiates insulin release. Overall, the results indicate that the actions of efaroxan at this distal site may be more important for control of insulin secretion than its effects on the KATP channel.
Redistribution of Sudomotor Responses Is an Early Sign of Sympathetic Dysfunction in Type 1 Diabetes
Authors: Hoeldtke Robert D. , Bryner Kimberly D. , Horvath Gabriella G. , Phares Robert W. , Broy Lance F. , Hobbs Gerald R.
Published: March 2007

Patients with diabetic neuropathy typically have decreased sweating in the feet but excessive sweating in the upper body. Previous studies of sudomotor function in diabetes have included patients with long-standing disease. The present study was designed to test for the early presence of sudomotor dysfunction and to characterize its relation to glycemic control and other aspects of peripheral nerve function. A total of 37 patients (10 males, 27 females) enrolled in a longitudinal study, in which autonomic function was evaluated annually for 3 years. Patients enrolled 2-22 months after the diagnosis of type 1 diabetes. Forty-one age- and sex-matched healthy control subjects were also studied. Sweat production in response to acetylcholine stimulation was dramatically increased in the forearm at the time of the first evaluation (1.67 ± 0.24 μl/cm2 in the diabetic patients vs. 1.04 ± 0.14 μl/cm2 in the control subjects, P < 0.05). Likewise, the ratio of sweating in the forearm to sweating below the waist was higher in the diabetic patients (0.553 ±0.07 μl/cm2) than in the control subjects (0.385 ± 0.04μl/cm2, P < 0.05). Forearm sweat was negatively associated with the renin-to-prorenin ratio and vanillylmandelic acid (VMA)excretion (P < 0.025), tests of sympathetic nerve function. The ratio of sweating in the forearm to sweating in the foot was likewise increased in diabetic patients with poor glycemic control. We interpret this redistribution of sudomotor responses to be indicative of sympathetic nerve injury and conclude 1) that the sympathetic nervous system is especially vulnerable to the adverse effects of chronic hyperglycemia and 2) that sympathetic dysfunction can be detected very early in type 1 diabetes.
The Effect of Diabetes on Expression of β1-,β2-, and β3-Adrenoreceptors in Rat Hearts
Authors: Dinçer Ü. Deniz , Bidasee Keshore R. , Güner Şahika , Tay Ayin , Özçelikay A. Tanju , Altan V. Melih
Published: March 2007

Diabetic hearts exhibit decreased responsiveness to stimulation byβ-adrenoreceptor (β-AR) agonists. This decrease in activity may be due to changes in expression and/or signaling of β-AR. Recently we showed that right atrial strips from 14-week streptozotocin (STZ)-induced diabetic rat hearts exhibit decreased responsiveness to β1-AR agonist stimulation, but not to β2-AR agonist. In the present study,we investigated the effects of long-term diabetes on the expression of cardiacβ1-, β2-, and β3-ARs and looked at whether these changes could be restored with insulin treatment. Using reverse transcription-polymerase chain reaction (RT-PCR), PAGE, and Western blot analysis, we found that β1-AR mRNA and protein levels decreased by 34.9 ± 5.8 and 44.4 ± 5.8%, respectively, in 14 week-STZ-treated diabetic rat hearts when compared with age-matched controls. On the other hand, mRNA levels encoding β2- andβ3-ARs increased by 72.5 ± 16.6 and 97.3 ±26.1%, respectively. Although the latter translated into a proportional increase in β3-AR protein levels (100.0 ± 17.0%),β2-AR protein levels decreased to 82.6 ± 1.1% of control. Insulin treatment for 2 weeks, after 12 weeks of untreated diabetes,partially restored β1-AR mRNA and protein levels to 60.1± 8.4 and 83.2 ± 5.0%, respectively, of control. Although insulin treatment minimally attenuated the rise in mRNA levels encodingβ2- and β3-ARs, the steady-state levels of these proteins returned to near control values. These data suggest that the decreased responsiveness of diabetic hearts to stimulation of β-AR agonists may be due to a decrease in β1-AR and an increaseβ3-AR expression.
Changes in the expression of transcription factors in pancreatic AR42J cells during differentiation into insulin-producing cells.
Authors: Zhang Y Q , Mashima H , Kojima I
Published: March 2007

Pancreatic AR42J cells possess both exocrine and neuroendocrine properties and convert to insulin-producing cells upon treatment with activin A and hepatocyte growth factor (HGF). We studied changes in the mRNA expression of various transcription factors during the course of differentiation. Among the transcription factors studied, expression levels of Pax4 and neurogenin3 changed significantly. These two factors were not detected in naive cells, whereas their mRNA levels were markedly increased after treatment with activin A and HGF. Thus, these two factors were induced by activin A. Transfection of Pax4 did not induce any changes in morphology or expression of pancreatic polypeptide (PP). Furthermore, introduction of antisense Pax4 did not affect the conversion into insulin-producing cells induced by activin A and HGF. In contrast, transfection of neurogenin3 induced morphological changes similar to those induced by activin A. In addition, transfection of neurogenin3 induced the expression of PP. Conversely, introduction of antisense neurogenin3 blocked the differentiation of AR42J cells induced by activin A and HGF. These results indicate that activin A regulates the expression of neurogenin3, which is critical for the differentiation of AR42J into endocrine cells.
Human type 2 diabetes: morphological evidence for abnormal beta-cell function.
Authors: Sempoux C , Guiot Y , Dubois D , Moulin P , Rahier J
Published: March 2007

The exact nature of the beta-cell defect in type 2 diabetic patients is still unclear. beta-Cell mass reduction has been reported but remains controversial. A preliminary study of a large series of patients has demonstrated that in most, the beta-cell defect is not related to a decreased beta-cell mass. Amyloid deposits are observed in the islets of some type 2 diabetic patients but also in normoglycemic subjects. Because it has been claimed that these deposits interfere with beta-cell function, we evaluated in situ the effect of insular amyloid deposits on beta-cell transcription and translation. Pancreases were obtained at autopsy from 28 normoglycemic patients and 41 type 2 diabetic patients. Staining with hemaluneosin and Congo red was used to analyze the general features of the islets and the presence of amyloid deposits, respectively. Immunohistochemistry for proinsulin was performed with an antibody recognizing the junction between B-chain and C-peptide, thus specifically labeling the Golgi area where proinsulin is produced. In seven patients, we evaluated insulin gene transcription by in situ hybridization of proinsulin mRNA combined with Congo red staining, and we evaluated insulin storage by double immunostaining for insulin and amylin. In many type 2 diabetic patients, the islets appeared entirely normal. Amyloid deposits were found in 57% of diabetic subjects and 33% of normoglycemic age-matched control subjects. The percentage of amyloid-infiltrated islets varied from 0.4 to 74%. beta-Cells from amyloid-containing islets still had specific Golgi proinsulin labeling. In obese type 2 diabetic patients, the number of beta-cells with abnormal expression of proinsulin in the whole cytoplasm was significantly higher than in normoglycemic control subjects. Proinsulin mRNA was significantly reduced in islets with amyloid deposits when compared with amyloid-free islets, but the mean reduction did not exceed 16%. Insulin was still present in the beta-cells of amyloid-containing islets, and its amount, estimated by measurement of the insulin-labeling optical density, was not statistically different from that in amyloid-free islets. In conclusion, even in amyloid-containing islets, beta-cells maintain active insulin transcription and translation and normal insulin storage. Taking into account that in most cases only a small proportion of islets are infiltrated by amyloid, the limited reduction in proinsulin mRNA is unlikely to play a major role in the pathogenesis of diabetes.
beta-cell apoptosis: stimuli and signaling.
Authors: Mandrup-Poulsen T
Published: March 2007

Pancreatic beta-cells are sensitive to a number of proapoptotic stimuli. Thus, apoptosis is an important part of the physiological neonatal remodeling of the endocrine pancreas, and a number of pathological stimuli involved in type 1 and type 2 diabetes have been shown to elicit beta-cell apoptosis. Factors of relevance to type 1 diabetes include proinflammatory cytokines, nitric oxide, and reactive oxygen species as well as Fas ligand. Recent findings that free fatty acids, glucose, sulfonylurea, and amylin cause beta-cell apoptosis in vitro suggest that programmed cell death may also be involved in the pathogenesis of type 2 diabetes. Furthermore, there is evidence favoring a convergence in signaling pathways toward common effectors of beta-cell apoptosis elicited by stimuli implicated in the pathogenesis of type 1 and type 2 diabetes. Therefore, recent studies involving the stimuli and signaling pathways of beta-cell apoptosis-in particular, mitogen- and stress-activated protein kinases-will be reviewed. It is concluded that immunological, inflammatory, and metabolic signals cause beta-cell apoptosis, and the possibility that these signals converge toward a common beta-cell death signaling pathway should be investigated further.