bluuebunny/crossref_metadata_2025 huggingface dataset:
Association and Haplotype Analysis of the Insulin-Degrading Enzyme (IDE) Gene, a Strong Positional and Biological Candidate for Type 2 Diabetes Susceptibility
Authors: Groves Christopher J. , Wiltshire Steven , Smedley Damian , Owen Katherine R. , Frayling Timothy M. , Walker Mark , Hitman Graham A. , Levy Jonathan C. , O’Rahilly Stephen , Menzel Stephan , Hattersley Andrew T. , McCarthy Mark I.
Published: March 2007

The gene for insulin-degrading enzyme (IDE) represents a strong positional and biological candidate for type 2 diabetes susceptibility. IDE maps to chromosome 10q23.3, a region linked to diabetes in several populations; the rat homolog has been directly implicated in diabetes susceptibility; and known functions of IDE support an important role in glucose homeostasis. We sought evidence for association between IDE variation and diabetes by mutation screening, defining local haplotype structure, and genotyping variants delineating common haplotypic diversity. An initial case-control analysis (628 diabetic probands from multiplex sibships and 604 control subjects) found no haplotypic associations, although one variant (IDE2, −179T→C) showed modest association with diabetes (odds ratio [OR]1.25, P = 0.03). Linkage partitioning analyses failed to support this association, but provided borderline evidence for a different variant (IDE10, IVS20–405A→G) (P = 0.06). Neither variant was associated with diabetes when replication was sought in 377 early onset diabetic subjects and 825 control subjects, though combined analysis of all typed cohorts indicated a nominally significant effect at IDE2 (OR 1.21 [1.04–1.40], P = 0.013). In the absence of convincing support for this association from linkage partitioning or analyses of continuous measures of glycemia, we conclude that analysis of over 2,400 samples provides no compelling evidence that variation in IDE contributes to diabetes susceptibility in humans.
Differential Effects of Rosiglitazone on Skeletal Muscle and Liver Insulin Resistance in A-ZIP/F-1 Fatless Mice
Authors: Kim Jason K. , Fillmore Jonathan J. , Gavrilova Oksana , Chao Lily , Higashimori Takamasa , Choi Hyejeong , Kim Hyo-Jeong , Yu Chunli , Chen Yan , Qu Xianqin , Haluzik Martin , Reitman Marc L. , Shulman Gerald I.
Published: March 2007

To determine the role of adipocytes and the tissue-specific nature in the insulin sensitizing action of rosiglitazone, we examined the effects of 3 weeks of rosiglitazone treatment on insulin signaling and action during hyperinsulinemic-euglycemic clamps in awake A-ZIP/F-1 (fatless), fat-transplanted fatless, and wild-type littermate mice. We found that 53 and 66% decreases in insulin-stimulated glucose uptake and insulin receptor substrate (IRS)-1–associated phosphatidylinositol (PI) 3-kinase activity in skeletal muscle of fatless mice were normalized after rosiglitazone treatment. These effects of rosiglitazone treatment were associated with 50% decreases in triglyceride and fatty acyl-CoA contents in the skeletal muscle of rosiglitazone-treated fatless mice. In contrast, rosiglitazone treatment exacerbated hepatic insulin resistance in the fatless mice and did not affect already reduced IRS-2–associated PI 3-kinase activity in liver. The worsening of insulin action in liver was associated with 30% increases in triglyceride and fatty acyl-CoA contents in the liver of rosiglitazone-treated fatless mice. In conclusion, these data support the hypothesis that rosiglitazone treatment enhanced insulin action in skeletal muscle mostly by its ability to repartition fat away from skeletal muscle.
Involvement of AMP-Activated Protein Kinase in Glucose Uptake Stimulated by the Globular Domain of Adiponectin in Primary Rat Adipocytes
Authors: Wu Xiangdong , Motoshima Hiroyuki , Mahadev Kalyankar , Stalker Timothy J. , Scalia Rosario , Goldstein Barry J.
Published: March 2007

Adiponectin is an abundant adipocyte-derived plasma protein with anti-atherosclerotic and insulin-sensitizing properties that suppresses hepatic glucose production and enhances glucose uptake into skeletal muscle. To characterize the potential effects of adiponectin on glucose uptake into adipose cells, we incubated isolated epididymal rat adipocytes with the globular domain of recombinant adiponectin purified from an E. coli expression system. Globular adiponectin increased glucose uptake in adipocytes without stimulating tyrosine phosphorylation of the insulin receptor or insulin receptor substrate-1, and without enhancing phosphorylation of Akt on Ser-473. Globular adiponectin further enhanced insulin-stimulated glucose uptake at submaximal insulin concentrations and reversed the inhibitory effect of tumor necrosis factor-α on insulin-stimulated glucose uptake. Cellular treatment with globular adiponectin increased the Thr-172 phosphorylation and catalytic activity of AMP-activated protein kinase and enhanced the Ser-79 phosphorylation of acetyl CoA carboxylase, an enzyme downstream of AMP kinase in adipose cells. Inhibition of AMP kinase activation using two pharmacological inhibitors (adenine 9-β-d-arabinofuranoside and compound C) completely abrogated the increase in glucose uptake stimulated by globular adiponectin, indicating that AMP kinase is integrally involved in the adiponectin signal transduction pathway. Coupled with recent evidence that the effects of adiponectin are mediated via AMP kinase activation in liver and skeletal muscle, the findings reported here provide an important mechanistic link in the signaling effects of adiponectin in diverse metabolically responsive tissues.
Starvation and Diabetes Reduce the Amount of Pyruvate Dehydrogenase Phosphatase in Rat Heart and Kidney
Authors: Huang Boli , Wu Pengfei , Popov Kirill M. , Harris Robert A.
Published: March 2007

The pyruvate dehydrogenase complex (PDC) is inactivated in many tissues during starvation and diabetes to conserve three-carbon compounds for gluconeogenesis. This is achieved by an increase in the extent of PDC phosphorylation caused in part by increased pyruvate dehydrogenase kinase (PDK) activity due to increased PDK expression. This study examined whether altered pyruvate dehydrogenase phosphatase (PDP) expression also contributes to changes in the phosphorylation state of PDC during starvation and diabetes. Of the two PDP isoforms expressed in mammalian tissues, the Ca2+-sensitive isoform (PDP1) is highly expressed in rat heart, brain, and testis and is detectable but less abundant in rat muscle, lung, kidney, liver, and spleen. The Ca2+-insensitive isoform (PDP2) is abundant in rat kidney, liver, heart, and brain and is detectable in spleen and lung. Starvation and streptozotocin-induced diabetes cause decreases in PDP2 mRNA abundance, PDP2 protein amount, and PDP activity in rat heart and kidney. Refeeding and insulin treatment effectively reversed these effects of starvation and diabetes, respectively. These findings indicate that opposite changes in expression of specific PDK and PDP isoenzymes contribute to hyperphosphorylation and therefore inactivation of the PDC in heart and kidney during starvation and diabetes.
Increased Phosphorylation of Skeletal Muscle Glycogen Synthase at NH2-Terminal Sites During Physiological Hyperinsulinemia in Type 2 Diabetes
Authors: Højlund Kurt , Stæhr Peter , Hansen Bo Falck , Green Kevin A. , Hardie D. Grahame , Richter Erik A. , Beck-Nielsen Henning , Wojtaszewski Jørgen F.P.
Published: March 2007

In type 2 diabetes, insulin activation of muscle glycogen synthase (GS) is impaired. This defect plays a major role for the development of insulin resistance and hyperglycemia. In animal muscle, insulin activates GS by reducing phosphorylation at both NH2- and COOH-terminal sites, but the mechanism involved in human muscle and the defect in type 2 diabetes remain unclear. We studied the effect of insulin at physiological concentrations on glucose metabolism, insulin signaling and phosphorylation of GS in skeletal muscle from type 2 diabetic and well-matched control subjects during euglycemic-hyperinsulinemic clamps. Analysis using phospho-specific antibodies revealed that insulin decreases phosphorylation of sites 3a + 3b in human muscle, and this was accompanied by activation of Akt and inhibition of glycogen synthase kinase-3α. In type 2 diabetic subjects these effects of insulin were fully intact. Despite that, insulin-mediated glucose disposal and storage were reduced and activation of GS was virtually absent in type 2 diabetic subjects. Insulin did not decrease phosphorylation of sites 2 + 2a in healthy human muscle, whereas in diabetic muscle insulin infusion in fact caused a marked increase in the phosphorylation of sites 2 + 2a. This phosphorylation abnormality likely caused the impaired GS activation and glucose storage, thereby contributing to skeletal muscle insulin resistance, and may therefore play a pathophysiological role in type 2 diabetes.
Low Circulating IGF-II Concentrations Predict Weight Gain and Obesity in Humans
Authors: Sandhu Manjinder S. , Gibson J. Martin , Heald Adrian H. , Dunger David B. , Wareham Nicholas J.
Published: March 2007

Results from experimental and gene-association studies suggest that IGF-II may influence body weight regulation and that individuals with low IGF-II levels may be more susceptible to weight gain and obesity. We therefore assessed the association between circulating concentrations of IGF-II and subsequent weight gain and progression to obesity. Participants in this study were 463 nonobese men and women aged between 45 and 60 years with normal glucose tolerance and with metabolic and anthropometric assessments at baseline and follow-up clinic visits. We examined the association between baseline concentrations of fasting serum IGF-II and risk of gaining ≥2.5 kg body wt or developing obesity using unconditional logistic regression. A total of 217 participants gained ≥2.5 kg body wt, and 29 developed obesity after >4 years of follow-up. In multivariate analysis, baseline IGF-II levels were significantly lower in participants who subsequently gained weight compared with individuals who remained stable or lost weight (P = 0.010). Similarly, individuals who developed obesity had lower baseline IGF-II levels (P = 0.006). Relatively higher IGF-II levels were also associated with a reduced risk of gaining weight (P for trend across quintiles of IGF-II = 0.006). Our data suggest that circulating IGF-II levels may play a role in body weight regulation and development of obesity in men and women with normal glucose tolerance.
Fetal or Neonatal Low-Glycotoxin Environment Prevents Autoimmune Diabetes in NOD Mice
Authors: Peppa Melpomeni , He Cijiang , Hattori Masakazu , McEvoy Robert , Zheng Feng , Vlassara Helen
Published: March 2007

Advanced glycation end products (AGEs) are implicated in β-cell oxidant stress. Diet-derived AGE (dAGE) are shown to contribute to end-organ toxicity attributed to diabetes. To assess the role of dAGE on type 1 diabetes, NOD mice were exposed to a high-AGE diet (H-AGE) and to a nutritionally similar diet with approximate fivefold-lower levels of Nε-carboxymethyllysine (CML) and methylglyoxal-derivatives (MG) (L-AGE). Suppression of serum CML and MG in L-AGE-fed mice was marked by suppression of diabetes (H-AGE mice >94% vs. L-AGE mice 33% in founder [F]0, 14% in F1, and 13% in F2 offspring, P < 0.006) and by a delay in disease onset (4-month lag). Survival for L-AGE mice was 76 vs. 0% after 44 weeks of H-AGE mice. Reduced insulitis in L-AGE versus H-AGE mice (P < 0.01) was marked by GAD- and insulin-unresponsive pancreatic interleukin (IL)-4-positive CD4+ cells compared with the GAD- and insulin-responsive interferon (IFN)-γ-positive T-cells from H-AGE mice (P < 0.005). Splenocytes from L-AGE mice consisted of GAD- and insulin-responsive IL-10-positive CD4+ cells compared with the IFN-γ-positive T-cells from H-AGE mice (P < 0.005). Therefore, high AGE intake may provide excess antigenic stimulus for T-cell-mediated diabetes or direct β-cell injury in NOD mice; both processes are ameliorated by maternal or neonatal exposure to L-AGE nutrition.
Increased Vulnerability of Brain Mitochondria in Diabetic (Goto-Kakizaki) Rats With Aging and Amyloid-β Exposure
Authors: Moreira Paula I. , Santos Maria S. , Moreno António M. , Seiça Raquel , Oliveira Catarina R.
Published: March 2007

This study evaluated the respiratory indexes (respiratory control ratio [RCR] and ADP/O ratio), mitochondrial transmembrane potential (ΔΨm), repolarization lag phase, repolarization level, ATP/ADP ratio, and induction of the permeability transition pore of brain mitochondria isolated from normal Wistar and GK diabetic rats of different ages (1.5, 12, and 24 months of age). The effect of amyloid β-peptides, 50 μmol/l Aβ25–35 or 2 μmol/l Aβ1–40, on mitochondrial function was also analyzed. Aging of diabetic mice induced a decrease in brain mitochondrial RCR, ADP/O, and ATP/ADP ratios but induced an increase in the repolarization lag phase. Brain mitochondria from older diabetic rats were more prone to the induction of the permeability transition pore, i.e., mitochondria from 24-month-old diabetic rats accumulated much less Ca2+ (20 μmol/l) than those isolated from 12-month-old rats (50 μmol/l) or 1.5-month-old rats (100 μmol/l). In the presence of 50 μmol/l Aβ25–35 or 2 μmol/l Aβ1–40, age-related mitochondrial effects were potentiated. These results indicate that diabetes-related mitochondrial dysfunction is exacerbated by aging and/or by the presence of neurotoxic agents such as amyloid β-peptides, supporting the idea that diabetes and aging are risk factors for the neurodegeneration induced by these peptides.
Pancreatic β-Cells Express Phagocyte-Like NAD(P)H Oxidase
Authors: Oliveira Henriette R. , Verlengia Rozangela , Carvalho Carla R.O. , Britto Luiz R.G. , Curi Rui , Carpinelli Angelo R.
Published: March 2007

The presence of a phagocyte-like NAD(P)H oxidase in pancreatic β-cells was investigated. Three NAD(P)H oxidase components were found in pancreatic islets by RT-PCR: gp91PHOX, p22PHOX, and p47PHOX. The components p67PHOX and p47PHOX were also demonstrated by Western blotting. Through immunohistochemistry, p47PHOX was mainly found in the central area of the islet, confirming the expression of this component by insulin-producing cells. Activation of NAD(P)H oxidase complex in the β-cells was also examined by immunohistochemistry. The pancreatic islets presented slower kinetics of superoxide production than HIT-T15 cells, neutrophils, and macrophages, but they reached 66% that of the neutrophil nitroblue tetrazolium (NBT) reduction after 2 h of incubation. Glucose (5.6 mmol/l) increased NBT reduction by 75% when compared with control. The involvement of protein kinase C (PKC) in the stimulatory effect of glucose was confirmed by incubation of islets with phorbol myristate acetate (a PKC activator) and bysindoylmaleimide (GF109203X) (a PKC-specific inhibitor). Diphenylene iodonium [an NAD(P)H oxidase inhibitor] abolished the increase of NBT reduction induced by glucose, confirming the NAD(P)H oxidase activity in pancreatic islets. Because reactive oxygen species are involved in intracellular signaling, the phagocyte-like NAD(P)H oxidase activation by glucose may play an important role for β-cell functioning.
Mechanisms of Abnormal Cardiac Repolarization During Insulin-Induced Hypoglycemia
Authors: Robinson Robert T.C.E. , Harris Nigel D. , Ireland Robert H. , Lee Stuart , Newman Christopher , Heller Simon R.
Published: March 2007

Prolonged cardiac repolarization causes fatal cardiac arrhythmias. There is evidence that these contribute to sudden death associated with nocturnal hypoglycemia in young people with diabetes. We measured cardiac repolarization (QT interval [QTc] and QT dispersion [QTd]) during experimental hypoglycemia with and without β-blockade and potassium infusion to establish possible mechanisms. Two groups of 10 nondiabetic men (study 1 and study 2) each underwent four hyperinsulinemic clamps: two euglycemic (5 mmol/l) and two hypoglycemic (5 mmol/l and 2.5 mmol/l for 60 min each). Study 1 was performed with and without potassium infusion to maintain normal concentrations and study 2 with and without β-blockade (atenolol, 100 mg/day for 7 days). QTd was unchanged during euglycemia but increased during hypoglycemia (55 ms, P < 0.0001 vs. baseline), which was prevented by potassium (6 ms, P = 0.78). QTc increased significantly during hypoglycemia alone (67 ms, P < 0.0001) and during potassium replacement (46 ms, P = 0.02). In study 2, the increase in QTd during hypoglycemia (68 ms, P < 0.0001) was prevented by β-blockade (3 ms, P = 0.88). The increase in QTc during hypoglycemia (55 ms, P < 0.0001) was prevented by β-blockade (1 ms, P = 0.98). Our data indicate that hypoglycemia causes an acquired long QT syndrome. Sympathoadrenal stimulation is the main cause, through mechanisms that involve but are not limited to catecholamine-mediated hypokalemia. These abnormalities are prevented by selective β-blockade.
The Natural History of Progression From Normal Glucose Tolerance to Type 2 Diabetes in the Baltimore Longitudinal Study of Aging
Authors: Meigs James B. , Muller Denis C. , Nathan David M. , Blake Deirdre R. , Andres Reubin
Published: March 2007

The natural history of progression from normal glucose tolerance (NGT) to impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and type 2 diabetes is not well defined. We studied this progression using biennial oral glucose tolerance tests performed in the Baltimore Longitudinal Study of Aging and survival analysis to assess progression from NGT to abnormal fasting plasma glucose (FPG; ≥6.1 mmol/l), abnormal 2-h plasma glucose (2hPG; ≥7.8 mmol/l), IFG (FPG 6.1–6.9 mmol/l, 2hPG ≤7.8 mmol/l), and IGT (FPG <6.1 mmol/l, 2hPG 7.8–11.0 mmol/l), and from IFG-IGT to diabetes (FPG ≥7.0 mmol/l or 2hPG ≥11.1 mmol/l). At baseline, the 815 subjects had a mean age of 57 years, 35% were women, and 60% had NGT. Of the 488 subjects with NGT, over half were followed for at least 10 years. By 10 years, 14% had progressed to abnormal FPG and 48% to abnormal 2hPG. Of the 267 subjects who progressed to IFG-IGT, 216 had additional follow-up. By 10 years, 8% of these progressed to diabetes by FPG whereas 27% progressed by 2hPG. In subsidiary analyses, we defined “abnormal” FPG as ≥5.55 mmol/l and “diabetic” FPG as ≥6.1 mmol/l, making the baseline prevalence of IFG similar to that of IGT. By these criteria, 43% progressed to abnormal FPG and 43% to abnormal 2hPG by 10 years of follow-up; among subjects developing impaired FPG or 2hPG, 22% progressed to diabetes by FPG whereas 17% progressed by 2hPG at 10 years. Nonetheless, 42% of subjects developing abnormal FPG did not develop abnormal 2hPG, and vice versa. We conclude that, although phenotypic differences in rates of progression are partly a function of diagnostic thresholds, fasting and postchallenge hyperglycemia may represent phenotypes with distinct natural histories in the evolution of type 2 diabetes.
A Role for Advanced Glycation End Products in Diminished Bone Healing in Type 1 Diabetes
Authors: Santana Ronaldo B. , Xu Lei , Chase Hermik Babakhanlou , Amar Salomon , Graves Dana T. , Trackman Philip C.
Published: March 2007

The effect of type 1 diabetes on bone healing and bone formation in standardized craniotomy defects created in BALB/cByJ mice was determined. The hypothesis that advanced glycation end products (AGEs) contribute to diminished bone healing in diabetes was evaluated by assessing for the presence of the receptor for advanced glycation end products (RAGE) by immunohistochemistry in healing craniotomy defects in diabetic animals. The effect of local application of a known RAGE protein ligand, Nε-(carboxymethyl)lysine (CML)−mouse serum albumin (MSA), on craniotomy defect healing in normal animals was then assessed and compared to the effects of control MSA. Finally, evidence in support of the expression of RAGE mRNA and protein in osteoblastic cells was obtained. The results indicated that craniotomy defects in diabetic animals healed ∼40% of the degree to which they healed in nondiabetic animals (P < 0.05). RAGE was expressed at higher levels in healing bone tissues in diabetic compared to control animals. Further studies in nondiabetic animals indicated that bone healing was reduced by 63 and 42% in lesions treated with 900 and 90 μg CML-MSA, respectively, compared to in animals treated with MSA alone (P < 0.05). Evidence for the expression of RAGE was obtained in mouse and rat osteoblastic cultures. These results support the contribution of AGEs to diminished bone healing in type 1 diabetes, possibly mediated by RAGE.
Identification of Interactive Loci Linked to Insulin and Leptin in Mice With Genetic Insulin Resistance
Authors: Almind Katrine , Kulkarni Rohit N. , Lannon Scott M. , Kahn C. Ronald
Published: March 2007

Mice double heterozygous (DH) for deletion of insulin receptor and insulin receptor substrate-1 are lean, insulin resistant, and have a phenotype that strongly depends on the genetic background of the mouse. On the C57BL/6 (B6) background, DH mice develop marked hyperinsulinemia and diabetes, whereas on the 129S6 background, DH mice exhibit only mild elevations of insulin and remain free of diabetes. F2 male mice created by an intercross between these two strains exhibit a 60% incidence of diabetes and a bell-shaped distribution of insulin levels as related to glucose, reminiscent of that in humans with type 2 diabetes. These mice also exhibit a wide range of leptin levels as related to body weight. A genome-wide scan of F2 mice reveals a quantitative trait locus (QTL) related to hyperinsulinemia on chromosome 14 (D14Mit55) with a peak logarithm of odds (LOD) score of 5.6, accounting for up to 69% of this trait. A QTL with a LOD score of 3.7 related to hyperleptinemia is present on chromosome 7 at D12Mit38 (a marker previously assigned to chromosome 12) in the area of the uncoupling protein 2/3 gene cluster. This locus also interacts synergistically with D14Mit55 in development of hyperinsulinemia and with a QTL on chromosome 12 (D12Mit231) related to hyperglycemia. These data demonstrate how multiple genetic modifiers can interact and influence the development of diabetes and the phenotype of animals with genetically programmed insulin resistance and provide evidence as to the location and nature of these genes.
Mechanisms by Which Liver-Specific PEPCK Knockout Mice Preserve Euglycemia During Starvation
Authors: She Pengxiang , Burgess Shawn C. , Shiota Masakazu , Flakoll Paul , Donahue E. Patrick , Malloy Craig R. , Sherry A. Dean , Magnuson Mark A.
Published: March 2007

Liver-specific PEPCK knockout mice, which are viable despite markedly abnormal lipid metabolism, exhibit mild hyperglycemia in response to fasting. We used isotopic tracer methods, biochemical measurements, and nuclear magnetic resonance spectroscopy to show that in mice lacking hepatic PEPCK, 1) whole-body glucose turnover is only slightly decreased; 2) whole-body gluconeogenesis from phosphoenolpyruvate, but not from glycerol, is moderately decreased; 3) tricarboxylic acid cycle activity is globally increased, even though pyruvate cycling and anaplerosis are decreased; 4) the liver is unable to synthesize glucose from lactate/pyruvate and produces only a minimal amount of glucose; and 5) glycogen synthesis in both the liver and muscle is impaired. Thus, although mice without hepatic PEPCK have markedly impaired hepatic gluconeogenesis, they are able to maintain a near-normal blood glucose concentration while fasting by increasing extrahepatic gluconeogenesis coupled with diminishing whole-body glucose utilization.
Induction of Adiponectin, a Fat-Derived Antidiabetic and Antiatherogenic Factor, by Nuclear Receptors
Authors: Iwaki Masanori , Matsuda Morihiro , Maeda Norikazu , Funahashi Tohru , Matsuzawa Yuji , Makishima Makoto , Shimomura Iichiro
Published: March 2007

Adiponectin is a fat-derived hormone with antidiabetic and antiatherogenic properties. Hypoadiponectinemia seen in obesity is associated with insulin-resistant diabetes and atherosclerosis. Thiazolidinediones, peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists, have been shown to increase plasma adiponectin levels by the transcriptional induction in adipose tissues. However, the precise mechanism of such action is unknown. In this study, we have identified a functional PPAR-responsive element (PPRE) in human adiponectin promoter. PPAR-γ/retinoid X receptor (RXR) heterodimer directly bound to the PPRE and increased the promoter activity in cells. In adipocytes, point mutation of the PPRE markedly reduced the basal transcriptional activity and completely blocked thiazolidinedione-induced transactivation of adiponectin promoter. We have also identified a responsive element of another orphan nuclear receptor, liver receptor homolog-1 (LRH-1), in adiponectin promoter. LRH-1 was expressed in 3T3-L1 cells and rat adipocytes. LRH-1 bound specifically to the identified responsive element (LRH-RE). LRH-1 augmented PPAR-γ-induced transactivation of adiponectin promoter, and point mutation of the LRH-RE significantly decreased the basal and thiazolidinedione-induced activities of adiponectin promoter. Our results indicate that PPAR-γ and LRH-1 play significant roles in the transcriptional activation of adiponectin gene via the PPRE and the LRH-RE in its promoter.
Expression of Peroxisome Proliferator-Activated Receptor-γ1 and Peroxisome Proliferator-Activated Receptor-γ2 in Visceral and Subcutaneous Adipose Tissue of Obese Women
Authors: Giusti Vittorio , Verdumo Chantal , Suter Michel , Gaillard Rolf Christian , Burckhardt Peter , Pralong Francois
Published: March 2007

Data regarding the expression of peroxisome proliferator-activated receptor (PPAR)-γ1 and PPAR-γ2 in human visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) are conflicting. To clarify this issue, we studied 50 women who had a BMI >35 kg/m2 were undergoing gastric reduction surgery. Phenotyping included recording of anthropometric parameters and of a biological profile. Quantification of the expression of PPAR-γ1 and PPAR-γ2 in samples of VAT and SAT was performed by real-time RT-PCR. In both SAT and VAT, the level of expression of PPAR-γ2 were >20-fold that of PPAR-γ1 (P < 0.001 for both). However, only PPAR-γ1 was differentially expressed, its levels in SAT being 216 ± 34% those in VAT (P < 0.001). In a stepwise, multivariate regression analysis, the levels of PPAR-γ1 in both SAT and VAT were the major determinants of waist circumference (R2 = 21% for both; P < 0.01). Finally, leptin but not PPARs appeared as the single parameter explaining the largest part of the variability of BMI in our cohort of patients (R2 = 22%, P < 0.001). These results are consistent with the putative roles of PPAR-γ1 and PPAR-γ2 in carbohydrate metabolism and energy homeostasis, respectively. As such, they constitute an important step toward the identification of potential targets for novel therapeutic strategies in the fields of obesity.
Diabetes Protection and Restoration of Thymocyte Apoptosis in NODIdd6Congenic Strains
Authors: Bergman Marie-Louise , Duarte Nadia , Campino Susana , Lundholm Marie , Motta Vinicius , Lejon Kristina , Penha-Gonçalves Carlos , Holmberg Dan
Published: March 2007

Type 1 diabetes in the nonobese diabetic (NOD) mouse is a multifactorial and polygenic disease. The NOD-derived genetic factors that contribute to type 1 diabetes are named Idd (insulin-dependent diabetes) loci. To date, the biological functions of the majority of the Idd loci remain unknown. We have previously reported that resistance of NOD immature thymocytes to depletion by dexamethazone (Dxm) maps to the Idd6 locus. Herein, we refine this phenotype using a time-course experiment of apoptosis induction upon Dxm treatment. We confirm that the Idd6 region controls apoptosis resistance in immature thymocytes. Moreover, we establish reciprocal Idd6 congenic NOD and B6 strains to formally demonstrate that the Idd6 congenic region mediates restoration of the apoptosis resistance phenotype. Analysis of the Idd6 congenic strains indicates that a 3-cM chromosomal region located within the distal part of the Idd6 region controls apoptosis resistance in NOD immature thymocytes. Together, these data support the hypothesis that resistance to Dxm-induced apoptosis in NOD immature thymocytes is controlled by a genetic factor within the region that also contributes to type 1 diabetes pathogenesis. We propose that the diabetogenic effect of the Idd6 locus is exerted at the level of the thymic selection process.
Glucagon, Catecholamine, and Symptom Responses to Hypoglycemia in Living Donors of Pancreas Segments
Authors: Robertson R. Paul , Sutherland David E.R. , Seaquist Elizabeth R. , Lanz Karla J.
Published: March 2007

Donors undergoing hemi-pancreatectomy to provide a pancreas segment for transplantation into a relative with type 1 diabetes acquire diminished insulin and glucagon responses to intravenous agonists. Some donors develop diabetes and require treatment for hyperglycemia. They become at risk for hypoglycemia when treatment includes sulfonylureas and insulin. However, no studies assessing the impact of hemi-pancreatectomy in humans on islet α-cell responses to hypoglycemia have been reported. Consequently, we performed stepped hypoglycemic clamps in 7 donors of varying glycemic control and compared their responses to 16 control subjects. Donors and control subjects reached similar nadirs of glycemia (45 ± 3 and 41 ± 1 mg/dl, respectively) during the clamp. The donors had significantly higher mean basal glucagon levels than control subjects (203 ± 27 vs. 135 ± 15 pg/ml; P < 0.03) but did not have significant differences in glucagon responses during the clamp. The donors also had significantly higher mean peak epinephrine responses during the clamp (1,231 ± 134 vs. 730 ± 68 pg/ml; P < 0.002), but there were no statistically significant differences in norepinephrine or symptom responses. The glucose thresholds at which hormonal and symptom responses began were not different. We conclude that although glucagon response to arginine and insulin response to glucose and arginine are diminished after hemi-pancreatectomy, no deficiency in glucagon responses were detected during hypoglycemia.
Mechanisms of the Age-Associated Deterioration in Glucose Tolerance
Authors: Basu Rita , Breda Elena , Oberg Ann L. , Powell Claudia C. , Dalla Man Chiara , Basu Ananda , Vittone Janet L. , Klee George G. , Arora Puneet , Jensen Michael D. , Toffolo Gianna , Cobelli Claudio , Rizza Robert A.
Published: March 2007

Glucose tolerance decreases with age. For determining the cause of this decrease, 67 elderly and 21 young (70.1 ± 0.7 vs. 23.7 ± 0.8 years) participants ingested a mixed meal and received an intravenous injection of glucose. Fasting glucose and the glycemic response above basal were higher in the elderly than in the young participants after either meal ingestion (P < 0.001) or glucose injection (P < 0.01). Insulin action (Si), measured with the meal and intravenous glucose tolerance test models, was highly correlated (r = 0.72; P < 0.001) and lower (P ≤ 0.002) in the elderly than in the young participants. However, when adjusted for differences in percentage body fat and visceral fat, Si no longer differed between groups. When considered in light of the degree of insulin resistance, all indexes of insulin secretion were lower (P < 0.01) in the elderly participants, indicating impaired β-cell function. Hepatic insulin clearance was increased (P < 0.002), whereas total insulin clearance was decreased (P < 0.002) in the elderly subjects. Multivariate analysis (r = 0.70; P < 0.001) indicated that indexes of insulin action (Si) and secretion (Phitotal) but not age, peak oxygen uptake, fasting glucose, degree of fatness, or hepatic insulin clearance predicted the postprandial glycemic response. We conclude that the deterioration in glucose tolerance that occurs in healthy elderly subjects is due to a decrease in both insulin secretion and action with the severity of the defect in insulin action being explained by the degree of fatness rather than age per se.
The GLP-1 Derivative NN2211 Restores β-Cell Sensitivity to Glucose in Type 2 Diabetic Patients After a Single Dose
Authors: Chang Annette M. , Jakobsen Grethe , Sturis Jeppe , Smith Marla J. , Bloem Cathie J. , An Bob , Galecki Andrzej , Halter Jeffrey B.
Published: March 2007

Glucagon-like peptide 1 (GLP-1) stimulates insulin secretion in a glucose-dependent manner, but its short half-life limits its therapeutic potential. We tested NN2211, a long-acting GLP-1 derivative, in 10 subjects with type 2 diabetes (means ± SD: age 63 ± 8 years, BMI 30.1 ± 4.2 kg/m2, HbA1c 6.5 ± 0.8%) in a randomized, double-blind, placebo-controlled, crossover study. A single injection (7.5 μg/kg) of NN2211 or placebo was administered 9 h before the study. β-cell sensitivity was assessed by a graded glucose infusion protocol, with glucose levels matched over the 5–12 mmol/l range. Insulin secretion rates (ISRs) were estimated by deconvolution of C-peptide levels. Findings were compared with those in 10 nondiabetic volunteers during the same glucose infusion protocol. In type 2 diabetic subjects, NN2211, in comparison with placebo, increased insulin and C-peptide levels, the ISR area under the curve (AUC) (1,130 ± 150 vs. 668 ± 106 pmol/kg; P < 0.001), and the slope of ISR versus plasma glucose (1.26 ± 0.36 vs. 0.54 ± 0.18 pmol · l[min−1 · mmol−1 · kg−1]; P < 0.014), with values similar to those of nondiabetic control subjects (ISR AUC 1,206 ± 99; slope of ISR versus plasma glucose, 1.44 ± 0.18). The long-acting GLP-1 derivative, NN2211, restored β-cell responsiveness to physiological hyperglycemia in type 2 diabetic subjects.
Insulin-Dependent Modulation of Plasma Ghrelin and Leptin Concentrations Is Less Pronounced in Type 2 Diabetic Patients
Authors: Anderwald Christian , Brabant Georg , Bernroider Elisabeth , Horn Rüdiger , Brehm Attila , Waldhäusl Werner , Roden Michael
Published: March 2007

The gastric peptide ghrelin augments and the adipocyte-derived hormone leptin reduces appetite and food intake. In the central nervous system, insulin directly decreases hunger sensation but could also act indirectly by modulating ghrelin and leptin secretion. This study examines dose-dependent effects of insulin on plasma ghrelin and leptin concentrations during hyperinsulinemic (1, 2, and 4 mU · kg−1 · min−1)-euglycemic clamp tests in six nondiabetic (control subjects) and six type 2 diabetic patients. Type 2 diabetic patients were studied before and after prolonged (12-h and 67-h) variable intravenous insulin treatment aiming at near-normoglycemia (115 ± 4 mg/dl). Nondiabetic subjects were also studied during saline infusion, which did not affect ghrelin but decreased leptin by 19 ± 6% (P < 0.03). In control subjects, plasma ghrelin decreased at all clamp steps (−17 ± 1, −27 ± 6, and −33 ± 4%, respectively; P < 0.006 vs. baseline), whereas leptin increased by 35 ± 11% (P < 0.05). In type 2 diabetic patients without insulin treatment, ghrelin decreased by 18 ± 7% (P < 0.05) only after 4 mU · kg−1 · min−1 insulin infusion and leptin increased by 19 ± 6% (P < 0.05). After prolonged insulin treatment and near-normoglycemia, ghrelin and leptin remained unchanged in type 2 diabetic patients during the clamps. In conclusion, insulin reduces plasma ghrelin in nondiabetic patients and, to a lesser extent, in type 2 diabetic patients before insulin therapy. These findings indicate an indirect effect of insulin via ghrelin on the suppression of hunger sensation and appetite.
Glucose Enhances Endothelial LOX-1 Expression
Authors: Li Ling , Sawamura Tatsuya , Renier Geneviève
Published: March 2007

Endothelial dysfunction is an early and key determinant of diabetic vascular complications that is elicited at least in part by oxidized LDL (oxLDL). The recent observation that lectin-like oxLDL receptor-1 (LOX-1) expression is increased in the vascular endothelium of diabetic rats suggests a role for LOX-1 in the pathogenesis of diabetic vascular dysfunction. Because postprandial plasma glucose has been recently proposed as an independent risk factor for cardiovascular diseases in patients with diabetes, we evaluated, in the current study, the in vitro effect of high glucose on LOX-1 expression by human aortic endothelial cells (HAECs) and the role of this receptor in glucose-induced human monocyte adhesion to endothelium. Exposure of HAECs to high d-glucose concentrations (5.6–30 mmol/l) enhanced, in a dose- and time-dependent manner, LOX-1 expression, both at the gene and protein levels. The stimulatory effect of glucose on LOX-1 gene expression in HAECs was abolished by antioxidants and inhibitors of nuclear factor (NF)-κB, protein kinase C (PKC), and mitogen-activated protein kinases (MAPKs). Electrophoretic mobility shift assay data demonstrated that high glucose enhanced, in HAECs, the nuclear protein binding to the NF-κB regulatory element of the LOX-1 gene. Finally, our results showed that incubation of HAECs with high glucose increased human monocyte adhesion to endothelium through a LOX-1—dependent signaling mechanism. Overall, these results demonstrate that high glucose induces endothelial LOX-1 expression. This effect appears to be exerted at the transcriptional level through increased oxidant stress and NF-κB, PKC, and MAPK activation. The study also suggests a role for LOX-1 as mediator of the stimulatory effect of high glucose on monocyte adhesion.
Impact of Aerobic Exercise Training on Age-Related Changes in Insulin Sensitivity and Muscle Oxidative Capacity
Authors: Short Kevin R. , Vittone Janet L. , Bigelow Maureen L. , Proctor David N. , Rizza Robert A. , Coenen-Schimke Jill M. , Nair K. Sreekumaran
Published: March 2007

Insulin resistance increases and muscle oxidative capacity decreases during aging, but lifestyle changes—especially physical activity—may reverse these trends. Here we report the effect of a 16-week aerobic exercise program (n = 65) or control activity (n = 37) performed by men and women aged 21–87 years on insulin sensitivity and muscle mitochondria. Insulin sensitivity, measured by intravenous glucose tolerance test, decreased with age (r = −0.32) and was related to abdominal fat content (r = −0.65). Exercise increased peak oxygen uptake (Vo2peak; 10%), activity of muscle mitochondrial enzymes (citrate synthase and cytochrome c oxidase, 45–76%) and mRNA levels of mitochondrial genes (COX4, ND4, both 66%) and genes involved in mitochondrial biogenesis (PGC-1α, 55%; NRF-1, 15%; TFAM, 85%). Exercise also increased muscle GLUT4 mRNA and protein (30–52%) and reduced abdominal fat (5%) and plasma triglycerides (25%). None of these changes were affected by age. In contrast, insulin sensitivity improved in younger people but not in middle-aged or older groups. Thus, the muscle mitochondrial response to 4 months of aerobic exercise training was similar in all age-groups, although the older people did not have an improvement in insulin sensitivity.
Chronic Endothelin-1 Treatment Leads to Insulin Resistance In Vivo
Authors: Wilkes Jason J. , Hevener Andrea , Olefsky Jerrold
Published: March 2007

We determined whether chronic endothelin-1 (ET-1) treatment could lead to in vivo insulin resistance. Like insulin, ET-1 acutely stimulated glucose transport in isolated soleus muscle strips of WKY rats. ET-1 pretreatment (1 h) decreased insulin-stimulated glucose transport in muscle strips (−23%). Both ET-1-mediated effects were generated through ETA receptors, because a specific ETA receptor antagonist (BQ610) blocked these effects of ET-1. Osmotic minipumps were used to treat normal rats with ET-1 for 5 days. Subsequent hyperinsulinemic-euglycemic clamps showed that ET-1 treatment led to an ∼30% decrease in insulin-stimulated glucose disposal rates in male and female rats. In addition, ex vivo study of soleus muscle strips showed decreased glucose transport into muscle from ET-1-treated animals. With respect to insulin signaling, chronic in vivo ET-1 treatment led to a 30–40% decrease in IRS-I protein content, IRS-I-associated p110α, and AKT activation. In summary, 1) in vitro ET-1 pretreatment leads to decreased insulin-stimulated glucose transport in skeletal muscle strips; 2) chronic ET-1 administration in vivo leads to whole-body insulin resistance, with decreased skeletal muscle glucose transport and impaired insulin signaling; and 3) elevated ET-1 levels may be a cause of insulin resistance in certain pathophysiologic states.
Insulin Resistance in Tetracycline-Repressible Munc18c Transgenic Mice
Authors: Spurlin Beth A. , Thomas Rhonda M. , Nevins Angela K. , Kim Hyo-Jeong , Kim Yoon-Jung , Noh Hye-Lim , Shulman Gerald I. , Kim Jason K. , Thurmond Debbie C.
Published: March 2007

To investigate the physiological effects of modulating the abundance of Munc18c or syntaxin 4 (Syn4) proteins on the regulation of glucose homeostasis in vivo, we generated tetracycline-repressible transgenic mice that overexpress either Munc18c or Syn4 proteins in skeletal muscle, pancreas and adipose tissue seven-, five-, and threefold over endogenous protein, respectively. Munc18c transgenic mice displayed whole-body insulin resistance during hyperinsulinemic-euglycemic clamp resulting from >41% reductions in skeletal muscle and white adipose tissue glucose uptake, but without alteration of hepatic insulin action. Munc18c transgenic mice exhibited ∼40% decreases in whole-body glycogen/lipid synthesis, skeletal muscle glycogen synthesis, and glycolysis. Glucose intolerance in Munc18c transgenic mice was reversed by repression of transgene expression using tetracycline or by simultaneous overexpression of Syn4 protein. In addition, Munc18c transgenic mice had depressed serum insulin levels, reflecting a threefold reduction in insulin secretion from islets isolated therefrom, thus uncovering roles for Munc18c and/or Syn4 in insulin granule exocytosis. Taken together, these results indicate that balance, more than absolute abundance, of Munc18c and Syn4 proteins directly affects whole-body glucose homeostasis through alterations in insulin secretion and insulin action.
A Peroxovanadium Compound Stimulates Muscle Glucose Transport as Powerfully as Insulin and Contractions Combined
Authors: Nolte Lorraine A. , Han Dong-Ho , Hansen Polly A. , Hucker Kathleen A. , Holloszy John O.
Published: March 2007

Stimulation of glucose transport by insulin involves tyrosine phosphorylation of the insulin receptor (IR) and IR substrates (IRSs). Peroxovanadates inhibit tyrosine phosphatases, also resulting in tyrosine phosphorylation of the IRSs. Muscle contractions stimulate glucose transport by a mechanism independent of the insulin-signaling pathway. We found that the peroxovanadate compound bis-peroxovanadium,1,10-phenanthrolene [bpV(phen)] stimulates glucose transport to the same extent as the additive effects of maximal insulin and contraction stimuli. Translocation of GLUT4 to the cell surface mediates stimulation of glucose transport. There is evidence suggesting there are separate insulin- and contraction-stimulated pools of GLUT4-containing vesicles. We tested the hypothesis that bpV(phen) stimulates both the insulin- and the contraction-activated pathways. Stimulation of glucose transport and GLUT4 translocation by bpV(phen) was completely blocked by the phosphatidylinositol 3-kinase (PI 3-K) inhibitors wortmannin and LY294002. The combined effect of bpV(phen) and contractions was no greater than that of bpV(phen) alone. Activation of the IRS-PI 3-K signaling pathway was much greater with bpV(phen) than with insulin. Our results suggest that the GLUT4 vesicles that are normally translocated in response to contractions but not insulin can respond to the signal generated via the IRS-PI 3-K pathway if it is sufficiently powerful.
Rosiglitazone Improves Downstream Insulin Receptor Signaling in Type 2 Diabetic Patients
Authors: Miyazaki Yoshinori , He Helen , Mandarino Lawrence J. , DeFronzo Ralph A.
Published: March 2007

Thiazolidinediones (TZDs) improve glycemic control and insulin sensitivity in patients with type 2 diabetes. To determine whether the TZD-induced improvement in glycemic control is associated with enhanced insulin receptor signaling in skeletal muscle, 20 type 2 diabetic patients received a 75-g oral glucose tolerance test (OGTT) and euglycemic insulin (80 mU · m−2 · min−1) clamp with [3-3H]glucose/indirect calorimetry/vastus lateralis muscle biopsies before and after 16 weeks of rosiglitazone treatment. Six age-matched nondiabetic subjects served as control subjects. RSG improved fasting plasma glucose (185 ± 8 to 139 ± 5 mg/dl), mean plasma glucose during the OGTT (290 ± 9 to 225 ± 6 mg/dl), HbA1c (8.5 ± 0.3 to 7.1 ± 0.3%), insulin-mediated total-body glucose disposal (TGD) (6.9 ± 0.7 to 9.2 ± 0.8 mg · kg−1 fat-free mass · min−1) (all P < 0.001), and decreased fasting plasma free fatty acid (FFA) (789 ± 59 to 656 ± 50 μEq/l) and mean FFA during the OGTT (644 ± 41 to 471 ± 35 μEq/l) (both P < 0.01). Before RSG treatment, insulin infusion did not significantly increase insulin receptor tyrosine phosphorylation (0.95 ± 0.10 to 1.08 ± 0.13 density units; NS) but had a small stimulatory effect on insulin receptor substrate (IRS)-1 tyrosine phosphorylation (1.05 ± 0.10 to 1.21 ± 0.12 density units; P < 0.01) and the association of p85 with IRS-1 (0.94 ± 0.06 to 1.08 ± 0.06 activity units; P < 0.01). RSG therapy had no effect on basal or insulin-stimulated insulin receptor tyrosine phosphorylation but increased insulin stimulation of IRS-1 tyrosine phosphorylation (1.13 ± 0.11 to 1.56 ± 0.17 density units; P < 0.01 vs. prerosiglitazone) and p85 association with IRS-1 (1.00 ± 0.06 to 1.27 ± 0.07 activity units; P < 0.05 vs. prerosiglitazone). In control and type 2 diabetic subjects, TGD/nonoxidative glucose disposal correlated positively with the insulin-stimulated increments in IRS-1 tyrosine phosphorylation (r = 0.52/r = 0.57, P < 0.01) and inversely with the plasma FFA concentration during the insulin clamp (r = −0.55/r = −0.53, P < 0.01). However, no significant association between plasma FFA concentrations during the insulin clamp and the increment in either IRS-1 tyrosine phosphorylation or the association of p85 with IRS-1 was observed. In conclusion, in type 2 diabetic patients, rosiglitazone treatment enhances downstream insulin receptor signaling in muscle and decreases plasma FFA concentration while improving glycemic control.
Central Pro-opiomelanocortin Gene Delivery Results in Hypophagia, Reduced Visceral Adiposity, and Improved Insulin Sensitivity in Genetically Obese Zucker Rats
Authors: Li Gang , Mobbs Charles V. , Scarpace Philip J.
Published: March 2007

Zucker (fa/fa) rats with defective leptin receptors are obese, hyperphagic, and hyperinsulinemic. For testing whether chronic activation of the central melanocortin pathway can bypass the defective leptin signaling and normalize altered energy homeostasis in these rats, recombinant adeno-associated virus encoding pro-opiomelanocortin (rAAV-POMC) or control vector was delivered bilaterally into the basal hypothalamus with coordinates targeting the arcuate nucleus. Thirty-eight days after POMC gene delivery, hypothalamic POMC expression increased fourfold and melanocortin signaling (indicated by phosphorylation of CREB) increased by 62% with respect to controls. There was a sustained reduction in food intake, a moderate but significant attenuation of weight gain, and a 24% decrease in visceral adiposity in rAAV-POMC rats. POMC gene delivery enhanced uncoupling protein 1 in brown adipose tissue (BAT) by more than fourfold. Fasting serum leptin, insulin, and cholesterol levels were also significantly reduced by rAAV-POMC treatment. This study demonstrates that targeted POMC gene delivery in the hypothalamus suppresses food intake and weight gain and reduces visceral adiposity and hyperinsulinemia in leptin-resistant obese Zucker rats. The mechanisms may involve the sustained hypophagia and the augmentation of thermogenesis in BAT.