bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Regulation of Protein Dynamics in Splanchnic and Skeletal Muscle Beds by Insulin and Amino Acids in Healthy Human Subjects
Authors: Nygren Jonas , Nair K. Sreekumaran
Published: March 2007

To determine the in vivo effect of amino acids (AAs) alone or in combination with insulin on splanchnic and muscle protein dynamics, we infused stable isotope tracers of AAs in 36 healthy subjects and sampled from femoral artery and vein and hepatic vein. The subjects were randomized into six groups and were studied at baseline and during infusions of saline (group 1), insulin (0.5 mU · kg−1 · min−1) (group 2), insulin plus replacement of AAs (group 3) insulin plus high-dose AAs (group 4), or somatostatin and baseline replacement doses of insulin, glucagon and GH plus high dose of AAs (group 5) or saline (group 6). Insulin reduced muscle release of AAs mainly by inhibition of protein breakdown. Insulin also enhanced AA-induced muscle protein synthesis (PS) and reduced leucine transamination. The main effect of AAs on muscle was the enhancement of PS. Insulin had no effect on protein dynamics or leucine transamination in splanchnic bed. However, AAs reduced protein breakdown and increased synthesis in splanchnic bed in a dose-dependent manner. AAs also enhanced leucine transamination in both splanchnic and muscle beds. Thus insulin’s anabolic effect was mostly on muscle, whereas AAs acted on muscle as well as on splanchnic bed. Insulin achieved anabolic effect in muscle by inhibition of protein breakdown, enhancing AA-induced PS, and reducing leucine transamination. AAs largely determined protein anabolism in splanchnic bed by stimulating PS and decreasing protein breakdown.
Discrete and Complementary Mechanisms of Protection of β-Cells Against Cytokine-Induced and Oxidative Damage Achieved by bcl-2 Overexpression and a Cytokine Selection Strategy
Authors: Tran Veronique Vien , Chen Guoxun , Newgard Christopher B. , Hohmeier Hans E.
Published: March 2007

We have been investigating the potential utility of engineered cell lines as surrogates for primary islet cells in treatment of type 1 diabetes. To this end, two strategies that have emerged for procuring cell lines with resistance to immune-mediated damage are 1) selection of cytokine-resistant cell lines by growth of INS-1 insulinoma cells in iteratively increasing concentrations of interleukin (IL)-1β + γ-interferon (IFN-γ), and 2) stable overexpression of the anti-apoptotic gene bcl-2 in INS-1 cells. Herein, we show that bcl-2−overexpressing cells are resistant to the cytotoxic effects of reactive oxygen and nitrogen species (ROS/RNS), but are only modestly protected against high concentrations of IL-1β + INF-γ, whereas the converse is true in cytokine selected cells. We also found that the combination of bcl-2 expression and cytokine selection confers a broader spectrum of resistance than either procedure alone, such that the resultant cells are highly resistant to cytokines and ROS/RNS, with no impairment in glucose-stimulated insulin secretion. INS-1−derived cells with combined bcl-2 expression and cytokine selection are also more resistant to damage induced by coculture with mitogen-activated peripheral blood mononuclear cells. Surprisingly, application of the cytokine selection procedure to bcl-2−overexpressing cells does not result in impairment of nuclear factor-κB translocation, iNOS expression, and NO production, as clearly occurs upon application of the selection procedure to cells without bcl-2 overexpression. Further investigation of the diverse pathways involved in the development of cytokine and ROS/RNS resistance may define simplified and specific strategies for preservation of β-cell mass.
The Degree of Phylogenetic Disparity of Islet Grafts Dictates the Reliance on Indirect CD4 T-Cell Antigen Recognition for Rejection
Authors: Rayat Gina R. , Johnson Zachary A. , Beilke Joshua N. , Korbutt Gregory S. , Rajotte Ray V. , Gill Ronald G.
Published: March 2007

Cellular xenograft rejection involves a pronounced contribution of CD4 T-cells recognizing antigens in association with recipient MHC class II molecules. However, the requirement for such “indirect” antigen recognition for acute islet xenograft is not clear, especially as a function of the phylogenetic disparity between the donor and recipient species. In vitro studies show that C57BL/6 (B6) mouse T-cells respond directly to either allogeneic BALB/c or phylogenetically related xenogeneic WF rat stimulator cells while having undetectable responses to phylogenetically disparate porcine stimulator cells. Although all types of grafts rejected acutely in wild-type mice, this response demonstrated markedly differing dependence on host MHC class II antigen presentation, depending on the donor species. While BALB/c islet allografts were acutely rejected in B6 MHC class II-deficient (C2D) recipients, WF rat xenografts demonstrated marked prolongation in C2D hosts relative to wild-type recipients. Interestingly, neonatal porcine islet (NPI) xenografts uniformly survived long term (>100 days) in untreated C2D hosts despite transfer of wild-type CD4 T-cells, demonstrating that survival in C2D recipients was not secondary to a lack of CD4 T-cells seen in such mice. Taken together, these results show a marked hierarchy in the requirement for host MHC class II-restricted indirect pathway in the rejection of pancreatic islet grafts. Thus, while cellular rejection of porcine xenografts is generally quite vigorous, this pathway is relatively finite, displaying a major reliance on host MHC class II-dependent antigen presentation for acute rejection.
Free Fatty Acid-Mediated Impairment of Glucose-Stimulated Insulin Secretion in Nondiabetic Oji-Cree Individuals From the Sandy Lake Community of Ontario, Canada
Authors: Carpentier André , Zinman Bernard , Leung Nathalie , Giacca Adria , Hanley Anthony J.G. , Harris Stewart B. , Hegele Robert A. , Lewis Gary F.
Published: March 2007

The Oji-Cree population of the Sandy Lake region of Ontario, Canada, has the third highest prevalence of type 2 diabetes in the world. Changes in their diet and physical activity over the past half-century, particularly the marked increase in consumption of dietary fats, are felt to be important factors accounting for this epidemic. The aim of the present study was to examine the β-cell response to a 48-h approximately twofold elevation of plasma free fatty acids (FFAs) (induced by Intralipid and heparin infusion) in members of the Sandy Lake Oji-Cree population (n = 12) and to compare the response to that in healthy age-matched nondiabetic Caucasian subjects (n = 16). The insulin secretion rate, insulin sensitivity index (SI), and disposition index (DI) (an index of insulin secretion that takes into account the ambient SI) were assessed in response to a 4-h graded intravenous glucose infusion followed by a 20 mmol/l 2-h hyperglycemic clamp. Total insulin secretory response to the graded glucose infusion did not change after a 48-h FFA elevation versus saline control in Caucasians and increased by ∼30% in Oji-Cree individuals (P = 0.04 for difference between the two groups). Infusion of heparin-Intralipid reduced SI by ∼40% in both groups (P = 0.002). Although DI was markedly reduced by heparin-Intralipid infusion in Caucasians (by ∼40%), it was reduced by only 15% in Oji-Cree individuals (P = 0.03 for difference of response between the two groups). However, SI and DI in the Oji-Cree individuals were already much lower than in Caucasians at baseline, in keeping with the very high risk of type 2 diabetes in this population. It is concluded that Oji-Cree individuals from a community at very high risk for developing type 2 diabetes are not more susceptible to the FFA-induced desensitization of glucose-stimulated insulin secretion than healthy non-Natives and, in fact, appear to be less susceptible. Whether this reflects an inherent resistance to lipotoxicity or an already-present lipotoxic effect in this population will require further study.
Differential Effects of Diabetes on Rat Choroid Plexus Ion Transporter Expression
Authors: Egleton Richard D. , Campos Christopher C. , Huber Jason D. , Brown Rachel C. , Davis Thomas P.
Published: March 2007

Though diabetes is a disease with vascular complications, little is known about its effects on the blood-brain barrier or the blood-cerebrospinal fluid barrier (BCSFB). The BCSFB is situated at choroid plexuses located in the lateral, third, and fourth ventricles. Choroid plexuses are the primary site of cerebrospinal fluid (CSF) production and express numerous ion transporters. Previous studies have shown a perturbation of ion transport in the periphery and brain during diabetes. In this study, we investigated the effect of diabetes on ion transporters in the choroid plexuses of streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in male Sprague-Dawley rats by intraperitoneal injection of STZ (60 mg/kg in citrate buffer, confirmed by glucose analysis: 601 ± 22 mg/dl diabetic rats, 181 ± 46 mg/dl age-matched controls); and at 28 days, rats were killed, choroid plexuses harvested, and protein extracted. Western blot analyses were carried out using antibodies for ion transporters, including Na+-K+-2Cl− cotransporter and the Na+-K+-ATPase α1-subunit. The efflux of the K+ analog 86Rb+ from choroid plexus was also studied. Diabetic rats showed an increase in expression of the Na+-K+-2Cl− cotransporter and the Na+-K+-ATPase α1-subunit, as compared with age-matched controls, a decrease in Na+-H+ exchanger expression, and no change in Na+-K+-ATPase β1- or β2-subunit. The net effect of these changes was a 66% increase in 86Rb+ efflux from diabetic choroid plexus compared with controls. These changes in expression may affect choroid plexus ion balance and thus significantly affect CSF production in diabetic rats.
Protein Kinase C β2-Dependent Phosphorylation of Core 2 GlcNAc-T Promotes Leukocyte-Endothelial Cell Adhesion
Authors: Chibber Rakesh , Ben-Mahmud Bahaedin M. , Mann Giovanni E. , Zhang Jin J. , Kohner Eva M.
Published: March 2007

Increased leukocyte-endothelial cell adhesion is a key early event in the development of retinopathy and atherogenesis in diabetic patients. We recently reported that raised activity of glycosylating enzyme [β]1,6 acetylglucosaminyltransferase (core 2 GlcNAc-T) is responsible for increased leukocyte-endothelial cell adhesion and capillary occlusion in retinopathy. Here, we demonstrate that elevated glucose increases the activity of core 2 GlcNAc-T and adhesion of human leukocytes to retinal capillary endothelial cells, in a dose-dependent manner, through diabetes-activated serine/threonine protein kinase C β2 (PKCβ2)-dependent phosphorylation. This regulatory mechanism, involving phosphorylation of core 2 GlcNAc-T, is also present in polymorphonuclear leukocytes isolated from type 1 and type 2 diabetic patients. Inhibition of PKCβ2 activation with the specific inhibitor, LY379196, attenuated serine phosphorylation of core 2 GlcNAc-T and prevented increased leukocyte-endothelial cell adhesion. Raised activity of core 2 GlcNAc-T was associated with a threefold increase in O-linked glycosylation of P-selectin glycoprotein ligand-1 on the surface of leukocytes of diabetic patients compared with age-matched control subjects. PKCβ2-dependent phosphorylation of core 2 GlcNAc-T may thus represent a novel regulatory mechanism for activation of this key enzyme in mediating increased leukocyte-endothelial cell adhesion and capillary occlusion in diabetic retinopathy.
Metabolic Effects of the Gly1057Asp Polymorphism in IRS-2 and Interactions With Obesity
Authors: Stefan Norbert , Kovacs Peter , Stumvoll Michael , Hanson Robert L. , Lehn-Stefan Angela , Permana Paska A. , Baier Leslie J. , Tataranni P. Antonio , Silver Kristi , Bogardus Clifton
Published: March 2007

Insulin receptor substrate (IRS)-2 plays an important role in insulin signaling and its disruption results in diabetes in mice. In humans, the IRS-2 Gly1057Asp substitution was associated with lower risk of type 2 diabetes in lean individuals, but with a higher risk in obese individuals. To clarify the role of IRS-2 on the development of type 2 diabetes and obesity in Pima Indians, and particularly to investigate whether the effects of the Gly1057Asp polymorphism on metabolism are mediated by obesity, molecular scanning of the gene for mutations was performed and interaction of the polymorphism with obesity was tested. We identified the previously described Gly1057Asp mutation as well as a rare Asp819His mutation and four silent polymorphisms. The effect of the Gly1057Asp mutation on type 2 diabetes and obesity was tested in a large cohort of Pima Indians (n = 998). A subgroup of nondiabetic full-heritage Pima Indians (n = 233) had measurements of body composition, glucose tolerance, insulin action (M), endogenous glucose production (EGP; hyperinsulinemic clamp), acute insulin response (AIR, 25-g intravenous glucose tolerance test, n = 118 normal glucose-tolerant subjects), and percutaneous fat biopsy specimens from the periumbilical region (n = 160). A total of 132 nondiabetic subjects were included in longitudinal analyses. The frequency of the Asp1057 allele was 0.6. In cross-sectional analyses, subjects homozygous for the Asp1057 allele (Asp/Asp) had a higher prevalence of type 2 diabetes than heterozygote individuals and subjects homozygous for the Gly1057 allele (X/Gly, P = 0.04). There was no effect on BMI (P = 0.78) or gene-BMI interaction on the prevalence of type 2 diabetes (P = 0.57). In the nondiabetic subgroup, subjects with Asp/Asp had higher percent body fat (P = 0.01), BMI (P = 0.02), and waist circumference (P = 0.004), but there was no difference in metabolic characteristics (all P > 0.2). However, the relationship between percent body fat and fasting glucose, basal EGP, EGP during the clamp, AIR, and subcutaneous abdominal adipocyte size was significantly different in the Asp/Asp group (P for interaction = 0.02, 0.06, 0.0007, 0.08, and 0.006, respectively) compared with the X/Gly group, suggesting a more detrimental effect of Asp homozygosity on these traits with increasing percent body fat. In longitudinal analyses, among subjects in the upper tertile of change in percent body fat, those with Asp/Asp had a larger increase in fasting and postprandial glycemia and basal EGP and a larger decrease in M and AIR than subjects with X/Gly, independent of change in obesity (all P < 0.05). In conclusion, our findings suggest that the association of homozygosity for the Asp1057 allele in IRS-2 with type 2 diabetes in Pima Indians may be mediated by interaction of the polymorphism with obesity on several diabetes-related traits.
Linkage and Linkage Disequilibrium Mapping of Genes Influencing Human Obesity in Chromosome Region 7q22.1–7q35
Authors: Li Wei-Dong , Li Ding , Wang Shuang , Zhang Shuanglin , Zhao Hongyu , Price R. Arlen
Published: March 2007

Linkage results suggest that the region of chromosome 7 containing the leptin gene cosegregates with extreme obesity; however, leptin coding region mutations are rare. To investigate whether the leptin flanking sequence and/or a larger 40-cM region (7q22.1–7q35) contributes to obesity, we genotyped individuals from 200 European American families segregating extreme obesity and normal weight (1,020 subjects) using 21 microsatellite markers and two single nucleotide polymorphisms (SNPs) and conducted nonparametric linkage (NPL) analyses. We also carried out transmission disequilibrium tests for 135 European American triads using 27 markers (including eight SNPs). Both quantitative (MERLIN-regress) and qualitative (GENEHUNTER and MERLIN-npl) analyses provided evidence for linkage for BMI (GENEHUNTER NPL = 2.98, 20 cM centromeric to leptin at the marker D7S692; MERLIN Z score = 3.56). Results for several other regions in 7q gave weak linkage. Transmission disequilibrium test (TDT) and quantitative TDT (and quantitative pedigree disequilibrium test) analyses suggest linkage disequilibrium near leptin and other regions of 7q. Our results suggested that there could be two or more genes in chromosome region 7q22.1–7q35 that influence obesity. A new region found by this study (D7S692-D7S523, 7q31.1) has the most consistent linkage results and could harbor obesity-related genes.
Pro12Ala of the Peroxisome Proliferator–Activated Receptor-γ2 Gene Is Associated With Lower Serum Insulin Levels in Nonobese African Americans
Authors: Kao W.H. Linda , Coresh Josef , Shuldiner Alan R. , Boerwinkle Eric , Bray Molly S. , Brancati Frederick L.
Published: March 2007

Recent research suggests that the Pro12Ala variant in peroxisome proliferator–activated receptor-γ2 (PPAR-γ2) is associated with diabetes- and obesity-related traits, and that its effects may be modified by obesity status. We characterized this variant in a population-based sample of 1,441 middle-aged African-American individuals with respect to diabetes-, obesity-, and other cardiovascular-related traits, both cross-sectionally and prospectively. The overall frequency of Ala12 was 1.9% (95% CI 1.5–2.5%), significantly lower than in Caucasian populations. Consistent with previous findings in Caucasians, African Americans with type 2 diabetes tended to be less likely to have the Pro/Ala genotype than those without (odds ratio [OR] 0.64, 95% CI 0.34–1.20); however, this OR was not statistically significant. Among nonobese individuals, the Pro/Ala genotype was associated with significantly lower ln(insulin) (P = 0.001), lower ln(HOMA-IR) (homeostasis model assessment of insulin resistance) (P = 0.002), higher fasting glucose-to-insulin ratio (P = 0.005), and lower diastolic blood pressure (P = 0.02). Among overweight individuals (BMI 25–29.9 kg/m2), the Pro/Ala genotype was associated with greater BMI (P = 0.02), waist-to-hip ratio (P = 0.01), and waist circumference (P = 0.04). Among obese individuals, there was no association between any of the diabetes- or obesity-related traits and the Pro12Ala PPAR-γ2 variant. We conclude that among nonobese African Americans, the Pro/Ala genotype is associated with markers of greater insulin sensitivity.
Prevalence of Mutations in AGPAT2 Among Human Lipodystrophies
Authors: Magré Jocelyne , Delépine Marc , Van Maldergem Lionel , Robert Jean-Jacques , Maassen J. Antonie , Meier Muriel , Panz Vanessa R. , Kim Chong Ae , Tubiana-Rufi Nadia , Czernichow Paul , Seemanova Eva , Buchanan Charles R. , Lacombe Didier , Vigouroux Corinne , Lascols Olivier , Kahn C. Ronald , Capeau Jacqueline , Lathrop Mark
Published: March 2007

Berardinelli-Seip congenital lipodystrophy (BSCL) is a heterogeneous genetic disease characterized by near absence of adipose tissue and severe insulin resistance. We have previously identified mutations in the seipin gene in a subset of our patients’ cohort. Recently, disease-causing mutations in AGPAT2 have been reported in BSCL patients. In this study, we have performed mutation screening in AGPAT2 and the related AGPAT1 in patients with BSCL or other forms of lipodystrophy who have no detectable mutation in the seipin gene. We found 38 BSCL patients from 30 families with mutations in AGPAT2. Three of the known mutations were frequently found in our families. Of the eight new alterations, six are null mutations and two are missense mutations (Glu172Lys and Ala238Gly). All the patients harboring AGPAT2 mutations presented with typical features of BSCL. We did not find mutations in patients with other forms of lipodystrophies, including the syndromes of Lawrence, Dunnigan, and Barraquer-Simons, or with type A insulin resistance. In conclusion, mutations in the seipin gene and AGPAT2 are confined to the BSCL phenotype. Because we found mutations in 92 of the 94 BSCL patients studied, the seipin gene and AGPAT2 are the two major genes involved in the etiology of BSCL.
Weight Loss-Induced Plasticity of Glucose Transport and Phosphorylation in the Insulin Resistance of Obesity and Type 2 Diabetes
Authors: Williams Katherine V. , Bertoldo Alessandra , Kinahan Paul , Cobelli Claudio , Kelley David E.
Published: March 2007

We tested the hypothesis that weight loss alleviates insulin resistance in skeletal muscle within the proximal steps of glucose metabolism, namely substrate delivery, glucose transport, and glucose phosphorylation. In obese subjects with and without type 2 diabetes, in vivo skeletal muscle assessments were obtained with dynamic positron emission tomography (PET) imaging performed during euglycemic clamps at moderate hyperinsulinemia (40 mU · min−1 · m−2), using [15O]H2O and [18F]fluoro-deoxyglucose ([18F]FDG) to quantify tissue perfusion and glucose metabolism. Dynamic [18F]FDG PET data were analyzed using both a novel muscle-specific compartmental model and a compartmental model originally developed for the brain and often used for [18F]FDG muscle image quantification. Weight loss in obese subjects with (n = 9) and without (n = 9) type 2 diabetes over a 4-month intervention was substantial (14 ± 2 kg, P < 0.05). Muscle insulin resistance, assessed by insulin-stimulated [18F]FDG uptake, decreased threefold in diabetic subjects and twofold in nondiabetic subjects (P < 0.001). Kinetic parameters for [18F]FDG transport and phosphorylation improved substantially in both groups, whereas tissue blood flow did not change. In particular, clinically significant weight loss fully corrected insulin resistance in type 2 diabetes at the step of glucose phosphorylation and largely, but incompletely, corrected insulin resistance at the glucose transport step.
Contraction-Induced Fatty Acid Translocase/CD36 Translocation in Rat Cardiac Myocytes Is Mediated Through AMP-Activated Protein Kinase Signaling
Authors: Luiken Joost J.F.P. , Coort Susan L.M. , Willems Jodil , Coumans Will A. , Bonen Arend , van der Vusse Ger J. , Glatz Jan F.C.
Published: March 2007

Contraction of rat cardiac myocytes induces translocation of fatty acid translocase (FAT)/CD36 and GLUT4 from intracellular stores to the sarcolemma, leading to enhanced rates of long-chain fatty acid (FA) and glucose uptake, respectively. Because intracellular AMP/ATP is elevated in contracting cardiac myocytes, we investigated whether activation of AMP-activated protein kinase (AMP kinase) is involved in contraction-inducible FAT/CD36 translocation. The cell-permeable adenosine analog 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) and the mitochondrial inhibitor oligomycin, similar to 4-Hz electrostimulation, evoked a more than threefold activation of cardiomyocytic AMP kinase. Both AICAR and oligomycin stimulated FA uptake into noncontracting myocytes by 1.4- and 2.0-fold, respectively, but were ineffective in 4 Hz-contracting myocytes. These findings indicate that both agents stimulate FA uptake by a similar mechanism as electrostimulation, involving activation of AMP kinase, as evidenced from phosphorylation of acetyl-CoA carboxylase. Furthermore, the stimulating effects of both AICAR and oligomycin were antagonized by blocking FAT/CD36 with sulfo-N-succinimidylpalmitate, but not by inhibiting phosphatidylinositol 3-kinase with wortmannin, indicating the involvement of FAT/CD36, but excluding a role for insulin signaling. Subcellular fractionation showed that oligomycin was able to mobilize intracellularly stored FAT/CD36 to the sarcolemma. We conclude that AMP kinase regulates cardiac FA use through mobilization of FAT/CD36 from a contraction-inducible intracellular storage compartment.
Glucose Autoregulates Its Uptake in Skeletal Muscle
Authors: Itani Samar I. , Saha Asish K. , Kurowski Theodore G. , Coffin Heather R. , Tornheim Keith , Ruderman Neil B.
Published: March 2007

Preexposure to a low concentration of glucose upregulates glucose transport into skeletal muscle, whereas exposure to a high concentration of glucose has the opposite effect. This autoregulatory process occurs independently of insulin, and the mechanism by which it operates is incompletely understood. Activation of the energy-sensing enzyme AMP-activated protein kinase (AMPK) has been shown to increase insulin-independent glucose transport into skeletal muscle in response to such stimuli as exercise and hypoxia. In the present study, we examined whether AMPK could also mediate glucose autoregulation. The activity of the α2 isoform of AMPK and 2-deoxyglucose uptake were assessed in incubated rat extensor digitorum longus muscle after preincubation for 4 h in media containing 0, 3, 6, or 25 mmol/l glucose. The principal findings were as follows. First, AMPK activity was highest in muscles incubated with no added glucose, and it decreased as the concentration of glucose was increased. In keeping with these findings, the concentration of malonyl CoA was increased, and acetyl CoA carboxylase phosphorylation at serine 79 was decreased as the medium glucose concentration was raised. Second, decreases in AMPK activity at the higher glucose concentrations correlated closely with decreases in glucose transport (2-deoxyglucose uptake), measured during a subsequent 20-min incubation at 6 mmol/l glucose (r2 = 0.93, P < 0.001). Third, the decrease in AMPK activity at the higher glucose concentrations was not associated with changes in whole-tissue concentrations of creatine phosphate or adenine nucleotides; however, it did correlate with increases in the rate of glycolysis, as estimated by lactate release. The results suggest that glucose autoregulates its own transport into skeletal muscle by a mechanism involving AMPK. They also suggest that this autoregulatory mechanism is not paralleled by changes in whole-tissue concentrations of creatine phosphate ATP, or AMP, but they leave open the possibility that alterations in a cytosolic pool of these compounds play a regulatory role.
Poly (ADP-Ribose) Polymerase Inhibition Prevents Spontaneous and Recurrent Autoimmune Diabetes in NOD Mice by Inducing Apoptosis of Islet-Infiltrating Leukocytes
Authors: Suarez-Pinzon Wilma L. , Mabley Jon G. , Power Robert , Szabó Csaba , Rabinovitch Alex
Published: March 2007

Poly (ADP-ribose) polymerase (PARP) is a nuclear enzyme that consumes NAD in response to DNA strand breaks. The PARP inhibitor nicotinamide prevents NAD consumption and protects islet β-cells from chemically induced necrosis but not cytokine-induced apoptosis. Therefore, it is unclear how nicotinamide protects NOD mice from autoimmune diabetes in which apoptosis is the mode of β-cell death. To investigate the mechanism of diabetes prevention by PARP inhibition, we studied the effects of a novel, potent PARP inhibitor, PJ34, a phenanthridinone derivative, on diabetes development in NOD mice and on diabetes recurrence in diabetic NOD mice transplanted with syngeneic islets. PJ34 administration from age 5 or 15 weeks significantly decreased insulitis, β-cell destruction and diabetes incidence, and protection from diabetes continued for 12 weeks after PJ34 therapy was stopped. Similarly, syngeneic islet graft survival was prolonged and outlasted therapy in PJ34-treated mice. Immunohistochemical studies revealed significantly fewer leukocytes in islet grafts of PJ34-treated mice, together with increased apoptosis of these cells and decreased expression of the T helper 1-type cytokine interferon (IFN)-γ. These results suggest that PARP inhibition protects against autoimmune β-cell destruction in NOD mice by inducing apoptosis of islet-infiltrating leukocytes and decreasing IFN-γ expression in the islets.
HIV Protease Inhibitors Acutely Impair Glucose-Stimulated Insulin Release
Authors: Koster Joseph C. , Remedi Maria S. , Qiu Haijun , Nichols Colin G. , Hruz Paul W.
Published: March 2007

HIV protease inhibitors (PIs) acutely and reversibly inhibit the insulin-responsive glucose transporter Glut 4, leading to peripheral insulin resistance and impaired glucose tolerance. Minimal modeling analysis of glucose tolerance tests on PI-treated patients has revealed an impaired insulin secretory response, suggesting additional pancreatic β-cell dysfunction. To determine whether β-cell function is acutely affected by PIs, we assayed glucose-stimulated insulin secretion in rodent islets and the insulinoma cell line MIN6. Insulin release from MIN6 cells and rodent islets was significantly inhibited by the PI indinavir with IC50 values of 1.1 and 2.1 μmol/l, respectively. The uptake of 2-deoxyglucose in MIN6 cells was similarly inhibited (IC50 of 2.0 μmol/l), whereas glucokinase activity was unaffected at drug levels as high as 1 mmol/l. Glucose utilization was also impaired at comparable drug levels. Insulin secretogogues acting downstream of glucose transport mostly reversed the indinavir-mediated inhibition of insulin release in MIN6 cells. Intravenous infusion of indinavir during hyperglycemic clamps on rats significantly suppressed the first-phase insulin response. These data suggest that therapeutic levels of PIs are sufficient to impair glucose sensing by β-cells. Thus, together with peripheral insulin resistance, β-cell dysfunction likely contributes to altered glucose homeostasis associated with highly active antiretroviral therapy.
Replication Increases β-Cell Vulnerability to Human Islet Amyloid Polypeptide-Induced Apoptosis
Authors: Ritzel Robert A. , Butler Peter C.
Published: March 2007

Type 2 diabetes is characterized by a relative β-cell deficit as a result of increased β-cell apoptosis and islet amyloid derived from the β-cell peptide islet amyloid polypeptide (IAPP). Human IAPP (h-IAPP) but not mouse IAPP (m-IAPP) induces apoptosis when applied to cells in culture, a property that depends on the propensity of h-IAPP to oligomerize. Since β-cell mass is regulated, the question arises as to why it is not adaptively increased in response to insulin resistance and hyperglycemia in type 2 diabetes. This adaptation might fail if dividing β-cells preferentially underwent apoptosis. We tested the hypothesis that β-cells are preferentially vulnerable to h-IAPP-induced apoptosis. We established a microculture environment to perform time-lapse video microscopy (TLVM) and studied β-cells (RIN) and HeLa cells undergoing replication or apoptosis. Sequential images (every 10 min for 36 h in RIN or 24 h in HeLa cells) of cells in vivo were analyzed, and each mitotic and apoptotic event was documented. Freshly dissolved h-IAPP caused a dose-dependent increased rate of apoptosis (P < 0.0001) in both cell types. At low and medium levels of toxicity, cells that had previously undergone mitosis were more vulnerable to h-IAPP-induced apoptosis than nondividing cells (P < 0.05). In the first 3 h after mitosis (full cell cycle length 26 ± 0.6 h), β-cells were particularly susceptible to h-IAPP-induced apoptosis (P < 0.05). Neither m-IAPP nor mature amyloid aggregates of h-IAPP were cytotoxic (P = 0.49). To corroborate these cell culture studies, we examined sections of human pancreatic tissue (five cases of type 2 diabetes) and human islets incubated for 48 h ± h-IAPP. Both were stained for apoptosis with the transferase-mediated dUTP nick-end labeling method and analyzed for the presence of paired apoptotic cells anticipated in the event of postmitotic apoptosis. In human pancreatic tissue 26 ± 5% (single plane of examination) and in human islets incubated with h-IAPP 44 ± 4% of apoptotic islet cells were paired. In conclusion, replicating β-cells are preferentially vulnerable to h-IAPP-induced apoptosis in cell culture. Postmitotic apoptosis was also documented in humans with type 2 diabetes and in human islet tissue. We postulate that β-cell deficiency in type 2 diabetes may result in part from failure to adaptively increase β-cell mass due to increased vulnerability of replicating β-cells to undergo apoptosis. If this postulate is correct, then inhibition of apoptosis should allow recovery of β-cell mass in type 2 diabetes.
The Daily Rhythm in Plasma Glucagon Concentrations in the Rat Is Modulated by the Biological Clock and by Feeding Behavior
Authors: Ruiter Marieke , La Fleur Susanne E. , van Heijningen Caroline , van der Vliet Jan , Kalsbeek Andries , Buijs Ruud M.
Published: March 2007

Plasma glucose concentrations display a daily rhythm generated by the hypothalamic biological clock, located in the suprachiasmatic nucleus (SCN). How the SCN orchestrates this rhythm is unknown. Because glucagon stimulates hepatic glucose production, we hypothesized that if glucagon has a daily rhythm, then it may be responsible for the glucose rhythm. From hourly blood samples, we determined daily glucagon concentrations for intact and SCN-lesioned rats. Intact ad libitum–fed rats showed a clear daily glucagon rhythm, and fasting resulted in an even more pronounced rhythm. It is interesting that a decrease in glucagon concentrations, instead of the expected increase, occurred already shortly after food removal. Toward the start of the active period, a peak in glucagon levels occurred, with concentrations similar to those measured in ad libitum–fed rats. SCN lesions abolished rhythmicity in plasma glucagon profiles. Scheduled-fed rats showed meal-induced glucagon peaks but also a daily rhythm in basal premeal glucagon concentrations. Plasma glucose concentrations of ad libitum–and scheduled-fed rats, however, were similar. In conclusion, feeding and the biological clock control 24-h plasma glucagon concentrations. In fed rats, glucagon is not responsible for the daily glucose rhythm. During fasting, however, glucagon may contribute to energy mobilization when the activity period starts.
PDX-1 Protein Containing Its Own Antennapedia-Like Protein Transduction Domain Can Transduce Pancreatic Duct and Islet Cells
Authors: Noguchi Hirofumi , Kaneto Hideaki , Weir Gordon C. , Bonner-Weir Susan
Published: March 2007

The pancreatic and duodenal homeobox factor-1 (PDX-1), also known as IDX-1/STF-1/IPF1, a homeodomain-containing transcription factor, plays a central role in regulating pancreatic development and insulin gene transcription. Furthermore, even in adults, PDX-1 is associated with islet neogenesis and differentiation of insulin-producing cells from progenitor cells. Here, we report for the first time that PDX-1 protein can permeate cells due to an Antennapedia-like protein transduction domain sequence in its structure and that transduced PDX-1 functions similarly to endogenous PDX-1; it binds to the insulin promoter and activates its expression. PDX-1 protein can also permeate into isolated pancreatic islets, which leads to stimulation of insulin gene expression. Moreover, PDX-1 protein transduced into cultures of pancreatic ducts, thought to be islet progenitor cells, induces insulin gene expression. These data suggest that PDX-1 protein transduction could be a safe and valuable strategy for enhancing insulin gene transcription and for facilitating differentiation of ductal progenitor cells into insulin-producing cells without requiring gene transfer technology.
Effect of Antecedent Hypoglycemia on Counterregulatory Responses to Subsequent Euglycemic Exercise in Type 1 Diabetes
Authors: Galassetti Pietro , Tate Donna , Neill Ray A. , Morrey Sachiko , Wasserman David H. , Davis Stephen N.
Published: March 2007

Exercise-related hypoglycemia is common in intensively treated patients with type 1 diabetes. The underlying mechanisms are not clearly defined. In nondiabetic subjects, hypoglycemia blunts counterregulatory responses to subsequent exercise. It is unknown whether this also occurs in type 1 diabetes. Therefore, the goal of this study was to test the hypothesis that prior hypoglycemia could result in acute counterregulatory failure during subsequent exercise in type 1 diabetes. A total of 16 type 1 diabetic patients (8 men and 8 women, HbA1c 7.8 ± 0.3%) were investigated during 90 min of euglycemic cycling exercise, following either two 2-h periods of previous-day hypoglycemia (2.9 mmol/l) or previous-day euglycemia. Patients’ counterregulatory responses (circulating levels of counterregulatory hormones, intermediary metabolites, substrate flux via indirect calorimetry, tracer-determined glucose kinetics, and cardiovascular measurements) were comprehensively assessed during exercise. Identical euglycemia and basal insulin levels were successfully maintained during all exercise studies, regardless of blood glucose levels during the previous day. After resting euglycemia, patients displayed normal counterregulatory responses to exercise. Conversely, when identical exercise was repeated after hypoglycemia, the glucagon response to exercise was abolished, and the epinephrine, norepinephrine, cortisol, endogenous glucose production, and lipolytic responses were reduced by 40–80%. This resulted in a threefold increase in the amount of exogenous glucose needed to maintain euglycemia during exercise. Our results demonstrate that antecedent hypoglycemia, in type 1 diabetes, can produce acute counterregulatory failure during a subsequent episode of prolonged moderate-intensity exercise. The metabolic consequence of the blunted neuroendocrine and autonomic nervous system counterregulatory responses was an acute failure of endogenous glucose production to match the increased glucose requirements during exercise. These data indicate that counterregulatory failure may be a significant in vivo mechanism responsible for exercise-associated hypoglycemia in type 1 diabetes.
Peroxisome Proliferator–Activated Receptor-α Agonist Treatment in a Transgenic Model of Type 2 Diabetes Reverses the Lipotoxic State and Improves Glucose Homeostasis
Authors: Kim Hyunsook , Haluzik Martin , Asghar Zeenat , Yau Daphne , Joseph Jamie W. , Fernandez Ana M. , Reitman Marc L. , Yakar Shoshana , Stannard Bethel , Heron-Milhavet Lisa , Wheeler Michael B. , LeRoith Derek
Published: March 2007

Abnormalities in insulin action are the characteristics of type 2 diabetes. Dominant-negative muscle-specific IGF-I receptor (MKR) mice exhibit elevated lipid levels at an early age and eventually develop type 2 diabetes. To evaluate the role of elevated lipids in the progression of the diabetic state, MKR mice were treated with WY14,643, a peroxisome proliferator–activated receptor (PPAR)-α agonist. WY14,643 treatment markedly reduced serum fatty acid and triglyceride levels within a few days, as well as muscle triglyceride levels, and subsequently normalized glucose and insulin levels in MKR mice. Hyperinsulinemic-euglycemic clamp analysis showed that WY14,643 treatment enhanced muscle and adipose tissue glucose uptake by improving whole-body insulin sensitivity. Insulin suppression of endogenous glucose production by the liver of MKR mice was also improved. The expression of genes involved in fatty acid oxidation was increased in liver and skeletal muscle, whereas gene expression levels of hepatic gluconeogenic enzymes were decreased in WY14,643-treated MKR mice. WY14,643 treatment also improved the pattern of glucose-stimulated insulin secretion from the perfused pancreata of MKR mice and reduced the β-cell mass. Taken together, these findings suggest that the reduction in circulating or intracellular lipids by activation of PPAR-α improved insulin sensitivity and the diabetic condition of MKR mice.
Relationship Between Diurnal Blood Pressure, Renal Hemodynamic Function, and the Renin-Angiotensin System in Type 1 Diabetes
Authors: Miller Judith A. , Curtis Jacqueline R. , Sochett Etienne B.
Published: March 2007

In patients with diabetes, altered diurnal blood pressure (BP) regulation (high night-to-day [N/D] ratio, or “nondipping”) is associated with increases in albumin excretion and a decline in the glomerular filtration rate (GFR) by an unknown mechanism. Because it is known that renin angiotensin system (RAS) activation and defective glucose control contribute to adverse renal outcomes, we examined renal responses to high glucose and to manipulation of the RAS in adolescents (mean age 14 ± 2 years) with uncomplicated type 1 diabetes, segregated into two groups on the basis of the presence or absence of normal N/D BP ratio. In the first experiment, renal hemodynamic comparisons were made during euglycemia (4–6 mmol/l) and hyperglycemia (9–11 mmol/l), maintained by modified clamp techniques. The induction of hyperglycemia resulted in a significant increase in GFR and filtration fraction (FF) in the high N/D ratio group. In the second experiment, we examined the renal response to graded angiotensin II (Ang II) infusion while subjects were euglycemic and salt replete. High N/D ratio was associated with an enhanced FF response to Ang II. In the third experiment, the N/D ratio and GFR were assessed after 3 weeks of ACE inhibition. This maneuver corrected the high N/D ratio, but it had no effect on glomerular hyperfiltration. These results suggest that RAS activation does not explain the hyperfiltration state, nor can it explain the poor outcomes, at least in this population. However, the observed deleterious hemodynamic responses to high glucose and Ang II and the insensitivity to ACE inhibition may, taken together, provide an explanation for the adverse renal outcomes in patients with type 1 diabetes and high N/D ratio.
Effects of Duration and Age at Onset of Type 1 Diabetes on Preclinical Manifestations of Nephropathy
Authors: Drummond Keith N. , Kramer Michael S. , Suissa Samy , Lévy-Marchal Claire , Dell’Aniello Sophie , Sinaiko Alan , Mauer Michael ,   for the *International Diabetic Nephropathy Study Group
Published: March 2007

Several studies have reported that the effect of type 1 diabetes disease duration on nephropathy may be greater during or after puberty than an equivalent number of years before puberty. The International Diabetic Nephropathy Study examined the effects of disease duration and age at onset on glomerular morphometry obtained from kidney biopsy in 243 young type 1 diabetic subjects with albumin excretion rates <100 μg/min: 184 with prepubertal onset, 35 with pubertal onset, and 24 with postpuberty onset. Outcomes included the volume fraction of the glomerulus occupied by the mesangium [Vv(Mes/glom)], glomerular basement membrane (GBM) width, and the surface density of peripheral glomerular capillary basement membrane per glomerulus Sv(PGBM/glom). Vv(Mes/glom) progressed slowly in the first 14 or 15 years after disease onset but more rapidly thereafter. GBM width increased, while Sv(PGBM/glom) decreased with increasing disease duration. No statistically significant differences in the effect of duration were observed among the three age-at-onset subgroups, even with multivariate adjustment for sex, center, baseline HbA1c concentration, diastolic blood pressure, height, and BMI. Our results may explain the conflicting results of previous studies regarding the effects of pre-versus postpuberty disease duration.
Variation in Type 2 Diabetes-Related Traits in Mouse Strains Susceptible to Diet-Induced Obesity
Authors: Rossmeisl Martin , Rim Jong S. , Koza Robert A. , Kozak Leslie P.
Published: March 2007

C57BL/6J (B6) and AKR/J (AKR) inbred strains of mice develop a comparable degree of obesity when fed a high-fat diet. However, although obese B6 mice are more glucose intolerant, obese AKR mice are more insulin resistant. To understand the basis for these strain differences, we characterized features of adiposity and glucose homeostasis in mice fed a high-fat diet for 8 weeks. The results indicated that despite hyperglycemia and impaired glucose tolerance, B6 mice have lower plasma insulin and are more insulin sensitive than AKR mice. Compared with adipose tissue of AKR mice, adipose tissue of B6 mice contained about threefold higher levels of total membrane-bound GLUT4 protein, whereas in skeletal muscle the levels were similar. Uptake of 2-[14C]deoxyglucose in vivo was reduced by a high-fat diet in adipose tissue, but not in skeletal muscle. Surprisingly, no significant differences in uptake occurred between the strains, despite the differences in GLUT4; however, glucose flux was calculated to be slightly higher in B6 mice. Higher expression of PEPCK in the liver of B6 mice, under both standard-diet and high-fat-diet conditions, suggests a plausible mechanism for elevated glycemia in these mice. In conclusion, phenotypic variation in insulin resistance and glucose production in the B6 and AKR strains could provide a genetic system for the identification of genes controlling glucose homeostasis.
Small-Conductance Calcium-Activated K+ Channels Are Expressed in Pancreatic Islets and Regulate Glucose Responses
Authors: Tamarina Natalia A. , Wang Yong , Mariotto Loris , Kuznetsov Andrey , Bond Chris , Adelman John , Philipson Louis H.
Published: March 2007

Glucose-stimulated insulin secretion is associated with transients of intracellular Ca2+ concentration [Ca2+]i in the pancreatic β-cell. We identified the expression and function of specific small-conductance Ca2+-activated K+ (SK) channel genes in insulin-secreting cells. The presence of mRNA for SK1, -2, -3, and -4 (intermediate-conductance Ca2+-activated K+ 1 [IK1]) channels was demonstrated by RT-PCR in rodent islets and insulinoma cells. SK2 and -3 proteins in mouse islets were detected by immunoblot and immunocytochemistry. In the tTA-SK3 tet-off mouse, a normal amount of SK3 protein was present in islets, but it became undetectable after exposure to doxycycline (DOX), which inhibits the transcription of the tTA-SK3 gene. The SK/IK channel-blockers apamin, dequalinium, and charybdotoxin caused increases in average [Ca2+]i levels and in frequency of [Ca2+]i oscillations in wild-type mouse islets. In SK3-tTA tet-off mice, the addition of apamin with glucose and tetraethylammonium (TEA) caused a similar elevation in [Ca2+]i, which was greatly diminished after DOX suppression of SK3 expression. We conclude that SK1, -2, -3, and IK1 (SK4) are expressed in islet cells and insulin-secreting cells and are able to influence glucose-induced calcium responses, thereby regulating insulin secretion.
Diabetogenic Potential of Human Pathogens Uncovered in Experimentally Permissive β-Cells
Authors: Flodström Malin , Tsai Devin , Fine Cody , Maday Amy , Sarvetnick Nora
Published: March 2007

Pancreatic β-cell antiviral defense plays a critical role in protection from coxsackievirus B4 (CVB4)-induced diabetes. In the present study, we tested the hypothesis that interferon (IFN)-induced antiviral defense determines β-cell survival after infection by the human pathogen CVB3, cytomegalovirus (CMV), and lymphocytic choriomeningitis virus (LCMV). We demonstrated that mice harboring β-cells that do not respond to IFN because of the expression of the suppressor of cytokine signaling-1 (SOCS-1) succumb to an acute form of type 1 diabetes after infection with CVB3. Interestingly, the tropism of the virus was altered in SOCS-1 transgenic (Tg) mice, and CVB3 was detected in islet cells of SOCS-1–Tg mice before β-cell loss and the onset of diabetes. Furthermore, insulitis was increased in SOCS-1–Tg mice after infection with murine CMV, and a minority of the mice developed overt diabetes. However, infection with LCMV failed to cause β-cell destruction in SOCS-1 Tg mice. These findings suggest that CVB3 can cause diabetes in a host lacking adequate β-cell antiviral defense, and that incomplete target cell antiviral defense may enhance susceptibility to diabetes triggered by CMV. In conclusion, suppressed β-cell antiviral defense reveals the diabetogenic potential of two pathogens previously linked to the onset of type 1 diabetes in humans.
Label-Retaining Cells in the Rat Pancreas
Authors: Duvillié Bertrand , Attali Myriam , Aiello Virginie , Quemeneur Eric , Scharfmann Raphael
Published: March 2007

Islets of Langerhans are micro-organs scattered throughout the pancreas that contain insulin-producing cells, called β-cells. Although new light has been recently shed on β-cell development, information on the phenotype and location of β-stem cells remains scarce. Here, we provide evidence that β-stem cells are slow-cycling cells located within and around the islets of Langerhans. First, using a bromodeoxyuridine (BrdU) pulse/chase approach, we detected BrdU-retaining cells in vivo in the islet area of rat pancreata. These cells were negative for endocrine markers but expressed Pdx1, a marker for pancreatic stem cells. Next, using an in vitro model that mimicked endocrine cell development, we found that BrdU-retaining cells were capable of differentiating into β-cells. Taken together, these observations demonstrate that BrdU retention is a property of β-stem cells.