bluuebunny/crossref_metadata_2025 huggingface dataset:
Palmitate Stimulation of Glucagon Secretion in Mouse Pancreatic α-Cells Results From Activation of l-Type Calcium Channels and Elevation of Cytoplasmic Calcium
Authors: Olofsson Charlotta S. , Salehi Albert , Göpel Sven O. , Holm Cecilia , Rorsman Patrik
Published: March 2007

We have investigated the short-term effects of the saturated free fatty acid (FFA) palmitate on pancreatic α-cells. Palmitate (0.5 or 1 mmol/l bound to fatty acid–free albumin) stimulated glucagon secretion from intact mouse islets 1.5- to 2-fold when added in the presence of 1–15 mmol/l glucose. Palmitate remained stimulatory in islets depolarized with 30 mmol/l extracellular K+ or exposed to forskolin, but it did not remain stimulatory after treatment with isradipine or triacsin C. The stimulatory action of palmitate on secretion correlated with a 3.5-fold elevation of intracellular free Ca2+ when applied in the presence of 15 mmol/l glucose, a 40% stimulation of exocytosis (measured as increases in cell capacitance), and a 25% increase in whole-cell Ca2+ current. The latter effect was abolished by isradipine, suggesting that palmitate selectively modulates l-type Ca2+ channels. The effect of palmitate on exocytosis was not mediated by palmitoyl-CoA, and intracellular application of this FFA metabolite decreased rather than enhanced Ca2+-induced exocytosis. The stimulatory effects of palmitate on glucagon secretion were paralleled by a ∼50% inhibition of somatostatin release. We conclude that palmitate increases α-cell exocytosis principally by enhanced Ca2+ entry via l-type Ca2+ channels and, possibly, relief from paracrine inhibition by somatostatin released by neighboring δ-cells.
Pioglitazone Reduces Islet Triglyceride Content and Restores Impaired Glucose-Stimulated Insulin Secretion in Heterozygous Peroxisome Proliferator–Activated Receptor-γ–Deficient Mice on a High-Fat Diet
Authors: Matsui Junji , Terauchi Yasuo , Kubota Naoto , Takamoto Iseki , Eto Kazuhiro , Yamashita Tokuyuki , Komeda Kajuro , Yamauchi Toshimasa , Kamon Junji , Kita Shunbun , Noda Mitsuhiko , Kadowaki Takashi
Published: March 2007

Heterozygous peroxisome proliferator–activated receptor-γ (PPAR-γ)-deficient (PPARγ+/−) mice were protected from high-fat diet–induced insulin resistance. To determine the impact of systemic reduction of PPAR-γ activity on β-cell function, we investigated insulin secretion in PPARγ+/− mice on a high-fat diet. Glucose-induced insulin secretion in PPARγ+/− mice was impaired in vitro. The tissue triglyceride (TG) content of the white adipose tissue, skeletal muscle, and liver was decreased in PPARγ+/− mice, but it was unexpectedly increased in the islets, and the increased TG content in the islets was associated with decreased glucose oxidation. Administration of a PPAR-γ agonist, pioglitazone, reduced the islet TG content in PPARγ+/− mice on a high-fat diet and ameliorated the impaired insulin secretion in vitro. Our results demonstrate that PPAR-γ protects islets from lipotoxicity by regulating TG partitioning among tissues and that a PPAR-γ agonist can restore impaired insulin secretion under conditions of islet fat accumulation.
Impact of Intra-Abdominal Fat and Age on Insulin Sensitivity and β-Cell Function
Authors: Utzschneider Kristina M. , Carr Darcy B. , Hull Rebecca L. , Kodama Keiichi , Shofer Jane B. , Retzlaff Barbara M. , Knopp Robert H. , Kahn Steven E.
Published: March 2007

The prevalence of glucose intolerance and type 2 diabetes increases with age. To determine whether the hyperbolic relationship between insulin sensitivity and the insulin response is affected by age and whether the decline in β-cell function with age is related to increases in intra-abdominal fat or age per se, we studied 220 healthy subjects with fasting glucose <6.1 mmol/l (89 men and 131 women, aged 26–75 years, BMI 18.7–40.4 kg/m2). The insulin sensitivity index (Si) and the acute insulin response to glucose (AIRg) were determined, and from these β-cell function was estimated as the disposition index (Si × AIRg). Intra-abdominal fat and subcutaneous fat areas were quantified by computed tomography. Si (5.40 ± 0.5 vs. 7.86 ± 0.7 ×10−5 min−1/[pmol/l]), P < 0.01) was decreased and intra-abdominal fat (117 ± 10 vs. 81 ± 9 cm2, P < 0.05) was increased in the oldest (age 60–75 years) versus the youngest (age 26–44 years) quartile. The hyperbolic relationship between Si and AIRg was present independent of age; thus, β-cell function measured as the disposition index (1,412 ± 120 vs. 2,125 ± 150 ×10−5 min−1, P < 0.01) was lower in the oldest versus the youngest quartile. In multiple regression, intra-abdominal fat (r = −0.470, P < 0.001) but not age was associated with Si, but both intra-abdominal fat (r = −0.198, P = 0.003) and age (r = −0.131, P = 0.05) were correlated with the disposition index. These data suggest that although intra-abdominal fat is a strong determinant of insulin sensitivity and β-cell function, age has an independent effect on β-cell function that may contribute to the increased prevalence of type 2 diabetes in older populations.
Interactions Between Hyperglycemia and Hypoxia
Authors: Nyengaard Jens R. , Ido Yassuo , Kilo Charles , Williamson Joseph R.
Published: March 2007

The primary aim of these experiments was to assess in vitro effects of hyperglycemia (30 mmol/l glucose) and hypoxia (Po2 = 36 torr) of 2-h duration, separately and in combination, on cytosolic and mitochondrial free NADH (NADHc and NADHm, respectively) in retinas from normal rats. NADH is the major carrier of electrons and protons that fuel ATP synthesis and several metabolic pathways linked to diabetic complications. Hyperglycemia and hypoxia increase free NADHc by different mechanisms that are additive. Hyperglycemia increases transfer of electrons and protons from sorbitol to NAD+c, reducing it to NADHc, but does not increase NADHm. Hypoxia increases NADHm by inhibiting its oxidation. Electrons and protons accumulating in NADHm restrain transfer of electrons and protons from NADHc to NAD+m via the malate-aspartate electron shuttle. Hyperglycemia and hypoxia also increase glycolysis by different mechanisms that are additive, and hyperglycemia increases ATP levels in hypoxic and in aerobic retinas. The additive effects of hyperglycemia and hypoxia on accumulation of electrons and protons in a common pool of free NADHc confirm the test hypothesis and the potential of a combination of these two risk factors to accelerate the onset and progression of diabetic retinopathy (and other complications of diabetes) by augmenting metabolic pathways fueled by free NADHc.
Podocyte-Derived Vascular Endothelial Growth Factor Mediates the Stimulation of α3(IV) Collagen Production by Transforming Growth Factor-β1 in Mouse Podocytes
Authors: Chen Sheldon , Kasama Yuki , Lee Joseph S. , Jim Belinda , Marin Maria , Ziyadeh Fuad N.
Published: March 2007

Podocyte-derived vascular endothelial growth factor (VEGF) is upregulated in diabetes and may contribute to albuminuria. Although believed to act upon the glomerular endothelium, VEGF may have pronounced effects on the podocyte itself. The functionality of this VEGF autocrine loop was investigated in conditionally immortalized mouse podocytes. Exogenous VEGF164 increased the production of α3(IV) collagen, an integral component of the glomerular basement membrane (GBM); this effect was completely prevented by SU5416, a pan-VEGF receptor inhibitor. The VEGF inhibitor also partially prevented the stimulation of α3(IV) collagen by transforming growth factor (TGF)-β1, establishing a novel role for endogenous VEGF. However, VEGF did not influence the production of another novel chain of collagen IV, α5(IV) collagen, and SU5416 failed to reverse the known inhibitory effect of TGF-β1 on α5(IV) collagen production. Cultured mouse podocytes possess at least the VEGFR-1 receptor, confirmed by RT-PCR, immunoblotting, and immunocytochemistry. By these techniques, however, VEGFR-2 is absent. VEGF signaling proceeds via autophosphorylation of VEGFR-1 and activation of the phosphatidylinositol 3-kinase (PI3K) pathway. Thus, podocyte-derived VEGF operates in an autocrine loop, likely through VEGFR-1 and PI3K, to stimulate α3(IV) collagen production. The TGF-β1–stimulated endogenous VEGF may have significant implications for podocyte dysfunction in diabetic glomerulopathy, manifesting as GBM thickening and altered macromolecular permeability.
Association of Protein Tyrosine Phosphatase 1B Gene Polymorphisms With Measures of Glucose Homeostasis in Hispanic Americans
Authors: Palmer Nicholette D. , Bento Jennifer L. , Mychaleckyj Josyf C. , Langefeld Carl D. , Campbell Joel K. , Norris Jill M. , Haffner Stephen M. , Bergman Richard N. , Bowden Donald W.
Published: March 2007

Protein tyrosine phosphatase (PTP)-1B, encoded by the PTPN1 gene, catalyzes the dephosphorylation of proteins at tyrosyl residues. PTP-1B has been implicated in negatively regulating insulin signaling by dephosphorylating the phosphotyrosine residues of the insulin receptor. The genetic contribution of PTPN1 to measures of glucose homeostasis has been assessed in 811 Hispanic subjects from the Insulin Resistance Atherosclerosis Study Family Study (IRASFS). Thirty-five single nucleotide polymorphisms (SNPs) spanning 161 kb and containing the PTPN1 gene were genotyped and tested for association. All 20 SNPs with minor allele frequencies >0.1 in a single haplotype block covering the PTPN1 genomic sequence show significant association with the insulin sensitivity index (Si) (P = 0.044–0.003) and fasting glucose (P = 0.029 to <0.001). In contrast, there is no evidence for association of PTPN1 polymorphisms with acute insulin response (a measure of β-cell function). Haplotype analysis of eight SNP haplotypes that have independently been shown to be associated with type 2 diabetes risk and protection in Caucasian type 2 diabetic subjects are associated with lower (P = 0.007) and higher (P = 0.0002) Si and higher (P = 0.00007) and lower (P = 0.001) fasting glucose, respectively, in the IRASFS. This comprehensive genetic analysis of PTPN1 reveals significant association with metabolic traits consistent with the proposed in vivo role for the PTP-1B protein.
Characterization of Mice Doubly Transgenic for Parathyroid Hormone-Related Protein and Murine Placental Lactogen
Authors: Fujinaka Yuichi , Sipula Darinka , Garcia-Ocaña Adolfo , Vasavada Rupangi C.
Published: March 2007

Transgenic overexpression of either parathyroid hormone-related peptide (PTHrP) or mouse placental lactogen type 1 (mPL1) in pancreatic β-cells, using the rat insulin II promoter (RIP), results in islet hyperplasia either through prolonged β-cell survival or through increased β-cell proliferation and hypertrophy, respectively. For determining whether the two proteins might exert complementary, additive, or synergistic effects on islet mass and function when simultaneously overexpressed in β-cells in vivo, RIP-PTHrP and RIP-mPL1 mice were crossed to generate mice doubly transgenic for PTHrP and mPL1. These double-transgenic mice displayed marked islet hyperplasia (threefold), hypoglycemia, increased β-cell proliferation (threefold), and resistance to the diabetogenic and cytotoxic effects of streptozotocin compared with their normal siblings. Although the phenotype of the double-transgenic mice was neither additive nor synergistic relative to their single-transgenic counterparts, it was indeed complementary, yielding the maximal salutary phenotypic features of both individual transgenes. Finally, mPL1, for the first time, was shown to exert a protective effect on the survival of β-cells, placing it among the few proteins that can improve function and proliferation and prolong the survival of β-cells. Placental lactogen 1 is an attractive target for future therapeutic strategies in diabetes.
Pancreatic-Specific Inactivation of IGF-I Gene Causes Enlarged Pancreatic Islets and Significant Resistance to Diabetes
Authors: Lu Yarong , Herrera Pedro L. , Guo Yubin , Sun David , Tang Zhengyi , LeRoith Derek , Liu Jun-Li
Published: March 2007

The dogma that IGF-I stimulates pancreatic islet growth has been challenged by combinational targeting of IGF or IGF-IR (IGF receptor) genes as well as β-cell–specific IGF-IR gene deficiency, which caused no defect in islet cell growth. To assess the physiological role of locally produced IGF-I, we have developed pancreatic-specific IGF-I gene deficiency (PID) by crossing Pdx1-Cre and IGF-I/loxP mice. PID mice are normal except for decreased blood glucose level and a 2.3-fold enlarged islet cell mass. When challenged with low doses of streptozotocin, control mice developed hyperglycemia after 6 days that was maintained at high levels for at least 2 months. In contrast, PID mice only exhibited marginal hyperglycemia after 12 days, maintained throughout the experiment. Fifteen days after streptozotocin, PID mice demonstrated significantly higher levels of insulin production. Furthermore, streptozotocin-induced β-cell apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL] assay) was significantly prevented in PID mice. Finally, PID mice exhibited a delayed onset of type 2 diabetes induced by a high-fat diet, accompanied by super enlarged pancreatic islets, increased insulin mRNA levels, and preserved sensitivity to insulin. Our results suggest that locally produced IGF-I within the pancreas inhibits islet cell growth; its deficiency provides a protective environment to the β-cells and potential in combating diabetes.
Phenotypic Characteristics of GAD Antibody-Positive Recently Diagnosed Patients With Type 2 Diabetes in North America and Europe
Authors: Zinman Bernard , Kahn Steven E. , Haffner Steven M. , O’Neill M. Colleen , Heise Mark A. , Freed Martin I. ,   ADOPT Study Group*
Published: March 2007

A number of patients with type 2 diabetes are GAD antibody positive. A Diabetes Outcome Progression Trial (ADOPT) is a randomized, double-blind clinical trial in recently diagnosed drug-naïve patients with type 2 diabetes that allows for the evaluation of GAD positivity in the context of anthropometric and biochemical characteristics. Of the 4,134 subjects enrolled in ADOPT for whom GAD status was obtained, 174 (4.2%) were GAD positive, with the prevalence of GAD antibodies being similar in North America (4.7%) and Europe (3.7%). Although BMI and age were similar, GAD-positive patients had a lower fasting insulin level, compatible with them being more insulin sensitive. The lower fasting insulin concentration was accompanied by a decreased early insulin response to oral glucose. However, when this insulin response was corrected for the degree of insulin sensitivity, GAD-positive and -negative patients had similar β-cell function. Consistent with the difference in insulin sensitivity, GAD-positive patients had higher HDL cholesterol and lower triglyceride levels. In the GAD-positive individuals, the prevalence of the metabolic syndrome as defined by NCEP ATP III (National Cholesterol Education Program Adult Treatment Panel III) was also lower (74.1 vs. 83.7%, P = 0.0009). These phenotypic differences may underlie a potential difference in the natural history of hyperglycemia and its clinical outcomes.
Hyperlipidemia in Concert With Hyperglycemia Stimulates the Proliferation of Macrophages in Atherosclerotic Lesions
Authors: Lamharzi Najib , Renard Catherine B. , Kramer Farah , Pennathur Subramaniam , Heinecke Jay W. , Chait Alan , Bornfeldt Karin E.
Published: March 2007

Hyperglycemia and hyperlipidemia are important risk factors for diabetes-accelerated atherosclerosis. Macrophage proliferation has been implicated in the progression of atherosclerosis. We therefore investigated the effects of hyperglycemia and hyperlipidemia on macrophage proliferation in murine atherosclerotic lesions and isolated primary macrophages. Hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-free diet for 12 weeks did not have elevated cholesterol levels compared with nondiabetic mice, and there was no evidence of increased macrophage proliferation in atherosclerotic lesions. Moreover, elevated glucose levels did not increase proliferation of isolated mouse peritoneal macrophages. In contrast, hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-rich diet showed increased cholesterol levels concomitant with macrophage proliferation in atherosclerotic lesions. Glucose promoted lipid and protein oxidation of LDL in vitro. Glucose-oxidized LDL resulted in phosphorylation of extracellular signal-regulated kinase and protein kinase B/Akt and stimulated proliferation of isolated macrophages. The mitogenic effect of glucose-oxidized LDL was mediated by CD36 and by extracellular signal-regulated kinase activation induced by protein kinase C-dependent and phosphatidylinositol 3-kinase-dependent pathways. Thus, hyperglycemia is not sufficient to stimulate macrophage proliferation in lesions of atherosclerosis or in isolated macrophages. A combination of hyperglycemia and hyperlipidemia, however, stimulates macrophage proliferation by a pathway that may involve the glucose-dependent oxidation of LDL.
Linkage Analysis of Diabetes Status Among Hypertensive Families
Authors: Avery Christy L. , Freedman Barry I. , Heiss Gerardo , Kraja Aldi , Rice Treva , Arnett Donna , Miller Michael B. , Pankow James S. , Lewis Cora E. , Myers Richard H. , Hunt Steven C. , Almasy Laura , North Kari E.
Published: March 2007

Type 2 diabetes susceptibility is determined by multiple genetic and environmental factors. Genome-wide linkage scans have localized common regions, possibly harboring susceptibility genes on chromosomes 1, 2, 12, and 20. Variability in linkage findings underscores the probable genetic heterogeneity of type 2 diabetes. Thus, we conducted a genome scan of diabetes status using maximum likelihood methods that model affection status by a liability threshold model. Hypertensive sibships and their offspring and/or parents in the Hypertension Genetic Epidemiology Network study were recruited from five field centers. The diabetes phenotype was derived using the World Health Organization criteria and adjusted for race/study center, age, age2, sex, and with and without percent body fat. In total, 567 diabetic participants were identified in 437 families. Variance component linkage analysis was performed among 1,545 Caucasians and 1,608 African Americans using race-specific marker allele frequencies. We detected a quantitative trait loci (QTLs) influencing diabetes variance (logarithm of odds = 3.4) on chromosome 22, which overlaps a positive type 2 diabetes finding among Canadian Oji-Cree Indians. We also observed suggestive evidence for linkage on chromosomes 1, 2, 5, 8, 14, 17, and 19. The identification and replication of type 2 diabetes QTLs will bring us closer to the detection of functional genes that influence diabetes susceptibility.
Variation in the Interleukin-6 Receptor Gene Associates With Type 2 Diabetes in Danish Whites
Authors: Hamid Yasmin H. , Urhammer Søren A. , Jensen Dorit P. , Glümer Charlotte , Borch-Johnsen Knut , Jørgensen Torben , Hansen Torben , Pedersen Oluf
Published: March 2007

Interleukin-6 (IL-6) is a pleiotropic cytokine involved in the pathophysiology of various human diseases such as type 2 diabetes and obesity. IL-6 signals via a heterodimeric receptor complex consisting of a soluble IL-6 α-subunit (IL-6 receptor [IL6R]) and a signal transducing subunit (gp130). The IL6R gene maps to an important candidate locus for type 2 diabetes on chromosome 1q21. An Asp358Ala polymorphism of the IL6R has been reported to associate with obesity in Pima Indians. We investigated the Asp358Ala polymorphism in relation to type 2 diabetes, obesity, and other pre-diabetic quantitative traits among Danish whites. By applying a recessive genetic model in a case-control study of 1,349 type 2 diabetic patients and 4,596 glucose-tolerant control subjects, we found a significant difference in genotype distribution (P = 0.008) and in allele frequency (Ala-allele 38.3% [95% CI 36.5–40.1] in diabetic subjects vs. 41.2% [40.2–42.2] in control subjects; P = 0.007). The odds ratio for the Asp/Asp carriers versus Ala/Ala carriers was 1.38 (1.09–1.71). Among 4,251 middle-aged glucose-tolerant subjects, the Asp358Ala polymorphism was not associated with estimates of obesity, post–oral glucose tolerance test serum insulin release, or the homeostasis model assessment of insulin resistance index. In conclusion, the Asp358Ala polymorphism of the IL6R associates with type 2 diabetes in Danish whites.
Autoimmune Diabetes and the Circle of Tolerance
Authors: Rossini Aldo A.
Published: March 2007

The concept of immunological tolerance is central to our understanding of type 1 diabetes and the development of strategies for its prediction, prevention, and cure. Tolerance simply refers to the absence of an immune response. Most of us are born with an immune system that develops tolerance to all the other systems of our bodies as well as to the things that we eat. It is the loss of immunological tolerance that leads to autoimmunity. And when that autoimmune response directly or indirectly targets the β-cell, type 1 diabetes is the result. In the U.S., 1 in 600 of us loses tolerance to pancreatic β-cells. Interference with T-cell function after the loss of tolerance, as can be achieved with immunosuppressive drugs like cyclosporin, arrests the disease, but the cost in side effects is high. Clearly, stopping the loss of tolerance would be preferable. If we can stop the loss of tolerance, we can prevent the disease. We and many others have investigated both approaches. But what of the people who already have diabetes? For them a separate but related strategy, tolerance induction, is required. Specifically, islet transplantation tolerance induction holds out the promise of being able to cure the disease. This has been the ultimate goal of our laboratory’s work for the past two decades.
Chronic Sympathetic Activation
Authors: Seals Douglas R. , Bell Christopher
Published: March 2007

Primary aging in adult humans is associated with a progressive, tonic activation of the peripheral sympathetic nervous system (SNS). The purpose of this SNS activation and its physiological impact are, however, unknown. We hypothesize that the chronic stimulation of the SNS with aging is driven in part by a progressive accumulation of body fat. This “error” is sensed by the central nervous system via increases in adiposity-sensitive humoral signals (e.g., leptin, insulin) that cross the blood-brain barrier, activate subcortical areas involved in the regulation of energy balance (e.g., ventromedial hypothalamus), and stimulate SNS outflow to peripheral tissues. The SNS activation is intended to increase β-adrenergic thermogenesis in order to expend excess energy as heat rather than by storage of fat. Recent evidence, however, indicates that these adjustments are not effective in augmenting energy expenditure with aging. Indeed, older sedentary adults demonstrate reduced, not increased, β-adrenergic stimulation of metabolic rate because of reduced tissue responsiveness, presumably mediated by SNS-induced impairment of β-adrenergic signaling. As a result, age-associated SNS activation, initiated as a consequence of accumulating adiposity with the intent of preventing further fat storage, ironically, may in time evolve into a potential mechanism contributing to the development of obesity with aging.
Suppression of Endogenous Glucose Production by Mild Hyperinsulinemia During Exercise Is Determined Predominantly by Portal Venous Insulin
Authors: Camacho Raul C. , Pencek R. Richard , Lacy D. Brooks , James Freyja D. , Wasserman David H.
Published: March 2007

Hyperinsulinemia during exercise in people with diabetes requiring exogenous insulin is a major clinical problem. The aim of this study was to assess the significance of portal vein versus arterial insulin to hepatic effects of hyperinsulinemia during exercise. Dogs had sampling (artery, portal vein, and hepatic vein) and infusion (vena cava and portal vein) catheters and flow probes (hepatic artery and portal vein) implanted >16 days before a study. Protocols consisted of equilibration (−130 to −30 min), basal (−30 to 0 min), and treadmill exercise (0–150 min) periods. Somatostatin was infused and glucagon and insulin were replaced in the portal vein to achieve basal arterial and portal vein levels at rest and simulated levels during the first 60 min of exercise. From 60 to 150 min of exercise, the simulated insulin infusion was sustained (C; n = 7), modified to selectively create a physiologic increment in arterial insulin (Pe; n = 7), or altered to increase arterial insulin as in Pe but with a concomitant increase in portal insulin (PePo; n = 7). Euglycemic clamps were performed in all studies. Portal and arterial insulin were 15 ± 2 and 4 ± 1 μU/ml (mean ± SE of all groups), respectively, at t = 60 min in all groups. Insulin levels were unchanged for the remainder of the exercise period in C. Arterial insulin was increased from 3 ± 1 to 14 ± 2 μU/ml, whereas portal insulin did not change in Pe after t = 60 min. Arterial insulin was increased from 3 ± 1 to 15 ± 2 μU/ml, and portal insulin was increased from 16 ± 3 to 33 ± 3 μU/ml in PePo after t = 60 min. Endogenous glucose production (Ra) rose similarly from basal during the first 60 min of exercise in all groups (mean ± SE of all groups was from 2.2 ± 0.1 to 6.8 ± 0.5 mg · kg−1 · min−1). The increase in Ra was sustained for the remainder of the exercise period in C. Ra was suppressed by ∼40%, but only after 60 min of hyperinsulinemia, and by ∼20% after 90 min of hyperinsulinemia in Pe. In contrast, the addition of portal venous hyperinsulinemia caused ∼90% suppression of Ra within 20 min and for the remainder of the experiment in PePo. Measurements of net hepatic glucose output were similar to Ra responses in all groups. Arterial free fatty acids (FFAs), a stimulus of Ra, were increased to 1,255 ± 258 μmol/l in C but were only 459 ± 67 and 312 ± 42 μmol/l in Pe and PePo, respectively, by 150 min of exercise. Thus, during exercise, the exquisite sensitivity of Ra to hyperinsulinemia is due entirely to portal venous hyperinsulinemia during the first 60 min, after which peripheral hyperinsulinemia may control ∼20–40%, possibly as a result of inhibition of the exercise-induced increase in FFA.
Effect of Moderate Exercise Training on Peripheral Glucose Effectiveness, Insulin Sensitivity, and Endogenous Glucose Production in Healthy Humans Estimated by a Two-Compartment-Labeled Minimal Model
Authors: Nishida Yuichiro , Tokuyama Kumpei , Nagasaka Shoichiro , Higaki Yasuki , Shirai Yoko , Kiyonaga Akira , Shindo Munehiro , Kusaka Ikuyo , Nakamura Tomoatsu , Ishibashi Shun , Tanaka Hiroaki
Published: March 2007

For examining the effects of moderate exercise training on peripheral glucose effectiveness (Sg2*), insulin sensitivity (Si2*), and endogenous glucose production (EGP), seven men and one woman (24.8 ± 1.8 years) participated in cycle ergometer training at lactate threshold intensity for 60 min/day, 5 days/week for 12 weeks. Stable-labeled frequently sampled intravenous glucose tolerance tests were performed before and 16 h and 1 week after the last training session. Sg2* (pre 0.71 ± 0.03 × 10−2, 16 h 0.85 ± 0.02 × 10−2 dl · kg−1 · min−1) and Si2* (pre 12.6 ± 2.6 × 10−4, 16 h 19.7 ± 3.3 × 10−4 dl · kg−1 · min−1 · [μU/ml]−1), analyzed using the two-compartment minimal model, were significantly elevated 16 h after the last training session. The elevated Sg2* remained higher despite the cessation of exercise training for 1 week (1.00 ± 0.03 × 10−2 dl · kg−1 · min−1). EGP was suppressed within 20 min after glucose bolus, and the suppression of EGP was followed by their overshoot. The time course of EGP during the intravenous glucose tolerance test remained similar after the training period. In conclusion, moderate exercise training at lactate threshold improves not only peripheral insulin sensitivity but also peripheral glucose effectiveness with no change in the effect of glucose and/or insulin to suppress EGP in healthy humans.
Ca2+ and AMPK Both Mediate Stimulation of Glucose Transport by Muscle Contractions
Authors: Wright David C. , Hucker Kathleen A. , Holloszy John O. , Han Dong Ho
Published: March 2007

It is now generally accepted that activation of AMP-activated protein kinase (AMPK) is involved in the stimulation of glucose transport by muscle contractions. However, earlier studies provided evidence that increases in cytosolic Ca2+ mediate the effect of muscle contractions on glucose transport. The purpose of this study was to test the hypothesis that both the increase in cytosolic Ca2+ and the activation of AMPK are involved in the stimulation of glucose transport by muscle contractions. Caffeine causes release of Ca2+ from the sarcoplasmic reticulum. Incubation of rat epitrochlearis muscles with a concentration of caffeine that raises cytosolic Ca2+ to levels too low to cause contraction resulted in an approximate threefold increase in glucose transport. Caffeine treatment also resulted in increased phosphorylation of calmodulin-dependent protein kinase (CAMK)-II in epitrochlearis muscle. The stimulation of glucose transport by caffeine was blocked by the Ca2+-CAMK inhibitors KN62 and KN93. Activation of AMPK with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) also resulted in an approximate threefold increase in glucose transport in the epitrochlearis. The increases in glucose transport induced by AICAR and caffeine were additive, and their combined effect was not significantly different from that induced by maximally effective contractile activity. KN62 and KN93 caused an ∼50% inhibition of the stimulation of glucose transport by contractile activity. Our results provide evidence that both Ca2+ and AMPK are involved in the stimulation of glucose transport by muscle contractions. They also suggest that the stimulation of glucose transport by Ca2+ involves activation of CAMK.
Stratification of Type 1 Diabetes Risk on the Basis of Islet Autoantibody Characteristics
Authors: Achenbach Peter , Warncke Katharina , Reiter Jürgen , Naserke Heike E. , Williams Alistair J.K. , Bingley Polly J. , Bonifacio Ezio , Ziegler Anette-G.
Published: March 2007

Family history of type 1 diabetes and autoantibodies to the islet antigens insulin (IAA), glutamate decarboxylase (GADA), and the protein tyrosine phosphatase-like protein IA-2 (IA-2A) are strong predictors of type 1 diabetes, but the rate of progression to diabetes in multiple islet autoantibody-positive relatives varies widely. We asked whether detailed characterization of islet autoantibodies that included determination of titer, epitope specificity, and IgG subclass would improve diabetes prediction in a large cohort of autoantibody-positive relatives. The study shows a strong association between risk and high titer, broad antibody responses to IA-2 and insulin. The highest risks were associated with high-titer IA-2A and IAA, IgG2, IgG3, and/or IgG4 subclass of IA-2A and IAA, and antibodies to the IA-2-related molecule IA-2β. Using models based on these antibody characteristics, autoantibody-positive relatives can be classified into groups with risks of diabetes ranging from 7 to 89% within 5 years.
Role for Plasma Membrane-Related Ca2+-ATPase-1 (ATP2C1) in Pancreatic β-Cell Ca2+ Homeostasis Revealed by RNA Silencing
Authors: Mitchell Kathryn J. , Tsuboi Takashi , Rutter Guy A.
Published: March 2007

Changes in intracellular Ca2+ concentration play a key role in the regulation of insulin secretion by glucose and other secretagogues. Here, we explore the importance of the secretory pathway Ca2+-ATPase, plasma membrane-related Ca2+-ATPase-1 (PMR1; human orthologue ATP2C1) in intracellular Ca2+ homeostasis in pancreatic islet β-cells. Endogenous PMR1 mRNA and protein were detected in both isolated rat islets and β-cell-derived lines (MIN6 and INS1). Subcellular fractionation of the cell lines revealed PMR1 immunoreactivity in both microsomal and dense-core secretory vesicle-enriched fractions. Correspondingly, depletion of cellular PMR1 with small interfering RNAs inhibited Ca2+ uptake into the endoplasmic reticulum and secretory vesicles by ∼20%, as assessed using organelle-targeted aequorins in permeabilized INS1 cells. In intact cells, PMR1 depletion markedly enhanced flux though l-type Ca2+ channels and augmented glucose-stimulated, but not basal, insulin secretion. Whereas average cytosolic [Ca2+] increases in response to 30.0 mmol/l glucose were unaffected by PMR1 depletion, [Ca2+] oscillation shape, duration, and decay rate in response to glucose plus tetraethylammonium were modified in PMR1-depleted single cells, imaged using fluo-3-acetoxymethylester. PMR1 thus plays an important role, which is at least partially nonoverlapping with that of sarco(endo-)plasmic reticulum Ca2+-ATPases, in the control of β-cell Ca2+ homeostasis and insulin secretion.
Absence of Inducible Nitric Oxide Synthase Reduces Myocardial Damage During Ischemia Reperfusion in Streptozotocin-Induced Hyperglycemic Mice
Authors: Marfella Raffaele , Di Filippo Clara , Esposito Katherine , Nappo Francesco , Piegari Elena , Cuzzocrea Salvatore , Berrino Liberato , Rossi Francesco , Giugliano Dario , D’Amico Michele
Published: March 2007

We investigated the role of inducible nitric oxide synthase (iNOS) on ischemic myocardial damage and angiogenic process in genetically deficient iNOS (iNOS−/−) mice and wild-type littermates (iNOS+/+), with and without streptozotocin-induced (70 mg/kg intravenously) diabetes. After ischemia (25 min) and reperfusion (120 min), both iNOS+/+ and iNOS−/− diabetic mice (blood glucose 22 mmol/l) had myocardial infarct size greater than their respective nondiabetic littermates (P < 0.01). Myocardial infarct size (P < 0.05), apoptotic index (P < 0.005), and tissue levels of tumor necrosis factor (P < 0.01), interleukin-6 (P < 0.01), and interleukin-18 (P < 0.01) were higher in nondiabetic iNOS−/− mice compared with nondiabetic iNOS+/+ mice. As compared with diabetic iNOS−/− mice, diabetic iNOS+/+ mice showed a greater infarct size (P < 0.01) associated with the highest tissue levels of nitrotyrosine and proinflammatory cytokines, as well as apoptosis. The beneficial role of iNOS in modulating defensive responses against ischemia/reperfusion injury seems to be abolished in diabetic mice.
Mitochondrial Diabetes
Authors: Maassen J. Antonie , ‘t Hart Leen. M. , van Essen Einar , Heine Rob J. , Nijpels Giel , Jahangir Tafrechi Roshan S. , Raap Anton K. , Janssen George M.C. , Lemkes Herman H.P.J.
Published: March 2007

Mutations in mitochondrial DNA (mtDNA) associate with various disease states. A few mtDNA mutations strongly associate with diabetes, with the most common mutation being the A3243G mutation in the mitochondrial DNA-encoded tRNA(Leu,UUR) gene. This article describes clinical characteristics of mitochondrial diabetes and its molecular diagnosis. Furthermore, it outlines recent developments in the pathophysiological and molecular mechanisms leading to a diabetic state. A gradual development of pancreatic β-cell dysfunction upon aging, rather than insulin resistance, is the main mechanism in developing glucose intolerance. Carriers of the A3243G mutation show during a hyperglycemic clamp at 10 mmol/l glucose a marked reduction in first- and second-phase insulin secretion compared with noncarriers. The molecular mechanism by which the A3243G mutation affects insulin secretion may involve an attenuation of cytosolic ADP/ATP levels leading to a resetting of the glucose sensor in the pancreatic β-cell, such as in maturity-onset diabetes of the young (MODY)-2 patients with mutations in glucokinase. Unlike in MODY2, which is a nonprogressive form of diabetes, mitochondrial diabetes does show a pronounced age-dependent deterioration of pancreatic function indicating involvement of additional processes. Furthermore, one would expect that all mtDNA mutations that affect ATP synthesis lead to diabetes. This is in contrast to clinical observations. The origin of the age-dependent deterioration of pancreatic function in carriers of the A3243G mutation and the contribution of ATP and other mitochondrion-derived factors such as reactive oxygen species to the development of diabetes is discussed.
Prevention of Mitochondrial Oxidative Damage as a Therapeutic Strategy in Diabetes
Authors: Green Katherine , Brand Martin D. , Murphy Michael P.
Published: March 2007

Hyperglycemia causes many of the pathological consequences of both type 1 and type 2 diabetes. Much of this damage is suggested to be a consequence of elevated production of reactive oxygen species by the mitochondrial respiratory chain during hyperglycemia. Mitochondrial radical production associated with hyperglycemia will also disrupt glucose-stimulated insulin secretion by pancreatic β-cells, because pancreatic β-cells are particularly susceptible to oxidative damage. Therefore, mitochondrial radical production in response to hyperglycemia contributes to both the progression and pathological complications of diabetes. Consequently, strategies to decrease mitochondrial radical production and oxidative damage may have therapeutic potential. This could be achieved by the use of antioxidants or by decreasing the mitochondrial membrane potential. Here, we outline the background to these strategies and discuss how antioxidants targeted to mitochondria, or selective mitochondrial uncoupling, may be potential therapies for diabetes.
Structure, Activation, and Biology of Calpain
Authors: Suzuki Koichi , Hata Shoji , Kawabata Yukiko , Sorimachi Hiroyuki
Published: March 2007

Variation in the calpain 10 gene has recently been shown to be associated with type 2 diabetes by positional cloning. Since then, studies on calpain 10 have been started in correlation with diabetes and insulin-mediated signaling. In this review, the activation mechanism of calpain by calcium ions, which is essential to understand its physiological functions, is discussed on the basis of recent X-ray structural analyses. Further, special features of the structure of calpain 10 that differ from those of typical μ- or m-calpain used in most studies are summarized together with discussion of the physiological function of calpain with respect to type 2 diabetes.
ALS/Lt: A New Type 2 Diabetes Mouse Model Associated With Low Free Radical Scavenging Potential
Authors: Mathews Clayton E. , Bagley Rebecca , Leiter Edward H.
Published: March 2007

Outbred CD-1 mice carry a spectrum of genetic susceptibilities for obesity and type 2 diabetes. ALS is an inbred strain with low antioxidant defenses produced by inbreeding CD-1 mice, with selection for susceptibility to alloxan, a generator of highly reactive oxygen free radicals and a potent β-cell toxin. The objective of this study was to determine if the low ability to diffuse free radical stress would contribute to spontaneous type 2 diabetes development in alloxan-untreated males. Indeed, both hyperinsulinemia and impaired glucose tolerance developed spontaneously between 6 and 8 weeks of age in alloxan-untreated males. Further aging was accompanied by increases in body mass, progressively more severe hyperinsulinemia, and development of overt hyperglycemia. Transition from impaired glucose tolerance to overt hyperglycemia correlated with a decreased ratio of reduced to oxidized glutathione. Evidence that the increased oxidative burden elicited the type 2 diabetes syndrome was obtained by the systemic elevation of the antioxidative capacity through daily administration of R-lipoic acid. R-lipoic acid (30 mg/kg) prevented hyperglycemia, reduced insulin levels, and increased free radical scavenging potential. This mouse model with reduced ability to diffuse free radical stress is of obvious interest because free radical-mediated damage is implicated in the pathogenesis and complications of both type 1 and type 2 diabetes.
The Biology of Mitochondrial Uncoupling Proteins
Authors: Rousset Sophie , Alves-Guerra Marie-Clotilde , Mozo Julien , Miroux Bruno , Cassard-Doulcier Anne-Marie , Bouillaud Frédéric , Ricquier Daniel
Published: March 2007

Uncoupling proteins (UCPs) are mitochondrial transporters present in the inner membrane of mitochondria. They are found in all mammals and in plants. They belong to the family of anion mitochondrial carriers including adenine nucleotide transporters. The term “uncoupling protein” was originally used for UCP1, which is uniquely present in mitochondria of brown adipocytes, the thermogenic cells that maintain body temperature in small rodents. In these cells, UCP1 acts as a proton carrier activated by free fatty acids and creates a shunt between complexes of the respiratory chain and ATP synthase. Activation of UCP1 enhances respiration, and the uncoupling process results in a futile cycle and dissipation of oxidation energy as heat. UCP2 is ubiquitous and highly expressed in the lymphoid system, macrophages, and pancreatic islets. UCP3 is mainly expressed in skeletal muscles. In comparison to the established uncoupling and thermogenic activities of UCP1, UCP2 and UCP3 appear to be involved in the limitation of free radical levels in cells rather than in physiological uncoupling and thermogenesis. Moreover, UCP2 is a regulator of insulin secretion and UCP3 is involved in fatty acid metabolism.
Chronic Effects of Fatty Acids on Pancreatic β-Cell Function
Authors: Biden Trevor J. , Robinson Darren , Cordery Damien , Hughes William E. , Busch Anna K.
Published: March 2007

Type 2 diabetes can be viewed as a failure of the pancreatic β-cell to compensate for peripheral insulin resistance with enhanced insulin secretion. This failure is explained by both a relative loss of β-cell mass as well as secretory defects that include enhanced basal secretion and a selective loss of sensitivity to glucose. These features are reproduced by chronic exposure of β-cells to fatty acids (FAs), suggesting that hyperlipidemia might contribute to decompensation. Using MIN6 cells pretreated for 48 h with oleate or palmitate, we have previously defined alterations in global gene expression by transcript profiling and described additional secretory changes to those already established (Busch A-K, Cordery D, Denyer G, Biden TJ: Diabetes 51:977–987, 2002). In contrast to a modest decoupling of glucose-stimulated insulin secretion, FA pretreatment markedly enhanced the secretory response to an acute subsequent challenge with FAs. We propose that this apparent switch in sensitivity from glucose to FAs would be an appropriate response to hyperlipidemia in vivo and thus plays a positive role in β-cell compensation for insulin resistance. Altered expression of dozens of genes could contribute to this switch, and allelic variations in any of these genes could (to varying degrees) impair β-cell compensation and thus contribute to conditions ranging from impaired glucose tolerance to frank diabetes.
β-Cell Calcium-Independent Group VIA Phospholipase A2 (iPLA2β)
Authors: Bao Shunzhong , Jin Chun , Zhang Sheng , Turk John , Ma Zhongmin , Ramanadham Sasanka
Published: March 2007

Evidence that group VIA cytosolic calcium-independent phospholipase A2 (iPLA2β) participates in β-cell signal transduction includes the observations that inhibition of iPLA2β with the bromoenol lactone suicide substrate suppresses glucose-stimulated insulin secretion and that overexpression of iPLA2β amplifies insulin secretory responses in INS-1 insulinoma cells. Immunofluorescence analyses also reveal that iPLA2β accumulates in the perinuclear region of INS-1 cells stimulated with glucose and forskolin. To characterize this phenomenon further, iPLA2β was expressed as a fusion protein with enhanced green fluorescent protein (EGFP) in INS-1 cells so that movements of iPLA2β are reflected by changes in the subcellular distribution of green fluorescence. Stimulation of INS-1 cells overexpressing iPLA2β-EGFP induced greater insulin secretion and punctate accumulation of iPLA2β-EGFP fluorescence in the perinuclear region. To determine the identity of organelles with which iPLA2β might associate, colocalization of green fluorescence with fluorophores associated with specific trackers targeted to different subcellular organelles was examined. Such analyses reveal association of iPLA2β-EGFP fluorescence with the ER and Golgi compartments. Arachidonate-containing plasmenylethanolamine phospholipid species are abundant in β-cell endoplasmic reticulum (ER) and are excellent substrates for iPLA2β. Arachidonic acid produced by iPLA2β-catalyzed hydrolysis of their substrates induces release of Ca2+ from ER stores—an event thought to participate in glucose-stimulated insulin secretion.
Linkage of Calpain 10 to Type 2 Diabetes
Authors: Cox Nancy J. , Hayes M. Geoffrey , Roe Cheryl A. , Tsuchiya Takafumi , Bell Graeme I.
Published: March 2007

The follow-up studies to the original report of association of variation at calpain 10 (CAPN10) with type 2 diabetes in the Mexican-American population of Starr County, Texas, encompass a broad range of science. There are association studies on genetic variation at CAPN10 in different human populations over a range of phenotypes related to type 2 diabetes, physiological studies on the biological functions of calpain proteases, and evolutionary studies on CAPN10 and the NIDDM1 region. We review here the studies published to date on CAPN10, as well as the latest findings from positional cloning studies on a number of other complex disorders. Collectively, these studies provide perspective on the challenges of moving from the linkage mapping and positional cloning studies on which we have been focused to an understanding of the biology shaping the relationship of genotype to phenotype at loci influencing susceptibility to complex disorders like type 2 diabetes.
Genetic Factors and Insulin Secretion
Authors: ’t Hart Leen M. , Fritsche Andreas , Rietveld Ingrid , Dekker Jacqueline M. , Nijpels Giel , Machicao Fausto , Stumvoll Michael , van Duijn Cornelia M. , Häring Hans U. , Heine Robert J. , Maassen J. Antonie , van Haeften Timon W.
Published: March 2007

IGFs are important regulators of pancreatic β-cell development, growth, and maintenance. Mutations in the IGF genes have been found to be associated with type 2 diabetes, myocardial infarction, birth weight, and obesity. These associations could result from changes in insulin secretion. We have analyzed glucose-stimulated insulin secretion using hyperglycemic clamps in carriers of a CA repeat in the IGF-I promoter and an ApaI polymorphism in the IGF-II gene. Normal and impaired glucose-tolerant subjects (n = 237) were independently recruited from three different populations in the Netherlands and Germany to allow independent replication of associations. Both first- and second-phase insulin secretion were not significantly different between the various IGF-I or IGF-II genotypes. Remarkably, noncarriers of the IGF-I CA repeat allele had both a reduced insulin sensitivity index (ISI) and disposition index (DI), suggesting an altered balance between insulin secretion and insulin action. Other diabetes-related parameters were not significantly different for both the IGF-I and IGF-II gene variant. We conclude that gene variants in the IGF-I and IGF-II genes are not associated with detectable variations in glucose-stimulated insulin secretion in these three independent populations. Further studies are needed to examine the exact contributions of the IGF-I CA repeat alleles to variations in ISI and DI.