bluuebunny/crossref_metadata_2025 huggingface dataset:
High White Blood Cell Count Is Associated With a Worsening of Insulin Sensitivity and Predicts the Development of Type 2 Diabetes
Authors: Vozarova Barbora , Weyer Christian , Lindsay Robert S. , Pratley Richard E. , Bogardus Clifton , Tataranni P. Antonio
Published: March 2007

Chronic low-grade inflammation may be involved in the pathogenesis of insulin resistance and type 2 diabetes. We examined whether a high white blood cell count (WBC), a marker of inflammation, predicts a worsening of insulin action, insulin secretory function, and the development of type 2 diabetes in Pima Indians. We measured WBC in 352 nondiabetic Pima Indians (215 men and 137 women, aged 27 ± 6 years [means ± SD], body fat 32 ± 8%, WBC 8,107 ± 2,022 cells/mm3) who were characterized for body composition (by hydrodensitometry or dual-energy X-ray absorptiometry), glucose tolerance (by 75-g oral glucose tolerance test), insulin action (M; by hyperinsulinemic clamp), and acute insulin secretory response (AIR; by 25-g intravenous glucose challenge). Among 272 subjects who were normal glucose tolerant (NGT) at baseline, 54 developed diabetes over an average follow-up of 5.5 ± 4.4 years. Among those who remained nondiabetic, 81 subjects had follow-up measurements of M and AIR. Cross-sectionally, WBC was related to percent body fat (r = 0.32, P < 0.0001) and M (r = −0.24, P < 0.0001), but not to AIR (r = 0.06, P = 0.4). In a multivariate analysis, when adjusted for age and sex, both percent body fat (P < 0.0001) and M (P = 0.03) were independently associated with WBC. A high WBC value predicted diabetes (relative hazard 90th vs. 10th percentiles [95%CI] of 2.7 [1.3–5.4], P = 0.007) when adjusted for age and sex. The predictive effect of WBC persisted after additional adjustment for established predictors of diabetes, i.e., percent body fat, M, and AIR (relative hazard 2.6 [1.1–6.2], P = 0.03). After adjustment for follow-up duration, a high WBC at baseline was associated with a subsequent worsening of M (P = 0.003), but not a worsening of AIR. A high WBC predicts a worsening of insulin action and the development of type 2 diabetes in Pima Indians. These findings are consistent with the hypothesis that a chronic activation of the immune system may play a role in the pathogenesis of type 2 diabetes.
Genetic Variation in the Gene Encoding Adiponectin Is Associated With an Increased Risk of Type 2 Diabetes in the Japanese Population
Authors: Hara Kazuo , Boutin Philippe , Mori Yasumichi , Tobe Kazuyuki , Dina Christian , Yasuda Kazuki , Yamauchi Toshimasa , Otabe Shuichi , Okada Terumasa , Eto Kazuhiro , Kadowaki Hiroko , Hagura Ryoko , Akanuma Yasuo , Yazaki Yoshio , Nagai Ryozo , Taniyama Matsuo , Matsubara Koichi , Yoda Madoka , Nakano Yasuko , Kimura Satoshi , Tomita Motowo , Kimura Satoshi , Ito Chikako , Froguel Philippe , Kadowaki Takashi
Published: March 2007

An adipocyte-derived peptide, adiponectin (also known as GBP28), is decreased in subjects with type 2 diabetes. Recent genome-wide scans have mapped a diabetes susceptibility locus to chromosome 3q27, where the adiponectin gene (APM1) is located. Herein, we present evidence of an association between frequent single nucleotide polymorphisms at positions 45 and 276 in the adiponectin gene and type 2 diabetes (P = 0.003 and P = 0.002, respectively). Subjects with the G/G genotype at position 45 or the G/G genotype at position 276 had a significantly increased risk of type 2 diabetes (odds ratio 1.70 [95% CI 1.09–2.65] and 2.16 [1.22–3.95], respectively) compared with those having the T/T genotype at positions 45 and 276, respectively. In addition, the subjects with the G/G genotype at position 276 had a higher insulin resistance index than those with the T/T genotype (1.61 ± 0.05 vs. 1.19 ± 0.12, P = 0.001). The G allele at position 276 was linearly associated with lower plasma adiponectin levels (G/G: 10.4 ± 0.85 μg/ml, G/T: 13.7 ± 0.87 μg/ml, T/T: 16.6 ± 2.24 μg/ml, P = 0.01) in subjects with higher BMIs. Based on these findings together with the observation that adiponectin improves insulin sensitivity in animal models, we conclude that the adiponectin gene may be a susceptibility gene for type 2 diabetes.
Physiological Consequences of Phasic Insulin Release in the Normal Animal
Authors: Cherrington Alan D. , Sindelar Dana , Edgerton Dale , Steiner Kurt , McGuinness Owen P.
Published: March 2007

The dose-response relationship between the hepatic sinusoidal insulin level and glucose production by the liver is such that a half-maximally effective concentration is at or slightly below the hormone levels seen basally after an overnight fast. In the normal individual, the direct effect of the hormone on the hepatocyte is far more important in restraining glucose production than its indirect effect mediated via a suppression of lipolysis. Because insulin regulates the liver in a direct fashion, its effect occurs within several minutes. Thus, the speed with which insulin works and the sensitivity of the liver to it predict that first-phase insulin release should have a significant effect in quickly suppressing hepatic glucose production. On the other hand, nonhepatic tissues are much less sensitive to insulin and respond slowly as a result of the need for insulin to cross the endothelial barrier. As a result, first-phase insulin is unlikely to significantly alter peripheral glucose disposal. Simulation studies in humans and dogs in which the effects of first-phase insulin were simulated confirmed the aforementioned predictions. In addition, they confirmed the ability of second-phase insulin release to have significant effects on both glucose production and utilization.
Role of Electrostatic and Hydrophobic Interactions in Ca2+-Dependent Phospholipid Binding by the C2A-Domain From Synaptotagmin I
Authors: Gerber Stefan H. , Rizo Josep , Südhof Thomas C.
Published: March 2007

Most C2-domains bind to phospholipid bilayers as a function of Ca2+. Although phospholipid binding is central for the normal functions of C2-domain proteins, the precise mechanism of phospholipid binding is unclear. One of the key questions is whether phospholipid binding by C2-domains is primarily governed by electrostatic or hydrophobic interactions. We have now examined this question for the C2A-domain of synaptotagmin I, a membrane protein of secretory vesicles with an essential function in Ca2+-triggered exocytosis. Our results confirm previous data showing that Ca2+-dependent phospholipid binding by the synaptotagmin C2A-domain is exquisitely sensitive to ionic strength, suggesting an essential role for electrostatic interactions. However, we find that hydrophobic interactions mediated by exposed residues in the Ca2+-binding loops of the C2A-domain, in particular methionine 173, are also essential for tight phospholipid binding. Furthermore, we demonstrate that the apparent Ca2+ affinity of the C2A-domain is determined not only by electrostatic interactions as shown previously, but also by hydrophobic interactions. Together these data indicate that phospholipid binding by the C2A-domain, although triggered by an electrostatic Ca2+-dependent switch, is stabilized by a hydrophobic mechanism. As a result, Ca2+-dependent phospholipid binding proceeds by a multimodal mechanism that mirrors the amphipathic nature of the phospholipid bilayer. The complex phospholipid binding mode of synaptotagmins may be important for its role in regulated exocytosis of secretory granules and synaptic vesicles.
Lipotoxicity in Human Pancreatic Islets and the Protective Effect of Metformin
Authors: Lupi Roberto , Del Guerra Silvia , Fierabracci Vanna , Marselli Lorella , Novelli Michela , Patanè Giovanni , Boggi Ugo , Mosca Franco , Piro Salvatore , Del Prato Stefano , Marchetti Piero
Published: March 2007

Human pancreatic islets from eight donors were incubated for 48 h in the presence of 2.0 mmol/l free fatty acid (FFA) (oleate to palmitate, 2 to 1). Insulin secretion was then assessed in response to glucose (16.7 mmol/l), arginine (20 mmol/l), and glyburide (200 μmol/l) during static incubation or by perifusion. Glucose oxidation and utilization and intra-islet triglyceride content were measured. The effect of metformin (2.4 μg/ml) was studied because it protects rat islets from lipotoxicity. Glucose-stimulated but not arginine- or glyburide-stimulated insulin release was significantly lower from FFA-exposed islets. Impairment of insulin secretion after exposure to FFAs was mainly accounted for by defective early-phase release. In control islets, increasing glucose concentration was associated with an increase in glucose utilization and oxidation. FFA incubation reduced both glucose utilization and oxidation at maximal glucose concentration. Islet triglyceride content increased significantly after FFA exposure. Addition of metformin to high-FFA media prevented impairment in glucose-mediated insulin release, decline of first-phase insulin secretion, and reduction of glucose utilization and oxidation without significantly affecting islet triglyceride accumulation. These results show that lipotoxicity in human islets is characterized by selective loss of glucose responsiveness and impaired glucose metabolism, with a clear defect in early-phase insulin release. Metformin prevents these deleterious effects, supporting a direct protective action on human β-cells.
Altered β-Cell Distribution of pdx-1 and GLUT-2 After a Short-Term Challenge With a High-Fat Diet in C57BL/6J Mice
Authors: Reimer Martina Kvist , Ahrén Bo
Published: March 2007

Mechanisms involved in the islet adaptation to insulin resistance were examined in mice of the C57BL/6J strain challenged with a high-fat (58%) diet for 8 weeks. Basal hyperglycemia commenced after 1 week, whereas hyperinsulinemia evolved after 8 weeks. Glucose elimination after an intravenous glucose challenge (1 g/kg) was significantly delayed after 1, 4, and 8 weeks on the high-fat diet compared with normal-diet–fed mice. This result was associated with unchanged insulin responses. However, glucose-stimulated insulin secretion from isolated islets was increased in a compensatory fashion at all glucose levels over a wide range (3.3–22 mmol/l) after 8 weeks on the high-fat diet, whereas no compensatory hypersecretion of insulin was evident after 1 or 4 weeks, except at 22 mmol/l glucose. Immunohistochemistry revealed that the islet architecture of insulin and glucagon cells remained intact in islets from mice fed a high-fat diet. However, the nuclear translocation of the homeobox transcription factor, pdx-1, and the plasma membrane translocation of GLUT2 were both impaired in high-fat–fed animals after 1 week. In contrast, the expression of the full-length leptin receptor (ObRb) was not affected by high-fat feeding. The study thus shows that 8 weeks are required for the development of a compensatory hypersecretion of insulin after high-fat feeding in mice, and even then the in vivo insulin secretion is insufficient to normalize impaired glucose tolerance. The early-onset islet dysfunction is accompanied by impaired β-cell trafficking of two factors, pdx-1 and GLUT-2, which are involved in β-cell proliferation and glucose recognition. The mechanisms compromising this β-cell trafficking remain to be established.
Fast and cAMP-Sensitive Mode of Ca2+-Dependent Exocytosis in Pancreatic β-Cells
Authors: Kasai Haruo , Suzuki Tomoyuki , Liu Ting-Ting , Kishimoto Takuya , Takahashi Noriko
Published: March 2007

The fast component (mode 1) of Ca2+-dependent exocytosis in pancreatic β-cells, unlike that in adrenal chromaffin cells, is regulated by cytosolic ATP in a concentration-dependent manner. This action of ATP is apparent within 3 min and does not require ATP hydrolysis; rather, it requires the production of cAMP by adenylate cyclase. Moreover, the effect of cAMP is ATP dependent, as revealed by the observation that the fast component of exocytosis is facilitated by ATP, even in the presence of a saturating concentration of cAMP (200 μmol/l). Thus, the amplitude of mode-1 exocytosis depends quadratically on the cytosolic ATP concentration and is facilitated by ATP, even in the absence of an increase in the concentration of cAMP. Given that high glucose concentrations increase the cytosolic ATP concentration, glucose-induced insulin secretion likely involves this action of ATP on mode-1 exocytosis, together with its effect on ATP-dependent K+ channels. In contrast to the fast component of exocytosis, the slow component (mode 2) of this process is independent of cAMP and ATP and can account for the slow component of insulin secretion, which does not require these nucleotides.
Quantification of Insulin Secretion in Relation to Insulin Sensitivity in Nondiabetic Postmenopausal Women
Authors: Ahrén Bo , Larsson Hillevi
Published: March 2007

To evaluate mechanisms underlying the close association between insulin secretion and insulin sensitivity, insulin sensitivity was evaluated by the euglycemic-hyperinsulinemic clamp technique (M/Iclamp) and insulin secretion was determined from the 75-g oral glucose tolerance test (OGTT) and from the glucose-dependent arginine-stimulation test in 81 nondiabetic postmenopausal women, all aged 61 years. M/Iclamp was normally distributed with mean ± SD of 69.9 ± 30.5 nmol glucose · kg−1 · min−1/pmol insulin · l−1. It was found that the several different measures of insulin secretion from the OGTT and the glucose-dependent arginine-stimulation test were all inversely related to M/Iclamp. However, measures determining the direct insulin responses were more markedly potentiated by low M/Iclamp than were measures determining glucose potentiation of insulin secretion. Moreover, the product of M/Iclamp times measures of insulin secretion (disposition index [DI]) was inversely related to the 2-h glucose value. Finally, surrogate insulin sensitivity measures quantified from OGTT and the glucose-dependent arginine-stimulation test only weakly correlated to M/Iclamp (R2 ≈ 0.25). Thus, 1) insulin secretion is adaptively increased when insulin sensitivity is low in nondiabetic postmenopausal women; 2) β-cell exocytotic ability shows more efficient adaptation than β-cell glucose recognition to low insulin sensitivity; 3) impaired β-cell adaptation (i.e., low DI) is associated with higher 2-h glucose values during OGTT, although other regulatory mechanisms also exist; and 4) indirect surrogate measures of insulin sensitivity only weakly correlate to insulin sensitivity as determined by the euglycemic-hyperinsulinemic clamp.
Insulin Release in Impaired Glucose Tolerance
Authors: Breda Elena , Toffolo Gianna , Polonsky Kenneth S. , Cobelli Claudio
Published: March 2007

The availability of quantitative indexes describing β-cell function in normal life conditions is important for the characterization of impaired mechanisms of insulin secretion in pathophysiological states. Recently, an oral C-peptide minimal model has been proposed and applied to subjects with normal glucose tolerance (NGT) during graded up-and-down glucose infusion protocols (40-min periods at 4, 8, 16, 8, 4, and 0 mg · kg−1 · min−1) and oral glucose tolerance tests. These tests are characterized by slow glucose and C-peptide dynamics, which reproduce prandial conditions. In view of the importance of β-cell dysfunction in the pathogenesis of type 2 diabetes, our aim was to test and use the oral minimal model in subjects with impaired glucose tolerance (IGT) to identify deranged mechanisms of β-cell function. Plasma C-peptide and glucose data from graded up-and-down glucose infusions were analyzed in nine NGT and four IGT subjects using the classic deconvolution approach and the oral minimal model, and indexes of β-cell function were derived. An index of insulin sensitivity was also obtained for each subject from minimal model analysis of glucose and insulin levels achieved during the test. Both deconvolution and minimal model analyses revealed that individuals with IGT have a relative defect in the ability to secrete enough insulin to adequately compensate for insulin resistance. Additionally, minimal model analysis suggests that insulin secretory defect in IGT arises from delays in the timing of the β-cell response to glucose.
Pulsatile Insulin Secretion: Detection, Regulation, and Role in Diabetes
Authors: Pørksen Niels , Hollingdal Malene , Juhl Claus , Butler Peter , Veldhuis Johannes D. , Schmitz Ole
Published: March 2007

Insulin concentrations oscillate at a periodicity of 5–15 min per oscillation. These oscillations are due to coordinate insulin secretory bursts, from millions of islets. The generation of common secretory bursts requires strong within-islet and within-pancreas coordination to synchronize the secretory activity from the β-cell population. The overall contribution of this pulsatile mechanism dominates and accounts for the majority of insulin release. This review discusses the methods involved in the detection and quantification of periodicities and individual secretory bursts. The mechanism by which overall insulin secretion is regulated through changes in the pulsatile component is discussed for nerves, metabolites, hormones, and drugs. The impaired pulsatile secretion of insulin in type 2 diabetes has resulted in much focus on the impact of the insulin delivery pattern on insulin action, and improved action from oscillatory insulin exposure is demonstrated on liver, muscle, and adipose tissues. Therefore, not only is the dominant regulation of insulin through changes in secretory burst mass and amplitude, but the changes may affect insulin action. Finally, the role of impaired pulsatile release in early type 2 diabetes suggests a predictive value of studies on insulin pulsatility in the development of this disease.
Effects of Fasting on Physiologically Pulsatile Insulin Release in Healthy Humans
Authors: Juhl Claus , Grøfte Thorbjørn , Butler Peter C. , Veldhuis Johannes D. , Schmitz Ole , Pørksen Niels
Published: March 2007

Insulin is released as secretory bursts superimposed on basal release. The overall contribution of secretory bursts was recently quantified as at least 75%, and the main regulation of insulin secretion is through perturbation of the amount of insulin released and the frequency of these secretory bursts. The mode of delivery of insulin into the circulation seems important for insulin action, and therefore physiological conditions that alter the pattern of insulin release may affect insulin action through this mechanism. To assess the mechanisms by which fasting changes the amount of insulin released and the frequency, amplitude, and overall contribution of pulsatile insulin secretion, we used a validated deconvolution model to examine pulsatile insulin secretion during 10 and 58 h of fasting in seven healthy subjects. The subjects were studied for 75 min before (0–75 min) and 75 min during (115–190 min) a glucose infusion (2.5 mg · kg−1 · min−1). We found that the pulsatile insulin release pattern was preserved and that, at fasting, overall insulin release is adjusted to needs by a reduced amount of insulin released (10.1 ± 1.7 vs. 16.0 ± 3.2 pmol/l/pulse, P < 0.05) but similar frequency (6.3 ± 0.4 vs. 6.1 ± 0.4 min/pulse) of the insulin secretory bursts. In both states, glucose infusion caused an increase (P < 0.05) in amount (100–200%) and frequency (∼20%). The impact of increased glucose concentration on pulse frequency seems distinct for in vivo versus in vitro pulsatile insulin secretion and may indicate the presence of a glucose-sensitive pacemaker, which initiates the coordinated secretory bursts. Increased insulin/C-peptide ratio at long-term fasting (6.0 vs. 9.1%, P < 0.01) indicates that the changes in insulin release patterns may be accompanied by changes in hepatic insulin extraction.
Intense Exercise Has Unique Effects on Both Insulin Release and Its Roles in Glucoregulation
Authors: Marliss Errol B. , Vranic Mladen
Published: March 2007

In intense exercise (>80% Vo2max), unlike at lesser intensities, glucose is the exclusive muscle fuel. It must be mobilized from muscle and liver glycogen in both the fed and fasted states. Therefore, regulation of glucose production (GP) and glucose utilization (GU) have to be different from exercise at <60% Vo2max, in which it is established that the portal glucagon-to-insulin ratio causes the less than or equal to twofold increase in GP. GU is subject to complex regulation by insulin, plasma glucose, alternate substrates, other humoral factors, and muscle factors. At lower intensities, plasma glucose is constant during postabsorptive exercise and declines during postprandial exercise (and often in persons with diabetes). During such exercise, insulin secretion is inhibited by β-cell α-adrenergic receptor activation. In contrast, in intense exercise, GP rises seven- to eightfold and GU rises three- to fourfold; therefore, glycemia increases and plasma insulin decreases minimally, if at all. Indeed, even an increase in insulin during α-blockade or during a pancreatic clamp does not prevent this response, nor does pre-exercise hyperinsulinemia due to a prior meal or glucose infusion. At exhaustion, GU initially decreases more than GP, which leads to greater hyperglycemia, requiring a substantial rise in insulin for 40–60 min to restore pre-exercise levels. Absence of this response in type 1 diabetes leads to sustained hyperglycemia, and mimicking it by intravenous infusion restores the normal response. Compelling evidence supports the conclusion that the marked catecholamine responses to intense exercise are responsible for both the GP increment (that occurs even during glucose infusion and postprandially) and the restrained increase of GU. These responses are normal in persons with type 1 diabetes, who often report exercise-induced hyperglycemia, and in whom the clinical challenge is to reproduce the recovery period hyperinsulinemia. Intense exercise in type 2 diabetes requires additional study.
Evidence for a Novel Type 1 Diabetes Susceptibility Locus on Chromosome 8
Authors: Sale Michèle M. , FitzGerald Liesel M. , Charlesworth Jacinta C. , Bowden Donald W. , Rich Stephen S.
Published: March 2007

Type 1 diabetes results from a combination of genetic susceptibility and environmental exposures. Susceptibility loci other than HLA and the insulin gene remain to be identified to account for the degree of familial clustering observed in this disorder. Early genome-wide scans provided suggestive evidence of linkage on chromosome 8q, prompting detailed analysis of this region. A total of 20 microsatellite markers spanning an 88-cM region of 8q11-24 were genotyped in 24 type 1 diabetes pedigrees from Wisconsin that contained 39 affected sib-pairs. Multipoint linkage analyses provided close to suggestive evidence of linkage, with a multipoint logarithm of odds score (MLS) of 2.4 and Genehunter nonparametric logarithm of odds score (NPL) of 2.7 (P = 0.003). There is also evidence of linkage disequilibrium at peak marker D8S1823 for the 217bp allele (P = 0.037) using the pedigree disequilibrium test. Although our sample size was small, the multiple tests were consistent and our preliminary results suggested that 8q24 may harbor a novel population-specific type 1 diabetes susceptibility gene. Continued investigation of this region for a novel type 1 diabetes susceptibility gene appears justified.
Experimental Models of Transcription Factor-Associated Maturity-Onset Diabetes of the Young
Authors: Wang Haiyan , Hagenfeldt-Johansson Kerstin , Otten Luc A. , Gauthier Benoit R. , Herrera Pedro L. , Wollheim Claes B.
Published: March 2007

Six monogenic forms of maturity-onset diabetes of the young (MODY) have been identified to date. Except for MODY2 (glucokinase), all other MODY subtypes have been linked to transcription factors. We have established a MODY3 transgenic model through the β-cell–targeted expression of dominant-negative HNF-1α either constitutively (rat insulin II promoter) or conditionally (Tet-On system). The animals display either overt diabetes or glucose intolerance. Decreased insulin secretion and reduced pancreatic insulin content contribute to the hyperglycemic state. The conditional approach in INS-1 cells helped to define new molecular targets of hepatocyte nuclear factor (HNF)-1α. In the cellular system, nutrient-induced insulin secretion was abolished because of impaired glucose metabolism. Conditional suppression of HNF-4α, the MODY1 gene, showed a similar phenotype in INS-1 cells to HNF-1α. The existence of a regulatory circuit between HNF-4α and HNF-1α is confirmed in these cell models. The MODY4 gene, IPF-1 (insulin promoter factor-1)/PDX-1 (pancreas duodenum homeobox-1), controls not only the transcription of insulin but also expression of enzymes involved in its processing. Suppression of Pdx-1 function in INS-1 cells does not alter glucose metabolism but rather inhibits insulin release by impairing steps distal to the generation of mitochondrial coupling factors. The presented experimental models are important tools for the elucidation of the β-cell pathogenesis in MODY syndromes.
Nucleotide Sensitivity of Pancreatic ATP-Sensitive Potassium Channels and Type 2 Diabetes
Authors: Schwanstecher Christina , Schwanstecher Mathias
Published: March 2007

Type 2 diabetes is generally perceived as a polygenic disorder, with disease development being influenced by both hereditary and environmental factors. However, despite intensive investigations, little progress has been made in identifying the genes that impart susceptibility to the common late-onset forms of the disease. E23K, a common single nucleotide polymorphism in KIR6.2, the pore-forming subunit of pancreatic β-cell ATP-sensitive K+ (KATP) channels, significantly enhances the spontaneous open probability of these channels, and thus modulates sensitivities toward inhibitory and activatory adenine nucleotides. Based on previous association studies, we present evidence that with an estimated attributable proportion of 15% in Caucasians, E23K in KIR6.2 appears to be the most important genetic risk factor for type 2 diabetes yet identified.
Sulfonylurea Stimulation of Insulin Secretion
Authors: Proks Peter , Reimann Frank , Green Nick , Gribble Fiona , Ashcroft Frances
Published: March 2007

Sulfonylureas are widely used to treat type 2 diabetes because they stimulate insulin secretion from pancreatic β-cells. They primarily act by binding to the SUR subunit of the ATP-sensitive potassium (KATP) channel and inducing channel closure. However, the channel is still able to open to a limited extent when the drug is bound, so that high-affinity sulfonylurea inhibition is not complete, even at saturating drug concentrations. KATP channels are also found in cardiac, skeletal, and smooth muscle, but in these tissues are composed of different SUR subunits that confer different drug sensitivities. Thus tolbutamide and gliclazide block channels containing SUR1 (β-cell type), but not SUR2 (cardiac, smooth muscle types), whereas glibenclamide, glimepiride, repaglinide, and meglitinide block both types of channels. This difference has been exploited to determine residues contributing to the sulfonylurea-binding site. Sulfonylurea block is decreased by mutations or agents (e.g., phosphatidylinositol bisphosphate) that increase KATP channel open probability. We now propose a kinetic model that explains this effect in terms of changes in the channel open probability and in the transduction between the drug-binding site and the channel gate. We also clarify the mechanism by which MgADP produces an apparent increase of sulfonylurea efficacy on channels containing SUR1 (but not SUR2).
β-Cell Mitochondria and Insulin Secretion
Authors: Wollheim Claes B. , Maechler Pierre
Published: March 2007

The β-cell mitochondria are known to generate metabolic coupling factors, or messengers, that mediate plasma membrane depolarization and the increase in cytosolic Ca2+, the triggering event in glucose-stimulated insulin secretion. Accordingly, ATP closes nucleotide-sensitive K+ channels necessary for the opening of voltage-gated Ca2+ channels. ATP also exerts a permissive action on insulin exocytosis. In contrast, GTP directly stimulates the exocytotic process. cAMP is considered to have a dual function: on the one hand, it renders the β-cell more responsive to glucose; on the other, it mediates the effect of glucagon and other hormones that potentiate insulin secretion. Mitochondrial shuttles contribute to the formation of pyridine nucleotides, which may also participate in insulin exocytosis. Among the metabolic factors generated by glucose, citrate-derived malonyl-CoA has been endorsed, but recent results have questioned its role. We have proposed that glutamate, which is also formed by mitochondrial metabolism, stimulates insulin exocytosis in conditions of permissive, clamped cytosolic Ca2+ concentrations. The evidence for the implication of these and other putative messengers in metabolism-secretion coupling is discussed in this review.
Gliclazide Directly Inhibits Arginine-Induced Glucagon Release
Authors: Cejvan Kenan , Coy David H. , Holst Jens Juul , Cerasi Erol , Efendic Suad
Published: March 2007

Arginine-stimulated insulin and somatostatin release is enhanced by the sulfonylurea gliclazide. In contrast, gliclazide inhibits the glucagon response. The aim of the present study was to investigate whether this inhibition of glucagon release was mediated by a direct suppressive effect of gliclazide or was secondary to the paracrine effect of released somatostatin. To eliminate the paracrine effects of somatostatin, we first perfused isolated rat pancreata with a medium supplemented with 23% of the standard calcium content. Second, we perifused isolated rat islets with a novel and highly specific antagonist of type 2 somatostatin receptor, DC-41-33 (2 μmol/l), which fully antagonizes the suppressive somatostatin effect on rat A cells. Gliclazide (30 μmol/l) inhibited glucagon release by 54% in the perfusion experiments, whereas the somatostatin response was nearly abolished. In islet perifusions with DC-41-33, arginine-induced glucagon release was inhibited by 66%. We therefore concluded that gliclazide inhibits glucagon release by a direct action on the pancreatic A cell.
Prolonged In Vitro Exposure to Autoantibodies Against CD38 Impairs the Function and Survival of Human Pancreatic Islets
Authors: Marchetti Piero , Antonelli Alessandro , Lupi Roberto , Marselli Lorella , Fallahi Poupak , Nesti Claudia , Baj Germano , Ferrannini Ele
Published: March 2007

Autoantibodies against CD38 (adenosine-5′-diphosphate[ADP]-ribosyl cyclase/cyclic ADP-ribose hydrolase) have been described in 10–12% of patients with type 2 diabetes. In human islets, anti-CD38 autoantibodies (CD38Abs) acutely stimulate insulin release (IR) and increase the cytosolic calcium concentration ([Ca2+]i). Whether CD38Abs affect human islet cell function and survival upon prolonged in vitro exposure is not known. We cultured human islets for up to 7 days in the presence of sera from 10 patients with type 2 diabetes that had neither CD38Ab- nor [Ca2+]i-mobilizing activity (−/−), sera from 6 patients with type 2 diabetes that was CD38Ab-positive and had [Ca2+]i-mobilizing activity (+/+), or no sera (control). At baseline, +/+ sera caused a significant (P < 0.002) acute stimulation of IR (IR at 3.3 mmol/l glucose was 45 ± 19, 84 ± 24, and 34 ± 12 μU/ml in control, +/+, and −/− sera, respectively; the corresponding IR at 16.7 mmol/l glucose was 72 ± 25, 204 ± 56, and 80 ± 32 μU/ml). At 3 days, IR at 3.3 mmol/l glucose was 42 ± 18, 27 ± 11, and 43 ± 24 μU/ml (P = 0.0003) for control, +/+, and −/− sera, respectively, whereas at 16.7 mmol/l glucose, it was 95 ± 76, 45 ± 35, and 76 ± 42 μU/ml, respectively. After 7 days of exposure, the corresponding IR at 3.3 mmol/l glucose was 40 ± 11, 28 ± 12, and 35 ± 15 μU/ml, respectively, whereas at 16.7 mmol/l glucose it was 79 ± 39, 39 ± 17, and 62 ± 39 μU/ml. At both 3 and 7 days, IR still increased when switching from 3.3 to 16.7 mmol/l glucose (P < 0.0003), and incubation with +/+ sera induced a significant decrease in the insulin response (P < 0.002). At 7 days, the number of dead cells (as evaluated by an enzyme-linked immunosorbent assay technique) differed significantly between control (1.2 ± 0.3 OD units) cells, islets exposed to −/− sera (1.4 ± 0.1), and islets coincubated with +/+ sera (1.9 ± 0.4, P < 0.01). We conclude that prolonged exposure of human islets to sera positive for the presence of CD38Abs with [Ca2+]i-mobilizing activity impairs β-cell function and viability in cultured human pancreatic islets.
Signals and Pools Underlying Biphasic Insulin Secretion
Authors: Henquin Jean-Claude , Ishiyama Nobuyoshi , Nenquin Myriam , Ravier Magalie A. , Jonas Jean-Christophe
Published: March 2007

Rapid and sustained stimulation of β-cells with glucose induces biphasic insulin secretion. The two phases appear to reflect a characteristic of stimulus-secretion coupling in each β-cell rather than heterogeneity in the time-course of the response between β-cells or islets. There is no evidence indicating that biphasic secretion can be attributed to an intrinsically biphasic metabolic signal. In contrast, the biphasic rise in cytoplasmic Ca2+ concentration ([Ca2+]i) induced by glucose is important to shape the two phases of secretion. The first phase requires a rapid and marked elevation of [Ca2+]i and corresponds to the release of insulin granules from a limited pool. The magnitude of the second phase is determined by the elevation of [Ca2+]i, but its development requires production of another signal. This signal corresponds to the amplifying action of glucose and may serve to replenish the pool of granules that are releasable at the prevailing [Ca2+]i. The species characteristics of biphasic insulin secretion and its perturbations in pathological situations are discussed.
Importance of Nonionic Signals for Glucose-Induced Biphasic Insulin Secretion
Authors: Aizawa Toru , Sato Yoshihiko , Komatsu Mitsuhisa
Published: March 2007

Glucose induces biphasic insulin secretion by the islet β-cell. Based on recent knowledge on glucose signaling in the β-cell, the underlying mechanisms for this biphasicity could be envisaged as follows. Glucose-induced elevation of cytosolic free Ca2+ concentration, which is due to the electrophysiological events that originate in closure of the ATP-sensitive K+ (KATP) channel, most likely triggers the first phase. The second phase is produced by gradual augmentation and potentiation of Ca2+-triggered insulin release by the KATP channel–independent, nonionic signals. Protein acylation may be involved in the nonionic signaling. In patients lacking functional KATP channels, however, the first phase of glucose-induced insulin secretion is clearly retained, casting doubt on the simplistic view outlined above. In this pathological condition, the KATP channel–independent, most likely nonionic, glucose action alone is sufficient for the first-phase response.
Dipeptidyl Peptidase IV-Resistant [d-Ala2]Glucose-Dependent Insulinotropic Polypeptide (GIP) Improves Glucose Tolerance in Normal and Obese Diabetic Rats
Authors: Hinke Simon A. , Gelling Richard W. , Pederson Raymond A. , Manhart Susanne , Nian Cuilan , Demuth Hans-Ulrich , McIntosh Christopher H.S.
Published: March 2007

The therapeutic potential of glucose-dependent insulinotropic polypeptide (GIP) for improving glycemic control has largely gone unstudied. A series of synthetic GIP peptides modified at the NH2-terminus were screened in vitro for resistance to dipeptidyl peptidase IV (DP IV) degradation and potency to stimulate cyclic AMP and affinity for the transfected rat GIP receptor. In vitro experiments indicated that [d-Ala2]GIP possessed the greatest resistance to enzymatic degradation, combined with minimal effects on efficacy at the receptor. Thus, [d-Ala2]GIP1–42 was selected for further testing in the perfused rat pancreas and bioassay in conscious Wistar and Zucker rats. When injected subcutaneously in normal Wistar, Fa/?, or fa/fa Vancouver Diabetic Fatty (VDF) Zucker rats, both GIP and [d-Ala2]GIP significantly reduced glycemic excursions during a concurrent oral glucose tolerance test via stimulation of insulin release. The latter peptide displayed greater in vivo effectiveness, likely because of resistance to enzymatic degradation. Hence, despite reduced bioactivity in diabetic models at physiological concentrations, GIP and analogs with improved plasma stability still improve glucose tolerance when given in supraphysiological doses, and thus may prove useful in the treatment of diabetic states.
Extreme Insulin Resistance of the Central Adipose Depot In Vivo
Authors: Mittelman Steven D. , Van Citters Gregg W. , Kirkman Erlinda L. , Bergman Richard N.
Published: March 2007

Despite the well-described association between obesity and insulin resistance, the physiologic mechanisms that link these two states are poorly understood. The present study was performed to elucidate the role of visceral adipose tissue in whole-body glucose homeostasis. Dogs made abdominally obese with a moderately elevated fat diet had catheters placed into the superior mesenteric artery so that the visceral adipose bed could be insulinized discretely. Omental insulin infusion was extracted at ∼27%, such that systemic insulin levels were lower than in control (portal vein) insulin infusions. Omental infusion did not lower systemic free fatty acid levels further than control infusion, likely because of the resistance of the omental adipose tissue to insulin suppression and the confounding lower systemic insulin levels. The arteriovenous difference technique showed that local infusion of insulin did suppress omental lipolysis, but only at extremely high insulin concentrations. The median effective dose for suppression of lipolysis was almost fourfold higher in the visceral adipose bed than for whole-body suppression of lipolysis. Thus, the omental adipose bed represents a highly insulin-resistant depot that drains directly into the portal vein. Increased free fatty acid flux to the liver may account for hepatic insulin resistance in the moderately obese state.
Albumin Binding of Acylated Insulin (NN304) Does Not Deter Action to Stimulate Glucose Uptake
Authors: Dea Melvin K. , Hamilton-Wessler Marianthe , Ader Marilyn , Moore Donna , Schäffer Lauge , Loftager Mette , Vølund Aage , Bergman Richard N.
Published: March 2007

NN304 [LysB29-tetradecanoyl des(B30) human insulin] is a potentially therapeutic insulin analog designed to exhibit protracted glucose-lowering action. In dogs with infusion rates similar to insulin itself, NN304 exhibits similar glucose uptake (Rd) stimulation with delayed onset of action. This compartmental modeling study was to determine if NN304 action could be accounted for by the ∼2% unbound NN304 concentration. NN304 (or human insulin) (n = 6 each) was infused at 10.2 pmol · min−1 · kg−1 under euglycemic clamp conditions in anesthetized dogs. NN304 appearance in lymph, representing interstitial fluid (ISF), was slow compared with insulin (t1/2 = 70 ± 7 vs. 14 ± 1 min, P < 0.001). Rd was highly correlated with the ISF concentration for insulin and NN304 (r = 0.86 and 0.93, respectively), suggesting that slow transendothelial transport (TET) is responsible for sluggish NN304 action. Insulin and NN304 concentration data were fit to a two-compartment (plasma and ISF) model. NN304 plasma elimination and TET were reduced to 10 and 7% of insulin, respectively. Thus, there was reduction of NN304 transport, but not to the degree expected. In ISF, there was no reduction in NN304 elimination. Thus, this acylated insulin analog demonstrates blunted kinetics in plasma, and full efficacy in the compartment of action, ISF.
Unprocessed Proinsulin Promotes Cell Survival During Neurulation in the Chick Embryo
Authors: Hernández-Sánchez Catalina , Rubio Eva , Serna José , de la Rosa Enrique J. , de Pablo Flora
Published: March 2007

We have chosen a vertebrate model accessible during neurulation, the chick, for analysis of endogenous insulin signaling and its contribution to early embryonic cell survival. Unlike rodents, humans and chickens have a single preproinsulin gene, facilitating its prepancreatic expression characterization. We show that in vivo interference with embryonic insulin signaling using antisense oligonucleotides against the insulin receptor increases apoptosis during neurulation. In contrast, high glucose administration does not increase the level of apoptosis in culture or in vivo. Exogenous insulin and, remarkably, proinsulin achieve similar survival protective effects at 10−8 mol/l. The low abundant preproinsulin mRNA from the prepancreatic embryo is translated to a protein that remains as unprocessed proinsulin. This concurs with the absence of prohormone convertase 2 (PC2) in the embryo, whereas PC2 is present later in embryonic pancreas. A C-peptide–specific antibody stains proinsulin-containing neuroepithelial cells of the chick embryo in early neurulation, as well as other cells in mesoderm- and endoderm-derived structures in the 2.5-day embryo. We have determined by 5′-RACE (rapid amplification of cDNA ends), and confirmed by RNase protection assay, that prepancreatic and pancreatic proinsulin mRNA differ in their first exon, suggesting differential transcriptional regulation. All these data support the role of endogenous proinsulin in cell survival in the chick embryo during important pathophysiologic periods of early development.
The Proline 12 Alanine Substitution in the Peroxisome Proliferator–Activated Receptor-γ2 Gene Is Associated With Lower Lipoprotein Lipase Activity in Vivo
Authors: Schneider Jochen , Kreuzer Joerg , Hamann Andreas , Nawroth Peter P. , Dugi Klaus A.
Published: March 2007

Lipoprotein lipase (LPL) plays a key role in lipid metabolism by hydrolyzing triglycerides in circulating lipoproteins. Low LPL activity has been linked to coronary artery disease (CAD), but the factors influencing LPL expression are not completely understood. Peroxisome proliferator–activated receptor (PPAR)-γ is a nuclear receptor regulating lipid and glucose metabolism, and a PPAR-responsive element is present in the LPL promoter. We determined the Pro12Ala polymorphism in the PPAR-γ2 gene in 194 male CAD patients because this allele is associated with decreased PPAR activity and reduced LPL promoter activity in vitro. Presence of 12Ala was associated with 20% lower LPL activity in postheparin plasma (141 ± 58 vs. 177 ± 77 nmol · ml−1 · min−1, P < 0.005). Remarkably, the influence of 12Ala on LPL was greater than that of the frequent polymorphisms (HindIII +9%, PvuII ±0%, 447stop +12%) in the LPL gene itself. To confirm these results in a different group of patients, we analyzed 100 diabetic patients in whom the 12Ala allele was also associated with lower LPL activity (12Ala: 132 ± 88 vs. 190 ± 129 nmol · ml−1 · min−1, P < 0.05). Our data demonstrate that the Pro12Ala substitution in PPAR-γ2 is associated with lower LPL activity in vivo and provides a new target for the analysis of genetic influences on LPL activity and CAD risk.
KIR6.2 Polymorphism Predisposes to Type 2 Diabetes by Inducing Overactivity of Pancreatic β-Cell ATP-Sensitive K+ Channels
Authors: Schwanstecher Christina , Meyer Ulrike , Schwanstecher Mathias
Published: March 2007

E23K, a common single nucleotide polymorphism in KIR6.2, the pore-forming subunit of pancreatic β-cell ATP-sensitive K+ channels, significantly enhanced open probability of these channels, thus reducing their sensitivity toward inhibitory ATP4− and increasing the threshold concentration for insulin release. Previous association studies and high allelic frequency suggest this effect to critically inhibit secretion and play a major role in pathogenesis of common type 2 diabetes. Based on evidence for functional relevance of E23K in both the heterozygous (E/K; with E in position 23 of KIR6.2 in one allele and K in the other) and homozygous (K/K; with K in position 23 of KIR6.2 in both alleles) genotype, we propose a model in which enhanced susceptibility to type 2 diabetes is associated with evolutionary advantage of the E/K state.
The Concurrent Accumulation of Intra-Abdominal and Subcutaneous Fat Explains the Association Between Insulin Resistance and Plasma Leptin Concentrations
Authors: Cnop Miriam , Landchild Melinda J. , Vidal Josep , Havel Peter J. , Knowles Negar G. , Carr Darcy R. , Wang Feng , Hull Rebecca L. , Boyko Edward J. , Retzlaff Barbara M. , Walden Carolyn E. , Knopp Robert H. , Kahn Steven E.
Published: March 2007

Obesity is associated with insulin resistance, particularly when body fat has a central distribution. However, insulin resistance also frequently occurs in apparently lean individuals. It has been proposed that these lean insulin-resistant individuals have greater amounts of body fat than lean insulin-sensitive subjects. Alternatively, their body fat distribution may be different. Obesity is associated with elevated plasma leptin levels, but some studies have suggested that insulin sensitivity is an additional determinant of circulating leptin concentrations. To examine how body fat distribution contributes to insulin sensitivity and how these variables are related to leptin levels, we studied 174 individuals (73 men, 101 women), a priori classified as lean insulin-sensitive (LIS, n = 56), lean insulin-resistant (LIR, n = 61), and obese insulin-resistant (OIR, n = 57) based on their BMI and insulin sensitivity index (SI). Whereas the BMI of the two lean groups did not differ, the SI of the LIR subjects was less than half that of the LIS group. The subcutaneous and intra-abdominal fat areas, determined by computed tomography, were 45 and 70% greater in the LIR subjects (P < 0.001) and 2.5- and 3-fold greater in the OIR group, as compared with the LIS group. Fasting plasma leptin levels were moderately increased in LIR subjects (10.8 ± 7.1 vs. 8.1 ± 6.4 ng/ml in LIS subjects; P < 0.001) and doubled in OIR subjects (21.9 ± 15.5 ng/ml; P < 0.001). Because of the confounding effect of body fat, we examined the relationships between adiposity, insulin sensitivity, and leptin concentrations by multiple regression analysis. Intra-abdominal fat was the best variable predicting insulin sensitivity in both genders and explained 54% of the variance in SI. This inverse relationship was nonlinear (r = −0.688). On the other hand, in both genders, fasting leptin levels were strongly associated with subcutaneous fat area (r = 0.760) but not with intra-abdominal fat. In line with these analyses, when LIS and LIR subjects were matched for subcutaneous fat area, age, and gender, they had similar leptin levels, whereas their intra-abdominal fat and insulin sensitivity remained different. Thus, accumulation of intra-abdominal fat correlates with insulin resistance, whereas subcutaneous fat deposition correlates with circulating leptin levels. We conclude that the concurrent increase in these two metabolically distinct fat compartments is a major explanation for the association between insulin resistance and elevated circulating leptin concentrations in lean and obese subjects.
Leptin Resistance During Aging Is Independent of Fat Mass
Authors: Gabriely Ilan , Ma Xiao Hui , Yang Xiao Man , Rossetti Luciano , Barzilai Nir
Published: March 2007

Increased fat mass, abdominal adiposity, and insulin resistance are typical findings in aging mammals and are frequently associated with leptin resistance and increased plasma leptin levels. To examine whether leptin’s failure in aging is due to aging per se or to changes in body fat mass or distribution, we studied aging rats that underwent calorie restriction throughout their lives, maintaining their youthful body fat pattern and metabolic profile. Leptin’s action was assessed by measuring its ability to regulate food intake, fat mass and its distribution, peripheral and hepatic insulin action, and its own gene expression in fat. Our results show that leptin’s action is markedly diminished in aging rats, independently of their body fat pattern. Leptin’s failure in this model suggests its causative role in the metabolic decline seen with aging.