bluuebunny/crossref_metadata_2025 huggingface dataset:
A 212-kb Region on Chromosome 6q25 Containing the TAB2 Gene Is Associated With Susceptibility to Type 1 Diabetes
Authors: Owerbach David , Piña Lazaro , Gabbay Kenneth H.
Published: March 2007

The IDDM5 gene, which is identified by whole-genome searches, is located on chromosome 6q25. TAB2 (MAP3K7IP2 [mitogen-activating protein kinase kinase kinase 7 interacting protein 2]) is a potential candidate gene for type 1 diabetes because it is located on chromosome 6q25 and is involved in nuclear factor (NF)-κB regulation. We have conducted familial association studies using 478 families and demonstrate that a type 1 diabetes susceptibility gene resides within a 212-kb region containing the TAB2 gene (Tsp = 1.0 × 10−2 to 4.0 × 10−4). No amino acid polymorphisms were detected in TAB2; however, multiple single nucleotide polymorphisms (SNPs) found within 5′ untranslated, 3′ untranslated, and intron regions were associated with type 1 diabetes susceptibility. Two additional genes, LOC340152, a predicted gene with currently unknown function, and SMT3, which has homology to SUMO (small ubiquitin-related modifier) were found within the 212-kb region and were associated with type 1 diabetes susceptibility. Functional studies of the three genes will be required to determine their biological relevance to type 1 diabetes. However, both TAB2 and SUMO are involved in NF-κB activation and may thus be involved in type 1 diabetes through apoptosis in pancreatic β-cells.
Hyperresponsiveness, Resistance to B-Cell Receptor—Dependent Activation-Induced Cell Death, and Accumulation of Hyperactivated B-Cells in Islets Is Associated With the Onset of Insulitis but not Type 1 Diabetes
Authors: Hussain Shabbir , Salojin Konstantin V. , Delovitch Terry L.
Published: March 2007

B-cells proliferate after B-cell receptor (BCR) stimulation and are deleted by activation-induced cell death (AICD) during negative selection. We report that B-cells from type 1 diabetes−susceptible NOD and type 1 diabetes−resistant but insulitis-prone congenic NOD.B6Idd4B and NOR mice, relative to B-cells from nonautoimmune disease−prone C57BL/6 and BALB/c mice, display a hyperproliferative response to BCR stimulation and lower activation threshold in the absence or presence of interleukin 4 (IL-4). This hyperproliferation is associated with an increased proportion of NOD and NOR B-cells that enter into the S phase of the cell cycle and undergo cell division. The relative resistance to BCR-induced AICD of B-cells from NOD, NOR, and NOD.B6Idd4B mice, all of which develop insulitis, correlates with the presence of a higher percentage of hyperactivated B-cells in the spleen and islets of these mice than in nonautoimmune disease−prone C57BL/6 and BALB/c mice. The NOD islet-infiltrated activated B-cells are more responsive to further stimulation by IL-4 than activated spleen B-cells. Our results suggest that resistance to AICD and accumulation of hyperactivated B-cells in islets is associated with the onset of an inflammatory insulitis, but not type 1 diabetes.
Autocrine Regulation of Single Pancreatic β-Cell Survival
Authors: Navarro-Tableros Víctor , Sánchez-Soto M. Carmen , García Santiago , Hiriart Marcia
Published: March 2007

Function and survival of cells depend in part on the presence of growth factors. We explored the autocrine regulation of insulin and nerve growth factor (NGF) on single adult rat pancreatic β-cell survival and hormone secretion. When NGF or insulin signaling were blocked in culture media, cell survival decreased compared with control cells, with apoptosis being the main mechanism of cell death. To further explore the role of glucose in β-cell survival, we cultured the cells for 16 h in 2.6 mmol/l glucose and observed that nearly 17% of the cells developed apoptosis; this effect was partially prevented by NGF and almost completely inhibited by insulin treatment. A high K+ concentration had the same effect, suggesting that insulin and NGF secretion by the cells was responsible for the survival effects and not glucose per se. Blocking NGF signaling with an NGF antibody or with K252a reduced insulin biosynthesis and secretion in the cells that survived the treatment. Moreover, the functional β-cell subpopulation with a higher insulin secretion rate is more susceptible to K252a. These results further indicate that NGF and insulin play important autoregulatory roles in pancreatic β-cell survival and function and strongly suggest the need to explore new focuses in diabetes treatment.
Splanchnic Cortisol Production Occurs in Humans
Authors: Basu Rita , Singh Ravinder J. , Basu Ananda , Chittilapilly Elizabeth G. , Johnson C. Michael , Toffolo Gianna , Cobelli Claudio , Rizza Robert A.
Published: March 2007

Glucocorticoids are potent regulators of protein, fat, and carbohydrate metabolism. To determine if cortisol production occurs within the splanchnic bed in humans, 11 nondiabetic subjects were studied using the hepatic/leg catheterization method along with an infusion of [9,11,12,12-2H4] cortisol (D4-cortisol) as proposed by Andrews et al. In the fasting state, there was net release (P < 0.05) of cortisol from the splanchnic bed (6.1 ± 2.6 μg/min) and net uptake (P < 0.05) by the leg (1.7 ± 0.7 μg/min). This, along with cortisol production by other tissues (e.g., the adrenals), resulted in a total-body cortisol appearance rate of 18.1 ± 1.9 μg/min. Fractional splanchnic D4-cortisol extraction averaged 12.9 ± 1.3% (P < 0.001), splanchnic cortisol uptake 14.8 ± 2.0 μg/min (P < 0.001), and splanchnic cortisol production 22.2 ± 3.3 μg/min (P < 0.001). On the other hand, fractional leg D4-cortisol extraction averaged 5.6 ± 1.8% (P < 0.02), leg cortisol uptake 2.3 ± 0.7 μg/min (P < 0.01), and leg cortisol production 0.4 ± 0.4 μg/min, which did not differ from zero. Because D4-cortisol loses a deuterium during conversion to [9,12,12-2H3] cortisone (D3-cortisone), which in turn generates [9,12,122H3] cortisol (D3-cortisol) via 11-β hydroxysteroid dehydrogenase (11β-HSD) type 1, D3-cortisol production can be used as an index of 11β-HSD type 1 activity. Net splanchnic D3-cortisol release (3.9 ± 0.4 μg/min) and splanchnic D3-cortisol production (7.1 ± 0.7 μg/min) occurred (P < 0.01) in all subjects. In contrast, there was minimal leg D3-cortisol production (0.04 ± 0.01 μg/min), resulting in a strong correlation between splanchnic D3-cortisol production and total-body 3D-cortisol production in both the fasting state (r = 0.84; P < 0.02) and during an infusion of insulin (r = 0.97; P < 0.01). Thus, splanchnic production of cortisol occurs in nondiabetic humans at rates approximating that which occurs in the remainder of the body. These data support the possibility that alterations in splanchnic cortisol production contribute to visceral fat accumulation and the hepatic insulin resistance of obesity or type 2 diabetes.
Vasomotor Responses to Hypoxia in Type 2 Diabetes
Authors: Weisbrod Cara J. , Eastwood Peter R. , O’Driscoll Gerard , Walsh Jennifer H. , Best Matthew , Halliwill John R. , Green Daniel J.
Published: March 2007

Type 2 diabetes is associated with vascular dysfunction, accelerated atherosclerotic morbidity, and mortality. Abnormal vasomotor responses to chemoreflex activation may contribute to the acceleration of atherosclerotic diabetes complications, but these responses have not previously been investigated. We measured forearm mean blood flow (MBF) and mean vascular conductance (MVC) responses to isocapnic hypoxia in seven healthy and eight type 2 diabetic subjects during local intra-arterial saline infusion and α-adrenergic blockade (phentolamine). The effects of hypoxia on saline and phentolamine responses significantly differed between groups; relative to normoxia, the %ΔMVC with hypoxia during saline was −3.3 ± 11.2% in control and 24.8 ± 13.3% in diabetic subjects, whereas phentolamine increased hypoxic %ΔMVC to similar levels (39.4 ± 9.7% in control subjects and 48.0 ± 11.8% in diabetic subjects, P < 0.05, two-way ANOVA). Absolute normoxic MBF responses during saline infusion were 91.9 ± 21.1 and 77.9 ± 15.3 in control and diabetic subjects, respectively, and phentolamine increased normoxic MBF to similar levels (165.2 ± 40.1 ml/min in control subjects and 175.9 ± 32.0 ml/min in diabetic subjects; both P < 0.05). These data indicate that diabetic and control subjects exhibit similar responses to hypoxia in the presence of α-adrenergic blockade despite evidence of exaggerated α-mediated vasoconstriction at rest.
Intra-Abdominal Fat Is a Major Determinant of the National Cholesterol Education Program Adult Treatment Panel III Criteria for the Metabolic Syndrome
Authors: Carr Darcy B. , Utzschneider Kristina M. , Hull Rebecca L. , Kodama Keiichi , Retzlaff Barbara M. , Brunzell John D. , Shofer Jane B. , Fish Brian E. , Knopp Robert H. , Kahn Steven E.
Published: March 2007

The underlying pathophysiology of the metabolic syndrome is the subject of debate, with both insulin resistance and obesity considered as important factors. We evaluated the differential effects of insulin resistance and central body fat distribution in determining the metabolic syndrome as defined by the National Cholesterol Education Program (NCEP) Adult Treatment Panel III. In addition, we determined which NCEP criteria were associated with insulin resistance and central adiposity. The subjects, 218 healthy men (n = 89) and women (n = 129) with a broad range of age (26–75 years) and BMI (18.4–46.8 kg/m2), underwent quantification of the insulin sensitivity index (Si) and intra-abdominal fat (IAF) and subcutaneous fat (SCF) areas. The metabolic syndrome was present in 34 (15.6%) of subjects who had a lower Si [median: 3.13 vs. 6.09 × 10−5 min−1/(pmol/l)] and higher IAF (166.3 vs. 79.1 cm2) and SCF (285.1 vs. 179.8 cm2) areas compared with subjects without the syndrome (P < 0.001). Multivariate models including Si, IAF, and SCF demonstrated that each parameter was associated with the syndrome. However, IAF was independently associated with all five of the metabolic syndrome criteria. In multivariable models containing the criteria as covariates, waist circumference and triglyceride levels were independently associated with Si and IAF and SCF areas (P < 0.001). Although insulin resistance and central body fat are both associated with the metabolic syndrome, IAF is independently associated with all of the criteria, suggesting that it may have a pathophysiological role. Of the NCEP criteria, waist circumference and triglycerides may best identify insulin resistance and visceral adiposity in individuals with a fasting plasma glucose <6.4 mmol/l.
Impaired Glucose Tolerance, but not Impaired Fasting Glucose, Is Associated With Increased Levels of Coronary Heart Disease Risk Factors
Authors: Blake Deirdre R. , Meigs James B. , Muller Denis C. , Najjar Samer S. , Andres Reubin , Nathan David M.
Published: March 2007

Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) identify individuals at high risk for progression to diabetes. Whether IFG and IGT have comparable coronary heart disease (CHD) risk factor profiles, independent of their progression to diabetes, is unclear. We determined CHD risk factor levels in 937 nondiabetic individuals at baseline and biannually over a mean follow-up period of 9.5 years. Subjects had no known CHD at baseline and had ≥2 (mean 4.2) oral glucose tolerance tests during follow-up. We classified glucose tolerance categories using American Diabetes Association diagnostic criteria or modified criteria that redefined IFG as 100–126 mg/dl, creating a similar baseline prevalence of IFG and IGT. Subjects who developed diabetes during follow-up were excluded from our analysis. Baseline CHD risk factors were similar in subjects with normal glucose tolerance (NGT) and IFG, but significantly more atherogenic in those with IGT or IFG + IGT. These findings were unchanged when the modified criteria were used, suggesting that IGT is phenotypically different from IFG and is associated with increased levels of CHD risk factors. Subjects with isolated IFG had similar levels of CHD risk factors as NGT subjects, even when IFG was redefined with a lower threshold. Although CHD risk factors were increased in the IGT group, the incidence of CHD events was not significantly different among groups, perhaps owing to the limited number of events. The differences in CHD risk factors among prediabetic groups may have clinical implications for screening strategies and CHD risk stratification of individuals with IFG and IGT.
Quantitative Trait Loci Near the Insulin-Degrading Enzyme (IDE) Gene Contribute to Variation in Plasma Insulin Levels
Authors: Gu Harvest F. , Efendic Suad , Nordman Sofia , Östenson Claes-Göran , Brismar Kerstin , Brookes Anthony J. , Prince Jonathan A.
Published: March 2007

Insulin-degrading enzyme (IDE) plays a principal role in the proteolysis of several peptides in addition to insulin and is encoded by IDE, which resides in a region of chromosome 10q that is linked to type 2 diabetes. Two recent studies presented genetic association data on IDE and type 2 diabetes (one positive and the other negative), but neither explored the fundamental question of whether polymorphism in IDE has a measurable influence on insulin levels in human populations. To address this possibility, 14 single nucleotide polymorphisms (SNPs) from a linkage disequilibrium block encompassing IDE have been genotyped in a sample of 321 impaired glucose tolerant and 403 nondiabetic control subjects. Analyses based on haplotypic genotypes (diplotypes), constructed with SNPs that differentiate common extant haplotypes extending across IDE, provided compelling evidence of association with fasting insulin levels (P = 0.0009), 2-h insulin levels (P = 0.0027), homeostasis model assessment of insulin resistance (P = 0.0001), and BMI (P = 0.0067), with effects exclusively evident in men. The strongest evidence for an effect of a single marker was obtained for rs2251101 (located near the 3′ untranslated region of IDE) on 2-h insulin levels (P = 0.000023). Diplotype analyses, however, suggest the presence of multiple interacting trait-modifying sequences in the region. Results indicate that polymorphism in/near IDE contributes to a large proportion of variance in plasma insulin levels and correlated traits, but questions of sex specificity and allelic heterogeneity will need to be taken into consideration as the molecular basis of the observed phenotypic effects unfolds.
Cholesterol Metabolism in Type 1 Diabetes
Authors: Gylling Helena , Tuominen Juha A. , Koivisto Veikko A. , Miettinen Tatu A.
Published: March 2007

Little information is available on cholesterol absorption and synthesis in human type 1 diabetes. We studied these variables using serum cholesterol precursor sterol ratios to cholesterol as surrogate markers of cholesterol synthesis and those of cholestanol and plant sterols to reflect cholesterol absorption in seven type 1 diabetic subjects and in five age- and body weight–matched control subjects. Total and lipoprotein cholesterol levels were similar, but triglycerides in intermediate-density lipoprotein (IDL) and LDL were higher in type 1 diabetic than in control subjects. Most of the marker sterols were transported by LDL and HDL in both groups. The percentage of esterified cholesterol was lower in triglyceride-rich lipoproteins in diabetic patients than in control subjects. The ratios of the absorption marker sterols in serum were higher, and those of the synthesis markers were lower in type 1 diabetic than in control subjects. The increased cholestanol ratios were seen in all lipoproteins, and those of free and total plant sterols were mainly in LDL, whereas the decreased free and total synthesis markers were mainly in all lipoproteins. In conclusion, high absorption and low synthesis marker sterols seem to characterize human type 1 diabetes. These findings could be related to low expression of ABC G/5 G/8 genes, resulting in high absorption of cholesterol and sterols in general and low synthesis of cholesterol compared with type 2 diabetes.
Normalization of Multiple Hemostatic Abnormalities in Uremic Type 1 Diabetic Patients After Kidney-Pancreas Transplantation
Authors: Fiorina Paolo , Folli Franco , D’Angelo Armando , Finzi Giovanna , Pellegatta Fabio , Guzzi Valeria , Fedeli Carlo , Valle Patrizia Della , Usellini Luciana , Placidi Claudia , Bifari Francesco , Belloni Daniela , Ferrero Elisabetta , Capella Carlo , Secchi Antonio
Published: March 2007

To evaluate the effects of kidney-pancreas transplantation on hemostatic abnormalities in uremic type 1 diabetic patients, we conducted a cross-sectional study involving 12 type 1 diabetic patients, 30 uremic type 1 diabetic patients, 27 uremic type 1 diabetic patients who had a kidney-pancreas transplant, 12 uremic type 1 diabetic patients who had a kidney-alone transplant, and 13 healthy control subjects. We evaluated platelet and clotting system. Platelets in the group of uremic type 1 diabetic patients were significantly larger than platelets in the other groups. Resting calcium levels were significantly higher in the uremic type 1 diabetic patients and uremic type 1 diabetic patients who had a kidney-alone transplant than in the type 1 diabetic patients who had a kidney-pancreas transplant and control subjects. CD41 expression was significantly reduced in platelets from the uremic type 1 diabetic patients compared with the other groups. Levels of hypercoagulability markers in the type 1 diabetic patients who had a kidney-pancreas transplant and, to a lesser extent, the uremic type 1 diabetic patients who had a kidney-alone transplant but not the uremic type 1 diabetic patients were similar to those of the control subjects. A reduction in natural anticoagulants was evident in the uremic type 1 diabetic patients, whereas near-normal values were observed in the type 1 diabetic patients who had a kidney-pancreas transplant and uremic type 1 diabetic patients who had a kidney-alone transplant. Hemostatic abnormalities were not observed in type 1 diabetic patients who had a kidney-pancreas transplant. This finding might explain the lower cardiovascular death rate observed in type 1 diabetic patients who had a kidney-pancreas transplant compared with uremic type 1 diabetic patients who had a kidney-alone transplant or uremic type 1 diabetic patients.
Polymorphisms in the Amino Acid Transporter Solute Carrier Family 6 (Neurotransmitter Transporter) Member 14 Gene Contribute to Polygenic Obesity in French Caucasians
Authors: Durand Emmanuelle , Boutin Philippe , Meyre David , Charles M. Aline , Clement Karine , Dina Christian , Froguel Philippe
Published: March 2007

Positional candidate gene analysis of the obesity-linked chromosome Xq24 locus identified two obesity-associated single nucleotide polymorphisms (SNPs) in the membrane amino acid transporter encoding the SLC6A14 (solute carrier family 6 [neurotransmitter transporter], member 14) gene in the Finnish population. Since we previously reported a modest evidence of linkage for this region in French obese families, we analyzed these SNPs in 1,267 obese adult case and 649 lean control subjects. SNPs 20649 C>T (odds ratio 1.23, 95% CI 1.04–1.45; P = 0.013) and 22510 C>G (1.36, 1.16–1.59; P = 0.0001) were shown to be associated with obesity in the French population. In addition, pedigree disequilibrium test results showed a modest excess of both at-risk SNP alleles in affected offspring (P = 0.05 and P = 0.08 for SNPs 20649 C>T and 22510 C>G, respectively). The SNP 22510 C>G at-risk G allele was associated, both in adult women with moderate obesity and in 234 obese girls, with higher body fat and modified perception of hunger and satiety (0.003 < P < 0.06). In conclusion, these data confirm an association of the SLC6A14 gene locus with obesity.
Toward Linking Structure With Function in ATP-Sensitive K+ Channels
Authors: Bryan Joseph , Vila-Carriles Wanda H. , Zhao Guiling , Babenko Audrey P. , Aguilar-Bryan Lydia
Published: March 2007

Advances in understanding the overall structural features of inward rectifiers and ATP-binding cassette (ABC) transporters are providing novel insight into the architecture of ATP-sensitive K+ channels (KATP channels) (KIR6.0/SUR)4. The structure of the KIR pore has been modeled on bacterial K+ channels, while the lipid-A exporter, MsbA, provides a template for the MDR-like core of sulfonylurea receptor (SUR)-1. TMD0, an NH2-terminal bundle of five α-helices found in SURs, binds to and activates KIR6.0. The adjacent cytoplasmic L0 linker serves a dual function, acting as a tether to link the MDR-like core to the KIR6.2/TMD0 complex and exerting bidirectional control over channel gating via interactions with the NH2-terminus of the KIR. Homology modeling of the SUR1 core offers the possibility of defining the glibenclamide/sulfonylurea binding pocket. Consistent with 30-year-old studies on the pharmacology of hypoglycemic agents, the pocket is bipartite. Elements of the COOH-terminal half of the core recognize a hydrophobic group in glibenclamide, adjacent to the sulfonylurea moiety, to provide selectivity for SUR1, while the benzamido group appears to be in proximity to L0 and the KIR NH2-terminus.
Chronic Exposure to GLP-1R Agonists Promotes Homologous GLP-1 Receptor Desensitization In Vitro but Does Not Attenuate GLP-1R–Dependent Glucose Homeostasis In Vivo
Authors: Baggio Laurie L. , Kim Jung-Guk , Drucker Daniel J.
Published: March 2007

Glucagon-like peptide-1 (GLP-1) stimulates glucose-dependent insulin secretion and inhibits food intake, gastric emptying, and glucagon secretion, actions that promote reduction of fasting and postprandial glycemia in subjects with type 2 diabetes. The rapid degradation of native GLP-1 has engendered interest in more stable longer-acting GLP-1 receptor agonists such as exendin-4 (Ex-4); however, the potential consequences of sustained GLP-1 receptor activation leading to receptor desensitization has not been extensively studied. We have now examined a range of GLP-1 receptor–dependent responses following treatment with Ex-4 using INS-1 cells in vitro and both wild-type control and MT–Ex-4 transgenic mice in vivo. Although both GLP-1 and Ex-4 acutely desensitized GLP-1 receptor–dependent cAMP accumulation in INS-1 cells, Ex-4 produced more sustained receptor desensitization, relative to GLP-1, in both acute (5–120 min) and chronic (24–72 h) experiments. PMA (4-phorbol 12-myristate 13-acetate) but not glucagon, glucose-dependent insulinotropic polypeptide (GIP), or epinephrine produced heterologous desensitization in vitro. MT–Ex-4 transgenic mice exhibited a reduced glycemic response to oral but not intraperitoneal glucose challenge following acute Ex-4 administration. In contrast, no differences in glycemic excursion or plasma insulin were observed after 1 week of twice-daily Ex-4 administration to wild-type versus MT–Ex-4 mice. Similarly, the levels of insulin, pdx-1, and GLP-1 receptor mRNA transcripts were comparable in wild-type and MT–Ex-4 transgenic mice after 1 week of Ex-4 administration. However, repeated Ex-4 administration significantly reduced food intake in MT–Ex-4 but not in wild-type mice. These findings illustrate that although Ex-4 is more potent than native GLP-1 in producing GLP-1 receptor desensitization in vitro, chronic exposure to Ex-4 in normal or transgenic mice is not associated with significant downregulation of GLP-1 receptor–dependent responses coupled to glucose homeostasis in vivo.
Suppression of Beta-Cell Secretion by Somatostatin Does Not Fully Reverse the Disproportionate Proinsulinemia of Type 2 Diabetes
Authors: Røder Michael E. , Kahn Steven E.
Published: March 2007

Disproportionate hyperproinsulinemia is a feature of β-cell dysfunction in type 2 diabetes. It has been hypothesized that this abnormality represents an intrinsic abnormality of the β-cell and/or may result from an increase in β-cell secretory demand. To address this, six patients with type 2 diabetes and six age- and BMI-matched normal subjects received a combined 3-h insulin and somatostatin clamp to decrease β-cell secretory demand. An arginine stimulation test was performed before and at the end of the clamp to measure β-cell peptide release. In keeping with the reduction in secretory demand, C-peptide levels were suppressed by 60–80% during the clamp, as were proinsulin (PI) levels. The arginine-stimulated PI/C-peptide ratio decreased in the diabetic subjects from 4.4 ± 1.5% before to 1.8 ± 0.5% after the clamp (P < 0.01). This latter ratio was similar to that observed in the normal subjects before the somatostatin infusion (1.5 ± 0.3%). In the normal subjects, after the clamp the PI/C-peptide ratio had decreased to 0.8 ± 0.3% (P < 0.01). Thus, the postclamp PI/C-peptide ratio in the subjects with type 2 diabetes was elevated compared with that in the normal subjects (P < 0.05). Based on these observations, while relief of secretory demand on β-cells by somatostatin decreases the disproportionate elevation in PI levels in patients with type 2 diabetes, the failure to normalize this measure suggests that an intrinsic abnormality of β-cell function exists in subjects with type 2 diabetes that may be aggravated by increased secretory demand.
Stimulation of Insulin Secretion by Intravenous Bolus Injection and Continuous Infusion of Gastric Inhibitory Polypeptide in Patients With Type 2 Diabetes and Healthy Control Subjects
Authors: Meier Juris J. , Gallwitz Baptist , Kask Bartholomaeus , Deacon Carolyn F. , Holst Jens J. , Schmidt Wolfgang E. , Nauck Michael A.
Published: March 2007

A reduced insulinotropic effect of gastric inhibitory polypeptide (GIP) is a characteristic of patients with type 2 diabetes. It was the aim of this study to determine the response of insulin secretion to different GIP doses administered by intravenous bolus injection and via continuous infusion in both healthy subjects and patients with type 2 diabetes. Eight patients with type 2 diabetes and eight healthy subjects participated in a 240-min hyperglycemic clamp (140 mg/dl) with intravenous infusion of placebo, GIP at a low dose, and GIP at a high dose, each administered continuously over 60 min. Boluses of placebo, 20 pmol GIP/kg, and 80 pmol GIP/kg were injected intravenously at 0, 60, and 120 min, respectively. Capillary and venous blood was drawn for glucose, insulin, C-peptide, and GIP. Plasma insulin and C-peptide concentrations were lower in patients than in control subjects during all infusion periods. GIP bolus administration evoked a significant increase in plasma insulin levels in both patients with type 2 diabetes and healthy subjects. In contrast, the continuous GIP infusion led to a weak increase in insulin secretion in both healthy subjects and type 2 diabetic patients. The dose-response relationship for the increase in insulin secretion after GIP bolus administration was similar in both groups, although at different degrees of β-cell function. The stimulation of insulin secretion by GIP is stronger after its bolus administration than during continuous infusion. Even though the insulin secretory capacity is generally impaired in patients with type 2 diabetes, the relative sensitivity of insulin secretion to a bolus administration of GIP is almost preserved. Therefore, the existence of a specific GIP receptor defect in type 2 diabetes appears unlikely.
Metabolic Syndrome and Robustness Tradeoffs
Authors: Kitano Hiroaki , Oda Kanae , Kimura Tomomi , Matsuoka Yukiko , Csete Marie , Doyle John , Muramatsu Masaaki
Published: March 2007

The metabolic syndrome is a highly complex breakdown of normal physiology characterized by obesity, insulin resistance, hyperlipidemia, and hypertension. Type 2 diabetes is a major manifestation of this syndrome, although increased risk for cardiovascular disease (CVD) often precedes the onset of frank clinical diabetes. Prevention and cure for this disease constellation is of major importance to world health. Because the metabolic syndrome affects multiple interacting organ systems (i.e., it is a systemic disease), a systems-level analysis of disease evolution is essential for both complete elucidation of its pathophysiology and improved approaches to therapy. The goal of this review is to provide a perspective on systems-level approaches to metabolic syndrome, with particular emphasis on type 2 diabetes. We consider that metabolic syndromes take over inherent dynamics of our body that ensure robustness against unstable food supply and pathogenic infections, and lead to chronic inflammation that ultimately results in CVD. This exemplifies how trade-offs between robustness against common perturbations (unstable food and infections) and fragility against unusual perturbations (high–energy content foods and low–energy utilization lifestyle) is exploited to form chronic diseases. Possible therapeutic approaches that target fragility of emergent robustness of the disease state have been discussed. A detailed molecular interaction map for adipocyte, hepatocyte, skeletal muscle cell, and pancreatic β-cell cross-talk in the metabolic syndrome can be viewed at http://www.systems-biology.org/001/003.html.
P2Y Purinergic Potentiation of Glucose-Induced Insulin Secretion and Pancreatic Beta-Cell Metabolism
Authors: Farret A. , Vignaud M. , Dietz S. , Vignon J. , Petit P. , Gross R.
Published: March 2007

Purine nucleotides and their analogs increase insulin secretion through activation of pancreatic β-cell P2Y receptors. The present study aimed at determining the role of glucose metabolism in the response to P2Y agonists and whether ATP-activated K+ channels (KATP channels) are involved in this response. The experiments were performed in the rat isolated pancreas, perfused with a Krebs-bicarbonate buffer supplemented with 2 g/l bovine serum albumin under dynamic glucose conditions from 5 mmol/l baseline to 11 mmol/l. ADPβS (0.5 μmol/l) was selected as a stable and selective P2Y agonist. This compound, ineffective on the 5 mmol/l glucose background, induced a significant threefold increase in insulin release triggered by the glucose challenge. The effect of ADPβS was markedly reduced (P < 0.001) in the presence of an inhibitor of glucose metabolism. In addition to glucose, the ADP analog also amplified the β-cell insulin response to 15 mmol/l methyl pyruvate (P < 0.05), but it was ineffective on the insulin response to 2.5 mmol/l methyl succinate. A nonmetabolic stimulus was applied using tolbutamide (185 μmol/l). Insulin secretion induced by the KATP channel blocker was strongly reinforced by ADPβS (P < 0.001), which prompted us to check a possible interplay of KATP channels in the effect of ADPβS. In the presence of diazoxide 250 μmol/l and 21 mmol/l KCl, ADPβS still amplified the second phase of glucose-induced insulin secretion (P < 0.001). We conclude that P2Y receptor activation is able to promote insulin secretion through a mechanism, involving β-cell metabolism and a rise in intracellular calcium; this effect does not result from a direct inhibitory effect on KATP channels.
AMP-Activated Protein Kinase: A New Beta-Cell Glucose Sensor?
Authors: Leclerc Isabelle , Rutter Guy A.
Published: March 2007

Stimulation of AMP-activated protein kinase (AMPK) in skeletal muscle and liver is seen as an exciting prospect for the treatment of type 2 diabetes. However, we have recently demonstrated that changes in AMPK activity accompany the exposure of pancreatic islet β-cells to elevated glucose concentrations and may be involved in the activation of insulin secretion. Here, we discuss this hypothesis and explore the potential role of changes in AMPK activity in the actions of other secretagogues. Amino acids decreased AMPK activity in MIN6 β-cells with an order of potency for inhibition: arg = leu < gln = leu + glu < glucose, which was closely correlated with the stimulation of insulin release (r2 = 0.76). By contrast, increases in intracellular Ca2+ concentration provoked by cell depolarization with KCl activated AMPK in the face of increased free intracellular ATP concentrations. Elevation of intracellular cAMP levels with isobutylmethyxanthine or forskolin had no effect on AMPK activity. We conclude that metabolizable amino acids regulate AMPK in the β-cell via increases in the cytosolic ATP/AMP ratio and via phosphorylation by the upstream kinase LKB1. Intracellular Ca2+ ions may activate AMPK by calmodulin kinase 1 kinase-mediated phosphorylation. The latter may act as a novel feedback mechanism to inhibit excessive insulin secretion under some circumstances.
Liver X Receptor Activation Stimulates Insulin Secretion via Modulation of Glucose and Lipid Metabolism in Pancreatic Beta-Cells
Authors: Efanov Alexander M. , Sewing Sabine , Bokvist Krister , Gromada Jesper
Published: March 2007

Liver X receptors (LXRs) α and β, transcription factors of a nuclear hormone receptor family, are expressed in pancreatic islets as well as glucagon-secreting and insulin-secreting cell lines. Culture of pancreatic islets or insulin-secreting MIN6 cells with a LXR specific agonist T0901317 caused an increase in glucose-dependent insulin secretion and islet insulin content. The stimulatory effect of T0901317 on insulin secretion was observed only after >72 h of islet culture with the compound. In MIN6 cells, T0901317 increased protein expression of lipogenic enzymes, fatty acid synthase, and acetyl-CoA carboxylase. LXR activation also produced an increase in glucokinase protein and pyruvate carboxylase (PC) activity levels. The PC inhibitor phenylacetic acid abolished the increase in insulin secretion in cells treated with T0901317. The results suggest that LXRs can control insulin secretion and biosynthesis via regulation of glucose and lipid metabolism in pancreatic β-cells.
Postprandial Hyperglycemia and Diabetes Complications
Authors: Ceriello Antonio
Published: March 2007

Increasing evidence suggests that the postprandial state is a contributing factor to the development of atherosclerosis. In diabetes, the postprandial phase is characterized by a rapid and large increase in blood glucose levels, and the possibility that the postprandial “hyperglycemic spikes” may be relevant to the onset of cardiovascular complications has recently received much attention. Epidemiological studies and preliminary intervention studies have shown that postprandial hyperglycemia is a direct and independent risk factor for cardiovascular disease (CVD). Most of the cardiovascular risk factors are modified in the postprandial phase in diabetic subjects and directly affected by an acute increase of glycemia. The mechanisms through which acute hyperglycemia exerts its effects may be identified in the production of free radicals. This alarmingly suggestive body of evidence for a harmful effect of postprandial hyperglycemia on diabetes complications has been sufficient to influence guidelines from key professional scientific societies. Correcting the postprandial hyperglycemia may form part of the strategy for the prevention and management of CVDs in diabetes.
Nuclear Factor-κB Activity in β-Cells Is Required for Glucose-Stimulated Insulin Secretion
Authors: Norlin Stefan , Ahlgren Ulf , Edlund Helena
Published: March 2007

Glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells depends on coordinated glucose uptake, oxidative metabolism, and Ca2+-triggered insulin exocytosis. Impaired GSIS is a hallmark of type 2 diabetes. However, at present we know very little about the molecular mechanisms that induce and maintain the expression of genes required for GSIS in β-cells. The transcription factor nuclear factor-κB (NF-κB) is activated by an increase in intracellular Ca2+ in β-cells. Here, we show that attenuation of NF-κB activation in β-cells generates mice with impaired GSIS, and that the β-cells show perturbed expression of genes required for glucose uptake, oxidative metabolism, and insulin exocytosis. Thus, NF-κB appears to be part of a positive regulatory circuit that maintains GSIS in pancreatic β-cells.
Delayed Transcapillary Delivery of Insulin to Muscle Interstitial Fluid After Oral Glucose Load in Obese Subjects
Authors: Sjöstrand Mikaela , Gudbjörnsdottir Soffia , Strindberg Lena , Lönnroth Peter
Published: March 2007

Obese subjects exhibit a delay in insulin action and delivery of insulin to muscle interstitial fluid during glucose/insulin infusion. The aim of the present study was to follow the distribution of insulin to skeletal muscle after an oral glucose load in obese subjects. We conducted an oral glucose tolerance test (OGTT) in 10 lean and 10 obese subjects (BMI 23 ± 0.6 vs. 33 ± 1.2 kg/m2; P < 0.001). Insulin measurements in muscle interstitial fluid were combined with forearm arteriovenous catheterization and blood flow measurements. In the obese group, interstitial insulin was significantly (35–55%) lower than plasma insulin (P < 0.05) during the 1st h after the OGTT, whereas in lean subjects, no significant difference was found between interstitial and plasma insulin levels during the same time period. The permeability surface area product for glucose, representing capillary recruitment, increased in the lean group (P < 0.05) but not in the obese group (NS). Obese subjects had a significantly higher plasma insulin level at 90–120 min after oral glucose (398 ± 57 vs. 224 ± 37 pmol/l in control subjects; P < 0.05). The significant gradient between plasma insulin and muscle interstitial insulin during the first hour after OGTT suggests a slow delivery of insulin in obese subjects. The hindered transcapillary transport of insulin may be attributable to a defect in insulin-mediated capillary recruitment.
Heritability of Insulin Secretion, Peripheral and Hepatic Insulin Action, and Intracellular Glucose Partitioning in Young and Old Danish Twins
Authors: Poulsen Pernille , Levin Klaus , Petersen Inge , Christensen Kaare , Beck-Nielsen Henning , Vaag Allan
Published: March 2007

The etiology of type 2 diabetes is multifactorial, including genetic as well as pre- and postnatal factors that influence several different defects of glucose homeostasis, primarily in muscle, β-cells, and liver. In the present twin study, we report heritability estimates (h2) for measures of insulin secretion, insulin resistance, hepatic glucose production (HGP), and intracellular glucose partitioning using gold standard methods (euglycemic-hyperinsulinemic clamp technique, tritiated glucose infusion, indirect calorimetry, and intravenous glucose tolerance testing) among 110 younger (22–31 years of age) and 86 older (57–66 years of age) twins. To obtain a valid estimate of β-cell function, insulin secretion was adjusted for the individual degree of insulin action (disposition index). In both age-groups there was a major genetic component in the etiology of insulin secretion that was statistically significantly higher among older twins (young h2 = 0.75 [0.55–0.86] and old h2 = 0.84 [0.69–0.92], P < 0.05). The heritability estimates for peripheral insulin sensitivity (young h2 = 0.53 [0.28–0.71] and old h2 = 0.55 [0.20–0.76]) and nonoxidative glucose metabolism (young h2 = 0.50 [0.32–0.64] and old h2 = 0.48 [0.04–0.72]) were similar in younger and older twins, supporting the notion of both genetic and environmental etiological factors in the control of insulin action and nonoxidative glucose metabolism. The results suggested that HGP was predominantly controlled by nongenetic factors in both young and old twins. In conclusion, we provide further evidence for a role of genes in controlling insulin secretion, insulin action, and nonoxidative glucose metabolism. The relative contribution of genes versus environment on in vivo insulin secretion exhibited an age dependency with a slightly greater relative impact of genes among older as compared with younger twins.
Islet-infiltrating B-Cells in Nonobese Diabetic Mice Predominantly Target Nervous System Elements
Authors: Carrillo Jorge , Puertas Maria Carmen , Alba Aurora , Ampudia Rosa Maria , Pastor Xavier , Planas Raquel , Riutort Nadal , Alonso Nuria , Pujol-Borrell Ricardo , Santamaria Pere , Vives-Pi Marta , Verdaguer Joan
Published: March 2007

B-cells accumulate in pancreatic islets during the autoimmune response that precedes the onset of type 1 diabetes. However, the role and antigenic specificity of these cells remain a mystery. To elucidate the antigenic repertoire of islet-infiltrating B-cells in type 1 diabetes, we generated hybridoma cell lines of islet-infiltrating B-cells from nonobese diabetic (NOD) mice and NOD mice expressing a diabetogenic T-cell receptor (8.3-NOD). Surprisingly, characterization of the tissue specificity of the antibodies secreted by these cells revealed that a predominant fraction of these hybridomas produce antibodies specific for the pancreatic nervous system. Similar results were obtained with B-cell hybridomas derived from mild insulitic lesions of diabetes-resistant (NOD × NOR)F1 and 8.3-(NOD × NOR)F1 mice. Immunoglobulin class analyses further indicated that most islet-derived hybridomas had arisen from B-cells that had undergone immunoglobulin class switch recombination, suggesting that islet-associated B-cells are involved in active, T-helper–driven immune responses against local antigenic targets. This is the first evidence showing the existence of a predominant active B-cell response in situ against pancreatic nervous system elements in diabetogenesis. Our data are consistent with the idea that this B-cell response precedes the progression of insulitis to overt diabetes, thus strongly supporting the idea that pancreatic nervous system elements are early targets in type 1 diabetes.
Plasma Visfatin Concentrations and Fat Depot–Specific mRNA Expression in Humans
Authors: Berndt Janin , Klöting Nora , Kralisch Susan , Kovacs Peter , Fasshauer Mathias , Schön Michael R. , Stumvoll Michael , Blüher Matthias
Published: March 2007

Visceral and subcutaneous adipose tissue display important metabolic differences that underlie the association of visceral obesity with obesity-related cardiovascular and metabolic alterations. Recently, visfatin was identified as an adipokine, which is predominantly secreted from visceral adipose tissue both in humans and mice. In this study, we examined whether visfatin plasma concentrations (using enzyme immunosorbent assay) and mRNA expression (using RT-PCR) in visceral and subcutaneous fat correlates with anthropometric and metabolic parameters in 189 subjects with a wide range of obesity, body fat distribution, insulin sensitivity, and glucose tolerance. Visfatin plasma concentration correlates positively with the visceral visfatin mRNA expression (r2 = 0.17, P < 0.0001), BMI (r2 = 0.062, P = 0.004), percent body fat (r2 = 0.048, P = 0.01), and negatively with subcutaneous visfatin mRNA expression (r2 = 0.18, P < 0.0001). However, in a subgroup of 73 individuals, in which visceral fat mass was calculated from computed tomography scans, there was no correlation between plasma visfatin concentrations and visceral fat mass. We found no significant correlation between visfatin plasma concentrations and parameters of insulin sensitivity, including fasting insulin, fasting plasma glucose concentrations, and the glucose infusion rate during the steady state of an euglycemic-hyperinsulinemic clamp independent of percent body fat. Visfatin gene expression was not different between visceral and subcutaneous adipose tissue in the entire study group nor in selected subgroups. We found a significant correlation between visceral visfatin gene expression and BMI (r2 = 0.06, P = 0.001) and percent body fat (measured using dual-energy X-ray absorptiometry) (r2 = 0.044, P = 0.004), whereas no significant association between BMI or percent body fat and subcutaneous visfatin mRNA expression existed (both P >0.5). In conclusion, visfatin plasma concentrations and visceral visfatin mRNA expression correlated with measures of obesity but not with visceral fat mass or waist-to-hip ratio. In addition, we did not find differences in visfatin mRNA expression between visceral and subcutaneous adipose tissue in humans.
Variants in Hepatocyte Nuclear Factor 4α Are Modestly Associated With Type 2 Diabetes in Pima Indians
Authors: Muller Yunhua Li , Infante Aniello M. , Hanson Robert L. , Love-Gregory Latisha , Knowler William , Bogardus Clifton , Baier Leslie J.
Published: March 2007

Single nucleotide polymorphisms (SNPs) within the hepatocyte nuclear factor 4α (HNF4α) gene are associated with type 2 diabetes in Finns and Ashkenazi Jews. Previous studies in both populations have reported linkage to type 2 diabetes near the HNF4α locus on chromosome 20q12-13. To investigate whether HNF4α is a diabetes susceptibility gene in Pima Indians, a population with the highest reported prevalence of type 2 diabetes but with no evidence for linkage of the disease on chromosome 20q, 19 SNPs across the promoter and coding region of HNF4α were genotyped for association analysis. In a group of 1,037 Pima Indians (573 diabetic and 464 nondiabetic subjects), three SNPs in HNF4α (rs3212183 and rs2071197 located in introns 3 and 1, respectively, and rs6031558, an extremely rare SNP located in the P2 promoter region) were modestly associated with type 2 diabetes (rs3212183 odds ratio [OR] 1.34 [95% CI 1.07–1.67], P = 0.009; rs2071197 1.34 [1.07–1.66], P = 0.008; and rs6031558 3.18 [1.03–9.84], P = 0.04, adjusted for age, sex, birth year, heritage, and family membership). We conclude that variants in HNF4α do not appear to be major determinants for type 2 diabetes in Pima Indians; however, HNF4α may have a minor role in type 2 diabetes susceptibility within this Native American population.
Common Polymorphisms in the USF1 Gene Are Not Associated With Type 2 Diabetes in French Caucasians
Authors: Gibson Fernando , Hercberg Serge , Froguel Philippe
Published: March 2007

Upstream transcription factor 1 (USF1) is a ubiquitously expressed transcription factor of the basic helix-loop-helix leucine zipper family that has been shown to regulate the expression of a raft of key genes involved in glucose and lipid metabolism. The USF1 gene is located at chromosome 1q22-q23, within the most consistently replicated type 2 diabetes susceptibility locus in the human genome. In this study, we have examined the contribution of eight common USF1 single nucleotide polymorphisms (SNPs) to type 2 diabetes susceptibility in the French Caucasian population. None of the USF1 SNPs genotyped, including two SNPs previously associated with familial combined hyperlipidemia (rs2073658 and rs3737787), showed evidence of association with type 2 diabetes. In addition, USF1 SNPs were not associated with plasma levels of glucose, triglycerides, total cholesterol, or apolipoproteins A1 or B in normoglycemic subjects. A total of four common USF1 haplotypes were identified, accounting for >99% of chromosomes. There was no significant difference in the USF1 haplotype distribution of the case and control subjects. In conclusion, we report here that we were unable to find any evidence to support the hypothesis that genetic variation in the USF1 gene makes a significant contribution to type 2 diabetes susceptibility in the French Caucasian population.