bluuebunny/crossref_metadata_2025 huggingface dataset:
Coordinated Regulation of Fat-Specific and Liver-Specific Glycerol Channels, Aquaporin Adipose and Aquaporin 9
Authors: Kuriyama Hiroshi , Shimomura Iichiro , Kishida Ken , Kondo Hidehiko , Furuyama Naoki , Nishizawa Hitoshi , Maeda Norikazu , Matsuda Morihiro , Nagaretani Hiroyuki , Kihara Shinji , Nakamura Tadashi , Tochino Yoshihiro , Funahashi Tohru , Matsuzawa Yuji
Published: March 2007

Plasma glycerol is a major substrate for hepatic gluconeogenesis. Aquaporin adipose (AQPap/7), an adipose-specific glycerol channel, provides fat-derived glycerol into plasma. In the present study, we cloned the coding and promoter regions of mouse aquaporin 9 (AQP9), a liver-specific glycerol channel. Fasting and refeeding of mice increased and decreased hepatic AQP9 mRNA levels, respectively. Insulin deficiency induced by streptozotocin resulted in increased hepatic AQP9 mRNA. These changes in hepatic AQP9 mRNA were accompanied by those of hepatic gluconeogenic mRNAs and plasma glycerol levels. In cultured hepatocytes, insulin downregulated AQP9 mRNA. The AQP9 promoter contained the negative insulin response element TGTTTTC at −496/−502, similar to the promoter of the AQPap/7 gene. In contrast, in insulin-resistant db+/db+ mice, AQPap/7 mRNA in fat and AQP9 mRNA in liver were increased, despite hyperinsulinemia, with high plasma glycerol and glucose levels. Glycerol infusion in the db+/db+ mice augmented hepatic glucose output. Our results indicate that coordinated regulations of fat-specific AQPap/7 and liver-specific AQP9 should be crucial to determine glucose metabolism in physiology and insulin resistance.
Effect of Weight Loss on Insulin Sensitivity and Intramuscular Long-Chain Fatty Acyl-CoAs in Morbidly Obese Subjects
Authors: Houmard Joseph A. , Tanner Charles J. , Yu Chunli , Cunningham Paul G. , Pories Walter J. , MacDonald Kenneth G. , Shulman Gerald I.
Published: March 2007

Increases in intramyocellular long-chain fatty acyl-CoAs (LCACoA) have been implicated in the pathogenesis of insulin resistance in skeletal muscle. To test this hypothesis, we measured muscle (vastus lateralis) LCACoA content and insulin action in morbidly obese patients (n = 11) before and after weight loss (gastric bypass surgery). The intervention produced significant weight loss (142.3 ± 6.8 vs. 79.6 ± 4.1 kg for before versus after surgery, respectively). Fasting insulin decreased by ∼ 84% (23.3 ± 3.8 vs. 3.8 ± 0.5 mU/ml), and insulin sensitivity, as determined by minimal model, increased by ∼360% (1.2 ± 0.3 vs. 4.1 ± 0.5 min−1 · [μ U/kg−1]) indicating enhanced insulin action. Muscle palmityl CoA (16:0; 0.54 ± 0.08 vs. 0.35 ± 0.04 nmol/g wet wt) concentration decreased by ∼35% (P < 0.05) with weight loss, whereas stearate CoA (18:0; −17%; 0.65 ± 0.05 vs. 0.54 ± 0.03 nmol/g wet wt) and linoleate CoA (18:2; −30%; 2.47 ± 0.27 vs. 1.66 ± 0.19 nmol/g wet wt) were also reduced (P < 0.05). There were no statistically significant declines in muscle palmitoleate CoA (16:1), oleate CoA (18:1), or total LCACoA content. These data suggest that a reduction in intramuscular LCACoA content may be responsible, at least in part, for the enhanced insulin action observed with weight loss in obese individuals.
Different Regulated Expression of the Tyrosine Phosphatase-Like Proteins IA-2 and Phogrin by Glucose and Insulin in Pancreatic Islets
Authors: Löbner Kristian , Steinbrenner Holger , Roberts Graham A. , Ling Zhidong , Huang Guo-Cai , Piquer Sandra , Pipeleers Daniel G. , Seissler Jochen , Christie Michael R.
Published: March 2007

IA-2 and phogrin are tyrosine phosphatase-like proteins that may mediate interactions between secretory granules and cytoskeleton in islets and neuroendocrine tissues. We investigated factors that regulate IA-2 and phogrin expression and their relationship to maturation of insulin secretory responses that occur after birth. Islet content of IA-2, but not phogrin, increased during the first 10 days of life in rats, when insulin secretion in response to glucose increased to adult levels. In cultured 5-day-old rat islets, IA-2 protein and mRNA was increased by glucose and agents that potentiate insulin secretion by the cAMP pathway. Addition of insulin increased IA-2 protein levels and insulin biosynthesis without affecting IA-2 mRNA. Blocking insulin secretion with diazoxide or insulin action with insulin receptor antibodies inhibited glucose-induced increases in IA-2 protein, but not those of mRNA. Phogrin expression was unchanged by all agents. Thus, IA-2 is regulated at the mRNA level by glucose and elevated cAMP, whereas locally secreted insulin modulates IA-2 protein levels by stimulating biosynthesis. In contrast, phogrin expression is insensitive to factors that modify β-cell function. These results demonstrate differential regulation of two closely related secretory granule components and identify IA-2 as a granule membrane protein subject to autocrine regulation by insulin.
C-Peptide Exerts Beneficial Effects on Myocardial Blood Flow and Function in Patients With Type 1 Diabetes
Authors: Hansen Alexander , Johansson Bo-Lennart , Wahren John , von Bibra Helene
Published: March 2007

Myocardial dysfunction, perfusion abnormalities, and the extent to which these abnormalities may be reversed by C-peptide administration was assessed in type 1 diabetic patients. Eight patients were studied before and during a 0.84-mg/kg dipyridamole administration using a randomized double-blind crossover protocol with infusion of C-peptide (6 pmol · kg−1 · min−1) or saline during 60 min on two different days. Myocardial function was measured as peak myocardial velocity during systole (Vs) and early diastole (Vd) by pulsed tissue Doppler imaging. Myocardial contrast echocardiography was used for assessment of myocardial blood volume (SImax) and myocardial blood flow index (MBFI) calculated from the relation between trigger interval and signal intensity. Eight age-matched healthy volunteers served as control subjects. In the basal state, Vd (13.8 ± 0.6 vs. 15.6 ± 0.5 cm/s, P < 0.04) and SImax (6.6 ± 0.6 vs. 8.2 ± 0.6 a.u. P < 0.04) were reduced in patients compared with control subjects. Dipyridamole administration significantly increased indexes of myocardial function and blood flow to a similar extent in patients and control subjects. During C-peptide administration, Vs and Vd increased by 12% (P = 0.03), SImax increased from 6.6 ± 0.6 to 8.1 ± 0.7 a.u. (P < 0.02), and MBFI increased from 3.3 ± 0.4 to 5.3 ± 0.9 (P < 0.05). The results demonstrate that type 1 diabetic patients have impaired myocardial function and perfusion in the basal state that can be improved by short-term replacement of C-peptide.
Amelioration of Long-Term Renal Changes in Obese Type 2 Diabetic Mice by a Neutralizing Vascular Endothelial Growth Factor Antibody
Authors: Flyvbjerg Allan , Dagnæs-Hansen Frederik , De Vriese An S. , Schrijvers Bieke F. , Tilton Ronald G. , Rasch Ruth
Published: March 2007

Diabetic nephropathy in type 2 diabetic patients is a frequent complication associated with increased morbidity and mortality. Various growth factors and cytokines have been implicated in the pathogenesis of diabetic kidney disease, including vascular endothelial growth factor (VEGF). To explore a role for VEGF in renal changes in type 2 diabetes, we examined the renal effects of a neutralizing murine VEGF antibody in the diabetic db/db mouse, a model of obese type 2 diabetes. One group of db/db mice was treated for 2 months with a VEGF antibody, while another db/db group was treated for the same period with an isotype-matched irrelevant IgG. A third group consisting of nondiabetic db/+ mice was treated with the same isotype-matched IgG for 2 months. Placebo-treated db/db mice showed a pronounced increase in kidney weight, glomerular volume, basement membrane thickness (BMT), total mesangial volume, urinary albumin excretion (UAE), and creatinine clearance (CrCl) when compared with nondiabetic controls. In VEGF antibody-treated db/db mice, increases in kidney weight, glomerular volume, BMT, and UAE were attenuated, whereas the increase in CrCl was abolished. VEGF antibody administration tended to reduce expansion in total mesangial volume. These effects in diabetic animals were seen without impact on body weight, blood glucose, insulin levels, or food consumption. In conclusion, chronic inhibition of VEGF in db/db mice ameliorates the diabetic renal changes seen in type 2 diabetes.
Impact of Duration of Infusion and Choice of Isotope Label on Isotope Recycling in Glucose Homeostasis
Authors: Tigas Stelios K. , Sunehag Agneta L. , Haymond Morey W.
Published: March 2007

The purposes of this study were to quantify the impact of the duration of infusion and choice of stable isotope of glucose on measures of glucose rate of appearance (glucose Ra) and to determine whether the differences observed were due to tracer recycling via the glycogen pool (direct pathway) or gluconeogenesis (indirect pathway). Six healthy adult volunteers were studied on four occasions in the postabsorptive state during infusions of [1-13C]glucose and [6,6-2H2]glucose: 2.5-h infusion of both (A), and 2.5-h infusion of one (B) and 14.5-h infusion of the other isotope (C), and 5-h infusion of [6,6-2H2]glucose and 2.5-h infusion of [1-13C]glucose (D). Infusion of both isotopes for 2.5 h resulted in similar glucose Ra values. When compared with a 14.5-h infusion, the 2.5-h glucose tracer infusion overestimated glucose Ra by 26–35%. Glucose 13C recycled via the Cori cycle, resulting in slower decay from the plasma pool and longer half-life of [1-13C]glucose compared with [6,6-2H2]glucose. There was no detectable release of [13C]glucose or [2H2]glucose tracer into the plasma pool after administration of glucagon. These data demonstrate that glucose Ra varies not as a result of isotope cycling but as a result of differences in duration of isotope infusion regardless of the isotope used. This is most likely due to incomplete isotope and substrate equilibration with the 2.5-h infusion. The potential error was reduced by nearly 80% using a 5-h infusion of [6,6-2H2]glucose. These studies demonstrate that the duration of isotope infusion has significantly greater impact on quantitation of glucose Ra than does the selection of isotope.
Dissociation of Obesity and Impaired Glucose Disposal in Mice Overexpressing Acyl Coenzyme A:Diacylglycerol Acyltransferase 1 in White Adipose Tissue
Authors: Chen Hubert C. , Stone Scot J. , Zhou Ping , Buhman Kimberly K. , Farese Robert V.
Published: March 2007

Acyl coenzyme A:diacylglycerol acyltransferase 1 (DGAT1) is one of two DGAT enzymes known to catalyze the final step in mammalian triglyceride synthesis. Mice deficient in DGAT1 are resistant to obesity and have enhanced insulin sensitivity. To understand better the relationship between triglyceride synthesis and energy and glucose metabolism, we generated transgenic (aP2-Dgat1) mice in which expression of murine DGAT1 in the white adipose tissue (WAT) was twofold higher than normal. aP2-Dgat1 mice that were fed a regular diet had larger adipocytes and greater total fat pad weight than wild-type (WT) mice. In response to a high-fat diet, aP2-Dgat1 mice became more obese (∼20% greater body weight after 15 weeks) than WT mice. However, the increase in adiposity in aP2-Dgat1 mice was not associated with impaired glucose disposal, as demonstrated by glucose and insulin tolerance tests. Correlating with this finding, triglyceride deposition in the liver and skeletal muscle, two major target tissues of insulin, was similar in aP2-Dgat1 and WT mice. Thus, DGAT1 overexpression in murine WAT provides a model in which obesity does not impair glucose disposal. Our findings support the lipotoxicity hypothesis that the deposition of triglycerides in insulin-sensitive tissues other than adipocytes causes insulin resistance.
SERCA3 Ablation Does Not Impair Insulin Secretion but Suggests Distinct Roles of Different Sarcoendoplasmic Reticulum Ca2+ Pumps for Ca2+ Homeostasis in Pancreatic β-cells
Authors: Arredouani Abdelilah , Guiot Yves , Jonas Jean-Christophe , Liu Lynne H. , Nenquin Myriam , Pertusa José A. , Rahier Jacques , Rolland Jean-François , Shull Gary E. , Stevens Martine , Wuytack Frank , Henquin Jean-Claude , Gilon Patrick
Published: March 2007

Two sarcoendoplasmic reticulum Ca2+-ATPases, SERCA3 and SERCA2b, are expressed in pancreatic islets. Immunocytochemistry showed that SERCA3 is restricted to β-cells in the mouse pancreas. Control and SERCA3-deficient mice were used to evaluate the role of SERCA3 in β-cell cytosolic-free Ca2+ concentration ([Ca2+]c) regulation, insulin secretion, and glucose homeostasis. Basal [Ca2+]c was not increased by SERCA3 ablation. Stimulation with glucose induced a transient drop in basal [Ca2+]c that was suppressed by inhibition of all SERCAs with thapsigargin (TG) but unaffected by selective SERCA3 ablation. Ca2+ mobilization by acetylcholine was normal in SERCA3-deficient β-cells. In contrast, [Ca2+]c oscillations resulting from intermittent glucose-stimulated Ca2+ influx and [Ca2+]c transients induced by pulses of high K+ were similarly affected by SERCA3 ablation or TG pretreatment of control islets; their amplitude was increased and their slow descending phase suppressed. This suggests that, during the decay of each oscillation, the endoplasmic reticulum releases Ca2+ that was pumped by SERCA3 during the upstroke phase. SERCA3 ablation increased the insulin response of islets to 15 mmol/l glucose. However, basal and postprandial plasma glucose and insulin concentrations in SERCA3-deficient mice were normal. In conclusion, SERCA2b, but not SERCA3, is involved in basal [Ca2+]c regulation in β-cells. SERCA3 becomes operative when [Ca2+]c rises and is required for normal [Ca2+]c oscillations in response to glucose. However, a lack of SERCA3 is insufficient in itself to alter glucose homeostasis or impair insulin secretion in mice.
Prevention of Hypoglycemia Using Risk Assessment With a Continuous Glucose Monitoring System
Authors: Choleau Carine , Dokladal Petr , Klein Jean-Claude , Ward W. Kenneth , Wilson George S. , Reach Gérard
Published: March 2007

Due to the lag between sugar intake and the beginning of recovery from hypoglycemia, it is necessary to intervene in an anticipatory way if one wants to prevent, not only detect, hypoglycemia. This article presents the principle of a hypoglycemia prevention system based on risk assessment. The risk situation can be defined as the moment when the system estimates that the glucose concentration is expected to reach a hypoglycemia threshold in less than a given time (e.g., 20 min). Since there are well-known discrepancies between blood and interstitial glucose concentrations, the aim of this experimental study performed in nondiabetic rats was first to validate this strategy, and second to determine whether it can work when the glucose concentration is estimated by a glucose sensor in subcutaneous tissue rather than in blood. We used a model of controlled decrease in blood glucose concentration. A glucose infusion, the profile of which mimicked the appearance of glucose from an intragastric load, was administered either when hypoglycemia was detected or on the basis of risk recognition. Despite the lag between the beginning of the load and that of the increase in blood glucose concentration, which was in all experiments 15–20 min, hypoglycemia was fully prevented without overshoot hyperglycemia in the groups of rats in which the glucose load was started when the hypoglycemia risk was detected, on the basis of either blood or interstitial glucose concentration. This was, of course, not the case when the same glucose load was infused at the detection of the hypoglycemia threshold.
ALT-946 and Aminoguanidine, Inhibitors of Advanced Glycation, Improve Severe Nephropathy in the Diabetic Transgenic (mREN-2)27 Rat
Authors: Wilkinson-Berka Jennifer L. , Kelly Darren J. , Koerner Suzanne M. , Jaworski Kassie , Davis Belinda , Thallas Vicki , Cooper Mark E.
Published: March 2007

The severe diabetic nephropathy that develops in the hypertensive transgenic (mRen-2)27 rat with streptozotocin (STZ) diabetes has previously been considered angiotensin II-dependent. Because metabolic pathways are also activated in the diabetic kidney, the present study aimed to determine whether renoprotection could be afforded with inhibitors of advanced glycation end products (AGEs), ALT-946, and aminoguanidine (AG). At 6 weeks of age, nondiabetic control and STZ diabetic Ren-2 rats were randomized to receive vehicle, ALT-946 (1 g/l), or AG (1 g/l) and were studied for 12 weeks. Systolic blood pressure was unchanged with diabetes, ALT-946, or AG. Both kidney weight and glomerular filtration rate were increased with diabetes and unchanged with ALT-946 or AG. ALT-946 and AG equally ameliorated glomerulosclerosis and medullary pathology; however, ALT-946 did reduce cortical tubular degeneration to a greater extent than AG. Albumin excretion rate, which was elevated with diabetes, was reduced with ALT-946 but not AG. AGE immunolabeling was increased in glomeruli and reduced with ALT-946 and AG. These findings indicate that even in the context of renal injury presumed to be primarily blood pressure- and/or angiotensin II-dependent, approaches that interfere with metabolic pathways such as inhibitors of AGE formation can confer renal protection in experimental diabetes.
STAT5 Activation Induced by Diabetic LDL Depends on LDL Glycation and Occurs Via src Kinase Activity
Authors: Brizzi Maria Felice , Dentelli Patrizia , Gambino Roberto , Cabodi Sara , Cassader Maurizio , Castelli Ada , Defilippi Paola , Pegoraro Luigi , Pagano Gianfranco
Published: March 2007

Advanced glycation end products (AGEs) have been implicated in the accelerated vascular injury occurring in diabetes. We recently reported that LDL prepared from type 2 diabetic patients (dm-LDL), but not normal LDL (n-LDL) triggered signal transducers and activators of transcription STAT5 activation and p21waf expression in endothelial cells (ECs). The aims of the present study were to investigate the role of LDL glycation in dm-LDL- mediated signals and to analyze the molecular mechanisms leading to STAT5 activation. We found that glycated LDL (gly-LDL) triggered STAT5 activation, the formation of a prolactin inducible element (PIE)-binding complex containing STAT5, and increased p21waf expression through the activation of the receptor for AGE (RAGE). We also demonstrated that dm-LDL and gly-LDL, but not n-LDL treatment induced the formation of a stable complex containing the activated STAT5 and RAGE. Moreover, gly-LDL triggered src but not JAK2 kinase activity. Pretreatment with the src kinase inhibitor PP1 abrogated both STAT5 activation and the expression of p21waf induced by gly-LDL. Consistently, gly-LDL failed to activate STAT5 in src−/− fibroblasts. Collectively, our results provide evidence for the role of glycation in dm-LDL-mediated effects and for a specific role of src kinase in STAT5-dependent p21waf expression.
No Association BetweenlckGene Polymorphisms and Protein Level in Type 1 Diabetes
Authors: Nervi Solange , Nicodeme Sandra , Gartioux Corinne , Atlan Catherine , Lathrop Marc , Reviron Denis , Naquet Philippe , Matsuda Fumihiko , Imbert Jean , Vialettes Bernard
Published: March 2007

We previously described a reduced expression of the protein tyrosine kinase Lck in T-cells from type 1 diabetic patients, the origin of which is still unknown. The human lck gene, located on chromosome 1p35-34.3, was evaluated as a candidate susceptibility gene for type 1 diabetes. A molecular scan of the sequence variations in the coding, the relevant promoter, and most of the intronic sequences of the lck gene (representing a total of 10.5 kb fragment) was performed in 187 Caucasian subjects including 91 type 1 diabetic patients and 96 normoglycemic control subjects. We identified 35 sequence variations, including one deletion and 34 single nucleotide polymorphisms (SNPs), 33 of them being new. Four variants were frequent but not significantly associated with diabetes or Lck protein level. Of the SNP variants, 11 were only found within the diabetic population and some were associated with low Lck protein levels. The low frequency of these polymorphisms did not permit any statistically significant correlations with the disease status, suggesting that the lck gene probably does not contribute to genetic susceptibility to type 1 diabetes.
The Rat Arcuate Nucleus Integrates Peripheral Signals Provided by Leptin, Insulin, and a Ghrelin Mimetic
Authors: Hewson Adrian K. , Tung Loraine Y.C. , Connell David W. , Tookman Laura , Dickson Suzanne L.
Published: March 2007

The hypothalamic circuits controlling food intake and body weight receive and integrate information from circulating satiety signals such as leptin and insulin and also from ghrelin, the only known circulating hormone that stimulates appetite following systemic injection. Activation of arcuate neurons by ghrelin and ghrelin mimetics (the growth hormone secretagogues) is augmented in 48-h-fasted rats compared with fed rats, as reflected by a greater number of cells expressing Fos protein in response to administration of the same maximally effective dose. Here we sought to determine whether this increased responsiveness in fasting might reflect or be influenced by low levels of circulating satiety factors such as leptin or insulin. Chronic central infusion of insulin or leptin during a 48-h fast suppressed the threefold increase in the Fos response to intravenous injection of a maximally effective dose of growth hormone-releasing peptide (GHRP)-6, a synthetic growth hormone secretagogue. This appears to be a direct central action of insulin and leptin because the marked decrease in plasma levels of insulin, leptin, and glucose during fasting were unaffected by central administration of either hormone. Furthermore, the GHRP-6-induced Fos response was twofold greater in obese leptin- and insulin-resistant Zucker rats compared with lean controls. These data provide evidence that the ghrelin-sensitive circuits in the hypothalamus are dynamically regulated by central insulin and leptin action.
A Novel Approach to Increase Human Islet Cell Mass While Preserving β-Cell Function
Authors: Beattie Gillian M. , Montgomery Anthony M.P. , Lopez Ana D. , Hao Ergeng , Perez Brandon , Just Margaret L. , Lakey Jonathan R.T. , Hart Marquis E. , Hayek Alberto
Published: March 2007

Human islet expansion in monolayer culture leads to loss of function and senescence. By maintaining the 3-D configuration of islets in fibrin gels, it is feasible to expand β-cells in response to hepatocyte growth factor (HGF) while preserving physiologic glucose responsiveness both in vitro and in vivo after transplantation into nude mice. Islets were cultured free floating with or without growth factors and nicotinamide and in fibrin gels with the same conditions. Proliferation was observed only in islets cultured in fibrin gels and the cocktail; total insulin increased by threefold, with a concomitant increase in β-cell mass by morphometry. Insulin release after glucose challenge was also preserved. Islets in fibrin gels gave rise in vivo to large grafts rich in insulin and glucagon, and grafts from free-floating islets were smaller with fewer endocrine cells. Circulating human C-peptide levels were higher than in the mice receiving free-floating islets. In summary, fibrin allows for HGF-mediated cell proliferation while preserving glucose responsiveness in an environment that preserves cell-cell contacts. Limited islet ex vivo expansion under these conditions may improve recipient-donor tissue ratios to equal the functional results of whole-organ transplants.
cAMP-Activated Protein Kinase-Independent Potentiation of Insulin Secretion by cAMP Is Impaired in SUR1 Null Islets
Authors: Nakazaki Mitsuhiro , Crane Ana , Hu Min , Seghers Victor , Ullrich Susanne , Aguilar-Bryan Lydia , Bryan Joseph
Published: March 2007

Whereas the loss of ATP-sensitive K+ channel (KATP channel) activity in human pancreatic β-cells causes severe hypoglycemia in certain forms of hyperinsulinemic hypoglycemia, similar channel loss in sulfonylurea receptor-1 (SUR1) and Kir6.2 null mice yields a milder phenotype that is characterized by normoglycemia, unless the animals are stressed. While investigating potential compensatory mechanisms, we found that incretins, specifically glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), can increase the cAMP content of Sur1KO islets but do not potentiate glucose-stimulated insulin release. This impairment is secondary to a restriction in the ability of Sur1KO β-cells to sense cAMP correctly. Potentiation does not appear to require cAMP-activated protein kinase (PKA) because H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) and KT5720, inhibitors of PKA, do not affect stimulation by GLP-1, GIP, or exendin-4 in wild-type islets, although they block phosphorylation of cAMP-response element-binding protein. The impaired incretin response in Sur1KO islets is specific; the stimulation of insulin release by other modulators, including mastoparan and activators of protein kinase C, is conserved. The results suggest that the defect responsible for the loss of cAMP-induced potentiation of insulin secretion is PKA independent. We hypothesize that a reduced release of insulin in response to incretins may contribute to the unexpected normoglycemic phenotype of Sur1KO mice versus the pronounced hypoglycemia seen in neonates with loss of KATP channel activity.
The Relative Contributions of Birth Weight, Weight Change, and Current Weight to Insulin Resistance in Contemporary 5-Year-Olds
Authors: Wilkin Terence J. , Metcalf Bradley S. , Murphy Michael J. , Kirkby Joanne , Jeffery Alison N. , Voss Linda D.
Published: March 2007

For more than a decade, the fetal programming hypothesis has taught that insulin resistance and its associated metabolic disturbances result from poor gestational environment, for which low birth weight is a surrogate. Low birth weight, however, is now uncommon in industrialized societies. We have investigated the relevance of birth weight, “catch-up” weight, and current weight to insulin resistance in 300 contemporary British children. Insulin resistance at 5 years was not related to birth weight but was correlated with current weight and weight catch-up in both sexes, more strongly so in girls (r = 0.33, P < 0.001 vs. r = 0.18, P = 0.03), who were intrinsically more insulin-resistant than boys. Weight change merely co-correlated with current weight (r = 0.67, P < 0.01 in both sexes) and did not improve on the prediction of insulin resistance. Most important, insulin resistance at 5 years was the same in children of heavier birth weight, whose weight SD score had not changed, as in those of lighter birth weight, matched for current weight, who had experienced so-called catch-up (boys 0.89 and 0.88 units, respectively, P = 0.96; girls 1.26 and 1.13 units, P = 0.41). Insulin resistance in contemporary children seems to be a function of excess current weight rather than of low birth weight or change in weight.
Rosiglitazone but Not Metformin Enhances Insulin- and Exercise-Stimulated Skeletal Muscle Glucose Uptake in Patients With Newly Diagnosed Type 2 Diabetes
Authors: Hällsten Kirsti , Virtanen Kirsi A. , Lönnqvist Fredrik , Sipilä Hannu , Oksanen Airi , Viljanen Tapio , Rönnemaa Tapani , Viikari Jorma , Knuuti Juhani , Nuutila Pirjo
Published: March 2007

Rosiglitazone, a thiazolidinedione, enhances peripheral insulin sensitivity in patients with type 2 diabetes. Because the synergic action of insulin and exercise has been shown to be decreased in insulin resistance, the aim of this study was to compare the effects of rosiglitazone and metformin on muscle insulin responsiveness at rest and during exercise in patients with type 2 diabetes. Therefore, 45 patients with newly diagnosed or diet-treated type 2 diabetes were randomized for treatment with rosiglitazone (4 mg b.i.d.), metformin (1 g b.i.d.), or placebo in a 26-week double-blind trial. Skeletal muscle glucose uptake was measured using fluorine-18-labeled fluoro-deoxy-glucose and positron emission tomography (PET) during euglycemic-hyperinsulinemic clamp and one-legged exercise before and after the treatment period. Rosiglitazone (P < 0.05) and metformin (P < 0.0001) treatment lowered the mean glycosylated hemoglobin. The skeletal muscle glucose uptake was increased by 38% (P < 0.01) and whole-body glucose uptake by 44% in the rosiglitazone group. Furthermore, the exercise-induced increment during insulin stimulation was enhanced by 99% (P < 0.0001). No changes were observed in skeletal muscle or whole-body insulin sensitivity in the metformin group. In conclusion, rosiglitazone but not metformin 1) improves insulin responsiveness in resting skeletal muscle and 2) doubles the insulin-stimulated glucose uptake rate during physical exercise in patients with type 2 diabetes. Our results suggest that rosiglitazone improves synergic action of insulin and exercise.
Insulin-Mediated Hemodynamic Changes Are Impaired in Muscle of Zucker Obese Rats
Authors: Wallis Michelle G. , Wheatley Catherine M. , Rattigan Stephen , Barrett Eugene J. , Clark Andrew D.H. , Clark Michael G.
Published: March 2007

Insulin-mediated hemodynamic effects in muscle were assessed in relation to insulin resistance in obese and lean Zucker rats. Whole-body glucose infusion rate (GIR), femoral blood flow (FBF), hindleg glucose extraction (HGE), hindleg glucose uptake (HGU), 2-deoxyglucose (DG) uptake into muscles of the lower leg (Rg), and metabolism of infused 1-methylxanthine (1-MX) to measure capillary recruitment were determined for isogylcemic (4.8 ± 0.2 mmol/l, lean; 11.7 ± 0.6 mmol/l, obese) insulin-clamped (20 mU · min−1 · kg−1 × 2 h) and saline-infused control anesthetized age-matched (20 weeks) lean and obese animals. Obese rats (445 ± 5 g) were less responsive to insulin than lean animals (322 ± 4 g) for GIR (7.7 ± 1.4 vs. 22.2 ± 1.1 mg · min−1 · kg−1, respectively), and when compared with saline-infused controls there was no increase due to insulin by obese rats in FBF, HGE, HGU, and Rg of soleus, plantaris, red gastrocnemius, white gastrocnemius, extensor digitorum longus (EDL), or tibialis muscles. In contrast, lean animals showed marked increases due to insulin in FBF (5.3-fold), HGE (5-fold), HGU (8-fold), and Rg (∼5.6-fold). Basal (saline) hindleg 1-MX metabolism was 1.5-fold higher in lean than in obese Zucker rats, and insulin increased in only that of the lean. Hindleg 1-MX metabolism in the obese decreased slightly in response to insulin, thus postinsulin lean was 2.6-fold that of the postinsulin obese. We conclude that muscle insulin resistance of obese Zucker rats is accompanied by impaired hemodynamic responses to insulin, including capillary recruitment and FBF.
Lower Heart Rate Variability Is Associated With the Development of Coronary Heart Disease in Individuals With Diabetes
Authors: Liao Duanping , Carnethon Mercedes , Evans Gregory W. , Cascio Wayne E. , Heiss Gerardo
Published: March 2007

The objective of this study was to test prospectively in a population sample whether individuals with impaired heart rate variability (HRV) are at increased risk of developing coronary heart disease (CHD) and of non-CHD mortality and to test whether this relationship is more pronounced among individuals with diabetes. We examined the association between HRV and incident CHD and non-CHD mortality in a cohort of 11,654 men and women aged 45–64 years at intake, from the biracial, population-based Atherosclerosis Risk in Communities Study. Supine, resting, 2-min beat-to-beat heart rate data were collected at the baseline examination. High frequency (HF; 0.15–0.40 Hz) and low frequency (LF; 0.04–0.15 Hz) spectral powers, LF/HF ratio, normalized HF and LF, the standard deviation of all normal R-R intervals (SDNN), and the mean of the sum of the squared differences between adjacent normal R-R intervals (MSSD) were used as the conventional indexes of HRV to measure cardiac autonomic control. From this cohort, 635 cases of incident CHD (including 346 cases of incident myocardial infarction [MI] and 82 cases of fatal CHD), and 623 non-CHD deaths were identified and validated after an average of 8 years of follow-up. Among individuals with diabetes, the multivariable adjusted proportional hazards ratios (95% CI) were 2.03 (1.28–3.23), 1.60 (1.12–2.27), 1.50 (0.65–3.42), and 1.27 (0.84–1.91) for incident MI, incident CHD, fatal CHD, and non-CHD deaths, respectively, comparing the lowest quartile to the upper most three quartiles of HF. A similar pattern of associations was found for LF, SDNN, and MSSD. By contrast, there was no consistent pattern of associations among individuals without diabetes. At the population level, a lower HRV (reflective of impaired cardiac autonomic control) is statistically significantly related to the development of CHD among individuals with diabetes, independent of markers of the duration/severity of the glucose metabolism impairment. These data suggest a contribution of an impaired cardiac autonomic control to the risk of CHD among individuals with diabetes.
Sex-Related Bias and Exclusion Mapping of the Nonrecombinant Portion of Chromosome Y in Human Type 1 Diabetes in the Isolated Founder Population of Sardinia
Authors: Contu Daniela , Morelli Laura , Zavattari Patrizia , Lampis Rosanna , Angius Efisio , Frongia Paola , Murru Daniela , Maioli Mario , Francalacci Paolo , Todd John A. , Cucca Francesco
Published: March 2007

A male excess in Sardinian type 1 diabetic cases has previously been reported and was largely restricted to those patients carrying the HLA-DR3/nonDR4 genotype. In the present study, we have measured the male- to-female (M:F) ratio in a sample set of 542 newly collected, early-onset type 1 diabetic Sardinian patients. This data not only confirm the excess of male type 1 diabetic patients overall (M:F ratio = 1.3, P = 3.9 × 10−3) but also that the bias in male incidence is largely confined to patients with the DR3/nonDR4 genotype (M:F ratio = 1.6, P = 2.0 × 10−4). These sex effects could be due to a role for allelic variation of the Y chromosome in the susceptibility to type 1 diabetes, but to date this chromosome has not been evaluated in type 1 diabetes. We, therefore, established the frequencies of the various chromosome Y lineages and haplotypes in 325 Sardinian male patients, which included 180 cases with the DR3/nonDR4 genotype, and 366 Sardinian male control subjects. Our results do not support a significant involvement of the Y chromosome in DR3/nonDR4 type 1 diabetic cases nor in early-onset type 1 diabetes as a whole. Other explanations, such as X chromosome-linked inheritance, are thus required for the male bias in incidence in type 1 diabetes in Sardinia.
Interleukin-1 Receptor Antagonist Genotype Is Associated With Coronary Atherosclerosis in Patients With Type 2 Diabetes
Authors: Marculescu Rodrig , Endler Georg , Schillinger Martin , Iordanova Nelly , Exner Markus , Hayden Evelyn , Huber Kurt , Wagner Oswald , Mannhalter Christine
Published: March 2007

Recently, inflammation has received considerable attention in the pathogenesis of both type 2 diabetes and atherosclerosis. The interleukin-1 receptor antagonist (IL-1ra) is a major modulator of the interleukin-1 pro-inflammatory pathway. We studied the relationship between a variable number tandem repeat (VNTR) polymorphism in intron 2 of the IL-1ra gene (IL1RN) and coronary artery disease (CAD) in patients with and without type 2 diabetes, following 787 consecutive patients admitted for suspected CAD. According to the current criteria of the American Diabetes Association, 250 patients had type 2 diabetes. In this group of patients, allele 2 carriers (n = 108) had an increased prevalence of CAD compared with noncarriers (85.2 vs. 73.2%), a difference that remained significant in a multivariate logistic regression model (odds ratio 2.2, 95% CI 1.1–4.3, P = 0.02). No association of CAD with allele 2 carrier status was present among nondiabetic patients (n = 537). Enzyme-linked immunosorbent assays showed decreased baseline plasma levels of IL-1ra in patients with type 2 diabetes, which may in part explain the role of the IL1RN VNTR in these patients.
PPARG F388L, a Transactivation-Deficient Mutant, in Familial Partial Lipodystrophy
Authors: Hegele Robert A. , Cao Henian , Frankowski Christy , Mathews Suresh T. , Leff Todd
Published: March 2007

Autosomal dominant familial partial lipodystrophy (FPLD) due to mutant LMNA encoding nuclear lamin A/C is characterized by adipose tissue repartitioning together with multiple metabolic disturbances, including insulin resistance and dyslipidemia. There is emerging evidence that some rare mutations in peroxisome proliferator-activated receptor-γ (PPAR-γ), encoded by PPARG, might be associated with human lipodystrophy. We report a three-generation Canadian kindred ascertained based upon partial lipodystrophy, with a normal LMNA gene sequence. Candidate gene sequencing showed that all four affected subjects were heterozygous for a novel T→A mutation at PPARG nucleotide 1164 in exon 5 that predicted substitution of phenylalanine at codon 388 by leucine (F388L). The mutation was absent from normal family members and normal unrelated subjects, and altered a highly conserved residue within helix 8 of the predicted ligand-binding pocket of PPAR-γ. The mutant receptor had significantly decreased basal transcriptional activity and impaired stimulation by a synthetic ligand. The germline transmission of a transactivation-deficient mutation in PPARG suggests that autosomal dominant partial lipodystrophy is genetically heterogeneous. Our findings are consistent with the idea that mutant PPARG can underlie the partial lipodystrophy phenotype.
Regulation of Pyruvate Dehydrogenase Kinase Expression by Peroxisome Proliferator–Activated Receptor-α Ligands, Glucocorticoids, and Insulin
Authors: Huang Boli , Wu Pengfei , Bowker-Kinley Melissa M. , Harris Robert A.
Published: March 2007

Pyruvate dehydrogenase kinase (PDK) catalyzes phosphorylation and inactivation of the pyruvate dehydrogenase complex (PDC). Two isoforms of this mitochondrial kinase (PDK2 and PDK4) are induced in a tissue-specific manner in response to starvation and diabetes. Inactivation of PDC by increased PDK activity promotes gluconeogenesis by conserving three-carbon substrates. This helps maintain glucose levels during starvation, but is detrimental in diabetes. Factors that regulate PDK2 and PDK4 expression were examined in Morris hepatoma 7800 C1 cells. The peroxisome proliferator−activated receptor-α (PPAR-α) agonist WY-14,643 and the glucocorticoid dexamethasone increased PDK4 mRNA levels. Neither compound affected the half-life of the PDK4 message, suggesting that both increase gene transcription. Fatty acids caused an increase in the PDK4 message comparable to that induced by WY-14,643. Insulin prevented and reversed the stimulatory effects of dexamethasone on PDK4 gene expression, but was less effective against the stimulatory effects of WY-14,643 and fatty acids. Insulin also decreased the abundance of the PDK2 message. The findings suggest that decreased levels of insulin and increased levels of fatty acids and glucocorticoids promote PDK4 gene expression in starvation and diabetes. The decreased level of insulin is likely responsible for the increase in PDK2 mRNA level in starvation and diabetes.
Bedtime Administration of NN2211, a Long-Acting GLP-1 Derivative, Substantially Reduces Fasting and Postprandial Glycemia in Type 2 Diabetes
Authors: Juhl Claus B. , Hollingdal Malene , Sturis Jeppe , Jakobsen Grethe , Agersø Henrik , Veldhuis Johannes , Pørksen Niels , Schmitz Ole
Published: March 2007

Glucagon-like peptide 1 (GLP-1) is a potent glucose-lowering agent of potential interest for the treatment of type 2 diabetes. To evaluate actions of NN2211, a long-acting GLP-1 derivative, we examined 11 patients with type 2 diabetes, age 59 ± 7 years (mean ± SD), BMI 28.9 ± 3.0 kg/m2, HbA1c 6.5 ± 0.6%, in a double-blind, placebo-controlled, crossover design. A single injection (10 μg/kg) of NN2211 was administered at 2300 h, and profiles of circulating insulin, C-peptide, glucose, and glucagon were monitored during the next 16.5 h. A standardized mixed meal was served at 1130 h. Efficacy analyses were performed for the fasting (7–8 h) and mealtime (1130–1530 h) periods. Insulin secretory rates (ISR) were estimated by C-peptide deconvolution analysis. Glucose pulse entrainment (6 mg · kg−1 · min−1 every 10 min) was evaluated by 1-min sampled measurements of insulin concentrations from 0930 to 1030 h and subsequent time series analysis of the insulin concentration profiles. All results are given as NN2211 versus placebo; statistical analyses were performed by analysis of variance. In the fasting state, plasma glucose was significantly reduced (6.9 ± 1.0 vs. 8.1 ± 1.0 mmol/l; P = 0.004), ISR was increased (179 ± 70 vs. 163 ± 66 pmol/min; P = 0.03), and plasma glucagon was unaltered (19 ± 4 vs. 20 ± 4 pg/ml; P = 0.17) by NN2211. Meal-related area under the curve (AUC)1130–1530 h for glucose was markedly reduced (30.6 ± 2.4 vs. 39.9 ± 7.3 mmol · l−1 · h−1; P < 0.001), ISR AUC1130–1530 h was unchanged (118 ± 32 vs. 106 ± 27 nmol; P = 0.13), but the increment (relative to premeal values) was increased (65 ± 22 vs. 45 ± 11 nmol; P = 0.04). Glucagon AUC1130–1530 h was suppressed (77 ± 18 vs. 82 ± 17 pmol · l−1 · h−1; P = 0.04). Gastric emptying was significantly delayed as assessed by AUC1130–1530 h of 3-ortho-methylglucose (400 ± 84 vs. 440 ± 70 mg · l−1 · h−1; P = 0.02). During pulse entrainment, there was a tendency to increased high frequency regularity of insulin release as measured by a greater spectral power and autocorrelation coefficient (0.05 < P < 0.10). The pharmacokinetic profile of NN2211, as assessed by blood samplings for up to 63 h postdosing, was as follows: T1/2 = 10.0 ± 3.5 h and Tmax = 12.4 ± 1.7 h. Two patients experienced gastrointestinal side effects on the day of active treatment. In conclusion, the long-acting GLP-1 derivative NN2211 effectively reduces fasting as well as meal-related (∼12 h postadministration) glycemia by modifying insulin secretion, delaying gastric emptying, and suppressing prandial glucagon secretion.
A Unique Defect in the Regulation of Visceral Fat Cell Lipolysis in the Polycystic Ovary Syndrome as an Early Link to Insulin Resistance
Authors: Ek Ingvar , Arner Peter , Rydén Mikael , Holm Cecilia , Thörne Anders , Hoffstedt Johan , Wahrenberg Hans
Published: March 2007

The etiology of polycystic ovary syndrome (PCOS) is unknown. However, PCOS has a strong resemblance to the insulin resistance (metabolic) syndrome, where an increased rate of visceral fat cell lipolysis is believed to play a pathophysiological role. We hypothesized that primary defects in visceral lipolysis might also exist in PCOS. Ten young, nonobese, and otherwise healthy PCOS women were compared with 13 matched control women. In vitro lipolysis regulation and stoichiometric properties of the final step in lipolysis activation, namely the protein kinase A (PKA)-hormone sensitive lipase (HSL) complex, were investigated in isolated visceral (i.e., omental) fat cells. Body fat distribution and circulating levels of insulin, glucose, and lipids were normal in PCOS women. However, in vivo insulin sensitivity was slightly decreased (P = 0.03). Catecholamine-induced adipocyte lipolysis was markedly (i.e., about twofold) increased in PCOS women due to changes at the postreceptor level, although there was no change in the antilipolytic properties of visceral fat cells. Western blot analyses of visceral adipose tissue showed twofold increased levels of the catalytic and the regulatory Iα components of PKA. In contrast, the regulatory RIIβ component of PKA was almost 50% decreased in visceral adipose tissue in PCOS women. Recent studies on genetically modified mice have shown that a similar transition in the regulatory PKA units induces an increased lipolytic response to catecholamines. Further analysis showed that the level of HSL-short, an enzymatically inactive splice form of HSL, was decreased in PCOS (P < 0.01). The altered lipolysis in PCOS is different from that observed in visceral fat cells in the insulin resistance syndrome that occurs at the level of adrenergic receptors. We concluded that increased catecholamine-induced lipolysis in visceral fat cells may be due to unique alterations in the stoichiometric properties of the adipose PKA-HSL holoenzymes. This could be an early and possibly primary lipolysis defect in PCOS.
Cellular Basis of Diabetic Nephropathy
Authors: Caramori M. Luiza , Kim Youngki , Huang Chunmei , Fish Alfred J. , Rich Stephen S. , Miller Michael E. , Russell Greg , Mauer Michael
Published: March 2007

This study was designed to elucidate the cellular basis of risk of or protection from nephropathy in patients with type 1 diabetes. Entry criteria included diabetes duration of ≥8 years (mean duration, 22.5 years) and glomerular filtration rate (GFR) >30 ml·min−1·1.73 m−2. Patients were classified, on the basis of the estimated rate of mesangial expansion, as “fast-track” (upper quintile) or “slow-track” (lower quintile). A total of 88 patients were normoalbuminuric, 17 were microalbuminuric, and 19 were proteinuric. All three groups had increased glomerular basement membrane (GBM) width and mesangial fractional volume [Vv(Mes/glom)], with increasing severity from normoalbuminuria to microalbuminuria to proteinuria but with considerable overlap among groups. Vv(Mes/glom) (r = 0.75, P < 0.001) and GBM width (r = 0.63, P < 0.001) correlated with albumin excretion rate (AER), whereas surface density of peripheral GBM per glomerulus [Sv(PGBM/glom)] (r = 0.50, P < 0.001) and Vv(Mes/glom) (r = −0.48, P < 0.001) correlated with GFR. Vv(Mes/glom) and GBM width together explained 59% of AER variability. GFR was predicted by Sv(PGBM/glom), AER, and sex. Fast-track patients had worse glycemic control, higher AER, lower GFR, more hypertension and retinopathy, and, as expected, worse glomerular lesions than slow-track patients. Thus, there are strong relationships between glomerular structure and renal function across the spectrum of AER, but there is considerable structural overlap among AER categories. Given that normoalbuminuric patients may have advanced glomerulopathy, the selection of slow-track patients based on glomerular structure may better identify protected patients than AER alone.