bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetics of Obesity and Type 2 Diabetes
Authors: Bougnères Pierre
Published: March 2007

The modern generalization of sedentary life and caloric abundance has created new physiological conditions capable of changing the level of expression of a number of genes involved in fuel metabolism and body weight regulation. It is likely that the genetic variants or alleles of these genes have in the past participated in the adaptation of human physiology to its evolutionary constraints. The nature and prevalence of polymorphisms responsible for the quantitative variation of complex metabolic traits may have been different among human populations, depending on their environment and ancestral genetic background. These polymorphisms could likely explain differences in disease susceptibility and prevalence among groups of humans. From complex traits to potentially complex alleles, understanding the molecular genetic basis underlying quantitative variation will continue to be a growing concern among geneticists dealing with obesity and type 2 diabetes, the main fuel disorders of the modern era. Genomics and genetic epidemiology now allow high-level linkage and association studies to be designed. But the pooling of large trans-geographic cohorts may in fact increase the genetic heterogeneity of studied traits and dilute genotype-phenotype associations. In this article, we underscore the importance of selecting the traits to be subjected to quantitative genetic analysis. Although this is not possible for most other multifactorial diseases, obesity and type 2 diabetes can be subjected to a pregenetic dissection of complexity into simpler quantitative traits (QTs). This dissection is based on the pathogenic mechanisms, and the time course of the traits, and the individuals’ age, within the predisease period rather than on descriptive parameters after disease diagnosis. We defend that this approach of phenotypes may ease future associations to be established between QTs of intermediate complexity and genetic polymorphisms.
Searching for Type 2 Diabetes Genes on Chromosome 20
Authors: Permutt Marshall Alan , Wasson Jonathan , Love-Gregory Latisha , Ma Jiyan , Skolnick Gary , Suarez Brian , Lin Jennifer , Glaser Benjamin
Published: March 2007

Genome scans in families with type 2 diabetes identified a putative locus on chromosome 20q. For this study, linkage disequilibrium mapping was used in an effort to narrow a 7.3-Mb region in an Ashkenazi type 2 diabetic population. The region encompassed a 1-logarithm of odds (LOD) interval around the microsatellite marker D20S107, which gave a LOD score of >3 in linkage analysis of a combined Caucasian population. This 7.3-Mb region contained 25 known and 99 predicted genes. Predicted single nucleotide polymorphisms (SNPs) were chosen from public databases and validated. Two SNPs were unique to the Ashkenazi. Here, 91 SNPs with a minor allele frequency of ≥10% were genotyped in pooled DNA from 150 case subjects and 150 control subjects of Ashkenazi Jewish descent. The SNP association study showed that SNP rs2664537 in the TIX1 gene had a significant P value of 0.035, but the finding did not replicate in an additional case pool. In addition, HNF4a and Mybl2 were screened for mutations and new polymorphisms. No mutations were identified, and a new nonsynonymous SNP (R687C in exon 14 of Mybl2) was found. The limits to this type of association study are discussed.
Sulfonylurea-Mediated Stimulation of Insulin Exocytosis via an ATP-Sensitive K+ Channel–Independent Action
Authors: Renström Erik , Barg Sebastian , Thévenod Frank , Rorsman Patrik
Published: March 2007

Several reports indicate that hypoglycemic sulfonylureas augment Ca2+-dependent insulin secretion via mechanisms other than inhibition of the ATP-sensitive K+ channel. The effect involves a 65-kd protein in the granule membrane and culminates in intragranular acidification. Lowering of granule pH is necessary for the insulin granule to gain release competence. Proton pumping into the granule is driven by a v-type H+-ATPase, but requires simultaneous Cl− uptake into the granule via metabolically regulated ClC-3 Cl− channels to maintain electroneutrality. Here we discuss the possibility that modulation of granule ClC-3 channels represents the mechanism whereby sulfonylureas directly potentiate the β-cell exocytotic machinery.
Stimulus/Secretion Coupling Factors in Glucose-Stimulated Insulin Secretion
Authors: Newgard Christopher B. , Lu Danhong , Jensen Mette Valentin , Schissler Jonathan , Boucher Anne , Burgess Shawn , Sherry A. Dean
Published: March 2007

There is a growing appreciation for the complexity of the pathways involved in glucose-stimulated insulin secretion (GSIS) from pancreatic islet β-cells. In our laboratory, this has stimulated the development of an interdisciplinary approach to the problem. In this study, we review recent studies combining the tools of recombinant adenovirus for gene delivery, the development of novel cell lines that exhibit either robust or weak GSIS, and nuclear magnetic resonance imaging for metabolic fingerprinting of glucose-stimulated cells. Using these tools, we demonstrate a potentially important role for pyruvate carboxylase−mediated pyruvate cycling pathways in the control of GSIS, and discuss potential coupling factors produced by such pathways.
The Multiple Actions of GLP-1 on the Process of Glucose-Stimulated Insulin Secretion
Authors: MacDonald Patrick E. , El-kholy Wasim , Riedel Michael J. , Salapatek Anne Marie F. , Light Peter E. , Wheeler Michael B.
Published: March 2007

The physiological effects of glucagon-like peptide-1 (GLP-1) are of immense interest because of the potential clinical relevance of this peptide. Produced in intestinal L-cells through posttranslational processing of the proglucagon gene, GLP-1 is released from the gut in response to nutrient ingestion. Peripherally, GLP-1 is known to affect gut motility, inhibit gastric acid secretion, and inhibit glucagon secretion. In the central nervous system, GLP-1 induces satiety, leading to reduced weight gain. In the pancreas, GLP-1 is now known to induce expansion of insulin-secreting β-cell mass, in addition to its most well-characterized effect: the augmentation of glucose-stimulated insulin secretion. GLP-1 is believed to enhance insulin secretion through mechanisms involving the regulation of ion channels (including ATP-sensitive K+ channels, voltage-dependent Ca2+ channels, voltage-dependent K+ channels, and nonselective cation channels) and by the regulation of intracellular energy homeostasis and exocytosis. The present article will focus principally on the mechanisms proposed to underlie the glucose dependence of GLP-1’s insulinotropic effect.
Glucagon-Like Peptide-1 Receptor Activation Antagonizes Voltage-Dependent Repolarizing K+ Currents in β-Cells
Authors: MacDonald Patrick E. , Salapatek Anne Marie F. , Wheeler Michael B.
Published: March 2007

Glucagon-like peptide-1 (GLP-1) acts through its G-protein-coupled receptor to enhance glucose-stimulated insulin secretion from pancreatic β-cells. This is believed to result from modulation of at least two ion channels: ATP-sensitive K+ (KATP) channels and voltage-dependent Ca2+ channels. Here, we report that GLP-1 receptor signaling also regulates the activity of β-cell voltage-dependent K+ (KV) channels, themselves potent glucose-dependent regulators of insulin secretion. GLP-1 receptor activation with exendin 4 (10−8 mol/l) in rat β-cells antagonized KV currents by 43.3 ± 6.3%, whereas the GLP-1 receptor antagonist exendin 9-39 had no effect. The effect of GLP-1 receptor activation on KV currents could be replicated (current reduction of 55.7 ± 6.0%) by G-protein activation with GMP-PNP (10 nmol/l). The cAMP pathway antagonist Rp-cAMPS (100 μmol/l) prevented current inhibition by exendin 4, implicating cAMP signaling in GLP-1 receptor modulation of β-cell KV currents. Finally, exendin 4 (10−8 mol/l) increased the amplitude (130 ± 5.7%) and duration (285 ± 15.9%) of the β-cell depolarization response to current injection, independent of any effect on KATP or Ca2+ channels. The present results demonstrate that GLP-1 receptor signaling can antagonize β-cell repolarization by reducing voltage-dependent K+ currents, an effect likely to contribute to GLP-1’s glucose-dependent insulinotropic effect.
Endoplasmic Reticulum Stress and the Development of Diabetes
Authors: Harding Heather P. , Ron David
Published: March 2007

The early steps of insulin biosynthesis occur in the endoplasmic reticulum (ER), and the β-cell has a highly developed and active ER. All cells regulate the capacity of their ER to fold and process client proteins and they adapt to an imbalance between client protein load and folding capacity (so-called ER stress). Mutations affecting the ER stress-activated pancreatic ER kinase (PERK) and its downstream effector, the translation initiation complex eukaryotic initiation factor 2 (eIF2), have a profound impact on islet cell development, function, and survival. PERK mutations are associated with the Wolcott-Rallison syndrome of infantile diabetes and mutations that prevent the α-subunit of eIF2 from being phosphorylated by PERK, block β-cell development, and impair gluconeogenesis. We will review this and other rare forms of clinical and experimental diabetes and consider the role of ER stress in the development of more common forms of the disease.
Effect of AICAR Treatment on Glycogen Metabolism in Skeletal Muscle
Authors: Aschenbach William G. , Hirshman Michael F. , Fujii Nobuharu , Sakamoto Kei , Howlett Kirsten F. , Goodyear Laurie J.
Published: March 2007

AMP-activated protein kinase (AMPK) is proposed to stimulate fat and carbohydrate catabolism to maintain cellular energy status. Recent studies demonstrate that pharmacologic activation of AMPK and mutations in the enzyme are associated with elevated muscle glycogen content in vivo. Our purpose was to determine the mechanism for increased muscle glycogen associated with AMPK activity in vivo. AMPK activity and glycogen metabolism were studied in red and white gastrocnemius muscles from rats treated with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) in vivo, and also in muscles incubated with AICAR in vitro. In vivo AICAR treatment reduced blood glucose and increased blood lactate compared with basal values. AICAR increased muscle α2 AMPK activity, glycogen, and glucose-6-phosphate concentrations. Glycogen synthase activity was increased in the red gastrocnemius but was decreased in the white gastrocnemius. Glycogen phosphorylase activity increased in both muscles, with an inhibition initially observed in the red gastrocnemius. In vitro incubation with AICAR activated α2 AMPK but had no effect on either glycogen synthase or glycogen phosphorylase. These results suggest that AICAR treatment does not promote glycogen accumulation in skeletal muscle in vivo by altering glycogen synthase and glycogen phosphorylase. Rather, the increased glycogen is due to the well-known effects of AICAR to increase glucose uptake.
Caffeine-Induced Impairment of Insulin Action but Not Insulin Signaling in Human Skeletal Muscle Is Reduced by Exercise
Authors: Thong Farah S.L. , Derave Wim , Kiens Bente , Graham Terry E. , Ursø Birgitte , Wojtaszewski Jørgen F.P. , Hansen Bo F. , Richter Erik A.
Published: March 2007

We investigated the effects of caffeine ingestion on skeletal muscle glucose uptake, glycogen synthase (GS) activity, and insulin signaling intermediates during a 100-min euglycemic-hyperinsulinemic (100 μU/ml) clamp. On two occasions, seven men performed 1-h one-legged knee extensor exercise at 3 h before the clamp. Caffeine (5 mg/kg) or placebo was administered in a randomized, double-blind fashion 1 h before the clamp. During the clamp, whole-body glucose disposal was reduced (P < 0.05) in caffeine (37.5 ± 3.1 μmol · min−1 · kg−1) vs. placebo (54.1 ± 2.9 μmol · min−1 · kg−1). In accordance, the total area under the curve over 100 min (AUC0–100 min) for insulin-stimulated glucose uptake in caffeine was reduced (P < 0.05) by ∼50% in rested and exercised muscle. Caffeine also reduced (P < 0.05) GS activity before and during insulin infusion in both legs. Exercise increased insulin sensitivity of leg glucose uptake in both caffeine and placebo. Insulin increased insulin receptor tyrosine kinase (IRTK), insulin receptor substrate 1-associated phosphatidylinositol (PI) 3-kinase activities, and Ser473 phosphorylation of protein kinase B (PKB)/Akt significantly but similarly in rested and exercised legs. Furthermore, insulin significantly decreased glycogen synthase kinase-3α (GSK-3α) activity equally in both legs. Caffeine did not alter insulin signaling in either leg. Plasma epinephrine and muscle cAMP concentrations were increased in caffeine. We conclude that 1) caffeine impairs insulin-stimulated glucose uptake and GS activity in rested and exercised human skeletal muscle; 2) caffeine-induced impairment of insulin-stimulated muscle glucose uptake and downregulation of GS activity are not accompanied by alterations in IRTK, PI 3-kinase, PKB/Akt, or GSK-3α but may be associated with increases in epinephrine and intramuscular cAMP concentrations; and 3) exercise reduces the detrimental effects of caffeine on insulin action in muscle.
Mechanism of Amino Acid-Induced Skeletal Muscle Insulin Resistance in Humans
Authors: Krebs Michael , Krssak Martin , Bernroider Elisabeth , Anderwald Christian , Brehm Attila , Meyerspeer Martin , Nowotny Peter , Roth Erich , Waldhäusl Werner , Roden Michael
Published: March 2007

Plasma concentrations of amino acids are frequently elevated in insulin-resistant states, and a protein-enriched diet can impair glucose metabolism. This study examined effects of short-term plasma amino acid (AA) elevation on whole-body glucose disposal and cellular insulin action in skeletal muscle. Seven healthy men were studied for 5.5 h during euglycemic (5.5 mmol/l), hyperinsulinemic (430 pmol/l), fasting glucagon (65 ng/l), and growth hormone (0.4 μg/l) somatostatin clamp tests in the presence of low (∼1.6 mmol/l) and increased (∼4.6 mmol/l) plasma AA concentrations. Glucose turnover was measured with d-[6,6-2H2]glucose. Intramuscular concentrations of glycogen and glucose-6-phosphate (G6P) were monitored using 13C and 31P nuclear magnetic resonance spectroscopy, respectively. A ∼2.1-fold elevation of plasma AAs reduced whole-body glucose disposal by 25% (P < 0.01). Rates of muscle glycogen synthesis decreased by 64% (180–315 min, 24 ± 3; control, 67 ± 10 μmol · l−1 · min−1; P < 0.01), which was accompanied by a reduction in G6P starting at 130 min (ΔG6P260–300 min, 18 ± 19; control, 103 ± 33 μmol/l; P < 0.05). In conclusion, plasma amino acid elevation induces skeletal muscle insulin resistance in humans by inhibition of glucose transport/phosphorylation, resulting in marked reduction of glycogen synthesis.
Insulin and Isoproterenol Differentially Regulate Mitogen-Activated Protein Kinase-Dependent Na+-K+-2Cl− Cotransporter Activity in Skeletal Muscle
Authors: Gosmanov Aidar R. , Thomason Donald B.
Published: March 2007

Recent studies have demonstrated that p44/42MAPK extracellular signal−regulated kinase (ERK)1 and −2-dependent Na+-K+-2Cl− co-transporter (NKCC) activity may contribute to total potassium uptake by skeletal muscle. To study the precise mechanisms regulating NKCC activity, rat soleus and plantaris muscles were stimulated ex vivo by insulin or isoproterenol (ISO). Both hormones stimulated total uptake of the potassium congener 86Rb by 25–70%. However, only ISO stimulated the NKCC-mediated 86Rb uptake. Insulin inhibited the ISO-stimulated NKCC activity, and this counteraction was sensitive to the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 in the predominantly slow-twitch soleus muscle. Pretreatment of the soleus muscle with the phosphatidylinositol (PI) 3-kinase inhibitors wortmannin and LY294002 or with SB203580 uncovered an insulin-stimulated NKCC activity and also increased the insulin-stimulated phosphorylation of ERK. In the predominantly fast-twitch plantaris muscle, insulin-stimulated NKCC activity became apparent only after inhibition of PI 3-kinase activity, accompanied by an increase in ERK phosphorylation. PI 3-kinase inhibitors also abolished insulin-stimulated p38 MAPK phosphorylation in the plantaris muscle and Akt phosphorylation in both muscles. These data demonstrated that insulin inhibits NKCC-mediated transport in skeletal muscle through PI 3-kinase−sensitive and SB203580-sensitive mechanisms. Furthermore, differential activation of signaling cascade elements after hormonal stimulation may contribute to fiber-type specificity in the control of potassium transport by skeletal muscle.
C2-Ceramide Influences the Expression and Insulin-Mediated Regulation of Cyclic Nucleotide Phosphodiesterase 3B and Lipolysis in 3T3-L1 Adipocytes
Authors: Mei Jie , Holst Lena Stenson , Landström Tova Rahn , Holm Cecilia , Brindley David , Manganiello Vincent , Degerman Eva
Published: March 2007

Cyclic nucleotide phosphodiesterase (PDE) 3B plays an important role in the antilipolytic action of insulin and, thereby, the release of fatty acids from adipocytes. Increased concentrations of circulating fatty acids as a result of elevated or unrestrained lipolysis cause insulin resistance. The lipolytic action of tumor necrosis factor (TNF)-α is thought to be one of the mechanisms by which TNF-α induces insulin resistance. Ceramide is the suggested second messenger of TNF-α action, and in this study, we used 3T3-L1 adipocytes to investigate the effects of C2-ceramide (a short-chain ceramide analog) on the expression and regulation of PDE3B and lipolysis. Incubation of adipocytes with 100 μmol/l C2-ceramide (N-acetyl-sphingosine) resulted in a time-dependent decrease of PDE3B activity, accompanied by decreased PDE3B protein expression. C2-ceramide, in a time- and dose-dependent manner, stimulated lipolysis, an effect that was blocked by H-89, an inhibitor of protein kinase A. These ceramide effects were prevented by 20 μmol/l troglitazone, an antidiabetic drug. In addition to downregulation of PDE3B, the antilipolytic action of insulin was decreased by ceramide treatment. These results, together with data from other studies on PDE3B and lipolysis in diabetic humans and animals, suggest a novel pathway by which ceramide induces insulin resistance. Furthermore, PDE3B is demonstrated to be a target for troglitazone action in adipocytes.
Assessment of the Role of Interstitial Glucagon in the Acute Glucose Secretory Responsiveness of In Situ Pancreatic β-Cells
Authors: Moens Karen , Berger Veerle , Ahn Jung-Mo , Van Schravendijk Chris , Hruby Victor J. , Pipeleers Daniel , Schuit Frans
Published: March 2007

Glucagon is a potent stimulator of insulin release in the presence of a permissive glucose concentration, activating β-cells in vitro via both glucagon- and glucagon-like peptide-1 (GLP-1)-receptors. It is still unclear whether locally released glucagon amplifies the secretory responsiveness of neighboring β-cells in the intact pancreas. The present study investigates this question in the perfused pancreas by examining the effects of antagonists for glucagon receptors ([des-His1,des-Phe6,Glu9]glucagon-NH2, 10 μmol/l) and GLP-1-receptors [exendin-(9-39)-NH2, 1 μmol/l] on the insulin secretory response to glucose. The specificity of both antagonists was demonstrated by their selective interaction with glucagon-receptor signaling in rat hepatocytes and GLP-1-receptor signaling in Chinese hamster lung (CHL) fibroblasts. In purified rat β-cells, the glucagon-receptor antagonist (10 μmol/l) inhibited the effect of 1 nmol/l glucagon upon glucose-induced insulin release by 78 ± 6%. In the perfused rat pancreas, neither of these antagonists inhibited the potent secretory response to 20 mmol/l glucose, although they effectively suppressed the potentiating effect of, respectively, an infusion of glucagon (1 nmol/l) or GLP-1 (1 nmol/l) on insulin release. When endogenous glucagon release was enhanced by isoproterenol (100 nmol/l), no amplification was seen in the simultaneous or subsequent insulin secretory response to glucose. It is concluded that, at least under the present selected conditions, the glucose-induced insulin release by the perfused rat pancreas seems to occur independent of an amplifying glucagon signal from neighboring α-cells.
Peroxisomal Proliferator-Activated Receptor-γ Upregulates Glucokinase Gene Expression in β-Cells
Authors: Kim Ha-il , Cha Ji-Young , Kim So-Youn , Kim Jae-woo , Roh Kyung Jin , Seong Je-Kyung , Lee Nam Taek , Choi Kang-Yell , Kim Kyung-Sup , Ahn Yong-ho
Published: March 2007

Thiazolidinediones, synthetic ligands of peroxisomal proliferator-activated receptor-γ (PPAR-γ), improve peripheral insulin sensitivity and glucose-stimulated insulin secretion in pancreatic β-cells. To explore the role of PPAR-γ in glucose sensing of β-cells, we have dissected the β-cell-specific glucokinase (βGK) promoter, which constitutes glucose-sensing apparatus in pancreatic β-cells, and identified a peroxisomal proliferator response element (PPRE) in the promoter. The βGK-PPRE is located in the region between +47 and +68 bp. PPAR-γ/retinoid X receptor-α heterodimer binds to the element and activates the βGK promoter. The βGK promoter lacking or having mutations in PPRE cannot be activated by PPAR-γ. PPAR-γ activates the βGK promoter in β-cells as well as non-β-cells. Furthermore, troglitazone increases endogenous GK expression and its enzyme activity in β-cell lines. These results indicate that PPAR-γ can regulate GK expression in β-cells. Taking these results together with our previous work, we conclude that PPAR-γ regulates gene expression of glucose-sensing apparatus and thereby improves glucose-sensing ability of β-cells, contributing to the restoration of β-cell function in type 2 diabetic subjects by troglitazone.
Gastrin Stimulates β-Cell Neogenesis and Increases Islet Mass From Transdifferentiated but Not From Normal Exocrine Pancreas Tissue
Authors: Rooman Ilse , Lardon Jessy , Bouwens Luc
Published: March 2007

It is still unclear which factors regulate pancreatic regeneration and β-cell neogenesis and which precursor cells are involved. We evaluated the role of intravenously infused gastrin in regenerating pancreas of duct-ligated rats. The ligation of exocrine ducts draining the splenic half of the pancreas resulted in acinoductal transdifferentiation within the ligated part but not in the unligated part. We found that infusion of gastrin from day 7 to 10 postligation resulted in a doubling of the β-cell mass in the ligated part as measured by morphometry. This increase in insulin-expressing cells was not associated with increased proliferation, hypertrophy, or reduced cell death of the β-cells. Furthermore, we found an increased percentage of single, extra-insular β-cells and small β-cell clusters induced by gastrin infusion. These changes occurred only in the ligated part of the pancreas, where transdifferentiation of the exocrine acinar cells to ductlike cells (metaplasia) had occurred, and was not found in the normal unaffected pancreatic tissue. In conclusion, we demonstrate that administration of gastrin stimulates β-cell neogenesis and expansion of the β-cell mass from transdifferentiated exocrine pancreas.
NFAT Regulates Insulin Gene Promoter Activity in Response to Synergistic Pathways Induced by Glucose and Glucagon-Like Peptide-1
Authors: Lawrence Michael C. , Bhatt Harshika S. , Easom Richard A.
Published: March 2007

Currently there is intense interest to define the mechanism of action of glucagon-like peptide-1 (GLP-1) in regulating β-cell function, including insulin gene transcription. In this study, GLP-1 (100 nmol/l), in the presence of glucose (11 mmol/l), induced a ∼71-fold increase in insulin gene promoter activity in INS-1 pancreatic β-cells, an effect that was an order of magnitude larger than with either stimulant alone. The response to GLP-1 was mimicked by forskolin and largely inhibited by the protein kinase A (PKA) inhibitors, H89 and myristoylated PKI(14–22) amide, indicating partial mediation via a cAMP/PKA pathway. Significantly, the actions of both GLP-1 and forskolin were abolished by the selective Ca2+/calmodulin-dependent phosphatase 2B (calcineurin) inhibitor, FK506, as well as by the chelation of intracellular Ca2+ by BAPTA (bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetate). Glucose and GLP-1 also synergistically activated NFAT (nuclear factor of activated T-cells)-mediated transcription from a minimal promoter construct containing tandem NFAT consensus sequences. Furthermore, two-point base pair mutations in any of the three identified NFAT sites within the rat insulin I promoter resulted in a significant reduction in the combined effect of glucose and GLP-1. These data suggest that the synergistic action of glucose and GLP-1 to promote insulin gene transcription is mediated through NFAT via PKA- and calcineurin-dependent pathways in pancreatic β-cells.
Primary In Vivo Oscillations of Metabolism in the Pancreas
Authors: Bergsten Peter , Westerlund Johanna , Liss Per , Carlsson Per-Ola
Published: March 2007

The role of metabolism in the generation of plasma insulin oscillations was investigated by simultaneous in vivo recordings of oxygen tension (pO2) in the endocrine and exocrine pancreas and portal blood insulin concentrations in the anesthetized rat. At the start of the experiment, the blood glucose concentration of seven rats was 6.2 ± 0.1 mmol/l and the arterial blood pressure was 116 ± 5 mmHg. These values did not differ from those obtained at the end of the experiment. Islet pO2 was measured by impaling superficially located islets with a miniaturized Clark electrode. The pO2 measurements revealed slow (0.21 ± 0.03 min−1) with superimposed rapid (3.1 ± 0.3 min−1) oscillations. The average pO2 was 39 ± 5 mmHg. Simultaneous recordings of pO2 in the exocrine pancreas were significantly lower (16 ± 6 mmHg), but showed a slow and a rapid oscillatory activity with similar frequencies as seen in the endocrine pancreas. Corresponding measurements of portal insulin concentrations revealed insulin oscillations at a frequency of 0.22 ± 0.02 min−1. The results are the first in vivo recordings of an oscillatory islet parameter with a frequency corresponding to that of plasma insulin oscillations; they support a primary role of metabolic oscillations in the induction of plasma insulin oscillations.
Counteraction of Type 1 Diabetic Alterations by Engineering Skeletal Muscle to Produce Insulin
Authors: Riu Efren , Mas Alex , Ferre Tura , Pujol Anna , Gros Laurent , Otaegui Pedro , Montoliu Lluis , Bosch Fatima
Published: March 2007

Insulin replacement therapy in type 1 diabetes is imperfect because proper glycemic control is not always achieved. Most patients develop microvascular, macrovascular, and neurological complications, which increase with the degree of hyperglycemia. Engineered muscle cells continuously secreting basal levels of insulin might be used to improve the efficacy of insulin treatment. Here we examined the control of glucose homeostasis in healthy and diabetic transgenic mice constitutively expressing mature human insulin in skeletal muscle. Fed transgenic mice were normoglycemic and normoinsulinemic and, after an intraperitoneal glucose tolerance test, showed increased glucose disposal. When treated with streptozotocin (STZ), transgenic mice showed increased insulinemia and reduced hyperglycemia when fed and normoglycemia and normoinsulinemia when fasted. Injection of low doses of soluble insulin restored normoglycemia in fed STZ-treated transgenic mice, while STZ-treated controls remained highly hyperglycemic, indicating that diabetic transgenic mice were more sensitive to the hypoglycemic effects of insulin. Furthermore, STZ-treated transgenic mice presented normalization of both skeletal muscle and liver glucose metabolism. These results indicate that skeletal muscle may be a key target tissue for insulin production and suggest that muscle cells secreting basal levels of insulin, in conjunction with insulin therapy, may permit tight regulation of glycemia.
Regional Differences in the Response of Human Pre-Adipocytes to PPARγ and RXRα Agonists
Authors: Sewter Ciaran P. , Blows Fiona , Vidal-Puig Antonio , O’Rahilly Stephen
Published: March 2007

We have previously reported that omental (OM) preadipocytes respond less well to the prodifferentiating effects of thiazolidinediones than do preadipocytes from subcutaneous (SC) depots. This finding is consistent with in vivo alterations in fat distribution that occur in humans treated with thiazolidinediones. To explore these site-related differences further, we used real-time RT-PCR to quantify the specific mRNAs encoding peroxisome proliferator-activated receptor (PPAR) γ1 and γ2 and found that both isoforms were more highly expressed in SC than in OM preadipocytes. After 10 days of thiazolidinedione treatment, preadipocytes from both depots showed a small and comparable increase in expression of PPARγ1 mRNA (1.7 ± 0.2-fold [P = 0.007]) and 1.3 ± 0.1-fold [P = 0.008] increase for SC and OM, respectively). There was a much larger increase in PPARγ2 expression, which was significantly greater in SC compared with OM preadipocytes (11.1 ± 2.8-fold [P = 0.0003] and 5.5 ± 1.7-fold [P = 0.0003], respectively; P = 0.014 for SC versus OM). To establish whether the refractoriness of OM preadipocytes to differentiation was unique to activators of the PPARγ pathway, we examined the effects of the retinoid X receptor (RXR) ligand LG100268. As assessed by glycerol-3-phosphate dehydrogenase activity, LG100268 had a greater effect on the differentiation of SC compared with OM preadipocytes when examined alone (SC = 5.7 ± 1.7-fold vs. OM = 1.9 ± 0.6-fold; P < 0.05) or in combination with rosiglitazone (SC = 27.0 ± 7.5 vs. OM = 10.6 ± 3.6-fold; P < 0.05). Consistent with this, RXRα mRNA levels were also higher in SC than in OM preadipocytes. In summary, the previously reported insensitivity of OM preadipocytes to the differentiating effects of thiazolidinediones may relate to their lower basal levels of PPARγ1 and γ2 mRNA and their diminished capacity to upregulate PPARγ2 expression in response to ligand. That omentally derived cells also show reduced responsiveness to the prodifferentiating actions of an RXR ligand and a lower expression of RXRα in the undifferentiated state suggests that they may have a more generalized resistance to differentiation.
Theophylline Improves Hypoglycemia Unawareness in Type 1 Diabetes
Authors: de Galan Bastiaan E. , Tack Cees J. , Lenders Jacques W. , Pasman Jaco W. , Elving Lammy D. , Russel Frans G. , Lutterman Jos A. , Smits Paul
Published: March 2007

Iatrogenic hypoglycemias and the subsequent occurrence of hypoglycemia unawareness are well-known complications of intensive insulin therapy in type 1 diabetic patients that limit glycemic management. From a pharmacological point of view, the adenosine-receptor antagonist theophylline might be beneficial in the management of hypoglycemia unawareness. Theophylline stimulates the release of catecholamines and reduces cerebral blood flow, thereby facilitating stronger metabolic responses to and a prompter perception of decreasing glucose levels. To test the effect of theophylline on responses to hypoglycemia, we performed paired hyperinsulinemic-hypoglycemic clamp studies in 15 diabetic patients with hypoglycemia unawareness and 15 matched healthy control subjects. In random order, we concurrently infused either theophylline or placebo. Measurements included counterregulatory hormones, symptoms, hemodynamic parameters, and sweat detection using a dew-point electrode. Additionally, middle cerebral artery velocities (VMCA) using transcranial Doppler were monitored as an estimate of cerebral blood flow. When compared with placebo, theophylline significantly enhanced responses of plasma epinephrine, norepinephrine, and cortisol levels in both diabetic patients and control subjects. Because of the theophylline, sweat production started at ∼0.3 mmol/l higher glucose levels in both groups (P < 0.01), and symptom scores in diabetic patients approached those in control subjects. Theophylline decreased VMCA in both groups (P < 0.001), but significantly greater in diabetic patients (P < 0.01), and prevented the hypoglycemia-induced increase of VMCA that occurred during the placebo studies. We conclude that theophylline improves counterregulatory responses to and perception of hypoglycemia in diabetic patients with impaired awareness of hypoglycemia.
The Effects of Rosiglitazone on Insulin Sensitivity, Lipolysis, and Hepatic and Skeletal Muscle Triglyceride Content in Patients With Type 2 Diabetes
Authors: Mayerson Adam B. , Hundal Ripudaman S. , Dufour Sylvie , Lebon Vincent , Befroy Douglas , Cline Gary W. , Enocksson Staffan , Inzucchi Silvio E. , Shulman Gerald I. , Petersen Kitt F.
Published: March 2007

We examined the effect of three months of rosiglitazone treatment (4 mg b.i.d.) on whole-body insulin sensitivity and in vivo peripheral adipocyte insulin sensitivity as assessed by glycerol release in microdialysis from subcutaneous fat during a two-step (20 and 120 mU · m−2 · min−1) hyperinsulinemic-euglycemic clamp in nine type 2 diabetic subjects. In addition, the effects of rosiglitazone on liver and muscle triglyceride content were assessed by 1H-nuclear magnetic resonance spectroscopy. Rosiglitazone treatment resulted in a 68% (P < 0.002) and a 20% (P < 0.016) improvement in insulin-stimulated glucose metabolism during the low- and high- dosage−insulin clamps, respectively, which was associated with ∼40% reductions in plasma fatty acid concentration (P < 0.05) and hepatic triglyceride content (P < 0.05). These changes were associated with a 39% increase in extramyocellular lipid content (P < 0.05) and a 52% increase in the sensitivity of peripheral adipocytes to the inhibitory effects of insulin on lipolysis (P = 0.04). In conclusion, these results support the hypothesis that thiazolidinediones enhance insulin sensitivity in patients with type 2 diabetes by promoting increased insulin sensitivity in peripheral adipocytes, which results in lower plasma fatty acid concentrations and a redistribution of intracellular lipid from insulin responsive organs into peripheral adipocytes.
Coronary Microvascular Adaptation to Myocardial Metabolic Demand Can Be Restored by Inhibition of Iron-Catalyzed Formation of Oxygen Free Radicals in Type 2 Diabetic Patients
Authors: Nitenberg Alain , Ledoux Séverine , Valensi Paul , Sachs Régis , Antony Isabelle
Published: March 2007

Dilation of coronary vessels is impaired in diabetic patients when myocardial metabolic demand is increased. Deferoxamine (DFX) restores a normal dilation of epicardial coronary arteries. To assess the effects of DFX on metabolic coronary microvascular dilation in type 2 diabetic patients, coronary blood flow was measured using intracoronary Doppler and quantitative angiography in 17 type 2 diabetic patients with normal coronary arteries and without any other coronary risk factors. Measurements were made at baseline and during a cold pressor test (CPT), before and after intravenous administration of DFX. With a similar rate-pressure product (RPP) increase during CPT before and after DFX (+21.1 ± 8.7 vs. +20.5 ± 8.9%, respectively), coronary blood flow increase was significantly enhanced after DFX (+31.8 ± 16.7 vs. +6.3 ± 12.9% before DFX, P < 0.001). Moreover, coronary resistance increased during CPT before DFX and decreased after DFX (+14.8 ± 21.9 vs. −7.9 ± 10.9%, respectively, P < 0.001). Lastly, the negative relationship between coronary blood flow and RPP before DFX (R = 0.546, P < 0.05) was changed in a positive relationship after DFX (R = 0.518, P < 0.05). In conclusion, in type 2 diabetic patients, inhibition of iron-catalyzed oxidative reactions by DFX restored dilation of the coronary microcirculation and a normal matching between myocardial metabolic demand and coronary blood flow.
A Genomewide Linkage Scan for Abdominal Subcutaneous and Visceral Fat in Black and White Families
Authors: Rice Treva , Chagnon Yvon C. , Pérusse Louis , Borecki Ingrid B. , Ukkola Olavi , Rankinen Tuomo , Gagnon Jacques , Leon Arthur S. , Skinner James S. , Wilmore Jack H. , Bouchard Claude , Rao D.C.
Published: March 2007

Abdominal visceral fat (AVF), abdominal subcutaneous fat (ASF), and abdominal total fat (ATF) were measured using a computed tomography scan, both before (baseline) and after (post) a 20-week endurance exercise training protocol in the HERITAGE Family Study. Each of the baseline and response (post minus baseline) measures was adjusted for several covariates, including total fat mass, and responses to training were further adjusted for baseline levels. Multipoint variance components linkage analysis using a genomewide scan of 344 markers was conducted separately by race using race-specific allele frequencies. Several promising results (P < 0.0023) were obtained. For baseline AVF, the best evidence was on 2q22.1 and 2q33.2-q36.3 (including the IRS1 locus) in whites, with suggestive findings on 7q22.2-q31.3 (including the LEP locus) in blacks. Although several regions were indicated for baseline ASF, only 4q31.22-q32.2 and 11p15.4-p11.2 replicated the results of another study. For responses to training, promising results were limited to ASF and ATF primarily on 7q36.2 (including NOS3) in blacks, with suggestive regions (P < 0.01) on 1q21.2-q24.1 (S100A, ATP1A2, and ATP1B1), 10q25.2 (ADRA2A), and 11p15.5 (IGF2). In summary, the 4q and 11p regions have now been implicated in two independent studies for ASF; further research is warranted to identify the genes and mutations in these regions that are responsible for fat accumulation in the abdominal depot. Additional work in an independent sample is needed to verify the linkages for baseline AVF as well as the response measures.
Association Between a Novel Variant of the Human Type 2 Deiodinase Gene Thr92Ala and Insulin Resistance
Authors: Mentuccia Daniela , Proietti-Pannunzi Laura , Tanner Keith , Bacci Vincenzo , Pollin Toni I. , Poehlman Eric T. , Shuldiner Alan R. , Celi Francesco S.
Published: March 2007

Thyroid hormone action is an important determinant of energy and glucose metabolism. T4 metabolism is regulated by the deiodinases of which type 2 is expressed in humans in skeletal muscle and brown adipose tissue, where its transcription is stimulated by the β-3 adrenergic pathway. We performed molecular scanning of the human type 2 deiodinase (DIO2) gene and evaluated a novel variant for associations with obesity and insulin resistance, assessing both the main effect and interaction with the Trp64Arg β-3–adrenergic receptor (ADRB3) variant. Molecular scanning of DIO2 in 50 obese Caucasians demonstrated a Thr92Ala variant. Association studies in 972 nondiabetic patients, 135 of whom underwent euglycemic-hyperinsulinemic clamps, showed that subjects with the Thr92Ala variant had lower glucose disposal rate (0.54 ± 0.02 mg · min−1 · kg−1 fat-free mass Ala92 homozygotes vs. 0.44 ± 0.02 Ala92 heterozygotes vs. 0.42 ± 0.04 Thr92 homozygotes, P = 0.0088). Association analysis of the entire group showed significant evidence for a synergistic effect between the Thr92Ala DIO2 and Trp64Arg ADRB3 variants on BMI (both variants 34.3 ± 0.9 kg/m2 vs. neither variant 33.1 ± 0.4 kg/m2, P = 0.04 for interaction). To our knowledge, Thr92Ala is the first description of a missense mutation of DIO2. This variant strongly associates with insulin resistance and, in subjects with the Trp64Arg ADRB3 variant, an increased BMI, suggesting an interaction between these two common gene variants.
Variations in Insulin Secretion in Carriers of Gene Variants in IRS-1 and -2
Authors: ’t Hart Leen M. , Nijpels Giel , Dekker Jacqueline M. , Maassen J. Antonie , Heine Robert J. , van Haeften Timon W.
Published: March 2007

Associations between type 2 diabetes (and/or parameters contributing to glucose homeostasis) and genetic variation in the genes encoding insulin receptor substrate (IRS)-1 and -2 have been reported in several populations. Recently, it has been reported that the Gly972Arg variant in IRS-1 was associated with reduced insulin secretion during hyperglycemic clamps in German subjects with normal glucose tolerance. We have examined glucose-stimulated insulin secretion in relation to gene variants in the IRS-1 (Gly972Arg) and IRS-2 (Gly1057Asp) genes in two Dutch cohorts. Subjects with normal (n = 64) or impaired (n = 94) glucose tolerance underwent 3-h hyperglycemic clamps at 10 mmol/l glucose. All subjects were genotyped for the IRS-1 and IRS-2 variants by PCR-RFLP–based methods. We did not observe any significant difference in both first- and second-phase insulin secretion between carriers and noncarriers of both gene variants, nor was there evidence for an association with other diabetes-related parameters. We conclude that the common gene variants in IRS-1 and IRS-2 are not associated with altered glucose-stimulated insulin secretion in two populations from the Netherlands.
Troglitazone Downregulates Δ-6 Desaturase Gene Expression in Human Skeletal Muscle Cell Cultures
Authors: Wahl Hans Günther , Kausch Christiana , Machicao Fausto , Rett Kristian , Stumvoll Michael , Häring Hans-Ulrich
Published: March 2007

Δ-6 Desaturase, one of the rate-limiting enzymes, catalyzes the conversion of linoleic acid (C18:2 ω6) into γ-linolenic acid (C18:3 ω6), arachidonic acid (C20:4 ω6), and further metabolites. Recently, it has been shown that human Δ-6 desaturase is expressed not only in liver but in a variety of human tissues, including muscle. Skeletal muscle is a major site of insulin action, and insulin sensitivity may be related to the fatty acid composition of muscle lipids. We examined the effects of troglitazone on the regulation of Δ-6 desaturase gene expression in human muscle cell cultures obtained from muscle biopsies (n = 15). Δ-6 Desaturase mRNA and peroxisome proliferator–activated receptor γ2 (PPARγ2) mRNA were quantified by two-step RT-PCR, and the activity of the Δ-6 desaturase enzyme was estimated by gas chromatographic analysis of the ω 6-C18:3/C18:2 fatty acids ratio. In cells treated with 11.5 μmol troglitazone for 4 days, PPARγ2 mRNA levels were significantly increased (301.0 ± 51.5%, P < 0.05) and Δ-6 desaturase mRNA levels were significantly decreased (41.7 ± 5.9%, P < 0.0005) compared with the untreated controls. In accordance with the decrease of Δ-6 desaturase mRNA, there was a significant decrease in the ω6-C18:3/C18:2 ratio down to 47.4 ± 7.5% in cholesterol esters, 54.2 ± 7.4% in phospholipids, 56.7 ± 6.5% in nonesterified fatty acids, and 67.7 ± 5.9% in triglycerides. The troglitazone-induced decrease in Δ-6 desaturase mRNA is associated with a change in the unsaturated fatty acid composition of the muscle cells. These results add new aspects to the known thiazolidinedione effects on lipid metabolism.
Increased Glucocorticoid Receptor Expression in Human Skeletal Muscle Cells May Contribute to the Pathogenesis of the Metabolic Syndrome
Authors: Whorwood Christopher B. , Donovan Stephen J. , Flanagan Daniel , Phillips David I.W. , Byrne Christopher D.
Published: March 2007

Altered glucocorticoid hormone action may contribute to the etiology of the metabolic syndrome, but the molecular mechanisms are poorly defined. Tissue sensitivity to glucocorticoid is regulated by expression of the glucocorticoid receptor (GR)-α and 11β-hydroxysteroid dehydrogenase type I (11β-HSD1)-mediated intracellular synthesis of active cortisol from inactive cortisone. We have analyzed GRα and 11β-HSD1 expression in skeletal myoblasts from men (n = 14) with contrasting levels of insulin sensitivity (euglycemic clamp measurements of insulin-dependent glucose disposal rate), blood pressure, and adiposity. Positive associations were evident between myoblast expression of GRα under basal conditions and levels of insulin resistance (r2 = 0.34, P < 0.05), BMI (r2 = 0.49, P < 0.01), percent body fat (r2 = 0.34, P < 0.02), and blood pressure (r2 = 0.86, P < 0.001). Similar associations were evident when myoblasts were incubated with physiological levels of cortisol (P < 0.01 for all). Importantly, GRα expression was unaffected by variations in in vivo concentrations of insulin, IGF-1, or glucose concentrations. In common with the GR, 11β-HSD1 expression in myoblasts incubated with physiological concentrations of cortisol in vitro was positively associated with levels of insulin resistance (r2 = 0.68, P < 0.001), BMI (r2 = 0.63, P < 0.005), and blood pressure (r2 = 0.27, P < 0.05). Regulation of GRα and 11β-HSD1 by cortisol was abolished by the GR antagonist RU38486. In summary, our data suggest that raised skeletal muscle cell expression of GRα and 11β -HSD1-mediated regulation of intracellular cortisol may play a fundamental role in mechanisms contributing to the pathogenesis of the metabolic syndrome.
A Tailored Therapy for the Metabolic Syndrome
Authors: Etgen Garret J. , Oldham Brian A. , Johnson William T. , Broderick Carol L. , Montrose Chahrzad R. , Brozinick Joseph T. , Misener Elizabeth A. , Bean James S. , Bensch William R. , Brooks Dawn A. , Shuker Anthony J. , Rito Christopher J. , McCarthy James R. , Ardecky Robert J. , Tyhonas John S. , Dana Sharon L. , Bilakovics James M. , Paterniti James R. , Ogilvie Kathleen M. , Liu Sha , Kauffman Raymond F.
Published: March 2007

A novel nonthiazolidinedione dual peroxisome proliferator- activated receptor (PPAR)-α/γ agonist, LY465608, was designed to address the major metabolic disturbances of type 2 diabetes. LY465608 altered PPAR-responsive genes in liver and fat of db/db mice and dose-dependently lowered plasma glucose in hyperglycemic male Zucker diabetic fatty (ZDF) rats, with an ED50 for glucose normalization of 3.8 mg · kg−1 · day−1. Metabolic improvements were associated with enhanced insulin sensitivity, as demonstrated in female obese Zucker (fa/fa) rats using both oral glucose tolerance tests and hyperinsulinemic-euglycemic clamps. Further characterization of LY465608 revealed metabolic changes distinct from a selective PPAR-γ agonist, which were presumably due to the concomitant PPAR-α agonism, lower respiratory quotient, and less fat accumulation, despite a similar impact on glycemia in male ZDF rats. In addition to these alterations in diabetic and insulin-resistant animals, LY465608 dose-dependently elevated HDL cholesterol and lowered plasma triglycerides in human apolipoprotein A-I transgenic mice, demonstrating that this compound significantly improves primary cardiovascular risk factors. Overall, these studies demonstrate that LY465608 beneficially impacts multiple facets of type 2 diabetes and associated cardiovacular risk, including those facets involved in the development of micro- and macrovascular complications, which are the major sources for morbidity and mortality in these patients.