bluuebunny/crossref_metadata_2025 huggingface dataset:
Platelet-Derived Growth Factor Stimulates Glucose Transport in Skeletal Muscles of Transgenic Mice Specifically Expressing Platelet-Derived Growth Factor Receptor in the Muscle, but It Does Not Affect Blood Glucose Levels
Authors: Yuasa Tomoyuki , Kakuhata Rei , Kishi Kazuhiro , Obata Toshiyuki , Shinohara Yasuo , Bando Yoshimi , Izumi Keisuke , Kajiura Fumiko , Matsumoto Mitsuru , Ebina Yousuke
Published: March 2007

Insulin stimulates the disposal of blood glucose into skeletal muscle and adipose tissues by the translocation of GLUT4 from intracellular pools to the plasma membrane, and consequently the concentration of blood glucose levels decreases rapidly in vivo. Phosphatidylinositol (PI) 3-kinase and Akt play a pivotal role in the stimulation of glucose transport by insulin, but detailed mechanisms are unknown. We and others reported that not only insulin but also platelet-derived growth factor (PDGF) and epidermal growth factor facilitate glucose uptake through GLUT4 translocation by activation of PI 3-kinase and Akt in cultured cells. However, opposite results were also reported. We generated transgenic mice that specifically express the PDGF receptor in skeletal muscle. In these mice, PDGF stimulated glucose transport into skeletal muscle in vitro and in vivo. Thus, PDGF apparently shares with insulin some of the signaling molecules needed for the stimulation of glucose transport. The degree of glucose uptake in vivo reached ∼60% of that by insulin injection in skeletal muscle, but blood glucose levels were not decreased by PDGF in these mice. Therefore, PDGF-induced disposal of blood glucose into skeletal muscle is insufficient for rapid decrease of blood glucose levels.
Free Fatty Acid Levels Modulate Microvascular Function
Authors: de Jongh Renate T. , Serné Erik H. , IJzerman Richard G. , de Vries Greetje , Stehouwer Coen D.A.
Published: March 2007

To test the hypothesis that free fatty acids (FFAs) modulate microvascular function and that this contributes to obesity-associated insulin resistance, hypertension, and microangiopathy, we examined the effects of both FFA elevation in lean women and FFA lowering in obese women on skin microvascular function. A total of 16 lean and 12 obese women underwent, respectively, Intralipid plus heparin (or saline) infusion and overnight acipimox (or placebo) treatment. We measured capillary recruitment with capillaroscopy and endothelium-(in)dependent vasodilation by iontophoresis of acetylcholine and sodium nitroprusside before and during hyperinsulinemia (40 mU · m−2 · min−1). FFA elevation impaired capillary recruitment and acetylcholine-mediated vasodilation before (44.6 ± 16.8 vs. 56.9 ± 18.9%, P < 0.05; and 338 ± 131 vs. 557 ± 162%, P < 0.01, respectively) and during (54.0 ± 21.3 vs. 72.4 ± 25.4%, P < 0.01; and 264 ± 186 vs. 685 ± 199%, P < 0.01, respectively) hyperinsulinemia. FFA lowering improved capillary recruitment before (50.9 ± 14.6 vs. 37.4 ± 9.3%, P < 0.01) and during (66.8 ± 20.6 vs. 54.8 ± 15.4%, P < 0.05) hyperinsulinemia. Changes in FFA levels were inversely associated with changes in capillary recruitment and insulin sensitivity in lean (r = −0.46, P = 0.08; and r = −0.56, P = 0.03) and in obese (r = −0.70, P = 0.02; and r = −0.62, P = 0.04) women. Regression analyses showed that changes in capillary recruitment statistically explained ∼29% of the association between changes in FFA levels and insulin sensitivity. In conclusion, FFA levels modulate microvascular function and may contribute to obesity-associated insulin resistance, hypertension, and microangiopathy.
Phloridzin Improves Hyperglycemia But Not Hepatic Insulin Resistance in a Transgenic Mouse Model of Type 2 Diabetes
Authors: Zhao Hong , Yakar Shoshana , Gavrilova Oksana , Sun Hui , Zhang Yang , Kim Hyunsook , Setser Jennifer , Jou William , LeRoith Derek
Published: March 2007

The chronic hyperglycemia that occurs in type 2 diabetes may cause deterioration of β-cell function and insulin resistance in peripheral tissues. Mice that express a dominant-negative IGF-1 receptor, specifically in skeletal muscle (MKR mice), exhibit severe insulin resistance, hyperinsulinemia, dyslipidemia, and hyper-glycemia. To determine the role of hyperglycemia in the worsening of the diabetes state in these animals, MKR mice were treated with phloridzin (PHZ), which inhibits intestinal glucose uptake and renal glucose reabsorption. Blood glucose levels were decreased and urine glucose levels were increased in response to PHZ treatment in MKR mice. PHZ treatment also increased food intake in MKR mice; however, the fat mass was decreased and lean body mass did not change. Serum insulin, fatty acid, and triglyceride levels were not affected by PHZ treatment in MKR mice. Hyperinsulinemic-euglycemic clamp analysis demonstrated that glucose uptake in white adipose tissue was significantly increased in response to PHZ treatment. Despite the reduction in blood glucose following PHZ treatment, there was no improvement in insulin-stimulated whole-body glucose uptake in MKR mice and neither was there suppression of endogenous glucose production by insulin. These results suggest that glucotoxicity plays little or no role in the worsening of insulin resistance that occurs in the MKR mouse model of type 2 diabetes.
Intranasal Insulin Reduces Body Fat in Men but not in Women
Authors: Hallschmid Manfred , Benedict Christian , Schultes Bernd , Fehm Horst-Lorenz , Born Jan , Kern Werner
Published: March 2007

Insulin acts in the central nervous system to reduce food intake and body weight and is considered a major adiposity signal. After intranasal administration, insulin enters the cerebrospinal fluid compartment and alters brain functions in the absence of substantial absorption into the blood stream. Here we report the effects of 8 weeks of intranasal administration of insulin (4 × 40 IU/day) or placebo to two groups of healthy human subjects (12 men and 8 women in each group). The insulin-treated men lost 1.28 kg body wt and 1.38 kg of body fat, and their waist circumference decreased by 1.63 cm. Plasma leptin levels dropped by an average of 27%. In contrast, the insulin-treated women did not lose body fat and gained 1.04 kg body wt due to a rise in extracellular water. Our results provide a strong, first confirmation in humans that insulin acts as a negative feedback signal in the regulation of adiposity and point to a differential sensitivity to the catabolic effects of insulin based on sex.
Absence of Lymph Nodes inNODMice Treated With Lymphotoxin-β Receptor Immunoglobulin Protects From Diabetes
Authors: Levisetti Matteo G. , Suri Anish , Frederick Katherine , Unanue Emil R.
Published: March 2007

Pregnant nonobese diabetic (NOD) mice were treated with lymphotoxin-β receptor immunoglobulin fusion protein (LTβR-Ig) or control human immunoglobulin on days embryonic day 11 (E11) and E14, and offspring were followed for the development of anti–β-cell antibodies, islet pathology, and hyperglycemia. The development of anti–β-cell surface antibodies was abrogated in treated mice compared with controls. Autopsy examination of the mice at 30 weeks of age revealed normal development of secondary lymphoid structures in the control animals; however, mice treated with LTβR-Ig had no axillary, inguinal, popliteal, or peripancreatic lymph nodes. Histological examination of the pancreata of the control mice revealed a severe and destructive mononuclear cellular infiltrate in the islets, whereas the islets of the LTβR-Ig–treated mice were devoid of any insulitis. None of the LTβR-Ig–treated mice (n = 22) developed diabetes; in contrast, 80% of the control mice (n = 46) developed diabetes at 1 year of age. The LTβR-Ig–treated mice did not contain diabetogenic T-cells. However, the treated mice developed diabetes upon inoculation with diabetogenic T-cells. In this model of spontaneous autoimmune diabetes, secondary lymphoid structures, most likely the peripancreatic lymph nodes, were essential for the development of pathologic anti–β-cell autoimmunity.
Stimulation of Insulin Release by Glucose Is Associated With an Increase in the Number of Docked Granules in the β-Cells of Rat Pancreatic Islets
Authors: Straub Susanne G. , Shanmugam Geetha , Sharp Geoffrey W.G.
Published: March 2007

Electron microscopy and quantitative stereological techniques were used to study the dynamics of the docked granule pool in the rat pancreatic β-cell. The mean number of granules per β-cell was 11,136. After equilibration in RPMI containing 5.6 mmol/l glucose, 6.4% of the granules (∼700) were docked at the plasma membrane (also measured as [means ± SE] 4.3 ± 0.6 docked granules per 10 μm of plasma membrane at the perimeter of the cell sections). After a 40-min exposure to 16.7 mmol/l glucose, 10.2% of the granules (∼1,060) were docked (6.4 ± 0.8 granules per 10 μm of plasma membrane). Thus, the docked pool increased by 50% during stimulation with glucose. Islets were also exposed to 16.7 mmol/l glucose in the absence or presence of 10 μmol/l nitrendipine. In the absence and presence of nitrendipine, there were 6.1 ± 0.7 and 6.3 ± 0.6 granules per 10 μm of membrane, respectively. Thus, glucose increased granule docking independently of increased [Ca2+]i and exocytosis. The data suggest a limit to the number of docking sites. As the rate of docking exceeded the rate of exocytosis, docking is not rate limiting for insulin release. Only with extremely high release rates, glucose stimulation after a 4-h incubation with a high concentration of fatty acid-free BSA, was the docked granule pool reduced in size.
A Novel Glucagon Receptor Antagonist Inhibits Glucagon-Mediated Biological Effects
Authors: Qureshi Sajjad A. , Rios Candelore Mari , Xie Dan , Yang Xiaodong , Tota Laurie M. , Ding Victor D.-H. , Li Zhihua , Bansal Alka , Miller Corin , Cohen Sheila M. , Jiang Guoqiang , Brady Ed , Saperstein Richard , Duffy Joseph L. , Tata James R. , Chapman Kevin T. , Moller David E. , Zhang Bei B.
Published: March 2007

Glucagon maintains glucose homeostasis during the fasting state by promoting hepatic gluconeogenesis and glycogenolysis. Hyperglucagonemia and/or an elevated glucagon-to-insulin ratio have been reported in diabetic patients and animals. Antagonizing the glucagon receptor is expected to result in reduced hepatic glucose overproduction, leading to overall glycemic control. Here we report the discovery and characterization of compound 1 (Cpd 1), a compound that inhibits binding of 125I-labeled glucagon to the human glucagon receptor with a half-maximal inhibitory concentration value of 181 ± 10 nmol/l. In CHO cells overexpressing the human glucagon receptor, Cpd 1 increased the half-maximal effect for glucagon stimulation of adenylyl cyclase with a KDB of 81 ± 11 nmol/l. In addition, Cpd 1 blocked glucagon-mediated glycogenolysis in primary human hepatocytes. In contrast, a structurally related analog (Cpd 2) was not effective in blocking glucagon-mediated biological effects. Real-time measurement of glycogen synthesis and breakdown in perfused mouse liver showed that Cpd 1 is capable of blocking glucagon-induced glycogenolysis in a dosage-dependent manner. Finally, when dosed in humanized mice, Cpd 1 blocked the rise of glucose levels observed after intraperitoneal administration of exogenous glucagon. Taken together, these data suggest that Cpd 1 is a potent glucagon receptor antagonist that has the capability to block the effects of glucagon in vivo.
Mapping Non–Class II H2-Linked Loci for Type 1 Diabetes in Nonobese Diabetic Mice
Authors: Deruytter Nathalie , Boulard Olivier , Garchon Henri-Jean
Published: March 2007

Major histocompatibility complex (MHC) plays a largely predominant role in the genetic predisposition to type 1 diabetes, in both humans and rodents. While class II loci have long been recognized as essential, they do not fully explain the MHC-linked genetic component of type 1 diabetes. In the present study, using new NOD congenic strains harboring defined chromosomal segments from C57BL/6 mice, we circumscribed three distinct loci influencing murine type 1 diabetes and tightly linked to but separated from the class II region. Our findings might guide the search for additional HLA-linked loci in human type 1 diabetes.
Quantitative Trait Loci for Obesity- and Diabetes-Related Traits and Their Dietary Responses to High-Fat Feeding in LGXSM Recombinant Inbred Mouse Strains
Authors: Cheverud James M. , Ehrich Thomas H. , Hrbek Tomas , Kenney Jane P. , Pletscher L. Susan , Semenkovich Clay F.
Published: March 2007

Genetic variation in response to high-fat diets is important in understanding the recent secular trends that have led to increases in obesity and type 2 diabetes. The examination of quantitative trait loci (QTLs) for both obesity- and diabetes-related traits and their responses to a high-fat diet can be effectively addressed in mouse model systems, including LGXSM recombinant inbred (RI) mouse strains. A wide range of obesity- and diabetes-related traits were measured in animals from 16 RI strains with 8 animals of each sex fed a high- or low-fat diet from each strain. Marker associations were measured at 506 microsatellite markers spread throughout the mouse genome using a nested ANOVA. Locations with significant effects on the traits themselves and/or trait dietary responses were identified after correction for multiple comparisons by limiting the false detection rate. Nonsyntenic associations of marker genotypes were common at QTL locations so that the significant results were limited to loci still significant in multiple QTL models. We discovered 91 QTLs at 39 locations. Many of these locations (n = 31) also showed genetic effects on dietary response, typically because the loci produced significantly larger effects on the high-fat diet. Fat depot weights, leptin levels, and body weight at necropsy tended to map to the same locations and were responsible for a majority of the dietary response QTLs. Basal glucose levels and the response to glucose challenge mapped together in locations distinct from those affecting obesity. These QTL locations form a panel for further research and fine mapping of loci affecting obesity- and diabetes-related traits and their responses to high-fat feeding.
Sterol Regulatory Element-Binding Protein-1 Mediates the Effect of Insulin on Hexokinase II Gene Expression in Human Muscle Cells
Authors: Gosmain Yvan , Lefai Etienne , Ryser Stephan , Roques Marina , Vidal Hubert
Published: March 2007

Insulin upregulates hexokinase II (HKII) expression in skeletal muscle, and this effect is altered in type 2 diabetic patients. This study was conducted to identify the transcription factors that mediate the effect of insulin on HKII gene expression in human muscle. We have cloned the promoter region of the HKII gene and investigated its regulation in a primary culture of human skeletal muscle cells. We defined a region (−369/−270) that conferred the transcriptional response to insulin. This region contains a sterol regulatory element (SRE) that interacted with the recombinant active form of SRE binding protein-1c (SREBP-1c) in electrophoretic mobility shift assays, and, using chromatin immunoprecipitation assay, we showed that endogenous SREBP-1 interacted directly with the promoter region of the HKII gene in human muscle cells. Mutation of the SRE sequence completely suppressed the response of the promoter to insulin stimulation. Finally, overexpression of the rodent mature form of SREBP-1c (adipocyte determination and differentiation factor-1 [ADD1]-403) was able to reproduce insulin action, whereas a dominant-negative form (ADD1-403R) prevented the effect of insulin on HKII promoter constructs. These results demonstrate that SREBP-1c is involved in the effect of insulin on HKII gene transcription and indicate that it is one of the mediators of insulin action on gene expression in human skeletal muscle.
Effect of Recurrent Hypoglycemia on Spatial Cognition and Cognitive Metabolism in Normal and Diabetic Rats
Authors: McNay Ewan C. , Sherwin Robert S.
Published: March 2007

The effects of recurrent hypoglycemia (RH) on cognition in human subjects remain controversial, perhaps in part due to difficulty in completely controlling previous hypoglycemic history. We used a model of RH in nondiabetic and diabetic rats to examine the effects of short-term (3 h daily for 3 days) RH on subsequent hippocampally dependent spatial memory, tested either at euglycemia or under acute hypoglycemia. Hippocampal metabolism was simultaneously measured using microdialysis. Antecedent RH improved task performance (79 ± 2% alternation in nondiabetic RH animals vs. 63 ± 3% in controls; P < 0.001) at euglycemia, accompanied by reversal of the task-associated dip (20 ± 1% below baseline) in hippocampal extracellular fluid (ECF) glucose seen in control animals. RH rats also had a larger rise in hippocampal ECF glucose, after intraperitoneal glucose injection, than did controls. However, RH animals tested at acute hypoglycemia (∼2.8 mmol/l) performed significantly worse than control animals. Results were similar in diabetic and nondiabetic rats. Our data suggest that RH causes improvement in subsequent cognitive performance at euglycemia, accompanied by alterations in cognitive metabolism. When glucose availability is limited, complex cognitive functioning seems to be adversely effected in RH animals, perhaps to better maintain and preserve basic brain functions.
Decrease in Glucose-Stimulated Insulin Secretion With Aging Is Independent of Insulin Action
Authors: Muzumdar Radhika , Ma Xiaohui , Atzmon Gil , Vuguin Patricia , Yang Xiaoman , Barzilai Nir
Published: March 2007

While the incidence of diabetes increases with age, a decrease in β-cell function independent of age-related insulin resistance has not been conclusively determined. We studied insulin secretion (by hyperglycemic clamp) in 3-, 9-, and 20-month-old chronically catheterized, awake, Sprague Dawley (SD) rats (n = 78). Insulin action was modulated in a group of old rats by caloric restriction (CR) or by surgical removal of visceral fat (VF−). During the first 2 h of the clamp (11 mmol/l glucose), insulin secretion and insulin resistance (Si hyper clamp) demonstrated the characteristic hyperbolic relationship. However, after hyperglycemia for an additional 2 h, the ability to maintain insulin secretion, commensurate with the degree of insulin resistance, was decreased in all aging rats (P < 0.05). Increasing plasma glucose levels to 18 mmol/l glucose, after clamp at 11 mmol/l, increased insulin secretion by approximately threefold in young rats, but failed to induce similar magnitude of response in the aging rats (∼50%). However, elevation of plasma free fatty acid (FFA) levels by twofold (by intralipid infusion during 11 mmol/l glucose clamp) resulted in a robust, approximate twofold response in both young and old rats. Thus, prolonged stimulation by hyperglycemia unveiled a functional defect in insulin secretion with aging. This age-related defect is independent of insulin action and is specific to glucose and not FFAs. We suggest that prolonged hyperglycemic stimulation can be a tool to identify functional defects in insulin secretion, particularly in the context of the hyperbolic relationship with insulin action, in elderly subjects or those at risk for type 2 diabetes.
Uncoupling Protein 2 Promoter Polymorphism −866G/A Affects Its Expression in β-Cells and Modulates Clinical Profiles of Japanese Type 2 Diabetic Patients
Authors: Sasahara Miyoshi , Nishi Masahiro , Kawashima Hiromichi , Ueda Kazuya , Sakagashira Setsuya , Furuta Hiroto , Matsumoto Eisaku , Hanabusa Tadashi , Sasaki Hideyuki , Nanjo Kishio
Published: March 2007

Common uncoupling protein 2 (UCP2) promoter polymorphism −866G/A is reported to be associated with its expression in adipose tissue and the risk of obesity in Caucasians. On the other hand, several studies suggested that UCP2 expression in β-cells is an important determinant of insulin secretion. In the Japanese population, morbid obesity is very rare, and insulin secretion capacity is relatively low as compared with Caucasians. Because UCP2 would link to insulin secretion and obesity, it might explain this ethnic difference. Here, we report that the UCP2 promoter with the A allele showed higher promoter activity in the INS-1 β-cell line. The frequency of the A allele is higher in our Japanese study than that in Caucasians. Type 2 diabetic patients with the A allele need insulin therapy earlier and showed higher frequency of insulin treatment. Moreover glucose-induced early insulin secretion is significantly lower in patients with the A allele. However, there was no difference in allele frequency between obese and lean type 2 diabetic patients. In conclusion, UCP2 promoter polymorphism −866G/A does not affect obesity in Japanese type 2 diabetic patients but affects its transcription in β-cells and modulates glucose-induced insulin secretion and eventually insulin requirement in Japanese type 2 diabetic patients. Higher A allele frequency in the Japanese population might partly explain the ethnic difference of insulin secretion capacity.
Messenger RNA Transcripts of the Hepatocyte Nuclear Factor-1α Gene Containing Premature Termination Codons Are Subject to Nonsense-Mediated Decay
Authors: Harries Lorna W. , Hattersley Andrew T. , Ellard Sian
Published: March 2007

Mutations in the hepatocyte nuclear factor-1α (HNF-1a) gene cause maturity-onset diabetes of the young (MODY). Approximately 30% of these mutations generate mRNA transcripts harboring premature termination codons (PTCs). Degradation of such transcripts by the nonsense-mediated decay (NMD) pathway has been reported for many genes. To determine whether PTC mutant transcripts of the HNF-1α gene elicit NMD, we have developed a novel quantitative RT-PCR assay. We performed quantification of ectopically expressed mutant transcripts relative to normal transcripts in lymphoblastoid cell lines using a coding single nucleotide polymorphism (cSNP) as a marker. The nonsense mutations R171X, I414G415ATCG→CCA, and P291fsinsC showed reduced mutant mRNA expression to 40% (P = 0.009), <0.01% (P ≤ 0.0001), and 6% (P = 0.001), respectively, of the normal allele. Transcript levels were restored using the translation inhibitor cycloheximide, indicating that the instability arises from NMD. The missense mutations G207D and R229P did not show NMD although R229P exhibited moderate RNA instability. This study provides the first evidence that HNF-1α PTC mutations may be subject to NMD. Mutations that result in significant reduction of protein levels due to NMD will not have dominant-negative activity in vivo. Haploinsufficiency is therefore likely to be the most important mutational mechanism of HNF-1α mutations causing MODY.
Uncoupling Protein 2 and Islet Function
Authors: Chan Catherine B. , Saleh Monique C. , Koshkin Vasilij , Wheeler Michael B.
Published: March 2007

Stressors such as chronic hyperglycemia or hyperlipidemia may lead to insufficient insulin secretion in susceptible individuals, contributing to type 2 diabetes. The molecules mediating this effect are just beginning to be identified. Uncoupling protein (UCP)-2 may be one such negative modulator of insulin secretion. Accumulating evidence shows that β-cell UCP2 expression is upregulated by glucolipotoxic conditions and that increased activity of UCP2 decreases insulin secretion. Mitochondrial superoxide has been identified as a posttranslational regulator of UCP2 activity in islets; thus, UCP2 may provide protection to β-cells at one level while simultaneously having detrimental effects on insulin secretion. Interestingly, the latter appears to be the dominant outcome, because UCP2 knockout mice display an increased β-cell mass and retained insulin secretion capacity in the face of glucolipotoxicity.
Single Nucleotide Polymorphisms in the Proximal Promoter Region of the Adiponectin (APM1) Gene Are Associated With Type 2 Diabetes in Swedish Caucasians
Authors: Gu Harvest F. , Abulaiti Adili , Östenson Claes-Göran , Humphreys Keith , Wahlestedt Claes , Brookes Anthony J. , Efendic Suad
Published: March 2007

Adiponectin (APM1) is an adipocyte-derived peptide. The APM1 gene is located on chromosome 3q27 and linked to type 2 diabetes. In patients with type 2 diabetes, the adiponectin level in plasma is decreased in comparison to healthy subjects. To identify genetic defects of the APM1 gene that contribute to the development of type 2 diabetes, we genotyped 13 single nucleotide polymorphisms (SNPs) in 106 patients with type 2 diabetes, 325 patients with impaired glucose tolerance (IGT), and 497 nondiabetic control subjects in Swedish Caucasians by using dynamic allele-specific hybridization (DASH). We found that SNPs −11426(A/G) and −11377(G/C) in the proximal promoter region had significant differences of allele frequencies between type 2 diabetic patients and nondiabetic control subjects (P = 0.02 and P = 0.04, respectively). SNP-11426(A/G) was significantly associated with fasting plasma glucose in type 2 diabetic patients (P = 0.02) and in IGT subjects (P = 0.04), while the patients carrying CC and CG genotypes for SNP-11377(G/C) had a higher BMI than the patients with the GG genotype (P = 0.03). Haplotype analysis of 13 SNPs in the APM1 gene showed that estimates of haplotype frequencies in Swedish Caucasians are similar to those estimated in French Caucasians. However, no significant association of haplotypes with type 2 diabetes and IGT was detected in our study. The present study provides additional evidence that SNPs in the proximal promoter region of the APM1 gene contribute to the development of type 2 diabetes.
Muscle-Type Specific Intramyocellular and Hepatic Lipid Metabolism During Starvation in Wistar Rats
Authors: Neumann-Haefelin Claudia , Beha Anja , Kuhlmann Johanna , Belz Ulrich , Gerl Martin , Quint Manfred , Biemer-Daub Gabriele , Broenstrup Mark , Stein Marion , Kleinschmidt Elke , Schaefer Hans-Ludwig , Schmoll Dieter , Kramer Werner , Juretschke Hans-Paul , Herling Andreas W.
Published: March 2007

The physiological dynamics of intramyocellular lipids (IMCLs) in different muscle types and of hepatocellular lipids (HepCLs) are still uncertain. The dynamics of IMCLs in the soleus, tibialis anterior, and extensor digitorum longus (EDL) muscles and HepCL during fed, 12- to 72-h starved, and refed conditions were measured in vivo by 1H-magnetic resonance spectroscopy (MRS) in Wistar rats. Despite significant elevations of free fatty acids (FFAs) during starvation, HepCLs and IMCLs in soleus remained constant. In tibialis anterior and EDL, however, IMCLs increased significantly by 170 and 450% after 72 h of starvation, respectively. After refeeding, elevated IMCLs dropped immediately in both muscles. Total muscle long-chain acyl-CoAs (LCACoAs) remained constant during the study period. Hepatic palmitoleoyl-CoA (C16:1) decreased significantly during starvation while total hepatic LCACoAs increased significantly. Consistent with constant values for FFAs, HepCLs, IMCLs, and muscle LCACoAs from 12–72 h of starvation, insulin sensitivity did not change. We conclude that during starvation-induced adipocytic lipolysis, oxidative muscles dispose elevated FFAs by oxidation, while nonoxidative ones neutralize FFAs by reesterification. Both mechanisms might prevent impairment of insulin signaling by maintaining low levels of LCACoAs. Hepatic palmitoleoyl-CoA might have a special role in lipid metabolism due to its unique dynamic profile during starvation.
Reduced Lipid Oxidation in Skeletal Muscle From Type 2 Diabetic Subjects May Be of Genetic Origin
Authors: Gaster Michael , Rustan Arild C. , Aas Vigdis , Beck-Nielsen Henning
Published: March 2007

Insulin resistance in skeletal muscle in vivo is associated with reduced lipid oxidation and lipid accumulation. It is still uncertain whether changes in lipid metabolism represent an adaptive compensation at the cellular level or a direct expression of a genetic trait. Studies of palmitate metabolism in human myotubes established from control and type 2 diabetic subjects may solve this problem, as genetic defects are preserved and expressed in vitro. In this study, total uptake of palmitic acid was similar in myotubes established from both control and type 2 diabetic subjects under basal conditions and acute insulin stimulation. Myotubes established from diabetic subjects expressed a primary reduced palmitic acid oxidation to carbon dioxide with a concomitantly increased esterification of palmitic acid into phospholipids compared with control myotubes under basal conditions. Triacylglycerol (TAG) content and the incorporation of palmitic acid into diacylglycerol (DAG) and TAG at basal conditions did not vary between the groups. Acute insulin treatment significantly increased palmitate uptake and incorporation of palmitic acid into DAG and TAG in myotubes established from both study groups, but no difference was found in myotubes established from control and diabetic subjects. These results indicate that the reduced lipid oxidation in diabetic skeletal muscle in vivo may be of genetic origin; it also appears that TAG metabolism is not primarily affected in diabetic muscles under basal physiological conditions.
Insulin-Independent Induction of Sterol Regulatory Element-Binding Protein-1c Expression in the Livers of Streptozotocin-Treated Mice
Authors: Matsuzaka Takashi , Shimano Hitoshi , Yahagi Naoya , Amemiya-Kudo Michiyo , Okazaki Hiroaki , Tamura Yoshiaki , Iizuka Yoko , Ohashi Ken , Tomita Sachiko , Sekiya Motohiro , Hasty Alyssa , Nakagawa Yoshimi , Sone Hirohito , Toyoshima Hideo , Ishibashi Shun , Osuga Jun-ichi , Yamada Nobuhiro
Published: March 2007

Insulin and glucose together have been previously shown to regulate hepatic sterol regulatory element-binding protein (SREBP)-1c expression. We sought to explore the nutritional regulation of lipogenesis through SREBP-1c induction in a setting where effects of sugars versus insulin could be distinguished. To do so, mice were insulin depleted by streptozotocin (STZ) administration and subjected to a fasting-refeeding protocol with glucose, fructose, or sucrose. Unexpectedly, the insulin-depleted mice exhibited a marked induction of SREBP-1c on all sugars, and this increase in SREBP-1c was even more dramatic than in the non-STZ-administered controls. The time course of changes in SREBP-1 induction varied depending on the type of sugars in both control and STZ-administered mice. Glucose refeeding gave a peak of SREBP-1c induction, whereas fructose refeeding caused slow and gradual increments, and sucrose refeeding fell between these two responses. Expression of various lipogenic enzymes were also gradually increased over time, irrespective of the types of sugars, with greater intensities in STZ-administered than in nontreated mice. In contrast, induction of hepatic glucokinase and suppression of phoshoenolpyruvate carboxykinase were insulin dependent in an early refed state. These data clearly demonstrate that nutritional regulation of SREBP-1c and lipogenic genes may be completely independent of insulin as long as sufficient carbohydrates are available.
Leptin Resistance and Enhancement of Feeding Facilitation by Melanin-Concentrating Hormone in Mice Lacking Bombesin Receptor Subtype-3
Authors: Maekawa Fumihiko , Quah Hun-Meng A. , Tanaka Kohichi , Ohki-Hamazaki Hiroko
Published: March 2007

Mice lacking either bombesin receptor subtype (BRS)-3 or gastrin-releasing peptide receptor (GRP-R) exhibit feeding abnormalities. However, it is unclear how these receptors are associated with feeding regulation. In BRS-3-deficient mice, we found hyperphagia, subsequent hyperleptinemia, and brain leptin resistance that occurred after the onset of obesity. To explore the cause of this phenomenon, we examined changes in feeding responses to appetite-related neuropeptides in BRS-3-deficient, GRP-R-deficient, and wild-type littermate mice. Among orexigenic neuropeptides, the hyperphagic response to melanin-concentrating hormone (MCH) was significantly enhanced in BRS-3-deficient mice but not in GRP-R-deficient mice. In addition, the levels of MCH-R and prepro-MCH mRNAs in the hypothalamus of BRS-3-deficient mice were significantly more elevated than those of wild-type littermates. There was no significant difference in feeding between BRS-3-deficient and wild-type littermate mice after treatment with bombesin (BN), although the hypophagic response to low-dose BN was significantly suppressed in the GRP-R-deficient mice. These results suggest that upregulation of MCH-R and MCH triggers hyperphagia in BRS-3-deficient mice. From these results, we assume that the BRS-3 gene deletion upsets the mechanism by which leptin decreases the expression of MCH-R and that this effect may be mediated through neural networks independent of BN-related peptides such as GRP-R.
Discrimination Between Obesity and Insulin Resistance in the Relationship With Adiponectin
Authors: Abbasi Fahim , Chu James W. , Lamendola Cindy , McLaughlin Tracey , Hayden John , Reaven Gerald M. , Reaven Peter D.
Published: March 2007

Insulin resistance and obesity are both associated with lower plasma adiponectin concentrations. Since insulin resistance and obesity are related, the extent to which the association of adiponectin with insulin resistance is dependent on its relationship with obesity is unclear. To address this issue, fasting plasma adiponectin concentrations were measured in 60 nondiabetic subjects, stratified into four equal groups on the basis of both their degree of adiposity and insulin resistance. Insulin resistance was quantified by determining the steady-state plasma glucose (SSPG) concentration in response to an infusion of octreotide, glucose, and insulin, and degree of adiposity was assessed by BMI. Subjects were defined as obese (BMI ≥30.0 kg/m2) or nonobese (<27.0 kg/m2) and as either insulin sensitive (SSPG <100 mg/dl) or insulin resistant (>190 mg/dl). Insulin-resistant subjects had significantly (P<0.001) lower (mean ± SD) adiponectin concentrations, whether they were obese (17.1 ± 5.9 μg/ml) or nonobese (16.3 ± 7.5 μg/ml) as compared with either obese, insulin-sensitive (34.3 ± 13.1 μg/ml) or nonobese, insulin-sensitive (29.8 ± 15.3 μg/ml) subjects. Finally, adiponectin levels in insulin-sensitive subjects varied to a significantly greater degree than in insulin-resistant subjects. These results suggest that adiponectin concentrations are more closely related to differences in insulin-mediated glucose disposal than obesity.
Ketosis-Prone Type 2 Diabetes in Patients of Sub-Saharan African Origin
Authors: Mauvais-Jarvis Franck , Sobngwi Eugène , Porcher Raphaël , Riveline Jean-Pierre , Kevorkian Jean-Philippe , Vaisse Christian , Charpentier Guillaume , Guillausseau Pierre-Jean , Vexiau Patrick , Gautier Jean-François
Published: March 2007

Nonautoimmune ketosis-prone diabetic syndromes are increasingly frequent in nonwhite populations. We have characterized a cohort of patients of sub-Saharan African origin who had ketosis-prone type 2 diabetes (n = 111), type 1 diabetes (n = 21), and type 2 diabetes (n = 88) and were admitted to a hospital for management of uncontrolled diabetes. We compared epidemiological, clinical, and metabolic features at diabetes onset and measured insulin secretion (glucagon-stimulated C-peptide) and insulin action (short intravenous insulin tolerance test) during a 10-year follow-up. Ketosis-prone type 2 diabetes shows a strong male predominance, stronger family history, higher age and BMI, and more severe metabolic decompensation than type 1 diabetes. In ketosis-prone type 2 diabetes, discontinuation of insulin therapy with development of remission of insulin dependence is achieved in 76% of patients (non–insulin dependent), whereas only 24% of patients remain insulin dependent. During evolution, ketosis-prone type 2 diabetes exhibit specific β-cell dysfunction features that distinguish it from type 1 and type 2 diabetes. The clinical course of non–insulin-dependent ketosis-prone type 2 diabetes is characterized by ketotic relapses followed or not by a new remission. Progressive hyperglycemia precedes and is a strong risk factor for ketotic relapses (hazard ratio 38). The probability for non–insulin-dependent ketosis-prone type 2 diabetes to relapse is 90% within 10 years, of whom ∼50% will become definitively insulin dependent. Insulin sensitivity is decreased in equal proportion in both ketosis-prone type 2 diabetes and type 2 diabetes, but improves significantly in non–insulin-dependent ketosis-prone type 2 diabetes, only after correction of hyperglycemia. In conclusion, ketosis-prone type 2 diabetes can be distinguished from type 1 diabetes and classical type 2 diabetes by specific features of clinical pathophysiology and also by the natural history of β-cell dysfunction and insulin resistance reflecting a propensity to glucose toxicity.
Inflammatory Markers and Risk of Developing Type 2 Diabetes in Women
Authors: Hu Frank B. , Meigs James B. , Li Tricia Y. , Rifai Nader , Manson JoAnn E.
Published: March 2007

We conducted a prospective, nested, case-control study of inflammatory markers as predictors of type 2 diabetes among 32,826 women who provided blood samples in 1989 through 1990 in the Nurses’ Health Study. Among women free of diabetes, cardiovascular disease, or cancer at baseline, 737 had developed diabetes by 2000. Control women (n = 785) were selected matched on age, fasting status, race, and BMI for cases in the top BMI decile. Baseline levels of tumor necrosis factor (TNF)-α receptor 2, interleukin (IL)-6, and C-reactive protein (CRP) were significantly higher among case than control subjects (all P ≤ 0.001). After adjusting for BMI and other lifestyle factors, all three biomarkers significantly predicted diabetes risk; the odds ratios (ORs) comparing extreme quintiles were 1.64 (95% CI 1.10–2.45) for TNF-αR2, 1.91 (1.27–2.86) for IL-6, and 4.36 (2.80–6.80) for CRP (P for trend <0.001 for all biomarkers). In a multivariate model simultaneously including the three biomarkers, only CRP levels were significantly associated with risk of diabetes (OR comparing extreme quintiles of CRP = 3.99, P for trend <0.001). These data support the role of inflammation in the pathogenesis of type 2 diabetes. Elevated CRP levels are a strong independent predictor of type 2 diabetes and may mediate associations of TNF-αR2 and IL-6 with type 2 diabetes.
Effect of Postprandial Hypertriglyceridemia and Hyperglycemia on Circulating Adhesion Molecules and Oxidative Stress Generation and the Possible Role of Simvastatin Treatment
Authors: Ceriello Antoniom , Quagliaro Lisa , Piconi Ludovica , Assaloni Roberta , Da Ros Roberto , Maier Amabile , Esposito Katherine , Giugliano Dario
Published: March 2007

Adhesion molecules, particularly intracellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and E-selectin, have been associated with cardiovascular disease. Elevated levels of these molecules have been reported in diabetic patients. Postprandial hypertriglyceridemia and hyperglycemia are considered risk factors for cardiovascular disease, and evidence suggests that postprandial hypertriglyceridemia and hyperglycemia may induce an increase in circulating adhesion molecules. However, the distinct role of these two factors is a matter of debate. Thirty type 2 diabetic patients and 20 normal subjects ate three different meals: a high-fat meal, 75 g of glucose alone, and a high-fat meal plus glucose. Glycemia, triglyceridemia, plasma nitrotyrosine, ICAM-1, VCAM-1, and E-selectin were assayed during the tests. Subsequently, diabetic subjects took simvastatin 40 mg/day or placebo for 12 weeks. The three tests were performed again at baseline, between 3 and 6 days after starting the study, and at the end of each study. High-fat load and glucose alone produced an increase of nitrotyrosine, ICAM-1, VCAM-1, and E-selectin plasma levels in normal and diabetic subjects. These effects were more pronounced when high fat and glucose were combined. Short-term simvastatin treatment had no effect on lipid parameters, but reduced the effect on adhesion molecules and nitrotyrosine, which was observed during every different test. Long-term simvastatin treatment was accompanied by a lower increase in postprandial triglycerides, which was followed by smaller variations in ICAM-1, VCAM-1, E-selectin, and nitrotyrosine during the tests. This study shows an independent and cumulative effect of postprandial hypertriglyceridemia and hyperglycemia on ICAM-1, VCAM-1, and E-selectin plasma levels, suggesting oxidative stress as a common mediator of such effects. Simvastatin shows a beneficial effect on oxidative stress and the plasma levels of adhesion molecules, which may be ascribed to a direct effect in addition to the lipid-lowering action of the drug.
Uncoupling Proteins Prevent Glucose-Induced Neuronal Oxidative Stress and Programmed Cell Death
Authors: Vincent Andrea M. , Olzmann James A. , Brownlee Michael , Sivitz W.I. , Russell James W.
Published: March 2007

The central role of mitochondria in most pathways leading to programmed cell death (PCD) has focused our investigations into the mechanisms of glucose-induced neuronal degeneration. It has been postulated that hyperglycemic neuronal injury results from mitochondria membrane hyperpolarization and reactive oxygen species formation. The present study not only provides further evidence to support our model of glucose-induced PCD but also demonstrates a potent ability for uncoupling proteins (UCPs) to prevent this process. Dorsal root ganglion (DRG) neurons were screened for UCP expression by Western blotting and immunocytochemistry. The abilities of individual UCPs to prevent hyperglycemic PCD were assessed by adenovirus-mediated overexpression of UCP1 and UCP3. Interestingly, UCP3 is expressed not only in muscle, but also in DRG neurons under control conditions. UCP3 expression is rapidly downregulated by hyperglycemia in diabetic rats and by high glucose in cultured neurons. Overexpression of UCPs prevents glucose-induced transient mitochondrial membrane hyperpolarization, reactive oxygen species formation, and induction of PCD. The loss of UCP3 in DRG neurons may represent a significant contributing factor in glucose-induced injury. Furthermore, the ability to prevent UCP3 downregulation or to reproduce the uncoupling response in DRG neurons constitutes promising novel approaches to avert diabetic complications such as neuropathy.
Divergent Pathways of Gene Expression Are Activated by the RAGE Ligands S100b and AGE-BSA
Authors: Valencia Jessica V. , Mone Manisha , Zhang Jin , Weetall Marla , Buxton Frank P. , Hughes Thomas E.
Published: March 2007

Activation of the receptor for advanced glycation end products (RAGE) reportedly triggers a variety of proinflammatory responses. However, our previous work revealed that RAGE-binding AGEs free of endotoxin were incapable of inducing vascular cell adhesion molecule-1 (VCAM-1) or tumor necrosis factor-α (TNF-α) expression. Thus, the objective of this study was to clarify the role of AGEs in cell activation through gene expression profiling using both in vitro and in vivo model systems. Endothelial cells treated with AGE-BSA, previously shown to bind RAGE with high affinity, did not show gene expression changes indicative of an inflammatory response. In contrast, the alternate RAGE ligand, S100b, triggered an increase in endothelial mRNA expression of a variety of immune-related genes. The effects of AGEs were studied in vivo using healthy mice exposed to two different treatment conditions: 1) intravenous injection of a single dose of model AGEs or 2) four intraperitoneal injections of model AGEs (once per day). In both cases, the liver was extracted for gene expression profiling. Both of the short-term AGE treatments resulted in a moderate increase in liver mRNA levels for genes involved in macrophage-based clearance/detoxification of foreign agents. Our findings using AGEs with strong RAGE-binding properties indicate that AGEs may not uniformly play a role in cellular activation.
Electrically Stimulated Axon Reflexes Are Diminished in Diabetic Small Fiber Neuropathies
Authors: Krämer Heidrun H. , Schmelz Martin , Birklein Frank , Bickel Andreas
Published: March 2007

Axon reflex mediated flare depends on the density and the function of cutaneous C-fibers and may be impaired in diabetic neuropathy. We induced neurogenic axon reflex flare by intracutaneous electrical stimulation and analyzed size and intensity of the flare on the dorsum of the foot and ventral thigh with laser Doppler imaging (LDI). We investigated 12 diabetic subjects with small fiber neuropathies (SFNs), 5 diabetic subjects without neuropathy (NO-Ns), and 14 healthy control subjects. Five of the normal subjects were reassessed after 12 months. In comparing patients with SFN to control subjects, we found that SFN flare size but not the intensity of vasodilation (flux) was reduced on the feet (P < 0.001) and thighs (P < 0.007). Furthermore, electrical thresholds for flare induction were increased (thighs P < 0.001 and feet P < 0.03). In NO-Ns, flare size at the feet (P < 0.02) and flux at both sites (thighs P < 0.001 and feet P < 0.002) were even increased. Test/retest evaluation of our method revealed a good correlation (r = 0.83, P < 0.004). Intracutaneous electrical stimulation of C-fibers and scanning the flare with LDI is a sensitive tool to reliably detect small fiber impairment in diabetic SFN subjects and even increased neuropeptide release in NO-Ns.
A Large Set of Finnish Affected Sibling Pair Families With Type 2 Diabetes Suggests Susceptibility Loci on Chromosomes 6, 11, and 14
Authors: Silander Kaisa , Scott Laura J. , Valle Timo T. , Mohlke Karen L. , Stringham Heather M. , Wiles Kerry R. , Duren William L. , Doheny Kimberly F. , Pugh Elizabeth W. , Chines Peter , Narisu Narisu , White Peggy P. , Fingerlin Tasha E. , Jackson Anne U. , Li Chun , Ghosh Soumitra , Magnuson Victoria L. , Colby Kimberly , Erdos Michael R. , Hill Jason E. , Hollstein Pablo , Humphreys Kathleen M. , Kasad Roshni A. , Lambert Jessica , Lazaridis Konstantinos N. , Lin George , Morales-Mena Anabelle , Patzkowski Kristin , Pfahl Carrie , Porter Rachel , Rha David , Segal Leonid , Suh Yong D. , Tovar Jason , Unni Arun , Welch Christian , Douglas Julie A. , Epstein Michael P. , Hauser Elizabeth R. , Hagopian William , Buchanan Thomas A. , Watanabe Richard M. , Bergman Richard N. , Tuomilehto Jaakko , Collins Francis S. , Boehnke Michael
Published: March 2007

The aim of the Finland-United States Investigation of NIDDM Genetics (FUSION) study is to identify genes that predispose to type 2 diabetes or are responsible for variability in diabetes-related traits via a positional cloning and positional candidate gene approach. In a previously published genome-wide scan of 478 Finnish affected sibling pair (ASP) families (FUSION 1), the strongest linkage results were on chromosomes 20 and 11. We now report a second genome-wide scan using an independent set of 242 Finnish ASP families (FUSION 2), a detailed analysis of the combined set of 737 FUSION 1 + 2 families (495 updated FUSION 1 families), and fine mapping of the regions of chromosomes 11 and 20. The strongest FUSION 2 linkage results were on chromosomes 6 (maximum logarithm of odds score [MLS] = 2.30 at 95 cM) and 14 (MLS = 1.80 at 57 cM). For the combined FUSION 1 + 2 families, three results were particularly notable: chromosome 11 (MLS = 2.98 at 82 cM), chromosome 14 (MLS = 2.74 at 58 cM), and chromosome 6 (MLS = 2.66 at 96 cM). We obtained smaller FUSION 1 + 2 MLSs on chromosomes X (MLS = 1.27 at 152 cM) and 20p (MLS = 1.21 at 20 cM). Among the 10 regions that showed nominally significant evidence for linkage in FUSION 1, four (on chromosomes 6, 11, 14, and X) also showed evidence for linkage in FUSION 2 and stronger evidence for linkage in the combined FUSION 1 + 2 sample.