bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Genes Regulated by the Insulin Sensitizer Rosiglitazone During Adipocyte Differentiation
Authors: Albrektsen Tatjana , Frederiksen Klaus Stensgaard , Holmes William E. , Boel Esper , Taylor Karen , Fleckner Jan
Published: March 2007

Thiazolidinediones (TZDs) are a new class of compounds that improve insulin sensitivity in type 2 diabetic patients as well as in rodent models of this disease. These compounds act as ligands for a member of the nuclear hormone receptor superfamily, peroxisome proliferator–activated receptor-γ (PPAR-γ), which is highly expressed in adipose tissue and, moreover, has been shown to play an important role in adipocyte differentiation. The strong correlation between the antidiabetic activity of TZDs and their ability to activate PPAR-γ suggests that PPAR-γ, through downstream-regulated genes, mediates the effects of TZDs. In this report, we present the isolation and characterization of 81 genes, encoding proteins of known function, differentially expressed during TZD-stimulated differentiation of 3T3-L1 cells. By the use of different reverse– Northern blot techniques, the differential expression of 50 of these genes could be verified, and 21 genes were specifically regulated by a potent TZD during the course of adipocyte differentiation, whereas no effect of a PPAR-γ antagonist could be observed in mature adipocytes. The differential expression of a large fraction of the isolated genes was also shown to occur in white adipose tissue of ob/ob mice treated with rosiglitazone; combined, our results suggest that an important effect of rosiglitazone in adipose tissue is based on activation of PPAR-γ in preexisting preadipocytes found among the mature adipocytes, resulting in subsequent adipocyte differentiation.
Thiazolidinedione Treatment Normalizes Insulin Resistance and Ischemic Injury in the Zucker Fatty Rat Heart
Authors: Sidell Robert J. , Cole Mark A. , Draper Nicholas J. , Desrois Martine , Buckingham Robin E. , Clarke Kieran
Published: March 2007

Obesity is associated with risk factors for cardiovascular disease, including insulin resistance, and can lead to cardiac hypertrophy and congestive heart failure. Here, we used the insulin-sensitizing agent rosiglitazone to investigate the cellular mechanisms linking insulin resistance in the obese Zucker rat heart with increased susceptibility to ischemic injury. Rats were treated for 7 or 14 days with 3 mg/kg per os rosiglitazone. Hearts were isolated and perfused before and during insulin stimulation or during 32 min low-flow ischemia at 0.3 ml · min−1 · grams wet wt−1 and reperfusion. d[2-3H]glucose was used as a tracer of glucose uptake, and phosphorus-31 nuclear magnetic resonance spectroscopy was used to follow energetics during ischemia. At 12 months of age, obese rat hearts were insulin resistant with decreased GLUT4 protein expression. During ischemia, glucose uptake was lower and depletion of ATP was greater in obese rat hearts, thereby significantly impairing recovery of contractile function during reperfusion. Rosiglitazone treatment normalized the insulin resistance and restored GLUT4 protein levels in obese rat hearts. Glucose uptake during ischemia was also normalized by rosiglitazone treatment, thereby preventing the greater loss of ATP and restoring recovery of contractile function to that of lean rat hearts. We conclude that rosiglitazone treatment, by normalizing glucose uptake, protected obese rat hearts from ischemic injury.
Elevated Levels of Acute-Phase Proteins and Plasminogen Activator Inhibitor-1 Predict the Development of Type 2 Diabetes
Authors: Festa Andreas , D’Agostino Ralph , Tracy Russell P. , Haffner Steven M.
Published: March 2007

Elevated serum levels of acute-phase proteins, indicating chronic subclinical inflammation, have been associated with cardiovascular disease as well as the insulin resistance syndrome. Chronic inflammation may also be a risk factor for developing type 2 diabetes. We studied the concentrations of C-reactive protein (CRP), fibrinogen, and plasminogen activator inhibitor-1 (PAI-1) in 1,047 nondiabetic subjects in relation to incident diabetes within 5 years in the Insulin Resistance Atherosclerosis Study. Subjects with diabetes at follow-up (n = 144) had higher baseline levels of fibrinogen (mean ± SD; 287.8 ± 58.8 vs. 275.1 ± 56.0 mg/dl; P = 0.013) as well as of CRP (median [interquartile range]; 2.40 [1.29, 5.87] vs. 1.67 mg/l [0.75, 3.41]; P = 0.0001) and PAI-1 (24 [15, 37.5] vs. 16 ng/ml [9, 27]; P = 0.0001) than nonconverters. The odds ratio (OR) of converting to diabetes was significantly increased with increasing baseline concentrations of the inflammatory markers. In contrast to PAI-1, the association of CRP and fibrinogen with incident diabetes was significantly attenuated after adjustment for body fat (BMI or waist circumference) or insulin sensitivity (SI), as assessed by a frequently sampled intravenous glucose tolerance test. In a logistic regression model that included age, sex, ethnicity, clinical center, smoking, BMI, SI, physical activity, and family history of diabetes, PAI-1 still remained significantly related to incident type 2 diabetes (OR [95% CI] for 1 SD increase: 1.61 [1.20–2.16]; P = 0.002). Chronic inflammation emerges as a new risk factor for the development of type 2 diabetes; PAI-1 predicts type 2 diabetes independent of insulin resistance and other known risk factors for diabetes.
Hepatic Expression of Microsomal Triglyceride Transfer Protein and In Vivo Secretion of Triglyceride-Rich Lipoproteins Are Increased in Obese Diabetic Mice
Authors: Bartels Emil D. , Lauritsen Morten , Nielsen Lars B.
Published: March 2007

Secondary hyperlipidemia is a major cardiovascular risk factor in individuals with type 2 diabetes. Increased hepatic production of apolipoprotein B (apoB)-containing lipoproteins contributes to the elevated plasma levels, but the mechanism is poorly understood. Recent results have established that microsomal triglyceride transfer protein (MTP) is rate limiting for the assembly and secretion of apoB-containing lipoproteins. To better understand the mechanism of type 2 diabetes-associated hyperlipidemia, we quantified hepatic MTP mRNA levels, hepatic microsomal triglyceride transfer activity, and in vivo triglyceride secretion from the liver in two diabetic mouse models. Obese diabetic (ob/ob) mice had 45% higher (P = 0.006) hepatic MTP mRNA levels, 54% higher (P < 0.0001) microsomal triglyceride transfer activity, and 70% higher (P < 0.0001) in vivo triglyceride secretion rates compared with ob/+ control mice. In contrast, in lean streptozotocin-treated diabetic mice, hepatic MTP mRNA levels were unchanged, whereas microsomal triglyceride transfer activity and in vivo triglyceride secretion rates were marginally decreased. These studies suggest that obesity-induced type 2 diabetes in mice confers increases in hepatic MTP expression and secretion of triglyceride-rich lipoproteins. High blood glucose and altered hepatic expression of sterol regulatory element binding protein genes play a minor role in this diabetic response.
Genome-Wide Search for Type 2 Diabetes in Japanese Affected Sib-Pairs Confirms Susceptibility Genes on 3q, 15q, and 20q and Identifies Two New Candidate Loci on 7p and 11p
Authors: Mori Yasumichi , Otabe Shuichi , Dina Christian , Yasuda Kazuki , Populaire Céline , Lecoeur Cécile , Vatin Vincent , Durand Emmanuelle , Hara Kazuo , Okada Terumasa , Tobe Kazuyuki , Boutin Philippe , Kadowaki Takashi , Froguel Philippe
Published: March 2007

The genetic background that predisposes the Japanese population to type 2 diabetes is largely unknown. Therefore, we conducted a 10-cM genome-wide scan for type 2 diabetes traits in the 359 affected individuals from 159 families, yielding 224 affected sib-pairs of Japanese origin. Nonparametric multipoint linkage analyses performed in the whole population showed one suggestive linked region on 11p13-p12 (maximum logarithm of odds score [MLS] 3.08, near Pax6) and seven potentially linked regions (MLS >1.17) at 1p36-p32, 2q34, 3q26-q28, 6p23, 7p22-p21, 15q13-q21, and 20q12-q13 (near the gene for hepatocyte nuclear factor-4α [HNF-4α]). Subset analyses according to maximal BMI and early age at diagnosis added suggestive evidence of linkage with type 2 diabetes at 7p22-p21 (MLS 3.51), 15q13-q21 (MLS 3.91), and 20q12-q13 (MLS 2.32). These results support previous indication for linkage found on chromosome 3q, 15q, and 20q in other populations and identifies two new potential loci on 7p and 11p that may confer genetic risk for type 2 diabetes in the Japanese population.
Association Studies of Genetic Variation in the WFS1 Gene and Type 2 Diabetes in U.K. Populations
Authors: Minton Jayne A.L. , Hattersley Andrew T. , Owen Katharine , McCarthy Mark I. , Walker Mark , Latif Farida , Barrett Timothy , Frayling Timothy M.
Published: March 2007

Mutations in the WFS1 gene cause β-cell death, resulting in a monogenic form of diabetes known as Wolfram syndrome. The role of variation in WFS1 in type 2 diabetes susceptibility is not known. We sequenced the WFS1 gene in 29 type 2 diabetic probands and identified 12 coding variants. We used 152 parent-offspring trios to look for familial association; the R allele at residue 456 (P = 0.04) and the H allele at residue 611 (P = 0.05) as well as the R456-H611 haplotype (P = 0.032) were overtransmitted to affected offspring from heterozygous parents. In a further cohort of 327 type 2 diabetic subjects and 357 normoglycemic control subjects, the H611 allele and the R456-H611 haplotype were present in more type 2 diabetic subjects than control subjects (one-tailed P = 0.06 and P = 0.023, respectively). In a combined analysis, the H611 allele was present in 60% of all diabetes chromosomes and 55% of all control chromosomes (odds ratio [OR] 1.24 [95% CI 1.03–1.48], P = 0.02), and the R456-H611 haplotype was significantly more frequent in type 2 diabetic subjects than in control subjects (60 vs. 54%, OR 1.29 [95% CI 1.08–1.54], P = 0.0053). Our results provide the first evidence that variation in the WFS1 gene may influence susceptibility to type 2 diabetes.
Independent Regulation of In Vivo Insulin Action on Glucose Versus K+ Uptake by Dietary Fat and K+ Content
Authors: Choi Cheol S. , Lee Felix N. , McDonough Alicia A. , Youn Jang H.
Published: March 2007

Insulin stimulates both glucose and K+ uptake, and high-fat feeding is known to decrease insulin-stimulated glucose uptake. The purpose of this study was to examine whether insulin’s actions on glucose and K+ uptake are similarly decreased by a high-fat diet. Wistar rats were fed a standard control (12.2% fat; n = 6) or high-fat (66.5% fat; n = 13) diet for 15 days. Because K+ content was 1% in the control and 0.5% in the high-fat diet and because the rats ate less of the high-fat diet, we also compared the high-fat diet with 0.5% K+ (HFD; n = 7) to a high-fat diet supplemented with 1.5% K+ (HFD+K; n = 6). K+ intake was matched between the control and HFD+K groups (246 ± 8 vs. 224 ± 2 mg/day), but was lower in the HFD group (78 ± 10 mg/day; P < 0.05). Insulin-stimulated glucose and K+ uptake were determined by hyperinsulinemic (5 mU · kg−1 · min−1) glucose and K+ clamps. The HFD depressed both insulin-stimulated glucose uptake compared to the control (133 ± 5 vs. 166 ± 7 μmol · kg−1 · min−1; P < 0.05) and K+ uptake (5.5 ± 0.9 vs. 8.9 ± 1.0 μmol · kg−1 · min−1; P < 0.05) compared to the control. However, insulin-stimulated K+ uptake was unchanged in the HFD+K versus in the control group (10.0 ± 0.6 vs. 8.9 ± 1.0 μmol · kg−1 · min−1; P > 0.05), whereas insulin-stimulated glucose uptake in the HFD+K group was decreased to a rate (137 ± 9 μmol · kg−1 · min−1), similar to that of the HFD group. We concluded that the decrease in insulin-stimulated K+ uptake during high-fat feeding was a result of decreased K+ intake, and that insulin’s actions on glucose uptake and K+ uptake are independently regulated by dietary fat and K+ content, respectively.
Long-Term Treatment With the Dipeptidyl Peptidase IV Inhibitor P32/98 Causes Sustained Improvements in Glucose Tolerance, Insulin Sensitivity, Hyperinsulinemia, and β-Cell Glucose Responsiveness in VDF (fa/fa) Zucker Rats
Authors: Pospisilik J.A. , Stafford S.G. , Demuth H-U. , Brownsey R. , Parkhouse W. , Finegood D.T. , McIntosh C.H.S. , Pederson R.A.
Published: March 2007

The incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are responsible for >50% of nutrient-stimulated insulin secretion. After being released into the circulation, GIP and GLP-1 are rapidly inactivated by the circulating enzyme dipeptidyl peptidase IV (DP IV). The use of DP IV inhibitors to enhance these insulinotropic hormonal axes has proven effective on an acute scale in both animals and humans; however, the long-term effects of these compounds have yet to be determined. Therefore, we carried out the following study: two groups of fa/fa Zucker rats (n = 6 each) were treated twice daily for 3 months with the DP IV inhibitor P32/98 (20 mg · kg−1 · day−1, p.o.). Monthly oral glucose tolerance tests (OGTTs), performed after drug washout, revealed a progressive and sustained improvement in glucose tolerance in the treated animals. After 12 weeks of treatment, peak OGTT blood glucose values in the treated animals averaged 8.5 mmol/l less than in the controls (12.0 ± 0.7 vs. 20.5 ± 1.3 mmol/l, respectively). Concomitant insulin determinations showed an increased early-phase insulin response in the treated group (43% increase). Furthermore, in response to an 8.8 mmol/l glucose perfusion, pancreata from controls showed no increase in insulin secretion, whereas pancreata from treated animals exhibited a 3.2-fold rise in insulin secretion, indicating enhanced β-cell glucose responsiveness. Also, both basal and insulin-stimulated glucose uptake were increased in soleus muscle strips from the treated group (by 20 and 50%, respectively), providing direct evidence for an improvement in peripheral insulin sensitivity. In summary, long-term DP IV inhibitor treatment was shown to cause sustained improvements in glucose tolerance, insulinemia, β-cell glucose responsiveness, and peripheral insulin sensitivity, novel effects that provide further support for the use of DP IV inhibitors in the treatment of diabetes.
Carbon Monoxide Protects Pancreatic β-Cells From Apoptosis and Improves Islet Function/Survival After Transplantation
Authors: Günther Lukas , Berberat Pascal O. , Haga Manabu , Brouard Sophie , Smith R. Neal , Soares Miguel P. , Bach Fritz H. , Tobiasch Edda
Published: March 2007

Pancreatic islets transplanted to treat autoimmune type 1 diabetes often fail to function (primary nonfunction), likely because of islet β-cell apoptosis. We show that carbon monoxide (CO), a product of heme oxygenase activity, protects β-cells from apoptosis. Protection is mediated through guanylate cyclase activation, generation of cyclic GMP (cGMP), and activation of cGMP-dependent protein kinases. This antiapoptotic effect is still observed when β-cells are exposed to CO for 1 h before the apoptotic stimulus. In a similar manner, mouse islets exposed to CO for just 2 h function significantly better after transplantation than islets not exposed to CO. These findings suggest a potential therapeutic application for CO in improving islet function/survival after transplantation in humans.
Prevention of Overt Hypoglycemia During Exercise
Authors: Coker Robert H. , Koyama Yoshiharu , Denny Joshua C. , Camacho Raul C. , Lacy D. Brooks , Wasserman David H.
Published: March 2007

These studies were conducted to determine the magnitude and mechanism of compensation for impaired glucagon and insulin responses to exercise. For this purpose, dogs underwent surgery >16 days before experiments, at which time flow probes were implanted and silastic catheters were inserted. During experiments, glucagon and insulin were fixed at basal levels during rest and exercise using a pancreatic clamp with glucose clamped (PC/GC; n = 5), a pancreatic clamp with glucose unclamped (PC; n = 7), or a pancreatic clamp with glucose unclamped + intraportal propranolol and phentolamine hepatic α- and β-adrenergic receptor blockade (PC/HAB; n = 6). Glucose production (Ra) was measured isotopically. Plasma glucose was constant in PC/GC, but fell from basal to exercise in PC and PC/HAB. Ra was unchanged with exercise in PC/GC, but was slightly increased during exercise in PC and PC/HAB. Despite minimal increases in epinephrine in PC/GC, epinephrine increased approximately sixfold in PC and PC/HAB during exercise. In summary, during moderate exercise, 1) the increase in Ra is absent in PC/GC; 2) only a moderate fall in arterial glucose occurs in PC, due to a compensatory increase in Ra; and 3) the increase in Ra is preserved in PC/HAB. In conclusion, stimulation of Ra by a mechanism independent of pancreatic hormones and hepatic adrenergic stimulation is a primary defense against overt hypoglycemia.
Insulin Expression Levels in the Thymus Modulate Insulin-Specific Autoreactive T-Cell Tolerance
Authors: Chentoufi Aziz Alami , Polychronakos Constantin
Published: March 2007

Type 1 diabetes results from autoimmune destruction of the insulin-producing pancreatic β-cells. Evidence from our laboratory and others has suggested that the IDDM2 locus determines diabetes susceptibility by modulating levels of insulin expression in the thymus: the diabetes-protective class III alleles at a repeat polymorphism upstream of the insulin gene are associated with higher levels than the predisposing class I. To directly demonstrate the effect of thymic insulin expression levels on insulin-specific autoreactive T-cell selection, we have established a mouse model in which there is graded thymic insulin deficiency in linear correlation with insulin gene copy numbers, while pancreatic insulin remains unaltered. We showed that mice expressing low thymic insulin levels present detectable peripheral reactivity to insulin, whereas mice with normal levels show no significant response. We conclude that thymic insulin levels play a pivotal role in insulin-specific T-cell self-tolerance, a relation that provides an explanation for the mechanism by which the IDDM2 locus predisposes to or protects from diabetes.
Insulin Secretory Function Is Impaired in Isolated Human Islets Carrying the Gly972→Arg IRS-1 Polymorphism
Authors: Marchetti Piero , Lupi Roberto , Federici Massimo , Marselli Lorella , Masini Matilde , Boggi Ugo , Del Guerra Silvia , Patanè Giovanni , Piro Salvatore , Anello Marcello , Bergamini Ettore , Purrello Francesco , Lauro Renato , Mosca Franco , Sesti Giorgio , Del Prato Stefano
Published: March 2007

Type 2 (non–insulin-dependent) diabetes results from decreased insulin action in peripheral target tissues (insulin resistance) and impaired pancreatic β-cell function. These defects reflect both genetic components and environmental risk factors. Recently, the common Gly972→Arg amino acid polymorphism of insulin receptor substrate 1 (Arg972 IRS-1) has been associated with human type 2 diabetes. In this study, we report on some functional and morphological properties of isolated human islets carrying the Arg972 IRS-1 polymorphism. Insulin content was lower in variant than control islets (94 ± 47 vs. 133 ± 56 μU/islet; P < 0.05). Stepwise glucose increase (1.7 to 16.7 mmol/l) significantly potentiated insulin secretion from control islets, but not Arg972 IRS-1 islets, with the latter also showing a relatively lower response to glyburide and a significantly higher response to arginine. Proinsulin release mirrored insulin secretion, and the insulin-to-proinsulin ratio in response to arginine was significantly lower from Arg972 IRS-1 islets than from control islets. Glucose utilization and oxidation did not differ in variant and wild-type islets at both low and high glucose levels. Electron microscopy showed that Arg972 IRS-1 β-cells had a severalfold greater number of immature secretory granules and a lower number of mature granules than control β-cells. In conclusion, Arg972 IRS-1 islets have reduced insulin content, impaired insulin secretion, and a lower amount of mature secretory granules. These alterations may account for the increased predisposition to type 2 diabetes in individuals carrying the Gly972→Arg amino acid polymorphism of IRS-1.
Persistent Improvement of Type 2 Diabetes in the Goto-Kakizaki Rat Model by Expansion of the β-Cell Mass During the Prediabetic Period With Glucagon-Like Peptide-1 or Exendin-4
Authors: Tourrel Cécile , Bailbe Danielle , Lacorne Matthieu , Meile Marie-Jo , Kergoat Micheline , Portha Bernard
Published: March 2007

In the Goto-Kakizaki (GK) rat, a genetic model of type 2 diabetes, the neonatal β-cell mass deficit is considered to be the primary defect leading to basal hyperglycemia, which is detectable for the first time 3 weeks after birth. We investigated in GK females the short- and the long-term effects of a treatment with glucagon-like peptide-1 (GLP-1) or its long-acting analog exendin-4 (Ex-4) during the first postnatal week (during the prediabetic period). GK rats were treated with daily injections of glucagon-like peptide-1 (400 μg · kg−1 · day−1) or Ex-4 (3 μg · kg−1 · day−1) from day 2 to day 6 after birth and were evaluated against Wistar and untreated GK rats. Under these conditions, on day 7 both treatments enhanced pancreatic insulin content and total β-cell mass by stimulating β-cell neogenesis and regeneration. Follow-up of biological characteristics from day 7 to adult age (2 months) showed that such a GLP-1 or Ex-4 treatment exerted long-term favorable influences on β-cell mass and glycemic control at adult age. As compared to untreated GK rats, 2-month-old treated rats exhibited significantly decreased basal plasma glucose. Their glucose-stimulated insulin secretion, in vivo after intravenous glucose load or in vitro using isolated perfused pancreas, was slightly improved. This contributed at least partly to improve the in vivo plasma glucose disappearance rate, which was found to be increased in both treated GK groups compared to the untreated GK group. These findings in the GK model indicated, for the first time, that GLP-1 or Ex-4 treatment limited to the prediabetic period delays the installation and limits the severity of type 2 diabetes. Under these conditions, GLP-1 represents a unique tool because of its β-cell replenishing effect in spontaneously diabetic rodents. It may prove to be an invaluable agent for the prevention of human type 2 diabetes.
A Potent and Highly Selective VPAC2 Agonist Enhances Glucose-Induced Insulin Release and Glucose Disposal
Authors: Tsutsumi Manami , Claus Thomas H. , Liang Yin , Li Yaxin , Yang Ling , Zhu Jian , Dela Cruz Fernando , Peng Xianbu , Chen Hongxing , Yung Stephanie L. , Hamren Sarah , Livingston James N. , Pan Clark Q.
Published: March 2007

Pituitary adenylate cyclase—activating peptide (PACAP) and vasoactive intestinal peptide (VIP) activate two shared receptors, VPAC1 and VPAC2. Activation of VPAC1 has been implicated in elevating glucose output, whereas activation of VPAC2 may be involved in insulin secretion. A hypothesis that a VPAC2-selective agonist would enhance glucose disposal by stimulating insulin secretion without causing increased hepatic glucose production was tested using a novel selective agonist of VPAC2. This agonist, BAY 55-9837, was generated through site-directed mutagenesis based on sequence alignments of PACAP, VIP, and related analogs. The peptide bound to VPAC2 with a dissociation constant (Kd) of 0.65 nmol/l and displayed >100-fold selectivity over VPAC1. BAY 55-9837 stimulated glucose-dependent insulin secretion in isolated rat and human pancreatic islets, increased insulin synthesis in purified rat islets, and caused a dose-dependent increase in plasma insulin levels in fasted rats, with a half-maximal stimulatory concentration of 3 pmol/kg. Continuous intravenous or subcutaneous infusion of the peptide reduced the glucose area under the curve following an intraperitoneal glucose tolerance test. The peptide had effects on intestinal water retention and mean arterial blood pressure in rats, but only at much higher doses. BAY 55-9837 may be a useful therapy for the treatment of type 2 diabetes.
Insulin and Rosiglitazone Regulation of Lipolysis and Lipogenesis in Human Adipose Tissue In Vitro
Authors: McTernan Philip G. , Harte Alison L. , Anderson Leah A. , Green Allan , Smith Stephen A. , Holder Julie C. , Barnett Anthony H. , Eggo Margaret C. , Kumar Sudhesh
Published: March 2007

Lipolysis is an important process determining fuel metabolism, and insulin regulates this process in adipose tissue. The aim of this study was to investigate the long-term effects of insulin, an insulin enhancer (rosiglitazone [RSG]), and insulin in combination with RSG on the regulation of lipolysis and lipogenesis in human abdominal subcutaneous fat. Lipolysis and lipogenesis were assessed by protein expression studies of hormone-sensitive lipase (HSL) (84 kDa) and lipoprotein lipase (LPL) (56 kDa), respectively. In addition, lipolytic rate was assessed by glycerol release assay and tumor necrosis factor (TNF)-α release measured by enzyme-linked immunosorbent assay (n = 12). In subcutaneous adipocytes, increasing insulin doses stimulated LPL expression, with maximal stimulation at 100 nmol/l insulin (control, 1.0 ± 0.0 [mean ± SE, protein expression relative to control]; 1 nmol/l insulin, 0.87 ± 0.13; 100 nmol/l insulin, 1.68 ± 0.19; P < 0.001). In contrast, insulin at the 100 nmol/l dose reduced the expression of HSL (100 nmol/l insulin, 0.49 ± 0.05; P < 0.05), while no significant reduction was observed at other doses. Higher doses of insulin stimulated both HSL (1,000 nmol/l insulin, 1.4 ± 0.07; P < 0.01) and LPL (control 1.00 ± 0.0; 1,000 nmol/l insulin, 2.66 ± 0.27; P < 0.01) protein expression. Cotreatment with RSG induced an increased dose response to insulin for LPL and HSL (P < 0.05); RSG alone also increased LPL and HSL expression (P < 0.05). Insulin stimulated TNF-α secretion in a dose-dependent manner (P < 0.01); the addition of RSG (10−8 mol/l) reduced TNF-α secretion (P < 0.05). In summary, chronic treatment of human adipocytes with insulin stimulates lipolysis and LPL protein expression. The addition of RSG reduced the lipolytic rate and TNF-α secretion. The increase in lipolysis is not explained by changes in HSL expression. These data, therefore, may explain in part why hyperinsulinemia coexists with increased circulating nonesterified free fatty acids and increased adiposity in obese and/or type 2 diabetic patients.
Associations of Insulin Levels With Left Ventricular Structure and Function in American Indians
Authors: Ilercil Arzu , Devereux Richard B. , Roman Mary J. , Paranicas Mary , O’Grady Michael J. , Lee Elisa T. , Welty Thomas K. , Fabsitz Richard R. , Howard Barbara V.
Published: March 2007

We evaluated the association of insulin and echocardiographic left ventricular (LV) measurements in 1,388 (45% men) nondiabetic American Indian participants in the Strong Heart Study (SHS). Significant (all P < 0.05) relations were found in men and women between log10 fasting insulin and LV mass (r = 0.24 and 0.26), left atrial diameter (r = 0.25 and 0.28), posterior wall thickness (r = 0.20 and 0.26), septal thickness (r = 0.19 and 0.24), LV diameter (r = 0.17 and 0.16), and cardiac output (r = 0.20 and 0.24) and in women relative wall thickness (r = 0.11) and peripheral resistance (r = −0.17). In regression analyses, adjusting for BMI, age, height, and systolic pressure, fasting insulin was independently correlated with cardiac output in men and relative wall thickness and septal thickness in women (all P < 0.05). The 97th percentiles of fasting insulin (25 μU/ml for men, and 23 μU/ml for women) in 163 apparently normal (BMI <26; blood pressure <140/90; and absence of diabetes, valvular disease, LV wall motion abnormality, or antihypertensive treatment) SHS participants were used to separate normal from elevated fasting insulin levels. Adjusting for age, BMI, and height, men with elevated insulin levels had larger LV diameters (5.41 vs. 5.16 cm; P = 0.05), higher cardiac output (5.5 vs. 4.9 l/min; P < 0.001), and lower peripheral resistance (1,487 vs. 1,666; P = 0.01), paralleling results of regression analyses. Positive relations between insulin and heart size in nondiabetic adults are largely due to associations with body size; after adjustments for covariates, fasting insulin levels are related to greater LV size and cardiac output in men and more concentric LV geometry in women.
Downregulation of Connexin 43 Expression by High Glucose Reduces Gap Junction Activity in Microvascular Endothelial Cells
Authors: Sato Tsuyoshi , Haimovici Robert , Kao Richard , Li An-Fei , Roy Sayon
Published: March 2007

Impairment of retinal vascular homeostasis is associated with the development and progression of diabetic retinopathy involving gap junction intercellular communication (GJIC) activity. The principal gap junction protein of intercellular communication, connexin, was investigated to determine the effects of high glucose concentrations on the expression of endothelial-specific connexins (Cx37, Cx40, and Cx43), connexin phosphorylation pattern, and GJIC activity. Rat microvascular endothelial (RME) cells grown in high (30 mmol/l)-glucose medium for 9 days had reduced Cx43 expression: Cx43 mRNA (68 ± 13% of control; P = 0.019, n = 5) and protein (55.6 ± 16% of control; P = 0.003, n = 5) levels were reduced; however, Cx37 and Cx40 expression was not affected. Using alkaline phosphatase and Western blot analyses, we identified three forms of Cx43: a nonphosphorylated form (P0) and two phosphorylated forms (P1 and P2). Expression of all three forms was decreased in cells grown in high-glucose medium: PO, 73 ± 15% of control (P = 0.04); P1, 57 ± 16% of control (P = 0.01); and P2, 42 ± 22% of control (P = 0.006). Using immunofluorescence microscopy, we observed Cx43 localization at specific sites of contact (plaques) between adjacent cells. In cells grown in high-glucose medium, we observed reduced plaque counts (63 ± 6% of control; P = 0.009) and decreased intensity of Cx43 immunofluorescence compared with cells grown in normal medium. Furthermore, using scrape load dye transfer (SLDT) technique, we found that these cells exhibited reduced GJIC activity (60% of control; P = 0.01, n = 5). The reduction in GJIC activity correlated with the decreased Cx43 protein levels (r = 0.9). These results indicate that high glucose concentrations inhibited GJIC activity by reducing Cx43 synthesis in RME cells. Impaired intercellular communication may contribute to breakdown of homeostatic balance in diabetic microangiopathy.
C-Reactive Protein Is an Independent Predictor of Risk for the Development of Diabetes in the West of Scotland Coronary Prevention Study
Authors: Freeman Dilys J. , Norrie John , Caslake Muriel J. , Gaw Allan , Ford Ian , Lowe Gordon D.O. , O’Reilly Denis St. J. , Packard Chris J. , Sattar Naveed ,   for the West of Scotland Coronary Prevention Study Group
Published: March 2007

Accumulating evidence implicates inflammation as a potential pathway in the pathogenesis of type 2 diabetes. The objective of the present study was to assess the ability of C-reactive protein (CRP) to predict the development of diabetes in middle-aged men in the West of Scotland Coronary Prevention Study. Baseline plasma samples for CRP measurement were available for 5,245 men of whom 127 were classified as having a transition from normal glucose control to overt diabetes during the study, based on American Diabetes Association criteria. Baseline CRP was an important predictor of the development of diabetes in univariate analysis (hazard ratio [HR] for an increase of 1 SD = 1.55; 95% CI 1.32–1.82; P < 0.0001). In multivariate analysis, CRP remained a predictor of diabetes development (HR 1.30; 95% CI 1.07–1.58; P = 0.0075) independent of other clinically employed predictors, including baseline BMI and fasting triglyceride and glucose concentrations. Moreover, there was a graded increase in risk across CRP quintiles throughout the study, evident at even 1 year of follow-up. The highest quintile (CRP >4.18 mg/l) was associated with a greater than threefold risk of developing diabetes (HR 3.07; 95% CI 1.33–7.10) in a multivariate analysis at 5 years. Thus, CRP predicts the development of type 2 diabetes in middle-aged men independently of established risk factors. Because CRP, the most commonly used acute-phase protein in clinical practice, is very stable in serum, our observations have clinical potential in helping to better predict individuals destined to develop type 2 diabetes. They also add to the notion that low-grade inflammation is important in the pathogenesis of type 2 diabetes.
Direct and Indirect Effects of Insulin on Glucose Uptake and Storage by the Liver
Authors: Satake Shosuke , Moore Mary Courtney , Igawa Kayano , Converse Margaret , Farmer Benjamin , Neal Doss W. , Cherrington Alan D.
Published: March 2007

Studies were conducted in conscious 42-h–fasted dogs to determine how much of insulin’s effect on hepatic glucose uptake arises from its direct hepatic action versus its indirect (extrahepatic) action. Each experiment consisted of equilibration, basal, and experimental periods. During the latter, somatostatin, basal intraportal glucagon, portal glucose (21.3 μmol · kg−1 · min−1), and peripheral glucose (to double the hepatic glucose load) were infused. During the experimental period, insulin was infused intraportally at a basal rate (BI, n = 6), at a fourfold basal rate (PoI, n = 6), or via a peripheral vein to create a selective increase in the arterial insulin level similar to that in PoI (PeI, n = 6). Arterial and hepatic sinusoidal insulin levels (in picomoles per liter) during the experimental period were 31 ± 5 and 113 ± 15 in BI, 97 ± 11 and 394 ± 66 in PoI, and 111 ± 13 and 96 ± 9 in PeI, respectively. Net hepatic glucose uptake (NHGU) averaged 7.0 ± 1.1 μmol · kg−1 · min−1, 15.7 ± 2.7 μmol · kg−1 · min−1 (P < 0.05 vs. BI), and 12.0 ± 2.4 μmol · kg−1 · min−1 (P < 0.05 vs. BI) in BI, PoI, and PeI, respectively. Net hepatic carbon retention was 4.4 ± 1.2 μmol glucose equivalents · kg−1 · min−1, 12.3 ± 2.5 μmol glucose equivalents · kg−1 · min−1 (P < 0.05 vs. BI, P < 0.05 vs. PeI), and 7.1 ± 1.0 μmol glucose equivalents · kg−1 · min−1 (P < 0.05 vs. BI) in BI, PoI, and PeI, respectively. Both direct and indirect insulin actions increase NHGU, but the rise in hepatic sinusoidal insulin appears critical for efficient storage of glucose as hepatic glycogen.
Role of the Insulin Receptor Substrate 1 and Phosphatidylinositol 3-Kinase Signaling Pathway in Insulin-Induced Expression of Sterol Regulatory Element Binding Protein 1c and Glucokinase Genes in Rat Hepatocytes
Authors: Matsumoto Michihiro , Ogawa Wataru , Teshigawara Kiyoshi , Inoue Hiroshi , Miyake Kazuaki , Sakaue Hiroshi , Kasuga Masato
Published: March 2007

The mechanism by which insulin induces the expression of the sterol regulatory element binding protein 1c (SREBP-1c) and glucokinase genes was investigated in cultured rat hepatocytes. Overexpression of an NH2-terminal fragment of IRS-1 that contains the pleckstrin homology and phosphotyrosine binding domains (insulin receptor substrate-1 NH2-terminal fragment [IRS-1N]) inhibited insulin-induced tyrosine phosphorylation of IRS-1 as well as the association of IRS-1 with phosphatidylinositol (PI) 3-kinase activity, whereas the tyrosine phosphorylation of IRS-2 and its association with PI 3-kinase activity were slightly enhanced. The equivalent fragment of IRS-2 (IRS-2N) prevented insulin-induced tyrosine phosphorylation of both IRS-1 and IRS-2, although that of IRS-1 was inhibited more efficiently. The insulin-induced increases in the abundance of SREBP-1c and glucokinase mRNAs, both of which were sensitive to a dominant-negative mutant of PI 3-kinase, were blocked in cells in which the insulin-induced tyrosine phosphorylation of IRS-1 was inhibited by IRS-1N or IRS-2N. A dominant-negative mutant of Akt enhanced insulin-induced tyrosine phosphorylation of IRS-1 (but not that of IRS-2) and its association with PI 3-kinase activity, suggesting that Akt contributes to negative feedback regulation of IRS-1. The Akt mutant also promoted the effects of insulin on the accumulation of SREBP-1c and glucokinase mRNAs. These results suggest that the IRS-1–PI 3-kinase pathway is essential for insulin-induced expression of SREBP-1c and glucokinase genes.
Humoral Regulation of Resistin Expression in 3T3-L1 and Mouse Adipose Cells
Authors: Shojima Nobuhiro , Sakoda Hideyuki , Ogihara Takehide , Fujishiro Midori , Katagiri Hideki , Anai Motonobu , Onishi Yukiko , Ono Hiraku , Inukai Kouichi , Abe Miho , Fukushima Yasushi , Kikuchi Masatoshi , Oka Yoshitomo , Asano Tomoichiro
Published: March 2007

Resistin is a hormone secreted by adipocytes that acts on skeletal muscle myocytes, hepatocytes, and adipocytes themselves, reducing their sensitivity to insulin. In the present study, we investigated how the expression of resistin is affected by glucose and by mediators known to affect insulin sensitivity, including insulin, dexamethasone, tumor necrosis factor-α (TNF-α), epinephrine, and somatropin. We found that resistin expression in 3T3-L1 adipocytes was significantly upregulated by high glucose concentrations and was suppressed by insulin. Dexamethasone increased expression of both resistin mRNA and protein 2.5- to 3.5-fold in 3T3-L1 adipocytes and by ∼70% in white adipose tissue from mice. In contrast, treatment with troglitazone, a thiazolidinedione antihyperglycemic agent, or TNF-α suppressed resistin expression by ∼80%. Epinephrine and somatropin were both moderately inhibitory, reducing expression of both the transcript and the protein by 30–50% in 3T3-L1 adipocytes. Taken together, these data make it clear that resistin expression is regulated by a variety of hormones and that cytokines are related to glucose metabolism. Furthermore, they suggest that these factors affect insulin sensitivity and fat tissue mass in part by altering the expression and eventual secretion of resistin from adipose cells.
A 12-Year Prospective Study of the Relationship Between Islet Antibodies and β-Cell Function At and After the Diagnosis in Patients With Adult-Onset Diabetes
Authors: Borg Henrik , Gottsäter Anders , Fernlund Per , Sundkvist Göran
Published: March 2007

To clarify the relationships between islet antibodies (islet cell antibody [ICA], GAD antibody [GADA], and IA-2 antibody [IA-2A]) versus the progression of β-cell dysfunction, we have followed a group of diabetic patients from their diagnosis at 21–73 years of age. Patients with ICA had high levels of GADA and/or IA-2A at diagnosis and a more severe β-cell dysfunction 5 years after diagnosis than those with only GADA in low concentrations. The aim of the current 12-year follow-up study was to examine the further progression of β-cell dysfunction in relation to islet antibodies at and after diagnosis. Among 107 patients, complete β-cell failure 12 years after diagnosis was restricted to those with islet antibodies at diagnosis (16 of 21 [77%] with multiple antibodies and 4 of 5 [80%] with only GADA). In contrast, among antibody-negative patients, fasting P-C-peptide levels were unchanged. Most GADA-positive patients (22 of 27 [81%]) remained GADA positive after 12 years. Associated with decreasing fasting P-C-peptide levels (0.85 nmol/l [0.84] at diagnosis vs. 0.51 nmol/l [0.21] 12 years after diagnosis, P < 0.05), ICA developed after diagnosis in 6 of 105 originally antibody negative mostly overweight patients. In conclusion, multiple islet antibodies or GADA alone at diagnosis of diabetes predict future complete β-cell failure. After diagnosis, GADA persisted in most patients, whereas ICA development in patients who were antibody negative at diagnosis indicated decreasing β-cell function.
Inhibition of Interleukin-1β-Induced COX-2 and EP3 Gene Expression by Sodium Salicylate Enhances Pancreatic Islet β-Cell Function
Authors: Tran Phuong Oanh T. , Gleason Catherine E. , Robertson R. Paul
Published: March 2007

Previous work has suggested that functional interrelationships may exist between inhibition of insulin secretion by interleukin (IL)-1β and the endogenous synthesis of prostaglandin E2 (PGE2) in the pancreatic islet. These studies were performed to ascertain the relative abundance of E prostaglandin (EP) receptor mRNAs in tissues that are major targets, or major degradative sites, of insulin; to identify which EP receptor type mediates PGE2 inhibition of insulin secretion in pancreatic islets; and to examine possible sites of action through which sodium salicylate might affect IL-1β/PGE2 interactions. Real-time fluorescence-based RT-PCR indicated that EP3 is the most abundant EP receptor type in islets, liver, kidney, and epididymal fat. EP3 mRNA is the least, whereas EP2 mRNA is the most, abundant type in skeletal muscle. Misoprostol, an EP3 agonist, inhibited glucose-induced insulin secretion from islets, an event that was prevented by preincubation with pertussis toxin, by decreasing cAMP. Electromobility shift assays demonstrated that sodium salicylate inhibits IL-1β-induced nuclear factor-κB (NF-κB) activation. Sodium salicylate also prevented IL-1β from inducing EP3 and cyclooxygenase (COX)-2 gene expression in islets and thereby prevented IL-1β from inhibiting glucose-induced insulin secretion. These findings indicate that the sites of action through which sodium salicylate inhibits these negative effects of IL-1β on β-cell function include activation of NF-κB as well as generation of PGE2 by COX-2.
β-Cell Neogenesis During Prolonged Hyperglycemia in Rats
Authors: Lipsett Mark , Finegood Diane T.
Published: March 2007

β-cell neogenesis from ductal precursors, and possibly from other pancreatic cell types, contributes to the expansion of β-cell mass during development and after diabetogenic insults in rodents. Using a mathematical model−based analysis of β-cell mass, replication, and size, we recently demonstrated that neogenesis is also quantitatively important to the expansion of β-cell mass during prolonged hyperglycemia. In the present study, we examined the morphological appearance of neogenic focal areas, duct cell replication, and β-cell cluster size distribution in male Sprague Dawley rats infused with either saline or 50% glucose (2 ml/h) for 0, 1, 2, 3, 4, 5, or 6 days. Pancreatic tissue characterized by a high density of small duct-like structures, previously described as neogenic focal areas, were present in glucose-infused rats after 2, 3, or 4 days of infusion. The cross-sectional area of the pancreas characterized as focal tissue peaked after 3 days of infusion at 2.9 ± 0.8%. In contrast to the partial pancreatectomy model of β-cell regeneration, duct cell replication was not increased before or during focal area formation. However, the replication rate of cells in the duct-like structures of the focal areas was twofold greater than in cells of the common pancreatic duct and 15- to 40-fold greater than in cells of small, medium, and large ducts. Duct-cell replication was significantly reduced in small, medium, and large ducts of glucose as compared to saline-infused rats (0.21 ± 0.02 vs. 0.48 ± 0.04%; P < 0.03). Duct-associated β-cell mass was not different in glucose- and saline-infused rats (P = 0.78), whereas the number of acinar-associated single β -cells increased by 70% after 3 and 4 days of glucose infusion. In addition to small duct-like structures, focal areas had considerable T-cell infiltration (151 ± 30 T-cells/ mm2). There was also an increase in T-cell infiltration in acinar tissue of glucose as compared to saline-infused rats (0.43 ± 0.11 vs. 0.03 ± 0. 01 T-cells/mm2; P < 0.0001). In conclusion, these data suggest that neogenic focal areas in these glucose-infused rats do not arise from replication and differentiation of ductal progenitor cells. Rather, acinar cell transdifferentiation into β-cells and acinar cell dedifferentiation into neogenic focal areas lead to new β-cell formation during prolonged hyperglycemia.
Plasma Adiponectin Concentration Is Associated With Skeletal Muscle Insulin Receptor Tyrosine Phosphorylation, and Low Plasma Concentration Precedes a Decrease in Whole-Body Insulin Sensitivity in Humans
Authors: Stefan Norbert , Vozarova Barbora , Funahashi Tohru , Matsuzawa Yuji , Weyer Christian , Lindsay Robert S. , Youngren Jack F. , Havel Peter J. , Pratley Richard E. , Bogardus Clifton , Tataranni P. Antonio
Published: March 2007

Adiponectin, the most abundant adipose-specific protein, has been found to be negatively associated with degree of adiposity and positively associated with insulin sensitivity in Pima Indians and other populations. Moreover, adiponectin administration to rodents has been shown to increase insulin-induced tyrosine phosphorylation of the insulin receptor (IR) and also increase whole-body insulin sensitivity. To further characterize the relationship between plasma adiponectin concentration and insulin sensitivity in humans, we examined 1) the cross-sectional association between plasma adiponectin concentration and skeletal muscle IR tyrosine phosphorylation and 2) the prospective effect of plasma adiponectin concentration at baseline on change in insulin sensitivity. Fasting plasma adiponectin concentration, body composition (hydrodensitometry or dual energy X-ray absorptiometry), insulin sensitivity (insulin-stimulated glucose disposal, hyperinsulinemic clamp), and glucose tolerance (75-g oral glucose tolerance test) were measured in 55 Pima Indians (47 men and 8 women, aged 31 ± 8 years, body fat 29 ± 8% [mean ± SD]; 50 with normal glucose tolerance, 3 with impaired glucose tolerance, and 2 with diabetes). Group 1 (19 subjects) underwent skeletal muscle biopsies for the measurement of basal and insulin-stimulated tyrosine phosphorylation of the IR (stimulated by 100 nmol/l insulin). The fold increase after insulin stimulation was calculated as the ratio between maximal and basal phosphorylation. Group 2 (38 subjects) had follow-up measurements of insulin-stimulated glucose disposal. Cross-sectionally, plasma adiponectin concentration was positively associated with insulin-stimulated glucose disposal (r = 0.58, P < 0.0001) and negatively associated with percent body fat (r = −0.62, P < 0.0001) in the whole group. In group 1 plasma adiponectin was negatively associated with the basal (r = −0.65, P = 0.003) and positively associated with the fold increase in IR tyrosine phosphorylation (r = 0.69, P = 0.001) before and after the adjustment for percent body fat (r = −0.58, P = 0.01 and r = 0.54, P = 0.02, respectively). Longitudinally, after adjustment for age, sex, and percent body fat, low plasma adiponectin concentration at baseline was associated with a decrease in insulin sensitivity (P = 0.04). In conclusion, our cross-sectional data suggest a role of physiological concentration of fasting plasma adiponectin in the regulation of skeletal muscle IR tyrosine phosphorylation. Prospectively, low plasma adiponectin concentration at baseline precedes a decrease in insulin sensitivity. Our data indicate that adiponectin plays an important role in regulation of insulin sensitivity in humans.