bluuebunny/crossref_metadata_2025 huggingface dataset:
Insulin, C-Peptide, and Leptin Concentrations Predict Increased Visceral Adiposity at 5- and 10-Year Follow-Ups in Nondiabetic Japanese Americans
Authors: Tong Jenny , Fujimoto Wilfred Y. , Kahn Steven E. , Weigle David S. , McNeely Marguerite J. , Leonetti Donna L. , Shofer Jane B. , Boyko Edward J.
Published: March 2007

We prospectively examined the relationship between leptin and markers of insulin resistance and secretion and future visceral adipose tissue accumulation. In this study, 518 nondiabetic Japanese-American men and women underwent the following measurements at baseline and at 5- and 10-year follow-ups: plasma glucose and insulin measured after an overnight fast and during a 75-g oral glucose tolerance test, insulin secretion ratio (ISR) [(30-min insulin − fasting insulin)/30-min glucose], fasting C-peptide levels, plasma leptin (baseline only), and fat areas (intra-abdominal and subcutaneous) measured by computed tomography. Predictors of future intra-abdominal fat (IAF) were determined using multiple linear regression. Fasting insulin and C-peptide levels at baseline were significantly associated with IAF area at 5 years (coefficient = 0.041, P = 0.001 and coefficient = 1.283, P < 0.001, respectively) and 10 years (coefficient = 0.031, P = 0.020 and coefficient = 0.221, P = 0.035, respectively). ISR was not significantly associated with IAF at 5 or 10 years. Leptin level at baseline was positively associated with IAF at 5 years (coefficient = 0.055, P = 0.002) and 10 years (coefficient = 0.059, P = 0.003). In conclusion, higher levels of fasting insulin, C-peptide, and circulating leptin level predicted visceral fat accumulation independent from subcutaneous fat accumulation in nondiabetic Japanese-American men and women in both short-term (5 years) and long-term (10 years) follow-up.
Deletion of the Angiotensin Type 2 Receptor (AT2R) Reduces Adipose Cell Size and Protects From Diet-Induced Obesity and Insulin Resistance
Authors: Yvan-Charvet Laurent , Even Patrick , Bloch-Faure May , Guerre-Millo Michèle , Moustaid-Moussa Naima , Ferre Pascal , Quignard-Boulange Annie
Published: March 2007

The renin-angiotensin system with its active metabolite angiotensin (Ang) II has been related not only to hypertension but also to obesity and insulin resistance. Recent evidence obtained in vitro suggests that the type 2 Ang II receptor (AT2R) mediates the trophic action of Ang II on adipocyte differentiation and lipogenesis. We used AT2Ry/− mice to delineate a potential role of AT2R in adipose tissue development and metabolism. AT2Ry/− mice had a normal adiposity but displayed a striking adipose tissue phenotype characterized by small adipocytes and an increase in cell number. In muscle, the expression of several genes involved in lipid metabolism, including fatty acid translocase, uncoupling protein-3, peroxisome proliferator–activated receptors (α, δ), and carnitine palmitoyl transferase-1, was increased in AT2R-deficient mice. In response to high-fat feeding, these mice were protected against obesity and obesity-related glucose intolerance, as assessed by glucose tolerance tests. Moreover, lipid oxidation assessed by indirect calorimetry was higher in AT2R-deficient mice than in wild-type mice, irrespective of the diet. This suggests that AT2R-dependent signaling exerts a direct or indirect negative control on lipid utilization in muscles. These data support the idea that AT2R-dependent Ang II signaling increases adipose cell mass and glucose intolerance and thus could participate to the deleterious effects of a high-fat diet.
Sphingosine Kinase Activity and Sphingosine-1 Phosphate Production in Rat Pancreatic Islets and INS-1 Cells
Authors: Mastrandrea Lucy D. , Sessanna Shawn M. , Laychock Suzanne G.
Published: March 2007

Sphingosine-1 phosphate (S1P) is a bioactive sphingolipid with the potential to mobilize Ca2+, to inhibit apoptosis, and to promote mitogenesis. Sphingosine kinase (SPHK) and S1P were characterized in INS-1 insulinoma cells and isolated rat islets of Langerhans. SPHK activity increased in INS-1 cell homogenates treated with interleukin-1β (IL-1β) or tumor necrosis factor-α (TNF-α), and responses were additive. IL-1β or TNF-α increased islet SPHK activity within 15 min to 1 h; activity remained elevated after 8 h. SPHK2 was the predominant active isoform in INS-1 cells; little or no SPHK1 activity was detected. Cytokines increased endogenous S1P biosynthesis in 32Pi-prelabeled INS-1 cells, and cycloheximide inhibited the response after 8 h, suggesting that protein synthesis mediated the response. There was no [32P]S1P release from cells. Compared with basal values, IL-1β and TNF-α induced increases in SPHK1a mRNA levels relative to 18S ribosomal RNA in INS-1 cells within 1 h; relative SPHK2 mRNA levels were unchanged after cytokine treatment. IL-1β, but not TNF-α, induced relative SPHK1a mRNA expression levels within 1 h in islets, whereas SPHK2 mRNA levels were unchanged. Thus, IL-1β and TNF-α induced an early and sustained increase in SPHK activity in INS-1 cells and isolated islets, suggesting that S1P plays a role in the pathological response of pancreatic β-cells to cytokines.
MnSOD and Catalase Transgenes Demonstrate That Protection of Islets From Oxidative Stress Does Not Alter Cytokine Toxicity
Authors: Chen Hainan , Li Xiaoyan , Epstein Paul N.
Published: March 2007

Reactive oxygen species (ROS) and nitric oxide (NO) are proposed mediators of cytokine-induced β-cell destruction in type 1 diabetes. We produced transgenic mice with increased β-cell expression of manganese superoxide dismutase (MnSOD) and catalase. Expression of these antioxidants increased β-cell ROS scavenging and improved β-cell survival after treatment with different sources of ROS. MnSOD or catalase conferred protection against streptozotocin (STZ)-induced β-cell injury. Coexpression of MnSOD and catalase provided synergistic protection against peroxynitrite and STZ. To determine the potential effect of these antioxidants on cytokine-induced toxicity, we exposed isolated islets to a cytokine mixture, including interleukin-1β and interferon-γ. Cytokine toxicity was measured as reduced metabolic activity after 6 days and reduced insulin secretion after 1 day. Cytokines increased ROS production, and both antioxidants were effective in reducing cytokine-induced ROS. However, MnSOD and/or catalase provided no protection against cytokine-induced injury. To understand this, the nuclear factor-κB (NF-κB) signaling cascade was investigated. Antioxidants reduced NF-κB activation by ROS, but none of the antioxidants altered activation by cytokines, as measured by inhibitor of κB phosphorylation, NF-κB translocation, inducible NO synthase activation, and NO production. Our data agree with previous reports that antioxidants benefit β-cell survival against ROS damage, but they are not consistent with reports that antioxidants reduce cytokine toxicity. ROS appear to have no role in cytokine toxicity in primary β-cells.
Mannose-Binding Lectin as a Predictor of Microalbuminuria in Type 1 Diabetes
Authors: Hovind Peter , Hansen Troels Krarup , Tarnow Lise , Thiel Steffen , Steffensen Rudi , Flyvbjerg Allan , Parving Hans-Henrik
Published: March 2007

Inflammation and complement activation via the mannose-binding lectin (MBL) pathway have been suggested to play a role in the pathogenesis of diabetic microvascular complications. The association between the complement-activating protein MBL and the development of persistent microalbuminuria was evaluated in an inception cohort of 286 newly diagnosed type 1 diabetic patients consecutively admitted to the Steno Diabetes Center between 1 September 1979 and 31 August 1984. Serum MBL was measured with an immunofluorometric assay in 270 of the patients (159 men) after 3 years of diabetes duration. During the median (range) follow-up period of 18.0 (1.0–21.8) years, 75 patients subsequently progressed to persistent micro- or macroalbuminuria (urinary albumin excretion rate >30 mg/24 h). In patients with MBL levels above the median (1,597 μg/l), the cumulative incidence of persistent micro- or macroalbuminuria was 41% (CI 31–50) as compared with 26% (CI 17–34) in patients with MBL levels below the median (log-rank test, P = 0.003). In a Cox proportional hazard model with sex and age as fixed covariates, MBL was independently associated with later development of persistent micro- or macroalbuminuria (hazard ratio 1.21 [CI 1.02–1.42] per 1,000 μg/l increase in MBL; P = 0.03) after adjusting for possible confounders. In our study, high levels of MBL early in the course of type 1 diabetes was significantly associated with later development of persistent micro- or macroalbuminuria, suggesting that complement activation initiated by MBL may be involved in the pathogenesis of diabetic microvascular complications.
Minocycline Reduces Proinflammatory Cytokine Expression, Microglial Activation, and Caspase-3 Activation in a Rodent Model of Diabetic Retinopathy
Authors: Krady J. Kyle , Basu Anirban , Allen Colleen M. , Xu Yuping , LaNoue Kathryn F. , Gardner Thomas W. , Levison Steven W.
Published: March 2007

Diabetes leads to vascular leakage, glial dysfunction, and neuronal apoptosis within the retina. The goal of the studies reported here was to determine the role that retinal microglial cells play in diabetic retinopathy and assess whether minocycline can decrease microglial activation and alleviate retinal complications. Immunohistochemical analyses showed that retinal microglia are activated early in diabetes. Furthermore, mRNAs for interleukin-1β and tumor necrosis factor-α, proinflammatory mediators known to be released from microglia, are also increased in the retina early in the course of diabetes. Using an in vitro bioassay, we demonstrated that cytokine-activated microglia release cytotoxins that kill retinal neurons. Furthermore, we showed that neuronal apoptosis is increased in the diabetic retina, as measured by caspase-3 activity. Minocycline represses diabetes-induced inflammatory cytokine production, reduces the release of cytotoxins from activated microglia, and significantly reduces measurable caspase-3 activity within the retina. These results indicate that inhibiting microglial activity may be an important strategy in the treatment of diabetic retinopathy and that drugs such as minocycline hold promise in delaying or preventing the loss of vision associated with this disease.
From the Periphery of the Glomerular Capillary Wall Toward the Center of Disease
Authors: Wolf Gunter , Chen Sheldon , Ziyadeh Fuad N.
Published: March 2007

Nephropathy is a major complication of diabetes. Alterations of mesangial cells have traditionally been the focus of research in deciphering molecular mechanisms of diabetic nephropathy. Injury of podocytes, if recognized at all, has been considered a late consequence caused by increasing proteinuria rather than an event inciting diabetic nephropathy. However, recent biopsy studies in humans have provided evidence that podocytes are functionally and structurally injured very early in the natural history of diabetic nephropathy. The diabetic milieu, represented by hyperglycemia, nonenzymatically glycated proteins, and mechanical stress associated with hypertension, causes downregulation of nephrin, an important protein of the slit diaphragm with antiapoptotic signaling properties. The loss of nephrin leads to foot process effacement of podocytes and increased proteinuria. A key mediator of nephrin suppression is angiotensin II (ANG II), which can activate other cytokine pathways such as transforming growth factor-β (TGF-β) and vascular endothelial growth factor (VEGF) systems. TGF-β1 causes an increase in mesangial matrix deposition and glomerular basement membrane (GBM) thickening and may promote podocyte apoptosis or detachment. As a result, the denuded GBM adheres to Bowman’s capsule, initiating the development of glomerulosclerosis. VEGF is both produced by and acts upon the podocyte in an autocrine manner to modulate podocyte function, including the synthesis of GBM components. Through its effects on podocyte biology, glomerular hemodynamics, and capillary endothelial permeability, VEGF likely plays an important role in diabetic albuminuria. The mainstays of therapy, glycemic control and inhibition of ANG II, are key measures to prevent early podocyte injury and the subsequent development of diabetic nephropathy.
Dose-Response Effect of Elevated Plasma Free Fatty Acid on Insulin Signaling
Authors: Belfort Renata , Mandarino Lawrence , Kashyap Sangeeta , Wirfel Kelly , Pratipanawatr Thongchai , Berria Rachele , DeFronzo Ralph A. , Cusi Kenneth
Published: March 2007

The dose-response relationship between elevated plasma free fatty acid (FFA) levels and impaired insulin-mediated glucose disposal and insulin signaling was examined in 21 lean, healthy, normal glucose-tolerant subjects. Following a 4-h saline or Liposyn infusion at 30 (n = 9), 60 (n = 6), and 90 (n = 6) ml/h, subjects received a 2-h euglycemic insulin (40 mU · m−2 · min−1) clamp. Basal plasma FFA concentration (∼440 μmol/l) was increased to 695, 1,251, and 1,688 μmol/l after 4 h of Liposyn infusion and resulted in a dose-dependent reduction in insulin-stimulated glucose disposal (Rd) by 22, 30, and 34%, respectively (all P < 0.05 vs. saline control). At the lowest lipid infusion rate (30 ml/h), insulin receptor and insulin receptor substrate (IRS)-1 tyrosine phosphorylation, phosphatidylinositol (PI) 3-kinase activity associated with IRS-1, and Akt serine phosphorylation were all significantly impaired (P < 0.05–0.01). The highest lipid infusion rate (90 ml/h) caused a further significant reduction in all insulin signaling events compared with the low-dose lipid infusion (P < 0.05–0.01) whereas the 60-ml/h lipid infusion caused an intermediate reduction in insulin signaling. However, about two-thirds of the maximal inhibition of insulin-stimulated glucose disposal already occurred at the rather modest increase in plasma FFA induced by the low-dose (30-ml/h) lipid infusion. Insulin-stimulated glucose disposal was inversely correlated with both the plasma FFA concentration after 4 h of lipid infusion (r = −0.50, P = 0.001) and the plasma FFA level during the last 30 min of the insulin clamp (r = −0.54, P < 0.001). PI 3-kinase activity associated with IRS-1 correlated with insulin-stimulated glucose disposal (r = 0.45, P < 0.01) and inversely with both the plasma FFA concentration after 4 h of lipid infusion (r = −0.39, P = 0.01) and during the last 30 min of the insulin clamp (r = −0.43, P < 0.01). In summary, in skeletal muscle of lean, healthy subjects, a progressive increase in plasma FFA causes a dose-dependent inhibition of insulin-stimulated glucose disposal and insulin signaling. The inhibitory effect of plasma FFA was already significant following a rather modest increase in plasma FFA and develops at concentrations that are well within the physiological range (i.e., at plasma FFA levels observed in obesity and type 2 diabetes).
Glucose-Stimulated Upregulation of GLUT2 Gene Is Mediated by Sterol Response Element–Binding Protein-1c in the Hepatocytes
Authors: Im Seung-Soon , Kang Seung-Youn , Kim So-Youn , Kim Ha-il , Kim Jae-Woo , Kim Kyung-Sup , Ahn Yong-Ho
Published: March 2007

GLUT2 is mainly expressed in the liver, β-cells of the pancreas, and the basolateral membrane of kidney proximal tubules and plays an important role in glucose homeostasis in living organisms. The transcription of the GLUT2 gene is known to be upregulated in the liver during postprandial hyperglycemic states or in type 2 diabetes. However, a molecular mechanism by which glucose activates GLUT2 gene expression is not known. In this study, we report evidence that sterol response element–binding protein (SREBP)-1c plays a key role in glucose-stimulated GLUT2 gene expression. The GLUT2 promoter reporter is activated by SREBP-1c, and the activation is inhibited by a dominant-negative form of SREBP-1c (SREBP-1c DN). Adenoviral expression of SREBP-1c DN suppressed glucose-stimulated GLUT2 mRNA level in primary hepatocytes. An electrophoretic mobility shift assay and mutational analysis of the GLUT2 promoter revealed that SREBP-1c binds to the −84/−76 region of the GLUT2 promoter. Chromatin immunoprecipitation revealed that the binding of SREBP-1c to the −84/−76 region was increased by glucose concentration in a dose-dependent manner. These results indicate that SREBP-1c mediates glucose-stimulated GLUT2 gene expression in hepatocytes.
Tissue Factor Produced by the Endocrine Cells of the Islets of Langerhans Is Associated With a Negative Outcome of Clinical Islet Transplantation
Authors: Johansson Helena , Lukinius Agneta , Moberg Lisa , Lundgren Torbjörn , Berne Christian , Foss Aksel , Felldin Marie , Källen Ragnar , Salmela Kaija , Tibell Annika , Tufveson Gunnar , Ekdahl Kristina Nilsson , Elgue Graciela , Korsgren Olle , Nilsson Bo
Published: March 2007

There are strong indications that only a small fraction of grafts successfully engraft in clinical islet transplantation. One explanation may be the instant blood-mediated inflammatory reaction (IBMIR) elicited by tissue factor, which is produced by the endocrine cells. In the present study, we show that islets intended for islet transplantation produce tissue factor in both the transmembrane and the alternatively spliced form and that the membrane-bound form is released as microparticles often associated with both insulin and glucagon granules. A low–molecular mass factor VIIa (FVIIa) inhibitor that indirectly blocks both forms of tissue factor was shown in vitro to be a promising drug to eliminate the IBMIR. Thrombin-antithrombin complex (TAT) and FVIIa-antithrombin complex (FVIIa-AT) were measured in nine patients who together received 20 infusions of isolated human islets. Both the TAT and FVIIa-AT complexes increased rapidly within 15–60 min after infusion. When the initial TAT and FVIIa-AT levels were plotted against the increase in C-peptide concentration after 7 days, patients with an initially strong IBMIR showed no significant increase in insulin synthesis after 7 days. In conclusion, tissue factor present in both the islets and the culture medium and elicits IBMIR, which affects the function of the transplanted islets.
Loss of Connexin36 Channels Alters β-Cell Coupling, Islet Synchronization of Glucose-Induced Ca2+ and Insulin Oscillations, and Basal Insulin Release
Authors: Ravier Magalie A. , Güldenagel Martin , Charollais Anne , Gjinovci Asllan , Caille Dorothée , Söhl Goran , Wollheim Claes B. , Willecke Klaus , Henquin Jean-Claude , Meda Paolo
Published: March 2007

Normal insulin secretion requires the coordinated functioning of β-cells within pancreatic islets. This coordination depends on a communications network that involves the interaction of β-cells with extracellular signals and neighboring cells. In particular, adjacent β-cells are coupled via channels made of connexin36 (Cx36). To assess the function of this protein, we investigated islets of transgenic mice in which the Cx36 gene was disrupted by homologous recombination. We observed that compared with wild-type and heterozygous littermates that expressed Cx36 and behaved as nontransgenic controls, mice homozygous for the Cx36 deletion (Cx36−/−) featured β-cells devoid of gap junctions and failing to exchange microinjected Lucifer yellow. During glucose stimulation, islets of Cx36−/− mice did not display the regular oscillations of intracellular calcium concentrations ([Ca2+]i) seen in controls due to the loss of cell-to-cell synchronization of [Ca2+]i changes. The same islets did not release insulin in a pulsatile fashion, even though the overall output of the hormone in response to glucose stimulation was normal. However, under nonstimulatory conditions, islets lacking Cx36 showed increased basal release of insulin. These data show that Cx36-dependent signaling is essential for the proper functioning of β-cells, particularly for the pulsatility of [Ca2+]i and insulin secretion during glucose stimulation.
Albumin Excretion Rate and Cardiovascular Risk
Authors: Strain W. David , Chaturvedi Nish , Bulpitt Christopher J. , Rajkumar Chakravarthi , Shore Angela C.
Published: March 2007

Elevated albumin excretion rate (AER) independently predicts total and cardiovascular mortality in a variety of conditions, although the exact mechanisms are unknown. Laser Doppler fluximetry was used to study associations with risk factors and renal damage (AER calculated from a timed overnight urine collection) in 188 people without diabetes and 117 individuals with diabetes. Skin flow (flux) in response to arterial occlusion (ischemia) was measured. Three distinct patterns of postischemic peak flow were observed: 1) gradual rise to peak (normal), 2) nondominant early peak, and 3) dominant early peak. Those with a dominant early peak were more likely to have diabetes (P = 0.01), hypertension (P = 0.001), and obesity (P < 0.001) and had a higher AER (12.6 μg/min [95% CI 7.8–20.2] vs. 7.2 [5.5–9.5] nondominant early peak group and 3.7 [3.2–4.1] normal group; P < 0.001 for trend). This could not be accounted for by conventional cardiovascular risk factors (P < 0.001 after adjustment). A rapid peak flow response after ischemia is associated with an elevated AER and increased cardiovascular risk. This may represent shared mechanistic pathways and causative or con-sequential changes in the microvasculature and supports the hypothesis that microvascular dysfunction may contribute to large vessel pathophysiology.
Nutritional Epigenomics of Metabolic Syndrome
Authors: Gallou-Kabani Catherine , Junien Claudine
Published: March 2007

Human epidemiological studies and appropriately designed dietary interventions in animal models have provided considerable evidence to suggest that maternal nutritional imbalance and metabolic disturbances, during critical time windows of development, may have a persistent effect on the health of the offspring and may even be transmitted to the next generation. We now need to explain the mechanisms involved in generating such responses. The idea that epigenetic changes associated with chromatin remodeling and regulation of gene expression underlie the developmental programming of metabolic syndrome is gaining acceptance. Epigenetic alterations have been known to be of importance in cancer for ∼2 decades. This has made it possible to decipher epigenetic codes and machinery and has led to the development of a new generation of drugs now in clinical trials. Although less conspicuous, epigenetic alterations have also been progressively shown to be relevant to common diseases such as atherosclerosis and type 2 diabetes. Imprinted genes, with their key roles in controlling feto-placental nutrient supply and demand and their epigenetic lability in response to nutrients, may play an important role in adaptation/evolution. The combination of these various lines of research on epigenetic programming processes has highlighted new possibilities for the prevention and treatment of metabolic syndrome.
A Multicompartmental Model of In Vivo Adipose Tissue Glycerol Kinetics and Capillary Permeability in Lean and Obese Humans
Authors: Coppack Simon W. , Chinkes David L. , Miles John M. , Patterson Bruce W. , Klein Samuel
Published: March 2007

Lipolysis of adipose tissue triglycerides releases glycerol. Twenty-four volunteers, of whom 6 were obese and 13 were women, received a primed-constant infusion of 2H5-glycerol for 120 min during postabsorptive steady-state conditions. Arterial, abdominal venous, and interstitial (microdialysis) samples were taken, and a four-compartment model was applied to assess subcutaneous abdominal adipose tissue glycerol kinetics. Adipose tissue blood flow was measured using 133Xe washout. Venous glycerol concentrations (median 230 μmol/l [interquartile range 210–268]) were consistently greater than those of arterial blood (69.1 μmol/l [56.5–85.5]), while glycerol isotopic enrichments (tracer-to-tracee ratio) were greater in arterial blood (8.34% [7.44–10.1]) than venous blood (2.34% [1.71–2.69], P < 0.01). Microdialysate glycerol enrichment was 1.44% (1.11–1.79), indicating incomplete permeability of glycerol between capillary blood and interstitium. Calculated interstitial glycerol concentrations were between 270 μmol/l (256–350) and 332 μmol/l (281–371) (examining different boundary conditions). The calculated capillary diffusion capacity (ps) was between 2.21 ml · 100 g tissue−1 · min−1 (1.31–3.13) and 3.09 ml · 100 g tissue−1 · min−1 (1.52–4.90) and correlated inversely with adiposity (Rs ≤ −0.45, P < 0.05). Our results support previous estimates of interstitial glycerol concentration within adipose tissue and reveal capillary diffusion capacity is reduced in obesity.
Obesity and Type 2 Diabetes Impair Insulin-Induced Suppression of Glycogenolysis as Well as Gluconeogenesis
Authors: Basu Rita , Chandramouli Visvanathan , Dicke Betty , Landau Bernard , Rizza Robert
Published: March 2007

To determine whether the hepatic insulin resistance of obesity and type 2 diabetes is due to impaired insulin-induced suppression of glycogenolysis as well as gluconeogenesis, 10 lean nondiabetic, 10 obese nondiabetic, and 11 obese type 2 diabetic subjects were studied after an overnight fast and during a hyperinsulinemic-euglycemic clamp. Gluconeogenesis and glycogenolysis were measured using the deuterated water method. Before the clamp, when glucose and insulin concentrations differed among the three groups, gluconeogenesis was higher in the diabetic than in the obese nondiabetic subjects (P < 0.05) and glycogenolysis was higher in the diabetic than in the lean nondiabetic subjects (P < 0.05). During the clamp, when glucose and insulin concentrations were matched and glucagon concentrations were suppressed, both glycogenolysis and gluconeogenesis were higher (P < 0.01) in the diabetic versus the obese and lean nondiabetic subjects. Furthermore, glycogenolysis and gluconeogenesis were higher (P < 0.01) in the obese than in the lean nondiabetic subjects. Plasma free fatty acid concentrations correlated (P < 0.001) with glucose production and gluconeogenesis both before and during the clamp and with glycogenolysis during the clamp (P < 0.01). We concluded that defects in the regulation of glycogenolysis as well as gluconeogenesis cause hepatic insulin resistance in obese nondiabetic and type 2 diabetic humans.
Dual Role of Phosphofructokinase-2/Fructose Bisphosphatase-2 in Regulating the Compartmentation and Expression of Glucokinase in Hepatocytes
Authors: Payne Victoria A. , Arden Catherine , Wu Chaodong , Lange Alex J. , Agius Loranne
Published: March 2007

Hepatic glucokinase is regulated by a 68-kDa regulatory protein (GKRP) that is both an inhibitor and nuclear receptor for glucokinase. We tested the role of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK2) in regulating glucokinase compartmentation in hepatocytes. PFK2 catalyzes formation or degradation of the regulator of glycolysis fructose 2,6-bisphosphate (fructose 2,6-P2), depending on its phosphorylation state (ser-32), and is also a glucokinase-binding protein. Incubation of hepatocytes at 25 mmol/l glucose causes translocation of glucokinase from the nucleus to the cytoplasm and an increase in fructose 2,6-P2. Glucagon caused phosphorylation of PFK2-ser-32, lowered the fructose 2,6-P2 concentration, and inhibited glucose-induced translocation of glucokinase. These effects of glucagon were reversed by expression of a kinase-active PFK2 mutant (S32A/H258A) that overrides the suppression of fructose 2,6-P2 but not by overexpression of wild-type PFK2. Overexpression of PFK2 potentiated glucokinase expression in hepatocytes transduced with an adenoviral vector–encoding glucokinase by a mechanism that does not involve stabilization of glucokinase protein from degradation. It is concluded that PFK2 has a dual role in regulating glucokinase in hepatocytes: it potentiates glucokinase protein expression by posttranscriptional mechanisms and favors its cytoplasmic compartmention. Thus, it acts in a complementary mechanism to GKRP, which also regulates glucokinase protein expression and compartmentation.
Distinct Forebrain and Caudal Brainstem Contributions to the Neuropeptide Y Mediation of Ghrelin Hyperphagia
Authors: Faulconbridge Lucy F. , Grill Harvey J. , Kaplan Joel M.
Published: March 2007

Neuropeptide Y (NPY) has been implicated in the downstream mediation of ghrelin hyperphagia, with the site of action for both peptides considered to be intrinsic to the hypothalamus. Here, however, we observed robust hyperphagia with caudal brainstem (CBS) (fourth intracerebroventricular) ghrelin delivery and, moreover, that this response was reversed with coadministration of either of two NPY receptor antagonists (1229U91 and d-Tyr27,36, d-Thr32 NPY27–36) with contrasting NPY receptor subtype–binding properties. The same results were obtained after forebrain (third intracerebroventricular) administration, but the sites for both ghrelin and antagonist action were open to question, given the caudal flow of cerebrospinal fluid (CSF) through the ventricular system. To control for this, we occluded the cerebral aqueduct to restrict CSF flow between the forebrain and CBS ventricles and tested all combinations (same and cross ventricle) of ghrelin (150 pmol/1 μl) and NPY receptor antagonist delivery. With fourth intracerebroventricular ghrelin delivery after aqueduct occlusion, preadministration of either of the two antagonists through the same cannula reversed the hyperphagic response but neither was effective when delivered to the third ventricle. With third intracerebroventricular ghrelin administration, however, 1229U91 reversed the ingestive response only when delivered to the fourth ventricle, whereas d-Tyr27,36, d-Thr32 NPY27–36 was effective only when delivered to the forebrain. These results demonstrate distinct mediating pathways (due to location and subtypes of relevant NPY receptor) for the hyperphagic response driven separately by forebrain and CBS ghrelin administration.
Autocrine Action of Adiponectin on Human Fat Cells Prevents the Release of Insulin Resistance-Inducing Factors
Authors: Dietze-Schroeder Daniela , Sell Henrike , Uhlig Mathias , Koenen Marlis , Eckel Jürgen
Published: March 2007

The adipocyte hormone adiponectin is negatively correlated with obesity and insulin resistance and may exert an important antidiabetes function. In this study, primary human skeletal muscle cells were cocultured with human fat cells or incubated with adipocyte-conditioned medium in the presence or absence of the globular domain of adiponectin (gAcrp30) to analyze its capacity to restore normal insulin signaling in the muscle cells. Human skeletal muscle cells cocultured with adipocytes or treated with adipocyte-conditioned medium showed an impaired Akt and glycogen synthase kinase 3 serine phosphorylation in response to insulin. Furthermore, insulin-stimulated GLUT4 translocation was reduced by adipocyte-conditioned medium. Impaired insulin signaling was normalized upon addition of gAcrp30 to the coculture. Further, adipocyte-conditioned medium generated in the presence of gAcrp30 was unable to perturb insulin-stimulated Akt phosphorylation. Concomitant addition of gAcrp30 and adipocyte-conditioned medium to the myocytes failed to restore normal insulin action. Protein array analysis of adipocyte-conditioned medium indicated that the secretion of at least eight different cytokines was diminished in response to gAcrp30. We therefore suggest that adiponectin operates as a key regulator of adipocyte secretory function. This autocrine action may prevent the induction of skeletal muscle insulin resistance and may partly explain the antidiabetes action of this hormone.
Peptide-Mediated Targeting of the Islets of Langerhans
Authors: Samli Kausar N. , McGuire Michael J. , Newgard Christopher B. , Johnston Stephen Albert , Brown Kathlynn C.
Published: March 2007

Strategies for restoring β-cell function in diabetic patients would be greatly aided by the ability to target genes, proteins, or small molecules specifically to these cells. Furthermore, the ability to direct imaging agents specifically to β-cells would facilitate diagnosis and monitoring of disease progression. To isolate ligands that can home to β-cells in vivo, we have panned a random phage-displayed 20-mer peptide library on freshly isolated rat islets. We have isolated two 20-mer peptides that bind to islets ex vivo. One of these peptides preferentially homes to the islets of Langerhans in a normal rat with clear differentiation between the endocrine and exocrine cells of the pancreas. Furthermore, this peptide does not target β-cells in a type 2 diabetes animal model, suggesting that the peptide can discriminate between glucose-stimulated insulin secretion–functional and -dysfunctional β-cells.
Overexpression of Glutathione Peroxidase With Two Isoforms of Superoxide Dismutase Protects Mouse Islets From Oxidative Injury and Improves Islet Graft Function
Authors: Mysore Tharun B. , Shinkel Trixie A. , Collins James , Salvaris Evelyn J. , Fisicaro Nella , Murray-Segal Lisa J. , Johnson Lucinda E.A. , Lepore Diana A. , Walters Stacey N. , Stokes Rebecca , Chandra Abhilash P. , O’Connell Philip J. , d’Apice Anthony J.F. , Cowan Peter J.
Published: March 2007

Primary nonfunction of transplanted islets results in part from their sensitivity to reactive oxygen species (ROS) generated during the isolation and transplantation process. Our aim was to examine whether coexpression of antioxidant enzymes to detoxify multiple ROS increased the resistance of mouse islets to oxidative stress and improved the initial function of islet grafts. Islets from transgenic mice expressing combinations of human copper/zinc superoxide dismutase (SOD), extracellular SOD, and cellular glutathione peroxidase (Gpx-1) were subjected to oxidative stress in vitro. Relative viability after hypoxanthine/xanthine oxidase treatment was as follows: extracellular SOD + Gpx-1 + Cu/Zn SOD > extracellular SOD + Gpx-1 > extracellular SOD > wild type. Expression of all three enzymes was the only combination protective against hypoxia/reoxygenation. Islets from transgenic or control wild-type mice were then transplanted into streptozotocin-induced diabetic recipients in a syngeneic marginal islet mass model, and blood glucose levels were monitored for 7 days. In contrast to single- and double-transgenic grafts, triple-transgenic grafts significantly improved control of blood glucose compared with wild type. Our results indicate that coexpression of antioxidant enzymes has a complementary beneficial effect and may be a useful approach to reduce primary nonfunction of islet grafts.
Polymorphisms in the SLC2A2 (GLUT2) Gene Are Associated With the Conversion From Impaired Glucose Tolerance to Type 2 Diabetes
Authors: Laukkanen Olli , Lindström Jaana , Eriksson Johan , Valle Timo T. , Hämäläinen Helena , Ilanne-Parikka Pirjo , Keinänen-Kiukaanniemi Sirkka , Tuomilehto Jaakko , Uusitupa Matti , Laakso Markku
Published: March 2007

Impaired insulin secretion is a fundamental defect in type 2 diabetes. The aim of this study was to investigate whether single nucleotide polymorphisms (SNPs) in the genes regulating insulin secretion (SLC2A2 [encoding GLUT2], GCK, TCF1 [encoding HNF-1α], HNF4A, GIP, and GLP1R) are associated with the conversion from impaired glucose tolerance (IGT) to type 2 diabetes in participants of the Finnish Diabetes Prevention Study. With the exception of SLC2A2, other genes were not associated with the risk of type 2 diabetes. All four SNPs of SLC2A2 predicted the conversion to diabetes, and rs5393 (AA genotype) increased the risk of type 2 diabetes in the entire study population by threefold (odds ratio 3.04, 95% CI 1.34–6.88, P = 0.008). The risk for type 2 diabetes in the AA genotype carriers was increased in the control group (5.56 [1.78–17.39], P = 0.003) but not in the intervention group. We conclude that the SNPs of SLC2A2 predict the conversion to diabetes in obese subjects with IGT.
Proopiomelanocortin-Deficient Mice Are Hypersensitive to the Adverse Metabolic Effects of Glucocorticoids
Authors: Coll Anthony P. , Challis Benjamin G. , López Miguel , Piper Sarah , Yeo Giles S.H. , O’Rahilly Stephen
Published: March 2007

Congenital lack of proopiomelanocortin (POMC) causes obesity and glucocorticoid deficiency. The responses of Pomc−/− and wild-type mice to the administration of corticosterone were compared. In study 1, mice were given corticosterone-supplemented water (CORT) for 10 days, resulting in plasma CORT levels within the physiological range, with partial suppression of hypothalamic corticotropin-releasing hormone expression to a similar degree between genotypes. Body weight, fat mass, and food intake increased in CORT-treated Pomc−/− but not wild-type mice. CORT increased plasma insulin levels 50-fold in Pomc−/− versus 14-fold in wild-type mice (P < 0.01) and increased hypothalamic agouti-related protein (AgRP) expression by more than 200% in Pomc−/− versus 40% in wild type (P < 0.05). In study 2, mice were given CORT from weaning, and Pomc−/− but not wild-type mice developed hyperglycemia, ketonuria, and hepatic steatosis by 8–12 weeks. Thus, Pomc−/− mice are hypersensitive to the adverse metabolic effects of glucocorticoids. Additionally, as the levels of plasma CORT achieved, especially in study 1, were not grossly supraphysiological, we conclude that glucocorticoid deficiency may afford Pomc−/− mice some protection from the full adverse consequences of melanocortin deficiency. This may occur through a mechanism involving the suppression of AgRP by the hypoadrenal state.
Association of Common Variation in the HNF1α Gene Region With Risk of Type 2 Diabetes
Authors: Winckler Wendy , Burtt Noël P. , Holmkvist Johan , Cervin Camilla , de Bakker Paul I.W. , Sun Maria , Almgren Peter , Tuomi Tiinamaija , Gaudet Daniel , Hudson Thomas J. , Ardlie Kristin G. , Daly Mark J. , Hirschhorn Joel N. , Altshuler David , Groop Leif
Published: March 2007

It is currently unclear how often genes that are mutated to cause rare, early-onset monogenic forms of disease also harbor common variants that contribute to the more typical polygenic form of each disease. The gene for MODY3 diabetes, HNF1α, lies in a region that has shown linkage to late-onset type 2 diabetes (12q24, NIDDM2), and previous association studies have suggested a weak trend toward association for common missense variants in HNF1α with glucose-related traits. Based on genotyping of 79 common SNPs in the 118 kb spanning HNF1α, we selected 21 haplotype tag single nucleotide polymorphisms (SNPs) and genotyped them in >4,000 diabetic patients and control subjects from Sweden, Finland, and Canada. Several SNPs from the coding region and 5′ of the gene demonstrated nominal association with type 2 diabetes, with the most significant marker (rs1920792) having an odds ratio of 1.17 and a P value of 0.002. We then genotyped three SNPs with the strongest evidence for association to type 2 diabetes (rs1920792, I27L, and A98V) in an additional 4,400 type 2 diabetic and control subjects from North America and Poland and compared our results with those of the original sample and of Weedon et al. None of the results were consistently observed across all samples, with the possible exception of a modest association of the rare (3–5%) A98V variant. These results indicate that common variants in HNF1α either play no role in type 2 diabetes, a very small role, or a role that cannot be consistently observed without consideration of as yet unmeasured genetic or environmental modifiers.
Skeletal Muscle AMP-Activated Protein Kinase Phosphorylation Parallels Metabolic Phenotype in Leptin Transgenic Mice Under Dietary Modification
Authors: Tanaka Tomohiro , Hidaka Shuji , Masuzaki Hiroaki , Yasue Shintaro , Minokoshi Yasuhiko , Ebihara Ken , Chusho Hideki , Ogawa Yoshihiro , Toyoda Taro , Sato Kenji , Miyanaga Fumiko , Fujimoto Muneya , Tomita Tsutomu , Kusakabe Toru , Kobayashi Nozomi , Tanioka Hideki , Hayashi Tatsuya , Hosoda Kiminori , Yoshimatsu Hironobu , Sakata Toshiie , Nakao Kazuwa
Published: March 2007

Leptin augments glucose and lipid metabolism independent of its effect on satiety. Administration of leptin in rodents increases skeletal muscle β-oxidation by activating AMP-activated protein kinase (AMPK). We previously reported that, as hyperleptinemic as obese human subjects, transgenic skinny mice overexpressing leptin in liver (LepTg) exhibit enhanced insulin sensitivity and lipid clearance. To assess skeletal muscle AMPK activity in leptin-sensitive and -insensitive states, we examined phosphorylation of AMPK and its target, acetyl CoA carboxylase (ACC), in muscles from LepTg under dietary modification. Here we show that phosphorylation of AMPK and ACC are chronically augmented in LepTg soleus muscle, with a concomitant increase in the AMP-to-ATP ratio and a significant decrease in tissue triglyceride content. Despite preexisting hyperleptinemia, high-fat diet (HFD)-fed LepTg develop obesity, insulin-resistance, and hyperlipidemia. In parallel, elevated soleus AMPK and ACC phosphorylation in regular diet–fed LepTg is attenuated, and tissue triglyceride content is increased in those given HFD. Of note, substitution of HFD with regular diet causes a robust recovery of soleus AMPK and ACC phosphorylation in LepTg, with a higher rate of body weight reduction and a regain of insulin sensitivity. In conclusion, soleus AMPK and ACC phosphorylation in LepTg changes in parallel with its insulin sensitivity under dietary modification, suggesting a close association between skeletal muscle AMPK activity and sensitivity to leptin.
β-Cell Function in Morbidly Obese Subjects During Free Living
Authors: Camastra Stefania , Manco Melania , Mari Andrea , Baldi Simona , Gastaldelli Amalia , Greco Aldo V. , Mingrone Gertrude , Ferrannini Ele
Published: March 2007

Insulin hypersecretion and insulin resistance are physiologically linked features of obesity. We tested whether extreme hypersecretion impairs β-cell function under free-living conditions and whether major weight loss modifies insulin hypersecretion, insulin sensitivity, and β-cell function. Plasma glucose, C-peptide, and free fatty acid concentrations were measured at hourly intervals during 24 h of normal life (including calorie-standardized meals) in 20 morbidly obese nondiabetic patients (BMI 48.4 ± 1.7 kg/m2) and 7 nonobese age- and sex-matched control subjects; 8 of the obese patients were restudied 6 months and 2 years following biliopancreatic diversion. Insulin secretion was reconstructed from C-peptide levels by deconvolution and related to concurrent glucose levels through a mathematical model incorporating key features of β-cell function: rate sensitivity, β-cell glucose sensitivity, and potentiation. Insulin sensitivity (by the euglycemic insulin clamp technique) was reduced by 50% in obese subjects (23.1 ± 2.5 of obese subjects vs. 52.9 ± 4.9 μmol · min−1 · kgFFM−1 of control subjects, means ± SE, P = 0.0004) as was mean 24-h insulin clearance (median 809 [interquartile range 451] vs. 1,553 [520] ml · min−1 · m−2, P < 0.001) due to a 50% reduction in hepatic insulin extraction (P < 0.01). Over 24 h, insulin secretion was doubled in obese subjects (468 nmol [202] in obese subjects vs. 235 [85] of control subjects, P = 0.0002). Despite the hypersecretion, β-cell glucose sensitivity, rate sensitivity, and potentiation were similar in obese and control subjects. Six months postoperatively (weight loss = 33 ± 3 kg), both insulin hypersecretion (282 nmol [213]) and insulin sensitivity (51.6 ± 3.7 μmol · min−1 · kgFFM−1) were normalized. At 2 years (weight loss = 50 ± 8 kg), insulin sensitivity was supernormal (68.7 ± 3.3 μmol · min−1 · kgFFM−1) and insulin secretion was lower than normal (167 nmol [37]) (both P < 0.05 vs. control subjects). In conclusion, severe uncomplicated obesity is characterized by gross insulin hypersecretion and insulin resistance, but the dynamic aspects of β-cell function are intact. Malabsorptive bariatric surgery corrects both the insulin hypersecretion and the insulin resistance at a time when BMI is still high. With continued weight loss over a 2-year period, moderately obese subjects become supersensitive to insulin and, correspondingly, insulin hyposecretors.
Subcutaneous Oxyntomodulin Reduces Body Weight in Overweight and Obese Subjects
Authors: Wynne Katie , Park Adrian J. , Small Caroline J. , Patterson Michael , Ellis Sandra M. , Murphy Kevin G. , Wren Alison M. , Frost Gary S. , Meeran Karim , Ghatei Mohammad A. , Bloom Stephen R.
Published: March 2007

This study investigated the effect of subcutaneously administered oxyntomodulin on body weight in healthy overweight and obese volunteers. Participants self-administered saline or oxyntomodulin subcutaneously in a randomized, double-blind, parallel-group protocol. Injections were self-administered for 4 weeks, three times daily, 30 min before each meal. The volunteers were asked to maintain their regular diet and level of physical exercise during the study period. Subjects’ body weight, energy intake, and levels of adipose hormones were assessed at the start and end of the study. Body weight was reduced by 2.3 ± 0.4 kg in the treatment group over the study period compared with 0.5 ± 0.5 kg in the control group (P = 0.0106). On average, the treatment group had an additional 0.45-kg weight loss per week. The treatment group demonstrated a reduction in leptin and an increase in adiponectin. Energy intake by the treatment group was significantly reduced by 170 ± 37 kcal (25 ± 5%) at the initial study meal (P = 0.0007) and by 250 ± 63 kcal (35 ± 9%) at the final study meal (P = 0.0023), with no change in subjective food palatability. Oxyntomodulin treatment resulted in weight loss and a change in the levels of adipose hormones consistent with a loss of adipose tissue. The anorectic effect was maintained over the 4-week period. Oxyntomodulin represents a potential therapy for obesity.
Compromised Arterial Function in Human Type 2 Diabetic Patients
Authors: Okon Elena B. , Chung Ada W.Y. , Rauniyar Pooja , Padilla Eugenia , Tejerina Teresa , McManus Bruce M. , Luo Honglin , van Breemen Cornelis
Published: March 2007

Diabetes is associated with a perturbation of signaling pathways in vascular tissue, which causes vasomotor dysfunction such as hypertension and accelerated atherosclerosis. In the present study, the mechanisms of vasomotor dysfunction, Akt (Thr308 and Ser473) phosphorylation and expression of endothelial NO (nitric oxide) synthase, and inducible NO synthase were investigated in human diabetic internal mammary arteries. The phospho-Akt (Thr308) level in arteries from diabetic patients was reduced to about one-half of the level in nondiabetic patients, suggesting impaired insulin signaling in human diabetic vascular tissue. Augmented vasoconstriction was observed in diabetic arteries, due in part to deficiency of basal and stimulated NO production. This correlated with decreased endothelial NO synthase expression and activity in diabetic vessels. The sensitivity of diabetic vessels to the NO donor, sodium nitroprusside, was reduced as well, suggesting that NO breakdown and/or decreased sensitivity of smooth muscle to NO are also responsible for abnormal vasoconstriction. In addition, the abnormal vasoconstriction in diabetic vessels was not completely abolished in the presence of Nω-nitro-l-arginine methyl ester, revealing that NO-independent mechanisms also contribute to vasomotor dysfunction in diabetes. In conclusion, diabetes downregulates the Akt-signaling pathway and compromises human arterial function through a decrease in NO availability as well as through NO-independent mechanisms.