bluuebunny/crossref_metadata_2025 huggingface dataset:
Elimination of glucagon-like peptide 1R signaling does not modify weight gain and islet adaptation in mice with combined disruption of leptin and GLP-1 action.
Authors: Scrocchi L A , Hill M E , Saleh J , Perkins B , Drucker D J
Published: March 2007

Leptin and glucagon-like peptide 1 (GLP-1) exhibit opposing actions in the endocrine pancreas. GLP-1 stimulates insulin biosynthesis, secretion, and islet growth, whereas leptin inhibits glucose-dependent insulin secretion and insulin gene transcription. In contrast, GLP-1 and leptin actions overlap in the central nervous system, where leptin has been shown to activate GLP-1 circuits that inhibit food intake. To determine the physiological importance of GLP-1 receptor (GLP-1R)-leptin interactions, we studied islet function and feeding behavior in ob/ob:GLP-1R(-/-) mice. Although GLP-1R actions are thought to be essential for glucose-dependent insulin secretion, the levels of fasting glucose, glycemic excursion after glucose loading, glucose-stimulated insulin, and pancreatic insulin RNA content were similar in ob/ob:GLP-1R(+/+) versus ob/ob:GLP-1R(-/-) mice. Despite evidence linking GLP-1R signaling to the regulation of islet neogenesis and proliferation, ob/ob:GLP-1R(-/-) mice exhibited significantly increased islet numbers and area and an increase in the number of large islets compared with GLP-1R(+/+) or (-/-) mice (P < -0.01 to 0.05). Similarly, growth rates and both shortand long-term control of food intake were comparable in ob/ob:GLP-1R(+/+) versus ob/ob:GLP-1R4(-/-) mice. Furthermore, leptin produced a similar inhibition of food intake in GLP-1R(-/-), ob/ob:GLP-1R(+/+), and ob/ob:GLP1R4(-/-) mice. These findings illustrate that although leptin and GLP-1 actions overlap in the brain and endocrine pancreas, disruption of GLP-1 signaling does not modify the response to leptin or the phenotype of leptin deficiency in the ob/ob mouse, as assessed by long-term control of body weight or the adaptive beta-cell response to insulin resistance in vivo.
Hexosamine-Induced Fibronectin Protein Synthesis in Mesangial Cells Is Associated With Increases in cAMP Responsive Element Binding (CREB) Phosphorylation and Nuclear CREB
Authors: Singh Lalit P. , Andy Jack , Anyamale Vivian , Greene Kennieth , Alexander Michelle , Crook Errol D.
Published: March 2007

Hyperglycemia-induced alterations in mesangial (MES) cell function and extracellular matrix protein accumulation are seen in diabetic glomerulopathy. Recent studies have demonstrated that some of the effects of high glucose (HG) on cellular metabolism are mediated by the hexosamine biosynthesis pathway (HBP), in which fructose-6-phosphate is converted to glucosamine 6-phosphate by the rate-liming enzyme glutamine:fructose-6-phosphate amidotransferase (GFA). In this study, we investigated the role of HBP on HG-stimulated fibronectin protein synthesis, a matrix component, in SV-40–transformed rat kidney MES cells. Treatment of MES cells with 25 mmol/l glucose (HG) for 48 h increases cellular fibronectin levels by two- to threefold on Western blots when compared with low glucose (5 mmol/l). Glucosamine (GlcN; 1.5 mmol/l), which enters the hexosamine pathway distal to GFA action, also increases fibronectin synthesis. Azaserine (AZA; 0.5 μmol/l), an inhibitor of GFA, blocks the HG- but not the GlcN-induced fibronectin synthesis. Fibronectin contains cAMP responsive element (CRE) consensus sequences in its promoter and the phosphorylation of CRE-binding protein (CREB) may regulate its expression. On Western blots, HG and GlcN stimulate two- to threefold the phosphorylation of CREB at Ser 133, whereas CREB protein content was unaltered by either HG or GlcN. In addition, nuclear CREB activity was increased by HG and GlcN on gel-shift assays using 32P-CRE oligonucleotides. AZA impeded the HG-enhanced CREB phosphorylation and CRE binding but had no effect on GlcN-mediated CREB phosphorylation and CRE binding. Pharmacologic inhibition of protein kinase C (PKC) and protein kinase A (PKA), which are involved in hexosamine-mediated matrix production, blocked the CREB phosphorylation and fibronectin synthesis seen in HG and GlcN conditions. We conclude that the effects of HG on fibronectin synthesis in the mesangium are mediated by the HBP possibly via hexosamine regulation of CREB and PKC/PKA signaling pathways. These results support the hypothesis that the HBP is a sensor and regulator of the actions of glucose in the kidney.
Pancreatic Response to Mild Non–Insulin-Induced Hypoglycemia Does Not Involve Extrinsic Neural Input
Authors: Sherck Stephanie M. , Shiota Masakazu , Saccomando James , Cardin Sylvain , Allen Eric J. , Hastings Jon R. , Neal Doss W. , Williams Phil E. , Cherrington Alan D.
Published: March 2007

Mild non–insulin-induced hypoglycemia achieved by administration of a glycogen phosphorylase inhibitor results in increased glucagon and decreased insulin secretion in conscious dogs. Our aim was to determine whether the response of the endocrine pancreas to this mild hypoglycemia can occur in the absence of neural input to the pancreas. Seven dogs underwent surgical pancreatic denervation (PDN [study group]), and seven dogs underwent sham denervation (control [CON] group). Each study consisted of a 100-min equilibration period, a 40-min control period, and a 180-min test period. At the start of the test period, Bay R3401 (10 mg/kg), a glycogen phosphorylase inhibitor, was administered orally. Arterial plasma glucose (mmol/l) fell to a similar minimum in CON (5.0 ± 0.1) and PDN (4.9 ± 0.3). Arterial plasma insulin also fell to similar minima in both groups (CON, 20 ± 6 pmol/l; PDN, 14 ± 5 pmol/l). Arterial plasma glucagon rose to a similar maximum in CON (73 ± 8 ng/l) and PDN (72 ± 9 ng/l). Insulin and glucagon secretion data support these plasma hormone results, and there were no significant differences in the responses in CON and PDN for any parameter. Pancreatic norepinephrine content in PDN was only 4% of that in CON, confirming successful sympathetic denervation. Pancreatic polypeptide levels tended to increase in CON and decrease in PDN in response to mild hypoglycemia, indicative of parasympathetic denervation. It thus can be concluded that the responses of α- and β-cells to mild non–insulin-induced hypoglycemia can occur in the absence of extrinsic neural input.
Mapping by Genetic Interaction
Authors: Lyons Paul A. , Armitage Nicola , Lord C.J. , Phillips Michael S. , Todd John A. , Peterson Laurence B. , Wicker Linda S.
Published: March 2007

As many of the linked chromosome regions that predispose to type 1 diabetes in the NOD mouse have been dissected, it has become apparent that the initially observed effect is in fact attributable to several loci. One such cluster of loci on distal chromosome 3, originally described as Idd10, is now known to comprise three separate loci, Idd10, Idd17, and Idd18. Although these loci have a significant combined effect on diabetes development, their individual effects are barely detectable when diabetes is used as a read-out, which makes fine-mapping them by use of a conventional congenic approach impractical. In this study, we demonstrate that it is possible to map loci, with modest effects, to regions small enough for systematic gene identification by capitalizing on the fact that the combined loci provide more profound, measurable protection. We have mapped the Idd10 and Idd18 loci to 1.3- and 2.0-cM intervals, respectively, by holding the Idd3 allele constant. In addition, we have excluded Csf1 and Nras as candidates for both loci.
Characterization of the Mouse Islet-Specific Glucose-6-Phosphatase Catalytic Subunit–Related Protein Gene Promoter by In Situ Footprinting
Authors: Bischof Larry J. , Martin Cyrus C. , Svitek Christina A. , Stadelmaier Beth T. , Hornbuckle Lauri A. , Goldman Joshua K. , Oeser James K. , Hutton John C. , O’Brien Richard M.
Published: March 2007

Glucose-6-phosphatase (G6Pase) is a multicomponent system located in the endoplasmic reticulum comprising a catalytic subunit and transporters for glucose-6-phosphate, inorganic phosphate, and glucose. We have recently cloned a novel gene that encodes an islet-specific G6Pase catalytic subunit–related protein (IGRP) (Ebert et al., Diabetes 48:543–551, 1999). To begin to investigate the molecular basis for the islet-specific expression of the IGRP gene, a series of truncated IGRP–chloramphenicol acetyltransferase (CAT) fusion genes were transiently transfected into the islet-derived mouse βTC-3 and hamster insulinoma tumor cell lines. In both cell lines, basal fusion gene expression decreased upon progressive deletion of the IGRP promoter sequence between −306 and −66, indicating that multiple promoter regions are required for maximal IGRP-CAT expression. The ligation-mediated polymerase chain reaction footprinting technique was then used to compare trans-acting factor binding to the IGRP promoter in situ in βTC-3 cells, which express the endogenous IGRP gene, and adrenocortical Y1 cells, which do not. Multiple trans-acting factor binding sites were selectively identified in βTC-3 cells that correlate with regions of the IGRP promoter identified as being required for basal IGRP-CAT fusion gene expression. The data suggest that hepatocyte nuclear factor 3 may be important for basal IGRP gene expression, as it is for glucagon, GLUT2, and Pdx-1 gene expression. In addition, binding sites for several trans-acting factors not previously associated with islet gene expression, as well as binding sites for potentially novel proteins, were identified.
Effect of 3 Years of Antihypertensive Therapy on Renal Structure in Type 1 Diabetic Patients With Albuminuria
Authors:   The European Study for the Prevention of Renal Disease in Type 1 Diabetes ESPRIT Study Group
Published: March 2007

In the treatment of diabetic nephropathy, ACE inhibitor therapy reduces albumin excretion and slows the rate of decline in glomerular filtration rate (GFR). Our study was designed to investigate whether these effects lay in amelioration of the underlying glomerular structural abnormalities. A total of 54 type 1 diabetic patients with albuminuria and blood pressure (BP) <150/90 mmHg were randomized to receive 10 mg enalapril once daily, 10 mg nifedipine retard twice daily, or placebo in a multicenter double-blind study of 3 years’ duration. Renal biopsy was performed at baseline and follow-up, and tissue was analyzed by standard morphometric methods. BP, GFR, albumin excretion rate (AER), and HbA1c were measured every 6 months. Enalapril lowered AER after 6 months by 26% (P < 0.05); however, this reduction was not sustained at 3 years. There was no significant effect of nifedipine or placebo on AER. GFR decreased by a similar average rate of 4.1 ml · min–1 · year–1 (95% CI 2.6–5.6) in all three groups. BP and HbA1c were unchanged throughout the study in all groups. At baseline, nearly all biopsies showed classic appearances of diabetic glomerulopathy. There was no detectable effect of enalapril compared with either nifedipine or placebo on renal structure over 3 years. However, we found that patients with increased AER have established glomerulopathy and a progressive average decline in GFR of 4.1 ml · min–1 · year–1 in the absence of overt hypertension, and baseline AER appeared predictive of subsequent mesangial volume fraction (r2 = 0.20, P = 0.0018). In this small cohort of nonhypertensive patients studied for 3 years, disease evolution appears unaffected by treatment with either enalapril or nifedipine.
A Key Role for β-Cell Cytosolic Phospholipase A2 in the Maintenance of Insulin Stores But Not in the Initiation of Insulin Secretion
Authors: Persaud Shanta J. , Roderigo-Milne Helen M. , Squires Paul E. , Sugden David , Wheeler-Jones Caroline P.D. , Marsh Phil J. , Belin Véronique D. , Luther Melanie J. , Jones Peter M.
Published: March 2007

Cytosolic phospholipase A2 (cPLA2) is a Ca2+-sensitive enzyme that has been implicated in insulin secretion in response to agents that elevate β-cell intracellular Ca2+ ([Ca2+]i). We generated clones of the MIN6 β-cell line that stably underexpress cPLA2 by transfection with a vector in which cPLA2 cDNA had been inserted in the antisense orientation. Reduced expression of cPLA2 was confirmed by Western blotting. The insulin content of cPLA2-deficient MIN6 cells was reduced by ∼90%, but they showed no decrease in preproinsulin mRNA expression. Measurements of stimulus-dependent changes in [Ca2+]i indicated that reduced expression of cPLA2 did not affect the capacity of MIN6 cells to show elevations in Ca2+ in response to depolarizing stimuli. Perifusion experiments indicated that cPLA2 underexpressing MIN6 pseudoislets responded to glucose, tolbutamide, and KCl with insulin secretory profiles similar to those of cPLA2 expressing pseudoislets, but that secretion was not maintained with continued stimulus. Analysis of the ultrastructure of cPLA2-deficient MIN6 cells by electron microscopy revealed that they contained very few mature insulin secretory granules, but there was an abundance of non–electron-dense vesicles. These data are consistent with a role for cPLA2 in the maintenance of insulin stores, but they suggest that it is not required for the initiation of insulin secretion from β-cells.
Fetal Insulin-Like Growth Factor-2 Production Is Impaired in the GK Rat Model of Type 2 Diabetes
Authors: Serradas Patricia , Goya Luis , Lacorne Matthieu , Gangnerau Marie-Noëlle , Ramos Sonia , Alvarez Carmen , Pascual-Leone Ana-Maria , Portha Bernard
Published: March 2007

At late fetal age (21.5 days postcoitum [dpc]), GK rats present a severely reduced β-cell mass compared with Wistar rats. This anomaly largely antedates the onset of hyperglycemia in GK rats. Thus, the β-cell mass deficit could represent the primary defect leading to type 2 diabetes in the adult. The aim of this work was to investigate, in GK fetuses at the end of fetal age (21.5 dpc), whether impaired availability of growth factors such as insulin, growth hormone, and IGFs and their IGF binding proteins (IGFBPs) could be instrumental in this anomaly. Although it confirms that GK fetuses are hypoinsulinemic despite enhanced plasma glucose level due to maternal hyperglycemia, the present study shows for the first time that IGF-2 expression in the liver and pancreas and IGF-2 serum levels are decreased in GK fetuses. Serum level as well as liver and pancreatic mRNA expression of IGFBP-2 were found to be normal in GK fetuses, whereas serum level and liver mRNA expression of IGFBP-1 were increased. Finally, we found that the maximal β-cell mitogenic response to IGFs in vitro is kept intact, therefore suggesting that the direct biological action of IGFs on fetal GK β-cells is not grossly impaired. In conclusion, in GK fetuses at 21.5 dpc, the defective IGF-2 production appears to be an early landmark in the pathological sequence leading to retardation of β-cell growth in the fetal GK rat.
Triggering and Augmentation Mechanisms, Granule Pools, and Biphasic Insulin Secretion
Authors: Bratanova-Tochkova Troitza K. , Cheng Haiying , Daniel Samira , Gunawardana Subhadra , Liu Yi-Jia , Mulvaney-Musa Jennifer , Schermerhorn Thomas , Straub Susanne G. , Yajima Hiroki , Sharp Geoffrey W.G.
Published: March 2007

The insulin secretory response by pancreatic β-cells to an acute “square wave” stimulation by glucose is characterized by a first phase that occurs promptly after exposure to glucose, followed by a decrease to a nadir, and a prolonged second phase. The first phase of release is due to the ATP-sensitive K+ (KATP) channel-dependent (triggering) pathway that increases [Ca2+]i and has been thought to discharge the granules from a “readily releasable pool.” It follows that the second phase entails the preparation of granules for release, perhaps including translocation and priming for fusion competency before exocytosis. The pathways responsible for the second phase include the KATP channel-dependent pathway because of the need for elevated [Ca2+]i and additional signals from KATP channel-independent pathways. The mechanisms underlying these additional signals are unknown. Current hypotheses include increased cytosolic long-chain acyl-CoA, the pyruvate-malate shuttle, glutamate export from mitochondria, and an increased ATP/ADP ratio. In mouse islets, the β-cell contains some 13,000 granules, of which ∼100 are in a “readily releasable” pool. Rates of granule release are slow, e.g., one every 3 s, even at the peak of the first phase of glucose-stimulated release. As both phases of glucose-stimulated insulin secretion can be enhanced by agents such as glucagon-like peptide 1, which increases cyclic AMP levels and protein kinase A activity, or acetylcholine, which increases diacylglycerol levels and protein kinase C activity, a single “readily releasable pool” hypothesis is an inadequate explanation for insulin secretion. Multiple pools available for rapid release or rapid conversion of granules to a rapidly releasable state are required.
Systemic and Local Adrenergic Regulation of Muscle Glucose Utilization During Hypoglycemia in Healthy Subjects
Authors: Hoffman Robert P. , Sinkey Christine A. , Dopp John M. , Phillips Bradley G.
Published: March 2007

Adrenergic responses are crucial for hypoglycemic recovery. Epinephrine increases glucose production, lipolysis, and peripheral insulin resistance as well as blood flow and glucose delivery. Sympathetic activation causes vasoconstriction and reduces glucose delivery. To determine the effects of α- and β-adrenergic activity on muscle glucose uptake during hypoglycemia, we studied forearm blood flow (FBF) (plethysmography), arteriovenous glucose difference (AV-diff), and forearm glucose uptake (FGU) during insulin infusion with 60 min of euglycemia followed by 60 min of hypoglycemia. Twelve healthy subjects (27 ± 5 years of age) were randomized to intravenous propranolol (IV PROP, 80 μg/min), intravenous phentolamine (IV PHEN, 500 μg/min), intra-arterial propranolol (IA PROP, 25 μg/min), intra-arterial phentolamine (IA PHEN, 12 μg/min per 100 ml forearm tissue), and saline (SAL). FBF increased during hypoglycemia with SAL (P < 0.001) but not with IA or IV PROP. FGU (P = 0.015) and AV-diff (P = 0.099) fell during hypoglycemia with IA PROP but not with IV PROP. FBF increased during hypoglycemia with IA and IV PHEN (P < 0.005). AV-diff fell during hypoglycemia with IA and IV PHEN (P < 0.01), but FGU was unchanged. Blood pressure fell (P < 0.001), and adrenergic and neuroglycopenic symptoms increased with IV PHEN (P < 0.01). Thus, systemic but not local propranolol prevents a decrease in forearm glucose extraction during hypoglycemia, suggesting that epinephrine increases peripheral muscular insulin resistance through systemic effects. α-Adrenergic activation inhibits vasodilation and helps maintain brain glucose delivery.
Fructose Amplifies Counterregulatory Responses to Hypoglycemia in Humans
Authors: Gabriely Ilan , Hawkins Meredith , Vilcu Cristian , Rossetti Luciano , Shamoon Harry
Published: March 2007

Glucokinase (GK) is required for cellular glucose sensing, although there is a paucity of data regarding its role in the counterregulatory response to hypoglycemia in humans. Because fructose has been shown to modulate GK activity, we examined the effects of an acute infusion of fructose on hypoglycemia counterregulation in seven lean nondiabetic subjects. Using stepped hypoglycemia clamp studies (5.0, 4.4, 3.9, and 3.3 mmol/l target plasma glucose steps, 50 min each), subjects were studied on two separate occasions, without (control) or with co-infusion of fructose (1.2 mg · kg−1 · min−1). Fructose induced a resetting of the glycemic thresholds for secretion of epinephrine (3.8 ± 0.1 mmol/l) and glucagon (3.9 ± 0.2 mmol/l) to higher plasma glucose concentrations (4.0 ± 0.1 mmol/l [P = 0.006] and 4.1 ± 0.1 mmol/l [P = 0.03], respectively). In addition, the magnitude of increase in epinephrine and glucagon concentrations was higher after administration of fructose (48 and 39%, respectively, P < 0.05 for both). The amplification of these hormonal responses was specific because plasma norepinephrine, growth hormone, and cortisol were comparable in both sets of studies. Endogenous glucose production, measured with [3-3H]glucose, increased by 47% (P < 0.05) in the fructose infusion studies compared with 14% (P = NS) in the control studies. In addition, glucose uptake was more suppressed with fructose infusion (by 33%, P < 0.05). In concert with these effects of fructose on glucose kinetics, average glucose infusion rate was markedly reduced in the fructose infusion studies during the 3.9-mmol/l glucose step (4.6 ± 0.9 vs. 7.4 ± 1.1 μmol · kg−1 · min−1, respectively, P = 0.03) and during the 3.3-mmol/l glucose step (0.5 ± 0.1 vs. 5.2 ± 1.2 μmol · kg−1 · min−1, respectively, P < 0.001), suggesting more potent glucose counterregulation and improved recovery from hypoglycemia with fructose infusion. We conclude that infusion of a catalytic dose of fructose amplifies the counterregulatory response to hypoglycemia by both increases in hormonal activation and augmentation of glucose counterregulation in humans.
Renal Perfusion and the Renal Hemodynamic Response to Blocking the Renin System in Diabetes
Authors: Lansang M. Cecilia , Hollenberg Norman K.
Published: March 2007

In three groups of subjects, those with type 2 diabetes and nephropathy, those with type 1 diabetes without nephropathy, and healthy volunteers subjected to short-term hyperglycemia, we observed a counterintuitive relationship. In all three groups, baseline renal plasma flow (RPF) was positively correlated with the RPF response to blocking the renin-angiotensin system (RAS). This seems paradoxical in that an opposite result would have been expected if angiotensin-dependent renal vasoconstriction was responsible for the renal vasodilator response to RAS blockade. This suggests a link between the renal vasodilator response, mediated by nitric oxide (NO), and the activation of the intrarenal RAS. The complex interrelationships between hyperglycemia, insulin, NO, and the RAS may result in phenotypes that indicate varying risk of diabetic nephropathy and underlying genetic polymorphisms.
Decreased Mitochondrial Proton Leak and Reduced Expression of Uncoupling Protein 3 in Skeletal Muscle of Obese Diet-Resistant Women
Authors: Harper Mary-Ellen , Dent Robert , Monemdjou Shadi , Bézaire Véronic , Van Wyck Lloyd , Wells George , Kavaslar Gul Nihan , Gauthier Andre , Tesson Frédérique , McPherson Ruth
Published: March 2007

Weight loss in response to caloric restriction is variable. Because skeletal muscle mitochondrial proton leak may account for a large proportion of resting metabolic rate, we compared proton leak in diet-resistant and diet-responsive overweight women and compared the expression and gene characteristics of uncoupling protein (UCP)2 and UCP3. Of 1,129 overweight women who completed the University of Ottawa Weight Management Clinic program, 353 met compliance criteria and were free of medical conditions that could affect weight loss. Subjects were ranked according to percent body weight loss during the first 6 weeks of a 900-kcal meal replacement protocol. The highest and lowest quintiles of weight loss were defined as diet responsive and diet resistant, respectively. After body weight had been stable for at least 10 weeks, 12 of 70 subjects from each group consented to muscle biopsy and blood sampling for determinations of proton leak, UCP mRNA expression, and genetic studies. Despite similar baseline weight and age, weight loss was 43% greater, mitochondrial proton leak-dependent (state 4) respiration was 51% higher (P = 0.0062), and expression of UCP3 mRNA abundance was 25% greater (P < 0.001) in diet-responsive than in diet-resistant subjects. There were no differences in UCP2 mRNA abundance. None of the known polymorphisms in UCP3 or its 5′ flanking sequence were associated with weight loss or UCP3 mRNA abundance. Thus, proton leak and the expression of UCP3 correlate with weight loss success and may be candidates for pharmacological regulation of fat oxidation in obese diet-resistant subjects.
Long-Term Treatment With Dipeptidyl Peptidase IV Inhibitor Improves Hepatic and Peripheral Insulin Sensitivity in the VDF Zucker Rat
Authors: Pospisilik John A. , Stafford Sara G. , Demuth Hans-Ulrich , McIntosh Christopher H.S. , Pederson Raymond A.
Published: March 2007

Upon release into circulation, the potent insulin secretagogues glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are rapidly cleaved and inactivated by the enzyme dipeptidyl peptidase IV (DP IV). Long-term administration of specific DP IV inhibitors, so as to enhance circulating active GIP and GLP-1 levels, has been shown to improve glucose tolerance and β-cell glucose responsiveness and to reduce hyperinsulinemia in the Vancouver diabetic fatty (VDF) rat model of type 2 diabetes. Using the VDF model, the current study was undertaken to examine the effects of long-term DP IV inhibitor treatment on insulin sensitivity. Euglycemic-hyperinsulinemic clamps were performed on two sets of conscious VDF rats treated with or without the DP IV inhibitor P32/98 (20 mg · kg−1 · day−1 for 12 weeks). The protocol consisted of three sequential 90-min periods with insulin infusion rates of 0, 5, and 15 mU · kg−1 · min−1 and included a constant infusion of [ 3H]glucose for measure of hepatic and peripheral insulin sensitivity. Relative to untreated littermates, the treated animals showed a left shift in the sensitivity of hepatic glucose output to insulin (average reduction ∼6 μmol · kg−1 · min−1) and a marked gain in peripheral responsiveness to insulin, with glucose disposal rates increasing 105 and 216% in response to the two insulin steps (versus 2 and 46% in controls). These results provide the first demonstration of improved hepatic and peripheral insulin sensitivity after DP IV inhibitor therapy, and coupled with apparent improvements in β-cell function, they offer strong support for the utility of these compounds in the treatment of diabetes.
The AGE Inhibitor Pyridoxamine Inhibits Development of Retinopathy in Experimental Diabetes
Authors: Stitt Alan , Gardiner Thomas A. , Anderson Nathan L. , Canning Paul , Frizzell Norma , Duffy Noel , Boyle Cliona , Januszewski Andrzej S. , Chachich Mark , Baynes John W. , Thorpe Suzanne R.
Published: March 2007

We examined the ability of pyridoxamine (PM), an inhibitor of formation of advanced glycation end products (AGEs) and lipoxidation end products (ALEs), to protect against diabetes-induced retinal vascular lesions. The effects of PM were compared with the antioxidants vitamin E (VE) and R-α-lipoic acid (LA) in streptozotocin-induced diabetic rats. Animals were given either PM (1 g/l drinking water), VE (2,000 IU/kg diet), or LA (0.05%/kg diet). After 29 weeks of diabetes, retinas were examined for pathogenic changes, alterations in extracellular matrix (ECM) gene expression, and accumulation of the immunoreactive AGE/ALE Nε-(carboxymethyl)lysine (CML). Acellular capillaries were increased more than threefold, accompanied by significant upregulation of laminin immunoreactivity in the retinal microvasculature. Diabetes also increased mRNA expression for fibronectin (2-fold), collagen IV (1.6-fold), and laminin β chain (2.6-fold) in untreated diabetic rats compared with nondiabetic rats. PM treatment protected against capillary drop-out and limited laminin protein upregulation and ECM mRNA expression and the increase in CML in the retinal vasculature. VE and LA failed to protect against retinal capillary closure and had inconsistent effects on diabetes-related upregulation of ECM mRNAs. These results indicate that the AGE/ALE inhibitor PM protected against a range of pathological changes in the diabetic retina and may be useful for treating diabetic retinopathy.
Cognitive Ability and Brain Structure in Type 1 Diabetes
Authors: Ferguson Stewart C. , Blane Annette , Perros Petros , McCrimmon Rory J. , Best Jonathan J.K. , Wardlaw Joanna , Deary Ian J. , Frier Brian M.
Published: March 2007

Type 1 diabetes is associated with chronic hyperglycemia and exposure to intermittent severe hypoglycemia. The long-term cerebral effects of these consequences of diabetes are ill defined. In this study, the history of preceding severe hypoglycemia and the presence of background retinopathy were examined in relation to cognitive ability (neuropsychological test battery) and brain structure (magnetic resonance imaging) in a cross-sectional evaluation of 74 young people with type 1 diabetes. Participants differed by their severe hypoglycemia exposure and degree of diabetic retinopathy and none had previous neuropsychological pathology. Severe hypoglycemia did not influence cognitive ability or brain structure. Background diabetic retinopathy was associated with small focal white-matter hyperintensities in the basal ganglia (33.3 vs. 4.7%, after correction for age, P = 0.005) and significant cognitive disadvantage, affecting fluid intelligence (P = 0.008, Eta2 = 0.14), information processing (P = 0.001, Eta2 = 0.22), and attention and concentration ability (P = 0.03, Eta2 = 0.09). In conclusion, recurrent exposure to severe hypoglycemia alone in young people with type 1 diabetes had no detrimental impact on brain structure or function over the duration of diabetes examined. Chronic hyperglycemia (inferred by the presence of background diabetic retinopathy) may affect brain structure and function.
NOD Congenic Mice Genetically Protected From Autoimmune Diabetes Remain Resistant to Transplantation Tolerance Induction
Authors: Pearson Todd , Markees Thomas G. , Wicker Linda S. , Serreze David V. , Peterson Laurence B. , Mordes John P. , Rossini Aldo A. , Greiner Dale L.
Published: March 2007

The loss of self-tolerance leading to autoimmune type 1 diabetes in the NOD mouse model involves at least 19 genetic loci. In addition to their genetic defects in self-tolerance, NOD mice resist peripheral transplantation tolerance induced by costimulation blockade using donor-specific transfusion and anti-CD154 antibody. Hypothesizing that these two abnormalities might be related, we investigated whether they could be uncoupled through a genetic approach. Diabetes-resistant NOD and C57BL/6 stocks congenic for various reciprocally introduced Idd loci were assessed for their ability to be tolerized. Surprisingly, in NOD congenic mice that are almost completely protected from diabetes, costimulation blockade failed to prolong skin allograft survival. In reciprocal C57BL/6 congenic mice with NOD-derived Idd loci, skin allograft survival was readily prolonged by costimulation blockade. These data indicate that single or multiple combinations of evaluated Idd loci that dramatically reduce diabetes frequency do not correct resistance to peripheral transplantation tolerance induced by costimulation blockade. We suggest that mechanisms controlling autoimmunity and transplantation tolerance in NOD mice are not completely overlapping and are potentially distinct, or that the genetic threshold for normalizing the transplantation tolerance defect is higher than that for preventing autoimmune diabetes.
T-Cell Compartments of Prediabetic NOD Mice
Authors: Berzins Stuart P. , Venanzi Emily S. , Benoist Christophe , Mathis Diane
Published: March 2007

Given the importance of the NOD mouse as a model of type 1 diabetes, there is a surprising lack of published information on the overall composition of the thymic and peripheral T-cell compartments. In this study, we revisited some earlier reports of T-cell abnormalities in this strain and examined a number of additional parameters to provide a global view of T-cells in prediabetic NOD mice. In some cases, we concur with past conclusions, but in other important areas, we find that NOD mice closely resemble nonautoimmune strains. Specifically, and contrary to published reports, the thymocyte subset distribution, the rate and composition of thymic export, and the composition of the peripheral T-cell pool, including the proportion of CD25+CD4+ T-cells, are essentially normal in prediabetic NOD mice. These factors are therefore unlikely to be involved in the loss of tolerance that leads to autoimmunity within this strain.
Accelerated Diabetes in Rat Insulin Promoter-Tumor Necrosis Factor-α Transgenic Nonobese Diabetic Mice Lacking Major Histocompatibility Class II Molecules
Authors: Rajagopalan Govindarajan , Kudva Yogish C. , Flavell Richard A. , David Chella S.
Published: March 2007

The major predisposing genetic component in type 1 diabetes maps to the major histocompatibility complex locus in both mice and humans. To verify the HLA class II association with disease pathogenesis, we adopted the transgenic approach. Expression of HLA-DQ8, the molecule showing the strongest association with human type 1 diabetes, in the diabetes-predisposing milieu of NOD mice in the absence of the endogenous class II molecule I-Ag7 did not render susceptibility to type 1 diabetes. To study if providing a local proinflammatory environment would lead to diabetes in these mice, Aβo.NOD.DQ8 were bred with C57BL/6 mice expressing tumor necrosis factor (TNF)-α in the β-cells of the islets of Langerhans. Surprisingly, although diabetes was evident in the F1 intercross expressing rat insulin promoter (RIP)-TNF, offspring lacking either endogenous or transgenic class II molecules developed accelerated diabetes with high frequency in both sexes. Moreover, expression of any functional class II molecule seemed to confer significant protection from diabetes in this model. Thus, neonatal expression of TNF-α in an islet-specific manner bypassed the requirement of CD4+ T-cells and resulted in diabetes that could be mediated by CD8+ T-cells. We also show for the first time that diabetes in NOD.RIP-TNF mice can occur independent of inheritance of NOD-derived idd1.
Increased Dietary Fat Promotes Islet Amyloid Formation and β-Cell Secretory Dysfunction in a Transgenic Mouse Model of Islet Amyloid
Authors: Hull Rebecca L. , Andrikopoulos Sofianos , Verchere C. Bruce , Vidal Josep , Wang Feng , Cnop Miriam , Prigeon Ronald L. , Kahn Steven E.
Published: March 2007

Transgenic mice expressing the amyloidogenic human islet amyloid polypeptide (hIAPP) in their islet β-cells are a model of islet amyloid formation as it occurs in type 2 diabetes. Our hIAPP transgenic mice developed islet amyloid when fed a breeder chow but not regular chow. Because the breeder chow contained increased amounts of fat, we hypothesized that increased dietary fat enhances islet amyloid formation. To test this hypothesis, we fed male hIAPP transgenic and nontransgenic control mice diets containing 15% (low fat), 30% (medium fat), or 45% (high fat) of calories derived from fat for 12 months, and we measured islet amyloid, islet endocrine cell composition, and β-cell function. Increased dietary fat in hIAPP transgenic mice was associated with a dose-dependent increase in both the prevalence (percentage of islets containing amyloid deposits; 34 ± 8, 45 ± 8, and 58 ± 10%, P < 0.05) and severity (percentage of islet area occupied by amyloid; 0.8 ± 0.5, 1.0 ± 0.5, and 4.6 ± 2.5%, P = 0.05) of islet amyloid. In addition, in these hIAPP transgenic mice, there was a dose-dependent decrease in the proportion of islet area comprising β-cells, with no significant change in islet size. In contrast, nontransgenic mice adapted to diet-induced obesity by increasing their islet size more than twofold. Increased dietary fat was associated with impaired insulin secretion in hIAPP transgenic (P = 0.05) but not nontransgenic mice. In summary, dietary fat enhances both the prevalence and severity of islet amyloid and leads to β-cell loss and impaired insulin secretion. Because both morphologic and functional defects are present in hIAPP transgenic mice, this would suggest that the effect of dietary fat to enhance islet amyloid formation might play a role in the pathogenesis of the islet lesion of type 2 diabetes in humans.
Pioglitazone Reduces Hepatic Fat Content and Augments Splanchnic Glucose Uptake in Patients With Type 2 Diabetes
Authors: Bajaj Mandeep , Suraamornkul Swangjit , Pratipanawatr Thongchai , Hardies Lou J. , Pratipanawatr Wilailak , Glass Leonard , Cersosimo Eugenio , Miyazaki Yoshinori , DeFronzo Ralph A.
Published: March 2007

The effect of pioglitazone on splanchnic glucose uptake (SGU), endogenous glucose production (EGP), and hepatic fat content was studied in 14 type 2 diabetic patients (age 50 ± 2 years, BMI 29.4 ± 1.1 kg/m2, HbA1c 7.8 ± 0.4%). Hepatic fat content (magnetic resonance spectroscopy) and SGU (oral glucose load- insulin clamp technique) were quantitated before and after pioglitazone (45 mg/day) therapy for 16 weeks. Subjects received a 7-h euglycemic insulin (100 mU · m−2 · min−1) clamp, and a 75-g oral glucose load was ingested 3 h after starting the insulin clamp. Following glucose ingestion, the steady-state glucose infusion rate during the insulin clamp was decreased appropriately to maintain euglycemia. SGU was calculated by subtracting the integrated decrease in glucose infusion rate during the 4 h after glucose ingestion from the ingested glucose load. 3-[3H]glucose was infused during the initial 3 h of the insulin clamp to determine rates of EGP and glucose disappearance (Rd). Pioglitazone reduced fasting plasma glucose (10.0 ± 0.7 to 7.5 ± 0.6 mmol/l, P < 0.001) and HbA1c (7.8 ± 0.4 to 6.7 ± 0.3%, P < 0.001) despite increased body weight (83 ± 3 to 86 ± 3 kg, P < 0.001). During the 3-h insulin clamp period before glucose ingestion, pioglitazone improved Rd (6.9 ± 0.5 vs. 5.2 ± 0.5 mg · kg−1 · min− 1, P < 0.001) and insulin-mediated suppression of EGP (0.21 ± 0.04 to 0.06 ± 0.02 mg · kg−1 · min−1, P < 0.01). Following pioglitazone treatment, hepatic fat content decreased from 19.6 ± 3.6 to 10.4 ± 2.1%, (P < 0.005), and SGU increased from 33.0 ± 2.8 to 46.2 ± 5.1% (P < 0.005). Pioglitazone treatment in type 2 diabetes 1) decreases hepatic fat content and improves insulin-mediated suppression of EGP and 2) augments splanchnic and peripheral tissue glucose uptake. Improved splanchnic/peripheral glucose uptake and enhanced suppression of EGP contribute to the improvement in glycemic control in patients with type 2 diabetes.
Prevalence and Characteristics of the Metabolic Syndrome in the San Antonio Heart and Framingham Offspring Studies
Authors: Meigs James B. , Wilson Peter W.F. , Nathan David M. , D’Agostino Ralph B. , Williams Ken , Haffner Steven M.
Published: March 2007

The metabolic syndrome may be a common phenotype increasing risk for type 2 diabetes and cardiovascular disease. We assessed the prevalence and characteristics of the metabolic syndrome among population-based samples of 3,224 white subjects attending Framingham Offspring Study (FOS) exam 5 (1991–1995) and 1,081 non-Hispanic white and 1,656 Mexican-American subjects attending the San Antonio Heart Study (SAHS) phase II follow-up exam (1992–1996). Subjects were ∼50% women, aged 30–79 years, without diabetes, and classified with the metabolic syndrome according to criteria for obesity, dyslipidemia, hyperglycemia, and hypertension proposed by the Third Report of the National Cholesterol Education Program’s Adult Treatment Panel (ATP III) or the World Health Organization (WHO). We used regression models to estimate rates across ethnic groups and to assess the association of the metabolic syndrome with insulin resistance and predicted 10-year coronary heart disease (CHD) risk. Among FOS white subjects, the age- and sex-adjusted prevalence of the metabolic syndrome was 24% by both ATP III and WHO criteria; among SAHS non-Hispanic white subjects, 23 and 21%, respectively; and among SAHS Mexican-American subjects, 31 and 30%. Rates were highest among Mexican-American women (ATP III, 33%) and lowest among white women (21%). Subjects with the metabolic syndrome by ATP III criteria had higher age-, sex-, and ethnicity-adjusted levels of fasting insulin (11.3 μU/ml), homeostasis model assessment of insulin resistance (2.7), and predicted CHD risk (11.8%) than those without the syndrome (5.9 μU/ml, 1.3, and 6.4%, respectively; all P = 0.0001); differences were similar using WHO criteria. We conclude that the metabolic syndrome typically affects 20–30% of middle-aged adults in the U.S. By any criteria, subjects with the metabolic syndrome are more insulin resistant and at increased predicted risk for CHD versus those without the metabolic syndrome.
Neurotrophin-3 Prevents the Proximal Accumulation of Neurofilament Proteins in Sensory Neurons of Streptozocin-Induced Diabetic Rats
Authors: Sayers Nicola M. , Beswick Lisa J. , Middlemas Alicia , Calcutt Nigel A. , Mizisin Andrew P. , Tomlinson David R. , Fernyhough Paul
Published: March 2007

The relation between neurofilament expression and/or phosphorylation in the proximal versus distal components of the sensory peripheral neuraxis was studied and related to disorders in structure and function of the distal axon of streptozocin (STZ)-induced diabetic rats studied for 14 weeks. The ability of neurotrophin-3 (NT-3) to prevent abnormalities in neurofilament biology was also investigated. Compared with age-matched controls, neurofilament heavy (NF-H) (3.3-fold) and neurofilament medium (NF-M) (2.5-fold), but not neurofilament light (NF-L), subunits accumulated in the proximal axon of sensory neurons of the lumbar dorsal root ganglia (DRG) in untreated diabetic rats. Neurofilament accumulation was prevented by NT-3. Small- and large-diameter sensory neurons exhibited elevated levels of NF-H protein accumulation and phosphorylation in the DRG of untreated diabetic rats, levels that were ameliorated by NT-3. The sural nerve of untreated diabetic rats showed a 50% decrease in the levels of NF-H and NF-M, but not NF-L, subunits; NT-3 only partially normalized the defect in NF-M expression. These observations were associated with significant lowering of motor and sensory nerve conduction velocity but no alteration in the mean axonal diameter of myelinated axons in the sural nerve in untreated diabetic rats. It is proposed that the accumulation of NF-H and NF-M subunits in the proximal axon is an etiologic factor in the distal axon degeneration observed in diabetes.
Transplantation of Reversibly Immortalized Insulin-Secreting Human Hepatocytes Controls Diabetes in Pancreatectomized Pigs
Authors: Okitsu Teru , Kobayashi Naoya , Jun Hee-Sook , Shin Seungjin , Kim Su-Jin , Han Jaeseok , Kwon Hyokjoon , Sakaguchi Masakiyo , Totsugawa Toshinori , Kohara Michinori , Westerman Karen A. , Tanaka Noriaki , Leboulch Philippe , Yoon Ji-Won
Published: March 2007

Type 1 diabetes results from the destruction of insulin-producing pancreatic β-cells by a β-cell–specific autoimmune process. Although converting other cell types into insulin-producing cells may compensate for the loss of the β-cell mass while evading β-cell–specific T-cell responses, proof-of-principle of this approach in large animal models is lacking. This investigation was initiated to determine whether an insulin-producing human hepatocyte line can control diabetes when transplanted into totally pancreatectomized diabetic pigs. We established a reversibly immortalized human hepatocyte line, YOCK-13, by transferring a human telomerase reverse transcriptase cDNA and a drug-inducible Cre recombinase cassette, followed by cDNA for a modified insulin under the control of the l-type pyruvate kinase (l-PK) promoter. YOCK-13 cells produced small amounts of modified insulin and no detectable endogenous l-PK at low glucose concentrations, whereas they produced large amounts of both modified insulin and l-PK in response to high glucose concentrations. Xenotransplantation of YOCK-13 cells via the portal vein into immunosuppressed, totally pancreatectomized pigs decreased hyperglycemia and prolonged survival without adverse effects such as portal thrombosis, liver necrosis, pulmonary embolism, and tumor development. We suggest that this reversibly immortalized, insulin-secreting human hepatocyte line may overcome the shortage of donor pancreata for islet transplantation into patients with type 1 diabetes.
Elevations in Markers of Liver Injury and Risk of Type 2 Diabetes
Authors: Hanley Anthony J.G. , Williams Ken , Festa Andreas , Wagenknecht Lynne E. , D’Agostino Ralph B. , Kempf Judy , Zinman Bernard , Haffner Steven M.
Published: March 2007

A limited number of studies have reported associations of markers of liver injury, including elevated concentrations of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), with prospective risk of type 2 diabetes. However, only one study has adjusted for a detailed measure of insulin sensitivity (insulin sensitivity index [Si]), which is important given associations of obesity and Si with nonalcoholic fatty liver disease (NAFLD). Our objective was to investigate the associations of elevated AST and ALT with incident type 2 diabetes among 906 participants in the Insulin Resistance Atherosclerosis Study who were nondiabetic at baseline. Si and acute insulin response (AIR) were measured directly from the frequently sampled intravenous glucose tolerance test among black, Hispanic, and non-Hispanic white participants aged 40–69 years. After 5.2 years, 148 individuals had developed type 2 diabetes. Baseline AST and ALT were positively correlated with fasting insulin (r = 0.22 and r = 0.35, respectively), waist circumference (r = 0.18 and r = 0.34), and fasting glucose (r = 0.13 and r = 0.29) and inversely with Si (r = −0.18 and r = −0.30; all P < 0.0001). In separate logistic regression models adjusting for age, sex, ethnicity, clinical center, and alcohol consumption, participants in the highest quartiles (Q4) of AST and ALT were at significantly increased risk of incident type 2 diabetes compared with those in the lowest three quartiles (Q1–Q3): AST: odds ratio (OR) 1.73 (95% CI 1.17–2.57); ALT: OR 2.32 (1.36–3.75). After further adjustment for smoking, waist circumference, triglyceride, HDL, impaired glucose tolerance, Si, and AIR, both AST and ALT remained significantly associated with incident type 2 diabetes: AST, Q4 vs. Q1–Q3: OR 1.98 (1.23–3.17); ALT, Q4 vs. Q1–Q3: OR 2.00 (1.22–3.28). There were no interactions of sex, ethnicity, obesity, impaired glucose tolerance, or Si with AST or ALT in the prediction of type 2 diabetes. When entered into the same model with adjustment for demographic variables, both C-reactive protein and ALT independently predicted type 2 diabetes. In addition, AST and ALT were positively associated with incident type 2 diabetes after excluding former and moderate to heavy drinkers. In conclusion, AST and ALT independently predict type 2 diabetes. Baseline elevations of these markers may reflect NAFLD or related pathologies.
Regulation of Peroxisome Proliferator–Activated Receptor-γ Activity by Mammalian Target of Rapamycin and Amino Acids in Adipogenesis
Authors: Kim Jae Eun , Chen Jie
Published: March 2007

Adipocyte differentiation is a developmental process that is critical for metabolic homeostasis and nutrient signaling. The mammalian target of rapamycin (mTOR) mediates nutrient signaling to regulate cell growth, proliferation, and diverse cellular differentiation. It has been reported that rapamycin, the inhibitor of mTOR and an immunosuppressant, blocks adipocyte differentiation, but the mechanism underlying this phenomenon remains unknown. Here we show that mTOR plays a critical role in 3T3-L1 preadipocyte differentiation and that mTOR kinase activity is required for this process. Rapamycin specifically disrupted the positive transcriptional feedback loop between CCAAT/enhancer-binding protein-α and peroxisome proliferator–activated receptor-γ (PPAR-γ), two key transcription factors in adipogenesis, by directly targeting the transactivation activity of PPAR-γ. In addition, we demonstrate for the first time that PPAR-γ activity is dependent on amino acid sufficiency, revealing a molecular link between nutrient status and adipogenesis. The results of our further investigation have led us to propose a model in which the mTOR pathway and the phosphatidylinositol 3-kinase/Akt pathway act in parallel to regulate PPAR-γ activation during adipogenesis by mediating nutrient availability and insulin signals, respectively. It is interesting that troglitazone (a thiazolidinedione drug) reversed the inhibitory effects of rapamycin and amino acid deprivation, implicating therapeutic values of thiazolidinedione drugs to counter certain side effects of rapamycin as an immunosuppressant.