bluuebunny/crossref_metadata_2025 huggingface dataset:
Both Subcutaneously and Intravenously Administered Glucagon-Like Peptide I Are Rapidly Degraded From the NH2-Terminus in Type II Diabetic Patients and in Healthy Subjects
Authors: Deacon Carolyn F , Nauck Michael A , Toft-Nielsen Maibritt , Pridal Lone , Willms Berend , Holst Jens J
Published: September 2013

To fate of exogenous glucagon-like peptide I (GLP-I)(7–36) amide was studied in nondiabetic and type II diabetic subjects using a combination of high-pressure liquid chromatography (HPLC), specific radioimmunoassays (RIAs), and a sensitive enzyme-linked immunosorbent assay (ELISA), whereby intact biologically active GLP-I and its metabolites could be determined. After GLP-I administration, the intact peptide could be measured using an NH2-terminally directed RIA or ELISA,while the difference in concentration between these assays and a COOH-terminal–specific RIA allowed determination of NH2-terminally truncated metabolites. Subcutaneous GLP-I was rapidlydegraded in a time-dependent manner, forming a metabolite, which co-eluted on HPLC with GLP-I(9–36) amide and had the same immunoreactive profile. Thirty minutes after subcutaneous GLP-I administration to diabetic patients (n = 8), the metabolite accounted for 88.5 ± 1.9% of the increase in plasma immunoreactivity determined by the COOH-terminal RIA, which was higher than the levels measured in healthy subjects (78.4 ± 3.2%; n = 8; P < 0.05). Intravenously infused GLP-I was also extensively degraded, but no significant differences were seen between the two groups. Intact GLP-I accounted for only 19.9 ± 3.4% of the increase in immunoreactivity measured with the COOH-terminal RIA in normal subjects (n = 8), and 25.0 ± 4.8% of the increase in diabetic subjects (n = 8), the remainder being the NH2-terminally truncated metabolite.
Effect of Prostaglandin E2 and Hyaluronan on Mesangial Cell Proliferation: A Potential Contribution to Glomerular Hypercellularity in Diabetes
Authors: Mahadevan Padmavathi , Larkins Richard G , Fraser J Robert E , Dunlop Marjorie E
Published: September 2013

Proliferation of mesangial cells is a feature of several forms of human and experimental glomerulopathy, including that seen in diabetes. The nonsulfated glycosaminoglycan hyaluronan participates in the regulation of pericellular matrix assembly and is a mitogen in some cell types. We have shown previously that hyaluronan production is increased in the glomerulus in a glucose- and prostaglandin-dependent manner. We have investigated the effect of diabetes and of addition of hyaluronan and prostaglandin E2 (PGE2) on the uptake of [3H]thymidine by glomerular core preparations enriched in mesangial cells. When compared with nondiabetic controls, it was shown that [3H]thymidine uptake was significantly increased in glomerular core preparations from streptozotocin-induced diabetic rats (to 169 ± 5%, P < 0.001). In glomerular cores from both experimental groups, hyaluronan (50–250 ng/ml) or PGE2 (10−12 to 10−8 mol/l) increased the uptake of [3H]thymidine. Further, mesangial cells from nondiabetic control glomerular cores, when maintained in culture in early passage, responded with increased [3H]thymidine uptake to raised glucose (5.6–25 mmol/l) and to added hyaluronan and PGE2. We propose that prostaglandin and hyaluronan production in response to a raised glucose environment in diabetes can contribute to mesangial hypercellularity.
Effect of Puberty on Markers of Glomerular Hypertrophy and Hypertension in IDDM
Authors: Lawson Margaret L , Sochett Etienne B , Chait Peter G , Balfe J Williamson , Daneman Denis
Published: September 2013

Epidemiological data implicate puberty as a factor in the initiation of diabetic nephropathy. However, the mechanism remains unclear. We hypothesized that puberty would result in an increase in glomerular hypertrophy and hypertension; these two early concomitant events are seen as pivotal to the pathophysiology of diabetic nephropathy. We studied the effect of pubertal duration on three surrogate markers of glomerular hypertrophy/hypertension: kidney volume (KV), microalbuminuria (MA), and Na-Li countertransport (CT). We recruited 177 subjects (87 female and 90 male; aged 6.2–22.1 years) with IDDM of 5 to 10 years' duration (6.8 ± 1.6 years) into three groups with different pubertal duration: prepubertal since IDDM diagnosis; prepubertal at diagnosis, now pubertal; or early puberty at diagnosis, now postpubertal. KV was measured by ultrasound and corrected for body surface area; MA was defined as urinary albumin excretion of 15–200 μg/min in two of three 24-h samples, and Na-Li CT was measured in erythrocytes. As pubertal duration increased, there was a disproportionate increase in mean KV (prepubertal, 247 ± 6 [SE] ml/1.73 m2; pubertal, 282 ± 7/1.73 m2; postpubertal, 295 ± 7/1.73 m2 P = 0.001), prevalence of nephromegaly (KV > 300 ml/1.73 m2) (14, 31, and 45%, respectively, P = 0.001), and prevalence of MA (0, 9.7, and 20.5%, respectively, P = 0.003). Subjects with KV > 300 ml/1.73 m2 were eight times more likely to have MA than those with KV <300 (odds ratio 8.1, 95% confidence interval 2.4–27.4, P = 0.0001). There was no effect of pubertal duration on Na-Li CT. Multiple regression with KV as the dependent variable found an association with pubertal duration, MA, Na-Li CT, and current HbA1c (P < 0.0001). Our findings indicate that pubertal duration is an important determinant of both KV and MA and suggest that nephromegaly precedes microalbuminuria. We postulate that these effects are attributable to the influence of the pubertal milieu on glomerular hypertrophy/hypertension.
The Antihyperglycemic Agent Englitazone Prevents the Defect in Glucose Transport in Rats Fed a High-Fat Diet
Authors: Stevenson Ralph W , McPherson R Kirk , Persson Lorna M , Genereux Paul E , Swick Andrew G , Spitzer Josephine , Herbst John J , Andrews Kim M , Kreutter David K , Gibbs E Michael
Published: September 2013

The effects of englitazone in male Wistar rats fed a high-fat diet (59% of calories as fat) were compared with control rats fed a high-carbohydrate diet (69% of calories as carbohydrate) (5–15 animals per group). Insulin-stimulated (17 nmol/l) 2-deoxy-D-glucose (2-DG) uptake was inhibited 31% in adipocytes isolated from rats on the high-fat diet for 3 weeks, but englitazone (50 mg/kg for the last 7 days) normalized the response. There was a selective decrease in GLUT4 (54 ± 5% of high-carbohydrate) in epididymal fat from rats on the high-fat diet for 3 weeks, but englitazone treatment did not reverse the defect in GLUT4 (43 ± 8% of high-carbohydrate) or increase GLUT1 (81 ± 12% of high-carbohydrate). Englitazone normalized oral glucose (1 g/kg body wt) intolerance and excessive (210% of high-carbohydrate) liver glycogen deposition (from [14C]glucose) caused by the high-fat diet. The high-fat diet tended to decrease insulin receptor substrate-1 (IRS-1) and phosphatidylinositol-3′-kinase (PI-3-kinase) expression in epididymal fat (26% decrease; P < 0.1). Englitazone did not reverse this decrease in IRS-1 and PI-3-kinase levels in fat from high-fat-fed rats (there was a further 25–30% decrease, P < 0.05), nor did it increase PI-3-kinase activity in 3T3-L1 adipocytes under conditions (48 h incubation) where it stimulated 2-DG uptake sixfold or enhanced insulin-stimulated 2-DG uptake. In summary, englitazone prevented the insulin resistance associated with a high-fat diet, but the mechanism of action does not involve changes in fat or muscle glucose transporter content and may not involve activation of the insulin signaling pathway via PI-3-kinase.
The Coupling of Glucose Metabolism and Perfusion in Human Skeletal Muscle: The Potential Role of Endothelium-Derived Nitric Oxide
Authors: Baron Alain D
Published: September 2013

Insulin-mediated glucose metabolism in skeletal muscle is associated with a commensurate increase in muscle perfusion. The link between insulin action and vasodilation may be mediated by endothelium-derived nitric oxide (EDNO). The evidence suggests that insulin causes an increase in the production of EDNO in insulin-sensitive but not insulin-resistant subjects. This defect in insulinmediated vasodilation may contribute to 1) enhanced presser sensitivity and 2) reduced rates of insulin-mediated glucose uptake. We propose that the endothelium is an insulin target tissue that exhibits an increase in the release of EDNO in response to insulin. We postulate that the insulin-resistant state of obesity is associated with insulin resistance at the level of the endothelium, reduced EDNO release, and impaired vasodilation. Thus EDNO may act as the mediator coupling glucose metabolism to vasodilation. The interaction between insulin and the endothelium to enhance EDNO release describes a novel insulin action that deserves further exploration.
Modulation of Insulin Receptor Signaling: Potential Mechanisms of a Cross Talk Between Bradykinin and the Insulin Receptor
Authors: Häring HU , Tippmer S , Kellerer M , Mosthaf L , Kroder G , Bossenmaier B , Berti L
Published: September 2013

Insulin resistance of the skeletal muscle plays a key role in the development of the metabolic endocrine syndrome and its further progression to type II diabetes. Impaired signaling from the insulin receptor to the glucose transport system and to glycogen synthase is thought to be the cause of skeletal muscle insulin resistance. An incomplete activation of the insulin receptor tyrosine kinase, which is found in type II diabetes, appears to contribute to the pathogenesis of the signaling defect. Available data suggest that the impaired tyrosine kinase function of the insulin receptor is not due to an inherited defect but rather is caused by a modulation of insulin receptor function. We used rat-1 fibroblasto and NIH-3T3 cells stably overexpressing human insulin receptor and 293 cells transiently overexpressing human insulin receptor to characterize conditions modulating the signaling function of the insulin receptor kinase. Using these cell models, we could demonstrate that activation of different protein kinase C (PKC) isoforms by high glucose levels or phorbol esters causes a rapid inhibition of the receptor tyrosine kinase activity. This effect is most likely mediated through serine phosphorylation of the receptor β-subunit. It can be prevented by PKC inhibitors and the new oral antidiabetic agent thiazolidindione. The data suggest that PKC might be an important negative regulator of insulin receptor function. Because we have recently shown that bradykinin activates different isoforms of PKC in these cell types, an inhibitory cross talk between the bradykinin receptor and the insulin receptor through PKC activation seemed possible. However, we were unable to observe an insulin receptor tyrosine kinase inhibition through bradykinin, suggesting that different isoforms of PKC are activated by hyperglycemia and bradykinin. On the other hand, a modulation of bradykinin signals by insulin could be demonstrated in these cells. Bradykinin-induced tyrosine phosphorylation of proteins of ∼130 and 70 kDa was inhibited by insulin treatment of rat-1 flbroblasts. These data suggest that signals from the insulin receptor modify signaling from the bradykinin receptor to tyrosine phosphorylation of different cellular proteins.
Kallikreins and Kinins: Molecular Characteristics and Cellular and Tissue Responses
Authors: Margolius Harry S
Published: September 2013

Kallikrein-kininogen-kinin systems are now topics of widespread interest. The long-standing appreciation of their diverse pharmacological properties and biochemical characteristics is being supplemented by modern definitions of their cellular receptors' signal-transduction mechanisms and physiological and pathological roles. The assignment of important homeostatic responsibilities for kinins, including those in autocrine and paracrine signaling for skeletal and cardiac muscle energy metabolism, is now subject to definitive experimental evaluation via the availability of better kallikrein inhibitors, specific kinin receptor antagonists, and techniques of genetic manipulation.
Immunolocalization of Bradykinin B2 Receptors on Skeletal Muscle Cells
Authors: Figueroa Carlos D , Dietze Günther , Müller-Esterl Werner
Published: September 2013

The kallikrein-kinin system has been implicated in the inflammatory process, blood pressure regulation, renal homeostasis, and glucose utilization. The effects of kallikrein and kinin on glucose uptake by the skeletal muscle are well established; however, the occurrence and the cellular distribution of the kinin receptor(s) mediating these effects in the striated muscle are unknown. Using anti-peptide antibodies raised against the predicted intra- and extracellular domains of the B2 receptor and the peroxidase/antiperoxidase system, we have been able to detect the B2 receptor on the plasma membrane of striated skeletal muscle cells of the rat hindlimb. A strong immunostaining appeared as a rim of immunoreactive material located on the periphery of striated muscle cells. Cross-sectioned and longitudinally sectioned cells revealed a similar staining pattern. Alternatively, the immunostaining with specific antibodies to tissue kallikrein and to T-kininogen did not yield a significant staining of the striated muscle cells. Localization of the B2 receptor on the surface of striated muscle cells provides a structural basis for the hypothesized physiological functions of the kinin system in the skeletal muscle.
B2 Bradykinin Receptors in Cultured Neonatal Rat Cardiomyocytes Mediate a Negative Chronotropic and Negative Inotropic Response
Authors: Kasel Albert M , Fauβner Alexander , Pfeifer Alexander , Müller Ursula , Werdan Karl , Roscher Adelbert A
Published: September 2013

Receptors for bradykinin (BK) were characterized in primary cultures of beating neonatal rat cardiomyocytes using [3H]BK as radioligand. Degradation studies demonstrated that [3H]BK was stable for at least 2 h when incubated with cardiomyocytes at 2 and 37°C in the presence of bacitracin in combination with captopril or ramiprilat. Without these inhibitors, >80% of the [3H]BK was degraded within 2 h at 37°C. This indicates that angiotensin-converting enzyme (ACE) is responsible for the main BK-degrading activity in cardiomyocytes. Scat-chard plots were linear and gave a Kd of 1.5 ± 0.8 nmol/1 (mean ± SD, n = 4) and a maximum binding capacity of 55–125 fmol/mg protein. Association and dissociation studies showed that binding of [3H]BK was saturable and reversible. Binding of [3H]BK at 37°C led to internaliza-tion of the ligand. Competition studies with B1 and B2agonists and antagonists were consistent with a B2 subtype of receptor. Addition of BK to beating cardiomyocytes (>1 nmol/1) at 37°C gave a strong but transient negative chronotropic effect. This response was paralleled by changes in the pulsation amplitude, which indicated a simultaneous negative inotropic effect of BK. These results provide a basis for the hypothesis that ACE inhibition exerts its cardioprotective effect at the level of a population of cardiomyocytes by virtue of kinin receptor-mediated mechanisms.
Inhibition of Angiotensin Type 1 Receptor Prevents Decline of Glucose Transporter (GLUT4) in Diabetic Rat Heart
Authors: Hoenack Carsten , Roesen Peter
Published: September 2013

There is some evidence that inhibition of angiotensinconverting enzyme (ACE) activity can improve the uptake and conversion of glucose by heart and skeletal muscle in diabetes. To study the underlying mechanisms, we treated streptozotocin-induced diabetic rats with the angiotensin type 1 receptor (AT1) antagonist ICI D8731 and the ACE inhibitor fosinopril for 4 months and determined the expression of the myocardial glucose transporter proteins. In diabetic rats, the expression of the insulin-regulated glucose transporter (GLUT4) was strongly diminished as shown by Western and Northern blots. ICI D8731 prevented the decrease of GLUT4 protein in diabetes but had no influence on the amount of mRNA encoding for GLUT1 and GLUT4. GLUT1 protein was hardly detected in the rat heart and was affected neither by diabetes nor by treatment with the AT1 antagonist. Additionally, ICI D8731 influenced the translocation of GLUT4 from the intracellular pool to the plasma membrane, because treatment increased the amount of GLUT4 protein in the plasma membranes as well as in intracellular membrane fractions compared with membranes of untreated diabetic control rats. In contrast, inhibition of ACE by fosinopril influenced neither the expression nor the translocation of the glucose transporter proteins. These observations indicate that angiotensin II has a distinct influence on the posttranscriptional regulation of the GLUT4 transporter protein, presumably indirectly as a consequence of hemodynamic effects and structural alterations of the vessel wall.
Glucosamine-Induced Inhibition of Liver Glucokinase Impairs the Ability of Hyperglycemia to Suppress Endogenous Glucose Production
Authors: Barzilai Nir , Hawkins Meredith , Angelov Ivo , Hu Meizhu , Rossetti Luciano
Published: September 2013

Although the kinetic characteristics of hepatic glucokinase (GK) suggest its potential role as the hepatic “glucose sensor,” its impact on the regulation of in vivo hepatic glucose production (HGP) is still controversial. Since decreased GK activity has been linked to experimental and human diabetes, we examined whether a moderate and transient inhibition of GK activity diminishes the ability of hyperglycemia to suppress HGP. We first determined the concentration of the competitive inhibitor, glucosamine (GlcN), which decreases hepatic GK activity by ∼ 60% in vitro. GlcN was then infused into conscious rats to achieve a similar inhibition of the in vivo GK activity (plasma GlcN levels = ∼ 2 mmol/l; rats infused with saline served as control, n = 20). To maintain equal plasma insulin and glucagon concentrations throughout the studies, somatostatin and insulin (basal replacement) were infused for 4 h. [3-(3H)]-glucose and [U-(14C)]-lactate were infused to measure HGP, gluconeogenesis, and glucose cycling (GC) during 2 h of euglycemia (glucose ∼ 8 mmol/l) followed by 2 h of hyperglycemia (glucose ∼ 18 mmol/l). Our results support the notion that hepatic GK activity is indeed decreased by GlcN in vivo. In fact, in response to hyperglycemia the “direct” pathway of hepatic glucose-6-phosphate (G-6-P) formation was ∼ 40% lower with GlcN compared with saline infusion (37 ± 3 vs. 63 ± 3%; P < 0.001). Furthermore, while hyperglycemia stimulated GC by ∼ 2.5-fold during saline infusion (from 3.0 ± 0.6 to 7.7 ± 1.4 mg.kg−1 · min−1, P < 0.001, euglycemia vs. hyperglycemia), this increase was blunted in the presence of GlcN (4.6 ± 0.6 mg.kg−1 · min−1, P = NS). Finally, in the presence of GlcN, the hepatic concentration of G-6-P was decreased by ∼ 40% compared with saline (234 ± 38 and 390 ± 24 nmol/g, P < 0.01). During the euglycemic studies, HGP was similar (12.6 ± 0.6 and 11.3 ± 0.2 mg .kg−1 · min−1 with GlcN or saline infusion, respectively). However, while hyperglycemia per se suppressed HGP by ∼ 65%, HGP was inhibited by ∼ 38% and it was ∼ twofold higher than in the saline-infused rats (7.8 ± 0.8 and 4.0 ± 0.3 mg.kg−1 · min−1, P < 0.01) in the presence of GlcN-induced inhibition of hepatic GK. This increase in HGP was largely accounted for by the decreased inhibition of hepatic net glycogenolysis by hyperglycemia (3.3 ± 0.8 and 1.1 ± 0.3 mg.kg−1 · min−1 with GlcN or saline infusion, respectively, P < 0.01). We conclude that intact GK activity is required for the normal suppression of HGP by hyperglycemia and its impairment may contribute to increased HGP in experimental and human diabetes.
Supraphysiological Hyperinsulinemia Increases Plasma Leptin Concentrations After 4 h in Normal Subjects
Authors: Utriainen Tapio , Malmström Raija , Mäkimattila Sari , Yki-Järvinen Hannele
Published: September 2013

In rodents, food intake and insulin increase ob gene expression and circulating leptin concentrations, but it is unknown whether insulin regulates plasma leptin concentrations in humans. We measured plasma leptin concentrations in 27 normal subjects (16 men, 11 women; age, 24 ± 1 years; BMI, 22.6 ± 0.5 kg/m2; body fat, 18 ± 1%) during a 6-h euglycemic hyperinsulinemic clamp (sequential insulin infusions of 1, 2, and 5 mU.kg−1 · min−1 for 2 h each). During these insulin infusions, plasma leptin increased from a basal concentration of 7.4 ± 1.6 ng/ml by -2 ± 2, 17 ± 4, and 50 ± 6% to 7.2 ± 1.5 (NS vs. basal), 8.5 ± 1.7 (P < 0.001), and 10.4 ± 2.0 ng/ml (P < 0.001), respectively. Of the subjects, eight also participated in a control study where saline was infused for 6 h. In these subjects, plasma leptin increased by 5 ± 4, 26 ± 10, and 62 ± 10% during the insulin infusions, and decreased by 9 ± 4 (P = 0.07 for change during saline vs. insulin), 13 ± 4 (P < 0.01), and 17 ± 4% (P < 0.001) after 2, 4, and 6 h of the saline infusion, respectively. Women had higher plasma leptin concentrations basally and during hyperinsulinemia (P < 0.001) than men, but this difference was entirely accounted for by greater adiposity in women (22 ± 2 vs. 14 ± 1%, P < 0.001). These data provide evidence for the insulin regulation of plasma leptin concentrations in humans. This effect requires hours of high insulin concentrations, implying that postprandial satiety is not regulated via changes in plasma leptin concentrations. Insulin may, however, be of importance in the long-term or diurnal regulation of plasma leptin concentrations.
The ApoB-100 Gene EcoRI Polymorphism Influences the Relationship Between Features of the Insulin Resistance Syndrome and the Hyper-ApoB and Dense LDL Phenotype in Men
Authors: Vohl Marie-Claude , Tchernof André , Dionne France T , Moorjani Sital , Prud'homme Denis , Bouchard Claude , Nadeau André , Lupien Paul J , Després Jean-Pierre
Published: September 2013

The aim of this study was to investigate whether the EcoRI polymorphism of the apolipoprotein B (apoB) gene influences the relationships between features of the insulin resistance syndrome and the dense LDL phenotype and apoB concentrations. A sample of 65 men was divided into two groups on the basis of the EcoRI genotype. Forty-four subjects were (+/+) homozygotes for the presence of the EcoRI restriction site that is associated with a glutamic acid at codon 4154. Twenty-one men were (+/−) heterozygotes for the absence of the restriction site resulting from a glutamic acid to a lysine substitution at codon 4154. In the (+/−) group, fasting plasma FFA levels were positively correlated with plasma apoB, LDL-apoB, and the LDL particle score that was calculated from the migration distances of LDL subspecies and their relative band intensities, reflecting the proportion of small dense LDL particles. However, these associations were not found among (+/+) subjects. The two genotypic groups were further divided into two subgroups on the basis of fasting FFA concentrations, and the LDL particle score and the LDL-apoB levels were compared. High FFA levels were associated with a higher proportion of small dense LDL particles, as reflected by a higher mean LDL particle score, irrespective of the genotype. However, the apoB-EcoRI polymorphism appeared to influence the association between high FFA levels and LDL-apoB concentrations because (+/−) heterozygotes with high FFA levels had higher LDL-apoB concentrations than (+/−) heterozygotes with low FFA levels. In addition, the integrated area under the curve of plasma insulin concentrations, measured in response to a 75-g oral glucose challenge, and the amount of visceral adipose tissue, measured by computed tomography, were positively associated with the LDL particle score only in (+/−) heterozygotes. When subjects were divided on the basis of insulin area (low vs. high) or visceral adipose tissue (low vs. high), (+/−) heterozygotes with high insulin area or with high levels of visceral adipose tissue had a higher mean LDL particle score than (+/−) heterozygotes with low insulin area or low visceral adipose tissue. However, among (+/+) homozygotes, low or high levels of insulin or visceral adipose tissue could not discriminate between men with large or small LDL particles. Therefore, (+/−) heterozygotes may be more susceptible to develop the dense LDL phenotype in presence of hyperinsulinemia and visceral obesity. Results of the present study suggest that the apoB-EcoRI polymorphism may exacerbate the alterations in the LDL particle (size and concentration) found among visceral obese-hyperinsulinemic men.
Pregnant Diabetic Rats Fed the Antioxidant Butylated Hydroxytoluene Show Decreased Occurrence of Malformations in Offspring
Authors: Eriksson Ulf J , Simán C Martin
Published: September 2013

The increased incidence of congenital malformations in diabetic pregnancy may be associated with an excess of free oxygen radicals in the embryo. We have previously blocked the dysmorphogenesis of rat embryos exposed to high glucose and β-hydroxybutyrate concentrations in vitro by increasing the antioxidant capacity of the conceptus. In the present study, we attempted to diminish the teratogenic process in vivo in a rat model of diabetic pregnancy. Thus, pregnant diabetic and normal rats were fed either a standard diet or a diet enriched with 1% of the antioxidant butylated hydroxytoluene (BHT). The fetuses of the diabetic rats were smaller than the fetuses of the normal rats (body weight 2.70 g vs. 3.68 g) when the mothers were fed a standard diet. The BHT diet increased the fetal weight in the offspring of diabetic rats (3.17 g), with no change in fetuses of the normal rats (3.65 g). The placentas of diabetic rats were heavier than the placentas of normal rats; this difference was not present in the BHT-fed rats. The BHT treatment had no effect on the rate of resorptions, which was increased in the diabetic rats compared with the normal rats. In contrast, the increased rate of congenital malformations in the offspring of diabetic rats (19%), compared with that in the normal rats (0%), was markedly decreased by the BHT diet (2.3%). No malformations were found in the normal rats treated with BHT. These data support the notion that an excess of free oxygen radicals in the embryo contributes to the teratogenic process of diabetic pregnancy and, thus, suggest an area for future preventive therapeutic treatment.
Altered Insulin Secretory Responses to Glucose in Diabetic and Nondiabetic Subjects With Mutations in the Diabetes Susceptibility Gene MODY3 on Chromosome 12
Authors: Byrne Maria M , Sturis Jeppe , Menzel Stephan , Yamagata Kazuya , Fajans Stefan S , Dronsfield Mark J , Bain Stephen C , Hattersley Andrew T , Velho Gilberto , Froguel Phillipe , Bell Graeme I , Polonsky Kenneth S
Published: September 2013

One form of maturity-onset diabetes of the young (MODY) results from mutations in a gene, designated MODY3, located on chromosome 12 in band q24. The present study was undertaken to define the interactions between glucose and insulin secretion rate (ISR) in subjects with mutations in MODY3. Of the 13 MODY3 subjects, six subjects with normal fasting glucose and glycosylated hemoglobin and seven overtly diabetic subjects were studied as were six nondiabetic control subjects. Each subject received graded intravenous glucose infusions on two occasions separated by a 42-h continuous intravenous glucose infusion designed to prime the β-cell to secrete more insulin in response to glucose. ISRs were derived by deconvolution of peripheral C-peptide levels. Basal glucose levels were higher and insulin levels were lower in MODY3 subjects with diabetes compared with nondiabetic subjects or with normal healthy control subjects. In response to the graded glucose infusion, ISRs were significantly lower in the diabetic subjects over a broad range of glucose concentrations. ISRs in the nondiabetic MODY3 subjects were not significantly different from those of the control subjects at plasma glucose levels <8 mmol/l. As glucose rose above this level, however, the increase in insulin secretion in these subjects was significantly reduced. Administration of glucose by intravenous infusion for 42 h resulted in a significant increase in the amount of insulin secreted over the 5–9 mmol/l glucose concentration range in the control subjects and nondiabetic MODY3 subjects (by 38 and 35%, respectively), but no significant change was observed in the diabetic MODY3 subjects. In conclusion, in nondiabetic MODY3 subjects insulin secretion demonstrates a diminished ability to respond when blood glucose exceeds 8 mmol/l. The priming effect of glucose on insulin secretion is preserved. Thus, β-cell dysfunction is present before the onset of overt hyperglycemia in this form of MODY. The defect in insulin secretion in the nondiabetic MODY3 subjects differs from that reported previously in nondiabetic MODY1 or mildly diabetic MODY2 subjects.
Imidazoline Compounds Stimulate Insulin Release by Inhibition of KATP Channels and Interaction With the Exocytotic Machinery
Authors: Zaitsev Sergei V , Efanov Alexandre M , Efanova Ioulia B , Larsson Olof , Ostenson Claes-Göran , Gold Gerald , Berggren Per-Olof , Efendić Suad
Published: September 2013

A novel imidazoline compound, RX871024, was used to investigate the mechanisms by which imidazoline derivatives promote insulin secretion in rat pancreatic β-cells and HIT T15 cells. RX871024 stimulated insulin release from rat pancreatic β-cells and HIT T15 cells in a glucose-dependent way. This effect was not related to α2-adrenergic, I1-, and I2-imidazoline receptors. RX871024 promoted insulin release by at least two modes of action. One included an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i), subsequent to blocking of ATP-dependent K+ channels, membrane depolarization, and activation of voltage-dependent Ca2+ channels. The other, a more distal effect of imidazoline, affected the exocytotic machinery and was unrelated to changes in membrane potential and [Ca2+]i. The mechanism of RX871024-induced insulin release was dependent on protein kinases A and C. The sensitizing effect of a low dose of RX871024 on glucose-induced insulin secretion suggests that imidazoline compounds of this kind may constitute the basis for development of a new class of oral hypoglycemic agents.
Low Mitochondrial Glycerol Phosphate Dehydrogenase and Pyruvate Carboxylase in Pancreatic Islets of Zucker Diabetic Fatty Rats
Authors: MacDonald Michael J , Tang Jiping , Polonsky Kenneth S
Published: September 2013

The enzyme activities of mitochondrial glycerol phosphate dehydrogenase (mGPD) (EC 1.1.99.5) and pyruvate carboxylase (PC) (EC 6.4.1.1) have been reported to be low in the pancreatic islet of several rodent models of NIDDM. The present study was undertaken to discern whether mGPD is abnormal in the Zucker diabetic fatty (ZDF) rat (ZDF/Gmi-fa/fa), an animal model of NIDDM in which insulin secretion is unable to counteract the insulin resistance associated with the obesity that characterizes this model. Experiments were performed in prediabetic 6-week-old ZDF rats in comparison with 12-week-old overtly hyperglycemic animals and, as controls, Zucker lean (ZL) rats (ZDF/Gmi-+/fa or -+/+) and Wistar rats (+/+) of the same ages. The enzyme activity of mGPD was 32 and 18% of normal in islets of 6- and 12-week-old ZDF rats, respectively (P < 0.001 by analysis of variance). The activity of PC, which like mGPD is relatively abundant in the pancreatic islet, was 17 and 10% of normal in the islets of 6- and 12-week-old ZDF rats, respectively (P < 0.001). The activity of mGPD was normal in islets from ZL rats. However, PC activity was slightly lower in islets of 6- (51% of normal, P = 0.007) and 12-week-old (67% of normal, P = 0.01) ZL rats. The amounts of mGPD protein, as judged from Western analysis, and of PC protein, as judged from probing transblots with streptavidin that binds to biotin-containing enzymes, roughly correlated with the enzyme activities. This indicates that the decreased enzyme activities are caused by the decreased net synthesis of these enzymes rather than by the decreased activity of a normal amount of enzyme. The enzyme activity of succinate dehydrogenase, a control for mGPD, was normal in the ZL and ZDF rats. An incidental finding of the current study was the discovery of beta-methylcrotonyl-CoA carboxylase and propionyl-CoA carboxylase in the islet. Levels of these enzymes were also normal. Although reductions in mGPD and PC may contribute to the abnormal insulin secretion present in overt diabetes, they are modest compared with the severe reductions seen in inherited inborn errors of metabolism. Because of this and because more than a single enzyme is affected and the enzymes in the islet are diminished in more than one rodent model of NIDDM, these reductions are unlikely to represent the primary genetic defect in the ZDF rat. Since ZDF rats are euglycemic at 6 weeks of age and ZL animals are euglycemic throughout life and since these animals demonstrate low enzyme activities, this evidence suggests that it is not hyperglycemia but rather some other component of the diabetic syndrome that is responsible for the reductions in these enzymes.
Leptin: A Significant Indicator of Total Body Fat but Not of Visceral Fat and Insulin Insensitivity in African-American Women
Authors: Dua Arnavaz , Hennes Magda I , Hoffmann Raymond G , Maas Diana L , Krakower Glenn R , Sonnenberg Gabriele E , Kissebah Ahmed H
Published: September 2013

The recently cloned adipose tissue hormone leptin has been proposed to be involved in the neuroendocrine regulation of adiposity and its metabolic sequelae. Visceral fat is known to predict reduced insulin sensitivity and associated adverse metabolic profiles. In this study, we report the first evaluation of the relationships between leptin levels and total body fat, visceral fat, and insulin sensitivity in a cohort of premenopausal African-American women. Thirty-four subjects were analyzed for total fat mass and visceral fat by dual-energy X-ray absorptiometry and computerized axial tomography, respectively. Insulin sensitivity (SI) was assessed using Bergman's minimal model. Results showed that fasting leptin levels strongly correlated with total body fat mass (r = 0.797, P < 0.001). Correlations of leptin with visceral fat (r = 0.54, P < 0.001) and SI (r = −0.419, P = 0.02) were dependent on total body fat. In conclusion, leptin levels reflect total body fat mass, and although visceral fat is known to predict reduced insulin sensitivity independently, leptin did not. Our data thus suggest that diverse mechanisms are responsible for the regulation of total body versus visceral fat distribution, with its metabolic and health risks.
Glomerular Hyperfiltration in the Prediction of Nephropathy in IDDM: A 10-Year Follow-Up Study
Authors: Yip Jeannie W , Jones Sharon L , Wiseman Martin J , Hill Caron , Viberti Giancarlo
Published: September 2013

Glomerular hyperfiltration has been proposed as an independent risk factor for the development of diabetic nephropathy in patients with IDDM. In a case-controlled prospective study of IDDM patients without albuminuria, serial glomerular filtration rate (GFR) measurements were performed over an observation period of 10 years. A group of 25 IDDM patients (20 men, 5 women; initial age, 29 [17–49] years) with glomerular hyperfiltration (GFR >135 ml · min−1 · 1.73 m−2) were matched for age, sex, and duration of diabetes with 25 IDDM patients (20 men, 5 women; initial age, 30 [17–48] years) with glomerular normofiltration (GFR 83–135 ml · min−1 · 1.73 m−2). GFR, urinary albumin excretion rate (AER), blood pressure, and glycated hemoglobin were measured at baseline and at 5, 8, and 10 years. The two groups had similar entry levels of blood pressure, AER, and glycated hemoglobin. Metabolic control was similar in the two groups during follow-up. The final GFR remained higher in the group with hyperfiltration (122 [109–135] vs. 103 [95–111] ml · min−1 · 1.73 m−2; P = 0.02) despite a nonsignificantly faster rate of fall of GFR compared with that of the control group (2.54 [1.20–3.88] vs. 1.50 [1.01–1.99] ml · min−1 · year−1; P = 0.14). A similar number of patients in each group progressed to either microalbuminuria or macroalbuminuria (n = 4 vs. n = 3) or developed hypertension (blood pressure, >160/95 mmHg; n = 3 vs. n = 4). End-of-study AER was, however, higher in the group with hyperfiltration (geometric mean [95% CI]: 18.9 [11.3–31.6] vs. 11.0 [8.1–15.0]; P = 0.05), and baseline glomerular hyperfiltration was an independent determinant of end-of-study blood pressure (P = 0.04). The strongest predictors of end-of-study AER and blood pressure were their baseline values (P < 0.04 and P < 0.01, respectively). In conclusion, levels of AER and blood pressure are the main risk factors for renal outcome, while glomerular hyperfiltration appears to play a lesser role.
Tissue-Specific Self-Peptides Bound by Major Histocompatibility Complex Class I Molecules of a Human Pancreatic β-cell Line
Authors: Papadopoulos Kyriakos P , Colovai Adrianna I , Maffei Antonella , Jaraquemada Dolores , Suciu-Foca Nicole , Harris Paul E
Published: September 2013

The process of β-cell destruction in IDDM is mediated, in part, by CD8+ T-cells. Structural characterization of HLA-I-bound self-peptides presented by the human β-cell line HP-62 was performed to identify possible tissue-specific autoantigens in the context of CD8+ T-cell/HLA-I interactions. The sequences of the β-cell line HLA-I-bound peptides were compared with sequence databases. Six of the obtained sequences showed homology to known precursor proteins, three of which—GLUT2 receptor, phosphatidylinositol-glycan-specific phospholipase D, and 5-hydroxytryptamine-1F receptor—have a limited, tissue-specific expression. These HLA-bound self-peptides may be part of a pool of autoantigens recognized by β-cell reactive cytotoxic T-cells.
Dual Functional Effects of Interleukin-1β on Purine Nucleotides and Insulin Secretion in Rat Islets and INS-1 Cells
Authors: Meredith Melissa , Rabaglia Mary E , Corbett John A , Metz Stewart A
Published: September 2013

Interleukin-1β (IL-1β) has been shown to inhibit glucose-induced insulin secretion from rat islets and purified β-cells, primarily through the generation of nitric oxide (NO). However, the mechanisms by which NO exerts its effects remain unclear. To examine the role of purine nucleotides, we cultured intact rat islets or INS-1 (glucose-responsive transformed rat) β-cells for 18 h in the presence or absence of IL-1β. In islets, the exposure to IL-1β (100 pmol/l) inhibited subsequent glucose-induced insulin secretion by 91% with no significant effect on insulin content or basal insulin release. IL-1β also diminished insulin secretion induced by pure mitochondrial fuels, 40 mmol/l K+, or a phorbol ester. Concomitantly, IL-1β significantly decreased islet ATP (–45%), GTP (–33%), ATP/ADP (–54%), and GTP/GDP (–46%). These effects were totally reversed by provision of Nω-nitro-L-arginine methyl ester (NAME) in arginine-free media that inhibited NO production. In contrast, in INS-1 cells, IL-1β (10 or 100 pmol/l) reduced both basal and glucose-induced insulin secretion by 50%, but insulin content was also reduced by 35%. Therefore, the INS-1 cells were still able to respond to glucose stimulation with a 1.8–2.0–fold increase in insulin release in either the presence or absence of IL-1β. Concomitantly, in INS-1 cells, IL-1β had no effect on ATP/ADP or GTP/GDP ratios, although it modestly decreased ATP (–25%) and GTP (–22%). As in islets, all effects of IL-1β in INS-1 cells were prevented by NAME. Thus, in rat islets, IL-1β (via the generation of NO) abolishes insulin exocytosis in association with large decreases in the ATP/ADP (and GTP/GDP) ratio, implying the impairment of mitochondrial function. Furthermore, IL-1β inhibits cytosolic synthesis of new purine nucleotides (via the salvage pathway), as assessed by a decrease in their specific activity after labeling with [3H]hypoxanthine. In contrast, in INS-1 cells, IL-1β appears to impair cytosolic synthesis of purine nucleotides and insulin biosynthesis selectively (both possibly reflecting decreased glycolysis) with little direct effect on insulin exocytosis itself.
Report of the American Diabetes Association's Task Force on Standardization of the Insulin Assay
Authors: Robbins David C , Andersen Lennart , Bowsher Ron , Chance Ron , Dinesen Bo , Frank Bruce , Gingerich Ron , Goldstein David , Widemeyer Hsaio-Mei , Haffner Steven , Hales C Nick , Jarett Leonard , Polonsky Kenneth , Porte Daniel , Skyler Jay , Webb George , Gallagher Kathy
Published: September 2013

Recent large-scale epidemiological studies demonstrate that blood concentrations of immunoreactive insulin predict the development of NIDDM and IDDM and are associated with the risk of several degenerative diseases, such as coronary and peripheral vessel atherosclerosis, hypertension, and dyslipidemia. The reliability of these measurements is dependent on a biological assay that has not been well standardized between laboratories. Recognizing this, the American Diabetes Association organized a task force to assess comparability of blood insulin measurements between laboratories and to suggest techniques to improve comparability. The task force found that identical serum and plasma samples measured in different laboratories produced widely disparate values that were unacceptable for population comparisons. Use of a single reference standard did little to improve comparability. Assay characteristics such as linearity, recovery, accuracy, and cross-reactivity to proinsulin and its primary conversion intermediates varied among the laboratories, and they did not readily explain differences in the measurements made from assay to assay. Use of the same assay kit in different laboratories did not always ensure comparable measurements. Linear regression of assay results from one laboratory to an arbitrarily chosen reference assay greatly improved comparability and demonstrated the potential value in comparing each assay to a reference method. The task force report defines acceptable assay characteristics and proposes a three-step process of insulin assay proficiency and comparability. A central reference assay and ongoing sample exchange will be needed to allow reliable comparisons of insulin measurements made in different laboratories. Rigorous quality control and continuous quality improvement are needed to maintain reliability of the insulin measurement.
Expression and Functional Activity of Glucagon, Glucagon-Like Peptide I, and Glucose-Dependent Insulinotropic Peptide Receptors in Rat Pancreatic Islet Cells
Authors: Moens Karen , Heimberg Harry , Flamez Daisy , Huypens Peter , Quartier Erik , Ling Zhidong , Pipeleers Daniel , Gremlich Sandrine , Thorens Bernard , Schuit Frans
Published: September 2013

Rat pancreatic α- and β-cells are critically dependent on hormonal signals generating cyclic AMP (cAMP) as a synergistic messenger for nutrient-induced hormone release. Several peptides of the glucagon-secretin family have been proposed as physiological ligands for cAMP production in β-cells, but their relative importance for islet function is still unknown. The present study shows expression at the RNA level in β-cells of receptors for glucagon, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide I(7-36) amide (GLP-I), while RNA from islet α-cells hybridized only with GIP receptor cDNA. Western blots confirmed that GLP-I receptors were expressed in β-cells and not in α-cells. Receptor activity, measured as cellular cAMP production after exposing islet β-cells for 15 min to a range of peptide concentrations, was already detected using 10 pmol/l GLP-I and 50 pmol/l GIP but required 1 nmol/l glucagon. EC50 values of GLP-I- and GIP-induced cAMP formation were comparable (0.2 nmol/l) and 45-fold lower than the EC50 of glucagon (9 nmol/l). Maximal stimulation of cAMP production was comparable for the three peptides. In purified α-cells, 1 nmol/l GLP-I failed to increase cAMP levels, while 10 pmol/l to 10 nmol/l GIP exerted similar stimulatory effects as in β-cells. In conclusion, these data show that stimulation of glucagon, GLP-I, and GIP receptors in rat β-cells causes cAMP production required for insulin release, while adenylate cyclase in α-cells is positively regulated by GIP.
Are the β-Cell Signaling Molecules Malonyl-CoA and Cystolic Long-Chain Acyl-CoA Implicated in Multiple Tissue Defects of Obesity and NIDDM?
Authors: Prentki Marc , Corkey Barbara E
Published: September 2013

Widely held theories of the pathogenesis of obesity-associated NIDDM have implicated apparently incompatible events as seminal: 1) insulin resistance in muscle, 2) abnormal secretion of insulin, and 3) increases in intra-abdominal fat. Altered circulating or tissue lipids are characteristic features of obesity and NIDDM. The etiology of these defectss is not known. In this perspective, we propose that the same metabolic events, elevated malonyl-CoA and long-chain acyl-CoA (LC-CoA), in various tissues mediate, in part, the pleiotropic alterations characteristic of obesity and NIDDM. We review the evidence in support of the emerging concept that malonyl-CoA and LC-CoA act as metabolic coupling factors in β-cell signal transduction, linking fuel metabolism to insulin secretion. We suggest that acetyl-CoA carboxylase, which synthesizes malonyl-CoA, a “signal of plenty,” and carnitine palmitoyl transferase 1, which is regulated by it, may perform as fuel sensors in the β-cell, integrating the concentrations of all circulating fuel stimuli in the β-cell as well as in muscle, liver, and adipose tissue. The target effectors of LC-CoA may include protein kinase C sub-types, complex lipid formation, genes encoding metabolic enzymes or transduction factors, and protein acylation. We support the concept that only under conditions in which both glucose and lipids are plentiful will the metabolic abnormality, which may be termed glucolipoxia, become apparent. If our hypothesis is correct that common signaling abnormalities in the metabolism of malonyl-CoA and LC-CoA contribute to altered insulin release and sensitivity, it offers a novel explanation for the presence of variable combinations of these defects in individuals with differing genetic backgrounds and for the fact that it has been difficult to determine whether one or the other is the primary event.