bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of Hepatic Sensitivity to Glucagon in NIDDM: Use as a Tool to Estimate the Contribution of the Indirect Pathway to Nocturnal Glycogen Synthesis
Authors: Nielsen Michael F , Wise Steven , Dinneen Sean F , Schwenk W Frederick , Basil Ananda , Rizza Robert A
Published: September 2013

NIDDM is associated with excessive rates of endogenous glucose production in both the postabsorptive and postprandial states. To determine whether this is due to an intrinsic increase in hepatic sensitivity to glucagon, 9 NIDDM and 10 nondiabetic subjects were studied on three occasions. On each occasion, glycogen was labeled the evening before the study with subjects ingesting meals containing [6-3H]galactose. Beginning at 6:00 A.M. on the following morning, somatostatin was infused to inhibit endogenous hormone secretion. Insulin concentrations were maintained constant at basal levels (defined as that necessary to keep glucose at ∼5 mmol/l) in each individual. On one occasion, glucagon was infused at a rate of 0.65 ng ∼ kg−1 · min−1 throughout the experiment, resulting in glucagon concentrations of ∼130 pg/ml and a slow but comparable fall in endogenous glucose production with time in both groups. On the other two occasions, the glucagon infusion was increased at 10:00 A.M. to either 1.5 or 3.0 ng · kg−1 · min−1, resulting in an increase in glucagon concentrations to ∼180 and 310 pg/ml, respectively. The increment in endogenous glucose production (i.e., area above basal) did not differ in diabetic and nondiabetic subjects during either the 1.5 ng · kg−1 · min−1 (0.75 ± 0.055 vs. 0.78 ± 0.048 mmol/kg) or 3.0 ng · kg−1 · min−1 (1.06 ± 0.066 vs. 1.10 ± 0.073 mmol/kg) glucagon infusions. In contrast, the amount of [6-3H]glucose released from glycogen was lower (P < 0.05) in the diabetic than nondiabetic subjects during both glucagon infusions. The specific activity of glycogen, calculated as the integrated release of [6-3H]glucose divided by the integrated release of unlabeled glucose, was lower (P < 0.05) in diabetic subjects than in nondiabetic subjects during both the 1.5 ng · kg−1 · min−1 (19.0 ± 3.9 vs. 41.4 ± 5.7 dpmμmol) and 3.0 ng · kg−1 · min−1 (19.1 ± 3.1 vs. 36.5 ± 7.2 dpm/μmol) glucagon infusions, implying that a greater portion of the glucose released from glycogen was derived from the indirect pathway. We concluded that although NIDDM is not associated with an intrinsic alteration in hepatic sensitivity to glucagon, it does alter the relative contributions of the direct and indirect pathways to nocturnal glycogen synthesis.
Intracerebroventricular Leptin Increases Lumbar and Renal Sympathetic Nerve Activity and Blood Pressure in Normal Rats
Authors: Dunbar Joseph C , Hu Yuange , Lu Huiqing
Published: September 2013

Obesity and hyperinsulinism are known to be major stimuli of leptin production by adipose tissue, leading to increased leptin levels in the circulation. It has also been demonstrated that increased leptin production leads to satiety, possibly by decreasing the levels of neuropeptide Y (NPY) in the central nervous system (CNS). Because obesity and hyperinsulinism are also frequently associated with hypertension, we studied the effect of the intracerebroventricular (ICV) administration of leptin on mean arterial pressure (MAP), heart rate, vascular flows, and lumbar and renal sympathetic nerve activity (SNA). Normal Wistar rats were implanted with an ICV cannula and allowed to recover. On the day of the study, the animals were fasted and anesthetized with chloralose/urethane. Catheters were placed in a femoral artery and vein, and Doppler flow probes were placed around the iliac, renal, and superior mesenteric arteries for measurement of MAP, heart rate, and blood flows. In other experiments, lumbar SNA and renal SNA were recorded. ICV leptin administration resulted in an MAP that was slowly but progressively increasing. Blood flows decreased in the iliac and superior mesenteric arteries, but not in the renal artery. Leptin injection increased the lumbar SNA and renal SNA. The plasma glucose and insulin levels were not changed. We concluded that ICV leptin increases MAP by decreasing arterial blood flow to the skeletal muscle and the splanchnic vascular bed. This increased peripheral resistance is the result of an increased activity of the sympathetic nerves. We suggest that increased leptin may serve as a link in the triad of obesity and hyperinsulinism and hypertension.
Circulating Vascular Cell Adhesion Molecule-1 (VCAM-1) in Atherosclerotic NIDDM Patients
Authors: Otsuki Michio , Hashimoto Kunihiko , Morimoto Yasuhiko , Kishimoto Tadamitsu , Kasayama Soji
Published: September 2013

Vascular cell adhesion molecule-1 (VCAM-1) has been shown to be highly expressed in atherosclerotic lesions. Although the soluble form of VCAM-1 (sVCAM-1) is detected in human sera, the relation between the degree of atherosclerosis and serum sVCAM-1 level has not been defined. In the present study, sVCAM-1 concentrations were measured in sera from 101 Japanese NIDDM patients. The mean ± SD serum sVCAM-1 concentration in 26 patients with symptomatic atherosclerotic vascular diseases (789 ± 187 ng/ml) was higher than that in 75 patients without the disease (664 ±175 ng/ml). Among the 101 NIDDM patients, 56 had atherosclerotic change of the carotid arteries, based on the evaluation by highresolution B-mode ultrasonography. Their sVCAM-1 level was 759 ± 201 ng/ml, higher than that in 45 patients without any detectable atherosclerosis of the carotid arteries (619 ± 130 ng/ml). In addition, there was a positive correlation between sVCAM-1 concentration and thickness of the intimal plus medial complex (IMT) of the carotid arteries in the NIDDM patients (r = 0.41, P < 0.0001). Multivariate regression analysis revealed significant predictors of mean IMT value to be sVCAM-1 concentration (F = 62.88, P = 0.0001) and age (F = 9.59, P = 0.0026). By contrast, sVCAM-1 concentration was not increased in nondiabetic patients with atherosclerotic change of the carotid arteries (668 ± 191 ng/ml; n = 36) compared with those without the atherosclerotic change (632 ± 177 ng/ml; n = 28), and there was no correlation between sVCAM-1 level and IMT of the carotid arteries in the nondiabetic subjects. These results indicate that circulating sVCAM-1 may be a marker of atherosclerotic lesions in NIDDM patients with symptomatic and asymptomatic atherosclerosis.
Improved Glucose Tolerance Restores Insulin-Stimulated Akt Kinase Activity and Glucose Transport in Skeletal Muscle From Diabetic Goto-Kakizaki Rats
Authors: Krook Anna , Kawano Yuichi , Song Xiao Mei , Efendić Suad , Roth Richard A , Wallberg-Henriksson Harriet , Zierath Juleen R
Published: September 2013

The serine/threonine kinase Akt (protein kinase B [PKB] or related to A and C protein kinase [RAC] has recently been implicated to play a role in the signaling pathway to glucose transport. However, little is known concerning the regulation of Akt activity in insulinsensitive tissues such as skeletal muscle. To explore the role of hyperglycemia on Akt kinase activity in skeletal muscle, normal Wistar rats or Goto-Kakizaki (GK) diabetic rats were treated with phlorizin. Phlorizin treatment normalized fasting blood glucose and significantly improved glucose tolerance (P < 0.001) in GK rats, whereas in Wistar rats, the compound had no effect on glucose homeostasis. In soleus muscle from GK rats, maximal insulin-stimulated (120 nmol/l) Akt kinase activity was reduced by 68% (P < 0.01) and glucose transport was decreased by 39% (P < 0.05), compared with Wistar rats. Importantly, the defects at the level of Akt kinase and glucose transport were completely restored by phlorizin treatment. There was no significant difference in Akt kinase protein expression among the three groups. At a submaximal insulin concentration (2.4 nmol/l), activity of Akt kinase and glucose transport were unaltered. In conclusion, improved glucose tolerance in diabetic GK rats by phlorizin treatment fully restored insulin-stimulated activity of Akt kinase and glucose transport. Thus, hyperglycemia may directly contribute to the development of muscle insulin resistance through alterations in insulin action on Akt kinase and glucose transport.
The Role of Enteroviral Infections in the Development of IDDM: Limitations of Current Approaches
Authors: Graves Patricia M , Norris Jill M , Pallansch Mark A , Gerling Ivan C , Rewers Marian
Published: September 2013

Enteroviruses have been examined for their possible role in the etiology of IDDM for nearly 40 years, yet the evidence remains inconclusive. The mechanism of acute cytolytic infection of β-cells, proposed by earlier studies, appears to be incompatible with the long preclinical period of autoimmunity preceding IDDM. Advances in molecular biology have improved our understanding of enteroviral biology and of potential alternative pathogenic mechanisms through which enteroviruses may cause diabetes. The focus of future human studies will likely shift from people with IDDM to those with prediabetic autoimmunity to determine whether acute enteroviral infections can promote progression from autoimmunity to overt diabetes. We propose that such studies use assays to detect enteroviral RNA, in addition to IgM serology. RNA assays can overcome sensitivity and type-specificity limitations of IgM assays as well as identify diabetogenic strains of enteroviruses, if such exist. Evaluation of the role of enteroviruses in triggering β-cell autoimmunity in humans will require large prospective studies of young children. The Diabetes Autoimmunity Study in the Young—one of very few such studies currently underway—is focusing on potential interactions between HLA class II genes and enteroviral infections. Future studies will likely examine interactions between viral infections and non-HLA IDDM candidate genes, including those that may determine β-cell tropism of candidate viruses.
Alterations in the Expression and Cellular Localization of Protein Kinase C Isozymes ε and θ Are Associated With Insulin Resistance in Skeletal Muscle of the High-Fat–Fed Rat
Authors: Schmitz-Peiffer Carsten , Browne Carol L , Oakes Nicholas D , Watkinson Allan , Chisholm Donald J , Kraegen Edward W , Biden Trevor J
Published: September 2013

We have tested the hypothesis that changes in the levels and cellular location of protein kinase C (PKC) isozymes might be associated with the development of insulin resistance in skeletal muscles from the highfat–fed rat. Lipid measurements showed that triglyceride and diacylglycerol, an activator of PKC, were elevated four- and twofold, respectively. PKC activity assays indicated that the proportion of membraneassociated calcium-independent PKC was also increased. As determined by immunoblotting, total (particulate plus cytosolic) PKC α, ε, and ζ levels were not different between control and fat-fed rats. However, the ratio of particulate to cytosolic PKC ε in red muscles from fat-fed rats was increased nearly sixfold, suggesting chronic activation. In contrast, the amount of cytosolic PKC θ was downregulated to 45% of control, while the ratio of particulate to cytosolic levels increased, suggesting a combination of chronic activation and downregulation. Interestingly, while insulin infusion in glucose-clamped rats increased the proportion of PKC θ in the particulate fraction of red muscle, this was potentiated by fat-feeding, suggesting that the translocation is a consequence of altered lipid flux rather than a proximal event in insulin signaling. PKC ε and θ measurements from individual rats correlated with triglyceride content of red gastrocnemius muscle; they did not correlate with plasma glucose, which was not elevated in fat-fed rats, suggesting that they were not simply a consequence of hyperglycemia. Our results suggest that these specific alterations in PKC ε and PKC θ might contribute to the link between increased lipid availability and muscle insulin resistance previously described using high-fat–fed rats.
Glucokinase Regulatory Protein May Interact With Glucokinase in the Hepatocyte Nucleus
Authors: Brown Karen S , Kalinowski Stephen S , Megill John R , Durham Stephen K , Mookhtiar Kasim A
Published: September 2013

Glucokinase (GK) plays a central role in the sensing of glucose in pancreatic β-cells and parenchymal cells of the liver. Glucokinase regulatory protein is a physiological inhibitor of GK in the liver. To understand the role of the interaction of these two proteins in glucose sensing, we carried out a series of experiments to localize the protein in the liver cell. The regulatory protein was found to be present mainly in the nucleus of the cell under a variety of conditions that mimicked the glucose status of the fed and fasted state. GK was localized in the nucleus when the cells were exposed to low glucose concentrations. At higher glucose concentrations or in the presence of low concentrations of fructose, GK translocated to the cytoplasm. The effect of fructose was more robust and rapid than the effect of high glucose concentrations. Furthermore, the effect of fructose and high glucose on the translocation of GK from the nucleus could be partially reversed by glucagon. This unusual localization and behavior suggests a role for GK and its regulatory protein in hepatic energy metabolism that may be broader than glucose phosphorylation.
Expression of the Functional Leptin Receptor mRNA in Pancreatic Islets and Direct Inhibitory Action of Leptin on Insulin Secretion
Authors: Emilsson Valur , Liu Yong-Ling , Cawthorne Michael A , Morton Nicholas M , Davenport Michelle
Published: September 2013

Leptin, encoded for by the mouse ob gene, regulates feeding behavior and energy metabolism. Its receptor (Ob-R) is encoded by the mouse diabetic (db) gene and is mutated in the db/db mouse so that it lacks the cytoplasmic domain. We show that the full-length leptin receptor (Ob-Rb), which is believed to transmit the leptin signal, is expressed in pancreatic islets of ob/ob and wild-type mice, as well as in hypothalamus, liver, kidney, spleen, and heart. Recombinant leptin inhibited basal insulin release in the perfused pancreas preparation from ob/ob mice but not in that from Zucker fa/fa rats. Leptin (1–100 nmol/l) also produced a dose-dependent inhibition of glucose-stimulated insulin secretion by isolated islets from ob/ob mice. In contrast, leptin at maximum effective concentration (100 nmol/l) did not inhibit glucose-stimulated insulin secretion by islets from db/db mice. These results provide evidence that a functional leptin receptor is present in pancreatic islets and suggest that leptin overproduction, particularly from abdominal adipose tissue, may modify directly both basal and glucose-stimulated insulin secretion.
Cotransplantation of Allogeneic Islets With Allogeneic Testicular Cell Aggregates Allows Long-Term Graft Survival Without Systemic Immunosuppression
Authors: Korbutt Gregory S , Elliott John F , Rajotte Ray V
Published: September 2013

We prepared single-cell suspensions of Lewis rat (RT11/1) testicular cells and cultured these in vitro for 48 h under conditions that promoted the formation of cellular aggregates. In the absence of systemic immunosuppression, the transplantation of a sufficient quantity of these aggregates (containing 11 × 106 cells, (75% Sertoli cells), together with 2,000 purified Lewis rat islets, reversed the diabetic state for >95 days in 100% (5/5) of the chemically diabetic Wistar-Furth (RT1u/u) recipients. Similar grafts consisting of islets alone or islets plus 50% fewer testicular cell aggregates survived for only 10 days. Functioning composite allografts harvested from normoglycemic animals at ü100 days showed healthy β-cells in close association with Fas ligand–expressing Sertoli cells. Because no gene therapy protocol is required, the transplantation of composite grafts consisting of purified human allogeneic islets plus human allogeneic testicular cell aggregates can be applied in clinical islet transplantation as soon as it has been proven in a large animal model.
Blood Glucose Control and Microvascular and Macrovascular Complications in Diabetes
Authors: Hanssen Kristian F
Published: September 2013

High blood glucose levels for several years is the major factor in the development and progression of microvascular complications in IDDM. Reducing mean blood glucose reduces the risk of progression of diabetic microvascular complications substantially. A curve-linear relationship exists between HbA1c levels and progression of diabetic retinopathy. Recent evidence also points to a close relationship between high blood glucose levels and progression of microvascular complications in NIDDM. The relationship between mean blood glucose and cardiovascular disease in diabetes has been unclear. Recent population-based studies give evidence for a linear association of glycemic control with the risk for cardiovascular disease in patients with NIDDM. However, randomized studies comparing different degrees of glycemic control in NIDDM and their impact on cardiovascular morbidity and mortality are urgently needed.
Impaired Coronary Flow Reserve in NIDDM: A Possible Role for Diabetic Cardiopathy in Humans
Authors: Strauer BE , Motz W , Vogt M , Schwartzkopff B
Published: September 2013

Diabetic cardiopathy represents a cardiac disorder with involvement of myocardial, interstitial, coronary, and neural structures. One of the main manifestations refers to coronary microangiopathy, which has not yet been clearly identified. Coronary hemodynamics, including the determination of coronary flow reserve, were therefore analyzed in normal subjects and in nine patients with NIDDM and clinically suspected coronary heart disease but normal coronary arteriogram. Coronary flow reserve was determined as the quotient of baseline and minimal coronary resistance after dipyridamole (0.5 mg/kg i.v.). Coronary blood flow was measured quantitatively by the argon method. Systolic left ventricular function was analyzed by ventriculography and diastolic function by M-mode and Doppler echocardiography. Twelve healthy normotensive subjects served as the control group (CON). In the diabetic patients, maximal coronary flow was significantly reduced (172 ± 50 vs. 395 ± 103 ml/min × 100 g; P < 0.001), and minimal coronary resistance was increased (0.60 ± 0.19 vs. 0.24 ± 0.06 mmHg × min × 100 g/ml; P < 0.001). Coronary reserve in the diabetic subjects was markedly reduced (1.84 ± 0.39 vs. 4.23 ± 0.52; P < 0.001). No difference existed with respect to myocardial oxygen consumption (12.4 ± 2.3 vs. 11.8 ± 2.8 ml 02/100 g × min; NS). Global systolic function was normal in all patients (ejection fraction: NIDDM 72 ± 13 vs. CON 77 ± 12%, NS; CI: NIDDM 3.2 ± 0.8 vs. CON 3.3 ± 1.2 1/min × m2, NS). Diastolic function was impaired in diabetic patients with an increase in relaxation time index (97 ± 23 vs. 45 ± 18 ms; P < 0.01) and an impaired diastolic inflow pattern, indicated by the ratio between early and late transmitrai flow (0.75 ± 0.14 vs. 1.66 ± 0.13; P < 0.05). We conclude that the markedly reduced coronary flow reserve in diabetic patients may play a key role in the induction and perpetuation of coronary insufficiency in myocardial ischemia, in diastolic and systolic dysfunction, and in the initiation of diabetic cardiopathy.
Growth Factor Alterations in Advanced Diabetic Retinopathy: A Possible Role of Blood Retina Barrier Breakdown
Authors: Pfeiffer Andreas , Spranger Joachim , Meyer-Schwickerath Rolf , Schatz Helmut
Published: September 2013

Chronic hyperglycemia may cause growth factor alterations that are likely to participate in tissue remodeling typical for diabetic late complications. However, few details of such events are known. The ocular vitreous fluid allows studies of growth factor levels in human eyes (after vitrectomy). The vitreous is highly inert and protected by the blood-retina barrier and thus probably reflects growth factor production by the normal retina. Vitreous from patients with proliferative diabetic retinopathy (PDR) was compared with vitreous obtained from patients with nonproliferative eye disease and with vitreous from patients without diabetes but with marked neovascular proliferations due to ischemia. This design permits us to distinguish diabetes-related from non-diabetes-related alterations. Insulin-like growth factor I (IGF-I), IGF-II, IGF binding protein 2 (IGFBP-2), and IGFBP-3 were elevated 3-to 13-fold in nondiabetic retinal ischemia and 1.5- to 3-fold in PDR, indicating that the changes were not restricted to diabetes. These changes may partially be explained by leakage of serum into the vitreous, since IGFs and IGFBPs are 20- to 50-fold higher in serum than in vitreous, and vitreous protein content was 1.5-fold elevated in PDR subjects and 5-fold in ischemia patients compared with control subjects. TGF-β is a proposed antiangiogenic factor in the eye. TGF-β2 was the predominant subtype in vitreous, and its total amount was not altered in PDR patients. More importantly, the active fraction of TGF-β was decreased by 30 and 70% in PDR and nondiabetic retinal ischemia patients, respectively. Since plasmin may control TGF-β activation, the serum protein α2-antiplasmin was measured and found to be significantly elevated to 150 and 250% of control values in PDR and ischemia patients, respectively. Thus, influx of serum proteins due to microvascular disturbances and hypoxia is proposed as a possible cause for vitreous alterations of IGF-I and of active TGF-β. These changes seem to occur late in the sequence of events leading to PDR and are not specific for diabetes, but they were also observed in other diseases characterized by retinal hypoxia.
Metabolic and Vascular Factors in the Pathogenesis of Diabetic Neuropathy
Authors: Cameron Norman E , Cotter Mary A
Published: September 2013

Reduced nerve perfusion is an important factor in the etiology of diabetic neuropathy. Studies in streptozotocin-induced diabetic rats show that nerve conduction velocity (NCV) and blood flow deficits are corrected by treatment with vasodilator drugs, with angiotensin II and endothelin-1 antagonists being particularly important. The AT1 antagonist ZD7155 also prevents diabetic deficits in regeneration following nerve damage, indicating that hypoperfusion is an important limitation for nerve repair. Metabolic changes include high polyol pathway flux, increased advanced glycosylation, elevated oxidative stress, and impaired ω-6 essential fatty acid metabolism. Aldose reductase inhibitors (ARIs) restore NCV via their effects on perfusion. ARI action probably depends on blocking the conversion of glucose to sorbitol, thus preventing depletion of vasa nervorum glutathione, an important endogenous free radical scavenger. Free radicals cause vascular endothelium damage and reduced nitric oxide vasodilation. Inhibition of advanced glycosylation and autoxidation (autoxidative glycosylation), major sources of free radicals, by aminoguanidine or transition metal chelators, corrects neurovascular dysfunction. Evening primrose oil supplies γ-linolenic acid (GLA) to improve vasodilator eicosanoid synthesis in diabetes, correcting nerve blood flow and NCV deficits. Interactions between some of these mechanisms have therapeutic implications. Thus, combined ARI and evening primrose oil treatment produced a 10-fold amplification of NCV and blood flow responses. Similarly, GLA effects are markedly enhanced when given in combination with ascorbate as ascorbyl-GLA. Thus, metabolic abnormalities combine to produce deleterious changes in nerve perfusion that make a major contribution to the etiology of diabetic neuropathy. The potential importance of multi-action therapy is stressed.
Approaches to Improve Epidemiological Studies of Diabetic Neuropathy: Insights from the Rochester Diabetic Neuropathy Study
Authors: Dyck Peter J , Melton L Joseph , O'Brien Peter C , Service F John
Published: September 2013

The quality of the epidemiological data on diabetic neuropathies remains poor for a variety of reasons. They include variability in 1) ascertainment of diabetes, 2 the clinical varieties of diabetic patients studied, 3) characterization of neurological dysfunction, 4) abnormal limits for neurological examinations and tests, 5) minimal criteria for neuropathy, 6) correct attribution of nondiabetic neurological disease, 7) correct attribution of type of neuropathy, 8) estimating neuropathy from use of multiple tests, and 9) estimating severity of polyneuropathy. We have tried to remedy these shortcomings in the Rochester Diabetic Neuropathy Study (RDNS). It was not possible to adequately characterize and quantitate diabetic polyneuropathies using only one or two clinical or test abnormalities. To estimate severity of diabetic polyneuropathy, the results of the neurological examination and abnormalities of nerve conduction, quantitative sensory tests, and quantitative autonomie tests were combined into a composite score. One begins by scoring a standard test of neurological deficits (impairments) of the lower limbs (NIS[LL]) and adds to this transformed numbers for percentile abnormality of seven good functional tests. This NIS(LL)+7 tests score appears to provide a much more comprehensive and stable numeric score by which to diagnose and grade severity of diabetic polyneuropathy than does the use of individual clinical or test results. This test score should be useful as a measure of change in diabetic polyneuropathy for purposes of medical practice, epidemiology studies, and controlled clinical trials. The staging approach that we introduced previously continues to provide an important measure of overall severity of diabetic polyneuropathy, taking into account both symptoms and impairments.
Endothelial Dysfunction: Cause of the Insulin Resistance Syndrome
Authors: Pinkney Jonathan H , Stehouwer Coen DA , Coppack Simon W , Yudkin John S
Published: September 2013

Insulin resistance has been proposed as the metabolic basis of atherogenesis. This hypothesis is based on the concept of the “insulin resistance syndrome,” according to which insulin resistance is viewed as the primary abnormality that gives rise to dyslipidemia, essential hypertension, impaired glucose tolerance, and NIDDM. However, this hypothesis takes no account of the wellestablished and central role of vascular endothelium in the atherogenic process. Although endothelial injury is an early and prominent feature of atherogenesis, relatively little attention has been given to its metabolic consequences. In subjects with NIDDM, we have shown that endothelial dysfunction is associated with insulin resistance, raising the question of whether this relationship could be causal. In this article, we review the factors that are considered to be responsible for the development of endothelial dysfunction during atherogenesis, together with the metabolic consequences of endothelial dysfunction. While dysfunction of the endothelium in large and medium-sized arteries plays a central role in atherogenesis, we argue that dysfunction of peripheral vascular endothelium, at arteriolar and capillary level, plays the primary role in the pathogenesis of both insulin resistance and the associated features of the insulin resistance syndrome. We propose that the insulin resistance syndrome, together with many aspects of atherogenesis, can be viewed as the diverse consequences of endothelial dysfunction in different vascular beds. This new and testable hypothesis accounts for both the endothelial and metabolic abnormalities associated with atherogenesis.
Depot- and Sex-Specific Differences in Human Leptin mRNA Expression: Implications for the Control of Regional Fat Distribution
Authors: Montague Carl T , Prins Johannes B , Sanders Louise , Digby Janet E , O'Rahilly Stephen
Published: September 2013

Obese subjects with excess intra-abdominal fat deposition suffer greater adverse metabolic consequences than do similarly overweight subjects with a predominantly subcutaneous distribution of adiposity. Little is known about the factors regulating the regional distribution of body fat. Leptin is a recently characterized protein secreted by adipocytes that appears to provide a long-term hormonal feedback signal regulating fat mass. No systematic evaluation of site-related differences in human adipocyte leptin expression has been reported to date. Levels of leptin mRNA were examined by quantitative reverse transcription-polymerase chain reaction in adipocytes isolated from omental and subcutaneous adipose depots of nonobese and mildly obese individuals undergoing elective surgery. In all individuals studied (n = 24), leptin mRNA levels were higher in subcutaneous than in omental adipocytes (P < 0.0001). In contrast, there were no consistent site-specific differences in the expression of glycerol-3-phosphate dehydrogenase mRNA. The subcutaneous-toomental ratio of leptin mRNA expression was markedly higher in women (5.5 ± 1.1-fold) than in men (1.9 ± 0.2-fold) (P < 0.02). A significant relationship between BMI and leptin mRNA expression was demonstrable in the subcutaneous adipocytes of women (P < 0.006). Thus, leptin mRNA appears to be expressed predominantly by subcutaneous adipocytes, particularly in women. These findings suggest a possible role for leptin in the control of adipose tissue distribution and mass.
The α2-Adrenergic Receptor Is More Effective Than the Galanin Receptor in Activating G-Proteins in RINm5F β-cell Membranes
Authors: Gillison Susan L , Straub Susanne G , Sharp Geoffrey W G
Published: September 2013

Activated receptors for galanin and norepinephrine, and for several other agonists, inhibit insulin release from pancreatic β-cells via pertussis toxin–sensitive Gi- and Go-proteins and by acting on at least four cellular mechanisms. These mechanisms include repolarization via activation of the ATP-sensitive potassium (KATP) channel, inhibition of adenylyl cyclase, and inhibition by unknown mechanism at a “distal” site. For norepinephrine and galanin there is also inhibition of the L-type Ca2+ channel. Consequently, during simultaneous activation by multiple agonists, the effectiveness with which a receptor interacts with the G-proteins will, to some extent, determine the responses. This could have important consequences for the β-cell. Therefore, the G-protein interactions of two activated receptors, those for norepinephrine and galanin, were compared in the same β-cell membranes. Measurements were made of the rates of receptor–G-protein interaction (by GTPγS binding) and of the rates of turnover of G-proteins (by GTPase activity). A comparison was also made of the ability of norepinephrine and galanin to facilitate ADP ribosylation of the α-subunits of Gi and Go by cholera toxin (CTX). Such CTX-induced ADP ribosylation of Gi and Go occurs during G-protein interaction with an activated receptor. By measurement of the number of receptors in the membrane preparation used, the relative effectiveness of the two receptors was assessed. The α2adrenergic receptor was found to be markedly more effective than the galanin receptor in activating G-proteins.
Increased Lipogenic Capacity of the Islets of Obese Rats: A Role in the Pathogenesis of NIDDM
Authors: Lee Young , Hiros Hiroshi , Zhou Yan-Ting , Esser Victoria , McGarry J Denis , Unger Roger H
Published: September 2013

The onset of NIDDM in obese Zucker diabetic fatty (fa/fa) rats is preceded by a striking increase in the plasma levels of free fatty acids (FFAs) and by a sixfold rise in triglyceride content in the pancreatic islets. The latter finding provides clear evidence of elevated tissue levels of long-chain fatty acyl CoA, which can impair β-cell cell function. To determine if the triglyceride accumulation is entirely the passive consequence of high plasma FFA levels or if prediabetic islets have an increased lipogenic capacity that might predispose to NIDDM, the metabolism of long-chain fatty acids was compared in islets of obese prediabetic and nonprediabetic Zucker diabetic fatty (ZDF) rats and of lean Wistar and lean ZDF rats. When cultured in 1 or 2 mmol/l FFA, islets of both female and male obese rats accumulated, respectively, 7 and 15 times as much triglyceride as islets from lean rats exposed to identical FFA concentrations. The esterification of [14C]palmitate and 9,10-[3H]palmitate was increased in islets of male obese rats and could not be accounted for by defective oxidation of 9,10-[3H]-palmitate. Glycerol-3-PO4 acyltransferase (GPAT) activity was 12 times that of controls. The mRNA of GPAT was increased in islets of obese rats. We conclude that, in the presence of comparable elevations in FFA concentrations, the islets of obese prediabetic rats have a higher lipogenic capacity than controls. This could be a factor in their high risk of diabetes.
Effects of Multiple Daily Insulin Injections and Intraperitoneal Insulin Therapy on Cholesteryl Ester Transfer and Lipoprotein Lipase Activities in NIDDM
Authors: Bagdade John D , Kelley David E , Henry Robert R , Eckel Robert H , Ritter Mary C
Published: September 2013

Although the relationship between the actions of cholesteryl ester transfer protein (CETP) and atherosclerosis is complex, a strong body of evidence suggests that its activity (cholesteryl ester transfer [CET]) is proatherogenic. We have previously shown that CET is increased in IDDM patients receiving conventional subcutaneous insulin treatment and normalized when systemic insulin levels are lowered with intraperitoneal insulin delivery (IP). Since CET has been found by many observers to also be accelerated in NIDDM, we sought to determine whether the same salutary effect could be achieved in insulin-requiring NIDDM men before and 7 months after randomization to an intensive treatment regimen (Rx) of either IP (n = 9) or multiple daily insulin injections (MDI; n = 13). HbA1c improved to the same degree in both groups (MDI group: 9.4 ± 1.1% pre-Rx vs. 7.2 ± 0.7% post-Rx [P < 0.001]; IP group: 9.2 ± 1.3% pre-Rx vs. 7.1 ± 0.5% post-Rx [P< 0.001]). Compared with pre-Rx levels, plasma triglycerides were not significantly changed by either treatment (MDI group: 136 ± 80 mg/dl pre-Rx vs. 139 ± 87 mg/dl post-Rx; IP group: 157 ± 63 mg/dl pre-Rx vs. 188 ± 89 mg/dl post-Rx), though an upward trend followed IP. Before randomization, CET estimated with both mass and isotopic assays was greater in the NIDDM subjects than in nondiabetic control subjects (P < 0.001). With improved glycemic control, CE mass transfer declined in both groups, but only reached normal levels in the IP group (MDI group at 2 h: 49.0 ± 13.7 [mean ± SD] μg pre-Rx vs. 29.5 ± 15.3 μg post-Rx [−39.7%, P < 0.01]; IP group at 2 h: 40.8 ± 23.3 μg pre-Rx vs. 10.9 ± 6.5 μg post-Rx [−73.2%, P < 0.05]) and remained abnormally increased (P < 0.005) in the subjects receiving MDI. Total lipolytic activity after intensive treatment was unchanged from pretreatment levels, which were similar to those of the reference group. Although directional changes in lipoprotein lipase (LpL) and hepatic triglyceride lipase (HTGL) similar to those found in IDDM after MDI and IP were observed, they were not statistically significant. Thus, while improved glycemic control alone achieved by either MDI or IP reduced the pathological increase in CET in these insulin-treated NIDDM men, normalization was only achieved in those treated with IP. Despite near-normal HbA1c levels, CET remained abnormally increased in NIDDM patients treated rigorously with conventional subcutaneous insulin delivery.
Visceral Fat and Race-Dependent Health Risks in Obese Nondiabetic Premenopausal Women
Authors: Albu Jeanine B , Murphy Laura , Frager David H , Johnson Julia A , Pi-Sunyer F Xavier
Published: September 2013

Our previous finding that a waist-to-hip ratio (WHR) >0.85 was not associated with similar health risks in black, compared with white, obese premenopausal nondiabetic women of similar fatness is attributed to either 1) a different relationship between WHR and visceral adiposity or 2) differences in the relationship between visceral adiposity and the metabolic abnormalities of obesity. We measured visceral (VAT) and subcutaneous adipose tissue (SCAT) areas at midwaist in 25 black and 25 white obese nondiabetic premenopausal women with similar BMI, percentage body fat, and wide range of WHR (0.7–0.95 for black women and 0.7–0.9 for white women) and then compared insulin sensitivity index (SI), glucose and insulin areas under the 2-h curve (AUCs) during an oral glucose tolerance test (OGTT), and blood lipids in the two groups before and after adjustments for total body and visceral adiposity. After adjusting for total body fat mass (FM), obese black women had significantly less VAT (by 32 cm2) and lower VAT/SCAT for any given WHR. The regression equations predicting the SI, the glucose and insulin AUCs, and the triglyceride and HDL cholesterol levels from regional adipose tissue measurements (VAT, SCAT, or VAT/SCAT) and from total body fat (FM or percentage body fat) had slopes that were not significantly different for black and white women. LDL cholesterol levels were independently related to VAT in black but not in white women. The black women had a similar SI insulin AUC, and triglyceride levels but significantly lower glucose AUC and higher HDL cholesterol levels (P < 0.001), after adjusting for VAT and FM. Regression analysis of the pooled data showed that high VAT and high VAT/SCAT, but not SCAT, predicted lower SI, higher glucose and insulin AUCs during OGTT, and higher triglyceride levels, independent of total adiposity. We conclude that while increases in VAT and VAT/SCAT adversely affect metabolism in both black and white obese premenopausal women, similar levels of total body and visceral adiposity are associated with different metabolic risk factors in these groups.
Phenotype of the Obese Koletsky (f) Rat Due to Tyr763Stop Mutation in the Extracellular Domain of the Leptin Receptor (Lepr): Evidence for Deficient Plasma-to-CSF Transport of Leptin in Both the Zucker and Koletsky Obese Rat
Authors: Wu-Peng X Sharon , C Chua Streamson , Okada Norichika , Liu Shun-Mei , Nicolson Margery , Leibel Rudolph L
Published: September 2013

The obese phenotypes of the diabetes (db) mouse and fatty (fa) rat are due to functional null mutations of the leptin receptor (Lepr). The recessive mutation in the Koletsky (f) obese rat maps to the same genetic intervals as db and fa and fails to complement the fa mutation. Comparison of the sequence of brain Lepr cDNA from +/+ and f/f animals reveals a T2349A transversion resulting in a Tyr763Stop nonsense mutation in the gene just before the transmembrane domain. Virtual absence of Lepr mRNA in whole brain from f/f animals is consistent with the presence of a null mutation. The predicted reduced cerebrospinal fluid (CSF) transport of leptin in both f/f and fa/fa mutants is reflected in the ∼10-fold lower ratio of CSF/plasma leptin concentration in the obese versus lean animals. However, equivalent CSF leptin concentration between lean and obese rats (fa/fa, f/f) indicates that leptin can enter the CSF through a non–Lepr-mediated mechanism, which may be saturated at normal physiological plasma leptin concentration.
Insulin Receptor Substrate-1 Phosphorylation and Phosphatidylinositol 3-Kinase Activity in Skeletal Muscle From NIDDM Subjects After In Vivo Insulin Stimulation
Authors: Björnholm Marie , Kawano Yuichi , Lehtihet Mikael , Zierath Juleen R
Published: September 2013

We examined the effect of physiological hyperinsulinemia on insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation and phosphatidylinositol (PI) 3-kinase activity in skeletal muscle from six lean–to–moderately obese NIDDM patients and six healthy subjects. A rise in serum insulin levels from ∼60 to ∼650 pmol/l increased IRS-1 tyrosine phosphorylation sixfold over basal levels in control muscle (P < 0.01), whereas no significant increase was noted in NIDDM muscle. The reduced IRS-1 phosphorylation in the NIDDM muscle was not related to changes in IRS-1 protein content, since IRS-1 protein expression was similar between control and NIDDM subjects (16.0 ± 1.7 vs. 22.9 ± 4.0 arbitrary units/mg protein for control and NIDDM, respectively; NS). Physiological hyperinsulinemia increased PI 3-kinase activity in control muscle twofold (P < 0.01), whereas no increase in insulin-stimulated PI 3-kinase activity was noted in the NIDDM muscle. Furthermore, in vitro insulin-stimulated (600 pmol/l) 3-O-methylglucose transport was 40% lower in isolated muscle from NIDDM subjects (P < 0.05). The present findings couple both reduced insulin-stimulated IRS-1 tyrosine phosphorylation and PI 3-kinase activity to the impaired insulin-stimulated glucose transport in skeletal muscle from lean–to–moderately obese NIDDM subjects.
New Insights Into the Role and Mechanism of Glycogen Synthase Activation by Insulin
Authors: Lawrence John C , Roach Peter J
Published: September 2013

The metabolism of the storage polysaccharide glycogen is intimately linked with insulin action and blood glucose homeostasis. Insulin activates both glucose transport and glycogen synthase in skeletal muscle. The central issue of a long-standing debate is which of these two effects determines the rate of glycogen synthesis in response to insulin. Recent studies with transgenic animals indicate that, under appropriate conditions, each process can contribute to determining the extent of glycogen accumulation. Insulin causes stable activation of glycogen synthase by promoting dephosphorylation of multiple sites in the enzyme. A model linking this action to the mitogen-activated protein kinase signaling pathway via the phosphorylation of the regulatory subunit of glycogen synthase phosphatase gained widespread acceptance. However, the most recent evidence argues strongly against this mechanism. A newer model, in which insulin inactivates the enzyme glycogen synthase kinase-3 via the protein kinase B pathway, has emerged. Though promising, this model still does not completely explain the molecular basis for the insulin-mediated activation of glycogen synthase, which remains one of the many unknowns of insulin action.
Bioavailability and Bioeffectiveness of Subcutaneous Human Insulin and Two of its Analogs—LysB28ProB29-Human Insulin and AspB10LysB28ProB29-Human Insulin—Assessed in a Conscious Pig Model
Authors: Radziuk Jerry M , Davies Jill C , Pye W Susan , Shields James E , DiMarchi Richard D , Chance Ronald E
Published: September 2013

In this study, human insulin was compared with two of its analogs—LysB28ProB29-human insulin and AspB10LysB28ProB29-human insulin—with respect to bioavailability and metabolic effectiveness. Absorption from the subcutaneous site was determined using kinetic parameters from the washout curve, following intravenous infusion of insulin or analog. Absorption was found to be more rapid for the two analogs, with 90% absorption by 100 min for the analogs and by 180 min for insulin. Total absorption was 97 ± 10% for insulin, 99 ± 7% for LysB28ProB29-human insulin, and 93 ± 12% for AspB10LysB28ProB29-human insulin. Bioactivity was assessed from the glucose infusion and using tracer-determined metabolic clearance rates (MCRs) and glucose production rates. The fractional glucose requirements (relative to the total amount infused) increased more rapidly for the two analogs than for insulin, with 50% of the glucose infused by 105 min for both analogs vs. 145 min for insulin. The total amount of glucose required was, however, significantly less (19.7 ± 1.5 mmol/kg) for AspB10LysB28ProB29-human insulin than for either LysB28ProB29-human insulin (25.9 ± 3.0 mmol/kg) or human insulin (27.8 ± 2.6 mmol/kg). The glucose requirements were reflected in a lower MCR for AspB10LysB28ProB29-human insulin but equivalent decreases in the rates of glucose production. Thus both analogs demonstrated more rapid rates of absorption, onset, and termination of action, but were not completely bioequivalent, with AspB10LysB28ProB29-human insulin demonstrating a 25% decrease in bioactivity.
Glutamate Decarboxylase–Reactive Peripheral Blood Lymphocytes From Patients With IDDM Express Gut-Specific Homing Receptor α4β7-Integrin
Authors: Paronen Johanna , Klemetti Paula , Kantele Jussi M , Savilahti Erkki , Perheentupa Jaakko , Åkerblom Hans K , Vaarala Outi
Published: September 2013

Migration of lymphocytes to the pancreas is a prerequisite for insulitis in IDDM. Mucosal vascular addressin (MAdCAM-1), involved in the recirculation of lymphocytes to the gut, has been found in the inflamed islets in NOD mice. In humans, triggers of the gut immune system (e.g., early exposure to cow's milk proteins in infancy, exposure to enteroviral infections) have been associated with IDDM. To study the possible link between the gut immune system and IDDM, we tested the expression of the α4β7-integrin, a homing receptor for MAdCAM-1, on GAD65-reactive lymphocytes. Using immunomagnetic cell sorting, we depleted the lymphocytes with high expression of α4β7-integrin in the peripheral blood mononuclear cell population from IDDM patients and patients with autoimmune polyendocrine disease type 1 (APD-I). The depletion led to a marked decrease (mean 70%) in the cellular response against GAD65 in three of six IDDM patients and in one subject at high risk for IDDM. A decrease of 37% in the GAD response was observed after depletion in the case of one APD-I patient who also had IDDM. Cellular response to tetanus toxoid increased in the majority of patients as well as in three control subjects studied. We demonstrated that a remarkable population of islet cell antigen–reactive lymphocytes express the gut-specific homing receptor, which emphasizes the role of gut immunity in IDDM. The manipulation of the gut immune system is therefore proposed as a tool for modulation of the autoimmunity against pancreatic β-cells in IDDM.
Mutations in the Hepatocyte Nuclear Factor–1α Gene Are a Common Cause of Maturity-Onset Diabetes of the Young in the U.K.
Authors: Frayling Timothy M , Bulman Michael P , Ellard Sian , Appleton Maggie , Dronsfield Mark J , Mackie Alasdair D R , Baird Joyce D , Kaisaki Pamela J , Yamagata Kazuya , Bell Graeme I , Bain Stephen C , Hattersley Andrew T
Published: September 2013

Mutations in the hepatocyte nuclear factor–1α (HNF-1α) gene have recently been shown to cause maturityonset diabetes of the young (MODY). We have examined 15 U.K. MODY families for mutations in the coding region of the HNF-1α gene. Eight different mutations, three frameshift (P291fsinsC, P379fsdelCT, and A443fsdelCA) and five missense mutations (P129T, R131W, R159W, P519L, and T620I), were identified in eleven families (73%). The previously reported mutation P291fsinsC was found in four pedigrees. A screen of a further 32 probands with early onset (<40 years of age) NIDDM showed the mutation in two additional families. This common mutation was present on at least three different haplotypes, suggesting that its high frequency is due to recurrent mutation rather than a founder effect. We have demonstrated that mutations in the HNF-1α gene are a common cause of MODY in U.K. families and result in early onset NIDDM with a progressive clinical course. Mutation-based genetic counseling can now be considered for the majority of patients with MODY.