bluuebunny/crossref_metadata_2025 huggingface dataset:
A Lesson in Metabolic Regulation Inspired by the Glucokinase Glucose Sensor Paradigm
Authors: Matschinsky Franz M
Published: September 2013

Special features of glucose metabolism in pancreatic β-cells are central to an understanding of the physiological role of these cells in glucose homeostasis. Several of these characteristics are emphasized: a high-capacity system for glucose transport; glucose phosphorylation by the high-Km glucokinase (GK), which is rate-limiting for glucose metabolism and determines physiologically the glucose dependency curves of many processes in β-cell intermediary and energy metabolism and of insulin release and is therefore viewed as glucose sensor; remarkably low activity of lactate dehydrogenase and the presence of effective hydrogen shuttles to allow virtually quantitative oxidation of glycolytic NADH; the near absence of glycogen and fatty acid synthesis and of gluconeogenesis, such that intermediary metabolism is primarily catabolic; a crucial role of mitochondrial processes, including the citric acid cycle, electron transport, and oxidative phosphorylation with FoF1 ATPase governing the glucose-dependent increase of the ATP mass-action ratio; a Ca2+-independent glucose-induced respiratory burst and increased ATP production in β-cells as striking manifestations of crucial mitochondrial reactions; control of the membrane potential by the mass-action ratio of ATP and voltage-dependent Ca2+ influx as signal for insulin release; accumulation of malonyl-CoA, acyl-CoA, and diacylglycerol as essential or auxiliary metabolic coupling factors; and amplification of the adenine nucleotide, lipid-related, and Ca2+ signals to recruit many auxiliary processes to maximize insulin biosynthesis and release. The biochemical design also suggests certain candidate diabetes genes related to fuel metabolism: low-activity and low-stability GK mutants that explain in part the maturity-onset diabetes of the young (MODY) phenotype in humans and mitochondrial DNA mutations of FoF1 ATPase components thought to cause late-onset diabetes in BHEcdb rats. These two examples are chosen to illustrate that metabolic reactions with high control strength participating in β-cell energy metabolism and generating coupling factors and intracellular signals are steps with great susceptibility to genetic, environmental, and pharmacological influences. Glucose metabolism of β-cells also controls, in addition to insulin secretion and insulin biosynthesis, an adaptive response to excessive fuel loads and may increase the β-cell mass by hypertrophy, hyperplasia, and neogenesis. It is probable that this adaptive response is compromised in diabetes because of the GK or ATPase mutants that are highlighted here. A comprehensive knowledge of β-cell intermediary and energy metabolism is therefore the foundation for understanding the role of these cells in fuel homeostasis and in the pathogenesis of the most prevalent metabolic disease, diabetes.
cAMP-Signaling Pathway Acts in Selective Synergism With Glucose or Tolbutamide to Increase Cytosolic Ca2+ in Rat Pancreatic β-Cells
Authors: Yaekura Kazuro , Kakei Masafumi , Yada Toshihiko
Published: September 2013

cAMP and the insulinotropic peptides that raise cAMP glucose-dependently increase the cytosolic free Ca2+ concentration ([Ca2+]i) in pancreatic β-cells, which is tightly linked to the potentiation of glucose-induced insulin release. We examined whether cAMP increases [Ca2+]i in specific cooperation only with glucose or also with other insulin secretagogues that act through different mechanisms. [Ca2+]i in single rat pancreatic β-cells was measured by dual-wavelength fura-2 microfluorometry. In the presence of a stimulatory concentration of glucose (8.3 mmol/l) and the moderate elevation in [Ca2+]i induced by it, forskolin, an activator of adenylyl cyclase, or dibutyryl cAMP produced a marked additional increase in [Ca2+]i but was ineffective at the basal 2.8 mmol/l glucose. These cAMP-elevating agents also potentiated the effect of tolbutamide on [Ca2+]i. The cAMP-induced increase in [Ca2+]i was completely and selectively inhibited by a blocker of cAMP-dependent protein kinase A (PKA), and by nitrendipine, a blocker of the L-type Ca2+ channel. However, in the presence of high KCl and the [Ca2+]i elevation induced by it, a rise in cAMP failed to further increase [Ca2+]i, whereas BAY K8644, an agonist of L-type Ca2+ channels, evoked an additional increase in [Ca2+]i. Under low Na+ conditions, the [Ca2+]i response to cAMP was observed in the majority of the cells. In the cells in which glucose at 4.5–5 mmol/l was inadequate to increase [Ca2+]i, the glucose together with a rise in cAMP often increased [Ca2+]i. Likewise, tolbutamide and a rise in cAMP acted in concert to increase [Ca2+]i. Thus, cAMP left-shifted the concentration-[Ca2+]i response relationship for glucose and tolbutamide. In conclusion, the cAMP-PKA pathway acts in selective synergism with glucose and tolbutamide to initiate [Ca2+]i signals in pancreatic β-cells. cAMP appears to regulate β-cell sensitivity to glucose and tolbutamide. In contrast, cAMP fails to cooperate with high KCl to increase [Ca2+]i. It is suggested that cAMP acts mainly on a site that is more proximal but functionally linked to the L-type Ca2+ channel, thereby finally increasing Ca2+ influx through this channel.
Effect of Pancreas Transplantation on Free Fatty Acid Metabolism in Uremic IDDM Patients
Authors: Luzi Livio , Groop Leif C , Perseghin Gianluca , Taskinen Marja-Ritta , Hilden Hannele , Bianchi Elda , Terruzzi Ileana , Dodesini Alessandro R , Carlo Valerio Di , Pozza Guido
Published: September 2013

To assess the effect of pancreas transplantation on free fatty acid (FFA) and glucose metabolism, we studied seven uremic IDDM patients (HbA1c 9.1%), nine IDDM patients after combined kidney-pancreas transplantation (HbA1c 5.8%), seven patients with chronic uveitis (HbA1c 5.6%), and nine normal control subjects (HbA1c 5.5%) by means of the [3-3H]glucose and [1-14C]palmitate infusion techniques combined with indirect calorimetry and euglycemic insulin clamp. In the postabsorptive state, pancreas-transplant patients had similar plasma glucose and FFA concentrations and non-statistically different rates of hepatic glucose production (HGP) and FFA turnover, while demonstrating a reduced rate of FFA oxidation (42 ± 5 vs. 73 ± 10 μmicromol · m−2 · min−1; P < 0.05) compared with control subjects. After 180 min of tracer equilibration, all subjects underwent a low-dose (100 min, 8 mU · m−2 · min−1) followed by a high-dose (100 min, 40 mU · m−2 · min−1) euglycemic insulin infusion. During insulin infusion, pancreas-transplant patients showed a greater inhibition of FFA concentration (609 ± 76 to 58 ± 15 micromol/l) compared with healthy subjects (681 ± 90 to 187 ± 25 micromol/l; P < 0.01 vs. pancreas-transplant patients). FFA turnover and oxidation rates during both low-dose and high-dose insulin infusions were lower in pancreas-transplant patients compared with healthy subjects (P < 0.03 and P < 0.01, for turnover and oxidation, respectively). Uremic IDDM patients demonstration altered basal and insulin-mediated glucose metabolism. Pancreas transplantation normalized only insulin-mediated glucose oxidation, leaving the stimulation of non-oxidative glucose disposal still markedly defective. In conclusion, patients after pancreas transplantation have normal basal FFA turnover and reduced basal FFA oxidation rates. During hyperinsulinemia, pancreas-transplant patients show a normal inhibition of FFA turnover and FFA oxidation. Insulin-mediated glucose metabolism remained abnormal after pancreas transplantation. Our findings may be related to the effect of chronic immunosuppressive therapy on glucose and FFA metabolism.
Linkage Studies of NIDDM with 23 Chromosome 11 Markers in a Sample of Whites of Northern European Descent
Authors: Elbein Steven C , Bragg Kelli L , Hoffman Michael D , Mayorga Rachel A , Leppert Mayorga F
Published: September 2013

Considerable data support a genetic basis to susceptibility for NIDDM, but previous analysis of candidate genes has failed to identify a major susceptibility locus. Among regions with multiple potential candidates is chromosome 11, which includes the apolipoprotein C3 cluster, muscle glycogen phosphorylase, two insulin-dependent diabetes loci, the sulfonylurea receptor, and ataxia telangiectasia. To test linkage, we initially typed 19 markers at 10- to 15-cM intervals along chromosome 11. Analyses carried out under parametric models in members of 16-19 families of northern European ancestry detected possible linkage of NIDDM to D11S916. Nonparametric methods detected possible linkage to NIDDM at D11S901, which was 5–10 cM distant, and at D11S935, which was ∼30 cM distant. Both D11S916 and D11S901 were near the IDDM4 locus. To further test linkage, we typed five additional markers within 5 cM of D11S916 in the initial 19 families. We also tested markers from the linked region in a second set of recently sampled additional families. Two additional markers (D11S527 and D11S534) showed possible linkage in the initial 19 families, but none of the markers were linked to NIDDM in a separate set of families from the same ethnic background. The best evidence for linkage in the combined data set of the initial 19 families and 26 additional families was at D11S534 under parametric analysis (Z = 1.20) and at D11S935 under nonparametric analysis (affected pedigree number, P = 0.0013). Our findings suggest marginal evidence for a diabetes susceptibility locus in the region between D11S901 and D11S935, with the best evidence for a locus at or near D11S935. Replication of these findings in other populations will be necessary to distinguish false-positive linkage from a true NIDDM susceptibility locus.
Biochemical and Molecular Mechanisms in the Development of Diabetic Vascular Complications
Authors: King George L , Kunisaki Makoto , Nishio Yoshihiko , Inoguchi Toyoshi , Shiba Teruo , Xia Pu
Published: September 2013

Hyperglycemia is the major causal factor in the development of diabetic vascular complications. The mechanism by which hyperglycemia causes the complications is not clear; however, it is very likely that hyperglycemia is mediating its adverse effects through multiple mechanisms. We have summarized some of these mechanisms in this review, with particular attention to the effect of hyperglycemia on the activation of diacylglycerol (DAG)-protein kinase C (PKC) pathway. We have reviewed existing information regarding various vascular tissues that show increased DAG and PKC levels. In addition, the mechanism by which hyperglycemia increases DAG as well as the cellular physiological consequences on the activation of PKC have been reviewed.
Mechanism on Disorders of Coagulation and Fibrinolysis in Diabetes
Authors: Matsuda Tamotsu , Morishita Eriko , Jokaji Hiroshi , Asakura Hidesaku , Saito Masanori , Yoshida Tomotaka , Takemoto Ken-ichi
Published: September 2013

Determination of various important parameters of coagulation and fibrinolysis, clinical characteristics, and levels of serum lipid were compared in 193 patients with NIDDM and 50 control subjects. Levels of fibrinogen, tissue factor pathway inhibitor (TFPI), thrombin-antithrombin complex, and plasminogen activator inhibitor 1 in plasma increased significantly in the diabetic patients. Levels of TFPI correlated significantly with levels of total cholesterol. In the patients with coronary heart disease or cerebral infarction, levels of lipoprotein(a) increased significantly. From these results, we have concluded that there is a thrombotic tendency or at least an imbalance between the hemostatic and thrombosis-protecting system in diabetic patients, especially in patients with angiopathy.
Augmented Contractile Function and Abnormal Ca2+ Handling in the Aorta of Zucker Obese Rats With Insulin Resistance
Authors: Ouchi Yasuyoshi , Han Shu-zhong , Kim Seungbum , Akishita Masahiro , Kozaki Koichi , Toba Kenji , Orimo Hajime
Published: September 2013

To investigate the role of hyperinsulinemia/msulin resistance in vasomotor tone regulation, we studied the effects of vasoactive substances on tension and intracellular free calcium concentration ([Ca2+]i) of aortic smooth muscle derived from rats that were made hyperinsulinemic by insulin infusion and from Zucker obese rats with insulin resistance. The tension and [Ca2+]i of fura 2-loaded aortic strip preparations without endothelium were simultaneously measured by using a fluorimeter. Ten male Wistar rats received a continuous subcutaneous infusion of insulin (18 nmol · kg−1 · day−1) for 2 weeks with osmotic minipumps (INS group). A control group of 10 rats received vehicle. The plasma imnranoreactive insulin concentration in the INS group increased to 930 ± 54 Pmol/1. The increase in [Ca2+]i and tension by KCI and phenylephrine (PE) were lower in the INS group without alteration of the [Ca2+]itension relationship. The responses to serotonin (5-HT) in the INS group were similar to those in the control group. In contrast, responses to KCI, PE, and 5-HT were markedly enhanced in Zucker obese rats compared with those in Zucker lean rats. The pretreatment of aortic preparations from lean rats with Bay K 8644 significantly enhanced the responses to KCI to the level observed in the preparations from obese rats; however, Bay K 8644 failed to affect the responses to KCI in obese rats. These results suggest that enhanced vascular contractile responses to vasoactive substances, possibly due to altered function of the voltage-dependent Ca2+ channel in vascular smooth muscle, may play an important role in the pathogenesis of hypertension in the insulin resistance syndrome.
The Mechanism of Collagen Cross-Linking in Diabetes: A Puzzle Nearing Resolution
Authors: Monnier Vincent M , Glomb Marcus , Elgawish Abdelhamid , Sell David R
Published: September 2013

Considerable interest has been focused in recent years on the mechanism of collagen cross-linking by high glucose in vitro and in vivo. Experiments in both diabetic humans and in animals have shown that over time collagen becomes less soluble, less digestible by collagenase, more stable to heat-induced denaturation, and more glycated. In addition, collagen becomes more modified by advanced products of the Maillard reaction, i.e., immunoreactive advanced glycation end products and the glycoxidation markers carboxymethyllysine and pentosidine. Mechanistic studies have shown that collagen cross-linking in vitro can be uncoupled from glycation by the use of antioxidants and chelating agents. Experiments in the authors' laboratory revealed that ∼50% of carboxymethyllysine formed in vitro originates from pathways other than oxidation of Amadori products, i.e., most likely the oxidation of Schiff base-linked glucose. In addition, the increase in thermal stability of rat tail tendons exposed to high glucose in vitro or in vivo was found to strongly depend on H202 formation. The final missing piece of the puzzle is that of the structure of the major cross-link. We speculate that it is a nonfluorescent nonultraviolet active cross-link between two lysine residues, which includes a fragmentation product of glucose linked in a nonreducible bond labile to both strong acids and bases.
Rage: A Novel Cellular Receptor for Advanced Glycation End Products
Authors: Schmidt Ann Marie , Hori Osamu , Cao Rong , Yan Shi Du , Brett Jerold , Wautier Jean-Luc , Ogawa Satoshi , Kuwabara Keisuke , Matsumoto Masayasu , Stern David
Published: September 2013

Exposure of proteins to reducing sugars results in nonenzymatic glycation with the ultimate formation of advanced glycation end products (AGEs). One means through which AGEs modulate cellular functions is through binding to specific cell surface acceptor molecules. The receptor for AGEs (RAGE) is such a receptor and is a newly identified member of the immunoglobulin superfamily expressed on endothelial cells (ECs), mononuclear phagocytes (MPs), and vascular smooth muscle cells (SMCs) in both vivo and in vitro. Binding of AGEs to RAGE results in induction of cellular oxidant stress, as exemplified by the generation of thiobarbituric acid-reactive substances, expression of heme oxygenase type I, and activation of the transcription factor NF-kB, with consequences for a range of cellular functions. AGEs on the surface of diabetic red cells enhance binding to endothelial RAGE and result in enhanced oxidant stress in the vessel wall. By using reagents to selectively block access to RAGE, the role of this receptor in AGE-mediated perturbation of cellular properties can be dissected in detail.
Characterization of Human DNA Topoisomerase II as an Autoantigen Recognized by Patients With IDDM
Authors: Chang Yih-Hsin , Hwang Jaulang , Shang Huey-Fang , Tsai Shih-Tzer
Published: September 2013

Autoantibodies against several cytoplasmic autoantigens such as glutamic acid decarboxylase, heat shock protein 65, insulin, and carboxypeptidase H have been identified in the sera of patients with IDDM. To investigate whether type II DNA topoisomerase (TopII) is an autoantigen in IDDM patients, we have constructed a series of overlapping DNA TopII fragments that covered the entire length of this enzyme. These fragments were used as antigens to screen sera of IDDM patients. We have examined 195 Chinese IDDM patients (mean age 14.2 ± 7.5 years, age at onset 9.2 ± 6.4 years, duration of diabetes 4.6 ± 3.4 years) and 51 nondiabetic individuals. The results showed that DNA TopII autoantibodies were detected in 49.2 and 47.2% of IDDM patients using purified TopII fragments and full-length TopII as antigens, respectively. The frequency of anti-TopII positivity was relatively stable irrespective of sex and disease duration. The patients were slightly older at onset and the prevalence of anti-thyroglobulin/anti-microsomal autoantibodies was twice that in the IDDM subgroup positive for anti-TopII than in IDDM patients who were negative for anti-TopII. We also characterized the epitopes of DNA TopII that were recognized by IDDM sera. Those epitopes resided mostly in three distinct domains. One resided in amino acid residues 1–147, another in amino acid residues 286–472, and the third in the COOH-terminal one-third of DNA TopII. Intriguingly, we found that these epitopes shared similarity (up to 36% identity and 63.6% homology) to previously identified epitopes of IDDM autoantigens.
A Variation at Position −30 of the β-Cell Glucokinase Gene Promoter Is Associated With Reduced β-Cell Function in Middle-Aged Japanese-American Men
Authors: Stone Lisa M , Kahn Steven E , Fujimoto Wilfred Y , Deeb Samir S , Porte Daniel
Published: September 2013

We sought to determine whether a G→A variant at position −30 of the β-cell promoter of the glucokinase (GCK) gene observed to be present more frequently in Japanese-American men with impaired glucose tolerance (IGT) than in Japanese-American men with normal glucose tolerance (NGT) is associated with impaired β-cell function. We studied 125 unrelated Japanese-American men (aged 46–74 years; mean 61 ± 0.5) who were nondiabetic by a 75-g oral glucose tolerance test (OGTT) (65 had NGT and 60 had IGT). The presence of the −30 β-cell GCK gene promoter variant was determined by single-strand conformation polymorphism analysis. β-cell function was assessed using the ratio of the incremental response in immunoreactive insulin (IRI) to that of glucose during the first 30 min of the OGTT (Δ IRI[30 min−0 min]/Δglucose[30 min−0 min]) performed at baseline and at 5 years of follow-up. β-cell function adjusted for basal IRI ([Δ IRI[30 min−0 min]/Δ glucose[30 min−0 min]]/basal IRI; the relative insulin response) was also evaluated. At baseline, the −30 β-cell GCK gene promoter variant was present in 15.4% of subjects with NGT vs. 38.3% of subjects with IGT (P < 0.01). Fasting IRI did not differ between groups. At baseline, ΔIRI[30 min−0 min]/Δglucose[30 min−0 min] was significantly lower in subjects with the promoter variant (57 × 10−9 to 95 × 10−9 to 95 × 10−9] vs. 77 × 10−9 [55 × 10−9 to 128 × 10−9]; median [interquartile range]; P < 0.01) as was the relative insulin response (0.97 [0.70–1.24] vs. 1.37 [0.95–2.03] l/mmol; P < 0.0005). Similarly, at 5 years of follow-up, ΔIRI[30 min−0 min]/Δglucose[30 min−0 min] and the relative insulin response were significantly reduced in the group with the variant. In the subgroups of subjects with IGT at baseline, IGT at 5 years, and NGT at 5 years, the relative insulin response was significantly lower in those with the variant. We conclude that the −30 β-cell GCK gene promoter variant is associated with reduced β-cell function in middle-aged Japanese-American men and may contribute to the high risk of abnormal glucose tolerance in this population.
Isokinetic Muscle Strength in Long-Term IDDM Patients in Relation to Diabetic Complications
Authors: Andersen Henning , Poulsen Per L , Mogensen Carl E , Jakobsen Johannes
Published: September 2013

The isokinetic muscle strength in 56 IDDM patients with > 20 years of diabetes duration and in their individually sex-, age-, weight-, and height-matched control subjects was assessed. Peak torque of foot dorsal and plantar flexion and knee and wrist extension and flexion was measured. The neuropathic condition was assessed by a neurological disability score, a neuropathy symptom score, nerve conduction studies, and quantitative sensory examination. All results were summed to obtain a neuropathy rank-sum score for each patient. According to their renal albumin excretion, the patients were classified to have normo-, micro-, or macroalbuminuria. In addition, according to their retinal status, patients were classified as having no, simple, or proliferative retinopathy. The IDDM patients had a 21% reduction of muscle strength of both ankle dorsal (P < 1 × 10™4) and plantar flexors (P < 0.01), compared with control subjects. A 16% reduction of knee extensors (P < 0.005) and a 17% reduction of knee flexors (P < 0.01) was found. In contrast, muscle strength in wrist flexors and extensors was not significantly reduced (10 and 11%, respectively [NS]). In patients with the most severe weakness, muscle strength of the calf muscles was only 50% of the expected performance. Correlations were found between the neuropathy rank-sum score and the muscle strength of ankle dorsal (r = −0.66, P < 1 × 10™7) and plantar flexors (r = −0.51, P < 0.0005), knee extensors (r = −0.51, P < 0.0005) and flexors (r = −0.44, P < 0.005), and wrist flexors (r = −0.41, P < 0.005). No correlation was found for wrist extensors (r = 0). Neither were there any relationships between muscle strength at the ankle and knee and the degree of albuminuria or retinopathy. In conclusion, motor performance is substantially impaired in long-term IDDM patients, and the weakness is related to the presence of neuropathy but not to albuminuria or retinopathy per se.
Gene Expression of Islet Cell Antigen p69 in Human, Mouse, and Rat
Authors: Karges Wolfram , Pietropaolo Massimo , Ackerley Cameron A , Dosch Hans-Michael
Published: September 2013

Based on the detection of specific antibodies and T-cell sensitization in patients with IDDM, islet cell antigen p69 (ICAp69) has been suggested to be a target antigen of diabetic autoimmunity. The biological function, tissue expression, and developmental kinetics of ICAp69 are largely unknown. We analyzed ICAp69 expression at the gene transcription and protein level in human and rodent tissues. By using template-calibrated quantitative reverse transcriptase polymerase chain reaction (RT-PCR), high levels of ICAp69 mRNA were found in human pancreatic islets and brain. In mouse and rat, ICAp69 gene expression peaked in islet cell lines followed by testis, islets, and brain. ICAp69 mRNA was found at low levels in other organs by RT-PCR but not by Northern blot analysis. In mice, ICAp69 transcription becomes detectable in fetal life, and fetal and adult gene expression patterns are similar. Western blot analysis of human and mouse tissues showed high expression of ICAp69 in brain, testis, pancreatic tissue, and islet cell lines. In these organs, ICAp69 immunoreactivity is predominately localized at the blood brain barrier (capillary endothelium), at the blood testis barrier (Sertoli cells and spermatids), and in pancreatic islets (β-cells). The subcellular localization of ICAp69 to endoplasmic reticulum, Golgi complex, and vesicles by immune electron microscopy suggests a role of this neuroendocrine molecule in cellular protein traffic and processing.
Specificity of Leptin Action on Elevated Blood Glucose Levels and Hypothalamic Neuropeptide Y Gene Expression in ob/ob Mice
Authors: Schwartz Michael W , Baskin Denis G , Bukowski Thomas R , Kuijper Joseph L , Foster Donald , Lasser Gerry , Prunkard Donna E , Porte Daniel , Woods Stephen C , Seeley Randy J , Weigle David S
Published: September 2013

Correction of the obese state induced by genetic leptin deficiency reduces elevated levels of both blood glucose and hypothalamic neuropeptide Y (NPY) mRNA in ob/ob mice. To determine whether these responses are due to a specific action of leptin or to the reversal of the obese state, we investigated the specificity of the effect of systemic leptin administration to ob/ob mice (n = 8) on levels of plasma glucose and insulin and on hypothalamic expression of NPY mRNA. Saline-treated controls were either fed ad libitum (n = 8) or pair-fed to the intake of the leptin-treated group (n = 8) to control for changes of food intake induced by leptin. The specificity of the effect of leptin was further assessed by 1) measuring NPY gene expression in db/db mice (n = 6) that are resistant to leptin, 2) measuring NPY gene expression in brain areas outside the hypothalamus, and 3) measuring the effect of leptin administration on hypothalamic expression of corticotropin-releasing hormone (CRH) mRNA. Five daily intraperitoneal injections of recombinant mouse leptin (150 μg) in ob/ob mice lowered food intake by 56% (P < 0.05), body weight by 4.1% (P < 0.05), and levels of NPY mRNA in the hypothalamic arcuate nucleus by 42.3% (P < 0.05) as compared with saline-treated controls. Pair-feeding of ob/ob mice to the intake of leptin-treated animals produced equivalent weight loss, but did not alter expression of NPY mRNA in the arcuate nucleus. Leptin administration was also without effect on food intake, body weight, or NPY mRNA levels in the arcuate nucleus of db/db mice. In ob/ob mice, leptin did not alter NPY mRNA levels in cerebral cortex or hippocampus or the expression of CRH mRNA in the hypothalamic paraventricular nucleus (PVN). Leptin administration to ob/ob mice also markedly reduced serum glucose (8.3 ± 1.2 vs. 24.5 ± 3.8 mmol/l; P < 0.01) and insulin levels (7,263 ± 1,309 vs. 3,150 ± 780 pmol/l), but was ineffective in db/db mice. Pair-fed mice experienced reductions of glucose and insulin levels that were < 60% of the reduction induced by leptin. The results suggest that in ob/ob mice, systemic administration of leptin inhibits NPY gene overexpression through a specific action in the arcuate nucleus and exerts a hypoglycemic action that is partly independent of its weight-reducing effects. Furthermore, both effects occur before reversal of the obesity syndrome. Defective leptin signaling due to either leptin deficiency (in ob/ob mice) or leptin resistance (in db/db mice) therefore leads directly to hyperglycemia and the overexpression of hypothalamic NPY that is implicated in the pathogenesis of the obesity syndrome.
The Search for IDDM Susceptibility Genes: The Next Generation
Authors: Owerbach David , Gabbay Kenneth H
Published: September 2013

Two human chromosomal regions, the HLA region on chromosome 6p21 and the insulin gene region on chromosome 11p15, have been investigated in detail for more than 10 years for the presence of IDDM susceptibility genes. Recent genome searches indicate the possible existence of many additional susceptibility genes in IDDM. The lengthy and protracted studies to prove the linkage and identity of the susceptibility genes in the HLA and insulin gene regions provide a perspective and background for understanding the complexities and time course for characterization of the putative additional IDDM susceptibility genes uncovered by genome searches.
Potentiation of Effects of Weight Loss by Monounsaturated Fatty Acids in Obese NIDDM Patients
Authors: Low Cecilia C , Grossman Eric B , Gumbiner Barry
Published: September 2013

Although moderate weight loss improves glycemic control in obese NIDDM patients, quite often it is not normalized. To determine whether the response to weight loss can be improved by altering the macronutrient composition of hypocaloric diets, 17 obese NIDDM patients were studied at 1) baseline, 2) after dieting for 6 weeks on a formula diet enriched in either monounsaturated fatty acids (MUFAs, n = 9) or carbohydrates (CHOs, n = 8) at a 50% caloric deficit, and 3) after 4 weeks of postdiet refeeding on the respective formulas with caloric intake titrated to achieve weight maintenance. Fasting, 24-h, and oral glucose tolerance test (OGTT) blood glucose, plasma insulin, and C-peptide levels were measured. All prediet parameters were similar between groups. After dieting, although weight loss was similar between groups, the fasting glucose level decreased significantly more in the MUFA group (−4.6 ± 0.7 mmol/l) than in the CHO group (−2.4 ± 1.0 mmol/l; P < 0.05). Twenty-four–hour glycemia decreased in both groups after dieting, but the MUFA group had a greater decrease than the CHO group (P < 0.05, analysis of variance [ANOVA]). Although decreases in fasting glycemia were maintained in both groups after refeeding, postprandial glycemia deteriorated after refeeding with the CHO- but not the MUFA-enriched formula (P < 0.05). After dieting and refeeding, fasting C-peptide increased 204 ± 47 pmol/l in the MUFA group, but the CHO group remained at prediet levels (P < 0.05). Twenty-four-hour C-peptide levels were similar between groups after dieting and refeeding, despite the lower glycemia and CHO content of the MUFA formula. However, when equal amounts of CHO were consumed during the OGTT, the MUFA group had significantly higher C-peptide levels after both dieting and refeeding (P < 0.05). Fasting, 24-h, and OGTT insulin levels were similar between groups throughout the study. These results indicate that macronutrient composition is an important determinant of the glycemic response to weight-loss therapy in obese NIDDM patients. Based on the C-peptide response during the OGTT, increased CHO-induced insulin secretion is one possible mechanism by which this occurs.
Islets of Langerhans Generate Wavelike Electric Activity Modulated by Glucose Concentration
Authors: Palti Yoram , David Galia Ben , Lachov Ela , Mika Yuval H , Omri Gila , Schatzberger Rachel
Published: September 2013

The electric activity of whole islets of Langerhans was monitored for the first time in this study. Measurements were made from single islets isolated from mice, hamsters, gerbils, and rats by means of external electrodes. Well-structured synchronized potential spikes up to 0.5 mV in amplitude with a stable frequency of 0.5–2 Hz were measured. Spike generation had a glucose concentration threshold. In the physiological range of each animal species, firing rate was an approximate linear function of glucose concentration. At low glucose concentrations, firing became intermittent, i.e., in bursts, while in the physiological range and above, firing was typically continuous. Simultaneous measurements from two locations on an islet indicate that the measured activity reflects the propagation of an excitation wave throughout the islet. This, together with signal synchronization, suggests that the islets contain a functional pacemaker (FPM) from which excitation propagates by means of gap junctions to the rest of the islet cells (mostly β-cells). Thus, the electric characteristics of the individual β-cells are functionally masked so that the islet acts as a single functional unit. In view of the dependency of insulin secretion on the islet's electric activity, the islet glucose-insulin dose-response characteristics must be determined by those of the FPM.
The Hemodynamic Abnormalities in Short-Term Insulin Deficiency: The Role of Prostaglandin Inhibition
Authors: Avogaro Angelo , Crepaldi Cristina , Piarulli Francesco , Milan Daniele , Valerio Anna , Pavan Paola , Sacerdoti David , Calabrò Alessio , Macdonald Ian , Crepaldi Gaetano , Scognamiglio Roldano , Tiengo Antonio
Published: September 2013

It has been suggested that the hemodynamic derangements present in diabetic ketoacidosis are the results not only of profound volume depletion but also of the effects of increased production of vasodilating prostaglandins (PGs), principally PGI2, released by adipose tissue. In animal and in vitro models, prostaglandin synthesis is increased during insulin deficiency. We assessed the effects of short-term ketosis on the metabolic and hemodynamic variables of 10 IDDM patients free from long-term complications and of 9 normal control subjects after a 7-day randomized double-blind indomethacin (INDO) (50 mg q.i.d.) or placebo treatment period. Calf blood flow (CBF), postocclusive reactive hyperemia (PORH), and recovery half-time (an index of overall perfusion) after PORH were measured by plethysmography. Left ventricular and myocardial functions were also studied in each different condition during placebo and INDO treatment in IDDM patients. During placebo treatment, the increase in CBF during ketosis was higher (1.75 ± 0.29 ml · min−1 · 100 ml muscle−1) than during INDO (0.85 ± 0.17 ml · min−1 · 100 ml muscle−1; P = 0.007). PORH was similar in baseline conditions, during ketosis, and in recovery in both the placebo and INDO arms. Recovery half-time significantly increased during placebo (10 ± 2; 200%; P < 0.01) but not during INDO (1 ± 1; 106%; NS) treatment. In normal control subjects, insulin deficiency did not induce any significant effect on hemodynamic variables. In IDDM patients, during placebo treatment, ketosis increased both the cardiac index (from 3.4 ± 0.7 to 4.1 ± 0.8 1 · min−1 · m−2; P < 0.01) and the stroke index (from 42 ± 8 to 49 ± 7 ml/m2; P < 0.01) without changes in left ventricular ejection fraction but with a significant increase in both left and right ventricular end-diastolic volumes. Metabolic recovery induced a normalization of these parameters. INDO treatment significantly blunted these alterations. In summary, we showed that during acute insulin deficiency, INDO-sensitive mechanisms mediate vascular disturbances. Moreover, INDO treatment was capable of completely preventing the cardiac venous return and the left ventricular alterations. INDO does not interfere with the overall ketogenetic process or with insulin-induced metabolic recovery.
Acute and Chronic Effect of Insulin on Leptin Production in Humans: Studies In Vivo and In Vitro
Authors: Kolaczynski Jerzy W , Nyce Mark R , Considine Robert V , Boden Guenther , Nolan John J , Henry Robert , Mudaliar Sunder R , Olefsky Jerrold , Caro Jose F
Published: September 2013

This study was undertaken to investigate the changes in obesity (OB) gene expression and production of leptin in response to insulin in vitro and in vivo under euglycemic and hyperglycemic conditions in humans. Three protocols were used: 1) euglycemic clamp with insulin infusion rates at 40, 120, 300, and 1,200 mU · m−2 · min−1 carried out for up to 5 h performed in 16 normal lean individuals, 30 obese individuals, and 31 patients with NIDDM; 2) 64-to 72-h hyperglycemic (glucose 12.6 mmol/l) clamp performed on 5 lean individuals; 3) long-term (96-h) primary culture of isolated abdominal adipocytes in the presence and absence of 100 nmol/l insulin. Short-term hyperinsulinemia in the range of 80 to > 10,000 μU/ml had no effect on circulating levels of leptin. During the prolonged hyperglycemic clamp, a rise in leptin was observed during the last 24 h of the study (P < 0.001). In the presence of insulin in vitro, OB gene expression increased at 72 h (P < 0.01), followed by an increase in leptin released to the medium (P < 0.001). In summary, insulin does not stimulate leptin production acutely; however, a long-term effect of insulin on leptin production could be demonstrated both in vivo and in vitro. These data suggest that insulin regulates OB gene expression and leptin production indirectly, probably through its trophic effect on adipocytes.
Are Insulin and Proinsulin Independent Risk Markers for Premature Coronary Artery Disease?
Authors: Katz Richard J , Ratner Robert E , Cohen Robert M , Eisenhower Ellen , Verme Dante
Published: September 2013

Controversy persists about whether hyperinsulinemia and hyperproinsulinemia are independent risk markers for coronary atherosclerosis. A common limitation of most previous studies has been imprecise categorization of disease status in normal and coronary artery disease (CAD) groups. We assessed the relationship of pancreatic β-cell secretory products and premature CAD in a casecontrol study of 134 nondiabetic subjects, aged ≤55 years old, carefully defined for CAD status by catheterization and/or thallium stress studies. Case patients comprised 66 patients with premature CAD, and control subjects (non-CAD group) included 68 patients without CAD but with traditional CAD risk factors and chest pain and/or abnormal electrocardiograms but normal catheterization and/or thallium stress studies. In addition to the CAD and non-CAD group comparison, both groups were compared with a reference group of 27 mixed lean and obese control volunteers. All CAD and non-CAD patients had a 3-h 75-g oral glucose tolerance test with measurement of fasting and post-glucose load immunoreactive insulin (IRI), specific insulin (INS), proinsulin-like material (PI), and C-peptide. Increased fasting insulin and fasting proinsulin levels both were statistically significantly associated with higher odds of being in either the premature CAD and the non-CAD groups when compared with the reference group in a polychotomous logistic regression model (odds ratio of at least 1.20 for a 20% increase in each β-cell secretory product in both comparisons, P ≤ 0.05). However, increased pancreatic β-cell secretory hormone levels did not show a statistically significant relative risk for being in the premature CAD group when compared with the non-CAD group. After adjustment for BMI, all statistically significant associations disappeared for IRI, INS, and PI when the odds favoring being in the CAD and non-CAD groups were compared versus the reference group. Furthermore, the odds of being in the premature CAD and non-CAD groups when compared with the reference group were not significantly associated to the ratio of PI to insulin and C-peptide. Thus, although there is a statistically significant association between the odds of having premature CAD with elevated insulin and proinsulin levels compared with the reference group, these findings are equally common in subjects with traditional CAD risk factors without detectable CAD. Furthermore, the association of higher insulin and proinsulin levels with the likelihood of a patient having or not having CAD disappears after adjustment for BMI, suggesting that insulin and proinsulin are not independent risk markers but are primarily dependent on obesity.
Reduced Myocardial 123I-Metaiodobenzylguanidine Uptake in Newly Diagnosed IDDM Patients
Authors: Schnell Oliver , Muhr Daniela , Weiss Mayo , Dresel Stefan , Haslbeck Manfred , Standl Eberhard
Published: September 2013

123I-labeled metaiodobenzylguanidine (123I-MIBG) scintigraphy is a novel technique for the assessment of cardiac sympathetic dysinnervation. To evaluate defects of the cardiac autonomic nervous system at the onset of IDDM, this technique together with conventional electrocardiogram (ECG)-based cardiac reflex tests and measurement of the QT interval was applied to 22 newly diagnosed metabolically stabilized IDDM patients without myocardial perfusion abnormalities (99mTc-labeled methoxyisobutylisonitrile scintigraphy) and 9 matched control subjects. Seventeen diabetic patients (77%), but none of the control subjects, were observed to have a reduced global myocardial uptake of 123I-MIBG. In contrast, only two diabetic patients (9%) demonstrated an ECG-based cardiac autonomic neuropathy (two or more of five age-related cardiac reflex tests abnormal) (P < 0.001). In newly diagnosed IDDM patients, the uptake of 123I-MIBG was reduced more in the posterior myocardial region compared with the lateral and apical region (P < 0.01, P = 0.03). The septal myocardial region exhibited a smaller uptake than the lateral myocardial region (P = 0.02). The maximum/minimum 30:15 ratio correlated with the global, anterior, lateral, and septal myocardial uptake of 123I-MIBG (P < 0.05, P < 0.05, P < 0.01, P < 0.05). A correlation between global and regional myocardial 123IMIBG uptake and HbAlc or QT interval was not observed. Newly diagnosed metabolically stabilized IDDM patients without myocardial perfusion defects show evidence of cardiac sympathetic dysinnervation, as indicated by a reduction of 123I-MIBG uptake, at a significant higher proportion than ECG-based cardiac autonomic neuropathy. Furthermore, they present with regional differences of myocardial 123I-MIBG uptake.
MHC Class I-Mediated Antigen Presentation and Induction of CD8+ Cytotoxic T-Cell Responses in Autoimmune Diabetes-Prone NOD Mice
Authors: Serreze David V , Leiter Edward H , Christianson Gregory J , Dudley Mark E , Roopenian Derry C , Scott Gallichan W , Snider Denis P , Croitoru Kenneth , Rosen thai Kenneth L
Published: September 2013

The common class I alleles (e.g., JC1 and Db) within the H2g7 major histocompatibility complex (MHC) clearly contribute to autoimmune IDDM in NOD mice, but the mechanism by which this occurs has been controversial. One laboratory has reported that the peptide transporter encoded by the Tapl gene within H2g7 is defective, and this contributes to IDDM by impairing MHC class I-mediated antigen presentation. If true, defective MHC class I-mediated antigen presentation should segregate with the H2g7 haplotype. NOD mice, related congenic stocks, and other control strains were used to test this hypothesis. H2g7-positive strains did not differ from those expressing other MHC haplotypes in ability to present MHC class I-restricted H3aa or H3ab minor histocompatibility (H) antigens to cytotoxic T-lymphocytes (CTL). The H2g7 haplotype was found to have a reduced capacity to mediate MHC class I-restricted presentation of the H47a minor H antigen. However, MHC class I-restricted presentation of H47a was found to be Tap independent. NOD mice and control strains also did not differ in ability to activate adenovirus-specific MHC class I restricted CTL. Thus, the H2g7 haplotype is not characterized by a Tap gene defect that only impairs the inductive phase of the immune response. In addition, MHC class I-restricted presentation of either minor H or adenoviral antigens was equivalent in male and female NOD mice. Therefore, while the class I alleles of the H2g7 haplotype exert diabetogenic functions in NOD mice, this is not elicited through a Tap gene defect. The absence of female-specific Tap gene defects also indicates this cannot account for the reduced male incidence of IDDM in some NOD mouse colonies.
Autonomic Mediation of Glucagon Secretion During Insulin-Induced Hypoglycemia in Rhesus Monkeys
Authors: Havel Peter J. , Valverde Celia
Published: September 2013

Autonomic activation mediates the majority of the increase of glucagon secretion during insulin-induced hypoglycemia in several species including dogs, mice, and rats. However, the role of the autonomic nervous system to increase glucagon during hypoglycemia in humans remains controversial, and investigations in nonhuman primates have not been previously conducted. The autonomic contribution to glucagon secretion during hypoglycemia in a nonhuman primate was examined by two independent pharmacological approaches. Glucagon responses to clamped insulin-induced hypoglycemia were compared in conscious rhesus monkeys in the presence or absence of ganglionic blockade with trimethaphan, or during combined muscarinic and adrenergic receptor blockade with atropine, propranolol, and tolazoline. Insulin- induced hypoglycemia (plasma glucose = 1.9 ± 0.1 mmol/l) activated parasympathetic nerves to the pancreas as assessed by increased plasma pancreatic polypeptide (PP) levels (δ= 135.0 ± 36.8 pmol/l, P < 0.01), produced sympathoadrenal activation as assessed by elevations of plasma epinephrine (EPI) (δ = 22.3 ± 2.95 nmol/l, P < 0.0005) and norepinephrine (NE) (δ = 3.72 ± 0.77 nmol/l, P < 0.0025) and increased plasma inununoreactive glucagon (IRG) (δ = 920 ± 294 ngfl, P < 0.025). Nicotinic ganglionic blockade with trimethaphan prevented parasympathetic (δPP = 16.5 ± 16.3 pmol/l, P < 0.01 vs. control) and sympathoadrenal (δEPI = 1.52 ± 0.98 nmol/l; δNE = -0.62 ± 0.24 nmol/l, both P < 0.0025 vs. control) activation during hypoglycemia and inhibited the IRG response by 70% (δ = 278 ± 67 ng/l,P < 0.025 vs. control). Combined muscarinic and adrenergic receptor blockade reduced parasympathetic activation (δPP = 48.3 ± 16.3 pmol/l, P < 0.01 vs. control) and inhibited the IRG response by a similar degree to ganglionic blockade (δIRG = 284 ± 60 ngfl, P < 0.025 vs. control). These results demonstrate by two independent pharmacological approaches that autonomic activation makes a substantial contribution to increased glucagon secretion during hypoglycemia of ∼2.0 mmol/l in a species of nonhuman primate.
The Inhibition of the Insulin Receptor by the Membrane Protein PC-1 Is Not Specific and Results From the Hydrolysis of ATP
Authors: Stefan Cristiana , Wera Stefaan , Stalmans Willy , Bollen Mathieu
Published: September 2013

The membrane protein plasma cell differentiation antigen 1 (PC-1) has been purified as an inhibitor of insulin receptor tyrosine kinase activity and has been implicated in the pathogenesis of NIDDM. However, we show here that PC-1 is a general protein kinase inhibitor in vitro and that this inhibition results from the hydrolysis of ATP by the intrinsic nucleotide pyrophosphatase activity of PC-1. Thus, the inhibition diminished with increasing ATP concentrations, and it was nullified when the ATP concentration was kept constant with a regenerating system or when ATP was added repetitively. When care was taken to avoid ATP depletion, PC-1 did not affect the insulin sensitivity of insulin receptor autophosphorylation. We conclude that the reported inhibition of insulin signaling by PC-1 does not result from a direct inhibition of the insulin receptor kinase activity.
β-Cell Destruction May Be a Late Consequence of the Autoimmune Process in Nonobese Diabetic Mice
Authors: Shimada Akira , Charlton Brett , Taylor-Edwards Cariel , Fathman C Garrison
Published: September 2013

The NOD mouse is an animal model of IDDM that shows many of the characteristics of human IDDM. It has been proposed that β-cell destruction in IDDM progresses over time in a linear manner. Recently, we and others have demonstrated that T helper type 1 (Thl) cells have pathogenic roles in the NOD model and proposed that cytokine balances change as the disease progresses. However, it has not been demonstrated how or when the cytokine balances change or how the β-cell destruction progresses. We have recently demonstrated that the cytokine profiles of CD45RBlow CD4+ cells correlate either with their pathogenic or with their protective roles in the NOD mouse. To further analyze this apparent correlation between the shift in cytokine level and IDDM, we examined the anti-CD3-induced cytokine profiles of this subset from NOD mice of various ages compared with that from age-matched I-Ak transgenic NOD and BALB/c mice as controls. A significantly higher ratio of anti-CD3–induced interferon-γ/interleukin-4 was found in diabetic NOD mice (P < 0.0001) but not in age-matched nondiabetic NOD mice. This cytokine ratio did not change significantly until the onset of diabetes in NOD mice. Based upon these results, we propose that IDDM in the NOD mouse progresses as a predominant inflammatory β-cell dysfunction without actual β-cell destruction until late in the disease process. This supports the possibility that late-stage immunotherapy may preserve islet β-cell mass.