BACKGROUNDAbnormal insulin secretion of pancreatic beta cells is now regarded as the more primary defect than the insulin function in the etiology of type 2 diabetes. Previous studies found impaired mitochondrial function and impaired Ca(2+) influx in beta cells in diabetic patients and animal models, suggesting a role for these processes in proper insulin secretion. The aim of this study was to investigate the detailed relationship of mitochondrial function, Ca(2+) influx, and defective insulin secretion.

METHODSWe investigated mitochondrial function and morphology in pancreatic beta cell of diabetic KK-Ay mice and C57BL/6J mice. Two types of Ca(2+) channel activities, L-type and store-operated Ca(2+) (SOC), were evaluated using whole-cell patch-clamp recording. The glucose induced Ca(2+) influx was measured by a non-invasive micro-test technique (NMT).

RESULTSMitochondria in KK-Ay mice pancreatic beta cells were swollen with disordered cristae, and mitochondrial function decreased compared with C57BL/6J mice. Ca(2+) channel activity was increased and glucose induced Ca(2+) influx was impaired, but could be recovered by genipin.

CONCLUSIONDefective mitochondrial function in diabetic mice pancreatic beta cells is a key cause of abnormal insulin secretion by altering Ca(2+) influx, but not via Ca(2+) channel activity.

Animals ; Calcium ; metabolism ; Diabetes Mellitus ; metabolism ; physiopathology ; Electrophysiology ; Insulin ; secretion ; Insulin-Secreting Cells ; metabolism ; Male ; Membrane Potential, Mitochondrial ; physiology ; Mice ; Mice, Inbred C57BL ; Mitochondria ; metabolism

The aim of this study was to assess the prevalence of diabetes and to study the effects of excess growth hormone (GH) on insulin sensitivity and beta-cell function in Korean acromegalic patients. One hundred and eighty-four acromegalic patients were analyzed to assess the prevalence of diabetes, and 52 naive acromegalic patients were enrolled in order to analyze insulin sensitivity and insulin secretion. Patients underwent a 75 g oral glucose tolerance test with measurements of GH, glucose, insulin, and C-peptide levels. The insulin sensitivity index and beta-cell function index were calculated and compared according to glucose status. Changes in the insulin sensitivity index and beta-cell function index were evaluated one to two months after surgery. Of the 184 patients, 17.4% were in the normal glucose tolerance (NGT) group, 45.1% were in the pre-diabetic group and 37.5% were in the diabetic group. The insulin sensitivity index (ISI0,120) was significantly higher and the HOMA-IR was lower in the NGT compared to the diabetic group (P = 0.001 and P = 0.037, respectively). The ISI0,120 and disposition index were significantly improved after tumor resection. Our findings suggest that both insulin sensitivity and beta-cell function are improved by tumor resection in acromegalic patients.
Acromegaly/*diagnosis/etiology/metabolism ; Adult ; Asian Continental Ancestry Group ; Blood Glucose/analysis ; C-Peptide/analysis ; Diabetes Mellitus/epidemiology ; Female ; Glucose Tolerance Test ; Human Growth Hormone/secretion ; Humans ; Insulin/blood/secretion ; *Insulin Resistance ; Insulin-Secreting Cells/cytology/*physiology ; Male ; Middle Aged ; Prediabetic State/epidemiology ; Republic of Korea

This study aimed to determine whether taurine supplementation improves metabolic disturbances and diabetic complications in an animal model for type 2 diabetes. We investigated whether taurine has therapeutic effects on glucose metabolism, lipid metabolism, and diabetic complications in Otsuka Long-Evans Tokushima fatty (OLETF) rats with long-term duration of diabetes. Fourteen 50-week-old OLETF rats with chronic diabetes were fed a diet supplemented with taurine (2%) or a non-supplemented control diet for 12 weeks. Taurine reduced blood glucose levels over 12 weeks, and improved OGTT outcomes at 6 weeks after taurine supplementation, in OLETF rats. Taurine significantly reduced insulin resistance but did not improve beta-cell function or islet mass. After 12 weeks, taurine significantly decreased serum levels of lipids such as triglyceride, cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol. Taurine significantly reduced serum leptin, but not adiponectin levels. However, taurine had no therapeutic effect on damaged tissues. Taurine ameliorated hyperglycemia and dyslipidemia, at least in part, by improving insulin sensitivity and leptin modulation in OLETF rats with long-term diabetes. Additional study is needed to investigate whether taurine has the same beneficial effects in human diabetic patients.
Adipokines/blood ; Animals ; Blood Glucose ; Diabetes Mellitus, Type 2/drug therapy ; Dietary Supplements ; Dyslipidemias/blood/*drug therapy ; Glucose Tolerance Test ; Hyperglycemia/blood/*drug therapy ; Hypoglycemic Agents/administration & dosage/*pharmacology ; Hypolipidemic Agents/administration & dosage/*pharmacology ; Insulin/physiology/secretion ; Insulin Resistance ; Insulin-Secreting Cells/physiology/secretion ; Leptin/*blood ; Lipid Metabolism/drug effects ; Lipids/blood ; Male ; Organ Specificity ; Rats ; Rats, Long-Evans ; Taurine/administration & dosage/*pharmacology

OBJECTIVETo elucidate GPR40/FFA1 and its downstream signaling pathways in regulating insulin secretion.

METHODSGPR40/FFA1 expression was detected by immunofluorescence imaging. We employed linoleic acid (LA), a free fatty acid that has a high affinity to the rat GPR40, and examined its effect on cytosolic free calcium concentration ([Ca2+]i) in primary rat beta-cells by Fluo-3 intensity under confocal microscopy recording. Downregulation of GPR40/FFA1 expression by antisense oligonucleotides was performed in pancreatic beta-cells, and insulin secretion was assessed by enzyme-linked immunosorbent assay.

RESULTSLA acutely stimulated insulin secretion from primary cultured rat pancreatic islets. LA induced significant increase of [Ca2+]i in the presence of 5.6 mmol/L and 11.1 mmol/L glucose, which was reflected by increased Fluo-3 intensity under confocal microscopy recording. LA-stimulated increase in [Ca2+]i and insulin secretion were blocked by inhibition of GPR40/FFA1 expression in beta-cells after GPR40/FFA1-specific antisense treatment. In addition, the inhibition of phospholipase C (PLC) activity by U73122, PLC inhibitor, also markedly inhibited the LA-induced [Ca2+]i increase.

CONCLUSIONLA activates GPR40/FFA1 and PLC to stimulate Ca2+ release, resulting in an increase in [Ca2+]i and insulin secretion in rat islet beta-cells.

Animals ; Calcium ; metabolism ; Enzyme Activation ; Insulin ; secretion ; Insulin-Secreting Cells ; drug effects ; metabolism ; secretion ; Linoleic Acid ; pharmacology ; Male ; Rats ; Rats, Sprague-Dawley ; Receptors, G-Protein-Coupled ; physiology ; Type C Phospholipases ; physiology

Animals ; Exocytosis ; drug effects ; physiology ; Glucose ; pharmacology ; Insulin ; secretion ; Insulin-Secreting Cells ; cytology ; drug effects ; metabolism ; Mice ; Microscopy, Fluorescence ; methods ; Potassium ; pharmacology ; Recombinant Fusion Proteins ; genetics ; metabolism ; Vesicle-Associated Membrane Protein 2 ; genetics ; metabolism

The purpose of the present study is to investigate the effects of urotensin II (UII) on insulin secretion in islet beta cells and the underlying mechanism. Glucose tolerance test was performed in Wistar rats to evaluate the effect of UII on the levels of plasma glucose and insulin. Static incubation experiment was employed to investigate the effect of UII on glucose-induced insulin secretion (GIIS) in betaTC-6 cells. After the incubation, insulin content and mRNA level in betaTC-6 cells were analyzed. Finally, Western blot was used to find out if UII could change the expression levels of pancreatic duodenal homeobox-1 (PDX-1) and glucokinase (GCK). It was observed that intravenous administration of UII (30, 300 nmol/kg) resulted in a significant decrease in insulin level 15 min after glucose load, and induced an obvious increase in plasma glucose 90 min after the load. In vitro, two hours of UII incubation inhibited GIIS in betaTC-6 cells without affecting insulin content and mRNA levels. The inhibitory effect of UII was blocked by UII receptor antagonist (urantide), and partially blunted by protein kinase C (PKC) inhibitor (chelerythrine) and somatostatin receptor antagonist (cyclosomatostatin). Moreover, we found that GCK protein level was significantly reduced by UII, while PDX-1, a key regulator of insulin gene transcription in beta cells, was not affected. These results suggest that UII-induced inhibition of GIIS in betaTC-6 cells are mediated by UII receptor and PKC pathway, as well as somatostatin receptor which could be activated by high dose of UII. The inhibitory effect of UII on insulin secretion is rather associated with a suppression of GCK expression than a regulation on PDX-1 expression.
Animals ; Blood Glucose ; metabolism ; Cell Line ; Glucokinase ; metabolism ; Homeodomain Proteins ; metabolism ; Insulin ; secretion ; Insulin-Secreting Cells ; metabolism ; physiology ; secretion ; Male ; Mice ; Rats ; Rats, Wistar ; Trans-Activators ; metabolism ; Urotensins ; pharmacology

BACKGROUNDUncoupling protein (UCP) 2 is related to the dysfunction of beta cells induced by fatty acids. However, whether UCP2 has similar effects on alpha cell is still not clear. This study aimed to investigate the effects of UCP2 and its possible mechanisms in lipotoxicity-induced dysfunction of pancreatic alpha cells.

METHODSThe alpha TC1-6 cells were used in this study to evaluate the effects of palmitate and/or UCP2 inhibit factors on the glucagon secretory function, glucagon content, the glucagon mRNA level and the nitrotyrosine level in the supernatant. Meantime, the expression levels of UCP2 and peroxisome proliferator-activated receptor-γ coactivator-1 alpha (PGC-1 alpha) were measured by real-time reverse transcription polymerase chain reaction (RT-PCR) and Western blotting. Furthermore, the possible relationship between UCP2 and insulin signal transduction pathway was analyzed.

RESULTSPalmitate stimulated alpha cell glucagon secretion and the expression of UCP2 and PGC-1 alpha, which could be partially decreased by the inhibition of UCP2. Palmitate increased nitrotyrosine level and suppressed insulin signal transduction pathway in alpha cells. Inhibition of UCP2 influenced the effects of free fatty acid on alpha cells and may relate to glucagon secretion.

CONCLUSIONUCP2 played an important role on alpha cell dysfunction induced by free fatty acid in vitro, which may be related to its effects on oxidative stress and insulin signal transduction pathway.

Animals ; Cells, Cultured ; Glucagon ; secretion ; Glucagon-Secreting Cells ; drug effects ; physiology ; Insulin ; pharmacology ; Insulin Receptor Substrate Proteins ; metabolism ; Ion Channels ; genetics ; physiology ; Iridoid Glycosides ; pharmacology ; Iridoids ; Mice ; Mitochondrial Proteins ; genetics ; physiology ; Oxidative Stress ; Palmitic Acid ; toxicity ; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha ; Phosphorylation ; RNA, Messenger ; analysis ; Signal Transduction ; Trans-Activators ; genetics ; physiology ; Transcription Factors ; Tyrosine ; analogs & derivatives ; metabolism ; Uncoupling Protein 2

As glucose is known to induce insulin secretion in pancreatic beta cells, this study investigated the role of a phospholipase D (PLD)-related signaling pathway in insulin secretion caused by high glucose in the pancreatic beta-cell line MIN6N8. It was found that the PLD activity and PLD1 expression were both increased by high glucose (33.3 mM) treatment. The dominant negative PLD1 inhibited glucose-induced Beta2 expression, and glucose-induced insulin secretion was blocked by treatment with 1-butanol or PLD1-siRNA. These results suggest that high glucose increased insulin secretion through a PLD1-related pathway. High glucose induced the binding of Arf6 to PLD1. Pretreatment with brefeldin A (BFA), an Arf inhibitor, decreased the PLD activity as well as the insulin secretion. Furthermore, BFA blocked the glucose-induced mTOR and p70S6K activation, while mTOR inhibition with rapamycin attenuated the glucose induced Beta2 expression and insulin secretion. Thus, when taken together, PLD1 would appear to be an important regulator of glucose-induced insulin secretion through an Arf6/PLD1/mTOR/p70S6K/Beta2 pathway in MIN6N8 cells.
ADP-Ribosylation Factors/metabolism/physiology ; Animals ; Basic Helix-Loop-Helix Transcription Factors/metabolism/physiology ; Cells, Cultured ; Gene Expression Regulation, Enzymologic/drug effects ; Glucose/*pharmacology ; Insulin/*secretion ; Insulin-Secreting Cells/*drug effects/enzymology/metabolism/secretion ; Intracellular Signaling Peptides and Proteins/metabolism/physiology ; Mice ; Models, Biological ; Oligodeoxyribonucleotides, Antisense/pharmacology ; Phospholipase D/antagonists & inhibitors/genetics/metabolism/*physiology ; Protein-Serine-Threonine Kinases/metabolism/physiology ; Ribosomal Protein S6 Kinases, 70-kDa/metabolism/physiology ; Signal Transduction/drug effects/genetics

This investigation was made to assess the effect of iron overload on function of pancreatic islet cells in Wistar rats. Sixty-five male rats were randomly divided into four groups: Group A received repeated intraperitoneal (i. p.) injections of ferric nitrilotriacetate (FeNTA); Group B received the equivalent dose of Na2 NTA; Group C received i. p. injection of Diethylenetriaminepentaacetic acid in addition to FeNTA; and Group D rats were untreated controls. Glucose tolerance tests were performed at the beginning, 5th week, and 10th week. Serum iron(SI) and serum ferritin (SF) were measured. The pancreatic tissues were taken for immunohistochemical exam; the levels of Insulin, Glucagon, ss in islets were also evaluated. At the 10th week, the levels of plasma glucose at 2 hours after glucose load in groups A and C were higher than those in groups B and D (P = 0.043); the granules of insulin in beta cells of group A were decreased obviously, the area of islets of group A was smaller than those of other groups (P = 0. 000). Iron overload might influence glycometabolism. And the beta cells' capability to secrete insulin was decreased obviously. Therefore, by way of removing iron, it is possible to protect the rat's glycometabolism to some extent.
Animals ; Glucose Tolerance Test ; Insulin ; secretion ; Insulin-Secreting Cells ; physiology ; secretion ; Iron Overload ; complications ; Male ; Random Allocation ; Rats ; Rats, Wistar

BACKGROUNDType 2 diabetes is a chronic disease characterized by a progressive loss of beta cell functions. However, the evaluation of beta cell functions is either expensive or inconvenient for clinical practice. We aimed to elucidate the association between the changes of insulin responsiveness and the fasting plasma glucose (FPG) during the development of diabetes.

METHODSA total of 1192 Chinese individuals with normal blood glucose or hyperglycemia were enrolled for the analysis. The early insulinogenic index (DeltaI30/DeltaG30), the area under the curve of insulin (AUC-I), and homeostasis model assessment were applied to evaluate the early phase secretion, total insulin secretion, and insulin resistance respectively. Polynomial regression analysis was performed to estimate the fluctuation of beta cell functions.

RESULTSThe DeltaI30/DeltaG30 decreased much more rapidly than the AUC-I accompanying with the elevation of FPG. At the FPG of 110 mg/dl (a pre-diabetic stage), the DeltaI30/DeltaG30 lost 50% of its maximum while the AUC-I was still at a compensated normal level. The AUC-I exhibited abnormal and decreased gradually at the FPG of from 130 mg/dl to higher (overt diabetes), while the DeltaI30/DeltaG30 almost remained at 25% of its maximum value. When hyperglycemia continuously existed at > 180 mg/dl, both the DeltaI30/DeltaG30 and AUC-I were totally lost.

CONCLUSIONThe increased fasting plasma glucose reflects progressive decompensation of beta cell functions, and could be used to guide the strategy of clinical treatments.

Adult ; Aged ; Aged, 80 and over ; Blood Glucose ; analysis ; Diabetes Mellitus ; blood ; physiopathology ; Fasting ; blood ; Female ; Humans ; Insulin ; secretion ; Insulin Resistance ; Insulin-Secreting Cells ; physiology ; Male ; Middle Aged