GPR40 activation initiates store-operated Ca2+ entry and potentiates insulin secretion via the IP3R1/STIM1/Orai1 pathway in pancreatic ß-cells.

The long-chain fatty acid receptor GPR40 plays an important role in potentiation of glucose-induced insulin secretion (GIIS) from pancreatic ß-cells. Previous studies demonstrated that GPR40 activation enhances Ca2+ release from the endoplasmic reticulum (ER) by activating inositol 1,4,5-triphosphate (IP3) receptors. However, it remains unknown how ER Ca2+ release via the IP3 receptor is linked to GIIS potentiation. Recently, stromal interaction molecule (STIM) 1 was identified as a key regulator of store-operated Ca2+ entry (SOCE), but little is known about its contribution in GPR40 signaling. We show that GPR40-mediated potentiation of GIIS is abolished by knockdown of IP3 receptor 1 (IP3R1), STIM1 or Ca2+-channel Orai1 in insulin-secreting MIN6 cells. STIM1 and Orai1 knockdown significantly impaired SOCE and the increase of intracellular Ca2+ by the GPR40 agonist, fasiglifam. Furthermore, ß-cell-specific STIM1 knockout mice showed impaired fasiglifam-mediated GIIS potentiation not only in isolated islets but also in vivo. These results indicate that the IP3R1/STIM1/Orai1 pathway plays an important role in GPR40-mediated SOCE initiation and GIIS potentiation in pancreatic ß-cells.

GLP1 Receptor Agonist Liraglutide Is an Effective Therapeutic Option for Perioperative Glycemic Control in Type 2 Diabetes within Enhanced Recovery After Surgery (ERAS) Protocols.

BACKGROUND: Enhanced Recovery After Surgery (ERAS) protocols are multimodal perioperative care pathways designed to achieve early recovery after surgical procedures by maintaining preoperative organ function and reducing profound stress responses following surgery [Wilmore and Kehlet: BMJ 2001; 322(7284): 473-6]. Glucagon-like peptide-1 receptor agonists (GLP-1RAgs), such as liraglutide, have recently been widely used as antidiabetic agents in patients with type 2 diabetes (T2D) because they maintain blood glucose at an ideal level throughout the day, including during postprandial periods, thereby improving hypoglycemia and body weight more than insulin therapies. Additionally, the administration of liraglutide may exert cardiovascular, renal, and cerebral protective effects in T2D patients. The use of GLP-1RAgs for perioperative glycemic control is sometimes considered to be controversial. METHODS: The efficacy and safety of liraglutide therapy during perioperative glycemic control in elective surgery patients within ERAS protocols were compared with those of insulin therapy. Ninety adult T2D patients scheduled to undergo elective surgery within ERAS protocols were randomized and analyzed. Forty-nine subjects were prescribed liraglutide and 41 insulin therapy. Procedures comprised orthopedic, thoracic, urological, otolaryngological, hepatic resection, and gynecological breast surgeries. RESULTS: Liraglutide was shown to be a more effective option than insulin therapy because (1) glycemic levels were more stable; (2) the number of patients requiring additional insulin according to the insulin sliding scale was significantly smaller (Fisher's exact test, p = 0.005); (3) the insulin dosage required on the day of surgery was significantly smaller (Fisher's exact, p = 0.004); (4) the additional insulin volume required was significantly less for patients throughout the perioperative period (Fisher's exact test, p = 0.001); and (5) while lean body mass remained the same, body fat measurements, particularly visceral fat, tended to decrease. CONCLUSIONS: Based on the results of the present study and a recent large-scale clinical study showing cardiovascular and renal protective effects in T2D patients, we consider the administration of liraglutide within ERAS protocols for T2D patients to represent a more comprehensive suite of patient protection measures as a perioperative non-insulin agent, particularly in patients with limited exercise ability and those at risk of hypoglycemia.

Oral Administration of Apple Procyanidins Ameliorates Insulin Resistance via Suppression of Pro-Inflammatory Cytokine Expression in Liver of Diabetic ob/ob Mice.

Procyanidins, the main ingredient of apple polyphenols, are known to possess antioxidative and anti-inflammatory effects associated closely with the pathophysiology of insulin resistance and type 2 diabetes. We investigated the effects of orally administered apple procyanidins (APCs) on glucose metabolism using diabetic ob/ob mice. We found no difference in body weight or body composition between mice treated with APCs and untreated mice. A 4 week oral administration of APCs containing water [0.5% (w/v)] ameliorated glucose tolerance, insulin resistance, and hepatic gluconeogenesis in ob/ob mice. APCs also suppressed the increase in the level of the pancreatic ß-cell. Insulin-stimulated Akt phosphorylation was significantly enhanced; pro-inflammatory cytokine expression levels were significantly decreased, and c-Jun N-terminal kinase phosphorylation was downregulated in the liver of those mice treated with APCs. In conclusion, APCs ameliorate insulin resistance by improving hepatic insulin signaling through suppression of hepatic inflammation in ob/ob mice, which may be a mechanism with possible beneficial health effects of APCs in disturbed glucose metabolism.

Src regulates insulin secretion and glucose metabolism by influencing subcellular localization of glucokinase in pancreatic ß-cells.

AIMS/INTRODUCTION: Src, a non-receptor tyrosine kinase, regulates a wide range of cellular functions, and hyperactivity of Src is involved in impaired glucose metabolism in pancreatic ß-cells. However, the physiological role of Src in glucose metabolism in normal, unstressed ß-cells remains unclear. In the present study, we investigated the role of Src in insulin secretion and glucose metabolism. MATERIALS AND METHODS: Src was downregulated using small interfering ribonucleic acid in INS-1 cells, and glucose-induced insulin secretion, adenosine triphosphate content, intracellular calcium concentration, glucose utilization and glucokinase activity were measured. Expression levels of messenger ribonucleic acid and protein of glucokinase were examined by semiquantitative real-time polymerase chain reaction and immunoblotting, respectively. Cells were fractionated by digitonin treatment, and subcellular localization of glucokinase was examined by immunoblotting. Interaction between glucokinase and neuronal nitric oxide synthase was estimated by immunoprecipitation. RESULTS: In Src downregulated INS-1 cells, glucose-induced insulin secretion was impaired, whereas insulin secretion induced by high K(+) was not affected. Intracellular adenosine triphosphate content and elevation of intracellular calcium concentration by glucose stimulation were suppressed by Src downregulation. Src downregulation reduced glucose utilization in the presence of high glucose, which was accompanied by a reduction in glucokinase activity without affecting its expression. However, Src downregulation reduced glucokinase in soluble, cytoplasmic fraction, and increased it in pellet containing intaracellular organelles. In addition, interaction between glucokinase and neuronal nitric oxide synthase was facilitated by Src downregulation. CONCLUSIONS: Src plays an important role in glucose-induced insulin secretion in pancreatic ß-cells through maintaining subcellular localization and activity of glucokinase.

Palmitate induces reactive oxygen species production and ß-cell dysfunction by activating nicotinamide adenine dinucleotide phosphate oxidase through Src signaling.

AIMS/INTRODUCTION: Chronic hyperlipidemia impairs pancreatic ß-cell function, referred to as lipotoxicity. We have reported an important role of endogenous reactive oxygen species (ROS) overproduction by activation of Src, a non-receptor tyrosine kinase, in impaired glucose-induced insulin secretion (GIIS) from diabetic rat islets. In the present study, we investigated the role of ROS production by Src signaling in palmitate-induced dysfunction of ß-cells. MATERIALS AND METHODS: After rat insulinoma INS-1D cells were exposed to 0.6 mmol/L palmitate for 24 h (palmitate exposure); GIIS, ROS production and nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity were examined with or without exposure to10 µmol/L 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a Src inhibitior, for 30 or 60 min. RESULTS: Exposure to PP2 recovered impaired GIIS and decreased ROS overproduction as a result of palmitate exposure. Palmitate exposure increased activity of NOX and protein levels of NOX2, a pathological ROS source in ß-cells. Palmitate exposure increased the protein level of p47 (phox) , a regulatory protein of NOX2, in membrane fraction compared with control, which was reduced by PP2. Transfection of small interfering ribonucleic acid of p47 (phox) suppressed the augmented p47 (phox) protein level in membrane fraction, decreased augmented ROS production and increased impaired GΙIS by palmitate exposure. In addition, exposure to PP2 ameliorated impaired GIIS and decreased ROS production in isolated islets of KK-A(y) mice, an obese diabetic model with hyperlipidemia. CONCLUSIONS: Activation of NOX through Src signaling plays an important role in ROS overproduction and impaired GΙIS caused by chronic exposure to palmitate, suggesting a lipotoxic mechanism of ß-cell dysfunction of obese mice.

A novel hook-shaped enhancement on contrast-enhanced sagittal magnetic resonance image in acute Sheehan's syndrome: a case report.

We report characteristic magnetic resonance (MR) image findings in a case of Sheehan's syndrome. A 37-year-old woman experienced complications of retained placenta and massive bleeding (3600 g) during delivery of a full-term baby. A pituitary function test demonstrated panhypopituitarism. MR image of the pituitary gland on postpartum day 10 revealed swelling of the anterior lobe. A hook-shaped enhancement was demonstrated on a sagittal image. The pituitary stalk, majority of the marginal zone of the anterior lobe, the anterior lobe just in front of the posterior lobe, and posterior lobe were well enhanced. In contrast, the central portion and the superior margin, just in front of the stalk insertion of the anterior lobe, were not enhanced. Anatomically, blood supply to these unenhanced portions of the anterior lobe was via the hypophyseal long portal vein and trabecular artery, which are tributaries of the superior hypophyseal artery that originate far from the internal carotid artery. Based on clinical history and MR image findings, the patient was diagnosed with Sheehan's syndrome and treated with hydrocortisone and levothyroxine. Follow-up MR image revealed marked atrophy of the anterior lobe. The characteristic hook-shaped enhancement in Sheehan's syndrome well reflected the vulnerability to massive bleeding based on the complex pituitary vasculature, which has not been reported previously. MR image with contrast enhancement is useful in the diagnosis of the acute phase of Sheehan's syndrome and in evaluating infarction of the anterior lobe.

Reduction of reactive oxygen species ameliorates metabolism-secretion coupling in islets of diabetic GK rats by suppressing lactate overproduction.

We previously demonstrated that impaired glucose-induced insulin secretion (IS) and ATP elevation in islets of Goto-Kakizaki (GK) rats, a nonobese model of diabetes, were significantly restored by 30-60-min suppression of endogenous reactive oxygen species (ROS) overproduction. In this study, we investigated the effect of a longer (12 h) suppression of ROS on metabolism-secretion coupling in ß-cells by exposure to tempol, a superoxide (O2(-)) dismutase mimic, plus ebselen, a glutathione peroxidase mimic (TE treatment). In GK islets, both H2O2 and O2(-) were sufficiently reduced and glucose-induced IS and ATP elevation were improved by TE treatment. Glucose oxidation, an indicator of Krebs cycle velocity, also was improved by TE treatment at high glucose, whereas glucokinase activity, which determines glycolytic velocity, was not affected. Lactate production was markedly increased in GK islets, and TE treatment reduced lactate production and protein expression of lactate dehydrogenase and hypoxia-inducible factor 1α (HIF1α). These results indicate that the Warburg-like effect, which is characteristic of aerobic metabolism in cancer cells by which lactate is overproduced with reduced linking to mitochondria metabolism, plays an important role in impaired metabolism-secretion coupling in diabetic ß-cells and suggest that ROS reduction can improve mitochondrial metabolism by suppressing lactate overproduction through the inhibition of HIF1α stabilization.

Role of mitochondrial phosphate carrier in metabolism-secretion coupling in rat insulinoma cell line INS-1.

In pancreatic ß-cells, glucose-induced mitochondrial ATP production plays an important role in insulin secretion. The mitochondrial phosphate carrier PiC is a member of the SLC25 (solute carrier family 25) family and transports Pi from the cytosol into the mitochondrial matrix. Since intramitochondrial Pi is an essential substrate for mitochondrial ATP production by complex V (ATP synthase) and affects the activity of the respiratory chain, Pi transport via PiC may be a rate-limiting step for ATP production. We evaluated the role of PiC in metabolism-secretion coupling in pancreatic ß-cells using INS-1 cells manipulated to reduce PiC expression by siRNA (small interfering RNA). Consequent reduction of the PiC protein level decreased glucose (10 mM)-stimulated insulin secretion, the ATP:ADP ratio in the presence of 10 mM glucose and elevation of intracellular calcium concentration in response to 10 mM glucose without affecting the mitochondrial membrane potential (Δψm) in INS-1 cells. In experiments using the mitochondrial fraction of INS-1 cells in the presence of 1 mM succinate, PiC down-regulation decreased ATP production at various Pi concentrations ranging from 0.001 to 10 mM, but did not affect Δψm at 3 mM Pi. In conclusion, the Pi supply to mitochondria via PiC plays a critical role in ATP production and metabolism-secretion coupling in INS-1 cells.