Factors influencing the durability of the glucose-lowering effect of sitagliptin combined with a sulfonylurea.

We analyzed the changes of glycemic control over 12 months and the factors influencing blood glucose in 162 Japanese patients with type 2 diabetes having inadequate glycemic control despite sulfonylurea-based therapy who received add-on sitagliptin. Hemoglobin A1c (HbA1c) decreased significantly after 4 weeks of treatment, and this improvement was maintained for 1 year, although HbA1c was slightly higher in week 52 than in week 24. Comparison of the patients showing a ≥0.4% increase of HbA1c between weeks 24 and 52 (n = 57) with the others (n = 105) showed a significant difference in the change of bodyweight, as well as the dose of glibenclamide (both P < 0.01). Although combined therapy with sitagliptin and a sulfonylurea seems to be effective for at least 1 year, blood glucose levels are more likely to increase again in patients who show greater weight gain after 24 weeks of treatment and those receiving a higher dose of glibenclamide.

Pitavastatin reduces elevated IL-18 levels in Japanese subjects with hypercholesterolemia: sub-analysis of Kansai investigation of statin for hyperlipidemic intervention in metabolism and endocrinology (KISHIMEN).

AIM: Pitavastatin significantly improved lipid profiles and reduced serum high-sensitivity C-reactive protein (hs-CRP) levels in a multi-center and prospective study. The aim of this study was to explore the effect of pitavastatin on serum levels of another inflammatory biomarker, interleukin-18 (IL-18), in a sub-analysis of the previous multi-center prospective study. METHODS: The subjects were 83 patients derived from the KISHIMEN study. Pitavastatin (1-2 mg/day) was administered for 12 months. Serum total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), remnant-like particle cholesterol (RLP-C), triglycerides (TG), IL-18, and high sensitivity C-reactive protein (hs-CRP) levels were measured. RESULTS: TC, LDL-C, and RLP-C levels were significantly reduced by 18.3%, 30.1%, and 21.0% (mean values) at 12 months after pitavastatin administration. TG levels were decreased by 9.8% in subjects whose basal TG levels were above 150 mg/dL. HDL-C levels were significantly increased at 6 months (11.9%). Pitavastatin did not significantly alter IL-18 levels in overall subjects, but reduced IL-18 levels in the highest quartile by 24.5% (median value) at 12 months. Pitavastatin significantly reduced hs-CRP levels by 28.6% in overall subjects and by 62.4% in the highest quartile at 12 months. There was a significant correlation between IL-18 and hs-CRP at baseline after both values were transformed into logarithms (Pearson's correlation coefficient, r = 0.259, p = 0.0181); however, percent changes in these levels were not significantly correlated. CONCLUSION: Pitavastatin significantly improves lipid profiles, and reduces enhanced inflammation monitored by IL-18, as well as by hs-CRP, in hypercholesterolemic subjects.

Secretory units of islets in transplantation index is a useful clinical marker to evaluate the efficacy of sitagliptin in treatment of type 2 diabetes mellitus.

We carried out a retrospective analysis of 40 Japanese patients with type 2 diabetes mellitus who received sitagliptin. Glycated hemoglobin (HbA1c) and fasting plasma glucose were significantly decreased from 7.53 ± 0.65% and 155.2 ± 29.4 mg/dL at baseline to 6.80 ± 0.60% (P < 0.01) and 131.2 ± 22.3 mg/dL (P < 0.01) at week 20, respectively. ß-Cell function was evaluated by the secretory units of islets in transplantation (SUIT) index, which was significantly increased from 28.5 ± 14.0 at baseline to 38.6 ± 17.0 at week 20 (P < 0.01). Multivariate analysis was carried out between ΔHbA1c and several parameters (age, the duration of diabetes, body mass index, triglyceride [TG], C-peptide [CPR], ΔCPR, HbA1c [baseline] and ΔSUIT), which showed HbA1c (baseline; ß = 0.580, P < 0.001) and ΔSUIT (ß = 0.308, P < 0.05) as significant independent determinants of ΔHbA1c. These two variables explained 53% of the variance in HbA1c response. These results suggest that SUIT index can be a clinical marker for the efficacy of sitagliptin in treatment of diabetes mellitus. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00109.x, 2011).

Usefulness of serum cystatin C in Japanese patients with type 2 diabetes mellitus and nephropathy.

We examined usefulness of serum cystatin C to detect chronic kidney disease (CKD) stage >or=3, which was defined by Modification of Diet in Renal Disease formula. Serum cystatin C could detect CKD stage >or=3 with high efficacy in 289 Japanese patients with type 2 diabetes and nephropathy.

Olmesartan reduced microalbuminuria in Japanese subjects with type 2 diabetes.

We investigated the effect of olmesartan on early diabetic nephropathy in hypertensive patients with type 2 diabetes by its replacement of other angiotensin II type 1 receptor blockers (ARBs) by olmesartan. The urinary albumin/creatinine ratio significantly decreased. The present result suggests a possibility that olmesartan may have more effect on early nephropathy than other ARBs.

Effects of pitavastatin on lipid profiles and high-sensitivity CRP in Japanese subjects with hypercholesterolemia: Kansai Investigation of Statin for Hyperlipidemic Intervention in Metabolism and Endocrinology (KISHIMEN) investigatars.

AIM: The effect of pitavastatin on high-sensitivity C-reactive protein (hs-CRP) has not been reported, yet, in humans. We, therefore, investigated the effects of pitavastatin on lipid profiles and hs-CRP in Japanese subjects with hypercholesterolemia. METHODS: The subjects were 178 Japanese with hypercholesterolemia, including 103 (58%) with type 2 diabetes. Pitavastatin (12 mg/day) was administered for 12 months. Serum low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), remnant-like particle cholesterol (RLP-C), triglycerides (TG) and hs-CRP levels were measured for 12 months. RESULTS: Serum LDL-C and RLP-C levels were significantly decreased by 30.3% and 22.8%, respectively. Serum TG levels were decreased by 15.9% in subjects with basal TG levels above 150 mg/dl. Serum HDL-C levels were significantly increased. The administration of pitavastatin reduced serum hs-CRP levels by 34.8%. No serious adverse events were observed, including changes in glycosylated hemoglobin levels of diabetic patients. CONCLUSION: These results suggest that pitavastatin significantly improves lipid profiles and reduces proinflammatory responses, without adverse effects, in Japanese subjects with hypercholesterolemia, including those with diabetes mellitus.

A case of lymphocytic panhypophysitis (LPH) during pregnancy.

A 37-year-old pregnant woman developed continuous headache in the 10th week of pregnancy, followed by bilateral visual field defect and general malaise in the 24th week. The brain magnetic resonance imaging showed a pituitary mass. In laboratory examination, plasma concentration of free thyroxine, thyroid stimulating hormone (TSH), cortisol, and adrenocorticotropic hormone (ACTH) was low. General malaise vanished shortly after the replacement therapy of glucocorticoid and thyroid hormone, but partial central diabetes insipidus (CDI) appeared, which could be treated with desmopressin acetate (DDAVP). The visual field defect having enlarged, transsphenoidal surgery was performed in the 31st week of pregnancy. Adenohypophysis could be resected, and it showed infiltration of mature lymphocytes. After the surgery, the visual defect had improved, but hormone replacement was still necessary. She delivered a baby in the 38th week without any trouble. Provocative tests after delivery revealed a low response in TSH, prolactin (PRL), and follicle stimulating hormone (FSH). Hormone replacement and DDAVP administration was necessary in the same doses after delivery. The diagnosis was lymphocytic panhypophysitis (LPH). In the case of pregnant woman, LPH should be included in the differential diagnosis of pituitary mass for the fetomaternal safety.

Impaired metabolism-secretion coupling in pancreatic beta-cells: role of determinants of mitochondrial ATP production.

Glucose-induced insulin secretion from beta-cells is often impaired in diabetic condition and by exposure to diabetogenic pharmacological agents. In pancreatic beta-cells, intracellular glucose metabolism regulates exocytosis of insulin granules, according to metabolism-secretion coupling in which glucose-induced mitochondrial ATP production plays an essential role. Impaired glucose-induced insulin secretion often results from impaired glucose-induced ATP elevation in beta-cells. Mitochondrial ATP production is driven by the proton-motive force including mitochondrial membrane potential (DeltaPsi(m)) generated by the electron transport chain. These electrons are derived from reducing equivalents, generated in the Krebs cycle and transferred from cytosol by the shuttles. Here, roles of the determinants of mitochondrial ATP production in impaired glucose-induced insulin secretion are discussed. Cytosolic alkalization, H(+) leak in the inner membrane by uncoupler (e.g. free fatty acid exposure), decrease in the supply of electron donors including NADH and FADH(2) to the respiratory chain, and endogenous mitochondrial ROS (e.g. Na(+)/K(+)-ATPase inhibition) all reduce hyperpolarlization of DeltaPsi(m) and ATP production, causing decresed glucose-induced insulin release. The decrease in the supply of NADH and FADH(2) to the respiratory chain derives from impairments in glucose metabolism including glycolysis (e.g. MODY2 and exposure to NO) and the shuttles (e.g. diabetic state and exposure to ketone body).

Diphenylhydantoin suppresses glucose-induced insulin release by decreasing cytoplasmic H+ concentration in pancreatic islets.

Diphenylhydantoin (DPH), which is clinically used in the treatment of epilepsy, inhibits glucose-induced insulin release from pancreatic islets by a mechanism that remains unknown. In the present study, DPH is shown to suppress glucose-induced insulin release concentration-dependently. In dynamic experiments, 20 microm DPH suppressed 16.7 mm glucose-induced biphasic insulin release. DPH also suppressed insulin release in the presence of 16.7 mm glucose, 200 microm diazoxide, and 30 mm K+ without affecting the intracellular Ca2+ concentration. DPH suppressed ATP content and mitochondrial membrane hyperpolarization in the presence of 16.7 mm glucose without affecting glucose utilization, glucose oxidation, and reduced nicotinamide adenine dinucleotide phosphate fluorescence. DPH increased cytoplasmic pH in the presence of high glucose, but the increase was abolished under Na+ -deprived conditions and HCO3- -deprived conditions, suggesting that Na+ and HCO3- transport across the plasma membrane are involved in the increase in cytoplasmic pH by DPH. Alkalization by adding NH4+ to the extracellular medium also suppressed insulin release, ATP content, and mitochondrial membrane hyperpolarization. Because ATP production from the mitochondrial fraction in the presence of substrates was decreased by increased pH in the medium, DPH suppresses mitochondrial ATP production by reducing the H+ gradient across mitochondrial membrane. Using permeabilized islets, the increase in pH was shown to decrease Ca2+ efficacy at a clamped concentration of ATP in the exocytotic system. Taken together, DPH inhibits glucose-induced insulin secretion not only by inhibiting mitochondrial ATP production, but also by reducing Ca2+ efficacy in the exocytotic system through its alkalizing effect on cytoplasm.

ATP enhances exocytosis of insulin secretory granules in pancreatic islets under Ca2+-depleted condition.

Glucose and other nutrients have been shown to stimulate insulin release from pancreatic islets under Ca2+-depleted condition when protein kinase A (PKA) and protein kinase C (PKC) are activated simultaneously. We investigated the role of metabolic nucleotide signals including ATP, ADP, and GTP in exocytosis of insulin secretory granules under Ca2+-depleted condition using electrically permeabilized rat islets. ATP under PKC activation augmented insulin release concentration-dependently by 100 nM 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in Ca2+-depleted condition, while ADP could not suppress ATP-dependent insulin release in this condition. Neither GTP nor activated PKA in the absence of PKC activation increased insulin release under Ca2+-depleted condition in the presence of ATP, but both enhanced insulin secretion in the presence of ATP when PKC was activated. In conclusion, activated PKC and the presence of ATP both are required in the insulin secretory process under Ca2+-depleted condition. While PKA activation and GTP cannot substitute for PKC activation and ATP, respectively, under Ca2+-depleted condition, they enhance ATP-dependent insulin secretion when PKC is activated.

Tacrolimus suppresses glucose-induced insulin release from pancreatic islets by reducing glucokinase activity.

Tacrolimus is widely used for immunosuppressant therapy, including various organ transplantations. One of its main side effects is hyperglycemia due to reduced insulin secretion, but the mechanism remains unknown. We have investigated the metabolic effects of tacrolimus on insulin secretion at a concentration that does not influence insulin content. Twenty-four-hour exposure to 3 nM tacrolimus reduced high glucose (16.7 mM)-induced insulin secretion (control 2.14 +/- 0.08 vs. tacrolimus 1.75 +/- 0.02 ng.islet(-1).30 min(-1), P < 0.01) without affecting insulin content. In dynamic experiments, insulin secretion and NAD(P)H fluorescence during a 20-min period after 10 min of high-glucose exposure were reduced in tacrolimus-treated islets. ATP content and glucose utilization of tacrolimus-treated islets in the presence of 16.7 mM glucose were less than in control (ATP content: control 9.69 +/- 0.99 vs. tacrolimus 6.52 +/- 0.40 pmol/islet, P < 0.01; glucose utilization: control 103.8 +/- 6.9 vs. tacrolimus 74.4 +/- 5.1 pmol.islet(-1).90 min(-1), P < 0.01). However, insulin release from tacrolimus-treated islets was similar to that from control islets in the presence of 16.7 mM alpha-ketoisocaproate, a mitochondrial fuel. Glucokinase activity, which determines glycolytic velocity, was reduced by tacrolimus treatment (control 65.3 +/- 3.4 vs. tacrolimus 49.9 +/- 2.8 pmol.islet(-1).60 min(-1), P < 0.01), whereas hexokinase activity was not affected. These results indicate that glucose-stimulated insulin release is decreased by chronic exposure to tacrolimus due to reduced ATP production and glycolysis derived from reduced glucokinase activity.

Chronic exposure to beta-hydroxybutyrate inhibits glucose-induced insulin release from pancreatic islets by decreasing NADH contents.

To investigate the effects of chronic exposure to ketone bodies on glucose-induced insulin secretion, we evaluated insulin release, intracellular Ca2+ and metabolism, and Ca2+ efficacy of the exocytotic system in rat pancreatic islets. Fifteen-hour exposure to 5 mM d-beta-hydroxybutyrate (HB) reduced high glucose-induced insulin secretion and augmented basal insulin secretion. Augmentation of basal release was derived from promoting the Ca2+-independent and ATP-independent component of insulin release, which was suppressed by the GDP analog. Chronic exposure to HB affected mostly the second phase of glucose-induced biphasic secretion. Dynamic experiments showed that insulin release and NAD(P)H fluorescence were lower, although the intracellular Ca2+ concentration ([Ca2+](i)) was not affected 10 min after exposure to high glucose. Additionally, [Ca2+](i) efficacy in exocytotic system at clamped concentrations of ATP was not affected. NADH content, ATP content, and ATP-to-ADP ratio in the HB-cultured islets in the presence of high glucose were lower, whereas glucose utilization and oxidation were not affected. Mitochondrial ATP production shows that the respiratory chain downstream of complex II is not affected by chronic exposure to HB, and that the decrease in ATP production is due to decreased NADH content in the mitochondrial matrix. Chronic exposure to HB suppresses glucose-induced insulin secretion by lowering the ATP level, at least partly by inhibiting ATP production by reducing the supply of NADH to the respiratory chain. Glucose-induced insulin release in the presence of aminooxyacetate was not reduced, which implies that chronic exposure to HB affects the malate/aspartate shuttle and thus reduces NADH supply to mitochondria.

Effect of high dietary fat on insulin secretion in genetically diabetic Goto-Kakizaki rats.

INTRODUCTION AND AIM: To clarify the effects of a high fat-diet on insulin secretion from genetically diabetic beta cells, Goto-Kakizaki rats and Wistar rats were subjected to oral glucose tolerance test (OGTT) after 12-week high-fat feeding. METHODOLOGY: We compared Wistar and Goto-Kakizaki (GK) rats fed a high-fat diet (45% fat content) for 12 weeks, measuring insulin secretion and insulin release. RESULTS: Insulin secretion during oral glucose tolerance test (OGTT) was enhanced in high-fat diet-fed Wistar rats (WF) with normal glucose tolerance. Insulin secretion in high-fat diet-fed GK rats (GF) during OGTT also was enhanced together with deteriorated glucose tolerance. Basal insulin release from the isolated perfused pancreas at 3.3 m glucose in WF was comparable to that in normal chow-fed Wistar rats (WN), but basal insulin release in GF was remarkably higher than in normal chow-fed GK rats (GN). Stimulated insulin release induced by 16.7 m glucose was remarkably increased in WF compared with WN. Total insulin release at 16.7 m glucose in both GK rat groups was similar and minimal. CONCLUSION: These results indicate that normal pancreatic beta-cells have the ability to secrete sufficient insulin to compensate for the insulin resistance induced by a high-fat diet. In contrast, glucose metabolism in diabetic rats after high-fat diet deteriorated partly because of insufficient insulin secretion caused by genetic defects and lipotoxicity due to chronically high FFA levels.