A novel mechanism of imeglimin-mediated insulin secretion via the cADPR-TRP channel pathway.

AIMS/INTRODUCTION: Imeglimin is a novel oral hypoglycemic agent that improves blood glucose levels through multiple mechanisms of action including the enhancement of glucose-stimulated insulin secretion (GSIS), however, the details of this mechanism have not been clarified. In the process of GSIS, activation of the transient receptor potential melastatin 2 (TRPM2) channel, a type of non-selective cation channel (NSCCs) in ß-cells, promotes plasma membrane depolarization. The present study aimed to examine whether imeglimin potentiates GSIS via the TRPM2 channel in ß-cells. MATERIALS AND METHODS: Pancreatic islets were isolated by collagenase digestion from male wild-type and TRPM2-knockout (KO) mice. Insulin release and nicotinamide adenine dinucleotide (NAD+ ) production in islets were measured under static incubation. NSCC currents in mouse single ß-cells were measured by patch-clamp experiments. RESULTS: Batch-incubation studies showed that imeglimin enhanced GSIS at stimulatory 16.6 mM glucose, whereas it did not affect basal insulin levels at 2.8 mM glucose. Imeglimin increased the glucose-induced production of NAD+ , a precursor of cADPR, in islets and the insulinotropic effects of imeglimin were attenuated by a cADPR inhibitor 8-Br-cADPR. Furthermore, imeglimin increased NSCC current in ß-cells, and abolished this current in TRPM2-KO mice. Imeglimin did not potentiate GSIS in the TRPM2-KO islets, suggesting that imeglimin's increase of NSCC currents through the TRPM2 channel is causally implicated in its insulin releasing effects. CONCLUSIONS: Imeglimin may activate TRPM2 channels in ß-cells via the production of NAD+ /cADPR, leading to the potentiation of GSIS. Developing approaches to stimulate cADPR-TRPM2 signaling provides a potential therapeutic tool to treat type 2 diabetes.

IgG4-related Pericarditis in which Oral Corticosteroid Therapy Was Effective.

IgG4-related diseases (IgG4-RDs) have recently been reported in many organs other than the salivary, pancreatic and hepatobiliary systems. A 64-year-old woman was referred to our department for her abdominal fullness and cardiomegaly on chest X-ray. After draining the pericardial fluid, her symptom promptly diminished, and pericardial friction rubbing became clearly audible. Elevated serum levels of IgG and IgG4 and ureteral wall thickening on computed tomography suggested IgG4-RD. After the initiation of oral corticosteroid therapy, the pericardial effusion was resolved, and she has been in a steady-state condition for the past two years.

Eicosapentaenoic acid shows anti-inflammatory effect via GPR120 in 3T3-L1 adipocytes and attenuates adipose tissue inflammation in diet-induced obese mice.

BACKGROUND: Saturated fatty acids have been shown to cause insulin resistance and low-grade chronic inflammation, whereas unsaturated fatty acids suppress inflammation via G-protein coupled receptor 120 (GPR120) in macrophages. However, the anti-inflammatory effects of unsaturated fatty acids in adipocytes have yet to be elucidated. Hence, the aims of the present study were to evaluate the anti-inflammatory effects of eicosapentaenoic acid (EPA) via GPR120 in adipocytes. METHODS: We used 250 µM palmitate as a representative saturated fatty acid. 3T3-L1 adipocytes were used for in vitro studies. We further evaluated the effect of EPA supplementation in a high-fat/high-sucrose (HFHS) diet-induced adipose tissue inflammatory mouse model. RESULTS: EPA attenuated palmitate-induced increases in inflammatory gene expression and NF-κB phosphorylation in 3T3-L1 adipocytes. Silencing of GPR120 abolished the anti-inflammatory effects of EPA. In GPR120 downstream signal analysis, EPA was found to decrease palmitate-induced increases in TAK1/TAB1 complex expression. EPA supplementation suppressed HFHS-induced crown-like structure formation in epididymal adipose tissue and altered macrophage phenotypes from M1 to M2 in the stromal vascular fraction. Moreover, the EPA-containing diet attenuated increases in adipose p-JNK and phospho-p65 NF-κB levels. CONCLUSIONS: In conclusion, the findings of the present study demonstrate that EPA suppresses palmitate-induced inflammation via GPR120 by inhibiting the TAK1/TAB1 interaction in adipocytes. EPA supplementation reduced HFHS diet-induced inflammatory changes in mouse adipose tissues. These results demonstrate adipose GPR120 as a potential therapeutic target for decreasing inflammation.

Effects of pitavastatin on walking capacity and CD34+/133+ cell number in patients with peripheral artery disease.

This multi-center prospective non-randomized comparative study investigated the effects of pitavastatin in patients with peripheral artery disease (PAD) in terms of exercise tolerance capacities and peripheral CD34+/133+ cell numbers. At baseline, a peripheral blood test was administered to 75 patients with PAD, along with a treadmill exercise test using the Skinner-Gardner protocol to measure asymptomatic walking distance (AWD) and maximum walking distance (MWD). Each patient was assigned to a 6-month pitavastatin treatment group (n = 53) or a control group (n = 22), according to the patient's preference. The tests were repeated in both groups at 3 and 6 months. Baseline AWD and MWD correlated positively with the ankle-brachial pressure index (r = 0.342, p = 0.0032 and r = 0.324, p = 0.0054, respectively). Both AWD and MWD values improved at 3 and 6 months compared with baseline, and the degrees of their improvement were higher in the pitavastatin treatment group. CD34+/133+ cell numbers did not change over time or between groups. Eighty-seven percent of patients in the treatment group attained low-density lipoprotein cholesterol levels below 100 mg/dL after 3 months. The study shows that pitavastatin may be effective in increasing exercise tolerance capacity in patients with PAD.

Pravastatin improves postprandial endothelial dysfunction and hemorheological deterioration in patients with effort angina pectoris.

Postprandial hypertriglyceridemia and hyperglycemia may promote endothelial and hemorheological dysfunction. The present study investigated the effects of pravastatin on endothelial function and hemorheology in patients with stable angina pectoris (AP) before and after eating a test meal. We recruited 26 patients with stable AP who had impaired glucose tolerance and mild dyslipidemia and six healthy men as controls to assess endothelial function and hemorheological behavior. In each group, we measured forearm blood flow (FBF) during post-ischemic reactive hyperemia and obtained blood samples before and 2 h after the test meal. Pravastatin 20 mg/day was then commenced in the 26 AP patients. The above tests were repeated after 2 days and 6 months. Maximum FBF during hyperemia in the baseline fasting phase was significantly lower in the AP patients than in the controls (p < 0.05). Fasting and postprandial FBF during reactive hyperemia time-dependently improved after pravastatin treatment (p < 0.05 vs. baseline data for each phase). Pravastatin treatment for 6 months, but not for 2 days, inhibited leukocyte activation and improved hemorheological parameters. In conclusion, pravastatin treatment for 6 months improved fasting and postprandial endothelial and hemorheological dysfunction in AP patients.

High-density lipoprotein and apolipoprotein A-I inhibit palmitate-induced translocation of toll-like receptor 4 into lipid rafts and inflammatory cytokines in 3T3-L1 adipocytes.

Saturated fatty acids (SFAs) activate toll-like receptor 4 (TLR4) signal transduction in macrophages and are involved in the chronic inflammation accompanying obesity. High-density lipoprotein (HDL) and apolipoprotein A-I (apoA-I) produce anti-inflammatory effects via reverse cholesterol transport. However, the underlying mechanisms by which HDL and apoA-I inhibit inflammatory responses in adipocytes remain to be determined. Here we examined whether palmitate increases the translocation of TLR4 into lipid rafts and whether HDL and apoA-I inhibit inflammation in adipocytes. Palmitate exposure (250 µM, 24 h) increased interleukin-6 and tumor necrosis factor-α gene expressions and translocation of TLR4 into lipid rafts in 3T3-L1 adipocytes. Pretreatment with HDL and apoA-I (50 µg/mL, 6 h) suppressed palmitate-induced inflammatory cytokine expression and TLR4 translocation into lipid rafts. Moreover, HDL and apoA-I inhibited palmitate-induced phosphorylation of nuclear factor-kappa B. HDL showed an anti-inflammatory effect via ATP-binding cassette transporter G1 and scavenger receptor class B, member 1, whereas apoA-I showed an effect via ATP-binding cassette transporter A1. These results demonstrated that HDL and apoA-I reduced palmitate-potentiated TLR4 trafficking into lipid rafts and its related inflammation in adipocytes via these specific transporters.

Erratum to: Decreased glucagon levels and decreased insulin secretion after sitagliptin versus mitiglinide administration with similar glycemic levels following an oral glucose load: a randomized crossover pharmaceutical mechanistic study.

[This corrects the article DOI: 10.1007/s13340-015-0207-1.].

Endogenous α2A-Adrenoceptor-Operated Sympathoadrenergic Tones Attenuate Insulin Secretion via cAMP/TRPM2 Signaling.

In pancreatic ß-cells, pharmacological concentrations of catecholamines, including adrenaline, have been used to inhibit insulin release and explore the multiple mechanisms involved. However, the significance of these signaling pathways for physiological adrenergic functions in ß-cells is largely unknown. In the process of glucose-induced insulin secretion, opening of background current through nonselective cation channels (NSCCs) might facilitate membrane depolarization by closure of the ATP-sensitive K+ channels. Here, we examined whether physiological insulinostatic adrenaline action is mediated via the transient receptor potential melastatin 2 (TRPM2) channel, a type of NSCC, in ß-cells. Results showed that physiological concentrations of adrenaline strongly suppressed glucose-induced and incretin-potentiated cAMP production and insulin secretion and inhibited NSCCs current and membrane excitability via the α2A-adrenoceptor in wild-type mice; however, insulin secretion was not attenuated in TRPM2-knockout (KO) mice. Administration of yohimbine, an α2-adrenoceptor antagonist, failed to affect glucose tolerance in TRPM2-KO mice, in contrast to an improved glucose tolerance in wild-type mice receiving the antagonist. The current study demonstrated that a physiological concentration of adrenaline attenuates insulin release via coupling of α2A-adrenoceptor to cAMP/TRPM2 signaling, thereby providing a potential therapeutic tool to treat patients with type 2 diabetes.

Glucose and GTP-binding protein-coupled receptor cooperatively regulate transient receptor potential-channels to stimulate insulin secretion [Review].

In pancreatic ß-cells, glucose-induced closure of the ATP-sensitive K+ (KATP) channel is an initial process triggering glucose-stimulated insulin secretion (GSIS). This KATP-channel dependent pathway has been believed to be a central mechanism for GSIS. However, since the resting membrane potential of cells is determined by the balance of the net result of current amplitudes in outward and inward directions, it must be taken into consideration that not only KATP channel inhibition but also inward current via the basal opening of non-selective cation channels (NSCCs) plays a crucial role in membrane potential regulation. The basal activity of NSCCs is essential to effectively evoke depolarization in concert with KATP channel closure that is dependent on glucose metabolism. The present study summarizes recent findings regarding the roles of NSCCs in GSIS and GTP-binding protein coupled receptor-(GPCR) operated potentiation of GSIS.

Decreased glucagon levels and decreased insulin secretion after sitagliptin versus mitiglinide administration with similar glycemic levels following an oral glucose load: a randomized crossover pharmaceutical mechanistic study.

AIMS: Both sitagliptin (SIT) and mitiglinide (MIT) can lower postprandial hyperglycemia. The purpose of this study was to examine differences in insulin and glucagon secretion after SIT or MIT administration when similar levels of plasma glucose (PG) were achieved for both agents following an oral glucose load. PATIENTS AND METHODS: We directly compared the effects of these two agents in 16 type-2 diabetic patients (M/F = 10/6, age 66 ± 3 years old, HbA1c 6.6 ± 0.5 %). Patients received SIT (50 mg qd for 1 week and 100 mg qd for an additional week) or MIT (10 mg tid for 2 weeks). After 2 weeks, patients crossed over to the other treatment. 75-g oral glucose tolerance tests were conducted before the study and after interventions. RESULTS: The area under the curve (AUC) up to 180 min for the PG response was similar for both agents. While basal insulin secretion rates (ISR) were similar, incremental AUC of ISR was significantly lower in the SIT treatment (522 ± 108 vs 702 ± 288 pmol/min min, p < 0.01), although the difference between the SIT and MIT treatments in the Matsuda index-which reflects insulin sensitivity-remained nonsignificant. Glucose-stimulated insulin secretion was similarly increased by the MIT and SIT treatments. Suppression of the AUC for glucagon was observed in the SIT treatment, while MIT treatment failed to suppress the glucagon concentration (-432 ± 2322 vs MIT 1116 ± 2520 pg/ml min, p < 0.05). The basal proinsulin/insulin ratio was lower in the SIT treatment (0.23 ± 0.04 vs MIT 0.26 ± 0.36, p < 0.05). CONCLUSIONS: Although either SIT or MIT can be employed to reduce postprandial hyperglycemia, SIT induces changes in hormonal profiles that are more favorable to islet functions than MIT does.

Involvement of cAMP/EPAC/TRPM2 activation in glucose- and incretin-induced insulin secretion.

In pancreatic ß-cells, closure of the ATP-sensitive K(+) (K(ATP)) channel is an initial process triggering glucose-stimulated insulin secretion. In addition, constitutive opening of background nonselective cation channels (NSCCs) is essentially required to effectively evoke depolarization as a consequence of K(ATP) channel closure. Thus, it is hypothesized that further opening of NSCC facilitates membrane excitability. We identified a class of NSCC that was activated by exendin (ex)-4, GLP-1, and its analog liraglutide at picomolar levels. This NSCC was also activated by increasing the glucose concentration. NSCC activation by glucose and GLP-1 was a consequence of the activated cAMP/EPAC-mediated pathway and was attenuated in TRPM2-deficient mice. The NSCC was not activated by protein kinase A (PKA) activators and was activated by ex-4 in the presence of PKA inhibitors. These results suggest that glucose- and incretin-activated NSCC (TRPM2) works in concert with closure of the KATP channel to effectively induce membrane depolarization to initiate insulin secretion. The current study reveals a new mechanism for regulating electrical excitability in ß-cells and for mediating the action of glucose and incretin to evoke insulin secretion, thereby providing an innovative target for the treatment of type 2 diabetes.

Comparison of three α-glucosidase inhibitors for glycemic control and bodyweight reduction in Japanese patients with obese type 2 diabetes.

AIMS/INTRODUCTION: α-Glucosidase inhibitors (αGIs) are widely used for the primary treatment of type 2 diabetes. We compared the clinical effects of three αGIs (miglitol, acarbose and voglibose) in patients with obese type 2 diabetes. MATERIALS AND METHODS: Japanese patients (n = 81) with obese type 2 diabetes (body mass index [BMI] ≥25 kg/m(2)) were enrolled in this multicenter, open-label study. The participants were randomized into the miglitol (n = 18), acarbose (n = 22), voglibose (n = 19) or control (n = 22) groups. Glycemic control (fasting blood glucose and glycated hemoglobin [HbA1c]), bodyweight, BMI, serum insulin, serum lipids (low-density lipoprotein and high-density lipoprotein cholesterol, and triacylglycerols) and adipocytokines (leptin and adiponectin) were evaluated every 4 weeks for 12 weeks. RESULTS: In the miglitol group, HbA1c was improved significantly from the baseline at all points. The changes in HbA1c at 8 and 12 weeks from baseline were greater in the miglitol group than the control group. The voglibose group showed significant improvements in HbA1c at 12 weeks. Bodyweight and BMI were decreased significantly in the miglitol group. In addition, significant correlations were observed between the decrements in HbA1c and bodyweights over 12 weeks in the miglitol (r = 0.759, P < 0.001) and voglibose groups (r = 0.667, P = 0.002). Serum lipid and adipocytokine levels were not altered in any groups. CONCLUSIONS: αGIs, especially miglitol, can effectively control blood glucose and bodyweight in obese type 2 diabetes. This study was registered with UMIN (no. UMIN000006465).

Combination therapy of angiotensin II receptor blocker and thiazide produces severe hyponatremia in elderly hypertensive subjects.

Thiazide diuretics are known to produce severe hyponatremia as well as hypokalemia. The present study demonstrated severe hyponatremia in three hypertensive patients who had received combination therapy consisting of an angiotensin II receptor blocker (ARB) and thiazide. The serum sodium (Na) levels in all three cases were markedly reduced to below 116 mmol/L, and the patients exhibited augmented urinary excretion of Na with a reduced circulatory blood volume. After withdrawing the ARB and thiazide treatment, the serum Na levels normalized within one to two weeks. Combination therapy with ARBs and thiazide may cause hyponatremia in elderly patients.

Suppression of coronary atherosclerosis by helix B surface Peptide, a nonerythropoietic, tissue-protective compound derived from erythropoietin.

Erythropoietin (EPO), a type I cytokine originally identified for its critical role in hematopoiesis, has been shown to have nonhematopoietic, tissue-protective effects, including suppression of atherosclerosis. However, prothrombotic effects of EPO hinder its potential clinical use in nonanemic patients. In the present study, we investigated the antiatherosclerotic effects of helix B surface peptide (HBSP), a nonerythropoietic, tissue-protective compound derived from EPO, by using human umbilical vein endothelial cells (HUVECs) and human monocytic THP-1 cells in vitro and Watanabe heritable hyperlipidemic spontaneous myocardial infarction (WHHLMI) rabbits in vivo. In HUVECs, HBSP inhibited apoptosis (≈70%) induced by C-reactive protein (CRP), a direct mediator of atherosclerosis. By using a small interfering RNA approach, Akt was shown to be a key molecule in HBSP-mediated prevention of apoptosis. HBSP also attenuated CRP-induced production of tumor necrosis factor (TNF)-α and matrix metalloproteinase-9 in THP-1 cells. In the WHHLMI rabbit, HBSP significantly suppressed progression of coronary atherosclerotic lesions as assessed by mean cross-sectional stenosis (HBSP 21.3 ± 2.2% versus control peptide 38.0 ± 2.7%) and inhibited coronary artery endothelial cell apoptosis with increased activation of Akt. Furthermore, TNF-α expression and the number of M1 macrophages and M1/M2 macrophage ratio in coronary atherosclerotic lesions were markedly reduced in HBSP-treated animals. In conclusion, these data demonstrate that HBSP suppresses coronary atherosclerosis, in part by inhibiting endothelial cell apoptosis through activation of Akt and in association with decreased TNF-α production and modified macrophage polarization in coronary atherosclerotic lesions. Because HBSP does not have the prothrombotic effects of EPO, our study may provide a novel therapeutic strategy that prevents progression of coronary artery disease.

Effects of long-term treatment with ranirestat, a potent aldose reductase inhibitor, on diabetic cataract and neuropathy in spontaneously diabetic torii rats.

We evaluated ranirestat, an aldose reductase inhibitor, in diabetic cataract and neuropathy (DN) in spontaneously diabetic Torii (SDT) rats compared with epalrestat, the positive control. Animals were divided into groups and treated once daily with oral ranirestat (0.1, 1.0, 10 mg/kg) or epalrestat (100 mg/kg) for 40 weeks, normal Sprague-Dawley rats, and untreated SDT rats. Lens opacification was scored from 0 (normal) to 3 (mature cataract). The combined scores (0-6) from both lenses represented the total for each animal. DN was assessed by measuring the motor nerve conduction velocity (MNCV) in the sciatic nerve. Sorbitol and fructose levels were measured in the lens and sciatic nerve 40 weeks after diabetes onset. Cataracts developed more in untreated rats than normal rats (P < 0.01). Ranirestat significantly (P < 0.01) inhibited rapid cataract development; epalrestat did not. Ranirestat significantly reversed the MNCV decrease (40.7 ± 0.6 m/s) in SDT rats dose-dependently (P < 0.01). Epalrestat also reversed the prevented MNCV decrease (P < 0.05). Sorbitol levels in the sciatic nerve increased significantly in SDT rats (2.05 ± 0.10 nmol/g), which ranirestat significantly suppressed dose-dependently, (P < 0.05, <0.01, and <0.01); epalrestat did not. Ranirestat prevents DN and cataract; epalrestat prevents DN only.

Association of serum osteoprotegerin with vascular calcification in patients with type 2 diabetes.

BACKGROUND: Osteoprotegerin is a member of the tumor necrosis factor-related family and inhibits RANK stimulation of osteoclast formation as a soluble decoy receptor. The goal of this study was to determine the relationship of serum osteoprotegerin with vascular calcification in patients with type 2 diabetes. METHODS: The subjects were 124 patients with type 2 diabetes mellitus, including 88 males and 36 females with a mean (± SD) age of 65.6 ± 8.2 years old. Serum levels of osteoprotegerin, osteocalcin, fibroblast growth factor 23 (FGF23), 25-hydroxyvitamin D3 and adiponectin were measured by ELISA. Vascular calcification in the cervical artery was examined by ultrasound sonography. The subjects were divided into 4 quartiles depending on serum osteoprotegerin levels. RESULTS: Vascular calcification was significantly higher in the 4th quartile and significantly lower in the 1st quartile of serum osteoprotegerin levels, compared to other quartiles. There were no differences in serum osteoprotegerin and vascular calcification among patients with different stages of diabetic nephropathy, but serum FGF23 levels were elevated in those with stage 4 diabetic nephropathy. Simple regression analysis showed that serum osteoprotegerin levels had significant positive correlations with age, systolic blood pressure and serum adiponectin levels, and significant negative correlations with BMI and serum 25-hydroxyvitamin D3. CONCLUSIONS: These findings suggest that elevated serum osteoprotegerin may be involved in vascular calcification independently of progression of diabetic nephropathy in patients with type 2 diabetes.

Inhibition of insulin secretion from rat pancreatic islets by dexmedetomidine and medetomidine, two sedatives frequently used in clinical settings.

The aim of this study was to determine whether dexmedetomidine (DEX) and medetomidine (MED), α2-adrenergic agonists clinically used as sedatives, influence insulin secretion from rat pancreatic islets. Islets were isolated from adult male Wistar rats after collagenase digestion. Static incubation was used to determine effects of DEX or MED on insulin secretion and ionic-channel currents of ß-cells. Results indicate that both drugs dose-dependently inhibit insulin secretion, DEX more potently than MED. The inhibitory effects were attenuated by addition of yohimbine or by pretreatment of rats with pertussis toxin (PTX). 10 nM DEX decreased the current amplitude of voltage-dependent Ca2+ channels, but this did not occur when the N-type Ca2+ channel blocker ω-conotoxin was added. In the presence of tetraethylammonium, a classical voltage-gated K+ channel (Kv channel) blocker, the magnitude of inhibition of insulin secretion by MED was reduced. However, when tolbutamide, a specific blocker of the ATP-sensitive K+ channel (KATP channel), was present, the magnitude of MED inhibition of insulin secretion was not influenced, suggesting that Kv-channel activity alteration, but not that of KATP channels, is involved in MED-associated insulin secretory inhibition. The Kv-channel currents were increased during 1 nM MED exposure at membrane potentials ranging from -30 mV to -10 mV, where action potentials were generated in response to glucose stimulation. These results indicate that DEX and MED inhibit insulin secretion through an α2-adrenoceptor and PTX-sensitive GTP-binding protein pathway that eventually involves Kv channel activation and Ca2+ channel inhibition.

Prompt increases in retinol-binding protein 4 and endothelial progenitor cells during acute exercise load in diabetic subjects.

The present study was undertaken to determine whether acute exercise load alters serum retinol-binding protein 4 (RBP4) and numbers of endothelial progenitor cells (EPC) in diabetic subjects. Sixty-two subjects with type 2 diabetes mellitus were enrolled in the present study. They were 50 males and 12 females with the ages of 65.1±8.1 (mean ± SD) years. Cardio-pulmonary exercise stress test (CPX) was carried out, and the numbers of EPC and serum RBP4 levels before and after the CPX were measured. RBP4 is a cytokine synthesized in hepatocytes, white adipose tissues and skeletal muscles, and serum RBP4 was determined by ELISA. EPC was determined as CD34(+)/133(+) cells by FACS. The subjects were subgrouped into two groups with or without nephropathy. Serum RBP4 levels promptly increased from 48.2±4.3 (mean±SEM) to 54.3±4.2 µg/mL after the CPX (mean exercise time of 8 min) in the diabetic subjects without nephropathy (p=0.0006), but did not in those with nephropathy. There was a positive correlation between changes in serum RBP4 during the exercise and estimated glomerular filtration rate (r=0.30, p=0.018). Also, an acute exercise load promptly increased the number of EPCs in the diabetic subjects with and without nephropathy. These findings suggest that a prompt increase in exercise-induced RBP4 is retarded by progression of nephropathy, and that an exercise-induced mobilization of EPCs could maintain endothelial cells in diabetic subjects.