Hiroshi Hashiguchi

Cyclic AMP/cAMP‐GEF pathway amplifies insulin exocytosis induced by Ca2+ and ATP in rat islet β‐cells

Cyclic AMP (cAMP) plays a pivotal role in insulin secretion induced by incretins. The effects of the second messenger extend to many sites and there has been much controversy on the mechanisms. The aim of this study was to examine how cAMP amplified insulin exocytosis.

Association of upregulated activity of KATP channels with impaired insulin secretion in UCP1-expressing insulinoma cells

Insulin‐secreting MIN6 cells overexpressing uncoupling protein‐1 (UCP1) were studied regarding insulin secretion in response to various secretagogues. Overexpression of UCP1 prevented an increase of cytosolic ATP levels induced by glucose. In contrast, glucose utilization was not affected, nor was glycerol phosphate flux. The UCP1‐expressing cells showed an inability to increase cytosolic Ca2+ concentration ([Ca2+]i) in response to glucose or α ketoisocaproate and this resulted in less insulin secretion, whereas initial reduction in [Ca2+]i occurring upon either nutrient addition was not affected. Moreover, the effectiveness of tolbutamide on [Ca2+]i increase was reduced and the dose‐response relations for insulin secretion induced by the agent was shifted toward the right in the UCP1‐expressing cells. The resting membrane potential of the UCP1‐expressing cells was significantly hyperpolarized by 6.2 mV compared with control cells. In the perforated and conventional whole‐cell patch‐clamp configurations, the conductance density of ATP‐sensitive K+ (KATP) channels of the UCP1‐expressing cells was 6‐fold and 1.7‐fold greater than that of the control cells, respectively. The sensitivity of KATP channels for tolbutamide was not different between two groups, indicating that in intact cells more than 6‐fold higher concentrations of tolbutamide were required to reduce the KATP channel currents of UCP1‐expressing cells to the same levels as of the control cells. The current density of the voltage‐dependent Ca2+ channels was not influenced. In conclusion, UCP1‐expressing cells showed a refractoriness to respond to tolbutamide as well as nutrients. An upregulated activity of KATP channels was associated with unresponsiveness to the agent in the cells with impaired mitochondrial function.

Effect of Channel Length on the Gas–Liquid Two-Phase Flow Phenomena in a Microchannel

An optical measurement system was used to investigate the effect of microchannel length and inlet geometery on adiabatic gas–liquid two-phase flow. Experiments were conducted with 146-mm- and 1571-mm-long, circular microchannels of 100 μm diameter. Void fraction and gas and liquid plug/slug lengths and their velocities were measured for two inlet configurations for gas–liquid mixing: (a) reducer and (b) T-junction. The superficial gas velocity was varied from 0.03 to 14 m/s, and superficial liquid velocity from 0.04 to 0.7 m/s. The test section length was found to have a significant effect on the two-phase flow characteristics measured at the same axial location (37 mm from the inlet) in both microchannels. The mean void fraction data for the short (146 mm) microchannel with the reducer inlet agreed well with the equation previously proposed by Kawahara et al. (2002). On the other hand, the mean void fraction data for the long (1571 mm) microchannel obeyed the homogeneous flow model and Armands equation for both the reducer and T-junction inlet configurations. Many long and rapidly moving gas plugs/slugs and long, slowly moving liquid plugs/slugs were observed in the short microchannel compared to the long microchannel, leading to the differences in the time-averaged void fraction data. The mean velocity of liquid plugs/slugs generally agreed well with Hughmarks equation and the homogeneous flow model predictions, regardless of the inlet configurations and microchannel lengths. Thus, both the microchannel length and inlet geometry were found to significantly affect the two-phase flow characteristics in a microchannel.

The Combination Therapy of Fenofibrate and Ezetimibe Improved Lipid Profile and Vascular Function Compared with Statins in Patients with Type 2 Diabetes

Aim: Elevated level of serum triglyceride (TG) is a characteristic of type 2 diabetes. We evaluated the clinical significance of intervention for the serum TG levels in the fasting and postprandial states in patients with type 2 diabetes. Methods: Fifty patients with type 2 diabetes, treated with statins, were selected and divided into two groups. One group was treated with a combination of fenofibrate and ezetimibe (F/E group) and the other group with statins (statin group) for 12 weeks. The lipoprotein profile of both groups was compared using high-performance liquid chromatography, and the vascular function was assessed using flow-mediated dilation (FMD) at the forearm. Results: The levels of very low-density lipoprotein (VLDL) cholesterol, malondialdehyde low-density lipoprotein (MDA-LDL), total TG, chylomicron-TG, VLDL-TG, and HDL-TG decreased in the F/E group, whereas those of HDL cholesterol increased. Furthermore, the peak particle size of LDL increased, but that of HDL decreased in the F/E group. The combination treatment significantly improved the FMD. The change in the cholesterol level in a very small fraction of HDL was a significant independent predictor for determining the improvement of FMD (p < 0.01). Conclusions: Compared with the treatment with statins, the treatment with the combination of fenofibrate and ezetimibe effectively controlled the LDL cholesterol and TG levels, increased the HDL cholesterol level, especially in its small fraction, and improved vascular function of patients with type 2 diabetes.

Investigation of the clinical significance of the growth hormone-releasing peptide-2 test for the diagnosis of secondary adrenal failure

The aim of this study was to evaluate the ability of the growth hormone-releasing peptide-2 (GHRP-2) test to clinically diagnose hypothalamo-pituitary-adrenal (HPA) axis failure. We performed an insulin tolerance test (ITT), CRH stimulation test, and GHRP-2 test on 47 patients suspected of having a hypothalamo-pituitary disorder. Patients with pituitary disorders had significantly lower ACTH responses to the GHRP-2 test compared to patients with hypothalamic disorders and the control group. In contrast, peak cortisol levels in response to the GHRP-2 test were significantly lower in both hypothalamic and pituitary disorder cases compared with the control group. Assignment of a cut-off value of 11.6 μg/dL for the peak serum cortisol level demonstrated that the GHRP-2 test was able to predict secondary hypoadrenalism with 88.9% specificity and 89.7% sensitivity. The responses of ACTH and cortisol to the GHRP-2 test had no correlation to the CRH test, suggesting the involvement of a different mechanism of ACTH secretion. These results indicate that the GHRP-2 test may induce ACTH secretion from the pituitary gland through direct stimulation. Although the GHRP-2 test does not have the same predictive value as the insulin tolerance test (ITT), it has similar diagnostic potential as the CRH stimulation test for evaluating HPA axis failure.

mRNA expression of platelet activating factor receptor (PAFR) in peripheral blood mononuclear cells is associated with albuminuria and vascular dysfunction in patients with type 2 diabetes

AIMS Renal dysfunction in addition to diabetes is a serious risk factor for cardiovascular events. We hypothesized that some of the changes in gene expression in blood cells cause renal dysfunction and macrovascular disease through impaired endothelial function. This study aimed to define which changes in gene expression in peripheral blood mononuclear cells (PBMCs) are related to renal function parameters and endothelial function of large arteries in patients with type 2 diabetes mellitus (T2DM). METHODS We recruited 95 patients with T2DM. After matching for gender, age, BMI and HbA1c levels, the patient cohort included 42 with normoalbuminuria, 28 with microalbuminuria, and 25 with macroalbuminuria. All patients in the three groups were assessed for urinary albumin to creatinine ratio (ACR), estimated glomerular filtration rate (eGFR), flow-mediated dilatation (FMD), and mRNA expression in PBMCs. RESULTS The mRNA expression of platelet activating factor receptor (PAFR) differed most markedly between the three groups and was significantly higher in the macroalbuminuric group (p < 0.001 vs. normoalbuminuric group; p < 0.05 vs. microalbuminuric group). PAFR mRNA expression significantly correlated with log transformed ACR (ρ = 0.424, p < 0.001) but not eGFR. PAFR mRNA expression also had a significant negative correlation with FMD (ρ = -0.379, p < 0.001). Furthermore, the prevalence of macrovascular complications, particularly stroke, was significantly higher in patients with elevated PAFR mRNA expression in PBMCs. CONCLUSIONS PAFR overexpression in PBMCs may link diabetic nephropathy to macroangiopathy through impairment of endothelial function in patients with T2DM.