Tomoaki Shimizu

The diabetes-susceptible gene SLC30A8/ZnT8 regulates hepatic insulin clearance.

Recent genome-wide association studies demonstrated that common variants of solute carrier family 30 member 8 gene (SLC30A8) increase susceptibility to type 2 diabetes. SLC30A8 encodes zinc transporter-8 (ZnT8), which delivers zinc ion from the cytoplasm into insulin granules. Although it is well known that insulin granules contain high amounts of zinc, the physiological role of secreted zinc remains elusive. In this study, we generated mice with β cell-specific Slc30a8 deficiency (ZnT8KO mice) and demonstrated an unexpected functional linkage between Slc30a8 deletion and hepatic insulin clearance. The ZnT8KO mice had low peripheral blood insulin levels, despite insulin hypersecretion from pancreatic β cells. We also demonstrated that a substantial amount of the hypersecreted insulin was degraded during its first passage through the liver. Consistent with these findings, ZnT8KO mice and human individuals carrying rs13266634, a major risk allele of SLC30A8, exhibited increased insulin clearance, as assessed by c-peptide/insulin ratio. Furthermore, we demonstrated that zinc secreted in concert with insulin suppressed hepatic insulin clearance by inhibiting clathrin-dependent insulin endocytosis. Our results indicate that SLC30A8 regulates hepatic insulin clearance and that genetic dysregulation of this system may play a role in the pathogenesis of type 2 diabetes.

Repetitive Fluctuations in Blood Glucose Enhance Monocyte Adhesion to the Endothelium of Rat Thoracic Aorta

Background—The aim of this study was to elucidate the effect of repetitive fluctuations in blood glucose concentrations on monocyte adhesion to the aortic endothelium. Methods and Results—Nonobese type 2 diabetes, Goto–Kakizaki (GK) rats were fed twice daily to induce repetitive postprandial glucose spikes. Then, we compared the number of monocytes adherent to the endothelium of thoracic aorta in these rats with that in rats fed ad libitum. To suppress the glucose spikes, rats were injected with an inhibitor of sodium–glucose transporter, phloridzin, just before each meal for 12 weeks. GK rats fed twice daily showed significantly lower HbA1c than GK rats fed ad libitum. However, the former group showed markedly higher number of monocytes adherent to the endothelium than the latter, together with increased arterial intimal thickening. Phloridzin significantly reduced the number of adherent monocytes in GK rats fed twice daily. Conclusion—Our data demonstrated that repetitive postprandial fluctuation in glucose concentration evokes monocyte adhesion to endothelial cells that was worse than that induced by stable hyperglycemia in vivo. Suppression of such fluctuations efficiently suppressed monocyte adhesion to the aortic endothelium.

Gut Dysbiosis and Detection of “Live Gut Bacteria” in Blood of Japanese Patients With Type 2 Diabetes

OBJECTIVE Mounting evidence indicates that the gut microbiota are an important modifier of obesity and diabetes. However, so far there is no information on gut microbiota and “live gut bacteria” in the systemic circulation of Japanese patients with type 2 diabetes. RESEARCH DESIGN AND METHODS Using a sensitive reverse transcription–quantitative PCR (RT-qPCR) method, we determined the composition of fecal gut microbiota in 50 Japanese patients with type 2 diabetes and 50 control subjects, and its association with various clinical parameters, including inflammatory markers. We also analyzed the presence of gut bacteria in blood samples. RESULTS The counts of the Clostridium coccoides group, Atopobium cluster, and Prevotella (obligate anaerobes) were significantly lower (P < 0.05), while the counts of total Lactobacillus (facultative anaerobes) were significantly higher (P < 0.05) in fecal samples of diabetic patients than in those of control subjects. Especially, the counts of Lactobacillus reuteri and Lactobacillus plantarum subgroups were significantly higher (P < 0.05). Gut bacteria were detected in blood at a significantly higher rate in diabetic patients than in control subjects (28% vs. 4%, P < 0.01), and most of these bacteria were Gram-positive. CONCLUSIONS This is the first report of gut dysbiosis in Japanese patients with type 2 diabetes as assessed by RT-qPCR. The high rate of gut bacteria in the circulation suggests translocation of bacteria from the gut to the bloodstream.

Effect of metformin on advanced glycation endproduct formation and peripheral nerve function in streptozotocin-induced diabetic rats

The effects of metformin treatment on advanced glycation endproduct formation and peripheral nerve function in streptozotocin-induced diabetic rats were examined. Streptozotocin-induced diabetic rats were treated with low dose metformin (50-65 mg kg(-1) daily) or high dose metformin (500-650 mg kg(-1) daily) for 10 weeks. While the metformin-untreated diabetic group showed a significant increase of advanced glycation endproducts (6.1-fold in the lens, 1.6-fold in the sciatic nerve, 2.3-fold in the renal cortex, and 1.9-fold in plasma; all P < 0.01) compared with the healthy control group, both metformin-treated groups had significantly less advanced glycation endproduct deposition. The % decrease in the diabetes-induced increase in advanced glycation endproduct formation by low and high dose metformin treatment was 25% and 72% in the lens (both P < 0.01), 31% and 42% in the sciatic nerve (both P < 0.05), and 16% and 33% in the renal cortex (P < 0.05 and P < 0.01), respectively. However, the plasma advanced glycation endproduct level showed no significant difference from that in the untreated diabetic group, in spite of slight decrease in plasma glucose and glycated hemoglobin levels in the metformin-treated groups. The diabetes-induced sciatic nerve conduction velocity deficits were improved by 46% and 42% by low and high dose metformin treatment, respectively (both P < 0.01). These data suggest that metformin may have a direct antiglycative action, which in turn contributes to amelioration of peripheral nerve function. Thus, metformin treatment may be effective in the prevention of diabetic complications through not only lowering plasma glucose, but also directly inhibiting advanced glycation endproduct formation.

Miglitol suppresses the postprandial increase in interleukin 6 and enhances active glucagon-like peptide 1 secretion in viscerally obese subjects

Visceral obesity and insulin resistance are regarded as risk factors for atherosclerosis. Epidemiologic studies have demonstrated long-term anti-atherosclerotic effects with administration of alpha-glucosidase inhibitors. Alpha-glucosidase inhibitors also have been reported to enhance glucagon-like peptide 1 (GLP-1) secretion. We compared the postprandial effects of a single administration of miglitol and acarbose on glucose and lipid metabolism, on insulin requirement, on GLP-1 secretion, and on inflammatory and endothelial markers in viscerally obese subjects. Twenty-four viscerally obese subjects with relative insulin resistance participated in this study. Subjects were given a single dose of miglitol (50 mg), acarbose (100 mg), or placebo blindly and randomly before a meal in a crossover design. The meal loads after drug administration were tested 3 times within 2 weeks. We measured glucose, insulin, lipids, lipoprotein lipase, interleukin 6, intracellular adhesion molecule 1, vascular cell adhesion molecule 1, and active GLP-1 at before and various minutes after the meal. Single administration of both alpha-glucosidase inhibitors had several beneficial effects in improving postprandial hyperglycemia and reducing postprandial insulin requirement approximately 25% of placebo without adversely affecting lipid profiles. Although lipoprotein lipase levels within 2 hours after the meal did not show differences among miglitol, acarbose, and placebo administrations, miglitol significantly suppressed the increases in triglycerides, remnant-like particle triglycerides, and remnant-like particle cholesterol compared to acarbose and placebo in the early phase. Miglitol also significantly enhanced active GLP-1 secretion to a greater extent than acarbose (P < .01) and placebo (P < .001), and significantly suppressed the postprandial increase in interleukin 6 compared to placebo (P < .01). The results point to the potential suitability of miglitol as an anti-atherosclerotic effect in viscerally obese subjects, in preference to acarbose. Further studies are needed to elucidate the long-term effects on enhanced GLP-1 secretion and anti-atherosclerosis.

Temporary hyperglycaemia provokes monocyte adhesion to endothelial cells in rat thoracic aorta

Aims/hypothesisSeveral epidemiological data suggest that patients with postprandial hyperglycaemia are at high risk of cardiovascular disease. The aim of this study was to elucidate the effect of a glucose ‘spike’ on monocyte adhesion to rat aortic endothelial cells.Materials and methodsMonocyte adhesion to endothelial cells in vivo was quantitated using an en face method for observation of endothelial surface after immunohistochemical staining for CD68 in the thoracic aortas of Sprague–Dawley rats after several kinds of blood glucose rises.ResultsThe number of monocytes adhering to endothelial cells increased at 30xa0min after injection of glucose in 8-week-old Sprague–Dawley rats. The increased adhesion returned to the basal level at 120xa0min after glucose injection, concomitantly with the return of blood glucose levels to normal. The infusion of octreotide to inhibit endogenous insulin secretion did not prevent the glucose-induced increase in monocyte adhesion to endothelial cells. On the other hand, the number of monocytes adhering to endothelial cells did not increase in rats with streptozotocin-induced diabetes and sustained hyperglycaemia.Conclusions/interpretationOur data demonstrate that a temporary rise in blood glucose levels can in itself promote a reversible increase in monocyte adhesion to arterial endothelial cells.

Comparison of effects of olmesartan and telmisartan on blood pressure and metabolic parameters in Japanese early-stage type-2 diabetics with hypertension.

Angiotensin II type-1 receptor blockers (ARBs) are regarded as first-line treatments for type-2 diabetes with hypertension. Despite the availability of various types of ARBs, there are no comparative studies of their effects on patients with diabetes. In this open-label prospective crossover study, we compared the effects of olmesartan (20 mg/day) and telmisartan (40 mg/day). Twenty Japanese early-stage type-2 diabetes patients with hypertension treated with valsartan (80 mg/day) for at least 8 weeks were recruited to this study. At study entry, valsartan was changed to olmesartan (20 mg/day) or telmisartan (40 mg/day) and administered for 8 weeks. The drugs were then switched and treatment was continued for another 8 weeks. We analyzed the blood pressure lowering effects of each drug by 24-h ambulatory blood pressure monitoring at 0, 8, and 16 weeks. Simultaneously, we measured metabolic parameters and inflammation markers. Olmesartan lowered mean systolic and diastolic blood pressure more significantly than did telmisartan. While there were no differences between the groups in metabolic parameters, including HbA1c and adiponectin, the decreases in serum interleukin-6 and highly sensitive C-reactive protein were more significant by olmesartan treatment. Our results indicate that olmesartan has more potent arterial blood pressure lowering and anti-inflammatory effects than telmisartan. (Hypertens Res 2008; 31: 7−13)

Combination of the Framingham Risk Score and Carotid Intima-Media Thickness Improves the Prediction of Cardiovascular Events in Patients With Type 2 Diabetes

OBJECTIVE The aim of this study was to investigate whether carotid intima-media thickness (IMT) and brachial-ankle pulse wave velocity (baPWV) add value to the Framingham risk score (FRS) in predicting the development of cardiovascular diseases (CVDs) in type 2 diabetic patients with a negative history of CVD. RESEARCH DESIGN AND METHODS Type 2 diabetic patients (n = 783) were retrospectively recruited and followed for CVD. RESULTS During a 5.4-year follow-up period, 85 incidences of CVD were recorded (10.9%). After adjustment for conventional arterial risk factors, multivariate analysis with the Cox proportional hazards model identified IMT, but not baPWV, as a significant determinant of CVD. In addition, the combination of FRS with IMT, but not with baPWV, improved the prediction of CVD. CONCLUSIONS Carotid IMT is a significant predictor of CVD in asymptomatic type 2 diabetic patients, and the combination of FRS and IMT improves the prediction of CVD in these patients.

Nateglinide Reduces Carotid Intima-Media Thickening in Type 2 Diabetic Patients Under Good Glycemic Control

Objective—Postprandial hyperglycemia observed in type 2 diabetes mellitus is a risk factor for atherosclerosis. The aim of this study was to investigate the effect of strict glycemic control by nateglinide on common carotid far wall intima-media thickness in type 2 diabetic patients who were already under good glycemic control. Methods and Results—We performed an open labeled randomized prospective trial on 78 drug-naive type 2 diabetic patients whose HbA1c was less than 6.5%. Thirty-eight patients were randomly assigned to receive nateglinide (270 mg/dL) and 40 to control group (no treatment). After 12 months, a significant reduction in HbA1c was observed in the nateglinide group, whereas a significant increase of HbA1c was observed in the untreated group. The carotid intima-media thickness at the end of 1-year follow-up was significantly reduced in the nateglinide group compared with the untreated group (−0.017±0.054 mm/year versus 0.024±0.066 mm/year, P=0.0064). Whereas nateglinide treatment also reduced triglyceride, highly-sensitive C-reactive protein, and E-selectin, multiple regression analysis identified HbA1c as the only significant independent determinant of the change in carotid intima-media thickness. Conclusion—In type 2 diabetic patients with good glycemic control, further strict glycemic control by nateglinide results in regression of carotid intima-media thickness.

Endothelial nitric oxide synthase gene and the development of diabetic nephropathy

BACKGROUNDnEndothelial nitric oxide synthase gene and the development of diabetic nephropathynnnBACKGROUNDnIntron 4 insertion/deletion polymorphism of the constitutive endothelial nitric oxide synthase (ecNOS) gene may be related to diabetic nephropathy.nnnMETHODSnA case-control study was performed in three groups of Japanese patients with Type 2 diabetes mellitus, which including 123 patients with advanced diabetic nephropathy, 107 patients with overt proteinuria and normal serum creatinine level, and a control group of 203 patients with normal renal function despite having diabetes for over 10 years. Additionally, logistic regression analysis was used to assess the findings.nnnRESULTSnWhen we examined the a-deletion/b-insertion in intron 4 of ecNOS gene, the genotype and allele frequencies were not significantly different between the patients with advanced diabetic nephropathy (a/a 2.4, a/b 21.9, b/b 75.5, a 13.4, b 86.6%), the patients with overt proteinuria (a/a 2.8, a/b 15.8, b/b 81.4, a 10.7, b 89.3%) and the control group (a/a 1.4, a/b 21.6, b/b 76.8, a 12.8, b 87.7%). Logistic regression analysis showed that the ecNOS intron4 a-allele frequency was not the related to nephropathy (P = 0.88).nnnCONCLUSIONnWe conclude that there is no association of the ecNOS gene polymorphism with the development of diabetic nephropathy in Japanese patients with type 2 diabetes.