Minako Kawaguchi

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.

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.

Efficacy and safety of modified Yale insulin infusion protocol in Japanese diabetic patients after open-heart surgery

To our knowledge, there is currently no insulin infusion protocol for critically ill patients especially designed for Asian diabetics although many such protocols are used in Western countries. In this study, we modified the Yale insulin infusion protocol taking into consideration the characteristics of Japanese diabetics and hospital environment. We tested the modified protocol in 40 type 2 diabetic patients after elective open-heart surgery (MY group) comparing with 35 type 2 diabetic patients under empirical blood glucose control (EC group). Analyses of 1656 blood glucose measurements during insulin infusion revealed that percentage of samples that showed achievement of target blood glucose level (80-140 mg/dl) was higher under MY (78+/-15%, n=870) than EC (57+/-23%, n=786, p<0.0001). On the other hand, the percentage of samples in which blood glucose was less than 60 mg/dl was comparable in the two groups (MY: 0.5+/-5.9 per thousand, EC: 5.1+/-18.5 per thousand). None of the patients with hypoglycemia showed significant clinical adverse effects. In conclusion, our modified Yale insulin infusion protocol is effective and safe for tight blood glucose control in Japanese diabetic patients after open-heart surgery.

Exercise-induced enhancement of insulin sensitivity is associated with accumulation of M2-polarized macrophages in mouse skeletal muscle.

Exercise enhances insulin sensitivity in skeletal muscle, but the underlying mechanism remains obscure. Recent data suggest that alternatively activated M2 macrophages enhance insulin sensitivity in insulin target organs such as adipose tissue and liver. Therefore, the aim of this study was to determine the role of anti-inflammatory M2 macrophages in exercise-induced enhancement of insulin sensitivity in skeletal muscle. C57BL6J mice underwent a single bout of treadmill running (20 m/min, 90 min). Twenty-four hours later, ex vivo insulin-stimulated 2-deoxy glucose uptake was found to be increased in plantaris muscle. This change was associated with increased number of CD163-expressing macrophages (i.e. M2-polarized macrophages) in skeletal muscle. Systemic depletion of macrophages by pretreatment of mice with clodronate-containing liposome abrogated both CD163-positive macrophage accumulation in skeletal muscle as well as the enhancement of insulin sensitivity after exercise, without affecting insulin-induced phosphorylation of Akt and AS160 or exercise-induced GLUT4 expression. These results suggest that accumulation of M2-polarized macrophages is involved in exercise-induced enhancement of insulin sensitivity in mouse skeletal muscle, independently of the phosphorylation of Akt and AS160 and expression of GLUT4.

Effects of sitagliptin on ectopic fat contents and glucose metabolism in type 2 diabetic patients with fatty liver: A pilot study

Recent data have shown that ectopic fat accumulation in the liver worsens hepatic glucose metabolism, suggesting that fatty liver in patients with type 2 diabetes is a therapeutic target. Glucagon‐like peptide (GLP)‐1 improves fatty liver, but the effect of dipeptidyl peptidase‐4 inhibitor on fatty liver is still unclear. The present pilot study determined the effects of 12‐week treatment with sitagliptin, a dipeptidyl peptidase‐4 inhibitor, on liver fat content in type 2 diabetes with fatty liver. We also evaluated intramyocellular lipid (IMCL) and glucose kinetics during oral glucose tolerance test (OGTT) before and after the treatment.

Association Between Expression of FABPpm in Skeletal Muscle and Insulin Sensitivity in Intramyocellular Lipid-Accumulated Nonobese Men

CONTEXT Intramyocellular lipid (IMCL) accumulation is observed in both insulin-resistant subjects and insulin-sensitive endurance athletes (athletes paradox). We hypothesized that the expression pattern of fatty acid transporters may influence oxidative capacity and determine the association between IMCL and insulin resistance. OBJECTIVE The objective of the study was to investigate the muscle expression of fatty acid transporters and their function related to insulin sensitivity in IMCL-accumulated subjects. DESIGN AND SETTING The study subjects were 36 nonobese healthy men. Their IMCL levels were measured by (1)H-magnetic resonance spectroscopy, and their insulin sensitivity was evaluated by steady-state glucose infusion rate (GIR) during a euglycemic-hyperinsulinemic clamp. Gene expression levels in the vastus lateralis were evaluated by quantitative RT-PCR. We compared the clinical phenotypes and the expression levels of genes involved in lipid metabolism in skeletal muscle between IMCL-accumulated high-GIR (H-GIR) subjects (n = 8) and low-GIR subjects (n = 9). The functions of candidate fatty acid transporters were determined by in vitro analyses. RESULTS Compared with the low-GIR group, body fat was lower and maximum oxygen uptake was higher in the H-GIR group. Several lipid oxidation genes in muscle were up-regulated in the H-GIR group, and this was associated with increased expression of higher plasma membrane-associated fatty acid-binding protein (FABPpm) and decreased expression of fatty acid transport protein (FATP)-1. Overexpression of FABPpm in C2C12 myotubes increased fatty acid oxidation coupled with the elevated expression of genes related to fatty acid oxidation. These changes were not observed in FATP1-overexpressed myotubes. CONCLUSIONS Differences in the gene expression of fatty acid transporters may, at least in part, affect insulin sensitivity in IMCL-accumulated nonobese men.

Increased intramyocellular lipid/impaired insulin sensitivity is associated with altered lipid metabolic genes in muscle of high responders to a high-fat diet

The accumulation of intramyocellular lipid (IMCL) is recognized as an important determinant of insulin resistance, and is increased by a high-fat diet (HFD). However, the effects of HFD on IMCL and insulin sensitivity are highly variable. The aim of this study was to identify the genes in muscle that are related to this inter-individual variation. Fifty healthy men were recruited for this study. Before and after HFD for 3 days, IMCL levels in the tibialis anterior were measured by (1)H magnetic resonance spectroscopy, and peripheral insulin sensitivity was evaluated by glucose infusion rate (GIR) during the euglycemic-hyperinsulinemic clamp. Subjects who showed a large increase in IMCL and a large decrease in GIR by HFD were classified as high responders (HRs), and subjects who showed a small increase in IMCL and a small decrease in GIR were classified as low responders (LRs). In five subjects from each group, the gene expression profile of the vastus lateralis muscle was analyzed by DNA microarray analysis. Before HFD, gene expression profiles related to lipid metabolism were comparable between the two groups. Gene Set Enrichment Analysis demonstrated that five gene sets related to lipid metabolism were upregulated by HFD in the HR group but not in the LR group. Changes in gene expression patterns were confirmed by qRT-PCR using more samples (LR, n = 9; HR, n = 11). These results suggest that IMCL accumulation/impaired insulin sensitivity after HFD is closely associated with changes in the expression of genes related to lipid metabolism in muscle.

Comparison of effects of cilnidipine and azelnidipine on blood pressure, heart rate and albuminuria in type 2 diabetics with hypertension: A pilot study.

Previous studies reported that both cilnidipine and azelnidipine have a renoprotective effect compared with amlodipine. The aim of this study was to compare the effects of cilnidipine and azelnidipine on blood pressure, heart rate and albuminuria. An open‐label prospective crossover trial was carried out. We recruited 19 type 2 diabetics treated with amlodipine (5 mg/day) at least for 12 weeks. At study entry, amlodipine was changed to cilnidipine (10 mg/day) or azelnidipine (16 mg/day) and each administered for 16 weeks. Then, the drugs were switched and the treatment was continued for another 16 weeks. Despite no differences in 24‐h blood pressure and heart rate between cilnidipine and azelnidipine, treatment with cilnidipine resulted in a greater reduction in urinary albumin:creatinine ratio than azelnidipine. Our results suggested that cilnidipine is more efficient in reducing albuminuria than azelnidipine independent of its blood pressure lowering effect in type 2 diabetic patients with hypertension. This trial was registered with UMIN (no. 000007201).

Effect of treatment guidance using a retrospective continuous glucose monitoring system on glycaemic control in outpatients with type 2 diabetes mellitus: A randomized controlled trial

Objectives To assess the effect of treatment guidance based on data from a continuous glucose monitoring (CGM) device on glycaemic control, and patient satisfaction, in patients with type 2 diabetes mellitus (T2DM). Methods Patients with poorly-controlled T2DM treated with insulin were randomly assigned to the intervention or nonintervention group. Continuous blood-glucose levels were recorded for 4–5 days using a CGM device on three separate occasions during the 8-month study period. The intervention group received treatment guidance based on the CGM data; the nonintervention group received advice based on blood glucose and glycosylated haemoglobin (HbA1c) levels. Results A total of 34 patients were enrolled in the study. The mean ± SD baseline HbA1c was 8.2 ± 1.2% in the intervention group and 8.2 ± 0.9% in the nonintervention group. At the study end, there was no significant difference in the change from baseline of HbA1c between the two groups. There was also no significant difference in the change from baseline in the Diabetes Treatment Satisfaction Questionnaire score between the two groups. Conclusions The present study did not demonstrate that treatment guidance using retrospective CGM data was effective for improving glycaemic control and therapeutic satisfaction in Japanese patients with T2DM.

Effects of alcohol abstinence on glucose metabolism in Japanese men with elevated fasting glucose: A pilot study

It has been demonstrated that moderate alcohol consumption provides protection against the development of type 2 diabetes. However, several other reports suggested that moderate alcohol intake may increase the risk of type 2 diabetes in non-obese Japanese. The aim of present study was to investigate the effect of 1-week alcohol abstinence on hepatic insulin sensitivity and fasting plasma glucose (FPG) in non-obese Japanese men. We recruited 8 non-obese Japanese men with mildly elevated FPG and drinking habits alcohol (mean frequency; 5.6 ± 2.5 times/week, mean alcohol consumption; 32.1 ± 20.0 g/day). Before and after the 1-week alcohol abstinence, we used the 2-step hyperinsulinemic-euglycemic clamp to measure endogenous glucose production (EGP) and insulin sensitivity (IS) in muscle and liver. One-week alcohol abstinence significantly reduced both FPG by 7% (from 105.5 ± 11.7 to 98.2 ± 7.8 mg/dl, P < 0.01) and fasting EGP by 6% (from 84.1 ± 4.2 to 77.6 ± 1.6 mg/m2 per min, P < 0.01), respectively. Two–step clamp study showed that alcohol abstinence significantly improved hepatic-IS, but not muscle-IS. In conclusion, one week alcohol abstinence improved hepatic IS and FPG in non-obese Japanese men with mildly elevated FPG and drinking habits alcohol.