Yuzuru Ito

Diet-Induced Adipose Tissue Inflammation and Liver Steatosis Are Prevented by DPP-4 Inhibition in Diabetic Mice

OBJECTIVE Diet composition alters the metabolic states of adipocytes and hepatocytes in diabetes. The effects of dipeptidyl peptidase-4 (DPP-4) inhibition on adipose tissue inflammation and fatty liver have been obscure. We investigated the extrapancreatic effects of DPP-4 inhibition on visceral fat and the liver. RESEARCH DESIGN AND METHODS We investigated diet-induced metabolic changes in β-cell–specific glucokinase haploinsufficient (Gck+/−) diabetic mice. We challenged animals with a diet containing a combination of sucrose and oleic acid (SO) or sucrose and linoleic acid (SL). Next, we assessed the effects of a DPP-4 inhibitor, des-fluoro-sitagliptin, on adipose tissue inflammation and hepatic steatosis. RESULTS The epididymal fat weight and serum leptin level were significantly higher in Gck+/− mice fed SL than in mice fed SO, although no significant differences in body weight or adipocyte size were noted. Compared with SO, SL increased the numbers of CD11c+ M1 macrophages and CD8+ T-cells in visceral adipose tissue and the expression of E-selectin, P-selectin, and plasminogen activator inhibitor-1 (PAI-1). DPP-4 inhibition significantly prevented adipose tissue infiltration by CD8+ T-cells and M1 macrophages and decreased the expression of PAI-1. The production of cytokines by activated T-cells was not affected by DPP-4 inhibition. Furthermore, DPP-4 inhibition prevented fatty liver in both wild-type and Gck+/− mice. DPP-4 inhibition also decreased the expressions of sterol regulatory element–binding protein-1c, stearoyl-CoA desaturase-1, and fatty acid synthase, and increased the expression of peroxisome proliferator–activated receptor-α in the liver. CONCLUSIONS Our findings indicated that DPP-4 inhibition has extrapancreatic protective effects against diet-induced adipose tissue inflammation and hepatic steatosis.

Metformin prevents liver tumorigenesis induced by high-fat diet in C57Bl/6 Mice

The prevalence of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) is increasing with the growing epidemics of obesity and diabetes. NAFLD encompasses a clinicopathologic spectrum of disease ranging from isolated hepatic steatosis to NASH, which is a more aggressive form of fatty liver disease, to cirrhosis and, finally, hepatocellular carcinoma (HCC). The exact mechanism behind the development of HCC in NASH remains unclear; however, it has been established that hepatic steatosis is the important risk factor in the development of HCC. Metformin has recently drawn attention because of its potential antitumor effect. Here, we investigated the effects of metformin on high-fat diet (HFD)-induced liver tumorigenesis, using a mouse model of NASH and liver tumor. Metformin prevented long-term HFD-induced liver tumorigenesis in C57Bl/6 mice. Of note, metformin failed to protect against liver tumorigenesis in mice that had already begun to develop NAFLD. Metformin improved short-term HFD-induced fat accumulation in the liver, associated with the suppression of adipose tissue inflammation. Collectively, these results suggest that metformin may prevent liver tumorigenesis via suppression of liver fat accumulation in the early stage, before the onset of NAFLD, which seems to be associated with a delay in the development of inflammation of the adipose tissue.

Trefoil Factor 2 Promotes Cell Proliferation in Pancreatic β-Cells through CXCR-4-Mediated ERK1/2 Phosphorylation

Decreased β-cell mass is a hallmark of type 2 diabetes, and therapeutic approaches to increase the pancreatic β-cell mass have been expected. In recent years, gastrointestinal incretin peptides have been shown to exert a cell-proliferative effect in pancreatic β-cells. Trefoil factor 2 (TFF2), which is predominantly expressed in the surface epithelium of the stomach, plays a role in antiapoptosis, migration, and proliferation. The TFF family is expressed in pancreatic β-cells, whereas the role of TFF2 in pancreatic β-cells has been obscure. In this study, we investigated the mechanism by which TFF2 enhances pancreatic β-cell proliferation. The effects of TFF2 on cell proliferation were evaluated in INS-1 cells, MIN6 cells, and mouse islets using an adenovirus vector containing TFF2 or a recombinant TFF2 peptide. The forced expression of TFF2 led to an increase in bromodeoxyuridine (BrdU) incorporation in both INS-1 cells and islets, without any alteration in insulin secretion. TFF2 significantly increased the mRNA expression of cyclin A2, D1, D2, D3, and E1 in islets. TFF2 peptide increased ERK1/2 phosphorylation and BrdU incorporation in MIN6 cells. A MAPK kinase inhibitor (U0126) abrogated the TFF2 peptide-mediated proliferation of MIN6 cells. A CX-chemokine receptor-4 antagonist also prevented the TFF2 peptide-mediated increase in ERK1/2 phosphorylation and BrdU incorporation in MIN6 cells. These results indicated that TFF2 is involved in β-cell proliferation at least partially via CX-chemokine receptor-4-mediated ERK1/2 phosphorylation, suggesting TFF2 may be a novel target for inducing β-cell proliferation.

The Alkalizer Citrate Reduces Serum Uric Acid Levels and Improves Renal Function in Hyperuricemic Patients Treated with the Xanthine Oxidase Inhibitor Allopurinol

Objective. Hyperuricemia, an integral component of metabolic syndrome, is a major health problem causing gout and renal damage. Urine alkalizers such as citrate preparations facilitate renal excretion of the uric acid, but its supportive effect on xanthine oxidase inhibitors has not been tested yet. We performed a randomized, prospective study of the effect of a combination of allopurinol and a citrate preparation on renal function in patients with hyperuricemia, employing 70 patients who had hyperuricemia with serum uric acid levels ≥7.0 mg/dL, or those diagnosed as having hyperuricemia in the past. Methods. They were randomly enrolled into two study groups: the allopurinol monotherapy (MT) group or combination treatment (CT) group with allopurinol and a citrate preparation. Allopurinol (100–200 mg/day) in the absence or presence of a citrate preparation (3 g/day) was administered for 12 weeks and levels of serum uric acid, its urinary clearance (Cua), and the renal glomerular filtration rates assessed with the creatinine clearance (Ccr) were evaluated before and after the treatment. Results. Serum levels of uric acid decreased significantly in both groups, whereas the change observed was much greater in CT group. Cua was significantly increased in CT group but not in MT group. Ccr was not altered in both groups in general, whereas it was significantly increased in a fraction of CT group with decreased renal function. Conclusions. These results indicate that an additional use of citrate preparations with xanthine oxidase inhibitors is beneficial for patients with hyperuricemia, reducing circulating uric acid and improving their glomerular filtration rates.

Glycemic control after addition of the dipeptidyl peptidase-4 inhibitor alogliptin in patients with type 2 diabetes showing inadequate response to thrice-a-day treatment with α-glucosidase inhibitors.

Objective: We investigated the effect of addition of alogliptin, while continuing the α-glucosidase inhibitor (αGI) administration at the same or reduced dose, or discontinuing the drug, on the glycemic control in type 2 diabetic patients showing inadequate response to αGI treatment. Research design and methods: A prospective, randomized, controlled, multicenter interventional study trial. Subjects were randomly assigned to treatment with alogliptin alone (Intake 0 group), or alogliptin in addition to an αGI administered once-/twice-/thrice-daily (Intake 1, 2 and 3 groups). Main outcome measures: Changes in glycemic control were measured. Results: The HbA1c and glycoalbumin levels at 1 and 3 months were significantly lower than the values at the baseline in the Intake 1, 2 and 3 groups, but not the Intake 0 group. The body weight at 3 months was significantly lower than that at the baseline in the Intake 3 group. There were no significant differences in the degree of satisfaction or participating volition recorded, before and after the start of the study treatments. Conclusions: Addition of alogliptin to once-/twice-daily administration of an αGI may be effective for obtaining improved glycemic control, without lowering the treatment satisfaction level, in type 2 diabetic patients.

Indicators of the need for insulin treatment and the effect of treatment for gestational diabetes on pregnancy outcomes in Japan.

This study assessed indicators of the need for insulin therapy and the effect of treatment on pregnancy outcomes in Japanese patients with gestational diabetes mellitus (GDM). All patients diagnosed with GDM were hospitalized for three days. Plasma glucose profiles in patients under strict dietary management and the characteristics of GDM patients with high daily glucose levels were investigated. Patients who failed to achieve glycemic targets were treated with insulin. Indicators of the need for insulin treatment were investigated. Pregnancy outcomes in patients prescribed dietary management and patients prescribed insulin treatment were compared. The study included 112 patients with GDM. GDM patients with high daily glucose levels in the hospital exhibited significantly higher 1-h and 2-h plasma glucose levels in oral glucose tolerance tests (OGTTs) at diagnosis. In our hospital, 102 GDM patients with singleton pregnancies were followed until delivery; 32 (31.3%) were treated with insulin. Univariate analysis identified significant associations of insulin requirement with family history of diabetes and with 1-h and 2-h OGTT values at diagnosis. Multivariate analysis showed that the 1-h OGTT plasma glucose level at diagnosis was an independent predictor of the need for insulin. In perinatal outcomes, insulin treatment was associated with low birth weight.

Protection of insulin receptor substrate-3 from staurosporine-induced apoptosis

In primary adipocytes, insulin receptor substrate (IRS)-1 and -3 are expressed in a comparable amount and play distinct roles in insulin signaling. To examine the roles of these IRS in apoptosis inhibition, we evaluated staurosporine-induced apoptosis in Chinese hamster ovary (CHO) cells overexpressing human insulin receptor and IRS-1 or IRS-3. Overexpression of both IRS protected CHO cells from staurosporine-induced apoptosis. Overexpressed IRS-3 as well as IRS-1 enhanced phosphoinositide (PI) 3-kinase activity in response to insulin and increased phosphorylation of protein kinase B (PKB) at S473 and phosphorylation of one of the members of the forkhead transcription factor FKHRL1 on T32 in both insulin-untreated and -treated states. Treatment of these cells with a PI 3-kinase inhibitor LY294002 suppressed apoptosis-inhibitory effects of IRS-1 and IRS-3 as well as the phosphorylation of PKB and FKHRL1. These results indicate that both IRS-1 and IRS-3 take part in apoptosis inhibition through the PI 3-kinase/PKB/forkhead cascade.

AMPK Is Involved in the Regulation of Incretin Receptors Expression in Pancreatic Islets under a Low Glucose Concentration

The precise role of AMP-activated protein kinase (AMPK), a target of metformin, in pancreatic β cells remains controversial, even though metformin was recently shown to enhance the expression of incretin receptors (GLP-1 and GIP receptors) in pancreatic β cells. In this study, we investigated the effect of AMPK in the regulation of incretin receptors expression in pancreatic islets. The phosphorylation of AMPK in the mouse islets was decreased by increasing glucose concentrations. We showed the expression of incretin receptors in bell-shaped response to glucose; Expression of the incretin receptors in the isolated islets showed higher levels under a medium glucose concentration (11.1 mM) than that under a low glucose concentration (2.8 mM), but was suppressed under a high glucose concentration (22.2 mM). Both treatment with an AMPK inhibitor and DN-AMPK expression produced a significant increase of the incretin receptors expression under a low glucose concentration. By contrast, in hyperglycemic db/db islets, the enhancing effect of the AMPK inhibitor on the expression of incretin receptors was diminished under a low glucose concentration. Taken together, AMPK is involved in the regulation of incretin receptors expression in pancreatic islets under a low glucose concentration.