Ectopic fat accumulation in the liver and glucose homeostasis

Liver fat is associated not only with enhanced hepatic glucose production but also with skeletal muscle insulin resistance, supporting a central role of fatty liver in systemic insulin resistance and existence of a network between the liver and skeletal muscle. Palmitate and cholesterol act as toxic lipids to cause hepatic insulin resistance via mitochondria-derived oxidative stress. Obesity-mediated disruption in crosstalk among protein-, glucose- and lipid-metabolism pathways results in hepatic insulin resistance, enhanced gluconeogenesis and liver steatosis by impairing proteasome function. The liver plays as an endocrine organ to produce functional hepatokines and thereby mediates fatty liver-associated skeletal muscle insulin resistance through unique mechanisms. Selenoprotein P is upregulated through FoxOs and hyperglycemia and causes resistance to insulin, angiogenesis and exercise through reductive stress. LECT2 is upregulated in satiety through AMPK inactivation and contributes to the development of muscle insulin resistance and obesity by activating JNK and by impairing myogenesis, respectively. Therefore, overnutrition evokes remodeling of nutrient homeostasis by toxic lipids and proteasome dysfunction in the liver. The remodeling also results in the overproduction of hepatokines that disrupt inter-organ network leading to pathology of diabetes. © Springer Japan 2016.Book Chapter / Embargo Period 12 month

Genes involved in oxidative phosphorylation are coordinately upregulated with fasting hyperglycaemia in livers of patients with type 2 diabetes

取得学位 : 博士（医学）, 学位授与番号 : 医博乙第1634号 , 学位授与年月日 : 平成19年9月5日, 学位授与大学 : 金沢大学, 主査教授 : 山本 博, 副査教授 : 山岸 正和 , 中尾 眞

Concentration-dependent Dual Effects of Hydrogen Peroxide on Insulin Signal Transduction in H4IIEC Hepatocytes

BACKGROUND: Oxidative stress induced by the accumulation of reactive oxygen species (ROS) has a causal role in the development of insulin resistance, whereas ROS themselves function as intracellular second messengers that promote insulin signal transduction. ROS can act both positively and negatively on insulin signaling, but the molecular mechanisms controlling these dual actions of ROS are not fully understood. METHODOLOGY/PRINCIPAL FINDINGS: Here, we directly treated H4IIEC hepatocytes with hydrogen peroxide (H2O2), a representative membrane-permeable oxidant and the most abundant ROS in cells, to identify the key factors determining whether ROS impair or enhance intracellular insulin signaling. Treatment with high concentrations of H2O2 (25-50 µM) for 3 h reduced insulin-stimulated Akt phosphorylation, and increased the phosphorylation of both JNK and its substrate c-Jun. In contrast, lower concentrations of H2O2 (5-10 µM) enhanced insulin-stimulated phosphorylation of Akt. Moreover, lower concentrations suppressed PTP1B activity, suggesting that JNK and phosphatases such as PTP1B may play roles in determining the thresholds for the diametrical effects of H2O2 on cellular insulin signaling. Pretreatment with antioxidant N-acetyl-L-cysteine (10 mM) canceled the signal-promoting action of low H2O2 (5 µM), and it canceled out further impairment of insulin of insulin signaling induced by high H₂O₂ (25 µM). CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that depending on its concentration, H2O2 can have the positive or negative effect on insulin signal transduction in H4IIEC hepatocytes, suggesting that the concentration of intracellular ROS may be a major factor in determining whether ROS impair or enhance insulin signaling

Liver steatosis is associated with insulin resistance in skeletal muscle rather than in the liver in Japanese patients with non-alcoholic fatty liver disease

Aims/Introduction: To examine the association between liver histological features and organ-specific insulin resistance indices calculated from 75-g oral glucose tolerance test data in patients with non-alcoholic fatty liver disease. Materials and Methods: Liver biopsy specimens were obtained from 72 patients with non-alcoholic fatty liver disease, and were scored for steatosis, grade and stage. Hepatic and skeletal muscle insulin resistance indices (hepatic insulin resistance index and Matsuda index, respectively) were calculated from 75-g oral glucose tolerance test data, and metabolic clearance rate was measured using the euglycemic hyperinsulinemic clamp method. Results: The degree of hepatic steatosis, and grade and stage of non-alcoholic steatohepatitis were significantly correlated with Matsuda index (steatosis r = -0.45, P < 0.001; grade r = -0.54, P < 0.001; stage r = -0.37, P < 0.01), but not with hepatic insulin resistance index. Multiple regression analyses adjusted for age, sex, body mass index and each histological score showed that the degree of hepatic steatosis (coefficient = -0.22, P < 0.05) and grade (coefficient = -0.40, P < 0.01) were associated with Matsuda index, whereas the association between stage and Matsuda index (coefficient = -0.07, P = 0.593) was no longer significant. A similar trend was observed for the association between steatosis and metabolic clearance rate (coefficient = -0.62, P = 0.059). Conclusions: Liver steatosis is associated with insulin resistance in skeletal muscle rather than in the liver in patients with non-alcoholic fatty liver disease, suggesting a central role of fatty liver in the development of peripheral insulin resistance and the existence of a network between the liver and skeletal muscle

Fat-free mass and calf circumference as body composition indices to determine non-exercise activity thermogenesis in patients with diabetes

Aims/Introduction: To investigate the clinical and anthropometrical parameters that are associated with non-exercise activity thermogenesis that is composed of basal energy expenditure (BEE) and diet-induced thermogenesis (DIT) in patients with diabetes. Materials and Methods: Body composition was assessed using bioelectrical impedance, and BEE and DIT were measured using indirect calorimetry in 40 Japanese patients with diabetes. Results: BEE correlated positively with bodyweight, body mass index, fat mass, and fat-free mass, and correlated negatively with age in both men and women. In multivariate logistic regression analysis, BEE correlated positively with both fat mass and fat-free mass independently of sex and age. In addition, DIT correlated positively with bodyweight, body mass index, fat mass and fat-free mass, and correlated negatively with age in women, but not men. Fat-free mass contributed to DIT at least partly, and an aging-related decrease in DIT was observed. The best anthropometric parameter that reflected fat mass and fat-free mass was hip circumference (HC) and calf circumference (CC), respectively, in both men and women. Indeed, both HC (men β = 0.600, P < 0.001; women β = 0.752, P < 0.001) and CC (men β = 0.810, P = 0.012; women β = 0.821, P = 0.002) were correlated with BEE independently of age and sex. In addition, CC (β = 0.653, P = 0.009), but not HC was correlated with DIT significantly only in females, independently of age. Conclusions: HC reflects fat mass and was positively associated with BEE, but not with DIT. In contrast, CC reflects fat-free mass, and was positively associated with BEE in both men and women, and with DIT in women. © 2015 Asian Association for the Study of Diabetes and Wiley Publishing Asia Pty Ltd

Vildagliptin vs liraglutide as a second-line therapy switched from sitagliptin-based regimens in patients with type 2 diabetes: A randomized, parallel-group study

Introduction: A step-up strategy for dipeptidyl peptidase (DPP)-4 inhibitor-based regimens has not yet been established. In addition, similarities and differences between DPP-4 inhibitors and glucagon-like peptide (GLP)-1 receptor agonists remain to be elucidated in humans. We investigated the pleiotropic effects of vildagliptin vs liraglutide in patients with type 2 diabetes on sitagliptin-based regimens in an open-label, randomized, clinical trial. Materials and Methods: A total of 122 patients with type 2 diabetes that was inadequately controlled by sitagliptin-based regimens were randomly assigned to either vildagliptin (50 mg, twice daily) or liraglutide treatment (0.9 mg, once daily) for 12 weeks. The primary outcomes were glycated hemoglobin and body mass index. Results: Both vildagliptin and liraglutide significantly lowered glycated hemoglobin within 12 weeks after switching from sitagliptin, but liraglutide produced a greater reduction (-0.67 ± 0.12% vs -0.36 ± 0.53%). Liraglutide lowered body mass index, whereas vildagliptin did not affect body mass index. Vildagliptin lowered fasting C-peptide immunoreactivity, but liraglutide did not. Vildagliptin increased serum levels of adiponectin, arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid, whereas liraglutide had no effect on these levels. Quality of life, assessed using the diabetes treatment satisfaction questionnaire, was not impaired in either group. The most common adverse events were gastrointestinal symptoms, which occurred with similar frequencies in both groups. Conclusions: Vildagliptin-mediated improvements in glycemic control did not correlate with indices for insulin secretion and insulin sensitivity. Switching from sitagliptin to liraglutide is useful in managing hyperglycemia and weight. Each agent exerts unique pleiotropic effects. This trial was registered with the University Hospital Medical Information Network Clinical Trials Registry (no. 000004953). © 2014 The Authors. Journal of Diabetes Investigation published by Asian Association of the Study of Diabetes (AASD) and Wiley Publishing Asia Pty Ltd

Association between coefficients of variation of the R-R intervals on electrocardiograms and post-challenge hyperglycemia in patients with newly diagnosed type 2 diabetes

The aim of the present study was to examine whether there is a relationship between autonomic function and post-challenge hyperglycemia in patients with type 2 diabetes. Subjects included 122 Japanese patients newly diagnosed with type 2 diabetes. Autonomic nerve function was assessed using coefficients of variation of the R-R intervals on electrocardiograms (CVRR). Unlike anthropometry, insulin secretion and insulin resistance, age (r =)0.209, P < 0.021) and post-challenge plasma glucose at 120 min (PG120; r =)0.219, P < 0.015) were the only variables significantly correlated with CVRR. Age was not significantly correlated with PG120. In multiple regression analyses, CVRR Z-score, but not age, was significantly correlated with PG120. The present results suggest that autonomic function affects post-challenge blood glucose levels independently of age. © 2011 Asian Association for the Study of Diabetes and Blackwell Publishing Asia Pty Ltd

Renoprotective effects of atorvastatin compared with pravastatin on progression of early diabetic nephropathy

Introduction: Several studies have shown that statins suppress the progression of diabetic nephropathy. However, few reports have directly compared the renoprotective effects between potent and conventional statins. Materials and Methods: Patients with diabetic nephropathy, selected as those with a serum creatinine level of 0.9-1.5 mg/dL and simultaneously having either microalbuminuria or positive proteinuria, were randomly assigned to one of three groups: a conventional diet therapy group, a group given 10 mg of pravastatin and a group given 10 mg of atorvastatin. Renal function was evaluated before and after a 12-month period of therapy. Results: The atorvastatin group had a significant decrease in low-density lipoprotein cholesterol at 3 months and thereafter compared with the other groups. The urinary albumin-to-creatinine ratio significantly decreased in the atorvastatin group; the degree of this decrease was significantly greater than that in the diet therapy group. The kidney function estimated with cystatin C (CysC) and the estimated glomerular filtration rate calculated from CysC were significantly preserved in the atorvastatin group compared with the pravastatin group. In a multivariate regression analysis, the use of atorvastatin was the only explanatory variable for the changes in CysC; this was independent of changes in low-density lipoprotein cholesterol. Conclusions: Atorvastatin is more effective than pravastatin for the prevention of increase in CysC, and this renoprotective effect was considered to a result of the pleiotropic effect of atorvastatin independent of its lipid-lowering effect. This study was registered with UMIN (no. UMIN 000001774). © 2014 The Authors

Inverse Correlation between Serum Levels of Selenoprotein P and Adiponectin in Patients with Type 2 Diabetes

Background: We recently identified selenoprotein P (SeP) as a liver-derived secretory protein that causes insulin resistance in the liver and skeletal muscle; however, it is unknown whether and, if so, how SeP acts on adipose tissue. The present study tested the hypothesis that SeP is related to hypoadiponectinemia in patients with type 2 diabetes. Methodology/Principal Findings: We compared serum levels of SeP with those of adiponectin and other clinical parameters in 36 patients with type 2 diabetes. We also measured levels of blood adiponectin in SeP knockout mice. Circulating SeP levels were positively correlated with fasting plasma glucose (r = 0.35, P = 0.037) and negatively associated with both total and high-molecular adiponectin in patients with type 2 diabetes (r = 20.355, P = 0.034; r = 20.367, P = 0.028). SeP was a predictor of both total and high-molecular adiponectin, independently of age, body weight, and quantitative insulin sensitivity index (b = 20.343, P = 0.022; b = 20.357, P = 0.017). SeP knockout mice exhibited an increase in blood adiponectin levels when fed regular chow or a high sucrose, high fat diet. Conclusions/Significance: These results suggest that overproduction of liver-derived secretory protein SeP is connected with hypoadiponectinemia in patients with type 2 diabetes

Increased oxidative stress precedes the onset of high-fat diet-induced insulin resistance and obesity

金沢大学医薬保健研究域医学系Insulin resistance is a key pathophysiological feature of metabolic syndrome. However, the initial events triggering the development of insulin resistance and its causal relations with dysregulation of glucose and fatty acids metabolism remain unclear. We investigated biological pathways that have the potential to induce insulin resistance in mice fed a high-fat diet (HFD). We demonstrate that the pathways for reactive oxygen species (ROS) production and oxidative stress are coordinately up-regulated in both the liver and adipose tissue of mice fed an HFD before the onset of insulin resistance through discrete mechanism. In the liver, an HFD up-regulated genes involved in sterol regulatory element binding protein 1c-related fatty acid synthesis and peroxisome proliferator-activated receptor α-related fatty acid oxidation. In the adipose tissue, however, the HFD down-regulated genes involved in fatty acid synthesis and up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. Furthermore, increased ROS production preceded the elevation of tumor necrosis factor-α and free fatty acids in the plasma and liver. The ROS may be an initial key event triggering HFD-induced insulin resistance. © 2008 Elsevier Inc. All rights reserved