Kyu-Chang Won

Endoplasmic Reticulum Stress-Induced Activation of Activating Transcription Factor 6 Decreases Insulin Gene Expression via Up-Regulation of Orphan Nuclear Receptor Small Heterodimer Partner

The highly developed endoplasmic reticulum (ER) structure of pancreatic beta-cells is a key factor in beta-cell function. Here we examined whether ER stress-induced activation of activating transcription factor (ATF)-6 impairs insulin gene expression via up-regulation of the orphan nuclear receptor small heterodimer partner (SHP; NR0B2), which has been shown to play a role in beta-cell dysfunction. We examined whether ER stress decreases insulin gene expression, and this process is mediated by ATF6. A small interfering RNA that targeted SHP was used to determine whether the effect of ATF6 on insulin gene expression is mediated by SHP. We also measured the expression level of ATF6 in pancreatic islets in Otsuka Long Evans Tokushima Fatty rats, a rodent model of type 2 diabetes. High glucose concentration (30 mmol/liter glucose) increased ER stress in INS-1 cells. ER stress induced by tunicamycin, thapsigargin, or dithiotreitol decreased insulin gene transcription. ATF6 inhibited insulin promoter activity, whereas X-box binding protein-1 and ATF4 did not. Adenovirus-mediated overexpression of active form of ATF6 in INS-1 cells impaired insulin gene expression and secretion. ATF6 also down-regulated pancreatic duodenal homeobox factor-1 and RIPE3b1/MafA gene expression and repressed the cooperative action of pancreatic duodenal homeobox factor-1, RIPE3b1/MafA, and beta-cell E box transactivator 2 in stimulating insulin transcription. The ATF6-induced suppression of insulin gene expression was associated with up-regulation of SHP gene expression. Finally, we found that expression of ATF6 was increased in the pancreatic islets of diabetic Otsuka Long Evans Tokushima Fatty rats, compared with their lean, nondiabetic counterparts, Long-Evans Tokushima Otsuka rats. Collectively, this study shows that ER stress-induced activation of ATF6 plays an important role in the development of beta-cell dysfunction.

Glucotoxicity in the INS-1 rat insulinoma cell line is mediated by the orphan nuclear receptor small heterodimer partner.

Prolonged elevations of glucose concentration have deleterious effects on β-cell function. One of the hallmarks of such glucotoxicity is a reduction in insulin gene expression, resulting from decreased insulin promoter activity. Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor that inhibits nuclear receptor signaling in diverse metabolic pathways. In this study, we found that sustained culture of INS-1 cells at high glucose concentrations leads to an increase in SHP mRNA expression, followed by a decrease in insulin gene expression. Inhibition of endogenous SHP gene expression by small interfering RNA partially restored high-glucose–induced suppression of the insulin gene. Adenovirus-mediated overexpression of SHP in INS-1 cells impaired glucose-stimulated insulin secretion as well as insulin gene expression. SHP downregulates insulin gene expression via two mechanisms: by downregulating PDX-1 and MafA gene expression and by inhibiting p300-mediated pancreatic duodenal homeobox factor 1–and BETA2-dependent transcriptional activity from the insulin promoter. Finally, the pancreatic islets of diabetic OLETF rats express SHP mRNA at higher levels than the islets from LETO rats. These results collectively suggest that SHP plays an important role in the development of β-cell dysfunction induced by glucotoxicity.

Association between diabetes-related factors and clinical periodontal parameters in type-2 diabetes mellitus

BackgroundEvidence consistently shows that diabetes is a risk factor for increased prevalence of gingivitis and periodontitis. But there is a controversy about the relationship between diabetes related factors and periodontal health. The aim of the present study is to explore the relationship between diabetes related factors such as glycosylated hemoglobin, fasting blood glucose, duration of diabetes and compliance to diabetes self management and periodontal health status.MethodsPeriodontal health of 125 participants with type-2 diabetes mellitus was measured by the number of missing teeth, community periodontal index (CPI), Russell’s periodontal index and papillary bleeding index. Information on sociodemographic factors, oral hygiene behavior, duration and compliance to self management of diabetes, levels of glycosylated hemoglobin(HbA1c) and fasting blood glucose(FBG) were collected by interview and hospital medical records. Statistically, independent t-test, an analysis of variance (ANOVA), chi-squared test and multiple regression analyses were used to assess the association between diabetes-related factors and periodontal health.ResultsPeriodontal parameters including the number of missing teeth and papillary bleeding index were significantly influenced by duration of diabetes, FBG and compliance to self management of diabetes. CPI was significantly influenced by duration of diabetes, FBG and HbA1C. And Russell’s periodontal index was significantly influenced by duration of diabetes, FBG, HbA1C and compliance to self management of diabetes. Results of multiple linear regression analysis showed that the duration of diabetes showed significant positive correlation with all of the periodontal health parameters, except for missing teeth. HbA1c was correlated with Russells periodontal and papillary bleeding index. FBG and compliance to self management of diabetes were correlated with missing teeth and papillary bleeding index respectively.ConclusionsDiabetes-related factors such as duration of diabetes, FBG, HbA1c and compliance to self management of diabetes were significantly correlated with periodontal health among individuals with type-2 diabetes.

Leptin-like effects of MTII are augmented in MSG-obese rats.

To evaluate whether MTII, a melanocortin receptor 3/4 agonist, is working in hypophagic and hypothermogenic obese model, we measured food intake, body weight, oxygen consumption, and fat mass following intracerebroventricular (i.c.v.) infusion of MTII in monosodium glutamate (MSG)-induced obese rats. MTII, or artificial cerebrospinal fluid (aCSF), was infused into i.c.v. with an osmotic minipump for 1 week. MSG-obese rats were induced by neonatal injection of MSG. Five-month-old MSG rats were characterized by hypophagia, lower oxygen consumption, hyperleptinemia, and obesity compared to age-matched control rats. The infusion of MTII decreased their food intake, visceral fat, and body weight in MSG-obese rats compared with aCSF-infused rats. The oxygen consumption was increased by MTII treatment in MSG-obese rats compared with aCSF as well as pair fed (PF) rats. Interestingly, these leptin-like effects of MTII were greater in MSG-obese rats than in controls, which might be related to the increased expression of melanocortin receptor 4 (MC4R) in the hypothalamus of MSG-obese rats. Our results suggested that both anorexic and thermogenic mechanisms were activated by MTII in the MSG-obese rats and contributed to the decrease in body weight and fat mass. Moreover, there was a sensitization to MTII caused by upregulation of the melanocortin receptor in the MSG-obese rats.

COMP-angiopoietin-1 enhances skeletal muscle blood flow and insulin sensitivity in mice

To test whether chronic enhanced blood flow alters insulin-stimulated glucose uptake, we measured skeletal muscle glucose uptake in chow-fed and high-fat-fed mice injected with adenovirus containing modified angiopoietin-1, COMP-Ang1, via euglycemic-hyperinsulinemic clamp. Blood flow rates and platelet endothelial cell adhesion molecule-1 positive endothelial cells in the hindlimb skeletal muscle were elevated in COMP-Ang1 compared with control LacZ. Whole body glucose uptake and whole body glycogen/lipid synthesis were elevated in COMP-Ang1 compared with LacZ in chow diet. High-fat diet significantly reduced whole body glucose uptake and whole body glycolysis in LacZ mice, whereas high-fat-fed COMP-Ang1 showed a level of whole body glucose uptake that was comparable with chow-fed LacZ and showed increased glucose uptake compared with high-fat-fed LacZ. Glucose uptake and glycolysis in gastrocnemius muscle of chow-fed COMP-Ang1 were increased compared with chow-fed LacZ. High-fat diet-induced whole body insulin resistance in the LacZ was mostly due to approximately 40% decrease in insulin-stimulated glucose uptake in skeletal muscle. In contrast, COMP-Ang1 prevented diet-induced skeletal muscle insulin resistance compared with high-fat-fed LacZ. Akt phosphorylation in skeletal muscle was increased in COMP-Ang1 compared with LacZ in both chow-fed and high-fat-fed groups. These results suggest that increased blood flow by COMP-Ang1 increases insulin-stimulated glucose uptake and prevents high-fat diet-induced insulin resistance in skeletal muscle.

Cross-cultural comparison of neurobehavioral performance in Asian workers.

Widely-used neurobehavioral tests have been developed and standardized on Western populations, but studies on subject factors for Asian populations have been very limited. For the effective application and interpretation of neurobehavioral tests in Asian populations, an evaluation of the effects of subject factors, including cultural background, is necessary. A cross-cultural study was conducted to evaluate the effects of cultural background and the interaction between cultural background and education on neurobehavioral tests in Asian populations. The Korean version of the Swedish Performance Evaluation System (Simple Reaction Time, Symbol Digit, and Finger Tapping Speed) and a pegboard test were administered to 537 workers who were not exposed to chemicals at work from Fareast (Korea and Chinese), Central (Uzbekistan and Tajikistan), and South Asia (Sri Lanka and Indonesia). The Fareast Asian group exhibited better performance in adjusted test scores than other Asian groups, achieving significance for Symbol Digit and Finger Tapping Speed in both genders. The magnitude of the effect of cultural background on Symbol Digit was comparable to the effect of about 10 years of education. Cultural background did not modify the relation between years of education and Symbol Digit in either males or females. This study may provide the first evidence that cultural background has a large impact on neurobehavioral test performance, even within Asian populations, and suggests that cultural background is a critical confounding factor that must be controlled in epidemiologic studies which include Asian populations in the sample.

Combined Treatment of Betulinic Acid, a PTP1B Inhibitor, with Orthosiphon stamineus Extract Decreases Body Weight in High-Fat–Fed Mice

Leptin resistance is a common feature of obesity and is accompanied by hyperleptinemia. Although leptin sensitizers improve leptin resistance, they also decrease plasma leptin levels that attenuate the leptin-associated antiobesity effect. We hypothesized that the combinational treatment of leptin sensitizer and endogenous leptin expression stimulant would synergistically induce an antiobesity effect in high-fat-fed obese animals. Betulinic acid (BA) isolated from Saussurea lappa suppressed the hypothalamic protein tyrosine phosphatase 1B in mice and enhanced the antiobesity effect of leptin in obese rats. Ethanol extract of Orthosiphon stamineus (OS) induced leptin expressions in both 3T3-L1 adipocytes and mice in a dose-dependent manner. To evaluate our hypothesis, we treated obese mice induced by 6 weeks of high-fat-diet feeding with BA and OS for 2 weeks. Although BA or OS alone did not decrease body weight in obese mice, the combinational treatment of BA and OS decreased body weight significantly compared to either BA- or OS-treated obese mice. These results suggest that combinational treatment of BA and OS would be effective for the treatment of obesity.

Hexane Extract of Orthosiphon stamineus Induces Insulin Expression and Prevents Glucotoxicity in INS-1 Cells

Background Hyperglycemia, a characteristic feature of diabetes, induces glucotoxicity in pancreatic β-cells, resulting in further impairment of insulin secretion and worsening glycemic control. Thus, preservation of insulin secretory capacity is essential for the management of type 2 diabetes. In this study, we evaluated the ability of an Orthosiphon stamineus (OS) extract to prevent glucotoxicity in insulin-producing cells. Methods We measured insulin mRNA expression and glucose-stimulated insulin secretion (GSIS) in OS-treated INS-1 cells after exposure to a high glucose (HG; 30 mM) concentration. Results The hexane extract of OS elevated mRNA expression of insulin as well as pancreatic and duodenal homeobox-1 of INS-1 cells in a dose-dependent manner. The hexane OS extract also increased the levels of phosphorylated phosphatidylinositol 3-kinase (PI3K) in a concentration-dependent manner. Additionally, Akt phosphorylation was elevated by treatment with 100 and 200 µmol of the hexane OS extract. Three days of HG exposure suppressed insulin mRNA expression and GSIS; these expressions were restored by treatment with the hexane OS extract. HG elevated peroxide levels in the INS-1 cells. These levels were unaffected by OS treatment under both normal and hyperglycemic conditions. Conclusion Our results suggested that the hexane extract of OS elevates insulin mRNA expression and prevents glucotoxicity induced by a 3-day treatment with HG. This was associated with the activation of PI-3K and Akt.

Hemorheologic Alterations in Patients with Type 2 Diabetes Mellitus Presented with an Acute Myocardial Infarction

Background Hemorheologic indices are known to be related to vascular complications in variable clinical settings. However, little is known about the associations between hemorheologic parameters and acute myocardial infarction (AMI) in type 2 diabetes mellitus (T2DM). The purpose of this study was to demonstrate the changes of hemorheologic environment inside of blood using hemorheologic parameters, especially the elongation index (EI) and critical shear stress (CSS) in diabetics with versus without AMI. Methods A total of 195 patients with T2DM were enrolled. Patients were divided into the study group with AMI (AMI+, n=77) and control group (AMI−, n=118) who had no history of coronary artery disease. Hemorheologic parameters such as EI and CSS were measured and compared between the two groups. Results The EI was lower (30.44%±1.77% in AMI+ and 31.47%±1.48% in AMI−, P<0.001) but the level of CSS was higher (316.13±108.20 mPa in AMI+ and 286.80±85.34 mPa in AMI−, P=0.040) in the AMI+. The CSS was significantly related to the erythrocyte sedimentation rate (R2=0.497, P<0.001) and use of dipeptidyl peptidase-4 inhibitors (R2=0.574, P=0.048). Conclusion Diabetics with AMI resulted in adverse hemorheologic changes with lower EI and higher CSS compared to diabetic subjects without AMI. Evaluation of the hemorheologic parameters may provide valuable supplementary information for managing patients with AMI and T2DM.

Letter: Lack of Association between Serum Cystatin C Levels and Coronary Artery Disease in Diabetic Patients (Korean Diabetes J 2010;34:95-100).

Cardiovascular disease, including coronary artery disease (CAD), is the major cause of morbidity and mortality for individuals with diabetes and the largest contributor to the direct and indirect costs of diabetes [1,2]. Patients with diabetes are affected by other risk factors such as dyslipidemia, hypertension, prothrombic and proinflammatory factors, and therefore atherosclerosis in type 2 diabetes mellitus is often accelerated [3]. However, the pathophysiologic mechanisms responsible for the substantially increased risk for CAD in adult type 2 diabetes remain unclear. Inflammation plays a pivotal role in atherosclerosis, and inflammatory markers such as C-reactive protein, platelet-derived growth factor, transforming growth factor-beta, and granulocyte-macrophage colony stimulating factor may help clinicians to identify high risk patients [4,5]. In many previous studies, the association between inflammatory markers and coronary atherosclerosis was weak and mostly explained by the concomitant burden of CAD risk factors. Cystatin C is a novel endogenous marker of kidney function that may be more sensitive than inflammatory markers for detection of mild to moderate decrements in glomerular filtration rate [6]. However, few data exist on the relationship between serum cystatin C level and cardiovascular disease in diabetic patients with or without diabetic nephropathy. Maahs et al. [7] reported a significant relationship between serum cystatin C level and CAD in type 1 diabetic patients, but they assessed surrogate markers of CAD rather than CAD events or death and more importantly did not consider urinary albumin excretion. In contrast with previous studies, Kim et al. [8] reported that they found no association between serum cystatin C level and CAD in diabetic patients and that serum cystatin C levels were significantly higher in patients with diabetic nephropathy than in patients without both in CAD patients and non-CAD patients. However, the study used a retrospective case-control design, the sample was relatively small, and they did not evaluate the relationship between cystatin C levels and other markers (inflammatory, structural, and functional), body mass index (BMI) or other variables. Recently, Maahs et al. [9] investigated whether the relationship between cystatin C and progression of CAD differed between individuals with type 1 diabetes and without diabetes. In results, the univariate associations of cystatin C to CAD progression were similar in type 1 diabetic patients and without diabetes mellitus. The association of cystatin C to progression of CAD differed in the expected direction (increased cystatin C as a biomarker of worsening renal function associated with CAD progression) by type 1 diabetes status (P = 0.01) after adjustment for other risk factors of cardiovascular disease. Therefore, Maahs et al. [7] suggested, which a complex relationship exists among cystatin C, BMI, and CAD progression, which requires further study. I appreciate the devotion of study investigators, who are conducting important research about the relationship between cystatin C and diabetes, and hope that they will continue to do so in the future.