Ji Sung Yoon

Increased Expression of Focal Adhesion Kinase in Thyroid Cancer: Immunohistochemical Study

Focal adhesion kinase (FAK) is a tyrosine kinase that is found in cellular structures called focal adhesions. FAK appears to be a key element in signal transduction pathways involved in cell adhesion and locomotion. FAK is overexpressed in various tumors, including tumors derived from regions of the head and neck, colon, breast, prostate, and liver. In this study, we investigated immunohistochemically whether FAK expression was increased in thyroid cancers. FAK staining was not seen in any of the 20 normal thyroid tissues or the 6 nodular hyperplasia specimens. In contrast, FAK staining was observed in all of 17 papillary carcinomas, 9 follicular carcinomas, 8 medullary carcinomas, and 2 anaplastic carcinomas. Nine of 17 follicular adenomas showed FAK immunoreactivity. FAK was not expressed in normal tissue and nodular hyperplasia, but was expressed in some of the follicular adenoma, and all of the follicular, papillary, medullary and anaplastic thyroid carcinoma. This result indicates that the up-regulation of FAK may play a role in the development of thyroid carcinogenesis.

Relative Skeletal Muscle Mass Is Associated with Development of Metabolic Syndrome

Background Visceral adiposity is related to insulin resistance. Skeletal muscle plays a central role in insulin-mediated glucose disposal; however, little is known about the association between muscle mass and metabolic syndrome (MS). This study is to clarify the clinical role of skeletal muscle mass in development of MS. Methods A total of 1,042 subjects were enrolled. Subjects with prior MS and chronic diseases were excluded. After 24 months, development of MS was assessed using NCEP-ATP III criteria. Skeletal muscle mass (SMM; kg), body fat mass (BFM; kg), and visceral fat area (VFA; cm2) were obtained from bioelectrical analysis. Then, the following values were calculated as follows: percent of SMM (SMM%; %): SMM (kg)/weight (kg), skeletal muscle index (SMI; kg/m2): SMM (kg)/height (m2), skeletal muscle to body fat ratio (MFR): SMM (kg)/BFM (kg), and skeletal muscle to visceral fat ratio (SVR; kg/cm2): SMM (kg)/VFA (cm2). Results Among 838 subjects, 88 (10.5%) were newly diagnosed with MS. Development of MS increased according to increasing quintiles of BMI, SMM, VFA, and SMI, but was negatively associated with SMM%, MFR, and SVR. VFA was positively associated with high waist circumference (WC), high blood pressure (BP), dysglycemia, and high triglyceride (TG). In contrast, MFR was negatively associated with high WC, high BP, dysglycemia, and high TG. SVR was negatively associated with all components of MS. Conclusion Relative SMM ratio to body composition, rather than absolute mass, may play a critical role in development of MS and could be used as a strong predictor.

A Protective Role for Heme Oxygenase-1 in INS-1 Cells and Rat Islets that are Exposed to High Glucose Conditions

Heme oxygenase-1 (HO-1) has been described as an inducible protein that is capable of cytoprotection via radical scavenging and the prevention of apoptosis. Chronic exposure to hyperglycemia can lead to cellular dysfunction that may become irreversible over time, and this process has been termed glucose toxicity. Yet little is known about the relation between glucose toxicity and HO-1 in the islets. The purposes of the present study were to determine whether prolonged exposure of pancreatic islets to a supraphysiologic glucose concentration disrupts the intracellular balance between reactive oxygen species (ROS) and HO-1, and so this causes defective insulin secretion; we also wanted to evaluate a protective role for HO-1 in pancreatic islets against high glucose levels. The intracellular peroxide levels of the pancreatic islets (INS-1 cell, rat islet) were increased in the high glucose media (30 mM glucose or 50 mM ribose). The HO-1 expression was induced in the INS-1 cells by the high glucose levels. Both the HO-1 expression and glucose stimulated insulin secretion (GSIS) was decreased simultaneously in the islets by treatment of the HO-1 antisense. The HO-1 was upregulated in the INS-1 cells by hemin, an inducer of HO-1. And, HO-1 upregulation induced by hemin reversed the GSIS in the islets at a high glucose condition. These results suggest HO-1 seems to mediate the protective response of pancreatic islets against the oxidative stress that is due to high glucose conditions.

The Role of Skeletal Muscle in Development of Nonalcoholic Fatty Liver Disease

Background Nonalcoholic fatty liver disease (NAFLD) is closely correlated with abnormal accumulation of visceral fat, but the role of skeletal muscle remains unclear. The aim of this study was to elucidate the role of skeletal muscle in development of NAFLD. Methods Among 11,116 subjects (6,242 males), we examined the effects of skeletal muscle mass and visceral fat area (VFA, by bioelectric impedance analysis) on NAFLD using by the fatty liver index (FLI). Results Of the total subjects (9,565 total, 5,293 males) included, 1,848 were classified as having NALFD (FLI ≥60). Body mass index, lipid profile, fasting plasma glucose, hemoglobin A1c, prevalence of type 2 diabetes (DM), hypertension (HTN), and metabolic syndrome were higher in males than females, but FLI showed no significant difference. The low FLI group showed the lowest VFA and highest skeletal muscle mass of all the groups. Skeletal muscle to visceral fat ratio (SVR) and skeletal muscle index had inverse correlations with FLI, when adjusted for age and gender. In multivariate regression analysis, SVR was negatively associated with FLI. Among SVR quartiles, the highest quartile showed very low risk of NAFLD when adjusted for age, gender, lipid profile, DM, HTN, and high sensitivity C-reactive protein from the lowest quartiles (odds ratio, 0.037; 95% confidence interval, 0.029 to 0.049). Conclusion Skeletal muscle mass was inversely associated with visceral fat area, and higher skeletal muscle mass may have a beneficial effect in preventing NAFLD. These results suggest that further studies are needed to ameliorate or slow the progression of sarcopenia.

Understanding the Cardiovascular Effects of Incretin

Cardiovascular disease (CVD), a leading cause of death in patients with diabetes mellitus, has several pathogenic mechanisms that are well established. However, the traditional hypoglycemic agents do not have proven positive effects on macrovascular disease. Novel therapeutic agents target the incretin pathway including the glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) agonists and the dipeptidyl peptidase-4 inhibitors. The glucose-regulatory actions of these agents function by increasing insulin secretion and suppressing glucagon. They also act to increase weight loss not only by inhibiting gastric emptying, but also by reducing appetite. Although GLP-1 and GLP-1R agonists have demonstrated beneficial effects on myocardium and vascular endothelium including coronary and peripheral mouse vessels, they also have anti-inflammatory and anti-atherogenic actions. These agents also have positive effects on the lipid profile and blood pressure. Although these cardioprotective actions seem to be beyond the effects of glucose control and weight loss, they are mediated through GLP-1R- or GLP-1R-independent actions of cleaved GLP-1 (9-36). Larger randomized controlled trials are necessary to elucidate the clinical promise of these beneficial CVD effects.

Diabetogenic effect of statins: a double-edged sword?

Statins are widely prescribed cholesterol-lowering agents, which have been demonstrated to significantly reduce cardiovascular morbidity and mortality. However, recent trials have reported that statins cause worsening of hyperglycemia and increase the risk of new-onset diabetes. The association between the diabetogenic effect of statins with intensive dose and accompanying major risk factors for diabetes has been demonstrated. However, statins do not appear to have a class effect on insulin sensitivity in non-diabetic patients. Numerous mechanisms have been suggested to explain how statins cause β-cell insulin secretory dysfunction and peripheral insulin resistance leading to incident diabetes. According to findings from an aggregate of large clinical trials, the benefits of statin treatment appear to outweigh the risk of new-onset diabetes. Therefore, it would be inappropriate to discontinue the use of statins for prevention of cardiovascular events because of its potential risk for development of incident diabetes. This review addresses the currently available evidence related to statin use and new-onset diabetes from a clinical perspective.

Inhibition of fatty acid translocase cluster determinant 36 (CD36), stimulated by hyperglycemia, prevents glucotoxicity in INS-1 cells.

The purpose of the present study was to determine whether exposure of pancreatic islets to glucotoxic conditions changes fatty acid translocase cluster determinant 36 (CD36) and examine the role of CD36 on the induction of glucotoxicity. We measured the changes of CD36 and insulin secretion in high glucose (30 mM) exposed INS-1 cells and CD36 suppressed INS-1 cells by transfection of CD36 siRNA. The intracellular peroxide level of INS-1 cells increased in the high glucose media compared to normal glucose (5.6mM) media. The mRNA levels of insulin and PDX-1, as well as glucose stimulated insulin secretion (GSIS) were decreased in INS-1 cells exposed to high glucose media compared to normal glucose media, while CD36 and palmitate uptake were significantly elevated with exposure to high glucose media for 12h. The inhibition of CD36 reversed the decreased GSIS and intracellular peroxide level in INS-1 cells. These results suggest that high glucose may exacerbate glucotoxicity via increasing fatty acid influx by elevation of CD36 expression, and that CD36 may be a possible target molecule for preventing glucotoxicity in pancreatic beta-cells.

The Relationship between Metformin and Cancer in Patients with Type 2 Diabetes

Background Recently, several studies reported that the cancer incidence in type 2 diabetes patients is higher than in the general population. Although a number of risks are shared between cancer and diabetes patients, there have been few studies of its correlation. We evaluated the influences of several factors including low density lipoprotein cholesterol (LDL-C), albuminuria and use of metformin on the risk of cancer in patients with type 2 diabetes. Methods We enrolled 1,320 patients with at least 5 years of follow-up and 73 patients were diagnosed with cancer during this period. The associations of the risk factors with cancer incidence were evaluated by multiple regression analysis. The subjects were placed into two subgroups based on metformin dosage (<1,000 mg/day, ≥1,000 mg/day) and we compared cancer incidence using analysis of covariance. Results LDL-C and albuminuria were not significantly correlated with cancer risk. In contrast, metformin showed a reverse correlation with cancer risk (P=0.006; relative risk, 0.574). In the metformin nonadministration group, smoking, male gender, and high triglyceride levels tended to be contributing factors without statistical significance. Cancer occurence was lower in the low dose metformin group (less than 1,000 mg/day) (P=0.00). Conclusion These results suggest that the administration of low dose metformin in patients with type 2 diabetes may be associated with a reduced risk of cancer.

Usefulness of Glycated Hemoglobin as Diagnostic Criteria for Metabolic Syndrome

The metabolic syndrome (MetS) is the clustering of cardiovascular risk factors and known as a powerful predictor of diabetes and cardiovascular disease. Glycated hemoglobin (HbA1c) is used as one of the diagnostic criteria for diabetes and category of increased risk for diabetes. We examined the usefulness of HbA1c as a diagnostic tool for MetS and to determine the cut-off value of HbA1c as a criterion for MetS, in non-diabetic Korean subjects. We analyzed 7,307 participants (male: 4,181, 57%) in a medical check-up program, and applied the newly recommended guidelines of the International Diabetes Federation for diagnosis of MetS. The mean HbA1c was 5.54% in all subjects and showed no significant difference between genders. Using receiver-operating characteristic curve, HbA1c value corresponding to the fasting plasma glucose value of 100 mg/dL was 5.65% (sensitivity 52.3%, specificity 76.7%). The prevalence of MetS was 8.5% according to the IDF guideline and 10.9% according to HbA1c value of 5.7%, showing 69.5% agreement rate. The detection rate of MetS increased to 25.7% using the HbA1c criterion of 5.7% instead of fasting hyperglycemia. This study suggests that HbA1c might be used as a diagnostic criterion for MetS and the appropriate cut-off value of HbA1c may be 5.65% in this Korean population.

Diagnostic Accuracy of 64-Slice MDCT Coronary Angiography for the Assessment of Coronary Artery Disease in Korean Patients with Type 2 Diabetes

Background A 64-slice multidetector computed tomography (MDCT) is well known to be a useful noninvasive form of angiography for the general population, but not for certain patients with diabetes. The aim of this study was to investigate the diagnostic accuracy and usefulness of 64-slice MDCT coronary angiography for detecting coronary artery disease in Korean patients with type 2 diabetes mellitus (T2DM). Methods A total of 240 patients were included, 74 of whom had type 2 diabetes (M:F=40:33; 41.8±9.5 years). We compared significant coronary stenosis (>50% luminal narrowing) in MDCT with invasive coronary angiography (ICA) by segment, artery, and patient. We also evaluated the influence of obesity and coronary calcium score on MDCT accuracy. Results Of the 4,064 coronary segments studied, 4,062 segments (T2DM=1,109) were assessed quantitatively by both MDCT and ICA, and 706 segments (T2DM=226) were detected as a significant lesion by ICA in all patients. Sensitivity, specificity, as well as positive and negative predictive values for the presence of significant stenosis in T2DM were: by segment, 89.4%, 96.4%, 85.8%, and 97.4%, respectively; by artery (n=222), 95.1%, 92.9%, 94.4%, and 93.8%, respectively; by patients (n=74), 98.4%, 100.0%, 98.4%, and 90.0%, respectively. Regardless of presence of diabetes, there was no significant difference in diagnostic accuracy. Obesity (≥25 kg/m2) and coronary calcium score did not also affect the diagnostic accuracy of MDCT. Conclusion The 64-slice MDCT coronary angiography was found to have similar diagnostic accuracy with ICA, regardless of diabetes. These results suggest MDCT may be helpful to reduce unnecessary invasive studies for patients with diabetes.