Byung-Wan Lee

Metformin alleviates hepatosteatosis by restoring SIRT1-mediated autophagy induction via an AMP-activated protein kinase-independent pathway

Metformin activates both PRKA and SIRT1. Furthermore, autophagy is induced by either the PRKA-MTOR-ULK1 or SIRT1-FOXO signaling pathways. We aimed to elucidate the mechanism by which metformin alleviates hepatosteatosis by examining the molecular interplay between SIRT1, PRKA, and autophagy. ob/ob mice were divided into 3 groups: one with ad libitum feeding of a standard chow diet, one with 300 mg/kg intraperitoneal metformin injections, and one with 3 g/d caloric restriction (CR) for a period of 4 wk. Primary hepatocytes or HepG2 cells were treated with oleic acid (OA) plus high glucose in the absence or presence of metformin. Both CR and metformin significantly improved body weight and glucose homeostasis, along with hepatic steatosis, in ob/ob mice. Furthermore, CR and metformin both upregulated SIRT1 expression and also stimulated autophagy induction and flux in vivo. Metformin also prevented OA with high glucose-induced suppression of both SIRT1 expression and SIRT1-dependent activation of autophagy machinery, thereby alleviating intracellular lipid accumulation in vitro. Interestingly, metformin treatment upregulated SIRT1 expression and activated PRKA even after siRNA-mediated knockdown of PRKAA1/2 and SIRT1, respectively. Taken together, these results suggest that metformin alleviates hepatic steatosis through PRKA-independent, SIRT1-mediated effects on the autophagy machinery.

The Associations of Total and Differential White Blood Cell Counts with Obesity, Hypertension, Dyslipidemia and Glucose Intolerance in a Korean Population

Although many studies have reported an association between total white blood cell count and metabolic syndrome, relatively few reports are available on the association between differential white blood cell counts and metabolic syndrome. The medical records of 15,654 subjects (age, median 46, range 14-90 yr; 8,380 men and 7,274 women) who visited the Center for Health Promotion were investigated. It was found that as total white blood cell (WBC) and differential WBC counts increased the frequencies of diabetes, hypertension, obesity, dyslipidemia, and metabolic syndrome also increased. Moreover, these significant relationships persisted after adjusting for age, gender, smoking, alcohol intake, educational background, and household income. The odds ratios (95% CI) for metabolic syndrome was 2.64 (2.30-3.04) in the highest quartile of total WBC count, with corresponding figures of 2.14 (1.88-2.44) for neutrophils, 2.32 (2.03-2.64) for lymphocytes, 1.56 (1.37-1.78) for monocytes, 1.36 (1.20-1.54) for basophils, and 1.82 (1.59-2.08) for eosinophils versus the lowest quartiles of the appropriate total and differential counts, respectively, after adjusting for the variables mentioned above. These independent associations were also observed by subgroup analyses according to the smoking status. Our data suggest that even within normal ranges, total WBC count and the differential WBC counts are associated with the presence of metabolic syndrome.

The favorable outcome of human islet transplantation in Korea: experiences of 10 autologous transplantations.

Background. Cystic neoplasms of the pancreas are an increasingly diagnosed entity, and surgical resection of the pancreas is advocated. Islet autotransplantation is a therapeutic approach used to prevent diabetes in cases of pathologically benign neoplasm after major pancreatectomy. Methods. A total of 10 patients underwent pancreatectomy with islet autotransplantation. To evaluate islet transplantation efficiency, the authors compared 23 subjects who did not undergo islet transplantation after partial pancreatectomy with 87 subjects with normal glucose tolerance and with 77 diabetic subjects that did not undergo pancreatectomy. Results. Ten female patients with nine cystic neoplasms and one patient with pancreatic injury underwent transplantation. Their mean islet equivalents (IEQ) was 3,159 IEQ/kg. During follow-up, two recipients required insulin or oral agents. At the 12-month follow-up, homeostasis model assessment (HOMA)-β was 77.36±17.68, the insulinogenic index (INSindex) was 0.49±0.11, and fasting C-peptide and hemoglobin A1c were 1.28±0.18 ng/mL and 5.73±0.26%, respectively. Islet replacement was found to increase HOMA-β by approximately 17% compared with distal pancreatectomy in normal glucose tolerance subjects without islet autotransplantation and by 46% compared with distal pancreatectomy diabetes subjects without islet autotransplantation. Factors different in the two insulin and oral hypoglycemic agent (OHA)-requiring recipients and the eight insulin- and OHA-free recipients were pancreatectomy extent, preoperative glucose metabolism insufficiency, age, and underlying cystic neoplasm disease. Conclusions. Even partial islet graft function can have a beneficial metabolic effect on the recipient in terms of metabolic parameters such as HOMA-β and INSindex. This study suggests that islet replacement should be considered for experimental procedures in benign pancreatic conditions.

Epicardial adipose tissue thickness is an indicator for coronary artery stenosis in asymptomatic type 2 diabetic patients: its assessment by cardiac magnetic resonance.

BackgroundWe used cardiovascular magnetic resonance (CMR) to investigate the association between epicardial adipose tissue (EAT) thickness and silent myocardial ischemia, as well as coronary artery stenosis, in asymptomatic type 2 diabetic patients.MethodsThe study included 100 type 2 diabetic subjects (51 male and 49 female; mean age: 56 ± 7 years). Silent myocardial ischemia, as determined by CMR, was defined as evidence of inducible ischemia or myocardial infarction. Signal reduction or stenosis of ≥ 50% in the vessel diameter was used as the criteria for significant coronary artery stenosis on coronary magnetic resonance (MR) angiography.ResultsEAT thickness was positively correlated with body mass index (BMI), waist-to-hip ratio, systolic blood pressure, postprandial glucose, fasting/postprandial triglyceride (TG), serum glycated hemoglobin (HbA1c) level, and homeostasis model assessment of insulin resistance (HOMA-IR) score. Significant coronary artery stenosis was found in 24 patients, while 14 patients had silent myocardial ischemia in CMR (1 with silent myocardial infarction, 11 with inducible ischemia, and 2 with both). EAT thickness was greater in patients who had coronary artery stenosis (13.0 ± 2.6 mm vs. 11.5 ± 2.1 mm, p = 0.01), but did not differ between the subjects with or without silent myocardial ischemia on CMR images (12.8 ± 2.1 vs. 11.7 ± 2.3 mm, p = 0.11). Multivariate logistic regression analysis indicated that EAT thickness was an independent indicator for significant coronary artery stenosis after adjusting for traditional risk factors (OR 1.403, p = 0.026).ConclusionsIncreased EAT thickness assessed by CMR is an independent risk factor for significant coronary artery stenosis in asymptomatic type 2 diabetes. However, EAT thickness was not associated with silent myocardial ischemia.

Transcription factor Snail is a novel regulator of adipocyte differentiation via inhibiting the expression of peroxisome proliferator-activated receptor γ

Snail belongs to the superfamily of zinc-finger transcription factors and plays a crucial role in processes regulating cell fate, such as the formation of mesoderm and initiation of epithelial–mesenchymal transition. We have previously discovered that Snail modulates adiponectin expression in 3T3-L1 cells during adipogenesis. In the present study, we elucidated the functional role of Snail in adipocyte differentiation and its underlying molecular mechanism. Snail expression was dramatically decreased during adipogenesis in 3T3-L1 cells. Overexpression of Snail blocked adipocyte differentiation by suppressing the expression of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT-enhancer-binding protein alpha, while knockdown of Snail expression stimulated adipogenesis in 3T3-L1 cells. Chromatin immunoprecipitation assay and luciferase assay showed that Snail inhibits the transcriptional activity of the PPARγ gene by directly binding to the E-box motifs in the PPARγ promoter. Wnt10b induced phosphorylation of glycogen synthase kinase 3 beta (GSK3β), leading to inhibition of adipogenesis in 3T3-L1 cells in accordance with increased expression of Snail, whereas adipogenic capacity was restored in Snail siRNA-transfected preadipocytes. LiCl (a GSK3β inhibitor)-treated cells also showed increased expression of Snail, with a reduced adipogenic potential. Snail-overexpressing 3T3-F442A cells did not differentiate into mature adipocytes in immunodeficient nude mice. Taken together, Snail is a novel regulator of adipocyte differentiation, which acts by direct suppression of PPARγ expression. Our data also indicate that the expression of Snail is mediated by the Wnt–GSK3β signaling pathway.

Korean Red Ginseng (Panax ginseng) Improves Insulin Sensitivity in High Fat Fed Sprague-Dawley Rats

Many studies have documented that ginseng has antidiabetic and antiobesity effects, but the mechanism of the effects has not been elucidated. The aim of this study was to determine the effect of Korean red ginseng (KRG, Panax ginseng) and investigate the mechanism of antidiabetic and antiobesity effects in obese insulin resistant animal models. Sprague‐Dawley (SD) rats were divided into three groups: a control group (group I) fed a normal diet, another group (group II) fed only high fat diet (HFD) and a third group (group III) fed HFD with KRG (200 mg/kg, oral) for 18 weeks. The body weight, food intake, adipose tissues, liver, kidney, pancreas, adiponectin, and leptin were measured. Blood glucose, insulin tolerance test, and hyperinsulinemic euglycemic clamp test were investigated. A significant weight reduction, especially fat mass reduction, was observed in the KRG treated group. Increased insulin sensitivity was found in the KRG treated group. We observed increased insulin signalling, increased phosphorylation of IR, IRS‐1, Akt, and membranous GLUT4 in muscle by Western blotting assay. In conclusion, KRG may have antidiabetic and antiobesity effects due to partly increased insulin sensitivity by increased adipokine and partly enhanced insulin signalling. Copyright

Effective glycemic control achieved by transplanting non-viral cationic liposome-mediated VEGF-transfected islets in streptozotocin-induced diabetic mice

Hypoxic damage is one of the major causes of islet graft failure and VEGF is known to play a crucial role in revascularization. To address the effectiveness of a cationic lipid reagent as a VEGF gene carrier, and the beneficial effect of VEGF-transfected islets on glycemic control, we used effectene lipid reagent in a transfection experiment using mouse islets. Transfection efficiencies were highest for 4 µg/µl cDNA and 25 µl effectene and cell viabilities were also satisfactory under this condition, and the overproduction of VEGF mRNA and protein were confirmed from conditioned cells. A minimal number of VEGF-transfected islets (100 IEQ/animal) were transplanted into streptozotocin (STZ)-induced diabetic mice. Hyperglycemia was not controlled in the islet transplantation (IT)-alone group (0/8) (non- diabetic glucose mice number/total recipient mice number) or in the IT-pJDK control vector group (0/8). However, hyperglycemia was completely abrogated in the IT-pJDK-VEGF transduced group (8/8), and viable islets and increased VEGF-transfected grafts vascularization were observed in renal capsules.

Lithospermic acid B protects beta-cells from cytokine-induced apoptosis by alleviating apoptotic pathways and activating anti-apoptotic pathways of Nrf2–HO-1 and Sirt1

Lithospermic acid B (LAB) has been reported to protect OLETF rats, an established type 2 diabetic animal model, from the development of diabetes-related vascular complications. We investigated whether magnesium lithospermate B (LAB) has a protective role under cytokine-induced apoptosis in INS-1 cells in vitro and whether it slows the development of diabetes in OLETF rats in vivo. Pretreatment with 50 μM LAB significantly reduced the 1000 U/mL INF-γ and 100 U/mL IL-1β-induced INS-1 cell death. LAB significantly alleviated cytokine-induced phosphorylations of p38 and JNK in accordance with a decrease in cleaved caspase-3 activity in beta-cells. LAB also protected against the cytokine-induced caspase-3 apoptotic pathway via significant activation of Nrf2-HO (heme-oxygenase)-1 and Sirt1 expression. OLETF rats treated with 40 mg/kg/day LAB showed a significant improvement in glucose tolerance compared to untreated OLETF control rats in vivo. Our results suggest that the cytoprotective effects of LAB on pancreatic β-cells are related with both alleviating apoptotic pathways and activating anti-apoptotic pathways of Nrf2-HO-1 and Sirt1.

Association between betatrophin/ANGPTL8 and non-alcoholic fatty liver disease: animal and human studies.

Betatrophin/angiopoietin-like protein 8 (ANGPTL8) is a liver-secreted protein recently identified as a potent stimulator of beta cell proliferation in mice. However, it is unclear how betatrophin is regulated in humans with non-alcoholic fatty liver disease (NAFLD). We investigated the role of betatrophin in mice and in humans with and without NAFLD. Serum betatrophin levels were examined by ELISA in 164 subjects, including 96 patients with NAFLD. Levels were significantly elevated in subjects with NAFLD compared with controls (1.301 ± 0.617 vs. 0.900 ± 0.574 μg/L, P < 0.001), even after stratification by diabetic or obesity status. Circulating betatrophin positively correlated with obesity or glycemic indices, liver enzyme profiles, and NAFLD status, and was confirmed by multivariate regression analyses (β = 0.195, P = 0.040). However, when including insulin resistance index in the model, the significant association between betatrophin level and NAFLD was diminished due to a mediation effect of insulin resistance on this relationship. Palmitate or tunicamycin increased betatrophin expression in HepG2 cells, while a chemical chaperone blocked its induction. Hepatic expression of betatrophin was elevated in mice with NAFLD including db/db or ob/ob mice and mice with a high-fat or methionine-choline deficient diet. In conclusion, circulating betatrophin was increased in mice and humans with NAFLD and its expression was induced by endoplasmic reticulum stress in hepatocytes (Clinical trial no. NCT02285218).

The effect of rosiglitazone on LRP1 expression and amyloid β uptake in human brain microvascular endothelial cells: a possible role of a low-dose thiazolidinedione for dementia treatment

Thiazolidinediones, such as rosiglitazone or pioglitazone, are anti-diabetic agents that have been expected to show a beneficial effect in Alzheimers disease (AD) because of their anti-inflammatory effect. However, these agents have failed to show a significant beneficial effect on AD in recent clinical trials. Here, we suggest that low-dose rosiglitazone treatment, and not the conventional doses, has an amyloid β (Aβ)-clearing effect by increasing LRP1, an Aβ outward transporter in the blood-brain barrier. Rosiglitazone up-regulated LRP1 mRNA and protein expression and LRP1 promoter activity in human brain microvascular endothelial cells (HBMECs). Aβ uptake through LRP1 in HBMECs was also increased by rosiglitazone. This increase in LRP1 and Aβ uptake was observed in up to 10 nm rosiglitazone concentration. At concentrations above 20 nm rosiglitazone, the LRP1 expression and Aβ uptake in HBMECs were not altered. The possible mechanism of this unusual dose response is discussed. This study suggests a new therapeutic application of thiazolidinediones for AD at a much lower dose than the doses used for diabetes treatment.