Inhibitory Effects of Metformin on TNF-α Induced Endothelial Inflammation and its Mechanisms

• Main Authors: Shu-Hui Chiang, 江書慧
• Other Authors: 賴凌平
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/22709062442149368960

碩士 === 國立臺灣大學 === 藥理學研究所 === 93 === Background：Type 2 diabetes is a disease with high morbidity and mortality in modern society, and nearly 80% of deaths in those with type 2 diabetes involve cardiovascular disease or stroke. Among many oral hypoglycemic drugs, metformin lowers blood glucose level through the improvement of insulin sensitivity. Clinical trials have demonstrated that metformin is unique in protecting patients with type 2 diabetes from macrovascular disease. The aim of the present study was to investigate whether metformin and other agents involved in insulin resistance modulated inflammatory reactions in endothelial cells. Methods and Results：The proinflammatory factor TNF-α can induce inflammatory reaction in endothelial cells and promote IL-6 secretion and ICAM-1 expression. Therefore, we used TNF-α induced inflammatory reactions in HUVECs as the experimental model. In our study, the secretion of IL-6 after TNF-α (10 ng/ml) treatment for 24hr was about 15 times that of basal level. Metformin concentration-dependently inhibited TNF-α induced IL-6 secretion. When pretreated with 100 μM metformin, the secretion of IL-6 induced by TNF-α was significantly reduced when compared with positive control (10 ng/ml TNF-α only). The secretion of IL-6 after 500 μM and 1000 μM metformin pretreatment were about 50% and 40% that of positive control respectively. We found that TNF-α induced IL-6 secretion was related to NF-κB activation because NF-κB inhibitors CAPE (pyrrolidine dithiocarbamate) (25 μg/ml) and PDTC (pyrrolidine dithiocarbamate) (20 μM) partially inhibited the IL-6 secretion induced by TNF-α. Moreover, metformin (500 μM) also inhibited TNF-α (10 ng/ml) induced IκB-α degradation and NF-κB p65 translocation to the nucleus, and these inhibitory effects were blocked by a PI3K inhibitor wortmanin (100 nM). Because the phosphorylation/activation of AMPK by metformin is PI3K- dependent, we speculated that the activation of AMPK might be concerned in the inhibitory effect of metformin. Similar to IL-6 secretion, metformin (30 μM) also inhibited TNF-α induced ICAM-1 expression. PPAR-γ agonist 15d-PGJ2 is an insulin sensitizer, too. We also found that 15d-PGJ2 inhibited TNF-α induced ICAM-1 expression. Resistin is an adipokine and is related to insulin resistant. We found that it did not change IL-6 secretion or ICAM-1 expression in HUVECs. Conclusions：In our study, metformin had inhibitory effects on TNF-α induced IL-6 secretion and ICAM-1 expression in HUVECs. We speculated that these effects were due to its ability to activate AMPK through a PI3K-dependent pathway and to inhibit TNF-α induced IκB-α degradation to prevent NF-κB p65 from translocation to the nucleus. We demonstrated that metformin had protective effects on endothelial inflammation. However, its precise mechanisms of action remain to be elucidated.