Metformin inhibits TNF-α-induced IκB kinase phosphorylation, IκB-α degradation and IL-6 production in endothelial cells through PI3K-dependent AMPK phosphorylation

Background: Metformin has been reported to reduce cardiovascular complications in diabetic patients. The purpose of the present study was to investigate the anti-inflammatory effects of metformin on endothelial cells and the related molecular mechanisms. Methods: Human umbilical vein endothelial cells (HUVEC) were used for the experiments. The effects of metformin on TNF-alpha-induced IL-6 production were investigated. Modulation of AMPK and related signal transduction pathways were also performed. Results: TNF-alpha increased IL-6 secretion by HUVEC in a dose-dependent manner but inhibitors of NF-kappa B abolished the TNF-alpha-induced IL-6 production. Pre-treatment with metformin (100-1000 mu mol/L) also inhibited TNF-alpha-induced IL-6 production, phosphorylation of I kappa B kinase (IKK) alpha/beta and I kappa B-alpha degradation. Metformin increased phosphorylation of AMP-activated kinase (AMPK) but wortmannin, a PI3K inhibitor, negated its effects on AMPK phosphorylation and TNF-alpha-induced I kappa B-alpha degradation. AICAR, a direct AMPK activator, had inhibitory effects on TNF-alpha-induced IL-6 production, similar to that of metformin. Transfection of siRNA against alpha 1-AMPK eradicated the inhibitory effects of metformin on TNF-alpha-induced IL-6, implying the essential role of AMPK. Conclusions: Metformin had anti-inflammatory effects on endothelial cells and inhibited TNF-alpha-induced IKK alpha/beta phosphorylation, I kappa B-alpha degradation and IL-6 production in HUVEC. This effect was related to PI3K-dependent AMPK phosphorylation. (c) 2008 Elsevier Ireland Ltd. All rights reserved.