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.

Human umbilical vein endothelial cells (HUVEC) were used for the experiments. The effects of metformin on TNF-α-induced IL-6 production were investigated. Modulation of AMPK and related signal transduction pathways were also performed.

TNF-α increased IL-6 secretion by HUVEC in a dose-dependent manner but inhibitors of NF-κB abolished the TNF-α-induced IL-6 production. Pre-treatment with metformin (100–1000 μmol/L) also inhibited TNF-α-induced IL-6 production, phosphorylation of IκB kinase (IKK) α/β and IκB-α degradation. Metformin increased phosphorylation of AMP-activated kinase (AMPK) but wortmannin, a PI3K inhibitor, negated its effects on AMPK phosphorylation and TNF-α-induced IκB-α degradation. AICAR, a direct AMPK activator, had inhibitory effects on TNF-α-induced IL-6 production, similar to that of metformin. Transfection of siRNA against α1-AMPK eradicated the inhibitory effects of metformin on TNF-α-induced IL-6, implying the essential role of AMPK.

Metformin had anti-inflammatory effects on endothelial cells and inhibited TNF-α-induced IKKα/β phosphorylation, IκB-α degradation and IL-6 production in HUVEC. This effect was related to PI3K-dependent AMPK phosphorylation.