Metformin inhibits TNF-alpha-induced IkappaB kinase phosphorylation, IkappaB-alpha 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-kappaB abolished the TNF-alpha-induced IL-6 production. Pre-treatment with metformin (100-1000 micromol/L) also inhibited TNF-alpha-induced IL-6 production, phosphorylation of IkappaB kinase (IKK) alpha/beta and IkappaB-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 IkappaB-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 alpha1-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 IKKalpha/beta phosphorylation, IkappaB-alpha degradation and IL-6 production in HUVEC. This effect was related to PI3K-dependent AMPK phosphorylation.
Huang
Nan-Lan
NL
Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Chiang
Shu-Hui
SH
Hsueh
Chia-Hsiang
CH
Liang
Yao-Jen
YJ
Chen
Yi-Jung
YJ
Lai
Ling-Ping
LP
D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D050197:Atherosclerosis / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D051550:I-kappa B Kinase / Q000378:metabolism*; D015850:Interleukin-6 / Q000378:metabolism*; D008687:Metformin / Q000494:pharmacology*; D016328:NF-kappa B / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D034741:RNA, Small Interfering; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014471:Umbilical Veins / Q000166:cytology
D055372:AMP-Activated Protein Kinases; D000893:Anti-Inflammatory Agents; D007004:Hypoglycemic Agents; D051550:I-kappa B Kinase; D015850:Interleukin-6; D008687:Metformin; D016328:NF-kappa B; D019869:Phosphatidylinositol 3-Kinases; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; C508600:IL6 protein, human; C526180:PRKAA1 protein, human