Anti-inflammatory mechanism of metformin and its effects in intestinal inflammation and colitis-associated colon cancer

Background and Aim: The aim of this study is to evaluate the effect of metformin on intestinal inflammation. Methods: COLO205 cells were pretreated with metformin and stimulated with tumor necrosis factor (TNF)-α. Expression of interleukin (IL)-8 was determined by luciferase assay and real-time PCR. Inhibitor of kappaB (IκB) phosphorylation/degradation and adenosine monohosphate-activated protein kinase (AMPK) activity were evaluated by Western blotting. DNA-binding activity of transcription factor nuclear factor-kappaB (NF-κB) was assessed by electrophoretic mobility shift assay. In an acute colitis model, mice were given 4% dextran sulfate sodium (DSS) for 5 days. IL-10^-/- mice were used to evaluate the effect of metformin on chronic colitis. In an inflamation-associated tumor model, mice were given a single intraperitoneal injection of azoxymethane followed by three cycles of 2% DSS for 5 days and 2 weeks of free water consumption. Results: Metformin significantly inhibited IL-8 induction in COLO 205 cells stimulated with TNF-α. Metformin attenuated IκBα phosphorylation and NF-κB DNA-binding activity. Administration of metformin significantly reduced the severity of DSS-induced colitis. In addition, DSS-induced IκB kinase (IKK) activation was significantly reduced in mice treated with metformin. Metformin significantly attenuated the severity of colitis in IL-10^-/- mice, induced AMPK activity in intestinal epithelial cells, and inhibited the development of colitic cancer in mice. Conclusions: These results indicate that metformin suppresses NF-κB activation in intestinal epithelial cells and ameliorates murine colitis and colitis-associated tumorigenesis in mice, suggesting that metformin could be a potential therapeutic agent for the treatment of inflammatory bowel disease.