Contributory role of 5-lipoxygenase and its association with angiogenesis in the promotion of inflammation-associated colonic tumorigenesis by cigarette smoking.

Our previous study shows that cigarette smoking can promote inflammation-associated adenoma formation in the mouse colon, but the underlying mechanism remains unknown. Several studies suggest that there is a link between 5-lipoxygenase (5-LOX) and carcinogenesis in humans and animals. In the present study, we aims to investigate whether the promoting action of cigarette smoke on inflammation-associated colon cancer formation is associated with 5-LOX activation in mice. Results showed that exposure to the mainstream smoke of unfiltered cigarettes enhanced the 5-LOX protein expression in the inflammation-associated colonic adenomas. It was accompanied with an up-regulation of matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF). Both are the key angiogenic factors for tumorigenesis. 5-LOX inhibitors decreased the incidence of colonic adenoma formation and reduced angiogenesis, MMP-2 activity and VEGF protein expression in the colons of these animals. Taken together, these results strongly suggest that cigarette smoke can induce 5-LOX expression which plays an important role in activation of MMP-2 and VEGF to induce angiogenic process and promotion of inflammation-associated adenoma formation in mice.