DOWN-REGULATION OF INDUCIBLE NITRIC OXIDE SYNTHASE EXPRESSION BY INOSITOL HEXAPHOSPHATE IN HUMAN COLON CANCER CELLS

Inflammatory bowel disease (IBD) is chronic inflammatory condition associated with increased risk of developing colorectal cancer. A number of mediators of inflammation, such as pro-inflammatory cytokines, prostaglandins and nitric oxide have been involved in carcinogenesis, especially in the promotion and progression stages. NO is synthesized from L-arginine by constitutively expressed endothelial and neuronal nitric oxide synthases (eNOS and nNOS, respectively) and an inducible NOS (iNOS) isoform expressed under inflammatory conditions. A selective inhibitors of iNOS could be, therefore, considered to be good candidates as chemopreventive agents against colon cancer. In this study, the effect of inositol hexaphosphate (IP6), dietary phytochemical, on the mRNA expression of iNOS stimulated with bacterial lipopolysaccharides (Escherichia coli and Salmonella typhimurium) and IL-1β in intestinal cells Caco-2 for 6 and 12 h was investigated. A transcription level of iNOS with the use real time QRT-PCR technique was determined in cells treated with 1 and 2.5 mM IP6. Stimulation of Caco-2 with pro-inflammatory factors (LPS and IL-1β) resulted in an up-expression of iNOS mRNA at 6 and 12 h. Cells exposed to IP6 only revealed significant reduction in iNOS gene transcription after 12 h. A decrease in iNOS transcription by IP6 following the gene induction by proinflammatory agents in 6 and 12 h lasting cultures was also determined. The findings of this study suggest that one of the anti-cancer and anti-inflammatory abilities of IP6 can be realized by suppressing the expression of gene encoding inducible nitric oxide synthase isoform at the transcriptional level.