Effects of cellular redox balance on induction of apoptosis by eicosapentaenoic acid in HT29 colorectal adenocarcinoma cells and rat colon in vivo

Background and aims-Epidemiological evidence suggests n-3 polyunsaturated l ipids may protect against colorectal neoplasia. Consumption of fish oil mod ulates crypt cytokinetics in humans, and crypt apoptosis in animal models. To explore these effects, we investigated involvement of caspase enzymes an d cellular redox balance in the induction of apoptosis by eicosapentaenoic acid (EPA) in HT29 cells, and in rat colon in vivo. Methods-Survival of HT29 cells grown with EPA in the presence Of caspase in hibitors, antioxidants, or buthionine sulphoximine, an inhibitor of glutath ione neosynthesis, was determined. The effects of EPA enriched fish oil and glutathione depletion on apoptosis in rat colon were assessed using microd issected crypts. Results-Treatment of HT29 cells with EPA reduced viable cell number and act ivated caspase 3, prior to cell detachment. Antioxidants and caspase inhibi tors blocked HT29 cell death whereas glutathione depletion increased it. Ra ts fed fish oil had higher crypt cell apoptosis than those fed corn oil, an d glutathione depletion enhanced this effect. Conclusions-Incorporation of EPA into colonic epithelial cell lipids increa ses apoptosis. The results of this study, using both an animal and cell lin e model, support the hypothesis that this effect is mediated via cellular r edox tone, and is sensitive to glutathione metabolism. The data suggest a m echanism whereby polyunsaturated fatty acids may influence the susceptibili ty of colorectal crypt cells to induction or progression of neoplasia.