Cancer Prevention by Different Forms of Tocopherols   全文下載

Cancer Prevention by Different Forms of Tocopherols

Low vitamin E nutritional status has been suggested to increase cancer risk. However, recent large-scale human trials with high doses of alpha-tocopherol (a-T) have produced disappointing results. This points out the need for a better understanding of the biological activities of different forms of tocopherols. Using a tocopherol mixture that is rich in g-T (g-TmT), we demonstrated the inhibition of colon carcinogenesis in mice, and the inhibition is associated with decreased levels of 8-isoprostane, nitrotyrosine, prostaglandin E2 and leukotriene B4. Dietary 0.3% g-TmT also inhibited chemically induced lung tumorigenesis in the A/J mice as well as the growth of lung cancer cells in xenograft or allograft tumors; the inhibition was associated with a reduction of oxidative/nitrosative stress. d-T was found to be more active than g-T in the inhibition of cancer cell growth in culture and lung cancer xenograft tumors as well as in azoxymethane-induced colon aberrant crypt foci formation in rats, whereas a-T was ineffective. Analysis of the levels of tocopherols and their metabolites in blood and tissues suggests that metabolites of d-T and g-T contribute to their inhibitory activity. These studies demonstrate the broad cancer preventive activity of g-TmT and higher activity of d-T.