Mammary cancer chemoprevention by inorganic and organic selenium: single agent treatment or in combination with vitamin E and their effects on in vitro immune functions.

The chemopreventive efficacies of selenate, selenite, selenium dioxide, selenomethionine and selenocystine were examined during the promotion phase of carcinogenesis in the 7,12-dimethylbenz[a]anthracene-induced mammary tumor model in rats. Each agent was added to the diet at a final concentration of 3 p.p.m. selenium. In general there was no significant difference in the potency of these five selenium compounds in inhibiting the development of mammary tumors. The interaction of vitamin E (500 p.p.m.) with either selenite or selenomethionine was further characterized in a second carcinogenesis study. Results of this experiment suggested that vitamin E enhanced the protective effect of selenite but not that of selenomethionine. In an attempt to explore the synergistic mechanism of selenium and vitamin E, the effects of these two agents on mitogen-induced blastogenesis and natural killer cytotoxic activity were also investigated. No consistent changes in these in vitro immune functions were detected resulting from supranutritional feeding of either selenite or vitamin E or both. The metabolism of inorganic versus organic selenium was discussed in relation to their role in the control of neoplastic growth as well as to their selective modulation by vitamin E.