Lack of chemopreventive efficacy of DL-selenomethionine in colon carcinogenesis

Epidemiologic observations and laboratory research have suggested that diet ary selenium reduces the risk of colon cancer. Selenium-enriched brewer's y east as a dietary supplement reduces the incidence of and mortality from ca ncer of the colon in humans. It is not clear whether the observed inhibitor y effect is due to selenomethionine, or to other forms of selenium, or to a mixture of the selenium compounds present in selenium-enriched brewer's ye ast. Therefore, bioassay described in this study examined the chemopreventi ve efficacy of 10 and 15 ppm selenomethionine, equivalent to 3.6 and 5.4 pp m as selenium, against azoxymethane (AOM)-induced colon carcinogenesis. At five weeks of age, groups of male F344 rats were fed diets containing 0 (co ntrol diet), 10 or 15 ppm selenomethionine. At seven and eight weeks of age , all rats except those in vehicle-treated groups received s.c. injections of AOM at a dose rate of 15 mg/kg body wt. The rats were maintained on thei r respective diets for 52 weeks and were then sacrificed. Colon tumors were processed and evaluated histopathologically. Colon tumor incidence and mul tiplicity were analyzed statistically. No obvious toxic effects were observ ed following dietary administration of 10 or 15 ppm selenomethionine as ind icated by body weight gain. Administration of 10 or 15 ppm selenomethionine had no significant effect on colon tumor incidence and multiplicity. This study suggests that i) selenomethionine lacks chemopreventive efficacy agai nst AOM-induced colon carcinogenesis and ii) other forms of selenium or a m ixture of selenium compounds present in selenium-enriched brewer's yeast ne ed to be evaluated for their chemopreventive efficacy.