Epidemiologic observations and laboratory research have suggested that dietary
selenium reduces the risk of
colon cancer.
Selenium-enriched brewer's yeast as a dietary supplement reduces the incidence of and mortality from
cancer of the colon in humans. It is not clear whether the observed inhibitory 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 yeast. Therefore, bioassay described in this study examined the chemopreventive efficacy of 10 and 15 ppm
selenomethionine, equivalent to 3.6 and 5.4 ppm as
selenium, against
azoxymethane (AOM)-induced colon
carcinogenesis. At five weeks of age, groups of male F344 rats were fed diets containing 0 (control 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 their respective diets for 52 weeks and were then sacrificed. Colon
tumors were processed and evaluated histopathologically. Colon
tumor incidence and multiplicity were analyzed statistically. No obvious toxic effects were observed following dietary administration of 10 or 15 ppm
selenomethionine as indicated 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 against AOM-induced colon
carcinogenesis and ii) other forms of
selenium or a mixture of
selenium compounds present in
selenium-enriched brewer's yeast need to be evaluated for their chemopreventive efficacy.