A comparison of the effect of selenium on the mutagenicity and metabolism of benzo[ a]pyrene in rat and hamster liver S9 activation systems

Abstract

When selenium (Na 2SeO 3) was included in the incubation mix containing rat or hamster liver S9 preparations both the metabolism and mutagenicity of benzo[ a]pyrene (BaP) and several of its metabolites were altered. At non-toxic concentrations selenium inhibited the S9 dependent mutagenicity of BaP and number of its metabolites on Salmonella typhimurium strain TA100 as indicated by the number of histidine independent revertants observed. High performance liquid chromatographic analysis of S9 generated metabolites of BaP from rat and hamster liver indicated that selenium caused quantitative differences in the amounts of the metabolic products. In hamster liver S9 differences were reflected in decreased amounts of strongly mutagenic BaP-7,8-dihydrodiol and increased amounts of 4,5- and 9,10-dihydrodiols that were weakly mutagenic to TA100 in that system. In rat liver S9 selenium caused quantitatively similar decreases in BaP-7,8- and 9,10-dihydrodiol and 3-hydroxy-BaP. When used as substrate 3-hydroxy-BaP was the most mutagenic to TA100 in the rat activation system whereas BaP-7,8-dihydrodiol was most mutagenic in the hamster S9 system. Assays that measured the formation of water-soluble conjugates of BaP indicated that selenium did not significantly alter the formation of sulfate ester or glutathione conjugates although a 12–17% reduction of labeled metabolites bound to the glucuronide fraction was observed. Results described in this report suggest that selenium modified the metabolism and hence the mutagenicity of BaP to TA100 by affecting mixed-function oxidase and/or epoxide hydratase activity in both the rat and hamster liver S9 activation systems.