Involvement of phenolic metabolites in the irreversible protein-binding of 14C-bromobenzene catalysed by rat liver microsomes.

During microsomal metabolism of 14C-bromobenzene, radioactive material was irreversibly bound to microsomal protein. Although primary monooxygenation of aromatic hydrocarbons leads to the formation of reactive epoxides which may bind to protein, our results indicate that reactive intermediates formed via oxidation of the phenolic metabolites substantially contribute to the overall binding. This conclusion is supported by the following observations: 1) The binding of radioactivity continued to increase even though the primary metabolism was terminated; 2) Addition of UDP-glucuronic acid largely reduced the amount of the free phenols in the incubation mixture and simultaneously decreased the binding; and 3) Inhibition of the epoxide hydratase by 1,1,1-trichloro-2-propene oxide (TCPO) completely prevented the formation of the dihydrodiols, but did not significantly affect the binding. Thus, the results are in agreement with our previous observations on the binding of 14C-naphthalene and 14C-dichlorobiphenyl, and suggest that phenols generated from these aromatic hydrocarbons are further metabolized to protein-binding species.