Stereoselective formation of bromobenzene glutathione conjugates

Abstract

Two bromobenzene-glutathione conjugates have been detected as both in vivo and in vitro metabolites of bromobenzene. Separation and purification by high pressure liquid chromatography (HPLC) and analysis by 13C and 1H-NMR spectroscopy indicated that the metabolites are trans-3-bromo-6-(glutathion-S-yl)-cyclohexa-2,4-dien-1-ol and trans-4-bromo-6-(glutathion-S-yl)-cyclohexa-2,4-dien-1-ol. The two conjugates are formed in unequal amounts; over a dose range of 25–500 mg/kg the ratio of the two conjugates excreted into bile in 6 h was 1.6 ± 0.1 (mean ± S.E.). Pretreatment of rats with either phenobarbital or 3-methyl-cholanthrene did not significantly alter the ratio of the two conjugates excreted into bile. When bromobenzene was incubated with rat liver microsomes and glutathione, the same two conjugates were formed in the presence but not in the absence of 100 000 × g supernatant. Furthermore, in the presence of 100 000 × g supernatant from control animals, microsomes from rats treated with phenobarbital formed both conjugates 6 times more rapidly than did microsomes from control rats, whereas microsomes from rats treated with 3-methylcholanthrene formed both conjugates less rapidly than did those from control rats. Thus, the data suggest that both conjugates are formed via bromobenzene 3,4-oxide and that their formation requires enzymes in liver cytosol.