Human CYP2E1-dependent and human sulfotransferase 1A1-modulated induction of micronuclei by benzene and its hydroxylated metabolites in Chinese hamster V79-derived cells.

Benzene is a ubiquitous environmental pollutant and a confirmed human carcinogen, which requires metabolic activation, primarily by CYP2E1, for most of its biological actions. Chromosome damages in benzene-exposed workers and rodents have been observed, and in their urine sulfo- and glucuronide-conjugates of phenol and hydroquinone were present. Yet, direct evidence for human CYP2E1-activated mutagenicity of benzene and the exact significance of phase II metabolism for inactivating benzene metabolites are still missing. In the present study, benzene and its oxidized metabolites (phenol, hydroquinone, catechol, 1,2,4-trihydroxybenzene and 1,4-benzoquinone) were investigated for induction of micronuclei in a V79-derived cell line genetically engineered for expression of both human CYP2E1 and human sulfotransferase (SULT) 1A1 (indicated by active micronuclei induction by 1-hydroxymethylpyrene). The results demonstrated concentration-dependent induction of micronuclei by benzene and phenol, though with lower potency or efficacy than the other metabolites. Inhibition of CYP2E1 by 1-aminobenzotriazole did not change the effect of benzoquinone, but completely abolished that of benzene and phenol, and attenuated that of the other compounds. Moreover, inhibition of SULT1A1 by pentachlorophenol potentiated the effects of benzene, hydroquinone, catechol and trihydroxybenzene. Ascorbic acid, a reducing and free radical-scavenging agent, significantly lowered the effects of hydroquinone, catechol, trihydroxybenzene as well as N-nitrosodimethylamine (a known CYP2E1-dependent promutagen), with that of benzoquinone unaffected. These results suggest that in addition to activating benzene and phenol, human CYP2E1 may further convert hydroquinone, catechol and trihydroxybenzene to more genotoxic metabolites, and sulfo-conjugation of the multi-hydroxylated metabolites of benzene by human SULT1A1 may represent an important detoxifying pathway.