REDUCTION OF BENZENE METABOLISM AND TOXICITY IN MICE THAT LACK CYP2E1EXPRESSION

Transgenic CYP2E1 knockout mice (cyp2e1(-/-)) were used to investigate the involvement of CYP2E1 in the in vivo metabolism of benzene and in the development of benzene-induced toxicity. After benzene exposure, absence of CYP2E1 protein was confirmed by Western blot analysis of mo use liver samples. For the metabolism studies, male cyp2e1(-/-) and wi ld-type control mice were exposed to 200 ppm benzene, along with a rad iolabeled tracer dose of [C-14]benzene (1.0 Ci/mol) by nose-only inhal ation for 6 hr. Total urinary radioactivity and all radiolabeled indiv idual metabolites were reduced in urine of cyp2e1(-/-) mice compared t o wildtype controls during the 48-hr period after benzene exposure. In addition, a significantly greater percentage of total urinary radioac tivity could be accounted for as phenylsulfate conjugates in cyp2e1(-/ -) mice compared to wild-type mice, indicating the importance of CYP2E 1 in oxidation of phenol following benzene exposure in normal mice. Fo r the toxicity studies, male cyp2e1(-/-), wildtype, and B6C3F1 mice we re exposed by whole-body inhalation to 0 ppm (control) or 200 ppm benz ene, 6 hr/day for 5 days. On Day 5, blood, bone marrow, thymus, and sp leen were removed for evaluation of micronuclei frequencies and tissue cellularities. No benzene-induced cytotoxicity or genotoxicity was ob served in cyp2e1(-/-) mice. In contrast, benzene exposure resulted in severe genotoxicity and cytotoxicity in both wild-type and B6C3F1 mice . These studies conclusively demonstrate that CYP2E1 is the major dete rminant of in vivo benzene metabolism and benzene-induced myelotoxicit y in mice. (C) 1996 Academic Press, Inc.