Reduction of Benzene Metabolism and Toxicity in Mice That Lack CYP2E1 Expression

Abstract

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 mouse liver samples. For the metabolism studies, male cyp2e1-/- and wild-type control mice were exposed to 200 ppm benzene, along with a radiolabeled tracer dose of [14C]benzene (1.0 Ci/mol) by nose-only inhalation for 6 hr. Total urinary radioactivity and all radiolabeled individual metabolites were reduced in urine of cyp2e1-/- mice compared to wild-type controls during the 48-hr period after benzene exposure. In addition, a significantly greater percentage of total urinary radioactivity could be accounted for as phenylsulfate conjugates in cyp2e1-/- mice compared to wild-type mice, indicating the importance of CYP2E1 in oxidation of phenol following benzene exposure in normal mice. For the toxicity studies, male cyp2e1-/-, wild-type, and B6C3F1 mice were exposed by whole-body inhalation to 0 ppm (control) or 200 ppm benzene, 6 hr/day for 5 days. On Day 5, blood, bone marrow, thymus, and spleen were removed for evaluation of micronuclei frequencies and tissue cellularities. No benzene-induced cytotoxicity or genotoxicity was observed 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 determinant of in vivo benzene metabolism and benzene-induced myelotoxicity in mice.

Cytochromes P450 involved with benzene metabolism in hepatic and pulmonary microsomes

“…Transgenic mice have been used to determine the cytochrome P450 isozyme responsible for benzene metabolism [25]. Knockout mice that did not express a functional CYP2E1 protein metabolized benzene to a lesser extent than wild-type controls, which supported the idea that CYP2E1 is the major cytochrome P450 isozyme.…”

Stress response, biotransformation effort, and immunotoxicity in captive birds exposed to inhaled benzene, toluene, nitrogen dioxide, and sulfur dioxide

“…Similarly, benzene, toluene, ethylbenzene and xylenes induce hepatic CYP 450 activity in mammals (Tamie and Rui-Sheng 1994;Valentine et al, 1996;Villard et al, 1994). In contrast, contaminants can suppress CYP 450 activity (Treinen-Moslen 2003).…”

Comparative metabolism of [ 14 C]benzene to excretable products and bioactivation to DNA-binding derivatives in maternal and neonatal mice

“…The relative contributions of the enzymes involved in benzene bioactivation, e.g. peroxidases (Sawata et al 1989;Smith et al 1989;Schattenberg et al 1994) and CYP2E1 (Snyder et al 1993;Valentine et al 1996;Kenyon et al 1998), to the formation of the reactive metabolites in the sucklings remain to be determined. Fig.…”

“…The hematotoxic eects of benzene require metabolic bioactivation of the compound (Andrews et al 1977), a process in which CYP2E1 is a principal catalyst (Snyder et al 1993;Valentine et al 1996;Kenyon et al 1998), and in which the liver plays a pivotal role (Sammet et al 1979). Cellular macromolecules to which the resulting reactive benzene metabolites bind include DNA (Creek et al 1997) and protein (Irons and Neptun 1980;Chen and Eastmond 1995 ).…”