Benzene is an occupational and environmental toxicant. The main human health concern associated with benzene exposure is leukemia. The toxic effects of benzene are dependent on its metabolism by the cytochrome P450 enzyme system. The cytochrome P450 enzymes CYP2E1 and CYP2F2 are the major contributors to the bioactivation of benzene in rats and mice. Although benzene metabolism has been shown to occur with mouse and human lung microsomal preparations, little is known about the ability of human CYP2F to metabolize benzene or the lung cell types that might activate this toxicant. Our studies compared bronchiolar derived (BEAS-2B) and alveolar derived (A549) human cell lines for benzene metabolizing ability by evaluating the roles of CYP2E1 and CYP2F1. BEAS-2B cells that overexpressed CYP2F1 and recombinant CYP2F1 were also evaluated. BEAS-2B cells overexpressing the enzyme CYP2F1 produced 47.4 ± 14.7 pmols hydroxylated metabolite/106 cells/45 min. The use of the CYP2E1-selective inhibitor diethyldithiocarbamate and the CYP2F2-selective inhibitor 5-phenyl-1-pentyne demonstrated that both CYP2E1 and CYP2F1 are important in benzene metabolism in the BEAS-2B and A549 human lung cell lines. The recombinant expressed human CYP2F1 enzyme had a Km value of 3.83 μM and a Vmax value of 0.01 pmol/pmol P450 enzyme/min demonstrating a reasonably efficient catalysis of benzene metabolism (Vmax/Km = 2.6). Thus, these studies have demonstrated in human lung cell lines that benzene is bioactivated by two lung-expressed P450 enzymes.
- Cytochromes P450
ASJC Scopus subject areas
- Molecular Medicine
- Molecular Biology
- Health, Toxicology and Mutagenesis