| Abstract: | Because DNA modification may be a prerequisite for chemical carcinogenesis, the DNA-damaging potential of benzene and its metabolites was examined in order to identify the proximate DNA-damaging agent associated with benzene exposure. A DNA synthesis inhibition assay previously identified p-benzoquinone as the most potent overall cellular toxin and inhibitor of DNA synthesis, but failed to discriminate among the hydroxylated metabolites. Therefore, the ability of benzene and its metabolites to induce DNA strand breaks in the mouse lymphoma cell line, L5178YS, was examined in order to provide a more accurate indication of the DNA damage associated with benzene and its metabolites. Cells were exposed to benzene, hydroquinone, catechol, phenol, 1,2,4-benzenetriol, or p-benzoquinone over a 1000-fold concentration range (1.0 microM-1.0 mM). Concentrations of benzene, phenol, or catechol as high as 1.0 mM did not increase the percentage of single-stranded DNA observed. Concentrations of hydroquinone as high as 0.1 mM were also ineffective. In contrast, both p-benzoquinone and 1,2,4-benzenetriol produced DNA breaks in a dose-related fashion. Of the two, benzoquinone proved to be more potent with an ED50 of approximately equal to 2.5 microM compared with 55.0 microM for benzenetriol. The DNA damage induced by 6.0 microM benzoquinone was maximal within 3 min of exposure and yielded approximately 70% single-stranded DNA after alkaline denaturation. By contrast, the single-stranded DNA observed after benzenetriol exposure required 60 min of exposure to achieve the same extent of damage as that found with benzoquinone. These results suggest that the benzene metabolites, benzenetriol and benzoquinone, may cause DNA damage and that the mechanisms responsible for the damage associated with these two compounds may be different. |
