DEP have been shown to induce a transient increase in CYP1A1 that returns to basal level at 7 days post-exposure, but to cause a sustained decrease in CYP2B1 in rat lung, whereas carbon black (CB) results only in a sustained decrease of CYP2B1. The present study examined the effects of DEP-altered pulmonary cytochrome P450 on the metabolization of mutagenic agents. Sprague Dawley rats were intratracheally instilled with saline or a single dose of DEP or CB at 35 mg/kg body weight. At 1, 3, or 7 days post-exposure, S9, microsomes, and cytosol were isolated from lung tissue. The mutagenicity of 2-aminoanthracene (2-AA) and 2-aminofluorene (2-AF) were monitored using the Ames test with S. typhimurium YG1024. The results show that S9 or microsomes, but not the cytosolic enzymes, activated the mutagenicity of 2-AA and 2-AF in a dose-dependent manner. The CB-exposed S9, with down-regulated CYP2B1, significantly reduced 2-AA mutagenicity compared to the control S9 at all time points. In contrast, the induction of 2-AA mutagenicity by DEP-exposed S9, with down-regulated CYP2B1 but induced CYP1A1 at 1 and 3 days post-exposure, decreased with increasing exposure time. At 1 day post-exposure, the DEP-S9 had a similar effect to that of control S9, but induced higher mutagenicity than the CB-S9. This DEP-derived S9 activated 2-AA mutagenicity decreased at 3 days post-exposure and further declined to the level of CB-S9 at 7 days post-exposure. Heat-inactivated S9 or addition of a CYP1A1 inhibitor, alpha-naphthoflavone, blocked 2-AA activation. These results suggest that both CYP1A1 and CYP2B1 activate 2-AA mutagenicity. At 3 days post exposure, DEP-S9 decreased, while CB-S9 increased 2-AF mutagenicity compared to control S9, suggesting that both CYP1A1 and CYP2B1 decrease 2-AF mutagenicity. These results show that mutagenic activation is substrate-specific, depending on competing metabolic pathways. DEP exposure, which alters the cytochrome P450 system, may have a profound effect on pulmonary handling of mutagenic agents.
The Toxicologist. Society of Toxicology 42nd Annual Meeting and ToxExpo, Cutting-Edge Science, Networking, New Perspectives, March 9-13, 2003, Salt Lake City, Utah