In vivo and in vitro comparison of cytochrome P-450 expression and DNA adduct formation in rat liver and lung treated with benzo(a)pyrene

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants produced from incomplete combustion of organic materials. Benzo(a)pyrene (BaP), a prototypical PAH, is a known animal carcinogen and a suspected human carcinogen. BaP is metabolized by the subsequent actions of cytochrome P-450 (CYP450) and epoxide hydrolase to its ultimate carcinogen BaP-7,8-diol-9,10-epoxide (BPDE). BPDE is a highly reactive electrophile that can form covalent adducts with DNA. Furthermore, BaP can induce expression of bioactivating enzymes CYP1A1 and CYP1B1 via the aryl hydrocarbon receptor. Chronic exposure to BaP is associated with the development of cancer at prominent sites, including the lung.; This dissertation investigated tissue-specific differences in bioactivation of BaP and subsequent BaP-DNA adduct formation in target (lung) and non-target (liver) tissues utilizing precision-cut rat liver and lung slices incubated in dynamic organ culture. Additionally, in vivo studies were employed to validate the use of the in vitro model.; The results from this dissertation demonstrate that rat liver and lung slices were viable in dynamic organ culture and that incubation with BaP did not result in cytotoxicity. Tissue slices were able to metabolize BaP to reactive intermediates that formed covalent adducts with DNA. Greater expression of CYP1A1 and CYP1B1 mRNA in lung slices following in vitro incubation with BaP correlated with higher levels of BaP-DNA adducts. Furthermore, in vivo treatment with BaP resulted in a similar (CYP1A1) or greater (CYP1B1) induction of mRNA levels in lung compared to liver, however, BaP-DNA adduct levels were similar or greater in the liver compared to the lung. While in vitro and in vivo exposure to BaP generated similar adduct profiles in a given tissue, qualitatively different BaP-DNA adducts were found in lung and liver tissue.; Together, these results suggest that higher expression of CYP1A1 and CYP1B1 bioactivating enzymes in the lung, and the unique BaP-DNA adducts produced, may contribute to the tissue specificity of BaP-mediated carcinogenesis. Furthermore, these studies serve to characterize and validate the use of precision-cut tissue slices incubated in dynamic organ culture as a model to investigate metabolic activation and subsequent chemical-DNA adduct formation, which is necessary for the genotoxic activity of chemical carcinogens.