P-32 POSTLABELING ANALYSIS OF DIBENZ[A,J]ACRIDINE-DNA ADDUCTS IN MICE- IDENTIFICATION OF PROXIMATE METABOLITES

N-Heterocyclic polynuclear aromatics are widely-occurring environmenta l pollutants formed during the pyrolysis of nitrogen-containing organi c chemicals. Dibenz[a,j]acridine (DBA), a member of this class, has be en shown to be a skin carcinogen in mice. We undertook studies to dete rmine the organ distribution of DBA-DNA adducts and to identify the DB A metabolites which lead to the formation of carcinogen-DNA adducts in vivo. DBA and its metabolites, trans-DBA-1,2-dihydrodiol (DBA-1,2-DHD ), trans-DBA-3,4-dihydrodiol (DBA-3,4-DHD) and trans-DBA-5,6-dihydrodi ol (DBA-5,6-DHD), were topically applied on mice. DNA was isolated usi ng enzyme-solvent extraction methods, and analyzed for carcinogen-DNA adducts using P-32-postlabelling. In skin, DBA produced two distinct a dducts(Adducts 1 and 2). The same two adducts were seen when DBA-3,4-D HD was applied. In addition, the total adduct level elicited by DBA-3, 4-DHD was twice that of the parent compound. Two adducts (Adducts 3 an d 4) were also seen in mouse skin when DBA-5,6-DHD was applied, but th ese differed chromatographically from adducts seen with DBA. However, when DBA-3,4-DHD was applied and analyzed using sensitive nuclease P-1 P-32-postlabelling, all four adducts could be detected. These results suggest that the major route of DBA activation to DNA-binding species in skin is through formation of DBA-3,4-DHD and subsequent metabolism of this compound to a bay-region diol-epoxide. However, we postulate that another activation pathway may proceed through a bis-dihydrodiol- epoxide.