Covalent DNA Adducts Formed in Mouse Epidermis from Dibenz[a,j]anthracene: Evidence for the Formation of Polar Adducts

The formation of deoxyribonucleoside adducts in mouse epidermis has been examined following topical application of [3H]dibenz[a,j]anthracene (DB[a,j]A) or by 32P-postlabeling following topical application of unlabeled DB[a,j]A, DB[a,j]A trans-3,4-diol or the anti- or syn-3,4-diol 1,2-epoxides. A single topical application of [3H]DB[a,j]A at a dose of 400 nmol per mouse led to the formation of 11 detectable covalent DNA adducts. Seven of these DNA adducts were tentatively identified based on cochromatography with marker adducts using high-pressure liquid chromatography (HPLC). The presence of both deoxyguanosine (dGuo) as well as deoxyadenosine (dAdo) adducts formed from bay-region anti- and syn-3,4-diol 1,2-epoxides of DB[a,j]A was revealed. The major bay-region diol epoxide DNA adduct formed in mouse epidermis following topical application of [3H]DB[a,j]A was tentatively identified as the (4R,3S)-diol (2S,1R)-epoxide bound through trans addition of the exocyclic amino group of dGuo, although substantial amounts of the corresponding dAdo adduct were also detected. In addition, a K-region 5,6-oxide-dAdo adduct was tentatively identified in HPLC chromatograms based on cochromatography with an authentic marker adduct. 32P-Postlabeling analysis of DB[a,j]A-DNA adducts formed in mouse epidermis after topical application of unlabeled compound confirmed the presence of bay-region diol epoxide DNA adducts similar to those observed after application of [3H]DB[a,j]A. However, 32P-postlabeling analysis also revealed the presence of more polar covalent DNA adducts in epidermal DNA samples from DB[a,j]A-treated mice. These more polar DNA adducts represented a significant proportion of the 32P-labeled material recovered in HPLC chromatograms. While the exact nature of these adducts remains unknown at present, they had retention times identical to polar DNA adducts formed following topical application of DB[a,j]A trans-3,4-diol and may represent bis-dihydrodiol epoxide DNA adducts. The present results indicate that a rather broad spectrum of DNA adducts arises following topical application of DB[a,j]A to mouse epidermis.