In vivo DNA adduct formation by benzo(a)pyrene in mouse and rat epidermal and dermal fibroblasts after topical application of an initiating dose of benzo(a)pyrene.

Abstract

In vivo adduct formation by benzo[a]pyrene (BP) has been compared in mouse and rat epidermal keratinocytes and dermal fibroblasts after topical application of an initiating dose of carcinogen. The BP-DNA adducts were analyzed by chromatography and acid hydrolysis of BP-deoxyribonucleoside adducts to BP-tetrols. BP was dissolved in acetone and applied, at similar doses per unit area (100 nmol/mouse and 240 nmol/rat), to 50-day-old Swiss mice and 35-day-old Wistar rats. Epidermal and dermal cells were isolated twenty four hours later. Reverse-phase HPLC of BP-deoxyribonucleoside adducts demonstrated the presence of three BP-deoxyribonucleosides adducts in mouse epidermal cells and one in mouse dermal cells. An unknown product (0.13 and 0.04 pmol/mg mouse epidermal and dermal cell DNA respectively) eluted before the BP-7,10/8,9-tetrol marker, at same relative position as 9-OH-BP-DNA adduct. The major adduct formed in mouse epidermal keratinocytes and dermal fibroblasts was dGuo modified by (+)-anti-BPDE and accounted for more than 70% of the adducts. Acid hydrolysis of the individual BP-DNA adducts was used to identify the BP-DNA adducts formed in mouse epidermal and dermal cells as anti- and syn-BPDE-dGuo. Twenty four hours after topical application of BP, the total levels of modified deoxyribonucleosides and (+)-BPDE-dGuo were 3 times greater in mouse epidermal cells than in dermal cells. The ratios of anti-BPDE to syn-BPDE was 17:1 and 12:1 in mouse epidermal and dermal cells DNA, respectively. This work provides the evidence that, at an initiating dose, 3H modified deoxyribonucleosides of rat epidermal keratinocytes and dermal fibroblasts are not detectable. This may be essential for the resistance of rat skin to the carcinogenic action of benzo[a]pyrene.