MODULATION OF OXIDANT FORMATION IN MOUSE SKIN IN-VIVO BY TUMOR-PROMOTING PHORBOL ESTERS

The pathways of oxidant generation in mouse epidermis were investigate d by P-32-postlabeling analysis of diastereomeric DNA adducts derived from oxidation of (7S,8S)-dihydroxy-7,8-dihydrobenzo(a)pyrene ((+)-BP- 7,8-diol). The pattern of deoxynucleoside-3'-5'-bis-phosphate adducts in epidermal scrapings from female CD-1 mice indicated that cytochrome P-450 was the major oxidant. When animals were pretreated with the tu mor-promoting phorbol ester, tetradecanoyl phorbol acetate (TPA), 24 h before coadministration of TPA and (+)-BP-7,8-diol, the pattern of DN A adducts indicated that peroxyl radicals made a major contribution to (+)-BP-7,8-diol epoxidation. Peroxyl radical-dependent epoxidation wa s maximal when the time between the 2 TPA administrations was 24-72 h. No increase in radical-derived adducts was observed when the non-tumo r-promoting phorbol ester 4-O-methyl-TPA was substituted for TPA. The calcium ionophore A23187 stimulated radical generation when substitute d for the first, but not the second, TPA treatment. The antiinflammato ry steroid fluocinolone acetonide inhibited (-)-anti-BPDE-DNA adduct f ormation when coadministered with the first but not the second TPA tre atment. In contrast, all-trans-retinoic acid inhibited (-)-anti-BPDE-D NA adduct formation when coadministered with the second but not the fi rst TPA treatment. These findings demonstrate that tumor promoting pho rbol esters stimulate oxygen radical generation in mouse skin and that radical generation is blocked by inhibitors of tumor promotion.