Oxygen radical-dependent epoxidation of (7S,8S)-dihydroxy-7,8-dihydrobenzo[a]pyrene in mouse skin in vivo. Stimulation by phorbol esters and inhibition by antiinflammatory steroids.
(7S,8S)--Dihydroxy--7,8--dihydrobenzo[a]pyrene ((+)-BP-7,8-diol) is epoxidized to (7S,8R)-dihydroxy-(9S,10R)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene ((+)-syn-BPDE) by cytochrome P-450 isoenzymes and to (7S,8R)-dihydroxy-(9R,10S)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene ((-)-anti-BPDE) by peroxyl free radicals. 32P postlabeling analysis of the diastereomeric BPDE-DNA adducts was used to investigate the pathways of (+)-BP-7,8-diol oxidation in mouse skin in vivo. The pattern of deoxynucleoside 3',5'-bisphosphate adducts in epidermal scrapings from female CD-1 mice indicated that cytochrome P-450 was the major oxidant. Similar results were obtained when the tumor-promoting phorbol ester tetradecanoylphorbolacetate (TPA) was coadministered with (+)-BP-7,8-diol. However, when animals were pretreated with TPA 24 h before coadministration of TPA and (+)-BP-7,8-diol, the pattern of BPDE-DNA adducts indicated that peroxyl radicals made a major contribution to (+)-BP-7,8-diol epoxidation. Peroxyl radical-dependent epoxidation was maximal when the time between the two TPA administrations was 24-72 h. No increase in (-)-anti-BPDE-DNA was observed when the non-tumor-promoting phorbol ester 4-O-methyl-TPA was substituted for TPA. The calcium ionophore A23187 stimulated peroxyl radical generation when substituted for the first, but not the second, TPA treatment. The antiinflammatory steroid fluocinolone acetonide inhibited (-)-anti-BPDE-DNA adduct formation when coadministered with the first but not the second TPA treatment. These findings demonstrate the existence of two independent pathways of metabolic activation of (+)-BP-7,8-diol in mouse epidermis, one dependent on cytochrome P-450 and the other dependent on peroxyl free radicals. The results also suggest that repetitive topical administration of tumor-promoting phorbol esters remodels epidermal metabolism leading to a significant increase in free radical generation.
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A. B. Hancock, Jr. Memorial Laboratory for Cancer Research, Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146.
Marnett
L J
LJ
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001711:Biotransformation; D002273:Carcinogens / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004247:DNA / Q000302:isolation & purification / Q000378:metabolism*; D004224:Diterpenes; D004305:Dose-Response Relationship, Drug; D005260:Female; D005446:Fluocinolone Acetonide / Q000494:pharmacology*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000494:pharmacology*; D012867:Skin / Q000187:drug effects / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D002273:Carcinogens; D004224:Diterpenes; D007527:Isoenzymes; D013729:Terpenes; D005446:Fluocinolone Acetonide; C011309:mezerein; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D000255:Adenosine Triphosphate; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D009195:Peroxidase; D013755:Tetradecanoylphorbol Acetate