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.
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| Abstract |
(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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| Authors | C Ji, L J Marnett |
| Journal | The Journal of biological chemistry (J Biol Chem) Vol. 267 Issue 25 Pg. 17842-8 (Sep 05 1992) ISSN: 0021-9258 [Print] United States |
| PMID | 1325452 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.) |
| Chemical References |
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