Metabolism of benzo(a)pyrene and its major metabolites to ethyl acetate-soluble and water-soluble metabolites by cultured rodent trachea.

The metabolism,by short-termorgancufturesof rat and hamstertrachea, of benzo(a)pyreneand its primaryme tabolites, 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene (4,5dihydrodiol), 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene (7,8dihydrodiol), 9,1O-dihydro-9,1O-dihydroxybenzo(a)pyrene (9,1 0-dihydrodiol), and 3-hydroxybenzo(a)pyrene, to their majorethylacetate-solubleandwater-solublemetabolites has been studied.The majorethylacetate-solublemetab olites formed from (3H]benzo(a)pyrene cochromato graphedwith and had fluorescenceexcitationand emis sion spectra similar to 9,10-dihydrodiol,7,8-dihydrodiol, and benzo(a)pyren-3-yIhydrogen sulfate, with smaller amountsof metabolitescochromatographingwith 4,5-di hydrodioland monohydroxybenzo(a)pyrenesalso being formed. In contrast to this, enzymic hydrolysisof the water-soluble metabolites by Ketodase suggested that the two majorwater-solubleglucuronideconjugateswere those of the monohydroxybenzo(a)pyrenesand 4,5-dihy drodiol,with smaller amountsof glucuronideconjugates of 7,8-dihydrodioland 9,1O-dihydroxybenzo(a)pyrene but lfttle or no 9,10-dihydrodiol being formed. These results were confirmed and extended by the studiesof the furthermetabolismof the individualmetab olites. 3-Hydroxybenzo(a)pyrenewas metabolizedbothto an ethyl acetate-soluble product, which cochromato graphedwith and had fluorescenceexcitationand emis sion spectra similar to benzo(a)pyren-3-ylhydrogensul fate, and to a water-solubleglucuronideconjugate. 4,5Dihydrodiol was metabolized to an unidentified ethyl ace tate-solublemetaboliteand to a water-solubleglucuronic acid conjugate. Both 7,8-dihydrodioland, to a smaller extent, 9,10-dihydrodiol were metabolized, presumably via their respective diol-epoxides,to an ethyl acetate soluble metabolite, which cochromatographedwith and had fluorescenceexcitationand emissionspectrasimilar to 7,8,9,1O-tetrahydro-7,8,9,1O-tetrahydroxybenzo(a)py rene. However, significantdifferenceswere observed in the water-solublemetabolitesformedfromthese metabo lites. A major pathwayof 7,8-dihydrodiolmetabolismwas to its water-solubleglucuronideconjugate,whereas lfttle or no9,10-dihydrodiol wasconjugateddirectlywithuridine diphosphate-glucuronicacid. Smallamountsof 9,10-dihy I This study was supported in part by grants from the Medical Research Council and Cancer Research Campaign of Great Britain. Part of this work has been presented in abstract form (39) and at the Second International Symposium on Polynuclear Aromatic Hydrocarbons. 2 To whom requests for reprints should be addressed, at the National Institute for Research in Dairying, Shinfield, Reading RG2 9AT, England. ReceivedJanuary16,1978;acceptedJune1, 1978. drodiolwere metabolizedto the catechol9,10-dihydroxy benzo(a)pyrene,which was rapidly conjugatedwith un dine diphosphate-glucunonicacid. These results have demonstrated that the rodent trachea, an area of the respiratory tract susceptible to hydrocarbon carcinogen esis, is capableof metabolizingbenzo(a)pyneneto a wide range of oxidative and conjugatedproducts.Factorsaf fecting the balance and activitiesof these enzyme sys tems may be of critical importance in determiningthe susceptibilityof the respiratorytract to carcinogenesis.