MICROSOME-MEDIATED BIOACTIVATION OF DIBENZO[A,L]PYRENE AND IDENTIFICATION OF DNA-ADDUCTS BY P-32 POSTLABELING

Dibenzo[a,l]pyrene (DBP) is one of the most potent bacterial mutagen a nd mammary carcinogens. When DBP (50 mu M) was incubated with calf thy mus DNA (300 mu g/ml) in the presence of liver microsomes from beta-na phthoflavone (beta-NF)- or Aroclor 1254-treated rats, at least eight a dduct spots were detected as analyzed by nuclease P1-enhanced P-32-pos tlabeling assay. DNA adduction was enhanced by nearly 20- and 60-fold with beta-NF- and Aroclor 1254-induced microsomes, respectively, as co mpared with uninduced microsomes, suggesting a possible involvement of CYP1A family in DBP activation. Inclusion of the selective P4501A1 in hibitor, alpha-naphthoflavone (50 mu M) in the activation reaction alm ost completely (>98 %) abolished adduct formation further supporting i nvolvement of P4501A in DBP activation, Analysis of DNA and 2'-deoxynu cleosides 3'-mononucleotide reacted with anti- and syn-DBP-11,12-diol- 13,14-epoxides (DBPDEs) and co-chromatography analyses in multiple sol vents showed that the microsomal DBP-DNA adducts were derived by inter action of both anti-and syn-DBPDEs with adenine and guanine in DNA in the following order: anti-DBPDE-dA similar to syn-DBPDE-dG much greate r than anti-DBPDE-dG similar to syn-DBPDE-dA, It is concluded that (i) most or all DBP adducts were P4501A-mediated; (ii) both the anti- and syn-stereoisomers were involved in the DNA adduct formation; and (iii ) both adenine and guanine in the DNA contributed equally to the forma tion of the major and minor adducts.