Benzo(a)pyrene:DNA adduct formation in early-passage Wistar rat embryo cell cultures: evidence for multiple pathways of activation of benzo(a)pyrene.

The benzo(a)pyrene (BaP):DNA adducts formed in cells are present at very low levels and are usually identified by reverse-phase high-performance liquid chromatography of tritium labeled BaP:deoxyribonucleoside adducts with known standards. To improve the identification of the BaP:DNA adducts formed, acid hydrolysis techniques were used to convert the BaP:deoxyribonucleoside adducts formed in Wistar rat embryo cell cultures to BaP:purine adducts and BaP:tetraols. Early passage Wistar rat embryo cell cultures were exposed to [3H]BaP. The BaP:deoxyribonucleoside adducts were isolated by immobilized boronate chromatography and reverse-phase high-performance liquid chromatography. Three adducts (MS1, MS2, MS3) bound to the immobilized boronate column indicating that they contained cis-vicinal hydroxyl groups, a configuration which would result from reaction of 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydroBaP (anti-BaPDE) with DNA. MS2 resulted from reaction of (+)-anti-BaPDE with deoxyguanosine (dGuo), for it cochromatographed with a [14C]-(+)-anti-BaPDE:dGuo marker at the deoxyribonucleoside level and after hydrolysis of MS2 and the marker to 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydroBaP (BaPDE):guanine and BaPDE:tetraol. MS1, an adduct that eluted in the same region as a (-)-anti-BaPDE:dGuo marker, was not formed by reaction of anti-BaPDE with DNA. Exposure of (-)-anti-BaPDE:dGuo to 0.1 N HCl for 24 h at 37 degrees C resulted in cleavage of the glycosidic bond to give an enantiomer that cochromatographed with the (+)-anti-BaPDE:dGuo hydrolysis product. Hydrolysis of MS1 under the same conditions yielded a product that eluted earlier than the hydrolysis product of anti-BaPDE:dGuo. Hydrolysis of MS1 at 80 degrees C under conditions which produce tetraols from BaPDE:deoxyribonucleoside adducts resulted in the formation of a product which did not elute with either 7 beta,8 alpha-dihydroxy-9 beta,10 beta-epoxy-7,8,9,10-tetrahydro-BaP (syn-BaPDE) or anti-BaPDE tetraols. MS1 was also not present in cells exposed to BaP-7,8-diol or 3-hydroxyBaP. These results demonstrated that MS1 is formed by a different mechanism of activation than a simple bay-region diol-epoxide. MS3 and its hydrolysis products had chromatographic properties identical to those of r-7,c-9,c-10,t-8-tetrahydroxy-7,8,9,10-tetrahydroBaP, a tetraol formed from syn-BaPDE. MS3 appears to result from spontaneous breakdown of a syn-BaPDE:DNA adduct to give a tetraol that contains cis-vicinal hydroxyls in the 9 and 10 positions and therefore binds to an immobilized boronate column.(ABSTRACT TRUNCATED AT 400 WORDS)