Transport of DNA-adducting metabolites in mouse serum following benzo [a]pyrene administration

Metabolic activation of benzo[]pyrene (BaP) by cellular enzymesis required for DNA adduct formation. In vivo DNA adducts mightalso arise from BaP metabolites supplied via the systemic circulation,rather than from in situ activation. We determined whether electrophilicmetabolites could be detected in mouse serum 4 h after BaP dosing(i.p.) by trapping metabolites with salmon sperm DNA (ssDNA),followed by ³²P-postlabeling analysis for DNA adducts. In vitrostudies demonstrated that mouse serum sequesters BaP-7,8-diol-9,10-epoxide(BPDE) and protects it from hydrolysis. BPDE was rapidly transferredfrom serum to ssDNA or splenocytes, with adduct levels in ssDNA4- to 7-fold greater than in splenocytes. After BaP administration,mouse serum produced two adduct spots when incubated with ssDNA.The major adduct (spot 3) co-chromatographed with a BPDE adductstandard, while the minor adduct (spot 2) was unrelated to BPDE.A BPDE standard curve in control serum was developed to quantitateBPDE levels in dosed serum. These levels ranged from 13.1 to19.1 nM. Tissue DNA contained three adduct spots: spots 2 and3 appeared identical to the respective adducts arising fromdosed serum. BPDE-DNA adducts in tisues were highest in liver,lung and spleen, with kidney and stomach levels significantlylower. Levels of adduct 2 did not correlate with levels of adduct3, especially in spleen where the adduct 2/adduct 3 ratio wasvery low. In vitro studies in which splenocytes were presentedwith both adducting metabolites suggested that splenocytes preferentiallyform adduct 3. These results indicate that two of the threeBaP electrophilic metabolites responsible for cellular DNA damageare present in mouse serum. The levels of BPDE in serum maybe sufficient to account for a substantial portion of the tissueload of BPDE-DNA adducts.