Formation and repair of benzo[a]pyrene—DNA adducts in cultured hamster tracheal epithelium determined by 32P-postlabeling analysis and unscheduled DNA synthesis

Hamster tracheal organ cultures were used to investigate the relationship between DNA adduct formation measured directly by the 32P-postlabeling assay, and the DNA damage measured indirectly by the unscheduled DNA synthesis (UDS) assay. Hamster tracheas were treated with three concentrations of benzo[a]pyrene (B[a]P) for 2 days. Postlabeling and UDS assays were also carried out a few days after removal of the B[a]P. Furthermore, the types of B[a]P-DNA adducts formed in the in vitro organ culture were qualitatively compared with those formed in vivo after intratracheal intubation of B[a]P attached to Fe2O3 particles. In vivo only one adduct was detected by 32P-postlabeling. This adduct cochromatographed with the trans-addition produce of dG and (+)-anti-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE). In vitro, a clear B[a]P-DNA adduct pattern was also found with the 32P-postlabeling assay. Four different adducts were found. The main adduct spot migrated to the same position on the thin-layer chromatogram as the in vivo adduct. B[a]P-DNA adduct formation was both time- and dose-dependent. During the first day after removal of B[a]P the adduct levels still increased, thereafter they decreased at all B[a]P concentrations. A time- and dose-dependent increase in UDS was observed in the tracheal epithelial cells treated with B[a]P in vitro. After removal of the B[a]P, UDS decreased immediately, in contrast to the formation of DNA adducts. The results of the present study show that B[a]P induces time- and dose-dependently both DNA adducts and UDS in hamster tracheal organ culture. Moreover, the main DNA adduct formed in vitro, dG-(+)-anti-BPDE, was the same as that found in vivo.