Assessment of chemically-induced DNA repair in rat tracheal epithelial cells

An assay for measuring chemically-induced DNA repair in primary cultures of rat tracheal epithelial (TE) cells has been developed and characterized. Chemical exposure may be either in vitro or in vivo. Epithelial cells were removed from the trachea by protease digestion, allowed to attach to collagen-coated glass slides, and incubated with [3H]-thymidine. DNA repair was assessed as unscheduled DNA synthesis by quantitative autoradiography. The direct acting genotoxicants methyl methanesulfonate (100 microM) and N-methyl-N'-nitro-N-nitrosoguanidine (10 microM) yielded a positive response in vitro. 1,6-Dinitropyrene (DNP) (0.05 microM) and dimethylnitrosamine (DMN) (1 mM) were also positive in vitro demonstrating that TE cells have the capacity to metabolically activate these compounds. 2-Acetylaminofluorene (AAF), aflatoxin B1 (AFB1), and benzo[a]pyrene (BP) were all negative in vitro, suggesting organ specific patterns of metabolic activation. DMN, which has been shown to induce DNA repair in TE cells following exposure by inhalation, was negative when administered by gavage. 1,6-DNP, BP and AAF did not induce DNA repair or alter the fraction of cells in S-phase when administered by gavage. Formaldehyde did not induce DNA repair or increase the fraction of cells in S-phase in TE cells following either in vivo exposure by inhalation (0.47, 2, 5.9 or 14.8 p.p.m. for 1, 3 or 5 days) or exposure of the cultured cells in vitro (100 microM). This assay provides the means to assess the genotoxic potential of environmental chemicals in the epithelial cells of the respiratory system.