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

Abstract

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 [ ³ H]-thymidine. DNA repair was assessed as unscheduled DNA synthesis by quantitative autoradiography. The direct acting genotoxicants methyl methanesulfonate (100 μM) and N-methyl-N'-nitro-N-nitrosoguanidine (10 μM) yielded a positive response in vitro . 1, 6-Dinitropyrene (DNP) (0.05 μM) 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 B ₁ (AFB ₁ ), 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 μM). This assay provides the means to assess the genotoxic potential of environmental chemicals in the epithelial cells of the respiratory system.