Potentials and mechanisms of genotoxicity of six pharmaceuticals frequently detected in freshwater environment.

Genotoxic potentials and the mechanisms of six pharmaceuticals, which are frequently detected in surface water worldwide, were investigated using isogenic chicken DT40 mutant cell lines. These pharmaceuticals include erythromycin, sulfamethazine, sulfathiazole, chlortetracycline, oxytetracycline, and diclofenac. The genotoxic effects of these pharmaceuticals were determined based on growth kinetics of several mutant cell lines. Genotoxic chemicals were expected to decrease the growth kinetics in at least one of the mutants more significantly than DNA-repair-proficient wild-type cells. The test pharmaceuticals sensitized the cells deficient in homologous recombination (HR) repair (RAD54⁻/⁻), nucleotide excision repair (XPA⁻/), or translesion DNA synthesis (REV3⁻/⁻), suggesting that these pharmaceuticals may induce bulky adducts covalently bound to duplex DNA, like ultraviolet (UV) light. Genotoxicity was confirmed again by analyzing chromosome aberrations (CAs) and γ-H2AX foci in both wild-type and the susceptible mutants (i.e., RAD54⁻/⁻ and XPA⁻/) following the exposure to all the test pharmaceuticals except for erythromycin. The data indicate that these pharmaceuticals induce the DNA damages that stall DNA replication, leading to chromosomal breaks as well as translesion DNA synthesis mediated mutagenesis in DT40 cells.