Investigations of DNA Damage Produced by Asbestos Fibers in Rat Pleural Mesothelial Cells

Asbestos fibers have long been considered nongenotoxic because of the absence of point asbestos-treated cells mutations in several assays. More recently, some studies have demonstrated that various kinds of DNA damage were observed in asbestos-treated cells, namely, base hydroxylation, DNA adducts, and DNA breaks. The occurrence of DNA breakage has been mostly suggested by indirect methods. We investigated DNA damage produced by Rhodesian chrysotile fibers in a model of normal rat pleural mesothelial cells (RPMC) developed in our laboratory, by different approaches. DNA breakage and repair of DNA damage were evidenced by the enhancement of the activity of poly(ADP)ribose polymerase (PARP) and of unscheduled DNA synthesis, and were suggested by cell cycle arrest in asbestos-exposed RPMC. In growing cells, a cell cycle arrest was observed at the G1-S transition. DNA breakage was also demonstrated by the formation of comets in single-cell gel electrophoresis (SCGE) assay. The results showed that comets were generated by asbestos, as assessed by the significant increase in mean tail length and mean tail moment after exposure to asbestos. In RPMC-TSV40 (i.e., RPMC in which the protein was p53 inactivated by infection with a retroviral recombinant encoding the large T antigen of the SV40 virus), the comet parameters were moderately enhanced. Regarding previous results of an impairment of DNA repair in RPMC-TSV40, the SCGE results suggest that chrysotile caused DNA breakage in both RPMC and RPMC-TSV40. Moreover, these findings lead to the hypothesis that DNA repair was impaired in RPMC-TSV40.