DNA breakage in asbestos-treated normal and transformed (TSV40) rat pleural mesothelial cells

Asbestos has been shown to induce cell cycle arrest, DNA repair and some abnormalities consistent with DNA damage but not DNA breakage. The purpose of the study was to investigate DNA breakage in asbestos-exposed rat pleural mesothelial cells (RPMC). RPMC were compared with their transformed counterparts, RPMC-TSV40 (i.e. p53-inactivated by infection with a retroviral recombinant encoding the SV40 large T antigen), as in the latter cells the cell cycle does not arrest and DNA repair is deficient due to ineffective p53-dependent cell cycle control. RPMC and RPMC-TSV40 were exposed to chrysotile and crocidolite asbestos and also to camptothecin for comparison. The presence of DNA breakage was determined using the single cell gel (Comet) assay with alkaline electrophoresis and quantified by measuring comet tail length (TL) and the percentage of total DNA in the tail and calculating tail moment (TM). We found that comets were generated by both types of asbestos in RPMC and in RPMC-TSV40 as well as by camptothecin in RPMC. On a per weight basis, chrysotile induced more abnormalities in comet parameters than did crocidolite. The comet TL and TM increased with fibre concentration, although less so with crocidolite than with chrysotile. When exposed to chrysotile at similar concentrations, RPMC consistently showed more abnormal comet parameters than did RPMC-TSV40. We concluded that asbestos causes DNA breakage and suggest that some of the DNA breakage measured was due to repair mechanisms in the normal RPMC.