Asbestos fibers induce DNA single strand breaks in human pleural mesothelial cells in vitro

Transformed human pleural mesothelial cells (MeT-5A) were exposed to 1-4 mu g/cm(2) crocidolite asbestos fibers, to 10-100 ng/ml tumor necrosis factor alpha (TNF-alpha) for up to 48 h, and studied for the induction of DNA dam age using the comet assay. Significant but reversible increases in the mean tail moments were observed, but not in the distribution of comet tails in the histograms in the cells exposed to 1 mu g/cm(2) crocidolite for 6 h. At higher concentrations of asbestos fibers all the indices in the Comet assa y showed significant and irreversible change. All the doses of TNF-alpha. c aused marginal increase in the mean tail moments. The mean tail moments wer e highest in the cells with concurrent treatment with TNF-alpha and crocido lite. In the cells pretreated with inhibitors of antioxidant enzymes (amino triazole for catalase and buthionine sulfoximine for gamma-glutamylcysteine synthetase) asbestos fibers slightly increased oxidant-related fluorescenc e of dichlorofluorescein (DCFH) but did not cause any further increases in the mean tail moments. This study shows that asbestos fibers cause DNA sing le strand breaks in human mesothelial cells. Since the inhibition of antiox idant enzymes did not have an effect on the DNA damage caused by fibers, ot her mechanisms than reactive oxygen metabolites may be involved in the indu ction of DNA damage by mineral fibers.