DNA single strand breaks induced by asbestos fibers in human pleural mesothelial cells in vitro

The mechanisms of the cellular effects and DNA damage caused by asbestos fi bers in human me sothelial cells are not well understood. We exposed transf ormed human pleural mesothelial cells to 1-4 mu g/cm(2) crocidolite and to 10-100 ng/ml tumor necrosis Factor alpha for up to 48 hr and studied the in duction of DNA damage using the Comet assay. As a positive control, 100 mu M H2O2 was used. The DNA single strand breaks were assessed as the mean tai l moments and as distributions of the tail DNA in the cell. The Comet assay showed significant but reversible increases in the mean tail moments, but not in the distribution of Comet tails in the histograms in cells exposed t o 1 mu g/cm(2) crocidolite for 6 hr. At higher concentrations of asbestos f ibers all the indices in the Comet assay showed significant and irreversibl e change. All the doses of TNF-alpha caused marginal increase in the mean t ail moments. The mean tail moments were highest in the cells with concurren t treatment to TNF-alpha. and crocidolite. In the cells pretreated with inh ibitors of antioxidant enzymes (aminotriazole for catalase and buthionine s ulfoximine for gamma-glutamylcysteine synthetase) asbestos fibers slightly increased oxidant-related fluorescence of dichlorofluorescein (DCFH) but di d not cause any further increases in the mean tail moments. This study show s that asbestos fibers cause DNA single strand breaks in human mesothelial cells. Since the inhibition of antioxidant enzymes did not have an effect o n the DNA damage caused by the fibers, other mechanisms than free radicals seem to be involved in the induction of DNA damage by mineral fibers. (C) 1 999 Wiley-Liss, Inc.