In vitro biodegradation of chrysotile fibres by alveolar macrophages and mesothelial cells in culture: comparison with a pH effect.

The modification of the chemistry of asbestos chrysotile fibres (Mg3(Si2O5)(OH)4) after their ingestion by cultured cells has been studied. Two types of cells involved in asbestos related pulmonary disease were used, rabbit alveolar macrophages (AM), recovered by bronchoalveolar lavage, and pleural mesothelial cells (PMC) obtained from the rat parietal pleura. Chemical characterisation of intracellular fibres was performed on unstained ultrathin sections by electron probe microanalysis. The results showed a progressive leaching of Mg, characterised by a time dependent decrease of Mg/Si. AM were more efficient than PMC at leaching intracellular chrysotile fibres since it took longer to obtain the same proportion of leached fibres with PMC than with AM. As in vitro Mg-leaching can be obtained by acid treatment, chrysotile fibres were incubated, either untreated or pretreated with cell membranes, at pH 4 or 7 for various times. The data show that the kinetic of leaching by AM was comparable with leaching at pH 4. The leaching by PMC was of the same order as leaching at pH 7. When membranes were adsorbed on to the fibres, a delayed leaching was observed. The results indicate that the solubilisation of chrysotile by AM could be an intraphagolysosomal event due to a pH effect. With PMC, however, it is not possible to draw this conclusion since nothing is known about the intracellular pH.