Fiber-Induced Hydroxyl Radical Formation and DNA Damage

Summary

We have measured the phagosomal pH (ppH) in tracheal epithelial cells, alveolar type II cells, and mesothelial cells. The ppH was measured using a flow cytometric procedure employing fluorescein-isothiocyanate-labeled, amorphous silica particles. The ppH for these cells ranged from 7.0 to 7.6, with no statistically significant difference in ppH between the cell types. We also compared the ability of a series of fibers to initiate hydroxyl radical formation in an acellular system at pH 4.0, an acidic pH similar to the reported ppH for rat alveolar macrophages, and at pH 7.0, the ppH determined in this study for epithelial and mesothelial cells. In general, for those fibers capable of initiating hydroxyl radical formation, the capacity of the fiber to generate hydroxyl radicals was dependent on the pH. Most of the fibers tested were more effective at initiating hydroxyl radicals at pH 7.0 than at pH 4.0. These results suggest that the ability of fibers to induce varying amounts of injury to different cell types may be due to differing pH effects within cellular regions. The capacity of crocidolite to induce DNA damage was determined by measuring p53 expression. Crocidolite induced expression of p53 in cultured lung epithelial cells. The induced p53 expression was extinguished by salicylic acid suggesting that hydroxyl radicals play a role in crocidolite-induced DNA damage.