Effects of simulated pulmonary surfactant on the cytotoxicity and DNA-damaging activity of respirable quartz and kaolin

Respirable-sized quartz and kaolin dusts were pretreated with simulated pul monary surfactant dispersions of dipalmitoyl phosphatidylcholine (DPPC) in saline to model the conditioning of particles depositing in alveolar region s of the lung. DPPC-treated and untreated dusts were used to challenge lava ged rat pulmonary alveolar macrophages in vitro. Cytotoxicity was determine d over a 5-d period using both total and viable cell counts from a fluoresc ence-based viability assay. DNA damage, as an indication of genotoxicity, w as determined over a 7-d period by the single-cell gel electrophoresis assa y. Untreated quartz and kaolin both expressed a significant and potent cyto toxicity, which increased with concentration and time. DPPC-surfactant pret reatment delayed significant expression of this cytotoxicity until 3 to 5 d after challenge. Untreated quartz also caused DNA damage, which increased with concentration and time. DPPC-surfactant treatment of quartz delayed mo st DNA damage expression to 5 and 7 d. Untreated kaolin expressed weaker ac tivity for DNA damage, significant at the highest concentration through 5 d , and at the higher concentrations on d 7. Surfactant treatment delayed mos t kaolin activity for DNA damage to 7 d after challenge.