Evaluation of cytotoxic concentration-time response in A549 cells exposed to respirable alpha-quartz.

A causal pathway between quartz, silicosis and lung cancer has been postulated. The aim of our study was to assess cytotoxic effects induced in a human lung epithelial cell line (A549) by exposure to alpha-quartz. Cells were exposed to respirable alpha-quartz (SRM1878a, NIST) at 25, 50 or 100 microg ml(-1 )for 24 h and at 50 or 100 microg ml(-1) for 48 h. Cytotoxic effects were analyzed by scanning electron microscopy (SEM), apoptotic morphology analysis with Hoechst staining and lactate dehydrogenase (LDH) release assay. In cells exposed to alpha-quartz for 24 h, a concentration-dependent bleb development and in particular the localization of blebs at the cell edge at higher concentrations were observed. The blebbing phenomenon was more evident after 48 h of exposure to 50 or to 100 microg ml(-1) of alpha-quartz and large blebs were localized at the cell edge. At the same concentrations surface smoothing was also observed. Moreover the presence of holes and tears was detected at the highest concentration both at 24 and 48 h. Results of morphological analysis with Hoechst stain evidenced an increase concentration-time dependent of apoptotic cell percentage that was more marked after 48 h exposure to 100 microg ml(-1) and a prevalence of late apoptosis stage with the increase of exposure time and concentration. Cells exposed to 50 or 100 microg ml(-1) of alpha-quartz for 24 and 48 h produced a significant increase in LDH release. The concentration-time-dependent bleb induction evidenced by SEM correlates with the increase of apoptotic cells and LDH activity release, demonstrating the onset of cytotoxic effects in human lung cells exposed to alpha-quartz.