Uptake of Native and Surface-Modified Quartz in Epithelial Cells and Macrophages

Abstract

Particle uptake by the pulmonary epithelium is an important mechanism of cell injury and may play an important role in particle-induced cytotoxicity. We have investigated the uptake of native and surface-modified silica in the epithelial cell line A549 and the macrophage cell line RAW 264.7. Cells were cultured in Petri dishes and incubated at 40 or 80 µg/cm2 with native, polyvinylpyridine N-oxide (PVNO)- or aluminium lactate (AL)-coated DQ12 for 2, 4 and 24 h. Native quartz was ingested by both cell types within 2 h after treatment. The phagocytosis rate for native quartz was highest in epithelial A549 cells (93% of total cells) and remained at that high level to the end of the time period. Modification of the quartz particle surfaces affected particle uptake in all monolayer cultures. The PVNO coating stimulated particle phagocytosis by the macrophages, whereas endocytosis was dramatically reduced in the lung epithelial cells. The AL coating, which changes binding of the quartz surface to membranes due to negative charges, did not affect the particle internalization process in A549 cells, but the MTT and lactate dehydrogenase assays showed reduced DQ12-induced cytotoxic effects. We suggest that the process of particle endocytosis is receptor mediated and is differently affected by coating of the particles in epithelial cells and macrophages.