Silica-induced cytokine release from A549 cells: importance of surface area versus size

Physical and chemical properties such as structure, composition and surface reactivity determine the biological activity of mineral particles. Long-te rm exposure to crystalline silica is known to cause persistent pulmonary in flammation leading to adverse health effects. There is less information abo ut the potential health effects of amorphous (noncrystalline) silica. In th is study, the inflammatory and cytotoxic potency of crystalline and amorpho us silica in relation to particle size and surface area was assessed. Human epithelial lung cells (A549) were exposed to different size fractions of q uartz (aerodynamic diameter 0.5, 2 and 10 mum) and amorphous silica (diamet er 0.3 mum). All particles induced increased release of the proinflammatory cytokines interleukin (IL)-6 and IL-8. When cells were exposed to equal ma sses of quartz, the smallest size fraction was the most potent. These diffe rences, however, disappeared when cytokine release was related to equal sur face areas. When amorphous silica and quartz were compared, the amorphous s ilica was most potent to induce IL-6 regardless of how exposure was express ed, whereas the smallest size fraction of quartz was the most potent induce r of IL-8. Thus, the surface area seems to be the critical determinant when potency of different sizes of quartz is compared.