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

Department of Environmental Medicine, National Institute of Public Health, P.O. Box 4404, Torshov, N-0403 Oslo, Norway

P E Schwarzel

National Institute of Public Health, Oslo, Norway

B V Johansen

National Institute of Public Health, Oslo, Norway; University of Oslo, Oslo, Norway

T Myran

SINTEF, University of Trondheim, Trondheim, Norway

N Uthus

Franzefoss Bruk A/S, Rud, Norway

M Refsnes

National Institute of Public Health, Oslo, Norway

Physical and chemical properties such as structure, composition and surface reactivity determine the biological activity of mineral particles. Long-term exposureto crystalline silica is known to cause persistent pulmonary inflammation leading to adverse health effects. There is less information about the potential health effects of amorphous (noncrystal-line) silica. In this study, the inflammatory and cytotoxic potency of crystalline and amorphous silica in relation to particle size and surface area was assessed. Human epithelial lung cells (A549) were exposed to different size fractions of quartz (aerodynamic diameter 0.5,2 and 10 sm) and amorphous silica (diameter 0.3 pm). All particles induced increased release ofthe proinflammatory cytokines interleukin (IL)-6 and IL-8. When cells were exposed to equal masses of quartz, the smallest size fraction was the most potent. These differences, however, disappeared when cytokine release was related to equal surface areas. When amorphous silica and quartz were compared, the amorphoussilicawas mostpotentto induce IL-6 regardless of how exposure was expressed, whereas the smallest size fraction of quartz was the most potent inducer of IL-8. Thus, the surface area seems to be the critical determinant when potency of different sizes of quartz is compared.

Key Words: Silica • size • surface area • cytokines • A549 cells

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