Mineral composition other than quartz is a critical determinant of the particle inflammatory potential

The aim of this study was to examine the inflammatory potential of stone quarry particles with differing mineral and metal composition and if the effects could be related to the leaching of metals from the particles and if antioxidants would reduce the cytokine release. After intratracheal instillation of rats with a type of mylonite (median size 8 microns) we found a stronger inflammatory potential of mylonite than of quartz at 20 h after treatment. In isolated rat type 2 cells and human epithelial lung cells (A549) mylonite induced a much greater release of MIP-2/IL-8 than quartz or a type of basalt and a feldspar. The mylonite particles were more potent even when compared to smaller size fractions of quartz. Thus mineral composition can be more important than size in eliciting acute inflammatory responses. The content of metals in basalt and mylonite showed minor variations with somewhat more metals present in basalt. The release of metals from the two particle types varied, but in general more metals were released from basalt than from mylonite particles. However, metal release was not related to the differences in proinflammatory effect. Antioxidants seemed to decrease the release of cytokines induced by mylonite particles, but a suppression of basal cytokine release by antioxidants was also observed, questioning the involvement of oxygen radicals in the mylonite-induced effects.