Tire particles of different sizes induce a proinflammatory response of varying intensity in lung cells

Pollution from road traffic contributes significantly to air pollution through pollutants from exhaust emissions (gases and particles) and non-exhaust emissions (tire wear particles, brake wear particles and the resuspension of road dust). This research examined the hazard of tire particles (TP) and in particular evaluated the effect of TP size on lung macrophages. TP were obtained by cryogenic grinding of a tire and subsequent sieving to obtain four groups of particles (TP70, TP30, TP15, TP5) of different sizes with average diameters of 107 µm, 55 µm, 22 µm, and 6 µm, respectively. A complete physicochemical characterization was performed to determine the size distribution, chemical composition and morphology of these particles. We then investigated the proinflammatory response, oxidative stress and cytotoxicity induced in RAW264.7 cells exposed to four different TP concentrations for 24 h. TP had no direct effect on cytotoxicity, nor did they increase reactive oxygen species (ROS) production in the cells. However, TP induced a significant and size-dependent proinflammatory effect, which was particularly pronounced with small particles. Moreover, this effect was concentration-dependent.