76 Combined Exposure to Road Wear Particles and Diesel Exhaust Particles Induces Enhanced Pro-Inflammatory Responses in Cells of the Human Airways

Ambient particulate matter (PM) is one of the leading environmental mortality risk factors worldwide. PM is not a single entity but consists of a complex and variable mixture of particles from multiple sources. Nevertheless, there is a paucity of experimental studies assessing the potential combinatory effects of different types of particles, and most focus on the effects of individual PM components or mixed PM samples. In the present study, the pro-inflammatory effects of combined exposure to road wear particles and diesel exhaust particles (DEP), two important constituents of traffic-derived PM, were assessed in vitro. Human bronchial epithelial cells (HBEC3-KT) and differentiated THP-1 macrophage-like cells were exposed to road wear particles and two different samples of DEP under submerged conditions, both alone and in combination. Particle-induced release of pro-inflammatory cytokines (CXCL8 and IL-1β) was measured by enzyme-linked immunosorbent assay. The results show that combined exposure to road wear particles and DEP induced enhanced release of pro-inflammatory cytokines compared with the effects of the individual particle samples. The combinatory effects appeared to depend on properties of the DEP samples and also differed between the HBEC3-KT cells and THP-1 macrophage-like cells. This study shows that the effects of combined exposure to different types of particles may surpass the effects anticipated by the effects of the individual particulates. These combinatory effects between types of particles could have implications when assessing measures to reduce PM-induced health effects.