Different toxicity of combustion particles on human lung A549 cells: A comparison between diesel exhaust and wood smoke

Background: Combustion particles are one of the main sources of particles with a diameter of 2.5 µm or less (PM2.5) in the environment. But they are heterogeneous depending on source, combustion conditions, aging and many other factors. This study compares the toxicity of two kinds of combustion particles from different sources, namely diesel exhaust (DE) and wood smoke (WS) using a human lung cell line. Methods: Two samples of DE were collected when a diesel engine was driving in urban cycles or rural cycles. Also two batches of WS were collected in climate chamber in Aarhus University, when wood was burning with good or poor oxygen supply. Particle samples were characterized by TEM and dynamic light scattering. A549 cells were exposed to suspended particles (100 µg/mL) for 24h. Carbon black (100 µg/mL) or LPS (100 ng/mL) served as reference groups, and unstimulated cells as control group. Then reactive oxygen species (ROS) formation were evaluated by DCF assay and cytokine concentrations (IL-1β, IL-8, IL-33 and thymic stromal lymphopoietin (TSLP)) in supernatant was measured by ELISA. Results: DE did not induce significant ROS generation, while both kinds of WS induced quite high level of ROS (about 10 fold increase comparing to control). According to the result of preliminary ELISA test, all particles induced a significant increase (about 2 fold comparing to control) of IL-8 (but not IL-1β, IL-33 or TSLP) secretion, among which WS burning with good oxygen supply seemed more potent. The difference between DE and WS was less remarkable than seen in ROS. Conclusion: ROS generation and IL-8 secretion was greater in A549 cells exposed to particles from WS than from DE.