Superoxide Release from Macrophages upon Exposure to Secondary Organic Aerosols, Biomass, and Plastic Burning...

Oxidative stress induced by reactive oxygen species (ROS) is a key process for adverse health effects upon respiratory deposition of particulate matter (PM). Alveolar macrophages can release superoxide upon phagocytosis of PM through a process called the respiratory burst. The release of cellular ROS should depend on both PM composition and dose, but the dose-response relationship for various types of PM remains poorly quantified. Here we measure cellular superoxide production by macrophage cells exposed to secondary organic aerosols (SOA) derived from oxidation of limonene, toluene, and naphthalene, as well as PM generated from biomass burning and flaming combustion of five different types of plastics. We quantify cellular superoxide production over the span of 4 h after an initial exposure of macrophages to PM suspensions by applying a chemiluminescence assay combined with electron paramagnetic resonance. We then define the activation threshold as the dose at which cells exhibit a clear increase in superoxide production. Limonene SOA is found to induce the largest amount of superoxide release (∼32 μM) but has the largest activation threshold of 300 μg mL^-1. Naphthalene and toluene SOA show smaller enhancement of superoxide production (∼2.5-7 μM) but have lower activation thresholds from 0.02 to 0.1 μg mL^-1. Biomass burning PM does not show a clear activation threshold. Plastic burning PM shows a varied response depending on the type of plastic, with PM derived from poly-(ethylene terephthalate) (PET) having the highest superoxide production (∼12 μM). The activation thresholds for polystyrene (PS), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) burning PM are very low (∼0.01 μg mL^-1), while those for poly-(vinyl chloride) (PVC) and PET burning PM are substantially higher (50-100 μg mL^-1). Our findings highlight the importance of employing dose-response relationships and superoxide activation thresholds, rather than single-dose comparisons, to evaluate and compare the oxidative stress potential of different PMs more accurately.