Prominent Contribution of Hydrogen Peroxide to Intracellular Reactive Oxygen Species Generated upon Exposure to Naphthalene Secondary Organic Aerosols

Exposure to particulate matter (PM) can induce the production of reactive oxygen and nitrogen species (ROS/RNS) in biological systems. Secondary organic aerosols (SOA) make up a substantial fraction of ambient fine PM. In this study, the contribution of hydrogen peroxide (H₂O₂) to intracellular ROS/RNS production upon exposure to naphthalene SOA was investigated using an oxidative stress indicator (carboxy-H₂DCFDA) and a H₂O₂ scavenger (catalase). With the addition of catalase, the ROS/RNS response was substantially suppressed, indicating that H₂O₂ was the main type of ROS contributing to the measured ROS/RNS. We also found that H₂O₂ in naphthalene SOA extracts (H₂O_2[SOA]) could rapidly diffuse into cells and contribute to intracellular ROS/RNS, while another contribution was from H₂O₂ produced by cells (H₂O_2[cell]). The contributions from H₂O_2[SOA] and H₂O_2[cell] were both determined. The results showed that H₂O_2[SOA] (3.16–4.20 ng/μg) was substantially higher than H₂O_2[cell] (1.03–1.27 ng/μg), assuming the production of H₂O₂ by cells was constant over time. These findings demonstrated that H₂O₂ was the main ROS accumulated in cells upon exposure to naphthalene SOA and that the diffusion of H₂O_2[SOA] into the cells could represent one of the main pathways contributing to intracellular ROS/RNS.