This New Investigator Study investigates the mechanisms of formation of reactive oxygen species (ROS) by different types of secondary organic aerosols (SOAs), distinguishing between ROS formed by pollutants entering lung lining fluid (chemically) and by macrophages producing ROS as an inflammatory response (biologically). He will measure concentrations of ROS in epithelial lung lining fluid in macrophages exposed to SOA produced in a reaction chamber, with or without transition metals, using electron paramagnetic resonance spectroscopy with a spin trapping technique or a chemiluminescence assay.
Abstract of the research proposal
Reactive oxygen species (ROS) play a central role in adverse health effects and oxidative stress of atmospheric air particulate matter. Respiratory particle deposition can lead to the release of ROS in the epithelial lining fluid due to catalytic reactions cycles of redox-active components with lung antioxidants. Secondary organic aerosols, a dominant fraction of fine particulate matter, may generate ROS including hydrogen peroxide and OH radicals in the epithelial lining fluid, which may be enhanced in the presence of transition metal ions due to Fenton-like reactions. However, the formation of other types of ROS including superoxide and organic radicals, which may play an important role in oxidative stress, has been hardly studied and quantified. It is urgent to conduct further studies to fully unravel kinetics and molecular mechanism of formation of ROS by different types of anthropogenic and biogenic SOA formed in various oxidation levels. Alveolar macrophages are the first cellular responders to inhaled air pollutants, which can release ROS biologically after phagocytosis of inhaled particles. Thus, ROS can be released both chemically and biologically upon particle deposition, but the relative importance of biological and chemical ROS is poorly understood and yet to be quantified. Specific aims of this proposal
are: 1) Elucidating the chemical mechanism and quantifying the formation kinetics of ROS (H2O2, OH, O2-, and organic radicals) in the epithelial lining fluid by redox-active multi-pollutants including secondary organic aerosols and transition metals; 2) Quantifying the relative importance of chemical ROS generated by redox reactions and biological ROS released by macrophages in the epithelial lining fluid.
SOA particles will be generated using a reaction chamber and ambient particles will be collected using the high flow impactor. Particles will be extracted into surrogate epithelial lining fluid containing lung antioxidants. To mimic co-respiratory deposition of SOA and transition metals and to investigate the effects of transition metals on ROS formation by SOA in the ELF, different concentrations of Fe2+ and Cu+ will be added. The generated radical forms of ROS will be quantified using electron paramagnetic resonance (EPR) spectroscopy with a spin trapping technique and H2O2 will be measured using the fluorimetric assay. Oxidative potential and redox activity will also be quantified using the dithiothreitol (DTT) assay. To quantify ROS release by macrophages, rat primary alveolar macrophages will be exposed to particles and the generated ROS will be measured using chemiluminescence and EPR with a spin probing technique. The kinetic multi-layer model for surface and bulk chemistry in the epithelial lining fluid (KM-SUB-ELF) will be applied for analysis and interpretation of experimental data to derive kinetic parameters such as reaction rate coefficients. The model will also be used for estimation of chemical ROS concentrations in the ELF upon size-dependent particle respiratory deposition, which will be compared with biological ROS released by macrophages. The results and implications of the proposed study should be useful for air quality regulators for the design of efficient control strategies against adverse aerosol health effects. The novelty of this proposal is to quantify and compare chemical and biological ROS production by multi-pollutants (e.g., SOA, transition metals) in epithelial lining fluid by experiments and kinetic modeling to advance fundamental understanding of formation and multiphase processes of ROS for a quantitative assessment of aerosol effects on oxidative stress.