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 for the 2019 HEI Annual Conference
Formation of Reactive Oxygen Species in Epithelial Lining Fluid by Particle Deposition and Comparisons with Oxidative Potential Measurements
Ting Fang, Pascale S. J. Lakey, Manabu Shiraiwa
University of California, Irvine, CA, USA
Background. 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 including soluble transition metal ions and organic compounds with lung antioxidants.
Methods. Size-segregated ambient particles were collected in Atlanta in 2016 and organic carbon and water-soluble metals were measured. A kinetic multi-layer model of surface and bulk chemistry in the lining fluid (KM-SUB-ELF) model was combined with a human respiratory tract model to estimate the concentrations and production rates of different types of ROS (hydroxyl radical [OHdot], superoxide radical [O2dot minus], hydrogen peroxide [H2O2]). The model considers ROS formation by redox reactions of metal ions and quinones as well as decomposition of organic hydroperoxides contained in secondary organic aerosols (SOA). The estimated ROS production rates were compared with oxidative potential measured with the dithiothreitol (DTT) and ascorbic acid assays.
Results. The extrathoracic region was found to have higher ROS concentrations compared to the bronchial and alveolar regions due to higher particle deposition into epithelial fluid with lower volume. Iron (Fe) and copper (Cu) ions contribute mainly to H2O2 and O2- production rates, which show strong correlation with measured oxidative potentials. In contrast, oxidative potential does not exhibit significant correlations with OH production rates, which are mainly driven by SOA decomposition and Fenton(-like) reactions of metal ions.
Conclusions. Oxidative potential is a good indicator of production of H2O2 and O2- but not OH in epithelial lining fluid. Combination of field measurements of chemical composition and oxidative potential with model simulation can provide critical insights into ROS formation by ambient particulate matter in the human respiratory tract.
Poster by Shiraiwa et al., for 2019 HEI Annual Conference