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Formation of reactive oxygen species by organic aerosols and transition metals in epithelial lining fluid

Principal Investigator: 

University of California, Irvine

This New Investigator Award 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. 

Funded under
In review

Abstract for HEI Annual Conference 2022

Cellular Superoxide Release Overwhelms Chemistry upon Lung Deposition of Particulate Matter

Ting Fang1, Yu-Kai Huang2, Jinlai Wei1, Jessica E. Monterrosa Mena3, Pascale S. J. Lakey1, Michael T. Kleinman3, Michelle A. Digman2, Manabu Shiraiwa1

1Department of Chemistry, University of California, Irvine, CA, USA; 2Department of Biomedical Engineering, University of California, Irvine, CA, USA; 3Division of Occupational and Environmental Medicine, University of California, Irvine, CA, USA

Background. Particulate matter associated with air pollution causes respiratory and cardiovascular diseases, leading to several millions of premature deaths annually; mechanistic pathways involving physiological changes and tissue injury driven by free radicals that cause oxidative stress are key factors. Deposition of particulate matter in the respiratory tract causes the formation of reactive oxygen species (ROS) by chemical and cellular processes, but their relative contributions are hardly quantified and their link to oxidative stress remains uncertain.

Methods. Here we quantify cellular and chemical superoxide generation by representative anthropogenic and biogenic particulate matter components. We apply a chemiluminescence assay combined with electron paramagnetic resonance spectroscopy as well as kinetic modeling to quantify chemical and cellular superoxide generation. RAW 264.7 macrophages, a common model for alveolar macrophages, are exposed to 9,10-phenanthrenequinone and isoprene-derived SOA. In addition, we apply state-of-the-art cellular imaging techniques including the phasor approach to fluorescence lifetime imaging microscopy and third harmonic generation microscopy to investigate the cellular mechanism for superoxide release and its impacts on lipids and membrane fluidity.

Results. We show that atmospherically-relevant doses of quinones and isoprene-derived secondary organic aerosols activate NADPH oxidase in macrophages to release massive amounts of superoxide via respiratory burst, overwhelming the superoxide formation by aqueous redox reactions in epithelial lining fluid. While higher and longer exposures trigger cellular antioxidant response elements, the released ROS cause lipid peroxidation to increase cell membrane fluidity, inducing oxidative damage and stress.

Conclusions. The mechanistic and quantitative understandings obtained in this study provide a basis for further elucidation of adverse aerosol health effects and oxidative stress by fine particulate matter.