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.
Iron-facilitated Organic Radical Formation from Secondary Organic Aerosols in Surrogate Lung Fluid
Jinlai Wei1, Ting Fang1, Pascale Lakey1, Manabu Shiraiwa1
1Department of Chemistry, University of California, Irvine, CA, 92697-2025, USA
Background. Reactive oxygen species (ROS) and free radicals play a central role in oxidative stress upon respiratory deposition of atmospheric particulate matter (PM). While secondary organic aerosols (SOA) and iron are major components of ambient PM, their interactions and underlying mechanisms of ROS formation are not well understood.
Methods. SOA particles were generated from •OH photooxidation of isoprene, α-terpineol and toluene using a potential aerosol mass reactor. A continuous-wave electron paramagnetic resonance (CW-EPR) spectrometer coupled with a spin-trapping technique was used for free radical quantification by mixtures of SOA and Fe ions in surrogate lung fluid. The total peroxide measurements were conducted using a modified iodometric-spectrophotometric method. A kinetic model was applied to simulate the radical formation by aqueous reactions of isoprene SOA with Fe2+.
Results. We demonstrate substantial formation of organic radicals by mixtures of iron ions and SOA in surrogate lung fluid. The molar yields of organic radicals by SOA are measured to be 0.03 – 0.5%, which are 5 – 10 times higher compared to those in water. We observe that Fe(II) enhances organic radical yields dramatically by a factor of 20 – 80, which can be attributed to Fe2+-facilitated decomposition of organic peroxides, in consistent with a positive correlation between peroxide contents and molar yields of organic radicals. Kinetic modeling, which reproduces time- and concentration-dependence of organic radical formation, indicates the role of antioxidants for mediating redox cycling of iron ions.
Conclusions. While highly reactive radicals including •OH and superoxide radicals are often assumed to cause oxidative damage, we found that they can be scavenged by lung antioxidants efficiently. These findings imply that relatively long-lived and reactive organic radicals may play a role in oxidative stress in human respiratory tract.