Inter-comparison of oxidative potential metrics for airborne particles identifies differences between acellular chemical assays

Abstract

Oxidative potential (OP) has been identified as an important factor underlying the health effects of airborne particulate matter (PM). OP denotes the ability of PM to deplete antioxidants and to form reactive oxygen species (ROS) in the lung. OP can be quantified using a variety of chemical assays and analytical techniques. Despite the widespread use of various OP metrics, there is no consensus or comprehensive inter-laboratory assessment on how these assays compare. In this work for the first time, we compared 11 OP indicators from acellular assays using standard reference material of urban PM. The OP indicators included ascorbic acid, glutathione, glutathione disulfide, cysteine, cystine, dithiothreitol, H2O2, •OH, O2•-, and empirical and theoretical redox potential of simulated lung lining fluid (SLF). The indicators showed first-order kinetics at low PM concentration (25 μg mL−1), whereas the kinetics were non-linear at higher PM concentrations. The indicators demonstrated mainly linear dose-response relationships at PM concentrations 25–100 μg mL−1, following similar trends with water-soluble transition metals, but they were not always proportional to PM concentrations, and demonstrated substantial differences in their sensitivities to PM. The results indicate the importance of using reduced reaction time for reliable OP quantification due to non-linearity in assay responses at high PM concentrations. This work shows that the choice of molecular probes and measurement techniques must be carefully considered when planning studies on OP of ambient air and should importantly include the association of OP metrics with health outcomes.