Development of an antioxidant assay to study oxidative potential of airborne particulate matter

Abstract

Abstract. Oxidative potential is a measure of redox activity of airborne\nparticulate matter (PM) and is often used as a surrogate to estimate one\nform of PM toxicity. The evaluation of oxidative potential in\na physiologically relevant environment is always challenging. In this work, we\ndeveloped a chromatographic method, employing an ultra-high-performance\nliquid chromatograph coupled to a triple–quadruple mass spectrometer, to\ndetermine the oxidative potential of PM from different sources. To this\npurpose, we measured the PM-induced oxidation of glutathione, cysteine, and\nascorbic acid, and formation of glutathione disulfide and cystine, following\nPM addition to simulated epithelial lining fluids, which, in addition to the\nantioxidants, contained inorganic salts, a phospholipid, and proteins. The\nnew method showed high precision and, when applied to standard reference PM,\nthe oxidative potential was found to increase with the reaction time and PM\nconcentration in the lung fluid. The antioxidant depletion rates were\nconsiderably higher than the rates found with the conventional\ndithiothreitol assay, indicating the higher sensitivity of the new method.\nThe presence of the lung fluid inorganic species increased the oxidative\npotential determined through glutathione and cysteine, but showed an\nopposite effect with ascorbic acid, whereas the presence of proteins\nresulted in a moderate decrease in the oxidative potential. In the presence\nof PM 2.5 , glutathione and cysteine demonstrated similar depletion\npatterns, which were noticeably different from that of ascorbic acid,\nsuggesting that cysteine could be used as an alternative to glutathione for\nprobing oxidative potential.