Effects of endogenous and exogenous reductants in lung fluid on the bioaccessible metal concentration and oxidative potential of ultrafine particles

Abstract

Health risk posed by ultrafine particles (UFPs) is potentially increased by reducing substances present in lung fluid, although knowledge of the underlying mechanisms is insufficient. Here, UFPs mainly consisting of metals and quinones were prepared. The reducing substances examined included lung endogenous and exogenous reductants. UFPs were extracted in simulated lung fluid containing reductants. Extracts were used to analyze metrics relevant to health effects, including the bioaccessible metal concentration (MeBA) and oxidative potential (OPDTT). The MeBA of Mn (974.5–9896.9 μg L−1) was higher than those of Cu (155.0–599.6 μg L−1) and Fe (79.9–500.9 μg L−1). Correspondingly, UFPs containing Mn had higher OPDTT (2.07–12.0 pmol min−1 μg−1) than those containing Cu (2.03–7.11 pmol min−1 μg−1) and Fe (1.63–5.34 pmol min−1 μg−1). Endogenous and exogenous reductants can increase MeBA and OPDTT, and the increments were generally higher for composite than pure UFPs. Positive correlations between OPDTT and MeBA of UFPs in the presence of most reductants emphasized the importance of the bioaccessible metal fraction in UFPs for inducing oxidative stress by reactive oxygen species (ROS)-generating reactions between quinones, metals, and lung reductants. Present findings provide novel insight into the toxicity and health risks of UFPs.