(612d) Bioavailable Metal Speciation and Surface Redox Capacity in Toxicity of Nanoparticles

Metal-mediated oxidative stress is an important mechanism of nanoparticle toxicity. Metal mediated oxidative stress is highly dependent on bioavailable metal speciation. However, currently the bioavailable metal speciation is not adequately characterized in toxicology of nanoparticles. In addition, the effect of surface redox capacity of elemental carbon nanometerials on bioavailable metal speciation is yet to be understood.

The objective of this study was to test the hypothesis that bioavailable iron speciation is a key factor of iron-mediated oxidative stress, and that carbon black nanoparticles can affect the bioavailable iron speciation through surface redox capacity. Cultured A549 human lung epithelial cells were exposed to (1) carbon black nanoparticles alone, (2) Fe2O3 nanoparticles alone, and (3) both types of particles simultaneously. Protein oxidation, lipid peroxidation, and cellular cell viability were measured after 25 hours of exposure. The reductive capacity of carbon black nanoparticles towards Fe3+ ions was measured separately in a cell-free assay.

Cells co-exposed to both carbon black and Fe2O3 particles showed significant oxidative stress. In the cell-free assay, significant reduction of Fe3+ ions by soot nanoparticle was found. On the other hand, surface oxidized carbon black particles did not show significant redox capacity, and co-exposure to Fe2O3 and oxidized carbon black particles did not generate significant oxidative stress. The results suggest that bioavailable metal speciation is an important parameter for assessing toxicity of nanoparticles, and that surface redox capacity should be characterized because it may play an important role in nanoparticle toxicity.