Cerium oxide nanoparticles accelerate the decay of peroxynitrite (ONOO-)

Cerium oxide nanoparticles (CeO2 NPs) have been shown to possess a substantial oxygen storage capacity via the interchangeable surface reduction and oxidation of cerium atoms, cycling between the Ce4+ and Ce3+ redox states. It has been well established in many studies that depending on their reactivity and surface chemistry, CeO2 NPs can effectively convert both reactive oxygen species (superoxide, O-2(center dot-), and hydrogen peroxide) into more inert species and scavenge reactive nitrogen species (RNS)(nitric oxide, center dot NO), both in vitro and in vivo. Since much of damage attributed to center dot NO and O-2(center dot-) is actually the result of oxidation or nitration by peroxynitrite or its breakdown products and due to the multiple species that these nanoparticles target in vivo, it was logical to test their interaction with the highly reactive molecule peroxynitrite (ONOO-). Here, we report that CeO2 NPs significantly accelerated the decay of ONOO- by three independent methods. Additionally, our data suggest the ability of CeO2 NPs to interact with ONOO- is independent of the Ce3+/Ce4+ ratio on the surface of the CeO2 NPs. The accelerated decay was not observed when reactions were carried out in an inert gas (argon), suggesting strongly that the decay of peroxynitrite is being accelerated due to a reaction of CeNPs with the carbonate radical anion. These results suggest that one of the protective effects of CeO2 NPs during RNS is likely due to reduction in peroxynitrite or its reactive breakdown products.