Quenching effect of cerium oxide nanoparticles on singlet oxygen: validation of the potential for reaction with multiple reactive oxygen species.

Here we studied cerium oxide nanoparticles (nanoceria) as an agent for the future treatment of oxidative damage by validating and evaluating its scavenging activity towards reactive oxygen species (ROS) in vitro. Nanoceria has been shown to mimic the activities of superoxide dismutase and catalase, degrading superoxide (O₂^•-) and hydrogen peroxide (H₂O₂). We examined the antioxidative activity of nanoceria, focusing on its ability to quench singlet oxygen (¹O₂) in an aqueous solution. Electron paramagnetic resonance (EPR) was used to determine the rates of second-order reactions between nanoceria and three ROS (¹O₂, O₂^•-, and H₂O₂) in aqueous solution, and its antioxidative abilities were demonstrated. Nanoceria shows a wide range of ultraviolet-light absorption bands and thus ¹O₂ was produced directly in a nanoceria suspension using high-frequency ultrasound. The quenching or scavenging abilities of nanoceria for ¹O₂ and hypoxanthine-xanthine oxidase reaction-derived O₂^•- were examined by EPR spin-trapping methods, and the consumption of H₂O₂ was estimated by the EPR oximetry method. Our results indicated that nanoceria interact not only with two previously reported ROS but also with ¹O₂. Nanoceria were shown to degrade O₂^•- and H₂O₂, and their ability to quench ¹O₂ may be one mechanism by which they protect against oxidative damage such as inflammation.