In‐vitro Analysis of Catalase‐, Oxidase‐ and SOD‐mimetic Activity of Commercially Available and Custom‐synthesized Cerium Oxide Nanoparticles and Assessment of Neuroprotective Effects in a Hippocampal Brain Slice Model of Ischemia
Authors: Estevez Ana Yesenia , Stadler Brad , Erlichman Joseph S. 
Published: November 2023

Oxidative stress has been implicated in many neurological conditions, from stroke to Alzheimer's disease. Cerium oxide (CeO2) nanoparticles (nanoceria or CeNPs) are potent antioxidants that are being explored as a potential therapeutic for these and other pathologies involving oxidative stress. Nanoceria are small, capable of catalytically neutralizing multiple types of reactive oxygen species (ROS), and, due to cycling between the Ce3+ and Ce4+ oxidation states, they can continually regenerate their ROS‐neutralizing capacity depending on the redox conditions. However, both therapeutic and toxic effects of CeNPs have been reported and we hypothesize that this stems from differences in the types of CeNPs used because the method of synthesis as well as the choice of stabilizers coating the particles can lead to disparate biological effects. Understanding which physical/chemical properties correlate with biological activity is critical in order to gain insight into the conditions that promote the positive effects and to understand under what circumstances toxic properties emerge. In the present study we begin to address these issues in a systematic way. Specifically, we tested the enzyme‐mimetic properties of two commercially available (Treibacher Industries and Nanophase) and one custom‐synthesized (CeNRx) CeNP formulation using commercially available enzymatic assay kits. These particles differed in size and method of stabilization. We detected significant differences in the catalase‐ and SOD‐mimetic activities across the three formulations with the Treibacher formulation displaying low levels of catalase‐mimetic activity and undetectable levels of SOD‐mimetic activity. The Nanophase formulation displayed intermediate levels of catalase‐mimetic and low levels of SOD mimetic activity. The custom‐synthesized CeNRx formulation displayed the highest levels of both catalase and SOD‐mimetic activity of the three formulations tested. None of the nanoparticle formulations displayed significant oxidase mimetic activity, demonstrating that there is not a high level of non‐selective oxidation with these CeNPs. We then tested the effects of these CeNPs in a mouse hippocampal brain slice model of ischemia where cell death was assessed using the fluorescence indicator SYTOX green. Fluorescence levels in the slices treated with Treibacher CeNPs were not significantly different from that in untreated slices. In contrast, there was a ~23% increase in cell death in slices treated with Nanophase CeNPs, and a 34% decrease in cell death in slices treated with CeNRx CeNPs. These results demonstrate that three CeNP formulations display different enzyme‐mimetic activity in vitro which correlates with different neuroprotective profiles in brain slices. Future studies will assess further CeNP modifications in order maximize beneficial and minimize toxic effects.

Support or Funding Information

Some funding for these studies was provided by CeNRx.