Cerium Oxide Nanoparticles as Antioxidant or Pro-oxidant Agents

This study was initiated to resolve the ambiguity of contradictory pro-oxidant (toxic) and antioxidant (protective) effects of cerium oxide nanoparticles (CeONPs) taking zebrafish as a model system. To carry out the investigation, different CeONPs having different surface charges (+ve/–ve) with similar shapes and sizes were synthesized at different pH conditions (acidic/basic) using different capping agents (lysine/citrate). Our findings show that the alteration of the capping agent or pH had a profound effect on the biological activity of CeONPs. CeONPs synthesized at alkaline pH showed almost no toxic effect on zebrafish larvae; on the contrary, CeONPs synthesized at acidic pH were found to be toxic, leading to mortality, morphological changes, and abnormal swimming behavior of the larvae and altered levels of reactive oxygen species (ROS), mitochondrial membrane potential, and DNA degradation in larval cells. Moreover, the level of toxicity further increased on coating the NPs with positively charged capping agents. Thus, the study will be very useful in designing CeONPs for killing or protecting biological cells as needed.