Biocompatible ligands modulate nanozyme activity of CeO2 nanoparticles

Abstract

The diversity of catalytic activities and antioxidant properties of cerium oxide nanoparticles (CeO₂ NPs) makes them promising materials for the theranostics of various diseases, especially those caused by disturbances in free radical homeostasis in living systems. Despite the fact that the functionalisation of nanoparticles’ surface plays a critical role in nanomedicine applications, the effect of different coatings on their enzyme-like behaviour and antioxidant properties is still poorly understood, which limits the biomedical application of CeO₂ NPs. This paper reports on the effect of low and high molecular weight biocompatible ligands on the SOD-like activity and radical scavenging properties of CeO₂ NPs, which was analysed using a phosphate-rich medium resembling a natural environment. The results obtained show that these ligands modulate the SOD-like properties of CeO₂ NPs as follows. Citrate and polysaccharide (maltodextrin and dextran) surface coatings increase the SOD-like activity of CeO₂ NPs by an average of 2.2 times, and the protein corona (γ-globulin, γ-IgG) increases this activity by an average of 1.8 times. Citrate-coated CeO₂ NPs and CeO₂ nanoparticles modified with polysaccharide molecules are more effective SOD mimetics than CeO₂@γ-IgG NPs. The SOD-like activity of phosphatidylcholine-coated CeO₂ and CeO₂@γ-IgG NPs is due to the combined action of nanoscale CeO₂ and ligands. The antioxidant activity of CeO₂ NPs after their modification with different ligands with respect to alkyl peroxyl radicals is multidirectional. Unexpectedly, citrate-, maltodextrin- and dextran-coated CeO₂ NPs are more effective antioxidants than bare CeO₂ NPs. CeO₂ NPs modified with phosphatidylcholine or γ-IgG exhibited less radical-scavenging ability than bare CeO₂ nanoparticles. Thus, common biocompatible ligands are able to regulate the biochemical activity of CeO₂ NPs.