Analysis of the antioxidant enzyme‐mimetic activity and neuroprotective effects of cerium oxide nanoparticles stabilized with varying ratios of citric acid and EDTA

Abstract

Cerium oxide (CeO2) nanoparticles (nanoceria or CeNPs) are potent antioxidants that are being explored as a potential therapeutic for diseases featuring oxidative stress. However, both beneficial and toxic effects of CeNPs have been reported. We hypothesize that the method of synthesis as well as the choice of stabilizers coating the particles can lead to disparate biological effects. In the present study we tested the antioxidant enzyme‐mimetic properties of a series of custom‐synthesized CeNPs that differed in the citric acid (CA) and EDTA ratio (CA:EDTA) used to stabilize them. We first spun each type of CeNP at 100,000 RPM (434,513 xg) in order to separate it into supernatant (SUP) and pellet (PEL) fractions. We then used commercially available enzymatic assay kits to assess the catalase‐ and superoxide dismutase (SOD)‐mimetic activity of each fraction. The CeNPs stabilized with only CA (CA:EDTA ratio of 100:0) exhibited significantly higher catalase‐mimetic activity in both the SUP and PEL fractions compared to the other samples. Varying the CA:EDTA ratio had opposing effects in the SOD‐mimetic activity of the SUP and PEL fractions. For example, CeNPs stabilized with only CA (CA:EDTA ratio of 100:0 ) displayed most of the SOD‐mimetic activity in the PEL. In contrast, CeNPs stabilized with only EDTA (CA:EDTA ratio of 0:100) showed highest level of SOD‐mimetic activity in the SUP. Intermediate ratios (CA:EDTA of 40:60) showed intermediate levels of SOD‐mimetic activity in the SUP and PEL fractions. 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. Interestingly, no significant neuroprotection was observed in brain slices treated with CeNPs stabilized with the extreme ratios of CA:EDTA (100:0 and 0:100). However, slices treated with CeNPs stabilized with intermediate ratios of CA:EDTA (50:50, 40:60, 30:70) showed significantly reduced ischemic cell death. When the SUP and PEL fractions of the CA:EDTA 50:50 sample were tested separately, only the slices treated with the pellet fraction showed significantly reduced cell death. These results demonstrate that CeNPs varying in the ratio of CA:EDTA used for stabilization display different enzyme‐mimetic activity. More importantly, our data suggest that CeNPs synthesized with intermediate CA:EDTA stabilization ratios demonstrate the best neuroprotection profile in ischemic brain slices and that the neuroprotective activity resides in the PEL fraction of the CeNPs.Support or Funding InformationThis work was supported by St. Lawrence University and Cerion Advanced Materials.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.