Nanoceria exhibit redox state-dependent catalase mimetic activity

Abstract

In this study we have found that cerium oxide nanoparticles exhibit catalase mimetic activity. Surprisingly, the catalase mimetic activity correlates with a reduced level of cerium in the +3 state, in contrast to the relationship between surface charge and superoxide scavenging properties.

Fig. 1

Nanoceria exhibit catalase mimetic activity at physiologically relevant hydrogen peroxide concentrations in a redox-state dependent manner. Hydrogen peroxide levels were quantified using the Amplex Red assay. Ceria preparation A (open triangle, 100 μM, filled circles, 300 μM), with a higher +3/+4 redox state ratio, exhibits no catalase mimetic activity at this concentration of hydrogen peroxide. Preparation B (filled squares, 100 μM and open circles, 300 μM), with relatively low +3/+4 redox-state ratios, exhibits substantial catalase mimetic activity.

Fig. 2

Nanoceria with higher levels of cerium in the +3 oxidative state are inefficient catalase mimetics. Any baseline changes that occur in a sample with peroxide alone (negative alone) have been subtracted from the raw data, hence normalized absorbance is plotted. Hydrogen peroxide was followed by changes in absorbance of the reaction monitoring absorbance at 240 nm. The slight changes in absorbance peroxide control (no nanoceria) filled circles; nanoceria preparation A with peroxide, open circles; nanoceria preparation B, filled inverted triangles. The mean of at least three independent experiments is plotted with the standard deviation of the mean shown as error.

Fig. 3

Nanoceria catalyze the conversion of hydrogen peroxide to oxygen. The level of dissolved oxygen was monitored using a standard Clark electrode in air-saturated buffer in the presence of 0.1 M hydrogen peroxide, DTPA and cerium oxide nanoparticles. Without the addition of nanoparticles no detectable changes in dissolved oxygen were observed. A dynamic Weibull peak fit curve was used to smooth the data from the raw probe data since the sensitivity of the instrument is only up to 0.1%, using SigmaPlot 10.