UV-shielding property, photocatalytic activity and photocytotoxicity of ceria colloid solutions

https://doi.org/10.1016/j.jphotobiol.2010.09.002Get rights and content

Abstract

UV-shielding property, photocatalytic activity and cytotoxicity (including photocytotoxicity) of citrate-stabilized ceria colloid solutions were studied. It was established that UV-shielding property (namely, the sun protection factor, the critical absorption wavelength and the UVA/UVB-ratio) of ceria nanoparticles are as good as those of titanium dioxide and zinc oxide nanoparticles. It was further demonstrated that ceria nanoparticles possesses substantially lower photocatalytic activity, which additionally decreases upon decrease in ceria particle size. It was found that colloid ceria solutions are non-toxic to mouse fibroblasts (L929) and fibroblast-like cells of African Green monkey (VERO). Moreover, ceria nanoparticles are capable to protect these cells from UV-irradiation-induced damage. It was proposed that nanocrystalline ceria could be used not only as UV-blocking material, but also as prophylactic and even therapeutic compound for sunburns treatment.

Introduction

Nanocrystalline semiconductor materials are widely used in sunscreen cosmetics. Nowadays, most of inorganic UV-blocking filters are based on titanium dioxide (TiO2) and zinc oxide (ZnO). However, a number of reports exist indicating the possibility of brain cells [1], blood lymphocytes [2] and lymphoblastic cells [3] damage by titania nanoparticles. Moreover, nanoparticles of zinc and titanium oxides possess enormous photocatalytic activity [4], [5], thus inducing the increase in their toxicity upon irradiation. Reactive oxygen species (ROS) forming during photocatalytic processes decompose not only components of cosmetics but even skin cells [6], [7]. It was demonstrated that under UV-irradiation TiO2 and ZnO nanoparticles being the part of sunscreen cosmetics generate hydroxyl radicals [8], [9], [10], [3] damaging DNA of skin cells [11]. Photocytotoxicity of titania against fibroblasts has been also confirmed [12].

Cerium dioxide (CeO2) is one of the today’s most promising nanobiomaterials [13], [14], [15], [16]. Ceria becomes strongly non-stoichiometric in nanocrystalline state and due to this reason is able to participate in various redox processes [17], [18], in particular, to inactivate some of the most toxic ROS, such as superoxide radical [13], hydrogen peroxide [14] and nitroxyl radical [19]. Due to the high concentration of oxygen defects in ceria lattice the recombination of free charge carriers (electrons and holes) forming upon UV-irradiation of ceria proceeds very rapidly. It should be also noted that UV-extinction coefficient of ceria is rather high; therefore this compound is considered as a promising UV-filter in sunscreen cosmetics [20], [21], [22]. Moreover, vacancy engineered ceria nanostructures can protect from radiation-induced cellular damage [23], radiation-induced pneumonitis [24] and can prevent retinal degeneration by photons of light [25].

Thus the aim of this work consists of thorough investigation of the possibility of nanocrystalline ceria use in sunscreen cosmetics, including study of its sunshielding properties, photocatalytic activity and cytotoxicity upon UV-irradiation.

Section snippets

Experimental

Colloid solutions of ceria nanoparticles (0.1 M) stabilized by sodium citrate were synthesized according to [26], [27]. Nanoparticles obtained were of ultra small size (⩽2 nm), stable in water, various buffer solutions, and biological fluids in a wide range of pH values (from 4 to 12). Our previous studies indicate also that such nanoparticles can participate in redox processes in aqueous media [27].

Ceria nanopowders of different particle size used hereafter for comparative studies of

UV-shielding property

UV-shielding properties of ceria nanoparticles were studied in comparison with the corresponding properties of TiO2- and ZnO-containing systems by measuring the light absorption in the middle (UVB) and near (UVA) ultraviolet regions.

To estimate the efficiency of skin protection in UVB region we used the value of Sun Protection Factor (SPF) defined by Sayre et al. [32] as:SPF=290400EA(λ)×SS(λ)290400EA(λ)×SS(λ)×T(λ).

Here, EA(λ) – erythemal action spectrum [33]; SS(λ) – standard solar spectrum

Conclusions

In the present study we have demonstrated that UV-shielding properties (namely, the sun protection factor, the critical absorption wavelength and the UVA/UVB-ratio) of ceria nanoparticles are comparable to those of titanium dioxide and zinc oxide nanoparticles. Nanoceria possesses substantially lower photocatalytic activity in comparison with TiO2 and ZnO, which additionally decreases upon decrease in ceria particle size. Colloid ceria solutions are non-toxic to mouse fibroblasts (L929) and

Acknowledgments

We thank S.I. Woychuk and Z.M. Olevinskaya for technical assistance. This work was supported partly by Russian Foundation for Basic Research (Project 08-03-00471) and Russian Education Agency (Project GK P-2440).

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