Cerium oxide nanoparticles, combining antioxidant and UV shielding properties, prevent UV-induced cell damage and mutagenesis

Efficient inorganic UV shields, mostly based on refracting TiO<inf>2</inf> particles, have dramatically changed the sun exposure habits. Unfortunately, health concerns have emerged from the pro-oxidant photocatalytic effect of UV-irradiated TiO<inf>2</inf>, which mediates toxic effects on cells. Therefore, improvements in cosmetic solar shield technology are a strong priority. CeO<inf>2</inf> nanoparticles are not only UV refractors but also potent biological antioxidants due to the surface 3+/4+ valency switch, which confers anti-inflammatory, anti-ageing and therapeutic properties. Herein, UV irradiation protocols were set up, allowing selective study of the extra-shielding effects of CeO<inf>2</inf>vs. TiO<inf>2</inf> nanoparticles on reporter cells. TiO<inf>2</inf> irradiated with UV (especially UVA) exerted strong photocatalytic effects, superimposing their pro-oxidant, cell-damaging and mutagenic action when induced by UV, thereby worsening the UV toxicity. On the contrary, irradiated CeO<inf>2</inf> nanoparticles, via their Ce3+/Ce4+ redox couple, exerted impressive protection on UV-treated cells, by buffering oxidation, preserving viability and proliferation, reducing DNA damage and accelerating repair; strikingly, they almost eliminated mutagenesis, thus acting as an important tool to prevent skin cancer. Interestingly, CeO<inf>2</inf> nanoparticles also protect cells from the damage induced by irradiated TiO<inf>2</inf>, suggesting that these two particles may also complement their effects in solar lotions. CeO<inf>2</inf> nanoparticles, which intrinsically couple UV shielding with biological and genetic protection, appear to be ideal candidates for next-generation sun shields. © The Royal Society of Chemistry 2015.