Cellular damage mechanism induced by dioxide titanium nanoparticles used in sunscreens

Abstract

Titanium dioxide (TiO 2 ) is widely used in sunscreens because it protects against UVradiation. Current ones are micronized or nanoparticle formulations (TiO 2 @NP), which blendwith the skin tone and attain a better cosmetic effect. Nanosized titanium dioxide is approvedby the Food and Drug Administration, but its biocompatibility is controversial. Concern aboutnegative effects has lately been raised. In fact, cytotoxicity and oxidative stress produced byTiO 2 @NP when exposed to sunlight were demonstrated in some studies.The goal of this work was to propose an alternative to the cellular damage generatedupon the interaction of TiO 2 @NP with sunlight.Antioxidant vitamins B 2 (riboflavin) and vitamin C were tried as functionalization agentsbecause their potential to bind to the nanoparticle and the capacity of neutralize the oxidativestress. Binding was achieved after a few minutes of sonication in aqueous media, followedby characterization. We used a model of prokaryotic cells (methicillin-sensitiveStaphylococcus aureus biofilm) exposed to light to study the protective capacity ofvitamins@TiO 2 NP. Viability was assessed using the XTT assay. The absorbance values areproportional to the metabolic activity of the cells and indicate cell survival.The TiO 2 @NP functionalized with vitamin B 2 were the more stable ones, and were chosento follow the experiments. The analysis of the supernatant by UV-Vis spectrometry showedthat every gram of TiO 2 @NP is loaded with 0.8 grams of vitamin B 2 . The IR spectrum ofvitaminB2@TiO 2 NP showed signs of binding between compounds. The OH bending peak(1634 cm -1 ) corresponding to bare nanoparticle disappeared and the NH 2 bending bandcharacteristic of vitamin B2 appeared (1650 cm -1 ).In samples treated with vitaminB2@TiO 2 NP irradiated for up to 6 h, the levels of reactiveoxygen species (NBT assay) and protein oxidation (AOPP assay) were completelydecreased. The lipid oxidation (MDA assay) was also remarkably lower when usingvitaminB2@TiO 2 NP (64 % less). The bare oxide NPs are harmful, in part, because bothanatase and rutile forms are semiconductors and produce high amounts of ROS uponsunlight. Moreover, the cell viability percent for prokaryotic cells improved when they weretreated with vitaminB2@TiO 2 NP (153 ± 9%) compared to the ones treated with bareTiO 2 @NP (82 ± 3%).Functionalization with vitamin B 2 proved to be a biocompatible and low-cost alternative toprotect the cells from this oxidative stress. Therefore, we plan to continue this study oneukaryotic cells and in vivo, to check the penetration and biodistribution of the nanoparticles.