TiO₂-nanoparticles shield HPEKs against ZnO-induced genotoxicity

Usage of sunscreens has become commonplace amongst outdoor sports. Recently, nanomaterials have gained increasing market share as ingredients in sunscreens (as well as other topically applied products). In particular ZnO and TiO₂ nanoparticles (ZNP and TNP) have found their niche in this application. This study investigated the safety aspects of these nanoparticles from a combinatorial exposure point of view. Focus was on investigating generation of oxidative stress and induction of DNA damage which the two nanoparticles caused. It was found that TNPs triggered stronger oxidative stress than ZNPs but ZNPs remained more potent at causing DNA damage. The individual mechanisms of DNA damage were found to be through oxidative stress for TNPs (indirect genotoxicity) and through Zn²⁺ ion nuclear uptake resulting in DNA damage for ZNP (direct genotoxicity). Interesting, it was found that intracellular TNPs could adsorb Zn²⁺ ions and lower their nuclear uptake in turn shielding the HPEKs from ZNP-induced genotoxicity. Toxicological assessments of dual nanoparticle systems remain an unstudied area and based on the results obtained deserves further consideration.