Cytotoxicity of ZnO nanoparticles in human melanocyte cells in the presence or absence of UV radiation: A preliminary comparative study with TiO2 nanoparticles

Abstract

Zinc oxide nanoparticles (ZnONPs) and titanium dioxide nanoparticles (TiO₂NPs), due to their nanometric size and photostability, are increasingly used as ingredients in sunscreens to absorb and scatter UV radiation. However, the current state of knowledge is insufficient to guarantee their safety. Therefore, the objectives of this study were to evaluate the cytotoxicity of ZnONPs and TiO₂NPs in the presence and absence of UV radiation in in vitro model of primary human melanocyte cells HEMas. Our research demonstrated that 47 nm TiO₂NPs exhibited lower toxicity compared to 25 nm ZnONPs. ZnONPs (5–12.5 ppm) affect various intracellular processes, including cell membrane integrity, proliferative processes, and the induction of morphological changes in cells at the ultrastructural level, particularly in mitochondria. The study highlights intricate mechanisms of cell death induced by ZnONPs, revealing a multifaceted interplay between apoptosis and necrosis. Additionally, we indicate the potential role of intracellular calcium ion influx, notably triggered by ZnONPs, in driving cell toxicity. This influx is linked to endoplasmic reticulum (ER) dysfunction, ultimately leading to cell death, offering valuable insights into the underlying mechanisms of nanoparticle-induced toxicity. Importantly, the co-exposure of both ZnONPs and TiO₂NPs with UV radiation (9 J/cm²) enhances the toxic effect on melanocyte cells, indicating an interaction between NPs and UV radiaton and raising potential concerns about their effects on melanocytes and overall skin health.