Investigation of micronized titanium dioxide penetration in human skin xenografts and its effect on cellular functions of human skin-derived cells

Titanium dioxide (TiO 2 ) nanoparticles are ubiquitously used materials in everyday life (e.g. paints, household products and plastic goods). However, despite the wide array of common applications, their pathogenetic role was also suggested under certain conditions (e.g. pulmonary neoplasias and lung fibrosis). From a dermatological point of view, it is also of great importance that TiO 2 also serves as a physical photoprotective agent in sunscreens and is widely used in various cosmetic products. However, the effect of TiO 2 on human cutaneous functions is still unknown. Therefore, in the current study, we investigated the in vivo penetration of TiO 2 via human skin transplanted to immunodeficient mice and, furthermore, we measured the in vitro effects of nanoparticles on various functional properties of numerous epidermal and dermal cells in culture. Hereby, using various nuclear microscopy methods, we provide the first evidence that TiO 2 nanoparticles in vivo do not penetrate through the intact epidermal barrier. However, we also report that TiO 2 , when exposed directly to cell cultures in vitro, exerts significant and cell-type dependent effects on such cellular functions as viability, proliferation, apoptosis and differentiation. Therefore, our novel findings will hopefully inspire one to systemically explore in future, clinically oriented trials whether there is indeed a risk from micronized TiO 2 -containing products on skin with an impaired stratum corneum barrier function.