Interactions of TiO2 nanoparticles with ingredients from modern lifestyle products and their effects on human skin cells.

The number of consumer products containing nanoparticles (NPs) experienced a rapid increase during the past decades. However, most studies of nanosafety have been conducted using only pure NPs produced in the laboratory while the interactions with other ingredients in consumer products have rarely been considered so far. In the present study, we investigated such interactions - with a special focus on modern lifestyle products (MLPs) used by adolescents. An extensive survey was undertaken at different high schools all over Austria to identify MLPs that either contain NPs or that could come easily in contact with NPs from other consumer products (such as TiO₂ from sunscreens). Based on the results from a survey among secondary schools students, we focused on ingredients from Henna tattoos (2-hydroxy-1,4-naphtochinone, HNQ, and p-phenylene diamine, PPD), fragrances (butylphenyl methylpropional, known as Lilial^®), cosmetics and skin-care products (four different parabens). As cellular model, we decided to use neonatal normal human dermal fibroblasts (nNHDF) since skin contact is the main route of exposure for these compounds. TiO₂ NPs interacted with these compounds as evidenced by alterations in their hydrodynamic diameter observed by nanoparticle tracking analysis. Combinations of TiO₂ NPs with the different MLP components did not show altered cytotoxicity profiles compared to MLP components without TiO₂ NPs. Nevertheless, altered cellular glutathione contents were detected after incubation of the cells with Lilial^®. This effect was independent of the presence of TiO² NPs. Testing mixtures of NPs with other compounds from consumer products is an important approach to achieve a more reliable safety assessment.