Food-grade titanium dioxide translocates across the buccal mucosa in pigs and induces genotoxicity in an in vitro model of human oral epithelium

The whitening and opacifying agent titanium dioxide (TiO₂) is used worldwide in various foodstuffs, toothpastes and pharmaceutical tablets. Its use as a food additive (E171 in EU) has raised concerns for human health. Although the buccal mucosa is the first area exposed, oral transmucosal passage of TiO₂ particles has not been documented. Here we analyzed E171 particle translocation in vivo through the pig buccal mucosa and in vitro on human buccal TR146 cells, and the effects on proliferating and differentiated TR146 cells. In the buccal floor of pigs, isolated TiO₂ particles and small aggregates were observed 30 min after sublingual deposition, and were recovered in the submandibular lymph nodes at 4 h. In TR146 cells, kinetic analyses showed high absorption capacities of TiO₂ particles. The cytotoxicity, genotoxicity and oxidative stress were investigated in TR146 cells exposed to E171 in comparison with two TiO₂ size standards of 115 and 21 nm in diameter. All TiO₂ samples were reported cytotoxic in proliferating cells but not following differentiation. Genotoxicity and slight oxidative stress were reported for the E171 and 115 nm TiO₂ particles. These data highlight the buccal mucosa as an absorption route for the systemic passage of food-grade TiO₂ particles. The greater toxicity on proliferating cells suggest potential impairement of oral epithelium renewal. In conclusion, this study emphasizes that buccal exposure should be considered during toxicokinetic studies and for risk assessment of TiO₂ in human when used as food additive, including in toothpastes and pharmaceutical formulations.