Impact of nano-titanium dioxide extracted from food products on Caco-2 cells using three-phase digestion model

Abstract

The prevalence of titanium dioxide in existing consumer products and food chains, globally, demands continued study of exposure and biological impact. This work characterises the nature and biological interactions of titanium dioxide nanoparticles commonly exposed to consumers through the food chain. We observed anatase titanium dioxide with mean particle size of 155 nm to be present in three foods readily available on the Australian market. Following the extraction and simulated digestion of these nanoparticles, we observed time-dependent changes to the complex nanoparticle protein corona and found the extracted particles to induce autophagy in Caco-2 cells. Importantly, we found contradictions in the results from different cytotoxicity methodologies, which warrant further critical review and consideration for future reliance on CCK-8 and fluorescence-based ROS probe assays. Elemental analysis indicated that exposure to the extracted titanium dioxide nanoparticles dysregulated cellular homeostasis, in particular Zn homeostasis, in Caco-2 cells. While debate surrounding the mechanism of nanoparticle toxicity continues, these findings contribute to the growing body of evidence which implicates Zn-mediated cellular processes in nanoparticle-induced oxidative stress, inflammation, and apoptosis. Further, in light of the increasing regulatory and risk assessment attention on TiO₂ and the recent ban mandated by the European Union on its use as a food additive, improved understanding of mechanism of toxicological action can aid in informing more proportionate and precautionary regulatory approaches.