<i>In situ</i> quantification of diverse titanium dioxide nanoparticles unveils selective endoplasmic reticulum stress-dependent toxicity

<p>Although titanium dioxide nanoparticles (TiO<sub>2</sub> NPs) have been extensively studied, their possible impact on health due to their specific properties supported by their size and geometry, remains to be fully characterized to support risk assessment. To further document NPs biological effects, we investigated the impact of TiO<sub>2</sub> NPs morphology on biological outcomes. To this end, TiO<sub>2</sub> NPs were synthesized as nanoneedles (NNs), titanate scrolled nanosheets (TNs), gel-sol-based isotropic nanoparticles (INPs) and tested for perturbation of cellular homeostasis (cellular ion content, cell proliferation, stress pathways) in three cell types and compared to the P25. We showed that TiO<sub>2</sub> NPs were internalized at various degrees and their toxicity depended on both titanium content and NPs shape, which impacted on intracellular calcium homeostasis thereby leading to endoplasmic reticulum stress. Finally, we showed that a minimal intracellular content of TiO<sub>2</sub> NPs was mandatory to induce toxicity enlightening once more the crucial notion of internalized dose threshold beside the well-recognized dose of exposure.</p>