Environmentally Relevant Concentrations of Commercial Titanium Dioxide Nanoparticles Induce Ferroptosis in <scp>HUVECs</scp>

Titanium dioxide nanoparticles (TiO₂-NPs) have been ever increasingly exposed to people through all possible routes, while studies focusing on their potential cardiovascular risks are relatively lacking, especially the underlying biological mechanisms that are not yet elucidated. In this study, the ferroptotic effect of TiO₂-NPs (30 nm) at environmentally relevant concentrations (0, 3, 12, and 48 μg/mL) on human umbilical vein endothelial cells (HUVECs) and the potential molecular mechanism were studied with the corresponding biochemical and molecular biology assays. The results showed that TiO₂-NPs at the tested concentrations could reduce HUVEC viability, but ferrostatin-1 might rescue this reduction in cell viability. Also, TiO₂-NPs exposure increased Fe²⁺, reactive oxygen species, and malondialdehyde, but decreased glutathione, mitochondrial membrane potential, and activities of anti-oxidative enzymes (catalase, superoxide dismutase, and glutathione peroxidase) in HUVECs through an integrated signaling pathway. Meanwhile, enhanced p38 protein phosphorylation and keap1 protein and decreased Nrf2 protein phosphorylation with reductions in mRNA expressions of downstream anti-oxidative enzyme genes (catalase, superoxide dismutase, glutathione peroxidase, and phospholipid hydroperoxidase) were identified in the TiO₂-NPs-exposed HUVECs. These indicated that TiO₂-NPs exposure induced ferroptosis in HUVECs via the p38/keap1 inhibiting Nrf2 pathway. EC ferroptosis will be a promising biomarker for assessing the cardiovascular health risks of environmental contaminants.