Amplification of arsenic genotoxicity by TiO2 nanoparticles in mammalian cells: new insights from physicochemical interactions and mitochondria

Titanium dioxide nanoparticles (TiO₂ NPs) have shown great adsorption capacity for arsenic (As); however, the potential impact of TiO₂ NPs on the behavior and toxic responses of As remains largely unexplored. In the present study, we focused on the physicochemical interaction between TiO₂ NPs and As(III) to clarify the underlying mechanisms involved in their synergistic genotoxic effect on mammalian cells. Our data showed that As(III) mainly interacted with TiO₂ NPs by competitively occupying the sites of hydroxyl groups on the surface of TiO₂ NP aggregates, resulting in more aggregation of TiO₂ NPs. Although TiO₂ NPs at concentrations used here had no cytotoxic or genotoxic effects on cells, they efficiently increased the genotoxicity of As(III) in human-hamster hybrid (A_L) cells. The synergistic genotoxicity of TiO₂ NPs and As(III) was partially inhibited by various endocytosis pathway inhibitors while it was completely blocked by an As(III)-specific chelator. Using a mitochondrial membrane potential fluorescence probe, a reactive oxygen species (ROS) probe together with mitochondrial DNA-depleted ρ⁰ A_L cells, we discovered that mitochondria were essential for mediating the synergistic DNA-damaging effects of TiO₂ NPs and As(III). These data provide novel mechanistic proof that TiO₂ NPs enhanced the genotoxicity of As(III) via physicochemical interactions, which were mediated by mitochondria-dependent ROS.