The use of titanium suboxides, known as Magnéli phase TiOx, is expected to increase in the near future due to their desirable properties. In order to use Magnéli phase TiOx nanoparticles safely, it is necessary to know how nanoparticles interact with biological systems. In this study, the cytotoxicity of three different Magnéli TiOx nanoparticles was evaluated using human lung A549 cells and the results were compared with hazard data on two different TiO₂ nanoparticles whose biological interactions have already been extensively studied. After A549 cells were exposed to nanoparticles, the metabolic activity was measured by the Resazurin assay, the amount of cellular proteins was measured by the Coomassie Blue assay, and lysosomal integrity was measured by the Neutral Red Uptake assay. In order to investigate possible modes of particle actions, intracellular Ca2+ level, reactive oxygen species (ROS) production, and photo-oxidative disruptions of lysosomal membranes were assessed. All experiments were performed in serum-containing and in serum-deprived cell culture mediums. In addition, the photocatalytic activity of Magnéli TiOx and TiO₂ nanoparticles was measured. The results show that Magnéli TiOx nanoparticles increase intracellular Ca2+ but not ROS levels. In contrast, TiO₂ nanoparticles increase ROS levels, resulting in a higher cytotoxicity. Although Magnéli TiOx nanoparticles showed a lower UV-A photocatalytic activity, the photo-stability of the lysosomal membranes was decreased by a greater extent, possibly due to particle accumulation inside lysosomes. We provide evidence that Magnéli TiOx nanoparticles have lower overall biological activity when compared with the two TiO₂ formulations. However, some unique cellular interactions were detected and should be further studied in line with possible Magnéli TiOx application. We conclude that Magnéli phase nanoparticles could be considered as low toxic material same as other forms of titanium oxide particles.
Keywords: A549 cells; ROS; calcium ions; cytotoxicity; lysosomes; nanoparticles; nanotoxicity.