Crystal Phase-Related Toxicity of One-Dimensional Titanium Dioxide Nanomaterials on Kidney Cells

One-dimensional (1D) nanomaterials are widely used in different fields, and the increased application of 1D nanomaterials has drawn concerns about their unknown toxicity. 1D titanium oxide (TiO₂) nanomaterials in different crystal phases are commonly applied in environmental remediation and solar energy conversion fields, but these materials pose a threat to human health, especially to the kidneys, an organ with abundant blood flow. To systematically evaluate the cytotoxicity to the kidneys, TiO₂ nanofibers with TiO₂(B), anatase, and rutile phases, as well as nanorods with anatase and rutile phases were synthesized and added to the culture medium of HK2 cells. Cell counting kit-8 assay, 2',7'-dichlorofluorescin diacetate assay, Hoechst 33342 staining experiments, and quantitative real-time reverse transcription polymerase chain reaction tests were used to explore the renal effects of the as-prepared TiO₂ nanomaterials in the short term or long term. In the short-term evaluation, all the added TiO₂ nanomaterials were toxic to HK2 cells, and the cytotoxicity was dose-dependent. Rutile TiO₂ can widely attach to the cell surface and displays the most serious cell-killing and proapoptotic ability, while anatase induces the most serious oxidative stress. In long-term evaluation, all the as-prepared TiO₂ nanomaterials led to epithelial mesenchymal transition (EMT), a mechanism of renal fibrosis. Consistent with the short-term results, rutile induced the most serious EMT. This study indicated that the renal toxicity of 1D TiO₂ nanomaterials is crystal phase-dependent and that rutile induced the most significant renal cell injury. Oxidative stress is a crucial but not the only contributor to the renal toxicity of TiO₂ nanomaterials in the short term.