Titanium Dioxide (TiO2) Nanoparticles Induce JB6 Cell Apoptosis Through Activation of the Caspase-8/Bid and Mitochondrial Pathways

Titanium dioxide (TiO2), a commercially important material, is used in a wide variety of products. Although TiO2 is generally regarded as nontoxic, the cytotoxicity, pathogenicity, and carcinogenicity of TiO2 nanoparticles have been recently recognized. The present study investigated TiO2 nanoparticle-induced cell apoptosis and molecular mechanisms involved in this process in a mouse epidermal (JB6) cell line. Using the 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assay, TiO2 nanoparticles were found to exhibit higher cytotoxicity than fine particles. YOPRO-1 iodide (YP) staining demonstrated that both TiO2 nanoparticles and fine particles induced cell death through apoptosis. The signaling pathways involved in TiO2 particle-induced apoptosis were investigated. Western-blot analysis showed an activation of caspase-8, Bid, BAX, and caspase-3 and a decrease of Bcl-2 in JB6 cells treated with TiO2 particles. Time-dependent poly(ADP) ribose polymerase (PARP) cleavage induced by TiO2 nanoparticles was observed. TiO2 particles also induced cytochrome c release from mitochondria to cytosol. Further studies demonstrated that TiO2 nanoparticles induced significant changes in mitochondrial membrane permeability, suggesting the involvement of mitochondria in the apoptotic process. In conclusion, evidence indicated that TiO2 nanoparticles exhibit higher cytotoxicity and apoptotic induction compared to fine particles in JB6 cells. Caspase-8/Bid and mitochondrial signaling may play a major role in TiO2 nanoparticle-induced apoptosis involving the intrinsic mitochondrial pathway. Unraveling the complex mechanisms associated with these events may provide further insights into TiO2 nanoparticle-induced pathogenicity and potential to induce carcinogenicity.