Titanium Dioxide Nanoparticles-Mediated In Vitro Cytotoxicity Does Not Induce Hsp70 and Grp78 Expression in Human Bronchial Epithelial A549 Cells

Titanium dioxide nanoparticles (TiO2NPs) are increasingly being used in various industrial applications including the production of paper, plastics, cosmetics and paints. With the increasing number of nano-related products, the concern of governments and the general public about the health and environmental risks, especially with regard to occupational and other environmental exposure, are gradually increasing. However, there is insufficient knowledge about the actual affects upon human health and the environment, as well as a lack of suitable biomarkers for assessing TiO2NP-induced cytotoxicity. Since the respiratory tract is likely to be the main exposure route of industrial workers to TiO2NPs, we investigated the cytotoxicity of the anatase and rutile crystalline forms of TiO2NPs in A549 cells, a human alveolar type II-like epithelial cell line. In addition, we evaluated the transcript and protein expression levels of two heat shock protein (HSP) members, Grp78 and Hsp70, to ascertain their suitability as biomarkers of TiO2NP-induced toxicity in the respiratory system. Ultrastructural observations confirmed the presence of TiO2NPs inside cells. In vitro exposure of A549 cells to the anatase or rutile forms of TiO2NPs led to cell death and induced intracellular ROS generation in a dose-dependent manner, as determined by the MTS and dichlorofluorescein (DCF) assays, respectively. In contrast, the transcript and protein expression levels of Hsp70 and Grp78 did not change within the same TiO2NPs dose range (25–500 μg/ml). Thus, whilst TiO2NPs can cause cytotoxicity in A549 cells, and thus potentially in respiratory cells, Hsp70 and Grp78 are not suitable biomarkers for evaluating the acute toxicological effects of TiO2NPs in the respiratory system.