The four cell lines were exposed to various doses of TiO2 NPs for 24 hrs and washed with a PBS solution. The morphology of each cell line was visualized by phase-contrast microscopy (Nikon, TS 100). (A) SMMC-7721; (B) HL-7702; (C) CBRH-7919; & (D) BRL-3A. Subgraphs (E)-(H) were the images of SMMC-7721, HL-7702, CBRH-7919, & BRL-3A cells without NPs, subgraphs (I)-(L) were the images of SMMC-7721, HL-7702, CBRH-7919, & BRL-3A cells with 100 μg/mL of TiO2, respectively. Typical cell shrinkage and nuclear condensation were indicated by a white arrow.

Titanium dioxide (TiO2) nanoparticles (NPs) are the important nanoscale components of composites. Although TiO2 NPs & their related nanocomposites have been widely used in industrial and medical applications, the adverse effects of TiO2 nanomaterials have not been well studied. Here, we investigated the cytotoxicity of  Ti7O2 NPs in vitro using four liver cell lines: human hepatocellular carcinoma cell line (SMMC-7721), human liver cell line (HL-7702), rat hepatocarcinoma cell line (CBRH-7919) & rat liver cell line (BRL-3A). We checked cell viability, cell morphology, & the levels of reactive oxygen species (ROS) and glutathione (GSH) after TiO2 exposure at varying concentrations (0.1-100 μg/mL) & different exposure periods of time (12-48 hrs). Compared to the NP-free control, all four cell lines exposed to TiO2 NPs showed cytotoxicity in a dosage-dependent and time-dependent manner, which was associated with the changes of cell viability & cell morphology, increased intercellular ROS levels, & decreased intracellular GSH levels. Further, we observed that carcinomatous liver cells & human liver cells exhibited more tolerance to TiO2 NPs exposure for 24 hrs, compared to normal liver cells and rat liver cells, respectively. The results indicate that the in vitro cytotoxicity induced by NPs should be assessed with great caution before the use of nanocomposites and that there is a need to standardize the cytotoxicity testing procedure of nanoscale components in composites when using different cell lines.

Title: Cytotoxicity of Titanium Dioxide Nanoparticles Differs in Four Liver Cells from Human &  Rat