Acute toxicity of intravenously administered titanium dioxide nanoparticles in mice

Abstract

Background: With a wide range of applications, titanium dioxide (TiO₂) nanoparticles (NPs) are manufactured worldwide in large quantities. Recently, in the field of nanomedicine, intravenous injection of TiO₂ nanoparticulate carriers directly into the bloodstream has raised public concerns on their toxicity to humans.

Methods: In this study, mice were injected intravenously with a single dose of TiO₂ NPs at varying dose levels (0, 140, 300, 645, or 1387 mg/kg). Animal mortality, blood biochemistry, hematology, genotoxicity and histopathology were investigated 14 days after treatment.

Results: Death of mice in the highest dose (1387 mg/kg) group was observed at day two after TiO₂ NPs injection. At day 7, acute toxicity symptoms, such as decreased physical activity and decreased intake of food and water, were observed in the highest dose group. Hematological analysis and the micronucleus test showed no significant acute hematological or genetic toxicity except an increase in the white blood cell (WBC) count among mice 645 mg/kg dose group. However, the spleen of the mice showed significantly higher tissue weight/body weight (BW) coefficients, and lower liver and kidney coefficients in the TiO₂ NPs treated mice compared to control. The biochemical parameters and histological tissue sections indicated that TiO₂ NPs treatment could induce different degrees of damage in the brain, lung, spleen, liver and kidneys. However, no pathological effects were observed in the heart in TiO₂ NPs treated mice.

Conclusions: Intravenous injection of TiO₂ NPs at high doses in mice could cause acute toxicity effects in the brain, lung, spleen, liver, and kidney. No significant hematological or genetic toxicity was observed.

Figure 1. The image of TiO₂ NPs was captured by SEM.

Figure 2. The image of TiO₂ NPs aggregates in saline under the light microscope.

TiO₂ NPs in saline solution was dropped onto a glass slide and the aggregates of TiO₂ NPs in solution was checked under the microscope (400×). After precipitation, the larger aggregates were in the size range of 100–500 nm, and the smaller aggregates were not visible under the light microscope at 400×.

Figure 3. Pathological morphology of different tissues observed under microscope.

In mice treated with TiO₂ NPs, neuronal cell degeneration was observed in the brain tissue; vacuoles were observed in the neurons of hippocampus and their number was increased in the high dose groups, which indicated fatty degeneration occurred in the hippocampus of brain tissue. In the lung tissues, perivascular infiltration of inflammatory cells, foamy cells as well as pulmonary fibrosis were observed; the granulomatous lesions were found at the doses of 645 and 1387 mg/kg. At the doses of 140 and 300 mg/kg, TiO₂ NPs showed vacuolar degeneration in the liver. At 645 mg/kg, inflammatory cells were found in the bile ducts of the liver, and hydropic degeneration around the central vein and spotty necrosis of hepatocytes were also observed. At 645 and 1387 mg/kg, multifocal lesions were observed in the liver. In the kidneys, swelling in the renal glomerulus was observed in TiO₂ NPs treated mice. In the spleen, minor lesions were observed due to increased proliferation of local macrophages. No obvious abnormality in histology was observed in the heart in TiO₂ NPs treated mice as seen under the microscope (400×).

Figure 4. Micronucleus test result.

Average of micronucleus cell number per thousand polychromatic erythrocytes in animals was analyzed. No significant difference was observed among the micronucleus cell number between TiO₂ NPs treated mice and the control.