The effect of titanium dioxide nanoparticles on mice midbrain substantia nigra

Widely used Titanium dioxide nanoparticles (TiO₂) enter into the body and cause various organ damages. Therefore, we aimed to study the effect of TiO₂ on the substantia nigra of midbrain.

40 male BALB/c mice were randomly divided into five groups: three groups received TiO₂ at doses of 10, 25, and 50 mg/kg, the fourth group received normal saline for 45 days by gavage, and control group (without intervention). Then, Motor tests including pole and hanging tests were done to investigate motor disorders. The animal brain was removed for histological purposes. Accordingly, immunohistochemistry was performed to detect tyrosine hydroxylase positive cells, and then toluidine blue staining was done to identify dark neurons in the substantia nigra. Eventually, the total number of these neurons were counted using stereological methods in different groups.

The results showed that the time recorded for mice to turn completely downward on the pole in the TiO₂-50 group increased and also the time recorded for animals to hang on the wire in the hanging test significantly decreased (P<0.05) in comparison with other groups. Also, the average number of tyrosine hydroxylase positive neurons in TiO₂-25 and TiO₂-50 groups significantly decreased as compared to the TiO₂-10 and control groups (P<0.05). The total number of dark neurons in the TiO₂-25 and TiO₂-50 groups was substantially higher than the TiO₂-10, control and normal saline groups (P<0.05).

Our findings indicated that TiO₂, depending on dose, can cause the destruction of dopaminergic neurons and consequently increase the risk of Parkinson's disease.