The effect of titanium dioxide nanoparticles on antioxidant gene expression in tilapia (Oreochromis niloticus)

The reactivity of nanoparticles (NPs) in biological systems is well recognized, but there are huge gaps in our understanding of NP toxicity in fish, despite a number of recent ecotoxicity studies. Therefore, the aim of this research was to evaluate the effect of titanium dioxide NPs (TiO₂-NPs) on antioxidant gene expression in the tilapia, Oreochromis niloticus. First, different sizes, shapes, and phases of TiO₂-NPs were synthesized and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and dynamic light scattering (DLS). Fish were injected intraperitoneally with different concentrations (0.1, 1.0, 10.0 mg/L), sizes (7, 14, and 21 nm), and phases (anatase and rutile) of TiO₂-NPs, and sacrificed 3, 6, 12, and 24 h after injection, when their livers were removed. Total RNA was extracted, and expression of the catalase (CAT), glutathione-S-transferase (GST), and superoxide dismutase (SOD) genes was assessed by real-time polymerase chain reaction (RT-PCR). The results showed that injection of 1.0 mg/L TiO₂-NPs induced an initial mild increase in CAT, GST, and SOD gene expression in tilapia, after which transcript levels decreased. Fish injected with 7 and 14 nm TiO₂-NPs showed an increase in antioxidant transcript levels 6 h after treatment. Finally, the rutile form generated stronger induction of the GST gene than anatase TiO₂-NPs during the first 6 h after injection, which suggests that exposure to rutile causes higher levels of reactive oxygen species to be produced.