Oxidative stress and hepatotoxicity in the frog, Rana chensinensis, when exposed to low doses of trichlorfon

Trichlorfon is an organophosphate insecticide that is widely used in aquaculture and agriculture against parasitic infestations and has caused aquatic toxicity to non-target organisms. To evaluate the effects of low doses of trichlorfon on the oxidative stress and hepatotoxicity in amphibians, Chinese brown frogs (Rana chensinensis) were exposed to trichlorfon at concentrations of 0, 0.01, 0.1, and 1.0 mg/L for 2 and 4 weeks. Then, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and the content of malondialdehyde (MDA) in hepatic tissue were examined to evaluate the effects of oxidative stress and lipid peroxidation. The histopathological alternations to the liver were observed through light and transmission electron microscopy (TEM). The results showed that SOD and CAT activities were increased in the livers of frogs exposed to various concentrations of trichlorfon. The GST activity showed no significant changes at any concentration after 2 weeks of exposure, whereas there was an initial increase after exposure to 0.1 mg/L of trichlorfon at 4 weeks. The content of MDA revealed a significant decrease after exposure. Histopathological and ultrastructural studies showed that trichlorfon induced hyalinization, vacuolation, nucleus necrosis, and cellular swelling in hepatocytes. These results suggest that low doses of trichlorfon could induce oxidative stress, lipid peroxidation, and hepatic lesions in frogs, which shows that even lower, non-lethal doses of trichlorfon are potentially toxic to amphibians.