We elucidated the effects of chlorpyrifos exposure on the morphology, oxidative stress and oxidative damage in zebrafish (Danio rerio) embryos. After exposed to concentration gradient of chlorpyrifos solution for 96hours, the rates of deformities and death were dramatically higher than those in the control groups, and the median lethal concentration of CPF was calculated to be 1.18mg/L after a 96h exposure. The expression levels of oxidative stress-related genes, antioxidant enzyme activities and malondialdehyde (MDA) content were investigated. In CPF treatment groups, the antioxidant enzyme (SOD, CAT) activities and the expression levels of their encoding genes (Cu/Zn-sod, Mn-sod, cat) significantly decreased, compared with the control groups. At low concentrations of chlorpyrifos, antioxidant enzyme activities were not affected significantly, while the expression levels of their encoding genes were more sensitive to chlorpyrifos. Chlorpyrifos could induce the expression of nrf2, which played an important role in increased expression of a group of genes encoding antioxidant and phaseⅡdetoxification enzymes, but the kinetics of GST and gstp2 were not consistent with each other. The down-regulation of expression levels of ucp2 and cox1 made contributions to reducing ROS generated by the respiratory chain in CPF treatment groups. Meanwhile, in CPF treatment groups, the expression level of bcl2 was significantly down-regulated, suggesting that the balance of apoptosis was destroyed. MDA content was significantly higher in CPF treatment groups than that in control, indicating that chlorpyrifos could cause oxidative damage in zebrafish embryos.
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