The Toxicity Effect And Mechanism Of Two Kinds Of APPson Zebrafish (Danio Rerio)

Chemical pesticides play an irreplaceable role in crop protection. However, long-term and unreasonable usage of pesticides may have permanent and irreversible detrimental effects on beneficial organisms (non-target organisms) in environment. Therefore, the work of environmental safety assessment for chemical pesticides is increasingly important.Due to its characteristics of high efficiency, low toxicity and safety to subsequent crop, aryloxyphenoxypropionate herbicides (APP) occupy an important position in the herbicide market. Cyhalofop-butyl and quizalofop-P-ethyl, two kinds of typical APP herbicides, are widely applied in the prevention and control of weeds. It is therefore significant to carry out further environmental assessment of evaluating their toxic effect on non-target organisms, especially aquatic organism.In this study, to investigat toxic effect and action mechanism in different life stages of zebrafish of cyhalofop-butyl and quizalofop-P-ethyl, experimental work which combines multiple toxicology technology was conducted:1 The acute toxicity of cyhalofop-butyl on and quizalofop-P-ethyl different stage of zebrafishThe 96h-LC50 of cyhalofop-butyl to zebrafish embryo, larvae and adult was 0.57n 1.32 and 4.05 mg/L, respectively. The results demonstrated that cyhalofop-butyl was middle toxic to zebrafish adluts and larvae, and highly toxic to zebrafish embryos. The most sensitivity stage of zebrafish life to cyhalofop-butyl is embryo. The 96h-LC50 of quizalofop-P-ethyl to zebrafish embryo was 0.23mg/L, and highly toxic to zebrafish embryos.2 The developmental toxicity of cyhalofop-butyl and quizalofop-P-ethyl on zebrafish embryosZebrafish embryos were exposed to 0.10,0.20,0.30,0.40,0.50.0.60mg/L cyhalofop-butyl and 0.10,0.20> 0.30,0.40,0.50 mg/L quizalofop-P-ethyl for 6 days and the embryonic mophorlogical indicators were tested. The results indicated that a large suite of symptoms was induced in embryonic development by different dosages of cyhalofop-butyl and quizalofop-P-ethyl, including hatching inhibition, abnormal spontaneous movement, slow heart rate, growth regression and morphological deformities.3 The action mechanism of cyhalofop-butyl developmental toxicity on zebrafish embryosExposure to cyhalofop-butyl resulted in significant increases in reactive oxygen species (ROS) production and cell apoptosis in heart area. Embryos were exposed to 0.10,0.20,0.30 mg/L cyhalofop-butyl for 4 days. Quantative PCR found that the mRNA levels of the genes related to oxidative stress Mn-Sod, Cu/Zn-Sod, Cat and Gpx were induced significantly. Meanwhile, a series of apoptosis related gene were also upregulated, including p53, Mdm2, Box, Puma, Caspase-3 and Caspase-9. Moreover, the activity of capspase-9 and caspase-3 were significantly increased.4 The cardiotoxic effects and the action mechanism of quizalofop-P-ethyl on zebrafish embryos6 days expoure test indicated that exposure to quizalofop-P-ethyl caused some cardiac morphogenetic defects, including pericardial edema, an abnormally looped heart, and malformed chambers. In addition, exposure to quizalofop-P-ethyl also led to cardiac performance dysfunction, such as slow heart rate, decreased cardiac output. Embryos were exposed to 0.10、0.20^ 0.30 mg/L quizalofop-P-ethyl for 4 days. Quantative PCR found that the mRNA levels of key cardiac genes were induced significantly, including Nkx2.5、Tbx5、GATA4、VEGF、vmhc、ANP、BNP、Moreover, the protein levels of TBX5, an important gene in mediating cardiac development, were induced.5 The immune toxicity and endocrine disruption of quizalofop-P-ethyl on zebrafish embryosQuantative PCR test found the mRNA levels of regulated the innate immune system-related genes, including CXCL-Clc、CC-chem、IL-1β、IL-8, IFN and TNFa, and endocrine genes, including VTG1、 Era、hhex and pax8 were induced significantly after quizalofop-P-ethyl expoure. Moreover, the protein levels of VTG were induced.6 The endocrine disruption effect of quizalofop-P-ethyl on zebrafish adultsAdult zebrafish were exposed to different dosage (2、20 and 200 μg/L) quizalofop-P-ethyl for 30d. In males, QpE exposure significantly increased plasma estradiol (E2) and vitellogenin (VTG) levels. In contrast, plasma sex hormone levels and vitellogenin concentrations were not altered significantly, concomitant with up-regulation of hepatic VTG and ERa gene expression. While down-regulation of VTG concentration was observed in females, concomitant with down-regulation of hepatic VTG1, VTG3, ER/51 and ERβ2 gene expression. Interestingly, QpE exposure significantly increased transcriptional profiles of some genes in the HPG axis and liver in males, while the majority of these genes were down-regulated in females. Docking studies showed that QpE has the possibility to interaction with the ligand-binding domain (LBD) of zebrafish Era at Ser350 and Ser428 and ERβ1 at Lys305, suggesting QpE possessing the capacity of binding to ER.