Lizhen Zhu

Occurrence and origin of sensitivity toward difenoconazole in zebrafish (Danio reio) during different life stages

We report here an investigation of the mechanisms contributing to the divergent sensitivity toward the triazole fungicide difenoconazole of zebrafish (Danio reio) during different life stages. Adult and embryonic zebrafish were exposed to three different concentrations of difenoconazole (0.01, 0.5 and 1.0mg/L). The death rate, bioaccumulation of difenoconazole, oxidative stress parameters and transcription of related genes were tested at 4 and 8 days post-exposure (dpe). The death rate for adult zebrafish was much higher than that of the embryos at an exposure concentration of 1.0mg/L at both 4 and 8 dpe. The concentrations of difenoconazole in both the embryos and adult fish were similar, except for the group exposed to 0.01mg/L difenoconazole. A decrease in antioxidant enzyme activities was observed in both the embryos and the livers of adult fish after exposure to difenoconazole. Significant lipid peroxidation was found in the livers of adult fish in all exposure groups at 8 dpe, but was not observed in the treated embryos. The gene transcription response of the embryos toward difenoconazole was different from that in the livers of adult fish at 4 dpe. At 8 dpe, the modification in the transcription of the tested genes in the embryos and adult fish was similar, except for the genes related to the synthesis of sterols.

Cyhalofop-butyl has the potential to induce developmental toxicity, oxidative stress and apoptosis in early life stage of zebrafish (Danio rerio)

Cyhalofop-butyl is a selective herbicide widely employed in paddy field, which can transfer into aquatic environments. However, details of the environmental risk and aquatic toxicity of cyhalofop-butyl have not been fully investigated. In this study, zebrafish (Danio rerio) embryos were exposed to a range of cyhalofop-butyl until 120 hour post-fertilization (hpf) to assess embryonic toxicity of the chemical. Our results demonstrated that cyhalofop-butyl was highly toxic to zebrafish embryos, with concentration-dependent negative effects in embryonic development. In addition, exposure to cyhalofop-butyl resulted in significant increases in reactive oxygen species (ROS) production and cell apoptosis in heart area. The mRNA levels of the genes related to oxidative stress and apoptosis were also altered significantly after cyhalofop-butyl exposure. Moreover, the activity of capspase-9 and caspase-3 were significantly increased. Therefore, we speculated that oxidative stress-induced apoptosis should be responsible for abnormal development during embryogenesis after cyhalofop-butyl exposure.

Toxic effects of thifluzamide on zebrafish (Danio rerio).

Thifluzamide is a fungicide widely used to control crop diseases, and it therefore constitutes a hazard to the environment. In this study, zebrafish were selected to assess the aquatic toxicity of thifluzamide. The acute and development toxicity of thifluzamide to embryos, larvae, and adult zebrafish were measured and the corresponding 96h-LC50 values were as follows: adult fish (4.19mg/L) <larvae (3.52mg/L) <embryos (3.08mg/L). A large suite of symptoms was found in these three stages of zebrafish, including abnormal spontaneous movement, slow heartbeat, hatching inhibition, growth regression, and morphological deformities. In addition, for adult zebrafish, distinct pathological changes were noted in liver and kidney 21 days post exposure (dpe) to 0.19, 1.33, and 2.76mg/L. Liver damage was more severe than kidney damage. In another 28 days exposure of adult zebrafish to 0.019, 0.19, and 1.90mg/L, negative changes in mitochondrial structure and enzymes activities [succinate dehydrogenase (SDH) and respiratory chain complexes] were found. These might be responsible for the adverse expansion of the apoptosis- and immune-related genes, which would facilitate the action of these factors in programmed cell death and might play a key role during the toxic events.

Impact of environmental concentrations of beta-cypermethrin on the antioxidant system in the brain and liver of zebrafish (Danio rerio)

Beta-cypermethrin (beta-CYP) is a widely used pyrethroid pesticide, the extensive application of which may potentially cause damage to non-target organisms. To investigate the effect of beta-CYP on the antioxidant system of aquatic animals, adult zebrafish were exposed to environmentally relevant dosages (0.01, 0.1 and 1.0 μg/L) of beta-CYP. The activities of four antioxidant enzymes in zebrafish liver and brain tissue were tested after 7, 15 and 30 days of exposure. Our results showed that exposure of beta-CYP could induce different levels of increase in hepatic superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GPx) activities at 7 and 15 days post exposure (dpe), but caused apparent inhibition of hepatic SOD, GR and GPx activities at 30 dpe. Unlike in liver tissue, SOD and CAT activities in zebrafish brain did not show any apparent response to beta-CYP during the whole treatment period. In addition, increased brain GPx activities were observed at 7 and 30 dpe.

Quizalofop-P-ethyl exposure increases estrogen axis activity in male and slightly decreases estrogen axis activity in female zebrafish (Danio rerio)

The herbicide Quizalofop-P-ethyl (QpE) exerts toxic effects in fish, but limited information is currently available on its effects on the endocrine system. In the current study, adult zebrafish (Danio rerio) were exposed to different concentrations (0, 2, 20, 200μg/L) of QpE for 30days. In males, QpE exposure significantly increased plasma estradiol (E2) and vitellogenin (VTG) levels, concomitant with up-regulation of hepatic esr1 and vtg gene expression. In females, plasma sex hormone levels and VTG concentrations were not altered significantly, but an increased expression of hepatic esr1 in addition to decreased expression of hepatic vtg, esr2a and esr2b was observed. Marked histological lesions were also observed in the gonads of both males and females. Moreover, 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 QpE forming stable interactions with the ligand-binding domain (LBD) of zebrafish ESR1 and ESR2a, suggesting QpE may bind to estrogen receptors (ESRs). This study for the first time reveals QpE as an endocrine-disrupting chemical (EDC) disrupting the zebrafish endocrine system in a sex-specific manner, whereby it increases estrogen axis activity in males and slightly decreases estrogen axis activity in females, which may be accounted for by QpE regulating steroidogenesis and/or activating ESR(s).

Neonicotinoid insecticides imidacloprid, guadipyr, and cycloxaprid induce acute oxidative stress in Daphnia magna

Cycloxaprid (CYC) and guadipyr (GUA) are two new and promising neonicotinoid insecticides whose effects on Daphnia magna are as yet unknown. In this study, the acute toxicities of CYC and GUA to D. magna, including immobilization and embryo-hatching inhibition, and their effects on antioxidant enzymes and related gene expression were determined after a 48-h exposure. Imidacloprid (IMI) was evaluated at the same time as a reference agent. The 48-h EC50 values of IMI, GUA, and CYC for neonate immobilization were 13.0-16.5mg/L and for embryo hatching were 11.3-16.2mg/L. The specific activity of the enzymes superoxide dismutase (SOD) and catalase (CAT) were interfered by IMI, but not by GUA and CYC, while the activity of acetylcholinesterase (AChE) was significantly increased by IMI, but inhibited by GUA and CYC. The relative expressions of the Sod-Cu/Zn, Sod-Mn, Cat, and Ache genes were usually inhibited by IMI, GUA, and CYC, except for Cat by CYC, Ache by GUA, and Sods by IMI. For vitellogenin genes with a SOD-like domain (Vtg1/2-sod), relative expression was increased by IMI and inhibited by GUA and CYC, indicating that IMI, GUA, and CYC have potential toxicity toward reproduction. CYC and GUA are highly active against IMI-resistant pests, and considering the similar toxicity of IMI to D. magna, CYC and GUA are suitable for use in future integrated pest management systems.

Racemic, R-, and S-tebuconazole altered chitinase and chitobiase activity of Daphnia magna

ABSTRACT Tebuconazole is a chiral trizole fungicide and widely used in many crops for controlling disease. Tebuconazole is potential toxic to some aquatic organisms but relative information of its isomers is scarce. To detect the endocrine disrupting effects and difference of rac-, R-, and S-tebuconazole, the chitinase activity in Daphnia magna and chitobiase activity in each test medium were used as biomonitors after a 14-day exposure. Results showed that chitinase activity was significantly reduced by rac-, R-, and S-tebuconazole. The chitobiase activity in the test medium was reduced by rac- and R-tebuconazole before day 10, and only one peak was observed at day 10 or day 12 compared with two obvious peaks in the control group (days 6 and 12). S-tebuconazole delayed and reduced the reproduction of D. magna, but did not delay the first chitobiase activity peak, whereas the second peak could not be characterized as the exposure concentration and time increased. Compared with chitinase activity, chitobiase activity can still be used as a rudimentary model for identifying molt-interfering xenobiotics, and further studies should focus on the analysis of correlations between these parameters.