Background Bromoacetamide (BAcAm) is a kind of disinfection by-products, and has been confirmed to have cytotoxicity and genetic toxicity, but its toxic effect on neurodevelopment is still unclear.
Objective This experiment aims to study the neurodevelopmental toxicity and its mechanism caused by BAcAm on zebrafish embryos.
Methods Wild-type zebrafish embryos were randomly divided into six groups (30 embryos in each group), namely a control group and five BAcAm exposure groups (0.625, 1.25, 2.5, 5, and 10 mg·L-1). The exposure period was from 2 h post-fertilization (hpf) to 96 hpf. The mortality of zebrafish embryos was detected every day, and the 72 hpf hatching rate and the 96 hpf mortality, deformity rate, and body length were calculated. The locomotor ability of zebrafish was tested at 120hpf. Reactive oxygen species (ROS) levels in zebrafish were detected by 2, 7-dichlorodi -hydrofluorescein diacetate (DCFH-DA) probe. The expression levels of neurodevelopment-related genes (dlx2, ngn1, elavl3, shha, mbp, and syn2a) and oxidative stress-related genes (Cu/Zn sod, gpx, cat, nrf2, and ho-1) were detected by fluorescence quantitative PCR.
Results At 72 hpf, the hatching rate of zebrafish embryos in the 10 mg·L-1 BAcAm exposure group was 88.40%, lower than the 100% hatching rate in the control group (P < 0.05). At 96 hpf, the mortality rates of zebrafish embryos in the 5 and 10 mg·L-1 BAcAm exposure groups were 48.10% and 96.06%, respectively, higher than 15.92% in the control group (P < 0.05); the malformation rates of embryos in the 2.5 and 5 mg·L-1 BAcAm exposure groups were 21.38% and 43.43%, respectively, which were higher than 1.94% in the control group (P < 0.05); the body lengths of embryos in the 2.5 and 5mg·L-1 BAcAm exposure groups were 5.21 and 4.94mm, respectively, lower than 5.40mm in the control group (P < 0.05). The locomotor ability test results found that compared with the control group, the BAcAm exposure groups showed decreasing movement distance and time (P < 0.05). ROS staining results revealed that the ROS expression levels in the head region of zebrafish embryos in the 1.25, 2.5, and 5 mg·L-1 BAcAm groups were significantly higher than those in the control group (P < 0.05). Quantitative PCR results showed that the expression levels of neurodevelopment-related genes dlx2 were down-regulated in the 2.5 and 5 mg·L-1 BAcAm groups, ngn1 was down-regulated in the 5 mg·L-1 BAcAm group, elavl3 and shha were down-regulated in the 1.25, 2.5, and 5mg·L-1 BAcAm groups, mbp was down-regulated in the 1.25 and 5mg·L-1 BAcAm groups, syn2a was down-regulated in all BAcAm groups (P < 0.05); the expression levels of oxidative stress-related genes Cu/Zn sod was up-regulated in the 2.5 and 5 mg·L-1 BAcAm groups, gpx was up-regulated in the 5 mg·L-1 BAcAm group, cat and nrf2 were up-regulated in the 1.25, 2.5, and 5 mg·L-1 BAcAm groups, and ho-1 was upregulated in all BAcAm groups (P < 0.05).
Conclusion BAcAm exposure may induce oxidative stress and inhibit the expression of neurodevelopment-related genes, thereby induce neurodevelopmental toxicity in zebrafish embryos.
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