Toxicity of o-phenylphenol on craniofacial cartilage development through ROS-induced oxidative stress in zebrafish embryos.

O-phenylphenol (OPP), a commonly used antiseptic and bactericide, has some threat to human health and the environment. Environmental exposure to OPP may cause potential health hazards in animals and humans, and the developmental toxicity of OPP needs to be assessed. Therefore, the zebrafish model was used to evaluate the ecological impact of OPP, and the zebrafish craniofacial skeleton is mainly derived from the cranial neural crest stem cells (NCCs). In this study, zebrafish were exposed to 1,2,4 mg/L OPP from10 to 80 h post-fertilization (hpf). Our study observed that OPP could cause the early disorder of craniofacial pharyngeal arch development and lead to behavioural abnormalities. In addition, qPCR and enzyme activity revealed that OPP exposure would induce the production of reactive oxygen species (ROS) and oxidative stress. And proliferation cell nuclear antigen (PCNA) indicated that the proliferation of NCCs was reduced. The mRNA expression of genes related to migration, proliferation, and differentiation of NCCs has changed significantly under OPP exposure. Astaxanthin (AST), a widely used antioxidant, could partially rescue the craniofacial cartilage development exposed to OPP. The results showed improvements in oxidative stress, gene transcription, NCCs proliferation, and protein expression in zebrafish, suggesting that OPP may reduce antioxidant capacity and subsequently inhibit migration, proliferation, and differentiation of the NCCs. In conclusion, our study found that OPP may produce reactive oxygen species, leading to developmental toxicity in zebrafish craniofacial cartilage.

Sulfoxaflor induces immunotoxicity in zebrafish (Danio rerio) by activating TLR4/NF-κB signaling pathway.

Sulfoxaflor is an insecticide that is widely used and affects the nervous system of sucking pests. However, studies on the molecular mechanism of the toxicity of sulfoxaflor to non-target species are limited. Zebrafish (Danio rerio) was used as an experimental subject in this study. Zebrafish embryos were exposed to 20, 25, and 30 mg/L sulfoxaflor solution to detect hatchability, mortality, heart rate, neutrophil count, oxidative stress, and expression of genes related to apoptosis and immune inflammation. The results showed that zebrafish embryos exposed to sulfoxaflor solution increased mortality and growth retardation, and the number of innate immune cells decreased significantly. In addition, the expression levels of apoptotic and proapoptotic genes increased significantly, and oxidative stress-related indexes changed significantly. Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signaling pathway was further studied, and the interleukin 6 (IL-6), interleukin 1 beta (IL-1ß), cyclooxygenase-2 (COX2), tumor necrosis factor-alpha (TNF-α), TLR4, and myeloid differentiation primary response 88 (MYD88) gene expression levels were significantly up-regulated. We used small molecule inhibitor QNZ for the rescue experiment and detected the expression of relevant target proteins in the QNZ signaling pathway. QNZ reduced the expression of TLR4/NF-κB signaling pathway-related protein NF-κB p65 in the cytoplasm and nucleus and rescued the number of innate immune cells. In summary, sulfoxaflor may induce developmental toxicity and immunotoxicity in zebrafish by activating the TLR4/NF-κB signaling pathway, which provides a basis for further studies on the molecular mechanism of sulfoxaflor action in the aquatic ecosystem and the development and utilization of QNZ.

Hematopoietic stem cell and immunotoxicity in zebrafish embryos induced by exposure to Metalaxyl-M.

Metalaxyl-M (MM), a protective and therapeutic fungicide, has been shown to be a promising candidate, but its toxicity toward aquatic organisms is unknown. In this study, we evaluated for the first time the immunotoxicity of MM in zebrafish embryos. Phenotypes (heart rate, body length, and yolk area) and the number of neutrophils, macrophages, and T cells in the thymus were analyzed in zebrafish embryo after exposure to MM. Our results showed that zebrafish embryos exposed to MM showed a concentration-dependent increase in the yolk area and a significant decrease in the number of neutrophils, macrophages, and thymus T cells. We detected upregulated expression of related immune signaling genes, such as tnfa, nfkb3, cxcl-c1c, il6, mmp9, and tgfb1. Additionally, we observed a significant decrease in HSCs in zebrafish larvae after exposure to MM. IWR-1 could restore the number of neutrophils and macrophages after exposure to MM. The results indicated that MM exerted developmental toxicity and immunotoxicity to zebrafish embryos, and these phenomena may be caused by MM's regulation of WNT signaling pathway.