Bisphenol A Analogues Induce Neuroendocrine Disruption via Gut-Brain Regulation in Zebrafish.

There is epidemiological evidence in humans that exposure to endocrine-disrupting chemicals such as bisphenol A (BPA) is tied to abnormal neuroendocrine function with both behavioral and intestinal symptoms. However, the underlying mechanism of this effect, particularly the role of gut-brain regulation, is poorly understood. We exposed zebrafish embryos to a concentration series (including environmentally relevant levels) of BPA and its analogues. The analogue bisphenol G (BPG) yielded the strongest behavioral impact on zebrafish larvae and inhibited the largest number of neurotransmitters, with an effective concentration of 0.5 µg/L, followed by bisphenol AF (BPAF) and BPA. In neurod1:EGFP transgenic zebrafish, BPG and BPAF inhibited the distribution of enteroendocrine cells (EECs), which is associated with decreased neurotransmitters level and behavioral activity. Immune staining of ace-α-tubulin suggested that BPAF inhibited vagal neural development at 50 and 500 µg/L. Single-cell RNA-Seq demonstrated that BPG disrupted the neuroendocrine system by inducing inflammatory responses in intestinal epithelial cells via TNFα-trypsin-EEC signaling. BPAF exposure activated apoptosis and inhibited neural developmental pathways in vagal neurons, consistent with immunofluorescence imaging studies. These findings show that both BPG and BPAF affect the neuroendocrine system through the gut-brain axis but by different mechanisms, revealing new insights into the modes of bisphenol-mediated neuroendocrine disruption.

Neural System Impairment and Involved Microglia-Neuron Regulation of Broflanilide in Zebrafish Larvae.

Broflanilide is widely used to control pests and has attracted attention due to its adverse effects on aquatic organisms. Our previous study showed that broflanilide has a negative impact on the central nervous system (CNS) at lethal dosages; however, its neural effects under practical situations and the underlying mechanisms remain unknown. To elucidate how broflanilide affects the CNS, we exposed zebrafish larvae to broflanilide at 16.9 and 88.0 µg/L (the environmentally relevant concentrations) for 120 h. Zebrafish locomotion was significantly disturbed at 88.0 µg/L, with a decreased moving distance and velocity accompanied by an inhibited neurotransmitter level. In vivo neuroimaging analysis indicated that the nerves of zebrafish larvae, including the axons, myelin sheaths, and neurons, were impaired. The number of neurons was significantly reduced after exposure, with an impaired morphological structure. These changes were accompanied by the abnormal transcription of genes involved in early CNS development. In addition, an increased total number of microglia and an elevated proportion of amoeboid microglia were observed after 88.0 µg/L broflanilide exposure, pointing out to an upstream role of microglia activation in mediating broflanilide neurotoxicity. Meanwhile, increased inflammatory cytokine levels and brain neutrophil numbers were observed, implicating significant inflammatory response and immune toxicity. Our findings indicate that broflanilide interferes with microglia-neuron regulation and induces neurodevelopmental disorders.

The neurobehavioral impacts of typical antibiotics toward zebrafish larvae.

Due to the widely usage in livestock, aquaculture and clinics, antibiotic residues are existed in aqueous environments and their potential toxicity to aquatic organisms is concerning. Here, we used zebrafish as the model to investigate the neurotoxicity and involved mechanism of seven antibiotics that were frequently detected in surface waters. The results revealed that the short-term exposure to clarithromycin (CLA), chlortetracycline (CTC) and roxithromycin (ROX) induced behavioral effects, with effective concentration of 1 µg/L (CTC and ROX) and 100 µg/L (CLA, CTC and ROX) respectively. A significant decrease in the travel distance and velocity as well as an increase in turn angle was measured. TUNEL assay identified increased cell apoptosis in brain sections of larvae exposed to three neurotoxic antibiotics, which raised the possibility that the behavioral symptoms were associated with neural damage. Transcriptome sequencing showed that the three antibiotics could affect the nervous system of zebrafish including the alteration of synaptogenesis and neurotransmission. Additionally, ROX and CTC affected pathways involved in mitochondrial stress response and endocrine system in zebrafish larvae. Besides, BDNF, ASCL1, and CREBBP are potential upstream regulatory factors that mediated these impacts. These findings indicated that exposure of CTC, ROX and CLA may cause abnormal behavior toward zebrafish larvae under environmental relevant concentration and revealed the potential role of neural cell apoptosis and synaptogenesis signaling in mediating this effect.

Bisphenol analogues induced social defects and neural impairment in zebrafish.

There is evidence in humans that endocrine disrupting chemicals exposure, such as bisphenol A (BPA), is tied to social behavior impacts when evaluated in early life stage. However, the potential social impact of BPA alternatives and its association with central nervous system (CNS) is poorly understood. Here, we performed behavioral test for zebrafish that are continuously exposed to environmental relevant concentrations (5 and 500 ng/L) of BPA, BPF, and BPAF since embryonic stage. Surprisingly, significant social behavior defects, including increased social distance and decreased contact time, were identified in zebrafish treated by 500 ng/L BPAF and BPA. These behavioral changes were accompanied by apparent histological injury, microglia activation, enhanced apoptosis and neuron loss in brain. The gut-brain transcriptional profile showed that genes involved in neuronal development pathways were up-regulated in all bisphenol analogs treatments, indicating a protective phenotype of CNS; however, these pathways were inhibited in gut. Besides, a variety of key regulators in the gut-brain regulation were identified based on protein interaction prediction, such as rac1-limk1, insrb1 and fosab. These findings implicated that the existence of bisphenol analogues in water would influence the social life of fish, and revealed a potential role of gut-brain transcriptional alteration in mediating this effect.