SDHI Fungicide Toxicity and Associated Adverse Outcome Pathways: What Can Zebrafish Tell Us?

Inhibition of human drug transporter activities by succinate dehydrogenase inhibitors

Succinate dehydrogenase inhibitors (SDHIs) are widely-used fungicides, to which humans are exposed and for which putative health risks are of concern. In order to identify human molecular targets for these environmental chemicals, the interactions of 15 SDHIs with activities of main human drug transporters implicated in pharmacokinetics were investigated in vitro. 5/15 SDHIs, i.e., benzovindiflupyr, bixafen, fluxapyroxad, pydiflumetofen and sedaxane, were found to strongly reduce activity of the renal organic anion transporter (OAT) 3, in a concentration-dependent manner (with IC50 values in the 1.0-3.9 μM range), without however being substrates for OAT3. Moreover, these 5/15 SDHIs decreased the membrane transport of estrone-3 sulfate, an endogenous substrate for OAT3, and sedaxane was predicted to inhibit in vivo OAT3 activity in response to exposure to the acceptable daily intake (ADI) dose. In addition, pydiflumetofen strongly inhibited the renal organic cation transporter (OCT) 2 (IC50 = 2.0 μM) and benzovindiflupyr the efflux pump breast cancer resistance protein (BCRP) (IC50 = 3.9 μM). Other human transporters, including organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 as well as multidrug and toxin extrusion protein (MATE) 1 and MATE2-K were moderately or weakly inhibited by SDHIs, whereas P-glycoprotein, multidrug resistance-associated protein (MRP), OCT1 and OAT1 activities were not or only marginally impacted. Then, some human drug transporters, especially OAT3, constitute molecular targets for SDHIs. This could have toxic consequences, notably with respect to levels of endogenous compounds and metabolites substrates for the considered transporters or to potential SDHI-drug interactions. This could therefore contribute to putative health risk of these fungicides.

3D-QSAR-Directed Synthesis of Halogenated Coumarin-3-Hydrazide Derivatives: Unveiling Their Potential as SDHI Antifungal Agents

The pursuit of new succinate dehydrogenase (SDH) inhibitors is a leading edge in fungicide research and development. The use of 3D quantitative structure-activity relationship (3D-QSAR) models significantly enhances the development of compounds with potent antifungal properties. In this study, we leveraged the natural product coumarin as a molecular scaffold to synthesize 74 novel 3-coumarin hydrazide derivatives. Notably, compounds 4ap (0.28 μg/mL), 6ae (0.32 μg/mL), and 6ah (0.48 μg/mL) exhibited exceptional in vitro effectiveness against Rhizoctonia solani, outperforming the commonly used fungicide boscalid (0.52 μg/mL). Furthermore, compounds 4ak (0.88 μg/mL), 6ae (0.61 μg/mL), 6ah (0.65 μg/mL), and 6ak (1.11 μg/mL) showed significant activity against Colletotrichum orbiculare, surpassing both the SDHI fungicide boscalid (43.45 μg/mL) and the broad-spectrum fungicide carbendazim (2.15 μg/mL). Molecular docking studies and SDH enzyme assays indicate that compound 4ah may serve as a promising SDHI fungicide. Our ongoing research aims to refine this 3D-QSAR model further, enhance molecular design, and conduct additional bioactivity assays.

Cardiac and neurobehavioral impairments in three phylogenetically distant aquatic model organisms exposed to environmentally relevant concentrations of boscalid

Boscalid (2-Chloro-N-(4'-chlorobiphenyl-2-yl) nicotinamide), a pyridine carboxamide fungicide, is an inhibitor of the complex II of the respiration chain in fungal mitochondria. As boscalid is only moderately toxic for aquatic organisms (LC50 > 1-10 mg/L), current environmental levels of this compound in aquatic ecosystems, in the range of ng/L-μg/L, are considered safe for aquatic organisms. In this study, we have exposed zebrafish (Danio rerio), Japanese medaka (Oryzias latipes) and Daphnia magna to a range of concentrations of boscalid (1-1000 μg/L) for 24 h, and the effects on heart rate (HR), basal locomotor activity (BLA), visual motor response (VMR), startle response (SR), and habituation (HB) to a series of vibrational or light stimuli have been evaluated. Moreover, changes in the profile of the main neurotransmitters have been determined. Boscalid altered HR in a concentration-dependent manner, leading to a positive or negative chronotropic effect in fish and D. magna, respectively. While boscalid decreased BLA and increased VMR in Daphnia, these behaviors were not altered in fish. For SR and HB, the response was more species- and concentration-specific, with Daphnia exhibiting the highest sensitivity. At the neurotransmission level, boscalid exposure decreased the levels of L-aspartic acid in fish larvae and increased the levels of dopaminergic metabolites in D. magna. Our study demonstrates that exposure to environmental levels of boscalid alters cardiac activity, impairs ecologically relevant behaviors, and leads to changes in different neurotransmitter systems in phylogenetically distinct vertebrate and invertebrate models. Thus, the results presented emphasize the need to review the current regulation of this fungicide.

Nontargeted metabolomic insights into the behavioral effects of 5-MeO-MiPT in zebrafish (Danio rerio)

5-Methoxy-N-methyl-N-isopropyltryptamine (5-MeO-MiPT) is a novel psychoactive substance exhibiting a tryptamine structure. Despite its increasing prevalence, the environmental impact of 5-MeO-MiPT remains unexplored. Our prior investigation revealed that 5-MeO-MiPT induced inhibited spontaneous movement and prompted anxiety-like behavior in adult zebrafish-a validated toxicological model. To elucidate this phenomenon and establish a correlation between metabolomics and behavioral changes induced by 5-MeO-MiPT, zebrafish were administered varying drug concentrations. Zebrafishes were subjected to injections of different 5-MeO-MiPT concentrations. Subsequent metabolomic analysis of endogenous metabolites affected by the drug unveiled substantial variations in metabolic levels between the control group and the drug-injected cohorts. A total of 22 distinct metabolites emerged as potential biomarkers. Further scrutiny identified seven pathways significantly influenced by 5-MeO-MiPT. A focused exploration into amino acid metabolism, lipid metabolism, and energy metabolism unveiled that the metabolic repercussions of 5-MeO-MiPT on zebrafish resulted in observable brain damage. Notably, the study identified a consequential disruption in the liver-brain pathway. The comprehensive metabolomic approach employed herein effectively discerned the impact of 5-MeO-MiPT on zebrafish metabolism. This approach also shed light on the mechanism underpinning the anxiety-like behavior observed in zebrafish post-drug injection. Specifically, our findings indicate that 5-MeO-MiPT induces brain damage, particularly within the liver-brain pathway.

Integrated histopathology and transcriptome metabolome profiling reveal the toxicity mechanism of phenazine-1-carboxylic acid in zebrafish

Phenazine-1-carboxylic acid (PCA) is a new type of agrochemical used to prevent plant diseases, but its effects on aquatic organisms are unclear. To comprehensively assess the impacts of PCA for aquatic organisms and its associated environmental risks, this study investigated, taking zebrafish as the research object, the toxicological mechanism of PCA by means of optical microscopy, hematoxylin and eosin (HE) staining, ultrastructural observation, physiological and biochemical testing, transcriptome sequencing, metabolome analysis, fluorescence quantitative PCR and molecular simulation. The results indicated that PCA was detrimental to zebrafish embryos, larvae and adults, with LC50 values at 96 h of 3.9093 mg/L, 8.5075 mg/L, and 13.6388 mg/L, respectively. PCA caused abnormal spontaneous movement, slowed the heart rate, delayed hatching, shortened the body length, slowed growth, and caused malformations. PCA mainly affected the brain, liver, heart, and ovaries. PCA distorted cell morphology, damaged mitochondrial membranes, disintegrated mitochondrial ridges, and dissociated nuclear membranes. PCA inhibited the enzyme activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX), decreased the malondialdehyde (MDA) content and disrupted antioxidant effects. The results of omics studies confirmed that PCA interfered with the transcriptional and metabolic network of zebrafish, downregulating most genes and metabolites. PCA mainly affected functions related to mitochondrial steroids, lipids, sterols, oxidoreductase activity and pathways involving cofactors, steroids, porphyrin, cytochromes, which specifically bound to targets such as panx3, agmat, and ace2. PCA was moderately toxic to zebrafish, and its usage should be strictly controlled to reduce toxic effects on aquatic organisms. The results of this study provide a new insights for ecotoxicology research.

Comprehensive evaluation of chiral sedaxane with four stereoisomers for risk reduction: Bioactivity, toxicity, and stereoselective dissipation in crop planting systems

A comprehensive evaluation of chiral pesticide at the stereoisomeric level is an effective strategy to improve efficiency and reduce risk on foods. For chiral sedaxane with four stereoisomers, there were 517-1013 fold differences in bioactivity for three kinds of phytopathogens and 3.73 fold differences in toxicity against model organism (Danio rerio) between the best (trans-1R2S-sedaxane) and worst stereoisomer (cis-1S2S-sedaxane). Trans-1R2S-sedaxane had the strongest affinity with the active site than other stereoisomers, which might contribute to the highest bioactivity. Trans-sedaxane was 28.2-331 fold more effective than cis-sedaxane. The dissipation half-lives of sedaxane stereoisomers ranged from 3.28 to 30.7 d in the test crops and soils. Trans-1S2R-sedaxane and cis-1S2S-sedaxane were preferentially dissipated in corn plants, while the preferential dissipation of trans-1R2S-sedaxane was found in wheat plants, potato plants and corn soil. The preferential dissipation of trans-sedaxane in corn plants, wheat plants, potato plants and corn soil would be environmentally friendly.

Evaluation of the toxic effects of fluindapyr, a novel SDHI fungicide, to the earthworms Eisenia fetida

The emergence of resistance to existing succinate dehydrogenase inhibitor fungicides (SDHIs) calls for the urgent innovation of novel formulations, but also results in an increase information gap on the ecological risks of novel SDHIs especially to non-target organisms. Herein, the environmental behavior and toxicological effects of a novel SDHI, fluindapyr (FIP), were evaluated using earthworm as model non-target organism. Results showed that FIP had a relatively shorter half-live (about 28 days) in artificial soil compared with traditional SDHIs. Besides, FIP exhibited a rapid uptake and bioaccumulation trend in earthworms. For the toxicological effects, FIP suppressed earthworm growth (≥ 5 mg/kg) and reproduction (≥ 1 mg/kg) whereas no lethal effects were observed up to the highest tested concentration of 25 mg/mg. FIP of high exposure concentrations also induced serious epidermis and intestines damage as well as oxidative stress to earthworms after 28-day exposure. In addition, expression of oxidative damage related genes (CAT, CRT, GST, HSP70, SOD) was further verified after FIP exposure. The earthworm Tier 1 RQ also indicated a potential risk for earthworm reproduction. Data presented here may be useful for the risk assessments of FIP in soil ecosystems and help to set appropriate precautions to ensure protection against novel SDHIs.

Neurobehavioral effects of fungicides in zebrafish: a systematic review and meta-analysis

Pesticides are widely used in global agriculture to achieve high productivity levels. Among them, fungicides are specifically designed to inhibit fungal growth in crops and seeds. However, their application often results in environmental contamination, as these chemicals can persistently be detected in surface waters. This poses a potential threat to non-target organisms, including humans, that inhabit the affected ecosystems. In toxicologic research, the zebrafish (Danio rerio) is the most commonly used fish species to assess the potential effects of fungicide exposure, and numerous and sometimes conflicting findings have been reported. To address this, we conducted a systematic review and meta-analysis focusing on the neurobehavioral effects of fungicides in zebrafish. Our search encompassed three databases (PubMed, Scopus, and Web of Science), and the screening process followed predefined inclusion/exclusion criteria. We extracted qualitative and quantitative data, as well as assessed reporting quality, from 60 included studies. Meta-analyses were performed for the outcomes of distance traveled in larvae and adults and spontaneous movements in embryos. The results revealed a significant overall effect of fungicide exposure on distance, with a lower distance traveled in the exposed versus control group. No significant effect was observed for spontaneous movements. The overall heterogeneity was high for distance and moderate for spontaneous movements. The poor reporting practices in the field hindered a critical evaluation of the studies. Nevertheless, a sensitivity analysis did not identify any studies skewing the meta-analyses. This review underscores the necessity for better-designed and reported experiments in this field.

The role of miRNA-26a-5p and target gene socs1a in flutolanil induced hepatotoxicity of zebrafish at environmental relevant levels

Flutolanil has been detected worldwide in aquatic environment and fish, which has become an undeniable stressor on ecosystem and human health. Flutolanil has been reported to be toxic to aquatic organisms. However, the pathophysiological and molecular mechanism behind the detrimental effects remains obscure. Here we reported hepatotoxicity induced by flutolanil in HepG2 cells and zebrafish, as revealed by toxicokinetic, HE staining, miRNAs-mRNAs sequencing, molecular dynamic simulations and dual luciferase reporter assays. Collectively, our results indicated that flutolanil could be absorbed by and accumulated in the liver of zebrafish, causing hepatic vacuolar degeneration, steatosis and nuclear condensation and abnormal liver function, where its exposure at environmental levels disrupted the expressions of miRNA-26a-5p and its target gene socs1a by mediating JAK-STAT signaling pathway, which was partially responsible for hepatotoxicity, correlated with oxidative stress, cell apoptosis, inflammation, cell cycle disorder and mitochondrial dysfunction. These findings suggest that miRNA-26a-5p/socs1a can serve as potential biomarkers of hepatotoxicity in zebrafish following exposure to flutolanil. This uncovered route will provide a new tool for the risk assessment of flutolanil and a guide to proper use of flutolanil and environmental remedy, and open up a new horizon for liver disease assessment.

Development of S-penthiopyrad for bioactivity improvement and risk reduction from the systemic evaluation at the enantiomeric level

For the purpose of screening high-efficiency and low-risk green pesticides, a systematic study on fungicide penthiopyrad was conducted at the enantiomeric level. The bioactivity of S-(+)-penthiopyrad (median effective concentration (EC50), 0.035 mg/L) against Rhizoctonia solani was 988 times higher than R-(-)-penthiopyrad (EC50, 34.6 mg/L), which would reduce 75% usage of rac-penthiopyrad under the same efficacy. Furthermore, their antagonistic interaction (toxic unit (TUrac), 2.07) indicated the existence of R-(-)-penthiopyrad would reduce the fungicidal activity of S-(+)-penthiopyrad. AlphaFold2 modeling and molecular docking illustrated that S-(+)-penthiopyrad had the higher binding ability with the target protein than R-(-)-penthiopyrad, showing higher bioactivity. For model organism Danio rerio, S-(+)-penthiopyrad (median lethal concentrations (LC50), 3.02 mg/L) and R-(-)-penthiopyrad (LC50, 4.89 mg/L) were both less toxic than rac-penthiopyrad (LC50, 2.73 mg/L), and the existence of R-(-)-penthiopyrad could synergistically enhance the toxicity of S-(+)-penthiopyrad (TUrac, 0.73), using S-(+)-penthiopyrad would reduce at least 23% toxicity to fish. The enantioselective dissipation and residues of rac-penthiopyrad were tested in three kinds of fruits, and their dissipation half-lives ranged from 1.91 to 23.7 d. S-(+)-penthiopyrad was dissipated preferentially in grapes, which was R-(-)-penthiopyrad in pears. On the 60th d, the residue concentrations of rac-penthiopyrad in grapes were still higher than its maximum residue limit (MRL), but the initial concentrations were lower than their MRL values in watermelons and pears. Thus, more tests in different cultivars of grapes and planting environments should be encouraged. Based on the acute and chronic dietary intake risk assessments, the risks in the three fruits were all acceptable. In conclusion, S-(+)-penthiopyrad is a high-efficiency and low-risk alternative to rac-penthiopyrad.

Bixafen causes hepatotoxicity and pancreas toxicity in zebrafish (Danio rerio)

Bixafen (BIX), a widely used succinate dehydrogenase inhibitor (SDHI) in agricultural disease control, has garnered significant attention due to its known hazardous effects on aquatic organisms. In this study, we exposed zebrafish embryos to 0.1, 0.2, and 0.3 μM BIX, to explore the impact of BIX on liver and pancreas. The results showed that BIX caused deformities and dysfunction in zebrafish embryos, including spinal curvature, pericardial edema, heart rate decrease, and hatching delay. Moreover, BIX significantly affected the development of the liver and pancreas in zebrafish and downregulated zebrafish fabp10a gene expression. Overall, this study presents strong evidence for BIX's potential toxicity to zebrafish liver and pancreas. The results may provide new insights into the evaluation of BIX'S impact on aquatic organisms.

Probing the Interaction between Isoflucypram Fungicides and Human Serum Albumin: Multiple Spectroscopic and Molecular Modeling Investigations

To better understand the potential toxicity risks of isoflucypram in humans, The interaction between isoflucypram and HSA (human serum albumin) was studied through molecular docking, molecular dynamics simulations, ultraviolet-visible absorption, fluorescence, synchronous fluorescence, three-dimensional fluorescence, Fourier transform infrared spectroscopies, and circular dichroism spectroscopies. The interaction details were studied using the molecular docking method and molecular dynamics simulation method. The results revealed that the effect of isoflucypram on human serum albumin was mixed (static and dynamic) quenching. Additionally, we were able to obtain important information on the number of binding sites, binding constants, and binding distance. The interaction between isoflucypram and human serum albumin occurred mainly through hydrogen bonds and van der Waals forces. Spectroscopic results showed that isoflucypram caused conformational changes in HSA (human serum albumin), in which the α-helix was transformed into a β-turn, β-sheet, and random coil, causing the HSA structure to loosen. By providing new insights into the mechanism of binding between isoflucypram and human serum albumin, our study has important implications for assessing the potential toxicity risks associated with isoflucypram exposure.

Adverse effects and potential mechanisms of fluxapyroxad in Xenopus laevis on carbohydrate and lipid metabolism

Fungicides are one of significant contributing factors to the rapid decline of amphibian species worldwide. Fluxapyroxad (FLX), an effective and broad-spectrum succinate dehydrogenase inhibitor fungicide, has attracted major concerns due to its long-lasting in the environment. However, the potential toxicity of FLX in the development of amphibians remains mostly unknown. In this research, the potential toxic effects and mechanisms of FLX on Xenopus laevis were investigated. In the acute toxicity test, the 96 h median lethal concentration (LC₅₀) of FLX to X. laevis tadpoles was 1.645 mg/L. Based on the acute toxicity result, tadpoles at the stage 51 were exposed to 0, 0.00822, 0.0822, and 0.822 mg/L FLX during 21 days. Results demonstrated that FLX exposure led to an apparent delay in the growth and development of tadpoles and associated with severe liver injury. Additionally, FLX induced glycogen depletion and lipid accumulation in the liver of X. laevis. The biochemical analysis of plasma and liver indicated that FLX exposure could perturb liver glucose and lipid homeostasis by altering enzyme activity related to glycolysis, gluconeogenesis, fatty acid synthesis, and oxidation. Consistent with the biochemical result, FLX exposure altered the liver transcriptome profile, and the enrichment analysis of differential expression genes highlighted the adverse effects of FLX exposure on steroid biosynthesis, PPAR signaling pathway, glycolysis/gluconeogenesis, and fatty acid metabolism in the tadpole liver. Overall, our study was the first to reveal that sub-lethal concentrations of FLX could induce liver damage and produce obvious interference effects on carbohydrate and lipid metabolism of Xenopus, providing new insight into the potential chronic hazards of FLX for amphibians.

Inhibition of Succinate Dehydrogenase by Pesticides (SDHIs) and Energy Metabolism

Succinate dehydrogenase (SDH) is one of the enzymes of the tricarboxylic acid cycle (Krebs cycle) and complex II of the mitochondrial respiratory chain. A class of fungicides (SDHIs) targets the complex II reaction in the SDH. A large number of those in use have been shown to inhibit SDH in other phyla, including humans. This raises questions about possible effects on human health and non-target organisms in the environment. The present document will address metabolic consequences in mammals; it is neither a review on SDH nor is it about the toxicology of SDHIs. Most clinically relevant observations are linked to a severe decrease in SDH activity. Here we shall examine the mechanisms for compensating a loss of SDH activity and their possible weaknesses or adverse consequences. It can be expected that a mild inhibition of SDH will be compensated by the kinetic properties of this enzyme, but this implies a proportionate increase in succinate concentration. This would be relevant for succinate signaling and epigenetics (not reviewed here). With regard to metabolism, exposure of the liver to SDHIs would increase the risk for non-alcoholic fatty liver disease (NAFLD). Higher levels of inhibition may be compensated by modification of metabolic fluxes with net production of succinate. SDHIs are much more soluble in lipids than in water; consequently, a different diet composition between laboratory animals and humans is expected to influence their absorption.

Succinate dehydrogenase complex subunit C: Role in cellular physiology and disease

Succinate dehydrogenase complex subunit C (SDHC) is a subunit of mitochondrial complex II (MCII), which is also known as succinate dehydrogenase (SDH) or succinate: ubiquinone oxidoreductase. Mitochondrial complex II is the smallest respiratory complex in the respiratory chain and contains four subunits. SDHC is a membrane-anchored subunit of SDH, which connects the tricarboxylic acid cycle and the electron transport chain. SDH regulates several physiological processes within cells, plays an important role in generating energy to maintain normal cell growth, and is involved in apoptosis. Currently, SDHC is generally recognized as a tumor-suppressor gene. SDHC mutations can cause oxidative damage in the body. It is closely related to the occurrence and development of cancer, neurodegenerative diseases, and aging-related diseases. Here, we review studies on the structure, biological function, related diseases of SDHC, and the mev-1 Animal Model of SDHC Mutation and its potential use as a therapeutic target of certain human diseases.

Chronic toxic effects of isoflucypram on reproduction and intestinal energy metabolism in zebrafish (Danio rerio)

The intestine is a vital organ involved in chemical and nutrient uptake and biotransformation. Intestinal dysfunction can impair energy and material supply for reproduction. Isoflucypram, a new succinate dehydrogenase inhibitor fungicide, is highly toxic to aquatic systems. However, the chronic toxic effects of isoflucypram on intestinal differentiation in aquatic organisms remain unknown. In this study, zebrafish (F0, 4-month-old) were exposed to 0, 0.008, or 0.08 μM isoflucypram for 120 days. After 90 days of exposure, F0 generations of adult zebrafish were paired, and the corresponding F1 generation embryos were obtained and observed. After 120 days of exposure, the gut of F0 generation zebrafish was collected, and intestinal histopathology and mitochondrial morphology were analyzed. Exposure to 0.08 μM isoflucypram resulted in significant death, hatching delay, and malformation (blood clot clustering, pericardial edema, and microphthalmia) of F1 embryos and larvae. Exposure to isoflucypram caused irregular and swollen villi in the zebrafish gut, accompanied by alterations in the intestinal mitochondrial ultrastructure. In addition, the differentially expressed genes involved in mitochondrial energy metabolism were significantly enriched. Overall, our data suggest that chronic exposure to isoflucypram is associated with reproductive and intestinal dysfunction in adult zebrafish.

Fluxapyroxad disrupt erythropoiesis in zebrafish (Danio rerio) embryos

Fluxapyroxad, a succinate dehydrogenase inhibitor (SDHI) fungicide, is commercialized worldwide to control a variety of fungal diseases. Growing evidence shows that fluxapyroxad is teratogenic to aquatic organisms. In this study, the influence of fluxapyroxad toward hematopoietic development was evaluated using zebrafish embryos which were exposed to fluxapyroxad (0.03 µM, 0.3 µM and 3 µM) from 3 h post fertilization (hpf) to 3 days post fertilization (dpf). Compared to the control groups, the hemoglobin was ectopic and decreased in response to fluxapyroxad treatment. The transcription levels of genes (hbbe1, hbbe2, and gata1a) involved in erythropoiesis were reduced after exposure to fluxapyroxad. In contrast, the distributions and expression of marker genes for myeloid lineage cells were unaffected by fluxapyroxad exposure. Our data suggested that fluxapyroxad might specifically affect erythropoiesis and hold great promise for the assessment of the toxicity of fluxapyroxad to aquatic organisms.

The adverse effects of fluxapyroxad on the neurodevelopment of zebrafish embryos

Fluxapyroxad (Flu), one of the succinate dehydrogenase-inhibited (SDHI) fungicides, has been extensively used in crop fungal disease control. Despite its increasing use in modern agriculture and long-term retention in the environment, the potentially toxic effects of Flu in vivo, especially on neurodevelopment, remain under-evaluated. In this study, zebrafish embryos were exposed to Flu at concentrations of 0.5, 0.75, and 1 mg/L for 96 h to evaluate the neurotoxicity of Flu. The results showed that Flu caused concentration-dependent malformations, including shorter body length, smaller head and eyes, and yolk sac edema. After exposure to Flu, larval zebrafish exhibited severe motor aberrations. Flu at a concentration of 1 mg/L significantly decreased dopamine level and notably altered acetylcholinesterase (AChE) activity and acetylcholine (ACh) content. Abnormal central nervous system (CNS) neurogenesis and disordered motor neuron development were observed in Tg (HUC-GFP) and Tg (hb9-GFP) zebrafish in Flu-treated groups. The expression of key genes involved in neurotransmission and neurodevelopment further proved that Flu impaired the zebrafish nervous system. This work contributes to our understanding of the neurotoxic effects and mechanisms induced by Flu in zebrafish and may help us take precautions against the neurotoxicity of Flu.