Neurodevelopmental toxicity and Parkinsonism-like symptoms induced by nano-alumina exposure in zebrafish

Background Nano-alumina (nano-Al₂O₃) is a widely utilized nanomaterial. Its impacts on the environment and biological systems have garnered significant attention. Zebrafish serves as a common model organism in scientific research due to its high homology with the human genome and is extensively used in toxicity studies.

Objective To investigate the developmental toxicity and neurotoxicity of nano-Al₂O₃ exposure in zebrafish and the corresponding mechanisms of action.

Method Zebrafish embryos at 6 h post-fertilization (hpf) were randomly assigned to a control group and five dose groups exposed to nano-Al₂O₃ at concentrations of 200, 400, 600, 800, and 1000 μg·mL⁻¹, respectively. Thirty embryos were included in each group, and the culture medium was replaced every 24 h until 144 hpf. The hatching rates at 48 and 72 hpf and the cumulative malformation rates up to 144 hpf were calculated. At 144 hpf, a zebrafish behavior analyzer was used to record the movement trajectories of the zebrafish, and the total distance traveled and average speed were analyzed for each group. At 144 hpf, the development of dopaminergic neurons in transgenic zebrafish expressing vmat2: GFP, brain vessels in those expressing vegf: GFP, and central nervous system neurons in those expressing elavl3: EGFP were observed under a fluorescence microscope, and statistical analysis was conducted using Image Pro Plus. Real-time quantitative PCR was employed to detect the expression levels of neuron development-related genes (syn2α, gap43, dat), Lewy body formation-related gene (α-syn), and autophagy-related genes (pink1, parkin) at 144 hpf.

Results Compared to the control group, the nano-Al₂O₃ exposed groups exhibited reduced hatching rates at 48 hpf and increased cumulative malformation rates (P<0.05), with phenomena such as delayed development, absence of the swim bladder, and body curvature. The autonomous behavioral tests revealed that the nano-Al₂O₃ exposed zebrafish showed a decrease in the total distance swum (P<0.001) and a significant reduction in average speed compared to the control group. The fluorescence observations indicated that the length of dopaminergic neurons in vmat2: GFP transgenic zebrafish was reduced in the nano-Al₂O₃ exposed groups (P<0.001). Additionally, vegf: GFP transgenic zebrafish exhibited a significant absence of brain vessels, while elavl3: EGFP transgenic zebrafish showed a weakened fluorescence intensity of central nervous system neurons (P<0.001) and a decreased length of these neurons (P<0.01). The real-time quantitative PCR analysis revealed that compared to the control group, the gene expression levels of α-syn, syn2α, dat, and gap43 were upregulated in the zebrafish exposed to nano-Al₂O₃ (except for the 400 μg·mL⁻¹ exposure group) (P<0.01), while the expression levels of parkin were downregulated in the 600 and 800 μg·mL⁻¹ nano-Al₂O₃ exposed groups, and the expression levels of pink1 were downregulated in all exposure groups except for the 200 μg·mL⁻¹ group (P<0.05).

Conclusion Exposure to nano-Al₂O₃ exhibits developmental toxicity in zebrafish larvae and induces Parkinsonism-like symptoms in zebrafish. The preliminary speculation of the mechanism suggests that it may be related to nano-Al₂O₃-induced mitochondrial autophagy impairment.