Developmental toxicities of albendazole and its metabolites in zebrafish (Danio rerio) embryos

Albendazole (ABZ) is a benzimidazole anthelmintic medicine widely used in livestock and, especially, aquaculture industries. Given its widespread use, ABZ commonly enters waterways, negatively impacting aquatic organisms. Classified as Pregnancy Category C because of its teratogenic properties, ABZ poses a high risk of developmental toxicity. In this study, zebrafish (Danio rerio) embryos were used to assess the developmental toxicity of ABZ and its two metabolites, ABZ-sulfoxide and ABZ-sulfone. Among these, only ABZ exhibited strong lethality, demonstrating an LC₅₀ value of 83.3 μg/L, and induced extensive phenotypic changes, including pericardial edema and reduced midbrain and eye areas. Using Tg(cmlc2:EGFP) embryos to assess cardiac morphology, 75 μg/L of ABZ was confirmed to induce a vertical alignment of the atrium and ventricle, instead of the normal S-shaped configuration, and significant reductions in heart rate and ejection fraction were observed. Using ABZ-treated Tg(HuC:EGFP) embryos, neurodevelopmental toxicity was confirmed, with 75 μg/L of ABZ eliminating both intraocular and cranial neuronal signaling. Moreover, early neural function, assessed using tail coiling frequency at 24 h post-fertilization, was significantly reduced in ABZ-treated embryos. Impaired optic neurogenesis was also confirmed, with significant decreases in pax2a and pax6a gene expression. Acridine orange staining identified apoptotic changes, mainly in the head, and inflammatory responses increased in ABZ-treated Tg(mpx:EGFP) embryos, accompanied by increases in mpx (neutrophil marker, 3-fold) and il1β (cytokine, 30-fold) expression. This study showed that ABZ induced severe developmental toxicity at low concentrations, demonstrating that its presence in the environment should be carefully monitored.