Assessment of thyroid endocrine disruption induced by florfenicol: Integrating in vivo zebrafish experiments and in silico molecular docking and dynamics simulations.

Florfenicol, a widely used veterinary antibiotic, is increasingly being detected in aquatic environments; however, its potential effects on thyroid hormone (TH) homeostasis remain unclear. This study integrated in vivo zebrafish assays with in silico molecular simulations to investigate the thyroid-disrupting effects of florfenicol and its underlying mechanisms. Exposure to environmentally relevant concentrations of florfenicol significantly reduced plasma T4 and T3 levels in zebrafish. This reduction was linked to dysregulated expression of the hypothalamus-pituitary-thyroid (HPT) axis genes, particularly transthyretin (TTR), deiodinase 2, and deiodinase 3. Additionally, molecular docking and dynamics simulations confirmed that florfenicol can stably bind to TTR and thyroid receptors α and β, with an affinity comparable to or higher than that of natural THs. Overall, these results demonstrate that florfenicol disrupts TH homeostasis by interfering with the HPT axis and directly affecting TH transport and receptor binding. Our study highlights the potential ecological risks of florfenicol to the thyroid endocrine system in aquatic wildlife.