Study effect and mechanism of ofloxacin and levofloxacin on development of Rana nigromaculata tadpoles based on the hypothalamus-pituitary-thyroid axis

Excessive antibiotics transferred into the aquatic environment may affect the development of amphibians. Pre-vious studies on the aquatic ecological risk of ofloxacin generally ignored its enantiomers. The purpose of this study was to compare the effects and mechanisms of ofloxacin (OFL) and levofloxacin (LEV) on the early development of Rana nigromaculata. After 28-day exposure at environmental levels, we found that LEV exerted more severe inhibitory effects on the development of tadpoles than OFL. According to the enrichment results of differentially expressed genes in the LEV and OFL treatments, LEV and OFL had different effects on the thyroid development of tadpoles. dio2 and trh were affected by the regulation of dexofloxacin instead of LEV. At the protein level, LEV was the main component that affected thyroid development-related protein, while dexo-floxacin in OFL had little effect on thyroid development. Furthermore, molecular docking results further confirmed that LEV was a major component affecting thyroid development-related proteins, including DIO and TSH. In summary, OFL and LEV regulated the thyroid axis by differential binding to DIO and TSH proteins, thereby exerting differential effects on the thyroid development of tadpoles. Our research is of great significance for comprehensive assessment of chiral antibiotics aquatic ecological risk.