Spirodiclofen inhibited melanin synthesis in zebrafish embryos

Spirodiclofen has been registered and marketed in more than 50 countries worldwide and are widely used because of their broad-spectrum acaricidal activity and long-lasting efficacy. However, its environmental toxicological assessment to fish remains poorly understood. In the present study, zebrafish embryos were modelled and exposed to series concentration of spirodiclofen. It has been found that spirodiclofen exposure induced zebrafish embryos abnormal pigmentation, the quantitative analysis of melanin in images using Image J showed a significant decrease in the proportion of melanin area in zebrafish exposed to 0.146 mg/L treatment group at 48 and 96 h, respectively. ELISA analysis illustrated that zebrafish embryos exposed to 0.146 mg/L exhibited a significant decrease in the levels of melanin, tyrosinase and dopachrome tautomerase content, and in constant with these results, the genes involved in melanin synthesis (Tyr, Dct and Pck-β) were significantly downregulated, indicating that melanin synthesis was inhibited. The molecular docking showed that spirodiclofen had a lower binding energy with tyrosinase compared to other compounds. The results demonstrated that spirodiclofen interfered zebrafish embryos melanin synthesis. This provided new insights into the mechanism of spirodiclofen toxicity to zebrafish embryos.