Virtual screening of FDA-approved drugs identifies amlodipine as a novel anti-Gyrodactylus kobayashii agent with therapeutic potential in aquaculture

Parasitic infestations remain a major challenge in aquaculture, causing substantial economic losses. Current treatments for gyrodactylosis predominantly rely on unapproved chemicals, which often exhibit suboptimal efficacy. In this study, a molecular docking approach was employed to elucidate interactions between FDA-approved drugs and key residues within the active site of Gyrodactylus kobayashii proteins. Using AutoDock Vina, we screened a library of FDA-approved compounds and identified amlodipine and colistin sulfate salt as the most potent candidates against G. kobayashii. The minimum concentrations required to achieve complete parasite eradication within 24 h were 13.0 mg/L for amlodipine and 16.0 mg/L for colistin sulfate salt. Given its lower toxicity to goldfish, amlodipine was selected for further investigation. In vitro assays demonstrated that amlodipine exhibited significant anthelmintic activity, with 18 mg/L eradicating 60.67 % of G. kobayashii within 2 h. Subsequent in vivo trials involving goldfish infected with G. kobayashii revealed that a 24-hour bath treatment with amlodipine reduced the total worm burden, achieving an EC₅₀ value of 10.537 mg/L, and 100 % efficacy at 13.0 mg/L. Acute toxicity assays determined an LC₅₀ of 19.653 mg/L for goldfish following 96 h of exposure to amlodipine. Furthermore, expression analyses of xenobiotic-sensitive genes (cyp1a and hsp70) indicated significant modulation post-treatment, with a gradual return to baseline levels over time. To further elucidate the mechanistic effects of amlodipine, we investigated the expression of key genes within the MAPK signaling pathway, including JNK, P53, SMAD4, JNK3, and C-JUN. Results showed that the expression of these genes was significantly influenced by both the concentration and duration of amlodipine exposure. These findings underscore the potential of virtual screening methodologies for identifying effective anthelmintic agents targeting specific proteins. This approach offers promising implications for the aquaculture industry, which has historically lagged behind other sectors in drug research and development.