Identification of plumbagin as an effective chemotherapeutic agent for treatment of Gyrodactylus infections

Abstract

Monogenean parasites are responsible for severe economic losses of both freshwater and marine aquaculture industries. Current chemotherapeutic treatments are consuming, expensive, and harmful to water quality and human health. Medicinal plants are a reliable source of alternative anthelmintic agents. In the pursuit of novel anti-monogenean drugs, in vivo anthelminthic efficacy of 26 selected phytochemical compounds was studied, by choosing Gyrodactylus kobayashi infecting goldfish (Carassius auratus) as a model. The screening results showed that four compounds (plumbagin (PLB), thymoquinone, osthole and psoralen) had the highest activity against G. kobayashii with EC99 value ranging from 0.4 to 4.0 mg/L after 48-h exposure. Among these active compounds, PLB was the most efficacious one and selected for the next study. In vitro trials revealed the clear anti-parasitic effects of PLB, with complete death at 45 min of exposure at a concentration of 2.0 mg/L, withdrawal of PLB afterward did not lead to the recovery of the exposed parasites. Bathing G. kobayashii infected goldfish in PLB also significantly reduced the worm burden, with an extremely low EC50 value of 0.09 mg/L after 48-h immersion. The results also showed that one short bath using very low concentrations of 0.4–0.7 mg/L for 30–60 min was effective in eliminating G. kobayashii infection with no visible fish toxicity. Acute toxicity assay indicated the 48-h LC50 of PLB against goldfish was 0.657 mg/L. Furthermore, SEM analysis displayed that PLB-mediated worm killing was associated with the tegumental damages. As seen by TEM, in vivo treatment against G. kobayashii with PLB also caused vacuolization and lysis of parasite's tegument, besides, differing degrees of damage to vitelline cells were observed in treated worms. Collectively, simple chemical structure along with the potent efficacy demonstrated that PLB could serve as an ideal leading compound in the development of a commercial drug to control Gyrodactylus infections in aquaculture