Arctigenin: An emerging candidate against infections of Gyrodactylus

Gyrodactylosis is a common parasitic disease that affects both farmed and wild fish. Current strategies of chemotherapy are not always satisfactory, requiring the discovery of new anthelmintic agents. Arctigenin is a natural dibenzylbutyrolactone lignin present in several plants with many biological activities. In this study, in vitro and in vivo anthelminthic efficacy of arctigenin against Gyrodactylus kobayashii in goldfish (Carassius auratus) is reported for the first time. In in vitro trials, exposure to arctigenin caused rapid declines in motility and ultimate death of worms. A positive correlation was seen between arctigenin concentrations and the time to parasite death, which, at the highest concentration of 8 mg/L occurred at 33 min. Bathing G. kobayashii-infected goldfish in arctigenin significantly reduced infection prevalences and intensities as compared to the control, with EC50 values of 1.85 and 1.58 mg/L after 24 and 48-h exposure, respectively, with 100% efficacy against G. kobayashii at 4.0 mg/L after only 4 h. Acute toxicity assay indicated that the LC50 of arctigenin against goldfish after 96-h exposure was 11.63 mg/L, which was 6.29 times higher than the 24 h EC50. The expression of four xenobiotic sensitive genes (cyp1a, hsp70, gst and sod) were significantly altered in the initial 48 h after arctigenin treatment, but had a tendency of returning to the initial level of gene expression after 96 h. In addition, SEM and TEM were used to study the specific action of arctigenin against gyrodactylids. SEM revealed that arctigenin-mediated worm killing was associated with tegumental damage and with damage seen by TEM to the mitochondria may be a cause of parasite death. Collectively, these findings demonstrate the potential of arctigenin as an alternative natural compound for controlling infections of Gyrodactylus. With further medicinal chemistry optimization, more potent arctigenin analogues offer promise for future combinatorial or replacement anthelmintic control