Isoimperatorin: A promising anti Gyrodactylus kobayashii natural compound from Angelica dahurica

Current gyrodactylids treatments using chemicals such as rotenone, piperazine and trichlorfon cause environmental and human health issues, especially their toxicity to the host. Therefore, search for alternative anthelmintic agents is urgent and natural compounds from herbs show promising solution to this problem. In our previous study, we screened 33 herbal medicines and found that Angelica dahurica has a good anthelmintic efficacy. In order to identify the active compounds from Angelica dahurica, bioassay-guided isolation was performed using a Carassius auratus - Gyrodactylus kobayashii model in this study. After extraction, purification and characterization step by step, isoimperatorin was eventually separated as the main active ingredient for eradicating G. kobayashii in goldfish. Compared to the control groups, bathing G. kobayashii-infected goldfish in isoimperatorin significantly reduced infection prevalence and intensity, with EC50 values of 0.63 (24 h) and 0.53 mg/L (48 h), respectively. Acute toxicity assays indicated that the LC50 (96 h) of isoimperatorin against goldfish was 10.16 mg/L, which was 19.17 times higher than EC50 (48 h). In addition, scanning electron microscope (SEM) and RT-qPCR were used to explore the anthelminthic mechanism of isoimperatorin. TEM results showed that after exposure to isoimperatorin, morphological alterations in the tegument of G. kobayashii were observed, which disrupted its homeostasis. Besides, isoimperatorin significantly downregulated the expression of ATPase genes (ATP5A1, ATP5C, ATP5F) and oxidative phosphorylation pathway genes (NDUFS8, NDUFA8, SDH). After treatment with isoimperatorin, the content of ATP in the worms decreased significantly. In summary, isoimperatorin showed promising anti G. kobayashii efficacy via damaging tegument, supplying insufficient energy to the G. kobayashii.