Epicatechin gallate: A promising agent isolated from Sargentodoxa cuneata for the treatment of ichthyophthiriasis in goldfish (Carassius auratus)

Abstract

Ichthyophthirius multifiliis is a pathogenic parasite of freshwater fish that threatens the sustainability of aquaculture industry globally. Our previous studies have identified Sargentodoxa cuneata ethanol extracts exhibited potent antiparasitic activity against I. multifiliis. However, the active ingredients in S. cuneata remain unknown. In this study, we isolated an active compound from S. cuneata by bioassay-guided fractionation and identified it as epicatechin gallate (ECG) by NMR, FT-IR and HR-MS spectroscopy. In vitro assays revealed that ECG was effective against all the free-living stages of I. multifiliis. ECG could cause 100% mortality of theronts at 0.3 mg/L within 30.6 ± 0.4 min, and terminate reproduction of protomonts and tomonts at concentrations of 2.0 and 10.0 mg/L, respectively. Morphologically, 2.0 mg/L ECG treatment for 2 h induced the loss of plasma membrane integrity and leakage of intracellular contents of the protomont. Moreover, an in vivo parasite‑goldfish infection model was applied to evaluate the efficacy of ECG on prevention and treatment of ichthyophthiriasis. The results showed that 2.0 mg/L ECG treatment for 12 days could cure goldfish ichthyophthiriasis and significantly increase the survival rate of the infected goldfish by 86.7%. Acute toxicity test revealed that ECG was relatively safe to goldfish, with a median lethal concentration (LC50) value of 63.7 mg/L, which was >30 times higher than effective concentration against I. multifiliis in vivo. Overall, our data indicated that ECG had the potential as a novel antiparasitic agent for the treatment of ichthyophthiriasis in aquaculture.