Antiparasitic efficacy of dihydrosanguinarine and dihydrochelerythrine from Macleaya microcarpa against Ichthyophthirius multifiliis in richadsin (Squaliobarbus curriculus)

Ichthyophthirius multifiliis is a holotrichous protozoan that invades the gills and skin surfaces of fish and can cause morbidity and high mortality in most species of freshwater fish worldwide. The present study was undertaken to investigate the antiparasitic activity of crude extracts and pure compounds from the leaves of Macleaya microcarpa. The chloroform extract showed a promising antiparasitic activity against I. multifiliis. Based on these finding, the chloroform extract was fractionated on silica gel column chromatography in a bioactivity-guided isolation affording two compounds showing potent activity. The structures of the two compounds were elucidated as dihydrosanguinarine and dihydrochelerythrine by hydrogen and carbon-13 nuclear magnetic resonance spectrum and electron ionization mass spectrometry. The in vivo tests revealed that dihydrosanguinarine and dihydrochelerythrine were effective against I. multifiliis with median effective concentration (EC50) values of 5.18 and 9.43 mg/l, respectively. The acute toxicities (LC50) of dihydrosanguinarine and dihydrochelerythrine for richadsin were 13.3 and 18.2 mg/l, respectively. The overall results provided important information for the potential application of dihydrosanguinarine and dihydrochelerythrine in the therapy of serious infection caused by I. multifiliis.