Saikosaponin D efficiently inhibits SVCV infection in vitro and in vivo

Spring viraemia of carp (SVC) triggered by spring viraemia of carp virus (SVCV), is an acute and highly lethal infectious disease for which there is currently no effective therapy. Saikosaponin D (SSD), one main constituent of Bupleurum yinchowense, increasingly draws attention for its extensive pharmacological activities. In this study, we explored the antiviral activity of SSD against SVCV in epithelioma papulosum cyprini (EPC) cells, zebrafish and common carp. By comparing inhibitory concentration at half-maximal activity (IC50), we found that SSD (IC50 = 0.21 mg/L) possessed higher anti-SVCV activity than all the natural products which had been reported until now. In accordance with its antiviral activity, SSD significantly reduced SVCV-induced apoptosis and recovered SVCV-activated caspase-3/8/9 activity. Compared with SVCV group, apoptotic cells were decreased by 17.63% and 32.16% after SSD treatment at 48 and 72 h post infection (pi), respectively. In addition, cellular morphological damage and reactive oxygen species (ROS) generation induced by SVCV were both inhibited by SSD treatment. More importantly, SSD was also effective to the treatment of SVCV infection in zebrafish and common carp. Intraperitoneal injection of SSD (6 mg/kg) increased the survival rate of zebrafish by 36% and inhibited SVCV nucleoprotein and glycoprotein gene expression by > 90% in kidney and spleen at 1th and 4th dpi. The survival rate of common carp was also increased by 32% after SSD (6 mg/kg) treatment. In summary, SSD is confirmed to be a natural product with the highest anti-SVCV activity up to now, and its application in the treatment of SVCV is promising in aquaculture.