This experiment was conducted to study the antiviral activities of sodium tanshinone IIA sulfonate (STS) against porcine reproductive and respiratory syndrome virus (PRRSV) and its mechanism. Anti-PRRSV activities of STS were observed on Marc-145 cells by using visualization of cytopathologic effect assay and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test, and its antiviral mechanism was determined by time-of-addition assay, adsorption inhibition assay, and virucidal assay. The results showed that STS could reduce the damage of PRRSV to Marc-145 cells, with the inhibition ratio exceeding to 100%, at the maximum non-cytotoxic concentration. The time-of-addition and virucidal assays indicated that the anti-PRRSV activities of STS could be due to inhibiting the virus replication or/and inactivating the virus directly. The inhibition of the virus attachment was not discovered in adsorption inhibition assay. The results proved that STS had strong anti-PRRSV activity and encouraged for further exploration of STS.

DG and STS have great potential for developing new anti-MDV drugs for clinic application.

Context: The prevalence of infectious bursal disease has brought about enormous financial losses to the world poultry industry. Chinese herb medicines can provide valuable materials for discovery and development of new drugs. Objective: To screen constituents derived from Chinese herb medicines for their antiviral activity against infectious bursal disease virus (IBDV) in vitro. Materials and methods: Twenty constituents derived from Chinese herb medicines and B87 strain of IBDV were used. The 50% cytotoxic concentration (CC 50 ) and 50% effective concentration (EC 50 ) were determined by visualization of cytopathologic effect (CPE) and 3-(4,5-dimethyithiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) test on chicken embryo fibroblast. Selectivity index (SI) and inhibition ratio (%I) were calculated from the data obtained from the MTT test. Results: Antiviral assays showed dipotassium glycyrrhizinate and ligustrazine hydrochloride among the 20 constituents tested exhibited significant inhibitory activity against IBDV in a dose-dependent manner. EC 50 of dipotassium glycyrrhizinate and ligustrazine hydrochloride were 663.2 AE 268.4 and 92.52 AE 21.13 mg/mL, and SI were 44.52 and 421.62, respectively. The time-of-addition and virucidal assay indicated that anti-IBDV activity of the two constituents could be due to their inhibiting virus replication and/or inactivating virus directly. The inhibition of virus attachment was not observed in the adsorption inhibition assay. Dipotassium glycyrrhizinate and ligustrazine hydrochloride exhibited more than 70% and 80% inhibition of IBDV, respectively, at the maximum safe concentration. Discussion and conclusion: We believe that dipotassium glycyrrhizinate and ligustrazine hydrochloride can be used to develop a new anti-IBDV compound, and it is worth applying the constituents in clinical practice.