In vivo and in vitro antiviral activity of five Tibetan medicinal plant extracts against herpes simplex virus type 2 infection

Extracts from five Tibetan medicinal plants collected from the Tibetan Plateau were evaluated for antiviral activity against herpes simplex virus type 2 (HSV-2) in vitro and in vivo. Viral plaque reduction assays showed that extracts from four out of five plants inhibited HSV-2 infection significantly with 50% effective concentrations (EC50) values ranging from 0.35 ± 0.11 to 1.83 ± 0.21 mg/mL. The other plant, Swertia mussotii Franch. (Gentianaceae), exhibited activity in inhibiting the viral biosynthesis. In the attachment assay, two plants, Dracocephalum heterophyllum Benth. (Lamiaceae) and Dracocephalum tanguticum Maxim. (Lamiaceae) reduced the attachment of HSV-2 to cell surface. Interestingly, all of the extracts showed virucidal activity. Analyzed by real-time PCR, three extracts showed strong inhibition of HSV DNA replication with Dracocephalum heterophyllum and Dracocephalum tanguticum at the concentration of 4 mg/mL and Lagotis brevituba Maxim. (Scrophulariaceae) at 1 mg/mL. BALB/c mice were used for determining in vivo efficacy. Mice encephalitis herpes models were established by infection with HSV-2. The extracts of Dracocephalum heterophyllum, Dracocephalum tanguticum, and Swertia mussotii at a dose of 1 g/kg per day significantly prolonged the mean survival times and reduced the mortality of HSV-2 infected mice compared with control group (P