[Antiviral activities against influenza virus (FM1) of bioactive fractions and representative compounds extracted from Banlangen (Radix Isatidis)].

To study the antiviral activities of clemastanin B (CB), epigoitrin, phenylpropanoids portion (PEP) and the mixture of phenylpropanoids, alkaloids and organic acid fractions (PEP+ALK+OA) from Banlangen (Radix Isatidis). The experiment consisted of four parts: therapeutic action, prophylaxsis action, inhibition of virus attachment, and direct virucidal action. Cytopathic effect (CPE) and 3-(4,5-Dimethylthiazol-2-yI)-2,5-diphenyltetrazolium (MTT) were used to assess antiviral activity. CB, epigoitrin, PEP and PEP + ALK +OA fractions from Banlangen (Radix Isatidis) extract significantly increased the viability of MDCK cells pre-infected with the virus compared with the virus control group in all the dilutions (P < 0.01). Pretreated with either pure compounds or chemical fractions of Banlangen (Radix Isatidis) extract in all the dilutions significantly improved the viability of MDCK cells (P < 0.01). The inhibition of virus absorption to the host cells by CB, epigoitrin and PEP was in a dose dependent manner. CB, epigoitrin, PEP and PEP+ ALK+ OA exert their anti-influenza activity by inhibiting the virus multiplication, prophylaxsis and blocking the virus attachment. The primary mode of action of PEP and PEP + ALK + OA is the inhibition of virus replication. The inhibitory effects on virus attachment and multiplication are the main modes for epigoitrin.