Strictinin, which is a member of the ellagitanin family of hydrolyzable tannins, prevented replication of human, duck and swine influenza A viruses (IAVs) in vitro at non-toxic concentrations. The addition of strictinin at the same time as IAV inoculation to MDCK cells inhibited viral replication in a dose-dependent manner. Strictinin showed 50% inhibitory concentrations for IAVs from 0.09±0.021 to 0.28±0.037μM (mean±S.E.M.) by the focus-forming assay. Treatment of MDCK cells with strictinin before and after viral inoculation resulted in no significant antiviral activity. Further studies showed that strictinin inhibited IAV-induced hemifusion. However, strictinin exhibited no inhibitory effect against receptor binding, sialidase activity. Strictinin also showed an antiviral effect on influenza B virus and human parainfluenza virus type-1 in vitro. The results indicate that strictinin is a useful antiviral agent.
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