Antiviral effect of polyphenol-enriched extract of Rumex Acetosa L. against Influenza A virus

Although effective antiviral drugs are available for the treatment of influenza A virus (IAV) infection, the need for intensified drug discovery towards antiviral active compounds is obvious.

A polyphenol-enriched extract of Rumex acetosa L. (Polygonaceae), standardized on galloylated oligomeric proanthocyanidins, was tested for antiviral activity against IAV in vitro using MTT, plaque reduction and hemagglutination assay. The extract inhibited IAV replication in a dose-dependent manner. IC₅₀ and CC₅₀ values, as determined by MTT assay, were 2.2µg/mL and 79.2µg/mL, respectively, indicating a CC₅₀/IC₅₀ selectivity ratio of 36. This antiviral activity was confirmed by plaque reduction assay. To determine the mechanism of this antiviral effect, the extract was added at different stages during the viral replication cycle. The strongest antiviral effect was observed when the extract was added before adsorption of IAV to the cells, but in high concentrations an effect was also detected when extract was added after adsorption of IAV to and even after penetration of IAV into the cells, indicating the antiviral effect being associated not only with viral adsorption and penetration. Structure-activity relation of flavan-3-ols and oligomeric proanthocyanidins indicated that trihydroxylation of ring B or alternatively galloylation at position O-3 potentiate the antiviral activity. Detailed studies using the model compound procyanidin-B2-digallate indicated this compound as a potent inhibitor of IAV.