Antiviral activity of organic solvent factions of Houttuynia cordata and Lespedeza cuneata against influenza A virus

Influenza virus infection remains considerable health threats to humans and animals.Currently approved antiviral treatments against influenza virus infection present several limitations such as occurrence of resistant viruses and side effects, precluding persistent uses in humans.To develop new antiviral agents against influenza virus infection, we examined antiviral activity of organic solvent fractions of Houttuynia cordata Thunb.(HC) and Lespedeza cuneata G. Don.(LC), which are widely used as medical herbs.Firstly, eight organic solvent fractions prepared from HC and LC were evaluated for in-vitro cytotoxicity and antioxidative activity by 2,2-diphenyl-1-picryl hydrazyl radical scavenging assay.To evaluate virucidal activity against influenza A virus, each organic solvent fraction was treated to influenza A virus and the residual virus titers were measured by viral plaque assay.At noncytotoxic concentrations, all the organic solvent fractions reduced viral infectivity in a dose-dependent manner, demonstrating robust virucidal activity against influenza A virus.In addition, three organic solvent fractions of LC inhibited hemagglutination by influenza virus, suggesting that the organic solvent fractions prevent the receptor binding of the viral hemagglutinin.Antiviral activity of the organic solvent fractions of HC and LC against influenza A viruses suggest that natural compounds contained in the plants provide valuable source for the development of new antiviral agents against influenza viruses.