Molecular investigation of the virucidal activity of proanthocyanidin from Alpinia zerumbet against the influenza A virus

Abstract Proanthocyanidins (PACs) have various bioactivities, such as being anti-bacterial, anti-cancer, and anti-oxidant. Consequently, they have been vigorously studied for the development of new natural bioactive compounds. Recently, AzPAC was isolated from the medicinal plant Alpinia zerumbet, and it was found to inhibit the infection of animal viruses, influenza A viruses (IAVs), and porcine epidemic diarrhea virus. The virucidal activity of AzPAC means that it can interact directly with viral particles. However, few studies have investigated the preventive mechanism utilized by AzPAC on influenza virus replication. In this study, the composition of AzPAC and the affinity between AzPAC and IAVs was investigated in detail. We found that AzPAC was composed of an epicatechin monomer, which was linked by inter-flavan bonds between the C4 and C8 positions (B2-type) and the C4 and C6 positions (B5-type) in the terminal units of the PAC. A quenching assay indicated that AzPAC interacted with IAV membrane proteins, hemagglutinin and neuraminidase. Additionally, circular dichroism analysis indicated that AzPAC affected the change in the secondary structure rate of the viral membrane proteins. AzPAC was able to impair the infective process of IAVs via direct interaction with their viral membrane proteins. These results indicate that A. zerumbet is an invaluable bioresource for the development of preventive drugs against IAV infection.