Aloe vera and its Components Inhibit Influenza A Virus-Induced Autophagy and Replication

Aloe vera ethanol extract (AVE) reportedly has significant anti-influenza virus activity, but its underlying mechanisms of action and constituents have not yet been completely elucidated. Previously, we have confirmed that AVE treatment significantly reduces the viral replication of green fluorescent protein-labeled influenza A virus in Madin-Darby canine kidney (MDCK) cells. In addition, post-treatment with AVE inhibited viral matrix protein 1 (M1), matrix protein 2 (M2), and hemagglutinin (HA) mRNA synthesis and viral protein (M1, M2, and HA) expressions. In this study, we demonstrated that AVE inhibited autophagy induced by influenza A virus in MDCK cells and also identified quercetin, catechin hydrate, and kaempferol as the active antiviral components of AVE. We also found that post-treatment with quercetin, catechin hydrate, and kaempferol markedly inhibited M2 viral mRNA synthesis and M2 protein expression. A docking simulation suggested that the binding affinity of quercetin, catechin hydrate, and kaempferol for the M2 protein may be higher than that of known M2 protein inhibitors. Thus, the inhibition of autophagy induced by influenza virus may explain the antiviral activity of AVE against H1N1 or H3N2. Aloe vera extract and its constituents may, therefore, be potentially useful for the development of anti-influenza agents.