Inhibitory effect of (+)-catechin on the growth of influenza A/PR/8 virus in MDCK cells

We investigated whether (+)-catechin, a building block of tannins contained in the extract of Ephedrae herba (EHext), exerts an inhibitory effect on t he acidification of intracellular compartments such as endosomes and lysoso mes (referred to as ELS), and thereby inhibits the growth of influenza A PR /8/34 (PR8) virus (H1N1 subtype) in Madin-Darby canine kidney cells. The vi tal fluorescence microscopic study with acridine orange showed that 1-h tre atment with (+)-catechin inhibited the acidification of ELS in a concentrat ion-dependent manner (1.0-10.0 mM), Moreover, the growth of PR8 virus was i nhibited markedly when the cells were treated with (+)-catechin (1.25-10.0 mM) for 1 h immediately after infection, or treated within as little as 5 t o 10 min after infection. Conversely, virus growth resumed within 3 h conco mitantly with the reappearance of acidified ELS after removal of (+)-catech in. Similar to EHext, (+)-catechin inhibited both the acidification of ELS and the influenza virus growth. It suggests that (+)-catechin is one of the active components in EHext.