Inhibitory effect of Ephedrae herba, an oriental traditional medicine, on the growth of influenza A/PR/8 virus in MDCK cells

Using several herbal extracts, we investigated whether certain Kampo medici nes exert an inhibitory effect on the acidification of intracellular compar tments such as endosomes and lysosomes (referred to as ELS), and thereby in hibit the growth of influenza A virus in Madin-Darby canine kidney cells. T he vital fluorescence microscopic study showed that the extract of Ephedrae herba (EHext) among five herbal extracts inhibited acidification of endoso mes and lysosomes in a concentration-dependent manner (100-400 mu g/ml). Mo reover the growth of influenza A/PR/8/34 (H1N1) (PR8) virus was inhibited w hen the cells were treated with EHext for 1 h immediately after infection, or treated as early as 5-10 min after infection. Conversely, virus growth r esumed concomitantly with the reappearance of acidified ELS after removal o f EHext. The fact that the inhibitory effect of EHext was completely or par tially reversed by FeCl3, a tannin-reactive agent, strongly suggests that t annin is one of the active components in the extract. (C) 1999 Elsevier Sci ence B.V. All rights reserved.