ABSTRACT
Objective To comparatively analyze the in vitro antiviral mechanism( s) of eugeniin and quercetin against varicella-zoster virus ( VZV) by using a novel antiviral assay based upon a reporter cell line (MV9G cells) for VZV. Methods Selection indexes (SIs) of potential antiviral compounds extracted from Chinese herbs or plants including eugeniin, eugenol, morin, curcumin, myricetin and quercetin for in vitro inhibition of VZV were calculated. The compounds with relatively higher SIs were screened out for fur-ther investigation of their in vitro inhibitory mechanisms with a cell-free virus ( CFVs) direct-infection assay and a cell-associated virus (CAVs) co-culture assay established with MV9G cells in our previous study. The inhibitory mechanisms analyzed in this study included direct inactivation of CFVs, inhibition of the adhesion and/or penetration capabilities of CFVs to MV9G cells, inhibition of the intracellular replication of CAVs and inhibition of the transcription and / or expression of viral immediate early gene 62 ( IE62 ) . Results Among the tested compounds, eugeniin and quercetin showed relatively higher SIs of 5. 82 and 8. 97, respec-tively. Eugeniin rather than quercetin directly but partly inactivated CFVs and inhibited their attachment to and penetration into MV9G cells in a concentration-dependent manner. Both eugeniin and quercetin revers-ibly inhibited the intracellular replication of CAVs and the transcription and expression of viral IE62 gene, for which eugeniin needed to be added within 12 hours after infection. Conclusion Eugeniin and quercetin had different in vitro inhibitory mechanisms against VZV, but inhibiting the transcription and expression of viral IE62 gene was a common mechanism shared by both of them.