Abstract: To study the inhibitory activity and mechanism of baicalin against H5N1 pseudovirus.Inhibition of viral-entry by baicalin was determined with H5N1 pseudoviruses system infected with different H5N1 pseudovirus strains,while VSVG pseudoviruses was used as negative control.Hemagglutination inhibition assay and enzyme-linked immunosorbent assay (ELISA) were performed to investigate the mechanism for its anti-influenza activity.The cytotoxicity of baicalin was measured using MTT assay.The results demonstrated that baicalin specifically inhibited the entry of H5N1 pseudovirus strains,including A/Anhui/1/2005,A/Xinjiang/1/2006,A/Hong Kong/156/1997,A/Qinghai/59/2005,A/Thailand/Kan353/2004,A/VietNam/1194/2004,and the IC₅₀ values were 65.76±5.61 μM,54.98±4.38 μM,46.81±5.12 μM,32.88±4.18 μM,63.30±1.59 μM and 43.23±3.43 μM,respectively.Moreover,baicalin targeted HA2 subunit of hemagglutinin with IC₅₀ of 35.86±3.09 μM.These findings suggested that baicalin blocked entry of H5N1 influenza virus directly.The action mechanisms may be potential target to HA2 submit of hemagglutinin.

Key words: baicalin, H5N1 subtype, hemagglutinin, HA2 subunit