Identification of Soybean Components that Prevent the Entry of Influenza Virus

We have previously demonstrated the anti-influenza virus activity of a soybean extract, indicating the presence of compounds that prevent viral entry into cells. In this study, we sought to identify the compounds in hydrothermal extracts of soybean that blocked viral entrance and analyzed their mechanisms of action. Hot aqueous extracts of roasted soybeans were separated by reverse-phase chromatography on an octadecylsilyl C18 column, and the antiviral activity of individual fractions was measured during the viral entry and culture phases. Fractions 2-5 were found to have a significantly high antiviral activity during the culture phase, whereas during the entry phase, fractions 2-4 showed strong antiviral activity, with fraction 4 having notably potent inhibitory effects. We accordingly analyzed fractions 3 and 4 using liquid chromatography quadrupole time-of-flight mass spectrometry and identified potential anti-viral compounds, including acacetin, 9,10,13-trihydroxy-11-octadencenoic acid, and soy saponin IV. Furthermore, the analysis of these active components revealed that acacetin and soyasaponin were active during the entry phase, and subsequent assessments of their inhibitory effects on influenza virus entry into cells revealed that acacetin inhibits the endocytosis process during viral uptake, whereas soyasaponin inhibits virus binding to its receptor. These findings thus indicate a novel mechanism for the anti-influenza activity of acacetin.