Antiviral activity of green tea catechins against feline calicivirus as a surrogate for norovirus

In this study, several medicinal plant extracts including spices, herb teas, and medical herbs were screened for antiviral activity against feline calicivirus (FCV), a surrogate of norovirus. Among them, a methanolic extract of green tea, Camellia sinensis, only exhibited a significant antiviral activity against FCV. The methanolic extract was further fractionated with several solvents such as methanol (MeOH), n-hexane, chloroform (CHCl3), ethyl acetate (EtOAc), n-butanol (n-BuOH), and water. EtOAc-soluble fraction exhibited the highest antiviral activity against FCV. Moreover, the analysis of the most active fraction using a HPLC led to the identification of 4 known catechins: (-)-epigallocatechin (EGC), (-)-epicatechin (EC), (-)-epigallocatechin gallate (EGCG), and (-)-epicatechin gallate (ECG). Among the catechins tested in this study, EGCG exhibited the most effective antiviral activity (EC50, 12 mg/mL) with relatively low cytotoxicity (CC50, 320 mg/ mL), resulting relatively high selectivity index value 26.67. To our knowledge, this is the first experimental verification showing antiviral activity of catechins from green tea against FCV.