Fig. 5.

Glycyrrhizic acid inhibition of coxsackievirus A16 infection by direct inactivation, while the inhibition of enterovirus 71 infection is linked to a post cell entry event. (A) Time-of-drug addition study. Glycyrrhizic acid at 5 mM was added at 2 h prior to (−2 h), during (0 h), or post virus inoculation at time points as indicated (0.5 h, 1 h, 2 h, 4 h, 6 h, 12 h and 24 h PI). Virus infection was determined at 72 h PI using MTT assay. An inhibition rate was calculated as described in Section 2 and was plotted against time-of-drug addition. Data are presented as mean±standard errors of triplicate samples. The results are representative of two independent experiments. (B, C) Glycyrrhizic acid directly deactivates coxsackievirus A16, but not EV71. Duplicate samples of CVA16 (B) or EV71 (C) in 100 μl culture medium were incubated with glycyrrhizic acid at 0, 3, and 5 mM in a 37 °C water bath for 60 min. Ten microliters of the pre-treated virus or equal amount of untreated virus (final MOI=0.3) were then added to Vero cells (final concentrations of GA applied to Vero cells were 0.03 and 0.05 mM for GA-treated samples). Preincubation of CVA16 with 5 mM GA resulted in a loss of infectious virion production by more than 3 logs, whereas the same treatment did not significantly affect EV71 infectivity. Data are presented as mean±standard errors of duplicate samples. The results are representative of two independent experiments.