Fig. 4.

Inhibition of coxsackievirus A16 and enterovirus 71 infection by glycyrrhizic acid. (A) Glycyrrhizic acid treatment blocks the cytopathic effect by virus infection. Vero cells in duplicate were untreated or treated with glycyrrhizic acid at concentrations as indicated for 2 h. The cells were then infected with CVA16 or EV71 (MOI=0.3). The cells were fixed with 3% paraformaldehyde at 72 h PI and stained with 0.5% crystal violet. Inhibition of CVA16 or EV71 infection prevents cell death and hence increased staining compared infected but untreated controls. The results are representative from two independent experiments. (B, C) Glycyrrhizic acid treatment reduces infectious virion production. To assay for inhibition of virion production, Vero cells were treated with glycyrrhizic acid at 1, 3, and 5 mM or remained untreated. The cells were then infected with CVA16 (B) or with EV71 (C) at MOI=0.3. The samples were harvested at 48 h PI and infectious virions in those samples were assayed with secondary infection assays. Data are presented as mean±standard errors of triplicate samples from three independent experiments. (D) Glycyrrhizic acid treatment inhibits VP1 protein expression of EV71. Vero cells were infected with EV71 in the presence or absence of glycyrrhizic acid at concentrations as indicated. The cells were harvested at 48 h PI and VP1 expression in the samples was detected by immunoblotting analysis. GAPDH was used as a loading control. The results are representative from two independent experiments.