Anti-hepatitis C virus compounds obtained from Glycyrrhiza uralensis and other Glycyrrhiza species

Abstract

Development of complementary and/or alternative drugs for treatment of hepatitis C virus (HCV) infection is still much needed from clinical and economic points of view. Antiviral substances obtained from medicinal plants are potentially good targets to study. Glycyrrhiza uralensis and G. glabra have been commonly used in both traditional and modern medicine. In this study, extracts of G. uralensis roots and their components were examined for anti-HCV activity using an HCV cell culture system. It was found that a methanol extract of G. uralensis roots and its chloroform fraction possess anti-HCV activity with 50%-inhibitory concentrations (IC(50)) of 20.0 and 8.0 μg/mL, respectively. Through bioactivity-guided purification and structural analysis, glycycoumarin, glycyrin, glycyrol and liquiritigenin were isolated and identified as anti-HCV compounds, their IC(50) being 8.8, 7.2, 4.6 and 16.4 μg/mL, respectively. However, glycyrrhizin, the major constituent of G. uralensis, and its monoammonium salt, showed only marginal anti-HCV activity. It was also found that licochalcone A and glabridin, known to be exclusive constituents of G. inflata and G. glabra, respectively, did have anti-HCV activity, their IC(50) being 2.5 and 6.2 μg/mL, respectively. Another chalcone, isoliquiritigenin, also showed anti-HCV activity, with an IC(50) of 3.7 μg/mL. Time-of-addition analysis revealed that all Glycyrrhiza-derived anti-HCV compounds tested in this study act at the post-entry step. In conclusion, the present results suggest that glycycoumarin, glycyrin, glycyrol and liquiritigenin isolated from G. uralensis, as well as isoliquiritigenin, licochalcone A and glabridin, would be good candidates for seed compounds to develop antivirals against HCV.

Keywords: antiviral substance; coumarin; hepatitis C virus.

Figure 1

Effects of glycycoumarin, glycyrin and glycyrol isolated from G. uralensis on HCV RNA replication and protein synthesis. (a) Huh 7.5 cells infected with HCV J6/JFH1 and treated with either glycycoumarin (20 μg/mL), glycyrin (15 μg/mL), glycyrol (10 μg/mL) or left untreated were subjected to western blot analysis using monoclonal antibody against the HCV NS3 protein at 1 and 2 days post‐infection. GAPDH served as an internal control to verify equal amounts of sample loading. Signal intensities of NS3 were normalized to the corresponding GAPDH signal. (b) Amounts of HCV RNA in the cells described in (a) were measured by real‐time quantitative RT‐PCR analysis. These amounts were normalized to GAPDH mRNA expression. Data represent means ± SEM of data from two independent experiments. The value for the untreated control at 1 day post‐infection is arbitrarily expressed as 1.0. ^* P < 0.001, compared with the control. (c) Amounts of HCV infectious particles in the supernatants of the cultures described in (a) and (b) were determined: data for glycycoumarin, glycyrin, glycyrol and the untreated control are shown. Data represent means ± SEM of data from two independent experiments. ^* P < 0.05; ^† P < 0.01, compared with the untreated control; dpi, days post infection.