Screening of hepatoprotective compounds from licorice against carbon tetrachloride and acetaminophen induced HepG2 cells injury

Licorice and its constituents, especially licorice flavonoids have been reported to possess significant hepatoprotective activities. However, previous studies mainly focus on the extract and major compounds, and few reports are available on other licorice compounds. This work aims to evaluate the in vitro hepatoprotective activities of licorice compounds and screen active compounds, and to establish the structure–activity relationship. A compound library consisting of 180 compounds from three medicinal licorice species, Glycyrrhiza uralensis, G. glabra and G. inflata was established. HepG2 cells were incubated with the compounds, together with the treatment of 0.35% CCl4 for 6 h and 14 mM APAP for 24 h, respectively. A total of 62 compounds at 10 µM showed protective effects against CCl4 to improve cell viability from 52.5% to >60%, and compounds 5 (licoflavone A), 104 (3,4-didehydroglabridin), 107 (isoliquiritigenin), 108 (3,4,3′,4′-tetrahydroxychalcone), and 111 (licochalcone B) showed the most potent activities, improving cell viability to >80%. And 64 compounds showed protective effects against APAP to improve cell viability from 52.0% to >60%, and compounds 47 (derrone), 76 (xambioona), 77 ((2S)-abyssinone I), 107 (isoliquiritigenin), 118 (licoagrochalcone A), and 144 (2′-O-demethybidwillol B) showed the most potent activities, improving cell viability to >80%. Preliminary structure–activity analysis indicated that free phenolics compounds especially chalcones showed relatively stronger protective activities than other types of compounds. Compounds 5, 76, 104, 107, 111, 118 and 144 possess potent activities against both CCl4 and APAP, and 5, 76 and 118 were reported for the first time. They could be the major active compounds of licorice for the treatment of liver injury.