In vitro anti-Helicobacter pylori activity of Extractum liquiritiae, glycyrrhizin and its metabolites.

Objective: To investigate the in vitro activity of Extractum liquiritiae (EL), glycyrrhizic acid (GL), glycyrrhetinic acid (GA) and a novel lipophilic derivative of glycyrrhetinic acid monoglucuronide (GAMG), acetylated GAMG (aGAMG), against 29 Helicobacter pylori strains.

Methods: The MIC of each compound was determined by the agar dilution method, and the killing kinetics were monitored in brain heart infusion broth ( approximately 10(6)-10(7) cfu/mL) at 0, 4, 24, 48, 72 and 96 h.

Results: GA was the most potent compound (MIC(50 /90), 50/100 mg/L), inhibiting 79.3% of the strains at MIC < or =50 mg/L. Clarithromycin-resistant strains were susceptible at 12.5 and 25 mg/L, and metronidazole-resistant strains at 25-50 and at 200 mg/L. The MIC distribution (mg/L) of aGAMG was < or =6.25 (29.2%), 50 (4.2%), 100-200 (12.5%) and > or =400 (54.1%). EL and GL were less active (MICs >400 mg/L). GA exhibited rapid, concentration and strain-dependent bactericidal activity.

Conclusions: The potent in vitro activity of GA against H. pylori provides a further explanation for its beneficial effect on peptic ulcers. Its effectiveness against clarithromycin-resistant strains provides hope that it can form the basis for an alternative therapeutic agent against H. pylori.