Identification of Escherichia coli enterotoxin inhibitors from traditional medicinal herbs by in silico, in vitro, and in vivo analyses

Ethnopharmacological relevance: Glycyrrhiza uralensis has been used for the treatment of gastrointestinal disorders, such as diarrhea, in several ancient cultures. Glycyrrhizin is the principal component of liquorice and lots of pharmacological effects have been demonstrated. Aim of the study: Heat-labile enterotoxin (UT), the virulence factor of enterotoxigenic Escherichia coli, induces diarrhea by initially binding to the G(M1) on the surfaces of intestinal epithelial cells and consequently leading to the massive loss of fluid and ions from cells. Therefore, we evaluated the inhibitory effects of traditional medicinal herbs (TMH) on the B subunit of LT (LTB) and Cm, interaction. Materials and methods: The inhibitory effects of TMH on LTB-G(M1), interaction were evaluated by G(M1)-enzyme-linked immunosorbent assay (ELISA). The likely active phytochemicals of these TMH were then predicted by in silica model (docking) and analyzed by in vitro (G(M1)-ELISA) and in vivo (patent mouse gut assay) models. Results: We found that various TMH, which have been ethnomedically used for the treatment of diarrhea, inhibited the LTB-G(M1), interaction. Docking data showed that triterpenoids were the most active phytochemicals and the oleanane-type triterpenoids presented better LTB-binding abilities than other types of triterpenoids. Moreover, by in vitro and in vivo models, we demonstrated that glycyrrhizin was the most effective oleanane-type triterpenoid that significantly suppressed both the LTB-binding ability (IC50 = 3.26 +/- 0.17 mM) and the LT-induced fluid accumulation in mice. Conclusions: We found an LT inhibitor, glycyrrhizin, from TMH by in silico, in vitro, and in vivo analyses. (c) 2008 Elsevier Ireland Ltd. All rights reserved.