Anti-diarrheal effect of Galla Chinensis on the Escherichia coli heat-labile enterotoxin and ganglioside interaction.

Enterotoxigenic Escherichia coli (ETEC) is the most frequently isolated enteropathogen, accounting for approximately 210 million diarrhea episodes annually. ETEC-induced diarrhea is initiated by the binding of B subunit of heat-labile enterotoxin (LTB) to the ganglioside G(M1) on the surface of intestinal epithelial cell. Therefore, we evaluated the inhibitory effects of 297 Chinese medicinal herbs on the LTB and G(M1) interaction by G(M1)-enzyme-linked immunosorbent assay. Galla Chinensis extract (GCE) exhibited anti-LT-induced diarrheal effect in the patent mouse gut assay, with IC50 value of 4.7+/-1.3 mg/ml. GCE also inhibited the binding of LTB to G(M1), suggesting that GCE suppressed the LT-induced fluid accumulation by blocking the binding of LTB to G(M1). Furthermore, the ethyl acetate (EA) soluble fraction was the most active fraction of Galla Chinensis that inhibiting the binding of LTB to G(M1) with an IC50 value of 153.6+/-3.4 microg/ml. The major components of the EA fraction should be phenolic derivatives according to a thin-layer chromatography analysis. Gallic acid, the major component of EA fraction, blocked the binding of LTB to G(M1), resulting in the suppression of LT-induced diarrhea. In conclusion, these data suggested that Galla Chinensis and gallic acid might be potent drugs for the treatment of LT-induced diarrhea.