Effect of hot water extract of a glycyrrhizin-deficient strain of Glycyrrhiza uralensis on contact hypersensitivity in mice.

To evaluate the medicinal properties of a glycyrrhizin (GL)-deficient strain of Glycyrrhiza uralensis, we investigated the anti-allergic effect of the hot water extract obtained from its roots on contact hypersensitivity in mice, and compared it with that of the hot water extract of a commercial crude drug, Glycyrrhiza Radix. The hot water root extract of the GL-deficient strain contained glucoglycyrrhizin (GGL) and rhaoglucoglycyrrhizin (RGL) instead of GL, and it showed anti-allergic activity against contact hypersensitivity in a fashion similar to that of the crude drug extract. We further confirmed the presence of glycyrrhetinic acid (GA), a major metabolite of GL, in mice serum after oral administration of the hot water root extract of a GL-deficient strain. We demonstrated that GGL underwent hydrolysis by intestinal microflora of mice to form GA. These results suggest that a GL-deficient strain of G. uralensis is a useful medicinal resource since the glycosides of GA work in a fashion similar to that of GL when orally administered.