Metabolites identification of bioactive licorice compounds in rats

Licorice (Glycyrrhiza uralensis Fisch.) is one of the most popular herbal medicines worldwide. This study aims to identify the metabolites of seven representative bioactive licorice compounds in rats. These compounds include 22β-acetoxyl glycyrrhizin (1), licoflavonol (2), licoricidin (3), licoisoflavanone (4), isoglycycoumarin (5), semilicoisoflavone B (6), and 3-methoxy-9-hydroxy-pterocarpan (7). After oral administration of 250mg/kg of 1 or 40mg/kg of 2-7 to rats, a total of 16, 43 and 31 metabolites were detected in the plasma, urine and fecal samples, respectively. The metabolites were characterized by HPLC/DAD/ESI-MS(n) and LC/IT-TOF-MS analyses. Particularly, two metabolites of 1 were unambiguously identified by comparing with reference standards, and 22β-acetoxyl glycyrrhizin-6″-methyl ester (1-M2) is a new compound. Compound 1 could be readily hydrolyzed to eliminate the glucuronic acid residue. The phenolic compounds (4-7) mainly undertook phase II metabolism (glucuronidation or sulfation). Most phenolic compounds with an isoprenyl group (chain or cyclized, 2-5) could also undertake hydroxylation reaction. This is the first study on in vivo metabolism of these licorice compounds.