Pharmacokinetics-based identification of pseudoaldosterogenic compounds originating from Glycyrrhiza uralensis roots (Gancao) after dosing LianhuaQingwen capsule.

LianhuaQingwen capsule, prepared from an herbal combination, is officially recommended as treatment for COVID-19 in China. Of the serial pharmacokinetic investigations we designed to facilitate identifying LianhuaQingwen compounds that are likely to be therapeutically important, the current investigation focused on the component Glycyrrhiza uralensis roots (Gancao). Besides its function in COVID-19 treatment, Gancao is able to induce pseudoaldosteronism by inhibiting renal 11ß-HSD2. Systemic and colon-luminal exposure to Gancao compounds were characterized in volunteers receiving LianhuaQingwen and by in vitro metabolism studies. Access of Gancao compounds to 11ß-HSD2 was characterized using human/rat, in vitro transport, and plasma protein binding studies, while 11ß-HSD2 inhibition was assessed using human kidney microsomes. LianhuaQingwen contained a total of 41 Gancao constituents (0.01-8.56 µmol/day). Although glycyrrhizin (1), licorice saponin G2 (2), and liquiritin/liquiritin apioside (21/22) were the major Gancao constituents in LianhuaQingwen, their poor intestinal absorption and access to colonic microbiota resulted in significant levels of their respective deglycosylated metabolites glycyrrhetic acid (8), 24-hydroxyglycyrrhetic acid (M2D; a new Gancao metabolite), and liquiritigenin (27) in human plasma and feces after dosing. These circulating metabolites were glucuronized/sulfated in the liver and then excreted into bile. Hepatic oxidation of 8 also yielded M2D. Circulating 8 and M2D, having good membrane permeability, could access (via passive tubular reabsorption) and inhibit renal 11ß-HSD2. Collectively, 1 and 2 were metabolically activated to the pseudoaldosterogenic compounds 8 and M2D. This investigation, together with such investigations of other components, has implications for precisely defining therapeutic benefit of LianhuaQingwen and conditions for its safe use.

3-Monoglucuronyl-glycyrrhretinic acid is a substrate of organic anion transporters expressed in tubular epithelial cells and plays important roles in licorice-induced pseudoaldosteronism by inhibiting 11ß-hydroxysteroid dehydrogenase 2.

Licorice (glycyrrhiza root) has been used as a herbal medicine worldwide with its main active constituent being glycyrrhizin (GL). Licorice sometimes causes adverse effects such as inducing pseudoaldosteronism by inhibiting type 2 11ß-hydroxysteroid dehydrogenase (11ß-HSD2) caused by glycyrrhetinic acid (GA), a major metabolite of GL. In this study we compared the inhibitory effects of GA, GL, and 3-monoglucuronyl-glycyrrhetinic acid (3MGA), another metabolite of GL, on 11ß-HSD2 activity by using microsomes and rat kidney tissue slices. GA, 3MGA, and GL inhibited 11ß-HSD2 in rat kidney microsomes, with IC(50) values of 0.32, 0.26, and 2.2 µM, respectively. However, the inhibitory activity of these compounds was reduced markedly, in the slices, in a medium containing 5% bovine serum albumin. Assays using human embryonic kidney 293 cells with transient transformation in transporter genes showed that 3MGA is a substrate of human organic anion transporter (OAT) 1, human OAT3, and human organic anion-transporting peptide 4C1, whereas GA is not. When GA (100 mg/kg/day) was administered orally for 16 days to Eisai hyperbilirubinemic rats, plasma concentrations and urinary excretion of 3MGA were significantly higher, whereas the activity of 11ß-HSD2 in kidney microsomes was significantly lower compared with Sprague Dawley rats. These results suggest that 3MGA is actively transported into tubules through OATs, resulting in the inhibition of 11ß-HSD2. Because the plasma level of 3MGA depends on the function of hepatic transporters, monitoring 3MGA levels in plasma or urine may be useful for preventing pseudoaldosteronism when licorice or GL is prescribed to patients.