Stereoisomerism at the 3-position of glycyrrhetinic acid affects pseudoaldosteronism-related toxicokinetics

Licorice-induced pseudoaldosteronism is attributed to the inhibition of 11β-hydroxysteroid dehydrogenase 2 in renal tubular cells by glycyrrhizic acid metabolites; however, the marked interindividual variability observed in toxic risk remains unclear. In this study, we established stereoselective toxicokinetic profiles for a recently identified metabolite, 3-epi-18β-glycyrrhetinic acid (3-epi-GA), which were compared with the parent compound, 18β-glycyrrhetinic acid (GA). Following a single intravenous administration of these 2 compounds in rats, 3-epi-GA exhibited a 7-fold longer half-life of the elimination phase and a 22-fold higher area under the curve compared with that of GA, based on a noncompartmental analysis. Two-compartment modeling indicated a 13-fold prolongation in the half-life of the elimination phase and an 18-fold increase in area under the curve for 3-epi-GA. The biliary excretion profiles in rats showed distinct differences between the 2 compounds. In rats administered with GA, 18β-glycyrrhetinyl-30-O-glucuronide, GA-3-O-sulfate-30-O-glucuronide (GA3S30G), and 18β-glycyrrhetinyl-3-O-sulfate (GA3S) were detected in the bile. In contrast, rats administered with 3-epi-GA predominantly excreted 3-epi-18β-glycyrrhetinyl-30-O-glucuronide in the bile, whereas 3-epi-GA3S30G and 3-epi-GA3S were present at trace levels. In vitro studies demonstrated that 3-epi-GA was a poor substrate for human sulfotransferase 2A1. Uptake studies revealed that 18β-glycyrrhetinyl-30-O-glucuronide and 3-epi-18β-glycyrrhetinyl-30-O-glucuronide, but not GA or 3-epi-GA, were actively transported into cells by organic anion transporter 3. Both metabolites exhibited strong binding to serum albumin; however, under hypoalbuminemic conditions, the unbound GA fraction was increased, facilitating passive diffusion into renal tubular cells. Collectively, C-3 epimerization of GA significantly attenuated phase II metabolism and biliary excretion, which resulted in prolonged systemic exposure and potential accumulation of 3-epi-GA and its glucuronide compared with GA. These stereochemical differences provide a mechanistic explanation for the marked interindividual variability observed in licorice-induced pseudoaldosteronism and highlight the importance of monitoring 3-epi-GA-derived compounds as potential biomarkers of licorice-related toxicity. SIGNIFICANCE STATEMENT: C-3 epimerization of 18β-glycyrrhetinic acid (GA) by enterobacteria attenuates phase II metabolism and biliary excretion, resulting in prolonged systemic and renal exposure to 3-epi-GA and its glucuronides compared with GA. This provides interindividual variability in GA-related toxicity.