Cell experiment:

Primary microglia cultures are used in this study. For treatment assay, microglia are incubated with complete DMEM and stimulated with or without 100 ng/mL IFN-γ in the presence or absence of 18β-Glycyrrhetinic acid (25 μM and 50 μM) at 37℃ in a humidified incubator with 5% CO2. For cell migration assay, the isolated primary microglia that seeded in complete DMEM medium are stimulated with or without IFN-γ (100 ng/mL), and treated with different doses of 18β-Glycyrrhetinic acid, 24 h later, the microglia culture supernatants are collected and added to the lower chambers of Transwell inserts[2].

Animal experiment:

Healthy Wistar rats (male, 200±20 g) are used and divided into five groups with 10 individuals for each group randomly. Animals in normal control (NC) group receive distilled water for 6 days and 0.5% CMC-Na for the last 3 days. Rats in Triptolide model group (TP), 18β-Glycyrrhetinic acid low-dose group (GAL+TP), and 18β-Glycyrrhetinic acid high-dose group (GAH+TP) receive distilled water, 18β-Glycyrrhetinic acid (50 mg/kg, p.o., dissolved in distilled water), or 18β-Glycyrrhetinic acid (100 mg/kg, p.o., dissolved in distilled water) for consecutive 6 days, respectively, and liver injury is induced by TP (2.4 mg/kg, p.o., suspended in 0.5% CMC-Na) for the last 3 days. Animals in the above three groups receive TP 6 hours after distilled water or 18β-Glycyrrhetinic acid treatment on the last 3 days[3].

Glycyrrhetinic acid (enoxolone) is a major component of a plant called licorice. It has been found to have both antiviral and antifungal activities. It is able to carboxilate the replication of DNA and inhibits the production of microbial toxins and enzymes [1] [2]. In rats, 18β-Glycyrrhetinic acid potently inhibited 11β-hydroxysteroid dehydrogenase (11β-HSD) activity of hepatic and renal homogenates with IC50 values of 0.09 μm and 0.36 μm, respectively [3].

Before glucocorticoids bind the mineralocorticoid receptor (MR), the selectivity of MR for aldosterone can be exerted by enzymes, and hence competing glucocorticoids is inactivated. 11β-HSD-1 and 11β-HSD-2 and 11β-HSD-3 are three of the enzymes. 11β-HSD-1 has bidirectional activity and a Km value in the micromolar range. It is NADP+-dependent. 11β-HSD-2 exhibits only oxidase activity and has a Km in the nanomolar range. It is NAD+-dependent. In the kidney, it colocalizes with the MR [4].

JEG-3 cell line was derived from a human choriocarcinoma. In this cell line, the enzyme activity of 11β-HSD-3 was inhibited by glycyrrhetinic acid [4].

In rats, 3 h after the administration of glycyrrhetinic acid at concentration of 200 mg/kg, p.o. significantly inhibited 11β-HSD activity in the kidney and the liver. In addition, glycyrrhetinic acid slightly increased the circulating corticosterone level. In differential inhibitory effects on 11β-HSD isozyme activity, the 11-, 24- and 30-positions of glycyrrhetinic acid may play important roles. This had been showed by Data [3].

References:
[1].  Salari MH, Sohrabi N, Kadkhoda Z, et al. Antibacterial Effects of Enoxolone on Periodontopathogenic and Capnophilic Bacteria Isolated from Specimens of Periodontitis Patients. Iranian Biomedical Journal, 2003, 7(1):39-42.
[2].  Bahmani M, Rafieian-Kopaei M, Jeloudari M, et al. A review of the health effects and uses of drugs of plant licorice (Glycyrrhiza glabra L.) in Iran. Asian Pacific Journal of Tropical Disease, 2015, 5: 127-29.
[3].  Shimoyama Y, Hirabayashi K, Matsumoto H, et al. Effects of glycyrrhetinic acid derivatives on hepatic and renal 11beta-hydroxysteroid dehydrogenase activities in rats. J Pharm Pharmacol, 2003, 55(6):811-7.
[4].  Gomez-Sanchez EP, Cox D, Foecking M, et al. 11 beta-hydroxysteroid dehydrogenases of the choriocarcinoma cell line JEG-3 and their inhibition by glycyrrhetinic acid and other natural substances. Steroids, 1996, 61(3):110-5.