Glycyrrhizin and long-term histopathologic changes in a murine model of asthma

Abstract

Background: Licorice root has been widely used to treat bronchial asthma for many years. However, the effect of this herb on lung histopathologic features is not fully understood.

Objective: In this study, we aimed to determine the effects of oral administration of glycyrrhizin, an active constituent of licorice root, on lung histopathologic features in BALB/c mice, in which the model of chronic asthma was established.

Methods: Twenty-eight BALB/c mice were divided into 4 groups: control, placebo, dexamethasone, and glycyrrhizin. Mice in the treatment and placebo groups were sensitized with 2 intraperitoneal injections of ovalbumin and then were exposed to aerosolized ovalbumin for 30 minutes per day on 3 days each week for 8 weeks beginning on the 21st study day. In the last week of inhalational exposure, mice in the placebo group received saline and those in the treatment groups received either dexamethasone, 1 mg/kg, or glycyrrhizin, 10 mg/kg, via orogastric gavage for 7 consecutive days. Animals were humanely killed 24 hours after the last ovalbumin and drug exposure. Lung histopathologic findings were evaluated using light and electron microscopy.

Results: As evaluated in the control, placebo, dexamethasone, and glycyrrhizin groups, respectively, the mean (SD) basement membrane thickness was 306.34 (36.91), 657.52 (98.99), 405.13 (96.1), and 465.01 (121.48) nm; subepithelial smooth muscle thickness was 7.22 (1.37), 11.24 (1.85), 5.62 (1.15), and 7.76 (1.11) μm; epithelium thickness was 19.48 (1.22), 41.62 (5.49), 22.59 (3.18), and 25.54 (4.68) μm; number of mast cells was 1.34 (0.19), 3.62 (0.5), 2.06 (0.77), and 2.77 (0.23)/16,400 μm(2); and number of goblet cells was 0.32 (0.1), 4.92 (0.82), 0.66 (0.06), and 0.98 (0.15)/100 μm. Evaluation of lung histopathologic features demonstrated that the chronic asthma model of mice was successfully established, with significantly higher numbers of goblet and mast cells and increased thickness of epithelium, basement membrane, and subepithelial smooth muscle layers (P < 0.001 for all) in the asthma group compared with in the control group. The number of goblet (P < 0.001) and mast (P < 0.02) cells and the thickness of basement membrane (P < 0.001), subepithelial smooth muscle layers (P ≤ 0.001), and epithelium of the lung (P < 0.001) were found to be significantly lower in the glycyrrhizin group compared with in the placebo group. When the glycyrrhizin and dexamethasone groups were compared, there was no statistically significant difference between the 2 groups in the histopathologic parameters, including thickness of basement membrane (P = 0.514), subepithelial smooth muscle (P = 0.054), and epithelium (P = 1.0) and number of mast (P = 0.075) and goblet (P = 0.988) cells.

Conclusions: The results of this study suggest that the group receiving glycyrrhizin had amelioration of all established chronic histopathologic changes of lung in the mouse model of asthma. Further studies are needed to evaluate the efficacy of glycyrrhizin in the management of asthma.

Keywords: BALB/c mice; Glycyrrhiza glabra; airway remodeling; asthma; glycyrrhizin; lung histopathology.

Figure 1

Effects of placebo, dexamethasone, and glycyrrhizin use on the thickness of (A) basement membrane, (B) subepithelial smooth muscle, and (C) epithelium and on the number of (D) mast cells and (E)goblet cells. Results represent the mean (SD). *P ≤ 0.001, compared with the placebo group. ^†P < 0.02 compared with the placebo group.

Figure 2

Light microscopic findings in the placebo, dexamethasone, and glycyrrhizin groups. (A) In the placebo (asthma) group, light microscopic findings revealed irregular respiratory epithelium. Subepithelial smooth muscle (Sm) was markedly thickened. Inflammatory cell infiltration is circled (hematoxylin-eosin). (B) In the dexamethasone group, respiratory epithelium appears regular, and the number of goblet cells (Gc) and the thickness of the smooth muscle layer are decreased (periodic acid–Schiff, ×20). (C) In the glycyrrhizin group, airway epithelium and parenchymal areas appear normal. The number of Gc is decreased (periodic acid–Schiff, ×20).

Figure 3

Electron microscopic findings in the placebo, dexamethasone, and glycyrrhizin groups. (A) In the asthma group, basement membrane (*) integrity was disrupted. Cells filled with secretion granules were detected in the electron microscopic evaluation. (B) In the dexamethasone group, basement membrane (*) was regular. Secretory cells were filled with secretion granules. (C) In the glycyrrhizin group, basement membrane (*) was regular, and cells with cilia and secretory cells were filled with dense secretion granules and were seen as normal.