Abstract
Background and Objective: Previous studies demonstrated that licorice (Glycyrrhiza glabra) inhibits airway hyperresponsiveness, inflammation and remodeling in murine models of asthma. However, licorice use is faced with many side effects including, increased adrenal hydrocortisone secretion and hypertension which are dose-dependent.This study aimed to test the effect of three different doses of licorice extract on, lung pathology, bronchoalveolar lavage oxidative stress markers, plasma immunoglobulin E (IgE) and Th2 cell cytokine in a model of ovalbumin (OVA)-induced bronchial asthma. Methodology: Mice were sensitized with 10 mg OVA on days 0 and 14. On days 21, 22 and 23, mice were challenged with 1% OVA solution. Six groups of mice were used in this study: 1-normal saline (S), 2-OVA-sensitized and challenged (OVA), 3-OVA+montelukast(M),4-OVA+10 mg kg(-1) licorice (L10), 5-OVA+20 mg kg(-1) licorice (L20) and 6-OVA+40 mg kg(-1) licorice extract (L40). Results: The results revealed that the lowest dose of licorice (10 mg kg(-1)) protected against OVA-induced lung inflammation and mucus secretion. It also, reduced interleukin (IL)-5, IL-13 and IgE. Moreover, it significantly reduced the raised malondialdehyde (MDA) and nitric oxide (NO) and restored superoxide dismutase (SOD) and catalase (CAT) activity. Conclusion:The results of this study offered clear evidence for the antioxidant and anti-inflammatory effects of licorice in a murine model of bronchial asthma. The lowest dose of licorice is the most effective and as the dose increase the antioxidant and anti-inflammatory action decrease. This provides an advantage as licorice has many side effects which appears with the high doses.