Glycyrrhizin alleviates experimental allergic asthma in mice

Asthma is a chronic respiratory disease, the incidence of which is increasing globally. The existing therapy is inadequate and has many adverse effects. It needs a better therapeutic molecule preferably of natural origin, which has negligible or no adverse effects. In view of this, we evaluated Glycyrrhizin (GRZ), a major constituent of a plant Glycyrrhiza glabra, for its efficacy on asthmatic features in a mouse model of asthma. BALB/c mice were sensitized and challenged with ovalbumin (OVA) to develop the asthmatic features such as airway hyperresponsiveness: allergen induced airway constriction and airway hyperreactivity (AHR) to methacholine (MCh), and pulmonary inflammation. The mice were orally treated with GRZ (2.5, 5, 10 and 20 mg/kg) during or after OVA-sensitization and OVA-challenge to evaluate its protective or reversal effect, respectively on the above asthmatic features. The status of airway hyperresponsiveness was measured by monitoring specific airway conductance (SGaw) using a non-invasive method and the pulmonary inflammation was assessed by haematoxylin and eosin staining of lung sections. Several other parameters associated with asthma such as interleukin (IL)-4, IL-5 interferon-γ (IFN-γ), OVA-specific IgE, total IgG2a and cortisol were measured by ELISA. GRZ (5 mg/kg) markedly inhibited OVA-induced immediate airway constriction, AHR to MCh (p < 0.01), lung inflammation, and infiltration of eosinophils in the peribronchial and perivascular areas. It prevented the reduction of IFN-γ (p < 0.02), and decreased IL-4 (p < 0.05), IL-5 (p < 0.05) and eosinophils (p < 0.0002) in the BAL fluid. Also, it reduced OVA-specific IgE levels (p < 0.01) and prevented the reduction of total IgG2a (p < 0.01) in serum. We have also showed that it has no effect on serum cortisol levels. Our results demonstrate that GRZ alleviates asthmatic features in mice and it could be useful towards developing a better therapeutic molecule in the future.