Inhibitory Effect of Nimbolide on Mast Cell Degranulation and Allergic Asthma in Mice

The Indian neem tree has been used for treating several medical conditions. Nimbolide, an active compound present in the leaves of the Indian neem tree, has shown anti-inflammatory effects in several animal models. However, its efficacy against allergic asthma has not been examined. Therefore, we investigated the effects of nimbolide on mast cell degranulation and ovalbumin-induced allergic asthma in mice. Nimbolide administration inhibited antigen-induced degranulation of RBL-2H3 cells in a concentration-dependent manner and reduced the immune cell numbers by suppressing the expression of inflammatory cytokines, such as IL-4, IL-13, IFN-γ, IL-33, and thymic stromal lymphopoietin (TSLP) in the bronchoalveolar lavage fluid. Histological studies also demonstrated the in vivo efficacy of nimbolide, evident from the reduced number of periodic acid-Schiff-stained cells and inflammatory scores in the lungs. Furthermore, nimbolide administration inhibited the increase of IL-13 levels, but not that of serum IgE levels. These results demonstrate the therapeutic potential of nimbolide against allergic asthma.