Abstract
Rhizome of Alisma orientale has been used as a traditional medicine for treating kidney diseases in East Asian countries. Its inhibitory effects on hypersensitivity responses have been reported for methanol extracts, with alisol B 23-acetate (AB23Ac) being the most active constituent among six terpenes in inhibiting the direct passive Arthus reaction. However, whether AB23Ac has efficacy against allergic asthma has not been tested to date. The in vivo efficacy of AB23Ac in an ovalbumin (OVA)-induced allergic asthma mouse model was evaluated by administrating AB23Ac before OVA sensitization or OVA challenge in BALB/c mice. AB23Ac suppressed antigen-induced degranulation of RBL-2H3 mast cells in a concentration-dependent manner. The administration of AB23Ac both before OVA sensitization and OVA challenge greatly lowered pulmonary resistance and the increase in immune cell counts and inflammatory responses around the peribronchial and perivascular regions. In addition, the inflammatory cytokine levels of Th1/Th2/Th17 cells in the bronchoalveolar lavage fluid decreased in the AB23Ac-treated groups. AB23Ac reduced the number of PAS-stained cells in the lungs. Furthermore, a computer modeling study indicated that AB23Ac can bind tightly to spleen tyrosine kinase (Syk). These results suggest that AB23Ac may ameliorate allergic asthma by suppressing immune responses in dendritic cells during sensitization and in mast cells during challenge periods.