The rhizomes of Alisma orientale and alisol derivatives inhibit allergic response and experimental atopic dermatitis.

The 70% ethanol extract of the rhizome of Alisma orientale (Alismatis rhizome) (AOE) was prepared and found to significantly inhibit 5-lipoxygenase (5-LOX)-catalyzed leukotriene (LT) production from rat basophilic leukemia (RBL)-1 cells and β-hexosaminidase release by antigen-stimulated RBL-2H3 cells. It also attenuated delayed-type hypersensitivity (DTH) reaction in mice. Among the three major triterpene constituents isolated (i.e., alisol B, alisol B 23-acetate, alisol C 23-acetate) as active principles, alisol B and its 23-acetate strongly and significantly inhibited LT production and β-hexosaminidase release between 1-10 µM. On the other hand, all these alisol derivatives significantly and strongly inhibited DTH response after oral administration. In addition, AOE (200 mg/kg/d) was for the first time found to considerably alleviate hapten-induced dermatitis symptoms in NC/Nga mice, an animal model of atopic dermatitis. These results indicate that alisol derivatives possess inhibitory activities on immediate-type as well as delayed-type hypersensitivity reactions and may contribute to the anti-allergic action of AOE.