Anti-allergic Principles from Thai Zedoary: Structural Requirements of Curcuminoids for Inhibition of Degranulation and Effect on the Release of TNF-alpha and IL-4 in RBL-2H3 Cells

The 80% aqueous acetone extract of the rhizomes of Curcuma zedoaria cultivated in Thailand (Thai zedoary) was found to inhibit release of beta-hexosaminidase, as a marker of antigen-IgE-mediated degranulation, in RBL-2H3 cells and passive cutaneous anaphylaxis reaction in mice. From the active fraction, four curcuminoids (curcumin, dihydrocurcumin, tetrahydrodemethoxycurcumin, and tetrahydrobisdemethoxycurcumin) were isolated together with two bisabolane-type sesquiterpenes, and the effects of four curcuminoids from Thai zedoary and several related compounds on the degranulation were examined. Among them, curcumin showed the highest activity against beta-hexosaminidase release with IC(50) of 5.3 microM, followed by bisdemethoxycurcumin (IC(50) = 11 microM). With regard to the structural requirements of curcuminoids for the activity, the conjugated olefins at the 1-7 positions and the 4'- or 4''-hydroxyl groups of curcuminoids were suggested to be essential for the strong activity, whereas the 3'- or 3''-methoxyl group only enhanced the activity. Furthermore, effects of curcumin and bisdemethoxycurcumin on calcium ionophores (A23187 and ionomycin)-induced degranulation and antigen-induced release of TNF-alpha and IL-4 were examined.