Koboku An Extract of Magnolia Bark, Inhibits Leukotriene Synthesis in Rat Basophilic Leukemia-1 Cells

To determine anti-allergic effects of Koboku, a Chinese herbal medicine, we investigated its inhibitory action on the production of cysteinyl leukotrienes (LT) and LTB4, which are important chemical mediators in the pathogenesis of allergic diseases. A231 87-stimulated synthesis of cysteinyl LT and LTB4 was measured by HPLC in the absence or presence of various concentrations of Koboku in rat basophilic leukemia-1 (RBL-1) cells. In a dose-dependent manner, Koboku inhibited synthesis of cysteinyl LT and LTB4 by up to 92.3 and 100%, respectively. Immunoglobulin E-mediated release of cysteinyl LT and LTB4, which was measured by specific radioimmunoassay (RIA) was also inhibited by Koboku in RBL-2H3 cells. Sites of inhibition of Koboku in the metabolic pathway of LT synthesis were phospholipase A2 (PLA2) and 5-lipoxygenase (5-LO), but not LTC4 synthase or LTA4 hydrolase. We conclude that the anti-allergic effect of Koboku may be attributable, at least in part, to the inhibition of LT synthesis.