Inhibition of leukotriene synthesis by honokiol in rat basophilic leukemia cells

The effects of honokiol, a diphenyl compound extracted from a Chinese herbal medicine, on leukotriene (LT) synthesis were evaluated in rat basophilic leukemia (RBL) cells. The production of LTC(4) and LTB(4) stimulated by the Ca2+ ionophore A23187 was measured in RBL-1 cells by high-performance liquid chromatography. Honokiol inhibited the production of LTC(4) and LTB(4) stimulated by A23187 in RBL-1 cells. Honokiol did not inhibit either phospholipase A(2) activity, measured by the release of H-3-arachidonic acid (AA), or LTC(4) synthase and LTA(4) hydrolase activities, measured with LTA(4)-free acid as substrate. The synthesis of LTC(4) and LTB(4) from AA in RBL-1 cell lysates in the presence of Ca2+ was inhibited by honokiol. These results indicate that honokiol blocks LT synthesis by inhibiting 5-lipoxygenase activity. Honokiol also inhibited immunoglobulin E-mediated production of these LTs in RBL-2H3 cells, which was measured by a specific radioimmunoassay (RIA). These results suggest that honokiol may exhibit antiallergic actions by inhibiting LT synthesis in immediate-type hyperreactivity.