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 b asophilic leukemia (RBL) cells. The production of LTC(4) and LTB(4) st imulated by the Ca2+ ionophore A23187 was measured in RBL-1 cells by h igh-performance liquid chromatography. Honokiol inhibited the producti on 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 re lease of H-3-arachidonic acid (AA), or LTC(4) synthase and LTA(4) hydr olase activities, measured with LTA(4)-free acid as substrate. The syn thesis of LTC(4) and LTB(4) from AA in RBL-1 cell lysates in the prese nce of Ca2+ was inhibited by honokiol. These results indicate that hon okiol blocks LT synthesis by inhibiting 5-lipoxygenase activity. Honok iol also inhibited immunoglobulin E-mediated production of these LTs i n RBL-2H3 cells, which was measured by a specific radioimmunoassay (RI A). These results suggest that honokiol may exhibit antiallergic actio ns by inhibiting LT synthesis in immediate-type hyperreactivity.