SAIBOKU-TO, A HERBAL EXTRACT MIXTURE, SELECTIVELY INHIBITS 5-LIPOXYGENASE ACTIVITY IN LEUKOTRIENE SYNTHESIS IN RAT BASOPHILIC LEUKEMIA-1 CELLS

Saiboku-To, a mixture of extracts from 10 medicinal herbs, has been us ed for the treatment of bronchial asthma in Japan. Inhibitory action o f this drug on arachidonate 5-lipoxygenase (5-LO) metabolism in rat ba sophilic leukemia cells (RBL-1 cells) was examined. Saiboku-To signifi cantly inhibited calcium ionophore-stimulated synthesis of cysteinyl l eukotrienes (cLTs) and leukotriene B-4 (LTB(4)). Inhibition appeared 1 0 min after addition of the substance and reached a maximal value afte r 3 h. Saiboku-To did not inhibit the release of [H-3]arachidonic acid (AA) from cell membrane by calcium ionophore stimulation, or the prod uction of cLTs and LTB(4) when LTA(4)-free acid was used as the substr ate. However, it significantly inhibited the production of cLTs and LT B(4) when free AA was used as the substrate. The production of thrombo xane A(2) (TXA(2)), a cyclooxygenase metabolite, was not inhibited whe n AA was used as the substrate in cell free study. These results indic ate that Saiboku-To selectively inhibits 5-LO activity in the metaboli c pathway of AA.