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 used for the treatment of bronchial asthma in Japan. Inhibitory action of this drug on arachidonate 5-lipoxygenase (5-LO) metabolism in rat basophilic leukemia cells (RBL-1 cells) was examined. Saiboku-To significantly inhibited calcium ionophore-stimulated synthesis of cysteinyl leukotrienes (cLTs) and leukotriene B4 (LTB4). Inhibition appeared 10 min after addition of the substance and reached a maximal value after 3 h. Saiboku-To did not inhibit the release of [3H]arachidonic acid (AA) from cell membrane by calcium ionophore stimulation, or the production of cLTs and LTB4 when LTA4-free acid was used as the substrate. However, it significantly inhibited the production of cLTs and LTB4 when free AA was used as the substrate. The production of thromboxane A2 (TXA2). a cyclooxygenase metabolite, was not inhibited when AA was used as the substrate in cell free study. These results indicate that Saiboku-To selectively inhibits 5-LO activity in the metabolic pathway of AA.