The Chinese herbal medicine,Shinpi-To,inhibits IgE-mediated leukotriene synthesis in rat basophilic leukemia-2H3 cells

We examined the action of Shinpi-To (Formula divinita; TJ-85), a granular extract of seven Chinese medicinal herbs that is used in treating childhood asthma, on the leukotriene synthesis in rat basophilic leukemia-2H3 cells (RBL-2H3 cells). IgE-loaded cells were stimulated with anti-IgE serum in the presence or absence of Shinpi-To. Released LTC₄ and LTB₄ were measured by radioimmunoassay (RIA). Shinpi-To significantly inhibited IgE-mediated synthesis of leukotriene (LT)C₄ and LTB₄. To identify the inhibitory sites, we investigated the action of this extract on four synthetic enzymes, phospholipase A₂ (PLA₂), 5-lipoxygenase (5-LO), LTC₄ synthase, and LTA₄ hydrolase. Shinpi-To inhibited the A23187-stimulated release of ³H]arachidonic acid (AA) from the cell membrane, reflecting an effect on PLA₂ activity. It also suppressed production of LTC₄ and LTB₄ when cell lysates were incubated with AA as substrate. It did not inhibit the production of LTC₄ and LTB₄ when LTA₄-free acid was used as the substrate. Shinpi-To did not inhibit the IgE-mediated increase of intracellular Ca²⁺ (Ca²⁺]_i) concentration. Results indicate that Shinpi-To inhibits LT synthesis by inhibiting PLA₂ and 5-LO activities without affecting the mobilization of Ca²⁺]_i.