Inhibitory effect of GBH on platelet aggregation through inhibition of intracellular Ca ²⁺ mobilization in activated human platelets

Geiji-Bokryung-Hwan (GBH) was studied on antiplatelet activity in human platelet suspensions. GBH consists of the 5 herbs Cinnamomi Ramulus, Poria Cocos, Mountan Cortex Radicis, Paeoniae Radix, and Persicae Semen, which have been used in herbal medicine for thousands of years for atherosclerosis. The mechanism involved in the antiplatelet activity of GBH in human platelet suspensions was investigated. GBH inhibited platelet aggregation and Ca ²⁺ mobilization in a concentration-dependent manner without increasing intracellular cyclic AMP and cyclic GMP. GBH had no inhibitory effect on thromboxane B2 (TXB2) production in cell-free systems. Collagen-related peptide (CRP)-induced Ca ²⁺ mobilization is regulated by phospholipase C-2 (PLC-γ2) activation. We evaluated the effect of GBH on tyrosine phosphorylation of PLC-γ2 and the production of inositol-1,4,5- trisphosphate (IP3). GBH at concentrations that inhibited platelet aggregation and Ca ²⁺ mobilization had no effects on tyrosine phosphorylation of PLC-γ2 or on the formation of IP3 induced by CRP. Similar results were obtained with thrombin-induced platelet activation. GBH inhibited platelet aggregation and Ca ²⁺ mobilization induced by thrombin without affecting the production of IP3. We then evaluated the effect of GBH on the binding of IP3 to its receptor. GBH at high concentrations partially blocked the binding of IP3 to its receptor. Therefore, the results suggested that GBH suppresses Ca ²⁺ mobilization at a step distal to IP3 formation. GBH may provide a good tool for investigating Ca ²⁺ mobilization.