| Cardiovascular diseases, including stroke, thrombosis, ischemic and coronary heart diseases, continue to be the leading cause of death. In particular, thrombotic diseases, are major cardiovascular complications in a majority of patients. Platelets play an important role in the development of thrombosis. Consequently, antiplatelet treatments have been developed as a cornerstone in the prevention of thrombosis. However, chemically synthesized antiplatelet drugs, including aspirin and clopidogrel, have adverse effects, such as internal bleeding and drug resistance. Therefore, we still need to identify novel antiplatelet agents, and natural bioactive compounds with antiplatelet effects have garnered much attention. Black tea is one of the most popular beverages worldwide and accounts for a substantial portion of polyphenol intake, as it contains high concentrations of theaflavins (TFs) and thearubigins (TRs). Many clinical studies have demonstrated the beneficial effects of black tea on cardiovascular diseases. However, the antiplatelet and antithrombotic activities effects of theaflavins remain unknown. In this study we aimed to investigate the effects of theaflavin (TF-1) on collagen-induced platelet activation and thrombosis formation.Platelets isolated from human blood were washed and analyzed using an aggregometer, flow cytometry, a thromboxane (Tx) B2 ELISA kit, western blotting and fluorescence microscopy. The effects of theaflavin on the hemostatic state and thrombosis formation were investigated in C57 mice based on the tail bleeding time and an FeCl3-induced arterial thrombus model. TF-1 dose-dependently inhibited collagen-induced platelet aggregation and reduced ATP release; it also attenuated P-selectin expression, fibrinogen binding, spreading and TxA2 formation. Western blot analysis showed that TF-1 potently inhibited spleen tyrosine kinase (Syk) and phospholipase (PL) C-y2 phosphorylation. The in vivo results further confirmed the inhibition by TF-1 of platelet activation according to the FeCl3-induced arterial thrombus formation model, in which TF-1 prolonged the arterial occlusion time from 15±1.1 minutes to 40±5.4 minutes in C57 mice.In the present study, we first discovered that TF-1 could inhibite collagen-induced platelet activation and the inhibition of Syk activation might explain the inhibitory effects of TF-1, as shown by reduced Syk, PLCy2 and Akt phosphorylation. The in vivo FeCl3 induced arterial thrombosis model showed TF-1 significantly prolonged the arterial occlusion time in C57 mice. Those findings indicated that long-term intake of black tea could prevent cardiovascular and thrombotic risks and TF-1 might be developed as a natural agent for the prevention of cardiovascular diseases. |
