Inhibitory mechanisms of cme-1, a novel polysaccharide from the mycelia of cordyceps sinensis, in platelet activation

Objective: CME-1 is a polysaccharide purified from the mycelia of medicinal mushroom Cordyceps sinensis, its molecular weight was determined to be 27.6 kDa by using nuclear magnetic resonance and gas chromatography-mass spectrometry. The initiation of arterial thromboses is relevant to various cardiovascular diseases (CVDs) and is believed to involve platelet activation. Our recent study exhibited that CME-1 has potent antiplatelet activity via the activation of adenylate cyclase/cyclic AMP ex vivo and in vivo. Methods: The aggregometry, and immunoblotting were used in this study. Results: In this study, the mechanisms of CME-1 in platelet activation is further investigated and found that CME-1 inhibited platelet aggregation as well as the ATP-release reaction, relative intracellular [Ca⁺] mobilization, and the phosphorylation of phospholipase C (PLC)y2 and protein kinase C (PKC) stimulated by collagen. CME-1 has no effects on inhibiting either convulxin, an agonist of glycoprotein VI, or aggretin, an agonist of integrin a₂p\ stimulated platelet aggregation. Moreover, this compound markedly diminished thrombin and arachidonic acid (AA) induced phosphorylation of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase 2, c-Jun N-terminal kinase 1, and Akt. Treatment with SQ22536, an inhibitor of adenylate cyclase, markedly diminished the CME-1-mediated increasing of cyclic AMP level and reversed prostaglandin E₁- or CME-1-mediated inhibition of platelet aggregation and p38 MAPK and Akt phosphorylation stimulated by thrombin or AA. Furthermore, phosphodiesterase activity of human platelets was not altered by CME-1. Conclusion: The crucial finding of this study is that the antiplatelet activity of CME-1 may initially inhibit the PLCy2-PKC-p47 cascade, and inhibit PI3-kinase/Akt and MAPK phosphorylation through adenylate cyclase/cyclic AMP activation, then inhibit intracellular [Ca⁺] mobilization, and, ultimately, inhibit platelet activation. The novel role of CME-1 in antiplatelet activity indicates that this compound exhibits high therapeutic potential for treating or preventing CVDs.