Antiplatelet Activity of Obovatol, a Biphenolic Component of Magnolia Obovata, in Rat Arterial Thrombosis and Rabbit Platelet Aggregation

Aim: Thrombosis occurs in the coronary arteries via the activation of platelets, and leads to acute myocardial infarction and sudden death. Obovatol, a major biphenolic component of Magnolia obovata leaves, displays anti-inflammatory and acyl Co-A cholesterol acyltrasferase inhibitory effects. The purpose of this study was to determine the effects of obovatol on thrombus formation in vivo and platelet activation in vitro and ex vivo. Methods: We investigated the antiplatelet and antithrombotic activities of obovatol in rat carotid arterial thrombosis in vivo along with platelet aggregation in vitro and ex vivo. Its possible cellular mechanism of antiplatelet activity was investigated by testing PLC-gamma 2 activation, arachidonic acid cascade, calcium mobilization and granule secretion. Results: Oral administration of obovatol prevented carotid thrombosis, but also significantly inhibited collagen-induced platelet aggregation. Obovatol did not change coagulation times, such as activated partial thromboplastin time and prothrombin time, indicating that the antithrombotic effect of obovatol might be due to antiplatelet activity rather than anticoagulation activity. Obovatol inhibited in vitro collagen-and arachidonic acid-induced rabbit platelet aggregation in a concentration-dependent manner (1-10 mu M), with IC50 values of 2.4 +/- 0.8 and 4.8 +/- 0.9 mu M, respectively. Obovatol blocked collagen-mediated phospholipase C-gamma 2 phosphorylation, cytoplasmic calcium mobilization, arachidonic acid liberation and serotonin secretion. Conclusion: Obovatol has a potent antithrombotic effect, which may be due to antiplatelet activity. The antiplatelet activity of obovatol is mediated by inhibition of PLC-gamma 2 phosphorylation. Thus, obovatol may be a potential candidate to treat cardiovascular disease.