Anti-platelet effect of ginkgolide a from Ginkgo biloba

Abstract

Effects of ginkgolide A (GA) from Ginkgo biloba leaves in collagen (10 μg/mL)-stimulated platelet aggregation were investigated. Zymographic analysis confirmed that pro-matrix metalloproteinase-9 (MMP-9) (92 kDa) was activated by GA to form an activated MMP-9 (86-kDa) on gelatinolytic activities. GA concentration-dependently inhibited platelet aggregation, intracellular Ca2+ mobilization, and thromboxane A2 (TXA2) formation by inhibiting the cyclooxygenase-1 (COX-1) activity in collagen-stimulated platelets. In addition, GA increased the formation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), which have an anti-platelet function in both resting and collagen-stimulated platelets. On the other hand, GA did not prolong prothrombin time (PT) and activated partial thromboplastin time (aPTT) associated with the extrinsic and intrinsic coagulation pathways on human plasma, respectively. Therefore, we suggest that the inhibitory effect of GA on platelet aggregation might involve the following pathway. GA may increase the MMP-9 activity and intracellular cAMP and cGMP production, inhibit intracellular Ca2+ mobilization, and decrease TXA2 production by down-regulating the COX-1, thereby leading to inhibition of platelet aggregation without cytotoxicity. These results strongly indicate that GA is a potent inhibitor of collagen-stimulated platelet aggregation. It may play an important role as a negative regulator during platelet activation.