| 摘要: | 血小板在止血與動脈血栓形成上扮演重要角色，透過黏附蛋白 (例如:collagen) 或是水溶性血小板刺激劑 (例如:thrombin) 活化血小板專一性受體促進血小板活化。不同的刺激劑會與各自專一性受體結合並引發一連串inside-out的訊息傳遞，促使血小板型態變化，導致纖維蛋白原 (fibrinogen) 與integrin αIIbβ3結合引起outside-in的訊息傳遞，造成血小板顆粒分泌和凝集作用。Garcinol由Garcinia indica乾果皮中萃取出的一種聚異戊二烯化二苯甲酮，雖然garcinol具有抗發炎、抗癌等多樣生物活性，但很少研究在探討garcinol對於血栓形成的影響，而血小板在血栓形成上扮演重要角色，因此本篇將探討garcinol對於血小板活化作用的影響。研究結果顯示garcinol會抑制由collagen、thrombin、arachidonic acid和U46619引起的血小板凝集作用。此外，Garcinol 抑制由collagen所刺激的integrin αIIbβ3 inside–out signaling，包括ATP 與鈣離子的釋出、P-selectin的表現量、Syk、PLC2/PKC、PI3K/Akt/GSK3β、MAPKs和NF-κB的蛋白磷酸化。同時garcinol能夠直接透過干擾FITC–PAC-1和FITC-triflavin與integrin αIIbβ3結合從而抑制integrin αIIbβ3 outside–in signaling中的integrin β3、Src、FAK和Syk蛋白磷酸化進而減少血小板在纖維蛋白原的貼附與展開的面積並且影響血小板的凝塊回縮。另外，在動物實驗中也證實garcinol 顯著降低ADP造成肺栓塞的死亡率，並延長了血栓形成的時間且不會延長出血時間。綜上所述，這項研究發現了 garcinol 透過干擾纖維蛋白原與integrin αIIbβ3結合，進而抑制血小板活化降低血栓的形成，因此garcinol可能是天然存在的integrin αIIbβ3的抑制劑並有機會發展成一種新型的抗血栓劑。
Platelets play a central role in physiological hemostasis and pathological arterial thrombosis. Upon stimulation by adhesive proteins like collagen or soluble platelet agonists such as thrombin, platelets initiate signaling cascades through specific receptors. The respective receptor–specific platelet activation signaling pathways cause common signaling events, resulting in platelet shape changes, and inside–out signaling, leading to the binding of fibrinogen to integrin αIIbβ3. This binding trigger outside–in signaling, resulting in platelet granule secretion and aggregation. Garcinol, a polyisoprenylated benzophenone, is extracted from Garcinia indica fruit rind. Despite the diverse bioactivities attributed to garcinol, there is a paucity of research examining its impact on platelet activation. Results from this study showed that garcinol inhibited collagen, thrombin, arachidonic acid and U46619-induced platelet aggregation. Besides, garcinol exerted notable inhibitory effects on integrin αIIbβ3 inside–out signaling, including decreased ATP release, cytosolic P-selectin expression, Ca2+ mobilization, and attenuated the phosphorylation of Syk, PLC2/PKC, PI3K/Akt/GSK3β, MAPKs, and NF-κB in response to collagen stimulation. Garcinol directly inhibited integrin αIIbβ3 activation by interfering with FITC–PAC-1 and FITC-triflavin binding stimulated by collagen. In addition, garcinol modulated integrin αIIbβ3-mediated outside–in signaling, resulting in reduced platelet adhesion and the single-platelet spreading area, suppressed phosphorylation of integrin β3, Src, FAK, and Syk on immobilized fibrinogen, and inhibited thrombin-stimulated fibrin clot retraction. Garcinol demonstrated a significant reduction in mortality resulting from ADP-induced pulmonary embolism in mice. Furthermore, garcinol exhibited a notable prolongation of the occlusion time for thrombotic platelet plug formation, without affecting bleeding time. These findings highlight the potential of garcinol as a novel antithrombotic agent, acting as a naturally occurring inhibitor of integrin αIIbβ3. |
