Garcinol acts as a novel integrin α_IIbβ₃ inhibitor in human platelets

Aims: Platelet activation plays a central role in arterial thrombosis. Platelets are activated by adhesive proteins (i.e., collagen) or soluble agonists (i.e., thrombin), the respective receptor-specific signaling cause inside-out signaling, leading to the binding of fibrinogen to integrin α_IIbβ₃. This binding triggers outside-in signaling, resulting in platelet aggregation. Garcinol, a polyisoprenylated benzophenone, is extracted from the fruit rind of Garcinia indica. Although garcinol exhibits considerable bioactivities, few studies have investigated the effect of garcinol on platelet activation.

Main methods: Aggregometry, immunoblotting, flow cytometer, confocal microscopic analysis, fibrin clot retraction, animal studies such as fluorescein-induced platelet plug formation in mesenteric microvessels, acute pulmonary thromboembolism, and tail bleeding time were performed in this study.

Key findings: This study indicates that garcinol inhibited platelet aggregation stimulated by collagen, thrombin, arachidonic acid, and U46619. Garcinol reduced integrin α_IIbβ₃ inside-out signaling, including ATP release; cytosolic Ca²⁺ mobilization; P-selectin expression; and Syk, PLCγ2/PKC, PI3K/Akt/GSK3β, MAPKs, and NF-κB activation stimulated by collagen. Garcinol directly inhibited integrin α_IIbβ₃ activation by interfering with FITC-PAC-1 and FITC-triflavin by collagen. Additionally, garcinol affected integrin α_IIbβ₃-mediated outside-in signaling, such as decreasing platelet adhesion and the single-platelet spreading area; suppressing integrin β₃, Src, FAK, and Syk phosphorylation on immobilized fibrinogen; and inhibiting thrombin-stimulated fibrin clot retraction. Garcinol substantially reduced mortality caused by pulmonary thromboembolism and prolonged the occlusion time of thrombotic platelet plug formation without extending bleeding time in mice.

Significance: This study identified that garcinol, a novel antithrombotic agent, acts as a naturally occurring integrin α_IIbβ₃ inhibitor.