6-[3-(dimethylamino)propylamino]-9-methoxy-11H-indeno[1,2-c]quinolin-11-one抑制血小板凝集作用機轉之探討

Abstract

本篇論文主要探討化合物TCH-201抑制人類血小板凝集的作用機轉。在人類血小板懸浮液（PS）中，TCH-201呈濃度相關性的抑制由U46619 (1 μM)、collagen (10 μg/ml)、arachidonic acid (AA, 200 μM)和thrombin (0.1 U/ml)引起的血小板凝集，其IC50分別為10.12±1.38、12.87±1.57、17.43±1.26和24.01±1.68 μM。TCH-201也會抑制由collagen和thrombin引起的P-selectin 表現量及thromboxane B2生成，對於蛋白質tyrosine phosphorylation訊息傳遞方面，在PLC、PI3K、Syk、Src、LAT這些位置都有抑制磷酸化的情形。 首先，我們檢驗影響血小板最終活化的GPIIb-IIIa，發現TCH-201不會抑制disintegrin對GPIIb-IIIa之結合作用，亦不影響纖維蛋白原 (fibrinogen)結合到經elastase處理後的GPIIb-IIIa。此顯示了TCH-201不會結合到非活化或活化態的GPIIb-IIIa，及對此部位產生拮抗作用。除此之外，TCH-201不會提升胞內cAMP與cGMP生成量，也不會干擾由AA引起的thromboxane B2生成及對cPLA2活性沒有直接的影響，其作用非來自對內生性cPLA2活性及arachidonate- thromboxane A2 生合成路徑上的抑制。 再者，在血小板內鈣離子濃度變化的實驗中，我們發現TCH-201呈劑量相關性的抑制collagen和thrombin引發的Ca2+ mobilization。更進一步將血小板先以EGTA處理後，發現TCH-201會抑制thrombin引發之內鈣釋出及外鈣的進入。以thapsigargin來釐清對SOCC的作用，顯示TCH-201只些微影響thapsigargin所引發鈣離子進入。 在血小板懸浮液中，TCH-201可抑制PMA引發的血小板凝集。以OAG（DAG 類似物）刺激造成外鈣進入的實驗中，發現TCH-201會抑制此現象；同時TCH-201亦減少以collagen和thrombin刺激之下的PKCα translocation。顯示TCH-201對DAG活化PKC這條路徑上有影響。 綜合上述結果，TCH-201影響Ca2+ mobilization的作用主要來自於抑制胞內的鈣離子釋出，並能抑制胞外鈣離子流入；且對Ca2+ mobilization的阻斷可能進而影響血小板內PKC的活性，兩者共同貢獻到TCH-201對於血小板功能的抑制作用。至於是否抑制 PLC活化和其上游則有待更進一步的探討。

In the present study, the mechanism of antiplatelet activity of TCH-201, a synthetic 6-[3-(dimethylamino)propylamino]-9-methoxy- 11H-indeno[1,2-c]quinolin-11-one, was investigated. TCH-201 concentration-dependently inhibited platelet aggregation stimulated by U46619 (1 μM), collagen (10 μg/ml), AA (200 μM) and thrombin (0.1 U/ml) with IC50 values of 10.12±1.38, 12.87±1.57, 17.43±1.26 and 24.01±1.68 μM in washed human platelets, respectively. TCH-201 also inhibited collagen and thrombin-induced P-selectin expression and thromboxane B2 formation. In addition, TCH-201 attenuated tyrosine phosphorylation of a number of proteins including PLC、PI3K、Syk、Src and LAT. Fibrinogen binding to activated glycoprotein (GP)IIb-IIIa is the final common pathway of platelet aggregation. However, TCH-201 did not influence disintegrin binding to GPIIb-IIIa and it did not affect fibrinogen binding to activated GPIIb-IIIa. This suggests that the inhibitory effect of TCH-201 is not through acting as a direct antagonist of GPIIb-IIIa. TCH-201 alone did not induce significant increase in cAMP and cGMP levels in platelets. TCH-201 failed to inhibit the biosynthesis of thromboxane B2 induced by arachidonic acid and it had no inhibitory effect on cytosolic phospholipase A2, suggesting that it dose not affect the endogenous cPLA2 activity, and arachidonate-thromboxane A2 biosynthetic pathway. In Fura-2 loaded platelets, TCH-201 inhibited intracellular calcium mobilization stimulated by collagen and thrombin. In the presence of EGTA, TCH-201 showed its inhibitory effects on both calcium release from intracellular stores and calcium influx in thrombin-stimulated platelets. Using thapsigargin as a tool to study SOCC, however, TCH-201 did not significantly affect [Ca2+]i level in thapsigargin-induced [Ca2+]i entry. In washed human platelets, TCH-201 inhibited platelet aggregation induced by PMA. Activation of OAG (DAG analog) mediated store-independent calcium entry was blocked by TCH-201. In addition, TCH-201 reduced translocation of PKCα to the cell membrane caused by collagen and thrombin. This suggests that TCH-201 may affect activation of PKC by DAG. Taken together, these data clearly indicate that the inhibitory mechanism on calcium mobilization in stimulated platelets of TCH-201 is due to blockade of calcium release from intracellular stores, the consequential calcium influx and the activation of PKC. However, if TCH-201 affects the activation of PLC and its upstream remains to be investigated.