Department of Medicine, University of Vermont, Burlington, Vermont, USA.
Platelets. 2010;21(2):85-93. doi: 10.3109/09537100903470298.
Vascular endothelial growth factor (VEGF) and endostatin are key protein modulators of angiogenesis found within platelets. The platelet activation pathways that control angiogenic protein release are incompletely elucidated. The differential release of pro-angiogenic and anti-angiogenic proteins from the platelet has been demonstrated for proteinase activated receptors (PARs). Given the ability of tumors to secrete ADP and the availability of ADP receptor antagonists clinically, we determined the influence of adenosine diphosphate (ADP) and the ADP receptors, P2Y(1) and P2Y(12), on platelet release of the angiogenic stimulator protein, VEGF, and the angiogenic inhibitor protein, endostatin. Minimally altered whole blood (WB) and platelet rich plasma (PRP) from healthy volunteers was stimulated with ADP alone (12.5 uM), in combination with a P2Y(1) antagonist (MRS2179) or a P2Y(12) antagonist (cangrelor). VEGF and endostatin protein concentrations were assessed by an ELISA assay. We report that maximally stimulating concentrations of ADP significantly increased VEGF release from platelets in both PRP and WB by 36+/-12% 36+/-12% 54+/-18% 36 +/- 12% (p < 0.05) respectively as compared to control. Both P2Y(1) and P2Y(12) receptor antagonism inhibited this release. Conversely, endostatin levels did not change following ADP stimulation in PRP, while a 4.7% (p = 0.03) increase was observed in WB. As compared to thrombin receptor activation, ADP activation was a weaker stimulus for VEGF release. We found that activation of platelets by ADP results in an increase in soluble VEGF concentrations with minimal effects on endostatin concentrations, suggesting ADP release in the tumor microenvironment may be, on balance, proangiogenic. P2Y receptor antagonism abrogates ADP mediated proangiogenic protein release and thus may represent a potential pharmacologic strategy for regulating platelet mediated angiogenesis.
血管内皮生长因子 (VEGF) 和内皮抑素是血小板中血管生成的关键蛋白调节剂。控制血管生成蛋白释放的血小板激活途径尚未完全阐明。蛋白酶激活受体 (PAR) 已经证明了从血小板中释放促血管生成和抗血管生成蛋白的差异。鉴于肿瘤能够分泌 ADP 以及临床上可获得 ADP 受体拮抗剂，我们确定了二磷酸腺苷 (ADP) 及其 ADP 受体 P2Y(1) 和 P2Y(12) 对血小板释放血管生成刺激蛋白 VEGF 和血管生成抑制剂蛋白内皮抑素的影响。从健康志愿者中获得的最小改变的全血 (WB) 和富含血小板的血浆 (PRP) 用 ADP 单独 (12.5 μM) 刺激，与 P2Y(1) 拮抗剂 (MRS2179) 或 P2Y(12) 拮抗剂 (cangrelor) 联合刺激。通过 ELISA 测定法评估 VEGF 和内皮抑素蛋白浓度。我们报告说，与对照相比，最大刺激浓度的 ADP 分别使 PRP 和 WB 中的血小板 VEGF 释放增加 36+/-12%36+/-12%54+/-18%36 +/- 12%（p < 0.05）。P2Y(1) 和 P2Y(12) 受体拮抗剂均抑制了这种释放。相反，ADP 刺激后 PRP 中的内皮抑素水平没有变化，而在 WB 中观察到 4.7%（p = 0.03）的增加。与凝血酶受体激活相比，ADP 激活是 VEGF 释放的较弱刺激物。我们发现，ADP 激活血小板会导致可溶性 VEGF 浓度增加，而内皮抑素浓度变化很小，这表明肿瘤微环境中的 ADP 释放可能总体上具有促血管生成作用。P2Y 受体拮抗剂可消除 ADP 介导的促血管生成蛋白释放，因此可能成为调节血小板介导的血管生成的潜在药物治疗策略。
