Alwayn I P, Appel J Z, Goepfert C, Buhler L, Cooper D K, Robson S C
Transplantation Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, USA.
Xenotransplantation. 2000 Nov;7(4):247-57. doi: 10.1034/j.1399-3089.2000.00965.x.
Activation of endothelial cells and platelet sequestration play major roles in rejection of xenografts. The histopathology of both hyperacute and acute vascular or delayed rejection of vascularized discordant xenografts is characterized by interstitial hemorrhage and intravascular thrombosis. Agents that prevent platelet activation and consequent microthrombus formation have proven beneficial in xenograft rejection but do not fully preclude vascular thrombosis. Recently, several new anti-platelet therapies have undergone extensive clinical testing for atherosclerotic thrombotic vascular disorders; other putative therapies are undergoing pre-clinical evaluation. We have investigated the effect of several of these novel agents on platelet aggregation in baboons in order to screen for future potential in xenograft rejection models.
Drugs tested in these experiments were aurintricarboxylic acid (ATA, von Willebrand Factor-GPIb inhibitor), fucoidin (a selectin-inhibitor), 1-benzylimidazole (1-BI, thromboxane synthase antagonist), prostacyclin (PGI2, endothelial stabilizer), heparin (thrombin antagonist), nitroprusside sodium or nicotinamide (NPN or NA, both NO-donors), and eptifibatide (EFT, GPIIb/IIIa receptor antagonist). These were infused intravenously to nine baboons. Coagulation parameters and platelet counts were monitored and baboons were observed for adverse side-effects. The efficacy of these agents in inhibiting platelet aggregation was assayed in a platelet aggregometer.
Treatment with ATA and fucoidin resulted in complete inhibition of platelet aggregation but also in major perturbation of coagulation parameters. 1-BI and PGI2 had no effect when administered alone, but in combination resulted in moderate inhibition of aggregation without disturbance in PT or PTT. NPN and NA had no substantive effects on platelet aggregation. Heparin resulted in specific inhibition of thrombin-induced platelet aggregation and, as anticipated, was associated with moderate prolongation of PTT. Importantly, EFT caused complete inhibition of platelet aggregation without changes in coagulation. Platelet counts, fibrinogen levels, and fibrinogen degradation products remained within the normal ranges in all experiments.
Although excellent inhibition of platelet activation was obtained with ATA and fucoidin, clinical use may be precluded by concomitant disturbances of coagulation. Combinations of heparin and EFT may prove beneficial in preventing the thrombotic disorders associated with xenograft rejection while maintaining adequate hemostatic responses. These agents are to be evaluated in our pig-to-primate xenotransplantation models.
内皮细胞的激活和血小板的扣押在异种移植排斥中起主要作用。超急性和急性血管性或延迟性血管化异种移植排斥的组织病理学特征为间质出血和血管内血栓形成。已证明预防血小板激活及随之而来的微血栓形成的药物在异种移植排斥中有益，但不能完全防止血管血栓形成。最近，几种新的抗血小板疗法已针对动脉粥样硬化性血栓性血管疾病进行了广泛的临床试验；其他假定的疗法正在进行临床前评估。我们研究了其中几种新型药物对狒狒血小板聚集的影响，以便筛选其在异种移植排斥模型中的未来潜力。
在这些实验中测试的药物有金精三羧酸（ATA，血管性血友病因子 - GPIb抑制剂）、岩藻依聚糖（一种选择素抑制剂）、1 - 苄基咪唑（1 - BI，血栓素合酶拮抗剂）、前列环素（PGI2，内皮稳定剂）、肝素（凝血酶拮抗剂）、硝普钠或烟酰胺（NPN或NA，均为一氧化氮供体）以及依替巴肽（EFT，GPIIb/IIIa受体拮抗剂）。将这些药物静脉注射给9只狒狒。监测凝血参数和血小板计数，并观察狒狒有无不良副作用。在血小板聚集仪中测定这些药物抑制血小板聚集的功效。
用ATA和岩藻依聚糖治疗导致血小板聚集完全抑制，但也导致凝血参数的严重紊乱。单独使用1 - BI和PGI2无效，但联合使用可适度抑制聚集，且不干扰PT或PTT。NPN和NA对血小板聚集无实质性影响。肝素特异性抑制凝血酶诱导的血小板聚集，并且如预期的那样，与PTT适度延长相关。重要的是，EFT导致血小板聚集完全抑制，而凝血无变化。在所有实验中，血小板计数、纤维蛋白原水平和纤维蛋白原降解产物均保持在正常范围内。
虽然ATA和岩藻依聚糖能很好地抑制血小板激活，但伴随的凝血紊乱可能使其无法用于临床。肝素和EFT联合使用可能在预防与异种移植排斥相关的血栓性疾病同时维持足够的止血反应方面证明是有益的。这些药物将在我们的猪 - 灵长类动物异种移植模型中进行评估。
