Bioengineering Catalytically Active Grafts for Vascular Surgery

描述(由申请人提供)： 治疗严重外周动脉疾病的金标准仍然是自体静脉搭桥术。然而，当静脉不可用时，必须使用假体移植物，并且与非常高的失败率相关，仅两年就接近70%。假体移植失败的主要原因是新生内膜增生。已有研究表明，一氧化氮(NO)是一种有效的抑制新生内膜增生的物质。用于局部抑制新生内膜增生的两类NO供体主要是二氮杂二醇和S-亚硝硫醇。由于NO释放的持续时间较短，任何一类NO供体的移植物修饰对移植物功能的改善都是有限的。然而，RSNO仍然具有吸引力，因为它们存在于人的血浆中，可以与光、金属离子或L-抗坏血酸(AA)反应释放NO。因此，为了克服药物传递时间的限制，我们建议开发和评价一种催化活性的移植物，通过将AA固定在移植物的管腔表面，在血液-材料界面上长时间释放NO。这一概念利用了循环RSNO的无限储存库，它将与接枝表面的AA反应释放NO。我们假设，在管腔表面加入AA的催化活性假体移植物将利用内源性循环RSNO在血液-材料界面产生NO，并抑制新生内膜增生的形成。为了验证我们方法的可行性，我们合成了第一代聚(1，8-辛二醇-柠檬酸-抗坏血酸)(POCA)共聚物，并在体外证明了与RSNO溶液接触时NO的生成延长。初步数据显示，POCA在2个月内降解了30%。这一点很重要，因为只要移植物上有POCA，NO就会释放出来。当POCA被完全降解时，NO将模拟移植物的内源性内皮化，从而消除了外部NO释放的需要。为了支持我们的方法，我们使用豚鼠主动脉间置模型植入了POCA移植物，在1个月时发现移植物增生较少。因此，鉴于我们有希望的初步数据，我们建议以以下具体目标来验证我们的假设：1)合成和表征生物相容的AA聚二柠檬酸共聚物，催化RSNO转化为NO，并使用这些共聚物来制备具有催化活性的ePTFE移植物；2)评估具有催化活性的POCA-ePTFE移植物在体内抑制新生内膜增生的安全性、生物相容性和有效性；以及3)评估优化的催化活性POCA-ePTFE移植物在体内抑制动脉粥样硬化动物模型中的新生内膜增生的生物相容性和有效性。目前，假体移植物是 作为自体静脉的不良替代品，有必要开发新的策略来提高假体移植物的通畅率。通过多学科合作，我们已经证明了我们方法的可行性。成功完成这项建议中描述的研究将提供一种创新的方法，在局部产生重要的治疗剂NO，同时克服其他移植物修饰方法的局限性，并直接导致临床前研究。一旦得到验证，这项技术有可能对退伍军人医疗保健产生积极影响。

DESCRIPTION (provided by applicant): The gold standard for the treatment of severe peripheral artery disease remains bypass grafting with autologous vein. However, when vein is not available, prosthetic grafts must be utilized and are associated with very high failure rates, approaching 70% at just 2 years. The primary cause of failure of prosthetic grafts is development of neointimal hyperplasia. It is well established tht nitric oxide (NO) is a potent inhibitor of neointimal hyperplasia. The two main classes of NO donors that have been used to inhibit neointimal hyperplasia locally are diazeniumdiolates and S-nitrosothiols (RSNO). Graft modifications with either class of NO donors have shown only limited improvement in graft function due to a short duration of NO release. However, RSNO remain attractive because they are present in human plasma and can release NO upon reaction with light, metal ions, or L-ascorbic acid (AA). Thus, to overcome the limitation of drug delivery duration, we propose to develop and evaluate a catalytically active graft that will release NO at the blood-material interface for an extended duration of time by immobilizing AA to the luminal surface of the graft. This concept takes advantage of the limitless reservoir of circulating RSNO that will react with AA on the graft surface to release NO. We hypothesize that a catalytically active prosthetic graft engineered to incorporate AA on the lumen surface will utilize endogenous circulating RSNO to generate NO at the blood-material interface and inhibit the formation of neointimal hyperplasia. To confirm the feasibility of our approach, we synthesized a first generation poly(1,8 octanediol-citrate-ascorbate) (POCA) copolymer and demonstrated prolonged generation of NO upon contact with RSNO solutions in vitro. Preliminary data show 30% POCA degradation at 2 months. This is important, as NO will be released as long as POCA is present on the graft. By the time POCA is completely degraded, the NO will have simulated endogenous endothelialization of the graft, thereby abrogating the need for external NO release. Supporting our approach, we implanted a POCA graft using a guinea pig aortic interposition model and found less graft hyperplasia at 1 month. Thus, given our promising preliminary data, we propose to investigate our hypothesis with the following Specific Aims: 1) synthesize and characterize biocompatible AA containing polydiolcitrate copolymers that catalyze the conversion of RSNO to NO and use these copolymers to fabricate catalytically active ePTFE grafts; 2) evaluate the safety, biocompatibility, and efficacy of the catalytically active POCA-ePTFE graft at inhibiting neointimal hyperplasia in vivo; and 3) evaluate the biocompatibility and efficacy of an optimized catalytically active POCA-ePTFE graft at inhibiting neointimal hyperplasia in an atherosclerotic animal model in vivo. Currently, prosthetic grafts are a poor substitute for autologous vein and there is a significant need to develop novel strategies to improve prosthetic graft patency rates. Through a multidisciplinary collaboration, we have demonstrated the feasibility of our approach. Successful completion of the studies described in this proposal will provide an innovative approach to locally generate NO, an important therapeutic agent, while overcoming limitations of other graft modification approaches, and directly lead to preclinical investigations. Once validated, this technology has the potential to positively impact veteran health care.