【作者】 李海伟；

【导师】 徐克；

【作者基本信息】 中国医科大学 ， 影像医学与核医学， 2010， 博士

【摘要】 阻塞性血管疾病包括心脑血管及外周血管疾病严重威胁着人类健康,而且发病率呈逐年上升趋势。血管内支架植入术已经成为冠状动脉和外周血管阻塞性疾病的主要治疗手段。但是支架的长期存留导致的内膜增生严重影响了支架置入术的中远期疗效。药物洗脱支架(Drug-Eluting Stent, DES)由于抗增殖药物的使用减轻了新生内膜的形成,但药物释放完毕后仍以异物永久存在于血管壁中,持续刺激血管壁导致再狭窄(In-Stent Restenosis, ISS)。如何缩短支架在体内的存留时间,减轻机械刺激是血管内支架研究的热点之一。可降解血管内支架几乎和永久性金属血管内支架同时提出。可降解血管内支架(Biodegradable Endovascular Stent,BES)具有暂时存留的特点,在人体内完成使命后降解消失,因此受到医学界关注。早在1988年,Stack等人就利用聚乳酸材料(Poly-Lactic Acid,PLA)研制开发了生物可降解支架。目前研究较多的可降解支架包括生物大分子支架,可降解铁支架及可降解镁合金支架(Biodegradable Magnesium Alloy Stent, BMS)。生物大分子支架机械性能差限制了它在小血管中的应用,可降解铁支架降解速度慢,近年来研究较少。镁合金支架较其他两种可降解支架具有支撑力强、炎症反应小等特点,近年来发展迅速。国外镁合金支架的动物实验及临床试验报道认为镁合金支架安全有效,但存在中度新生内膜增生以及降解速度过快等问题,因此如何延长降解时间、减轻新生内膜增生摆在了广大研究者的面前。中科院金属研究所研制出了一种雷帕霉素涂层AZ31可降解镁合金支架,表面经过(1)电抛光以增加支架表面光滑程度,减少血栓形成；(2)化学钝化处理以延长降解时间。同时在支架的表面涂以雷帕霉素,旨在抑制新生内膜增生,药物载体为聚(乳酸-三亚甲基碳酸酯)(Poly (Lactic Acid-co-Trimethylene Carbonate)，P(LA-TMC))。该支架的机械性能、血液相容性、血小板黏附实验、模拟血浆中的降解性能实验已完成,试验结果理想。本实验的目的在于初步研究该支架在兔腹主动脉中的降解时间及抑制新生内膜的性能。目前国内外尚没有药物涂层可降解镁合金支架的相关实验及临床报道。本研究分为以下两个方面：第一部分：雷帕霉素涂层AZ31可降解镁合金支架在兔腹主动脉的降解性能研究。目的：初步评价雷帕霉素涂层AZ31可降解镁合金支架在兔腹主动脉的降解性能。方法：将20枚雷帕霉素涂层AZ31可降解镁合金支架置入20只新西兰大白兔肾下腹主动脉中。分别于术后1个月(n=5)、两个月(n=5)、3个月(n=5)及4个月(n=5)处死动物。对支架段血管进行钼靶照相及病理处理。(1)通过钼靶照相评价支架在降解过程中的大体形态改变。(2)对病理图像进行计算机图像分析,计算支架不同时间段剩余支杆的截面积。对截面积进行直线回归分析,得到支架完全降解所需要的时间。结果：20只大白兔在随访期存活良好。钼靶照相显示1个月时支架形态完整,扩张完全；2个月时支架部分支杆降解断裂,失去支撑作用；3个月时大部分支架支杆降解,4个月时所有支架完全降解。计算机病理图像分析示平均每天支架支杆降解面积为0.00192mm2,支架在兔腹主动脉中完全降解所需时间为105.0天。结论：雷帕霉素涂层可降解AZ31镁合金支架在兔主动脉中2个月内失去支撑作用,完全降解所需时间为105.0天。降解时间较已报道的其他镁合金支架有所延长,但仍有待于进一步延长。第二部分：雷帕霉素涂层AZ31可降解镁合金支架在兔腹主动脉抑制新生内膜性能研究。目的：初步评价雷帕霉素涂层AZ31可降解镁合金支架在兔腹主动脉抑制新生内膜的性能。方法：术前一周常规喂养。AZ31可降解镁合金支架及雷帕霉素涂层AZ31可降解镁合金支架各22枚配对置入22只新西兰大白兔腹主动脉中,前者置于肾下腹主动脉近端,后者置于肾下腹主动脉远端。术后青霉素抗炎,阿司匹林抗凝。分别于术后第3天(n=2),1个月(n=5),2个月(n=5),3个月(n=5),4个月(n=5)处死动物。术后3天随访观察有无急性血栓形成。其余随访期将支架段血管取出后进行病理学及血管数字形态计量分析。结果：22只新西兰大白兔术后存活良好。造影及病理未见血栓形成。随访期间,雷帕霉素涂层AZ31可降解镁合金支架的新生内膜面积明显小于AZ31可降解镁合金支架新生内膜面积。1个月时二者为0.60±0.22mm2 vs.1.44±0.04mm2,P<0.05。第2、3、4个月时,二者比分别为0.63±0.27mm2 vs. 1.41±0.08mm2、0.57±0.14mm2 vs.1.43±0.02mm2、0.58±0.10mm2 vs. 1.47±0.03mm2,P值均小于0.05。药物涂层镁合金支架新生内膜厚度明显小于裸镁合金支架,第1、2、3、4个月时,二者分别110.32±65.31μm vs.250.36±114.39μm、91.28±35.31μm vs.225.12±75.14μm、89.32±38.82μm vs.214.08±75.13μm、116.95±10.44μm vs.239.37±9.49μm,P值均小于0.05。与之对应,随访期内,前者的血管管腔面积明显小于后者,2.44±0.64mm2 vs.1.58±0.43mm2、2.64±0.17mm2 vs.1.93±0.27mm2、2.84±0.54mm2 vs.2.04±0.34mm2、3.00±0.13mm2 vs.2.16±0.08mm2,P值均小于0.05。术后第1个月,雷帕霉素涂层组的内皮化评分低于裸支架,为1.0±0.21 vs.2.45±0.35,P<0.05。术后第2、3、4个月,二者分别为：2.57±0.39vs.2.25±0.36、2.46±0.11 vs.2.56±0.39、2.56±0.28 vs.2.38±0.31,P值均大于0.05。证明雷帕霉素涂层造成血管内皮化延迟。随访期内,两组支架在内弹力膜下面积、炎性评分、损伤评分无明显差别,P值均大于0.05。结论：与AZ31镁合金支架相比,雷帕霉素涂层AZ31可降解镁合金支架能减少新生内膜面积形成,增加管腔面积,但会延缓血管的内皮化。更多还原

【Abstract】 Cardiovascular disease has became more and more common because of the development of economy and the diet of people, and threatened people’s health seriously. According to statistics, some scholars have anticipated that cardiovascular disease will be the most frequent fatality factor in 2020. Clinically, the use of intravascular stents has gained popularity and becomes an eatablished mode of treatment in percutaneous cardiovascular interventions. However, mural thrombus, elastic recoil and neointimal hyperplasia limit the long-term effectiveness of this treatment. While thrombosis has been controlled with antiplatelet therapy, elastic recoil has been solved with the high radial force of permanent stents, and neointimal hyperplasia has been reduced with the use of drug-eluting stents(paclitaxel and rapamycin). But when the drug is eluted, drug-eluting stents pose problems similar to that of bare metal stents, as permanent foreign bodies in vessel wall which have the risk of continuous interaction between the stent and the surrounding tissue, leading to long-term endothelial dysfunction or chronic inflammatory reaction. These interactions are known as the possible factors for in-stent restenosis(ISS). So how to lessen the mechanical stimulation is one of the hotest points in endovascular stent study. Biodegradable Endovascular Stent(BES) may act as a new biomedical tool which are "fulfilling the mission and stepping away" because of its more physiological repair, reconstitution of local vascular compliance, and a temprory, limited, longitudinal, and radial straightening effect, including the possibility of growth. In 1988, Stack developed the original biodegradable endovascular stent made of poly-lactic acid(PLA). At present, there are three types of BES which are studied most frequently: biodegradable polymers stent, biodegradable iron stent and biodegradable magnesium alloy stent(BMS). Stents made of biodegradable polymers have limited success because of their low radial strength and local inflammation, thus leaving corrodible metals as the best alternatives. BMS’s strong radial force, less inflammatory reaction makes it become the most promising biodegradable stent. In earlier studies, biodegradable magnesium alloy stents were proved to be safe and efficient. However, preliminary preclinical and clinical trials had demonstrated that these stents resulted in higher restenosis rates than seen in drug-eluting stents for a modest degree of neointima formation, late recoil and faster degradation. So how to prolong the degradation and lessess the intimal hyperplasia faces reserchers. A new style of BMS called rapamycin-eluting AZ31 biodegradable magnesium alloy stent has been developed by the Institute of Metal Research Chinese Academy of Sciences(Shenyang, China). The stent’s surface is electropolished so as to prolong cloting time and decrease thrombosis, also inactivated to lengthen corrosion period. The stent was coated by rapamycin whose carrier is poly (lactic acid-co-trimethylene carbonate) (P(LA-TMC)). The mechanical parameter, blood compatibility, plate adhesion experiment and degradation performance have been completed, and the result is ideal. The purpose of present study was to evaluate the degradation time and the character of inhibiting intimal hyperplasia of rapamycin-eluting AZ31 biodegradable magnesium alloy stent. There have been no reports of drug-eluting magnesium alloy stent all over the world. The study included two parts:Part I:The degradable performance of rapamycin-eluting AZ31 biodegradable magnesium alloy stents in rabit abdominal aorta. Objective:The purpose of this study was to study the degradable performance of rapamycin-eluting AZ31 bioabsorbable magnesium alloy stents in rabbit abdominal aortas. Method:Twenty AZ31 biodegradable magnesium alloystents were deployed in infrarenal abdominal aortas of twelve New Zealand white rabbits. Rabbits were sacrificed in one month (n=5), two months(n=5), three months (n=5) and four months (n=5) after stents implantation. Vessels were harvested, radiographed,and then treated with pathology in order to evaluate degradable performance. Radiography of stented vessel was made to show the whole figure, and the pathology was analyzed by computer in order to anticipate the corrosion time. Results:All animals survived in the scheduled follow-up period. Radiography showed stents were expanded fully in one month, most struts had been already corroded partly in two months and completely in three months, all struts were corroded completely in four months. The corrosion period of AZ31 magnesium alloy stents in rabbit aorta was 105.0 days. Conclusion:Rapamycin-eluting AZ31 bioabsorbable magnesium alloy stents lose radial force in rabbit abdominal aorta in two months, and the corrosion period is 105.0 days.PartⅡ:The study of inhibiting intimal hyperplasia character of rapamycin-eluting AZ31 biodegradable magnesium alloy stent. Objective:The purpose of this study was to evaluate inhibiting intimal hyperplasia character of rapamycin-eluting AZ31 biodegradable magnesium alloy stent in rabbit aortas. Methods:Rapamycin-eluting AZ31 biodegradable magnesium alloy stent (n=22) and AZ31 magnesium alloy stents (n=22) were deployed in aortas of 22 New Zealand white rabbits (2 stents each rabbit). Rabbits were sacrificed in 3 days (n=2),1 month (n=5),2 months (n=5),3 months (n=5) and 4 months (n=5) after stents implantation. Stented vessels were harvested to be made pathology and then calculated with computer. Results:All rabbits survived during follow-up period. No evidence of thrombosis was found in angiography and pathology. Neointimal area in the segment deployed with rapamycin-eluting AZ31 magnesium alloy stent was smaller than that deployed with magnesium alloy stent during follow-up period(1 month:0.60±0.22mm2 vs.1.44±0.04mm2, P<0.05; 2、3、4 months after operation:0.63±0.27mm2 vs.1.41±0.08mm2、0.57±0.14mm2 vs.1.43±0.02mm2、0.58±0.10mm2 vs.1.47±0.03mm2, all P＜0.05). Neointimal thichness in the segment deployed with rapamycin-eluting AZ31 magnesium alloy stent was shorter than that deployed with magnesium alloy stent during follow-up period. The data of two groups are:110.32±65.31μm vs.250.36±114.39μm、91.28±35.31μm vs. 225.12±75.14μm、89.32±38.82μm vs.214.08±75.13μm、116.95±10.44μm vs. 239.37±9.49μm, all P<0.05 in 1、2、3、4 months. So the lumen area was significantly larger in the rapamycin-eluting AZ31 magnesium alloy stents group when compared with AZ31 magnesium alloy stents group. The data of every follow-up time was baned as following:2.44±0.64mm2 vs.1.58±0.43mm2 (1 month)、2.64±0.17mm2 vs. 1.93±0.27mm2 (2 months)、2.84±0.54mm2 vs.2.04±0.34mm2、(3 months)、3.00±0.13mm2vs.2.16±0.08mm2 (4 months), all P<0.05。The endothelialization score of two groups was different obviously in 1 month(1.0±0.21 (experiment group) vs.2.45±0.35(contral group), P<0.05),contrasting with the performance in 2、3、4 months(2.57±0.39 vs.2.25±0.36、2.46±0.11 vs. 2.56±0.39、2.56±0.28 vs.2.38±0.31, all P＜0.05.), which suggested that rapamycin-eluting AZ31 magnesium alloy stents group had delayed endothelialization. There was no obvious difference in internal elastic lamina(IEL) area, injury score, inflammation score between two groups during follow-up period. Conclusion: Rapamycin-eluting AZ31 biodegradable magnesium alloy stent obviously reduces the neointimal hyperplasia and improves the lumen area when compared to AZ31 magnesium alloy stent, but it delays vessel’s healing and endothelialization.更多还原