Sequential studies of arterial wall regeneration in microporous, compliant, biodegradable small-caliber vascular grafts in rats

Microporous, compliant, biodegradable vascular grafts prepared from a mixture of polyurethane (95% weight) and poly-L-lactic acid (5% weight) can function as a temporary scaffold for the regeneration of the arterial wall in small-caliber arteries. This study was undertaken to document the sequential events leading to this regeneration. Therefore, polyurethane/poly-L-lactic acid vascular grafts were implanted into the abdominal aorta of rats (N = 28) and were harvested at regular intervals from 1 hour up to 12 weeks after implantation. The implants were evaluated by means of light and electron microscopy. At each time of harvesting, the implants were patent and showed arterial pulsations. No stenosis or dilatation was observed. Endothelial cells grew from the adjacent aortic intima across the anastomoses, from day 6 onward, to form an almost complete neointima after 6 weeks of implantation. Smooth muscle cells also grew from the adjacent aortic media over the graft lattice through the platelet-fibrin coagulum from day 6 onward. The smooth muscle cells, predominantly longitudinally arranged at week 6, but also circularly arranged in some areas at week 12, formed a neomedia in which elastic laminae regenerated. Polymorphonuclear leukocytes and monocytes initially invaded the graft lattices. Fibroblasts, histiocytes, and capillaries grew from the perigraft tissue into the polyurethane/poly-L-lactic acid lattices from day 6 onward, which resulted in the formation of a neoadventitia. The polyurethane/poly-L-lactic acid lattices started to disintegrate from day 12 onward. The regenerative processes in the disintegrating polyurethane/poly-L-lactic acid grafts resulted in the formation of neoarteries, which were of sufficient strength, compliance, and thromboresistance to function as small-caliber arterial substitutes.     

Smooth muscle cell seeding in biodegradable grafts in rats: a new method to enhance the process of arterial wall regeneration

In this study a smooth muscle cell seeding technique was developed and evaluated in biodegradable vascular grafts in rats. Cultured smooth muscle cells (3.5 to 5 X 10(6) in 0.1 ml whole blood) were seeded by means of a one-step preclotting technique in microporous, compliant, biodegradable vascular grafts (internal diameter 1.3 mm, length 1 cm; n = 16). Four seeded grafts as well as four nonseeded preclotted control grafts were histologically evaluated immediately after seeding and on preclotting; the other seeded grafts (n = 12) as well as nonseeded preclotted control grafts (n = 12) were implanted into the abdominal aorta of rats and were evaluated after 2 hours (n = 4), 2 days (n = 4), and 1 week (n = 4) with regard to the process of arterial wall regeneration. All grafts, except one seeded graft harvested at 1 week, were patent. All nonseeded control grafts showed no (at 2 hours and at 2 days) or limited (at 1 week) smooth muscle cell ingrowth. Of the 11 patent seeded grafts three also showed poor or limited neomedia development, probably because of improper preclotting. However, eight of the 11 patent seeded grafts showed fast and uniform noemedia development (clearly discernible at 2 days). Moreover, in two patent 1-week seeded grafts there were neomedia comparable in thickness and architecture (circularly arranged smooth muscle cells) to that of normal rat media, and a neointima had already lined 30% to 40% of the lumen. These results clearly demonstrate that smooth muscle cell seeding in biodegradable grafts is feasible and indicate that this seeding can enhance the process of arterial wall regeneration in these grafts.     

分化生长因子-8对大鼠移植腹主动脉肌纤维化的作用及其机制

目的探讨分化生长因子(GDF)-8对移植大鼠腹主动脉肌纤维化的抑制作用。方法建立雄性Wistar大鼠至雄性SD大鼠腹主动脉原位移植模型,实验动物随机分为两组:延长冷缺血组(PCI)和对照组,测定术后7、14、21、28 d血管内膜厚度,逆转录-聚合酶链反应(RT-PCR)检测移植血管GDF-8的表达,免疫组织化学(IHC)检测Smad4的表达。结果 PCI组内膜14 d开始增厚,28 d至(381．952±44．334)μm,对照组为(56．898±17．543)μm,差异有统计学意义(P<0．05), 术后PCI组GDF-8 mRNA为对照组的3．6％-33.8％,Smad4蛋白表达高于对照组。结论 GDF-8 在移植动脉肌纤维化过程中发挥重要作用,延长冷缺血时间可下调GDF-8的表达而加速肌纤维化进程。     

The myofibrosis mechanism of differentiation growth factor-8 on rat abdominal aorta grafts

OBJECTIVE: The objective of this study was to investigate the role of differentiation growth factor-8 (GDF-8) in inhibiting myofibrosis of abdominal aorta grafts. METHODS: Male Spague-Dawley (SD) rats that received abdominal aorta grafts from male Wistar rats were randomly divided into 2 groups: prolonged cold ischemia (PCI) and control groups. Hematoxylin-eosin (HE) staining was performed to examine aortic graft morphology and to measure neointimal thickness. RT-PCR demonstrated the expression of GDF-8. Immunohistochemical staining (IHC) was performed to detect the expression of Smad4, a pivotal molecule of the transforming, growth factor-beta (TGF-beta)/Smad signal pathway. RESULTS: The intimal thickness increased by 14 days following transplantation in the PCI group (P<.05), reaching 381.952+/-44.334 microm at 28 days, which was higher than that of the control group (56.898+/-17.543 microm; P<.05). The GDF-8 expression in the PCI group was only 3.6%-33.8% of that among the control group. There was a much higher expression of Smad4 on the endothelium of the PCI than the control group at the same time. CONCLUSIONS: Prolonged cold ischemia accelerated grafts myofibrosis by down-regulating the expression of GDF-8, which plays a key role in the myofibrosis process of rat abdominal aortic grafts.     

Arterial wall regeneration in small-caliber vascular grafts in rats. Neoendothelial healing and prostacyclin production

Clinically available synthetic graft materials frequently fail when used as a small-caliber arterial substitute. Therefore, we developed a new type of graft material, prepared from a mixture of polyurethane and poly-L-lactic acid, to be used as a scaffold for the regeneration of the arterial wall. In this study microporous, compliant, biodegradable polyurethane/poly-L-lactic acid grafts (n = 16) and polytetrafluoroethylene grafts (n = 16) were implanted in the rat abdominal aorta and evaluated 3, 6, and 12 weeks after implantation. First, we evaluated the extent of neoendothelial healing (n = 8) by means of light microscopy and scanning electron microscopy. Next, we studied the ability of the neoendothelial cells to produce prostacyclin (n = 8) by means of bioassay for prostacyclin and radioimmunoassay for its stable hydrolysis product, 6-oxo-prostaglandin F1 alpha. There were no significant differences between the two graft types in the amount of prostacyclin production per unit graft area covered with neoendothelium, and this amount was the same as for normal endothelium. However, the polytetrafluoroethylene grafts showed incomplete neoendothelial healing, even after 12 weeks of implantation, in contrast to the polyurethane/poly-L-lactic acid grafts. The better healing characteristics of the polyurethane/poly-L-lactic acid grafts ensured the fast development of a complete neoarterial wall, possessing strength, compliance, and thromboresistance equivalent to normal arterial wall tissue. These results demonstrate that arterial wall tissue regeneration in polyurethane/poly-L-lactic acid grafts may open new perspectives in the field of arterial reconstructive surgery.     

Long-term results of cryopreserved arterial allograft reconstruction in infected prosthetic grafts and mycotic aneurysms of the abdominal aorta.

PURPOSE: This prospective, observational study determined the long-term outcome in patients with abdominal aortic infection (primary or prosthetic graft) who were treated with simultaneous aortic/graft excision and cryopreserved arterial allograft reconstruction. METHODS: From April 1992 to March 2000, patients with abdominal aortic infection underwent complete or partial excision of the infected aorta/prosthetic graft and cryopreserved arterial allograft reconstruction. Arterial allografts were harvested from multiple organ donors and cryopreserved at -80 degrees C without rate-controlled freezing. The patients were observed for survival, limb salvage, persistence and/or recurrence of infection, and allograft patency. The results were calculated with life-table methods. RESULTS: During the 8-year study period, 28 consecutive patients (27 men, 1 woman; mean age, 64 years) underwent treatment for abdominal aortic infection (23 graft infections, including 7 graft-enteric fistulas and 5 primary aortic infections). Allograft reconstruction was performed as an emergency procedure in 13 patients (46%). The mean follow-up period was 35.4 months (range, 6-101 months). The overall treatment-related mortality rate was 17.8% (17% for graft infection, 20% for primary aortic infection). The overall 3-year survival was 67%. There was no early or late amputation. There was no persistent or recurrent infection, and none of the patients received long-term (> 3 months) antibiotic therapy. Reoperation for allograft revision, excision, or replacement was necessary in four patients (17%) who were available for examination, with no reoperative perioperative death. The 3-year primary and secondary allograft patency rates were 81% and 96%, respectively. CONCLUSION: Our experience with cryopreserved arterial allograft in the management of abdominal aortic infection suggests that this technique seems to be a useful option for treating one of the most dreaded vascular complications.     

The use of microvascular graft as an arterial substitute in the abdominal aorta of the rat

The purpose of this study was to compare by means of microsurgical techniques a porous with an interiorly smooth siliconized vascular graft. Compatibility and patency of the graft were examined in a long term followup. A microvascular prosthesis with a particular fibrous texture was used. The fibres consisted of polyurethane (PUR), a new prosthetic material. The lumen of the prosthesis measured 1.6 mm; the outer diameter was 2.4 mm. In group A an in- and exteriorly microporous graft was applied; in group B the inner surface of the prosthesis was smoothed by a silicon layer. 30 SPFWistar rats were randomized in group A (n = 15) and B (n = 15), and both prosthetic materials were implanted as a substitute for an infrarenal part of the abdominal aorta. Monofile suture material (Mirafil^R—DR 5) size 10:0 was used for the anastomosis. The mean pressure of the aorta amounted to 108 ± 30 mm Hg. After 4 ± 2 months the total survival rate was 77% (n = 23): in group A, 80% (n = 12); in group B, 73% (n = 11). Cause of death was early thrombosis due to technical mistakes. The following results were obtained by angiography: highest patency—group A, 8; group B, 1; constriction—group A, 6; group B, 9; occlusion—group A, 1; group B, 4; total—group A, 15; group B, 14; 1 angiography technically failed. Arterial substitution in the abdominal aorta of the rat by PUR-grafts is possible and is a suitable model for further experiments. Prosthetic material with porous structure is significantly better than that with an impermeable smooth inner surface (significance 10%, test by Bross¹³). The low number of experiments allows only trend information and therefore must be considered as a pilot study, though histopathological findings undoubtly point to the superiority of the porous texture of the vascular prosthesis.     

生物可降解支架在修复腹壁缺损中的应用

<正>腹壁缺损作为外科的常见症状,其发生率在过去的75年里仍维持在一定的水平。统计表明美国每年约施行200万例腹部手术,而其中约10万人需要在术后进行腹壁缺损的修复[1-2]。使用不可降解的合成材料(聚丙烯、聚四氟     

基质衍生因子在大鼠腹主动脉移植术后介导的修复重构机制

目的 探讨基质衍生因子-1（SDF-1）在大鼠腹主动脉移植术后介导的修复重构机制。方法 雄性Wistar大鼠为供者，雄性SD大鼠为受者，建立腹主动脉原位移植模型。免疫组织化学技术检测受者移植动脉内皮细胞上SDF-1的表达以及血管内膜的厚度；逆转录-聚合酶链法（RT-PCR）检测移植动脉血管中SDF-1受体CXCR4的表达。结果 受者移植的腹主动脉内皮细胞上持续表达SDF-1，且其表达水平与术后血管内膜增生厚度密切相关。结论 SDF-1能动员干细胞至移植的腹主动脉，并分化成平滑肌样细胞。SDF-1可能成为预警血管硬化、慢性移植物功能丧失发生和发展的指标。     

Neointima formation in expanded polytetrafluoroethylene vascular grafts with different fibril lengths following implantation in the rat aorta

Expanded polytetrafluoroethylene (PTFE) prostheses with fibril lengths of 30 and 60 microns were implanted in the rat infrarenal aorta. Sequential scanning electron and light microscopic studies of the prostheses after implantation demonstrated a different pattern of endothelialization. Prostheses with a fibril length of 60 microns had a continuous multilayered neointima at week 25 postimplantation, whereas prostheses with a 30-microns fibril length had a discontinuous and single layer of endothelium after the same interval. It was concluded, therefore, that a prerequisite for the development of a lining in a vascular prosthesis is for the inner surface of the prosthesis to have adequate pores for effective anchoring of the invading endothelioid cells. Expanded PTFE prostheses with an internodular distance of 60 microns provided sufficient anchoring possibilities for invading endothelioid cells to form a continuous neointima.     

Laser-assisted vessel repair in the rat abdominal aorta

The use of laser energy to thermally denature proteins and produce tissue bonding has potential applications in both the repair and anastomosis of small arteries. The repair of longitudinal arteriotomies in the rat abdominal aorta using the argon laser has been studied in 42 animals with survival times of up to ten weeks. This was compared to vessel repair by conventional suture techniques in 15 animals.Vessels subjected to laser repair showed a high incidence of failure (40%) within the first eight days post operatively compared to no failures in the sutured group. There were no failures of the repaired vessels in the animals surviving longer than eight days. Mechanical bursting pressures of greater than 500 mm Hg were found in both groups of animals at 3 and 10 weeks. Angiography prior to sacrifice showed satisfactory patency of vessels subjected to both types of repair with negligible constriction. Histological examination of the repaired aorta revealed pseudo-aneurysm formation in (29%) of the vessels subjected to laser repair, while the sutured vessels showed greater foreign body tissue reaction.     

SDF-1 plays a key role in the repairing and remodeling process on rat allo-orthotopic abdominal aorta grafts

BACKGROUND: Our previous study demonstrated that prolonged cold preservation promoted neointima formation and remodeling but delayed the subsequent arteriosclerosis of rat abdominal aorta grafts. The mechanisms of this phenomenon remain obscure. In this study, we investigated whether stromal cell derived factor-1 (SDF-1) could play a role in recruiting stem cells to repair and remodel the damaged intima of abdominal aorta grafts. METHODS: Male Spague-Dawley rats received abdominal aorta grafts from male Wistar rats. Hematoxylin and eosin staining was performed to assess the structure of graft aortas by measuring the neointimal thickness. Immunohistochemical staining detected SDF-1 expression. RT-PCR demonstrated the expression of CXCR4, the only known natural receptor of SDF-1 expression on stem cells. RESULTS: The neointimal thickness of the SDF-1 antibody-treated group was inconspicuous; a significant relationship existed between the expression of SDF-1 and the neointimal thickness of the grafts. Furthermore, no CXCR4 was detected in normal abdominal aortas, but it was observed in the grafted abdominal aorta. CONCLUSION: Prolonged cold ischemia may delay the graft's arteriosclerosis by selectively chemoattracting stem cells to the damaged intima through SDF-1, the presence of which may predict graft arteriosclerosis and the subsequent development of chronic graft dysfunction (CGD). The SDF-1 antibody slowed the endothelial chimerism by blocking this chemoattration. In addition to mycophenolate mofetil and FK 506, SDF-1 antibody might be a new potential effective strategy to decrease the frequency of CGD.     

Ligation and extraanatomic arterial reconstruction for the treatment of aneurysms of the abdominal aorta

Purpose: Since Blaisdell et al. first described axillobifemoral bypass and aortic exclusion to treat patients at high risk with abdominal aortic aneurysms in 1965, this approach has been controversial. To help define the appropriate application of this procedure, the recent experience of the authors was reviewed. Methods: Twenty-six patients underwent operation between March 1980 and August 1992. Mean age was 71 ± 7 years. Average aneurysm diameter was 7.0 ± 1.5 cm. Sixty-nine percent of the aneurysms were symptomatic; 21% were suprarenal. All patients had serious comorbid factors. All underwent axillobifemoral bypass with iliac artery ligation; the infrarenal aorta was also ligated in 62%. Results: There were two postoperative deaths (7.7%). One- and two-year survival rates were 59% and 38%, respectively. Three patients died of aneurysm rupture (11.5%); the aorta had not been ligated in two of these patients. The remaining late deaths were due to comorbid conditions. Extraanatomic bypass grafts thrombosed in five patients; no limbs were lost. Conclusions: Axillobifemoral bypass without aortic ligation does not effectively reduce the risk of aneurysm rupture. However, axillobifemoral bypass with aortic ligation is an acceptable treatment for patients with severe medical problems and symptomatic, anatomically complicated, or large abdominal aortic aneurysms. Because the risk of aneurysm rupture is not completely eliminated, this procedure should be reserved for patients with high-risk aneurysms who would not tolerate direct aortic replacement. (J VASC SURG 1994;20:629-36.)     

Long-term biologic fate of neoarteries regenerated in microporous, compliant, biodegradable, small-caliber vascular grafts in rats

Microporous, compliant, biodegradable vascular grafts prepared from a mixture of polyurethane [( PU], 95% weight) and poly-L-lactide [( PLLA] 5% weight) can function as temporary scaffolds for the regeneration of the arterial wall of small-caliber arteries. The purpose of this study was to determine the long-term biologic fate of these neoarteries that were regenerated in PU/PLLA vascular grafts. The PU/PLLA vascular grafts (1.5 mm internal diameter [ID]) were implanted into the abdominal aortas of rats (N = 8) and were evaluated 1 year after implantation by means of macroscopic inspection, light microscopy, and electron microscopy. All implants were patent; three implants were normally shaped, two were slightly dilated (+/- 10% of the original ID), and three implants were aneurysmal. Arterial pulsations were reduced but still visible in the normally shaped implants and absent in the other implants. In all implants, the neointima was complete. The neomedia varied among the implants: In the normally shaped implants, smooth muscle cells were predominantly circularly arranged as in normal arterial tissue; in the other implants, smooth muscle cells were predominantly longitudinally arranged. The neoadventitia showed a completely fragmented graft lattice, which was organized by fibrohistiocytic tissue. These results suggest that the pattern of arrangement of smooth muscle cells in the neomedia determines the ultimate biologic fate of neoarteries regenerated in microporous, compliant, biodegradable vascular grafts. Only those neoarteries with predominantly circularly arranged smooth muscle cells in the neomedia were able to function normally as an arterial substitute for a 1-year period after implantation into the rat abdominal aorta.     

Predictive factors for the intermediate-term patency of arterial grafts in aorta no-touch off-pump coronary revascularization.

OBJECTIVE: Graft flow is one of the important determinants of the arterial graft patency. To establish the optimal graft design, we examined detailed characteristics of the arterial composite and sequential grafts, and sought to delineate the risk factors of graft occlusion due to insufficient bypass flow. METHODS: Angiograms of 2547 bypass grafts in 677 consecutive patients who underwent total arterial off-pump CABG without aortic manipulation followed by early postoperative angiography since December 2000 were reviewed. The angiographic flow was graded as A (antegrade), B (competitive), C (reversal), and O (occlusion). RESULTS: The overall early graft patency rate was 98.2% (2502/2547). The rate of grade A was 91.3% (2325/2547), while the rates of grades B and C were 2.9% (73/2547) and 4.1% (104/2547), respectively. For the main trunk of the anterior descending branch (LAD), the graft patency rate was 99.3% (674/679). The grade A rate of the internal thoracic artery (ITA) grafts to LAD in an individual fashion was 99.5% (203/204), being comparable with that in the sequential or composite grafting which had two distal anastomoses (98.1%, 159/162; p=0.33). The actuarial patency rates at 3 years were 84.7% for the bypass grafts with grade A flow and 33.9% for those with grade B/C flow, respectively (p<0.0001). The multivariate Cox-regression analysis demonstrated that grade B/C (p<0.0001, HR=4.19) and 51-75% stenosis of the native coronary artery (p=0.02, HR=2.86) were significant predictors of graft occlusion. CONCLUSIONS: For the LAD, the results of graft flow in sequential ITA grafting or composite grafting with two distal anastomoses were comparable with that in individual ITA grafting. Prediction and prevention of competitive and reverse flow are mandatory for achieving the advantages of the arterial materials.