Extravascular perivenous fibrin support leads to aneurysmal degeneration and intimal hyperplasia in arterialized vein grafts in the rat

Background and aims  External support of vein grafts by fibrin glue possibly prevents overdistension, vascular remodeling, and neointimal hyperplasia. Previous animal models of neointimal hyperplasia showed conflicting results. Here, long-term effects of external fibrin glue support were studied in a new rat model of jugular vein to abdominal aorta transposition. Materials and methods and methods  In male Wistar rats (250–300 g) right jugular vein (1.0–1.5 cm) was transposed to the infrarenal aorta. Fibrin glue (0.25 ml) covered the vein before releasing the vascular clamps (n = 6). Control vein grafts were exposed directly to blood pressure. After 16 weeks vein grafts were pressure-fixed for histology. Intima thickness, luminal and intimal area were measured by planimetry and elastic fibers demonstrated by Elastica van Giesson staining. Results  Intimal thickness (74.04 ± 6.7 μm vs 1245 ± 187 μm, control vs fibrin treatment; p < 0.001), intimal area (2517.16 ± 355 mm² vs 18424 ± 4927 mm², control vs fibrin treatment; p < 0.05) and luminal area (2184.75 ± 347 mm² vs 7231.85 ± 1782 mm², control vs fibrin treatment; p < 0.05) were significantly increased, elastic fibers in the vessel wall were diminished and the vessel wall infiltrated by mononuclear cells in fibrin glue supported veins. Conclusion  External support of vein grafts by fibrin glue leads to aneurysmal degeneration and intimal hyperplasia, thereby possibly jeopardizing long-term graft patency.     

Hemagglutinating virus of Japan-liposome–mediated gene transfer of endothelial cell nitric oxide synthase inhibits intimal hyperplasia of canine vein grafts under conditions of poor runoff

Purpose: Late graft failure is a critical problem, particularly in the presence of poor runoff vessels. Intimal hyperplasia is considered to be the main cause of graft failure. We have already reported that intimal thickening of experimental vein grafts in dogs with poor runoff vessels is more pronounced than that in dogs with normal vessels. We and others also have reported that production of nitric oxide (NO) in the endothelium of canine vein grafts is impaired. In the present study, we asked whether in vivo gene transfer of endothelial cell NO synthase (ecNOS) would inhibit intimal hyperplasia of autogenous vein grafts implanted in limbs with poor distal runoff in dogs. Methods: After exposing femoral veins, the nuclear-targeted lac Z gene, bovine ecNOS cDNA, or control vector plasmid encapsulated in the hemagglutinating virus of Japan-liposomes was infused intraluminally, followed by incubation for 10 minutes at room temperature under a distending pressure of 100 mm Hg. Twenty reversed vein grafts were implanted under normal runoff conditions, and 4 days later these were used to confirm gene transfer to the vein grafts. Twelve reversed vein grafts were implanted under conditions of poor runoff, and 4 weeks after the operation intimal thickening was evident. Results: In vein grafts under normal runoff conditions, lac Z gene transfer exhibited diffuse and frequent X-Gal-positive signals in both medial and adventitial layers 4 days after implantation (n = 3). In case of the ecNOS gene–transferred vein grafts, bovine ecNOS protein was mainly detected in medial smooth muscle cells and adventitial cells 4 days after implantation, determined using immunohistochemical techniques and bovine ecNOS specific antibody (n = 3). In addition, ecNOS-transferred vessels showed intense purple signals by reduced nicotinamide adenine dinucleotide phosphate diaphorase and nitroblue tetrazolium reaction, in both medial and adventitial layers, whereas weak NOS activity was recognized at the adventitial vasa vasorum of the untreated veins or control vector transferred veins (n = 3, respectively). In vein grafts under poor runoff conditions, the intimal thickness at 4 weeks after implantation was significantly reduced by ecNOS gene transfer (n = 4; 90.0 ± 7.6 μm and 1.18 ± 0.07 mm²) in comparison with buffer-treated vessels (n = 4; 195.8 ± 25.7 μm and 2.62 ± 0.48 mm²) or vector vehicle–treated vessels (n = 4; 193.0 ± 15.8 μm and 2.65 ± 0.22 mm²). Conclusions: Our findings show that gene transfer of ecNOS inhibited intimal hyperplasia of canine vein grafts caused by poor runoff conditions, as a result of an increased local production of NO. Thus ecNOS gene transfer warrants further study as a possible approach to prevent late graft failure. (J Vasc Surg 1998;27:135-44.)     

Site-specific therapeutic angiogenesis after systemic administration of vascular endothelial growth factor

Purpose: Recent experimental studies have established the feasibility of therapeutic angiogenesis; in all cases, this has been achieved with local administration of angiogenic growth factors. This study was designed to investigate the hypothesis that systemic administration of an angiogenic growth factor specifically mitogenic for endothelial cells — vascular endothelial growth factor (VEGF) — could augment collateral vessel development in a rabbit ischemic hindlimb model.Methods: Ten days after the ligation of the external iliac artery and excision of the common and superficial femoral arteries in one limb of New Zealand white rabbits, heparin (800 IU, n = 13), VEGF (1 mg, n = 3; 5 mg, n = 5), heparin (800 IU) + VEGF (1 mg, n = 5; 5 mg, n = 7), or saline solution (n = 8) was injected as a single bolus in a marginal ear vein. Collateral vessel formation and limb perfusion were assessed 10 and 30 days after treatment.Results: Animals in both VEGF-treated groups had a significantly higher (p < 0.01) increase in calf blood pressure ratio at day 10 (control, 0.44 ± 0.02; heparin, 0.47 ± 0.02; VEGF, 0.60 ± 0.01; heparin + VEGF, 0.61 ± 0.02) and day 30 (control, 0.49 ± 0.05; heparin, 0.48 ± 0.02; VEGF, 0.70 ± 0.03; heparin + VEGF, 0.73 ± 0.03). Both VEGF-treated groups had a significantly higher (p < 0.05) angiographic score at day 30 (control, 0.28 ± 0.01; heparin, 0.28 ± 0.01; VEGF, 0.37 ± 0.01; heparin + VEGF, 0.38 ± 0.02). Maximum flow reserve at day 30 in the ischemic limb was higher (p < 0.05) in VEGF-treated rabbits (control, 1.87 ± 0.07; heparin, 1.92 ± 0.08; VEGF, 2.42 ± 0.16; heparin + VEGF, 2.33 ± 0.12). Capillary density was higher (p < 0.01) in the ischemic muscles of VEGF-treated rabbits (control, 156 ± 10/mm²; heparin, 178 ± 8/mm²; VEGF, 230 ± 10/mm²; heparin + VEGF, 233 ± 8/mm²).Conclusions: This series of in vivo experiments demonstrates that intravenous administration of VEGF, with or without heparin, results in both anatomic and physiologic evidence of enhanced collateral vessel formation in the rabbit ischemic hindlimb. Single-bolus systemic administration of VEGF may be a feasible therapeutic strategy in patients with lower-extremity ischemia. (J VASC SURG 1995;21:314-25.)     

Endothelial cell seeding fails to attenuate intimal thickening in balloon-injured rabbit arteries

Background: Restenosis of arteries or bypass grafts after vascular reconstruction is a common clinical entity that significantly limits long-term patency. This process, termed intimal hyperplasia (IH), is characterized by smooth muscle cell proliferation in the intima and subsequent accumulation of intercellular matrix. This study was designed to test the hypothesis that endothelial cell (EC) seeding of acutely injured arteries accelerates reendothelialization of the flow surface and limits the development of IH.Methods: ECs were harvested from jugular veins of New Zealand white rabbits (n = 13) and were amplified in tissue culture. Each animal subsequently underwent bilateral balloon catheter injury of the iliofemoral arteries; one side was immediately seeded with cultured autologous ECs at supraconfluent density, whereas the contralateral vessel served as a nonseeded control. Animals were killed 33 ± 5 days after balloon injury. Intimal thickening was quantitated on histologic sections of vessels (three sections per vessel, total of 60 sections) and percent endothelialization was assessed by SEM; measurements were obtained by use of computer-aided morphometry performed by a blinded observer. Data were analyzed by use of a paired t test for comparison between seeded and control vessels.Results: Seeded vessels exhibited a greater degree of reendothelialization (93.9% ± 7.6% of the surface) than their unseeded counterparts (65.1% ± 22.5%, p < 0.01). Intimal cross-sectional area and the ratio of intimal area to medial area were not significantly different between seeded and control vessels (intima: 0.32 ± 0.19 vs 0.37 ± 0.11 mm², p = 0.28; intimal area to medial area ratio: 0.84 ± 0.35 vs 1.02 ± 0.2, p = 0.24).Conclusions: We conclude that seeding with autologous venous ECs accelerated restoration of the endothelial monolayer but failed to attenuate IH in balloon-injured rabbit arteries. Further studies are necessary to determine the functional properties of seeded endothelium and to examine the effect of EC seeding on intimal thickening in other clinically relevant models. (J VASC SURG 1995;21:413-21.)     

Celiprolol reduces the intimal thickening of autogenous vein grafts via an enhancement of nitric oxide function through an inhibition of superoxide production

BACKGROUND: Beta-adrenoceptor antagonist celiprolol has been widely used as an effective antihypertensive agent. Some studies reported that celiprolol enhances nitric oxide production. The purpose of the present study is to examine the effects of celiprolol on vein graft intimal hyperplasia and endothelium-dependent nitric oxide (NO)-mediated relaxation. METHODS: Japanese white rabbits were randomized to a control group that was fed regular rabbit chow or to a celiprolol group that was fed regular rabbit chow supplemented with 100 mg/body celiprolol sodium. The reversed jugular vein was implanted into the carotid artery. At 2 and 4 weeks after the operation, vein grafts in both groups were harvested, and intimal hyperplasia of the vein grafts was assessed. At 4 weeks after the operation, harvested vein grafts from both the groups were examined on the endothelium-dependent relaxation by application of Ach and were examined to detect for endothelial NO synthase (eNOS) expression and superoxide anion production. RESULTS: Celiprolol inhibited intimal hyperplasia of carotid interposition-reversed jugular vein grafts 4 weeks after implantation (Intima/media index of celiprolol group, 0.48 +/- 0.01 vs control group, 1.07 +/- 0.08, P < .05) and suppressed cell proliferation in the neointima 2 weeks after implantation. In addition, celiprolol significantly enhanced endothelium-dependent NO-mediated relaxation in the vein graft with no change in eNOS expression and a reduction in superoxide production. CONCLUSIONS: These novel findings clearly demonstrate that beta-adrenoceptor antagonist celiprolol can suppress intimal hyperplasia of the vein graft, which may be due to the enhancement of nitric oxide function through an inhibition of superoxide production. These results strongly support the clinical usefulness of celiprolol administration for preventing intimal hyperplasia of the vein graft after bypass grafting.     

Long-term performance of an external stent for saphenous vein grafts: the VEST IV trial

Background

Externally stenting saphenous vein grafts reduces intimal hyperplasia, improves lumen uniformity and reduces oscillatory shear stress 1 year following surgery. The present study is the first to present the longer-term (4.5 years) performance and biomechanical effects of externally stented saphenous vein grafts.

Methods

Thirty patients previously implanted with the VEST external stent in the randomized, within-patient-controlled VEST I study were followed up for adverse events; 21 of these were available to undergo coronary angiography and intravascular ultrasound.

Results

Twenty-one stented and 29 nonstented saphenous vein grafts were evaluated by angiography and ultrasound at 4.5?±?0.3 years. Vein graft failure rates were comparable between stented and nonstented grafts (30 and 23% respectively; p?=?0.42). All failures were apparent at 1 year except for one additional nonstented failure at 4.5 years. In patent vein grafts, Fitzgibbon perfect patency remained significantly higher in the stented versus nonstented vein grafts (81 and 48% respectively, p?=?0.002), while intimal hyperplasia area (4.27 mm²?±?1.27 mm² and 5.23 mm²?±?1.83 mm² respectively, p?<?0.001) and thickness (0.36 mm?±?0.09 mm and 0.42 mm?±?0.11 mm respectively, p?<?0.001) were significantly reduced. Intimal hyperplasia proliferation correlated with lumen uniformity and with the distance between the stent and the lumen (p?=?0.04 and p?<?0.001 respectively).

Conclusions

External stenting mitigates saphenous vein graft remodeling and significantly reduces diffuse intimal hyperplasia and the development of lumen irregularities 4.5 years after coronary artery bypass surgery. Close conformity of the stent to the vessel wall appears to be an important factor.

Trial registration

NCT01415245. Registered 11 August 2011.

     

Nonporous silicone polymer coating of expanded polytetrafluoroethylene grafts reduces graft neointimal hyperplasia in dog and baboon models

Purpose: Neointimal hyperplasia frequently develops after placement of prosthetic vascular grafts and is a major cause of graft failure. This study was an attempt to prevent vascular lesion formation by coating the graft luminal surface with a thin layer of nonporous silicone polymer, and subsequently with an ultrathin layer of vapor phase (plasma gas) deposited fluoropolymer, thereby providing a smooth and chemically uniform surface that was postulated to limit pannus tissue ingrowth across the graft anastomoses.Methods: Bilateral femoral arteriovenous (AV) conduits were constructed in four dogs using expanded polytetrafluoroethylene graft materials (ePTFE; 6-mm inside diameter, 2.5-cm long). In each animal, one femoral AV shunt was constructed from a graft whose luminal surface was entirely coated with polymer. On the contralateral side, an uncoated graft served as a control. Bilateral aortoiliac grafts were placed in three baboons using 5-cm segments of ePTFE (4-mm inside diameter). One end (1 cm) of each graft had been coated with polymer. In each animal, the coated end of one graft was placed proximally and the coated end of the second graft was placed distally in the contralateral vessels.Results: All grafts were patent at 30 days. In the dog model, there was a significant reduction in graft neointimal area at the venous anastomoses for the coated grafts compared with the uncoated grafts (0.03 ± 0.02 mm ² and 1.11 ± 0.54 mm ² , respectively; p < 0.05). In the baboon model, the silicone coating significantly reduced the graft neointimal thickness (0.003 ± 0.003 mm vs 0.21 ± 0.05 mm; p < 0.05) and neointimal area (0.05 ± 0.08 mm ² vs 0.82 ± 0.58 mm ² ; p < 0.05).Conclusions: These data demonstrate that healing of ePTFE grafts can be effectively modified by altering the physical properties of the graft surface. Neointimal hyperplasia within ePTFE grafts is significantly reduced by the local application of a fluorocarbon-coated, silicone-based polymer. The resulting graft flow surface effectively prevents tissue ingrowth from the adjacent native vessel, thereby preserving the anastomosis luminal area. This approach could represent a new strategy for limiting graft surface anastomotic neointimal hyperplasia. (J Vasc Surg 1996;24:825-33.)     

Clinical in vitro endothelialization of femoropopliteal bypass grafts: An actuarial follow-up over three years

Purpose: The creation of an endothelial coverage on prosthetic vascular surfaces may improve the performance of synthetic small diameter vascular grafts. In vitro lining with cultured autologous endothelial cells offers a confluent endothelium at the time of implantation.Methods: Between June 1989 and December 1991, 49 patients who had no saphenous vein available entered the study. Indication for operation was disabling claudication in 37 patients and critical ischemia in 12 patients. With a random 1:2 assignment, 33 patients were admitted to the endothelialized group and 16 control patients received an untreated polytetrafluoroethylene prosthesis. Cultured autologous endothelial cells from the external jugular vein were confluently lined onto polytetrafluoroethylene grafts precoated with fibrinolytically inhibited fibrin glue. The follow-up was based on angiography, platelet labeling studies with indium 111 – labeled oxine, assessment of the ankle-brachial index, and duplex sonography.Results: First-passage mass cultures of 16 million endothelial cells — required for the confluent lining of a 70 cm long 6 mm graft — were reached 25.1 ± 11.2 days after vein excision. Growth failure occurred in 27.3%. After 32 months, the actuarial patency was 84.7% for endothelialized grafts and 55.4% for control grafts (p < 0.041 by Breslow test; p < 0.068 by Mantel-Cox test). The ankle-brachial index was continually diverging, reaching significantly lower values in the control group at 24 months (0.98 ± 0.14 in the endothelialized group versus 0.70 ± 0.12 in the control; p < 0.0023). The uptake of indium 111–labeled platelets — measured at 9 days, 3 months, 6 months, and 12 months — was significantly lower in the endothelialized group during the entire observation period.Conclusions: Our initial 3-year data demonstrate the early superiority of endothelialized synthetic grafts over commonly used untreated expanded polytetrafluoroethylene prostheses. (J VASC SURG 1994;19:540-8.)     

Endothelial seeding of polytetrafluoroethylene femoral popliteal bypasses: The failure of low-density seeding to improve patency

Purpose: We compared 66 seeded polytetrafluoroethylene and 53 autologous vein grafts to determine whether endothelial seeding could improve the patency of polytetrafluoroethylene femoral popliteal bypass grafts and to determine whether endothelial seeding could be performed consistently in multiple institutions. Methods: Nine surgeons at four hospitals randomized patients to receive either a seeded polytetrafluoroethylene or a vein graft, but if no satisfactory vein (n = 26) existed, an "obligatory" seeded polytetrafluoroethylene graft was used. Results: Scanning electron microscopy confirmed satisfactory initial attachment of endothelium on the discarded ends of the grafts. Patency was compared with the use of log rank analysis and revealed better patency in vein grafts at 30 months (vein = 91.6% ± 4.1%; seeded polytetrafluoroethylene = 37.8% ± 9.4%; p = 0.006). Failed grafts revealed anastomotic hyperplasia. Conclusions: (1) Vein graft patency was better than seeded polytetrafluoroethylene grafts; (2) seeding did not improve patency in below-the-knee bypasses as suggested by pilot studies; (3) the failure of seeded grafts was associated with anastomotic hyperplasia but not with the failure of initial endothelial attachment; and (4) each institution reported similar results. (J VASC SURG 1994;20:650-5.)     

Alterations in wall tension and shear stress modulate tyrosine kinase signaling and wall remodeling in experimental vein grafts

Purpose: Hemodynamic alterations have been implicated as major stimuli for the development of intimal hyperplasia in vein grafts that are implanted in the arterial circulation. Tyrosine kinase is known to mediate cell signaling. However, its role with in vivo mechanotransduction is not yet well defined. We used a novel bioprosthetic collagen tube to provide an external support to vein grafts and examined the subsequent changes in hemodynamics, tyrosine kinase signaling, wall remodeling, and vasomotor function. Methods: Carotid interposition bypass grafting was performed with the reversed jugular vein in New Zealand white rabbits. In the experimental group (n = 15), after the completion of the proximal anastomosis, the vein was passed through a 4-mm collagen tube and the distal anastomosis was performed. The tube support was fashioned to completely cover the vein grafts. The control animals (n = 14) had no tube support. After surgery, the blood pressure and flow rate were measured and the wall tension and shear stress were calculated in the vein grafts on day 3 or day 28 (n = 5 per group). Tyrosine phosphorylation was assessed with the Western blot test in vein grafts at day 3 (n = 4 per group). The intimal and medial dimensions of the vein grafts were assessed with videomorphometry on day 28 (n = 5 per group). The cumulative dose response curves of the vein grafts to contractile and relaxant agonists were determined in isometric tension studies on day 28 (n = 5 per group). Results: The use of tube support reduced wall tension 1.7-fold (P < .01) and increased shear stress 4.8-fold (P < .001) without altering the flow rate or blood pressure. The tyrosine kinase activity was reduced 15-fold (P < .001) in the tube-supported vein grafts. The intimal thickness was reduced by 45% in the tube-supported vein grafts as compared with the control grafts (46 ± 2 mm vs 84 ± 5 mm, respectively; P < .0001), and the media thickness was reduced by 20% (63 ± 8 mm vs 79 ± 4 mm, respectively; P < .05). Isometric tension studies showed preservation of contractile function and modulation of endothelial-dependent dysfunctional relaxation in tube-supported vein grafts. Conclusion: These results show that reduced wall tension and increased shear stress with an external tube support can effectively modulate the signaling, functional, and hyperplastic responses in vein grafts. We conclude that this simple strategy deserves further study and clinical consideration. (J Vasc Surg 1999;29:334-44.)     

Development and Validation of Small-diameter Vascular Tissue From a Decellularized Scaffold Coated With Heparin and Vascular Endothelial Growth Factor

To overcome shortcomings of current small‐diameter vascular prostheses, we developed a novel allogenic vascular graft from a decellularized scaffold modified through heparin immobilization and vascular endothelial growth factor (VEGF) coating. The VEGF coating and release profiles were assayed by enzyme‐linked immunosorbent assay, the biological activity of modified surface was validated by human umbilical vein endothelial cells seeding and proliferation for 10 days in vitro. In vivo, we implanted either a modified or a nonmodified scaffold as bilateral carotid allogenic graft in canines (n = 15). The morphological examination of decellularized scaffolds showed complete removal of cellular components while the extracellular matrix structure remained intact. After modification, the scaffolds possessed local sustained release of VEGF up to 20 days, on which the cells cultured showed significantly higher proliferation rate throughout the time after incubation compared with the cells cultured on nonmodified scaffolds (P < 0.0001). After 6 months of implantation, the luminal surfaces of modified scaffolds exhibited complete endothelium regeneration, however, only a few disorderly cells and thrombosis overlay the luminal surfaces of nonmodified scaffolds. Specifically, the modified scaffolds exhibited significantly smaller hyperplastic neointima area compared with the nonmodified, not only at midportion (0.56 ± 0.07 vs. 2.04 ± 0.12 mm², P < 0.0001), but also at anastomotic sites (1.76 ± 0.12 vs. 3.67 ± 0.20 mm², P < 0.0001). Moreover, modified scaffolds had a significantly higher patency rate than the nonmodified after 6 months of implantation (14/15 vs. 7/15, P = 0.005). Overall, this modified decellularized scaffold provides a promising direction for fabrication of small‐diameter vascular grafts.     

Vein adaptation to the hemodynamic environment of infrainguinal grafts

Purpose: Although arteries appear to remodel in response to changes in hemodynamic parameters such as shear stress, little is known about functioning human vein grafts. This study was designed to explore diameter changes in human saphenous vein grafts after infrainguinal bypass.Methods: We used duplex ultrasonography to measure hemodynamic variables that might affect the diameter of 48 in situ saphenous vein grafts during the first year after infrainguinal arterial bypass. Volumetric flow rate, average velocity, peak systolic velocity, and vein diameter in the proximal and distal thirds of these grafts were each measured at 1 week and at 3, 6, and 12 months after operation. Veins were divided into three groups based on initial size (1 week after bypass) in the below-knee segment: small, < 3.5 mm diameter; medium, 3.5 to 4 mm diameter; and large, > 4 mm diameter.Results: Distal vein diameters at 1 week for small, medium, and large grafts were 2.9 ± 0.1, 3.7 ± 0.1, and 4.3 ± 0.1 mm, respectively (p < 0.001), but by 12 months these diameters were 3.6 ± 0.2, 3.8 ± 0.2, and 3.9 ± 0.2 mm, respectively (p = 0.54). Large veins decreased in diameter, whereas small veins increased in diameter, as confirmed by linear regression of percent change in diameter versus initial vein graft diameter (r = -0.62, p < 0.001). Volumetric flow rate, peak systolic velocity, and shear stress also tended to approach uniform values over time. Of the hemodynamic variables studied, the best predictor of diameter change was shear stress (linear regression of percent change in diameter vs shear stress, r = 0.67, p < 0.001). Veins with a diameter increase greater than 10% over time had significantly higher initial shear stress than veins with a diameter decrease greater than 10% over time (28.6 ± 3.8 vs 13.1 ± 1.8 dynes/cm², p < 0.01), whereas initial volumetric flow rates in these two groups were similar (135 ± 23 vs 130 ± 15 ml/min).Conclusions: Infrainguinal in situ vein graft diameter, volume flow rate, peak systolic velocity, and shear stress all tend to stabilize at uniform values regardless of the initial vein graft diameter. Of the hemodynamic variables studied, shear stress is most strongly associated with the change in diameter over time. Thus human saphenous vein appears to be capable of adapting to its hemodynamic environment after arterial grafting by modulating diameter to normalize shear stress. (J VASC SURG 1994;19:970–9.)     

Improved in vivo endothelialization of prosthetic grafts by surface modification with fibronectin

Endothelial cell growth in vitro is enhanced by coating with fibronectin the surface on which cells grow. Similar coating of prosthetic arterial grafts may promote in vivo graft endothelialization if graft patency is not adversely affected. In each of 15 dogs, two fibronectin-coated polytetrafluoroethylene grafts and two grafts that were not coated were implanted. One graft in each pair was seeded with autologous endothelial cells, so that four different grafts were studied in each animal: a coated, seeded graft; a coated graft that was not seeded; a seeded graft that was not coated; a graft that was neither coated nor seeded. At 2, 4, and 8 weeks, grafts from five animals were examined for patency, surface endothelialization, and indium 111 platelet reactivity. After seeding, surface coverage by endothelium of coated grafts was more complete and more rapid than in uncoated grafts (64% ± 23% vs 31% ± 13% at 4 weeks, p < 0.05). Without seeding, coated grafts also appeared to have increased endothelial cell ingrowth compared with plain grafts (48.8% ± 15.1% vs 37.6% ± 1.5% at 8 weeks). Early (2-week) platelet reactivity of coated grafts was increased (p = 0.06), but patency was not adversely affected. Thus fibronectin coating of prosthetic grafts promotes surface endothelialization in vivo without altering graft patency. (J VASC SURG 1988;8:476-82.)     

Enhancement of tissue factor expression by vein segments exposed to coronary arterial hemodynamics

Purpose: Although saphenous vein is the most reliable conduit for arterial interposition procedures in the coronary circulation, graft thrombosis remains a clinical problem. We hypothesized that an important factor in early graft thrombosis is sudden change in the hemodynamic environment of the vein as it is placed in the coronary circulation. Methods: We used an ex vivo perfusion system to study freshly excised segments of human saphenous vein (HSV) and pig internal jugular vein. For coronary graft (CAVG) simulation, sections of HSV were subjected to arterial pulsatile pressure and flow and twisting and stretching to mimic deformations caused by the beating heart. Using functional and immunohistochemical assays, we investigated the effect of these conditions on expression of tissue factor (TF), an important prothrombotic surface molecule. Results: In each of 11 experiments (6 human, 5 porcine), vein segments from a single donor were subjected to venous conditions (VEN), CAVG perfusion, or no perfusion. Expression of TF was measured as the amount of factor Xa generated per unit area of luminal vein surface. VEN perfusion did not cause a significant change in mean TF expression over nonperfused control values (human: 14.3 ± 1.5 versus 11.4 ± 2.3 U/cm², p = 0.31; pig: 11.6 ± 1.5 versus 12.5 ± 1.4 U/cm², p = 0.70). CAVG perfusion led to significant enhancement of TF expression over VEN perfusion (human: 36.8 ± 6.2 versus 14.3 ± 1.5 U/cm², p < 0.05; pig: 40.0 ± 9.9 versus 11.6 ± 1.5 U/cm², p < 0.05). Immunohistochemical analysis showed positive TF staining on the luminal side of a CAVG-stimulated HSV segment, but not on a VEN-stimulated segment. In four additional studies, HSV segments were subjected to arterial perfusion without twist and stretch to mimic lower extremity arterial interposition grafts. TF expression for lower extremity venous graft perfusion was significantly higher than for VEN perfusion (25.3 ± 2.5 versus 14.3 ± 1.5, p < 0.01) but not significantly different from CAVG perfusion. Conclusions: Our studies in a unique perfusion system suggest that exposure of vein to coronary arterial hemodynamic conditions results in elevated expression of the important prothrombotic molecule TF. This phenomenon may contribute to early graft thrombosis. (J Vasc Surg 1998;27:521-7.)     

Photodynamic therapy of vein grafts: Suppression of intimal hyperplasia of the vein graft but not the anastomosis

Purpose: There is no clinically useful therapy for the suppression of vein bypass graft intimal hyperplasia (IH). Photodynamic therapy (PDT), a technique that uses light to activate otherwise biologically inert photosensitizers to produce cytotoxic effects, has been demonstrated to successfully inhibit experimental IH in balloon-injured arteries. The purpose of this study was to investigate the efficacy of PDT as a method to reduce vein graft IH.Methods: Reversed external jugular vein bypass grafts of the common carotid artery were performed in 28 male Sprague-Dawley rats. The animals received either chloroaluminum sulfonated phthalocyanine (2.5 mg/kg intravenously) 24 hours before the ex vivo irradiation of the vein grafts (VG) with 100 joule/cm² at 675 nm (PDT VG) or saline solution as control (CON VG). Preharvest bromodeoxyuridine was administered to label proliferating cells. All vein grafts were perfusion fixed within 96 hours for a pilot study or at 2 and 4 weeks for the main study. Histology, immunohistochemistry, and morphometric analysis were performed.Results: There was no acute thrombus formation in the hypocellular PDT VG with occasional platelets but no leukocytes adherent to the luminal surface. Intimal areas of the PDT VG were 18% at 2 weeks and 53% at 4 weeks of the CON VGs (p < 0.05). Medial areas and percent of stenoses were also significantly less in PDT than in CON VG. However, intimal hyperplasia noted in the longitudinal sections within 2 mm of the anastomoses did not demonstrate a difference between PDT and CON VG. Intimal hyperplasia of both PDT and CON VG consisted of smooth muscle cells, verified by immunohistochemistry. Bromodeoxyuridine-labeled cells were more abundant in 2-week than in 4-week specimens, were found most frequently in the intimal areas of the CON VG body, and were equivalent in the anastomoses of PDT VG and CON VG.Conclusions: These data suggest that PDT of vein grafts suppresses the development of IH in the body of the vein graft but does not affect IH adjacent to the anastomoses. The artery may be the source of proliferating smooth muscle cells that contribute to the anastomotic vein graft IH. (J VASC SURG 1995;21:882-90.)     

Hydrophilic statin suppresses vein graft intimal hyperplasia via endothelial cell-tropic Rho-kinase inhibition

BACKGROUND: Recent studies suggest that statins can protect the vasculature in a manner that is independent of their lipid-lowering activity through inhibition of the small guanosine triphosphate-binding protein, Rho, and Rho-associated kinase. Little information is available on the inhibitory effect of statins on vein graft intimal hyperplasia, the main cause of late graft failure after bypass grafting. We therefore examined the effects of a hydrophilic statin on vein graft intimal hyperplasia in vivo and Rho-kinase activity in vitro. METHODS: In the first experiment, rabbits were randomized to a control group (n = 7) that was fed regular rabbit chow or to a pravastatin group (n = 7) that was fed regular rabbit chow supplemented with 10 mg/kg pravastatin sodium. The branches of the jugular vein were ligated and an approximately 3-cm segment of the jugular vein was taken for an autologous reversed-vein graft. The carotid artery was cut and replaced with the harvested autologous jugular vein. At 2 and 4 weeks after the operation, vein grafts in both groups were harvested, and intimal hyperplasia of the vein grafts was assessed. In the second experiment, human umbilical vein endothelial cells and vascular smooth muscle cells were cultured and then treated with 1 micromol/L and 30 micromol/L pravastatin for 24 hours and harvested. Immunoblotting was performed on the resulting precipitates. Quantitative evaluation of phosphorylated myosin binding subunit and endothelial nitric oxide synthase was performed by densitometric analysis. RESULTS: We demonstrated that oral administration of the hydrophilic statin pravastatin to normocholesterolemic rabbits inhibited intimal hyperplasia of carotid interposition-reversed jugular vein grafts 4 weeks after implantation (pravastatin group, 39.5 +/- 3.5 microm vs control group, 64.0 +/- 7.1 microm; n = 7; P < .05) and suppressed cell proliferation and apoptosis in the neointima 2 weeks after implantation. In addition, we found that pravastatin inhibited Rho-kinase activity and accelerated endothelial nitric oxide synthase expression in human umbilical vein endothelial cells but did not inhibit Rho-kinase activity in vascular smooth muscle cells. CONCLUSIONS: These novel findings clearly demonstrate that a hydrophilic statin can suppress intimal hyperplasia of the vein graft in vivo and also show endothelial cell-tropic inhibition of Rho-kinase in vitro. Furthermore, these results strongly support the clinical use of hydrophilic statins to prevent intimal hyperplasia of the vein graft after bypass grafting. CLINICAL RELEVANCE: Late graft failure caused by neointimal hyperplasia limits the efficacy of vein grafting. Various treatments were examined to reduce neointimal hyperplasia, but a standard clinical treatment has not yet been established. We report here the inhibitory effect of pravastatin on the development of vein graft intimal hyperplasia. In addition, we demonstrate that pravastatin showed endothelial cell-tropic benefits through both the inhibition of Rho-kinase activity and acceleration of eNOS expression in vitro. Because the clinical benefits and safety of pravastatin have been established to a certain extent through long-term clinical usage, pravastatin may soon become standard treatment after vein bypass grafting.     

Reduction of lipid peroxidation with intraoperative superoxide dismutase treatment decreases intimal hyperplasia in experimental vein grafts.

BACKGROUND: Vein graft failure is commonly attributed to the development of intimal hyperplastic lesions. Oxidative stress has been implicated in the initiation and progression of atherosclerosis. In this study we examined the effects of local intraoperative treatment with polyethylene glycolated superoxide dismutase (PEG-SOD) on lipid peroxidation and on the development of intimal hyperplasia in experimental vein grafts. MATERIALS AND METHODS: Forty-one New Zealand White male rabbits had a right carotid interposition bypass graft using the ipsilateral reversed jugular vein. Sixteen animals received local PEG-SOD (4,100 units) treatment; 9 animals received the polyethylene glycol (PEG) vehicle without SOD; 16 animals were used as controls. Postoperatively, malondialdehyde (MDA, a product of lipid peroxidation) concentration and SOD activity were assessed in 3-day vein grafts by colorimetric spectrophotometry. To determine wall dimensions and vasomotor function, morphometric and isometric tension studies were performed on 28-day vein grafts. RESULTS: MDA concentration was increased 5. 7-fold (P < 0.05) in 3-day control vein grafts compared to ungrafted jugular veins. Intraoperative PEG-SOD treatment raised SOD activity 5.0-fold (P < 0.05) and reduced MDA concentration 8-fold (P < 0.05) in 3-day vein grafts compared to controls. At 28 days, intimal thickness was reduced by 35% with PEG-SOD treatment (54 +/- 4 vs 83 +/- 5; P < 0.001) compared to control vein grafts, without a change in medial thickness (77 +/- 4 vs 88 +/- 5; P = ns). The vasomotor functions of 28-day PEG-SOD-treated vein grafts to norepinephrine, serotonin, bradykinin, nitroprusside, and acetylcholine were not significantly changed when compared to controls. Treatment with PEG alone did not significantly alter lipid peroxidation, wall dimensions, or vasomotor function of vein grafts. CONCLUSION: This study demonstrates that intraoperative local treatment of vein grafts with PEG-SOD increases SOD activity and decreases lipid peroxidation for at least 3 days, resulting in reduced intimal hyperplasia at 28 days. These findings further implicate oxidative stress in the hyperplastic response of vein grafts and suggest a potential therapeutic role for PEG-SOD in the prevention of vein graft failure.     

A prospective study of the determinants of vein graft flow velocity: Implications for graft surveillance

Purpose: Serial monitoring of vein graft peak systolic flow velocity (PSFV) has been endorsed as a technique for vein graft surveillance with low values (<45 cm/sec) considered a marker for impending graft failure. Optimal application of this method requires an understanding of the factors affecting PSFV in normal grafts. A prospective evaluation of 46 consecutive elective infrainguinal vein grafts (6 popliteal/29 tibial/11 pedal) was undertaken to assess the major determinants of PSFV.Methods: Factors recorded for each patient included vein graft diameter (VGD), measured outflow resistance (MOR), conduit length, outflow level (popliteal/tibial/pedal), inflow level (femoral/popliteal), systolic blood pressure, cardiac ejection fraction, the presence of a patent plantar arch, and Society for Vascular Surgery/International Society for Cardiovascular Surgery resistance scoring. MOR was measured by occluding graft inflow and infusing saline solution through a proximal graft cannula at 60 cc/min while simultaneously recording the pressure at the distal anastomosis via a separate cannula. MOR was calculated by dividing the resultant pressure by the infusion rate. MORs were expressed in resistance units and were measured before and after the infusion of papaverine (MOR_(PAP)). PSFVs and VGDs were measured 4 to 6 cm from the distal anastomosis 3 weeks after surgery with duplex scanning (60 degree angle with midstream sample volume).Results: PSFVs ranged from 22 to 148 cm/sec and averaged 83.4 ± 4.8 cm/sec. Pedal bypass grafts had significantly lower PSFVs (64 ± 10 vs 89.5 ± 5 cm/sec, p = 0.02) and significantly higher MOR_(PAP)s (0.86 ± 0.15 vs 0.51 ± 0.05 resistance units, p = 0.05) than bypasses to the popliteal/tibial level. When subjected to univariate analysis the factors correlating with PSFV were MOR (r = -0.59, p = 0.0001), MOR_(PAP) (r = -0.69, p = 0.0001) VGD (r = -0.31, p = 0.06), the Society for Vascular Surgery/International Society for Cardiovascular Surgery score (r = -0.35, p = 0.04), inflow level (r = -0.47, p = 0.002), and outflow level (r = -0.35, p = 0.03). When subjected to multiple regression analysis, only MOR_(PAP) (r ² = 0.51, p = 0.001) and VGD (r ² = 0.14, p =0.001) contributed significantly to the overall model (r ² = 0.65, p = 0.0001) withMOR_(PAP)) eliminating the effect of the other variables. The multiple regression model predicts PSFV as follows: PSFV = 176 + VGD_(mm)( -11.7) + MOR_(PAP))( -63.4).Conclusions: Clinically successful and hemodynamically normal vein grafts have widely variable, yet predictable flow characteristics that are influenced primarily by outflow resistance and VGD. This wide variability suggests that no single lower threshold value for PSFV is universally applicable in identifying all grafts at risk for failure. Detection of focal areas of flow acceleration within the graft may be more accurate in identifying grafts at risk for failure. (J VASC SURG 1994;19:259-67.)     

Characterization of dopamine-mediated relaxation in experimental vein bypass grafts

BACKGROUND: Dopamine is an endogenous inotropic agent commonly used during coronary artery surgery and in the medical therapy of a revascularized patient. In this study the responses of intimal hyperplastic vein grafts to dopamine are examined. METHODS: The in vitro isometric tension responses to dopamine of common carotid jugular vein bypass grafts in New Zealand White rabbits were determined. The responses were compared to those obtained in the jugular vein and in the common carotid artery. Both endothelialized and denuded vessels were precontracted with prostaglandin F(2alpha) and the responses to dopamine were assessed. The contributions of nitric oxide and prostanoids to the response were also determined. RESULTS: Each vessel showed a biphasic dose response to dopamine with relaxation at low concentrations followed by contraction at high concentrations. Dopamine relaxation in the jugular vein was endothelial independent while in the carotid artery it was endothelial dependent and decreased. The sensitivity of both vessels was significantly greater than the vein graft (6.62 +/- 0.12; P < 0. 05); however, after endothelial denudation, the sensitivity of dopamine-mediated relaxation of the vein graft (8.91 +/- 0.09) was significantly enhanced. Preincubation with L-NMMA (to block NO synthesis) inhibited vein graft relaxation to dopamine and preincubation with indomethacin (to block cyclooxygenase activity) inhibited carotid artery relaxation to dopamine. Addition of phenoxybenzamine, a broad alpha-adrenergic antagonist, enhanced dopamine relaxation in the jugular vein and depressed the relaxation in the carotid artery. There was no effect on the dopamine response in the vein graft. Jugular vein and carotid artery responded to dopamine with cholera toxin-sensitive (Galpha(s)) responses. In contrast, dopamine relaxation in the vein graft was enhanced by inhibition of Galpha(s). CONCLUSION: Dopamine relaxation in vein grafts is mediated in part by NO but not by either prostanoids or alpha-adrenergic receptor activation. It is diminished compared to native vessels due to an endothelium-dependent, Galpha(s)-mediated pathway.