Journal of Vascular Surgery
Volume 47, Issue 3 , Pages 608-615, March 2008

Inhibition of experimental neointimal hyperplasia by recombinant human thrombomodulin coated ePTFE stent grafts

Presented at the Thirty-second Annual Meeting of the New England Society for Vascular Surgery, Stowe, Vt, Sept 17, 2005.

  • Geoffrey Wong, MD

      Affiliations

    • Division of Vascular Surgery, University of Massachusetts Medical School and the UMass Memorial Health Care, Worcester, Mass
    • ,
  • Jian-ming Li, MD

      Affiliations

    • Division of Vascular Surgery, University of Massachusetts Medical School and the UMass Memorial Health Care, Worcester, Mass
    • ,
  • Gregory Hendricks, PhD

      Affiliations

    • Department of Cell Biology, University of Massachusetts Medical School and the UMass Memorial Health Care, Worcester, Mass.
    • ,
  • Mohammad H. Eslami, MD

      Affiliations

    • Division of Vascular Surgery, University of Massachusetts Medical School and the UMass Memorial Health Care, Worcester, Mass
    • ,
  • Michael J. Rohrer, MD

      Affiliations

    • Division of Vascular Surgery, University of Massachusetts Medical School and the UMass Memorial Health Care, Worcester, Mass
    • ,
  • Bruce S. Cutler, MD

      Affiliations

    • Division of Vascular Surgery, University of Massachusetts Medical School and the UMass Memorial Health Care, Worcester, Mass
    • Corresponding Author InformationReprint requests: Bruce S. Cutler, MD, Division of Vascular Surgery, UMass Memorial Health Care, 55 Lake Avenue North, Worcester, MA 01655.

Received 4 June 2007; accepted 11 November 2007.

Article Outline

Objectives

The goal of this study was to evaluate the ability of recombinant human thrombomodulin (rTM) to inhibit neointimal hyperplasia when bound to expanded polytetrafluoroethylene (ePTFE) stent grafts placed in a porcine balloon injured carotid artery model.

Methods

The left carotid artery of male pigs, weighing 25 to 30 Kg, was injured with an angioplasty balloon. Two weeks later either a non-coated standard ePTFE stent graft (Viabahn, 6 × 25 mm, W. L. Gore & Associates) or a rTM coated stent graft was implanted into the balloon-injured segment using an endovascular technique. Carotid angiography was performed at the time of the balloon injury, two weeks later and then at 4 weeks to assess the degree of luminal stenosis. One month after stent graft deployment, the grafts were explanted following in situ perfusion fixation for histological analysis. The specimens were then cross-sectioned into proximal, middle and distal segments, and the residual arterial lumen and intimal to media (I/M) ratios were calculated with computerized planimetry.

Results

rTM binding onto ePTFE-grafts was confirmed by functional activation of protein C and histopathology with immuno-scanning electron microscopy, backscatter electron emission imaging and x-ray microanalysis. All seven of the rTM coated stent grafts and six of the seven uncoated stent grafts were patent at the time of explantation. The mean luminal diameter of the rTM coated stents was 93% ± 2.0% of the original diameter, compared with 67% ± 23% (P = .006) in the control group. Histological analysis demonstrated that the area obliterated by intimal hyperplasia at the proximal portion of the rTM stent was −27% compared with the control group: (2.73 ± 0.69 mm2, vs 3.47 ± 0.67 mm2, P <.05).

Conclusions

Neointimal hyperplasia is significantly inhibited in ePTFE stent grafts coated with rTM compared with uncoated grafts, as documented by improved luminal diameter by angiography and by computerized planimetry measurements of residual lumen area. These findings suggest that binding of recombinant human thrombomodulin onto ePTFE grafts may improve the long-term patency of covered stents grafts.

Clinical Relevance

Decrease of neointimal hyperplasia of the magnitude observed in this study could significantly improve blood flow and patency of small caliber prosthetic grafts. If the durability of these results can be confirmed by long-term studies, this technique may prove useful in preventing graft stenosis and arterial thrombosis following angioplasty or vascular bypass procedures.

 

Since its clinical introduction in 1976, expanded polytetrafluoroethylene (ePTFE) has been widely used as a substitute for autogenous saphenous vein bypass grafts.1 However, its usefulness in small vessel and distal revascularization continues to be hindered by luminal stenosis due to neointimal hyperplasia.2

Neointimal hyperplasia (NH) is the predominant pathological process leading to graft failure, mediated by smooth muscle cell (SMC) migration and proliferation leading to matrix deposition in response to arterial manipulation and intimal trauma. Polymers3, 4 and biosynthetic grafts5, 6, 7, 8, 9, 10, 11, 12 have been used in an attempt to inhibit the progression of neointimal hyperplasia with limited success. Anticoagulants such as heparin 5, 7, 8, 10, 11 prostaglandins6 and thrombolytic derivatives9, 12 have no significant effect on the development of neointimal hyperplasia.7

Thrombomodulin (TM) is an endothelial cell surface glycoprotein,13 whose anticoagulant properties arise from binding thrombin. The thrombomodulin-thrombin complex inhibits the procoagulant properties of thrombin, which in turn activates the anticoagulant zymogen protein C, which potently inhibits thrombus formation. The anticoagulant properties of thrombomodulin13, 14, 15, 16, 17 and molecular structure15, 16, 17 have been studied extensively. Our laboratory demonstrated that recombinant human thrombomodulin (rTM) was also a potent antimitogenic molecule. It inhibits smooth muscle cell proliferation in vitro,18 and decreases neointimal hyperplasia in a rabbit femoral artery balloon-injury model.19 We also reported that rTM can be bonded to ePTFE material in vitro and still function to activate protein C after a period of continuous flow simulation.20 A preliminary study of rTM bound to ePTFE grafts demonstrated an inhibitory effect on neointimal formation in a porcine carotid artery bypass model (data not shown). The purpose of this study was to evaluate the feasibility of binding rTM to ePTFE stent grafts and to study its ability to inhibit neointimal hyperplasia in a porcine balloon injured carotid artery model.

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Methods 

Stent graft preparation and evaluation 

Binding of rTM to ePTFE stent grafts 

Viabahn ePTFE stents (6 × 25 mm, internodal distance 25 microns, stent bound to the outside of the ePTFE graft, W. L. Gore & Associates, Inc, Flagstaff, Ariz),were coated with recombinant human-soluble thrombomodulin TMD1 (CS+) (rTM, donated by Eli Lilly and Co, Indianapolis, Ind) using a two step binding technique.18 The stent grafts were initially treated with a carbodiimide cross-reacting agent (EDAC, 1-ethyl-3-(3-diamethylaminoprophyl) carbodiimide, Sigma, St. Louis, MO) at a concentration of 10 mg/ml in water (Milli-Q water, Millipore Corp., Billerica, Mass) for 60 minutes at 4°C. After washing the stents twice with water, they were then incubated with rTM 15 μg/cm2 in Tris-HCL buffer (pH 7.4, Sigma) for 48 hours at 4°C.

Evaluation of rTM Bound ePTFE stents 

The presence of functional rTM on the ePTFE stent grafts was evaluated with an activated protein C (APC) assay.18 One rTM coated ePTFE stent graft was cross-sectioned into three segments for analysis. Two segments were assessed for APC activity, and the other was subjected to immuno-SEM evaluation. Of the two stent segments for APC activity study, the first was evaluated for binding of rTM to the luminal surface and the second for whole stent segment rTM binding. The first segment was opened longitudinally and the inner surface exposed to evaluate the luminal surface. It was then fixed to the base of a 24-well plate (Corning Inc., Corning, NY). For whole stent evaluation, the entire section of the stent was placed into the 24-well plate with both the luminal and stent strut surfaces exposed.

Both rTM coated stent graft segments were then incubated with 1 unit/ml of human plasma thrombin (Sigma) at 37°C for 60 minutes followed by incubation with 5 μg/ml of human protein C (Enzyme Research Laboratories, South Bend, Ind) at 37°C for 60 minutes. Then, 150 μl of each sample solution was transferred to a 96-well plate in triplicate. An aliquot of hirudin was added to each well (final concentration 30 nM) for 4 minutes to stop thrombin function. Chromogenic substrate S2366 (Chromogenix, DiaPharma Group Inc., West Chester, Ohio) was then added to each well (final concentration 0.4 mM). The reaction was stopped using 30 μl of 20% acetic acid in each well after 30 minutes, and the samples were immediately analyzed for optical density at 405 nm with a spectrophotometer (SLT Spectra, TECAN US, Inc., Durham, NC).

Immunoscanning electron microscopy 

The rTM coated ePTFE stent segments were incubated with monoclonal mouse antihuman endothelium thrombomodulin antibody QBEND/40 (Harlan Sera-Lab Limited, San Francisco, Calif) at a 1:10 dilution in incubation buffer (PBS plus 0.1% bovine serum albumin) at 4°C overnight, followed by incubation with a second antibody, AURION immunogold goat anti-mouse IgG (Electron Microscopy Sciences [EMS], Hatfield, Pa) at 22°C for 2 hours. After washing with incubation buffer and water, the samples were subjected to R-GENT developer and silver enhancer (EMS) for 20 minutes followed by water wash and then kept in water for scanning electron microscopy (SEM) evaluation.

Scanning electron microscopy and x-ray microanalysis with energy dispersive spectroscopy 

Immunogold stained and silver impregnated enhanced stent graft samples with and without rTM coating were dehydrated with ethanol and critical-point-dried with CO2. The samples were then mounted onto aluminum stubs with silver conductive paste and sputtered-coated with gold/palladium. The inner surface of the samples was examined using an ETEC autoscan scanning electron microscope (ETEC Corporation Inc., Hayward, Calif) at 20 kV accelerating voltage.

The immunogold stained and silver enhanced rTM coated stent graft samples were also secured to SEM stubs with pure carbon tape and conductive colloidal graphite. Approximately 10 nm of carbon was evaporated onto the surface to stabilize the material in the electron probe. The ePTFE stent samples were then examined using back scatter electron emission imaging (BSI) at X1000. Atomic contrast images were recorded using a Cameca SX50 electron microprobe equipped with a Robinson fast scan BSI detector (Cameca Inc., Courbevoie, France). Metal particles identified in BSI were analyzed using a PGT PRISM digital energy dispersive detector (Princeton-Gamma-Tech Inc., Princeton, NJ) and their x-ray spectrums were recorded. Microanalyses were counted for 30 seconds over an energy range of 0 to 10 keV. The detector resolution was approximately 150 eV.

Surgical procedures 

Male Yorkshire pigs weighing 25 to 30 Kg were anesthetized with Telazol 5 mg/Kg, ketamine 2.5 mg/Kg, and xylazine 2.5 mg/Kg intramuscularly, and general anesthesia maintained with isoflurane 1% to 3%. The left common femoral artery was cannulated with an 8F introducer. A bolus of heparin 5000 IU was administered intra-arterially after sheath insertion and an additional 2500 IU was given just prior to stent graft deployment. A 5F pigtail catheter was directed over a guidewire, under fluoroscopic guidance, into the aortic arch where a flush aortic arch angiogram was obtained. Next, a selective arteriogram of the left common carotid artery was obtained using a 5F Berstein catheter and marker wire. Arterial dimensions were obtained with a Phillips (Phillips, Orlando, Fla) BV300 C-arm, and electronic calipers, prior to arterial injury. A 6.0 × 20 mm ultra-soft angioplasty balloon (Boston Scientific Corp., Natick, Mass) was then positioned in the left common carotid artery between the second and third cervical vertebrae. The balloon was expanded to 6.4 mm at 10 atmospheres, rotated 360 degrees, moved up and down 0.5 cm, and deflated and re-inflated twice to stimulate neointimal hyperplasia. Completion angiograms were obtained in the anterior-posterior (AP) and lateral anterior oblique (LAO) projections.

The ePTFE stent grafts were deployed 4 weeks after balloon injury through a surgical incision to expose the left common femoral artery. The pigs were randomly assigned to receive either a rTM coated or non-coated 6 × 25 mm ePTFE stent graft delivered over a 0.035 inch Amplatz guidewire, and deployed in the left common carotid artery between the second and third cervical vertebrae. Completion arteriograms were obtained in AP and LAO projections for comparative analysis (Fig 1, A, B, and C). All pigs received acetylsalicylic acid 325 mg daily until termination.

  • View full-size image.
  • Fig 1. 

    Angiographic digital images of the left carotid artery. A, Digital subtraction image of the balloon injury site 2 weeks after angioplasty, prior to stent graft deployment. B and C, Unsubstracted images of a 6 × 25 mm ePTFE covered stent graft deployed in the left common carotid artery at the balloon-injured site.

Specimen collection 

The animals were sacrificed 4 weeks after stent graft placement. After inducing general anesthesia, selective left common carotid arteriograms were obtained through surgical exposure of the artery. An 8F infusion catheter was inserted into the proximal left common carotid artery and, using inflow occlusion, an arteriogram was obtained in two views. The animals were then exsanguinated, followed by fixation of the common carotid artery by antegrade perfusion with 4% paraformaldehyde at 120 to 140 mm Hg pressure for 30 minutes. The entire left common carotid artery including the stent graft was resected en bloc and stored in 4% paraformaldehyde for histopathological evaluation. Arteriographic data were recorded for comparison with preoperative measurements to assess the development of neointimal hyperplasia.

After 24 hours of fixation, the specimens were dehydrated and embedded in araldite in a cylindrical mold with the long axis perpendicular to the cutting plane. Transverse sections 100 μm were cut with a diamond wafering blade from the proximal, middle and distal segments of each stent graft. The ePTFE and the stent wires were left in place to avoid potential artifact or damage to the stent graft. The cut sections were then polished to approximately 30 μm and mounted on glass slides.

Histopathological analysis 

One of the rTM-coated and one of the uncoated stent grafts were sectioned longitudinally for gross inspection. Cross-sectional images were obtained using a Leica MZ 7.5 dissecting stereomicroscope (Leica Microsystems, Bannockburn, Ill) at X2.5 magnification. The imaging system was calibrated with a stage micrometer. The cross-sectional areas of the vessel lumen, stent lumen, intima, media, and whole artery were measured using Image J software National Center for Biotechnology Information (NCBI, Bethesda, Md). The ratios of intima to media (I/M) were calculated.

Statistical analysis 

The data were analyzed using variance for mixed models by restricted maximum likelihood estimation (REML) using the SAS proc mixed procedure.21, 22 Compliance with the assumption of normality for the distribution of residuals was evaluated graphically using frequency histograms as well as by the Kolmogorov-Smirnov goodness of fit test.23, 24 Differences were considered significant at the 95% confidence level (P < .05).

The results of luminal area, neointimal area, media area, whole artery area, and I/M ratio and lumen to whole artery (L/A) ratio are expressed as the mean ± SD of proximal, middle, and distal segments, n = 5. The effect of ratios vs left carotid artery segment (proximal 1/3, middle 1/3, distal 1/3), and treatment (rTM-coated and uncoated stent graft) were evaluated using analysis of variance for mixed models. The effect of luminal diameter of angiograms vs segment (proximal 1/3, middle 1/3, distal 1/3), and treatment (rTM-coated and uncoated stent graft) were evaluated using analysis of univariate analysis of variance for mixed models two-pair t test, n = 7. Results are reported after applying a Bonferroni adjustment to compensate for chance false discoveries presuming 100 multiple comparisons.

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Results 

A total of 14 stent grafts were deployed in the left common carotid artery of 14 pigs; seven rTM coated and seven uncoated. There were no periprocedural complications or deaths. At the time the grafts were harvested, all of the rTM coated stents were patent, while one of the seven uncoated stents had thrombosed.

Bonding of rTM to stent grafts 

Scanning electron microscopy, both secondary imaging and backscatter (ie, atomic contrast) imaging, was performed on the immuno-stained and silver enhanced luminal surfaces of the ePTEF stent graft (Fig 2, A, B, C, and D). The presence of silver enhanced-immuno labeled rTM molecules bound to the nodal and internodal strands of the ePTFE are easily seen in the backscatter image (Fig 2, C) as bright spots throughout the image. The stent graft that we used in this study was a Nitinol stent (Boston Scientific Corp., Natick, Mass). The titanium and nickel are components of Nitinol. X-ray microanalysis of the bright objects (Fig 2, D) and the elemental spectrum for silver (Ag) confirms the presence of silver enhanced, immuno-labeled rTM on the luminal surface of the stent graft.

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  • Fig 2. 

    SEM and back scatter electron emission image (BSI). A, SEM of normal ePTFE. B, SEM of rTM molecules bound to ePTFE. C, BSI demonstrates silver tagged rTM molecules (white particles); D, X-ray microanalysis shows the presence of Ag bonded rTM molecules.

The presence of activated protein C was used to confirm the bonding of functional rTM to the stent grafts (Fig 3). No protein C activity could be demonstrated for control ePTFE grafts placed in buffered saline, whereas the rTM coated stent grafts showed 77.5% increase in APC activity on the luminal surface, and 86.8% on whole stent graft, indicating that both surfaces of the stent graft were coated with functional rTM. Thus, the combination of electron microscopy and activated protein C analysis demonstrated the presence of active molecules of rTM on all surfaces of the coated stent grafts.

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  • Fig 3. 

    Optical density of activated protein C. The functional presence of rTM on the luminal surface of the rTM coated stent graft and the whole rTM coated stent graft was evaluated with activated protein C. The whole structure of rTM-coated stent graft expressed significantly more activated protein C than the luminal surface alone.

Histopathological analysis 

The residual luminal diameter was measured by angiography. For the rTM coated stent graft group the residual diameter was 93% ± 2.0% of the pre-stent value. The luminal diameter of the uncoated group was reduced to 67.2% ± 22.7% (P = .006).

On gross inspection of the harvested grafts 4 weeks after deployment, the rTM coated stents were covered with a thin, glistening white layer (Fig 4, A and B). There was no mural thrombus or fibrin present. The proximal and distal margins of the stent graft had a smooth tapering layer onto the native vessel (Fig 4, A). By contrast, an irregularly thickened yellowish intraluminal layer covered the uncoated stent grafts. There were focal areas of red blood clot and fibrin deposition. The inner surface of the stent grafts was irregular at both the proximal and distal ends (Fig 4, B). As noted above, one of the uncoated stent grafts had thrombosed prior to harvest.

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  • Fig 4. 

    Gross photographs of the luminal surface of ePTFE covered stent grafts explanted at 4 weeks. A, The rTM-coated ePTFE stent graft is covered with a smooth, glistening white thin layer with minimal surface deposition. B, The uncoated ePTFE stent graft is covered with an irregular thick yellow-brown layer with scattered blood clots.

Light microscopy combined with computerized planimetry was used to measure cross-sectional areas and to calculate I/M ratios for rTM treated and control specimens. The rTM coated stent graft had a larger lumen area and less neointimal thickening than the control stent graft. (Fig 5, A, B, C, D, and F) The data for lumen, neointima, media and whole artery areas, and I/M ratio and L/A ratio are listed in the Table. The cross-sectional areas of neointimal thickening observed for the proximal, middle, and distal segments of the rTM stent grafts and the control groups are shown in Fig 6, A. There was a −27% (P < .05) reduction in neointimal thickening of the proximal segment, −15.8% (NS) for the middle, and −12.9% not significant (NS) for the distal segment. The results for the I/M ratios were similar (Fig 6, B). There was −39% (P < .05) reduction for the proximal, −7.95% (NS) for the middle, and −18.7% (NS) for the distal segments. Consequently, histological analysis showed that rTM effectively reduced neointimal hyperplasia and that the effect was most pronounced in the proximal segment of the coated stent graft.

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  • Fig 5. 

    Light microscopic images of a representative transverse section of uncoated and rTM-coated ePTFE stent graft 4 weeks after deployment in the left carotid artery. Uncoated ePTFE covered stent graft. A, Proximal. B, Middle. C, Distal. rTM-coated ePTFE covered stent graft. D, Proximal. E, Middle. F, Distal.

Table. Histomorphometric measurement: Areas of lumen, neointima, media, and whole artery (mean ± SD)
(Stent graft)LocationLumen (mm2)Neointima (mm2)Media (mm2)Whole artery (mm2)I/M ratioL/A ratio
UncoatedProximal7.34±0.993.74±0.675.05±1.1519.65±2.660.77±0.050.37±0.08
Middle9.94±0.673.79±1.615.98±1.2922.96±2.030.63±0.210.37±0.08
Distal8.96±0.562.93±0.705.85±1.4821.95±2.830.52±0.120.43±0.04
rTM boundProximal9.02±0.392.73±0.696.01±1.4020.07±2.630.47±0.150.36±0.07
Middle11.31±0.473.19±0.806.17±2.5324.03±3.150.58±0.170.41±0.08
Distal10.14±0.662.56±1.406.02±2.2121.80±2.410.42±0.180.41±0.11

rTM, Recombinant human thrombomodulin; I/M, intimal to media; L/A, lumen to whole artery.

The luminal area of the proximal, middle, and distal stent graft cross sectional segments is shown in Fig 7. The luminal areas of the rTM coated stents were 9.02 ± 0.39 mm2, 11.31 ± 0.47 mm2, and 10.14 ± 0.66 mm2, respectively. In the corresponding segments of the uncoated stent graft group, the values were 7.34 ± 0.99 mm2, 9.94 ± 0.67 mm2, and 8.96 ± 0.56 mm2, respectively. The overall difference between the luminal areas of the two groups was 1.176 mm2 (P < .05). Angiographically, the luminal diameter was 4.81 ± 0.05 mm prior to balloon injury, and 4.29 ± 0.15 mm 2 weeks after balloon injury, P < .001. Four weeks after stent graft placement, the diameter of the control stent graft group was 3.16 ± 0.22 mm, and the rTM coated stent graft group was 4.48 ± 0.03 mm, P < .02.

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  • Fig 7. 

    Luminal area of the rTM-coated and uncoated ePTFE stent grafts. The mean luminal area of each segment of the rTM-coated stent graft was larger in each segment compared with uncoated stent graft with an overall luminal area difference of 1.176 mm2 (P < .05).

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Discussion 

Re-stenosis produced by neointimal hyperplasia limits the success of angioplasty and stenting of small caliber peripheral arteries. Patency rates as low as 38% and 8% for 1 and 3 years, respectively, have been reported for angioplasty and stenting of the femoropopliteal segment.25 There have been no reports of successful stent grafting for femoropopliteal occlusive disease.26 Previous studies have shown that rTM is a potent inhibitor of neointimal hyperplasia, because of its antithrombotic and antimitogenic properties.20 To take advantage of the favorable characteristics of rTM requires a delivery system that can place a high concentration of rTM at the site of arterial injury. Systemic therapy is not practical because rTM is rapidly diluted by the circulating blood volume, metabolized by the liver, and excreted by the kidney. The present study evaluated covalent bonding rTM to endovascular ePTFE stent grafts, so as to deliver a high concentration of rTM directly to the site of arterial injury.

In order to control neointimal hyperplasia, it is important to prevent arterial spasm and remodeling after injury, as well as the inflammatory reaction and proliferative effects of smooth muscle cells. The rTM coated ePTFE stent graft circumvents the problems associated with systemic therapy as well as the uncontrolled leaching of the drug from the surface of a polymer based delivery device. By coating all surfaces of ePTFE stent grafts with rTM, the anticoagulant, antimitogenic, and anti-inflammatory properties of rTM are concentrated at the site of tissue injury, thereby maximizing the local suppressant effect on the smooth muscle cells and inflammatory reaction that initiate the hyperplastic process.

This study demonstrated the feasibility of bonding rTM to 6 mm ePTFE covered stent grafts as confirmed by immuno-scanning electron microscopy, back scatter imaging, and x-ray microanalysis. The presence of functional rTM bound to ePTFE grafts was verified by demonstrating the presence of activated protein C. The rTM coated stent grafts reduced neointimal hyperplasia, compared with non-coated stents in a porcine balloon injury model, as judged by the gross appearance, angiographically maintained luminal diameter, histological analysis of residual luminal, and improved I/M ratios.

Following implantation of a stent graft, flow turbulence occurs preferentially in the proximal segment. The resultant change in hemodynamics may explain the observed increase in neointimal formation in this segment shown in Fig 6 of the control group. Compared with the control group, the neointima and I/M ratio in the proximal segment of the rTM coated stent group was significantly less. The primary limitations of this study are the relatively small number of experimental animals and the short duration of follow-up. It is possible that a larger study might have shown significant inhibition of hyperplasia in the middle and distal segments as well as the proximal segments of the rTM coated stent grafts. On the other hand, a more extensive study could confirm that the primary inhibitory effect of neointimal hyperplasia indeed is in the proximal segment where the most active hyperplasia appears to occur. The encouraging results noted here, have prompted us to undertake a larger study with longer follow-up to answer this question and to evaluate the duration of the antihyperplastic effects of rTM.

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Conclusion 

Thrombomodulin, by virtue of its anticoagulant, antimitogenic, and anti-inflammatory properties, appears to be an attractive choice as a surface-binding agent. The preliminary findings of this study suggest that coating a 6 mm diameter ePTFE stent graft with recombinant human thrombomodulin will inhibit neointimal hyperplasia and preserve luminal patency as confirmed by angiography and cross-sectional morphometric evaluation. This technique may prove to be a practical means to prevent restenosis and early procedural failure following angioplasty or open vascular bypass operations.

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Author contributions 


Conception and design: JML

Analysis and interpretation: GW, JML, GH

Data collection: GW, JML, GH

Writing the article: GW, JML, BC, GH

Critical revision of the article: JML, BC, MR, ME

Final approval of the article: BC, JML

Statistical analysis: GW, JML

Obtained funding: BC, JML

Overall responsibility: BC

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The authors thank Stephen Baker, MScPH, Senior Biostatistician, Departments of Cell Biology and Information Resources, the University of Massachusetts Medical School for assistance of statistical analysis. The authors also acknowledge grant supports from the Ellinwood Research Endowment (BSC) and the Bugher Foundation (JML).

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References 

  1. Veith FJ, Gupta SK, Ascer E, White-Flores S, Samson RH, Scher LA, et al. Six-year prospective multicenter randomized comparison of autologous saphenous vein and expanded polytetrafluoroethylene grafts in infrainguinal arterial reconstructions. J Vasc Surg. 1986;3:104–114
  2. Quinones-Baldrich WJ, Prego AA, Ucelay-Gomez R, Freischlag JA, Ahn SS, Baker JD, et al. Long-term results of infrainguinal revascularization with polytetrafluoroethylene: a ten-year experience. J Vasc Surg. 1992;16:209–217
  3. Boyce B. Physical characteristics of expanded polytetrafluoroethylene grafts. In:  Stanley JC editors. Biological and synthetic vascular prostheses. New York: Grune and Straton; 1982;p. 553–561
  4. Ikada Y. Surface modification of polymers for medical applications. Biomaterials. 1994;15:725–736
  5. Bjorck . Thrombin uptake and inhibition on heparinized polytetrafluoroethylene (PTFE) grafts and native sheep vessels. Thromb Res. 1986;42:605
  6. Ebert CD, Lee ES, Kim SW. The antiplatelet activity of immobilized prostacyclin. J Biomed Mater Res. 1982;16:629–638
  7. Geary RL, Koyama N, Wang TW, Vergel S, Clowes AW. Failure of heparin to inhibit intimal hyperplasia in injured baboon arteries (The role of heparin-sensitive and -insensitive pathways in the stimulation of smooth muscle cell migration and proliferation). Circulation. 1995;91:2972–2981
  8. Ito Y, Imanishi Y, Sisido M. In vitro platelet adhesion and in vivo antithrombogenicity of heparinized polyetherurethaneureas. Biomaterials. 1988;9:235–240
  9. Ohshiro T, Kosaki G. Urokinase immobilized on medical polymeric materials: Fundamental and clinical studies. Artific Organs. 1980;4:58–64
  10. Piao AZ, Jacobs HA, Park KD, Kim SW. Heparin immobilization by surface amplification. ASAIO J. 1992;38:M638–M643
  11. Ritter EF, Fata MM, Rudner AM, Klitzman B. Heparin bonding increases patency of long microvascular prostheses. Plast Reconstr Surg. 1998;101:142–146
  12. Senatore F, Bernath F, Meisner K. Clinical study of urokinase-bound fibrocollagenous tubes. J Biomed Mater Res. 1986;20:177–188
  13. Esmon CT, Owen WG. Identification of an endothelial cell cofactor for thrombin-catalyzed activation of protein C. Proc Natl Acad Sci U S A. 1981;78:2249–2252
  14. Esmon CT. Thrombomodulin as a model of molecular mechanisms that modulate protease specificity and function at the vessel surface. FASEB J. 1995;9:946–955
  15. Jackman RW, Beeler DL, VanDeWater L, Rosenberg RD. Characterization of a thrombomodulin cDNA reveals structural similarity to the low density lipoprotein receptor. Proc Natl Acad Sci U S A. 1986;83:8834–8838
  16. Suzuki K, Kusumoto H, Deyashiki Y, Nishioka J, Maruyama I, Zushi M, et al. Structure and expression of human thrombomodulin, a thrombin receptor on endothelium acting as a cofactor for protein C activation. EMBO J. 1987;6:1891–1897
  17. Wen D, Dittman WA, Ye RD, Deaven LL, Majerus PW, Sadler JE. Human thrombomodulin: complete cDNA sequence and chromosome localization of the gene. Biochemistry (Mosc). 1987;26:4350–4357
  18. Li JM, Singh MJ, Nelson PR, Hendricks GM, Itani M, Rohrer MJ, et al. Immobilization of human thrombomodulin to expanded polytetrafluoroethylene. J Surg Res. 2002;105:200–208
  19. Li JM, Garnette CS, Cahn M, Claytor RB, Rohrer MJ, Dobson JG, et al. Recombinant thrombomodulin inhibits arterial smooth muscle cell proliferation induced by thrombin. J Vasc Surg. 2000;32:804–813
  20. Li JM, Singh MJ, Itani M, Vasiliu C, Hendricks G, Baker SP, et al. Recombinant human thrombomodulin inhibits arterial neointimal hyperplasia after balloon injury. J Vasc Surg. 2004;39:1074–1083
  21. Verbeke G, Lesaffre E. The linear mixed model: a critical investigation in the context of longitudinal data. In:  Gregoire T editors. Proceedings of the Nantucket Conference on Modeling Longitudinal and Spatially Correlated Data: Methods, Applications, and Future Directions. New York: Springer Verlag; 1997;p. 89–99
  22. Littell RC, Milliken GA, Stroup WW, Wolfinger RD. The SAS system for mixed models. Cary, NC: SAS Institute Inc; 1996;
  23. Bailar JC, Mosteller F. Medical uses of statistics. Boston: The New England Journal of Medicine Books; 1992;
  24. Daniel WW. Applied Nonparametric Statistics. PWS-Kent, Boston: Chapman and Hall; 1990;
  25. Bui TD, Gordon IL, Nguyen T, Fujitani RM, Wilson SE, Conroy RC. Transluminal stenting for femoropopliteal occlusive disease: analysis of restenosis by serial arteriography. Ann Vasc Surg. 2006;20:200–208
  26. Ansel GM, Botti CF, Silver MJ. The use of femoropopliteal stent grafts for critical limb ischemia. Techniques in vascular and interventional radiology. 2005;8:140–145

 Competition of interest: none.

PII: S0741-5214(07)01778-8

doi:10.1016/j.jvs.2007.11.025

Journal of Vascular Surgery
Volume 47, Issue 3 , Pages 608-615, March 2008

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