The Role of Immunomodulation in Vein Graft Remodeling and Failure.

Obstructive arterial disease is a major cause of morbidity and mortality in the developed world. Venous bypass graft surgery is one of the most frequently used revascularization strategies despite its considerable short and long time failure rate. Due to vessel wall remodeling, inflammation, intimal hyperplasia, and accelerated atherosclerosis, vein grafts may (ultimately) fail to revascularize tissues downstream to occlusive atherosclerotic lesions. In the past decades, little has changed in the prevention of vein graft failure (VGF) although new insights in the role of innate and adaptive immunity in VGF have emerged. In this review, we discuss the pathophysiological mechanisms underlying the development of VGF, emphasizing the role of immune response and associated factors related to VG remodeling and failure. Moreover, we discuss potential therapeutic options that can improve patency based on data from both preclinical studies and the latest clinical trials. This review contributes to the insights in the role of immunomodulation in vein graft failure in humans. We describe the effects of immune cells and related factors in early (thrombosis), intermediate (inward remodeling and intimal hyperplasia), and late (intimal hyperplasia and accelerated atherosclerosis) failure based on both preclinical (mouse) models and clinical data.

Endothelin-1, endothelin receptor antagonists, and vein graft occlusion in coronary artery bypass surgery: 20 years on and still no journey from bench to bedside.

The saphenous vein is the most commonly used bypass graft in patients with coronary artery disease. During routine coronary artery bypass, grafting the vascular damage inflicted on the vein is likely to stimulate the release of endothelin-1, a potent endothelium-derived vasoconstrictor that also possesses cell proliferation and inflammatory properties, conditions associated with vein graft failure. In both in vitro and in vivo studies, endothelin receptor antagonists reduce neointimal thickening. The mechanisms underlying these observations are multifactorial and include an effect on cell proliferation and cell/tissue damage. Much of the data supporting the beneficial action of endothelin-1 receptor antagonism at reducing intimal thickening and occlusion in experimental vein grafts were published over 20 years ago. The theme of the recent ET-16 conference in Kobe was "Visiting Old and Learning New". This short review article provides an overview of studies showing the potential of endothelin receptor antagonists to offer an adjuvant therapeutic approach for reducing saphenous vein graft failure and poses the question why this important area of research has not been translated from bench to bedside given the potential benefit for coronary artery bypass patients.

Evaluation of a Bovine Vascular Graft in Sheep.

The study objective was to determine safety and efficacy of a treated bovine vascular xenograft, in two Good Laboratory Practice compliant studies in sheep following carotid graft implantation. In one study, a 3- to 5-mm diameter xenograft was implanted into the right carotid artery of male sheep and compared to autologous jugular vein and a polymeric grafts similarly implanted. In a second study, a 9.5- to 14-mm diameter xenograft similarly implanted into the right carotid artery was compared to an autologous saphenous vein. Monthly Doppler ultrasound evaluation of implant patency and flow in implants and contralateral control carotid arteries was performed. The small vessel cohort 6 month xenograft patency was equivalent (or better) than animals with polymeric vascular graft or autologous vein implants; the aneurysm incidence was less than that of autologous vein grafts. In the large vessel cohort, all 15 xenografts and 12/15 saphenous vein implants were patent at 6 month follow-up. Tissue histology showed mild inflammatory responses in the xenografts that was slightly greater than suture material. In summary, treated bovine xenograft performance in this small study suggests it may be superior to polymeric autologous vein grafts, and may have a similar failure rate as autologous vein grafts after implantation.

Increased levels of lysosomal cysteinyl cathepsins in human varicose veins: a histology study.

Varicose veins are a major chronic venous disease characterised by extensive remodelling of the extracellular matrix architecture in the vascular wall. Although matrix metalloproteinases have been implicated in these pathologic events, little is known about the functional relevance of other protease family members. Here, we studied the distribution of lysosomal cysteine proteases, cathepsins B, L, K, and S, and their endogenous inhibitor, cystatin C, in long saphenous vein specimens from nine normal donors and 18 patients with varicose veins (VVs). Immunohistochemical analysis demonstrated increased levels of cathepsins L, K, B, and S and reduced levels of cystatin C in VVs. This imbalance between cysteinyl cathepsins and cystatin C may favour VV remodelling. To investigate the inflammatory mechanism of their expression, we examined a detailed inflammatory cell profile in VVs, including macrophages, T lymphocytes, and mast cells. Increased numbers of CD3-positive T cells and tryptase-positive mast cells were found in VVs, and enhanced levels of cysteinyl cathepsins were detected from lesion CD3-positive T cells, chymase-positive mast cells, endothelial cells, and smooth-muscle cells. Elevated cathepsins, and their co-localisation to infiltrated inflammatory cells and to vascular cells, suggest that these proteases participate in extracellular matrix degradation in response to inflammation during VV pathogenesis.

Comparison of conventional and no-touch techniques in harvesting saphenous vein for coronary artery bypass grafting in view of endothelial damage.

BACKGROUND: Optimization of saphenous vein patency for myocardial revascularization. OBJECTIVE: The goal of this study was to present the no-touch technique of saphenous vein preparation. This technique consists of harvesting the vein with a pedicle of surrounding tissue, which protects the vein from distension pressure. METHODS: We performed a prospective, randomized study that compared 2 techniques for harvesting saphenous vein-conventional and no-touchin 40 patients undergoing coronary artery bypass grafting. We carried out a morphologic study of the endothelium with the aid of light and transmission electron microscopy and an immunohistochemical assessment to identify adenosine, inducible nitric oxide synthase (iNOS), and vascular endothelial growth factor (VEGF) in the vein wall. RESULTS: The integrity of endothelial cell and all vascular layers was maintained better with the no-touch technique than with the conventional procedure. The immunohistochemical assessment revealed that adenosine receptor, iNOS, and VEGF immunoexpression levels were normal or lower in the no-touch group than in the conventional-harvest group, as shown by the staining densities in all layers of the vein wall. CONCLUSION: Endothelial integrity and adenosine, iNOS, and VEGF immunoreactivities were better preserved when the no-touch technique was used for vein graft harvesting. The mechanical protection provided by the cushion of surrounding tissue in the no-touch group and the vasorelaxation and thromboresistant activities of nitric oxide may be responsible for the reduction in vasospasms and the improved patency rate.

Inflammation modulates murine venous thrombosis resolution in vivo: assessment by multimodal fluorescence molecular imaging.

OBJECTIVE: Assessment of thrombus inflammation in vivo could provide new insights into deep vein thrombosis (DVT) resolution. Here, we develop and evaluate 2 integrated fluorescence molecular-structural imaging strategies to quantify DVT-related inflammation and architecture and to assess the effect of thrombus inflammation on subsequent DVT resolution in vivo. METHODS AND RESULTS: Murine DVT were created with topical 5% FeCl(3) application to thigh or jugular veins (n=35). On day 3, mice received macrophage and matrix metalloproteinase activity fluorescence imaging agents. On day 4, integrated assessment of DVT inflammation and architecture was performed using confocal fluorescence intravital microscopy. Day 4 analyses showed robust relationships among in vivo thrombus macrophages, matrix metalloproteinase activity, and fluorescein isothiocyanate-dextran deposition (r>0.70; P<0.01). In a serial 2-time point study, mice with DVT underwent intravital microscopy at day 4 and day 6. Analyses revealed that the intensity of thrombus inflammation at day 4 predicted the magnitude of DVT resolution at day 6 (P<0.05). In a second approach, noninvasive fluorescence molecular tomography-computed tomography was used and detected macrophages within jugular DVT (P<0.05 versus sham controls). CONCLUSIONS: Integrated fluorescence molecular-structural imaging demonstrates that the DVT-induced inflammatory response can be readily assessed in vivo and can inform the magnitude of thrombus resolution.

C1-esterase inhibitor protects against early vein graft remodeling under arterial blood pressure.

OBJECTIVES: Arterial pressure induced vein graft injury can result in endothelial loss, accelerated atherosclerosis and vein graft failure. Inflammation, including complement activation, is assumed to play a pivotal role herein. Here, we analyzed the effects of C1-esterase inhibitor (C1inh) on early vein graft remodeling. METHODS: Human saphenous vein graft segments (n=8) were perfused in vitro with autologous blood either supplemented or not with purified human C1inh at arterial pressure for 6h. The vein segments and perfusion blood were analyzed for cell damage and complement activation. In addition, the effect of purified C1inh on vein graft remodeling was analyzed in vivo in atherosclerotic C57Bl6/ApoE3 Leiden mice, wherein donor caval veins were interpositioned in the common carotid artery. RESULTS: Application of C1inh in the in vitro perfusion model resulted in significantly higher blood levels and significantly more depositions of C1inh in the vein wall. This coincided with a significant reduction in endothelial loss and deposition of C3d and C4d in the vein wall, especially in the circular layer, compared to vein segments perfused without supplemented C1inh. Administration of purified C1inh significantly inhibited vein graft intimal thickening in vivo in atherosclerotic C57Bl6/ApoE3 Leiden mice, wherein donor caval veins were interpositioned in the common carotid artery. CONCLUSION: C1inh significantly protects against early vein graft remodeling, including loss of endothelium and intimal thickening. These data suggest that it may be worth considering its use in patients undergoing coronary artery bypass grafting.

Limb salvage with CryoVein cadaver saphenous vein allografts used for peripheral arterial bypass: role of blood compatibility.

Patients suffering from limb-threatening ischemia often have scarce or inadequate autogenous veins for complex lower limb revascularization. One option for such patients is to use conduit consisting of cadaver saphenous vein allograft (CSVA) as a final surgical option before limb amputation. This study reviewed retrospectively the patency of CryoVein CSVA allografts, processed by CryoLife, Inc., in 54 implant cases of lower extremity arterial bypass over a span of 6 years. Patient demographics, graft patency, limb salvage, and blood type matching of donor to recipient were analyzed. Kaplan-Meier analysis showed postoperative primary patency rates of 89, 63%, 30%, 17%, and 9% at 1, 3, 6, 12, and 18 months, respectively. Secondary patency rates were 89%, 74%, 63%, 63%, and 54% at 1, 3, 6, 12, and 18 months, respectively. Limb salvage rates were 67% at 12 months and 54% at 18 months. Median follow-up was 467 days. Of the 34 cases where the patient received a blood-group compatible CSVA, 30 had limb salvage and only six of 20 noncompatible grafts offered limb salvage (p = 0.05). Although primary patency rate was poor at 1 year, high secondary patency and limb salvage rates support the use of CSVA as a peripheral bypass conduit alternative. Cases with donor-recipient ABO blood type compatibility had significantly better limb salvage.

Chronic homocysteine exposure upregulates endothelial adhesion molecules and mediates leukocyte: endothelial cell interactions under flow conditions.

AIMS: Homocysteine upregulates expression of adhesion molecules on endothelial cells which recruits leukocytes and initiates atherosclerosis. Endothelial cells in hyperhomocysteinemic patients are continuously exposed to high levels of homocysteine. This study exposed adult endothelial cells and endothelial cells from immune naïve foetal tissue to homocysteine chronically and studied effects on cellular adhesion molecule expression under static and flow conditions. METHODS: Human umbilical vein endothelial cells (HUVEC) and human saphenous vein endothelial cells (HSVEC) were cultured in medium containing 1 mM dl-homocysteine or l-cysteine for 5-9 days. Proliferation was assessed. Cells were subjected to flowing neutrophils and numbers of tethered, rolled fixed and transmigrated neutrophils on endothelial cells were counted and compared to controls. Immunofluorescence staining with antibodies against Intercellular adhesion molecule-1 (ICAM-1), E-selectin and P-selectin were used to quantify expression. RESULTS: Chronic treatment with 1 mM homocysteine inhibited proliferation of HUVEC and HSVEC. Homocysteine treated cells showed significantly increased expression of ICAM-1, E-selectin and to a lesser extent P-selectin. In both cell types, homocysteine significantly increased interactions between neutrophils and endothelial cells under flow conditions (p < 0.05) while cysteine had no effect. CONCLUSION: Endothelial cells from adult and immune naïve foetal tissue showed similar responses to chronic treatment with homocysteine.

Ex vivo pulsatile perfusion of human saphenous veins induces intimal hyperplasia and increased levels of the plasminogen activator inhibitor 1.

Vessel wall trauma induces vascular remodeling processes including the development of intimal hyperplasia (IH). To assess the development of IH in human veins, we have used an ex vivo vein support system (EVVSS) allowing the perfusion of freshly isolated segments of saphenous veins in the presence of a pulsatile flow which reproduced arterial conditions regarding shear stress, flow rate and pressure during a period of 7 and 14 days. Compared to the corresponding freshly harvested human veins, histomorphometric analysis showed a significant increase in the intimal thickness which was already maximal after 7 days of perfusion. Expression of the endothelial marker CD31 demonstrated the presence of endothelium up to 14 days of perfusion. In our EVVSS model, the activity as well as the mRNA and protein expression levels of plasminogen activator inhibitor 1, the inhibitor of urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), were increased after 7 days of perfusion, whereas the expression levels of tPA and uPA were not altered. No major change was observed between 7 and 14 days of perfusion. These data show that our newly developed EVVSS is a valuable setting to study ex vivo remodeling of human veins submitted to a pulsatile flow.

Varicose veins show enhanced chemokine expression.

OBJECTIVES: Leucocyte infiltration in the wall of varicose veins has been reported previously. This study was designed to investigate the expression of pro-inflammatory cytokines and chemokines in control and in patients with varicose veins and to test the effect of treating varicose vein patients with acetylsalicylic acid (ASA) on cytokine expression prior to removal of varices. MATERIAL AND METHODS: Sections of vein were removed during operation from both patient groups, and ribonuclease protection assays (RPAs) were performed to assess the expression of chemokines. Group I included non-varicose saphenous veins from healthy patients undergoing amputation for trauma. Varicose veins were obtained from patients with primary varicose undergoing surgical treatment who received no drug (group II) or treatment with 300 mg day(-1) of ASA for 15 days before surgery (group III). RESULTS: Non-varicose veins constitutively expressed low levels of monocyte-chemoattractant protein (MCP-1) and interleukin (IL)-8 mRNA. Varicose veins had a distinct chemokine expression pattern, since significant up-regulation of MCP-1 and IL-8 and a marked expression of IP-10, RANTES, MIP-1alpha and MIP-1beta mRNA were detected. Removal of the endothelium did not alter this pattern. Varicose veins obtained from patients treated with ASA showed a consistent decrease in chemokine expression, although it did not reach statistical significance. CONCLUSIONS: Varicose veins showed increased expression of several chemokines compared to control veins. A non-significant reduction of activation was observed following treatment with ASA for 15 days.

Inflammatory cell infiltrates in vessels with different susceptibility to atherosclerosis in rheumatic and non-rheumatic patients: a controlled study of biopsy specimens obtained at coronary artery surgery.

BACKGROUND: The main aim of the present study was to compare the occurrence of inflammatory cell infiltrates in the aorta, a vessel with a high occurrence of atherosclerosis, with that in the saphenous vein (SV) and internal mammary artery (IMA), which are protected from atherosclerosis. METHODS AND RESULTS: Samples from the aorta, SV, and IMA of 65 patients with inflammatory rheumatic diseases (IRD) and from 51 control patients undergoing coronary artery bypass graft surgery were examined for the presence and location of inflammatory cell infiltrates and atherosclerotic lesions. Mononuclear cell infiltrates (MCIs) in the media or adventitia were observed in 2% IMAs, 17% SVs, and 35% aortic specimens (SV vs IMA: p=0.006; SV vs aorta: p=0.001). Atherosclerotic lesions were present in none IMA, 3% SVs and 18% aortic specimens. IRD and smoking increased the odds of MCI in the aorta (odds ratio (OR)=3.6, 95% confidence interval (CI): 1.6-8.5 and OR=4.0, 95% CI: 1.5-10.9), but not in the SV or IMA. CONCLUSIONS: The occurrence of medial and adventitial MCI in the aorta, SV, and IMA paralleled each vessel's susceptibility to atherosclerosis: it was highest in the aorta and lowest in IMA. Local vascular inflammation may be involved in atherogenesis, and influence the patency of vascular grafts.

[Application of irradiated allograft vascular in the liver transplantation].

OBJECTIVE: To study the substitute portal vein by irradiated allograft saphenous vein during liver transplantation and investigate the changes in morphology and immunology. METHODS: All the recipients were divided into 3 groups randomly:irradiated allograft group (n = 11) (group A), fresh allograft group (n = 9) (group B) and fresh self-graft group (n = 14) (group C). The number of non-jam graft vessels in each group was explored at 1st week, 2nd week, 1st month, 2nd month and 3rd month post-operation. Also, the infiltration of CD(4)(+), CD(8)(+) T cells and histological changes in grafted vessels were detected. RESULTS: No obvious histological changes were observed in group A, as well as under naked eyes. There were 9, 3 and 12 non-jam vessels in group A, B and C and there were significant differences between group A and B (P < 0.05). The endothelial cells of graft vessels were observed both in group A and C two weeks post-operation and covered the graft vessels two months later. There were infiltration of lymphocytes and inflammatory cells at early stage, obvious damage and no endothelial cells growth in graft vessels in group B. Compared with group B, the percentage of CD(4)(+), CD(8)(+) T cells in group A was lower significantly, but higher slightly than that in group C. CONCLUSIONS: Irradiated allograft saphenous veins have the quality of ideal vascular transplantation prosthesis and weak antigenicity at the same time. The changes of CD(4)(+), CD(8)(+) T cells after allograft vessels can be detected as immunology index for acute immunological rejection.

Vein graft harvesting induces inflammation and impairs vessel reactivity.

BACKGROUND: Saphenous veins are often used for coronary artery bypass grafting (CABG), but loss of patency is a problem. The surgical procedure may contribute to graft injury. Our aim was to study the impact of surgical handling of saphenous veins on graft inflammation and vascular function. METHODS: Biopsy samples of saphenous veins were taken from 9 patients undergoing elective CABG at the start of vein harvesting (open technique) and after the last proximal anastomosis was sutured. Messenger RNA was extracted and amplified with semiquantitative reverse transcription polymerase chain reaction. Gene expression of proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta), leukocyte adhesion molecules (E-selectin, intercellular adhesion molecule-1), and vasoactive substances (endothelin-1, inducible and endothelial nitric oxide synthase) was investigated. Translocation of nuclear factor-kappaB (NFkappaB) was evaluated with electrophoretic mobility shift assay. Immunostaining for von Willebrand factor was performed to evaluate loss of endothelium, and in vitro vein reactivity to phenylephrine and endothelin-1 was studied. RESULTS: Gene expression of cytokines and leukocyte adhesion molecules increased after graft harvesting and storage, whereas vasoactive substances did not change. Nuclear translocation of NFkappaB occurred after surgical handling, concurrent with partial loss of endothelium and impaired contractile function. CONCLUSIONS: Standard surgical handling of vein grafts induces NFkappaB-driven inflammation in the vessel wall and impairs vascular function. This may potentially contribute to both early and late graft occlusion.

Immunocytochemical characterisation of the inflammatory cell infiltrate of varicose veins.

OBJECTIVES: To characterise the inflammatory cell infiltrate in varicose vein wall, and its relationship to the valve complex. DESIGN: A comparative study of the distribution of inflammatory cells in normal and varicose vein. MATERIALS: Specimens of proximal human long saphenous vein were obtained from patients with duplex Doppler confirmed long saphenous vein reflux (n=14). Control vein was obtained from patients undergoing coronary artery bypass without clinical evidence of venous insufficiency (n=6). Longitudinal 7 microm frozen sections of vein, displaying valve, were prepared. METHODS: Using immunohistochemistry, T-lymphocytes (CD3), macrophage/monocytes (CD68), neutrophils (CD15s) and mast cells (anti-mast cell tryptase) were identified. The number of cells per unit length vein were counted using light microscopy. RESULTS: There were significantly more mast cells and macrophage/monocytes in varicose vein as compared to control. There was a non-significant trend towards more T-lymphocytes in varicose vein. Few neutrophils were present in varicose or normal vein. The distribution of inflammatory cells with respect to the valve was not found to be significant. CONCLUSIONS: Varicose veins display a greater inflammatory cell infiltrate than normal vein. The key role of macrophage/monocytes and mast cells in tissue damage and remodelling should stimulate further research into whether they play a significant role in the development of chronic venous insufficiency.

Venous hypertension, inflammation and valve remodeling.

OBJECTIVES: To identify possible mechanisms for destruction of valves in chronic venous hypertension and the results of treatment with an anti-inflammatory micronized purified flavonoid fraction. MATERIAL AND METHODS: The saphenous vein valves in a rat model of venous hypertension caused by a femoral arterial-venous fistula were studied. Studies included femoral venous pressure, valve morphology, femoral venous reflux and selected molecular inflammatory markers as examined by immunohistochemistry. The effects of treatment with the anti-inflammatory micronized purified flavonoid fraction (S 5628, Servier, 50 and 100 mg/kg/day) were investigated. RESULTS: The femoral venous pressure was elevated close to arterial values for a period of 3 weeks. We then examined the morphology of the veins and selected molecular inflammatory markers were assessed. The results show that in this model venous reflux develops in response to venous hypertension. This can be inhibited by the administration of the anti-inflammatory micronized purified flavonoid fraction (S 5628, Servier, 50 and 100 mg/kg/day). The valve becomes incompetent by a combination of venous dilation and shortening of the valve leaflets. This is not inhibited by treatment with S 5628. The valve leaflets are infiltrated with granulocytes, monocytes and T-lymphocytes, and the endothelial cells express enhanced levels of P-selectin and ICAM-1. Cells in the valves are subject to extensive apoptosis although no enhancement of MMP 2,9 expression could be detected at the three-week time point examined in this study. CONCLUSIONS: These results indicate that in this model chronic elevation of venous pressure is associated with an inflammatory reaction in venous valves, a process that may lead to their dysfunction, reflux, and upstream elevation of venous pressure. These effects are mitigated by the anti-inflammatory micronized purified flavonoid fraction in a dose dependent manner.

Clinical, angiographic, and intravascular ultrasound characteristics of early saphenous vein graft failure.

OBJECTIVES: We sought to examine saphenous vein graft (SVG) lesions that fail within the first year after operation. BACKGROUND: Saphenous vein grafts remain patent for approximately 10 years; however, up to 15% to 20% of SVGs become occluded within the first year. METHODS: We studied 100 patients who underwent percutaneous coronary intervention (PCI) for early (<1 year post-implantation) SVG failure lesions and compared them with a diabetes- and hypercholesterolemia-matched cohort of late SVG failures (>1 year). Coronary angiography and intravascular ultrasound images were analyzed. RESULTS: The majority of patients in both groups were males who presented with unstable angina; 36% were diabetic. Graft ages were 6.0 +/- 2.9 months and 105.4 +/- 50.8 months, respectively. The early SVG failure lesion location was more often ostial or proximal (62% vs. 42%, respectively). Early SVG failures were angiographically smaller than late failures (reference: 2.47 +/- 0.86 mm vs. 3.26 +/- 0.83 mm, p < 0.001) but had similar lesion lengths. Intravascular ultrasound showed that early failure lesions had smaller proximal and distal reference lumen areas (7.3 +/- 6.8 mm2 vs. 10.6 +/- 3.8 mm2, p = 0.026) and greater reference plaque burden than late failures (52.3% vs. 36.1%, p < 0.001). After PCI, 20.6% of early and 30.6% of late failure lesions had creatine kinase-myocardial band (CK-MB) greater than twice normal. CONCLUSIONS: Early SVG failure is mostly proximal or ostial, lesions appear focal, and early SVGs appear smaller than late SVGs. Intravascular ultrasound shows significant reference segment plaque burden, suggesting more severe, diffuse SVG disease.

Matrix metalloproteinase-9 and urokinase-type plasminogen activator in varicose veins.

The purpose of this study was to evaluate the roles of matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA) with regard to varicose veins (VVs). Immunohistochemical staining and ELISA were performed on samples from 73 patients with the following leg VVs: 82 greater saphenous veins (GSV) from the groin (GSV groin), 28 GSV from the ankle (GSV ankle), 85 VVs, and 13 normal GSV groin (control [CR]) obtained during coronary artery bypass surgery. Immunohistochemically, MMP-9 was localized in the smooth muscle cells (SMCs) in the tunica media. The ratio of immunopositive cells of MMP-9 in the GSV groin, VVs, and GSV ankle were significantly higher than that of CR. The ratios of immunopositive cells of uPA and uPA receptor (uPAR) were not significantly different among the groups. uPA and uPAR were found to be positive in a different set of SMCs of the MMP-9-positive cells. An ELISA showed that the amount of uPA in the culture of the GSV groin was significantly higher than that in CR. For the remodeling process, MMP-9 may be produced in the VV wall and degrade elastic lamellae and other extracellular components of the venous wall. uPA may be produced by groin tissue of the GSV and flow downward because of valvular incompetence, activating MMP-9 at VV tissues.

Cyclooxygenase-2 regulates granulocyte-macrophage colony-stimulating factor, but not interleukin-8, production by human vascular cells: role of cAMP.

Vascular smooth muscle is now recognized as an important site of mediator generation under inflammatory conditions. Indeed, the release of leukocyte activators, such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-8, by human arterial smooth muscle cells has recently been demonstrated. However, the potential for venous cells to release GM-CSF has not been addressed. We have shown that human vascular smooth muscle cells express the "inflammatory" form of cyclooxygenase (COX), cyclooxygenase-2 (COX-2), when stimulated with cytokines. In some nonvascular cell types, the COX activity has been shown to regulate the release of GM-CSF and IL-8, although the nature of the isoform responsible was not addressed. We show that human venous smooth muscle cells, like their arterial counterparts, release GM-CSF after stimulation with IL-1beta. Similarly, both cell types released IL-8. Under the same conditions, we found that COX-2 activity suppressed GM-CSF, but not IL-8, release by both types of human vascular cells. Moreover, the prostacyclin mimetic, cicaprost, and the cAMP analogue, dibutyryl cAMP, inhibited GM-CSF release from these cells. These observations suggest that COX-2 activity suppresses GM-CSF release via a cAMP-dependent pathway in human vascular cells and illustrates a novel mechanism by which this enzyme can modulate immune and inflammatory events.

Human saphenous vein allograft bypass grafts: immune response.

Although it has been claimed that allografts of blood vessels might be successful because of minimal immunogenicity, they are subject to frequent and early failure, the cause of which has not been thoroughly investigated. We sought to define the immune response to allograft bypass. In a prospective trial, 40 patients underwent cryopreserved venous allograft bypass. Allograft biopsies were performed at implantation and at allograft explantation in instances of graft failure. Tissues were evaluated in a blinded manner by means of standard histologic examination and paraffin immunohistochemical analysis with monoclonal antibodies against a variety of immune markers. During the 31-month follow-up period, 22 allografts were removed, and 19 were suitable for immunohistochemical study. Of these 19, 6 (32%) had moderate or severe infiltrates, which were evenly distributed throughout the intima, media, and adventitia. Immunohistochemical study of the explants demonstrated all of these infiltrates to be leukocytes (+LCA), which were predominantly activated T lymphocytes (+CD3, CD8, CR3) containing cytotoxic granules (+TIA-1). Macrophages were uncommon (+CD68); B cells (+L26, CD79) and natural killer cells (+CD56) were rare. Immunosuppression was associated with decreased presence of cytotoxic granules (TIA-1). Human venous allografts are immunogenic and prompt a T cell-mediated response. Allografts also fail without strong evidence of rejection, presumably because of local injury, hypercoagulability, or stasis. It may be possible to modify the contribution of rejection to venous allograft failure by means of immunosuppression and to modify the contribution of local hypercoagulability by means of anticoagulation.