Differential stimulation of macrophage procoagulant activity by vascular grafts

Short- and midterm results for internal jugular vein extension for short right renal vein kidney transplant

Renal transplantation remains the definitive treatment for end-stage renal disease (ESRD). The shorter renal vein in right donor nephrectomies is associated with higher incidence of technical failure. We present here our experience with autologous internal jugular vein (IJV) conduits to facilitate living-donor transplants. Six patients underwent right, living-donor kidney transplant with simultaneous IJV harvest over a 1-year period. All had bilateral jugular duplex scans preoperatively and were placed on aspirin 81 mg postoperatively. Patient demographics, comorbidities, and laboratories were retrospectively queried. Postoperative follow-up and examination were performed per institutional protocol. The mean age and BMI were 51 ± 4.6 years and 30 ± 1.4 kg/m² , respectively. An average 4.5 ± 0.5 cm of IJV was taken, and anastomosed exsitu, end to end to the renal vein. One patient developed a perinephric hematoma requiring reexploration and another expired during follow-up from septic shock of unknown etiology; there were no harvest site complications or deep vein thrombosis. All had immediate and stable graft function at 3.8 ± 1.7 (range: 0.7-11.3) months follow-up. Mean serum creatinine and estimated glomerular filtration rate were 1.3 ± 0.1 mg/dL and 55 ± 2.4 mL/min/1.73 m² , respectively. Internal jugular vein extension of short right renal veins for kidney transplant is a viable technique for ESRD patients with promising results.

Two-Center German Experience with Aortic Endografting

Purpose:

To report the results of a two-center study of endovascular abdominal aortic aneurysm (AAA) exclusion using a polyester-covered nitinol stent-graft.

Methods:

Candidates were evaluated with arteriography and computed tomography. Criteria for endovascular therapy were a proximal aortic neck > 10 mm in length and < 25 mm in diameter, no bilateral internal iliac artery involvement in the aneurysm, no markedly tortuous common iliac arteries (CIAs) or CIAs < 7 mm in diameter, and no superior mesenteric artery occlusive disease. Patients were treated with the Mialhe Stentor and Vanguard stent-grafts in either tube or bifurcated versions.

Results:

Between August 1994 and November 1996, 149 patients (mean age 67 years, range 49 to 90) were admitted to the study. Overall primary technical success (aneurysm exclusion without endoleak) was 87% (130 patients): 78% (7 patients) for tube grafts and 88% (123 patients) for bifurcated endografts. The rate of local, remote, or systemic complications was 10.8%, with a 30-day mortality rate of 0.7%. During an average 13.5-month follow-up, there were no late deaths. Four of 20 endoleaks sealed spontaneously, 14 were treated with endoluminal techniques, and 2 remain untreated by patient request. Three graft limb thromboses occurred; one was treated surgically, one with lytic therapy, and one was untreated. Secondary patency was 96%.

Conclusions:

Endoluminal repair of infrarenal AAAs using straight or bifurcated grafts is a feasible alternative to conventional surgical repair. Longer follow-up and more experience with refined endograft models will elucidate the durability of this endovascular approach to treating AAAs.

Effects of adsorbed proteins and surface chemistry on foreign body giant cell formation, tumor necrosis factor alpha release and procoagulant activity of monocytes

The adhesion and activation of monocytes and macrophages are thought to affect the foreign body response to implanted medical devices. However, these cells interact with devices indirectly, because of the prior adsorption of proteins. Therefore, we preadsorbed several "model" biomaterial surfaces with proteins and then measured foreign body giant cell (FBGC) formation, tumor necrosis factor alpha (TNFalpha) release, and procoagulant activity. The model surfaces were tissue culture polystyrene (TCPS), untreated polystyrene (PS), and Primaria, whereas the proteins used were albumin, fibronectin, fibrinogen, and immunoglobulin. FBGC formation, TNFalpha release, and procoagulant activity of monocytes were the highest for surfaces preadsorbed with IgG. FBGC formation was lower on surfaces with adsorbed fibrinogen and fibronectin than on uncoated surfaces. TNFalpha release and procoagulant activity of monocytes were similar on surface adsorbed with fibrinogen, fibronectin, or albumin. Monocyte activation was also affected by the surface chemistry of the substrates, because FBGC formation was the highest on PS and the lowest on TCPS. Monocyte procoagulant activity was the highest on Primaria. Adsorbed proteins and surface chemistry were found to have strong effects on FBGC formation, monocyte TNFalpha release, and procoagulant activity in vitro, providing support for the idea that these same variables could affect macrophage-mediated foreign body response to biomaterials in vivo.

Evaluation of tissue-factor production by human endothelial cells incubated with three acrylic bone cements

The effect of three methacrylate-based cements used for the fixation of joint prostheses on tissue-factor production by human umbilical vein endothelial cells was evaluated in vitro. The extracts in the culture medium of the cements were tested after 1-h and 7-day curing. The endothelial cells were incubated with the cement extracts for 4 h, and then the tissue factor was determined in cell lysates with both the recalcification time and enzyme immuno assay. The cements did not induce significant production of tissue factor and, therefore, did not activate the extrinsic pathway of coagulation within the limits of the mechanism considered.

A retrospective study of late outcome in patients with peripheral arterial occlusive disease: an association between prosthetic vascular graft and cancer death?

The authors assessed the relationship between cause of death and treatment modality in patients with peripheral arterial occlusive disease. A total of 273 patients were treated with percutaneous transluminal angioplasty, surgical reconstruction, amputation, or medical therapy. We evaluated the outcome in various patient subgroups divided by treatments with a mean follow-up of 4.9 years. Most patients died because of cardiovascular or cerebrovascular events, and cancer was the second most frequent cause of death. Furthermore, there was a significant difference in cancer deaths between patients who received prosthetic vascular grafts and those with other types of treatment (9.3% vs. 2.8%, p<0.01, odds ratio = 3.34). It is noteworthy that patients with peripheral arterial occlusive disease succumbed to cancer, especially the patients with prosthetic vascular grafts.

Blood and tissue compatibility of modified polyester: thrombosis, inflammation, and healing

Poly(ethylene terephthalate) (PET) has been reported in literature to be moderately inflammatory and thrombogenic. To moderate the inflammatory response, PET fabric was surface modified by either Fluoropassiv fluoropolymer (FC), or an RGD-containing peptide (RGD). Samples were subsequently autoclave sterilized and implanted subcutaneously in Sprague Dawley rats for 2 to 4 weeks. Retrieved samples were evaluated histopathologically for indications of material toxicity and healing. Minimal acute or chronic inflammation was associated with the fabrics after 2 and 4 week implant duration. However, fibroblast proliferation into FC modified fabric (PET/FC) was less than that into unmodified (PET) and RGD modified fabric (PET/RGD) after 4 weeks, suggesting that FC modification of PET may inhibit excessive tissue growth. Additional samples of modified and unmodified fabrics were placed in stainless steel mesh cages, which were then implanted subcutaneously for 4 weeks. Cellular exudate was extracted weekly and cell concentrations within the exudate measured. Total leukocyte count (TLC) (reflective of local inflammation) at 1 week for PET/RGD was greater than that for PET/FC and PET. TLCs after 4 week implant decreased for all sample groups. In a separate experiment, PET vascular grafts surface modified by either FC or RGD were contacted 1 h with blood using the baboon arteriovenous (AV) shunt model of thrombosis in both the presence and absence of heparin. Accumulation of 111In labeled platelets (reflective of thrombus accumulation) upon grafts was less in the presence of heparin (effect significant at p = 1.2 x 10(-6), two-way ANOVA). Accumulation (in the presence of heparin) upon PET/RGD was less (p = 0.19), and upon PET/FC significantly less (p = 0.016) than that upon the unmodified PET control, suggesting that FC modification of PET may inhibit thrombus accumulation.

Leukocyte-polytetrafluoroethylene interaction enhances proliferation of vascular smooth muscle cells via tumor necrosis factor-alpha secretion

Intimal hyperplasia of vascular smooth muscle cells (VSMC) at the venous anastomosis of arteriovenous grafts represents the most common cause of vascular access failure in hemodialysis patients. Upstream release of growth factors from leukocytes activated by adhesion to the graft material may play a role in this lesion. We evaluated the effect of interaction of peripheral blood mononuclear cells (PBMC) with polytetrafluoroethylene (PTFE) on proliferation of VSMC. Vascular smooth muscle cell proliferation was significantly increased by conditioned media from human PBMC incubated with PTFE. Peripheral blood mononuclear cell adhesion to PTFE could not be antagonized by the beta 1 integrin ligand-containing peptide GRGDSP, but was attenuated by EDTA consistent with beta 2 integrin-mediated adhesion. Soluble scavenger receptor ligands at high concentrations had no effect on adhesion to PTFE excluding any contributory role of scavenger receptors in this interaction. Neutralizing antibodies to TNF-alpha significantly attenuated the mitogenic effect of PBMC/PTFE conditioned media and a marked increase in TNF-alpha secretion by PBMC on PTFE was detected by ELISA. These studies demonstrate that PBMC interaction with PTFE can promote proliferation of VSMC via increased production of TNF-alpha and perhaps other cytokines. Leukocyte interaction with PTFE causing enhanced secretion of TNF-alpha and consequent VSMC proliferation may account for the development of venous intimal hyperplasia in hemodialysis patients with arteriovenous grafts.

Blood-biomaterial interactions in a flow system in the presence of bacteria: effect of protein adsorption

An in vitro continuous flow system with whole human blood was used to study blood-biomaterial interactions on a base polyurethane and three modified surfaces in the presence and absence of circulating Staphylococcus epidermidis. We hypothesized that the composition of the protein layer adsorbed on the surface of the biomaterial would influence the response of blood components and bacteria. We examined the test surfaces for adsorption of nine plasma proteins and adsorption profiles differed on the four surfaces. The positively charged surface, UC, adsorbed significantly higher amounts of fibronectin (P < .01), von Willebrand factor (P < .01), and fibrinogen (P < .05) than the other materials. As a consequence of increased adsorption of these adhesive proteins, the adhesion of platelets and bacteria was greater on UC than on any other surface. On the base polyurethane, BC, and the negatively charged surface, UA, protein adsorption was low, and these materials were largely free of adherent blood cells and bacteria. The heparinized surface, UH, adsorbed higher quantities (P < .01) of Hageman factor and high molecular weight kininogen relative to the other surfaces. Platelet adhesion, and surface coagulation were prominent on UC, and may have contributed to increased bacterial adhesion on this surface. In the presence of circulating bacteria, adsorption was generally lower than in the absence of bacteria. The pattern of protein adsorption was largely unaffected by the strain of circulating bacteria, but platelet responses (adhesion and activation) were greater in the presence of slime-producing S. epidermidis as compared to the non-slime-producing strain, suggesting that slime may have a direct activating effect on platelets.

Procoagulant human monocytes mediate tissue factor/factor VIIa-dependent platelet-thrombus formation when exposed to flowing nonanticoagulated human blood

Tissue factor (TF) on monocyte and macrophage surfaces is a nonproteolytic cofactor for factor VIIa (FVIIa)-induced coagulation. Monocyte-derived macrophages in atherosclerotic plaques express TF, which, after plaque disruption or rupture, may complex with FVII/VIIa from the bloodstream, resulting in activation of extrinsic coagulation. We studied the effect of TF expression on human monocytes on arterial thrombus formation in a model system of thrombogenesis. Thawed, cryopreserved human monocytes adherent to plastic coverslips were stimulated with lipopolysaccharide (0.5 microgram/mL) to express TF and subsequently exposed to flowing nonanticoagulated human blood in a parallel-plate perfusion chamber. The wall shear rate at the cell surface was 650 seconds-1, corresponding to that of average-sized coronary arteries. The stimulated monocytes elicited pronounced fibrin deposition and platelet-thrombus formation. The platelet-thrombus volume was as large as that triggered by human type III collagen fibrils under similar experimental conditions. In contrast, the monocytes elicited much more fibrin deposition than the collagen surface. However, inclusion of an anti-TF monoclonal antibody that blocks the complexation of FVII/FVIIa with TF virtually abolished the fibrin deposition (P < .03) and reduced platelet-thrombus formation by more than 70% (P < .04). Thus, arterial thrombus formation induced by stimulated monocytes was almost completely blocked by the anti-TF antibody, suggesting that inhibition of TF/FVIIa complex formation on monocytes and macrophages at sites of plaque rupture or after percutaneous transluminal coronary angioplasty procedures may reduce intravascular thrombotic complications.

Transplantation of autologous tissue fragments into an e-PTFE graft with long fibrils

An expanded polytetrafluoroethylene (e-PTFE) graft with long fibrils transplanted with bone marrow showed rapid and uniform neointima formation in a dog study. The e-PTFE grafts (fibril length, 90 microns; 6 mm internal diameter; length, 6-8 cm) transplanted with autologous bone marrow were implanted in the abdominal aortae of 10 dogs and retrieved at 3 weeks and 3 months after implantation. Control e-PTFE grafts without bone marrow treatment were also implanted in the same manner in 8 dogs. Macroscopically the treated graft wall appeared red in color; however, there was no thrombus deposition on the surface. Light microscopic observation revealed that the treated grafts were completely lined with endothelial cells at 3 weeks. The neointima was uniform without intimal hyperplasia at the anastomotic sites. Inside the graft wall many capillary blood vessels were observed. At 3 months moderate intimal hyperplasia throughout the graft with complete endothelialization was observed. In the control grafts, endothelialization was observed at the anastomotic sites; however, half of the other areas were covered with a fibrin layer devoid of endothelial cells even in the 3-month grafts. These results indicated that neointima formation was effectively accelerated with the autologous bone marrow transplantation, but moderate intimal hyperplasia throughout the graft was inevitable in e-PTFE grafts even after complete endothelialization.