External-beam radiation therapy for improved dialysis access patency: feasibility and early safety.

Rectenwald, J. E., Pretus, H. A., Seeger, J. M., Huber, T. S., Mendenhall, N. P., Zlotecki, R. A., Palta, J. R., Li, Z. F., Hook, S. Y., Sarac, T. P., Welborn, M. B., Klingman, N. V., Abouhamze, Z. S. and Ozaki, C. K. External-Beam Radiation Therapy for Improved Dialysis Access Patency: Feasibility and Early Safety. Radiat. Res. 156, 53-60 (2001).Prosthetic dialysis access grafts fail secondary to neointimal hyperplasia at the venous anastomosis. We hypothesized that postoperative single-fraction external-beam radiation therapy to the venous anastomosis of hemodialysis grafts can be used safely in an effort to improve access patency. Dogs (n = 8) underwent placement of expanded polytetrafluoroethylene grafts from the right carotid artery to the left jugular vein. Five dogs received single-fraction external-beam photon irradiation (8 Gy) to the venous anastomosis after surgery. Controls were not irradiated. Shunt angiograms were completed 3 and 6 months postoperatively. Anastomoses, mid-graft, and the surrounding tissues were analyzed. Immunohistochemistry for smooth muscle cell alpha-actin, proliferating cellular nuclear antigen (PCNA), and apoptosis was performed. Incisions healed well, though all animals developed wound seromas. One control suffered graft thrombosis 4 months postoperatively. Angiography/histology confirmed severe neointimal hyperplasia at the venous anastomosis. The remaining seven dogs developed similar amounts of neointimal hyperplasia. PCNA studies showed no accelerated fibroproliferative response at irradiated anastomoses compared to controls. Skin incisions and soft tissues over irradiated anastomoses revealed no radiation-induced changes or increase in apoptosis. Thus we conclude that postoperative single-fraction external-beam irradiation of the venous anastomosis of a prosthetic arteriovenous graft that mimics the situation in humans is feasible and safe with regard to early wound healing.

Hydrophilic surface modification of metallic endoluminal stents.

PURPOSE: Stainless steel endovascular stents are inherently thrombogenic so that thrombus accumulates on these devices, leading to acute vessel occlusion. A potential solution to this problem is stent surface modification with hydrophilic polymers, which might limit platelet adhesion and reactivity. METHODS: N-vinylpyrrolidone (NVP) and potassium sulfopropyl acrylate (KSPA) hydrophilic monomers were gamma graft polymerized onto 1 cm2 stainless steel slabs and 4 mm Palmaz stainless steel stents. Surface characteristics of modified and plain stainless steel stents were then investigated with contact angle and x-ray photoelectron spectroscopy measurements, and in vitro and in vivo platelet reactivity was assessed as 111Indium platelet accumulation expressed as counts/min/cm2. RESULTS: Surface modification of stainless steel slabs and stents with both NVP and KSPA hydrophilic polymers significantly reduced in vitro platelet adhesion (plain = 2249 +/- 723 counts/min/cm2, NVP = 428 +/- 156 counts/min/cm2, KSPA = 958 +/- 223 counts/min/cm2) and in vivo platelet accumulation after 1 hour of blood flow exposure (plain = 1407 +/- 796 counts/min/cm2, NVP = 426 +/- 175 counts/min/cm2, KSPA = 399 +/- 124 counts/min/cm2. In addition, platelet accumulation on modified stents indexed to plain stents was lowest in KSPA-modified stents (NVP = 79.3% +/- 31.7% of plain, KSPA = 51.2% +/- 36.2% of plain). Surface analysis confirmed surface grafting with both monomers, and SEM documented smoothing of the irregular surfaces of the stainless steel stents after grafting. CONCLUSION: Hydrophilic polymer surface modification of stainless steel stents decreases initial stent surface platelet accumulation, which may decrease the risk of vessel thrombosis associated with the use of these devices.

The relationship between carotid plaque composition, plaque morphology, and neurologic symptoms.

Variations in plaque composition could make carotid artery plaques prone to ulceration, subintimal hemorrhage, plaque progression, or embolization and, thus, increase the risk of ipsilateral ischemic neurologic events. Seventy-eight carotid endarterectomy specimens from 74 patients (38 symptomatic and 36 asymptomatic) were analyzed. Prior to analysis, 43 of the 78 plaques were divided into sections based on disease severity and examined by light microscopy for surface ulceration and subintimal hemorrhage. Extracted lipid, cholesterol, collagen, and calcium content were determined in all 78 plaques and compared to clinical presentation and/or morphologic observations. Plaques removed from symptomatic patients contained more extracted lipid and cholesterol than those from asymptomatic patients. In addition, compared to the remainder of the plaque, the most stenotic portion of the plaque contained more cholesterol, more calcium, and less collagen. Finally, irrespective of clinical presentation, plaque sections found to have surface ulceration and subintimal hemorrhage contained more cholesterol and less collagen than plaques without these changes. Lipid-laden plaques with low levels of collagen are associated with plaque ulceration, subintimal hemorrhage, and ischemic neurologic symptoms. This suggests that plaque composition may be an important factor in the pathophysiology of carotid atherosclerosis.

Glutamine preserves gut glutathione levels during intestinal ischemia/reperfusion.

Intestinal ischemia/reperfusion (I/R) causes formation of reactive oxygen intermediates (ROI) which lead to mucosal cell injury. Glutathione (GSH), an ROI scavenger, protects tissues from ROI-mediated cell injury. Since GSH biosynthesis is partially dependent on glutamine (Gln) levels, we tested the hypothesis that intravenous Gln infusion will assist in maintaining mucosal cell GSH levels and decrease membrane lipid peroxidation during intestinal I/R. The external jugular vein of male Sprague-Dawley rats was cannulated and infused with normal saline (NS) at 2 cc/hr. After 3 days, matched pairs of rats received either NS alone or NS+ 3% Gln for an additional 24 hr. Next, mucosal GSH levels were measured after a sham I/R in 6 rats and after either 30 or 60 min of ischemia/60 min of reperfusion in a group of 8 and 12 rats, respectively. Finally, conjugated diene (CD), a byproduct of membrane lipid peroxidation, was measured following 60 min of ischemia/60 min of reperfusion in a separate group of 12 rats. Control rats had the highest GSH levels and there was no difference between NS vs NS + 3% Gln rats (2.50 +/- 0.48 vs 2.50 +/- 0.43, P = NS). With 30 and 60 min of ischemia/60 min of reperfusion, GSH levels were significantly lower in NS-infused rats compared to those in NS + 3% Gln-infused rats (30 min: 1.54 +/- 0.14 vs 1.80 +/- 0.16, P < 0.05; 60 min: 1.27 +/- 0.15 vs 1.52 +/- 0.20, P < 0.04). In addition, CD levels were lower in NS + 3% Gln-infused rats compared to those in NS alone-infused rats (5.58 +/- 0.87 vs 7.94 +/- 0.55, P < 0.04). In conclusion, Gln supplementation partially maintains gut GSH levels during bowel I/R, which in turn lessens I/R-induced cell membrane lipid peroxidation.

In vitro laser recanalization of chronically occluded prosthetic grafts.

Polytetrafluoroethylene (PTFE) and Dacron grafts were implanted in canine femoral and carotid arteries using PTFE and Prolene suture, respectively. Arteries containing occluded grafts were explanted and laser recanalization was attempted in vitro. Laser recanalization was successful in 78% of PTFE grafts compared to 30% of Dacron grafts. Recanalization was complete (residual stenosis less than 5%) in opened PTFE grafts, whereas residual stenosis averaged 60% in recanalized Dacron grafts. PTFE graft/PTFE suture anastomotic tensile strength was unchanged after recanalization, while Dacron graft/Prolene suture anastomotic tensile strength decreased significantly. In addition, anastomotic bursting pressure was significantly higher for lased PTFE grafts with PTFE sutures (300 mg Hg) compared to lased Dacron grafts with Prolene sutures (70 mm Hg). Chronically occluded PTFE grafts with PTFE suture can be safely and effectively opened by laser recanalization. In contrast, attempted laser recanalization of Dacron grafts sutured with Prolene suture is seldom successful, significantly weakens the graft artery anastomosis, and should be avoided.

Lipid risk factors in patients requiring arterial reconstruction.

Progressive peripheral atherosclerosis commonly leads to failure of a bypass graft. Lowering blood cholesterol retards coronary atherosclerosis and similar treatment might limit peripheral atherosclerosis. To identify lipid risk factors for peripheral atherosclerosis, 144 patients with peripheral atherosclerosis (98 with severe disease and 46 with stable claudication) and 61 age-matched control subjects were studied. Fasting lipid (cholesterol and triglycerides) and lipoprotein (high-density lipoprotein [HDL], low-density lipoprotein [LDL], and very-low-density lipoprotein [VLDL] cholesterol [C]) levels were measured. The incidence of hypertension and diabetes mellitus, amount of previous tobacco use, and location and severity of the peripheral atherosclerosis were also determined. Patients with peripheral atherosclerosis had higher VLDL-C and lower HDL-C levels than controls had, but serum cholesterol and plasma LDL-C levels were similar. Patients with peripheral atherosclerosis also had a higher incidence of diabetes mellitus and hypertension. Predictors of peripheral atherosclerosis by regression analysis were diabetes mellitus, low HDL-C levels, and tobacco use, with diabetes mellitus being the strongest variable. Peripheral atherosclerosis below the inguinal ligament was strongly predicted by low HDL-C and increased VLDL-C levels but not by increased cholesterol or LDL-C levels. Thus lipid risk factors for peripheral atherosclerosis are different, and attempts at limiting late graft failure by lowering lipid levels should be directed toward these lipoproteins.

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 less than 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.

Laser radiation in the treatment of prosthetic graft stenosis. A preliminary study of prosthesis damage by laser energy.

Transluminal laser recanalization is potentially an important new treatment of anastomotic intimal hyperplasia. However, currently used grafts or sutures may be damaged by laser radiation at power and energy levels required for plaque removal. To investigate this problem, two commonly used grafts (Dacron and polytetrafluoroethylene [PTFE]) and two types of vascular suture (polypropylene and PTFE) were exposed to argon laser radiation in vitro. Dacron and PTFE grafts recovered from amputations were also studied to determine whether graft "healing" affected graft resistance to laser damage. Power and energy levels required to perforate atherosclerotic superficial femoral arteries were determined for comparison. PTFE grafts were significantly (1.5 to 7 times) more resistant to perforation by laser energy than atherosclerotic arteries under all conditions. In contrast, Dacron grafts perforated at power and energy levels one half to one third of that required for vaporization of atherosclerotic plaque. PTFE sutures remained intact at power and energy levels above the levels that perforated atherosclerotic arteries, whereas polypropylene sutures were destroyed by very low levels of power and energy (0.5 joules at 0.5 watts). Because of the variable levels of power and energy that damage different types of prosthetic grafts and sutures, laser angioplasty should only be investigated clinically as a therapy for anastomotic intimal hyperplasia when PTFE grafts and sutures are present.

The relationship between carotid plaque composition and neurologic symptoms.

Variations in plaque composition, particularly an increased lipid concentration, could make carotid plaques unstable and prone to embolization. To investigate this hypothesis, 35 carotid bifurcation plaques from 31 patients undergoing carotid endarterectomy (20 symptomatic, 11 asymptomatic) were prospectively analyzed. Plaque total lipid, cholesterol, collagen, and Ca2+ content were determined, and the plaque collagen was fractionated into pepsin-soluble collagen (PSC) (indicative of less crosslinked, more recently synthesized collagen) and pepsin-insoluble collagen. Preoperative serum lipid and plasma lipoprotein levels were also obtained in all patients. Results revealed that plaques removed from symptomatic patients contained significantly more total lipid and cholesterol (P less than 0.001) than those removed from asymptomatic patients. There was also an increased amount of pepsin-soluble collagen in symptomatic plaques, potentially indicating increased metabolic activity (P less than 0.05). In addition, mean plasma low-density lipoprotein cholesterol was higher in symptomatic patients than in asymptomatic patients (P less than 0.05). Since lipid-laden plaques can potentially be identified by B-mode ultrasound, it may be important to remove these plaques in asymptomatic patients or, alternatively, to attempt to lower the plaque cholesterol by lipid-lowering maneuvers.

Improved endothelial cell seeding with cultured cells and fibronectin-coated grafts.

A possible approach to the low seeding efficiency of endothelial cells into prosthetic grafts is to increase the number of cells to be seeded in cell culture and improve seeding efficiency by graft precoating with fibronectin. The effect of cell culture on cell adhesion is unknown, however, and fibronectin also binds fibrin, which may increase the thrombogenicity of the graft luminal surface. To investigate these questions, freshly harvested canine jugular vein endothelial cells from six animals and similar cells harvested from six primary and eight secondary cell cultures were labeled with 111Indium and seeded into 5 cm, 4 mm PTFE grafts coated with fibronectin, using similar uncoated PTFE grafts as controls. Platelet accumulation and distribution on six similar coated and uncoated grafts placed in canine carotid, external jugular arterial venous shunts for 2 hr were also determined using autogenous 111Indium-labeled platelets. Significant differences between group means were determined using the paired Student's t test. Results reveal that seeding efficiency is significantly better in all groups of coated grafts compared to uncoated grafts (P less than 0.01). Cells derived from cell culture also had significantly higher seeding efficiencies than freshly harvested cells when seeded into coated grafts (P less than 0.05) and tended to have higher seeding efficiencies than harvested cells when seeded into uncoated grafts (P = 0.53). Fibronectin coating increased mean platelet accumulation on the entire graft luminal surface, but not to a statistically significant degree (P greater than 0.1). Whether this increased seeding efficiency will improve graft endothelialization remains to be investigated.