Drug-eluting stents for infrainguinal occlusive disease: progress and challenges

Pilot safety study of perivascular injection of tissue-engineered allogeneic aortic endothelial cells in patients undergoing minimally invasive peripheral revascularization

OBJECTIVE

Restenosis is a limitation of endovascular interventions performed in the superficial femoral artery (SFA). Preclinical studies have demonstrated that the perivascular delivery of tissue-engineered allogeneic aortic endothelial cells (PVS-10200) reduced stenosis in porcine models of SFA revascularization. The purpose of this study was to investigate the safety and feasibility of percutaneous PVS-10200 delivery after angioplasty and stenting in the SFA of patients with peripheral artery disease.

METHODS

In this phase I open-label trial, 21 patients (average lesion length of 10.10 ± 2.36 cm and ≥70% stenosis) were treated with PVS-10200: 11 in a low-dose cohort (cohort A) and 10 in a high-dose cohort (cohort B). The primary objective was to demonstrate the safety (incidence of major adverse events) of PVS-10200 within 4 weeks after surgery. Secondary end points included assessments of resting ankle-brachial index (ABI) in the treated leg, Fontaine class, and time to target lesion revascularization (TLR).

RESULTS

No patient had a major adverse event within 4 weeks. One patient required a limb amputation at 30 weeks. At 48 weeks, cohort A and cohort B patients maintained a 37% and 62% increase in ABI compared with baseline, respectively; 70% of cohort A and 78% of cohort B improved by ≥1 Fontaine classification stage, and the TLR rate was 39% for cohort A and 20% for cohort B.

CONCLUSIONS

Percutaneous local delivery of PVS-10200 is a well-tolerated and novel therapeutic approach that may be a suitable treatment for patients after endovascular intervention of the SFA. Larger randomized trials are needed to determine if PVS-10200 can improve ABI and reduce TLR rates.

Ultrasound-guided percutaneous delivery of tissue-engineered endothelial cells to the adventitia of stented arteries controls the response to vascular injury in a porcine model

OBJECTIVE

High restenosis rates are a limitation of peripheral vascular interventions. Previous studies have shown that surgical implantation of a tissue-engineered endothelium onto the adventitia surface of injured vessels regulates vascular repair. In the present study, we developed a particulate formulation of tissue-engineered endothelium and a method to deliver the formulation perivascular to injured blood vessels using a percutaneous, minimally invasive technique.

METHODS

Stainless steel stents were implanted in 18 balloon-injured femoral arteries of nine domestic swine, followed by ultrasound-guided percutaneous perivascular injection of gelatin particles containing cultured allogeneic porcine aortic endothelial cells (PAE). Controls received injections of empty particles (matrix) or no perivascular injection (sham) after stent deployment. Animals were sacrificed after 90 days.

RESULTS

Angiographic analysis revealed a significantly greater lumen diameter in the stented segments of arteries treated with PAE/matrix (4.72 ± 0.12 mm) compared with matrix (4.01 ± 0.20 mm) or sham (4.03 ± 0.16 mm) controls (P < .05). Similarly, histologic analysis revealed that PAE/matrix-treated arteries had the greatest lumen area (20.4 ± 0.7 mm(2); P < .05) compared with controls (16.1 ± 0.9 mm(2) and 17.1 ± 1.0 mm(2) for sham and matrix controls, respectively) and the smallest intimal area (3.3 ± 0.4 mm(2); P < .05) compared with controls (6.2 ± 0.5 mm(2) and 4.4 ± 0.5 mm(2) for sham and matrix controls, respectively). Overall, PAE-treated arteries had a 33% to 50% decrease in percent occlusion (P < .05) compared with controls. Histopathological analysis revealed fewer leukocytes present in the intima in the PAE/matrix group compared with control groups, suggesting that the biological effects were in part due to inhibition of the inflammatory phase of the vascular response to injury.

CONCLUSIONS

Minimally invasive, perivascular delivery of PAE/matrix to stented arteries was performed safely using ultrasound-guided percutaneous injections and significantly decreased stenosis. Application at the time of or subsequent to peripheral interventions may decrease clinical restenosis rates.

[Evolution of stents for the treatment of femoral artery lesions]

Endovascular treatment and stent implantation in the superficial femoral artery have been proposed for over 20 years. However, the first experiments with stainless stents were relatively disappointing. The first improvement consisted in the introduction of nitinol self-expanding stents. This technology allowed an initial improvement of clinical performances, but the first generation of nitinol stents demonstrated a relatively high rate of fractures. Better knowledge of the femoral artery biomechanics and advances in technology allowed to propose a second generation of nitinol stents with improved flexibility, which decreased the rates of fracture. In-stent restenosis related to neointimal hyperplasia has also led to the development of new concepts to improve patency rates after stenting of the femoral artery: drug-eluting stents (coated-stents), biodegradable stents, and covered stents. These technologies will help to treat more complex lesions of the femoral artery in the future, with comparable results to those obtained with femoropopliteal bypasses, but we are still waiting for results of ongoing studies.

A dual-inhibition study on vascular smooth muscle cells with meclofenamic acid and β-irradiation for the prevention of restenosis

PURPOSE

Restenosis is still one of the major limitations after angioplasty. A therapeutic treatment combining β-irradiation and pharmacologic cyclooxygenase-2 inhibition was employed to study the impact on vascular smooth muscle cells (SMCs).

MATERIALS AND METHODS

The effects of meclofenamic acid in combination with yttrium-90 ((90)Y) on cell growth, clonogenic activity, cell migration, and cell cycle distribution of human aortic SMCs were investigated. Treatment was sustained over a period of 4 days and recovery of cells was determined until day 20 after initiation. The hypothesis was that there is no difference between control and treated groups.

RESULTS

A dose-dependent growth inhibition was observed in single and combined treatment groups for meclofenamic acid and β-irradiation. Cumulative radiation dosage of 8 Gy completely inhibited colony formation. This was also observed for 200 μM meclofenamic acid alone or in combination with minor β-irradiation dosages. Results of the migration tests showed also a dose dependency with additive effects of combined therapy. Meclofenamic acid 200 μM alone and with cumulative β-irradiation dosages resulted in an increased G2/M-phase share.

CONCLUSIONS

Incubating human SMCs with meclofenamic acid and (90)Y for a period of 4 d (ie, 1.5 half-life times) resulted in an effective inhibition of smooth muscle cell proliferation, colony formation, and migration.

[New stent developments for peripheral arterial occlusive disease]

Infrainguinal peripheral occlusive disease is increasingly being treated by endovascular techniques. Bare metal stainless steel, self-expanding nitinol stents, drug-eluting and covered stents (stent grafts) are becoming increasingly more important adjuncts to percutaneous translumninal angioplasty in the treatment of peripheral artery disease. In this article the available evidence supporting the use of stents in the femoropopliteal and tibial arteries will be described as well as their limitations. Future stent developments will also be discussed.

Endovascular treatment of peripheral vascular disease

Peripheral arterial disease (PAD) affects about 27 million people in North America and Europe, accounting for up to 413,000 hospitalizations per year with 88,000 hospitalizations involving the lower extremities and 28,000 involving embolectomy or thrombectomy of lower limb arteries. Many patients are asymptomatic and, among symptomatic patients, atypical symptoms are more common than classic claudication. Peripheral arterial disease also correlates strongly with risk of major cardiovascular events, and patients with PAD have a high prevalence of coexistent coronary and cerebrovascular disease. Because the prevalence of PAD increases progressively with age, PAD is a growing clinical problem due to the increasingly aged population in the United States and other developed countries. Until recently, vascular surgical procedures were the only alternative to medical therapy in such patients. Today, endovascular practice, percutaneous transluminal angioplasty with or without stenting, is used far more frequently for all types of lower extremity occlusive lesions, reflecting the continuing advances in imaging techniques, angioplasty equipment, and endovascular expertise. The role of endovascular intervention in the treatment of limb-threatening ischemia is also expanding, and its promise of limb salvage and symptom relief with reduced morbidity and mortality makes percutaneous transluminal angioplasty/stenting an attractive alternative to surgery and, as most endovascular interventions are performed on an outpatient basis, hospital costs are cut considerably. In this monograph we discuss current endovascular intervention for treatment of occlusive PAD, aneurysmal arterial disease, and venous occlusive disease.

Delivery site of perivascular endothelial cell matrices determines control of stenosis in a porcine femoral stent model

PURPOSE

Endothelial cells, grown within gelatin matrices and implanted onto the adventitia of injured vessels, inhibit stenosis in experimental models. To determine if this technology could be adapted for minimally invasive procedures, the authors compared the effects of cells in an implantable sponge to that of an injectable formulation and investigated the importance of delivery site in a stent model.

MATERIALS AND METHODS

Stents were implanted in the femoral arteries of 30 pigs. This was followed by perivascular implantation of sponges or injection of particles containing allogeneic endothelial cells. Controls received acellular matrices or nothing. The effects of delivery site were assessed by injecting cellular matrices into or adjacent to the perivascular tissue or into the neighboring muscle. Animals were sacrificed after 28 days. Pre-sacrifice angiograms and tissue sections were evaluated for stenosis.

RESULTS

Arteries treated with cellular matrices had a 55%-63% decrease in angiographic stenosis (P < .05) and a 38%-43% reduction in histologic stenoses (P < .05) compared to controls. Intimal area was greatest when cellular matrices were delivered into the muscle (6.35 mm(2) +/- 0.95) rather than into or adjacent to the perivascular tissue (4.05 mm(2) +/- 0.56 and 4.73 mm(2) +/- 0.53, respectively; P < .05).

CONCLUSIONS

Perivascular endothelial cell matrices reduced stenosis after stent-induced injury. The effects were not dependent on the formulation but appeared to be dependent on delivery site. Minimally invasive injections of endothelial cell matrices to the adventitia of arteries following peripheral interventions may decrease restenosis rates.

Characterization of primary and restenotic atherosclerotic plaque from the superficial femoral artery: Potential role of Smad3 in regulation of SMC proliferation

OBJECTIVE

To characterize and compare primary and restenotic lesions of the superficial femoral artery and analyze the contribution of TGF-beta/Smad3 signaling to the pathophysiology of peripheral artery occlusive disease.

METHODS AND RESULTS

Immunohistochemical studies were performed on specimens retrieved from the superficial femoral artery of patients undergoing either atherectomy for primary atherosclerotic or recurrent disease after stenting and/or prior angioplasty. Immunohistochemical analysis revealed a significantly higher smooth muscle cell (SMC) content (alpha-actin+) and expression of Smad3 in restenotic lesions while primary lesions contained significantly more leukocytes (CD45+) and macrophages (CD68+). Further studies demonstrated colocalization of Smad3 with alpha-actin and PCNA, suggesting a role for Smad3 in the proliferation observed in restenotic lesions. To confirm a role for Smad3 in SMC proliferation, we both upregulated Smad3 via adenoviral mediated gene transfer (AdSmad3) and inhibited Smad3 through transfection with siRNA in human aortic SMCs, then assessed cell proliferation with tritiated thymidine. Overexpression of Smad3 enhanced whereas inhibition of Smad3 decreased cell proliferation.

CONCLUSION

Differences in cellular composition and cell proliferation in conjunction with the finding that Smad3 is expressed exclusively in restenotic disease suggest that TGF-beta, through Smad3 signaling, may play an essential role in SMC proliferation and the pathophysiology of restenosis in humans.