Porous balloon catheters for local delivery: assessment of vascular damage in a rabbit iliac angioplasty model

Macromolecular approaches to prevent thrombosis and intimal hyperplasia following percutaneous coronary intervention

Cardiovascular disease remains one of the largest contributors to death worldwide. Improvements in cardiovascular technology leading to the current generation of drug-eluting stents, bioresorbable stents, and drug-eluting balloons, coupled with advances in antirestenotic therapeutics developed by pharmaceutical community, have had a profound impact on quality of life and longevity. However, these procedures and devices contribute to both short- and long-term complications. Thus, room for improvement and development of new, alternative strategies exists. Two major approaches have been investigated to improve outcomes following percutaneous coronary intervention including perivascular delivery and luminal paving. For both approaches, polymers play a major role as controlled research vehicles, carriers for cells, and antithrombotic coatings. With improvements in catheter delivery devices and increases in our understanding of the biology of healthy and diseased vessels, the time is ripe for development of novel macromolecular coatings that can protect the vessel lumen following balloon angioplasty and promote healthy vascular healing.

Water soluble polymer films for intravascular drug delivery of antithrombotic biomolecules

Over the past 10 years, the number of percutaneous coronary intervention (PCI) procedures performed in the United States has increased by 33%; however, restenosis, which inhibits complete functional recovery of the vessel wall, remains a complication of this procedure. To traverse the complications associated with PCI, the investigation of therapeutic delivery has become an integral topic in modern research. One such therapeutic, a mimic of the proteoglycan decorin, termed DS-SILY, can mask exposed collagen and thereby effectively decrease platelet activation, has recently been developed by our lab. Drawing inspiration from coating technologies developed by the pharmaceutical industry, a fast-dissolving polymer film has been developed to deliver active therapeutic agents from a balloon catheter during PCI. This research investigates the release of DS-SILY from fast-dissolving polymer films composed of poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG). Thin, uniform polymer films were produced via spin coating technique. The dissolution speed of the polymer films was found to be dependent on the concentration of polymer solution, where at least 65% of the films were shown to dissolve into nanometer sized polymer fragments within 2 min. DS-SILY, up to 6.26 μg/cm(2), was loaded into the films and functional release of the mimic was demonstrated by its successful binding to collagen upon release. Furthermore, DS-SILY released from films resulted in increased platelet inhibition. These results indicate that use of fast-dissolving polymer films allow for the successful release of biomolecules and further investigation of their use for localized drug delivery during PCI procedures is warranted.

Nanotechnology in interventional cardiology

High-grade atherosclerotic stenoses are reduced to zero or minimal residual stenosis grades by a single or a series of balloon angioplasties. Currently, stents are implanted to prevent immediate vascular recoil and elution of an antimitotic drug from the stent struts minimizes restenosis. An unwanted side-effect of this drug elution is delayed re-endothelialization which requires treatment with two anti-platelet drugs, in many cases for a minimum of 1 year to prevent acute in-stent thrombosis. Advances in stent design and drug elution technology, now in its fourth generation, have not abated this issue. Nanotechnology-based local drug delivery has the potential to achieve restenosis prevention while not impeding endothelial healing. Molecularly targeted drugs can be aimed to specifically bind to epitopes in the injured media and adventitia. Thus, endothelial healing may progress unhindered. To prevent restenosis, this technology may be used with bare metal or biodegradable stents. In this article novel nanoparticulate agents will be compared regarding their potential to deliver drugs to molecular targets within the vascular wall. Potential molecular targets, targeting mechanisms, drug-delivery propensities, and biocompatibility will be reviewed.

Efficiency of drug delivery to the coronary arteries in swine is dependent on the route of administration: assessment of luminal, intimal, and adventitial coronary artery and venous delivery methods

PURPOSE

To compare the efficiency of five different drug delivery methods to the coronary artery in swine.

MATERIALS AND METHODS

A nanoparticle-albumin-bound, nonradioactive isotopic marker was administered within the left anterior descending coronary artery (LAD) through a microinfusion catheter (MIC: adventitial, n = 8, and luminal, n = 4), a porous drug infusion balloon (DIB: intimal, n = 4), and a straight catheter (SC: luminal, n = 2) and within the superior vena cava (SC: intravenous, luminal, n = 2). The distribution of the marker in heart, lung, liver, kidney, muscle, blood, urine, and bile was determined 68-84 minutes after delivery. The heart was sectioned into six axial slices and each slice divided into four quadrants. The marker content was assayed by neutron bombardment and the total counts of disintegrations per minute (DPM) expressed as a percentage of the control for each device delivery control.

RESULTS

After luminal delivery with the nonactuated MIC (MIC-NA) or intimal delivery with the DIB, 0.17% ± 0.07 and 0.39% ± 0.09, respectively, less than 0.39% of the total marker was detected in the heart. After adventitial delivery with the actuated MIC (MIC-A), 63.1% ± 9.9 of the total marker was detected in the heart. Marker was only detected in quadrants containing the coronary LAD, with the highest level in the middle slice and lower marker levels in consecutive proximal and distal heart slices. The nonactuated MIC-NA and DIB drug infusion balloon patterns of marker distribution were similar to those of actuated MIC-A, although with reduced levels. These delivery methods were also associated with considerably more marker detected in the lungs and liver: at least 22% compared with 1.34% ± 1.34 for the actuated MIC-A There was one delivery failure with the actuated MIC.

CONCLUSIONS

Catheter-based adventitial delivery with the MIC-A represents a more efficient delivery method for retention of vascular therapeutics.

Local administration of NF-kappa B decoy oligonucleotides to prevent restenosis after balloon angioplasty: an experimental study in New Zealand white rabbits

PURPOSE

To evaluate the efficacy of NF-kappa B oligonucleotides (ODN) administered by local administration with the channeled balloon catheter to prevent restenosis after balloon angioplasty in restenotic iliac arteries of New Zealand white rabbits.

MATERIALS AND METHODS

In vitro, 8000 rabbit vascular smooth muscle cells (rVSMC) where transfected with a liposomal carrier (TfX50) with 100 ng of decoy and scrambled ODN. Inhibition of proliferation was measured using a MTT assay after 24 hours in comparison to control. In vivo, 22 male New Zealand White rabbits were fed a 1% cholesterol diet and received denudation of both common iliac arteries with a 3 mm balloon catheter to induce an arterial stenosis. Four weeks after stenosis induction, local application of NF-kappa B in two different concentrations (1 mug: n = 14; 10 mug: n = 8) was performed randomly on one common iliac artery. Scrambled oligonucleotides without specific binding capacities were injected into the contralateral side. The channeled balloon catheter allows simultaneous balloon dilation (8 atm) of the stenosis and local application of a drug solution (2 atm). Four weeks after local drug delivery the animals were killed and the vessels were excised and computerized morphometric measurements were performed.

RESULTS

NF-kappa B decoy ODN but not scrambled ODN inhibited proliferation of rVSMC in vitro. Following local ODN application in the animals, no acute vascular complications were seen. NF-kappa B ODN resulted in a statistically non significant reduction of neointimal area compared to the control group. The neointimal area was 0.97 mm(2) using 1 mug NF-kappa B ODN compared to 0.98 mm(2) in the control group. The higher dose resulted in a neointimal area of 0.97 mm(2) compared to 1.07 mm(2) at the control side.

CONCLUSIONS

Local drug delivery of NF-kappa B ODN using the "channeled balloon" catheter could not reduce neointimal hyperplasia in stenostic rabbit iliac arteries. Application modalities have to be improved to enhance the effect of the local application to prevent restenosis after balloon angioplasty.

Effects of altering infusion parameters on intimal hyperplasia following local catheter-based delivery into the rabbit iliac artery

BACKGROUND

Efficient local gene or drug therapy requires optimized application modalities to avoid vessel damage, which might lead to increased neointimal hyperplasia. Aim of the study was to evaluate different application parameters for local delivery using the channeled balloon catheter in order to minimize vessel trauma induced by local application.

METHODS AND RESULTS

Sixty cholesterol fed rabbits were randomly enrolled into twelve groups of different local application parameters: group I, application pressure 2atm/application volume 1ml physiologic saline; group II, 2atm/2ml; group III, 2atm/5ml; group IV, 4atm/1ml; group V, 4atm/2ml; group VI, 4atm/5ml. The other six groups received Ringer's solution instead of saline. Administration of the solution was randomly performed in one iliac artery using the channeled balloon catheter with simultaneous balloon angioplasty (8atm). The contralateral iliac artery served as a control and was treated with balloon angioplasty only. Four weeks after local therapy, calibrated angiography was performed; the animals were sacrificed, vessel segments were excised and quantitative morphometric measurements were obtained. In none of the animals acute complications, e.g. dissection, thrombosis or perforation of the vessel, was noted. Up to an application pressure of 4atm and an application volume of 5ml, no significant neointima formation was seen compared to arteries which underwent angioplasty only. Additionally, no significant differences between saline and Ringer's solution were detected. In a multivariate analysis, neither application pressure nor volume were found to have a statistically significant influence on the amount of neointimal hyperplasia.

CONCLUSIONS

Local application of "drugs" using the channeled balloon catheter is safe and feasible without significant induction of neointimal hyperplasia compared to angioplasty, if an application volume of 5ml and a pressure of 4atm is not exceeded.

Comparative Trial of Local Pharmacotherapy withl-Arginine, r-Hirudin, and Molsidomine to Reduce Restenosis after Balloon Angioplasty of Stenotic Rabbit Iliac Arteries

PURPOSE

To determine if local application of L-arginine, r-hirudin, or molsidomine significantly reduces restenosis after balloon angioplasty in stenotic rabbit iliac arteries.

MATERIALS AND METHODS

Thirty-one male cholesterol-fed New Zealand white rabbits underwent balloon dilation of both common iliac arteries to induce arterial stenosis. Four weeks later, one stenotic iliac artery was simultaneously dilated and received local application of L-arginine (210 mg/mL, n = 7), r-hirudin (0.5 mg/mL, n = 8), or molsidomine (0.2 mg/mL, n = 8) with a channeled balloon catheter. On the contralateral side, 0.9% saline was injected as a control. In eight sham animals, saline was applied to one iliac artery and balloon dilation to only the contralateral artery. Six weeks after local treatment, vessels were harvested, and computerized morphometric and immunohistologic analyses were performed.

RESULTS

Application of drugs resulted in a significant reduction of neointimal area as follows: 53% with L-arginine (1.01 mm(2) vs. 2.17 mm(2), P <.05), 43% with molsidomine (1.04 mm(2) vs. 1.89 mm(2), P <.05), and 20% with r-hirudin (1.79 mm(2) vs. 2.24 mm(2), P <.05). Infusion of saline led to a significant increase (50%, 1.21 mm(2) vs. 1.93 mm(2), P <.05) in neointimal area compared with balloon dilation alone. Immunohistologic findings showed a significant reduction of macrophages (5.0% vs. 10.2%, P <.05) and proliferating cells (6.2% vs. 10.6%, P <.05) in the neointima after local application of L-arginine.

CONCLUSION

Reduction of neointimal area was significant for L-arginine and molsidomine but not for r-hirudin. Saline infusion caused significant arterial trauma, resulting in additional neointimal proliferation.

Local intra-arterial drug delivery for prevention of restenosis: comparison of the efficiency of delivery of different radiopharmaceuticals through a porous catheter

RATIONALE AND OBJECTIVES

Several radiopharmaceuticals were administered through a porous balloon catheter to compare the absolute amount deposited and the retention in the vessel wall. The reported efficiency of local drug delivery ranges from 0.001% to 0.1%, with poor retention after 24 hours.

METHODS

An endothelin derivative (n = 6), pertechnetate (n = 6), hexamethylpropylene amineoxime (HMPAO) (n = 5), ethyl cysteinate dimer (ECD) (n = 5), and tin colloid (n = 5) were labeled with 185 MBq/mL 99m-technetium. After balloon denudation of the infrarenal aorta in 27 New Zealand White rabbits, 100 microL of each agent was administered through a porous balloon at a pressure of 4 bar. Dynamic and static whole-body scintigrams were obtained for 24 hours. The infrarenal aorta was excised and the activity calculated in a gamma counter.

RESULTS

Apart from their retention in the region of local administration, the radiopharmaceuticals showed different distribution patterns. The highest regional tracer retention was observed with HMPAO. After administration of HMPAO, a significant difference between regional (vessel wall plus surrounding tissue: 14.5% of injected dose [ID]/24 hours) and local (vessel wall: 1.8% ID/24 hours) delivery was found. In contrast, ECD was eliminated quickly (local retention after 24 hours = 0% ID). The retention efficiencies were HMPAO > endothelin derivative > tin colloid > pertechnetate > ECD.

CONCLUSIONS

The different physicochemical and pharmacokinetic properties of radiopharmaceuticals resulted in different delivery efficiencies after local application.

Local photodynamic therapy with Zn(II)-phthalocyanine in an experimental model of intimal hyperplasia

Photodynamic therapy (PDT) appears to be a novel promising modality to prevent intimal hyperplasia (IH) and restenosis after angioplasty. Local PDT, that consists of local delivery of photosensitizing agents followed by intraluminal local irradiation, represents a recent advancement. This methodology requires optimization in order to achieve the best prompt outcome especially in terms of pharmacokinetics of the photosensitizing agent. We studied the pharmacokinetic properties by using the photosensitizing agent Zn(II)-phthalocyanine (ZnPc), locally released by a channeled balloon. The efficacy of local PDT in reducing IH was evaluated in an experimental rabbit model of arterial injury. The maximum accumulation of ZnPc was found at 30 min: the injured portion of the artery gave a ZnPc recovery of 1.18 micromol/mg, as compared with undetectable amounts of ZnPc in the non injured arteries; within 90 min after the local delivery, clearance of the agent was almost complete. Local PDT produced an effective reduction of IH in our vascular injury model: at 7, 14, 21 and 28 days IH and intima/media ratio (IMR) was significantly reduced as compared with balloon injured arteries. The local delivery of ZnPc showed favourable pharmacokinetic properties, that allow the performance of PDT immediately after the vascular injury. Local PDT performed in these conditions represents a promising approach to prevent IH after balloon injury. Further studies are needed to better clarify the biological response of the injured arterial wall to local PDT.

Heparin infusion prior to stenting (HIPS) trial: final results of a prospective, randomized, controlled trial evaluating the effects of local vascular delivery on intimal hyperplasia

BACKGROUND

Local delivery of pharmacologic agents or genes at the site of angioplasty is a promising approach to reduce restenosis. However, there are unresolved questions concerning the safety and feasibility of local vascular delivery in clinical practice as well as the efficacy of delivered drug. To this end, the safety, feasibility, and efficacy of local delivery of heparin were evaluated in the Heparin Infusion Prior to Stenting (HIPS) trial.

METHODS AND RESULTS

A total of 179 patients were enrolled in this multicenter, randomized, prospective, core laboratory-evaluated trial. Patients were randomly assigned to 5000 U heparin either administered to the coronary artery lumen or infused into the arterial wall immediately after angioplasty and before stent placement. End points included procedural events and clinical, angiographic, and intravascular ultrasound events at 6 months. Patient groups were evenly matched. There was no difference in the incidence of arterial injury, defined as an increase in arterial dissection, acute closure, or decrease in Thrombolysis In Myocardial Infarction grade blood flow in the group receiving local delivery. At follow-up there was no difference in the major adverse event rate between intraluminal (22.7%) and local groups (24.7%). There was no difference between intraluminal and local therapy in the angiographic in-stent restenosis rate (12.5%, 12.7%) or the in-stent volumetric analysis by intravascular ultrasound (IVUS) (37.19 +/- 20. 86 mm(3) vs 43.79 +/- 25.52 mm(3)).

CONCLUSIONS

Local delivery of 5000 U heparin into the arterial wall before stent implantation is safe and feasible. There was not a favorable effect of locally delivered heparin on clinical, angiographic, or IVUS end points of restenosis. The use of IVUS to measure volume of intimal hyperplasia in a multicenter, core laboratory-controlled trial is feasible.

Vascular remodeling and the local delivery of cytochalasin B after coronary angioplasty in humans

OBJECTIVES

This study sought to determine the safety, feasibility and outcome of local delivery of cytochalasin B at the site of coronary angioplasty.

BACKGROUND

Previous failures in the pharmacologic prevention of restenosis may have been related to inadequate dosing at the angioplasty site as a result of systemic drug administration. Alternatively, although previous experimental protocols have typically targeted control of excess tissue growth (intimal hyperplasia), it now appears that overall arterial constriction (vascular remodeling) is the major contributor to late lumen loss. Cytochalasin B inhibits the polymerization of actin and has proved to be a potent inhibitor of vascular remodeling in animal models.

METHODS

In this phase I, multicenter, randomized, controlled trial, cytochalasin B (or matching placebo) was administered to the site of a successful balloon angioplasty using a microporous local delivery infusion balloon.

RESULTS

The rate of drug delivery at a constant infusion pressure varied significantly from patient to patient (range 1.7 to 20.2 ml/min), perhaps related to a variable constricting effect of the atherosclerotic plaque on the infusion balloon. The minimal stenosis diameter after the procedure was slightly better in the active drug group (1.86 +/- 0.44 vs. 1.49 +/- 0.63 mm, p < 0.03), but this difference was not seen at four to six weeks. Although the study was not powered for clinical outcomes (n = 43), the combined end point (death, nonfatal infarction or repeat revascularization) was encountered in 20% of the patients receiving cytochalasin B and in 38% of the patients receiving placebo. Clinical restenosis occurred in 18% of the treatment group and 22% of the placebo group. There were no significant differences between groups in biochemical or electrocardiographic variables.

CONCLUSIONS

Cytochalasin B can be safely administered by local delivery after successful coronary angioplasty and warrants further study of its efficacy in reducing restenosis.

Local administration of ramiprilat is less effective than oral ramipril in preventing restenosis after balloon angioplasty in an animal model

PURPOSE

To test the hypothesis that local administration of angiotensin converting enzyme (ACE) inhibitor via a microporous balloon catheter would be more effective than oral administration of ACE inhibitor in preventing neointima formation after balloon angioplasty.

MATERIALS AND METHODS

Neointima formation was induced by balloon denudation followed by 0.5% cholesterol diet in 29 New Zealand White rabbits. Directly after denudation, local administration of 1.8 mg of ramiprilat (n = 7) or saline (n = 7) with a microporous balloon catheter at a pressure of 3 atm was performed. Both groups additionally received ramipril orally (1 mg/d). Seven animals were treated exclusively with oral ramipril. The control group was fed a 0.5% cholesterol diet and given no medication (n = 8). Six weeks after intervention, the animals were killed and morphometric and immunohistologic analyses were performed.

RESULTS

Oral administration of ramipril resulted in a significant reduction of placque area (-66%, P < .05). Oral and local administration of the ACE inhibitor was followed by a nonsignificant reduction of the neointimal area (-17%). Local administration of saline combined with oral ramipril failed to prevent neointimal formation (reduction of 6%, NS).

CONCLUSION

Oral administration of ramipril resulted in a significant reduction of neointimal proliferation in New Zealand White rabbits. The possible benefit of an additional administration of local ramiprilat was diminished by an excessive neointimal hyperplasia, which was most likely caused by the inherent vessel trauma with use of the microporous balloon catheter.

Quantification of horseradish peroxidase delivery into the arterial wall in vivo as a model of local drug treatment: comparison between a porous and a gel-coated balloon catheter

PURPOSE

To quantify horseradish peroxidase (HRP) delivery into the arterial wall, as a model of local drug delivery, and to compare two different percutaneous delivery balloons.

METHODS

Perforated and hydrophilic hydrogel-coated balloon catheters were used to deliver HRP in aqueous solution into the wall of porcine iliac arteries in vivo. HRP solutions of 1 mg/ml were used together with both perforated and hydrophilic hydrogel-coated balloon catheters and 40 mg/ml HRP solutions were used with the hydrogel-coated balloon only. The amount of HRP deposited in the arterial wall was then determined photospectrometrically.

RESULTS

Using the 1 mg/ml HRP solution, the hydrogel-coated balloon absorbed 0.047 mg HRP into the coating. Treatment with this balloon resulted in a mean vessel wall concentration of 7.4 microg HRP/g tissue +/- 93% (standard deviation) (n = 7). Treatment with the hydrogel-coated balloon that had absorbed 1.88 mg HRP into the coating (using the 40 mg/ml HRP solution) led to a mean vessel wall concentration of 69.5 microg HRP/g tissue +/- 74% (n = 7). Treatment with the perforated balloon using 1 mg/ml aqueous HRP solution led to a mean vessel wall concentration of 174 microg/g +/- 81% (n = 7). Differences between the hydrogel-coated and perforated balloons (1 mg/g solutions of HRP) and between hydrogel-coated balloons (0.047 mg vs 1.88 mg absorbed into the balloon coating) were significant (p < 0.05; two-sided Wilcoxon test).

CONCLUSIONS

The use of a perforated balloon catheter allowed the delivery of a higher total amount of HRP compared with the hydrogel-coated balloon, but at the cost of a higher systemic HRP application. To deliver 174 microg HRP per gram of vessel wall with the perforated balloon, 6.5 +/- 1.5 mg HRP were lost into the arterial blood (delivery efficiency range = 0.2%-0.3%). With 0.047 mg HRP loaded into the coating of the hydrogel balloon, 7.4 microg HRP could be applied to 1 g of vessel wall (delivery efficiency 1.7%), and with 1.88 mg HRP loaded into the coating of the hydrogel balloon, 69.5 microg HRP could be applied per gram of vessel wall (delivery efficiency 0.6%).

Local delivery infusion pressure is a key determinant of vascular damage and intimal thickening

Local drug delivery following percutaneous transluminal coronary angioplasty (PTCA) may prevent restenosis by achieving higher local tissue concentrations of drugs than systemic administration. However, it remains unknown whether vascular damage and the ensuing intimal thickening is associated with the degree of infusion pressure achieved by local delivery. Therefore, local delivery of normal saline was performed using a channeled balloon catheter (Transport) to the rabbit iliac artery with different infusion pressures of 0, 3, 5, 7, and 12 atm (n=4 for each). The extent of vascular damage and the development of intimal thickening were determined histopathologically 14 days after the procedure. In 10 additional rabbits, to assess the degree of vessel penetration, local delivery of indocyanine green dye solution was performed in a similar fashion. After 1 h, the green dye penetrated deeply at the higher infusion pressures of 7 and 12 atm. The incidence of internal clastic lamina laceration and occurrence of total occlusion as a result of thrombus formation demonstrated an increase proportional to the degree of local infusion pressure. When the vascular injury score in each arterial section was plotted against the infusion pressure, a significant relation was observed (r=0.717, p<0.0001). At 0, 3, 5, 7, and 12 atm, neointimal areas of 0.160+/-0.005, 0.163+/-0.008, 0.189+/-0.017, 0.260+/-0.027, and 0.329+/-0.033 mm2, respectively, were observed. Smooth muscle cell (SMC) proliferative activity also increased in proportion to the local infusion pressure. We have demonstrated for the first time that local delivery infusion pressure itself is related to the severity of vascular damage, resulting in the development of intimal thickening and an associated increase in SMC proliferative activity. Therefore, we suggest that infusion pressure is a key determinant of vascular injury during local drug delivery, with lower pressure causing the least neointimal response.

Intramural injection of biodegradable microspheres as a local drug-delivery system to inhibit neointimal thickening in a rabbit model of balloon angioplasty

Restenosis remains the major limitation of coronary angioplasty. The objective of this study was to develop microspheres able to be delivered at the angioplasty site for long-term drug release and to test their effects in a model of balloon angioplasty. Polylactic-co-glycolide acid microspheres (5-10 microm in diameter) were prepared by using an oil-in-water emulsion-solvent evaporation method. In vitro experiments with hydrocortisone-loaded microspheres revealed a hydrocortisone release for 4 weeks. We studied the in vivo effect of injection of microspheres into the arterial wall of New Zealand White rabbits by using a perforated balloon. Deep penetration of microspheres in the arterial wall was documented immediately after angioplasty. Intimal hyperplasia was assessed in iliac arteries 4 weeks after angioplasty. The morphometric analysis was performed in four groups of animals; the first group was subjected only to conventional angioplasty (control, n = 10), whereas the other three groups after conventional angioplasty were received perforated balloon angioplasty with saline (n = 10), microspheres (n = 10), or hydrocortisone-loaded microspheres (n = 7). Intramural injection of saline did not induce greater intimal hyperplasia compared with control (0.17 +/- 0.03 vs. 0.18 +/- 0.03 mm2, respectively). Microspheres injection was associated with a trend toward a greater degree of intimal hyperplasia that did not reach statistical significance. Hydrocortisone-loaded microspheres were associated with a significant reduction in intimal hyperplasia compared with unloaded microspheres (0.16 +/- 0.02 vs. 0.26 +/- 0.03 mm2, respectively). The polylactic-co-glycolide acid microspheres are well tolerated, easily injected into the arterial wall, and the increase of intimal hyperplasia is easily inhibited by release of hydrocortisone for 4 weeks after initial injury.

Endovascular catheter-delivered photodynamic therapy in an experimental response to injury model

BACKGROUND

The effectiveness of local endovascular photodynamic therapy (PDT) in preventing tissue hyperplasia was evaluated in a vascular injury model.

METHODS

Standardized unidirectional arterial injury with a directional atherectomy catheter was performed in porcine arteries (n = 180). Animals (n = 72) were randomly allocated to unidirectional injury only (Group 1), injury followed by drug delivery of photosensitizer with a porous balloon (Group 2), or by local exposure to monochromatic light (Group 3). In Group 4, injury was followed by local drug delivery of photosensitizer and subsequent exposure to light (PDT). Up to 21 days after treatment, all experimental vessels were excised, fixed and processed for histology, immunohistochemistry and transmission electron microscopy.

RESULTS

After vascular injury an inflammatory and myoproliferative response was observed in Groups 1, 2 and 3 (mean tissue hyperplasia/media ratio 1.0 +/- 0.5 at 21 days; area tissue hyperplasia: 1.57 +/- 0.9 mm2). Proliferation in injured vascular segments (Group 1-3) reached a maximum at 7 days, with 6%. Only in Group 4, after injury followed by photodynamic therapy, was there no significant vascular response (mean tissue hyperplasia/media ratio 0.3 +/- 0.2: area tissue hyperplasia: 0.1 +/- 0.05 mm2 p < 0.001, proliferating cells 0.3%).

CONCLUSION

Vascular response after unidirectional injury was suppressed only by endovascular photodynamic therapy.

Time course of smooth muscle cell proliferation after local drug delivery of low-molecular-weight heparin using a porous balloon catheter

It has been reported previously that systemic application of low molecular weight heparin (LMWH) suppresses smooth muscle cell (SMC) proliferation after balloon angioplasty in experimental studies. However, the high concentration of heparin required for a beneficial effect may cause severe bleeding complications. The ideal situation to overcome the systemic side effects would be to administer LMWH locally and deep into the arterial wall, which became possible by the development of porous balloon catheters. The in vivo feasibility of local delivery of LMWH using the porous balloon has been assessed by delivering tritium-marked LMWH into rabbit carotid arteries. The efficacy of the system was investigated by using a second injury animal model. After development of an intimal plaque by electrical stimulation, 61 rabbits were treated with the porous balloon after balloon angioplasty. In 23 rabbits, local drug delivery was accomplished with a porous balloon catheter (35 holes, hole diameter 75 microns, 2.5 mm catheter diameter). LMWH was locally administered with 4 ml (solution 375 anti-Xa-units/ml) and 2 atm. To study the extent of restenosis and morphological changes, these animals were killed 3, 7, 14, 28, or 56 d after intervention. After staining (hematoxylin, van Gieson, BrdU, RAM 11, alpha-actin) procedures to quantify SMC proliferation, intimal macrophages and morphological analysis were performed. Porous balloon treatment led to an increase in intimal SMC proliferation rate in the early stage after intervention. However, during the following time period, a significant decrease of the proliferation rate as compared with the animals treated with balloon angioplasty alone could be observed, which resulted in an only moderate increase of the intimal layer after local drug delivery compared with balloon angioplasty alone.

Local alcohol delivery may reduce phenotype conversion of smooth muscle cells and neointimal formation in rabbit iliac arteries after balloon injury

Local delivery of pharmacological agents into the vessel wall has been extensively studied to prevent restenosis after coronary angioplasty. Alcohol solution was found to affect cellular responses to growth stimulation. This study was carried out to examine the effect of local delivery of alcohol solution on intimal proliferation following balloon injury. New Zealand white rabbits of 2-3 kg underwent balloon denudation of bilateral iliac arteries. Following denudation, 2 ml 10% or 15% alcohol solution was infused into one iliac arterial wall using a Wolinsky porous balloon catheter. The other iliac artery of the same animal received local delivery of normal saline and was used as the control. The animals were killed at 2 weeks. The neointimal areas of alcohol treated vascular segments were significantly less than those of control segments in both 10% (n = 10) and 15% (n = 11) groups (65 +/- 16 versus 113 +/- 20 x 10(3) microns2 in 10% group, P < 0.0001; 48 +/- 15 versus 107 +/- 10 x 10(3) microns2 in 15% group, P = 0.002). In order to determine the effect of alcohol solution on smooth muscle cell proliferation, a method of quantifying phenotypic conversion of smooth muscle cells was chosen. This consists of a measurement of volume fraction of the synthetic organelles (VFSO) of vascular smooth muscle cell profiles (SMC) using transmission electron micrographs taken in the animals killed at day 8. The VFSO of SMC of the control sites were significantly greater than those of paired 10% alcohol treated arteries in both intima (0.39 +/- 0.02 versus 0.21 +/- 0.01, P < 0.0001) and media (0.33 +/- 0.03 versus 0.19 +/- 0.02, P < 0.0001). Similar findings were noted in the 15% alcohol treated group. It is concluded that intramural alcohol delivery using porous balloon catheter is effective in reducing neointimal proliferation in rabbit iliac arteries after balloon injury. The mechanisms of action may involve direct inhibition of cellular responses to growth stimulation.

Local photodynamic therapy reduces tissue hyperplasia in an experimental restenosis model

Local photodynamic therapy may have potential in preventing myointimal hyperplasia after angioplasty. In this study, the effect of photodynamic therapy was evaluated in an experimental model of restenosis. Standardized unidirectional arterial injury with a directional atherectomy catheter was performed in porcine arteries. Animals were randomly allocated to four groups: group 1, unidirectional injury only; group 2, injury followed by local delivery of photosensitizer; group 3, injury followed by local exposure to monochromatic light; and group 4, where injury was followed by local drug delivery of photosensitizer and subsequent exposure to light (photodynamic therapy). Seven, 14 or 21 days after treatment, all experimental vessels were excised, fixed and processed for histology. An inflammatory and myoproliferative response was observed after injury in vessels from groups 1, 2 and 3. In group 4, after injury followed by photodynamic therapy, the myoproliferative response was significantly reduced. Thus, in this study, tissue hyperplasia after unidirectional injury was effectively suppressed by photodynamic therapy.

Comparison of local intravascular drug-delivery catheter systems

Systemic and local delivery of the photosensitive drug Photofrin polyporphyrin was investigated in normal porcine arteries (n = 192). A macroporous balloon and a novel needle injection catheter were used for local drug delivery and compared with systemic delivery. Fluorescence microscopy combined with digital image analysis was used to quantify the drug-related fluorescence. Systemic delivery showed a maximum in the intima at 4 hours. Application with the porous balloon revealed maximum indicator-related fluorescence intensity in the intima after 5 minutes; delivery with the needle injection catheter resulted in a several-fold enhanced maximum in adventitia after 30 minutes compared with the maximum achieved with either systemic injection or porous balloon application. After 21 days fluorescence was detectable in arteries treated with the new needle injection catheter. Local drug delivery is feasible with either system, but prolonged delivery was achieved only with the needle injection catheter.

Vascular gene therapy

Gene therapy is emerging as a new and exciting therapeutic modality for cardiovascular pathology. The work reported here was carried out in the National Heart, Lung and Blood Institute (NHLBI) in Bethesda, MD, USA, where genetically engineered endothelial cells were used to seed endovascular prostheses and cell adhesion to the prostheses was tested both in vitro and in vivo. Two catheter based systems were used to deliver genes to the arterial wall cells in vivo, employing retroviral and adenoviral vectors. Efficient gene transfer to vascular cells in vivo was achieved with adenoviral vectors.