Localized intramural drug delivery during balloon angioplasty using hydrogel-coated balloons and pressure-augmented diffusion

Intracoronary Administration of Drugs in Clinical Practice

Intracoronary administration of drugs allows to achieve the fastest possible effect in interventional cardiology. This allows to avoid all the biological filters of the body and achieve the required concentration of the active substance at the injection site. Also, given the local action, systemic side effects are nearly absent. The aim. To study the literature data of the leading countries of the world in the field of intracoronary drug administration. To analyze the experience of different centers on the use of various medications in the treatment of the phenomenon of distal microembolization. Results. One of the first drugs administered intracoronary was streptokinase for the treatment of acute myocardial infarction. After that, it became clear that this method of delivering drugs is possible and can be used. With the beginning of the treatment of acute coronary syndromes by stenting, one of the possible complications arose in the form of no-reflow. At the same time, realizing that this is a local problem, they began to use the possibility of intracoronary administration of drugs to treat this phenomenon. The main advantage of this method is quick response to drug administration. Today, the drugs of choice in the treatment of no-reflow are verapamil, adenosine, nitroprusside, adrenaline. On the other hand, probably the most common drug that is administered intracoronary is nitroglycerin. It is used as a vasodilator in the event of spasm of the coronary arteries. Subsequently, it has been recommended to deliver drugs via a microcatheter or aspiration catheter to achieve even more selective effect in the area of the affected vessel, and this also minimizes drug loss due to coronary reflux into the aortic sinuses while usinga guiding catheter. Work is also underway on the use of intracoronary insulin in acute coronary syndrome in order to reduce the area of damage in myocardial infarction. It is also very promising to study the introduction of stem cells directlyinto the myocardium through a microcatheter in order to regenerate the myocardium after a heart attack. Conclusions. Intracoronary administration of drugs allows to achieve the maximum effect in the shortest possible time. Today, many drugs can be used in this way, starting from the treatment of the phenomenon of distal microembolization and ending with myocardial regeneration after myocardial infarction.

Functional hydrogel coatings

Hydrogels—natural or synthetic polymer networks that swell in water—can be made mechanically, chemically and electrically compatible with living tissues. There has been intense research and development of hydrogels for medical applications since the invention of hydrogel contact lenses in 1960. More recently, functional hydrogel coatings with controlled thickness and tough adhesion have been achieved on various substrates. Hydrogel-coated substrates combine the advantages of hydrogels, such as lubricity, biocompatibility and anti-biofouling properties, with the advantages of substrates, such as stiffness, toughness and strength. In this review, we focus on three aspects of functional hydrogel coatings: (i) applications and functions enabled by hydrogel coatings, (ii) methods of coating various substrates with different functional hydrogels with tough adhesion, and (iii) tests to evaluate the adhesion between functional hydrogel coatings and substrates. Conclusions and outlook are given at the end of this review.

Nanoparticle eluting-angioplasty balloons to treat cardiovascular diseases

Nanoparticles (NPs) can be used to locally deliver anti-restenosis drugs when they are infused directly to the injured arteries after intervention procedures such as angioplasty. However, the efficacy of transferring NPs via infusion to the arterial wall is limited, at least partially, due to poor NP retention on the inner artery wall. To improve NP retention, angioplasty balloons coated with drug-loaded NPs were fabricated via either layer-by-layer (LbL) electrostatic coating or acrylic-based hydrogel (AAH) coating techniques. Three types of NPs, namely poly (lactide-co-glycolide) (PLGA), biodegradable photo-luminescent PLGA and urethane doped polyester were studied. The transfer efficacy of NPs from various coatings to the arterial wall were further evaluated to find the optimal coating conditions. The ex vivo NP transfer studies showed significantly more NPs being transferred to the rat arterial wall after the angioplasty procedure by the AAH coating (95% transfer efficiency) compared to that of the LbL technique (60%) and dip coating (20%) under flow conditions (10 dyn/cm²). Our results suggest that the AAH coating of drug-loaded NPs on the angioplasty balloon could potentially provide superior retention of drug-loaded NPs onto the arterial wall for a better local delivery of drug-loaded NPs to effectively treat arterial diseases.

Local Endovascular Delivery, Gene Therapy, and Cell Transplantation for Peripheral Arterial Disease

Advances in catheter technology, gene identification, and cell biology may provide novel treatment options for patients with peripheral arterial disease (PAD) who are not candidates for standard revascularization procedures. Animal studies and recent results in human beings suggest that transfer of growth factors or regulatory genes and transplantation of progenitor cells may provide novel therapy options by inducing therapeutic angiogenesis or by inhibiting restenosis. This review will discuss the development of a variety of catheters for localized endovascular delivery, as well as the various cellular and genetic strategies that exist to restore blood flow to ischemic tissue and to reduce neointimal hyperplasia.

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 endovascular delivery, gene therapy, and cell transplantation for peripheral arterial disease

Advances in catheter technology, gene identification, and cell biology may provide novel treatment options for patients with peripheral arterial disease (PAD) who are not candidates for standard revascularization procedures. Animal studies and recent results in human beings suggest that transfer of growth factors or regulatory genes and transplantation of progenitor cells may provide novel therapy options by inducing therapeutic angiogenesis or by inhibiting restenosis. This review will discuss the development of a variety of catheters for localized endovascular delivery, as well as the various cellular and genetic strategies that exist to restore blood flow to ischemic tissue and to reduce neointimal hyperplasia.

Effects of different application parameters on penetration characteristics and arterial vessel wall integrity after local nanoparticle delivery using a porous balloon catheter

Catheter-based local delivery of drug loaded nanoparticles agents offers a potential therapeutic approach to reducing restenosis. However, high delivery pressures and large volumes of infusates may cause severe vascular damage and increase intimal thickening. Therefore, we investigated the penetration pattern and vessel wall integrity of fluorescence-labelled nanoparticles (217 nm in diameter) into the non-atherosclerotic aorta abdominalis of New Zealand white rabbits in dependence of the volume (2.5 and 5 ml) and concentration (0.5 and 1 mg/ml) of the nanoparticle suspension, as well as the infusion pressure (2 and 4 atm) using a channelled balloon catheter (SCIMED REMEDY model RC 20/2.5). The location and penetration characteristics of nanoparticles in the arterial vessel wall were visualized using confocal laser scanning microscopy and transmission electron microscopy (TEM). Catheter design and infusion pressure form a radial particle stream through intima and media into the adventitial layer of the aorta abdominalis. Infusion pressures of 4 atm in combination with high particle concentrations lead to effective nanoparticle delivery without severe vessel wall disruptions. Endothelium of the treated vessel segments was slightly affected during catheter insertion showing partly denudation of the innermost cell layer. TEM micrographs underlines transport functional properties of the vasa vasorum inside the vessel wall. Consequently, local delivery efficiency of nanoparticulate carriers is critically affected by infusion pressure, and concentration of carrier suspensions. These factors need to be taken into consideration for the design of in vivo experiments.

Local drug delivery in restenosis injury: thermoresponsive co-polymers as potential drug delivery systems

The success of percutaneous transluminal coronary angioplasty in treatment of acute coronary syndromes has been compromised by the incidence of restenosis. The physical insult of balloon insertion can damage or remove the endothelial monolayer, thereby generating a prothrombotic surface. The resulting inappropriate response to injury can also lead to penetration of inflammatory cells, conversion of the underlying media to a synthetic phenotype, deposition of extracellular matrix, constrictive remodeling, and neointimal hyperplasia. While stent implantation at the time of balloon insertion has offset some of these events, inflammatory responses to the implanted biomaterial (stent) and intimal hyperplasia are still prominent features of the procedure, leading in 20-30% of cases to in-stent restenosis within a year. Systemic delivery of drugs designed to offset in-stent restenosis injury has been largely unsuccessful, which has led to the development of strategies for coating stents with drugs for local delivery. Drug-eluting stents constitute an innovative means of further reducing the incidence of restenosis injury and clinical trials have shown encouraging results. This review focuses on properties of a class of environment-sensitive hydrogels, the N-isopropylacrylamide-based thermoresponsive co-polymers, on their potential roles as stent coatings, on their demonstrated ability to incorporate and release drugs that modify vascular endothelial and smooth muscle cell functions, and on issues that still await clarification, prior to their adoption in a clinical setting.

Novel Echogenic Drug-Immunoliposomes for Drug Delivery

RATIONALE AND OBJECTIVES

We have developed novel echogenic immunoliposomes (ELIPs) that can be antibody-conjugated for the specific highlighting of atheroma and atheroma components. The utility of these agents for regional drug delivery has not been evaluated previously. We chose to use an antibiotic as the prototype drug. The concept that an infectious agent may affect the development and progression of atherosclerosis has stimulated trials on the use of antibiotics for coronary syndromes. However, these agents are given systemically with concomitant problems. Development of an agent for local drug delivery may obviate adverse effects and improve treatment efficacy. The aim of this study was to evaluate the potential of our ELIPs for drug incorporation and to demonstrate efficient drug delivery to cultured cells.

METHODS

Azithromycin was incorporated into the ELIPs during development. Free drug was removed with a Sephadex G-50 column. Acoustic properties were evaluated using an intravascular ultrasound catheter and quantified by computer-assisted videodensitometry. Human umbilical arterial endothelial cells were infected with Chlamydia pneumoniae. Cells were treated with the drug-ELIP complexes, and infection-forming units were counted using fluorescence techniques.

RESULTS

We were able to incorporate a drug into the ELIPs with retention of acoustic properties. The drug-ELIP complex demonstrated effective inhibition of microbial growth in endothelial cells (P < 0.001 vs. empty liposomes and control).

CONCLUSIONS

We have developed a novel acoustic drug-liposomal agent that can deliver drugs to cultured cells. Although in vivo translation is required, this technique has potential for site-specific drug delivery.

Biodegradable nanoparticles for drug and gene delivery to cells and tissue

Biodegradable nanoparticles formulated from poly (D,L-lactide-co-glycolide) (PLGA) have been extensively investigated for sustained and targeted/localized delivery of different agents including plasmid DNA, proteins and peptides and low molecular weight compounds. Research about the mechanism of intracellular uptake of nanoparticles, their trafficking and sorting into different intracellular compartments, and the mechanism of enhanced therapeutic efficacy of nanoparticle-encapsulated agent at cellular level is more recent and is the primary focus of the review. Recent studies in our laboratory demonstrated rapid escape of PLGA nanoparticles from the endo-lysosomal compartment into cytosol following their uptake. Based on the above mechanism, various potential applications of nanoparticles for delivery of therapeutic agents to the cells and tissue are discussed.

Polylysine as a vehicle for extracellular matrix-targeted local drug delivery, providing high accumulation and long-term retention within the vascular wall

We present the first steps in the elaboration of an approach of extracellular matrix-targeted local drug delivery (ECM-LDD), designed to provide a high concentration, ubiquitous distribution, and long-term retention of a drug within the vessel wall after local intravascular delivery. The approach is based on the concept of a bifunctional drug comprising a "therapeutic effector" and an "affinity vehicle," which should bind to an abundant component of the vessel wall. The aim of the present study was to select molecules suitable for the role of affinity vehicles for ECM-LDD and to study their intravascular delivery and retention ex vivo and in an animal model. By use of fluorescence microscopy, the following molecules were selected on the basis of strong binding to cross sections of human vessels: protamine, polylysine, polyarginine, a glycosaminoglycan-binding peptide from vitronectin, and a synthetic dendrimer. With polylysine as a prototypic affinity vehicle, we showed that after intravascular delivery, polylysine was concentrated throughout a luminal layer of the vascular wall to an extremely high concentration of 20 g/L and was retained therein for at least 72 hours of perfusion without noticeable losses. Low molecular weight (fluorescein) and high molecular weight (hirudin) compounds could be chemically conjugated to polylysine and were retained in the vessel wall after intravascular delivery of the conjugates. In conclusion, by use of the ECM-LDD method, an extremely high concentration and long-term retention of locally delivered drug can be reached. Polycationic molecules can be considered as potential affinity vehicles for ECM-LDD.

Local drug delivery: an emerging approach in the treatment of restenosis

Very limited success has been demonstrated with systemic pharmacological treatment to reduce the incidence of restenosis following angioplasty in patients. The lack of success of many of the pharmacotherapeutic agents in reducing the restenosis rates post-angioplasty and following stent implementation is believed to arise from inadequate concentrations of the agents at the lesion site. This has led to the development of various local delivery devices that would ideally deliver and retain adequate amounts of drug to the vessel wall for sufficient periods of time to ensure a therapeutic effect without inducing further injury or compromising blood flow. Local dosing would avoid systemic toxicity, and the use of modified balloon catheters or coated stents might enable percutaneous approaches.

Gene Therapy for Cardiovascular Disease

During the past decade, gene therapy for the treatment of many inherited and acquired medical problems has become the subject of increasing focus in both the scientific litera ture and the lay press. This review examines the history and current status of gene therapy for advanced chronic periph eral and myocardial ischemia.

Local paclitaxel delivery for the prevention of restenosis: biological effects and efficacy in vivo

OBJECTIVE

The aim of this study was to evaluate the potential of paclitaxel to prevent restenosis in vivo.

BACKGROUND

Paclitaxel (Taxol) is a microtubule-stabilizing compound with potent antitumor activity. It influences the cytoskeleton equilibrium by increasing the assembly of altered microtubules, thereby inducing cellular modifications that result in reduced proliferation, migration and signal transduction.

METHODS

Before the in vivo study, delivery efficiency was determined with radiolabeled paclitaxel in porcine hearts. After induction of a defined plaque in the right carotid arteries of 76 New Zealand rabbits by electrical stimulation, 27 animals underwent balloon dilation and subsequent local paclitaxel delivery (10 ml, 10 micromol/liter) with a double-balloon catheter. Twenty-nine animals served as control with angioplasty only, 10 animals underwent local delivery of vehicle only (0.9% NaCl solution) and 10 animals were solely electrostimulated. Vessels were excised one, four, and eight weeks after intervention.

RESULTS

The extent of stenosis in paclitaxel-treated animals was significantly reduced compared with balloon-dilated control animals (p = 0.0012, one, four and eight weeks after intervention: 14.6%, 24.6% and 20.5%, vs. 24.9%, 33.8% and 43.1%, respectively). Marked vessel enlargement compared with balloon-dilated control animals could be observed (p = 0.0001, total vessel area after one, four and eight weeks: paclitaxel group: 1.983, 1.700 and 1.602 mm2, control: 1.071, 1.338 and 1.206 mm2, respectively). Tubulin staining and electron microscopy revealed changes in microtubule assembly, which were limited to the intimal area. Vasocontractile function after paclitaxel treatment showed major impairment.

CONCLUSIONS

Local delivery of paclitaxel resulted in reduced neointimal stenosis and enlargement in vessel size. Both these effects contribute to a preservation of vessel shape and are likely to be caused by a structural alteration of the cytoskeleton.

Surface modification of polyethylene balloon catheters for local drug delivery

Local drug delivery is an attractive approach to the associated problems of percutaneous transluminal coronary angioplasty (PTCA), including arterial injury. The objective of the present research was to deliver a high concentration of a potent anti-thrombin agent, argatroban (ARG), to the vessel wall in order to reduce arterial injury. Local delivery was accomplished by the ionic attachment of drug particles to a modified balloon surface. Surface graft polymerization of ionic monomers to a high-density poly(ethylene) (PE) substrate was performed utilizing ultra-violet (UV) methods. Acrylic acid (AAc) and 2(dimethylamino) ethyl methacrylate (DMAEMA) were successfully grafted onto PE surfaces. Surface grafting was verified by contact angle, X-ray photoelectron spectroscopy, and zeta potential measurements. The amount of ARG adsorbed onto the modified PE surface was highly dependent on the pH of the drug media for both anionic and cationic grafted monomers. The efficacy of local drug delivery to the arterial wall was analyzed using drug-immobilized PE balloon catheters in the rabbit common carotid artery model. High concentrations of ARG (280 nmol/g tissue) were found within the ballooned arterial segment immediately after angioplasty, followed by a decrease after blood flow was restored.

Local delivery of nadroparin via hydrogel-coated angioplasty balloon: effect on platelet deposition and smooth muscle cell proliferation--an experimental study

PURPOSE

To assess the feasibility of intravascular delivery of nadroparin, a low-molecular-weight heparin, via hydrogel-coated angioplasty balloons, and the effects of nadroparin delivered in this manner on platelet deposition and smooth muscle cell (SMC) proliferation.

MATERIALS AND METHODS

Tritiated nadroparin was used to determine the nadroparin-carrying capacity of the hydrogel-coating, kinetics of release from the balloons, and, in four pigs, delivery of the nadroparin to the iliac arterial wall. Platelet deposition in nadroparin-treated iliac arteries versus contralateral iliac arteries dilated with saline-loaded, hydrogel-coated balloons was quantified in seven pigs using 111Indium-labeled platelets. Smooth muscle cell proliferation in nadroparin and saline-treated iliac arteries in 10 pigs was evaluated 7 days after angioplasty with use of proliferating cell nuclear antigen.

RESULTS

Approximately 98 international units of nadroparin were delivered by the hydrogel-coated balloon, the majority to the angioplasty site and distal vessel. There was a trend toward decreased platelet deposition in nadroparin-treated arteries, but statistical significance was not achieved (P = .1563). Medial SMC proliferation was decreased in the nadroparin-treated arteries in nine of 10 pigs (P = .0137).

CONCLUSIONS

Hydrogel-coated balloons may be used to deliver nadroparin to the arterial wall, with measurable levels of the drug delivered to the site of angioplasty, and with resultant decrease in SMC proliferation.

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%).

Arterial uptake of biodegradable nanoparticles: effect of surface modifications

Restenosis is the reobstruction of an artery following interventional procedures such as balloon angioplasty or stenting. Local pharmacotherapeutic approaches using controlled release systems are under investigation to inhibit the regional pathophysiologic process of restenosis. We have been investigating biodegradable nanoparticles (100 +/- 39 nm in diameter, mean +/- sd) for the local intra-arterial drug delivery. The purpose of this study was to investigate nanoparticle surface modifications (see Table 1) to enhance their arterial uptake. The PLGA (polylactic polyglycolic acid copolymer) nanoparticles were formulated by an oil-in-water emulsion solvent evaporation technique using a 2-aminochromone (U-86983, Upjohn and Pharmacia) (U-86) as a model antiproliferative agent. The various formulations of nanoparticles were evaluated for the arterial wall uptake by using an ex-vivo dog femoral artery model. The selected formulations were then tested in vivo in acute dog femoral artery and pig coronary artery models. The nanoparticles surface modified with a cationic compound, didodecyldimethylammonium bromide (DMAB), demonstrated 7-10-fold greater arterial U-86 levels compared to the unmodified nanoparticles in different ex-vivo and in-vivo studies. The mean U-86 levels were 10.7 +/- 1.7 microg/10 mg (dog) and 6.6 +/- 0.6 microg/10 mg (pig) in the artery segments ( approximately 2 cm) which were infused with the nanoparticles. The pig coronary studies further demonstrated that the infusion of nanoparticles with higher U-86 loading reduced the arterial U-86 levels, whereas increasing the nanoparticle concentration in the infusion solutions increased the arterial U-86 levels. The biodistribution studies in pigs following coronary arterial administration of nanoparticles demonstrated disposition of U-86 in the myocardium and distally in the liver and the lung. The mechanism of enhanced arterial uptake of the DMAB surface modified nanoparticles seems to be due to the alteration in the nanoparticle surface charge. The unmodified nanoparticles had a zeta potential of -27.8 +/- 0.5 mV (mean +/- sem, n = 5), whereas the DMAB modified nanoparticles demonstrated a zeta potential of +22.1 +/- 3.2 mV (mean +/- sem, n = 5). The adsorption of DMAB to the nanoparticle surface followed the Freundlich isotherm with binding capacity k = 28.1 microg/mg and affinity constant p = 2. 33. In conclusion, surface modified nanoparticles have potential applications for intra-arterial drug delivery to localize therapeutic agents in the arterial wall to inhibit restenosis.

Site-specific delivery of iloprost during experimental angioplasty suppresses smooth muscle cell proliferation

PURPOSE

The authors have previously reported that intramural delivery of iloprost during angioplasty suppresses local platelet aggregation at 1 hour in undiseased porcine arteries. In this study, the authors sought to quantify the effect of such treatment on medial vascular smooth muscle cell proliferation, an event implicated in the development of intimal hyperplasia.

MATERIALS AND METHODS

Three Yorkshire pigs underwent percutaneous transluminal angioplasty with hydrogel-coated balloons for a total of 10 iloprost-treated (experimental) and 10 saline-treated (control) arterial sites. The balloons were prepared with previously reported techniques and loaded with 2.25 microg of iloprost for the experimental sites. On the eighth day after angioplasty, these sites were harvested and prepared for immunohistochemical staining. Thin (4 microm) sections of the specimens were stained with use of monoclonal antibody to proliferating cell nuclear antigen (PCNA). Appropriate positive and negative controls were used. Approximately 350-500 vascular smooth muscle cells were randomly counted under high power (100x) by an experienced physician who was blinded to the origin of the specimen. A PCNA index (%) was calculated as follows: [(#PCNA [+] cells)/(#PCNA [+] cells + #PCNA [-] cells)]x 100. A paired t test was used for statistical comparison.

RESULTS

The PCNA indices for eight (n = 8) paired large vessels (iliac, carotid, subclavian) were 7.98 (+/- 1.8)%, for the iloprost-treated experimental sites, and 14.58 (+/- 3.8)% for the saline-treated control sites. This difference was statistically significant (P = .003). One large vessel pair was not available for analysis. When the pair of renal arteries of animal 3 were included (n = 9), the PCNA indices were 8.32 (+/- 2.3)% for the experimental sites, and 13.79 (+/- 4.2)% for the control sites. The differences were again significant (P = .01).

CONCLUSION

Intraarterial site-specific delivery of iloprost during angioplasty with drug-loaded, hydrogel-coated balloons significantly suppresses medial smooth muscle cells in swine at the expected peak period of proliferation of 7 days after angioplasty.

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.

Prevention of acute inducible atrial flutter in dogs by using an ibutilide-polymer-coated pacing electrode

Atrial arrhythmias (atrial fibrillation or atrial flutter) after coronary artery bypass graft surgery are difficult to prevent or treat and often result in significant morbidity. Prior experimental studies by our group showed improved therapeutic efficacy for antiarrhythmic drugs delivered via controlled-release polymeric matrices implanted on the epicardial surface. These experiments were conducted to test the hypothesis that direct atrial epicardial administration of ibutilide from a controlled-release system (compared with intravenous administration) can reduce the inducibility of atrial flutter in the acute postoperative atrial myocardium. Polymeric sustained-release preparations were formulated by solvent casting of an ibutilide and polyurethane (Pellathane) solution in tetrahydrofurane. Multilayer solvent-casted coatings on pacing electrode wires were carried out to fabricate a sustained-release electrode system. In animal model studies, each dog underwent a thoracotomy, followed by a right atriotomy that was repaired. Induction of atrial flutter was attempted by burst pacing with the bipolar pacing catheter. Sinus rhythm was restored with overdrive pacing. After determining the induction rate (percentage) of atrial flutter in the baseline state, a stainless-steel wire coated with the drug-delivery system, 10% ibutilide/90% polyurethane (n = 7), or without drug (polyurethane coating without ibutilide, n = 5; control) was sewn onto the right atrium. Systemic intravenous administration of ibutilide (1.2 microg/kg/h) also was carried out in a separate group of animals after atriotomy (n = 5). For ibutilide (at an estimated dose of 1.2 microg/kg/h), the atrial-flutter results were 41.85 +/- 2.21% induction for baseline compared with 12.42 +/- 5.26% (p = 0.02) after the ibutilide wire implant. In the control dogs, atrial flutter was induced 29.4 +/- 4.7% at baseline and 25.2 +/- 5.1% after implantation of the control wire (p = 0.4). Ibutilide coronary venous serum concentrations at the end of the ibutilide-polyurethane electrode experiments were 2.25 +/- 0.2 ng/ml (mean +/- SEM) versus systemic levels that were below the limits of detection. Systemic intravenous ibutilide infusions had no effect on the inducibility of atrial flutter. In conclusion, an epicardial implantable electrode coating with an ibutilide controlled drug-release system significantly reduced the inducibility of atrial flutter in an experimental atriotomy model. These results suggest that atrial arrhythmias occurring after coronary bypass surgery may be prevented by local atrial administration of ibutilide from a controlled-release pacing electrode.

Effect of atherosclerosis on transmural convection an arterial ultrastructure. Implications for local intravascular drug delivery

Local infusion of agents through perforated catheters may reduce neointimal formation following vascular angioplasty. Such treatment will succeed only if the drug is retained within the arterial intima long enough to promote repair. Drugs will be dispersed throughout the wall predominantly by transmural convection instead of diffusion if the Peclet number, Pe = J (1-delta f)/P, is greater than unity, where J is the transmural fluid flow per unit surface area and delta(f) and P are the reflection and permeability coefficients to the drug, respectively. Although the targets of local drug delivery will be atherosclerotic vessels, little is known about the transport properties of these vessels. Accordingly, we evaluated the effects of hypercholesterolemia and atherosclerosis on J per unit pressure (hydraulic conductance, Lp) and on ultrastructure in femoral arteries. Measurements were made at 30, 60, and 90 mm Hg in anesthetized New Zealand white rabbits fed a normal diet (n = 6) and after 3 weeks of lipid feeding (n = 19). Atherosclerosis was induced in six lipid-fed animals by air desiccation of a femoral artery. Hydraulic conductance was significantly greater in vessels from hypercholesterolemic than from normal animals and decreased with pressure only in hypercholesterolemic arteries. Atherosclerosis did not augment hydraulic conductance compared with hypercholesterolemia alone. Electron microscopic examination demonstrated damaged endothelium in hypercholesterolemic arteries and both altered endothelium and less tightly packed medial tissue, compared with controls, in atherosclerotic vessels, at least at lower pressures. Peclet numbers for macromolecules exceeded unity for all three groups of arteries and reached 0.3 to 0.4 for molecules as small as heparin. Thus, convection plays a dominant role in the distribution of macromolecular agents following local delivery and may result in their rapid transport to the adventitia in the femoral artery.

Mural delivery of iloprost with use of hydrogel-coated balloon catheters suppresses local platelet aggregation

PURPOSE

To develop reproducible and quantifiable methods for mural delivery of iloprost, a potent agent against platelet aggregation, with use of hydrogel-coated angioplasty balloons, and to determine the in vivo effect of direct iloprost delivery on platelet aggregation at the angioplasty site.

MATERIALS AND METHODS

Drug loading of tritiated iloprost from an immersion solution onto hydrogel-coated balloons was evaluated as a function of balloon size (3 mm x 2 cm, 6 mm x 2 cm, 8 mm x 3 cm; n = 4 each), drug concentration (0.0715 mg/mL, 0.1072 mg/mL, 0.1430 mg/mL; n = 3 each), and duration of immersion (40 seconds, 60 seconds, 120 seconds; n = 3 each). In another set of experiments, optimal drying methods were tested to minimize drug loss within a protective delivery sheath (n = 3 each). Ex vivo angioplasty was performed on excised swine arteries to estimate how much of the drug present on the balloon could be delivered to the wall (n = 3 iliac segments). Finally, in vivo angioplasty was performed in three Yorkshire pigs (n = 6 iloprost-treated and 6 control arteries) and indium-111-labeled platelet aggregation was measured at these sites, which were harvested 1 hour after the procedure.

RESULTS

In the initial set of experiments, the authors found that the volume of drug loaded is determined by the wet-volume of the hydrogel coating, that the majority of volume loading occurs within the first 2 minutes, and that the volume uptake is independent of the drug concentration. The optimal drying method resulting in the least loss of iloprost within the sheath (only 4%) was prolonged drying (5 hours) under ambient conditions. Ex vivo angioplasty experiments showed that approximately 33% of the drug present on the balloon can be delivered to the wall. Finally, in vivo experiments showed that platelet aggregation is significantly suppressed at treated sites (by approximately 33% compared to control sites; P = .03) by minuscule mural doses of iloprost (roughly estimated at under 1 microg).

CONCLUSION

Quantifiable and reproducible methods for loading iloprost onto hydrogel-coated angioplasty balloons were developed. The best of these methods was able to deliver enough iloprost into the wall to significantly reduce local platelet aggregation.

Quantitative evaluation of local drug delivery using the InfusaSleeve catheter

BACKGROUND

Restenosis is the most common long-term complication after angioplasty. Local delivery of pharmacologic agents at the site of angioplasty holds promise as a means of achieving higher concentrations of drug in the arterial wall than can be obtained by systemic infusion. In this study, a novel local drug delivery catheter system, the InfusaSleeve catheter, was evaluated in a porcine coronary balloon injury model. The purpose of the study was to evaluate the efficacy of solute transfer to the arterial wall and the influence of varying supporting angioplasty balloon pressure.

METHODS AND RESULTS

Ten pigs (total of 22 arterial segments) underwent overstretch balloon injury (artery/balloon ratio 1:1.29) with a standard angioplasty balloon. In 7 animals (16 arterial segments) horseradish peroxidase (HRP; 10 mg/ml) was administered locally after injury, by tracking the local infusion catheter as a sheath over the angioplasty balloon to the intended site of arterial drug delivery. Supporting angioplasty balloons were inflated to one of the three different pressures. In 3 pigs HRP (10 mg/ml) was administered intravenously. No significant arterial injury caused by the local delivery device was evident on histological examination (disruption of the internal lamina elastica, arterial media, or thrombosis). Radial concentrations of the HRP reaction product in the first 150 microns of the arterial wall were quantified against known standards by measurement of light transmission through tissue sections. Mean HRP concentrations were not significantly different from those obtained by intravenous infusion using a supporting pressure of 1 atm or a supporting pressure of 3 atm of the underlying angioplasty balloon. However, a supporting pressure of 6 atm resulted in a 6-fold greater mean HRP concentration in the arterial wall than that which could be achieved by systemic administration of an equal volume of tracer (P < 0.001).

CONCLUSION

Thus solute can be delivered throughout the coronary media by the InfusaSleeve, with the magnitude of wall uptake related to support pressure. Local delivery at 6 atm support pressure produced substantially greater uptake than did systemic delivery.

Local delivery of heparin to balloon angioplasty sites with a new angiotherapy catheter: pharmacokinetics and effect on platelet deposition in the porcine model

The purpose of this study was to assess the efficacy of local heparin delivery to balloon angioplasty sites in an in vivo porcine model by using a newly designed angiotherapy catheter that allows for prolonged drug infusion while maintaining distal arterial perfusion. Protocols were designed to assess the safety of intracoronary drug delivery, the effect of infusion time and drug concentration on intramural heparin deposition, the distribution of heparin within the arterial wall, the histologic effects of local heparin delivery, the wash-out of intramurally deposited heparin, and the effect of heparin delivery on early platelet deposition following balloon injury in peripheral and coronary vessels. Local intracoronary delivery of heparin was well tolerated in all animals. Between 0.04 and 0.08% of infused heparin was intramurally deposited at the time of drug delivery, with longer infusion durations and higher concentrations of heparin resulting in greater intramural deposition. Autoradiography demonstrated homogenous distribution of heparin throughout the intima, media, and adventitia, with localization in the nuclei, cytoplasm, and extracellular space. Histologic analysis demonstrated no additional vessel trauma from local drug delivery beyond that seen with conventional angioplasty. Wash-out studies demonstrated a biexponential disappearance of intramurally deposited drug, with rapid release of heparin over the first 60 min and persistence of small amounts of drug for at least 7 d. Locally delivered heparin significantly attenuated the deposition of platelets in peripheral vessels, although a similar decrease in platelet deposition in the coronary arteries was not statistically significant. Local delivery of heparin directly to coronary angioplasty sites is possible with the use of a new angiotherapy catheter. Wash-out of heparin from the arterial wall is initially rapid, although drug is detectable for up to 1 wk following delivery. In porcine peripheral arteries, use of this technique significantly decreases early platelet deposition following balloon injury.

Local drug delivery with porous balloons in the rabbit: assessment of vascular injury for an improvement of application parameters

OBJECTIVES

Sufficient intramural drug concentrations with the use of porous balloon catheters can be achieved with additional vascular trauma only. However, effective delivery of a potent drug even in deeper layers of the vessel wall might outweigh these traumatic side effects. Given the porous balloon catheter, the parameters of injection pressure and applied fluid volume will influence the interventional result.

METHODS

We tested a 2.5-mm porous balloon (35 75-micron pores) in the right carotid artery of New Zealand rabbits and used injection pressures of 1, 2, and 5 atm and fluid volumes of 2 and 4 ml of low-molecular-weight heparin solution in combination with the different parameters (n = 5 animals/group). In 50 rabbits, an intimal fibromuscular plaque was induced by using the electrostimulation model. Balloon dilatation and then application of the porous balloon was performed in 30 animals, 10 animals were only electrostimulated, and 10 animals served as a control group with balloon dilatation only. The vessels were excised 7 d after intervention, stained, and analyzed histomorpologically. Anti-Xa assays revealed the extent of systemically escaped drug, and serial cuts allowed for exact determination of vessel wall injuries.

RESULTS

Effective local drug delivery could not be achieved with an injection pressure of less than 2 atm. Specific pressure-driven effects such as jet injuries could be identified. When the pressure was high enough for disruptive drug delivery (> or = 2 atm), fluid volumes of 4 ml led to loose elastic membranes and local thickening within the media.

CONCLUSIONS

Sufficient intramural drug distribution using porous balloon catheters can be achieved with low injection pressures. Different fluid volumes strongly determine the extent of additional vascular injury.

Localized delivery of heparin to angioplasty sites with iontophoresis

Drug delivery by iontophoresis involves the application of an electric field to move selectively charged drug molecules across biological membranes. The purpose of this study was to assess the efficacy of intravascular iontophoresis in the local delivery of heparin to balloon angioplasty sites by using a recently designed iontophoretic catheter. In vivo heparin iontophoresis was assessed in 33 rats and 21 pigs in four protocols designed to measure the technical determinants of intramural drug deposition, the pharmacokinetics and localization of coronary delivery, and the effect of this technique on platelet deposition following balloon injury. First, iontophoresis of 3H-heparin into the aorta of 33 rats was performed to determine the effects of iontophoretic current, iontophoretic membrane balloon initiation pressure, iontophoresis time, and heparin concentration on intramural drug deposition. Second, iontophoresis of 3H-heparin was performed in 16 porcine coronary arteries to quantitate immediate drug delivery and subsequent wash-out over 24 h. Third, iontophoresis of fluorescent heparin was performed in 8 porcine coronary arteries to define intramural localization of locally delivered drug. Fourth, 111In-labeled platelet deposition was measured 1 h following balloon angioplasty and local iontophoretic heparin delivery in 16 porcine carotid and iliac vessels. Contralateral control vessels that were dilated with the same size balloon and treated with iontophoresis of saline served as controls. Rat aortic studies demonstrated that iontophoresis resulted in 13 times more intramural heparin deposition than passive delivery (passive: 0.3 +/- 0.4 microgram, iontophoresis: 4.6 +/- 1.6 micrograms, P < 0.0004). Iontophoretic membrane balloon inflation pressure had no significant effect on intramural drug deposition, but longer iontophoresis times and higher heparin concentrations resulted in higher levels of intramural heparin (P < 0.05). Porcine coronary studies demonstrated successful intramural deposition of heparin in all arteries without adverse electrical or hemodynamic sequelae, with persistence of the drug for at least 24 h. Localization studies demonstrated immediate deposition of fluorescent heparin in the intima and internal elastic lamina, with subsequent rapid diffusion of the drug into the media. Porcine platelet studies demonstrated that heparin iontophoresis decreased platelet deposition following balloon injury by approximately 66% compared with saline-treated control vessels (heparin-treated: 1.46 +/- 2.51 x 10(8), control: 4.27 +/- 7.02 x 10(8), P = 0.001). This study has demonstrated that local intramural heparin delivery is feasible with an intravascular iontophoretic catheter. Following intracoronary heparin iontophoresis in the porcine model, intramural drug is detected for at least 24 h. Local delivery of heparin with this technique significantly decreases early platelet deposition following balloon injury in peripheral porcine arteries.

Site-specific intracoronary heparin delivery in humans after balloon angioplasty. A radioisotopic assessment of regional pharmacokinetics

BACKGROUND

Demonstration and quantification of site-specific intracoronary administration of compounds has been confined thus far to the experimental animal laboratory. The aim of this study was to describe a scintigraphic method to demonstrate site-specific intracoronary drug delivery in humans. The methods allow on-line visualization and off-line quantification of site-specifically infused gamma-emitting compounds.

METHODS AND RESULTS

In 12 patients after balloon angioplasty, 99mTc-labeled heparin was administered at the site of dilatation by use of a coil balloon. Both the infusion period and the washout period after the end of infusion were monitored with a gamma-camera. A curve of counts per pixel as a function of time was derived that showed an accumulation phase during infusion followed by washout phase after the end of infusion. Both phases were fitted by regression analysis and showed a linear accumulation pattern and a biexponential washout pattern. After correction for background counts, 99mTc decay, and body attenuation, peak heparin amount and regional bioavailability were calculated. Peak amount was defined as the initial point of the slow washout component of the biexponential curve (elimination component), and regional bioavailability was defined as the area under the curve of accumulation and washout phase. Half-life and retention time, define as seven half-lives, were obtained by use of the elimination component after correction for 99mTc decay. Mean peak delivered amount was 45 +/- 44 IU (236 +/- 228 micrograms), corresponding to an efficiency of delivery ranging from 1% to 8% of the totally infused dose. Total regionally bioavailable heparin reached 244 +/- 194 IU.h (1.28 +/- 1.01 mg.h). Retention time varied from 12 to 90 hours (mean, 50:33 +/- 22:50 hours:minutes).

CONCLUSIONS

Site-specific intracoronary heparin delivery after angioplasty by means of the coil balloon was demonstrated in humans, and regional pharmacokinetics was quantified by use of a radioisotopic technique.

Site-specific intravascular administration of drugs: history of a method applicable in humans

Demonstration and quantification of site-specific intracoronary administration of pharmacological compounds has been limited thus far to animal experimental models. Recently, a method applicable in humans has been developed. The aim of this study is to give an overview on the available methods to visualize and quantify intravascularly administered "labeled" drugs in animals and to describe the historical development of a method now applied in the clinical arena. The potential of this approach is briefly summarized.

Local delivery of c-myb antisense oligonucleotides during balloon angioplasty

Intraluminal delivery of antisense oligonucleotides to c-myb was assessed following balloon angioplasty in swine peripheral arteries. Successful delivery and intramural persistence of oligonucleotide for over 24 h were demonstrated following angioplasty with hydrogel balloons coated with 32P-labeled antisense. Delivery of fluorescein-labeled antisense demonstrated further localization within the arterial media and intracellularly. Preliminary in vitro studies demonstrated the feasibility of inhibition of porcine lymphocyte proliferation using the murine antisense to c-myb. Twelve iliac or carotid arteries underwent angioplasty with antisense-coated balloons, while the contralateral vessels underwent angioplasty with the same-sized balloons coated with the complementary sense strand. Six to seven days later, dilated arterial segments were surgically isolated. In 10 of 12 vessel pairs, antisense-treated vessels demonstrated less cellular proliferation than did contralateral sense-treated vessels, as assessed by quantitative immunohistochemical staining of proliferating cell nuclear antigen, and smooth muscle cell proliferation was reduced 18% in antisense-treated vessels compared to the contralateral sense-treated vessels (PCNA-positive nuclear area: 7.7 +/- 4.9% vs. 9.3 +/- 5.2%, P < 0.04)-intraluminal delivery of antisense oligonucleotides to c-myb is feasible with a catheter-based system and may reduce smooth muscle cell proliferation following arterial injury.

Intramural drug delivery by direct injection within the arterial wall: first clinical experience with a novel intracoronary delivery-infiltrator system

Local drug delivery at the lesion site in patients with coronary artery disease is being intensively studied to prevent restenosis after percutaneous coronary intervention. However, the effective penetration of the delivered agents into the vessel wall and delivery time remain considerable problems for all currently existing devices. A unique, new catheter has been invented, the infiltrator Angioplasty Balloon Catheter (IABC), which has the capability to allow intramural drug delivery by direct injection within the arterial wall. We describe the first clinical experience with this catheter. IABC is an angioplasty catheter with 3 lumens: one for inflating the balloon, one central for the guidewire, and a third for drug delivery. On the surface of the balloon there are 3 longitudinal strips of 6 injection needles, which on inflation stand 0.01" high, and are connected to the drug-delivery lumen. With inflation of the balloon, the needles penetrate the lesion, allowing drug delivery into the media of the vessel wall. We used the IABC in 17 patients (age = 58 +/- 9 years) undergoing coronary angioplasty. All patients were symptomatic, with significant lesions (13 LAD, 3 LCX, 1 RCA) and documented ischemia. Following initial dilatation with a conventional angioplasty balloon (stenosis from 72 +/- 8% to 26 +/- 14%, P < 0.001), the IABC was used to infiltrate the lesion with 0.4 ml (6,000 IU) of low-molecular-weight heparin (Fraxiparine). For the delivery, the IABC was inflated to 1-2 atm for 30-45 s, and the heparin was injected by hand in 5 s. Lesion residual stenosis and morphology remained unchanged after IABC use (26 +/- 14% to 22 +/- 11%, P = NS). In 10 patients, stent placement followed the IABC use. The decision to proceed with stent placement was made after the initial dilatation with the conventional balloon, and it was not influenced by the IABC use. Stent placement greatly improved the final result (for the whole patient group: 22 +/- 11% to 5 +/- 18%, for the stented patients: 22 +/- 13% to -7 +/- 10%, P < 0.001 for both). Hospital course was uneventful, with no electrocardiogram changes and normal cardiac enzymes for all patients. We have shown that the use of a unique new catheter (IABC) for intramural drug delivery in human patients undergoing coronary angioplasty is feasible and safe. This catheter is the first of a new generation of catheters and represents a significant step in local drug delivery. It is very promising as a vehicle to modify plaque behavior and potentially influence restenosis after angioplasty.

Restenosis: is there a pharmacologic fix in the pipeline?

One of the most frustrating aspects of restenosis is that it is the result of advances in medical care (there was no restenosis before the days of balloon angioplasty), yet it seems to be resistant to all that science has to offer. Still we believe there is reason to be optimistic. We are at last beginning to see some promise from clinical trials, and data being generated confirm some of the hypotheses previously generated from animal experiments. Thus the effects seen with the GP IIb/IIIa antibody 7E3 suggest that thrombosis may be as important in its long-term sequelae as it is for acute reocclusion. The jury is still out on whether antiproliferative approaches will be a therapeutic option, but local delivery paradigms using novel formulations delivered by catheter or impregnated in stents may allow the concept to be tested without the risk of systemic toxicity. Plans are also underway for gene therapy trials, although we may have to wait for better vector technology before taking these into the coronary bed. Perhaps we should move away from the "single pill" approach and accept that, like many infections, malignancies, or even heart failure, a multifaceted approach with combination therapy will provide the first glimmer of that brighter tomorrow.

Local delivery of heparin with balloon angioplasty: results of a prospective randomized trial

PURPOSE

To evaluate the effectiveness of local delivery of heparin via hydrogel-coated balloons in the treatment of vascular stenoses associated with hemodialysis access.

MATERIALS AND METHODS

This was a randomized, prospective trial comparing treatment with hydrogel-coated balloon catheters delivered with heparin coating (n = 33) and without (n = 26). All patients were undergoing hemodialysis, and all stenoses involved the venous anastomosis of a dialysis graft or a native vein. The heparin-treated balloons were soaked in concentrated heparin and delivered in a protected manner to help prevent washout of heparin.

RESULTS

The mean primary patencies were 143 days with heparin treatment and 214 days without heparin (P = .174). The mean assisted primary patencies were 165 days with heparin and 194 days without (P = .315). The mean secondary patencies were 351 days with heparin and 384 without (P = .81).

CONCLUSION

In this population with this technique, the treatment outcome of venous outflow stenosis in patients with dialysis grafts is not improved with local delivery of heparin.

Prevention of Restenosis by Local Drug Delivery

Local drug therapy for preventing restenosis after angioplasty has been investigated for over a decade. Biologically active agents ranging from drugs to genes can be delivered locally using a wide variety of catheters. Microspheres, liposomes, and polymers have been used to enhance drug retention at the delivery site. More recently stents have been investigated as devices to attain local drug delivery, either by coating with polymers, seeding with genetically modified cells or by using them as a source of local radiation. Though the best method of delivering agents locally remains undefined, this approach is likely to emerge as an essential mode of therapy in the near future.

Intramural delivery of agent via a novel drug-delivery sleeve. Histological and functional evaluation

BACKGROUND

The infusion sleeve is a novel drug-delivery catheter system designed to deliver an agent under controlled conditions into the arterial wall at the site of angioplasty. The purpose of the present study was to characterize the delivery agent via the infusion sleeve in ex vivo and in vivo models.

METHODS AND RESULTS

The delivery of horseradish peroxidase via the infusion sleeve was studied in a porcine explanted heart model. Under physiological conditions, arteries underwent balloon injury (approximately 10% overstretch), after which horseradish peroxidase (2.5 mL) was delivered at specific pressures. Cross-sectional analysis demonstrated greater staining when the agent was delivered at increasing pressures. The infusion sleeve was evaluated in an in vivo canine coronary model. With an infusion sleeve loaded over a standard dilatation catheter through a 9F guide, overstretch balloon injury was performed, after which fluoresceinated heparin was delivered. Animals were killed 2 hours after delivery. Fluoresceinated heparin-treated segments demonstrated high fluorescence signals, localizing with smooth muscle cell nuclei with less activity in the interstitium. The functional significance of intramural heparin delivery was studied in a porcine carotid model. In the presence of 111In-labeled platelets, arteries underwent overstretch injury followed by delivery of heparin (50 or 100 units/kg) or vehicle. Platelet deposition was reduced at 30 minutes (57%, P < .01) and 12 hours (39%, P = .06) compared with saline controls.

CONCLUSIONS

Agent delivery via the infusion sleeve is pressure dependent; transmural delivery is possible with minimal disruption of arterial wall architecture; the infusion sleeve is compatible with standard angioplasty equipment; and heparin delivery at the site of balloon injury significantly reduces platelet deposition in a porcine model for a minimum of 12 hours.

Adenoviral mediated gene transfer to atherosclerotic arteries after balloon angioplasty

The purpose of this study was to examine the pattern of catheter-mediated adenoviral gene transfer into atherosclerotic vessels subjected to balloon injury. Atherosclerotic lesions were created in the iliac arteries of New Zealand white rabbits fed with cholesterol. Balloon dilatation was performed at the angiographically defined region of maximal stenosis. Instillation of a recombinant adenoviral vector encoding beta Galactosidase was performed at the angioplasty site with either (1) a double-balloon catheter (n = 7 arterial segments), (2) a hydrogel-coated balloon (n = 3), (3) a perforated balloon (n = 3), or (4) a catheter with an inflatable circumferential helical ring (n = 4). Successful gene transfer reflected by expression of nuclear-localizing beta-galactosidase activity was observed in all sections displaying angioplasty effect. Genetically modified cells were located in pockets within the deep portions of the neointima, the media, and the adventitia immediately adjacent to dissection planes. Gene transfer to an atherosclerotic vessel subjected to balloon angioplasty is feasible with recombinant adenovirus vectors and currently available delivery catheters. The regions of the vessel wall that express the foreign protein are those which contribute most importantly to the proliferative cellular response which characterizes postangioplasty restenosis.

Regional and arterial localization of radioactive microparticles after local delivery by unsupported or supported porous balloon catheters

Catheter-mediated intramural delivery of pharmaceutical agents after angioplasty is a potential method to reduce postangioplasty restenosis. The efficacy of such delivery has been limited both by an incomplete initial intramural deposition of delivered agents and by rapid diffusion of soluble agents from the site of delivery. The local delivery of microparticulate agents results in prolonged retention of material at the delivery site. Accordingly this study was designed to evaluate the complementary issue of the initial delivery efficiency and pattern of localization of microparticles after local catheter-mediated delivery with two types of porous balloons. These two types were a "standard" porous balloon (PB) in which hydraulic pressure both inflated the balloon and infused the agents and a porous balloon with a mechanical undergirding that permitted mechanical expansion (PB/ME) before agent infusion. Radioactive cerium 141-labeled microparticles (11.4 microns diameter) were locally delivered into atherosclerotic rabbit femoral arteries after angioplasty to test the hypothesis that use of the PB/ME apparatus would yield enhanced intramural particle deposition and decreased systemic administration by increased balloon-wall contact before microparticle infusion. Six animals underwent infusion with the PB catheter, and seven animals underwent infusion with the PB/ME catheter. An image of the in vivo particle distribution was obtained with a gamma camera during infusion, immediately after infusion, and 1, 3, and 7 days after infusion. Tissue samples from the artery, periadventitia, thigh, calf, and foot musculature, and liver were obtained at animal death, and retained radioactivity was measured with a well counter.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of platelet deposition and lysis of intracoronary thrombus during balloon angioplasty using urokinase-coated hydrogel balloons

BACKGROUND

Conventional balloon angioplasty of intracoronary thrombus is associated with a high incidence of abrupt closure, distal embolization, and no-reflow phenomenon. The purpose of this study was to assess a new technique for treating intracoronary thrombus consisting of the local delivery of urokinase directly to the angioplasty site with urokinase-coated hydrogel balloons.

METHODS AND RESULTS

We assessed local urokinase delivery using hydrogel balloons in four protocols. First, we evaluated the pharmacokinetics of urokinase delivery in vitro using 125I-labeled urokinase to measure drug loading onto hydrogel balloons, drug retention by the hydrogel polymer during blood exposure, and drug transfer from the balloon surface to the arterial wall during balloon dilatation. Second, we measured 125I-urokinase washoff from the hydrogel balloon in the intact circulation and intramural drug delivery during in vivo balloon angioplasty in 10 anesthetized New Zealand rabbits. Third, we assessed the effect of local urokinase delivery on 111In-labeled platelet deposition after balloon angioplasty in vivo in 13 porcine carotid or iliac arteries dilated with urokinase-coated balloons and compared them with contralateral control arteries dilated with saline-coated balloons. Finally, we determined the clinical efficacy of urokinase-coated balloons in 15 patients with intracoronary thrombus, including 7 who demonstrated abrupt thrombotic closure after conventional angioplasty. Between 241 and 1509 U urokinase could be loaded onto hydrogel balloons ranging in size from 2 to 8 mm. In vitro and in vivo studies demonstrated that hydrogel balloons absorbed significantly more urokinase and demonstrated less drug wash-off than nonhydrogel balloons (P < .01). Similarly, both in vitro and in vivo studies demonstrated urokinase transfer from the hydrogel to the arterial wall during balloon angioplasty, with greater intramural drug deposition with larger balloons (P < .01). Local urokinase delivery after in vivo porcine angioplasty decreased 111In-labeled platelet deposition by 47% compared with contralateral control vessels (P = .03). Use of urokinase-coated balloons in patients with intracoronary thrombus resulted in thrombus dissolution and reversal of abrupt closure in all cases, without evidence of distal embolization.

CONCLUSIONS

With the use of hydrogel-coated balloons, urokinase can be delivered locally to an angioplasty site. This technique decreases platelet deposition after in vivo balloon angioplasty and is efficacious in treating intracoronary thrombus in patients, including those with abrupt thrombotic closure.