Intramural methotrexate therapy for the prevention of neointimal thickening after balloon angioplasty

Endovascular Drug Delivery

Drug-eluting stents (DES) and balloons revolutionize atherosclerosis treatment by targeting hyperplastic tissue responses through effective local drug delivery strategies. This review examines approved and emerging endovascular devices, discussing drug release mechanisms and their impacts on arterial drug distribution. It emphasizes the crucial role of drug delivery in modern cardiovascular care and highlights how device technologies influence vascular behavior based on lesion morphology. The future holds promise for lesion-specific treatments, particularly in the superficial femoral artery, with recent CE-marked devices showing encouraging results. Exciting strategies and new patents focus on local drug delivery to prevent restenosis, shaping the future of interventional outcomes. In summary, as we navigate the ever-evolving landscape of cardiovascular intervention, it becomes increasingly evident that the future lies in tailoring treatments to the specific characteristics of each lesion. By leveraging cutting-edge technologies and harnessing the potential of localized drug delivery, we stand poised to usher in a new era of precision medicine in vascular intervention.

Current concepts regarding drug dosing for peripheral stents

Drug-eluting stent (DES) are the mainstay therapy for the treatment of coronary artery disease. Stent design and drug-elution strategies have evolved over the years leading to the last generation DES which shows optimal safety and efficacy outcome. Peripheral arteries have different mechanical and biological features and the lessons learned from the coronary field have been difficult to introduce into the development of peripheral vascular technologies. First, due to its complex biomechanical behavior the use of metallic stents is limited in some vascular segments (i.e., distal superficial fermoral artery [SFA]). Also, peripheral vascular atherosclerosis is different containing higher levels of plaque burden and calcium. Finally, peripheral arterial disease tends to be more aggressive including longer lesions and higher incidence of total chronic occlusion. In general terms, restenosis in the peripheral vascular territory is more aggressive and occurs at a later time (~12 months) requiring a different pharmacokinetic profile compared to coronary technologies. Several strategies have been evaluated in the peripheral arteries raging from the bare metal stent to the drug coated balloon and drug eluting stent with outcome varying depending on the different field of application (i.e. SFA and below-the-knee). Results coming from the clinical trial are encouraging but further studies and direct comparison among the different technologies are demanded to determine the best therapy for peripheral vascular disease.

Effects of Methotrexate on Carotid Intima-media Thickness in Patients with Rheumatoid Arthritis

The purpose of this study was to evaluate the effects of rheumatoid arthritis (RA) and antirheumatic drugs on atherosclerosis by comparing carotid intima-media thickness (CIMT) as an indicator for cardiovascular diseases (CVD). This study included 44 female RA patients who met the 2010 ACR/EULAR criteria and age-matched 22 healthy females. CIMT was measured on both carotid arteries using a B-mode ultrasound scan. The mean value of both sides was taken as the CIMT of the subject. The CIMT was evaluated according to the use of drugs, disease activity and CVD risk factors in RA patients as a case-control study. Higher CIMT was observed in RA patients as compared with healthy subjects (0.705 ± 0.198 mm, 0.611 ± 0.093 mm, respectively, P < 0.05). With adjustment for the CVD risk factors, disease activity and the use of anti-rheumatic drugs, methotrexate (MTX) only showed a favorable effect on CIMT in RA. A significantly lower CIMT was observed in RA with MTX as compared with RA without MTX (0.644 ± 0.136 mm, 0.767 ± 0.233 mm, respectively, P < 0.05). The effects were correlated with MTX dosage (β = -0.029, P < 0.01). The use of MTX should be considered in high priority not only to control arthritis but also to reduce the RA-related CVD risk to mortality.

Perivascular delivery of neomycin inhibits the activation of NF-κB and MAPK pathways, and prevents neointimal hyperplasia and stenosis after arterial injury

The nuclear transcription factor kappaB (NF-kappaB) is a cytoplasmic dimer that, as the family of mitogen-activated protein kinase (MAPK), can directly regulate the expression of early genes and genes involved in the stress response, following a variety of physiological or pathological stimuli. Both of them stimulate the transcription of many proteins, which are considered important during inflammation. A crucial role has been assigned to these factors in cellular proliferation and in neointimal hyperplasia secondary to the endothelial lesion of arterial vessels. On the other hand, it has been described that neomycin can have an inhibitory function on tumor cell proliferation, through the inhibition of different intracellular pathways of signaling, among them the NF-kappaB and MAPK pathways. Rat common carotid artery was subjected to balloon angioplasty. Neomycin sulfate (18 mg) was applied using pluronic acid gel on the adventitial surface of the injured vessel. MAPK and NF-kappaB activation was quantified after 24 hours with immunohistochemical staining. Neointimal formation was quantified after 14 days with morphometry. Immunohistochemistry results demonstrating MAPK and NF-kappaB activation reveal that both transcription factors are activated in the media of the control vessel wall. In contrast, the immunoreactivity for MAPK and NF-kappaB in the sections obtained from arteries treated with neomycin over 24 hours was insufficient or nonexistent. Treatment with neomycin on adventitia over 14 days in arteries on which angioplasty was performed shows a neointimal index (intimal area/medial area) decrease of 71% in comparison with arteries that were not treated. The adventitial neomycin treatment over 14 days produces a very significant increase (287.5%; p<0.0001) in the arterial luminal circumference in comparison with arteries treated with vehicle. These results support the theory that neomycin plays an important role against neointimal hyperplasia through the inhibition of MAPK and NF-kappaB activation.

Local drug delivery to prevent restenosis

INTRODUCTION

Despite significant advances in vascular biology, bioengineering, and pharmacology, restenosis remains a limitation to the overall efficacy of vascular reconstructions, both percutaneous and open. Although the pathophysiology of intimal hyperplasia is complex, a number of drugs and molecular tools have been identified that can prevent restenosis. Moreover, the focal nature of this process lends itself to treatment with local drug administration. This article provides a broad overview of current and future techniques for local drug delivery that have been developed to prevent restenosis after vascular interventions.

METHODS

A systematic electronic literature search using PubMed was performed for all accessible published articles through September 2012. In an effort to remain current, additional searches were performed for abstracts presented at relevant societal meetings, filed patents, clinical trials, and funded National Institutes of Health awards.

RESULTS

The efficacy of local drug delivery has been demonstrated in the coronary circulation with the current clinical use of drug-eluting stents. Until recently, however, drug-eluting stents were not found to be efficacious in the peripheral circulation. Further pursuit of intraluminal devices has led to the development of balloon-based technologies, with a recent surge in trials involving drug-eluting balloons. Early data appear encouraging, particularly for treatment of superficial femoral artery lesions, and several devices have recently received the Conformité Européene mark in Europe. Investigators have also explored the periadventitial application of biomaterials containing antirestenotic drugs, an approach that could be particularly useful for surgical bypass or endarterectomy. In the past, systemic drug delivery has been unsuccessful; however, there has been recent exploration of intravenous delivery of drugs designed specifically to target injured or reconstructed arteries. Our review revealed a multitude of additional interesting strategies, including >65 new patents issued during the past 2 years for approaches to local drug delivery focused on preventing restenosis.

CONCLUSIONS

Restenosis after intraluminal or open vascular reconstruction remains an important clinical problem. Success in the coronary circulation has not translated into solutions for the peripheral arteries. However, our literature review reveals a number of promising approaches, including drug-eluting balloons, periadventitial drug delivery, and targeted systemic therapies. These and other innovations suggest that the future is bright and that a solution for preventing restenosis in peripheral vessels will soon be at hand.

Pharmacokinetics and consistency of pericardial delivery directed to coronary arteries: direct comparison with endoluminal delivery

BACKGROUND AND HYPOTHESIS

Pharmacologic modulation of the contents of the pericardial space has been shown to influence the response of coronary arteries to balloon injury. Endoluminal (EL) local delivery of various drugs into coronaries has been found to be limited by short residence time, as well as by highly variable deposited agent concentration. We hypothesized that compounds placed into the pericardial space (P) would penetrate into coronary tissue with greater consistency than seen after EL delivery and provide for prolonged coronary exposure to agents.

METHODS AND RESULTS

125I-labeled basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), albumin, or 131I-labeled diazeniumdiolated albumin (NONO-albumin) were delivered as model/therapeutic proteins into the porcine pericardial space (n = 15 pigs) or into coronaries using an EL delivery catheter (n = 48 arteries). In subjects receiving 125I-labeled proteins, the delivery target or mid-regions of the left anterior descending (LAD) and left circumflex (LCx) arteries were harvested at 1 h or 24 h for gamma-counting and autoradiography, and fractional intramural delivery (FID) or retention measured as percent agent in 100 mg artery/agent in infusate for both time points. In the animals receiving 131I-labeled NONO-albumin, serial gamma imaging was employed to evaluate the rate of redistribution in individual animals following either pericardial or endoluminal delivery. At 1 h, FID values ranged from 0.00064 to 0.0052% for P delivery (median 0.0022%), and from 0.00021 to 6.7 for EL delivery (median 0.27%). At 24 h, FID values ranged from 0.00011 to 0.003 for P delivery (median 0.0013), and from 0.0002 to 1.4 for EL delivery. The estimated T1/2 for bFGF redistribution from the vascular tissue was 22 h (P) and 7 h (EL), respectively, while the directly determined T1/2 values for NONO-albumin redistribution from the delivery region were 22.2 h (P) and 2.5 h (EL).

CONCLUSIONS

These data show that pericardial fluid contents can access coronary arteries with intramural concentrations which typically vary by 10-15-fold, while EL delivery results in a remarkably wide intramural concentration range with up to 33,000-fold variability. The apparent redistribution rate is more rapid following EL delivery, possibly due to sustained diffusive tissue loading from the pericardial space. Pericardial delivery appears to offer substantial advantages over EL administration with respect to residence time and reproducibility.

Poly(vinyl alcohol)-graft-poly(lactide-co-glycolide) nanoparticles for local delivery of paclitaxel for restenosis treatment

Catheter-based local delivery of biodegradable nanoparticles (NP) with sustained release characteristics represents a therapeutic approach to reduce restenosis. Paclitaxel-loaded NP consisting of poly(vinyl alcohol)-graft-poly(lactide-co-glycolide) (PVA-g-PLGA) with varying PLGA chain length as well as poly(lactide-co-glycolide) (PLGA), were prepared by a solvent evaporation technique. NP of <180 nm in diameter characterized by photon correlation spectroscopy (PCS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) are spherical and show smooth surfaces. Yields typically range from 80 to 95% with encapsulation efficiencies between 77 and 87%. The extent of initial in vitro paclitaxel release was affected by the PVA-g-PLGA composition. Blank nanoparticles from PVA(300)-g-PLGA(30) and PVA(300)-g-PLGA(15) showed excellent biocompatibility in rabbit vascular smooth muscle cells (RbVSMC) at polymer concentrations of 0.37 mg/ml. Paclitaxel-loaded NP have an increased antiproliferative effect on cells in comparison to free drug. Confocal laser scanning microscopy of RbVSMC confirmed cellular uptake of nanoparticles composed of fluorescently labeled PVA(300)-g-PLGA(15) loaded with Oregon Green labeled paclitaxel. Cells showed a clearly increased fluorescence activity with a co-localization of paclitaxel and polymer nanoparticles during incubation with particle suspension. To evaluate the antirestenotic effect in vivo, paclitaxel-loaded nanoparticles were administered locally to the wall of balloon-injured rabbit iliac arteries using a porous balloon catheter. As a result a 50% reduction in neointimal area in vessel segments treated with paclitaxel-loaded nanoparticles compared to control vessel segments could be observed (local paclitaxel nanoparticle treated segments 0.80+/-0.19 mm(2), control segments 1.58+/-0.6 mm(2); p<0.05).

Modified Paclitaxel-loaded Nanoparticles for Inhibition of Hyperplasia in a Rabbit Arterial Balloon Injury Model

PURPOSE

This study tested the possibility of localized intravascular infusion of positive charged paclitaxel-loaded nanoparticles (NPs) to better prevent neointimal formation in a rabbit carotid artery injury model.

MATERIALS AND METHODS

NPs were prepared by oil-water emulsion/solvent evaporation technique using biodegradable poly (lactide-co-glycolide) (PLGA). A cationic surfactant, didodecyldimethylammonium bromide (DMAB), was absorbed on the NP surface by electrostatic attraction between positive and negative charges. NPs were characterized in such aspects as size, surface morphology, surface charges as well as in vitro drug release profile. Balloon injured rabbit carotid arteries were treated with single infusion of paclitaxel-loaded NP suspension and observed for 28 days. The inhibitory effects of NPs on neointima formation were evaluated as end-point.

RESULTS

NPs showed spherical shape with a diameter ranging from 200 to 500 nm. Negatively charged PLGA NPs shifted to positive after the DMAB modification. The in vitro drug release profile showed a biphasic release pattern. Morphometric analyses on the retrieved artery samples revealed that the inhibitory effect of intima proliferation was dose-dependent. At a concentration of 30 mg ml(-1), NP infusion completely inhibited intima proliferation in a rabbit vascular injury model.

CONCLUSIONS

Paclitaxel-loaded NPs with DMAB modification were proven an effective means of inhibiting proliferative response to vascular injury in a rabbit model.

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.

Methotrexate loaded SAE coated coronary stents reduce neointimal hyperplasia in a porcine coronary model

OBJECTIVE

To evaluate the effect of stent based methotrexate delivery on neointimal hyperplasia.

METHODS

Stainless steel coronary stents and biological polymer coated (SAE) stents were randomly implanted in coronary arteries of pigs with a stent to artery ratio of 1.1:1. The pigs were killed after five days (10 stents) or four weeks (20 stents). Second, stainless steel coronary stents were dip coated in a 10 mg/ml methotrexate-SAE polymer solution, resulting in a total load of 150 microg methotrexate/stent. SAE coated stents and methotrexate loaded stents were randomly implanted in porcine coronary arteries with a stent to artery ratio of 1.2:1 and followed up to four weeks.

RESULTS

SAE coated stents and bare stents elicited a similar tissue response at five days. At four weeks, neointimal hyperplasia induced by the coated stents was less pronounced than with the bare stents (1.32 (0.66) v 1.73 (0.93) mm2, p > 0.05). In vitro drug release studies showed that 50% of the methotrexate was released in 24 hours, and all drug was released within four weeks. No impact on vascular smooth muscle cell proliferation or viability was observed in in vitro cell cultures. At four weeks the arteries with methotrexate loaded stents had decreased peristrut inflammation and neointimal hyperplasia (1.22 (0.34) v 2.25 (1.28) mm2, p < 0.01).

CONCLUSIONS

SAE coating had an excellent biocompatibility with vascular tissue. Stent based delivery of methotrexate in the SAE coating effectively reduced neointimal hyperplasia in a porcine coronary stent model, potentially due to reduced peristrut inflammation.

Rapamycin in cardiovascular medicine

The cellular action of rapamycin (sirolimus), a natural fermentation product produced by Streptomyces hygroscopicus, is mediated by binding to the FK506 binding protein. By inhibiting a kinase known as the target of rapamycin, it restricts the proliferation of smooth-muscle cells by blocking cell-cycle progression at the G1/S transition. The finding that rapamycin possesses both anti-proliferative and antimigratory activity suggests that it could contribute to the control of arterial re-narrowing after percutaneous intervention and control the vascular manifestations of chronic rejection in transplanted hearts. The first clinical trials of implantation of rapamycin- coated stents in obstructive coronary artery lesions have been reported and, in selected patient groups, it appears that the restenosis process has been abolished. Studies are underway to establish the benefits of rapamycin-coated stents in day-to-day interventional practice, including small vessels, long lesions and patients with multivessel disease. With the addition of novel antiplatelet agents and delivery systems, it is possible that the two major limitations of percutaneous coronary intervention - restenosis and stent thrombosis - will be overcome. Cardiac graft loss due to intimal hyperplasia and accelerated atherosclerosis remains the major limitation to long-term survival following cardiac transplantation. Animal studies of rapamycin have suggested that this process can be reduced or abolished. Human studies of the efficacy of rapamycin in preventing both acute rejection and allograft arterial disease are in progress. Concerns regarding toxicity, carcinogenicity, delayed healing and endothelialization remain. As with any new agent or technology, we must remain vigilant to late adverse side-effects.

Deposition of nanoparticles in the arterial vessel by porous balloon catheters: localization by confocal laser scanning microscopy and transmission electron microscopy

Restenosis remains the major limitation of percutaneous transluminal angioplasty (PTA) and stenting in the treatment of patients with atherosclerotic disease. Catheter-based local delivery of pharmacologic agents offers a potential therapeutic approach to reducing restenosis and minimizing undesirable systemic side effects. However, the intramural retention of liquid agents is low. Therefore, to achieve a sustained and regional release of the therapeutic agent it must be encapsulated in nanoparticle carrier systems. The purpose of this study was to investigate the size dependence of the penetration of nanoparticles after local delivery into the vessel wall of the aorta abdominalis of New Zealand white rabbits. Two milliliters of a 0.025% fluorescence-labeled polystyrene nanoparticle suspension with diameters ranging from 110 to 514 nm were infused at 2 atm and at constant PTA pressure of 8 atm into the aorta abdominalis. After the infused segments were removed, the location of nanoparticles was visualized using confocal laser scanning microscopy and transmission electron microscopy. The study demonstrates a size-dependent nanoparticle penetration into the intact vessel wall. While nanoparticles of about 100 and 200 nm were deposited in the inner regions of the vessel wall, 514-nm nanoparticles accumulated primarily at the luminal surface of the aorta. The observations confirm that size plays a critical role in the distribution of particles in the arterial vessel wall. It is additionally influenced by the formation of pressure-induced infusion channels, as well as by the existence of anatomic barriers, such as plaques, at the luminal surface of the aorta or the connective elastic tissue.

Propionyl-L-carnitine reduces intimal hyperplasia after injury in normocholesterolemic rabbit carotid artery by modulating proliferation and caspase 3-dependent apoptosis of vascular smooth muscle cells

Previously we documented that propionyl-L-carnitine (PLC) reduces the growth of atherosclerotic lesions in cholesterol-fed aged rabbits in association with a decrease of plaque smooth muscle cell (SMC) proliferation and plasma triglycerides. To clarify whether PLC might influence SMC growth through mechanisms other than triglyceride lowering, we investigated the effect of a daily treatment per os with PLC on carotid intimal hyperplasia after ballooning in normocholesterolemic rabbits. PLC did not induce variations of plasma triglyceride and cholesterol. One week later, the number of proliferating SMCs was reduced in PLC as compared with controls. After 3 weeks, morphometric analysis demonstrated a reduced neointimal relative volume and percentage of stenosis but not vessel area in PLC as compared with controls. This associated with an intimal reduced SMC number and an increased apoptotic rate as detected by nick-end labelling (TUNEL) and ligation-mediated polymerase chain reaction (PCR). Western blotting also demonstrated an increase of caspase-3 cleavage in PLC carotids. Antiproliferative and pro-apoptotic effects of PLC were confirmed in vitro on actively proliferating and serum deprived SMCs, respectively. Molecules with an additional cell-specific, pro-apoptotic action may represent a new therapeutic tool in reducing intimal SMC hyperplasia following angioplasty or stenting procedures.

Stent development and local drug delivery

Stent implantation has become the new standard angioplasty procedure. In-stent re-stenosis remains the major limitation of coronary stenting. Re-stenosis is related to patient-, lesion- and procedure-specific factors. Patient-specific factors can not be influenced to any extent. Procedure-specific factors are affected by implantation technique and stent characteristics. Design and material influence vascular injury and humoral and cellular response. Radiation has been shown to have inhibitory effects on smooth muscle cell growth and neo-intima formation, but in clinical trials the outcome has been hampered by re-stenosis at the edges of the radioactive stent ('candy wrapper'). New approaches target pharmacological modulation of local vascular biology by local administration of drugs. This allows for drug application at the precise site and time of vessel injury. Systemic release is minimal and this may reduce the risk of toxicity. The drug and the delivery vehicle must fulfil pharmacological, pharmacokinetic and mechanical requirements and the application of eluting degradable matrices seems to be a possible solution. Numerous pharmacological agents with antiproliferative properties are currently under clinical investigation, e.g. actinomycin D, rapamycin or paclitaxel. Another approach is for stents to be made of biodegradable materials as an alternative to metallic stents. Their potential long-term complications, such as in-stent re-stenosis and the inaccessibility of the lesion site for surgical revascularization, needs to be assessed. Current investigational devices and the line of (pre)clinical investigation are discussed in detail. Currently, there is little experimental, and only preliminary clinical, understanding of the acute and long-term effects of drug-eluting or biodegradable stents in coronary arteries. The clinical benefit of these approaches still has to be proven.

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.

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.

Gene therapy for restenosis: getting nearer the heart of the matter

Intensive work over the past decade has been directed to the study of vascular gene transfer as an approach to the unresolved problem of restenosis. This effort has resulted in a significant foundation of knowledge relative to the activities of potentially therapeutic gene products as well as the capabilities and limitations of vector systems and mechanical delivery modalities available for effecting the vascular expression of these gene products. In several instances, significant progress has been made by experiments highlighting unexpected difficulties and the need for more comprehensive understanding. It is thus now possible to clearly define and address specific challenges that must be overcome in order to make feasible progress from the preclinical to the clinical arena. The key challenges at present appear to include the evolution of clinically practical delivery methods that meet the kinetic requirements of achieving efficient gene transduction and the availability of vectors that maximize efficiency while minimizing undesirable host responses. Emerging data suggest that approaches to solving each of these issues may have recently been developed. Basic research evaluating these new delivery mechanisms and molecular vectors is essential to establish their true potential for use in the clinical arena.

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.

Local delivery of ethanol inhibits intimal hyperplasia in pig coronary arteries after balloon injury

BACKGROUND

Smooth muscle cell (SMC) hyperplasia is an important mechanism of restenosis after coronary angioplasty and the primary mechanism of restenosis within coronary stents. Ethanol has been shown to reduce the response of SMCs to local growth stimulants in vitro. This study was carried out to determine whether local delivery of ethanol solution could reduce intimal hyperplasia induced by balloon injury.

METHODS AND RESULTS

Three groups of juvenile domestic pigs underwent oversized balloon dilation injury of the left anterior descending and left circumflex coronary arteries. Immediately after the balloon injury, one of the arteries was randomized to local delivery of 15% ethanol with a local delivery balloon catheter, and the other received no further treatment. Histological and morphometric studies were carried out at 2 weeks in group 1 (n=16) and at 4 weeks in group 2 (n=10). In the third group (n=15), animals were killed at days 4, 8, and 14 after balloon injury, and coronary artery segments were studied by immunohistochemical staining against proliferating cell nuclear antigen (PCNA) and bromodeoxyuridine (BrdU). Histological injury scores were not different between the ethanol-treated and untreated arterial segments in either group 1 or 2. The neointimal areas were significantly smaller in the ethanol-treated arterial segments than in the untreated segments (0.25+/-0.08 versus 0.57+/-0.08 mm2, P=.004, at 2 weeks; 0.33+/-0.05 versus 0.54+/-0.07 mm2, P=.03, at 4 weeks). SMC proliferative activity was significantly lower in ethanol-treated arteries than in untreated arteries at 4 and 8 days after injury by BrdU and PCNA staining.

CONCLUSIONS

Local delivery of 15% ethanol solution to pig coronary arteries significantly decreased the SMC proliferative activity and neointimal formation induced by balloon dilation injury.

Postangioplasty restenosis: a practical model in the porcine carotid artery

Transluminal coronary angioplasty is a routine therapeutic intervention in coronary heart disease. Despite the high rate of primary success, restenosis continues to be its major limitation. Porcine models have been considered to be the most adequate experimental models for studying restenosis. One limitation of porcine models is the need for radiological guidance and the expenses involved. The objective of the present study was to adapt an experimental model of angioplasty in the porcine carotid artery that does not require radiological equipment. Eight animals were used to develop the technique of balloon injury to the common carotid artery by dissection without radiological guidance. This technique was then employed in six other animals. Under anesthesia, the left common carotid artery was dissected and incised at the carotid sinus for insertion of an over-the-wire angioplasty balloon towards the aorta. Overstretch injury of the carotid artery was performed under direct visualization. After 30 days, the arteries were excised and pressure-fixated. Uninjured carotid arteries from 3 additional animals were used as controls. A decreased luminal area associated with intimal hyperplasia and medial reaction was observed in all injured arteries. Immunohistochemistry identified the intimal hyperplastic cells as smooth muscle cells. Computerized morphometry of the ballooned segments revealed the following mean areas: lumen 2.12 mm2 (+/- 1.09), intima 0.22 mm2 (+/- 0.08), media 3.47 mm2 (+/- 0.67), and adventitia 1.11 mm2 (+/- 0.34). Our experimental model of porcine carotid angioplasty without radiological guidance induced a vascular wall reaction and permitted the quantification of this response. This porcine model may facilitate the study of vascular injury and its response to pharmacological interventions.

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.

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.

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 intramural delivery of L-arginine enhances nitric oxide generation and inhibits lesion formation after balloon angioplasty

BACKGROUND

Long-term oral administration of L-arginine has been shown to enhance production of nitric oxide (NO) and to reduce lesion formation. The goal of this study was to determine whether local intramural administration of L-arginine could enhance NO generation and reduce intimal thickening.

METHODS AND RESULTS

New Zealand White rabbits (n = 27) received a 1% cholesterol diet. For the short-term study, after 1 week of diet, both iliac arteries were balloon injured. Four weeks later, vasoreactivity was assessed angiographically during infusion of acetylcholine (Ach) before and after delivery of L-arginine or saline into the right or left iliac artery (800 mg/5 mL; 0.2 mL/min, 15 minutes) by use of a local drug-delivery balloon. Vessels were then harvested for measurements of NO. For the long-term study, after balloon injury, drugs were delivered as above into the iliac arteries. Two and 4 weeks after L-arginine delivery, vasoreactivity was determined. Subsequently, the iliac arteries were harvested for histomorphometric analysis and measurements of NO. In the short-term study, local delivery of L-arginine restored endothelium-dependent vasodilatation (Ach 10(-5) mol/L; L-arginine +35 +/- 10%; saline -14 +/- 5%; P < .001) and enhanced local production of nitrogen oxides (L-arginine 152 +/- 28; saline 78 +/- 12 nmol/L per milligram of tissue per hour; P < .04). In the long-term study, local administration of L-arginine enhanced vascular NO production as long as 1 week after the injury (L-arginine 394.4 +/- 141.6; saline 86.3 +/- 34.3 nmol/L per milligram of tissue per hour; P < .01) and reduced intimal thickening 4 weeks later (intima/ media ratio: L-arginine 0.56 +/- 0.1; saline 1.40 +/- 0.2; P < .001), largely due to suppression of macrophage accumulation.

CONCLUSIONS

A single intramural administration of L-arginine enhances vascular NO generation and inhibits lesion formation. Local augmentation of NO production at the site of balloon angioplasty may be a novel strategy to prevent restenosis.

High dose rate intracoronary radiation for inhibition of neointimal formation in the stented and balloon-injured porcine models of restenosis: angiographic, morphometric, and histopathologic analyses

PURPOSE

We examined the effects of intracoronary irradiation delivered at a high dose rate on neointimal hyperplasia after injury induced by two methods: balloon overstretch injury, and stent implantation in a porcine model of coronary restenosis.

METHODS AND MATERIALS

In 34 Hanford miniature swine, a segment of each coronary artery was targeted for injury and treatment. The artery segments were treated with 192Ir at doses of 10 Gy over 4 min (eight animals), 15 Gy over 6 min (nine animals), 25 Gy over 10 min (nine animals) or control (simulation wire only; eight animals). The treated segments were subjected to stent implantation (left anterior descending and right coronary artery) or balloon overstretch (circumflex) injury. Twenty-eight days later, repeat coronary angiography and sacrifice were done. Quantitative coronary angiography, morphometry, and extensive histopathologic analyses were carried out in a blinded fashion.

RESULTS

The change in minimal lumen diameter from postinjury to presacrifice in the stent-injured left anterior descending was -0.79 +/- 0.34 (mean: +/- SD) mm in the control group, compared to -0.43 +/- 0.35 mm in the 15 Gy (p = 0.04) and -0.21 +/- 0.50 mm in the 25 Gy (p = 0.01) groups; and in the balloon-injured circumflex was -0.31 +/- 0.22 mm in the control group compared to -0.03 +/- 0.18 mm in the 10 Gy (p = 0.05) and 0.00 +/- 0.33 in the 15 Gy (p = 0.01) groups. Percent area stenosis in the left anterior descending was 36 +/- 9% in the control group compared to 18 +/- 12% in the 15 Gy (p = 0.003) and 11 +/- 11% in the 25 Gy (p < 0.001) groups; and in the circumflex was 16 +/- 10% in the control groups, compared to 5 +/- 5% in the 15 Gy (p = 0.02) and 2 +/- 2% in the 25 Gy (p = 0.009) groups. Histopathology showed a striking reduction in the amount of neointima in the irradiated arteries compared with control vessels. Other radiation effects were stromal fibrin exudate, thinning of the media, and adventitial fibrosis and leukocyte infiltration in the radiated arterial segments.

CONCLUSIONS

High dose rate intracoronary irradiation with 192Ir effectively inhibits intimal proliferation after stent-induced as well as balloon-overstretch injury. This shorter treatment time (4 to 10 min) may provide a clinically practical approach to the prevention of restenosis after angioplasty.

Age-related changes affecting atherosclerotic risk. Potential for pharmacological intervention

The incidence of cardiovascular diseases that are related to the atherosclerotic process increases exponentially with age. Organ lesions, the clinical manifestation of atherosclerotic disease, are late events due to complications in the plaque (ulceration, thrombosis, calcification) which are the result of an increased vulnerability to disruption of a previously stable plaque. The higher incidence of age-related clinical events could be explained by a rising sensitivity of plaques to destabilising factors, both parietal and humoral. The increased probability that a plaque in an elderly patient will became vulnerable could be related to those destabilising factors that significantly increase with aging, such as advanced glycation end-products. For these reasons, it seems most important that the analysis of these age-related destabilising factors, rather than those factors that promote the development of early atherosclerotic plaques, should be undertaken. Taking the point of view of a pharmacological intervention, this should eventually lead to a more complete understanding of this process.

Effect of thrombin inhibition with desulfatohirudin on early kinetics of cellular proliferation after balloon angioplasty in atherosclerotic rabbits

BACKGROUND

Thrombin may have a pivotal role in restenosis after angioplasty. Hirudin, a potent thrombin inhibitor, reduces luminal narrowing by plaque after angioplasty in a rabbit model of atherosclerosis. Because cellular proliferation is believed to be an important mechanism for restenosis and thrombin has been shown to be a potent smooth muscle cell mitogen in vitro, we hypothesized that the mechanism of the effect of hirudin on limiting luminal narrowing by plaque occurs via inhibition of cellular proliferation.

METHODS AND RESULTS

Femoral atherosclerosis was induced in 108 rabbits, and balloon angioplasty was performed. At angioplasty, group 1 rabbits (n=38) were treated with a 2-hour infusion of hirudin, and group 2 rabbits (n=41) were treated with heparin. Group 3 rabbits (n=29) were treated with hirudin (n=15) or heparin (n=14) and killed at 7 or 28 days to determine cross-sectional area narrowing by plaque and cellular proliferation with the use of bromodeoxyuridine labeling. At 29, 71, or 167 hours after angioplasty, group 1 and 2 rabbits were injected with 3H-thymidine and killed 1 hour later, and labeling indexes were determined. A significant increase in the index of 3H-thymidine-labeled nuclei was observed in the intima of "ballooned" arteries compared with "nonballooned" atherosclerotic arteries at both 30 hours (0.06+/-0.05 versus 0.01+/-0.01, P<.01) and 72 hours (0.10+/-0.06 versus 0.004+/-0.004, P<.01). By 7 days, the index of labeled cells was similar to baseline (0.04+/-0.03 versus 0.01+/-0.01, P=.12). Hirudin had no effect on the 3H-thymidine labeling indexes at any of the time points studied despite the fact that hirudin treatment in group 3 rabbits resulted in less cross-sectional area narrowing by plaque at both 7 and 28 days after angioplasty (41+/-16 versus 24+/-12 at 7 days and 60+/-21 versus 44+/-17 at 28 days, heparin versus hirudin; P<.03).

CONCLUSIONS

Balloon angioplasty resulted in a marked increase in cellular proliferation that peaked at 72 hours. A 2-hour infusion of hirudin failed to reduce early 3H-thymidine labeling, suggesting that inhibition of cell proliferation within the first 7 days after angioplasty is not the predominant mechanism by which hirudin exerts its effect on limiting luminal narrowing by plaque 28 days after balloon angioplasty in this animal model.

Local delivery of biodegradable microparticles containing colchicine or a colchicine analogue: effects on restenosis and implications for catheter-based drug delivery

OBJECTIVES

This study sought to evaluate the delivery efficiency, intramural retention and antirestenotic efficacy of soluble colchicine or colchicine analogue delivered into the arterial wall after angioplasty as well as the efficacy of these medications after prolonged local release from biodegradable microparticles.

BACKGROUND

Local delivery of pharmacologic agents is a potential treatment for restenosis. However, the delivery efficiency of the technique and the choice of agent to modulate cellular proliferation are unknown. It was hypothesized that restenosis would be unaffected by colchicine or a hydrophobic colchicine analogue with short intramural retention, whereas it would be reduced after prolonged local release.

METHODS

Rabbit atherosclerotic femoral arteries underwent angioplasty followed by local delivery. Delivery efficiency and intramural retention of 3H-colchicine were evaluated. The effect of agents in soluble formulation or released from microparticles on angiographic and morphometric restenosis was evaluated at 2 weeks and compared with that in the control groups (angioplasty only and local infusion of carrier solution).

RESULTS

Delivery of efficiency was 0.01% and intramural retention < 24 h. Neither soluble colchicine formulation reduced restenosis. Microparticles releasing the colchicine analogue reduced restenosis compared with control and colchicine microparticles but not angioplasty alone (p = 0.002). Delivery outside the artery was observed, and the long-term release of both colchicine resulted in toxicity to the adjacent musculature.

CONCLUSIONS

Colchicine or the colchicine analogue did not reduce restenosis, although the long-term local release of the colchicine analogue reduced neointimal proliferation resulting from local delivery. Local delivery of cytotoxic agents with insufficient vascular specificity may be limited by toxicity to adjacent tissues resulting from a larger than expected delivery area and prolonged agent retention.

A prescreening system for potential antiproliferative agents: implications for local treatment strategies of postangioplasty restenosis

BACKGROUND

Recent advances in the understanding of the biology of restenosis indicate that it is predominantly caused by a multifactorial stimulation of smooth muscle cell proliferation. The aim of this study was to investigate the in vitro effect of five potential antiproliferative agents on smooth muscle cells from human atherosclerotic femoral arteries.

METHODS AND RESULTS

Primary stenosing plaque material of 24 patients (aged 63 +/- 14 years) and restenosing plaque material of 7 patients (aged 65 +/- 9 years) was selectively extracted from femoral arteries by the Simpson atherectomy device. Cells were isolated by enzymatic disaggregation and identified as smooth muscle cells by positive reaction with smooth muscle alpha-actin. Dalteparin sodium (0.001-100 anti-Xa units/ml), cyclosporine A (0.005-500 micrograms/ml), colchicine (0.00004-4 pg/ml), etoposide (0.002-200 micrograms/ml), and doxorubicin (0.0005-50 micrograms/ml) were added to the cultures. Six days after seeding, cells were trypsinized and cell number was measured by a cell counter. All five agents tested exhibited a significant inhibition of smooth muscle cell proliferation (P < 0.001). After an incubation time of 48 h, the cytoskeletal components, alpha-actin, vimentin, and microtubules were investigated. At peak concentrations, all five tested agents except dalteparin sodium caused severe damage to the cytoskeleton.

CONCLUSIONS

All five potential antiproliferative agents exhibited a significant inhibition of smooth muscle cell proliferation. The development of new intravascular delivery systems may open the way for local antiproliferative treatment strategies in interventional cardiology.

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)

Localized drug delivery in atherosclerotic arteries via a new balloon angioplasty catheter with intramural channels for simultaneous local drug delivery

A dual-purpose angioplasty catheter with intramural channels and exterior pores for local drug delivery ("channeled balloon") was studied in eight atherosclerotic human necropsy arteries and in 22 rabbits with atherosclerotic peripheral arteries, in which markers (0.005 microns to 15 microns) were infused locally at 2 atmospheres during simultaneous angioplasty at 6 atmospheres. Thirteen of the rabbits were sacrificed at 4 or 24 h after procedure to determine the intramural retention over time. Histology confirmed effective angioplasty and revealed presence of markers in the arterial wall in 29 of 43 treated arteries (67%), whereas all control segments without local delivery had no marker staining. majority of the ineffective local delivery (12/14) occurred when 15 micron particles were infused (12/13 arteries without intramural markers), especially when examined 4 or 24 h later. Thus, in atherosclerotic arteries, the channeled balloon enabled simultaneous local drug delivery at low pressure during effective angioplasty, although particle size may play a role in successful intramural impregnation and retention.

Experimental therapeutics and clinical studies in (re)stenosis

Restenosis is defined functionally as loss of luminal vessel patency following various methods of interventional cardiology, but ultrastructurally, it represents a wound healing response that involves smooth muscle migration, proliferation and matrix deposition at the site of injury. Currently, despite intensive experimental and clinical studies, there are no therapeutic agents that are able to suppress pharmacologically the clinical restenosis. Ultrastructural pathology and animal modeling have played a pivotal role in defining new experimental therapies and rationales for clinical trials. However, concerns regarding the lack of suitable animal models persist and of the many compounds reported efficacious preclinically, none have demonstrated clinical benefit in preventing restenosis. Animal modeling studies now include the use of true restenosis studies, which may be more clinically relevant and pharmacologically predictive of clinical performance.

Local delivery of r-hirudin by a double-balloon perfusion catheter prevents mural thrombosis and minimizes platelet deposition after angioplasty

BACKGROUND

The major morbidity of percutaneous transluminal coronary angioplasty is acute thrombosis and restenosis of the dilated lesion. Platelet-thrombus deposition occurs within minutes after injury, is primarily mediated by thrombin, causes acute occlusion, and contributes to late restenosis. Experimentally, specific thrombin inhibitors have prevented mural thrombosis. However, local therapy may be more effective than systemic treatment. We tested the hypothesis that high local concentrations of an antithrombin drug at the site of arterial injury following balloon angioplasty inhibit platelet thrombus formation equally or better than conventional systemic treatment and at lower systemic anticoagulant levels.

METHODS AND RESULTS

Balloon angioplasty of the carotid arteries of 29 pigs was performed using systemic intravenous treatment with heparin (100 U/kg, groups I and II), suboptimal r-hirudin (0.3 mg/kg, group III), and higher-dose r-hirudin (0.7 mg/kg, group IV), which is the lowest dose that completely inhibited arterial thrombosis in the pig. Immediately after balloon angioplasty of the first carotid, additional local therapy with placebo (group I) or r-hirudin (groups II, III, and IV; 0.3 mg/kg in 1 mL) was administered with distal perfusion through a new percutaneous double-balloon catheter. After 1 hour of local drug delivery, angioplasty of the contralateral carotid was performed. Reflow for 1 hour was permitted to both carotids to compare the short-term effect of local plus systemic treatment with systemic treatment on quantitative 111In-labeled platelet deposition and macroscopic mural thrombus formation on deeply injured carotid segments. Local drug delivery of placebo compared with systemic heparin treatment resulted in no change of platelet deposition (x 10(6)/cm2, mean +/- SEM) in controls (group I, 91.0 +/- 23.5 versus 80.8 +/- 19.4), but local delivery of r-hirudin resulted in a significant reduction in group II (15 +/- 2.5 versus 71.3 +/- 14.5; P < .02) and group III (11.4 +/- 2.5 versus 80.5 +/- 11.4; P < .01) and was borderline in group IV (7.4 +/- 1.8 versus 14.1 +/- 7.4; P = .05), respectively. The incidence of macroscopic mural thrombus formation with local and systemic treatment was 86% and 75% in group I, 16% and 70% in group II, 14% and 71% in group III, and 0% and 16% in group IV, respectively.

CONCLUSIONS

Local therapy with the specific thrombin inhibitor r-hirudin significantly reduces short-term quantitative platelet deposition and macroscopic mural thrombus formation following balloon angioplasty compared with systemic treatment of conventional doses of heparin and hirudin and requires a significantly smaller amount of the recombinant drug.

Percutaneous transluminal in vivo gene transfer by recombinant adenovirus in normal porcine coronary arteries, atherosclerotic arteries, and two models of coronary restenosis

BACKGROUND

Gene therapy has been proposed as a possible solution to the problem of restenosis after coronary angioplasty. The current study was undertaken to assess conventional methods of gene transfer and to develop percutaneous techniques for introducing genes directly into the coronary arteries of large mammals. Since the anticipated targets of gene therapy against restenosis include atherosclerotic and previously instrumented arteries, we also evaluated gene transfer in atherosclerotic coronary arteries and in two porcine models of restenosis: one using intracoronary stents and a second using balloon overstretch angioplasty.

METHODS AND RESULTS

The conventional method of using perforated balloon catheters to deliver Lipofectin-DNA complexes directly into the coronary arteries of intact animals was applied to 18 porcine coronary arteries including normal arteries, hypercholesterolemic arteries, and those simulating restenosis. The results of this study were consistent with previously published results indicating that only low levels of luciferase gene expression could be obtained by Lipofectin-mediated gene transfer. We therefore undertook a second, parallel study to evaluate percutaneous transluminal in vivo gene transfer using a replication-deficient adenoviral vector. A comparison of the two studies revealed that the mean level of reporter gene expression in the cohort undergoing adenoviral infection was 100-fold higher than in the cohort undergoing Lipofection. Analysis of luciferase activity over time in normal arteries revealed that recombinant gene expression was half-maximal after 1 day, peaked within 1 week, was still half-maximal at 2 weeks, and declined to low levels by 4 weeks. Histochemical analysis of coronary arteries treated with a second adenovirus expressing a nuclear-localized beta-galactosidase gene demonstrated gene transfer to a limited number of cells in the media and adventitia. Immunohistochemical analysis of Ad5-infused arteries using a monoclonal antibody directed against CD44 identified a periadventitial infiltrate composed of leukocytes.

CONCLUSIONS

The recombinant adenoviral vectors proved to be far more effective than Lipofectin at delivering foreign genes directly into the coronary arteries of living mammals. Furthermore, the influences of hypercholesterolemia and arterial injury appeared to have little effect on the levels of gene expression obtained using either method. The results demonstrate that low-level recombinant gene expression, the major obstacle impeding gene therapy for the prevention of restenosis, can potentially be overcome by using adenoviral vectors to mediate coronary gene transfer in vivo. The duration of gene expression provided by these vectors and their effective deployment in atherosclerotic, balloon-overstretched, and stented coronary arteries suggest that recombinant adenovirus may have potential for evaluating gene therapy in the clinically informative porcine models of coronary restenosis.

The etiology of intimal hyperplasia

Injury of an arterial wall results in the growth of a neointima which can cause significant luminal narrowing. Current theories do not adequately explain the experimental and clinical data. We propose the hypothesis that some substance produced by the media is inhibitory to smooth muscle cell proliferation. This substance cannot cross the normal intima. Following an injury which removes the intima this substance quickly diffuses out of the arterial wall into the blood, its concentration in the arterial wall falls and proliferation of smooth muscle cells begins. Later, as the arterial wall volume increases and the lumen (and, thus, area for diffusion) decreases, the substance returns to inhibitory levels and intimal hyperplasia ceases.

Drug delivery into the arterial wall: a time-course study with use of a lipophilic dye

PURPOSE

One potential approach to the prevention of restenosis after angioplasty is to deliver antiproliferative agents directly to the angioplasty site. The purpose of this study was to determine the time course of drug penetration into the media of the balloon-dilated artery.

MATERIALS AND METHODS

Balloon angioplasty of the left and right iliac arteries was performed once for 1 minute in each of five rabbits. A double-balloon catheter was then positioned at the site of angioplasty, and the fluorescent dye PKH26 (molecular weight, 961) was delivered under pressure to simulate drug delivery. Afterward, the arteries were removed and dye penetration into the media was measured on frozen cross sections by epifluorescence microscopy.

RESULTS

Delivery of the dye was performed for periods ranging from 5 to 50 minutes at a mean pressure of 189 mm Hg. The depth of dye penetration (D, micrometers) was directly related to dye perfusion time (T, minutes) (D = 0.348T + 11.958, r = 0.496, P < .01). This equation predicts complete medial dye penetration in 81 minutes assuming an average intima-media thickness (40 microns).

CONCLUSION

This study demonstrates that PKH26 can be delivered to the media of the dilated artery. However, the time required to obtain complete penetration may limit the utility of this double-balloon catheter approach to drug delivery.

Inhibition of smooth muscle cell proliferation by visible light-activated psoralen

The present study was designed to evaluate the effect of 8-methoxypsoralen (8-MOP) activated with visible light (419 nm) on the suppression of smooth muscle cell (SMC) proliferation in vitro. We hypothesize that if visible light (VL) instead of UVA is used to photoactivate 8-MOP, cytotoxic 8-MOP-DNA cross-link formation can be minimized. Bovine aorta SMCs (2 x 10(4)/cm2) were incubated with 8-MOP (1 micrograms/mL) for 30 minutes (in the dark) and exposed to a range of VL (2 to 69 J/cm2) to determine the dose of VL that inhibits SMC proliferation with minimal toxicity. The results show that 8-MOP in combination with 2 to 12 J/cm2 VL reversibly inhibited SMC proliferation for up to 5 days after treatment. SMC viability was confirmed by trypan blue exclusion. 8-MOP in combination with 23- or 69-J/cm2 VL irreversibly inhibited SMC proliferation. In cell cycle studies, 12-J/cm2 VL was used to activate 8-MOP. A phase-specific G2 blockade that correlated temporally with recovery of SMC replication was observed. Photoadduct repair studies showed that cell proliferation rates recovered when 60% of the adducts had been removed. These results demonstrate for the first time the possibility of using VL to activate 8-MOP to inhibit cell proliferation and suggest that 8-MOP/VL photochemotherapy can be used to control SMC growth.

Cell proliferation after balloon injury of iliac arteries in the cholesterol-fed New Zealand White rabbit

Acute mechanical injury of an artery results in neointimal hyperplasia that is due at least in part to cell proliferation within the vessel wall. The purpose of this study was to quantify cell proliferation activity in the iliac artery of New Zealand White rabbits after balloon injury and cholesterol feeding. Retrograde pullback balloon injury of iliac arteries was performed, and the animals were then fed a 2% cholesterol diet. At intervals from day 1 through day 35 postinjury, iliac arteries were obtained for histological analysis. Intimal and medial areas were measured morphometrically. Total number of cells within the intima and media was counted. Smooth muscle cell-predominant or macrophage-predominant regions of the intima and media were identified using HHF-35 and RAM-11 immunocytochemical markers, respectively. Number of cells in the proliferative phase of the cell cycle was measured by using the proliferating cell nuclear antigen and bromodeoxyuridine techniques. Thirty-one arteries from 16 rabbits were available for analysis. Total number of cells and number of cells per square millimeter within the media did not change significantly from day 1 through day 35 postinjury. Total number of cells within the intima increased significantly, but the number of cells per square millimeter of intima decreased significantly during the same time period. Proliferative activity was identified in the media between days 3 and 35 with peak activity at day 3 postinjury. Proliferative activity in the intima was present in all specimens from day 8 through day 35. Proliferative activity was present in both HHF-35- and RAM-11-predominant regions of the intima.(ABSTRACT TRUNCATED AT 250 WORDS)

Biodegradable microspheres containing a colchicine analogue inhibit DNA synthesis in vascular smooth muscle cells

BACKGROUND

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Local application of agents capable of modulating vascular responses, including smooth muscle cell proliferation, has been achieved, but difficulty in maintaining active levels locally has been a factor limiting the efficacy of such approaches. One strategy to maintain adequate levels is the local delivery of microspheres that release active agents over sustained time periods.

METHODS AND RESULTS

We incorporated a colchicine analogue into biodegradable microspheres composed of a lactic acid/glycolic acid copolymer and characterized their drug release behavior as well as their effects on bovine aortic smooth muscle cells (BASMCs) in culture. Drug release was evaluated by spectrophotometric assay. Drug effects on DNA synthesis were measured by thymidine incorporation after addition of serum to subconfluent cells synchronized by serum withdrawal as well as in asynchronous cell populations. Polymeric microspheres incorporating 10% to 17% drug by weight and averaging 6 microns in size were found to release the colchicine analog in buffered saline solutions over more than several weeks. Drug-loaded particles inhibited DNA synthesis completely, with EC50 values ranging from 0.001 to 0.005 g% (wt/wt). Morphological changes suggesting microtubule depolymerization were observed after drug particle treatment, with similar EC50 values. Microspheres allowed to contact the cell surface demonstrated effects similar to those seen with microspheres suspended in the nutrient medium by porous polycarbonate filters, at EC50 values approximately fivefold lower. In contrast, control microspheres composed only of polymer with no incorporated active drug demonstrated no observable toxicity to BASMCs and < 40% inhibition of thymidine incorporation even in suspensions containing up to 0.5 g% particles.

CONCLUSIONS

Biodegradable microspheres were fashioned that release a colchicine analogue and inhibit DNA synthesis in smooth muscle cells. Drug-loaded polymeric particles are candidates for local delivery at sites of arterial injury to decrease restenosis.