Localized arterial wall drug delivery from a polymer-coated removable metallic stent. Kinetics, distribution, and bioactivity of forskolin

The cyclic adenosine monophosphate elevating medicine, forskolin, reduces neointimal formation and atherogenesis in mice

Neointimal formation and atherogenesis are major vascular complications following percutaneous coronary intervention, and there is lack of pharmacological therapy. This study was aimed to examine the effect of forskolin (FSK), a cyclic adenosine monophosphate (cAMP)‐elevating agent, on vascular response to angioplasty wire injury and on atherogenesis in mice. Forskolin treatment reduced neointima formation at 7 and 28 days after wire injury. Early morphometrics of the injured vessels revealed that FSK treatment enhanced endothelial repair and reduced inflammatory cell infiltration. In vitro treatment of primary aortic cells with FSK, at 3‐100 μmol/L, increased endothelial cell proliferation, whereas FSK, at 30‐100 μmol/L, inhibited smooth muscle cell proliferation. FSK inhibited lipopolysaccharide‐induced leucocyte‐endothelial interaction in vitro and in vivo. In a mouse model of atherosclerosis driven by dyslipidaemia and hypertension, FSK administration increased endothelial repair and reduced atherosclerotic plaque formation, without affecting blood pressure, plasma lipids or aortic aneurysms formation. In summary, FSK, at doses relevant to human therapeutic use, protects against neointimal hyperplasia and atherogenesis, and this is attributable to its activities on pro‐endothelial repair and anti‐inflammation. This study raises a potential of clinical use of FSK as an adjunct therapy to prevent restenosis and atherosclerosis after percutaneous coronary intervention.

Development of Microporous Covered Stents: Geometrical Design of the Luminal Surface

To reduce in-stent restenosis rates we have developed newly designed covered stents, in which a stent strut is buried into a microporous elastomeric cover film to provide a physical barrier against tissue ingrowth and a pharmacological reservoir for drug-eluting.

The covered stents were prepared by dip-coating balloon expandable stents mounted on a stainless steel rod in a segmented polyurethane (SPU) solution, and were subsequently subjected to laser-processed microporing (pore diameter, 100 μm; interpore distance, 200 μm). The covered stents, which possessed flat luminal surfaces and micropores that were homogeneously arranged on the whole surface of the covering film, were deployed into the bilateral common carotid arteries of normal New Zealand white rabbits. Angiography after one month of implantation showed all stents were patent with little thrombus formation. The mean thickness of the formed neointimal layers was 292 ± 177 μm (n=8), which was close to the size in non-covered bare stent (231 ± 58 μm, n=7), but markedly decreased (about 2/3) from that in the previously developed wrapping-type covered stents (415 ± 173 μm, P<0.01, n=8).

Effect of strut distribution on neointimal coverage of everolimus-eluting bioresorbable scaffolds: an optical coherence tomography study

The thick struts of bioresorbable vascular scaffolds (BRS) are associated with changes in wall shear stress and contribute to neointimal proliferation. We aimed to evaluate the relationship between the BRS strut distribution and the neointimal proliferation. 50 lesions underwent optical coherence tomography, 12 months after BRS implantation. Scaffold area and neointimal thickness were evaluated in each cross-sectional area (CSA). Scaffold eccentricity was defined as follows: (maximum diameter - minimum diameter) × 100/maximum diameter. CSAs of BRS were divided into four quadrants. The maximal neointimal thickness (Maximal-NIT), Minimal-NIT and the number of struts in each quadrant were measured. The number of struts were classified as 1, 2, 3 and ≥ 4. Furthermore, the mean-NIT acquired in each quadrant was divided by the average-NIT of all struts in the same CSA, which was defined as the unevenness score. In addition, Maximal-NIT minus Minimal-NIT was divided by the average-NIT of all struts in the same CSA, which was defined as heterogenicity of neointimal proliferation. There was a significant difference in the association between the number of struts and not only the unevenness score (no. of strut = 1 (N = 440), unevenness score 1.04 ± 0.34; 2 (N = 696), 0.98 ± 0.27; 3 (N = 994), 0.96 ± 0.23; ≥4 (N = 1202), 1.04 ± 0.22, P < 0.01) but also Maximal-NIT and Minimal-NIT. Furthermore, a significant correlation was observed between scaffold eccentricity in each CSA and the heterogeneity of neointimal proliferation in the same CSA (N = 892, R = 0.38, p = 0.01). Crowding of struts is associated with increased neointimal proliferation after BRS implantation. The scaffold eccentricity causes heterogeneity of neointimal proliferation.

Crosslinked Polyurethane Coating on Vascular Stents for Enhanced X-ray Contrast

A coating of polyurethaneurea was made from a solution on the surface of metal stents. The influence of cleaning, etching, chemical and ion beam modification (plasma immersion ion implantation) of the metal surface on the adhesion strength of the polyurethaneurea was analysed. Polyurethaneurea films imbedded with tantalum particles as a radiopaque filler maintained their strength and elasticity and produced clear X-ray contrast images of vascular stents.

Comparison of failure rates of crossing side branch with pressure vs. coronary guidewire: a meta-analysis

OBJECTIVES

The aim of this study was to compare the failure rates of crossing side branch (SB) with pressure guidewire vs. coronary guidewire after main vessel (MV) stenting in coronary bifurcation lesions (CBL).

BACKGROUND

Percutaneous coronary intervention of CBL is technically difficult. The European Bifurcation Club recommends performing either fractional flow reserve (FFR) estimation of the SB or final kissing balloon inflation (FKBI) after the MV stenting when a significant SB ostial stenosis is present. Even though FFR is recommended in CBL, there is concern about SB crossing with pressure guidewire among interventionists.

MATERIALS AND METHODS

We undertook a comprehensive literature search to identify all relevant studies reporting the failure rates of SB crossing after MV stenting with either pressure or coronary guidewire. A random effects model was used to compare the failure rates between the two approaches.

RESULTS

Our search identified six studies that reported failure rates of SB crossing with a pressure guidewire (n = 648) and 11 studies that reported failure rates of SB crossing with a coronary guide-wire (n = 2601). Estimated pooled failure rate was 3·9% (95% CI: 1·5% to 9·6%) for inability to cross SB with pressure guidewire. Estimated pooled failure rate of SB crossing with coronary guidewire was 3·1% (95% CI: 1·5% to 6·2%). There was no significant difference between the failure rates in the two groups (P = 0·70).

CONCLUSION

The failure rates of SB crossing after MV stenting are low with both pressure and coronary guidewire procedures, with no significant difference between the two approaches.

Role of Animal Models in Coronary Stenting

Coronary angioplasty initially employed balloon dilatation only. This technique revolutionized the treatment of coronary artery disease, although outcomes were compromised by acute vessel closure, late constrictive remodeling, and restenosis due to neointimal proliferation. These processes were studied in animal models, which contributed to understanding the biology of endovascular arterial injury. Coronary stents overcome acute recoil, with improvements in the design and metallurgy since then, leading to the development of drug-eluting stents and bioresorbable scaffolds. These devices now undergo computer modeling and benchtop and animal testing before evaluation in clinical trials. Animal models, including rabbit, sheep, dog and pig are available, all with individual benefits and limitations. In smaller mammals, such as mouse and rabbit, the target for stenting is generally the aorta; whereas in larger animals, such as the pig, it is generally the coronary artery. The pig coronary stenting model is a gold-standard for evaluating safety; but insights into biomechanical properties, the biology of stenting, and efficacy in controlling neointimal proliferation can also be gained. Intra-coronary imaging modalities such as intravascular ultrasound and optical coherence tomography allow precise serial evaluation in vivo, and recent developments in genetically modified animal models of atherosclerosis provide realistic test beds for future stents and scaffolds.

Coronary bifurcation lesions: Present status and future perspectives

Coronary bifurcation lesions (CBLs) are challenging and associated with a higher rate of adverse events than non-bifurcation lesions. In the era of drug-eluting stents, 2 primary interventional strategies for treating CBL include the complex strategy the main vessel (MV) and side-branch (SB) stenting, and the simple strategy MV stenting combined with provisional SB stenting. The meta-analysis of the simple vs. complex strategies demonstrated an increased incidence of myocardial infarction in the complex strategy. Likewise, the Tryton dedicated bifurcation stents, as compared with the simple strategy, increased the rate of myocardial infarction. In contrast, the Nordic-Baltic Bifurcation Study IV demonstrated that event rates were not significantly different comparing the simple vs. complex strategies in true bifurcation lesions involving a large SB. Fractional flow reserve (FFR) has emerged as a powerful catheter based tool for the functional assessment of a stenosis, but the role of FFR on the long-term outcomes of patients with CBL has not been studied. Given the recent evidence that Tryton stents (a dedicated bifurcation stent) increased event rates, and the lack of benefit from using 2-stent techniques (the Nordic Baltic Bifurcation Study IV) in true CBL, assessing the FFR of the SB seems now of outmost importance, but randomized data are lacking. An intravascular study showed that kissing balloon inflation (KBI) significantly reduced SB stenosis, restored stent lumen at the carina, and expanded stent in the proximal segment. However, a recent randomized study showed no significant benefit of routine KBI. This review highlights current concepts and future perspectives in patients with CBL.

Controlled release for local delivery of drugs: barriers and models

Controlled release systems are an effective means for local drug delivery. In local drug delivery, the major goal is to supply therapeutic levels of a drug agent at a physical site in the body for a prolonged period. A second goal is to reduce systemic toxicities, by avoiding the delivery of agents to non-target tissues remote from the site. Understanding the dynamics of drug transport in the vicinity of a local drug delivery device is helpful in achieving both of these goals. Here, we provide an overview of controlled release systems for local delivery and we review mathematical models of drug transport in tissue, which describe the local penetration of drugs into tissue and illustrate the factors - such as diffusion, convection, and elimination - that control drug dispersion and its ultimate fate. This review highlights the important role of controlled release science in development of reliable methods for local delivery, as well as the barriers to accomplishing effective delivery in the brain, blood vessels, mucosal epithelia, and the skin.

Impact of kissing balloon inflation on the main vessel stent volume, area, and symmetry after side-branch dilation in patients with coronary bifurcation lesions: a serial volumetric intravascular ultrasound study

OBJECTIVES

Intravascular ultrasound (IVUS) was performed to investigate the impact of kissing balloon inflation (KBI) on the main vessel (MV) stent volume, area, and symmetry after side-branch (SB) dilation in patients with coronary bifurcation lesions (CBL).

BACKGROUND

It remains controversial whether KBI would restore the MV stent area and symmetry loss after SB dilation.

METHODS

A total of 88 serial IVUS examinations of the MV were performed after MV angioplasty, MV stenting, SB dilation, and KBI in 22 patients with CBL. The MV stent was divided into proximal, bifurcation, and distal segments; the stent volume index (SVI), minimal stent area (MSA), stent symmetry index (SSI), and external elastic membrane (EEM) volume index were measured in 198 stent segments and compared after MV stenting, SB dilation, and KBI.

RESULTS

In the bifurcation segment, SVI, MSA, and SSI were significantly smaller after SB dilation than after MV stenting and KBI (SVI was 6.10 ± 1.50 mm(3)/mm vs. 6.68 ± 1.60 mm(3)/mm and 6.57 ± 1.60 mm(3)/mm, respectively, p < 0.05; MSA was 5.15 ± 1.30 mm(2) vs. 6.08 ± 1.40 mm(2) and 5.86 ± 1.50 mm(2), respectively, p < 0.05; and SSI was 0.78 ± 0.02 mm(2) vs. 0.87 ± 0.03 mm(2) and 0.84 ± 0.03 mm(2), respectively, p < 0.05). KBI restored the MV SVI, MSA, and SSI after SB dilation. In the proximal segment, SVI, MSA, and EEM volume index were significantly larger, but SSI was smaller after KBI than after MV stenting and SB dilation. In the distal segment, neither SB dilation nor KBI had a significant impact on the MV stent volume or symmetry.

CONCLUSIONS

This is the first comprehensive volumetric IVUS analysis of CBL, to our knowledge, demonstrating that KBI restores the MV stent volume, area, and symmetry loss after SB dilation in the bifurcation segment, and induces asymmetric stent expansion in the proximal segment.

Synthesis, characterization, and paclitaxel release from a biodegradable, elastomeric, poly(ester urethane)urea bearing phosphorylcholine groups for reduced thrombogenicity

Biodegradable polymers with high elasticity, low thrombogenicity, and drug loading capacity continue to be pursued for vascular engineering applications, including vascular grafts and stents. A biodegradable elastomeric polyurethane was designed as a candidate material for use as a drug-eluting stent coating, such that it was nonthrombogenic and could provide antiproliferative drug release to inhibit smooth muscle cell proliferation. A phosphorylcholine containing poly(ester urethane) urea (PEUU-PC) was synthesized by grafting aminated phosphorylcholine onto backbone carboxyl groups of a polyurethane (PEUU-COOH) synthesized from a soft segment blend of polycaprolactone and dimethylolpropionic acid, a hard segment of diisocyanatobutane and a putrescine chain extender. Poly(ester urethane) urea (PEUU) from a soft segment of polycaprolactone alone was employed as a control material. All of the synthesized polyurethanes showed high distensibility (>600%) and tensile strengths in the 20-35 MPa range. PEUU-PC experienced greater degradation than PEUU or PEUU-COOH in either a saline or lipase enzyme solution. PEUU-PC also exhibited markedly inhibited ovine blood platelet deposition compared with PEUU-COOH and PEUU. Paclitaxel loaded in all of the polymers during solvent casting continued to release for 5 d after a burst release in a 10% ethanol/PBS solution, which was utilized to increase the solubility of the releasate. Rat smooth muscle cell proliferation was significantly inhibited in 1 wk cell culture when releasate from the paclitaxel-loaded films was present. Based on these results, the synthesized PEUU-PC has promising functionality for use as a nonthrombogenic, drug eluting coating on metallic vascular stents and grafts.

Comparisons of the effects of stent eccentricity on the neointimal hyperplasia between sirolimus-eluting stent versus paclitaxel-eluting stent

PURPOSE

Previous studies suggested that asymmetric stent expansion did not affect suppression of neointimal hyperplasia (NIH) after sirolimus-eluting stents (SES) implantation. The aim of this study was to evaluate the effects of stent eccentricity (SE) on NIH between SES versus paclitaxel-eluting stents (PES) using an intravascular ultrasound (IVUS) analysis from the randomized trial.

MATERIALS AND METHODS

Serial IVUS data were obtained from Post-stent Optimal Expansion (POET) trial, allocated randomly to SES or PES. Three different SE (minimum stent diameter divided by maximum stent diameter) were evaluated; SE at the lesion site with maximal %NIH area (SE-NIH), SE at the minimal stent CSA [SE-minimal stent area (SE-MSA)], and averaged SE through the entire stent (SE-mean). We classified each drug-eluting stents (DES) into the concentric (≥ mean SE) and eccentric groups (< mean SE) based on the mean value of SE.

RESULTS

Among 301 enrolled patients, 233 patients [SES (n = 108), PES (n = 125)] underwent a follow-up IVUS. There was no significant correlation between %NIH area and SE-NIH (r = - 0.083, p = 0.391) or SE-MSA (r = - 0.109, p = 0.259) of SES. However, SE-NIH of PES showed a weak but significant correlation with %NIH area (r = 0.269, p < 0.01). As to the associations between SEmean and NIH volume index, SES revealed no significant correlation (r = - 0.001, p = 0.990), but PES showed a weak but significant correlation (r = 0.320, p < 0.01). However, there was no difference in the restenosis rate between the eccentric versus concentric groups of both DES.

CONCLUSION

This study suggests that lower SE of both SES and PES, which means asymmetric stent expansion, may not be associated with increased NIH.

Local determinants of thrombus formation following sirolimus-eluting stent implantation assessed by optical coherence tomography

OBJECTIVES

We conducted this study to assess the prevalence and determinants of subclinical thrombus after sirolimus-eluting stent (SES) implantation.

BACKGROUND

Angioscopic analyses have demonstrated the presence of thrombus is more common than the clinical incidence of SES thrombosis.

METHODS

Fifty-three patients (53 lesions) underwent 6-month follow-up optical coherence tomography. A stent eccentricity index ([SEI] minimum/maximum stent diameter) was determined in each cross section. To evaluate unevenness of neointimal thickness, a neointimal unevenness score ([NUS] maximum neointimal thickness in the cross section/average neointimal thickness of the same cross section) was calculated for each cross section. Average SEI and NUS were calculated for each stent. Major adverse cardiac events were defined as a composite of death, myocardial infarction, and target vessel revascularization.

RESULTS

Fourteen cases of thrombus (26%) were detected by optical coherence tomography (thrombus: n = 14 vs. nonthrombus: n = 39). The percentage of thrombus was associated with longer stents (36.4 +/- 20.2 mm vs. 25.1 +/- 9.8 mm; p = 0.008), a larger number of uncovered struts (17 +/- 16 vs. 8 +/- 11; p = 0.03), smaller average SEI (0.89 +/- 0.04 vs. 0.92 +/- 0.03; p = 0.001), and greater average NUS (2.22 +/- 0.24 vs. 2.00 +/- 0.33; p = 0.03). A significant relationship existed between average SEI and average NUS (p < 0.0001, R = 0.68), and between average SEI and the number of uncovered struts (p < 0.0006, R = 0.46). There was no significant difference in major adverse cardiac events during follow-up (median: 485 days, 7.1% vs. 12.8%; p > 0.99).

CONCLUSIONS

Longer stents and greater asymmetric stent expansion may be important determinants of thrombus formation after SES implantation. In this small cohort, the presence of thrombus did not increase the risk of major adverse cardiac events.

Influence of unsaturated carbonic acids on hemocompatibility and cytotoxicity of poly-vinylacetate based co-polymers

The aim of this study was to investigate hemocompatibility and cytotoxicity properties of synthetic polymer coatings containing various unsaturated carbonic acids with vinylacetate. Co-polymers of vinylacetate and crotonic acid (CA), maleic acid (MA), and itaconic acid (IA) were made. The materials were characterized in terms of their adhesion to metal supports (titanium and stainless steel) as well as hemocompatibility (% hemolysis, wettability, erythrocyte aggregation, hemoglobin content, thrombocyte count and lipid peroxidation levels) and cytotoxicity (human endothelial cell activity in vitro and chromosome aberrations, bone marrow proliferation and cell ploidy in rats). Co-polymers of unsaturated carbonic acids with vinylacetate exhibited good hemocompatibility properties, as opposed to vinylacetate homopolymer for which substantial levels of hemolysis were observed. By coating the metal supports with co-polymers the cytotoxic effects associated with the bare metal samples were markedly reduced. MA samples showed excellent hemocompatibility and no cytotoxicity, yet they lacked good adhesion properties to metal substrate, probably due to high water content. CA samples, having the highest density of carboxylic groups among the samples under investigation, showed increased bone marrow proliferation activity and cell ploidy in rats, as compared to controls. The most promising results in the present study were obtained for the samples with IA, which showed good adhesion to metal substrates, good hemocompatibility and low cytotoxicity. Thus, co-polymers of vinylacetate and IA rich in carboxylic groups are promising materials for the design of novel drug-eluting stents.

In-vitro assays of polymer-coated stents eluting platelet glycoprotein IIb/IIIa receptor monoclonal antibody

The monoclonal antibody (mAb) to the platelet glycoprotein (GP) IIb/IIIa receptor has potent antiplatelet and antithrombotic characteristics shown to reduce thrombus-related major complications after coronary angioplasty. This mAb can be incorporated in drug-eluting stents capable of releasing single or multiple bioactive agents into the bloodstream and surrounding tissues. Stents eluting the monoclonal mouse anti-human platelet glycoprotein IIb/IIIa antibody SZ-262 were tested for their effectiveness in improving the blood compatibility and the antithrombotic characteristics by immunofluorescence and scanning electron microscopy (SEM). The SEM results convincingly demonstrated that the surface of the mAb eluting-stents was completely free of platelet uptake without any sign of cellular debris or proteinaceous deposits, compared with controls. The deformation index of platelets on the L-polylactic acid (L-PLA) coated stents were higher than bare Nitinol intravascular stents, as shown by SEM images. Monoclonal antibody to the platelet GP IIb/IIIa receptor, when eluting from L-PLA polymer-coated stents, effectively inhibits platelet aggregation in the stent microenvironment, thus demonstrating a potential capacity of reducing thrombosis, improving blood flow and arterial patency rates, and inhibiting cyclic blood flow variations. These results highlight the possibility of such monoclonal antibody-eluting stents to reduce or possibly eliminate thrombosis and in-stent restenosis.

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.

Vascular delivery of c-myc antisense from cationically modified phosphorylcholine coated stents

c-Myc is involved in the formation of neointimal hyperplasia. We investigated in vitro, ex vivo and in vivo release of antisense c-myc from cationically modified phosphorylcholine-coated stents, as well as the effects on c-Myc expression and neointima formation in a porcine coronary stent model. In vitro experiments were performed to determine optimal loading of stents with antisense. Stents loaded with labelled antisense were deployed in porcine arteries ex vivo and in vivo. Antisense was detected in the vessel wall directly surrounding the stent of pig carotid and coronary artery up to 48 h after stent deployment. Nuclear uptake was observed in endothelial and vascular smooth muscle cells. Labelled antisense within peripheral tissues in vivo was <1.0% of that within stented arterial segments. Control and antisense loaded stents implanted into 10 pig coronary arteries and analysed at 28 days post-stenting showed that lumen area within the antisense stents was significantly increased (i.e. 30.5% greater, P<0.01), whilst both neointimal area and neointimal thickness were significantly reduced (17.5% and 19.5%, respectively, P<0.01) compared to control stents. Cationically modified phosphorylcholine coated stent-based delivery of c-myc antisense is feasible with minimal systemic delivery and is associated with a reduction of in-stent neointimal hyperplasia in pig coronary arteries.

Coronary stents: a materials perspective

The objective of this review is to describe the suitability of different biomaterials as coronary stents. This review focuses on the following topics: (1) different materials used for stents, (2) surface characteristics that influence stent-biology interactions, (3) the use of polymers in stents, and (4) drug-eluting stents, especially those that are commercially available.

Drug-eluting stents: factors governing local pharmacokinetics

Stent-based drug delivery system is a revolutionary approach to mitigate the negative affects of balloon angioplasty, improve immune responsiveness and prevent hyperplastic growth of smooth muscle in the restenotic state. Its success is therefore empirically associated with effective delivery of potent therapeutics to the target site at a therapeutic concentration, for a sufficient time, and in a biologically active form. However, local delivery with drug-eluting stents imparts large dynamic concentration gradients across tissues that can be difficult to identify, characterize and control. This review explores the factors such as physiological transport forces, drug physicochemical properties, local biological tissue properties and stent design that governs the local pharmacokinetics within the arterial wall by drug-eluting stent. Rational design and optimization of drug-eluting stents for local delivery thus requires a careful consideration of all these factors.

Impact of asymmetric stent expansion on neointimal hyperplasia following sirolimus-eluting stent implantation

To assess whether asymmetric stent expansion affects suppression of neointimal hyperplasia after sirolimus-eluting stent implantation, 64 patients in the SIRolImUS-coated Bx Velocity stent trial who underwent single 18-mm stent implantation and 3-dimensional intravascular ultrasonography at 8-month follow-up were enrolled. To assess the longitudinal stent asymmetric expansion, 2 cross sections with a maximal/minimal stent area were chosen in each patient. To assess for tomographic stent asymmetric expansion, stent eccentricity was determined by dividing the minimum stent diameter by the maximum stent diameter. At the 2 cross sections with a maximal/minimal stent area, a sirolimus-eluting stent reduced neointimal hyperplasia significantly with no interaction between the treatment and stent areas. A sirolimus-eluting stent also significantly reduced neointimal hyperplasia in the concentric and eccentric stent groups.

Small-scale systems for in vivo drug delivery

Recent developments in the application of micro- and nanosystems for drug administration include a diverse range of new materials and methods. New approaches include the on-demand activation of molecular interactions, novel diffusion-controlled delivery devices, nanostructured 'smart' surfaces and materials, and prospects for coupling drug delivery to sensors and implants. Micro- and nanotechnologies are enabling the design of novel methods such as radio-frequency addressing of individual molecules or the suppression of immune response to a release device. Current challenges include the need to balance the small scale of the devices with the quantities of drugs that are clinically necessary, the requirement for more stable sensor platforms, and the development of methods to evaluate these new materials and devices for safety and efficacy.

Separate and combined effects of local and continuous intravenous administration of beta-cyclodextrin tetradecasulfate on intimal hyperplasia after angioplasty in porcine coronary arteries

BACKGROUND

Beta-Cyclodextrin tetradecasulfate binds fibroblast growth factors and possesses anticoagulant properties. This study was designed to assess the separate and combined effects of local intramural delivery and intravenous administration of beta-cyclodextrin tetrade-casulfate on neointimal formation and arterial damage following angioplasty.

METHODS AND RESULTS

Fifty-two pigs randomized into four groups underwent coronary artery angioplasty: 1) control, 2) continuous intravenous infusion of 100 mg/kg/d of beta-cyclodextrin tetradecasulfate, 3) intramural delivery of 1250 mg beta-cyclodextrin tetradecasulfate, 4) intramural delivery of 1250 mg beta-cyclodextrin tetradecasulfate followed by continuous intravenous infusion of 100 mg/kg/d. Fourteen days after injury, morphometric analysis revealed that arteries randomized to the intravenous beta-cyclodextrin tetradecasulfate groups had a decreased normalized neointima area: control, 3.03 +/- 0.75 mm(2); intravenous, 1.67 +/- 0.73 mm(2) (40% decrease; P < 10(-7)); intravenous plus local, 1.95 +/- 0.76 mm(2) (30% decrease; P < 10(-5)). There was no difference in neointimal response following local beta-cyclodextrin tetradecasulfate delivery only (2.82 +/- 1.14 mm(2)). Coronary arterial damage, defined as aneurysm, dissection, adventitial rupture, and retromedial hematoma was similar in all groups (12% in control and local groups, 10% in the intravenous group, 14% in the intravenous plus local; NS). Bleeding complications were more frequent in the intravenous and intravenous plus local groups compared to the local and control groups (23%vs 7.6% and 0%, respectively; P < 0.05).

CONCLUSIONS

Continuous intravenous administration of beta-cyclodextrin tetradecasulfate substantially reduced intimal hyperplasia, while intramural delivery had no effect, indicating that a single bolus of beta-cyclodextrin tetradecasulfate did not reduce intimal hyperplasia. There was no additive effect of local intramural delivery of beta-cyclodextrin tetradecasulfate. However, local delivery of beta-cyclodextrin tetradecasulfate induced less bleeding complications and did not lead to additional arterial injury, indicating that local delivery of an anticoagulant does not cause additional arterial injury.

Fabrication of micropored elastomeric film-covered stents and acute-phase performances

To prevent thrombus formation in the acute phase and restenosis in the subacute to chronic phase after stenting of atherosclerotic arteries, we developed a covered stent with a micropored elastomeric film, the blood-contacting surface of which was coated with a photocured gelatin layer immobilized with heparin. Segmented polyurethane (SPU) film (30 microm in wall thickness) as a cover material was multiply micropored by excimer laser-directed microprocessing (pore diameter, 30 microm; interpore distance, 125 microm). An aqueous mixed solution of benzophenone-derivatized gelatin and heparin was coated on the micropored SPU film. Upon ultraviolet light irradiation, a thin layer of a gelatin gel immobilized with heparin was formed and simultaneously fixed on the SPU film. The fully covered stents were assembled by wrapping a balloon-expandable stent with gelatin/heparin gel-layered SPU film and subsequently suturing and then gluing. To assess the validity of this covered stent in vivo, "half-covered" stents, in which half at the distal side was covered with the gel-layered SPU film, was implanted in rabbit common carotid arteries (about 3 mm in diameter). After 3 months of implantation, all the half-covered stents (n = 7) were patent. Regardless of the covered or noncovered region of the stents, the entire luminal surface of the stents was fully endothelialized and a thin neointimal tissue was formed. The potential advantages of a covered stent as designed above are discussed.

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.

Transforming growth factor-beta: a promising target for anti-stenosis therapy

Transforming growth factor-beta (TGF-beta) is the general name for a family of cytokines which have widespread effects on many aspects of growth and development. The TGF-beta isoforms are produced by most cell types and exert a wide range of effects in a context-dependent autocrine, paracrine or endocrine fashion via interactions with distinct receptors on the cell surface. TGF-beta is involved in the wound healing process and, thus plays a significant role in the formation of a restenotic lesion after percutaneous transluminal coronary angioplasty (PTCA) or stenting. Perhaps because of its wide-ranging effects, TGF-beta is usually released from cells in a latent form, and its activation and signaling are complex. Manipulation of the TGF-beta1, TGF-beta2, and TGF-beta3 isoforms by inhibiting their expression, activation, or signaling reduces scarring and fibrosis in animal models. However, to date, few have reached clinical trial. This review summarizes current knowledge on the activation and signaling of TGF-beta, and focuses on the anti-TGF-beta strategies which may lead to clinical applications in the prevention of restenosis following PTCA or stenting.

Antiproliferative effects of the antiallergic agent azelastine on human aortic smooth-muscle cells: an in vitro study

RATIONALE AND OBJECTIVES

The aim of the study was to examine the effects of azelastine on proliferation, clonogenic activity, cell-cycle, and migration of human aortic smooth-muscle cells (haSMCs) in vitro.

METHODS

HaSMCs were treated for 4 days with azelastine (1 micromol/L, 25 micromol/L, 50 micromol/L). Half of the treated groups were incubated again with azelastine, the other half received azelastine-free medium every 4 days until day 20. The growth kinetics and clonogenic activity were assessed. The cell-cycle distribution was investigated by FACS -- analysis and the migratory ability was evaluated.

RESULTS

Azelastine inhibited the proliferation and the clonogenic activity of haSMCs in a dose dependent manner. A G2/M-phase block was induced and the migratory ability was significantly impaired.

CONCLUSION

Azelastine has the potential to inhibit the proliferation of haSMCs. If a sufficient dose can be applied either systemically or locally it could be a valuable substance to prevent restenosis.

Carrier proteins determine local pharmacokinetics and arterial distribution of paclitaxel

The growing use of local drug delivery to vascular tissues has increased interest in hydrophobic compounds. The binding of these drugs to serum proteins raises their levels in solution, but hinders their distribution through tissues. Inside the arterial interstitium, viscous and steric forces and binding interactions impede drug motion. As such, this might be the ideal scenario for increasing the amount of drug delivered to, and residence time within, arterial tissues. We quantified carrier-mediated transport for paclitaxel, a model hydrophobic agent with potential use in proliferative vascular diseases, by determining, in the presence or absence of carrier proteins, the maximum concentration of drug in aqueous solution, the diffusivity in free solution, and the diffusivity in arterial tissues. Whereas solubility of paclitaxel was raised 8.1-, 21-, and 57-fold by physiologic levels of alpha(1)-acid glycoproteins, bovine serum albumin, and calf serum over that in protein-free solution, diffusivity of paclitaxel in free solution was reduced by 41, 49, and 74%, respectively. When paclitaxel mixed in these solutions was applied to arteries both in vitro and in vivo, drug was more abundant at the tissue interface, but protein carriers tended to retain drug in the lumen. Once within the tissue, these proteins did not affect the rate at which drug traverses the tissue because this hydrophobic drug interacted with the abundant fixed proteins and binding sites. The protein binding properties of hydrophobic compounds allow for beneficial effects on transvascular transport, deposition, and distribution, and may enable prolonged effect and rationally guide local and systemic strategies for their administration.

Intravascular and intracardiac stents used in congenital heart disease

Intravascular or intracardiac stenoses occur in many forms of congenital heart disease or after attempted surgical repair. Although balloon dilation is one option for management, restenosis can occur due to elastic recoil immediately after the procedure. To address to such stenotic lesions, many reports support implanting endovascular stents to provide a framework for vessel expansion. Both balloon-expandable fixed tubular mesh stainless steel devices, and self-expandable stents have had an extensive clinical application. In pediatric patients, stents are used for a variety of stenoses, such as systemic venous obstruction pathways (eg, Mustard, Fontan baffle, or bidirectional cavopulmonary connections), pulmonary artery, right ventricular to pulmonary conduits, aortic coarctation, the arterial duct, aorticopulmonary collaterals, or postoperative systemic to pulmonary shunts. Because of improvements in device profile, implantation rates have increased. Complications such as stent fracture, migration, aneurysm formation, and in-stent restenosis occur but only rarely. This latter event may be because of intimal hyperplasia and/or continued vessel (and patient) growth related to the stent diameter. As such, some instances require redilation to manage the acquired lesion. Stent application has importantly altered management algorithms in congenital heart disease.

Neointimal thickening after stent delivery of paclitaxel: change in composition and arrest of growth over six months

OBJECTIVES

The purpose of this study was to determine long-term effects of stent-based paclitaxel delivery on amount, rate and composition of neointimal thickening after stent implantation.

BACKGROUND

Paclitaxel prevents vascular smooth muscle cell proliferation and migration in vitro and in vivo. These actions, coupled with low solubility, make it a viable candidate for modulating vascular responses to injury and prolonged effects after local delivery. We asked whether local delivery of paclitaxel for a period of weeks from a stent coated with a bioerodible polymer could produce a sustained reduction in neointimal hyperplasia for up to six months after stenting.

METHODS

Stainless steel stents were implanted in the iliac arteries of rabbits after endothelial denudation. Stents were uncoated or coated with a thin layer of poly(lactide-co-sigma-caprolactone) copolymer alone or containing paclitaxel, 200 microg.

RESULTS

Paclitaxel release in vitro followed first-order kinetics for two months. Tissue responses were examined 7, 28, 56 or 180 days after implantation. Paclitaxel reduced intimal and medial cell proliferation three-fold seven days after stenting and virtually eliminated later intimal thickening. Six months after stenting, long after drug release and polymer degradation were likely complete, neointimal area was two-fold lower in paclitaxel-releasing stents. Tissue responses in paclitaxel-treated vessels included incomplete healing, few smooth muscle cells, late persistence of macrophages and dense fibrin with little collagen.

CONCLUSIONS

Poly(lactide-co-sigma-caprolactone) copolymer-coated stents permit sustained paclitaxel delivery in a manner that virtually abolishes neointimal hyperplasia for months after stent implantation, long after likely completion of drug delivery and polymer degradation.

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.

Correlation of transarterial transport of various dextrans with their physicochemical properties

Local vascular drug delivery provides elevated concentrations of drug in the target tissue while minimizing systemic side effects. To better characterize local pharmacokinetics we examined the arterial transport of locally applied dextran and dextran derivatives in vivo. Using a two-compartment pharmacokinetic model to correct the measured transmural flux of these compounds for systemic redistribution and elimination as delivered from a photopolymerizable hydrogel surrounding rat carotid arteries, we found that the diffusivities and the transendothelial permeabilities were strongly dependent on molecular weight and charge. For neutral dextrans, the effective diffusive resistance in the media increased with molecular weight approximately 4.1-fold between the molecular weights of 10 and 282 kDa. Similarly, endothelial resistance increased 28-fold over the same molecular weight range. The effective medial diffusive resistance was unaffected by cationic charge as such molecules moved identically to neutral compounds, but increased approximately 40% when dextrans were negatively charged. Transendothelial resistance was 20-fold lower for the cationic dextrans, and 11-fold higher for the anionic dextrans, when both were compared to neutral counterparts. These results suggest that, while low molecular weight drugs will rapidly traverse the arterial wall with the endothelium posing a minimal barrier, the reverse is true for high molecular weight agents. With these data, the deposition and distribution of locally released vasotherapeutic compounds might be predicted based upon chemical properties, such as molecular weight and charge.

Biocompatibility of phosphorylcholine coated stents in normal porcine coronary arteries

OBJECTIVE

To improve the biocompatibility of stents using a phosphorylcholine coated stent as a form of biomimicry.

INTERVENTIONS

Implantation of phosphorylcholine coated (n = 20) and non-coated (n = 21) stents was performed in the coronary arteries of 25 pigs. The animals were killed after five days (n = 6), four weeks (n = 7), and 12 weeks (n = 8), and the vessels harvested for histology, scanning electron microscopy, and morphometry.

MAIN OUTCOME MEASURES

Stent performance was assessed by studying early endothelialization, neointima formation, and vessel wall reaction to the synthetic coating.

RESULTS

Stent thrombosis did not occur in either group. Morphometry showed no significant differences between the two study groups at any time point. At five days both the coated and non-coated stents were equally well endothelialised (91% v 92%, respectively). At four and 12 weeks there was no difference in intimal thickness between the coated and non-coated stents. Up to 12 weeks postimplant the phosphorylcholine coating was still discernible in the stent strut voids, and did not appear to elicit an adverse inflammatory response.

CONCLUSION

In this animal model the phosphorylcholine coating showed excellent blood and tissue compatibility, unlike a number of other polymers tested in a similar setting. Given that the coating was present up to 12 weeks postimplant with no adverse tissue reaction, it may be a potential candidate polymer for local drug delivery.

Polymeric-based perivascular delivery of a nitric oxide donor inhibits intimal thickening after balloon denudation arterial injury: role of nuclear factor-kappaB

OBJECTIVES

To examine the effect of a polymeric-based periadventitial delivery of a nitric oxide (NO)-releasing diazeniumdiolate, spermine/NO (SPER/NO), on balloon injury-induced neointimal hyperplasia in rat ileofemoral arteries.

BACKGROUND

Reduced local bioavailability and adverse side effects limit systemic administration of NO to modulate vascular response to injury.

METHODS

A polylactic-polyglycolic acid polymeric matrix containing 2.5% SPER/NO (w/w) was applied around the injured arteries. Quantitative histomorphometry was performed at day 14, proliferating cell nuclear antigen (PCNA) immunohistochemistry at day 3 to assess effects on smooth muscle proliferation and electrophoretic mobility shift assay to evaluate effects on transcription factor, nuclear factor-kappaB (NF-kappaB).

RESULTS

Treatment with SPER/NO reduced the intimal area (0.011 +/- 0.009 vs. 0.035 +/- 0.006 mm2 control, p < 0.01) and the intima to media ratio (0.089 +/- 0.062 vs. 0.330 +/- 0.057 control, p < 0.005). Spermine/nitric oxide produced a profound inhibition of PCNA-positive cells (>75%, p < 0.005) and significantly suppressed the injury-induced activation of NF-kappaB. Vascular cyclic guanosine monophosphate (cGMP) levels were elevated after treatment with the SPER/NO (0.28 +/- 0.03 vs. 0.17 +/- 0.02 pmol/mg tissue control, p < 0.01). The inhibitory effects on neointimal proliferation were localized to the site of application of SPER/NO and were not associated with any changes in platelet aggregation or bleeding time. Neither SPER nor polymer alone had any significant effects on any of the variables examined.

CONCLUSIONS

Polymeric-based perivascular delivery of a NO donor produces a marked localized inhibition of neointimal proliferation in balloon-injured arteries. This phenomenon is associated with suppression of NF-kappaB activation and elevation of the vascular cGMP at the site of injury.

Sustained release of heparin from polymeric particles for inhibition of human vascular smooth muscle cell proliferation

Vascular smooth muscle cell (SMC) growth plays an important role in atherosclerosis, restenosis and venous bypass graft disease. With systemic drug administration no effective therapy for restenosis and venous bypass graft disease is available. This could be due to low local concentrations of the drugs at the target site. A directed delivery of drugs to tissues with a sustained release system during percutaneous transluminal coronary angioplasty (PTCA) or during bypass surgery could provide high concentrations of drugs at the target site and avoid systemic side effects. In the present study heparin was encapsulated by spray-drying into biodegradable poly(D, L-lactic-co-glycolic acid) (PLGA) to obtain a system for prolonged drug release. SMC were cultured from saphenous vein explants obtained from patients undergoing coronary bypass surgery. Cell proliferation was measured by [(3)H]thymidine incorporation. Heparin release from PLGA 50:50 microspheres in an isoosmolar PBS buffer (pH=7.4) showed a triphasic profile with an initial burst (completed after 24 h), a dormant period and a final stage with increased release rate, which lasted about 10-14 days. Cell proliferation as measured by [(3)H]thymidine incorporation was markedly stimulated by platelet-derived growth factor-BB (PDGF-BB) (5 ng/ml) or serum (5%). Proliferation of SMC was equally reduced (50%; P<0.05; n=9-11) by native heparin or heparin released from PLGA microspheres, while PLGA microspheres without heparin loading had no effect on [(3)H]thymidine incorporation in human SMC. Similar results were also obtained when SMC were stimulated with 5% serum instead of PDGF-BB (50%; P<0.05; n=6). Thus, heparin encapsulated into PLGA microspheres was released over a prolonged period of time and thereby effectively reduced human SMC proliferation stimulated either with PDGF or serum. Biodegradable PLGA microspheres may also be used to encapsulate other antiproliferative agents and provide a new approach for local drug delivery after PTCA. This may help to prevent restenosis after PTCA or to reduce graft disease after coronary bypass graft surgery.

Gene therapy as a therapeutic intervention for vascular disease

Gene therapy for the treatment of many medical problems, including vascular disease, has become the subject of increasing discussion in both the scientific literature and the national press over the past decade. This review will examine the history and current status of gene therapy for vascular proliferative disorders and advanced chronic peripheral and cardiac ischemia.

Intravascular ultrasound-guided balloon angioplasty for treatment of in-stent restenosis

We investigated the usefulness of intravascular ultrasound (IVUS)-guided balloon angioplasty for in-stent restenosis in 37 lesions of 34 consecutive patients. We divided these patients into two groups: a group in which the balloon size was determined by quantitative coronary angiography (QCA group; 17 patients, 19 lesions) and a group in which the balloon size was determined by IVUS (IVUS group; 17 patients, 18 lesions). We compared short-term and 6-month outcomes for these groups. In the IVUS group, we used a balloon of a size equal to 95% of the media-to-media diameter at the distal to the stent, as determined by IVUS. No significant differences were observed in patient or lesion characteristics between the two groups. The clinical success rate was 100% in both groups, and no clinical events were observed in either of the groups. The balloon/artery ratio was larger in the IVUS group than in the QCA group (1.33 +/- 0.35 vs. 1.16 +/- 0.13, P < 0.05), and the recurrent restenosis rate was lower (17% vs. 53%, P < 0.05). These results suggest that repeat balloon angioplasty using a balloon size determined by IVUS is useful for in-stent restenosis. Cathet. Cardiovasc. Intervent. 47:298-303, 1999.

Increased Intramural Retention After Local Delivery of Molecules with Increased Binding Properties: Implications for Regional Delivery of Pharmacologic Agents

BACKGROUND: Catheter-based local vascular delivery results in concentrated qualtities of pharmaceutical agents or genes into focal areas of the arterial wall. However, intramural retention is short and has reduced the potential efficacy of this approach. It was postulated that agents that possess increased intramural binding would show increased intramural retention. Platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) were models of agents with increased cellular and extracellular matrix binding properties. METHODS AND RESULTS: The delivery efficiency and intramural retention of 2 mL of saline containing I(125) labeled PDGF (n = 35 arteries) and bFGF (n = 24) were compared with albumin (n = 21) after local delivery into porcine coronary arteries. Animals were sacrificed at three or more prespecified timepoints: immediately after delivery, 1 day, or 3 days after delivery and if necessary at 5 or 7 days to document prolonged retention. Autoradiograms of the arterial sections were evaluated for the extent of delivery. Delivery efficiency, defined as the amount leaving the catheter and retrieved from the arterial wall, was 0.60% +/- 0.42% for albumin, 1.98% +/- 0.88% for PDGF (P =.001), and 0.31% +/- 0.11% for bFGF. The calculated intramural half-life of albumin was 7.4 hours, 56.2 hours for PDGF, and 14.9 hours for bFGF (P =.0001 for PDGF). Infusate covering >50% of the medial area was observed in 85% of arteries immediately after delivery. Although myocardial delivery was similar for albumin, PDGF, and bFGF, myocardial retention was significantlylonger for bFGF (P <.001). CONCLUSIONS: Molecules that exhibit preferential intramural binding show a longer intramural residence duration than solutes without such binding properties. In addition, delivery and subsequent prolonged retention in the myocardium can be obtained by local delivery via the arterial lumen of solutions with preferential binding properties.

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.

Biocompatibility of polyurethane-coated stents: tissue and vascular aspects

To assess the arterial injury triggered by polyurethane-coated vs. uncoated stents, six polyurethane-coated and six bare nitinol stents were implanted in rabbit carotid arteries. All animals were sacrificed 4 wk after stent placement. Sections were evaluated by histology and morphometric analysis. At 4 wk, both the coated and uncoated stent struts were entirely endothelialized. The spaces between the struts showed a relatively mild proliferative response, with a few sections demonstrating neovascularization around the struts. Polyurethane coating was associated with an inflammatory tissue response consisting of lymphocytic infiltration and foreign-body reaction, with the appearance of multinucleated giant cells. Lumen, intimal, and medial cross-sectional areas varied little between coated and uncoated stented vessels (2.45+/-0.19 vs. 2.47+/-0.47 mm2, 1.17+/-0.52 vs. 0.78+/-0.30 mm2, and 0.66+/-0.18 vs. 0.58+/-0.27 mm2, respectively). In the rabbit carotid artery model, polyurethane coating does not affect the degree of neointimal proliferation after endovascular stenting compared with the conventional stenting approach. However, the inflammatory tissue response may indicate a low intrinsic biocompatibility of this stable polymer, so that it may not be an ideal material for coating intravascular devices.