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

Recent developments in drug eluting devices with tailored interfacial properties

Drug eluting devices have greatly evolved during past years to become fundamental products of great marketing importance in the biomedical field. There is currently a large diversity of highly specialized devices for specific applications, making the development of these devices an exciting field of research. The replacement of the former bare metal devices by devices loaded with drugs allowed the sustained and controlled release of drugs, to achieve the desired local therapeutic concentration of drug. The newer devices have been "engineered" with surfaces containing micro- and nanoscale features in a well-controlled manner, that have shown to significantly affect cellular and subcellular function of various biological systems. For example, the topography can be structured to form an antifouling surface mimicking the defense mechanisms found in nature, like the skin of the shark. In the case of bone implants, well-controlled nanostructured interfaces can promote osteoblast differentiation and matrix production, and enhance short-term and long-term osteointegration. In any case, the goal of current research is to design implants that induce controlled, guided, and rapid healing. This article reviews recent trends in the development of drug eluting devices, as well as recent developments on the micro/nanotechnology scales, and their future challenges. For this purpose medical devices have been divided according to the different systems of the body they are focused to: orthopedic devices, breathing stents, gastrointestinal and urinary systems, devices for cardiovascular diseases, neuronal implants, and wound dressings.

The metamorphosis of vascular stents: passive structures to smart devices

The role of nanotechnology enabled techniques in the evolution of vascular stents.

Emerging technologies: polymer-free phospholipid encapsulated sirolimus nanocarriers for the controlled release of drug from a stent-plus-balloon or a stand-alone balloon catheter

Drug-eluting stents have proven to be effective in reducing the risk of late restenosis. In order to achieve a controlled and prolonged release of the antiproliferative agent, current drug-eluting stents utilise various biodegradable as well as non-erodible polymeric blends to coat the stent surface and to serve as drug carriers. The utilisation of polymeric compounds in current drug-eluting stents may eventually limit their performance as well as their clinical applicability due to the potential induction of undesirable local reactions. The development of alternative, polymer-free drug carriers has the potential to overcome some of the limitations of current drug-eluting stent formulations. Moreover, improvements in drug carriers may also result in an expansion of the technological possibilities for other intravascular drug delivery systems, such as metal-free or even implant-free solutions. This article describes the structure and the preclinical validation profile of a novel phospholipid encapsulated sirolimus nanocarrier, used as a coating in two formulations: a coronary stent-plus-balloon system and a stand-alone balloon catheter. The nanoparticles provided a stable, even and homogenous coating to the devices in both formulations. Dose-finding studies allowed the most appropriate identification of the best nanoparticle structure associated with an extremely efficient transfer of drug to all layers of the vessel wall, achieving high tissue concentrations that persisted days after the application, with low systemic drug leaks.

Nanoparticle-based drug delivery: case studies for cancer and cardiovascular applications

Nanoparticles (NPs) comprised of nanoengineered complexes are providing new opportunities for enabling targeted delivery of a range of therapeutics and combinations. A range of functionalities can be included within a nanoparticle complex, including surface chemistry that allows attachment of cell-specific ligands for targeted delivery, surface coatings to increase circulation times for enhanced bioavailability, specific materials on the surface or in the nanoparticle core that enable storage of a therapeutic cargo until the target site is reached, and materials sensitive to local or remote actuation cues that allow controlled delivery of therapeutics to the target cells. However, despite the potential benefits of NPs as smart drug delivery and diagnostic systems, much research is still required to evaluate potential toxicity issues related to the chemical properties of NP materials, as well as their size and shape. The need to validate each NP for safety and efficacy with each therapeutic compound or combination of therapeutics is an enormous challenge, which forces industry to focus mainly on those nanoparticle materials where data on safety and efficacy already exists, i.e., predominantly polymer NPs. However, the enhanced functionality affordable by inclusion of metallic materials as part of nanoengineered particles provides a wealth of new opportunity for innovation and new, more effective, and safer therapeutics for applications such as cancer and cardiovascular diseases, which require selective targeting of the therapeutic to maximize effectiveness while avoiding adverse effects on non-target tissues.

Nanotechnology in interventional cardiology

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

Osteopontin expression during early cerebral ischemia-reperfusion in rats: enhanced expression in the right cortex is suppressed by acetaminophen

Osteopontin (OPN) is a pleiotropic protein implicated in various inflammatory responses including ischemia-reperfusion (I-R) injury. Two distinct forms of the protein have been identified: an extensively studied secreted form (sOPN) and a less-well-known intracellular form (iOPN). Studies have shown that increased OPN expression parallels the time course of macrophage infiltration into injured tissue, a late event in the development of cerebral infarcts. sOPN has been suggested to promote remodeling of the extracellular matrix in the brain; the function of iOPN may be to facilitate certain signal transduction processes. Here, we studied OPN expression in adult male Sprague-Dawley rats subjected to global forebrain I-R injury. We found iOPN in the cytoplasm of both cortices and the hippocampus, but unexpectedly only the right cortex exhibited a marked increase in the iOPN level after 45 min of reperfusion. Acetaminophen, a drug recently shown to decrease apoptotic incidence, caspase-9 activation, and mitochondrial dysfunction during global I-R, significantly inhibited the increase in iOPN protein in the right cortex, suggesting a role for iOPN in the response to I-R injury in the right cortex.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

New approach for local delivery of rapamycin by bioadhesive PLGA-carbopol nanoparticles

Local delivery of antiproliferative drugs encapsulated in biodegradable nanoparticles has shown promise as an experimental strategy for preventing vascular restenosis development. The general aim of this work was to develop polymeric nanoparticle carriers with bioadhesive properties, and to evaluate its adjuvant potential for local, intramural delivery of rapamycin for inhibition of restenosis. The bioadhesive rapamycin-loaded PLGA nanoparticles were obtained by applying carbopol 940 of different concentrations as stabilizer and bioadhesive agent. The resultant nanoparticles were characterized concerning physicochemical properties such as morphology, particle size, zeta potential, entrapment efficiency, drug loading, drug release in vitro, stability in vitro as well as the arterial uptake and retention ability in an ex-vivo model. The results revealed that carbopol could serve as a better stabilizer in the preparation of rapamycin-loaded PLGA nanoparticles compared with PVA, and the physicochemical characteristics of the obtained PLGA nanoparticles were affected by the concentration of carbopol. Furthermore, it was found that carbopol could impart the nanoparticles with bioadhesive properties, improving the rentention and uptake of nanoparticles in the arterial wall, benefiting the nanoparticles for efficient localization of therapeutic agents in restenosis site. Cell viability assay results showed that blank PLGA-carbopol nanoparticles exhibited low toxicity and excellent biocompatibility and rapamycin-loaded nanoparticles with a smaller particle size (< 200 nm) had an increased antiproliferative effect on cells in comparison to free drug. These results indicated that this research might provide a potential experimental basis for the further study of carbopol stabilized bioadhesive nanoparticles against restenosis in vivo.

Inhibition of Apoptosis Through Localized Delivery of Rapamycin-Loaded Nanoparticles Prevented Neointimal Hyperplasia and Reendothelialized Injured Artery

Background— A significant fraction of vascular smooth muscle cells (VSMCs) undergo rapid apoptosis after balloon angioplasty. In this study, we tested the hypothesis that protecting VSMCs from undergoing apoptosis prevents the cascade of events that lead to intimal hyperplasia.

Methods and Results— Rapamycin-loaded gel-like nanoparticles (mean diameter, 54�5 nm) were infused locally in a rat carotid artery model of vascular injury. The drug has both antiapoptotic and antiproliferative effects on VSMCs and hence was selected for the current study. Localized delivery of nanoparticles sustained the drug level in the target artery for >2 weeks; demonstrated significant inhibition of hyperplasia (intima/media ratio, 1.5�0.02 versus 2.7�0.6; P <0.01); and most importantly, reendothelialized the injured artery (endothelium coverage: treated 82% versus control 28%). We also demonstrated inhibition of activation of caspase-3/7 enzymes in the treated artery, preventing VSMCs from undergoing apoptosis and subsequent infiltration of macrophages.

Conclusions— It may be postulated that the localized delivery of rapamycin inhibited apoptosis of VSMCs, minimizing the inflammatory response to the injury and, thus, creating conditions conducive to vascular repair (reendothelialization). Unlike stenting, which can lead to thrombosis and increased risk for in-stent restenosis, our approach could eliminate or minimize long-term complications because the injured artery undergoes a natural process of reendothelialization.

Targeting microspheres and cells to polyethylene glycol-modified biological surfaces

It has previously been demonstrated that damaged arterial tissue can be acutely modified with protein-reactive polyethylene glycol (PEG) to block undesirable platelet deposition. This concept might be expanded by employing PEG-biotin and its strong interaction with avidin for site-specific targeted delivery. Toward this end, cultured endothelial cells (ECs) were surface modified with PEG-biotin and the available biotin was quantified with flow cytometry. NeutrAvidin-coated microspheres and PEG-biotin modified ECs with NeutrAvidin as a bridging molecule were delivered under arterial shear stress to PEG-biotin modified ECs on a coverslip as well as scrape-damaged bovine carotid arteries. After incubation with a 10 mM solution for 1 min, 8 x 10(7) PEG-biotin molecules/EC were found and persisted for up to 120 h. Perfused microspheres adhered to NHS-PEG-biotin treated bovine carotid arteries with 60 +/- 16 microspheres/mm(2) versus 11 +/- 4 microspheres/mm(2) for control arteries (p < 0.015). Similarly, 22 +/- 5 targeted ECs/mm(2) adhered to NHS-PEG-biotin treated bovine carotid arteries versus 6 +/- 2 ECs/mm(2) for control arteries (p < 0.01). The targeting strategy demonstrated here might ultimately find application for drug delivery, gene therapy, or cell therapy where localization to specific labeled vascular regions is desired following catheter-based or surgical procedures.

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).

Adenoviral gene vector tethering to nanoparticle surfaces results in receptor-independent cell entry and increased transgene expression

The present studies investigated the hypothesis that affinity immobilization of replication-defective adenoviruses (Ad) on the surfaces of biodegradable nanoparticles (NP) can improve transduction through uncoupling cellular uptake from the coxsackie-adenovirus receptor (CAR). Ad was tethered to the surfaces of polylactide-based NP that were surface-activated using a photoreactive polyallylamine-benzophenone-pyridyldithiocarboxylate polymer, which enabled (via thiol chemistry) the covalent attachment of Ad-binding proteins, either the recombinant D1 domain of CAR or an adenoviral knob-specific monoclonal antibody. Gene transfer by NP-Ad complexes was studied in relation to cellular uptake as a function of cell type and the character of NP-Ad binding. NP-Ad complexes, but not Ad applied with or without control nonimmune IgG-modified NP, significantly increased green fluorescent protein reporter expression in endothelioma and endothelial and arterial smooth muscle cells (SMC) in direct correlation to the extent of NP-Ad internalization. CAR-independent uptake of NP-Ad was confirmed by demonstrating inhibition of free Ad- but not NP-Ad complex-mediated transduction by knob protein. Complexes formulated with an Ad encoding inducible nitric oxide synthase inhibited growth of cultured SMC to a significantly greater extent than those with (GFP)Ad or (NULL)Ad or free vector. It is concluded that Ad-specific affinity tethering to biodegradable NP can significantly increase the level of gene expression via a CAR-independent uptake mechanism.

Nanoparticle-induced platelet aggregation and vascular thrombosis

Ever increasing use of engineered carbon nanoparticles in nanopharmacology for selective imaging, sensor or drug delivery systems has increased the potential for blood platelet-nanoparticle interactions. We studied the effects of engineered and combustion-derived carbon nanoparticles on human platelet aggregation in vitro and rat vascular thrombosis in vivo. Multiplewall (MWNT), singlewall (SWNT) nanotubes, C60 fullerenes (C60CS) and mixed carbon nanoparticles (MCN) (0.2-300 microg ml(-1)) were investigated. Nanoparticles were compared with standard urban particulate matter (SRM1648, average size 1.4 microm). Platelet function was studied using lumi aggregometry, phase-contrast, immunofluorescence and transmission electron microscopy, flow cytometry, zymography and pharmacological inhibitors of platelet aggregation. Vascular thrombosis was induced by ferric chloride and the rate of thrombosis was measured, in the presence of carbon particles, with an ultrasonic flow probe. Carbon particles, except C60CS, stimulated platelet aggregation (MCN>or=SWNT>MWNT>SRM1648) and accelerated the rate of vascular thrombosis in rat carotid arteries with a similar rank order of efficacy. All particles resulted in upregulation of GPIIb/IIIa in platelets. In contrast, particles differentially affected the release of platelet granules, as well as the activity of thromboxane-, ADP, matrix metalloproteinase- and protein kinase C-dependent pathways of aggregation. Furthermore, particle-induced aggregation was inhibited by prostacyclin and S-nitroso-glutathione, but not by aspirin. Thus, some carbon nanoparticles and microparticles have the ability to activate platelets and enhance vascular thrombosis. These observations are of importance for the pharmacological use of carbon nanoparticles and pathology of urban particulate matter.