Local delivery: let's keep our eyes on the wall

Endoluminal reconstruction of the arterial wall with endothelial cell/glue matrix reduces restenosis in an atherosclerotic rabbit

OBJECTIVES

The objectives of this study were 1) to improve the attachment of reimplanted endothelial cells (EC) using a fibrin glue, and 2) to assess the impact of endothelial reseeding on restenosis eight weeks after balloon angioplasty.

BACKGROUND

A possible mechanism contributing to restenosis after balloon angioplasty is the loss of the EC lining. Previous attempts to reseed EC had little effect due to rapid loss of the seeded cells.

METHODS

Twelve atherosclerotic rabbits were subjected to angioplasty of iliac arteries and reseeding procedure. One iliac artery was subjected to EC/glue reconstruction and a contralateral site to EC seeding without glue. The animals were sacrificed after 4 h. In another series 12 rabbits were treated in the same fashion and were restudied at eight weeks. Additionally, in 10 animals one iliac was subjected to glue treatment, and another served as control.

RESULTS

Histological examination demonstrated the ability of this method to reattach the EC/glue matrix circumferentially to 68.0 +/- 6.7% of the arterial wall in comparison with 13.5 +/- 3.9% reattachment after EC seeding. Morphometry at eight weeks showed that the lumen area was significantly greater in the EC/glue group (1.23 +/- 0.35 mm2) than in the EC seeding alone (0.65 +/- 0.02 mm2) and 0.72 +/- 0.41 mm2 in the glue group. This was principally accounted for by the statistically significant differences in the intimal area (0.76 +/- 0.18 mm vs. 1.25 +/-0.26 mm2 and 1.01 +/- 0.53 mm2, respectively).

CONCLUSIONS

The attachment of EC after angioplasty can be greatly improved with fibrin glue matrix. The near 70% endothelial coverage achieved by this method resulted in a significant reduction of restenosis in atherosclerotic rabbit.

Photodynamic therapy with local photosensitizer delivery inhibits experimental intimal hyperplasia

BACKGROUND

Photodynamic therapy (PDT), the light activation of photosensitizer dyes for the production of free radicals, effectively inhibits experimental intimal hyperplasia with systemic administration of the photosensitizer. The local application of the photosensitizer directly into a vascular lesion to avoid systemic side effects and tightly control dose administration has theoretical appeal. The aim of this study was to quantify serum and arterial tissue uptake after site-specific photosensitizer delivery and, following PDT, determine its effectiveness at inhibiting intimal hyperplasia.

STUDY DESIGN/MATERIALS AND METHODS

The rat common carotid artery was balloon-injured, pressurized at 400 mm Hg for 2 minutes with the photosensitizer dye benzoporphyrin-derivative (BPD), and irradiated with 690 nm laser light at a fluence of 100 J/cm2. Control animals were pressurized with saline only, or received no additional treatment than balloon-injury.

RESULTS

Pressurization with BPD resulted in complete penetration of the intima and media and was associated with relatively high tissue, but almost no detectable serum BPD concentrations. No skin photosensitization or other systemic side effects were observed with photosensitizer administration. After 9 days, PDT-treated arteries displayed a significantly lower number of smooth muscle cells in the arterial wall than balloon-injured (P < 0.001) or saline-pressurized arteries (P < 0.0002), and no intimal hyperplasia. At 21 days, IH after PDT was significantly reduced as compared with balloon-injured (P < 0.0004), or saline-pressurized arteries (P < 0.003) with no arterial dilatation.

CONCLUSIONS

Site-specific delivery of liposomal BPD followed by PDT represents a safe method to treat arteries, and may be effectively used in vivo to inhibit the development of intimal hyperplasia.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Measurement of drug distribution in vascular tissue using quantitative fluorescence microscopy

Quantitative tools to assess vascular macromolecular distributions have been limited by low signal-to-noise ratios, reduced spatial resolution, postexperimental motion artifact, and the inability to provide multidimensional drug distribution profiles. Fluorescence microscopy offers the potential of identifying exogenous compounds within intact tissue by reducing autofluorescence, the process by which endogenous compounds emit energy at the same wavelength as fluorescent labels. A new technique combining fluorescence microscopy with digital postprocessing has been developed to address these limitations and is now described in detail. As a demonstration, histologic cross-sections of calf carotid arteries that had been loaded endovascularly with FITC-Dextran (20 kD) ex vivo were imaged at two different locations of the electromagnetic spectrum, one exciting only autofluorescent structures and the other exciting both autofluorescent elements and exogenous fluorescent labels. The former image was used to estimate the autofluorescence in the latter. Subtraction of the estimated autofluorescence resulted in an autofluorescence-corrected image. A standard curve, constructed from arteries that were incubated until equilibrium in different bulk phase concentrations of FITC-Dextran, was used to convert fluorescent intensities to tissue concentrations. This resulted in a concentration map with spatial resolution superior to many of the previous methods used to quantify macromolecular distributions. The transvascular concentration profiles measured by quantitative fluorescence microscopy compared favorably with those generated from the proven en face serial sectioning technique, validating the former. In addition, the fluorescence method demonstrated markedly increased spatial resolution. This new technique may well prove to be a valuable tool for elucidating the mechanisms of macromolecular transport, and for the rational design of drug delivery systems.

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.

Drug clearance and arterial uptake after local perivascular delivery to the rat carotid artery

OBJECTIVES

We attempted to characterize how drug released into the perivascular space enters the arterial wall and how it is cleared from the local environment.

BACKGROUND

Drug released into the perivascular space can enter the artery either from the adventitial aspect or from the lumen after absorption by the extraarterial capillaries and mixing within the systemic circulation. Some investigators suggest that this latter mechanism dominates, and they question whether local drug release is synonymous with local deposition.

METHODS

We investigated both the pathways by which adventitially released drug is cleared from the perivascular space and those by which drug enters the blood vessel wall. Inulin was used to follow drug release from implanted devices and subsequent entry to the circulation, because of its first-pass urinary excretion. Heparin was used to follow arterial deposition because of its vasoactivity and tissue-binding properties. The different potential pathways of drug entry and egress were systematically removed and the effects on metabolism and deposition determined.

RESULTS

Ligature occlusion of the artery did not decrease inulin excretion or heparin deposition. Extravascular wraps designed to shield the device from extramural capillaries reduced inulin excretion rates 10-fold but did not alter heparin deposition into the vessel wall. The deposition of drug after perivascular delivery was 500 times higher than after intraperitoneal administration.

CONCLUSIONS

Although almost all the drug released into the perivascular space is cleared through the extravascular capillaries, virtually all the deposited drug diffuses directly from the perivascular space, and little arrives from the endovascular aspect. These data support the view that local drug release leads directly to increased local drug concentration.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Controlled delivery of a tyrphostin inhibits intimal hyperplasia in a rat carotid artery injury model

We examined the inhibitory effect of AG-17, a potent inhibitor of protein tyrosine kinase activity on injury-induced vascular SMC proliferation by polymeric-based, periadventitial controlled release implant in the balloon catheter carotid injury model in rats. The AG-17 delivery system was formulated from ethylenevinyl acetate copolymer and the release kinetics as well as drug stability were determined. Polymeric matrices containing 2 or 10% AG-17 were implanted perivascularly in rats following balloon catheter injury. Western blot analysis of explanted arterial segments revealed enhanced tyrosine phosphorylation in injured arteries that was essentially reduced to normal levels in treated arteries. The mean neointima to media ratios were significantly reduced in both 2% (0.79 +/- 0.17, n = 9, P < 0.02) and 10% AG-17 (0.59 +/- 0.09, n = 12, P < 0.001) groups in comparison to the control group (1.38 +/- 0.18, n = 16). The mean areas of the media in the control and the 2% AG-17 group did not differ significantly but a significant reduction of the mean area of the media was observed in 10% AG-17 group. Embedding of the unstable tyrphostin compound, AG-17, in a hydrophobic matrix stabilizes the drug both in vitro and in vivo, and allows delivery-rate modulation as well as protracted site-specific therapy. Perivascular controlled release delivery of the tyrphostin AG-17 inhibits neointimal formation in the rat carotid injury model.

Mechanisms of transmural heparin transport in the rat abdominal aorta after local vascular delivery

Local vascular drug delivery systems provide elevated concentrations in target arterial tissues, while minimizing systemic side effects. Drug can now be released to isolated arterial segments from the endovascular or perivascular aspects of the blood vessel, yet the forces that determine drug distribution and deposition for these different modes of delivery have not been rigorously investigated. This study examines mechanisms of transmural transport of a model vasoactive drug, heparin, and compares estimates of the distribution after administration from either aspect of the artery. We showed that (1) heparin traversed the arterial wall rapidly; (2) diffusion far outweighed convection in the control of transmural heparin transport in the normal artery, but after endothelial injury, convective forces rose to one quarter the magnitude of diffusive forces; (3) the endothelium posed a minimal diffusive barrier to heparin; and (4) the diffusive barrier imposed by the adventitia depended on its thickness. These findings strongly suggest that vasoregulatory compounds can be administered to target tissue by either perivascular or endovascular means with equal efficacy, because the forces governing transport of heparin from either aspect of the blood vessel wall are not significantly different. Furthermore, the differences in arterial transport properties between heparin and other macromolecules suggest that distribution and the optimal aspect of delivery will depend just as much on the physicochemical properties of the drug as the state of the blood vessel wall.