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

Location-dependent coronary artery diffusive and convective mass transport properties of a lipophilic drug surrogate measured using nonlinear microscopy

PURPOSE

Arterial wall mass transport properties dictate local distribution of biomolecules or locally delivered dugs. Knowing how these properties vary between coronary artery locations could provide insight into how therapy efficacy is altered between arterial locations.

METHODS

We introduced an indocarbocyanine drug surrogate to the lumens of left anterior descending and right coronary (LADC; RC) arteries from pigs with or without a pressure gradient. Interstitial fluorescent intensity was measured on live samples with multiphoton microscopy. We also measured binding to porcine coronary SMCs in monoculture.

RESULTS

Diffusive transport constants peaked in the middle sections of the LADC and RC arteries by 2.09 and 2.04 times, respectively, compared to the proximal and distal segments. There was no statistical difference between the average diffusivity value between LADC and RC arteries. The convection coefficients had an upward trend down each artery, with the RC being higher than the LADC by 3.89 times.

CONCLUSIONS

This study demonstrates that the convective and diffusive transport of lipophilic molecules changes between the LADC and the RC arteries as well as along their length. These results may have important implications in optimizing drug delivery for the treatment of coronary artery disease.

Immunolocalization of proliferating cells in the rabbit iliac artery after balloon angioplasty

PURPOSE

Experiments were performed to characterize the location of proliferating cells in the balloon-dilated rabbit iliac artery.

MATERIALS AND METHODS

Balloon angioplasty was performed on the external iliac arteries in each of four rabbits. The arteries were removed 3 days later, frozen, cryosectioned, and immunostained with Ki-67, an antibody that identifies proliferating cells. The sections were then examined to determine the patterns of cell proliferation within the arterial media and the ratio of proliferating to nonproliferating cells.

RESULTS

Of the 31 arterial cross-sections examined, cell proliferation was circumferential in five (16%), and focal in 26 (84%). Of the 86 foci of proliferation examined within the 31 cross-sections, proliferation was localized to the inner media in 30 (35%), to the outer media in four (5%), and was transmural in 52 (60%). The internal elastica lamina (IEL) appeared normal at 22 foci (26%), but appeared stretched or torn at 64 (74%). Proliferation was usually confined to the inner media at foci having no IEL injury (18 of 22; 82%), but was most often transmural where the IEL was stretched or torn (49 of 64; 77%). The ratio of proliferating to nonproliferating cells, which averaged 0.31 +/- .20, was greater (P < .01) in areas with IEL injury than in areas without IEL injury.

CONCLUSION

These results suggest that angioplasty-induced cell proliferation is typically focal rather than circumferential and is associated with stretching or tearing of the IEL.

Local administration of ramiprilat is less effective than oral ramipril in preventing restenosis after balloon angioplasty in an animal model

PURPOSE

To test the hypothesis that local administration of angiotensin converting enzyme (ACE) inhibitor via a microporous balloon catheter would be more effective than oral administration of ACE inhibitor in preventing neointima formation after balloon angioplasty.

MATERIALS AND METHODS

Neointima formation was induced by balloon denudation followed by 0.5% cholesterol diet in 29 New Zealand White rabbits. Directly after denudation, local administration of 1.8 mg of ramiprilat (n = 7) or saline (n = 7) with a microporous balloon catheter at a pressure of 3 atm was performed. Both groups additionally received ramipril orally (1 mg/d). Seven animals were treated exclusively with oral ramipril. The control group was fed a 0.5% cholesterol diet and given no medication (n = 8). Six weeks after intervention, the animals were killed and morphometric and immunohistologic analyses were performed.

RESULTS

Oral administration of ramipril resulted in a significant reduction of placque area (-66%, P < .05). Oral and local administration of the ACE inhibitor was followed by a nonsignificant reduction of the neointimal area (-17%). Local administration of saline combined with oral ramipril failed to prevent neointimal formation (reduction of 6%, NS).

CONCLUSION

Oral administration of ramipril resulted in a significant reduction of neointimal proliferation in New Zealand White rabbits. The possible benefit of an additional administration of local ramiprilat was diminished by an excessive neointimal hyperplasia, which was most likely caused by the inherent vessel trauma with use of the microporous balloon catheter.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

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.