Introduction: The main cause of loss of patency in arteriovenous fistula (AVF) vascular accesses is venous neointimal hyperplasia, which is the accumulation of vascular smooth muscle cells (VSMCs) in the vessel intima. Perfusion catheters are a novel liquid drug delivery device that can administer therapeutic agents directly into the vascular wall. Aptamer 14 (Apt14) is an RNA “smart drug” that specifically targets VSMCs to inhibit their migration and has been shown to reduce neointimal formation in porcine arterial injury models. The purpose of this study was to determine the acute delivery efficacy of Apt14 delivery with a perfusion catheter via visualization of the depth of drug penetration in porcine venous tissue using a novel AVF benchtop model.
Materials and
Methods: The AVF benchtop bioreactor consists of a circulation media reservoir, gear pump, transparent vessel housing, and a signal generator. Porcine jugular veins harvested from a local abattoir were used as the test vessels. The average flow rate and systolic/diastolic pressures measured in the bioreactor were 665 ± 85 mL/min and 146/87 mmHg. The delivery catheter used in this study was the occlusion perfusion catheter (OPC, Advanced Catheter Therapies) which can isolate a treatment zone in the vessel using two occlusion balloons and allow pressure-driven liquid delivery into the target region (Figure 1). The OPC catheter has a built-in pressure transducer that enables monitoring in real-time of the delivery pressure in the treatment zone during infusion. We used a fluorescent formulation of Apt14 to enable visualization of the depth of delivery penetration via fluorescent microscopy. The aptamer solution was prepared at 100 nM and delivered at 0.4 atm for 2 minutes. After drug delivery, the OPC was withdrawn from the bioreactor, and the veins exposed to AVF-level pulsatile flow for 1 hour. Treated segments of the veins were removed after the time point, stained with phalloidin-Alexa Fluor 488 (Thermo Fisher Scientific) to visualize smooth muscle, and imaged. Depth of drug penetration was measured from the internal elastic lamina to the maximum depth of penetration and normalized to the thickness of the venous medial layer. All data are expressed mean +/-standard deviation.
Results, Conclusions, and Discussions: Fluorescent microscopy showed that Apt14 delivery with the OPC resulted in successful acute retention of the drug in the medial layer of the porcine veins (Figure 2). Average depth of penetration was 13.65 +/- 5.02 µm (n = 3), which was 77 +/- 16% of the medial layer thickness. This study is the first to evaluate the liquid delivery of an RNA aptamer in venous tissue under simulated AVF flow. We demonstrated feasibility delivering a liquid therapeutic into porcine venous using a perfusion catheter. Future work will include measuring aptamer accumulation and optimizing delivery parameters, including drug concentration, pressure, and duration.
Acknowledgements (Optional): This project is supported in part by funding from the American Society of Diagnostic and Interventional Nephrology and the National Institute of Health [1R01EB028798].
.jpg "Linda B. Liu, BS photo")
