Comparison of methods for local delivery of tissue factor pathway inhibitor to balloon-injured arteries in rabbits

Background. Prolonged intravenous infusions of recombinant tissue factor pathway inhibitor (rTFPI) have been shown to attenuate markedly neointimal formation and stenosis after balloon-induced injury to the carotid arteries in minipigs. Design. Because local delivery of rTFPI to the injury site would be clinically advantageous, we designed this study to compare the local delivery and retention of rTFPI in balloon-injured arteries using three catheter-based systems. Methods. Similar amounts (range 3-4.5 mg) of a mixture of ¹²⁵I-labeled and unlabeled rTFPI were delivered by either passive diffusion at moderate pressure (5 x 10⁵ Pa with the LocalMed InfusaSleeve, or 4 x 10⁵ Pa with the SciMed Dispatch device), or facilitated diffusion combining lower pressure (2 x 10⁵ Pa) and electrical current (3.5 mA/cm²; e^-MED, iontophoresis) to balloon-injured carotid arteries in anesthetized rabbits. Results. Comparable amounts of rTFPI were retained on the injured vessels immediately after delivery (t = 0) with the LocalMed (628 ± 68 μg/g per cm², n = 4), SciMed (522 ± 167 μg/g per cm², n = 4), and e^-MED (497 ± 142 μg/g per cm², n = 4) catheters (NS). However, rTFPI was decreased by 37% after 24 h compared with t = 0 (P < 0.02) in the e^-MED group, but was increased 1.5-fold (P = 0.02) and 1.3-fold in the SciMed and LocalMed groups, respectively, presumably because of redistribution of rTFPI from remote endothelial or perivascular sites. Retention of rTFPI was six to nine times higher for injured compared with non-injured arteries, and persisted for at least 48 h after delivery with the LocalMed catheter. Conclusions. Sustained, marked retention of rTFPI delivered locally at the site of balloon-induced arterial injury appears to result from catheter-based systems that use passive diffusion at moderate pressure.