A Novel All-Trans Retinoic Acid Perivascular Wrap Reduces Neointimal Hyperplasia Following Arterial Balloon Injury

Abstract

Introduction: All-trans retinoic acid (ATRA) is a vitamin A derivative that has many beneficial effects on the vasculature, including inhibition of vascular smooth muscle cell (VSMC) proliferation and stimulation of nitric oxide (NO) release. Thus, through a multidisciplinary collaboration, we developed a novel ATRA perivascular wrap utilizing a biodegradable citric-acid based polymer, poly (diol-citrate) (POC). The goal of our current study was to characterize the properties of ATRA wraps in vitro and evaluate the efficacy of our ATRA wrap to inhibit neointimal hyperplasia in vivo. We hypothesized that treatment with ATRA perivascular wraps would decrease the formation of neointimal hyperplasia with a concomitant decrease in proliferation. Methods: ATRA wraps were fabricated using POC wraps loaded with ATRA dissolved in DMSO to a final concentration of 20 mg/ml. ATRA release was measured over time and was confirmed using HPLC. VSMC proliferation was assessed by measuring DNA content. The rat carotid injury model was performed in 10 week old male Sprague Dawley rats. Treatment groups included: control, injury, and injury +ATRA wrap (1cm x 1cm). n=6-7/group. Arteries were harvested at 14 days. Morphometric analysis was performed on H&E stained cross-sections utilizing Image J software. Immunohistochemistry was performed to assess for BrdU incorporation and macrophage infiltration (ED1 staining). Results: In vitro, ATRA release from the wraps occurred for 14 days, with the greatest release in the first 7 days. ATRA wraps inhibited VSMC proliferation by approximately 75% at 7 days (p<0.05) compared to controls. In vivo, ATRA wraps resulted in significant inhibition of neointimal hyperplasia, with a 56.3% reduction in intimal area (p<0.001) and a 57% reduction in the intima/media area ratio (p<0.001) as compared to injury alone. We observed no significant changes in the lumen or medial area. With respect to proliferation, ATRA wraps resulted in a decreasing trend in proliferation for both the intimal and medial layers, with a slight increase in the adventitia. However, none of these changes reached statistical significance. With respect to inflammation, treatment with ATRA wraps resulted in increased macrophage infiltration compared to injury alone (1.8-fold, p<0.001). Conclusions: Neointimal hyperplasia was significantly inhibited by the citric acid-based biodegradable ATRA-eluting perivascular wrap without significant effect on vessel wall remodeling. This therapy represents a novel method to deliver ATRA to the vasculature to inhibit neointimal hyperplasia. the increased inflammatory response, while not anticipated, is mostly likely due to mass effect of the wrap in the small neck of the rat. Further study of this therapy is warranted in a large animal model.