Percutaneous transluminal angioplasty with stent implantation is used to dilate arteries narrowed by atherosclerotic plaques and to revascularize coronary arteries occluded by atherothrombosis in myocardial infarction. Commonly applied drug-eluting stents release anti-proliferative or anti-inflammatory agents to reduce the incidence of restenosis. However, these stents may still lead to in-stent stenosis and late stent thrombosis; one of the reasons may be that endothelial recovery process is impaired and thus endothelium fails to heal after arterial injury. Neutrophils immigrate to the site of injury during the initial state of inflammation and secrete a wide array of granule proteins which may modulate the process underlying restenosis and neointima formation.
Here we examined the contribution of neutrophils and neutrophilic granule proteins to arterial healing after injury. We focused on the involvement of neutrophil-derived cathelicidin (human LL-37 and mouse CRAMP) in re-endothelialization and neointima formation with the aim to develop a cathelicidin coated stent that reduces restenosis following vascular injury.
Atherosclerotic mice with intact white blood cell count or neutropenia were subjected to wire-induced injury of the carotid artery mimicking arterial injury. Neutropenic mice exhibited larger neointima sizes with reduced endothelial coverage. By use of intravital microscopy it was shown that neutrophils rapidly adhere following wire injury and locally deposit cathelicidins. These rapidly activate endothelial early outgrowth cells (EOCs, also known as endothelial progenitor cells) via ligation of formyl peptide receptor 2 (fpr2) as indicated by intracellular Ca2+ mobilization and adhesion. In line, mice deficient in cathelicidin show reduced EOC adhesion, re-endothelialization following wire injury and increased neointima areas. We then translated these findings into an animal model using a biofunctionalized, miniaturized Nitinol stent coated with cathelicidin and found that neutrophil-instructing stent reduced in-stent stenosis, providing a novel concept that cathelicidin may promote vascular healing after interventional therapy.
We conclude that neutrophil-borne cathelicidin effectively promotes re-endothelialization and thereby limits neointima formation after stent implantation. These findings warrant investigation of the applicability of this strategy in large animal models and its translation into clinical trials.