Vascular neutral endopeptidase inhibition improves endothelial function and reduces intimal hyperplasia

Neutral endopeptidase (NEP, EC 3.4.24.11) metabolises endogenous vasoactive peptides that may protect against atherogenesis. Since NEP is found in the adventitia of arteries, we investigated the anti-atherogenic effects of chronic adventitial NEP inhibition. Intimal hyperplasia of rabbit carotid arteries was induced by placement of soft, non-occlusive, peri-arterial silastic collars. NEP localisation was studied with autoradiography 7 and 14 days after collar placement. Vascular NEP was inhibited in vivo by local superfusion of one collared carotid artery with Candoxatrilat (50 pmol/h), for 7 days (n = 7). The contralateral collar was filled with saline vehicle. After 7 days, ring segments of collared and normal (proximal to the collar) arteries were obtained and in vitro functional measurements, immunohistochemical determination of the pro-atherogenic factor plasminogen activator inhibitor-1 (PAI-1), localization of macrophages and morphometric analyses were carried out. Vascular NEP radiolabelled substrate binding, mainly in the media, was increased by approximately 50% after 7 days (n = 5; p < 0.05) and by approximately 300% after 14 days of collar placement (n = 5; p < 0.05). Compared with normal artery segments from the same animal, vehicle-filled collared sections displayed significantly impaired vasorelaxation to acetylcholine (endothelium-independent vasodilatation was preserved), increased PAI-1 immunostaining, macrophage accumulation and intimal thickening. In Candoxatrilat-treated collared arteries, vasorelaxation to acetylcholine was improved, along with reductions in PAI-1 levels, macrophage numbers and intimal area (all p < 0.05). Enhancing the activity of local, endogenous peptides by adventitial inhibition of vascular NEP may protect against early atherogenesis. This is of particular relevance to using adventitial therapies to prevent intimal hyperplasia leading to restenosis.