Inhibition of neointima formation in an organ culture of human saphenous vein: A comparison of dual endothelin-converting enzyme/neutral endopeptidase and selective neutral endopeptidase inhibition

Purpose: Endothelin-1 (ET-1) has been implicated in a variety of vascular p athologic conditions, although there is considerable controversy as to whet her such effects are mediated by the ET-(A) or ET-(B) receptor. This study investigated whether inhibition of big ET-1 processing by inhibition of end othetin-converting enzyme (ECE) could, therefore, offer an alternative ther apeutic strategy in the prevention of vein graft intimal hyperplasia. Methods: Human saphenous vein (3 equal segments from 10 patients) were main tained in organ culture for 14 days with either 50 mu mol/L CGS 26303 (a du al ECE/neutral endopeptidase [NEP] inhibitor), 50 mu mol/L CGS 24592 (a sel ective NEP inhibitor), or vehicle (control). They were then processed for i mmunostaining and neointimal thickness measurements, and conditioned media was collected for enzyme-linked immunosorbent assay analysis. Results: Neointimal thickness in the ECE/NEP-inhibited veins did not differ significantly from that of control segments. However, there was a highly s ignificant augmentation in the NEP-inhibited segments, consistent with an i nhibition of ET-1 degradation (median difference, 16.8; 95% CI, -23.5, -10. 4; P = .002, Wilcoxon). ECE immunostaining was reduced in the ECE/NEP-inhib ited veins, although ET-1 staining was also present. ET-1 expression was in tense in the thickened neointimas of NEP-inhibited veins, which also showed significant ECE staining. Elevated levels of big ET-1 were measured in the ECE/NEP-inhibited veins, consistent with reduced ECE activity. However, ma ture ET-1 was still detectable in these segments. Conclusion: There is a requirement for potent and selective inhibitors of E CE to evaluate fully the potential therapeutic benefits of blocking ET-1 bi osynthesis. The use of dual inhibitors complicates the interpretation of re sults, because the observed response is likely to be a combination of both ECE and NEP inhibition.