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.
OBJECTIVE
Endothelin-1 (ET-1) has been implicated in a variety of vascular pathologic conditions, although there is considerable controversy as to whether 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 endothelin-converting enzyme (ECE) could, therefore, offer an alternative therapeutic strategy in the prevention of vein graft intimal hyperplasia.


METHODS
Human saphenous vein (3 equal segments from 10 patients) were maintained in organ culture for 14 days with either 50 micromol/L CGS 26303 (a dual ECE/neutral endopeptidase [NEP] inhibitor), 50 micromol/L CGS 24592 (a selective NEP inhibitor), or vehicle (control). They were then processed for immunostaining 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 significant augmentation in the NEP-inhibited segments, consistent with an inhibition 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-inhibited veins, although ET-1 staining was also present. ET-1 expression was intense 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, mature ET-1 was still detectable in these segments.


CONCLUSIONS
There is a requirement for potent and selective inhibitors of ECE to evaluate fully the potential therapeutic benefits of blocking ET-1 biosynthesis. The use of dual inhibitors complicates the interpretation of results, because the observed response is likely to be a combination of both ECE and NEP inhibition.
Porter
K E
KE
Department of Surgery, Robert Kilpatrick Clinical Sciences Building, Leicester University, Leicester Royal Infirmary, United Kingdom.
Dickinson
T
T
London
N J
NJ
D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors*; D000072396:Endothelin-Converting Enzymes; D006801:Humans; D008666:Metalloendopeptidases; D015260:Neprilysin / Q000037:antagonists & inhibitors*; D009924:Organ Culture Techniques; D012501:Saphenous Vein / Q000254:growth & development*; D017539:Tunica Intima / Q000254:growth & development*
D016282:Aspartic Acid Endopeptidases; D008666:Metalloendopeptidases; D015260:Neprilysin; D000072396:Endothelin-Converting Enzymes