Vascular endothelin converting enzyme-1 expression and activity is upregulated in clinical diabetes

Circulating and vascular endothelin-1 (ET-1) levels are elevated in diabetes, but the molecular components of the enzymatic activation of ET-1 in the vasculature remains unknown. Furthermore, the distribution of ET receptors favors a contractile phenotype in African Americans with diabetes. Whether there is any difference in local ET-1 activation in this population is unknown. This study examined the expression and activity of ET converting enzyme-1 subisoforms (ECE-1) in the internal mammary artery specimens obtained from patients undergoing coronary artery bypass grafting. The study groups included African-American (AA) and Caucasian (CA), nondiabetic (ND) and diabetic (D) patients: AAND N=10, CAND N=9, AAD N=9, and CAD N=11. The expression of ECE-1a, ECE-1b and ECE-1c subisoforms was studied by RT-PCR. ECE-1a was upregulated 2- and 4-fold in the CAD and AAD groups, respectively (P<.05). In African-American patient groups, ECE-1 activity (fmol/mg protein.h) was augmented from 2,804 ± 185 in nondiabetic tissue samples to 6,857 ± 393 in the diabetic tissue (P<.05). There was a similar increase in the CAD group, which did not significantly differ from AA diabetics. ECE-1 inhibitors, phosphoramidon and FR-901533, inhibited vascular ECE-1 activity by more than 80%. While neutral endopeptidase (NEP) and matrix metalloproteinase-2 (MMP-2) are able to process big ET-1, inhibitors of NEP (thiorphan) and MMP (batimistat) did not affect ECE-1 activity. In conclusion, the enzymatic pathway essential for generating vascular ET-1 is activated in the vasculature of both AA and CA diabetic patients and this activation is highly specific for ECE-1.