Abstract-CGS 26303 is a vasopeptidase inhibitor that simultaneously inhibits endothelin-converting enzyme (ECE) and neutral endopeptidase (NEP). We compared the effects of chronic treatment with CGS 26303 to the selective inhibition of angiotensin-converting enzyme (ACE) and NEP during the transition from left ventricular hypertrophy (LVH) to congestive heart failure (CHF) in hypertensive rats. LV geometry and function were assessed in Dahl salt-sensitive rats placed on a high-salt diet from age 6 weeks (hypertensive rats) and in control rats fed a low-salt diet. The hypertensive rats were randomized into groups that received no treatment or were treated with an ACE inhibitor (temocapril), an ECE/NEP inhibitor (CGS 26303), or a NEP inhibitor (CGS 24592) from the LVH stage (11 weeks) to the CHF stage (17 weeks). All treatments decreased the systolic blood pressure equally and significantly improved LV fractional shortening. Both temocapril and CGS 26303 ameliorated LV perivascular fibrosis, reduced mRNA levels of types I and III collagen, and decreased the heart weight/body weight ratio. CHF rats had increased plasma ET-1 levels compared with control rats. Only CGS 26303 reduced ET-1 to normal levels. ET-1 levels were found to correlate with heart/body weight, right ventricle/body weight and perivascular fibrosis ratios. During the transition to CHF, CGS 26303 produces effects that are comparable to temocapril and superior to CGS 24592. The beneficial effects of CGS 26303 are likely caused in part by the greater reduction of plasma ET-1. Dual ECE/NEP inhibitor may provide a new strategy for the treatment of human heart failure.

Endothelin-1 (ET-1) is generated from big ET-1 by endothelin converting enzyme-1 (ECE-1). This process is inhibited by phosphoramidon through binding to the catalytic domain of ECE-1. There are four isoforms of human ECE-1 (ECE-1a, ECE-1b, ECE-1c and ECE-1d) which possess a conserved catalytic domain. Interestingly, a recent study has shown that in ECE-1b-transfected CHO cells phosphoramidon increases the expression and activity of ECE-1b. It is not known, however, whether phosphoramidon has similar effects on the expression of other ECE-1 isoforms. To address this point, we have established recombinant CHO cell lines that permanently express either human ECE-1a, ECE-1b or ECE-1c. Incubation of CHO/ECE-1a, -1b, and -1c with phosphoramidon (100 microM) for 16 hours markedly elevated the intracellular expression of ECE-1a and ECE-1b, but not ECE-1c protein, as indicated by Western blotting and immunocytochemistry. These increases appear to be due to inhibition of intracellular degradation of the protein because metabolic labeling followed by immunoprecipitation showed ECE-1a and ECE-1b proteins had prolonged half-lives in the phosphoramidon-treated cells. This is further supported by the finding that ECE-1 mRNA levels were unchanged following phosphoramidon treatment. Taken together, our results demonstrate that phosphoramidon differentially affects the expression of three human ECE-1 isoforms.