Regulation of endothelin-converting enzyme-1 (ECE-1) by the calcimimetic R-568

Although calcimimetics were developed to block parathyroid hormone synthesis, some reports suggest that they may also reduce blood pressure by unknown mechanisms. Calcimimetic-induced changes in the synthesis of endothelial vasoactive factors could be involved. Wistar rats were treated with the calcimimetic R-568, and systolic blood pressure (SBP) was registered with a tail-cuff sphygmomanometer, the content of endothelial nitric oxide synthase (eNOS) and endothelin-converting enzyme (ECE-1) in tissue was evaluated by immunohistochemistry and Western blot, circulating levels of endothelin-1 (ET-1) were measured by ELISA. R-568 reduced SBP and circulating levels of ET-1, without changes in eNOS expression. In contrast, R-568 increased the lung and vascular content of ECE-1. In order to analyze the mechanisms involved, we studied the effect of R-568 on human endothelial cells. R-568 did not modify neither eNOS protein content nor pre-pro-ET-1 mRNA expression, but increased ECE-1 protein content, and decreased ET-1 synthesis and ECE-1 activity. The inhibition of ECE-1 activity was very strong, similar to the classic ECE inhibitor phosphoramidon, the addition of exogenous zinc restored enzymatic activity. Moreover, the amount of zinc in immunoprecipitated ECE from R-568 treated cells was 3-fold less than in control cells. In conclusion, R-568 inhibits ECE by expelling zinc from the enzyme, with the subsequent decrease in enzymatic activity and reducing circulating levels of ET-1, which may be responsible for the lower SBP observed in R-568-treated rats. This descent would be partially compensated by the increased synthesis of the ECE-1 itself, and by other homeostatic mechanisms that regulate SBP.

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