Abstract 9: The Virtually Mature BNP1-32 Is a Precursor for the Biologically More Active BNP1-30

The mature B-type natriuretic peptide (BNP1-32), mainly released from ventricular myocardium, has antifibrotic effects and exerts vasorelaxant and natriuretic activity leading to a reduction of blood volume and pressure. Thus, BNP is used as a drug for the treatment of decompensated heart failure. Here we show the discovery of a new murine BNP metabolite, BNP1-30, exerting higher biological activity compared to the mature BNP1-32, in vitro and in vivo. By mass spectrometric analysis of murine lung tissues incubated with BNP1-32 and of elution fractions of BNP1-32-perfused livers, we discovered a distinct BNP1-32 cleavage product, identified as the C-terminally truncated BNP1-30. We identified endothelin-converting enzyme (ECE) as the peptidase generating BNP1-30 from BNP1-32 by the hydrolysis of the two C-terminal leucine. This new metabolite is significantly more efficient compared to BNP1-32 in stimulating the natriuretic peptide receptor (NPR) A. Interestingly it is also stimulating the C-type natriruretic peptide specific receptor NPRB. In parallel, dose-response curves in NPRA & -B co-transfected cell lines and stimulation of primary smooth muscle cells, endothelial cells and mesangial cells showed better efficacy for BNP1-30. In vivo, BNP1-30 reduced the mean arterial blood pressure of normotensive mice after acute infusion significantly more than BNP1-32. Additionally, BNP1-30 was also significantly more potent compared to the rodent derived pro-BNP cleavage product BNP1-45. Even more important, in a 3-day infusion experiment using spontaneously hypertensive rats (SHR), BNP1-30 was able to reduce systolic blood pressure by 30 mmHg and decreased cardiac BNP mRNA, a marker for cardiac failure, while BNP1-32 was without significant effect. We show for the first time the occurrence of a BNP metabolite being a more efficient antihypertensive peptide than the virtually mature BNP1-32 that has been described as ‘the’ circulating biologically active form of BNP. Our results suggest that BNP1-32 is only the precursor for the more biologically active BNP1-30 leading to a fundamental revision of the natriuretic peptide system and also opens the avenue for the identification of more effective targets in the treatment of cardiovascular diseases.