Brain Natriuretic Peptide

Overview

Brain natriuretic peptide (BNP) is a 32-amino-acid cardiac natriuretic peptide originally isolated from porcine brain in 1988 by Sudoh and colleagues. Despite its name, BNP is primarily synthesized in ventricular cardiomyocytes and released in response to myocardial wall stress. The human BNP sequence consists of a 17-residue disulfide-bonded ring (Ser-Leu-Arg-Arg-Ser-Ser-Cys-Phe-Gly-Gly-Arg-Met-Asp-Arg-Ile-Gly-Ser) followed by a 15-amino-acid C-terminal tail.

Biosynthesis and Secretion

BNP is synthesized as a 108-amino-acid preproBNP that is cleaved during secretion to produce a 76-amino-acid proBNP fragment (NT-proBNP) and the mature 32-amino-acid BNP. This cleavage occurs via furin-like prohormone convertases within the secretory pathway. The molar ratio of BNP to NT-proBNP in circulation is approximately 1:1, though BNP has a shorter half-life (20 minutes) compared to NT-proBNP (120 minutes) due to receptor-mediated clearance.

Receptor Signaling

BNP binds preferentially to natriuretic peptide receptor-A (NPR-A), a transmembrane guanylyl cyclase receptor. NPR-A activation generates cyclic guanosine monophosphate (cGMP), which mediates vasodilation, natriuresis, and inhibition of cardiac fibroblast proliferation. BNP exhibits approximately 10-fold selectivity for NPR-A over NPR-B (the CNP receptor) and does not bind NPR-C (the clearance receptor).

Physiological Functions

BNP produces dose-dependent natriuresis and diuresis by inhibiting sodium reabsorption in the collecting duct. It relaxes vascular smooth muscle through both endothelium-dependent and -independent pathways. BNP antagonizes the renin-angiotensin-aldosterone system by suppressing renin secretion and aldosterone synthesis. Additionally, it exerts direct antifibrotic and antihypertrophic effects on the myocardium.

Clinical Utility as Biomarker

Plasma BNP and NT-proBNP levels correlate directly with ventricular filling pressures and are gold-standard biomarkers for heart failure diagnosis and prognosis. A BNP cutoff of 100 pg/mL and NT-proBNP cutoff of 300 pg/mL have high negative predictive value for excluding acute heart failure. Serial measurements guide therapeutic optimization and predict outcomes.

Therapeutic Applications

Recombinant BNP (nesiritide) is approved for acute decompensated heart failure. Novel approaches including neprilysin inhibitors (sacubitril) that prevent BNP degradation have transformed heart failure pharmacotherapy when combined with angiotensin receptor blockers.

References

1. Sudoh, T., et al. (1988). BNP: identification in the brain of a novel natriuretic peptide. Nature, 332(6159), 78-81.
2. Hall, C. (2004). NT-proBNP: the rationale for use in heart failure. Journal of Cardiovascular Pharmacology, 44(Suppl 1), S27-S33.
3. McMurray, J.J., et al. (2014). ESC guidelines for the diagnosis and treatment of heart failure. European Heart Journal, 35(34), 2333-2387.