Circulating N-terminal fragments of A- and B-type natriuretic peptides: molecular heterogeneity, measurement and clinical application

Abstract

Natriuretic peptides have emerged as important candidates for the development of diagnostic tools in cardiovascular disease. Their increased concentrations have been found to be useful for ruling out disease of cardiac origin, as prognostic indicators, and in the follow-up of patients with heart failure. In order for natriuretic peptides to be efficient biomarkers, analytical problems in assay specificity and calibration need to be resolved. The aim of the present study was to elucidate circulating molecular components of N-terminal fragments of A- and B-type natriuretic peptides (NT-proANP and NT-proBNP) in human blood, and to develop reliable and novel assays for their measurement with clinical application.

Reliable immunoassays for NT-proANP and NT-proBNP were set up based on recombinant calibrators and antisera against different epitopes. A novel immunoassay for detecting the activation of A- and/or B-type natriuretic peptide systems, referred to as NT-proXNP, was also developed. The chromatographic results of human plasma and serum samples indicated that NT-proANP and especially NT-proBNP are heterogeneous in human circulation. They are truncated at both termini, causing a serious risk of preanalytical errors. Further studies with recombinant peptides confirmed that the central parts of NT-proANP and NT-proBNP are stable in plasma and serum even at harsh storage conditions. Thus the most reliable assays are directed at the central portions of the molecule only.

All developed assays were applicable to clinical samples of cardiac patients. NT-proXNP showed a diagnostic efficiency equal to or slightly better compared to individual NT-proANP and NT-proBNP assays. Furthermore, the prognostic value of NT-proANP and NT-proBNP was investigated in a population-based sample of men. Both peptides were strong predictors of mortality and its co-morbidities, adding to the prognostic value of conventional risk factors.