Special Japanese-Western Consensus Meeting on Biomarkers Executive Summary

On November 21, 2009, biomarker leaders from Europe and America met with leading biomarker and cardiac leaders of Japan to discuss and come to consensus on state-of-the-art natriuretic peptide research. Natriuretic peptides, brain natriuretic peptide (BNP) and N-terminal probrain natriuretic peptide (NT-proBNP), have revolutionized the way we look at patients presenting with dyspnea. While not considered stand-alone tests, natriuretic peptide (NP) testing clearly adds value to the workup and follow-up of patients. In order to use NP levels correctly, physicians need to be aware of the molecular biology of the peptides, appropriate cutoffs in various conditions, and important caveats for using natriuretic peptide levels. These were all discussed at the meeting. Additionally, natriuretic peptide testing as portrayed in guidelines from the participating countries were compared and contrasted. When describing BNP values in Japan and in the United States in parallel, each BNP value was calculated by using the correlation data of Fischer et al. (Int Heart J 2011; 52: 253-265) State-of-the-art BNP research: Brain natriuretic peptide (BNP) first isolated from the porcine brain is a cardiac hormone secreted mainly from the ventricle of the heart. Human BNP consists of 32 amino acids, and its molecular size differs from those of other species. The primary structure of BNP also shows marked species difference as shown in Figure 1, indicating that the specificity of the antibody used for the assay system should be carefully considered. Metabolic clearance of natriuretic peptide family, atrial natriuretic peptide (ANP), BNP and C-type natriuretic peptide (CNP) comprises two systems, neutral endopeptidase-mediated degradation and clearance receptor-mediated internalization. The rank order in affinity for human clearance receptor is ANP > CNP > BNP, indicating that the half life of BNP in the bloodstream is longer than those of ANP and CNP. In striking contrast with molecular forms of ANP in plasma and the heart, the molecular forms of BNP consist of proBNP and BNP in humans as well as in rats. Table I shows a comparison of BNP and ANP in various aspects. Although a recent paper reported that BNP does not circulate in patients with heart failure, which indicates proBNP functions as a circulating form of BNP-like immunoreactivity in human plasma, this misleading result can be explained by the very poor recovery of BNP-32 extraction and peptidase digestion of BNP-32. The posttranslational processing of proBNP is more advanced in the central nervous system. The modification by O-glycosylation of the N-terminal part of proBNP, which interferes with the processing of proBNP, makes precise analysis of molecular forms of circulating BNP-like and N-terminal proBNP-like immunoreactivities very difficult for clinical biomarkers. Since the functional molecule of BNP is BNP32, and BNP-32 is not modified by O-glycosylation and other modifications, BNP-32 should be measured as a biomarker for heart failure (HF), like insulin for diabetes mellitus as shown in Table II. Complex BNP species in human plasma: BNP is a clinically useful diagnostic marker for pathophysiological conditions of heart disease, including HF, ventricular remodeling, and pulmonary hypertension. BNP-32 (active form), proBNP (proBNP[1-108], weakly active form), and NT-proBNP (proBNP[1-76], inactive form) circulate in the plasma of healthy subjects in contrast with atrial natriuretic peptide (ANP) (Figure 2). Although plasma levels of these BNP species increase in HF patients, recent studies have revealed that the plasma proBNP level shows a higher elevation than that of BNP-32. In the plasma of HF patients, furthermore, proBNP is O-glycosylated in the NT-proBNP region, and O-glycosylated (Glyco-) proBNP with weak activity circulates along with Glyco-NTproBNP and other known BNP species (Figures 2 and 3). Commercially available BNP assay kits, such as from Shionogi and Abbott, utilize antibodies directed against a ring or a Cterminal portion of BNP-32, which cross-react with proBNP to comparable or lesser extents. Glyco-NT-proBNP is less reactive in NT-proBNP assay kits, such as from Roche, and is underestimated as indicated by recovery of its immunoreactiv-