Background: Multiple B-type natriuretic peptide (BNP) fragments circulate in patients with heart failure (HF) but the types and relative quantities, particularly in relation to bioactive BNP 1-32, remain poorly defined. The purpose of the study was to relate clinically available BNP values with quantitative information on the concentration of pre-secretion and post-processed fragments of BNP detected by mass spectrometry.
Methods and results: Seventy Class I-IV patients were prospectively enrolled with blood drawn into tubes containing a preservative to protect against BNP degradation. Samples were analyzed by quantitative mass spectrometry (MS) immunoassay for intact BNP 1-32 and its fragments. Clinical BNP 1-2 was measured by standard clinical laboratory methods. ProBNP 1-108, corin, and clinically measured BNP levels were elevated, but MS BNP 1-32 levels were low and differed from clinical BNP (P=0.01). Intact MS BNP 1-32 correlated modestly with clinical BNP (r=0.46, P<0.001). MS BNP fragments 3-32, 4-32, and 5-32 demonstrated the best associations with clinical BNP; fragment 5-32 with a correlation coefficient of r=0.81 (P<0.001).
Conclusions: ProBNP 1-108 is measured by clinical BNP assays and contributes to the cumulative results of the BNP assay. However, the observation that clinically measured BNP correlates best with MS degradation fragments and relatively poorly with MS BNP 1-32 suggests that a significant component of circulating clinical BNP is composed of such fragments that are known to demonstrate little biological activity. There appear to be multiple pathways involved in the dysregulation of proBNP in HF, and both the processing of proBNP and the downstream degradation to BNP 1-32 appear to be critical.