Detection of Endogenous B-Type Natriuretic Peptide at Very Low Concentrations in Patients with Heart Failure

Background— The myocardium secretes B-type natriuretic peptide (BNP) in response to stimuli associated with heart failure (HF). However, high immunoreactive-BNP levels in patients with HF are associated with a paradoxical lack of natriuretic response. We hypothesized that commercially available assays for immunoreactive BNP do not reflect the bioactivity of the natriuretic peptide system, because they measure both unprocessed inactive pro-BNP and mature BNP 1-32. We describe an assay for the detection of bioactive BNP 1-32 and confirm very low concentrations in plasma from HF patients. Methods and Results— We developed a quantitative mass spectrometry immunoassay to capture endogenous BNP peptides using high affinity antibodies. Bound BNP and its truncated fragments were detected by matrix assisted laser desorption ionization–time of flight mass spectrometry based on their predicted masses. Mass spectrometry immunoassay revealed rapid in vitro degradation of BNP 1-32 in plasma, which requires plasma colle...