Plasma Neprilysin in Heart Failure: Response Dynamics and Clinical Associations Are Immunoassay Dependent

Discordance among published findings on the plasma concentrations, response dynamics, and clinical associations of plasma neprilysin (NEP) in health and heart failure (HF) require clarification.

Using a newly developed glycosylation-sensitive monoclonal antibody sandwich ELISA (NEPCVRI), plasma NEP was measured in 99 non-HF controls, 95 HF patients with preserved ejection fraction, and 104 patients with reduced ejection fraction. Results were compared with those from 2 commercial polyclonal antibody-based AlphaLISA (NEPPE) and ELLA (NEPELLA) immunoassays and a fluorometric activity [NEP activity (NEPACT)] assay.

NEPCVRI did not correlate with NEPPE, NEPELLA, or NEPACT while the latter 3 assays correlated strongly and directly with each other. Compared with non-HF, NEPCVRI was significantly downregulated in HF, while NEPPE, NEPELLA, and NEPACT were significantly upregulated. Strikingly, NEPCVRI concentration was perturbed by comorbidities (hypertension, diabetes, or atrial fibrillation) and exhibited inverse relationships with clinical variables and functional biomarkers compared with those of NEPPE, NEPELLA, or NEPACT. On univariate and multivariate analyses, NEPPE, NEPELLA, and NEPACT were associated with all-cause death and the composite endpoint of HF admission and all-cause death, while NEPCVRI had no prognostic value.

Plasma NEPCVRI, NEPPE, NEPELLA, and NEPACT display altered dynamics in HF, with NEPCVRI displaying inverse trends to those exhibited by the latter 3 assays. Conflicting data in NEP research may be explained by the heterogeneity of plasma NEP and the antibodies used to detect its varied glycosylated and nonglycosylated fragments. Well-characterized and validated immunoassays are crucial for understanding changes in NEP concentrations and activity in its biological and clinical contexts.