Analysis of peptides derived from Pro Atrial Natriuretic Peptide that circulate in man and increase in heart disease

The present investigation was designed to determine the levels and circulating forms of peptides derived from Pro Atrial Natriuretic Peptide (ProANP) and to assess their usefulness as markers for severity of heart disease. A sensitive and specific "two-site" immunoradiometric assay (IRMA) for the measurement of C-terminal ProANP 99-126 (alpha ANP) and two radioimmunoassays (RIAs) for the measurement of N-terminal ProANP 31-67 and ProANP 79-98 were developed. Immunoassays were validated by measurement of circulating peptide concentrations in 15 normal volunteers and 44 patients with varying degrees of heart disease. Mean concentrations of immunoreactive (ir) alpha ANP, ProANP 79-98 and ProANP 31-67 in normal volunteers (n = 15) were 8.5 +/- 1.1, 143 +/- 16 and 587 +/- 83 pmoles/l, respectively, increasing in patients with mild heart disease (NYHA I to II; n = 22) to 17.1 +/- 2.1, 691 +/- 197 and 2160 +/- 540 pmoles/l with greatest increases being observed in patients with severe heart disease (NYHA III to IV; n = 22) of 103 +/- 23, 4550 +/- 590 and 10,600 +/- 1350 pmoles/l, respectively. RP-HPLC of pooled plasma revealed peaks corresponding to alpha ANP, beta ANP, ProANP 1-126, ProANP 1-98, ProANP 31-67 and ProANP 79-98, all apparently increased in heart disease. In conclusion, using a series of immunoassays, we observed the graded increase of alpha ANP, irProANP 31-67 and irProANP 79-98 with increasing severity of heart disease. All peptides proved useful markers, but only ProANP 79-98 levels were able to distinguish patients with mild heart disease (NYHA I) from normals. Finally, RP-HPLC analysis indicated that ProANPs 31-67 and 79-98 circulate as distinct entities, in addition to ProANP 1-98.