ANP-28 (Atrial Natriuretic Peptide): cardiac hormone research overview

ANP-28 (atrial natriuretic peptide-28, also called ANF or atriopeptin) is a 28-amino acid cardiac hormone secreted primarily by atrial cardiomyocytes in response to atrial wall stretch caused by increased blood volume and pressure. First described by Adolfo de Bold and colleagues in 1981, ANP-28's discovery fundamentally revised the understanding of the heart — establishing it as an endocrine organ capable of directly regulating blood pressure and fluid homeostasis in addition to its mechanical pumping function. ANP-28 is the founding member of the natriuretic peptide family and the endogenous peptide whose recombinant form constitutes carperitide, approved in Japan for acute decompensated heart failure since 1995.

What is ANP-28?

ANP-28 is a 28-amino acid cyclic peptide (MW approximately 3,080 Da) encoded by the NPPA gene on chromosome 1p36.2, in close proximity to the NPPB gene encoding BNP. Like BNP-32, ANP-28 contains a 17-amino acid ring structure formed by an intramolecular disulfide bond between two cysteine residues (Cys-7 and Cys-23 in the 28-residue numbering). The peptide is synthesized as a 151-amino acid prepropeptide, processed to a 126-amino acid prohormone (proANP) stored in atrial granules, and cleaved to the mature 28-amino acid ANP-28 plus the N-terminal 98-amino acid fragment (NT-proANP) upon secretion. Corin is the primary prohormone convertase responsible for ANP processing in the heart.

The landmark discovery of ANP-28 came from Adolfo de Bold and colleagues at Queen's University, Ontario. Their 1981 paper in Life Sciences demonstrated that intravenous injection of crude atrial extracts in rats produced a rapid, potent natriuretic and diuretic response, showing for the first time that the heart secretes a blood pressure-regulating hormone. De Bold's work overturned the prevailing model of the heart as a purely mechanical organ and launched the natriuretic peptide field. The active peptide was subsequently isolated and sequenced, with human ANP-28 identified and the proANP storage mechanism characterized through the mid-1980s.

ANP-28 is predominantly produced in atrial cardiomyocytes, where proANP is stored in large dense-core secretory granules and rapidly released upon atrial wall distension. Ventricular ANP production is low under normal conditions but upregulated in heart failure. Unlike BNP-32, whose expression is more strongly upregulated by ventricular stress, ANP-28 has a more acute secretion profile tied to moment-to-moment atrial filling pressure. Both peptides are components of the endogenous counter-regulatory system opposing volume overload and RAAS activation.

Mechanism of action

ANP-28 signals primarily through natriuretic peptide receptor type A (NPR-A / guanylyl cyclase A), the same receptor as BNP-32. NPR-A binding increases intracellular cyclic GMP (cGMP), activating protein kinase G (PKG) in target tissues. The downstream consequences are: vascular smooth muscle relaxation and vasodilation (reducing both preload and afterload); natriuresis and diuresis through direct renal tubular effects — including inhibition of sodium reabsorption in the inner medullary collecting duct and increased GFR; suppression of renin secretion from juxtaglomerular cells; inhibition of aldosterone secretion from the adrenal glomerulosa; and inhibition of vasopressin (ADH) release from the posterior pituitary.

ANP-28 also acts on NPR-C (clearance receptor / natriuretic peptide receptor-3), which mediates its removal from the circulation through receptor-mediated endocytosis and intracellular degradation. Neutral endopeptidase (neprilysin, encoded by MME) further degrades circulating ANP-28. The development of neprilysin inhibitors (sacubitril, co-formulated with valsartan as sacubitril-valsartan / Entresto) is based in part on the rationale of preserving endogenous ANP and BNP signaling by blocking their enzymatic degradation — illustrating ANP-28's continued clinical relevance to heart failure pharmacology even when the peptide itself is not administered directly.

Beyond cardiovascular effects, ANP-28 has anti-proliferative and anti-fibrotic effects on cardiac fibroblasts (opposing TGF-β-mediated collagen deposition), suppresses endothelin-1 production, and has been shown in preclinical models to modulate immune cell activity and reduce inflammatory cytokine production. These pleiotropic effects have generated interest beyond the acute HF context.

What the research shows

ANP-28 has an extensive clinical literature as a cardiac biomarker, though NT-proBNP and BNP-32 have largely supplanted ANP and NT-proANP in most clinical algorithms due to superior analytical characteristics and larger validating studies. A comprehensive 2015 PMC review (PMC4496260, Atrial Natriuretic Peptide in Cardiovascular Biology and Disease) details ANP's physiology and biomarker roles across cardiovascular conditions. Mid-regional proANP (MR-proANP), a more stable fragment of proANP, has been validated as a sensitive heart failure biomarker in large studies including the BACH trial, which found MR-proANP non-inferior to BNP for diagnosing acute heart failure in dyspneic patients.

Carperitide (recombinant human ANP-28, α-hANP, trade name Hanp) is approved in Japan for the treatment of acute decompensated heart failure and has been used clinically there since 1995. Carperitide is administered by continuous intravenous infusion due to its short plasma half-life. Japanese clinical experience with carperitide has been documented in observational and prospective studies, including the JCARE-CARD registry, though large randomized controlled trials comparing carperitide to other acute HF therapies have been limited. Carperitide's clinical use is essentially restricted to Japan; it has not received regulatory approval in the United States, European Union, or Australia.

The rationale for sacubitril-valsartan (LCZ696/Entresto) — which inhibits neprilysin to preserve endogenous ANP/BNP while blocking the RAAS with valsartan — is directly grounded in ANP-28/BNP-32 biology. The PARADIGM-HF trial (McMurray et al., NEJM 2014) demonstrated that sacubitril-valsartan reduced cardiovascular death and HF hospitalization versus enalapril in HFrEF, representing a therapeutic application of natriuretic peptide pathway biology. ANP-28 genetic variants (NPPA gene polymorphisms) have also been associated with atrial fibrillation risk and hypertension susceptibility in GWAS studies.

ANP-28 versus carperitide: an important distinction

Carperitide (α-hANP, Daiichi Sankyo, Japan) is recombinant human ANP-28 — the identical 28-amino acid peptide sequence to endogenous human ANP-28, produced by recombinant DNA technology. The distinction is one of source, formulation, and regulatory status: endogenous ANP-28 is the naturally secreted atrial hormone; carperitide is the pharmaceutical-grade recombinant form approved for intravenous use in Japan. Carperitide has not been approved by the FDA, EMA, or TGA. Research-grade synthetic ANP-28 is available from peptide suppliers for laboratory use. As with BNP-32/nesiritide, researchers should specify whether their reference is to endogenous ANP-28 (biomarker context), carperitide (pharmacologic context, Japan-approved), or research-grade peptide (experimental context).

Pharmacokinetics

ANP-28 has a plasma half-life of less than 5 minutes in humans — among the shortest of any known peptide hormones — due to rapid clearance via NPR-C receptor-mediated endocytosis and neprilysin proteolysis. This extremely short half-life necessitates continuous intravenous infusion when carperitide is used pharmacologically; bolus dosing would produce only a transient effect. Fasting plasma ANP-28 concentrations in healthy adults range from approximately 5–25 pmol/L (roughly 15–77 pg/mL), rising substantially with exercise, atrial distension, and heart failure. NT-proANP and MR-proANP have longer half-lives and are used as biomarker surrogates in clinical practice.

Physiologic levels and pharmacologic dose data

Not medical advice. These are ranges reported in research literature, not personalized recommendations. Consult your physician.

Endogenous ANP-28: normal plasma concentrations in healthy adults are approximately 5–25 pmol/L (15–77 pg/mL) at rest; exercise and atrial distension produce rapid increases. Heart failure patients may have concentrations 5–10 times above normal. These are physiologic values, not administered doses. For pharmacologic context (carperitide): the approved Japanese prescribing information specifies intravenous infusion at 0.025–0.2 mcg/kg/min, typically initiated at 0.025–0.05 mcg/kg/min and titrated. Carperitide is administered only by intravenous infusion under physician supervision in a hospital setting due to the risk of hypotension.

Research-grade ANP-28 peptide has no approved human therapeutic dosing outside Japan's carperitide program. In vitro studies and preclinical research use ANP-28 at concentrations matching physiologic (picomolar) and pharmacologic (nanomolar) receptor occupancy. Any exogenous administration outside the carperitide drug program would be investigational.

Storage and handling

Research-grade ANP-28 peptide is supplied lyophilized and should be stored at −20 °C or below, protected from moisture and light. The intramolecular disulfide bond forming the 17-residue ring structure is essential for biological activity; reducing agents (DTT, beta-mercaptoethanol) and oxidizing conditions should be avoided. Reconstitution in physiologic saline or PBS at neutral pH is recommended. Solutions should be aliquoted to minimize freeze-thaw cycling and stored at −80 °C for long-term stability. ANP-28 is highly susceptible to neprilysin; protease inhibitors should be considered in assay contexts requiring prolonged peptide stability.

What ANP-28 is NOT

ANP-28 is not carperitide, though carperitide IS recombinant ANP-28 — the distinction is regulatory status (pharmaceutical versus endogenous/research compound). ANP-28 is not BNP-32: BNP (B-type natriuretic peptide) is a related 32-amino acid peptide encoded by a different gene (NPPB vs NPPA), secreted predominantly from the ventricles rather than the atria, regulated differently (primarily by ventricular wall stress rather than atrial stretch), and measured separately in clinical biomarker assays. Both signal through NPR-A but are distinct hormones. ANP-28 is not NT-proANP or MR-proANP, which are N-terminal fragments of the prohormone used as biomarker surrogates due to their greater stability in plasma. ANP-28 is not sacubitril-valsartan (Entresto); sacubitril-valsartan works by blocking neprilysin (thus preserving endogenous ANP/BNP) and blocking AT1 receptors — it is a pharmacologic strategy targeting the ANP/BNP pathway, not the peptide itself.

References

Primary sources include: de Bold et al.'s original 1981 Life Sciences paper demonstrating the natriuretic hormone activity of atrial extracts; the 2015 PMC review on ANP in cardiovascular biology (PMC4496260); the PMC review of natriuretic peptide structures, receptors, and therapeutic applications (PMC4855512); StatPearls on atrial natriuretic peptide (NCBI Bookshelf NBK562257); and relevant literature on carperitide clinical use in Japan. The PARADIGM-HF trial (McMurray et al., NEJM 2014) documents the clinical translation of ANP/BNP pathway biology into the sacubitril-valsartan therapeutic.