Atrial natriuretic peptide

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File:ANP Granules in a Mouse Model.png
Electron micrograph of ventricular (left) and atrial myocyte (right) showing location of ANP storage granules in a mouse model. Captured by Dr. Stephen C. Pang from Queen's University.

Atrial natriuretic peptide (ANP) or atrial natriuretic factor (ANF) is a natriuretic peptide hormone secreted from the cardiac atria.[1] Natriuretic peptides (ANP, BNP, and CNP) are a family of hormone/paracrine factors that are structurally related.[2] The main function of ANP is causing a reduction in expanded extracellular fluid (ECF) volume by increasing renal sodium excretion. ANP is synthesized, and secreted by cardiac muscle cells in the walls of the atria in the heart. These cells contain volume receptors which respond to increased stretching of the atrial wall due to increased atrial blood volume.

Reduction of blood volume by ANP can result in secondary effects such as reduction of extracellular fluid (ECF) volume (edema), improved cardiac ejection fraction with resultant improved organ perfusion, decreased blood pressure, and increased serum potassium. These effects may be blunted or negated by various counter-regulatory mechanisms operating concurrently on each of these secondary effects.

Brain natriuretic peptide (BNP) – a misnomer; it is secreted by cardiac muscle cells in the heart ventricles – is similar to ANP in its effect. It acts via the same receptors as ANP does, but with 10-fold lower affinity than ANP. The biological half-life of BNP, however, is twice as long as that of ANP, and that of NT-proBNP is even longer, making these peptides better choices than ANP for diagnostic blood testing.

Discovery

The discovery of ANP was reported in 1981, when rat atrial extracts were found to contain a substance that increased salt and urine output in the kidney.[3] Later, the substance was purified from heart tissue by several groups and named atrial natriuretic factor (ANF) or ANP.[4]

Structure

ANP is a 28-amino acid peptide with a 17-amino acid ring in the middle of the molecule. The ring is formed by a disulfide bond between two cysteine residues at positions 7 and 23. ANP is closely related to BNP (brain natriuretic peptide) and CNP (C-type natriuretic peptide), which all share a similar amino acid ring structure. ANP is one of a family of nine structurally similar natriuretic hormones: seven are atrial in origin.[5]

Production

ANP is synthesized as an inactive preprohormone, encoded by the human NPPA gene located on the short arm of chromosome 1.[2] The NPPA gene is expressed primarily in atrial myocytes and consists of two introns and three exons, with translation of this gene yielding a high molecular mass 151 amino acid polypeptide known as preproANP.[6] The preprohormone is activated via post-translational modification that involves cleavage of the 25 amino acid signal sequence to produce proANP, a 126 amino acid peptide that is the major form of ANP stored in intracellular granules of the atria.[6] Following stimulation of atrial cells, proANP is released and rapidly converted to the 28-amino-acid C-terminal mature ANP on the cell surface by the cardiac transmembrane serine protease corin.[7][8]

ANP is secreted in response to:

Receptors

Three types of atrial natriuretic peptide receptors have been identified on which natriuretic peptides act. They are all cell surface receptors and designated:

  • guanylyl cyclase-A (GC-A) also known as natriuretic peptide receptor-A (NPRA/ANPA) or NPR1
  • guanylyl cyclase-B (GC-B) also known as natriuretic peptide receptor-B (NPRB/ANPB) or NPR2
  • natriuretic peptide clearance receptor (NPRC/ANPC) or NPR3

NPR-A and NPR-B have a single membrane-spanning segment with an extracellular domain that binds the ligand.[citation needed] The intracellular domain maintains two consensus catalytic domains for guanylyl cyclase activity. Binding of a natriuretic peptide induces a conformational change in the receptor that causes receptor dimerization and activation.[citation needed]

The binding of ANP to its receptor causes the conversion of GTP to cGMP and raises intracellular cGMP. As a consequence, cGMP activates a cGMP-dependent kinase (PKG or cGK) that phosphorylates proteins at specific serine and threonine residues. In the medullary collecting duct, the cGMP generated in response to ANP may act not only through PKG but also via direct modulation of ion channels.[10]

NPR-C functions mainly as a clearance receptor by binding and sequestering ANP from the circulation. All natriuretic peptides are bound by the NPR-C.[citation needed]

Physiological effects

Maintenance of the ECF volume (space), and its subcompartment the vascular space, is crucial for survival.[citation needed] These compartments are maintained within a narrow range, despite wide variations in dietary sodium intake. There are three volume regulating systems: two salt saving systems, the renin angiotensin aldosterone system (RAAS) and the renal sympathetic system (RSS); and the salt excreting natriuretic peptide (NP) hormone system. When the vascular space contracts, the RAAS and RSS are "turned on" ; when the atria expand, NP's are "turned on". Each system also suppresses its counteracting system(s). NP's are made in cardiac, intestinal, renal, and adrenal tissue: ANP in one of a family of cardiac NP's: others at BNP, CNP, and DNP.[5]

ANP binds to a specific set of receptors – ANP receptors. Receptor-agonist binding causes the increase in renal sodium excretion, which results in a decreased ECF and blood volume. Secondary effects may be an improvement in cardiac ejection fraction and reduction of systemic blood pressure.[citation needed]

Renal

ANP acts on the kidney to increase sodium and water excretion (natriuresis) in the following ways:[11][12]

  • ANP increases glomerular filtration rate and glomerular permeability.[13]  ANP directly dilates the afferent arteriole and counteracts the norepinephrine induced vasoconstriction of the afferent arteriole.[14]  Some studies suggest that ANP also constricts the efferent arteriole, but this is not a unanimous finding.[14]  ANP inhibits the effect of Angiotensin II on the mesangial cells, thereby relaxing them.[14]  ANP increases the radius and number of glomerular pores, thereby increasing glomerular permeability and resulting in greater filter load of sodium and water.[13]
  • Increases blood flow through the vasa recta, which will wash the solutes (sodium chloride (NaCl), and urea) out of the medullary interstitium. The lower osmolarity of the medullary interstitium leads to less reabsorption of tubular fluid and increased excretion.{{
  • Decreases sodium reabsorption in the distal convoluted tubule (interaction with NCC) and cortical collecting duct of the nephron via guanosine 3',5'-cyclic monophosphate(cGMP) dependent phosphorylation of ENaC. The medullary collecting duct is the main site of ANP regulation of sodium excretion.[13] ANP effects sodium channels at both the apical and basolateral sides.[13]  ANP inhibits ENaCon the apical side and the Sodium Potassium ATPase pump on the basolateral side in a cGMP PKG dependent manner resulting in less sodium re-absorption and more sodium excretion.[14]
  • It inhibits renin secretion, thereby inhibiting the production of angiotensin and aldosterone.
  • It inhibits the renal sympathetic nervous system. ANP has the opposite effect of aldosterone on the kidney: aldosterone increases renal sodium retention and ANP increases renal sodium loss.

Its natriuretic effect is affected by dopamine and dopamine receptor D1 activity in vivo [15]

Adrenal

Vascular

Relaxes vascular smooth muscle in arterioles and venules by:

  • Membrane Receptor-mediated elevation of vascular smooth muscle cGMP
  • Inhibition of the effects of catecholamines

Promotes uterine spiral artery remodeling, which is important for preventing pregnancy-induced hypertension.[16]

Cardiac

  • ANP inhibits cardiac hypertrophy in heart failure as well as fibrosis.[17] Fibrosis is inhibited by preventing fibroblasts from entering heart tissue and replicating, as well as decreasing inflammation.[17] ANP prevents hypertrophy by inhibiting calcium influx that is caused by norepinephrine.[17]
  • Re-expression of NPRA rescues the phenotype.[citation needed]

Adipose tissue

  • Increases the release of free fatty acids from adipose tissue. Plasma concentrations of glycerol and nonesterified fatty acids are increased by i.v. infusion of ANP in humans.
  • Activates adipocyte plasma membrane type A guanylyl cyclase receptors NPR-A
  • Increases intracellular cGMP levels that induce the phosphorylation of a hormone-sensitive lipase and perilipin A via the activation of a cGMP-dependent protein kinase-I (cGK-I)
  • Does not modulate cAMP production or PKA activity.

Immune System

ANP is produced locally by several immune cells. ANP is shown to regulate several functions of innate and adaptive immune system as well as shown to have cytoprotective effects.[18]

  • ANP modulates innate immunity by raising defence against extracellular microbes and inhibiting the release of pro-inflammatory markers and expression of adhesion molecules.[18]
  • There is evidence of cytoprotective effects of ANP in myocardial, vascular smooth, endothelial, hepatocytes and tumour cells.[18]

Degradation

Modulation of the effects of ANP is achieved through gradual degradation of the peptide by the enzyme neutral endopeptidase (NEP). Recently, NEP inhibitors have been developed, such as Sacubitril and Sacubitril/valsartan. They may be clinically useful in treating patients in heart failure with reduced ejection fraction .

Biomarker

Fragments derived from the ANP precursor, including the signal peptide, N-terminal pro-ANP and ANP, have been detected in human blood.[19] ANP and related peptides are used as biomarkers for cardiovascular diseases such as stroke, coronary artery disease, myocardial infarction and heart failure.[20][21][22][23] A specific ANP precursor called mid-regional pro-atrial natriuretic peptide (MRproANP) is a highly sensitive biomarker in heart failure.[24] MRproANP levels below 120 pmol/L can be used to effectively rule out acute heart failure.[24]

Large amounts of ANP secretion has been noted to cause electrolyte disturbances (hyponatremia) and polyuria. These indications can be a marker of a large atrial myxoma.[25]

Therapeutic use and drug development

Opinions regarding the use of ANP for the treatment of acute heart failure and kidney disease are varied.[26] While this molecule has been shown to successfully restore some hemodynamic parameters following heart failure, and yield clinical improvement for kidney injury, whether it ultimately reduces mortality and its long-term effects are unknown.[27] Therefore, more studies need to be conducted to better understand the therapeutic effects of ANP.[27] Newly synthesized homologues of ANP molecule are being assessed for the treatment of acute heart failure.[28] Preliminary research on one of such molecules, ularitide, has shown that this drug is safe, well tolerated, and effective in the treatment of acute heart failure.[28]

Other natriuretic peptides

Brain natriuretic peptide (BNP) – a misnomer; it is secreted by ventricular myocytes – is similar to ANP in its effect. It acts via atrial natriuretic peptide receptors but with 10-fold lower affinity than ANP. The biological half-life of BNP, however, is twice as long as that of ANP, and that of NT-proBNP is even longer, making these peptides better choices than ANP for diagnostic blood testing.

In addition to the mammalian natriuretic peptides (ANP, BNP, CNP), other natriuretic peptides with similar structure and properties have been isolated elsewhere in the animal kingdom. A salmon natriuretic peptide known as salmon cardiac peptide has been described,[29] and dendroaspis natriuretic peptide (DNP) has been found in the venom of the green mamba, as well as an NP in a species of African snake.[30]

Beside these four, five additional natriuretic peptides have been identified: long-acting natriuretic peptide (LANP), vessel dilator, kaliuretic peptide, urodilatin, and adrenomedullin.[5]

Pharmacological modulation

Neutral endopeptidase (NEP) also known as neprilysin is the enzyme that metabolizes natriuretic peptides. Several inhibitors of NEP are currently being developed to treat disorders ranging from hypertension to heart failure. Most of them are dual inhibitors (NEP and ACE). In 2014, PARADIGM-HF study was published in NEJM. This study considered as a landmark study in treatment of heart failure. The study was double blinded; compared LCZ696 versus enalapril in patients with heart failure. The study showed lower all cause mortality, cardiovascular mortality and hospitalization in LCZ696 arm.[31] Omapatrilat (dual inhibitor of NEP and angiotensin-converting enzyme) developed by BMS did not receive FDA approval due to angioedema safety concerns. Other dual inhibitors of NEP with ACE/angiotensin receptor are (in 2003) being developed by pharmaceutical companies.[32]

Synonyms

ANP is also called atrial natriuretic factor (ANF), atrial natriuretic hormone (ANH), cardionatrine, cardiodilatin (CDD), and atriopeptin.

Notes


References

  1. ↑ Macchia DD (December 1987). "Atrial natriuretic factor: a hormone secreted by the heart". Pharmaceutisch Weekblad. Scientific Edition. 9 (6): 305–14. doi:10.1007/bf01956510. PMID 2829109.
  2. ↑ 2.0 2.1 Potter LR, Yoder AR, Flora DR, Antos LK, Dickey DM (2009). "Natriuretic peptides: their structures, receptors, physiologic functions and therapeutic applications". Handbook of Experimental Pharmacology. cGMP: Generators, Effectors and Therapeutic Implications. Springer Berlin Heidelberg (191): 341–66. doi:10.1007/978-3-540-68964-5_15. ISBN 9783540689607. PMC 4855512. PMID 19089336.
  3. ↑ de Bold AJ, Borenstein HB, Veress AT, Sonnenberg H (January 1981). "A rapid and potent natriuretic response to intravenous injection of atrial myocardial extract in rats". Life Sciences. 28 (1): 89–94. doi:10.1016/0024-3205(81)90370-2. PMID 7219045.
  4. ↑ de Bold AJ (November 1985). "Atrial natriuretic factor: a hormone produced by the heart". Science. 230 (4727): 767–70. Bibcode:1985Sci...230..767D. doi:10.1126/science.2932797. PMID 2932797.
  5. ↑ 5.0 5.1 5.2 Vesely DL (2013). "Chapter 39, Antinatriureic peptides,". Seldin and Giebisch’s The Kidney (Fifth ed.). Elsevier Inc. p. 1242. doi:10.1016/B978-0-12-381462-3.00037-9.
  6. ↑ 6.0 6.1 Stryjewski PJ, Kuczaj A, Kulak Ł, Nowak J, Nessler B, Nessler J (2014-02-20). "Twiddler's syndrome: a rare complication of pacemaker implantation". Polskie Archiwum Medycyny Wewnetrznej. 124 (4): 209. doi:10.20452/pamw.2196. PMID 24556875.
  7. ↑ Yan W, Sheng N, Seto M, Morser J, Wu Q (May 1999). "Corin, a mosaic transmembrane serine protease encoded by a novel cDNA from human heart". The Journal of Biological Chemistry. 274 (21): 14926–35. doi:10.1074/jbc.274.21.14926. PMID 10329693.
  8. ↑ Yan W, Wu F, Morser J, Wu Q (July 2000). "Corin, a transmembrane cardiac serine protease, acts as a pro-atrial natriuretic peptide-converting enzyme". Proceedings of the National Academy of Sciences of the United States of America. 97 (15): 8525–9. Bibcode:2000PNAS...97.8525Y. doi:10.1073/pnas.150149097. PMC 26981. PMID 10880574.
  9. ↑ name="Widmaier" >Widmaier EP, Raff H, Strang KT (2008). Vander's Human Physiology (11th ed.). McGraw-Hill. pp. 291, 509–10. ISBN 978-0-07-304962-5.
  10. ↑ Mohler ER, Finkbeiner WE (2011). Medical Physiology (Boron) (2 ed.). Philadelphia: Saunders. ISBN 1-4377-1753-5.
  11. ↑ Hoehn K, Marieb EN (2013). "16". Human anatomy & physiology (9th ed.). Boston: Pearson. p. 629. ISBN 978-0-321-74326-8. question number 14
  12. ↑ Goetz KL (January 1988). "Physiology and pathophysiology of atrial peptides". The American Journal of Physiology. 254 (1 Pt 1): E1–15. doi:10.1152/ajpendo.1988.254.1.E1. PMID 2962513.
  13. ↑ 13.0 13.1 13.2 13.3 Theilig F, Wu Q (May 2015). "ANP-induced signaling cascade and its implications in renal pathophysiology". American Journal of Physiology. Renal Physiology. 308 (10): F1047–55. doi:10.1152/ajprenal.00164.2014. PMC 4436998. PMID 25651559.
  14. ↑ 14.0 14.1 14.2 14.3 Fu S, Ping P, Wang F, Luo L (2018-01-12). "Synthesis, secretion, function, metabolism and application of natriuretic peptides in heart failure". Journal of Biological Engineering. 12 (1): 2. doi:10.1186/s13036-017-0093-0. PMID 29344085.
  15. ↑ Fernandes-Cerqueira C, Sampaio-Maia B, Quelhas-Santos J, Moreira-Rodrigues M, Simões-Silva L, Blazquez-Medela AM, Martinez-Salgado C, Lopez-Novoa JM, Pestana M (2013). "Concerted action of ANP and dopamine D1-receptor to regulate sodium homeostasis in nephrotic syndrome". BioMed Research International. 2013: 397391. doi:10.1155/2013/397391. PMC 3727124. PMID 23956981.
  16. ↑ Cui Y, Wang W, Dong N, Lou J, Srinivasan DK, Cheng W, Huang X, Liu M, Fang C, Peng J, Chen S, Wu S, Liu Z, Dong L, Zhou Y, Wu Q (March 2012). "Role of corin in trophoblast invasion and uterine spiral artery remodelling in pregnancy". Nature. 484 (7393): 246–50. Bibcode:2012Natur.484..246C. doi:10.1038/nature10897. PMC 3578422. PMID 22437503.
  17. ↑ 17.0 17.1 17.2 Fu S, Ping P, Wang F, Luo L (2018-01-12). "Synthesis, secretion, function, metabolism and application of natriuretic peptides in heart failure". Journal of Biological Engineering. 12 (1): 2. doi:10.1186/s13036-017-0093-0. PMC 5766980. PMID 29344085.
  18. ↑ 18.0 18.1 18.2 De Vito P (August 2014). "Atrial natriuretic peptide: an old hormone or a new cytokine?". Peptides. 58: 108–16. doi:10.1016/j.peptides.2014.06.011. PMID 24973596.
  19. ↑ Goetze JP, Hansen LH, Terzic D, Zois NE, Albrethsen J, Timm A, Smith J, Soltysinska E, Lippert SK, Hunter I (March 2015). "Atrial natriuretic peptides in plasma". Clinica Chimica Acta; International Journal of Clinical Chemistry. 443: 25–8. doi:10.1016/j.cca.2014.08.017. PMID 25158019.
  20. ↑ Wang TJ, Larson MG, Levy D, Benjamin EJ, Leip EP, Omland T, Wolf PA, Vasan RS (February 2004). "Plasma natriuretic peptide levels and the risk of cardiovascular events and death". The New England Journal of Medicine. 350 (7): 655–63. doi:10.1056/NEJMoa031994. PMID 14960742.
  21. ↑ Sabatine MS, Morrow DA, de Lemos JA, Omland T, Sloan S, Jarolim P, Solomon SD, Pfeffer MA, Braunwald E (January 2012). "Evaluation of multiple biomarkers of cardiovascular stress for risk prediction and guiding medical therapy in patients with stable coronary disease". Circulation. 125 (2): 233–40. doi:10.1161/CIRCULATIONAHA.111.063842. PMC 3277287. PMID 22179538.
  22. ↑ Mäkikallio AM, Mäkikallio TH, Korpelainen JT, Vuolteenaho O, Tapanainen JM, Ylitalo K, Sotaniemi KA, Huikuri HV, Myllylä VV (May 2005). "Natriuretic peptides and mortality after stroke". Stroke. 36 (5): 1016–20. doi:10.1161/01.STR.0000162751.54349.ae. PMID 15802631.
  23. ↑ Barbato E, Bartunek J, Marchitti S, Mangiacapra F, Stanzione R, Delrue L, Cotugno M, Di Castro S, De Bruyne B, Wijns W, Volpe M, Rubattu S (March 2012). "NT-proANP circulating level is a prognostic marker in stable ischemic heart disease". International Journal of Cardiology. 155 (2): 311–2. doi:10.1016/j.ijcard.2011.11.057. PMID 22177588.
  24. ↑ 24.0 24.1 Roberts E, Ludman AJ, Dworzynski K, Al-Mohammad A, Cowie MR, McMurray JJ, Mant J (March 2015). "The diagnostic accuracy of the natriuretic peptides in heart failure: systematic review and diagnostic meta-analysis in the acute care setting". BMJ. 350: h910. doi:10.1136/bmj.h910. PMC 4353288. PMID 25740799.
  25. ↑ Anbar M, Loonsk JW (2011). "Computer emulated oral exams: rationale and implementation of cue-free interactive computerised tests". Medical Teacher. 10 (2): 175–80. doi:10.1186/cc9788. PMC 3067042.
  26. ↑ Nigwekar SU, Navaneethan SD, Parikh CR, Hix JK (February 2009). "Atrial natriuretic peptide for management of acute kidney injury: a systematic review and meta-analysis". Clinical Journal of the American Society of Nephrology. 4 (2): 261–72. doi:10.2215/CJN.03780808. PMC 2637582. PMID 19073785.
  27. ↑ 27.0 27.1 Kobayashi D, Yamaguchi N, Takahashi O, Deshpande GA, Fukui T (January 2012). "Human atrial natriuretic peptide treatment for acute heart failure: a systematic review of efficacy and mortality". The Canadian Journal of Cardiology. 28 (1): 102–9. doi:10.1016/j.cjca.2011.04.011. PMID 21908161.
  28. ↑ 28.0 28.1 Yandrapalli S, Jolly G, Biswas M, Rochlani Y, Harikrishnan P, Aronow WS, Lanier GM (January 2018). "Newer hormonal pharmacotherapies for heart failure". Expert Review of Endocrinology & Metabolism. 13 (1): 35–49. doi:10.1080/17446651.2018.1406799. PMID 30063443.
  29. ↑ Tervonen V, Arjamaa O, Kokkonen K, Ruskoaho H, Vuolteenaho O (September 1998). "A novel cardiac hormone related to A-, B- and C-type natriuretic peptides". Endocrinology. 139 (9): 4021–5. doi:10.1210/en.139.9.4021. PMID 9724061.
  30. ↑ Schweitz H, Vigne P, Moinier D, Frelin C, Lazdunski M (July 1992). "A new member of the natriuretic peptide family is present in the venom of the green mamba (Dendroaspis angusticeps)". The Journal of Biological Chemistry. 267 (20): 13928–32. PMID 1352773.
  31. ↑ McMurray JJ, Packer M, Desai AS, Gong J, Lefkowitz MP, Rizkala AR, Rouleau JL, Shi VC, Solomon SD, Swedberg K, Zile MR (September 2014). "Angiotensin-neprilysin inhibition versus enalapril in heart failure". The New England Journal of Medicine. 371 (11): 993–1004. doi:10.1056/NEJMoa1409077. PMID 25176015.
  32. ↑ Venugopal J (2003). "Pharmacological modulation of the natriuretic peptide system". Expert Opinion on Therapeutic Patents. 13 (9): 1389–1409. doi:10.1517/13543776.13.9.1389.

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