Adenosine

Adenosine is both a chemical found in many living systems and a medication. As a medication it is used to treat certain forms of supraventricular tachycardia that do not improve with vagal maneuvers.[1] Common side effects include chest pain, feeling faint, shortness of breath along with tingling of the senses.[1] Serious side effects include a worsening dysrhythmia and low blood pressure.[1] It appears to be safe in pregnancy.[1]

It is a purine nucleoside composed of a molecule of adenine attached to a ribose sugar molecule (ribofuranose) moiety via a β-N9-glycosidic bond.[2][3][4] Derivatives of adenosine are widely found in nature and play an important role in biochemical processes, such as energy transfer—as adenosine triphosphate (ATP) and adenosine diphosphate (ADP)—as well as in signal transduction as cyclic adenosine monophosphate (cAMP). Adenosine itself is a neuromodulator, believed to play a role in promoting sleep and suppressing arousal. Adenosine also plays a role in regulation of blood flow to various organs through vasodilation.[5][6][7]

Adenosine
Adenosin
Adenosine-3D-balls
Clinical data
Trade namesAdenocard; Adenocor; Adenic; Adenoco; Adeno-Jec; Adenoscan; Adenosin; Adrekar; Krenosin
SynonymsSR-96225 (developmental code name)
AHFS/Drugs.comMonograph
Pregnancy
category
  • C

(adenosine may be safe to the fetus in pregnant women)

Routes of
administration
Intravenous
ATC code
Legal status
Legal status
  • In general: ℞ (Prescription only)
Pharmacokinetic data
BioavailabilityRapidly cleared from circulation via cellular uptake
Protein bindingNo
MetabolismRapidly converted to inosine and adenosine monophosphate
Elimination half-lifecleared plasma <30 seconds – half-life <10 seconds
Excretioncan leave cell intact or can be degraded to hypoxanthine, xanthine, and ultimately uric acid
Identifiers
CAS Number
PubChem CID
IUPHAR/BPS
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
Chemical and physical data
FormulaC10H13N5O4
Molar mass267.241 g/mol g·mol−1
3D model (JSmol)
 ☒☑ (what is this?)  (verify)

Medical uses

Supraventricular tachycardia

In individuals with supraventricular tachycardia (SVT), adenosine is used to help identify and convert the rhythm.

Certain SVTs can be successfully terminated with adenosine.[8] This includes any re-entrant arrhythmias that require the AV node for the re-entry, e.g., AV reentrant tachycardia (AVRT), AV nodal reentrant tachycardia (AVNRT). In addition, atrial tachycardia can sometimes be terminated with adenosine.

Fast rhythms of the heart that are confined to the atria (e.g., atrial fibrillation, atrial flutter) or ventricles (e.g., monomorphic ventricular tachycardia) and do not involve the AV node as part of the re-entrant circuit are not typically converted by adenosine. However, the ventricular response rate is temporarily slowed with adenosine in such cases.

Because of the effects of adenosine on AV node-dependent SVTs, adenosine is considered a class V antiarrhythmic agent. When adenosine is used to cardiovert an abnormal rhythm, it is normal for the heart to enter ventricular asystole for a few seconds. This can be disconcerting to a normally conscious patient, and is associated with angina-like sensations in the chest.[9]

Nuclear stress test

Adenosine is used as an adjunct to thallium (TI 201) or technetium (Tc99m) myocardial perfusion scintigraphy (nuclear stress test) in patients unable to undergo adequate stress testing with exercise.[10]

Dosage

When given for the evaluation or treatment of a supraventricular tachycardia (SVT), the initial dose is 6 mg to 12 mg, depending on standing orders or provider preference,[11] given as a rapid parenteral infusion. Due to adenosine's extremely short half-life, the IV line is started as proximal (near) to the heart as possible, such as the antecubital fossa. The IV push is often followed with an immediate flush of 10-20 ccs of saline. If this has no effect (i.e., no evidence of transient AV block), a dose of 12 mg can be given 1–2 minutes after the first dose. When given to dilate the arteries, such as in a "stress test", the dosage is typically 0.14 mg/kg/min, administered for 4 or 6 minutes, depending on the protocol.

The recommended dose may be increased in patients on theophylline, since methylxanthines prevent binding of adenosine at receptor sites. The dose is often decreased in patients on dipyridamole (Persantine) and diazepam (Valium) because adenosine potentiates the effects of these drugs. The recommended dose is also reduced by half in patients presenting congestive heart failure, myocardial infarction, shock, hypoxia, and/or hepatic or renal insufficiency, and in elderly patients.

Drug interactions

Dipyridamole potentiates the action of adenosine, requiring the use of lower doses.

Caffeine and adenosine
Caffeine's principal mode of action is as an antagonist of adenosine receptors in the brain.

Methylxanthines (e.g., caffeine, found in coffee, or theophylline in tea, or theobromine, as found in chocolate) competitively antagonize adenosine's effects; an increased dose of adenosine may be required. By nature of caffeine's purine structure,[12] it binds to some of the same receptors as adenosine.[12] The pharmacological effects of adenosine may be blunted in individuals taking large quantities of methylxanthines.[13]

Contraindications

Common contraindications for adenosine include

  • Asthma, traditionally considered an absolute contraindication. This is being contended and it is now considered a relative contraindication (however, selective adenosine antagonists are being investigated for use in treatment of asthma)[14]
  • Decompensated heart failure
  • Long QT syndrome
  • Poison/drug-induced tachycardia
  • Second- or third-degree heart block (without a pacemaker)
  • Severe hypotension
  • Sick sinus syndrome (without a pacemaker)

When administered via a central lumen catheter, adenosine has been shown to initiate atrial fibrillation because of its effect on atrial tissue. In individuals with accessory pathways, the onset of atrial fibrillation can lead to a life-threatening ventricular fibrillation. However, adenosine may be administered if equipment for cardioversion is immediately available as a backup.

Side effects

Many individuals experience facial flushing, a temporary rash on the chest, lightheadedness, diaphoresis, or nausea after administration of adenosine due to its vasodilatory effects. Metallic taste is a hallmark side-effect of adenosine administration. These symptoms are transitory, usually lasting less than one minute. It is classically associated with a sense of "impending doom", more prosaically described as apprehension. This lasts a few seconds after administration of a bolus dose, during transient asystole induced by intravenous administration. In some cases, adenosine can make patients' limbs feel numb for about 2–5 minutes after administration intravenously depending on the dosage (usually above 12 mg).

Pharmacological effects

Adenosine is an endogenous purine nucleoside that modulates many physiological processes. Cellular signaling by adenosine occurs through four known adenosine receptor subtypes (A1, A2A, A2B, and A3).[15]

Extracellular adenosine concentrations from normal cells are approximately 300 nM; however, in response to cellular damage (e.g. in inflammatory or ischemic tissue), these concentrations are quickly elevated (600–1,200 nM). Thus, in regard to stress or injury, the function of adenosine is primarily that of cytoprotection preventing tissue damage during instances of hypoxia, ischemia, and seizure activity. Activation of A2A receptors produces a constellation of responses that in general can be classified as anti-inflammatory.[16]

Adenosine receptors

All adenosine receptor subtypes (A1, A2A, A2B, and A3) are G-protein-coupled receptors. The four receptor subtypes are further classified based on their ability to either stimulate or inhibit adenylate cyclase activity. The A1 receptors couple to Gi/o and decreases cAMP levels, while the A2 adenosine receptors couple to Gs, which stimulates adenylate cyclase activity. In addition, A1 receptors couple to Go, which has been reported to mediate adenosine inhibition of Ca2+ conductance, whereas A2B and A3 receptors also couple to Gq and stimulate phospholipase activity. Researchers at Cornell University have recently shown adenosine receptors to be key in opening the blood-brain barrier (BBB). Mice dosed with adenosine have shown increased transport across the BBB of amyloid plaque antibodies and prodrugs associated with Parkinson's disease, Alzheimer's, multiple sclerosis, and cancers of the central nervous system.[17]

Ghrelin/growth hormone secretagogue receptor

Adenosine is an endogenous agonist of the ghrelin/growth hormone secretagogue receptor.[18] However, while it is able to increase appetite, unlike other agonists of this receptor, adenosine is unable to induce the secretion of growth hormone and increase its plasma levels.[18]

Mechanism of action

When it is administered intravenously, adenosine causes transient heart block in the atrioventricular (AV) node. This is mediated via the A1 receptor, inhibiting adenylyl cyclase, reducing cAMP and so causing cell hyperpolarization by increasing K+ efflux via inward rectifier K+ channels, subsequently inhibiting Ca2+ current.[19] It also causes endothelial-dependent relaxation of smooth muscle as is found inside the artery walls. This causes dilation of the "normal" segments of arteries, i.e. where the endothelium is not separated from the tunica media by atherosclerotic plaque. This feature allows physicians to use adenosine to test for blockages in the coronary arteries, by exaggerating the difference between the normal and abnormal segments.

The administration of adenosine also reduces blood flow to coronary arteries past the occlusion. Other coronary arteries dilate when adenosine is administered while the segment past the occlusion is already maximally dilated, which is a process called coronary steal. This leads to less blood reaching the ischemic tissue, which in turn produces the characteristic chest pain.

Metabolism

Adenosine used as a second messenger can be the result of de novo purine biosynthesis via adenosine monophosphate (AMP), though it is possible other pathways exist.[20]

When adenosine enters the circulation, it is broken down by adenosine deaminase, which is present in red cells and the vessel wall.

Dipyridamole, an inhibitor of adenosine nucleoside transporter, allows adenosine to accumulate in the blood stream. This causes an increase in coronary vasodilatation.

Adenosine deaminase deficiency is a known cause of immunodeficiency.

Research

Viruses

The adenosine analog NITD008 has been reported to directly inhibit the recombinant RNA-dependent RNA polymerase of the dengue virus by terminating its RNA chain synthesis. This suppresses peak viremia and rise in cytokines and prevented lethality in infected animals, raising the possibility of a new treatment for this flavivirus.[21] The 7-deaza-adenosine analog has been shown to inhibit the replication of the hepatitis C virus.[22] BCX4430 is protective against Ebola and Marburg viruses.[23] Such adenosine analogs are potentially clinically useful since they can be taken orally.

Anti-inflammatory properties

Adenosine is believed to be an anti-inflammatory agent at the A2A receptor.[24][25] Topical treatment of adenosine to foot wounds in diabetes mellitus has been shown in lab animals to drastically increase tissue repair and reconstruction. Topical administration of adenosine for use in wound-healing deficiencies and diabetes mellitus in humans is currently under clinical investigation.

Methotrexate's anti-inflammatory effect may be due to its stimulation of adenosine release.[26]

Central nervous system

In general, adenosine has an inhibitory effect in the central nervous system (CNS). Caffeine's stimulatory effects are credited primarily (although not entirely) to its capacity to block adenosine receptors, thereby reducing the inhibitory tonus of adenosine in the CNS. This reduction in adenosine activity leads to increased activity of the neurotransmitters dopamine and glutamate.[27] Experimental evidence suggests that adenosine and adenosine agonists can activate Trk receptor phosphorylation through a mechanism that requires the adenosine A2A receptor.[28]

Hair

Adenosine has been shown to promote thickening of hair on people with thinning hair.[29][30] A 2013 study compared topical adenosine with minoxidil in male androgenetic alopecia, finding it was not superior to minoxidil and further trials were needed.[31]

Sleep

The principal component of marijuana, delta-9-tetrahydrocannabinol (THC) and the endocannabinoid anandamide (AEA) induce sleep in rats by increasing adenosine levels in the basal forebrain. They also significantly increase slow-wave sleep during the third hour, mediated by CB1 receptor activation. These findings identify a potential therapeutic use of cannabinoids to induce sleep in conditions where sleep may be severely attenuated.[32]

See also

References

  1. ^ a b c d "Adenosine". The American Society of Health-System Pharmacists. Retrieved Jan 12, 2015.
  2. ^ I.K. Morton; Judith M. Hall (6 December 2012). Concise Dictionary of Pharmacological Agents: Properties and Synonyms. Springer Science & Business Media. pp. 106–. ISBN 978-94-011-4439-1.
  3. ^ J. Buckingham (1987). Dictionary of Organic Compounds. CRC Press. pp. 75–. ISBN 978-0-412-54090-5.
  4. ^ Index Nominum 2000: International Drug Directory. Taylor & Francis. January 2000. pp. 18–. ISBN 978-3-88763-075-1.
  5. ^ Sato, A (April 2005). "Mechanism of vasodilation to adenosine in coronary arterioles from patients with heart disease". American Journal of Physiology. Heart and Circulatory Physiology. 288 (4): H1633–40. doi:10.1152/ajpheart.00575.2004. PMID 15772334.
  6. ^ Costa, F; Biaggioni, I (May 1998). "Role of nitric oxide in adenosine-induced vasodilation in humans". Hypertension. 31 (5): 1061–4. doi:10.1161/01.HYP.31.5.1061. PMID 9576114.
  7. ^ Morgan, JM; McCormack, DG; Griffiths, MJ; Morgan, CJ; Barnes, PJ; Evans, TW (September 1991). "Adenosine as a vasodilator in primary pulmonary hypertension". Circulation. 84 (3): 1145–9. doi:10.1161/01.CIR.84.3.1145. PMID 1884445.
  8. ^ Mitchell J, Lazarenko G (November 2008). "Wide QRS complex tachycardia. Diagnosis: Supraventricular tachycardia with aberrant conduction; intravenous (IV) adenosine". CJEM. 10 (6): 572–3, 581. PMID 19000353.
  9. ^ Pijls, Nico H. J.; Bernard De Bruyne (2000). Coronary Pressure. Springer. ISBN 0-7923-6170-9.
  10. ^ O'Keefe, JH; Bateman, TM; Silverstri, R; et al. (1992). "Safety and diagnostic accuracy of adenosine thallium-201 scintigraphy in patients unable to exercise and those with left bundle branch block". Am. Heart J. 124 (3): 614–21. doi:10.1016/0002-8703(92)90268-z. PMID 1514488.
  11. ^ http://www.regionsems.com/wp-content/uploads/2016/04/2014-Guidelines.pdf
  12. ^ a b "Caffeine". Chemistry Explained.
  13. ^ "Vitamin B4". R&S Pharmchem. April 2011. Archived from the original on 2011-07-15.
  14. ^ Brown RA, Spina D, Page CP (March 2008). "Adenosine receptors and asthma". Br. J. Pharmacol. 153 Suppl 1 (S1): S446–56. doi:10.1038/bjp.2008.22. PMC 2268070. PMID 18311158.
  15. ^ Haskó G, Linden J, Cronstein B, Pacher P (September 2008). "Adenosine receptors: therapeutic aspects for inflammatory and immune diseases". Nat Rev Drug Discov. 7 (9): 759–70. doi:10.1038/nrd2638. PMC 2568887. PMID 18758473.
  16. ^ Haskó, G (January 2004). "Adenosine: an endogenous regulator of innate immunity". Trends in Immunology. 25 (1): 33–39. doi:10.1016/j.it.2003.11.003. PMID 14698282.
  17. ^ Carman, A. J.; Mills, J. H.; Krenz, A; Kim, D. G.; Bynoe, M. S. (2011). "Adenosine receptor signaling modulates permeability of the blood-brain barrier". J. Neurosci. 31 (37): 13272–80. doi:10.1523/JNEUROSCI.3337-11.2011. PMC 3328085. PMID 21917810.
  18. ^ a b Claude Kordon; I. Robinson; Jacques Hanoune; R. Dantzer (6 December 2012). Brain Somatic Cross-Talk and the Central Control of Metabolism. Springer Science & Business Media. pp. 42–. ISBN 978-3-642-18999-9.
  19. ^ Katzung, Bertram (2012). Basic & Clinical Pharmacology (12th ed.). McGraw Hill. p. 245. ISBN 978-0-07-176402-5.
  20. ^ Miller-Patrick K, Vincent DL, Early RJ, et al. (1993). "Effects of the purine biosynthesis pathway inhibitors azaserine, hadacidin, and mycophenolic acid on the developing ovine corpus luteum". Chin J Physiol. 36 (4): 245–52. PMID 8020339.
  21. ^ Yin, Z; Chen, YL; Schul, W; Wang, QY; Gu, F; Duraiswamy, J; Reddy Kondreddi, R; Niyomrattanakit, P; Lakshminarayana, SB; Goh, A; Xu, HY; Liu, W; Liu, B; Lim, JY; Ng, CY; Qing, M; Lim, CC; Yip, A; Wang, G; Chan, WL; Tan, HP; Lin, K; Zhang, B; Zou, G; Bernard, KA; Garrett, C; Beltz, K; Dong, M; Weaver, M; He, H; Pichota, A; Dartois, V; Keller, TH; Shi, PY (2009). "An adenosine nucleoside inhibitor of dengue virus". Proc Natl Acad Sci U S A. 106 (48): 20435–20439. Bibcode:2009PNAS..10620435Y. doi:10.1073/pnas.0907010106. PMC 2787148. PMID 19918064.
  22. ^ Olsen, DB; Eldrup, AB; Bartholomew, L; Bhat, B; Bosserman, MR; Ceccacci, A; Colwell, LF; Fay, JF; Flores, OA; Getty, K. L.; Grobler, J. A.; Lafemina, R. L.; Markel, E. J.; Migliaccio, G.; Prhavc, M.; Stahlhut, M. W.; Tomassini, J. E.; MacCoss, M.; Hazuda, D. J.; Carroll, S. S. (2004). "A 7-Deaza-Adenosine Analog Is a Potent and Selective Inhibitor of Hepatitis C Virus Replication with Excellent Pharmacokinetic Properties". Antimicrobial Agents and Chemotherapy. 48 (10): 3944–53. doi:10.1128/AAC.48.10.3944-3953.2004. PMC 521892. PMID 15388457.
  23. ^ Warren, T. K.; Wells, J.; Panchal, R. G.; Stuthman, K. S.; Garza, N. L.; Van Tongeren, S. A.; Dong, L.; Retterer, C. J.; Eaton, B. P.; Pegoraro, G.; Honnold, S.; Bantia, S.; Kotian, P.; Chen, X.; Taubenheim, B. R.; Welch, L. S.; Minning, D. M.; Babu, Y. S.; Sheridan, W. P.; Bavari, S. (2014). "Protection against filovirus diseases by a novel broad-spectrum nucleoside analogue BCX4430". Nature. 508 (7496): 402–5. Bibcode:2014Natur.508..402W. doi:10.1038/nature13027. PMID 24590073.
  24. ^ Nakav S, Chaimovitz C, Sufaro Y (2008). Bozza P, ed. "Anti-Inflammatory Preconditioning by Agonists of Adenosine A1 Receptor". PLoS ONE. 3 (5): e2107. Bibcode:2008PLoSO...3.2107N. doi:10.1371/journal.pone.0002107. PMC 2329854. PMID 18461129. open access
  25. ^ Trevethick MA, Mantell SJ, Stuart EF, Barnard A, Wright KN, Yeadon M (October 2008). "Treating lung inflammation with agonists of the adenosine A2A receptor: promises, problems and potential solutions". Br. J. Pharmacol. 155 (4): 463–74. doi:10.1038/bjp.2008.329. PMC 2579671. PMID 18846036.
  26. ^ Cronstein B (2010). "How does methotrexate suppress inflammation?". Clin Exp Rheumatol. 28 (5 Suppl 61): S21–3. PMID 21044428.
  27. ^ Solinas, M; Ferré, S; You, Z. B; Karcz-Kubicha, M; Popoli, P; Goldberg, S. R (2002). "Caffeine induces dopamine and glutamate release in the shell of the nucleus accumbens". The Journal of Neuroscience. 22 (15): 6321–4. PMID 12151508.
  28. ^ Lee, FS; Chao, MV; Lee (March 2001). "Activation of Trk neurotrophin receptors in the absence of neurotrophins". PNAS. 98 (6): 3555–3560. Bibcode:2001PNAS...98.3555L. doi:10.1073/pnas.061020198. PMC 30691. PMID 11248116.
  29. ^ Oura, H; Iino, M; Nakazawa, Y; Tajima, M; Ideta, R; Nakaya, Y; Arase, S; Kishimoto, J (December 2008). "Adenosine increases anagen hair growth and thick hairs in Japanese women with female pattern hair loss: a pilot, double-blind, randomized, placebo-controlled trial". The Journal of dermatology. 35 (12): 763–7. doi:10.1111/j.1346-8138.2008.00564.x. PMID 19239555.
  30. ^ Hwang, KA; Hwang, YL; Lee, MH; Kim, NR; Roh, SS; Lee, Y; Kim, CD; Lee, JH; Choi, KC (February 2012). "Adenosine stimulates growth of dermal papilla and lengthens the anagen phase by increasing the cysteine level via fibroblast growth factors 2 and 7 in an organ culture of mouse vibrissae hair follicles". International Journal of Molecular Medicine. 29 (2): 195–201. doi:10.3892/ijmm.2011.817. PMID 22020741.
  31. ^ Faghihi, G; Iraji, F; Rajaee Harandi, M; Nilforoushzadeh, M. A.; Askari, G (2013). "Comparison of the efficacy of topical minoxidil 5% and adenosine 0.75% solutions on male androgenetic alopecia and measuring patient satisfaction rate". Acta Dermatovenerol Croat. 21 (3): 155–9. PMID 24183218.
  32. ^ Murillo-Rodriguez, Eric; Blanco-Centurion, Carlos; Sanchez, Cristina; Daniele, Piomelli; Shiromani, Priyattam J. (2003). "Anandamide Enhances Extracellular Levels of Adenosine and Induces Sleep: An In Vivo Microdialysis Study". Sleep. 26 (8): 943–947. doi:10.1093/sleep/26.8.943. ISSN 0161-8105.
8-Cyclopentyl-1,3-dimethylxanthine

8-Cyclopentyl-1,3-dimethylxanthine (8-Cyclopentyltheophylline, 8-CPT, CPX) is a drug which acts as a potent and selective antagonist for the adenosine receptors, with some selectivity for the A1 receptor subtype, as well as a non-selective phosphodiesterase inhibitor. It has stimulant effects in animals with slightly higher potency than caffeine.

8-Phenyltheophylline

8-Phenyltheophylline (8-phenyl-1,3-dimethylxanthine, 8-PT) is a drug derived from the xanthine family which acts as a potent and selective antagonist for the adenosine receptors A1 and A2A, but unlike other xanthine derivatives has virtually no activity as a phosphodiesterase inhibitor. It has stimulant effects in animals with similar potency to caffeine. Coincidentally 8-phenyltheophylline has also been found to be a potent and selective inhibitor of the liver enzyme CYP1A2 which makes it likely to cause interactions with other drugs which are normally metabolised by CYP1A2.

ATPase

ATPases (EC 3.6.1.3, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, SV40 T-antigen, adenosine 5'-triphosphatase, ATP hydrolase, complex V (mitochondrial electron transport), (Ca2+ + Mg2+)-ATPase, HCO3−-ATPase, adenosine triphosphatase) are a class of enzymes that catalyze the decomposition of ATP into ADP and a free phosphate ion or the inverse reaction. This dephosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life.

Some such enzymes are integral membrane proteins (anchored within biological membranes), and move solutes across the membrane, typically against their concentration gradient. These are called transmembrane ATPases.

Adenine

Adenine (A, Ade) is a nucleobase (a purine derivative). It is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The three others are guanine, cytosine and thymine. Its derivatives have a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). It also has functions in protein synthesis and as a chemical component of DNA and RNA. The shape of adenine is complementary to either thymine in DNA or uracil in RNA.

The adjacent image shows pure adenine, as an independent molecule. When connected into DNA, a covalent bond is formed between deoxyribose sugar and the bottom left nitrogen, so removing the hydrogen. The remaining structure is called an adenine residue, as part of a larger molecule. Adenosine is adenine reacted with ribose as used in RNA and ATP; deoxyadenosine, adenine attached to deoxyribose, as is used to form DNA.

Adenosine A1 receptor

The adenosine A1 receptor is one member of the adenosine receptor group of G protein-coupled receptors with adenosine as endogenous ligand.

Adenosine A2A receptor

The adenosine A2A receptor, also known as ADORA2A, is an adenosine receptor, and also denotes the human gene encoding it.

Adenosine A2B receptor

The adenosine A2B receptor, also known as ADORA2B, is a G-protein coupled adenosine receptor, and also denotes the human adenosine A2b receptor gene which encodes it.

== Mechanism ==

This integral membrane protein stimulates adenylate cyclase activity in the presence of adenosine. This protein also interacts with netrin-1, which is involved in axon elongation.

== Gene ==

The gene is located near the Smith-Magenis syndrome region on chromosome 17.

Adenosine A3 receptor

The adenosine A3 receptor, also known as ADORA3, is an adenosine receptor, but also denotes the human gene encoding it.

Adenosine deaminase

Adenosine deaminase (also known as adenosine aminohydrolase, or ADA) is an enzyme (EC 3.5.4.4) involved in purine metabolism. It is needed for the breakdown of adenosine from food and for the turnover of nucleic acids in tissues.

Its primary function in humans is the development and maintenance of the immune system. However, the full physiological role of ADA is not yet completely understood.

Adenosine diphosphate

Adenosine diphosphate (ADP), also known as adenosine pyrophosphate (APP), is an important organic compound in metabolism and is essential to the flow of energy in living cells. ADP consists of three important structural components: a sugar backbone attached to adenine and two phosphate groups bonded to the 5 carbon atom of ribose. The diphosphate group of ADP is attached to the 5’ carbon of the sugar backbone, while the adenosine attaches to the 1’ carbon.ADP can be interconverted to adenosine triphosphate (ATP) and adenosine monophosphate (AMP). ATP contains one more phosphate group than does ADP. AMP contains one fewer phosphate group. Energy transfer used by all living things is a result of dephosphorylation of ATP by enzymes known as ATPases. The cleavage of a phosphate group from ATP results in the coupling of energy to metabolic reactions and a by-product of ADP. Being the "molecular unit of currency", ATP is continually being reformed from lower-energy species ADP and AMP. The biosynthesis of ATP is achieved throughout processes such as substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation, all of which facilitating the addition of a phosphate group to ADP.

Adenosine monophosphate

Adenosine monophosphate (AMP), also known as 5'-adenylic acid, is a nucleotide. AMP consists of a phosphate group, the sugar ribose, and the nucleobase adenine; it is an ester of phosphoric acid and the nucleoside adenosine. As a substituent it takes the form of the prefix adenylyl-.

AMP plays an important role in many cellular metabolic processes, being interconverted to ADP and/or ATP. AMP is also a component in the synthesis of RNA.

Adenosine receptor

The adenosine receptors (or P1 receptors) are a class of purinergic G protein-coupled receptors with adenosine as endogenous ligand. There are four known types of adenosine receptors in humans: A1, A2A, A2B and A3; each is encoded by a different gene.

The adenosine receptors are commonly known for their antagonists caffeine and theophylline, whose action on the receptors produces the stimulating effects of coffee, tea and chocolate.

Adenosine triphosphate

Adenosine triphosphate (ATP) is a complex organic chemical that provides energy to drive many processes in living cells, e.g. muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer. When consumed in metabolic processes, it converts either to adenosine diphosphate (ADP) or to adenosine monophosphate (AMP). Other processes regenerate ATP so that the human body recycles its own body weight equivalent in ATP each day. It is also a precursor to DNA and RNA, and is used as a coenzyme.

From the perspective of biochemistry, ATP is classified as a nucleoside triphosphate, which indicates that it consists of three components: a nitrogenous base (adenine), the sugar ribose, and the triphosphate.

Aminophylline

Aminophylline is a compound of the bronchodilator theophylline with ethylenediamine in 2:1 ratio. The ethylenediamine improves solubility, and the aminophylline is usually found as a dihydrate.Aminophylline is less potent and shorter-acting than theophylline. Its most common use is in the treatment of airway obstruction from asthma or COPD. Aminophylline is a nonselective adenosine receptor antagonist and phosphodiesterase inhibitor.

CGS-15943

CGS-15943 is a drug which acts as a potent and reasonably selective antagonist for the adenosine receptors A1 and A2A, having a Ki of 3.3nM at A2A and 21nM at A1. It was one of the first adenosine receptor antagonists discovered that is not a xanthine derivative, instead being a triazoloquinazoline. Consequently, CGS-15943 has the advantage over most xanthine derivatives that it is not a phosphodiesterase inhibitor, and so has more a specific pharmacological effects profile. It produces similar effects to caffeine in animal studies, though with higher potency.

Caffeine

Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is the world's most widely consumed psychoactive drug. Unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world. There are several known mechanisms of action to explain the effects of caffeine. The most prominent is that it reversibly blocks the action of adenosine on its receptor and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also stimulates certain portions of the autonomic nervous system.

Caffeine is a bitter, white crystalline purine, a methylxanthine alkaloid, and is chemically related to the adenine and guanine bases of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). It is found in the seeds, nuts, or leaves of a number of plants native to Africa, East Asia and South America, and helps to protect them against predator insects and to prevent germination of nearby seeds. The most well-known source of caffeine is the coffee bean, a misnomer for the seed of Coffea plants. Beverages containing caffeine are ingested to relieve or prevent drowsiness and to improve performance. To make these drinks, caffeine is extracted by steeping the plant product in water, a process called infusion. Caffeine-containing drinks, such as coffee, tea, and cola, are very popular; as of 2014, 85% of American adults consumed some form of caffeine daily, consuming 164 mg on average.Caffeine can have both positive and negative health effects. It can treat and prevent the premature infant breathing disorders bronchopulmonary dysplasia of prematurity and apnea of prematurity. Caffeine citrate is on the WHO Model List of Essential Medicines. It may confer a modest protective effect against some diseases, including Parkinson's disease. Some people experience sleep disruption or anxiety if they consume caffeine, but others show little disturbance. Evidence of a risk during pregnancy is equivocal; some authorities recommend that pregnant women limit consumption to the equivalent of two cups of coffee per day or less. Caffeine can produce a mild form of drug dependence – associated with withdrawal symptoms such as sleepiness, headache, and irritability – when an individual stops using caffeine after repeated daily intake. Tolerance to the autonomic effects of increased blood pressure and heart rate, and increased urine output, develops with chronic use (i.e., these symptoms become less pronounced or do not occur following consistent use).Caffeine is classified by the US Food and Drug Administration as generally recognized as safe (GRAS). Toxic doses, over 10 grams per day for an adult, are much higher than the typical dose of under 500 milligrams per day. A cup of coffee contains 80–175 mg of caffeine, depending on what "bean" (seed) is used and how it is prepared (e.g., drip, percolation, or espresso). Thus it requires roughly 50–100 ordinary cups of coffee to reach the toxic dose. However, pure powdered caffeine, which is available as a dietary supplement, can be lethal in tablespoon-sized amounts.

Cyclic adenosine monophosphate

Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes. cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transduction in many different organisms, conveying the cAMP-dependent pathway. It should not be confused with 5'-AMP-activated protein kinase (AMP-activated protein kinase).

Nucleoside

Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (either ribose or deoxyribose), whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and one or more phosphate groups. In a nucleoside, the anomeric carbon is linked through a glycosidic bond to the N9 of a purine or the N1 of a pyrimidine. Examples of nucleosides include cytidine, uridine, adenosine, guanosine, thymidine and inosine.

SCH-58261

SCH-58261 is a drug which acts as a potent and selective antagonist for the adenosine receptor A2A, with more than 50x selectivity for A2A over other adenosine receptors. It has been used to investigate the mechanism of action of caffeine, which is a mixed A1 / A2A antagonist, and has shown that the A2A receptor is primarily responsible for the stimulant effects of caffeine, but blockade of both A1 and A2A receptors is required to accurately replicate caffeine's effects in animals. SCH-58261 has also shown antidepressant and neuroprotective effects in a variety of animal models, and has been investigated as a possible treatment for Parkinson's disease.

Amino acid-derived
Lipid-derived
Nucleobase-derived
Vitamin-derived
Miscellaneous
Nucleic acid constituents
Nucleobase
Nucleoside
Nucleotide
(Nucleoside monophosphate)
Nucleoside diphosphate
Nucleoside triphosphate
Channel blockers
Receptor agonists
and antagonists
Ion transporters
Receptor
(ligands)
Transporter
(blockers)
Enzyme
(inhibitors)
Others
GH
(somatotropin)
GHIH
(somatostatin)
GHRH
(somatocrinin)
GHS
(ghrelin)
IGF-1
(somatomedin)

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.