Adenosine

Absorption

Data regarding the absorption of adenosine are not readily available.

Toxicity

Patients experiencing an overdose of adenosine may present with asystole, heart block, or cardiac ischemia; though the effects are generally short lived. Patients experiencing an overdose should be treated with symptomatic and supportive care, which may include a slow intravenous injection of theophylline.
The LD50 in mice is >20 g/kg subcutaneously, 500mg/kg intraperitoneally, and 39.6 μg/kg subcutaneously.

Description

Adenosine is a nucleoside composed of a molecule of adenine attached to a ribose sugar molecule (ribofuranose) moiety via a β-N9-glycosidic bond. Adenosine works in the energy transfer-as adenosine triphosphate (ATP) and adenosine diphosphate (ADP)-as well as in signal transduction as cyclic adenosine monophosphate, cAMP. It shows neuromodulatory, cytoprotective, anti-inflammatory and cardioprotective actions.

Description

Adenosine is a nucleoside found widely in nature, and it is one of the components of the important energy-transfer coenzymes adenosine triphosphate (ATP) and diphosphate (ADP). It was first isolated from yeast nucleic acid; several researchers reported its structure in the 1930s. More recently, M. Nedergaard and co-workers showed that adenosine released during acupuncture acts as a painkiller.

Chemical properties

White or almost white, crystalline powder.

Chemical properties

Adenosine is an important nucleoside composed of adenine and ribose. White, crystalline, odorless powder, mild, saline, or bitter taste, quite soluble in hot water, practically insoluble in alcohol. Formed by isolation following hydrolysis of yeast nucleic acid.

The Uses of Adenosine

adenosine is an amino acid. Studies indicate anti-wrinkle and skinsmoothing capacities. Although little is written about its direct skin benefit, adenosine plays an important role in biochemical processes. As adenosine triphosphate (ATP) and adenosine diphosphate (ADP), it is involved in energy transfer, and as cyclic adenosine monophosphate (cAMP) in signal transduction.

The Uses of Adenosine

antiarrhythmic, cardiac depressant

What are the applications of Application

Adenosine is an apoptosis inducer and an Adenosine A Receptor activator

Indications

Adenosine is indicated as an adjunct to thallium-201 in myocardial perfusion scintigraphy in patients unable to adequately exercise. It is also indicated to convert sinus rhythm of paroxysmal supraventricular tachycardia.

Background

The structure of adenosine was first described in 1931, though the vasodilating effects were not described in literature until the 1940s. Adenosine is indicated as an adjunct to thallium-201 in myocardial perfusion scintigraphy, though it is rarely used in this indication, having largely been replaced by dipyridamole and [regadenson]. Adenosine is also indicated in the treatment of supraventricular tachycardia.
Adenosine was granted FDA approval on 30 October 1989.

Definition

ChEBI: Adenosine is a ribonucleoside composed of a molecule of adenine attached to a ribofuranose moiety via a beta-N(9)-glycosidic bond. It has a role as an anti-arrhythmia drug, a vasodilator agent, an analgesic, a human metabolite and a fundamental metabolite. It is a purines D-ribonucleoside and a member of adenosines. It is functionally related to an adenine.

brand name

Adenocard (Astellas); Adenoscan (Astellas).

Origin

Adenosine may be generated intracellularly in the central nervous system from degradation of AMP or from the hydrolysis of S-adenosyl homocysteine, and then exit via bi-directional nucleoside transporters, or extracellularly by the metabolism of released nucleotides. Inactivation of extracellular adenosine occurs by transport into neurons or neighboring cells, followed by either phosphorylation to AMP by adenosine kinase or deamination to inosine by adenosine deaminase[1].

Biological Functions

Adenosine regulates multiple physiological and pathophysiological processes, by acting both through G-protein coupled adenosine receptors and intracellularly. It modulates neuronal plasticity, astrocytic activity , learning and memory, food intake, motor function, sleep/wake cycle, pain, immunosupression, proliferation, and aging. Adenosine is involved in ischemia and stroke, epilepsy, and neurodegenerative pathologies such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). Extracellular adenosine, interacting with P1 receptors (A1R, A2AR, A2BR, and A3R) regulates metabolism through different signaling pathways[1].

Biological Functions

[1] Mercedes Garcia-Gil. “Metabolic Aspects of Adenosine Functions in the Brain.” Frontiers in Pharmacology (2021): 672182.

General Description

Adenosine is a purine nucleoside and a building block of RNA and many other biomolecules such as adenosine triphosphate and nicotinamide adenine dinucleotide. In the extracellular space, ecto-5′-nucleotidase (CD73) dephosphorylates adenosine triphosphate (ATP) to produce adenosine. Adenosine has four receptors namely A1R, A2AR A2BR and A3R. Adenosine plays a key role in the osteogenic differentiation. A1R induces osteoclast differentiation and A2AR induces osteoblast differentiation.

Biological Activity

Neurotransmitter that acts as the preferred endogenous agonist at all adenosine receptor subtypes.

Biochem/physiol Actions

Endogenous neurotransmitter at adenosine receptors. Cardioprotective effects may relate to activation of A1 adenosine receptors. The antiplatelet and anti?inflammatory actions of adenosine appear to be mediated via the A2 adenosine receptor. In contrast, adenosine appears to be a pro-inflammatory mediator in asthma and chronic obstructive pulmonary disease (COPD).

Pharmacokinetics

Adenosine is indicated as an adjunct to thallium-201 in myocardial perfusion scintigraphy and also indicated for conversion of sinus rhythm of paroxysmal supraventricular tachycardia. Adenosine has a short duration of action as the half life is <10 seconds, and a wide therapeutic window. Patients should be counselled regarding the risk of cardiovascular side effects, bronchoconstriction, seizures, and hypersensitivity.

Clinical Use

Adenosine (Adenocard) is an endogenous nucleoside that is a product of the metabolism of adenosine triphosphate. It is used for the rapid termination of supraventricular arrhythmias following rapid bolus dosing.
Adenosine is approved for the acute management and termination of supraventricular tachyarrhythmias, including A-V nodal reentrant tachycardia and A-V reciprocating tachycardia. Adenosine may be helpful in the diagnosis of atrial flutter.

Side Effects

Adverse reactions to the administration of adenosine are fairly common; however, the short half-life of the drug limits the duration of such events.The most common adverse effects are flushing, chest pain, and dyspnea. Adenosine may induce profound bronchospasm in patients with known reactive airway disease. The mechanism for bronchospasm is unclear, and the effect may last for up to 30 minutes despite the short half-life of the drug.

Drug interactions

Metabolism of adenosine is slowed by dipyridamole, indicating that in patients stabilized on dipyridamole the therapeutically effective dose of adenosine may have to be increased. Methylxanthines antagonize the effects of adenosine via blockade of the adenosine receptors.

Metabolism

Adenosine can be phosphorylated by adenosine kinase to form adenosine monophosphate. From there, it is phosphorylated again by adenylate kinase 1 to form adenosine diphosphate, and again by nucleoside diphosphate kinase A or B to form adenosine triphosphate.
Alternatively, adenosine can be deaminated by adenosine deaminase to form inosine. Iosine is phosphorylated by purine nucleoside phosphorylase to form hypoxanthine. Hypoxanthine undergoes oxidation by xanthine dehydrogenase twice to form the metabolites xanthine, followed by uric acid.

Metabolism

It is impossible to study adenosine in classical pharmacokinetic studies, since it is present in various forms in all the cells of the body. An efficient salvage and recycling system exists in the body, primarily in erythrocytes and blood vessel endothelial cells. The halflife in vitro is estimated to be less than 10 seconds, and may be even shorter in vivo.

storage

-20°C

Purification Methods

Crystallise adenosine from distilled water and dry it at 110o. It has been purified via the picrate, where ethanolic picric acid is added to adenosine and the picrate is filtered off and recrystallised from EtOH. It has m 180-185o(dec). Adenosine is recovered by dissolving 0.4g of the picrate in 80mL of hot H2O, treated with a small quantity of Dowex 1 anion exchange resin in the chloride form, and the resin is filtered off. The filtrate is treated with more resin and filtered again. One equivalent of aqueous NaOH is added to the colourless filtrate which is evaporated to 4mL and cooled to give 0.176g of adenosine m 236o. [Davoll et al. J Chem Soc 967 1948, Davoll & Lowy J Am Chem Soc 73 1650 1951, Beilstein 26 III/IV 3598.]

Precautions

Patients with second- or third-degree A-V block should not receive adenosine. As indicated previously, the use of adenosine in asthmatic patients may exacerbate the asthmatic symptoms.