Adenosinerelated

Adenosine-related refers to processes, molecules, and pathways centered on the nucleoside adenosine and its derivatives. Adenosine is a purine nucleoside composed of adenine attached to ribose. It plays roles as a building block of energy carriers and as a signaling molecule that coordinates cellular responses to energy status, stress, and inflammation.

Biochemical origin and metabolism: Adenosine is produced intracellularly from AMP and can be generated extracellularly by surface enzymes such as CD39 and CD73. It is cleared from the extracellular space by uptake into cells via nucleoside transporters and by enzymatic degradation to inosine through adenosine deaminase. These pathways regulate the local concentration and signaling outcomes of adenosine.

Adenosine acts mainly through four G protein–coupled receptors: A1, A2A, A2B, and A3. A1 and A3 generally inhibit adenylyl cyclase, lowering cAMP, while A2A and A2B stimulate it, increasing cAMP. Receptor distribution and affinity create tissue-specific effects, including modulation of heart rate and conduction, vasodilation, neuroprotection, and anti-inflammatory actions. Caffeine, a nonselective antagonist, can enhance wakefulness by blocking adenosine signaling.

Clinical uses and pharmacology: Adenosine itself is used acutely to terminate certain supraventricular tachycardias due to transient AV node block and very short half-life, administered intravenously. In diagnostic imaging, selective A2A agonists such as regadenoson are used as vasodilators in myocardial perfusion tests, while agents that affect adenosine uptake, like dipyridamole, enhance endogenous adenosine signaling.

Research and broader relevance: The adenosine pathway is implicated in tumor immunology and inflammatory disease, where high extracellular adenosine can suppress immune responses via A2A receptors. Therapeutic strategies include adenosine pathway inhibitors or receptor antagonists to modulate inflammation or enhance anti-tumor immunity.