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MSX-3, MSX-4, and MSX-2 are xanthines and are derivatives of the non-selective adenosine receptor antagonist caffeine. [5] [6] MSX-2 has been extensively studied due to its high affinity and selectivity for the adenosine A 2A receptor, but use of MSX-2 itself has been limited by its poor water solubility.
Caffeine is an antagonist of all four adenosine receptor subtypes (A 1, A 2A, A 2B, and A 3), although with varying potencies. [5] [167] The affinity (K D) values of caffeine for the human adenosine receptors are 12 μM at A 1, 2.4 μM at A 2A, 13 μM at A 2B, and 80 μM at A 3. [167]
Caffeine keeps you awake by blocking adenosine receptors. Each type of adenosine receptor has different functions, although with some overlap. [3] For instance, both A 1 receptors and A 2A play roles in the heart, regulating myocardial oxygen consumption and coronary blood flow, while the A 2A receptor also has broader anti-inflammatory effects throughout the body. [4]
It is a xanthine and a derivative of the non-selective adenosine receptor antagonist caffeine. [ 1 ] [ 2 ] The affinities (K i ) of MSX-2 for the human adenosine receptors are 5.38 to 14.5 nM for the adenosine A 2A receptor, 2,500 nM for the adenosine A 1 receptor (172- to 465-fold lower than for the A 2A receptor), and >10,000 nM for the ...
DMPX (3,7-dimethyl-1-propargylxanthine) is a caffeine analog which displays affinity for A 2 adenosine receptors, in contrast to the A 1 subtype receptors. [1] DMPX had 28 times and 15 times higher potency than caffeine in blocking, respectively, the peripheral and central effects of the adenosine agonist NECA.
A crystal structure of the A 2A receptor bound with the agonist NECA and a G protein-mimic has been published in 2016 (PDB code: 5g53). [20] The encoded protein (the A 2A receptor) is abundant in basal ganglia, vasculature, T lymphocytes, and platelets and it is a major target of caffeine, which is a competitive antagonist of this protein. [21]
Caffeine exerts its psychoactive and sympathomimetic effects by acting as an antagonist at adenosine receptors. [9] d9-Caffeine was assessed for human adenosine receptor antagonism at the four receptor subtypes: A1, A2A, A2B, and A3, and found to have similar adenosine receptor affinity as caffeine. [3]
Studies indicate that, similar to caffeine, simultaneous antagonism of adenosine receptors [9] is responsible for paraxanthine's stimulatory effects. Paraxanthine adenosine receptor binding affinity (21 μM for A1, 32 μM for A2 A, 4.5 μM for A2 B, and >100 for μM for A3) is similar or slightly stronger than caffeine, but weaker than theophylline.