Spare Adenosine A2a Receptors Are Associated with Positive Exercise Stress Test in Coronary Artery Disease

Abstract

During exercise, cardiac oxygen consumption increases and the resulting low oxygen level in the myocardium triggers coronary vasodilation. This response to hypoxia is controlled notably by the vasodilator adenosine and its A 2A receptor (A 2A R). According to the "spare receptor" pharmacological model, a strong A 2A R-mediated response can occur in the context of a large number of receptors remaining unoccupied, the activation of only a weak fraction of A 2A R (evaluated using K D ), which results in maximal cAMP production (evaluated using EC 50 ), and hence in maximal coronary vasodilation. In coronary artery disease (CAD), myocardial ischemia limits adaptation to exercise, which is commonly detected using the exercise stress test (EST). We hypothesized that spare A 2A R is present in CAD patients to correct ischemia. Seventeen patients with angiographically documented CAD and 17 control subjects were studied. We addressed adenosine-plasma concentration and A 2A R-expression at the mononuclear cell-surface, which reflects cardiovascular expression. The presence of spare A 2A R was tested using an innovative pharmacological approach based on a homemade monoclonal antibody with agonist properties. EST was positive in 82% of patients and in none of the controls. Adenosine plasma concentration increased by 60% at peak exercise in patients and in none of the controls (p < 0.01). Most patients (65%), and none of the controls, had spare A 2A R (identified when EC 50 /K D ≤ 0.1) and a low A 2A R-expression (mean: -37% versus controls; p < 0.01). All patients with spare A 2A R had a positive EST whereas the subjects without spare A 2A R had a negative EST (p < 0.05). Spare A 2A R is therefore associated with positive EST in CAD patients and its detection may be used as a diagnostic marker.

Extracellular vesicles with ubiquitinated adenosine A2A receptor in plasma of patients with coronary artery disease

“…In CAD, one could hypothesize that A 2A R circulate from donor cells to target cells as a salvage pathway to be stimulated by adenosine when vasodilation is required for oxygen delivery in failing artery tissues. This mechanism may explain the low expression of A 2A R with spare receptor characteristics (EC 50 < K D ) found in PBMC from CAD patients presenting a major cardiovascular risk by a release from the cells into the blood of EV carrying A 2A R, constituting a circulating pool of receptors.…”

“…Extracellular vesicles and PBMC were analysed by Western blotting as previously reported. [11][12][13][14][15] Briefly, freeze-dried EV corresponding to 100 µL of plasma and cell pellets corresponding to 0.25 × 10 6 PBMC were solubilized in 15 µL Laemmli sample buffer (BioRad) with 5% SDS, 5% 2-mercaptoethanol and a complete set of protease inhibitors (Roche), heated for 5 minutes at 95°C and loaded on 12% SDS-PAGE minigel (BioRad). Prestained molecular weight markers (BioRad) have always been loaded onto the gel.…”

“…10 A 2A R from patients with coronary artery disease (CAD) is poorly expressed and, consequently, produces low level of cAMP, two characteristics that are associated with myocardial ischaemia, as documented by positive exercise stress testing or reduced flow reserve. [11][12][13] The down-regulation of A 2A R expression in CAD patients is related to the homocysteine (HCy) metabolism via its degradation product H 2 S. 14 Circulating EV can be considered as a reserve of functional G protein-coupled receptors as previously suggested from data obtained on a mouse model of heart cellular stress for angiotensin II type 1 receptor. 16 Taking into account the major role of A 2A R in cardiovascular disease and the potential contribution of circulating EV in delivering cell receptor from donor to target cells, we searched for the presence of A 2A R in EV from plasma of patients with CAD and culture supernatant of human lymphoblastoid T cells cultured in CAD-like conditions.…”

“…Among them, the A 2A receptor (A 2A R) is strongly expressed in coronary cells and its activation increases coronary blood flow, partly through the production of cAMP in target cells . A 2A R from patients with coronary artery disease (CAD) is poorly expressed and, consequently, produces low level of cAMP, two characteristics that are associated with myocardial ischaemia, as documented by positive exercise stress testing or reduced flow reserve . The down‐regulation of A 2A R expression in CAD patients is related to the homocysteine (HCy) metabolism via its degradation product H 2 S .…”

Rapid Measurement of Adenosine Concentration in Human Blood Using Fixed Potential Amperometry: Comparison with Mass Spectrometry and High- Performance Liquid Chromatography

“…Adenosine is an ATP derivative that is implicated in a lot of cardiovascular and neurological diseases including neurocardiogenic syncope [1][2][3], coronary artery diseases [4,5], neuropathic pain [6], septic shock [7] and severe systemic inflammatory response [8]. Thus, measurig adenosine in blood may be helpful for some pathologies.…”