Low basal expression of A2A adenosine receptors and increase in adenosine plasma concentration are associated with positive exercise stress testing

Adenosine Receptors Profile in Fibromuscular Dysplasia

Fibromuscular dysplasia (FMD) is a non-inflammatory vascular disease that is characterized by unexplained systemic hypertension occurring in young people, associated with arterial stenosis, aneurysm rupture, intracranial/renal infarction, and stroke. Although the gold standard for the diagnosis remains catheter-angiography, biological markers would be helpful due to the delay from first symptom to diagnosis. Adenosine is an ATP derivative, that may be implicated in FMD pathophysiology. We hypothesized that changes in adenosine blood level (ABL) and production of adenosine receptors may be associated with FMD. Using peripheral blood mononuclear cells, we evaluated A1, A2A, and A2B receptor production by Western blot, in 67 patients (17 men and 50 women, mean (range) age 55 (29−77) years and 40 controls, 10 men and 30 women, mean (range) age 56 (37−70)). ABL was evaluated by liquid chromatography, mass spectrometry. ABL was significantly higher in patients vs. controls, mean (range): 1.7 (0.7−3) µmol/L vs. controls 0.6 (0.4−0.8) µmol/L (+180%) p < 0.001. While A1R and A2AR production did not differ in patients and controls, we found an over-production of A2BR in patients: 1.70 (0.90−2.40; arbitrary units) vs. controls = 1.03 (0.70−1.40), mean + 65% (p < 0.001). A2BR production with a cut off of 1.3 arbitrary units, gives a good sensitivity and specificity for the diagnosis. Production measurement of A2BR on monocytes and ABL could help in the diagnosis, especially in atypical or with poor symptoms.

HILIC-MS/MS Analysis of Adenosine in Patient Blood

Adenosine is a purine ribonucleoside with important roles in various physiological processes. A number of studies have indicated the importance of adenosine in cardiovascular diseases including syncope; however, the accurate determination of adenosine in human blood is challenging due to the molecule’s instability. In the present study, we report a simple method for the pre-treatment of blood samples and the development of a fast and efficient hydrophilic interaction chromatographic tandem mass spectrometry method for the analysis of adenosine in patient blood. During collection, samples were mixed directly with a solvent mixture containing 95% acetonitrile and 10 mM ammonium formate in a Vacutainer tube, resulting in successful prevention of adenosine metabolic processes and direct blood sample deproteinization. The method was validated according to bioanalytical industry guidelines and found to be accurate, repeatable, specific and sensitive with LLOQ 0.005 μg/mL, thus allowing its application in the analysis of real clinical samples.

Hyperhomocysteinemia and Cardiovascular Disease: Is the Adenosinergic System the Missing Link?

The influence of hyperhomocysteinemia (HHCy) on cardiovascular disease (CVD) remains unclear. HHCy is associated with inflammation and atherosclerosis, and it is an independent risk factor for CVD, stroke and myocardial infarction. However, homocysteine (HCy)-lowering therapy does not affect the inflammatory state of CVD patients, and it has little influence on cardiovascular risk. The HCy degradation product hydrogen sulfide (H2S) is a cardioprotector. Previous research proposed a positive role of H2S in the cardiovascular system, and we discuss some recent data suggesting that HHCy worsens CVD by increasing the production of H2S, which decreases the expression of adenosine A2A receptors on the surface of immune and cardiovascular cells to cause inflammation and ischemia, respectively.

Recent advances in the role of the adenosinergic system in coronary artery disease

Adenosine is an endogenous nucleoside that plays a major role in the physiology and physiopathology of the coronary artery system, mainly by activating its A2A receptors (A2AR). Adenosine is released by myocardial, endothelial, and immune cells during hypoxia, ischaemia, or inflammation, each condition being present in coronary artery disease (CAD). While activation of A2AR improves coronary blood circulation and leads to anti-inflammatory effects, down-regulation of A2AR has many deleterious effects during CAD. A decrease in the level and/or activity of A2AR leads to: (i) lack of vasodilation, which decreases blood flow, leading to a decrease in myocardial oxygenation and tissue hypoxia; (ii) an increase in the immune response, favouring inflammation; and (iii) platelet aggregation, which therefore participates, in part, in the formation of a fibrin-platelet thrombus after the rupture or erosion of the plaque, leading to the occurrence of acute coronary syndrome. Inflammation contributes to the development of atherosclerosis, leading to myocardial ischaemia, which in turn leads to tissue hypoxia. Therefore, a vicious circle is created that maintains and aggravates CAD. In some cases, studying the adenosinergic profile can help assess the severity of CAD. In fact, inducible ischaemia in CAD patients, as assessed by exercise stress test or fractional flow reserve, is associated with the presence of a reserve of A2AR called spare receptors. The purpose of this review is to present emerging experimental evidence supporting the existence of this adaptive adenosinergic response to ischaemia or inflammation in CAD. We believe that we have achieved a breakthrough in the understanding and modelling of spare A2AR, based upon a new concept allowing for a new and non-invasive CAD management.

Homocysteine concentration and adenosine A2A receptor production by peripheral blood mononuclear cells in coronary artery disease patients

Hyperhomocysteinemia is associated with coronary artery disease (CAD). The mechanistic aspects of this relationship are unclear. In CAD patients, homocysteine (HCy) concentration correlates with plasma level of adenosine that controls the coronary circulation via the activation of adenosine A_2A receptors (A_2AR). We addressed in CAD patients the relationship between HCy and A_2AR production, and in cellulo the effect of HCy on A_2AR function. 46 patients with CAD and 20 control healthy subjects were included. We evaluated A_2AR production by peripheral blood mononuclear cells using Western blotting. We studied in cellulo (CEM human T cells) the effect of HCy on A_2A R production as well as on basal and stimulated cAMP production following A_2A R activation by an agonist‐like monoclonal antibody. HCy concentration was higher in CAD patients vs controls (median, range: 16.6 [7‐45] vs 8 [5‐12] µM, P < 0.001). A_2A R production was lower in patients vs controls (1.1[0.62‐1.6] vs 1.53[0.7‐1.9] arbitrary units, P < 0.001). We observed a negative correlation between HCy concentration and A_2A R production (r = −0.43; P < 0.0001), with decreased A_2A R production above 25 µM HCy. In cellulo, HCy inhibited A_2AR production, as well as basal and stimulated cAMP production. In conclusion, HCy is negatively associated with A_2A R production in CAD patients, as well as with A_2A R and cAMP production in cellulo. The decrease in A_2A R production and function, which is known to hamper coronary blood flow and promote inflammation, may support CAD pathogenesis.

Relationship between adenosine A2a receptor polymorphism rs5751876 and fractional flow reserve during percutaneous coronary intervention

Fractional flow reserve (FFR) assessed during adenosine-induced maximal hyperemia has emerged as a useful tool for the guidance of percutaneous coronary interventions (PCI). However, interindividual variability in the response to adenosine has been claimed as a major limitation to the use of adenosine for the measurement of FFR, carrying the risk of underestimating the severity of coronary stenoses, with potential negative prognostic consequences. Genetic variants of the adenosine receptor A2a (ADORA2A gene), located in the coronary circulation, have been involved in the modulation of the hyperemic response to adenosine. However, no study has so far evaluated the impact of the single nucleotide polymorphism rs5751876 of ADORA2A on the measurement of FFR in patients undergoing percutaneous coronary intervention that was, therefore, the aim of our study. We included patients undergoing coronary angiography and FFR assessment for intermediate (40-70%) coronary lesions. FFR measurement was performed by pressure-recording guidewire (Prime Wire, Volcano), after induction of hyperemia with intracoronary boli of adenosine (from 60 to 1440 μg, with dose doubling at each step). Restriction fragment length polymorphism (RFLP) analysis was performed to assess the presence of rs5751876 C>T polymorphism of ADORA2a receptor. We included 204 patients undergoing FFR measurement of 231 coronary lesions. A total of 134 patients carried the polymorphism (T allele), of whom 41 (30.6%) in homozygosis (T/T).Main clinical and angiographic features did not differ according to ADORA2A genotype. The rs5751876 C>T polymorphism did not affect mean FFR values (p = 0.91), the percentage of positive FFR (p = 0.54) and the duration of maximal hyperemia. However, the time to recovery to baseline FFR values was more prolonged among the T-allele carriers as compared to wild-type patients (p = 0.04). Based on these results, in patients with intermediate coronary stenoses undergoing FFR assessment with adenosine, the polymorphism rs5751876 of ADORA2A does not affect the peak hyperemic response to adenosine and the results of FFR. However, a more prolonged effect of adenosine was observed in T-carriers.

Adenosine Receptor Profiling Reveals an Association between the Presence of Spare Receptors and Cardiovascular Disorders

Adenosine and its receptors exert a potent control on the cardiovascular system. This review aims to present emerging experimental evidence supporting the existence and implication in cardiovascular disorders of specific adenosinergic pharmacological profiles, conforming to the concept of "receptor reserve", also known as "spare receptors". This kind of receptors allow agonists to achieve their maximal effect without occupying all of the relevant cell receptors. In the cardiovascular system, spare adenosine receptors appear to compensate for a low extracellular adenosine level and/or a low adenosine receptor number, such as in coronary artery disease or some kinds of neurocardiogenic syncopes. In both cases, the presence of spare receptors appears to be an attempt to overcome a weak interaction between adenosine and its receptors. The identification of adenosine spare receptors in cardiovascular disorders may be helpful for diagnostic purposes.

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

Extracellular vesicles (EV) can transfer cellular molecules for specific intercellular communication with potential relevance in pathological conditions. We searched for the presence in plasma from coronary artery disease (CAD) patients of EV containing the adenosine A_2A receptor (A_2AR), a signalling receptor associated with myocardial ischaemia and whose expression is related to homocysteine (HCy) metabolism. Using protein organic solvent precipitation for plasma EV preparation and Western blotting for protein identification, we found that plasma from CAD patients contained various amounts of EV with ubiquitin bound to A_2AR. Interestingly, the presence of ubiquitinated A_2AR in EV from patients was dependent on hyperhomocysteinemia, the amount being inversely proportional to A_2AR expression in peripheral mononuclear cells in patients with the highest levels of HCy. CEM, a human T cell line, was also found to released EV containing various amounts of ubiquitinated A_2AR in stimulated conditions depending on the hypoxic status and HCy level of culture medium. Together, these data show that ubiquitinated A_2AR‐containing EV circulate in the plasma of CAD patients and that this presence is related to hyperhomocysteinemia. A_2AR in plasma EV could be a useful tool for diagnosis and a promising drug for the treatment of CAD.

Uric acid levels are associated with endothelial dysfunction and severity of coronary atherosclerosis during a first episode of acute coronary syndrome

The role of serum uric acid in coronary artery disease has been extensively investigated. It was suggested that serum uric acid level (SUA) is an independent predictor of endothelial dysfunction and related to coronary artery lesions. However, the relationship between SUA and severity of coronary atherosclerosis evaluated via endothelial dysfunction using peripheral arterial tone (PAT) and the reactive hyperhemia index (RHI) has not been investigated during a first episode of acute coronary syndrome (ACS). The aim of our study was to address this point. We prospectively enrolled 80 patients with a first episode of ACS in a single-center observational study. All patients underwent coronary angiography, evaluation of endothelial function via the RHI, and SUA measurement. The severity of the coronary artery lesion was assessed angiographically, and patients were classified in three groups based on the extent of disease and Gensini and SYNTAX scores. Endothelial function was considered abnormal if RHI < 1.67. We identified a linear correlation between SUA and RHI (R² = 0.66 P < 0.001). In multivariable analyses, SUA remained associated with RHI, even after adjustment for traditional cardiovascular risk factors and renal function. SUA was associated with severity of coronary artery disease. SUA is associated with severity of coronary atherosclerosis in patients with asymptomatic hyperuricemia. This inexpensive, readily measured biological parameter may be useful to monitor ACS patients.

Specific Pharmacological Profile of A2A Adenosine Receptor Predicts Reduced Fractional Flow Reserve in Patients With Suspected Coronary Artery Disease

Background

The rapid and reliable exclusion of myocardial revascularization is a major unmet clinical need in patients with suspected coronary artery disease (CAD) and non‐contributive electrocardiography and troponin. Non‐invasive tests have high rates of false positives and negatives, and there is no biomarker to assess myocardial ischemia. The presence of spare adenosine A_2A receptors (A_2AR)—characterized by a high dissociation constant/half maximal effective concentration (K_D/EC₅₀) ratio—expressed on peripheral blood mononuclear cells (PBMC) has been associated with ischemia during exercise stress testing in patients with CAD. In this work, we investigated the diagnostic accuracy of spare A_2AR versus fractional flow reserve (FFR) in patients with suspected CAD.

Methods and Results

Sixty patients with suspected CAD, but non‐contributive electrocardiography and troponin, were consecutively enrolled in this prospective study. The binding (K_D), functional response (cyclic adenosine monophosphate [cAMP] production; EC₅₀) on PBMC A_2AR were compared with FFR results. Patients were divided into 3 groups: 17 (group 1) with normal coronary angiography (n=13) or stenosis <20% (n=4); 21 with CAD and non‐significant FFR (group 2); and 22 with CAD and significant FFR (group 3). Median K_D/EC₅₀ was 6‐fold higher in group 3 (4.20; interquartile range: 2.81–5.00) than group 2 (0.66; interquartile range: 0.47–1.25) and 7‐fold higher than group 1 (0.60; interquartile range: 0.30–0.66).

Conclusions

In patients with suspected CAD and non‐contributive electrocardiography and troponin, the absence of spare A_2AR on PBMC may help to rule out myocardial ischemia.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT03218007.

Uric acid levels are associated with endothelial dysfunction and severity of coronary atherosclerosis during a first episode of acute coronary syndrome

The role of serum uric acid in coronary artery disease has been extensively investigated. It was suggested that serum uric acid level (SUA) is an independent predictor of endothelial dysfunction and related to coronary artery lesions. However, the relationship between SUA and severity of coronary atherosclerosis evaluated via endothelial dysfunction using peripheral arterial tone (PAT) and the reactive hyperhemia index (RHI) has not been investigated during a first episode of acute coronary syndrome (ACS). The aim of our study was to address this point. We prospectively enrolled 80 patients with a first episode of ACS in a single-center observational study. All patients underwent coronary angiography, evaluation of endothelial function via the RHI, and SUA measurement. The severity of the coronary artery lesion was assessed angiographically, and patients were classified in three groups based on the extent of disease and Gensini and SYNTAX scores. Endothelial function was considered abnormal if RHI < 1.67. We identified a linear correlation between SUA and RHI (R² = 0.66 P < 0.001). In multivariable analyses, SUA remained associated with RHI, even after adjustment for traditional cardiovascular risk factors and renal function. SUA was associated with severity of coronary artery disease. SUA is associated with severity of coronary atherosclerosis in patients with asymptomatic hyperuricemia. This inexpensive, readily measured biological parameter may be useful to monitor ACS patients.

Expressions of adenosine A2A receptors in coronary arteries and peripheral blood mononuclear cells are correlated in coronary artery disease patients

BACKGROUND

Altered coronary blood flow occurs in patients with coronary artery disease (CAD). Adenosine strongly impacts blood flow mostly via adenosine A_2A receptor (A_2AR) expressed in coronary tissues. As part of a systemic regulation of the adenosinergic system, we compared A_2AR expression in situ, and on peripheral blood mononuclear cells (PBMC) in CAD patients.

METHODS AND RESULTS

Aortic and coronary tissues, and PBMC were sampled in 20 CAD patients undergoing coronary artery bypass surgery and consecutively included. Controls were PBMC obtained from 15 healthy subjects. Expression and activity of A_2AR were studied by Western blotting and cAMP measurement, respectively. A_2AR expression on PBMC was lower in patients than in controls (0.83±0.31 vs 1.2±0.35 arbitrary units; p<0.01), and correlated with A_2AR expression in coronary and aortic tissues (Pearson's r: 0.77 and 0.59, p<0.01, respectively). Basal and maximal cAMP productions following agonist stimulation of PBMC were significantly lower in patients than in controls (120±42 vs 191±65 and 360±113 vs 560±215pg/10⁶ cells, p<0.05, respectively). In CAD patients, the increase from basal to maximal cAMP production in PBMC and aortic tissues was similar (+300% and +246%, respectively).

CONCLUSION

Expression of A_2AR on PBMC correlated with those measured in coronary artery and aortic tissues in CAD patients, A_2AR activity of PBMC matched that observed in aorta, and A_2AR expression and activity in PBMC were found reduced as compared to controls. Measuring the expression level of A_2AR on PBMC represents a good tool to address in situ expression in coronary tissues of CAD patients.

Spare Adenosine A2a Receptors Are Associated With Positive Exercise Stress Test In Coronary Artery Disease

During exercise, cardiac oxygen-consumption increases and the resulting low oxygen level in myocardium triggers coronary vasodilation. This response to hypoxia is controlled notably by the vasodilator adenosine and its A_2A receptor (A_2AR). According to the "spare receptor" pharmacological model, a strong A_2AR-mediated response can occur in the context of a large number of receptors remaining unoccupied, activation of only a weak fraction of A_2AR (evaluated using K_D) resulting in maximal cAMP production (evaluated using EC₅₀), 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_2AR are 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_2AR-expression at the mononuclear cell-surface, which reflects cardiovascular expression. The presence of spare A_2AR 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 only (p<0.01). Most patients (65%), and none of the controls, had spare A_2AR (identified when EC₅₀/K_D≤0.1) and a low A_2AR-expression (mean: -37% vs controls; p<0.01). All patients with spare A_2AR had a positive EST whereas the subjects without spare A_2AR had a negative EST (p<0.05). Spare A_2AR are therefore associated with positive EST in CAD patients and their detection may be used as a diagnostic marker.