Adenosine-mediated Protection Research Articles

Ticagrelor for the primary prevention of stroke in patients with coronary artery disease: a systematic review and meta-analysis of randomized controlled trials.

Coronary artery disease (CAD) patients had a higher risk of first-ever stroke than general population even when they were on antiplatelet treatment. It was unknown whether more potent antiplatelet inhibitor ticagrelor which also provided adenosine-mediated protection would improve the primary stroke prevention for CAD. PubMed, Embase, Web of Science and CERNTRAL were searched for randomized clinical trials (RCTs) comparing efficacy and safety outcomes of over 30-day use of ticagrelor versus other antiplatelet drugs or placebo in patients with acute or chronic coronary syndrome. RCTs involving patients with any stroke history were excluded. Based on 5 RCTs with 45,843 patients, ticagrelor-involving regimens significantly reduced first-ever strokes (risk ratio [RR] 0.81; 95% confidential interval [CI] 0.71-0.94; I2 = 0%) in comparison to other antiplatelet regimens in CAD, where the benefits in reducing ischemic strokes (IS) (RR 0.80; 95% CI 0.68-0.94; I2 = 0%) was not canceled out by the increase of intracranial hemorrhage (ICH) (RR 1.41; 95% CI 1.05-1.89; I2 = 0%). According to results of subgroup analyses, the protective effects of ticagrelor on first-ever stroke were more significant with treatment duration of more than 1year, dosage of 60mg twice daily, and in clinical settings of chronic coronary syndrome. In conclusion, available evidence from aggregate data supported a modest advantage of ticagrelor-involving regimens for the primary stroke prevention in CAD compared with other antiplatelet regimens after the trade-off between reducing IS and inducing ICH, where more benefits might be expected from long-term and low-dose use of ticagrelor among patients with chronic coronary syndrome. Further collaborative meta-analysis of individual participant data from well-designed and statistically-powered trials would be needed to generate high quality evidence on this issue.

Epithelial-specific A2B adenosine receptor signaling protects the colonic epithelial barrier during acute colitis.

Central to inflammatory bowel disease (IBD) pathogenesis is loss of mucosal barrier function. Emerging evidence implicates extracellular adenosine signaling in attenuating mucosal inflammation. We hypothesized that adenosine-mediated protection from intestinal barrier dysfunction involves tissue-specific signaling through the A2B adenosine receptor (Adora2b) at the intestinal mucosal surface. To address this hypothesis, we combined pharmacologic studies and studies in mice with global or tissue-specific deletion of the Adora2b receptor. Adora2b(-/-) mice experienced a significantly heightened severity of colitis, associated with a more acute onset of disease and loss of intestinal epithelial barrier function. Comparison of mice with Adora2b deletion on vascular endothelial cells (Adora2b(fl/fl)VeCadCre(+)) or intestinal epithelia (Adora2b(fl/fl)VillinCre(+)) revealed a selective role for epithelial Adora2b signaling in attenuating colonic inflammation. In vitro studies with Adora2b knockdown in intestinal epithelial cultures or pharmacologic studies highlighted Adora2b-driven phosphorylation of vasodilator-stimulated phosphoprotein (VASP) as a specific barrier repair response. Similarly, in vivo studies in genetic mouse models or treatment studies with an Adora2b agonist (BAY 60-6583) recapitulate these findings. Taken together, our results suggest that intestinal epithelial Adora2b signaling provides protection during intestinal inflammation via enhancing mucosal barrier responses.

The conundrum of protection from AKI by adenosine in rodent clamp ischemia models

Kim et al. show that isoflurane uses a tubule-based transforming growth factor-β/CD73-dependent process that generates adenosine to protect mice from ischemic acute kidney injury (AKI) with effects to prevent the 'no-reflow phenomenon' and decrease inflammation. While direct cytoprotection occurred in culture, extensive research suggests that in vivo adenosine protection from rodent ischemic AKI is mediated by a mutually cooperative mechanism involving blood flow, inflammation, and innate immunity through multiple adenosine receptors with promiscuous actions on diverse cell types.

Differential cardioprotective effects of cardiac and non-cardiac adenosine during global ischemia and reperfusion

Simultaneous inhibition of adenosine deaminase with 9-erythro(2-hydroxy-3nonyl)adenine (EHNA)] and nucleoside transport (es-ENT1) system with p-nitrobenzylmercapto-purine riboside (NBMPR) before ischemia allows diffrentiation between cardiac and non-cardiac adenosine-mediated protection, in vivo. Methods: Hearts of anesthetized dogs (n=45) were instrumented to measure global function, in vivo. A vehicle solution (Series A) or a vehicle solution containing 100 μM EHNA and 25 μM of NBMPR (Series B) was infused into the CPB before subjecting the hearts to 30 min of normothermic aortic cross clamping (NACC) and 60 min of reperfusion. Animals in Series A and B were divided to receive a single intracoronary infusion of saline (Control group), 100 μM 8-SPT or 10 μM DPCPX immediately following NACC. ATP pool intermediates were determined using HPLC. Results: Adenosine/inosine ration during ischemia was 10-folds higher in B groups than in series A groups. At the end of reperfusion, both 8-SPT and DPPX treatments resulted in an equal reduction in LV function regardless of ENA/NBMPR treatment (Series A vs. B). Conclusion: Blockade of surface A1-R slightly reduced but failed to totally abolish cardioprotection offered by entrapment of cardiac adenosine. Non-cardiac adenosine plays a modest role in the overall myocardial recovery with EHNA/NBMPR. Entrapment of cardiac adenosine play a major role in EHNA/NBMPR mediated cardioprotection independent of surface A1-R.

Ischaemic tolerance in aged mouse myocardium: the role of adenosine and effects of A1 adenosine receptor overexpression.

The genesis of the ischaemia intolerant phenotype in aged myocardium is poorly understood. We tested the hypothesis that impaired adenosine-mediated protection contributes to ischaemic intolerance, and examined whether this is countered by A1 adenosine receptor (A1AR) overexpression. Responses to 20 min ischaemia and 45 min reperfusion were assessed in perfused hearts from young (2-4 months) and moderately aged (16-18 months) mice. Post-ischaemic contractility was impaired by ageing with elevated ventricular diastolic (32 +/- 2 vs. 18 +/- 2 mmHg in young) and reduced developed (37 +/- 3 vs. 83 +/- 6 mmHg in young) pressures. Lactate dehydrogenase (LDH) loss was exaggerated (27 +/- 2 vs. 16 +/- 2 IU g-1 in young) whereas the incidence of tachyarrhythmias was similar in young (15 +/- 1 %) and aged hearts (16 +/- 1 %). Functional analysis confirmed equipotent effects of 50 micro M adenosine at A1 and A2 receptors in young and aged hearts. Nonetheless, while 50 micro M adenosine improved diastolic (5 +/- 1 mmHg) and developed pressures (134 +/- 7 mmHg) and LDH loss (6 +/- 2 IU g-1) in young hearts, it did not alter these variables in the aged group. Adenosine did attenuate arrhythmogenesis for both ages (to ~10 %). In contrast to adenosine, 50 micro M diazoxide reduced ischaemic damage and arrhythmogenesis for both ages. Contractile and anti-necrotic effects of adenosine were limited by 100 micro M 5-hydroxydecanoate (5-HD) and 3 micro M chelerythrine. Anti-arrhythmic effects were limited by 5-HD but not chelerythrine. Non-selective (100 micro M 8-sulfophenyltheophylline) and A1-selective (150 nM 8-cyclopentyl-1,3-dipropylxanthine) adenosine receptor antagonism impaired ischaemic tolerance in young but not aged hearts. Quantitative real-time PCR and radioligand analysis indicated that impaired protection is unrelated to changes in A1AR mRNA transcription, or receptor density (~8 fmol mg-1 protein in both age groups). However, A1AR overexpression improved tolerance for both ages, restoring adenosine-mediated protection. These data reveal impaired protection via exogenous and endogenous adenosine contributes to ischaemic intolerance with ageing. This is independent of A1AR expression, and involves ineffective activation of a 5-HD-/diazoxide-sensitive process. The effects of A1AR overexpression indicate that the age-related failure in signalling can be overcome.

Receptor and non-receptor-dependent mechanisms of cardioprotection with adenosine.

The relative roles of mitochondrial (mito) ATP-sensitive K(+) (mitoK(ATP)) channels, protein kinase C (PKC), and adenosine kinase (AK) in adenosine-mediated protection were assessed in Langendorff-perfused mouse hearts subjected to 20-min ischemia and 45-min reperfusion. Control hearts recovered 72 +/- 3 mmHg of ventricular pressure (50% preischemia) and released 23 +/- 2 IU/g lactate dehydrogenase (LDH). Adenosine (50 microM) during ischemia-reperfusion improved recovery (149 +/- 8 mmHg) and reduced LDH efflux (5 +/- 1 IU/g). Treatment during ischemia alone was less effective. Treatment with 50 microM diazoxide (mitoK(ATP) opener) during ischemia and reperfusion enhanced recovery and was equally effective during ischemia alone. A(3) agonism [100 nM 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide], A(1) agonism (N(6)-cyclohexyladenosine), and AK inhibition (10 microM iodotubercidin) all reduced necrosis to the same extent as adenosine, but less effectively reduced contractile dysfunction. These responses were abolished by 100 microM 5-hydroxydecanoate (5-HD, mitoK(ATP) channel blocker) or 3 microM chelerythrine (PKC inhibitor). However, the protective effects of adenosine during ischemia-reperfusion were resistant to 5-HD and chelerythrine and only abolished when inhibitors were coinfused with iodotubercidin. Data indicate adenosine-mediated protection via A(1)/A(3) adenosine receptors is mitoK(ATP) channel and PKC dependent, with evidence for a downstream location of PKC. Adenosine provides additional and substantial protection via phosphorylation to 5'-AMP, primarily during reperfusion.

Adenosine Preconditioning of Human Myocardium is Dependent upon the ATP-sensitive K+Channel

Evidence supports the involvement of adenosine receptor stimulation and activation of KATPchannels in ischemic preconditioning of human myocardium. It is unknown, however, whether protection mediated by adenosine receptors is dependent upon the KATPchannel in the human heart. The purpose of this study was to determine whether adenosine-mediated protection against a simulated ischemia–reperfusion injury in human myocardium is dependent upon KATPchannels. Isolated human right atrial trabeculae were placed in tissue baths at 37°C, oxygenated with a modified Tyrode solution, and field stimulated at 1 Hz. Trabeculae were subjected to 45 min of normothermic simulated ischemia (hypoxic, substrate-free buffer with pacing at 3 Hz.) and 60 min of reperfusion (I/R trabeculae). Trabeculae were preconditioned with simulated ischemia (IPC trabeculae) or adenosine receptor stimulation (adenosine, 125 μmol/l) for 5 min (ADO trabeculae) prior to simulated ischemic–reperfusion injury. Inhibition of the KATPchannel with glibenclamide (10 μmol/l) was combined with adenosine pretreatment (ADO+GLI trabeculae) or alone (GLI trabeculae) prior to simulated ischemic–reperfusion injury. Developed force (DF) at end reperfusion (mean±s.e.) was compared to baseline developed force, and tissue creatine kinase (CK) activity at end reperfusion was measured. I/R trabeculae showed 27±2% of baseline DF, whereas IPC trabeculae or ADO trabeculae showed 50±4% and 43±3% of baseline DF, respectively. ADO+GLI trabeculae showed 25±2% and GLI trabeculae showed 23±4% of baseline DF. Tissue CK activity was enhanced in the IPC and ADO trabeculae (433±63 U/g wet myocardium, and 415±28 U/g wet myocardium, respectively). I/R trabeculae had 196±26 U/g wet myocardium and ADO+GLI trabeculae had 277±38 U/g wet myocardium at end reperfusion. The results suggest that ischemic preconditioning and adenosine receptor stimulation confer functional protection against simulated ischemic-reperfusion, and adenosine mediated protection is eliminated by KATPchannel inhibition in human myocardium.

Protective effects of adenosine in the reversibly injured heart

There is substantial evidence that the nucleoside adenosine reduces postischemic ventricular dysfunction (ie, myocardial stunning). Studies performed in our laboratory have attempted to address the mechanism of adenosine-mediated protection of the reversibly injured heart. Experiments were performed in isolated perfused rat and rabbit hearts and in in situ canine and porcine preparations. The role of adenosine A1 receptors was assessed by using adenosine A1 receptor agonists and antagonists, and by measuring interstitial fluid purine levels with the cardiac microdialysis technique. In isolated perfused hearts, treatment immediately before ischemia with adenosine and adenosine A1 receptor analogues significantly improved postischemic ventricular function, effects that were blocked by a selective adenosine A1 receptor antagonist. In in situ canine and porcine preparations, pretreatment with adenosine and an adenosine deaminase inhibitor increased preischemic interstitial fluid adenosine levels and attenuated regional myocardial stunning. Adenosine treatment was also associated with improved myocardial phosphorylation potential in isolated guinea pig hearts and in the in situ porcine preparation. These results suggest that adenosine-induced attenuation of myocardial stunning is mediated via adenosine A1 receptor activation and enhancement of postischemic myocardial phosphorylation potential.

G-protein control of cardiac potassium channels

Two cardiac potassium (K +) channels are activated by pertussis toxin (PTX)-sensitive G proteins either directly or in a “membrane-delimited” manner. They are muscarinic K +(K ACH) and ATP-sensitive K +(K ATP) channels. K ACH channels are responsible for acetylcholine (ACh)- or adenosine-induced deceleration of the heartbeat and atrioventricular conduction, while K ATP channels are responsible for the ischemia-induced shortening of the cardiac action potential and possibly for the adenosine-mediated protection from ischemic damage. Distinct molecular mechanisms underlie G-protein activation of these cardiac K + channels; the α subunit of PTX-sensitive G proteins activates the K ATP channels, while βγ subunits activate the K ACh channel. The physiologic significance of this heterogeneous mechanism remains to be determined.