Additive protection against lung ischemia-reperfusion injury by adenosine A2A receptor activation before procurement and during reperfusion

Transient receptor potential vanilloid 4 channel inhibition attenuates lung ischemia-reperfusion injury in a porcine lung transplant model

OBJECTIVE

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel important in many physiological and pathophysiological processes, including pulmonary disease. Using a murine model, we previously demonstrated that TRPV4 mediates lung ischemia-reperfusion injury, the major cause of primary graft dysfunction after transplant. The current study tests the hypothesis that treatment with a TRPV4 inhibitor will attenuate lung ischemia-reperfusion injury in a clinically relevant porcine lung transplant model.

METHODS

A porcine left-lung transplant model was used. Animals were randomized to 2 treatment groups (n = 5/group): vehicle or GSK2193874 (selective TRPV4 inhibitor). Donor lungs underwent 30 minutes of warm ischemia and 24 hours of cold preservation before left lung allotransplantation and 4 hours of reperfusion. Vehicle or GSK2193874 (1 mg/kg) was administered to the recipient as a systemic infusion after recipient lung explant. Lung function, injury, and inflammatory biomarkers were compared.

RESULTS

After transplant, left lung oxygenation was significantly improved in the TRPV4 inhibitor group after 3 and 4 hours of reperfusion. Lung histology scores and edema were significantly improved, and neutrophil infiltration was significantly reduced in the TRPV4 inhibitor group. TRPV4 inhibitor-treated recipients had significantly reduced expression of interleukin-8, high mobility group box 1, P-selectin, and tight junction proteins (occludin, claudin-5, and zonula occludens-1) in bronchoalveolar lavage fluid as well as reduced angiopoietin-2 in plasma, all indicative of preservation of endothelial barrier function.

CONCLUSIONS

Treatment of lung transplant recipients with TRPV4 inhibitor significantly improves lung function and attenuates ischemia-reperfusion injury. Thus, selective TRPV4 inhibition may be a promising therapeutic strategy to prevent primary graft dysfunction after transplant.

Adenosinergic metabolism pathway: an emerging target for improving outcomes of solid organ transplantation

Extracellular nucleotides are widely recognized as crucial modulators of immune responses in peripheral tissues. Adenosine triphosphate (ATP) and adenosine are key components of extracellular nucleotides, the balance of which contributes to immune homeostasis. Under tissue injury, ATP exerts its pro-inflammatory function, while the adenosinergic pathway rapidly degrades ATP to immunosuppressive adenosine, thus inhibiting excessive and uncontrolled inflammatory responses. Previous reviews have explored the immunoregulatory role of extracellular adenosine in various pathological conditions, especially inflammation and malignancy. However, current knowledge regarding adenosine and adenosinergic metabolism in the context of solid organ transplantation remains fragmented. In this review, we summarize the latest information on adenosine metabolism and the mechanisms by which it suppresses the effector function of immune cells, as well as highlight the protective role of adenosine in all stages of solid organ transplantation, including reducing ischemia reperfusion injury during organ procurement, alleviating rejection, and promoting graft regeneration after transplantation. Finally, we discuss the potential for future clinical translation of adenosinergic pathway in solid organ transplantation.

Primary graft dysfunction following lung transplantation: From pathogenesis to future frontiers

Lung transplantation is the treatment of choice for patients with end-stage lung disease. Currently, just under 5000 lung transplants are performed worldwide annually. However, a major scourge leading to 90-d and 1-year mortality remains primary graft dysfunction. It is a spectrum of lung injury ranging from mild to severe depending on the level of hypoxaemia and lung injury post-transplant. This review aims to provide an in-depth analysis of the epidemiology, pathophysiology, risk factors, outcomes, and future frontiers involved in mitigating primary graft dysfunction. The current diagnostic criteria are examined alongside changes from the previous definition. We also highlight the issues surrounding chronic lung allograft dysfunction and identify the novel therapies available for ex-vivo lung perfusion. Although primary graft dysfunction remains a significant contributor to 90-d and 1-year mortality, ongoing research and development abreast with current technological advancements have shed some light on the issue in pursuit of future diagnostic and therapeutic tools.

Shufeng Jiedu capsule inhibits inflammation and apoptosis by activating A2AAR and inhibiting NF-κB to alleviate LPS-induced ALI

ETHNOPHARMACOLOGICAL RELEVANCE

Shufeng Jiedu capsule (SFJDC) is a pure form of traditional Chinese medicine (TCM) that contains eight medicinal plants. Known for its anti-inflammatory and antipyretic effects, it is mostly used to treat upper respiratory tract infections and other infectious diseases, such as colds, pharyngitis, laryngitis, and tonsillitis. Both acute lung injury (ALI) and COVID-19 are closely related to lung damage, primarily manifesting as lung inflammation and epithelial cell damage. However, whether SFJDC can improve ALI and by what mechanism remain unclear. The purpose of this study was to explore whether SFJDC could be used as a prophylactic treatment for COVID-19 by improving acute lung injury.

AIM OF THE STUDY

The purpose of this study was to determine whether SFJDC could protect against ALI caused by lipopolysaccharide (LPS), and we wanted to determine how SFJDC reduces inflammation and apoptosis pharmacologically and molecularly.

MATERIALS AND METHODS

Preadministering SFJDC at 0.1 g/kg, 0.3 g/kg, or 0.5 g/kg for one week was followed by 5 mg/kg LPS to induce ALI in mice. Observations included the study of lung histomorphology, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) secretion, as well as the ratio of lung wet/dry weights. In addition, RAW264.7 cells were treated for 24 h with 1 μg/mL LPS after being pretreated for 1 h with 0.5 mg/mL SFJDC. In the samples, we detected TNF-α, IL-1β, and IL-6. Cell apoptosis was detected by stimulating A549 cells for 24 h with RAW264.7 supernatant. Both in vitro and in vivo, the levels of A2A adenosine receptor (A2AAR), PKA, IκB, p-IκB, NF-κB P65 (P65), p-NF-κB P65 (p-P65), cleaved caspases-3 (Cc3), Bcl-2 associated X protein (Bax), and B-cell lymphoma-2 (Bcl-2) proteins were determined using Western blot analysis.

RESULTS

Lung tissue morphology was improved as SFJDC decreased cytokine secretion, the ratio of lung wet/dry weights, and lung tissue secretion of proinflammatory cytokines. The expression of A2AAR was increased by SFJDC, and the phosphorylation of NF-κB was inhibited. TUNEL staining and flow cytometry showed that SFJDC inhibited apoptosis by reducing the expression of Cc3 and the ratio of Bax/Bcl-2.

CONCLUSIONS

According to the results of this study, SFJDC can reduce inflammation and inhibit apoptosis. A2AAR activation and regulation of NF-κB expression are thought to make SFJDC anti-inflammatory and anti-apoptotic. A wide range of active ingredients may result in an anti-inflammatory and antipyretic effect with SFJDC.

Role of the purinergic signaling network in lung ischemia-reperfusion injury

PURPOSE OF REVIEW

Primary graft dysfunction (PGD) is the leading cause of early mortality following lung transplantation and is typically caused by lung ischemia-reperfusion injury (IRI). Current management of PGD is largely supportive and there are no approved therapies to prevent lung IRI after transplantation. The purinergic signaling network plays an important role in this sterile inflammatory process, and pharmacologic manipulation of said network is a promising therapeutic strategy. This review will summarize recent findings in this area.

RECENT FINDINGS

In the past 18 months, our understanding of lung IRI has improved, and it is becoming clear that the purinergic signaling network plays a vital role. Recent works have identified critical components of the purinergic signaling network (Pannexin-1 channels, ectonucleotidases, purinergic P1 and P2 receptors) involved in inflammation in a number of pathologic states including lung IRI. In addition, a functionally-related calcium channel, the transient receptor potential vanilloid type 4 (TRPV4) channel, has recently been linked to purinergic signaling and has also been shown to mediate lung IRI.

SUMMARY

Agents targeting components of the purinergic signaling network are promising potential therapeutics to limit inflammation associated with lung IRI and thus decrease the risk of developing PGD.

Secondary Burn Progression Mitigated by an Adenosine 2A Receptor Agonist

BACKGROUND

Current burn therapy is largely supportive with limited therapies to curb secondary burn progression. Adenosine 2A receptor (A2AR) agonists have anti-inflammatory effects with decreased inflammatory cell infiltrate and release of pro-inflammatory mediators. Using a porcine comb burn model, we examined whether A2AR agonists could mitigate burn progression.

STUDY DESIGN

Eight full-thickness comb burns (4 prongs with 3 spaces per comb) per pig were generated with the following specifications: temperature 115° C, 3 kg force, and 30 second application time. In a randomized fashion, animals (4 per group) were then treated with A2AR agonist (ATL-1223, 3 ng/kg/min, intravenous infusion over 6 hours) or vehicle control. Necrotic interspace development was the primary outcome and additional histologic assessments were conducted.

RESULTS

Analysis of unburned interspaces (72 per group) revealed that ATL-1223 treatment decreased the rate of necrotic interspace development over the first 4 days following injury (p<0.05). Treatment significantly decreased dermal neutrophil infiltration at 48 hours following burn (14.63±4.30 vs 29.71±10.76 neutrophils/high-power field, p=0.029). Additionally, ATL-1223 treatment was associated with fewer interspaces with evidence of microvascular thrombi through post-burn day 4 (18.8% vs 56.3%, p=0.002). Two weeks following insult, the depth of injury at distinct burn sites (adjacent to interspaces) was significantly reduced by ATL-1223 treatment (2.91±0.47 vs 3.28±0.58 mm, p=0.038).

CONCLUSION

This work demonstrates the ability of an A2AR agonist to mitigate burn progression through dampening local inflammatory processes. Extended dosing strategies may yield additional benefit and improve cosmetic outcome in those with severe injury.

CD3+CD4-CD8- Double-negative αβ T cells attenuate lung ischemia-reperfusion injury

OBJECTIVE

Lung ischemia-reperfusion injury (IRI) is a common complication after lung transplantation, and immune cells have been implicated in modulating outcomes. We hypothesized that a newly described subset of αβ T-cell receptor positive cells; that is, CD4-CD8- (double negative [DN]) T cells, are found in lungs and can protect against lung IRI.

METHODS

Ischemia was induced in C57BL/6 mice by left pulmonary artery and vein occlusion for 30 minutes followed by 180 minutes of reperfusion. These mice were paired with sham hilar dissected surgical controls. In mice undergoing IRI, adoptive transfer of DN T cells or conventional T cells was performed 12 hours before occlusion. Flow cytometry was used to quantify T cells and inflammatory cytokines, and apoptotic signaling pathways were evaluated with immunoblotting. Lung injury was assessed with Evans blue dye extravasation.

RESULTS

DN T cells were significantly higher (5.29% ± 1% vs 2.21% ± 3%; P < .01) in IRI lungs and secreted higher levels of interleukin-10 (30% ± 5% vs 6% ± 1%; P < .01) compared with surgical sham controls. Immunoblotting, hematoxylin and eosin staining and Evans blue dye demonstrated that adoptive transfer of DN T cells significantly decreased interstitial edema (P < .01) and attenuated apoptosis/cleaved caspase-3 expression in the lungs following lung IRI (P < .01).

CONCLUSIONS

DN T cells traffic into lungs during IRI, and have tissue protective functions regulating inflammation and apoptosis. We propose a potential novel immunoregulatory function of DN T cells during lung IRI.

Transplanting Marginal Organs in the Era of Modern Machine Perfusion and Advanced Organ Monitoring

Organ transplantation is undergoing profound changes. Contraindications for donation have been revised in order to better meet the organ demand. The use of lower-quality organs and organs with greater preoperative damage, including those from donation after cardiac death (DCD), has become an established routine but increases the risk of graft malfunction. This risk is further aggravated by ischemia and reperfusion injury (IRI) in the process of transplantation. These circumstances demand a preservation technology that ameliorates IRI and allows for assessment of viability and function prior to transplantation. Oxygenated hypothermic and normothermic machine perfusion (MP) have emerged as valid novel modalities for advanced organ preservation and conditioning. Ex vivo prolonged lung preservation has resulted in successful transplantation of high-risk donor lungs. Normothermic MP of hearts and livers has displayed safe (heart) and superior (liver) preservation in randomized controlled trials (RCT). Normothermic kidney preservation for 24 h was recently established. Early clinical outcomes beyond the market entry trials indicate bioenergetics reconditioning, improved preservation of structures subject to IRI, and significant prolongation of the preservation time. The monitoring of perfusion parameters, the biochemical investigation of preservation fluids, and the assessment of tissue viability and bioenergetics function now offer a comprehensive assessment of organ quality and function ex situ. Gene and protein expression profiling, investigation of passenger leukocytes, and advanced imaging may further enhance the understanding of the condition of an organ during MP. In addition, MP offers a platform for organ reconditioning and regeneration and hence catalyzes the clinical realization of tissue engineering. Organ modification may include immunological modification and the generation of chimeric organs. While these ideas are not conceptually new, MP now offers a platform for clinical realization. Defatting of steatotic livers, modulation of inflammation during preservation in lungs, vasodilatation of livers, and hepatitis C elimination have been successfully demonstrated in experimental and clinical trials. Targeted treatment of lesions and surgical treatment or graft modification have been attempted. In this review, we address the current state of MP and advanced organ monitoring and speculate about logical future steps and how this evolution of a novel technology can result in a medial revolution.

Extracellular nucleotide signaling in solid organ transplantation

The role of extracellular purine nucleotides, including adenosine triphosphate (ATP) and adenosine, as modulators of posttransplantation outcome and ischemia-reperfusion injury is becoming increasingly evident. Upon pathological release of ATP, binding and activation of P2 purinergic surface receptors promote tissue injury and inflammation, while the expression and activation of P1 receptors for adenosine have been shown to attenuate inflammation and limit ischemia-induced damage, which are central to the viability and long-term success of allografts. Here we review the current state of the transplant field with respect to the role of extracellular nucleotide signaling, with a focus on the sources and functions of extracellular ATP. The connection between ischemia reperfusion, purinergic signaling, and graft preservation, as well as the role of ATP and adenosine as driving factors in the promotion and suppression of posttransplant inflammation and allograft rejection, are discussed. We also examine novel therapeutic approaches that take advantage of the ischemia-reperfusion-responsive and immunomodulatory roles for purinergic signaling with the goal of enhancing graft viability, attenuating posttransplant inflammation, and minimizing complications including rejection, graft failure, and associated comorbidities.

Adenosine A2A receptor agonist (regadenoson) in human lung transplantation

BACKGROUND

Currently, there are no clinically approved treatments for ischemia-reperfusion injury after lung transplantation. Pre-clinical animal models have demonstrated a promising efficacy of adenosine _2A receptor (A_2AR) agonists as a treatment option for reducing ischemia-reperfusion injury. The purpose of this human study, is to conduct a Phase I clinical trial for evaluating the safety of continuous infusion of an A_2AR agonist in lung transplant recipients.

METHODS

An adaptive, two-stage continual reassessment trial was designed to evaluate the safety of regadenoson (A_2AR agonist) in the setting of lung transplantation. Continuous infusion of regadenoson was administered to lung transplant recipients that was started at the time of skin incision. Adverse events and dose-limiting toxicities, as pre-determined by a study team and assessed by a clinical team and an independent safety monitor, were the primary end-points for safety in this trial.

RESULTS

Between January 2018 and March 2019, 14 recipients were enrolled in the trial. Of these, 10 received the maximum infused dose of 1.44 µg/kg/min for 12 hours. No dose-limiting toxicities were observed. The steady-state plasma regadenoson levels sampled before the reperfusion of the first lung were 0.98 ± 0.46 ng/ml. There were no mortalities within 30 days.

CONCLUSIONS

Regadenoson, an A_2AR agonist, can be safely infused in the setting of lung transplantation with no dose-limiting toxicities or drug-related mortality. Although not powered for the evaluation of secondary end-points, the results of this trial and the outcome of pre-clinical studies warrant further investigation with a Phase II randomized controlled trial.

ATP and T-cell-mediated rejection

PURPOSE OF REVIEW

Purine nucleosides and nucleotides are released in the extracellular space following cell injury and act as paracrine mediators through a number of dedicated membrane receptors. In particular, extracellular ATP (eATP) significantly influences T-lymphocyte activation and phenotype. The purpose of this review is to discuss the role of ATP signaling in the T-cell-mediated alloimmune response.

RECENT FINDINGS

In various animal models of solid transplantation, the purinergic axis has been targeted to prevent acute rejection and to promote long-term graft tolerance. The inhibition of ATP-gated P2X receptors has been shown to halt lymphocyte activation, to downregulate both Th1 and Th17 responses and to promote T-regulatory (Treg) cell differentiation. Similarly, the inhibition of ATP signaling attenuated graft-versus-host disease in mice undergoing hematopoietic cell transplantation. Significantly, different drugs targeting the purinergic system have been recently approved for human use and may be a viable therapeutic option for transplant patients.

SUMMARY

The inhibition of eATP signaling downregulates the alloimmune response, expands Treg cells and promotes graft survival. This robust preclinical evidence and the recent advances in pharmacological research may lead to intriguing clinical applications.

Imatinib Is Protective Against Ischemia-Reperfusion Injury in an Ex Vivo Rabbit Model of Lung Injury

BACKGROUND

Ischemia-reperfusion injury is characterized by an increase in oxidative stress and leads to significant morbidity and death. The tyrosine kinase c-Abl is activated by oxidative stress and mediates processes that affect endothelial barrier function. We hypothesized treatment with the c-Abl inhibitor imatinib would be protective against ischemia-reperfusion injury in our ex vivo rabbit model.

METHODS

Heart-lung blocs were harvested from rabbits and stored in cold in Perfadex (Vitrolife, Englewood, CO) for 18 hours. Blocs were reperfused for 2 hours in an ex vivo circuit with donor rabbit blood alone (untreated group, n = 7) or donor rabbit blood and 4 mg imatinib (treatment group, n = 10). Serial clinical variables measured every 15 minutes (arterial oxygen and carbon dioxide tension and mean pulmonary artery pressures) and biochemistry of tissue samples before and after reperfusion were assessed.

RESULTS

Compared with untreated lungs, imatinib treatment improved physiologic parameters, including oxygen, carbon dioxide, and pulmonary artery pressures. Imatinib-treated lungs had less vascular barrier dysfunction as quantified by wet-to-dry weight ratios and bronchoalveolar lavage protein concentrations. Treated lungs showed less inflammation as measured by bronchoalveolar lavage myeloperoxidase assay, less mitochondrial reactive oxygen species production, and increased antioxidant catalase levels. Finally, imatinib protected lungs from DNA damage and p53 upregulation.

CONCLUSIONS

Imatinib treatment significantly improved the physiologic performance of reperfused lungs and biochemical indicators associated with reperfusion injury in this ex vivo model. Further study is necessary to elucidate the mechanism of tyrosine kinase inhibition in lungs exposed to ischemia and reperfusion.

NOX2 Activation of Natural Killer T Cells Is Blocked by the Adenosine A2A Receptor to Inhibit Lung Ischemia-Reperfusion Injury

RATIONALE

Ischemia-reperfusion (IR) injury after lung transplantation, which affects both short- and long-term allograft survival, involves activation of NADPH oxidase 2 (NOX2) and activation of invariant natural killer T (iNKT) cells to produce IL-17. Adenosine A2A receptor (A2AR) agonists are known to potently attenuate lung IR injury and IL-17 production. However, mechanisms for iNKT cell activation after IR and A2AR agonist-mediated protection remain unclear.

OBJECTIVES

We tested the hypothesis that NOX2 mediates IL-17 production by iNKT cells after IR and that A2AR agonism prevents IR injury by blocking NOX2 activation in iNKT cells.

METHODS

An in vivo murine hilar ligation model of IR injury was used, in which left lungs underwent 1 hour of ischemia and 2 hours of reperfusion.

MEASUREMENTS AND MAIN RESULTS

Adoptive transfer of iNKT cells from p47(phox-/-) or NOX2(-/-) mice to Jα18(-/-) (iNKT cell-deficient) mice significantly attenuated lung IR injury and IL-17 production. Treatment with an A2AR agonist attenuated IR injury and IL-17 production in wild-type (WT) mice and in Jα18(-/-) mice reconstituted with WT, but not A2AR(-/-), iNKT cells. Furthermore, the A2AR agonist prevented IL-17 production by murine and human iNKT cells after acute hypoxia-reoxygenation by blocking p47(phox) phosphorylation, a critical step for NOX2 activation.

CONCLUSIONS

NOX2 plays a key role in inducing iNKT cell-mediated IL-17 production and subsequent lung injury after IR. A primary mechanism for A2AR agonist-mediated protection entails inhibition of NOX2 in iNKT cells. Therefore, agonism of A2ARs on iNKT cells may be a novel therapeutic strategy to prevent primary graft dysfunction after lung transplantation.

Improved metabolism and redox state with a novel preservation solution: implications for donor lungs after cardiac death (DCD)

Lungs donated after cardiac death (DCD) are an underutilized resource for a dwindling donor lung transplant pool. Our study investigates the potential of a novel preservation solution, Somah, to better preserve statically stored DCD lungs, for an extended time period, when compared to low-potassium dextran solution (LPD). We hypothesize that Somah is a metabolically superior organ preservation solution for hypothermic statically stored porcine DCD lungs, possibly improving lung transplant outcomes. Porcine DCD lungs (n = 3 per group) were flushed with and submerged in cold preservation solution. The lungs were stored up to 12 h, and samples were taken from lung tissue and the preservation medium throughout. Metabolomic and redox potential were analyzed using high performance liquid chromatography, mass spectrometry, and RedoxSYS®, comparing substrate and pathway utilization in both preservation solutions. Glutathione reduction was seen in Somah but not in LPD during preservation. Carnitine, carnosine, and n-acetylcarnosine levels were elevated in the Somah medium compared with LPD throughout. Biopsies of Somah exposed lungs demonstrated similar trends after 2 h, up to 12 h. Adenosine gradually decreased in Somah medium over 12 h, but not in LPD. An inversely proportional increase in inosine was found in Somah. Higher oxidative stress levels were measured in LPD. Our study suggests suboptimal metabolic preservation in lungs stored in LPD. LPD had poor antioxidant potential, cytoprotection, and an insufficient redox potential. These findings may have immediate clinical implications for human organs; however, further investigation is needed to evaluate DCD lung preservation in Somah as a viable option for transplant.

Oxidative and nitrosative stress during pulmonary ischemia-reperfusion injury: from the lab to the OR

Oxidative and nitrosative stress are an umbrella term for pathophysiological processes that involve free radical generation during inflammation. In this review, the involvement of reactive oxygen and nitrogen species is evaluated during lung ischemia-reperfusion injury (LIRI) from a surgical point of view. The main biochemical and cellular mechanisms behind free radical generation are discussed, together with surgical procedures that may cause reperfusion injury. Finally, different therapeutic strategies are further explored. A literature search was performed, searching for "lung ischemia reperfusion injury", "reperfusion injury", "large animal model" and different search terms for each section: "surgery", "treatment", "cellular mechanism", or "enzyme". Although reperfusion injury is not an uncommon entity and there is a lot of evidence concerning myocardial ischemia-reperfusion injury, in the lung this phenomenon is less extensively described and studies in large animals are not easy to come by. With increasing number of patients on waiting lists for lung transplant, awareness for this entity should all but rise.

Lung injury pathways: Adenosine receptor 2B signaling limits development of ischemic bronchiolitis obliterans organizing pneumonia

Purpose/Aim of the Study: Adenosine signaling was studied in bronchiolitis obliterans organizing pneumonia (BOOP) resulting from unilateral lung ischemia.

MATERIALS AND METHODS

Ischemia was achieved by either left main pulmonary artery or complete hilar ligation. Sprague-Dawley (SD) rats, Dahl salt sensitive (SS) rats and SS mutant rat strains containing a mutation in the A2B adenosine receptor gene (Adora2b) were studied. Adenosine concentrations were measured in bronchoalveolar lavage (BAL) by HPLC. A2A (A2AAR) and A2B adenosine receptor (A2BAR) mRNA and protein were quantified.

RESULTS

Twenty-four hours after unilateral PA ligation, BAL adenosine concentrations from ischemic lungs were increased relative to contralateral lungs in SD rats. A2BAR mRNA and protein concentrations were increased after PA ligation while miR27a, a negatively regulating microRNA, was decreased in ischemic lungs. A2AAR mRNA and protein concentrations remained unchanged following ischemia. A2BAR protein was increased in PA ligated lungs of SS rats after 7 days, and 4 h after complete hilar ligation in SD rats. SS-Adora2b mutants showed a greater extent of BOOP relative to SS rats, and greater inflammatory changes.

CONCLUSION

Increased A2BAR and adenosine following unilateral lung ischemia as well as more BOOP in A2BAR mutant rats implicate a protective role for A2BAR signaling in countering ischemic lung injury.

Role of inflammatory cells and adenosine in lung ischemia reoxygenation injury using a model of lung donation after cardiac death

AIM

The objective of this study is to analyze the role of inflammation in the lung ischemia reperfusion (IR) injury and determine the protective role of adenosine in an in vitro lung transplantation model.

MATERIALS AND METHODS

We used a hybrid model of lung donor after cardiac death, with warm ischemia in corpo of varying duration (2 h, 4 h) followed by in vitro lung slices culture for reoxygenation (1 h, 4 h and 24 h), in the presence or not of lymphocytes and of adenosine. To quantify the inflammatory lesions, we performed TNFα, IL2 assays, and histological analysis.

RESULTS

In this model of a nonblood perfused system, the addition of lymphocytes during reoxygenation lead to higher rates of TNFα and IL2 after 4 h than after 2 h of warm ischemia (P < .05). These levels increased with the duration of reoxygenation and were maximum at 24 h (P < .05). In the presence of adenosine TNFα and IL2 decreased. After 2 h of warm ischemia, we observed a significant inflammatory infiltration, alveolar thickening and a necrosis of the bronchiolar cells. After 4 h of warm ischemia, alveolar cells necrosis was associated.

CONCLUSION

This model showed that lymphocytes increased the inflammatory response and the histological lesions after 4 h of warm ischemia and that adenosine could have an anti-inflammatory role with potential reconditioning action when used in the pneumoplegia solution.

Ex Vivo Perfusion With Adenosine A2A Receptor Agonist Enhances Rehabilitation of Murine Donor Lungs After Circulatory Death

BACKGROUND

Ex vivo lung perfusion (EVLP) enables assessment and rehabilitation of marginal donor lungs before transplantation. We previously demonstrated that adenosine A2A receptor (A2AR) agonism attenuates lung ischemia-reperfusion injury. The current study utilizes a novel murine EVLP model to test the hypothesis that A2AR agonist enhances EVLP-mediated rehabilitation of donation after circulatory death (DCD) lungs.

METHODS

Mice underwent euthanasia and 60 minutes warm ischemia, and lungs were flushed with Perfadex and underwent cold static preservation (CSP, 60 minutes). Three groups were studied: no EVLP (CSP), EVLP with Steen solution for 60 minutes (EVLP), and EVLP with Steen solution supplemented with ATL1223, a selective A2AR agonist (EVLP + ATL1223). Lung function, wet/dry weight, cytokines and neutrophil numbers were measured. Microarrays were performed using the Affymetrix GeneChip Mouse Genome 430A 2.0 Array.

RESULTS

Ex vivo lung perfusion significantly improved lung function versus CSP, which was further, significantly improved by EVLP + ATL1223. Lung edema, cytokines, and neutrophil counts were reduced after EVLP and further, significantly reduced after EVLP + ATL1223. Gene array analysis revealed differential expression of 1594 genes after EVLP, which comprise canonical pathways involved in inflammation and innate immunity including IL-1, IL-8, IL-6, and IL-17 signaling. Several pathways were uniquely regulated by EVLP + ATL1223 including the downregulation of genes involved in IL-1 signaling, such as ADCY9, ECSIT, IRAK1, MAPK12, and TOLLIP.

CONCLUSIONS

Ex vivo lung perfusion modulates proinflammatory genes and reduces pulmonary dysfunction, edema, and inflammation in DCD lungs, which are further reduced by A2AR agonism. This murine EVLP model provides a novel platform to study rehabilitative mechanisms of DCD lungs.

Inflammatory targets of therapy in sickle cell disease

Sickle cell disease (SCD) is a monogenic globin disorder characterized by the production of a structurally abnormal hemoglobin (Hb) variant Hb S, which causes severe hemolytic anemia, episodic painful vaso-occlusion, and ultimately end-organ damage. The primary disease pathophysiology is intracellular Hb S polymerization and consequent sickling of erythrocytes. It has become evident for more than several decades that a more complex disease process contributes to the myriad of clinical complications seen in patients with SCD with inflammation playing a central role. Drugs targeting specific inflammatory pathways therefore offer an attractive therapeutic strategy to ameliorate many of the clinical events in SCD. In addition, they are useful tools to dissect the molecular and cellular mechanisms that promote individual clinical events and for developing improved therapeutics to address more challenging clinical dilemmas such as refractoriness to opioids or hyperalgesia. Here, we discuss the prospect of targeting multiple inflammatory pathways implicated in the pathogenesis of SCD with a focus on new therapeutics, striving to link the actions of the anti-inflammatory agents to a defined pathobiology, and specific clinical manifestations of SCD. We also review the anti-inflammatory attributes and the cognate inflammatory targets of hydroxyurea, the only Food and Drug Administration-approved drug for SCD.

Ex vivo lung perfusion with adenosine A2A receptor agonist allows prolonged cold preservation of lungs donated after cardiac death

OBJECTIVE

Ex vivo lung perfusion has been successful in the assessment of marginal donor lungs, including donation after cardiac death (DCD) donor lungs. Ex vivo lung perfusion also represents a unique platform for targeted drug delivery. We sought to determine whether ischemia-reperfusion injury would be decreased after transplantation of DCD donor lungs subjected to prolonged cold preservation and treated with an adenosine A2A receptor agonist during ex vivo lung perfusion.

METHODS

Porcine DCD donor lungs were preserved at 4°C for 12 hours and underwent ex vivo lung perfusion for 4 hours. Left lungs were then transplanted and reperfused for 4 hours. Three groups (n = 4/group) were randomized according to treatment with the adenosine A2A receptor agonist ATL-1223 or the dimethyl sulfoxide vehicle: Infusion of dimethyl sulfoxide during ex vivo lung perfusion and reperfusion (DMSO), infusion of ATL-1223 during ex vivo lung perfusion and dimethyl sulfoxide during reperfusion (ATL-E), and infusion of ATL-1223 during ex vivo lung perfusion and reperfusion (ATL-E/R). Final Pao2/Fio2 ratios (arterial oxygen partial pressure/fraction of inspired oxygen) were determined from samples obtained from the left superior and inferior pulmonary veins.

RESULTS

Final Pao2/Fio2 ratios in the ATL-E/R group (430.1 ± 26.4 mm Hg) were similar to final Pao2/Fio2 ratios in the ATL-E group (413.6 ± 18.8 mm Hg), but both treated groups had significantly higher final Pao2/Fio2 ratios compared with the dimethyl sulfoxide group (84.8 ± 17.7 mm Hg). Low oxygenation gradients during ex vivo lung perfusion did not preclude superior oxygenation capacity during reperfusion.

CONCLUSIONS

After prolonged cold preservation, treatment of DCD donor lungs with an adenosine A2A receptor agonist during ex vivo lung perfusion enabled Pao2/Fio2 ratios greater than 400 mm Hg after transplantation in a preclinical porcine model. Pulmonary function during ex vivo lung perfusion was not predictive of outcomes after transplantation.

Anti-inflammatory, antioxidant, and antiparkinsonian effects of adenosine A2A receptor antagonists

The purpose of the study was to examine derivatives of annelated xanthines (imidazo-, pyrimido-, and diazepino-purinediones) for potential anti-inflammatory effects in carrageenan-induced paw edema in mice. Additionally, their antioxidant activity using the FRAP (ferric-reducing ability of plasma) assay and lipid peroxidation in rat brain homogenate were analyzed. All the studied derivatives showed affinity for adenosine A_2A receptor. The preliminary assays found that five (KD-114, KD-57, KD-129, KD-50, and KD-358) pyrimidopurinedione derivatives, administered intraperitoneally (i.p.) at a dose of 100mg/kg, had stronger anti-inflammatory effects. At a concentration of 10^-5M, three of the derivatives KD-57, KD-114, and KD-129 most influenced the total antioxidant ability. The most efficient anti-inflammatory compound, KD-114, also showed the strongest binding to A_2A receptors and when administered at a dose of 5mg/kg (i.p.), effectively reversed haloperidol-induced catalepsy and significantly increased the striatal extracellular dopamine level in the rat striatum. This effect was weaker than the one produced by CSC (1mg/kg i.p.), and only slightly weaker than that produced by ZM 241385 (3mg/kg i.p.) used as reference drugs. From the results of the present studies, it may be concluded that anti-inflammatory and antiparkinsonian effects of the examined compounds correlate with their influence on adenosine A_2A receptors, the most probable antagonism to these subtype receptors.

Therapeutic applications

The current treatments offered to patients with chronic respiratory diseases are being re-evaluated based on the loss of potency during long-term treatments or because they only provide significant clinical benefits to a subset of the patient population. For instance, glucocorticoids are considered the most effective anti-inflammatory therapies for chronic inflammatory and immune diseases, such as asthma. But they are relatively ineffective in asthmatic smokers, and patients with chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF). As such, the pharmaceutical industry is exploring new therapeutic approaches to address all major respiratory diseases. The previous chapters demonstrated the widespread influence of purinergic signaling on all pulmonary functions and defense mechanisms. In Chap. 8, we described animal studies which highlighted the critical role of aberrant purinergic activities in the development and maintenance of chronic airway diseases. This last chapter covers all clinical and pharmaceutical applications currently developed based on purinergic receptor agonists and antagonists. We use the information acquired in the previous chapters on purinergic signaling and lung functions to scrutinize the preclinical and clinical data, and to realign the efforts of the pharmaceutical industry.

The Role of Ectonucleotidases CD39 and CD73 and Adenosine Signaling in Solid Organ Transplantation

Extracellular adenosine is a potent immunomodulatory molecule that accumulates in states of inflammation. Nucleotides such as adenosine triphosphate and adenosine diphosphate are release from injured and necrotic cells and hydrolyzed to adenosine monophosphate and adenosine by the concerted action of the ectonucleotidases CD39 and CD73. Accumulating evidence suggest that purinergic signaling is involved in the inflammatory response that accompanies acute rejection and chronic allograft dysfunction. Modification of the purinergic pathway has been shown to alter graft survival in a number of solid organ transplant models and the response to ischemia–reperfusion injury (IRI). Furthermore, the purinergic pathway is intrinsically involved in B and T cell biology and function. Although T cells have traditionally been considered the orchestrators of acute allograft rejection, a role for B cells in chronic allograft loss is being increasingly appreciated. This review focuses on the role of the ectonucleotidases CD39 and CD73 and adenosine signaling in solid organ transplantation including the effects on IRI and T and B cell biology.

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

Role of adenosine A2A receptor in organ-specific vascular reactivity following hemorrhagic shock in rats

BACKGROUND

Previous studies have demonstrated differences among organs in terms of shock-induced vascular reactivity and a role for adenosine A2A receptors (A2ARs) in protection against ischemia/reperfusion injury. However, the contributions of A2ARs to organ-specific vascular reactivity and the protection of vascular responsiveness following shock are currently unknown.

METHODS

We investigated the role of A2ARs in different arteries, including the left femoral artery (LFA), thoracic aorta (TA), superior mesenteric artery (SMA), right renal artery (RRA), pulmonary artery (PA), and middle cerebral artery (MCA), in hemorrhagic-shock rats.

RESULTS

The vascular reactivities of the LFA, SMA, RRA, and MCA increased slightly during early shock and then gradually decreased, whereas those of the PA and TA decreased from the start of shock. Different blood vessels lost vascular reactivity at different rates compared with controls; the LFA had the highest rate of loss (64.51%), followed by the SMA (44.69%), TA (36.06%), PA (37.83%), and RRA (32.33%), whereas the MCA had the lowest rate (18.45%). The rate of loss of vascular reactivity in the different vessels was negatively correlated with A2AR expression levels in normal and shock conditions. The highly selective A2AR agonist CGS 21680 significantly improved vascular reactivity, hemodynamic parameters, and animal survival, whereas the specific antagonist SCH58261 further decreased the shock-induced reduction in vascular reactivity and hemodynamic parameters.

CONCLUSIONS

A2ARs are involved in the regulation and protection of vascular reactivity following shock. A2AR activation may have a beneficial effect on hemorrhagic shock by improving vascular reactivity and hemodynamic parameters.

Adenosine A3 receptor activation attenuates lung ischemia-reperfusion injury

BACKGROUND

Severe ischemia-reperfusion (IR) injury leads to primary graft dysfunction after lung transplantation. Adenosine receptors modulate inflammation after IR, and the adenosine A3 receptor (A3R) is expressed in lung tissue and inflammatory cells. This study tests the hypothesis that A3R agonism attenuates lung IR injury by a neutrophil-dependent mechanism.

METHODS

Wild-type and A3R knockout (A3R-/-) mice underwent 1-hour left lung ischemia followed by 2-hours reperfusion (IR). A selective A3R agonist, Cl-IB-MECA, was administered (100 μg/kg intravenously) 5 minutes prior to ischemia. Study groups included sham, IR, and IR+Cl-IB-MECA (n = 6/group). Lung injury was assessed by measuring lung function, pulmonary edema, histopathology, and proinflammatory cytokines, and myeloperoxidase levels in bronchoalveolar lavage fluid. Parallel in vitro experiments were performed to evaluate neutrophil chemotaxis, and neutrophil activation was measured after exposure to acute hypoxia and reoxygenation.

RESULTS

Treatment of wild-type mice with Cl-IB-MECA significantly improved lung function and decreased edema, cytokine expression, and neutrophil infiltration after IR. The Cl-IB-MECA had no effects in A3R-/- mice; Cl-IB-MECA significantly decreased activation of wild-type, but not A3R-/-, neutrophils after acute hypoxia and reoxygenation and inhibited chemotaxis of wild-type neutrophils.

CONCLUSIONS

Exogenous activation of A3R by Cl-IB-MECA attenuates lung dysfunction, inflammation, and neutrophil infiltration after IR in wild-type but not A3R-/- mice. Results with isolated neutrophils suggest that the protective effects of Cl-IB-MECA are due, in part, to the prevention of neutrophil activation and chemotaxis. The use of A3R agonists may be a novel therapeutic strategy to prevent lung IR injury and primary graft dysfunction after transplantation.

Sinomenine protects against lipopolysaccharide-induced acute lung injury in mice via adenosine A(2A) receptor signaling

Sinomenine (SIN) is a bioactive alkaloid extracted from the Chinese medicinal plant Sinomenium acutum, which is widely used in the clinical treatment of rheumatoid arthritis (RA). However, its role in acute lung injury (ALI) is unclear. In this study, we investigate the role of SIN in lipopolysaccharide (LPS)-induced ALI in mice. After ALI, lung water content and histological signs of pulmonary injury were attenuated, whereas the PaO₂/FIO₂ (P/F) ratios were elevated significantly in the mice pretreated with SIN. Additionally, SIN markedly inhibited inflammatory cytokine TNF-α and IL-1β expression levels as well as neutrophil infiltration in the lung tissues of the mice. Microarray analysis and real-time PCR showed that SIN treatment upregulated adenosine A_2A receptor (A_2AR) expression, and the protective effect of SIN was abolished in A_2AR knockout mice. Further investigation in isolated mouse neutrophils confirmed the upregulation of A_2AR by SIN and showed that A_2AR-cAMP-PKA signaling was involved in the anti-inflammatory effect of SIN. Taken together, these findings demonstrate an A_2AR-associated anti-inflammatory effect and the protective role of SIN in ALI, which suggests a potential novel approach to treat ALI.

Ex vivo rehabilitation of non-heart-beating donor lungs in preclinical porcine model: delayed perfusion results in superior lung function

OBJECTIVES

Ex vivo lung perfusion (EVLP) is a promising modality for the evaluation and treatment of marginal donor lungs. The optimal timing of EVLP initiation and the potential for rehabilitation of donor lungs with extended warm ischemic times is unknown. The present study compared the efficacy of different treatment strategies for uncontrolled non-heart-beating donor lungs.

METHODS

Mature swine underwent hypoxic arrest, followed by 60 minutes of no-touch warm ischemia. The lungs were harvested and flushed with 4°C Perfadex. Three groups (n = 5/group) were stratified according to the preservation method: cold static preservation (CSP; 4 hours of 4°C storage), immediate EVLP (I-EVLP: 4 hours EVLP at 37°C), and delayed EVLP (D-EVLP; 4 hours of CSP followed by 4 hours of EVLP). The EVLP groups were perfused with Steen solution supplemented with heparin, methylprednisolone, cefazolin, and an adenosine 2A receptor agonist. The lungs then underwent allotransplantation and 4 hours of recipient reperfusion before allograft assessment for resultant ischemia-reperfusion injury.

RESULTS

The donor blood oxygenation (partial pressure of oxygen/fraction of inspired oxygen ratio) before death was not different between the groups. The oxygenation after transplantation was significantly greater in the D-EVLP group than in the I-EVLP or CSP groups. The mean airway pressure, pulmonary artery pressure, and expression of interleukin-8, interleukin-1β, and tumor necrosis factor-α were all significantly reduced in the D-EVLP group. Post-transplant oxygenation exceeded the acceptable clinical levels only in the D-EVLP group.

CONCLUSIONS

Uncontrolled non-heart-beating donor lungs with extended warm ischemia can be reconditioned for successful transplantation. The combination of CSP and EVLP in the D-EVLP group was necessary to obtain optimal post-transplant function. This finding, if confirmed clinically, will allow expanded use of nonheart-beating donor lungs.

Adenosine A₂A agonist improves lung function during ex vivo lung perfusion

BACKGROUND

Ex vivo lung perfusion (EVLP) is a novel technique than can be used to assess and potentially repair marginal lungs that may otherwise be rejected for transplantation. Adenosine has been shown to protect against pulmonary ischemia-reperfusion (IR) injury through its A(2A) receptor. We hypothesized that combining EVLP with adenosine A(2A) receptor agonist treatment would enhance lung functional quality and increase donor lung use.

METHODS

Eight bilateral pig lungs were harvested and flushed with cold Perfadex (Vitrolife, Englewood, CO). After 14 hours of storage at 4°C, EVLP was performed for 5 hours on 2 explanted lung groups: (1) control group lungs (n = 4) were perfused with Steen Solution (Vitrolife) and dimethyl sulfoxide and (2) treated group lungs (n = 4) received 10 μM CGS21680, a selective A(2A) receptor agonist, in a Steen solution-primed circuit. Lung histologic features, tissue cytokines, gas analysis, and pulmonary function were compared between groups.

RESULTS

Treated lungs demonstrated significantly less edema as reflected by wet-dry weight ratio (6.6 versus 5.2; p < 0.03) and confirmed by histologic examination. In addition, treated lung demonstrated significantly lower levels of interferon-γ (IFN- γ) (45.1 versus 88.5; p < 0.05). Other measured tissue cytokine levels (interleukin [IL]-1β, IL-6, and IL-8) were lower in the treatment group, but values failed to reach statistical significance. The oxygenation index was improved in the treated group (1.5 versus 2.3; p < 0.01) as was mean airway pressure (10.3 versus 13; p < 0.009).

CONCLUSIONS

Combined use of adenosine A(2A) agonist and EVLP significantly attenuates the inflammatory response in acutely injured lungs after IR and enhances pulmonary function. This combination may improve donor lung quality and could increase the donor lung pool for transplantation.

Interplay of hypoxia and A2B adenosine receptors in tissue protection

That adenosine signaling can elicit adaptive tissue responses during conditions of limited oxygen availability (hypoxia) is a long-suspected notion that recently gained general acceptance from genetic and pharmacologic studies of the adenosine signaling pathway. As hypoxia and inflammation share an interdependent relationship, these studies have demonstrated that adenosine signaling events can be targeted to dampen hypoxia-induced inflammation. Here, we build on the hypothesis that particularly the A(2B) adenosine receptor (ADORA(2B)) plays a central role in tissue adaptation to hypoxia. In fact, the ADORA(2B) requires higher adenosine concentrations than any of the other adenosine receptors. However, during conditions of hypoxia or ischemia, the hypoxia-elicited rise in extracellular adenosine is sufficient to activate the ADORA(2B). Moreover, several studies have demonstrated very robust induction of the ADORA(2B) elicited by transcriptional mechanisms involving hypoxia-dependent signaling pathways and the transcription factor "hypoxia-induced factor" 1. In the present chapter, genetic and pharmacologic evidence is presented to support our hypothesis of a tissue protective role of ADORA(2B) signaling during hypoxic conditions, including hypoxia-elicited vascular leakage, organ ischemia, or acute lung injury. All these disease models are characterized by hypoxia-elicited tissue inflammation. As such, the ADORA(2B) has emerged as a therapeutic target for dampening hypoxia-induced inflammation and tissue adaptation to limited oxygen availability.

Pretreatment strategy with adenosine A2A receptor agonist attenuates reperfusion injury in a preclinical porcine lung transplantation model

OBJECTIVE

Adenosine A(2A) receptor activation after lung transplantation attenuates ischemia-reperfusion injury by reducing inflammation. However, the effect of adenosine A(2A) receptor activation in donor lungs before transplant remains ill defined. This study compares the efficacy of 3 different treatment strategies for adenosine A(2A) receptor agonist in a clinically relevant porcine lung transplantation model.

METHODS

Mature porcine lungs underwent 6 hours of cold ischemia before allotransplantation and 4 hours of reperfusion. Five groups (n = 6/group) were evaluated on the basis of treatment with ATL-1223, a selective adenosine A(2A) receptor agonist: thoracotomy alone (sham), transplant alone (ischemia-reperfusion), donor pretreatment via ATL-1223 bolus (ATL-D), recipient treatment via ATL-1223 infusion (ATL-R), and a combination of both ATL-1223 treatments (ATL-D/R). Lung function and injury were compared.

RESULTS

Blood oxygenation was significantly higher among ATL-D, ATL-R, and ATL-D/R groups versus ischemia-reperfusion (392.0 ± 52.5, 428.9 ± 25.5, and 509.4 ± 25.1 vs 77.2 ± 17.0 mm Hg, respectively, P < .001). ATL-1223-treated groups had lower pulmonary artery pressures (ATL-D = 30.5 ± 1.8, ATL-R = 30.2 ± 3.3, and ATL-D/R = 29.3 ± 4.5 vs IR = 45.2 ± 2.1 mm Hg, P < .001) and lower mean airway pressures versus ischemia-reperfusion (ATL-D = 9.1 ± 0.8, ATL-R = 9.1 ± 2.6, and ATL-D/R = 9.6 ± 1.3 vs IR = 21.1 mm Hg, P < .001). Likewise, ATL-1223-treated groups had significantly lower lung wet/dry weight, proinflammatory cytokine expression, and lung injury scores by histology compared with ischemia-reperfusion. All parameters of lung function and injury in ATL-1223-treated groups were similar to sham (all P > .05).

CONCLUSIONS

Pretreatment of donor lungs with ATL-1223 was as efficacious as other treatment strategies in protecting against ischemia-reperfusion injury. If necessary, supplemental treatment of recipients with ATL-1223 may provide additional protection. These results support the development of pharmacologic A(2A)R agonists for use in human clinical trials for lung transplantation.

Targeting iNKT cells for the treatment of sickle cell disease

Sickle cell disease (SCD) causes widely disseminated vaso-occlusive episodes. Building on evidence implicating invariant NKT (iNKT) cells in the pathogenesis of ischemia/reperfusion injury, recent studies demonstrate that blockade of iNKT cell activation in mice with SCD reduces pulmonary inflammation and injury. In patients with SCD, iNKT cells in blood are increased in absolute number and activated in comparison to healthy controls. iNKT cell activation is reduced by agonists of adenosine 2A receptors (A(2A)Rs) such as the clinically approved coronary vasodilator, regadenoson. An ongoing multi-center, dose-finding and safety trial of infused regadenoson, has been initiated and is providing preliminary data about its safety and efficacy to treat SCD. Very high accumulation of adenosine may have deleterious effects in SCD through activation of adenosine 2B receptors that are insensitive to regadenoson. Future possible therapeutic approaches for treating SCD include selective A(2B)R antagonists and antibodies that deplete iNKT cells.

Adenosine signaling via the adenosine 2B receptor is involved in bronchiolitis obliterans development

BACKGROUND

Adenosine is produced in response to ischemia or inflammation and protects tissues from injury. Four adenosine receptors are critical in the physiologic negative-feedback mechanism for limitation and termination of tissue-specific and systemic inflammatory responses. Accumulating evidence has focused on the anti-inflammatory and immunosuppressive role of the adenosine 2A receptor (A(2A)R), and we have previously reported on its role in the development of bronchiolitis obliterans (BO) after lung transplantation. Few studies, however, have reported the role of the adenosine 2B receptor (A(2B)R) in BO. Data suggests that the A(2B)R has pro-inflammatory and pro-fibrotic roles. We hypothesized that adenosine signaling through A(2B)R is involved in the development of BO.

METHODS

A murine heterotopic tracheal model across a total alloantigenic mismatch was used to study A(2B)R signaling in BO. Tracheal transplants consisted of Balb/c donor tracheas transplanted into wild-type or A(2B)R knockout (KO) C57BL/6 recipients. Transplanted tracheas were removed 3, 7, 12, and 21 days after transplantation. The luminal obliteration was evaluated through hematoxylin and eosin staining, and the cellular infiltration (macrophage, neutrophil, CD3+ and Foxp3+ regulatory T cell) was detected by immunohistochemical staining.

RESULTS

Compared with allografts in wild-type recipients, tracheas transplanted into A(2B)R KO mice displayed less BO development on Day 21. A(2B)R KO mice had an increase in CD3+ T cells and CD4+/CD25+/Foxp3+ regulatory T cells than did wild-type mice on Day 7. By Day 12, more CD3+ T cells were present in the wild-type trachea compared with the A(2B)R KO, but the percentage of CD4+/CD25+/Foxp3+ regulatory T cells remained higher in the tracheas of A(2B)R KO mice.

CONCLUSIONS

A(2B)R stimulation may promote the development of BO by inhibiting CD4+/CD25+/Foxp3+ regulatory T-cell infiltration.

Regulation of leukocyte function by adenosine receptors

The immune system responds to cues in the microenvironment to make acute and chronic adaptations in response to inflammation and injury. Locally produced purine nucleotides and adenosine provide receptor-mediated signaling to all bone-marrow derived cells of the immune system to modulate their responses. This review summarizes recent advances in our understanding of the effects of adenosine signaling through G protein-coupled adenosine receptors on cells of the immune system. Adenosine A(2A) receptors (A(2A)Rs) have a generally suppressive effect on the activation of immune cells. Moreover, their transcription is strongly induced by signals that activate macrophages or dendritic cells through toll-like receptors, or T cells through T cell receptors. A(2A)R induction is responsible for producing a gradual dissipation of inflammatory responses. A(2A)R activation is particularly effective in limiting the activation of invariant NKT (iNKT) cells that play a central role in acute reperfusion injury. A(2A) agonists have clinical promise for the treatment of vaso-occlusive tissue injury. Blockade of A(2A) receptors may be useful to enhance immune-mediated killing of cancer cells. A(2B)R expression also is transcriptionally regulated by hypoxia, cytokines, and oxygen radicals. Acute A(2B)R activation attenuates the production of proinflammatory cytokines from macrophages, but sustained activation facilitates macrophage and dendritic cell remodeling and the production of acute phase proteins and angiogenic factors that may participate in evoking insulin resistance and tissue fibrosis. A(2B)R activation also influences macrophage and neutrophil function by influencing expression of the anti-inflammatory netrin receptor, UNC5B. The therapeutic significance of adenosine-mediated effects on the immune system is discussed.

Targeting of adenosine receptors in ischemia-reperfusion injury

IMPORTANCE OF THE FIELD

Ischemia-reperfusion (IR) injury is a common problem after transplantation as well as myocardial infarction and stroke. IR initiates an inflammatory response leading to rapid tissue damage. Adenosine, produced in response to IR, is generally considered a protective signaling molecule and elicits its physiological responses through four distinct adenosine receptors. The short half-life, lack of specificity and rapid metabolism limits the use of adenosine as a therapeutic agent. Thus, intense research efforts have focused on the synthesis and implementation of specific adenosine receptor agonists and antagonists as potential therapeutic agents for a variety of inflammatory conditions including IR injury.

AREAS COVERED IN THIS REVIEW

Current knowledge on IR injury with a focus on lung, heart and kidney and studies that have advanced our understanding of the role of adenosine receptors and the therapeutic potential of adenosine receptor agonists and antagonists for the prevention of IR injury.

WHAT THE READER WILL GAIN

Insight into the role of adenosine receptor signaling in IR injury.

TAKE HOME MESSAGE

No therapies are currently available that specifically target IR injury; however, targeting of specific adenosine receptors may offer therapeutic strategies in this regard.

Tissue-derived proinflammatory effect of adenosine A2B receptor in lung ischemia-reperfusion injury

OBJECTIVE

Ischemia-reperfusion injury after lung transplantation remains a major source of morbidity and mortality. Adenosine receptors have been implicated in both pro- and anti-inflammatory roles in ischemia-reperfusion injury. This study tests the hypothesis that the adenosine A(2B) receptor exacerbates the proinflammatory response to lung ischemia-reperfusion injury.

METHODS

An in vivo left lung hilar clamp model of ischemia-reperfusion was used in wild-type C57BL6 and adenosine A(2B) receptor knockout mice, and in chimeras created by bone marrow transplantation between wild-type and adenosine A(2B) receptor knockout mice. Mice underwent sham surgery or lung ischemia-reperfusion (1 hour ischemia and 2 hours reperfusion). At the end of reperfusion, lung function was assessed using an isolated buffer-perfused lung system. Lung inflammation was assessed by measuring proinflammatory cytokine levels in bronchoalveolar lavage fluid, and neutrophil infiltration was assessed via myeloperoxidase levels in lung tissue.

RESULTS

Compared with wild-type mice, lungs of adenosine A(2B) receptor knockout mice were significantly protected after ischemia-reperfusion, as evidenced by significantly reduced pulmonary artery pressure, increased lung compliance, decreased myeloperoxidase, and reduced proinflammatory cytokine levels (tumor necrosis factor-α; interleukin-6; keratinocyte chemoattractant; regulated on activation, normal T-cell expressed and secreted; and monocyte chemotactic protein-1). Adenosine A(2B) receptor knockout → adenosine A(2B) receptor knockout (donor → recipient) and wild-type → adenosine A(2B) receptor knockout, but not adenosine A(2B) receptor knockout → wild-type, chimeras showed significantly improved lung function after ischemia-reperfusion.

CONCLUSIONS

These results suggest that the adenosine A(2B) receptor plays an important role in mediating lung inflammation after ischemia-reperfusion by stimulating cytokine production and neutrophil chemotaxis. The proinflammatory effects of adenosine A(2B) receptor seem to be derived by adenosine A(2B) receptor activation primarily on resident pulmonary cells and not bone marrow-derived cells. Adenosine A(2B) receptor may provide a therapeutic target for prevention of ischemia-reperfusion-related graft dysfunction in lung transplant recipients.

Activation of A1, A2A, or A3 adenosine receptors attenuates lung ischemia-reperfusion injury

OBJECTIVE

Adenosine and the activation of specific adenosine receptors are implicated in the attenuation of inflammation and organ ischemia-reperfusion injury. We hypothesized that activation of A(1), A(2A), or A(3) adenosine receptors would provide protection against lung ischemia-reperfusion injury.

METHODS

With the use of an isolated, ventilated, blood-perfused rabbit lung model, lungs underwent 18 hours of cold ischemia followed by 2 hours of reperfusion. Lungs were administered vehicle, adenosine, or selective A(1), A(2A), or A(3) receptor agonists (CCPA, ATL-313, or IB-MECA, respectively) alone or with their respective antagonists (DPCPX, ZM241385, or MRS1191) during reperfusion.

RESULTS

Compared with the vehicle-treated control group, treatment with A(1), A(2A), or A(3) agonists significantly improved function (increased lung compliance and oxygenation and decreased pulmonary artery pressure), decreased neutrophil infiltration by myeloperoxidase activity, decreased edema, and reduced tumor necrosis factor-alpha production. Adenosine treatment was also protective, but not to the level of the agonists. When each agonist was paired with its respective antagonist, all protective effects were blocked. The A(2A) agonist reduced pulmonary artery pressure and myeloperoxidase activity and increased oxygenation to a greater degree than the A(1) or A(3) agonists.

CONCLUSION

Selective activation of A(1), A(2A), or A(3) adenosine receptors provides significant protection against lung ischemia-reperfusion injury. The decreased elaboration of the potent proinflammatory cytokine tumor necrosis factor-alpha and decreased neutrophil sequestration likely contribute to the overall improvement in pulmonary function. These results provide evidence for the therapeutic potential of specific adenosine receptor agonists in lung transplant recipients.

Role of extracellular adenosine in acute lung injury

Acute lung injury (ALI) is a lung disease characterized by pulmonary edema and severe hypoxia. The past decade hosted a search for endogenous mechanisms controlling lung inflammation and pulmonary edema during ALI. As such, recent evidence indicates extracellular adenosine in orchestrating the resolution of pulmonary edema and inflammation during ALI.

ATL 313, A Selective A(2A) Adenosine Receptor Agonist, Reduces Myocardial Infarct Size in a Rat Ischemia/Reperfusion Model

Objective:

The cardioprotective effects of activation of the A_2A adenosine receptor (A_2AAR) on ischemia/reperfusion injury in the heart remain controversial. We investigated whether ATL 313, a new selective A_2AAR agonist, could reduce myocardial infarct size in a rat ischemia/reperfusion model.

Methods:

Sprague-Dawley rats were subjected to a 40 minute occlusion of the left coronary artery followed by 3 hours reperfusion. Hemodynamics were monitored during the procedure. The rats were divided into 3 groups: Group 1 received continuous intravenous infusion of saline given 10 min prior to ischemia and throughout reperfusion (n=8); Group 2 received continuous intravenous infusion of 10 ng/kg/min of ATL 313 given 10 min prior to ischemia, and throughout reperfusion (n=8); and group 3 received an intravenous bolus of ATL 313 (900 ng/Kg body weight) given 10 min prior to ischemia, and continuous intravenous infusion of 10 ng/kg/min of ATL 313 started at 20 min after ischemia and throughout reperfusion (n=8). After euthanasia of the rats, the hearts were harvested for the assessment of risk zone and zone of necrosis of the left ventricle.

Results:

The percentage of risk zone in the left ventricle was similar among group 1 (47 ± 3.7 %), group 2 (41.5 ± 4.2 %) and group 3 (42.4 ± 3.8 %). However, the infarct size, expressed as a percentage of the risk zone, was significantly decreased in group 3 (30.6 ± 5 %, P=0.01) compared with group 1 (53.8 ± 6.2 %) and group 2 (52.1 ± 4.8 %). In group 3, the bolus injection of ATL 313 caused a reduction in blood pressure during the procedure, and decreased heart rate and LV ±dp/dt before coronary artery occlusion; but increased LV +dp/dt at the end of reperfusion compared to the other 2 groups.

Conclusion:

A_2AAR agonist ATL313 significantly reduced infarct size and improved LV contractility at the end of reperfusion assessed by LV dp/dt at a dose of 900 ng/Kg. The mechanisms for the observed cardioprotection effect of ATL313 remain to be determined.

Adenosine A2A receptor activation on CD4+ T lymphocytes and neutrophils attenuates lung ischemia-reperfusion injury

OBJECTIVE

Adenosine A(2A) receptor activation potently attenuates lung ischemia-reperfusion injury. This study tests the hypothesis that adenosine A(2A) receptor activation attenuates ischemia-reperfusion injury by inhibiting CD4+ T cell activation and subsequent neutrophil infiltration.

METHODS

An in vivo model of lung ischemia-reperfusion injury was used. C57BL/6 mice were assigned to either sham group (left thoracotomy) or 7 study groups that underwent ischemia-reperfusion (1 hour of left hilar occlusion plus 2 hours of reperfusion). ATL313, a selective adenosine A(2A) receptor agonist, was administered 5 minutes before reperfusion with or without antibody depletion of neutrophils or CD4+ T cells. After reperfusion, the following was measured: pulmonary function using an isolated, buffer-perfused lung system, T cell infiltration by immunohistochemistry, myeloperoxidase and proinflammatory cytokine/chemokine levels in bronchoalveolar lavage fluid, lung wet/dry weight, and microvascular permeability.

RESULTS

ATL313 significantly improved pulmonary function and reduced edema and microvascular permeability after ischemia-reperfusion compared with control. Immunohistochemistry and myeloperoxidase content demonstrated significantly reduced infiltration of neutrophils and CD4+ T cells after ischemia-reperfusion in ATL313-treated mice. Although CD4+ T cell-depleted and neutrophil-depleted mice displayed significantly reduced lung injury, no additional protection occurred when ATL313 was administered to these mice. Expression of tumor necrosis factor-alpha, interleukin 17, KC, monocyte chemotactic protein-1, macrophage inflammatory protein-1, and RANTES were significantly reduced in neutrophil- and CD4+ T cell-depleted mice and reduced further by ATL313 only in neutrophil-depleted mice.

CONCLUSIONS

These results demonstrate that CD4+ T cells play a key role in mediating lung inflammation after ischemia-reperfusion. ATL313 likely exerts its protective effect largely through activation of adenosine A(2A) receptors on CD4+ T cells and neutrophils.

The role of adenosine A2A receptor signaling in bronchiolitis obliterans

BACKGROUND

Binding of adenosine to the anti-inflammatory Gs-coupled adenosine 2A receptor (A(2A)R) inhibits the activity of most inflammatory cells. Extensive preclinical evidence exists for the use of A(2A)R agonists in the prevention of acute ischemia-reperfusion injury. Activation of A(2A)Rs on lymphocytes and antigen-presenting cells also attenuates the alloimmune response. Because ischemia-reperfusion injury and alloimmunity are risk factors for the development of bronchiolitis obliterans (BO), the objective of this study was to determine the effect of A(2A)R signaling on tracheal rejection in a mouse model of BO.

METHODS

A non-revascularized heterotopic tracheal model across a total alloantigenic mismatch was used to study A(2A)R signaling in a mouse model of BO. Tracheal transplants were performed using Balb/c donors into wild-type or A(2A)R knockout C57BL/6 recipient mice. Another group of Balb/c transplants into C57BL/6 recipients were also treated with a selective A(2A)R agonist. Tracheas were assessed at 3, 7, 12, 21, and 28 days after transplantation by hematoxylin and eosin staining, immunohistochemical staining, and collagen staining.

RESULTS

Compared with allograft tracheas in wild-type recipients, allografts in A(2A)R knockout recipients had increased inflammation and more severe BO development. Recipient wild-type mice treated with a selective A(2A)R agonist were significantly protected from lymphocyte infiltration and luminal occlusion, but fibro-obliteration still developed by 28 days after transplantation.

CONCLUSIONS

Endogenous adenosine signals through the A(2A)R to attenuate inflammatory and immune factors involved in BO development. Synthetic A(2A)R agonists may provide a novel treatment strategy to prevent BO.

Protection from pulmonary ischemia-reperfusion injury by adenosine A2A receptor activation

Background

Lung ischemia-reperfusion (IR) injury leads to significant morbidity and mortality which remains a major obstacle after lung transplantation. However, the role of various subset(s) of lung cell populations in the pathogenesis of lung IR injury and the mechanisms of cellular protection remain to be elucidated. In the present study, we investigated the effects of adenosine A_2A receptor (A_2AAR) activation on resident lung cells after IR injury using an isolated, buffer-perfused murine lung model.

Methods

To assess the protective effects of A_2AAR activation, three groups of C57BL/6J mice were studied: a sham group (perfused for 2 hr with no ischemia), an IR group (1 hr ischemia + 1 hr reperfusion) and an IR+ATL313 group where ATL313, a specific A_2AAR agonist, was included in the reperfusion buffer after ischemia. Lung injury parameters and pulmonary function studies were also performed after IR injury in A_2AAR knockout mice, with or without ATL313 pretreatment. Lung function was assessed using a buffer-perfused isolated lung system. Lung injury was measured by assessing lung edema, vascular permeability, cytokine/chemokine activation and myeloperoxidase levels in the bronchoalveolar fluid.

Results

After IR, lungs from C57BL/6J wild-type mice displayed significant dysfunction (increased airway resistance, pulmonary artery pressure and decreased pulmonary compliance) and significant injury (increased vascular permeability and edema). Lung injury and dysfunction after IR were significantly attenuated by ATL313 treatment. Significant induction of TNF-α, KC (CXCL1), MIP-2 (CXCL2) and RANTES (CCL5) occurred after IR which was also attenuated by ATL313 treatment. Lungs from A_2AAR knockout mice also displayed significant dysfunction, injury and cytokine/chemokine production after IR, but ATL313 had no effect in these mice.

Conclusion

Specific activation of A_2AARs provides potent protection against lung IR injury via attenuation of inflammation. This protection occurs in the absence of circulating blood thereby indicating a protective role of A_2AAR activation on resident lung cells such as alveolar macrophages. Specific A_2AAR activation may be a promising therapeutic target for the prevention or treatment of pulmonary graft dysfunction in transplant patients.

CD4+ T lymphocytes mediate acute pulmonary ischemia-reperfusion injury

OBJECTIVE

Postischemic reperfusion of the lung triggers proinflammatory responses that stimulate injurious neutrophil chemotaxis. We hypothesized that T lymphocytes are recruited and activated during reperfusion and mediate subsequent neutrophil-induced lung ischemia-reperfusion injury.

METHODS

An in vivo mouse model of lung ischemia-reperfusion injury was used. C57BL/6 mice were assigned to either the sham group (left thoracotomy) or 7 study groups that underwent 1-hour left hilar occlusion followed by 1 to 24 hours of reperfusion. After in vivo reperfusion, the lungs were perfused ex vivo with buffer whereby pulmonary function was assessed. Lung vascular permeability, edema, neutrophil accumulation, and cytokine/chemokine production (tumor necrosis factor alpha, interleukin 17, CCL3, and CXCL1) were assessed based on Evans blue dye leak, wet/dry weight ratio, myeloperoxidase level, and enzyme-linked immunosorbent assay, respectively.

RESULTS

A preliminary study showed that 2 hours of reperfusion resulted in greater pulmonary dysfunction than 1 or 24 hours of reperfusion. The 2-hour reperfusion period was thus used for the remaining experiments. Comparable and significant protection from ischemia-reperfusion injury-induced lung dysfunction and injury occurred after antibody depletion of neutrophils or CD4(+) T cells but not CD8(+) T cells (P < .05 vs immunoglobulin G control). Lung ischemia-reperfusion injury was proportional to the infiltration of neutrophils but not T cells. Moreover, pulmonary neutrophil infiltration and the production of CXCL1 (KC) were significantly diminished by CD4(+) T-cell depletion but not vice versa.

CONCLUSIONS

Both CD4(+) T lymphocytes and neutrophils accumulate during reperfusion and contribute sequentially to lung ischemia-reperfusion injury. The data suggest that neutrophils mediate ischemia-reperfusion injury; however, CD4(+) T cells play a critical role in stimulating chemokine production and neutrophil chemotaxis during ischemia-reperfusion injury.

Adenosine deaminase-adenosine pathway in hemolysis-associated pulmonary hypertension

Hemolysis-associated pulmonary hypertension (HA-PH) is a serious clinical complication of various hemolytic disorders, and pulmonary hypertension (PH) is considered the greatest risk factor for death in patients with a hemolytic disorder. It is now well established that hemolysis causes the release of soluble hemoglobin and arginase from injured erythrocytes into plasma. This leads to nitric oxide (NO) deficiency, oxidative stress and a state of endothelial dysfunction that is associated with clinical development of PH. We challenge this concept and propose that in addition to the NO-arginase pathway, the adenosine deaminase-adenosine pathway plays a significant role in HA-PH and that modulation of this pathway may offer protective/therapeutic effects in HA-PH. Our preliminary data suggest that in HA-PH adenosine deaminase (ADA) is released from injured erythrocytes into plasma and that metabolic conversion of adenosine (ADO) to inosine by ADA reduces extracellular ADO levels. Adenosine, mainly via activation of adenosine A(2A) receptors, mediates a number of biological responses that may reduce hemolysis-induced vasculopathy and the risk of PH. Hypoxia is the strongest stimulus for ADO synthesis, and this increased ADO production counteracts some of the tissue/vascular injury caused by hypoxia itself. Unfortunately, under hypoxic conditions (anemia, vasoconstriction, and vaso-occlusion) in HA-PH, this "ADO negative-feed back" is abolished and the vascular protective effects of ADO are severely diminished by ADA released from injured erythrocytes. We hypothesize that in hemolytic anemia the repetitive release of ADA increases the risk for vaso-occlusive events and PH. We also propose that increase in extracellular ADO levels or activation of adenosine A(2A) receptors attenuates HA-PH, and we suggest further preclinical and clinical investigation of ADA inhibitors and ADO agonists in HA-PH.

Attenuation of gastric mucosal inflammation induced by indomethacin through activation of the A2A adenosine receptor in rats

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin induce gastric mucosal lesions in part by the activation of inflammatory cells and the production of proinflammatory cytokines. The activation of adenosine A(2A) receptors inhibits inflammation by increasing cyclic AMP in leukocytes and reducing both the production of various proinflammatory cytokines and neutrophil chemotaxis. The aim of present study was to determine whether administration of an orally active adenosine A(2A) receptor agonist (4-[3-[6-amino-9-(5-cyclopropylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl]-piperidine-1-carboxylic acid methyl ester; ATL-313) ameliorated indomethacin-induced gastric mucosal lesions in rats.

METHODS

Gastric lesions were produced by oral gavage of indomethacin (30 mg/kg). ATL-313 (1-10 microg/kg) was given orally just before the indomethacin administration.

RESULTS

The ulcer index induced by indomethacin was significantly (>50%) reduced by pretreatment with ATL-313 and this effect was blocked completely by the addition of equimolar ZM241385, a selective A(2A) receptor antagonist. The gastric content of myeloperoxidase (MPO) and proinflammatory cytokines was significantly reduced by 10 microg/kg ATL-313, but gastric mucosal prostaglandin 2 (PGE2) was not affected.

CONCLUSION

We conclude that ATL-313 does not inhibit the mucosal damaging effect of indomethacin, but it does block secondary injury due to stomach inflammation. A(2A) agonists may represent a class of new therapeutic drugs for NSAID-induced gastric ulcers.

Inflammatory lung injury after cardiopulmonary bypass is attenuated by adenosine A(2A) receptor activation

OBJECTIVE

Cardiopulmonary bypass has been shown to exert an inflammatory response within the lung, often resulting in postoperative pulmonary dysfunction. Several studies have shown that adenosine A(2A) receptor activation attenuates lung ischemia-reperfusion injury; however, the effect of adenosine A(2A) receptor activation on cardiopulmonary bypass-induced lung injury has not been studied. We hypothesized that specific adenosine A(2A) receptor activation by ATL313 would attenuate inflammatory lung injury after cardiopulmonary bypass.

METHODS

Adult male Sprague-Dawley rats were randomly divided into 3 groups: 1) SHAM group (underwent cannulation + heparinization only); 2) CONTROL group (underwent 90 minutes of normothermic cardiopulmonary bypass with normal whole-blood priming solution; and 3) ATL group (underwent 90 minutes of normothermic cardiopulmonary bypass with ATL313 added to the normal priming solution).

RESULTS

There was significantly less pulmonary edema and lung injury in the ATL group compared with the CONTROL group. The ATL group had significant reductions in bronchoalveolar lavage interleukin-1, interleukin-6, interferon-gamma, and myeloperoxidase levels compared with the CONTROL group. Similarly, lung tissue interleukin-6, tumor necrosis factor-alpha, and interferon-gamma were significantly decreased in the ATL group compared with the CONTROL group. There was no significant difference between the SHAM and ATL groups in the amount of pulmonary edema, lung injury, or levels of proinflammatory cytokines.

CONCLUSION

The addition of a potent adenosine A(2A) receptor agonist to the normal priming solution before the initiation of cardiopulmonary bypass significantly protects the lung from the inflammatory effects of cardiopulmonary bypass and reduces the amount of lung injury. Adenosine A(2A) receptor agonists could represent a new therapeutic strategy for reducing the potentially devastating consequences of the inflammatory response associated with cardiopulmonary bypass.