A2B adenosine receptor signaling attenuates acute lung injury by enhancing alveolar fluid clearance in mice

Modafinil exerts anti-inflammatory and anti-fibrotic effects by upregulating adenosine A2A and A2B receptors

Adenosine receptor (AR) suppresses inflammation and fibrosis by activating cyclic adenosine monophosphate (cAMP) signaling. We investigated whether altered AR expression contributes to the development of fibrotic diseases and whether A2AAR and A2BAR upregulation inhibits fibrotic responses. Primary human lung fibroblasts (HLFs) from normal (NHLFs) or patients with idiopathic pulmonary fibrosis (DHLF) were used for in vitro testing. Murine models of fibrotic liver or pulmonary disease were developed by injecting thioacetamide intraperitoneally, by feeding a high-fat diet, or by intratracheal instillation of bleomycin. Modafinil, which activates cAMP signaling via A2AAR and A2BAR, was administered orally. The protein amounts of A2AAR, A2BAR, and exchange protein directly activated by cAMP (Epac) were reduced, while collagen and α-smooth muscle actin (α-SMA) were elevated in DHLFs compared to NHLFs. In liver or lung tissue from murine models of fibrotic diseases, A2AAR and A2BAR were downregulated, but A1AR and A3AR were not. Epac amounts decreased, and amounts of collagen, α-SMA, KCa2.3, and KCa3.1 increased compared to the control. Modafinil restored the amounts of A2AAR, A2BAR, and Epac, and reduced collagen, α-SMA, KCa2.3, and KCa3.1 in murine models of fibrotic diseases. Transforming growth factor-β reduced the amounts of A2AAR, A2BAR, and Epac, and elevated collagen, α-SMA, KCa2.3, and KCa3.1 in NHLFs; however, these alterations were inhibited by modafinil. Our investigation revealed that A2AAR and A2BAR downregulation induced liver and lung fibrotic diseases while upregulation attenuated fibrotic responses, suggesting that A2AAR and A2BAR-upregulating agents, such as modafinil, may serve as novel therapies for fibrotic diseases.

Circadian Influences on Myocardial Ischemia-Reperfusion Injury and Heart Failure

The impact of circadian rhythms on cardiovascular function and disease development is well established, with numerous studies in genetically modified animals emphasizing the circadian molecular clock's significance in the pathogenesis and pathophysiology of myocardial ischemia and heart failure progression. However, translational preclinical studies targeting the heart's circadian biology are just now emerging and are leading to the development of a novel field of medicine termed circadian medicine. In this review, we explore circadian molecular mechanisms and novel therapies, including (1) intense light, (2) small molecules modulating the circadian mechanism, and (3) chronotherapies such as cardiovascular drugs and meal timings. These promise significant clinical translation in circadian medicine for cardiovascular disease. (4) Additionally, we address the differential functioning of the circadian mechanism in males versus females, emphasizing the consideration of biological sex, gender, and aging in circadian therapies for cardiovascular disease.

TR4 worsen urosepsis by regulating GSDMD

BACKGROUND

Urosepsis is a life-threatening organ disease in which pathogenic microorganisms in the urine enter the blood through the vessels, causing an imbalance in the immune response to infection. The aim of this study was to elucidate the role of testicular orphan receptor 4 (TR4) in urosepsis.

METHODS

The role of TR4 in the progression and prognosis of urosepsis was confirmed by analyzing data from online databases and clinical human samples. To mimic urosepsis, we injected E. coli bacteria into the renal pelvis of mice to create a urosepsis model. Hematoxylin and eosin staining was used to observe histopathological changes in urosepsis. The effects of the upregulation or downregulation of TR4 on macrophage pyroptosis were verified in vitro. Chromatin immunoprecipitation assay was used to verify the effect of TR4 on Gasdermin D (GSDMD) transcription.

RESULTS

TR4 was more highly expressed in the nonsurviving group than in the surviving group. Furthermore, overexpressing TR4 promoted inflammatory cytokine expression, and knocking down TR4 attenuated inflammatory cytokine expression. Mechanistically, TR4 promoted pyroptosis by regulating the expression of GSDMD in urosepsis. Furthermore, we also found that TR4 knockdown protected mice from urosepsis induced by the E. coli.

CONCLUSIONS

TR4 functions as a key regulator of urosepsis by mediating pyroptosis, which regulates GSDMD expression. Targeting TR4 may be a potential strategy for urosepsis treatment.

Protective effect of olopatadine hydrochloride against LPS-induced acute lung injury: via targeting NF-κB signaling pathway

BACKGROUND

Morbidity and mortality rates associated with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) are high (30-40%). Nuclear factor-kappa B (NF-κB) is a transcription factor, associated with transcription of numerous cytokines leading to cytokine storm, and thereby, plays a major role in ALI/ARDS and in advanced COVID-19 syndrome.

METHODS

Considering the role of NF-κB in ALI, cost-effective in silico approaches were utilized in the study to identify potential NF-κB inhibitor based on the docking and pharmacokinetic results. The identified compound was then pharmacologically validated in lipopolysaccharide (LPS) rodent model of acute lung injury. LPS induces ALI by altering alveolar membrane permeability, recruiting activated neutrophils and macrophages to the lungs, and compromising the alveolar membrane integrity and ultimately impairs the gaseous exchange. Furthermore, LPS exposure is associated with exaggerated production of various proinflammatory cytokines in lungs.

RESULTS

Based on in silico studies Olopatadine Hydrochloride (Olo), an FDA-approved drug was found as a potential NF-κB inhibitor which has been reported for the first time, and considered further for the pharmacological validation. Intraperitoneal LPS administration resulted in ALI/ARDS by fulfilling 3 out of the 4 criteria described by ATS committee (2011) published workshop report. However, treatment with Olo attenuated LPS-induced elevation of proinflammatory markers (IL-6 and NF-κB), oxidative stress, neutrophil infiltration, edema, and damage in lungs. Histopathological studies also revealed that Olo treatment significantly ameliorated LPS-induced lung injury, thus conferring improvement in survival. Especially, the effects produced by Olo medium dose (1 mg/kg) were comparable to dexamethasone standard.

CONCLUSION

In nutshell, inhibition of NF-κB pathway by Olo resulted in protection and reduced mortality in LPS- induced ALI and thus has potential to be used clinically to arrest disease progression in ALI/ARDS, since the drug is already in the market. However, the findings warrant further extensive studies, and also future studies can be planned to elucidate its role in COVID-19-associated ARDS or cytokine storm.

Hypoxia-adenosine axis as therapeutic targets for acute respiratory distress syndrome

The human respiratory and circulatory systems collaborate intricately to ensure oxygen delivery to all cells, which is vital for ATP production and maintaining physiological functions and structures. During limited oxygen availability, hypoxia-inducible factors (HIFs) are stabilized and play a fundamental role in maintaining cellular processes for hypoxia adaptation. First discovered during investigations of erythropoietin production regulation, HIFs influence physiological and pathological processes, including development, inflammation, wound healing, and cancer. HIFs promote extracellular adenosine signaling by enhancing adenosine generation and receptor signaling, representing an endogenous feedback mechanism that curbs excessive inflammation, supports injury resolution, and enhances hypoxia tolerance. This is especially important for conditions that involve tissue hypoxia, such as acute respiratory distress syndrome (ARDS), which globally poses significant health challenges without specific treatment options. Consequently, pharmacological strategies to amplify HIF-mediated adenosine production and receptor signaling are of great importance.

The resurgence of the Adora2b receptor as an immunotherapeutic target in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense desmoplastic stroma that impedes drug delivery, reduces parenchymal blood flow, and suppresses the anti-tumor immune response. The extracellular matrix and abundance of stromal cells result in severe hypoxia within the tumor microenvironment (TME), and emerging publications evaluating PDAC tumorigenesis have shown the adenosine signaling pathway promotes an immunosuppressive TME and contributes to the overall low survival rate. Hypoxia increases many elements of the adenosine signaling pathway, resulting in higher adenosine levels in the TME, further contributing to immune suppression. Extracellular adenosine signals through 4 adenosine receptors (Adora1, Adora2a, Adora2b, Adora3). Of the 4 receptors, Adora2b has the lowest affinity for adenosine and thus, has important consequences when stimulated by adenosine binding in the hypoxic TME. We and others have shown that Adora2b is present in normal pancreas tissue, and in injured or diseased pancreatic tissue, Adora2b levels are significantly elevated. The Adora2b receptor is present on many immune cells, including macrophages, dendritic cells, natural killer cells, natural killer T cells, γδ T cells, B cells, T cells, CD4+ T cells, and CD8+ T cells. In these immune cell types, adenosine signaling through Adora2b can reduce the adaptive anti-tumor response, augmenting immune suppression, or may contribute to transformation and changes in fibrosis, perineural invasion, or the vasculature by binding the Adora2b receptor on neoplastic epithelial cells, cancer-associated fibroblasts, blood vessels, lymphatic vessels, and nerves. In this review, we discuss the mechanistic consequences of Adora2b activation on cell types in the tumor microenvironment. As the cell-autonomous role of adenosine signaling through Adora2b has not been comprehensively studied in pancreatic cancer cells, we will also discuss published data from other malignancies to infer emerging therapeutic considerations for targeting the Adora2b adenosine receptor to reduce the proliferative, invasive, and metastatic potential of PDAC cells.

Pulmonary drug delivery for acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a life-threatening condition that causes respiratory failure. Despite numerous clinical trials, there are no molecularly targeted pharmacologic therapies to prevent or treat ARDS. Drug delivery during ARDS is challenging due to the heterogenous nature of lung injury and occlusion of lung units by edema fluid and inflammation. Pulmonary drug delivery during ARDS offers several potential advantages including limiting the off-target and off-organ effects and directly targeting the damaged and inflamed lung regions. In this review we summarize recent ARDS clinical trials using both systemic and pulmonary drug delivery. We then discuss the advantages of pulmonary drug delivery and potential challenges to its implementation. Finally, we discuss the use of nanoparticle drug delivery and surfactant-based drug carriers as potential strategies for delivering therapeutics to the injured lung in ARDS.

Human Neutrophil Defensins Disrupt Liver Interendothelial Junctions and Aggravate Sepsis

Human neutrophil peptides 1-3 (HNP1-3), also known as human α-defensins, are the most abundant neutrophil granule proteins. The genes that encode HNP1-3, DEFA1/DEFA3, exhibit extensive copy number variations, which correlate well with their protein levels. Human and mouse studies have shown that increased copy numbers of DEFA1/DEFA3 worsen sepsis outcomes. Additionally, high concentrations of HNP1-3 in body fluids have been reported in patients with sepsis. However, direct evidence for the pathogenic role of HNP1-3 proteins during sepsis progression is lacking. In current study, sepsis was induced by means of cecal puncture and ligation. Various doses of HNP-1 (low dose with 0.5 mg/kg body weight and high dose with 10 mg/kg body weight) or phosphate buffer saline were intraperitoneally administered to mice at six hours after sepsis onset. Survival rate was monitored, and vascular permeability, endothelial cell pyroptosis, and immunofluorescence of endothelial adherens junction protein vascular endothelial-cadherin were evaluated. The administration of a high dose of HNP-1 after sepsis onset led to increased mortality, more severe liver injury, and increased vascular permeability in the liver and mesentery. The injection of high dose of HNP-1 did not directly induce liver endothelial cell death but destroyed interendothelial junctions in the liver. Moreover, genetic deficiency of nucleotide-binding oligomerization domain-like receptor protein-3 or caspase-1 abrogated the high mortality and disrupted liver interendothelial junctions caused by high dose of HNP-1 during sepsis. This study directly demonstrates that neutrophil defensins play a key role in regulating endothelial stability during sepsis development.

Alternative adenosine Receptor activation: The netrin-Adora2b link

During hypoxia or inflammation, extracellular adenosine levels are elevated. Studies using pharmacologic approaches or genetic animal models pertinent to extracellular adenosine signaling implicate this pathway in attenuating hypoxia-associated inflammation. There are four distinct adenosine receptors. Of these, it is not surprising that the Adora2b adenosine receptor functions as an endogenous feedback loop to control hypoxia-associated inflammation. First, Adora2b activation requires higher adenosine concentrations compared to other adenosine receptors, similar to those achieved during hypoxic inflammation. Second, Adora2b is transcriptionally induced during hypoxia or inflammation by hypoxia-inducible transcription factor HIF1A. Studies seeking an alternative adenosine receptor activation mechanism have linked netrin-1 with Adora2b. Netrin-1 was originally discovered as a neuronal guidance molecule but also functions as an immune-modulatory signaling molecule. Similar to Adora2b, netrin-1 is induced by HIF1A, and has been shown to enhance Adora2b signaling. Studies of acute respiratory distress syndrome (ARDS), intestinal inflammation, myocardial or hepatic ischemia and reperfusion implicate the netrin-Adora2b link in tissue protection. In this review, we will discuss the potential molecular linkage between netrin-1 and Adora2b, and explore studies demonstrating interactions between netrin-1 and Adora2b in attenuating tissue inflammation.

Effects of Hypoxia on Respiratory Diseases: Perspective View of Epithelial Ion Transport

The balance of gas exchange and lung ventilation is essential for the maintenance of body homeostasis. There are many ion channels and transporters in respiratory epithelial cells, including epithelial sodium channel, Na,K-ATPase, cystic fibrosis transmembrane conductance regulator, and some transporters. These ion channels/transporters maintain the capacity of liquid layer on the surface of respiratory epithelial cells, and provide an immune barrier for the respiratory system to clear off foreign pathogens. However, in some harmful external environment and/or pathological conditions, the respiratory epithelium is prone to hypoxia, which would destroy the ion transport function of the epithelium and unbalance the homeostasis of internal environment, triggering a series of pathological reactions. Many respiratory diseases associated with hypoxia manifest an increased expression of hypoxia-inducible factor-1, which mediates the integrity of the epithelial barrier and affects epithelial ion transport function. It is important to study the relationship between hypoxia and ion transport function, whereas the mechanism of hypoxia-induced ion transport dysfunction in respiratory diseases is not clear. This review focuses on the relationship of hypoxia and respiratory diseases, as well as dysfunction of ion transport and tight junctions in respiratory epithelial cells under hypoxia.

Therapeutic Targeting of Hypoxia-A2-Adenosinergic Pathway in COVID-19 Patients

The hypoxia-hypoxia-inducible factor (HIF)-1α-A2-adenosinergic pathway protects tissues from inflammatory damage during antipathogen immune responses. The elimination of this physiological tissue-protecting mechanism by supplemental oxygenation may contribute to the high mortality of oxygen-ventilated COVID-19 patients by exacerbating inflammatory lung damage. Restoration of this pathway with hypoxia-adenosinergic drugs may improve outcomes in these patients.

A novel definition and treatment of hyperinflammation in COVID-19 based on purinergic signalling

Hyperinflammation plays an important role in severe and critical COVID-19. Using inconsistent criteria, many researchers define hyperinflammation as a form of very severe inflammation with cytokine storm. Therefore, COVID-19 patients are treated with anti-inflammatory drugs. These drugs appear to be less efficacious than expected and are sometimes accompanied by serious adverse effects. SARS-CoV-2 promotes cellular ATP release. Increased levels of extracellular ATP activate the purinergic receptors of the immune cells initiating the physiologic pro-inflammatory immune response. Persisting viral infection drives the ATP release even further leading to the activation of the P2X7 purinergic receptors (P2X7Rs) and a severe yet physiologic inflammation. Disease progression promotes prolonged vigorous activation of the P2X7R causing cell death and uncontrolled ATP release leading to cytokine storm and desensitisation of all other purinergic receptors of the immune cells. This results in immune paralysis with co-infections or secondary infections. We refer to this pathologic condition as hyperinflammation. The readily available and affordable P2X7R antagonist lidocaine can abrogate hyperinflammation and restore the normal immune function. The issue is that the half-maximal effective concentration for P2X7R inhibition of lidocaine is much higher than the maximal tolerable plasma concentration where adverse effects start to develop. To overcome this, we selectively inhibit the P2X7Rs of the immune cells of the lymphatic system inducing clonal expansion of Tregs in local lymph nodes. Subsequently, these Tregs migrate throughout the body exerting anti-inflammatory activities suppressing systemic and (distant) local hyperinflammation. We illustrate this with six critically ill COVID-19 patients treated with lidocaine.

Re-Du-Ning injection ameliorates LPS-induced lung injury through inhibiting neutrophil extracellular traps formation

BACKGROUND

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening diseases and could occur in severe COVID-19 patients. Re-Du-Ning injection (RDN) is a tradition Chinese medicine preparation which has been clinically used for treatment of respiratory diseases including COVID-19.

PURPOSE

To elucidate the potential mechanisms of RDN for the treatment of ALI.

METHODS

Female C57BL/6J mice were used to establish ALI model by intraperitoneal injection 10 mg/kg LPS, and RDN injection was intraperitoneally administered with the dose of 5 and 10 ml/kg. The cytokines were measured by ELISA and qPCR. The data related to NETs were analyzed by ELISA, immunofluorescence, Western blotting and network pharmacological approach.

RESULTS

RDN robustly alleviated LPS-induced ALI. Meanwhile, RDN downregulated the expression of pro-inflammatory cytokines, such as IL-1β, IL-6 and TNF-α. Specifically, RDN treatment inhibited the formation of neutrophil extracellular traps (NETs) and remarkably suppressed the protein of PAD4. The active compound from RDN decreased the phosphorylation of ERK1/2.

CONCLUSION

These findings demonstrate that RDN ameliorates LPS-induced ALI through suppressing MAPK pathway to inhibit the formation of NETs.

Targeting circadian PER2 as therapy in myocardial ischemia and reperfusion injury

The cycle of day and night dominates life on earth. Therefore, almost all living organisms adopted a molecular clock linked to the light-dark cycles. It is now well established that this molecular clock is crucial for human health and wellbeing. Disruption of the molecular clockwork directly results in a myriad of disorders, including cardiovascular diseases. Further, the onset of many cardiovascular diseases such as acute myocardial infarction exhibits a circadian periodicity with worse outcomes in the early morning hours. Based on these observations, the research community became interested in manipulating the molecular clock to treat cardiovascular diseases. In recent years, several exciting discoveries of pharmacological agents or molecular mechanisms targeting the molecular clockwork have paved the way for circadian medicine's arrival in cardiovascular diseases. The current review will outline the most recent circadian therapeutic advances related to the circadian rhythm protein Period2 (PER2) to treat myocardial ischemia and summarize future research in the respective field.

Alcohol inhibits alveolar fluid clearance through the epithelial sodium channel via the A2 adenosine receptor in acute lung injury

Chronic alcohol abuse increases the risk of mortality and poor outcomes in patients with acute respiratory distress syndrome. However, the underlying mechanisms remain to be elucidated. The present study aimed to investigate the effects of chronic alcohol consumption on lung injury and clarify the signaling pathways involved in the inhibition of alveolar fluid clearance (AFC). In order to produce rodent models with chronic alcohol consumption, wild‑type C57BL/6 mice were treated with alcohol. A2a adenosine receptor (AR) small interfering (si)RNA or A2bAR siRNA were transfected into the lung tissue of mice and primary rat alveolar type II (ATII) cells. The rate of AFC in lung tissue was measured during exposure to lipopolysaccharide (LPS). Epithelial sodium channel (ENaC) expression was determined to investigate the mechanisms underlying alcohol‑induced regulation of AFC. In the present study, exposure to alcohol reduced AFC, exacerbated pulmonary edema and worsened LPS‑induced lung injury. Alcohol caused a decrease in cyclic adenosine monophosphate (cAMP) levels and inhibited α‑ENaC, β‑ENaC and γ‑ENaC expression levels in the lung tissue of mice and ATII cells. Furthermore, alcohol decreased α‑ENaC, β‑ENaC and γ‑ENaC expression levels via the A2aAR or A2bAR‑cAMP signaling pathways in vitro. In conclusion, the results of the present study demonstrated that chronic alcohol consumption worsened lung injury by aggravating pulmonary edema and impairing AFC. An alcohol‑induced decrease of α‑ENaC, β‑ENaC and γ‑ENaC expression levels by the A2AR‑mediated cAMP pathway may be responsible for the exacerbated effects of chronic alcohol consumption in lung injury.

Characterization of a Murine Model System to Study MicroRNA-147 During Inflammatory Organ Injury

Inflammatory organ injury and sepsis have profound impacts on the morbidity and mortality of surgical and critical care patients. MicroRNAs are small RNAs composed of 20-25 nucleotides that have a significant contribution to gene regulation. MicroRNA-147 (miR-147), in particular, has been shown to have an emerging role in different physiological functions such as cell cycle regulation and inflammatory responses. However, animal model systems to study tissue-specific functions of miR-147 during inflammatory conditions in vivo are lacking. In the present study, we characterize miR-147 expression in different organs and cell types. Next, we generated a transgenic mouse line with a floxed miR-147 gene. Subsequently, we used this mouse line to generate mice with whole-body deletion of miR-147 (miR-147 -/-) by crossing "floxed" miR-147 mice with transgenic mice expressing Cre recombinase in all tissues (CMVcre mice). Systematic analysis of miR-147 -/- mice demonstrates normal growth, development, and off-spring. In addition, deletion of the target gene in different organs was successful at baseline or during inflammation, including the heart, intestine, stomach, liver, spleen, bone marrow, lungs, kidneys, or stomach. Moreover, miR-147 -/- mice have identical baseline inflammatory gene expression compared to C57BL/6 mice, except elevated IL-6 expression in the spleen (7.5 fold, p < 0.05). Taken together, our data show the successful development of a transgenic animal model for tissue and cell-specific deletion of miR-147 that can be used to study the functional roles of miR-147 during inflammatory organ injury.

Adenosine and Inflammation: Here, There and Everywhere

Adenosine is a ubiquitous endogenous modulator with the main function of maintaining cellular and tissue homeostasis in pathological and stress conditions. It exerts its effect through the interaction with four G protein-coupled receptor (GPCR) subtypes referred as A1, A2A, A2B, and A3 adenosine receptors (ARs), each of which has a unique pharmacological profile and tissue distribution. Adenosine is a potent modulator of inflammation, and for this reason the adenosinergic system represents an excellent pharmacological target for the myriad of diseases in which inflammation represents a cause, a pathogenetic mechanism, a consequence, a manifestation, or a protective factor. The omnipresence of ARs in every cell of the immune system as well as in almost all cells in the body represents both an opportunity and an obstacle to the clinical use of AR ligands. This review offers an overview of the cardinal role of adenosine in the modulation of inflammation, showing how the stimulation or blocking of its receptors or agents capable of regulating its extracellular concentration can represent promising therapeutic strategies for the treatment of chronic inflammatory pathologies, neurodegenerative diseases, and cancer.

Late Protective Effect of Netrin-1 in the Murine Acetaminophen Hepatotoxicity Model

Acetaminophen (APAP) overdose-induced acute liver failure is an important clinical problem in the United States and the current antidote N-acetylcysteine, has a short early therapeutic window. Since most patients present late to the clinic, there is need for novel late-acting therapeutic options. Though the neuronal guidance cue netrin-1, has been shown to promote hepatic repair and regeneration during liver ischemia/reperfusion injury, its effect in APAP-induced hepatotoxicity is unknown. In the quest for a late-acting therapeutic intervention in APAP-induced liver injury, we examined the role of netrin-1 in a mouse model of APAP overdose. Male C57BL/6J mice were cotreated with exogenous netrin-1 or vehicle control, along with 300 mg/kg APAP and euthanized at 6, 12, and 24 h. Significant elevations in alanine aminotransferase indicative of liver injury were seen in control mice at 6 h and this was not affected by netrin-1 administration. Also, netrin-1 treatment did not influence mitochondrial translocation of phospho-JNK, or peroxynitrite formation indicating that there was no interference with APAP-induced injury processes. Interestingly however, netrin-1 administration attenuated liver injury at 24 h, as seen by alanine aminotransferase levels and histology, at which time significant elevations in the netrin-1 receptor, adenosine A2B receptor (A2BAR) as well as macrophage infiltration was evident. Removal of resident macrophages with clodronate liposomes or treatment with the A2BAR antagonist PSB1115 blocked the protective effects of netrin-1. Thus, our data indicate a previously unrecognized role for netrin-1 in attenuation of APAP hepatotoxicity by enhancing recovery and regeneration, which is mediated through the A2BAR and involves resident liver macrophages.

Machine Learning-Based Discovery of a Gene Expression Signature in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

To identify differentially expressed genes and networks from the airway cells within 72 hours of intubation of children with and without pediatric acute respiratory distress syndrome. To test the use of a neutrophil transcription reporter assay to identify immunogenic responses to airway fluid from children with and without pediatric acute respiratory distress syndrome.

DESIGN

Prospective cohort study.

SETTING

Thirty-six bed academic PICU.

PATIENTS

Fifty-four immunocompetent children, 28 with pediatric acute respiratory distress syndrome, who were between 2 days to 18 years old within 72 hours of intubation for acute hypoxemic respiratory failure.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We applied machine learning methods to a Nanostring transcriptomics on primary airway cells and a neutrophil reporter assay to discover gene networks differentiating pediatric acute respiratory distress syndrome from no pediatric acute respiratory distress syndrome. An analysis of moderate or severe pediatric acute respiratory distress syndrome versus no or mild pediatric acute respiratory distress syndrome was performed. Pathway network visualization was used to map pathways from 62 genes selected by ElasticNet associated with pediatric acute respiratory distress syndrome. The Janus kinase/signal transducer and activator of transcription pathway emerged. Support vector machine performed best for the primary airway cells and the neutrophil reporter assay using a leave-one-out cross-validation with an area under the operating curve and 95% CI of 0.75 (0.63-0.87) and 0.80 (0.70-1.0), respectively.

CONCLUSIONS

We identified gene networks important to the pediatric acute respiratory distress syndrome airway immune response using semitargeted transcriptomics from primary airway cells and a neutrophil reporter assay. These pathways will drive mechanistic investigations into pediatric acute respiratory distress syndrome. Further studies are needed to validate our findings and to test our models.

Hyperinflammation and airway surface liquid dehydration in cystic fibrosis: purinergic system as therapeutic target

OBJECTIVE AND DESIGN

The exacerbate inflammatory response contributes to the progressive loss of lung function in cystic fibrosis (CF), a genetic disease that affects the osmotic balance of mucus and mucociliary clearance, resulting in a microenvironment that favors infection and inflammation. The purinergic system, an extracellular signaling pathway characterized by nucleotides, enzymes and receptors, may have a protective role in the disease, through its action in airway surface liquid (ASL) and anti-inflammatory response.

MATERIALS AND METHODS

To make up this review, studies covering topics of CF, inflammation, ASL and purinergic system were selected from the main medical databases, such as Pubmed and ScienceDirect.

CONCLUSION

We propose several ways to modulate the purinergic system as a potential therapy for CF, like inhibition of P2X7, activation of P2Y2, A2A and A2B receptors and blocking of adenosine deaminase. Among them, we postulate that the most suitable strategy is to block the action of adenosine deaminase, which culminates in the increase of Ado levels that presents anti-inflammatory actions and improves mucociliary clearance. Furthermore, it is possible to maintain the physiological levels of ATP to control the hydration of ASL. These therapies could correct the main mechanisms that contribute to the progression of CF.

PMN-derived netrin-1 attenuates cardiac ischemia-reperfusion injury via myeloid ADORA2B signaling

Previous studies implicated the neuronal guidance molecule netrin-1 in attenuating myocardial ischemia-reperfusion injury. However, the tissue-specific sources and receptor signaling events remain elusive. Neutrophils are among the first cells responding to an ischemic insult and can be associated with tissue injury or rescue. We found netrin-1 levels were elevated in the blood of patients with myocardial infarction, as well as in mice exposed to myocardial ischemia-reperfusion. Selectively increased infarct sizes and troponin levels were found in Ntn1loxP/loxP Lyz2 Cre+ mice, but not in mice with conditional netrin-1 deletion in other tissue compartments. In vivo studies using neutrophil depletion identified neutrophils as the main source for elevated blood netrin-1 during myocardial injury. Finally, pharmacologic studies using treatment with recombinant netrin-1 revealed a functional role for purinergic signaling events through the myeloid adenosine A2b receptor in mediating netrin-1-elicited cardioprotection. These findings suggest an autocrine signaling loop with a functional role for neutrophil-derived netrin-1 in attenuating myocardial ischemia-reperfusion injury through myeloid adenosine A2b signaling.

Targeting alveolar-specific succinate dehydrogenase A attenuates pulmonary inflammation during acute lung injury

Acute lung injury (ALI) is an inflammatory lung disease, which manifests itself in patients as acute respiratory distress syndrome (ARDS). Previous studies have implicated alveolar-epithelial succinate in ALI protection. Therefore, we hypothesized that targeting alveolar succinate dehydrogenase SDH A would result in elevated succinate levels and concomitant lung protection. Wild-type (WT) mice or transgenic mice with targeted alveolar-epithelial Sdha or hypoxia-inducible transcription factor Hif1a deletion were exposed to ALI induced by mechanical ventilation. Succinate metabolism was assessed in alveolar-epithelial via mass spectrometry as well as redox measurements and evaluation of lung injury. In WT mice, ALI induced by mechanical ventilation decreased SDHA activity and increased succinate in alveolar-epithelial. In vitro, cell-permeable succinate decreased epithelial inflammation during stretch injury. Mice with inducible alveolar-epithelial Sdha deletion (Sdha^loxp/loxp SPC-CreER mice) revealed reduced lung inflammation, improved alveolar barrier function, and attenuated histologic injury. Consistent with a functional role of succinate to stabilize HIF, Sdha^loxp/loxp SPC-CreER experienced enhanced Hif1a levels during hypoxia or ALI. Conversely, Hif1a^loxp/loxp SPC-CreER showed increased inflammation with ALI induced by mechanical ventilation. Finally, wild-type mice treated with intra-tracheal dimethlysuccinate were protected during ALI. These data suggest that targeting alveolar-epithelial SDHA dampens ALI via succinate-mediated stabilization of HIF1A. Translational extensions of our studies implicate succinate treatment in attenuating alveolar inflammation in patients suffering from ARDS.

Allosterism vs. Orthosterism: Recent Findings and Future Perspectives on A2B AR Physio-Pathological Implications

The development of GPCR (G-coupled protein receptor) allosteric modulators has attracted increasing interest in the last decades. The use of allosteric modulators in therapy offers several advantages with respect to orthosteric ones, as they can fine-tune the tissue responses to the endogenous agonist. Since the discovery of the first A₁ adenosine receptor (AR) allosteric modulator in 1990, several efforts have been made to develop more potent molecules as well as allosteric modulators for all adenosine receptor subtypes. There are four subtypes of AR: A₁, A_2A, A_2B, and A₃. Positive allosteric modulators of the A₁ AR have been proposed for the cure of pain. A₃ positive allosteric modulators are thought to be beneficial during inflammatory processes. More recently, A_2A and A_2B AR allosteric modulators have also been disclosed. The A_2B AR displays the lowest affinity for its endogenous ligand adenosine and is mainly activated as a consequence of tissue damage. The A_2B AR activation has been found to play a crucial role in chronic obstructive pulmonary disease, in the protection of the heart from ischemic injury, and in the process of bone formation. In this context, allosteric modulators of the A_2B AR may represent pharmacological tools useful to develop new therapeutic agents. Herein, we provide an up-to-date highlight of the recent findings and future perspectives in the field of orthosteric and allosteric A_2B AR ligands. Furthermore, we compare the use of orthosteric ligands with positive and negative allosteric modulators for the management of different pathological conditions.

Enhancing Extracellular Adenosine Levels Restores Barrier Function in Acute Lung Injury Through Expression of Focal Adhesion Proteins

Background: Acute respiratory distress syndrome (ARDS) is a clinical presentation of acute lung injury (ALI) with often fatal lung complication. Adenosine, a nucleoside generated following cellular stress provides protective effects in acute injury. The levels of extracellular adenosine can be depleted by equilibrative nucleoside transporters (ENTs). ENT inhibition by pharmaceutical agent dipyridamole promotes extracellular adenosine accumulation and is protective in ARDS. However, the therapeutic potential of dipyridamole in acute lung injury has not yet been evaluated. Methods: Adenosine acts on three adenosine receptors, the adenosine A1 (Adora1), A2a (Adora2a), the A2b (Adora2b) or the adenosine A3 (Adora 3) receptor. Accumulation of adenosine is usually required to stimulate the low-affinity Adora2b receptor. In order to investigate the effect of adenosine accumulation and the contribution of epithelial-specific ENT2 or adora2b expression in experimental ALI, dipyridamole, and epithelial specific ENT2 or Adora2b deficient mice were utilized. MLE12 cells were used to probe downstream Adora2b signaling. Adenosine receptors, transporters, and targets were determined in ARDS lungs. Results: ENT2 is mainly expressed in alveolar epithelial cells and is negatively regulated by hypoxia following tissue injury. Enhancing adenosine levels with ENT1/ENT2 inhibitor dipyridamole at a time when bleomycin-induced ALI was present, reduced further injury. Mice pretreated with the ADORA2B agonist BAY 60-6583 were protected from bleomycin-induced ALI by reducing vascular leakage (558.6 ± 50.4 vs. 379.9 ± 70.4, p < 0.05), total bronchoalveolar lavage fluid cell numbers (17.9 ± 1.8 to 13.4 ± 1.4 e4, p < 0.05), and neutrophil infiltration (6.42 ± 0.25 vs. 3.94 ± 0.29, p < 0.05). While mice lacking Adora2b in AECs were no longer protected by dipyridamole. We also identified occludin and focal adhesion kinase as downstream targets of ADORA2B, thus providing a novel mechanism for adenosine-mediated barrier protection. Similarly, we also observed similar enhanced ADORA2B (3.33 ± 0.67 to 16.12 ± 5.89, p < 0.05) and decreased occludin (81.2 ± 0.3 to 13.3 ± 0.4, p < 0.05) levels in human Acute respiratory distress syndrome lungs. Conclusion: We have highlighted a role of dipyridamole and adenosine signaling in preventing or treating ALI and identified Ent2 and Adora2b as key mediators in important for the resolution of ALI.

Purinergic Regulation of Endothelial Barrier Function

Increased vascular permeability is a hallmark of several cardiovascular anomalies, including ischaemia/reperfusion injury and inflammation. During both ischaemia/reperfusion and inflammation, massive amounts of various nucleotides, particularly adenosine 5'-triphosphate (ATP) and adenosine, are released that can induce a plethora of signalling pathways via activation of several purinergic receptors and may affect endothelial barrier properties. The nature of the effects on endothelial barrier function may depend on the prevalence and type of purinergic receptors activated in a particular tissue. In this review, we discuss the influence of the activation of various purinergic receptors and downstream signalling pathways on vascular permeability during pathological conditions.

Adenosine at the Interphase of Hypoxia and Inflammation in Lung Injury

Hypoxia and inflammation often coincide in pathogenic conditions such as acute respiratory distress syndrome (ARDS) and chronic lung diseases, which are significant contributors to morbidity and mortality for the general population. For example, the recent global outbreak of Coronavirus disease 2019 (COVID-19) has placed viral infection-induced ARDS under the spotlight. Moreover, chronic lung disease ranks the third leading cause of death in the United States. Hypoxia signaling plays a diverse role in both acute and chronic lung inflammation, which could partially be explained by the divergent function of downstream target pathways such as adenosine signaling. Particularly, hypoxia signaling activates adenosine signaling to inhibit the inflammatory response in ARDS, while in chronic lung diseases, it promotes inflammation and tissue injury. In this review, we discuss the role of adenosine at the interphase of hypoxia and inflammation in ARDS and chronic lung diseases, as well as the current strategy for therapeutic targeting of the adenosine signaling pathway.

Sodium-coupled neutral amino acid transporter SNAT2 counteracts cardiogenic pulmonary edema by driving alveolar fluid clearance

The constant transport of ions across the alveolar epithelial barrier regulates alveolar fluid homeostasis. Dysregulation or inhibition of Na⁺ transport causes fluid accumulation in the distal airspaces resulting in impaired gas exchange and respiratory failure. Previous studies have primarily focused on the critical role of amiloride-sensitive epithelial sodium channel (ENaC) in alveolar fluid clearance (AFC), yet activation of ENaC failed to attenuate pulmonary edema in clinical trials. Since 40% of AFC is amiloride-insensitive, Na⁺ channels/transporters other than ENaC such as Na⁺-coupled neutral amino acid transporters (SNATs) may provide novel therapeutic targets. Here, we identified a key role for SNAT2 (SLC38A2) in AFC and pulmonary edema resolution. In isolated perfused mouse and rat lungs, pharmacological inhibition of SNATs by HgCl₂ and α-methylaminoisobutyric acid (MeAIB) impaired AFC. Quantitative RT-PCR identified SNAT2 as the highest expressed System A transporter in pulmonary epithelial cells. Pharmacological inhibition or siRNA-mediated knockdown of SNAT2 reduced transport of l-alanine across pulmonary epithelial cells. Homozygous Slc38a2^-/- mice were subviable and died shortly after birth with severe cyanosis. Isolated lungs of Slc38a2^+/- mice developed higher wet-to-dry weight ratios (W/D) as compared to wild type (WT) in response to hydrostatic stress. Similarly, W/D ratios were increased in Slc38a2^+/- mice as compared to controls in an acid-induced lung injury model. Our results identify SNAT2 as a functional transporter for Na⁺ and neutral amino acids in pulmonary epithelial cells with a relevant role in AFC and the resolution of lung edema. Activation of SNAT2 may provide a new therapeutic strategy to counteract and/or reverse pulmonary edema.

Hypoxia-Inducible Factor-1: A Potential Target to Treat Acute Lung Injury

Acute lung injury (ALI) is an acute hypoxic respiratory insufficiency caused by various intra- and extrapulmonary injury factors. Presently, excessive inflammation in the lung and the apoptosis of alveolar epithelial cells are considered to be the key factors in the pathogenesis of ALI. Hypoxia-inducible factor-1 (HIF-1) is an oxygen-dependent conversion activator that is closely related to the activity of reactive oxygen species (ROS). HIF-1 has been shown to play an important role in ALI and can be used as a potential therapeutic target for ALI. This manuscript will introduce the progress of HIF-1 in ALI and explore the feasibility of applying inhibitors of HIF-1 to ALI, which brings hope for the treatment of ALI.

Adenosine and ATPγS protect against bacterial pneumonia-induced acute lung injury

Lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, disrupts the alveolar-capillary barrier, triggering pulmonary vascular leak thus inducing acute lung injury (ALI). Extracellular purines, adenosine and ATP, protected against ALI induced by purified LPS. In this study, we investigated whether these purines can impact vascular injury in more clinically-relevant E.coli (non-sterile LPS) murine ALI model. Mice were inoculated with live E. coli intratracheally (i.t.) with or without adenosine or a non-hydrolyzable ATP analog, adenosine 5'-(γ-thio)-triphosphate (ATPγS) added intravenously (i.v.). After 24 h of E. coli treatment, we found that injections of either adenosine or ATPγS 15 min prior or adenosine 3 h after E.coli insult significantly attenuated the E.coli-mediated increase in inflammatory responses. Furthermore, adenosine prevented weight loss, tachycardia, and compromised lung function in E. coli-exposed mice. Accordingly, treatment with adenosine or ATPγS increased oxygen saturation and reduced histopathological signs of lung injury in mice exposed to E. coli. Lastly, lung-targeting gene delivery of adenosine or ATPγS downstream effector, myosin phosphatase, significantly attenuated the E. coli-induced compromise of lung function. Collectively, our study has demonstrated that adenosine or ATPγS mitigates E. coli-induced ALI in mice and may be useful as an adjuvant therapy in future pre-clinical studies.

Potential mechanism and key genes involved in mechanical ventilation and lipopolysaccharide‑induced acute lung injury

Mechanical ventilation (MV) and lipopolysaccharide (LPS) infection are common causes of acute lung injury. The aim of the present study was to identify the key genes and potential mechanisms involved in mechanical ventilation (MV) and lipopolysaccharide (LPS)-induced acute lung injury (ALI). Gene expression data of adult C57BL/6 mice with ALI induced by inhaling LPS, MV and LPS + MV were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) associated with MV, LPS and LPS + MV were screened, followed by functional enrichment analysis, protein-protein interaction network construction, and prediction of transcription factors and small molecule drugs. Finally, the expression of key genes was verified in vivo using reverse transcription-quantitative PCR. A total of 63, 538 and 1,635 DEGs were associated with MV, LPS and LPS + MV, respectively. MV-associated genes were significantly enriched in the ‘purine ribonucleotide metabolic process’. LPS and LPS + MV-associated genes were significantly enriched in ‘cellular response to cytokine stimulus’ and ‘cell chemotaxis’. All three conditions were enriched in ‘TNF signaling pathway’ and ‘IL-17 signaling pathway’. Expression levels of C-X-C motif chemokine ligand (CXCL)2, CXCL3 and CXCL10 were upregulated in the LPS and LPS + MV groups. Adenosine A2b receptor, zinc finger and BTB domain-containing 16 and hydroxycarboxylic acid receptor 2 were identified as DEGs in the MV group. Compared with the control group, Early growth response 1 and activating TF 3 was upregulated in all three groups. Similarities and differences were observed among the MV- and LPS-induced ALI, and MV may enhance the effects of LPS on gene expression. MV may affect urine ribonucleotide metabolic-related processes, whereas LPS may cause cell chemotaxis and cytokine stimulus responses in ALI progression. The inflammatory response was shared by MV and LPS. The results of the present study may provide insight into a theoretical basis for the study and treatment of ALI.

Sustained adenosine exposure causes endothelial mitochondrial dysfunction via equilibrative nucleoside transporters

Adenosine is a potent signaling molecule that has paradoxical effects on lung diseases. We have previously demonstrated that sustained adenosine exposure by inhibition of adenosine degradation impairs lung endothelial barrier integrity and causes intrinsic apoptosis through equilibrative nucleoside transporter_1/2-mediated intracellular adenosine signaling. In this study, we further demonstrated that sustained adenosine exposure increased mitochondrial reactive oxygen species and reduced mitochondrial respiration via equilibrative nucleoside transporter_1/2, but not via adenosine receptor-mediated signaling. We have previously shown that sustained adenosine exposure activates p38 and c-Jun N-terminal kinases in mitochondria. Here, we show that activation of p38 and JNK partially contributed to sustained adenosine-induced mitochondrial reactive oxygen species production. We also found that sustained adenosine exposure promoted mitochondrial fission and increased mitophagy. Finally, mitochondria-targeted antioxidants prevented sustained adenosine exposure-induced mitochondrial fission and improved cell survival. Our results suggest that inhibition of equilibrative nucleoside transporter_1/2 and mitochondria-targeted antioxidants may be potential therapeutic approaches for lung diseases associated with sustained elevated adenosine.

Exploiting the Indole Scaffold to Design Compounds Binding to Different Pharmacological Targets

Several indole derivatives have been disclosed by our research groups that have been collaborating for nearly 25 years. The results of our investigations led to a variety of molecules binding selectively to different pharmacological targets, specifically the type A γ-aminobutyric acid (GABA_A) chloride channel, the translocator protein (TSPO), the murine double minute 2 (MDM2) protein, the A_2B adenosine receptor (A_2B AR) and the Kelch-like ECH-associated protein 1 (Keap1). Herein, we describe how these works were conceived and carried out thanks to the versatility of indole nucleus to be exploited in the design and synthesis of drug-like molecules.

Therapeutic Potentials of A2B Adenosine Receptor Ligands: Current Status and Perspectives

BACKGROUND

Adenosine receptors (ARs) are classified as A1, A2A, A2B, and A3 subtypes belong to the superfamily of G-protein coupled receptors (GPCRs). More than 40% of modern medicines act through either activation or inhibition of signaling processes associated with GPCRs. In particular, A2B AR signaling pathways are implicated in asthma, inflammation, cancer, ischemic hyperfusion, diabetes mellitus, cardiovascular diseases, gastrointestinal disorders, and kidney disease.

METHODS

This article reviews different disease segments wherein A2B AR is implicated and discusses the potential role of subtype-selective A2B AR ligands in the management of such diseases or disorders. All the relevant publications on this topic are reviewed and presented scientifically.

RESULTS

This review provides an up-to-date highlight of the recent advances in the development of novel and selective A2B AR ligands and their therapeutic role in treating various disease conditions. A special focus has been given to the therapeutic potentials of selective A2B AR ligands in the management of airway inflammatory conditions and cancer.

CONCLUSIONS

This systematic review demonstrates the current status and perspectives of A2B AR ligands as therapeutically useful agents that would assist medicinal chemists and pharmacologists in discovering novel and subtype-selective A2B AR ligands as potential drug candidates.

A Role for the Adenosine ADORA2B Receptor in Midazolam Induced Cognitive Dysfunction

BACKGROUND

We recently reported a role for the circadian rhythm protein Period 2 (PER2) in midazolam induced cognitive dysfunction. Based on previous studies showing a critical role for the adenosine A2B receptor (ADORA2B) in PER2 regulation, we hypothesized that hippocampal ADORA2B is crucial for cognitive function.

METHODS

Midazolam treated C57BL/6J mice were analyzed for Adora2b hippocampal mRNA expression levels, and spontaneous T-maze alternation was determined in Adora2b-/- mice. Using the specific ADORA2B agonist BAY-60-6583 in midazolam treated C57BL/6J mice, we analyzed hippocampal Per2 mRNA expression levels and spontaneous T-maze alternation. Finally, Adora2b-/- mice were assessed for mRNA expression of markers for inflammation or cognitive function in the hippocampus.

RESULTS

Midazolam treatment significantly downregulated Adora2b or Per2 mRNA in the hippocampus of C57BL/6J mice, and hippocampal PER2 protein expression or T-maze alternation was significantly reduced in Adora2b-/- mice. ADORA2B agonist BAY-60-6583 restored midazolam mediated reduction in spontaneous alternation in C57BL/6J mice. Analysis of hippocampal Tnf-α or Il-6 mRNA levels in Adora2b-/- mice did not reveal an inflammatory phenotype. However, C-fos, a critical component of hippocampus-dependent learning and memory, was significantly downregulated in the hippocampus of Adora2b-/- mice.

CONCLUSION

These results suggest a role of ADORA2B in midazolam induced cognitive dysfunction. Further, our data demonstrate that BAY-60-6583 treatment restores midazolam induced cognitive dysfunction, possibly via increases of Per2. Additional mechanistic studies hint towards C-FOS as another potential underlying mechanism of memory impairment in Adora2b-/- mice. These findings suggest the ADORA2B agonist as a potential therapy in patients with midazolam induced cognitive dysfunction.

CD73's Potential as an Immunotherapy Target in Gastrointestinal Cancers

CD73, a cell surface 5'nucleotidase that generates adenosine, has emerged as an attractive therapeutic target for reprogramming cancer cells and the tumor microenvironment to dampen antitumor immune cell evasion. Decades of studies have paved the way for these findings, starting with the discovery of adenosine signaling, particularly adenosine A2A receptor (A2AR) signaling, as a potent suppressor of tissue-devastating immune cell responses, and evolving with studies focusing on CD73 in breast cancer, melanoma, and non-small cell lung cancer. Gastrointestinal (GI) cancers are a major cause of cancer-related deaths. Evidence is mounting that shows promise for improving patient outcomes through incorporation of immunomodulatory strategies as single agents or in combination with current treatment options. Recently, several immune checkpoint inhibitors received FDA approval for use in GI cancers; however, clinical benefit is limited. Investigating molecular mechanisms promoting immunosuppression, such as CD73, in GI cancers can aid in current efforts to extend the efficacy of immunotherapy to more patients. In this review, we discuss current clinical and basic research studies on CD73 in GI cancers, including gastric, liver, pancreatic, and colorectal cancer, with special focus on the potential of CD73 as an immunotherapy target in these cancers. We also present a summary of current clinical studies targeting CD73 and/or A2AR and combination of these therapies with immune checkpoint inhibitors.

Focusing on Adenosine Receptors as a Potential Targeted Therapy in Human Diseases

Adenosine is involved in a range of physiological and pathological effects through membrane-bound receptors linked to G proteins. There are four subtypes of adenosine receptors, described as A1AR, A2AAR, A2BAR, and A3AR, which are the center of cAMP signal pathway-based drug development. Several types of agonists, partial agonists or antagonists, and allosteric substances have been synthesized from these receptors as new therapeutic drug candidates. Research efforts surrounding A1AR and A2AAR are perhaps the most enticing because of their concentration and affinity; however, as a consequence of distressing conditions, both A2BAR and A3AR levels might accumulate. This review focuses on the biological features of each adenosine receptor as the basis of ligand production and describes clinical studies of adenosine receptor-associated pharmaceuticals in human diseases.

Maresin Conjugates in Tissue Regeneration 1 improves alveolar fluid clearance by up-regulating alveolar ENaC, Na, K-ATPase in lipopolysaccharide-induced acute lung injury

Maresin Conjugates in Tissue Regeneration 1 (MCTR1) is a newly identified macrophage‐derived sulfido‐conjugated mediator that stimulates the resolution of inflammation. This study assessed the role of MCTR1 in alveolar fluid clearance (AFC) in a rat model of acute lung injury (ALI) induced by lipopolysaccharide (LPS). Rats were intravenously injected with MCTR1 at a dose of 200 ng/rat, 8 hours after administration of 14 mg/kg LPS. The level of AFC was then determined in live rats. Primary rat ATII (Alveolar Type II) epithelial cells were also treated with MCTR1 (100 nmol/L) in a culture medium containing LPS for 8 hours. MCTR1 treatment improved AFC (18.85 ± 2.07 vs 10.11 ± 1.08, P < .0001) and ameliorated ALI in rats. MCTR1 also significantly promoted AFC by up‐regulating epithelial sodium channel (ENaC) and Na⁺‐K⁺‐adenosine triphosphatase (Na, K‐ATPase) expressions in vivo. MCTR1 also activated Na, K‐ATPase and elevated phosphorylated‐Akt (P‐Akt) by up‐regulating the expression of phosphorylated Nedd4‐2 (P‐Nedd4‐2) in vivo and in vitro. However, BOC‐2 (ALX inhibitor), KH7 (cAMP inhibitor) and LY294002 (PI3K inhibitor) abrogated the improved AFC induced by MCTR1. Based on the findings of this study, MCTR1 may be a novel therapeutic approach to improve reabsorption of pulmonary oedema during ALI/acute respiratory distress syndrome (ARDS).

Inhibition of CXCR4 and CXCR7 Is Protective in Acute Peritoneal Inflammation

Our previous studies revealed a pivotal role of the chemokine stromal cell-derived factor (SDF)-1 and its receptors CXCR4 and CXCR7 on migratory behavior of polymorphonuclear granulocytes (PMNs) in pulmonary inflammation. Thereby, the SDF-1-CXCR4/CXCR7-axis was linked with adenosine signaling. However, the role of the SDF-1 receptors CXCR4 and CXCR7 in acute inflammatory peritonitis and peritonitis-related sepsis still remained unknown. The presented study provides new insight on the mechanism of a selective inhibition of CXCR4 (AMD3100) and CXCR7 (CCX771) in two models of peritonitis and peritonitis-related sepsis by injection of zymosan and fecal solution. We observed an increased expression of SDF-1, CXCR4, and CXCR7 in peritoneal tissue and various organs during acute inflammatory peritonitis. Selective inhibition of CXCR4 and CXCR7 reduced PMN accumulation in the peritoneal fluid and infiltration of neutrophils in lung and liver tissue in both models. Both inhibitors had no anti-inflammatory effects in A_2B knockout animals (A_2B–/–). AMD3100 and CCX771 treatment reduced capillary leakage and increased formation of tight junctions as a marker for microvascular permeability in wild type animals. In contrast, both inhibitors failed to improve capillary leakage in A_2B–/– animals, highlighting the impact of the A_2B-receptor in SDF-1 mediated signaling. After inflammation, the CXCR4 and CXCR7 antagonist induced an enhanced expression of the protective A_2B adenosine receptor and an increased activation of cAMP (cyclic adenosine mono phosphate) response element-binding protein (CREB), as downstream signaling pathway of A_2B. The CXCR4- and CXCR7-inhibitor reduced the release of cytokines in wild type animals via decreased intracellular phosphorylation of ERK and NFκB p65. In vitro, CXCR4 and CXCR7 antagonism diminished the chemokine release of human cells and increased cellular integrity by enhancing the expression of tight junctions. These protective effects were linked with functional A_2B-receptor signaling, confirming our in vivo data. In conclusion, our study revealed new protective aspects of the pharmacological modulation of the SDF-1-CXCR4/CXCR7-axis during acute peritoneal inflammation in terms of the two hallmarks PMN migration and barrier integrity. Both anti-inflammatory effects were linked with functional adenosine A_2B-receptor signaling.

miRNA-129/FBW7/NF-κB, a Novel Regulatory Pathway in Inflammatory Bowel Disease

F-box and WD repeat domain-containing protein 7 (FBW7) has been documented to be implicated in nuclear factor κB (NF-κB) signaling and inflammation, but its role in the pathogenesis of inflammatory bowel disease (IBD) remains unknown. FBW7 was increased both in colon tissues from IBD patients and trinitrobenzene sulphonic acid (TNBS)-induced colitis mice. Immunoprecipitation assay identified that FBW7 as a novel inhibitor of κBα (IκBα)-binding partner. FBW7 upregulation promoted IκBα ubiquitin-dependent degradation, NF-κB activation, and subsequent intestinal inflammation in intestinal epithelial cells, whereas inhibition of FBW7 produced the opposite effects. Computational analysis revealed that microRNA-129 (miR-129) directly targets at 3' UTR of FBW7. The miR-129-suppressed proteasome pathway mediated the degradation of IκBα by negatively regulating FBW7. The in vivo study demonstrated that upregulation of miR-129 ameliorated intestinal inflammation in TNBS-induced colitis mice through inhibition of the NF-κB signaling pathway. In conclusion, FBW7 is a novel E3 ubiquitin ligase for IκBα and thereby leads to NF-κB activation and inflammation. miR-129 negatively regulates FBW7 expression, resulting in secondary inhibition of the NF-κB pathway and amelioration of intestinal inflammation. Our findings provide new insight into the development of therapeutic strategies for the treatment of IBD.

Adenosine A2B receptor activation stimulates alveolar fluid clearance through alveolar epithelial sodium channel via cAMP pathway in endotoxin-induced lung injury

Clinical studies have established that the capacity of removing excess fluid from alveoli is impaired in most patients with acute respiratory distress syndrome. Impaired alveolar fluid clearance (AFC) correlates with poor outcomes. Adenosine A_2B receptor (A_2BAR) has the lowest affinity with adenosine among four adenosine receptors. It is documented that A_2BAR can activate adenylyl cyclase (AC) resulting in elevated cAMP. Based on the understanding that cAMP is a key regulator of epithelial sodium channel (ENaC), which is the limited step in sodium transport, we hypothesized that A_2BAR signaling may affect AFC in acute lung injury (ALI) through regulating ENaC via cAMP, thus attenuating pulmonary edema. To address this, we utilized pharmacological approaches to determine the role of A_2BAR in AFC in rats with endotoxin-induced lung injury and further focused on the mechanisms in vitro. We observed elevated pulmonary A_2BAR level in rats with ALI and the similar upregulation in alveolar epithelial cells exposed to LPS. A_2BAR stimulation significantly attenuated pulmonary edema during ALI, an effect that was associated with enhanced AFC and increased ENaC expression. The regulatory effects of A_2BAR on ENaC-α expression were further verified in cultured alveolar epithelial type II (ATII) cells. More importantly, activation of A_2BAR dramatically increased amiloride-sensitive Na⁺ currents in ATII cells. Moreover, we observed that A_2BAR activation stimulated cAMP accumulation, whereas the cAMP inhibitor abolished the regulatory effect of A_2BAR on ENaC-α expression, suggesting that A_2BAR activation regulates ENaC-α expression via cAMP-dependent mechanism. Together, these findings suggest that signaling through alveolar epithelial A_2BAR promotes alveolar fluid balance during endotoxin-induced ALI by regulating ENaC via cAMP pathway, raising the hopes for treatment of pulmonary edema due to ALI.

A2B adenosine receptor inhibition by the dihydropyridine calcium channel blocker nifedipine involves colonic fluid secretion

The adenosine A_2B receptor is a critical protein in intestinal water secretion. In the present study, we screened compound libraries to identify inhibitors of the A_2B receptor and evaluated their effect on adenosine-induced intestinal fluid secretion. The screening identified the dihydropyridine calcium antagonists nifedipine and nisoldipine. Their respective affinities for the A_2B receptor (K_i value) were 886 and 1,399 nM. Nifedipine and nisoldipine, but not amlodipine or nitrendipine, inhibited both calcium mobilization and adenosine-induced cAMP accumulation in cell lines. Moreover, adenosine injection into the lumen significantly increased fluid volume in the colonic loop of wild-type mice but not A_2B receptor-deficient mice. PSB-1115, a selective A_2B receptor antagonist, and nifedipine prevented elevated adenosine-stimulated fluid secretion in mice. Our results may provide useful insights into the structure–activity relationship of dihydropyridines for A_2B receptor. As colonic fluid secretion by adenosine seems to rely predominantly on the A_2B receptor, nifedipine could be a therapeutic candidate for diarrhoea-related diseases.

Blockade of equilibrative nucleoside transporter 1/2 protects against Pseudomonas aeruginosa-induced acute lung injury and NLRP3 inflammasome activation

Pseudomonas aeruginosa infections are increasingly multidrug resistant and cause healthcare-associated pneumonia, a major risk factor for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Adenosine is a signaling nucleoside with potential opposing effects; adenosine can either protect against acute lung injury via adenosine receptors or cause lung injury via adenosine receptors or equilibrative nucleoside transporter (ENT)-dependent intracellular adenosine uptake. We hypothesized that blockade of intracellular adenosine uptake by inhibition of ENT1/2 would increase adenosine receptor signaling and protect against P. aeruginosa-induced acute lung injury. We observed that P. aeruginosa (strain: PA103) infection induced acute lung injury in C57BL/6 mice in a dose- and time-dependent manner. Using ENT1/2 pharmacological inhibitor, nitrobenzylthioinosine (NBTI), and ENT1-null mice, we demonstrated that ENT blockade elevated lung adenosine levels and significantly attenuated P. aeruginosa-induced acute lung injury, as assessed by lung wet-to-dry weight ratio, BAL protein levels, BAL inflammatory cell counts, pro-inflammatory cytokines, and pulmonary function (total lung volume, static lung compliance, tissue damping, and tissue elastance). Using both agonists and antagonists directed against adenosine receptors A2AR and A2BR, we further demonstrated that ENT1/2 blockade protected against P. aeruginosa -induced acute lung injury via activation of A2AR and A2BR. Additionally, ENT1/2 chemical inhibition and ENT1 knockout prevented P. aeruginosa-induced lung NLRP3 inflammasome activation. Finally, inhibition of inflammasome prevented P. aeruginosa-induced acute lung injury. Our results suggest that targeting ENT1/2 and NLRP3 inflammasome may be novel strategies for prevention and treatment of P. aeruginosa-induced pneumonia and subsequent ARDS.

Purinergic Signaling in Pulmonary Inflammation

Purine nucleotides and nucleosides are at the center of biologic reactions. In particular, adenosine triphosphate (ATP) is the fundamental energy currency of cellular activity and adenosine has been demonstrated to play essential roles in human physiology and pathophysiology. In this review, we examine the role of purinergic signaling in acute and chronic pulmonary inflammation, with emphasis on ATP and adenosine. ATP is released into extracellular space in response to cellular injury and necrosis. It is then metabolized to adenosine monophosphate (AMP) via ectonucleoside triphosphate diphosphohydrolase-1 (CD39) and further hydrolyzed to adenosine via ecto-5'-nucleotidase (CD73). Adenosine signals via one of four adenosine receptors to exert pro- or anti-inflammatory effects. Adenosine signaling is terminated by intracellular transport by concentrative or equilibrative nucleoside transporters (CNTs and ENTs), deamination to inosine by adenosine deaminase (ADA), or phosphorylation back into AMP via adenosine kinase (AK). Pulmonary inflammatory and hypoxic conditions lead to increased extracellular ATP, adenosine diphosphate (ADP) and adenosine levels, which translates to increased adenosine signaling. Adenosine signaling is central to the pulmonary injury response, leading to various effects on inflammation, repair and remodeling processes that are either tissue-protective or tissue destructive. In the acute setting, particularly through activation of adenosine 2A and 2B receptors, adenosine signaling serves an anti-inflammatory, tissue-protective role. However, excessive adenosine signaling in the chronic setting promotes pro-inflammatory, tissue destructive effects in chronic pulmonary inflammation.

mSphere of Influence: Adenosine in Host Defense against Bacterial Pneumonia-Friend or Foe?

Elsa N. Bou Ghanem works in the field of innate immune senescence, inflammation, and host defense. In this mSphere of Influence article, she reflects on how "Adenosine A2B receptor deficiency promotes host defenses against Gram-negative bacterial pneumonia" by Barletta et al. (K. E. Barletta, R. E. Cagnina, M. D. Burdick, J. Linden, and B. Mehrad, Am J Respir Crit Care Med 186:1044-1050, 2012, https://doi.org/10.1164/rccm.201204-0622OC) impacted her own work examining the role of the extracellular adenosine pathway in neutrophil responses and host defense against pneumococcal pneumonia.

Cardioprotective role of APIP in myocardial infarction through ADORA2B

In ischemic human hearts, the induction of adenosine receptor A2B (ADORA2B) is associated with cardioprotection against ischemic heart damage, but the mechanism underlying this association remains unclear. Apaf-1-interacting protein (APIP) and ADORA2B transcript levels in human hearts are substantially higher in patients with heart failure than in controls. Interestingly, the APIP and ADORA2B mRNA levels are highly correlated with each other (R = 0.912). APIP expression was significantly increased in primary neonatal cardiomyocytes under hypoxic conditions and this induction reduced myocardial cell death via the activation of the AKT-HIF1α pathway. Accordingly, infarct sizes of APIP transgenic mice after left anterior descending artery ligation were significantly reduced compared to those of wild-type mice. Strikingly, knockdown of APIP expression impaired the cytoprotective effects of ADORA2B during hypoxic damage. Immunoprecipitation and proximity ligation assays revealed that APIP interacts with ADORA2B, leading to the stabilization of both proteins by interfering with lysosomal degradation, and to the activation of the downstream PKA-CREB signaling pathways. ADORA2B levels in the hearts of APIP^Tg/Tg, APIP^Tg/+, and Apip^+/- mice were proportionally downregulated. In addition, ADORA2B D296G derived from the rs200741295 polymorphism failed to bind to APIP and did not exert cardioprotective activity during hypoxia. Moreover, Adora2b D296G knock-in mice were more vulnerable than control mice to myocardial infarction and intentional increases in APIP levels overcame the defective protection of the ADORA2B SNP against ischemic injury. Collectively, APIP is crucial for cardioprotection against myocardial infarction by virtue of binding to and stabilizing ADORA2B, thereby dampening ischemic heart injury.

Capturing the multifactorial nature of ARDS - "Two-hit" approach to model murine acute lung injury

Severe acute respiratory distress syndrome (ARDS) presents typically with an initializing event, followed by the need for mechanical ventilation. Most animal models of ALI are limited by the fact that they focus on a singular cause of acute lung injury (ALI) and therefore fail to mimic the complex, multifactorial pathobiology of ARDS. To better capture this scenario, we provide a comprehensive characterization of models of ALI combining two injuries: intra tracheal (i.t.) instillation of LPS or hypochloric acid (HCl) followed by ventilator‐induced lung injury (VILI). We hypothesized, that mice pretreated with LPS or HCl prior to VILI and thus receiving a (“two‐hit injury”) will sustain a superadditive lung injury when compared to VILI. Mice were allocated to following treatment groups: control with i.t. NaCl, ventilation with low peak inspiratory pressure (PIP), i.t. HCl, i.t. LPS, VILI (high PIP), HCl i.t. followed by VILI and LPS i.t. followed by VILI. Severity of injury was determined by protein content and MPO activity in bronchoalveolar lavage (BAL), the expression of inflammatory cytokines and histopathology. Mice subjected to VILI after HCl or LPS instillation displayed augmented lung injury, compared to singular lung injury. However, mice that received i.t. LPS prior to VILI showed significantly increased inflammatory lung injury compared to animals that underwent i.t. HCl followed by VILI. The two‐hit lung injury models described, resulting in additive but differential acute lung injury recaptures the clinical relevant multifactorial etiology of ALI and could be a valuable tool in translational research.

Integrating molecular pathogenesis and clinical translation in sepsis-induced acute respiratory distress syndrome

Sepsis-induced acute respiratory distress syndrome (ARDS) has high morbidity and mortality and arises after lung infection or infection at extrapulmonary sites. An aberrant host response to infection leads to disruption of the pulmonary alveolar-capillary barrier, resulting in lung injury characterized by hypoxemia, inflammation, and noncardiogenic pulmonary edema. Despite increased understanding of the molecular biology underlying sepsis-induced ARDS, there are no targeted pharmacologic therapies for this devastating condition. Here, we review the molecular underpinnings of sepsis-induced ARDS with a focus on relevant clinical and translational studies that point toward novel therapeutic strategies.

A2BAR activation attenuates acute lung injury by inhibiting alveolar epithelial cell apoptosis both in vivo and in vitro

The epithelial barrier of the lung is destroyed during acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) due to the apoptosis of alveolar epithelial cells (AECs). Therefore, treatments that block AEC apoptosis might be a therapeutic strategy to ameliorate ALI. Based on recent evidence, A2B adenosine receptor (A2BAR) plays an important role in ALI in several different animal models, but its exact function in AECs has not been clarified. We investigated the role of A2BAR in AEC apoptosis in a mouse model of oleic acid (OA)-induced ALI and in hydrogen peroxide (H2O2)-induced AEC (A549 cells and MLE-12 cells) injury. Mice treated with BAY60-6583, a selective A2BAR agonist, showed lower AEC apoptosis rates than mice treated with OA. However, the role of BAY60-6583 in OA-induced ALI was attenuated by a specific blocker of A2BAR, PSB1115. A2BAR activation decreased H2O2-induced cell apoptosis in vitro, as characterized by the translocation of apoptotic proteins, the release of cytochrome c, and the activation of caspase-3 and poly (ADP ribose) polymerase 1 (PARP-1). In addition, apoptosis was required for the phosphorylation of ERK1/2, p38, and JNK. Importantly, compared with cells transfected with the A2BAR-siRNA, an ERK inhibitor or p38 inhibitor exhibited decreased apoptotic ratios and cleaved caspase-9 and cleaved PARP-1 levels, whereas the JNK inhibitor displayed increases in these parameters. In conclusion, A2BAR activation effectively attenuated OA-induced ALI by inhibiting AEC apoptosis and mitigated H2O2-induced AEC injury by suppressing the p38 and ERK1/2-mediated mitochondrial apoptosis pathway.