Alveolar Epithelial A2B Adenosine Receptors in Pulmonary Protection during Acute Lung Injury

Adenosine A2B receptor agonist improves epidermal barrier integrity in a murine model of epidermal hyperplasia

Adenosine regulates multiple physiological processes through the activation of four receptor subtypes, of which the A2B adenosine receptor (A2BAR) has the lowest affinity for adenosine. Being the adenosine receptor subtype most prominently expressed in epidermis, we recently described the antiproliferative and anti-inflammatory effect of the selective A2BAR agonist BAY60-6583 (BAY) in human keratinocytes stimulated with 12-O-tetradecanoylphorbol-13-acetate (TPA), so we sought to establish the effect of topical application of BAY in a model of murine epidermal hyperplasia. Topical application of BAY (1 or 10 μg/site) prevented the inflammatory reaction and skin lesions induced by TPA, minimizing hyperproliferation and acanthosis, as well as the expression of specific markers of proliferative keratinocytes. On the other hand, pre-treatment with the selective A2BAR antagonist, PSB-1115 (PSB, 5 or 50 μg/site) reversed these beneficial effects. Additionally, BAY application normalized the expression of epidermal barrier proteins, whose integrity is altered in inflammatory skin diseases, while treatment with the antagonist alone worsened it. Our results, besides confirming the anti-inflammatory and antiproliferative effects of the A2BAR agonist, further demonstrate a role of A2BAR activation to preserve the epidermal barrier. Therefore, the activation of A2BAR may constitute a possible new pharmacological target for the treatment of skin inflammatory diseases such as psoriasis.

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.

Therapeutic targeting of hypoxia inducible factor in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by bilateral chest infiltration and acute hypoxic respiratory failure. ARDS carries significant morbidity and mortality despite advancements in medical management, calling for the development of novel therapeutic targets. Hypoxia-inducible factor (HIF) is a heterodimeric protein involved in various essential pathways, including metabolic reprogramming, immune modulation, angiogenesis and cell cycle regulation. HIF is routinely degraded in homeostasis conditions via the prolyl hydroxylase domain/von Hippel-Lindau protein pathway. However, HIF is stabilized in ARDS via various mechanisms (oxygen-dependent and independent) as an endogenous protective pathway and plays multifaceted roles in different cell populations. This review focuses on the functional role of HIF and its target genes during ARDS, as well as how HIF has evolved as a therapeutic target in current medical management.

Adenosine receptor signalling as a driver of pulmonary fibrosis

Pulmonary fibrosis is a debilitating and life-limiting lung condition in which the damage- response mechanisms of mixed-population cells within the lungs go awry. The tissue microenvironment is drastically remodelled by aberrantly activated fibroblasts which deposit ECM components into the surrounding lung tissue, detrimentally affecting lung function and capacity for gas exchange. Growing evidence suggests a role for adenosine signalling in the pathology of tissue fibrosis in a variety of organs, including the lung, but the molecular pathways through which this occurs remain largely unknown. This review explores the role of adenosine in fibrosis and evaluates the contribution of the different adenosine receptors to fibrogenesis. Therapeutic targeting of the adenosine receptors is also considered, along with clinical observations pointing towards a role for adenosine in fibrosis. In addition, the interaction between adenosine signalling and other profibrotic signalling pathways, such as TGFβ1 signalling, is discussed.

Targeting myocardial equilibrative nucleoside transporter ENT1 provides cardioprotection by enhancing myeloid Adora2b signaling

Previous studies implicate extracellular adenosine signaling in attenuating myocardial ischemia and reperfusion injury (IRI). This extracellular adenosine signaling is terminated by its uptake into cells by equilibrative nucleoside transporters (ENTs). Thus, we hypothesized that targeting ENTs would function to increase cardiac adenosine signaling and concomitant cardioprotection against IRI. Mice were exposed to myocardial ischemia and reperfusion injury. Myocardial injury was attenuated in mice treated with the nonspecific ENT inhibitor dipyridamole. A comparison of mice with global Ent1 or Ent2 deletion showed cardioprotection only in Ent1-/- mice. Moreover, studies with tissue-specific Ent deletion revealed that mice with myocyte-specific Ent1 deletion (Ent1loxP/loxP Myosin Cre+ mice) experienced smaller infarct sizes. Measurements of cardiac adenosine levels demonstrated that postischemic elevations of adenosine persisted during reperfusion after targeting ENTs. Finally, studies in mice with global or myeloid-specific deletion of the Adora2b adenosine receptor (Adora2bloxP/loxP LysM Cre+ mice) implied that Adora2b signaling on myeloid-inflammatory cells in cardioprotection provided by ENT inhibition. These studies reveal a previously unrecognized role for myocyte-specific ENT1 in cardioprotection by enhancing myeloid-dependent Adora2b signaling during reperfusion. Extension of these findings implicates adenosine transporter inhibitors in cardioprotection against ischemia and reperfusion injury.

A2B Adenosine Receptor in Idiopathic Pulmonary Fibrosis: Pursuing Proper Pit Stop to Interfere with Disease Progression

Purine nucleotides and nucleosides are involved in various human physiological and pathological mechanisms. The pathological deregulation of purinergic signaling contributes to various chronic respiratory diseases. Among the adenosine receptors, A2B has the lowest affinity such that it was long considered to have little pathophysiological significance. Many studies suggest that A2BAR plays protective roles during the early stage of acute inflammation. However, increased adenosine levels during chronic epithelial injury and inflammation might activate A2BAR, resulting in cellular effects relevant to the progression of pulmonary fibrosis.

HIF1A-dependent induction of alveolar epithelial PFKFB3 dampens acute lung injury

Acute lung injury (ALI) is a severe form of lung inflammation causing acute respiratory distress syndrome in patients. ALI pathogenesis is closely linked to uncontrolled alveolar inflammation. We hypothesize that specific enzymes of the glycolytic pathway could function as key regulators of alveolar inflammation. Therefore, we screened isolated alveolar epithelia from mice exposed to ALI induced by injurious ventilation to assess their metabolic responses. These studies pointed us toward a selective role for isoform 3 of the 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3). Pharmacologic inhibition or genetic deletion of Pfkfb3 in alveolar epithelia (Pfkfb3loxP/loxP SPC-ER-Cre+ mice) was associated with profound increases in ALI during injurious mechanical ventilation or acid instillation. Studies in genetic models linked Pfkfb3 expression and function to Hif1a. Not only did intratracheal pyruvate instillation reconstitute Pfkfb3loxP/loxP or Hif1aloxP/loxP SPC-ER-Cre+ mice, but pyruvate was also effective in ALI treatment of wild-type mice. Finally, proof-of-principle studies in human lung biopsies demonstrated increased PFKFB3 staining in injured lungs and colocalized PFKFB3 to alveolar epithelia. These studies reveal a specific role for PFKFB3 in counterbalancing alveolar inflammation and lay the groundwork for novel metabolic therapeutic approaches during ALI.

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.

Update on the recent development of allosteric modulators for adenosine receptors and their therapeutic applications

Adenosine receptors (ARs) have been identified as promising therapeutic targets for countless pathological conditions, spanning from inflammatory diseases to central nervous system disorders, from cancer to metabolic diseases, from cardiovascular pathologies to respiratory diseases, and beyond. This extraordinary therapeutic potential is mainly due to the plurality of pathophysiological actions of adenosine and the ubiquitous expression of its receptors. This is, however, a double-edged sword that makes the clinical development of effective ligands with tolerable side effects difficult. Evidence of this is the low number of AR agonists or antagonists that have reached the market. An alternative approach is to target allosteric sites via allosteric modulators, compounds endowed with several advantages over orthosteric ligands. In addition to the typical advantages of allosteric modulators, those acting on ARs could benefit from the fact that adenosine levels are elevated in pathological tissues, thus potentially having negligible effects on normal tissues where adenosine levels are maintained low. Several A1 and various A3AR allosteric modulators have been identified so far, and some of them have been validated in different preclinical settings, achieving promising results. Less fruitful, instead, has been the discovery of A2A and A2BAR allosteric modulators, although the results obtained up to now are encouraging. Collectively, data in the literature suggests that allosteric modulators of ARs could represent valuable pharmacological tools, potentially able to overcome the limitations of orthosteric ligands.

Dipyridamole and adenosinergic pathway in Covid-19: a juice or holy grail

Background

Coronavirus disease 2019 (Covid-19) is an infectious worldwide pandemic triggered by severe acute respiratory coronavirus 2 (SARS-CoV-2). This pandemic disease can lead to pro-inflammatory activation with associated acute lung injury and acute respiratory distress syndrome.

Main body of the abstract

SARS-CoV-2 infection is linked with inhibition of adenosine and activation of phosphodiesterase. Dipyridamole (DIP) is a nucleoside transport and phosphodiesterase inhibitor so that it may potentially affect SARS-CoV-2 infection and its accompanying inflammations. Therefore, the primary objective of this mini-review study was to elucidate the potential beneficial impacts of DIP on the adenosinergic pathway in Covid-19. A systemic search was done using online databases with relevant keywords. The findings of the present study illustrated that DIP directly or indirectly, through augmentation of adenosine and inhibition of phosphodiesterase, mitigates Covid-19 outcomes.

Conclusion

Our study concluded that DIP has a potential therapeutic effect in the management and treatment of Covid-19. This could be attained either directly, through anti-SARS-CoV-2, anti-inflammatory, and anti-platelets properties, or indirectly, through augmentation of extracellular adenosine, which has anti-inflammatory and immune-regulatory effects. However, extensive randomized clinical trials, and clinical and prospective research in this area are required to demonstrate the safety and therapeutic efficacy of DIP and adenosine modulators in the treatment of Covid-19.

Recrystallization of Adenosine for Localized Drug Delivery

Adenosine (ADO) is an endogenous metabolite with immense potential to be repurposed as an immunomodulatory therapeutic, as preclinical studies have demonstrated in models of epilepsy, acute respiratory distress syndrome, and traumatic brain injury, among others. The currently licensed products Adenocard and Adenoscan are formulated at 3 mg/mL of ADO for rapid bolus intravenous injection, but the systemic administration of the saline formulations for anti-inflammatory purposes is limited by the nucleoside's profound hemodynamic effects. Moreover, concentrations that can be attained in the airway or the brain through direct instillation or injection are limited by the volumes that can be accommodated in the anatomical space (<5 mL in humans) and the rapid elimination by enzymatic and transport mechanisms in the interstitium (half-life <5 s). As such, highly concentrated formulations of ADO are needed to attain pharmacologically relevant concentrations at sites of tissue injury. Herein, we report a previously uncharacterized crystalline form of ADO (rcADO) in which 6.7 mg/mL of the nucleoside is suspended in water. Importantly, the crystallinity is not diminished in a protein-rich environment, as evidenced by resuspending the crystals in albumin (15% w/v). To the best of our knowledge, this is the first report of crystalline ADO generated using a facile and organic solvent-free method aimed at localized drug delivery. The crystalline suspension may be suitable for developing ADO into injectable formulations for attaining high concentrations of the endogenous nucleoside in inflammatory locales.

The Hypoxia-Adenosine Link during Myocardial Ischemia-Reperfusion Injury

Despite increasing availability and more successful interventional approaches to restore coronary reperfusion, myocardial ischemia-reperfusion injury is a substantial cause of morbidity and mortality worldwide. During myocardial ischemia, the myocardium becomes profoundly hypoxic, thus causing stabilization of hypoxia-inducible transcription factors (HIF). Stabilization of HIF leads to a transcriptional program that promotes adaptation to hypoxia and cellular survival. Transcriptional consequences of HIF stabilization include increases in extracellular production and signaling effects of adenosine. Extracellular adenosine functions as a signaling molecule via the activation of adenosine receptors. Several studies implicated adenosine signaling in cardioprotection, particularly through the activation of the Adora2a and Adora2b receptors. Adenosine receptor activation can lead to metabolic adaptation to enhance ischemia tolerance or dampen myocardial reperfusion injury via signaling events on immune cells. Many studies highlight that clinical strategies to target the hypoxia-adenosine link could be considered for clinical trials. This could be achieved by using pharmacologic HIF activators or by directly enhancing extracellular adenosine production or signaling as a therapy for patients with acute myocardial infarction, or undergoing cardiac surgery.

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.

Enteric glial adenosine 2B receptor signaling mediates persistent epithelial barrier dysfunction following acute DSS colitis

Intestinal epithelial barrier function is compromised in inflammatory bowel disease and barrier dysfunction contributes to disease progression. Extracellular nucleotides/nucleosides generated in gut inflammation may regulate barrier function through actions on diverse cell types. Enteric glia modulate extracellular purinergic signaling and exert pathophysiological effects on mucosal permeability. These glia may regulate inflammation with paracrine responses, theoretically mediated via adenosine 2B receptor (A2BR) signaling. As the cell-specific roles of A2BRs in models of colitis and barrier dysfunction are unclear, we studied glial A2BRs in acute dextran sodium sulfate (DSS) colitis. We performed and validated conditional ablation of glial A2BRs in Sox10CreERT2+/-;Adora2bf/f mice. Overt intestinal disease activity indices in DSS-colitis were comparable between Sox10CreERT2+/-;Adora2bf/f mice and littermate controls. However, ablating glial A2BRs protected against barrier dysfunction following acute DSS-colitis. These benefits were associated with the normalization of tight junction protein expression and localization including claudin-1, claudin-8, and occludin. Glial A2BR signaling increased levels of proinflammatory mediators in the colon and cell-intrinsic regulation of genes including Csf3, Cxcl1, Cxcl10, and Il6. Our studies show that glial A2BR signaling exacerbates immune responses during DSS-colitis and that this adenosinergic cell-specific mechanism contributes to persistent gut epithelial barrier dysfunction.

Sevoflurane Dampens Acute Pulmonary Inflammation via the Adenosine Receptor A2B and Heme Oxygenase-1

Acute respiratory distress syndrome is a life-threatening disease associated with high mortality. The adenosine receptor A2B (Adora2b) provides anti-inflammatory effects, which are also associated with the intracellular enzyme heme oxygenase-1 (HO-1). Our study determined the mechanism of sevoflurane’s protective properties and investigated the link between sevoflurane and the impact of a functional Adora2b via HO-1 modulation during lipopolysaccharide (LPS)-induced lung injury. We examined the LPS-induced infiltration of polymorphonuclear neutrophils (PMNs) into the lung tissue and protein extravasation in wild-type and Adora2b−/− animals. We generated chimeric animals, to identify the impact of sevoflurane on Adora2b of hematopoietic and non-hematopoietic cells. Sevoflurane decreased the LPS-induced PMN-infiltration and diminished the edema formation in wild-type mice. Reduced PMN counts after sevoflurane treatment were detected only in chimeric mice, which expressed Adora2b exclusively on leukocytes. The Adora2b on hematopoietic and non-hematopoietic cells was required to improve the permeability after sevoflurane inhalation. Further, sevoflurane increased the protective effects of HO-1 modulation on PMN migration and microvascular permeability. These protective effects were abrogated by specific HO-1 inhibition. In conclusion, our data revealed new insights into the protective mechanisms of sevoflurane application during acute pulmonary inflammation and the link between sevoflurane and Adora2b, and HO-1 signaling, respectively.

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.

From Anti-SARS-CoV-2 Immune Response to the Cytokine Storm via Molecular Mimicry

The aim of this study was to investigate the role of molecular mimicry in the cytokine storms associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human proteins endowed with anti-inflammatory activity were assembled and analyzed for peptide sharing with the SARS-CoV-2 spike glycoprotein (gp) using public databases. It was found that the SARS-CoV-2 spike gp shares numerous pentapeptides with anti-inflammatory proteins that, when altered, can lead to cytokine storms characterized by diverse disorders such as systemic multiorgan hyperinflammation, macrophage activation syndrome, ferritinemia, endothelial dysfunction, and acute respiratory syndrome. Immunologically, many shared peptides are part of experimentally validated epitopes and are also present in pathogens to which individuals may have been exposed following infections or vaccinal routes and of which the immune system has stored memory. Such an immunologic imprint might trigger powerful anamnestic secondary cross-reactive responses, thus explaining the raging of the cytokine storm that can occur following exposure to SARS-CoV-2. In conclusion, the results support molecular mimicry and the consequent cross-reactivity as a potential mechanism in SARS-CoV-2-induced cytokine storms, and highlight the role of immunological imprinting in determining high-affinity, high-avidity, autoimmune cross-reactions as a pathogenic sequela associated with anti-SARS-CoV-2 vaccines.

Targeting purinergic receptors to suppress the cytokine storm induced by SARS-CoV-2 infection in pulmonary tissue

The etiological agent of coronavirus disease (COVID-19) is the new member of the Coronaviridae family, a severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2), responsible for the pandemic that is plaguing the world. The single-stranded RNA virus is capable of infecting the respiratory tract, by binding the spike (S) protein on its viral surface to receptors for the angiotensin II-converting enzyme (ACE2), highly expressed in the pulmonary tissue, enabling the interaction of the virus with alveolar epithelial cells promoting endocytosis and replication of viral material. The infection triggers the activation of the immune system, increased purinergic signaling, and the release of cytokines as a defense mechanism, but the response can become exaggerated and prompt the so-called “cytokine storm”, developing cases such as severe acute respiratory syndrome (SARS). This is characterized by fever, cough, and difficulty breathing, which can progress to pneumonia, failure of different organs and death. Thus, the present review aims to compile and correlate the mechanisms involved between the immune and purinergic systems with COVID-19, since the modulation of purinergic receptors, such as A2A, A2B, and P2X7 expressed by immune cells, seems to be effective as a promising therapy, to reduce the severity of the disease, as well as aid in the treatment of acute lung diseases and other cases of generalized inflammation.

Akt-independent effects of triciribine on ACE2 expression in human lung epithelial cells: Potential benefits in restricting SARS-CoV2 infection

The severe acute respiratory syndrome coronavirus 2 that causes coronavirus disease 2019 (COVID-19) binds to the angiotensin-converting enzyme 2 (ACE2) to gain cellular entry. Akt inhibitor triciribine (TCBN) has demonstrated promising results in promoting recovery from advanced-stage acute lung injury in preclinical studies. In the current study, we tested the direct effect of TCBN on ACE2 expression in human bronchial (H441) and lung alveolar (A549) epithelial cells. Treatment with TCBN resulted in the downregulation of both messenger RNA and protein levels of ACE2 in A549 cells. Since HMGB1 plays a vital role in the inflammatory response in COVID-19, and because hyperglycemia has been linked to increased COVID-19 infections, we determined if HMGB1 and hyperglycemia have any effect on ACE2 expression in lung epithelial cells and whether TCBN has any effect on reversing HMGB1- and hyperglycemia-induced ACE2 expression. We observed increased ACE2 expression with both HMGB1 and hyperglycemia treatment in A549 as well as H441 cells, which were blunted by TCBN treatment. Our findings from this study, combined with our previous reports on the potential benefits of TCBN in the treatment of acute lung injury, generate reasonable optimism on the potential utility of TCBN in the therapeutic management of patients with COVID-19.

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.

Simvastatin attenuates acute lung injury by activation of A2B adenosine receptor

To explore the protective mechanism of simvastatin in acute lung injury (ALI), the lipopolysaccharide (LPS) induced (5 mg/kg) ALI rat model was used to examine the effects of simvastatin. Following simvastatin treatment, the histopathological evaluation of lung tissues was made using hematoxylin and eosin (H&E) staining. Also, myeloperoxidase (MPO) activity and the levels of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and IL-10 were determined by ELISA. Blood gas analyses of arterial blood samples were performed to assess the pulmonary gas exchange. Moreover, the neutrophil count and total protein content were determined in the bronchoalveolar lavage (BAL) fluid. The ratio of wet lung to dry lung (W/D) and the alveolar fluid clearance (AFC) were calculated to estimate the severity of edema. Lastly, the levels of A2BAR, CFTR, claudin4, and claudin18 were also measured by qRT-PCR and Western blotting. Simvastatin treatment, in a dose-related manner, markedly improved the lung histological injury and decreased the levels of TNF-α, IL-1β, and increased IL-10 in LPS induced ALI. Also, pulmonary neutrophil count was alleviated. Besides, a decreased ratio of W/D lung also confirmed the simvastatin intervention. Notably, simvastatin reduced the levels of A2BAR, CFTR, and claudin18 but upregulated claudin4 in lung tissues. Additionally, treatment with PSB1115, an antagonist of A2BAR, countered the protective effect of simvastatin in ALI. Our study demonstrates that simvastatin has a protective effect against LPS-induced ALI by activating A2BAR and should be exploited as a novel therapeutic target for the treatment of ALI.

Adenosine Signaling in Mast Cells and Allergic Diseases

Adenosine is a nucleoside involved in the pathogenesis of allergic diseases. Its effects are mediated through its binding to G protein-coupled receptors: A1, A2a, A2b and A3. The receptors differ in the type of G protein they recruit, in the effect on adenylyl cyclase (AC) activity and the downstream signaling pathway triggered. Adenosine can produce both an enhancement and an inhibition of mast cell degranulation, indicating that adenosine effects on these receptors is controversial and remains to be clarified. Depending on the study model, A1, A2b, and A3 receptors have shown anti- or pro-inflammatory activity. However, most studies reported an anti-inflammatory activity of A2a receptor. The precise knowledge of the adenosine mechanism of action may allow to develop more efficient therapies for allergic diseases by using selective agonist and antagonist against specific receptor subtypes.

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.

How Genetics Might Explain the Unusual Link Between Malaria and COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-associated coronavirus disease 2019 (COVID-19) pandemic has been the subject of a large number of studies in recent times. Here, starting from the evidence that in Italy, the areas with the lowest number of COVID-19 cases were those with the highest incidence of malaria in the early 1900's, we explore possible inverse relationships between malaria and COVID-19. Indeed, some genetic variants, which have been demonstrated to give an advantage against malaria, can also play a role in the incidence and severity of SARS-CoV-2 infections (e.g., the ACE2 receptor). To verify this scientific hypothesis, we here use public data from whole-genome sequencing (WGS) experiments to extrapolate the genetic information of 46 world populations with matched COVID-19 data. In particular, we focus on 47 genes, including ACE2 and genes which have previously been reported to play a role in malaria. Only common variants (>5%) in at least 30% of the selected populations were considered, and, for this subset, we correlate the intra-population allele frequency with the COVID-19 data (cases/million inhabitants), eventually pinpointing meaningful variants in 6 genes. This study allows us to distinguish between positive and negative correlations, i.e., variants whose frequency significantly increases with increasing or decreasing COVID-19 cases. Finally, we discuss the possible molecular mechanisms associated with these variants and advance potential therapeutic options, which may help fight and/or prevent COVID-19.

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.

Genetic and epigenetic regulation of the non-muscle myosin light chain kinase isoform by lung inflammatory factors and mechanical stress

RATIONALE

The myosin light chain kinase gene, MYLK, encodes three proteins via unique promoters, including the non-muscle isoform of myosin light chain kinase (nmMLCK), a cytoskeletal protein centrally involved in regulation of vascular integrity. As MYLK coding SNPs are associated with severe inflammatory disorders (asthma, acute respiratory distress syndrome (ARDS)), we explored clinically relevant inflammatory stimuli and promoter SNPs in nmMLCK promoter regulation.

METHODS

Full-length or serially deleted MYLK luciferase reporter promoter activities were measured in human lung endothelial cells (ECs). SNP-containing non-muscle MYLK (nmMYLK) DNA fragments were generated and nmMYLK promoter binding by transcription factors (TFs) detected by protein-DNA electrophoretic mobility shift assay (EMSA). Promoter demethylation was evaluated by 5-aza-2'-deoxycytidine (5-Aza). A preclinical mouse model of lipopolysaccharide (LPS)-induced acute lung injury (ALI) was utilized for nmMLCK validation.

RESULTS

Lung EC levels of nmMLCK were significantly increased in LPS-challenged mice and LPS, tumor necrosis factor-α (TNF-α), 18% cyclic stretch (CS) and 5-Aza each significantly up-regulated EC nmMYLK promoter activities. EC exposure to FG-4592, a prolyl hydroxylase inhibitor that increases hypoxia-inducible factor (HIF) expression, increased nmMYLK promoter activity, confirmed by HIF1α/HIF2α silencing. nmMYLK promoter deletion studies identified distal inhibitory and proximal enhancing promoter regions as well as mechanical stretch-, LPS- and TNFα-inducible regions. Insertion of ARDS-associated SNPs (rs2700408, rs11714297) significantly increased nmMYLK promoter activity via increased transcription binding (glial cells missing homolog 1 (GCM1) and intestine-specific homeobox (ISX), respectively). Finally, the MYLK rs78755744 SNP (-261G/A), residing within a nmMYLK CpG island, significantly attenuated 5-Aza-induced promoter activity.

CONCLUSION

These findings indicate nmMYLK transcriptional regulation by clinically relevant inflammatory factors and ARDS-associated nmMYLK promoter variants are consistent with nmMLCK as a therapeutic target in severe inflammatory disorders.

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.

Co-inhibition of CD73 and ADORA2B Improves Long-Term Cigarette Smoke Induced Lung Injury

Adenosine (ADO) involvement in lung injury depends on the activation of its receptors. The ADO A_2A receptor (ADORA2A) and A_2B receptor (ADORA2B) are best described to have both tissue-protective and tissue-destructive processes. However, no approach has been effective in delineating the mechanism(s) involved with ADO shifting from its tissue-protective to tissue-destructive properties in chronic airway injury. Using cigarette smoke (CS) as our model of injury, we chronically exposed Nuli-1 cells to 5% CS extract (CSE) for 3 years establishing a long-term CSE exposure model (LTC). We found significant morphological changes, decreased proliferation, and migration resulting in impaired airway wound closure in LTC. Further investigations showed that long-term CSE exposure upregulates CD73 and ADORA2B expression, increases ADO production, inhibits PKC alpha activity and p-ERK signaling pathway. Knocking down ADORA2B and/or CD73 in LTC activates PKC alpha and increases p-ERK signaling. Knocking down both showed better improvement in wound repair than either alone. In vivo experiments also showed that double knockout CD73 and ADORA2B remarkably improved CS-induced lung injury by activating PKC alpha, reducing the inflammatory cell number in bronchoalveolar lavage fluid and the production of inflammatory mediator IL-6, inhibiting the fibrosis-like lesions and decreasing collagen deposition surrounding bronchioles. Collectively, long-term CSE exposure upregulates CD73 expression and increases ADO production, which promotes low affinity ADORA2B activation and subsequent diminution of PKC alpha activity and ERK signaling pathway, and inhibition of airway wound repair. Moreover, the data suggesting ADORA2B and CD73 as potential therapeutic targets may be more efficacious in improving chronic CS lung diseases and impaired wound repair.

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.

Alkaline phosphatase in pulmonary inflammation-a translational study in ventilated critically ill patients and rats

Background

Alkaline phosphatase (AP), a dephosphorylating enzyme, is involved in various physiological processes and has been shown to have anti-inflammatory effects.

Aim

To determine the correlation between pulmonary AP activity and markers of inflammation in invasively ventilated critically ill patients with or without acute respiratory distress syndrome (ARDS), and to investigate the effect of administration of recombinant AP on pulmonary inflammation in a well-established lung injury model in rats

Methods

AP activity was determined and compared with levels of various inflammatory mediators in bronchoalveolar lavage fluid (BALF) samples obtained from critically ill patients within 2 days of start of invasive ventilation. The endpoints of this part of the study were the correlations between AP activity and markers of inflammation, i.e., interleukin (IL)-6 levels in BALF. In RccHan Wistar rats, lung injury was induced by intravenous administration of 10 mg/kg lipopolysaccharide, followed by ventilation with a high tidal volume for 4 h. Rats received either an intravenous bolus of 1500 IU/kg recombinant AP or normal saline 2 h after intravenous LPS administration, right before start of ventilation. Endpoints of this part of the study were pulmonary levels of markers of inflammation, including IL-6, and markers of endothelial and epithelial dysfunction.

Results

BALF was collected from 83 patients; 10 patients had mild ARDS, and 15 had moderate to severe ARDS. AP activity correlated well with levels of IL-6 (r = 0.70), as well as with levels of other inflammatory mediators. Pulmonary AP activity between patients with and without ARDS was comparable (0.33 [0.14–1.20] vs 0.55 [0.21–1.42] U/L; p = 0.37). Animals with acute lung injury had markedly elevated pulmonary AP activity compared to healthy controls (2.58 [2.18–3.59] vs 1.01 [0.80–1.46] U/L; p < 0.01). Intravenous administration of recombinant AP did neither affect pulmonary inflammation nor endothelial and epithelial dysfunction.

Conclusions

In ventilated critically ill patients, pulmonary AP activity correlates well with markers of pulmonary inflammation, such as IL-6 and IL-8. In animals with lung injury, pulmonary AP activity is elevated. Administration of recombinant AP does not alter pulmonary inflammation and endothelial or epithelial dysfunction in the acute phase of a murine lung injury model.

Role of microRNA-15a-5p/TNFAIP3-interacting protein 2 axis in acute lung injury induced by traumatic hemorrhagic shock

The present study aimed to investigate the role of microRNA (miR)-15a-5p in the pathogenesis of acute lung injury induced by traumatic hemorrhagic shock (THS), and to explore the underlying molecular mechanism. The expression level of miR-15a-5p was detected using reverse transcription-quantitative (RT-qPCR) and the association between miR-15a-5p and TNFAIP3-interacting protein 2 (TNIP2) was revealed using TargetScan and dual luciferase reporter assays. To investigate the effect of miR-15a-5p on THS-induced acute lung injury, a THS rat model was established. Lung capillary permeability and lung edema were then determined. Moreover, proinflammatory factors in the bronchoalveolar lavage fluid (BALF) and serum of the THS rat model were detected using ELISA. In addition, protein levels in the current study were measured via western blotting. It was revealed that miR-15a-5p was significantly upregulated in both patients with THS and samples from the THS rat model. TNIP2 represents a direct target of miR-15a-5p, and it was downregulated in both patients with THS and the THS rat model. Further analyses indicated that downregulation of miR-15a-5p significantly relieved acute lung injury induced by THS, evidenced by a decreased ratio of Evan's blue dye (EBD) in the BALF to EBD in plasma of THS rats, decreased lung permeability index and reduced lung wet/dry ratio. Inhibition of miR-15a-5p also decreased THS-induced upregulation of pro-inflammatory factors. Furthermore, the data revealed that THS-induced NF-κB activation in the lung tissues of rats was inhibited by miR-15a-5p knockdown. Moreover, it was demonstrated that all the effects of miR-15a-5p on THS rats were ablated following TNIP2 silencing. Taken together, the data of the current study indicate that miR-15a-5p downregulation serves a protective role in THS-induced acute lung injury via directly targeting TNIP2.

Can Adenosine Fight COVID-19 Acute Respiratory Distress Syndrome?

Coronavirus disease 2019 (COVID-19) patients can develop interstitial pneumonia, which, in turn, can evolve into acute respiratory distress syndrome (ARDS). This is accompanied by an inflammatory cytokine storm. severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) has proteins capable of promoting the cytokine storm, especially in patients with comorbidities, including obesity. Since currently no resolutive therapy for ARDS has been found and given the scientific literature regarding the use of adenosine, its application has been hypothesized. Through its receptors, adenosine is able to inhibit the acute inflammatory process, increase the protection capacity of the epithelial barrier, and reduce the damage due to an overactivation of the immune system, such as that occurring in cytokine storms. These features are known in ischemia/reperfusion models and could also be exploited in acute lung injury with hypoxia. Considering these hypotheses, a COVID-19 patient with unresponsive respiratory failure was treated with adenosine for compassionate use. The results showed a rapid improvement of clinical conditions, with negativity of SARS-CoV2 detection.

Hypoxia and HIF Signaling: One Axis with Divergent Effects

The correct concentration of oxygen in all tissues is a hallmark of cellular wellness, and the negative regulation of oxygen homeostasis is able to affect the cells and tissues of the whole organism. The cellular response to hypoxia is characterized by the activation of multiple genes involved in many biological processes. Among them, hypoxia-inducible factor (HIF) represents the master regulator of the hypoxia response. The active heterodimeric complex HIF α/β, binding to hypoxia-responsive elements (HREs), determines the induction of at least 100 target genes to restore tissue homeostasis. A growing body of evidence demonstrates that hypoxia signaling can act by generating contrasting responses in cells and tissues. Here, this dual and controversial role of hypoxia and the HIF signaling pathway is discussed, with particular reference to the effects induced on the complex activities of the immune system and on mechanisms determining cell and tissue responses after an injury in both acute and chronic human diseases related to the heart, lung, liver, and kidney.

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.

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.

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.

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.

A1 adenosine receptor signaling reduces Streptococcus pneumoniae adherence to pulmonary epithelial cells by targeting expression of platelet-activating factor receptor

Extracellular adenosine production is crucial for host resistance against Streptococcus pneumoniae (pneumococcus) and is thought to affect antibacterial immune responses by neutrophils. However, whether extracellular adenosine alters direct host-pathogen interaction remains unexplored. An important determinant for lung infection by S. pneumoniae is its ability to adhere to the pulmonary epithelium. Here we explored whether extracellular adenosine can directly impact bacterial adherence to lung epithelial cells. We found that signaling via A1 adenosine receptor significantly reduced the ability of pneumococci to bind human pulmonary epithelial cells. A1 receptor signaling blocked bacterial binding by reducing the expression of platelet-activating factor receptor, a host protein used by S. pneumoniae to adhere to host cells. In vivo, A1 was required for control of pneumococcal pneumonia as inhibiting it resulted in increased host susceptibility. As S. pneumoniae remain a leading cause of community-acquired pneumonia in the elderly, we explored the role of A1 in the age-driven susceptibility to infection. We found no difference in A1 pulmonary expression in young versus old mice. Strikingly, triggering A1 signaling boosted host resistance of old mice to S. pneumoniae pulmonary infection. This study demonstrates a novel mechanism by which extracellular adenosine modulates resistance to lung infection by targeting bacterial-host interactions.

Optimization and anti-inflammatory evaluation of methyl gallate derivatives as a myeloid differentiation protein 2 inhibitor

Myeloid differentiation protein 2 (MD2) is a co-receptor of toll-like receptor 4 (TLR4) responsible for the recognition of lipopolysaccharide (LPS) and mediates a series of TLR4-dependent inflammatory responses in inflammatory lung diseases including acute lung injury (ALI). Targeting MD2 thus may provide a therapeutic strategy against these lung diseases. In this study, we identified a novel compound 4k with the potent anti-inflammatory activity among 39 methyl gallate derivatives (MGDs). MGD 4k exhibited a high binding affinity to MD2, which in turn prevented the formation of the LPS/MD2/TLR4 complex. In addition, MGD 4k significantly reversed the upregulation of LPS-induced inflammatory mediators such as tumor necrosis factor-α, interleukin-6, intracellular adhesion molecule-1, vascular cell adhesion molecule-1, and monocyte chemoattractant protein-1 in vitro and in vivo. Mechanistically, MGD 4k performed anti-inflammatory function by inactivating JNK, ERK and p38 signaling pathways. Taken together, our study identified MGD 4k as a novel potential therapeutic agent for ALI through inhibiting MD2, inflammatory responses, and major inflammation-associated signaling pathways.

Non-Nucleoside Agonists of the Adenosine Receptors: An Overview

Potent and selective adenosine receptor (AR) agonists are of pharmacological interest for the treatment of a wide range of diseases and conditions. Among these derivatives, nucleoside-based agonists represent the great majority of molecules developed and reported to date. However, the limited availability of compounds selective for a specific AR subtype (i.e., A2BAR) and a generally long and complex synthetic route for largely substituted nucleosides are the main drawbacks of this category of molecules. Non-nucleoside agonists represent an alternative set of compounds able to stimulate the AR function and based on simplified structures. This review provides an updated overview on the structural classes of non-nucleoside AR agonists and their biological activities, with emphasis on the main derivatives reported in the literature. A focus is also given to the synthetic routes employed to develop these derivatives and on molecular modeling studies simulating their interaction with ARs.

Propofol reduces acute lung injury by up-regulating gamma-aminobutyric acid type a receptors

BACKGROUND

We used a two-hit lung injury rat model that involves mechanical ventilation (MV) following lipopolysaccharide exposure to investigate the effects of propofol on the expression of GABA_A receptors (GABA_AR) and cytokine responses, and we then determined the specific effects of GABA on cytokine responses in vitro in alveolar epithelial cells (AECs).

METHODS

Forty-eight adult male Wister rats were equally and randomly divided into the following 4 groups (n = 12) using a random number table: sham group, sham+propofol group, lipopolysaccharide (LPS) + VILI group, and LPS + VILI + propofol group. All animals were anesthetized, and the animals received a 3.75 mg/kg intratracheal instillation of endotoxins or phosphate-buffered saline (PBS) as the control, as described previously. After 30 min, rats were ventilated for 5 h in a volume-controlled ventilation mode. In the LPS + VILI group, animals were ventilated with a tidal volume (Vt) of 22 ml/kg and zero positive end-expiratory pressure (PEEP) at a respiratory rate of 16-18 breaths/min, whereas control (sham) rats were ventilated with a Vt of 6 ml/kg and PEEP of 5 cmH₂O at a rate of 45-55 breaths/min. The FiO₂ remained constant as 0.4, propofol was administered intravenously in the LPS + VILI + propofol and sham + propofol groups at a rate of 10 mg·kg^-1·h^-1 while normal saline at the same rate was intravenously administered in the LPS + VILI and sham groups during the entire mechanical ventilation period. Five hours after mechanical ventilation, the rats were killed. Survival rates, histopathology, concentrations of inflammatory mediators in bronchoalveolar lavage fluid (BALF), wet weight/dry weight (W/D) ratio of the lung, myeloperoxidase (MPO) activity in lung tissues, and expression of GAD and GABA_AR by immunohistochemical detection and Western blotting were assessed. Then, human type II-like alveolar epithelial cells (A549 cells) were cultured to full confluence and incubated with GABA (100 nM) alone, picrotoxin alone, a GABA_AR antagonist (PTX, 50 nM), or GABA + PTX for 10 min, followed by stimulation with LPS (control) at 100 ng/ml for 4 h. The concentrations of IL-1β, IL-2, IL-8, and IL-10 were then measured.

RESULTS

Administration of propofol in a two-hit lung injury rat model can increase survival rates and the expression of GAD and GABA_AR (P < .05). The administration of propofol can attenuate the release of pro-inflammatory cytokines both in vivo and in vitro, and the administration of propofol can attenuate histopathological changes, the W/D ratio, and MPO activity (P < .05).

CONCLUSIONS

In this study, we found that the administration of propofol improved lung function, alleviated lung injury, and up-regulated the GAD and GABA_AR expressions in a two-hit model of acute lung injury (ALI) characterized by intratracheal instillation of an endotoxin and prolonged MV. Therefore, the protective effects of propofol may be associated with the up-regulation of GABA_A receptors in AECs.

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.

Ventilation following established ARDS: a preclinical model framework to improve predictive power

BACKGROUND

Despite advances in understanding the pathophysiology of acute respiratory distress syndrome, effective pharmacological interventions have proven elusive. We believe this is a consequence of existing preclinical models being designed primarily to explore biological pathways, rather than predict treatment effects. Here, we describe a mouse model in which both therapeutic intervention and ventilation were superimposed onto existing injury and explored the impact of β-agonist treatment, which is effective in simple models but not clinically.

METHODS

Mice had lung injury induced by intranasal lipopolysaccharide (LPS), which peaked at 48 hours post-LPS based on clinically relevant parameters including hypoxaemia and impaired mechanics. At this peak of injury, mice were treated intratracheally with either terbutaline or tumour necrosis factor (TNF) receptor 1-targeting domain antibody, and ventilated with moderate tidal volume (20 mL/kg) to induce secondary ventilator-induced lung injury (VILI).

RESULTS

Ventilation of LPS-injured mice at 20 mL/kg exacerbated injury compared with low tidal volume (8 mL/kg). While terbutaline attenuated VILI within non-LPS-treated animals, it was ineffective to reduce VILI in pre-injured mice, mimicking its lack of clinical efficacy. In contrast, anti-TNF receptor 1 antibody attenuated secondary VILI within pre-injured lungs, indicating that the model was treatable.

CONCLUSIONS

We propose adoption of a practical framework like that described here to reduce the number of ultimately ineffective drugs reaching clinical trials. Novel targets should be evaluated alongside interventions which have been previously tested clinically, using models that recapitulate the (lack of) clinical efficacy. Within such a framework, outperforming a failed pharmacologic should be a prerequisite for drugs entering trials.

Hypoxia signaling in human diseases and therapeutic targets

Since the discovery of hypoxia-inducible factor (HIF), numerous studies on the hypoxia signaling pathway have been performed. The role of HIF stabilization during hypoxia has been extended from the induction of a single gene erythropoietin to the upregulation of a couple of hundred downstream targets, which demonstrates the complexity and importance of the HIF signaling pathway. Accordingly, HIF and its downstream targets are emerging as novel therapeutic options to treat various organ injuries. In this review, we discuss the current understanding of HIF signaling in four different organ systems, including the heart, lung, liver, and kidney. We also discuss the divergent roles of HIF in acute and chronic disease conditions and their revealed functions. Finally, we introduce some of the efforts that are being performed to translate our current knowledge in hypoxia signaling to clinical medicine.

A protein family that plays diverse roles in acute and chronic hypoxia (low oxygen) may prove valuable in developing novel therapies for different diseases. Hypoxia, the short- or long-term depletion of oxygen in cells, tissues and organs, is involved in many disease conditions. Holger Eltzschig at the McGovern Medical School in Houston, USA, and co-workers reviewed research into the roles of a key hypoxia regulator, the hypoxia-inducible factor (HIF) protein group, in diseases affecting the heart, lung, liver and kidneys. HIF protein activity is often beneficial in acute conditions such as myocardial ischemia, sending signals to protect cells and increasing tissue tolerance to hypoxia. However, during chronic hypoxia, HIF signaling may contribute to the progression of disease, for example in pulmonary fibrosis. HIF stabilizers and HIF-induced targets as drugs could prove valuable in future treatments.

Targeting the Immunomodulatory CD73/Adenosine System to Improve the Therapeutic Gain of Radiotherapy

Extracellular adenosine is a potent endogenous immunosuppressive mediator critical to the maintenance of homeostasis in various normal tissues including the lung. Adenosine is either released from stressed or injured cells or generated from extracellular adenine nucleotides by the concerted action of the ectoenzymes ectoapyrase (CD39) and 5′ ectonucleotidase (CD73) that catabolize ATP to adenosine. An acute CD73-dependent increase of adenosine in normal tissues mostly exerts tissue protective functions whereas chronically increased adenosine-levels in tissues exposed to DNA damaging chemotherapy or radiotherapy promote pathologic remodeling processes and fibrosis for example in the skin and the lung. Importantly, cancer cells also express CD73 and high CD73 expression in the tumor tissue has been linked to poor overall survival and recurrence free survival in patients suffering from breast and ovarian cancer. CD73 and adenosine support growth-promoting neovascularization, metastasis, and survival in cancer cells. In addition, adenosine can promote tumor intrinsic or therapy-induced immune escape by various mechanisms that dampen the immune system. Consequently, modulating CD73 or cancer-derived adenosine in the tumor microenvironment emerges as an attractive novel therapeutic strategy to limit tumor progression, improve antitumor immune responses, avoid therapy-induced immune deviation, and potentially limit normal tissue toxicity. However, the role of CD73/adenosine signaling in the tumor and normal tissue responses to radiotherapy and its use as therapeutic target to improve the outcome of radiotherapy approaches is less understood. The present review will highlight the dual role of CD73 and adenosine in tumor and tissue responses to radiotherapy with a special focus to the lung. It will also discuss the potential benefits and risks of pharmacologic modulation of the CD73/adenosine system to increase the therapeutic gain of radiotherapy or combined radioimmunotherapy in cancer treatment.

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.

Effects of Lung Protective Ventilation on the Cognitive Function Level of Patients with Esophageal Cancer

BACKGROUND

We intended to investigate the effects of lung protective ventilation on the cognitive function level of patients with esophageal cancer.

METHODS

Overall, 132 patients with esophageal cancer admitted to Taian Central Hospital, Taian China from January 2013 to January 2017 were enrolled in the study. According to the random number table method, they were divided into observation group and control group, 66 cases each. All patients underwent general anesthesia for thoracoscopic esophageal cancer radical operation, and lung protective ventilation and conventional positive pressure ventilation were used respectively. The levels of SOD, NSE and MDA, MMSE score and WMS memory quotient in the blood of the elbow vein were compared between the two groups at different times.

RESULTS

The levels of SOD and MMSE in the observation group at T2 and T3 were higher than those in the control group, and the NSE and MDA levels were lower than those in the control group (P=0.013, 0.033, 0.015, 0.044, 0.034, 0.029, 0.014, 0.017). The incidence of postoperative cognitive impairment was lower in the observation group than in the control group (P=0.007). The WMS memory quotient scores of the patients in the T2, T3, and T4 observation groups were higher than those in the control group (p=0.009, 0.032, 0.040).

CONCLUSION

Lung protective ventilation can reduce the oxidative stress injury for patients and improve their postoperative cognitive function and memory ability.