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1.  Adenosine mediates IL-13–induced inflammation and remodeling in the lung and interacts in an IL-13–adenosine amplification pathway 
Journal of Clinical Investigation  2003;112(3):332-344.
IL-13 is an important mediator of inflammation and remodeling. We hypothesized that adenosine accumulation, alterations in adenosine receptors, and adenosine–IL-13 autoinduction are critical events in IL-13–induced pathologies. To test this, we characterized the effects of IL-13 overexpression on the levels of adenosine, adenosine deaminase (ADA) activity, and adenosine receptors in the murine lung. We also determined whether adenosine induced IL-13 in lungs from ADA-null mice. IL-13 induced an inflammatory and remodeling response that caused respiratory failure and death. During this response, IL-13 caused a progressive increase in adenosine accumulation, inhibited ADA activity and mRNA accumulation, and augmented the expression of the A1, A2B, and A3 but not the A2A adenosine receptors. ADA enzyme therapy diminished the IL-13–induced increase in adenosine, inhibited IL-13–induced inflammation, chemokine elaboration, fibrosis, and alveolar destruction, and prolonged the survival of IL-13–transgenic animals. In addition, IL-13 was strongly induced by adenosine in ADA-null mice. These findings demonstrate that adenosine and adenosine signaling contribute to and influence the severity of IL-13–induced tissue responses. They also demonstrate that IL-13 and adenosine stimulate one another in an amplification pathway that may contribute to the nature, severity, progression, and/or chronicity of IL-13 and/or Th2-mediated disorders.
doi:10.1172/JCI200316815
PMCID: PMC166289  PMID: 12897202
2.  Role of A2B adenosine receptor signaling in adenosine-dependent pulmonary inflammation and injury  
The Journal of Clinical Investigation  2006;116(8):2173-2182.
Adenosine has been implicated in the pathogenesis of chronic lung diseases such as asthma and chronic obstructive pulmonary disease. In vitro studies suggest that activation of the A2B adenosine receptor (A2BAR) results in proinflammatory and profibrotic effects relevant to the progression of lung diseases; however, in vivo data supporting these observations are lacking. Adenosine deaminase–deficient (ADA-deficient) mice develop pulmonary inflammation and injury that are dependent on increased lung adenosine levels. To investigate the role of the A2BAR in vivo, ADA-deficient mice were treated with the selective A2BAR antagonist CVT-6883, and pulmonary inflammation, fibrosis, and airspace integrity were assessed. Untreated and vehicle-treated ADA-deficient mice developed pulmonary inflammation, fibrosis, and enlargement of alveolar airspaces; conversely, CVT-6883–treated ADA-deficient mice showed less pulmonary inflammation, fibrosis, and alveolar airspace enlargement. A2BAR antagonism significantly reduced elevations in proinflammatory cytokines and chemokines as well as mediators of fibrosis and airway destruction. In addition, treatment with CVT-6883 attenuated pulmonary inflammation and fibrosis in wild-type mice subjected to bleomycin-induced lung injury. These findings suggest that A2BAR signaling influences pathways critical for pulmonary inflammation and injury in vivo. Thus in chronic lung diseases associated with increased adenosine, antagonism of A2BAR-mediated responses may prove to be a beneficial therapy.
doi:10.1172/JCI27303
PMCID: PMC1501110  PMID: 16841096
3.  Interleukin-6 Contributes to Inflammation and Remodeling in a Model of Adenosine Mediated Lung Injury 
PLoS ONE  2011;6(7):e22667.
Background
Chronic lung diseases are the third leading cause of death in the United States due in part to an incomplete understanding of pathways that govern the progressive tissue remodeling that occurs in these disorders. Adenosine is elevated in the lungs of animal models and humans with chronic lung disease where it promotes air-space destruction and fibrosis. Adenosine signaling increases the production of the pro-fibrotic cytokine interleukin-6 (IL-6). Based on these observations, we hypothesized that IL-6 signaling contributes to tissue destruction and remodeling in a model of chronic lung disease where adenosine levels are elevated.
Methodology/Principal Findings
We tested this hypothesis by neutralizing or genetically removing IL-6 in adenosine deaminase (ADA)-deficient mice that develop adenosine dependent pulmonary inflammation and remodeling. Results demonstrated that both pharmacologic blockade and genetic removal of IL-6 attenuated pulmonary inflammation, remodeling and fibrosis in this model. The pursuit of mechanisms involved revealed adenosine and IL-6 dependent activation of STAT-3 in airway epithelial cells.
Conclusions/Significance
These findings demonstrate that adenosine enhances IL-6 signaling pathways to promote aspects of chronic lung disease. This suggests that blocking IL-6 signaling during chronic stages of disease may provide benefit in halting remodeling processes such as fibrosis and air-space destruction.
doi:10.1371/journal.pone.0022667
PMCID: PMC3143181  PMID: 21799929
4.  Metabolic Consequences of Adenosine Deaminase Deficiency in Mice Are Associated with Defects in Alveogenesis, Pulmonary Inflammation, and Airway Obstruction 
Adenosine deaminase (ADA) is a purine catabolic enzyme that manages levels of the biologically active purines adenosine and 2′-deoxyadenosine in tissues and cells. ADA-deficient mice die at 3 wk of age from severe respiratory distress. This phenotype is progressive and is linked to perturbations in pulmonary purine metabolism. The inflammatory changes found in the lungs of ADA-deficient mice included an accumulation of activated alveolar macrophages and eosinophils. These changes were accompanied by a pronounced enlargement of alveolar spaces and increases in mucus production in the bronchial airways. The alveolar enlargement was found to be due in part to abnormal alveogenesis. Lowering adenosine and 2′-deoxyadenosine levels using ADA enzyme therapy decreased the pulmonary eosinophilia and resolved many of the lung histopathologies. In addition, genetically restoring ADA to the forestomach of otherwise ADA-deficient mice prevented adenine metabolic disturbances as well as lung inflammation and damage. These data suggest that disturbances in purinergic signaling mediate the lung inflammation and damage seen in ADA-deficient mice.
PMCID: PMC2193256  PMID: 10899903
eosinophil; asthma; emphysema; alveolar macrophage; adenosine deaminase
5.  A protective role for the A1 adenosine receptor in adenosine-dependent pulmonary injury 
Adenosine is a signaling nucleoside that has been implicated in the regulation of asthma and chronic obstructive pulmonary disease. Adenosine signaling can serve both pro- and anti-inflammatory functions in tissues and cells. In this study we examined the contribution of A1 adenosine receptor (A1AR) signaling to the pulmonary inflammation and injury seen in adenosine deaminase–deficient (ADA-deficient) mice, which exhibit elevated adenosine levels. Experiments revealed that transcript levels for the A1AR were elevated in the lungs of ADA-deficient mice, in which expression was localized predominantly to alveolar macrophages. Genetic removal of the A1AR from ADA-deficient mice resulted in enhanced pulmonary inflammation along with increased mucus metaplasia and alveolar destruction. These changes were associated with the exaggerated expression of the Th2 cytokines IL-4 and IL-13 in the lungs, together with increased expression of chemokines and matrix metalloproteinases. These findings demonstrate that the A1AR plays an anti-inflammatory and/or protective role in the pulmonary phenotype seen in ADA-deficient mice, which suggests that A1AR signaling may serve to regulate the severity of pulmonary inflammation and remodeling seen in chronic lung diseases by controlling the levels of important mediators of pulmonary inflammation and damage.
doi:10.1172/JCI200522656
PMCID: PMC539198  PMID: 15630442
6.  Adenosine Deaminase Enzyme Therapy Prevents and Reverses the Heightened Cavernosal Relaxation in Priapism 
The journal of sexual medicine  2010;7(9):3011-3022.
Introduction
Priapism featured with painful prolonged penile erection is dangerous and commonly seen in sickle cell disease (SCD). The preventive approaches or effective treatment options for the disorder are limited because of poor understanding of its pathogenesis. Recent studies have revealed a novel role of excess adenosine in priapism caused by heightened cavernosal relaxation, and therefore present an intriguing mechanism-based therapeutic possibility.
Aim
The aim of this study was to determine the therapeutic effects of adenosine deaminase (ADA) enzyme therapy to lower adenosine in priapism.
Methods
Both ADA-deficient mice and SCD transgenic (Tg) mice display priapism caused by excessive adenosine. Thus, we used these two distinct lines of mouse models of priapism as our investigative tools. Specifically, we treated both of these mice with different dosages of polyethylene glycol–modified ADA (PEG–ADA) to reduce adenosine levels in vivo. At the end points of the experiments, we evaluated the therapeutic effects of PEG–ADA treatment by measuring adenosine levels and monitoring the cavernosal relaxation.
Main Outcome Measures
Adenosine levels in penile tissues were measured by high-performance liquid chromatography, and cavernosal relaxation was quantified by electrical field stimulation (EFS)-induced corporal cavernosal strip (CCS) assays.
Results
We found that lowering adenosine levels in penile tissues by PEG–ADA treatment from birth in ADA-deficient mice prevented the increased EFS-induced CCS relaxation associated with priapism. Intriguingly, in both ADA-deficient mice and SCD Tg mice with established priapism, we found that normalization of adenosine levels in penile tissues by PEG–ADA treatment relieved the heightened EFS-induced cavernosal relaxation in priapism.
Conclusions
Our studies have identified that PEG–ADA is a novel, safe, and mechanism-based drug to prevent and correct excess adenosine-mediated increased cavernosal relaxation seen in two independent priapic animal models, and suggested its therapeutic possibility in men suffering from priapism.
doi:10.1111/j.1743-6109.2009.01552.x
PMCID: PMC2906644  PMID: 19845544
Adenosine Signaling; Priapism; Novel Therapies; Pharmacologic Treatment of Priapism
7.  A3 Adenosine Receptor Signaling Influences Pulmonary Inflammation and Fibrosis 
Adenosine is a signaling molecule produced during conditions that cause cellular stress or damage. This signaling pathway is implicated in the regulation of pulmonary disorders through the selective engagement of adenosine receptors. The goal of this study was to examine the involvement of the A3 adenosine receptor (A3R) in a bleomycin model of pulmonary inflammation and fibrosis. Results demonstrated that A3R-deficient mice exhibit enhanced pulmonary inflammation that included an increase in eosinophils. Accordingly, there was a selective up-regulation of eosinophil-related chemokines and cytokines in the lungs of A3R-deficient mice exposed to bleomycin. This increase in eosinophil numbers was accompanied by a decrease in the amount of extracellular eosinophil peroxidase activity in lavage fluid from A3R-deficient mice exposed to bleomycin, an observation suggesting that the A3R is necessary for eosinophil degranulation in this model. Despite an increase in inflammatory metrics associated with A3R-deficient mice treated with bleomycin, there was little difference in the degree of pulmonary fibrosis. Examination of fibrotic mediators demonstrated enhanced transforming growth factor (TGF)-β1 expression, but not a concomitant increase in TGF-β1 activity. This was associated with the loss of expression of matrix metalloprotease 9, an activator of TGF-β1, in alveolar macrophages and airway mast cells in the lungs of A3R-deficient mice. Together, these results suggest that the A3R serves antiinflammatory functions in the bleomycin model, and is also involved in regulating the production of mediators that can impact fibrosis.
doi:10.1165/rcmb.2007-0419OC
PMCID: PMC2586045  PMID: 18587054
pulmonary fibrosis; adenosine receptors; inflammation; eosinophil; extracellular matrix
8.  A gene expression signature of emphysema-related lung destruction and its reversal by the tripeptide GHK 
Genome Medicine  2012;4(8):67.
Background
Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease consisting of emphysema, small airway obstruction, and/or chronic bronchitis that results in significant loss of lung function over time.
Methods
In order to gain insights into the molecular pathways underlying progression of emphysema and explore computational strategies for identifying COPD therapeutics, we profiled gene expression in lung tissue samples obtained from regions within the same lung with varying amounts of emphysematous destruction from smokers with COPD (8 regions × 8 lungs = 64 samples). Regional emphysema severity was quantified in each tissue sample using the mean linear intercept (Lm) between alveolar walls from micro-CT scans.
Results
We identified 127 genes whose expression levels were significantly associated with regional emphysema severity while controlling for gene expression differences between individuals. Genes increasing in expression with increasing emphysematous destruction included those involved in inflammation, such as the B-cell receptor signaling pathway, while genes decreasing in expression were enriched in tissue repair processes, including the transforming growth factor beta (TGFβ) pathway, actin organization, and integrin signaling. We found concordant differential expression of these emphysema severity-associated genes in four cross-sectional studies of COPD. Using the Connectivity Map, we identified GHK as a compound that can reverse the gene-expression signature associated with emphysematous destruction and induce expression patterns consistent with TGFβ pathway activation. Treatment of human fibroblasts with GHK recapitulated TGFβ-induced gene-expression patterns, led to the organization of the actin cytoskeleton, and elevated the expression of integrin β1. Furthermore, addition of GHK or TGFβ restored collagen I contraction and remodeling by fibroblasts derived from COPD lungs compared to fibroblasts from former smokers without COPD.
Conclusions
These results demonstrate that gene-expression changes associated with regional emphysema severity within an individual's lung can provide insights into emphysema pathogenesis and identify novel therapeutic opportunities for this deadly disease. They also suggest the need for additional studies to examine the mechanisms by which TGFβ and GHK each reverse the gene-expression signature of emphysematous destruction and the effects of this reversal on disease progression.
doi:10.1186/gm367
PMCID: PMC4064320  PMID: 22937864
9.  Enhanced Airway Inflammation and Remodeling in Adenosine Deaminase-Deficient Mice Lacking the A2B Adenosine Receptor1 
Adenosine is a signaling nucleoside that is generated in response to cellular injury and orchestrates the balance between tissue protection and the progression to pathological tissue remodeling. Adenosine deaminase (ADA)-deficient mice develop progressive airway inflammation and remodeling in association with adenosine elevations, suggesting that adenosine can promote features of chronic lung disease. Furthermore, pharmacological studies in ADA-deficient mice demonstrate that A2BR antagonism can attenuate features of chronic lung disease, implicating this receptor in the progression of chronic lung disease. This study examines the contribution of A2BR signaling in this model by generating ADA/A2BR double-knockout mice. Our hypothesis was that genetic removal of the A2BR from ADA-deficient mice would lead to diminished pulmonary inflammation and damage. Unexpectedly, ADA/A2BR double-knockout mice exhibited enhanced pulmonary inflammation and airway destruction. Marked loss of pulmonary barrier function and excessive airway neutrophilia are thought to contribute to the enhanced tissue damage observed. These findings support an important protective role for A2BR signaling during acute stages of lung disease.
doi:10.4049/jimmunol.0900515
PMCID: PMC3631106  PMID: 19494329
10.  Alterations in Adenosine Metabolism and Signaling in Patients with Chronic Obstructive Pulmonary Disease and Idiopathic Pulmonary Fibrosis 
PLoS ONE  2010;5(2):e9224.
Background
Adenosine is generated in response to cellular stress and damage and is elevated in the lungs of patients with chronic lung disease. Adenosine signaling through its cell surface receptors serves as an amplifier of chronic lung disorders, suggesting adenosine-based therapeutics may be beneficial in the treatment of lung diseases such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Previous studies in mouse models of chronic lung disease demonstrate that the key components of adenosine metabolism and signaling are altered. Changes include an up-regulation of CD73, the major enzyme of adenosine production and down-regulation of adenosine deaminase (ADA), the major enzyme for adenosine metabolism. In addition, adenosine receptors are elevated.
Methodology/Principal Findings
The focus of this study was to utilize tissues from patients with COPD or IPF to examine whether changes in purinergic metabolism and signaling occur in human disease. Results demonstrate that the levels of CD73 and A2BR are elevated in surgical lung biopsies from severe COPD and IPF patients. Immunolocalization assays revealed abundant expression of CD73 and the A2BR in alternatively activated macrophages in both COPD and IPF samples. In addition, mediators that are regulated by the A2BR, such as IL-6, IL-8 and osteopontin were elevated in these samples and activation of the A2BR on cells isolated from the airways of COPD and IPF patients was shown to directly induce the production of these mediators.
Conclusions/Significance
These findings suggest that components of adenosine metabolism and signaling are altered in a manner that promotes adenosine production and signaling in the lungs of patients with COPD and IPF, and provide proof of concept information that these disorders may benefit from adenosine-based therapeutics. Furthermore, this study provides the first evidence that A2BR signaling can promote the production of inflammatory and fibrotic mediators in patients with these disorders.
doi:10.1371/journal.pone.0009224
PMCID: PMC2821921  PMID: 20169073
11.  Transgenic Modeling of Transforming Growth Factor-β1 
Inflammation and tissue remodeling with pathologic fibrosis are common consequences of Th2 responses in the lung and other organs. Interleukin (IL)-13 and transforming growth factor-β1 (TGF-β1) are frequently coexpressed in these responses and are believed to play important roles in the pathogenesis of Th2-induced pathologies. To shed light on the mechanisms of these responses, overexpression transgenic approaches were used to selectively target each of these cytokines to the murine lung. IL-13 proved to be a potent stimulator of eosinophilic inflammation, mucus metaplasia, tissue fibrosis, and alveolar remodeling. CC chemokines, specific chemokine receptors (CCR2, CCR1), adenosine metabolism, vascular endothelial growth factor, and IL-11 contributed to the genesis of these responses. IL-13 also induced tissue fibrosis, at least in part, via its ability to induce and activate TGF-β1. In the TGF-β1 transgenic mouse, epithelial apoptosis preceded the onset of tissue fibrosis and alveolar remodeling. In addition, chemical (Z-VAD-fmk) and genetic (null mutations of early growth response gene 1) interventions blocked apoptosis and ameliorated TGF-β1–induced fibrosis and alveolar restructuring. These studies define an IL-13–TGF-β1 pathway of tissue remodeling that regulates inflammation, mucus metaplasia, apoptosis, vascular responses, and fibrosis in the lung. They also highlight the intimate relationship between apoptosis and fibrosis induced by TGF-β1. By defining the complexities of this pathway, these studies highlight sites at which therapies can be directed to control these important responses.
doi:10.1513/pats.200602-017AW
PMCID: PMC2658706  PMID: 16799085
asthma; fibrosis; interleukin-13; transforming growth factor-β; 1; transgenic
12.  Attenuation of Chronic Pulmonary Inflammation in A2B Adenosine Receptor Knockout Mice 
Pharmacologic evidence suggests that activation of A2B adenosine receptors results in proinflammatory effects relevant to the progression of asthma, a chronic lung disease associated with elevated interstitial adenosine concentrations in the lung. This concept has been challenged by the finding that genetic removal of A2B receptors leads to exaggerated responses in models of acute inflammation. Therefore, the goal of our study was to determine the effects of A2B receptor gene ablation in the context of ovalbumin-induced chronic pulmonary inflammation. We found that repetitive airway allergen challenge induced a significant increase in adenosine levels in fluid recovered by bronchoalveolar lavage. Genetic ablation of A2B receptors significantly attenuated allergen-induced chronic pulmonary inflammation, as evidenced by a reduction in the number of bronchoalveolar lavage eosinophils and in peribronchial eosinophilic infiltration. The most striking difference in the pulmonary inflammation induced in A2B receptor knockout (A2BKO) and wild-type mice was the lack of allergen-induced IL-4 release in the airways of A2BKO animals, in line with a significant reduction in IL-4 protein and mRNA levels in lung tissue. In addition, attenuation of allergen-induced transforming growth factor–β release in airways of A2BKO mice correlated with reduced airway smooth muscle and goblet cell hyperplasia/hypertrophy. In conclusion, genetic removal of A2B adenosine receptors in mice leads to inhibition of allergen-induced chronic pulmonary inflammation and airway remodeling. These findings are in agreement with previous pharmacologic studies suggesting a deleterious role for A2B receptor signaling in chronic lung inflammation.
doi:10.1165/rcmb.2008-0391OC
PMCID: PMC2874442  PMID: 19556606
adenosine; asthma; pulmonary inflammation; IL-4; transforming growth factor–β
13.  Adenosine Deaminase Inhibition Prevents Clostridium difficile Toxin A-Induced Enteritis in Mice ▿  
Infection and Immunity  2010;79(2):653-662.
Toxin A (TxA) is able to induce most of the classical features of Clostridium difficile-associated disease in animal models. The objective of this study was to determine the effect of an inhibitor of adenosine deaminase, EHNA [erythro-9-(2-hydroxy-3-nonyl)-adenine], on TxA-induced enteritis in C57BL6 mice and on the gene expression of adenosine receptors. EHNA (90 μmol/kg) or phosphate-buffered saline (PBS) was injected intraperitoneally (i.p.) 30 min prior to TxA (50 μg) or PBS injection into the ileal loop. A2A adenosine receptor agonist (ATL313; 5 nM) was injected in the ileal loop immediately before TxA (50 μg) in mice pretreated with EHNA. The animals were euthanized 3 h later. The changes in the tissue were assessed by the evaluation of ileal loop weight/length and secretion volume/length ratios, histological analysis, myeloperoxidase assay (MPO), the local expression of inducible nitric oxide synthase (NOS2), pentraxin 3 (PTX3), NF-κB, tumor necrosis factor alpha (TNF-α), and interleukin-1β (IL-1β) by immunohistochemistry and/or quantitative reverse transcription-PCR (qRT-PCR). The gene expression profiles of A1, A2A, A2B, and A3 adenosine receptors also were evaluated by qRT-PCR. Adenosine deaminase inhibition, by EHNA, reduced tissue injury, neutrophil infiltration, and the levels of proinflammatory cytokines (TNF-α and IL-1β) as well as the expression of NOS2, NF-κB, and PTX3 in the ileum of mice injected with TxA. ATL313 had no additional effect on EHNA action. TxA increased the gene expression of A1 and A2A adenosine receptors. Our findings show that the inhibition of adenosine deaminase by EHNA can prevent Clostridium difficile TxA-induced damage and inflammation possibly through the A2A adenosine receptor, suggesting that the modulation of adenosine/adenosine deaminase represents an important tool in the management of C. difficile-induced disease.
doi:10.1128/IAI.01159-10
PMCID: PMC3028843  PMID: 21115723
14.  Is neutrophil elastase the missing link between emphysema and fibrosis? Evidence from two mouse models 
Respiratory Research  2005;6(1):83.
Background
The separation of emphysema from fibrosis is not as clear-cut as it was thought in early studies. These two pathologies may be present at the same time in human lungs and in mice either instilled with elastolytic enzymes or bleomycin or exposed to cigarette-smoke. According to a current view, emphysema originates from a protease/antiprotease imbalance, and a role for antiproteases has also been suggested in the modulation of the fibrotic process. In this study we investigate in experimental animal models of emphysema and fibrosis whether neutrophil elastase may constitute a pathogenic link between these two pathologies.
Methods
This study was done in two animal models in which emphysema and fibrosis were induced either by bleomycin (BLM) or by chronic exposure to cigarette-smoke. In order to assess the protease-dependence of the BLM-induced lesion, a group mice was treated with 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride, a serine proteinase inhibitor active toward neutrophil elastase. Lungs from each experimental group were used for the immunohistochemical assessment of transforming growth factor-β (TGF-β) and transforming growth factor-α (TGF-α) and for determination of the mean linear intercept as well as the percent volume densities of fibrosis and of emphysematous changes. Additionally, the lungs were also assessed for desmosine content and for the determination of elastase levels in the pulmonary interstitium by means of immunoelectron microscopy.
Results
We demonstrate that in BLM-treated mice (i) the development of elastolytic emphysema precedes that of fibrosis; (ii) significant amount of elastase in alveolar interstitium is associated with an increased expression of TGF-β and TGF-α; and finally, (iii) emphysematous and fibrotic lesions can be significantly attenuated by using a protease inhibitor active against neutrophil elastase.
Also, in a strain of mice that develop both emphysema and fibrosis after chronic cigarette-smoke exposure, the presence of elastase in alveolar structures is associated with a positive immunohistochemical reaction for reaction for both TGF-β and TGF-α.
Conclusion
The results of the present study strongly suggest that neutrophil elastase may represent a common pathogenic link between emphysema and fibrosis. Proteases and in particular neutrophil elastase could act as regulatory factors in the generation of soluble cytokines with mitogenic activity for mesenchymal cells resulting either in emphysema or in fibrosis or both.
doi:10.1186/1465-9921-6-83
PMCID: PMC1184102  PMID: 16045796
15.  The Reno-Vascular A2B Adenosine Receptor Protects the Kidney from Ischemia 
PLoS Medicine  2008;5(6):e137.
Background
Acute renal failure from ischemia significantly contributes to morbidity and mortality in clinical settings, and strategies to improve renal resistance to ischemia are urgently needed. Here, we identified a novel pathway of renal protection from ischemia using ischemic preconditioning (IP).
Methods and Findings
For this purpose, we utilized a recently developed model of renal ischemia and IP via a hanging weight system that allows repeated and atraumatic occlusion of the renal artery in mice, followed by measurements of specific parameters or renal functions. Studies in gene-targeted mice for each individual adenosine receptor (AR) confirmed renal protection by IP in A1−/−, A2A−/−, or A3AR−/− mice. In contrast, protection from ischemia was abolished in A2BAR−/− mice. This protection was associated with corresponding changes in tissue inflammation and nitric oxide production. In accordance, the A2BAR-antagonist PSB1115 blocked renal protection by IP, while treatment with the selective A2BAR-agonist BAY 60–6583 dramatically improved renal function and histology following ischemia alone. Using an A2BAR-reporter model, we found exclusive expression of A2BARs within the reno-vasculature. Studies using A2BAR bone-marrow chimera conferred kidney protection selectively to renal A2BARs.
Conclusions
These results identify the A2BAR as a novel therapeutic target for providing potent protection from renal ischemia.
Using gene-targeted mice, Holger Eltzschig and colleagues identify the A2B adenosine receptor as a novel therapeutic target for providing protection from renal ischemia.
Editors' Summary
Background.
Throughout life, the kidneys perform the essential task of filtering waste products and excess water from the blood to make urine. Each kidney contains about a million small structures called nephrons, each of which contains a filtration unit consisting of a glomerulus (a small blood vessel) intertwined with a urine-collecting tube called a tubule. If the nephrons stop working for any reason, the rate at which the blood is filtered (the glomerular filtration rate or GFR) decreases and dangerous amounts of waste products such as creatinine build up in the blood. Most kidney diseases destroy the nephrons slowly over years, producing an irreversible condition called chronic renal failure. But the kidneys can also stop working suddenly because of injury or poisoning. One common cause of “acute” renal failure in hospital patients is ischemia—an inadequate blood supply to an organ that results in the death of part of that organ. Heart surgery and other types of surgery in which the blood supply to the kidneys is temporarily disrupted are associated with high rates of acute renal failure.
Why Was This Study Done?
Although the kidneys usually recover from acute failure within a few weeks if the appropriate intensive treatment (for example, dialysis) is provided, acute renal failure after surgery can be fatal. Thus, new strategies to protect the kidneys from ischemia are badly needed. Like other organs, the kidneys can be protected from lethal ischemia by pre-exposure to several short, nonlethal episodes of ischemia. It is not clear how this “ischemic preconditioning” increases renal resistance to ischemia but some data suggest that the protection of tissues from ischemia might involve a signaling molecule called extracellular adenosine. This molecule binds to proteins called receptors on the surface of cells and sends signals into them that change their behavior. There are four different adenosine receptor—A1AR, A2AAR, A2BAR, and A3AR—and in this study, the researchers use ischemic preconditioning as an experimental strategy to investigate which of these receptors protects the kidneys from ischemia in mice, information that might provide clues about how to protect the kidneys from ischemia.
What Did the Researchers Do and Find?
The researchers first asked whether ischemic preconditioning protects the kidneys of mice strains that lack the genes for individual adenosine receptors (A1AR−/−, A2AAR−/−, A2BAR−/−, and A3AR−/− mice) from subsequent ischemia. Using a hanging-weight system, they intermittently blocked the renal artery of these mice before exposing them to a longer period of renal ischemia. Twenty-four hours later, they assessed the renal function of the mice by measuring their blood creatinine levels, GFRs, and urine production. Ischemic preconditioning protected all the mice from ischemia-induced loss of kidney function except the A2BAR−/− mice. It also prevented ischemia-induced structural damage and inflammation in the kidneys of wild-type but not A2BAR−/− mice. These results suggest that A2BAR may help to protect the kidneys from ischemia. Consistent with this idea, ischemic preconditioning did not prevent ischemia-induced renal damage in wild-type mice treated with a compound that specifically blocks the activity of A2BAR. However, wild-type mice (but not A2BAR−/− mice) treated with an A2BAR agonist (which activates the receptor) retained their kidney function after renal ischemia without ischemic preconditioning. Finally, the researchers report that A2BAR has to be present on the blood vessels in the kidney to prevent ischemia-induced acute renal failure.
What Do These Findings Mean?
These findings suggest that the protection of the kidneys from ischemia and the renal resistance to ischemia that is provided by ischemic preconditioning involve adenosine signaling through A2BAR. They also suggest that adenosine might provide protection against ischemia-induced damage by blocking inflammation in the kidney although other possible mechanisms of action need to be investigated. Importantly, these findings suggest that A2BAR might be a therapeutic target for the prevention of renal ischemia. However, results obtained in animals do not always reflect the situation in people, so before A2BAR agonists can be used to reduce the chances of patients developing acute renal failure after surgery, these results need confirming in people and the safety of A2BAR agonists need to be thoroughly investigated.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050137.
The US National Institute of Diabetes and Digestive and Kidney Diseases provides information on how the kidneys work and what can go wrong with them, including a list of links to further information about kidney disease
The MedlinePlus encyclopedia has a page on acute kidney failure (in English and Spanish)
Wikipedia has pages on acute renal failure, ischemia, ischemic preconditioning, and adenosine (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
doi:10.1371/journal.pmed.0050137
PMCID: PMC2504049  PMID: 18578565
16.  Dependence on O2- generation by xanthine oxidase of pathogenesis of influenza virus infection in mice. 
Journal of Clinical Investigation  1990;85(3):739-745.
We evaluated various biochemical parameters in influenza virus-infected mice and focused on adenosine catabolism in the supernatant of bronchoalveolar lavage fluid (s-BALF), lung tissue, and serum (plasma). The activities of adenosine deaminase (ADA) and xanthine oxidase (XO), which generates O2-, were elevated in the s-BALF, lung tissue homogenate, and serum (plasma). The elevations were most remarkable in s-BALF and in lung tissue: We found a 170-fold increase in ADA activity and a 400-fold increase in XO activity as measured per volume of alveolar lavage fluid. The ratio of activity of XO to activity of xanthine dehydrogenase in s-BALF increased from 0.15 +/- 0.05 (control; no infection) to 1.06 +/- 0.13 on day 6 after viral infection. Increased levels of various adenosine catabolites (i.e., inosine, hypoxanthine, xanthine, and uric acid) in serum and s-BALF were confirmed. We also identified O2- generation from XO in s-BALF obtained on days 6 and 8 after infection, and the generation of O2- was enhanced remarkably in the presence of adenosine. Lastly, treatment with allopurinol (an inhibitor of XO) and with chemically modified superoxide dismutase (a scavenger of O2-) improved the survival rate of influenza virus-infected mice. These results indicate that generation of oxygen-free radicals by XO, coupled with catabolic supply of hypoxanthine from adenosine catabolism, is a pathogenic principle in influenza virus infection in mice and that a therapeutic approach by elimination of oxygen radicals thus seems possible.
PMCID: PMC296490  PMID: 2155924
17.  Excess adenosine in murine penile erectile tissues contributes to priapism via A2B adenosine receptor signaling  
The Journal of Clinical Investigation  2008;118(4):1491-1501.
Priapism, abnormally prolonged penile erection in the absence of sexual excitation, is associated with ischemia-mediated erectile tissue damage and subsequent erectile dysfunction. It is common among males with sickle cell disease (SCD), and SCD transgenic mice are an accepted model of the disorder. Current strategies to manage priapism suffer from a poor fundamental understanding of the molecular mechanisms underlying the disorder. Here we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected priapic activity. ADA enzyme therapy successfully corrected the priapic activity both in vivo and in vitro, suggesting that it was dependent on elevated adenosine levels. Further genetic and pharmacologic evidence demonstrated that A2B adenosine receptor–mediated (A2BR-mediated) cAMP and cGMP induction was required for elevated adenosine–induced prolonged penile erection. Finally, priapic activity in SCD transgenic mice was also caused by elevated adenosine levels and A2BR activation. Thus, we have shown that excessive adenosine accumulation in the penis contributes to priapism through increased A2BR signaling in both Ada–/– and SCD transgenic mice. These findings provide insight regarding the molecular basis of priapism and suggest that strategies to either reduce adenosine or block A2BR activation may prove beneficial in the treatment of this disorder.
doi:10.1172/JCI33467
PMCID: PMC2267015  PMID: 18340377
18.  Insights into thymic purine metabolism and adenosine deaminase deficiency revealed by transgenic mice overexpressing ecto-5'-nucleotidase (CD73). 
Journal of Clinical Investigation  1997;99(4):676-683.
The adenosine producing enzyme ecto-5'-nucleotidase (5'-NT) is not normally expressed during thymocyte development until the medullary stage. To determine whether earlier expression would lead to adenosine accumulation and/or be deleterious for thymocyte maturation, thymic purine metabolism, and T cell differentiation were studied in lckNT transgenic mice overexpressing 5'-NT in cortical thymocytes under the control of the lck proximal promoter. In spite of a 100-fold elevation in thymic 5'-NT activity, transgenic adenosine levels were unchanged and T cell immunity was normal. Inosine, the product of adenosine deamination, was elevated more than twofold, however, indicating that adenosine deaminase (ADA) can prevent the accumulation of adenosine, even with a dramatic increase in 5'-NT activity, and demonstrating the availability of 5'-NT substrates in the thymus for the first time. Thymic adenosine concentrations of mice treated with the ADA inhibitor 2'-deoxycoformycin (dCF) were elevated over 30-fold, suggesting that high ADA activity, rather than an absence of 5'-NT, is mainly responsible for low thymic adenosine levels. The adenosine concentrations in dCF-treated mice are sufficient to cause adenosine receptor-mediated thymocyte apoptosis in vitro, suggesting that adenosine accumulation could play a role in ADA-deficient severe combined immunodeficiency.
PMCID: PMC507850  PMID: 9045870
19.  IL-18 Induces Emphysema and Airway and Vascular Remodeling via IFN-γ, IL-17A, and IL-13 
Rationale: Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation, alveolar destruction, and airway and vascular remodeling. However, the mechanisms that lead to these diverse alterations have not been defined.
Objectives: We hypothesized that IL-18 plays a central role in the pathogenesis of these lesions.
Methods: We generated and characterized lung-specific, inducible IL-18 transgenic mice.
Measurements and Main Results: Here we demonstrate that the expression of IL-18 in the mature murine lung induces inflammation that is associated with the accumulation of CD4+, CD8+, CD19+, and NK1.1+ cells; emphysema; mucus metaplasia; airway fibrosis; vascular remodeling; and right ventricle cardiac hypertrophy. We also demonstrate that IL-18 induces type 1, type 2, and type 17 cytokines with IFN-γ–inhibiting macrophage, lymphocyte, and eosinophil accumulation while stimulating alveolar destruction and genes associated with cell cytotoxicity and IL-13 and IL-17A inducing mucus metaplasia, airway fibrosis, and vascular remodeling. We also highlight interactions between these responses with IL-18 inducing IL-13 via an IL-17A–dependent mechanism and the type 1 and type17/type 2 responses counterregulating each another.
Conclusions: These studies define the spectrum of inflammatory, parenchymal, airway, and vascular alterations that are induced by pulmonary IL-18; highlight the similarities between these responses and the lesions in COPD; and define the selective roles that type 1, type 2, and type 17 responses play in the generation of IL-18–induced pathologies.
doi:10.1164/rccm.201108-1545OC
PMCID: PMC3373071  PMID: 22383501
IL-18; chronic obstructive pulmonary disease; airway fibrosis; mucus metaplasia; vascular remodeling
20.  IL-17A is essential to the development of elastase-induced pulmonary inflammation and emphysema in mice 
Respiratory Research  2013;14(1):5.
Background
Pulmonary emphysema is characterized by alveolar destruction and persistent inflammation of the airways. Although IL-17A contributes to many chronic inflammatory diseases, it’s role in the inflammatory response of elastase-induced emphysema remains unclear.
Methods
In a model of elastase-induced pulmonary emphysema we examined the response of IL-17A-deficient mice, monitoring airway inflammation, static compliance, lung histology and levels of neutrophil-related chemokine and pro-inflammatory cytokines in bronchoalveolar lavage (BAL) fluid.
Results
Wild-type mice developed emphysematous changes in the lung tissue on day 21 after elastase treatment, whereas emphysematous changes were decreased in IL-17A-deficient mice compared to wild-type mice. Neutrophilia in BAL fluid, seen in elastase-treated wild-type mice, was reduced in elastase-treated IL-17A-deficient mice on day 4, associated with decreased levels of KC, MIP-2 and IL-1 beta. Elastase-treated wild-type mice showed increased IL-17A levels as well as increased numbers of IL-17A+ CD4 T cells in the lung in the initial period following elastase treatment.
Conclusions
These data identify the important contribution of IL-17A in the development of elastase-induced pulmonary inflammation and emphysema. Targeting IL-17A in emphysema may be a potential therapeutic strategy for delaying disease progression.
doi:10.1186/1465-9921-14-5
PMCID: PMC3564829  PMID: 23331548
IL-17; Elastase; Emphysema; Chronic obstructive pulmonary disease
21.  120 The Features of Airway Remodeling Are More Severe in Female Mice 
Background
Epidemiological studies have already shown that females are dominant in terms of the sex ratio of adult asthma prevalence and severe asthma. It has also been reported that female mice are more susceptible to the development of allergic airway inflammation and airway hyperresponsiveness (AHR) than males. However, there have been few reports of studies on sex difference in the pathogenesis of severe asthma, especially airway remodeling in an animal model. In this study, we investigated sex difference in formation of airway remodeling using a long-term antigen challenged asthma model.
Methods
Following ovalbumin (OVA)/alum intraperitoneal injection, male or female mice (BALB/c) were challenged with aerosolized 1% OVA on 3 days/week for 5 weeks, and we investigated the sex difference in AHR, airway inflammation, as well as airway remodeling.
Results
In OVA-sensitized and -challenged (OVA/OVA) female mice, AHR, the number of eosinophils and lymphocytes, as well as Th2 cytokines and growth factors in BAL fluid were increased compared with OVA/OVA male mice. On the other hand, there is no significant difference in the level of eotaxin in BAL fluid. The histological features of airway remodeling, including goblet cell hyperplasia, subepithelial fibrosis and myofibroblast hypertrophy, were also increased in OVA/OVA female mice. Moreover, serum total and OVA-specific IgE were significantly elevated in OVA/OVA female mice.
Conclusions
These results indicate that female mice are dominant in terms of forming airway remodeling as compared with male mice. The involvement of sex difference for sensitization and growth factor release in lung tissue based on inflammatory cell infiltration is indicated for the mechanism of sex difference of airway remodeling.
doi:10.1097/01.WOX.0000411865.43631.44
PMCID: PMC3513133
22.  Oxidative Damage to Nucleic Acids in Severe Emphysema* 
Chest  2008;135(4):10.1378/chest.08-2257.
Background
Oxidative stress is a key element in the pathogenesis of emphysema, but oxidation of nucleic acids has been largely overlooked. The aim of this study was to investigate oxidative damage to nucleic acids in severe emphysematous lungs.
Methods
Thirteen human severe emphysematous lungs, including five with α1-antitrypsin deficiency (AATD), were obtained from patients receiving lung transplantation. Control lung tissue was obtained from non-COPD lungs (n = 8) and donor lungs (n = 8). DNA and RNA oxidation were investigated by immunochemistry. Morphometry (mean linear intercept [Lm] and CT scan) and immunostaining for CD68 and neutrophil elastase also were performed.
Results
Nucleic acid oxidation was increased in alveolar wall cells in emphysematous lungs compared to non-COPD and donor lungs (p < 0.01). In emphysematous lungs, oxidative damage to nucleic acids in alveolar wall cells was increased in the more severe emphysematous areas assessed by histology (Lm, > 0.5 mm; p < 0.05) and CT scan (< −950 Hounsfield units; p < 0.05). Compared to classic emphysema, AATD lungs exhibited higher levels of nucleic acid oxidation in macrophages (p < 0.05) and airway epithelial cells (p < 0.01). Pretreatments with DNase and RNase demonstrated that RNA oxidation was more prevalent than DNA oxidation in alveolar wall cells.
Conclusions
We demonstrated for the first time that nucleic acids, especially RNA, are oxidized in human emphysematous lungs. The correlation between the levels of oxidative damage to nucleic acids in alveolar wall cells and the severity of emphysema suggest a potential role in the pathogenesis of emphysema.
doi:10.1378/chest.08-2257
PMCID: PMC3864580  PMID: 19118262
α1-antitrypsin deficiency; emphysema; nucleic acids; oxidative stress; RNA
23.  The antiinflammatory mechanism of methotrexate. Increased adenosine release at inflamed sites diminishes leukocyte accumulation in an in vivo model of inflammation. 
Journal of Clinical Investigation  1993;92(6):2675-2682.
Methotrexate, a folate antagonist, is a potent antiinflammatory agent when used weekly in low concentrations. We examined the hypothesis that the antiphlogistic effects of methotrexate result from its capacity to promote intracellular accumulation of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) that, under conditions of cell injury, increases local adenosine release. We now present the first evidence to establish this mechanism of action in an in vivo model of inflammation, the murine air pouch model. Mice were injected intraperitoneally with either methotrexate or saline for 3-4 wk during induction of air pouches. Pharmacologically relevant doses of methotrexate increased splenocyte AICAR content, raised adenosine concentrations in exudates from carrageenan-inflamed air pouches, and markedly inhibited leukocyte accumulation in inflamed air pouches. The methotrexate-mediated reduction in leukocyte accumulation was partially reversed by injection of adenosine deaminase (ADA) into the air pouch, completely reversed by a specific adenosine A2 receptor antagonist, 3,7-dimethyl-1-propargylxanthine (DMPX), but not affected by an adenosine A1 receptor antagonist, 8-cyclopentyl-dipropylxanthine. Neither ADA nor DMPX affected leukocyte accumulation in the inflamed pouches of animals treated with either saline or the potent antiinflammatory steroid dexamethasone. These results indicate that methotrexate is a nonsteroidal antiinflammatory agent, the antiphlogistic action of which is due to increased adenosine release at inflamed sites.
Images
PMCID: PMC288465  PMID: 8254024
24.  A Role for Adenosine Deaminase in Drosophila Larval Development 
PLoS Biology  2005;3(7):e201.
Adenosine deaminase (ADA) is an enzyme present in all organisms that catalyzes the irreversible deamination of adenosine and deoxyadenosine to inosine and deoxyinosine. Both adenosine and deoxyadenosine are biologically active purines that can have a deep impact on cellular physiology; notably, ADA deficiency in humans causes severe combined immunodeficiency. We have established a Drosophila model to study the effects of altered adenosine levels in vivo by genetic elimination of adenosine deaminase-related growth factor-A (ADGF-A), which has ADA activity and is expressed in the gut and hematopoietic organ. Here we show that the hemocytes (blood cells) are the main regulator of adenosine in the Drosophila larva, as was speculated previously for mammals. The elevated level of adenosine in the hemolymph due to lack of ADGF-A leads to apparently inconsistent phenotypic effects: precocious metamorphic changes including differentiation of macrophage-like cells and fat body disintegration on one hand, and delay of development with block of pupariation on the other. The block of pupariation appears to involve signaling through the adenosine receptor (AdoR), but fat body disintegration, which is promoted by action of the hemocytes, seems to be independent of the AdoR. The existence of such an independent mechanism has also been suggested in mammals.
Adenosine deaminase is critically important to survival; congenital deficiency in humans leads to severe immunodeficiency. Here, the authors demonstrate that adenosine deaminase deficiency in flies results in severe developmental defects.
doi:10.1371/journal.pbio.0030201
PMCID: PMC1135298  PMID: 15907156
25.  Soluble Ecto-5′-nucleotidase (5′-NT), Alkaline Phosphatase, and Adenosine Deaminase (ADA1) Activities in Neonatal Blood Favor Elevated Extracellular Adenosine*  
The Journal of Biological Chemistry  2013;288(38):27315-27326.
Background: Newborns have elevated plasma adenosine levels, which may influence their immunological function.
Results: Compared with adults, newborns have elevated plasma 5′-NT and alkaline phosphatase activities and lower adenosine deaminase activity.
Conclusion: Soluble enzymes significantly influence extracellular purine metabolism in blood, and the levels of these enzymes in newborns promote elevated adenosine.
Significance: Higher adenosine generation in newborn blood may promote an anti-inflammatory immunological status.
Extracellular adenosine, a key regulator of physiology and immune cell function that is found at elevated levels in neonatal blood, is generated by phosphohydrolysis of adenine nucleotides released from cells and catabolized by deamination to inosine. Generation of adenosine monophosphate (AMP) in blood is driven by cell-associated enzymes, whereas conversion of AMP to adenosine is largely mediated by soluble enzymes. The identities of the enzymes responsible for these activities in whole blood of neonates have been defined in this study and contrasted to adult blood. We demonstrate that soluble 5′-nucleotidase (5′-NT) and alkaline phosphatase (AP) mediate conversion of AMP to adenosine, whereas soluble adenosine deaminase (ADA) catabolizes adenosine to inosine. Newborn blood plasma demonstrates substantially higher adenosine-generating 5′-NT and AP activity and lower adenosine-metabolizing ADA activity than adult plasma. In addition to a role in soluble purine metabolism, abundant AP expressed on the surface of circulating neonatal neutrophils is the dominant AMPase on these cells. Plasma samples from infant observational cohorts reveal a relative plasma ADA deficiency at birth, followed by a gradual maturation of plasma ADA through infancy. The robust adenosine-generating capacity of neonates appears functionally relevant because supplementation with AMP inhibited whereas selective pharmacologic inhibition of 5′-NT enhanced Toll-like receptor-mediated TNF-α production in neonatal whole blood. Overall, we have characterized previously unrecognized age-dependent expression patterns of plasma purine-metabolizing enzymes that result in elevated plasma concentrations of anti-inflammatory adenosine in newborns. Targeted manipulation of purine-metabolizing enzymes may benefit this vulnerable population.
doi:10.1074/jbc.M113.484212
PMCID: PMC3779727  PMID: 23897810
Adenosine; Adenosine Receptor; ADP; AMP; ATP; Immunology; Infectious Diseases; Innate Immunity; Purine; Purinergic Agonists

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