Purinergic P2Y₂ receptors promote neutrophil infiltration and hepatocyte death in mice with acute liver injury

Salivary metabolites are promising noninvasive biomarkers of drug-induced liver injury

BACKGROUND

Drug-induced liver injury (DILI) is one of the most common adverse events of medication use, and its incidence is increasing. However, early detection of DILI is a crucial challenge due to a lack of biomarkers and noninvasive tests.

AIM

To identify salivary metabolic biomarkers of DILI for the future development of noninvasive diagnostic tools.

METHODS

Saliva samples from 31 DILI patients and 35 healthy controls (HCs) were subjected to untargeted metabolomics using ultrahigh-pressure liquid chromatography coupled with tandem mass spectrometry. Subsequent analyses, including partial least squares-discriminant analysis modeling, t tests and weighted metabolite coexpression network analysis (WMCNA), were conducted to identify key differentially expressed metabolites (DEMs) and metabolite sets. Furthermore, we utilized least absolute shrinkage and selection operato and random fores analyses for biomarker prediction. The use of each metabolite and metabolite set to detect DILI was evaluated with area under the receiver operating characteristic curves.

RESULTS

We found 247 differentially expressed salivary metabolites between the DILI group and the HC group. Using WMCNA, we identified a set of 8 DEMs closely related to liver injury for further prediction testing. Interestingly, the distinct separation of DILI patients and HCs was achieved with five metabolites, namely, 12-hydroxydodecanoic acid, 3-hydroxydecanoic acid, tetradecanedioic acid, hypoxanthine, and inosine (area under the curve: 0.733-1).

CONCLUSION

Salivary metabolomics revealed previously unreported metabolic alterations and diagnostic biomarkers in the saliva of DILI patients. Our study may provide a potentially feasible and noninvasive diagnostic method for DILI, but further validation is needed.

Bioinformatics-led discovery of liver-specific genes and macrophage infiltration in acute liver injury

Background

Acute liver injury (ALI) is an important global health concern, primarily caused by widespread hepatocyte cell death, coupled with a complex immune response and a lack of effective remedies. This study explores the underlying mechanisms, immune infiltration patterns, and potential targets for intervention and treatment ALI.

Methods

The datasets of acetaminophen (APAP), carbon tetrachloride (CCl4), and lipopolysaccharide (LPS)-induced ALI were obtained from the GEO database. Differentially expressed genes (DEGs) were individually identified using the limma packages. Functional enrichment analysis was performed using KEGG, GO, and GSEA methods. The overlapping genes were extracted from the three datasets, and hub genes were identified using MCODE and CytoHubba algorithms. Additionally, PPI networks were constructed based on the String database. Immune cell infiltration analysis was conducted using ImmuCellAI, and the correlation between hub genes and immune cells was determined using the Spearman method. The relationship between hub genes, immune cells, and biochemical indicators of liver function (ALT, AST) was validated using APAP and triptolide (TP) -induced ALI mouse models.

Results

Functional enrichment analysis indicated that all three ALI models were enriched in pathways linked to fatty acid metabolism, drug metabolism, inflammatory response, and immune regulation. Immune analysis revealed a significant rise in macrophage infiltration. A total of 79 overlapping genes were obtained, and 10 hub genes were identified that were consistent with the results of the biological information analysis after screening and validation. Among them, Clec4n, Ms4a6d, and Lilrb4 exhibited strong associations with macrophage infiltration and ALI.

P2Y2 purinergic receptor gene deletion protects mice from bacterial endotoxin and sepsis-associated liver injury and mortality

The liver plays a significant role in regulating a wide range of metabolic, homeostatic, and host-defense functions. However, the impact of liver injury on the host's ability to control bacteremia and morbidity in sepsis is not well understood. Leukocyte recruitment and activation lead to cytokine and chemokine release, which, in turn, trigger hepatocellular injury and elevate nucleotide levels in the extracellular milieu. P2Y2 purinergic receptors, G protein-coupled and activated by extracellular ATP/UTP, are expressed at the cell surface of hepatocytes and nonparenchymal cells. We sought to determine whether P2Y2 purinergic receptor function is necessary for the maladaptive host response to bacterial infection and endotoxin-mediated inflammatory liver injury and mortality in mice. We report that P2Y2 purinergic receptor knockout mice (P2Y2-/-) had attenuated inflammation and liver injury, with improved survival in response to LPS/galactosamine (LPS/GalN; inflammatory liver injury) and cecal ligation and puncture (CLP; polymicrobial sepsis). P2Y2-/- livers had attenuated c-Jun NH2-terminal kinase activation, matrix metallopeptidase-9 expression, and hepatocyte apoptosis in response to LPS/GalN and attenuated inducible nitric oxide synthase and nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3 protein expression in response to CLP. Implicating liver injury in the disruption of amino acid homeostasis, CLP led to lower serum arginine and higher bacterial load and morbidity in the WT mice, whereas serum arginine levels were comparable to sham-operated controls in P2Y2-/- mice, which had attenuated bacteremia and improved survival. Collectively, our studies highlight the pathophysiological relevance of P2Y2 purinergic receptor function in inflammatory liver injury and dysregulation of systemic amino acid homeostasis with implications for sepsis-associated immune dysfunction and morbidity in mice.NEW & NOTEWORTHY Our studies provide experimental evidence for P2Y2 purinergic receptor-mediated potentiation of inflammatory liver injury, morbidity, and mortality, in two well-established animal models of inflammatory liver injury. Our findings highlight the potential to target P2Y2 purinergic signaling to attenuate the induction of "cytokine storm" and prevent its deleterious consequences on liver function, systemic amino acid homeostasis, host response to bacterial infection, and sepsis-associated morbidity and mortality.

CD73 mediates the therapeutic effects of endometrial regenerative cells in concanavalin A-induced hepatitis by regulating CD4+ T cells

BACKGROUND

As a kind of mesenchymal-like stromal cells, endometrial regenerative cells (ERCs) have been demonstrated effective in the treatment of Concanavalin A (Con A)-induced hepatitis. However, the therapeutic mechanism of ERCs is not fully understood. Ecto-5`-nucleotidase (CD73), an enzyme that could convert immune-stimulative adenosine monophosphate (AMP) to immune-suppressive adenosine (ADO), was identified highly expressed on ERCs. The present study was conducted to investigate whether the expression of CD73 on ERCs is critical for its therapeutic effects in Con A-induced hepatitis.

METHODS

ERCs knocking out CD73 were generated with lentivirus-mediated CRISPR-Cas9 technology and identified by flow cytometry, western blot and AMPase activity assay. CD73-mediated immunomodulatory effects of ERCs were investigated by CD4+ T cell co-culture assay in vitro. Besides, Con A-induced hepatitis mice were randomly assigned to the phosphate-buffered saline treated (untreated), ERC-treated, negative lentiviral control ERC (NC-ERC)-treated, and CD73-knockout-ERC (CD73-KO-ERC)-treated groups, and used to assess the CD73-mediated therapeutic efficiency of ERCs. Hepatic histopathological analysis, serum transaminase concentrations, and the proportion of CD4+ T cell subsets in the liver and spleen were performed to assess the progression degree of hepatitis.

RESULTS

Expression of CD73 on ERCs could effectively metabolize AMP to ADO, thereby inhibiting the activation and function of conventional CD4+ T cells was identified in vitro. In addition, ERCs could markedly reduce levels of serum and liver transaminase and attenuate liver damage, while the deletion of CD73 on ERCs dampens these effects. Furthermore, ERC-based treatment achieved less infiltration of CD4+ T and Th1 cells in the liver and reduced the population of systemic Th1 and Th17 cells and the levels of pro-inflammatory cytokines such as IFN-γ and TNF-α, while promoting the generation of Tregs in the liver and spleen, while deletion of CD73 on ERCs significantly impaired their immunomodulatory effects locally and systemically.

CONCLUSION

Taken together, it is concluded that CD73 is critical for the therapeutic efficiency of ERCs in the treatment of Con A-induced hepatitis.

Cell-type-specific role of P2Y2 receptor in HDM-driven model of allergic airway inflammation

Allergic airway inflammation (AAI) is a chronic respiratory disease that is considered a severe restriction in daily life and is accompanied by a constant risk of acute aggravation. It is characterized by IgE-dependent activation of mast cells, infiltration of eosinophils, and activated T-helper cell type 2 (Th2) lymphocytes into airway mucosa. Purinergic receptor signaling is known to play a crucial role in inducing and maintaining allergic airway inflammation. Previous studies in an ovalbumin (OVA)-alum mouse model demonstrated a contribution of the P2Y2 purinergic receptor subtype (P2RY2) in allergic airway inflammation. However, conflicting data concerning the mechanism by which P2RY2 triggers AAI has been reported. Thus, we aimed at elucidating the cell-type-specific role of P2RY2 signaling in house dust mite (HDM)-driven model of allergic airway inflammation. Thereupon, HDM-driven AAI was induced in conditional knockout mice, deficient or intact for P2ry2 in either alveolar epithelial cells, hematopoietic cells, myeloid cells, helper T cells, or dendritic cells. To analyze the functional role of P2RY2 in these mice models, flow cytometry of bronchoalveolar lavage fluid (BALF), cytokine measurement of BALF, invasive lung function measurement, HDM re-stimulation of mediastinal lymph node (MLN) cells, and lung histology were performed. Mice that were subjected to an HDM-based model of allergic airway inflammation resulted in reduced signs of acute airway inflammation including eosinophilia in BALF, peribronchial inflammation, Th2 cytokine production, and bronchial hyperresponsiveness in mice deficient for P2ry2 in alveolar epithelial cells, hematopoietic cells, myeloid cells, or dendritic cells. Furthermore, the migration of bone-marrow-derived dendritic cells and bone-marrow-derived monocytes, both deficient in P2ry2, towards ATP was impaired. Additionally, we found reduced levels of MCP-1/CCL2 and IL-8 homologues in the BALF of mice deficient in P2ry2 in myeloid cells and lower concentrations of IL-33 in the lung tissue of mice deficient in P2ry2 in alveolar epithelial cells. In summary, our results show that P2RY2 contributes to HDM-induced airway inflammation by mediating proinflammatory cytokine production in airway epithelial cells, monocytes, and dendritic cells and drives the recruitment of lung dendritic cells and monocytes.

Purinergic signaling during Marek's disease in chickens

Purinergic receptors (PRs) have been reported as potential therapeutic targets for many viral infections including herpesviruses, which urges the investigation into their role in Marek's disease (MD), a herpesvirus induced cancer in chickens that is an important pathogen for the poultry industry. MD is caused by MD virus (MDV) that has a similar viral life cycle as human varicella zoster virus in that it is shed from infected epithelial skin cells and enters the host through the respiratory route. In this report, PR responses during natural MDV infection and disease progression was examined in MD-resistant white Leghorns (WL) and MD-susceptible Pure Columbian (PC) chickens during natural infection. Whole lung lavage cells (WLLC) and liver tissue samples were collected from chickens infected but showing no clinical signs of MD (Infected) or presenting with clinical disease (Diseased). RNA was extracted followed by RT-qPCR analysis with gene specific primers against members of the P1, P2X, and P2Y PR families. Differential expression (p < 0.05) was observed in breed and disease conditions. Some PRs showed tissue specific expression (P1A1, P2X1, and P2X6 in WLLC) whereas others responded to MDV infection only in MD-susceptible (PC) chickens (P1A2A, P2X1, P2X5, P2X7). P2Y PRs had differential expression in both chicken lines in response to MDV infection and MD progression. This study is the first to our knowledge to examine PR responses during MDV infection and disease progression. These results suggest PR signaling may an important area of research for MDV replication and MD.

P2X7 Receptor in Alcoholic Steatohepatitis and Alcoholic Liver Fibrosis

Alcoholic liver disease is one of the most common chronic liver diseases in the world. It is a liver disease caused by prolonged heavy drinking and its main clinical features are nausea, vomiting, enlargement of the liver, and jaundice. Recent studies suggest that Kupffer cell-mediated inflammatory response is a core driver in the development of alcoholic steatohepatitis and alcoholic liver fibrosis. As a danger signal, extracellular ATP activates the assembly of NLPR3 inflammasome by acting on purine P2X7 receptor, the activated NLRP3 inflammasome prompts ASC to cleave pro-cCaspase-1 into active caspase-1in KCs. Active caspase-1 promotes the conversion of pro-IL-1β to IL-1β, which further enhances the inflammatory response. Here, we briefly review the role of the P2X7R-NLRP3 inflammasome axis in the pathogenesis of alcoholic liver disease and the evolution of alcoholic steatohepatitis and alcoholic liver fibrosis. Regulation of the inflammasome axis of P2X7R-NLRP3 may be a new approach for the treatment of alcoholic liver disease.

Liver infiltration of multiple immune cells during the process of acute liver injury and repair

BACKGROUND

Immune cells, including neutrophils, natural killer (NK) cells, T cells, NKT cells and macrophages, participate in the progression of acute liver injury and hepatic recovery. To date, there has been no systematic study on the quantitative changes in these different immune cells from initial injury to subsequent recovery.

AIM

To investigate the infiltration changes of various immune cells in acute liver injury models over time, and to study the relationship between the changes in leukocyte cell-derived chemotaxin 2 (LECT2) and the infiltration of several immune cells.

METHODS

Carbon tetrachloride- and concanavalin A-induced acute liver injury models were employed to mimic toxin-induced and autoimmune-mediated liver injury respectively. The quantitative changes in various immune cells were monitored at different time points. Serum samples were collected, and liver tissues were harvested. Ly6G, CD161, CD4, CD8 and F4/80 staining were used to indicate neutrophils, NK/NKT cells, CD4⁺ T cells, CD8⁺ T cells and macrophages, respectively. Lect2-KO mice were used to detect the function of LECT2.

RESULTS

During the injury and repair process, different types of immune cells began to increase, reached their peaks and fell into decline at different time points. Furthermore, when the serum alanine transaminase (ALT) and aspartate transaminase (AST) indices reverted to normal levels 7 d after the injury, the infiltration of immune cells still existed even 14 d after the injury, showing an obvious lag effect. We found that the expression of LECT2 was upregulated in acute liver injury mouse models, and the liver injuries of Lect2-KO mice were less severe than those of wild-type mice. Compared with wild-type mice, Lect2-KO mice had different immune cell infiltration.

CONCLUSION

The recovery time of immune cells was far behind that of serum ALT and AST during the process of liver repair. LECT2 could regulate monocyte/macrophage chemotaxis and might be used as a therapeutic target for acute liver injury.

Therapeutic potential for P2Y2 receptor antagonism

G protein-coupled receptors are the target of more than 30% of all FDA-approved drug therapies. Though the purinergic P2 receptors have been an attractive target for therapeutic intervention with successes such as the P2Y₁₂ receptor antagonist, clopidogrel, P2Y₂ receptor (P2Y₂R) antagonism remains relatively unexplored as a therapeutic strategy. Due to a lack of selective antagonists to modify P2Y₂R activity, studies using primarily genetic manipulation have revealed roles for P2Y₂R in a multitude of diseases. These include inflammatory and autoimmune diseases, fibrotic diseases, renal diseases, cancer, and pathogenic infections. With the advent of AR-C118925, a selective and potent P2Y₂R antagonist that became commercially available only a few years ago, new opportunities exist to gain a more robust understanding of P2Y₂R function and assess therapeutic effects of P2Y₂R antagonism. This review discusses the characteristics of P2Y₂R that make it unique among P2 receptors, namely its involvement in five distinct signaling pathways including canonical Gα_q protein signaling. We also discuss the effects of other P2Y₂R antagonists and the pivotal development of AR-C118925. The remainder of this review concerns the mounting evidence implicating P2Y₂Rs in disease pathogenesis, focusing on those studies that have evaluated AR-C118925 in pre-clinical disease models.

The Dual Role of Innate Immune Response in Acetaminophen-Induced Liver Injury

Acetyl-para-aminophenol (APAP), a commonly used antipyretic analgesic, is becoming increasingly toxic to the liver, resulting in a high rate of acute hepatic failure in Europe and the United States. Excessive APAP metabolism in the liver develops an APAP-protein adduct, which causes oxidative stress, MPTP opening, and hepatic necrosis. HMGB-1, HSP, nDNA, mtDNA, uric acid, and ATP are DMAPs released during hepatic necrosis. DMAPs attach to TLR4-expressing immune cells such KCs, macrophages, and NK cells, activating them and causing them to secrete cytokines. Immune cells and their secreted cytokines have been demonstrated to have a dual function in acetaminophen-induced liver injury (AILI), with a role in either proinflammation or pro-regeneration, resulting in contradicting findings and some research confusion. Neutrophils, KCs, MoMFs, NK/NKT cells, γδT cells, DCs, and inflammasomes have pivotal roles in AILI. In this review, we summarize the dual role of innate immune cells involved in AILI and illustrate how these cells initiate innate immune responses that lead to persistent inflammation and liver damage. We also discuss the contradictory findings in the literature and possible protocols for better understanding the molecular regulatory mechanisms of AILI.

The roles of nucleotide signaling and platelets in inflammation

Nucleotides and platelets have been associated with a wide range of activities that affect the host inflammatory response. The main goal of this study is to examine the roles of nucleotide signaling and platelets in inflammation. The study analysis entailed conducting a systematic search to identify relevant articles in PsycINFO, PubMed, Web of Science, and CINAHL. The evidence gathered from the identified articles shows the roles of nucleotides and platelets in inflammation. In the extracellular environment, nucleotides act as signaling molecules that can activate nucleotide receptors to promote inflammation. Inflammation is an essential process through which the innate immune system responds to pathogens, microbes, and damage-associated molecular patterns. Moreover, research evidence shows that the mechanisms through which platelets affect inflammatory responses and regulate hemostasis are the same. The roles of nucleotides and platelets in inflammation have been explored in several studies worldwide. Although platelets and nucleotides have unique structures, both of them influence the host response to pathogens and tumors. Analysis of platelets and nucleotides will offer valuable insight for the development of new treatments for infectious and inflammatory diseases.

Targeting innate immune responses to attenuate acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) hepatotoxicity is an important cause of acute liver failure, resulting in massive deaths in many developed countries. Currently, the metabolic process of APAP in the body has been well studied. However, the underlying mechanism of APAP-induced liver injury remains elusive. Increasing clinical and experimental evidences indicate that the innate immune responses are involved in the pathogenesis of APAP-induced acute liver injury (AILI), in which immune cells have dual roles of inducing inflammation to exacerbate hepatotoxicity and removing dead cells and debris to help liver regeneration. In this review, we summarize the latest findings of innate immune cells involved in AILI, particularly emphasizing the activation of innate immune cells and their different roles during the injury and repair phases. Moreover, current available treatments are discussed according to the different roles of innate immune cells in the development of AILI. This review aims to update the knowledge about innate immune responses in the pathogenesis of AILI, and provide potential therapeutic interventions for AILI.

Combined exercise training improved exercise capacity and lung inflammation in rats with hepatopulmonary syndrome

AIM

Physical exercise training attenuates pulmonary inflammation, but its effects on impaired respiratory function caused by hepatopulmonary syndrome (HPS) have not been evaluated. We determined if the combination of moderate intensity aerobic and resistance training during HPS development modifies exercise capacity, respiratory system mechanics, and lung inflammation responses.

MAIN METHODS

Wistar rats were randomly divided into sham, HPS, and HPS + combined exercise training groups. Fifteen days after HPS induction, a moderate intensity aerobic plus resistance exercise training protocol was performed five times a week for 5 weeks on alternate days. Exercise capacity, respiratory system mechanics, lung inflammation, pulmonary morphology, and immunohistochemistry were evaluated.

KEY FINDINGS

Overall, our findings indicated that combined exercise training efficiently increased the maximal running and resistance capacity of HPS animals. The training regimen reduced the expression of P2X7 in parenchymal leukocytes (P < 0.01), partially restored the expression of interleukin-10 in airway epithelium (P < 0.01), and increased the expression of TFPI in the airway epithelium (P < 0.01) as well as reduced its expression in parenchymal leukocytes (P < 0.01). However, exercise training did not attenuate HPS-induced respiratory mechanical derangements or lung tissue remodeling.

SIGNIFICANCE

Combined exercise training can elicit adaptation with regard to both maximal running capacity and maximum strength and modify the expression of P2X7 and TFPI in parenchymal leukocytes and that of IL-10 in airway epithelium.

Hepatic Adenosine Triphosphate Reduction Through the Short-Chain Fatty Acids-Peroxisome Proliferator-Activated Receptor γ-Uncoupling Protein 2 Axis Alleviates Immune-Mediated Acute Hepatitis in Inulin-Supplemented Mice

How liver tolerance is disrupted in immune-mediated liver injury is currently unclear. There is also insufficient information available regarding susceptibility, precipitation, escalation, and perpetuation of autoimmune hepatitis. To explore how dietary fiber influences hepatic damage, we applied the concanavalin A (ConA)-induced acute immune-mediated liver injury model in mice fed a diet supplemented with 6.8% inulin, a water-soluble fermentable fiber. Twelve hours after ConA administration, inulin-supplemented diet-fed mice demonstrated significantly alleviated hepatic damage histologically and serologically, with down-regulation of hepatic interferon-γ and tumor necrosis factor and reduced myeloperoxidase (MPO)-producing neutrophil infiltration. Preconditioning with an inulin-supplemented diet for 2 weeks significantly reduced hepatic adenosine triphosphate (ATP) content; suramin, a purinergic P2 receptor antagonist, abolished the protective effect. Of note, the portal plasma derived from mice fed the inulin-supplemented diet significantly alleviated ConA-induced immune-mediated liver injury. Mechanistically, increased portal short-chain fatty acid (SCFA) levels, such as those of acetate and butyrate, by inulin supplementation leads to up-regulation of hepatic γ-type peroxisome proliferator-activated receptor (Pparg) and uncoupling protein 2 (Ucp2), which uncouples mitochondrial ATP synthesis downstream of PPARγ. Pparg down-regulating small interfering RNA cancelled the protective effect of inulin supplementation against MPO-producing neutrophil infiltration and the subsequent immune-mediated liver injury, suggesting that the SCFA-PPARγ-UCP2 axis plays a key role in the protective effect by inulin supplementation. Moreover, significant changes in the gut microbiota, including increased operational taxonomic units in genera Akkermansia and Allobaculum, also characterized the protective effect of the inulin-supplemented diet. Conclusion: There is a possible unraveled etiopathophysiological link between the maintenance of liver tolerance and dietary fiber. The SCFA-PPARγ-UCP2 axis may provide therapeutic targets for immune-mediated liver injury in the future.

CD39-mediated ATP-adenosine signalling promotes hepatic stellate cell activation and alcoholic liver disease

CD39 is associated with diverse physiological and pathological processes, including cell proliferation and differentiation. Adenosine triphosphate (ATP) is hydrolysed to adenosine by different enzymes including ecto-nucleoside triphosphate diphosphohydrolase-1/ENTPD1 (CD39) and ecto-5'-nucleotidase (CD73), regulating many physiological and pathological processes in various diseases, but these changes and functions in alcoholic liver disease are generally unknown. In this study, an alcoholic liver disease model in vivo was induced by ethanol plus carbon tetrachloride(CCl4) administered to C57BL/6 mice, who were the intraperitoneally injected with the CD39 inhibitor sodium polyoxotungstate (POM1) or colchicine from the 5th week to the 8th week. Meanwhile, hepatic stellate cells were stimulated by acetaldehyde to replicate alcoholic liver fibrosis models in vitro. Exogenous ATP and POM1 were added in turn to the culture system. Pharmacological blockade of CD39 largely prevents liver damage and collagen deposition. We found that blockade or silencing of CD39 prevented acetaldehyde-induced proliferation of HSC-T6 cells and the expression of fibrogenic factors. Moreover, blockade or silencing of CD39 could block the activation of the adenosine A2A and adenosine A2B receptors and the TGF-β/Smad3 pathway, which are essential events in HSC activation. Thus, blockade of CD39 to inhibit the transduction of ATP to adenosine may prevent HSC activation, alleviating alcoholic hepatic fibrosis. The findings from this study suggest ATP-adenosine signalling is a novel therapeutic and preventive target for alcoholic liver disease.

P2Y2R Deficiency Ameliorates Hepatic Steatosis by Reducing Lipogenesis and Enhancing Fatty Acid β-Oxidation through AMPK and PGC-1α Induction in High-Fat Diet-Fed Mice

Non-alcoholic fatty liver disease (NAFLD) is a chronic metabolic liver disease associated with obesity and insulin resistance. Activation of the purinergic receptor P2Y2R has been reported to promote adipogenesis, inflammation and dyslipidemia in adipose tissues in obese mice. However, the role of P2Y2R and its mechanisms in NAFLD remain unknown. We hypothesized that P2Y2R deficiency may play a protective role in NAFLD by modulating lipid metabolism in the liver. In this study, we fed wild type and P2Y2R knockout mice with a high-fat diet (HFD) for 12 weeks and analyzed metabolic phenotypes. First, P2Y2R deficiency effectively improved insulin resistance with a reduction in body weight and plasma insulin. Second, P2Y2R deficiency attenuated hepatic lipid accumulation and injury with reduced alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Third, P2Y2R deficiency decreased the expression of fatty acid synthesis mediators (cluster of differentiation (CD36), fatty acid synthase (FAS), and stearoyl-CoA desaturase 1 (SCD1)); and increased the expression of adipose triglyceride lipase (ATGL), a lipolytic enzyme. Mechanistically, P2Y2R deficiency increased the AMP-activated protein kinase (AMPK) activity to improve mitochondrial fatty acid β-oxidation (FAO) by regulating acetyl-CoA carboxylase (ACC) and carnitine palmitoyltransferase 1A (CPT1A)-mediated FAO pathway. In addition, P2Y2R deficiency increased peroxisome proliferator-activated gamma co-activator-1α (PGC-1α)-mediated mitochondrial biogenesis. Conclusively, P2Y2R deficiency ameliorated HFD-induced hepatic steatosis by enhancing FAO through AMPK signaling and PGC-1α pathway, suggesting P2Y2R as a promising therapeutic target for NAFLD.

The complex roles of neutrophils in APAP-induced liver injury

Acetaminophen (APAP) is a widely applied drug for the alleviation of pain and fever, which is also a dose‐depedent toxin. APAP‐induced acute liver injury has become one of the primary causes of liver failure which is an increasingly serious threat to human health. Neutrophils are the major immune cells in human serving as the first barrier against the invasion of pathogen. It has been reported that neutrophils patriciate in the occurrence and development of APAP‐induced liver injury. However, evolving evidences suggest that neutrophils also contribute to tissue repair and actively orchestrate resolution of inflammation. Here, we addressed the complex roles in APAP‐induced liver injury on the basis of brief introduction of neutrophil's activation, recruitment and migration.

The role of P2Y receptors in regulating immunity and metabolism

P2Y receptors are G protein-coupled receptors whose physiological agonists are the nucleotides ATP, ADP, UTP, UDP and UDP-glucose. Eight P2Y receptors have been cloned in humans: P2Y₁R, P2Y₂R, P2Y₄R, P2Y₆R, P2Y₁₁R, P2Y₁₂R, P2Y₁₃R and P2Y₁₄R. P2Y receptors are expressed in lymphoid tissues such as thymus, spleen and bone marrow where they are expressed on lymphocytes, macrophages, dendritic cells, neutrophils, eosinophils, mast cells, and platelets. P2Y receptors regulate many aspects of immune cell function, including phagocytosis and killing of pathogens, antigen presentation, chemotaxis, degranulation, cytokine production, and lymphocyte activation. Consequently, P2Y receptors shape the course of a wide range of infectious, autoimmune, and inflammatory diseases. P2Y₁₂R ligands have already found their way into the therapeutic arena, and we envision additional ligands as future drugs for the treatment of diseases caused by or associated with immune dysregulation.

Potential Therapeutic Applications of P2 Receptor Antagonists: From Bench to Clinical Trials

BACKGROUND

Extracellular purines and pyrimidines have important physiological functions in mammals. Purines and pyrimidines act on P1 and P2 purinergic receptors, which are widely expressed in the plasma membrane in various cell types. P2 receptors act as important therapeutic targets and are associated with several disorders, such as pain, neurodegeneration, cancer, inflammation, and thrombosis. However, the use of antagonists for P2 receptors in clinical therapy, with the exception of P2Y12, is a great challenge. Currently, many research groups and pharmaceutical companies are working on the development of specific antagonist molecules for each receptor subtype that could be used as new medicines to treat their respective disorders.

OBJECTIVE

The present review compiles some interesting findings on the application of P2 receptor antagonists in different in vitro and in vivo experimental models as well as the progress of advanced clinical trials with these compounds.

CONCLUSION

Despite all of the exciting results obtained on the bench, few antagonists of P2 receptors advanced to the clinical trials, and once they reach this stage, the effectiveness of the therapy is not guaranteed, as in the example of P2X7 antagonists. Despite this, P2Y12 receptor antagonists have a history of success and have been used in therapy for at least two decades to prevent thrombosis in patients at risk for myocardial infarctions. This breakthrough is the motivation for scientists to develop new drugs with antagonistic activity for the other P2 receptors; thus, in a matter of years, we will have an evolution in the field of purinergic therapy.

Purinergic signalling in liver diseases: Pathological functions and therapeutic opportunities

Extracellular nucleotides, including ATP, are essential regulators of liver function and serve as danger signals that trigger inflammation upon injury. Ectonucleotidases, which are expressed by liver-resident cells and recruited immune cells sequentially hydrolyse nucleotides to adenosine. The nucleotide/nucleoside balance orchestrates liver homeostasis, tissue repair, and functional restoration by regulating the crosstalk between liver-resident cells and recruited immune cells. In this review, we discuss our current knowledge on the role of purinergic signals in liver homeostasis, restriction of inflammation, stimulation of liver regeneration, modulation of fibrogenesis, and regulation of carcinogenesis. Moreover, we discuss potential targeted therapeutic strategies for liver diseases based on purinergic signals involving blockade of nucleotide receptors, enhancement of ectonucleoside triphosphate diphosphohydrolase activity, and activation of adenosine receptors.

The role of the CD39-CD73-adenosine pathway in liver disease

Extracellular adenosine triphosphate (ATP) is a danger signal released by dying and damaged cells, and it functions as an immunostimulatory signal that promotes inflammation. The ectonucleotidases CD39/ectonucleoside triphosphate diphosphohydrolase-1 and CD73/ecto-5'-nucleotidase are cell-surface enzymes that breakdown extracellular ATP into adenosine. This drives a shift from an ATP-driven proinflammatory environment to an anti-inflammatory milieu induced by adenosine. The CD39-CD73-adenosine pathway changes dynamically with the pathophysiological context in which it is embedded. Accumulating evidence suggests that CD39 and CD73 play important roles in liver disease as critical components of the extracellular adenosinergic pathway. Recent studies have shown that the modification of the CD39-CD73-adenosine pathway alters the liver's response to injury. Moreover, adenosine exerts different effects on the pathophysiology of the liver through different receptors. In this review, we aim to describe the role of the CD39-CD73-adenosine pathway and adenosine receptors in liver disease, highlighting potential therapeutic targets in this pathway, which will facilitate the development of therapeutic strategies for the treatment of liver disease.

Update of P2Y receptor pharmacology: IUPHAR Review 27

Eight G protein-coupled P2Y receptor subtypes respond to extracellular adenine and uracil mononucleotides and dinucleotides. P2Y receptors belong to the δ group of rhodopsin-like GPCRs and contain two structurally distinct subfamilies: P2Y₁ , P2Y₂ , P2Y₄ , P2Y₆ , and P2Y₁₁ (principally G_q protein-coupled P2Y₁ -like) and P2Y_12-14 (principally G_i protein-coupled P2Y₁₂ -like) receptors. Brain P2Y receptors occur in neurons, glial cells, and vasculature. Endothelial P2Y₁ , P2Y₂ , P2Y₄ , and P2Y₆ receptors induce vasodilation, while smooth muscle P2Y₂ , P2Y₄ , and P2Y₆ receptor activation leads to vasoconstriction. Pancreatic P2Y₁ and P2Y₆ receptors stimulate while P2Y₁₃ receptors inhibits insulin secretion. Antagonists of P2Y₁₂ receptors, and potentially P2Y₁ receptors, are anti-thrombotic agents, and a P2Y₂ /P2Y₄ receptor agonist treats dry eye syndrome in Asia. P2Y receptor agonists are generally pro-inflammatory, and antagonists may eventually treat inflammatory conditions. This article reviews recent developments in P2Y receptor pharmacology (using synthetic agonists and antagonists), structure and biophysical properties (using X-ray crystallography, mutagenesis and modelling), physiological and pathophysiological roles, and present and potentially future therapeutic targeting.

Increased Purinergic Responses Dependent on P2Y2 Receptors in Hepatocytes from CCl4-Treated Fibrotic Mice

Inflammatory and wound healing responses take place during liver damage, primarily in the parenchymal tissue. It is known that cellular injury elicits an activation of the purinergic signaling, mainly by the P2X7 receptor; however, the role of P2Y receptors in the onset of liver pathology such as fibrosis has not been explored. Hence, we used mice treated with the hepatotoxin CCl₄ to implement a reversible model of liver fibrosis to evaluate the expression and function of the P2Y2 receptor (P2Y2R). Fibrotic livers showed an enhanced expression of P2Y2R that eliminated its zonal distribution. Hepatocytes from CCl₄-treated mice showed an exacerbated ERK-phosphorylated response to the P2Y2R-specific agonist, UTP. Cell proliferation was also enhanced in the fibrotic livers. Hepatic transcriptional analysis by microarrays, upon CCl₄ administration, showed that P2Y2 activation regulated diverse pathways, revealing complex action mechanisms. In conclusion, our data indicate that P2Y2R activation is involved in the onset of the fibrotic damage associated with the reversible phase of the hepatic damage promoted by CCl₄.

Cellular Interplay as a Consequence of Inflammatory Signals Leading to Liver Fibrosis Development

Inflammation has been known to be an important driver of fibrogenesis in the liver and onset of hepatic fibrosis. It starts off as a process meant to protect the liver from further damage, but it can become the main promoter of liver fibrosis. There are many inflammation-related pathways activated during liver fibrosis that lead to hepatic stellate cells (HSCs) activation and collagen-deposition in the liver. Such events are mostly modulated upstream of HSCs and involve signals from hepatocytes and innate immune cells. One particular event is represented by cell death during liver injury that generates multiple inflammatory signals that further trigger sterile inflammation and enhancement of inflammatory response. The assembly of inflammasome that responds to danger-associated molecular patterns (DAMPs) stimulates the release of pro-inflammatory cytokines and at the same time, initiates programmed cell death called pyroptosis. This review focuses on cellular and molecular mechanisms responsible for initiation and progress of inflammation in the liver.

Purine signaling regulating HSCs inflammatory cytokines secretion, activation, and proliferation plays a critical role in alcoholic liver disease

Purine signaling pathway plays an important role in inflammation and tissue damage. To investigate the role of purine signaling pathway in acute alcoholic liver injury and chronic alcoholic liver fibrosis, we replicated two animal models and two cellular models. We found that body weights, liver indexes, serum biochemical parameters, serum fibrosis indexes, and pathological and immunohistochemical results had significant changes in two treatment groups compared with two control groups. In addition, gene expressions of purine receptors, inflammatory cytokines, fibrogenic cytokines, and inflammasomes increased obviously in two animal models and two cellular models. Furthermore, purine receptor inhibitors could significantly inhibit protein expressions of purine receptors and reduce protein expressions of inflammatory cytokines, fibrogenic cytokines, and inflammasomes. Besides, P2X7R small interfering ribonucleic acid (siRNA) had the same effects. Meanwhile, we detected protein expressions of inflammatory cytokines secreted by inflammasomes, and we found that purine receptor-mediated inflammasomes activation was a key event in the process of chronic alcoholic liver fibrosis. In summary, this study shows that inhibition of purine receptors can alleviate acute alcoholic liver injury and chronic alcoholic liver fibrosis in mice. Therefore, purine receptor is a potential new target for the treatment of acute alcoholic liver injury and chronic alcoholic fibrosis.

Extracellular ATP and Purinergic P2Y2 Receptor Signaling Promote Liver Tumorigenesis in Mice by Exacerbating DNA Damage

Release of ATP to the extracellular compartment and subsequent activation of purinergic receptors is a conserved mechanism mediating inflammatory responses and cell fate decisions in various organs including the liver. Previous findings suggest that extracellular ATP may promote liver tumorigenesis, however, the underlying mechanisms are poorly understood. Therefore, our aim was to dissect the functions of extracellular ATP and P2Y₂ receptors (P2Y₂R) during hepatocarcinogenesis. Liver tumors were induced in wild-type and P2y₂r ^-/- knockout mice by intraperitoneal diethylnitrosamine (DEN) injection. Tumorigenesis was analyzed after 8 to 10 months and molecular analyses were performed at different stages of tumorigenesis in vivo, as well as in primary mouse hepatocytes in vitro. Liver tumor incidence and tumor numbers were strongly reduced in P2y₂r ^-/- mice, whereas tumor size and morphology were comparable to wild-type controls, suggesting that P2Y₂R contributes to tumor initiation. Mechanistically, hepatocyte proliferation in DEN-treated P2y₂r ^-/- mice was reduced, which correlated with reduced c-JUN and CCND1 but increased p21 expression. Moreover, DNA damage as determined by hepatocellular expression of γH2A.X and of genes related to genotoxic stress, as well as STAT3 phosphorylation, was reduced in the absence of P2y₂r. Administration of genotoxic agents to primary hepatocytes in vitro confirmed that DNA damage was indeed exacerbated by extracellular ATP, subsequent P2Y₂R activation, and downstream intracellular calcium-dependent signal transduction. In conclusion, our data reveal that extracellular ATP and subsequent P2Y₂R function stimulate DNA damage responses and hepatocyte proliferation, thereby promoting hepatocarcinogenesis. Targeting this pathway may be an attractive approach for chemoprevention of hepatocellular carcinoma. SIGNIFICANCE: Extracellular ATP and subsequent P2Y₂ receptor function stimulate DNA damage responses and hepatocyte proliferation, thereby promoting hepatocarcinogenesis in mice. Targeting this pathway may be an attractive approach for chemoprevention of hepatocellular carcinoma. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/4/699/F1.large.jpg.

Regulation of CD39 expression in ATP-P2Y2R-mediated alcoholic liver steatosis and inflammation

Inflammation plays a central role in the progression of alcoholic liver disease. ATP-P2Y2R signaling and CD39 play an important role in various diseases, but little is known about their role in alcoholic liver steatosis and inflammation. As a transmembrane hydrolase, CD39 hydrolyzes ATP, while the mutual regulation of CD39 and ATP-P2Y2R in alcoholic steatohepatitis is poorly understood. Here, we found that the expression of ATP, P2Y2R, and CD39 is increased significantly both in the liver of alcohol-fed mice and alcohol-induced RAW264.7 cell lines. In this study, C57BL/6 mice were intrapretationally injected with P2Y2R inhibitor suramin from day 4 until day 10 during the induction of a chronic/binge drinking model. Pharmacological blockade of P2Y2R largely prevents liver damage, lipid accumulation, and inflammation, with concomitant down-expression of CD39 in liver. We found that the inhibition of P2Y2R in vitro reduces inflammation via down-expression of interleukin 6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α), and the expression of CD39 was reduced, whereas the activation of P2Y2R showed an opposite effect. Silencing of CD39 promoted the expression of ATP and P2Y2R. These results indicate that CD39 attenuates alcohol-induced steatohepatitis by scavenging extracellular ATP to indirectly regulate the expression of P2Y2R. Interestingly, P2Y2R paradoxically boosts CD39 activity. Thus, blockade of the extracellular ATP-P2Y2R signalling represents a potential therapeutic approach against alcoholic liver disease, and CD39 is a potential therapeutic target.

Purinergic signaling in hepatic disease

Extracellular purines (ATP and adenosine) are ubiquitous intercellular messengers. During tissular damage, they function as damage-associated molecular patterns (DAMPs). In this context, purines announce tissue alterations to initiate a reparative response that involve the formation of the inflammasome complex and the recruitment of specialized cells of the immune system. The present review focuses on the role of the purinergic system in liver damage, mainly during the onset and development of fibrosis. After hepatocellular injury, extracellular ATP promotes a signaling cascade that ameliorates tissue alterations to restore the hepatic function. However, if cellular damage becomes chronic, ATP orchestrates an aberrant reparative process that results in severe liver diseases such as fibrosis and cirrhosis. ATP and adenosine, their receptors, and extracellular ectonucleotidases are mediators of unique processes that will be reviewed in detail.

The role of inflammasome activation in Triptolide-induced acute liver toxicity

Triptolide (TP), the major active compound derived from the traditional Chinese medicine Tripterygium wilfordii Hook. F, possesses an excellent pharmacological profile of immunomodulatory and anti-tumor activities. However, the application of TP was restricted due to its narrow therapeutic window and side effects, especially its hepatotoxicity. This study was designed to investigate the role of inflammasome in TP-induced acute liver toxicity. After the administration of TP at the dose of 600 μg/kg for 12 h or 24 h, we examined the serum biochemical parameters, liver histopathological changes, the expression of liver inflammatory factors, and the activation of NLRP3 inflammasome. Mice treated with TP displayed liver injury with a time-dependent increase of serum transaminases and activation of NLRP3 inflammasome, accompanied by the elevation of neutrophils infiltration. Further results implied that the activation of TLR4-Myd88-NF-κB pathway and oxidative stress induced by a single dose of TP (600 μg/kg) might participate in the activation of NLRP3 inflammasome. To investigate whether the activation of inflammasome participates in the liver damage induced by TP, a single dose of Ac-Yvad-Cmk (Caspase-1 inhibitor) was injected before TP administration. Ac-Yvad-Cmk pretreatment effectively prevented the increase of Cleaved Caspase-1 and inhibited the maturity of IL-1β. Additional studies revealed that Ac-Yvad-Cmk pretreatment decreased the recruitment of neutrophils and inhibited the production of massive pro-inflammatory factors. Taken together, our results revealed that activation of inflammasome aggravated the acute liver toxicity induced by TP. Inhibition of inflammasome could serve as a novel therapeutic target for the amelioration of TP-induced hepatotoxicity.

Pharmacology of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes divided into two subgroups (P2Y₁, P2Y₂, P2Y₄, P2Y₆, and P2Y₁₁) and (P2Y₁₂, P2Y₁₃, and P2Y₁₄). The P2Y receptors are expressed in various cell types and play important roles in physiology and pathophysiology including inflammatory responses and neuropathic pain. The antagonism of P2Y₁₂ receptors is used in pharmacotherapy for the prevention and therapy of cardiovascular events. The nucleoside analogue ticagrelor and active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel inhibit platelet P2Y₁₂ receptors and reduce thereby platelet aggregation. The P2Y₂ receptor agonist diquafosol is used for the treatment of the dry eye syndrome. The P2Y receptor subtypes differ in their amino acid sequences, their pharmacological profiles and their signaling transduction pathways. Recently, selective receptor ligands have been developed for all subtypes. The published crystal structures of the human P2Y₁ and P2Y₁₂ receptors as well as receptor models will facilitate the development of novel drugs for pharmacotherapy.

New Insights in Purinergic Therapy: Novel Antagonists for Uridine 5'-Triphosphate-Activated P2Y Receptors from Brazilian Flora

P2Y2 and P2Y4 receptors are physiologically activated by uridine 5'-triphosphate (UTP) and are widely expressed in many cell types in humans. P2Y2 plays an important role in inflammation and proliferation of tumor cells, which could be attenuated with the use of antagonists. However, little is known about the physiological functions related to P2Y4, due to the lack of selective ligands for these receptors. This can be solved through the search for novel compounds with antagonistic activity. The aim of this study was to discover new potential antagonist candidates for P2Y2 and P2Y4 receptors from natural products. We applied a calcium measurement methodology to identify new antagonist candidates for these receptors. First, we established optimal conditions for the calcium assay using J774.G8, a murine macrophage cell line, which expresses functional P2Y2 and P2Y4 receptors and then, we performed the screening of plant extracts at a cutoff concentration of 50 μg/mL. ATP and ionomycin, known intracellular calcium inductors, were used to stimulate cells. The calculated EC₅₀ were 11 μM and 103 nM, respectively. These cells also responded to the UTP stimulation with an EC₅₀ of 1.021 μM. Screening assays were performed and a total of 100 extracts from Brazilian plants were tested. Joannesia princeps Vell. (stem) and Peixotoa A. Juss (flower and leaf) extracts stood out due to their ability to inhibit UTP-induced responses without causing cytotoxicity, and presented an IC₅₀ of 32.32, 14.99, and 12.98 μg/mL, respectively. Collectively, our results point to the discovery of potential antagonist candidates from Brazilian flora for UTP-activated receptors.

P2Y2R Signaling Is Involved in the Onset of Glomerulonephritis

Endogenously released adenosine-5’-triphosphate (ATP) is a key regulator of physiological function and inflammatory responses in the kidney. Genetic or pharmacological inhibition of purinergic receptors has been linked to attenuation of inflammatory disorders and hence constitutes promising new avenues for halting and reverting inflammatory renal diseases. However, the involvement of purinergic receptors in glomerulonephritis (GN) has only been incompletely mapped. Here, we demonstrate that induction of GN in an experimental antibody-mediated GN model results in a significant increase of urinary ATP-levels and an upregulation of P2Y2R expression in resident kidney cells as well as infiltrating leukocytes pointing toward a possible role of the ATP/P2Y2R-axis in glomerular disease initiation. In agreement, decreasing extracellular ATP-levels or inhibition of P2R during induction of antibody-mediated GN leads to a reduction in all cardinal features of GN such as proteinuria, glomerulosclerosis, and renal failure. The specific involvement of P2Y2R could be further substantiated by demonstrating the protective effect of the lack of P2Y2R in antibody-mediated GN. To systematically differentiate between the function of P2Y2R on resident renal cells versus infiltrating leukocytes, we performed bone marrow-chimera experiments revealing that P2Y2R on hematopoietic cells is the main driver of the ATP/P2Y2R-mediated disease progression in antibody-mediated GN. Thus, these data unravel an important pro-inflammatory role for P2Y2R in the pathogenesis of GN.

The purinergic receptor subtype P2Y2 mediates chemotaxis of neutrophils and fibroblasts in fibrotic lung disease

Idiopathic pulmonary fibrosis (IPF) is a devastating disease with few available treatment options. Recently, the involvement of purinergic receptor subtypes in the pathogenesis of different lung diseases has been demonstrated. Here we investigated the role of the purinergic receptor subtype P2Y2 in the context of fibrotic lung diseases.The concentration of different nucleotides was measured in the broncho-alveolar lavage (BAL) fluid derived from IPF patients and animals with bleomycin-induced pulmonary fibrosis. In addition expression of P2Y2 receptors by different cell types was determined. To investigate the functional relevance of P2Y2 receptors for the pathogenesis of the disease the bleomycin model of pulmonary fibrosis was used. Finally, experiments were performed in pursuit of the involved mechanisms.Compared to healthy individuals or vehicle treated animals, extracellular nucleotide levels in the BAL fluid were increased in patients with IPF and in mice after bleomycin administration, paralleled by a functional up-regulation of P2Y2R expression. Both bleomycin-induced inflammation and fibrosis were reduced in P2Y2R-deficient compared to wild type animals. Mechanistic studies demonstrated that recruitment of neutrophils into the lungs, proliferation and migration of lung fibroblasts as well as IL6 production are key P2Y2R mediated processes.Our results clearly demonstrate the involvement of P2Y2R subtypes in the pathogenesis of fibrotic lung diseases in humans and mice and hence support the development of selective P2Y2R antagonists for the treatment of IPF.

Purinergic Regulation of Neutrophil Function

Purinergic signaling, which utilizes nucleotides (particularly ATP) and adenosine as transmitter molecules, plays an essential role in immune system. In the extracellular compartment, ATP predominantly functions as a pro-inflammatory molecule through activation of P2 receptors, whereas adenosine mostly functions as an anti-inflammatory molecule through activation of P1 receptors. Neutrophils are the most abundant immune cells in circulation and have emerged as an important component in orchestrating a complex series of events during inflammation. However, because of the destructive nature of neutrophil-derived inflammatory agents, neutrophil activation is fine-tuned, and purinergic signaling is intimately involved in this process. Indeed, shifting the balance between P2 and P1 signaling is critical for neutrophils to appropriately exert their immunologic activity. Here, we review the role of purinergic signaling in regulating neutrophil function, and discuss the potential of targeting purinergic signaling for the treatment of neutrophil-associated infectious and inflammatory diseases.

P2rx4 deficiency in mice alleviates allergen-induced airway inflammation

Compelling evidences point out a crucial role for extracellular nucleotides such as adenosine triphosphate (ATP) during inflammatory conditions. Once released into the extracellular space, ATP modulates migration, maturation and function of various inflammatory cells via activating of purinergic receptors of the P2Y- and P2X- family. P2RX4 is an ATP-guided ion channel expressed on structural cells such as alveolar epithelial and smooth muscle cells as well as inflammatory cells including macrophages, dendritic cells (DCs) and T cells. P2RX4 has been shown to interact with P2RX7 and promote NLRP3 inflammasome activation. Although P2RX7 has already been implicated in allergic asthma, the role of P2RX4 in airway inflammation has not been elucidated yet. Therefore, we used a selective pharmacological antagonist and genetic ablation to investigate the role of P2RX4 in an ovalbumin (OVA) driven model of allergen-induced airway inflammation (AAI). Both, P2RX4 antagonist 5-BDBD treatment and P2rx4 deficiency resulted in an alleviated broncho alveolar lavage fluid eosinophilia, peribronchial inflammation, Th2 cytokine production and bronchial hyperresponsiveness. Furthermore, P2rx4-deficient bone marrow derived DCs (BMDCs) showed a reduced IL-1ß production in response to ATP accompanied by a decreased P2rx7 expression and attenuated Th2 priming capacity compared to wild type (WT) BMDCs in vitro. Moreover, mice adoptively transferred with P2rx4-deficient BMDCs exhibit a diminished AAI in vivo. In conclusion our data suggests that P2RX4-signaling contributes to AAI pathogenesis by regulating DC mediated Th2 cell priming via modulating IL-1ß secretion and selective P2RX4-antagonists might be a new therapeutic option for allergic asthma.

Distinct roles of ecto-nucleoside triphosphate diphosphohydrolase-2 (NTPDase2) in liver regeneration and fibrosis

Ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) are cell surface-located transmembrane ecto-enzymes of the CD39 superfamily which regulate inflammation and tissue repair by catalyzing the phosphohydrolysis of extracellular nucleotides and modulating purinergic signaling. In the liver, NTPDase2 is reportedly expressed on portal fibroblasts, but its functional role in regulating tissue regeneration and fibrosis is incompletely understood. Here, we studied the role of NTPDase2 in several models of liver injury using global knockout mice. Liver regeneration and severity of fibrosis were analyzed at different time points after exposure to carbon tetrachloride (CCl₄) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or partial hepatectomy in C57BL/6 wild-type and globally NTPDase2-deficient (Entpd2 null) mice. After chronic CCl₄ intoxication, Entpd2 null mice exhibit significantly more severe liver fibrosis, as assessed by collagen content and histology. In contrast, deletion of NTPDase2 does not have a substantial effect on biliary-type fibrosis in the setting of DDC feeding. In injured livers, NTPDase2 expression extends from the portal areas to fibrotic septae in pan-lobular (CCl₄-induced) liver fibrosis; the same pattern was observed, albeit to a lesser extent in biliary-type (DDC-induced) fibrosis. Liver regeneration after partial hepatectomy is not substantively impaired in global Entpd2 null mice. NTPDase2 protects from liver fibrosis resulting from hepatocellular injury induced by CCl₄. In contrast, Entpd2 deletion does not significantly impact fibrosis secondary to DDC injury or liver regeneration after partial hepatectomy. Our observations highlight mechanisms relating to purinergic signaling in the liver and indicate possible therapeutic avenues and new cellular targets to test in the management of hepatic fibrosis.

Efferocytosis and Outside-In Signaling by Cardiac Phagocytes. Links to Repair, Cellular Programming, and Intercellular Crosstalk in Heart

Phagocytic sensing and engulfment of dying cells and extracellular bodies initiate an intracellular signaling cascade within the phagocyte that can polarize cellular function and promote communication with neighboring non-phagocytes. Accumulating evidence links phagocytic signaling in the heart to cardiac development, adult myocardial homeostasis, and the resolution of cardiac inflammation of infectious, ischemic, and aging-associated etiology. Phagocytic clearance in the heart may be carried out by professional phagocytes, such as macrophages, and non-professional cells, including myofibrolasts and potentially epithelial cells. During cardiac development, phagocytosis initiates growth cues for early cardiac morphogenesis. In diseases of aging, including myocardial infarction, heightened levels of cell death require efficient phagocytic debridement to salvage further loss of terminally differentiated adult cardiomyocytes. Additional risk factors, including insulin resistance and other systemic risk factors, contribute to inefficient phagocytosis, altered phagocytic signaling, and delayed cardiac inflammation resolution. Under such conditions, inflammatory presentation of myocardial antigen may lead to autoimmunity and even possible rejection of transplanted heart allografts. Increased understanding of these basic mechanisms offers therapeutic opportunities.

Myeloid P2Y2 receptor promotes acute inflammation but is dispensable for chronic high-fat diet-induced metabolic dysfunction

The purinergic receptor P2Y2 binds ATP to control chemotaxis of myeloid cells, and global P2Y2 receptor knockout mice are protected in models of acute inflammation. Chronic inflammation mediated by macrophages and other immune cells in adipose tissue contributes to the development of insulin resistance. Here, we investigate whether mice lacking P2Y2 receptors on myeloid cells are protected against acute and chronic inflammation. Wild-type mice were transplanted with either wild-type or P2Y2 receptor null bone marrow and treated with a sublethal dose of endotoxin as a model of acute inflammation, or fed a high-fat diet to induce obesity and insulin resistance as a model of chronic inflammation. P2Y2^-/- chimeric mice were protected against acute inflammation. However, high-fat diet feeding induced comparable inflammation and insulin resistance in both WT and P2Y2^-/- chimeric mice. Of note, confocal microscopy revealed significantly fewer crown-like structures, assemblies of macrophages around adipocytes, in P2Y2^-/- chimeric mice compared to WT chimeric mice. We conclude that P2Y2 receptors on myeloid cells are important in mediating acute inflammation but are dispensable for the development of whole body insulin resistance in diet-induced obese mice.

Molecular Recognition of Agonists and Antagonists by the Nucleotide-Activated G Protein-Coupled P2Y2 Receptor

A homology model of the nucleotide-activated P2Y₂R was created based on the X-ray structures of the P2Y₁ receptor. Docking studies were performed, and receptor mutants were created to probe the identified binding interactions. Mutation of residues predicted to interact with the ribose (Arg110) and the phosphates of the nucleotide agonists (Arg265, Arg292) or that contribute indirectly to binding (Tyr288) abolished activity. The Y114F, R194A, and F261A mutations led to inactivity of diadenosine tetraphosphate and to a reduced response of UTP. Significant reduction in agonist potency was observed for all other receptor mutants (Phe111, His184, Ser193, Phe261, Tyr268, Tyr269) predicted to be involved in agonist recognition. An ionic lock between Asp185 and Arg292 that is probably involved in receptor activation interacts with the phosphate groups. The antagonist AR-C118925 and anthraquinones likely bind to the orthosteric site. The updated homology models will be useful for virtual screening and drug design.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

P2X7 receptor antagonism prevents IL-1β release from salivary epithelial cells and reduces inflammation in a mouse model of autoimmune exocrinopathy

Salivary gland inflammation is a hallmark of Sjögren's syndrome (SS), a common autoimmune disease characterized by lymphocytic infiltration of the salivary gland and loss of saliva secretion, predominantly in women. The P2X7 receptor (P2X7R) is an ATP-gated nonselective cation channel that induces inflammatory responses in cells and tissues, including salivary gland epithelium. In immune cells, P2X7R activation induces the production of proinflammatory cytokines, including IL-1β and IL-18, by inducing the oligomerization of the multiprotein complex NLRP3-type inflammasome. Here, our results show that in primary mouse submandibular gland (SMG) epithelial cells, P2X7R activation also induces the assembly of the NLRP3 inflammasome and the maturation and release of IL-1β, a response that is absent in SMG cells isolated from mice deficient in P2X7Rs (P2X7R^-/-). P2X7R-mediated IL-1β release in SMG epithelial cells is dependent on transmembrane Na⁺ and/or K⁺ flux and the activation of heat shock protein 90 (HSP90), a protein required for the activation and stabilization of the NLRP3 inflammasome. Also, using the reactive oxygen species (ROS) scavengers N-acetyl cysteine and Mito-TEMPO, we determined that mitochondrial reactive oxygen species are required for P2X7R-mediated IL-1β release. Lastly, in vivo administration of the P2X7R antagonist A438079 in the CD28^-/-, IFNγ^-/-, NOD.H-2^h4 mouse model of salivary gland exocrinopathy ameliorated salivary gland inflammation and enhanced carbachol-induced saliva secretion. These findings demonstrate that P2X7R antagonism in vivo represents a promising therapeutic strategy to limit salivary gland inflammation and improve secretory function.

Endotoxin-induced autocrine ATP signaling inhibits neutrophil chemotaxis through enhancing myosin light chain phosphorylation

Although the neutrophil recruitment cascade during inflammation has been well described, the molecular players that halt neutrophil chemotaxis remain unclear. In this study, we found that lipopolysaccharide (LPS) was a potent stop signal for chemotactic neutrophil migration. Treatment with an antagonist of the ATP receptor (P2X1) in primary human neutrophils or knockout of the P2X1 receptor in neutrophil-like differentiated HL-60 (dHL-60) cells recovered neutrophil chemotaxis. Further observations showed that LPS-induced ATP release through connexin 43 (Cx43) hemichannels was responsible for the activation of the P2X1 receptor and the subsequent calcium influx. Increased intracellular calcium stopped neutrophil chemotaxis by activating myosin light chain (MLC) through the myosin light chain kinase (MLCK)-dependent pathway. Taken together, these data identify a previously unknown function of LPS-induced autocrine ATP signaling in inhibiting neutrophil chemotaxis by enhancing MLC phosphorylation, which provides important evidence that stoppage of neutrophil chemotaxis at infectious foci plays a key role in the defense against invading pathogens.

The Protective Effect of Cordycepin on D-Galactosamine/Lipopolysaccharide-Induced Acute Liver Injury

As the major active ingredient of Cordyceps militaris, cordycepin (3′-deoxyadenosine) has been well documented to alleviate inflammation and oxidative stress both in vitro and in vivo. To explore the potential protective effect of cordycepin in fulminant hepatic failure, mice were pretreated with cordycepin for 3 weeks followed by D-galactosamine (GalN)/lipopolysaccharide (LPS) injection. Then we found cordycepin (200 mg/kg) administration elevated survival rate, improved liver function, and suppressed hepatocyte apoptosis and necrosis in mice with severe hepatic damage by GalN/LPS treatment. Further, cordycepin inhibited hepatic neutrophil and macrophage infiltration and prevented proinflammatory cytokine production possibly through suppressing TLR4 and NF-κB signaling transduction. The blockade of reactive oxygen species (ROS) and lipid peroxidation production by cordycepin was associated with the decrease of NAD(P)H oxidase (NOX) activity. Besides, cordycepin significantly prevented excessive autophagy induced by GalN/LPS in the liver. These data suggested that cordycepin could be a promising therapeutic agent for GalN/LPS-induced hepatotoxicity.

Upregulation of P2Y2 nucleotide receptor in human hepatocellular carcinoma cells

Objective

To examine if hypoxia inducible factor-1α (HIF-1α) can induce the upregulation of the purinergic receptor P2Y2 (P2Y2) and thereby promote the viability of human hepatocellular carcinoma (HCC) cells under hypoxic conditions.

Methods

Archival HCC tumour specimens and corresponding non-cancerous tissues were examined immunohistochemically for P2Y2 protein. A series of in vitro experiments were undertaken using HCC cell lines to determine the effect of hypoxia on HIF-1α and P2Y2 levels, the effect of HIF-1α upregulation on P2Y2 levels, and the effect of P2Y2 upregulation on cell viability under hypoxic conditions.

Results

Human HCC specimens were positive for P2Y2. Hypoxia and upregulated HIF-1α both upregulated the P2Y2 levels in HCC cell lines. P2Y2 upregulation using plasmid transfection resulted in enhanced cell viability under hypoxia. Treatment of HepG2 cells with the selective P2Y2 antagonist MRS2312 downregulated P2Y2 and reduced cell viability in five HCC cell lines. P2Y2 knockdown reduced HepG2 cell viability under hypoxia.

Conclusions

These present results suggest that HCC cells upregulate P2Y2 levels during hypoxia, which in turn promotes their growth. P2Y2 could be a potential therapeutic target for treating HCC.

The Role of Purine Metabolites as DAMPs in Acute Graft-versus-Host Disease

Acute graft-versus-host disease (GvHD) causes high mortality in patients undergoing allogeneic hematopoietic cell transplantation. An early event in the classical pathogenesis of acute GvHD is tissue damage caused by the conditioning treatment or infection that consecutively leads to translocation of bacterial products [pathogen-associated molecular patterns (PAMPs)] into blood or lymphoid tissue, as well as danger-associated molecular patterns (DAMPs), mostly intracellular components that act as pro-inflammatory agents, once they are released into the extracellular space. A subtype of DAMPs is nucleotides, such as adenosine triphosphate released from dying cells that can activate the innate and adaptive immune system by binding to purinergic receptors. Binding to certain purinergic receptors leads to a pro-inflammatory microenvironment and promotes allogeneic T cell priming. After priming, T cells migrate to the acute GvHD target organs, mainly skin, liver, and the gastrointestinal tract and induce cell damage that further amplifies the release of intracellular components. This review summarizes the role of different purinergic receptors in particular P2X7 and P2Y2 as well as nucleotides in the pathogenesis of GvHD.

The Role of Extracellular Adenosine Triphosphate in Ischemic Organ Injury

OBJECTIVES

Ischemic tissue injury contributes to significant morbidity and mortality and is implicated in a range of pathologic conditions, including but not limited to myocardial infarction, ischemic stroke, and acute kidney injury. The associated reperfusion phase is responsible for the activation of the innate and adaptive immune system, further accentuating inflammation. Adenosine triphosphate molecule has been implicated in various ischemic conditions, including stroke and myocardial infarction.

STUDY SELECTION

Adenosine triphosphate is a well-defined intracellular energy transfer and is commonly referred to as the body's "energy currency." However, Laboratory studies have demonstrated that extracellular adenosine triphosphate has the ability to initiate inflammation and is therefore referred to as a damage-associated molecular pattern. Purinergic receptors-dependent signaling, proinflammatory cytokine release, increased Ca influx into cells, and subsequent apoptosis have been shown to form a common underlying extracellular adenosine triphosphate molecular mechanism in ischemic organ injury.

CONCLUSIONS

In this review, we aim to discuss the molecular mechanisms behind adenosine triphosphate-mediated ischemic tissue injury and evaluate the role of extracellular adenosine triphosphate in ischemic injury in specific organs, in order to provide a greater understanding of the pathophysiology of this complex process. We also appraise potential future therapeutic strategies to limit damage in various organs, including the heart, brain, kidneys, and lungs.

Important roles of P2Y receptors in the inflammation and cancer of digestive system

Purinergic signaling is important for many biological processes in humans. Purinoceptors P2Y are widely distributed in human digestive system and different subtypes of P2Y receptors mediate different physiological functions from metabolism, proliferation, differentiation to apoptosis etc. The P2Y receptors are essential in many gastrointestinal functions and also involve in the occurrence of some digestive diseases. Since different subtypes of P2Y receptors are present on the same cell of digestive organs, varying subtypes of P2Y receptors may have opposite or synergetic functions on the same cell. Recently, growing lines of evidence strongly suggest the involvement of P2Y receptors in the pathogenesis of several digestive diseases. In this review, we will focus on their important roles in the development of digestive inflammation and cancer. We anticipate that as the special subtypes of P2Y receptors are studied in depth, specific modulators for them will have good potentials to become promising new drugs to treat human digestive diseases in the near future.

Clinical Effects and Safety of 3% Diquafosol Ophthalmic Solution for Patients With Dry Eye After Cataract Surgery: A Randomized Controlled Trial

PURPOSE

To compare the efficacies and safety profiles of 3% diquafosol and 0.1% sodium hyaluronate in patients with dry eye after cataract surgery.

DESIGN

Randomized controlled trial.

METHODS

setting: Soonchunhyang University Hospital, Seoul, South Korea.

STUDY POPULATION

In all, 130 eyes of 86 dry eye patients who had undergone cataract surgery between January 2014 and January 2015 were enrolled and randomly divided into a diquafosol group and a sodium hyaluronate group.

INTERVENTION

The diquafosol group used diquafosol 6 times a day and the hyaluronate group used sodium hyaluronate 6 times a day after cataract surgery.

MAIN OUTCOME MEASURES

Evaluations of efficacy were conducted based on an Ocular Surface Disease Index questionnaire, tear breakup time (TBUT), Schirmer I test, corneal fluorescein and conjunctival lissamine green staining scores, serial measurement of ocular higher-order aberrations (HOAs), corneal HOAs, and uncorrected distance visual acuity test. Safety evaluations were based on anterior chamber inflammation and discontinuation of the eye drops.

RESULTS

Objective signs and subjective symptoms were aggravated at 1 week postoperatively and began to recover significantly 4 weeks after surgery. The diquafosol group showed significantly superior TBUT (P < .001), corneal fluorescein (P = .045), and conjunctival staining (P = .001) compared to the sodium hyaluronate group throughout the study period. TBUT (P < .001) and the change in HOAs (P = .018) recovered significantly more quickly in the diquafosol group. The safety evaluations showed no intergroup differences.

CONCLUSIONS

Eye drops of 3% diquafosol may be an effective and safe treatment for the management of cataract surgery-induced dry eye aggravation in patients with preexisting dry eye.

NTPDase1/CD39 and aberrant purinergic signalling in the pathogenesis of COPD

Purinergic receptor activation via extracellular ATP is involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). Nucleoside triphosphate diphosphohydrolase-1/CD39 hydrolyses extracellular ATP and modulates P2 receptor signalling.We aimed to investigate the expression and function of CD39 in the pathogenesis of cigarette smoke-induced lung inflammation in patients and preclinical mouse models. CD39 expression and soluble ATPase activity were quantified in sputum and bronchoalveolar lavage fluid (BALF) cells in nonsmokers, smokers and COPD patients or mice with cigarette smoke-induced lung inflammation. In mice, pulmonary ATP and cytokine concentrations, inflammation and emphysema were analysed in the presence or absence of CD39.Following acute cigarette smoke exposure CD39 was upregulated in BALF cells in smokers with further increases in COPD patients. Acute cigarette smoke exposure induced CD39 upregulation in murine lungs and BALF cells, and ATP degradation was accelerated in airway fluids. CD39 inhibition and deficiency led to augmented lung inflammation; treatment with ATPase during cigarette smoke exposure prevented emphysema.Pulmonary CD39 expression and activity are increased in COPD. CD39 deficiency leads to enhanced emphysema in mice, while external administration of a functional CD39 analogue partially rescues the phenotype. The compensatory upregulation of pulmonary CD39 might serve as a protective mechanism in cigarette smoke-induced lung damage.