Nucleotide receptors: an emerging family of regulatory molecules in blood cells

Metabolic Checkpoints in Differentiation of Helper T Cells in Tissue Inflammation

Naïve CD4⁺ T cell differentiate into effector and regulatory subsets of helper T (Th) cells in various pathophysiological conditions and modulate tissue inflammation in autoimmune diseases. While cytokines play a key role in determining the fate of Th cells differentiation, metabolites, and metabolic pathways profoundly influence Th cells fate and their functions. Emerging literature suggests that interplay between metabolic pathways and cytokines potentiates T cell differentiation and functions in tissue inflammation in autoimmune diseases. Metabolic pathways, which are essential for the differentiation and functions of Th cell subsets, are regulated by cytokines, nutrients, growth factors, local oxygen levels, co-activation receptors, and metabolites. Dysregulation of metabolic pathways not only alters metabolic regulators in Th cells but also affect the outcome of tissue inflammation in autoimmune and allergic diseases. Understanding the modulation of metabolic pathways during T cells differentiation may potentially lead to a therapeutic strategy for immune-modulation of autoimmune and allergic diseases. In this review, we summarize the role of metabolic checkpoints and their crosstalk with different master transcription factors and signaling molecules in differentiation and function of Th subsets, which may potentially unravel novel therapeutic interventions for tissue inflammation and autoimmune disorders.

Activation of the P2X7 receptor in midbrain periaqueductal gray participates in the analgesic effect of tramadol in bone cancer pain rats

Background

Cancer pain is a well-known serious complication in metastatic or terminal cancer patients. Current pain management remains unsatisfactory. The activation of spinal and supraspinal P2X₇ receptors plays a crucial role in the induction and maintenance mechanisms of various kinds of acute or chronic pain. The midbrain periaqueductal gray is a vital supraspinal site of the endogenous descending pain-modulating system. Tramadol is a synthetic, centrally acting analgesic agent that exhibits considerable efficacy in clinically relieving pain. The purpose of this study was to determine whether the activation of P2X₇ receptor in the ventrolateral region of the periaqueductal gray (vlPAG) participates in the analgesic mechanisms of tramadol on bone cancer pain in rats. The bone cancer pain rat model was established by intratibial cell inoculation of SHZ-88 mammary gland carcinoma cells. The analgesic effects of different doses of tramadol (10, 20, and 40 mg/kg) were assessed by measuring the mechanical withdrawal threshold and thermal withdrawal latency values in rats by using an electronic von Frey anesthesiometer and radiant heat stimulation, respectively. Alterations in the number of P2X₇ receptor-positive cells and P2X₇ protein levels in vlPAG were separately detected by using immunohistochemistry and Western blot assay. The effect of intra-vlPAG injection of A-740003 (100 nmol), a selective competitive P2X₇ receptor antagonist, on the analgesic effect of tramadol was also observed.

Results

The expression of P2X₇ receptor in the vlPAG on bone cancer pain rats was mildly elevated, and the tramadol (10, 20, and 40 mg/kg) dose dependently relieved pain-related behaviors in bone cancer pain rats and further upregulated the expression of P2X₇ receptor in the vlPAG. The intra-vlPAG injection of A-740003 pretreatment partly but significantly antagonized the analgesic effect of tramadol on bone cancer pain rats.

Conclusions

The injection of tramadol can dose dependently elicit analgesic effect on bone cancer pain rats by promoting the expression of the P2X₇ receptor in vlPAG.

Sulfated Glycosides from the Sea Cucumbers Block Ca2+ Flow in Murine Neuroblastoma Cells

Recently the ability of triterpene glycosides from sea cucumbers to interact with purinergic receptors of P2X family on the membranes of immune cells enhancing the reversible ATP-dependent Ca2+ intake and therefore modulating (stimulating) the receptor's activity was discovered. As a result the activation of cellular immunity on the organism level was observed. Purinergic receptors are associated with a series of important functions in normal and pathophysiology, thus the searching of its new modulators (both stimulants and blockers) seems to be very important medical and scientific task. The cytotoxic activity of four triterpene glycosides isolated from different species of sea cucumbers: liouvilloside A (1) from Pseudocolochirus violaceus, fallaxoside D1 (2) from Cucumaria fallax and magnumosides C3 (3) and C4 (4) from Massinium (=Neothynidium) magnum against neuroblastoma Neuro 2A cells was tested. The glycosides 1 and 4 were the most cytotoxic in the series (EC50 5.0 μM and 21.5 μM, correspondingly). Moreover, non-cytotoxic concentration (1 μM) of these compounds inhibited ATP-dependent Ca2+ intake into the Neuro 2A cells, containing P2X7 receptors on the surface, by 53 and 47%, correspondingly. The ability of sea cucumbers triterpene glycosides to block the purinergic receptors in vitro is first discovered.

Adenosinergic signaling inhibits oxalate transport by human intestinal Caco2-BBE cells through the A2B adenosine receptor

Most kidney stones (KS) are composed of calcium oxalate, and small increases in urine oxalate affect the stone risk. Intestinal oxalate secretion mediated by anion exchanger SLC26A6 (PAT1) plays a crucial role in limiting net absorption of ingested oxalate, thereby preventing hyperoxaluria and related KS, reflecting the importance of understanding regulation of intestinal oxalate transport. We previously showed that ATP and UTP inhibit oxalate transport by human intestinal Caco2-BBE cells (C2). Since ATP is rapidly degraded to adenosine (ADO), we examined whether intestinal oxalate transport is regulated by ADO. We measured [¹⁴C]oxalate uptake in the presence of an outward Cl gradient as an assay of Cl-oxalate exchange activity, ≥49% of which is PAT1-mediated in C2 cells. We found that ADO significantly inhibited oxalate transport by C2 cells, an effect completely blocked by the nonselective ADO receptor antagonist 8- p-sulfophenyltheophylline. ADO also significantly inhibited oxalate efflux by C2 cells, which is important since PAT1 mediates oxalate efflux in vivo. Using pharmacological antagonists and A_2B adenosine receptor (A_2B AR) siRNA knockdown studies, we observed that ADO inhibits oxalate transport through the A_2B AR, phospholipase C, and PKC. ADO inhibits oxalate transport by reducing PAT1 surface expression as shown by biotinylation studies. We conclude that ADO inhibits oxalate transport by lowering PAT1 surface expression in C2 cells through signaling pathways including the A_2B AR, PKC, and phospholipase C. Given higher ADO levels and overexpression of the A_2B AR in inflammatory bowel disease (IBD), our findings have potential relevance to pathophysiology of IBD-associated hyperoxaluria and related KS.

Platelets and cancer angiogenesis nexus

There has been remarkable insight into the importance of platelets in a wide range of pathophysiologic events, including inflammation and cancer progression. Thrombocytosis in cancer patients is a common finding. Tumor cells induce platelet activation and subsequent aggregation through direct and indirect mechanisms. Platelets are recognized to contribute to metastatic dissemination. There is plenty of evidence that components of the hemostatic system contribute to the process of angiogenesis. Furthermore, there are accumulated data on the substantial influence of blood platelets in the process of blood vessel formation during malignancy. Platelets appear to be the main physiologic transporters of proangiogenic and antiangiogenic factors. Moreover, they influence the process of angiogenesis through platelet-derived microparticles, microRNA, lipids, and variety of surface receptors. Platelets contribute to early and late stages of angiogenesis. Available data support the overall stimulatory effect of platelets on tumor angiogenesis. It raises the possibility that interfering with platelet function may be an effective antineoplastic treatment strategy.

Crucial role of P2X7 receptor for effector T cell activation in experimental autoimmune uveitis

PURPOSE

To investigate the roles of P2X7 receptors (P2RX7) in the pathogenesis of experimental autoimmune uveoretinitis (EAU).

STUDY DESIGN

Experimental.

METHODS

Either wild-type (P2rx7 ^+/+ ) or P2rx7-deficient (P2rx7 ^-∕- ) mice were immunized with interphotoreceptor retinoid-binding protein (IRBP) peptide 1-20. Severity of EAU was evaluated clinically and histopathologically. The induction of IRBP-specific proliferation and cytokines in draining lymph nodes was assessed by enzyme-linked immunosorbent assays (ELISA). The frequency of activation markers was examined by flow cytometry. Furthermore, inhibitory roles of systemic administration of Brilliant Blue G (BBG), an antagonist for P2RX7, in EAU were also assessed in the wild-type mice.

RESULTS

The severity of EAU in P2rx7 ^-∕- mice was reduced as compared with that in P2rx7 ^+/+ mice, both clinically and histopathologically. IRBP-specific proliferation in P2rx7 ^-∕- on day 16 was slightly decreased compared to that in P2rx7 ^+/+ mice. The induction of IRBP-specific interferon (IFN)-γ and interleukin (IL)-17 in P2rx7 ^-∕- mice on day 16 was lower than that in P2rx7 ^+/+ mice. The up-regulation of surface expression of activation markers such as CD25, CD44, and CD69 in response to TCR stimulation in P2rx7 ^-∕- mice was decreased as compared with that in P2rx7 ^+/+ mice. Furthermore, neutralization of P2RX7 in vivo by BBG suppressed EAU clinically and histopathologically. IRBP-specific IFN-γ and IL-17 induction in BBG-treated mice was significantly lower than that in vehicle-treated mice.

CONCLUSION

The results suggest that P2RX7 is a novel preventative therapeutic target for uveitis as it suppresses the effector functions of both Th1 and Th17 cell responses.

Lipophosphoglycan 3 From Leishmania infantum chagasi Binds Heparin With Micromolar Affinity

Leishmania infantum chagasi is an intracellular protozoan parasite responsible for visceral leishmaniasis, a fatal disease in humans. Heparin-binding proteins (HBPs) are proteins that bind to carbohydrates present in glycoproteins or glycolipids. Evidence suggests that HBPs present on Leishmania surface participate in the adhesion and invasion of parasites to tissues of both invertebrate and vertebrate hosts. In this study, we identified the product with an HSP90 (heat shock protein 90) domain encoded by lipophosphoglycan (LPG3) gene as a L infantum chagasi HBP (HBPLc). Structural analysis using the LPG3 recombinant protein suggests that it is organized as a tetramer. Binding analysis confirms that it is capable of binding heparin with micromolar affinity. Inhibition of adenosine triphosphatase activity in the presence of heparin, molecular modeling, and in silico docking analysis suggests that heparin-binding site superimposes with the adenosine triphosphate–binding site. Together, these results show new properties of LPG3 and suggest an important role in leishmaniasis.

Functional variant of the P2X7 receptor gene is associated with human papillomavirus-16 positive cervical squamous cell carcinoma

Human papillomavirus (HPV) infection and the fate of HPV infected cervical epithelial cells are strictly associated with cervical cancer development. P2X7 receptor has been implicated in both the regulation of immune responses and apoptosis of cervical cancer cells. The study aims to investigate if polymorphisms in the P2RX7 gene are associated with the risk of cervical cancer in Taiwanese women. P2RX7 253 T/C, 835 G/A, and 1513 A/C loss-of-function polymorphisms were genotyped in a hospital-based study of 507 women with cervical squamous cell carcinoma (CSCC) and 1619 age-matched healthy control women. The presence and genotypes of HPV in CSCC was determined. The frequency of 253 C/C genotype was found to increase significantly in patients with HPV-16 positive CSCC compared with controls (odds ratio = 10.2, 95% confidence interval 1.39–87.8, P_c = 0.03). No significant associations were found for other 2 polymorphisms. Analysis of haplotypes also revealed no significant differences among women with CSCC, those with HPV-16 positive CSCC and controls. In conclusion, inheritance of the C/C genotype at position 253 in the P2RX7 gene may contribute to the risk of HPV-16 associated CSCC in Taiwanese women.

The P2X7 Receptor in Inflammatory Diseases: Angel or Demon?

Under physiological conditions, adenosine triphosphate (ATP) is present at low levels in the extracellular milieu, being massively released by stressed or dying cells. Once outside the cells, ATP and related nucleotides/nucleoside generated by ectonucleotidases mediate a high evolutionary conserved signaling system: the purinergic signaling, which is involved in a variety of pathological conditions, including inflammatory diseases. Extracellular ATP has been considered an endogenous adjuvant that can initiate inflammation by acting as a danger signal through the activation of purinergic type 2 receptors-P2 receptors (P2Y G-protein coupled receptors and P2X ligand-gated ion channels). Among the P2 receptors, the P2X7 receptor is the most extensively studied from an immunological perspective, being involved in both innate and adaptive immune responses. P2X7 receptor activation induces large-scale ATP release via its intrinsic ability to form a membrane pore or in association with pannexin hemichannels, boosting purinergic signaling. ATP acting via P2X7 receptor is the second signal to the inflammasome activation, inducing both maturation and release of pro-inflammatory cytokines, such as IL-1β and IL-18, and the production of reactive nitrogen and oxygen species. Furthermore, the P2X7 receptor is involved in caspases activation, as well as in apoptosis induction. During adaptive immune response, P2X7 receptor modulates the balance between the generation of T helper type 17 (Th17) and T regulatory (Treg) lymphocytes. Therefore, this receptor is involved in several inflammatory pathological conditions. In infectious diseases and cancer, P2X7 receptor can have different and contrasting effects, being an angel or a demon depending on its level of activation, cell studied, type of pathogen, and severity of infection. In neuroinflammatory and neurodegenerative diseases, P2X7 upregulation and function appears to contribute to disease progression. In this review, we deeply discuss P2X7 receptor dual function and its pharmacological modulation in the context of different pathologies, and we also highlight the P2X7 receptor as a potential target to treat inflammatory related diseases.

Crucial factors of the inflammatory microenvironment (IL-1β/TNF-α/TIMP-1) promote the maintenance of the malignant hemopoietic clone of myelofibrosis: an in vitro study

Along with molecular abnormalities (mutations in JAK2, Calreticulin (CALR) and MPL genes), chronic inflammation is the major hallmark of Myelofibrosis (MF). Here, we investigated the in vitro effects of crucial factors of the inflammatory microenvironment (Interleukin (IL)-1β, Tumor Necrosis Factor (TNF)-α, Tissue Inhibitor of Metalloproteinases (TIMP)-1 and ATP) on the functional behaviour of MF-derived circulating CD34⁺ cells.

We found that, regardless mutation status, IL-1β or TNF-α increases the survival of MF-derived CD34⁺ cells. In addition, along with stimulation of cell cycle progression to the S-phase, IL-1β or TNF-α ± TIMP-1 significantly stimulate(s) the in vitro clonogenic ability of CD34⁺ cells from JAK2^V617 mutated patients. Whereas in the JAK2^V617F mutated group, the addition of IL-1β or TNF-α + TIMP-1 decreased the erythroid compartment of the CALR mutated patients. Megakaryocyte progenitors were stimulated by IL-1β (JAK2^V617F mutated patients only) and inhibited by TNF-α. IL-1β + TNF-α + C-X-C motif chemokine 12 (CXCL12) ± TIMP-1 highly stimulates the in vitro migration of MF-derived CD34+ cells. Interestingly, after migration toward IL-1β + TNF-α + CXCL12 ± TIMP-1, CD34⁺ cells from JAK2^V617F mutated patients show increased clonogenic ability.

Here we demonstrate that the interplay of these inflammatory factors promotes and selects the circulating MF-derived CD34⁺ cells with higher proliferative activity, clonogenic potential and migration ability. Targeting these micro-environmental interactions may be a clinically relevant approach.

Glia and hemichannels: key mediators of perinatal encephalopathy

Perinatal encephalopathy remains a major cause of disability, such as cerebral palsy. Therapeutic hypothermia is now well established to partially reduce risk of disability in late preterm/term infants. However, new and complementary therapeutic targets are needed to further improve outcomes. There is increasing evidence that glia play a key role in neural damage after hypoxia-ischemia and infection/inflammation. In this review, we discuss the role of astrocytic gap junction (connexin) hemichannels in the spread of neural injury after hypoxia-ischemia and/or infection/inflammation. Potential mechanisms of hemichannel mediated injury likely involve impaired intracellular calcium handling, loss of blood-brain barrier integrity and release of adenosine triphosphate (ATP) resulting in over-activation of purinergic receptors. We propose the hypothesis that inflammation-induced opening of connexin hemichannels is a key regulating event that initiates a vicious cycle of excessive ATP release, which in turn propagates activation of purinergic receptors on microglia and astrocytes. This suggests that developing new neuroprotective strategies for preterm infants will benefit from a detailed understanding of glial and connexin hemichannel responses.

POM-1 inhibits P2 receptors and exhibits anti-inflammatory effects in macrophages

Extracellular nucleotides can modulate the immunological response by activating purinergic receptors (P2Rs) on the cell surface of macrophages, dendritic, and other immune cells. In particular, the activation of P2X7R can induce release of cytokines and cell death as well as the uptake of large molecules through the cell membrane by a mechanism still poorly understood. Polyoxotungstate-1 (POM-1) has been proposed as a potent inhibitor of ecto-nucleotidases, enzymes that hydrolyze extracellular nucleotides, regulating the activity of P2Rs. However, the potential impact of POM-1 on P2Rs has not been evaluated. Here, we used fluorescent dye uptake, cytoplasmic free Ca2+ concentration measurement, patch-clamp recordings, scanning electron microscopy, and quantification of inflammatory mediators to investigate the effects of POM-1 on P2Rs of murine macrophages. We observed that POM-1 blocks the P2YR-dependent cytoplasmic Ca2+ increase and has partial effects on the cytoplasmic Ca2+, increasing dependence on P2XRs. POM-1 can inhibit the events related with ATP-dependent inflammasome activation, anionic dye uptake, and also the opening of large conductance channels, which are associated with P2X7R-dependent pannexin-1 activation. On the other hand, this compound has no effects on cationic fluorescent dye uptake, apoptosis, and bleb formation, also dependent on P2X7R. Moreover, POM-1 can be considered an anti-inflammatory compound, because it prevents TNF-α and nitric oxide release from LPS-treated macrophages.

Pretreatment with quercetin prevents changes in lymphocytes E-NTPDase/E-ADA activities and cytokines secretion in hyperlipidemic rats

Hyperlipidemia (HL) is a condition associated with endothelial dysfunction and inflammatory disorders. Purinergic system ectoenzymes play an important role in modulating the inflammatory and immune response. This study investigated whether the preventive treatment with quercetin is able to prevent changes caused by hyperlipidemia in the purinergic system, through the activities of E-NTPDase and E-ADA in lymphocytes, and quantify the nucleotides and nucleoside, and the secretion of anti- and proinflammatory cytokines. Animals were divided into saline/control, saline/quercetin 5 mg/kg, saline/quercetin 25 mg/kg, saline/quercetin 50 mg/kg, saline/simvastatin (0.04 mg/kg), hyperlipidemia, hyperlipidemia/quercetin 5 mg/kg, hyperlipidemia/quercetin 25 mg/kg, hyperlipidemia/quercetin 50 mg/kg, and hyperlipidemia/simvastatin. Animals were pretreated with quercetin for 30 days and hyperlipidemia was subsequently induced by intraperitoneal administration of 500 mg/kg of poloxamer-407. Simvastatin was administered after the induction of hyperlipidemia. Lymphocytes were isolated and E-NTPDase and E-ADA activities were determined. Serum was separated for the cytokines and nucleotide/nucleoside quantification. E-NTPDase and E-ADA activities were increased in lymphocytes from hyperlipidemic rats and pretreatment with quercetin was able to prevent the increase in the activities of these enzymes caused by hyperlipidemia. Hyperlipidemic rats when receiving pretreatment with quercetin and treatment with simvastatin showed decreased levels of ATP and ADP when compared to the untreated hyperlipidemic group. The IFN-γ and IL-4 cytokines were increased in the hyperlipidemic group when compared with control group, and decreased when hyperlipidemic rats received the pretreatment with quercetin. However, pretreatment with quercetin was able to prevent the alterations caused by hyperlipidemia probably by regulating the inflammatory process. We can suggest that the quercetin is a promising compound to be used as an adjuvant in the treatment of hyperlipidemia.

Electron Pathways through Erythrocyte Plasma Membrane in Human Physiology and Pathology: Potential Redox Biomarker?

Erythrocytes are involved in the transport of oxygen and carbon dioxide in the body. Since pH is the influential factor in the Bohr-Haldane effect, pHi is actively maintained via secondary active transports Na+/H+ exchange and HC3–/Cl– anion exchanger. Because of the redox properties of the iron, hemoglobin generates reactive oxygen species and thus, the human erythrocyte is constantly exposed to oxidative damage. Although the adult erythrocyte lacks protein synthesis and cannot restore damaged proteins, it is equipped with high activity of protective enzymes. Redox changes in the cell initiate various signalling pathways. Plasma membrane oxido-reductases (PMORs) are trans-membrane electron transport systems that have been found in the membranes of all cells and have been extensively characterized in the human erythrocyte. Erythrocyte PMORs transfer reducing equivalents from intracellular reductants to extracellular oxidants, thus their most important role seems to be to enable the cell respond to changes in intra- and extra-cellular redox environments.

So far the activity of erythrocyte PMORs in disease states has not been systematically investigated. This review summarizes present knowledge on erythrocyte electron transfer activity in humans (health, type 1 diabetes, diabetic nephropathy, and chronic uremia) and hypothesizes an integrated model of the functional organization of erythrocyte plasma membrane where electron pathways work in parallel with transport metabolons to maintain redox homeostasis.

Hematopoietic stem cells under pressure

PURPOSE OF REVIEW

Hematopoietic stem cells (HSCs) and progenitors are tasked with maintaining hematopoietic homeostasis in the face of numerous insults and challenges, including infection, inflammation, and exsanguination. HSCs possess the remarkable ability to reconstitute the entire hematopoietic system of an organism whose own hematopoietic system has been ablated. This ability is exploited routinely in the clinic via HSC transplantation (HSCT). Here, we focus on the physiological and molecular bottlenecks overcome by HSCs during transplantation.

RECENT FINDINGS

During transplantation, HSCs encounter a damaged bone marrow niche, characterized molecularly by increases in oxygen concentrations and an altered cytokine milieu. New mechanisms and pathways have been recently implicated during HSCT, including transplanted HSC-dependent secretion of conditioning molecules that facilitate engraftment and pathways that protect HSCs from perturbed organelle homeostasis.

SUMMARY

Better understanding the molecular processes HSCs employ to withstand the stress of transplant will illuminate novel targets for further improving conditioning regimens and engraftment during HSCT.

Sepsis induced by cecal ligation and perforation (CLP) alters nucleotidase activities in platelets of rats

Sepsis is a potentially lethal condition, and it is associated with platelet alterations. The present study sought to investigate the activity of ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase), E-5'-nucleotidase, and ecto-adenosine deaminase (E-ADA) in the platelets of rats that were induced with sepsis. Male Wistar rats were divided into three groups of ten animals each: a negative control group (normal; NC); a group that underwent surgical procedures (sham); and a group that underwent cecal ligation and perforation (CLP). The induction of sepsis was confirmed by bacteremia, and the causative pathogen identified was Escherichia coli. Hematological parameters showed leukocytosis and thrombocytopenia in animals in the septic group. The results also revealed that there were significant (p < 0.05) increases in adenosine triphosphate (ATP) and adenosine monophosphate (AMP) hydrolyses, and in the deamination of adenosine in the CLP group compared to the sham and control groups. Conversely, ADP hydrolysis was significantly decreased (p < 0.05) in the CLP group compared to the sham and control groups. Purine levels were analyzed by high-performance liquid chromatography (HPLC) in serum samples from control, sham, and CLP groups. Increased concentrations of ATP, adenosine, and inosine were found in the CLP group compared to the sham and control groups. Conversely, the concentrations of ADP and AMP in the CPL group were not significantly altered. We suggest that alterations in hematological parameters, nucleotide hydrolysis in platelets, and nucleotide concentrations in serum samples of rats with induced sepsis may be related to thromboembolic events.

Ectonucleotidase inhibitors: a patent review (2011-2016)

INTRODUCTION

Ectonucleotidases are a broad family of metallo-ectoenzymes that are responsible for hydrolysing a variety of nucleotides to nucleosides, hence orchestrating the activation of P1 and P2 cell receptors via controlled release of nucleotides and nucleosides. Many disorders such as impaired calcification including aortic calcification, neurological and immunological disorders, platelet aggregation, cell proliferation and metastasis. are characterized by an increase in expression of these ectonucleotidases. Consequently, selective inhibitors of ectonucleotidases are required for therapeutic intervention. Area covered: Several classes of compounds such as purine, nucleotide derivatives (e.g., ARL67156) and monoclonal antibodies, have shown promising ectonucleotidase inhibitory potential. This review discusses chemistry and therapeutic applications of ectonucleotidase inhibitors patented from 2011 to 2016. Expert opinion: All eukaryotic cells express nucleotide and nucleoside receptors on their cell surface and are capable of releasing extracellular nucleotides. Ectonucleotidases are a broad family of metallo-ectoenzymes that hydrolyze a variety of nucleotides to nucleosides. These extracellular nucleotides and nucleosides are important cell signalling molecules and mediate a variety of (patho)physiological processes by acting upon their respective P1 and/or P2 receptors. Discovery of molecules that can selectively inhibit or activate ectonucleotidases is crucial from therapeutic point of view, since it allows human intervention into purinergic cell signalling, thereby allowing us to modulate related (patho)physiological processes as desired.

Connexin hemichannel blockade improves survival of striatal GABA-ergic neurons after global cerebral ischaemia in term-equivalent fetal sheep

Basal ganglia injury at term remains a major cause of disability, such as cerebral palsy. In this study we tested the hypotheses that blockade of astrocytic connexin hemichannels with a mimetic peptide would improve survival of striatal phenotypic neurons after global cerebral ischaemia in term-equivalent fetal sheep, and that neuronal survival would be associated with electrophysiological recovery. Fetal sheep (0.85 gestation) were randomly assigned to receive a short or long (1 or 25 h) intracerebroventricular infusion of a mimetic peptide or vehicle, starting 90 minutes after 30 minutes of cerebral ischaemia. Sheep were killed 7 days after ischaemia. Cerebral ischaemia was associated with reduced numbers of calbindin-28k, calretinin, parvalbumin and GAD positive striatal neurons (P < 0.05 ischaemia + vehicle, n = 6 vs. sham ischaemia, n = 6) but not ChAT or nNOS positive neurons. Short infusion of peptide (n = 6) did not significantly improve survival of any striatal phenotype. Long infusion of peptide (n = 6) was associated with increased survival of calbindin-28k, calretinin, parvalbumin and GAD positive neurons (P < 0.05 vs. ischaemia + vehicle). Neurophysiological recovery was associated with improved survival of calbindin-28k, calretinin and parvalbumin positive striatal neurons (P < 0.05 for all). In conclusion, connexin hemichannel blockade after cerebral ischaemia in term-equivalent fetal sheep improves survival of striatal GABA-ergic neurons.

Neuronal P2X7 receptor-induced reactive oxygen species production contributes to nociceptive behavior in mice

ATP can activate a variety of pathways through P2 purinoreceptors, leading to neuroprotection and pathology in the CNS. Among all P2X receptors, the P2X7 receptor (P2X7R) is a well-defined therapeutic target for inflammatory and neuropathic pain. Activation of P2X7R can generate reactive oxygen species (ROS) in macrophages and microglia. However, the role of ROS in P2X7R–induced pain remains unexplored. Here, we investigated the downstream effects of neuronal P2X7R activation in the spinal cord. We found that ATP induces ROS production in spinal cord dorsal horn neurons, an effect eliminated by ROS scavenger N-tert-butyl-α-phenylnitrone (PBN) and P2X7R antagonist A438079. A similar effect was observed with a P2X7R agonist, BzATP, and was attenuated by a NADPH oxidase inhibitor apocynin. Intrathecal administration of BzATP resulted in ROS production in the spinal cord and oxidative DNA damage in dorsal horn neurons. BzATP also induced robust biphasic spontaneous nociceptive behavior. Pre-treatment with A438079 abolished all BzATP-induced nociceptive behaviors, while ROS scavengers dose-dependently attenuated the secondary response. Here, we provide evidence that neuronal P2X7R activation leads to ROS production and subsequent nociceptive pain in mice. Together, the data indicate that P2X7R-induced ROS play a critical role in the P2X7R signaling pathway of the CNS.

Purinergic Signaling in the Cardiovascular System

There is nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory-motor nerves, as well as in intracardiac neurons. Centers in the brain control heart activities and vagal cardiovascular reflexes involve purines. Adenine nucleotides and nucleosides act on purinoceptors on cardiomyocytes, AV and SA nodes, cardiac fibroblasts, and coronary blood vessels. Vascular tone is controlled by a dual mechanism. ATP, released from perivascular sympathetic nerves, causes vasoconstriction largely via P2X1 receptors. Endothelial cells release ATP in response to changes in blood flow (via shear stress) or hypoxia, to act on P2 receptors on endothelial cells to produce nitric oxide, endothelium-derived hyperpolarizing factor, or prostaglandins to cause vasodilation. ATP is also released from sensory-motor nerves during antidromic reflex activity, to produce relaxation of some blood vessels. Purinergic signaling is involved in the physiology of erythrocytes, platelets, and leukocytes. ATP is released from erythrocytes and platelets, and purinoceptors and ectonucleotidases are expressed by these cells. P1, P2Y₁, P2Y₁₂, and P2X1 receptors are expressed on platelets, which mediate platelet aggregation and shape change. Long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides promote migration and proliferation of vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis, vessel remodeling during restenosis after angioplasty and atherosclerosis. The involvement of purinergic signaling in cardiovascular pathophysiology and its therapeutic potential are discussed, including heart failure, infarction, arrhythmias, syncope, cardiomyopathy, angina, heart transplantation and coronary bypass grafts, coronary artery disease, diabetic cardiomyopathy, hypertension, ischemia, thrombosis, diabetes mellitus, and migraine.

Inosine Released from Dying or Dead Cells Stimulates Cell Proliferation via Adenosine Receptors

Introduction

Many antitumor therapies induce apoptotic cell death in order to cause tumor regression. Paradoxically, apoptotic cells are also known to promote wound healing, cell proliferation, and tumor cell repopulation in multicellular organisms. We aimed to characterize the nature of the regenerative signals concentrated in the micromilieu of dead and dying cells.

Methods

Cultures of viable melanoma B16F10 cells, mouse fibroblasts, and primary human fibroblast-like synoviocytes (FLS) in the presence of dead and dying cells, their supernatants (SNs), or purified agonists and antagonists were used to evaluate the stimulation of proliferation. Viable cell quantification was performed by either flow cytometry of harvested cells or by crystal violet staining of adherent cells. High-performance liquid chromatography and liquid chromatography coupled with mass spectrometry of cell SNs were deployed to identify the nature of growth-promoting factors. Coimplantation of living cells in the presence of SNs collected from dead and dying cells and specific agonists was used to evaluate tumor growth in vivo.

Results

The stimulation of proliferation of few surviving cells by bystander dead cells was confirmed for melanoma cells, mouse fibroblasts, and primary FLS. We found that small soluble molecules present in the protein-free fraction of SNs of dead and dying cells were responsible for the promotion of proliferation. The nucleoside inosine released by dead and dying cells acting via adenosine receptors was identified as putative inducer of proliferation of surviving tumor cells after irradiation and heat treatment.

Conclusion

Inosine released by dead and dying cells mediates tumor cell proliferation via purinergic receptors. Therapeutic strategies surmounting this pathway may help to reduce the rate of recurrence after radio- and chemotherapy.

Bone Marrow Homing and Engraftment Defects of Human Hematopoietic Stem and Progenitor Cells

Homing of hematopoietic stem cells (HSC) to their microenvironment niches in the bone marrow is a complex process with a critical role in repopulation of the bone marrow after transplantation. This active process allows for migration of HSC from peripheral blood and their successful anchoring in bone marrow before proliferation. The process of engraftment starts with the onset of proliferation and must, therefore, be functionally dissociated from the former process. In this overview, we analyze the characteristics of stem cells (SCs) with particular emphasis on their plasticity and ability to find their way home to the bone marrow. We also address the problem of graft failure which remains a significant contributor to morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). Within this context, we discuss non-malignant and malignant hematological disorders treated with reduced-intensity conditioning regimens or grafts from human leukocyte antigen (HLA)-mismatched donors.

Activities of ectonucleotidases and adenosine deaminase in platelets of cattle experimentally infected by Fasciola hepatica

The enzymatic activities of NTPDase, 5'-nucleotidase and adenosine deaminase (ADA) are important in regulating the concentration of adenine nucleotides, molecules known to be involved on platelet aggregation. Fasciolosis causes coagulation disorders that have not been completely elucidated. Taking into consideration the association between the purinergic system and hemostasis, this study aimed to evaluate the enzymatic activities of NTPDase (hydrolyze ATP and ADP), 5'-nucleotidase (hydrolyze AMP) and ADA (deamination of adenosine) in platelets from cattle experimentally infected by Fasciola hepatica on days 20, 40, 60 and 80 post-infection (PI). For this study, 10 healthy Friesian steers were separated into two groups: the group A (n = 5) was used as uninfected control, and the group B was composed of steers experimentally infected by F. hepatica (n = 5). The number of platelets did not differ between groups in the periods evaluated. Reduction of NTPDase (p < 0.05) hydrolysing ATP (days 20, 40 and 60 PI), and ADP (days 40, 60 and 80 PI), and on 5'-nucleotidase hydrolyzing AMP (days 40 and 60 PI) was observed. A reduction (p < 0.05) in ADA activity on day 20 PI, as well as an increase (p < 0.05) in ADA activity on days 40 and 60 PI was observed when compared to the control. Based on these results, we can conclude that ATP, ADP and AMP hydrolysis and adenosine deamination were altered in platelets of cattle infected by F. hepatica. Considering the importance of the purinergic system in hemostasis, it is believed that those changes may contribute to the coagulation impairment observed in acute fasciolosis described in the literature.

Characterization of E-NTPDase (EC 3.6.1.5) activity in hepatic lymphocytes: A different activity profile from peripheral lymphocytes

The activity of ectonucleoside triphosphate diphosphohydrolase (E-NTPDase; EC 3.6.1.5) was characterized in hepatic lymphocytes (HL) of rats. For this purpose, a specific method for the isolation of lymphocytes from hepatic tissue was developed. Subsequently, E-NTPDase activity of rat HL was compared with that of rat peripheral lymphocytes. The HL showed high cell count and viability. Also, the characterization test revealed that the optimal E-NTPDase activities were attained at 37°C and pH 8.0 in the presence of Ca²⁺ . In addition, in the presence of specific E-NTPDase inhibitors (20mM sodium azide and 0.3mM suramin), there were significant inhibitions in nucleotide hydrolysis. However, there was no significant change in adenosine triphosphate (ATP) or adenosine diphosphate (ADP) hydrolysis in the presence of inhibitors of other E-ATPase (0.1mM Ouabain, 0.5mM orthovanadate, and 1mM, 5mM, and 10mM sodium azide). Furthermore, the kinetic behavior of the enzyme in HL showed apparent Km of 134.90 ± 0.03μM and 214.40 ± 0.06μM as well as Vmax of 345.0 ± 28.32 and 242.0 ± 27.55 ƞmol Pi/min/mg of protein for ATP and ADP, respectively. The Chevillard plot revealed that ATP and ADP were hydrolyzed at the same active site of the enzyme. Our results suggest that the degradation of extracellular nucleotides in HL may have been primarily accomplished by E-NTPDase. The higher E-NTPDase activity observed in HL may be attributed to the important physiological functions of ATP and ADP in HL.

SIGNIFICANCE OF THE STUDY

Extracellular purine nucleotides are able to interact with specific receptors and trigger a number of important physiological functions in cells. This interaction is controlled by ectonucleoside triphosphate diphosphohydrolase (E-NTPDase), enzyme that present their catalytic site at the extracellular space and degrades nucleotides. This purinergic signaling has important functions in peripheral lymphocytes and may represent an important new therapeutic target for the treatment of immunological diseases. However, there is dearth of information on the involvement of E-NTPDase in liver lymphocytes. The liver is an important organ, which performs both metabolic and toxicological roles in living organism, and hepatic lymphocytes may play crucial action in the regulation of immune responses in the liver tissue. Furthermore, various chronic diseases such as cirrhosis may be treated with novel pharmacotherapy by targeting the modulation of hepatic lymphocytes. Thus, the significance of this study is to evaluate the activity of E-NTPDase in liver lymphocyte and compare its activity with the peripheral lymphocytes.

Quercetin changes purinergic enzyme activities and oxidative profile in platelets of rats with hypothyroidism

Diseases related to thyroid hormones have been extensively studied because affect a large number of individuals, and these hormones participate in the regulation of the whole organism homeostasis. However, little is known about the involvement of purinergic signaling related to oxidative stress in hypothyroidism and possible therapeutic adjuncts for treatment of this disorder. Thus, the present study investigates the effects of quercetin on NTPDase, 5'-nucleotidase and adenosine deaminase activities, platelet aggregation and oxidative profile in platelets of rats with methimazole (MMI)-induced hypothyroidism. Methimazole at a concentration of 20mg/100mL was administered for 90days. From the second month the animals received quercetin 10 or 25mg/kg for 60days. Results showed that: Ecto-5'-nucleotidase activity decreased in methimazole/water group and the treatment with quercetin 25mg/kg decreased NTPDase, 5'-nucleotidase and adenosine deaminase activities. Moreover, platelet aggregation increased in methimazole/water group. Lipid peroxidation increased while superoxide dismutase and catalase activities decreased, but, interestingly, the treatment with quercetin reversed these changes. These results demonstrated that quercetin modulates adenine nucleotide hydrolysis decreasing the ADP formation and adenosine deamination. At the same time quercetin improves the oxidative profile, as well as reduces platelet aggregation, which together with the modulation in the nucleotides levels can contribute to the prevention of platelet disorders.

Two P2X1 receptor transcripts able to form functional channels are present in most human monocytes

To characterize the presence and general properties of P2X1 receptors in single human monocytes we used RT-PCR, flow cytometry, and the patch-clamp and the two-electrode voltage-clamp techniques. Most human monocytes expressed the canonical P2X1 (90%) and its splicing variant P2X1del (88%) mRNAs. P2X1 receptor immunoreactivity was also observed in 70% of these cells. Currents mediated by P2X1 (EC₅₀=1.9±0.8µm) and P2X1del (EC₅₀ >1000µm) channels, expressed in Xenopus leavis oocytes, have different ATP sensitivity and kinetics. Both currents mediated by P2X1 and P2X1del channels kept increasing during the continuous presence of high ATP concentrations. Currents mediated by the native P2X1 receptors in human monocytes showed an EC₅₀=6.3±0.2µm. Currents have kinetics that resemble those observed for P2X1 and P2X1del receptors in oocytes. Our study is the first to demonstrate the expression of P2X1 transcript and its splicing variant P2X1del in most human monocytes. We also, for the first time, described functional homomeric P2X1del channels and demonstrated that currents mediated by P2X1 or P2X1del receptors, during heterologous expression, increased in amplitude when activated with high ATP concentrations in a similar fashion to those channels that increase their conductance under similar conditions, such as P2X7, P2X2, and P2X4 channels.

Purinergic receptor regulation of LPS-induced signaling and pathophysiology

Macrophages express several lipopolysaccharide (LPS) binding proteins and are potently activated by LPS to produce inflammatory mediators. Recent studies have shown that receptors for exogenous nucleotides (P2X and P2Y purinergic receptors) can modulate macrophage production of TNF-α , IL-1β and nitric oxide (NO) following LPS exposure. Macrophages and LPS-stimulated monocytes express elevated levels of P2Y1, P2Y2 and P2X7 mRNA, suggesting that both P2Y and P2X receptors can contribute to LPS-induced pathophysiology. In addition, oxidized-ATP treatment (which inhibits P2X7) of macrophages blocks LPS-induced NO production, NF-κB and ERK-1/2 activation. Also, an LPS-binding domain located in the P2X7 C-terminus appears important for receptor trafficking/function. Moreover, the purinergic receptor ligand 2-MeS-ATP attenuates LPS-induced cytokine and NO production in vivo and ex vivo. These data suggest that P2X7 and certain P2Ys are linked to LPS effects, although their relative contribution in vivo is unclear. Accordingly, we tested the capacity of several adenine nucleotides to modulate LPS-induced mortality in mice. We found that the P2X7-directed ligand BzATP was unable to prevent LPS-induced death, whereas 2-MeS-ATP and 2-Cl-ATP, which bind to multiple P2X and P2Y receptors were able to protect mice from LPS-induced death. These data suggest that the co-ordinate action of P2Y and P2X7 receptors are critical for controlling LPS responses in vivo and that agents directed against both receptor classes may provide the greatest therapeutic advantage.

A novel assay to detect nucleotide receptor P2X7 genetic polymorphisms influencing numerous innate immune functions

The importance of accessory signaling pathways amplifying endotoxin responses has recently been highlighted by genetic studies describing LPS-hyporesponsive individuals despite carrying the common allele for TLR4. The nucleotide receptor P2X7 modulates the production of numerous LPS-stimulated inflammatory mediators. We have recently described the largest phenotypic screen known for genetic polymorphisms associated with the nucleotide receptor P2X7, a global regulator of leukocyte function. This required the development of a novel monocyte pore assay with numerous advantages over previous methods and with the potential to facilitate rapid (< 3 h), multiplex analysis of clinical samples. This paper addresses aspects pertinent to the development of the monocyte pore assay, briefly summarizes our results suggestingthat P2X7 alleles modulate LPSstimulated cytokine production, and discusses a model wherein P2X7 may serve as an amplification loop of innate immunity.

P2X Receptor-Mediated Modulation of Sensory Transmission to the Spinal Cord Dorsal Horn

In the somatosensory system, P2X receptors are expressed on both peripheral and central terminals of primary afferent neurons. Those expressed on peripheral terminals are activated in response to both nociceptive and innocuous stimuli, whereas those at central terminals (“central terminal P2X receptors”) play an important role in modulating sensory transmission to the spinal cord dorsal horn. The author reviews recent studies on the central terminal P2X receptors. It is proposed that central terminal P2X receptors, once activated, may be involved in both central sensitization and initiation of pain. Thus, these receptors may repesent a promising target for therapeutic management of pathological pain.

P2X6 Knockout Mice Exhibit Normal Electrolyte Homeostasis

ATP-mediated signaling is an important regulator of electrolyte transport in the kidney. The purinergic cation channel P2X6 has been previously localized to the distal convoluted tubule (DCT), a nephron segment important for Mg²⁺ and Na⁺ reabsorption, but its role in ion transport remains unknown. In this study, P2x6 knockout (P2x6^-/-) mice were generated to investigate the role of P2X6 in renal electrolyte transport. The P2x6^-/- animals displayed a normal phenotype and did not differ physiologically from wild type mice. Differences in serum concentration and 24-hrs urine excretion of Na⁺, K⁺, Mg²⁺ and Ca²⁺ were not detected between P2x6^+/+, P2x6^+/- and P2x6^-/- mice. Quantitative PCR was applied to examine potential compensatory changes in renal expression levels of other P2x subunits and electrolyte transporters, including P2x1-5, P2x7, Trpm6, Ncc, Egf, Cldn16, Scnn1, Slc12a3, Slc41a1, Slc41a3, Cnnm2, Kcnj10 and Fxyd2. Additionally, protein levels of P2X2 and P2X4 were assessed in P2x6^+/+ and P2x6^-/- mouse kidneys. However, significant changes in expression were not detected. Furthermore, no compensatory changes in gene expression could be demonstrated in heart material isolated from P2x6^-/- mice. Except for a significant (P<0.05) upregulation of P2x2 in the heart of P2x6^-/- mice compared to the P2x6^+/+ mice. Thus, our data suggests that purinergic signaling via P2X6 is not significantly involved in the regulation of renal electrolyte handling under normal physiological conditions.

Blockade of Extracellular ATP Effect by Oxidized ATP Effectively Mitigated Induced Mouse Experimental Autoimmune Uveitis (EAU)

Various pathological conditions are accompanied by ATP release from the intracellular to the extracellular compartment. Extracellular ATP (eATP) functions as a signaling molecule by activating purinergic P2 purine receptors. The key P2 receptor involved in inflammation was identified as P2X7R. Recent studies have shown that P2X7R signaling is required to trigger the Th1/Th17 immune response, and oxidized ATP (oxATP) effectively blocks P2X7R activation. In this study we investigated the effect of oxATP on mouse experimental autoimmune uveitis (EAU). Our results demonstrated that induced EAU in B6 mice was almost completely abolished by the administration of small doses of oxATP, and the Th17 response, but not the Th1 response, was significantly weakened in the treated mice. Mechanistic studies showed that the therapeutic effects involve the functional change of a number of immune cells, including dendritic cells (DCs), T cells, and regulatory T cells. OxATP not only directly inhibits the T cell response; it also suppresses T cell activation by altering the function of DCs and Foxp3⁺ T cell. Our results demonstrated that inhibition of P2X7R activation effectively exempts excessive autoimmune inflammation, which may indicate a possible therapeutic use in the treatment of autoimmune diseases.

Impaired P2X1 Receptor-Mediated Adhesion in Eosinophils from Asthmatic Patients

Eosinophils play an important role in the pathogenesis of asthma and can be activated by extracellular nucleotides released following cell damage or inflammation. For example, increased ATP concentrations were reported in bronchoalveolar lavage fluids of asthmatic patients. Although eosinophils are known to express several subtypes of P2 receptors for extracellular nucleotides, their function and contribution to asthma remain unclear. In this article, we show that transcripts for P2X1, P2X4, and P2X5 receptors were expressed in healthy and asthmatic eosinophils. The P2X receptor agonist α,β-methylene ATP (α,β-meATP; 10 μM) evoked rapidly activating and desensitizing inward currents (peak 18 ± 3 pA/pF at -60 mV) in healthy eosinophils, typical of P2X1 homomeric receptors, which were abolished by the selective P2X1 antagonist NF449 (1 μM) (3 ± 2 pA/pF). α,β-meATP-evoked currents were smaller in eosinophils from asthmatic patients (8 ± 2 versus 27 ± 5 pA/pF for healthy) but were enhanced following treatment with a high concentration of the nucleotidase apyrase (17 ± 5 pA/pF for 10 IU/ml and 11 ± 3 pA/pF for 0.32 IU/ml), indicating that the channels are partially desensitized by extracellular nucleotides. α,β-meATP (10 μM) increased the expression of CD11b activated form in eosinophils from healthy, but not asthmatic, donors (143 ± 21% and 108 ± 11% of control response, respectively). Furthermore, α,β-meATP increased healthy (18 ± 2% compared with control 10 ± 1%) but not asthmatic (13 ± 1% versus 10 ± 0% for control) eosinophil adhesion. Healthy human eosinophils express functional P2X1 receptors whose activation leads to eosinophil αMβ2 integrin-dependent adhesion. P2X1 responses are constitutively reduced in asthmatic compared with healthy eosinophils, probably as the result of an increase in extracellular nucleotide concentration.

Free and nanoencapsulated vitamin D3 : effects on E-NTPDase and E-ADA activities in an animal model with induced arthritis

The effect of vitamin D3 in oral solution (VD3 ) and vitamin D3 -loaded nanocapsules (NC-VD3 ) was analysed in animals with complete Freund's adjuvant (CFA) induced arthritis (AR). For this purpose, we evaluated scores for arthritis, thermal hyperalgesia and paw oedema, as well as histological analyses and measurements of the activity of the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) and ecto-adenosine deaminase (E-ADA) enzymes in rat lymphocytes. Haematological and biochemical parameters were also determined. The doses administered were 120 UI/day of VD3 and 15.84 UI/day of NC-VD3 . Fifteen days after the induction of AR, the groups were treated for 15 days with vitamin D3 . The results demonstrated that VD3 was able to reduce arthritis scores, thermal hyperalgesia and paw oedema in rats with CFA-induced arthritis. However, treatment with NC-VD3 did not reduce arthritis scores. The histological analyses showed that both formulations were able to reduce the inflammatory changes induced by CFA. The activity of E-NTPDase in rat lymphocytes was higher in the AR compared with the control group, while the activity of E-ADA was lower. This effect was reversed after the 15-day treatment. Data from this study indicates that both forms of vitamin D3 seem to contribute to decreasing the inflammatory process induced by CFA, possibly altering the activities of ectoenzymes. Copyright © 2016 John Wiley & Sons, Ltd.

SIGNIFICANCE OF THE STUDY

The effects promoted by both formulations of vitamin D3 , either in oral solution or nanoencapsulated form, strongly suggests the softening of the inflammatory process induced by complete Freund's adjuvant (CFA), possibly altering the E-NTPDase and E-ADA activities. However, it is known that vitamin D has a beneficial effect on the modulation of the immune system components responsible for the inflammatory process. Moreover, the establishment of responses to treatment with vitamin D3 may provide an alternative for inhibiting the proinflammatory response, assisting in our understanding of the immunopathology of this disease and possibly improving the signs and symptoms that hinder the quality of life of patients with rheumatoid arthritis.

HIGHLIGHTS

Evaluation of the effects on the E-NTPDase and E-ADA activities in an animal model of induced arthritis. Two formulations of vitamin D3 were used: form oral solution and nanoencapsulated. Vitamin D3 seems to contribute to the inflammatory process induced by CFA. Vitamin D3 possibly alters the E-NTPDase and E-ADA activities. Vitamin D3 may be an alternative supplementary treatment for chronic arthritis.

ATP release through pannexon channels

Extracellular adenosine triphosphate (ATP) serves as a signal for diverse physiological functions, including spread of calcium waves between astrocytes, control of vascular oxygen supply and control of ciliary beat in the airways. ATP can be released from cells by various mechanisms. This review focuses on channel-mediated ATP release and its main enabler, Pannexin1 (Panx1). Six subunits of Panx1 form a plasma membrane channel termed 'pannexon'. Depending on the mode of stimulation, the pannexon has large conductance (500 pS) and unselective permeability to molecules less than 1.5 kD or is a small (50 pS), chloride-selective channel. Most physiological and pathological stimuli induce the large channel conformation, whereas the small conformation so far has only been observed with exclusive voltage activation of the channel. The interaction between pannexons and ATP is intimate. The pannexon is not only the conduit for ATP, permitting ATP efflux from cells down its concentration gradient, but the pannexon is also modulated by ATP. The channel can be activated by ATP through both ionotropic P2X as well as metabotropic P2Y purinergic receptors. In the absence of a control mechanism, this positive feedback loop would lead to cell death owing to the linkage of purinergic receptors with apoptotic processes. A control mechanism preventing excessive activation of the purinergic receptors is provided by ATP binding (with low affinity) to the Panx1 protein and gating the channel shut.

Deletion of P2X7 attenuates hyperoxia-induced acute lung injury via inflammasome suppression

Increasing evidence shows that hyperoxia is a serious complication of oxygen therapy in acutely ill patients that causes excessive production of free radicals leading to hyperoxia-induced acute lung injury (HALI). Our previous studies have shown that P2X7 receptor activation is required for inflammasome activation during HALI. However, the role of P2X7 in HALI is unclear. The main aim of this study was to determine the effect of P2X7 receptor gene deletion on HALI. Wild-type (WT) and P2X7 knockout (P2X7 KO) mice were exposed to 100% O2 for 72 h. P2X7 KO mice treated with hyperoxia had enhanced survival in 100% O2 compared with the WT mice. Hyperoxia-induced recruitment of inflammatory cells and elevation of IL-1β, TNF-α, monocyte chemoattractant protein-1, and IL-6 levels were attenuated in P2X7 KO mice. P2X7 deletion decreased lung edema and alveolar protein content, which are associated with enhanced alveolar fluid clearance. In addition, activation of the inflammasome was suppressed in P2X7-deficient alveolar macrophages and was associated with suppression of IL-1β release. Furthermore, P2X7-deficient alveolar macrophage in type II alveolar epithelial cells (AECs) coculture model abolished protein permeability across mouse type II AEC monolayers. Deletion of P2X7 does not lead to a decrease in epithelial sodium channel expression in cocultures of alveolar macrophages and type II AECs. Taken together, these findings show that deletion of P2X7 is a protective factor and therapeutic target for the amelioration of hyperoxia-induced lung injury.

P2X ion channel receptors and inflammation

Neuroinflammation limits tissue damage in response to pathogens or injury and promotes repair. There are two stages of inflammation, initiation and resolution. P2X receptors are gaining attention in relation to immunology and inflammation. The P2X7 receptor in particular appears to be an essential immunomodulatory receptor, although P2X1 and P2X4 receptors also appear to be involved. ATP released from damaged or infected cells causes inflammation by release of inflammatory cytokines via P2X7 receptors and acts as a danger signal by occupying upregulated P2X receptors on immune cells to increase immune responses. The purinergic involvement in inflammation is being explored for the development of novel therapeutic strategies.

Involvement of purinergic system in the release of cytokines by macrophages exposed to glioma-conditioned medium

Macrophages are involved in cancer progression. M1 macrophages have an antitumor effect, whereas M2 phenotype are associated with tumor growth. The progression of gliomas involves the participation of an inflammatory microenvironment. Adenosine triphosphate (ATP) can act as pro-inflammatory signal, whereas adenosine has opposite properties. The biological effects of extracellular nucleotides/nucleosides mediated by purinergic receptors are controlled by ectonucleotidases. In the present work, we evaluated whether glioma-conditioned medium (GL-CM) modulates macrophage differentiation and the participation of ATP and adenosine in the release of pro-and anti-inflammatory cytokines by these cells. The results show that macrophages exposed to GL-CM were modulated to an M2-like phenotype. HPLC analysis of GL-CM demonstrated the presence of significant amounts of ATP and its metabolites. Macrophages exposed to GL-CM presented decreased ATP and AMP hydrolysis and increased IL-10 and MCP-1 secretion, effects that were diminished by P1 or P2 antagonists. GL-CM did not alter the release of IL-6 by macrophages, although treatment with ATP promoted an increase in the release of IL-6, which was prevented by a P2X7 antagonist. In summary, we found that A2A and P2X7 activation is necessary for IL-10, MCP-1, and IL-6 release by macrophages exposed to GL-CM, which, in turn, modulates the macrophages to M2-phenotype. The present study establishes a relationship between M2-like polarization, cytokine release and purinergic receptor activation in macrophages exposed to GL-CM. Therefore, the data presented herein contributes to advancing in the field of cancer-related inflammation and point specific purinergic receptors as targets for modulation of the phenotype of glioma-associated macrophages.

Blood cells: an historical account of the roles of purinergic signalling

The involvement of purinergic signalling in the physiology of erythrocytes, platelets and leukocytes was recognised early. The release of ATP and the expression of purinoceptors and ectonucleotidases on erythrocytes in health and disease are reviewed. The release of ATP and ADP from platelets and the expression and roles of P1, P2Y(1), P2Y(12) and P2X1 receptors on platelets are described. P2Y(1) and P2X(1) receptors mediate changes in platelet shape, while P2Y(12) receptors mediate platelet aggregation. The changes in the role of purinergic signalling in a variety of disease conditions are considered. The successful use of P2Y(12) receptor antagonists, such as clopidogrel and ticagrelor, for the treatment of thrombosis, myocardial infarction and stroke is discussed.

Extracellular ATP and other nucleotides-ubiquitous triggers of intercellular messenger release

Extracellular nucleotides, and ATP in particular, are cellular signal substances involved in the control of numerous (patho)physiological mechanisms. They provoke nucleotide receptor-mediated mechanisms in select target cells. But nucleotides can considerably expand their range of action. They function as primary messengers in intercellular communication by stimulating the release of other extracellular messenger substances. These in turn activate additional cellular mechanisms through their own receptors. While this applies also to other extracellular messengers, its omnipresence in the vertebrate organism is an outstanding feature of nucleotide signaling. Intercellular messenger substances released by nucleotides include neurotransmitters, hormones, growth factors, a considerable variety of other proteins including enzymes, numerous cytokines, lipid mediators, nitric oxide, and reactive oxygen species. Moreover, nucleotides activate or co-activate growth factor receptors. In the case of hormone release, the initially paracrine or autocrine nucleotide-mediated signal spreads through to the entire organism. The examples highlighted in this commentary suggest that acting as ubiquitous triggers of intercellular messenger release is one of the major functional roles of extracellular nucleotides. While initiation of messenger release by nucleotides has been unraveled in many contexts, it may have been overlooked in others. It can be anticipated that additional nucleotide-driven messenger functions will be uncovered with relevance for both understanding physiology and development of therapy.

Hypercholesterolemia and Ecto-enzymes of Purinergic System: Effects of Paullinia cupana

Hypercholesterolemia is a metabolic disorder characterized by high levels of low-density lipoprotein and blood cholesterol, causing inflammatory lesion. Purinergic signaling modulates the inflammatory and immune responses through adenine nucleotides and nucleoside. Guaraná has hypocholesterolemic and antiinflammatory properties. Considering that there are few studies demonstrating the effects of guaraná powder on the metabolism of adenine nucleotides, we investigated its effects on the activity of ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase) and ecto-adenosine deaminase activity in lymphocytes of rats with diet-induced hypercholesterolemia. The rats were divided into hypercholesterolemic and normal diet groups. Each group was subdivided by treatment: saline, guaraná powder 12.5, 25, or 50 mg/kg/day and caffeine concentration equivalent to highest dose of guaraná, fed orally for 30 days. An increase in adenosine triphosphate hydrolysis was observed in the lymphocytes of rats with hypercholesterolemia and treated with 25 or 50 mg/kg/day when compared with the other groups. The hypercholesterolemic group treated with the highest concentration of guaraná powder showed decreased ecto-adenosine deaminase activity compared with the normal diet groups. Guaraná was able to reduce the total cholesterol and low-density lipoprotein cholesterol to basal levels in hypercholesterolemic rats. High concentrations of guaraná associated with a hypercholesterolemic diet are likely to have contributed to the reduction of the inflammatory process.

Rotenone-induced Impairment of Mitochondrial Electron Transport Chain Confers a Selective Priming Signal for NLRP3 Inflammasome Activation

Mitochondrial dysfunction is considered crucial for NLRP3 inflammasome activation partly through its release of mitochondrial toxic products, such as mitochondrial reactive oxygen species (mROS)(2) and mitochondrial DNA (mtDNA). Although previous studies have shown that classical NLRP3-activating stimulations lead to mROS generation and mtDNA release, it remains poorly understood whether and how mitochondrial damage-derived factors may contribute to NLRP3 inflammasome activation. Here, we demonstrate that impairment of the mitochondrial electron transport chain by rotenone primes NLRP3 inflammasome activation only upon costimulation with ATP and not with nigericin or alum. Rotenone-induced priming of NLRP3 in the presence of ATP triggered the formation of specklike NLRP3 or ASC aggregates and the association of NLRP3 with ASC, resulting in NLRP3-dependent caspase-1 activation. Mechanistically, rotenone confers a priming signal for NLRP3 inflammasome activation only in the context of aberrant high-grade, but not low-grade, mROS production and mitochondrial hyperpolarization. By contrast, rotenone/ATP-mediated mtDNA release and mitochondrial depolarization are likely to be merely an indication of mitochondrial damage rather than triggering factors for NLRP3 inflammasome activation. Our results provide a molecular insight into the selective contribution made by mitochondrial dysfunction to the NLRP3 inflammasome pathway.

Human β Defensin-3 Increases CD86 Expression on Monocytes by Activating the ATP-Gated Channel P2X7

Human β defensin-3 (hBD-3), an epithelial cell-derived antimicrobial peptide, mediates chemotaxis and activation of myeloid cells. In this study, we provide evidence that hBD-3 induces the costimulatory molecule CD86 on primary human monocytes by a mechanism involving autocrine activation of ionotropic P2X7 receptors (P2X7R) by ATP. Incubation of monocytes with hBD-3 resulted in increased expression of both the CD80 and CD86 costimulatory molecules. Treatment of monocytes with a selective P2X7R antagonist inhibited the ability of hBD-3 to induce expression of CD86 but not CD80. The hBD-3-dependent upregulation of CD86 was also attenuated in monocytes incubated with apyrase, a potent scavenger of extracellular ATP. Finally, direct activation of monocyte P2X7R by exogenous ATP mimicked the ability of hBD-3 to induce CD86 expression. These data suggest that hBD-3 induces monocyte activation by both P2X7-dependent (CD86 upregulation) and P2X7-independent (CD80 upregulation) signaling mechanisms and raise the possibility that activation of P2X7R could play an important role in shaping the inflammatory microenvironment in conditions where hBD-3 is highly expressed, such as psoriasis or oral carcinoma.

Purinergic signaling during macrophage differentiation results in M2 alternative activated macrophages

Macrophages represent a highly heterogenic cell population of the innate immune system, with important roles in the initiation and resolution of the inflammatory response. Purinergic signaling regulates both M1 and M2 macrophage function at different levels by controlling the secretion of cytokines, phagocytosis, and the production of reactive oxygen species. We found that extracellular nucleotides arrest macrophage differentiation from bone marrow precursors via adenosine and P2 receptors. This results in a mature macrophage with increased expression of M2, but not M1, genes. Similar to adenosine and ATP, macrophage growth arrested with LPS treatment resulted in an increase of the M2-related marker Ym1. Recombinant Ym1 was able to affect macrophage proliferation and could, potentially, be involved in the arrest of macrophage growth during hematopoiesis.

Role of P2X7 receptor in Clostridium perfringens beta-toxin-mediated cellular injury

BACKGROUND

Clostridium perfringens beta-toxin is a pore-forming toxin (PFT) and an important agent of necrotic enteritis and enterotoxemia. We recently reported that beta-toxin strongly induced cell death in THP-1 cells via the formation of oligomers. We here describe that the P2X(7) receptor, which is an ATP receptor, interacts with beta-toxin.

METHODS

We tested the role of P2X(7) receptor in beta-toxin-induced toxicity using specific inhibitors, knockdown of receptor, expression of the receptor and interaction by dot-blot assay. The potency of P2X(7) receptor was further determined using an in vivo mouse model.

RESULTS

Selective P2X(7) receptor antagonists (oxidized ATP (o-ATP), oxidized ADP, and Brilliant Blue G (BBG)) inhibited beta-toxin-induced cytotoxicity in THP-1 cells. o-ATP also blocked the binding of beta-toxin to cells. The P2X(7) receptor and beta-toxin oligomer were localized in the lipid rafts of THP-1 cells. siRNA for the P2X(7) receptor inhibited toxin-induced cytotoxicity and binding of the toxin. In contrast, the siRNA knockdown of P2Y(2) or P2Y(6) had no effect on beta-toxin-induced cytotoxicity. The addition of beta-toxin to P2X(7)-transfected HEK-293 cells resulted in binding of beta-toxin oligomer. Moreover, beta-toxin specifically bound to immobilized P2X(7) receptors in vitro and colocalized with the P2X(7) receptor on the THP-1 cell surface. Furthermore, beta-toxin-induced lethality in mice was blocked by the preadministration of BBG.

CONCLUSIONS

The results of this study indicate that the P2X(7) receptor plays a role in beta-toxin-mediated cellular injury.

GENERAL SIGNIFICANCE

P2X(7) receptor is a potential target for the treatment of C. perfringens type C infection.

Expression and function of P2 receptors in hematopoietic stem and progenitor cells

Nucleotides have unambiguously emerged as a family of mediators of intercellular communication, which bind to a class of plasma membrane receptors, P2 receptors, to trigger intercellular signaling. P2 receptors can be further divided into P2X and P2Y subfamilies based on structure and function. Different hematopoietic cells express diverse spectrums of P2 receptors at different levels, including hematopoietic stem and progenitor cells (HSPCs). Extracellular adenosine triphosphate (ATP) exerts different effects on HSPCs, regulating cell proliferation, differentiation, migration, and chemotaxis, release of cytokines or lysosomal constituents, and generation of reactive oxygen or nitrogen species. The relationship between abnormal P2 receptor function and human diseases attracts more and more attention. This review summarizes the expression and function of P2 receptors in HSPCs and the relationship to hematopoietic diseases.

CD73 and CD39 ectonucleotidases in T cell differentiation: Beyond immunosuppression

Extracellular ATP is a danger signal released by dying and damaged cells, and it functions as an immunostimulatory signal that promotes inflammation. However, extracellular adenosine acts as an immunoregulatory signal that modulates the function of several cellular components of the adaptive and innate immune response. Consequently, the balance between ATP and adenosine concentration is crucial in immune homeostasis. CD39 and CD73 are two ectonucleotidases that cooperate in the generation of extracellular adenosine through ATP hydrolysis, thus tilting the balance towards immunosuppressive microenvironments. Extracellular adenosine can prevent activation, proliferation, cytokine production and cytotoxicity in T cells through the stimulation of the A2A receptor; however, recent evidence has shown that adenosine may also affect other processes in T-cell biology. In this review, we discuss evidence that supports a role of CD73 and CD39 ectonucleotidases in controlling naive T-cell homeostasis and memory cell survival through adenosine production. Finally, we propose a novel hypothesis of a possible role of these ectonucleotidases and autocrine adenosine signaling in controlling T-cell differentiation.

Metabolic faecal fingerprinting of trans-resveratrol and quercetin following a high-fat sucrose dietary model using liquid chromatography coupled to high-resolution mass spectrometry

Faecal non-targeted metabolomics deciphers metabolic end-products resulting from the interactions among food, host genetics, and gut microbiota. Faeces from Wistar rats fed a high-fat sucrose (HFS) diet supplemented with trans-resveratrol and quercetin (separately or combined) were analysed by liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS). Metabolomics in faeces are categorised into four clusters based on the type of treatment. Tentative identification of significantly differing metabolites highlighted the presence of carbohydrate derivatives or conjugates (3-phenylpropyl glucosinolate and dTDP-D-mycaminose) in the quercetin group. The trans-resveratrol group was differentiated by compounds related to nucleotides (uridine monophosphate and 2,4-dioxotetrahydropyrimidine D-ribonucleotide). Marked associations between bacterial species (Clostridium genus) and the amount of some metabolites were identified. Moreover, trans-resveratrol and resveratrol-derived microbial metabolites (dihydroresveratrol and lunularin) were also identified. Accordingly, this study confirms the usefulness of omics-based techniques to discriminate individuals depending on the physiological effect of food constituents and represents an interesting tool to assess the impact of future personalized therapies.