Recent patents on novel P2X(7) receptor antagonists and their potential for reducing central nervous system inflammation

The analgesic and gastroprotective activities of the three fungal extracts and their possible correlation with the inhibition of the P2X7 receptor

P2X7 is a purinergic receptor physiologically activated by extracellular ATP. Its activation induces proinflammatory responses, including cytokine release, reactive oxygen species formation, and cell death. Previous in vivo experimental models demonstrated that P2X7 blockade has anti-inflammatory effects; however, there are no drugs used in clinical therapy that act on the P2X7 receptor. In the context of inflammatory diseases, nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used as the first-line treatment; however, their major side effects include stomach ulcer formation, which increases patient morbidity and mortality. Here, we analyzed for the first time the analgesic and gastroprotective activities of three fungal extracts that showed antagonistic effects on P2X7 in vitro. The Antarctic fungal extracts obtained from Vishniacozyma victoriae, Metschnikowia australis, and Ascomycota sp. were tested in animal models of acute pain and ethanol-induced ulceration. These three extracts reduced paw licking by approximately 50 %, which is related to pain behavior, and reduced the number of stomach ulcers 3-7 times compared with the control (70 % ethanol), making them more efficient than the lansoprazole, an NSAID drug, and Brilliant Blue G (BBG), a known P2X7 antagonist, which only halves the number of ulcers. Furthermore, the extracts also protected the gastric mucosa and significantly reduced the levels of liver and renal enzymes compared with those in the ethanol group. Taken together, the fungal extracts presented both analgesic and possibly anti-inflammatory activities and had a protective effect on the gastric epithelium.

A current review on P2X7 receptor antagonist patents in the treatment of neuroinflammatory disorders: a patent review on antagonists

Chronic inflammation is defined by an activated microglial state linked to all neurological disorders, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (a motor neuron disease that affects the brain and spinal cord). P2X7 receptors (P2X7R) are ATP-activated ion-gated channels present on microglial surfaces. Prolonged ATP release under pathological settings results in sustained P2X7R activation, which leads to inflammasome development and cytokine release. P2X7R and its enabling roles have recently been linked to neurodegenerative diseases, making it a potential research subject. This research provides an overview of current patents for chemicals, biologics, and medicinal applications. The World Intellectual Property Organization (WIPO), European Patent Office (EPO, Espacenet), and the United States Patent and Trademark Office (USPTO) databases were searched for patents using the keywords "P2X7R and Neuroinflammation." During the study period from 2015 to 2021, 103 patents were examined. The countries that protected these innovations were the United States, PCT (Patent Cooperation Treaty states), Europe, Canada, Australia, and India. Janssen Pharmaceutica NV had the most applications, followed by Acetelion Pharmaceuticals LTD., Renovis Inc., Kelly Michael G, Kincaid Jhon, Merck Patent GMBH, H Lundbeck A/S, and many more. The P2X7R is a possible diagnostic and therapeutic target for cancer, pain disorders, and inflammation. For P2X7 R, several compounds have been discovered and are presently the subject of clinical trial investigations. This study featured patents for P2X7R antagonists, which help treat conditions including neuroinflammation.

Insight into the pathophysiological advances and molecular mechanisms underlying cerebral stroke: current status

Molecular pathways involved in cerebral stroke are diverse. The major pathophysiological events that are observed in stroke comprises of excitotoxicity, oxidative stress, mitochondrial damage, endoplasmic reticulum stress, cellular acidosis, blood-brain barrier disruption, neuronal swelling and neuronal network mutilation. Various biomolecules are involved in these pathways and several major proteins are upregulated and/or suppressed following stroke. Different types of receptors, ion channels and transporters are activated. Fluctuations in levels of various ions and neurotransmitters have been observed. Cells involved in immune responses and various mediators involved in neuro-inflammation get upregulated progressing the pathogenesis of the disease. Despite of enormity of the problem, there is not a single therapy that can limit infarction and neurological disability due to stroke. This is because of poor understanding of the complex interplay between these pathophysiological processes. This review focuses upon the past to present research on pathophysiological events that are involved in stroke and various factors that are leading to neuronal death following cerebral stroke. This will pave a way to researchers for developing new potent therapeutics that can aid in the treatment of cerebral stroke.

A Hybrid Approach Combining Shape-Based and Docking Methods to Identify Novel Potential P2X7 Antagonists from Natural Product Databases

P2X7 is an ATP-activated purinergic receptor implicated in pro-inflammatory responses. It is associated with the development of several diseases, including inflammatory and neurodegenerative conditions. Although several P2X7 receptor antagonists have recently been reported in the literature, none of them is approved for clinical use. However, the structure of the known antagonists can serve as a scaffold for discovering effective compounds in clinical therapy. This study aimed to propose an improved virtual screening methodology for the identification of novel potential P2X7 receptor antagonists from natural products through the combination of shape-based and docking approaches. First, a shape-based screening was performed based on the structure of JNJ-47965567, a P2X7 antagonist, using two natural product compound databases, MEGx (~5.8 × 103 compounds) and NATx (~32 × 103 compounds). Then, the compounds selected by the proposed shape-based model, with Shape-Tanimoto score values ranging between 0.624 and 0.799, were filtered for drug-like properties. Finally, the compounds that met the drug-like filter criteria were docked into the P2X7 allosteric binding site, using the docking programs GOLD and DockThor. The docking poses with the best score values were submitted to careful visual inspection of the P2X7 allosteric binding site. Based on our established visual inspection criteria, four compounds from the MEGx database and four from the NATx database were finally selected as potential P2X7 receptor antagonists. The selected compounds are structurally different from known P2X7 antagonists, have drug-like properties, and are predicted to interact with key P2X7 allosteric binding pocket residues, including F88, F92, F95, F103, M105, F108, Y295, Y298, and I310. Therefore, the combination of shape-based screening and docking approaches proposed in our study has proven useful in selecting potential novel P2X7 antagonist candidates from natural-product-derived compounds databases. This approach could also be useful for selecting potential inhibitors/antagonists of other receptors and/or biological targets.

Agonists, Antagonists, and Modulators of P2X7 Receptors

The P2X7 receptor has been proposed as a novel drug target for different types of diseases associated with inflammation, including brain diseases, peripheral inflammation, and cancers. Structurally diverse P2X7 receptor antagonists, mainly negative allosteric modulators (NAMs), have been developed in recent years, and several P2X7 receptor antagonists are currently evaluated in clinical trials. The P2X7 receptor requires high micro- to even millimolar ATP concentrations to be activated. Selective agonists for the P2X7 receptor are not available. Positive allosteric modulators (PAMs) have been described, but PAMs with high potency and selectivity are still lacking. This chapter discusses medicinal chemistry approaches toward the development of P2X7 receptor modulators and presents a selection of recommended tool compounds for studying P2X7 receptors in humans and rodents.

Synthesis of Sulfonamide Tethered (Hetero)aryl ethylidenes as Potential Inhibitors of P2X Receptors: A Promising Way for the Treatment of Pain and Inflammation

P2X receptors have the ability to regulate various physiological functions like neurotransmission, inflammatory responses, and pain sensation. Such physiological properties make these receptors a new target for the treatment of pain and inflammation. Several antagonists of P2X receptors have been studied for the treatment of neuropathic pain and neurodegenerative disorders but potency and selectivity are the major issues with these known inhibitors. Sulfonamide derivatives were reported to be potent inhibitors of P2X receptors. In this study, sulfonamide carrying precursor hydrazide was synthesized by a facile method that was subsequently condensed with methyl (hetero)arylketones to obtain a series of new (hetero)aryl ethylidenes. These compounds were screened for inhibitory potential against h-P2X2, h-P2X4, h-P2X5, and h-P2X7 receptors to find their potency and selectivity. Computational studies were performed to confirm the mode of inhibition as well as type of interaction between ligand and target site. In calcium signaling experiments, compound 6h was found to be the most potent and selective inhibitor of h-P2X2 and h-P2X7 receptors with IC₅₀ ± standard error of the mean (SEM) values of 0.32 ± 0.01 and 1.10 ± 0.21 μM, respectively. Compounds 6a and 6c exhibited selective inhibition for h-P2X7 receptor, whereas 6e, 7a, and 7b expressed selective inhibitions toward h-P2X2 receptor that were comparable to the positive control suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS).

Metformin alleviates hydrogen peroxide-induced inflammation and oxidative stress via inhibiting P2X7R signaling in spinal cord tissue cells neurons

Metformin, the first medication that is often prescribed for the treatment of type 2 diabetes mellitus, was recently found to be neuroprotective. To study the mechanism underlying the neuroprotective effect of metformin, we pretreated primary spinal cord neurons with 50 µM or 100 µM metformin for 2 h prior to treatment with hydrogen peroxide (H2O2) for up to 48 h. Our results showed that H2O2 increased the expression of purinergic receptor P2X7 (P2X7R) in spinal cord neurons, which promoted the downstream pro-inflammatory cytokines release and oxidative stress. We found that metformin could reverse these pro-inflammatory and pro-oxidative effects of H2O2. Besides, P2X7R knockdown by siRNA suppressed H2O2-induced pro-inflammatory cytokine release and oxidative stress response. In conclusion, our results show that metformin can alleviate H2O2-induced inflammation and oxidative stress via modulating the P2X7R signaling pathway.

P2X7 Receptors in Neurodegeneration: Potential Therapeutic Applications From Basic to Clinical Approaches

Purinergic receptors play important roles in central nervous system (CNS), where the bulk of these receptors are implicated in neuroinflammatory responses and regulation of cellular function of neurons, microglial and astrocytes. Within the P2X receptor family, P2X₇ receptor is generally known for its inactivity in normal conditions and activation by moderately high concentrations (>100 μM) of extracellular adenosine 5′-triphosphate (ATP) released from injured cells as a result of brain injury or pathological conditions. Activation of P2X₇R contributes to the activation and proliferation of microglia and directly contribute to neurodegeneration by provoking microglia-mediated neuronal death, glutamate-mediated excitotoxicity, and NLRP3 inflammasome activation that results in initiation, maturity and release of the pro-inflammatory cytokines and generation of reactive oxygen and nitrogen species. These components of the inflammatory response play important roles in many neural pathologies and neurodegeneration disorders. In CNS, expression of P2X₇R on microglia, astrocytes, and oligodendrocytes are upregulated under neuroinflammatory conditions. Several in vivo studies have demonstrated beneficial effects of the P2X₇ receptor antagonists in animal model systems of neurodegenerative diseases. A number of specific and selective P2X₇ receptor antagonists have been developed, but only few of them have shown efficient brain permeability. Finding potent and selective P2X₇ receptor inhibitors which are also CNS penetrable and display acceptable pharmacokinetics (PK) has presented challenges for both academic researchers and pharmaceutical companies. In this review, we discuss the role of P2X₇ receptor function in neurodegenerative diseases, the pharmacological inhibition of the receptor, and PET radiopharmaceuticals which permit non-invasive monitoring of the P2X₇ receptor contribution to neuroinflammation associated with neurodegeneration.

Purinergic P2X7 Receptor: A Cation Channel Sensitive to Tumor Microenvironment

Objective:

Current review was conducted to check involvement of P2X7R use in cancer treatment.

Methods:

We review the most recent patents focused on the use of P2X7R in the treatment of cancer.

Results:

P2X7R is an intriguing purinergic receptor that plays different roles in tumor progression.

Conclusion:

Powerful strategies able to selectively interfere with its expression and function should reveal helpful in the development of new anti-cancer therapies.

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.

Neuroimmune and Inflammatory Signals in Complex Disorders of the Central Nervous System

An extensive microglial-astrocyte-monocyte-neuronal cross talk seems to be crucial for normal brain function, development, and recovery. However, under certain conditions neuroinflammatory interactions between brain cells and neuroimmune cells influence disease outcome and brain pathology. Microglial cells express a range of functional states with dynamically pleomorphic profiles from a surveilling status of synaptic transmission to an active player in major events of development such as synaptic elimination, regeneration, and repair. Also, inflammation mediates a series of neurotoxic roles in neuropsychiatric conditions and neurodegenerative diseases. The present review discusses data on the involvement of neuroinflammatory conditions that alter neuroimmune interactions in four different pathologies. In the first section of this review, we discuss the ability of the early developing brain to respond to a focal lesion with a rapid compensatory plasticity of intact axons and the role of microglial activation and proinflammatory cytokines in brain repair. In the second section, we present data of neuroinflammation and neurodegenerative disorders and discuss the role of reactive astrocytes in motor neuron toxicity and the progression of amyotrophic lateral sclerosis. In the third section, we discuss major depressive disorders as the consequence of dysfunctional interactions between neural and immune signals that result in increased peripheral immune responses and increase proinflammatory cytokines. In the last section, we discuss autism spectrum disorders and altered brain circuitries that emerge from abnormal long-term responses of innate inflammatory cytokines and microglial phenotypic dysfunctions.

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.

P2X7 Participates in Intracerebral Hemorrhage-Induced Secondary Brain Injury in Rats via MAPKs Signaling Pathways

This study aimed to study the role of P2X7 in intracerebral hemorrhage (ICH)-induced secondary brain injury (SBI) and the underlying mechanisms. An autologous blood injection was used to induce ICH model in Sprague-Dawley rats, and cultured primary rat cortical neurons were exposed to oxyhemoglobin to mimic ICH in vitro. siRNA interference and over-expression of P2X7, agonists and antagonists of P2X7, p38 MAPK and ERK were exploited. The protein levels were assessed using Western blotting and immunofluorescence staining. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining and Fluoro-Jade B were conducted to detect apoptotic and degenerating neurons. The protein levels of P2X7, phosphorylated p38, ERK, active caspase-3 and NF-κB were significantly increased by ICH, which could be further increased by BzATP (P2X7 agonist) and reduced by BBG (P2X7 antagonist). And BzATP demonstrated a significant increase in cell death ratio and brain water content, while BBG led to a reverse results. In addition, Over- P2X7 increased the levels of P2X7, phosphorylated p38, ERK, active caspase-3 and NF-κB, and aggravated cell apoptosis, while si P2X7 resulted in opposite effects. Finally, the protein levels of phosphorylated P38 and active caspase 3 were decreased by BzATP plus Hydrochloride (p38 MAPK antagonist) and increased vy BBG plus Asiatic acid (p38 MAPK agonist), while the protein levels of phosphorylated ERK and NF-κB were decreased with BzATP plus Nimbolide (ERK antagonist) and increased with BBG plus Saikosaponin C (ERK agonist). This study demonstrates that inhibition of P2X7 could prevent ICH-induced SBI via MAPKs signaling pathway.

Escape from adamantane: Scaffold optimization of novel P2X7 antagonists featuring complex polycycles

The adamantane scaffold, despite being widely used in medicinal chemistry, is not devoid of problems. In recent years we have developed new polycyclic scaffolds as surrogates of the adamantane group with encouraging results in multiple targets. As an adamantane scaffold is a common structural feature in several P2X7 receptor antagonists, herein we report the synthesis and pharmacological evaluation of multiple replacement options of adamantane that maintain a good activity profile. Molecular modeling studies support the binding of the compounds to a site close to the central pore, rather than to the ATP-binding site and shed light on the structural requirements for novel P2X7 antagonists.

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.

P2X7 Receptor as a Therapeutic Target

P2X7 receptor is an ATP-gated cation channel that upon agonist interaction leads to cellular influx of Na(+) and Ca(2+) and efflux of K(+). P2X7 is expressed by a wide variety of cells and its activation mediates a large number of biological processes like inflammation, neuromodulation, cell death or cell proliferation and it has been associated to related pathological conditions including infectious, inflammatory, autoimmune, neurological, and musculoskeletal disorders and, in the last years, to cancer. This chapter describes structural features of P2X7, chemical properties of its agonist, antagonist, and allosteric modulators and summarizes recent advances on P2X7 receptor as therapeutic target in the aforementioned diseases. We also give an overview on recent literature suggesting that P2X7 single-nucleotide polymorphisms could be exploited as diagnostic biomarkers for the development of tailored therapies.

Emerging role of P2X7 receptors in CNS health and disease

Purinergic signalling in the brain is becoming an important focus in the study of CNS health and disease. Various purinergic receptors are found to be present in different brain cells in varying extent, which get activated upon binding of ATP or its analogues. Conventionally, ATP was considered only as a major metabolic fuel of the cell but its recognition as a neurotransmitter in early 1970s, brought meaningful insights in neuron glia crosstalk, participating in various physiological functions in the brain. P2X7R, a member of ligand gated purinergic receptor (P2X) family, is gaining attention in the field of neuroscience because of its emerging role in broad spectrum of ageing and age related neurological disorders. The aim of this review is to provide an overview about the structure and function of P2X7R highlighting its unique features which distinguish it from the other members of its family. This review critically analyzes the literature mentioning the details about the agonist and antagonist of the P2X7R. It also emphasizes the advancements in understanding the dual role of P2X7R in brain development and disorders inviting meaningful insights about its involvement in Alzheimer's disease, Huntington's disease, Multiple Sclerosis, Neuropathic pain, Spinal Cord Injury and NeuroAIDS. Exploring the roles of P2X7R in detail is critical to identify its therapeutic potential in the treatment of acute and chronic neurodegenerative diseases. Moreover, this review also helps to raise more interest in the neurobiology of the purinergic receptors and thus providing new avenues for future research.

Crosstalk between purinergic receptors and canonical signaling pathways in the mouse salivary gland

Isolated clusters of mouse parotid acinar cells in combination with live cell imaging were used to explore the crosstalk in molecular signaling between purinergic, cholinergic and adrenergic pathways that integrate to control fluid and protein secretion. This crosstalk was manifested by (1) β-adrenergic receptor activation and amplification of P2X4R evoked Ca(2+) signals, (2) β-adrenergic-induced amplification of P2X7R-evoked Ca(2+) signals and (3) muscarinic receptor induced activation of P2X7Rs via exocytotic activity. The findings from our study reveal that purinoceptor-mediated Ca(2+) signaling is modulated by crosstalk with canonical signaling pathways in parotid acinar cells. Integration of these signals are likely important for dynamic control of saliva secretion to match physiological demand in the parotid gland.

Hydrogen sulfide intervention in focal cerebral ischemia/reperfusion injury in rats

The present study aimed to explore the mechanism underlying the protective effects of hydrogen sulfide against neuronal damage caused by cerebral ischemia/reperfusion. We established the middle cerebral artery occlusion model in rats via the suture method. Ten minutes after middle cerebral artery occlusion, the animals were intraperitoneally injected with hydrogen sulfide donor compound sodium hydrosulfide. Immunofluorescence revealed that the immunoreactivity of P2X₇ in the cerebral cortex and hippocampal CA1 region in rats with cerebral ischemia/reperfusion injury decreased with hydrogen sulfide treatment. Furthermore, treatment of these rats with hydrogen sulfide significantly lowered mortality, the Longa neurological deficit scores, and infarct volume. These results indicate that hydrogen sulfide may be protective in rats with local cerebral ischemia/reperfusion injury by down-regulating the expression of P2X₇ receptors.

Paeoniflorin down-regulates ATP-induced inflammatory cytokine production and P2X7R expression on peripheral blood mononuclear cells from patients with primary Sjögren's syndrome

This study determined the effects of paeoniflorin (PF) on the expression of purinergic receptor P2X ligand-gated ion channel 7 (P2X7R) expressed on peripheral blood mononuclear cells (PBMCs) and production of ATP-induced pro-inflammatory cytokines released by PBMCs in patients with primary Sjögren's syndrome (pSS). The pharmacological functions and cytotoxic effects of PF were dose dependent in PBMCs from 20 newly diagnosed pSS patients and 20 normal individuals. The optimum dose of PF was 100μM. PF significantly down-regulated the production of interleukin (IL)-1β and IL-6 from pSS PBMCs, and significantly inhibited ATP-induced expression of P2X7R, that might contribute to reduced IL-1β and IL-6. mRNA and protein levels of P2X7R on pSS PBMCs were significantly higher than in normal individuals (p=0.03, p<0.001). When PBMCs from subjects were stimulated in vitro with ATP in the presence of PF, P2X7R mRNA and protein levels were decreased significantly (p<0.001, p<0.001, respectively versus ATP group) in the pSS. Supernatant IL-1β and IL-6 levels were significantly lower in the PF group compared with ATP group (p<0.001, p<0.001). We show for the first time that PF-mediated reduction of IL-1β and IL-6 was due in part to the reduced expression and activation of the ATP sensor P2X7R on pSS PBMCs, indicating that PF might be useful for the management of pSS via down-regulating P2X7R expression. Thus, PF may provide a new therapeutic approach to regulate P2X7R-mediated pathologic responses of pSS.

Targeting P(2)X(7) receptor for the treatment of central post-stroke pain in a rodent model

Stroke is a leading cause of death and disability in industrialized countries. Approximately 8-14% of stroke survivors suffer from central post-stroke pain (CPSP) when hemorrhagic stroke occurs in lateral thalamic regions, which severely affects their quality of life. Because the mechanisms of CPSP are not well understood, effective treatments have not been developed. In the present study, we tested the hypothesis that persistent CPSP is caused by P(2)X(7)receptor activation after brain tissue damage and subsequent elevations in inflammatory cytokines. A thalamic hemorrhagic rat model was used, characterized by thermal and mechanical allodynia that develops in the subacute to chronic phases upon CPSP onset. We found a significant increase in P(2)X(7) expression in reactive microglia/macrophages in thalamic peri-lesion tissues at 5 weeks post-hemorrhage. Thalamic P(2)X(7) receptors were directly involved in pain transmission and hypersensitivity. The systemic targeting of P(2)X(7) receptors during the acute stage of hemorrhage rescued abnormal pain behaviors and neuronal activity in the thalamocingulate pathway by reducing reactive microglia/macrophage aggregation and associated inflammatory cytokines. After CPSP onset, the targeting of interleukin-1β reversed abnormal pain sensitivity. The aberrant spontaneous thalamocortical oscillations in rats with CPSP were modulated by blocking P(2)X(7) receptors. Taken together, our results suggest that targeting P(2)X(7) may be bi-effective in the treatment of CPSP, as both a pain blocker and immunosuppressant that inhibits inflammatory damage to brain tissue. P(2)X(7)receptors may serve as a potential target to prevent the occurrence of CPSP and may be beneficial for the recovery of patients from stroke.

Discovery of novel 2,5-dioxoimidazolidine-based P2X(7) receptor antagonists as constrained analogues of KN62

Novel 2,5-dioxoimidazolidine-based conformationally constrained analogues of KN62 (1) were developed as P2X7 receptor (P2X7R) antagonists using a rigidification strategy of the tyrosine backbone of 1. SAR analysis of the 2,5-dioxoimidazolidine scaffold indicated that piperidine substitution at the N3 position and no substitution at N1 position were preferable. Further optimization of the substituents at the piperidine nitrogen and the spacer around the skeleton resulted in several superior antagonists to 1, including 1-adamantanecarbonyl analogue 21i (IC50 = 23 nM in ethidium uptake assay; IC50 = 14 nM in IL-1β ELISA assay) and (3-CF3-4-Cl)benzoyl analogue (-)-21w (54 nM in ethidium uptake assay; 9 nM in IL-1β ELISA assay), which was more potent than the corresponding (+) isomer. Compound 21w displayed potent inhibitory activity in an ex vivo model of LTP-induced pain signaling in the spinal cord and significant anti-inflammatory activity in in vivo models of carrageenan-induced paw edema and type II collagen-induced joint arthritis.

The P2X7 receptor channel: recent developments and the use of P2X7 antagonists in models of disease

The P2X7 receptor is a trimeric ATP-gated cation channel found predominantly, but not exclusively, on immune cells. P2X7 activation results in a number of downstream events, including the release of proinflammatory mediators and cell death and proliferation. As such, P2X7 plays important roles in various inflammatory, immune, neurologic and musculoskeletal disorders. This review focuses on the use of P2X7 antagonists in rodent models of neurologic disease and injury, inflammation, and musculoskeletal and other disorders. The cloning and characterization of human, rat, mouse, guinea pig, dog, and Rhesus macaque P2X7, as well as recent observations regarding the gating and permeability of P2X7, are discussed. Furthermore, this review discusses polymorphic and splice variants of P2X7, as well as the generation and use of P2X7 knockout mice. Recent evidence for emerging signaling pathways downstream of P2X7 activation and the growing list of negative and positive modulators of P2X7 activation and expression are also described. In addition, the use of P2X7 antagonists in numerous rodent models of disease is extensively summarized. Finally, the use of P2X7 antagonists in clinical trials in humans and future directions exploring P2X7 as a therapeutic target are described.

ATP-P2X7 Receptor Modulates Axon Initial Segment Composition and Function in Physiological Conditions and Brain Injury

Axon properties, including action potential initiation and modulation, depend on both AIS integrity and the regulation of ion channel expression in the AIS. Alteration of the axon initial segment (AIS) has been implicated in neurodegenerative, psychiatric, and brain trauma diseases, thus identification of the physiological mechanisms that regulate the AIS is required to understand and circumvent AIS alterations in pathological conditions. Here, we show that the purinergic P2X7 receptor and its agonist, adenosine triphosphate (ATP), modulate both structural proteins and ion channel density at the AIS in cultured neurons and brain slices. In cultured hippocampal neurons, an increment of extracellular ATP concentration or P2X7-green fluorescent protein (GFP) expression reduced the density of ankyrin G and voltage-gated sodium channels at the AIS. This effect is mediated by P2X7-regulated calcium influx and calpain activation, and impaired by P2X7 inhibition with Brilliant Blue G (BBG), or P2X7 suppression. Electrophysiological studies in brain slices showed that P2X7-GFP transfection decreased both sodium current amplitude and intrinsic neuronal excitability, while P2X7 inhibition had the opposite effect. Finally, inhibition of P2X7 with BBG prevented AIS disruption after ischemia/reperfusion in rats. In conclusion, our study demonstrates an involvement of P2X7 receptors in the regulation of AIS mediated neuronal excitability in physiological and pathological conditions.

Pathological pain and the neuroimmune interface

Reciprocal signalling between immunocompetent cells in the central nervous system (CNS) has emerged as a key phenomenon underpinning pathological and chronic pain mechanisms. Neuronal excitability can be powerfully enhanced both by classical neurotransmitters derived from neurons, and by immune mediators released from CNS-resident microglia and astrocytes, and from infiltrating cells such as T cells. In this Review, we discuss the current understanding of the contribution of central immune mechanisms to pathological pain, and how the heterogeneous immune functions of different cells in the CNS could be harnessed to develop new therapeutics for pain control. Given the prevalence of chronic pain and the incomplete efficacy of current drugs--which focus on suppressing aberrant neuronal activity--new strategies to manipulate neuroimmune pain transmission hold considerable promise.

P2X7-dependent, but differentially regulated release of IL-6, CCL2, and TNF-α in cultured mouse microglia

ATP is an important regulator of microglia and its effects on microglial cytokine release are currently discussed as important contributors in a variety of brain diseases. We here analyzed the effects of ATP on the production of six inflammatory mediators (IL-6, IL-10, CCL2, IFN-γ, TNF-α, and IL-12p70) in cultured mouse primary microglia. Stimulation of P2X7 receptor by ATP (1 mM) or BzATP (500 µM) evoked the mRNA expression and release of proinflammatory cytokines IL-6, TNF-α, and the chemokine CCL2 in WT cells but not in P2X7(-/-) cells. The effects of ATP and BzATP were inhibited by the nonselective P2 receptor antagonists PPADs and suramin. Various selective P2X7 receptor antagonists blocked the P2X7-dependent release of IL-6 and CCL2, but, surprisingly, had no effect on BzATP-induced release of TNF-α in microglia. Calcium measurements confirmed that P2X7 is the main purine receptor activated by BzATP in microglia and showed that all P2X7 antagonists were functional. It is also presented that pannexin-1 hemichannel function and potential P2X4/P2X7 heterodimers are not involved in P2X7-dependent release of IL-6, CCL2, and TNF-α in microglia. How P2X7-specific antagonists only affect P2X7-dependent IL-6 and CCL2 release, but not TNF-α release is at the moment unclear, but indicates that the P2X7-dependent release of cytokines in microglia is differentially regulated.

The P2X7 receptor: a key player in immune-mediated bone loss?

Inflammatory diseases are often multiorganic diseases with manifestations not related directly to the primary affected organ. They are often complicated by a generalized bone loss that subsequently leads to osteoporosis and bone fractures. The exact mechanism for the accompanying bone loss is not understood in full detail, but factors such as glucocorticoid treatment, immobilization, malnutrition, and insufficient intake of vitamin D play a role. However, it has become evident that the inflammatory process itself is involved and the resulting bone loss is termed immune-mediated bone loss. It stems from an increase in bone resorption and the pro-inflammatory cytokines tumor necrosis factor alpha and interleukin 1 beta and has been shown to not only mediate the inflammatory response but also to strongly stimulate bone degradation. The purinergic P2X7 receptor is central in the processing of these two cytokines and in the initiation of the inflammatory response, and it is a key molecule in the regulation of both bone formation and bone resorption. The aim of this review is therefore to provide evidence-based novel hypotheses of the role of ATP-mediated purinergic signalling via the P2X7 receptor in immune-mediated bone loss and -osteoporosis.

Natural compounds with P2X7 receptor-modulating properties

The adenosine 5'-triphosphate (ATP)-gated P2X7 receptor is a membrane-bound, non-selective cation channel, expressed in a variety of cell types. The P2X7 senses high extracellular ATP concentrations and seems to be implicated in a wide range of cellular functions as well as pathophysiological processes, including immune responses and inflammation, release of gliotransmitters and cytokines, cancer cell growth or development of neurodegenerative diseases. In the present study, we identified natural compounds and analogues that can block or sensitize the ATP (1 mM)-induced Ca(2+) response using a HEK293 cell line stably expressing human P2X7 and fluorometric imaging plate reader technology. For instance, teniposide potently blocked the human P2X7 at sub-miromolar concentrations, but not human P2X4 or rat P2X2. A marked block of ATP-induced Ca(2+) entry and Yo-Pro-1 uptake was also observed in human A375 melanoma cells and mouse microglial cells, both expressing P2X7. On the other hand, agelasine (AGL) and garcinolic acid (GA) facilitated the P2X7 response to ATP in all three cell populations. GA also enhanced the YO-PRO-1 uptake, whereas AGL did not affect the ATP-stimulated intracellular accumulation of this dye. According to the pathophysiological role of P2X7 in various diseases, selective modulators may have potential for further development, e.g. as neuroprotective or antineoplastic drugs.

Physiological roles and potential therapeutic applications of the P2X7 receptor in inflammation and pain

The P2X7 receptor (P2X7R) is a nonselective cation channel that is activated by extracellular ATP and triggers the secretion of several proinflammatory substances, such as IL-1β, IL-18, TNF-α, and nitric oxide. Recently, several preclinical studies have demonstrated that this receptor participates in inflammation and pain mechanisms. Taken together, these results indicate that P2X7R is a promising pharmacological target, and compounds that modulate the function of this receptor show potential as new anti-inflammatory medicines. In this review, we discuss aspects of P2X7R pharmacology and the participation of this protein in inflammation and pain and provide an overview of some promising compounds that have been tested as antagonists of P2X7R, with clinical applicability.

P2X7 receptor activation regulates microglial cell death during oxygen-glucose deprivation

Brain-resident microglia may promote tissue repair following stroke but, like other cells, they are vulnerable to ischemia. Here we identify mechanisms involved in microglial ischemic vulnerability. Using time-lapse imaging of cultured BV2 microglia, we show that simulated ischemia (oxygen-glucose deprivation; OGD) induces BV2 microglial cell death. Removal of extracellular Ca(2+) or application of Brilliant Blue G (BBG), a potent P2X7 receptor (P2X7R) antagonist, protected BV2 microglia from death. To validate and extend these in vitro findings, we assessed parenchymal microglia in freshly isolated hippocampal tissue slices from GFP-reporter mice (CX3CR1(GFP/+)). We confirmed that calcium removal or application of apyrase, an ATP-degrading enzyme, abolished OGD-induced microglial cell death in situ, consistent with involvement of ionotropic purinergic receptors. Indeed, whole cell recordings identified P2X7R-like currents in tissue microglia, and OGD-induced microglial cell death was inhibited by BBG. These pharmacological results were complemented by studies in tissue slices from P2X7R null mice, in which OGD-induced microglia cell death was reduced by nearly half. Together, these results indicate that stroke-like conditions induce calcium-dependent microglial cell death that is mediated in part by P2X7R. This is the first identification of a purinergic receptor regulating microglial survival in living brain tissues. From a therapeutic standpoint, these findings could help direct novel approaches to enhance microglial survival and function following stroke and other neuropathological conditions.

P2X(7) receptors in cerebral ischemia

Cerebral ischemia is one of the most common diseases resulting in death and disability in aged people. It leads immediately to rapid energy failure, ATP depletion, and ionic imbalance, which increase extracellular ATP levels and accordingly activate P2X7 receptors. These receptors are ATP-gated cation channels and widely distributed in nerve cells, especially in the immunocompetent cells of the brain. Currently, interest in the roles of P2X7 receptors in ischemic brain injury is growing. In this review, we discuss recent research progress on the actions of P2X7 receptors, their possible mechanisms in cerebral ischemia, and the potential therapeutic value of P2X7 receptor antagonists which may provide a new target both for clinical and for research purposes.

P2X7 receptor activation induces inflammatory responses in salivary gland epithelium

Inflammation of the salivary gland is a well-documented aspect of salivary gland dysfunction that occurs in Sjogren's syndrome (SS), an autoimmune disease, and in γ-radiation-induced injury during treatment of head and neck cancers. Extracellular nucleotides have gained recognition as key modulators of inflammation through activation of cell surface ionotropic and metabotropic receptors, although the contribution of extracellular nucleotides to salivary gland inflammation is not well understood. In vitro studies using submandibular gland (SMG) cell aggregates isolated from wild-type C57BL/6 mice indicate that treatment with ATP or the high affinity P2X7R agonist 3'-O-(4-benzoyl)benzoyl-ATP (BzATP) induces membrane blebbing and enhances caspase activity, responses that were absent in SMG cell aggregates isolated from mice lacking the P2X7R (P2X7R(-/-)). Additional studies with SMG cell aggregates indicate that activation of the P2X7R with ATP or BzATP stimulates the cleavage and release of α-fodrin, a cytoskeletal protein thought to act as an autoantigen in the development of SS. In vivo administration of BzATP to ligated SMG excretory ducts enhances immune cell infiltration into the gland and initiates apoptosis of salivary epithelial cells in wild-type, but not P2X7R(-/-), mice. These findings indicate that activation of the P2X7R contributes to salivary gland inflammation in vivo, suggesting that the P2X7R may represent a novel target for the treatment of salivary gland dysfunction.

Astrocytic CX43 hemichannels and gap junctions play a crucial role in development of chronic neuropathic pain following spinal cord injury

Chronic neuropathic pain is a frequent consequence of spinal cord injury (SCI). Yet despite recent advances, upstream releasing mechanisms and effective therapeutic options remain elusive. Previous studies have demonstrated that SCI results in excessive ATP release to the peritraumatic regions and that purinergic signaling, among glial cells, likely plays an essential role in facilitating inflammatory responses and nociceptive sensitization. We sought to assess the role of connexin 43 (Cx43) as a mediator of CNS inflammation and chronic pain. To determine the extent of Cx43 involvement in chronic pain, a weight-drop SCI was performed on transgenic mice with Cx43/Cx30 deletions. SCI induced robust and persistent neuropathic pain including heat hyperalgesia and mechanical allodynia in wild-type control mice, which developed after 4 weeks and was maintained after 8 weeks. Notably, SCI-induced heat hyperalgesia and mechanical allodynia were prevented in transgenic mice with Cx43/Cx30 deletions, but fully developed in transgenic mice with only Cx30 deletion. SCI-induced gliosis, detected as upregulation of glial fibrillary acidic protein in the spinal cord astrocytes at different stages of the injury, was also reduced in the knockout mice with Cx43/Cx30 deletions, when compared with littermate controls. In comparison, a standard regimen of post-SCI treatment of minocycline attenuated neuropathic pain to a significantly lesser degree than Cx43 deletion. These findings suggest Cx43 is critically linked to the development of central neuropathic pain following acute SCI. Since Cx43/Cx30 is expressed by astrocytes, these findings also support an important role of astrocytes in the development of chronic pain.

Activated human CD4+CD45RO+ memory T-cells indirectly inhibit NLRP3 inflammasome activation through downregulation of P2X7R signalling

Inflammasomes are multi-protein complexes that control the production of pro-inflammatory cytokines such as IL-1β. Inflammasomes play an important role in the control of immunity to tumors and infections, and also in autoimmune diseases, but the mechanisms controlling the activation of human inflammasomes are largely unknown. We found that human activated CD4+CD45RO+ memory T-cells specifically suppress P2X7R-mediated NLRP3 inflammasome activation, without affecting P2X7R-independent NLRP3 or NLRP1 inflammasome activation. The concomitant increase in pro-IL-1β production induced by activated memory T-cells concealed this effect. Priming with IFNβ decreased pro-IL-1β production in addition to NLRP3 inflammasome inhibition and thus unmasked the inhibitory effect on NLRP3 inflammasome activation. IFNβ suppresses NLRP3 inflammasome activation through an indirect mechanism involving decreased P2X7R signaling. The inhibition of pro-IL-1β production and suppression of NLRP3 inflammasome activation by IFNβ-primed human CD4+CD45RO+ memory T-cells is partly mediated by soluble FasL and is associated with down-regulated P2X7R mRNA expression and reduced response to ATP in monocytes. CD4+CD45RO+ memory T-cells from multiple sclerosis (MS) patients showed a reduced ability to suppress NLRP3 inflammasome activation, however their suppressive ability was recovered following in vivo treatment with IFNβ. Thus, our data demonstrate that human P2X7R-mediated NLRP3 inflammasome activation is regulated by activated CD4+CD45RO+ memory T cells, and provide new information on the mechanisms mediating the therapeutic effects of IFNβ in MS.

Inhibition of P2X7 receptor ameliorates transient global cerebral ischemia/reperfusion injury via modulating inflammatory responses in the rat hippocampus

Background

Neuroinflammation plays an important role in cerebral ischemia/reperfusion (I/R) injury. The P2X7 receptor (P2X7R) has been reported to be involved in the inflammatory response of many central nervous system diseases. However, the role of P2X7Rs in transient global cerebral I/R injury remains unclear. The purpose of this study is to determine the effects of inhibiting the P2X7R in a rat model of transient global cerebral I/R injury, and then to explore the association between the P2X7R and neuroinflammation after transient global cerebral I/R injury.

Methods

Immediately after infusion with the P2X7R antagonists Brilliant blue G (BBG), adenosine 5′-triphosphate-2′,3′-dialdehyde (OxATP) or A-438079, 20 minutes of transient global cerebral I/R was induced using the four-vessel occlusion (4-VO) method in rats. Survival rate was calculated, neuronal death in the hippocampal CA1 region was observed using H & E staining, and DNA cleavage was observed by deoxynucleotidyl transferase-mediated UTP nick end labeling TUNEL). In addition, behavioral deficits were measured using the Morris water maze, and RT-PCR and immunohistochemical staining were performed to measure the expression of IL-1β, TNF-α and IL-6, and to identify activated microglia and astrocytes.

Results

The P2X7R antagonists protected against transient global cerebral I/R injury in a dosage-dependent manner. A high dosage of BBG (10 μg) and A-0438079 (3 μg), and a low dosage of OxATP (1 μg) significantly increased survival rates, reduced I/R-induced learning memory deficit, and reduced I/R-induced neuronal death, DNA cleavage, and glial activation and inflammatory cytokine overexpression in the hippocampus.

Conclusions

Our study indicates that inhibiting P2X7Rs protects against transient global cerebral I/R injury by reducing the I/R-induced inflammatory response, which suggests inhibition of P2X7Rs may be a promising therapeutic strategy for clinical treatment of transient global cerebral I/R injury.

P2 receptors for extracellular nucleotides in the central nervous system: role of P2X7 and P2Y₂ receptor interactions in neuroinflammation

Extracellular nucleotides induce cellular responses in the central nervous system (CNS) through the activation of ionotropic P2X and metabotropic P2Y nucleotide receptors. Activation of these receptors regulates a wide range of physiological and pathological processes. In this review, we present an overview of the current literature regarding P2X and P2Y receptors in the CNS with a focus on the contribution of P2X7 and P2Y(2) receptor-mediated responses to neuroinflammatory and neuroprotective mechanisms.

Roles of white matter in central nervous system pathophysiologies

The phylogenetic enlargement of cerebral cortex culminating in the human brain imposed greater communication needs that have been met by the massive expansion of WM (white matter). Damage to WM alters brain function, and numerous neurological diseases feature WM involvement. In the current review, we discuss the major features of WM, the contributions of WM compromise to brain pathophysiology, and some of the mechanisms mediating WM injury. We will emphasize the newly appreciated importance of neurotransmitter signalling in WM, particularly glutamate and ATP signalling, to understanding both normal and abnormal brain functions. A deeper understanding of the mechanisms leading to WM damage will generate much-needed insights for developing therapies for acute and chronic diseases with WM involvement.

[The role of ecto-purines in inflammation leading to demyelination - new means for therapies against multiple sclerosis]

Nucleotides released from activated and/or injured cells activate P2 receptors. Extracellular nucleotides serve as danger signals or damage-associated molecular patterns (DAMPs) that trigger various immune responses. Indeed, P2 receptors are highly expressed in the astrocytes, microglia and other immune cells such as T and B lymphocytes that migrate to the central nervous system. The activation of P2 receptors triggers the secretion of proinflammatory cytokines and chemokines as well as immune cell migration and proliferation that contribute to demyelination and axonal damage. The activation of P2 receptors is controlled by the ectonucleotidases which hydrolyze extracellular nucleotides. Ecto-NTPDases and ecto-5'-nucleotidase are expressed in the astrocytes, oligodendrocytes, microglia, endothelial cells and activated T cells. The hydrolysis of extracellular ATP and ADP by enzymes results in the generation of extracellular adenosine. This nucleoside interacts with P1 receptors and activates anti-inflammatory and immunosuppressive responses in the cells involved in MS.

Role of purinergic P2X receptors in the control of liver homeostasis

It is now accepted that extracellular ATP and other nucleotides are potent signaling molecules, akin to neurotransmitters, hormones and lipid mediators. In the liver, several clues support a significant role for extracellular ATP-induced signaling pathways in the control of tissue homeostasis. First, ATP and other nucleotides are physiologically detected in extracellular fluids within the liver, including sinusoidal blood and intraductular bile, in various mammalian species including human and rodents. Moreover, finely tuned mechanisms of ATP release by different liver cell types have been described, under physiological cellular changes. In addition, most hepatic cells constitutively express, at the membrane level, several ATP-metabolizing ectoenzymes and ATP-sensitive receptors that modulate and transduce these mediator signals respectively. Finally, hepatic cells also express numerous membrane transporters that actively contribute to purinergic salvage pathways. Once released in the extracellular medium, unmetabolised ATP molecules can bind to purinergic P2X and P2Y receptors, and subsequently trigger various intracellular signal transduction pathways collectively referred to as purinergic signaling. In the liver, purinergic signaling has been shown to regulate key basic cellular functions, such as glucose/lipid metabolism, protein synthesis and ionic secretion, and homeostatic processes, such as cell cycle, inflammatory response and immunity. Whilst the functional relevance of P2Y receptors in liver physiology has been well documented, limited information is available regarding the potential role of hepatic P2X receptors in the modulation of liver homeostasis.

Astrocytes promote peripheral nerve injury-induced reactive synaptogenesis in the neonatal CNS

Neonatal damage to the trigeminal nerve leads to "reactive synaptogenesis" in the brain stem sensory trigeminal nuclei. In vitro models of brain injury-induced synaptogenesis have implicated an important role for astrocytes. In this study we tested the role of astrocyte function in reactive synaptogenesis in the trigeminal principal nucleus (PrV) of neonatal rats following unilateral transection of the infraorbital (IO) branch of the trigeminal nerve. We used electrophysiological multiple input index analysis (MII) to estimate the number of central trigeminal afferent fibers that converge onto single barrelette neurons. In the developing PrV, about 30% of afferent connections are eliminated within 2 postnatal weeks. After neonatal IO nerve damage, multiple trigeminal inputs (2.7 times that of the normal inputs) converge on single barrelette cells within 3-5 days; they remain stable up to the second postnatal week. Astrocyte proliferation and upregulation of astrocyte-specific proteins (GFAP and ALDH1L1) accompany reactive synaptogenesis in the IO nerve projection zone of the PrV. Pharmacological blockade of astrocyte function, purinergic receptors, and thrombospondins significantly reduced or eliminated reactive synaptogenesis without changing the MII in the intact PrV. GFAP immunohistochemistry further supported these electrophysiological results. We conclude that immature astrocytes, purinergic receptors, and thrombospondins play an important role in reactive synaptogenesis in the peripherally deafferented neonatal PrV.

Emerging role of extracellular nucleotides and adenosine in multiple sclerosis

Extracellular nucleotides and adenosine play important roles in inflammation. These signaling molecules interact with the cell-surface-located P2 and P1 receptors, respectively, that are widely distributed in the central nervous system and generally exert opposite effects on immune responses. Indeed, extracellular ATP, ADP, UTP, and UDP serve as alarmins or damage-associated molecular patterns that activate mainly proinflammatory mechanisms, whereas adenosine has potent anti-inflammatory and immunosuppressive effects. This review discusses the actual and potential role of extracellular nucleotides and adenosine in multiple sclerosis (MS).

ALS: focus on purinergic signalling

Amyotrophic lateral sclerosis (ALS) is one of the most common neuromuscular diseases. It is devastating and fatal, causing progressive paralysis of all voluntary muscles and eventually death, while sparing cognitive functions. A pathological hallmark of ALS is neuroinflammation mediated by non-neuronal cells in the nervous system, such as microglia and astrocytes that accelerate the disease progression. Scientists have neither found a unique key mechanism, nor an effective treatment against ALS, supposedly because it is a multi-factorial and multi-systemic disease. Extracellular purines and pyrimidines are widespread and powerful physiopathological molecules, signalling to most cell types and directing cell-to-cell communication networks. They are instrumental for instance for neurotransmission, muscle contraction and immune surveillance. Recent work has reported the crucial involvement of purinergic pathways in many neurodegenerative and neuroinflammatory diseases, comprising ALS. Especially P2 receptors for ATP, P1 receptors for adenosine, and nucleotide transporters were found to be modulated in ALS cells and tissues, playing a potential role in the disease. Given the composite cellular cross-talk occurring during ALS and the established action of extracellular purines/pyrimidines as neuron-to-glia alarm signal in the nervous system, a mutual query in these two fields should now be whether, how and when purinergic would meet ALS. In this review, we will highlight the early cellular and molecular purinergic cross-talk that participates to ALS etiopathology, with the conviction that better understanding of purinergic dynamics might provide original research perspectives, stimulate alternative disease modelling, and the design and testing of more powerful targeted therapeutics against this relentlessly progressive disorder.

The P2 receptor antagonist PPADS supports recovery from experimental stroke in vivo

BACKGROUND

After ischemia of the CNS, extracellular adenosine 5'-triphosphate (ATP) can reach high concentrations due to cell damage and subsequent increase of membrane permeability. ATP may cause cellular degeneration and death, mediated by P2X and P2Y receptors.

METHODOLOGY/PRINCIPAL FINDINGS

The effects of inhibition of P2 receptors by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on electrophysiological, functional and morphological alterations in an ischemia model with permanent middle cerebral artery occlusion (MCAO) were investigated up to day 28. Spontaneously hypertensive rats received PPADS or vehicle intracerebroventricularly 15 minutes prior MCAO for up to 7 days. The functional recovery monitored by qEEG was improved by PPADS indicated by an accelerated recovery of ischemia-induced qEEG changes in the delta and alpha frequency bands along with a faster and sustained recovery of motor impairments. Whereas the functional improvements by PPADS were persistent at day 28, the infarct volume measured by magnetic resonance imaging and the amount of TUNEL-positive cells were significantly reduced by PPADS only until day 7. Further, by immunohistochemistry and confocal laser scanning microscopy, we identified both neurons and astrocytes as TUNEL-positive after MCAO.

CONCLUSION

The persistent beneficial effect of PPADS on the functional parameters without differences in the late (day 28) infarct size and apoptosis suggests that the early inhibition of P2 receptors might be favourable for the maintenance or early reconstruction of neuronal connectivity in the periinfarct area after ischemic incidents.

Glutamate and ATP signalling in white matter pathology

Excessive signalling by excitatory neurotransmitters like glutamate and ATP can be deleterious to neurons and oligodendroglia, and cause disease. In particular, sustained activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainate and N-methyl-d-aspartate (NMDA) receptors damages oligodendrocytes, a feature that depends entirely on Ca(2+) overload of the cytoplasm and that can be initiated by disruption of glutamate homeostasis. Thus, inhibition of glutamate uptake by activated microglia can compromise glutamate homeostasis and induce oligodendrocyte excitotoxicity. Moreover, non-lethal, brief activation of kainate receptors in oligodendrocytes rapidly sensitizes these cells to complement attack as a consequence of oxidative stress. In addition to glutamate, ATP signalling can directly trigger oligodendrocyte excitotoxicity via activation of Ca(2+) -permeable P2X7 purinergic receptors, which mediates ischaemic damage to white matter (WM) and causes lesions that are reminiscent of multiple sclerosis (MS) plaques. Conversely, blockade of P2X7 receptors attenuates post-ischaemic injury to WM and ameliorates chronic experimental autoimmune encephalomyelitis, a model of MS. Importantly, P2X7 expression is elevated in normal-appearing WM in patients with MS, suggesting that signalling through this receptor in oligodendrocytes may be enhanced in this disease. Altogether, these observations reveal novel mechanisms by which altered glutamate and ATP homeostasis can trigger oligodendrocyte death. This review aims at summarizing current knowledge about the mechanisms leading to WM damage as a consequence of altered neurotransmitter signalling, and their relevance to disease. This knowledge will generate new therapeutic avenues to treat more efficiently acute and chronic WM pathology.