Structural and Functional Basis for Understanding the Biological Significance of P2X7 Receptor

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.

Unravelling the complexities of non-alcoholic steatohepatitis: The role of metabolism, transporters, and herb-drug interactions

Nonalcoholic fatty liver disease (NAFLD) is a mainstream halting liver disease with high prevalence in North America, Europe, and other world regions. It is an advanced form of NAFLD caused by the amassing of fat in the liver and can progress to the more severe form known as non-alcoholic steatohepatitis (NASH). Until recently, there was no authorized pharmacotherapy reported for NASH, and to improve the patient's metabolic syndrome, the focus is mainly on lifestyle modification, weight loss, ensuring a healthy diet, and increased physical activity; however, the recent approval of Rezdiffra (Resmetirom) by the US FDA may change this narrative. As per the reported studies, there is an increased articulation of uptake and efflux transporters of the liver, including OATP and MRP, in NASH, leading to changes in the drug's pharmacokinetic properties. This increase leads to alterations in the pharmacokinetic properties of drugs. Furthermore, modifications in Cytochrome P450 (CYP) enzymes can have a significant impact on these properties. Xenobiotics are metabolized primarily in the liver and constitute liver enzymes and transporters. This review aims to delve into the role of metabolism, transport, and potential herb-drug interactions in the context of NASH.

Intrathecal Fumagillin Alleviates Chronic Neuropathy-Induced Nociceptive Sensitization and Modulates Spinal Astrocyte-Neuronal Glycolytic and Angiogenic Proteins

Nociceptive sensitization is accompanied by the upregulation of glycolysis in the central nervous system in neuropathic pain. Growing evidence has demonstrated glycolysis and angiogenesis to be related to the inflammatory processes. This study investigated whether fumagillin inhibits neuropathic pain by regulating glycolysis and angiogenesis. Fumagillin was administered through an intrathecal catheter implanted in rats with chronic constriction injury (CCI) of the sciatic nerve. Nociceptive, behavioral, and immunohistochemical analyses were performed to evaluate the effects of the inhibition of spinal glycolysis-related enzymes and angiogenic factors on CCI-induced neuropathic pain. Fumagillin reduced CCI-induced thermal hyperalgesia and mechanical allodynia from postoperative days (POD) 7 to 14. The expression of angiogenic factors, vascular endothelial growth factor (VEGF) and angiopoietin 2 (ANG2), increased in the ipsilateral lumbar spinal cord dorsal horn (SCDH) following CCI. The glycolysis-related enzymes, pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA) significantly increased in the ipsilateral lumbar SCDH following CCI on POD 7 and 14 compared to those in the control rats. Double immunofluorescence staining indicated that VEGF and PKM2 were predominantly expressed in the astrocytes, whereas ANG2 and LDHA were predominantly expressed in the neurons. Intrathecal infusion of fumagillin significantly reduced the expression of angiogenic factors and glycolytic enzymes upregulated by CCI. The expression of hypoxia-inducible factor-1α (HIF-1α), a crucial transcription factor that regulates angiogenesis and glycolysis, was also upregulated after CCI and inhibited by fumagillin. We concluded that intrathecal fumagillin may reduce the expression of ANG2 and LDHA in neurons and VEGF and PKM2 in the astrocytes of the SCDH, further attenuating spinal angiogenesis in neuropathy-induced nociceptive sensitization. Hence, fumagillin may play a role in the inhibition of peripheral neuropathy-induced neuropathic pain by modulating glycolysis and angiogenesis.

P2X7 receptors and pannexin1 hemichannels shape presynaptic transmission

Over the last decades, since the discovery of ATP as a transmitter, accumulating evidence has been reported about the role of this nucleotide and purinergic receptors, in particular P2X7 receptors, in the modulation of synaptic strength and plasticity. Purinergic signaling has emerged as a crucial player in orchestrating the molecular interaction between the components of the tripartite synapse, and much progress has been made in how this neuron-glia interaction impacts neuronal physiology under basal and pathological conditions. On the other hand, pannexin1 hemichannels, which are functionally linked to P2X7 receptors, have appeared more recently as important modulators of excitatory synaptic function and plasticity under diverse contexts. In this review, we will discuss the contribution of ATP, P2X7 receptors, and pannexin hemichannels to the modulation of presynaptic strength and its impact on motor function, sensory processing, synaptic plasticity, and neuroglial communication, with special focus on the P2X7 receptor/pannexin hemichannel interplay. We also address major hypotheses about the role of this interaction in physiological and pathological circumstances.

Functional role of P2X7 purinergic receptor in cancer and cancer-related pain

Numerous studies have revealed that the ATP-gated ion channel purinergic 2X7 receptor (P2X7R) plays an important role in tumor progression and the pathogenesis of cancer pain. P2X7R requires activation by extracellular ATP to perform its regulatory role functions. During tumor development or cancer-induced pain, ATP is released from tumor cells or other cells in the tumor microenvironment (such as tumor-associated immune cells), which activates P2X7R, opens ion channels on the cell membrane, affects intracellular molecular metabolism, and regulates the activity of tumor cells. Furthermore, peripheral organs and receptors can be damaged during tumor progression, and P2X7R expression in nerve cells (such as microglia) is significantly upregulated, enhancing sensory afferent information, sensitizing the central nervous system, and inducing or exacerbating pain. These findings reveal that the ATP-P2X7R signaling axis plays a key regulatory role in the pathogenesis of tumors and cancer pain and also has a therapeutic role. Accordingly, in this study, we explored the role of P2X7R in tumors and cancer pain, discussed the pharmacological properties of inhibiting P2X7R activity (such as the use of antagonists) or blocking its expression in the treatment of tumor and cancer pain, and provided an important evidence for the treatment of both in the future.

The role of the purinergic ligand-gated ion channel 7 receptor in common digestive system cancers

The incidence of digestive malignancies has increased in recent years, including colorectal cancer (CRC), hepatocellular carcinoma (HCC) and pancreatic cancer. Advanced stages of these cancers are prone to metastasis, which seriously reduce the standard of living of patients and lead to decline in the survival rate of patients. So far there are no good specific drugs to stop this phenomenon. It is very important and urgent to find new biomarkers and therapeutic targets. Purinergic ligand-gated ion channel 7 receptor (P2X7R) is ATP-gated and nonselective ion channel receptor involved in many inflammatory processes and cancer progression. P2X7R is present in many cancer cells and promotes or inhibits cancer development through signal transduction. Studies have presented that P2X7R plays a role in the proliferation and migration of digestive system cancers, such as CRC, HCC and pancreatic cancer. Therefore, P2X7R may serve as a biomarker or therapeutic target for digestive system cancers. This paper describes the structure and function of P2X7R, and mainly reviews the research progress on the role of P2X7R in CRC, HCC and pancreatic cancer.

Role and therapeutic targets of P2X7 receptors in neurodegenerative diseases

The P2X7 receptor (P2X7R), a non-selective cation channel modulated by adenosine triphosphate (ATP), localizes to microglia, astrocytes, oligodendrocytes, and neurons in the central nervous system, with the most incredible abundance in microglia. P2X7R partake in various signaling pathways, engaging in the immune response, the release of neurotransmitters, oxidative stress, cell division, and programmed cell death. When neurodegenerative diseases result in neuronal apoptosis and necrosis, ATP activates the P2X7R. This activation induces the release of biologically active molecules such as pro-inflammatory cytokines, chemokines, proteases, reactive oxygen species, and excitotoxic glutamate/ATP. Subsequently, this leads to neuroinflammation, which exacerbates neuronal involvement. The P2X7R is essential in the development of neurodegenerative diseases. This implies that it has potential as a drug target and could be treated using P2X7R antagonists that are able to cross the blood-brain barrier. This review will comprehensively and objectively discuss recent research breakthroughs on P2X7R genes, their structural features, functional properties, signaling pathways, and their roles in neurodegenerative diseases and possible therapies.

Characterization of Common Genetic Variants in P2RX7 and Their Contribution to Chronic Pain Conditions

The adenosine triphosphate (ATP)-gated channel P2X7 is encoded by a gene enriched for common nonsynonymous variants. Many of these variants have functional cellular effects, and some have been implicated in chronic pain. In this study, we first systematically characterized all 17 common nonsynonymous variants using whole-cell patch clamp electrophysiology. Then, we analyzed these variants for statistical association with chronic pain phenotypes using both individual P2RX7 variants as predictors and cumulative allele counts of same-direction cellular effect in univariate models. Association and validation analyses were conducted in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) cohort (N = 3260) and in the Complex Persistent Pain Conditions (CPPC) cohort (N = 900), respectively. Our results showed an association between allele A of rs7958311 and an increased risk of chronic pelvic pain, with convergent evidence for contribution to fibromyalgia and irritable bowel syndrome, confirmed in a meta-analysis. This allelic variant produced a unique cellular phenotype: a gain-of-function in channel opening, and a loss-of-function in pore opening. A computational study using a 12-state Markov model of ATP binding to the P2X7 receptor suggested that this cellular phenotype arises from an increased ATP binding affinity and an increased open channel conductance combined with a loss of sensitization. Cumulative allele count analysis did not provide additional insights. In conclusion, our results go beyond reproducing association for rs7958311 with chronic pain and suggest that its unique combination of gain-of-function in channel and loss-of-function in pore activity may explain why it is likely the only common P2RX7 variant with contribution to chronic pain. PERSPECTIVE: This study characterizes all common P2RX7 variants using cellular assays and statistical association analyses with chronic pain, with Markov state modeling of the most robustly associated variant.

Role of the P2 × 7 receptor in neurodegenerative diseases and its pharmacological properties

Neurodegenerative diseases seriously affect patients' physical and mental health, reduce their quality of life, and impose a heavy burden on society. However, their treatment remains challenging. Therefore, exploring factors potentially related to the pathogenesis of neurodegenerative diseases and improving their diagnosis and treatment are urgently needed. Recent studies have shown that P2 × 7R plays a crucial role in regulating neurodegenerative diseases caused by neuroinflammation. P2 × 7R is an adenosine 5'-triphosphate ligand-gated cation channel receptor present in most tissues of the human body. An increase in P2 × 7R levels can affect the progression of neurodegenerative diseases, and the inhibition of P2 × 7R can alleviate neurodegenerative diseases. In this review, we comprehensively describe the biological characteristics (structure, distribution, and function) of this gene, focusing on its potential association with neurodegenerative diseases, and we discuss the pharmacological effects of drugs (P2 × 7R inhibitors) used to treat neurodegenerative diseases.

Indoleamine 2,3-dioxygenase controls purinergic receptor-mediated ischemia-reperfusion injury in renal tubular epithelial cells

OBJECTIVES

Ischemia-reperfusion (I-R) injury is the most common cause of acute kidney injury (AKI). Experimental studies have shown that indoleamine 2,3-dioxygenase 1 (IDO) and the purinergic receptor P2X7 contribute to kidney I-R injury. We evaluated whether there is an interplay between IDO and P2X7 in the pathogenesis of I-R injury.

METHODS

Primary renal proximal tubular epithelial cells (RPTECs) were subjected to anoxia or reoxygenation with or without specific inhibitors. Cell imaging, colorimetric assays, and Western blotting were used.

RESULTS

Cell imaging revealed that inhibition of IDO, or all the purinergic receptors with an ATPase, or specific inhibition of P2X7 rescued the cells from anoxia or reoxygenation-induced cell death. This was confirmed with LDH release assay, which also detected the ferroptotic nature of cell death due to reoxygenation. On the contrary, activated cleaved caspase 3 increased during anoxia, showing that apoptosis prevails. All the aforementioned treatments prevented caspase increase. Both anoxia and reoxygenation increased extracellular ATP, IDO, and P2X7 expression. IDO remained unaffected by the above-mentioned treatments. On the contrary, treatment with apyrase or inhibition of P2X7decreased extracellular ATP and P2X7 expression, which are also decreased by inhibition of IDO. The first indicates a positive feedback loop regarding P2X7 activation, expression and function, while the latter implies that IDO controls P2X7 expression.

CONCLUSIONS

In RPRECs subjected to anoxia or reoxygenation, IDO is upregulated, increasing P2X7 and contributing to anoxia or reoxygenation-induced cell death. Clarifying the molecular mechanisms implicated in kidney I-R injury is of particular interest since it may lead to new therapeutic strategies against AKI.

Tumour immune escape via P2X7 receptor signalling

While P2X7 receptor expression on tumour cells has been characterized as a promotor of cancer growth and metastasis, its expression by the host immune system is central for orchestration of both innate and adaptive immune responses against cancer. The role of P2X7R in anti-tumour immunity is complex and preclinical studies have described opposing roles of the P2X7R in regulating immune responses against tumours. Therefore, few P2X7R modulators have reached clinical testing in cancer patients. Here, we review the prognostic value of P2X7R in cancer, how P2X7R have been targeted to date in tumour models, and we discuss four aspects of how tumours skew immune responses to promote immune escape via the P2X7R; non-pore functional P2X7Rs, mono-ADP-ribosyltransferases, ectonucleotidases, and immunoregulatory cells. Lastly, we discuss alternative approaches to offset tumour immune escape via P2X7R to enhance immunotherapeutic strategies in cancer patients.

The antidepressant effect of short- and long-term zinc exposition is partly mediated by P2X7 receptors in male mice

Background: As a member of the purinergic receptor family, divalent cation-regulated ionotropic P2X7 (P2rx7) plays a role in the pathophysiology of psychiatric disorders. This study aimed to investigate whether the effects of acute zinc administration and long-term zinc deprivation on depression-like behaviors in mice are mediated by P2X7 receptors. Methods: The antidepressant-like effect of elevated zinc level was studied using a single acute intraperitoneal injection in C57BL6/J wild-type and P2rx7 gene-deficient (P2rx7 -/-) young adult and elderly animals in the tail suspension test (TST) and the forced swim test (FST). In the long-term experiments, depression-like behavior caused by zinc deficiency was investigated with the continuous administration of zinc-reduced and control diets for 8 weeks, followed by the same behavioral tests. The actual change in zinc levels owing to the treatments was examined by assaying serum zinc levels. Changes in monoamine and brain-derived neurotrophic factor (BDNF) levels were measured from the hippocampus and prefrontal cortex brain areas by enzyme-linked immunosorbent assay and high-performance liquid chromatography, respectively. Results: A single acute zinc treatment increased the serum zinc level evoked antidepressant-like effect in both genotypes and age groups, except TST in elderly P2rx7 -/- animals, where no significant effect was detected. Likewise, the pro-depressant effect of zinc deprivation was observed in young adult mice in the FST and TST, which was alleviated in the case of the TST in the absence of functional P2X7 receptors. Among elderly mice, no pro-depressant effect was observed in P2rx7 -/- mice in either tests. Treatment and genotype changes in monoamine and BDNF levels were also detected in the hippocampi. Conclusion: Changes in zinc intake were associated with age-related changes in behavior in the TST and FST. The antidepressant-like effect of zinc is partially mediated by the P2X7 receptor.

The P2X7 Receptor in Autoimmunity

The P2X7 receptor (P2X7R) is an ATP-gated nonselective cationic channel that, upon intense stimulation, can progress to the opening of a pore permeable to molecules up to 900 Da. Apart from its broad expression in cells of the innate and adaptive immune systems, it is expressed in multiple cell types in different tissues. The dual gating property of P2X7R is instrumental in determining cellular responses, which depend on the expression level of the receptor, timing of stimulation, and microenvironmental cues, thus often complicating the interpretation of experimental data in comprehensive settings. Here we review the existing literature on P2X7R activity in autoimmunity, pinpointing the different functions in cells involved in the immunopathological processes that can make it difficult to model as a druggable target.

Inhibition of Galectins and the P2X7 Purinergic Receptor as a Therapeutic Approach in the Neurovascular Inflammation of Diabetic Retinopathy

Diabetic retinopathy (DR) is the most frequent microvascular retinal complication of diabetic patients, contributing to loss of vision. Recently, retinal neuroinflammation and neurodegeneration have emerged as key players in DR progression, and therefore, this review examines the neuroinflammatory molecular basis of DR. We focus on four important aspects of retinal neuroinflammation: (i) the exacerbation of endoplasmic reticulum (ER) stress; (ii) the activation of the NLRP3 inflammasome; (iii) the role of galectins; and (iv) the activation of purinergic 2X7 receptor (P2X7R). Moreover, this review proposes the selective inhibition of galectins and the P2X7R as a potential pharmacological approach to prevent the progression of DR.

P2X7 Receptor in microglia contributes to propofol-induced unconsciousness by regulating synaptic plasticity in mice

Propofol infusion is processed through the wake-sleep cycle in neural connections, and the ionotropic purine type 2X7 receptor (P2X7R) is a nonspecific cation channel implicated in sleep regulation and synaptic plasticity through its regulation of electric activity in the brain. Here, we explored the potential roles of P2X7R of microglia in propofol-induced unconsciousness. Propofol induced loss of the righting reflex in male C57BL/6 wild-type mice and increased spectral power of the slow wave and delta wave of the medial prefrontal cortex (mPFC), all of which were reversed with P2X7R antagonist A-740003 and strengthened with P2X7R agonist Bz-ATP. Propofol increased the P2X7R expression level and P2X7R immunoreactivity with microglia in the mPFC, induced mild synaptic injury and increased GABA release in the mPFC, and these changes were less severe when treated with A-740003 and were more obvious when treated with Bz-ATP. Electrophysiological approaches showed that propofol induced a decreased frequency of sEPSCs and an increased frequency of sIPSCs, A-740003 decrease frequency of sEPSCs and sIPSCs and Bz-ATP increase frequency of sEPSCs and sIPSCs under propofol anesthesia. These findings indicated that P2X7R in microglia regulates synaptic plasticity and may contribute to propofol-mediated unconsciousness.

Roles of inflammasomes in viral myocarditis

Viral myocarditis (VMC), characterized by viral infection-induced inflammation, is a life-threatening disease associated with dilated cardiomyopathy or heart failure. Innate immunity plays a crucial role in the progression of inflammation, in which inflammasomes provide a platform for the secretion of cytokines and mediate pyroptosis. Inflammasomes are rising stars gaining increasing attention. The nucleotide oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, the caspase recruitment domain-containing protein 8 (CARD8) inflammasome, and the caspase-11 inflammasome are three inflammasomes that were reported to affect the process and prognosis of VMC. These inflammasomes can be activated by a wide range of cellular events. Accumulating evidence has suggested that inflammasomes are involved in different stages of VMC, including the trigger and progression of myocardial injury and remodeling after infection. In this review, we summarized the pathways involving inflammasomes in VMC and discussed the potential therapies targeting inflammasomes and related pathways.

Research progress on the P2X7 receptor in liver injury and hepatocellular carcinoma

Purinergic ligand-gated ion channel 7 receptor (P2X7 receptor) is an adenosine triphosphate (ATP)-gated ion channel that is widely distributed on the surfaces of immune cells and tissues such as those in the liver, kidney, lung, intestine, and nervous system. Hepatocellular carcinoma (HCC) is one of the most common malignancies with increasing incidence and mortality. Although many treatments for liver cancer have been studied, the prognosis for liver cancer is still very poor. Therefore, new liver cancer treatments are urgently needed. P2X7 receptor activation can secrete proinflammatory factors through the P2X7 receptor-NLRP3 signaling pathway, thereby affecting the progression of liver injury. The P2X7 receptor may be a target for growth inhibition of HCC cells and may affect the invasion and migration of HCC cells through the PI3K/AKT and AMPK signaling pathways. In recent years, P2X7 receptor antagonists or inhibitors have attracted widespread attention as therapeutic targets for hepatocellular carcinoma and liver injury. Therefore, this review covers the basic concepts of the P2X7 receptor and role of the P2X7 receptor in liver cancer and liver injury, providing new potential therapeutic targets for hepatocellular carcinoma and liver injury.

Research Progress in the Relationship Between P2X7R and Cervical Cancer

Cervical cancer is one of the most common and serious tumors in women. Finding new biomarkers and therapeutic targets plays an important role in the diagnosis, prognosis, and treatment of cervical cancer. Purinergic ligand-gated ion channel 7 receptor (P2X7R) is a purine ligand cation channel, activated by adenosine triphosphate (ATP). Studies have shown that P2X7R plays an important role in a variety of diseases and cancers. More and more studies have shown that P2X7R is also closely related to cervical cancer; therefore, the role of P2X7R in the development of cervical cancer deserves further discussion. The expression level of P2X7R in uterine epithelial cancer tissues was lower than that of the corresponding normal tissues. P2X7R plays an important role in the apoptotic process of cervical cancer through various mechanisms of action, and both antagonists and agonists of P2X7R can inhibit the proliferation of cervical cancer cells, while P2X7R is involved in the antitumor effect of Atr-I on cervical cancer cells. This review evaluates the current role of P2X7R in cervical cancer in order to develop more specific therapies for cervical cancer. In conclusion, P2X7R may become a biomarker for cervical cancer screening, and even a new target for clinical treatment of cervical cancer.

Spotlight on P2X7 Receptor PET Imaging: A Bright Target or a Failing Star?

The homotrimeric P2X7 receptor (P2X7R) is expressed by virtually all cells of the innate and adaptive immune system and plays a crucial role in various pathophysiological processes such as autoimmune and neurodegenerative diseases, inflammation, neuropathic pain and cancer. Consequently, the P2X7R is considered a promising target for therapy and diagnosis. As the development of tracers comes hand-in-hand with the development of potent and selective receptor ligands, there is a rising number of PET tracers available in preclinical and clinical studies. This review analyzes the development of P2X7R positron emission tomography (PET) tracers and their potential in various PET imaging applications.

Abacavir causes leukocyte/platelet crosstalk by activating neutrophil P2X7 receptors thus releasing soluble lectin-like oxidized low-density lipoprotein receptor-1

BACKGROUND AND PURPOSE

Abacavir, an antiretroviral drug used in HIV therapy associated with myocardial infarction, promotes thrombosis through P2X7 receptors. The role of platelets as pro-thrombotic cells is acknowledged whereas that of neutrophils-due to their secretory capacity-is gaining recognition. This study analyses the role of neutrophils-specifically the secretome of abacavir-treated neutrophils (SN_ABC )-in platelet activation that precedes thrombosis.

EXPERIMENTAL APPROACH

Effects of abacavir or SN_ABC on platelet activation and platelet-leukocyte interactions and expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) were analysed by flow cytometry. The secretome was analysed by proteomics. The role of leukocytes in the actions of abacavir was evaluated in a mouse model of thrombosis.

KEY RESULTS

Abacavir induced platelet-leukocyte interactions, not directly via effects of abacavir on platelets, but via activation of neutrophils, which triggered interactions between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1 (PSGL-1). SN_ABC stimulated platelet activation and platelet-leukocyte interactions through a process that was dependent on LOX-1, neutrophil P2X7 and platelet P2Y1, P2Y12 and P2X1 receptors. Abacavir induced the expression of LOX-1 on neutrophils and of the soluble form of LOX-1 (sLOX-1) in SN_ABC . Neutrophils, LOX-1, P2X7, P2Y1, P2Y12 and P2X1 receptors were required for the pro-thrombotic actions of abacavir in vivo.

CONCLUSION AND IMPLICATIONS

Neutrophils are target cells in abacavir-induced thrombosis. Abacavir released sLOX-1 from neutrophils via activation of their P2X7 receptors, which in turn activated platelets. Hence, sLOX-1 could be the missing link in the cardiovascular risk associated with abacavir.

Purinergic ionotropic P2X7 and metabotropic glutamate mGlu5 receptors crosstalk influences pro-inflammatory conditions in microglia

Microglia represent the resident immune system in the brain. They mediate neuroinflammatory processes and have been described as important regulators of homeostasis in the central nervous system (CNS). Among several players and mechanisms contributing to microglial function in inflammation, ATP and glutamate have been shown to be involved in microgliosis. In this study, we focused on receptor subtypes that respond to these neurotransmitters, purinergic ionotropic P2X7 receptor and metabotropic glutamate mGlu₅ receptor. We found that both receptors are functionally expressed in a murine microglia cell line, BV2 cells, and we performed patch-clamp experiments to measure purinergic ionotropic P2X7 receptor ion flux in control condition and after metabotropic glutamate mGlu₅ receptor activation. The selective purinergic ionotropic P2X7 receptor agonist, 2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate (BzATP, 100 μM), elicited a robust current that was prevented by the selective purinergic ionotropic P2X7 receptor antagonist A438079 (10 μM). When BV2 cells were acutely stimulated with the selective metabotropic glutamate mGlu₅ agonist, (RS)-2-chloro-5-hydroxyphenylglycine (CHPG, 200 μM), purinergic ionotropic P2X7 receptor current was increased. This positive modulation was prevented by the selective metabotropic glutamate mGlu₅ receptor antagonist 3-((2-Methyl-4-thiazolyl)ethynyl)pyridine (MTEP, 1 μM). Moreover, nitric oxide synthesis elicited by purinergic ionotropic P2X7 receptor activation was enhanced by metabotropic glutamate mGlu₅ receptor co-stimulation. Taken together, our results suggest an important crosstalk between ATP and glutamate in inflammation. Pro-inflammatory effects mediated by purinergic ionotropic P2X7 receptor might be exacerbated by simultaneous exposure of microglia to ATP and glutamate, suggesting new pharmacological targets to modulate neuroinflammation.

Hypoxia-inducible factor 1 alpha (HIF-1α) stimulated and P2X7 receptor activated by COVID-19, as a potential therapeutic target and risk factor for epilepsy

Based on available evidence, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a neuroinvasive virus. According to the centers for disease control and prevention (CDC), coronavirus disease 2019 (COVID-19) may cause epilepsy. In this line, COVID-19 can stimulate hypoxia-inducible factor-1 alpha (HIF-1α) and activate P2X7 receptor. Both HIF-1α and P2X7 receptors are linked to epileptogenesis and seizures. Therefore, in the current study, we suggested that COVID-19 may have a role in epileptogenesis and seizure through HIF-1α stimulation and P2X7 receptor activation. Consequently, pharmacological targeting of these factors could be a promising therapeutic approach for such patients.

Pyroptosis and Its Role in Autoimmune Disease: A Potential Therapeutic Target

Autoimmune diseases are a group of heterogeneous diseases with diverse clinical manifestations that can be divided into systemic and organ-specific. The common etiology of autoimmune diseases is the destruction of immune tolerance and the production of autoantibodies, which attack specific tissues and/or organs in the body. The pathogenesis of autoimmune diseases is complicated, and genetic, environmental, infectious, and even psychological factors work together to cause aberrant innate and adaptive immune responses. Although the exact mechanisms are unclear, recently, excessive exacerbation of pyroptosis, as a bond between innate and adaptive immunity, has been proven to play a crucial role in the development of autoimmune disease. Pyroptosis is characterized by pore formation on cell membranes, as well as cell rupture and the excretion of intracellular contents and pro-inflammatory cytokines, such as IL-1β and IL-18. This overactive inflammatory programmed cell death disrupts immune system homeostasis and promotes autoimmunity. This review examines the molecular structure of classical inflammasomes, including NLRP3, AIM2, and P2X7-NLRP3, as the switches of pyroptosis, and their molecular regulation mechanisms. The sophisticated pyroptosis pathways, including the canonical caspase-1-mediated pathway, the noncanonical caspase-4/5/11-mediated pathway, the emerging caspase-3-mediated pathway, and the caspase-independent pathway, are also described. We highlight the recent advances in pyroptosis in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, Sjögren's syndrome and dermatomyositis, and attempt to identify its potential advantages as a therapeutic target or prognostic marker in these diseases.

The Role of Purinergic P2X7 Receptor in Inflammation and Cancer: Novel Molecular Insights and Clinical Applications

The purinergic P2X7 receptor (P2X7R) is a transmembrane protein whose expression has been related to a variety of cellular processes, while its dysregulation has been linked to inflammation and cancer. P2X7R is expressed in cancer and immune system cell surfaces. ATP plays a key role in numerous metabolic processes due to its abundance in the tumour microenvironment. P2X7R plays an important role in cancer by interacting with ATP. The unusual property of P2X7R is that stimulation with low doses of ATP causes the opening of a permeable channel for sodium, potassium, and calcium ions, whereas sustained stimulation with high doses of ATP favours the formation of a non-selective pore. The latter effect induces a change in intracellular homeostasis that leads to cell death. This evidence suggests that P2X7R has both pro- and anti-tumour proprieties. P2X7R is increasingly recognised as a regulator of inflammation. In this review, we aimed to describe the most relevant characteristics of P2X7R function, activation, and its ligands, while also summarising the role of P2X7R activation in the context of inflammation and cancer. The currently used therapeutic approaches and clinical trials of P2X7R modulators are also described.

Purinergic P2 receptors: Involvement and therapeutic implications in diabetes-related glomerular injury

The purinergic activation of P2 receptors initiates a powerful and rapid signaling cascade that contributes to the regulation of an array of physiological and pathophysiological processes in many organs, including the kidney. P2 receptors are broadly distributed in both epithelial and vascular renal cells. Disturbances of purinergic signaling can lead to impairments in renal function. A growing body of evidence indicates changes in P2 receptor expression and nucleotide metabolism in chronic renal injury and inflammatory diseases. Increasing attention has focused on purinergic P2X7 receptors, which are not normally expressed in healthy kidney tissue but are highly expressed at sites of tissue damage and inflammation. Under hyperglycemic conditions, several mechanisms that are linked to purinergic signaling and involve nucleotide release and degradation are disrupted, resulting in the accumulation of adenosine 5'-triphosphate in the bloodstream in diabetes. Dysfunction of the purinergic system might be associated with serious vascular complications in diabetes, including diabetic nephropathy. This review summarizes our current knowledge of the role of P2 receptors in diabetes-related glomerular injury and its implications for new therapeutics for diabetic nephropathy.

Function of the P2X7 receptor in hematopoiesis and leukemogenesis

Adenosine triphosphate (ATP) accumulates at tissue injury and inflammation sites. The P2X7 receptor is an ATP-gated ion channel known for its cytotoxic activity. However, P2X7 receptors also play important roles in the growth of cancer and the immune regulation. Functional P2X7 receptor is widely expressed in murine and human hematopoietic stem cells and their lineages, including monocytes, macrophages, mast cells, and B or T lymphocytes, and participates in various physiological and pathologic activities. Therefore, it is not surprising that the P2X7 receptor is important for the normal hematopoiesis and leukemogenesis. Here, we summarize the biological functions of P2X7 receptor during both normal hematopoiesis and leukemogenesis. In particular, we found that ATP levels are dramatically increased in the leukemic bone marrow niche and the fates of leukemia-initiating cells of acute myeloid leukemia are tightly controlled by P2X7 expression and ATP-P2X7-mediated signaling pathways. These findings strongly indicate that the P2X7 receptor may be considered a potential biomarker of hematological malignancies in bone marrow niches, and its antagonists may be useful for the leukemia treatment in addition to the traditional chemotherapy.

The P2X7 purinergic receptor in intervertebral disc degeneration

Mechanisms involved in the development of intervertebral disc (IVD) degeneration are only partially known, thus making the implementation of effective therapies very difficult. In this study, we investigated P2X7 purinergic receptor (P2X7R), NLRP3 inflammasome, and interleukin (IL)-1β expression in IVD specimens at different stages of disease progression, and during the in vitro dedifferentiation process of the primary cells derived thereof. We found that P2X7R, NLRP3, and IL-1β expression was higher in the IVD samples at a more advanced stage of degeneration and in the expanded IVD cells in culture which partially recapitulated the in vivo degeneration process. In IVD cells, the P2X7R showed a striking nuclear localization, while NLRP3 was mainly cytoplasmic. Stimulation with the semiselective P2X7R agonist benzoyl ATP together with lipopolysaccharide treatment triggered P2X7R transfer to the cytoplasm and P2X7R/NLRP3 colocalization. Taken together, these findings support pathophysiological evidence that the degenerated disc is a highly inflamed microenvironment and highlight the P2X7R/NLRP3 axis as a suitable therapeutic target. The immunohistochemical analysis and the assessment of subcellular localization revealed a substantial expression of P2X7R also in normal disc tissue. This gives us the opportunity to contribute to the few studies performed in natively expressed human P2X7R so far, and to understand the possible physiological ATP-mediated P2X7R homeostasis signaling. Therefore, collectively, our findings may offer a new perspective and pave the way for the exploration of a role of P2X7R-mediated purinergic signaling in IVD metabolism that goes beyond its involvement in inflammation.

Cancer Metabostemness and Metabolic Reprogramming via P2X7 Receptor

The heterogeneity of tumor cell mass and the plasticity of cancer cell phenotypes in solid tumors allow for the insurgence of resistant and metastatic cells, responsible for cancer patients' clinical management's main challenges. Among several factors that are responsible for increased cancer aggression, metabolic reprogramming is recently emerging as an ultimate cancer hallmark, as it is central for cancer cell survival and self-renewal, metastasis and chemoresistance. The P2X7 receptor, whose expression is upregulated in many solid and hematological malignancies, is also emerging as a good candidate in cancer metabolic reprogramming and the regulation of stem cell proliferation and differentiation. Metabostemness refers to the metabolic reprogramming of cancer cells toward less differentiated (CSCs) cellular states, and we believe that there is a strong correlation between metabostemness and P2X7 receptor functions in oncogenic processes. Here, we summarize important aspects of P2X7 receptor functions in normal and tumor tissues as well as essential aspects of its structure, regulation, pharmacology and its clinical use. Finally, we review current knowledge implicating P2X7 receptor functions in cancer-related molecular pathways, in metabolic reprogramming and in metabostemness.

Abacavir Increases Purinergic P2X7 Receptor Activation by ATP: Does a Pro-inflammatory Synergism Underlie Its Cardiovascular Toxicity?

The cardiovascular toxicity of Abacavir is related to its purinergic structure. Purinergic P2X7-receptors (P2X7R), characterized by activation by high concentrations of ATP and with high plasticity, seem implicated. We appraise the nature of the interplay between Abacavir and P2X7R in generating vascular inflammation. The effects of Abacavir on leukocyte-endothelium interactions were compared with those of its metabolite carbovir triphosphate (CBV-TP) or ATP in the presence of apyrase (ATP-ase) or A804598 (P2X7R-antagonist). CBV-TP and ATP levels were evaluated by HPLC, while binding of Abacavir, CBV-TP and ATP to P2X7R was assessed by radioligand and docking studies. Hypersensitivity studies explored a potential allosteric action of Abacavir. Clinical concentrations of Abacavir (20 µmol/L) induced leukocyte-endothelial cell interactions by specifically activating P2X7R, but the drug did not show affinity for the P2X7R ATP-binding site (site 1). CBV-TP levels were undetectable in Abacavir-treated cells, while those of ATP were unaltered. The effects of Abacavir were Apyrase-dependent, implying dependence on endogenous ATP. Exogenous ATP induced a profile of proinflammatory actions similar to Abacavir, but was not entirely P2X7R-dependent. Docking calculations suggested ATP-binding to sites 1 and 2, and Abacavir-binding only to allosteric site 2. A combination of concentrations of Abacavir (1 µmol/L) and ATP (0.1 µmol/L) that had no effect when administered separately induced leukocyte-endothelium interactions mediated by P2X7R and involving Connexin43 channels. Therefore, Abacavir acts as a positive allosteric modulator of P2X7R, turning low concentrations of endogenous ATP themselves incapable of stimulating P2X7R into a functional proinflammatory agonist of the receptor.

P2X7 receptor: a critical regulator and potential target for breast cancer

Breast cancer is currently the most common cancer and the leading cause of cancer death among women worldwide. Advanced breast cancer is prone to metastasis, and there is currently no drug to cure metastatic breast cancer. The purinergic ligand-gated ion channel 7 receptor is an ATP-gated nonselective cation channel receptor and is involved in signal transduction, growth regulation, cytokine secretion, and tumor cell development. Recent studies have shown that upregulation of the P2X7 receptor in breast cancer can mediate AKT signaling pathways, Ca2 þ-activated SK3 potassium channels, and EMT and regulate the secretion of small extracellular vesicles to promote breast cancer invasion and migration, which are affected by factors such as hypoxia and ATP. In addition, studies have shown that microRNAs can bind to the 3' untranslated region of the P2X7 receptor, which affects the occurrence and development of breast cancer by upregulating and downregulating P2X7 receptor expression. Studies have shown that new P2X7 receptor inhibitors, such as emodin and Uncaria tomentosa, can inhibit P2X7 receptor-mediated breast cancer invasion and are expected to be used clinically. This article reviews the research progress on the relationship between the P2X7 receptor and breast cancer to provide new ideas and a basis for clinical diagnosis and treatment.