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

Role of Pyroptosis in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a serious chronic condition marked by persistent and recurrent intestinal ulcers. Although the exact cause of IBD remains unclear, it is generally accepted that a complex interaction among dietary factors, gut microbiota, and immune responses in genetically predisposed individuals contributes to its development. Pyroptosis, an inflammatory form of programmed cell death activated by inflammasomes, is marked by the rupture of cell membranes and the subsequent release of inflammatory mediators. Emerging evidence indicates that pyroptosis plays a crucial role in the pathogenesis of IBD. Moderate pyroptosis activation can enhance intestinal immune defenses, while excessive inflammasome activation can trigger an inflammatory cascade, resulting in increased damage to intestinal tissues. This article reviews the molecular mechanisms underlying pyroptosis and highlights its role in the onset and progression of IBD. Furthermore, We explore recent advancements in IBD treatment, focusing on small molecule compounds that specifically target and inhibit pyroptosis.

ATP-Gated P2X7-Ion Channel on Kidney-Resident Natural Killer T Cells and Memory T Cells in Intrarenal Inflammation

Key Points

Parenchymal T cells in the kidney expressed much higher levels of P2X7 than vascular T cells. P2X7-blocking nanobodies uncover a large fraction of kidney-resident natural killer T and tissue-resident memory T cells. These cells were lost during cell preparation because of activation of P2X7 by NAD+ released from damaged cells, unless blocked by nanobodies.

Background

The P2X7 ion channel, a key sensor of sterile inflammation, has been implicated as a therapeutic target in GN, and P2X7-antagonistic nanobodies can attenuate experimental GN. However, little is known about the expression of P2X7 on renal immune cells.

Methods

We used conventional immunofluorescence of kidney sections and intraperitoneal injection of nanobodies in mice followed by flow cytometry analysis of parenchymal T cells and RNA sequencing to elucidate the expression and function of P2X7 on parenchymal and vascular immune cells in the mouse kidney.

Results

Our study showed that parenchymal T cells, including a large subset of natural killer T cells and CD69+ tissue-resident memory T cells, display much higher cell surface levels of P2X7 than vascular T cells. After a single intraperitoneal injection of P2X7-blocking nanobodies, P2X7 on parenchymal T cells was fully occupied by the injected nanobodies within 30 minutes. This resulted in an effective protection of these cells from nicotinamide adenine dinucleotide–induced cell death during cell preparation. Conversely, systemic injection of nicotinamide adenine dinucleotide that mimics sterile inflammation results in the selective depletion of P2X7hiCD69hi T cells from the kidney parenchyma.

Conclusions

Our study uncovered a novel purinergic regulatory mechanism affecting kidney-resident T-cell populations.

Non-coding RNAs affecting NLRP3 inflammasome pathway in diabetic cardiomyopathy: a comprehensive review of potential therapeutic options

Cardiomyopathies are a heterogeneous group of disorders that can lead to fulminant heart failure and sudden cardiac death. In recent years, the prevalence of all types of cardiomyopathies has shown an upward trend globally. Up to 40% of patients with cardiomyopathy-related heart failure have diabetes mellitus (DM). With the fast global spread of DM, the prevalence of DCM is increasing accordingly and it remains the leading cause of morbidity and mortality in chronic diabetic patients. NLRP3 inflammasome significantly contributes to the development and pathological progression of DCM. Targeting the inflammasome or any of the mediators along its activation pathway provides new potential therapeutic targets for developing specialized drugs to treat DCM.In this comprehensive review, we sought to introduce and summarize the non-coding RNAs with potential therapeutic effects targeting NLRP3 inflammasome signaling in DCM. We hope this general overview can aid future research in developing new therapies for DCM.

Ligand-receptor interactions: A key to understanding microglia and astrocyte roles in epilepsy

Epilepsy continues to pose significant social and economic challenges on a global scale. Existing therapeutic approaches predominantly revolve around neurocentric mechanisms, and fail to control seizures in approximately one-third of patients. This underscores the pressing need for novel and complementary treatment approaches to address this gap. An increasing body of literature points to a role for glial cells, including microglia and astrocytes, in the pathogenesis of epilepsy. Notably, microglial cells, which serve as pivotal inflammatory mediators within the epileptic brain, have received increasing attention over recent years. These immune cells react to epileptogenic insults, regulate neuronal processes, and play diverse roles during the process of epilepsy development. Additionally, astrocytes, another integral non-neuronal brain cells, have garnered increasing recognition for their dynamic contributions to the pathophysiology of epilepsy. Their complex interactions with neurons and other glial cells involve modulating synaptic activity and neuronal excitability, thereby influencing the aberrant networks formed during epileptogenesis. This review explores the alterations in microglial and astrocytic function and their mechanisms of communication following an epileptogenic insult, examining their contribution to epilepsy development. By comprehensively studying these mechanisms, potential avenues could emerge for refining therapeutic strategies and ameliorating the impact of this complex neurological disease.

Synthesis and in vitro evaluation of novel compounds and discovery of a promising iodine-125 radioligand for purinergic P2X7 receptor (P2X7R)

The purinergic P2X ligand-gated ion channel 7 receptor (P2X7R) plays a critical role in various inflammatory processes and other diseases. Fast determination of compounds P2X7R binding potency and discovery of a promise PET radiotracer for imaging P2X7R require a P2X7R suitable radioligand for radioactive competitive binding assay. Herein, we designed and synthesized thirteen new P2X7R ligands and determined the in vitro binding potency. The fluorescence screening assay identified the iodide compound 1c with high potency and specificity toward P2X7R with an IC50 of 0.25 ± 0.05 nM. Therefore, 1c was 125I-labeled to afford [125I]1c with a good radiochemical yield (44 ± 12 %, n = 3) and high radiochemical purity (>95 %). Radioligand saturation binding assay showed that [125I]1c specifically bound to human P2X7R with high affinity (Kd = 1.68 nM and Bmax = 94 fmol/mg). A radioactive high throughput binding assay using [125I]1c for our new compounds demonstrated that the imidazole compounds 1b, 1c, and 1d exhibited high inhibition for >70 %, while the analogues of GSK314181A exhibited low inhibition for <35 %. In addition, our radioligand competitive binding assays using [125I]1c demonstrated that 1b, 1c, and 1d have high potency with IC50 values of 7.91 ± 0.22, 7.06 ± 1.68, and 7.16 ± 0.41 nM toward P2X7R, respectively.Together, compounds 1b, 1c, and 1d are highly potent for P2X7R, and [125I]1c has great potential to be a radioligand for screening P2X7R binding potency of the new compounds and investigating the P2X7R expression in animal models of human disease.

Mechanisms of mitochondrial damage-associated molecular patterns associated with inflammatory response in cardiovascular diseases

Cardiovascular diseases (CVDs) continue to be a substantial global healthcare burden despite considerable progress in therapies. The inflammatory response during the progression of CVD has attracted considerable attention. Mitochondria serve as the principal energy source for the heart. In cardiovascular illnesses, mitochondrial homeostasis is disrupted, accompanied by structural and functional impairments. During mitochondrial stress or injury, mitochondrial damage-associated molecular patterns (mtDAMPs), such as mitochondrial DNA, cardiolipin, N-formyl peptide, and adenosine triphosphate, are released to activate pattern recognition receptors and trigger immunological responses. Inflammatory responses mediated by mtDAMPs substantially contribute to the pathophysiology of cardiovascular illnesses. In this review, we discuss the molecular mechanisms by which different mtDAMPs control the inflammatory response, address the pathological consequences of mtDAMPs in inducing or exacerbating the inflammatory response in CVDs, and summarize potential therapeutic targets in relevant experimental studies. Preventing or reducing mtDAMP release may play a role in CVD progression by alleviating the inflammatory response.

Imaging neuroglia

Imaging can help us understand the role neuroglia plays in health and during the course of neurologic disorders. In vivo microscopy has had a great impact on our understanding of how neuroglia behaves during health and disease. While initially the technique was hindered by the limited penetration depth in brain tissue, recent advancements lead to increasing possibilities for imaging of deeper brain structures, even at super-resolution. Unfortunately, in vivo microscopy cannot be applied in a clinical setting and thus cannot be used to study neuroglia in patient populations. However, noninvasive imaging techniques like positron emission tomography (PET) and magnetic resonance imaging (MRI) can. PET has provided valuable information on the involvement of neuroglia in neurologic disorders. To more specifically image microglia and astrocytes, many new PET biomarkers have been defined for which PET tracers are continuously developed, evaluated, and improved. A cell-type specific PET tracer with favorable imaging characteristics can have a huge impact on neuroglia research. While being less sensitive than PET, MRI is a more accessible imaging technique. Initially, only general neuroinflammation processes could be imaged with MRI, but newly developed methods and sequences allow for increasing cell-type specificity. Overall, while each imaging method comes with limitations, improvements are continuously made, all with the aim to truly understand the role that neuroglia play in health and disease.

Oxidized ATP Suppresses B Lymphocyte Activity to Attenuate Antibody-mediated Rejection of Kidney Allografts in Mice

BACKGROUND

Antibody-mediated rejection (AMR) is a major cause of renal allograft dysfunction and loss. Targeting B cells and/or donor-specific antibody removal using plasma exchange and anti-CD20 antibodies are increasingly used in clinical practice, but the efficacy remains limited. Recent studies suggest that targeting purinergic P2X7 receptor/ATP axis can have profound immune regulatory effects in transplant models, but the mechanisms involved remain incompletely defined.

METHODS

Purified B cells were isolated from the spleen of Balb/C mice and cultured with oxidized ATP at different concentrations. Proliferation and differentiation of B cells were examined. Effects of oxidized ATP were examined in a presensitized animal model where kidney allograft rejection mimics aspects of clinical AMR. Histopathology was assessed at the time of rejection or on day 5 after kidney transplantation. Infiltrating immune cells in renal allografts were detected by flow cytometry.

RESULTS

Oxidized ATP inhibited B-cell activation and proliferation in vitro, significantly attenuated histological signs of graft injury and prolonged kidney allograft survival. Mechanistically, oxidized ATP inhibited antibody secretion by activated B cells in response to lipopolysaccharide stimulation and markedly suppressed the production of donor-specific antibody in kidney allograft recipients. Oxidized ATP also reduced graft infiltration by other inflammatory cells.

CONCLUSIONS

These findings provide evidence for the involvement of the purinergic P2X7 receptor pathway in AMR and suggest that targeting this pathways may have important clinical implications.

A shared mechanism for TNP-ATP recognition by members of the P2X receptor family

P2X receptors (P2X1-7) are non-selective cation channels involved in many physiological activities such as synaptic transmission, immunological modulation, and cardiovascular function. These receptors share a conserved mechanism to sense extracellular ATP. TNP-ATP is an ATP derivative acting as a nonselective competitive P2X antagonist. Understanding how it occupies the orthosteric site in the absence of agonism may help reveal the key allostery during P2X gating. However, TNP-ATP/P2X complexes (TNP-ATP/human P2X3 (hP2X3) and TNP-ATP/chicken P2X7 (ckP2X7)) with distinct conformations and different mechanisms of action have been proposed. Whether these represent species and subtype variations or experimental differences remains unclear. Here, we show that a common mechanism of TNP-ATP recognition exists for the P2X family members by combining enhanced conformation sampling, engineered disulfide bond analysis, and covalent occupancy. In this model, the polar triphosphate moiety of TNP-ATP interacts with the orthosteric site, while its TNP-moiety is deeply embedded in the head and dorsal fin (DF) interface, creating a restrictive allostery in these two domains that results in a partly enlarged yet ion-impermeable pore. Similar results were obtained from multiple P2X subtypes of different species, including ckP2X7, hP2X3, rat P2X2 (rP2X2), and human P2X1 (hP2X1). Thus, TNP-ATP uses a common mechanism for P2X recognition and modulation by restricting the movements of the head and DF domains which are essential for P2X activation. This knowledge is applicable to the development of new P2X inhibitors.

Ionotropic purinergic receptor 7 (P2X7) channel structure and pharmacology provides insight regarding non-nucleotide agonism

P2X7 is a member of the Ionotropic Purinergic Receptor (P2X) family. The P2X family of receptors is composed of seven (P2X1-7), ligand-gated, nonselective cation channels. Changes in P2X expression have been reported in multiple disease models. P2Xs have large complex extracellular domains that function as receptors for a variety of ligands, including endogenous and synthetic agonists and antagonists. ATP is the canonical agonist. ATP affinity ranges from nanomolar to micromolar for most P2XRs, but P2X7 has uniquely poor ATP affinity. In many physiological settings, it may be difficult to achieve the millimolar extracellular ATP concentrations needed for P2X7 channel activation; however, channel function is implicated in pain sensation, immune cell function, cardiovascular disease, cancer, and osteoporosis. Multiple high-resolution P2X7 structures have been solved in apo-, ATP-, and antagonist-bound states. P2X7 structural data reveal distinct allosteric and orthosteric antagonist-binding sites. Both allosteric and orthosteric P2X7 antagonists are well documented to inhibit ATP-evoked channel current. However, a growing body of evidence supports P2X7 activation by non-nucleotide agonists, including extracellular histone proteins and human cathelicidin-derived peptides (LL-37). Interestingly, P2X7 non-nucleotide agonism is not inhibited by allosteric antagonists, but is inhibited by orthosteric antagonists. Herein, we review P2X7 function with a focus on the efficacy of available pharmacology on P2X7 channel current activation by non-nucleotide agonists in effort to understand agonist/antagonist efficacy, and consider the impact of these data on the current understanding of P2X7 in physiology and disease given these limitations of P2X7-selective antagonists and incomplete knockout mouse models.

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.

Astrocytic P2X7 receptor regulates depressive-like behavioral reactions of mice in response to acute stressful stimulation

Acute stress causes depressive-like reactions in the tail suspension (TST) and forced swim tests (FST) of mice. Similarly, inescapable foot shock is able to promote the development of anhedonia as indicated by decreased sucrose consumption of treated mice in the sucrose preference test (SPT). The astrocyte-specific deletion of the P2X7R by a conditional knockout strategy or its knockdown by the intracerebroventricular (i.c.v.) delivery of an adeno-associated virus (AAV) expressing P2X7R-specific shRNA in astrocytes significantly prolonged the immobility time in TST and FST. In contrast, the shRNA-induced downregulation of the P2X7R in neurons, oligodendrocytes, or microglia had no detectable effect on the behavior of treated mice in these tests. Moreover, sucrose consumption in the SPT was not altered following inescapable foot shock treatment in any of these cell type-specific approaches. Immunohistochemistry indicated that the administered astrocyte-specific AAV efficiently conveyed expression of shRNA by hippocampal CA1 astrocytes, but not by neurons. In conclusion, P2X7R in astrocytes of this area of the brain appears to be involved in depressive-like reactions to acute stressors.

Techniques for evaluating the ATP-gated ion channel P2X7 receptor function in macrophages and microglial cells

Resident macrophages are tissue-specific innate immune cells acting as sentinels, constantly patrolling their assigned tissue to maintain homeostasis, and quickly responding to pathogenic invaders or molecular danger signals molecules when necessary. Adenosine triphosphate (ATP), when released to the extracellular medium, acts as a danger signal through specific purinergic receptors. Interaction of ATP with the purinergic receptor P2X7 activates macrophages and microglial cells in different pathological conditions, triggering inflammation. The highly expressed P2X7 receptor in these cells induces cell membrane permeabilization, inflammasome activation, cell death, and the production of inflammatory mediators, including cytokines and nitrogen and oxygen-reactive species. This review explores the techniques to evaluate the functional and molecular aspects of the P2X7 receptor, particularly in macrophages and microglial cells. Polymerase chain reaction (PCR), Western blotting, and immunocytochemistry or immunohistochemistry are essential for assessing gene and protein expression in these cell types. Evaluation of P2X7 receptor function involves the use of ATP and selective agonists and antagonists and diverse techniques, including electrophysiology, intracellular calcium measurements, ethidium bromide uptake, and propidium iodide cell viability assays. These techniques are crucial for studying the role of P2X7 receptors in immune responses, neuroinflammation, and various pathological conditions. Therefore, a comprehensive understanding of the functional and molecular aspects of the P2X7 receptor in macrophages and microglia is vital for unraveling its involvement in immune modulation and its potential as a therapeutic target. The methodologies presented and discussed herein offer valuable tools for researchers investigating the complexities of P2X7 receptor signaling in innate immune cells in health and disease.

Microglial NLRP3 inflammasome-mediated neuroinflammation and therapeutic strategies in depression

Previous studies have demonstrated a bidirectional relationship between inflammation and depression. Activation of the nucleotide-binding oligomerization domain, leucine-rich repeat, and NLR family pyrin domain-containing 3 (NLRP3) inflammasomes is closely related to the pathogenesis of various neurological diseases. In patients with major depressive disorder, NLRP3 inflammasome levels are significantly elevated. Understanding the role that NLRP3 inflammasome-mediated neuroinflammation plays in the pathogenesis of depression may be beneficial for future therapeutic strategies. In this review, we aimed to elucidate the mechanisms that lead to the activation of the NLRP3 inflammasome in depression as well as to provide insight into therapeutic strategies that target the NLRP3 inflammasome. Moreover, we outlined various therapeutic strategies that target the NLRP3 inflammasome, including NLRP3 inflammatory pathway inhibitors, natural compounds, and other therapeutic compounds that have been shown to be effective in treating depression. Additionally, we summarized the application of NLRP3 inflammasome inhibitors in clinical trials related to depression. Currently, there is a scarcity of clinical trials dedicated to investigating the applications of NLRP3 inflammasome inhibitors in depression treatment. The modulation of NLRP3 inflammasomes in microglia holds promise for the management of depression. Further investigations are necessary to ascertain the efficacy and safety of these therapeutic approaches as potential novel antidepressant treatments.

Molecular mechanisms of resveratrol and its silver nanoparticle conjugate in addressing sepsis-induced lung injury

Sepsis is a life-threatening condition characterized by a systemic inflammatory response to infection. Despite extensive research on its pathophysiology, effective therapeutic approaches remain a challenge. This study investigated the potential of resveratrol (RV) and silver nanoparticle-enhanced resveratrol (AgNP-RV) as treatments for sepsis-induced lung injury using a rat model of polymicrobial sepsis induced by cecal ligation and puncture (CLP). The study focused on evaluating changes in oxidative status (TAS, TOS, and OSI) and the expression of inflammatory and apoptotic markers (IL-1β, TNF-α, P2X7R, TLR4, Caspase-3, and Bcl-2) in lung tissue. Both RV and AgNP-RV demonstrated potential in mitigating oxidative stress, inflammation, and apoptosis, with AgNP-RV exhibiting greater efficacy than RV alone (p < 0.05). These findings were corroborated by histopathological analyses, which revealed reduced tissue damage in the RV- and AgNP-RV-treated groups. Our study highlights the therapeutic potential of RV and, particularly, AgNP-RV in combating sepsis-induced oxidative stress, inflammation, and apoptosis. It also underscores the promise of nanoparticle technology in enhancing therapeutic outcomes. However, further investigations are warranted to fully understand the mechanisms of action, especially concerning the role of the P2X7 receptor in the observed effects. Nonetheless, our research suggests that RV and AgNP-RV hold promise as novel strategies for sepsis management.

Association of polymorphisms within P2RX4 with type 2 diabetes mellitus: a preliminary case-control study

OBJECTIVE

Type 2 diabetes mellitus (T2DM) is a complex heterogenic metabolic with a wide range of etiology. Purinergic receptors have pivotal roles in different processes and are hypothesized to have roles in the pathogenesis of T2DM.

MATERIALS AND METHODS

Three hundred subjects affected by T2DM and 300 healthy subjects were genotyped by amplification refractory mutation system polymerase chain reaction (ARMS-PCR). SPSS V16.0 was recruited for statistical analysis.

RESULTS

The findings showed that the G allele of rs25644A > G increases the risk of T2DM in our population statistically (OR = 1.51, 95% CI = 1.14-1.99, p = 0.003). This allele in some genotype models, including the dominant model, caused an increase in the risk of T2DM. The interaction of genotypes between studied variants in the P2XR4 gene increased the risk of T2DM. Haplotype analysis showed that Ars1169727/Grs25644 haplotype caused an increase in the risk of T2DM.

CONCLUSIONS

The findings suggest that rs25644A > G plays a role in our population's increased risk of T2DM.

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.

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.

ALPL regulates pro-angiogenic capacity of mesenchymal stem cells through ATP-P2X7 axis controlled exosomes secretion

BACKGROUND

Early-onset bone dysplasia is a common manifestation of hypophosphatasia (HPP), an autosomal inherited disease caused by ALPL mutation. ALPL ablation induces prototypical premature bone ageing characteristics, resulting in impaired osteogenic differentiation capacity of human bone marrow mesenchymal stem cells (hBMMSCs). As angiogenesis is tightly coupled with osteogenesis, it also plays a necessary role in sustaining bone homeostasis. We have previously observed a decrease in expression of angiogenesis marker gene CD31 in the metaphysis of long bone in Alpl+/- mice. However, the role of ALPL in regulation of angiogenesis in bone has remained largely unknown.

METHODS

Exosomes derived from Normal and HPP hBMMSCs were isolated and identified by ultracentrifugation, transmission electron microscopy, and nanoparticle size measurement. The effects of ALPL on the angiogenic capacity of hBMMSCs from HPP patients were assessed by immunofluorescence, tube formation, wound healing and migration assay. exo-ELISA and Western Blot were used to evaluate the exosomes secretion of hBMMSCs from HPP, and the protein expression of VEGF, PDGFBB, Angiostatin and Endostatin in exosomes respectively.

RESULTS

We verified that ALPL ablation resulted in impaired pro-angiogenic capacity of hBMMSCs, accounting for reduced migration and tube formation of human umbilical vein endothelial cells, as the quantities and proteins composition of exosomes varied with ALPL expression. Mechanistically, loss of function of ALPL enhanced ATP release. Additional ATP, in turn, led to markedly elevated level of ATP receptor P2X7, which consequently promoted exosomes secretion, resulting in a decreased capacity to promote angiogenesis. Conversely, inhibition of P2X7 increased the angiogenic induction capacity by preventing excessive release of anti-angiogenic exosomes in ALPL deficient-hBMMSCs.

CONCLUSION

The ALPL-ATP axis regulates the pro-angiogenic ability of hBMMSCs by controlling exosomes secretion through the P2X7 receptor. Thus, P2X7 may be proved as an effective therapeutic target for accelerating neovascularization in ALPL-deficient bone defects.

Finding new analgesics: Computational pharmacology faces drug discovery challenges

Despite the worldwide prevalence and huge burden of pain, pain is an undertreated phenomenon. Currently used analgesics have several limitations regarding their efficacy and safety. The discovery of analgesics possessing a novel mechanism of action has faced multiple challenges, including a limited understanding of biological processes underpinning pain and analgesia and poor animal-to-human translation. Computational pharmacology is currently employed to face these challenges. In this review, we discuss the theory, methods, and applications of computational pharmacology in pain research. Computational pharmacology encompasses a wide variety of theoretical concepts and practical methodological approaches, with the overall aim of gaining biological insight through data acquisition and analysis. Data are acquired from patients or animal models with pain or analgesic treatment, at different levels of biological organization (molecular, cellular, physiological, and behavioral). Distinct methodological algorithms can then be used to analyze and integrate data. This helps to facilitate the identification of biological molecules and processes associated with pain phenotype, build quantitative models of pain signaling, and extract translatable features between humans and animals. However, computational pharmacology has several limitations, and its predictions can provide false positive and negative findings. Therefore, computational predictions are required to be validated experimentally before drawing solid conclusions. In this review, we discuss several case study examples of combining and integrating computational tools with experimental pain research tools to meet drug discovery challenges.

DUSP1/MKP-1 represents another piece in the P2X7R intracellular signaling puzzle in cerebellar cells: our last journey with Mª Teresa along the purinergic pathways of Eden

The P2X7 receptor (P2X7R) stands out within the purinergic family as it has exclusive pharmacological and regulatory features, and it fulfills distinct roles depending on the type of stimulation and cellular environment. Tonic activation of P2X7R promotes cell proliferation, whereas sustained activation is associated with cell death. Yet strikingly, prolonged P2X7R activation in rat cerebellar granule neurons and astrocytes does not affect cell survival. The intracellular pathways activated by P2X7Rs involve proteins like MAPKs, ERK1/2 and p38, and interactions with growth factor receptors could explain their behavior in populations of rat cerebellar cells. In this study, we set out to characterize the intracellular mechanisms through which P2X7Rs and Trk receptors, EGFR (epidermal growth factor receptor) and BDNFR (brain-derived neurotrophic factor receptor), regulate the dual-specificity phosphatase DUSP1. In cerebellar astrocytes, the regulation of DUSP1 expression by P2X7R depends on ERK and p38 activation. EGFR stimulation can also induce DUSP1 expression, albeit less strongly than P2X7R. Conversely, EGF was virtually ineffective in regulating DUSP1 in granule neurons, a cell type in which BDNF is the main regulator of DUSP1 expression and P2X7R only induces a mild response. Indeed, the regulation of DUSP1 elicited by BDNF reflects the balance between both transcriptional and post-transcriptional mechanisms. Importantly, when the regulation of DUSP1 expression is compromised, the viability of both astrocytes and neurons is impaired, suggesting this phosphatase is essential to maintain proper cell cytoarchitecture and functioning.

P2X7 receptor of olfactory bulb microglia plays a pathogenic role in stress-related depression in mice with allergic rhinitis

The aim of this study was to explore the role and mechanism of the olfactory bulb (OB) microglial P2X7 receptor (P2X7R) in allergic rhinitis (AR)-related depression, with the objective of identifying a potential clinical target. An AR mouse model was induced using ovalbumin (OVA), while chronic stress was employed to induce depression. The study used P2X7R-specific antagonists and OB microglia-specific P2X7R knockdown mice as crucial tools. The results showed that mice in the OVA + stress group exhibited more pronounced depressive-like phenotypes. Furthermore, there was an observed increase in microglial activation in the OB, followed by a rise in the level of inflammation. The pharmacological inhibition of P2X7R significantly mitigated the depression-like phenotype and the OB inflammatory response in OVA + stress mice. Notably, the specific knockdown of microglial P2X7R in the OB resulted in a similar effect, possibly linked to the regulation of IL-1β via the "ATP-P2X7R-Caspase 1" axis. These findings collectively demonstrate that microglial P2X7R in the OB acts as a direct effector molecule in AR-related depression, and its inhibition may offer a novel strategy for clinical prevention and treatment.

P2X7 receptors: a bibliometric review from 2002 to 2023

For many years, there has been ongoing research on the P2X7 receptor (P2X7R). A comprehensive, systematic, and objective evaluation of the scientific output and status of P2X7R will be instrumental in guiding future research directions. This study aims to present the status and trends of P2X7R research from 2002 to 2023. Publications related to P2X7R were retrieved from the Web of Science Core Collection database. Quantitative analysis and visualization tools were Microsoft Excel, VOSviewer, and CiteSpace software. The analysis content included publication trends, literature co-citation, and keywords. 3282 records were included in total, with the majority of papers published within the last 10 years. Based on literature co-citation and keyword analysis, neuroinflammation, neuropathic pain, gastrointestinal diseases, tumor microenvironment, rheumatoid arthritis, age-related macular degeneration, and P2X7R antagonists were considered to be the hotspots and frontiers of P2X7R research. Researchers will get a more intuitive understanding of the status and trends of P2X7R research from this study.

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.

Emerging Microglial Therapies and Targets in Clinical Trial

Modulation of microglia function for treatment of neurodegenerative and neuropsychiatric disorders is an emerging field of neuroscience drug development. This is largely attributed to human genetic association studies combined with biological evidence indicating that the innate immune system acts as a causal contributor superimposed on the reactive component of neuronal loss in neurological dysfunction. The identification of disease risk gene variants that encode immune-modulatory proteins in microglia provides tools to evaluate how microglia cellular function or dysfunction affect neuronal health. The development of clinical stage therapeutic compounds that modify myeloid cell function enables us to investigate how modulating microglia function could become a transformational approach to mitigate neurological disorders. Improving our ability to boost microglia-promoting homeostatic and reparative functions hopefully will translate into achieving a better outcome for patients affected by neurological diseases. In this chapter, we aim to provide an overview of the microglial emerging therapies and targets being studied in current clinical trials.

Microglial Positron Emission Tomography Imaging In Vivo : Positron Emission Tomography Radioligands: Utility in Research and Clinical Practice

Microglia, the resident immune cells of the central nervous system (CNS) play a key role in regulating and maintaining homeostasis in the brain. However, the CNS is also vulnerable to infections and inflammatory processes. In response to CNS perturbations, microglia become reactive, notably with expression of the translocator protein (TSPO), primarily on their outer mitochondrial membrane. Despite TSPO being commonly used as a marker for microglia, it is also present in other cell types such as astrocytes. Positron emission tomography (PET) ligands that target the TSPO enable the noninvasive detection and quantification of glial reactivity. While some limitations were raised, TSPO PET remains an attractive biomarker of CNS infection and inflammation. This book chapter delves into the development and application of microglial PET imaging with a focus on the TSPO PET. First, we provide an overview of the evolution of TSPO PET radioligands from first-generation to second-generation ligands and their applications in studying neuroinflammation (or CNS inflammation). Subsequently, we discuss the limitations and challenges associated with TSPO PET. Then we go on to explore non-TSPO targets for microglial PET imaging. Finally, we conclude with future directions for research and clinical practice in this field.

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.

Gene-Level Analysis of Anthracycline-Induced Cardiomyopathy in Cancer Survivors: A Report From COG-ALTE03N1, BMTSS, and CCSS

Background

Anthracyclines are highly effective in treating cancer, albeit with increased cardiomyopathy risk. Although risk is attributed to associations with single nucleotide polymorphisms (SNPs), multiple SNPs on a gene and their interactions remain unexamined.

Objectives

This study examined gene-level associations with cardiomyopathy among cancer survivors using whole-exome sequencing data.

Methods

For discovery, 278 childhood cancer survivors (129 cases; 149 matched control subjects) from the COG (Children's Oncology Group) study ALTE03N1 were included. Logic regression (machine learning) was used to identify gene-level SNP combinations for 7,212 genes and ordinal logistic regression to estimate gene-level associations with cardiomyopathy. Models were adjusted for primary cancer, age at cancer diagnosis, sex, race/ethnicity, cumulative anthracycline dose, chest radiation, cardiovascular risk factors, and 3 principal components. Statistical significance threshold of 6.93 × 10-6 accounted for multiple testing. Three independent cancer survivor populations (COG study, BMTSS [Blood or Marrow Transplant Survivor Study] and CCSS [Childhood Cancer Survivor Study]) were used to replicate gene-level associations and examine SNP-level associations from discovery genes using ordinal logistic, conditional logistic, and Cox regression models, respectively.

Results

Median age at cancer diagnosis for discovery cases and control subjects was 6 years and 8 years, respectively. Gene-level association for P2RX7 (OR: 0.10; 95% CI: 0.04-0.27; P = 2.19 × 10-6) was successfully replicated (HR: 0.65; 95% CI: 0.47-0.90; P = 0.009) in the CCSS cohort. Additional signals were identified on TNIK, LRRK2, MEFV, NOBOX, and FBN3. Individual SNPs across all discovery genes, except FBN3, were replicated.

Conclusions

In our study, SNP sets having 1 or no copies of P2RX7 variant alleles were associated with reduced risk of cardiomyopathy, presenting a potential therapeutic target to mitigate cardiac outcomes in cancer survivors.

Synthetic molecules as P2X7 receptor antagonists: A medicinal chemistry update focusing the therapy of inflammatory diseases

Stimulation of the P2X7 receptor by extracellular adenosine 5'-triphosphate induces a series of responses in the organism, exceptionally protein cascades related to the proinflammatory process. This has made P2X7 a target for research on inflammatory diseases such as rheumatoid arthritis. Thus, the incessant search for new prototypes that aim to antagonize the action of P2X7 has been remarkable in recent decades, a factor that has already led to numerous clinical studies in humans. In this review, we present the key molecules developed over the years with potential inhibition of P2X7 and inflammation. In addition, an update with newly developed chemical classes with promising activity and results in clinical studies for human pathologies focusing on P2X7 inhibition.

Leveraging the ATP-P2X7 receptor signalling axis to alleviate traumatic CNS damage and related complications

The P2X7 receptor is an exceptional member of the P2X purinergic receptor family, with its activation requiring high concentrations of extracellular adenosine 5'-triphosphate (ATP) that are often associated with tissue damage and inflammation. In the central nervous system (CNS), it is highly expressed in glial cells, particularly in microglia. In this review, we discuss the role and mechanisms of the P2X7 receptor in mediating neuroinflammation and other pathogenic events in a variety of traumatic CNS damage conditions, which lead to loss of neurological and cognitive functions. We raise the perspective on the steady progress in developing CNS-penetrant P2X7 receptor-specific antagonists that leverage the ATP-P2X7 receptor signaling axis as a potential therapeutic strategy to alleviate traumatic CNS damage and related complications.

P2X7-Receptor Pathway Involvement in the Anti-Inflammatory Activity of Medicinal Plants

Medicinal plants used in European folk medicine attached to Lamiales, Gentianales or Asterales orders are used to treat inflammatory disorders. Many targets have been identified but to date, implication of purinergic receptor P2X7 activation has not yet been investigated. We managed to evaluate the protective effect on P2X7 activation by plant extracts used as anti-inflammatory in European folk medicine by the YO-PRO-1 uptake dye in vitro bioassay. Results revealed that among our selected plants, species from Scrophularia and Plantago genus were able to decrease significantly P2X7 activation (>50 % at 0.1 and 1 μg/mL). UPLC/MS, dereplication and metabolomic analysis of Scrophularia extracts, allowed us to identify the cinnamoyl-iridoid harpagoside as putative inhibitor of P2X7 activation. These results open a new research field regarding the anti-inflammatory mechanism of cinnamoyl-iridoids bearing plants, which may involve the P2X7 receptor.

The P2X7 Receptor, a Multifaceted Receptor in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by impaired episodic memory and two pathological lesions: amyloid plaques and neurofibrillary tangles. In AD, damaged neurons and the accumulation of amyloid β (Aβ) peptides cause a significant release of high amounts of extracellular ATP, which acts as a danger signal. The purinergic receptor P2X7 is the main sensor of high concentrations of ATP, and P2X7 has been shown to be upregulated in the brains of AD patients, contributing to the disease's pathological processes. Further, there are many polymorphisms of the P2X7 gene that impact the risk of developing AD. P2X7 can directly modulate Aβ plaques and Tau protein lesions as well as the inflammatory response by regulating NLRP3 inflammasome and the expression of several chemokines. The significant role of microglial P2X7 in AD has been well established, although other cell types may also be important in P2X7-mediated mechanisms. In this review, we will discuss the different P2X7-dependent pathways involved in the development of AD.

The neuroinflammatory astrocytic P2X7 receptor: Alzheimer's disease, ischemic brain injury, and epileptic state

INTRODUCTION

Astrocytes have previously been considered as cells supporting neuronal functions, but they are now recognized as active players in maintaining central nervous system (CNS) homeostasis. Astrocytes can communicate with other CNS cells, i.e. through the gliotransmitter ATP and P2X7 receptors (Rs).

AREAS COVERED

In this review, we will discuss how the P2X7R initiates the release of gliotransmitters and proinflammatory cytokines/chemokines, thereby establishing a dialog between astrocytes and neurons and, in addition, causing neuroinflammation. In astrocytes, dysregulation of P2X7Rs has been associated with neurodegenerative illnesses such as Alzheimer's disease (AD), as well as the consequences of cerebral ischemic injury and status epilepticus (SE).

EXPERT OPINION

Although all CNS cells are possible sources of ATP release, the targets of this ATP are primarily at microglial cells. However, astrocytes also contain ATP-sensitive P2X7Rs and have in addition the peculiar property over microglia to continuously interact with neurons via not only inflammatory mediators but also gliotransmitters, such as adenosine 5'-triphosphate (ATP), glutamate, γ-amino butyric acid (GABA), and D-serine. Cellular damage arising during AD, cerebral ischemia, and SE via P2X7R activation is superimposed upon the original disease, and their prevention by blood-brain barrier permeable pharmacological antagonists is a valid therapeutic option.

The potential role of T-cell metabolism-related molecules in chronic neuropathic pain after nerve injury: a narrative review

Neuropathic pain is a common type of chronic pain, primarily caused by peripheral nerve injury. Different T-cell subtypes play various roles in neuropathic pain caused by peripheral nerve damage. Peripheral nerve damage can lead to co-infiltration of neurons and other inflammatory cells, thereby altering the cellular microenvironment and affecting cellular metabolism. By elaborating on the above, we first relate chronic pain to T-cell energy metabolism. Then we summarize the molecules that have affected T-cell energy metabolism in the past five years and divide them into two categories. The first category could play a role in neuropathic pain, and we explain their roles in T-cell function and chronic pain, respectively. The second category has not yet been involved in neuropathic pain, and we focus on how they affect T-cell function by influencing T-cell metabolism. By discussing the above content, this review provides a reference for studying the direct relationship between chronic pain and T-cell metabolism and searching for potential therapeutic targets for the treatment of chronic pain on the level of T-cell energy metabolism.

Animal Models for the Investigation of P2X7 Receptors

The P2X7 receptor is a trimeric ligand-gated cation channel activated by extracellular adenosine 5'-triphosphate. The study of animals has greatly advanced the investigation of P2X7 and helped to establish the numerous physiological and pathophysiological roles of this receptor in human health and disease. Following a short overview of the P2X7 distribution, roles and functional properties, this article discusses how animal models have contributed to the generation of P2X7-specific antibodies and nanobodies (including biologics), recombinant receptors and radioligands to study P2X7 as well as to the pharmacokinetic testing of P2X7 antagonists. This article then outlines how mouse and rat models have been used to study P2X7. These sections include discussions on preclinical disease models, polymorphic P2X7 variants, P2X7 knockout mice (including bone marrow chimeras and conditional knockouts), P2X7 reporter mice, humanized P2X7 mice and P2X7 knockout rats. Finally, this article reviews the limited number of studies involving guinea pigs, rabbits, monkeys (rhesus macaques), dogs, cats, zebrafish, and other fish species (seabream, ayu sweetfish, rainbow trout and Japanese flounder) to study P2X7.

Astrocyte adaptation in Alzheimer's disease: a focus on astrocytic P2X7R

Astrocytes are key homeostatic and defensive cells of the central nervous system (CNS). They undertake numerous functions during development and in adulthood to support and protect the brain through finely regulated communication with other cellular elements of the nervous tissue. In Alzheimer's disease (AD), astrocytes undergo heterogeneous morphological, molecular and functional alterations represented by reactive remodelling, asthenia and loss of function. Reactive astrocytes closely associate with amyloid β (Aβ) plaques and neurofibrillary tangles in advanced AD. The specific contribution of astrocytes to AD could potentially evolve along the disease process and includes alterations in their signalling, interactions with pathological protein aggregates, metabolic and synaptic impairments. In this review, we focus on the purinergic receptor, P2X7R, and discuss the evidence that P2X7R activation contributes to altered astrocyte functions in AD. Expression of P2X7R is increased in AD brain relative to non-demented controls, and animal studies have shown that P2X7R antagonism improves cognitive and synaptic impairments in models of amyloidosis and tauopathy. While P2X7R activation can induce inflammatory signalling pathways, particularly in microglia, we focus here specifically on the contributions of astrocytic P2X7R to synaptic changes and protein aggregate clearance in AD, highlighting cell-specific roles of this purinoceptor activation that could be targeted to slow disease progression.

Exploration of the link between gut microbiota and purinergic signalling

Growing evidence reveals that microorganisms in the gut are linked to metabolic health and disease risk in human beings to a considerable extent. The focus of research at this stage must tend to focus on cause-and-effect studies. In addition to being a component of DNA and RNA, purine metabolites can be involved in purine signalling in the body as chemical messengers. Abnormalities in purinergic signalling may lead to neuropathy, rheumatic immune diseases, inflammation, tumors, and a wide range of other diseases. It has proved that gut microbes are involved in purinergic signalling. The relationship between these gut-derived purinergic signalling molecules and host metabolism may be one of the important clues to our understanding of the mechanisms by which the microbiota affects host metabolism.

Purinergic P2X7R as a potential target for pancreatic cancer

Pancreatic cancer is one of the deadliest types of cancer, with a death rate nearly equal to the incidence. The P2X7 receptor (P2X7R) is a kind of extracellular adenosine triphosphate (ATP)-gated ion channel with special permeability, which exists in most tissues of human body and mediates inflammation-related signaling pathways and immune signal transduction after activation. P2X7R is also present on the surface of several tumor cells and is involved in tumor growth and progression. P2X7R expression in pancreatic cancer has also been identified in recent studies. Activation of P2X7R in pancreatic cancer can support the proliferation of pancreatic stellate cells, participate in protein interactions, and mediate ERK1/2, IL-6/STAT3, hCAP-18/LL-37, PI3K/AKT signaling pathways to promote pancreatic cancer progression. Inhibitors targeting P2X7R can inhibit the development of pancreatic cancer and are expected to be used in clinical therapy. Therefore, P2X7R is promising as a potential therapeutic target for pancreatic cancer. This article reviews the progress of research on P2X7R in pancreatic cancer.

The P2X7 receptor in mood disorders: Emerging target in immunopsychiatry, from bench to bedside

Psychiatric disorders are among the most burdensome disorders worldwide. Though therapies have evolved over the last decades, treatment resistance still affects many patients. Recently, neuroimmune systems have been identified as important factors of mood disorder biology. The underlying dysregulation in neuroimmune cross-talk is driven by genetic risk factors and accumulating adverse environmental influences like chronic psychosocial stress. These result in a cluster of proinflammatory cytokines and quantitative and functional changes of immune cell populations (e.g., microglia, monocytes, T cells), varying by disease entity and state. Among the emerging immune targets, purinergic signalling revolving around the membranous and ATP specific P2X7 receptor (P2X7R) has gained wider attention and clinical studies making use of antagonistic drugs are on-going. Still, no clinically meaningful applications have been identified so far. A major problem is the often overly simplified approach taken to translate findings from bench to bedside. Therefore, the present review focuses on purinergic signalling via P2X7R in the context of recent advances in immunopsychiatric mood disorder research. Our aim is to provide an overview of the current P2X7R-related findings, from bench to bedside. First, we summarize the characteristics of purinergic signalling and P2X7R, followed by a depiction of genetic and clinical data connecting P2X7R to mood disorders. We close with our perspective on current developments and discuss changes necessary to translate the evident potential of P2X7R signalling modulation into meaningful clinical application. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

Purinergic signaling: Diverse effects and therapeutic potential in cancer

Regardless of improved biological insights and therapeutic advances, cancer is consuming multiple lives worldwide. Cancer is a complex disease with diverse cellular, metabolic, and physiological parameters as its hallmarks. This instigates a need to uncover the latest therapeutic targets to advance the treatment of cancer patients. Purines are building blocks of nucleic acids but also function as metabolic intermediates and messengers, as part of a signaling pathway known as purinergic signaling. Purinergic signaling comprises primarily adenosine triphosphate (ATP) and adenosine (ADO), their analogous membrane receptors, and a set of ectonucleotidases, and has both short- and long-term (trophic) effects. Cells release ATP and ADO to modulate cellular function in an autocrine or paracrine manner by activating membrane-localized purinergic receptors (purinoceptors, P1 and P2). P1 receptors are selective for ADO and have four recognized subtypes-A1, A2A, A2B, and A3. Purines and pyrimidines activate P2 receptors, and the P2X subtype is ligand-gated ion channel receptors. P2X has seven subtypes (P2X1-7) and forms homo- and heterotrimers. The P2Y subtype is a G protein-coupled receptor with eight subtypes (P2Y1/2/4/6/11/12/13/14). ATP, its derivatives, and purinoceptors are widely distributed in all cell types for cellular communication, and any imbalance compromises the homeostasis of the cell. Neurotransmission, neuromodulation, and secretion employ fast purinergic signaling, while trophic purinergic signaling regulates cell metabolism, proliferation, differentiation, survival, migration, invasion, and immune response during tumor progression. Thus, purinergic signaling is a prospective therapeutic target in cancer and therapy resistance.

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.

Synthesis, Biological Evaluation and Molecular Modeling Studies of Naphthoquinone Sulfonamides and Sulfonate Ester Derivatives as P2X7 Inhibitors

ATP acts in the extracellular environment as an important signal, activating a family of receptors called purinergic receptors. In recent years, interest in the potential therapeutics of purinergic components, including agonists and antagonists of receptors, has increased. Currently, many observations have indicated that ATP acts as an important mediator of inflammatory responses and, when found in high concentrations in the extracellular space, is related to the activation of the P2X7 purinergic receptor. In this sense, the search for new inhibitors for this receptor has attracted a great deal of attention in recent years. Sulfonamide derivatives have been reported to be potent inhibitors of P2X receptors. In this study, ten naphthoquinone sulfonamide derivatives and five naphthoquinone sulfonate ester derivatives were tested for their inhibitory activity on the P2X7 receptor expressed in peritoneal macrophages. Some compounds showed promising results, displaying IC₅₀ values lower than that of A740003. Molecular docking and dynamic studies also indicated that the active compounds bind to an allosteric site on P2X7R. The binding free energy indicates that sulfonamides have an affinity for the P2X7 receptor similar to A740003. Therefore, the compounds studied herein present potential P2X7R inhibition.

Anti-Inflammatory Activity of 1,4-Naphthoquinones Blocking P2X7 Purinergic Receptors in RAW 264.7 Macrophage Cells

P2X7 receptors are ligand-gated ion channels activated by ATP and play a significant role in cellular immunity. These receptors are considered as a potential therapeutic target for the treatment of multiple inflammatory diseases. In the present work, using spectrofluorimetry, spectrophotometry, Western blotting and ELISA approaches, the ability of 1,4-naphthoquinone thioglucoside derivatives, compounds U-286 and U-548, to inhibit inflammation induced by ATP/LPS in RAW 264.7 cells via P2X7 receptors was demonstrated. It has been established that the selected compounds were able to inhibit ATP-induced calcium influx and the production of reactive oxygen species, and they also exhibited pronounced antioxidant activity in mouse brain homogenate. In addition, compounds U-286 and U-548 decreased the LPS-induced activity of the COX-2 enzyme, the release of pro-inflammatory cytokines TNF-α and IL-1β in RAW 264.7 cells, and significantly protected macrophage cells against the toxic effects of ATP and LPS. This study highlights the use of 1,4-naphthoquinones as promising purinergic P2X7 receptor antagonists with anti-inflammatory activity. Based on the data obtained, studied synthetic 1,4-NQs can be considered as potential scaffolds for the development of new anti-inflammatory and analgesic drugs.

The ATP-dependent Pathways and Human Diseases

Adenosine triphosphate (ATP) is one of the most important molecules of life, present both inside the cells and extracellularly. It is an essential building block for nucleic acids biosynthesis and crucial intracellular energy storage. However, one of the most interesting functions of ATP is the role of a signaling molecule. Numerous studies indicate the involvement of ATP-dependent pathways in maintaining the proper functioning of individual tissues and organs. Herein, the latest data indicating the ATP function in the network of intra- and extracellular signaling pathways including purinergic signaling, MAP kinase pathway, mTOR and calcium signaling are collected. The main ATP-dependent processes maintaining the proper functioning of the nervous, cardiovascular and immune systems, as well as skin and bones, are summarized. The disturbances in the ATP amount, its cellular localization, or interaction with target elements may induce pathological changes in signaling pathways leading to the development of serious diseases. The impact of an ATP imbalance on the development of dangerous health dysfunctions such as neurodegeneration diseases, cardiovascular diseases (CVDs), diabetes mellitus, obesity, cancers and immune pathogenesis are discussed here.

Aluminum induces neuroinflammation via P2X7 receptor activating NLRP3 inflammasome pathway

INTRODUCTION

Aluminum is everywhere in nature and is a recognized neurotoxicant closely associated with various neurodegenerative diseases. Neuroinflammation occurs in the early stage of neurodegenerative diseases, but the underlying mechanism by which aluminum induces neuroinflammation remains unclear.

MATERIAL AND METHODS

A 3-month subchronic aluminum exposure mouse model was established by drinking water containing aluminum chloride (AlCl₃). Microglia BV2 cells and hippocampal neuron HT22 cells were treated with AlCl₃ in vitro. BBG and YC-1 were used as intervention agents.

RESULTS

Aluminum could activate microglia and increase the level of extracellular ATP, stimulate P2X7 receptor, HIF-1α, activate NLRP3 inflammasome and CASP-1, release more cytokine IL-1β, and induce an inflammatory response in nerve cells. There was a mutual regulatory relationship between P2X7 and HIF-1α at mRNA and protein levels. The co-culture system of BV2-HT22 cells observed that conditioned medium from microglia treated with aluminum could aggravate neuronal morphological damage, inflammatory response and death. While BBG and YC-1 intervention could rescue these injuries to some extent.

CONCLUSION

The P2X7-NLRP3 pathway was involved in aluminum-induced neuroinflammation and injury. P2X7 and HIF-1α might mutually regulate and promote the progression of neuroinflammation, both BBG and YC-1 could relieve it.

P2X7 receptor activation mediates superoxide dismutase 1 (SOD1) release from murine NSC-34 motor neurons

Mutant superoxide dismutase 1 (SOD1) can be constitutively released from motor neurons and transmitted to naïve motor neurons to promote the progression of amyotrophic lateral sclerosis (ALS). However, the biological impacts of this process and the precise mechanisms of SOD1 release remain to be fully resolved. Using biochemical and fluorescent techniques, this study aimed to determine if P2X7 receptor activation could induce mutant SOD1 release from motor neurons and whether this released SOD1 could be transmitted to motor neurons or microglia to mediate effects associated with neurodegeneration in ALS. Aggregated SOD1^G93A, released from murine NSC-34 motor neurons transiently transfected with SOD1^G93A, could be transmitted to naïve NSC-34 cells and murine EOC13 microglia to induce endoplasmic reticulum (ER) stress and tumour necrosis factor-alpha (TNFα) release, respectively. Immunoblotting revealed NSC-34 cells expressed P2X7. Extracellular ATP induced cation dye uptake into these cells, which was blocked by the P2X7 antagonist AZ10606120, demonstrating these cells express functional P2X7. Moreover, ATP induced the rapid release of aggregated SOD1^G93A from NSC-34 cells transiently transfected with SOD1^G93A, a process blocked by AZ10606120 and revealing a role for P2X7 in this process. ATP-induced SOD1^G93A release coincided with membrane blebbing. Finally, aggregated SOD1^G93A released via P2X7 activation could also be transmitted to NSC-34 and EOC13 cells to induce ER stress and TNFα release, respectively. Collectively, these results identify a novel role for P2X7 in the prion-like propagation of SOD1 in ALS and provide a possible explanation for the therapeutic benefits of P2X7 antagonism previously observed in ALS SOD1^G93A mice.

Origin, distribution, and function of three frequent coding polymorphisms in the gene for the human P2X7 ion channel

P2X7, an ion channel gated by extracellular ATP, is widely expressed on the plasma membrane of immune cells and plays important roles in inflammation and apoptosis. Several single nucleotide polymorphisms have been identified in the human P2RX7 gene. In contrast to other members of the P2X family, non-synonymous polymorphisms in P2X7 are common. Three of these occur at overall frequencies of more than 25% and affect residues in the extracellular “head”-domain of P2X7 (155 Y/H), its “lower body” (270 R/H), and its “tail” in the second transmembrane domain (348 T/A). Comparison of the P2X7 orthologues of human and other great apes indicates that the ancestral allele is Y—R—T (at 155–270–348). Interestingly, each single amino acid variant displays lower ATP-sensitivity than the ancestral allele. The originally published reference sequence of human P2X7, often referred to as “wildtype,” differs from the ancestral allele at all three positions, i.e. H—H—A. The 1,000 Genome Project determined the sequences of both alleles of 2,500 human individuals, including roughly 500 persons from each of the five major continental regions. This rich resource shows that the ancestral alleles Y155, R270, and T348 occur in all analyzed human populations, albeit at strikingly different frequencies in various subpopulations (e.g., 25%–59% for Y155, 59%–77% for R270, and 13%–47% for T348). BLAST analyses of ancient human genome sequences uncovered several homozygous carriers of variant P2X7 alleles, possibly reflecting a high degree of inbreeding, e.g., H—R—T for a 50.000 year old Neanderthal, H—R—A for a 24.000 year old Siberian, and Y—R—A for a 7,000 year old mesolithic European. In contrast, most present-day individuals co-express two copies of P2X7 that differ in one or more amino acids at positions 155, 270, and 348. Our results improve the understanding of how P2X7 structure affects its function and suggest the importance of considering P2X7 variants of participants when designing clinical trials targeting P2X7.

A Possible Causal Involvement of Neuroinflammatory, Purinergic P2X7 Receptors in Psychiatric Disorders

P2X7 receptors (Rs) are prominent members of the P2XR family, which after binding ATP, open non-selective cationic channels, thereby allowing the transmembrane passage of Na+, Ca²⁺, and K+. Long-lasting and repetitive stimulation of the receptor by its agonist leads to the formation of large membrane pores permeable for organic cations of up to 900 Da molecular size. These pores are believed to play a role in apoptosis and inflammation. P2X7Rs are located primarily at peripheral macrophages and microglial cells, the resident macrophages of the CNS. The coactivation of toll-like receptors 4 (TLR4) by lipopolysaccharide, a constituent of the cell membrane of gram-negative bacteria, and the P2X7R by ATP leads to the generation and release of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α. Together with the microglial release of chemokines, reactive oxygen and nitrogen species, proteases, and excitotoxic glutamate, these cytokines result in neurodegeneration. P2X7Rs were found not only to amplify various neurodegenerative illnesses, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis, but also to participate in a range of psychiatric diseases, such as major depression, bipolar disorder, schizophrenia, and autism spectrum disorder. Based on the prevention/reversal of neuroinflammation, pharmacological antagonists of P2X7Rs and their genetic deletion in animal experiments counteract these deleterious psychiatric conditions. Hence, brain penetrant P2X7R antagonists are potential therapeutics for psychiatric diseases, although the available evidence still needs to be extended and validated by further clinical data.

Evaluation of nanobody-based biologics targeting purinergic checkpoints in tumor models in vivo

Adenosine triphosphate (ATP) represents a danger signal that accumulates in injured tissues, in inflammatory sites, and in the tumor microenvironment. ATP promotes tumor growth but also anti-tumor immune responses notably via the P2X7 receptor. ATP can also be catabolized by CD39 and CD73 ecto-enzymes into immunosuppressive adenosine. P2X7, CD39 and CD73 have attracted much interest in cancer as targets offering the potential to unleash anti-tumor immune responses. These membrane proteins represent novel purinergic checkpoints that can be targeted by small drugs or biologics. Here, we investigated nanobody-based biologics targeting mainly P2X7, but also CD73, alone or in combination therapies. Blocking P2X7 inhibited tumor growth and improved survival of mice in cancer models that express P2X7. P2X7-potentiation by a nanobody-based biologic was not effective alone to control tumor growth but enhanced tumor control and immune responses when used in combination with oxaliplatin chemotherapy. We also evaluated a bi-specific nanobody-based biologic that targets PD-L1 and CD73. This novel nanobody-based biologic exerted a potent anti-tumor effect, promoting tumor rejection and improving survival of mice in two tumor models. Hence, this study highlights the importance of purinergic checkpoints in tumor control and open new avenues for nanobody-based biologics that may be further exploited in the treatment of cancer.