Pharmacological blockade of the P2X7 receptor reverses retinal damage in a rat model of type 1 diabetes

An improved understanding of pediatric chronic nonbacterial osteomyelitis pathophysiology informs current and future treatment

Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disease that primarily affects children and young people. It can cause significant pain, reduced function, bone swelling, and even (vertebral body) fractures. Because of a limited understanding of its pathophysiology, the treatment of CNO remains empiric and is based on relatively small case series, expert opinion, and personal experience. Several studies have linked pathological NOD-kike receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome activation and the resulting imbalance between pro- and anti-inflammatory cytokine expression with CNO. This agrees with elevated pro-inflammatory (mostly) monocyte-derived protein signatures in the blood of CNO patients that may be used as future diagnostic and/or prognostic biomarkers. Recently, rare variants in the P2RX7 gene, encoding for an ATP-dependent transmembrane channel, were linked with increased NLRP3 inflammasome assembly and prolonged monocyte/macrophage survival in CNO. Although the exact molecular mechanisms remain unclear, this will inform future target-directed and individualized treatment. This manuscript reviews most recent developments and their impact on diagnostic and therapeutic strategies in CNO.

A comprehensive review of natural product-derived compounds acting on P2X7R: The promising therapeutic drugs in disorders

BACKGROUND

The P2X7 receptor (P2X7R) is known to play a significant role in regulating various pathological processes associated with immune regulation, neuroprotection, and inflammatory responses. It has emerged as a potential target for the treatment of diseases. In addition to chemically synthesized small molecule compounds, natural products have gained attention as an important source for discovering compounds that act on the P2X7R.

PURPOSE

To explore the research progress made in the field of natural product-derived compounds that act on the P2X7R.

METHODS

The methods employed in this review involved conducting a thorough search of databases, include PubMed, Web of Science and WIKTROP, to identify studies on natural product-derived compounds that interact with P2X7R. The selected studies were then analyzed to categorize the compounds based on their action on the receptor and to evaluate their therapeutic applications, chemical properties, and pharmacological actions.

RESULTS

The natural product-derived compounds acting on P2X7R can be classified into three categories: P2X7R antagonists, compounds inhibiting P2X7R expression, and compounds regulating the signaling pathway associated with P2X7R. Moreover, highlight the therapeutic applications, chemical properties and pharmacological actions of these compounds, and indicate areas that require further in-depth study. Finally, discuss the challenges of the natural products-derived compounds exploration, although utilizing compounds from natural products for new drug research offers unique advantages, problems related to solubility, content, and extraction processes still exist.

CONCLUSION

The detailed information in this review will facilitate further development of P2X7R antagonists and potential therapeutic strategies for P2X7R-associated disorders.

Pyroptosis in renal inflammation and fibrosis: current knowledge and clinical significance

Pyroptosis is a novel inflammatory form of regulated cell death (RCD), characterized by cell swelling, membrane rupture, and pro-inflammatory effects. It is recognized as a potent inflammatory response required for maintaining organismal homeostasis. However, excessive and persistent pyroptosis contributes to severe inflammatory responses and accelerates the progression of numerous inflammation-related disorders. In pyroptosis, activated inflammasomes cleave gasdermins (GSDMs) and generate membrane holes, releasing interleukin (IL)-1β/18, ultimately causing pyroptotic cell death. Mechanistically, pyroptosis is categorized into caspase-1-mediated classical pyroptotic pathway and caspase-4/5/11-mediated non-classical pyroptotic pathway. Renal fibrosis is a kidney disease characterized by the loss of structural and functional units, the proliferation of fibroblasts and myofibroblasts, and extracellular matrix (ECM) accumulation, which leads to interstitial fibrosis of the kidney tubules. Histologically, renal fibrosis is the terminal stage of chronic inflammatory kidney disease. Although there is a multitude of newly discovered information regarding pyroptosis, the regulatory roles of pyroptosis involved in renal fibrosis still need to be fully comprehended, and how to improve clinical outcomes remains obscure. Hence, this review systematically summarizes the novel findings regarding the role of pyroptosis in the pathogenesis of renal fibrosis and discusses potential biomarkers and drugs for anti-fibrotic therapeutic strategies.

Purinergic signaling via P2X receptors and mechanisms of unregulated ATP release in the outer retina and age-related macular degeneration

Age-related macular degeneration (AMD) is a chronic and progressive inflammatory disease of the retina characterized by photoceptor loss and significant central visual impairment due to either choroidal neovascularization or geographic atrophy. The pathophysiology of AMD is complex and multifactorial, driven by a combination of modifiable and non-modifiable risk factors, molecular mechanisms, and cellular processes that contribute to overall disease onset, severity, and progression. Unfortunately, due to the structural, cellular, and pathophysiologic complexity, therapeutic discovery is challenging. While purinergic signaling has been investigated for its role in the development and treatment of ocular pathologies including AMD, the potential crosstalk between known contributors to AMD, such as the complement cascade and inflammasome activation, and other biological systems, such as purinergic signaling, have not been fully characterized. In this review, we explore the interactions between purinergic signaling, ATP release, and known contributors to AMD pathogenesis including complement dysregulation and inflammasome activation. We begin by identifying what is known about purinergic receptors in cell populations of the outer retina and potential sources of extracellular ATP required to trigger purinergic receptor activation. Next, we examine evidence in the literature that the purinergic system accelerates AMD pathogenesis leading to apoptotic and pyroptotic cell death in retinal cells. To fully understand the potential role that purinergic signaling plays in AMD, more research is needed surrounding the expression, distribution, functions, and interactions of purinergic receptors within cells of the outer retina as well as potential crosstalk with other systems. By determining how these processes are affected in the context of purinergic signaling, it will improve our understanding of the mechanisms that drive AMD pathogenesis which is critical in developing treatment strategies that prevent or slow progression of the disease.

P2X7 Is Involved in the Mouse Retinal Degeneration via the Coordinated Actions in Different Retinal Cell Types

Adenosine triphosphate (ATP) released from dying cells with high concentrations is sensed as a danger signal by the P2X7 receptor. Sodium iodate (NaIO3) is an oxidative toxic agent, and its retinal toxicity has been used as the model of dry age-related macular degeneration (AMD). In this study, we used NaIO3-treated mice and cultured retinal cells, including BV-2 microglia, 661W photoreceptors, rMC1 Müller cells and ARPE-19 retinal epithelial cells, to understand the pathological action of P2X7 in retinal degeneration. We found that NaIO3 can significantly decrease the photoreceptor function by reducing a-wave and b-wave amplitudes in electroretinogram (ERG) analysis. Optical coherence tomography (OCT) analysis revealed the degeneration of retinal epithelium and ganglion cell layers. Interestingly, P2X7-/- mice were protected from the NaIO3-induced retinopathy and inflammatory NLRP3, IL-1β and IL-6 gene expression in the retina. Hematoxylin and eosin staining indicated that the retinal epithelium was less deteriorated in P2X7-/- mice compared to the WT group. Although P2X7 was barely detected in 661W, rMC1 and ARPE-19 cells, its gene and protein levels can be increased after NaIO3 treatment, leading to a synergistic cytotoxicity of BzATP [2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate tri(triethyleneammonium)salt] and NaIO3 administration in ARPE-19 cells. In conclusion, the paracrine action of the ATP/P2X7 axis via cell-cell communication is involved in NaIO3-induced retinal injury. Our results show that P2X7 antagonist might be a potential therapy in inflammation-related retinal degeneration.

Predictive Power of Tissue and Circulating Biomarkers for the Severity of Biopsy-Validated Chronic Liver Diseases

Background: Although liver biopsy remains the gold standard for the diagnosis and the monitoring of liver disease, non-invasive biomarkers have been recently suggested to predict liver disease severity, progression, and response to therapy. We investigated multiple tissue and circulating markers of angiogenesis in predicting the severity of biopsy-validated chronic liver diseases in patients with chronic hepatitis C virus (HCV) and in NAFLD/NASH patients. Methods: We studied samples from forty-six patients with HCV and/or NAFLD who underwent liver biopsy, liver ultrasonography, and liver stiffness measurement. Ishak and Brunt scores were calculated. Expression of selective genes and luminex analyses of 17 different circulating pro-angiogenic factors were performed. Results: The phenotype of NAFLD/NASH or HCV subjects was similar, except for insulin, which was expressed at higher levels in NAFLD/NASH patients. A Mann−Whitney test showed significant differences for the circulating levels of HB-EGF and for follistatin between HCV and NAFLD/NASH patients. In HCV patients, we found an inverse correlation between disease stage and BMP-9 and VEGF-A circulating levels, while in NASH/NAFLD direct correlations between stage and BMP-9 and VEGF-A circulating levels were noted. The K-means algorithm divided HCV and NASH/NAFLD patients in two clusters with significant differences between them. Logistic regression models showed a positive relationship with BMP-9 levels for NASH/NAFLD and with HB-EGF circulating concentrations for HCV. ROC analysis showed for BMP-9 > 1188 pg/mL a worse disease in NASH/NAFLD, whereas for HB-EGF < 61 pg/mL a higher severity of disease in HCV. Conclusion: Our data show that circulating biomarker profiles can identify the severity of chronic liver disease of NAFLD/NASH or HCV origin.

Emerging role of neutrophil extracellular traps in the complications of diabetes mellitus

Immune dysfunction is widely regarded as one of the central tenants underpinning the pathophysiology of diabetes mellitus (DM) and its complications. When discussing immunity, the role of neutrophils must be accounted for: neutrophils are the most abundant of the circulating immune cells and are the first to be recruited to sites of inflammation, where they contribute to host defense via phagocytosis, degranulation, and extrusion of neutrophil extracellular traps (NETs). NETs are composed of DNA associated with nuclear and cytosolic neutrophil proteins. Although originally reported as an antimicrobial strategy to prevent microbial dissemination, a growing body of evidence has implicated NETs in the pathophysiology of various autoimmune and metabolic disorders. In these disorders, NETs propagate a pathologic inflammatory response with consequent tissue injury and thrombosis. Many diabetic complications—such as stroke, retinopathy, impaired wound healing, and coronary artery disease—involve these mechanisms. Therefore, in this review, we discuss laboratory and clinical data informing our understanding of the role of NETs in the development of these complications. NET markers, including myeloperoxidase, citrullinated histone H3, neutrophil elastase, and cell-free double-stranded DNA, can easily be measured in serum or be detected via immunohistochemical/immunocytochemical staining of tissue specimens. Therefore, NET constituents potentially constitute reliable biomarkers for use in the management of diabetic patients. However, no NET-targeting drug is currently approved for the treatment of diabetic complications; a candidate drug will require the outcomes of well-designed, robust clinical trials assessing whether NET inhibition can benefit patients in terms of morbidity, quality of life, health expenditures, and mortality. Therefore, much work remains to be done in translating these encouraging pieces of data into clinical trials for NET-targeting medications to be used in the clinic.

Signalling by extracellular nucleotides in health and disease

Nucleotides are released from all cells through regulated pathways or as a result of plasma membrane damage or cell death. Outside the cell, nucleotides act as signalling molecules triggering multiple responses via specific plasma membrane receptors of the P2 family. In the nervous system, purinergic signalling has a key function in neurotransmission. Outside the nervous system, purinergic signalling is one of the major modulators of basal tissue homeostasis, while its dysregulation contributes to the pathogenesis of various disease, including inflammation and cancer. Pre-clinical and clinical evidence shows that selective P2 agonists or antagonists are effective treatments for many pathologies, thus highlighting the relevance of extracellular nucleotides and P2 receptors as therapeutic targets.

Neutrophils and neutrophil extracellular trap components: Emerging biomarkers and therapeutic targets for age-related eye diseases

Age-related eye diseases, including dry eye, glaucoma, age-related macular degeneration, and diabetic retinopathy, represent a major global health issue based on their increasing prevalence and disabling action. Unraveling the molecular mechanisms underlying these diseases will provide novel opportunities to reduce the burden of age-related eye diseases and improve eye health, contributing to sustainable development goals achievement. The impairment of neutrophil extracellular traps formation/degradation processes seems to be one of these mechanisms. These traps formed by a meshwork of DNA and neutrophil cytosolic granule proteins may exacerbate the inflammatory response promoting chronic inflammation, a pivotal cause of age-related diseases. In this review, we describe current findings that suggest the role of neutrophils and their traps in the pathogenesis of the above-mentioned age-related eye diseases. Furthermore, we discuss why these cells and their constituents could be biomarkers and therapeutic targets for dry eye, glaucoma, age-related macular degeneration, and diabetic retinopathy. We also examine the therapeutic potential of some neutrophil function modulators and provide several recommendations for future research in age-related eye diseases.

Administration of P2X7 Receptor Blockers in Oncological Experimental Models

The tumor microenvironment is rich in components that strongly influence cancer cell survival. One of the pivotal molecules present at the tumor bed is ATP, which has an essential role in promoting cancer proliferation and metastasis and immune responses via its receptor P2X7. Several studies have proved the efficacy of P2X7 pharmacological blockade in inhibiting primary and metastatic tumor growth in preclinical models. Here we describe the experimental procedures that we optimized to test P2X7 roles in carcinogenesis by antagonist administration. Special attention is paid to their concentrations and routes of administration. The depicted in vitro models include cell count and viability assays, which are useful to test P2X7 roles in cell proliferation and vitality, and the soft agar colony formation test that allows investigation of the transforming and invading abilities of tumor cells. We also describe systemic and intramass administration of P2X7 blockers in murine models of melanoma and leukemia. Both xenotransplant and syngeneic experimental tumor models are detailed.

Piperazine squaric acid diamides, a novel class of allosteric P2X7 receptor antagonists

The P2X7 receptor (P2X7R) stands out among the purinergic receptors due to its strong involvement in the regulation of tumor growth and metastasis formation as well as in innate immune responses and afferent signal transmission. Numerous studies have pointed out the beneficial effects of P2X7R antagonism for the treatment of a variety of cancer types, inflammatory diseases, and chronic pain. Herein we describe the development of novel P2X7R antagonists, incorporating piperazine squaric diamides as a central element. Besides improving the antagonists' potency from pIC₅₀ values of 5.7-7.6, ADME properties (logD_7.4 value, plasma protein binding, in vitro metabolic stability) of the generated compounds were investigated and optimized to provide novel P2X7R antagonists with drug-like properties. Furthermore, docking studies revealed the antagonists binding to the allosteric binding pocket in two distinct binding poses, depending on the substitution of the central piperazine moiety.

Rapid morphologic changes to microglial cells and upregulation of mixed microglial activation state markers induced by P2X7 receptor stimulation and increased intraocular pressure

BACKGROUND

The identification of endogenous signals that lead to microglial activation is a key step in understanding neuroinflammatory cascades. As ATP release accompanies mechanical strain to neural tissue, and as the P2X7 receptor for ATP is expressed on microglial cells, we examined the morphological and molecular consequences of P2X7 receptor stimulation in vivo and in vitro and investigated the contribution of the P2X7 receptor in a model of increased intraocular pressure (IOP).

METHODS

In vivo experiments involved intravitreal injections and both transient and sustained elevation of IOP. In vitro experiments were performed on isolated mouse retinal and brain microglial cells. Morphological changes were quantified in vivo using Sholl analysis. Expression of mRNA for M1- and M2-like genes was determined with qPCR. The luciferin/luciferase assay quantified retinal ATP release while fura-2 indicated cytoplasmic calcium. Microglial migration was monitored with a Boyden chamber.

RESULTS

Sholl analysis of Iba1-stained cells showed retraction of microglial ramifications 1 day after injection of P2X7 receptor agonist BzATP into mouse retinae. Mean branch length of ramifications also decreased, while cell body size and expression of Nos2, Tnfa, Arg1, and Chil3 mRNA increased. BzATP induced similar morphological changes in ex vivo tissue isolated from Cx3CR1+/GFP mice, suggesting recruitment of external cells was unnecessary. Immunohistochemistry suggested primary microglial cultures expressed the P2X7 receptor, while functional expression was demonstrated with Ca2+ elevation by BzATP and block by specific antagonist A839977. BzATP induced process retraction and cell body enlargement within minutes in isolated microglial cells and increased Nos2 and Arg1. While ATP increased microglial migration, this required the P2Y12 receptor and not P2X7 receptor. Transient elevation of IOP led to microglial process retraction, cell body enlargement, and gene upregulation paralleling changes observed with BzATP injection, in addition to retinal ATP release. Pressure-dependent changes were reduced in P2X7-/- mice. Death of retinal ganglion cells accompanied increased IOP in C57Bl/6J, but not P2X7-/- mice, and neuronal loss showed some association with microglial activation.

CONCLUSIONS

P2X7 receptor stimulation induced rapid morphological activation of microglial cells, including process retraction and cell body enlargement, and upregulation of markers linked to both M1- and M2-type activation. Parallel responses accompanied IOP elevation, suggesting ATP release and P2X7 receptor stimulation influence the early microglial response to increased pressure.

P2X7 Receptor Antagonist Attenuates Retinal Inflammation and Neovascularization Induced by Oxidized Low-Density Lipoprotein

Age-related macular degeneration (AMD) is a common and severe blinding disease among people worldwide. Retinal inflammation and neovascularization are two fundamental pathological processes in AMD. Recent studies showed that P2X7 receptor was closely involved in the inflammatory response. Here, we aim to investigate whether A740003, a P2X7 receptor antagonist, could prevent retinal inflammation and neovascularization induced by oxidized low-density lipoprotein (ox-LDL) and explore the underlying mechanisms. ARPE-19 cells and C57BL/6 mice were treated with ox-LDL and A740003 successively for in vitro and in vivo studies. In this research, we found that A740003 suppressed reactive oxygen species (ROS) generation and inhibited the activation of Nod-like receptor pyrin-domain protein 3 (NLRP3) inflammasome and nuclear factor-κB (NF-κB) pathway. A740003 also inhibited the generation of angiogenic factors in ARPE-19 cells and angiogenesis in mice. The inflammatory cytokines and phosphorylation of inhibitor of nuclear factor-κB alpha (IKBα) were repressed by A740003. Besides, ERG assessment showed that retinal functions were remarkably preserved in A740003-treated mice. In summary, our results revealed that the P2X7 receptor antagonist reduced retinal inflammation and neovascularization and protected retinal function. The protective effects were associated with regulation of NLRP3 inflammasome and the NF-κB pathway, as well as inhibition of angiogenic factors.

The P2X7 Receptor: A Promising Pharmacological Target in Diabetic Retinopathy

Diabetes is a worldwide emergency. Its chronic complications impose a heavy burden on patients, health systems, and on society as a whole. Diabetic retinopathy is one of the most common and serious complications of diabetes, and an established risk factor for blindness in adults. Over 15 years of investigation led to the identification of vascular endothelial growth factor (VEGF) as a main pathogenic factor in diabetic retinopathy and to the introduction of highly effective anti-VEGF-based therapies, such as the monoclonal antibody bevacizumab or its fragment ranibizumab, which helped to prevent diabetes-related blindness in millions of patients. Recently, a pathogenic role for uncontrolled increases in the extracellular ATP concentration (eATP) and for overactivation of the purinergic receptor P2X7 (P2X7R) has been suggested. The P2X7R is an eATP-gated plasma membrane channel expressed in multiple tissues and organs, with a pleiotropic function in inflammation, immunity, cancer, and hormone and growth factor release. P2X7R stimulation or overexpression positively regulate the secretion and buildup of VEGF, thus promoting neo-angiogenesis in a wide variety of disease processes. In this review, we explore current evidence that supports the role of P2X7R receptor signaling in the pathogenesis of diabetic retinopathy, as well as the most appealing current therapeutical options for P2X7R targeting.

P2X7 receptor in multifaceted cellular signalling and its relevance as a potential therapeutic target in different diseases

P2X7 receptor, a purinergic receptor family member, is abundantly expressed on many cells, including immune, muscle, bone, neuron, and glia. It acts as an ATP-activated cation channel that permits the influx of Ca²⁺, Na⁺ and efflux of K⁺ ions. The P2X7 receptor plays crucial roles in many physiological processes including cytokine and chemokine secretion, NLRP3 inflammasome activation, cellular growth and differentiation, locomotion, wound healing, transcription factors activation, cell death and T-lymphocyte survival. Past studies have demonstrated the up-regulation and direct association of this receptor in many pathophysiological conditions such as cancer, diabetics, arthritis, tuberculosis (TB) and inflammatory diseases. Hence, targeting this receptor is considered a worthwhile approach to lessen the afflictions associated with the disorders mentioned above by understanding the receptor architecture and downstream signalling processes. Here, in the present review, we have dissected the structural and functional aspects of the P2X7 receptor, emphasizing its role in various diseased conditions. This information will provide in-depth knowledge about the receptor and help to develop apt curative methodologies for the betterment of humanity in the coming years.

H3 Relaxin Alleviates Migration, Apoptosis and Pyroptosis Through P2X7R-Mediated Nucleotide Binding Oligomerization Domain-Like Receptor Protein 3 Inflammasome Activation in Retinopathy Induced by Hyperglycemia

Introduction: P2X7R excitation-interrelated NLRP3 inflammasome activation induced by high glucose contributes to the pathogenesis of diabetic retinopathy (DR). Relaxin-3 is a bioactive peptide with a structure similar to insulin, which has been reported to be effective in diabetic cardiomyopathy models in vivo and in vitro. However, it is not known whether relaxin-3 has a beneficial impact on DR, and the underlying mechanisms of the effect are also remain unknown.

Methods and Results: The retinas of male streptozotocin (STZ)-induced diabetic Sprague-Dawley (SD) rats were characterized. Human retinal microvascular endothelial cells (HRMECs) were used to evaluate the anti-inflammatory, antiapoptotic, antipyroptotic and anti-migration effects of H3 relaxin by transmission electron microscopy, wound-healing assay, transwell assay, flow cytometry, cytokine assays and western-blot analysis. After H3 relaxin treatment, changes of the ultrastructure and expression of NLRP3 inflammasome related proteins in the retinas of rats were compared with those in the diabetic group. In vitro, H3 relaxin played a beneficial role that decreased cell inflammation, apoptosis, pyroptosis and migration stimulated by advanced glycation end products (AGEs). Moreover, inhibition of P2X7R and NLRP3 inflammasome activation decreased NLRP3 inflammasome-mediated injury that similar to the effects of H3 relaxin. H3 relaxin suppressed the stimulation of apoptosis, pyroptosis and migration of HRMECs in response to AGEs mediated by P2X7R activation of the NLRP3 inflammasome.

Conclusion: Our findings provide new insights into the mechanisms of the inhibitory effect of H3 relaxin on AGE-induced retinal injury, including migration, apoptosis and pyroptosis, mediated by P2X7R-dependent activation of the NLRP3 inflammasome in HRMECs.

Dihydrotanshinone, a Natural Diterpenoid, Preserves Blood-Retinal Barrier Integrity via P2X7 Receptor

Activation of P2X7 signaling, due to high glucose levels, leads to blood retinal barrier (BRB) breakdown, which is a hallmark of diabetic retinopathy (DR). Furthermore, several studies report that high glucose (HG) conditions and the related activation of the P2X7 receptor (P2X7R) lead to the over-expression of pro-inflammatory markers. In order to identify novel P2X7R antagonists, we carried out virtual screening on a focused compound dataset, including indole derivatives and natural compounds such as caffeic acid phenethyl ester derivatives, flavonoids, and diterpenoids. Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) rescoring and structural fingerprint clustering of docking poses from virtual screening highlighted that the diterpenoid dihydrotanshinone (DHTS) clustered with the well-known P2X7R antagonist JNJ47965567. A human-based in vitro BRB model made of retinal pericytes, astrocytes, and endothelial cells was used to assess the potential protective effect of DHTS against HG and 2′(3′)-O-(4-Benzoylbenzoyl)adenosine-5′-triphosphate (BzATP), a P2X7R agonist, insult. We found that HG/BzATP exposure generated BRB breakdown by enhancing barrier permeability (trans-endothelial electrical resistance (TEER)) and reducing the levels of ZO-1 and VE-cadherin junction proteins as well as of the Cx-43 mRNA expression levels. Furthermore, HG levels and P2X7R agonist treatment led to increased expression of pro-inflammatory mediators (TLR-4, IL-1β, IL-6, TNF-α, and IL-8) and other molecular markers (P2X7R, VEGF-A, and ICAM-1), along with enhanced production of reactive oxygen species. Treatment with DHTS preserved the BRB integrity from HG/BzATP damage. The protective effects of DHTS were also compared to the validated P2X7R antagonist, JNJ47965567. In conclusion, we provided new findings pointing out the therapeutic potential of DHTS, which is an inhibitor of P2X7R, in terms of preventing and/or counteracting the BRB dysfunctions elicited by HG conditions.

P2X receptors in cancer growth and progression

It is increasingly appreciated that ion channels have a crucial role in tumors, either as promoters of cancer cell growth, or modulators of immune cell functions, or both. Among ion channels, P2X receptors have a special status because they are gated by ATP, a common and abundant component of the tumor microenvironment. Furthermore, one P2X receptor, i.e. P2X7, may also function as a conduit for ATP release, thus fuelling the increased extracellular ATP level in the tumor interstitium. These findings show that P2X receptors and extracellular ATP are indissoluble partners and key regulators of tumor growth, and suggest the exploitation of the extracellular ATP-P2X partnership to develop innovative therapeutic approaches to cancer.

P2X7 Receptors: An Untapped Target for the Management of Cardiovascular Disease

Chronic low-grade inflammation contributes to the development of several diseases, including cardiovascular disease. Adequate strategies to target inflammation in cardiovascular disease are in their infancy and remain an avenue of great interest. The purinergic receptor P2X7 is a ubiquitously expressed receptor that predominately mediates inflammation and cellular death. P2X7 is a ligand-gated cation channel that is activated in response to high concentrations of extracellular ATP, triggering the assembly and activation of the NLRP3 (nuclear oligomerization domain like receptor family pyrin domain containing 3) inflammasome and subsequent release of proinflammatory cytokines IL (interleukin)-1β and IL-18. Increased P2X7 activation and IL-1β and IL-18 concentrations have been implicated in the development of many cardiovascular conditions including hypertension, atherosclerosis, ischemia/reperfusion injury, and heart failure. P2X7 receptor KO (knockout) mice exhibit a significant attenuation of the inflammatory response, which corresponds with reduced disease severity. P2X7 antagonism blunts blood pressure elevation in hypertension and progression of atherosclerosis in animal models. IL-1β and IL-18 inhibition has shown efficacy in clinical trials reducing major adverse cardiac events, including myocardial infarction, and heart failure. With several P2X7 antagonists available with proven safety margins, P2X7 antagonism could represent an untapped potential for therapeutic intervention in cardiovascular disorders.

A rationale for targeting the P2X7 receptor in Coronavirus disease 19

Severe pneumonia which shares several of the features of acute respiratory distress syndrome (ARDS) is the main cause of morbidity and mortality in Coronavirus disease 19 (Covid‐19) for which there is no effective treatment, so far. ARDS is caused and sustained by an uncontrolled inflammatory activation characterized by a massive release of cytokines (cytokine storm), diffuse lung oedema, inflammatory cell infiltration, and disseminated coagulation. Macrophage and T lymphocyte dysfunction plays a central role in this syndrome. In several experimental in vitro and in vivo models, many of these pathophysiological changes are triggered by stimulation of the P2X7 receptor. We hypothesize that this receptor might be an ideal candidate to target in Covid‐19‐associated severe pneumonia.

Linked Articles

This article is part of a themed issue on The Pharmacology of COVID‐19. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.21/issuetoc

Increased expression of hypoxia inducible factor-1 alpha and vascular endothelial growth factor is associated with diabetic gastroparesis

BACKGROUND

Gastroparesis is a recognized complication of diabetes but its pathogenic mechanism incompletely understood. Our aim was to determine whether HIF-1α and VEGF are secreted from gastric tissue is a fundamental factor that drives diabetic gastroparesis.

METHODS

Diabetes was induced in Sprague-Dawley by a single intraperitoneal injection of 65 mg/kg streptozotocin. After 4 and 12 weeks, rats were euthanized for assaying body weight, blood glucose, gastric acid secretion and gastric emptying. Morphologic changes in gastric mucosa were observed by the light microscope. Expression of HIF-1α and VEGF were assessed using immunohistochemistry, RT-PCR and Western blot analyses.

RESULTS

Compared with control group, blood glucose were significantly increased and body weight were markedly decreased in streptozotocin-induced diabetes. Gastric emptying was significantly decreased in diabetic rats compared to the control group at different times. The number of parietal cells was obviously decreased, and vacuolated degeneration in diabetic rats. Gastric acid secretion in diabetic group was significantly decreased, and expression of HIF-1α and VEGF were significantly increased in the diabetic group.

CONCLUSION

These results indicated that overexpression of HIF-1α and VEGF in the gastric mucosa and played a pivotal role in the progression of diabetic gastroparesis.

Purinergic signaling, DAMPs, and inflammation

Danger sensing is one of the most fundamental evolutionary features enabling multicellular organisms to perceive potential threats, escape from risky situations, fight actual intruders, and repair damage. Several endogenous molecules are used to "signal damage," currently referred to as "alarmins" or "damage-associated molecular patterns" (DAMPs), most being already present within all cells (preformed DAMPs), and thus ready to be released, and others neosynthesized following injury. Over recent years it has become overwhelmingly clear that adenosine 5'-triphosphate (ATP) is a ubiquitous and extremely efficient DAMP (thus promoting inflammation), and its main metabolite, adenosine, is a strong immunosuppressant (thus dampening inflammation). Extracellular ATP ligates and activates the P2 purinergic receptors (P2Rs) and is then degraded by soluble and plasma membrane ecto-nucleotidases to generate adenosine acting at P1 purinergic receptors (P1Rs). Extracellular ATP, P2Rs, ecto-nucleotidases, adenosine, and P1Rs are basic elements of the purinergic signaling network and fundamental pillars of inflammation.

Alteration of purinergic signaling in diabetes: Focus on vascular function

Diabetes is an important risk factor for the development of cardiovascular disease including atherosclerosis and ischemic heart disease. Vascular complications including macro- and micro-vascular dysfunction are the leading causes of morbidity and mortality in diabetes. Disease mechanisms at present are unclear and no ideal therapies are available, which urgently calls for the identification of novel therapeutic targets/agents. An altered nucleotide- and nucleoside-mediated purinergic signaling has been implicated to cause diabetes-associated vascular dysfunction in major organs. Alteration of both purinergic P1 and P2 receptor sensitivity rather than the changes in receptor expression accounts for vascular dysfunction in diabetes. Activation of P2X₇ receptors plays a crucial role in diabetes-induced retinal microvascular dysfunction. Recent findings have revealed that both ecto-nucleotidase CD39, a key enzyme hydrolyzing ATP, and CD73, an enzyme regulating adenosine turnover, are involved in the renal vascular injury in diabetes. Interestingly, erythrocyte dysfunction in diabetes by decreasing ATP release in response to physiological stimuli may serve as an important trigger to induce vascular dysfunction. Nucleot(s)ide-mediated purinergic activation also exerts long-term actions including inflammatory and atherogenic effects in hyperglycemic and diabetic conditions. This review highlights the current knowledge regarding the altered nucleot(s)ide-mediated purinergic signaling as an important disease mechanism for the diabetes-associated vascular complications. Better understanding the role of key receptor-mediated signaling in diabetes will provide more insights into their potential as targets for the treatment.

Effect of P2X7 receptor on tumorigenesis and its pharmacological properties

The occurrence and development of tumors is a multi-factor, multi-step, multi-gene pathological process, and its treatment has been the most difficult problem in the field of medicine today. Therefore, exploring the relevant factors involved in the pathogenesis of tumors, improving the diagnostic rate, treatment rate, and prognosis survival rate of tumors have become an urgent problem to be solved. A large number of studies have shown that the P2X7 receptor (P2X7R) and the tumor microenvironment play an important role in regulating the growth, apoptosis, migration and invasion of tumor cells. P2X7R is an ATP ligand-gated cationic channel receptor, which exists in most tissues of the human body. The main function of P2X7R is to regulate the relevant cells (such as macrophages, lymphocytes, and glial cells) to release damaging factors and induce apoptosis and cell death. In recent years, with continuous research and exploration of P2X7R, it has been found that P2X7R exists on the surface of most tumor cells and plays an important role in tumor pathogenesis. The activation of the P2X7R can open the ion channels on the tumor cell membrane (sodium ion, calcium ion influx and potassium ion outflow), trigger rearrangement of the cytoskeleton and changes in membrane fluidity, allow small molecule substances to enter the cell, activate enzymes and kinases in related signaling pathways in cells (such as PKA, PKC, ERK1/2, AKT, and JNK), thereby affecting the development of tumor cells, and can also indirectly affect the growth, apoptosis and migration of tumor cells through tumor microenvironment. At present, P2X7R has been widely recognized for its important role in tumorigenesis and development. In this paper, we give a comprehensive description of the structure and function of the P2X7R gene. We also clarified the concept of tumor microenvironment and its effect on tumors, discussed the relevant pathological mechanisms in the development of tumors, and revealed the intrinsic relationship between P2X7R and tumors. We explored the pharmacological properties of P2X7R antagonists or inhibitors in reducing its expression as targeted therapy for tumors.

A new research hot spot: The role of NLRP3 inflammasome activation, a key step in pyroptosis, in diabetes and diabetic complications

Pyroptosis is a form of cell death mediated by gasdermin D (GSDMD); it is characterised by NLRP3 inflammasome activation, caspase activation, cell membrane pore formation, and the release of interleukin-1β and interleukin-18. NLRP3 inflammasome activation plays a central role in pyroptosis. Recent research has suggested that NLRP3 inflammasome activation may be involved in the occurrence and development of diabetes mellitus and its associated complications. This finding provided the impetus for us to clarify the significance of pyroptosis in diabetes. In this review, we summarise the current understanding of the molecular mechanisms involved in pyroptosis, as well as recent advances in the role of NLRP3 inflammasome activation and pyroptosis in the development of diabetes and diabetic complications.