P2X7 receptor activation amplifies lipopolysaccharide-induced vascular hyporeactivity via interleukin-1 beta release

THE effect of P2X7 receptor activation on functional responses of human left internal mammary artery

The Purinoreceptor 7 (P2X7R) has become a promising drug target in many cardiovascular diseases, including coronary artery disease, since prolonged activation of P2X7R could promote vascular dysfunction, atherosclerosis, and thrombosis. Thus, we aimed to study the effects of P2X7R activation on vascular relaxation responses of the human left internal mammary artery (LIMA). Sections of redundant human LIMA were cut into 3-mm wide rings,, suspended in 20-mL organ baths containing physiologic salt solution, and attached to an isometric force transducer connected to a computer-based data acquisition system. Long-term (60 min) incubation with specific P2X7R agonist Bz-ATP caused significant reductions in relaxation responses of LIMA to ATP and acetylcholine, which were reversed by selective P2X7R antagonists Brilliant Blue G or AZ11645373, whereas there were no changes in relaxation responses to endothelium-independent vasodilators isoprenaline, cAMP analog 8-Br-cAMP, and nitric oxide donor sodium nitroprusside. The impairment in relaxant responses of LIMA to endothelium-dependent vasodilators following activation of P2X7R for the long-term may contribute to postoperative LIMA vasospasm and hypertension. Modulation of P2X7R activity with selective agents may represent a new potential therapeutic approach in patients undergoing coronary artery bypass grafting surgery.

Adenosine and ATPγS protect against bacterial pneumonia-induced acute lung injury

Lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, disrupts the alveolar-capillary barrier, triggering pulmonary vascular leak thus inducing acute lung injury (ALI). Extracellular purines, adenosine and ATP, protected against ALI induced by purified LPS. In this study, we investigated whether these purines can impact vascular injury in more clinically-relevant E.coli (non-sterile LPS) murine ALI model. Mice were inoculated with live E. coli intratracheally (i.t.) with or without adenosine or a non-hydrolyzable ATP analog, adenosine 5'-(γ-thio)-triphosphate (ATPγS) added intravenously (i.v.). After 24 h of E. coli treatment, we found that injections of either adenosine or ATPγS 15 min prior or adenosine 3 h after E.coli insult significantly attenuated the E.coli-mediated increase in inflammatory responses. Furthermore, adenosine prevented weight loss, tachycardia, and compromised lung function in E. coli-exposed mice. Accordingly, treatment with adenosine or ATPγS increased oxygen saturation and reduced histopathological signs of lung injury in mice exposed to E. coli. Lastly, lung-targeting gene delivery of adenosine or ATPγS downstream effector, myosin phosphatase, significantly attenuated the E. coli-induced compromise of lung function. Collectively, our study has demonstrated that adenosine or ATPγS mitigates E. coli-induced ALI in mice and may be useful as an adjuvant therapy in future pre-clinical studies.

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.

Protective Effect of Astragaloside IV on High Glucose-Induced Endothelial Dysfunction via Inhibition of P2X7R Dependent P38 MAPK Signaling Pathway

Vascular endothelial dysfunction is associated with increased mortality in patients with diabetes. Astragaloside IV (As-IV) is a bioactive saponin with therapeutic potential as an anti-inflammatory and antiendothelial dysfunction. However, the underlying mechanism for how As-IV ameliorated endothelial dysfunction is still unclear. Therefore, in this study, we examined the protective effect of As-IV against endothelial dysfunction and explored potential molecular biology mechanism. In vivo, rats were intraperitoneally injected with streptozotocin (STZ) at a dose of 65 mg/kg body weight to establish a diabetic model. In vitro studies, rat aortic endothelial cells (RAOEC) were pretreated with As-IV, SB203580 (p38 MAPK inhibitor) for 2 h prior to the addition of high glucose (33 mM glucose). Our findings indicated that As-IV improved impaired endothelium-dependent relaxation and increased the levels of endothelial NO synthase (eNOS) and nitric oxide (NO) both in vivo and in vitro. Besides, As-IV treatment inhibited the elevated inflammation and oxidative stress in diabetic model both in vivo and in vitro. Moreover, As-IV administration reversed the upregulated expression of P2X7R and p-p38 MAPK in vivo and in vitro. Additionally, the effects of both P2X7R siRNA and SB203580 on endothelial cells were similar to As-IV. Collectively, our study demonstrated that As-IV rescued endothelial dysfunction induced by high glucose via inhibition of P2X7R dependent p38 MAPK signaling pathway. This provides a theoretical basis for the further study of the vascular endothelial protective effects of As-IV.

Non-coding RNAs in aortic dissection: From biomarkers to therapeutic targets

Aortic dissection (AD) is the rupture of the aortic intima, causing the blood in the cavity to enter the middle of the arterial wall. Without urgent and proper treatment, the mortality rate increases to 50% within 48 hours. Most patients present with acute onset of symptoms, including sudden severe pain and complex and variable clinical manifestations, which can be easily misdiagnosed. Despite this, the molecular mechanisms underlying AD are still unknown. Recently, non‐coding RNAs have emerged as novel regulators of gene expression. Previous studies have proven that ncRNAs can regulate several cardiovascular diseases; therefore, their potential as clinical biomarkers and novel therapeutic targets for AD has aroused widespread interest. To date, several studies have reported that microRNAs are crucially involved in AD progression. Additionally, several long non‐coding RNAs and circular RNAs have been found to be differentially expressed in AD samples, suggesting their potential roles in vascular physiology and disease. In this review, we discuss the functions of ncRNAs in AD pathophysiology and highlight their potential as biomarkers and therapeutic targets for AD. Meanwhile, we present the animal models previously used for AD research, as well as the specific methods for constructing mouse or rat AD models.

Natural compounds acting at P2 receptors alleviate peripheral neuropathy

Neuropathic pain is generally resistant to currently available treatments, and it is often a consequence of nerve injury due to surgery, diabetes or infection. Myocardial ischemic nociceptive signaling increases the sympathoexcitatory reflex to aggravate myocardial injury. Elucidation of the pathogenetic factors might provide a target for optimal treatment. Abundant evidence in the literature suggests that P2X and P2Y receptors play important roles in signal transmission. Traditional Chinese medicines, such as emodin, puerarin and resveratrol, antagonize nociceptive transmission mediated by purinergic 2 (P2) receptors in primary afferent neurons. This review summarizes recently published data on P2 receptor-mediated neuropathic pain and myocardial ischemia in dorsal root ganglia (DRG), superior cervical ganglia (SCG) and stellate ganglia (SG), with a special focus on the beneficial role of natural compounds.

P2X7, a critical regulator and potential target for bone and joint diseases

Abundant evidence indicted that P2X7 receptor show a essential role in human health and some human diseases including hypertension, atherosclerosis, pulmonary inflammation, tuberculosis infection, psychiatric disorders, and cancer. P2X7 receptor also has an important role in some central nervous system diseases such as neurodegenerative disorders. Recently, more research suggested that P2X7 receptor also plays a crucial role in bone and joint diseases. But the effect of P2X7 receptor on skeletal and joint diseases has not been systematically reviewed. In this article, the role of P2X7 receptor in skeletal and joint diseases is elaborated. The activation of P2X7 receptor can ameliorate osteoporosis by inducing a fine balance between osteoclastic resorption and osteoblastic bone formation. The activation of P2X7 receptor can relieve the stress fracture injury by increasing the response to mechanical loading and inducing osteogenesis. But the activation of P2X7 receptor mediates the cell growth and cell proliferation in bone cancer. In addition, the activation of P2X7 receptor can aggravate the process of some joint diseases such as osteoarthritis, rheumatoid arthritis, and acute gouty arthritis. The inhibition of P2X7 receptor can alleviate the pathological process of joint disease to some extent. In conclusion, P2X7 receptor may be a critical regulator and therapeutic target for bone and joint diseases.

LncRNA and mRNA interaction study based on transcriptome profiles reveals potential core genes in the pathogenesis of human thoracic aortic dissection

The aim of the present study was to determine the potential core genes in the pathogenesis of human thoracic aortic dissection (TAD) by analyzing microarray profiles of long non‑coding (lnc)‑RNAs between TAD and normal thoracic aorta (NTA). The differentially expressed lncRNA profiles of the aorta tissues between TAD patients (TAD group, n=6) and age‑matched donors with aortic diseases (NTA group, n=6) were analyzed by lncRNAs microarray. Gene ontology (GO), pathway and network analyses were used to further investigate candidate lncRNAs and mRNAs. Differentially expressed lncRNAs and mRNAs were validated by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). In total, the present study identified 765 lncRNAs and 619 mRNAs with differential expression between TAD and NTA (fold change >2.0, P<0.01). GO analysis demonstrated that the differentially upregulated lncRNAs are associated with cell differentiation, homeostasis, cell growth and angiogenesis. Kyoto Encyclopedia of Gene and Genomes pathway analysis demonstrated that the differentially downregulated lncRNAs are mainly associated with arrhythmogenic right ventricular cardiomyopathy, hypertrophic cardiomyopathy and dilated cardiomyopathy. To reduce the lncRNAs for further investigation and to enrich those potentially involved in TAD, a total of 16 candidate lncRNAs with a significant expression (fold change >4, P<0.01) were selected, that were associated with an annotated protein‑coding gene through the GO term and scientific literatures. Then a set of significantly expressed lncRNAs [purinergic receptor P2X7 (P2RX7), hypoxia inducing factor (HIF)‑1A‑AS2, AX746823, RP11‑69I8.3 and RP11‑536K7.5) and the corresponding mRNAs (P2RX7, cyclin dependent kinase inhibitor 2B, HIF‑1A, runt‑related transcription factor 1, connective tissue growth factor and interleukin 2 receptor a chain] were confirmed using RT‑qPCR. The present study revealed that the expression profiles of lncRNAs and mRNAs in aorta tissues from TAD were significantly altered. These results may provide important insights into the pathogenesis of TAD disease.

Role of the Purinergic Receptor P2XR4 After Blunt Chest Trauma in Cigarette Smoke-Exposed Mice

Both acute and chronic lung injury are associated with up-regulation of the pulmonary expression of the purinergic receptors P2XR4 and P2XR7. Genetic deletion or blockade of P2XR7 attenuated pulmonary hyperinflammation, but simultaneous P2XR4 up-regulation compensated for P2XR7 deletion. Therefore, we tested the hypothesis whether genetic P2XR4 deletion would attenuate the pulmonary inflammatory response and thereby improve organ function after blunt chest trauma in mice with and without pretraumatic cigarette smoke (CS) exposure.After 3 weeks to 4 weeks of exposure to CS, anesthetized wildtype or P2XR4 mice (n = 32) underwent a blast wave-induced blunt chest trauma followed by 4 h of lung-protective mechanical ventilation, fluid resuscitation, and noradrenaline support to maintain mean arterial pressure >55 mm Hg. Hemodynamics, lung mechanics, gas exchange, and acid-base status were measured together with blood and tissue cytokine and chemokine concentrations, heme oxygenase-1, B-cell lymphoma-extra large (Bcl-xL), endogenous nuclear factor-κB inhibitor (IκBα) expression, nitrotyrosine formation, purinergic receptor expression, and histological scoring.Despite a significant increase in the histopathology score in both CS-exposed groups, neither CS exposure nor P2XR4 deletion had any significant effect on post-traumatic pulmonary function and inflammatory response. However, P2XR4 deletion was associated with attenuated impairment of glucose homeostasis and acid-base-status after CS exposure and chest trauma.In conclusion, genetic P2XR4 deletion failed to attenuate the acute post-traumatic pulmonary inflammatory response. The improved glucose homeostasis and acid-base-status after CS exposure in the P2XR4 group was possibly due to less alveolar hypoxia-induced right ventricular remodeling resulting in preserved liver metabolic capacity.

The P2X7 purinergic receptor: An emerging therapeutic target in cardiovascular diseases

The P2X7 purinergic receptor, a calcium permeable cationic channel, is activated by extracellular ATP. Most studies show that P2X7 receptor plays an important role in the nervous system diseases, immune response, osteoporosis and cancer. Mounting evidence indicates that P2X7 receptor is also associated with cardiovascular disease. For example, the P2X7 receptor activated by ATP can attenuate myocardial ischemia-reperfusion injury. By contrast, inhibition of P2X7 receptor decreases arrhythmia after myocardial infarction, prolongs cardiac survival after a long term heart transplant, alleviates the dilated cardiomyopathy and the autoimmune myocarditis process. The P2X7 receptor also mitigates vascular diseases including atherosclerosis, hypertension, thrombosis and diabetic retinopathy. This review focuses on the latest research on the role and therapeutic potential of P2X7 receptor in cardiovascular diseases.

Blunt Chest Trauma in Mice after Cigarette Smoke-Exposure: Effects of Mechanical Ventilation with 100% O2

Cigarette smoking (CS) aggravates post-traumatic acute lung injury and increases ventilator-induced lung injury due to more severe tissue inflammation and apoptosis. Hyper-inflammation after chest trauma is due to the physical damage, the drop in alveolar PO₂, and the consecutive hypoxemia and tissue hypoxia. Therefore, we tested the hypotheses that 1) CS exposure prior to blunt chest trauma causes more severe post-traumatic inflammation and thereby aggravates lung injury, and that 2) hyperoxia may attenuate this effect. Immediately after blast wave-induced blunt chest trauma, mice (n=32) with or without 3-4 weeks of CS exposure underwent 4 hours of pressure-controlled, thoraco-pulmonary compliance-titrated, lung-protective mechanical ventilation with air or 100 % O₂. Hemodynamics, lung mechanics, gas exchange, and acid-base status were measured together with blood and tissue cytokine and chemokine concentrations, heme oxygenase-1 (HO-1), activated caspase-3, and hypoxia-inducible factor 1-α (HIF-1α) expression, nuclear factor-κB (NF-κB) activation, nitrotyrosine formation, purinergic receptor 2X₄ (P2XR₄) and 2X₇ (P2XR₇) expression, and histological scoring. CS exposure prior to chest trauma lead to higher pulmonary compliance and lower PaO₂ and Horovitz-index, associated with increased tissue IL-18 and blood MCP-1 concentrations, a 2-4-fold higher inflammatory cell infiltration, and more pronounced alveolar membrane thickening. This effect coincided with increased activated caspase-3, nitrotyrosine, P2XR₄, and P2XR₇ expression, NF-κB activation, and reduced HIF-1α expression. Hyperoxia did not further affect lung mechanics, gas exchange, pulmonary and systemic cytokine and chemokine concentrations, or histological scoring, except for some patchy alveolar edema in CS exposed mice. However, hyperoxia attenuated tissue HIF-1α, nitrotyrosine, P2XR₇, and P2XR₄ expression, while it increased HO-1 formation in CS exposed mice. Overall, CS exposure aggravated post-traumatic inflammation, nitrosative stress and thereby organ dysfunction and injury; short-term, lung-protective, hyperoxic mechanical ventilation have no major beneficial effect despite attenuation of nitrosative stress, possibly due to compensation of by regional alveolar hypoxia and/or consecutive hypoxemia, resulting in down-regulation of HIF-1α expression.

Altered expression of P2Y2 and P2X7 purinergic receptors in the isolated rat heart mediates ischemia-reperfusion injury

The aim of this study is to analyze the expression of purinergic receptors in the heart after ischemia-reperfusion, and their possible role in ischemia-reperfusion injury. Rat hearts were perfused according to the Langendorff technique and subjected to 30 min ischemia followed by 15 min reperfusion. Ischemia-reperfusion reduced the gene expression and protein content of purinergic receptors of the P2Y2 subtype, and increased the gene expression and protein content of the P2X7 subtype. Treatment with the agonist of the P2Y2 subtype 2-thio-UTP and with the antagonist of the P2X7 subtype Brilliant Blue improved myocardial function parameters, reduced cell death and increased the myocardial expression of antiapoptotic markers after ischemia-reperfusion. These results suggest that the myocardial expression of the protective P2Y2 subtype of purinergic receptors is reduced, whereas that of the harmful subtype P2X7 subtype is increased during coronary ischemia-reperfusion. This may contribute to myocardial injury in this condition.

Vascular and inflammatory actions of P2X receptors in renal injury

P2 purinergic receptors are activated by extracellular ATP and subserve a plethora of roles in the body, including metabolism, inflammation and neuronal signalling. This review focuses on renal purinergic receptors and how different roles that they play may contribute to renal dysfunction and the progression of chronic kidney disease. Numerous studies have linked P2 receptors, particularly the P2X4R and P2X7R subtypes, to kidney injury and damage. However, the mechanisms underlying this association are not fully defined. Several studies show that activation of P2X4R and particularly P2X7R can have a pro-inflammatory effect, causing or exacerbating damage to renal tissue. However, clinical trials aiming to utilise P2X7R antagonists to treat inflammatory disease have been unsuccessful, and it is possible that other mechanisms besides inflammation tie P2X7R activation to disease progression. In this context, purinergic signalling is also involved in the control of vascular tone and our recent studies suggest that activation of P2X4R/P2X7R causes renal vascular dysfunction and contributes to chronic kidney disease. This brief review aims to summarise the complementary inflammatory and vascular roles of P2X receptors in the kidney, with emphasis on the subtypes P2X4R and P27XR, and how each contributes to and presents therapeutic targets in the progression of chronic kidney disease.

The Beneficial Effects of P2X7 Antagonism in Rats with Bile Duct Ligation-induced Cirrhosis

Splanchnic angiogenesis in liver cirrhosis often leads to complications as gastroesophageal variceal hemorrhage and the treatment efficacy is adversely affected by poor portal-systemic collateral vasoresponsiveness related to nitric oxide (NO). Purinergic receptor subtype P2X7 participates in the modulation of inflammation, angiogenesis, fibrogenesis and vasoresponsiveness, but the relevant influence in cirrhosis is unknown. Common bile duct-ligated (CBDL) or sham-operated Spraque-Dawley rats received brilliant blue G (BBG, a P2X7 antagonist and food additive) or vehicle from the 15th to 28th day after operations, then hemodynamics, mesenteric angiogenesis, portal-systemic shunting, liver fibrosis, and protein expressions of angiogenic and fibrogenic factors were evaluated. The influence of oxidized ATP (oATP, another P2X7 receptor antagonist) on the collateral vasoresponsiveness to arginine vasopressin (AVP) was also surveyed. BBG decreased superior mesenteric artery (SMA) flow, portal-systemic shunting, mesenteric vascular density, and mesenteric protein expressions of vascular endothelial growth factor (VEGF), VEGF receptor 2 (VEGFR2), phospho (p)-VEGFR2, platelet-derived growth factor (PDGF), PDGF receptor beta (PDGFRβ), cyclooxygenase (COX)-1, COX-2, and endothelial NO synthase (eNOS) in CBDL rats. BBG also ameliorated liver fibrosis and down-regulated hepatic interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), PDGF, IL-1β, transforming growth factor-beta (TGF-β), p-extracellular-signal-regulated kinases (ERK), and alpha-smooth muscle actin (α-SMA) expressions in CBDL rats. The collateral vasocontractility to AVP was enhanced by oATP. oATP down-regulated eNOS, inducible NOS (iNOS), VEGF, Akt, p-Akt, and nuclear factor-kappa B (NF-κB) expressions in splenorenal shunt, the most prominent intra-abdominal collateral vessel in rodents. P2X7 antagonism alleviates splanchnic hyperemia, severity of portal-systemic shunting, mesenteric angiogenesis, liver fibrosis, and enhances portal-systemic collateral vasoresponsiveness in cirrhotic rats. P2X7 blockade may be a feasible strategy to control cirrhosis and complications.

Mitochondrial damage-associated molecular patterns and vascular function

Immune system activation occurs not only due to foreign stimuli, but also due to endogenous molecules. As such, endogenous molecules that are released into the circulation due to cell death and/or injury alarm the immune system that something has disturbed homeostasis and a response is needed. Collectively, these molecules are known as damage-associated molecular patterns (DAMPs). Mitochondrial DAMPs (mtDAMPs) are potent immunological activators due to the bacterial ancestry of mitochondria. Mitochondrial DAMPs are recognized by specific pattern recognition receptors of the innate immune system, some of which are expressed in the cardiovascular system. Cell death leads to release of mtDAMPs that may induce vascular changes by mechanisms that are currently not well understood. This review will focus on recently published evidence linking mtDAMPs and immune system activation to vascular dysfunction and cardiovascular disease.

Andrographolide protects against lipopolysaccharide-induced vascular hyporeactivity by suppressing the expression of inducible nitric oxide in periaortic adipose

This study investigated the role of perivascular adipose tissue (PVAT) in the beneficial effects of andrographolide on vascular reactivity in endotoxaemic rats. After being challenged by lipopolysaccharide (4 mg/kg intraperitoneally), the rats were treated with andrographolide (1 mg/kg intraperitoneally). The response to phenylephrine of aortic rings with or without PVAT was recorded. Vascular relaxing effect of PVAT was determined by bioassay experiments. Inducible nitric oxide synthase (iNOS) in aortic PVAT was tested by Western blot, immunofluorescence, and quantitative polymerase chain reaction. Lipopolysaccharide injection lowered the contraction force induced by phenylephrine in aortic rings with or without PVAT and andrographolide treatment reversed these effects. In bioassay experiments, transferring bathing solution incubated with a PVAT+ ring to a PVAT- ring induced relaxation in the recipient. This relaxing effect of PVAT from endotoxaemic rats was more potent than the rats treated with vehicles. Andrographolide treatment decreased the relaxing effect of PVAT in endotoxaemic rats. The levels of iNOS protein and messenger RNA in PVAT were significantly higher in endotoxaemic rats than in the rats treated with vehicles. Andrographolide treatment decreased PVAT iNOS protein and messenger RNA levels in endotoxaemic rats. Our results suggest that andrographolide restores vascular reactivity in endotoxaemic rats by downregulation of iNOS in PVAT.

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

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

P2X7 receptor activation contributes to an initial upstream mechanism of lipopolysaccharide-induced vascular dysfunction

Pro-inflammatory cytokines, chemokines and ROS (reactive oxygen species) are excessively produced in endotoxaemia. However, attempting to inhibit all of these inflammatory signalling pathways at the same time in order to prevent endotoxaemia is difficult. In a previous study we observed that activation of P2X7 receptors elicited the release of IL (interleukin)-1β from LPS (lipopolysaccharide)-incubated vessels. In the present study, we hypothesize that P2X7 receptor activation is the initial event leading to vascular dysfunction following LPS treatment. LPS-induced decreases in MAP (mean arterial pressure) and pressor responses to NE (noradrenaline) were attenuated in P2X7KO (P2X7-knockout) mice. Hyporeactivity in response to PE (phenylephrine) in isolated mesenteric arteries by LPS treatment was also observed in C57BL/6 [WT (wild-type)] mice, which was prevented by IL1ra (IL-1 receptor antagonist), L-NAME (N(G)-nitro-L-arginine methyl ester) and indomethacin and in P2X7KO mice. In addition, treatment with IL1ra plus L-NAME produced an additive inhibition of LPS-induced vascular hyporeactivity, suggesting different signalling pathways between IL-1β and NOS (NO synthase). LPS-induced plasma levels of IL-1β, TNFα (tumour necrosis factor α), IL-10, vascular eNOS (endothelial NOS) and COX2 (cyclo-oxygenase 2) protein expression, as determined by ELISA and Western blot, observed in WT mice were inhibited by IL1ra and in P2X7KO mice. These results suggest that P2X7 receptor activation involves an initial upstream mechanism of LPS-induced vascular dysfunction, which is associated with IL-1β-mediated eNOS, COX2 activation and TNFα release.

Action of natural products on p2 receptors: a reinvented era for drug discovery

Natural products contribute significantly to available drug therapies and have been a rich source for scientific investigation. In general, due to their low cost and traditional use in some cultures, they are an object of growing interest as alternatives to synthetic drugs. With several diseases such as cancer, and inflammatory and neuropathic diseases having been linked to the participation of purinergic (P2) receptors, there has been a flurry of investigations on ligands within natural products. Thirty-four different sources of these compounds have been found so far, that have shown either agonistic or antagonistic effects on P2 receptors. Of those, nine different plant sources demonstrated effects on P2X2, P2X3, P2X7, and possibly P2Y12 receptor subtypes. Microorganisms, which represent the largest group, with 26 different sources, showed effects on both receptor subtypes, ranging from P2X1 to P2X4 and P2X7, and P2Y1, P2Y2, P2Y4, and P2Y6. In addition, there were seventeen animal sources that affected P2X7 and P2Y1 and P2Y12 receptors. Natural products have provided some fascinating new mechanisms and sources to better understand the P2 receptor antagonism. Moreover, current investigations should clarify further pharmacological mechanisms in order to consider these products as potential new medicines.

Effects of LPS on P2X3 receptors of trigeminal sensory neurons and macrophages from mice expressing the R192Q Cacna1a gene mutation of familial hemiplegic migraine-1

A knockin (KI) mouse model with the R192Q missense mutation in the Cacna1a gene commonly detected in familial hemiplegic migraine was used to study whether trigeminal ganglia showed a basal inflammatory profile that could be further enhanced by the lipopolysaccharide (LPS) toxin. Adenosine-5'-triphosphate (ATP)-gated purinergic ionotropic receptor 3 (P2X3) currents expressed by the large majority of trigeminal sensory neurons were taken as functional readout. Cultured R192Q KI trigeminal ganglia showed higher number of active macrophages, basal release of tumor necrosis factor alpha (TNFα), and larger P2X3 receptor currents with respect to wild type (WT) cells. After 5 h application of LPS in vitro, both WT and R192Q KI cultures demonstrated significant increase in macrophage activation, very large rise in TNFα mRNA content, and ambient protein levels together with fall in TNFα precursor, suggesting potent release of this inflammatory mediator. Notwithstanding the unchanged expression of P2X3 receptor protein in WT or R192Q KI cultures, LPS evoked a large rise in WT neuronal currents that recovered faster from desensitization. Basal R192Q KI currents were larger than WT ones and could not be further augmented by LPS. These data suggest that KI cultures had a basal neuroinflammatory profile that might facilitate the release of endogenous mediators (including ATP) to activate constitutively hyperfunctional P2X3 receptors and amplify nociceptive signaling by trigeminal sensory neurons.

A potential therapeutic role for P2X7 receptor (P2X7R) antagonists in the treatment of inflammatory diseases

INTRODUCTION

The P2X7 receptor (P2X7R) has an important role in inflammation and immunity, but until recently, clinical application has been limited by a lack of specific antagonists. Recent studies using P2X7R knockout mice and specific receptor antagonists have shown that the P2X7R is an important therapeutic target in inflammatory diseases.

AREAS COVERED

We have reviewed the current literature on the role of the P2X7R in inflammatory diseases, focusing on potential therapeutic applications of selective P2X7R antagonists as anti-inflammatory agents. Particular emphasis has been placed on the potential role of P2X7R in common inflammatory diseases. The latest developments in Phase I and II clinical trials of P2X7R antagonists are covered.

EXPERT OPINION

Recent studies using gene knockout mice and selective P2X7R antagonists suggest that P2X7R is a viable therapeutic target for inflammatory diseases. However, efficacious P2X7R antagonists for use in clinical studies are still at an early stage of development. Future challenges include: identifying potential toxicity and side effects of treatment, timing of treatment initiation and its duration in chronic inflammatory conditions, optimum dosage and development of a functional assay for P2X7R that would help to guide treatment.

C terminus of the P2X7 receptor: treasure hunting

P2X receptor (P2XR) is a family of the ATP-gated ion channel family and can permeabilize the plasma membrane to small cations such as potassium, sodium, and calcium, resulting in cellular depolarization. There are seven P2XR that have been described and cloned, with 45% identity in amino acid sequence. Each P2X receptors has two transmembrane domains that are separated by an extracellular loop and an intracellular N and C terminus. Unlike the other P2X receptors, the P2X7R has a larger C terminus with an extra 200 amino acid residues compared with the other receptors. The C terminus of the P2X7R has been implicated in regulating receptor function including signaling pathway activation, cellular localization, protein-protein interactions, and post-translational modification (PTM). In the present review, we discuss the role of the P2X7R C terminus in regards to receptor function, describe the specific domains and motifs found therein and compare the C terminus sequence with others proteins to discover predicted domains or sites of PTM.

Purinergic receptor functionality is necessary for infection of human hepatocytes by hepatitis delta virus and hepatitis B virus

Hepatitis B virus (HBV) and hepatitis delta virus (HDV) are major sources of acute and chronic hepatitis. HDV requires the envelope proteins of HBV for the processes of assembly and infection of new cells. Both viruses are able to infect hepatocytes though previous studies have failed to determine the mechanism of entry into such cells. This study began with evidence that suramin, a symmetrical hexasulfated napthylurea, could block HDV entry into primary human hepatocytes (PHH) and was then extrapolated to incorporate findings of others that suramin is one of many compounds that can block activation of purinergic receptors. Thus other inhibitors, pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonate (PPADS) and brilliant blue G (BBG), both structurally unrelated to suramin, were tested and found to inhibit HDV and HBV infections of PHH. BBG, unlike suramin and PPADS, is known to be more specific for just one purinergic receptor, P2X7. These studies provide the first evidence that purinergic receptor functionality is necessary for virus entry. Furthermore, since P2X7 activation is known to be a major component of inflammatory responses, it is proposed that HDV and HBV attachment to susceptible cells, might also contribute to inflammation in the liver, that is, hepatitis.

Oxidized ATP inhibits T-cell-mediated autoimmunity

T cells directed against self antigens play an important role in several autoimmune diseases. The available immunosuppressive compounds used to treat autoimmune diseases are limited, and often they have side effects that limit their application. T cells express ATP receptors, which could be new target molecules to treat autoimmune disease. Here we analyzed the effect of oxidized ATP (oxATP), an inhibitor of the ATP receptor P2rx7, in different murine models of T-cell-mediated autoimmune diseases. Treatment with oxATP inhibited proliferation and effector function of T cells. In the systems we used, oxATP did not obviously interfere with the innate immune response, but strongly reduced antigen-specific T-cell responses. This treatment ameliorated T-cell-mediated autoimmune type I diabetes and autoimmune encephalitis in mice. In conclusion, oxATP was found to strongly inhibit activated T cells and could thus be used to target T-cell-mediated autoimmune disease.

P2X(7) receptor at the heart of disease

Purinergic signaling is a crucial component of disease whose pathophysiological basis is now well established. This review focuses on P2X(7), a unique bifunctional purinoreceptor that either opens a non selective cation channel or forms a large, cytolytic pore depending on agonist application and leading to membrane blebbing and to cell death either by necrosis or apoptosis.Activation of P2X(7) receptor has been shown to stimulate the release of multiple proinflammatory cytokines by activated macrophages, with the IL-1b to be the most extensively studied among them. These findings were verified by the use of knockout P2X(7) ((-/-)) mice.Update information coming from all fields of research implicate this receptor at the very heart of diseases such as rheumatoid arthritis, multiple sclerosis, depression, Alzheimer disease, and to kidney damage, in renal fibrosis and experimental nephritis.Clinical studies are currently underway with the newly developed selective antagonists for P2X(7) receptor, the results of which are eagerly anticipated. These studies together with data from in-vivo experiments with the P2X(7) knockout mice and in-vitro experiments will shed light in this exciting area.

P2X(7) Receptors in Neurological and Cardiovascular Disorders

P2X receptors are ATP-gated cation channels that mediate fast excitatory transmission in diverse regions of the brain and spinal cord. Several P2X receptor subtypes, including P2X(7), have the unusual property of changing their ion selectivity during prolonged exposure to ATP, which results in a channel pore permeable to molecules as large as 900 daltons. The P2X(7) receptor was originally described in cells of hematopoietic origin, and mediates the influx of Ca(2+) and Na(+) and Ca(2+) and Na(+) ions as well as the release of proinflammatory cytokines. P2X(7) receptors may affect neuronal cell death through their ability to regulate the processing and release of interleukin-1beta, a key mediator in neurodegeneration, chronic inflammation, and chronic pain. Activation of P2X(7), a key mediator in neurodegeneration, chronic inflammation, and chronic pain. Activation of P2X(7) receptors provides an inflammatory stimulus, and P2X(7) receptor-deficient mice have substantially attenuated inflammatory responses, including models of neuropathic and chronic inflammatory pain. Moreover, P2X(7) receptor activity, by regulating the release of proinflammatory cytokines, may be involved in the pathophysiology of depression. Apoptotic cell death occurs in a number of vascular diseases, including atherosclerosis, restenosis, and hypertension, and may be linked to the release of ATP from endothelial cells, P2X(7) receptor activation, proinflammatory cytokine production, and endothelial cell apoptosis. In this context, the P2X(7) receptor may be viewed as a gateway of communication between the nervous, immune, and cardiovascular systems.

Late, but not early, inhibition of soluble guanylate cyclase decreases mortality in a rat sepsis model

Overproduction of nitric oxide and activation of soluble guanylate cyclase (sGC) are important in sepsis-induced hypotension and hyporesponsiveness to vasoconstrictors. A time course of the expression and activity of sGC in a sepsis model [cecal ligation and puncture (CLP)] was evaluated in rats. Soluble GC alpha-1 and beta-1 subunit mRNA levels increased in the lungs, but not in the aorta. However, in both tissues, the protein levels increased 24 h after sepsis and remained high for up to 48 h. Sodium nitroprusside-stimulated cGMP accumulation was higher 48 h after CLP in the lung and aorta. NOS-2 protein expression peaked 24 h after CLP, decreasing thereafter. The impact of inhibiting the expression of sGC early (8 h) or late (20 h) on vascular reactivity and the indexes of organ damage and mortality were also studied. Late administration of methylene blue (MB) or ODQ (1H-[1,2,4]-oxadiazole[4,3-a]quinoxalin-1-one) restored the blood pressure and vascular responsiveness to vasoconstrictors to normal levels but was ineffective in early sepsis. Late MB injection reduced the plasma levels of urea, creatinine, and lactate. MB improved the survival if administered late, but it increased the mortality when administrated early after sepsis onset. The increased sGC expression/activity may be relevant for the late hypotension and hyporesponsiveness to vasoconstrictors in sepsis. In accordance, MB increased survival if administered in late sepsis, but not in early sepsis. Therefore, differential responsiveness to sGC during the course of sepsis may determine the success or failure of treatment with sGC inhibitors.