Ecto-nucleotidases of the CD39/NTPDase family modulate platelet activation and thrombus formation: Potential as therapeutic targets

Cytokine storm in human monkeypox: A possible involvement of purinergic signaling

Some evidence has indicated that monkeypox can induce a cytokine storm. Purinergic signaling is a cell pathway related to the cytokine storm. However, the precise mechanisms that lead to cytokine storms in monkeypox infections and the possible involvement of purinergic signaling in the immune response to this virus remain unknown. In this review article, we aimed to highlight a body of scientific evidence that consolidates the role of the cytokine storm in monkeypox infection and proposes a new hypothesis regarding the roles of purinergic signaling in this immune-mediated mechanism. We further suggested some purinergic signaling modulators to mitigate the deleterious and aggravating effects of immune dysregulation in human monkeypox virus infection by inhibiting P2X3, P2X7, P2Y2, and P2Y12, reducing inflammation, and activating A1 and A2A receptors to promote an anti-inflammatory response.

Platelet P2Y12 signalling pathway in the dysregulated immune response during sepsis

Sepsis is a complicated pathological condition in response to severe infection. It is characterized by a strong systemic inflammatory response, where multiple components of the immune system are involved. Currently, there is no treatment for sepsis. Blood platelets are known for their role in haemostasis, but they also participate in inflammation through cell-cell interaction and the secretion of inflammatory mediators. Interestingly, an increase in platelet activation, secretion, and aggregation with other immune cells (such as monocytes, T-lymphocytes and neutrophils) has been detected in septic patients. Therefore, antiplatelet therapy in terms of P2Y12 antagonists has been evaluated as a possible treatment for sepis. It was found that blocking P2Y12 receptors decreased platelet marker expression and limited attachment to immune cells in some studies, but not in others. This review addresses the role of platelets in sepsis and discusses whether antagonizing P2Y12 signalling pathways can alter the disease outcome. Challenges in studying P2Y12 antagonists in sepsis also are discussed. LINKED ARTICLES: This article is part of a themed issue on Platelet purinergic receptor and non-thrombotic disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.4/issuetoc.

Effect of Regular Training on Platelet Function in Untrained Thoroughbreds

Training has a significant effect on the physiology of blood coagulation in humans and in horses. Several hemostatic changes have been reported after exercise in the horse but data available are inconclusive. The aim of this study was to investigate platelet activation and primary platelet-related hemostasis modifications in young never-trained Thoroughbreds in the first incremental training period in order to improve knowledge on this topic. Twenty-nine clinically healthy, untrained, 2-year-old Thoroughbred racehorses were followed during their incremental 4-month sprint exercise training. Blood collection was performed once a month, five times in total (T-30, T0, T30, T60, and T90). Platelet aggregation was measured by light transmission aggregometry in response to various agonists: adenosine diphosphate (ADP), collagen, and calcium ionophore A23187. Platelet function was evaluated using a platelet function analyzer (PFA-100®) using collagen/ADP and collagen/adrenaline cartridges. Nitrite-nitrate (NOx) plasma concentrations were measured via a colorimetric assay to assess in vivo nitric oxide bioavailability. Platelet activation was also investigated through gene expression analyses (selectin P-SELP, ectonucleotidase CD39-ENTPD1, prostaglandin I2 synthase-PTGIS, endothelial nitric oxide synthase 3-NOS3). Differences among the time points were analyzed and mean ± SEM were calculated. Significant modifications were identified compared with T-30, with an increase in platelet aggregation (collagen:32.6 ± 4.8 vs. 21.6 ± 4.9%; ADP: 35.5 ± 2.0 vs. 24.5 ± 3.1%; A23187: 30 ± 4.7 vs. 23.8 ± 4%) and a shorter closure time of C-ADP cartridges (75.6 ± 4.4 vs. 87.7 ± 3.4 s) that tended to return to the baseline value at T90. NOx concentrations in plasma significantly increased after 30 days of the training program compared with the baseline. The first long-term training period seems to induce platelet hyperactivity after 30 days in never-trained Thoroughbreds. Regular physical training reduces the negative effects of acute efforts on platelet activation.

Platelets in Renal Disease

Kidney disease is a major global health concern, affecting millions of people. Nephrologists have shown interest in platelets because of coagulation disorders caused by renal diseases. With a better understanding of platelets, it has been found that these anucleate and abundant blood cells not only play a role in hemostasis, but also have important functions in inflammation and immunity. Platelets are not only affected by kidney disease, but may also contribute to kidney disease progression by mediating inflammation and immune effects. This review summarizes the current evidence regarding platelet abnormalities in renal disease, and the multiple effects of platelets on kidney disease progression. The relationship between platelets and kidney disease is still being explored, and further research can provide mechanistic insights into the relationship between thrombosis, bleeding, and inflammation related to kidney disease, and elucidate targeted therapies for patients with kidney disease.

CD39 abrogates platelet-derived factors induced IL-1β expression in the human placenta

Tissue insults in response to inflammation, hypoxia and ischemia are accompanied by the release of ATP into the extracellular space. There, ATP modulates several pathological processes, including chemotaxis, inflammasome induction and platelet activation. ATP hydrolysis is significantly enhanced in human pregnancy, suggesting that increased conversion of extracellular ATP is an important anti-inflammatory process in preventing exaggerated inflammation, platelet activation and hemostasis in gestation. Extracellular ATP is converted into AMP, and subsequently into adenosine by the two major nucleotide-metabolizing enzymes CD39 and CD73. Here, we aimed to elucidate developmental changes of placental CD39 and CD73 over gestation, compared their expression in placental tissue from patients with preeclampsia and healthy controls, and analyzed their regulation in response to platelet-derived factors and different oxygen conditions in placental explants as well as the trophoblast cell line BeWo. Linear regression analysis showed a significant increase in placental CD39 expression, while at the same time CD73 levels declined at term of pregnancy. Neither maternal smoking during first trimester, fetal sex, maternal age, nor maternal BMI revealed any effects on placental CD39 and CD73 expression. Immunohistochemistry detected both, CD39 and CD73, predominantly in the syncytiotrophoblast layer. Placental CD39 and CD73 expression were significantly increased in pregnancies complicated with preeclampsia, when compared to controls. Cultivation of placental explants under different oxygen conditions had no effect on the ectonucleotidases, whereas presence of platelet releasate from pregnant women led to deregulated CD39 expression. Overexpression of recombinant human CD39 in BeWo cells decreased extracellular ATP levels after culture in presence of platelet-derived factors. Moreover, platelet-derived factors-induced upregulation of the pro-inflammatory cytokine, interleukin-1β, was abolished by CD39 overexpression. Our study shows that placental CD39 is upregulated in preeclampsia, suggesting an increasing demand for extracellular ATP hydrolysis at the utero-placental interface. Increased placental CD39 in response to platelet-derived factors may lead to enhanced conversion of extracellular ATP levels, which in turn could represent an important anti-coagulant defense mechanism of the placenta.

Application of Nanotechnology in Thrombus Therapy

A thrombus is a blood clot that forms in the lumen of an artery or vein, restricting blood flow and causing clinical symptoms. Thrombosis is associated with many life-threatening cardiovascular diseases. However, current clinical therapeutic technologies still have many problems in targeting, enrichment, penetration, and safety to meet the thrombosis treatment needs. Therefore, researchers devote themselves to developing nanosystems loaded with antithrombotic drugs to address this paradox in recent years. Herein, the existing thrombosis treatment technologies are first reviewed; and then, their advantages and disadvantages are outlined based on a brief discussion of thrombosis's definition and formation mechanism. Furthermore, the need and application cases for introducing nanotechnology are discussed, focusing on thrombus-specific targeted ligand modification technology and microenvironment-triggered responsive drug release technology. Then, nanomaterials that can be used to design antithrombotic nanotherapeutic systems are summarized. Moreover, a variety of drug delivery technologies driven by nanomotors in thrombosis therapy is also introduced. Last of all, a prospective discussion on the future development of nanotechnology for thrombosis therapy is highlighted.

A Comprehensive Review of Risk Factors for Venous Thromboembolism: From Epidemiology to Pathophysiology

Venous thromboembolism (VTE) is the third most common cause of death worldwide. The incidence of VTE varies according to different countries, ranging from 1-2 per 1000 person-years in Western Countries, while it is lower in Eastern Countries (<1 per 1000 person-years). Many risk factors have been identified in patients developing VTE, but the relative contribution of each risk factor to thrombotic risk, as well as pathogenetic mechanisms, have not been fully described. Herewith, we provide a comprehensive review of the most common risk factors for VTE, including male sex, diabetes, obesity, smoking, Factor V Leiden, Prothrombin G20210A Gene Mutation, Plasminogen Activator Inhibitor-1, oral contraceptives and hormonal replacement, long-haul flight, residual venous thrombosis, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, trauma and fractures, pregnancy, immobilization, antiphospholipid syndrome, surgery and cancer. Regarding the latter, the incidence of VTE seems highest in pancreatic, liver and non-small cells lung cancer (>70 per 1000 person-years) and lowest in breast, melanoma and prostate cancer (<20 per 1000 person-years). In this comprehensive review, we summarized the prevalence of different risk factors for VTE and the potential molecular mechanisms/pathogenetic mediators leading to VTE.

Overexpression of TcNTPDase-1 Gene Increases Infectivity in Mice Infected with Trypanosoma cruzi

Ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) are enzymes located on the surface of the T. cruzi plasma membrane, which hydrolyze a wide range of tri-/-diphosphate nucleosides. In this work, we used previously developed genetically modified strains of Trypanosoma cruzi (T. cruzi), hemi-knockout (KO +/−) and overexpressing (OE) the TcNTPDase-1 gene to evaluate the parasite infectivity profile in a mouse model of acute infection (n = 6 mice per group). Our results showed significantly higher parasitemia and mortality, and lower weight in animals infected with parasites OE TcNTPDase-1, as compared to the infection with the wild type (WT) parasites. On the other hand, animals infected with (KO +/−) parasites showed no mortality during the 30-day trial and mouse weight was more similar to the non-infected (NI) animals. In addition, they had low parasitemia (45.7 times lower) when compared with parasites overexpressing TcNTPDase-1 from the hemi-knockout (OE KO +/−) group. The hearts of animals infected with the OE KO +/− and OE parasites showed significantly larger regions of cardiac inflammation than those infected with the WT parasites (p < 0.001). Only animals infected with KO +/− did not show individual electrocardiographic changes during the period of experimentation. Together, our results expand the knowledge on the role of NTPDases in T. cruzi infectivity, reenforcing the potential of this enzyme as a chemotherapy target to treat Chagas disease (CD).

Reversible Platelet Integrin αIIbβ3 Activation and Thrombus Instability

Integrin αIIbβ3 activation is essential for platelet aggregation and, accordingly, for hemostasis and arterial thrombosis. The αIIbβ3 integrin is highly expressed on platelets and requires an activation step for binding to fibrinogen, fibrin or von Willebrand factor (VWF). A current model assumes that the process of integrin activation relies on actomyosin force-dependent molecular changes from a bent-closed and extended-closed to an extended-open conformation. In this paper we review the pathways that point to a functional reversibility of platelet αIIbβ3 activation and transient aggregation. Furthermore, we refer to mouse models indicating that genetic defects that lead to reversible platelet aggregation can also cause instable thrombus formation. We discuss the platelet agonists and signaling pathways that lead to a transient binding of ligands to integrin αIIbβ3. Our analysis points to the (autocrine) ADP P2Y₁ and P2Y₁₂ receptor signaling via phosphoinositide 3-kinases and Akt as principal pathways linked to reversible integrin activation. Downstream signaling events by protein kinase C, CalDAG-GEFI and Rap1b have not been linked to transient integrin activation. Insight into the functional reversibility of integrin activation pathways will help to better understand the effects of antiplatelet agents.

Platelets and the Cybernetic Regulation of Ischemic Inflammatory Responses through PNC Formation Regulated by Extracellular Nucleotide Metabolism and Signaling

Ischemic events are associated with severe inflammation and are here referred to as ischemic inflammatory response (IIR). Recent studies identified the formation of platelet–neutrophil complexes (PNC) as key players in IIR. We investigated the role of extracellular platelet nucleotide signaling in the context of IIR and defined a cybernetic circle, including description of feedback loops. Cybernetic circles seek to integrate different levels of information to understand how biological systems function. Our study specifies the components of the cybernetic system of platelets in IIR and describes the theoretical progression of IIR passing the cybernetic cycle with positive and negative feedback loops based on nucleotide-dependent signaling and functional regulation. The cybernetic components and feedback loops were explored by cytometry, immunohistological staining, functional blocking antibodies, and ADP/ATP measurements. Using several ex vivo and in vivo approaches we confirmed cybernetic parameters, such as controller, sensor, and effector (VASP phosphorylation, P2Y₁₂, ADORAs and GPIIb/IIIa activity), as well as set points (ADP, adenosine) and interfering control and disturbance variables (ischemia). We demonstrate the impact of the regulated platelet–neutrophil complex (PNC) formation in blood and the resulting damage to the affected inflamed tissue. Taken together, extracellular nucleotide signaling, PNC formation, and tissue damage in IIR can be integrated in a controlled cybernetic circle of platelet function, as introduced through this study.

Effects of physical exercise on the functionality of human nucleotidases: A systematic review

Nucleotidases contribute to the regulation of inflammation, coagulation, and cardiovascular activity. Exercise promotes biological adaptations, but its effects on nucleotidase activities and expression are unclear. The objective of this study was to review systematically the effects of exercise on nucleotidase functionality in healthy and unhealthy subjects. The MEDLINE, EMBASE, Cochrane Library, and Web of Science databases were searched to identify, randomized clinical trials, non-randomized clinical trials, uncontrolled clinical trials, quasi-experimental, pre-, and post-interventional studies that evaluated the effects of exercise on nucleotidases in humans, and was not limited by language and date. Two independent reviewers performed the study selection, data extraction, and assessment of risk of bias. Of the 203 articles identified, 12 were included in this review. Eight studies reported that acute exercise, in healthy and unhealthy subjects, elevated the activities or expression of nucleotidases. Four studies evaluated the effects of chronic training on nucleotidase activities in the platelets and lymphocytes of patients with metabolic syndrome, chronic kidney disease, and hypertension and found a decrease in nucleotidase activities in these conditions. Acute and chronic exercise was able to modify the blood plasma and serum levels of nucleotides and nucleosides. Our results suggest that short- and long-term exercise modulate nucleotidase functionality. As such, purinergic signaling may represent a novel molecular adaptation in inflammatory, thrombotic, and vascular responses to exercise.

CoCl2-Mimicked Endothelial Cell Hypoxia Induces Nucleotide Depletion and Functional Impairment That Is Reversed by Nucleotide Precursors

Chronic hypoxia drives vascular dysfunction by various mechanisms, including changes in mitochondrial respiration. Although endothelial cells (ECs) rely predominantly on glycolysis, hypoxia is known to alter oxidative phosphorylation, promote oxidative stress and induce dysfunction in ECs. Our work aimed to analyze the effects of prolonged treatment with hypoxia-mimetic agent CoCl₂ on intracellular nucleotide concentration, extracellular nucleotide breakdown, mitochondrial function, and nitric oxide (NO) production in microvascular ECs. Moreover, we investigated how nucleotide precursor supplementation and adenosine deaminase inhibition protected against CoCl₂-mediated disturbances. Mouse (H5V) and human (HMEC-1) microvascular ECs were exposed to CoCl₂-mimicked hypoxia for 24 h in the presence of nucleotide precursors: adenine and ribose, and adenosine deaminase inhibitor, 2′deoxycoformycin. CoCl₂ treatment decreased NO production by ECs, depleted intracellular ATP concentration, and increased extracellular nucleotide and adenosine catabolism in both H5V and HMEC-1 cell lines. Diminished intracellular ATP level was the effect of disturbed mitochondrial phosphorylation, while nucleotide precursors effectively restored the ATP pool via the salvage pathway and improved endothelial function under CoCl₂ treatment. Endothelial protective effects of adenine and ribose were further enhanced by adenosine deaminase inhibition, that increased adenosine concentration. This work points to a novel strategy for protection of hypoxic ECs by replenishing the adenine nucleotide pool and promoting adenosine signaling.

Novel possibility for cutaneous melanoma treatment by means of rosmarinic acid action on purinergic signaling

Cancer cases have increased significantly in Brazil and worldwide, with cutaneous melanoma (CM) being responsible for nearly 57,000 deaths in the world. Thus, this review article aims at exploring and proposed hypotheses with respect to the possibility that RA can be a promising and alternative compound to be used as an adjuvant in melanoma treatment, acting on purinergic signaling. The scarcity of articles evidencing the action of this compound in this signaling pathway requires further studies. Considering diverse evidence found in the literature, we hypothesize that RA can be an effective candidate for the treatment of CM acting as a modulating molecule of purinergic cellular pathway through P2X7 blocking, mitigating the Warburg effect, and as antagonic molecule of the P2Y12 receptor, reducing the formation of adhesive molecules that prevent adherence in tumor cells. In this way, our proposals for CM treatment based on targeting purinergic signaling permeate the integral practice, going from intracell to extracell. Undoubtedly, much is still to be discovered and elucidated about this promising compound, this paper being an interesting work baseline to support more research studies.

Tannic Acid Attenuates Peripheral and Brain Changes in a Preclinical Rat Model of Glioblastoma by Modulating Oxidative Stress and Purinergic Signaling

Glioblastoma (GB) is a highly aggressive and invasive brain tumor; its treatment remains palliative. Tannic acid (TA) is a polyphenol widely found in foods and possesses antitumor and neuroprotective activities. This study aimed to investigate the effect of TA on oxidative stress parameters and the activity of ectonucleotidases in the serum, platelets, and lymphocytes and/or in the brain of rats with preclinical GB. Rats with GB were treated intragastrically with TA (50 mg/kg/day) for 15 days or with a vehicle. In the platelets of the animals with glioma, the adenosine triphosphate (ATP) and adenosine monophosphate (AMP) hydrolysis and the catalase (CAT) activity decreased. Besides, the adenosine diphosphate (ADP) hydrolysis, adenosine (Ado) deamination, and the reactive oxygen species (ROS) and nitrite levels were increased in glioma animals; however, TA reversed ROS and nitrite levels and AMP hydrolysis alterations. In lymphocytes from animals with glioma, the ATP and ADP hydrolysis, as well as Ado deamination were increased; TA treatment countered this increase. In the brain of the animals with glioma, the ROS, nitrite, and thiobarbituric acid reactive substance (TBARS) levels increased and the thiol (SH) levels and CAT and superoxide dismutase (SOD) activities were decreased; TA treatment decreased the ROS and TBARS levels and restored the SOD activity. In the serum of the animals with glioma, the ATP hydrolysis decreased; TA treatment restored this parameter. Additionally, the ROS levels increased and the SH and SOD activity decreased by glioma implant; TA treatment enhanced nitrite levels and reversed SOD activity. Altogether, our results suggest that TA is an important target in the treatment of GB, as it modulates purinergic and redox systems.

Electroacupuncture relieves neuropathic pain by inhibiting degradation of the ecto-nucleotidase PAP in the dorsal root ganglions of CCI mice

BACKGROUND

Although electroacupuncture is widely used in chronic pain management, it is quite controversial due to its unclear mechanism. We hypothesised that EA alleviates pain by inhibiting degradation of the ecto-nucleotidase prostatic acid phosphatase (PAP) and facilitating ATP dephosphorylation in dorsal root ganglions (DRGs).

METHODS

We applied EA in male C57 mice subjected to chronic constriction injury (CCI) and assessed extracellular ATP and 5'-nucleotidease expression in DRGs. Specifically, we used a luminescence assay, quantitative reverse transcriptase-polymerase chain reaction, western blotting, immunohistochemistry and nociceptive-related behavioural changes to gather data, and we tested for effects after PAP expression was inhibited with an adeno-associated virus (AAV). Moreover, membrane PAP degradation was investigated in cultured DRG neurons and the inhibitory effects of EA on this degradation were assessed using immunoprecipitation.

RESULTS

EA treatment alleviated CCI surgery induced mechanical pain hypersensitivity. Furthermore, extracellular ATP decreased significantly in both the DRGs and dorsal horn of EA-treated mice. PAP protein but not mRNA increased in L4-L5 DRGs, and inhibition of PAP expression via AAV microinjection reversed the analgesic effect of EA. Membrane PAP degradation occurred through a clathrin-mediated endocytosis pathway in cultured DRG neurons; EA treatment inhibited the phosphorylation of adaptor protein complex 2, which subsequently reduced the endocytosis of membrane PAP.

CONCLUSIONS

EA treatment alleviated peripheral nerve injury-induced mechanical pain hypersensitivity in mice by inhibiting membrane PAP degradation via reduced endocytosis and subsequently promote ATP dephosphorylation in DRGs.

The secreted tyrosine kinase VLK is essential for normal platelet activation and thrombus formation

Tyrosine phosphorylation of extracellular proteins is observed in cell cultures and in vivo, but little is known about the functional roles of tyrosine phosphorylation of extracellular proteins. Vertebrate lonesome kinase (VLK) is a broadly expressed secretory pathway tyrosine kinase present in platelet α-granules. It is released from platelets upon activation and phosphorylates substrates extracellularly. Its role in platelet function, however, has not been previously studied. In human platelets, we identified phosphorylated tyrosines mapped to luminal or extracellular domains of transmembrane and secreted proteins implicated in the regulation of platelet activation. To determine the role of VLK in extracellular tyrosine phosphorylation and platelet function, we generated mice with a megakaryocyte/platelet-specific deficiency of VLK. Platelets from these mice are normal in abundance and morphology but have significant changes in function both in vitro and in vivo. Resting and thrombin-stimulated VLK-deficient platelets exhibit a significant decrease in several tyrosine phosphobands. Results of functional testing of VLK-deficient platelets show decreased protease-activated receptor 4-mediated and collagen-mediated platelet aggregation but normal responses to adenosine 5'-diphosphate. Dense granule and α-granule release are reduced in these platelets. Furthermore, VLK-deficient platelets exhibit decreased protease-activated receptor 4-mediated Akt (S473) and Erk1/2 (T202/Y204) phosphorylation, indicating altered proximal signaling. In vivo, mice lacking VLK in megakaryocytes/platelets display strongly reduced platelet accumulation and fibrin formation after laser-induced injury of cremaster arterioles compared with control mice but with normal bleeding times. These studies show that the secretory pathway tyrosine kinase VLK is critical for stimulus-dependent platelet activation and thrombus formation, providing the first evidence that a secreted protein kinase is required for normal platelet function.

Thrombo-Inflammation: A Focus on NTPDase1/CD39

There is increasing evidence for a link between inflammation and thrombosis. Following tissue injury, vascular endothelium becomes activated, losing its antithrombotic properties whereas inflammatory mediators build up a prothrombotic environment. Platelets are the first elements to be activated following endothelial damage; they participate in physiological haemostasis, but also in inflammatory and thrombotic events occurring in an injured tissue. While physiological haemostasis develops rapidly to prevent excessive blood loss in the endothelium activated by inflammation, hypoxia or by altered blood flow, thrombosis develops slowly. Activated platelets release the content of their granules, including ATP and ADP released from their dense granules. Ectonucleoside triphosphate diphosphohydrolase-1 (NTPDase1)/CD39 dephosphorylates ATP to ADP and to AMP, which in turn, is hydrolysed to adenosine by ecto-5'-nucleotidase (CD73). NTPDase1/CD39 has emerged has an important molecule in the vasculature and on platelet surfaces; it limits thrombotic events and contributes to maintain the antithrombotic properties of endothelium. The aim of the present review is to provide an overview of platelets as cellular elements interfacing haemostasis and inflammation, with a particular focus on the emerging role of NTPDase1/CD39 in controlling both processes.

Role of Purinergic Signalling in Endothelial Dysfunction and Thrombo-Inflammation in Ischaemic Stroke and Cerebral Small Vessel Disease

The cerebral endothelium is an active interface between blood and the central nervous system. In addition to being a physical barrier between the blood and the brain, the endothelium also actively regulates metabolic homeostasis, vascular tone and permeability, coagulation, and movement of immune cells. Being part of the blood–brain barrier, endothelial cells of the brain have specialized morphology, physiology, and phenotypes due to their unique microenvironment. Known cardiovascular risk factors facilitate cerebral endothelial dysfunction, leading to impaired vasodilation, an aggravated inflammatory response, as well as increased oxidative stress and vascular proliferation. This culminates in the thrombo-inflammatory response, an underlying cause of ischemic stroke and cerebral small vessel disease (CSVD). These events are further exacerbated when blood flow is returned to the brain after a period of ischemia, a phenomenon termed ischemia-reperfusion injury. Purinergic signaling is an endogenous molecular pathway in which the enzymes CD39 and CD73 catabolize extracellular adenosine triphosphate (eATP) to adenosine. After ischemia and CSVD, eATP is released from dying neurons as a damage molecule, triggering thrombosis and inflammation. In contrast, adenosine is anti-thrombotic, protects against oxidative stress, and suppresses the immune response. Evidently, therapies that promote adenosine generation or boost CD39 activity at the site of endothelial injury have promising benefits in the context of atherothrombotic stroke and can be extended to current CSVD known pathomechanisms. Here, we have reviewed the rationale and benefits of CD39 and CD39 therapies to treat endothelial dysfunction in the brain.

Acute moderate-intensity aerobic exercise promotes purinergic and inflammatory responses in sedentary, overweight and physically active subjects

NEW FINDING

What is the central question of this study? How does moderate-intensity aerobic exercise affect the behaviour of purinergic enzymes in sedentary, overweight and physically active subjects? What is the relationship between purinergic and inflammatory responses triggered by exercise? What is the main finding and its importance? Moderate-intensity aerobic exercise modifies the activity of purinergic enzymes and the levels of nucleotides and nucleosides. These results are similar in subjects with different biological characteristics. 5'-Nucleotidase activity and adenosine levels are associated with inflammatory responses. This study suggests that a purinergic pathway is related to the inflammatory responses triggered by exercise.

ABSTRACT

Purinergic signalling is a mechanism of extracellular communication that modulates events related to exercise, such as inflammation and coagulation. Herein, we evaluated the effects of acute moderate-intensity exercise on the activities of purinergic enzymes and plasma levels of adenine nucleotides in individuals with distinct metabolic characteristics. We analysed the relationship between purinergic parameters, inflammatory responses and cardiometabolic markers. Twenty-four healthy males were assigned to three groups: normal weight sedentary (n = 8), overweight sedentary (n = 8) and normal weight physically active (n = 8). The volunteers performed an acute session of moderate-intensity aerobic exercise on a treadmill at 70% of V ̇ O 2 peak ; blood samples were drawn at baseline, immediately post-exercise and at 1 h post-exercise. Immediately post-exercise, all subjects showed increases in ATP, ADP, AMP and p-nitrophenyl thymidine 5'-monophosphate hydrolysis, while AMP hydrolysis remained increased at 1 h after exercise. High-performance liquid chromatography analysis demonstrated lower levels of ATP and ADP at post- and 1 h post-exercise in all groups. Conversely, adenosine and inosine levels increased at post-exercise, but only adenosine remained augmented at 1 h after exercise in all groups. With regard to inflammatory responses, the exercise protocol increased tumour necrosis factor α (TNF-α) and interleukin 8 (IL-8) concentrations in all subjects, but only TNF-α remained elevated at 1 h after exercise. Significant correlations were found between the activity of 5'-nucleotidase, adenosine levels, V ̇ O 2 peak , triglyceride, TNF-α and IL-8 levels. Our findings suggest a purinergic signalling pathway that participates, at least partially, in the inflammatory responses triggered by acute moderate-intensity exercise. The response of soluble nucleotidases to acute moderate exercise appears to be similar between subjects of different biological profiles.

Adenosine metabolism in the vascular system

The concept of extracellular purinergic signaling was first proposed by Geoffrey Burnstock in the early 1970s. Since then, extracellular ATP and its metabolites ADP and adenosine have attracted an enormous amount of attention in terms of their involvement in a wide range of immunomodulatory, thromboregulatory, angiogenic, vasoactive and other pathophysiological activities in different organs and tissues, including the vascular system. In addition to significant progress in understanding the properties of nucleotide- and adenosine-selective receptors, recent studies have begun to uncover the complexity of regulatory mechanisms governing the duration and magnitude of the purinergic signaling cascade. This knowledge has led to the development of new paradigms in understanding the entire purinome by taking into account the multitude of signaling and metabolic pathways involved in biological effects of ATP and adenosine and compartmentalization of the adenosine system. Along with the "canonical route" of ATP breakdown to adenosine via sequential ecto-nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39) and ecto-5'-nucleotidase/CD73 activities, it has now become clear that purine metabolism is the result of concerted effort between ATP release, its metabolism through redundant nucleotide-inactivating and counteracting ATP-regenerating ectoenzymatic pathways, as well as cellular nucleoside uptake and phosphorylation of adenosine to ATP through complex phosphotransfer reactions. In this review I provide an overview of key enzymes involved in adenosine metabolic network, with special emphasis on the emerging roles of purine-converting ectoenzymes as novel targets for cancer and vascular therapies.

Structural and functional characterization of engineered bifunctional fusion proteins of CD39 and CD73 ectonucleotidases

Extracellular diphosphate and triphosphate nucleotides are released from activated or injured cells to trigger vascular and immune P₂ purinergic receptors, provoking inflammation and vascular thrombosis. These metabokines are scavenged by ectonucleoside triphosphate diphosphohydrolase-1 (E-NTPDase1 or CD39). Further degradation of the monophosphate nucleoside end products occurs by surface ecto-5'-nucleotidase (NMPase) or CD73. These ectoenzymatic processes work in tandem to promote adenosinergic responses, which are immunosuppressive and antithrombotic. These homeostatic ectoenzymatic mechanisms are lost in the setting of oxidative stress, which exacerbates inflammatory processes. We have engineered bifunctional enzymes made up from ectodomains (ECDs) of CD39 and CD73 within a single polypeptide. Human alkaline phosphatase-ectodomain (ALP-ECD) and human acid phosphatase-ectodomain (HAP-ECD) fusion proteins were also generated, characterized, and compared with these CD39-ECD, CD73-ECD, and bifunctional fusion proteins. Through the application of colorimetrical functional assays and high-performance liquid chromatography kinetic assays, we demonstrate that the bifunctional ectoenzymes express high levels of CD39-like NTPDase activity and CD73-like NMPase activity. Chimeric CD39-CD73-ECD proteins were superior in converting triphosphate and diphosphate nucleotides into nucleosides when compared with ALP-ECD and HAP-ECD. We also note a pH sensitivity difference between the bifunctional fusion proteins and parental fusions, as well as ectoenzymatic property distinctions. Intriguingly, these innovative reagents decreased platelet activation to exogenous agonists in vitro. We propose that these chimeric fusion proteins could serve as therapeutic agents in inflammatory diseases, acting to scavenge proinflammatory ATP and also generate anti-inflammatory adenosine.

Implications of CD39 in immune-related diseases

Extracellular adenosine triphosphate (eATP) mediates pro-inflammatory responses by recruiting and activating inflammatory cells. CD39 can hydrolyze eATP into adenosine monophosphate (AMP), while CD73 can convert AMP into the immunosuppressive nucleoside adenosine (ADO). CD39 is a rate-limiting enzyme in this cascade, which is regarded as an immunological switch shifting the ATP-mediated pro-inflammatory environment to the ADO- mediated anti-inflammatory status. The CD39 expression can be detected in a wide spectrum of immunocytes, which is under the influence of environmental and genetic factors. It is increasingly suggested that, CD39 participates in some pathophysiological processes, like inflammatory bowel disease (IBD), sepsis, multiple sclerosis (MS), allergic diseases, ischemia-reperfusion (I/R) injury, systemic lupus erythematosus (SLE), diabetes and cancer. Here, we focus on the current understanding of CD39 in immunity, and comprehensively illustrate the diverse CD39 functions within a variety of disorders.

HIV Antivirals Affect Endothelial Activation and Endothelial-Platelet Crosstalk

RATIONALE

People living with HIV on effective antiretroviral therapy are at increased risk of cardiovascular complications, possibly due to off-target drug effects. Some studies have associated antiretroviral therapy with increased risk of myocardial infarction and endothelial dysfunction, but a link between endothelial function and antiretrovirals has not been established.

OBJECTIVE

To determine the effects of antiretrovirals in common clinical use upon in vitro endothelial function to better understand cardiovascular risk in people living with HIV.

METHODS AND RESULTS

Human umbilical cord vein endothelial cells or human coronary artery endothelial cells were pretreated with the antiretrovirals abacavir sulphate (ABC), tenofovir disoproxil fumarate, or tenofovir alafenamide. Expression of adhesion molecules, ectonucleotidases (CD39 and CD73), tissue factor (TF), endothelial-derived microparticle (EMP) numbers and phenotype, and platelet activation were evaluated by flow cytometry. TF and ectonucleotidase activities were measured using colourimetric plate-based assays. ABC-treated endothelial cells had higher levels of ICAM (intercellular adhesion molecule)-1 and TF expression following TNF (tumor necrosis factor)-α stimulation. In contrast, tenofovir disoproxil fumarate and tenofovir alafenamide treatment gave rise to greater populations of CD39⁺CD73⁺ cells. These cell surface differences were also observed within EMP repertoires. ABC-treated cells and EMP had greater TF activity, while tenofovir disoproxil fumarate- and tenofovir alafenamide-treated cells and EMP displayed higher ectonucleotidase activity. Finally, EMP isolated from ABC-treated cells enhanced collagen-evoked platelet integrin activation and α-granule release.

CONCLUSIONS

We report differential effects of antiretrovirals used in the treatment of HIV upon endothelial function. ABC treatment led to an inflammatory, prothrombotic endothelial phenotype that promoted platelet activation. In contrast, tenofovir disoproxil fumarate and tenofovir alafenamide conferred potentially cardioprotective properties associated with ectonucleotidase activity. These observations establish a link between antiretrovirals and specific functional effects that provide insight into cardiovascular disease in people living with HIV.

Nucleotide ecto-enzyme metabolic pattern and spatial distribution in calcific aortic valve disease; its relation to pathological changes and clinical presentation

BACKGROUND

Extracellular nucleotide metabolism contributes to chronic inflammation, cell differentiation, and tissue mineralization by controlling nucleotide and adenosine concentrations and hence its purinergic effects. This study investigated location-specific changes of extracellular nucleotide metabolism in aortic valves of patients with calcific aortic valve disease (CAVD). Individual ecto-enzymes and adenosine receptors involved were analyzed together with correlation with CAVD severity and risk factors.

RESULTS

Nucleotide and adenosine degradation rates were adversely modified on the aortic surface of stenotic valve as compared to ventricular side, including decreased ATP removal (1.25 ± 0.35 vs. 2.24 ± 0.61 nmol/min/cm2) and adenosine production (1.32 ± 0.12 vs. 2.49 ± 0.28 nmol/min/cm2) as well as increased adenosine deamination (1.28 ± 0.31 vs. 0.67 ± 0.11 nmol/min/cm2). The rates of nucleotide to adenosine conversions were lower, while adenosine deamination was higher on the aortic sides of stenotic vs. non-stenotic valve. There were no differences in extracellular nucleotide metabolism between aortic and ventricular sides of non-stenotic valves. Furthermore, nucleotide degradation rates, measured on aortic side in CAVD (n = 62), negatively correlated with echocardiographic and biochemical parameters of disease severity (aortic jet velocity vs. ATP hydrolysis: r = - 0.30, p < 0.05; vs. AMP hydrolysis: r = - 0.44, p < 0.001; valvular phosphate concentration vs. ATP hydrolysis: r = - 0.26, p < 0.05; vs. AMP hydrolysis: r = - 0.25, p = 0.05) while adenosine deamination showed positive correlation trend with valvular phosphate deposits (r = 0.23, p = 0.07). Nucleotide and adenosine conversion rates also correlated with CAVD risk factors, including hyperlipidemia (AMP hydrolysis vs. serum LDL cholesterol: r = - 0.28, p = 0.05; adenosine deamination vs. total cholesterol: r = 0.25, p = 0.05; LDL cholesterol: r = 0.28, p < 0.05; triglycerides: r = 0.32, p < 0.05), hypertension (adenosine deamination vs. systolic blood pressure: r = 0.28, p < 0.05) and thrombosis (ATP hydrolysis vs. prothrombin time: r = - 0.35, p < 0.01). Functional assays as well as histological and immunofluorescence, flow cytometry and RT-PCR studies identified all major ecto-enzymes engaged in nucleotide metabolism in aortic valves that included ecto-nucleotidases, alkaline phosphatase, and ecto-adenosine deaminase. We have shown that changes in nucleotide-converting ecto-enzymes were derived from their altered activities on valve cells and immune cell infiltrate. We have also demonstrated a presence of A1, A2a and A2b adenosine receptors with diminished expression of A2a and A2b in stenotic vs. non-stenotic valves. Finally, we revealed that augmenting adenosine effects by blocking adenosine deamination with deoxycoformycin decreased aortic valve thickness and reduced markers of calcification via adenosine-dependent pathways in a mouse model of CAVD.

CONCLUSIONS

This work highlights profound changes in extracellular nucleotide and adenosine metabolism in CAVD. Altered extracellular nucleotide hydrolysis and degradation of adenosine in stenotic valves may affect purinergic responses to support a pro-stenotic milieu and valve calcification. This emphasizes a potential mechanism and target for prevention and therapy. .

Ectonucleoside Triphosphate Diphosphohydrolase-1/CD39 Affects the Response to ADP of Female Rat Platelets

There is evidence that an imbalance of extracellular purine levels may be associated with increased cardiovascular risk. Platelets play a pivotal role in vascular homeostasis and thrombosis and are important source of purine nucleotides and nucleosides. Hydrolysis of nucleotides ATP and ADP is regulated by two ectonucleotidases, triphosphate diphosphohydrolase-1 (NTPDase-1/CD39) and ecto-5’-nucleotidase (ecto-5’-NT/CD73). CD39 enzyme is expressed on the endothelium, circulating blood cells, and smooth muscle cells; there is evidence that changes in CD39 expression and activity affects the potential thrombogenic of a tissue. Gender difference in the cardiovascular risk has been extensively observed; however, while the age-dependent difference in the prevalence of cardiovascular events between men and women has been attributed to the loss of the protective effect of estrogens in the postmenopausal period, the physiological mechanism behind gender disparity is still unclear. Here, we evaluated comparatively male and female rat platelet reactivity and considered the possible role of CD39 at the basis of difference observed. We found a reduced in vitro response to ADP (1–30 µM) of female compared to male platelets, associated to increased platelet CD39 expression and activity. Platelet response to ADP was strongly increased by incubation (10 min) with the CD39 inhibitor, ARL67156 (100 µM), while male platelet response was unaffected. Rat treatment with clopidogrel (30 mg/kg, per os) inhibited ex vivo platelet aggregation. Bleeding time was prolonged in female compared to male. Taken together, our results suggest that platelet ATPase and ADPase activity might be a reliable predictor of platelet reactivity.

Lambda-cyhalothrin exposure alters purine nucleotide hydrolysis and nucleotidase gene expression pattern in platelets and liver of rats

Lambda-cyhalothrin (LCT) is a broad-spectrum pesticide widely used in agriculture throughout the world. This pesticide is considered a potential contaminant of surface and underground water as well as food, posing a risk to ecosystems and humans. In this sense, we decided to evaluate the activity of enzymes belonging to the purinergic system, which is linked with regulation of extracellular nucleotides and nucleosides, such as adenosine triphosphate (ATP) and adenosine (Ado) molecules involved in the regulation of inflammatory response. However, there are no data concerning the effects of LCT exposure on the purinergic system, where extracellular nucleotides act as signaling molecules. The aim of this study was to evaluate nucleotide hydrolysis by E-NTPDase (ecto-nucleoside triphosphate diphosphohydrolase), Ecto-NPP (ecto-nucleotide pyrophosphatase/phosphodiesterase), ecto-5'-nucleotidase and ecto-adenosine deaminase (E-ADA) in platelets and liver of adult rats on days 7, 30, 45 and 60 after daily gavage with 6.2 and 31.1 mg/kg bw of LCT. Gene expression patterns of NTPDases1-3 and 5'-nucleotidase were also determined in those tissues. In parallel, lambda-cyhalothrin metabolites [3-(2-chloro-3,3,3- trifluoroprop-1-enyl)-2,2-dimethyl-cyclopropane carboxylic acid (CFMP), 4-hydroxyphenoxybenzoic acid (4-OH-3-PBA), and 3-phenoxybenzoic acid (3-PBA)] were measured in plasma. Results showed that exposure rats to LCT caused a significant increase in the assessed enzymes activities. Gene expression pattern of ectonucleotidases further revealed a significant increase in E-NTPDase1, E-NTPDase2, and E-NTPDase3 mRNA levels after LCT administration at all times. A dose-dependent increase in LCT metabolite levels was also observed but there no significant variations in levels from weeks to week, suggesting steady-steady equilibrium. Correlation analyses revealed that LCT metabolites in the liver and plasma were positively correlated with the adenine nucleotides hydrolyzing enzyme, E-ADA and E-NPP activities in platelets and liver of rats exposed to lambda-cyhalothin. Our results show that LCT and its metabolites may affect purinergic enzymatic cascade and cause alterations in energy metabolism.

Kinetic study of NTPDase immobilization and its effect of haemocompatibility on polyethylene terephthalate

Poor haemocompatibility of material surfaces is a serious limitation that can lead to failure of blood-contacting devices and implants. In this work, we have improved the haemocompatibility of polyethylene terephthalate (PET) surfaces by immobilizing apyrase/ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) on to the carboxylated PET. NTPDase immobilized PET surfaces scavenge the ADP released by activated platelets, which prevents further platelet activation and aggregation. The surface properties of the modified PET were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDAX), and contact angle measurement. The enzyme attachment and stability on the modified PET surfaces were evaluated. The kinetics of free enzyme and immobilized enzyme were studied and fitted using the Michaelis-Menten kinetic model. Both free and immobilized NTPDase followed Michaelis-Menten kinetics with similar Michaelis-Menten constants (K_m). This suggests that the activity of NTPDase was unchanged upon immobilization. Protein adsorption and %hemolysis was significantly reduced for carboxylated PET and NTPDase immobilized PET surfaces compared to unmodified PET. Lactate dehydrogenase assay showed that the number of adhered platelets reduced by more than an order of magnitude for the NTPDase immobilized PET surface compared to unmodified PET. These results clearly indicate that NTPDase immobilization significantly enhances the haemocompatibility of PET surfaces.

Koala and Wombat Gammaherpesviruses Encode the First Known Viral NTPDase Homologs and Are Phylogenetically Divergent from All Known Gammaherpesviruses

There is a large taxonomic gap in our understanding of mammalian herpesvirus genetics and evolution corresponding to those herpesviruses that infect marsupials, which diverged from eutherian mammals approximately 150 million years ago (mya). We compare the genomes of two marsupial gammaherpesviruses, Phascolarctid gammaherpesvirus 1 (PhaHV1) and Vombatid gammaherpesvirus 1 (VoHV1), which infect koalas (Phascolarc tos cinereus) and wombats (Vombatus ursinus), respectively. The core viral genomes were approximately 117 kbp and 110 kbp in length, respectively, sharing 69% pairwise nucleotide sequence identity. Phylogenetic analyses showed that PhaHV1 and VoHV1 formed a separate branch, which may indicate a new gammaherpesvirus genus. The genomes contained 60 predicted open reading frames (ORFs) homologous to those in eutherian herpesviruses and 20 ORFs not yet found in any other herpesvirus. Seven of these ORFs were shared by the two viruses, indicating that they were probably acquired prespeciation, approximately 30 to 40 mya. One of these shared genes encodes a putative nucleoside triphosphate diphosphohydrolase (NTPDase). NTPDases are usually found in mammals and higher-order eukaryotes, with a very small number being found in bacteria. This is the first time that an NTPDase has been identified in any viral genome. Interrogation of public transcriptomic data sets from two koalas identified PhaHV1-specific transcripts in multiple host tissues, including transcripts for the novel NTPDase. PhaHV1 ATPase activity was also demonstrated in vitro, suggesting that the encoded NTPDase is functional during viral infection. In mammals, NTPDases are important in downregulation of the inflammatory and immune responses, but the role of the PhaHV1 NTPDase during viral infection remains to be determined.IMPORTANCE The genome sequences of the koala and wombat gammaherpesviruses show that the viruses form a distinct branch, indicative of a novel genus within the Gammaherpesvirinae Their genomes contain several new ORFs, including ORFs encoding a β-galactoside α-2,6-sialyltransferase that is phylogenetically closest to poxvirus and insect homologs and the first reported viral NTPDase. NTPDases are ubiquitously expressed in mammals and are also present in several parasitic, fungal, and bacterial pathogens. In mammals, these cell surface-localized NTPDases play essential roles in thromboregulation, inflammation, and immune suppression. In this study, we demonstrate that the virus-encoded NTPDase is enzymatically active and is transcribed during natural infection of the host. Understanding how these enzymes benefit viruses can help to inform how they may cause disease or evade host immune defenses.

Allergic sensitization increases the amount of extracellular ATP hydrolyzed by guinea pig leukocytes

Increased levels of ATP have been found in the bronchoalveolar lavage of patients with asthma, and subjects with this disease, but not healthy subjects, develop bronchospasm after nebulization with ATP. Because the main mechanism for controlling the noxious effects of extracellular ATP is its enzymatic hydrolysis, we hypothesized that allergic sensitization is accompanied by a decreased functioning of such hydrolysis. In the present study, peripheral blood leukocytes from sensitized and non-sensitized guinea pigs were used for determining the extracellular metabolism (as assessed by inorganic phosphate production) of ATP, ADP, AMP, or adenosine, and for detecting possible changes in the expression (qPCR and Western blot) of major ectonucleotidases (NTPDase1, NTPDase3, and NPP1) and purinoceptors (P2X₁, P2X₇, P2Y₄, and P2Y₆). Contrary to our hypothesis, we found that leukocytes from allergic animals produced higher amounts of inorganic phosphate after stimulation with ATP and ADP, as compared with leukocytes from non-sensitized animals. Although at first glance, this result suggested that sensitization caused higher efficiency of ectonucleotidases, their mRNA and protein expressions were unaffected. On the other hand, after sensitization, we found a significant increase in the protein expression of P2X₇ and P2Y₄, two purinoceptors known to be responsible for ATP release after activation. We concluded that allergic sensitization increased the amount of ATP hydrolyzed by ectonucleotidases, the latter probably not due to the enhanced efficiency of its enzymatic breakdown, but rather due to an increased release of endogenous ATP or other nucleotides, partly mediated by enhanced expression or P2X₇ and P2Y₄ receptors.

Alpl prevents bone ageing sensitivity by specifically regulating senescence and differentiation in mesenchymal stem cells

Mutations in the liver/bone/kidney alkaline phosphatase (Alpl) gene cause hypophosphatasia (HPP) and early-onset bone dysplasia, suggesting that this gene is a key factor in human bone development. However, how and where Alpl acts in bone ageing is largely unknown. Here, we determined that ablation of Alpl induces prototypical premature bone ageing characteristics, including bone mass loss and marrow fat gain coupled with elevated expression of p16INK4A (p16) and p53 due to senescence and impaired differentiation in mesenchymal stem cells (MSCs). Mechanistically, Alpl deficiency in MSCs enhances ATP release and reduces ATP hydrolysis. Then, the excessive extracellular ATP is, in turn, internalized by MSCs and causes an elevation in the intracellular ATP level, which consequently inactivates the AMPKα pathway and contributes to the cell fate switch of MSCs. Reactivating AMPKα by metformin treatment successfully prevents premature bone ageing in Alpl+/- mice by improving the function of endogenous MSCs. These results identify a previously unknown role of Alpl in the regulation of ATP-mediated AMPKα alterations that maintain MSC stemness and prevent bone ageing and show that metformin offers a potential therapeutic option.

CD39 and CD73 in the aortic valve-biochemical and immunohistochemical analysis in valve cell populations and its changes in valve mineralization

BACKGROUND

The calcific aortic valve disease (CAVD) is a common heart pathology that involves inflammation, fibrosis, and calcification of aortic valve leaflets. All these processes could be affected by changes in the extracellular purinergic signaling that depend on the activity of ectonucleotidases, mainly ectonucleoside triphosphate diphosphohydrolase 1 (CD39, eNTPD1) and ecto-5'nucleotidase (CD73, e5NT).

OBJECTIVE AND METHODS

We investigated the localization of CD39 and CD73 proteins in human noncalcified and calcified aortic valves using immunohistochemistry together with analysis of NTPDases and e5NT activities in aortic valve homogenates by analysis of substrate into product conversion by high-performance liquid chromatography. We also measured the rates of extracellular nucleotide catabolism on the surface of isolated cultured aortic valve endothelial (hAVECs) and interstitial cells (hAVICs) as well as characterized cellular CD39 and CD73 distribution.

RESULTS

In noncalcified valves, CD39 and CD73 were expressed in both endothelial and interstitial cells, while in calcified valves, the expressions of CD39 and CD73 were significantly down-regulated with the exception of calcified regions where the expression of CD73 was maintained. This correlated with activities in valve homogenates. NTPDase was reduced by 35% and e5NT activity by 50% in calcified vs. noncalcified valve. CD39 and CD73 were present mainly in the cell membrane of hAVECs, but in hAVICs, these proteins were also present intracellularly. The rates of extracellular adenosine triphosphate and adenosine monophosphate hydrolysis in isolated hAVECs and hAVICs were comparable.

CONCLUSION

The presence of ectonucleotidases in valves and especially in aortic valve interstitial cells highlights important local role of purinergic signaling and metabolism. Changes in the local expression and hence the activity of CD39 and CD73 in calcified valves suggest their potential role in CAVD.

CD39-adenosinergic axis in renal pathophysiology and therapeutics

Extracellular ATP interacts with purinergic type 2 (P2) receptors and elicits many crucial biological functions. Extracellular ATP is sequentially hydrolyzed to ADP and AMP by the actions of defined nucleotidases, such as CD39, and AMP is converted to adenosine, largely by CD73, an ecto-5'-nucleotidase. Extracellular adenosine interacts with P1 receptors and often opposes the effects of P2 receptor activation. The balance between extracellular ATP and adenosine in the blood and extracellular fluid is regulated chiefly by the activities of CD39 and CD73, which constitute the CD39-adenosinergic axis. In recent years, several studies have shown this axis to play critical roles in transport of water/sodium, tubuloglomerular feedback, renin secretion, ischemia reperfusion injury, renal fibrosis, hypertension, diabetic nephropathy, transplantation, inflammation, and macrophage transformation. Important developments include global and targeted gene knockout and/or transgenic mouse models of CD39 or CD73, biological or small molecule inhibitors, and soluble engineered ectonucleotidases to directly impact the CD39-adenosinergic axis. This review presents a comprehensive picture of the multiple roles of CD39-adenosinergic axis in renal physiology, pathophysiology, and therapeutics. Scientific advances and greater understanding of the role of this axis in the kidney, in both health and illness, will direct development of innovative therapies for renal diseases.

Changes in inflammatory/cardiac markers of HIV positive patients

HIV replication promotes atherogenesis and participates in the immune response to the virus, thereby influencing the inflammatory profile. These changes may, in turn, contribute to the risk of cardiovascular diseases with involvement of platelets. However, adenine nucleotides and nucleosides involved in thromboregulation and modulation of immune response may therefore be affected by these alterations.

OBJECTIVES

This study sought to evaluate the profile of pro and anti-inflammatory cytokines (IL-10, IL-6, IL-17, TNF, IL-4, IL-2 and IFN-gamma), cardiac markers (troponin, CK, CK MB, LDH, CRP) in HIV-positive patients and assess the in vitro effect of antiretroviral therapy on the activities of ectonucleotidases (E-NTPDase and E-5'-nucleotidase) in human platelets.

DESIGN AND METHODS

Blood samples were obtained from ten HIV positive patients at the Infectious Disease Clinic of the University Hospital of Santa Maria, Brazil and ten HIV negative individuals (control group) for this study.

RESULTS

The results revealed that there were significant (P < 0.05) increases in serum levels of IL-6 and IFN-gamma with no significant (P > 0.05) changes in the serum levels of the cardiac markers investigated (CK, CK-MB, troponin, LDH and CRP). In addition, the ectonucleotidases (E-NTPDase and E-5'-nucleotidase) activities were not altered (P > 0.05) in human platelets when incubated with different antiretroviral drugs in vitro.

CONCLUSIONS

The results of this study suggest that, despite successful treatment, a proinflammatory state is not altered in HIV patients, and that antiretroviral therapy per se does not change the purinergic profile.

Sepsis induced by cecal ligation and perforation (CLP) alters nucleotidase activities in platelets of rats

Sepsis is a potentially lethal condition, and it is associated with platelet alterations. The present study sought to investigate the activity of ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase), E-5'-nucleotidase, and ecto-adenosine deaminase (E-ADA) in the platelets of rats that were induced with sepsis. Male Wistar rats were divided into three groups of ten animals each: a negative control group (normal; NC); a group that underwent surgical procedures (sham); and a group that underwent cecal ligation and perforation (CLP). The induction of sepsis was confirmed by bacteremia, and the causative pathogen identified was Escherichia coli. Hematological parameters showed leukocytosis and thrombocytopenia in animals in the septic group. The results also revealed that there were significant (p < 0.05) increases in adenosine triphosphate (ATP) and adenosine monophosphate (AMP) hydrolyses, and in the deamination of adenosine in the CLP group compared to the sham and control groups. Conversely, ADP hydrolysis was significantly decreased (p < 0.05) in the CLP group compared to the sham and control groups. Purine levels were analyzed by high-performance liquid chromatography (HPLC) in serum samples from control, sham, and CLP groups. Increased concentrations of ATP, adenosine, and inosine were found in the CLP group compared to the sham and control groups. Conversely, the concentrations of ADP and AMP in the CPL group were not significantly altered. We suggest that alterations in hematological parameters, nucleotide hydrolysis in platelets, and nucleotide concentrations in serum samples of rats with induced sepsis may be related to thromboembolic events.

Ectonucleotidase inhibitors: a patent review (2011-2016)

INTRODUCTION

Ectonucleotidases are a broad family of metallo-ectoenzymes that are responsible for hydrolysing a variety of nucleotides to nucleosides, hence orchestrating the activation of P1 and P2 cell receptors via controlled release of nucleotides and nucleosides. Many disorders such as impaired calcification including aortic calcification, neurological and immunological disorders, platelet aggregation, cell proliferation and metastasis. are characterized by an increase in expression of these ectonucleotidases. Consequently, selective inhibitors of ectonucleotidases are required for therapeutic intervention. Area covered: Several classes of compounds such as purine, nucleotide derivatives (e.g., ARL67156) and monoclonal antibodies, have shown promising ectonucleotidase inhibitory potential. This review discusses chemistry and therapeutic applications of ectonucleotidase inhibitors patented from 2011 to 2016. Expert opinion: All eukaryotic cells express nucleotide and nucleoside receptors on their cell surface and are capable of releasing extracellular nucleotides. Ectonucleotidases are a broad family of metallo-ectoenzymes that hydrolyze a variety of nucleotides to nucleosides. These extracellular nucleotides and nucleosides are important cell signalling molecules and mediate a variety of (patho)physiological processes by acting upon their respective P1 and/or P2 receptors. Discovery of molecules that can selectively inhibit or activate ectonucleotidases is crucial from therapeutic point of view, since it allows human intervention into purinergic cell signalling, thereby allowing us to modulate related (patho)physiological processes as desired.

Simultaneous overexpression of human E5NT and ENTPD1 protects porcine endothelial cells against H2O2-induced oxidative stress and cytotoxicity in vitro

Ischemia-reperfusion injury (IRI) and oxidative stress still limit the survival of cells and organs in xenotransplantation models. Ectonucleotidases play an important role in inflammation and IRI in transplantation settings. We tested the potential protective effects derived by the co-expression of the two main vascular ectonucleotidases, ecto-5'-nucleotidase (E5NT) and ecto nucleoside triphosphate diphosphohydrolase 1 (ENTPD1), in an in vitro model of H₂O₂-induced oxidative stress and cytotoxicity. We produced a dicistronic plasmid (named pCX-DI-2A) for the co-expression of human E5NT and ENTPD1 by using the F2A technology. pCX-DI-2A-transfected porcine endothelial cells simultaneously overexpressed hE5NT and hENTPD1, which were correctly processed and localized on the plasma membrane. Furthermore, such co-expression system led to the synergistic enzymatic activity of hE5NT and hENTPD1 as shown by the efficient catabolism of pro-inflammatory and pro-thrombotic extracellular adenine nucleotides along with the enhanced production of the anti-inflammatory molecule adenosine. Interestingly, we found that the hE5NT/hENTPD1 co-expression system conferred protection to cells against H₂O₂-induced oxidative stress and cytotoxicity. pCX-DI-2A-transfected cells showed reduced activation of caspase 3/7 and cytotoxicity than mock-, hE5NT- and hENTPD1-transfected cells. Furthermore, pCX-DI-2A-transfected cells showed decreased H₂O₂-induced production of ROS as compared to the other control cell lines. The cytoprotective phenotype observed in pCX-DI-2A-transfected cells was associated with higher detoxifying activity of catalase as well as increased activation of the survival signaling molecules Akt, extracellular signal-regulated kinases 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). Our data add new insights to the protective effects of the combination of hE5NT and hENTPD1 against oxidative stress and constitute a proof of concept for testing this new genetic combination in pig-to-non-human primates xenotransplantation models.

The ENTPD1 promoter polymorphism -860 A > G (rs3814159) is associated with increased gene transcription, protein expression, CD39/NTPDase1 enzymatic activity, and thromboembolism risk

Ectonucleoside triphosphate diphosphohydrolase 1 (NTPDase1) degrades the purines ATP and ADP that are key regulators of inflammation and clotting. We hypothesized that NTPDase1 polymorphisms exist and that they regulate this pathway. We sequenced the ENTPD1 gene (encoding NTPDase1) in 216 subjects then assessed genotypes in 2 cohorts comprising 2213 humans to identify ENTPD1 polymorphisms associated with venous thromboembolism (VTE). The G allele of the intron 1 polymorphism rs3176891 was more common in VTE vs. controls (odds ratio 1.26-1.9); it did not affect RNA splicing, but it was in strong linkage disequilibrium with the G allele of the promoter polymorphism rs3814159, which increased transcriptional activity by 8-fold. Oligonucleotides containing the G allele of this promoter region bound nuclear extracts more avidly. Carriers of rs3176891 G had endothelial cells with increased NTPDase1 activity and protein expression, and had platelets with enhanced aggregation. Thus, the G allele of rs3176891 marks a haplotype associated with increased clotting and platelet aggregation attributable to a promoter variant associated with increased transcription, expression, and activity of NTPDase1. We term this gain-of-function phenotype observed with rs3814159 G "CD39 Denver."-Maloney, J. P., Branchford, B. R., Brodsky, G. L., Cosmic, M. S., Calabrese, D. W., Aquilante, C. L., Maloney, K. W., Gonzalez, J. R., Zhang, W., Moreau, K. L., Wiggins, K. L., Smith, N. L., Broeckel, U., Di Paola, J. The ENTPD1 promoter polymorphism -860 A > G (rs3814159) is associated with increased gene transcription, protein expression, CD39/NTPDase1 enzymatic activity, and thromboembolism risk.

Activities of ectonucleotidases and adenosine deaminase in platelets of cattle experimentally infected by Fasciola hepatica

The enzymatic activities of NTPDase, 5'-nucleotidase and adenosine deaminase (ADA) are important in regulating the concentration of adenine nucleotides, molecules known to be involved on platelet aggregation. Fasciolosis causes coagulation disorders that have not been completely elucidated. Taking into consideration the association between the purinergic system and hemostasis, this study aimed to evaluate the enzymatic activities of NTPDase (hydrolyze ATP and ADP), 5'-nucleotidase (hydrolyze AMP) and ADA (deamination of adenosine) in platelets from cattle experimentally infected by Fasciola hepatica on days 20, 40, 60 and 80 post-infection (PI). For this study, 10 healthy Friesian steers were separated into two groups: the group A (n = 5) was used as uninfected control, and the group B was composed of steers experimentally infected by F. hepatica (n = 5). The number of platelets did not differ between groups in the periods evaluated. Reduction of NTPDase (p < 0.05) hydrolysing ATP (days 20, 40 and 60 PI), and ADP (days 40, 60 and 80 PI), and on 5'-nucleotidase hydrolyzing AMP (days 40 and 60 PI) was observed. A reduction (p < 0.05) in ADA activity on day 20 PI, as well as an increase (p < 0.05) in ADA activity on days 40 and 60 PI was observed when compared to the control. Based on these results, we can conclude that ATP, ADP and AMP hydrolysis and adenosine deamination were altered in platelets of cattle infected by F. hepatica. Considering the importance of the purinergic system in hemostasis, it is believed that those changes may contribute to the coagulation impairment observed in acute fasciolosis described in the literature.

Red Wine Inhibits Aggregation and Increases ATP-diphosphohydrolase (CD39) Activity of Rat Platelets in Vitro

Moderate consumption of red wine has been shown to exert a peculiar cardioprotective effect compared with other alcoholic beverages; inhibition of platelet aggregation seems to be one of the mechanisms underlying this beneficial effect. CD39/ATP-diphosphohydrolase is an integral membrane glycoprotein metabolizing ATP and ADP to AMP; in concert with CD73/ecto-5′-nucleotidase, it contributes to extracellular adenosine accumulation. CD39 is considered a key modulator of thrombus formation; it inhibits platelet aggregation by promoting ADP hydrolysis. There is evidence that red wine consumption increases CD39 activity in platelets from streptozotocin-induced diabetic rats. Here we show that two kinds of Aglianico red wines inhibit aggregation and increase ATP-and ADPase activity in rat platelets.

Effect of antiretroviral therapy in thromboregulation through the hydrolysis of adenine nucleotides in platelets of HIV patients

The human immunodeficiency virus (HIV) infection results in biochemical and vascular dysfunctions. The highly active antiretroviral therapy (HAART) markedly reduces mortality and opportunistic diseases associated with acquired immunodeficiency syndrome (AIDS). This increased survival time predisposes the development of cardiovascular diseases. Platelets present purinergic system ectoenzymes such as E-NTPDase, E-5'-nucleotidase and E-ADA on its surface. In view of this, the aim of this study was to evaluate the activity of these ectoenzymes in platelets as well as the platelet aggregation and lipid profile of patients with HIV infection and also patients receiving HAART. The results showed an increase in the E-NTPDase activity for ATP hydrolysis in the HIV group compared with the control group and the HIV/HAART group. When assessing the activity E-NTPDase hydrolysis to ADP, the results revealed an increase in activity in the HIV group when compared to the control group, and a decrease in activity when in the HIV/HAART group when compared to the control and HIV groups. The activity of E-5'-nucleotidase revealed an increase in AMP hydrolysis in the HIV group, as the results from control and HIV/HAART groups showed no statistical difference. Regarding the E-ADA activity, the HIV and HIV/HAART groups revealed a decreased deamination of adenosine when compared with the control group. Furthermore, we observed an increased platelet aggregation of HIV/HAART group compared with the control group. Thus, our results suggest that antiretroviral treatment against HIV has a significant effect on the activity of purinergic system ectoenzymes demonstrating that thromboregulation is involved in the process.

Altered E-NTPDase/E-ADA activities and CD39 expression in platelets of sickle cell anemia patients

Sickle cell anemia (SCA) is a hemoglobinopathy characterized by hemolysis and vaso-occlusions caused by rigidly distorted red blood cells. Sickle cell crisis is associated with extracellular release of nucleotides and platelets, which are critical mediators of hemostasis participating actively in purinergic thromboregulatory enzymes system.This study aimed to investigate the activities of purinergic system ecto-enzymes present on the platelet surface as well as CD39 and CD73 expressions on platelets of SCA treated patients. Fifteen SCA treated patients and 30 health subjects (control group) were selected. Ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase), ecto-5'-nucleotidase (E-5'-NT) and ecto-adenosine deaminase (E-ADA) activities were measured in platelets isolated from these individuals. Results demonstrated an increase of 41 % in the E-NTPDase for ATP hydrolysis, 52% for ADP hydrolysis and 60 % in the E-ADA activity in SCA patients (P<0.05); however, a two folds decrease in the CD39 expression in platelets was observed in the same group (P<0.01). The increased E-NTPDase activity could be a compensatory mechanism associated with the low expression of CD39 in platelets. Besides, alteration of these enzymes activities suggests that the purinergic system could be involved in the thromboregulatory process in SCA patients.

Nucleotide Catabolism on the Surface of Aortic Valve Xenografts; Effects of Different Decellularization Strategies

Extracellular nucleotide metabolism controls thrombosis and inflammation and may affect degeneration and calcification of aortic valve prostheses. We evaluated the effect of different decellularization strategies on enzyme activities involved in extracellular nucleotide metabolism. Porcine valves were tested intact or decellularized either by detergent treatment or hypotonic lysis and nuclease digestion. The rates of ATP hydrolysis, AMP hydrolysis, and adenosine deamination were estimated by incubation of aorta or valve leaflet sections with substrates followed by HPLC analysis. We demonstrated relatively high activities of ecto-enzymes on porcine valve as compared to the aortic wall. Hypotonic lysis/nuclease digestion preserved >80 % of ATP and AMP hydrolytic activity but reduced adenosine deamination to <10 %. Detergent decellularization completely removed (<5 %) all these activities. These results demonstrate high intensity of extracellular nucleotide metabolism on valve surface and indicate that various valve decellularization techniques differently affect ecto-enzyme activities that could be important in the development of improved valve prostheses.

Calcium Signalling through Ligand-Gated Ion Channels such as P2X1 Receptors in the Platelet and other Non-Excitable Cells

Ligand-gated ion channels on the cell surface are directly activated by the binding of an agonist to their extracellular domain and often referred to as ionotropic receptors. P2X receptors are ligand-gated non-selective cation channels with significant permeability to Ca(2+) whose principal physiological agonist is ATP. This chapter focuses on the mechanisms by which P2X1 receptors, a ubiquitously expressed member of the family of ATP-gated channels, can contribute to cellular responses in non-excitable cells. Much of the detailed information on the contribution of P2X1 to Ca(2+) signalling and downstream functional events has been derived from the platelet. The underlying primary P2X1-generated signalling event in non-excitable cells is principally due to Ca(2+) influx, although Na(+) entry will also occur along with membrane depolarization. P2X1 receptor stimulation can lead to additional Ca(2+) mobilization via a range of routes such as amplification of G-protein-coupled receptor-dependent Ca(2+) responses. This chapter also considers the mechanism by which cells generate extracellular ATP for autocrine or paracrine activation of P2X1 receptors. For example cytosolic ATP efflux can result from opening of pannexin anion-permeable channels or following damage to the cell membrane. Alternatively, ATP stored in specialised secretory vesicles can undergo quantal release via the process of exocytosis. Examples of physiological or pathophysiological roles of P2X1-dependent signalling in non-excitable cells are also discussed, such as thrombosis and immune responses.

Synthesis of 2-arylated thiadiazolopyrimidones by Suzuki–Miyaura cross-coupling: a new class of nucleotide pyrophosphatase (NPPs) inhibitors

Over expression of nucleotide pyrophosphatase (NPPs) activity is associated with chondrocalcinosis, osteoarthritis, type 2 diabetes, neurodegenerative diseases, allergies and cancer metastasis.

Blood cells: an historical account of the roles of purinergic signalling

The involvement of purinergic signalling in the physiology of erythrocytes, platelets and leukocytes was recognised early. The release of ATP and the expression of purinoceptors and ectonucleotidases on erythrocytes in health and disease are reviewed. The release of ATP and ADP from platelets and the expression and roles of P1, P2Y(1), P2Y(12) and P2X1 receptors on platelets are described. P2Y(1) and P2X(1) receptors mediate changes in platelet shape, while P2Y(12) receptors mediate platelet aggregation. The changes in the role of purinergic signalling in a variety of disease conditions are considered. The successful use of P2Y(12) receptor antagonists, such as clopidogrel and ticagrelor, for the treatment of thrombosis, myocardial infarction and stroke is discussed.