Nucleoside triphosphates inhibit ADP, collagen, and epinephrine-induced platelet aggregation: role of P2Y₁ and P2Y₁₂ receptors

Skin Telocytes Could Fundament the Cellular Mechanisms of Wound Healing in Platelet-Rich Plasma Administration

For more than 40 years, autologous platelet concentrates have been used in clinical medicine. Since the first formula used, namely platelet-rich plasma (PRP), other platelet concentrates have been experimented with, including platelet-rich fibrin and concentrated growth factor. Platelet concentrates have three standard characteristics: they act as scaffolds, they serve as a source of growth factors and cytokines, and they contain live cells. PRP has become extensively used in regenerative medicine for the successful treatment of a variety of clinical (non-)dermatological conditions like alopecies, acne scars, skin burns, skin ulcers, muscle, cartilage, and bone repair, and as an adjuvant in post-surgery wound healing, with obvious benefits in terms of functionality and aesthetic recovery of affected tissues/organs. These indications were well documented, and a large amount of evidence has already been published supporting the efficacy of this method. The primordial principle behind minimally invasive PRP treatments is the usage of the patient's own platelets. The benefits of the autologous transplantation of thrombocytes are significant, representing a fast and economic method that requires only basic equipment and training, and it is biocompatible, thus being a low risk for the patient (infection and immunological reactions can be virtually disregarded). Usually, the structural benefits of applying PRP are attributed to fibroblasts only, as they are considered the most numerous cell population within the interstitium. However, this apparent simplistic explanation is still eluding those different types of interstitial cells (distinct from fibroblasts) that are residing within stromal tissue, e.g., telocytes (TCs). Moreover, dermal TCs have an already documented potential in angiogenesis (extra-cutaneous, but also within skin), and their implication in skin recovery in a few dermatological conditions was attested and described ultrastructurally and immunophenotypically. Interestingly, PRP biochemically consists of a series of growth factors, cytokines, and other molecules, to which TCs have also proven to have a positive expression. Thus, it is attractive to hypothesize and to document any tissular collaboration between cutaneous administered PRP and local dermal TCs in skin recovery/repair/regeneration. Therefore, TCs could be perceived as the missing link necessary to provide a solid explanation of the good results achieved by administering PRP in skin-repairing processes.

Biomedical application of TiO2NPs can cause arterial thrombotic risks through triggering procoagulant activity, activation and aggregation of platelets

BACKGROUND

Titanium dioxide nanoparticles (TiO2NPs) are widely used in medical application. However, the relevant health risk has not been completely assessed, the potential of inducing arterial thrombosis (AT) in particular.

METHODS

Alterations in platelet function and susceptibility to arterial thrombosis induced by TiO2NPs were examined using peripheral blood samples from healthy adult males and an in vivo mouse model, respectively.

RESULTS

Here, using human platelets (hPLTs) freshly isolated from health volunteers, we demonstrated TiO2NP treatment triggered the procoagulant activity of hPLTs through phosphatidylserine exposure and microvesicles generation. In addition, TiO2NP treatment increased the levels of glycoprotein IIb/IIIa and P-selectin leading to aggregation and activation of hPLTs, which were exacerbated by providing physiology-mimicking conditions, including introduction of thrombin, collagen, and high shear stress. Interestingly, intracellular calcium levels in hPLTs were increased upon TiO2NP treatment, which were crucial in TiO2NP-induced hPLT procoagulant activity, activation and aggregation. Moreover, using mice in vivo models, we further confirmed that TiO2NP treatment a reduction in mouse platelet (mPLT) counts, disrupted blood flow, and exacerbated carotid arterial thrombosis with enhanced deposition of mPLT.

CONCLUSIONS

Together, our study provides evidence for an ignored health risk caused by TiO2NPs, specifically TiO2NP treatment augments procoagulant activity, activation and aggregation of PLTs via calcium-dependent mechanism and thus increases the risk of AT.

Non-clinical investigations about cytotoxic and anti-platelet activities of gamma-terpinene

Gamma-terpinene (γ-TPN) is a cyclohexane monoterpene isolated from plant essential oils, such as tea tree (Melaleuca alternifolia), oregano (Origanum vulgare), rosemary (Rosmarinus officinalis L.), thyme (Thymus vulgaris Marchand), and eucalyptus (Eucalyptus sp.). Terpenes are widely studied molecules pharmacologically active on the cardiovascular system, hemostasis, and antioxidant actions. Herein, it was investigated the cytotoxic and antiplatelet activity of γ-TPN using different non-clinical laboratory models. For in silico evaluation, the PreADMET, SwissADME, and SwissTargetPrediction softwares were used. Molecular docking was performed using the AutoDockVina and BIOVIA Discovery Studio databases. The cytotoxicity of γ-TPN was analyzed by the MTT assay upon normal murine endothelial SVEC4-10 and fibroblast L-929 cells. Platelet aggregation was evaluated with platelet-rich (PRP) and platelet-poor (PPP) plasma from spontaneously hypertensive rats (SHR), in addition to SVEC4-10 cells pre-incubated with γ-TPN (50, 100, and 200 µM) for 24 h. SHR animals were pre-treated by gavage with γ-TPN for 7 days and divided into four groups (negative control, 25, 50, and 100 mg/kg). Blood samples were collected to measure nitrite using the Griess reagent. Gamma-TPN proved to be quite lipid-soluble (Log P = +4.50), with a qualified profile of similarity to the drug, good bioavailability, and adequate pharmacokinetics. It exhibited affinity mainly for the P2Y12 receptor (6.450 ± 0.232 Kcal/mol), moderate cytotoxicity for L-929 (CC50 = 333.3 µM) and SVEC 4-10 (CC50 = 366.7 µM) cells. The presence of γ-TPN in SVEC 4-10 cells was also able to reduce platelet aggregation by 51.57 and 44.20% at lower concentrations (50 and 100 µM, respectively). Then, γ-TPN has good affinity with purinergic receptors and an effect on the reversal of platelet aggregation and oxidative stress, being promising and safe for therapeutic targets and subsequent studies on the control of thromboembolic diseases.

Purinergic signaling in the battlefield of viral infections

Purinergic signaling has been associated with immune defenses against pathogens such as bacteria, protozoa, fungi, and viruses, acting as a sentinel system that signals to the cells when a threat is present. This review focuses on the roles of purinergic signaling and its therapeutic potential for viral infections. In this context, the purinergic system may play potent antiviral roles by boosting interferon signaling. In other cases, though, it can contribute to a hyperinflammatory response and disease severity, resulting in poor outcomes, such as during flu and potentially COVID-19. Lastly, a third situation may occur since viruses are obligatory intracellular parasites that hijack the host cell machinery for their infection and replication. Viruses such as HIV-1 use the purinergic system to favor their infection and persistence within the host cell. Therefore, understanding the particular nuances of purinergic signaling in each viral infection may contribute to designing proper therapeutic strategies to treat viral diseases.

Antiplatelet Action of Chloramine Derivatives of Adenosine Phosphates and Their Chemical Activity in Relation to Sulfur-Containing Compounds

We studied the properties of N6-chloroadenosine phosphates (ATP, ADP, and AMP chloramines) as compounds with potentially increased antiplatelet efficacy determined by their binding to the plasma membrane of platelets. Chloramine derivatives of ATP, ADP, and AMP do not differ in their optical absorption characteristics: their absorption spectra are in the range of 220-340 nm with a maximum at 264 nm. Chloramines of adenosine phosphates are characterized by high reactivity with respect to thiol compounds. In particular, the rate constants of the reaction of N6-chloroadenosine-5'-diphosphate with N-acetylcysteine, reduced glutathione, dithiothreitol, and cysteine reach 59,000, 250,000, 340,000, and 1,250,000 M^-1×sec^-1, respectively, and only 1.10±0.02 M^-1×sec^-1 with methionine. It has been found that N6-chloradenosine-5'-triphosphate is a strong inhibitor of platelet functions: it effectively suppresses ADP-induced cell aggregation (IC₅₀ in the whole blood is 5 μM) and inhibits aggregation of preactivated platelets and induces dissociation of their aggregates.

Effects of uridine and nucleotides on hemostasis parameters

Several purinergic receptors have been identified on platelets which are involved in hemostatic and thrombotic processes. The aim of the present study was to investigate the effects of uridine and its nucleotides on platelet aggregation and hemostasis in platelet-rich plasma (PRP) and whole blood. The effects of uridine, UMP, UDP, and UTP at different final concentrations (1 to 1000 µM) on platelet aggregation were studied using an aggregometer. In PRP samples, platelet aggregation was induced by ADP, collagen and epinephrine 3 min after addition of uridine, UMP, UDP, UTP and saline (as a control). All thromboelastogram experiments were performed at 1000 µM final concentrations of uridine and its nucleotides in whole blood. UDP and UTP were also tested in thromboelastogram with PRP. Our results showed that UDP, and especially UTP, inhibited ADP- and collagen-induced aggregation in a concentration-dependent manner. In whole blood thromboelastogram experiments, UDP stimulated clot formation while UTP suppressed clot formation. When thromboelastogram experiments were repeated with PRP, UTP's inhibitory effect on platelets was confirmed, while UDP's stimulated clot forming effect disappeared. Collectively, our data showed that UTP inhibited platelet aggregation in a concentration-dependent manner and suppressed clot formation. On the other hand, UDP exhibited distinct effects on whole blood or PRP in thromboelastogram. These data suggest that the difference on effects of UTP and UDP might have arisen from the different receptors that they stimulate and warrant further investigation with regard to their in vivo actions on platelet aggregation and hemostasis.

Four-Week Supplementation of Water-Soluble Tomato Extract Attenuates Platelet Function in Chinese Healthy Middle-Aged and Older Individuals: A Randomized, Double-Blinded, and Crossover Clinical Trial

Background and Aims

Platelets are linked to atherosclerotic development and pathological thrombosis. Single dose of water-soluble tomato extract (WTE) which is a natural extraction can exert anti-platelet effects after 3 or 7 h in British healthy people. However, the effects of WTE supplementation on platelet function in Chinese healthy middle-aged and older individuals have not been studied, and the effects or safety of 4-week WTE supplementation also remain unclear. The present study aims to determine the effects of WTE on platelet function, and explore the safety of 4-week WTE supplementation in Chinese healthy middle-aged and older individuals.

Methods

A randomized, double-blinded, and crossover clinical trial was conducted. Firstly, 105 individuals were randomly divided into two groups that received WTE (150 mg/day) or placebo for 4 weeks. Then, after a washout period of 2 weeks, two groups exchanged groups and continued for another 4-week intervention. Platelet aggregation, P-selectin, activated GPIIbIIIa, plasma platelet factor 4 (PF4), β-thromboglobulin (β-TG), and thromboxane B₂ (TXB₂) were tested at baseline, 4, 6, and 10 weeks.

Results

Compared with the placebo group, 150 mg/day WTE supplement for 4 weeks significantly reduced ADP-induced or collagen-induced platelet aggregation (−10.8 ± 1.8 or −3.9 ± 1.5%, P < 0.05), ADP-induced or collagen-induced platelet P-selectin expression (−6.9 ± 1.5 or −6.6 ± 1.3%, P < 0.05), ADP-induced or collagen-induced activated GPIIbIIIa (−6.2 ± 2.0 or −3.8 ± 2.0%, P < 0.05). Besides, 4-week intervention of 150 mg WTE per day also resulted in significant reductions in plasma PF4 (−120.6 ± 33.2 ng/mL, P < 0.05) and β-TG (−129.7 ± 27.5 ng/mL, P < 0.05) and TXB₂ (−42.0 ± 4.0 ng/mL, P < 0.05), while had no effects on coagulation function and liver or renal function. Interestingly, 2-week washout period is enough to reverse the inhibitory effect of 4-week WTE supplementation on platelet function.

Conclusion

WTE supplementation for 4 weeks could moderately reduce platelet activation, aggregation, and granule secretion in Chinese healthy middle-aged and older individuals, and these effects are safe. After 2-week washout period, the inhibitory effect of 4-week WTE on platelet function can be eliminated.

Clinical Trial Registration

[http://www.chictr.org.cn/], identifier [ChiCTR-POR-17012927].

Platelet transfusion for cancer secondary thrombocytopenia: Platelet and cancer cell interaction

Chemoradiotherapy and autoimmune disorder often lead to secondary thrombocytopenia in cancer patients, and thus, platelet transfusion is needed to stop or prevent bleeding. However, the effect of platelet transfusion remains controversial for the lack of agreement on transfusion strategies. Before being transfused, platelets are stored in blood banks, and their activation is usually stimulated. Increasing evidence shows activated platelets may promote metastasis and the proliferation of cancer cells, while cancer cells also induce platelet activation. Such a vicious cycle of interaction between activated platelets and cancer cells is harmful for the prognosis of cancer patients, which results in an increased tumor recurrence rate and decreased five-year survival rate. Therefore, it is important to explore platelet transfusion strategies, summarize mechanisms of interaction between platelets and tumor cells, and carefully evaluate the pros and cons of platelet transfusion for better treatment and prognosis for patients with cancer with secondary thrombocytopenia.

Purinergic Regulation of Endothelial Barrier Function

Increased vascular permeability is a hallmark of several cardiovascular anomalies, including ischaemia/reperfusion injury and inflammation. During both ischaemia/reperfusion and inflammation, massive amounts of various nucleotides, particularly adenosine 5'-triphosphate (ATP) and adenosine, are released that can induce a plethora of signalling pathways via activation of several purinergic receptors and may affect endothelial barrier properties. The nature of the effects on endothelial barrier function may depend on the prevalence and type of purinergic receptors activated in a particular tissue. In this review, we discuss the influence of the activation of various purinergic receptors and downstream signalling pathways on vascular permeability during pathological conditions.

Nucleotide P2Y1 receptor agonists are in vitro and in vivo prodrugs of A1/A3 adenosine receptor agonists: implications for roles of P2Y1 and A1/A3 receptors in physiology and pathology

Rapid phosphoester hydrolysis of endogenous purine and pyrimidine nucleotides has challenged the characterization of the role of P2 receptors in physiology and pathology. Nucleotide phosphoester stabilization has been pursued on a number of medicinal chemistry fronts. We investigated the in vitro and in vivo stability and pharmacokinetics of prototypical nucleotide P2Y₁ receptor (P2Y₁R) agonists and antagonists. These included the riboside nucleotide agonist 2-methylthio-ADP and antagonist MRS2179, as well as agonist MRS2365 and antagonist MRS2500 containing constrained (N)-methanocarba rings, which were previously reported to form nucleotides that are more slowly hydrolyzed at the α-phosphoester compared with the ribosides. In vitro incubations in mouse and human plasma and blood demonstrated the rapid hydrolysis of these compounds to nucleoside metabolites. This metabolism was inhibited by EDTA to chelate divalent cations required by ectonucleotidases for nucleotide hydrolysis. This rapid hydrolysis was confirmed in vivo in mouse pharmacokinetic studies that demonstrate that MRS2365 is a prodrug of the nucleoside metabolite AST-004 (MRS4322). Furthermore, we demonstrate that the nucleoside metabolites of MRS2365 and 2-methylthio-ADP are adenosine receptor (AR) agonists, notably at A₃ and A₁ARs. In vivo efficacy of MRS2365 in murine models of traumatic brain injury and stroke can be attributed to AR activation by its nucleoside metabolite AST-004, rather than P2Y₁R activation. This research suggests the importance of reevaluation of previous in vitro and in vivo research of P2YRs and P2XRs as there is a potential that the pharmacology attributed to nucleotide agonists is due to AR activation by active nucleoside metabolites.

In silico Approach for Anti-Thrombosis Drug Discovery: P2Y1R Structure-Based TCMs Screening

Cardiovascular diseases (CVDs), including thrombosis, which is induced by platelet aggregation, are the leading cause of mortality worldwide. The P2Y1 receptor (P2Y1R) facilitates platelet aggregation and is thus an important potential anti-thrombotic drug target. The P2Y1R protein structure contains a binding site for receptor antagonist MRS2500 within its seven-transmembrane bundle, which also provides suitable pockets for numerous other ligands to act as nucleotide antagonists of P2Y1R. The Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) comprises 499 Chinese Pharmacopoeia-registered herbs and the structure information for 29,384 ingredients. In silico docking of these compounds into the P2Y1R protein structure within the MRS2500 pocket can identify potential antithrombotic drugs from natural medicinal plants. Docking studies were performed and scored to evaluate ligand-binding affinities. In this study, a total of 8987 compounds from Traditional Chinese Medicine (TCM) were filtered by Lipinski's rule of five, and their ideal oral-intake properties were evaluated. Of these, 1656 compounds distributed in 443 herbs docked into the P2Y1R-MRS2500 structure in 16,317 poses. A total of 38 compounds were ranked with a DockScore above 70, and these may have significant potential for development into anti-thrombosis drugs. These computational results suggested that licorice (Glycyrrhiza uralensis Fisch), cimicifugae (Cimicifuga foetida L.), and ganoderma (Ganoderma lucidum Karst) and their chemical constituents, which have not previously been widely used for anti-thrombosis, may have unexpected effects on platelet aggregation. Moreover, two types of triterpene scaffolds summarized from 10 compounds were distributed in these three herbs and also docked into P2Y1R. These scaffold structures may be utilized for the development of drugs to inhibit platelet aggregation.

Purinergic P2Y1 Receptors Control Rapid Expression of Plasma Membrane Processes in Hippocampal Astrocytes

Astrocytes regulate neuronal activity and blood brain barrier through tiny plasma membrane branches or astrocytic processes (APs) making contact with synapses and brain vessels. Several transmitters released by astrocytes and exerting their action on several receptor classes expressed by astrocytes themselves influence their physiology. Here we found that APs are dynamically modulated by purines. In live imaging experiments carried out in rat hippocampal astrocytes, Gq-coupled P2Y1 receptor blockade with the selective antagonist MRS2179 (1 μM) or inhibition of its effector phospholipase C using U73122 (3 μM) produced APs retraction, while stimulation of the same receptor with the selective agonist 2MeSADP (100 μM) increased their number. Since astrocytes, among other transmitters, release ATP by several mechanisms including connexin hemichannels, we used the connexin hemichannel inhibitor carbenoxolone (100 μM) and APs retraction was observed. In our system we then measured expression or function of channels important for modulation of volume transmission and K+ buffering, aquaporin-4, and K+ inward rectifying (Kir) channels, respectively. Aquaporin-4 expression level did not change whereas, in whole-cell patch-clamp recordings performed to measure Kir current, we observed an increase in K+ current in all conditions where APs number was reduced. These data are supporting the idea of a dynamic modulation of astrocytic processes by purinergic signal, strengthening the role of purines in brain homeostasis.

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.

Leishmania infantum ecto-nucleoside triphosphate diphosphohydrolase-2 is an apyrase involved in macrophage infection and expressed in infected dogs

Background

Visceral leishmaniasis is an important tropical disease, and Leishmania infantum chagasi (synonym of Leishmania infantum) is the main pathogenic agent of visceral leishmaniasis in the New World. Recently, ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) were identified as enablers of infection and virulence factors in many pathogens. Two putative E-NTPDases (∼70 kDa and ∼45 kDa) have been found in the L. infantum genome. Here, we studied the ∼45 kDa E-NTPDase from L. infantum chagasi to describe its natural occurrence, biochemical characteristics and influence on macrophage infection.

Methodology/Principal Findings

We used live L. infantum chagasi to demonstrate its natural ecto-nucleotidase activity. We then isolated, cloned and expressed recombinant rLicNTPDase-2 in bacterial system. The recombinant rLicNTPDase-2 hydrolyzed a wide variety of triphosphate and diphosphate nucleotides (GTP> GDP  =  UDP> ADP> UTP  =  ATP) in the presence of calcium or magnesium. In addition, rLicNTPDase-2 showed stable activity over a pH range of 6.0 to 9.0 and was partially inhibited by ARL67156 and suramin. Microscopic analyses revealed the presence of this protein on cell surfaces, vesicles, flagellae, flagellar pockets, kinetoplasts, mitochondria and nuclei. The blockade of E-NTPDases using antibodies and competition led to lower levels of parasite adhesion and infection of macrophages. Furthermore, immunohistochemistry showed the expression of E-NTPDases in amastigotes in the lymph nodes of naturally infected dogs from an area of endemic visceral leishmaniasis.

Conclusions/Significance

In this work, we cloned, expressed and characterized the NTPDase-2 from L. infantum chagasi and demonstrated that it functions as a genuine enzyme from the E-NTPDase/CD39 family. We showed that E-NTPDases are present on the surface of promastigotes and in other intracellular locations. We showed, for the first time, the broad expression of LicNTPDases in naturally infected dogs. Additionally, the blockade of NTPDases led to lower levels of in vitro adhesion and infection, suggesting that these proteins are possible targets for rational drug design.

Visceral leishmaniasis is a dangerous and important, but neglected, tropical disease that affects millions of people, mainly in underdeveloped and developing countries. Presently, there are no vaccines against Leishmaniasis, and the few drugs with which the disease is treated have low efficacy and high side effects. The pathogenic agent of this disease in the New World is Leishmania infantum chagasi. In this work, we studied a protein from this parasite named ENTPDase-2. We expressed it in a bacterial system, purified it and characterized it as a genuine nucleotidase of the ENTPDase family. This protein seems to be localized at the surface of the parasite and in other intracellular locations. ENTPDase seems to facilitate in vitro infection because its blockade leads to lower levels of infection of macrophages. In addition, the protein is found in naturally infected dogs. A previous study demonstrated that ENTPDase-2 from L. infantum chagasi is a good antigen for immunodiagnosis of canine visceral leishmaniasis. We have now studied this protein in greater depth and suggest that it may be a good target for drug development.

The purinergic neurotransmitter revisited: a single substance or multiple players?

The past half century has witnessed tremendous advances in our understanding of extracellular purinergic signaling pathways. Purinergic neurotransmission, in particular, has emerged as a key contributor in the efficient control mechanisms in the nervous system. The identity of the purine neurotransmitter, however, remains controversial. Identifying it is difficult because purines are present in all cell types, have a large variety of cell sources, and are released via numerous pathways. Moreover, studies on purinergic neurotransmission have relied heavily on indirect measurements of integrated postjunctional responses that do not provide direct information for neurotransmitter identity. This paper discusses experimental support for adenosine 5'-triphosphate (ATP) as a neurotransmitter and recent evidence for possible contribution of other purines, in addition to or instead of ATP, in chemical neurotransmission in the peripheral, enteric and central nervous systems. Sites of release and action of purines in model systems such as vas deferens, blood vessels, urinary bladder and chromaffin cells are discussed. This is preceded by a brief discussion of studies demonstrating storage of purines in synaptic vesicles. We examine recent evidence for cell type targets (e.g., smooth muscle cells, interstitial cells, neurons and glia) for purine neurotransmitters in different systems. This is followed by brief discussion of mechanisms of terminating the action of purine neurotransmitters, including extracellular nucleotide hydrolysis and possible salvage and reuptake in the cell. The significance of direct neurotransmitter release measurements is highlighted. Possibilities for involvement of multiple purines (e.g., ATP, ADP, NAD(+), ADP-ribose, adenosine, and diadenosine polyphosphates) in neurotransmission are considered throughout.