Aggregation Of Washed Platelets Research Articles

Quantification of cyclic AMP and cyclic GMP levels in Krebs-Henseleit solution by LC-MS/MS: Application in washed platelet aggregation samples

Cyclic Nucleotides are important in regulating platelet function. Increases in 3′5′-cyclic adenosine monophosphate (cAMP) and 3′5′-cyclic guanosine monophosphate (cGMP) inhibit platelet aggregation and are pharmacological targets for antiplatelet therapy. Here we report an improved method for determining cAMP and cGMP concentrations and, for the first time, in washed platelet supernatants by combining high-performance liquid chromatography and tandem mass spectrometry (LC-MS/MS). Characteristic peaks of the substrates, cGMP or cAMP and their internal standards were identified in negative-ion electrospray ionisation using multiple reaction monitoring. Compared with previously reported methods, the method presented here shows high precision with the lowest lower limit of quantification (LLoQ) to date (10 pg/mL). The effect of a novel catecholamine, 6-nitrodopamine, on cyclic nucleotide levels was quantified. Our results showed that this new method was fast, sensitive, and highly reproducible.

Quantification of Cyclic Amp and Cyclic Gmp Levels in Krebs-Henseleit's Solution by Lc-Ms/Ms: Application in Washed Platelet Aggregation Samples

Quantification of Cyclic Amp and Cyclic Gmp Levels in Krebs-Henseleit's Solution by Lc-Ms/Ms: Application in Washed Platelet Aggregation Samples

Effects of novel Btk and Syk inhibitors on platelet functions alone and in combination in vitro and in vivo

BackgroundInhibitors of tyrosine kinases downstream of the B‐cell receptor, such as Bruton's tyrosine kinase (Btk) or Spleen tyrosine kinase (Syk), used alone or in combination are new therapeutic options in the treatment of B‐cell malignancies. A challenge in the development of second‐generation Btk inhibitors is to limit their side effects such as the increased bleeding risk. Considering the pivotal role of Syk in immunoreceptor tyrosine‐based activation motif mediated platelet signaling, the impact of inhibiting this kinase on platelet functions is also worth analyzing. ObjectivesWe investigated the effect of a novel Btk inhibitor, tirabrutinib, and a Syk inhibitor, entospletinib, alone and in combination on platelet signaling and functions in vitro and ex vivo. MethodsPlatelet aggregation, secretion, and signaling responses as well as thrombus growth under flow were analyzed in the presence of the inhibitors alone or in combination in vitro, at clinically relevant doses, and ex vivo in patients treated with these inhibitors in the context of a phase I trial. ResultsAlthough tirabrutinib alone had modest effects on platelet activation in vitro and ex vivo, entospletinib alone efficiently inhibited washed platelet aggregation in response to collagen. However, entospletinib weakly affected platelet activation in platelet‐rich plasma, in whole blood and ex vivo. Importantly, the combination of tirabrutinib and entospletinib induced a significant decrease in platelet response to collagen in vitro and ex vivo correlating with mild bleedings reported in some of the treated patients. ConclusionThese new results should contribute to improve the safety of these targeted therapies.

Comparative In Vitro Study of Various α2-Adrenoreceptor Agonist Drugs for Ticagrelor Reversal

Ticagrelor, an antiplatelet adenosine diphosphate (ADP)-P2Y12 receptor antagonist, increases the risk of bleeding. Its management is challenging because platelet transfusion is ineffective and no specific antidote is currently available. Epinephrine, a vasopressor catecholamine prescribed during shock, restores platelet functions inhibited by ticagrelor through stimulation of α2A-adrenoreceptors. It subsequently inhibits cyclic adenosine monophosphate (cAMP) pathway and PI3K signaling. However, since epinephrine may expose a patient to deleterious hemodynamic effects, we hypothesized that other α2-adrenoreceptor agonist drugs used in clinical practice with fewer side effects could reverse the antiplatelet effects of ticagrelor. We compared in vitro the efficacy of clonidine, dexmedetomidine, brimonidine, and norepinephrine with epinephrine to restore ADP- and PAR-1-AP-induced washed platelet aggregation inhibited by ticagrelor, as well as resulting platelet cAMP levels. In ticagrelor-free samples, none of the α2-adrenoreceptor agonists induced aggregation by itself but all of them potentiated ADP-induced aggregation. Compared with epinephrine, norepinephrine, and brimonidine partially restored ADP- and fully restored PAR-1-AP-induced aggregation inhibited by ticagrelor while clonidine and dexmedetomidine were ineffective. Indeed, this lack of effect resulted from a lower decrease in cAMP concentration elicited by these partial α2-adrenoreceptor agonists, clonidine, and dexmedetomidine, compared with full α2-agonists. Our results support the development of specific full and systemic α2-adrenoreceptor agonists for ticagrelor reversal.

Epinephrine restores platelet functions inhibited by ticagrelor: A mechanistic approach

Ticagrelor, an antagonist of the platelet adenosine diphosphate (ADP)-P2Y12 receptor is recommended for patients with acute coronary syndromes. However, ticagrelor exposes to a risk of bleeding, the management of which is challenging because platelet transfusion is ineffective, and no antidote is yet available. We hypothesized that the vasopressor drug epinephrine could counter the antiplatelet effects of ticagrelor and restore platelet functions. We assessed in vitro the efficiency of epinephrine in restoring platelet aggregation inhibited by ticagrelor and investigated the underlying mechanisms. Washed platelet aggregation and secretion were measured upon stimulation by epinephrine alone or in combination with ADP, in the presence or absence of ticagrelor. Mechanistic investigations used P2Y1 and phosphoinositide 3-kinase (PI3K) inhibitors and included vasodilator-stimulated phosphoprotein (VASP) and Akt phosphorylation assays as well as measurement of Ca2+ mobilisation. We found that epinephrine restored ADP-induced platelet aggregation, but not dense granule release. Epinephrine alone failed to induce aggregation whereas it fully induced VASP dephosphorylation and Akt phosphorylation regardless of the presence of ticagrelor. In the presence of ticagrelor, blockage of the P2Y1 receptor prevented restoration of platelet aggregation by the combination of epinephrine and ADP, as well as intracellular Ca2+ mobilisation. In combination with ADP, epinephrine induced platelet aggregation of ticagrelor-treated platelets through inhibition of the cAMP pathway and activation of the PI3K pathway, thus enabling the P2Y1 receptor signalling and subsequent Ca2+ mobilisation. This proof-of-concept study needs to be challenged in vivo for the management of bleeding in ticagrelor-treated patients.

Effect of Size and Concentration of PLGA-PEG Nanoparticles on Activation and Aggregation of Washed Human Platelets.

Nanotechnology is being increasingly utilised in medicine as diagnostics and for drug delivery and targeting. The small size and high surface area of nanoparticles (NPs), desirable properties that allow them to cross biological barriers, also offer potential for interaction with other cells and blood constituents, presenting possible safety risks. While NPs investigated are predominantly based on the biodegradable, biocompatible, and FDA approved poly-lactide-co-glycolide (PLGA) polymers, pro-aggregatory and antiplatelet effects have been reported for certain NPs. The potential for toxicity of PLGA based NPs remains to be examined. The aims of this study were to determine the impact of size-selected PLGA-PEG (PLGA-polyethylene glycol) NPs on platelet activation and aggregation. PLGA-PEG NPs of three average sizes of 112, 348, and 576 nm were formulated and their effect at concentrations of 0.0–2.2 mg/mL on the activation and aggregation of washed human platelets (WP) was examined. The results of this study show, for the first time, NPs of all sizes associated with the surface of platelets, with >50% binding, leading to possible internalisation. The NP-platelet interaction, however, did not lead to platelet aggregation nor inhibited aggregation of platelets induced by thrombin. The outcome of this study is promising, suggesting that these NPs could be potential carriers for targeted drug delivery to platelets.

Thrombomodulin alfa prevents the decrease in platelet aggregation in rat models of disseminated intravascular coagulation

IntroductionDisseminated intravascular coagulation (DIC), a deadly complication characterized by uncontrolled hypercoagulation, causes a decrease in the platelet count and impairs platelet aggregation. Thrombomodulin (TM) alfa, a recombinant human soluble TM, reduces hypercoagulation in DIC patients. However, the effects of TM alfa on impaired platelet aggregation remain to be determined. In this study, we aim to investigate the effects of TM alfa on platelet aggregation using lipopolysaccharide (LPS)-induced and tissue factor (TF)-induced DIC rat models. Materials and methodsSprague–Dawley rats were administered TF or LPS intravenously, with or without TM alfa before the injection. Six hours after LPS injection or 1 h after TF infusion, blood samples were obtained, and platelet-rich plasma was prepared. Collagen or adenosine diphosphate-induced platelet aggregation was measured using an aggregometer. In the other experiments, platelets were transfused 1 h after the TF infusion. Five minutes after transfusion, collagen-induced platelet aggregation was also measured. ResultsThe amplitude of platelet aggregation in platelet-rich plasma was decreased in LPS- and TF-treated rats. TM alfa inhibited the decrease in platelet aggregation in a dose-dependent manner. The washed platelet aggregation amplitude was not decreased in TF-treated rats. Suspension of normal platelets in plasma obtained from TF-treated rats reduced platelet aggregation. Platelet transfusion for TF-treated rats increased the platelet count but was unable to improve platelet aggregation. ConclusionsTM alfa attenuated impairment of platelet aggregation in LPS- and TF-induced DIC rat models. The changes in plasma composition played a role in the decrease of platelet aggregation in TF-treated rats.

The Role of Human Platelet Preparation for Toll-Like Receptors 2 and 4 Related Platelet Responsiveness.

Background Like immune cells, platelets express the repertoire of toll-like receptors (TLR), among them TLR2 and TLR4, which are important for the recognition of bacterial patterns. Receptor-mediated functional effects in platelets have been investigated, but reliable conclusions are tampered due to heterogeneous study designs with variable platelet preparation methods. This study compares TLR2- and TLR4-dependent platelet responsiveness in platelet-rich plasma (PRP) and in washed platelets (WPs). Material and Methods Fresh peripheral blood samples from healthy donors served for the preparation of PRP and WP. Basal and agonist-stimulated TLR2 and TLR4 expression levels were evaluated by flow cytometry. Light transmission aggregometry was used to investigate functional effects of TLR2 and TLR4 stimulation with Pam3CSK4 or LPS (lipopolysaccharides from Escherichia coli ) as ligands. The capacity of chemokine release was determined by immunoassays. Results Pam3CSK4 and LPS (in combination with thrombin) were able to induce aggregation in WP, but not in PRP, with threshold concentrations of 15 µg/mL. Basal expression levels of TLR2 and TLR4 were higher in WP than in PRP, increasing several-fold rapidly and persistently upon platelet activation with potent agonists. Pam3CSK4 (15 µg/mL) or LPS led to the submaximal release of RANTES, PF4, PDGF, NAP-2, and sCD40L from WP. In PRP, secretory effects are less pronounced for RANTES, PDGF, or PF4, and not detectable for NAP-2 or sCD40L. Conclusion The effects mediated by TLR2 and TLR4 stimulation are dependent on platelet preparation, an important issue for experimental designs and for manufacturing of platelet concentrates in transfusion medicine.

Methylglyoxal potentiates thrombin and collagen‐induced human platelet aggregation.

ObjectivesMethylglyoxal (MGO), a metabolite of the glycolysis pathway, is a precursor of advanced glycation end products (AGE). Levels of MGO are elevated in pre‐diabetic and diabetic patients (Dornadula 2015 et al. Chem Res Toxicol. 2015;28:1666–74). Because increased AGE formation has been proposed as one mechanism involved in vascular complications and platelet activation of diabetes (Hadas K et al, Plos One, 8:e74401; 2013), this study aimed to evaluate the effects of MGO on the human washed platelet aggregation induced by thrombin and collagen.MethodsThe study was approved by the local Ethics Committee (Protocol No. 66299817.4.0000.5137). Platelets were isolated from peripheral blood of human healthy volunteers (7 men and 10 women, aged 27.8±1.9 y.o.). Platelet samples (200 μL) were incubated with MGO (0.08–0.64 mM), and subsequently activated with either thrombin (0.01 to 1.0 U/ml) or collagen (0.2 to 20 μg/ml). Platelet aggregation was performed with an optical aggregometer (PAP‐8E Platelet Aggregation Profiler, PA, USA).ResultsThrombin produced concentration‐dependent platelet aggregation, achieving a maximum response at 0.3 and 1 U/ml (0.8 ± 0.5, 15.7±4.7, 27.8±5.5, 59.6±5.4 and 63.9±3.3% for 0.01, 0.03, 0.1, 0.3 and 1 U/ml, respectively). Pre‐incubation with MGO (0.08 mM) markedly increased (p<0.001) the thrombininduced platelet aggregation (14.0±13.5, 50.6±4.7, 72.4±4.2, 79.4±4.4 and 77.2±2.7%, respectively). Similar data were observed using higher concentrations of MGO (0.16 and 0.64 mM). In separate samples, addition of collagen induced concentration‐dependent platelet aggregation (0.2±0.2, 8.6±3.7, 14.4±4.4, 41.4±4.9 and 53.2±5.3 for 0.2, 1.0, 2.0, 10.0 and 20.0ug respectively). Pre‐incubation with MGO (0.08 mM) significantly increased (p<0.001) the collagen‐induced aggregation (0.5±0.3, 38.7±11.5, 38.3±6.8, 56.8±4.9 and 57.1±4.9 respectively). Higher concentrations of MGO (0.16 and 0.64 mM) also significantly potentiated collagen‐induced aggregation. MGO incubated had no effect in the absence of thrombin or collagen. Next, we evaluated if the potentiation of thrombin‐ and collagen‐induced platelet aggregation by MGO was due to inactivation of nitric oxide (NO) – cyclic GMP signaling Incubation of the NO donor sodium nitroprusside (3uM) inhibited by 32,7% a 60,9% (p<0.05) the thrombin‐ and collagen‐induced aggregation, respectively. However, MGO (0.08 e 0.16 mM) had no effect on the inhibitory effect of SNP on thrombin‐ and collagen‐induced aggregation. We also evaluated the protein expression by western blotting of both α1 and β1 subunits of soluble guanylate cyclase in the absence and presence of MGO. However, MGO did not significantly modify the expression of either subunits.ConclusionMGO enhances human platelet aggregation induced by thrombin and collagen by mechanisms independent of inactivation of NO‐cGMP signaling.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

MMP‐13 binds to platelet receptors αIIbβ3 and GPVI and impairs aggregation and thrombus formation

Unlabelled Box BackgroundAcute thrombotic syndromes lead to atherosclerotic plaque rupture with subsequent thrombus formation, myocardial infarction and stroke. Following rupture, flowing blood is exposed to plaque components, including collagen, which triggers platelet activation and aggregation. However, plaque rupture releases other components into the surrounding vessel which have the potential to influence platelet function and thrombus formation. ObjectivesHere we sought to elucidate whether matrix metalloproteinase‐13 (MMP‐13), a collagenolytic metalloproteinase up‐regulated in atherothrombotic and inflammatory conditions, affects platelet aggregation and thrombus formation. ResultsWe demonstrate that MMP‐13 is able to bind to platelet receptors alphaIIbbeta3 (αIIbβ3) and platelet glycoprotein (GP)VI. The interactions between MMP‐13, GPVI and αIIbβ3 are sufficient to significantly inhibit washed platelet aggregation and decrease thrombus formation on fibrillar collagen. ConclusionsOur data demonstrate a role for MMP‐13 in the inhibition of both platelet aggregation and thrombus formation in whole flowing blood, and may provide new avenues of research into the mechanisms underlying the subtle role of MMP‐13 in atherothrombotic pathologies.

Comparative Anti-Platelet Profiling Reveals a Potent Anti-Aggregatory Effect of CD34+ Progenitor Cell-Derived Late-Outgrowth Endothelial Cells in vitro

Background/Aims: Platelets affect endothelial progenitor cell (EPC) functionality, inducing their differentiation into mature endothelial cells. However, it remains to be established whether EPCs can influence platelet functionality. Methods: Mononuclear proangiogenic cells (MPCs) and early outgrowth cells (EOCs) were prepared from peripheral blood mononuclear cells, whereas late-outgrowth endothelial cells (OECs) were prepared from cord blood CD34+ cells. The effect of the above cells and their supernatants on washed platelet aggregation was studied. The effect of OECs and their supernatant on the adenosine diphosphate (ADP)-induced magnitude of platelet integrin receptor α_IIbβ₃ activation and on P-selectin membrane expression was investigated. The levels of nitric oxide (NO) and prostacyclin (PGI₂) that were secreted from EOCs, OECs, and human umbilical vein endothelial cells (HUVECs) were also assessed. Results: Among all progenitors, OECs and their supernatant exhibited the most potent inhibitory activity towards platelet aggregation. Furthermore, OECs and their supernatant, but not CD34+ cells, reduced α_IIbβ₃ activation and P-selectin membrane expression. Finally, OECs secreted higher NO and PGI₂ levels than EOCs did. Conclusion: The anti-platelet effect of EPCs depends highly on the degree of their endothelial phenotype, with OECs expressing the highest potency. Therefore, the induction of OEC generation and the enhancement of their functionality in vivo could be a new approach for the treatment of patients at a high thrombotic risk.

Molecular requirements involving the human platelet protease-activated receptor-4 mechanism of activation by peptide analogues of its tethered-ligand

Thrombin is the most potent agonist of human platelets and its effects are primarily mediated through the protease-activated receptors (PARs)-1 and -4. Although PAR-1 has higher affinity for thrombin than PAR-4, both receptors contribute to thrombin-mediated actions on platelets. Recently, a potent and selective PAR-1 antagonist (vorapaxar) was approved for clinical use in selected patients. In contrast, despite the fact that several PAR-4 antagonists have been developed, few of them have been tested in clinical trials.The aim of the present study was to elucidate the molecular requirements involving the PAR-4 mechanism of activation by peptide analogues of its tethered-ligand.Eight synthetic PAR-4 tethered-ligand peptide analogues were synthesized and studied for their agonistic/antagonistic potency and selectivity toward human washed platelet aggregation, using light transmittance aggregometry. In addition, in silico studies were conducted to describe the receptor–peptide interactions that are developed following PAR-4 exposure to the above analogues. To provide a first structure-activity relationship rationale on the bioactivity profiles recorded for the studied analogues, molecular docking was applied in a homology model of PAR-4, derived using the crystal structure of PAR-1.The following peptide analogues were synthesized: AYPGKF-NH2 (1), GYPGKF-NH2 (2), Ac-AYPGKF-NH2 (3), trans-cinnamoyl-AYPGKF-NH2 (4), YPGKF-NH2 (5), Ac-YPGKF-NH2 (6), trans-cinnamoyl-YPGKF-NH2 (7), and caffeoyl-YPGKF-NH2 (8). Peptide (1) is a selective PAR-4 agonist inducing platelet aggregation with an IC50 value of 26.2 μM. Substitution of Ala-1 with Gly-1 resulted in peptide (2), which significantly reduces the agonistic potency of peptide (1) by 25-fold. Importantly, substitution of Ala-1 with trans-cinnamoyl-1 resulted in peptide (7), which completely abolishes the agonistic activity of peptide (1) and renders it with a potent antagonistic activity toward peptide (1)-induced platelet aggregation. All other peptides tested were inactive. Tyr-2, residue, along with its neighboring environment was a key determinant in the PAR-4 recognition mode. When the neighboring residues to Tyr-2 provided an optimum spatial ability for the ligand to enter into the binding site of the transmembrane receptor, a biological response was propagated. These results were compared with the predicted binding poses of small molecule antagonists of PAR-4, denoted as YD-3, ML-354, and BMS-986120. π–π stacking interaction with Tyr-183 appears to be critical and common for both small molecules antagonists and the peptide trans-cinnamoyl-YPGKF-NH2.Conclusively, the lipophilicity, size, and aromatic nature of the residue preceding Tyr-2 are determining factors on whether a human platelet PAR-4 tethered-ligand peptide analogue will exert an agonistic or antagonistic activity.

Trans-fused 5-[(tert-Butoxtycarbonyl)amino]octahydroindenes as a protease activated receptor-1 (PAR1) antagonist.

Protease activated receptor 1 (PAR1) has been considered as a promising antiplatelet target to prevent thrombotic cardiovascular events in patients with prior myocardial infarction or peripheral arterial diseases. Previously, we found a series of octahydroindene analogues to have high potency on PAR1 and no significant cytotoxicity but poor metabolic stability in human and rat liver microsomes. We designed and synthesized substituted analogues of octahydroindenes at C5 or C6 aiming to improvement of metabolic stability, and identified that trans-fused 5-[(tert-butoxtycarbonyl)amino]octahydroindene analogues showed improved metabolic stability with maintaining good activity on PAR1. Especially, 2-methanesulfonate 57 (IC50=0.006 μM; R50=126.3min in human, 83.3min in rat), sulfamate 58 (IC50=0.020 μM; R50=52.8min in human, 106.0min in rat), and N-(cyclopropyl)methylsufonamide 63 (IC50=0.010 μM; R50=51.4min in human, 90.5min in rat) exhibited excellent activity and metabolic stability both on human and rat liver microsomes, comparable to those obtained for varapaxar (IC50=0.0015 μM; R50=83.2min in human, 32.4min in rat). Additionally, these compounds (57, 58, and 63) represented significant efficacy (IC50=0.0022, 0.0062, and 0.015 μM, each) in human washed platelet aggregation (WPA) assay without cytotoxicity and CYP3A4 inhibitory activity.

Discovery and antiplatelet activity of a selective PI3Kβ inhibitor (MIPS-9922)

A series of amino-substituted triazines were developed and examined for PI3Kβ inhibition and anti-platelet function. Structural adaptations of a morpholine ring of the prototype pan-PI3K inhibitor ZSTK474 yielded PI3Kβ selective compounds, where the selectivity largely derives from an interaction with the non-conserved Asp862 residue, as shown by site directed mutagenesis. The most PI3Kβ selective inhibitor from the series was studied in detail through a series of in vitro and in vivo functional studies. MIPS-9922, 10 potently inhibited ADP-induced washed platelet aggregation. It also inhibited integrin αIIbβ3 activation and αIIbβ3 dependent platelet adhesion to immobilized vWF under high shear. It prevented arterial thrombus formation in the in vivo electrolytic mouse model of thrombosis without inducing prolonged bleeding or excess blood loss.

Human Apolipoprotein a-I Decreases Platelet Activation Responses and Protects Mice from Arterial Thrombosis

Introduction: High-density lipoprotein (HDL) protects against thromboembolic coronary disease via reverse cholesterol transport mediated by HDL’s primary lipoprotein subunit, apolipoprotein A-I (apoA-I), binding to scavenger receptor BI (SR-BI). Absence of SR-BI increases platelet aggregation and venous/arterial thrombosis in mice, consistent with an antithrombotic role of this signaling axis. To date, the effects of the isolated apoA-I subunit on platelet activation remain unknown. We hypothesize that the antithrombotic effect is mediated by apoA-I signaling through platelet-specific SR-BI.Methods: Platelet function assays were performed on samples from healthy human volunteers (n=3). ApoA-I levels were determined using an ELISA kit. Microfluidic analysis of platelet aggregate formation on collagen under physiologic flow conditions (650 sec-1) was carried out in whole blood samples. Light transmission platelet aggregation in response to collagen and ristocetin was conducted using both platelet rich plasma (PRP) and washed platelets (WP). Venous and arterial thromboses were induced in wild type C57Bl/6 mice in a collagen (0.3 mg/kg)/epinephrine (0.03 mg/kg)-induced pulmonary embolism model and a 6% ferric chloride (FeCl3)-induced carotid artery thrombosis model, respectively. Recombinant human apoA-I was used with a final concentration of 300 µg/mL.Results/Discussion: ApoA-I plasma levels in the subjects studied fell within previously published ranges. Microfluidic analysis of platelet aggregate formation on collagen under shear stress did not demonstrate significant difference in total surface area coverage (n=3 in quadruplicate), but apoA1-treated samples demonstrated a significantly greater proportion of small aggregates (3-10 platelets/aggregate, 40.2% vs 31.8%, p<0.0001), compared to controls which had a significantly greater proportion of large aggregates (51-100 plts/agg, 6.3 vs 2.3%, p<0.001 and >100 plts/agg, 2.3% vs 0.7%, p<0.05). Platelet aggregation studies (Fig. 1) revealed significantly decreased collagen-induced aggregation in platelets treated with apoA-I compared to vehicle-treated controls in both PRP and WP samples, suggesting direct action of apoA-I on platelets. The difference was less pronounced in ristocetin-induced aggregation, though still significant, consistent with decreased activation of VWF, which has been recently shown to bind apoA-I. Apoa-I-treated PRP samples also had significantly decreased dense granule (ATP) release compared to non-treated samples. Pre-treatment with native HDL had no significant effect, consistent with studies demonstrating that only oxidized HDL inhibits aggregation. Recombinant human SR-BI (rhSR-BI) alone had little effect in PRP but inhibited collagen-induced aggregation in WP. Addition of rhSR-BI and apoA-I together inhibited aggregation in both PRP and WP to a greater degree than either component alone. Rabbit anti-human SR-BI alone had little effect in PRP but inhibited collagen-induced aggregation in WP. FeCl3 applicationinduced initial arterial occlusion within 8.8 +/-0.8 minutes in apoA-I-treated mice treated (n=3) compared to 6.1 +/- 0.3 minutes in vehicle-treated controls (n=3, p<0.01, t-test). Systemic thrombosis resulting in pulmonary embolism was induced by injection of collagen/epinephrine. Median time of survival after injection in mice pre-treated with apoA-I (n=5) was 30 +/- 0 minutes, compared to 3.3 +/- 0.4 minutes in vehicle-treated controls (n=5, p<0.001, t-test). Experiments were stopped after 30 minutes, at which time all apoA-1-treated mice were still alive, compared to zero controls.Conclusion: Though the mechanism is not yet completely understood, the data show an inhibitory effect of isolated human apoA-I on human platelet activation and murine arterial/venous thrombosis, likely through platelet inhibition. The increased inhibition seen with rhSR-BI and apoA-I together is consistent with previous studies demonstrating SR-BI’s regulatory role in platelet function. Ongoing studies include increasing sample size for human platelet function assays and murine venous/arterial thrombosis models in wild type mice with and without infusion of apoA-I compared to SR-BI-/- and apoA-I-/- mice with and without infusion of apoA-I. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Antiplatelet and anticoagulant effects of diterpenes isolated from the marine alga, Dictyota menstrualis.

Cardiovascular diseases represent a major cause of disability and death worldwide. Therapeutics are available, but they often have unsatisfactory results and may produce side effects. Alternative treatments based on the use of natural products have been extensively investigated, because of their low toxicity and side effects. Marine organisms are prime candidates for such products, as they are sources of numerous and complex substances with ecological and pharmacological effects. In this work, we investigated, through in vitro experiments, the effects of three diterpenes (pachydictyol A, isopachydictyol A and dichotomanol) from the Brazilian marine alga, Dictyota menstrualis, on platelet aggregation and plasma coagulation. Results showed that dichotomanol inhibited ADP- or collagen-induced aggregation of platelet-rich plasma (PRP), but failed to inhibit washed platelets (WP). In contrast, pachydictyol A and isopachydictyol A failed to inhibit the aggregation of PRP, but inhibited WP aggregation induced by collagen or thrombin. These diterpenes also inhibited coagulation analyzed by the prothrombin time and activated partial thromboplastin time and on commercial fibrinogen. Moreover, diterpenes inhibited the catalytic activity of thrombin. Theoretical studies using the Osiris Property Explorer software showed that diterpenes have low theoretical toxicity profiles and a drug-score similar to commercial anticoagulant drugs. In conclusion, these diterpenes are promising candidates for use in anticoagulant therapy, and this study also highlights the biotechnological potential of oceans and the importance of bioprospecting to develop medicines.

Chalcone derivatives inhibit human platelet aggregation and inhibit growth in human bladder cancer cells.

In an effort to develop potent cyclooxygenase-1 (COX-1) inhibitors used as anticancer agent, a series of 2',5'-dimethoxychalcones was screened to evaluate their antiplatelet effect on human washed platelets suspension. Compound 2 exhibited potent inhibition of human washed platelet aggregation induced by collagen, significantly inhibited collagen- and arachidonic acid-induced thromboxane B2 release, and revealed inhibitory effect on COX-1 activity. Molecular docking studies showed that 1, 2, and 4 were bound in the active site of COX-1. These indicated that the antiplatelet effect of these compounds were mainly mediated through the suppression of COX-1 activity and reduced the thromboxane formation. To investigate the mechanistic action of COX-1 inhibitor enhanced the cytotoxic effect against human bladder cancer cells, NTUB1, we assessed the cytotoxic effect of 2 against NTUB1. Treatment of NTUB1 cells with various concentrations of 2 led to a concentration-dependent increase of cell death and decrease of reactive oxygen species levels. The flow-cytometric analysis showed that 2 induced a G1 phase cell cycle arrest but did not accompany an appreciable sub-G1 phase in NTUB1 cells. In addition, compound 2 increased p21 and p27 expressions and did not inhibit the expression of COX-1 in NTUB1 cells. Our results suggested that 2 enhanced cell growth inhibition or antiproliferative activity in NTUB1 cells through G1 arrest by COX-1 independent mechanism.

Antithrombotic and antiplatelet activities of Soshiho-tang extract

BackgroundSoshiho-tang (SH; Chinese name, Xiao-Chai-Hu-Tang; Japanese name, Shosaiko-to) is a traditional Korean, Chinese, and Japanese medicine, which has been used to treat various conditions, including hepatitis, liver cirrhosis, and chronic and acute liver disease. SH consists of seven herbal components, of which Scutellaria baicalensis Georgi and Zingiber officinale Roscoe, are reported to have antithrombotic and antiplatelet activities. We investigated the antithrombotic activity of SH, including S. baicalensis and Z. officinale, as an integrative therapy.MethodsTo identify the antithrombotic activity of SH, we used a FeCl3-induced thrombus formation model. The mechanism of SH-mediated antithrombotic activity was assessed by determining platelet aggregation and coagulation times ex vivo, washed platelet aggregation, serotonin secretion, and thromboxane B2 formation.ResultsSH prolonged the occlusion time of thrombus formation when applied in a FeCl3-induced thrombus formation model. SH also inhibited collagen-induced platelet aggregation ex vivo in a concentration-dependent manner; however, it did not affect coagulation. Hence, to identify the antiplatelet effect of SH, we investigated washed platelet aggregations in vitro. SH significantly inhibited various agonist-induced platelet aggregations, and it completely inhibited serotonin secretion and thromboxane B2 formation.ConclusionsThe findings suggest that SH inhibited FeCl3-induced thrombus formation through antiplatelet activity, including inhibition of platelet aggregation, and serotonin and TXB2 production. Thus, SH may be useful as an integrative herbal formula for the treatment of thrombosis.

α(1,3)-Fucosyltransferases FUT4 and FUT7 Control Murine Susceptibility to Thrombosis

The α(1,3)-fucosyltransferases, types IV and VII (FUT4 and FUT7, respectively), are required for the synthesis of functional selectin-type leukocyte adhesion molecule ligands. The selectins and their ligands modulate leukocyte trafficking, and P-selectin and its ligand, P-selectin glycoprotein ligand-1, can modulate hemostasis and thrombosis. Regulation of thrombosis by FUT4 and/or FUT7 activity was examined in mouse models of carotid artery thrombosis and collagen/epinephrine-induced thromboembolism. Mice lacking both FUT4 and FUT7 (Fut(-/-) mice) had a shorter time to occlusive thrombus formation in the injured carotid artery and a higher mortality due to collagen/epinephrine-induced pulmonary thromboemboli. Mice lacking P-selectin or P-selectin glycoprotein ligand-1 did not have a prothrombotic phenotype. Whole blood platelet aggregation was enhanced, and plasma fibrinogen content, clot weight, and clot strength were increased in Fut(-/-) mice, and invitro clot lysis was reduced compared with wild type. Fut4(-/-), but not Fut7(-/-), mice had increased pulmonary thromboembolism-induced mortality and decreased thromboemboli dissolution invivo. These data show that FUT4 and FUT7 activity regulates thrombosis in a P-selectin- and P-selectin glycoprotein ligand-1-independent manner and suggest that FUT4 activity is important for thrombolysis.

The novel NOX inhibitor 2‐acetylphenothiazine impairs collagen‐dependent thrombus formation in a GPVI‐dependent manner

NADPH oxidases (NOXs) contribute to platelet activation by a largely unknown mechanism. Here, we studied the effect of the novel NOX inhibitor 2-acetylphenothiazine (2-APT) on human platelet functional responses and intracellular signaling pathways. The generation of superoxide ions was assessed by single cell imaging on adhering platelets using dihydroethidium (DHE), while other reactive oxygen species (ROS) were detected with 5-(and-6)-carboxy-2',7'-dichlorodihydrofluorescein diacetate (CM-H(2)-DCFDA). Whole blood thrombus formation, washed platelet aggregation, integrin αIIbβ3 inside-out signalling, Syk phosphorylation and PKC activation were analysed to understand the functional consequences of NOX inhibition by 2-APT in platelets. Superoxide ion generation stimulated by platelet adhesion on collagen and fibrinogen was significantly inhibited by 2-APT in concentration-dependent manner (IC(50) = 306 nM and 227 nM, respectively), whereas cumulative ROS accumulation was not affected by this pharmacological agent. 2-APT also abolished collagen-dependent whole blood thrombus formation and washed platelet aggregation in response to collagen but not thrombin. The activation of integrin αIIbβ3 and PKC in response to the GPVI-specific agonist collagen-related peptide (CRP) was significantly reduced, whereas the same responses to thrombin were not significantly affected by 2-APT. Finally, Syk activation in response to collagen but not thrombin was inhibited by 2-APT. Taken together, our results suggest that 2-APT attenuates GPVI-specific signalling and is a novel inhibitor of collagen-induced platelet responses. Therefore, NOXs could represent a novel target for the discovery of anti-thrombotic drugs.