PLATELET TXA2 SYNTHETASE INHIBITION AND TXA2/PROSTAGLANDIN ENDOPEROXIDE RECEPTOR BLOCKADE COMBINED IN ONE MOLECULE (R 68070)

F 68070, an oxime-alkane carboxylic acid derivative (Janssen Pharmaceutica), is a potent inhibitor of thromboxane A2 (TXA2) synthetase activity (IC50 in vitro against thrombin-stimulated human platelets in plasma : R 68070 : 2.9 x 10-8 M; CGS 13080 : 6 x 10-8 M; OKY-1581 : 8.2 x 10-8 M; dazmegrel : 2.6 x 10-8 M; dazoxiben : 2.3 x 10-8 M).The compound specifically inhibits platelet TXA2 synthetase activity (14C-arachidonic acid metabolism by washed human platelets) without effect on the cyclo-oxygenase, lipoxygenase (platelets, RBL cells) or prostacyclin synthetase activities (rat aortic rings).The inhibitory effect of R 68070 against human platelet TXA2 synthetase activity increases upon prolongation of the contact time (ICsg at 0.5 min of contact : 5.2 x 10-7 M; at 5 min : 8.3 x 10-8 M; at 30 min : 2.5 x 10-8 M) and is reversed by washing of the platelets.In vivo, the compound has a comparatively strong inhibitory effect on platelet TXA2 synthetase activity after oral administration to rats (ED50 - 2 h : R 68070 0.013 mg/kg; CGS-13080 : 0.8 mg/kg; OKY-1581 : 0.61 mg/kg; dazmegrel : 1 mg/kg; dazoxiben : 4.1 mg/kg) and a protracted duration of action in rats and dogs (inhibition 8 h after 1.25 mg/kg orally > 80 %).In vitro, R 68070 inhibits the aggregation of human platelets in plasma stimulated with collagen (IC50 : 4 x 10-6 M), but also with U 46619 (IC50 : 3.8 x 10-6 M) without affecting the primary aggregation reaction elicited by ADP, 5-HT or adrenaline. The compound thus also produces platelet TXA2/prostaglandin endoperoxide receptor blockade.In rats and in dogs R 68070 (1.25 mg/kg I.V.) potently prevents thrombus formation in carotid and coronary arteries damaged by electrical stimulation.The combination of platelet TXA2 synthetase inhibition with TXA2/prostaglandin endoperoxide blockade in one molecule thus might offer an improved anti-thrombotic effectiveness.

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Inhibitory Effect of Piracetam on Platelet-rich Thrombus Formation in an Animal Model

Thrombosis and Haemostasis ◽

10.1055/s-0037-1614243 ◽

1998 ◽

Vol 79 (01) ◽

pp. 222-227 ◽

Cited By ~ 8

Author(s):

F. Stockmans ◽

W. Deberdt ◽

Å. Nyström ◽

E. Nyström ◽

J. M. Stassen ◽

...

Keyword(s):

Platelet Aggregation ◽

Ex Vivo ◽

Peak Plasma ◽

Thrombus Formation ◽

Plasma Concentrations ◽

Inhibitory Effect ◽

Human Platelets ◽

Cell Deformability

SummaryIntravenous administration of piracetam to hamsters reduced the formation of a platelet-rich venous thrombus induced by a standardised crush injury, in a dose-dependent fashion with an IC50 of 68 ± 8 mg/kg. 200 mg/kg piracetam also significantly reduced in vivo thrombus formation in rats. However, in vitro aggregation of rat platelets was only inhibited with piracetam-concentrations at least 10-fold higher than plasma concentrations (6.2 ± 1.1 mM) obtained in the treated animals. No effects were seen on clotting tests.In vitro human platelet aggregation, induced by a variety of agonists, was inhibited by piracetam, with IC50’s of 25-60 mM. The broad inhibition spectrum could be explained by the capacity of piracetam to prevent fibrinogen binding to activated human platelets. Ex vivo aggregations and bleeding times were only minimally affected after administration of 400 mg/kg piracetam i.v. to healthy male volunteers, resulting in peak plasma levels of 5.8 ± 0.3 mM.A possible antiplatelet effect of piracetam could be due to the documented beneficial effect on red blood cell deformability leading to a putative reduction of ADP release by damaged erythrocytes. However similarly high concentrations were needed to prevent stirring-induced “spontaneous” platelet aggregation in human whole blood.It is concluded that the observed antithrombotic action of piracetam cannot satisfactorily be explained by an isolated direct effect on platelets. An additional influence of piracetam on the rheology of the circulating blood and/or on the vessel wall itself must therefore be taken into consideration.

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Abstract 13598: The G-protein BetaGamma Subunits Regulate Platelet Function

Circulation ◽

10.1161/circ.142.suppl_3.13598 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Ahmed Alarabi ◽

Zubair Karim ◽

Victoria Hinojos ◽

Patricia A Lozano ◽

Keziah Hernandez ◽

...

Keyword(s):

G Protein ◽

Platelet Function ◽

Thrombus Formation ◽

Human Platelets ◽

Inhibitory Effects ◽

Clot Retraction ◽

Betagamma Subunits

Platelet activation involves tightly regulated processes to ensure a proper hemostasis response, but when unbalanced, can lead to pathological consequences such as thrombus formation. G-protein coupled receptors (GPCRs) regulate platelet function by interacting with and mediating the response to various physiological agonists. To this end, an essential mediator of GPCR signaling is the G protein Gαβγ heterotrimers, in which the βγ subunits are central players in downstream signaling pathways. While much is known regarding the role of the Gα subunit in platelet function, that of the βγ remains poorly understood. Therefore, we investigated the role of Gβγ subunits in platelet function using a Gβγ (small molecule) inhibitor, namely gallein. We observed that gallein inhibits platelet aggregation and secretion in response to agonist stimulation, in both mouse and human platelets. Furthermore, gallein also exerted inhibitory effects on integrin αIIbβ3 activation and clot retraction. Finally, gallein’s inhibitory effects manifested in vivo , as documented by its ability to modulate physiological hemostasis and delay thrombus formation. Taken together, our findings demonstrate, for the first time, that Gβγ directly regulates GPCR-dependent platelet function, in vitro and in vivo . Moreover, these data highlight Gβγ as a novel therapeutic target for managing thrombotic disorders.

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Mobilization of Fibrinogen Receptor Sites on Human Platelets Stimulated with ADP is Prevented by Prostacyclin

10.1055/s-0039-1687387 ◽

1979 ◽

Author(s):

J. Hawiger ◽

S. Parkinson ◽

S. Timmons

Keyword(s):

Inhibitory Effect ◽

Human Platelets ◽

Affinity Constant ◽

Human Fibrinogen ◽

Fibrinogen Receptor ◽

Receptor Sites ◽

Plasma Factor ◽

Potent Inhibitory Effect

Fibrinogen is a plasma factor required for aggregation of human platelets by ADP. The mechanism of platelet-ADP-fibrinogen interaction was studied by measuring the equilibrium binding of 125I-fibrinogen to human platelets separated from plasma proteins. Binding of 125I-fibrinogen to platelets not stimulated with ADP was low and unaffected by an excess of unlabel led fibrinogen. However, when platelets were stimulated with 4μM of ADP, there was an eightfold increase In the number of available binding sites for human fibrinogen, with affinity constant of 1.9 x 109M-1. This striking increase in fibrinogen receptor sites on human platelets was specific for ADP as contrasted to ATP, AMP, and adenosine. Prostacyclin (Prostaglandin I2, PGI2), a novel prostaglandin produced by the blood vessel wall, completely blocked this ADP-induced increase in fibrinogen receptor sites on human platelets. The effect of PGI2 was prompt and concentration dependent, reaching maximum at 10-9M. 6-keto PGF2 a stable derivative ot PGI2, did not have such an effect. Thus movement of fibrinogen receptor sites on human platelet membrane stimulated with ADP is prevented by PGI2. This represents a new biologic property of this vascular hormone and contributes to better understanding of its potent inhibitory effect in vitro and in vivo on ADP-induced platelet aggregation requiring mobilization of fibrinogen receptor.

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IκB kinase 2 is not essential for platelet activation

Blood Advances ◽

10.1182/bloodadvances.2019001044 ◽

2020 ◽

Vol 4 (4) ◽

pp. 638-643

Author(s):

Manuel Salzmann ◽

Sonja Bleichert ◽

Bernhard Moser ◽

Marion Mussbacher ◽

Mildred Haase ◽

...

Keyword(s):

Platelet Activation ◽

Active Site ◽

Bleeding Time ◽

Thrombus Formation ◽

Human Platelets ◽

Iκb Kinase ◽

Specific Deletion

Abstract Platelets are small anucleate cells that release a plethora of molecules to ensure functional hemostasis. It has been reported that IκB kinase 2 (IKK2), the central enzyme of the inflammatory NF-κB pathway, is involved in platelet activation, because megakaryocyte/platelet-specific deletion of exons 6 and 7 of IKK2 resulted in platelet degranulation defects and prolonged bleeding. We aimed to investigate the role of IKK2 in platelet physiology in more detail, using a platelet-specific IKK2 knockout via excision of exon 3, which makes up the active site of the enzyme. We verified the deletion on genomic and transcriptional levels in megakaryocytes and were not able to detect any residual IKK2 protein; however, platelets from these mice did not show any functional impairment in vivo or in vitro. Bleeding time and thrombus formation were not affected in platelet-specific IKK2-knockout mice. Moreover, platelet aggregation, glycoprotein GPIIb/IIIa activation, and degranulation were unaltered. These observations were confirmed by pharmacological inhibition of IKK2 with TPCA-1 and BMS-345541, which did not affect activation of murine or human platelets over a wide concentration range. Altogether, our results imply that IKK2 is not essential for platelet function.

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Anticoagulant and antithrombotic properties of platelet protease nexin-1

Blood ◽

10.1182/blood-2009-04-217240 ◽

2010 ◽

Vol 115 (1) ◽

pp. 97-106 ◽

Cited By ~ 45

Author(s):

Yacine Boulaftali ◽

Frédéric Adam ◽

Laurence Venisse ◽

Véronique Ollivier ◽

Benjamin Richard ◽

...

Keyword(s):

Ex Vivo ◽

Thrombus Formation ◽

Human Platelets ◽

Platelet Surface ◽

Type Plasminogen Activator ◽

Healthy Donors ◽

Protease Nexin ◽

Deficient Mice

AbstractProtease nexin–1 (PN-1) is a serpin that inhibits plasminogen activators, plasmin, and thrombin. PN-1 is barely detectable in plasma but is expressed by platelets. Here, we studied platelet PN-1 in resting and activated conditions and its function in thrombosis. Studies on human platelets from healthy donors and from patients with a Gray platelet syndrome demonstrate that PN-1 is present both at the platelet surface and in α-granules. The role of PN-1 was investigated in vitro using human platelets incubated with a blocking antibody and using platelets from PN-1–deficient mice. Both approaches indicate that platelet PN-1 is active on thrombin and urokinase-type plasminogen activator. Blockade and deficiency of platelet PN-1 result in accelerated and increased tissue factor-induced thrombin generation as indicated by calibrated automated thrombography. Moreover, platelets from PN-1–deficient mice respond to subthreshold doses of thrombin, as assessed by P-selectin expression and platelet aggregation. Thrombus formation, induced ex vivo by collagen in blood flow conditions and in vivo by FeCl3-induced injury, is significantly increased in PN-1–deficient mice, demonstrating the antithrombotic properties of platelet PN-1. Platelet PN-1 is thus a key player in the thrombotic process, whose negative regulatory role has been, up to now, markedly underestimated.

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The Inhibitory Effect of GR32191, a Thromboxane Receptor Blocking Drug, on Human Platelet Aggregation, Adhesion and Secretion

Thrombosis and Haemostasis ◽

10.1055/s-0038-1646609 ◽

1989 ◽

Vol 61 (03) ◽

pp. 429-436 ◽

Cited By ~ 29

Author(s):

E J Hornby ◽

M R Foster ◽

P J McCabe ◽

L E Stratton

Keyword(s):

Platelet Aggregation ◽

Thrombus Formation ◽

Rabbit Aorta ◽

Inhibitory Effect ◽

Human Platelets ◽

Camp Phosphodiesterase ◽

Platelet Protein ◽

Thromboxane Receptor ◽

Serotonin Secretion

SummaryGR32191, a potent selective thromboxane receptor antagonist, has been shown to inhibit completely prostaglandin endoperoxide and thromboxane A2 (TxA2)-induced platelet aggregation, [14C]-serotonin secretion and β-thromboglobulin secretion. Deposition of human platelets onto damaged rabbit aorta in vitro is reduced in the presence of GR32191 which appears to inhibit aggregation of platelets but not direct adhesion of platelets to subendothelium. The effects of non-prostanoid platelet activating agents whose mode of action requires the biosynthesis of TxA2 are also inhibited by GR32191. Prostanoids which inhibit platelet function, such as prostacyclin or PGD2, retain their inhibitory properties in the presence of GR32191 which does not inhibit phospholipase A2, prostaglandin cyclooxygenase, thromboxane synthase, 12-lipoxygenase or cAMP phosphodiesterase activity. The inhibitory action of GR32191 on platelet aggregation, mural thrombus formation and platelet protein storage granule secretion suggests that it has potential in treatingthrombotic disease in man.

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L-641,953 (R-8-fluoro-dibenzo[b, f]thiepin-3-carboxylic acid-5-oxide): a novel thromboxane–prostaglandin endoperoxide antagonist

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y87-087 ◽

1987 ◽

Vol 65 (4) ◽

pp. 509-514 ◽

Cited By ~ 3

Author(s):

R. A. Hall ◽

J. R. Rokach ◽

P. Bélanger ◽

L. Bianchi ◽

D. Ethier ◽

...

Keyword(s):

Carboxylic Acid ◽

Pulmonary Artery ◽

Guinea Pig ◽

Significant Inhibition ◽

Response Curves ◽

Duration Of Action ◽

Prostaglandin Endoperoxide ◽

Guinea Pig Pulmonary Artery

The effects of L-641,953 (R-8-fluoro-dibenzo[b, f)thiepin-3-carboxylic acid-5-oxide) have been studied on pulmonary and other smooth muscle preparations in vitro and in vivo. When studied in vitro on guinea-pig tracheal chains, L-641,933 produced significant shifts in the dose–response curves to the prostaglandin endoperoxide analogues, U-44069 (pA2 7.06) and U-46619 (pA2 7.14), and prostaglandin (PG) F2α (pA2 6.33) had minimal activity against contractions induced by histamine (pA2 4.38), 5-hydroxytryptamine (pA2 4.63), and acetylcholine (pA2 4.56) and slightly enhanced relaxation induced by PGE2. When tested on the guinea-pig gall bladder strip in vitro, L-641,953 antagonized contractions induced by U-44069 (pA2 7.03) but was less active against those induced by PGF2α (pA2 6.03), PGE1 (pA2 5.62), and histamine (pA2 4.84). When tested in vitro on the guinea-pig pulmonary artery, L-651-953 significantly antagonized contractions induced by U-44069 (pA2 7.04), U-46619 (pA2 7.14), and PGF2α (pA2 7.16) but was less effective against contractions induced by histamine (pA2 4.19). Schild analysis indicated that L-641,953 was fully competitive against contractions of either the guinea-pig tracheal chain induced by U-46619 or the guinea-pig pulmonary artery induced by U-44069 and U-46619. When tested on human platelets in vitro L-641,953 inhibited aggregation induced by U-44069 (IC50 1.3 × 10−6 M) but not ADP. In vivo L-641,953 administered i.v. inhibited increases in pulmonary resistance induced by U-44069 (ED50 0.026 mg/kg) but not histamine in the guinea pig and U-44069 (ED50 0.15 mg/kg) but not histamine or PGF2α in the dog. When L-641,953 was administered by the intraduodenal route to dogs (3 mg/kg) significant inhibition of bronchoconstriction induced by U-44069 or arachidonic acid was observed with a duration of action [Formula: see text]. It is concluded that L-641,953 is a novel, relatively selective, and orally active antagonist of the thromboxane–prostaglandin endoperoxide receptor.

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Direct and Continuous Inhibition of ADAM17 Using a Novel Selective Inhibitor Restores Functional Platelet Yield From Human Pluripotent Stem Cells

Blood ◽

10.1182/blood.v118.21.2323.2323 ◽

2011 ◽

Vol 118 (21) ◽

pp. 2323-2323

Author(s):

Shinji Hirata ◽

Ryoko Jono-Ohnishi ◽

Satoshi Nishimura ◽

Naoya Takayama ◽

Sou Nakamura ◽

...

Keyword(s):

Stem Cells ◽

Pluripotent Stem Cells ◽

Imaging System ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Thrombus Formation ◽

Human Platelets ◽

P38 Map Kinase

Abstract Abstract 2323 Platelet transfusion is therapeutically important for patients with thrombocytopenia and/or bleeding disorders. Problems associated with a lack of donors and unknown infections in the blood have not been fully resolved, however. In that context, human induced pluripotent stem cells (hiPSCs) are a potentially abundant source of infection-free platelets. The pluripotent state of hiPSCs and their differentiation depend upon appropriate culture conditions defined in part by oxygen and temperature. We therefore initially examined whether temperatures at or below 24°C, which are required for preservation of platelet concentrates ex vivo, allow hiPSC differentiation to generate platelets. We found that only at 37°C were platelets generated. But at 37°C in vitro, platelets are subject to degradation exemplified by the shedding of GPIbα, a receptor for von Willebrand factor (vWF), which is caused by a disintegrin and metalloprotease (ADAM) 17. We therefore developed KP-457, a novel ADAM17 inhibitor that has a reverse hydroxamic acid structure and has been found safe in rats and dogs. Although inhibition of p38 MAP kinase, putatively upstream of ADAM17, reportedly inhibits GPIbα shedding in stored human platelets, even at 37°C, administration of the p38 inhibitor SB203580 induces cytotoxicity during differentiation, leading to a loss of platelet yield from hiPSCs. By contrast, KP-457 significantly protected GPIbα expression in platelets from hiPSCs and in aged human platelets in culture at 37°C. Moreover, iPSC-derived platelets generated in the presence of KP-457 displayed improved hemostatic function when studied using an imaging system that enables characterization of single-platelet kinetics during thrombus formation after laser-induced injury in vivo. We propose this new drug could markedly improve the maintenance of functional platelets generated in culture, particularly those derived from hiPSCs. Disclosures: No relevant conflicts of interest to declare.

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An Antithrombotic Strategy by Targeting Phospholipase D in Human Platelets

Journal of Clinical Medicine ◽

10.3390/jcm7110440 ◽

2018 ◽

Vol 7 (11) ◽

pp. 440 ◽

Cited By ~ 3

Author(s):

Wan Lu ◽

Chi Chung ◽

Ray Chen ◽

Li Huang ◽

Li Lien ◽

...

Keyword(s):

Platelet Aggregation ◽

Platelet Activation ◽

Phospholipase D ◽

Thrombus Formation ◽

Human Platelets ◽

Platelet Activity ◽

Clot Retraction ◽

First Time

Phospholipase D (PLD) is involved in many biological processes. PLD1 plays a crucial role in regulating the platelet activity of mice; however, the role of PLD in the platelet activation of humans remains unclear. Therefore, we investigated whether PLD is involved in the platelet activation of humans. Our data revealed that inhibition of PLD1 or PLD2 using pharmacological inhibitors effectively inhibits platelet aggregation in humans. However, previous studies have showed that PLD1 or PLD2 deletion did not affect mouse platelet aggregation in vitro, whereas only PLD1 deletion inhibited thrombus formation in vivo. Intriguingly, our data also showed that the pharmacological inhibition of PLD1 or PLD2 does not affect mouse platelet aggregation in vitro, whereas the inhibition of only PLD1 delayed thrombus formation in vivo. These findings indicate that PLD may play differential roles in humans and mice. In humans, PLD inhibition attenuates platelet activation, adhesion, spreading, and clot retraction. For the first time, we demonstrated that PLD1 and PLD2 are essential for platelet activation in humans, and PLD plays different roles in platelet function in humans and mice. Our findings also indicate that targeting PLD may provide a safe and alternative therapeutic approach for preventing thromboembolic disorders.

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Non-genomic effects of the Pregnane X Receptor negatively regulate platelet functions, thrombosis and haemostasis

Scientific Reports ◽

10.1038/s41598-019-53218-x ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 1

Author(s):

Gagan D. Flora ◽

Khaled A. Sahli ◽

Parvathy Sasikumar ◽

Lisa-Marie Holbrook ◽

Alexander R. Stainer ◽

...

Keyword(s):

Platelet Function ◽

Thrombus Formation ◽

Pregnane X Receptor ◽

Human Platelets ◽

Regulatory Effects ◽

Granule Secretion ◽

Species Specific ◽

Platelet Functions

AbstractThe pregnane X receptor (PXR) is a nuclear receptor (NR), involved in the detoxification of xenobiotic compounds. Recently, its presence was reported in the human vasculature and its ligands were proposed to exhibit anti-atherosclerotic effects. Since platelets contribute towards the development of atherosclerosis and possess numerous NRs, we investigated the expression of PXR in platelets along with the ability of its ligands to modulate platelet activation. The expression of PXR in human platelets was confirmed using immunoprecipitation analysis. Treatment with PXR ligands was found to inhibit platelet functions stimulated by a range of agonists, with platelet aggregation, granule secretion, adhesion and spreading on fibrinogen all attenuated along with a reduction in thrombus formation (both in vitro and in vivo). The effects of PXR ligands were observed in a species-specific manner, and the human-specific ligand, SR12813, was observed to attenuate thrombus formation in vivo in humanised PXR transgenic mice. PXR ligand-mediated inhibition of platelet function was found to be associated with the inhibition of Src-family kinases (SFKs). This study identifies acute, non-genomic regulatory effects of PXR ligands on platelet function and thrombus formation. In combination with the emerging anti-atherosclerotic properties of PXR ligands, these anti-thrombotic effects may provide additional cardio-protective benefits.

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