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Paul DS, Blatt TN, Schug WJ, Clark EG, Kawano T, Mackman N, Murcia S, Poe KO, Mwiza JMN, Harden TK, Bergmeier W, Nicholas RA. Loss of P2Y 1 receptor desensitization does not impact hemostasis or thrombosis despite increased platelet reactivity in vitro. J Thromb Haemost 2023; 21:1891-1902. [PMID: 36958516 PMCID: PMC10809801 DOI: 10.1016/j.jtha.2023.03.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 02/20/2023] [Accepted: 03/09/2023] [Indexed: 03/25/2023]
Abstract
BACKGROUND The hemostatic plug formation at sites of vascular injury is strongly dependent on rapid platelet activation and integrin-mediated adhesion and aggregation. However, to prevent thrombotic complications, platelet aggregate formation must be a self-limiting process. The second-wave mediator adenosine diphosphate (ADP) activates platelets via Gq-coupled P2Y1 and Gi-coupled P2Y12 receptors. After ADP exposure, the P2Y1 receptor undergoes rapid phosphorylation-induced desensitization, a negative feedback mechanism believed to be critical for limiting thrombus growth. OBJECTIVE The objective of this study was to examine the role of rapid P2Y1 receptor desensitization on platelet function and thrombus formation in vivo. METHODS We analyzed a novel knock-in mouse strain expressing a P2Y1 receptor variant that cannot be phosphorylated beyond residue 340 (P2Y1340-0P), thereby preventing the desensitization of the receptor. RESULTS P2Y1340-0P mice followed a Mendelian inheritance pattern, and peripheral platelet counts were comparable between P2Y1340-0P/340-0P and control mice. In vitro, P2Y1340-0P/340-0P platelets were hyperreactive to ADP, showed a robust activation response to the P2Y1 receptor-selective agonist, MRS2365, and did not desensitize in response to repeated ADP challenge. We observed increased calcium mobilization, protein kinase C substrate phosphorylation, alpha granule release, activation of the small GTPase Rap1, and integrin inside-out activation/aggregation. This hyperreactivity, however, did not lead to increased platelet adhesion or excessive plug formation under physiological shear conditions. CONCLUSION Our studies demonstrate that receptor phosphorylation at the C-terminus is critical for P2Y1 receptor desensitization in platelets and that impaired desensitization leads to increased P2Y1 receptor signaling in vitro. Surprisingly, desensitization of the P2Y1 receptor is not required for limiting platelet adhesion/aggregation at sites of vascular injury, likely because ADP is degraded quickly or washed away in the bloodstream.
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Affiliation(s)
- David S Paul
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. https://twitter.com/David_S_Paul
| | - Tasha N Blatt
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Wyatt J Schug
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Emily G Clark
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Tomohiro Kawano
- UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Nigel Mackman
- UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Sebastian Murcia
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Kathryn O Poe
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Jean Marie N Mwiza
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - T Kendall Harden
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Wolfgang Bergmeier
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
| | - Robert A Nicholas
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
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Upregulation of P2Y12 inhibits chondrocyte apoptosis in lumbar osteoarthritis through the PI3K/AKT signaling pathway. Mol Biol Rep 2022; 49:6459-6466. [PMID: 35581507 DOI: 10.1007/s11033-022-07467-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Revised: 04/05/2022] [Accepted: 04/08/2022] [Indexed: 10/18/2022]
Abstract
Lumbar facet osteoarthritis (FJOA) is a major cause of severe lower back pain and disability worldwide. However, the mechanism underlying cartilage degeneration in FJOA remains unclear. The purpose of this study was to investigate the regulation and mechanism of P2Y12 on chondrocyte apoptosis in FJOA. The experimental rats were randomly divided into non-operation (n = 20) and operation groups (n = 20). In the operation group, Sodium iodoacetate (MIA, Sigma, 200 mg/mL) was injected into the right L4/5 facet process using a blunt nanoneedle 26 (WPI, Sarasota, FL, USA) under the control of an injection pump. The final injection volume was 5µL and the injection rate was 2µL/min. The facet joint was removed four weeks after surgery. After the operation, samples were stored at -80 °C until further use, whereby the right facet joints in each group were tested. Hematoxylin and eosin (HE) and iron-red solid green staining were used to observe the degeneration of articular chondrocytes in rats. Immunohistochemistry and western blotting were used to observe the expressions of P2Y12, Matrix metalloproteinase 13 (MMP13), Collagen II (COL2), and other cartilage degeneration and apoptosis-related genes. Co-localization of P2Y12-cleaved caspase-3 in the apoptosis model was detected by dual-standard immunofluorescence staining. Apoptosis was also detected by flow cytometry and TUNEL assay.P2Y12 is highly expressed in OA cartilage tissue, and inhibits IL-1β -induced chondrocyte apoptosis through PI3K/AKT signaling pathway, thus playing a certain protective role on cartilage.
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Fernández DI, Provenzale I, Cheung HY, van Groningen J, Tullemans BM, Veninga A, Dunster JL, Honarnejad S, van den Hurk H, Kuijpers MJ, Heemskerk JW. Ultra-high-throughput Ca 2+ assay in platelets to distinguish ITAM-linked and G-protein-coupled receptor activation. iScience 2022; 25:103718. [PMID: 35072010 PMCID: PMC8762394 DOI: 10.1016/j.isci.2021.103718] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 11/12/2021] [Accepted: 12/29/2021] [Indexed: 12/30/2022] Open
Abstract
Antiplatelet drugs targeting G-protein-coupled receptors (GPCRs), used for the secondary prevention of arterial thrombosis, coincide with an increased bleeding risk. Targeting ITAM-linked receptors, such as the collagen receptor glycoprotein VI (GPVI), is expected to provide a better antithrombotic-hemostatic profile. Here, we developed and characterized an ultra-high-throughput (UHT) method based on intracellular [Ca2+]i increases to differentiate GPVI and GPCR effects on platelets. In 96-, 384-, or 1,536-well formats, Calcium-6-loaded human platelets displayed a slow-prolonged or fast-transient [Ca2+]i increase when stimulated with the GPVI agonist collagen-related peptide or with thrombin and other GPCR agonists, respectively. Semi-automated curve fitting revealed five parameters describing the Ca2+ responses. Verification of the UHT assay was done with a robustness compound library and clinically relevant platelet inhibitors. Taken together, these results present proof of principle of distinct receptor-type-dependent Ca2+ signaling curves in platelets, which allow identification of new inhibitors in a UHT way.
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Affiliation(s)
- Delia I. Fernández
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, 6229 ER Maastricht, The Netherlands
- Platelet Proteomics Group, Center for Research in Molecular Medicine and Chronic Diseases (CiMUS), Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain
| | - Isabella Provenzale
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, 6229 ER Maastricht, The Netherlands
- Institute for Cardiovascular and Metabolic Research, University of Reading, RG6 6AX Reading, UK
| | - Hilaire Y.F. Cheung
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, 6229 ER Maastricht, The Netherlands
- ISASLeibniz-Institut fur Analytische Wissenschaften-ISAS-e.V., 44227 Dortmund, Germany
- Institute of Cardiovascular Sciences, Institute of Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | | | - Bibian M.E. Tullemans
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Alicia Veninga
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Joanne L. Dunster
- Institute for Cardiovascular and Metabolic Research, University of Reading, RG6 6AX Reading, UK
| | | | | | - Marijke J.E. Kuijpers
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, 6229 ER Maastricht, The Netherlands
- Thrombosis Expertise Centre, Heart and Vascular Centre, Maastricht University Medical Centre, Maastricht, the Netherlands
| | - Johan W.M. Heemskerk
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, 6229 ER Maastricht, The Netherlands
- Synapse Research Institute, Kon. Emmaplein 7, 6214 AC, Maastricht, the Netherlands
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Fernández DI, Kuijpers MJE, Heemskerk JWM. Platelet calcium signaling by G-protein coupled and ITAM-linked receptors regulating anoctamin-6 and procoagulant activity. Platelets 2020; 32:863-871. [PMID: 33356720 DOI: 10.1080/09537104.2020.1859103] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Most agonists stimulate platelet Ca2+ rises via G-protein coupled receptors (GPCRs) or ITAM-linked receptors (ILRs). Well studied are the GPCRs stimulated by the soluble agonists thrombin (PAR1, PAR4), ADP (P2Y1, P2Y12), and thromboxane A2 (TP), signaling via phospholipase (PLC)β isoforms. The platelet ILRs glycoprotein VI (GPVI), C-type lectin-like receptor 2 (CLEC2), and FcγRIIa are stimulated by adhesive ligands or antibody complexes and signal via tyrosine protein kinases and PLCγ isoforms. Marked differences exist between the GPCR- and ILR-induced Ca2+ signaling in: (i) dependency of tyrosine phosphorylation; (ii) oscillatory versus continued Ca2+ rises by mobilization from the endoplasmic reticulum; and (iii) smaller or larger role of extracellular Ca2+ entry via STIM1/ORAI1. Co-stimulation of both types of receptors, especially by thrombin (PAR1/4) and collagen (GPVI), leads to a highly enforced Ca2+ rise, involving mitochondrial Ca2+ release, which activates the ion and phospholipid channel, anoctamin-6. This highly Ca2+-dependent process causes swelling, ballooning, and phosphatidylserine expression, establishing a unique platelet population swinging between vital and necrotic (procoagulant 'zombie' platelets). Additionally, the high Ca2+ status of procoagulant platelets induces a set of additional events: (i) Ca2+ dependent cleavage of signaling proteins and receptors via calpain and ADAM isoforms; (ii) microvesiculation; (iii) enhanced coagulation factor binding; and (iv) fibrin-coat formation involving transglutaminases. Given the additive roles of GPCR and ILR in Ca2+ signal generation, high-throughput screening of biomolecules or small molecules based on Ca2+ flux measurements provides a promising way to find new inhibitors interfering with prolonged high Ca2+, phosphatidylserine expression, and hence platelet procoagulant activity.
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Affiliation(s)
- Delia I Fernández
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, Maastricht, The Netherlands
| | - Marijke J E Kuijpers
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, Maastricht, The Netherlands
| | - Johan W M Heemskerk
- Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, Maastricht, The Netherlands
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Anderson R, Theron AJ, Steel HC, Nel JG, Tintinger GR. ADP-Mediated Upregulation of Expression of CD62P on Human Platelets Is Critically Dependent on Co-Activation of P2Y1 and P2Y12 Receptors. Pharmaceuticals (Basel) 2020; 13:ph13120420. [PMID: 33255391 PMCID: PMC7760858 DOI: 10.3390/ph13120420] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 11/18/2020] [Accepted: 11/20/2020] [Indexed: 12/17/2022] Open
Abstract
This study probed the differential utilization of P2Y1 and P2Y12 receptors in mobilizing CD62P (P-selectin) from intracellular granules following activation of human platelets with adenosine 5′-diphosphate (ADP, 100 µmol·L−1) Platelet-rich plasma (PRP) was prepared from the blood of adult humans. CD62P was measured by flow cytometry following activation of PRP with ADP in the absence and presence of the selective antagonists of P2Y1 and P2Y12 receptors, MRS2500 and PSB0739 (both 0.155–10 µmol·L−1), respectively. Effects of the test agents on ADP-activated, CD62P-dependent formation of neutrophil:platelet (NP) aggregates were also measured by flow cytometry, while phosphatidylinositol 3-kinase (PI3K) activity was measured according to Akt1 phosphorylation in platelet lysates. Treatment with MRS2500 or PSB0739 at 10 µmol·L−1 almost completely attenuated (94.6% and 86% inhibition, respectively) ADP-activated expression of CD62P and also inhibited NP aggregate formation. To probe the mechanisms involved in P2Y1/P2Y12 receptor-mediated expression of CD62P, PRP was pre-treated with U73122 (phospholipase C (PLC) inhibitor), 2-aminoethoxy-diphenyl borate (2-APB, inositol triphosphate receptor antagonist), calmidazolium chloride (calmodulin inhibitor), or wortmannin (PI3K inhibitor). U73122, 2-APB, and wortmannin caused almost complete inhibition of ADP-activated expression of CD62P, while calmidazolium chloride caused statistically significant, partial inhibition. PSB0739, but not MRS2500, caused potent inhibition of PI3K-mediated phosphorylation of Akt1. Optimal mobilization of CD62P by ADP-stimulated platelets is critically dependent on the co-activation of platelet P2Y1 and P2Y12 receptors. P2Y12 receptor activation is the key event in activation of PI3K, while activation of the P2Y1 receptor appears to create a high cytosolic Ca2+ environment conducive to optimum PI3K activity.
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Affiliation(s)
- Ronald Anderson
- Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa; (A.J.T.); (H.C.S.)
- Correspondence: ; Tel.: +27-12-318-2425; Fax: +27-12-323-0732
| | - Annette J. Theron
- Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa; (A.J.T.); (H.C.S.)
| | - Helen C. Steel
- Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa; (A.J.T.); (H.C.S.)
| | - Jan G. Nel
- Department of Haematology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa;
- Tshwane Academic Division of the National Laboratory Health Service of South Africa, Pretoria 0001, South Africa
| | - Gregory R. Tintinger
- Department of Internal Medicine, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa;
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Filippin KJ, de Souza KFS, de Araujo Júnior RT, Torquato HFV, Dias DA, Parisotto EB, Ferreira AT, Paredes-Gamero EJ. Involvement of P2 receptors in hematopoiesis and hematopoietic disorders, and as pharmacological targets. Purinergic Signal 2020; 16:1-15. [PMID: 31863258 PMCID: PMC7166233 DOI: 10.1007/s11302-019-09684-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 11/12/2019] [Indexed: 12/11/2022] Open
Abstract
Several reports have shown the presence of P2 receptors in hematopoietic stem cells (HSCs). These receptors are activated by extracellular nucleotides released from different sources. In the hematopoietic niche, the release of purines and pyrimidines in the milieu by lytic and nonlytic mechanisms has been described. The expression of P2 receptors from HSCs until maturity is still intriguing scientists. Several reports have shown the participation of P2 receptors in events associated with modulation of the immune system, but their participation in other physiological processes is under investigation. The presence of P2 receptors in HSCs and their ability to modulate this population have awakened interest in exploring the involvement of P2 receptors in hematopoiesis and their participation in hematopoietic disorders. Among the P2 receptors, the receptor P2X7 is of particular interest, because of its different roles in hematopoietic cells (e.g., infection, inflammation, cell death and survival, leukemias and lymphomas), making the P2X7 receptor a promising pharmacological target. Additionally, the role of P2Y12 receptor in platelet activation has been well-documented and is the main example of the importance of the pharmacological modulation of P2 receptor activity. In this review, we focus on the role of P2 receptors in the hematopoietic system, addressing these receptors as potential pharmacological targets.
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Affiliation(s)
- Kelly Juliana Filippin
- Faculdade de Ciências Farmacêuticas, Alimentos e Nutrição, Universidade Federal de Mato Grosso do Sul, Campo Grande, MS, 79070-900, Brazil
| | - Kamylla F S de Souza
- Departamento de Bioquímica, Universidade Federal de São Paulo, R. Três de Maio 100, São Paulo, SP, 04044-020, Brazil
| | | | - Heron Fernandes Vieira Torquato
- Departamento de Bioquímica, Universidade Federal de São Paulo, R. Três de Maio 100, São Paulo, SP, 04044-020, Brazil
- Universidade Braz Cubas, Av. Francisco Rodrigues Filho 1233, Mogi das Cruzes, SP, 08773-380, Brazil
| | - Dhébora Albuquerque Dias
- Faculdade de Ciências Farmacêuticas, Alimentos e Nutrição, Universidade Federal de Mato Grosso do Sul, Campo Grande, MS, 79070-900, Brazil
| | - Eduardo Benedetti Parisotto
- Faculdade de Ciências Farmacêuticas, Alimentos e Nutrição, Universidade Federal de Mato Grosso do Sul, Campo Grande, MS, 79070-900, Brazil
| | - Alice Teixeira Ferreira
- Departamento de Biofísica, Universidade Federal de São Paulo, R. Botucatu 862, São Paulo, SP, 04023-062, Brazil.
- Faculdade de Ciências Farmacêuticas, Alimentos e Nutrição (FACFAN), Laboratório de Biologia Molecular e Culturas Celulares, Av. Costa e Silva, s/n Bairro Universitário, Campo Grande, MS, CEP: 79070-900, Brazil.
| | - Edgar J Paredes-Gamero
- Faculdade de Ciências Farmacêuticas, Alimentos e Nutrição, Universidade Federal de Mato Grosso do Sul, Campo Grande, MS, 79070-900, Brazil.
- Departamento de Bioquímica, Universidade Federal de São Paulo, R. Três de Maio 100, São Paulo, SP, 04044-020, Brazil.
- Faculdade de Ciências Farmacêuticas, Alimentos e Nutrição (FACFAN), Laboratório de Biologia Molecular e Culturas Celulares, Av. Costa e Silva, s/n Bairro Universitário, Campo Grande, MS, CEP: 79070-900, Brazil.
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Adrenoceptor α 2A signalling countervails the taming effects of synchronous cyclic nucleotide-elevation on thrombin-induced human platelet activation and aggregation. Cell Signal 2019; 59:96-109. [PMID: 30926386 DOI: 10.1016/j.cellsig.2019.03.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Revised: 03/22/2019] [Accepted: 03/25/2019] [Indexed: 11/24/2022]
Abstract
The healthy vascular endothelium constantly releases autacoids which cause an increase of intracellular cyclic nucleotides to tame platelets from inappropriate activation. Elevating cGMP and cAMP, in line with previous reports, cooperated in the inhibition of isolated human platelet intracellular calcium-mobilization, dense granules secretion, and aggregation provoked by thrombin. Further, platelet alpha granules secretion and, most relevant, integrin αIIaβ3 activation in response to thrombin are shown to be prominently affected by the combined elevation of cGMP and cAMP. Since stress-related sympathetic nervous activity is associated with an increase in thrombotic events, we investigated the impact of epinephrine in this setting. We found that the assessed signalling events and functional consequences were to various extents restored by epinephrine, resulting in full and sustained aggregation of isolated platelets. The restoring effects of epinephrine were abolished by either interfering with intracellular calcium-elevation or with PI3-K signalling. Finally, we show that in our experimental setting epinephrine likewise reconstitutes platelet aggregation in heparinized whole blood, which may indicate that this mechanism could also apply in vivo.
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Moschos MM, Laios K, Androudi S, Ladas DS, Chatziralli IP. Anti-platelet effects of vitamin supplements in age-related macular degeneration: an in vitro study. Cutan Ocul Toxicol 2017; 37:207-209. [PMID: 29171298 DOI: 10.1080/15569527.2017.1409754] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
OBJECTIVE The purpose of this experimental study was to investigate the role of vitamin supplements (Ocuvite, Vitalux Omega, and Nutrof Total) as possible inhibitors of the onset of age-related macular degeneration (AMD). MATERIALS AND METHODS The anti-aggregating effect of each vitamin was determined against four accumulative factors namely, platelet activating factor (PAF), adenosine diphosphate (ADP), thrombin receptor-activating peptide (TRAP), and arachidonic acid (AA) in the platelet rich plasma (PRP) of healthy volunteers. RESULTS Ocuvite, Vitalux Omega, and Nutrof Total were more potent inhibitors against PAF and ADP compared to TRAP and AA. Among the three vitamins, Nutrof Total displayed more potent inhibitions against TRAP and AA, while against PAF and ADP all the three vitamins revealed similar IC50 values. CONCLUSIONS The vitamins Ocuvite, Vitalux Omega, and Nutrof Total have anti-aggregating effects and therefore can be used against AMD in healthy volunteers.
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Affiliation(s)
- Marilita M Moschos
- a Laboratory of Electrophysiology, 1st Department of Ophthalmology , University of Athens , Athens , Greece
| | - Konstantinos Laios
- a Laboratory of Electrophysiology, 1st Department of Ophthalmology , University of Athens , Athens , Greece
| | - Sofia Androudi
- b Department of Ophthalmology , University of Thessaly , Larissa , Greece
| | - Dimitrios S Ladas
- a Laboratory of Electrophysiology, 1st Department of Ophthalmology , University of Athens , Athens , Greece
| | - Irini P Chatziralli
- a Laboratory of Electrophysiology, 1st Department of Ophthalmology , University of Athens , Athens , Greece
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Role of P2Y 12 Receptor in Thrombosis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 906:307-324. [PMID: 27628007 DOI: 10.1007/5584_2016_123] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
P2Y12 receptor is a 342 amino acid Gi-coupled receptor predominantly expressed on platelets. P2Y12 receptor is physiologically activated by ADP and inhibits adenyl cyclase (AC) to decrease cyclic AMP (cAMP) level, resulting in platelet aggregation. It also activates PI3 kinase (PI3K) pathway leading to fibrinogen receptor activation, and may protect platelets from apoptosis. Abnormalities of P2Y12 receptor include congenital deficiencies or high activity in diseases like diabetes mellitus (DM) and chronic kidney disease (CKD), exposing such patients to a prothrombotic condition. A series of clinical antiplatelet drugs, such as clopidogrel and ticagrelor, are designed as indirect or direct antagonists of P2Y12 receptor to reduce incidence of thrombosis mainly for patients of acute coronary syndrome (ACS) who are at high risk of thrombotic events. Studies on novel dual-/multi-target antiplatelet agents consider P2Y12 receptor as a promising part in combined targets. However, the clinical practical phenomena, such as "clopidogrel resistance" due to gene variations of cytochrome P450 or P2Y12 receptor constitutive activation, call for better antiplatelet agents. Researches also showed inverse agonist of P2Y12 receptor could play a better role over neutral antagonists. Personalized antiplatelet therapy is the most ideal destination for antiplatelet therapy in ACS patients with or without other underlying diseases like DM or CKD, however, there is still a long way to go.
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Gerrits AJ, Jakubowski JA, Sugidachi A, Michelson AD, Frelinger AL. Incomplete reversibility of platelet inhibition following prolonged exposure to ticagrelor. J Thromb Haemost 2017; 15:858-867. [PMID: 28092426 DOI: 10.1111/jth.13627] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Indexed: 01/03/2023]
Abstract
Essentials Irreversible platelet inhibition persists after reversibly-binding ticagrelor is discontinued. Reversibility of platelet inhibition by ticagrelor and its active metabolite was assessed. Incomplete recovery was observed after prolonged exposure to ticagrelor. Activated GPIIb-IIIa and P-selectin, not platelet reactivity index, showed irreversibility. SUMMARY Introduction Ticagrelor is described as a reversible P2Y12 antagonist. However, residual platelet inhibition persists after discontinuation of ticagrelor when plasma levels are undetectable. We assessed the reversibility of platelet inhibition by ticagrelor and its active metabolite (T-AM) in comparison with cangrelor and prasugrel's active metabolite (P-AM). Methods Whole blood was treated in vitro with ~ 50% inhibitory concentrations of ticagrelor, T-AM, cangrelor, P-AM and assessed for ADP-stimulated activated GPIIb-IIIa and P-selectin and vasodilator-stimulated phosphoprotein (VASP) platelet reactivity index (PRI) before and after 100-fold dilution. Results Platelets exposed for 30 min to ticagrelor, T-AM or cangrelor showed full recovery of activated GPIIb-IIIa but only partial recovery of P-selectin. Longer exposure (24 h) to the drug decreased reversibility of activated GPIIb-IIIa by ticagrelor (65.1% [49.5-80.6], % of vehicle with 95% confidence interval [CI]) and T-AM (88.8% [79.2-98.3]), but not by cangrelor (101.4% [96.4-106.4]). Compared with 30 min exposure, the reversibility of P-selectin further decreased after 24 h exposure to ticagrelor (from 91.8% [82.1-101.5] to 51.8% [45.5-85.0]), but not T-AM (from 79.0% [67.8-90.3] to 77.4% [61.8-93.1]) or cangrelor (from 76.0% [67.6-84.4] to 76.2% [70.6-81.8]). In contrast, 24 h exposure to ticagrelor, T-AM and cangrelor resulted in full recovery of platelet reactivity as measured by PRI. Platelets exposed to P-AM showed no recovery of ADP reactivity. Conclusions Incomplete recovery after prolonged exposure to ticagrelor, observed by activated GPIIb-IIIa and P-selectin but not upstream VASP signaling, suggests that P2Y12 regains functionality and irreversible changes occur independent of VASP signaling.
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Affiliation(s)
- A J Gerrits
- Center for Platelet Research Studies, Division of Hematology/Oncology, Boston Children's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
| | - J A Jakubowski
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN, USA
| | - A Sugidachi
- Biological Research Laboratories, Daiichi Sankyo Co., Ltd., Tokyo, Japan
| | - A D Michelson
- Center for Platelet Research Studies, Division of Hematology/Oncology, Boston Children's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
| | - A L Frelinger
- Center for Platelet Research Studies, Division of Hematology/Oncology, Boston Children's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
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Seo HS, Choi SH, Han M, Kim KA, Cho CH, An SSA, Lim CS, Shin S. Measurement of platelet aggregation functions using whole blood migration ratio in a microfluidic chip. Clin Hemorheol Microcirc 2016; 62:151-63. [PMID: 26444593 DOI: 10.3233/ch-151961] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Platelets play a major role in maintaining endothelial integrity and hemostasis. Of the various soluble agonists, ADP is an important in vivo stimulus for inducing platelet aggregation. In this study, a simple, rapid, and affordable method was designed for testing bleeding time (BT) and platelet aggregation with a two-channel microfluidic chip. Whole blood migration ratio (MR) from a microchip system was evaluated in comparison to the closure time (CT) from PFA-100 assays (Siemens, Germany) and CD62P expression on platelets. To induce platelet aggregation, a combination of collagen (1.84 mg/ml) and ADP (37.5 mg/ml) were used as agonists. After adding the agonists to samples, whole blood MR from the microchip system was measured. The outcome of the assessment depended on reaction time and agonist concentration. MR of whole blood from the microchip system was significantly correlated with CT from PFA-100 (r = 0.61, p < 0.05, n = 60). In addition, MR was negatively correlated with CD62P expression (r =-0.95, p < 0.05, n = 60). These results suggest that the measurement of MR using agonists is an easy, simple and efficient method for monitoring platelet aggregation in normal and ADP-receptors defective samples, along with the BT test. Thus, usage of the current microfluidic method could expand to diverse applications, including efficacy assessments in platelet therapy.
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Affiliation(s)
- Hong Seog Seo
- KU-KIST Graduate School of Converging Science and Technology, Seoul, Korea
| | - Sung Hyuk Choi
- Department of Emergency Medicine, College of Medicine, Korea University, Guro Gu, Seoul, Korea
| | - Miran Han
- Department of Laboratory Medicine, College of Medicine, Korea University, Guro Gu, Seoul, Korea
| | - Kyeong Ah Kim
- Department of Laboratory Medicine, College of Medicine, Korea University, Guro Gu, Seoul, Korea
| | - Chi Hyun Cho
- Department of Laboratory Medicine, College of Medicine, Korea University, Guro Gu, Seoul, Korea
| | - Seong Soo A An
- College of Bionano Technology, Gachon Bionano Research Institute, Gachon University, Seongnam-si, Gyeonggi Do, Korea
| | - Chae Seung Lim
- Department of Laboratory Medicine, College of Medicine, Korea University, Guro Gu, Seoul, Korea
| | - Sehyun Shin
- School of Mechanical Engineering, Korea University, Seoul, Korea
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12
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Burke N, Flood K, Muellers S, Murray A, Dempsey M, Geary M, Kenny D, Malone F. An overview of platelet function in normal and complicated pregnancies. ACTA ACUST UNITED AC 2014. [DOI: 10.1586/17474108.2013.811934] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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13
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Medina C, Harmon S, Inkielewicz I, Santos-Martinez MJ, Jones M, Cantwell P, Bazou D, Ledwidge M, Radomski MW, Gilmer JF. Differential inhibition of tumour cell-induced platelet aggregation by the nicotinate aspirin prodrug (ST0702) and aspirin. Br J Pharmacol 2012; 166:938-49. [PMID: 22122360 DOI: 10.1111/j.1476-5381.2011.01794.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND AND PURPOSE Tumour cell-induced platelet aggregation (TCIPA) facilitates cancer cell invasion, angiogenesis and the formation of metastatic foci. TCIPA can be modulated by pharmacological inhibitors of MMP-2 and ADP; however, the COX inhibitor aspirin did not prevent TCIPA. In this study, we have tested the pharmacological effects of a new group of isosorbide-based aspirin prodrugs on TCIPA. EXPERIMENTAL APPROACH TCIPA was induced in human platelets by mixing with human adenocarcinoma or fibrosarcoma cells under no flow and flow conditions. The release of gelatinases and P-selectin expression during TCIPA were studied by zymography and flow cytometry respectively. KEY RESULTS Tumour cells caused platelet aggregation. This aggregation resulted in the release of MMP-2 and a significant up-regulation of P-selectin on platelets, indicative of platelet activation. Pharmacological modulation of TCIPA revealed that ST0702, one of the aspirin prodrugs, down-regulated TCIPA while aspirin was ineffective. The deacetylated metabolite of ST0702, 5-nicotinate salicylate (ST0702 salicylate), down-regulated both ADP-stimulated platelet aggregation and TCIPA. CONCLUSIONS AND IMPLICATIONS Our results show that ST0702 was an effective inhibitor of TCIPA in vitro. Its deacetylated metabolite may contribute to the effects of ST0702 by inhibiting ADP-mediated TCIPA.
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Affiliation(s)
- Carlos Medina
- School of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin, Dublin, Ireland.
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14
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Elvers M, Grenegård M, Khoshjabinzadeh H, Münzer P, Borst O, Tian H, Di Paolo G, Lang F, Gawaz M, Lindahl TL, Fälker K. A novel role for phospholipase D as an endogenous negative regulator of platelet sensitivity. Cell Signal 2012; 24:1743-52. [DOI: 10.1016/j.cellsig.2012.04.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Accepted: 04/25/2012] [Indexed: 02/01/2023]
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15
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Protease-activated receptor 1 (PAR1) signalling desensitization is counteracted via PAR4 signalling in human platelets. Biochem J 2011; 436:469-80. [PMID: 21391917 DOI: 10.1042/bj20101360] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
PARs (protease-activated receptors) 1 and 4 belong to the family of G-protein-coupled receptors which induce both G(α12/13) and G(αq) signalling. By applying the specific PAR1- and PAR4-activating hexapeptides, SFLLRN and AYPGKF respectively, we found that aggregation of isolated human platelets mediated via PAR1, but not via PAR4, is abolished upon homologous receptor activation in a concentration- and time-dependent fashion. This effect was not due to receptor internalization, but to a decrease in Ca²⁺ mobilization, PKC (protein kinase C) signalling and α-granule secretion, as well as to a complete lack of dense granule secretion. Interestingly, subthreshold PAR4 activation rapidly abrogated PAR1 signalling desensitization by differentially reconstituting these affected signalling events and functional responses, which was sufficient to re-establish aggregation. The lack of ADP release and P2Y₁₂ receptor-induced G(αi) signalling accounted for the loss of the aggregation response, as mimicking G(αi/z) signalling with 2-MeS-ADP (2-methylthioadenosine-5'-O-diphosphate) or epinephrine (adrenaline) could substitute for intermediate PAR4 activation. Finally, we found that the re-sensitization of PAR1 signalling-induced aggregation via PAR4 relied on PKC-mediated release of both ADP from dense granules and fibrinogen from α-granules. The present study elucidates further differences in human platelet PAR signalling regulation and provides evidence for a cross-talk in which PAR4 signalling counteracts mechanisms involved in PAR1 signalling down-regulation.
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16
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Johnston-Cox HA, Yang D, Ravid K. Physiological implications of adenosine receptor-mediated platelet aggregation. J Cell Physiol 2010; 226:46-51. [PMID: 20717958 DOI: 10.1002/jcp.22379] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Adenosine is an important mediator of inhibition of platelet activation. This metabolite is released from various cells, as well as generated via activity of ecto-enzymes on the cell surface. Binding of adenosine to A(2) subtypes (A(2A) or A(2B)), G-protein coupled adenosine receptors, results in increased levels of intracellular cyclic adenosine monophosphate (cAMP), a strong inhibitor of platelet activation. The role and importance of adenosine and its receptors in platelet physiology are addressed in this review, including recently identified roles for the A(2B) adenosine receptor as a modulator of platelet activation through its newly described role in the control of expression of adenosine diphosphate (ADP) receptors.
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Affiliation(s)
- Hillary A Johnston-Cox
- Departments of Medicine and Biochemistry, Whitaker Cardiovascular Institute, Evans Center for Interdisciplinary Biomedical Research, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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17
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Abstract
Antiplatelet therapy is critical in the prevention of thrombotic complications of acute coronary syndrome and percutaneous coronary interventions. Current antiplatelet agents (aspirin, clopidogrel and glycoprotein IIb/IIIa antagonists) have demonstrated the capacity to reduce major adverse cardiac events. However, these agents have limitations that compromise their clinical utility. The platelet P2Y12 receptor plays a central role in platelet function and is a focus in the development of antiplatelet therapies. Cangrelor is a potent, competitive inhibitor of the P2Y12 receptor that is administered by intravenous infusion and rapidly achieves near complete inhibition of ADP-induced platelet aggregation. This investigational drug has been studied for use during coronary procedures and the management of patients experiencing acute coronary syndrome and is undergoing evaluation for use in the prevention of perioperative stent thrombosis.
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Affiliation(s)
- Nicholas B Norgard
- University at Buffalo, School of Pharmacy and Pharmaceutical Sciences, 313 Cooke Hall, Buffalo, NY 14260-1200, USA.
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18
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Lahiri P, Roy S, Sardar P, Deb S, Chakrabarti P, Guha P, Guha S, Chaudhuri U, Dasgupta AK. Platelet responsiveness to yohimbine hydrochloride and MRS2179 in the context of the interaction between collagen and epinephrine in acute coronary syndrome. Blood Cells Mol Dis 2009; 43:105-10. [PMID: 19272818 DOI: 10.1016/j.bcmd.2009.02.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Accepted: 02/05/2009] [Indexed: 10/21/2022]
Abstract
Acute coronary syndrome (ACS) covers a spectrum of clinical conditions ranging from unstable angina, Non-ST segment elevation myocardial infarction (NSTEMI), or ST segment elevation myocardial infarction (STEMI). This study encompasses patients with acute coronary syndrome, who were receiving the dual antiplatelet therapy of aspirin and clopidogrel. The focus of the study was to gain insight into the role of selective P2Y1 antagonism using MRS2179 in such cases as well as its effects, if any, on collagen-epinephrine interaction. All the cases showed greater potency of inhibition of the interaction when yohimbine hydrochloride (YH), a blocker of alpha2A-adrenoreceptor, was used compared to MRS2179, a P2Y1 antagonist, although there was variability in responsiveness to the antiplatelet drugs. These findings indicate that alpha2A-adrenoreceptors of platelets in this group play a major role in precipitating the interactive effect of collagen and epinephrine. The dose-response effect as studied by platelet aggregometry showed that the required molar concentration to block the interactive effect in the case of YH was less than that of MRS2179. Hence, it is postulated that although there may be an impairment of collagen-induced aggregation by MRS2179, the interactive effect of collagen-epinephrine may not be impaired by MRS2179 as efficaciously as YH.
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Affiliation(s)
- Prabir Lahiri
- Institute of Hematology and Transfusion Medicine, Medical College, Kolkata, West Bengal, India.
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19
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Douglass JG, Patel RI, Yerxa BR, Shaver SR, Watson PS, Bednarski K, Plourde R, Redick CC, Brubaker K, Jones AC, Boyer JL. Lipophilic modifications to dinucleoside polyphosphates and nucleotides that confer antagonist properties at the platelet P2Y12 receptor. J Med Chem 2008; 51:1007-25. [PMID: 18232657 DOI: 10.1021/jm701348d] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Platelet P2Y12 receptors play a central role in the regulation of platelet function and inhibition of this receptor by treatment with drugs such as clopidogrel results in a reduction of atherothrombotic events. We discovered that modification of natural and synthetic dinucleoside polyphosphates and nucleotides with lipophilic substituents on the ribose and base conferred P2Y12 receptor antagonist properties to these molecules producing potent inhibitors of ADP-mediated platelet aggregation. We describe methods for the preparation of these functionalized dinucleoside polyphosphates and nucleotides and report their associated activities. By analysis of these results and by deconstruction of the necessary structural elements through selected syntheses, we prepared a series of highly functionalized nucleotides, resulting in the selection of an adenosine monophosphate derivative (62) for further clinical development.
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Affiliation(s)
- James G Douglass
- Departments of Chemistry, Inspire Pharmaceuticals, Inc., 4222 Emperor Boulevard, Suite 200, Durham, North Carolina 27703-8466, USA.
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20
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Jurk K, Kehrel BE. Inherited and Acquired Disorders of Platelet Function. Transfus Med Hemother 2007. [DOI: 10.1159/000098178] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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21
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Cauwenberghs S, Feijge MAH, Hageman G, Hoylaerts M, Akkerman JWN, Curvers J, Heemskerk JWM. Plasma ectonucleotidases prevent desensitization of purinergic receptors in stored platelets: importance for platelet activity during thrombus formation. Transfusion 2006; 46:1018-28. [PMID: 16734820 DOI: 10.1111/j.1537-2995.2006.00837.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND Platelets (PLTs) contain purinergic receptors for ATP (P2X1) and ADP (P2Y1 and P2Y12) that rapidly desensitize upon stimulation with these nucleotides. In vivo, this is antagonized by ectonucleotidases on the surface of endothelial cells and white blood cells (WBCs). The receptor desensitization of ATP- and ADP-induced responses of PLTs stored in plasma without WBCs was investigated. STUDY DESIGN AND METHODS ATP- and ADP-induced PLT shape change (shear-induced) aggregation and Ca2+ signaling were measured in the presence or absence of plasma. Degradation of nucleotides in plasma was quantified by high-performance liquid chromatography. RESULTS Washed PLTs became refractory for ATP and ADP in shape change, aggregation, and Ca2+ responses during a 90-minute incubation at 37 degrees C. The PLT responses mediated by P2X1, P2Y1, and P2Y12 receptors gradually reduced or disappeared. When plasma was present, however, the PLTs persistently showed high responses to ATP and ADP. Heat treatment of plasma abolished this effect. Also under conditions of flow and high shear, PLTs in plasma kept high P2X1 activity, mediating aggregate formation. In isolated plasma, not containing WBCs, nucleotides were degraded in the order of ADP/UDP>ATP/UTP. Degradation of ATP was partly inhibited by blocking the ecto-NTPDase CD39, whereas degradation of both ATP and ADP was inhibited by blocking ectopyrophosphatase/phosphodiesterase activity. Part of the nucleotide-degrading activities appeared to be membrane-bound. CONCLUSION Ectonucleotidases in plasma preserve the functionality of P2X1 and P2Y receptors. Upon PLT storage, these plasma activities are essential to ensure adequate (shear-dependent) formation of aggregates and thrombi.
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Affiliation(s)
- Sandra Cauwenberghs
- Department of Biochemistry (CARIM), the Sanquin Blood Bank South-East, the Department of Health Risk Analysis and Toxicology (NUTRIM), Maastricht University, Maastricht, the Netherlands
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22
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Oury C, Daenens K, Hu H, Toth-Zsamboki E, Bryckaert M, Hoylaerts MF. ERK2 activation in arteriolar and venular murine thrombosis: platelet receptor GPIb vs. P2X. J Thromb Haemost 2006; 4:443-52. [PMID: 16420578 DOI: 10.1111/j.1538-7836.2006.01745.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The functional significance of extracellular signal-regulated kinase 2 (ERK2) activation was investigated during shear induced human platelet aggregation (SIPA) in vitro and during shear controlled thrombosis in vivo in intestinal arterioles and venules of wild type (WT) and transgenic (TG) mice with platelet-specific overexpression of human P2X(1) (TG). In SIPA, ERK2 was rapidly phosphorylated during GPIb stimulation, its activation contributing to SIPA for 50%, independently of P2X(1) regulation. Thrombotic occlusion of injured arterioles occurred considerably faster in TG (4.3 +/- 2.3 min) than in WT (38 +/- 8 min) arterioles, but occlusion times in TG (19 +/- 12) and WT (48 +/- 4.5 min) venules differed less. Both the alphabeta-meATP triggered desensitization of platelet P2X(1), as well as P2X(1) antagonism by NF279 or NF449 prolonged mean occlusion to about 75 min in WT and 65 min in TG arterioles, but venular occlusion times were less affected. Preventing ERK2 activation by U0126 prolonged occlusion times in TG (41 +/- 10 min) and WT (51 +/- 17) arterioles more than in TG (46 +/- 5 min) and WT (56 +/- 6 min) venules, uncovering a role for ERK2 in shear controlled thrombosis. Antagonism of GPIb by a recombinant murine von Willebrand factor (VWF)-A1 fragment prolonged occlusion times to comparable values, ranging from 55 to 58 min, both in TG and WT arterioles and venules. Further inhibition strategies, combining VWF-A1, U0126 and NF449 in WT and TG mice and resulting in occlusion in various time windows, identified that inhibition by VWF-A1 largely abrogated the ERK2 contribution to thrombosis. In conclusion, P2X(1) and ERK2 both participate in shear stress controlled thrombosis, but ERK2 activation is initiated predominantly via GPIb-VWF interactions.
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Affiliation(s)
- C Oury
- Center for Molecular and Vascular Biology, University of Leuven, Leuven, Belgium
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23
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Léon C, Freund M, Latchoumanin O, Farret A, Petit P, Cazenave JP, Gachet C. The P2Y(1) receptor is involved in the maintenance of glucose homeostasis and in insulin secretion in mice. Purinergic Signal 2005; 1:145-51. [PMID: 18404499 PMCID: PMC2096536 DOI: 10.1007/s11302-005-6209-x] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2004] [Accepted: 10/18/2004] [Indexed: 11/21/2022] Open
Abstract
Pancreatic β cells express several P2 receptors including P2Y1 and the modulation of insulin secretion by extracellular nucleotides has suggested that these receptors may contribute to the regulation of glucose homeostasis. To determine whether the P2Y1 receptor is involved in this process, we performed studies in P2Y1 mice. In baseline conditions, P2Y1-mice exhibited a 15% increase in glycemia and a 40% increase in insulinemia, associated with a 10% increase in body weight, pointing to a role of the P2Y1 receptor in the control of glucose metabolism. Dynamic experiments further showed that P2Y1-mice exhibited a tendency to glucose intolerance. These features were associated with a decrease in the plasma levels of free fatty acid and triglycerides. When fed a lipids and sucrose enriched diet for 15 weeks, the two genotypes no longer displayed any significant differences. To determine whether the P2Y1 receptor was directly involved in the control of insulin secretion, experiments were carried out in isolated Langerhans islets. In the presence of high concentrations of glucose, insulin secretion was significantly greater in islets from P2Y1-mice. Altogether, these results show that the P2Y1 receptor plays a physiological role in the maintenance of glucose homeostasis at least in part by regulating insulin secretion.
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Affiliation(s)
- Catherine Léon
- Institut National de la Santé et de la Recherche Médicale U.311, Etablissement Français du Sang-Alsace, Strasbourg Cedex, France
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24
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Jagroop IA, Matsagas MI, Geroulakos G, Mikhailidis DP. The effect of clopidogrel, aspirin and both antiplatelet drugs on platelet function in patients with peripheral arterial disease. Platelets 2004; 15:117-25. [PMID: 15154604 DOI: 10.1080/09537105310001645960] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Peripheral arterial disease (PAD) is associated with platelet hyperactivity. Aspirin and clopidogrel, two platelet inhibitors, act by different mechanisms. Aspirin inhibits thromboxane A2 synthesis and clopidogrel acts on the P2Y12 platelet ADP receptor. We evaluated the effect of clopidogrel (75 mg/day), aspirin (75 mg/day) and then both drugs on several platelet function indices in patients with PAD (n = 20). There was a significant (P = 0.0001) decrease in ADP-induced aggregation, after clopidogrel but not after taking aspirin. Clopidogrel plus aspirin significantly decreased spontaneous platelet aggregation (SPA) (P = 0.01 to P = 0.002) but SPA was not significantly altered by either aspirin or clopidogrel monotherapy. Similarly, monotherapy did not inhibit serotonin (5HT)-induced aggregation but there was a sigificant inhibition (P = 0.03 to P < 0.02) after combination therapy. ADP (0.8 microM)-induced platelet shape change (PSC) was significantly inhibited by clopidogrel (P = 0.004) or aspirin (P = 0.01). This was also true for 5HT-induced PSC (clopidogrel, P = 0.01; aspirin, P = 0.03). Soluble P-selectin decreased significantly (from 32 +/- 24 to 25 +/- 17 ng/ml, P = 0.04) with combination therapy. Plasma platelet-derived growth factor and intraplatelet 5HT levels were not altered by combination therapy. In PAD, clopidogrel is a more potent inhibitor of ADP-induced platelet activation than aspirin; combination therapy is more effective than clopidogrel or aspirin monotherapy. These potentially clinically relevant findings should be evaluated in appropriately designed trials.
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Affiliation(s)
- I Anita Jagroop
- Department of Clinical Biochemistry, Royal Free University College Medical School, University College, Royal Free Campus, London NW3 2QG, UK
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25
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Abstract
The platelet surface membrane possesses three P2 receptors activated by extracellular adenosine nucleotides; one member of the ionotropic receptor family (P2X(1)) and two members of the G-protein-coupled receptor family (P2Y(1) and P2Y(12)). P2Y(1) and P2Y(12) receptors have firmly established roles in platelet activation during thrombosis and haemostasis, whereas the importance of the P2X(1) receptor has been more controversial. However, recent studies have demonstrated that P2X(1) receptors can generate significant functional platelet responses alone and in synergy with other receptor pathways. In addition, studies in transgenic animals indicate an important role for P2X(1) receptors in platelet activation, particularly under conditions of shear stress and thus during arterial thrombosis. This review discusses the background behind discovery of P2X(1) receptors in platelets and their precursor cell, the megakaryocyte, and how signalling via these ion channels may participate in platelet activation.
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Affiliation(s)
- Martyn P Mahaut-Smith
- Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK.
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26
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Mathieu R, Baurand A, Schmitt M, Gachet C, Bourguignon JJ. Synthesis and biological activity of 2-alkylated deoxyadenosine bisphosphate derivatives as P2Y(1) receptor antagonists. Bioorg Med Chem 2004; 12:1769-79. [PMID: 15028267 DOI: 10.1016/j.bmc.2003.12.041] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2003] [Accepted: 12/22/2003] [Indexed: 11/23/2022]
Abstract
A previous study around adenine nucleotides afforded the reference N(6)-methyl-2'-deoxyadenosine-3',5'-bisphosphate (1a, MRS 2179) as a selective human P2Y(1) receptor antagonist (pA(2)=6.55+/-0.05) with antithrombotic properties. In the present paper, we have synthesized and tested in vitro various 2-substituted derivatives with the goal of exploring the 2-position binding region and developing more potent P2Y(1) receptor antagonists. Thus, we have adopted a novel and versatile chemical pathway using a palladium-catalyzed cross-coupling reaction with the 2-iodinated derivative 7 as a common intermediate for a very efficient synthesis of the 2-alkyl-N(6)-methyl-2'-deoxyadenosine-3',5'-bisphosphate nucleotides 1e-i. The biological activity was evaluated through the ability of compounds to inhibit ADP-induced platelet aggregation, intracellular calcium rise and to displace the specific binding of [(33)P]2-MeSADP. 2-Ethyl and 2-propyl groups appeared to be tolerated, whereas a bulky group or a C(3) linear substituent dramatically decreased potency of antagonists. The 2-ethynyl derivative 1h (pA(2)=7.54+/-0.10) was significantly more potent (10-fold) as an antagonist when compared to the reference 1a, revealing a potential electronic interaction highly favorable between triple bond orbitals and the P2Y(1) receptor at this position.
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Affiliation(s)
- Romain Mathieu
- Laboratoire de Pharmacochimie de la Communication Cellulaire (CNRS, UMR 7081), Faculté de Pharmacie, Université Louis Pasteur, 74 route du Rhin, BP24, 67401 Illkirch cedex, France
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27
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Joseph SM, Pifer MA, Przybylski RJ, Dubyak GR. Methylene ATP analogs as modulators of extracellular ATP metabolism and accumulation. Br J Pharmacol 2004; 142:1002-14. [PMID: 15210578 PMCID: PMC1575113 DOI: 10.1038/sj.bjp.0705865] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
1 Transient accumulation of extracellular ATP reflects both release of ATP from intracellular stores and altered rates of ATP metabolism by ecto-enzymes. Ecto-nucleoside triphosphate diphosphohydrolases (eNTPDases) and ecto-nucleotide pyrophosphatases (eNPPs) degrade ATP, while ecto-nucleotide diphosphokinases (eNDPKs) synthesize ATP from ambient ADP. 2 Although the methylene ATP analogs betagamma-meATP and alphabeta-meATP are widely used as metabolically stable tools for the analysis of purinergic signaling, their specific effects on eNTPDase, eNPP, and eNDPK activities have not been defined. This study compared the actions of these analogs on extracellular ATP metabolism by human 1321N1 astrocytes, rat PC12 pheochomocytoma cells, and rat C6 glioma cells. 3 Both analogs significantly reduced clearance of extracellular ATP by 1321N1 cells that express both eNTPDases and eNPPs, as well as by C6 cells that exclusively express eNPPs. In contrast, both analogs were much less efficacious in inhibiting ATP clearance by PC12 cells that predominantly express eNTPDases. Betagamma-meATP, but not alphabeta-meATP, was effectively hydrolyzed by the 1321N1 and C6 cells; PC12 cells did not significantly degrade this analog. 4 Alphabeta-meATP, but not betagamma-meATP, acted as a substrate for purified yeast NDPK to generate ATP via trans-phosphorylation of ADP. alphabeta-meATP also acted as substrate for the eNDPK activities expressed by 1321N1, PC12, and C6 cells and thereby induced extracellular ATP accumulation in the presence of ambient or exogenously added ADP. 5 These results indicate that methylene ATP analogs exert complex and cell-specific effects on extracellular ATP metabolism that can significantly modify interpretation of studies that use these reagents as probes of purinergic signal transduction in intact tissues.
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Affiliation(s)
- Sheldon M Joseph
- Department of Physiology and Biophysics, E565, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, U.S.A
| | - Matthew A Pifer
- Department of Physiology and Biophysics, E565, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, U.S.A
| | - Ronald J Przybylski
- Department of Anatomy, E565, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, U.S.A
| | - George R Dubyak
- Department of Physiology and Biophysics, E565, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, U.S.A
- Author for correspondence:
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28
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Coleman LG, Polanowska-Grabowska RK, Marcinkiewicz M, Gear ARL. LDL oxidized by hypochlorous acid causes irreversible platelet aggregation when combined with low levels of ADP, thrombin, epinephrine, or macrophage-derived chemokine (CCL22). Blood 2004; 104:380-9. [PMID: 15054038 DOI: 10.1182/blood-2003-08-2961] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The in vitro oxidation of low-density lipoprotein (LDL) by hypochlorous acid produces a modified form (HOCl-LDL) capable of stimulating platelet function. We now report that HOCl-LDL is highly effective at inducing platelet function, causing stable aggregation and alpha-granule secretion. Such stimulation depended on the presence of low levels of primary agonists such as adenosine diphosphate (ADP) and thrombin, or others like epinephrine (EPI) and macrophage-derived chemokine (MDC, CCL22). Agonist levels, which by themselves induced little or reversible aggregation, caused strong stable aggregation when combined with low levels of HOCl-LDL. Platelet activation by HOCl-LDL and ADP (1 microM) caused P-selectin (CD62P) exposure, without serotonin or adenosine triphosphate (ATP) secretion. Intracellular calcium levels rose slowly (from 100 to 200 nM) in response to HOCl-LDL alone and rapidly when combined with ADP to about 300 nM. p38 mitogen-activated protein kinase (MAPK) became phosphorylated in response to HOCl-LDL alone. This phosphorylation was not blocked by the protein kinase C (PKC) inhibitor bisindolylmaleimide, which reduced the extent of aggregation and calcium increase. However, the p38 MAPK inhibitor SB203580 blocked platelet aggregation and phosphorylation of p38 MAPK. These findings suggest that HOCl-LDL exposed during atherosclerotic plaque rupture, coupled with low levels of primary agonists, can rapidly induce extensive and stable thrombus formation.
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Affiliation(s)
- Leon G Coleman
- Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, VA 22908, USA
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Alonso-Escolano D, Strongin AY, Chung AW, Deryugina EI, Radomski MW. Membrane type-1 matrix metalloproteinase stimulates tumour cell-induced platelet aggregation: role of receptor glycoproteins. Br J Pharmacol 2003; 141:241-52. [PMID: 14691052 PMCID: PMC1574193 DOI: 10.1038/sj.bjp.0705606] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
1. Matrix metalloproteinase-2 (MMP-2) plays a role in agonist- and tumour cell-induced platelet aggregation (TCIPA). 2. MMP-2 is synthesized as a proenzyme and is activated at the cell surface by membrane type-1 matrix metalloproteinase (MT1-MMP, MMP-14). 3. The significance of tumour cell-associated MT1-MMP for TCIPA was investigated using human breast carcinoma MCF7 cells stably coexpressing the integrin alphavbeta3 with MT1-MMP, cells expressing alphavbeta3 alone and mock-transfected cells. 4. Western blot and zymography confirmed that alphavbeta3/MT1-MMP cells expressed MT1-MMP and efficiently processed proMMP-2 to MMP-2. 5. Aggregometry, phase-contrast and transmission electron microscopy and flow cytometry were used to characterize TCIPA induced by MCF7 cell lines. 6. The aggregating potency of cells was: alphavbeta3/MT1-MMP >alphavbeta3=mock cells, as shown by aggregometry and phase-contrast microscopy. 7. Electron microscopy revealed close, membrane-membrane interactions between activated platelets and alphavbeta3/MT1-MMP cells during TCIPA. 8. Inhibition of MMP-2 with the neutralizing anti-MMP-2 antibody (5 microg ml(-1)) and o-phenanthroline (100 microm) reduced aggregation induced by alphavbeta3/MT1-MMP cells. 9. TCIPA induced by alphavbeta3/MT1-MMP cells was also reduced by inhibiting the generation and actions of ADP with apyrase (250 microg ml(-1)) and 2-methylthio-AMP (2-MeSAMP) (30 microm), but not N(6)-methyl-2'-deoxyadenosine-3',5'-bisphosphate (MRS2179) (30 microm). 10. Flow cytometry demonstrated that TCIPA enhanced expression of glycoprotein (GP) Ib and IIb/IIIa receptors not only on platelets but also on breast cancer cells. 11. Thus, (a) human breast carcinoma cell surface-associated MT1-MMP, via activating proMMP-2, stimulates TCIPA; (b) ADP amplifies the effects of MMPs via stimulation of P2Y(12) receptors and (c) both tumour- and platelet-derived GPIb and GPIIb/IIIa are involved in the aggregatory effects of MT1-MMP.
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Affiliation(s)
- David Alonso-Escolano
- Department of Integrative Biology and Pharmacology, University of Texas, Houston, TX 77030, USA
- Institute of Molecular Medicine for the Prevention of Human Diseases, University of Texas, Houston, TX 77030, USA
- University of Alberta, Edmonton, AB T6G2H7, Canada
| | - Alex Y Strongin
- Cancer Research Center, The Burnham Institute, La Jolla, CA 92037, USA
| | - Ada W Chung
- University of Alberta, Edmonton, AB T6G2H7, Canada
| | - Elena I Deryugina
- Cancer Research Center, The Burnham Institute, La Jolla, CA 92037, USA
| | - Marek W Radomski
- Department of Integrative Biology and Pharmacology, University of Texas, Houston, TX 77030, USA
- Institute of Molecular Medicine for the Prevention of Human Diseases, University of Texas, Houston, TX 77030, USA
- University of Alberta, Edmonton, AB T6G2H7, Canada
- Author for correspondence:
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30
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Kaneko M, Cuyun-Lira O, Takafuta T, Suzuki-Inoue K, Satoh K, Ohtsuki K, Ohnishi M, Arai M, Yatomi Y, Ozaki Y. Mechanisms of platelet retention in the collagen-coated-bead column. ACTA ACUST UNITED AC 2003; 142:258-67. [PMID: 14625532 DOI: 10.1016/s0022-2143(03)00133-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Although the glass-bead column has been used to measure platelet adhesion, whether platelet interaction with glass beads represents physiologic processes remains unsettled. In an attempt to obtain more physiologic platelet responses, plastic beads coated with type I collagen have been recently developed to replace glass beads. In this study, we analyzed the factors responsible for platelet retention in the collagen-coated-bead column and investigated its possible clinical applications. We pumped citrated whole-blood samples into columns at a fixed speed with an injection pump and calculated platelet-retention rates by measuring platelet counts before and after passage through the columns. The platelet-retention rates, which were highly reproducible with samples from healthy donors, were reduced in a patient with glycoprotein (GP) VI deficiency but not in patients with type III von Willebrand disease. Anti-GPIIb/IIIa antibody and GRGDS peptide markedly inhibited platelet retention, whereas inhibition of the GPIb-von Willebrand factor or GPIa/IIa-collagen interaction had no effect. Data on the effects of various antiplatelet agents (including the antithrombin agent argatroban, prostacyclin, acetylsalicylic acid, and the ADP scavenger creatine phosphate/creatine phosphokinase) support the usefulness of this assay method in clinical application. Our findings suggest that GPVI and GPIIb/IIIa but not the GPIb-von Willebrand factor interaction are mainly involved in platelet retention in this column.
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Affiliation(s)
- Makoto Kaneko
- Department of Clinical and Laboratory Medicine, Yamanashi Medical University, Nakakoma, Yamanashi, Japan
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Leon C, Ravanat C, Freund M, Cazenave JP, Gachet C. Differential involvement of the P2Y1 and P2Y12 receptors in platelet procoagulant activity. Arterioscler Thromb Vasc Biol 2003; 23:1941-7. [PMID: 12933533 DOI: 10.1161/01.atv.0000092127.16125.e6] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE In vivo, activated platelets contribute to the initiation of thrombin generation through the exposure of phosphatidylserine to form a procoagulant catalytic surface and through platelet-leukocyte interactions, which lead to the exposure of leukocyte tissue factor (TF). On the basis of observations that the platelet P2Y1 and P2Y12 receptors both contribute to thrombosis and thrombin formation in an in vivo model of TF-induced thromboembolism, we further characterized the role of these receptors in thrombin generation. METHODS AND RESULTS By using the selective P2 antagonists MRS2179 and AR-C69931MX, the P2Y12 receptor was found to be involved in thrombin-induced exposure of PS on isolated platelets and consequently in TF-induced thrombin formation in platelet-rich plasma. By contrast, the P2Y1 receptor was not involved in phosphatidylserine exposure nor in thrombin generation in platelet-rich plasma. In addition, both receptors were found to contribute to the interactions between platelets and leukocytes mediated by platelet P-selectin exposure, which result in TF exposure at the surface of leukocytes. CONCLUSIONS Overall, these results point to a differential involvement of the 2 platelet ADP receptors in the generation of thrombin and provide further evidence for the relevance of molecules targeting these receptors as antithrombotic agents.
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Affiliation(s)
- Catherine Leon
- Institut National de la Santé et de la Recherche Médicale U.311, Etablissement Français du Sang-Alsace, 10 rue Spielmann, 67065 Strasbourg Cédex, France
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Jackson SP, Schoenwaelder SM. Antiplatelet therapy: in search of the 'magic bullet'. Nat Rev Drug Discov 2003; 2:775-89. [PMID: 14526381 DOI: 10.1038/nrd1198] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The central importance of platelets in the development of arterial thrombosis and cardiovascular disease is well established. No other single cell type is responsible for as much morbidity and mortality as the platelet and, as a consequence, it represents a major target for therapeutic intervention. The growing awareness of the importance of platelets is reflected in the increasing number of patients receiving antiplatelet therapy, a trend that is likely to continue in the future. There are, however, significant drawbacks with existing therapies, including issues related to limited efficacy and safety. The discovery of a 'magic bullet' that selectively targets pathological thrombus formation without undermining haemostasis remains elusive, although recent progress in unravelling the molecular events regulating thrombosis has provided promising new avenues to solve this long-standing problem.
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Affiliation(s)
- Shaun P Jackson
- The Australian Centre for Blood Diseases, Department of Medicine, Monash University, Arnold Street, Box Hill Hospital, Box Hill, Victoria 3128, Australia.
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Matsagas M, Jagroop IA, Geroulakos G, Mikhailidis DP. The effect of a loading dose (300 mg) of clopidogrel on platelet function in patients with peripheral arterial disease. Clin Appl Thromb Hemost 2003; 9:115-20. [PMID: 12812379 DOI: 10.1177/107602960300900204] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Clopidogrel acts on the P2Y12 adenosine diphosphate (ADP) purinergic receptors on human platelets. The aim of this study was to establish if a loading dose of clopidogrel inhibits platelet activation in patients with peripheral arterial disease (PAD). Two indices of platelet activation were considered: platelet shape change (PSC) and aggregation. Citrated blood was collected from ten PAD patients who were not on aspirin, at baseline (0 hours) and 2 and 4 hours after these patients ingested a loading dose (300 mg) of clopidogrel. ADP (5 micromo/L)-induced platelet aggregation in whole blood was inhibited after 2 hours (free platelet count, 47% +/- 19% vs. 68% +/- 15%; p < or = 0.001) and 4 hours (47% +/- 19% vs. 66% +/- 16%; p < or = 0.001). There was also a significant inhibition of 5- hydroxytryptamine (SHT, 5.0 micromol/L)-induced platelet aggregation at 2 hours. This trend was also observed for 10-micomol/L ADP-induced aggregation. ADP (0.3-0.4 micromol/L)-induced PSC was significantly inhibited at 4 hours (increase in median platelet volume, 6.3%, 1.8-10.7 vs. 1.2%, 0-5.3; p = 0.01). 5HT (0.5 micromol/L)-induced PSC at 4 hours was also significantly inhibited (8.1, 5.3-10.6 vs. 3.0, 0-8.2; p = 0.03). A loading dose of clopidogrel (300 mg) inhibits platelet activation in PAD patients, as early as 2 hours. To the authors' knowledge, no other study considered the effect of a loading dose of clopidogrel in PAD.
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Affiliation(s)
- Miltiadis Matsagas
- Department Clinical Biochemistry, Royal Free University College School of Medicine, University of London, Royal Free Campus, UK
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