Activation of Platelets in Platelet-rich Plasma by Rotablation Is Speed Dependent and Can Be Inhibited by Abciximab (c7E3 Fab; ReoProTM

Morphological and cytochemical studies of platelets have reported a surface coat, or glycocalyx, external to the plasma membrane (1). Biochemical analyses have likewise confirmed the highly adsorptive properties of platelets as transporters of coagulation factors (2). However, visualization of the platelet membrane by conventional EM procedures does not reflect this special relationship between the platelet and its plasma environment. By the routine method of alcohol-propylene oxide dehydration for Epon embedding, the lipid bilayer nature of the platelet membrane appears similar to other blood cells (Fig. 1). A new rapid embedding technique using dimethoxypropane (DMP) as dehydrating agent (13) has permitted ultrastructural analyses of the surface features of the platelet-plasma interface.Aliquots of human or rabbit platelet-rich plasma (PRP) were added to equal volumes of 6% glutaraldehyde in Millonig's buffer at 37° for 45 minutes, rinsed in buffer and postfixed in 1% osmium in Millonig's buffer for 45 minutes.

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Functional Characterization of PM6/13, a β3-specific (GPIIIa/CD61) Monoclonal Antibody that Shows Preferential Inhibition of Fibrinogen Binding over Fibronectin Binding to Activated Human Platelets

Thrombosis and Haemostasis ◽

10.1055/s-0037-1614247 ◽

1998 ◽

Vol 79 (01) ◽

pp. 177-185 ◽

Cited By ~ 10

Author(s):

Ashia Siddiqua ◽

Michael Wilkinson ◽

Vijay Kakkar ◽

Yatin Patel ◽

Salman Rahman ◽

...

Keyword(s):

Monoclonal Antibody ◽

Platelet Aggregation ◽

Platelet Rich Plasma ◽

Functional Characterization ◽

Human Platelets ◽

Western Blots ◽

Activated Platelets ◽

Reducing Conditions ◽

Fibronectin Binding

SummaryWe report the characterization of a monoclonal antibody (MAb) PM6/13 which recognises glycoprotein IIIa (GPIIIa) on platelet membranes and in functional studies inhibits platelet aggregation induced by all agonists examined. In platelet-rich plasma, inhibition of aggregation induced by ADP or low concentrations of collagen was accompanied by inhibition of 5-hydroxytryptamine secretion. EC50 values were 10 and 9 [H9262]g/ml antibody against ADP and collagen induced responses respectively. In washed platelets treated with the cyclooxygenase inhibitor, indomethacin, PM6/13 inhibited platelet aggregation induced by thrombin (0.2 U/ml), collagen (10 [H9262]g/ml) and U46619 (3 [H9262]M) with EC50 = 4, 8 and 4 [H9262]g/ml respectively, without affecting [14C]5-hydroxytryptamine secretion or [3H]arachidonate release in appropriately labelled cells. Studies in Fura 2-labelled platelets revealed that elevation of intracellular calcium by ADP, thrombin or U46619 was unaffected by PM6/13 suggesting that the epitope recognised by the antibody did not influence Ca2+ regulation. In agreement with the results from the platelet aggregation studies, PM6/13 was found to potently inhibit binding of 125I-fibrinogen to ADP activated platelets. Binding of this ligand was also inhibited by two other MAbs tested, namely SZ-21 (also to GPIIIa) and PM6/248 (to the GPIIb-IIIa complex). However when tested against binding of 125I-fibronectin to thrombin stimulated platelets, PM6/13 was ineffective in contrast with SZ-21 and PM6/248, that were both potent inhibitors. This suggested that the epitopes recognised by PM6/13 and SZ-21 on GPIIIa were distinct. Studies employing proteolytic dissection of 125I-labelled GPIIIa by trypsin followed by immunoprecipitation with PM6/13 and analysis by SDS-PAGE, revealed the presence of four fragments at 70, 55, 30 and 28 kDa. PM6/13 did not recognize any protein bands on Western blots performed under reducing conditions. However Western blotting analysis with PM6/13 under non-reducing conditions revealed strong detection of the parent GP IIIa molecule, of trypsin treated samples revealed recognition of an 80 kDa fragment at 1 min, faint recognition of a 60 kDa fragment at 60 min and no recognition of any product at 18 h treatment. Under similar conditions, SZ-21 recognized fragments at 80, 75 and 55 kDa with the 55kDa species persisting even after 18 h trypsin treatment. These studies confirm the epitopes recognised by PM6/13 and SZ-21 to be distinct and that PM6/13 represents a useful tool to differentiate the characteristics of fibrinogen and fibronectin binding to the GPIIb-IIIa complex on activated platelets.

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Phospholipase C from Clostridium Perfringens Induces Human Platelet Aggregation in Plasma

Thrombosis and Haemostasis ◽

10.1055/s-0038-1642761 ◽

1988 ◽

Vol 59 (02) ◽

pp. 236-239 ◽

Cited By ~ 2

Author(s):

Giovanna Barzaghi ◽

Chiara Cerletti ◽

Giovanni de Gaetano

Keyword(s):

Platelet Aggregation ◽

Receptor Antagonist ◽

Phospholipase C ◽

Clostridium Perfringens ◽

Human Platelet ◽

Ex Vivo ◽

Platelet Rich Plasma ◽

Platelet Activating Factor ◽

Inhibitory Effect ◽

Thromboxane Receptor Antagonist

SummaryWe studied the aggregating effect of different concentrations of phospholipase C (PLC) (extracted from Clostridium perfringens) on human platelet-rich plasma (PRP). PRP was preincubated with PLC for 3 min at 37° C and the platelet aggregation was followed for 10 min. The threshold aggregating concentration (TAG) of PLC was 3-4 U/ml.We also studied the potentiation of PLC with other stimuli on platelet aggregation. Potentiating stimuli, such as arachidonic acid (AA), ADP. Platelet Activating Factor (PAF) and U-46619 (a stable analogue of cyclic endoperoxides) were all used at subthreshold concentrations. We also studied the possible inhibitory effect of aspirin, apyrase, TMQ, a prostaglandin endoper- oxide/thromboxane receptor antagonist and BN-52021, a PAF receptor antagonist. Only aspirin and apyrase were able to reduce aggregation induced by PLC alone and PLC + AA and PLC + ADP respectively. TMQ and BN-52021 were inactive. In ex vivo experiments oral aspirin (500 mg) partially inhibited platelet aggregation induced by PLC alone, PLC + AA and PLC + ADP 2 and 24 h after administration. Aspirin 20 mg for 7 days also reduced aggregation induced by PLC + AA.

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Time Dependence of Whole Blood Aggregation in Response to Platelet Activating Factor (PAF)

Thrombosis and Haemostasis ◽

10.1055/s-0038-1642746 ◽

1988 ◽

Vol 59 (02) ◽

pp. 162-163 ◽

Cited By ~ 5

Author(s):

R R Taylor ◽

J Strophair ◽

M Sturm ◽

R Vandongen ◽

L J Beilin

Keyword(s):

Time Dependence ◽

Whole Blood ◽

Platelet Rich Plasma ◽

Platelet Activating Factor ◽

Sampling Time ◽

Blood Sampling ◽

Impedance Aggregometry

SummaryThe aggregation/adhesion response to platelet activating factor (PAF) was studied in diluted whole blood by impedance aggregometry. The extent of aggregation varied directly with the interval between blood sampling and aggregation measurement over the first 30 minutes from sampling, then remained stable for the next 60 minutes of observation. This is an effect opposite to that described for aggregation to PAF in platelet rich plasma which, however, cannot be studied soon after sampling. Time dependence of aggregation is important and comparative measurements should be made during the period of stable aggregability.

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Platelet-Bound Prekallikrein Promotes Pro-Urokinase-Induced Clot Lysis: A Mechanism for Targeting the Factor XII Dependent Intrinsic Pathway of Fibrinolysis

Thrombosis and Haemostasis ◽

10.1055/s-0038-1642441 ◽

1994 ◽

Vol 71 (03) ◽

pp. 347-352 ◽

Cited By ~ 36

Author(s):

Jean-Pierre Loza ◽

Victor Gurewich ◽

Michael Johnstone ◽

Ralph Pannell

Keyword(s):

Platelet Rich Plasma ◽

Specific Inhibitor ◽

Specific Effect ◽

Clot Lysis ◽

Factor Xii ◽

Intrinsic Pathway ◽

Clot Retraction ◽

Enzymatic Mechanism ◽

Low Concentrations ◽

Factor Xiia

SummaryClots formed from platelet rich plasma were found to be lysed more readily by low concentrations of pro-urokinase (pro-UK) than clots formed from platelet poor plasma. This was not a non-specific effect since the reverse occurred with tissue plasminogen activator. A mechanical explanation due to platelet-mediated clot retraction was excluded by experiments in which retraction was inhibited with cyto-chalasin B. Therefore, a platelet-mediated enzymatic mechanism was postulated to explain the promotion of fibrinolysis. Casein autography of isolated platelets revealed a ≈ 90 kDa band of activity which comigrated with plasma prekallikrein (PK)/kallikrein, a known activator of pro-UK. Furthermore, treatment of platelets with plasma PK activator (PPA), consisting essentially of factor XIIa, induced activation of pro-UK and of chromomgenic substrate for kallikrein (S-2302). This activity corresponded to approximately 40-200 pM kallikrein per 10 8 washed and gel filtered platelets per ml. The activation of pro-UK by PPA-pretreated platelets was dose-dependent and inhibited by soybean trypsin inhibitor but not by bdellin, a specific inhibitor of plasmin, nor by the corn inhibitor of factor XIIa. Kinetic analysis of pro-UK activation by kallikrein showed promotion of the reaction by platelets. The KM of the reaction was reduced by platelets by ≈ 7-fold, while the kcat was essentially unchanged. In conclusion, PK was shown to be tightly associated with platelets where it can be activated by factor XIIa during clotting. The activation of pro-UK by platelet-bound kallikrein provides an explanation for the observed platelet mediated promotion of pro-UK-induced clot lysis. Since pro-UK and plasminogen have also been shown to be associated with platelets, the present findings suggest a mechanism by which the factor Xlla-dependent intrinsic pathway of fibrinolysis can be localized and targeted to a thrombus.

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Conditions Affecting the Responses of Human Platelets to Epinephrine

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647031 ◽

1988 ◽

Vol 60 (02) ◽

pp. 209-216 ◽

Cited By ~ 23

Author(s):

Chantal Lalau Keraly ◽

Raelene L Kinlough-Rathbone ◽

Marian A Packham ◽

Hidenori Suzuki ◽

J Fraser Mustard

Keyword(s):

Platelet Rich Plasma ◽

Shape Change ◽

Human Platelets ◽

Dense Granule ◽

Primary Phase ◽

Lag Phase ◽

Acid Citrate Dextrose ◽

Two Phases ◽

Citrate Dextrose ◽

Thromboxane Formation

SummaryConditions affecting the responses of human platelets to epinephrine were examined. In platelet-rich plasma prepared from blood anticoagulated with hirudin or PPACK (D-pheny- lalanyl-L-prolyl-L-arginine chloromethyl ketone), epinephrine did not cause shape change or aggregation. In a Tyrode-albumin- apyrase solution containing a concentration of Ca2+ in the physiological range, and fibrinogen, epinephrine in concentrations as high as 40 μM did not induce platelet shape change, caused either no primary aggregation or very slight primary aggregation, and did not induce thromboxane formation, release of dense granule contents, or secondary aggregation. In contrast, in citrated platelet-rich plasma, epinephrine induced two phases of aggregation. This is not attributable to the generation of traces of thrombin since the same effects were evident when blood was taken into a combined citrate-hirudin anticoagulant or a combined citrate-PPACK anticoagulant. In a modified Tyrode-albu- min-apyrase solution containing approximately 20 μM Ca2+, 1 mM Mg2+, and fibrinogen, epinephrine induced extensive aggregation after a lag phase, but no primary phase was evident; thromboxane formation and release of dense granule contents accompanied the aggregation response. These responses were also observed when PPACK was included with the acid-citrate- dextrose anticoagulant, and in the washing and resuspending fluids. In the presence of aspirin or the thromboxane receptor blocker BM 13.177 a few small aggregates were detected by particle counting and by scanning electron microscopy; with the latter inhibitor, the platelets in the aggregates retained their disc shape; secondary aggregation and the responses associated with it did not occur. Thus thromboxane A2 formation is not necessary for the formation of these small aggregates, but is required for extensive aggregation and release. As with other weak agonists, the close platelet-to-platelet contact in the low Ca2+ medium appears to be necessary for full secondary aggregation. Omission of fibrinogen from the low Ca2+ medium prevented both primary and secondary aggregation in response to epinephrine. An antibody (10E5) to the glycoprotein Ilb/IIIa complex was completely inhibitory in the presence of fibrinogen. Thus the response of human platelets to epinephrine is influenced by the concentration of Ca2+ and the presence of fibrinogen in the medium in which they are suspended.

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Extraction of Protein-Bound ATP and ADP from Human Platelets in Plasma

Thrombosis and Haemostasis ◽

10.1055/s-0038-1645211 ◽

1990 ◽

Vol 63 (02) ◽

pp. 286-290 ◽

Cited By ~ 3

Author(s):

Christina Beurling-Harbury ◽

Pehr B Harbury

Keyword(s):

Specific Activity ◽

Platelet Rich Plasma ◽

Binding Protein ◽

Human Platelets ◽

Luciferase Assay ◽

First Time ◽

Plasma Extraction

SummaryActin is the major ATP and ADP binding protein in platelets, 0.9–1.3 nmol/108 cells, 50–70% in the unpolymerized state. The goal of these experiments was to develop a method for extracting all protein-bound ATP and ADP from undisturbed platelets in plasma. Extraction of actin-bound ADP is routine while extraction of actin-bound ATP from platelets in buffer has been unsuccessful. Prior to extraction the platelets were exposed to 14-C adenine, to label the metabolic and actin pools of ATP and ADP. The specific activity was determined from the actin-bound ADP in the 43% ethanol precipitate. Sequential ethanol and perchlorate extractions of platelet rich plasma, and the derived supernatants and precipitates were performed. ATP concentrations were determined with the luciferase assay, and radioactive nucleotides separated by TLC. A total of 1.18 nmol/108 cells of protein-bound ATP and ADP was recovered, 52% ATP (0.61 nmol). The recovery of protein-bound ADP was increased from 0.3 to 0.57 nmol/108 cells. This approach for the first time successfully recovered protein bound ATP and ADP from platelets in a concentration expected for actin.

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Enhancement of ADP-induced Platelet Aggregation by Adrenaline in Vivo and Its Prevention

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647788 ◽

1973 ◽

Vol 29 (02) ◽

pp. 490-498 ◽

Cited By ~ 6

Author(s):

Hiroh Yamazaki ◽

Itsuro Kobayashi ◽

Tadahiro Sano ◽

Takio Shimamoto

Keyword(s):

Platelet Count ◽

Platelet Aggregation ◽

Platelet Rich Plasma ◽

The Other ◽

Endothelial Surface ◽

Important Interaction ◽

Blood Coagulability ◽

The Difference

SummaryThe authors previously reported a transient decrease in adhesive platelet count and an enhancement of blood coagulability after administration of a small amount of adrenaline (0.1-1 µg per Kg, i. v.) in man and rabbit. In such circumstances, the sensitivity of platelets to aggregation induced by ADP was studied by an optical density method. Five minutes after i. v. injection of 1 µg per Kg of adrenaline in 10 rabbits, intensity of platelet aggregation increased to 115.1 ± 4.9% (mean ± S. E.) by 10∼5 molar, 121.8 ± 7.8% by 3 × 10-6 molar and 129.4 ± 12.8% of the value before the injection by 10”6 molar ADP. The difference was statistically significant (P<0.01-0.05). The above change was not observed in each group of rabbits injected with saline, 1 µg per Kg of 1-noradrenaline or 0.1 and 10 µg per Kg of adrenaline. Also, it was prevented by oral administration of 10 mg per Kg of phenoxybenzamine or propranolol or aspirin or pyridinolcarbamate 3 hours before the challenge. On the other hand, the enhancement of ADP-induced platelet aggregation was not observed in vitro, when 10-5 or 3 × 10-6 molar and 129.4 ± 12.8% of the value before 10∼6 molar ADP was added to citrated platelet rich plasma (CPRP) of rabbit after incubation at 37°C for 30 second with 0.01, 0.1, 1, 10 or 100 µg per ml of adrenaline or noradrenaline. These results suggest an important interaction between endothelial surface and platelets in connection with the enhancement of ADP-induced platelet aggregation by adrenaline in vivo.

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Storage of Human Blood Platelets

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647709 ◽

1974 ◽

Vol 32 (02/03) ◽

pp. 405-416 ◽

Cited By ~ 3

Author(s):

M. R Hardeman ◽

Carina J L. Heynens

Keyword(s):

Storage Temperature ◽

Platelet Rich Plasma ◽

Blood Platelets ◽

Storage Period ◽

Serotonin Uptake ◽

Hypotonic Shock ◽

Glycolytic Intermediates

SummaryStorage experiments were performed at 4°, 25° and 37° C with platelet-rich plasma under sterile conditions. In some experiments also the effect of storing platelets at 4° C in whole blood was investigated.Before, during and after three days of storage, the platelets were tested at 37° C for their serotonin uptake and response to hypotonic shock. In addition some glycolytic intermediates were determined.A fair correlation was noticed between the serotonin uptake and hypotonic shock experiments. Both parameters were best maintained at 25° C. Also platelet counting, performed after the storage period, indicated 25° C as the best storage temperature. Determination of glycolytic intermediates did not justify any conclusion regarding the optimal storage temperature. Of the various anticoagulants studied, ACD and heparin gave the best results as to the serotonin uptake and hypotonic shock response, either with fresh or stored platelets. The use of EDTA resulted in the lowest activity, especially after storage.The results of these storage experiments in vitro, correspond well with those in vivo reported in the literature.

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The Effect of Lysed Platelets on Neutralization of Heparin In Vitro with Protamine as Measured by the Activated Coagulation Time (ACT)

Thrombosis and Haemostasis ◽

10.1055/s-0038-1646392 ◽

1991 ◽

Vol 66 (02) ◽

pp. 213-217 ◽

Cited By ~ 7

Author(s):

Arthur P Bode ◽

William J Castellani ◽

Edna D Hodges ◽

Susan Yelverton

Keyword(s):

Platelet Rich Plasma ◽

Coagulation Time ◽

Platelet Factor ◽

Platelet Suspension ◽

Antiheparin Activity ◽

Unit Increase ◽

Heparin Anticoagulation ◽

Heparin Activity ◽

Activated Coagulation Time

SummaryThe effect of lysed platelets on the activated coagulation time (ACT) was studied in heparinized whole blood during titration with protamine. Frozen-thawed washed platelet suspension, or a chromatography fraction thereof, or autologous frozen-thawed platelet-rich plasma was added in various dilutions to freshly drawn blood anticoagulated with 3,000 USP units/1 heparin. After a 10 min incubation, the amount of protamine needed to restore the ACT to baseline ("protamine titration dose") was determined. We found that the protamine titration dose decreased in proportion to the amount of lysed platelet material added; expressed as a percentage of the total number of platelets present, each unit increase in lysed platelets produced a 1.7% ±0.8 (SD) reduction in the protamine dose needed to normalize the ACT. A heparin activity assay showed that this effect was not due to antiheparin activity of lysed platelets such as platelet factor 4 (PF4). Our data indicate that the procoagulant activity of platelet membranes reduced the sensitivity of the ACT to heparin. These findings suggest that membranous platelet microparticles may cause an inaccurate calculation, based on the ACT, of a protamine dose to reverse heparin anticoagulation in cardiopulmonary bypass procedures.

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