Arachidonic Acid-Induced Aggregation of Platelets from Human Cord Blood Compared with Platelets from Adults

PAF-acether-aggregated rabbit platelets did not respond to a second challenge with the same agonist after their spontaneous disaggregation, but still aggregated in the presence of arachidonic acid (AA). When using 1 nM of PAF-acether in the first stimulation, aggregation in response to a second challenge with the same dose was nil. However, when 0.34 nM was used in the first step, aggregation in response to 0.64 nM PAF-acether was 59 96, as compared to control platelets. By contrast, aggregation of platelets pretreated with 1 nM PAF-acether was 72 % in the presence of 2.8 uM AA. Adding fibrinogen (0.34 mg/ml) before the second stimulation did not modify the desensitization pehnom- enon. Supernatants from platelets desensitized with 1 nM PAF- acether exhibited neither aggregating nor inhibitory activity. PAF-acether-induced desensitization could always be overcome, since aspirin-pretreated platelets first stimulated with 10 nM PAF-acether still aggregated with 100 nM of the same agonist, i.e. when using 100 times the amount which induced maximal aggregation. All our experiments were performed in the presence of ADP scavengers and, except for AA-induced aggregation, aspirin. We tested PAF-acether from 4 different cell origins and the semi-synthetic and synthetic compounds. Platelets were cross- desensitized towards PAF-acether from any source. Totally synthetic PAF-acether bearing aC,, alkyl chain at position 1 of the glycerol moiety desensitized platelets as well as the C.g synthetic analog. Lyso-PAF-acether (i.e. a compound lackifig tne acetyl group at the position 2 of the glycerol) (0.5-10.0 nM) and PAF-acether enantiomer (0.5-5.0 nM) neither aggregated nor desensitized platelets to PAF-acether. These results indicate that 1) PAF-acether from any source exhibit at least an identical active molecular site ; 2) the presence and the stereospecific position of the 2-acetyl group are critical for the interaction of PAF-acether with platelets, a result which could indicate the existence of a platelet acceptor (receptor) for PAF-acether. However, these postulated platelet membrane acceptors were never saturated even using very high amounts of the agonist.

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Differential Inhibition of Arachidonic Acid Mediated Aggregation of Platelets by Branded and Generic Argatroban Preparations

Blood ◽

10.1182/blood.v116.21.5131.5131 ◽

2010 ◽

Vol 116 (21) ◽

pp. 5131-5131

Author(s):

Christopher Aranda ◽

Debra Hoppensteadt ◽

Omer Iqbal ◽

Bruce E Lewis ◽

Jawed Fareed

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Platelet Activation ◽

Serotonin Release ◽

Final Concentration ◽

Release Mechanism ◽

Clinical Effects ◽

Induced Aggregation ◽

Aggregation Of Platelets ◽

Inhibition Of Thrombin

Abstract Abstract 5131 Argatroban represents a parentral antithrombin agent which is used in the management of anticoagulation in heparin compromised patients. Its main mechanism of action is mediated via inhibition of thrombin and its generation. While its effect on platelet activation inhibition by thrombin have been reported, very little information on the effects of this drug on thromboxane formation and Arachidonic Acid mediated activation of platelets is available. Argatroban and its generic versions namely Slovastan, Argaron and Gartban, may modulate Arachidonic Acid mediated platelet aggregation and release processes. To test this hypothesis a branded version of Argatroban (Mitsubishi – Tanade, Tokyo, Japan) and three generic versions of Argatroban namely Slovastan, Gartban, and Slovastan were compared for their effects on Arachidonic Acid mediated aggregation of platelets in normal healthy male and female volunteers (and n = 4). Other agonists such as Epinephrine, Collagen, and ADP were also used. The effect of Arachidonic Acid on serotonin release was also measured using an Elisa technique for the measurement of serotonin. All of the generic and branded versions of Argatroban produce varying levels of the inhibition of the Arachidonic Acid mediated aggregation of platelets, ranging from the 24 to 36 percent in comparison to the control at a concentration of 1 mg/ mL (p value < 0.05). Interestingly all of the Argatrobans produced a relatively weaker inhibition of the Arachidonic Acid mediated aggregation of platelets 24–26 percent inhibition versus 36 percent at the final concentration of 1 mg/mL. No differences were noted in the aggregation profile of ADP, Collagen, and Epinephrine between the control and the Argatrboban at a final concentration of 1 mg /mL. No differences were noted between the generic and branded Argatroban on all of the other agonists induced aggregation. In the serotonin release assays, all of the generic and branded Argatroban produced a concentration dependent inhibition of serotonin release which was stronger with the branded version of Argatroban. These results indicate that besides the inhibition of thrombin Argatroban is capable of inhibiting platelet activation via other mechanisms. Moreover, the generic versions of Argatroban exhibit a weaker inhibition of Arachidonic Acid mediated platelet aggregation and release. These studies suggest that beside thrombin mediated aggregation Argatroban and its generic versions can modulate platelet activation and release reactions. Furthermore a difference is observed between the generic and branded product which may impact the safety inefficacy profile in these agents. Argatroban is used commonly in the management of patients with heparin induced thrombocytopenia where multiple mechanisms of platelet activation are contributory to the pathogenesis of this syndrome. Modulation of thrombanxane formation and platelet release mechanism by Argatroban may represent an additional mechanism of the clinical effects of this parentral antithrombin agent. Disclosures: No relevant conflicts of interest to declare.

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Dose-Response Aggregometry in Maternal/Neonatal Platelets

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647052 ◽

1988 ◽

Vol 60 (02) ◽

pp. 314-318 ◽

Cited By ~ 34

Author(s):

A M A Gader ◽

H Bahakim ◽

F A Jabbar ◽

A L Lambourne ◽

T H Gaafar ◽

...

Keyword(s):

Arachidonic Acid ◽

Dose Response ◽

Lag Phase ◽

Phase Slope ◽

Multiple Doses ◽

Nonpregnant Adult ◽

Aggregation Of Platelets

SummaryThe aggregation of platelets collected from maternal/neonatal pairs (n = 240) at the time of childbirth, was studied in response to multiple doses of ADP, collagen, arachidonic acid and ristocetin. Similar responses were obtained from healthy nonpregnant adult controls for comparison. The lag phase, slope of the aggregation curves as well as maximum aggregation (MA%) were recorded and analysed. Neonatal and adult platelets exhibited more enhanced responses to decreasing doses of ADP, arachidonic acid and ristocetin, than maternal platelets. These enhanced responses were exhibited more consistantly in the slopes of the aggregation curves than in MA%. Although neonatal platelets have shown longer lag phase in their responses to collagen, the rate of the aggregation reaction was significantly faster than maternal platelets, with no differences in MA%. These results contradict many previous reports suggesting impaired aggregation responses of neonatal platelets to these agonist. The possible reasons for these contradictions were discussed.

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Inhibition by Glaucocalyxin A of Aggregation of Rabbit Platelets Induced by ADP, Arachidonic Acid and Platelet-Activating Factor, and Inhibition of [3H]-PAF Binding

Thrombosis and Haemostasis ◽

10.1055/s-0038-1648470 ◽

1992 ◽

Vol 67 (04) ◽

pp. 458-460 ◽

Cited By ~ 12

Author(s):

Zhang Bin ◽

Long Kun

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Platelet Activating Factor ◽

Northeastern China ◽

Ethereal Extract ◽

Ic50 Value ◽

Rabbit Platelets ◽

Ic50 Values ◽

Induced Aggregation

SummaryGlaucocalyxin A is a new diterpenoid isolated from the ethereal extract of the leaves of Rabdosia japonica (Burm f) Hara var glaucocalyx (Maxim) Hara (Labiatae) collected in the northeastern China. When it was incubated with washed rabbit platelets, glaucocalyxin A inhibited ADP- or arachidonic acid-induced platelet aggregation with IC50 values of 4.4 μmol/1, 14.1 μmol/1 respectively. Glaucocalyxin A also inhibited PAF-induced aggregation of rabbit platelets which were refractory to ADP and arachidonic acid with an IC50 value of 13.7 μmol/1. Analysis of [3H]-PAF binding showed that glaucocalyxin A prevented [3H]-PAF binding to intact washed rabbit platelets with an IC50 value of 8.16 μmol/1, which was consistent with its inhibition of PAF-induced platelet aggregation.

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On The Mechanism Of Heparin-Induced Potentiation Of Platelet Aggregation

10.1055/s-0038-1652598 ◽

1981 ◽

Author(s):

M Yamamoto ◽

K Watanabe ◽

Y Ando ◽

H Iri ◽

N Fujiyama ◽

...

Keyword(s):

Platelet Aggregation ◽

Platelet Activation ◽

Coagulation Factors ◽

Marked Enhancement ◽

Matrix Bound ◽

Induced Aggregation ◽

Aggregation Of Platelets ◽

Plasma Heparin

It has been suggested that heparin caused potentiation of aggregation induced by ADP or epinephrine. The exact mechanism of heparin-induced platelet activation, however, remained unknown. In this paper, we have investigated the role of anti-thrombin III ( AT ) in heparin-induced platelet activation using purified AT and AT depleted plasma. When ADP or epinephrine was added to citrated PRP one minute after addition of heparin ( 1 u/ml, porcine intestinal mucosal heparin, Sigma Co. USA ), marked enhancement of platelet aggregation was observed, compared with the degree of aggregation in the absence of heparin. However, in platelet suspensions prepared in modified Tyrode’s solution, heparin exhibited no potentiating effect on platelet aggregation induced by epinephrine or ADP. Potentiation of epinephrine- or ADP-induced platelet aggregation by heparin was demonstrated when purified AT was added to platelet suspensions at a concentration of 20 μg/ml. AT depleted plasma, which was prepared by immunosorption using matrix-bound antibodies to AT, retained no AT, while determination of α1-antitrypsinα2- macroglobulin and fibrinogen in AT depleted plasma produced values which corresponded to those of the original plasma when dilution factor was taken into account. The activities of coagulation factors were also comparable to those of the original plasma. Heparin exhibited potentiating effect on ADP- or epinephrine-induced aggregation of platelets in original plasma, but no effect in AT depleted plasma. When purified AT was added back to AT depleted plasma at a concentration of 20 μg/ml, potentiation of platelet aggregation by heparin was clearly demonstrated.Our results suggest that effect of heparin on platelet aggregation is also mediated by anti-thrombin III.

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Testosterone Potentiation of Ionophore and ADP Induced Platelet Aggregation : Relationship to Arachidonic Acid Metabolism

Thrombosis and Haemostasis ◽

10.1055/s-0038-1653405 ◽

1981 ◽

Vol 46 (02) ◽

pp. 538-542 ◽

Cited By ~ 42

Author(s):

R Pilo ◽

D Aharony ◽

A Raz

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Unsaturated Fatty Acids ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Arachidonic Acid Metabolism ◽

Ionophore A23187 ◽

Low Concentrations ◽

Induced Aggregation

SummaryThe role of arachidonic acid oxygenated products in human platelet aggregation induced by the ionophore A23187 was investigated. The ionophore produced an increased release of both saturated and unsaturated fatty acids and a concomitant increased formation of TxA2 and other arachidonate products. TxA2 (and possibly other cyclo oxygenase products) appears to have a significant role in ionophore-induced aggregation only when low concentrations (<1 μM) of the ionophore are employed.Testosterone added to rat or human platelet-rich plasma (PRP) was shown previously to potentiate platelet aggregation induced by ADP, adrenaline, collagen and arachidonic acid (1, 2). We show that testosterone also potentiates ionophore induced aggregation in washed platelets and in PRP. This potentiation was dose and time dependent and resulted from increased lipolysis and concomitant generation of TxA2 and other prostaglandin products. The testosterone potentiating effect was abolished by preincubation of the platelets with indomethacin.

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Pretreatment of Human Platelets with Plasmin Inhibits Responses toThrombin, but Potentiates Responses to Low Concentrations of Aggregating Agents, Including the Thrombin Receptor Activating Peptide, SFLLRN

Thrombosis and Haemostasis ◽

10.1055/s-0038-1656044 ◽

1997 ◽

Vol 77 (04) ◽

pp. 741-747 ◽

Cited By ~ 12

Author(s):

R L Kinlough-Rathbone ◽

D W Perry ◽

M L Rand ◽

M A Packham

Keyword(s):

Arachidonic Acid ◽

Platelet Activating Factor ◽

Human Platelets ◽

Thrombin Receptor ◽

Fibrinolytic Agents ◽

Albumin Solution ◽

Fibrinogen Receptor ◽

Low Concentrations ◽

Induced Aggregation

SummaryEffects of plasmin on platelets, that influence subsequent responses to aggregating agents, are relevant to attempts to prevent rethrombosis following administration of fibrinolytic agents. We describe plasmin-induced inhibition of platelet responses to thrombin, but potentiation of responses to other aggregating agents. Washed human platelets were labeled with 14C-serotonin, treated for 30 min at 37° C with 0, 0.1 or 0.2 CU/ml of plasmin, followed by aprotinin, washed and resuspended in a Tyrode-albumin solution with apyrase. Incubation with 0.2 CU/ml of plasmin almost completely inhibited thrombin-induced (0.1 U/ml) aggregation, release of 14C-serotonin, and increase in cytosolic [Ca2+]. In contrast, with plasmin-pretreated platelets, aggregation and release of 14C-serotonin were strongly potentiated in response to low concentrations of the thrombin receptor-activating peptide SFLLRN, ADP, platelet-activating factor, collagen, arachidonic acid, the thromboxane mimetic U46619, and the calcium ionophores A23187 and ionomycin. Aspirin or RGDS partially inhibited potentiation. Plasmin-pretreated platelets resuspended in plasma anticoagulated with FPRCH2C1 (PPACK) also showed enhanced responses to aggregating agents other than thrombin. The contrasting effects on responses to thrombin and SFLLRN are noteworthy. Plasmin cleaves GPIIb/IIIa so that it becomes a competent fibrinogen receptor, and binding of 125I-fibrinogen during ADP-induced aggregation was greatly potentiated within 10 s. Potentiation of aggregation by other agonists may be due to increased binding of released fibrinogen. Thus, platelets freed from a thrombus may have increased responsiveness to low concentrations of aggregating agents other than thrombin. These results provide further support for the use of inhibitors of platelet reactions in conjunction with administration of fibrinolytic agents.

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