The Effect of the Phospholipase Inhibitor Mepacrine on Platelet Aggregation, the Platelet Release Reaction and Fibrinogen Binding to the Platelet Surface

1981 ◽  
Vol 45 (03) ◽  
pp. 257-262 ◽  
Author(s):  
P D Winocour ◽  
R L Kinlough-Rathbone ◽  
J F Mustard
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Surface ◽  
Release Reaction ◽  
Fibrinogen Binding ◽  
Platelet Release

SummaryWe have examined whether inhibition by mepacrine of freeing of arachidonic acid from platelet phospholipids inhibits platelet aggregation to collagen, thrombin or ADP, and the release reaction induced by thrombin or collagen. Loss of arachidonic acid was monitored by measuring the amount of 14 C freed from platelets prelabelled with 14 C-arachidonic acid. Mepacrine inhibited 14 C loss by more than 80% but did not inhibit thrombin-induced platelet aggregation and had a small effect on release. ADP-induced platelet aggregation did not cause 14 C loss. Mepacrine inhibited ADP-induced platelet aggregation by inhibiting the association of fibrinogen with platelets during aggregation. The effect of mepacrine on fibrinogen binding could be considerably decreased by washing the platelets but the inhibition of 14 C loss persisted. Platelets pretreated with mepacrine and then washed show restoration of aggregation to collagen. Thus, mepacrine has two effects; 1. it inhibits phospholipases, 2. it inhibits fibrinogen binding. Freeing of arachidonic acid is not necessary for platelet aggregation or the release reaction.

Inhibition Of Platelet Release Reaction By Cytidine Monophosphate (CMP): Correlation With Inhibition Of Membrane Sialyltransferase Activity

1981 ◽  
Author(s):  
K K Wu ◽  
C S L Ku
Keyword(s):  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Dose Response ◽  
Response Curve ◽  
Inhibitory Effect ◽  
Dose Response Curve ◽  
Platelet Surface ◽  
Release Reaction ◽  
Significant Difference ◽  
Platelet Release

To provide further evidence for the contention that platelet surface sialyltransferase plays a major role in platelet release reaction, we evaluated the effect of CMP, a sialyltransferase inhibitor, on platelet aggregation and release. CMP exerted a dose-related inhibitory effect (IC5050=1.5mM) on the basal enzyme activity of intact washed platelets or membrane preparation. It blocks the enzyme stimulation by collagen, thrombin, ADP and U46619, a thromboxane A2 agonist. Serial experiments were then carried out in a lumiaggregometer to determine its effect on platelet release and aggregation. Pretreatment of platelet rich plasma or washed platelet suspension with CMP resulted in a significant reduction of ATP release induced by thrombin, collagen, ADP, U46619 and arachidonate. The dose-response curve of release inhibition was parallel to the enzyme inhibition. Platelet aggregation induced by ADP, collagen and sodium arachidonate was significantly inhibited by CMP but the dose-response curve shifted to the right. Platelet aggregation induced by thrombin or U46619 was unaffected. To determine whether the inhibitory effect of CMP might be mediated through stimulation of adenylate cyclase, platelet cyclic AMP content was determined by radioimmunoassay. There was no significant difference in the cyclic AMP content between CMP-treated and control platelets. CMP did not cause liberation of lactic dehydrogenase from platelets. These findings clearly indicate that inhibition of release reaction by CMP is linked to the inhibition of surface sialyltransferase and is independent of cyclic AMP. This study confirms the notion that platelet membrane sialyltransferase is involved in the initiation of platelet release reaction.

Release, Aggregation and Lysis of Human Platelets by Antilymphocyte Globulin and Antiplatelet Serum

1976 ◽  
Vol 36 (02) ◽  
pp. 411-423 ◽  
Author(s):  
Nicholas Lekas ◽  
J. C Rosenberg
Keyword(s):  
Platelet Aggregation ◽  
Gamma Globulin ◽  
Human Platelets ◽  
Plasma Medium ◽  
Release Reaction ◽  
Clinical Events ◽  
Thrombotic Complications ◽  
Platelet Release ◽  
Free Media

SummaryHuman platelets labeled with 51Cr were used to determine the contribution made by platelet lysis to the platelet release reaction and platelet aggregation induced by rabbit antihuman platelet serum (APS) and equine antihuman thymocyte globulin (ATG). Platelets were tested in both plasma (PRP) and non-plasma containing media. Antibodies directed against platelets, either as APS or ATG, induced significant amounts of platelet release and aggregation, as well as some degree of lysis, in the absence of complement. The presence of complement increased platelet lysis and aggregation, but not the release reaction. Non-immune horse gamma globulin produced different responses depending upon whether platelets were investigated in PRP or non-plasma containing media. Aggregation was seen in the latter but not the former. These differences can be explained by the presence of plasma components which prevent non-specific immune complexes from causing platelet aggregation. Since platelets in vivo are always in a plasma medium, one must be wary of utilizing data from platelet studies in synthetic plasma-free media as the basis of explaining clinical events. These observations demonstrate at least two, and possibly three, different mechanisms whereby ATG could activate platelets causing thrombotic complications and thrombocytopenia, i.e., via 1) specific and, 2) non-specific non-lytic pathways and 3) a lytic pathway.

THROMBOSPONDIN SPECIFICALLY INTERACTS WITH AMINO ACID SEQUENCES WITHIN THE A α- AND B β- CHAINS OF FIBRINOGEN

1987 ◽  
Author(s):  
Theresa Bacon-Baguley ◽  
Suzanne Kendra-Franczak ◽  
Daniel Walz
Keyword(s):  
Platelet Aggregation ◽  
Cyanogen Bromide ◽  
Gel Filtration ◽  
Amino Acid Sequences ◽  
Reverse Phase ◽  
Platelet Surface ◽  
Chain Component ◽  
Fibrinogen Binding ◽  
Platelet Aggregate ◽  
Single Peptide

Thrombospondin (TSP) is responsible for the secretion-dependent phase of platelet aggregation. The mechanism of this action is believed to be through the binding of TSP to fibrinogen, resulting in the stabilization of the platelet aggregate. It has been established that the binding of fibrinogen to the platelet surface is dependent upon peptide sequences present, respectively, in the Aa- and y-chains. We have hypothesized that the binding of TSP to fibrinogen is also dependent upon unique fibrinogen peptide sequences. To test this hypothesis we have examined the interaction of TSP and f.ih.r.inogen. using..a.-blat-b.inding assaLy of reduced fibrinogen, the separated fibrinogen chains, selected fibrinogen domains or peptides generated from cyanogen bromide cleaved chains. Iodinated TSP bound specifically to the Aα - and Bβ - chains. Binding to these chains was calcium independent, mutually exclusive and could be blocked either by preincubation of TSP with 9.4 μ M fibrinogen or by preincubation of fibrinogen with 1.1 nM thrombospondin. TSP bound to the D and DD plasmin fragment of fibrinogen; TSP interacted exclusively with the B-chain component of the DD fragment. The cyanogen bromide fragments of the separated Aα - and Bβ -chains were resolved through a combination of gel filtration and reverse-phase chromatography. TSP was found to bind to a single peptide within these fibrinogen chains. These studies demonstrate that thrombospondin interacts with at least two distinct sites on fibrinogen, and these sites differ from those already described for fibrinogen binding to platelets.

Extracellular fibrinogen binding protein, Efb, from Staphylococcus aureus binds to platelets and inhibits platelet aggregation

2004 ◽  
Vol 91 (04) ◽  
pp. 779-789 ◽  
Author(s):  
Oonagh Shannon ◽  
Jan-Ingmar Flock
Keyword(s):  
Platelet Aggregation ◽  
Potent Inhibitor ◽  
Specific Binding ◽  
Binding Protein ◽  
Dependent Manner ◽  
Platelet Surface ◽  
Putative Receptor ◽  
Activated Platelets ◽  
Fibrinogen Binding ◽  
Dose Dependent

Summary S. aureus produces and secretes a protein, extracellular fibrinogen binding protein (Efb), which contributes to virulence in wound infection. We have shown here that Efb is a potent inhibitor of platelet aggregation. Efb can bind specifically to platelets by two mechanisms; 1) to fibrinogen naturally bound to the surface of activated platelets and 2) also directly to a surface localized component on the platelets. This latter binding of Efb is independent of fibrinogen. The specific binding of Efb to the putative receptor on the platelet surface results in a stimulated, non-functional binding of fibrinogen in a dose dependent manner, distinct from natural binding of fibrinogen to platelets. The natural binding of fibrinogen to GPIIb/IIIa on activated platelets could be blocked by a monoclonal antibody against this integrin, whereas the Efb-mediated fibrinogen binding could not be blocked. The enhanced Efb-dependent fibrinogen binding to platelets is of a nature that does not promote aggregation of the platelets; instead it inhibits aggregation. The anti-thrombotic action of Efb may explain the effect of Efb on wound healing, which is delayed in the presence of Efb.

Pyridoxal phosphate inhibition of platelet function

1980 ◽  
Vol 238 (1) ◽  
pp. H54-H60 ◽  
Author(s):  
E. Kornecki ◽  
H. Feinberg
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Function ◽  
Pyridoxal Phosphate ◽  
Shape Change ◽  
Serotonin Release ◽  
Platelet Surface ◽  
Partial Inhibition ◽  
Induced Aggregation

The effect of pyridoxal phosphate (PLP) on human platelet function in vitro was studied. PLP inhibited adenosine diphosphate (ADP)-induced shape change, aggregation, and the potentiation by ADP of arachidonic acid-induced aggregation. This inhibition could easily be reversed by increasing concentrations of ADP or by removing PLP. The addition of sodium borohydride to PLP-treated platelets produced an irreversible inhibition of ADP aggregation. Thus it is possible that PLP inhibited ADP-induced platelet function by forming a Schiff base with platelet-surface amino groups. PLP also produced a partial inhibition of platelet aggregation to epinephrine, arachidonic acid, A23187, and a dose-dependent inhibition of [14C]serotonin release to epinephrine and arachidonic acid. PLP did not inhibit [14C]serotonin release to A23187, nor did it suppress arachidonic acid-induced malondialdehyde production. The conclusion is drawn that the partial inhibition by PLP of platelet aggregation observed to epinephrine, arachidonic acid, and A23187 resulted from PLP's inhibition of the effect of released ADP.

scholarly journals Effect of anti-P1A1 antibody on human platelets. II. Mechanism of the complement-dependent release reaction

Blood ◽  
1979 ◽  
Vol 53 (4) ◽  
pp. 578-587 ◽  
Author(s):  
AD Schreiber ◽  
DB Cines ◽  
C Zmijewski ◽  
RW Colman
Keyword(s):  
Human Platelets ◽  
Metabolic Energy ◽  
Igg Antibody ◽  
Platelet Surface ◽  
Release Reaction ◽  
Platelet Release ◽  
High Concentrations ◽  
Antibody Levels ◽  
Pharmacologic Agents

Abstract We studied the mechanism by which complement activated by anti-P1A1 antibody elicits the platelet release reaction. Anti-P1A1 antibody mediates its action through the classic complement pathway, and its effect depends on the concentration of IgG antibody on the platelet surface. At relatively high concentrations of anti-P1A1 antibody the release reaction was mediated by a mechanism in part independent of extracellular ADP and metabolic energy and inhibited by only high concentrations of PGE1. However, at lower concentrations of anti-P1A1 antibody the release reaction was dependent on metabolic energy and ADP, and the concentration of PGE1 required to inhibit platelet release was similar to that required to inhibit ADP-induced release. The cyclooxygenase inhibitor acetylsalicylic acid inhibited the release reaction at all nonlytic antibody levels studied. None of the agents studied inhibited the induction of platelet lysis by very high concentrations of anti-P1A1 antibody, and no effect of antibody on platelet 14C-serotonin uptake was observed at antibody concentrations that did not mediate direct in vitro alteration. These studies suggest the possible use of pharmacologic agents in modifying some complement- mediated platelet alterations.

Requirement Of Fibrinogen And Calcium For Inter-Platelet Bridges In Platelet Aggregation: A Hypothesis

1981 ◽  
Author(s):  
Elizabeth Kornecki ◽  
Stefan Niewiarowski
Keyword(s):  
Platelet Aggregation ◽  
Binding Sites ◽  
Proteolytic Enzymes ◽  
Divalent Cations ◽  
Platelet Surface ◽  
Fibrinogen Binding ◽  
Platelet Aggregates ◽  
High Concentrations ◽  
Induced Aggregation ◽  
Aggregation Of Platelets

Fibrinogen and calcium are required for the aggregation of platelets stimulated by ADP or pre-treated with proteolytic enzymes. Specific platelet surface fibrinogen binding sites (receptors) are exposed after platelets are stimulated by ADP or pre-treated with Chymotrypsin or pronase. It has previously been shown in our laboratory that an intact, symmetrical fibrinogen molecule is essential for fibrinogen binding and fibrinogen-induced aggregation of both ADP-stimulated and proteolytically-treated platelets. Here we propose that the mechanism by which fibrinogen and calcium aggregate platelets is by forming inter-platelet bridges linking the fibrinogen receptors of adjacent platelets together. In support of this proposition are the following new lines of evidence: 1) The fibrinogen-induced aggregations of ADP-stfiliulated or proteolytically-treated platelets are inhibited by high concentrations of fibrinogen (Ki=2.6 and 8.5 × 10 5M, respectively). The fibrinogen binding sites on adjacent platelets, at these concentrations, would be saturated by fibrinogen and therefore no inter-platelet fibrinogen bridges could be formed to hold the platelets together. 2) ADP-stimulated or chymotrypsin-treated platelets aggregated by fibrinogen are deaggregated by Chymotrypsin or pronase and this deaggregation coincides with the loss of 125I-fibrinogen from the platelet surface. 3) Preincubation of platelets with EDTA results in inhibition of both platelet aggregation and 125I-fibrinogen binding. Following the aggregations of ADP-stimulated or of chymotrypsin-treated platelets by fibrinogen, the addition of EDTA to the platelet aggregates results in both their deaggregation and their loss of bound 125I-fibrinogen. Thus it appears that divalent cations, especially calcium, are essential for the formation of fibrinogen-linked platelet aggregates.

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