Platelet Aggregating Factor Research Articles

Platelet aggregating IgG antibody to platelet surface glycoproteins associated with thrombosis and thrombocytopenia

Previously described platelet-aggregating antibodies associated with thrombosis and thrombocytopenia required heparin for their in vivo and in vitro expression. We have observed a patient with thrombosis who became thrombocytopenic during heparin treatment, but who suffered further thrombotic events and continued thrombocytopenia for 3 months after heparin withdrawal. The patient's plasma contained a potent platelet aggregating factor reactive with both his own and normal platelets in the absence of heparin. It also caused [14C]serotonin secretion from labelled platelets from normal donors and patients with either Glanzmann's thrombasthenia or Bernard-Soulier syndrome. This factor was an IgG and was neutralized by antibody specific for IgG lambda light chains. While the patient was thrombocytopenic an IgG paraprotein with lambda light chains was detected by isoelectrofocussing. After corticosteroid treatment it disappeared and the patient recovered. The active, but not the recovery serum contained IgG which immunoprecipitated a glycoprotein with characteristics of Glycoprotein IV from platelets labelled with Na[3H]BH4/periodate. Thus platelet-aggregating IgG antibodies with direct specificity for platelet surface glycoproteins may be associated with thrombosis/thrombocytopenia.

Thrombopénie induite par l'héparine et chirurgie cardiaque sous circulation extracorporelle

A case of mitral and aortic valvular replacement combined with double coronary artery bypass grafting is reported in a 64-year-old woman who presented with a history of heparin-induced thrombocytopenia. The use of a conventional dose of heparin did not induce the formation of a plasma platelet-aggregation factor. The necessity of postoperative anticoagulation was ensured by the prescription of antivitamin K, started on the morning of the operative day.

Multifactorial genesis of enhanced platelet aggregability in patients with nephrotic syndrome

Platelet aggregation, beta-thromboglobulin (beta-TG) and platelet factor 4 (PF 4) release and thromboxane B2 (TxB2) formation in stimulated platelet-rich plasma were investigated in 13 patients with nephrotic syndrome who had normal serum creatinine levels (creatinine clearance greater than 70 ml/min/1.73 m2). In contrast to 13 sex- and age-matched controls, spontaneous platelet aggregation only occurred in patients with nephrotic syndrome with correlation to serum albumin and plasma fibrinogen levels. The EC50 (estimated concentration of aggregating agent to cause half maximum velocity of primary aggregation) for ADP and collagen and threshold concentration of arachidonic acid (threshold AA) were decreased in patients with nephrotic syndrome, reflecting a hyperaggregable state. In patients with nephrotic syndrome EC50 ADP values were significantly correlated to serum albumin, serum cholesterol and plasma fibrinogen, however, EC50 collagen or threshold AA did not correlate to these parameters. Plasma beta-TG levels were increased in patients, whereas plasma PF 4 levels were not significantly changed in patients compared to controls. In vitro TxB2 formation was elevated in patients only after stimulation with AA. Nevertheless, after stimulation with collagen and ADP, TxB2 formation was unchanged in patients compared to controls. Platelet hyperaggregability in nephrotic patients was confirmed in our study. However, unchanged thromboxane B2 formation after collagen stimulus as well as missing correlations between EC50 collagen or threshold AA and serum albumin were contradictory to the hypothesis that enhanced AA availability due to hypoalbuminemia is responsible for platelet hyperaggregability. Platelet hyperaggregability in terms of EC50 ADP being associated with serum albumin levels as well as to serum cholesterol and plasma fibrinogen indicate a multifactorial genesis.

Thrombotic Thrombocytopenic Purpura: Successful Treatment Unlocks Etiologic Secrets

The cause of platelet agglutination in thrombotic thrombocytopenic purpura has been an enigma. Current evidence indicates that the interaction of platelets with a platelet-aggregating factor or unusually large multimers of factor VIII: von Willebrand factor, or both, may cause the abnormal platelet agglutination. Recent success in the treatment of thrombotic thrombocytopenic purpura with intravenous infusion of immunoglobulin suggests that the abnormal platelet agglutination in thrombotic thrombocytopenic purpura may reflect a deficiency of immunoglobulins that normally inhibit platelet-aggregating factors or large multimers of factor VIII: von Willebrand factor.

Regulation of Na+ and K+ contents in rat thymocytes

A modified nystatin technique allowed the investigation of the initial rate of Na+ efflux as a function of internal Na+ content under steady-state conditions in rat thymocytes. This kinetic study showed that 1) ouabain-sensitive Na+ efflux as a function of internal Na+ can be adjusted by a three-sites kinetic model, with a maximal pump rate of 581 +/- 79 mmol.l cells-1.h-1 and an apparent dissociation constant for internal Na+ of 10.0 +/- 1.0 mmol/l cells (mean +/- SE of 3 experiments), 2) bumetanide-sensitive Na+ efflux was extremely low compared with the pump efflux (approximately 1%), and 3) ouabain- and bumetanide-resistant Na+ efflux was almost a linear function of internal Na+ content (as expected for a Na+ leak). This "all-pump" mechanism of thymocyte Na+ regulation was confirmed by non-steady-state experiments showing that 1) ouabain induced a rapid net Na+ gain and K+ depletion in fresh thymocytes and completely blocked the recovery of normal cation contents in Na+-loaded-K+-depleted thymocytes, and 2) bumetanide was unable to modify thymocyte Na+ and K+ contents. Na+ extrusion by Na+-loaded thymocytes was unaffected by prostaglandin E2, isoproterenol, or platelet-aggregating factor (PAF) and was slightly impaired in the adult spontaneously hypertensive rat of the Okamoto strain (10% lower rate constant for net Na+ extrusion, P less than 0.05). Concerning cell Na+ regulation, our results do not support the concept that rat thymocytes are more representative of vascular cells than enucleated erythrocytes.

Inhibition of cyclooxygenase-independent platelet aggregation by sodium salicylate

The effect of acetylsalicylic acid (ASA) on platelet aggregation (PA) and thromboxane A 2 (TxA 2) formation was investigated in vitro and ex vivo after 1 g or 300 mg ASA administration to healthy subjects. 50–100 μM ASA inhibited PA by single aggregating agent such as platelet aggregating factor (PAF) or epinephrine and reduced to ⩽5% of control platelet TxB 2 formation, but did not influence PA by epinephrine plus PAF. The latter was inhibited by increasing ASA concentration. In samples incubated with 100 μM ASA and stimulated with epinephrine plus PAF, PA could be inhibited by the addition of 100–300 μM sodium salicylate. After 300 mg-1 g ASA administration to healthy subjects, the inhibition of PA by epinephrine plus PAF was more marked by highest doses of ASA. This study suggests that aspirin inhibits PA with a cy clooxygenase-independent mechanism; this effect is mediated, at least in vitro, by salicylic acid.

Relationships between chemical structure and inhibition of ADP-stimulated human thrombocyte release of serotonin and platelet factor 4

The inhibitory potencies of carbamoylpiperidinoalkane and N-alkylnipecotoylpiperazine derivatives on ADP-stimulated human blood platelet aggregation, serotonin (5-HT) release and platelet factor 4 (PF-4) release were evaluated. The procedure was designed to allow concurrent determination of all three sets of values. Most compounds were more than twice as potent in blocking PF-4 (X = 91 +/- 1 (S.E., n = 7)%) compared to their inhibition of 5-HT (X = 38 +/- 1(S.E., n = 6)%) release; the one compound which failed to meet these criteria was still decidedly more powerful in impeding PF-4 than 5-HT release. Since the compounds' platelet aggregation-inhibitory values were within the same range as their 5-HT release-blocking potencies, but had a strikingly greater impact in arresting PF-4 release, it is suggested that the platelet plasma membrane and the lining enveloping the dense bodies may share certain commonalities, while the sheathing encasing the alpha-granules may differ from both in a tangible manner.

The biochemical pharmacology of fenofibrate.

Fenofibrate is metabolized in several stages. First, the carboxyl ester moiety is cleaved by hydrolysis, resulting in fenofibric acid, the main pharmacologically active compound. Fenofibric acid, in turn, undergoes carbonyl reduction, resulting in a pharmacologically active metabolite referred to as reduced fenofibric acid. Both fenofibric acid and reduced fenofibric acid may be conjugated to form glucuronides. There are important species differences in the metabolism and elimination patterns of fenofibrate. In the rat and dog, fenofibric acid and reduced fenofibric acid are the principal metabolites. In humans, the glucuronide of fenofibric acid is predominant. In the rat and dog, approximately 70-80% of fenofibrate and its metabolites are recovered in the feces, whereas in humans approximately 65% of the dose is excreted in the urine. Several mechanisms contribute to fenofibrate's hypolipidemic action, including inhibition of fatty acid synthesis, stimulation of fatty acid beta-oxidation, inhibition of triglyceride synthesis, and enhancement of lipoprotein lipase activity. Fenofibrate's hypocholesterolemic action is a result of both decreased biosynthesis of cholesterol through inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and increased low-density lipoprotein (LDL) clearance via modulation of hepatic LDL receptors. Fenofibrate also has three other actions that may result in the prevention or at least slowing of atherogenesis, namely inhibition of cholesterol esterification, platelet aggregation, and platelet-derived growth factor. The native acyl glucuronide of fenofibric acid is very stable, and is unlikely to have any toxic potential. Although the elimination half-life of fenofibrate is prolonged in the elderly and in patients with impaired hepatic function, the area under the curve and its clearance are not altered because of compensatory changes in the volume of distribution.

Arterial Thrombosis Associated with Immune Thrombocytopenia: Presence of a Platelet Aggregating IgG Synergistic with Thrombin and Adrenalin

We report the case of a 50-year-old lady who presented with arterial thrombosis in the setting of thrombocytopenia. Investigations confirmed the diagnosis of idiopathic thrombocytopenic purpura. A spontaneous platelet aggregating factor (SPAF) was isolated from the immunoglobulin fraction of the patient's plasma. The isolated IgG irreversibly aggregated platelet-rich plasma and washed platelets, an effect abolished by pretreating the platelets with aspirin. The activity of the IgG was greatly enhanced by subaggregatory concentrations of thrombin and adrenalin and was localized to the F(ab')2 of the molecule. Plasmapheresis in combination with anti-platelet therapy resulted in an increase in the patient's platelet count, reduced platelet aggregating activity of plasma and significant clinical improvement. We suggest that the presence of this platelet aggregating IgG contributed to the development of thrombosis in our patient and postulate that a similar factor may explain the paradox of thrombosis observed in a select group of thrombocytopenic patients.

Venom from southern copperhead snake ( Agkistrodon contortrix contortrix). II. A unique phospholipase A 2 that induces platelet aggregation

J. Takagi, F. Sekiya, K. Kasahara, Y. Inada and Y. Saito. Venom from southern copperhead snake ( Agkistrodon contortrix contortrix). II. A unique phospholipase A 2 that induces platelet aggregation. Toxicon 26, 199 – 206, 1988. — A platelet aggregation factor was purified from the venom of southern copperhead snake ( Agkistrodon controtrix contortrix) by DEAE-cellulose ionexchange chromatography, precipitation with ammonium sulfate, affinity chromatography using bovine serum albumin as ligand, and gel filtration on Cellulofine GCL-2000. It had molecular weights of 11,000 and 14,000, as determined by gel filtration chromatography and sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS - PAGE), respectively. It consists of a single polypeptide, and was identified as a phospholipase A 2. It was quite resistant to heat and various denaturing reagents including urea and SDS. It lost both phospholipase A 2 activity and platelet aggregating activity upon modification of histidine residue(s) with p-bromophenacyl bromide. Its specificity towards the β-position of phospholipid in esterolytic reaction was confirmed by gas - liquid chromatography using a pure synthetic phosphatidylcholine. Platelet aggregation by this phospholipase A 2 was completely inhibited by prostacyclin, but was little inhibited by aspirin which indicates almost no direct participation of released arachidonic acid in the aggregation mechanism.

Platelet-type von willebrand disease platelet aggregating factor: A novel functional assay of von willebrand factor

Blood platelets from patients with platelet-type von Willebrand disease (vWD) aggregate upon the addition of human von Willebrand factor (vWf) in the absence of ristocetin or other stimulating factors. We measured quantitatively the ability of vWf to induce directly aggregation of platelet-type vWD platelets (platelet-type vWD platelet aggregating factor [PT-PAF]). Cryoprecipitate and factor VIII concentrates were used as a source of vWf of various multimeric composition. The PT-PAF activity was dependent on the multimer size of vWf, like in the case of ristocetin cofactor (RCof) activity. However, PT-PAF activity was not equivalent to RCof activity and the relative PT-PAF/RCof ratio ranged from 1.00 to 0.18 in the materials studied. The preparations containing the higher-molecular-weight multimers had higher PT-PAF/RCof ratio. These findings suggest that PT-PAF activity is a functional expression of more highly polymerized multimers of vWf as compared with RCof activity. Measurement of PT-PAF would serve as a novel functional assay of vWf.

Heparin-associated Thrombocytopenia in Maintenance Hemodialysis Patients

Thrombocytopenia associated with the presence of a heparin-dependent platelet aggregating factor developed in two patients after hemodialysis with heparin. It resolved in one patient after heparin was stopped; but persisted in the other during a two-week heparin-free period and intermittently thereafter. We suggest that when heparin causes thrombocytopenia in dialysis patients the heparin should be stopped whenever possible, but this may not be necessary in all patients.

Relationship between platelet aggregating factor and von Willebrand factor in thrombotic thrombocytopenic purpura.

The pathophysiology of the platelet thrombotic disorder, thrombotic thrombocytopenic purpura (TTP), is not well understood. Two apparently unrelated laboratory abnormalities have recently been described in patients with TTP: a platelet aggregating factor and abnormalities in von Willebrand factor (vWF). Although an interaction between these two abnormalities has been postulated to participate in the disease, this has not been proved. In this report we describe studies on a patient with relapsing TTP. These studies demonstrate that a consistent relationship exists between the platelet aggregating factor present in the patient's serum and vWF. The patient had chronic low-grade thrombocytopenic and schistocytic haemolytic anaemia that could be temporarily cured by infusions of plasma and certain other blood products. During acute exacerbations of the illness, a platelet aggregating factor was detectable in the patient's serum and this was associated with the loss of the larger multimers of vWF. During remissions of the illness, abnormally large multimers of vWF were present. The results of this study support the concept that a platelet aggregating factor plus large multimers of vWF participate in the acute platelet thrombi that characterize TTP.

Relevance of platelet factor four (PF4) plasma levels in multiple sclerosis.

In order to study the role of platelets in Multiple Sclerosis (MS) we assessed, in a group of patients during a quiescent phase of the disease, the plasma levels of beta-thromboglobulin (beta-TG) and platelet factor four (PF4) both in absence of treatment and during administration of aspirin (ASA) at the dose of 50 mg/daily. In the MS patients studied, the basal plasma levels of beta-TG and PF4 were significantly higher than in control subjects. The increase in the beta-TG plasma levels occurred independently of the age, sex and severity of the disease, whereas the modification in the PF4 plasma levels was significantly correlated with the severity of the disease. Administration to the patients of ASA, at the dose that does not affect prostacyclin production, determined a decrease of beta-TG in 77% of the patients. Mean PF4 plasma levels remained unchanged. These results suggest that PF4 in the plasma of MS patients may originate not only from the platelets but also from the mast cells following platelet aggregating factor (PAF) stimulation and immunocomplex formation.

Control of the proliferation and differentiation of GEJ under platelet aggregating factor treatment

Control of the proliferation and differentiation of GEJ under platelet aggregating factor treatment

ChemInform Abstract: Resolution of Oxiranes. Application to the Synthesis of the Platelet Aggregation Factor.

AbstractThe racemic epoxides (I) are optically resolved via the diastereomeric sulfonium tartrates (IV).

A Novel Platelet Aggregating Factor Found in a Patient With Defective Collagen-Induced Platelet Aggregation and Autoimmune Thrombocytopenia

We found a novel platelet aggregating factor in a patient with steroid-responsive immune thrombocytopenic purpura that is associated with defective collagen-induced platelet functions. The aggregating factor and platelet functions were analyzed. The patient, a 58-year-old female, had purpura and prolonged bleeding time despite adequate platelet counts (greater than 140,000/microL) after steroid therapy. The patient's platelets responded normally to all agonists except collagen. Platelet adhesion to collagen fibrils was decreased. The patient's plasma induced irreversible aggregation and ATP release in normal platelet-rich plasma (PRP). This platelet aggregating factor was found in F(ab')2 fragments of the patient's IgG, which caused thromboxane B2 synthesis, elevation of cytoplasmic Ca2+ levels, and phosphorylation of 40 kDa protein in normal platelets. Platelet aggregation by the patient's IgG was inhibited by prostacyclin, dibutyryl cAMP, diltiazem, disodium ethylenediaminetetraacetate, and antimycin A plus iodoacetate, but ADP scavengers, cyclo-oxygenase inhibitors, and heparin had little or no effect. The aggregating activity of the patient's IgG absorbed to and eluted from normal platelets. The patient's Fab fragments did not induce platelet aggregation in eight of ten normal PRP but specifically inhibited aggregation induced by collagen and by the patient's IgG. The major component of an immunoprecipitate made with the patient's IgG from radiolabeled membrane proteins of normal platelet extract had a 62 kDa mol wt, while no such precipitate appeared in extracts of the patient's platelets. These results indicated that platelet aggregation by the patient's IgG was induced by the reaction of an antibody with a specific antigen on the normal platelet membrane through stimulus-response coupling. This antigen may be a collagen receptor on the platelet, most likely a polypeptide of 62 kDa under reducing condition. The defect of collagen-induced aggregation of the patient's platelets seemed to be due to alteration of the membrane protein related to this putative collagen receptor.

A novel platelet aggregating factor found in a patient with defective collagen-induced platelet aggregation and autoimmune thrombocytopenia

We found a novel platelet aggregating factor in a patient with steroid- responsive immune thrombocytopenic purpura that is associated with defective collagen-induced platelet functions. The aggregating factor and platelet functions were analyzed. The patient, a 58-year-old female, had purpura and prolonged bleeding time despite adequate platelet counts (greater than 140,000/microL) after steroid therapy. The patient's platelets responded normally to all agonists except collagen. Platelet adhesion to collagen fibrils was decreased. The patient's plasma induced irreversible aggregation and ATP release in normal platelet-rich plasma (PRP). This platelet aggregating factor was found in F(ab')2 fragments of the patient's IgG, which caused thromboxane B2 synthesis, elevation of cytoplasmic Ca2+ levels, and phosphorylation of 40 kDa protein in normal platelets. Platelet aggregation by the patient's IgG was inhibited by prostacyclin, dibutyryl cAMP, diltiazem, disodium ethylenediaminetetraacetate, and antimycin A plus iodoacetate, but ADP scavengers, cyclo-oxygenase inhibitors, and heparin had little or no effect. The aggregating activity of the patient's IgG absorbed to and eluted from normal platelets. The patient's Fab fragments did not induce platelet aggregation in eight of ten normal PRP but specifically inhibited aggregation induced by collagen and by the patient's IgG. The major component of an immunoprecipitate made with the patient's IgG from radiolabeled membrane proteins of normal platelet extract had a 62 kDa mol wt, while no such precipitate appeared in extracts of the patient's platelets. These results indicated that platelet aggregation by the patient's IgG was induced by the reaction of an antibody with a specific antigen on the normal platelet membrane through stimulus- response coupling. This antigen may be a collagen receptor on the platelet, most likely a polypeptide of 62 kDa under reducing condition. The defect of collagen-induced aggregation of the patient's platelets seemed to be due to alteration of the membrane protein related to this putative collagen receptor.

Management of Patients with Heparin-Associated Thrombocytopenia and Thrombosis Requiring Cardiac Surgery

Heparin-associated thrombocytopenia and thrombosis (HATT) is a serious complication of heparin therapy that results in intravascular platelet aggregation with arterial or venous thrombosis. Platelet aggregation to heparin in vitro is used to confirm the diagnosis. Cessation of heparin therapy with avoidance of reexposure to heparin is an important principle in the management of HATT. However, certain patients with HATT may require reexposure to heparin for emergency cardiac operations requiring cardiopulmonary bypass while still demonstrating positive in vitro platelet aggregation with heparin. The present report describes the management of 2 such patients. In each patient aspirin was shown to inhibit platelet aggregation to heparin in vitro; therefore, aspirin and dipyridamole were administered to each patient before heparin reexposure and continued throughout the perioperative period. Cardiopulmonary bypass with full heparinization was achieved without thrombotic or hemorrhagic complications in both patients. Despite the presence of a heparin-dependent platelet-aggregating factor in the plasma of these 2 patients, inhibition of platelet aggregation with aspirin and dipyridamole allowed uneventful reexposure to heparin.

Studies Investigating Platelet Aggregation and Release Initiated by Sera From Patients With Thrombotic Thrombocytopenic Purpura

Abstract Many patients with thrombotic thrombocytopenic purpura (TTP) have a platelet aggregating factor in their serum that may be pathologically linked with the disease process. To help characterize the type of platelet aggregation and platelet release induced by the sera from seven TTP patients, we measured the ability of a variety of inhibitors of platelet function as well as the ability of monoclonal antibodies (MoAbs) against platelet glycoproteins to inhibit TTP sera-induced platelet aggregation and release. These results were compared with the ability of the same inhibitors to block platelet aggregation induced by ristocetin, collagen, ADP, thrombin, and IgG-immune complexes. Monoclonal antibody directed against platelet glycoprotein Ib totally inhibited ristocetin-induced aggregation and release but had no effect on aggregation and release induced by the TTP sera or by any of the other platelet agonists. However, the MoAb against glycoproteins IIb/IIIa inhibited aggregation and release caused by TTP sera as well as by collagen, thrombin, and ADP but had no effect on aggregation and release induced by ristocetin. The aggregating activity could be abolished by heparin but not by the serine protease inhibitor PMSF (1 mmol/L). And although monomeric human IgG and purified Fc fragments of IgG inhibited IgG-immune complex-induced aggregation and release, they had no effect on TTP sera-induced aggregation and release nor on aggregation and release induced by any of the other agonists. Consistent with these in vitro studies showing no effect of IgG were the in vivo observations that intravenous (IV) IgG was without effect when administered to three patients with TTP. This study indicates that although a von Willebrand factor (vWF)-rich preparation of cryoprecipitate enhances the in vitro platelet aggregation and release caused by sera from the seven TTP patients we studied, the pathway of aggregation and release is not via platelet glycoprotein Ib. Also the aggregating factor of TTP sera is not neutralized in vitro or in vivo by IgG.