Enhancement of platelet factor 3 activity in vitro and in vivo

Incubation of rabbit platelet-rich plasma with bacterial endotoxin results in activation of platelet factor 3, a precursor of blood thromboplastin. This platelet-endotoxin interaction is dose- and temperature-dependent, and is similar to the effects of antigen-antibody union in the presence of platelets. Injection of endotoxin intravenously is associated with a transient increase in platelet factor 3. Since platelet factor 3 can be demonstrated in platelet-poor plasma as well as platelet-rich plasma after endotoxin injection, it seems likely that an actual transfer of factor 3 from platelets to plasma occurs and that this activity is then rapidly inactivated or cleared from the blood stream.

Plasma platelet aggregating factor and platelet aggregation studies in pre-eclampsia

OBJECTIVE

A plasma platelet aggregation factor (PAF) has been implicated in the pathogenesis of platelet activation in thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). Similar mechanism may be operative in pre-eclampsia.

METHODS

Coagulation profile and detailed in vitro platelet aggregation with various agonists were studied. PAF was demonstrated by spontaneous aggregation of normal platelets with test plasma. Non-parametric Wilcoxon's rank sum test and Krauskal Wally's one way analysis of variance were applied.

RESULT

Twenty-two pre-eclamptic patients and 20 normal pregnant controls were studied. Anti-thrombin III levels were within normal range and fibrin degradation products were only border line raised ( > 10 < 40 micrograms/ml) in 14 (65.4%) patients. In vitro platelet aggregation was abnormal in 17 (77.2%) patients. PAF was demonstrable in 10 of 22 (45.5%) patients.

CONCLUSION

Platelet aggregation studies indicated the presence of both activated (hyperaggregable) as well as exhausted (hypoaggregable) platelets in circulation. PAF demonstrable in 45.4% pre-eclampsia patients would suggest its role in the pathogenetic mechanism of platelet activation in this disease.

Biological properties of the venom of the Papuan black snake (Pseudechis papuanus): presence of a phospholipase A2 platelet inhibitor

The whole venom of Pseudechis papuanus, in addition to its anticoagulant activity, powerfully inhibited platelet aggregation induced by ADP, adrenaline, collagen, ristocetin and thrombin. High levels of phospholipase A2 (PLA2) activity were detected. A mild procoagulant activity was also observed. Following exposure of platelets to P. papuanus venom, platelet factor 3 (procoagulant platelet phospholipid) showed decreased cofactor activity in factor X activation by Russell's viper, venom suggesting that the venom PLA2 plays a major role in the inhibition of the coagulation mechanism. In vivo rodent assays confirmed the inhibitory effect on platelets and the haemorrhagic and neurotoxic activities. It is possible that PLA2 is responsible for anticoagulation and that this, combined with the effect on platelet aggregation, a mild procoagulant and a moderately potent haemorrhagin, is responsible for the haemorrhagic diathesis observed in systemically envenomed patients. Polyvalent (Australia-Papua New Guinea) Commonwealth Serum Laboratories antivenom, currently used for clinical treatment of snakebite in Papua New Guinea, proved highly effective against P. papuanus venom in rodent and in vitro assays, despite the absence of this particular venom from the immunising mixture.

On the clot-promoting activity of human platelets in a one-stage prothrombinase assay

The procoagulant activity of activated platelets in a one-stage prothrombinase assay is reevaluated. It is shown that the apparent procoagulant activity of platelets activated by ADP or collagen can be explained by minor cell lysis accompanying platelet activation. The reduction in clotting time observed with thrombin activated platelets can be explained by a combined effect of minor cell lysis and release and activation of factor V from the platelets. Platelets stimulated by ionophore A23187 or by the combined action of collagen plus thrombin show a much shorter clotting time than can be accounted for by minor platelet lysis or release and activation of factor V from the platelets. The results with this clotting assay essentially confirm previous observations [Bevers et al.: Eur. J. Biochem. 122:429-436, 1982] using a spectrophotometric method with highly purified coagulation factors and a chromogenic substrate to measure the rate of thrombin formation with activated platelets.

Influence of risk factors and coagulation phenomena on the fluidity of blood in chronic arterial occlusive disease

The fluidity of blood is a significant factor for the functioning and maintenance of the microcirculation. In chronic arterial occlusive disease (COAD) the fluidity of erythrocytes is markedly reduced assessed by flow rates through a 5-micrometer pore filter system in simulation of microcirculatory conditions. Risk factors such as heavy smoking, hyperfibrinogenaemia and hypertriglyceridaemia as well as hyperfibrinogenaemia result in flow rates similar to those in patients with COAD. Isolated coagulation phenomena typical for hypercoagulability in such patients produce significantly reduced flow rates and indicate the necessity for therapeutic elimination of risk factors as well as improvement of erythrocyte fluidity, reduction of platelet hyper-reagibility and removal of hypercoagulability. Pentoxifylline effects increases in erythrocyte fluidity, decreases platelet hyper-reactivity and plasmatic hypercoagulability, and improves the fibrinolytic capacity of blood in patients with COAD.

Human platelet acetylcholinesterase: the effects of anticholinesterases on platelet function

Platelet acetylcholinesterase (AChE) activity was measured in gel-filtered platelet preparations. Three different anticholinesteratic agents (eserine, neostigmine, and diisopropylphosphorofluoridate) at final concentrations of 10 muM caused complete inhibition of AChE activity after 30 min incubation at room temperature with either platelet-rich plasma or gel-filtered platelets. Complete inhibition of platelet AChE had no effect on platelet aggregation, factor-3 availability, and plasma clot retraction. We conclude that platelet membrane AChE activity is not required for normal platelet function as measured by these in vitro parameters.

Correlations between age-dependent protein and lipid concentrations in plasma and platelet functions in children

The correlations between the levels of various plasma proteins and lipids and platelet function on glass and platelet factor 3 (PF 3)-availability in children of different age-groups were investigated. Several statistically significant positive and some significant negative correlations were found. Although conclusions based solely on such correlations should be considered with reservation, in our opinion the following factors should stimulate platelet function: prealbumin (adhesion and PF 3-availability in all age-groups, aggregation--specifically for children in puberty); alpha 1-antitrypsin (PF 3-availability); alpha 2-macroglobulin (platelet spreading capacity, PF 3-availability); plasminogen (platelet adhesion and aggregation--specifically for boys in puberty); caeruloplasmin (number of "free adhering platelets" spreading capacity); lysolecithin and lecithin (time-dependent increase of spontaneous platelet adhesion and aggregation, PF 3-availability); and free fatty acids (FFA) (PF 3-availability). Plasminogen and complement component C'3 show a negative relationship to the time-dependent increase of spontaneous platelet adhesiveness and aggregability in platelet-rich plasma.

Isolated deficiency of platelet procoagulant activity

This is a study of a 34 year old woman with a moderate to severe bleeding disorder in whom impaired platelet procoagulant activity (PPA) was found by several methods, including tests of factor 3 availability (PF-3a), prothrombin consumption and contact activation. No deficiencies of platelet adhesion, aggregation, secretion, metabolism or granule-bound substances were detectable. Under adequate platelet coverage, this woman underwent two surgical procedures without difficulty. These findings demonstrate the role of PPA in hemostasis and indicate that a defect in PPA can be an isolated occurrence. The abnormalities in PF-3a found in this patient could be due to the diminished number of factor V binding sites, resulting in impaired factor Xa binding, found in separate studies by Majerus et al.

Posttransfusional immunologic thrombocytopenia. A case report

A case of posttransfusional immunologic thrombocytopenia is reported in a 75-year-od PlA1-negative woman. This was the second episode of postoperative and posttransfusion thrombocytopenia in the same patient who had had only one pregnancy. Both thrombocytopenic episodes were subclinical and discovered by systematical hematologic study. A potent anti-PlA1-antibody (titer 1/128) was demonstrated by the platelet-indirect radioactive Coombs test which appeared more sensitive than other platelet immunological assays used. The very long duration of the thrombocytopenia is discussed as well as the therapeutic possibilities in such cases.

The action mechanism of the purified platelet aggregation principle of Trimeresurus mucrosquamatus venom

The minimal concentration of the platelet aggregation principle (Platelet Aggregoserpentin, PAS) necessary to induce platelet aggregation was 10 ng/ml, about one-hundredth of that of the crude venom. PAS induced the release of platelet factors 3 and 4 from platelets, but the released platelet factor 3 was easily inactivated by the anti-phospholipid effect of PAS. Pretreatment of platelets with neuraminidase potentiated PAS-induced platelet aggregation. PAS-induced platelet aggregation was independent on released ADP; it could occur in the ADP-removing systems, such as apyrase or a combination of phosphoenolpyruvate and pyruvate kinase. However, PAS-induced platelet aggregation could be inhibited by adenine nucleotides and adenosine. PAS-induced platelet aggregation was inhibited by some anti-inflammatory agents, antimalarial drugs, local anesthetics, antihistamine and smooth muscle relaxants. After deaggregation of PAS-treated platelets, thrombin and sodium arachidonate could further induce platelet aggregation, but ADP and second dose of PAS could not. It is concluded that PAS-induced platelet aggregation is due to prostaglandin synthesis. Recent literatures on the mechanism of platelet aggregation were surveyed and the actions of PAS were discussed.

Red cell stroma, a stable standard for assessment of platelet procoagulant release

Platelet function in vitro may be investigated in various ways. One of the accepted methods involves examination of platelet procoagulant release. Optimal conditions relating to maximal release have not been defined. Red cell stroma phospholipid can substitute for the platelet procoagulant in many in vitro tests (Quick et al., 1954, 1957; Margolis, 1961; Lovric & Margolis, 1964). Using a multiple channel coagulation meter, an assay system was developed for testing both red cell stroma and platelet procoagulants. Maximum procoagulant release was obtained by lysing in alkaline hypotonic solutions or by sonication. The system was tested in a one-stage kaolin-activated platelet-free plasma substrate, obtained from fresh pooled citrated plasma. With this method the amount of available procoagulant could be related to the numbers of red blood cells or platelets. The results indicated that one platelet provided procoagulant equivalent to that derived from 0.7 red cells. Procoagulant release was studied under various conditions and expressed in terms of stable (red cell) standard. Platelets subjected to hypotonic stress or factor 3 release (Hardisty test) were studied quantitatively. The addition of sulphinpyrazone (Anturan) had no observable effect on platelet release in this system.

The platelet function profile. A new format for recording platelet function tests

A platelet function profile that provides a concise record of platelet function tests has been developed. This format can be easily modified to meet local requirements or to include hematologic tests unique to each laboratory.

Plateletpheresis by discontinuous centrifugation: effect of collecting methods on the in vitro function of platelets

The in vitro function of platelets collected by two different methods during centrifugal plateletpheresis was compared. The RBC method involves collecting platelets with red cells followed by a supplementary spin to remove them, whereas the no-RBC method requires collecting platelets only from the buffy coat without red cells. Platelet response to adenosine diphosphate (ADP), epinephrine and collagen was slightly reduced in platelet-rich plasma (PRP) prepared by no-RBC technique and was markedly decreased in samples obtained by the RBC technique when compared to prepheresis controls. The decrease in platelet response to ADP, epinephrine and collagen was apparent in three testing systems: aggregation, release of serotonin and reptilase clot retraction. Both plasma and platelets appeared to be affected by the pheresis procedure. Platelet preparations obtained by both RBC and no-RBC techniques showed an increase of platelet factor 3 activity and an enhancement of aggregation, release of serotonin and clot retraction induced by thrombin as compared to prepheresis controls. Postpheresis platelet-poor plasma contains platelet membrane fragments which exhibit a high platelet factor 3 activity. The results showed that the RBC method, although providing a higher platelet yield, caused more qualitative alterations in platelets than in those obtained by no-RBC method, and that both methods of collecting platelets activated the procoagulant activity of platelets.

Platelet preservation. IV. Preparation and cryopreservation of platelet concentrates from fresh and overnight-stored human blood

Two methods were used for the preparation of platelet concentrates from fresh and overnight-stored human ACD blood. In a two-step method prostoglandin E1 was added to platelet rich plasma and the mixture was centrifuged to obtain platelet concentrate. The IBM 2991 Blood Cell Processor was used in a one-step method. The concentrates were stored in the frozen state. Concentrates prepared with the two-step method had a higher platelet recovery and a lower leukocyte contamination than did concentrates prepared with the one-step method. Based on serotonin uptake volocity, response to hypotonic stress and available platelet factor 3, no essential differences were observed between platelet concentrates prepared from fresh and overnight-stored blood. Concentrates prepared with the one-step method had a higher serotonin uptake velocity than those prepared with the two-step method. This did not result in a better recovery after cryopreservation.

Evaluation of the platelet factor 3 availability test for their detection

To assess two modifications of the platelet factor 3 (PF3) test for platelet antibody detection, an analysis of test conditions was performed with normal test material (serum, plasma, globulin fraction), defined HLA-specific, complement-fixing antisera and a quinidine-induced antiserum. It was shown that, under standardized conditions, the PF3 test revealed known platelet antibodies confirming earlier results. Its reproducibility and, to a lesser degree, its sensitivity were inferior to platelet complement fixation. In contrast, the test did not permit the reliable determination of platelet autoantibodies in sera of 89 thrombocytopenic patients including 36 cases of idiopathic thrombocytopenic purpura. Positive results loosely corresponded to the presence of HLA antibodies in sera.

Complement-dependence of platelet serotonin release test in polytransfused patients

The research of platelet isoantibodies in patients with Cooley's anaemia was performed by simultaneous determination of the platelet-complement fixation test, platelet factor 3 availability assay and 14C-serotonin release test. In 93% of the examined patients we obtained positive results with the 5HT-release test, which appeared to be a complement-dependent reaction in most of the sera-containing isoantibodies, different from sera of patients affected by autoimmune thrombocytopenia.

[Relations between complement and blood coagulation (author's transl)]

The complement system as well as the blood coagulation system are involved in several disease processes so that it seems to be of interest to search for direct or indirect functional relations. Both systems can be activated in vitro as well as in vivo by the same substances, as e.g. endotoxin or antigen antibody complexes. In spite of these common characteristics a direct functional relationship between complement and plasmatic blood coagulation could not be established. Complement and blood coagulation do not interact with each other. Activated complement components, however, can induce platelet aggregation and release reaction both of which may accelerate but not trigger intravascular coagulation. Therefore, indirect relations between complement and blood coagulation can be found in patients or in animal experiments, especially after activation of intravascular coagulation. These interactions depend on further mediator sugstances of both systems.

Influence of cytostatics on some platelet functions in vitro. V. Hydroxyurea

Hydroxyurea added to citrated platelet-rich plasma in vitro did not influence the aggregation of the platelets, their adhesion to glass, their release of aggregating activity, platelet factor 4 or availability of platelet factor 3. Neither did it have any effect on the uptake of 14C-serotonin, the reptilase clot retraction or the coagulation system.

The effect of phospholipase C on platelet factor 3 in human blood platelets

Intact human platelets isolated by gel filtration have been treated with purified phospholipase C. The effect of the enzyme on available and total platelet factor 3 has been tested. The available procoagulant platelet factor 3 was very low. A further small reduction was observed after incubation with phospholipase C when the enzyme was washed away before testing. External attack on platelets by phospholipase C led to a marked inactivation of total platelet factor 3.

Influence of cytotoxic drugs on platelet functions and coagulation in vitro. IV. Melphalan

Influence of melphalan on some platelet functions, plasmatic coagulation and fibrinolysis "in vitro" was investigated, using different concentrations of the drug (25, 50 and 250 mug/ml). The lowest concentration slightly inhibited adrenaline and/or collagen-induced platelet aggregation. Following the highest concentration of the drug, strong inhibition of aggregation was recorded, regardless of the inducer used. Melphalan was also shown to inhibit release of aggregating activity and release of platelet factor 4, as well as availability of platelet factor 3 and platelet acid phosphatase. The intensity of inhibition depended on both, melphalan concentration and the time of preincubation. In contrast to this, adhesion of platelets to glass slide was not found to be influenced by melphalan. Similarly, melphalan did not induce (in any concentration) loss of LDH from platelet cytoplasma, while triton X-100 or freezing and thawing of platelets caused significant increase of LDH activity. From coagulation tests studied, only thrombin time and reptilase time was found to be moderately prolonged in the presence of melphalan. Authors assumed that melphalan acts as a specific inhibitor of release reaction and can induce an acquired thrombocytopathy. The platelet membrane is not damaged by the drug, as was confirmed by the investigation of LDH activity. Influence on coagulation indicates some antithrombin effect of the drug. Although presented results were obtained in vitro, analogous changes in vivo could be suspected. Thus, impairement of platelet functions might play a part in haemorrhagic complications accompanying, in some cases, melphalan therapy.

Detection in various clinical disorders, including immunologic drug-induced and neonatal thrombocytopenias

A modified version of the platelet factor 3 immunoinjury technique for the detection of antiplatelet antibody is described in detail; heat-inactivated sera and frozen platelets are employed. The modification allows the results of the test to be available within 4 to 5 hours after drawing the blood sample, in contrast to the 3 days required in the original method. The technical work involved is significantly reduced. The reproducibility of the technique is improved. Results obtained with the two tests correlate well. Data accumulated in 458 cases of clinical disorders associated with antiplatelet antibody are reported. Drug-dependent antiplatelet antibody was demonstrated in 26 cases of thrombocytopenia associated with 19 different drugs. Data are also presented for 23 cases of neonatal thrombocytopenia.

[Effects of premedication, narcosis and surgery on the coagulation and fibrinolysis systems and the platelets. The influence of dextran and hydroxyethyl starch (hes) during and after operation (author's transl)]

Patients who had undergone orthopaedic surgery were investigated. The changes attributable to premedication and narcosis were characterized by a primary fibrinolysis which was accompanied by a slight hypercoagulability. This increased fibrinolytic activity was more pronounced immediately after the beginning of the operation. The post operative changes are characterized by increased ADP-induced aggregation, increased release of platelet factors 3 and 4 and hypercoagulability with reduced fibrinolysis. The reduction in platelets during the operation could be prevented due to the influence of dextran and hydroxyethyl starch (HES). It came further to a slight increase in the activity of factor VII, to an increased fibrinogen polymerization and also to an increased release of platelet factor 4.

Oestrogen-associated disease of the renal microcirculation

The effect of oestrogen-containing compounds on platelet factor 3, platelet life span, renal platelet localization and the fibrinolytic activity of forearm venous blood has been studied in eleven women with the renal vascular abnormalities of the loin pain and haematuria syndrome. The results were compared with those obtained in twenty-nine healthy female volunteer subjects. 2. Platelet factor 3 (PF3) availability was found to be increased in patients with the loin pain and haematuria syndrome during normal menstrual cycles. Oestrogens produced an increase in PF3 availability in both patients and control subjects. 3. Platelet life span was shortened and the index of renal platelet localization increased when patients with the loin pain and haematuria syndrome received oestrogens. No change in platelet kinetics was found in the healthy control subjects receiving oestrogens. 4. The fibrinolytic activity of forearm venous blood, both at rest and after venous occlusion, was increased in the healthy control subjects in response to oestrogens. No such response was seen in the patients with the loin pain and haematuria syndrome. 5. It is suggested that the change in platelet function may be causally related to the intrarenal vascular abnormalities. 6. The possible role of oestrogens in causing these disturbances or unmasking pre-existing abnormalities of platelet function or fibrinolysis is discussed.

Congenital release thrombocytopathy: pathophysiology and management

Congenital release thrombocytopathy must be included in the differential diagnosis of bleeding diatheses in women. A review of the coagulation profiles of 7 patients with congenital release thrombocytopathy suggests that more sophisticated platelet aggregation studies must be performed when routine screening procedures fail to determine the cause of a clinically suspected bleeding disorder. Establishing the diagnosis helps to avoid the use of medications which cause an acquired platelet dysfunction, and contributes to adequate prophylaxis against surgical and obstetric hemorrhage.

Heparin-induced immune thrombocytopenia

We studied five patients in whom severe thrombocytopenia developed during intermittent intravenous heparin treatment of arterial and venous thrombosis. Platelet aggregation was demonstrated when heparin (0.5 U per milliliter) was incubated with the patients' citrated platelet-rich plasma or with normal platelet-rich plasma in the presence of the patients' serum. Antiplatelet antibody was not detected in the patient globulin fractions prepared from serum collected within one week after heparin withdrawal by use of the platelet factor 3 availability technic. When the studies were repeated with modifications to detect heparin-dependent antiplatelet antibodies, positive results were obtained in four of five patients. The data suggest that a casual relation, mediated by an immune mechanism, existed between heparin therapy and thrombocytopenia, and that this syndrome may occur more often than has previously.

Detection of antiplatelet antibody in serum and on megakaryocytes of dogs with autoimmune thrombocytopenia

Blood and bone marrow samples from 13 thrombocytopenic dogs were examined to determine whether immunologic thrombocytopenia existed. Antiplatelet antibody was detected in serum of 8 of the dogs by platelet factor 3 test or its modification. Moderate to strong immunofluorescence of megakaryocytes was noticed in bone marrow smears stained with rabbit anticanine globulin conjugated with fluorescin isothiocyanate. Negative results were obtained with serum and bone marrow samples collected from 6 of the dogs during therapy for autoimmune thrombocytopenia. Clinical and laboratory findings varied in individual patients with circulating antiplatelet antibodies. Thrombocytopenia was present in all the dogs, with platelet counts ranging from less than 3,000 to 20,000/mu1 of blood. Signs of bleeding in tissues and body cavities were present in all dogs, but anemia was evidenced in only 3 dogs. Differential leukocyte counts were variable. Morphologic abnormalities such as vacuolation and reduced or absence of granulation of the cytoplasm and nuclear fragmentation were seen in some megakaryocytes.

Impairment of platelet adhesiveness and platelet factor 3 activity in cyanotic congenital heart disease

In 33 children with cyanotic congenital heart disease the platelet function has been studied. The most significant changes were reduced platelet adhesiveness to glass and impaired availability of platelet factor 3 in nearly 50% of the patients. Although clot retraction was poor in 84% of them, thrombocytopenia and prolonged bleeding time were not significant features.

Platelet function tests in uraemia and under acetylsalicylic acid administration

Procollagen-induced platelet aggregation, platelet retention (Hellem II), and platelet factor 3 availability (PF-3) were determinded in a group of healthy volunteers,acetylsalicylic acid (ASA) treated patients and in uraemic patients. ASA ingestion did not influence platelet retention and PF-3 availability. Uraemic patients had apronounced decrease in platelet aggregation and retention and PF-3 availability revealed inconsistent alterations. The relevance of the tests and the benefit of an ASA treatment for prophylaxis of thrombosis in Climino fistulae are discussed.