Plasma Fibrinopeptide A and Beta-Thromboglobulin in Patients with Chest Pain

Role of thrombogenic factors in the development of atherosclerosis

Hemostatic factors play a crucial role in generating thrombotic plugs at sites of vascular damage (atherothrombosis). However, whether hemostatic factors contribute directly or indirectly to the pathogenesis of atherosclerosis remains uncertain. Autopsy studies have revealed that intimal thickening represents the first stage of atherosclerosis and that lipid-rich plaque arises from such lesions. Several factors contribute to the start of intimal thickening. Platelets release several growth factors and bioactive agents that play a central role in development of not only thrombus but also of intimal thickening. We have been investigating which coagulation factors simultaneously, or subsequently with platelet aggregation, participate in thrombus formation. Tissue factor (TF) is an essential initiator of blood coagulation that is expressed in various stages of atherosclerotic lesions in humans and other animals. Factors including thrombin and fibrin, which are downstream of the coagulation cascade activated by TF, also contribute to atherosclerosis. TF is involved in cell migration, embryogenesis and angiogenesis. Thus TF, in addition to factors downstream of the coagulation cascade and the protease-activated receptor 2 activation system, would be a multifactorial regulator of atherogenesis.

Haemostatic variables in patients with unstable angina

To assess the contribution of thrombus formation in the pathogenesis of unstable angina, we employed the recently developed assays of small fragments which reflect the degree of activation of various components of the haemostatic system. Such haemostatic measurements were undertaken in patients with unstable angina (n = 47) from the time of their admission to the coronary care unit (CCU) at 8-h intervals in the first 24 h and then daily for a total of 5 days. The results obtained were compared with healthy control values. Patients exhibited lower ATIII, prolongation of the APTT and TT, but not PT or the reptilase time, which is a consequence of heparinization. There was significant elevation of fibrinogen, factor VIII:C, von Willebrand factor:antigen and von Willebrand factor:ristocetin cofactor throughout the study period. There was also evidence of thrombin generation as indicated by the elevated levels of fibrinopeptide A (FPA) and thrombin-antithrombin complexes. The platelet release proteins, beta-thromboglobulin (BTG) and platelet factor 4 (PF4), were markedly elevated in the first 2 days and dropped gradually thereafter. The fibrinolytic inhibitor, plasminogen activator inhibitor (PAI), levels were elevated throughout. Proteins C and S, plasminogen and alpha 2-antiplasmin remained unchanged. It was concluded that in patients with unstable angina, there is significant activation of the clotting system and inhibition of fibrinolysis which confirms the existence of a tendency towards thrombus formation in patients with unstable angina.

Flow cytometric assessment of platelet function in patients with peripheral arterial occlusive disease

This study compared new and traditional measures of platelet function in 16 patients with severe peripheral arterial occlusive disease and 15 age-matched controls. Circulating platelets were characterized by the use of fluorescence flow cytometry to assess platelet aggregate formation and expression of the secretion-dependent alpha granule membrane protein GMP-140, by measurement of plasma beta-thromboglobulin (beta-TG), and by performance of platelet-rich plasma aggregation studies. In addition, blood samples were treated with graded concentrations of adenosine diphosphate (ADP; 0 to 10 mumols/L) to characterize by fluorescence flow cytometry the secretory and aggregatory responses to mild stimulation. No differences were detected between the two groups with regard to platelet function in unstimulated circulating blood by use of these techniques. Values (mean +/- SEM) observed were: GMP-140-positive platelets, 11% +/- 3% versus 13% +/- 2%; platelet aggregates in circulating whole blood, 4% +/- 1% versus 9% +/- 3%; plasma beta-TG, 92 +/- 12 versus 94 +/- 22 ng/ml; and ED50 (concentration of ADP required to produce half maximal aggregation), 3.8 +/- 1.1 versus 3.1 +/- 0.5 mumol/L in the patients with peripheral arterial occlusive disease and controls, respectively. Treatment with ADP caused a dose-related increase in GMP-140 expression in both groups, without significant differences in this parameter between the groups at any given concentration. However, stimulation with ADP concentrations greater than 1 mumol/L resulted in more frequent aggregate formation in the control than in the peripheral arterial occlusive disease group (25% +/- 4% versus 11% +/- 2%, respectively at 5.0 mumols/L, p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Coagulation-fibrinolysis abnormalities in acute and chronic phases of cerebral thrombosis and embolism

We assayed plasma concentrations of fibrinogen, fibrinopeptide A, plasmin-alpha 2 plasmin inhibitor complex, D dimer, and antithrombin III activity in 40 patients with cerebral thrombosis and nine patients with cerebral embolism during the acute (less than 7 days), subacute (7-27 days), and chronic (greater than or equal to 28 days) periods and compared these with 69 controls. In cerebral thrombosis, fibrinogen and fibrinopeptide A levels were elevated significantly in all stages (p less than 0.001), whereas plasmin-alpha 2 plasmin inhibitor complex and D dimer levels were elevated significantly in the subacute and chronic periods. The antithrombin III activity was significantly decreased in the acute stage. The elevation of fibrinogen and plasmin-alpha 2 plasmin inhibitor complex levels in the acute stage was significantly greater in patients with an infarct size greater than 10 mm2 compared to patients with an infarct size less than 10 mm2. We observed similar changes in patients with cerebral embolism. These results suggest that enhanced coagulation exists at all stages and endogenous fibrinolysis is activated in the subacute and chronic periods in a large proportion of patients with cerebral thrombosis and embolism.

Thrombin and plasmin activity in coronary artery disease

Basal plasmin and thrombin activity in plasma were assessed by radioimmunoassay of the fibrinogen derivatives containing the sequence B beta 15-42 and of fibrinopeptide A respectively in a cross sectional controlled study of men with coronary artery disease. Compared with healthy controls (n = 33) men with angiographically defined coronary artery disease (n = 98) had a modest but significant increase in concentrations of fibrinopeptide A, indicating an activated coagulation system. Concentrations of B beta 15-42 were similar in those with coronary artery disease and in the controls. The enhanced thrombin activity in coronary artery disease is in keeping with current evidence suggesting an association between coronary artery disease and a hypercoagulable state.

Raised concentrations of glucose and adrenaline and increased in vivo platelet activation after myocardial infarction

Plasma concentration of beta thromboglobulin was used as an index of in vivo platelet activation in 36 patients after acute myocardial infarction. Twelve patients had diabetes, seven had pulmonary oedema or cardiogenic shock (pump failure) or both, and 17 had uncomplicated infarcts. On the first day of admission, concentrations of beta thromboglobulin were higher in the patients with diabetes and those with pump failure than in those with uncomplicated infarcts. Concentrations of beta thromboglobulin in the non-diabetic patients were studied by multiple regression analysis and were significantly associated with plasma concentrations of adrenaline, pump failure, and glucose but not with noradrenaline or infarct size. When all subjects were considered together, glucose, adrenaline, and pump failure were associated with the beta thromboglobulin concentration but diabetes was without significant effect. Hyperglycaemia and raised plasma adrenaline concentration after myocardial infarction may activate platelets, and this could contribute to poor outcome in such patients.

Possible interaction of platelets and adrenaline in the early phase of myocardial infarction

It is known that in most cases of transmural acute myocardial infarction a platelet clot originates within a coronary artery. In acute myocardial infarction patients increased levels of the plasma catecholamines adrenaline and noradrenaline as well as the platelet release proteins platelet factor 4 and beta-thromboglobulin have been reported. In this study, significantly higher values were found of platelet factor 4 (P less than 0.0001) and beta-thromboglobulin (P less than 0.002) in 17 acute myocardial infarction patients as compared to 17 control patients (on intensive care due to non-cardiac disorders), while the plasma levels of adrenaline and noradrenaline were not different. Positive correlations were obtained between the two catecholamines and the platelet products in the control group and between adrenaline and both platelet factor 4 (r = 0.715, P less than 0.01) and beta-thromboglobulin (r = 0.547, P less than 0.05) in the acute myocardial infarction patients. The data suggest that a stimulation of the platelets by adrenaline may facilitate in vitro activation during sampling in patients with high catecholamine load. On the other hand, a "preactivation" of the platelets by an increase of adrenaline might be of significance for thrombus formation in acute myocardial infarction.

Plasma levels of platelet secretory proteins

Platelets contain three types of secretory organelles: the dense granules, the alpha granules, and the lysosomes. Most of the proteins secreted from platelets are stored in the alpha granules, whereas the dense granules contain substances such as adenine nucleotides, serotonin, Ca++, and inorganic pyrophosphate types as well as a heparatinase. Three of the secreted alpha granule proteins have been measured by radioimmunoassay and it has been suggested that levels of these proteins in patient plasmas provide an index of in vivo platelet activation and secretion. These three are beta-thromboglobulin, platelet factor 4, and thrombospondin. In this chapter the chemistry of these proteins will be considered briefly, as will their clearance from the circulation, and then the clinical studies will be reviewed critically. Since radioimmunoassays were developed for these proteins (the first was reported in 1975), there has been a profusion of reports on levels of one or another of these proteins in a wide range of disease states, and these reports have indicated secreted platelet protein levels ranging from normal to grossly elevated in a given disease state. Possible reasons for such variability will be discussed.