Harvey J. Weiss

Thrombogenic Factors and Recurrent Coronary Events

BACKGROUND Thrombosis is a pivotal event in the pathogenesis of coronary disease. We hypothesized that the presence of blood factors that reflect enhanced thrombogenic activity would be associated with an increased risk of recurrent coronary events during long-term follow-up of patients who have recovered from myocardial infarction. METHODS AND RESULTS We prospectively enrolled 1045 patients 2 months after an index myocardial infarction. Baseline thrombogenic blood tests included 6 hemostatic variables (D-dimer, fibrinogen, factor VII, factor VIIa, von Willebrand factor, and plasminogen activator inhibitor-1), 7 lipid factors [cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, lipoprotein(a), apolipoprotein (apo)A-I, and apoB], and insulin. Patients were followed up for an average of 26 months, with the primary end point being coronary death or nonfatal myocardial infarction, whichever occurred first. The hemostatic, lipid, and insulin parameters were dichotomized into their top and the lower 3 risk quartiles and evaluated for entry into a Cox survivorship model. High levels of D-dimer (hazard ratio, 2.43; 95% CI, 1.49, 3.97) and apoB (hazard ratio, 1.82; 95% CI, 1.10, 3.00) and low levels of apoA-I (hazard ratio, 1.84; 95% CI, 1.10, 3.08) were independently associated with recurrent coronary events in the Cox model after adjustment for 6 relevant clinical covariates. CONCLUSIONS Our findings indicate that a procoagulant state, as reflected in elevated levels of D-dimer, and disordered lipid transport, as indicated by low apoA-1 and high apoB levels, contribute independently to recurrent coronary events in postinfarction patients.

Studies of the Release from Human Platelets of the Growth Factor for Cultured Human Arterial Smooth Muscle Cells

Platelets contain a growth-promoting factor for arterial smooth muscle cells (SMC) that may play a major role in atberogenesis. We have studied some of the effects of the platelet-derived growth factor (PDGF) on human arterial SMC in culture and the release of PDGF from human platelets in relationship to other released substances. Material released from platelets was highly potent in stimulating human SMC to proliferate. A substantial portion of the growth-promoting activity of human serum could be attributed to a factor(s) released from platelets. Similar dose-response patterns to PDGF were observed with human SMC and with mouse 3T3 cells. The time-course of release of PDGF and its concentration dependence on human thrombin were determined in comparison with serotonin, ADP, ATP, an acid bydrolase, platelet factor 4 (PF4), and β-thromboglobulln (βJTG). PDGF activity was assayed by stimulation of the incorporation of +-H-thymidine into DNA of 3T3 cells; PF4 and βJTG were measured by newly developed radioimmunoassays. PDGF, PF4, and βJTG were released from platelets by lower concentrations of thrombin than those required for release of the other components. The results suggest that PDGF, PF4, and βTG are localized in the platelet in granules different from either the dense bodies (that contain serotonin, ADP, ATP) or the acid hydrolase-containing granules, possibly in α-granules. The contents of these PDGF- containlng a-granules are actively released during the release reaction and are particularly sensitive to release by low doses of thrombin.

Decreased adhesion of giant (Bernard-Soulier) platelets to subendothelium: Further implications on the role of the von Willebrand factor in hemostasis

Abstract The platelets of two patients with the Bernard-Souller (giant platelet) syndrome were not aggregated by bovine factor VIII. Platelet aggregation by rlstocetin was also absent and, in contrast to the findings in von Willebrands disease, this defect was not corrected by human factor VIII. The platelets of patients with the Bernard-Soulier syndrome may lack a receptor for the von Willebrand factor activity of factor VIII (VIII VWF ), whereas the abnormal platelet function in von Willebrands disease is due to a decreased level of VIII VWF in their plasma. As in the latter disorder, the adhesion of platelets to subendothellum was impalred in the two patients with the Bernard-Souller syndrome that we studied. These findings provide further evidence that VIII VWF , through its effect on platelets, plays an important role during the primary arrest of bleeding.

Defective Ristocetin-Induced Platelet Aggregation in von Willebrand's Disease and its Correction by Factor VIII

The antibiotic ristocetin, in concentrations of 1.0-1.5 mg/ml, aggregated normal platelets in citrated platelet-rich plasma by a mechanism in which the release reaction played only a minor role. Platelet aggregation by ristocetin in a concentration of 1.2 mg/ml was absent or markedly decreased in 10 patients with von Willebrands disease. Lesser degrees of abnormality were obtained with a concentration of 1.5 mg/ml. The magnitude of the defect in ristocetin-induced platelet aggregation correlated well with the degree of abnormality of the bleeding time and the levels of antihemophilic factor (AHF, VIII(AHF)) procoagulant activity. In all patients, the defect in ristocetin-induced platelet aggregation was corrected in vitro by normal plasma. Correction was also obtained with a fraction of normal cryoprecipitate that eluted in the void volume with VIII(AHF) after chromatography on a gel that excludes molecules larger than 5 x 10(6). A similar fraction, devoid of VIII(AHF) activity, obtained from patients with von Willebrands disease had no corrective effect, but fractions obtained from patients with hemophilia were just as effective as those obtained from normal subjects. The correction activity of plasma and partially purified factor VIII was inhibited by a rabbit antibody to human factor VIII but not by a human antibody against VIII(AHF) procoagulant activity. The studies provide further evidence that patients with von Willebrands disease are deficient in a plasma factor that is necessary for normal platelet function. The activity of this factor appears to be associated with factor VIII but is unrelated to VIII(AHF) procoagulant activity.

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.

Platelet interaction with rabbit subendothelium in von Willebrand's disease: altered thrombus formation distinct from defective platelet adhesion.

Blood interaction with the subendothelium of rabbit aorta was investigated in an annular perfusion chamber using patients with von Willebrands disease, hemophilia, and afibrinogenemia. The vessels were exposed to nonanticoagulated blood for a range of flow conditions (wall shear rates of 650-3,300 s-1) and exposure times (1.5-10 min). The resultant platelet and fibrin interaction was quantified by the use of several morphometric techniques, one of which was developed to measure more precisely the dimensions (height and volume) of platelet thrombi attached to the subendothelium. A major finding was that under flow conditions in which little or no defect in platelet adhesion was observed in von Willebrands disease, platelet thrombus height and volume in this disorder were significantly reduced as compared with normal controls or patients with hemophilia. Thus, Factor VIII/von Willebrand factor (VIII/VWF) may mediate not only the adhesion of platelets to subendothelium but also platelet-platelet attachments necessary for normal thrombus development. The level of Factor VIII:coagulant activity (VIII: C) was also observed to influence the resultant thrombus height and volume deposited on subendothelium, presumably through the generation of thrombin or some other procoagulant factor preceding fibrin formation, since normal values of thrombus dimensions were always observed in a patient with a fibrinogen deficiency. The influence of VIII:C became greater as shear rate was reduced, whereas as shear rate was increased, VIII/VWF was more dominant in determining the resultant platelet deposition on subendothelium. Thus, the deficiencies of VIII:C and VIII/VWF in hemophilia and von Willebrands disease can lead to various abnormalities in platelet and fibrin association with subendothelium. The importance of a particular deficiency will depend strongly on the local blood flow conditions.

Role of shear rate and platelets in promoting fibrin formation on rabbit subendothelium: studies utilizing patients with quantitative and qualitative platelet defects

The deposition of platelets on subendothelium of rabbit aortic segments exposed to non-anticoagulated human blood increased progressively with increasing wall shear rates (50-2,600 s-1), whereas fibrin deposition decreased. Studies in normal subjects and patients with platelet disorders suggested that, under the conditions used, platelets were essential for fibrin deposition at intermediate (650 s-1) but not low (50 s-1) shear rates. Fibrin deposition was markedly diminished in a patient with Scott syndrome whose platelets have a diminished capacity to bind Factor Xa and activate Factors IX and II. In glycoprotein IIb-IIIa deficiency, fibrin deposition was normal (or somewhat increased), whereas in glycoprotein Ib deficiency the association of fibrin with platelets, but not subendothelium, was decreased. The findings indicate that platelets, perhaps through surface localization of coagulation proteins, promote fibrin deposition on subendothelium at arterial shear rates and suggest that agents directed against platelet coagulant properties could be antithrombotic.

Von Willebrand factor: dissociation from antihemophilic factor procoagulant activity.

Factor VIII corrects both the clotting defect in hemophilia A and an abnormality of platelet aggregation in von Willebrands disease. These two activities of factor VIII (antihemophilic factor and von Willebrand factor) are both detected in the void volume when human plasma or cryoprecipitate is chromatographed on Bio-Gel 5M under conditions of isotonic salt concentration. In contrast, antihemophilic factor procoagulant activity is detected with proteins of lower molecular weight when the chromatography is performed with a buffer containing 0.8M NaCl. In this way, the two activities of factor VIII can be dissociated. It remains to be determined whether these components are separate molecules associated as a complex of high molecular weight in plasma or whether they are subunits of a complex macromolecule.

Impaired interaction (adhesion-aggregation) of platelets with the subendothelium in storage-pool disease and after aspirin ingestion. A comparison with von Willebrand's disease.

Possible defects in the interaction of platelets with the subendothelial surface were evaluated in six patients with storeage-pool disease, nine patients with von Willebrands disease and seven normal subjects who ingested aspirin. Citrated blood was perfused through a chamber containing everted segments of rabbit aorta previously denuded of endothelium by means of a ballon catheter. With normal blood, 83.3 +/- 1.9 per cent (S.E.M.) of the surface was covered by adherent platelets. Platelet adhesion was normal after aspirin ingestion (89.7 +/- 4.6 per cent) and decreased in some patients with storage-pool disease. The most striking defect in both circumstances was the virtual absence of platelet thrombi. In contrast, decreased adhesion (57.3 +/- 3.4 per cent), but normal thrombus formation, was characteristic of von Willebrands disease. These types of defects in platelet adhesion and aggregation may account for the hemostatic defects in a variety of bleeding disorders. The findings further suggest the possible usefulness of aspirin as an antithrombotic agent.

Fibrinogen and platelets in the primary arrest of bleeding. Studies in two patients with congenital afibrinogenemia.

Abstract Two patients with a congenital absence of fibrinogen and a prolonged bleeding time were studied to determine the role of fibrinogen in the primary arrest of bleeding and for further clarification of the fibrinogen requirement for platelet function. The retention of platelets, sampled directly from venous blood, in glass-bead filters was consistently decreased and was markedly increased by pretreatment of the beads with fibrinogen. Adhesion of platelets to connective tissue, however, was normal. In citrated platelet-rich plasma (PRP), abnormalities in primary platelet aggregation by ADP and epinephrine were optimally corrected by fibrinogen in concentrations of 10 to 20 mg per 100 ml. In contrast to the abnormal findings in citrated PRP, both primary platelet aggregation and the release reaction were normal in heparinized PRP. The studies leave unanswered the question of the fibrinogen requirements for platelet aggregation, but indicate that fibrinogen is required as a cofactor in the interaction ...