Karen L. Kaplan

Identification and distribution of fibrinogen, fibrin, and fibrin(ogen) degradation products in atherosclerosis. Use of monoclonal antibodies.

Samples of normal and atherosclerotic vessels obtained from vascular and cardlothoraclc surgery were examined for the distribution of flbrlnogen/flbrln I, fibrin II, and flbrin(ogen) degradation products (Fragment D/DD) by using recently characterized monoclonal antibodies that recognize and distinguish the three molecular forms (MAbs I8C6, T2G1, and GC4, respectively) with the ABC-immunoperoxidase technique. In normal aortas, little flbrlnogen/flbrln I or fibrin II was present and no ftbrln(ogen) degradation products could be detected. In early lesions and In fibrous plaques, flbrlnogen/flbrln I and fibrin II were distributed in long threads and surrounding vessel wall cells and macrophages. Rbrln(ogen) degradation products were not seen In early lesions. In fibrous and advanced plaques, flbrlnogen/flbrin I, fibrin II, and flbrin(ogen) degradation products were detected In areas of loose connective tissue, In thrombus, and around cholesterol crystals. The results of this study suggest that Increased fibrin formation and degradation may be associated with progression of atherosclerotic disease. The observed distribution of the different molecular forms of fibrinogen also suggests the possibility that the cells present In the lesions actively participate In the flbrinogen-to-fibrln transition within the vessel wall.

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.

Radioimmunoassay of Platelet Factor 4 and β-Thromboglobulin: Development and Application to Studies of Platelet Release in Relation to Fibrinopeptide A Generation

Summary. Platelet and fibrinogen survival and turnover studies have shown that platelet activation and fibrin formation may occur to different degrees in different thrombotic disorders. More direct evidence of differential involvement of platelet activation and fibrin formation should be provided by specifically measuring the products of these reactions, i.e. released platelet proteins and fibrinopeptide A. Two platelet proteins, platelet factor 4 (PF4) and β‐thromboglobulin (βTG), were isolated and characterized, and sensitive and specific radioimmunoassays were developed to measure them. These assays were employed, along with the radioimmunoassay for fibrinopeptide A (FPA), to study the release of PF4 and βTG in relation to FPA cleavage. PF4 and βTTG were released by ADP and collagen with time course and concentration dependence similar to that of [14C]serotonin release. FPA was not cleaved from fibrinogen during ADP or collagen‐induced platelet release. Thrombin caused release of PF4 and βTTG as well as cleavage of FPA. Cleavage of FPA occurred with concentrations of thrombin about 100 times less than did release of PF4 and βTG, and release of [14C]serotinin required still higher thrombin concentrations. Release of [14C]serotonin and platelet proteins was similar as a function of time. Sodium citrate was found to inhibit platelet release induced by thrombin.

The generation of fibrinopeptide A in clinical blood samples: evidence for thrombin activity.

Plasma fibrinopeptide A (FPA) concentrations were measured in clinical blood samples incubated in the collecting syringe for different time periods before addition to heparin and Trasylol, and the rate of in vitro generation of FPA was calculated as the mean increment in FPA concentration per minute over the linear portion of the generation curve. 36 normal individuals had a mean plasma FPA level of 0.64 +/- 0.56 pmol/ml and an FPA generation rate of less than 0.5 pmol/ml per min. Clinical samples with elevated plasma FPA levels manifested slow (less than 1 pmol/ml per min) (28 patients) or rapid FPA generation (greater than 1 pmol/ml per min) (33 patients). Slow FPA generation was found in 10/10 patients with venous thrombosis, in 4/4 with aortic aneurysm, and in several patients with acquired hypofibrinogenemia. In one such patient, addition of fibrinogen resulted in rapid FPA generation whereas thrombin addition was without effect. Rapid FPA generation was generally linear, was usually associated with slower fibrinopeptide B generation and was inhibited by parenteral or in vitro heparin. It is thought to reflect increased thrombin activity and was seen in patients with pulmonary embolism, active systemic lupus erythematosus, renal transplant rejection, and after infusion of prothrombin concentrates. The initial rate of FPA cleavage by thrombin at fibrinogen concentrations from 0.05 to 4 mg/ml showed little change between 2 and 4 mg/ml with a Km of 2.99 muM. At a fibrinogen concentration of 2.5 mg/ml the FPA cleavage rate was 49.2 +/- 1.6 nmol/ml per min per U of thrombin. Exogenous thrombin added to normal blood generated 21.7 nmol/ml per U of thrombin FPA in the first minute with a nonlinear pattern reflecting inactivation of thrombin and the presence of alternative substrates. Hence, the thrombin concentration in the blood cannot be calculated from the FPA generation rate. The FPA generation rates in clinical samples with rapid generation (1-28 pmol/ml per min) could be produced by 2 X 10(-5) to 5.6 X 10(-4) thrombin U/ml acting on purified fibrinogen at physiological conditions of pH, ionic strength, and temperature.

Sequence of Fibrinogen Proteolysis and Platelet Release after Intrauterine Infusion of Hypertonic Saline

Plasma fibrinopeptide B (Bbeta1-14 or FPB) immunoreactivity was studied by radioimmunoassay in patients who received intrauterine infusion of hypertonic saline to terminate pregnancy. FPB immunoreactivity increased with thrombin treatment (TIFPB) suggesting the presence of a larger FPB-containing peptide, since purified FPB is not altered by thrombin, whereas thrombin increases the immunoreactivity of Bbeta1-42 (which includes FPB) 10-fold. TIFPB immunoreactivity in plasma, drawn 4 h after hypertonic saline infusion eluted from Sephadex G-50 similarly to isolated Bbeta1-42. Streptokinase, incubated with normal plasma progressively generated TIFPB immunoreactivity, which showed a major component which eluted from Sephadex G-50 similarly to Bbeta1-42. Streptokinase generated TIFPB much more rapidly in reptilase-treated plasma that contains fibrin I, (which still includes FPB), indicating that fibrin I is preferred over fibrinogen as a substrate for plasmin cleavage of arginine (Bbeta42)-alanine (Bbeta43). Serial studies were then made in 10 patients receiving intrauterine hypertonic saline. Fibrinopeptide A (FPA) levels rose immediately, reached a peak between 1 and 2 h, were declining at 4 h, and were normal at 24 and 48 h. TIFPB levels rose slightly in the 1st h, reached a peak at 4 h, and had returned to base-line values at 24 h. Serum fibrinogen degradation product levels were unchanged at 1 h, reached their highest level at 4 h, and were still markedly elevated at 24 and 48 h. Fibrinogen levels dropped slightly being lowest at 4 and 24 h. Platelet counts declined in parallel with the fibrinogen levels over the first 4 h, but continued to decrease through 48 h. Beta thromboglobulin (betaTG) levels generally paralleled FPA levels whereas platelet factor 4 (PF4) levels showed only slight changes. The data indicate that immediately after intrauterine hypertonic saline infusion thrombin is formed that cleaves FPA from fibrinogen to produce fibrin I and releases betaTG and PF4 from platelets. Later plasmin cleaves Bbeta1-42 from fibrin I to produce fragment X, which is further degraded to form serum fibrinogen degradation products. This sequence of proteolysis indicates that plasmin action on fibrin I serves as a mechanism that regulates fibrin II formation by removing the Bbeta chain cleavage site, which is required for thrombin action in converting fibrin I to fibrin II.

The hermansky-Pudlak syndrome: Report of three cases and review of pathophysiology and management considerations

Three Puerto Rican siblings with the Hermansky-Pudlak syndrome are described, and the literature on this syndrome is reviewed with regard to clinical factors, pathology, pathophysiology, and management of the disorder. The three patients all manifested oculocutaneous albinism and platelet storage pool disease with a moderate bleeding tendency. The oldest sibling died from restrictive lung disease and another has evidence of reduced functional residual capacity, although he is asymptomatic. None of the patients had evidence of inflammatory bowel disease, which has been reported in some cases. All of the patients had an increased incidence of bacterial infections, and they were anergic. Whether their immunological defect(s) is related to the Hermansky-Pudlak syndrome is not known. Two of the patients were treated with oral vitamin E. Bleeding symptoms in both were markedly reduced, although major changes in platelet aggregation were not seen. Vitamin E therapy did not appear to affect the progression of lung disease in the patient with fatal restrictive lung disease.

Venous thromboembolism in patients with diffuse large B-cell lymphoma

We conducted a retrospective record review to determine the frequency of venous thromboembolism (VTE) in patients with diffuse large B-cell lymphoma (DLBCL). All records from 1990 to 2001 of patients with the diagnosis of DLBCL at a tertiary care hospital were reviewed. Those with transformation from low-grade lymphoma, central nervous system lymphoma, HIV-related lymphoma or with incomplete records were excluded. All episodes of symptomatic VTE confirmed by imaging studies that were either present at diagnosis or occurred during initial treatment were identified. VTE occurred in 27 of 211 patients (12.8%). Stage I disease was associated with a low risk, whereas a high international prognostic index score increased risk. Of patients with VTE, thrombosis was present at diagnosis in 37% and occurred during the first chemotherapy cycle in 22% and during the first three cycles in 82%. The median survival of patients with VTE was 1.04 years [95% confidence interval (CI) = 0.75 – 1.33] compared to 5.2 years (95% CI 1.8 – 8.6) for those without VTE (P = 0.038). We conclude that VTE is a frequent complication of DLBCL that occurs particularly at diagnosis and during initial therapy, and it is associated with a worse prognosis.

Acquired storage pool deficiency with increased platelet-associated IgG: Report of five cases

Acquired abnormalities of platelet aggregation have been reported with increasing frequency. We studied five patients (including two with systemic lupus erythematosus and one with compensated chronic idiopathic thrombocytopenic purpura) in whom platelet aggregation responses to collagen, epinephrine and ADP are impaired; in all cases, we found that levels of platelet-associated immunoglobulin G (IgG) were increased. In all five patients substances stored in platelet-dense granules (ATP, ADP, serotonin and calcium) were diminished. The content of the alpha-granule substance, beta-thromboglobulin, was also decreased in most cases, whereas the levels of two secretable acid hydrolase enzymes (beta-glucuronidase and beta-N-acetyl glucosaminidase) were within normal limits. These findings are similar to those observed in subtypes of congenital storage pool deficiency. However, in contrast to the congenital disorder, a membrane-bound (nonsecretable) acid phosphatase was also decreased in the patients with acquired storage pool deficiency. These findings suggest that impaired platelet aggregation on an acquired basis may, in some patients, be due to immune platelet damage resulting in a distinctive type of platelet storage pool deficiency.

Effect of fibrin on endothelial cell production of prostacyclin and tissue plasminogen activator.

Fibrin formed on endothelial cells has previously been shown to have deleterious effects on the cells. Additionally, substances that cause endothelial cell damage have been reported to Induce cultured endothelial cells to synthesize prostacyclin and tissue plasminogen activator (t-PA). The present studies were undertaken to determine whether fibrin formed on cultured human umbilical vein endothelial cells would alter synthesis of prostacyclin and t-PA by the cells. Fibrin was found to Increase synthesis of both prostacyclin and t-PA In a dose and time dependent manner. Stimulation of prostacyclin synthesis was completely Inhibited by Indomethacln; partially inhibited by actinomycln D, cyclohexlmide, and trifluoperazine; and not affected by cytochalasln D or vlnblastine. In contrast, stimulation of t-PA synthesis was completely Inhibited by actinomycln D and cyclohexlmide; partially Inhibited by cytochalasln D, vlnblastine, and trtfluoperazlne; and not affected by indomethacin. Fibrin I, formed with Reptilase, caused only slight stimulation of t-PA production, but virtually no stimulation of prostacyclin synthesis. Neither collagen polymerization on the cells nor thrombin added In concentrations that did not Induce fibrin polymer formation stimulated production of either substance. Furthermore, soluble fibrin II generated In the presence of the fibrin polymerization Inhibitor gly-pro-arg-pro also failed to stimulate either prostacyclin or t-PA production. The presence of platelets in the plasma from which the fibrin was formed did not affect the amount of stimulation of the cells. Fibrin-Induced stimulation of endothelial cell production of prostacyclin and t-PA could act to limit vascular occlusion in vivo by Inhibiting platelet function and by stimulating flbrlnolysls via t-PA.

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.