The kinetics of inhibition of alpha-thrombin in human plasma.

Methods have been developed for kinetic studies of the inhibition of exogenous unmodified thrombin in human plasma containing normal levels of fibrinogen and calcium ion. To prevent interference by other proteases, factor VIII-deficient plasma was used and contained 50 nM Phe-Phe-Arg-chloromethyl ketone and 1 kallikrein-inactivating unit/ml aprotinin; neither inhibited thrombin at these levels. Two independent assays were used. The first was the discontinuous amidolytic assay of thrombin activity, which measures both free thrombin and thrombin-alpha 2-macroglobulin complex, and was used to estimate the rates of inhibition both by "inactivating" inhibitors, such as anti-thrombin and alpha 1-protease inhibitor, and by alpha 2-macroglobulin (alpha 2M). The contribution of alpha 2M was confirmed by a second method, which measured with time the generation of amidolytic activity due to the thrombin-alpha 2M complex. The total rate of thrombin inhibition in plasma containing 4 mM free Ca2+ was of the order of 1.9 min-1, of which 0.4 min-1 was due to alpha 2M and 0.9 min-1 was due to inhibitors that were removed when plasma was passed through heparin-agarose. Thrombin inhibition was also measured in varying dilutions of plasma and confirmed that total inhibition rate is approximately linearly related to plasma (and thus inhibitor) concentration. Negatively charged phospholipid micelles had very little effect on thrombin inhibition rate, but platelets accelerated inhibition to more than 2.5 min-1.

Fibronectin binding to thrombin-stimulated platelets: evidence for fibrin(ogen) independent and dependent pathways.

Plasma fibronectin binds in a specific and saturable manner to thrombin-stimulated platelets. gamma-Thrombin stimulated 80% as much fibronectin binding to platelets as alpha-thrombin with conversion of less than or equal to 1% of platelet fibrinogen to fibrin. Afibrinogenemic and normal platelets bound similar quantities of fibronectin in the presence of calcium or magnesium-ethylene glycol tetra-acetic acid (EGTA). These observations indicate that fibronectin can interact with platelets without involvement of fibrin or fibrinogen. Nevertheless, two different effects of fibrin(ogen) on fibronectin binding were observed. First, exogenous fibrinogen inhibited fibronectin binding to thrombin-stimulated platelets. This inhibition was unidirectional, as fibronectin did not inhibit fibrinogen binding to ADP or thrombin-stimulated cells. Second, formaldehyde-fixed cells with surface-associated fibrin bound significant quantities of fibronectin. This interaction required calcium and did not occur on fixed cells with or without surface-bound fibrinogen. A portion of the ligand bound to fixed cells with surface-associated fibrin was modified to form a derivative with a molecular weight identical to that of the fibronectin subunit cross-linked to the alpha-chain of fibrin. This high mol wt derivative was also observed to a variable extent with living cells in the presence of magnesium or calcium but not in the presence of magnesium-EGTA. Thus, fibronectin binds to platelets by at least two mechanisms: (1) a fibrin(ogen)-independent pathway that requires divalent ions and is inhibited by exogenous fibrinogen; and (2) a fibrin-dependent pathway with an absolute calcium requirement. With nonaggregated, thrombin-stimulated platelets, the former pathway appears to predominate.

Fibrinolytic response to trauma.

The fibrinolytic response to trauma was investigated in 23 patients. Patients were triaged upon arrival in the emergency center into three groups; group I-patients with significant trauma who maintained normal vital signs, had a good prognosis, and tolerated the trauma well (mean injury severity score 8, range 4 to 12); group II--patients with significant trauma and transient episodes of hypotension, hypoxia, or acidosis who recovered (mean injury severity score 22, range 9 to 38); and group III--patients with profound or continued hypoxia and hypotension who eventually died of the trauma (mean injury severity score 41, range 30 to 50). Serial measurements of prothrombin time, activated partial thromboplastin time, and platelet count; concentrations of fibrinogen, plasminogen, and fibrin degradation products; and assays of euglobulin fraction fibrinolytic activity on plasminogen-free and plasminogen-rich fibrin plates were obtained on all patients. Coagulation studies documented a trauma-related coagulopathy that correlated with the degree of trauma. Plasminogen concentrations were initially depressed in all three groups; however by 24 hours group III patients were noted to have significantly elevated plasminogen concentrations while group I and group II patients had normal plasminogen concentrations. Fibrinolytic activity measured on plasminogen-free and plasminogen-rich fibrin plates was initially increased in all three groups with group III patients demonstrating the greatest increase. Over the succeeding 14 hours fibrinolytic activity returned to baseline values in group I and group II patients while group III patients demonstrated no detectable fibrinolytic activity for the remainder of the study period. This absence of fibrinolytic activity and increase in plasminogen concentrations in group III patients is thought to be caused by depletion of the intravascular plasminogen activator with the subsequent development of a hypofibrinolytic state.

Thrombus-related uptake and vascular clearance of 131 I-fibrin des-AABB as compared to 125 I-fibrinogen in patients with established venous thrombosis.

Thrombus-related uptake of 131 I-fibrin des-AABB has been compared to that of 125 I-fibrinogen in 13 patients with established venous thrombosis. Both tracers originated from a common pool of beta-alanine precipitated fibrinogen. Scan-recordings were performed as a radiofibrin (ogen) uptake test. Uptake characteristics of des-AABB fibrin were similar to those of fibrinogen, when measured as percentage of concomitant radioactivity over the heart. Due to its longer circulation time, fibrinogen was superior to fibrin des-AABB for the detection of venous thrombi. Circulating des-AABB fibrin was cleared biphasically, with an initial rapid decline followed by a gradual exponential decrease. Mean half-lives were 5.5 +/- SD 3.5 hr and 10 +/- SD 3.5 hr, respectively. The elimination rates were uninfluenced by thrombus activity, as judged by the fibrin(ogen) uptake test. Metabolic half-life of fibrinogen in the total material was 62 +/- SD 19 hr. Dissociation of fibrinogen and soluble des-AABB fibrin clearance rates was evident, describing their own, independent elimination patterns, probably reflecting different clearing mechanisms.

Evidence for circulating fibrin in familial Mediterranean fever.

Cryofibrinogenemia was found in 10 of 24 plasma samples (42%) from subjects with FMF. This precipitate was found during active disease as well as during intervals between crises. We found a higher incidence of cryofibrinogenemia in subjects with mild to moderately severe disease not being treated with colchicine (six of eight) as compared with colchicine-treated subjects who were in partial or complete clinical remission (four or 16; p less than 0.02). All cryofibrinogen precipitates contained fibrin, as assessed by electrophoretic analyses showing the presence of multimeric crosslinked forms of fibrin(ogen) linked by gamma-dimers. This finding in clinical specimens supports the hypothesis that fibrin in an obligatory component of cryofibrinogen. Fibrin was also found in HPF (two of six specimens) prepared from cryofibrinogen-negative FMF plasmas, thus showing that soluble forms of fibrin are even more prevalent in this disorder than is indicated by the frequent finding of cryofibrinogenemia.

Homologous controlled-viscosity fibrin for endovascular embolization. Part II: catheterization technique, animal experiments.

Part I of the present paper described the development of a substance for endovascular embolization from homologous fibrinogen, aprotinin, thrombin, metrizamide and CaCl2. Part II deals with the applicability of a controlled-viscosity fibrin mixture via different types of arterial catheters. In a flow-dynamic model the embolizing medium injected via a double syringe was shown to block a blood flow corresponding approximately to the flow encountered in cerebral angioma vessels. In the course of animal experiments the embolization of mesenteric arteries of rabbits showed the distribution of the embolizing medium to be dependent on its viscosity; the action of an embolizing medium applied by means of a double syringe was studied in the femoral arteries of rabbits. Scintigraphy was used to study the distribution of the substance in the body of the experimental animal after intravenous (i.v.) application; long-term studies of embolized auricular arteries in rabbits revealed parchment-like necroses after 5 to 10 days and the presence of radiopaque substances in the ear stumps after 6 weeks.

Platelet inhibition of renal cortical fibrinolytic activity in the rabbit.

A fibrin slide test was utilized to study the effect of platelets and endotoxin on renal cortical fibrinolysis in rabbits. Cortical lysis was absent in kidney from animals made markedly thrombocytopenic with goat antirabbit platelet serum or endotoxin; light microscopy was normal and immunofluorescent microscopy for fibrin was negative. No loss of lysis was detected in kidney of animals given goat anti-rabbit albumin or isotonic saline. Plasma from animals with endotoxin or antiplatelet antibody-induced thrombocytopenia demonstrated an increased capacity to inhibit cortical fibrinolytic activity of normal rabbit kidney. Antiplatelet antibody could be substituted for the preparatory injection of endotoxin in the generalized Shwartzman reaction; a parallel rise in lysis inhibitory titer was detected in plasma from animals prepared with antibody or endotoxin. Although lysis was absent following incubation of normal renal cortex with washed platelets, no inhibition of lysis was found after incubation of normal cortex with endotoxin, histamine, serotonin, platelet membranes, or granules. Using a modified fibrin slide technique, a diffusable platelet inhibitor of lysis could be demonstrated. These studies indicate that platelets contain an inhibitor to renal cortical fibrinolysis which is released into the circulation upon platelet destruction. The findings also suggest that platelet destruction is the mechanism through which endotoxin inhibits cortical lysis.

Disseminated intravascular coagulation and head injury.

Blood coagulation tests were performed on admission to the hospital and on consecutive days after severe and moderate head injury in 34 patients. Platelet counts and fibrinogen were normal at admission and raised thereafter. The partial thromboplastin time was shortened at admission and lengthened in the following days. Fibrinolytic activity was enhanced at admission. The ethanol gelation test was negative in all patients during the post-traumatic time course. It was concluded that, in the first 24 hours after injury, activated coagulation was present after head injury. In contrast with data of other authors, disseminated intravascular coagulation did not occur in these series.

Serum and urinary fibrin-fibrinogen degradation products in glomerulonephritis.

The serum and urine concentrations of fibrin/fibrinogen degradation products (F.D.P.) were estimated in 172 patients with glomerulonephritis. In each case the diagnosis was established on the basis of clinical, renal histological, and ultrastructural findings. Serum F.D.P. concentrations were often raised in all types of glomerulonephritis, though more consistently in active proliferative forms. The urinary concentration provided a reliable and sensitive index of activity, progression, and natural history in proliferative glomerulonephritis. In these forms the urinary F.D.P. content was thought to reflect predominantly lysis of intraglomerular fibrin deposits. In minimal lesion and membranous glomerulonephritis low but abnormal concentrations of urinary F.D.P. were consistently found. It is suggested that in these cases the products are derived from limited proteolysis of fibrinogen filtered through an abnormally permeable basement membrane.Daily measurement of urinary F.D.P. concentration is of potential value in the differential diagnosis of patients with glomerulonephritis and at the same time provides a sensitive assessment of the activity and natural history of proliferative disease.