Textilinins from Pseudonaja textilis textilis. Characterization of two plasmin inhibitors that reduce bleeding in an animal model.

The incidence of vein-graft occlusion associated with myocardial infarction and thrombosis following the use of the plasmin inhibitor, aprotinin, to reduce blood loss during vascular surgery has prompted the isolation of an alternative kinetically distinct inhibitor of plasmin from the venom of Pseudonaja textilis. This inhibitor has been called textilinin (Txln) and two distinct forms have been isolated from the Brown-snake venom (molecular weight, 6688 and 6692). A comparison of plasmin inhibitor constants for aprotinin and the Txlns 1 and 2 indicated that the former bound very tightly (inhibitor constant, Ki approximately 10(-11) mol/l), while both of the latter bound less tightly (Ki approximately 10(-9) mol/l). Homogeneity of Txlns 1 and 2 was confirmed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and mass spectrometry. A sequence difference of six amino acids was observed between the two forms of Txln. Txln 1 and 2 showed, respectively, 45 and 43% homology with aprotinin, while there was 58 and 55% homology, respectively, with a plasmin inhibitor from the venom of eastern Taipan, Oxyuranus scutellatus. Both Txlns have six cysteines, like other inhibitors of this group, and homology was determined by alignment of these cysteines. Both have been shown to reduce blood loss by about 60% in a murine tail vein bleeding model. It is proposed that the kinetic profiles of Txln 1 and 2 for plasmin allow the arrest of haemorrhage without the possible threat of thrombosis.

Focused antithrombotic therapy: novel anti-platelet salicylates with reduced ulcerogenic potential and higher first-pass detoxification than aspirin in rats.

The use of aspirin as an anti-platelet drug is limited by its propensity to induce gastric injury and by its adverse effect on vascular prostacyclin formation. Two phenolic non-steroidal anti-inflammatory drugs (salicylic acid and diflunisal) were modified by esterification with a series of O-acyl moieties. The short-term ulcerogenic in vitro and in vivo anti-platelet properties, pharmacodynamic profiles, and extent of hepatic extraction of these phenolic esters were compared with aspirin (acetylsalicylic acid). The more lipophilic esters (longer carbon chain length in O-acyl group) show significantly less gastrotoxicity in stressed rats than does aspirin after a single oral dose. The in vitro and in vivo anti-platelet studies show that these phenolic esters inhibited (1) arachidonate-triggered human platelet aggregation and (2) thrombin-stimulated rat serum thromboxane A2 production by platelets in the clotting process almost as effectively as aspirin. The hepatic extractions of these O-acyl derivatives are significantly higher than those of aspirin. The pharmacodynamic studies show that these O-acyl derivatives of salicylic acid and diflunisal probably bind to, or combine with, the same site on the platelet cyclooxygenase as aspirin. Replacing the O-acetyl group with longer chain O-acyl moiety in this series of phenolic esters markedly reduced the potential of these agents to induce short-term gastric injury but did not lessen their activity as inhibitors of platelet aggregation. These non-acetyl salicylates may therefore represent a novel class of anti-platelet drugs with less ulcerogenic potential.

Brown snakes (Pseudonaja genus): venom yields, prothrombin activator neutralization and implications affecting antivenom usage.

The recent high prevalence of fatal bites by Brown snakes (Pseudonaja genus) has led to this study of venom yields from 66 brown snake milkings over 15 months. The amount of venom obtained from all species was higher than reported previously. Electrophoretic and Western blotting analyses of their venoms showed significantly lower avidity of Brown snake antivenom (BS-AV) for the prothrombin activator (PA) component (190 kD) than for other venom components, including the neurotoxins. The LD50 of P. inframacula has been determined for the first time. SDS-PAGE (sodium dodecyl sulphate-polyacrylamide gel electrophoresis) and Western blotting studies have shown that the Pseudonaja venoms contained proportionately more PA component than venoms of the Taipan (Oxyuranus scutellatus) or the Fierce snake (O. microlepidotus). Neutralization of the prothrombin activator of the Common Brown snake (P. textilis) (Pt-PA) by BS-AV was found to be time dependent and 40% remained unneutralized after 30 minutes incubation. Adult rats administered quantities of Pt-PA (IV) died with acute disseminated intravascular coagulation. Rats were made resistant to Pt-PA by preheparinization or by induction of tolerance to increasing quantities of Pt-PA. There is no evidence that Pt-PA has intrinsic toxicity apart from being a procoagulant. The improvement of BS-AV by addressing its deficiencies should be canvassed.

Hypercoagulability and hypofibrinolysis in primary osteoarthritis.

Histologic evidence of venous thrombosis and lipid abnormalities have previously been reported in osteoarthritis. Hypofibrinolysis has been recorded in patients with ischemic necrosis of bone, and it has been proposed as a major cause of osteonecrosis. This study determines whether systemic evidence of coagulation and lipid abnormalities could be detected in osteoarthritis. Global and specific tests were used to assess coagulability and fibrinolysis in 44 patients with degenerative osteoarthritis of the hip and 52 matched control subjects. In patients with osteoarthritis, an increase in factor VIIlc, increased platelet sensitivity over a range of adenosine diphosphate concentrations (0.05 micromol/L-4 micromol/L) and elevated D dimer levels were found. Euglobulin clot lysis time was prolonged in this group and plasminogen activator inhibitor Type 1 activity was increased. Relative hyperlipidemia was observed in the osteoarthritis group, with increased cholesterol, low density lipoprotein cholesterol, and triglyceride levels. It is concluded that there is a hypercoagulable and prothrombotic condition in osteoarthritis, with hypofibrinolysis and indirect evidence of increased fibrin generation. The possible contribution of lipid abnormalities to hemostatic imbalance in osteoarthritis is discussed.

Measurement of crosslinked fibrin derivatives in patients undergoing abdominal surgery: use in the diagnosis of postoperative venous thrombosis.

Levels of plasma crosslinked fibrin derivatives, a sensitive and direct marker of the lysis of intravascular crosslinked fibrin, were measured serially in 135 patients undergoing major abdominal surgery to determine their behavior and their use as a screening test for postoperative venous thrombosis. Preoperative levels and levels on the first postoperative day were significantly higher by both enzyme immunoassay and latex assay in 31 patients who developed venous thrombosis (positive venography) than in 104 patients who did not (negative 125I fibrinogen leg scan). Preoperative XLFDP levels 400 ng/ml (enzyme immunoassay) had a sensitivity to the diagnosis of postoperative venous thrombosis of 58%, specificity 74%, positive predictive value 41% and negative predictive value of 85%. The sensitivity of XLFDP levels over 1200 ng/ml on the first postoperative day was 65%, specificity 73%, positive predictive value 38% and negative predictive value 89%. These cutoff values were chosen (high negative predictive value) to allow identification of patients who were unlikely to have venous thrombosis. Measurement of plasma XLFDP, a simple inexpensive test, could be used as a screen to select patients for surveillance procedures (IPG or duplex ultrasonography). A substantial increase in XLFDP levels (greater than 500 ng/ml) occurred in virtually all patients, suggesting that fibrinolysis is not 'shutdown' postoperatively and that these assays reflect lytic activity at the fibrin surface more accurately than do measurements of plasminogen activators and their inhibitors.

Plasma cross-linked fibrin degradation product (XLFbDP) assays in an in vivo model of fibrinolysis.

Assumptions regarding the elaboration of plasma cross-linked fibrin degradation products (XLFbDPs) in vivo were tested using an experimental model in which particulate human fibrin was infused into rabbits and the products of lysis monitored with an immunoassay utilizing DD-3B6/22, a monoclonal antibody to human cross-linked derivatives. XLFbDPs were generated following the infusion of a suspension of cross-linked fibrin, attaining a peak between 40 and 60 min, then falling at a rate approximating a plasma half-life of 2 h. The major in vivo products of lysis of cross-linked fibrin, identified by SDS-PAGE of immunoextracted plasma, were D-dimer and high-molecular-weight moieties. Peak levels of XLFbDPs achieved correlated with the amount of fibrin administered. Since XLFbDP levels were no higher when fibrin infusion was followed by infusions of streptokinase and human plasminogen, it is concluded that endogenous mechanisms of lysis were already maximally stimulated. Infusions of non-cross-linked (NXL) fibrin or of fibrinogen led to much smaller, but measurable, rises in XLFbDP. In the latter group, XLFbDP levels rose further following fibrinolytic therapy. Treatment with epsilon aminocaproic acid (EACA) caused partial (greater than 50%) inhibition of lysis while pre-treatment with nitrogen mustard, inducing leucopenia, virtually abolished the appearance of XLFbDPs in the circulation. This implies that fibrinolytic responses are substantially dependent upon cellular functions sensitive to nitrogen mustard.

Fibrinolysis as a feature of disseminated intravascular coagulation (DIC) after Pseudonaja textilis textilis envenomation.

Blood was obtained from four patients envenomated by the Australian common brown snake, Pseudonaja textilis textilis. This elapid snake has one of the most toxic venoms in the world, containing extremely potent neurotoxic and coagulant components. The latter is a potent complete prothrombinase, converting prothrombin to alpha-thrombin, and comprises more than 30% of the total venom protein. The four envenomated patients developed a typical consumption coagulopathy. Serial serum and plasma samples from patients were studied by immunoaffinity adsorption, 2-alanine precipitation of fibrinogen and fibrinogen-related products and 2-dimensional immunoelectrophoresis, and assayed for crosslinked fibrin degradation products as D dimer, using the monoclonal antibody, DD-3B6/22. These procedures showed the virtually complete disappearance of fibrinogen, accompanied by the appearance of large quantities of fibrinogen and fibrin degradation products consisting of both crosslinked and noncrosslinked species. With recovery, a homogeneous high molecular weight fibrinogen was observed. The data suggest that the prothrombin activator of this venom causes the generation of thrombin which subsequently converts fibrinogen to fibrin and stimulates partial crosslinking of both alpha and gamma-chains. The resultant disseminated intravascular coagulation is accompanied by very active secondary fibrinolysis which apparently limits the extent of any microvascular thrombosis but which may contribute to a bleeding tendency.

Plasma cross linked fibrin degradation products in pulmonary embolism.

Plasma concentrations of cross linked fibrin degradation products, a marker of intravascular thrombosis and fibrinolysis, were measured in 495 patients with suspected pulmonary embolism referred for ventilation-perfusion lung scanning to determine whether concentrations are increased in pulmonary embolism and their potential use in diagnosis. Lung scans were described as normal (n = 66) or as showing a low (n = 292), indeterminate (n = 58), or high probability (n = 79) of pulmonary embolism. There was a difference between the mean levels of cross linked fibrin degradation products in each scan category: normal scans, 142 ng/ml; low probability scans, 295 ng/ml; indeterminate probability scans, 510 ng/ml; high probability scans, 952 ng/ml (p less than 0.001). Of the patients with high probability scans, 96% had raised concentrations. Explanations for discrepant low results include incorrect scan diagnosis, delay in blood sampling, and anticoagulation. Of the patients with a low or indeterminate probability of pulmonary embolism, 43% had increased concentrations of cross linked fibrin degradation products that could be attributed in most cases to another illness. Owing to the wide range of values in each lung scan diagnostic category, raised concentrations of these fibrin degradation products cannot be used without reference to the patient's clinical state as a discriminatory test for pulmonary embolism. Further evaluation of the significance of normal concentrations in excluding a diagnosis of pulmonary embolism appears to be warranted.

Partial purification and characterisation of a synovial fluid inhibitor of osteoblasts.

A polypeptide inhibitor of osteoblast proliferation is described which occurs in synovial effusions of patients with rheumatoid arthritis. Partial purification of the inhibitor showed a molecular weight of approximately 81,000 by gel electrophoresis. This polypeptide seems to be unique as no inhibitor of osteoblasts of similar molecular weight has been previously described in rheumatoid synovial effusions.

Purification and characterization of a prothrombin activator from the venom of the Australian brown snake, Pseudonaja textilis textilis.

A simple procedure, involving chromatography on concanavalin A-Sepharose and gel filtration, has been developed for the purification of a prothrombin activator from the venom of the Australian brown snake Pseudonaja textilis textilis. The prothrombin activator, which is a major venom component, is a high molecular weight protein (Mr greater than or equal to 200,000) which yields a number of subunits when examined by SDS-PAGE. It is related antigenically to the venom prothrombin activator of the taipan Oxyuranus scutellatus. P. textilis prothrombin activator is able to coagulate citrated plasma, warfarin plasma, and Factor V- and Factor X-deficient plasmas; to convert purified human prothrombin to thrombin; and to hydrolyse the peptide p-nitroanilide substrate S-2222. Calcium ions and phospholipids had little if any effect on the rates of coagulation of citrated plasma or S-2222 hydrolysis catalysed by this enzyme.

Measurement of crosslinked fibrin derivatives--use in the diagnosis of venous thrombosis.

The measurement of crosslinked fibrin derivatives in plasma has received evaluation as a screening test in the diagnosis of venous thrombosis. Plasma samples were taken from 104 patients undergoing venography because of clinical suspicion of lower limb venous thrombosis. The samples were assayed using a monoclonal antibody identifying an epitope on D dimer and larger crosslinked fibrin derivatives in an enzyme immunoassay. 100% of patients with positive venograms had elevated levels of these molecules. While a percentage of patients with negative venograms also had increased levels, alternative clinical explanations were apparent in most. A normal D dimer value excludes the diagnosis of venous thrombosis, while an increased value supports it. The measurement of crosslinked fibrin derivatives in plasma may play a role in the selection of patients for venography.

Rapid detection of cross-linked fibrin degradation products in plasma using monoclonal antibody-coated latex particles.

Conformational and structural changes on conversion of fibrinogen to fibrin and its cross-linking by Factor XIIIa lead to the development of new antigenic determinants that permit differentiation between their plasminolytic cleavage products. A monoclonal antibody (DD-3B6/22) that is specific for cross-linked fibrin derivatives containing the D dimer configuration has been used in developing a latex agglutination procedure that can detect fibrin degradation products in either plasma or serum. Fibrinogen or its degradation products do not cross-react with this antibody. Results were calibrated with an enzyme immunoassay, which used a purified D dimer standard. Plasmas from 40 normal subjects, all having D dimer levels below 250 ng/mL measured by enzyme immunoassay, were all negative by latex assay. In contrast, positive latex agglutination titers were obtained with 87 of 88 patients with demonstrated deep venous thrombosis, pulmonary embolism, or disseminated intravascular coagulation. Compared to enzyme immunoassay, latex agglutination assay is less sensitive, but this latex procedure provides a rapid and less elaborate test for elevated levels of cross-linked fibrin degradation products in patients with thrombosis. Plasma assays for fibrin degradation products are preferable to those using serum.

A simple chromatographic procedure for the purification of the D dimer fragment from crosslinked fibrin.

An improved procedure for the purification of fragment D dimer derived from crosslinked plasma fibrin is described which entails chromatofocusing chromatography using PBE 94 and polybuffer 74, and gel chromatography on Sephacryl S-300. The procedure provides a preparation of D dimer which behaves as a single macromolecular entity with molecular weight 190,000 in sedimentation equilibrium studies. Only a single protein band is observed in polyacrylamide gel electrophoresis conducted in the presence or absence of sodium dodecyl sulfate, while patterns characteristic of gamma'-gamma' chains are observed under denaturing conditions after reduction of the preparation with beta-mercaptoethanol. The D dimer contains no demonstrable E antigen by a range of electrophoretic and immunologic techniques. Advantages of this method for obtaining D dimer in high yield include the use of plasma as starting material, the use of a simple lysis regimen in the presence of Ca2+, and the use of simple chromatographic techniques performed under nondenaturing conditions.

Measurement of autoantibodies against fibrinogen and fibrin degradation products by enzyme-linked immunoassay.

We have devised a simple enzyme immunoassay to detect and quantitate autoantibodies against derivatives of fibrinogen. This assay has been applied with a range of antigens including a fibrinogen lysate (containing X, Y, D and E), D dimer, D dimer-E and a preparation of high molecular weight complexes derived from crosslinked fibrin. We have found that autoantibodies interacting with these antigens can be detected in varying concentrations in most sera from both normal subjects and patients with a variety of diseases and are evidently of mixed Ig class. These autoantibodies are directed against at least several cryptic antigens which appear during fibrinogen/fibrin degradation and some appear to be directed specifically against cross-linked fibrin derivatives. No clear disease correlates have yet emerged but a relationship between elevated levels and prior infective, thrombotic, inflammatory or traumatic disorders is likely. It is suggested that these autoantibodies may contribute to the catabolism of fibrinogen derivatives, provide a marker of thrombosis, and sometimes produce pathologic effects.

Measurement of cross linked fibrin derivatives in plasma: an immunoassay using monoclonal antibodies.

Fibrinogen degradation, fibrin polymerisation, and the insertion of cross links into fibrin by fibrin stabilising factor lead to the appearance of new antigenic determinants. Antibodies against these antigenic sites may react specifically with the derivatives but not with the parent molecules. We have utilised a monoclonal antibody, which interacts with the cross linked fragment D dimer and related high molecular weight fibrin derivatives, to develop an enzyme immunoassay which measures cross linked fibrin derivatives in plasma and serum using D dimer as standard. Mean concentration in plasma from normal subjects was 75 ng/ml with an upper limit of about 144 ng/ml. Concentrations in patients with pulmonary embolism, deep venous thrombosis, arterial thromboembolism, and disseminated intravascular coagulation were raised in all cases. Confirmation of the specific increase of cross linked fibrin derivatives in patients with disseminated intravascular coagulation was obtained by parallel monitoring of their fibrin degradation products in serum using affinity chromatography and sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. In many patients the plasma concentrations greatly exceeded the serum values of cross linked fibrin degradation products, suggesting that the procedure can measure fibrin derivatives in plasma which are absent from serum.

An immunoassay for human D dimer using monoclonal antibodies.

Monoclonal antibodies (MAb) were raised against human D dimer. The hybridomas were screened with a solid phase enzyme immunoassay against D dimer and fibrinogen degradation products. Among the panel of MAb identified, two distinct patterns emerged; the majority belonging to a panspecific class reacting against epitopes present on both D dimer and fibrinogen degradation product Dcate and a monospecific class reacting with determinants apparently present only on D dimer. A number of MAb were further characterised for their ability to specifically capture antigen in a solid phase enzyme immunoassay and assays were developed which have a sensitivity of 10 ng/ml for D dimer or crosslinked fibrin derivatives and may be suitable for detection of crosslinked derivatives in serum and plasma samples in a clinical situation.

Measurement of crosslinked fibrin degradation products - an immunoassay using monoclonal antibodies.

We have prepared a monoclonal antibody which recognises an antigenic determinant on D dimer, a specific fragment resulting from the degradation of crosslinked fibrin. This antibody has been used in the development of an enzyme-linked immunoassay for D dimer and related degradation products containing crosslinked gamma-gamma chains, to provide a simple assay of circulating crosslinked fibrin degradation products suitable for clinical use. Since these crosslinked fibrin degradation products are characteristic of fibrinolysis, as distinct from fibrinogenolysis, their measurement should aid in the diagnosis, evaluation and monitoring of thrombotic and thrombolytic states. In preliminary studies, low concentrations of crosslinked fibrin derivatives were detected in normal sera. High levels were found in 30/30 patients with disseminated intravascular coagulation and in the majority of patients having deep venous thrombosis or pulmonary embolism.

The influence of various combinations of plasminogen and streptokinase on fibrinolysis. II. A mechanistic study.

The components found in 125I-labelled cross-linked plasma fibrin lysates obtained by alternate treatments with streptokinase (SK) and plasminogen (plgn) were examined by immunological and physicochemical methods. The more rapid and complete lysis achieved with the sequence SK leads to plgn was reflected by the near absence of the electrophoretically stable D dimer-E complex and high molecular weight soluble aggregates (greater than 3 x 10(5) molecular weight), while these components were present in considerable amounts during the plgn leads to SK regimen. An assessment of the data from the rapid and slow regimens suggested that cross-linked high molecular weight complexes wer initially released from fibrin, these being rapidly degraded to the D dimer-E complex which was subsequently converted to pure D dimer and E fragments. Two forms of the D dimer-E complex are proposed, probably varying in stability according to the number of attachment sites between the D dimer and E domains.

The influence of various combinations of plasminogen and streptokinase on fibrinolysis.

The lysis rates of 125I cross-linked plasma fibrin clots have been investigated following immersion in various buffered concentration of streptokinase (SK), prior to (called the SK leads to plgn regimen) and after (called the plgn leads to SK regimen) enrichment with 2.0 U of plasminogen (plgn, lys-type). The SK leads to plgn regimen usually achieved total clot lysis with the most active lysis occurring following enrichment in 125-130 IU SK solutions, while only partial lysis was observed during the plgn leads to SK procedure. The effect of SK concentration was marked during the SK leads to plgn regimen while, during the plgn leads to SK treatment, its lytic rate never exceeded a factor of 2.0 over a wide concentration range of SK (8.0-20,000 IU/ml. The availability of plasminogen to perfuse the activator-rich clot seemed to be the prevailing influence on clot lysis and lysis of clots in plasma was inhibited by serum inhibitors, SK antibodies and plasma fibrinogen.