Fibrin Binding of Plasminogen Coated Liposomes In Vitro

In this study, the fibrin binding properties of liposomes containing a number of plasminogen (Pig) molecules on the outside were compared to those of free (non-liposomal) Pig in an in vitro model system. Fibrin monolayer coated 96-wells plates were used, containing fibrin monomer at a density of around 3.4 to 3.9 × 10-4 nmol/cm2. These densities are similar to liposomal Plg-densities, thus allowing multivalent interactions to occur.

In the panel of experimental conditions that was chosen, binding of free Pig and liposomes with Pig showed three main differences in characteristics. Firstly, in the fibrin binding of Plg-liposomes not all Pig may be involved, but on the average 40% of the total amount of liposomal Pig. This was shown by lysing the liposomes after binding to the fibrin and estimation of truly bound Pig. With Plg-densities on the liposomes below the fibrin binding sites density, the maximal number of bound Pig molecules remains below the amount of available fibrin binding sites. Secondly, a higher binding rate by at least one order of magnitude was observed for liposomes with Pig compared to free Pig. Thirdly, liposomes with Pig exhibit a fibrin binding affinity which increases with Plg-density, because of the multivalent character of interaction. Liposomal Pig can successfully compete for fibrin binding sites with a 100 fold higher concentration of free Pig.

These in vitro findings indicate that in view of avid and rapid fibrin binding, liposomes with attached plasminogen may be suitable for in vivo targeting to fibrin based thrombi.

Factor XII-Dependent Fibrinolysis: A Double Function of Plasma Kallikrein and the Occurrence of a Previously Undescribed Factor XII- and Kallikrein-Dependent Plasminogen Proactivator

Fibrinolytic studies in euglobulin fractions of Fletcher trait plasma (deficient in prekallikrein) revealed reduced activities as compared to normal plasma. A quantitative assay for total plasminogen activator plus proactivator in plasma showed that the amount in Fletcher trait patients is about half of normal (normal = ± 100 blood activator units [BAU]/ ml). Plasma kallikrein partially purified in a high and low molecular weight form exerted plasminogen activator activity amounting to 10–15 BAU/ml plasma. So, the absence of kallikrein in the deficient plasma can not fully account for the reduction in activator activity. Additions of kallikrein preparations or normal plasma fractions resulted in additional activator activity in Fletcher trait plasma which was assessed at 30–40 BAU/ml. This activity was assumed to originate from a previously undescribed plasminogen proactivator whose activation is kallikrein- and factor XH-dependent.

Fractionation experiments demonstrated the presence of two major activities and a minor activity caused by kallikrein in normal plasma.

It is concluded that plasma kallikrein has two functions in the generation of factor XII- dependent fibrinolytic activity: one as a direct plasminogen activator and another as a factor in the activation of a major factor XH-dependent plasminogen proactivator.

Protection of Single-chain Urokinase-type Plasminogen Activator (scu-PA) in Aprotinin Treated Cardiac Surgical Patients Undergoing Cardiopulmonary Bypass

Intraoperative high-dose aprotinin administration has been shown to reduce the intra-and postoperative blood loss in cardiac surgery. The haemostatic effect has been attributed to platelet preserving properties and to inhibition of contact activation reducing thrombotic and fibrinolytic activity during and after cardiopulmonary bypass (CPB).

Here we report on the effects of aprotinin on urokinase-type plasminogen activator, especially on the protection of the zymogen singlechain urokinase-type plasminogen activator (scu-PA). scu-PA occurs cell associated as well as free in the circulation (concentration 50 pM, half-life 5 min), and is potentially activated by kallikrein and plasmin, both potent targets for aprotinin. The generated active two-chain u-PA (tcu-PA) is a powerful activator of fibrinolysis.

Sixteen male patients undergoing myocardial revascularization were randomly assigned to aprotinin treatment (A) or control group (C).

Plasma concentration of total u-PA antigen and of the specific forms scu-PA(zymogen) and tcu-PA(active enzyme) were measured at different stages intraoperatively and two hours postoperatively. After an initial drop due to haemodilution at the onset of CPB, the concentrations of circulating u-PA forms restored intraoperatively in A, but remained subnormal in C until the end of the observation period. The concentration of total u-PA antigen of shed mediastinal blood was both in A and C two-fold higher than in the circulation, but the antigen was preserved as the zymogen scu-PA in A and largely converted to an inactive, non activatable form in C. Intra- and postoperative blood losses were less than half the amount in A as compared to C.

It is concluded that without aprotinin administration activation of circulatory scu-PA occurs, accompanied by stimulation of fibrinolysis and bleeding, finally resulting in elimination of tcu-PA complexed with endogenous inhibitors. Furthermore, cellular release of scu-PA occurs at or near the bleeding sites, as evidenced by the two-fold higher u-PA antigen concentration in the shed mediastinal blood. The released scu-PA is also activated and subsequently converted to an inactive form unless aprotinin is administered. High-dose aprotinin application during CPB effectively protects circulating and released scu-PA from activation and attenuates bleeding consequences.

Studies on the Fibrinolytic System in Human Plasma: Quantitative Determination of Plasminogen Activators and Proactivators

Effects due to plasma plasminogen activators and proactivators are usually studied in assay systems where inhibitors influence the activity and where the degree of activation of proactivators is unknown. Quantitative information on activator and proactivator levels in plasma is therefore not available

Studies on the precipitating and activating properties of dextran sulphate in euglobulin fractionation presented in this paper resulted in the preparation of a fraction in which there was optimal recovery and optimal activation of a number of plasminogen activators and proactivators from human plasma. The quantitative assay of these activators on plasminogen-rich fibrin plates required the addition of flufenamate to eliminate inhibitors. The response on the fibrin plates (lysed zones) could be coverted to arbitrary blood activator units (BAU). Consequently, a new activator assay which enables one to quantitatively determine the plasma level of plasminogen activators and proactivators together is introduced.

Two different contributions could be distinguished: an activity originating from extrinsic activator and one originating from intrinsic proactivators. The former could be assayed separately by means of its resistance to inhibition by Cl-inactivator. Considering the relative concentrations of extrinsic and intrinsic activators, an impression of the pattern of activator content in plasma was gained. In morning plasma with baseline levels of fibrinolysis, the amount of extrinsic activator was negligible as compared to the level of potentially active intrinsic activators. Consequently, the new assay nearly exclusively determines the level of intrinsic activators in morning plasma. A pilot study gave a fairly stable level of 100 ± 15 BAU/ml (n = 50). When fibrinolysis was stimulated by venous occlusion (15 min), the amount of extrinsic activator was greatly increased, reaching a total activator level of 249 ± 27 BAU/ml (n = 7).

On the Role of C1-Inhibitor as Inhibitor of Tissue-type Plasminogen Activator in Human Plasma

An enzyme immuno assay was developed to measure complexes of tissue-type plasminogen activator (t-PA) with C1-inhibitor in order to study the role of C1-inhibitor as an inhibitor of t-PA in plasma. In vitro experiments with melanoma and recombinant t-PA learned that purified C1-inhibitor reacts with both single chain t-PA and two chain t-PA. The rate constants ranged from 3.0 to 5.2 M-1s-1 In plasma, melanoma and recombinant two chain t-PA were hardly inhibited by C1-inhibitor, in contrast to melanoma and recombinant single chain t-PA which were inhibited to the same extent by endogenous C1-inhibitor as they were by purified C1-inhibitor. In vivo, t-PA/C1-inhibitor complex could be measured in plasma in a few cases in healthy volunteers (0.62 ± 0.43 ng/ml t-PA equivalents), after exercise (0.84 ± 0.25 ng/ml t-PA equivalents) and after a desmopressin infusion (0.26 ± 0.04 ng/ml t-PA equivalents). However, t-PA/C1-inhibitor complex was found in plasma in all cases after venous occlusion (1.7 ± 0.5 ng/ml t-PA equivalents), in peritoneal fluid from patients suffering from peritoneal inflammatory disease (2.2 ± 1.3 ng/ml t-PA equivalents) and in plasma from healthy volunteers during a t-PA infusion (27.7 ± 18.5 ng/ml t-PA equivalents at peak level). In the last case, about 8 % of the infused dose of recombinant t-PA (alteplase) was inhibited by C1-inhibitor at peak level. The half-life (t1/2α) of t-PA antigen in plasma was found not to be altered when t-PA was inhibited by C1-inhibitor (4.0 min and 4.2 min, respectively). Thus, in vivo, t-PA/C1-inhibitor complex is mostly present when t-PA escapes rapid liver clearance and accumulates in one place (e.g. during venous occlusion or in peritoneal fluid) or when it circulates in high concentrations (e.g. during t-PA infusion).

Effect of Isotretinoin on Endogenous Tissue-Type Plasminogen Activator (t-PA) and Plasminogen Activator Inhibitor 1 (PAI-1) in Humans

The effect of isotretinoin on fibrinolysis was investigated in 10 healthy, male volunteers in a randomized, double-blind, crossover-designed study. Isotretinoin (40 mg) was administered in the morning and in the evening for 5 days. t-PA, u-PA and PAI-1 antigen and activity in plasma were measured every morning at 9 a.m. on days 1 to 4 and every 3 hours over 24 hours on day 5. Isotretinoin treatment had no significant stimulatory effect on endogenous t-PA antigen and activity in morning plasma samples nor on their circadian variation. Also, u-PA antigen levels did not change after isotretinoin treatment. Mean PAI-1 antigen and PAI activity in 9 a.m. plasma samples were non-significantly higher during isotretinoin than during placebo treatment. After treatment with isotretinoin a significant rise of fasting triglyceride plasma levels was observed as compared to placebo. The study shows that isotretinoin has no clinically significant effect on endogenous fibrinolysis.

Hereditary Increase of Plasma Histidine-Rich Glycoprotein Associated with Abnormal Heparin Binding (HRG Eindhoven)

Plasma histidine-rich glycoprotein (HRG) was found to be persistently increased in a patient with a history of recurrent arterial thromboembolic events. The mean concentration was 270% of normal pooled plasma. Increased HRG was found in eight of the 17 relatives studied, but none of them has experienced thrombo-embolism yet. Apparently, increased HRG was hereditary with autosomal dominant inheritance. A significant correlation was found between the increased plasma concentration of the protein and the age of the subjects (P<0.02), whereas no such relation is present in a normal population.

The plasma HRG of the proposita and 9 of her family members displayed abnormal binding to heparin, as assessed in a crossed affinity immuno-electrophoresis system: the usual increase in mobility after binding to heparin was absent. The binding of this variant HRG to plasminogen was normal. This case represents the first abnormal HRG variant reported and it is proposed to designate it: HRG Eindhoven.

Treatment of Hereditary Protein C Deficiency with Stanozolol

Five type I protein C deficient male patients received 5 mg stanozolol b.i.d. during 4 weeks. After four weeks of treatment plasma protein C activity increased from 0.42 to 0.74 U/ml and protein C antigen from 0.49 to 0.75 U/ml. This approximately 1.6 fold increase in plasma protein C was accompanied by an increase in factor II antigen (1.5 fold), factor V activity (1.6 fold), factor X antigen (1.1 fold), antithrombin III antigen (1.3 fold) and heparin cofactor II antigen (1.5 fold), while the concentration of factor VII, factor VIII, and factor IX activity, and of protein S antigen remained unchanged. Prothrombin fragment F1+2, measured in two patients, increased 1.3 fold. In addition to its effect on procoagulant and anticoagulant factors stanozolol had profibrinolytic effects, reflected in an increase in tPA activity and in the concentration of plasminogen. These data indicate that in type I protein C deficient patients stanozolol increases the concentrations of both procoagulant and anticoagulant factors and favours fibrinolysis. The efficacy of stanozolol in preventing thrombotic disease in type I protein C deficient patients, however, remains to be established. During the four weeks of stanozolol treatment no thrombotic manifestations were observed in the protein C deficient patients.

Multicentre Evaluation of Commercial Kit Methods: Plasminogen Activator Inhibitor Activity

In order to study the analytical performance of different commercial kits for determination of plasminogen activator inhibitor (PAI) activity we distributed eight selected split samples to 11 European laboratories experienced with haemostasis testing. Three different laboratories were involved in the production of data from each of the commercial kits tested. A considerable variation of PAI activity results reported from the laboratories testing the same commercial kits was observed. The range of reported results could in individual samples exceed the median value indicating an interlaboratory variation of more than 100%.

When we harmonized the results reported from different kits in different laboratories by means of an international standard from National Institute for Biological Standards and Control (NIBSC) we still observed that the results produced by some kits deviated systematically from results produced by other kits. Also, the harmonized results were used to estimate the overall coefficient of variation (CV) of PAI activity determined in various laboratories by different kits. We observed an inverse correlation between the PAI activity level and the CV with a CV of about 10Q% for low PAI activity levels and a CV of about 16% for high PAI activity levels. The high imprecision of the kits in the low concentration range of PAI activity indicates that unspecific factors in plasma may interfere with determination of active PAI. This was confirmed by the evaluation of the results from one of the plasma samples, which was PAI-1 depleted. The laboratories involved in the testing reported for this sample a mean value of 6.1 IU/ml.

In conclusion, the currently available kits for determination of PAI activity are not accurate for measurement of PAI-1 in plasma, and the kits give imprecise results particularly at low activity levels.

Multicenter Evaluation of Commercially Available Methods for the Immunological Determination of Plasminogen Activator Inhibitor-1 (PAI-1)

In order to evaluate the comparability of data obtained with various available kits for the immunological determination of PAI-1 antigen in plasma and in order to investigate the underlying cause of observed differences, e. g. problems of specificity or of proper calibration of the provided standard, a multicenter study was organised in the framework of the Subcommittee of Fibrinolysis of the Scientific and Standardization Committee.

Eight different plasma samples were distributed among 16 laboratories: a pooled normal plasma, NIBSC 87/512, PAI-1 antigen depleted plasma, PAI-1 depleted plasma supplemented with 59 ng/ml active PAI-1 and four different individual plasma samples. A considerable variation in absolute values is observed between the various kits, e.g. in pooled normal plasma a value is found ranging between 7.4 and 28 ng/ml. Harmonization of all data relative to the PAI-l-depleted plasma supplemented with an exact amount of active PAI-1 (59 ng/ml), followed by a statistical analysis using a two way analysis of variance, revealed that 6 out of 7 kits yielded values that were not significantly different with coefficients of variation around 30%. Correlations between the values obtained with these kits yielded slopes between 0.75 and 1.44 with correlation coefficients between 0.973 and 0.999. Values obtained with one kit appeared to be significantly different (even after harmonization) from the other kits (p <0.001 to p <0.05). Comparison of PAI-1 antigen with the PAI activity values in the analysed samples suggests that one kit may deal with a problem of a difference in reactivity between active and latent PAI-1.

In conclusion 6 different kits yield results that, only after harmonization, are comparable and do correlate very well. Thus proper calibration of the provided standards may solve the majority of the problems observed with PAI-1 antigen kits. Differential specificity towards different conformational forms of PAI-1, as a consequence of the use of different monoclonal antibodies, is a minor, but a potential problem, that needs to be considered when comparing data obtained with various methods.

A Parent-Twin Study of Plasma Levels of Histidine-Rich Glycoprotein (HRG)

Histidine-rich glycoprotein (HRG) is a non-enzymatic glycoprotein that acts as a modulator of several plasma proteins involved in coagulation and fibrinolysis. The contributions of genetic and environmental influences to inter-individual variation in plasma levels of HRG were studied in 160 Dutch families consisting of adolescent twin pairs and their parents. Results showed that 69% of the variance in plasma HRG concentrations could be accounted for by genetic factors. Heritability was the same in males and females and in parents and their offspring. There was no association between HRG levels of husband and wife and no evidence was found for the influence of shared family environment on the resemblance between relatives.

Pharmacokinetics of Saruplase, a Recombinant Unglycosylated Human Single-Chain Urokinase-Type Plasminogen Activator and Its Effects on Fibrinolytic and Haemostatic Parameters in Healthy Male Subjects

Pharmacokinetics of two doses of the recombinant single-chain urokinase-type plasminogen activator (r-scu-PA) saruplase (40 and 20 mg) and its effect on fibrinolytic and haemostatic parameters were studied in six healthy male subjects using a randomized, double-blind, placebo-controlled, cross-over study. Special precautions were taken to prevent artefactual in vitro effects on fibrinolytic activity.

The clearance of saruplase ranged from 310 to 862 ml/min and the apparent volume of distribution of the central compartment was about 8 1. Both doses of saruplase caused α2-antiplasmin consumption, indicating some systemic fibrinolytic activation. However, the 20 mg dose caused no detectable fibrinogen breakdown and only a small increase in total fibrin/fibrinogen degradation products (TDP) (from 0.16 μg/ml [range 0.14 to 0.19] to 0.78 μg/ml [range 0.56 to 1.26]), while the 40 mg dose produce a fibrinogen breakdown to an average value of 44% (range 19 to 60%) and TDP increased from 0.12 μg/ml (range 0.11–0.12) to 2.29 μg/ml (range 0.45 to 5.55). The breakdown of fibrinogen was related to the quantity of saruplase converted to active two-chain u-PA (tcu-PA) in vivo (6 to 22% conversion). There were no important effects of saruplase on overall blood coagulation (activated partial thromboplastin time) and platelet function (collagen induced platelet aggregation, urinary [2,3-dinor]-thromboxane B2 excretion and plasminogen activator inhibitor 1 [PAI-1] release from platelets).

Saruplase is cleared rapidly from the plasma and a variable amount is converted to tcu-PA. This two-chain form of u-PA probably causes the dose-dependent systemic fibrinolytic activation.

Influence of Heparin and a Low Molecular Weight Heparinoid on Specific Endogenous and Exogenous Fibrinolytic Factors during Rest and Exercise

The effects of heparin (5,000 IU i.v.) and the low molecular weight heparinoid Org 10172 (Orgaran®) (3,250 anti-Xa units i. v.) on components of the fibrinolytic system were studied in two double-blind, randomised, placebo-controlled, cross-over trials using healthy subjects. In study A (n = 6) the effects were studied during rest and standardized exercise and in study B (n = 6) during a low dose infusion of recombinant tissue-type plasminogen activator (rt-PA; 80 µg over 16 min). At rest, heparin and Org 10172 did not influence the plasma concentrations of endogenous t-PA antigen, and activity, urokinase-type PA (u-PA) antigen, plasmin activatable pro-urokinase (scu-PA), active urokinase (tcu-PA) and plasminogen activator inhibitor-1 (PAI-1) antigen. Recombinant t-PA antigen and activity during rt-PA infusion were also not affected. During exercise, neither heparin nor Org 10172 influenced the area under the curve (AUC) of t-PA and u-PA antigen and t-PA activity when compared with placebo. Unexpectedly, after heparin the AUC of t-PA activity was 49% larger (range +19 to +245%) than after Org 10172 (p <0.05). The last difference was considered spurious. scu-PA, tcu-PA and PAI-1 antigen levels at 2 min after termination of exercise were unaffected by both compounds (p >0.05). Sulphated polysaccharides do not increase fibrinolytic activity of the plasma by changing the concentrations of the components of the fibrinolytic system.

Hereditary Cerebral Hemorrhage with Amyloidosis -Dutch Type: A Study of Fibrinolysis

In view of reported associations between increased bleeding tendency and systemically decreased α2-antiplasmin in patients with systemic amyloid deposition we studied α2-antiplasmin, fibrinogen, C-reactive protein and blood levels of locally produced endothelial hemostasis factors in the acute and quiescent phase in 16 patients with hereditary cerebral hemorrhage with amyloidosis - Dutch type (HCHWA-D).

None of the factors measured in the quiescent phase of the disease was abnormal. In the acute phase, shortly after a stroke, only factor VIII: Ag was evidently elevated. We concluded that systemic abnormalities in the part of the fibrinolysis system studied are not likely to be responsible for multifocal and recurrent cerebral hemorrhages in HCHWA-D. The role of an elevated factor VIII: Ag level in the acute phase is unclear.

Physical Exercise Induces Enhancement of Urokinase-Type Plasminogen Activator (u-PA) Levels in Plasma

The enhancement of the blood fibrinolytic potential by physical exercise is generally attributed to the release of tissue-type plasminogen activator (t-PA) from the vessel wall. In this study we have investigated the possible contribution of urokinase-type plasminogen activator (u-PA).

Six healthy male volunteers (age 21–25 years) were screened for their ability to perform maximal exercise for their age-group for 12 min on a bicycle ergometer. Subsequently, on one occasion they were required to remain supine for 2 h (from 8.30 a. m. onwards) and on another they performed maximal exercise (from 9.00 a.m. onwards). During exercise an increase in u-PA antigen and plasmin-activatable pro-urokinase (proUK) activity, concurrent with t-PA antigen and euglobulin t-PA activity, was observed in all six volunteers, while at rest these parameters remained unaffected. Mean u-PA- and t-PA antigen increased, respectively, from 4.2 ± 1.0 ng/ml and 5.8 ± 2.1 ng/ml before exercise to 9.8 ± 3.0 ng/ml and 18.3 ± 3.8 ng/ml (peak). Mean plasminactivatable proUK activity and t-PA activity increased, respectively, from 2.1 ± 0.4 ng/ml and 0.3 ± 0.2 ng/ml before exercise to 4.3 ± 1.7 ng/ml and 7.2 ± 4.0 ng/ml (peak). The increases were statistically significant throughout (paired t-test, pre vs post, antigen P <0.005 and activity P <0.02). After cessation of exercise u-PA and t-PA declined concurrently to normal values with a 50"/" decay in about 5 min. In conclusion, we found that both u-PA antigen and plasmin-activatable proUK activity are, concurrently with t-PA, enhanced upon exercise and, therefore, we consider that u-PA also contributes to – and co-operates in – the enhancement of the blood fibrinolytic potential and activity under these conditions.

Modified Crossed Immunoelectrophoresis to Study with Whole Plasma the Reversible Complex Formation of Histidine-Rich Glycoprotein with Plasminogen

To study the reversible complex formation between the plasma protein histidine-rich glycoprotein (HRG) and plasminogen, crossed immunoelectrophoresis of HRG was modified. In the modification, purified plasminogen was introduced into the gel of the first dimension electrophoresis.

Two molecular forms of plasminogen, Glu- and Lys-plasmino-gen, induced a dose-dependent reduction of the electrophoretic mobility of HRG, with a half maximal retardation for both plasminogens at 0.50–0.55 μM of added plasminogen to the agarose gel. HRG in plasma behaved as a uniform fraction with respect to plasminogen binding. In contrast, with the same modified technique another plasma protein, β2-antiplasmin, separated into a retarded plasminogen-binding form and a nonretarded non-plasminogen-binding form.

The method can be used to assess several aspects of reversible complex formation between plasma proteins, as demonstrated for plasminogen binding of HRG and α2-antiplasmin in whole plasma.

Effects of Moderate Alcohol Consumption on Platelet Function, Tissue-Type Plasminogen Activator and Plasminogen Activator Inhibitor

Short-term effects of moderate alcohol consumption on platelet function, tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI) were studied in two age groups of volunteers (20–30 and 45–55 years), each consisting of eight healthy males. The alcohol (30 g in red port and wine) was consumed during a standard dinner. Two blood samples were drawn: one in the postprandial phase, and one the next morning after fasting overnight. Alcohol consumption tended to increase platelet aggregation and production of hydroxy fatty acids, reduced plasma t-PA activity and increased PAI activity in the postprandial phase. After the overnight fast the effects on t-PA and PAI had disappeared whereas at that time alcohol consumption tended to decrease platelet function. The effects of alcohol on t-PA and PAI activity appeared mainly in the older age group, whereas the t-PA activity in this group was already much lower, irrespective of alcohol consumption.

Quantitation of Plasma Levels of Tetranectin - Effects of Oral Contraceptives, Pregnancy, Treatment with L-Asparaginase and Liver Cirrhosis

Tetranectin is a tetrameric protein that binds to kringle 4 of plasminogen. Increase of electrophoretic mobility of the otherwise slowly migrating tetranectin in the presence of ethylenediaminetetraacetate was used to develop a reproducible electroimmunoassay to quantify plasma levels. Plasma levels in normals were found within narrow limits of 100 ± 16 (SD)%, (100% =0.15 pmol/1). There was no difference between males and females, smokers and non-smokers, and there were no significant changes with age from 20 to 49 years.

Patients with severe liver cirrhosis showed a large variation in plasma tetranectin levels but no systematic or average reduction, in contrast to strong reductions in plasma levels of other proteins. Patients treated with L-asparaginase showed a gradual reduction in time in plasma levels of various proteins, though tetranectin showed no significant reduction.

It is concluded that tetranectin can be assayed reproducibly in plasma and has a well regulated plasma level. This level is not sensitive to conditions with reductions in synthesis of many proteins, such as during cirrhosis of the liver and during L-asparaginase therapy. The reductions in plasma levels during the use of oral contraceptives and pregnancy indicate involvement of sex steroids in the metabolism of tetranectin.

Elevated Plasminogen Activator Inhibitor (PAI), a Cause of Thrombophilia? – A Study in 203 Patients with Familial or Sporadic Venous Thrombophilia

Two hundred and three patients with venous thrombophilia were investigated in order to find out whether an elevated plasma concentration of plasminogen activator inhibitor (PAI) could be a cause of their tendency to thrombosis. The patients were studied in an asymptomatic period about 3 months after their last thromboembolic episode. PAI activity was found to be elevated in 19 patients (9%), and a corresponding elevation of PAI-1 antigen was observed.

In 16 out of the 19 patients with elevated PAI activity, followup could be performed after an additional asymptomatic period of about 1 year: in eight patients the elevation of PAI was transient and in eight it was persistent. Out of the eight patients with a persistent elevation of PAI, seven had a positive family history of thrombosis. Investigation of these families excluded a hereditary elevation of PAI activity in two families. In only two other families was elevated PAI activity also found among family members. The occurrence of elevated PAI activity, however, did not coincide with the occurrence of thrombosis in these individuals: except for the probands, all investigated family members who had a history of thrombosis had a normal PAI activity.

We therefore conclude that, at least in our material, familial thrombophilia can not be attributed to an inherited, persistent elevation of the blood level of PAI.

Influence of Factor Xllla Activity on Human Whole Blood Clot Lysis In Vitro

We studied the influence of Factor XIII a (F XIII a) activity on the lysis rate of fresh whole human blood clots, without using anticoagulants. Clotting was induced by exogenous thrombin, lysis by tissue-type Plasminogen Activator (t-PA) added before clotting. After various periods of time, lysis rates were determined by measuring the radioactivity in the supernatant of the clot originating from 125I-Fibrinogen added before clotting.

Lysis rates were determined in the presence of endogenous F XHIa and compared with those obtained after specific inhibition of F XIII a activity. We used an IgG fraction of an antiserum quenching the F XIII a activity. Addition of increasing amounts of the antibodies to normal blood resulted in a dramatic increase in clot lysis rate, concomitant with loss of F XIII activity. Lysis of blood clots from a patient with a congenital, homozygous, functional α2-Antiplasmin (α2-AP) deficiency (α2-AP-Enschede) was not or slightly increased by the anti F XIII antibodies indicating that fibrin-fibrin crosslinking per se does not contribute essentially to resistance of the blood clot against fibrinolysis. Both active α2-AP and F XIII a are required for the major part of the F XIII-dependent resistance of whole blood clots against lysis.

Daytime Fluctuations in Blood of Tissue-Type Plasminogen Activator (t-PA) and Its Fast-Acting Inhibitor (PAI-1)

Circadian fluctuation in blood fibrinolytic activity was studiedin 10 volunteers in the day-time period at 09.00, 12.00 and15.0 h. Activity of tissue-type plasminogen activator (t-PA) wasfound to increase from 09.00 to 15.00 h in accordance with knownresults with global assays of blood activity.

Mild Haemostatic Problems Associated with Congenital Heterozygous α2-Antiplasmin Deficiency

A Dutch family, of which 13 members are heterozygotes, deficient for α2-antiplasmin (α2-AP) is reported. Clinical studies showed that 2 heterozygotes had a mild bleeding tendency, which presented as bleeding episodes after tooth extraction and after surgery and, in one patient, also as excessive menstruation. Laboratory investigations revealed an α2-AP activity of 62% (51-71) (median and range) and an antigen level of 60% (60-66). The plasminogen binding as well as the fibrin binding properties of α2-AP were normal. Plasminogen concentrations were significantly higher in the heterozygotes compared to the other family members. However, free plasminogen not bound to histidine-rich glycoprotein was not significantly different between these two groups. We propose that in this family the deficiency of α2-AP is due to a decreased synthesis of a normal α2-AP molecule. This present study brings the frequency of heterozygous α2-AP deficient patients with a bleeding tendency to 13 out of 59 heterozygotes reported in the literature.

Activation Products of the Haemostatic System in Coronary, Cerebrovascular and Peripheral Arterial Disease

To determine the presence of a ‘hypercoagulable state’ as assessed by indices of thrombin and plasmin generation and of the amount of fibrin that is lysed, in patients with stable coronary, cerebral and peripheral arterial disease a population-based cross-sectional study was performed. From a population-based cohort comprising 7983 men and women aged 55 years and over, we randomly selected 127 subjects with a history of myocardial infarction, 124 with a history of stroke and/or transient ischemic attack, 131 patients with peripheral arterial disease and 263 control subjects in the same age group without arterial disease. Subjects using anticoagulant drugs were not selected. F1+2, TAT, and PAP were not associated with a history of cardiovascular events, nor with peripheral arterial disease. In contrast, positive associations were found for D-Dimer. Mean D-Dimer level was 40 μg/l (95% CI 35,44) in control subjects; 53 μg/l (47, 61) in those with a history of myocar-dial infarction and 51 μg/l (45, 58) in those with a history of stroke and or transient ischemic attack. D-Dimer increased gradually with increasing severity of peripheral atherosclerosis; a decrease in ankle/arm systolic blood pressure ratio of 0.1 was associated with an increase in D-Dimer of 3.9 μg/l (p<0.01). This was more pronounced in subjects with higher F1+2, TAT and PAP concentration. In conclusion, the markers of onset of coagulation F1+2, TAT and PAP are not associated with the presence of arterial disease, but increased levels of these markers are necessary for the positive association between D-Dimer and arterial disease.