Fibrinolysis in pre-eclampsia

State-of-the-Art Review: Usefulness of Laboratory Techniques for Evaluating Antithrombotic Efficacy of New Therapeutic Strategies

New drugs and new therapeutic strategies are being introduced for the prevention and the management of cardiovascular and thromboembolic disorders. Extensive clinical studies and large-scale epidemiological investigations are conducted to demonstrate the efficacy of these therapeutic approaches. Laboratory assays are invaluable tools for this exploration. We discuss how the new understanding concerning the regulation of the coagulolytic equilibrium offers novel investigation tools. Parameters reflecting the activities of new drugs targeted to their impact site and presenting few side effects are available. In addition to global clotting methods and chromogenic substrate-based assays, introduction of immunoassays has allowed measurement of most of the molecular markers of hemostatic activation. We recommend use of a panel of markers exploring the endothelial damage, the blood cell involvement, the early coagulant pathways' activation (XIIa and VIIa), the thrombin-formation pathways, the fibrin formation, and the evaluation of the global fibrinolytic capacity. When related to the clinical end points, all these laboratory assays offer useful and reliable monitoring of new drugs. They contribute to the establishment of new therapeutic strategies. Key Words: Hemostasis—Activation—Antithrombotic—Therapy— Laboratory monitoring.

Levels of plasminogen activators and their inhibitors in maternal and umbilical cord plasma in severe preeclampsia

OBJECTIVE

The purpose of this study was to evaluate the plasminogen activator system in maternal and umbilical cord plasma in patients with severe preeclampsia compared with control subjects with normotensive pregnancies.

STUDY DESIGN

Maternal blood was sampled from 42 patients at a median gestational age of 32 weeks; after delivery, arterial and venous umbilical cord blood was sampled from 37 and 36 of these patients, respectively. Maternal blood from women with uncomplicated pregnancies was sampled at the gestational age of 32 weeks (n = 18, group I), and umbilical cord blood was sampled after premature deliveries of normotensive pregnancies (n = 5, group II). Data were analyzed with the use of Mann-Whitney U tests.

RESULTS

Patients had significantly higher tissue plasminogen activator (P <.01) and unchanged urokinase plasminogen activator plasma levels compared with control subjects at 32 weeks of gestation; lower plasminogen activator inhibitor type 2 (P < 0.01) and no different plasminogen activator inhibitor type 1 concentrations were observed compared to control subjects at 32 weeks of gestation. In the arterial and venous umbilical cord plasma of patients, plasminogen activator inhibitor type 1 levels were significantly higher(P <.01) compared with control subjects at 32 weeks of gestation, although urokinase plasminogen activator levels in arterial and venous umbilical cord plasma (P < 0.01) were significantly lower.

CONCLUSION

Lower plasminogen activator inhibitor type 2 levels are associated with placental insufficiency, and higher tissue plasminogen activator levels are associated with endothelial dysfunction in patients with severe preeclampsia. The higher plasminogen activator inhibitor type 1 levels and lower urokinase plasminogen activator levels in umbilical cord of these patients are suggestive of decreased fibrinolysis in the fetal circulation.

Disseminated intravascular coagulation

Healthy pregnancy is accompanied by changes in the haemostatic system which convert it into a hypercoagulable state vulnerable to a spectrum of disorders ranging from venous thromboembolism to disseminated intravascular coagulation (DIC). This latter is always a secondary phenomenon triggered by specific disorders such as abruptio placentae and amniotic fluid embolism due to release of thromboplastin intravascularly or endothelial damage resulting from pre-eclampsia and sepsis. In modern obstetric practice the most common cause is haemorrhagic shock with delay in resuscitation leading to endothelial damage. The initial management of massive obstetric haemorrhage is the same whether associated with coagulopathy initially or not. Low-grade DIC, associated with pre-eclampsia, is monitored haematologically by serial platelet counts and serum fibrin degradation products (FDPs). Supportive measures and removal of the triggering mechanism are the key to successful management. Outcome depends primarily on our ability to deal with the trigger and not on direct attempts to correct the coagulation deficit.

Pregnancy zone protein-tissue-type plasminogen activator complexes bind to low-density lipoprotein receptor-related protein (LRP)

Tissue-type plasminogen activator (t-PA), is a serine proteinase that catalyzes the initial and rate-limiting step in the fibrinolytic cascade. Its plasma activity is determined by the rate of release into the bloodstream, the rate of inhibition by plasminogen-activator inhibitor type 1 (PAI-1) and the rate of hepatic clearance. Two receptor systems contribute to the clearance of t-PA: the mannose receptor and the low-density lipoprotein receptor-related protein (LRP) that removes free t-PA as well as t-PA-PAI-1 complexes from the blood. During pregnancy a significant rise in the plasma levels of pregnancy zone protein (PZP) is observed, while alpha(2)-macroglobulin (alpha(2)-M) remains constant. Interestingly, the fibrinolytic activity is decreased during this period. In this context, we have recently demonstrated the in vitro formation of PZP-t-PA complexes. Here, we purified LRP from human placenta by affinity chromatography and then analyzed the binding specificity and affinity of PZP-proteinase complexes to the receptor by enzyme immunoassay (EIA). Our results clearly established that the binding of PZP-t-PA complexes to LRP was specific, saturable, and with K(d) = 337 +/- 31 nM. Moreover, by using the same EIA, we further observed that this binding was inhibited by receptor-associated protein. These data suggest that PZP, by binding to t-PA and promoting its clearance via LRP, might contribute in vivo to the downregulation of the fibrinolytic activity during pregnancy.

Plasminogen activator of urokinase type and its inhibitor of placental type in hypertensive pregnancies and in intrauterine growth retardation: possible markers of placental function

OBJECTIVE

Our purpose was to study the plasma concentrations of the plasminogen activator of urokinase type and its specific inhibitor of placental type in pregnancies complicated by hypertension or fetal growth retardation.

STUDY DESIGN

Consecutive patients with pregnancy-induced hypertension (n = 17), mild preeclampsia (n = 17), severe preeclampsia (n = 19), and intrauterine growth retardation (n = 19) were studied. Blood samples were obtained just before delivery (mean 2 days). Women with normal pregnancies (n = 40), longitudinally followed between the tenth and fortieth gestational weeks, served as a control group.

RESULTS

The plasma concentrations of the urokinase type antigen were significantly lower in women with severe preeclampsia or intrauterine growth retardation than those in women with normal pregnancies (p < 0.001). In all four groups with complicated pregnancies the antigen concentrations of the urokinase type and its inhibitor were significantly correlated with both placental weight and birth weight.

CONCLUSIONS

The plasma concentration of the urokinase type antigen would appear to reflect placental function, and both the antigen and its inhibitor concentrations are correlated with placental and fetal growth.

Plasminogen activator inhibitors (PAI-1 and PAI-2) in normal pregnancies, pre-eclampsia and hydatidiform mole

OBJECTIVE

To examine the behaviour of the major inhibitors of fibrinolysis (PAI-1 and PAI-2) in normal pregnancy and pregnancy complicated by either pre-eclampsia or hydatidiform mole.

DESIGN

Prospective study.

SETTING

Antenatal Clinic and Maternity Hospital.

SUBJECTS

Eleven women with established pre-eclampsia and eleven women, matched by age, parity, and duration of pregnancy who were undergoing uncomplicated pregnancy. Two women having surgery for hydatidiform mole.

MAIN OUTCOME MEASURE

Plasma levels of PAI-1 and PAI-2 antigens determined by sensitive specific ELISA. Functional identification of PAI-2 by nondenaturing gel electrophoresis with overlay zymography.

RESULTS

In pre-eclampsia PAI-2 antigen was significantly lower than in normal pregnancy (105.3 +/- 34.9 versus 187.1 +/- 67.9 ng/ml; P < 0.001). In contrast PAI-1 antigen was significantly higher in pre-eclampsia than in normal pregnancy (170.7 +/- 71.2 versus 113.8 +/- 35.6 ng/ml; P < 0.05). In consequence the ratio of PAI-1/PAI-2 increased markedly in pre-eclampsia (2.5 versus 0.6). No PAI-2 was detected in plasma of women with hydatidiform moles.

CONCLUSIONS

PAI-2 levels fell significantly in pre-eclampsia probably as a result of decreased placental mass or function. The raised PAI-1 level in pre-eclampsia may reflect a response to hypertension or renal damage that is not specific to pregnancy or may reflect altered placental function. The use of the ratio of PAI-1/PAI-2 assists in separating normal from abnormal pregnancies.

Fibrinolytic parameters in normotensive pregnancy with intrauterine fetal growth retardation and in severe preeclampsia

In pregnancy a decrease in fibrinolytic activity, which is due to an increase in plasminogen activator inhibitor activity and plasminogen activator inhibitor type 1 and type 2, has been described. Because the placenta is a source of both type 1 and type 2 plasminogen activator inhibitor, we have studied them and other fibrinolytic parameters in a group of normotensive pregnant women with intrauterine fetal growth retardation and in two groups of women with preeclampsia, with or without intrauterine growth retardation. A significant increase in plasminogen activator inhibitor type 1 antigen and plasminogen activator inhibitor activity was observed in preeclampsia, with or without intrauterine growth retardation, but not in normotensive pregnancy with intrauterine growth retardation, when compared with normal pregnancy. Plasminogen activator inhibitor type 2 antigen levels showed a significant decrease in both groups of pregnant women (normotensive or preeclamptic) with intrauterine growth retardation when compared with pregnancies without intrauterine growth retardation. A significant correlation between plasminogen activator inhibitor type 2 levels and fetal weight has been observed in the clinical groups.

Complexes of activated protein C with alpha 1-antitrypsin in normal pregnancy and in severe preeclampsia

Protein C is a vitamin K-dependent regulator of blood coagulation. Activated protein C is regulated in plasma in large part by two inhibitors, protein C inhibitor and alpha 1-antitrypsin. Complexes of activated protein C with both inhibitors in plasma samples from subjects with normal or pathologic pregnancy were measured. In normal pregnancy we observed a progressive and significant increase in activated protein C/alpha 1-antitrypsin complex levels, from 9 +/- 3 ng/ml in the first trimester to 16 +/- 3 ng/ml in the third trimester, as well as an increase in alpha 1-antitrypsin plasma levels. In severe preeclampsia, but not in chronic hypertension with superimposed severe preeclampsia, there was a greater increase in activated protein C/alpha 1-antitrypsin levels (25 +/- 10 ng/ml) (p less than 0.001) and a decrease in protein C and protein C inhibitor levels as compared with normal pregnant women at similar gestational ages. These data show an increase in the activation of the protein C pathway in both normal and pathologic pregnancy and provide evidence for an enhancement of thrombin generation in severe preeclampsia compared with chronic hypertension with superimposed severe preeclampsia.

Determination of plasminogen activator inhibitor (PAI) capacity of human plasma in presence of oxidants: a novel principle

A new functional assay of PAI-activity in human plasma is described. Hitherto known assays for fast acting PAI have some disadvantages: predilution and/or acidification steps of the sample to afford the required inactivation of alpha-2-antiplasmin (A2-PI). This approach in contrast implicates test performance in presence of chloramine T (CT), an oxidant that destroys plasma antiplasmin activity without impairing significantly the activity of urokinase (u-PA) or plasmin. The following reaction conditions were found optimal: 50 microliter of undiluted plasma, anticoagulated with citrate or EDTA, were first incubated with 1 IU u-PA in a Tris-buffer, pH 8.4 and then with Glu-plasminogen (0.85 mumol/l final), CT (2.5 mmol/l final), tranexamic acid (0.9 mmol/l final) for 5 min. at 37 degrees C. After addition of 0.3 mmol/l of the chromogenic plasmin substrate H-D-Nva-CHA-Lys-pNA (pNA = para nitroanilide) and of NaCl (250 mmol/l final) a linear kinetic with delta A405/t in the range of 0.2/min for normal plasma was recorded. In an endpoint version of the test the chromogenic substrate can be added together with plasminogen resulting an A/t2-kinetic. Dilution studies showed a linear calibration curve from 0 to 14 arbitrary u-PA inhibiting units (AU)/ml plasma. By means of PAI-standard plasmas PAI-capacity values of 20 healthy volunteers (10 males/10 females) (x = 26 years, sigma = 4.2) were determined. They ranged from 0.4 - 6.9 (x = 1.3, sigma = 0.9) AU/ml plasma. Plasma samples containing more than 14 AU/ml were prediluted with PAI-deficient plasma. Intra- and inter-assay coefficients of variation (CV) were determined to be 1.3 +/- 0.6 and 4.3 +/- 0.5%, respectively. The values of this assay correlate well with those obtained by acidification of the samples. However, the possibility of measuring plasma PAI (and PA) activities by means of a simple and direct approach can be considered as an important progress with regard to routine hospital practice. The presented oxidative inactivation of A2-PI mimics the leukocyte attack phase, suggesting that activated leukocytes create a microenvironment of uncontrolled plasmin activity.

Measurement of tPA and tPA-PAI-1 complexes by ELISA, using monoclonal antibodies: clinical relevance

Two ELISA methods using monoclonal antibodies, are described for the measurement of tPA:Ag and tPA-PAI-1 complexes. On normal population tPA:Ag was found with a mean value of 5 ng/ml. Furthermore, despite that tPA activity was very low, only 50% (mean value) was measured as stable complexes with PAI-1. Important increase of tPA:Ag was observed in various pathologies (cardiac infarction, septicemia, respiratory distress syndrome). In liver disease, tPA:Ag reached high levels up to 100 ng/ml. Impaired liver clearance can potentiate the increased concentration which results from endothelial release. In all patients with elevated tPA:Ag level, 70 to 100% of tPA was complexed to PAI-1. Excess release of PAI-1 accompanys the increased release of tPA as it is proved by presence of high residual PAI-1 activity. Addition of exogeneous tPA to these pathological plasmas induced a high increase in tPA-PAI-1 complexes. Venous stasis in normal population resulted in a parallel increase of tPA:Ag and tPA-PAI-1 complexes. Although about a two fold increase was obtained for both parameters, post venous stasis plasma presented a much higher fibrinolytic activity while PAI-1 activity was moderately elevated. tPA:Ag and tPA-PAI-1 complexes have diagnosis and prognosis value in various pathologies as indicators of stimulated release of fibrinolysis activator and inhibitor.