The anticoagulant action of recombinant human activated protein C (rhAPC, Drotrecogin alpha activated): comparison between cord and adult plasma

Differential Contributions of Intrinsic and Extrinsic Pathways to Thrombin Generation in Adult, Maternal and Cord Plasma Samples

Background

Thrombin generation (TG) is a pivotal process in achieving hemostasis. Coagulation profiles during pregnancy and early neonatal period are different from that of normal (non-pregnant) adults. In this ex vivo study, the differences in TG in maternal and cord plasma relative to normal adult plasma were studied.

Methods

Twenty consented pregnant women and ten consented healthy adults were included in the study. Maternal and cord blood samples were collected at the time of delivery. Platelet-poor plasma was isolated for the measurement of TG. In some samples, anti-FIXa aptamer, RB006, or a TFPI inhibitor, BAX499 were added to elucidate the contribution of intrinsic and extrinsic pathway to TG. Additionally, procoagulant and inhibitor levels were measured in maternal and cord plasma, and these values were used to mathematically simulate TG.

Results

Peak TG was increased in maternal plasma (393.6±57.9 nM) compared to adult and cord samples (323.2±38.9 nM and 209.9±29.5 nM, respectively). Inhibitory effects of RB006 on TG were less robust in maternal or cord plasma (52% vs. 12% respectively) than in adult plasma (81%). Likewise the effectiveness of BAX499 as represented by the increase in peak TG was much greater in adult (21%) than in maternal (10%) or cord plasma (12%). Further, BAX499 was more effective in reversing RB006 in adult plasma than in maternal or cord plasma. Ex vivo data were reproducible with the results of the mathematical simulation of TG.

Conclusion

Normal parturient plasma shows a large intrinsic pathway reserve for TG compared to adult and cord plasma, while TG in cord plasma is sustained by extrinsic pathway, and low levels of TFPI and AT.

Activated protein C resistance in cord blood from healthy and complicated newborns

OBJECTIVES

Newborns are susceptible to thrombosis secondary to the immature hemostatic system and maternal and fetal complications. The contribution of activated protein C resistance (APCR) to thrombosis tendency has not yet been established. This study was conducted to investigate the effects of maternal and fetal complications on APCR levels.

METHODS

APCR levels were determined in cord blood from healthy term infants and compared with those in healthy preterm and complicated neonates as well as that in adult venous blood.

RESULTS

The mean value of APCR in cord blood from healthy term infants (166 +/- 40 s) was not significantly different from that in adult venous blood (173 +/- 40 s). No significant differences in the mean cord blood APCR values were observed between healthy term and preterm infants, infants with vaginal and cesarean delivery, infants from preeclamptic and non-eclamptic mothers, and infants with or without perinatal asphyxia. The activity levels of protein C, protein S, and antithrombin III were not significantly different between these groups except for lower levels in preterm babies.

CONCLUSIONS

The level of APCR in cord blood is comparable to that in adults and not influenced by maternal and fetal complications. It appears that APCR does not contribute to the thrombotic tendency in newborns.

Clot strength: a comparison between cord and adult blood by means of thrombelastometry

OBJECTIVE

To evaluate the clot strength in cord versus adult blood.

METHOD

Thrombelastometry (TEM) was the method of choice as it provides information on the clot strength in terms of the maximum clot firmness (MCF) and on the fibrin polymerization process in terms of the clot formation time and the alpha angle.

RESULTS

The MCFs were significantly lower in cord versus adult platelet rich plasma (PRP, 63.0+/-3.8 vs. 67.0+/-3.9 mm, P=0.006) and in cord versus adult whole blood (WB, 55.3+/-3.8 vs. 59.3+/-3.6 mm, P=0.001) employing the thrombelastometry with extrinsic activator assay. We suggest that the diminished clot strength in cord versus adult blood and plasma samples is attributable to an impaired polymerization of neonatal fibrin: (i) the thrombelastometry with extrinsic activator and inactivated platelets (FIBTEM) assay revealed significantly lower MCFs in cord versus adult PRP (23.0+/-3.1 mm vs. 27.3+/-3.9 mm, P=0.002) and in cord versus adult WB (11.6+/-2.3 mm vs. 15.3+/-3.3 mm, P<0.001); (ii) the alpha angle in the FIBTEM assay was significantly lower in cord versus adult WB (39.0+/-12.8 degrees vs. 55.5+/-12.3 degrees, P=0.02); (iii) the clot formation times in the FIBTEM assay were significantly longer in cord versus adult PRP (248.0+/-143.5 s vs. 81.5+/-39.8 s, P=0.001).

CONCLUSIONS

Neonatal fibrin shows impaired polymerization properties under our experimental conditions resulting in reduced clot strength compared with fibrin of adult origin.

Thrombin generation determined by calibrated automated thrombography (CAT) in pediatric patients with congenital heart disease

INTRODUCTION

Thrombin generation was studied in pediatric patients with congenital heart disease (CHD) undergoing cardiac surgery using the calibrated automated thrombography (CAT) in terms of the lag time until the onset of thrombin formation, time to thrombin peak maximum (TTP), endogenous thrombin potential (ETP), and thrombin peak height. The possible suitability to determine the coagulation status of these patients was investigated.

MATERIALS AND METHODS

CAT data of 40 patients with CHD (age range from newborn to 18 years) were compared to data using standard coagulation parameters such as prothrombin (FII), antithrombin (AT), tissue factor pathway inhibitor (TFPI), prothrombin fragment 1.2 (F 1.2), thrombin-antithrombin (TAT), activated partial thromboplastin time (aPTT), and prothrombin time (PT).

RESULTS

A significant positive correlation was seen between ETP and FII (p<0.01; r=0.369), as well as between peak height and F II (p<0.01; r=0.483). A significant negative correlation was seen between ETP and TFPI values (p<0.05; r=-0.225) while no significant correlation was seen between peak height and TFPI. A significant negative correlation was seen between F 1.2 generation and ETP (p<0.05; r=-0.254) and between F 1.2 generation and peak height (p<0.05; r=-0.236). No correlation was seen between AT and ETP or peak.

CONCLUSIONS

Our data indicate that CAT is a good global test reflecting procoagulatory and inhibitory factors of the hemostatic system in pediatric patients with CHD.

The respective and combined anticoagulant effects of recombinant human activated protein C, melagatran and heparins using CAT

INTRODUCTION

Combinations of anticoagulants might be beneficial in some patients with sepsis, but most anticoagulants require specific clotting assays for monitoring. Thrombin generation assay, however, is a global function test of hemostasis.

MATERIALS AND METHODS

We performed an in vitro investigation of the respective effects of recombinant human activated protein C (rhAPC) alone and in combination with either melagatran (a new direct thrombin inhibitor), unfractionated heparin (UH) or low molecular weight heparin (LMWH) in varying concentrations on the thrombin generation (TG) using the calibrated automated thrombography.

RESULTS

RhAPC, UH, LMWH and melagatran dose-dependently prolonged the lag time and the time to peak, and significantly suppressed the endogenous thrombin potential (ETP). Combined application of rhAPC with either melagatran, UH or LMWH induced an additive prolongation of the lag time; this effect was more pronounced in a combination of rhAPC with UH or LMWH.

CONCLUSION

In our in vitro study adding either melagatran, UH or LMWH augmented the capacity of rhAPC to suppress thrombin generation in human plasma. These findings suggest that patients with severe sepsis might benefit from a treatment with combinations of anticoagulant agents.

Protein S modulates the anticoagulant action of recombinant human activated protein C: a comparison between neonates and adults

Recombinant human-activated protein C (rhAPC, Drotrecogin alpha (activated), Xigris) has been shown to reduce organ damage and decrease mortality in severe sepsis. Since protein S (PS) serves as a potentiating cofactor of activated protein C and since PS levels are low in neonatal plasma, we hypothesized that the anticoagulant effect of rhAPC would be decreased in cord plasma compared to adult plasma. We demonstrate that the anticoagulant action of 0.3 microg ml(-1) rhAPC (5 nmol l(-1)) was decreased in cord plasma compared to adult plasma, and dose dependently increased in cord plasma in the presence of increasing activities of PS. Correspondingly, the anticoagulant action of rhAPC decreased in adult plasma in the presence of decreasing activities of PS. The low anticoagulant action of rhAPC in cord compared to adult plasma is attributable to low neonatal levels of PS, and as previously shown, to low neonatal levels of TFPI and AT. Our laboratory experiments do not allow definite conclusions for clinical situations. However, we speculate that the anticoagulant efficacy of rhAPC is impaired in neonates and in clinical situations associated with consumption and/or inhibition of PS, AT, and TFPI, such as severe sepsis.

Recombinant human activated protein C, heparin and melagatran in umbilical cord versus adult plasma

AIM

We investigated the anticoagulant effects of recombinant human activated protein C (rhAPC), unfractionated heparin (UH) and melagatran (a new direct thrombin inhibitor [DTI]), when administered individually and in combinations of rhAPC with either UH or melagatran, in umbilical cord and adult plasma. rhAPC is a promising candidate treatment to improve the outcome of severe sepsis in neonates and adults; the DTI melagatran represents a potential advance in antithrombotic therapy.

METHODS

The anticoagulant efficacy of these drugs was measured using the standard coagulation assays activated partial thromboplastin time (aPTT) and prothrombin time (PT).

RESULTS

Administered individually, rhAPC, UH and melagatran dose-dependently prolonged aPTT to a significantly greater extent in umbilical cord than in adult plasma. Melagatran alone, but not rhAPC or UH alone, dose-dependently prolonged the PT in both umbilical cord and adult plasma. Combining rhAPC with either UH or melagatran significantly augmented aPTT prolongation in both umbilical cord and adult plasma.

CONCLUSION

Our results, which facilitate estimation of rhAPC and melagatran dose requirements in umbilical cord plasma, may be of benefit in critically sick newborns with severe sepsis.

Drotrecogin alfa activated (recombinant human activated protein C) in combination with heparin or melagatran

Recombinant human activated protein C (rhAPC) has recently been demonstrated to be a promising candidate to improve the outcome for patients with severe sepsis. Plasma-derived activated protein C and unfractionated heparin (UH) exert anticoagulant synergy due to mechanisms that simultaneously decrease thrombin generation. Melagatran, a new direct thrombin inhibitor, does not bind to plasma proteins or requires antithrombin as a cofactor. The latter is often consumed in patients with severe sepsis. We investigated the anticoagulant efficiency in combined administration of rhAPC and UH or melagatran in terms of prolongation of the standard clotting assays activated partial thromboplastin time (aPTT) and prothrombin time (PT) in pooled plasma samples in vitro. RhAPC dose-dependently prolonged the aPTT but not the PT. The ability of UH and melagatran to prolong the aPTT was significantly enhanced in combination with rhAPC. The combined administration of rhAPC and melagatran, but not UH, resulted in additive prolongation of the PT. In control measurements the capability of rhAPC to suppress prothrombin fragment 1.2 generation dose-dependently increased in combination with heparin and melagatran. Our study demonstrates the respective effects of rhAPC, UH, melagatran and further different additive effects in combined administration of rhAPC and UH or melagatran on the prolongation of the aPTT and PT clotting assays usually used to monitor anticoagulant treatment.