Anticoagulant and fibrinolytic activities are promoted, not retarded, in vivo after thrombin generation in the presence of a monoclonal antibody that inhibits activation of protein C

Abstract

This study examines the assumption that both the anticoagulant and fibrinolytic activity that follow the generation of thrombin induced by infusion of factor Xa/PCPS are due to generation of activated protein C. Untreated controls or animals given unrelated antibody were compared with animals pretreated with a specific monoclonal antibody to protein C (HPC4). Compared with untreated controls excess HPC4 substantially reduced the level of protein C activation as observed by protein C immunoblotting and enzyme-linked immunosorbent assay for antitrypsin/activated protein C complexes. Despite this, the anticoagulant activity as reflected by the decline of factors Va and VIIIa levels (as observed by coagulation assays and by factor V immunoblotting) was significantly greater than controls. The fibrinolytic activity (as observed by assays of tissue plasminogen activator, D-Dimer, alpha 2-antiplasmin) also was significantly greater than controls. We conclude that neutralization of the protein C anticoagulant system while resulting in a significantly more intense coagulant response to Xa/PCPS does not preclude inactivation of factors Va and VIIIa and the full expression of the fibrinolytic response. We conclude further that after thrombin generation in vivo, protein C activation is not a prerequisite for the promotion of the fibrinolytic response previously observed, and that the inactivation of factors Va/VIIIa may be mediated by enzymes other than activated protein C. The reduction in alpha 2-antiplasmin levels in association with increased tissue plasminogen activator activity suggests that plasmin is a likely candidate.

In vivo–generated thrombin and plasmin do not activate the complement system in baboons

“…Baboon model of E coli sepsis and FXa/PCPS infusion Plasma samples were derived from studies approved by the Institutional Animal Care and Use Committee of the Oklahoma Medical Research Foundation. Papio anubis baboons were IV infused with a single bolus of FXa/PCPS (36.6 pmol/kg body weight FXa and 56.3 nmol/kg body weight PCPS) 9 or LD100 E coli (1 3 10 10 colony-forming units [CFUs]/kg to 3 3 10 10 CFU/kg). 11,15 Baboon blood samples and physiological parameters were collected before (T0) and at the indicated times after challenge with FXa/PCPS or E coli.…”

“…To test the in vivo role of thrombin and plasmin on complement activation in primates, we used plasma samples from baboons infused with factor Xa (FXa) and phosphatidylcholine-phosphatidylserine (PCPS) vesicles (FXa/PCPS) that trigger a robust burst of thrombin and subsequent plasmin generation in vivo. 8,9 For comparison, we used plasma from baboons infused with LD100 Escherichia coli 10 that leads to activation of the complement, 11,12 coagulation, and fibrinolytic systems. 13,14 We found that bacteria and lipopolysaccharide (LPS) were the main activators of the complement system in E coli sepsis.…”

Overexpressing endothelial cell protein C receptor alters the hemostatic balance and protects mice from endotoxin

“…For lipopolysaccharide (LPS) challenge, mice were injected intraperitoneally with 40 mg kg )1 LPS from E. coli O127: B8 (Sigma, St. Louis, MO, USA). Factor Xa/phosphatidylcholine (80%) phosphatidylserine (20%) (PCPS) vesicles were prepared as previous described [10]. Two doses of factor Xa/PCPS were used: the low dose was 23.5 pmol kg )1 factor Xa and 36.1 nmol kg )1 PCPS, and the high dose was 70.4 pmol kg )1 factor Xa and 108.3 nmol kg )1 PCPS.…”

Current Pathological and Laboratory Considerations in the Diagnosis of Disseminated Intravascular Coagulation

“…One example of disease-specific tailoring of DIC is the significantly more intense coagulant response in early trauma. Together with the extensiveness of endothelial cell activation, the excessive surge in thrombin leads to overdrive of tPA-triggered fibrinolysis and indiscriminate fibrin(ogen)olysis, as observed in a baboon model of DIC following blockade of the PC anticoagulant pathway to enhance thrombin generation [ 11 ].…”