Increased factor VIII plays a significant role in plasma hypercoagulability phenotype of patients with cirrhosis

Essentials The role of increased factor VIII in cirrhosis-induced hypercoagulability has never been demonstrated. Factor VIII and protein C effects were characterized by thrombin generation with thrombomodulin. Factor VIII elevation plays a significant role in cirrhosis-induced plasma hypercoagulability. Only protein C and factor VIII normalization led to thrombin generation similar to controls.

SUMMARY

Background In cirrhosis, thrombin generation (TG) studied in the presence of thrombomodulin (TM) indicates plasma hypercoagulability. Although the role of protein C (PC) deficiency has been investigated, the influence of an increase in the factor VIII level has never been addressed. Objectives We investigated the roles of high FVIII and low PC levels in increased TG in the presence of TM. Methods Blood samples were prospectively collected from 35 healthy controls and 93 patients with cirrhosis (Child-Turcotte-Pugh [CTP]-A, n = 61; CTP-B, n = 19; and CTP-C, n = 13) and FVIII levels > 150% (n = 48) and/or PC levels < 70% (n = 88). TG was performed with tissue factor (5 pm), phospholipids, and TM (4 nm). FVIII and PC levels were normalized by adding an inhibitory anti-FVIII antibody and exogenous PC, respectively. Results The endogenous thrombin potential (ETP) in the presence of TM was higher in patients than in controls. After FVIII normalization, the ETP (median) decreased from 929 nm min to 621 nm min (CTP-A), 1122 nm min to 1082 nm min (CTP-B), and 1221 nm min to 1143 nm min (CTP-C); after PC normalization, it decreased from 776 nm min to 566 nm min (CTP-A), 1120 nm min to 790 nm min (CTP-B), and 995 nm min to 790 nm min (CTP-C). The ETP was reduced by 17% and 30%, respectively, but normal TG was not restored. When both FVIII and PC levels were normalized, the ETP decreased from 929 nm min to 340 nm min (CTP-A), 1122 nm min to 506 nm min (CTP-B), and 1226 nm min to 586 nm min (CTP-C), becoming similar to control levels. Conclusion Cirrhosis-induced plasma hypercoagulability, as demonstrated in these experimental conditions, can be partly explained by opposite changes in two factors: PC level (decrease) and FVIII level (increase).

A novel protein C-factor VII chimera provides new insights into the structural requirements for cytoprotective protease-activated receptor 1 signaling

Essentials The basis of cytoprotective protease-activated receptor 1 (PAR1) signaling is not fully understood. Activated protein C chimera (APCFVII-82 ) was used to identify requirements for PAR1 signaling. APCFVII-82 did not initiate PAR1 signaling, but conferred monocyte anti-inflammatory activity. APC-specific light chain residues are required for cytoprotective PAR1 signaling.

SUMMARY

Background Activated protein C (APC) cell signaling is largely reliant upon its ability to mediate protease-activated receptor (PAR) 1 proteolysis when bound to the endothelial cell (EC) protein C (PC) receptor (EPCR). Furthermore, EPCR-bound PC modulates PAR1 signaling by thrombin to induce APC-like EC cytoprotection. Objective The molecular determinants of EPCR-dependent cytoprotective PAR1 signaling remain poorly defined. To address this, a PC-factor VII chimera (PCFVII-82 ) possessing FVII N-terminal domains and conserved EPCR binding was characterized. Methods Activated PC-FVII chimera (APCFVII-82 ) anticoagulant activity was measured with calibrated automated thrombography and activated FV degradation assays. APCFVII-82 signaling activity was characterized by the use of reporter assays of PAR1 proteolysis and EC barrier integrity. APCFVII-82 anti-inflammatory activity was assessed according to its inhibition of nuclear factor-κB (NF-κB) activation and cytokine secretion from monocytes. Results PCFVII-82 was activated normally by thrombin on ECs, but was unable to inhibit plasma thrombin generation. Surprisingly, APCFVII-82 did not mediate EPCR-dependent PAR1 proteolysis, confer PAR1-dependent protection of thrombin-induced EC barrier disruption, or limit PAR1-dependent attenuation of interleukin-6 release from lipopolysaccharide (LPS)-stimulated macrophages. Interestingly, EPCR occupation by active site-blocked APCFVII-82 was, like FVII, unable to mimic EC barrier stabilization induced by PC upon PAR1 proteolysis by thrombin. APCFVII-82 did, however, diminish LPS-induced NF-κB activation and tumor necrosis factor-α release from monocytes in an apolipoprotein E receptor 2-dependent manner, with similar efficacy as wild-type APC. Conclusions These findings identify a novel role for APC light chain amino acid residues outside the EPCR-binding site in enabling cytoprotective PAR1 signaling.

Anti-protein C antibodies are associated with resistance to endogenous protein C activation and a severe thrombotic phenotype in antiphospholipid syndrome

BACKGROUND

Antiphospholipid antibodies may interfere with the anticoagulant activity of activated protein C (APC) to induce acquired APC resistance (APCr).

AIMS

To investigate the frequency and characteristics of APCr by using recombinant human APC (rhAPC) and endogenous protein C activation in antiphospholipid syndrome (APS).

METHODS

APCr was assessed in APS and non-APS venous thromboembolism (VTE) patients on warfarin and normal controls with rhAPC or Protac by thrombin generation. IgG anti-protein C and anti-protein S antibodies and avidity were assessed by ELISA.

RESULTS

APS patients showed greater resistance to both rhAPC and Protac than non-APS patients and normal controls (median normalized endogenous thrombin potential inhibition): APS patients with rhAPC, 81.3% (95% confidence interval [CI] 75.2-88.3%; non-APS patients with rhAPC, 97.7% (95% CI 93.6-101.8%; APS patients with Protac, 66.0% (95% CI 59.5-72.6%); and non-APS patients with Protac, 80.7 (95% CI 74.2-87.2%). APS patients also had a higher frequency and higher levels of anti-protein C antibodies, with 60% (15/25) high-avidity antibodies. High-avidity anti-protein C antibodies were associated with greater APCr and with a severe thrombotic phenotype (defined as the development of recurrent VTE while patients were receiving therapeutic anticoagulation or both venous and arterial thrombosis). Twelve of 15 (80%) patients with high-avidity anti-protein C antibodies were classified as APS category I.

CONCLUSION

Thrombotic APS patients showed greater APCr to both rhAPC and activation of endogenous protein C by Protac. High-avidity anti-protein C antibodies, associated with greater APCr, may provide a marker for a severe thrombotic phenotype in APS. However, in patients with category I APS, it remains to be established whether anti-protein C or anti-β2 -glycoprotein I antibodies are responsible for APCr.

Group V secretory phospholipase A2 impairs endothelial protein C receptor-dependent protein C activation and accelerates thrombosis in vivo

BACKGROUND

Endothelial protein C receptor (EPCR) must be bound to a molecule of phosphatidylcholine (PC) to be fully functional, i.e. to interact with protein C/activated protein C (APC) properly. PC can be replaced with other lipids, such as lysophosphatidylcholine or platelet-activating factor, by the action of group V secretory phospholipase A2 (sPLA2-V), an enzyme that is upregulated in a variety of inflammatory conditions. Studies in purified systems have demonstrated that the substitution of PC notably impairs EPCR function in a process called EPCR encryption.

OBJECTIVES

To analyze whether sPLA2-V was able to regulate EPCR-dependent protein C activation in vivo, and its impact on thrombosis and the hemostatic system.

METHODS

Mice were transfected with sPLA2-V by hydrodynamic gene delivery. The effects on thrombosis were studied with the laser carotid artery occlusion model, and APC generation capacity was measured with ELISA. Global hemostasis was analyzed with thromboelastometry.

RESULTS

We found that sPLA2-V overexpression in mice significantly decreased their ability to generate APC. Furthermore, a murine carotid artery laser thrombosis model revealed that higher sPLA2-V levels were directly associated with faster artery thrombosis.

CONCLUSIONS

sPLA2-V plays a thrombogenic role by impairing the ability of EPCR to promote protein C activation.