Targeted gene sequencing identifies variants in the protein C and endothelial protein C receptor genes in patients with unprovoked venous thromboembolism.

OBJECTIVE: The interaction of protein C (PC) with the endothelial PC receptor (EPCR) enhances activated PC generation. We performed targeted gene sequencing of the PC gene (PROC) and EPCR genes (PROCR) in patients with unprovoked venous thromboembolism (VTE) to determine whether mutations that impair PC-EPCR interactions are associated with an increased risk of VTE. APPROACH AND RESULTS: We sequenced exon 3 of PROC and exons 2 and 3 of PROCR (the exons that encode the protein-protein binding domains of PC and EPCR) in 653 patients with unprovoked VTE and in 627 healthy controls. Five single nucleotide variants, each in individual patients, were identified that result in abnormal PC (Arg9Cys, Val34Met, and Arg-1Cys) or abnormal EPCR proteins (Arg96Cys and Val170Leu). We did not detect any nonsynonymous coding variants in the controls. When the PC variants were expressed in human embryonic kidney 293 cells, all exhibited decreased synthesis, and 2 of the variants had reduced capacity for activated PC generation. When expressed on the surface of human embryonic kidney 293 cells, the EPCR variants showed reduced affinity for fluorescently labeled PC. In addition, the previously reported EPCR A3 haplotype, which promotes cellular shedding of EPCR, is over-represented in the patient group (P=0.001). CONCLUSIONS: This is the first targeted DNA sequencing analysis of PROC and PROCR in a large group of patients with unprovoked VTE. Our data suggest that mutations that impair PC-EPCR interactions may be associated with an increased risk of VTE.

Procoagulant effects of lung cancer chemotherapy: impact on microparticles and cell-free DNA.

Lung cancer is the second leading type of cancer, with venous thromboembolism being the second leading cause of death. Studies have shown increased levels of microparticles and cell-free DNA (CFDNA) in cancer patients, which can activate coagulation through extrinsic and intrinsic pathways, respectively. However, the impact of lung cancer chemotherapy on microparticle and/or CFDNA generation is not completely understood. The aim of the study was to study the effects of platinum-based chemotherapeutic agents on generation of procoagulant microparticles and CFDNA in vitro and in vivo. Microparticles were isolated from chemotherapy-treated monocytes, human umbilical vein endothelial cells, or cancer cells. Tissue factor (TF) and phosphatidylserine levels were characterized and thrombin/factor Xa generation assays were used to determine microparticle procoagulant activity. CFDNA levels were isolated from cell supernatants and plasma. A murine xenograft model of human lung carcinoma was used to study the procoagulant effects of TF microparticles and CFDNA in vivo. In vitro, platinum-based chemotherapy induced TF/phosphatidylserine microparticle shedding from A549 and A427 lung cancers cells, which enhanced thrombin generation in plasma in a FVII-dependent manner. CFDNA levels were increased in supernatants of chemotherapy-treated neutrophils and plasma of chemotherapy-treated mice. TF microparticles were elevated in plasma of chemotherapy-treated tumour-bearing mice. Plasma CFDNA levels are increased in chemotherapy-treated tumour-free mice and correlate with increased thrombin generation. In tumour-bearing mice, chemotherapy increases plasma levels of CFDNA and TF/phosphatidylserine microparticles. Platinum-based chemotherapy induces the shedding of TF/phosphatidylserine microparticles from tumour cells and the release of CFDNA from host neutrophils.

Extracellular Histones Increase Tissue Factor Activity and Enhance Thrombin Generation by Human Blood Monocytes.

OBJECTIVES: Sepsis is characterized by systemic activation of inflammatory and coagulation pathways in response to infection. Recently, it was demonstrated that histones released into the circulation by dying/activated cells may contribute to sepsis pathology. Although the ability of extracellular histones to modulate the procoagulant activities of several cell types has been investigated, the influence of histones on the hemostatic functions of circulating monocytes is unknown. To address this, we investigated the ability of histones to modulate the procoagulant potential of THP-1 cells and peripheral blood monocytes, and examined the effects of plasmas obtained from septic patients to induce a procoagulant phenotype on monocytic cells. METHODS/RESULTS: Tissue factor (TF) activity assays were performed on histone-treated THP-1 cells and blood monocytes. Exposure of monocytic cells to histones resulted in increases in TF activity, TF antigen, and phosphatidylserine exposure. Histones modulate the procoagulant activity via engagement of Toll-like receptors 2 and 4, and this effect was abrogated with inhibitory antibodies. Increased TF activity of histone-treated cells corresponded to enhanced thrombin generation in plasma determined by calibrated automated thrombography. Finally, TF activity was increased on monocytes exposed to plasma from septic patients, an effect that was attenuated in plasma from patients receiving unfractionated heparin (UFH). CONCLUSIONS: Our studies suggest that increased levels of extracellular histones found in sepsis contribute to dysregulated coagulation by increasing TF activity of monocytes. These procoagulant effects can be partially ameliorated in sepsis patients receiving UFH, thereby identifying extracellular histones as a potential therapeutic target for sepsis treatment.

Lung cancer chemotherapy agents increase procoagulant activity via protein disulfide isomerase-dependent tissue factor decryption.

Lung cancer patients undergoing chemotherapy have an elevated risk for thrombosis. However, the mechanisms by which chemotherapy agents increase the risk for thrombosis remains unclear. The aim of this study was to determine the mechanism(s) by which lung cancer chemotherapy agents cisplatin, carboplatin, gemcitabine, and paclitaxel elicit increased tissue factor activity on endothelial cells, A549 cells, and monocytes. Tissue factor activity, tissue factor antigen, and phosphatidylserine exposure were measured on chemotherapy-treated human umbilical vein endothelial cells (HUVEC), A549 cells, and monocytes. Cell surface protein disulfide isomerase (PDI) and cell surface free thiol levels were measured on HUVEC and A549 non-small cell lung carcinoma cells. Treatment of HUVECs, A549 cells, and monocytes with lung cancer chemotherapy significantly increased cell surface tissue factor activity. However, elevated tissue factor antigen levels were observed only on cisplatin-treated and gemcitabine-treated monocytes. Cell surface levels of phosphatidylserine were increased on HUVEC and monocytes treated with cisplatin/gemcitabine combination therapy. Chemotherapy also resulted in increased cell surface levels of PDI and reduced cell surface free thiol levels. Glutathione treatment and PDI inhibition, but not phosphatidylserine inhibition, attenuated tissue factor activity. Furthermore, increased tissue factor activity was reversed by reducing cysteines with dithiothreitol. These studies are the first to demonstrate that lung cancer chemotherapy agents increase procoagulant activity on endothelial cells and A549 cells by tissue factor decryption through a disulfide bond formation in a PDI-dependent mechanism.