Multisite Thrombosis in a Patient with Paroxysmal Nocturnal Hemoglobinuria.

CASE: Paroxysmal nocturnal hemoglobinuria (PNH) is an extremely rare bone marrow disorder caused by acquired mutations in the phosphatidylinositol glycan class A gene, which lead to a partial or total loss of the cellular complement regulators CD55 and CD59.1 In addition to complement-mediated hemolysis and cytopenia, venous and arterial thromboses at multiple and/or unusual sites are a common complication and occur in up to 44% of patients in historic PNH cohorts.1 2.

Effect of factor XI inhibition on tumor cell-induced coagulation activation.

BACKGROUND: Cancer-associated thrombosis is a frequent complication in patients with malignancies. While factor XI (FXI)/FXIa inhibition is efficacious in preventing postoperative venous thromboembolism, its role in tumor cell-induced coagulation is less defined. OBJECTIVES: We thus aimed to provide mechanistic insights into FXI/FXIa inhibition in tumor cell-induced coagulation activation. METHODS: Procoagulant activity (PCA) of 4 different tissue factor (TF) expressing tumor cell lines was analyzed by single-stage clotting and thrombin generation assay in the presence of a FXIa inhibitor, BMS-262084 (BMS), an inhibitory FXI antibody (anti-FXI), or peak and trough concentrations of rivaroxaban or tinzaparin. Further, tumor cell-induced platelet aggregation was recorded. Recombinant human TF served as positive control. RESULTS: Although BMS and anti-FXI potently inhibited FXIa amidolytic activity, both inhibitors efficiently mitigated recombinant human TF- and tumor cell-induced fibrin clot formation and platelet aggregation only in the presence of low TF PCA. The anticoagulant effects showed an inverse correlation with the magnitude of cellular TF PCA expression. Similarly, BMS markedly interfered with tumor cell-induced thrombin generation, with the most prominent effects on peak and total thrombin. In addition, anticoagulant effects of FXIa inhibition by 10 µM BMS were in a similar range to those obtained by 600 nM rivaroxaban and 1.6 µM tinzaparin at low TF PCA levels. However, rivaroxaban and tinzaparin also exerted marked anticoagulant activity at high TF PCA levels. CONCLUSION: Our findings indicate that FXI/FXIa inhibition interferes with tumor cell-induced coagulation activation only at low TF PCA expression levels, a finding with potential implications for future in vivo studies.

Regulation of coagulation activation in newly diagnosed AML by the heme enzyme myeloperoxidase.

INTRODUCTION: Patients with acute myeloid leukemia (AML) are at increased risk of thrombohemorrhagic complications. Overexpressed tissue factor (TF) on AML blasts contributes to systemic coagulation activation. We have recently shown that the heme enzyme myeloperoxidase (MPO) negatively regulates TF procoagulant activity (PCA) on myelomonocytic cells in vitro. We now aimed to further characterize the functional interaction of MPO and TF in AML in vivo. METHODS: We prospectively recruited 66 patients with newly diagnosed AML. TF PCA of isolated peripheral blood mononuclear cells (PBMC) was assessed by single-stage clotting assay in the presence or absence of inhibitors against MPO catalytic activity (ABAH) or against MPO-binding integrins (anti-CD18). MPO in plasma and in AML blasts was measured by ELISA, and plasma D-dimers and prothrombin fragment F1+2 were quantified by automated immunoturbidimetric and chemiluminescence assays, respectively. RESULTS: Patients with AML had significantly higher MPO plasma levels compared to healthy controls and exhibited increased levels of D-dimers and F1+2. In vivo thrombin generation was mediated by TF PCA on circulating PBMC. Ex vivo incubation of isolated PBMC with ABAH or anti-CD18 antibody resulted in either increased or decreased TF PCA. The strong and robust correlation of F1+2 with TF PCA of circulating PBMC was abrogated at MPO plasma levels higher than 150 ng/mL, indicating a modulatory role for MPO on TF-mediated in vivo thrombin generation above this threshold. CONCLUSION: Our study indicates that catalytically active MPO released by circulating myeloblasts regulates TF-dependent coagulation in patients with newly diagnosed AML in a CD18-dependent manner.

Expression and Release of Tumor Cell Tissue Factor Triggers Recurrent Thromboembolism in a Patient with Endometrial Cancer.

Although cancer-associated thrombosis (CAT) is a frequent complication in patients with malignancies, its treatment remains a challenge in daily practice. Here, we report the clinical course of a 51-year-old woman presenting with a highly thrombogenic paraneoplastic coagulopathy. Despite therapeutic anticoagulation with various agents, including rivaroxaban, fondaparinux, and low-molecular-weight heparin, the patient suffered from recurrent venous and arterial thromboembolism. Locally advanced endometrial cancer was identified. Tumor cells showed strong expression of tissue factor (TF), and significant concentrations of TF-bearing microvesicles were detected in patient plasma. Coagulopathy was controlled only by continuous intravenous anticoagulation with the direct thrombin inhibitor, argatroban. Multimodal antineoplastic treatment, including neoadjuvant chemotherapy followed by surgery and postoperative radiotherapy, resulted in clinical cancer remission, which was paralleled by normalization of tumor markers, CA125 and CA19-9, D-dimer levels, and TF-bearing microvesicles. In summary, continuous anticoagulation with argatroban and multimodal anticancer treatment may be necessary to control TF-driven coagulation activation with recurrent CAT in endometrial cancer.

Inhibition of protein disulfide isomerase with PACMA-31 regulates monocyte tissue factor through transcriptional and posttranscriptional mechanisms.

INTRODUCTION: Protein disulfide isomerase (PDI) contributes to tissue factor (TF) regulation in monocytes. While bacitracin and quercetin-3-rutinoside mitigate myeloid TF production, the effect of PACMA-31, a more specific PDI inhibitor with distinct pharmacologic properties, remains unclear. MATERIALS AND METHODS: Lipopolysaccharide (LPS) stimulation of peripheral blood mononuclear cells (PBMCs) or citrate-anticoagulated whole blood was carried out in the presence of PACMA-31 or DMSO vehicle before monocytes were analyzed for TF expression, including antigen, procoagulant activity (PCA) and mRNA, release of IL-6 and TNFα, and LPS-induced signaling pathways. RESULTS: While PACMA-31 alone had no effect, coincubation with LPS and PACMA-31 (25 µM) enhanced LPS-induced monocyte TF production in whole blood. The effect was at least partially regulated on the transcriptional level and could not be explained by increased phosphatidylserine membrane exposure. In contrast, the same PACMA-31 concentrations were cytotoxic in isolated PBMCs. A lower dose of PACMA-31, however, restored the stimulating effect by enhancing IκB-NFκB signaling that also increased the release of IL-6 and TNFα. The protease-activated receptor 2 (PAR2) inhibitor ENMD547 but not TF antibody 10H10 or factor Xa inhibitor rivaroxaban prevented the stimulatory effect of PACMA-31 on inflammatory monocytes. In sharp contrast, short time incubation of LPS-stimulated PBMCs with 25 µM PACMA-31 was non-cytotoxic and significantly inhibited cellular TF PCA but not surface antigen expression. CONCLUSIONS: PACMA-31 regulates monocyte TF in a concentration-dependent manner by opposing transcriptional and posttranscriptional mechanisms. While low concentrations of PACMA-31 augment monocyte TF production by amplifying LPS-dependent PAR2 signaling, high concentrations convert monocyte TF into its non-coagulant state.

Bacitracin and Rutin Regulate Tissue Factor Production in Inflammatory Monocytes and Acute Myeloid Leukemia Blasts.

Aberrant expression of tissue factor (TF) by transformed myeloblasts and inflammatory monocytes drives coagulation activation in acute myeloid leukemia (AML). Although regulation of TF procoagulant activity (PCA) involves thiol-disulfide exchange reactions, the specific role of protein disulfide isomerase (PDI) and other thiol isomerases in AML-associated TF biology is unclear. THP1 cells and peripheral blood mononuclear cells (PBMCs) from healthy controls or AML patients were analyzed for thiol isomerase-dependent TF production under various experimental conditions. Total cellular and membrane TF antigen, TF PCA and TF mRNA were analyzed by ELISA, flow cytometry, clotting or Xa generation assay and qPCR, respectively. PBMCs and THP1 cells showed significant insulin reductase activity, which was inhibited by bacitracin or rutin. Co-incubation with these thiol isomerase inhibitors prevented LPS-induced TF production by CD14-positive monocytes and constitutive TF expression by THP1 cells and AML blasts. Downregulation of the TF antigen was mainly restricted to the cryptic pool of TF, efficiently preventing phosphatidylserine-dependent TF activation by daunorubicin, and at least partially regulated on the mRNA level in LPS-stimulated monocytes. Our study thus delineates a complex role of thiol isomerases in the regulation of myeloid TF PCA, with PDI being a promising therapeutic target in the management of AML-associated coagulopathies.

Monocyte activation and acquired autoimmune protein S deficiency promote disseminated intravascular coagulation in a patient with primary antiphospholipid syndrome.

Autoimmune protein S (PS) deficiency is a highly thrombotic, potentially life-threatening disorder. Its pathophysiological relevance in the context of primary antiphospholipid syndrome (APS) is unclear. Here, we report the case of a 76-year-old woman, who presented with a painful reticular skin erythema caused by microvascular thromboses. Disseminated intravascular coagulation (DIC) with consumptive coagulopathy was controlled only by continuous anticoagulation. While significantly elevated IgM antibodies to cardiolipin and ß2-glycoprotein-I were consistent with primary APS, a function-blocking PS autoantibody of the IgG isotype was detected. Robust microvesicle (MV)-associated tissue factor (TF) procoagulant activity (PCA) was isolated from patient plasma. Moreover, patient IgG, but not IgM, induced expression of TF PCA and release of TF-bearing MVs by peripheral blood mononuclear cells from healthy donors. In primary APS, induction of monocyte TF in combination with an acquired PS inhibitor may provoke a deleterious imbalance of procoagulant and anticoagulant pathways with evolution of thrombotic DIC.

Myeloperoxidase has no effect on the low procoagulant activity of silica-free DNA.

Blood coagulation and innate immunity are closely interrelated. At sites of inflammation, DNA and myeloperoxidase (MPO) are released from polymorphonuclear leukocytes (PMNs) as an integral component of neutrophil extracellular traps (NETs). NETs exert pleiotropic thrombogenic effects, with DNA-mediated contact activation of factor XII (FXII) likely playing a role. We have previously shown that MPO, a highly cationic protein, regulates coagulation through heteromolecular interactions with various negatively charged structures, including membrane phospholipids and low-molecular-weight heparin. The aims of our current study were to confirm that DNA activates coagulation and to investigate whether its procoagulant activity (PCA) is regulated by PMN-derived MPO. To this end, we used thrombin generation and FXIIa amidolytic activity assays to analyze the PCA of cell-free DNA isolated with silica membrane-based (cfDNA) or silica-free procedures (PaxDNA). cfDNA potently activated FXII and promoted thrombin generation in a concentration-dependent manner, but its PCA was largely attributable to contaminating silica particles. In contrast, pure, i.e. silica-free, PaxDNA was markedly less procoagulant. Although PaxDNA amplified thrombin generation in plasma, it was devoid of any direct FXII activating activity. MPO supershifted both cfDNA and PaxDNA in gel electrophoresis, but only silica-associated PCA of cfDNA was neutralized by MPO independently of its catalytic properties. Moreover, pretreatment with DNase I abolished silica-induced thrombin generation. In summary, we show that pure DNA has rather weak PCA, which is not further inhibited by heteromolecular complex formation with exogenous MPO. Our study thus provides novel mechanistic insights into the regulation of coagulation by extracellular DNA under inflammatory conditions.

Prevalence of definite antiphospholipid syndrome in carriers of the JAK2V617F mutation.

INTRODUCTION: Patients with Philadelphia-negative myeloproliferative neoplasms (MPNs), particularly those carrying the JAK2V617F mutation, are at increased risk of thrombosis. While an association of MPNs with autoimmune disorders has been established, the prevalence of inherited or acquired thrombophilias in JAK2V617F-positive patients remains obscure. We therefore investigated the coincidence of the JAK2V617F mutation with additional thrombogenic risk factors. METHODS: In a retrospective study, we analyzed all patients referred for thrombophilia work-up between 01/2011 and 08/2019, in whom additional JAK2V617F mutation analysis was performed because of thromboembolic events that were recurrent, atypically located and/or associated with abnormal blood counts. RESULTS: Of 472 tested patients, 49 (10.4%) were JAK2V617F-positive. While the frequency of inherited thrombophilias (factor V Leiden and prothrombin G20210A mutation, deficiency of antithrombin, protein C, protein S) was not different between the two groups, the prevalence of definite antiphospholipid syndrome (APS), mostly associated with a moderate- or high-risk antibody profile, was significantly higher in patients with (22.4%) than in those without (8.4%) JAK2V617F mutation (p < 0.01). All evaluable JAK2V617F-positive patients with APS were subsequently diagnosed with MPN. In patients with JAK2V617F mutation, presence of concomitant APS was associated with a significantly younger age (49 ± 14 vs. 60 ± 15 years) at the time of thrombophilia work-up (p < 0.05). CONCLUSION: We found a significant association between JAK2V617F-positive MPN and definite APS. The presence of concomitant APS in patients carrying the JAK2V617F mutation may lead to earlier manifestation of thromboembolic events and may warrant more aggressive antithrombotic treatment strategies to prevent recurrence.

Effect of myeloperoxidase on the anticoagulant activity of low molecular weight heparin and rivaroxaban in an in vitro tumor model.

BACKGROUND: Inflammation with leukocyte activation is a hallmark of cancer-associated thrombosis (CAT), and elevated leukocytes predict venous thromboembolism in cancer outpatients. In a recent trial, rivaroxaban was more efficacious than dalteparin in preventing CAT recurrence. OBJECTIVES: In a proof-of-concept study, we aimed to provide a mechanistic basis for improved efficacy of rivaroxaban compared to low molecular weight heparin in CAT treatment. METHODS: We studied the effects of rivaroxaban, dalteparin, and tinzaparin at peak and trough levels on tumor cell-induced procoagulant activity and platelet aggregation in the presence or absence of the cationic leukocyte-derived enzyme, myeloperoxidase (MPO). Furthermore, pro-inflammatory conditions were generated by stimulating whole blood with lipopolysaccharide (LPS) or phorbol-myristate-acetate (PMA), before measuring thrombin generation in plasma supernatants. RESULTS: All three anticoagulants inhibited thrombin generation, fibrin clot formation, and platelet aggregation induced by the tissue factor-expressing prostate carcinoma cell line, 22Rv1. Pre-incubation with MPO partially attenuated the anticoagulant activity of dalteparin and tinzaparin, but not rivaroxaban, at trough levels. The effect of MPO did not involve the enzyme's catalytic properties, but required its structural integrity, as indicated by heat denaturation. In plasma obtained from LPS- or PMA-stimulated whole blood, elevated MPO antigen levels inversely correlated with the ability of tinzaparin to inhibit 22Rv1-induced thrombin generation. CONCLUSIONS: Myeloperoxidase release may partially attenuate the anticoagulant activity of trough levels of dalteparin and tinzaparin in the context of paraneoplastic leukocyte activation. However, this effect is likely not sufficient to explain the improved efficacy of rivaroxaban, and possibly other oral factor Xa inhibitors, in CAT treatment.

LPS-induced expression and release of monocyte tissue factor in patients with haemophilia.

In haemophilia, thrombin generation and fibrin deposition upon vascular injury critically depend on the tissue factor (TF)-driven coagulation pathway. TF expression by monocytes/macrophages and circulating microvesicles contributes to haemostasis, thrombosis and inflammation. Inflammation is a hallmark of blood-induced joint disease. The aim of this study is to correlate TF production by whole-blood monocytes with inflammatory markers and clinical parameters in patients with moderate-to-severe haemophilia A or B (n = 43) in comparison to healthy males (n = 23). Monocyte TF antigen and microvesicle-associated TF procoagulant activity (MV TF PCA) were measured immediately after blood draw (baseline) and following incubation of whole blood with buffer or lipopolysaccharide (LPS) using two-colour flow cytometry and chromogenic FXa generation assay, respectively. Patients with HIV or uncontrolled HBV/HCV infections were excluded. TF was hardly detectable and not different in baseline and buffer-treaded samples from both groups. Stimulation with LPS, however, induced monocyte TF production, with increased TF-specific mean fluorescence intensity (P = 0.08) and MV TF PCA (P < 0.05) in patients compared to controls. Patients also had elevated hs-CRP and IL-6 serum levels (P < 0.001), which correlated with LPS-induced TF parameters. Further exploratory analyses revealed that the presence of systemic (low-grade) inflammation and boosted LPS-induced monocyte TF production were mainly restricted to patients with clinically controlled HBV and/or HCV infection (n = 16), who were older and also had a significantly worse orthopaedic joint score than patients with no history of viral hepatitis (P < 0.01). Our study delineates a previously unrecognised link between systemic inflammation and inducible monocyte TF production in patients with haemophilia A or B.

Myeloperoxidase Is a Negative Regulator of Phospholipid-Dependent Coagulation.

Myeloperoxidase (MPO) is a cationic heme enzyme stored in neutrophilic polymorphonuclear leukocytes (PMNs) that has recently been implicated in inflammatory cell signaling and tissue damage. Although PMNs play a critical role in both innate immunity and vascular thrombosis, no previous study has systematically investigated the effect of MPO on blood coagulation. Here, we show that PMN-derived MPO inhibits the procoagulant activity (PCA) of lipidated recombinant human tissue factor (rhTF) in a time- and concentration-dependent manner that involves, but is not entirely dependent on the enzyme's catalytic activity. Similarly, MPO together with its substrate, H2O2, inhibited the PCA of plasma microvesicles isolated from lipopolysaccharide (LPS)-stimulated whole blood, an effect additive to that of a function blocking TF antibody. Treatment of whole blood with LPS or phorbol-myristate-acetate dramatically increased MPO plasma levels, and co-incubation with 4-ABAH, a specific MPO inhibitor, significantly enhanced the PCA in plasma supernatants. MPO and MPO/H2O2 also inhibited the PCA of activated platelets and purified phospholipids (PLs), suggesting that modulation of negatively charged PLs, i.e., phosphatidylserine, rather than direct interference with the TF/FVIIa initiation complex was involved. Consistently, pretreatment of activated platelets with MPO or MPO/H2O2 attenuated the subsequent binding of lactadherin, which specifically recognizes procoagulant PS on cell membranes. Finally, endogenously released MPO regulated the PCA of THP1 cells in an autocrine manner dependent on the binding to CD11b/CD18 integrins. Collectively, these findings indicate that MPO is a negative regulator of PL-dependent coagulation and suggest a more complex role of activated PMNs in haemostasis and thrombosis.