Endothelial PTP1B Deletion Promotes VWF Exocytosis and Venous Thromboinflammation.

Background: Endothelial activation promotes the release of procoagulant extracellular vesicles and inflammatory mediators from specialized storage granules. Endothelial membrane exocytosis is controlled by phosphorylation. We hypothesized that the absence of PTP1B (protein tyrosine phosphatase 1B) in endothelial cells promotes venous thromboinflammation by triggering endothelial membrane fusion and exocytosis.

Blood Coagulation and Beyond: Position Paper from the Fourth Maastricht Consensus Conference on Thrombosis.

The Fourth Maastricht Consensus Conference on Thrombosis included the following themes. Theme 1: The "coagulome" as a critical driver of cardiovascular disease. Blood coagulation proteins also play divergent roles in biology and pathophysiology, related to specific organs, including brain, heart, bone marrow, and kidney.

Granulocyte microvesicles with a high plasmin generation capacity promote clot lysis and improve outcome in septic shock.

Microvesicles (MVs) have previously been shown to exert profibrinolytic capacity, which is increased in patients with septic shock (SS) with a favorable outcome. We, therefore, hypothesized that the plasmin generation capacity (PGC) could confer to MVs a protective effect supported by their capacity to lyse a thrombus, and we investigated the mechanisms involved. Using an MV-PGC kinetic assay, ELISA, and flow cytometry, we found that granulocyte MVs (Gran-MVs) from SS patients display a heterogeneous PGC profile driven by the uPA (urokinase)/uPAR system.

A new hybrid immunocapture bioassay with improved reproducibility to measure tissue factor-dependent procoagulant activity of microvesicles from body fluids.

Background: The procoagulant activity of tissue factor-bearing microvesicles (MV-TF) has been associated with the risk of developing venous thrombosis in cancer patients. However, MV-TF assays are limited either by i) a lack of specificity, ii) a low sensitivity, or iii) a lack of repeatability when high-speed centrifugation (HS-C) is used to isolate MV. Therefore, our objective was to develop a new hybrid "capture-bioassay" with improved reproducibility combining MV immunocapture from biofluids and measurement of their TF activity.

Increasing the sensitivity of the human microvesicle tissue factor activity assay.

Introduction: The TF-FVIIa complex is the primary activator of coagulation. Elevated levels of microvesicle (MV) bearing tissue factor (TF)-dependent procoagulant activity are detectable in patients with an increased risk of thrombosis. Several methods have been described to measure MV TF activity but they are hampered by limited sensitivity and specificity.

Tissue factor pathway inhibitor primes monocytes for antiphospholipid antibody-induced thrombosis.

Antiphospholipid antibodies (aPLs) with complex lipid and/or protein reactivities cause complement-dependent thrombosis and pregnancy complications. Although cross-reactivities with coagulation regulatory proteins contribute to the risk for developing thrombosis in patients with antiphospholipid syndrome, the majority of pathogenic aPLs retain reactivity with membrane lipid components and rapidly induce reactive oxygen species-dependent proinflammatory signaling and tissue factor (TF) procoagulant activation. Here, we show that lipid-reactive aPLs activate a common species-conserved TF signaling pathway.

A new assay to evaluate microvesicle plasmin generation capacity: validation in disease with fibrinolysis imbalance.

Among extracellular vesicles, leukocyte-derived microvesicles (LMVs) have emerged as complex vesicular structures. Primarily identified as procoagulant entities, they were more recently ascribed to plasmin generation capacity (MV-PGC). The objectives of this work were (1) to develop a new hybrid bio-assay combining the specific isolation of LMVs and measurement of their PGC, and compare its performance to the original method based on centrifugation, (2) to validate MV-PGC in septic shock, combining increased levels of LMVs and fibrinolytic imbalance.

Platelet function and microparticle levels in atrial fibrillation: Changes during the acute episode.

Background: Thrombotic risk constitutes a major complication of atrial fibrillation (AF). Platelets and microparticles (MPs) are important for hemostasis and thrombosis, however their participation during AF is not well known. The aim of this study was to characterize platelet function and MPs procoagulant and fibrinolytic activity in AF patients and to determine the effects of an acute-AF episode.

Tips and tricks for flow cytometry-based analysis and counting of microparticles.

Submicron-sized extra-cellular vesicles generated by budding from the external cell membranes, microparticles (MPs) are important actors in transfusion as well as in other medical specialties. After briefly positioning their role in the characterization of labile blood products, this technically oriented chapter aims to review practical points that need to be considered when trying to use flow cytometry for the analysis, characterization and absolute counting of MP subsets. Subjects of active discussions relative to instrumentation will include the choice of the trigger parameter, possible standardization approaches requiring instrument quality-control, origin and control of non-specific background and of coincidence artifacts, choice of the type of electronic signals, optimal sheath fluid and sample speed.

High-sensitivity flow cytometry provides access to standardized measurement of small-size microparticles--brief report.

Objective: Cellular microparticles (MP) are promising biomarkers in many pathological situations. Although flow cytometry (FCM) is widely used for their measurement, it has raised controversies because the smallest MP size falls below the detection limit of standard FCM (sd-FCM). Following recent technological improvements leading to high sensitivity FCM (hs-FCM), our objectives were (1) to evaluate the potential of hs-FCM for extended MP detection, (2) to set up a standardized protocol for MP enumeration, and (3) to compare MP counts obtained with both sensitivity levels.

Phase I studies of AVE9633, an anti-CD33 antibody-maytansinoid conjugate, in adult patients with relapsed/refractory acute myeloid leukemia.

The efficacy of anti-CD33 immunoconjugates had been previously demonstrated for gemtuzumab-ozogamicin. AVE9633 is an anti-CD33-maytansine conjugate created by ImmunoGen Inc. Phase I trials of AVE9633 were performed in patients with AML to evaluate tolerability, pharmacokinetics and pharmacodynamics.

Overcoming limitations of microparticle measurement by flow cytometry.

Circulating microparticles are submicron vesicles released from cell membranes in response to activation or apoptosis. Acknowledgment of their role both as markers and pathogenic effectors in thrombosis, inflammation, and the spread of cancer has increased the interest of their measurement in clinical practice. However, assessment of their clinical use is impeded by technological issues.