Romaric Lacroix

Tumor-Derived Tissue Factor–Bearing Microparticles Are Associated With Venous Thromboembolic Events in Malignancy

Purpose: Despite the strong association between malignant disease and thromboembolic disorders, the molecular and cellular basis of this relationship remains uncertain. We evaluated the hypothesis that tumor-derived tissue factorbearing microparticles in plasma contribute to cancer-associated thrombosis. Experimental Design: We developed impedance-based flow cytometry to detect, quantitate, and size microparticles in platelet-poor plasma. We evaluated the number of tissue factorbearing microparticles in a cohort of cancer patients of different histologies (N = 96) and conducted a case-control study of 30 cancer patients diagnosed with an acute venous thromboembolic event (VTE) compared with 60 cancer patients of similar age, stage, sex, and diagnosis without known VTE, as well as 22 patients with an idiopathic VTE. Results: Tissue factorbearing microparticles were detected in patients with advanced malignancy, including two thirds of patients with pancreatic carcinoma. Elevated levels of tissue factorbearing microparticles were associated VTE in cancer patients (adjusted odds ratio, 3.72; 95 confidence interval, 1.18-11.76; P = 0.01). In cancer patients without VTE, a retrospective analysis revealed a 1-year cumulative incidence of VTE of 34.8 in patients with tissue factorbearing microparticles versus 0 in those without detectable tissue factorbearing microparticles (Gray test P = 0.002).The median number of tissue factorbearing microparticles in the cancer VTE cohort (7.1 104 microparticles/L) was significantly greater than both the idiopathic VTE and cancerno VTE groups (P = 0.002 and P = 0.03, respectively). Pancreatectomy in three patients eliminated or nearly eliminated these microparticles which coexpressed the epithelial tumor antigen, MUC-1. Conclusion: We conclude that tumor-derived tissue factorbearing microparticles are associated with VTE in cancer patients and may be central to the pathogenesis of cancer-associated thrombosis. (Clin Cancer Res 2009;15(22):683040)

Standardization of platelet‐derived microparticle enumeration by flow cytometry with calibrated beads: results of the International Society on Thrombosis and Haemostasis SSC Collaborative workshop

Microparticles (MPs) are sub-micrometer sized vesicles released from cell membranes in response to activation or apoptosis [1]. MPs originating from several cell sources have been described in human plasma. Among them, plateletderivedMPs (PMPs) are believed to account for themajority of circulating MPs in healthy subjects [2]. Their levels are increased in several prothrombotic and inflammatory disorders [1]. In these clinical settings, PMP counts may be useful for identifying patients at risk for vascular disorders and for monitoring response to treatment [3]. However, their clinical use is not fully established, because standardized methodologies for PMP counting are lacking. A previous International Society on Thrombosis and Haemostasis (ISTH) Vascular Biology Subcommittee survey indicated that approximately 75% of laboratories use flow cytometry (FCM) to enumerate MPs in clinical samples. However, a wide variety of preanalytic variables and analytic variables have been reported in the literature, resulting in a wide range of PMP values in platelet-free plasma (PFP) of healthy subjects (100–4000 PMPs lL). This lack of consensus stresses the need for standardization [4]. Three ISTH Scientific and Standardization Subcommittees (SSC Vascular Biology, DIC, and Haemostasis &Malignancy) have initiated a project aimed at standardizing the enumeration of cellularMPs by FCM.Afirstcollaborative workshopwas set up, to: first, establish the resolution and the level of background noise of the flow cytometers currently used in laboratories with respect to the strategy requirements; and second, define the interinstrument reproducibility of PMP enumeration in human plasma. This strategy was based on the use of fluorescent calibrated sub-micrometer beads (Megamix beads; BioCytex, Marseille, France), which allow the window of MP analysis to be reproducibly set [5]. The study included 40 laboratories accounting for 59 flow cytometers, and was performed in two stages (Fig. S1): in stage A, participating laboratories received Megamix beads and were asked to set up the FCM protocol and to validate an instrument protocol adapted from a previously described method [5]. On the basis of forward scatter (FS)/FS channeling (FSC) resolution and background characteristics, stage A results led to acceptance or rejection of the tested instruments, with some time being allowed for technical intervention in order to improve any deficient performance. In stage B, selected laboratories received PFP samples prepared as frozen aliquots by the core laboratory, and were asked to analyze them with the previously validated instrument(s), common reagents, and the FCM protocol established in stage A. A detailed description of the methodology is available in the Supporting Information (Data S1). The purpose of this initial phase was to check whether the instrument to be used to enumerate PMPs demonstrated the required performance with a blend of fluorescent beads with well-known sizes and relative amounts. The instruments were validated on the basis of their capacity to discriminate between 0.5-lm and 0.9-lm Megamix beads using the FS/FSC parameter, as well as their background noise. Instruments detecting < 0.1% of fluorescent bead events among total events were rejected, because such a level of background may impede the electronics functions and induce amajor loss of events owing to coincidences and electronic aborts (Fig. S2A,B). Analysis of the results demonstrated that instruments were heterogeneous with respect to FS/FSC resolution and background noise. Furthermore, the level of performance could vary over time (Fig. S2C). Some of the parameters affecting FS/FSC resolution were identified with Megamix beads. Among them, FS/ FSC gain, FS/FSCmode, neutral density (intensity scavenging) Correspondence: Francoise Dignat-George, UMR-S608, 27 Bd Jean Moulin, 13005 Marseille, France. Tel.: +33 491 385600; fax: +33 491 385602. E-mail: francoise.dignat-george@univmed.fr Journal of Thrombosis and Haemostasis, 8: 2571–2574 DOI: 10.1111/j.1538-7836.2010.04047.x

Standardization of platelet-derived microparticle counting using calibrated beads and a Cytomics FC500 routine flow cytometer: a first step towards multicenter studies?

Summary.  Background: Platelet microparticles (PMPs) have proved useful to identify patients with vascular risk. However, PMP counting, which is currently done by flow cytometry (FCM), needs to be standardized. Objectives: The objectives were (i) to standardize FCM settings for PMP counts on a routine instrument (Cytomics FC500) using size‐calibrated fluorescent beads; (ii) to determine intra‐instrument and interinstrument reproducibility; and (iii) to establish PMP values in healthy subjects. Methods: Using a blend of size‐calibrated fluorescent beads (0.5 and 0.9 μm) in a fixed numerical ratio (Megamix), we gated PMPs in a restricted size window. To test intra‐instrument and inter‐instrument reproducibility, annexin V and CD41 coexpression were used to count PMPs in frozen aliquots of the same platelet‐free plasma (PFP) over 4 months and in PFP from 10 healthy subjects on three independent flow cytometers. Results: This calibrated‐bead strategy allowed full long‐term control of the FCM‐based microparticle protocol and reproducible PMP counts over time [coefficient of variation (CV) < 10%]. Optimal settings were easily transferred from one instrument to another, using Megamix as a stable template. Similar PMP counts (CV < 12%) were obtained using the three instruments. With such a standardized FCM protocol, PMP values were established in healthy subjects (n = 60) with significantly higher levels in women than in men [median (1st quartile to 3rd quartile): 1775 μL−1 (1014–3039 μL−1) vs. 656 μL−1 (407–962 μL−1)]. Conclusions: The present strategy provides a new option for PMP count standardization and thus opens the way for multicenter studies.

Impact of pre‐analytical parameters on the measurement of circulating microparticles: towards standardization of protocol

Summary.  Background:  Microparticles (MP) are small vesicles of 0.1–1 μm, released in response to activation or apoptosis. Over the past decade, they received an increasing interest both as biomarkers and biovectors in coagulation, inflammation and cancer. Clinical studies were conducted to assess their contribution to the identification of patients at cardiovascular risk. However, among the limitation of such studies, pre‐analytical steps remains an important source of variability and artifacts in MP analysis.

Standardization of pre-analytical variables in plasma microparticle determination: results of the International Society on Thrombosis and Haemostasis SSC Collaborative workshop

Microparticles (MP) are sub-micron sized vesicles released by activated or apoptotic cells. They are generally defined as 0.1 to 1 μm membrane particles that expose the anionic phospholipid phosphatidylserine (PS) and membrane antigens representative of their cellular origin [1]. It is now well recognized that MP behave as vectors of bioactive molecules, playing a role in blood coagulation, inflammation, cell activation and cancer metastasis. In clinical practice, circulating MP originating from blood and vascular cells are elevated in a variety of prothrombotic and inflammatory disorders, cardiovascular diseases, autoimmune conditions, infectious diseases and cancer [1-3].

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. Among the different methodologies available, flow cytometry is the most commonly used technique. This review addresses flow cytometry limitations in microparticle measurement that may be subdivided into three domains: sizing, probing, and counting. This article also covers the various standardization strategies and technological improvements that have been proposed to overcome these limitations. New tools using size-calibrated beads and recent progress in instrumentation have opened new avenues to improve detection of microparticle populations of smaller sizes. Significant optimization in microparticle detection is also expected from the use of new fluorescent dyes and the establishment of practical recommendations. Finally, absolute counting of microparticles will also benefit from adapted bead-based strategies or, alternatively, from the generalized availability of volumetric systems. Overall, recent technological improvements maintain flow cytometry as a highly competitive analytical method to measure microparticles. Challenging these evolutions in pathological situations is a mandatory step to validate their real impact in clinical practice.

Endothelial-derived microparticles: Biological conveyors at the crossroad of inflammation, thrombosis and angiogenesis

Endothelial microparticles (EMP) are complex vesicular structures that can be shed by activated or apoptotic endothelial cells. EMP are composed of a phospholipid bilayer that exposes transmembrane proteins and receptors and encloses cytosolic components such as enzymes, transcription factors and mRNA derived from their parent cells. Thus, EMP behave as biological conveyors playing a key role in the tuning of vascular homeostasis. This review focuses on the multifaceted roles of EMP, notably in coagulation, inflammation and angiogenesis and also on the mechanisms that trigger their formation. In this context, EMP could compromise vascular homeostasis and then represent key players in the pathogenesis of several inflammatory and thrombotic diseases. Consequently, elucidating their role and their mechanisms of formation will bring new insights into the understanding of endothelial-associated diseases. Moreover, in the future, it can open novel therapeutic perspectives based on the inhibition of EMP release.

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. Methods and Results—Compared with sd-FCM, hs-FCM displayed improved forward scatter resolution and lower background noise, allowing us to discriminate previously undetectable small MP in plasma samples. Using fluorescent beads with appropriate sizes (0.1/0.3/0.5/0.9 &mgr;m) and relative amounts, a new standardized hs-FCM MP protocol was set up and provided reproducible MP counts. Applied to coronary patient samples, it resulted into 8- to 20-fold increases in MP counts as compared with sd-FCM. Interestingly, the ratio between small and large MP varied according to clinical status but also depending on MP subset, suggesting access to new biological information. Conclusion—Recent improvements in FCM provide access to previously undetectable MP and represent a new opportunity to enhance their impact as biomarkers in clinical practice.

Methodological guidelines to study extracellular vesicles

Owing to the relationship between extracellular vesicles (EVs) and physiological and pathological conditions, the interest in EVs is exponentially growing. EVs hold high hopes for novel diagnostic and translational discoveries. This review provides an expert-based update of recent advances in the methods to study EVs and summarizes currently accepted considerations and recommendations from sample collection to isolation, detection, and characterization of EVs. Common misconceptions and methodological pitfalls are highlighted. Although EVs are found in all body fluids, in this review, we will focus on EVs from human blood, not only our most complex but also the most interesting body fluid for cardiovascular research.

Revisited role of microparticles in arterial and venous thrombosis

Microparticles (MPs) represent a heterogeneous population of submicronic vesicles that are released in response to cell activation or apoptosis. MPs harbor a large repertoire of cell surface receptors and mRNA and biological activities representative of their parent cells and related to their involvement in many biological functions. Although MP generation is a physiological response, a dramatic increase in circulating MPs is detectable in a variety of thrombosis‐associated disorders compared with healthy individuals. In this review, we will discuss a new vision of MPs as complex and ambivalent structures that express both activators and inhibitors of coagulation but also convey fibrinolytic properties. After summarizing our current knowledge about the role of MPs in venous and arterial thrombosis, this review will explore how this new vision of MPs influences their definition as emergent biomarkers in thrombotic diseases. Among the studies that have aimed to establish a link between thrombosis and MPs, a few studies have demonstrated a predictive value of MPs. So far, it is unclear whether this limited causative association is the result of current technical concerns and limited standardization or has to be integrated into a more complex vision of the role of MPs as key systems for regulating the balance between coagulation and fibrinolysis.