Microparticles in COVID-19 as a link between lung injury extension and thrombosis.

Procoagulant microparticles are associated with the extent of lung injuries in #COVID19 and pulmonary thrombosis https://bit.ly/3eX2LPc.

Microparticles are new biomarkers of septic shock-induced disseminated intravascular coagulopathy.

PURPOSE: Septic shock-induced disseminated intravascular coagulopathy (DIC) contributes to multiple organ failure. Mechanisms governing vascular responses to open occurrence of DIC have not yet been established. Circulating plasma microparticles (MPs), released upon cell stress, constitute a catalytic procoagulant surface and are surrogates of vascular cell activation/injury. Herein, MPs were assessed as possible markers of haemostatic and vascular dysfunction in the DIC time course. METHODS: One hundred patients with septic shock from three ICUs were enrolled and their haemostatic status evaluated at admission (D1), D2, D3 and D7. Circulating procoagulant MPs were isolated, quantified by prothrombinase assay and their cellular origin determined. DIC diagnosis was made according to the JAAM 2006 score. RESULTS: Ninety-two patients were analysed and 40 had DIC during the first 24 h. Routine clotting times and factor/inhibitor activity did not allow assessing vascular cell involvement. At admission, thrombin generation and fibrinolysis were observed in both groups while impaired fibrin polymerisation was evidenced only in DIC patients. Sustained thrombin generation persisted over time in both groups at D7. While total microparticle concentrations were in the same range regardless of DIC diagnosis, specific phenotypes were already detected at admission in DIC patients. Endothelial- and leucocyte-derived MPs were higher in DIC while an increased soluble glycoprotein V/platelet ratio was delayed, underscoring the first involvement of endothelial cells and leucocytes whereas platelet activation was delayed. Endothelium-derived CD105-MPs (OR 6.55) and CD31-MPs (OR 0.49) were strongly associated with early DIC in multivariate analysis. CONCLUSION: Endothelial-derived microparticles are relevant biomarkers of septic shock-induced DIC and could be used to evaluate early vascular injury.

Increased oxidative stress induces apoptosis in human cystic fibrosis cells.

Oxidative stress results in deleterious cell function in pathologies associated with inflammation. Here, we investigated the generation of superoxide anion as well as the anti-oxidant defense systems related to the isoforms of superoxide dismutases (SOD) in cystic fibrosis (CF) cells. Pro-apoptotic agents induced apoptosis in CF but not in control cells that was reduced by treatment with SOD mimetic. These effects were associated with increased superoxide anion production, sensitive to the inhibition of IκB-α phosphorylation, in pancreatic but not tracheal CF cells, and reduced upon inhibition of either mitochondrial complex I or NADPH oxidase. CF cells exhibited reduced expression, but not activity, of both Mn-SOD and Cu/Zn-SOD when compared to control cells. Although, expression of EC-SOD was similar in normal and CF cells, its activity was reduced in CF cells. We provide evidence that high levels of oxidative stress are associated with increased apoptosis in CFTR-mutated cells, the sources being different depending on the cell type. These observations underscore a reduced anti-oxidant defense mechanism, at least in part, via diminished EC-SOD activity and regulation of Cu/Zn-SOD and Mn-SOD expressions. These data point to new therapeutic possibilities in targeting anti-oxidant pathways to reduce oxidative stress and apoptosis in CF cells.

Microparticles: a critical component in the nexus between inflammation, immunity, and thrombosis.

Plasma membrane remodeling characterized by phosphatidylserine exposure and consecutive microparticle (MP) shedding is an ubiquitous process enabling the clearance of senescent cells and the maintenance of tissue homeostasis. MPs are released as fragments from the budding plasma membrane of virtually all eukaryotic cell types undergoing stimulation or apoptosis and may be considered a broad primitive response to stress. MP release is dependent on cytoskeleton degradation pathways involving caspases, requires a sustained increase in intracellular calcium triggering K+ and Cl- efflux and is possibly tuned by mitochondria permeability changes. Because they convey a broad spectrum of bioactive molecules, circulating MPs may serve as shuttles promoting cellular cross talk in various pathological settings such as inflammation or immunity-induced thrombotic disorders. If the drastic shedding of procoagulant MPs appears clearly noxious in thrombotic disorders or in some models of inflammation-induced coagulopathy, this does not necessarily endorse their invariably harmful nature. In the vessel, endothelial cytoprotection reported in the early regulation of inflammation-induced coagulopathy is emblematic of the beneficial effects provided by MPs. In addition, MPs would prove beneficial in the prevention of blood leakage. Because of their multiple properties that are characteristic of a private response of the parental cell, MPs could act as cytoprotective and anti-inflammatory agents through the delivery of activated protein C or annexin 1 and could contribute to the limitation of vascular hyporeactivity. Owing to their ability to cargo bioactive signals, MPs could be viewed as an integrated communication network enabling the coordination of complex cellular responses in biological fluids and the maintenance of the homeostasis equation. A better understanding of the molecular mechanisms involved in MP shedding would pave the way of a new pharmacological approach aiming at the control of MP-driven cellular responses.

Significance of membrane microparticles in solid graft and cellular transplantation.

Microparticles (MPs) are submicron vesicles released from stimulated or apoptotic cells after plasma membrane remodeling. In body fluids, they constitute relevant hallmarks of cell damage. Having long been considered inert debris reflecting cellular activation or damage, MPs are now considered as cellular effectors involved in cell-cell crosstalk. This review focuses on the pathophysiologic significance of MPs in the particular setting of solid graft and cellular transplantation.

A method to assess the migration properties of cell-derived microparticles within a living tissue.

BACKGROUND: Cells undergoing activation or apoptosis exhibit plasma membrane changes, leading to the formation of shed vesicles (microparticles, MP). Although their effects on recipient cells in vitro, and their ability to support inflammatory or thrombotic events in the circulation have been studied, the spreading of such vesicles in tissues is still elusive. Our aim was to set up a method to examine the behavior of these vesicles in vivo. METHODS: We examined the persistence of green-fluorescent microparticles (fMP), prepared after Ca2+ ionophore activation (iono-fMP) or apoptogenic treatment (eto-fMP) of human Jurkat T lymphoblastic or non-hematopoietic embryonic kidney (HEK) cell lines, following injection in zebrafish embryos 2h after egg fertilization. RESULTS: One hour post-injection, iono-fMP issued from both cell types formed a fluorescent dispersal in the intercellular space of embryos. In contrast, eto-fMP or MP deprived of sialic acid at their membrane, gathered together at the site of injection. CONCLUSIONS: We propose a method characterizing the abilities of MP to spread in the intercellular space. We showed that MP produced by apoptosis of T cells and those deprived of sialic acid at their membrane do not diffuse within the living cells. On the contrary, MP shed upon calcium induced activation of T and HEK cells, diffuse at a distance and spread in the intercellular space. GENERAL SIGNIFICANCE: The fate of injected MP relies on the type of induction rather than the cell species and results provide a model to test the ability of vesicles to interact locally or to spread outside of the site of production.

Circulating procoagulant microparticles in cancer patients.

Accumulating evidence indicates that microparticles (MPs) are important mediators of the interaction between cancer and the hemostatic system. We conducted a large prospective cohort study to determine whether the number of circulating procoagulant MPs is elevated in cancer patients and whether the elevated MP levels are predictive of occurrence of venous thrombembolism (VTE). We analyzed plasma samples of 728 cancer patients from the ongoing prospective observational Vienna Cancer and Thrombosis Study. Study endpoint was the occurrence of symptomatic VTE. Sixty-five age- and sex-matched healthy controls were recruited for defining the cut-off point for elevated MPs (4.62 nanomolar phosphatidylserine [nM PS]), which was set at the 95th percentile of MP levels in healthy controls. The measurement of MPs was performed after capture onto immobilized annexin V, and determination of their procoagulant activity was quantified with a prothrombinase assay. During a median observation period of 710 days, 53 patients developed VTE. MP levels (nM PS) were significantly higher in cancer patients than in healthy controls (median [25th-75th percentile], 3.95 [1.74-7.96] vs. 1.19 [0.81-1.67], p<0.001). Multivariate analysis including age, sex, surgery, chemo- and radiotherapy showed no statistically significant association of the hazard ratio of elevated MPs with VTE (0.95 [95% CI, 0.55-1.64], p=0.856). In conclusion, MP levels were elevated in cancer patients compared to healthy individuals in this study. However, elevated MP levels were not predictive of VTE.

Cellular mechanisms underlying the formation of circulating microparticles.

Microparticles (MPs) derived from platelets, monocytes, endothelial cells, red blood cells, and granulocytes may be detected in low concentrations in normal plasma and at increased levels in atherothrombotic cardiovascular diseases. The elucidation of the cellular mechanisms underlying the generation of circulating MPs is crucial for improving our understanding of their pathophysiological role in health and disease. The flopping of phosphatidylserine (PS) to the outer leaflet of the plasma membrane is the key event that will ultimately lead to the shedding of procoagulant MPs from activated or apoptotic cells. Research over the last few years has revealed important roles for calcium-, mitochondrial-, and caspase-dependent mechanisms leading to PS exposure. The study of Scott cells has unraveled different molecular mechanisms that may contribute to fine-tuning of PS exposure and MP release in response to a variety of specific stimuli. The pharmacological modulation of MP release may have a substantial therapeutic impact in the management of atherothrombotic vascular disorders. Because PS exposure is a key feature in pathological processes different from hemostasis and thrombosis, the most important obstacle in the field of MP-modulating drugs seems to be carefully targeting MP release to relevant cell types at an optimal level, so as to achieve a beneficial action and limit possible adverse effects.

Mechanisms of microparticle generation: on the trail of the mitochondrion!

Membrane remodeling, phosphatidylserine (PS) exposure, and subsequent microparticle (MP) shedding regulation is a critical step in maintaining vascular homeostasis. Shed MP, more particularly those of platelet origin, could be viewed as a way to increase the catalytic procoagulant surface relying on the essential presence of PS for optimal hemostatic response. Whether "flip-flop" is mandatory for the release of MP is suggested from the phenotype of Scott's syndrome, a rare bleeding disorder in which both PS exposure and MP shedding are deficient. PS exposure results from a specific cytoskeleton degradation pathway involving caspases, tuned by mitochondria permeability changes, and requiring a sustained increase in intracellular calcium. The actual roles of transmembrane ion transport or transient transmembrane pores in PS exposure remain to be more firmly established. Considering that an excess of plasma membrane procoagulant activity is associated with an increased risk of thrombosis, the identification of effectors of PS exposure and MP release appear relevant targets in thrombosis research and focused drug design. In this view, animal models of Scott's syndrome should prove of primary importance for the characterization of the genetic trait(s) accounting for the associated defect that would provide an important hint toward the control of PS exposure and subsequent MP release.

Factors influencing the level of circulating procoagulant microparticles in acute pulmonary embolism.

BACKGROUND: Flow cytometry has shown levels of platelet-derived microparticles (PMPs) and endothelial-derived microparticles (EMPs) to be elevated in deep-vein thrombosis. Cardiovascular risk factors can also contribute to hypercoagulability due to circulating procoagulant microparticles (CPMPs). AIMS: To investigate in a case-control study the respective contribution of pulmonary embolism and cardiovascular risk factors to the level of hypercoagulability due to CPMPs. METHODS: CPMP, PMP and EMP levels were measured in 45 consecutive patients (age 67.9 +/- 11.6 years; 66.7% men) admitted to an intensive care unit for acute pulmonary embolism (APE), 45 healthy control subjects with no history of venous thromboembolism or vascular risk factors (Controls(noCVRFs)), and 45 patients with cardiovascular risk factors (Controls(CVRFs)). APE was diagnosed by spiral computed tomography or scintigraphy. CPMP levels were assessed using a prothrombinase assay on platelet-depleted plasma (results expressed as nmol/L equivalent). RESULTS: CPMP levels were higher in APE patients than in Controls(noCVRFs) (medians 4.7 vs 3.2 nmol/L, interquartile ranges [IQRs] 2.9-11.1 vs 2.3-4.6 nmol/L; p=0.02). Similar results were reported for PMPs (medians 2.2 vs 1.9 nmol/L, IQRs 1.7-5.8 vs 1.4-2.4 nmol/L; p=0.02), whereas EMP levels were not significantly different. However, CPMP procoagulant activity was not significantly different in APE patients and Controls(CVRFs). CONCLUSIONS: CPMPs and PMPs were significantly elevated in APE patients vs Controls(noCVRFs), but this correlation was not significant when APE patients were compared with Controls(CVRFs). Our observations highlight the importance of adjusting for the presence of cardiovascular risk factors in conditions in which microparticle levels are raised.

Membrane microvesicles: macromessengers in cancer disease and progression.

Thrombotic complications have been documented in patients with cancer, and associated with tumor progression. Cancer patients have an increased level of circulating submicrometric (0.1-1 microm) membrane fragments termed microvesicles (MV) or microparticles. Variations in MV levels and phenotypes make them relevant pathogenic markers of thrombotic disorders and vascular damage. MV are released from the plasma membrane of activated or apoptotic cells, and are considered efficient effectors of the hemostatic or thrombotic responses. They are mostly characterized by the presence of procoagulant phospholipids at their surface and eventually that of tissue factor depending on the cells they originate from. These procoagulant entities allow them to initiate and propagate thrombotic reactions within the blood vessels. MV are also recognized as proximal or remote mediators of cell-to-cell communication. The mechanisms through which MV interact with target cells remain unclear although a number of studies suggest involvement of MV-cell fusion and/or ligand-receptor interactions. It has however to be emphasized that MV do not necessarily elicit deleterious responses. This review focuses on the role of MV in cancer-associated thrombosis.

Formation of procoagulant microparticles and properties.

The platelet procoagulant response consists of providing a catalytic surface where vitamin K-dependent clotting factors can interact with cofactors to form the characteristic enzyme complexes of the cascade culminating in the generation of sufficient thrombin for effective hemostasis. The essential element allowing such a local concentration is the anionic aminophospholipid phosphatidylserine, sequestered in the inner leaflet of the plasma membrane of resting cells but swiftly translocated to the outer leaflet after stimulation. Phosphatidylserine egress is followed by the shedding of membrane fragments, the so-called microparticles or microvesicles, also endowed with procoagulant properties more particularly when they harbor tissue factor, the major initiator of blood coagulation reactions. Furthermore, because microparticles hijack a number of membrane and cytoplasmic components from the cells they derive, they can elicit various responses in proximal or remote cells they interact with and can therefore be viewed as intercellular "macromessengers". Although several regulatory mechanisms have been proposed, the main actors responsible for the whole process of phosphatidylserine transmembrane redistribution and subsequent microparticle release remain to be identified.

Circulating microparticles may influence early carotid artery remodeling.

OBJECTIVES: To test associations of circulating microparticles with large artery remodeling before atherosclerosis is detectable. METHODS: In 232 untreated symptom-free individuals, we measured microparticles of various cellular origins (platelet, endothelial and leukocyte) by specific anti-GPIb (glycoprotein Ib), anti-cluster of differentiation (CD) 105 and anti-CD11a antibodies, and common carotid artery intima-media thickness (IMT), internal and external diameters by ultrasound. RESULTS: Except for CD105 microparticles with IMT to lumen ratio (IMT/D, P < 0.05), microparticles correlated with no carotid dimensions. Significant interactions existed between each microparticle type and IMT on internal and external diameters (GPIb, P < 0.01; CD105 and CD11a microparticles P < 0.001) consisting of lower trend in increased diameter with increasing IMT in individuals with high than in those with low microparticle level (according to the median) of each origin. As a result, individuals within the third IMT tertile had lower internal diameter in the presence of high than in the presence of low level of GPIb, CD105 or CD11a microparticles (P = 0.001, <0.05 or 0.01, respectively), and lower external diameter in the presence of high than in the presence of low level of GPIb and CD11a microparticles (P = 0.001 and 0.01). Also, individuals within third IMT tertile exhibited positive correlations of IMT with CD105 and CD11a microparticles (P < 0.05), negative correlations of internal diameter with GPIb (P < 0.05), CD105 (P < 0.05) and CD11a microparticles (P < 0.01) and of external diameter with GPIb and CD11a microparticles (P < 0.05), and positive correlations of IMT/D with CD105 and CD11a microparticles (P < 0.001). CONCLUSION: Increased levels of leukocyte and endothelial-derived microparticles are associated with carotid inward remodeling in individuals with the greatest IMT before atherosclerosis is detectable.

Circulating procoagulant microparticles in acute pulmonary embolism: a case-control study.

We investigated whether circulating procoagulant microparticles (CPMPs) contributed to hypercoagulability in 45 patients with acute pulmonary embolism (APE) and in 45 controls with and 45 controls without cardiovascular risk factors. Concentrations of CPMPs and platelet-derived microparticles (PMPs) were statistically significantly higher in patients with APE than in controls without cardiovascular risk factors. PMPs appeared to be the main source of procoagulant microparticle release in APE, but this correlation disappeared when APE patients were compared to controls with cardiovascular risk factors. CPMPs may have a role in venous thrombosis as mediators of cardiovascular risk factors.

Increased levels of circulating microparticles in primary Sjögren's syndrome, systemic lupus erythematosus and rheumatoid arthritis and relation with disease activity.

INTRODUCTION: Cell stimulation leads to the shedding of phosphatidylserine (PS)-rich microparticles (MPs). Because autoimmune diseases (AIDs) are characterized by cell activation, we investigated level of circulating MPs as a possible biomarker in primary Sjögren's syndrome (pSS), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). METHODS: We measured plasma levels of total, platelet and leukocyte MPs by prothrombinase capture assay and flow cytometry in 43 patients with pSS, 20 with SLE and 24 with RA and in 44 healthy controls (HCs). Secretory phospholipase A2 (sPLA2) activity was assessed by fluorometry. Soluble CD40 ligand (sCD40L) and soluble P-selectin (sCD62P), reflecting platelet activation, were measured by ELISA. RESULTS: Patients with pSS showed increased plasma level of total MPs (mean +/- SEM 8.49 +/- 1.14 nM PS equivalent (Eq), P < 0.0001), as did patients with RA (7.23 +/- 1.05 n PS Eq, P = 0.004) and SLE (7.3 +/- 1.25 nM PS Eq, P = 0.0004), as compared with HCs (4.13 +/- 0.2 nM PS Eq). Patients with AIDs all showed increased level of platelet MPs (P < 0.0001), but only those with pSS showed increased level of leukocyte MPs (P < 0.0001). Results by capture assay and flow cytometry were correlated. In patients with high disease activity according to extra-glandular complications (pSS), DAS28 (RA) or SLEDAI (SLE) compared with low-activity patients, the MP level was only slightly increased in comparison with those having a low disease activity. Platelet MP level was inversely correlated with anti-DNA antibody level in SLE (r = -0.65; P = 0.003) and serum beta2 microglobulin level in pSS (r = -0.37; P < 0.03). The levels of total and platelet MPs were inversely correlated with sPLA2 activity (r = -0.37, P = 0.0007; r = -0.36, P = 0.002, respectively). sCD40L and sCD62P concentrations were significantly higher in pSS than in HC (P < or = 0.006). CONCLUSIONS: Plasma MP level is elevated in pSS, as well as in SLE and RA, and could be used as a biomarker reflecting systemic cell activation. Level of leukocyte-derived MPs is increased in pSS only. The MP level is low in case of more severe AID, probably because of high secretory phospholipase A2 (sPLA2) activity, which leads to consumption of MPs. Increase of platelet-derived MPs, sCD40L and sCD62P, highlights platelet activation in pSS.

Translocator protein (18 kDa) is involved in primitive erythropoiesis in zebrafish.

The translocator protein (18 kDa) (TSPO), also known as peripheral-type benzodiazepine receptor, is directly or indirectly associated with many biological processes. Although extensively characterized, the specific function of TSPO during development remains unclear. It has been reported that TSPO is involved in a variety of mechanisms, including cell proliferation, apoptosis, regulation of mitochondrial functions, cholesterol transport and steroidogenesis, and porphyrin transport and heme synthesis. Although the literature has reported a murine knockout model, the experiment did not generate information because of early lethality. We then used the zebrafish model to address the function of tspo during development. Information about spatiotemporal expression showed that tspo has a maternal and a zygotic contribution which, during somatogenesis, seems to be erythroid restricted to the intermediate cell mass. Genetic and pharmacological approaches used to invalidate Tspo function resulted in embryos with specific erythropoietic cell depletion. Although unexpected, this lack of blood cells is independent of the Tspo cholesterol binding site and reveals a new in vivo key role for Tspo during erythropoiesis.

Mechanisms of the noxious inflammatory cycle in cystic fibrosis.

Multiple evidences indicate that inflammation is an event occurring prior to infection in patients with cystic fibrosis. The self-perpetuating inflammatory cycle may play a pathogenic part in this disease. The role of the NF-kappaB pathway in enhanced production of inflammatory mediators is well documented. The pathophysiologic mechanisms through which the intrinsic inflammatory response develops remain unclear. The unfolded mutated protein cystic fibrosis transmembrane conductance regulator (CFTRDeltaF508), accounting for this pathology, is retained in the endoplasmic reticulum (ER), induces a stress, and modifies calcium homeostasis. Furthermore, CFTR is implicated in the transport of glutathione, the major antioxidant element in cells. CFTR mutations can alter redox homeostasis and induce an oxidative stress. The disturbance of the redox balance may evoke NF-kappaB activation and, in addition, promote apoptosis. In this review, we examine the hypotheses of the integrated pathogenic processes leading to the intrinsic inflammatory response in cystic fibrosis.

Microparticle-induced release of B-lymphocyte regulators by rheumatoid synoviocytes.

INTRODUCTION: In the present study, we investigated the ability of microparticles isolated from synovial fluids from patients with rheumatoid arthritis or osteoarthritis to induce the synthesis and release of key cytokines of B-lymphocyte modulation such as B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor by rheumatoid fibroblast-like synoviocytes. METHODS: Microparticles were analyzed in synovial fluids from patients with rheumatoid arthritis, osteoarthritis, microcristalline arthritis, and reactive arthritis. In addition, microparticle release after activation from various cell lines (CEM lymphocyte and THP-1 cells) was assessed. Microparticles were isolated by differential centrifugation, and quantitative determinations were carried out by prothrombinase assay after capture on immobilized annexin V. B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor release was evaluated by enzyme-linked immunosorbent assay. RESULTS: Microparticles isolated from synovial fluids obtained from rheumatoid arthritis and osteoarthritis patients or microparticles derived from activated THP-1 cells were able to induce B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor release by rheumatoid arthritis fibroblast-like synoviocytes. Conversely, CEM-lymphocytes-derived microparticles generated by treatment with a combination of PHA, PMA and Adt-D did not promote the release of B cell-activating factor but favored the secretion of thymic stroma lymphopoietin and secretory leukocyte protease inhibitor by rheumatoid arthritis fibrobast-like synoviocytes. However, microparticles isolated from actinomycin D-treated CEM lymphocytes were not able to induce B cell-activating factor, thymic stroma lymphopoietin, or secretory leukocyte protease inhibitor release, indicating that microparticles derived from apoptotic T cells do not function as effectors in B-cell activation. CONCLUSIONS: These results demonstrate that microparticles are signalling structures that may act as specific conveyors in the triggered induction and amplification of autoimmunity. This study also indicates that microparticles have differential effects in the crosstalk between B lymphocytes and target cells of autoimmunity regarding the parental cells from which they derive.