Endothelial and platelet microparticles in patients with antiphospholipid antibodies

Prevention of Venous Thromboembolism in Medical Patients with Thrombocytopenia or with Platelet Dysfunction: The Last 10 Years

Current guideline recommendations for primary prophylaxis of venous thromboembolism (VTE) are based on randomized clinical trials that usually exclude subjects at a potentially high risk of bleeding complications. For this reason, no specific guideline is available for thromboprophylaxis in hospitalized patients with thrombocytopenia and/or platelet dysfunction. However, except in patients with absolute contraindications to anticoagulant drugs, antithrombotic prophylaxis should always be considered, for example, in hospitalized cancer patients with thrombocytopenia, especially in those with multiple VTE risk factors. Low platelet number, platelet dysfunction, and clotting abnormalities are also very common in patients with liver cirrhosis, but these patients have a high incidence of portal venous thrombosis, implying that cirrhotic coagulopathy does not fully protect against thrombosis. These patients may benefit from antithrombotic prophylaxis during hospitalization. Patients hospitalized for COVID-19 need prophylaxis, but frequently experience thrombocytopenia or coagulopathy. In patients with antiphospholipid antibodies, a high thrombotic risk is usually present, even in the presence of thrombocytopenia. VTE prophylaxis in high-risk conditions is thus suggested in these patients. At variance with severe thrombocytopenia (< 50,000/mm3), mild/moderate thrombocytopenia (≥ 50,000/mm3) should not interfere with VTE prevention decisions. In patients with severe thrombocytopenia, pharmacological prophylaxis should be considered on an individual basis. Aspirin is not as effective as heparins in lowering the risk of VTE. Studies in patients with ischemic stroke demonstrated that thromboprophylaxis with heparins is safe in these patients also during antiplatelet treatment. The use of direct oral anticoagulants in the prophylaxis of VTE in internal medicine patients has been recently evaluated, but no specific recommendation exists for patients with thrombocytopenia. The need for VTE prophylaxis in patients on chronic treatment with antiplatelet agents should be evaluated after assessing the individual risk of bleeding complications. Finally, the selection of patients who require post-discharge pharmacological prophylaxis remains debated. New molecules currently under development (such as the inhibitors of factor XI) may contribute to improve the risk/benefit ratio of VTE primary prevention in this setting of patients.

Platelets and Thrombotic Antiphospholipid Syndrome

Antiphospholipid antibody syndrome (APS) is an autoimmune disorder characterised by thrombosis and the presence of antiphospholipid antibodies (aPL): lupus anticoagulant and/or IgG/IgM anti-β2-glycoprotein I and anticardiolipin antibodies. APS carries significant morbidity for a relatively young patient population from recurrent thrombosis in any vascular bed (arterial, venous, or microvascular), often despite current standard of care, which is anticoagulation with vitamin K antagonists (VKA). Platelets have established roles in thrombosis at any site, and platelet hyperreactivity is clearly demonstrated in the pathophysiology of APS. Together with excess thrombin generation, platelet activation and aggregation are the common end result of all the pathophysiological pathways leading to thrombosis in APS. However, antiplatelet therapies play little role in APS, reserved as a possible option of low dose aspirin in addition to VKA in arterial or refractory thrombosis. This review outlines the current evidence and mechanisms for excessive platelet activation in APS, how it plays a central role in APS-related thrombosis, what evidence for antiplatelets is available in clinical outcomes studies, and potential future avenues to define how to target platelet hyperreactivity better with minimal impact on haemostasis.

The pathogenesis of obstetric APS: a 2023 update

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the persistent presence of antibodies directed against phospholipids and phospholipid-binding proteins that are associated with thrombosis and pregnancy-related morbidity. The latter includes fetal deaths, premature birth and maternal complications. In the early 1990s, a distinct set of autoantibodies, termed collectively antiphospholipid antibodies (aPL), were identified as the causative agents of this disorder. Subsequently histological analyses of the placenta from APS pregnancies revealed various abnormalities, including inflammation at maternal-fetal interface and poor placentation manifested by reduced trophoblast invasion and limited uterine spiral artery remodeling. Further preclinical investigations identified the molecular targets of aPL and the downstream intracellular pathways of key placental cell types. While these discoveries suggest potential therapeutics for this disorder, definitive clinical trials have not been completed. This concise review focuses on the recent developments in the field of basic and translational research pursuing novel mechanisms underlying obstetric APS.

Small-Extracellular-Vesicle-Derived miRNA Profile Identifies miR-483-3p and miR-326 as Regulators in the Pathogenesis of Antiphospholipid Syndrome (APS)

Primary antiphospholipid syndrome (PAPS) is a systemic autoimmune disease associated with recurrent thrombosis and/or obstetric morbidity with persistent antiphospholipid antibodies (aPL). Although these antibodies drive endothelial injury and thrombophilia, the underlying molecular mechanism is still unclear. Small extracellular vesicles (sEVs) contain miRNAs, key players in intercellular communication. To date, the effects of miRNA-derived sEVs in PAPS are not well understood. We characterised the quantity, cellular origin and miRNA profile of sEVs isolated from thrombotic APS patients (PAPS, n = 50), aPL-carrier patients (aPL, n = 30) and healthy donors (HD, n = 30). We found higher circulating sEVs mainly of activated platelet origin in PAPS and aPL patients compared to HD, that were highly engulfed by HUVECs and monocyte. Through miRNA-sequencing analysis, we identified miR-483-3p to be differentially upregulated in sEVs from patients with PAPS and aPL, and miR-326 to be downregulated only in PAPS sEVs. In vitro studies showed that miR-483-3p overexpression in endothelial cells induced an upregulation of the PI3K-AKT pathway that led to endothelial proliferation/dysfunction. MiR-326 downregulation induced NOTCH pathway activation in monocytes with the upregulation of NFKB1, tissue factor and cytokine production. These results provide evidence that miRNA-derived sEVs contribute to APS pathogenesis by producing endothelial cell proliferation, monocyte activation and adhesion/procoagulant factors.

Platelet-Derived Microparticles and Autoimmune Diseases

Extracellular microparticles provide a means of cell-to-cell communication and can promote information exchanges between adjacent or distant cells. Platelets are cell fragments that are derived from megakaryocytes. Their main functions are to stop bleeding, regulate inflammation, and maintain the integrity of blood vessels. When platelets are activated, they can perform related tasks by secreting platelet-derived microparticles that contain lipids, proteins, nucleic acids, and even organelles. There are differences in the circulating platelet levels in many autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, antiphospholipid antibody syndrome, and Sjogren's syndrome. In this paper, the latest findings in the research field of platelet-derived microparticles are reviewed, including the potential pathogenesis of platelet-derived microparticles in various types of immune diseases, their potential as related markers, and for monitoring the progress and prognosis of disease treatment are expounded.

The role of monocytes in thrombotic diseases: a review

Cardiovascular and cerebrovascular diseases are the number one killer threatening people's life and health, among which cardiovascular thrombotic events are the most common. As the cause of particularly serious cardiovascular events, thrombosis can trigger fatal crises such as acute coronary syndrome (myocardial infarction and unstable angina), cerebral infarction and so on. Circulating monocytes are an important part of innate immunity. Their main physiological functions are phagocytosis, removal of injured and senescent cells and their debris, and development into macrophages and dendritic cells. At the same time, they also participate in the pathophysiological processes of pro-coagulation and anticoagulation. According to recent studies, monocytes have been found to play a significant role in thrombosis and thrombotic diseases of the immune system. In this manuscript, we review the relationship between monocyte subsets and cardiovascular thrombotic events and analyze the role of monocytes in arterial thrombosis and their involvement in intravenous thrombolysis. Finally, we summarize the mechanism and therapeutic regimen of monocyte and thrombosis in hypertension, antiphospholipid syndrome, atherosclerosis, rheumatic heart disease, lower extremity deep venous thrombosis, and diabetic nephropathy.

Interaction between endothelial cell-derived extracellular vesicles and monocytes: A potential link between vascular thrombosis and pregnancy-related morbidity in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disease driven by a wide group of autoantibodies primarily directed against phospholipid-binding proteins (antiphospholipid antibodies). APS is defined by two main kinds of clinical manifestations: vascular thrombosis and pregnancy-related morbidity. In recent years, in vitro and in vivo assays, as well as the study of large groups of patients with APS, have led some authors to suggest that obstetric and vascular manifestations of the disease are probably the result of different pathogenic mechanisms. According to this hypothesis, the disease could be differentiated into two parallel entities: Vascular APS and obstetric APS. Thus, vascular APS is understood as an acquired thrombophilia in which a generalised phenomenon of endothelial activation and dysfunction (coupled with a triggering factor) causes thrombosis at any location. In contrast, obstetric APS seems to be due to an inflammatory phenomenon accompanied by trophoblast cell dysfunction. The recent approach to APS raises new issues; for instance, the mechanisms by which a single set of autoantibodies can lead to two different clinical entities are unclear. This review will address the monocyte, a cell with well-known roles in haemostasis and pregnancy, as a potential participant in vascular thrombosis and pregnancy-related morbidity in APS. We will discuss how in a steady state the monocyte-endothelial interaction occurs via extracellular vesicles (EVs), and how antiphospholipid antibodies, by inducing endothelial activation and dysfunction, may disturb this interaction to promote the release of monocyte-targeted procoagulant and inflammatory messages.

Hematological manifestations of antiphospholipid syndrome: Going beyond thrombosis

Thrombotic complications are a hallmark of antiphospholipid syndrome (APS). These vascular - arterial, venous, and/or small vessel - complications are well described and known to hematologists and healthcare providers caring for patients with this disease. In this review, we shed light on other hematological manifestations of the disease, including bleeding, thrombocytopenia, autoimmune hemolytic anemia, and thrombotic microangiopathy syndromes. While these manifestations are not bona fide clinical criteria for the diagnosis of APS, they frequently interact and contribute to the complexity of clinical management of APS.

Targeting thromboinflammation in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is a systemic autoimmune disease, where persistent presence of antiphospholipid antibodies (aPL) leads to thrombotic and obstetric complications. APS is a paradigmatic thromboinflammatory disease. Thromboinflammation is a pathophysiological mechanism coupling inflammation and thrombosis, which contributes to the pathophysiology of cardiovascular disease. APS can serve as a model to unravel mechanisms of thromboinflammation and the relationship between innate immune cells and thrombosis. Monocytes are activated by aPL into a proinflammatory and procoagulant phenotype, producing proinflammatory cytokines such as tumor necrosis factor α, interleukin 6, as well as tissue factor. Important cellular signaling pathways involved are the NF-κB-pathway, mammalian target of rapamycin (mTOR) signaling, and the NOD-, LRR-, and pyrin domain-containing protein 3 inflammasome. All of these may serve as future therapeutic targets. Neutrophils produce neutrophil extracellular traps in response to aPL, and this leads to thrombosis. Thrombosis in APS also stems from increased interaction of neutrophils with endothelial cells through P-selectin glycoprotein ligand-1. NETosis can be targeted not only with several experimental therapeutics, such as DNase, but also through the redirection of current therapies such as defibrotide and the antiplatelet agent dipyridamole. Activation of platelets by aPL leads to a procoagulant phenotype. Platelet-leukocyte interactions are increased, possibly mediated by increased levels of soluble P-selectin and soluble CD40-ligand. Platelet-directed future treatment options involve the inhibition of several platelet receptors activated by aPL, as well as mTOR inhibition. This review discusses mechanisms underlying thromboinflammation in APS that present targetable therapeutic options, some of which may be generalizable to other thromboinflammatory diseases.

Extracellular vesicles released upon stimulation with antiphospholipid antibodies: An actual direct procoagulant mechanism or a new factor in the lupus anticoagulant paradox?

Antiphospholipid antibodies (aPL) lead to a hypercoagulable state in vivo. Paradoxically, some of these autoantibodies perform as inhibitors of the coagulation cascade in vitro (a phenomenon referred to as "lupus anticoagulant"). The presence of lupus anticoagulant has been related to an increased quantity of plasma extracellular vesicles, which may constitute a direct procoagulant mechanism in antiphospholipid syndrome. This study investigates whether or not endothelial cell-derived extracellular vesicles released upon stimulation with aPL (aPL-EDEVs) are related to a higher direct coagulation activity. Using an in vitro model of endothelium, flow cytometry and a recalcified plasma-based assay, we found that the coagulation activity of aPL-EDEVs is mainly conditioned by the lupus anticoagulant-like activity of autoantibodies. Nevertheless, in the presence of β2 glycoprotein I, a cofactor of aPL during the stimulation of endothelial cells, the coagulation activity of EDEVs is restored in a mitogen-activated protein kinase kinases 1 and 2 (MEK1/2)-dependent manner. This phenomenon was especially evident when using immunoglobulins G from patients with vascular and obstetric primary antiphospholipid syndrome who manifest refractoriness to treatment. Our findings suggest that the role of aPL-EDEVs in the antiphospholipid syndrome-related hypercoagulable state may not rely on their capacity to enhance clotting directly. While β2 glycoprotein I performs as a procoagulant cofactor and restores the coagulation activity of extracellular vesicles via MEK1/2 pathway, proportionally, autoantibodies interact with aPL-EDEVs and exhaust their coagulation properties. Further analysis is required to establish whether lupus anticoagulant-like autoantibodies opsonise extracellular vesicles and whether opsonised vesicles may lead to thrombosis by indirect means.

Platelet- and endothelial-derived microparticles in the context of different antiphospholipid antibody profiles

Objectives

Studies on microparticles (MPs) in patients with antiphospholipid antibodies (aPL) are sparse and inconclusive. The relation between MPs and different aPL antibody profiles has never been tested. We evaluated the presence of platelet and endothelial microparticles in patients positive for IgG anti-β2-glycoprotein I (aβ2GPI) antibodies according to triple, double and single positive aPL profiles.

Methods

Megamix (Biocytex) was used to set up the MPs gating according to the datasheet. Markers of Platelet Microparticles (PMPs) were CD41a-PE and annexin-V-FITC that was used to determine phosphatidylserine (PS) exposure. CD144-FITC was used as a marker of Endothelial Microparticles (EMPs).

Results

The number of total MPs and EMPs was significantly higher in triple positive groups with respect to single positive group and showed a significant correlation with IgG aβ2GPI titers. The number PMPs was the lowest in triple positive group and inversely correlated with IgG aβ2GPI titers.

Conclusions

Elevated levels of total MPs and EMPs suggest a state of vascular activation in IgG aβ2GPI positive individuals according to the number of positive tests. PMPs may be fast cleared from circulation in high risk triple positive patients.

Microparticles in Autoimmunity: Cause or Consequence of Disease?

Microparticles (MPs) are small (100 nm - 1 um) extracellular vesicles derived from the plasma membrane of dying or activated cells. MPs are important mediators of intercellular communication, transporting proteins, nucleic acids and lipids from the parent cell to other cells. MPs resemble the state of their parent cells and are easily accessible when released into the blood or urine. MPs also play a role in the pathogenesis of different diseases and are considered as potential biomarkers. MP isolation and characterization is technically challenging and results in different studies are contradictory. Therefore, uniform guidelines to isolate and characterize MPs should be developed. Our understanding of MP biology and how MPs play a role in different pathological mechanisms has greatly advanced in recent years. MPs, especially if derived from apoptotic cells, possess strong immunogenic properties due to the presence of modified proteins and nucleic acids. MPs are often found in patients with autoimmune diseases where MPs for example play a role in the break of immunological tolerance and/or induction of inflammatory conditions. In this review, we describe the main techniques to isolate and characterize MPs, define the characteristics of MPs generated during cell death, illustrate different mechanism of intercellular communication via MPs and summarize the role of MPs in pathological mechanisms with a particular focus on autoimmune diseases.

Differences in Endothelial Activation and Dysfunction Induced by Antiphospholipid Antibodies Among Groups of Patients With Thrombotic, Refractory, and Non-refractory Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by pregnancy morbidity or thrombosis and persistent antiphospholipid antibodies (aPL) that bind to the endothelium and induce endothelial activation, which is evidenced by the expression of adhesion molecules and the production of reactive oxygen species (ROS) and subsequent endothelial dysfunction marked by a decrease in the synthesis and release of nitric oxide (NO). These endothelial alterations are the key components for the development of severe pathological processes in APS. Patients with APS can be grouped according to the presence of other autoimmune diseases (secondary APS), thrombosis alone (thrombotic APS), pregnancy morbidity (obstetric APS), and refractoriness to conventional treatment regimens (refractory APS). Typically, patients with severe and refractory obstetric APS exhibit thrombosis and are classified as those having primary or secondary APS. The elucidation of the mechanisms underlying these alterations according to the different groups of patients with APS could help establish new therapies, particularly necessary for severe and refractory cases. Therefore, this study aimed to evaluate the differences in endothelial activation and dysfunction induced by aPL between patients with refractory obstetric APS and other APS clinical manifestations. Human umbilical vein endothelial cells (HUVECs) were stimulated with polyclonal immunoglobulin-G (IgG) from different groups of patients n = 21), including those with primary (VTI) and secondary thrombotic APS (VTII) and refractory primary (RI+), refractory secondary (RII+), and non-refractory primary (NR+) obstetric APS. All of them with thrombosis. The expression of adhesion molecules; the production of ROS, NO, vascular endothelial growth factor (VEGF), and endothelin-1; and the generation of microparticles were used to evaluate endothelial activation and dysfunction. VTI IgG induced the expression of adhesion molecules and the generation of microparticles and VEGF. RI+ IgG induced the expression of adhesion molecules and decreased NO production. RII+ IgG increased the production of microparticles, ROS, and endothelin-1 and reduced NO release. NR+ IgG increased the production of microparticles and endothelin-1 and decreased the production of VEGF and NO. These findings reveal differences in endothelial activation and dysfunction among groups of patients with APS, which should be considered in future studies to evaluate new therapies, especially in refractory cases.

Antiphospholipid antibodies and risk of post-COVID-19 vaccination thrombophilia: The straw that breaks the camel's back?

Antiphospholipid antibodies (aPLs), present in 1–5 % of healthy individuals, are associated with the risk of antiphospholipid syndrome (APS), which is the most common form of acquired thrombophilia. APLs may appear following infections or vaccinations and have been reported in patients with COronaVIrus Disease-2019 (COVID-19). However, their association with COVID-19 vaccination is unclear. Notably, a few cases of thrombocytopenia and thrombotic events resembling APS have been reported to develop in recipients of either adenoviral vector- or mRNA-based COVID-19 vaccines.

The aim of this review is therefore to speculate on the plausible role of aPLs in the pathogenesis of these rare adverse events.

Adenoviral vector-based vaccines can bind platelets and induce their destruction in the reticuloendothelial organs. Liposomal mRNA-based vaccines may instead favour activation of coagulation factors and confer a pro-thrombotic phenotype to endothelial cells and platelets. Furthermore, both formulations may trigger a type I interferon response associated with the generation of aPLs. In turn, aPLs may lead to aberrant activation of the immune response with participation of innate immune cells, cytokines and the complement cascade. NETosis, monocyte recruitment and cytokine release may further support endothelial dysfunction and promote platelet aggregation. These considerations suggest that aPLs may represent a risk factor for thrombotic events following COVID-19 vaccination, and deserve further investigations.

Microparticles: An Alternative Explanation to the Behavior of Vascular Antiphospholipid Syndrome

Antiphospholipid syndrome is an autoimmune disease characterized by the persistent presence of antiphospholipid antibodies, along with occurrence of vascular thrombosis and pregnancy morbidity. The variety of antiphospholipid antibodies and their related mechanisms, as well as the behavior of disease in wide groups of patients, have led some authors to propose a differentiation of this syndrome into two independent entities: vascular and obstetric antiphospholipid syndrome. Thus, previous studies have discussed whether specific autoantibodies may be responsible for this differentiation or, in contrast, how the same antibodies are able to generate two different clinical presentations. This discussion is yet to be settled. The capability of serum IgG from patients with vascular thrombosis to trigger the biogenesis of endothelial cell-derived microparticles in vitro is one of the previously discussed differences between the clinical entities of antiphospholipid syndrome. These vesicles constitute a prothrombotic mechanism as they can directly lead to clot activation in murine models and recalcified human plasma. Nevertheless, other indirect mechanisms by which microparticles can spread a procoagulant phenotype could be critical to understanding their role in antiphospholipid syndrome. For this reason, questions regarding the cargo of microparticles, and the signaling pathways involved in their biogenesis, are of interest in attempting to explain the behavior of this autoimmune disease.

Extracellular Vesicles and Antiphospholipid Syndrome: State-of-the-Art and Future Challenges

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by thromboembolism, obstetric complications, and the presence of antiphospholipid antibodies (aPL). Extracellular vesicles (EVs) play a key role in intercellular communication and connectivity and are known to be involved in endothelial and vascular pathologies. Despite well-characterized in vitro and in vivo models of APS pathology, the field of EVs remains largely unexplored. This review recapitulates recent findings on the role of EVs in APS, focusing on their contribution to endothelial dysfunction. Several studies have found that APS patients with a history of thrombotic events have increased levels of EVs, particularly of endothelial origin. In obstetric APS, research on plasma levels of EVs is limited, but it appears that levels of EVs are increased. In general, there is evidence that EVs activate endothelial cells, exhibit proinflammatory and procoagulant effects, interact directly with cell receptors, and transfer biological material. Future studies on EVs in APS may provide new insights into APS pathology and reveal their potential as biomarkers to identify patients at increased risk.

Extracellular Vesicles Tune the Immune System in Renal Disease: A Focus on Systemic Lupus Erythematosus, Antiphospholipid Syndrome, Thrombotic Microangiopathy and ANCA-Vasculitis

Extracellular vesicles (EV) are microparticles released in biological fluids by different cell types, both in physiological and pathological conditions. Owing to their ability to carry and transfer biomolecules, EV are mediators of cell-to-cell communication and are involved in the pathogenesis of several diseases. The ability of EV to modulate the immune system, the coagulation cascade, the angiogenetic process, and to drive endothelial dysfunction plays a crucial role in the pathophysiology of both autoimmune and renal diseases. Recent studies have demonstrated the involvement of EV in the control of renal homeostasis by acting as intercellular signaling molecules, mediators of inflammation and tissue regeneration. Moreover, circulating EV and urinary EV secreted by renal cells have been investigated as potential early biomarkers of renal injury. In the present review, we discuss the recent findings on the involvement of EV in autoimmunity and in renal intercellular communication. We focused on EV-mediated interaction between the immune system and the kidney in autoimmune diseases displaying common renal damage, such as antiphospholipid syndrome, systemic lupus erythematosus, thrombotic microangiopathy, and vasculitis. Although further studies are needed to extend our knowledge on EV in renal pathology, a deeper investigation of the impact of EV in kidney autoimmune diseases may also provide insight into renal biological processes. Furthermore, EV may represent promising biomarkers of renal diseases with potential future applications as diagnostic and therapeutic tools.

Early Detection of Negative Smoking Impacts: Vascular Adaptation Deviation Based on Quantification of Circulated Endothelial Activation Markers

Introduction

Smoking can cause vascular damage in the form of an inflammatory reaction characterized by endothelial activation. Endothelial activation forms a pathological adaptation pattern so that it can induce the atherogenesis process. Several markers, such as E-selectin, platelet-derived micro particles (PMPs) and hematopoietic stem cell (HSC) can identify the activation of endothelial in circulating blood. Therefore, the deviation of vascular adaptation due to smoking can be detected early through the feedback mechanism between E-selectin, PMPs, and HSC.

Purpose

This study aims to analyze the initial picture of the negative impact of smoking on vascular adaptation by measuring E-selectin, PMPs, and HSC in the peripheral blood circulation. Participant criteria and methods: Peripheral blood samples (5 mL) were taken from each participant, both the smoking group (n = 30) and the non-smoker group (n = 31) to obtain peripheral blood mononuclear cells (PBMNC). PBMNC was isolated using ficoll-based gradient centrifugation. The flow cytometry assay method used to measure the E-selectin, PMPs and hematopoietic stem cells.

Results

The mean of circulating E-selectin in smokers was higher than that of non-smokers. On the other hand, the average number of PMPs and HSCs in smokers was lower than non-smokers.

Conclusion

Smoking increases the risk of accelerated vascular block formation, as indicated by an increase in the amount of circulating E-selectin. The increase in E-selectin in the blood vessels mediates the increased adhesion of PMPs in the vascular area so that the number of circulating PMPs in smokers decreases. The decrease in circulating PMPs decreases the signal of vascular repair, which is characterized by a decline in the number of HSCs.

Antiphospholipid antibodies and extracellular vesicles in pregnancy

Antiphospholipid antibodies (aPL) are autoantibodies that target phospholipid-binding proteins, such as β2 glycoprotein I (β2GPI), and can induce thrombosis systemically, as well as increase the risk of obstetric complications such as recurrent miscarriage and preeclampsia. Due to the expression of β2GPI by placental trophoblasts, aPL readily target the maternal-fetal interface during pregnancy and many studies have investigated the deleterious effects of aPL on placental trophoblast function. This review will focus on studies that have examined the effects of aPL on the production and modification of extracellular vesicles (EVs) from trophoblasts, as EVs are a key mode of feto-maternal communication in both normal and pathological pregnancy. A more comprehensive understanding of the effects of aPL on the quantity and cargo of EVs extruded by the human placenta may contribute to our current knowledge of how aPL induce both systemic and obstetric disease.

Expression of tissue factor mRNA in thrombosis associated with antiphospholipid syndrome

Tissue factor (TF) is a procoagulant protein associated with increased risk of thrombotic events in antiphospholipid syndrome (t-APS). The mechanisms by which TF levels are increased in APS have not yet been established. The aim of this study was to investigate whether TF mRNA expression is associated with TF levels and thrombosis in APS. We compared levels of circulating TF and high sensitivity C-reactive protein (hs-CRP) between t-APS and controls (individuals without thrombosis). The association between TF mRNA expression, quantified by real time quantitative polymerase chain reaction, and t-APS was accessed using regression analysis. We included 41 controls and 42 t-APS patients, mean age was 41 years old (SD 14) in both groups. Hs-CRP and TF levels were higher in t-APS patients (mean hs-CRP levels 0.81 mg/dL [SD 1.88] and median TF levels 249.0 pg/mL [IQR 138.77-447.61]) as compared to controls (mean hs-CRP levels 0.24 mg/dL [SD 0.26] and median TF levels 113.0 pg/mL [IQR 81.17-161.53]; P = 0.02 and P < 0.0001, respectively). There was no correlation between TF mRNA expression and TF levels in t-APS (r - 0.209, P = 0.19). TF mRNA expression was not associated with t-APS (adjusted OR 1.16; 95%CI 0.72-1.87). Despite circulating TF levels being higher in patients with t-APS than in controls, TF mRNA expression was similar between groups. The results demonstrate that TF mRNA expression is not associated with levels of circulating TF and hypercoagulability in t-APS.

Platelet-derived microparticles from recurrent miscarriage associated with antiphospholipid antibody syndrome influence behaviours of trophoblast and endothelial cells

Platelet-derived microparticles (PMPs) are a type of microparticle budding from platelets undergoing activation or apoptosis in many autoimmune diseases, including antiphospholipid antibody syndrome (APS). PMPs may also contribute to recurrent miscarriage, although the exact mechanism is unclear. The aim of this study was to determine the potential biological mechanism by which abnormal PMP activation may affect recurrent miscarriage. PMPs were counted by fluorescence-activated cell sorting (FACS) and compared between the healthy control (HC) and recurrent miscarriage/APS groups. Different effects of PMPs isolated by FACS from patients with recurrent miscarriage/APS and HCs were explored. Capillary electrophoresis immunoquantification, RT-qPCR, Luminex xMAP and immunofluorescence staining were performed to investigate all these different effects of PMPs. We found that the difference in the counts of PMP was not significant. However the expression of the inflammatory cytokine tumour necrosis factor-α (TNF-α) and the adhesion molecules intracellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) were increased by PMPs derived from the recurrent miscarriage/APS group. PMPs isolated from patients with recurrent miscarriage/APS also more potently stimulated monocyte recruitment, inhibited angiogenesis and promoted human umbilical vein endothelial cell (HUVEC) apoptosis, in comparison to PMPs from HCs matched for gestational week. Moreover, PMPs could be ternalized by HTR-8/SVneo cells and could increase apoptosis of these cells and decrease trophoblastic invasion and migration. To supplement our work, the limited sample size needs to be increased, and further in-vivo work is necessary. Findings from this study indicate that abnormal activation of PMPs contributes to recurrent miscarriage/APS progression and provides potential therapeutic targets.

Characterization of Plasma-Derived Small Extracellular Vesicles Indicates Ongoing Endothelial and Platelet Activation in Patients with Thrombotic Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is a systemic autoimmune disease, characterized by thrombosis, obstetric complications and the presence of antiphospholipid antibodies (aPL), which drive endothelial injury and thrombophilia. Extracellular vesicles (EVs) have been implicated in endothelial and thrombotic pathologies. Here, we characterized the quantity, cellular origin and the surface expression of biologically active molecules in small EVs (sEVs) isolated from the plasma of thrombotic APS patients (n = 14), aPL-negative patients with idiopathic thrombosis (aPL-neg IT, n = 5) and healthy blood donors (HBD, n = 7). Nanoparticle tracking analysis showed similar sEV sizes (110–170 nm) between the groups, with an increased quantity of sEVs in patients with APS and aPL-neg IT compared to HBD. MACSPlex analysis of 37 different sEV surface markers showed endothelial (CD31), platelet (CD41b and CD42a), leukocyte (CD45), CD8 lymphocyte and APC (HLA-ABC) cell-derived sEVs. Except for CD8, these molecules were comparably expressed in all study groups. sEVs from APS patients were specifically enriched in surface expression of CD62P, suggesting endothelial and platelet activation in APS. Additionally, APS patients exhibited increased CD133/1 expression compared to aPL-neg IT, suggesting endothelial damage in APS patients. These findings demonstrate enhanced shedding, and distinct biological properties of sEVs in thrombotic APS.

Increased circulating microparticles in women with preeclampsia

INTRODUCTION

Preeclampsia (PE) is associated with hypercoagulability, endothelial dysfunction and inflammation, which generate microparticles (MPs). Therefore, MPs may be important for PE.

METHODS

We established a verified MP measurement procedure to detect MPs in nonpregnant women (n = 25), healthy pregnant women (n = 29) and PE women (n = 73) and compared their MP levels.

RESULTS

Microparticles prepared from platelets (PMPs), endothelial cells (EMPs) and leucocytes (LMPs) were confirmed by transmission electron microscopy and were analysed by our established flow cytofluorimetric approach, which showed good specificity for determining the cell origin and level of MPs. The levels of total MPs (tMPs) and PMPs in the healthy pregnant group were significantly higher than those in the nonpregnant group (158.78 vs 93.00 and 45.04 vs 17.41, P = .004 and P = .007, respectively) but were not significantly different from those of the PE group. However, EMPs and LMPs were significantly higher in the PE group than in the healthy pregnant group (14.62 vs 11.48 and 8.94 vs 5.03, P = .015 and P < .001, respectively). Furthermore, the area under the receiver operating characteristic curves (AUC) for EMPs, LMPs and the combined sum of EMPs and LMPs were 0.661, 0.746 and 0.718, respectively (P < . 05); at their optimal cut-off values, the sensitivities were 50.68%, 87.67% and 46.58%, respectively, and the specificities were 80.77%, 58.33% and 95.65%, respectively.

CONCLUSION

Determining the MP level, especially that of EMPs and LMPs, by a specificity-verified method may reflect the endothelial dysfunction and inflammation involved in PE pathogenesis.

Platelet-derived microparticles analysis: Techniques, challenges and recommendations

Platelet-derived microparticles (PMP) are nano size fragments (100-1000 nm) released from platelets under various physiological and pathological conditions. PMP are the most abundant microparticles present in human blood. In recent past years PMP have caught attention of many clinicians as well as researchers for being associated with many diseases like cardio-vascular diseases, infections etc; and have emerged as potential biomarkers. Owing to their small size and diverse phenotype, structure and functions, microparticles including PMP render many challenges during sample handling, estimation and characterization. PMP can be analyzed for many parameters like absolute count, size distribution, functions, content, surface proteins and other phenotypic characteristics. Many techniques have been invented to analyze PMP and other extracellular vesicles for these parameters, but none of them is capable of examining all parameters alone. Apart from it, every technique has its own advantages, limitations and sets of recommendations while using it. This often leads to applying multiple techniques in combination for accurately measuring various parameters and user has to decide cautiously which technique has to be used for their selected parameter testing. This review compiles various methods, techniques, challenges during PMP analysis and recommendations based on previous studies, aimed at guiding users for selecting the most suitable techniques for their experiments with PMP.

Networks of enzymatically oxidized membrane lipids support calcium-dependent coagulation factor binding to maintain hemostasis

Blood coagulation functions as part of the innate immune system by preventing bacterial invasion, and it is critical to stopping blood loss (hemostasis). Coagulation involves the external membrane surface of activated platelets and leukocytes. Using lipidomic, genetic, biochemical, and mathematical modeling approaches, we found that enzymatically oxidized phospholipids (eoxPLs) generated by the activity of leukocyte or platelet lipoxygenases (LOXs) were required for normal hemostasis and promoted coagulation factor activities in a Ca²⁺- and phosphatidylserine (PS)-dependent manner. In wild-type mice, hydroxyeicosatetraenoic acid-phospholipids (HETE-PLs) enhanced coagulation and restored normal hemostasis in clotting-deficient animals genetically lacking p12-LOX or 12/15-LOX activity. Murine platelets generated 22 eoxPL species, all of which were missing in the absence of p12-LOX. Humans with the thrombotic disorder antiphospholipid syndrome (APS) had statistically significantly increased HETE-PLs in platelets and leukocytes, as well as greater HETE-PL immunoreactivity, than healthy controls. HETE-PLs enhanced membrane binding of the serum protein β2GP1 (β2-glycoprotein 1), an event considered central to the autoimmune reactivity responsible for APS symptoms. Correlation network analysis of 47 platelet eoxPL species in platelets from APS and control subjects identified their enzymatic origin and revealed a complex network of regulation, with the abundance of 31 p12-LOX-derived eoxPL molecules substantially increased in APS. In summary, circulating blood cells generate networks of eoxPL molecules, including HETE-PLs, which change membrane properties to enhance blood coagulation and contribute to the excessive clotting and immunoreactivity of patients with APS.

Increased levels of CCR7(lo)PD-1(hi) CXCR5+ CD4+ T cells, and associated factors Bcl-6, CXCR5, IL-21 and IL-6 contribute to repeated implantation failure

In vitro fertilization-embryo transfer (IVF-ET) can be used by infertile couples to assist with reproduction; however, failure of the embryo to implant into the endometrial lining results in failure of the IVF treatment. The present study investigated the expression of chemokine receptor 7 (CCR7)(lo) programmed death-1(PD-1)(hi) chemokine receptor type 5 (CXCR5)⁺ cluster of differentiation 4 (CD4)⁺ T cells and associated factors in patients with repeated implantation failure (RIF). A total of 30 females with RIF and 30 healthy females were enrolled in the current study. Flow cytometry was used to detect the proportion of CCR7(lo)PD-1(hi) CXCR5⁺ CD4⁺ T cells in the peripheral blood. Cytokine bead arrays were performed to detect the levels of interleukin (IL)-6, −4 and −2 in the serum. ELISAs were used to detect the level of IL-21 in the serum. Quantitative real time polymerase chain reaction analysis and immunohistochemistry were used to investigate the expression of B-cell lymphoma 6 (Bcl-6), chemokine receptor type 5 (CXCR5) and IL-21 in the endometrium. The results revealed that the percentage of CCR7(lo)PD-1(hi) CXCR5⁺ CD4⁺ T cells was increased in the RIF group compared with the control group during the mid luteal phase. The mRNA and protein levels of Bcl-6, IL-21 and CXCR5 in the endometrium and the concentrations of IL-21 and IL-6 in the serum were significantly increased in the RIF group; however, no significant difference was observed between the two groups in regards to the expression of IL-4 and IL-2. Furthermore, a significant positive correlation was identified between the percentage of CCR7(lo)PD-1(hi) CXCR5⁺ CD4⁺ T cells and IL-21 and IL-6 levels. The expression of IL-21 also had a positive correlation with Bcl-6 and CXCR5 expression in the RIF group. These results suggest that increased levels of CCR7(lo)PD-1(hi) CXCR5⁺ CD4⁺ T cells and associated factors contribute to RIF and could therefore be a potential therapeutic target.

Vascular Manifestations in Antiphospholipid Syndrome (APS): Is APS a Thrombophilia or a Vasculopathy?

PURPOSE OF REVIEW

Antiphospholipid antibody syndrome (APS) is characterized primarily by thrombosis and pregnancy morbidity. Chronic vascular lesions can also occur. While the underlying mechanisms of these vascular lesions are not entirely known, there have been multiple theories describing the potential process of vasculopathy in APS and the various clinical manifestations associated with it.

RECENT FINDINGS

Recently, it has been demonstrated that endothelial proliferation in kidneys can be explained by the activation of the mammalian target of rapamycin complex (mTORC) pathway by antiphospholipid antibodies (aPL). These data support the existence of an APS-related vasculopathy in different locations which can explain-in part-the different manifestations of APS. This review focuses on the various manifestations of APS as a result of APS-related vasculopathy, as well as pathophysiology, current screening, and treatment options for clinicians to be aware of.

Altered β2 -glycoprotein I expression on microparticles in the presence of antiphospholipid antibodies

Essentials β2 glycoprotein-I (β2 GPI) is a scavenger molecule that binds to microparticles (MPs). β2 GPI expression on MPs was measured in systemic lupus erythematosus (SLE) patients and controls. β2 GPI positive MPs is depressed among SLE patients positive for antiphospholipid antibodies. Complex formation between β2 GPI on MPs and patients own anti-β2 GPI may disturb MP clearance. Click to hear an ISTH Academy presentation on antiphospholipid antibody syndrome by Drs de Laat and Bertolaccini SUMMARY: Background Antiphospholipid antibodies (aPLs) together with thrombosis and/or pregnancy morbidities characterize the antiphospholipid syndrome. β2 -Glycoprotein I (β2 GPI), the most important antigen for aPLs, is a scavenger molecule that specifically binds to phosphatidylserine (PS) expressed on microparticles (MPs). Objectives To evaluate β2 GPI-expressing MPs in patients with systemic lupus erythematosus (SLE) stratified for aPL status, and in healthy controls. Patients/Methods We investigated 18 aPL/anti-β2 GPI-positive and 22 aPL-negative patients from a large SLE cohort and 19 healthy controls. β2 GPI-positive MPs and IgG-positive MPs were detected by flow cytometry. We measured plasma levels of β2 GPI, and performed in vitro experiments to investigate the binding properties of β2 GPI on MPs. Results SLE patients had more MPs and IgG-positive MPs than controls. We observed fewer β2 GPI-positive MPs in aPL/anti-β2 GPI-positive patients than in aPL/anti-β2 GPI-negative patients and controls (approximately two-fold). β2 GPI levels in plasma did not differ with aPL/anti-β2 GPI status in patients; however, controls had slightly higher levels of β2 GPI than aPL/anti-β2 GPI-positive patients. In vitro experiments revealed that β2 GPI preferentially binds to PS-positive MPs. Conclusions Despite abundant total MPs and MPs in immune complexes, β2 GPI-positive MPs were depleted in SLE patients, and the levels were especially low in aPL/anti-β2 GPI-positive patients. We suggest that anti-β2 GPI antibodies bind to β2 GPI-PS complexes expressed on MPs. Consequent loss of β2 GPI-PS expression on MPs may impair scavenging and contribute to the accumulation of circulating PS-negative MPs, a possible source of autoantigens. Autoantibodies delaying MP clearance may thus constitute an important mechanism underlying autoimmunity.

Modulating thrombotic diathesis in hereditary thrombophilia and antiphospholipid antibody syndrome: a role for circulating microparticles?

Over the past decades, there have been great advances in the understanding of the pathogenesis of venous thromboembolism (VTE) in patients with inherited and acquired thrombophilia [mainly antiphospholipid antibody syndrome (APS)]. However, a number of questions remain unanswered. Prognostic markers capable of estimating the individual VTE risk would be of great use. Microparticles (MPs) are sub-micron membrane vesicles constitutively released from the surface of cells after cellular activation and apoptosis. The effects of MPs on thrombogenesis include the exposure of phopshatidylserine and the expression of tissue factor and MPs have been described in clinical studies as possible diagnostic and prognostic biomarkers for VTE. This review will provide a novel perspective on the current knowledge and research trends on the possible role of MPs in hereditary thrombophilia and APS. Basically, the published data show that circulating MPs may contribute to the development of VTE in thrombophilic carriers, both in mild and severe states. Moreover, the presence of endothelial-MPs and platelet-MPs has been described in antiphospholipid syndrome and seems to be directly linked to antiphospholipid antibodies and not to other underlying autoimmune disorders or the thrombotic event itself. In conclusion, circulating MPs may constitute an epiphenomenon of thrombophilia itself and could be up-regulated in acute particular conditions, promoting a global prothrombotic state up to the threshold of the clinical relevant thrombotic event.

A importância de reconhecer a síndrome antifosfolípide na medicina vascular

A síndrome antifosfolipíde (SAF) é uma doença autoimune sistêmica caracterizada por trombose arterial ou venosa recorrente e/ou morbidade gestacional e pela presença dos anticorpos antifosfolipídeos, podendo apresentar outras manifestações vasculares, como microangiopatia, arteriopatia crônica e SAF catastrófica. Determinados testes laboratoriais para a síndrome (por exemplo, o anticoagulante lúpico) podem sofrer interferência do uso de medicações anticoagulantes, dificultando o diagnóstico. A fisiopatologia da SAF é complexa, sendo enumerados no texto diversos mecanismos patogênicos relacionados à coagulação, ao endotélio e às plaquetas. Por fim, discutimos o tratamento da SAF de acordo com a presença e o tipo de manifestações clínicas, o uso dos anticoagulantes orais diretos e o manejo perioperatório de pacientes com SAF.

The role of platelets in antiphospholipid syndrome

Despite extensive research, the pathogenesis of antiphospholipid syndrome (APS) remains obscure in many aspects. However, it is widely accepted that thrombosis is the result of a hypercoagulable state caused by antibodies directed against β2-glycoprotein I (β2-GPI), a protein whose physiological role is unknown. Although underestimated, platelets may be involved in APS and its thrombotic manifestations, especially arterial, in several ways. Thrombocytopenia is the most relevant non-criteria manifestation of APS, possibly caused by direct binding of anti-β2-GPI antibodies or anti-β2-GPI-β2-GPI complexes. On the other hand, platelets may have a key role in APS-related thrombosis due to the presence of multiple receptors that can interact with anti-β2-GPI antibodies (especially apolipoprotein E receptor 2' (apoER2') and glycoprotein Ibα (GPIbα)) with consequent release of different procoagulant mediators such as thromboxane B2, platelet factor 4 (PF4), and platelet factor 4 variant (CXCL4L1). The aim of this review is to put together evidence on the possible role of platelets in APS and to stimulate further research on the issue.

Extracellular vesicles and blood diseases

Extracellular vesicles (EVs) are small membrane vesicles released from many different cell types by the exocytic budding of the plasma membrane in response to cellular activation or apoptosis. EVs disseminate various bioactive effectors originating from the parent cells and transfer functional RNA and protein between cells, enabling them to alter vascular function and induce biological responses involved in vascular homeostasis. Although most EVs in human blood originate from platelets, EVs are also released from leukocytes, erythrocytes, endothelial cells, smooth muscle cells, and cancer cells. EVs were initially thought to be small particles with procoagulant activity; however, they can also evoke cellular responses in the immediate microenvironments and transport microRNAs (miRNA) into target cells. In this review, we summarize the recent literature relevant to EVs, including a growing list of clinical disorders that are associated with elevated EV levels. These studies suggest that EVs play roles in various blood diseases.

From trash to treasure: The untapped potential of endothelial microparticles in neurovascular diseases

Discovered in 1947, microparticles (MP) represent a group of sub-micron cell-derived particles isolated by high speed centrifugation. Once regarded as cellular 'trash', in the past decade MP have gained tremendous attention in both basic sciences and medical research both as biomarkers and mediators of infection, injury and response to therapy. Because MP bear cell surface markers derived from parent cells, accumulate in extracellular fluids (plasma, serum, milk, urine, cerebrospinal fluid) MP based tests are being developed commercially as important components in 'liquid biopsy' approaches, providing valuable readouts in cardiovascular disease and cancer, as well as stroke, Alzheimer's disease and Multiple Sclerosis. Importantly, MP have been reported as mobile transport vectors in the intercellular transfer of mRNAs, microRNAs, lipids and proteins. Here we discuss MP structure, properties and functions with particular relevance to neurological and neurovascular diseases.

Endothelial microparticles: Pathogenic or passive players in endothelial dysfunction in autoimmune rheumatic diseases?

Autoimmune rheumatic diseases are characterised by systemic inflammation and complex immunopathology, with an increased risk of cardiovascular disease, initiated by endothelial dysfunction in a chronic inflammatory environment. Endothelial microparticles (EMPs) are released into the circulation from activated endothelial cells and may therefore, reflect disease severity, vascular and endothelial dysfunction, that could influence disease pathogenesis via autocrine/paracrine signalling. The exact function of EMPs in rheumatic disease remains unknown, and this has initiated research to elucidate EMP composition and function, which may be determined by the mode of endothelial activation and the micro environment. To date, EMPs are thought to play a role in angiogenesis, thrombosis and inflammation by transferring specific proteins and microRNAs (miRs) to target cells. Here, we review the mechanisms underlying the generation and composition of EMPs and the clinical and experimental studies describing the involvement of EMPs in rheumatic diseases, since we have previously shown endothelial dysfunction and an elevated risk of cardiovascular disease are characteristics in systemic lupus erythematosus. We will also discuss the potential of EMPs as future biomarkers of cardiovascular risk in these diseases.

Possible roles of platelet-derived microparticles in atherosclerosis

Platelets and platelet-derived microparticles (PMPs) play important roles in cardiovascular diseases, especially atherosclerosis. Continued research has revealed that PMPs have numerous functions in atherosclerosis, not only in thrombosis formation, but also by induction of inflammation. PMPs also induce formation of foam cells. Recent evidence strongly indicates a significant role of PMPs in atherosclerosis. Here, current research on the function of PMPs in atherosclerosis is reviewed.

A new cytofluorimetric approach to evaluate the circulating microparticles in subjects with antiphospholipid antibodies

INTRODUCTION

Growing evidence supports the idea that microparticles (MPs) could contribute to the pathogenesis of the thrombotic phenomena associated with antiphospholipid antibody syndrome (APS), inducing a hypercoagulable state. But, to date, different approaches to evaluate circulating MPs and conflicting results have been reported.

MATERIALS AND METHODS

We have characterized the different circulating subpopulations of MPs in APS patients, and in asymptomatic aPL-positive subjects (carriers) by examining the correlation between the amount and phenotype of MPs and the clinical parameters. Forty-eight subjects were enrolled: 16 with primary APS, 16 aPL-positive, but without clinical criteria for APS (carriers), and 16 healthy subjects. The levels of MPs were evaluated using a new cytofluorimetric approach based on BD Horizon Violet Proliferation dye (VPD) 450.

RESULTS AND CONCLUSIONS

Using a new detection cytofluorimetric approach, we demonstrated that the AnnV-negative MPs, underestimated/or excluded in the previous studies, are a large subset of circulating MPs. Also, the levels of MPs in the plasma of aPL positive subjects indicate a state of cellular activation, which is much more pronounced in patients with APS compared to aPL carriers. Moreover, the preliminary data of our pilot study suggest that the evaluation of circulating MPs, in particular PMPs and EMPs, could be used as a surrogate biomarker for platelet and vascular damage monitoring and, if confirmed in a more numerous cohort of patients, it could be used as a prognostic factor to identify aPL positive subjects at higher risk of developing thrombosis.