Comparison of assays measuring extracellular vesicle tissue factor in plasma samples: communication from the ISTH SSC Subcommittee on Vascular Biology.

BACKGROUND: Scientific and clinical interest in extracellular vesicles (EVs) is growing. EVs that expose tissue factor (TF) bind factor VII/VIIa and can trigger coagulation. Highly procoagulant TF-exposing EVs are detectable in the circulation in various diseases, such as sepsis, COVID-19, or cancer. Many in-house and commercially available assays have been developed to measure EV-TF activity and antigen, but only a few studies have compared some of these assays. OBJECTIVES: The International Society on Thrombosis and Haemostasis Scientific and Standardization Committee Subcommittee on Vascular Biology initiated a multicenter study to compare the sensitivity, specificity, and reproducibility of these assays. METHODS: Platelet-depleted plasma samples were prepared from blood of healthy donors. The plasma samples were spiked either with EVs from human milk or EVs from TF-positive and TF-negative cell lines. Plasma was also prepared from whole human blood with or without lipopolysaccharide stimulation. Twenty-one laboratories measured EV-TF activity and antigen in the prepared samples using their own assays representing 18 functional and 9 antigenic assays. RESULTS: There was a large variability in the absolute values for the different EV-TF activity and antigen assays. Activity assays had higher specificity and sensitivity compared with antigen assays. In addition, there was a large intra-assay and interassay variability. Functional assays that used a blocking anti-TF antibody or immunocapture were the most specific and sensitive. Activity assays that used immunocapture had a lower coefficient of variation compared with assays that isolated EVs by high-speed centrifugation. CONCLUSION: Based on this multicenter study, we recommend measuring EV-TF using a functional assay in the presence of an anti-TF antibody.

Plasma levels of E-selectin are associated with retinopathy in sickle cell disease.

BACKGROUND: The vascular endothelium is markedly disrupted in sickle cell disease (SCD) and is the converging cascade of the complex pathophysiologic processes linked to sickle cell vasculopathy. Circulating endothelial activation and/or apoptotic markers may reflect this endothelial activation/damage that contributes to the pathophysiology of the SCD vascular complications. METHODS: Plasmatic levels of circulating endothelial cells (CECs), E-selectin, progenitor's endothelial cells (EPCs), and circulating extracellular vesicles (EVs) were evaluated in 50 SCD patients, 16 with vasculopathy. The association between these markers and the occurrence of disease-related microvascular injuries of the eye (retinopathy), kidney (nephropathy), and skin (chronic active ulcers) was explored. RESULTS: Among the endothelial activation markers studied, only higher plasma levels of E-selectin were found in SCD patients with vasculopathy (p = .015). Increased E-selectin levels were associated with retinopathy (p < .001) but not with nephropathy or leg ulcers. All patients, at steady state, with or without vasculopathy, did not display a high count of CEC and EPC, markers of endothelial injury and repair. We did not show any significant differences in EVs levels between vasculopathy and not vasculopathy SCD patients. CONCLUSIONS: Further studies will be required to determine whether the E-selectin could be used as an early biomarker of retinopathy sickle cell development.

Rheopheresis Performed in Hemodialysis Patients Targets Endothelium and Has an Acute Anti-Inflammatory Effect.

Background: Rheopheresis is a double-filtration plasmapheresis that removes a defined spectrum of high-molecular-weight proteins to lower plasma viscosity and improves microcirculation disorders. This technique can be performed in hemodialysis (HD) patients with severe microischemia. Interestingly, some studies showed that rheopheresis sessions improve endothelial function. Methods: Our study evaluated the inflammatory and endothelial biomarker evolution in 23 HD patients treated or not with rheopheresis. A p value ≤ 0.001 was considered statistically significant. Results: Thirteen HD patients treated by rheopheresis either for a severe peripheral arterial disease (N = 8) or calciphylaxis (N = 5) were analyzed. Ten control HD patients were also included in order to avoid any misinterpretation of the rheopheresis effects in regard to the HD circuit. In the HD group without rheopheresis, the circulating endothelial adhesion molecules, cytokines, angiogenic factor concentrations, and circulating levels were not modified. In the HD group with rheopheresis, the circulating endothelial adhesion molecules (sVCAM-1, sP-selectin, and sE-selectin) experienced a significant reduction, except sICAM-1. Among the pro-inflammatory cytokines, TNF-α was significantly reduced by 32.6% [(−42.2)−(−22.5)] (p < 0.0001), while the anti-inflammatory cytokine IL-10 increased by 674% (306−1299) (p < 0.0001). Among the angiogenic factors, only sEndoglin experienced a significant reduction. The CEC level trended to increase from 13 (3−33) cells/mL to 43 (8−140) cells/mL (p = 0.002). We did not observe any difference on the pre-session values of the molecules of interest between the first rheopheresis session and the last rheopheresis session. Conclusion: Rheopheresis immediately modified the inflammation balance and the endothelial injury biomarkers. Further studies are needed to understand the mechanisms underlying these biological observations.

Dissemination of extreme levels of extracellular vesicles: tissue factor activity in patients with severe COVID-19.

Coronavirus disease 2019 (COVID-19) has become one of the biggest public health challenges of this century. Severe forms of the disease are associated with a thrombo-inflammatory state that can turn into thrombosis. Because tissue factor (TF) conveyed by extracellular vesicles (EVs) has been implicated in thrombosis, we quantified the EV-TF activity in a cohort of hospitalized patients with COVID-19 (n = 111) and evaluated its link with inflammation, disease severity, and thrombotic events. Patients with severe disease were compared with those who had moderate disease and with patients who had septic shock not related to COVID-19 (n = 218). The EV-TF activity was notably increased in patients with severe COVID-19 compared with that observed in patients with moderate COVID-19 (median, 231 [25th to 75th percentile, 39-761] vs median, 25 [25th to 75th percentile, 12-59] fM; P < .0001); EV-TF was correlated with leukocytes, D-dimer, and inflammation parameters. High EV-TF values were associated with an increased thrombotic risk in multivariable models. Compared with patients who had septic shock, those with COVID-19 were characterized by a distinct coagulopathy profile with significantly higher EV-TF and EV-fibrinolytic activities that were not counterbalanced by an increase in plasminogen activator inhibitor-1 (PAI-1). Thus, this article is the first to describe the dissemination of extreme levels of EV-TF in patients with severe COVID-19, which supports the international recommendations of systematic preventive anticoagulation in hospitalized patients and potential intensification of anticoagulation in patients with severe disease.

Circulating Endothelial Cells as a Marker of Endothelial Injury in Severe COVID -19.

Beside the commonly described pulmonary expression of the coronavirus disease 2019 (COVID-19), major vascular events have been reported. The objective of this study was to investigate whether increased levels of circulating endothelial cells (CECs) might be associated with severe forms of COVID-19. Ninety-nine patients with COVID-19 were enrolled in this retrospective study. Patients in the intensive care units (ICU) had significantly higher CEC counts than non-ICU patients and the extent of endothelial injury was correlated with putative markers of disease severity and inflammatory cytokines. Together, these data provide in vivo evidence that endothelial injury is a key feature of COVID-19.