Circulating endothelial cells in essential thrombocythemia and polycythemia vera: correlation with JAK2-V617F mutational status, angiogenic factors and coagulation activation markers

Circulating endothelial cells in pathophysiology

PURPOSE OF REVIEW

The purpose of this review is to synthesize recent insights into the roles and importance of circulating endothelial cells (CECs) as indicators of the severity, progression, and prognosis of vascular-related diseases.

RECENT FINDINGS

Recent studies have identified elevated counts of CECs in pathological conditions, notably inflammatory or cardiovascular diseases such as acute myocardial infarction and heart failure, underscoring their potential as sensitive indicators of disease. Furthermore, the rise in CEC levels in cancer patients, particularly with disease advancement, points to their role in cancer-associated angiogenesis and response to treatment.

SUMMARY

This review underscores the evolving significance of CECs as markers for evaluating the gravity and advancement of diseases with vascular injury, including cardiovascular diseases, cancer, inflammatory conditions, and thromboembolic events. These last years, efforts made to standardize flow cytometry detection of CEC and the development of highly sensitive techniques to isolate, quantify or phenotype rare cells open promising avenues for clinical application. This may yield extensive knowledge regarding the mechanisms by which endothelial cells contribute to a variety of vascular-related disorders and their clinical value as emerging biomarkers.

Vascular endothelial growth factor and the risk of venous thromboembolism: a genetic correlation and two-sample Mendelian randomization study

Background

The relationship between vascular endothelial growth factor (VEGF) and the risk of venous thromboembolism (VTE) has always been one of the concerns in the medical field. However, the causal inferences from published observational studies on this issue may be affected by confounders or reverse causality. We performed a two-sample bidirectional Mendelian randomization (MR) to infer the associations between VEGF and VTE.

Methods

Summary statistics from genome-wide association studies (GWAS) for VEGF and VTE were obtained from published meta-analysis studies and the FinnGen consortium, respectively. Independent genetic variables significantly associated with exposure were selected as instrumental variables. Linkage disequilibrium score regression (LDSC) and five robust MR analytical approaches were conducted to estimate the genetic correlations and causal inference. The MR-Egger intercept, Cochran’s Q, and MR pleiotropy residual sum and outlier (MR-PRESSO) were performed to evaluate the horizontal pleiotropy, heterogeneities, and stability of these genetic variants on outcomes. Notably, replication analyses were performed using different subgroups of VTE.

Results

LDSC failed to identify genetic correlations between VEGF and VTE. Based on 9 SNPs, the circulating VEGF level was positively related to the risk of VTE using inverse variance weighting (IVW) method (odds ratio (OR) = 1.064, 95% confidence interval (CI), 1.009–1.122). Reverse MR analyses showed that genetic liability for VTE was not associated with increased VEGF level (β = -0.021, 95% CI, -0.087-0.045). Pleiotropy-robust methods indicated no bias in any estimates.

Conclusions

Our findings failed to detect coheritability between VEGF and VTE. The suggestive positive effect of the higher VEGF level on the VTE risk may have clinical implications, suggesting that VEGF as a possible predictor and therapeutic target for VTE prevention need to be further warranted.

Thromboinflammation in Myeloproliferative Neoplasms (MPN)-A Puzzle Still to Be Solved

Myeloproliferative neoplasms (MPNs), a group of malignant hematological disorders, occur as a consequence of somatic mutations in the hematopoietic stem cell compartment and show excessive accumulation of mature myeloid cells in the blood. A major cause of morbidity and mortality in these patients is the marked prothrombotic state leading to venous and arterial thrombosis, including myocardial infarction (MI), deep vein thrombosis (DVT), and strokes. Additionally, many MPN patients suffer from inflammation-mediated constitutional symptoms, such as fever, night sweats, fatigue, and cachexia. The chronic inflammatory syndrome in MPNs is associated with the up-regulation of various inflammatory cytokines in patients and is involved in the formation of the so-called MPN thromboinflammation. JAK2-V617F, the most prevalent mutation in MPNs, has been shown to activate a number of integrins on mature myeloid cells, including granulocytes and erythrocytes, which increase adhesion and drive venous thrombosis in murine knock-in/out models. This review aims to shed light on the current understanding of thromboinflammation, involvement of neutrophils in the prothrombotic state, plausible molecular mechanisms triggering the process of thrombosis, and potential novel therapeutic targets for developing effective strategies to reduce the MPN disease burden.

Thromboinflammation in Myeloproliferative Neoplasms (MPN)-A Puzzle Still to Be Solved

Myeloproliferative neoplasms (MPNs), a group of malignant hematological disorders, occur as a consequence of somatic mutations in the hematopoietic stem cell compartment and show excessive accumulation of mature myeloid cells in the blood. A major cause of morbidity and mortality in these patients is the marked prothrombotic state leading to venous and arterial thrombosis, including myocardial infarction (MI), deep vein thrombosis (DVT), and strokes. Additionally, many MPN patients suffer from inflammation-mediated constitutional symptoms, such as fever, night sweats, fatigue, and cachexia. The chronic inflammatory syndrome in MPNs is associated with the up-regulation of various inflammatory cytokines in patients and is involved in the formation of the so-called MPN thromboinflammation. JAK2-V617F, the most prevalent mutation in MPNs, has been shown to activate a number of integrins on mature myeloid cells, including granulocytes and erythrocytes, which increase adhesion and drive venous thrombosis in murine knock-in/out models. This review aims to shed light on the current understanding of thromboinflammation, involvement of neutrophils in the prothrombotic state, plausible molecular mechanisms triggering the process of thrombosis, and potential novel therapeutic targets for developing effective strategies to reduce the MPN disease burden.

Liquid Biopsy and Potential Liquid Biopsy-Based Biomarkers in Philadelphia-Negative Classical Myeloproliferative Neoplasms: A Systematic Review

Myeloproliferative neoplasms (MPNs) are rare, clonal disorders of the hematopoietic stem cell in which an uncontrolled proliferation of terminally differentiated myeloid cells is noted. Polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) are included in the category of Philadelphia-negative, so-called classical MPNs. The potential applications of liquid biopsy and liquid biopsy-based biomarkers have not been explored in MPNs until now. Thus, a systematic search was computed in PubMed/MEDLINE, Web of Science and The Cochrane Library and, in total, 198 potentially relevant papers were detected. Following the removal of duplicates (n = 85), 113 records were screened. After the exclusion of irrelevant manuscripts based on the screening of their titles and abstracts (n = 81), we examined the full texts of 33 manuscripts. Finally, after we applied the exclusion and inclusion criteria, 27 original articles were included in this review. Overall, the data analyzed in this review point out that liquid biopsy and liquid biopsy-based biomarkers (cell-free DNA, extracellular vesicles, microparticles, circulating endothelial cells) could be used in MPNs for diagnostic and prognostic purposes. Future research is needed to clarify whether this technique can be employed to differentiate between MPN subtypes and secondary causes of erythrocytosis, thrombocytosis and myelofibrosis, as well as to predict the development of thrombosis.

Assessment of endothelial progenitor cells, VEGF-A and SDF-1α in Hodgkin's lymphoma

Recently, there is great interest in vasculogenesis, a process of the formation of new blood vessels from progenitor cells or angioblasts, in the pathogenesis of cancer. To the best of our knowledge, the evaluation of endothelial progenitor cells (EPCs) in Hodgkin's lymphoma has not yet been reported. The aim of the present study was to assess the number of EPCs and selected cytokines, such as vascular endothelial growth factor (VEGF-A) and stromal cell-derived factor (SDF-1α) involved in vasculogenesis in Hodgkin's lymphoma patients. The study was conducted in a group of 42 patients with Hodgkin's lymphoma (eight patients with relapsed Hodgkin's lymphoma and 34 patients before the first treatment) and 30 healthy controls. The number of EPCs defined as CD31(+), CD34(+), CD45(-), CD133(+) was analysed on FacsCalibur flow cytometer and the concentration of VEGF-A and SDF-1α was assessed by ELISA. The study showed that there was a significantly higher EPCs number and VEGF-A concentration in the blood of Hodgkin's lymphoma patients compared to healthy individuals (8.20 vs. 0.55 cells/μl; P < 0.000001; 85.10 vs. 25.33 pg/ml, P = 0.000017; respectively). Detailed analysis revealed that there was elevated EPCs number in both study subgroups as compared to the control group. However, there was no difference in VEGF concentration between recurrent Hodgkin's lymphoma patients and the control group. A significant positive correlation was found between the number of EPCs and VEGF-A concentration (R = 0.31, P = 0.047). Significantly higher EPCs number combined with increased VEGF-A concentration, found in Hodgkin's lymphoma patients before the first treatment, suggest stimulation of new blood vessels formation, which may in turn contribute to tumour growth and metastasis in these patients.

Bone Marrow Soluble Mediator Signatures of Patients With Philadelphia Chromosome-Negative Myeloproliferative Neoplasms

Background

Essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF) are clonal hematological diseases classified as Philadelphia chromosome-negative myeloproliferative neoplasms (MPN). MPN pathogenesis is associated with the presence of somatic driver mutations, bone marrow (BM) niche alterations, and tumor inflammatory status. The relevance of soluble mediators in the pathogenesis of MPN led us to analyze the levels of cytokines, chemokines, and growth factors related to inflammation, angiogenesis and hematopoiesis regulation in the BM niche of MPN patients.

Methods

Soluble mediator levels in BM plasma samples from 17 healthy subjects, 28 ET, 19 PV, and 16 PMF patients were determined using a multiplex assay. Soluble mediator signatures were created from categorical analyses of high mediator producers. Soluble mediator connections and the correlation between plasma levels and clinic-laboratory parameters were also analyzed.

Results

The soluble mediator signatures of the BM niche of PV patients revealed a highly inflammatory and pro-angiogenic milieu, with increased levels of chemokines (CCL2, CCL5, CXCL8, CXCL12, CXCL10), and growth factors (GM-CSF M-CSF, HGF, IFN-γ, IL-1β, IL-6Ra, IL-12, IL-17, IL-18, TNF-α, VEGF, and VEGF-R2). ET and PMF patients presented intermediate inflammatory and pro-angiogenic profiles. Deregulation of soluble mediators was associated with some clinic-laboratory parameters of MPN patients, including vascular events, treatment status, risk stratification of disease, hemoglobin concentration, hematocrit, and red blood cell count.

Conclusions

Each MPN subtype exhibits a distinct soluble mediator signature. Deregulated production of BM soluble mediators may contribute to MPN pathogenesis and BM niche modification, provides pro-tumor stimuli, and is a potential target for future therapies.

Expression of CD markers in JAK2V617F positive myeloproliferative neoplasms: Prognostic significance

Myeloproliferative neoplasms (MPNs) are clonal stem cell disorders characterized by the presence of JAK2^V617F mutation. Thrombohemorrhagic as well as autoimmune or inflammatory phenomena are common clinical outcomes of these disorders. Recent studies have shown that abnormality in frequency and function of blood cells manifested by an alteration in CD markers' expression patterns play a key role in these complications. So, there may be a relationship between CD markers' expressions and prognosis of JAK2^V617F positive MPNs. Therefore, in this review, we have focused on these abnormalities from the perspective of changing expressions of CD markers and assessment of the relationship between these changes with prognosis of JAK2^V617F positive MPNs. It can be stated that the abnormal expression of a large number of CD markers can be used as a prognostic biomarker for clinical outcomes including thrombohememorrhagic events, as well as autoimmune and leukemic transformation in JAK2^V617F positive MPNs. Considering the possible role of CD markers' expressions in JAK2^V617F MPNs prognosis, further studies are needed to confirm the relationship between the expression of CD markers with prognosis to be able to find an appropriate therapeutic approach via targeting CD markers.

Selected Parameters of Angiogenesis and the JAK2, CALR, and MPL Mutations in Patients With Essential Thrombocythemia

The aim of the study was to evaluate selected angiogenic factors in patients with essential thrombocythemia (ET) depending on JAK2V617F, calreticulin gene (CALR) and myeloproliferative leukemia virus oncogene (MPL) mutations. Sixty ET patients and 20 healthy volunteers were enrolled in the study. The following tests were performed: vascular endothelial growth factor- A (VEGF-A), soluble vascular endothelial growth factor receptor-1 (sVEGFR-1),soluble vascular endothelial growth factor receptor-2 (sVEGFR-2), platelet-derived growth factor( PDGF-BB), and stromal-derived factor-1α (SDF-1α). We observed an increased PDGF-BB level in patients with ET compared to the controls. Patients with CALR mutation had significantly higher concentration of PDGF-BB and lower concentration of SDF-1α than patients with JAK2V617F mutation. High concentration of PDGF-BB and low concentration of SDF-1α in patients with CALR(+) ET may indicate a contribution of these chemokines in disturbed Ca²⁺ metabolism in platelets.

Phosphatidylserine-exposing blood and endothelial cells contribute to the hypercoagulable state in essential thrombocythemia patients

The mechanisms of thrombogenicity in essential thrombocythemia (ET) are complex and not well defined. Our objective was to explore whether phosphatidylserine (PS) exposure on blood cells and endothelial cells (ECs) can account for the increased thrombosis and distinct thrombotic risks among mutational subtypes in ET. Using flow cytometry and confocal microscopy, we found that the levels of PS-exposing erythrocytes, platelets, leukocytes, and serum-cultured ECs were significantly higher in each ET group [JAK2, CALR, and triple-negative (TN) (all P < 0.001)] than those in controls. Among ET patients, those with JAK2 mutations showed higher levels of PS-positive erythrocytes, platelets, neutrophils, and serum-cultured ECs than TN patients or those with CALR mutations, which show similar levels. Coagulation function assays showed that higher levels of PS-positive blood cells and serum-cultured ECs led to markedly shortened coagulation time and dramatically increased levels of FXa, thrombin, and fibrin production. This procoagulant activity could be largely blocked by addition of lactadherin (approx. 70% inhibition). Confocal microscopy showed that the FVa/FXa complex and fibrin fibrils colocalized with PS on ET serum-cultured ECs. Additionally, we found a relationship between D-dimer, prothrombin fragment F1 + 2, and PS exposure. Our study reveals a previously unrecognized link between hypercoagulability and exposed PS on cells, which might also be associated with distinct thrombotic risks among mutational subtypes in ET. Thus, blocking PS-binding sites may represent a new therapeutic target for preventing thrombosis in ET.

VEGF-A, sVEGFR-1, and sVEGFR-2 in BCR-ABL negative myeloproliferative neoplasms

BACKGROUND AND OBJECTIVE

Data from the literature indicate the relationship between the bone marrow microvessel density and the blood parameters of angiogenesis. The aim of this study was to evaluate selected parameters of angiogenesis (VEGF-A, sVEGFR-1, and sVEGFR-2) and their correlations with white blood cells, platelets, and red blood cells.

MATERIALS AND METHODS

The study included 72 patients (mean age, 61.84 years) with myeloproliferative neoplasms (MPNs): essential thrombocythemia (ET) (n=46), polycythemia vera (PV) (n=19), and primary myelofibrosis (PMF) (n=7). Serum VEGF-A, sVEGFR-1, and sVEGFR-2 were determined using the ELISA assay.

RESULTS

We observed a significantly higher level of VEGF-A and reduced concentrations of sVEGFR-1 and sVEGFR-2 in the whole group of patients with MPNs as compared to controls. Detailed analysis confirmed significantly higher level of VEGF-A and lower concentration of sVEGFR-2 in each subgroups of MPNs patients. However, sVEGFR-1 concentrations were significantly lower only in PV and ET patients.

CONCLUSIONS

The study showed an increased level of VEGF-A, which may indicate the intensity of neoangiogenesis in the bone marrow. Decreased sVEGFR-1 and sVEGFR-2 in the blood of patients with MPNs may reflect consumption of these soluble receptors.

New potential diagnostic biomarkers for pulmonary hypertension

This study aimed to determine whether the vascular endothelial growth factor (VEGF) family members soluble VEGF receptor 1 (also called soluble fms-like tyrosine kinase 1 (sFlt-1)) and placental growth factor (PlGF) could be used as biomarkers for pulmonary hypertension (PH).

Consecutive patients undergoing right heart catheterisation were enrolled (those with mean pulmonary arterial pressure ≥25 mmHg were classed as having PH; those with mean pulmonary arterial pressure <25 mmHg acted as non-PH controls). Plasma from the time of PH diagnosis was analysed for PlGF and sFlt-1 using enzyme immunoassays.

In total, 247 patients with PH were enrolled: 62 with idiopathic pulmonary arterial hypertension (IPAH), 14 with associated pulmonary arterial hypertension (APAH), 21 with collagen vascular disease (CVD), 26 with pulmonary venous hypertension, 67 with lung disease-associated PH and 57 with chronic thromboembolic PH. The non-PH control group consisted of 40 patients. sFlt-1 plasma levels were significantly higher in patients with IPAH, APAH, CVD and lung disease-associated PH versus controls; PlGF levels were significantly higher in all PH groups versus controls. The combination of sFlt-1 and PlGF resulted in a sensitivity of 83.7% with specificity of 100% for pulmonary arterial hypertension. There was no association between sFlt-1 or PlGF and haemodynamic parameters, 6-min walking distance or survival.

In summary, PlGF and sFlt-1 are promising diagnostic biomarkers for PH.

Circulating endothelial cells in patients with venous thromboembolism and myeloproliferative neoplasms

Background

Circulating endothelial cells (CEC) may be a biomarker of vascular injury and pro-thrombotic tendency, while circulating endothelial progenitor cells (CEP) may be an indicator for angiogenesis and vascular remodelling. However, there is not a universally accepted standardized protocol to identify and quantify these cells and its clinical relevancy remains to be established.

Objectives

To quantify CEC and CEP in patients with venous thromboembolism (VTE) and with myeloproliferative neoplasms (MPN), to characterize the CEC for the expression of activation (CD54, CD62E) and procoagulant (CD142) markers and to investigate whether they correlate with other clinical and laboratory data.

Patients and Methods

Sixteen patients with VTE, 17 patients with MPN and 20 healthy individuals were studied. The CEC and CEP were quantified and characterized in the blood using flow cytometry, and the demographic, clinical and laboratory data were obtained from hospital records.

Results

We found the CEC counts were higher in both patient groups as compared to controls, whereas increased numbers of CEP were found only in patients with MPN. In addition, all disease groups had higher numbers of CD62E+ CEC as compared to controls, whereas only patients with VTE had increased numbers of CD142+ and CD54+ CEC. Moreover, the numbers of total and CD62+ CEC correlated positively with the white blood cells (WBC) counts in both groups of patients, while the numbers of CEP correlated positively with the WBC counts only in patients with MPN. In addition, in patients with VTE a positive correlation was found between the numbers of CD54+ CEC and the antithrombin levels, as well as between the CD142+ CEC counts and the number of thrombotic events.

Conclusions

Our study suggests that CEC counts may reveal endothelial injury in patients with VTE and MPN and that CEC may express different activation-related phenotypes depending on the disease status.

Circulating endothelial cell kinetics and their potential predictive value during mobilization procedure

OBJECTIVE

Circulating endothelial cells (CECs) in patients with hematological malignancies are assessed as a noninvasive marker of angiogenesis. The aim of this study was to evaluate the numbers of CECs and their subsets during mobilization of hematopoietic stem cells.

PATIENTS AND METHODS

Thirty-eight patients were enrolled to the study (19 females and 19 males) at median age of 56.5 years. The group consisted of patients with multiple myeloma (26), lymphoma (10), and acute myeloid leukemia (2). Blood samples were collected before chemotherapy (0), 1 day after chemotherapy (Cht+1), on the day G-CSF commenced (G0), after 1 day of G-CSF (G+1), and on the day of the first apheresis. CECs were evaluated by four-color flow cytometry. Circulating progenitor cells were defined as CD45-/CD34+/CD31+/CD133+. Apoptotic CECs (ApoCECs) were defined as CD146+/AnnexinV+.

RESULTS

Median (Me) CECs number was 10.5/µl and it decreased after chemotherapy (Me = 8.3/µl, P < 0.001 when compared with baseline). Based on the number of aphereses needed to obtain 2 × 10(6)/kg CD34+ cells, patients were divided into "highly efficient" (one apheresis) and "poorly efficient" mobilizers (two or more aphereses). Median ApoCEC at Day G+1 was lower in highly efficient than in poorly efficient mobilizers (Me = 3.1/µl vs. Me = 5.1/µl, P = 0.02). ApoCEC at Day G+1 correlated with the number of aphereses (r = 0.48, P = 0.03). In multivariate analysis, ApoCEC at Day G+1 was an independent factor for successful mobilization during one apheresis.

CONCLUSIONS

CECs and their subsets change significantly during mobilization of HSCs. ApoCECs measured at the time of G-CSF commencement can predict the efficacy of HSC collection.