New insights into the causes of thrombotic events in patients with myeloproliferative neoplasms raise the possibility of novel therapeutic approaches

Endothelial Damage in JAK2V617F Myeloproliferative Neoplasms with Splanchnic Vein Thrombosis

BACKGROUND

 JAK2V617F-mutated myeloproliferative neoplasms (MPN) exhibit abnormal proliferation of bone marrow progenitors and increased risk of thrombosis, specifically in splanchnic veins (SVT). The contribution of the endothelium to the development of the prothrombotic phenotype was explored.

MATERIAL AND METHODS

 Plasma and serum samples from JAK2V617F MPN patients with (n=26) or without (n=7) thrombotic debut and different treatments, were obtained (n=33). Cultured endothelial cells (ECs) were exposed to serum samples from these patients and from healthy donors as controls. Changes in markers of inflammation (VCAM-1, ICAM-1), cell permeability (VE-cadherin), production of VWF, extracellular matrix (ECM) reactivity, and activation of intracellular signaling pathways related to stress, proliferation, inflammation (Akt, p44/42, IkBa), and JAK2/STAT3 pathway, were assessed by immunofluorescence, flow adhesion, SDS-PAGE and immunoblot. Additionally, circulating markers of endothelial activation and damage (VWF, sVCAM-1, sTNFRI, thrombomodulin, angiopoietin-2, a2-antiplasmin activity, PAI-1) were evaluated in Patients' plasma.

RESULTS

 The in vitro studies showed that EC exposure to MPN thrombotic patients' sera resulted in increased VCAM-1 and ICAM-1, and reduced VE-cadherin expression (p<0.05) at the cell surface. Production and release of VWF to the ECM were higher (p<0.05), with increased platelet adhesion after perfusing whole blood, being more noticeable in response to sera from non-treated patients. Furthermore, intracellular activation of Akt, p44/42, IkBa and JAK2/STAT3 was observed. Moreover, plasma levels of VWF, TNF-R1, VCAM-1, thrombomodulin, and angiopoietin-2 were higher in JAK2V617F+ MPN patients with thrombosis.

CONCLUSION

 The present findings suggest that circulating factors in MPNs with SVT debut induce endothelial proinflammatory and prothrombotic phenotypes, which are modulated in vitro with MPN treatment.

A Review About the Assessment of the Bleeding and Thrombosis Risk for Patients With Myeloproliferative Neoplasms Scheduled for Surgery

Myeloproliferative neoplasms (MPNs) present a unique challenge in surgical management due to their inherent predisposition to both bleeding and thrombosis. MPNs are a heterogenous group of acquired clonal conditions. The three classic MPNs are essential thrombocythemia (ET), myelofibrosis (PMF), and polycythemia vera (PV). All subtypes of MPN are associated with both thrombotic and bleeding complications. There are four risk categories for thrombosis in MPN patients: age, thrombosis history, and JAK-2 mutation. They are further classified as very low, low, intermediate, and high risk. The genetic landscape of MPN is fascinating and complex like all myeloid disorders. Bleeding risk can be assessed through leukocytosis, thrombocytosis, acquired von Willebrand syndrome (AVWS), and a previous history of bleeding in a patient. Risk assessment and perioperative management are important aspects of improving the quality of life and preventing complications in surgeries. Preoperative management includes a risk assessment of venous thromboembolism, use of appropriate pharmacological treatment, platelet count control, and correction and cardiovascular risk factors. This review summarizes the assessment of bleeding and thrombosis risk for patients with MPNs scheduled for surgery. Furthermore, this review discusses various tools that can be used to identify MPN patients at risk of thrombosis prior to surgery.

Impact of Tyrosine Kinase Inhibitors Applied for First-Line Chronic Myeloid Leukemia Treatment on Platelet Function in Whole Blood of Healthy Volunteers In Vitro

The tyrosine kinase inhibitors (TKIs) imatinib, dasatinib, bosutinib, and nilotinib are established for first-line treatment of chronic myeloid leukemia (CML) but may cause side effects such as bleeding and thrombotic complications. We investigated the impact of TKIs on platelet function ex vivo in anticoagulated whole blood (WB) samples from healthy adults by lumiaggregometry and PFA-100 test. Samples (n = 15 per TKI) were incubated for 30 minutes with TKI at therapeutically relevant final concentrations. Aggregation and ATP release were induced by collagen (1 µg/mL), arachidonic acid (0.5 mmol/L), and thrombin (0.5 U/mL). Imatinib, bosutinib, and nilotinib significantly increased collagen-induced aggregation compared with controls. In addition, for bosutinib and nilotinib, a significant increase in aggregation after induction with arachidonic acid was detected. ATP-release and PFA-100 closure times were not influenced significantly by these three TKI. In contrast, dasatinib demonstrated a concentration-dependent inhibition of collagen-induced aggregation and ATP release and a significant prolongation of the PFA-100 closure time with the collagen/epinephrine cartridge. Aggregation and ATP release by other agonists as well as closure time with the collagen/ADP cartridge were not influenced significantly. In conclusion, we clearly show a concentration-dependent inhibition of collagen-induced platelet function in WB by dasatinib confirming prior results obtained in platelet-rich plasma. Bosutinib and nilotinib exerted no impairment of platelet activation. On the contrary, both TKI showed signs of platelet activation. When comparing our results with existing data, imatinib in therapeutic relevant concentrations does not impair platelet function.

JAK2V617F mutation and circulating extracellular vesicles in essential thrombocythemia

The clinical course of essential thrombocythemia (ET) is complicated with thrombosis which significantly impacts patients' mortality. Studies have identified JAK2V617F mutation as an independent risk factor for thrombosis. Circulating extracellular vesicles (EVs) were evaluated in several studies regarding myeloproliferative neoplasms and thrombosis as potential biomarkers. The present study investigates the relationship between JAK2V617F mutation and EVs levels in 119 ET patients. Our analyses revealed that JAK2V617F-positive patients are at a significantly increased risk of thrombosis within five years before the ET diagnosis (hazard ratio [95% CI]: 11.9 [1.7-83.7], P = 0.013), and that JAK2V617F mutation is an independent risk factor for thrombosis at ET diagnosis or during the follow-up (hazard ratio [95% CI]: 3.56 [1.47-8.62], P = 0.005). ET patients have higher levels of platelet-EVs, erythrocyte-EVs and procoagulant activity of EVs than the healthy population. Absolute and relative counts of platelet-EVs are increased in the presence of JAK2V617F mutation (P = 0.018, P = 0.024, respectively). In conclusion, our results support the role of JAK2V617F mutation in the pathogenesis of thrombosis in essential thrombocythemia through enhancing platelet activation.

Philadelphia-negative myeloproliferative neoplasms display alterations in monocyte subpopulations frequency and immunophenotype

Philadelphia-negative myeloproliferative neoplasms (MPN) are clonal hematological diseases associated with driver mutations in JAK2, CALR, and MPL genes. Moreover, several evidence suggests that chronic inflammation and alterations in stromal and immune cells may contribute to MPN’s pathophysiology. We evaluated the frequency and the immunophenotype of peripheral blood monocyte subpopulations in patients with polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (MF). Peripheral blood monocytes from PV (n = 16), ET (n = 16), and MF (n = 15) patients and healthy donors (n = 10) were isolated and submitted to immunophenotyping to determine the frequency of monocyte subpopulations and surface markers expression density. Plasma samples were used to measure the levels of soluble CD163, a biomarker of monocyte activity. PV, ET, and MF patients presented increased frequency of intermediate and non-classical monocytes and reduced frequency of classical monocytes compared to controls. Positivity for JAK2 mutation was significantly associated with the percentage of intermediate monocytes. PV, ET, and MF patients presented high-activated monocytes, evidenced by higher HLA-DR expression and increased soluble CD163 levels. The three MPN categories presented increased frequency of CD56⁺ aberrant monocytes, and PV and ET patients presented reduced frequency of CD80/86⁺ monocytes. Therefore, alterations in monocyte subpopulations frequency and surface markers expression pattern may contribute to oncoinflammation and may be associated with the pathophysiology of MPN.

Comparative Mutational Profiling of Hematopoietic Progenitor Cells and Circulating Endothelial Cells (CECs) in Patients with Primary Myelofibrosis

A role of endothelial cells (ECs) in Primary Myelofibrosis (PMF) was supposed since JAK2 mutation was found in endothelial precursor cells (EPCs) and in ECs captured by laser microdissection. By Cell Search method, the circulating endothelial cells (CECs) from 14 PMF patients and 5 healthy controls have been isolated and compared by NGS with CD34+Hematopoietic stem and progenitors cells (HSPCs) for panel of 54 myeloid-associated mutations. PMF patients had higher levels of CECs. No mutation was found in HSPCs and CECs from controls, while CECs from PMF patients presented several somatic mutations. 72% of evaluable patients shared at least one mutation between HSPCs and CECs. 2 patients shared the JAK2 mutation, together with ABL1, IDH1, TET2 and ASXL1, KMT2A, respectively. 6 out of 8 shared only NON MPN-driver mutations: TET2 and NOTCH1 in one case; individual paired mutations in TP53, KIT, SRSF2, NOTCH1 and WT1, in the other cases. In conclusion, 70% of PMF patients shared at least one mutation between HSPCs and CECs. These latter harbored several myeloid-associated mutations, besides JAK2V617F mutation. Our results support a primary involvement of EC in PMF and provide a new methodological approach for further studies exploring the role of the “neoplastic” vascular niche.

Causes of erythrocytosis and its impact as a risk factor for thrombosis according to etiology: experience in a referral center in Mexico City

Background

Thrombotic events are well documented in primary erythrocytosis, but it is uncertain if secondary etiologies increase the risk of thrombosis. This study aimed to determine the causes of erythrocytosis and to identify its impact as a risk factor for thrombosis.

Methods

Data were obtained from patients with erythrocytosis between 2000 and 2017 at a referral hospital in Mexico City. Erythrocytosis was defined according to the 2016 WHO classification. Time to thrombosis, major bleeding, or death were compared among groups of patients defined by the etiology of erythrocytosis using a Cox regression model, adjusting for cardiovascular risk factors.

Results

In total, 330 patients with erythrocytosis were studied. The main etiologies of erythrocytosis were obstructive sleep apnea (OSA) in 29%, polycythemia vera (PV) in 18%, and chronic lung disease (CLD) in 9.4% of the patients. The incidence rate of thrombosis was significantly higher in patients with PV and CLD than that in patients with OSA (incidence rates of 4.51 and 6.24 vs. 1.46 cases per 100 person-years, P=0.009), as well as the mortality rate (mortality rates of 2.72 and 2.43 vs. 0.17 cases per 100 person-years, P =0.003).

Conclusion

The risk of thrombosis in CLD with erythrocytosis was comparable to that in patients with PV. Further larger-scale studies are needed to confirm these findings and evaluate the benefits of preventive management of COPD with erythrocytosis similar to PV.

Impact of platelets on major thrombosis in patients with a normal white blood cell count in essential thrombocythemia

Objectives

Cell counts have a significant impact on the complex mechanism of thrombosis in patients with essential thrombocythemia (ET). We recently demonstrated a considerable impact of white blood cell (WBC) counts on thrombotic risk in patients with optimized platelet counts by analysing a large anagrelide registry. In contrast, the current analysis of the registry aimed to estimate the influence of platelet counts on thrombotic risk in patients with optimized WBC counts.

Methods

Cox regression analysis and Kaplan‐Meier plot were applied on all patients in the registry with optimized WBC counts.

Results

By using the calculated cut‐off of 593 G/L for platelets, Cox regression analysis revealed a clear influence of elevated platelet counts on the occurrence of a major thrombotic event (P < .001). A Kaplan‐Meier plot revealed a markedly shorter time to a major thrombotic event for patients with platelet counts above the cut‐off (P < .001).

Conclusions

The data show clear impact of platelet lowering on the thrombotic risk in ET patients with normal WBC counts. Therefore, selective platelet lowering with anagrelide appears sufficient for thrombotic risk reduction in WHO‐diagnosed ET patients lacking leukocytosis.

Thrombotic, inflammatory, and HIF-regulated genes and thrombosis risk in polycythemia vera and essential thrombocythemia

Thrombosis is a major cause of morbidity and mortality in polycythemia vera (PV) and essential thrombocythemia (ET). The pathophysiology of thrombosis in these disorders remains unclear, and we hypothesized that upregulation of thrombotic, inflammatory, and hypoxia-inducible factor (HIF)-regulated genes may play a role in it. We performed unbiased RNA sequencing in granulocytes and platelets of PV patients and found differential expression of several thrombotic, inflammatory, and HIF-regulated genes. The expression of many of these genes positively correlated with JAK2 expression and JAK2V617F allelic burden. We then validated these findings by quantitative polymerase chain reaction analyses of selected gene transcripts in a larger number of PV and ET granulocytes and platelets (58 patients) and in 28 controls, and we compared these findings in patients with and without thrombosis. The study included 29 females and 29 males; of these, 28 had a history of thrombosis. We found that transcripts of several selected genes were upregulated in patients with PV or ET compared with controls. In granulocytes, the expression levels of F3, SELP, VEGFA, and SLC2A1 were significantly higher in patients with a history of thrombosis compared with those who did not have thrombosis. Patients with a history of thrombosis have significantly higher expression of IL1RAP (P < .05) in platelets compared with those without thrombosis. Our study confirms the presence of a thrombo-inflammatory state and augmented HIF activity in PV and ET and its role in thrombosis. These data may provide the background for targeted therapies in PV and ET.

From Budd-Chiari syndrome to acquired von Willebrand syndrome: thrombosis and bleeding complications in the myeloproliferative neoplasms

Thrombotic and hemorrhagic complications are prevalent in patients with essential thrombocythemia, polycythemia vera, and myelofibrosis. Given the impact on morbidity and mortality, reducing the risk of thrombosis and/or hemorrhage is a major therapeutic goal. Historically, patients have been risk stratified on the basis of traditional factors, such as advanced age and thrombosis history. However, multiple factors contribute to the thrombotic tendency, including gender, mutational profile, inflammatory stress, and abnormal cell adhesion. Management includes cardiovascular risk reduction and use of antiplatelet therapy, depending on myeloproliferative neoplasm subtype and mutational status. Anticoagulation is a mainstay of therapy for those with venous thrombosis, but practice patterns remain heterogeneous. Cytoreduction is indicated for higher-risk patients, but efficacy may depend on the involved vascular bed. Management of special situations, such as unusual site thrombosis, bleeding, the perioperative period, and pregnancy, are especially challenging. In this article, risk factors and treatment strategies for myeloproliferative neoplasm thrombosis and bleeding, including special situations, are reviewed. Insights gained from recent studies may lead to the development of a more precise risk classification and tailored therapy.

From Budd-Chiari syndrome to acquired von Willebrand syndrome: thrombosis and bleeding complications in the myeloproliferative neoplasms

Thrombotic and hemorrhagic complications are prevalent in patients with essential thrombocythemia, polycythemia vera, and myelofibrosis. Given the impact on morbidity and mortality, reducing the risk of thrombosis and/or hemorrhage is a major therapeutic goal. Historically, patients have been risk stratified on the basis of traditional factors, such as advanced age and thrombosis history. However, multiple factors contribute to the thrombotic tendency, including gender, mutational profile, inflammatory stress, and abnormal cell adhesion. Management includes cardiovascular risk reduction and use of antiplatelet therapy, depending on myeloproliferative neoplasm subtype and mutational status. Anticoagulation is a mainstay of therapy for those with venous thrombosis, but practice patterns remain heterogeneous. Cytoreduction is indicated for higher-risk patients, but efficacy may depend on the involved vascular bed. Management of special situations, such as unusual site thrombosis, bleeding, the perioperative period, and pregnancy, are especially challenging. In this article, risk factors and treatment strategies for myeloproliferative neoplasm thrombosis and bleeding, including special situations, are reviewed. Insights gained from recent studies may lead to the development of a more precise risk classification and tailored therapy.

Polycythemia Vera-Associated Complications: Pathogenesis, Clinical Manifestations, And Effects On Outcomes

Polycythemia vera is a Philadelphia-negative chronic myeloproliferative neoplasm, characterized by erythrocytosis, which is unique, compared to essential thrombocytosis and primary myelofibrosis. Though longevity can usually be expected, vascular morbidity is associated with this condition, as well as a propensity to evolve into myelofibrosis (post-PV MF) and acute myeloid leukemia. In addition, patients can have a pronounced symptom burden. Herein, contributors to the symptomatic burden, as well as the thrombotic and transformative tendencies are reviewed. From a symptom perspective, some are explained by cytokine release, others by microvascular complications, whereas certain symptoms can herald disease evolution. Thrombosis has multifactorial contributors, including but not limited to gender, and inflammatory stress; investigators have recently hypothesized that microparticles and Neutrophil Extracellular Trap Formations may add to thrombotic burden. Finally, we examine the progression to post-PV MF as well as leukemic transformation, highlighting well-established risk factors including age and leukocytosis, certain treatments, and the presence of “non-driver” mutations.

Bleeding signs due to acquired von Willebrand syndrome at diagnosis of chronic myeloid leukaemia in children

A considerable proportion of patients with chronic myeloid leukaemia (CML) may present at diagnosis with high platelet counts. This may result in thrombosis or bleeding complications due to binding of von Willebrand factor (VWF) multimers to platelets. Paediatric CML is very rare and no systematic investigation on clinical complications of elevated platelets has been reported. Data on platelet count and associated haemostaseological complications were retrospectively analysed in a cohort of 156 children with CML. Fifty-one percent (81/156) patients presented with thrombocytosis (platelet count> 500 × 10⁹ /l), and were extreme (>1 000 × 10⁹ /l) in 23/156 (16%). There were no cases of thrombosis but mild bleeding signs were present in 12% (n = 9) children with thrombocytosis. Bleeding occurred without correlation to elevated platelet counts and was associated with reduced large VWF multimers, indicating a diagnosis of acquired von Willebrand syndrome (AVWS), which resolved after initiation of CML treatment. Patients with paediatric CML frequently exhibit high platelet counts not resulting in thrombosis. In patients with thrombocytosis mild bleeding signs due to a low percentage of large VWF multimers can be demonstrated. AVWS may be underdiagnosed in paediatric CML (Clinical-Trials.gov NCT00445822, 9 March 2007).

Re-evaluation of hematocrit as a determinant of thrombotic risk in erythrocytosis

Here we critically evaluate the role of elevated hematocrit as the principal determinant of thrombotic risk in polycythemia and erythrocytosis, defined by an expansion of red cell mass. Since red cell volume determination is no longer readily available, in clinical practice, polycythemia and erythrocytosis are defined by elevated hemoglobin and hematocrit. Thrombosis is common in Chuvash erythrocytosis and polycythemia vera. Although the increased thrombotic risk is assumed to be due to the elevated hematocrit and an associated increase in blood viscosity, thrombosis does not accompany most types of erythrocytosis. We review studies indicating that the occurrence of thrombosis in Chuvash erythrocytosis is independent of hematocrit, that the thrombotic risk is paradoxically increased by phlebotomy in Chuvash erythrocytosis, and that, when compared to chemotherapy, phlebotomy is associated with increased thrombotic risk in polycythemia vera. Inherited and environmental causes that lead to polycythemia and erythrocytosis are accompanied by diverse cellular changes that could directly affect thrombotic risk, irrespective of the elevated hematocrit. The pressing issue in these disorders is to define factors other than elevated hematocrit that determine thrombotic risk. Defining these predisposing factors in polycythemia and erythrocytosis should then lead to rational therapies and facilitate development of targeted interventions.