Impact of white blood cells on thrombotic risk in patients with optimized platelet count in essential thrombocythemia

The role of leukocytes in myeloproliferative neoplasm thromboinflammation

Classic myeloproliferative neoplasms lacking the Philadelphia chromosome are stem cell disorders characterized by the proliferation of myeloid cells in the bone marrow and increased counts of peripheral blood cells. The occurrence of thrombotic events is a common complication in myeloproliferative neoplasms. The heightened levels of cytokines play a substantial role in the morbidity and mortality of these patients, establishing a persistent proinflammatory condition that culminates in thrombosis. The etiology of thrombosis remains intricate and multifaceted, involving blood cells and endothelial dysfunction, the inflammatory state, and the coagulation cascade, leading to hypercoagulability. Leukocytes play a pivotal role in the thromboinflammatory process of myeloproliferative neoplasms by releasing various proinflammatory and prothrombotic factors as well as interacting with other cells, which contributes to the amplification of the clotting cascade and subsequent thrombosis. The correlation between increased leukocyte counts and thrombotic risk has been established. However, there is a need for an accurate biomarker to assess leukocyte activation. Lastly, tailored treatments to address the thrombotic risk in myeloproliferative neoplasms are needed. Therefore, this review aims to summarize the potential mechanisms of leukocyte involvement in myeloproliferative neoplasm thromboinflammation, propose potential biomarkers for leukocyte activation, and discuss promising treatment options for controlling myeloproliferative neoplasm thromboinflammation.

Philadelphia chromosome-negative myeloproliferative chronic neoplasms: is clonal hematopoiesis the main determinant of autoimmune and cardio-vascular manifestations?

In this article, we reviewed the possible mechanisms linking the clonal hematopoiesis of indeterminate potential (CHIP) to chronic myeloproliferative neoplasms (MPNs), autoimmune diseases (ADs), and cardiovascular diseases (CADs). CHIP is characterized by the presence of clonal mutations with an allelic frequency >2% in the peripheral blood without dysplasia, overt hematological neoplasms, or abnormalities in blood cell count. The prevalence may reach 20% of elderly healthy individuals and is considered a risk factor for myelodysplastic neoplasms and acute leukemia. In MPNs, CHIP is often associated with mutations such as JAK2V617F or DNMT3A, TET2, or ASXL1, which exhibit a 12.1- and 1.7-2-fold increase in CADs. Specifically, JAK2-mutated cells produce excessive cytokines and reactive oxygen species, leading to proinflammatory modifications in the bone marrow microenvironment. Consequently, the likelihood of experiencing thrombosis is influenced by the variant allele frequency (VAF) of the JAK2V617F mutation, which also appears to be correlated with anti-endothelial cell antibodies that sustain thrombosis. However, DNMT3A mutations induce pro-inflammatory T-cell polarization and activate the inflammasome complex, while TET2 downregulation leads to endothelial cell autophagy and inflammatory factor upregulation. As a result, in patients with TET2 and DNMT3A-related CHIP, the inflammasome hyperactivation represents a potential cause of CADs. CHIP also occurs in patients with large and small vessel vasculitis, while ADs are more frequently associated with MPNs. In these diseases, monocytes and neutrophils play a key role in the formation of neutrophil extracellular trap (NET) as well as anti-endothelial cell antibodies, resulting in a final procoagulant effect. ADs, such as systemic lupus erythematosus, psoriasis, and arthritis, are also characterized by an overexpression of the Rho-associated coiled-coil containing protein kinase 2 (ROCK2), a serine/threonine kinase that can hyperactivate the JAK-STAT pathway. Interestingly, hyperactivation of ROCK2 has also been observed in myeloid malignancies, where it promotes the growth and survival of leukemic cells. In summary, the presence of CHIP, with or without neoplasia, can be associated with autoimmune manifestations and thrombosis. In the presence of these manifestations, it is necessary to consider a "disease-modifying therapy" that may either reduce the clonal burden or inhibit the clonally activated JAK pathway.

The pathobiology of thrombosis, microvascular disease, and hemorrhage in the myeloproliferative neoplasms

Thrombotic, vascular, and bleeding complications are the most common causes of morbidity and mortality in the Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). In these disorders, circulating red cells, leukocytes, and platelets, as well as some vascular endothelial cells, each have abnormalities that are cell-intrinsic to the MPN driver mutations they harbor (eg, JAK2 V617F). When these cells are activated in the MPNs, their interactions with each other create a highly proadhesive and prothrombotic milieu in the circulation that predisposes patients with MPN to venous, arterial, and microvascular thrombosis and occlusive disease. Bleeding problems in the MPNs are caused by the MPN blood cell-initiated development of acquired von Willebrand disease. The inflammatory state created by MPN stem cells in their microenvironment extends systemically to amplify the clinical thrombotic tendency and, at the same time, preferentially promote further MPN stem cell clonal expansion, thereby generating a vicious cycle that favors a prothrombotic state in these diseases.

Austrian recommendations for the management of essential thrombocythemia

According to the World Health Organization (WHO) classification, essential (primary) thrombocythemia (ET) is one of several Bcr-Abl negative chronic myeloproliferative neoplasms (MPN). The classical term MPN covers the subcategories of MPN: ET, polycythemia vera (PV), primary myelofibrosis (PMF), and prefibrotic PMF (pPMF). ET is marked by clonal proliferation of hematopoietic stem cells, leading to a chronic overproduction of platelets. At the molecular level a JAK2 (Janus Kinase 2), calreticulin, or MPL mutation is found in the majority of patients. Typical ongoing complications of the disease include thrombosis and hemorrhage. Primary and secondary prevention of these complications can be achieved with platelet function inhibitors and various cytoreductive drugs including anagrelide, hydroxyurea and interferon. After a long follow up, in a minority of ET patients the disease transforms into post-ET myelofibrosis or secondary leukemia. Overall, life expectancy with ET is only slightly decreased.

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.

Genetic polymorphisms and expression of NLRP3 inflammasome-related genes are associated with Philadelphia chromosome-negative myeloproliferative neoplasms

Inflammation plays a crucial role in the initiation, progression and prognosis of Philadelphia chromosome-negative myeloproliferative neoplasms (MPN), which could be clinically subdivided into polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Nucleotide binding domain (NOD)-like receptor protein 3 (NLRP3) inflammasomes affect inflammatory diseases and carcinomas by excessive production of cytokines. To investigate a possible association of NLRP3 inflammasome signaling with MPN, we investigated the expression of selected inflammasome-related genes from bone marrow cells of 67 MPN patients as well as gene polymorphisms in NLRP3 (rs35829419), NF-κB1 (rs28362491), CARD8 (rs2043211), IL-1β (rs16944), and IL-18 (rs1946518). It showed that inflammasome-related genes (NLRP3, NF-κB1, CARD8, IL-1β, and IL-18) were highly expressed in BM cells from MPN patients and the increased expression was associated with JAK2^V617F mutation, white blood cell counts and splenomegaly. Analysis of genetic polymorphisms in 269 MPN patients and 291 healthy controls demonstrated that NF-κB1 (rs28362491) was associated with MPN and increased expression of NF-κB1, NLRP3 and IL-1β. This research provided novel biomarkers and potential targets for MPN.

Essential Thrombocythemia and Acquired von Willebrand Syndrome: The Shadowlands between Thrombosis and Bleeding

Over the past decade, new insights have emerged on the pathophysiology of essential thrombocythemia (ET), its clinical management, and associated thrombohemostatic disturbances. Here, we review the latest diagnostic and risk stratification modalities of ET and its therapeutics. Moreover, we discuss the clinical evidence-based benefits, deriving from major clinical trials, of using cytoreductive therapy and antiplatelet agents to lower the risk of fatal vascular events. Also, we focus on the condition of extreme thrombocytosis (>1000 × 10⁹/L) and bleeding risk, the development and pathogenesis of acquired von Willebrand syndrome, and the clinical approach to this paradoxical scenario in ET.

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.

Efficacy and safety of anagrelide as a first-line drug in cytoreductive treatment-naïve essential thrombocythemia patients in a real-world setting

Objective

This study aimed to retrospectively assess the efficacy and safety of anagrelide in cytoreduction therapy‐naïve essential thrombocythemia (ET) patients in a real‐world setting.

Method

Data from 53 ET patients who received anagrelide as a first‐line therapy were reviewed for patient characteristics, antiplatelet status, cytoreduction status, therapeutic effects, adverse events, thrombohemorrhagic event development, progression to myelofibrosis or acute leukemia, and cause of death.

Results

The rate of achieving a platelet count of <600 × 10⁹/L during anagrelide monotherapy was 83.0%. Adverse events occurred in 32 of 53 patients, and tended to be slightly more severe in patients with cardiac failure; however, they were mostly tolerable. The therapeutic effect of anagrelide was consistent, regardless of genetic mutation profiles. The incidence of anemia as an adverse event was significantly higher in the CALR mutation‐positive group. Favorable platelet counts were also achieved in patients for whom hydroxyurea was introduced as a replacement for anagrelide or in addition to anagrelide because of unresponsiveness or intolerance to treatment.

Conclusion

In Japanese cytoreduction therapy‐naïve ET patients, anagrelide administration as a first‐line therapy demonstrated favorable effects in reducing platelet counts, and its safety profile that was generally consistent with those in previous reports.

Response to aspirin therapy in patients with myeloproliferative neoplasms depends on the platelet count

Patients with myeloproliferative neoplasms (MPN) are at an increased risk of thrombotic events even during antiplatelet therapy with aspirin. In the current study, we sought to investigate the association of the platelet count with the inhibitory potential of antiplatelet therapy in MPN. We determined arachidonic acid (AA)- and adenosine diphosphate (ADP)-inducible platelet reactivity by multiple electrode aggregometry in 93 patients with essential thrombocythemia, polycythemia vera or primary myelofibrosis. In patients without aspirin therapy (n = 44), the platelet count did not correlate with platelet aggregation. In aspirin-treated patients (n = 49), we observed a moderate correlation of residual AA-inducible platelet aggregation with the platelet count (r = 0.49; P < 0.001). Further, patients with high on-treatment residual platelet reactivity to AA (HRPR AA) had a significantly higher platelet count than patients without HRPR AA (547 × 10⁹/L [340 - 644 × 10⁹/L] vs 358 × 10⁹/L [242 - 501 × 10⁹/L], P = 0.01). Receiver-operating characteristic curve analysis revealed a platelet count of ≥317 × 10⁹/L as best threshold to distinguish between patients without and with HRPR AA (area under the curve: 0.73). After adding the direct ADP P2Y₁₂ inhibitor cangrelor to blood samples from all 93 patients in vitro, residual ADP-inducible platelet reactivity correlated weakly with the platelet count (r = 0.26, P = 0.01), but the platelet count did not differ significantly between patients with and without HRPR ADP (396 × 10⁹/L [316 - 644 × 10⁹/L] vs 340 × 10⁹/L [241 - 489 × 10⁹/L]; P = 0.2). In conclusion, our findings suggest that the extent of platelet inhibition by aspirin in patients with MPN at least in part depends on their individual platelet count.