Relationship between clotting activity and phosphatidylserine expression on erythrocyte membranes in polycythemia vera patients with the JAK2 V617F mutation

Eryptosis in polycythemia vera and essential thrombocythemia*

Aim: Polycythemia vera (PV) and essential thrombocythemia (ET) are Philadelphia–negative myeloproliferative neoplasms with documented apoptosis impairment at the level of hematopoietic stem cell. However, so far no study has evaluated apoptosis of circulating blood neoplastic cells, including the suicidal death of erythrocytes – eryptosis. Material/Methods: Erythrocytes from 61 patients (24 PV and 37 ET) naïve to and treated with hydroxyurea (HU) and 13 healthy individuals were analysed using flow cytometry to quantify phosphatidylserine (PS) externalization from Annexin-V-binding, calpain activity from 7-amino-4-chloromethylcoumarin (CMAC)-fluorescence, cell volume from forward scattered light (FSC) and cell shape from side scattered light (SSC). Results: Significantly increased levels of calpain activity and PS exposure were observed in both ET and PV naïve patients, indicating enhanced eryptosis. Among HU-treated patients, a significant increase in calpain activity in the ET group and a decrease in the PV group were observed compared to patients without cytoreductive therapy. Among PV patients, FSC was substantially higher in the HU-treated group than in the naïve group, whereas no significant differences were found between HU-treated and HU-naïve groups of ET patients. Conclusions: The enhanced eryptosis in ET and PV patients may be a form of systemic compensation of the pathological bone marrow overproduction of erythrocytes. HU, the basic cytoreductive drug used in ET and PV, may affect eryptosis in PV and ET in different ways depending on disease. The JAK2V617F mutation was not observed to have any effect on eryptosis in ET.

Cerebral thrombosis and myeloproliferative neoplasms

Myeloproliferative neoplasms (MPN) are acquired clonal disorders characterized by the proliferation of bone marrow myeloid cells. Different somatic mutations have been recently associated with MPN, the most common being JAK-2 V617F. Among MPN, polycythemia vera and essential thrombocythemia are particularly associated with an increased risk to develop thrombotic complications, either arterial or venous. Cerebrovascular events (stroke and transient ischemic attacks) are prevalent, accounting for approximately two-thirds of all events. Also cerebral vein thrombosis can complicate MPN and can be the first manifestation of the disease. Risk factors for thrombosis in patients with MPN are related or unrelated to the disease. Among the former there are cellular risk factors, such as increased white blood cell counts, vascular cell activation, endothelial dysfunction, and plasmatic risk factors, such as increased plasma viscosity, reduced levels of protein S, increased thrombin generation. The latter include increased age and previous thrombotic events. In addition, common cardiovascular risk factors (smoking, hypertension, diabetes, dyslipidemia, obesity) contribute to the pathogenesis of arterial events, whereas circumstantial risk factors (particularly oral contraceptive use and pregnancy/puerperium) to that of venous events. Primary prevention of arterial thrombosis with antiplatelet therapy is warranted in the majority of patients with MPN, whereas primary prevention of venous thrombosis is limited to anticoagulant prophylaxis during high-risk situations. Secondary prevention includes long-term antiplatelet therapy for arterial and short- or long-term anticoagulant therapy for venous thrombosis, depending on the risk factors present at the first event.

Hypocholesterolemia in patients with polycythemia vera

Polycythemia vera (PV) is characterized by low serum total cholesterol despite its association with vascular events such as myocardial and cerebral infarction. Serum cholesterol level has not been used as a diagnostic criterion for PV since the 2008 revision of the WHO classification. Therefore, we revisited the relationship between serum lipid profile, including total cholesterol level, and erythrocytosis. The medical records of 34 erythrocytosis patients (hemoglobin : men, > 18.5 g/dL ; women, > 16.5 g/dL) collected between August 2005 and December 2011 were reviewed for age, gender, and lipid profiles. The diagnoses of PV and non-PV erythrocytosis were confirmed and the in vitro efflux of cholesterol into plasma in whole blood examined. The serum levels of total cholesterol, low-density-lipoprotein cholesterol (LDL-Ch), and apolipoproteins A1 and B were lower in PV than in non-PV patients. The in vitro release of cholesterol into the plasma was greater in PV patients than in non-PV and non-polycythemic subjects. Serum total cholesterol, LDL-Ch, and apolipoproteins A1 and B levels are lower in patients with PV than in those with non-PV erythrocytosis. The hypocholesterolemia associated with PV may be attributable to the sequestration of circulating cholesterol into the increased number of erythrocytes.