Clinical Significance Of Circulating Microparticles In Ph^- Myeloproliferative Neoplasms (MPN)

Microparticles (MPs) are small membrane vesicles that are classified as red blood cell MPs (RMPs), platelet-derived MPs (PMPs), tissue factor MPs (TF⁺MPs) and endothelial MPs (EMPs) based on their origins. Philadelphia chromosome-negative myeloproliferative neoplasms (Ph^-MPN) are disorders characterized by abnormal hematopoiesis, thrombosis, JAK2V617F mutation. Although MPs are considered as biomarkers reflecting procoagulant state in cancer patients, their involvement in the patients with Ph^-MPN remains unclear. Our objective in this study was to measure the alterations of the four MPs types in the patients with MPN and to evaluate their correlations with JAK2V617F mutation and some clinical complications, especially for thrombosis and splenomegaly.

Sixty-seven patients with MPN were enrolled in this study, including 12 polycythaemia vera (PV), 49 essential thrombocythemia (ET) and 6 primary myelofibrosis (PMF). 30 healthy donors were selected as normal controls. Venous blood was anticoagulated with sodium citrate (1:9). Using flow cytometry, plasma samples were measured for RMPs, PMPs, TF⁺MPs and EMPs with phycoerythrin (PE)-conjugated monoclonal antibodies CD235a, CD61, CD142, and CD62E, respectively. Forward scatter was set in scale using fluorescent microspheres of 0.8μm and standard fluorescent microbeads (0-0.8μm) in diameter were used to set the microparticle gate. Data were expressed as median (M) and interquartile range (IQR). Meanwhile, genomic DNA was extracted from mononuclear cells and amplified by allele specific polymerase chain reaction (PCR).

(1) Patients with MPN showed significantly higher plasma levels for all four MPs compared with healthy donors (P<0.05), namely 49.0/μl (15.8-109.5/μl) vs 21.0/μl (13.8-32.6/μl) for RMPs, 181.2/μl(75.8-1111.6/μl) vs 74.9/μl (55.5-115.4/μl) for PMPs, 48.1/μl (13.1-72.4/μl) vs 31.0/μl (14.9-47.6/μl) for TF⁺MPs and 310.2/μl (128.6-1130.5/μl) vs 155.9/μl (100.3-227.6/μl) for EMPs. (2) Among different subtypes of MPN, PMPs were higher in patients with PMF than patients with PV and ET (P<0.05), but there was no significant difference between PV and ET group. No obvious difference was found in RMPs, TF⁺MPs and EMPs among different subtypes of MPN patients. (3) MPN patients with JAK2V617F mutation (n=34) were found to have higher plasma levels of TF⁺MPs and RMPs than those without mutation (P<0.05) and this difference was not found for PMPs and EMPs. (4) MPN patients with various thrombotic complications (n=10) showed higher levels of all four types of MPs than those without thrombotic complications (n=31) (P<0.05). Elevated MP levels were also found in patients with splenomegaly (n=19) compared to those without splenomegaly (n=14) (P<0.05).

Higher levels of MPs were observed in MPN patients compared with healthy controls, especially in patients complicated with thrombosis and splenomegaly, which reflects a prothrombotic state. Moreover, significantly increased TF⁺MPs and RMPs were found in MPN patients with JAK2V617F mutatioin.

No relevant conflicts of interest to declare.