Membrane Fluidity's Role In Platelet Function In Patients with Myeloproliferative Neoplasms

Patients with myeloproliferative neoplasms (MPN) frequently present thrombotic or haemorrhagic accidents, due to platelet function alterations. There are few published data referring to the biochemical alterations of platelet membrane in patients with MPN. The aim of our study was to determine whether changes of platelet membrane fluidity may be correlated with the modified expression of platelet receptors and altered platelet function in MPN.

This retrospective study included 71 patients with MPN: 21 chronic myeloid leukemia (CML), 13 primary myelofibrosis (PM), 24 essential thrombocytemia (ET) and 13 primary polycytemia (PP), as well as 10 healthy volunteers. Platelet function was analyzed by optical platelet aggregometry using as agonists ADP, collagen, ristocetin and epinephrine. The determination of platelet membrane fluidity was performed by fluorescence anisotropy measurements using as marker 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate (TMA DPH). Depending on platelet response to different reagents used for platelet aggregation, we divided the MPN patients into two groups: patients with normal response (amplitude greater than 60%) and patients with absent/ low response. Platelet receptor expression was analyzed by flowcytometry for adhesion markers (CD 42a and CD 42b) and aggregation markers (CD61, CD41).

Patients with MPN have a lower membrane fluorescence anisotropy (high fluidity) compared to controls (0.1528 vs 0.2531, P< 0.0001). The results are similar to those reported in literature (Breuer et all., Haemostasis, 1981). Patients with altered response for ristocetin (altered response of GP Ib receptor) have a higher membrane anisotropy corresponding to a decrease in membrane fluidity (altered response 0.2286 vs normal response 0.1391, P = 0.006). Patients with abnormal response for ristocetin have a platelet fluorescence anisotropy close to that obtained in the control group (0.228 vs 0.268, P=0.15). No statistically significant differences were obtained for other reagents (ADP 0.1425 vs. 0.1581, collagen 0.1557 vs. 0.1489, epinephrine 0.1430 vs. 0.1534). The ristocetin‘s amplitude curve correlates with decreased membrane fluorescence anisotropy (increased fluidity), with a nonlinear correlation (r = -0.6373, P=0.04). The CD42b expression (GP Ib) is low in patients versus controls (median: 14.57% vs 96.26%, P<0.01), unaccompanied by a similar difference in the CD42a value range (P=0.448). The CD61/CD41 expression (GP IIbIIIa) presents also lower values in patients (median: CD 61= 87.14%; CD 41=74.56%) versus controls (median: CD 61= 98.98%; CD 41=91.27%) but only the differences for CD61 are statistically significant (P=0.05 versus 0.064 for CD41).

MPN patients have a lower expression of platelet receptors and an increased membrane fluidity. Increased fluidity of platelet membranes correlates with a better response to ristocetin, although platelet receptor expressions are low. Possible explanations are the abnormal expression of GP Ib receptors and/or the altered signaling pathways in patients with MPN.

No relevant conflicts of interest to declare.