Platelet Functions and Risk Prognosis in Myelodysplastic Syndromes,

Abstract 3806

The myelodysplastic syndromes (MDS) are a heterogenous group of clonal stem cell disorders with peripheral cytopenias and increased incidence of leukemic transformation.

The prognosis of MDS is determined by several factors, including the presence of specific cytogenetic abnormalities, the percentage of blastoid cells in bone marrow and peripheral blood, the number of affected cell lineages, and transfusion dependency. The most commonly used risk stratification system is the International Prognostic Scoring System (IPSS). This score divides patients into a lower risk subset (low and intermediate-1) and a higher risk subset (intermediate-2 and high).

Patients with MDS may have hemorrhagic complications with serious outcomes that are among the major causes of death in this population. These bleeding episodes that are often related to thrombocytopenia also occur in MDS patients with normal platelet count.

The aim of this work was to study functional characteristics of platelets in MDS patients and their relationship to risk evaluated as indicated by IPSS.

Eighty diagnosed MDS patients risk-stratified according to IPSS were included: 40 with low-risk, 29 with intermediate-1-risk (I-1), 8 with intermediate-2-risk (I-2) and 3 with high-risk. Eighty healthy donors were included as control group.

Platelet-related primary haemostasis was evaluated with an automated platelet function analyzer (PFA-100®, Siemens Healthcare Diagnostics). Samples of citrated blood were aspirated under a shear rate of 4,000–5,000/s through a 150-μm aperture cut into a collagen-ADP (COL-ADP) or collagen-epinephrine (COL-EPI) coated membrane. The platelet haemostatic capacity is indicated by the time required for the platelet plug to occlude the aperture (closure time, CT), which is expressed in seconds.

Platelet activation was determined through FITC-PAC-1 (a mAb that recognizes activated conformation of fibrinogen receptor) and FITC-P-selectin mAb binding to quiescent and 100 μM TRAP activated platelets by flow cytometry. Surface expression of fibrinogen receptor (αIIb and β3 subunits) was determined by flow cytometry with specific mAbs.

Apoptosis was determined by flow cytometry analysis through FITC-annexin V binding to platelet membrane phosphatidylserine (PS) exposed in basal conditions.

I-2 and high-risk patients were gathered together in a high-risk group in order to analyze experimental results. Statistical analysis was performed with one-way ANOVA and Tukey test.

CTs obtained with COL-EPI and COL-ADP cartridges in controls and low risk patients were similar and significantly shorter than CTs observed in I-1-risk and high-risk MDS patients (p<0.05).

Platelets from all MDS patients showed a reduced capability for being activated by 100 μM TRAP. This impairment was more evident in I-1-risk and high-risk patients: PAC-1 binding, in arbitrary units (AU), was 11368±1017 in controls; 7849±789 in low-risk MDS (p<0.05); 4161±591 in I-1-risk MDS (p<0.01 versus control and p<0.05 versus low-risk) and 492±184 in high-risk MDS (p<0.01 versus control and p<0.05 versus low-risk). The platelet surface expression of P-selectin induced by 100 μM TRAP was also reduced: 5102±340 AU in controls, 3318±400 AU in low-risk MDS (p<0.05); 1880 ±197 AU in I-1-risk MDS (p<0.05 versus control and versus low-risk), and 1211±130 AU in high-risk MDS (p<0.05 versus control and versus low-risk). Diminished responses to TRAP were not due to a reduction in surface expression of fibrinogen receptor in platelets from MDS patients.

Platelets from MDS patients expressed more PS than controls under basal conditions. Mean fluorescence values for FITC-annexin binding were: 383±16 in controls; 444±21 in low-risk (p<0.05); 575±52 in I-1-risk MDS (p<0.05 versus control and versus low-risk); 611±17 in high-risk MDS (p<0.05 versus control and versus low-risk).

Our results indicated that platelets from MDS patients had less ability to be activated and were more apoptotic than control ones. These dysfunctions were more pronounced when the risk of the disease was higher according to IPSS.