Hemorrhagic risk due to platelet dysfunction in myelodysplastic patients, correlations with anemia severity and iron overload.

Platelet function is influenced by changes in membrane fluidity that has an important role in the expression of platelet receptors and in modulating the activity of proteins like phospholipase C or proteinkinase C. In freshly prepared platelets, membrane fluidity modifies the aggregation/agglutination function. Reactive oxygen species (ROS) represent another important parameter involved in platelet receptor activation. There is a certain association of high levels of ROS and iron overload. Patients with hemochromatosis have low platelet aggregation induced by thrombin; little is known about the anemia and effects of iron overload on platelet activation in myelodysplastic syndromes (MDS) patients. Study of platelet membrane fluidity and ROS production changes in patients with MDS and possible correlations with altered platelet function as reflected in aggregation curves and platelet receptor expression. To find out possible correlations of fluidity of platelet membrane and ROS level with hematologic parameters and iron levels. The prospective study included 34 patients with myelodysplastic syndromes classified according to French-American-British cooperative group proposals and 29 healthy volunteers. Platelet membrane fluidity was quantified by fluorescence anisotropy measurements using the marker 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate. ROS production was evaluated by fluorescence measurements using 2',7'-dichlorodihydrofluorescein diacetate. Platelet function was analyzed by optical aggregometry using the agonists adenosine diphosphate, collagen, ristocetin and epinephrine. The expression of platelet receptors CD41/CD61, CD42a/CD42b and CD62P/CD63 was evaluated by flow cytometry. Platelet membrane fluidity in patients with MDS was similar to that of healthy volunteers and did not vary according to the risk category. Patients with MDS had increased platelet ROS production compared with the control group without statistical correlation with membrane fluidity. We found a negative correlation of ROS levels with the severity of anemia (R =  -0.587, P = 0.017). Platelet response was reduced in patients with MDS compared with volunteers, for all reagents. The response was different according to the risk category only in case of ristocetin or collagen. Patients with anemia presented a decreased platelet aggregation induced by collagen or ristocetin (collagen: R = 0.395, P = 0.003; ristocetin: R = 0.420, P = 0.002). The membrane fluidity of platelets from MDS patients appeared unmodified, but the ROS production was increased in all risk categories of MDS. The levels of ROS were correlated with the degree of anemia, which, in turn, had a negative impact on the platelet aggregation function induced by collagen or ristocetin.

Assessment of changes in membrane properties of platelets from patients with chronic myeloid leukaemia in different stages of the disease.

Patients with chronic myeloproliferative leukemia (CML) have frequent haemorrhage and/or thrombosis in their medical history. The mechanisms of these major and life-threatening complications remain unclear. Membrane organization influences many of the unique cellular functions and is strongly correlated, among other factors, to the membrane lipid composition; it may be evaluated by following up the membrane fluidity and aggregation properties of the platelet. In this study, we evaluated the platelet aggregation, the expression of platelet surface receptors, the membrane fluidity (as evaluated by fluorescence anisotropy) and its correlation to reactive oxygen species (ROS) production, in patients with chronic myeloid leukaemia (CML). It was found that the patients in accelerated and blastic phase of CML present an altered platelet aggregation response to all reagents except for ristocetin as compared with chronic phase group, which shows only epinephrine-altered response. We also found that BCR/ABL transcript leads to higher levels of ROS in accelerated and blastic CML phases. Patients without molecular remission have lower platelet membrane fluidity. We obtained a positive correlation between ROS level and membrane fluorescence anisotropy changes. The CD41 expression was decreased in CML patients and P selectin expression was found to be higher in these patients than in healthy volunteers. Platelets of CML patients have altered aggregation parameters in accelerated and blastic phases, in which BCR/ABL transcript level is increased. The increased level of ROS in CML patients without molecular remission is associated with a decrease in fluidity of platelet membrane and expression of CD41/CD61 receptors. These findings may contribute to understanding the mechanism of the altered platelet response reported in CML patients.