Study on Membrane Fluidity and Oxidative Stress of Platelets with Function Abnormalities in Myelodysplastic Syndromes

Platelet function is influenced by changes in membrane fluidity (MF) which has an important role in the expression of platelet receptors and in modulating the activity of proteins like phospholipase C or proteinkinase C (Koner et al, Int J Biochem Cell Biol. 1998). It also modifies the aggregation/agglutination of freshly prepared platelets from volunteers (Vlasic et al, Life Sci. 1993). Reactive oxygen species (ROS) are involved in integrin αIIbβ3 activation (Begonja et al, Blood Cells, Mol. and Dis. 2006; Clutton et al, Arterioscler. Thromb. Vasc Biol. 2004). Moreover, bursts of ROS are generated in platelets exposed to thrombin (Wachowicz et al, Platelets. 2002). The MF and ROS have been studied in platelets of patients with Alzheimer disease (Cardoso SM et al, Neurobiol Aging. 2004) or chronic myeloproliferative neoplasms (Popov et al, Blood, ASH abstr.), but to our knowledge, not yet in patients with myelodysplastic syndromes (MDS).

Study of platelet MF changes and ROS production in patients with MDS and eventual correlation with altered platelet function as it is reflected in aggregation curves.

The retrospective study included 34 patients with MDS classified according to FAB proposals and 29 healthy volunteers. Platelet MF was quantified by fluorescence anisotropy measurements using the marker 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate (TMA DPH). ROS production was evaluated by fluorescence measurements using dichlorodihydrofluorescein diacetate(DCFDA-H2). Platelet function was analyzed by optical aggregometry using the agonists: ADP, collagen, ristocetin and epinephrine.

Platelet MF in patients with MDS was similar to that of healthy volunteers and did not vary according to the category of risk (mean anisotropy: r_MDS = 0.155 +/− 0.043 vs. r_control= 0.144 +/− 0.040, p = 0.37; r _{low risk MDS} =0.156 +/− 0.050 vs. r _{high risk MDS}= 0.170 +/− 0.051, p = 0.52.) Patients with MDS have increased platelet ROS production compared to control group (mean AUC: MDS=657.66 +/− 51.10 vs control= 575.59 +/− 76.56, p = 0.02.) without statistical correlation with MF. ROS level was proportional to the severity of anemia (R =- 0.587, p = 0.0169). Platelet response to ADP, epinephrine was reduced in patients with MDS comparatively to volunteers. Median amplitude A _ADP-MDS=37 (95% CI = 25.21–49.36) vs. A _ADP-control=74 (95% CI 62.24–76,5), p <0.0001; A _{epinephrine-MDS}=6 (95% CI 4.71– 11.23) vs. A _{epinephrine-control}=71 (95% CI = 67–79), p <0.0001, but did not differ according to the category of risk. Both the ristocetin and the collagen induced responses differed from platelets' response of the control group and moreover they were statistically different according to FAB category of risk: A _{collagen-high risk MDS}=2 (95% CI = 0–35.12) vs A _{collagen-low risk-MDS}=42.5 (95% CI = 14.39–62), p = 0.01; A _{collagen-control}=72.5 (95% CI = 67.49–80.25), p <0.0001; A _{ristocetin-low risk-MDS} =65 (95% CI = 51.79–76) vs A _{ristocetin-high risk-MDS}=42 (95% CI = 6.2–79.82), A _{ristocetin-control} =78 (95% CI = 69.74–80.25). Anemia decreased the platelet aggregation induced by collagen or by ristocetin (collagen R=0.395, p=0.0029; ristocetin R=0.420, p=0.002.)

The MF of platelets from MDS patients appeared unmodified, but the ROS production was increased in all risk categories of MDS. The levels of ROS correlated with the degree of anemia which was a negative-impact factor on the platelet aggregation function induced by collagen or by ristocetin. By affecting the signaling pathway, the increased ROS level may be involved in the lower platelet aggregation response and consequently in the decreased platelet function clinically reported in patients with MDS.

No relevant conflicts of interest to declare.