Hydroxyurea Therapy Is Associated with Decreased Platelet Aggregation Responses and Activation in Sickle Cell Disease

• Published in: Blood 2009-11, Vol.114 (22), p.2565-2565
• Main Authors: Proença-Ferreira, Renata, Machado, Tania F.G.S., Traina, Fabiola, Saad, Sara T.O., Costa, Fernando Ferreira, Conran, Nicola
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V114.22.2565.2565

Abstract 2565 Poster Board II-542 Sickle cell disease (SCD) is characterized by a hypercoagulable state that may contribute to the initiation and propagation of vaso-occlusion. Platelets (PLTs) circulate in an activated state in SCD individuals and both increased and unaltered platelet aggregation responses to adenosine phosphate (ADP) stimulation have been reported in SCD adults. PLTs play an important role in vascular inflammation, where platelet adhesion to the inflamed vascular wall and thrombus formation can, in turn, trigger platelet release of inflammatory substances that can further activate the endothelium and leukocytes. This study compared the aggregation responses of PLTs from healthy control individuals (CON), steady-state SCD and SCD patients on hydroxyurea therapy (SCDHU; 20–30mg/kg/day) following stimulation with three soluble agonists. Venous blood from CON, SCD and SCDHU subjects was collected in sodium citrate. Platelet rich plasma (PRP; 250 000 PLTs/ml) was separated and preincubated for 3 min (37°C) with 5μM ADP, 1 μg/ml human collagen type I (Col) or 500 mU/ml thrombin (TB). Aggregation was then determined (5 min, 37°C, constant stirring at 1000 rpm) using a Chrono-log® 700 aggregometer and platelet-poor plasma as a reference. PAC-1 and anti-CD49b antibody binding were determined by flow cytometry. Following ADP stimulation, CON and SCD PLTs presented statistically similar aggregations (77.7±4.8%, n=14; 70.8±8.9%, n=5, respectively, p>0.05, ANOVA, Bonferroni); in contrast SCDHU PLT platelet aggregation was significantly lower (60.4±8.2%, n=7; p0.05), whilst SCDHU PLT aggregation was significantly lower than CON PLT aggregation (70.0±6.6%, n=7). ADP and TB stimulate PLT aggregation largely by activation of the αIIbβ3 integrin. Accordingly, αIIbβ3-integrin activation, as determined by PAC-1 antibody binding was found to be significantly lower on SCDHU PLTs than on SCD PLTs (11.1±3.7%; 28.6±6.4%; 12.4±4.2% PAC-1 binding for CON, SCD, SCDHU PLT, respect., n≥13, p