Presentation Details
| Red Blood Cell Haemolysis and platelet activation : the forgotten players of hypercoagulability Neha Thomas, Stipo Jurcevic. University of Westminster, London, United Kingdom |
Abstract
Background Platelets play a major role in haemostasis, as they rapidly bind to damaged vessels, aggregate to form thrombi, prevents excessive bleeding and maintains the constant blood flow. Several studies have demonstrated the correlation between diseases that involve haemolysis and increased platelet activation causing hypercoagulability (Figure 1). Even though, the high risk of thrombosis in intravascular haemolytic conditions such as sickle cell disease and thalassaemia is widely accepted, the precise mechanisms responsible for the hypercoagulable state remains largely unknown. This study is aimed at understanding the molecular mechanisms of platelet activation in patients with haemolysis. This may help to determine an optimal therapeutic approach to prevent occurrence of thrombotic events in such conditions. Material and Methods The effects of haemolysis on platelet activation are studied by making use of an in vitro model. This model mimics haemolytic platelet activation using citrated whole blood samples, red blood cell (RBC) haemolysate and addition of the well-defined platelet agonist such as Protease-Activated Receptor-1 (PAR-1) agonist (a peptide that represents receptor binding sequence from thrombin molecule). PAR-1 is the main platelet receptor for thrombin. The levels of platelet activation are analysed using flow cytometry method. Results The presence of low concentration of PAR-1 agonist at 0.5mM resulted in a modest platelet activation (7%) as shown by expression of CD-62P (P-selectin) on platelet surface. Expectedly, the addition of higher concentrations of PAR-1 agonist resulted in moderate (22.0% at 1mM) or strong (92.5% at 5mM) platelet activation. The effects of RBC haemolysate on platelet activation were dose dependent with measurable activation (9.5%) determined at 0.04% RBC lysate (equivalent to 50 mg/L of free Haemoglobin) and strong effects at 0.2% RBC lysate (51% activation). Importantly, the combination of PAR-1 agonist (0.5mM) and RBC lysate (0.2% lysate – equivalent to 250 mg/L of free Haemoglobin) has shown a strong synergistic effect with a striking 68.9% activation. Conclusion Preliminary results using this in vitro model based on whole blood samples have established that RBC haemolysate at concentrations that are similar to those observed in patients causes striking platelet activation. Furthermore, a combination of agonist that binds to PAR-1 receptor (peptide from thrombin sequence) and RBC lysate have strong synergistic effects on platelet activation. This suggests that haemolytic crisis conditions in patients can cause hypercoagulable state. Notably, the platelet agonist such as thrombin acts synergistically with RBC lysate, which could be relevant in patients with comorbidities that trigger thrombin formation.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.