Mechanisms of hemolysis‐associated platelet activation

Abstract

Summary Background Intravascular hemolysis occurs after blood transfusion, in hemolytic anemias and other conditions, and is associated with hypercoagulable states. Hemolysis has been shown to potently activate platelets in vitro and in vivo and several mechanisms have been suggested to account for this including (1) direct activation by hemoglobin, (2) increase in reactive oxygen species (ROS), (3) scavenging of nitric oxide by released hemoglobin, and (4) release of intraerythrocytic ADP. Objective The aim of the current study is to elucidate the mechanism of hemolysis-mediated platelet activation. Methods We used flow cytometry to detect PAC-1 binding to activated platelets for in vitro experiments and a Siemens’ Advia 120 hematology system to assess platelet aggregation using platelet counts from in vivo experiments in a rodent model. Results We show that Hb does not directly activate platelets. However, ADP bound to Hb can cause platelet activation. Furthermore, platelet activation due to shearing of RBCs is reduced in the presence of apyrase which metabolizes ADP to AMP. Use of ROS scavengers did not affect platelet activation. We also show that cell free Hb does enhance platelet activation by abrogating the inhibitory effect of NO on platelet activation. In vivo infusions of ADP and purified (ADP-free) Hb as well as hemolysate result in platelet aggregation as evidenced by decreased platelet counts. Conclusion Two primary mechanisms account for red blood cell hemolysis-associated platelet activation: ADP release which activates platelets and cell-free hemoglobin release which enhances platelet activation by lowering NO bioavailability.

Effects of Aged Stored Autologous Red Blood Cells on Human Endothelial Function

“…Platelets are activated during red cell storage through adenosine diphosphate and CFPHb release, which enhances platelet activation by lowering NO bioavailability and stimulating purinurgic receptors (38). There was no observed effect of red cell transfusion on platelet activation, possibly related to the citrate preservative in the stored blood (see Figure E3).…”

Effects of haemolysis, icterus and lipaemia on coagulation tests as performed on Stago STA‐Compact‐Max analyser

“…For instance, phospholipid membranes from haemolytic red cells may interfere with the coagulation reaction by providing a phospholipid-rich surface that accelerates coagulation reactions [4]. Platelet activation by haemolysed red cells can impact on coagulation test results, indicating that effects will not be restricted to those induced by change in the colour of the plasma samples under analysis [13]. In contrast to photo-optical detection systems, viscosity-based detection systems (VBDS) also referred to as mechanical or electromechanical detection systems may overcome at least some of the analytical interference limitations.…”

New perspectives on the thrombotic complications of haemolysis

“…ADP induces platelet activation and may also contribute to transfusion-related vascular thrombosis. ADP released from haemolysed RBCs induces CD40LG release from platelets and lymphocytes, thereby contributing to the pro-inflammatory and pro-thrombotic environment (Helms et al, 2013).…”