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Mechanisms of hemolysis‐associated platelet activation
Author(s) -
Helms C. C.,
Marvel M.,
Zhao W.,
Stahle M.,
Vest R.,
Kato G. J.,
Lee J. S.,
Christ G.,
Gladwin M. T.,
Hantgan R. R.,
KimShapiro D. B.
Publication year - 2013
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.12422
Subject(s) - platelet , platelet activation , hemolysis , apyrase , chemistry , in vivo , nitric oxide , pharmacology , biochemistry , immunology , medicine , biology , microbiology and biotechnology , organic chemistry
Summary Background Intravascular hemolysis occurs after blood transfusion, in hemolytic anemias, and in 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: (i) direct activation by hemoglobin ( H b); (ii) increase in reactive oxygen species ( ROS ); (iii) scavenging of nitric oxide ( NO ) by released H b; and (iv) release of intraerythrocytic ADP . Objective 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 S iemens' A dvia 120 hematology system to assess platelet aggregation by using platelet counts from in vivo experiments in a rodent model. Results We found that H b did not directly activate platelets. However, ADP bound to H b could cause platelet activation. Furthermore, platelet activation caused by shearing of red blood cells ( RBC s) was reduced in the presence of apyrase, which metabolizes ADP to AMP . The use of ROS scavengers did not affect platelet activation. We also found that cell‐free H b enhanced platelet activation by abrogating the inhibitory effect of NO on platelet activation. In vivo infusions of ADP and purified ( ADP ‐free) H b, as well as hemolysate, resulted in platelet aggregation, as shown by decreased platelet counts. Conclusion Two primary mechanisms account for RBC hemolysis‐associated platelet activation: ADP release, which activates platelets; and cell‐free H b release, which enhances platelet activation by lowering NO bioavailability.