Hemoglobin A_o and α-Crosslinked Hemoglobin (α-DBBF) Potentiate Agonist-Induced Platelet Aggregation Through the Platelet Thromboxane Receptor

Abstract

Chemically modified hemoglobins are potential oxygen-carrying blood substitutes, but their in vivo administration has been associated with a variety of unexpected side events, including increased platelet reactivity. We studied the effects of hemoglobin A₀ (HbA₀) and α-crosslinked hemoglobin (α-DBBF) on platelets in vitro. Neither hemoglobin A₀ nor α-DBBF activated platelets when added alone, but both proteins potentiated submaximal agonist-induced platelet aggregation without increasing other markers of platelet activation such as serotonin secretion. Only agonists that are known to cause release of platelet arachidonic acid (AA) were potentiated while aggregation induced by ADP, which does not release AA, was not potentiated. Blockade of the thromboxane receptor with SQ-29,548 prevented the HbA₀-induced and the α-DBBF-induced potentiation suggesting that the AA/thromboxane signaling pathway mediates the interaction of platelets with hemoglobin.