Summary
Deep Hypothermic Circulatory Arrest (DHCA) is employed during thoracic aortic and
congenital heart surgery, and can induce postoperative neurological damage probably
caused by microthrombembolism. Hypothermia has been reported to induce platelet activation
and aggregation. The platelet activation marker P-selectin mediates binding of platelets
to leukocytes. Tirofiban and eptifibatide, short-acting inhibitors of the platelet
fibrinogen receptor GP IIb/IIIa, have recently been shown to protect platelet function
without increasing bleeding during heart surgery using cardiopulmonary bypass. The
aim of this study was to investigate the effect of tirofiban and eptifibatide on platelets
and platelet-leukocyte interaction under DHCA conditions in vitro.Platelet aggregation, binding of the GP IIb/IIIa activation specific antibody PAC-1,
P-selectin expression as well as monocyte and granulocyte content of aggregates were
investigated in un-stimulated and ADP-stimulated samples using flow cytometry. Tirofiban
and eptifibatide inhibited massive platelet aggregation and PAC-1 binding which were
induced by DHCA conditions. P-selectin expression was inhibited by tirofiban but increased
by eptifibatide at hypothermia. Platelet-bound leukocytes were present in all samples.
Eptifibatide increased granulocyte content of aggregates at hypothermia in ADP-stimulated
samples. We conclude that under conditions of DHCA both tirofiban and eptifibatide
inhibit platelet aggregation but have different effects on platelet P-selectin expression
and platelet-leukocyte interaction. Application of a short-acting and non-activating
GP IIb/IIIa inhibitor should be considered during DHCA in vivo to prevent occlusion of the microvasculature and subsequent organ damage.
Keywords
Platelet physiology - cell-cell interactions - coagulation inhibitors - platelet pharmacology