Background: Repeated ischemia/reperfusion in a tissue/organ remote from the heart (remote ischemic conditioning, RIC) protects against injury from sustained myocardial ischemia/reperfusion (I/R). Platelets are considered as mediators/targets of RIC´s protection. We have recently reported that infusion of washed platelets, taken from healthy volunteers after RIC, reduced infarct size (IS) in isolated rat hearts (FASEB Journal 2021; 35; S1; DOI: 10.1096/fasebj.2021.35.S1.03444). Anti-platelet drugs are potential confounders of RIC.

Aim: To study the impact of anti-platelet drugs, the cyclooxygenase inhibitor aspirin and the P2Y₁₂ inhibitor ticagrelor, on the platelet-mediated transfer of cardioprotection.

Methods: We included 18 healthy volunteers. As a contemporary control, volunteers were subjected to RIC through 3 x 5 min blood pressure cuff inflation at 200 mmHg on the left upper arm/ 5 min deflation. After at least 2 weeks, these volunteers were again subjected to RIC 3 hours after pretreatment with oral aspirin (500-1000 mg) and again at least another 2 weeks later 2 hours after pretreatment with oral ticagrelor (180 mg). Venous blood samples were taken before RIC and 60 min after RIC, respectively. Washed platelets were prepared using apyrase, prostaglandin E₁ and citrated Tyrode-buffer. The platelet count was adjusted to 2.5 x 10⁵ platelets/µL. The functionality of washed platelets was tested in response to thrombin (1U/ml), aggregation measured with turbodimetric light transmission aggregometry and expressed as the increase in light transmission in percent of control. Platelet preparations with an aggregation <60% were discarded. Male Lewis rats were sacrificed, their hearts isolated and perfused at constant pressure with buffer. Washed platelets before and after RIC, respectively, were infused for 8 min (2.5 x 10⁴ platelets/µL) into rat hearts before global 30 min/ 120 min I/R. IS was demarcated by triphenyl tetrazolium chloride staining and calculated in percent of ventricular mass.

Results: We confirm, that infusion of platelets after RIC reduces IS in isolated hearts with global I/R (Figure). This platelet-mediated transfer of cardioprotection was abrogated by aspirin-pretreatment of the volunteers (Figure). Platelets before RIC from ticagrelor-pretreated volunteers reduced IS per se; nevertheless, platelets after RIC further reduced IS (Figure).

Conclusion: Human platelets serve as carriers for RIC’s cardioprotective signal through an aspirin-sensitive and thus cyclooxygenase-dependent mechanism. The P2Y₁₂ inhibitor ticagrelor per se induces a cardioprotective platelet-dependent signal, which is further enhanced by RIC. The precise signal transfer from the platelets to the myocardium and the nature of the platelet-derived factors remain to be further identified.