LAUSR

INTRODUCTION Transfusion of "older" packed red blood cells (PRBCs) in patients with cardiovascular disorders (CVD) may be associated with an increased risk of pro-thrombotic events, but the underlying mechanisms are poorly understood. We hypothesized that the PRBC supernatant can activate blood platelets due to hemolysis-induced oxidative stress. METHODS Effects of the PRBC supernatants, and their filtrates (containing the soluble substances of molecular weight <10 kDa) prepared at day 1 and 42 of storage, from non-leukoreduced (D1 NLR, D42 NLR) and leukoreduced (D1 LR, D42 LR) PRBCs on PLT activation/reactivity and collagen-induced aggregation were measured by flow cytometry and turbidimetry, respectively. RESULTS Supernatants display a stimulating effect on PLTs, which was manifested by a release of PLT-derived microparticles, generation of PLT aggregates, increased P-selectin expression on the membrane surface, and activation of integrin αIIbβ3. Moreover, supernatants interacted in a way that may be additive or synergistic with collagen or with ADP. The pre-storage LR did not affect the levels of PLT activation markers. The enhanced PLT activation was presumably mediated by free hemoglobin and/or the products of its breakdown, accumulating in the PRBC milieu, and their ability to trigger the ROS generation. Additionally, collagen-induced PLT aggregation was increased by low molecular weight substances possibly derived from the residual leukocytes and PLTs present in PRBCs. CONCLUSION Transfusion of aged PRBCs may result in the hyper-activity of PLTs, which, at least in part, could be a cause of transfusion-related thrombotic complications reported in CVD patients.