Transfusion-induced functional and metabolic shifts in stored platelets: limitations of in vitro assessment

The impact of the stored platelet extracellular environment on function and the ability of platelets to change their function upon transfer into in vivo environments remain poorly understood. Human platelets were stored ex vivo at 20°C to 24°C (room temperature-stored platelets [RTPs]) or 1°C to 6°C (cold-stored platelets [CSPs]) and tested for function in the concomitant storage plasma or fresh plasma. In mice, we tested platelet function after ex vivo storage in concomitant plasma and after transfusion to mice ex vivo and in vivo. We also investigated stored platelet-rich plasma before and after transfusion to mice for metabolomics by liquid chromatography-tandem mass spectrometry. In in vitro, human RTPs showed a greater ability than CSPs to improve α_IIbβ₃ integrin activation upon dilution with fresh frozen plasma. Mouse RTPs' in vitro integrin activation improved more than that for CSPs after transfusion. Surprisingly, in mice, CSPs facilitated significantly greater platelet accumulation than RTPs in vivo. In contrast, fibrin generation was significantly more robust in RTPs than in CSPs during the early stages of hemostasis. In mouse RTPs, more metabolites changed significantly upon transfusion than in mouse CSPs. Transfusion decreased carnitine species, fatty acid metabolites, and amino acids only in RTPs, whereas polyamines decreased only in CSPs. The recovery from storage-induced oxidative stress was more complete in RTPs than in CSPs. Our findings highlight the severe limitations of in vitro testing of stored platelets. Platelet-rich plasma undergoes profound changes in metabolomic composition following transfusion. We further demonstrate the ability of platelets to undergo marked changes upon transfusion in RTPs more so than CSPs.