Biotin labeling allows for post-transfusion functional assessment of stored human platelets in mice

BackgroundPlatelet radiolabeling with radioisotopes is currently used for human platelet recovery and survival studies. Biotinylation enables ex vivo post-transfusion platelet function testing. Whether platelet biotinylation itself affects platelet function is controversial.Study Design and MethodsPlatelet concentrates from healthy humans were stored for 6 days. Samples were obtained at 1 or 2 and 6 days, and platelets were labeled following a radiolabeling protocol using saline instead of radioactive indium-111 (sham radiolabeling [sham-RL]). Alternatively, a newly developed biotinylation protocol, a washing protocol, or an unmanipulated control sample were used. Platelet function was assessed by flow cytometry after stimulation with platelet agonists and labeling of platelets with platelet activation markers. To test whether platelets can be activated after transfusion, labeled platelets were transfused into nonobese diabetic/severe combined immunodeficiency mice, and samples were obtained 1 h after transfusion.ResultsThe activation profile of biotinylated platelets was comparable to sham-RL platelets before transfusion except for significantly less alpha-degranulation and more phosphatidyl serine exposure on storage day 1/2. There was no significant difference between sham-RL and biotinylated platelets on storage day 6. Sham-RL and biotinylated platelets were significantly less activatable than washed and unmanipulated control platelets. After transfusion, the activation profile of biotinylated platelets was largely indistinguishable from unmanipulated ones.DiscussionThe decrease in activation level in biotinylated platelets we and others observed appears mainly due to the physical manipulation during the labeling process. In conclusion, biotinylated platelets allow for post-transfusion function assessment, a major advantage over radiolabeling.