Apoptotic markers are increased in platelets stored at 37°C

BACKGROUND: PLTs for transfusion lose viability during storage in blood banking. This loss of viability is accelerated at 37 degreesC, as is the risk of bacterial contamination, and has led to the selection of 22 degreesC as the routine storage temperature. Because PLTs contain an intact apoptotic mechanism, we sought to determine whether PLTs undergo apoptosis during storage and whether storage at 37 degreesC accelerated this process. STUDY DESIGN AND METHODS: PLT-rich plasma from PLT concentrates was stored at 37 or 22 degreesC in small aliquots or whole bags, with and without cell-permeable caspase inhibitors. Number of PLTs, pH, LDH level, and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H- tetrazolium activity were analyzed over time. PLT lysates were prepared and tested for the presence and activation of apoptotic proteins by enzyme assay and Western blotting. RESULTS: PLT viability was greatly reduced after 1 to 2 days of storage at 37 degreesC; however, signs of apoptosis were evident by 3 hours after temperature shift. In temperature-stressed PLTs only, a gradual rise in caspase-3 activity was detected that correlated with the appearance of the 17- to 20-kDa cleavage products of caspase-3. Gelsolin, a caspase-3 substrate, underwent cleavage within the same time frame. Bcl-x(L) and caspase-2 also declined significantly; caspase-9 activity rose. Specific caspase inhibitors could prevent caspase activation but did not improve PLT cellular viability at 37 degreesC. CONCLUSIONS: PLTs contain apoptotic proteins that are activated during PLT storage at 37 degreesC and may account for the rapid decline in PLT cellular viability. Although ineffective here, inhibition of PLT apoptosis may improve PLT cellular viability.