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BACKGROUND: The potential for bacterial contamination limits the storage of platelets at 22 degrees C to 5 days. This creates an inventory problem, which could be overcome by the use of cryopreservation to allow long-term storage of platelets. It has been demonstrated that the addition to platelets of a mixture of second- messenger effectors (platelet storage solution), allows these cells to retain significant in vitro functional activity following cold storage. Analysis is needed of the ability of this second messenger effector mixture both to protect platelets during cryopreservation and to reduce the need for a cryoprotectant. STUDY DESIGN AND METHODS: Fresh single- donor platelet units (n = 8) were divided into three samples and treated with 6-percent dimethyl sulfoxide (DMSO), 2-percent DMSO or the platelet storage solution and 2-percent DMSO. The samples were placed directly into a −80 degrees C freezer and stored for 1 week, after which they were thawed and analyzed for in vitro functional activity. RESULTS: Platelets cryopreserved with the platelet storage solution and 2-percent DMSO displayed statistically higher retention of functional activity and viability-including cell number, percent of discoid cells, extent of shape change, and hypotonic shock response-than did platelets stored by the method using 6-percent DMSO. In addition, the treated platelets displayed statistically lower expression of p- selectin. The treated platelets showed no loss of cell number, > 88- percent retention of discoid morphology, and > 75-percent retention of ristocetin-induced aggregation as compared to values for these measures in fresh platelets. CONCLUSION: The use of this platelet storage solution in the cryopreservation of platelets yields a significant improvement in their postthaw in vitro recovery and allows for a reduction of the DMSO concentration from 6 to 2 percent, with superior maintenance of in vitro viability and function.