Frozen thawed platelets: Importance of osmotic tolerance and platelet subpopulations

Me2SO cryopreserved platelets circulate in vivo, reduce bleeding time, and have hemostatic properties but their functional recovery is only half that of the fresh material. Poor osmotic response is often reported as the cause of the freezing injury. Osmotic excursions on 1- and 5-day-old platelets h ave been studied. Platelets stored for 5 days have a lesser capability to r egulate their volume particularly after an initial swelling. This is attrib uted to the reduction of discoid cell number, 80% vs 62% for 1-day-old and 5-day-old platelets, respectively. After freezing, hypotonic stress respons e is reduced from 86 to 39% for 1-day-old and 73 to 31% for 5-day-old plate lets. This reduction in function is supported by a similar reduction of dis coid cells from 80 to 40% for 1-day-old and 62 to 32% for 5-day-old platele ts. The integrity of the cytoskeleton is critical for the osmotic response. Freezing recovery is significantly lowered in the presence of propylene gl ycol, which alters actin. This contrasts with the recovery of platelets tre ated with anti-aggregating agents. Platelets show a greater viability after freezing and thawing when PGI(2) is added. It is postulated that freshly c ollected platelets, which are heterogeneous, contain populations of cells t hat are more sensitive to freezing than others. More tolerant cells remain discoid after freezing and are also less susceptible to storage lesions. Th erefore, the maintenance of the integrity of the membrane and the cytoskele ton should be considered for the development of preservation methodologies. (C) 1999 Academic Press.