Antifreeze protein modulates cell survival during cryopreservation: mediation through influence on ice crystal growth.
Antifreeze proteins (AFPs) are extremely efficient at inhibiting ice recrystallization in frozen solutions. Knight and Duman [Knight, C. A. & Duman, J. G. (1986) Cryobiology 23, 256-263] have proposed that this may be an important function of the proteins in freeze-tolerant organisms. We have tested this proposal in vitro by characterizing the influence of AFP on the recovery of cryopreserved cells, which often can survive cooling and yet subsequently be damaged by ice crystal growth during warming. Relatively low concentrations (e.g., 5-150 micrograms/ml) of winter flounder (Pseudopleuronectes americanus) AFP enhance survival of red blood cells cryopreserved in hydroxyethyl starch solutions. This effect is most apparent in samples warmed at suboptimal rates, i.e., where ice recrystallization would be exaggerated. Cryomicroscopy demonstrates that AFP inhibits ice recrystallization in the extracellular regions during the latter stages of the warming cycle. AFP concentrations that enhance survival of red cells confer partial inhibition of recrystallization. Relatively high concentrations of AFP (e.g., 1.54 mg/ml) are much more effective at inhibiting extracellular recrystallization. However, extensive growth of ice around the cell, and concomitant cell damage, is noted. The mechanism for this AFP-induced ice growth is unknown. We propose that there is a delicate balance between AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell damage and that this balance hinges on the degrees of inhibition of ice recrystallization and of preferential growth of ice around the cells. We conclude that, under appropriate conditions, one of the proposed functions of AFPs in nature can be emulated, and perhaps have application, in cryopreservation of materials of biomedical interest.