Interactions between cryoprotectors and cryosensitizers

Abstract When cryoprotected or unprotected mammalian cells are exposed to multiple freeze-thaw (FT) cycles, survival decreases exponentially, even when combinations of cryoprotector (CP) agents are used. This enables one to calculate independence or synergistic interactions between different CP (and/or cryosensitizers) agents. However, theoretical and practical considerations restrict the accuracy and interpretation of these experiments to a limited range of survivals. For example, low concentrations of CPs act independently until the concentration is increased so that competition for the “FT targets” occurs. While the standard CP agents, DMSO, propylene glycol (PG), HES, and glycerol interact with each other as cryoprotectants, glutamine acts independently when used in combination with any of the above CP agents. If cryosensitizers (CS) are used, some differences between standard CPs are observed. For example, DMSO and PG are better protectants than HES against FT sensitization by protein denaturants like ethanol or guanidine HCl. Some of the CSs (ethanol, A23187, BHT, zinc sulfate) interact with CPs, while others (guanidine HCl, DTNB, europium) act independently. These interactions, or lack of interaction, may help us determine how various CPs protect the many different targets of FT damage.