For example, some species of plants and animals produce substances with anti-freeze properties to help them survive cold environments.
This article has been corrected. This article has been cited by other articles in PMC. Abstract High levels of penetrating cryoprotectants CPAs can eliminate ice formation during cryopreservation of cells, tissues, and organs to cryogenic temperatures.
But CPAs become increasingly toxic as concentration increases. Many strategies have been attempted to overcome the problem of eliminating ice while minimizing toxicity, such as attempting to optimize cooling and warming rates, or attempting to optimize time of adding individual CPAs during cooling.
Because strategies currently used are not adequate, CPA toxicity remains the greatest obstacle to cryopreservation. CPA toxicity stands in the way of cryogenic cryopreservation of human organs, a procedure that has the potential to save many lives.
Critical analysis and suggestions are also included.
|Introduction||But cryoprotectant toxicity in cryobiology and cryonics is not related to long-term, high-temperature systemic effects — particularly liver breakdown products like ethylene glycol metabolites. Ethylene glycol itself has low systemic toxicity.|
But the demand for transplantable organs greatly exceeds the supply. Reversible cryopreservation of transplantable organs at cryogenic temperatures could substantially increase their availability.
This review will attempt to present an overview of CPA toxicity on the broadest possible level. Many, if not most, cryopreservation researchers seem to have the view that CPA toxicity follows different rules for different cells, tissues, or organisms.
Understanding the reasons for differing toxicities in different biological environments can lead to understanding the mechanisms of CPA toxicity. If erythrocytes or embryos of one species show very different CPA toxicities from erythrocytes or embryos of another species, understanding the reasons for those differences should provide insight into toxicity mechanisms.
This review does not presume to explain the many puzzling differences seen in cryopreservation of different biological systems with different CPAs, but rather attempts to present results seen empirically in the hope of serving as an impetus for others to discover explanations.
Many of the differences in the results of CPA toxicity research arise because of different experimental conditions, such as temperature, CPA concentration, CPA exposure time, CPA carrier solution, and type of toxicity assays viability assay. CPAs may be deemed toxic if cell membranes are breached or damaged, if enzyme function is impaired, if cell or embryo development is diminished, if sperm motility is impaired, if mitochondrial function is reduced, or if DNA, protein, or other macromolecules are damaged.
Some effects deemed to be due to CPA toxicity may actually be due to osmotic shock, oxidative stress, chilling injury, or other causes of damage. Toxicity can be specific to a particular CPA specific toxicity or toxicity that is a consequence of being a CPA non-specific toxicity.
The review begins with a description of specific CPA toxicities and specific forms of damage. Some comparative CPA studies follow.
CPA-Specific Toxicities Although some of the specific CPA toxicities discussed only occur at high temperature or to particular cells or organs, it is possible that awareness of these effects could shed light on injuries associated with these CPAs during their use for cryopreservation.
EG is metabolized primarily in the liver by alcohol dehydrogenase to glycoaldehyde and then by aldehyde dehydrogenase to produce glycolic acid, which can result in metabolic acidosis.
Glycolic acid can be further metabolized to oxalic acid, which precipitates with calcium to form calcium oxalate crystals in many tissues, notably the kidney.Penetrating cryoprotectants are able to travel across cell membranes (Muldrew, ) and make the environment for a decrease of cell H2O content at temperatures sufficiently low to cut down the detrimental consequence of the concentrated solutes on the cells (Mc Gann, ).
Extracellular cryoprotectants are non-penetrating molecules that function by reducing hyperosmotic cell lysis that occurs during the freezing process. Intracellular cryoprotectants penetrate the cell membrane and prevent the formation of ice crystals, which rupture cell membranes.
A Review and Application of Cryoprotectant: The Science of Cryonics can penetrate the cell membrane.
(3) Hyperbaric cryopreservation Penetrating cryoprotectants are small molecules that easily penetrate cell membranes. The molecular mass of penetrating cryoprotectants is typically less. Penetrating cryoprotectants are able to move across cell membranes (Muldrew, ) and create the environment for a reduction of cell water content at temperatures sufficiently low to reduce the damaging effect of the concentrated solutes on the cells (Mc Gann, ).
Such cryoprotectants would be hydrophobic enough to cross cell membranes readily — cryoprotectants cross cell membranes far more readily than would be predicted by their molecular weight [Figure 5, PHYSIOLOGICAL CHEMISTRY AND PHYSICS AND MEDICAL NMR ()] — and would be hydrophilic enough to readily mix with water.
Isotonicity in the presence of penetrating cryoprotectants - ing solute that must be present to provide osmotic support to the cell after the cryo- protectant has equilibrated across the cell membrane. It is not uncommon for such solutions to be made up simply by diluting an isotonic salt solution with cryoprotec- tant.
A 20% by volume.