Background: The application of cryopreservation in human and animal reproductive medicine has stimulated several studies
about the effects of low temperatures and freezing processes on cells and tissues, in order to develop efficient protocols for
gamete and embryo preservation. Moreover, cryopreservation is a fundamental tool for the establishment of animal germplasm
banks, allowing the preservation of genetic material from several species and breeds or for further study and/or recovery of
desirable characteristics. For the success of cryopreservation, the addition of an intracellular cryoprotectant agent in the freezing
solution is indispensable. However, issues related to intracellular cryoprotectant agents used, e.g., their metabolism and potential
toxicity, must be examined carefully so we can choose the cryoprotectant most suitable for a specific structure.
Review: In this regard, this review introduces several aspects of cryopreservation, such as basic principles and methods used
(slow freezing and vitrification), describing the fundamental steps of cryoprotectant agent’s exposure, cooling, storage, thawing
or warming and removal of the cryoprotectant agent. The addition of an intracellular cryoprotectant to the freezing solution is
essential, but does not guarantee the success of the cryopreservation protocol, due to its toxic effect, which requires a perfect
balance between cryoprotectant concentration, temperature and exposure time to the structure which will be cryopreserved.
Some studies attribute the toxicity of these agents mainly to the secondary metabolites formed when the cell resumes its activity
and gradually begins to metabolize the cryoprotectant agent. These secondary metabolites, such as lactate resulting from the
degradation of propanediol and the production of oxalic acid after the catalysis of ethylene glycol, can interfere in a number ways
on cellular homeostasis, resulting from an acid-base imbalance with cellular acidosis until the uncoupling of oxidative
phosphorylation in the mitochondrial membrane, preventing the production of adenosine triphosphate. In addition, there are
characteristics of tissue’s formation and metabolic peculiarities inherent to each species, resulting in differences in optimal
conditions required to maintain the biological properties of cells after thawing. Therefore, in addition to the knowledge about the
chemical and biological characteristics of the most suitable cryoprotectant agent for a given species, it is also necessary to adjust
the concentration and exposure time to it, allowing a more efficient preservation of various cell types.
Conclusion: Cryopreservation is a valuable tool for female gametes preservation, providing support for several reproductive
biotechnologies allowing safeguard the genetic material and facilitating its propagation. However, the success of this procedure
depends on the proper use of a cryoprotectant agent, which application, although essential, can cause irreversible cell damage
that can result in cellular death. Although there is no ideal cryoprotectant agent, able to protect completely the cell at low
temperatures and also to be free of toxicity, it has been demonstrated that the cryoprotectants currently employed enabled the
preservation of oocytes and ovarian tissue allowing the in vitro production of embryos and the restoration of fertility after
transplantation.
