Background: Antioxidants are molecules or substances able to convert the reactive oxygen species (ROS) in water, preventing
its overproduction. In an attempt to reduce or eliminate oxidative stress during cryopreservation, antioxidants, especially
catalase and trolox®, have been added to the freezing medium to maximize cell survival after the process of freezing / thawing.
These substances have been used mainly in the cryopreservation of semen, embryos and oocytes. Given the importance of
adding these agents in cryopreservation of mammal germ cells, this review aims to describe issues related to the addition of
catalase and trolox® for maintaining the viability of these cells in the cryopreservation process.
Review: Numerous protocols for germ cells cryopreservation have achieved satisfactory results in different species, although
some points of these protocols still require adjustments in order to succeed in the repeatability of results. Cryopreservation can
affect negativelly cell and / or tissues viability by several factors, including the formation of intracellular ice crystals, solution
effect and toxicity caused by the inappropriate use of cryoprotective agents. Currently, several studies have emphasized the
damage caused by the formation of ROS during cryopreservation processes, leading to oxidative stress. ROS formed during the
cryopreservation process can degrade essential molecules to cells, including the polyunsaturated lipids present in the cell
membrane (lipid peroxidation), leading them to death. In order to prevent oxidative stress that occurs during cryopreservation,
some researchers have tested the addition of antioxidants to the freezing medium in order to achieve higher rates of cell
survival after the thawing process. Antioxidants are substances that can neutralize ROS, thus reducing its power of chemical
reaction. These substances act by two systems: a non-enzymatic, including various hydrophilic and lipophilic compounds
such as α-tocopherol, and an enzyme, which is usually the first system to act in the cell, such as catalase. Antioxidants can act
in two ways, i.e., repairing the injuries occurred, or even more efficiently, eliminating the ROS before they cause damage to
cells, as is the case of α-tocopherol and catalase. Because of its great importance, these antioxidants (catalase and α-tocopherol,
and its analogue trolox®) have been tested successfully in cryopreservation protocols and in vitro culture, especially in semen,
embryos and oocytes. However, the use of these agents should be studied carefully, since some studies have demonstrated
dose-dependent toxicity.
Discussion: Cryopreservation is a technique that guarantees the preservation of gametes, for an indefinite period, to later use
in assisted reproductive technologies. However, the application of this technique can lead to oxidative stress, mainly due to
lipid peroxidation and consequently irreversible cell damages. An alternative to the elimination or reduction of these effects
is the addition of antioxidants such as catalase and trolox® in cryopreservation protocols, which has shown promising results
to increase the rate of cell viability after thawing. However, further studies are needed in this area to determine the type and the
optimal concentrations of these substances for each structure to be cryopreserved.
