Vitrification as an alternative means of cryopreserving ovarian tissue

Abstract

Because of the simplicity of vitrification, many authors have investigated it as an alternative to slow freezing for cryopreserving ovarian tissue. In the last decade, numerous studies have evaluated vitrification of ovarian tissue from both humans and animals. Different vitrification solutions and protocols, mostly adapted from embryo and oocyte vitrification, have been applied. The results have been discrepant from species to species and even within the same species, but lately they appear to indicate that vitrification can achieve similar or even superior results to conventional freezing. Despite the encouraging results obtained with vitrification of ovarian tissue from humans and different animal species, it is necessary to understand how vitrification solutions and protocols can affect ovarian tissue, notably preantral follicles. In addition, it is important to bear in mind that the utilization of different approaches to assess tissue functionality and oocyte quality is essential in order to validate the promising results already obtained with vitrification procedures. This review summarizes the principles of vitrification, discusses the advantages of vitrification protocols for ovarian tissue cryopreservation and describes different studies conducted on the vitrification of ovarian tissue in humans and animal species. Cryopreservation of ovarian tissue has proved to be a promising technique to safeguard fertility in women at risk of premature ovarian failure. For this aim, conventional freezing protocols have been successfully applied. However, it is known that such procedures can potentially damage the ovarian tissue mainly due to the formation of extra- and intracellular ice. In order to avoid this risk, ovarian tissue may be cryopreserved using vitrification protocols, where no ice crystals are formed. In addition to this advantage, vitrification is also a simple and fast protocol that is easy to master and does not require special equipment. Attracted by such positive characteristics, in the last decade, many researchers have been developing studies on vitrification of ovarian tissue from both humans and animals. However, the results have been discrepant from species to species and even within the same species. Nevertheless, lately they seem to indicate that vitrification can achieve similar or even superior results to conventional freezing. Despite the encouraging results obtained with vitrification, it is necessary to understand how vitrification solutions and protocols can affect the ovarian tissue. Here, we summarize the principles of vitrification, discuss the advantages of vitrification protocols for ovarian tissue cryopreservation, and describe different studies on the vitrification of ovarian tissue in humans and animal species.