Effects of new synthetic cryoprotectant agents on histological characteristics of various classes of vitrified bovine pre-antral follicles

Systematic review and meta-analysis on patented and non-patented vitrification processes to ovarian tissue reported between 2000 and 2021

Due to the great interest in ovarian cryopreservation and, consequently conservation and restoration of female fertility in the last decades, different vitrification procedures (vitrification devices or solutions) have been developed, patented, and used both for academic research purposes and for clinical use. Therefore, the present study aimed to provide a systematic review and meta-analysis of data obtained from the application of different patented and non-patented vitrification devices and solutions in different countries. For this purpose, relevant observational studies published between the years 2000 to 2021 were selected to verify the efficiency of ovarian vitrification processes on parameters such as morphology, viability, and apoptosis in preantral ovarian follicles after transplantation or in vitro culture. Our research revealed that, although several countries were considered in the study, the United States and Japan were the countries that registered the most processes, and 22 and 16 vitrification devices and solutions out of a total of 51, respectively were patented. Sixty-two non-patented processes were also considered in the study in all countries. We also observed that transplantation and in vitro ovarian culture were the techniques predominantly used to evaluate the efficiency of the devices and vitrification solutions, respectively. In conclusion, this review showed that patented or non-patented protocols available in the literature are able to successfully preserve preantral follicles present in ovarian tissue. Despite the satisfactory results reported so far, adjustments in ovarian vitrification protocols in order to minimize cryoinjuries to the follicles remain one of the goals of cryopreservation and preservation of the female reproductive function. We found that vitrification alters the morphology and viability, and offers risks leading in some cases to follicular apoptosis. However, adjustments to current protocols to develop an optimal procedure can minimize damage by not compromising follicular development after vitrification/warming.

Vitrification of caprine secondary and early antral follicles as a perspective to preserve fertility function

The present study aimed to evaluate the structure, survival and development of isolated caprine (secondary-SEC and early antral-EANT) follicles, after vitrification in the presence of synthetic polymers and in vitro culture. Additionally, transzonal projections (TZPs) and p450 aromatase enzyme were evaluated. After isolation, SEC and EANT follicles were in vitro cultured for six days or vitrified. After one week, SEC and EANT follicles were warmed and also in vitro cultured for six days. Data revealed that the percentage of morphologically normal follicles was similar between fresh and vitrified follicles in both follicular categories and antrum formation rate was similar between fresh and vitrified SEC follicles. Fluorescence by calcein-AM did not show difference between fresh and vitrified (SEC and EANT) follicles, however, the trypan blue test showed low viability for vitrified follicles. The integrity of TZPs was not affected between fresh and vitrified SEC follicles, however, in vitrified EANT follicles, there were signs of TZPs loss. Regarding steroidogenic function, it was observed a positive staining for p450 aromatase enzyme in fresh and vitrified SEC and EANT follicles. It was concluded that SEC follicles seem to be more resistant to vitrification than EANT follicles, as shown by the trypan blue test and TZPs assay. Future studies may confirm this hypothesis, in order to consolidate the use of SEC and EANT follicles as an alternative to ovary cryopreservation.