The effect of different vitrification protocols on cell survival in human ovarian tissue: a pilot study

Optimization of freezing and thawing protocols for human ovarian tissue cryopreservation through thermophysical characterisation of freezing medium by differential scanning calorimetry

Fertility preservation should be offered to patients facing gonadotoxic therapy. The method for preserving prepubescent girls' fertility, which is also suitable for women, is ovarian tissue cryopreservation (OTC). Although 200 births have been reported worldwide with this approach, significant improvements are needed. The literature indeed reports numerous protocols for freezing and thawing ovarian tissue, with no clear rationale for selection criteria. This study aims to optimize human OTC protocols by characterizing the thermodynamic properties of freezing medium. The freezing medium associated with most live births after autograft (Leibovitz L-15 medium with 4 mg/mL human serum albumin (HSA), 1.5M DMSO, and 0.1M sucrose) was characterized using differential scanning calorimetry. We obtained -120.49 °C for glass transition temperature (Tg'), -20 °C for crystallization temperature when cooling at 2.5 °C/min (Tc) and -4.11 °C for melting temperature (Tm). With these parameters, we optimized a freezing protocol in a programmable freezer (Nano-Digitcool, Cryo Bio System) and a thawing protocol. The freezing curve was as follows: 5 min at 4 °C, 1 °C/min to -7 °C, seeding: 60 °C/min to -32 °C, and 10 °C/min to -15 °C, 0.3 °C/min to -40 °C, 10 °C/min to -140 °C. The thawing protocol consisted in a 3.5-min step in a cold chamber to reach slowly Tg', limiting thermal and mechanical shocks, and then a 2-min incubation at 37 °C to quickly reach Tm. Ovarian tissue frozen-thawed according to these protocols had a similar quality to that of fresh tissue and could resume folliculogenesis during organotypic culture. Our study will contribute to improve human OTC and optimize women fertility preservation.

Comparative effectiveness of vitrification and slow freezing after heterotopic transplantation of human ovarian tissues

BACKGROUND

The aim of this study was to compare the effectiveness of two different vitrification methods and slow freezing in terms of the recovery of endocrine function, follicular morphology and proliferation, apoptosis of stromal cells, and angiogenesis after heterotopic transplantation of human ovarian tissue.

METHODS

Ovarian tissue from young women aged 29 to 40 was subjected to two vitrification methods and one slow freezing method. The thawed ovarian tissue was then transplanted into nude mice and divided into three groups (VF1 group, VF2 group, SF group) according to the different freezing methods. Ovarian tissue samples were collected at 4 and 6 weeks post-transplantation. The recovery of ovarian function was evaluated by observing the estrous cycle and measuring estradiol levels using Elisa. Histological evaluation was performed to assess the integrity of ovarian follicles. TUNEL assay was used to detect stromal cell apoptosis, and immunohistochemistry was conducted to evaluate follicular proliferation and tissue angiogenesis.

RESULTS

After heterotopic transplantation, mice in the experimental groups exhibited restoration of the estrous cycle. Hormone levels showed an increasing trend in the vitrification groups. At 6 weeks post-transplantation, the VF2 group had significantly higher hormone levels compared to the VF1 group and the slow freezing (SF) group (P < 0.05). At 4 weeks post-transplantation, the proportion of normal follicles was higher in the VF2 group compared to the other two groups (P > 0.05), and at 6 weeks post-transplantation, the VF2 group was significantly higher than the SF group (P < 0.05) and slightly higher than the VF1 group. Immunohistochemistry analysis indicated a higher proportion of proliferating follicles in the vitrification groups compared to the slow freezing group (P > 0.05). CD31 expression was established in all groups at 4 and 6 weeks post-transplantation, with better results in the slow freezing group compared to the vitrification group. TUNEL analysis showed that stromal cell apoptosis was higher in the SF group compared to the vitrification group at 4 weeks post-transplantation (P < 0.05), while there was no significant statistical difference among the groups at 6 weeks post-transplantation.

CONCLUSIONS

Vitrification showed better results than slow freezing, with the VF2 group performing slightly better than the VF1 group. Considering the lower economic and time costs associated with vitrification, it may be more suitable for ovarian tissue cryopreservation in major research centers in the future.

Vitrification alters growth differentiation factor 9 and follicle-stimulating hormone receptor expression in human cumulus-mural granulosa cells

OBJECTIVE

Ovarian tissue vitrification is widely utilized for fertility preservation in prepubertal and adolescent female patients with cancer. The current literature includes reports of successful pregnancy and live birth following autografting. However, the effects of the vitrification process on cumulus-mural granulosa cells (C-mGCs)-somatic cells in ovarian tissue crucial for oocyte maturation and early embryonic development-remain unclear. This study was conducted to explore the impact of vitrification on the cellular function of C-mGCs by quantifying the expression of growth differentiation factor 9 (GDF-9), bone morphogenetic protein 15 (BMP-15), follicle-stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR), connexin 37, survivin, and caspase 3.

METHODS

Mature and immature C-mGCs were obtained from 38 women with polycystic ovary syndrome who participated in an in vitro fertilization program. The C-mGCs were then divided into two groups: fresh and vitrified. The expression levels of target genes were assessed using real-time quantitative polymerase chain reaction.

RESULTS

After vitrification, GDF-9 expression was significantly decreased among both mature and immature C-mGCs, with 0.2- and 0.1-fold changes, respectively (p<0.01). Similarly, FSHR expression in the mature and immature groups was reduced by 0.1- and 0.02-fold, respectively, following vitrification (p<0.01). The expression levels of the other genes, including BMP-15, LHR, connexin 37, survivin, and caspase 3, remained similar across the examined groups (p>0.05).

CONCLUSION

Vitrification may compromise oocyte maturation through reduced GDF-9 and FSHR expression in C-mGCs after warming.

Investigating the impact of vitrification on bovine ovarian tissue morphology, follicle survival, and transcriptomic signature

PURPOSE

Ovarian tissue cryopreservation is vital for fertility preservation, yet its effect on ovarian tissue follicle survival and transcriptomic signature requires further investigation. This study delves into the effects of vitrification on tissue morphology, function, and transcriptomic changes, helping to find possibilities for vitrification protocol improvements.

METHODS

Ovarian cortex from 19 bovine animals were used to conduct pre- and post-vitrification culture followed by histological assessment, immunohistochemistry, and TUNEL assay. Follicles' functionality was assessed for viability and growth within the tissue and in isolated cultures. RNA-sequencing of ovarian tissue was used to explore the transcriptomic alterations caused by vitrification.

RESULTS

Follicle density, cell proliferation, and DNA damage in ovarian stroma were unaffected by vitrification. However, vitrified cultured tissue exhibited reduced follicle density of primordial/primary and antral follicles, while freshly cultured tissue manifested reduction of antral follicles. Increased stromal cell proliferation and DNA damage occurred in both groups post-culture. Isolated follicles from vitrified tissue exhibited similar viability to fresh follicles until day 4, after which the survival dropped. RNA-sequencing revealed minor effects of vitrification on transcriptomic signatures, while culture induced significant gene expression changes in both groups. The altered expression of WNT and hormonal regulation pathway genes post-vitrification suggests the molecular targets for vitrification protocol refinement.

CONCLUSION

Vitrification minimally affects tissue morphology, follicle density, and transcriptomic signature post-thawing. However, culture revealed notable changes in vitrified tissue samples, including reduced follicle density, decreased isolated follicle survival, and alteration in WNT signalling and ovarian hormonal regulation pathways, highlighted them as possible limitations of the current vitrification protocol.

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.

Different Impacts of Cryopreservation in Endothelial and Epithelial Ovarian Cells

The aim of our laboratory-based study was to investigate the extent of delayed-onset cell death after cryopreservation in endothelial and epithelial cell lines of ovarian origin. We found differences in percentages of vital cells directly after warming and after cultivation for 48 to 72 h. A granulosa cell line of endothelial origin (KGN) and an epithelial cell line (OvCar-3) were used. In both DMSO-containing and DMSO-free protocols, significant differences in vitality rates between the different cell lines when using open and closed vitrification could be shown (DMSO-containing: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.001; DMSO-free: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.031). Furthermore, there was a marked difference in the percentage of vital cells immediately after warming and after cultivation for 48 to 72 h; whereas the KGN cell line showed a loss of cell viability of 41% using a DMSO-containing protocol, the OvCar-3 cell loss was only 11% after cultivation. Using a DMSO-free protocol, the percentages of late-onset cell death were 77% and 48% for KGN and OvCar-3 cells, respectively. Our data support the hypothesis that cryopreservation-induced damage is cell type and cryoprotective agent dependent.