Slow freezing versus vitrification technique for human ovarian tissue cryopreservation: An evaluation of histological changes, WNT signaling pathway and apoptotic genes expression

Cryopreservation of canine ovarian tissue by slow freezing and vitrification: Evaluation of follicular morphology and apoptosis rate

In this study, we aimed to evaluate the efficacy of cryopreserving canine ovarian tissue using vitrification and slow freezing methods while investigating potential differences in cryotolerance based on follicular type and cryopreservation technique. Twenty-eight ovaries were collected from 14 anoestrus bitches of various breeds, aged between 2 and 5 years, and undergoing elective ovariohysterectomy. The ovaries were sectioned into small fragments and randomly assigned to three groups: vitrification, slow freezing, and a control group (fresh tissue). Vitrification was performed using cryotubes containing DAP 213 solution (2M DMSO, 1M acetamide, 3M propylene glycol) in two stages, while slow freezing involved cryotubes with 1.5M DMSO solution inserted into a programmable machine. The effects of cryopreservation were evaluated by histology and immunohistochemistry (cleaved caspase-3), to determine the percentage of cells undergoing apoptosis. Histological examination revealed that the slow freezing group exhibited a significantly higher percentage of intact follicles (45.75 %) compared to those subjected to vitrification (38.17 %; P = 0.01). Immunohistochemical evaluation further indicated that 84.21 % of the follicles in the slow freezing group did not express caspase-3, suggesting the absence of apoptosis. Conversely, vitrified samples exhibited significantly more apoptotic cells compared to other groups (P < 0.001). Furthermore, early antral follicles displayed a higher susceptibility to degeneration regardless of the cryopreservation method employed. Nevertheless, when comparing the cryopreserved groups, early antral follicles showed greater degeneration in slow freezing group, while preantral follicles were the most affected in the vitrification group. In conclusion, slow freezing demonstrated superior preservation of viable follicles compared to vitrification and emerged as the preferred technique for cryopreserving canine ovarian tissue. These findings contribute valuable insights into optimizing cryopreservation methods for canine ovarian tissue, potentially benefiting reproductive technologies and fertility preservation in canines.

The Influences of Cryopreservation Methods on RNA, Protein, Microstructure and Cell Viability of Skeletal Muscle Tissue

Background: Different experiments require different sample storage methods. The commonly used preservation methods in biobank practice cannot fully meet the multifarious requirements of experimental techniques. Programmable controlled slow freezing (PCSF) can maintain the viability of tissue. In this study, we hypothesized that PCSF-preserved samples have potential advantages in matching subsequent experiments compared with existing methods. Methods: We compared the differences on skeletal muscle tissue RNA integrity, protein integrity, microstructure integrity, and cell viability between four existing cryopreservation methods: liquid nitrogen (LN2) snap-freezing, LN2-cooled isopentane snap-freezing, RNAlater®-based freezing, and PCSF. RNA integrity was evaluated using agarose gel electrophoresis and RNA integrity number. Freezing-related microstructural damage in the muscle tissue was evaluated using ice crystal diameter and muscle fiber cross-sectional area. Protein integrity was evaluated using immunofluorescence staining. Cell viability was evaluated using trypan blue staining after primary muscle cell isolation. Results: PCSF preserved RNA integrity better than LN2 and isopentane, with a statistically significant difference. RNAlater preserved RNA integrity best. PCSF best controlled ice crystal size in myofibers, with a significant difference compared with LN2. The PCSF method best preserved the integrity of protein epitopes according to the mean fluorescence intensity results, with a significant difference. Cell viability was best preserved in the PCSF method compared with the other three methods, with a significant difference. Conclusion: PCSF protected the RNA integrity, microstructural integrity, protein integrity, and cell viability of skeletal muscle tissue. The application of PCSF in biobank practice is recommended as a multi-experiment-compatible cryopreservation method.

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.

Nanowarming improves survival of vitrified ovarian tissue and follicular development in a sheep model

Tissue cryopreservation has allowed long term banking of biomaterials in medicine. Ovarian tissue cryopreservation in particular helps patients by extending their fertility window. However, protection against tissue injury during the thawing process has proven to be challenging. This is mainly due to the heterogenous and slow distribution of the thermal energy across the vitrified tissue during a conventional warming process. Nanowarming is a technique that utilizes hyperthermia of magnetic nanoparticles to accelerate this process. Herein, hyperthermia of synthesized PEGylated silica-coated iron oxide nanoparticles was used to deter the injury of cryopreserved ovarian tissue in a sheep model. When compared to the conventional technique, our findings suggest that follicular development and gene expression in tissues warmed by the proposed technique have been improved. In addition, Nanowarming prevented cellular apoptosis and oxidative stress. We therefore conclude that Nanowarming is a potential complementary candidate to increase efficiency in the ovarian cryopreservation field.

Co-culture of human cryopreserved fragmented ovarian tissue with theca progenitor cells derived from theca stem cells

PURPOSE

Despite the significant advances in the in vitro development of human primordial follicles, it is still a challenging approach with great potential for improvements. Therefore, the present study aimed to investigate the effect of a feeder layer of human theca progenitor cells (hTPCs) on the development of primordial follicles embedded in human ovarian tissue.

METHODS

Fragments of frozen-thawed ovarian tissue were activated using the vanadate-derivative dipotassium bisperoxo (5-hydroxy-pyridine-2-carboxylic) oxovanadate (V) and kit ligand for 24 h. Then, the specimens were divided into the co-culture and mono-culture groups and were cultured with and without a hTPC feeder layer for 6 days, respectively. Afterward, the follicles were counted and classified, and the hormone levels and expression levels of apoptosis- and folliculogenesis-related genes were assessed.

RESULTS

Both culture groups showed significant follicle growth (P < 0.05). However, the co-culture group had a significantly higher number of growing follicles compared to the other group (P < 0.05). Moreover, the expression levels of ZP1, ZP2, ZP3, BMP-7, AMH, and GDF9 were significantly higher in the co-culture group compared to the other group (P < 0.05), while the expression levels of P53 and CASP3 were significantly lower (P < 0.05). Also, the concentrations of estradiol, progesterone, testosterone, and androstenedione were significantly higher in the co-culture group compared to the other group (P < 0.05).

CONCLUSION

The present study results provided novel evidence on the direct role of hTPCs in the growth and development of human primordial follicles. However, there is a need for future studies to illustrate the underlying mechanisms. Schematic summary of the results. According to our results, the expression of ZP1, ZP2, ZP3, and GDF9 in the oocytes, AMH in the granulosa cells, and BMP4 in the theca cells of the co-culture group were significantly higher than those of the mono-culture and non-culture groups, while the expression of apoptotic genes (BAX, CASP3, and P53) was significantly lower. Moreover, the co-culture group showed significantly increased levels of estradiol, progesterone, testosterone, and androstenedione in its culture media compared to the mono-culture groups.

Fertility preservation in pediatric healthcare: a review

Survival rates for children and adolescents diagnosed with malignancy have been steadily increasing due to advances in oncology treatments. These treatments can have a toxic effect on the gonads. Currently, oocyte and sperm cryopreservation are recognized as well-established and successful strategies for fertility preservation for pubertal patients, while the use of gonadotropin-releasing hormone agonists for ovarian protection is controversial. For prepubertal girls, ovarian tissue cryopreservation is the sole option. However, the endocrinological and reproductive outcomes after ovarian tissue transplantation are highly heterogeneous. On the other hand, immature testicular tissue cryopreservation remains the only alternative for prepubertal boys, yet it is still experimental. Although there are several published guidelines for navigating fertility preservation for pediatric and adolescent patients as well as transgender populations, it is still restricted in clinical practice. This review aims to discuss the indications and clinical outcomes of fertility preservation. We also discuss the probably effective and efficient workflow to facilitate fertility preservation.

Cryopreservation of African painted dog (Lycaon pictus) ovarian tissue

Development of techniques for the preservation and use of gonadal tissues are increasingly needed for the genetic management of the endangered African painted dog (Lycaon pictus). Here we evaluated two cryopreservation techniques for ovarian tissue (2 × 2 × 1 mm3 fragments, n = 11 individuals): needle immersed vitrification (NIV), with equilibration in a 7.5% dimethyl sulfoxide (DMSO) and 7.5% ethylene glycol (EG) solution, and vitrification in a 15% DMSO, 15% EG, and 0.5 M sucrose solution, and slow freezing in cryovials with either the equilibration (SF-E) or vitrification (SF-V) solutions. Following warming, tissues were either fixed and embedded for evaluation of density of morphologically normal follicles, semi-quantitative scoring of stromal cell preservation, and apoptotic index (TUNEL stain), and/or flash-frozen for expression of proliferation (PCNA), apoptosis (CASP3, BCL2), or oxidative stress (GPX3, SOD1, SOD2) pathway genes (n = 4). Needle immersed vitrification maintained higher density of morphologically normal follicles compared to the slow freezing protocols applied (p &lt; 0.05), with no significant changes in expression of select genes among treatment groups. A slight increase in apoptotic index was observed in all cryopreservation groups, but only reached significance in SF-E compared with fresh tissue controls (p &lt; 0.05). Future research should be dedicated to developing improved methods for ovarian tissue culture in the species, both as a means to evaluate the efficacy of tissue cryopreservation techniques and for the production of viable oocytes from banked ovarian tissue in the endangered African painted dog.

The effect of mTOR activation and PTEN inhibition on human primordial follicle activation in ovarian tissue culture

PURPOSE

The effect of PTEN inhibitor (Bpv(HOpic); Bpv) and mTOR activators (phosphatidic acid (PA) and propranolol (PP)), were evaluated on the activation and subsequent development of human primordial follicles in ovarian tissue culture.

METHODS

Slow frozen-thawed human ovarian cortical strips were incubated for 24 h in different groups: (1) Control (base medium), (2) Bpv (100 µM), (3) PA (200 µM), (4) PA + PP (50 µm), and (5) Bpv + PA + PP. Afterward, the medium was exchanged, and all groups were cultured without stimulators for 6 additional days. The proportion of normal and degenerated follicles, estradiol secretion, and expression of RPS6, FOXO3a, and AKT proteins was evaluated and compared between groups.

RESULTS

After 24 h of culture, there was no significant difference between the proportion of primordial and growing follicles in either of the experimental groups. This non-significant change was also observed for the phosphorylated protein to total protein ratios of RPS6, FOXO3a, and AKT proteins. After 7 days of culture, the proportion of the transitional follicles was significantly higher in comparison to the primordial follicles for the PA, PA + PP, and Bpv + PA + PP groups. The estradiol level was significantly higher on the last day compared to the first day, in PA, PA + PP, and Bpv + PA + PP groups. Hormonal secretion was significantly higher in the PA and PA + PP groups and lower in the Bpv and Bpv + PA + PP groups compared to the control on day 7 of culture.

CONCLUSION

Temporary in vitro treatment of human ovarian tissue with mTOR activators enhances the initiation of primordial follicle development and positively influences steroidogenesis after short-term culture.

Fertility preservation in female cancer sufferers: (only) a moral obligation?

PURPOSE

Advances in cancer diagnostics and therapeutics have thankfully led to high numbers of young cancer survivors, although some interventions may sometimes threaten fertility. The authors aimed to assess how evidence-based oncofertility counselling can be adequately fulfilled for the sake of female cancer patients, in light of its complexities and multidisciplinary nature, which require thorough counselling and consent pathways.

MATERIALS AND METHODS

A search has been conducted in the databases PubMed/MEDLINE, Web of Science, Scopus, EMBASE and Google Scholar via search strings such as fertility preservation, reproductive counselling, oncofertility, cancer survivors, in order to identify relevant meaningful sources spanning the 2010-2021 period.

RESULTS

Counselling needs to be implemented in compliance with international guidelines, so as to avoid medicolegal repercussions. Albeit fertility preservation is supported by most health care institutions, actual conditions at health care facilities often reflect several lingering difficulties in the oncofertility process. Oncofertility counselling should foster access to fertility preservation procedures. To best serve that purpose, it should be implemented in a manner consistent with ethical and legal standards, so that patients can make an informed decision based on comprehensive and relevant data.

CONCLUSIONS

Counselling needs to be rooted in a close cooperation of oncologists, reproductive endocrinologists, mental health counsellors and clinical researchers. The provision of oncofertility services is grounded in the moral obligation to uphold individual autonomy, which is essential in a free society, unless the exercise thereof could pose a risk to the children conceived or to others.

Thermally conductive graphene-based nanofluids, a novel class of cryosolutions for mouse blastocysts vitrification

Limited heating and cooling rates have long been recognized as bottlenecks in improving embryo cryopreservation. As a result, efforts to achieve higher heat transfer rates gave rise to milestones like open cryodevices and minimal media loading. A crucial but commonly ignored variable is heat conduction by cryosolutions. The low heat conductivity of the aqueous media surrounding embryos slows down cooling and heating rates of the embryo, imposing the risk of preventable damages. In this study, we introduce a novel thermally conductive cryosolution based on graphene oxide nanoparticles and test its performance against conventional sucrose-based solutions for vitrification of mouse blastocysts. Replacing sucrose with graphene oxide brought about similar re-expansion, hatching, and implantation rates of post-vitrification embryos while also preventing an array of cellular and molecular stresses. Our results showed significantly reduced oxidative stress, characterized by control-level expression of Sod1 and significant downregulation of Sod2 transcription when graphene oxide was used instead of sucrose. This molecular response was in agreement with the reduced level of reactive oxygen species produced in vitrified/warmed embryos using graphene-based solutions. The downstream impacts of this stress reduction manifested in significant downregulation of two major pro-apoptotic genes, Bax and Trp53, down to the same level as fresh embryos. Interestingly, embryos maintained their spherical shape during dehydration in graphene-based solutions and did not "collapse" when shrinking, like in sucrose-based solutions. These results provide new insights into the benefits of thermally conductive cryosolutions and showcase the potential of graphene oxide as a cryoprotectant in embryo vitrification.

Evaluating the Expression of Wnt Pathway Related Genes in Mouse Vitrified Preantral Follicles: An Experimental Study

Background

Wnt signaling pathway plays critical role in ovarian follicle development. Therefore, the aim of this study was to evaluate the effects of vitrification on the expression of Wnt pathway related genes in preantral follicles (PFs).

Methods

Isolated PFs (n=982) of 14-16 day old female mice (n=45: 15 for each group) were divided into fresh (n=265), toxicity (n=272), and vitrified (n=265). The mRNA levels of Wnt2, Wnt4, Lrp5 and Fzd3 were evaluated by real-time PCR on the 2nd and 6th days of culture period. One-way ANOVA was conducted to analyze the data. Post hoc Tukey's HSD was used for multiple comparisons and p-value less than 0.05 was considered statistically significant.

Results

The developmental parameters of fresh PFs were significantly higher than those of vitrified (p<0.001). There were no differences between fresh and vitrified PFs on the 2nd day of culture (p<0.001). Wnt4 expression levels decreased significantly in vitrified groups compared with fresh ones (p<0.001). Fzd3 and Lrp expression levels increased significantly in vitrified groups compared with those in the fresh group on the 2nd day (p<0.001). On the 6th day of culture period, the expression levels of Wnt2 and Fzd3 increased significantly in vitrified group compared to those of fresh group (p<0.001). Moreover, the expression levels of Wnt4 and Lrp increased significantly in toxicity groups compared to those of the control group (p<0.001).

Conclusion

Vitrification increase the expression levels of Wnt2, Lrp and Fzd3 genes of PFs during in vitro culture.

Review of ovarian tissue cryopreservation techniques for fertility preservation

Ovarian failure and ovarian malfunction are among major fertility problems in women of reproductive age (18-35 years). It is known that various diseases, such as ovarian cancer and premature ovarian failure, besides certain treatments, such as radiotherapy and chemotherapy of other organs, can affect the normal process of folliculogenesis and cause infertility. In recent years, various procedures have been proposed for the treatment of infertility. One of the newest methods is the use of cryopreservation ovarian fragments after cancer treatment. According to some studies, this method yields very satisfactory results. Although ovarian tissue cryopreservation (OTC) is an accepted technique of fertility preservation, the relative efficacy of cryopreservation protocols remains controversial. Considering the controversies about these methods and their results, in this study, we aimed to compare different techniques of ovarian cryopreservation and investigate their advantages and disadvantages. Reviewing the published articles may be possible to identify appropriate strategies and improve infertility treatment in these patients.

Female Oncofertility: Current Understandings, Therapeutic Approaches, Controversies, and Future Perspectives

Recent advances in early detection and oncological therapies have ameliorated the survival rate of young cancer patients. Yet, ovarian impairment induced by chemotherapy and radiotherapy is still a challenging issue. This review, based on clinical and lab-based studies, summarizes the evidence of gonadotoxicity of chemoradiotherapy, the recent approaches, ongoing controversies, and future perspectives of fertility preservation (FP) in female patients who have experienced chemo- or radio-therapy. Existing data indicate that chemotherapeutic agents induce DNA alterations and massive follicle activation via the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. Meanwhile, the radiation causes ionizing damage, leading to germ cell loss. In addition to the well-established methods, numerous therapeutic approaches have been suggested, including minimizing the follicle loss in cryopreserved ovarian grafts after transplantation, in vitro activation or in vitro growing of follicles, artificial ovarian development, or fertoprotective adjuvant to prevent ovarian damage from chemotherapy. Some reports have revealed positive outcomes from these therapies, whereas others have demonstrated conflictions. Future perspectives are improving the live birth rate of FP, especially in patients with adverse ovarian reserve, eliminating the risk of malignancy reintroducing, and increasing society’s awareness of FP importance.

Post-thawing and culture comparison of three routine slow freezing methods for human ovarian tissue cryopreservation: Histological, molecular, and hormonal aspects

To find the gold standard out of three pre-established routine slow freezing (SF) methods, ovarian cortex tissues of nine transsexual individuals were cryopreserved and compared to each other, as well as the control (fresh) samples. Histological, genomic, and endocrinological effects of the SFs were assessed post-thawing and after a seven-day culture period. SF1 included 10% dimethyl-sulfoxide (Me2SO) in the base medium (BM), SF2 had 1.5 M/L ethylene-glycol (EG) and 0.1 M/L sucrose in the BM, and SF3 consisted of 6% Me2SO, 6% EG and 0.15 M/L sucrose in the BM. The cortical tissue strips went under a programmed cooling process and were stored in liquid nitrogen. Histological criteria (tissue damage and follicular quality), as well as gene expression levels, were assessed in the thawed and control tissues. Half of the thawed and control tissues were cultured for seven days and their histology, genetic profile, and hormonal status were examined as the reflection of the avascular tension effect. Post-thawing tissue damage was similar between all groups but significantly increased post-culture (P < 0.05). The percentages of high-quality follicles diminished in all SFs after thawing and culture (P < 0.05) except for the similarity of post-thawing SF3, compared to control. The genetic profile of the tissue after thawing and culture suggested quiescence/activation balance in SF1 and 2 and significant down-regulation in SF3, compared to the control specimens (P < 0.05). Post-thawing BAX:BCL2 was higher than control in SF1 and SF3 (P < 0.05), while this ratio in SF2 was similar to the control. However, after culture this ratio was similar to that of control in SF3 and diminished in SF1 and 2 (P < 0.05). The expression levels of gap-junction genes showed dramatic pre- and post-thawing fluctuations in all groups. After culture, estradiol in SF3 was significantly higher than SF1 and 2 (P < 0.05). In addition, progesterone in SF3 was similar to control but significantly lower in SF1 and 2 (P < 0.05). In conclusion, all SFs showed advantages and disadvantages, and the follicular quality and its function depend on the type of cryoprotectant and the speed of thawing. The effects of freezing/thawing continue to appear during the seven days of culture. According to the results of this study, SF3 seems to be more promising in keeping the follicles functional and safe from cell damage during culture.

Cryopreservation of Gametes and Embryos and Their Molecular Changes

The process of freezing cells or tissues and depositing them in liquid nitrogen at -196 °C is called cryopreservation. Sub-zero temperature is not a physiological condition for cells and water ice crystals represent the main problem since they induce cell death, principally in large cells like oocytes, which have a meiotic spindle that degenerates during this process. Significantly, cryopreservation represents an option for fertility preservation in patients who develop gonadal failure for any condition and those who want to freeze their germ cells for later use. The possibility of freezing sperm, oocytes, and embryos has been available for a long time, and in 1983 the first birth with thawed oocytes was achieved. From the mid-2000s forward, the use of egg vitrification through intracytoplasmic sperm injection has improved pregnancy rates. Births using assisted reproductive technologies (ART) have some adverse conditions and events. These risks could be associated with ART procedures or related to infertility. Cryopreservation generates changes in the epigenome of gametes and embryos, given that ART occurs when the epigenome is most vulnerable. Furthermore, cryoprotective agents induce alterations in the integrity of germ cells and embryos. Notably, cryopreservation extensively affects cell viability, generates proteomic profile changes, compromises crucial cellular functions, and alters sperm motility. This technique has been widely employed since the 1980s and there is a lack of knowledge about molecular changes. The emerging view is that molecular changes are associated with cryopreservation, affecting metabolism, cytoarchitecture, calcium homeostasis, epigenetic state, and cell survival, which compromise the fertilization in ART.

Comparison of open and a novel closed vitrification system with slow freezing for human ovarian tissue cryopreservation

PURPOSE

To investigate the differences concerning post-thawing/warming follicle survival, DNA damage and apoptosis in human ovarian tissues cryopreserved by slow freezing, open, or closed vitrification methods.

METHODS

A total of 50 pieces of 5 × 5 × 1 mm ovarian cortical pieces were harvested (5 donor ovaries; mean age 31 ± 6.62 years). From each donor, one cortical piece was used as baseline; the remaining were randomly assigned to slow freezing (SF), vitrification using open device (VF-open), or closed device (VF-closed) groups. After 8-10 weeks of cryostorage, tissues were evaluated 4 h after thawing/warming. Histological analysis was evaluated for follicle survival (primordial and primary follicle densities) by H&E staining. The percentages of primordial and primary follicles with DNA double-strand breaks (γH2AX) and apoptotic cell death pathway activation (AC3) were immunohistochemically assessed. Data were analysed using one-way ANOVA and LSD post hoc comparison.

RESULTS

Compared to the baseline, primordial follicle (pdf) densities significantly declined in all cryopreserved groups (SF, VF-open, and VF-closed, P < 0.05). However, the total and non-apoptotic pdf densities were similar among SF, VF-open, and VF-closed. SF and VF with either open or closed devices did not increase the percentages of primordial or primary follicles with DNA double-strand breaks (DSBs) or apoptosis compared to the baseline or among the freezing methods in the present study.

CONCLUSION

Based on the intact primordial follicle survival, DNA damage, and apoptosis rates after thawing/warming, SF vs VF with either open or newly developed closed devices appear to be comparable.

Methods of Ovarian Tissue Cryopreservation: Is Vitrification Superior to Slow Freezing?-Ovarian Tissue Freezing Methods

After cancer treatment, female survivors often develop ovarian insufficiency or failure. Oocyte and embryo freezing are well-established fertility preservation options, but cannot be applied in pre-pubescent girls, in women with hormone-sensitive malignancies, or when gonadotoxic treatment cannot be delayed. Although ovarian tissue cryopreservation (OTC) has been used to restore fertility and endocrine function, the relative efficacy of its two major protocols, slow freezing and vitrification, remains controversial. This literature review evaluates clinical and lab-based studies published between January 2012 and June 2020 to determine whether vitrification, the optimal technique for oocyte and embryo cryopreservation, preserves ovarian tissue more effectively than slow freezing. Due to limited clinical data involving ovarian tissue vitrification, most clinical studies focus on slow freezing. Only 9 biochemical studies that directly compare the effects of slow freezing and vitrification of human ovarian tissue were noted. Most studies report no significant difference in follicular morphology and distribution between cryopreservation methods, but these findings must be interpreted in the context of high methodological variability. Discrepant findings regarding the effects of cryopreservation method on follicle viability, gene expression, and hormone production require further evaluation. Early clinical outcomes appear favorable for vitrification, but additional studies and longer term follow-up are needed to establish its efficacy. Sharing data through national or international registries would expedite this analysis. However, even if research corroborates conclusions of no clinical or biochemical difference between cryopreservation methods, the decreased costs and increased efficiency associated with vitrification make this method more accessible and cost-effective.

Comparison between two cryopreservation techniques of human ovarian cortex: morphological aspects and the heat shock response (HSR)

This study was tailored to compare the cryopreservation of the human ovarian cortex using closed metal container vitrification or the slow-freezing technique. Superficial ovarian cortical tissue biopsies were collected from 12 participants who underwent gynaecological videolaparoscopy. The fragmented samples were allocated to three experimental conditions: (a) fresh ovarian tissue, (b) slow-freezing, and (c) vitrification with a metal closed container. After thawing or rewarming, cellular morphological analyses were performed to determine tissue viability. The cellular response to thermal stress was measured by a putative increase in the immune quantification of the heat shock protein 70 kDa (heat shock protein 70 kDa response - HSR) after a heat challenge (2 h exposure at 42 °C). Both the total number of intact follicles and the frequency of primordial follicles were higher in fresh ovarian tissue than in the preserved samples, regardless of the technique employed. There was a trend towards an increase in the absolute number of intact follicles in the tissue preserved by vitrification. After cryopreservation, a higher HSR was obtained after slow-freezing. These results indicate that both cryopreservation techniques present advantages and may be used as alternatives to ovarian tissue cryopreservation.

Diverse Approaches to Ovarian Tissue Cryopreservation Have Equivalent Outcomes in Markers of Tissue Viability

Ovarian tissue cryopreservation (OTC) is an accepted method of fertility preservation. However, OTC is not standardized and many variations exist in the freezing strategy, tissue processing, and surgical approach. In this pilot study, we used a sheep model to compare slow freezing versus vitrification techniques, as well as the feasibility of processing ovarian tissue into a hyaluronan suspension of small ovarian units. Twelve ovaries were harvested from six female ewes. Paired tissues from each animal were assigned to different treatments and underwent freezing, thawing, autotransplantation, and second-look surgery, for a total of 18 surgical procedures and 3 measured time points. Treatments included whole tissue strips versus gel suspension and slow freezing versus vitrification. At each of the time points, tissue viability was measured by immunohistochemical analysis of CD31 and cleaved caspase-3 (CCASP3). CD31 and CCASP3 expression levels were equivalent between slow freezing and vitrification, and between whole ovarian tissue strips and gel suspension of fragmented ovarian tissue, at all time points. These preliminary data using a sheep model suggest that ovarian tissue is robust and likely to be minimally affected by aggressive fragmentation using a hyaluronan suspension. Furthermore, we provide evidence in support of vitrification as a viable option in OTC. Hyaluronan suspension of ovarian cortical fragments is novel and may represent a desirable method for reimplantation of frozen-thawed ovarian tissue in patients where occult malignant cells are a concern.

Passive slow freezing is an efficacious and cost-effective alternative to controlled slow freezing for ovarian tissue cryopreservation

We aimed to assess the feasibility of passive slow freezing (PSF using Mr. Frosty container, Nalgene) as an alternative to controlled slow rate freezing (CSF using (Freezal™, Air liquide)) for human ovarian tissue (OT) cryopreservation. Validation studies needed were determined after assessing the risk associated (EuroGTP-II ART tool) and were conducted in 66 OT samples from 10 transgender men aged 23.4 ± 5.1 y. Folliculogenesis was assessed in vitro (after 2 h and 2 days of culture) and in vivo (2, 4 and 6 weeks xenotransplantation in Balbc/nude mice) by haematoxilin-eosin staining. Fibrosis was assessed by Masson's trichrome staining. Immunohistochemistry was used to study cell proliferation (PCNA and Ki-67) and apoptosis (caspase-3 and TUNEL). Differences in percentages were estimated using a generalized estimated equations method. After 2 days of in vitro culture, higher odds of primordial follicles (PF) (OR 1.626; 95%CI (1.162-2.266); P = 0.004) and lower odds of growing follicles (GF) (OR 0.616; 95%CI (0.441-0.861); P = 0.004) were associated with the established CSF technique. No statistical differences were found in the mean estimated proportion of proliferating (Ki-67+ or PCNA+) or apoptotic (caspase-3+ or Tunel+) follicles. Two and 6 weeks after xenotransplantation, respectively lower odds of GF (OR 0.419; 95%CI (0.217-0.809); P = 0.010) and secondary follicles (OR 0.135; 95%CI (0.071-0.255); P < 0.001) were associated with CSF. Proportion of fibrosis was similar. This validation study shows a higher follicle activation after 2 days in vitro and after 2 weeks following xenotransplantation in mice using PSF. PSF may be an easy, cost-effective low-risk alternative to CSF for cryopreservation of human OT.

Ovarian tissue cryopreservation and novel bioengineering approaches for fertility preservation

PURPOSE OF REVIEW

Breast cancer patients who cannot delay treatment or for whom hormone stimulation and egg retrieval are contraindicated require alternative methods of fertility preservation prior to gonadotoxic treatment. Ovarian tissue cryopreservation is an alternative approach that may offer patients the opportunity to preserve fertility and carry biologically-related children later in life. Various experimental approaches are being explored to obtain mature gametes from cryopreserved and thawed ovarian tissue for fertilization and implantation using biomimetic tissue culture in vitro. Here we review the most recent developments in ovarian tissue cryopreservation and exciting advances in bioengineering approaches to in vitro tissue and ovarian follicle culture.

RECENT FINDINGS

Slow freezing is the most widely accepted method for ovarian tissue cryopreservation, but efforts have been made to modify vitrification for this application as well. Numerous approaches to in vitro tissue and follicle culture are in development, most prominently two-step culture systems for ovarian cortical tissue and encapsulation of ovarian follicles in biomimetic matrices for in vitro culture.

SUMMARY

Refinements to slow freeze and vitrification protocols continue to address challenges associated with cryopreservation, such as ice crystal formation and damage to the stroma. Similarly, improvements to in vitro tissue and follicle culture show promise for utilizing patients' cryopreserved tissues to obtain mature gametes after disease treatment and remission. Development of an effective and reproducible culture system for human ovarian follicles will serve as a broad assisted reproductive technology for cancer survivors who cryopreserved tissue prior to treatment.

ESHRE guideline: female fertility preservation

STUDY QUESTION

What is the recommended management for women and transgender men with regards to fertility preservation (FP), based on the best available evidence in the literature?

SUMMARY ANSWER

The ESHRE Guideline on Female Fertility Preservation makes 78 recommendations on organization of care, information provision and support, pre-FP assessment, FP interventions and after treatment care. Ongoing developments in FP are also discussed.

WHAT IS KNOWN ALREADY

The field of FP has grown hugely in the last two decades, driven by the increasing recognition of the importance of potential loss of fertility as a significant effect of the treatment of cancer and other serious diseases, and the development of the enabling technologies of oocyte vitrification and ovarian tissue cryopreservation (OTC) for subsequent autografting. This has led to the widespread, though uneven, provision of FP for young women.

STUDY DESIGN SIZE DURATION

The guideline was developed according to the structured methodology for development of ESHRE guidelines. After formulation of key questions by a group of experts, literature searches and assessments were performed. Papers published up to 1 November 2019 and written in English were included in the review.

PARTICIPANTS/MATERIALS SETTING METHODS

Based on the collected evidence, recommendations were formulated and discussed until consensus was reached within the guideline group. A stakeholder review was organized after finalization of the draft. The final version was approved by the guideline group and the ESHRE Executive Committee.

MAIN RESULTS AND THE ROLE OF CHANCE

This guideline aims to help providers meet a growing demand for FP options by diverse groups of patients, including those diagnosed with cancer undergoing gonadotoxic treatments, with benign diseases undergoing gonadotoxic treatments or those with a genetic condition predisposing to premature ovarian insufficiency, transgender men (assigned female at birth), and women requesting oocyte cryopreservation for age-related fertility loss.The guideline makes 78 recommendations on information provision and support, pre-FP assessment, FP interventions and after treatment care, including 50 evidence-based recommendations-of which 31 were formulated as strong recommendations and 19 as weak-25 good practice points and 3 research only recommendations. Of the evidence-based recommendations, 1 was supported by high-quality evidence, 3 by moderate-quality evidence, 17 by low-quality evidence and 29 by very low-quality evidence. To support future research in the field of female FP, a list of research recommendations is provided.

LIMITATIONS REASONS FOR CAUTION

Most interventions included are not well studied in FP patients. As some interventions, e.g. oocyte and embryo cryopreservation, are well established for treatment of infertility, technical aspects, feasibility and outcomes can be extrapolated. For other interventions, such as OTC and IVM, more evidence is required, specifically pregnancy outcomes after applying these techniques for FP patients. Such future studies may require the current recommendations to be revised.

WIDER IMPLICATIONS OF THE FINDINGS

The guideline provides clinicians with clear advice on best practice in female FP, based on the best evidence currently available. In addition, a list of research recommendations is provided to stimulate further studies in FP.

STUDY FUNDING/COMPETING INTERESTS

The guideline was developed and funded by ESHRE, covering expenses associated with the guideline meetings, with the literature searches and with the dissemination of the guideline. The guideline group members did not receive payment. R.A.A. reports personal fees and non-financial support from Roche Diagnostics, personal fees from Ferring Pharmaceuticals, IBSA and Merck Serono, outside the submitted work; D.B. reports grants from Merck Serono and Goodlife, outside the submitted work; I.D. reports consulting fees from Roche and speaker's fees from Novartis; M.L. reports personal fees from Roche, Novartis, Pfizer, Lilly, Takeda, and Theramex, outside the submitted work. The other authors have no conflicts of interest to declare.

DISCLAIMER

This guideline represents the views of ESHRE, which were achieved after careful consideration of the scientific evidence available at the time of preparation. In the absence of scientific evidence on certain aspects, a consensus between the relevant ESHRE stakeholders has been obtained. Adherence to these clinical practice guidelines does not guarantee a successful or specific outcome, nor does it establish a standard of care. Clinical practice guidelines do not replace the need for application of clinical judgment to each individual presentation, nor variations based on locality and facility type. ESHRE makes no warranty, express or implied, regarding the clinical practice guidelines and specifically excludes any warranties of merchantability and fitness for a particular use or purpose. (Full disclaimer available at  www.eshre.eu/guidelines.) ^†ESHRE Pages content is not externally peer reviewed. The manuscript has been approved by the Executive Committee of ESHRE.

Low KLOTHO level related to aging is associated with diminished ovarian reserve

OBJECTIVE

To explore the relationship between KLOTHO expression and diminished ovarian reserve (DOR).

DESIGN

A case-control study.

SETTING

Reproductive medicine center.

PATIENT(S)

A total of 157 patients with DOR and 159 control women were recruited from the Centre of Reproductive Medicine, Peking University Third Hospital.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The granulosa cells were isolated from follicular fluid after oocyte retrieval, and the KLOTHO level of granulosa cell was measured using a modified quantitative polymerase chain reaction technique. The serum KLOTHO level was measured by solid-phase sandwich enzyme-linked immunosorbent assay.

RESULT(S)

In both granulosa cells and serum derived from women with DOR, KLOTHO expressions were significantly lower compared with normal ovarian reserve controls. Moreover, KLOTHO expression diminished with advancing age.

CONCLUSION(S)

Diminished KLOTHO expression was associated with DOR. Further longitudinal studies in a similar population accompanying disease progression and mechanism exploration are needed to substantiate the rules of KLOTHO in reproductive aging.

Impacts of different synthetic polymers on vitrification of ovarian tissue

Type and concentration of cryoprotective agents (CPAs) are important factors which influence the likelihood of a successful ovarian tissue vitrification outcome. In an attempt to address this factor, the present study was conducted to evaluate the impacts of different synthetic polymers (Supercool X-1000, Supercool Z-1000 and PVP K-12) on vitrification of bovine ovarian tissue. From each ovarian pair, fragments were recovered and immediately fixed for analysis (fresh control) or submitted to vitrification, either or not followed by in vitro culture for one or five days. Vitrification was performed using the ovarian tissue cryosystem (OTC) system. The ovarian tissues were intended for histological and viability analysis [Reactive oxygen species (ROS) production and degenerate cells assay (Ethidium homodimer-1)], as well as immunolocalization of AQP3 and AQP9 were measured. The results showed that during almost all the periods after warming, in treatment groups which contain polymer (X-1000, Z-1000 and PVP), the percentage of morphologically normal follicles was the highest in the X-1000 samples. Furthermore, post-thawed X-1000 group revealed stronger labeling for AQP9 in primordial and transitional follicles, when compared with others. However, morphology after cryopreservation did not correlate with follicle viability and function where the levels of degeneration and tissue damage of PVP K-12 group were lower in comparison with X-1000 group and only in PVP K-12 group, ROS level was similar to that of the fresh control group. We believe that in addition to permeating CPAs, the addition of one (Supercool X-1000) or maybe a combination (Supercool X-1000 and PVP K-12) of non-permeating polymers could be useful to improve the outcome for vitrified bovine ovarian tissue.

Fertility Preservation in Women: Indications and Options for Therapy

Fertility preservation (FP) is a vital issue for individuals in either reproductive or prepubescent stage of life when future fertility may be compromised. The objective of any FP intervention is to minimize or eliminate primary disease burden and to ensure maintaining or preserving reproductive health. Fertility potential can be affected by cancer therapy and numerous other factors, including advancing age, metabolic conditions, autoimmune diseases, specific surgical interventions, and sex affirmation procedures. A paradigm shift focusing on quality-of-life issues and long-term survivorship has emerged, especially because of advances in cancer diagnostics and treatment. Several FP techniques have been widely distributed, while others are still in the research stage. In addition, specific procedures and some potentially fertoprotective agents are being developed, aiming to minimize the hazards of gonadal damage caused by cancer therapy and decrease the need for more costly, invasive, and time-consuming FP methods. This review highlights the advances, indications, and options for FP, both experimental and well-established, in females of various age groups. An electronic search in PubMed, Embase, and Google Scholar databases was conducted, including retrospective studies, prospective clinical trials, meta-analyses, original reviews, and online abstracts published up to June 30, 2019. The search terms used included fertility preservation, oncofertility, embryo cryopreservation, oocyte cryopreservation, and ovarian tissue cryopreservation. The meeting proceedings of the American Society for Reproductive Medicine and the European Society of Human Reproduction and Embryology were also hand searched.

Stepped vitrification technique for human ovarian tissue cryopreservation

The advantage of stepped vitrification (SV) is avoiding ice crystal nucleation, while decreasing the toxic effects of high cryoprotectant concentrations. We aimed to test this method for human ovarian tissue cryopreservation. Ovarian cortex was taken from 7 fertile adult women. Samples were subjected to an SV protocol performed in an automatic freezer, which allowed sample transfer to ever higher concentrations of dimethyl sulfoxide (DMSO) as the temperature was reduced. Histological evaluation of the vitrified-warmed tissue showed large numbers of degenerated follicles after 24 hours of in vitro culture. We therefore evaluated DMSO perfusion rates by X-ray computed tomography, ice crystal formation by freeze-substitution, and cell toxicity by transmission electron microscopy, seeking possible reasons why follicles degenerated. Although cryoprotectant perfusion was considered normal and no ice crystals were formed in the tissue, ultrastructural analysis detected typical signs of DMSO toxicity, such as mitochondria degeneration, alterations in chromatin condensation, cell vacuolization and extracellular matrix swelling in both stromal and follicular cells. The findings indicated that the method failed to preserve follicles due to the high concentrations of DMSO used. However, adaptations can be made to avoid toxicity to follicles caused by elevated levels of cryoprotectants.

Slow Freezing Versus Vitrification of Mouse Ovaries: from Ex Vivo Analyses to Successful Pregnancies after Auto-Transplantation

Slow freezing (SF) is the reference method for ovarian tissue cryopreservation. Vitrification (VT) constitutes an alternative but controversial method. This study compares SF and VT (open [VTo] and closed [VTc] systems) in terms of freezing damage and fertility restoration ability. In vitro analyses of C57Bl/6 SF or VTo-ovaries, immediately after thawing/warming or after culture (cult), revealed that event though follicular density was similar between all groups, nuclear density was decreased in VTo-ovaries compared to CT-ovaries (CT = 0.50 ± 0.012, SF = 0.41 ± 0.03 and VTo = 0.29 ± 0.044, p < 0.01). Apoptosis was higher in VTo-cult ovaries compared to SF-cult ovaries (p < 0.001) whereas follicular Bmp15 and Amh gene expression levels were decreased in the ovaries after culture, mostly after VTo (p < 0.001). Natural mating after auto-transplantation of SF, VTo and VTc-ovaries revealed that most mice recovered their oestrous cycle. Fertility was only restored with SF and VTo ovaries (SF: 68%; VTo: 63%; VTc: 0%; p < 0.001). Mice auto-transplanted with SF and VTo-ovaries achieved the highest number of pregnancies. In conclusion, in vitro, no differences between SF and VTo were evident immediately after thawing/warming but VTo ovaries displayed alterations in apoptosis and follicular specific proteins after culture. In vivo, SF and VTo ovary auto-transplantation fully restored fertility whereas with VTc-ovary auto-transplantation no pregnancies were achieved.

In vitro survival of follicles in prepubertal ewe ovarian cortex cryopreserved by slow freezing or non-equilibrium vitrification

PURPOSE

Vitrification is a well-accepted fertility preservation procedure for cryopreservation of oocytes and embryos but little is known regarding ovarian tissue, for which slow freezing is the current convention. The aim of the present study was to assess the efficiency of non-equilibrium vitrification compared to conventional slow freezing for ovarian cortex cryopreservation.

METHODS

Using prepubertal sheep ovaries, the capacity of the tissue to sustain folliculogenesis following cryopreservation and in vitro culture was evaluated. Ovarian cortex fragments were cultured in wells for 9 days, immediately or after cryopreservation by conventional slow freezing or non-equilibrium vitrification in straws. During culture, follicular populations within cortex were evaluated by histology and immunohistochemistry for PCNA and TUNEL. Steroidogenic activity of the tissue was monitored by assay for progesterone and estradiol in spent media.

RESULTS

No significant differences in follicle morphology, PCNA, or TUNEL labeling were observed between cryopreservation methods at the initiation of culture. Similar decreases in the proportion of primordial follicle population, and increases in the proportion of growing follicles, were observed following culture of fresh or cryopreserved ovarian tissue regardless of cryopreservation method. At the end of culture, PCNA and TUNEL-positive follicles were not statistically altered by slow freezing or vitrification in comparison to fresh cultured fragments.

CONCLUSIONS

Overall, for both cryopreservation methods, the cryopreserved tissue showed equal capacity to fresh tissue for supporting basal folliculogenesis in vitro. Taken together, these data confirm that both non-equilibrium vitrification and slow-freezing methods are both efficient for the cryopreservation of sheep ovarian cortex fragments.

Is the pre-antral ovarian follicle the 'holy grail'for female fertility preservation?

Fertility preservation is not only a concern for humans with compromised fertility after cancer treatment. The preservation of genetic material from endangered animal species or animals with important genetic traits will also greatly benefit from the development of alternative fertility preservation strategies. In humans, embryo cryopreservation and mature-oocyte cryopreservation are currently the only approved methods for fertility preservation. Ovarian tissue cryopreservation is specifically indicated for prepubertal girls and women whose cancer treatment cannot be postponed. The cryopreservation of pre-antral follicles (PAFs) is a safer alternative for cancer patients who are at risk of the reintroduction of malignant cells. As PAFs account for the vast majority of follicles in the ovarian cortex, they represent an untapped potential, which could be cultivated for reproduction, preservation, or research purposes. Vitrification is being used more and more as it seems to yield better results compared to slow freezing, although protocols still need to be optimized for each specific cell type and species. Several methods can be used to assess follicle quality, ranging from simple viability stains to more complex xenografting procedures. In vitro development of PAFs to the pre-ovulatory stage has not yet been achieved in humans and larger animals. However, in vitro culture systems for PAFs are under development and are expected to become available in the near future. This review will focus on recent developments in (human) fertility preservation strategies, which are often accomplished by the use of in vitro animal models due to ethical considerations and the scarcity of human research material.

Impact of vitrification on granulosa cell survival and gene expression

INTRODUCTION

Cryopreservation of ovarian tissue is an essential step in Ovarian Tissue Banking. In order to prevent the formation of ice crystals, typically the tissue is slowly frozen using a cryoprotectant. As an alternative the method of ultra-fast freezing by vitrification becomes more attention for freezing ovarian tissue because it has successfully been used for oocytes, embryos and sperm. However the impact of vitrification on granulosa cells, which are an essential part of ovarian tissue is uncertain.

AIM

In this study, we have therefore analysed the influence of vitrification on the survival rates of granulosa cells, the impact of DMSO or ethylenglycol containing vitrification protocols and investigated to what extent the gene expression of apoptosis- and temperature-sensitive genes changes.

MATERIAL AND METHODS

We used the human granulosa cell line KGN as a model for human granulosa cells and determined the survival rate and cell cycle stages by FACS analyses. The change in gene expression was determined by quantitative PCR analyses.

RESULTS

Our results show that vitrification is possible in granulosa cells but it reduces cell viability and leads to fluctuations in the cell cycle. The DMSO containing protocol results in a lower amount of dead cells than the ethylenglycol containing protocol. Gene expression analysis reveals that TNF-alpha expression is strongly increased after vitrification, while other apoptosis or temperature-related genes seem to stay unaffected.

CONCLUSION

We conclude that vitrification influences the viability of human granulosa cells. Furthermore, our results suggest that this could be mediated by a change in TNF-alpha gene expression.

Innovative multi-protectoral approach increases survival rate after vitrification of ovarian tissue and isolated follicles with improved results in comparison with conventional method

Background

In recent years, autotransplantation of cryopreserved ovarian tissue became a promising approach to preserve female fertility. The slow freezing is the most effective technique which resulted in greater live birth incidence so far. Despite that, interest to vitrification of the ovarian tissue is swiftly growing, thereby undermining the necessity for further improvements in the technique. In present study, we evaluated possibilities to increase follicle survival rates adopting innovative multi-protectoral vitrification protocols, applied to the slivers of ovarian cortex or isolated early-antral follicles, frozen individually. These experimental protocols have been compared with with validated vitrification and slow freezing ones, clinically used for female fertility preservation.

Results

The results showed that third tested variation of experimental vitrification protocol, with four cryoprotectants in relatively low concentrations and applied to pieces of ovarian tissue at 0 °C during equilibration, increased survival rate of ovine ovarian tissue and improved results in comparison with conventional vitrification method. This variation of experimental protocol showed significant increase in percentage of follicles with good morphology (69,3%) in comparison with only commercially available vitrification protocol for ovarian tissue (62,1%). Morphology results were confirmed by TUNEL assay. Analysis of estradiol and progesterone production by cultured individual follicles after freezing/thawing revealed that steroids secretion remained significantly higher after multi-protectoral vitrification and slow freezing protocol, when follicles after standard vitrification protocol demonstrated decline in steroidogenic activity.

Conclusions

The multi-protectoral approach represents a workable solution to improve vitrification outcome on ovarian tissue and isolated follicles. The reduction of individual cryoprotectants concentrations, while maintaining their sufficient cumulative level in the final freezing solution, helps to increase efficiency of the procedure. Moreover, equilibration with lower temperatures helped to decrease even further the toxic effects of cryoprotectants and preserve original quality of ovarian tissue. Therefore, multi-protectoral vitrification can be suggested as an improved method for the clinical cryopreservation of ovarian tissue.