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.

Prior exposure to chemotherapy does not reduce the in vitro maturation potential of oocytes obtained from ovarian cortex in cancer patients

STUDY QUESTION

Does chemotherapy exposure affect IVM potential of immature oocytes retrieved from the ovarian cortex following ovarian tissue cryopreservation (OTC) for fertility preservation?

SUMMARY ANSWER

The IVM potential of oocyte retrieved from ovarian cortex following OTC is not affected by prior exposure to chemotherapy but primarily dependent on patient's age, while successful retrieval of immature oocytes from the ovarian tissue is negatively affected by chemotherapy and its timing.

WHAT IS KNOWN ALREADY

The potential and feasibility of IVM in premenarche patients was previously demonstrated, in smaller studies. The scarce data that exist on the IVM potential of oocytes retrieved during OTC following chemotherapy support the feasibility of this process, however, this was not previously shown in the premenarche cancer patients population or in larger cohorts.

STUDY DESIGN, SIZE, DURATION

A retrospective cohort study evaluating 229 cancer patients aged 1-39 years with attempted retrieval of oocytes from the ovarian tissue and the medium following OTC in a university affiliated fertility preservation unit between 2002 and 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 172 chemotherapy naïve and 57 chemotherapy exposed patients aged 1-39 years underwent OTC in university affiliated tertiary infertility and IVF center. OTC and IVM outcomes were compared between the chemotherapy naïve and exposed groups. The main outcome measure was mean IVM rate per patient in the chemotherapy naïve and exposed groups, with subgroup analysis of a 1:1 chemotherapy exposed group matched for age at OTC and type of malignancy. We additionally analyzed premenarche and postmenarche patients' outcomes separately and investigated the effect of time from chemotherapy to IVM, malignancy type and chemotherapy regimen on oocyte number and IVM outcomes in the chemotherapy exposed group.

MAIN RESULTS AND THE ROLE OF CHANCE

While the number of retrieved oocytes and percentage of patients with at least one oocyte retrieved was higher in the chemotherapy naïve group (8.7 ± 7.9 versus 4.9 ± 5.6 oocytes and 87.2% versus 73.7%, P < 0.001 and P = 0.016, respectively), IVM rate and number of mature oocytes were comparable between the groups (29.0 ± 25.0% versus 28. 9 ± 29.2% and 2.8 ± 3.1 versus 2.2 ± 2.8, P = 0.979 and P = 0.203, respectively). Similar findings were shown in subgroup analyses for premenarche and postmenarche groups. The only parameter found to be independently associated with IVM rate in a multivariable model was menarche status (F = 8.91, P = 0.004). Logistic regression models similarly showed that past chemotherapy exposure is negatively associated with successful retrieval of oocytes while older age and menarche are predictive of successful IVM. An age and the type of malignancy matched (1:1) chemotherapy naïve and exposed groups were created (25 patients in each group). This comparison demonstrated similar IVM rate (35.4 ± 30.1% versus 31.0 ± 25.2%, P = 0.533) and number of matured oocytes (2.7 ± 3.0. versus 3.0 ± 3.9 oocytes, P = 0.772). Type of malignancy and chemotherapy regimen including alkylating agents were not associated with IVM rate.

LIMITATIONS, REASONS FOR CAUTION

This study's inherited retrospective design and the long study period carries the possible technological advancement and differences. The chemotherapy exposed group was relatively small and included different age groups. We could only evaluate the potential of the oocytes to reach metaphase II in vitro but not their fertilization potential or clinical outcomes.

WIDER IMPLICATIONS OF THE FINDINGS

IVM is feasible even after chemotherapy broadening the fertility preservation options of cancer patients. The use of IVM for fertility preservation, even after exposure to chemotherapy, should be further studied for optimal postchemotherapy timing safety and for the in vitro matured oocytes potential for fertilization.

STUDY FUNDING/COMPETING INTEREST(S)

No funding was received for this study by any of the authors. The authors report that no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Chemotherapy and female fertility

Chemotherapy to treat cancer is usually responsible for early ovarian follicle depletion. Ovarian damage induced by cancer treatments frequently results in infertility in surviving patients of childbearing age. Several fertility preservation techniques have been developed. Nowadays, oocyte or embryo cryopreservation with or without ovarian stimulation and cryopreservation of the ovarian cortex are the most commonly used. However, these methods may be difficult to implement in some situations, and subsequent use of the cryopreserved germ cells remains uncertain, with no guarantee of pregnancy. Improved knowledge of the molecular mechanisms and signaling pathways involved in chemotherapy-induced ovarian damage is therefore necessary, to develop new strategies for fertility preservation. The effects of various chemotherapies have been studied in animal models or in vitro on ovarian cultures, suggesting various mechanisms of gonadotoxicity. Today the challenge is to develop molecules and techniques to limit the negative impact of chemotherapy on the ovaries, using experimental models, especially in animals. In this review, the various theories concerning ovarian damage induced by chemotherapy will be reviewed and emerging approaches for ovarian protection will be explained.

Irinotecan (CPT-11) Treatment Induces Mild Gonadotoxicity

BACKGROUND

Gonadal toxicity following chemotherapy is an important issue among the population of young cancer survivors. The inhibitor of DNA topoisomerase I, irinotecan (CPT-11), is widely used for several cancer types. However, little is known about the effect of irinotecan on the fertility of both genders. Thus, the aim of the present study was to evaluate irinotecan gonadotoxicity, using a mouse model.

METHODS

Mature male and female mice were injected intraperitoneally with either saline (), irinotecan (100 mg/kg) or cyclophosphamide (100 mg/kg); and sacrificed one week or three months later for an acute or long-term toxicity assessment, respectively. We used thorough and advanced fertility assessment by already established methods: Gonadal and epididymal weights, as well as sperm count and sperm motility were determined; serum anti-Müllerian hormone (AMH) was measured by ELISA. Immunohistochemistry (Ki-67), immunofluorescence (PCNA, CD34), terminal transferase-mediated deoxyuridine 5-triphosphate nick-end labeling (TUNEL) and computerized analysis were performed to examine gonadal proliferation, apoptosis and vascularization. qPCR was used to assess the amount of testicular spermatogonia (Id4 and Gafra1 mRNA) and ovarian primordial oocytes reserves (Sohlh2, Nobox and Figla mRNA).

RESULTS

Females: Irinotecan administration induced acute ovarian apoptosis and decreased vascularity, as well as a mild, statistically significant, long-term decrease in the number of growing follicles, ovarian weight, and ovarian reserve. Males: Irinotecan administration caused an acute testicular apoptosis and reduced testicular spermatogenesis, but had no effect on vascularity. Irinotecan induced long-term decrease of testicular weight, sperm count and testicular spermatogonia and caused elevated serum AMH.

CONCLUSION

Our findings imply a mild, though irreversible effect of irinotecan on mice gonads.

Perinatal hypoxia leads to primordial follicle activation and premature depletion of ovarian reserve

BACKGROUND

The human ovary contains 6-million follicles during the 20th week of embryonic development and 1 million at birth. Girls born at small for gestational age weight demonstrate higher FSH levels during infancy, an earlier onset of puberty, and menarche. In light of these observations, we hypothesized that exposure to hypoxia at the early neonatal period might impact the primordial follicular pool and lead to premature depletion of ovarian reserve.

METHODS

Ovarian development in the rat model at days 1-5 postpartum reflects its human counterpart in the late perinatal period. We exposed newborn rat pups (n = 5) to controlled hypoxia, (5% oxygen/95% nitrogen) for 10 min three times daily for days 1-5 postpartum. On day 5, ovaries were harvested, H&E, Ki-67, and TUNEL staining were performed.

RESULTS

The percentage of primordial follicles out of total follicles in ovaries of pups exposed to hypoxia was lower compared to control (76 ± 8.2% and 90.33 ± 6.3% respectively, p < .05). Correspondingly the percentage of primary and secondary follicles was higher than in control. The mean stromal Ki67 staining score was significantly lower in the study group (1.67 ± 0.58 and 2.5 ± 0.55 respectively, p < .05). TUNEL staining demonstrated no difference in stromal apoptosis rates between both groups.

CONCLUSIONS

We provide evidence for the first time that perinatal hypoxia causes premature activation and growth initiation of dormant follicles. These changes were associated with decreased stromal cell proliferation, suggesting hypoxia-induced impairment of the support cell pool as a possible mechanism for accelerated follicular activation.

The role of gonadotropin-releasing hormone agonists in female fertility preservation

Advances in anticancer treatments have resulted in increasing survival rates among cancer patients. Accordingly, the quality of life after treatment, particularly the preservation of fertility, has gradually emerged as an essential consideration. Cryopreservation of embryos or unfertilized oocytes has been considered as the standard method of fertility preservation among young women facing gonadotoxic chemotherapy. Other methods, including ovarian suppression and ovarian tissue cryopreservation, have been considered experimental. Recent large-scale randomized controlled trials have demonstrated that temporary ovarian suppression using gonadotropin-releasing hormone agonists (GnRHa) during chemotherapy is beneficial for preventing chemotherapy-induced premature ovarian insufficiency in breast cancer patients. It should also be emphasized that GnRHa use during chemotherapy does not replace established fertility preservation methods. All young women facing gonadotoxic chemotherapy should be counseled about and offered various options for fertility preservation, including both GnRHa use and cryopreservation of embryos, oocytes, and/or ovarian tissue.

Use of Simvastatin, Fibrin Clots, and Their Combination to Improve Human Ovarian Tissue Grafting for Fertility Restoration After Anti-Cancer Therapy

Anticancer treatments, particularly chemotherapy, induce ovarian damage and loss of ovarian follicles. There are limited options for fertility restoration, one of which is pre-chemotherapy cryopreservation of ovarian tissue. Transplantation of frozen-thawed human ovarian tissue from cancer survivors has resulted in live-births. There is extensive follicular loss immediately after grafting, probably due to too slow graft revascularization. To avoid this problem, it is important to develop methods to improve ovarian tissue neovascularization. The study's purpose was to investigate if treatment of murine hosts with simvastatin or/and embedding human ovarian tissue within fibrin clots can improve human ovarian tissue grafting (simvastatin and fibrin clots promote vascularization). There was a significantly higher number of follicles in group A (ungrafted control) than in group B (untreated tissue). Group C (simvastatin-treated hosts) had the highest levels of follicle atresia. Group C had significantly more proliferating follicles (Ki67-stained) than groups B and E (simvastatin-treated hosts and tissue embedded within fibrin clots), group D (tissue embedded within fibrin clots) had significantly more proliferating follicles (Ki67-stained) than group B. On immunofluorescence study, only groups D and E showed vascular structures that expressed both human and murine markers (mouse-specific platelet endothelial cell adhesion molecule, PECAM, and human-specific von Willebrand factor, vWF). Peripheral human vWF expression was significantly higher in group E than group B. Diffuse human vWF expression was significantly higher in groups A and E than groups B and C. When grafts were not embedded in fibrin, there was a significant loss of human vWF expression compared to groups A and E. This protocol may be tested to improve ovarian implantation in cancer survivors.

Impact of first-line cancer treatment on the follicle quality in cryopreserved ovarian samples from girls and young women

STUDY QUESTION

Does first-line chemotherapy affect the quality of ovarian pre-antral follicles and stromal tissue in a population of young patients?

SUMMARY ANSWER

Exposure to first-line chemotherapy significantly impacts follicle viability, size of residual intact follicles, steroid secretion in culture and quality of the stromal compartment.

WHAT IS KNOWN ALREADY

First-line chemotherapy is considered to have a low gonadotoxic potential, and as such, does not represent an indication for fertility preservation. Studies investigating the effects of chemotherapy on the quality of ovarian tissue stored for fertility preservation in young patients are limited and the results sometimes contradictory.

STUDY DESIGN, SIZE, DURATION

We conducted a retrospective cohort study including young patients referred to three centers (Helsinki, Oslo and Tampere) to perform ovarian tissue cryopreservation for fertility preservation between 2003 and 2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 43 patients (age 1-24 years) were included in the study. A total of 25 were exposed to first-line chemotherapy before cryopreservation, whereas 18 patients were not. Density and size of follicles divided by developmental stages, prevalence of atretic follicles, health of the stromal compartment and functionality of the tissue in culture were evaluated and related to age and chemotherapy exposure. Activation of dormant follicles and DNA damage were also assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Patients exposed to first-line chemotherapy showed a significantly higher density of atretic primordial and intermediary follicles than untreated patients. The intact primordial and intermediary follicles were significantly smaller in size in patients exposed to chemotherapy. Production of steroids in culture was also significantly impaired and a higher content of collagen and DNA damage was observed in the stromal compartment of treated patients. Collectively, these observations may indicate reduced quality and developmental capacity of follicles as a consequence of first-line chemotherapy exposure. Neither increased activation of dormant follicles nor elevated levels of DNA damage in oocyte nuclei were found in patients exposed to chemotherapy.

LIMITATIONS, REASONS FOR CAUTION

The two groups were not homogeneous in terms of age and the patients were exposed to different treatments, which did not allow us to distinguish the effect of specific agents. The limited material availability did not allow us to perform all the analyses on the entire set of patients.

WIDER IMPLICATION OF THE FINDINGS

This study provides for the first time a comprehensive analysis of the effects of first-line chemotherapy on the health, density and functionality of follicles categorized according to the developmental stage in patients under 24 years of age. When exposed to these treatments, patients were considered at low/medium risk of infertility. Our data suggest a profound impact of these relatively safe therapies on ovarian health and encourages further exploration of this effect in follow-up studies in order to optimize fertility preservation for young cancer patients.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Swedish Childhood Cancer Foundation, the Finnish Cancer Society, the Finnish Pediatric Research Foundation, the Väre Foundation for Pediatric Cancer Research, The Swedish Research Council, the Stockholm County Council (ALF project) and Karolinska Institutet. The authors have no conflict of interest to declare.

The Impact of Chemotherapy on the Ovaries: Molecular Aspects and the Prevention of Ovarian Damage

Cancer treatment, such as chemotherapy, induces early ovarian follicular depletion and subsequent infertility. In order to protect gametes from the gonadotoxic effects of chemotherapy, several fertility preservation techniques—such as oocyte or embryo cryopreservation with or without ovarian stimulation, or cryopreservation of the ovarian cortex—should be considered. However, these methods may be difficult to perform, and the future use of cryopreserved germ cells remains uncertain. Therefore, improving the methods currently available and developing new strategies to preserve fertility represent major challenges in the area of oncofertility. Animal and ovarian culture models have been used to decipher the effects of different cytotoxic agents on ovarian function and several theories regarding chemotherapy gonadotoxicity have been raised. For example, cytotoxic agents might (i) have a direct detrimental effect on the DNA of primordial follicles constituting the ovarian reserve and induce apoptosis; (ii) induce a massive growth of dormant follicles, which are then destroyed; or (ii) induce vascular ovarian damage. Thanks to improvements in the understanding of the mechanisms involved, a large number of studies have been carried out to develop molecules limiting the negative impact of chemotherapy on the ovaries.

Anti-Müllerian Hormone in Fertility Preservation: Clinical and Therapeutic Applications

Anti-Müllerian hormone (AMH) is a member of the transforming growth factor (TGF)-beta family and a key regulator of sexual differentiation and folliculogenesis. While the serum AMH level has been used in reproductive medicine as a biomarker of quantitative ovarian reserve for more than 20 years, new potential therapeutic applications of recombinant AMH are emerging, notably in the field of oncofertility. Indeed, it is well known that chemotherapy, used to treat cancer, induces ovarian follicular depletion and subsequent infertility. Animal models have been used widely to understand the effects of different cytotoxic agents on ovarian function, and several hypotheses regarding chemotherapy gonadotoxicity have been proposed, that is, it might have a direct detrimental effect on the primordial follicles constituting the ovarian reserve and/or on the pool of growing follicles secreting AMH. Recently, a new mechanism of chemotherapy-induced follicular depletion, called the “burn-out effect,” has been proposed. According to this theory, chemotherapeutic agents may lead to a massive growth of dormant follicles which are then destroyed. As AMH is one of the factors regulating the recruitment of primordial follicles from the ovarian reserve, recombinant AMH administration concomitant with chemotherapy might limit follicular depletion, therefore representing a promising option for preserving fertility in women suffering from cancer. This review reports on the potential usefulness of AMH measurement as well as AMH’s role as a therapeutic agent in the field of female fertility preservation.

Imatinib mesylate does not counteract ovarian tissue fibrosis in postnatal rat ovary

Chemotherapy may result in ovarian atrophy, a depletion of the primordial follicle pool, diminished ovarian weight, cortical and stromal fibrosis. Imatinib mesylate is an anticancer agent that inhibits competitively several receptor tyrosine kinases (RTKs). RTKs play important roles in cell metabolism, proliferation, and apoptosis. In clinic, imatinib mesylate is also known as an anti-fibrotic medicine. In the present study, the impact of imatinib on the ovarian tissue was investigated by assessing ovarian tissue fibrosis in postnatal rat administered with or without imatinib for three days. Fibrosis in the ovarian tissue was determined by histology (Picrosirius and Masson's trichrome staining) and the protein expression of vimentin and alpha-smooth muscle actin (α-SMA). Furthermore, mRNA expression of Forkhead box transcription factor O1 and O3 (FOXO1 and FOXO3), which are markers of cell proliferation was quantified. A short-term exposure to imatinib showed to increase tissue fibrosis in ovaries. This was observed by Masson's trichrome staining. Exposure to imatinib led also to a down-regulation of vimentin protein expression and up-regulation mRNA expression of FOXO3. This may indicate a role of FOXO3 in ovarian tissue fibrosis in postnatal rat ovaries.

Co-transplantation of Human Ovarian Tissue with Engineered Endothelial Cells: A Cell-based Strategy Combining Accelerated Perfusion with Direct Paracrine Delivery

Infertility is a frequent side effect of chemotherapy and/or radiotherapy and for some patients, cryopreservation of oocytes or embryos is not an option. As an alternative, an increasing number of these patients are choosing to cryopreserve ovarian tissue for autograft following recovery and remission. Despite improvements in outcomes among patients undergoing auto-transplantation of cryopreserved ovarian tissue, efficient revascularization of grafted tissue remains a major obstacle. To mitigate ischemia and thus improve outcomes in patients undergoing auto-transplantation, we developed a vascular cell-based strategy for accelerating perfusion of ovarian tissue. We describe a method for co-transplantation of exogenous endothelial cells (ExECs) with cryopreserved ovarian tissue in a mouse xenograft model. We extend this approach to employ ExECs that have been engineered to constitutively express Anti-Mullerian hormone (AMH), thus enabling sustained paracrine signaling input to ovarian grafts. Co-transplantation with ExECs increased follicular volume and improved antral follicle development, and AMH-expressing ExECs promoted retention of quiescent primordial follicles. This combined strategy may be a useful tool for mitigating ischemia and modulating follicular activation in the context of fertility preservation and/or infertility at large.

The past, present and future of fertility preservation in cancer patients

Fertility preservation strategies have been developed for men and women whose fertility is compromised for medical reasons, especially in case of cancer therapy. At present, many reliable options for preserving fertility are available. However, a part of these fertility preservation methods, despite being promising, are still considered experimental. Nevertheless, there are still situations where no methods can be offered. Remarkable scientific progress is currently underway to improve available techniques and to develop new technologies to solve problems with current fertility strategies. These new options may drastically change reproductive options for young patients facing germ cell loss and hence sterility. Therefore, oncofertility counseling by a specialist is recommended for all young cancer patients having to undergo treatment that may reduce fertility potential.