The mTOR Inhibitor Rapamycin Counteracts Follicle Activation Induced by Ovarian Cryopreservation in Murine Transplantation Models

Ovarian cryopreservation with rapamycin improves fertility restoration in a murine orthotopic transplantation model

Currently, the only fertility preservation option of prepubertal patients is ovarian tissue cryopreservation followed by autotransplantation (OTCTP). Once in remission and patients desire to conceive, autotransplantation of frozen/thawed tissue is performed. A major issue of this technique is follicular loss directly after transplantation, mainly due to follicle activation. Our previous research showed that adding rapamycin to the freezing medium counteracted follicle proliferation and activation induced by OTCTP in heterotopic autotransplantation of ovaries in mice. Our current study aimed to test the potential of this approach to improve fertility restoration in mice. Forty 4-week-old female C57BL/6 mice underwent unilateral oophorectomy followed by slow-freezing of ovaries with or without rapamycin. After chemically disabling the remaining ovary, orthotopic autotransplantation was performed. After recovery, estrous cycle analysis was conducted using daily vaginal smears. The mice were mated with males for 4 months, and pregnancy outcomes were recorded. After mating, half the females were super-ovulated for oocyte quantification and ovarian analysis, while the others had their ovaries collected for analysis of remaining primordial follicles using immunohistochemistry. Female mice whose ovaries were cryopreserved with rapamycin prior to chemically disabling the remaining ovary and orthotopic autotransplantation, gave birth to more pups (102 rapamycin, 48 control). The live birth rate was also higher (P = 0.0025) when ovaries were cryopreserved in rapamycin compared to control medium. Additionally, more mice in the rapamycin group gave birth (13 rapamycin, 8 control) with a higher average litter size (P = 0.0837). More mice had primordial follicles left at the end of the experiment in the rapamycin group (P = 0.0397). Superovulation showed a similar number of oocytes collected (P = 0.4462). While rapamycin did not influence cyst formation after autotransplantation, mice that developed ovarian cysts gave birth to fewer pups per dam (P = 0.0119) with a lower live birth rate compared to mice without ovarian cysts (P = 0.0032). The use of rapamycin improved fertility restoration in mice. Using rapamycin during OTCTP in humans could potentially resolve the massive follicular loss directly after grafting, and thus eventually lead to better opportunities for women to become pregnant.

mTOR inhibitors potentially preserve fertility in female patients with haematopoietic malignancies: a narrative review

Haematologic malignancies are considered among the more common adolescent and young adult (AYA) cancers. Many female AYA patients with haematopoietic malignancies face impaired fertility. Haematologic malignancies patients tend to be treated with more aggressive systemic chemotherapy than that of solid tumours. In adult women, treatment-related contraception causes age-related fertility loss. Graft-versus-host disease (GVHD) after allogeneic haematopoietic stem cell transplantation is associated with decreased fertility. Ovarian cryopreservation is often indicated for haematopoietic malignancies; however, follicle loss associated with ovarian cryopreservation and ovarian minimal residual disease, which result in the withdrawal of the transplantation, are important issues. These problems may not be fully addressed by conventional methods of fertility preservation, such as oocyte, embryo, and ovarian cryopreservation, leaving room for research into new treatment approaches, such as fertility preservation drugs. In recent years, preclinical studies have shown that mTOR inhibitors may preserve chemotherapy-induced follicular loss, may have follicle-preserving effects on follicle loss associated with cryopreservation and transplantation of ovarian tissue, may have fertility-preserving effects on aging-related infertility. Clinical studies have shown that mTOR inhibitors may have the potential for indirect fertility preservation by controlling GVHD, have a limited anti-tumor effect against haematopoietic malignancies. The purpose of this article is to outline the various issues faced by female survivors of haematopoietic malignancies and discuss the potential of mTOR inhibitors as a safe treatment option. Based on current research, mTOR inhibitors seem promising and innovative fertility preservation agents regarding preclinical conditions, and further study, including clinical trials, should be expected.

Current Challenges and Future Prospects in Human Reproduction and Infertility

Human reproduction is a captivating yet intricate field, constantly presenting new challenges and discoveries [...].

Prospective solutions to ovarian reserve damage during the ovarian tissue cryopreservation and transplantation procedure

Birth rates continue to decline as more women experience fertility issues. Assisted reproductive technologies are available for patients seeking fertility treatment, including cryopreservation techniques. Cryopreservation can be performed on gametes, embryos, or gonadal tissue and can be used for patients who desire to delay in vitro fertilization treatment. This review focuses on ovarian tissue cryopreservation, the freezing of ovarian cortex containing immature follicles. Ovarian tissue cryopreservation is the only available treatment for the restoration of ovarian function in patients who undergo gonadotoxic treatments, and its wide adoption has led to its recent designation as "no longer experimental" by the American Society for Reproductive Medicine. Ovarian tissue cryopreservation and subsequent transplantation can restore native endocrine function and can support the possibility of pregnancy and live birth for the patient. Importantly, there are multiple steps in the procedure that put the ovarian reserve at risk of damage. The graft is highly susceptible to ischemic reperfusion injury and mass primordial follicle growth activation, resulting in a "burnout" phenomenon. In this review, we summarize current efforts to combat the loss of primordial follicles in grafts through improvements in freeze and thaw protocols, transplantation techniques, and pharmacologic adjuvant treatments. We conducted a review of the literature, with emphasis on emergent research in the last 5 years. Regarding freeze and thaw protocols, we discuss the widely accepted slow freezing approach and newer vitrification protocols. Discussion of improved transplantation techniques includes consideration of the transplantation location of the ovarian tissue and the importance of graft sites in promoting neovascularization. Finally, we discuss pharmacologic treatments being studied to improve tissue performance postgraft. Of note, there is significant research into the efficacy of adjuvants used to reduce ischemic injury, improve neovascularization, and inhibit hyperactivation of primordial follicle growth activations. Although the "experimental" label has been removed from ovarian tissue cryopreservation and subsequent transplantation, there is a significant need for further research to better understand sources of ovarian reserve damage to improve outcomes. Future research directions are provided as we consider how to reach the most hopeful results for women globally.

The Low Survivability of Transplanted Gonadal Grafts: The Impact of Cryopreservation and Transplantation Conditions on Mitochondrial Function

Advances in tissue preservation techniques have allowed reproductive medicine and assisted reproductive technologies (ARTs) to flourish in recent years. Because radio- and chemotherapy procedures are often gonadotoxic, irreversible damage can preclude future gamete production and endocrine support. Accordingly, in recent years, the freezing and storage of gonadal tissue fragments prior to the first oncological treatment appointment and autologous transplantation post-recovery have been considered improved solutions for fertility recovery in cancer survivors. Nevertheless, the cryopreservation and transplantation of thawed tissues is still very limited, and positive outcomes are relatively low. This review aims to discuss the limitations of oncofertility protocols with a focus on the impacts of mitochondrial dysfunction, oxidative stress, and the loss of antioxidant defense in graft integrity.

Research progress on the prevention and treatment of chemotherapy-induced ovarian damage

Chemotherapy is a main treatment option for malignant tumors, but it may cause various adverse effects, including dysfunction of female endocrine system and fertility. Chemotherapy-induced ovarian damage has been concerned with ovarian preservation but also the prevention and treatment of ovarian dysfunction. In this article, the mechanisms of ovarian injury caused by chemotherapy, including apoptosis of the follicle and supporting cells, follicle "burn out", ovarian stromal and microvascular damage; and influencing factors, including age at diagnosis, initial low pre-treatment anti-Müllerian hormone levels, toxicity, dose and regimen of chemotherapy drugs are reviewed based on the latest research results and clinical practice. The article also discusses measures and frontier therapies for the prevention and treatment of ovarian injury, including the application of gonadotropin releasing hormone agonists or antagonists, tyrosine kinase inhibitors, antioxidants, sphingosine-1-phosphate, ceramide-1-phosphate, mammalian target of rapamycin inhibitors, granulocyte-colony stimulating factor, stem cell therapy and artificial ovaries.

Research progress on mechanism of follicle injury after ovarian tissue transplantation and protective strategies

Ovarian tissue cryopreservation and transplantation is the only way to preserve fertility for female cancer patients in prepubertal ages and those who cannot delay radiotherapy or chemotherapy. However, the success rate of cryopreservation and transplantation of ovarian tissue is still low at present due to the risk of ischemia and hypoxia of the grafted tissues. Abnormal activation of primordial follicles and ischemia-reperfusion injury after blood supply recovery also cause massive loss of follicles in grafted ovarian tissues. Various studies have explored the use of different drugs to reduce the damage of follicles during freezing and transplantation as well as to extend the duration of endocrine and reproductive function in patients with ovarian transplantation. For example, melatonin, N-acetylcysteine, erythropoietin or other antioxidants have been used to reduce oxidative stress; mesenchymal stem cells derived from different tissues, basic fibroblast growth factor, vascular endothelial growth factor, angiopoietin 2 and gonadotropin have been used to promote revascularization; anti-Müllerian hormone and rapamycin have been used to reduce abnormal activation of primordial follicles. This article reviews the research progress on the main mechanisms of follicle loss after ovarian tissue transplantation, including hypoxia, ischemia-reperfusion injury and associated cell death, and abnormal activation of follicles. The methods for reducing follicle loss in grafted ovarian tissues are further explored to provide a reference for improving the efficiency of ovarian tissue cryopreservation and transplantation.