Ovarian and oocyte cryopreservation

Microenvironmentally Responsive Chemotherapeutic Prodrugs and CHEK2 Inhibitors Self-Assembled Micelles: Protecting Fertility and Enhancing Chemotherapy

Chemotherapy is a widely used and effective adjuvant treatment for cancer, and it has unavoidable damage to female fertility, with statistics showing 38% of women who have received chemotherapy are infertile. How to reduce fertility toxicity while enhancing the oncologic chemotherapy is a clinical challenge. Herein, co-delivery micelles (BML@PMP) are developed, which are composed of a reduction-sensitive paclitaxel prodrug (PMP) for chemotherapy and a CHEK2 inhibitor (BML277) for both fertility protection and chemotherapy enhancement. BML@PMP achieves fertility protection through three actions: (1) Due to the enhanced permeability and retention (EPR) effect, BML@PMP is more enriched in the tumor, while very little in the ovary (about 1/10th of the tumor). (2) Glutathione (GSH) triggers the release of PTX, and with low levels of GSH in the ovary, the amount of PTX released in the ovary is correspondingly reduced. (3) BML277 inhibits oocyte apoptosis by inhibiting the CHEK2-TAp63α pathway. Because of the different downstream targets of CHEK2 in tumor cells and oocytes, BML277 also enhances chemotherapeutic efficacy by reducing DNA damage repair which is activated through the CHEK2 pathway. This bidirectional effect of CHEK2 inhibitor-based co-delivery system represents a promising strategy for improving oncology treatment indices and preventing chemotherapy-associated fertility damage.

Freeze/thaw stress induces organelle remodeling and membrane recycling in cryopreserved human mature oocytes

PURPOSE

Our aim was to evaluate the ultrastructure of human metaphase II oocytes subjected to slow freezing and fixed after thawing at different intervals during post-thaw rehydration.

METHODS

Samples were studied by light and transmission electron microscopy.

RESULTS

We found that vacuolization was present in all cryopreserved oocytes, reaching a maximum in the intermediate stage of rehydration. Mitochondria-smooth endoplasmic reticulum (M-SER) aggregates decreased following thawing, particularly in the first and intermediate stages of rehydration, whereas mitochondria-vesicle (MV) complexes augmented in the same stages. At the end of rehydration, vacuoles and MV complexes both diminished and M-SER aggregates increased again. Cortical granules (CGs) were scarce in all cryopreserved oocytes, gradually diminishing as rehydration progressed.

CONCLUSIONS

This study also shows that such a membrane remodeling is mainly represented by a dynamic process of transition between M-SER aggregates and MV complexes, both able of transforming into each other. Vacuoles and CG membranes may take part in the membrane recycling mechanism.

Vitrification by Cryotop and the Maturation, Fertilization, and Developmental Rates of Mouse Oocytes

Background:

Oocyte cryopreservation is an important part of modern fertility treatment. The effect of vitrification on the fertilization and developmental rates of embryo is still a matter of debate.

Objectives:

This study aimed to investigate the effect of vitrification on the success of mouse oocyte maturation, fertilization, and preimplantation development in vitro.

Materials and Methods:

In this experimental study, a total of 200 germinal vesicle (GV) and 200 metaphase II (MII) oocytes were obtained from ovaries and fallopian tubes of NMRI mice, respectively and divided into two control and experimental (vitrified) groups. Oocytes in the experimental group were vitrified by Cryotop using vitrification medium (Origio, Denmark) and kept in liquid nitrogen for one month. Then, they were cultured in maturation medium for 24 hours. In vitro maturated metaphase 2 (IVM-MII) and ovulated metaphase 2 (OV-MII) oocytes were inseminated and the fertilized embryos assessed until the hatching blastocyst stage. Outcomes were assessed for statistical significance by Chi-square test using SPSS software.

Results:

Vitrification caused a significant reduction in the maturation rate of oocytes. Of those that matured, the fertilization rate of vitrified IVM-MII (44.1%) and OV-MII oocytes (50%) was not significantly different from each other but both were significantly lower than the control group (P < 0.05). There was no significant difference in developmental rates of both vitrified groups and the control group.

Conclusions:

The present study showed that vitrification using Cryotop and freezing medium can damage oocytes by reducing the maturation and fertilization rates in both developmental stages.

Ultrastructure of human mature oocytes after vitrification

Since the introduction of human assisted reproduction, oocyte cryopreservation has been regarded as an attractive option to capitalize the reproductive potential of surplus oocytes and preserve female fertility. However, for two decades the endeavor to store oocytes has been limited by the not yet optimized methodologies, with the consequence of poor clinical outcome or of uncertain reproducibility. Vitrification has been developed as the promising technology of cryopreservation even if slow freezing remains a suitable choice. Nevertheless, the insufficiency of clinical and correlated multidisciplinary data is still stirring controversy on the impact of this technique on oocyte integrity. Morphological studies may actually provide a great insight in this debate. Phase contrast microscopy and other light microscopy techniques, including cytochemistry, provided substantial morpho-functional data on cryopreserved oocyte, but are unable to unraveling fine structural changes. The ultrastructural damage is one of the most adverse events associated with cryopreservation, as an effect of cryo-protectant toxicity, ice crystal formation and osmotic stress. Surprisingly, transmission electron microsco py has attracted only limited attention in the field of cryopreservation. In this review, the subcellular structure of human mature oocytes following vitrification is discussed at the light of most relevant ultrastructural studies.

Cryopreservation and fertility: current and prospective possibilities for female cancer patients

With the evolution of the treatment of malignant neoplasms, the survival rates of patients undergoing chemo- or radiotherapy are increasing. The continuous development of techniques of assisted human reproduction has led to important strategies in an attempt to maintain reproductive function in patients subjected to treatment of neoplastic diseases, among them cryopreservation of embryos, gametes, and ovarian cortical tissue. The freezing of ovarian tissue is currently being proposed with the primary purpose of preserving ovarian function in these patients. Currently, the major challenge of groups working with preservation of fertility is the use of cryopreserved ovarian tissue after disease remission. The main alternatives presented today are the implantation of hetero- or orthotopic tissue and isolation of immature follicles from ovarian tissue followed by in vitro maturation and assisted reproduction procedures.

Reproduction after breast cancer

Breast cancer is the most frequently occurring cancer in women of developed countries, and as a result of new developments in breast cancer treatment, more women are cured after being diagnosed with this disease. It is important that fertility preservation strategies are addressed before chemotherapy, because chemotherapy may induce premature ovarian failure (depending on the woman's age, the drugs used, the dosage and duration of treatment). Among possible solutions are embryos or oocytes cryopreservation, ovarian tissue cryopreservation-freezing with a subsequent orthotopic and heterotopic autotransplantation, whole ovary cryopreservation, ovarian suppression with gonadotropin-releasing hormone (GnRH) analogues, which inhibit ovarian follicular depletion induced by chemotherapeutic agents and in vitro fertilisation (IVF) after ovulation induction with aromatase inhibitors or tamoxifen.

Vitrification of immature mouse oocyte using stepwise equilibration before or after in vitro maturation

Immature mouse oocytes before or after in vitro maturation (IVM) were vitrified by the use of either conventional one-step or three-step equilibration. Although vitrification after IVM using the stepwise method does not affect the cleavage rate, the early embryonic development was profoundly impaired in both protocols.

Cryopreservation and autotransplantation of human ovarian tissue prior to cytotoxic therapy--a technique in its infancy but already successful in fertility preservation

Increasing survival rates in young cancer patients, new reproductive techniques and the growing interest in quality of life after gonadotoxic cancer therapies have placed fertility preservation as an important issue to oncologists, fertility specialists and patients. Several techniques are now available for fertility preservation in these patients. A new promising method is cryopreservation and transplantation of ovarian cortex. Ovarian tissue can be extracted by laparoscopy without any significant delay of gonadotoxic therapy. The tissue can be cryopreserved by specialised centres of reproductive medicine and transplanted in case the women experience premature ovarian failure (POF). This review summarises the European expertise on cryopreservation and transplantation of ovarian tissue, following around 30 reported transplantations globally, resulting in six live births and several ongoing pregnancies. It emphasises that fertility preservation by the cryopreservation of ovarian tissue is a new but already a successful clinical option, which can be considered for selected cancer patients.

GnRH-analogues and oral contraceptives for fertility preservation in women during chemotherapy

BACKGROUND

For preserving fertility in women during chemotherapy, the character of invasive techniques, such as ovarian cryopreservation and other techniques, await further experience. Meanwhile, non-invasive techniques have attempted to minimize the gonadotoxic effect of chemotherapy, by using gonadotrophin-releasing hormone-analogues (GnRH-a) or oral contraceptives (OC).

METHODS

We performed a computerized MEDLINE search to identify articles published on fertility preservation using GnRH-a or OCs.

RESULTS

Nine human-controlled studies reported the use of GnRH-a and four reported the use of OCs in parallel to chemotherapy. All nine studies analysing the effect of GnRH-a found lower rates of premature ovarian failure (POF) in patients receiving GnRH-a compared with the controls. Summarizing the studies resulted in 11.1% incidence of POF in patients who received GnRH-a compared with 55.5% incidence in the controls. Evidence using the fertility preserving effect of OC is limited. Two studies showed lower POF rates in OC-treated patients. The summarized data revealed a POF rate of 13.2% in patients who received OCs compared with that of 29.8% in the controls.

CONCLUSIONS

The published clinical studies provide evidence, but do not prove statistically, that GnRH-a co-treatment reduces gonadotoxicity. Owing to the retrospective and non-randomized nature of most of the studies, definite conclusions concerning the reduction of POF by GnRH-a can still not be unequivocally drawn. As GnRH-a and OC have no serious side effects and as GnRH-a can even reduce chemotherapy-induced complications, such as severe menometrorrhagia, GnRH-a are considered by many clinicians as a clinically useful co-treatment in chemotherapy. The published clinical studies on OC also suggest a possible effect on the reduction of POF under certain conditions.

Morphology and function of cryopreserved whole ovine ovaries after heterotopic autotransplantation

BACKGROUND

The objective of this study was to perform complex characterization of cryopreserved and then autotransplanted ovaries including determination of the ability to respond to in vivo follicle stimulating hormone (FSH)-treatment, fertilizability of retrieved oocytes, and morphology, vascularization, cellular proliferation and apoptosis in sheep.

METHODS

Mature crossbred ewes were divided into two groups; an intact (control) group (n = 4), and autotransplanted group (n = 4) in which oophorectomy was performed laparoscopically and ovaries with intact vascular pedicles frozen, thawed and transplanted back into the same animal at a different site. Approximately five months after autotransplantation, estrus was synchronized, ewes were treated with FSH, and ovaries were collected. For all ovaries, number of visible follicles was determined, and collected cumulus oocyte complexes (COC) were matured and fertilized in vitro. Remaining ovarian tissues were fixed for evaluation of morphology, expression of factor VIII (marker of endothelial cells), vascular endothelial growth factor (VEGF; expressed by pericytes and smooth muscle cells), and smooth muscle cell actin (SMCA; marker of pericytes and smooth muscle cells), and cellular proliferation and apoptosis. Two fully functional ovaries were collected from each control ewe (total 8 ovaries).

RESULTS

Out of eight autotransplanted ovaries, a total of two ovaries with developing follicles were found. Control ewes had 10.6 +/- 2.7 follicles/ovary, oocytes were in vitro fertilized and developed to the blastocyst stage. One autotransplanted ewe had 4 visible follicles from which 3 COC were collected, but none of them was fertilized. The morphology of autotransplanted and control ovaries was similar. In control and autotransplanted ovaries, primordial, primary, secondary, antral and preovulatory follicles were found along with fully functional vascularization which was manifested by expression of factor VIII, VEGF and SMCA. Proliferating cells were detected in follicles, and the rate of apoptosis was minimal in ovaries of control and autotransplanted ovaries.

CONCLUSION

These data demonstrate successful autotransplantation of a portion of frozen/thawed ovaries manifested by restoration of selected ovarian function including in vitro maturation of collected oocytes, presence of follicles from several stages of folliculogenesis and blood vessels expressing specific markers of vascularization, and proliferation and apoptosis of ovarian cells. Thus, heterotopic autotransplantation of a whole frozen/thawed ovary allows for development of preovulatory follicles, oocyte growth, and for restoration of vascularization and cellular function. However, additional improvements are required to enhance the efficiency of autotransplantation of frozen/thawed ovaries to produce more oocytes.