Cryopreservation of embryos and oocytes in human assisted reproduction

The Effect of Vitrification on Expression and Histone Marks of Igf2 and Oct4 in Blastocysts Cultured from Two-Cell Mouse Embryos

OBJECTIVES

Vitrification is increasingly used in assisted reproductive technology (ART) laboratories worldwide. In this study the effect of vitrification on the expression and modifications of H3 histones of Igf2 and Oct4 was investigated in blastocysts cultured from vitrified and non-vitrified two-cell embryos.

MATERIALS AND METHODS

In this experimental study, two-cell embryos were cultured in KSOM medium to reach the blastocyst stage. Expression of Igf2 and Oct4 and modifications of H3 histones in regulatory regions of both genes were compared with in vivo blastocysts, which comprise the control group. To gene expression evaluation, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and the ChIP assay method were carried out to assess expression and histone modifications of the two genes.

RESULTS

The expression level of Igf2 was significantly higher in both experimental groups than the control group. In the regulatory region of Igf2, H3K9 methylation decreased whereas H3K9 acetylation increased in the experimental group compared with the control group. In contrast, the expression level of Oct4 was significantly lower in experimental groups. The Oct4 gene promoter showed a significant increase in H3K9 methylation and decrease in H3K9 acetylation (P<0.05).

CONCLUSIONS

According to our results, both vitrification and cultivation conditions may lead to changes in expression level and modification of histones in Igf2 and Oct4. However, these effects were the same in vitrified and non-vitrified groups. Indeed, the embryo is most affected by culture environment and in vitro culture. Therefore, vitrification may be used as a low-risk technique for embryo cryopreservation in ART.

Vitrification of human immature oocytes before and after in vitro maturation: a review

The use of immature oocytes subjected to in vitro maturation (IVM) opens interesting perspectives for fertility preservation where ovarian reserves are damaged by pathologies or therapies, as in PCO/PCOS and cancer patients. Human oocyte cryopreservation may offer some advantages compared to embryo freezing, such as fertility preservation in women at risk of losing fertility due to oncological treatment or chronic disease, egg donation and postponing childbirth. It also eliminates religious and/or other ethical, legal, and moral concerns of embryo freezing. In addition, a successful oocyte cryopreservation program could eliminate the need for donor and recipient menstrual cycle synchronization. Recent advances in vitrification technology have markedly improved the oocyte survival rate after warming, with fertilization and implantation rates comparable with those of fresh oocytes. Healthy live births can be achieved from the combination of IVM and vitrification, even if vitrification of in vivo matured oocytes is still more effective. Recently, attention is given to highlight whether vitrification procedures are more successful when performed before or after IVM, on immature GV-stage oocytes, or on in vitro matured MII-stage oocytes. In this review, we emphasize that, even if there are no differences in survival rates between oocytes vitrified prior to or post-IVM, reduced maturation rates of immature oocytes vitrified prior to IVM can be, at least in part, explained by underlying ultrastructural and biomolecular alterations.

Bio-inspired solute enables preservation of human oocytes using minimum volume vitrification

The ability to cryopreserve human oocytes has significant potential for fertility preservation. Current cryopreservation methods still suffer from the use of conventional cryoprotectants, such as dimethyl sulphoxide (DMSO), causing loss of viability and function. Such injuries result from the toxicity and high concentration of cryoprotectants, as well as mechanical damage of cells due to ice crystal formation during the cooling and rewarming processes. Here we report the preservation of human oocytes following vitrification using an innovative bio-inspired cryoprotectant integrated with a minimum volume vitrification approach. The results demonstrate that the recovered human oocytes maintained viability following vitrification and rewarming. Moreover, when this approach was used to vitrify mouse oocytes, the recovered oocytes preserved their viability and function following vitrification and rewarming. This bio-inspired approach substitutes DMSO, a well-known toxic cryoprotectant, with ectoine, a non-toxic naturally occurring solute. The bio-inspired vitrification approach has the potential to improve fertility preservation for women undergoing cancer treatment and endangered mammal species.

A microfluidic perfusion approach for on-chip characterization of the transport properties of human oocytes

Accurate characterization of the cell membrane transport properties of human oocytes is of great significance to reproductive pharmacology, fertility preservation, and assisted reproduction. However, the commonly used manual method for quantifying the transport properties is associated with uncontrolled operator-to-operator and run-to-run variability. Here, we report a novel sandwich structured microfluidic device that can be readily fabricated for characterizing oocyte membrane transport properties. Owing to its capacity for excellent control of both solution replacement and temperature in the microchannel, the temperature-dependent permeability of the oocyte membrane can be precisely characterized. Furthermore, the fertilization and developmental competence analysis post perfusion indicate that our approach does not compromise the physiological function of in vitro matured human oocytes. Collectively, we present the development of a novel sandwich structured microfluidic device based approach that allows on-chip characterization of the transport properties of human oocytes under innocuous osmotic shock or injury to the cells.

Glycine increases preimplantation development of mouse oocytes following vitrification at the germinal vesicle stage

Ice-free cryopreservation, referred to as vitrification, is receiving increased attention in the human and animal assisted reproduction. However, it introduces the detrimental osmotic stress by adding and removing high contents of cryoprotectants. In this study, we evaluated the effects of normalizing cell volume regulation by adding glycine, an organic osmolyte, during vitrification of mouse germinal vesicle stage oocyte and/or subsequent maturation on its development. The data showed that glycine supplementation in either vitrification/thawing or maturation medium significantly improved the cytoplasmic maturation of MII oocytes manifested by spindle assembly, chromosomal alignment, mitochondrial distribution, euploidy rate, and blastocyst development following fertilization in vitro, compared to the control without glycine treatment. Furthermore, glycine addition during both vitrification/thawing and maturation further enhanced the oocyte quality demonstrated by various markers, including ATP contents and embryo development. Lastly, the effect of anti-apoptosis was also observed when glycine was added during vitrification. Our result suggests that reducing osmotic stress induced by vitrification could improve the development of vitrified mouse oocyte.

Vitrification of embryos and oocytes for fertility preservation in cancer patients

As survival rates and the life expectancy of those with malignancy have increased, more women in their reproductive years are referred for fertility preservation. Chemotherapy and radiotherapy can severely affect ovarian function, and the effect is irreversible. Therefore, it is optimal to attempt fertility preservation before chemotherapy and radiotherapy are initiated. Oocyte and embryo cryopreservation is the most common option for fertility preservation in women. Several reports have proven that embryo and oocyte cryopreservation can achieve a successful pregnancy. This review discusses the impact of chemotherapy and radiotherapy on ovarian function, and the importance of oocyte and embryo cryopreservation for fertility preservation. In addition, the current status of pregnancy outcomes and potential for cryopreserved oocytes to result in live births in cancer patients was reviewed. This may provide useful information for decision-making in cancer patients regarding oocyte and embryo cryopreservation and fertility preservation.

Fertility preservation and reproductive health in the pediatric, adolescent, and young adult female cancer patient

PURPOSE OF REVIEW

As treatments for malignancies become increasingly successful, emphasis on quality of life in survivorship becomes important. Of equal importance is the role of gonadotoxic agents in the management of chronic medical conditions, such as nonmalignant blood disorders and rheumatologic and genetic conditions. Gonadotoxic agents have long-term effects to include ovarian insufficiency, pubertal arrest and subsequent infertility.

RECENT FINDINGS

In 2004, ovarian tissue cryopreservation emerged as an investigational but viable option for prepubertal patients and those unable to undergo ovarian stimulation. In 2012, oocyte preservation became standard therapy for patients without a partner or who elected not to use donor sperm or freeze embryos. Ovarian reserve testing with antimullerian hormone to assess fertility after gonadotoxic therapy is a rapidly growing area of interest with potentially significant benefits in personalizing the approach to fertility preservation.

SUMMARY

A systematic approach to fertility preservation prior to treatment in all patients receiving gonadotoxic agents optimizes care. Fertility preservation strategies can restore hormonal function and preserve reproductive potential. Future research in personalizing approach to care is critical to meeting the needs of this patient population.

Challenges and considerations in optimizing ovarian stimulation protocols in oncofertility patients

The scope of cancer treatment in women of childbearing age has changed in the last decade. Fertility preservation is no longer an afterthought but central to multi-disciplinary cancer treatment planning and should be addressed due to the cytotoxic effects of cancer therapy. However, oncology patients present as a unique treatment challenge as the physician must balance the urgency of fertility preservation with the risks of delaying cancer therapy. Controlled ovarian stimulation (COS) is routinely applied in assisted reproductive technology but can be contraindicated in women with estrogen-receptor-positive tumors. This paper reviews some of the challenges to consider when using COS and newer stimulation protocols to minimize risks and optimize outcomes in oncofertility patients.

Evaluation of the impact of vitrification on the actin cytoskeleton of in vitro matured ovine oocytes by means of Raman microspectroscopy

PURPOSE

Investigation of the changes induced by vitrification on the cortical F-actin of in vitro matured ovine oocytes by Raman microspectroscopy (RMS).

METHODS

Cumulus-oocyte complexes, recovered from the ovaries of slaughtered sheep, were matured in vitro and vitrified following the Minimum Essential Volume method using cryotops. The cortical region of metaphase II (MII) oocytes (1) exposed to vitrification solutions but not cryopreserved (CPA-exp), (2) vitrified/warmed (VITRI), and (3) untreated (CTR) was analyzed by RMS. A chemical map of one quadrant of single CPA-exp, VITRI and CTR oocytes was, also, performed. In order to identify the region of Raman spectra representative of the cortical F-actin modification, a group of in vitro matured oocytes were incubated with latrunculin-A (LATA), a specific F-actin destabilizing drug, and processed for RMS analysis. Thereafter, all the oocytes were stained with rhodamine phalloidin and evaluated by fluorescence confocal microscopy. Raman spectra of the oocytes were, statistically, analyzed using Principal Component Analysis (PCA).

RESULTS

The PCA score plots showed a marked discrimination between CTR oocytes and CPA-exp/ VITRI groups. The main differences, highlighted by PCA loadings, were referable to proteins (1657, 1440 and 1300 cm(-1)) and, as indicated by LATA experiments, also included the changes of the F-actin. Analysis by confocal microscopy revealed a clear alteration of the cortical F-actin of CPA-exp and VITRI oocytes confirming RMS results.

CONCLUSIONS

Raman microspectroscopy may represent an alternative analytical tool for investigating the biochemical modification of the oocyte cortex, including the F-actin cytoskeleton, during vitrification of in vitro matured ovine oocytes.