Effect of vitrification on human oocytes: a metabolic profiling study

Factors influencing the success of cryopreserved parathyroid autotransplantation: A systematic review

Permanent hypoparathyroidism is a postoperative complication of thyroid and parathyroid surgery and can be cured by cryopreserved parathyroid autotransplantation (CPAT). However, due to the lack of unified and standardized guidelines, the limited ability of the parathyroid tissue itself to withstand cryopreservation, and some yet-to-be-defined processes or technologies, the success rate of cryopreserved parathyroid autotransplantation varies between institutions; it is low for some institutions and high for others. Due to the sparsity of data, views vary on which factors most influence the success rate of cryopreserved parathyroid autotransplantation. In this review, we analyzed the following probable influencing factors: ischemic period before cryopreservation; processes of cryopreservation and thawing, including freezing medium; freezing and thawing methods; duration of cryopreservation; examination of the graft before transplantation; graft site; mass of transplanted tissue fragments; blood calcium level; and the evaluation criteria for cryopreserved parathyroid autotransplantation success. Although the effects of these factors are debatable, we hypothesized that examining them in the above-given order to determine whether they affect the success rate of cryopreserved parathyroid autotransplantation could be beneficial to maximizing the success rate. Our findings led us to conclude that cryopreserved parathyroid autotransplantation operations should be standardized. Standardized guidelines for cryopreserved parathyroid autotransplantation that include such factors as ischemic period time, freezing and thawing methods, and recipient status should be established based on a comprehensive analysis of these factors.

[The impact of oocyte cryopreservation time in oocyte donation on the clinical success rate]

OBJECTIVES

To evaluate the impact of the cryopreservation time of vitrified oocytes on the success rates in oocyte donation cycles.

METHODS

A retrospective study was carried out on 156 cycles with donated oocytes from January 2012 to September 2021. All the cycles were sorted according to the storage time of the oocytes (25 in the group 1:<3 months, 32 in the group 2: between 3 and 6 months, 39 in the group 3: between 6 and 12 months, 38 in the group 4: between 12 and 24 months and 22 in the group 5:>24 months). Clinical outcomes after ART, survival rates at thawing and oocyte fertilization rates were compared between the different cohorts stratified according to oocyte storage duration. A binary multivariate logistic regression was performed adjusting for the identified confounders.

RESULTS

Prolonged storage time of vitrified oocytes had an effect on their survival post-thawing rates, but no significant effect was identified on fertilization rates or clinical outcomes. After adjusting for the confounders, the relationships between clinical outcomes and oocytes storage time did not reach statistical significance. Our study was characterized by a limited cohort with data from a single ART center.

CONCLUSIONS

Our study doesn't highlight any significant difference in the use of long-stored vitrified oocytes (more than 2 years) on clinical issues in ART. The conclusion of our study needs to be verified in further studies with larger cohorts.

Melatonin Improves Parthenogenetic Development of Vitrified⁻Warmed Mouse Oocytes Potentially by Promoting G1/S Cell Cycle Progression

This study aimed to investigate the effect of melatonin on the cell cycle of parthenogenetic embryos derived from vitrified mouse metaphase II (MII) oocytes. Fresh oocytes were randomly allocated into three groups: untreated (control), or vitrified by the open-pulled straw method without (Vitrification group) or with melatonin (MT) supplementation (Vitrification + MT group). After warming, oocytes were parthenogenetically activated and cultured in vitro, then the percentage of embryos in the G1/S phase, the levels of reactive oxygen species (ROS) and glutathione (GSH), and the mRNA expression of cell cycle-related genes (P53, P21 and E2F1) in zygotes and their subsequent developmental potential in vitro were evaluated. The results showed that the vitrification/warming procedures significantly decreased the frequency of the S phase, markedly increased ROS and GSH levels and the expression of P53 and P21 genes, and decreased E2F1 expression in zygotes at the G1 stage and their subsequent development into 2-cell and blastocyst stage embryos. However, when 10⁻⁹ mol/L MT was administered for the whole duration of the experiment, the frequency of the S phase in zygotes was significantly increased, while the other indicators were also significantly improved and almost recovered to the normal levels shown in the control. Thus, MT might promote G1-to-S progression via regulation of ROS, GSH and cell cycle-related genes, potentially increasing the parthenogenetic development ability of vitrified–warmed mouse oocytes.

Effect of oocyte vitrification on embryo quality: time-lapse analysis and morphokinetic evaluation

OBJECTIVE

To analyze whether oocyte vitrification may affect subsequent embryo development from a morphokinetic standpoint by means of time-lapse imaging.

DESIGN

Observational cohort study.

SETTING

University-affiliated private IVF center.

PATIENT(S)

Ovum donation cycles conducted with the use of vitrified (n = 631 cycles; n = 3,794 embryos) or fresh oocytes (n = 1,359 cycles; n = 9,935 embryos) over 2 years.

INTERVENTIONS(S)

None.

MAIN OUTCOME MEASURE(S)

Embryo development was analyzed in a time-lapse imaging incubator. The studied variables included time to 2 cells (t2), 3 cells (t3), 4 cells (t4), 5 cells (t5), morula (tM), and cavitated, early, and hatching blastocyst (tB, tEB, tHB) as well as 2nd cell cycle duration (cc2 = t3 - t2). All of the embryos were classified according to the hierarchic tree model currently used for embryo selection. The analyzed variables were compared with the use of analysis of variance or chi-square and included 95% confidence intervals (CIs).

RESULT(S)

The embryos that originated from vitrified oocytes showed a delay of ∼1 hour from the first division to 2 cells (t2) to the time of blastulation (tB). The embryos that originated from vitrified oocytes showed a delay of ∼1 hour from the 1st division to 2 cells (t2) to the time of blastulation (tB) (P<.05). The proportions of embryos allocated to categories A-E in the hierarchical tree were similar between groups. No differences in implantation rates between the fresh (51.3% [95% CI 47.1%-55.7%]) and vitrified (46.4% [95% CI 38.4%-54.4%]) groups were found.

CONCLUSION(S)

The embryo quality of vitrified oocytes was not impaired: cc2, quality according to our hierarchic morphokinetic model, and implantation rates were similar between fresh and vitrified oocytes. However, morphokinetic differences were observed from t2 to tB. Our main study limitation was the retrospective nature of the analysis, although a large database was studied.

Safety and efficiency of oocyte vitrification

As the oocyte is the starting point for a new life, artificial reproductive technology (ART) techniques should not affect the (ultra) structural and functional integrity, or the developmental competence. Oocyte vitrification -one of the most significant achievements in human ART during the past decade- should therefore be a safe and efficient technique. This review discusses the principles and developments of the existing and future techniques, applications possibilities and safety concerns. The broad range of vitrification media and devices that are currently available, show differences in their effects on the oocyte ultrastructure and preimplantation development. It is not yet fully decided whether this has an influence on the obstetric and neonatal outcome, since only limited information is available with different media and devices. For autologous oocytes, the obstetric and neonatal outcomes appear promising and comparable to pregnancies obtained with fresh oocytes. This however, is not the case for heterologous fresh or vitrified oocytes, where the immunological foreign foetus induces adverse obstetric and neonatal outcomes. Besides the oocyte vitrification process itself, the effect of multiple stimulations (for oocyte banking or for oocyte donors), seems to influence the possibility to develop gynaecological cancers further in life. Automated vitrification/warming should offer a consistent, cross-contamination free process that offers the highest safety level for the users. They should also produce more consistent results in survival, development and clinical pregnancies between different IVF clinics.

Random-start ovarian stimulation in women desiring elective cryopreservation of oocytes

The current study investigates the utility of random-start ovarian stimulation in women desiring elective oocyte cryopreservation. Women in the study cohort underwent random-start ovarian stimulation, and were subdivided based on the phase of the menstrual cycle that ovarian stimulation began, i.e. early follicular, late follicular or luteal phase. Women undergoing conventional cycle day (CD) 2/3 ovarian stimulation start were controls. A total of 1302 women were included - 859 (66.0%) conventional CD 2/3, 342 (26.3%) early follicular, 42 (3.2%) late follicular and 59 (4.5%) luteal ovarian stimulation starts. There was no difference in the demographics or baseline ovarian stimulation characteristics. The duration of ovarian stimulation (11 versus 9 days; P < 0.001) and total dosage of gonadotrophins administered (4095.5 versus 3155 IU; P < 0.001) was higher in the random-start group. The number of total and MII oocytes in the control and random-start groups was similar. A non-significant trend towards increased cycle cancellation was noted in the late follicular start group (7.1%). Study findings indicate the number of total and MII oocytes derived from random-start protocols initiated during any phase of the menstrual cycle is similar to conventional CD 2/3 ovarian stimulation start protocols in women desiring elective oocyte cryopreservation.

Improved cryotolerance and developmental potential of in vitro and in vivo matured mouse oocytes by supplementing with a glutathione donor prior to vitrification

STUDY QUESTION

Can supplementation of media with a glutathione (GSH) donor, glutathione ethyl ester (GEE), prior to vitrification protect the mouse oocyte from oxidative damage and critical changes in redox homeostasis, and thereby improve cryotolerance?

SUMMARY ANSWER

GEE supplementation supported redox regulation, rapid recovery of spindle and chromosome alignment after vitrification/warming and improved preimplantation development of mouse metaphase II (MII) oocytes.

WHAT IS KNOWN ALREADY

Cryopreservation may affect mitochondrial functionality, induce oxidative stress, and thereby affect spindle integrity, chromosome segregation and the quality of mammalian oocytes. GEE is a membrane permeable GSH donor that promoted fertilization and early embryonic development of macaque and bovine oocytes after IVM.

STUDY DESIGN, SIZE, DURATION

Two experimental groups consisted of (i) denuded mouse germinal vesicle (GV) oocytes that were matured in vitro in the presence or absence of 1 mM GEE (IVM group 1) and (ii) in vivo ovulated (IVO) MII oocytes that were isolated from the ampullae and exposed to 1 mM GEE for 1 h prior to vitrification (IVO group 2). Recovery of oocytes from both groups was followed after CryoTop vitrification/warming for up to 2 h and parthenogenetic activation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Reactive oxygen species (ROS), spindle morphology and chromosome alignment were analyzed by confocal laser scanning microscopy (CLSM) and polarization microscopy in control and GEE-supplemented MII oocytes. The relative overall intra-oocyte GSH content was assessed by analysis of monochlorobimane (MBC)-GSH adduct fluorescence in IVM MII oocytes. The GSH-dependent intra-mitochondrial redox potential (E^m_GSH) of IVM MII oocytes was determined after microinjection with specific mRNA at the GV stage to express a redox-sensitive probe within mitochondria (mito-Grx1-roGFP2). The absolute negative redox capacity (in millivolts) was determined by analysis of fluorescence of the oxidized versus the reduced form of sensor by CLSM and quantification according to Nernst equation. Proteome analysis was performed by quantitative 2D saturation gel electrophoresis (2D DIGE). Since microinjection and expression of redox sensor mRNA required removal of cumulus cells, and IVM of denuded mouse oocytes in group 1 induces zona hardening, the development to blastocysts was not assessed after IVF but instead after parthenogenetic activation of vitrified/warmed MII oocytes from both experimental groups.

MAIN RESULTS AND ROLE OF CHANCE

IVM of denuded mouse oocytes in the presence of 1 mM GEE significantly increased intra-oocyte GSH content. ROS was not increased by CryoTop vitrification but was significantly lower in the IVM GEE group compared to IVM without GEE before vitrification and after recovery from vitrification/warming (P < 0.001). Vitrification alone significantly increased the GSH-dependent intra-mitochondrial redox capacity after warming (E^m_GSH, P < 0.001) in IVM oocytes, presumably by diffusion/uptake of cytoplasmic GSH into mitochondria. The presence of 1 mM GEE during IVM increased the redox capacity before vitrification and there was no further increase after vitrification/warming. None of the reproducibly detected 1492 spots of 2D DIGE separated proteins were significantly altered by vitrification or GEE supplementation. However, IVM of denuded oocytes significantly affected spindle integrity and chromosome alignment right after warming from vitrification (0 h) in group 1 and spindle integrity in group 2 (P < 0.05). GEE improved recovery in IVM group as numbers of oocytes with unaligned chromosomes and aberrant spindles was not significantly increased compared to unvitrified controls. The supplementation with GEE for 1 h before vitrification also supported more rapid recovery of spindle birefringence. GEE improved significantly development to the 2-cell stage for MII oocytes that were activated directly after vitrification/warming in both experimental groups, and also the blastocyst rate in the IVO GEE-supplemented group compared to the controls (P < 0.05).

LARGE SCALE DATA

None LIMITATIONS, REASONS FOR CAUTION: The studies were carried out in a mouse model, in IVM denuded rather than cumulus-enclosed oocytes, and in activated rather than IVF MII oocytes. Whether the increased GSH-dependent intra-mitochondrial redox capacity also improves male pronuclear formation needs to be studied further experimentally. The influence of GEE supplementation requires also further examination and optimization in human oocytes before it can be considered for clinical ART.

WIDER IMPLICATIONS OF THE FINDINGS

Although GEE supplementation did not alter the proteome at MII, the GSH donor may support cellular homeostasis and redox regulation and, thus, increase developmental competence. While human MII oocyte vitrification is an established procedure, GEE might be particularly beneficial for oocytes that suffer from oxidative stress and reduced redox capacity (e.g. aged oocytes) or possess low GSH due to a reduced supply of GSH from cumulus. It might also be of relevance for immature human oocytes that develop without cumulus to MII in vitro (e.g. in ICSI cycles) for ART.

STUDY FUNDING AND COMPETING INTERESTS

The study has been supported by the German Research Foundation (DFG FOR 1041; EI 199/3-2). There are no conflict of interests.

The Metabolomic Profile of Spent Culture Media from Day-3 Human Embryos Cultured under Low Oxygen Tension

Despite efforts made to improve the in vitro embryo culture conditions used during assisted reproduction procedures, human embryos must adapt to different in vitro oxygen concentrations and the new metabolic milieu provided by the diverse culture media used for such protocols. It has been shown that the embryo culture environment can affect not only cellular metabolism, but also gene expression in different species of mammalian embryos. Therefore we wanted to compare the metabolic footprint left by human cleavage-stage embryos under two types of oxygen atmospheric culture conditions (6% and 20% O2). The spent culture media from 39 transferred and implanted embryos from a total of 22 patients undergoing egg donation treatment was analyzed; 23 embryos came from 13 patients in the 6% oxygen concentration group, and 16 embryos from 9 patients were used in the 20% oxygen concentration group. The multivariate statistics we used in our analysis showed that human cleavage-stage embryos grown under both types of oxygen concentration left a similar metabolic fingerprint. We failed to observe any change in the net depletion or release of relevant analytes, such as glucose and especially fatty acids, by human cleavage-stage embryos under either type of culture condition. Therefore it seems that low oxygen tension during embryo culture does not alter the global metabolism of human cleavage-stage embryos.

Label-free characterization of vitrification-induced morphology changes in single-cell embryos with full-field optical coherence tomography

Vitrification is an increasingly popular method of embryo cryopreservation that is used in assisted reproductive technology. Although vitrification has high post-thaw survival rates compared to other freezing techniques, its long-term effects on embryo development are still poorly understood. We demonstrate an application of full-field optical coherence tomography (FF-OCT) to visualize the effects of vitrification on live single-cell (2 pronuclear) mouse embryos without harmful labels. Using FF-OCT, we observed that vitrification causes a significant increase in the aggregation of structures within the embryo cytoplasm, consistent with reports in literature based on fluorescence techniques. We quantify the degree of aggregation with an objective metric, the cytoplasmic aggregation (CA) score, and observe a high degree of correlation between the CA scores of FF-OCT images of embryos and of fluorescence images of their mitochondria. Our results indicate that FF-OCT shows promise as a label-free assessment of the effects of vitrification on embryo mitochondria distribution. The CA score provides a quantitative metric to describe the degree to which embryos have been affected by vitrification and could aid clinicians in selecting embryos for transfer.

Vitrification versus slow freezing for women undergoing oocyte cryopreservation

BACKGROUND

Oocyte cryopreservation is a technique with considerable potential in reproductive medicine, including  fertility preservation, as a way of delaying childbearing and as part of oocyte donation programs. Although the technique was relatively ineffective at first more recently numerous modifications have led to higher success rates.

OBJECTIVES

To compare the effectiveness and safety of vitrification and slow freezing as oocyte cryopreservation techniques for fertility outcomes in women undergoing assisted reproduction.

SEARCH METHODS

We searched electronic databases, trial registers and websites, including the Cochrane Menstrual Disorders and Subfertility Group Specialised Register of controlled trials, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and PsycINFO (date of search 3 March 2014).

SELECTION CRITERIA

Two review authors independently selected randomised controlled trials (RCTs) comparing vitrification and slow freezing for oocyte preservation in women undergoing assisted reproduction.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted the data from eligible studies and assessed their risk of bias. Any disagreements were resolved by discussion or by a third review author. Data extracted included study characteristics and outcome data. The overall quality of the evidence was assessed using GRADE methods.

MAIN RESULTS

Two RCTs were included in the review (106 participants). Neither study reported live birth rate. Vitrification was associated with an increased clinical pregnancy rate compared to slow freezing (RR 3.86, 95% CI 1.63 to 9.11, P = 0.002, 2 RCTs, 106 women, I(2) = 8%, moderate quality evidence). The effect of vitrification compared to slow freezing on ongoing pregnancy rates was only reported in one small study, with inconclusive findings (RR 6.07, 95% CI 0.86 to 43.04, P = 0.07, one RCT, 28 women, low quality evidence).No data were reported on adverse effects, nor were any other outcomes reported in the included trials. The evidence was limited by imprecision. We assessed the included studies as at low to unclear risk of bias as the methods were not well described.

AUTHORS' CONCLUSIONS

Oocyte vitrification compared to slow freezing probably increases clinical pregnancy rates in women undergoing assisted reproduction. However, the total number of women and pregnancies were low and the imprecision is high which limits applicability. The effect on ongoing pregnancy is uncertain as data were sparse. No data were available on live births or adverse effects.

MicroRNA and implantation

We provide a review of microRNA (miRNA) related to human implantation which shows the potential diagnostic role of miRNAs in impaired endometrial receptivity, altered embryo development, implantation failure after assisted reproduction technology, and in ectopic pregnancy and pregnancies of unknown location. MicroRNAs may be emerging diagnostic markers and potential therapeutic tools for understanding implantation disorders. However, further research is needed before miRNAs can be used in clinical practice for identifying and treating implantation failure.

New tools for embryo selection: comprehensive chromosome screening by array comparative genomic hybridization

The objective of this study was to evaluate the usefulness of comprehensive chromosome screening (CCS) using array comparative genomic hybridization (aCGH). The study included 1420 CCS cycles for recurrent miscarriage (n = 203); repetitive implantation failure (n = 188); severe male factor (n = 116); previous trisomic pregnancy (n = 33); and advanced maternal age (n = 880). CCS was performed in cycles with fresh oocytes and embryos (n = 774); mixed cycles with fresh and vitrified oocytes (n = 320); mixed cycles with fresh and vitrified day-2 embryos (n = 235); and mixed cycles with fresh and vitrified day-3 embryos (n = 91). Day-3 embryo biopsy was performed and analyzed by aCGH followed by day-5 embryo transfer. Consistent implantation (range: 40.5–54.2%) and pregnancy rates per transfer (range: 46.0–62.9%) were obtained for all the indications and independently of the origin of the oocytes or embryos. However, a lower delivery rate per cycle was achieved in women aged over 40 years (18.1%) due to the higher percentage of aneuploid embryos (85.3%) and lower number of cycles with at least one euploid embryo available per transfer (40.3%). We concluded that aneuploidy is one of the major factors which affect embryo implantation.