Understanding cellular disruptions during early embryo development that perturb viability and fetal development

Temperature fluctuations during embryo transfer can be mitigated by optimizing transfer protocol

RESEARCH QUESTION

What impact do variations in embryo transfer catheter loading and movement procedures have on temperature and pH fluctuations during embryo transfer?

DESIGN

Mock embryo transfers were conducted to test the impact of air flow/movement, use of catheter coverings, and the type of workstation used for catheter loading on catheter temperature. A thermocouple probe inserted into the tip of the outer catheter or taped to the exterior of the inner catheter recorded temperature within the catheter every 5 s from time of mock embryo loading (TL) to 60 s (TL + 60 s) or from the start of transit (TT). Fluctuations in culture medium pH in embryo transfer dishes were monitored.

RESULTS

The rate of cooling during transit was faster (all P < 0.05) when catheters were uncovered compared with all covering methods tested. This resulted in a lower catheter temperature at TL + 20 s (28.43 ± 0.30 °C) compared with catheters covered by plastic tubing (31.4 ± 0.30 °C), paper (31.0 ± 0.26 °C) or paper + thumb (31.1 ± 0.78 °C; all P ≤ 0.05). Temperature was maintained more effectively when catheters were loaded in a crib compared with a heated stage, until initiation of transit, when the rate of temperature decrease was similar. Culture medium pH increased more rapidly when embryo transfer dishes remained on a heated stage during the procedure compared with in an open crib.

CONCLUSIONS

Temperature loss during the embryo transfer procedure can be mitigated by reducing the transit time and using catheter coverings. Use of a crib for catheter loading only improved temperature stability while the catheter remained in the crib, not during transit, and reduced pH fluctuations during the procedure.

No major differences in perinatal and maternal outcomes between uninterrupted embryo culture in time-lapse system and conventional embryo culture

STUDY QUESTION

Is embryo culture in a closed time-lapse system associated with any differences in perinatal and maternal outcomes in comparison to conventional culture and spontaneous conception?

SUMMARY ANSWER

There were no significant differences between time-lapse and conventional embryo culture in preterm birth (PTB, <37 weeks), low birth weight (LBW, >2500 g) and hypertensive disorders of pregnancy for singleton deliveries, the primary outcomes of this study.

WHAT IS KNOWN ALREADY

Evidence from prospective trials evaluating the safety of time-lapse incubation for clinical use show similar embryo development rates, implantation rates, and ongoing pregnancy and live birth rates when compared to conventional incubation. Few studies have investigated if uninterrupted culture can alter risks of adverse perinatal outcomes presently associated with IVF when compared to conventional culture and spontaneous conceptions.

STUDY DESIGN, SIZE, DURATION

This study is a Swedish population-based retrospective registry study, including 7379 singleton deliveries after fresh embryo transfer between 2013 and 2018 from selected IVF clinics. Perinatal outcomes of singletons born from time-lapse-cultured embryos were compared to singletons from embryos cultured in conventional incubators and 71 300 singletons from spontaneous conceptions. Main perinatal outcomes included PTB and LBW. Main maternal outcomes included hypertensive disorders of pregnancy (pregnancy hypertension and preeclampsia).

PARTICIPANTS/MATERIALS, SETTING, METHODS

From nine IVF clinics, 2683 singletons born after fresh embryo transfer in a time-lapse system were compared to 4696 singletons born after culture in a conventional incubator and 71 300 singletons born after spontaneous conception matched for year of birth, parity, and maternal age. Patient and treatment characteristics from IVF deliveries were cross-linked with the Swedish Medical Birth Register, Register of Birth Defects, National Patient Register and Statistics Sweden. Children born after sperm and oocyte donation cycles and after Preimplantation Genetic testing cycles were excluded. Odds ratio (OR) and adjusted OR were calculated, adjusting for relevant confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

In the adjusted analyses, no significant differences were found for risk of PTB (adjusted OR 1.11, 95% CI 0.87-1.41) and LBW (adjusted OR 0.86, 95% CI 0.66-1.14) or hypertensive disorders of pregnancy; preeclampsia and hypertension (adjusted OR 0.99, 95% CI 0.67-1.45 and adjusted OR 0.98, 95% CI 0.62-1.53, respectively) between time-lapse and conventional incubation systems. A significantly increased risk of PTB (adjusted OR 1.31, 95% CI 1.08-1.60) and LBW (adjusted OR 1.36, 95% CI 1.08-1.72) was found for singletons born after time-lapse incubation compared to singletons born after spontaneous conceptions. In addition, a lower risk for pregnancy hypertension (adjusted OR 0.72 95% CI 0.53-0.99) but no significant difference for preeclampsia (adjusted OR 0.87, 95% CI 0.68-1.12) was found compared to spontaneous conceptions. Subgroup analyses showed that some risks were related to the day of embryo transfer, with more adverse outcomes after blastocyst transfer in comparison to cleavage stage transfer.

LIMITATIONS, REASONS FOR CAUTION

This study is retrospective in design and different clinical strategies may have been used to select specific patient groups for time-lapse versus conventional incubation. The number of patients is limited and larger datasets are required to obtain more precise estimates and adjust for possible effect of additional embryo culture variables.

WIDER IMPLICATIONS OF THE FINDINGS

Embryo culture in time-lapse systems is not associated with major differences in perinatal and maternal outcomes, compared to conventional embryo culture, suggesting that this technology is an acceptable alternative for embryo incubation.

STUDY FUNDING/COMPETING INTEREST(S)

The study was financed by a research grant from Gedeon Richter. There are no conflicts of interest for all authors to declare.

TRIAL REGISTRATION NUMBER

N/A.

Enhancement of preimplantation mouse embryo development with optimized in vitro culture dish via stabilization of medium osmolarity

OBJECTIVE

We evaluated the efficacy of the newly developed optimized in vitro culture (OIVC) dish for cultivating preimplantation mouse embryos. This dish minimizes the need for mineral oil and incorporates microwells, providing a stable culture environment and enabling independent monitoring of individual embryos.

METHODS

Mouse pronuclear (PN) zygotes and two-cell-stage embryos were collected at 18 and 46 hours after human chorionic gonadotropin injection, respectively. These were cultured for 120 hours using potassium simplex optimized medium (KSOM) to reach the blastocyst stage. The embryos were randomly allocated into three groups, each cultured in one of three dishes: a 60-mm culture dish, a microdrop dish, and an OIVC dish that we developed.

RESULTS

The OIVC dish effectively maintained the osmolarity of the KSOM culture medium over a 5-day period using only 2 mL of mineral oil. This contrasts with the significant osmolarity increase observed in the 60-mm culture dish. Additionally, the OIVC dish exhibited higher blastulation rates from two-cell embryos (100%) relative to the other dish types. Moreover, blastocysts derived from both PN zygotes and two-cell embryos in the OIVC dish group demonstrated significantly elevated mean cell numbers.

CONCLUSION

Use of the OIVC dish markedly increased the number of cells in blastocysts derived from the in vitro culture of preimplantation mouse embryos. The capacity of this dish to maintain medium osmolarity with minimal mineral oil usage represents a breakthrough that may advance embryo culture techniques for various mammals, including human in vitro fertilization and embryo transfer programs.

A comparison of culture and cooling for the short term preservation of in vivo derived dromedary camel embryos of varying morphological quality

Despite recent advancements in the cryopreservation of dromedary camel embryos, widespread application of the technique is still limited by the need for specialised vitrification equipment and supplies. Temporary, liquid-phase embryo storage methods provide a useful tool for short-term preservation of camel embryos. In the current study, we compared the use of in vitro embryo culture with cold liquid storage in order to maintain both high- (Grade 1- Excellent and 2-Good) and low- (Grade 3- Moderate and 4-Poor) morphological grade Day-7 dromedary camel embryos in vitro for up to 3 days. Embryos were either cooled and placed in Hams-F10 medium supplemented with HEPES and 10% FBS and then kept at 4 °C; or placed in Hams-F10 supplemented with sodium bicarbonate and 10% FBS and then cultured in a humidified atmosphere of 6% CO2 at 37 °C before being assessed for viability at 24 h. In high-morphological grade embryos, both cold storage and culture supported 100% viability (maintenance of normal morphology) over this period (Cooled n = 22, Cultured n = 20). In low-morphological grade embryos, culture supported higher viability (16/18, 88.9%) than did cooling (4/18, 22.2%). We then evaluated the effect of up to 3 days of cold storage or culture on embryo morphological grade, diameter, and developmental competence following embryo transfer. High-grade embryos were divided between culture and cold storage; low-grade embryos were evaluated only after culture. Over 3 days of culture, both high- and low-grade embryos tended to either maintain or improve upon their initial morphological score (P < 0.05) and increased in diameter (P < 0.001). Embryos subjected to cooling tended to have reduced morphological scores by 48 h of storage and decreased in diameter by 72 h (P < 0.05). No significant influence of storage method (cooling vs. culture), duration (24-72 h), or embryo grade (high vs low) was observed on pregnancy establishment at Day-60 (22.2%-57.2% pregnancy rates for all treatments). Overall, rates of pregnancy establishment were similar for transferred cultured (n = 45) and cooled (n = 45) embryos (pregnancy rates at Day 18, 48% vs 51.1%; at Day 60, 37.7% vs 37.7%). Rates of embryonic loss also were similar (22.7% vs 26%). In conclusion, whilst similar rates of pregnancy and pregnancy loss were observed following the transfer of both cooled and cultured embryos held in vitro for up to 3 days, amongst the two methods, only embryo culture appears to provide a means of effectively preserving Day- 7 dromedary camel embryos with reduced morphological values in vitro. Considering these embryos appear to show poor tolerance to the cooling procedure and are unlikely candidates for vitrification, embryo culture may provide an effective method for deriving pregnancies from low-morphological grade embryos when immediate transfer is not possible on the day of flushing.

Opening the black box: why do euploid blastocysts fail to implant? A systematic review and meta-analysis

BACKGROUND

A normal chromosomal constitution defined through PGT-A assessing all chromosomes on trophectoderm (TE) biopsies represents the strongest predictor of embryo implantation. Yet, its positive predictive value is not higher than 50-60%. This gap of knowledge on the causes of euploid blastocysts' reproductive failure is known as 'the black box of implantation'.

OBJECTIVE AND RATIONALE

Several embryonic, maternal, paternal, clinical, and IVF laboratory features were scrutinized for their putative association with reproductive success or implantation failure of euploid blastocysts.

SEARCH METHODS

A systematic bibliographical search was conducted without temporal limits up to August 2021. The keywords were '(blastocyst OR day5 embryo OR day6 embryo OR day7 embryo) AND (euploid OR chromosomally normal OR preimplantation genetic testing) AND (implantation OR implantation failure OR miscarriage OR abortion OR live birth OR biochemical pregnancy OR recurrent implantation failure)'. Overall, 1608 items were identified and screened. We included all prospective or retrospective clinical studies and randomized-controlled-trials (RCTs) that assessed any feature associated with live-birth rates (LBR) and/or miscarriage rates (MR) among non-mosaic euploid blastocyst transfer after TE biopsy and PGT-A. In total, 41 reviews and 372 papers were selected, clustered according to a common focus, and thoroughly reviewed. The PRISMA guideline was followed, the PICO model was adopted, and ROBINS-I and ROB 2.0 scoring were used to assess putative bias. Bias across studies regarding the LBR was also assessed using visual inspection of funnel plots and the trim and fill method. Categorical data were combined with a pooled-OR. The random-effect model was used to conduct the meta-analysis. Between-study heterogeneity was addressed using I2. Whenever not suitable for the meta-analysis, the included studies were simply described for their results. The study protocol was registered at http://www.crd.york.ac.uk/PROSPERO/ (registration number CRD42021275329).

OUTCOMES

We included 372 original papers (335 retrospective studies, 30 prospective studies and 7 RCTs) and 41 reviews. However, most of the studies were retrospective, or characterized by small sample sizes, thus prone to bias, which reduces the quality of the evidence to low or very low. Reduced inner cell mass (7 studies, OR: 0.37, 95% CI: 0.27-0.52, I2 = 53%), or TE quality (9 studies, OR: 0.53, 95% CI: 0.43-0.67, I2 = 70%), overall blastocyst quality worse than Gardner's BB-grade (8 studies, OR: 0.40, 95% CI: 0.24-0.67, I2 = 83%), developmental delay (18 studies, OR: 0.56, 95% CI: 0.49-0.63, I2 = 47%), and (by qualitative analysis) some morphodynamic abnormalities pinpointed through time-lapse microscopy (abnormal cleavage patterns, spontaneous blastocyst collapse, longer time of morula formation I, time of blastulation (tB), and duration of blastulation) were all associated with poorer reproductive outcomes. Slightly lower LBR, even in the context of PGT-A, was reported among women ≥38 years (7 studies, OR: 0.87, 95% CI: 0.75-1.00, I2 = 31%), while obesity was associated with both lower LBR (2 studies, OR: 0.66, 95% CI: 0.55-0.79, I2 = 0%) and higher MR (2 studies, OR: 1.8, 95% CI: 1.08-2.99, I2 = 52%). The experience of previous repeated implantation failures (RIF) was also associated with lower LBR (3 studies, OR: 0.72, 95% CI: 0.55-0.93, I2 = 0%). By qualitative analysis, among hormonal assessments, only abnormal progesterone levels prior to transfer were associated with LBR and MR after PGT-A. Among the clinical protocols used, vitrified-warmed embryo transfer was more effective than fresh transfer (2 studies, OR: 1.56, 95% CI: 1.05-2.33, I2 = 23%) after PGT-A. Lastly, multiple vitrification-warming cycles (2 studies, OR: 0.41, 95% CI: 0.22-0.77, I2 = 50%) or (by qualitative analysis) a high number of cells biopsied may slightly reduce the LBR, while simultaneous zona-pellucida opening and TE biopsy allowed better results than the Day 3 hatching-based protocol (3 studies, OR: 1.41, 95% CI: 1.18-1.69, I2 = 0%).

WIDER IMPLICATIONS

Embryo selection aims at shortening the time-to-pregnancy, while minimizing the reproductive risks. Knowing which features are associated with the reproductive competence of euploid blastocysts is therefore critical to define, implement, and validate safer and more efficient clinical workflows. Future research should be directed towards: (i) systematic investigations of the mechanisms involved in reproductive aging beyond de novo chromosomal abnormalities, and how lifestyle and nutrition may accelerate or exacerbate their consequences; (ii) improved evaluation of the uterine and blastocyst-endometrial dialogue, both of which represent black boxes themselves; (iii) standardization/automation of embryo assessment and IVF protocols; (iv) additional invasive or preferably non-invasive tools for embryo selection. Only by filling these gaps we may finally crack the riddle behind 'the black box of implantation'.

How and when to measure pH in IVF culture media: validation of a portable blood gas analyzer in two IVF culture dishes for time lapse and conventional incubators

PURPOSE

Maintaining a stable pH at optimal level in human embryo culture media is crucial for embryo development but poses a challenge for all IVF laboratories. We validate analytically reliable conditions for pH measurement that are as close as possible to the embryo microenvironment during IVF.

METHODS

This was a multicentric study. A Siemens EPOC portable blood gas analyzer was used. The analytical validation was carried out under the culture medium (Global Total HSA®) conditions of use (microdroplets, under oil overlay, in a IVF incubator with (EmbryoScope®) or without a time lapse system (K system G210+®) and using IVF dishes. The validation included repeatability ("within-run" precision), total precision (between-day precision), trueness based on inter-laboratory comparison, inaccuracy based on external quality assessment and comparison to the reference technique. We also assessed the pre-analytical medium incubation time required to obtain a target value.

RESULTS

A measurement after an incubation period of 24 to 48 h is more representative of the pH to which the embryo will be exposed throughout the culture. The "within-run" and "between-day" precision show very low coefficients of variation (CV%): 0.17 to 0.22% and 0.13 to 0.34%, respectively, with IVF culture media. Trueness (% bias) range from - 0.07 to - 0.03%. We demonstrate good correlation between EPOC and reference pH electrode with an overestimation of 0.03 pH units of EPOC.

CONCLUSION

Our method demonstrates good analytical performance for IVF laboratories wishing to implement a robust quality assurance system to monitor pH in embryo culture media. Compliance with stringent pre-analytical and analytical conditions is essential.

Haploid Parthenogenetic Embryos Exhibit Unique Stress Response to pH, Osmotic and Oxidative Stress

Preimplantation-stage embryos are susceptible to various types of stress when cultured in vitro. Parthenogenetic embryos that lack spermatozoa contribution exhibit aberrant developmental dynamics due to their uniparental origin. Herein, we assessed whether the absence of paternal genome affects the susceptibility of the embryos to pH, osmotic and oxidative stress. Haploid parthenogenetic embryos (HPE) (activated oocytes with 1 pronucleus and 2 polar bodies) were generated by incubating cumulus oocyte complexes of Swiss albino mice with 10 mM strontium chloride for 3 h. Normally fertilized embryos (NFE) (fertilized oocytes with 2 pronuclei and 2 polar bodies) were derived using in vitro fertilization. At 2-cell stage, both HPE and NFE were exposed to various stressors including pH (6.8 to 8.2), osmotic (isotonic, hypotonic, and hypertonic), and peroxidatic oxidative (H2O2, 25 µM) stress. Endoplasmic reticulum stress response, mitochondrial membrane potential, and the rate of blastocyst development were assessed. HPE were susceptible to alteration in the pH that was well tolerated by NFE. Similarly, HPE displayed remarkable difference in sensitivity to hypertonic stress and oxidative stress compared to NFE. The results clearly indicate that the oocytes that develop into embryos in the absence of paternal contribution are more vulnerable to environmental stressors, further highlighting the importance of spermatozoa contribution and/or the ploidy status in mitigating these stressors and towards healthy early embryo development.

Hyperoxic exposure alters intracellular bioenergetics distribution in human pulmonary cells

AIMS

Pulmonary oxygen toxicity is caused by exposure to a high fraction of inspired oxygen, which damages multiple cell types within the lung. The cellular basis for pulmonary oxygen toxicity includes mitochondrial dysfunction. The aim of this study was to identify the effects of hyperoxic exposure on mitochondrial bioenergetic and dynamic functions in pulmonary cells.

MAIN METHODS

Mitochondrial respiration, inner membrane potential, dynamics (including motility), and distribution of mitochondrial bioenergetic capacity in two intracellular regions were quantified using cultured human lung microvascular endothelial cells, human pulmonary artery endothelial cells and A549 cells. Hyperoxic (95 % O₂) exposures lasted 24, 48 and 72 h, durations relevant to mechanical ventilation in intensive care settings.

KEY FINDINGS

Mitochondrial motility was altered following all hyperoxic exposures utilized in experiments. Inhomogeneities in inner membrane potential and respiration parameters were present in each cell type following hyperoxia. The partitioning of ATP-linked respiration was also hyperoxia-duration and cell type dependent. Hyperoxic exposure lasting 48 h or longer provoked the largest alterations in mitochondrial motility and the greatest decreases in ATP-linked respiration, with a suggestion of decreases in respiration complex protein levels.

SIGNIFICANCE

Hyperoxic exposures of different durations produce intracellular inhomogeneities in mitochondrial dynamics and bioenergetics in pulmonary cells. Oxygen therapy is utilized commonly in clinical care and can induce undesirable decrements in bioenergy function needed to maintain pulmonary cell function and viability. There may be adjunctive or prophylactic measures that can be employed during hyperoxic exposures to prevent the mitochondrial dysfunction that signals the presence of oxygen toxcity.

Incubator type affects human blastocyst formation and embryo metabolism: a randomized controlled trial

STUDY QUESTION

Does the type of incubator used to culture human preimplantation embryos affect development to the blastocyst stage and alter amino acid utilization of embryos in assisted reproduction?

SUMMARY ANSWER

Culturing embryos in a time lapse system (TLS) was associated with a higher Day 5 blastocyst formation rate and altered amino acid utilization when measured from Day 3 to Day 5 compared to the standard benchtop incubator.

WHAT IS KNOWN ALREADY

Culture environment is known to be important for the developing preimplantation embryo. TLSs provide a stable milieu allowing embryos to be monitored in situ, whereas embryos cultured in standard benchtop incubators experience environmental fluctuations when removed for morphological assessment.

STUDY DESIGN, SIZE, DURATION

A prospective clinical trial randomizing 585 sibling embryos to either the TLS (289 embryos) or the standard benchtop incubator (296 embryos) over a 23-month period in a UK University Hospital Fertility Clinic.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Participants were aged 42 years or under, had an antral follicle count of ≥12 and ≥6 2 pronucleate zygotes. Zygotes were cultured individually in 25 µl of medium. Randomized embryos were graded and selected for transfer or cryopreservation on Day 5. For those embryos produced by women who underwent stimulation with recombinant FSH injections and were triggered with hCG, spent medium was collected on Day 5 for amino acid analysis by high pressure liquid chromatography. Clinical pregnancy was defined as the presence of a foetal heart beat on ultrasound scan at 7 weeks.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, blastocyst formation rate on Day 5 was significantly higher in embryos cultured in the TLS (55%) compared to the standard incubator (45%; P = 0.013). Similarly, there was an increase in the number of blastocysts suitable for cryopreservation in the TLS (31%) compared to the standard incubator (23%; P = 0.032). There was a significant difference in the utilization of 12 amino acids by blastocysts cultured from Day 3 to Day 5 in the TLS compared to the standard incubator. Embryos cultured in the TLS displayed an increased total amino acid utilization (P < 0.001) and reduced amino acid production (P < 0.001) compared to those in the standard incubator. Irrespective of incubator used, embryos fertilized by ICSI depleted significantly more amino acids from the medium compared to those fertilized by conventional IVF. There was no difference in the mean score of blastocysts transferred, or the clinical pregnancy rate after transfer of embryos from either of the incubators.

LIMITATIONS, REASONS FOR CAUTION

The study was not powered to discern significant effects on clinical outcomes.

WIDER IMPLICATIONS OF THE FINDINGS

The metabolism and development of preimplantation embryos is impacted by the type of incubator used for culture. Further research is required to investigate the long-term implications of these findings.

STUDY FUNDING/COMPETING INTEREST(S)

NIHR Southampton Biomedical Research Centre Commercial and Enterprise Incubator Fund funded this study. The TLS was provided on loan for the study by Vitrolife. The authors declare no conflict of interests.

TRIAL REGISTRATION NUMBER

ISRCTN73037149.

TRIAL REGISTRATION DATE

12 January 2012.

DATE OF FIRST PATIENT’S ENROLMENT

21 January 2012.

Hypoxic in vitro culture reduces histone lactylation and impairs pre-implantation embryonic development in mice

BACKGROUND

Dynamic changes of histone posttranslational modifications are important contexts of epigenetic reprograming after fertilization in pre-implantation embryos. Recently, lactylation has been reported as a novel epigenetic modification that regulates various cellular processes, but its role during early embryogenesis has not been elucidated.

RESULTS

We examined nuclear accumulation of H3K23la, H3K18la and pan histone lactylation in mouse oocytes and pre-implantation embryos by immunofluorescence with specific antibodies. All of the three modifications were abundant in GV stage oocytes, and both H3K23la and pan histone lactylation could be detected on the condensed chromosomes of the MII oocytes, while H3K18la were not detected. After fertilization, the nuclear staining of H3K23la, H3K18la and pan histone lactylation was faint in zygotes but homogeneously stained both of the parental pronuclei. The signal remained weak in the early cleavage stage embryos and increased remarkably in the blastocyst stage embryos. Comparison of the embryos cultured in four different conditions with varying concentrations of oxygen found that H3K23la, H3K18la and pan histone lactylation showed similar and comparable staining pattern in embryos cultured in atmospheric oxygen concentration (20% O₂), gradient oxygen concentration (5% O₂ to 2% O₂) and embryos obtained from in vivo, but the modifications were greatly reduced in embryos cultured in hypoxic condition (2% O₂). In contrast, nuclear accumulation of H3K18ac or H3K23ac was not significantly affected under hypoxic condition. Moreover, the developmental rate of in vitro cultured embryo was significantly reduced by low oxygen concentration and small molecule inhibition of LDHA activity led to decreased lactate production, as well as reduced histone lactylation and compromised developmental rate.

CONCLUSIONS

We provided for the first time the dynamic landscape of H3K23la, H3K18la and pan histone lactylation in oocytes and pre-implantation embryos in mice. Our data suggested that histone lactylation is subjected to oxygen concentration in the culture environment and hypoxic in vitro culture reduces histone lactylation, which in turn compromises developmental potential of pre-implantation embryos in mice.

Banking of AT-MSC and its Influence on Their Application to Clinical Procedures

Processing of MSCs to obtain a therapeutic product consists of two main steps: 1) the in vitro expansion of the cells until an appropriate number of them is obtained, and 2) freezing and storage of the expanded cells. The last step is critical and must be optimized so that after thawing the cells retain all their physiological properties including the secretory function. In this paper, we evaluated physiological parameters of AT-MSC's after a full cycle of their processing, particularly freezing and storing at the liquid nitrogen vapor temperature. Based on the recovered proliferative and secretory capacities of the thawed cells, we have designed the optimal technique for processing of MSCs for clinical applications. In our work, we tried to select the best DMSO-based cryoprotectant mixture on the base of post thawing fully retain their properties. We have demonstrated the effectiveness of the use of DMSO in various configurations of the constituent cryoprotective fluids. We have also shown that AT-MSCs that show control levels in most standard tests (viability, shape, culture behaviour, and proliferative properties) after thawing, may show transient variations in some important physiological properties, such as the level of secreted growth factors. Obtained results let us to indicate how to optimize the AT-MSC preparation process for clinical applications. We suggest that before their clinical application the cells should be cultured for at least one passage to recover their physiological stability and thus assure their optimal therapeutic potential.

Raman Spectrum of Follicular Fluid: A Potential Biomarker for Oocyte Developmental Competence in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disorder in reproductive women where abnormal folliculogenesis is considered as a common characteristic. Our aim is to evaluate the potential of follicular fluid (FF) Raman spectra to predict embryo development and pregnancy outcome, so as to prioritize the best promising embryo for implantation, reducing both physiological and economical burdens of PCOS patients. In addition, the altered metabolic profiles will be identified to explore the aetiology and pathobiology of PCOS. In this study, follicular fluid samples obtained from 150 PCOS and 150 non-PCOS women were measured with Raman spectroscopy. Individual Raman spectrum was analyzed to find biologic components contributing to the occurrence of PCOS. More importantly, the Raman spectra of follicular fluid from the 150 PCOS patients were analyzed via machine-learning algorithms to evaluate their predictive value for oocyte development potential and clinical pregnancy. Mean-centered Raman spectra and principal component analysis (PCA) showed global differences in the footprints of follicular fluid between PCOS and non-PCOS women. Two Raman zones (993-1,165 cm^-1 and 1,439-1,678 cm^-1) were identified for describing the largest variances between the two groups, with the former higher and the latter lower in PCOS FF. The tentative assignments of corresponding Raman bands included phenylalanine and β -carotene. Moreover, it was found that FF, in which oocytes would develop into high-quality blastocysts and obtain high clinical pregnancy rate, were detected with lower quantification of the integration at 993-1,165 cm^-1 and higher quantification of the integration at 1,439-1,678 cm^-1 in PCOS. In addition, based on Raman spectra of PCOS FF, the machine-learning algorithms via the fully connected artificial neural network (ANN) achieved the overall accuracies of 90 and 74% in correctly assigning oocyte developmental potential and clinical pregnancy, respectively. The study suggests that the PCOS displays unique metabolic profiles in follicular fluid which could be detected by Raman spectroscopy. Specific bands in Raman spectra have the biomarker potential to predict the embryo development and pregnancy outcome for PCOS patients. Importantly, these data may provide some valuable biochemical information and metabolic signatures that will help us to understand the abnormal follicular development in PCOS.

Metabolic activity of human blastocysts correlates with their morphokinetics, morphological grade, KIDScore and artificial intelligence ranking

STUDY QUESTION

Is there a relationship between blastocyst metabolism and biomarkers of embryo viability?

SUMMARY ANSWER

Blastocysts with higher developmental potential and a higher probability of resulting in a viable pregnancy consume higher levels of glucose and exhibit distinct amino acid profiles.

WHAT IS KNOWN ALREADY

Morphological and morphokinetic analyses utilized in embryo selection provide insight into developmental potential, but alone are unable to provide a direct measure of embryo physiology and inherent health. Glucose uptake is a physiological biomarker of viability and amino acid utilization is different between embryos of varying qualities.

STUDY DESIGN, SIZE, DURATION

Two hundred and nine human preimplantation embryos from 50 patients were cultured in a time-lapse incubator system in both freeze all and fresh transfer cycles. A retrospective analysis of morphokinetics, morphology (Gardner grade), KIDScore, artificial intelligence grade (EmbryoScore), glucose and amino acid metabolism, and clinical pregnancies was conducted.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ICSI was conducted in all patients, who were aged ≤37 years and previously had no more than two IVF cycles. Embryos were individually cultured in a time-lapse incubator system, and those reaching the blastocyst stage had their morphokinetics annotated and were each assigned a Gardner grade, KIDScore and EmbryoScore. Glucose and amino acid metabolism were measured. Clinical pregnancies were confirmed by the presence of a fetal heartbeat at 6 weeks of gestation.

MAIN RESULTS AND THE ROLE OF CHANCE

Glucose consumption was at least 40% higher in blastocysts deemed of high developmental potential using either the Gardner grade (P < 0.01, n = 209), KIDScore (P < 0.05, n = 207) or EmbryoScore (P < 0.05, n = 184), compared to less viable blastocysts and in blastocysts that resulted in a clinical pregnancy compared to those that failed to implant (P < 0.05, n = 37). Additionally, duration of cavitation was inversely related to glucose consumption (P < 0.05, n = 200). Total amino acid consumption was significantly higher in blastocysts with an EmbryoScore higher than the cohort median score (P < 0.01, n = 185). Furthermore, the production of amino acids was significantly lower in blastocysts with a high Gardner grade (P < 0.05, n = 209), KIDScore (P < 0.05, n = 207) and EmbryoScore (P < 0.01, n = 184).

LIMITATIONS, REASONS FOR CAUTION

Samples were collected from patients who had ICSI treatment and from only one clinic.

WIDER IMPLICATIONS OF THE FINDINGS

These results confirm that metabolites, such as glucose and amino acids, are valid biomarkers of embryo viability and could therefore be used in conjunction with other systems to aid in the selection of a healthy embryo.

STUDY FUNDING/COMPETING INTEREST(S)

Work was supported by Virtus Health. D.K.G is contracted with Virtus Health. The other authors have no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

MicroRNA-210 Regulates Endoplasmic Reticulum Stress and Apoptosis in Porcine Embryos

Simple Summary

The purpose of this study was to explore the effect of miR-210 on in vitro embryo development, mRNA expression related endoplasmic reticulum (ER) stress. Treatment with a miR-210-inhibitor significantly improved in vitro embryo development and total blastocyst cell number (TCN). Furthermore, miR-210-inhibitor treatment downregulated ER stress and apoptosis-related gene expression, while simultaneously improving embryo capacity. In contrast, a miR-210-mimic decreased in vitro embryo development, TCN, upregulated ER stress and apoptosis genes, and concomitantly impaired embryo quality. Therefore, we suggest that miR-210 plays an important role in porcine in vitro embryo development.

Abstract

Endoplasmic reticulum (ER) stress can be triggered during in vitro embryo production and is a major obstacle to embryo survival. MicroRNA (miR)-210 is associated with cellular adaptation to cellular stress and inflammation. An experiment was conducted to understand the effects of miR-210 on in vitro embryo development, ER stress, and apoptosis; to achieve this, miR-210 was microinjected into parthenogenetically activated embryos. Our results revealed that miR-210 inhibition significantly enhanced the cleavage rate, blastocyst formation rate, and total cell number (TCN) of blastocysts, and reduced expression levels of XBP1 (p < 0.05). miR-210 inhibition greatly reduced the expression of ER stress-related genes (uXBP1, sXBP1, ATF4, and PTPN1) and Caspase 3 and increased the levels of NANOG and SOX2 (p < 0.05). A miR-210-mimic significantly decreased the cleavage, blastocyst rate, TCN, and expression levels of XBP1 compared with other groups (p < 0.05). The miR-210-mimic impaired the expression levels of uXBP1, sXBP1, ATF4, PTPN1, and Caspase 3 and decreased the expression of NANOG and SOX2 (p < 0.05). In conclusion, miR-210 plays an essential role in porcine in vitro embryo development. Therefore, we suggest that miR-210 inhibition could alleviate ER stress and reduce apoptosis to support the enhancement of in vitro embryo production.

Reducing time to pregnancy and facilitating the birth of healthy children through functional analysis of embryo physiology†

An ever-increasing number of couples rely on assisted reproductive technologies (ART) in order to conceive a child. Although advances in embryo culture have led to increases in the success rates of clinical ART, it often takes more than one treatment cycle to conceive a child. Ensuring patients conceive as soon as possible with a healthy embryo is a priority for reproductive medicine. Currently, selection of embryos for transfer relies predominantly on the morphological assessment of the preimplantation embryo; however, morphology is not an absolute link to embryo physiology, nor the health of the resulting child. Non-invasive quantitation of individual embryo physiology, a key regulator of both embryo viability and health, could provide valuable information to assist in the selection of the most viable embryo for transfer, hence reducing the time to pregnancy. Further, according to the Barker Hypothesis, the environment to which a fetus is exposed to during gestation affects subsequent offspring health. If the environment of the preimplantation period is capable of affecting metabolism, which in turn will affect gene expression through the metaboloepigenetic link, then assessment of embryo metabolism should represent an indirect measure of future offspring health. Previously, the term viable embryo has been used in association with the potential of an embryo to establish a pregnancy. Here, we propose the term healthy embryo to reflect the capacity of that embryo to lead to a healthy child and adult.

Effects of Supplementation with Natural Antioxidants on Oocytes and Preimplantation Embryos

For most infertile couples, in vitro fertilization (IVF) represents the only chance to conceive. Given the limited success of IVF procedures, novel approaches are continuously tested with the aim of improving IVF outcomes. Growing attention is devoted today to the potential benefit of natural antioxidants in the optimization of infertility treatments. This review summarizes current data in this context, focusing on both experimental studies on oocytes/embryos and clinical trials on antioxidants supplementation. Based on information gained from experimental studies, antioxidant supplementation may have beneficial effects on IVF outcomes in terms of quality and cryotolerance of in vitro produced embryos, together with positive effects on in vitro maturation oocytes and on early embryonic development. Unfortunately, from the clinical side, there is a paucity of evidence favoring the protective qualities of antioxidants. Among the antioxidants considered, coenzyme Q10 may be regarded as one of the most promising for its positive role in rescuing the oxidative stress-induced damages, but further data are needed. It is concluded that further trials are necessary to characterize the potential clinical value of antioxidants in IVF treatments.

A novel culture medium with reduced nutrient concentrations supports the development and viability of mouse embryos

Further refinement of culture media is needed to improve the quality of embryos generated in vitro. Previous results from our laboratory demonstrated that uptake of nutrients by the embryo is significantly less than what is supplied in traditional culture media. Our objective was to determine the impact of reduced nutrient concentrations in culture medium on mouse embryo development, metabolism, and quality as a possible platform for next generation medium formulation. Concentrations of carbohydrates, amino acids, and vitamins could be reduced by 50% with no detrimental effects, but blastocyst development was impaired at 25% of standard nutrient provision (reduced nutrient medium; RN). Addition of pyruvate and L-lactate (+PL) to RN at 50% of standard concentrations restored blastocyst development, hatching, and cell number. In addition, blastocysts produced in RN + PL contained more ICM cells and ATP than blastocysts cultured in our control (100% nutrient) medium; however, metabolic activity was altered. Similarly, embryos produced in the RN medium with elevated (50% control) concentrations of pyruvate and lactate in the first step medium and EAA and Glu in the second step medium were competent to implant and develop into fetuses at a similar rate as embryos produced in the control medium. This novel approach to culture medium formulation could help define the optimal nutrient requirements of embryos in culture and provide a means of shifting metabolic activity towards the utilization of specific metabolic pathways that may be beneficial for embryo viability.

Need for choosing the ideal pH value for IVF culture media

PURPOSE

Monitoring the pH of IVF culture media is a good practice, but the required pH levels have been "arbitrarily" set. Assisted reproductive technology centers around the world are spending time and money on pH monitoring without any consensus to date. The objective of this narrative review was to evaluate the importance of pH monitoring during IVF, discover how the oocyte and embryo regulate their intracellular pH and try to determine the optimal pH to be applied.

METHODS

A narrative literature review was performed on publications in the PubMed database reporting on the impact of pH on cellular function, oocyte and embryo development, IVF outcomes and pathophysiology, or on physiological pH in the female reproductive tract.

RESULTS

Intracellular pH regulates many cellular processes such as meiotic spindle stability of the oocyte, cell division and differentiation, embryo enzymatic activities, and blastocoel formation. The internal pH of the human embryo is maintained by regulatory mechanisms (mainly Na⁺/H⁺ and HCO₃^-/Cl^- exchangers) that can be exceeded, particularly in the oocyte and early-stage embryos. The opinion that the optimal pH for embryo culture is physiological pH is not correct since several physicochemical parameters specific to IVF culture conditions (temperature, medium composition, duration of culture, or implication of CO₂) can modify the intracellular pH of the embryo and change its needs and adaptability.

CONCLUSIONS

Because correct and stable extracellular pH is essential to embryo health and development, monitoring pH is imperative. However, there is a lack of clinical data on choosing the ideal pH for human IVF culture media.

The impact of embryo quality on singleton birthweight in vitrified-thawed single blastocyst transfer cycles

STUDY QUESTION

Does the quality of a single transferred blastocyst affect singleton birthweight in frozen-embryo transfer (FET) cycles?

SUMMARY ANSWER

The transfer of a poor-quality blastocyst was associated with lower mean birthweight and gestation-adjusted birthweight (Z-scores) when compared with the transfer of an excellent-quality blastocyst during FET cycles.

WHAT IS KNOWN ALREADY

Embryo quality is a strong predictor of IVF success rates. However, very few studies have examined the effect of embryo quality on singleton birthweight.

STUDY DESIGN, SIZE, DURATION

This retrospective study involved singleton live births born to women undergoing frozen-thawed single blastocyst transfers during the period from January 2010 to December 2017 at a tertiary care centre.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 1207 women who fulfilled the inclusion criteria were included and were grouped into four groups depending on the blastocyst quality: excellent, good, average and poor. The primary outcome measure was singleton birthweight. The Z-score was employed to calculate the birthweight adjusted for gestational age and newborn gender. Multiple linear regression analysis was performed to investigate the relationship between embryo quality and neonatal birthweight after adjustment for some potential confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

In the primary multivariable model, singletons from the poor-quality blastocyst group weighed 183.5 g less than those from the excellent-quality blastocyst group (95% CI: −295.1 to −71.9 g, P = 0.001) in terms of mean birthweight after accounting for patient characteristics, IVF treatment parameters, the year of treatment and newborn gender. Likewise, poor-quality blastocyst transfer was associated with lower gestation-adjusted Z-scores than the transfer of excellent-quality blastocysts (β = −0.35, 95% CI: −0.59 to −0.12, P = 0.003).

LIMITATIONS AND REASONS FOR CAUTION

The current study was limited by its retrospective design and the fact that our analysis was restricted to women with singleton births from single blastocyst transfers. Future prospective studies are required to confirm our findings.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings provide new insight into the relationship between embryo quality and neonatal outcomes by showing that poor-quality blastocyst transfer was associated with a decrease in singleton birthweight.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Key Research and Development Program of China (grant no. 2018YFC1003000), the National Natural Science Foundation of China (grant nos. 81771533, 81571397 and 31770989), and the China Postdoctoral Science Foundation (Grant no. 2018M630456). The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

Not applicable.

Systematic Development, Validation and Optimization of a Human Embryo Culture System

Objective: To develop and validate a reliable in vitro culture system for human embryos. Design: Retrospective analyses of a series of four studies were conducted between 2006 and 2010 to assess the effect of incubator type (CO2 box versus Tri-gas minibox), media type, oil type, and hyaluronate supplementation. Optimization of in vitro blastocyst development was verified by assessing our National CDC/ART Surveillance reports between 2010 and 2016. Material and Methods: All patients experienced controlled ovarian hyperstimulation, followed by egg retrieval 35 h post-hCG. Cumulus-oocyte complexes were temporarily cultured in P1 or LG Fert medium plus HSA. Eggs were moved to a more complex media (G-medium or Global®-LG medium) containing a synthetic protein and embryo adhesion supplement (SPS and EAS, respectively; mLG) post-ICSI insemination. Zygotes were assigned to group culture in 25 µl droplets under oil (light mineral oil or paraffin oil; 37 °C) and embryo development was evaluated on Days 3, 5, and 6 and transferred on Day 3 to 5 depending on the number/quality of embryos available and the IVF history of the patient. Transfers were performed under ultrasound guidance, primarily using a Sureview-Wallace catheter, and enriched ET medium containing 500 µg/mL EAS. Results: Pilot study results (Expt. 1) showed that a mLG single-step medium could be effectively used in combination with Sanyo MCO-5 tri-gas (TG) incubators. Once adapted to SCIRS Lab in 2007 (Expt. 2), the latter culture system yielded improved blastocyst production and pregnancy outcomes compared to CO2 in air sequential incubation in P1/Multi-blast medium. In Expt. 3, the mLG/TG system yielded high levels of ≥2BB quality blastocysts (51 to 66%) across all age groups, and greater (p < 0.05) pregnancy success/live birth rates using fewer embryos transferred on Day 5 versus Day 3. After validating its clinical effectiveness, mLG was then prospectively compared to a new generation G-media (1.5 & 2.5; Expt. 4) and determined that the crossover treatment using paraffin oil (Ovoil™) allowed the mLG system to be optimized. Subsequently, a compilation of our Annual CDC/ART reported data over six years verified the overall viability of in vitro cultured and vitrified blastocysts produced in the mLG/TG system. Conclusion: By systematically evaluating and implementing various components of an embryo culture system we were able to optimize blastocyst development over the last decade. Our mLG/TG culture system modified an exceptionally well designed KSOMAA LG medium using endotoxin-free EAS and SPS additives to support cellular membrane wellness under stressful in vitro conditions (e.g., culture, cell biopsy, vitrification). Our use of the mLG/TG culture system has proven to be effective, creating reliably high blastocyst production, implantation, and healthy live births.

Applications of omics and nanotechnology to improve pig embryo production in vitro

An appropriate environment to optimize porcine preimplantation embryo production in vitro is required as genetically modified pigs have become indispensable for biomedical research and agriculture. To provide suitable culture conditions, omics technologies have been applied to elucidate which metabolic substrates and pathways are involved during early developmental processes. Metabolomic profiling and transcriptional analysis comparing in vivo- and in vitro-derived embryos have demonstrated the important role of amino acids during preimplantation development. Transcriptional profiling studies have been helpful in assessing epigenetic reprogramming agents to allow for the correction of gene expression during the cloning process. Along with this, nanotechnology, which is a highly promising field, has allowed for the use of engineered nanoplatforms in reproductive biology. A growing number of studies have explored the use of nanoengineered materials for sorting, labeling, and targeting purposes; which demonstrates their potential to become one of the solutions for precise delivery of molecules into gametes and embryos. Considering the contributions of omics and the recent progress in nanoscience, in this review, we focused on their emerging applications for current in vitro pig embryo production systems to optimize the generation of genetically modified animals.

The effects of glycine-glutamine dipeptide replaced l-glutamine on bovine parthenogenetic and IVF embryo development

Relative to alanine and serine amino acid levels, glutamine is highly abundant in follicular fluid, and is an important source of energy required for oocyte maturation and embryo development. Thus, glutamine is an essential component of in vitro embryo culture media. However, glutamine has poor stability and degrades spontaneously in solution to form ammonia and pyrrolidonecarboxylic acid. In the present study, we aimed to explore the effect of substituting l-glutamine with glycine-glutamine, a more stable glutamine, on development of early parthenogenetic embryos and in vitro fertilization (IVF) embryos in bovine. Results revealed that glycine-glutamine can significantly increase cleavage rate (parthenogenetic embryos:87.24% vs. 72.61%, IVF embryos:89.33% vs. 83.79%, P < 0.01), blastocyst number (parthenogenetic embryos:24.98% vs. 18.07%, IVF embryos:33.53% vs. 27.29%, P < 0.01), and blastocyst number (parthenogenetic embryos:96 vs. 76, IVF embryos:114 vs. 109, P < 0.01), reduce blastocyst apoptosis (parthenogenetic embryos:3.72% vs. 6.65%, IVF embryos:2.53% vs.6.23%, P < 0.01), alleviate embryo ammonia toxicity, and reduce the content of reactive oxygen species (ROS) compared with the l-glutamine. In addition, glycine-glutamine can alter epigenetic reprogramming by increasing the expression of HDAC1 (Histone Deacetylase 1) and decreasing the relative expression levels of H3K9 acetylation in early parthenogenetic embryos and IVF embryos. From our present study, we concluded that glycine-glutamine is an effective substitute of glutamine in modified synthetic oviduct fluid with amino acids (mSOFaa).

DMSO induces drastic changes in human cellular processes and epigenetic landscape in vitro

Though clinical trials for medical applications of dimethyl sulfoxide (DMSO) reported toxicity in the 1960s, later, the FDA classified DMSO in the safest solvent category. DMSO became widely used in many biomedical fields and biological effects were overlooked. Meanwhile, biomedical science has evolved towards sensitive high-throughput techniques and new research areas, including epigenomics and microRNAs. Considering its wide use, especially for cryopreservation and in vitro assays, we evaluated biological effect of DMSO using these technological innovations. We exposed 3D cardiac and hepatic microtissues to medium with or without 0.1% DMSO and analyzed the transcriptome, proteome and DNA methylation profiles. In both tissue types, transcriptome analysis detected >2000 differentially expressed genes affecting similar biological processes, thereby indicating consistent cross-organ actions of DMSO. Furthermore, microRNA analysis revealed large-scale deregulations of cardiac microRNAs and smaller, though still massive, effects in hepatic microtissues. Genome-wide methylation patterns also revealed tissue-specificity. While hepatic microtissues demonstrated non-significant changes, findings from cardiac microtissues suggested disruption of DNA methylation mechanisms leading to genome-wide changes. The extreme changes in microRNAs and alterations in the epigenetic landscape indicate that DMSO is not inert. Its use should be reconsidered, especially for cryopreservation of embryos and oocytes, since it may impact embryonic development.

Endoplasmic Reticulum (ER) Stress and Unfolded Protein Response (UPR) in Mammalian Oocyte Maturation and Preimplantation Embryo Development

Mammalian oocytes and early embryos derived from in vitro production are highly susceptible to a variety of cellular stresses. During oocyte maturation and preimplantation embryo development, functional proteins must be folded properly in the endoplasmic reticulum (ER) to maintain oocyte and embryo development. However, some adverse factors negatively impact ER functions and protein synthesis, resulting in the activation of ER stress and unfolded protein response (UPR) signaling pathways. ER stress and UPR signaling have been identified in mammalian oocytes and embryos produced in vitro, suggesting that modulation of ER stress and UPR signaling play very important roles in oocyte maturation and the development of preimplantation embryos. In this review, we briefly describe the current state of knowledge regarding ER stress, UPR signaling pathways, and their roles and mechanisms in mammalian (excluding human) oocyte maturation and preimplantation embryo development.

Culture of the Mouse Preimplantation Embryo

The first culture media designed specifically to support development of the preimplantation mouse embryo were formulated over 50 years ago and were based on balanced salt solutions, containing the carbohydrates pyruvate, lactate, and glucose as the sole energy sources. Such media used a bicarbonate-carbon dioxide buffer system to maintain the desired pH, and were typically supplemented with serum albumin, but lacked free amino acids. In contrast to the complexity of a tissue culture medium, these original formulations of mouse embryo culture media were very simplistic. Over the intervening decades, as our understanding of the physiology and metabolism of the preimplantation embryo increased, together with a greater understanding of the environment within the female reproductive tract, culture media to support mouse embryo development in vitro have become more physiological and consequently more complex. A main addition to such media has been an array of amino acids. Although the media of today contain more components than their predecessors, their preparation remains relatively easy to accomplish, made feasible through the use of stock solutions, which also readily facilitates any changes to formulations to be made, an essential prerequisite for experimentation. As well as changes in media formulations, there have been exciting developments in incubator technology and design, such as the inclusion of time-lapse capability, redefining our ability to both culture and monitor embryo development in vitro.

Antioxidants improve IVF outcome and subsequent embryo development in the mouse

STUDY QUESTION

What is the effect of a combination of three antioxidants (Acetyl-L-Carnitine, N-Acetyl-L-Cysteine and α-Lipoic Acid), present in IVF medium during mouse oocyte and sperm collection, on fertilization and subsequent IVF embryo development?

SUMMARY ANSWER

A combination of antioxidants resulted in faster developmental times from the 2-cell stage through to expanded blastocyst stage, accompanied by a significant increase in blastocyst cell number and a reduction of intracellular hydrogen peroxide (H2O2) levels.

WHAT IS KNOWN ALREADY

The antioxidant combination Acetyl-L-Carnitine, N-Acetyl-L-Cysteine and α-Lipoic Acid, when present in embryo culture media, has a significant beneficial effect on in vitro fertilized mouse pronucleate oocyte development, especially under oxidative stress.

STUDY DESIGN, SIZE, DURATION

IVF was conducted with combined antioxidants supplemented in IVF medium that was used for mouse oocyte collection and fertilization (oocyte IVF medium, 4 h exposure) and sperm collection and preparation (sperm IVF medium, 1 h exposure).

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

IVF was conducted under 20% oxygen, in the presence or absence of a combination of antioxidants (10 μM Acetyl-L-Carnitine, 10 μM N-Acetyl-L-Cysteine, 5 μM α-Lipoic Acid) and resultant embryos cultured with and without antioxidants under 20% oxygen. Subsequently, the effects of antioxidants on either oocytes or sperm was evaluated. Embryo development was analysed through time-lapse microscopy followed by differential nuclear staining to determine cell allocation in the blastocyst. Intracellular levels of H2O2 were assessed using an aryl boronate probe after 4 h of incubation with antioxidants. Controls were gametes and embryos that had no antioxidants in the medium. In a separate series of experiments, pronucleate oocytes were collected in handling medium with and without antioxidants for 20 min and subsequent cell numbers analysed.

MAIN RESULTS AND THE ROLE OF CHANCE

Antioxidant treatment during both IVF and culture resulted in significantly faster development times to two cell cleavage (P < 0.01), which continued through to the expanded blastocyst stage (P < 0.05). Resultant blastocysts had a significant increase in both trophectoderm (TE) cell numbers, inner cell mass (ICM) and total cell numbers (P < 0.001). The addition of antioxidants to IVF medium or embryo culture media exclusively also resulted in a significant increase in both blastocyst TE and ICM numbers leading to an increase in total cell numbers (P < 0.001). Antioxidant supplementation of either oocyte IVF medium alone, or in both oocyte and sperm IVF medium, lead to significantly faster times to two cell cleavage, which continued through to the expanded blastocyst stage. Blastocyst cell number in both these groups had significantly higher TE cell numbers resulting in an increase in total cell numbers. In contrast, there were no differences in embryo developmental rates and blastocyst cell number when antioxidants were present only in the sperm IVF medium. Levels of H2O2 were significantly reduced in pronucleate oocytes that were cultured in the presence of antioxidants (P < 0.001) compared to control, untreated embryos. Similarly, pronucleate oocytes treated with the combined antioxidants during pronucleate oocyte collection resulted in significantly increased blastocyst ICM numbers compared with controls (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

Embryo development was only examined in the mouse.

WIDER IMPLICATIONS OF THE FINDINGS

These findings suggest that supplementation of antioxidants to the IVF medium, as well as to embryo culture media, may further assist in maintaining the viability of human embryos in ART, conceivably through the reduction of oxidative stress.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by a research grant from Vitrolife AB (Sweden). The authors have no conflict of interest to declare.

Physiological oxygen culture reveals retention of metabolic memory in human induced pluripotent stem cells

Reprogramming somatic cells to a pluripotent cell state (induced Pluripotent Stem (iPS) cells) requires reprogramming of metabolism to support cell proliferation and pluripotency, most notably changes in carbohydrate turnover that reflect a shift from oxidative to glycolytic metabolism. Some aspects of iPS cell metabolism differ from embryonic stem (ES) cells, which may reflect a parental cell memory, or be a consequence of the reprogramming process. In this study, we compared the metabolism of 3 human iPS cell lines to assess the fidelity of metabolic reprogramming. When challenged with reduced oxygen concentration, ES cells have been shown to modulate carbohydrate use in a predictably way. In the same model, 2 of 3 iPS cell lines failed to regulate carbohydrate metabolism. Oxygen is a well-characterized regulator of cell function and embryo viability, and an inability of iPS cells to modulate metabolism in response to oxygen may indicate poor metabolic fidelity. As metabolism is linked to the regulation of the epigenome, assessment of metabolic responses of iPS cells to physiological stimuli during characterization is warranted to ensure complete cell reprogramming and as a measure of cell quality.

Reduced glutathione alleviates tunicamycin-induced endoplasmic reticulum stress in mouse preimplantation embryos

Endoplasmic reticulum (ER) stress, a dysfunction in protein-folding capacity, is involved in many pathological and physiological responses, including embryonic development. This study aims to determine the developmental competence, apoptosis, and stress-induced gene expression in mouse preimplantation embryos grown in an in vitro culture medium supplemented with different concentrations of the ER stress inducer tunicamycin (TM) and the antioxidant glutathione (GSH). Treatment of zygotes with 0.5 µg/ml TM significantly decreased (P < 0.05) the rate of blastocyst formation, whereas 1 mM GSH supplementation improved the developmental rate of blastocysts. Furthermore, TM treatment significantly increased (P < 0.05) the apoptotic index and reduced the total number of cells, whereas GSH significantly increased the total number of cells and decreased the apoptotic index. The expression levels of ER chaperones, including immunoglobulin-binding protein, activating transcription factor 6, double-stranded activated protein kinase-like ER kinase, activating transcription factor 4, and C/EBP homologous protein were significantly increased (P < 0.05) by TM, but significantly decreased (P < 0.05) by GSH treatment. A similar pattern was observed in the case of the pro-apoptotic gene, B cell lymphoma-associated X protein. The expression level of the anti-apoptotic gene B cell lymphoma 2, was decreased by TM, but significantly increased after co-treatment with GSH. In conclusion, GSH improves the developmental potential of mouse embryos and significantly alleviates ER stress.

Pluripotent Stem Cell Metabolism and Mitochondria: Beyond ATP

Metabolism is central to embryonic stem cell (ESC) pluripotency and differentiation, with distinct profiles apparent under different nutrient milieu, and conditions that maintain alternate cell states. The significance of altered nutrient availability, particularly oxygen, and metabolic pathway activity has been highlighted by extensive studies of their impact on preimplantation embryo development, physiology, and viability. ESC similarly modulate their metabolism in response to altered metabolite levels, with changes in nutrient availability shown to have a lasting impact on derived cell identity through the regulation of the epigenetic landscape. Further, the preferential use of glucose and anaplerotic glutamine metabolism serves to not only support cell growth and proliferation but also minimise reactive oxygen species production. However, the perinuclear localisation of spherical, electron-poor mitochondria in ESC is proposed to sustain ESC nuclear-mitochondrial crosstalk and a mitochondrial-H₂O₂ presence, to facilitate signalling to support self-renewal through the stabilisation of HIFα, a process that may be favoured under physiological oxygen. The environment in which a cell is grown is therefore a critical regulator and determinant of cell fate, with metabolism, and particularly mitochondria, acting as an interface between the environment and the epigenome.

Reactive oxygen species-mediated unfolded protein response pathways in preimplantation embryos

Excessive production of reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress-mediated responses are critical to embryonic development in the challenging in vitro environment. ROS production increases during early embryonic development with the increase in protein requirements for cell survival and growth. The ER is a multifunctional cellular organelle responsible for protein folding, modification, and cellular homeostasis. ER stress is activated by a variety of factors including ROS. Such stress leads to activation of the adaptive unfolded protein response (UPR), which restores homeostasis. However, chronic stress can exceed the toleration level of the ER, resulting in cellular apoptosis. In this review, we briefly describe the generation and impact of ROS in preimplantation embryo development, the ROS-mediated activation mechanism of the UPR via the ER, and the subsequent activation of signaling pathways following ER stress in preimplantation embryos.

Impact of the IVF laboratory environment on human preimplantation embryo phenotype

The phenotype of the human embryo conceived through in vitro fertilization (IVF), that is its morphology, developmental kinetics, physiology and metabolism, can be affected by numerous components of the laboratory and embryo culture system (which comprise the laboratory environment). The culture media formulation is important in determining embryo phenotype, but this exists within a culture system that includes oxygen, temperature, pH and whether an embryo is cultured individually or in a group, all of which can influence embryo development. Significantly, exposure of an embryo to one suboptimal component of the culture system of laboratory typically predisposes the embryo to become more vulnerable to a second stressor, as has been well documented for atmospheric oxygen and individual culture, as well as for oxygen and ammonium. Furthermore, the inherent viability of the human embryo is derived from the quality of the gametes from which it is created. Patient age, aetiology, genetics, lifestyle (as well as ovarian stimulation in women) are all known to affect the developmental potential of gametes and hence the embryo. Thus, as well as considering the impact of the IVF laboratory environment, one needs to be aware of the status of the infertile couple, as this impacts how their gametes and embryos will respond to an in vitro environment. Although far from straight forward, analysing the interactions that exist between the human embryo and its environment will facilitate the creation of more effective and safer treatments for the infertile couple.

Impacts of and interactions between environmental stress and epigenetic programming during early embryo development

The processes of assisted reproductive technologies (ART) involve a variety of interventions that impact on the oocyte and embryo. Critically, these interventions cause considerable stress and coincide with important imprinting events throughout gametogenesis, fertilisation and early embryonic development. It is now accepted that the IVM and in vitro development of gametes and embryos can perturb the natural course of development to varying degrees of severity. Altered gene expression and, more recently, imprinting disorders relating to ART have become a focused area of research. Although various hypotheses have been put forward, most research has been observational, with little attempt to discover the mechanisms and periods of sensitivity during embryo development that are influenced by the culture conditions following fertilisation. The embryo possesses innate survival factor signalling pathways, yet when an embryo is placed in culture, this signalling in response to in vitro stress becomes critically important in mitigating the effects of stresses caused by the in vitro environment. It is apparent that not all embryos possess this ability to adequately adapt to the stresses experienced in vitro, most probably due to an inadequate oocyte. It is speculated that it is important that embryos use their survival signalling mechanisms to maintain normal epigenetic programming. The seeming redundancy in the function of various survival signalling pathways would support this notion. Any invasion into the natural, highly orchestrated and dynamic process of sexual reproduction could perturb the normal progression of epigenetic programming. Therefore the source of gametes and the subsequent culture conditions of gametes and embryos are critically important and require careful attention. It is the aim of this review to highlight avenues of research to elucidate the effects of stress and the relationship with epigenetic programming. The short- and long-term health and viability of human and animal embryos derived in vitro will also be discussed.

Endoplasmic Reticulum Stress and Homeostasis in Reproductive Physiology and Pathology

The endoplasmic reticulum (ER), comprises 60% of the total cell membrane and interacts directly or indirectly with several cell organelles i.e., Golgi bodies, mitochondria and proteasomes. The ER is usually associated with large numbers of attached ribosomes. During evolution, ER developed as the specific cellular site of synthesis, folding, modification and trafficking of secretory and cell-surface proteins. The ER is also the major intracellular calcium storage compartment that maintains cellular calcium homeostasis. During the production of functionally effective proteins, several ER-specific molecular steps sense quantity and quality of synthesized proteins as well as proper folding into their native structures. During this process, excess accumulation of unfolded/misfolded proteins in the ER lumen results in ER stress, the homeostatic coping mechanism that activates an ER-specific adaptation program, (the unfolded protein response; UPR) to increase ER-associated degradation of structurally and/or functionally defective proteins, thus sustaining ER homeostasis. Impaired ER homeostasis results in aberrant cellular responses, contributing to the pathogenesis of various diseases. Both female and male reproductive tissues undergo highly dynamic cellular, molecular and genetic changes such as oogenesis and spermatogenesis starting in prenatal life, mainly controlled by sex-steroids but also cytokines and growth factors throughout reproductive life. These reproductive changes require ER to provide extensive protein synthesis, folding, maturation and then their trafficking to appropriate cellular location as well as destroying unfolded/misfolded proteins via activating ER-associated degradation mediated proteasomes. Many studies have now shown roles for ER stress/UPR signaling cascades in the endometrial menstrual cycle, ovarian folliculogenesis and oocyte maturation, spermatogenesis, fertilization, pre-implantation embryo development and pregnancy and parturition. Conversely, the contribution of impaired ER homeostasis by severe/prolong ER stress-mediated UPR signaling pathways to several reproductive tissue pathologies including endometriosis, cancers, recurrent pregnancy loss and pregnancy complications associated with pre-term birth have been reported. This review focuses on ER stress and UPR signaling mechanisms, and their potential roles in female and male reproductive physiopathology involving in menstrual cycle changes, gametogenesis, preimplantation embryo development, implantation and placentation, labor, endometriosis, pregnancy complications and preterm birth as well as reproductive system tumorigenesis.

Applying metabolomic analyses to the practice of embryology: physiology, development and assisted reproductive technology

The advent of metabolomics technology and its application to small samples has allowed us to non-invasively monitor the metabolic activity of embryos in a complex culture environment. The aim of this study was to apply metabolomics technology to the analysis of individual embryos from several species during in vitro development to gain an insight into the metabolomics pathways used by embryos and their relationship with embryo quality. Alanine is produced by both in vivo- and in vitro-derived human, murine, bovine and porcine embryos. Glutamine is also produced by the embryos of these four species, but only those produced in vitro. Across species, blastocysts significantly consumed amino acids from the culture medium, whereas glucose was not significantly taken up. There are significant differences in the metabolic profile of in vivo- compared with in vitro-produced embryos at the blastocyst stage. For example, in vitro-produced murine embryos consume arginine, asparagine, glutamate and proline, whereas in vivo-produced embryos do not. Human embryos produce more alanine, glutamate and glutamine, and consume less pyruvate, at the blastocyst compared with cleavage stages. Glucose was consumed by human blastocysts, but not at a high enough level to reach significance. Consumption of tyrosine by cleavage stage human embryos is indicative of blastocyst development, although tyrosine consumption is not predictive of blastocyst quality. Similarly, although in vivo-produced murine blastocysts consumed less aspartate, lactate, taurine and tyrosine than those produced in vitro, consumption of these four amino acids by in vitro-derived embryos with high octamer-binding transcription factor 4 (Oct4) expression, indicative of high quality, did not differ from those with low Oct4 expression. Further application of metabolomic technologies to studies of the consumption and/or production of metabolites from individual embryos in a complete culture medium could transform our understanding of embryo physiology and improve our ability to produce developmentally competent embryos in vitro.

In vitro culture of individual mouse preimplantation embryos: the role of embryo density, microwells, oxygen, timing and conditioned media

Single embryo culture is suboptimal compared with group culture, but necessary for embryo monitoring, and culture systems should be improved for single embryos. Pronucleate mouse embryos were used to assess the effect of culture conditions on single embryo development. Single culture either before or after compaction reduced cell numbers (112.2 ± 3.1; 110.2 ± 3.5) compared with group culture throughout (127.0 ± 3.4; P < 0.05). Reduction of media volume from 20 µl to 2 µl increased blastocyst cell numbers in single embryos cultured in 5% oxygen (84.4 ± 3.2 versus 97.8 ± 2.8; P < 0.05), but not in 20% oxygen (55.2 ± 2.9 versus 57.1 ± 2.8). Culture in microwell plates for the EmbryoScope and Primo Vision time-lapse systems changed cleavage timings and increased inner cell mass cell number (24.1 ± 1.0; 23.4 ± 1.2) compared with a 2 µl microdrop (18.4 ± 1.0; P < 0.05). Addition of embryo-conditioned media to single embryos increased hatching rate and blastocyst cell number (91.5 ± 4.7 versus 113.1 ± 4.4; P < 0.01). Single culture before or after compaction is therefore detrimental; oxygen, media volume and microwells influence single embryo development; and embryo-conditioned media may substitute for group culture.

Roles of Grp78 in Female Mammalian Reproduction

The glucose-regulated protein (GRP78) also referred to as immunoglobulin heavy chain binding protein (Bip) is one of the best characterized endoplasmic reticulum (ER) chaperone proteins, which belongs to the heat-shock protein (HSP) family. GRP78 as a central regulator of ER stress (ERS) plays many important roles in cell survival and apoptosis through controlling the activation of transmembrane ERS sensors: PKR-like ER-associated kinase (PERK), inositol requiring kinase 1 (IRE1), and activating transcription factor 6 (ATF6). Many studies have reported that GRP78 is involved in the physiological and pathological process in female reproduction, including follicular development, corpus luteum (CL), oviduct, uterus, embryo, preimplantation development, implantation/decidualization, and the placenta. The present review summarizes the biological or pathological roles and signaling mechanisms of GRP78 during the reproductive processes. Further study on the functions and mechanisms of GRP78 may provide new insight into mammalian reproduction, which not only enhance the understanding of the physiological roles but also support therapy target against infertility.

Tauroursodeoxycholic acid improves pre-implantation development of porcine SCNT embryo by endoplasmic reticulum stress inhibition

The aim of this study is to investigate whether endoplasmic reticulum (ER) stress attenuation could improve porcine somatic cell nuclear transfer (SCNT) embryo developmental competence. We treated porcine SCNT embryos with TUDCA (tauroursodeoxycholic acid, an inhibitor of ER stress) and/or TM (tunicamycin, an ER stress inducer), and examined embryonic developmental potential, embryo quality, the levels of ER stress markers (XBP1 protein and mRNA) and apoptosis-related-genes (BAX and BCL2 mRNA). Immunostaining detected X-box-binding protein (XBP1), a key gene regulator during ER stress, at all stages of SCNT embryo development. Embryo development analysis revealed that TUDCA treatment markedly increased (p<0.05) blastocyst formation rate, total cell number and inner cell mass (ICM) cell number compared to untreated control group. The TUDCA and TM groups showed significant alterations in XBP1 protein and XBP1-s mRNA levels compared to controls (lower and higher, respectively; p<0.05). Also, TUDCA treatment reduced oxidative stress by up-regulation of the antioxidant, GSH. TUNEL assay showed that TUDCA treatment significantly reduced apoptosis in porcine SCNT blastocysts confirmed by decreased pro-apoptotic BAX and increased anti-apoptotic BCL2 mRNA levels. Collectively, our results indicated that TUDCA can enhance the developmental potential of porcine SCNT embryos by attenuating ER-stress and reducing apoptosis.

Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro

Embryos are routinely cultured individually, although this can reduce blastocyst development. Culture in atmospheric (20%) oxygen is also common, despite multiple detrimental effects on embryos. Although frequently occurring together, the consequences of this combination are unknown. Mouse embryos were cultured individually or grouped, under physiological (5%) or atmospheric (20%) oxygen. Embryos were assessed by time-lapse and blastocyst cell allocation. Compared with the control group (5% oxygen group culture), 5-cell cleavage (t5) was delayed in 5% oxygen individual culture and 20% oxygen group culture (59.91 ± 0.23, 60.70 ± 0.29, 63.06 ± 0.32 h post-HCG respectively, P < 0.05). Embryos in 20% oxygen individual culture were delayed earlier (3-cell cleavage), and at t5 cleaved later than embryos in other treatments (66.01 ± 0.40 h, P < 0.001), this delay persisting to blastocyst hatching. Compared with controls, hatching rate and cells per blastocyst were reduced in 5% oxygen single culture and 20% oxygen group culture (134.1 ± 3.4, 104.5 ± 3.2, 73.4 ± 2.2 cells, P < 0.001), and were further reduced in 20% oxygen individual culture (57.0 ± 2.8 cells, P < 0.001), as was percentage inner cell mass. These data indicate combining individual culture and 20% oxygen is detrimental to embryo development.

From Embryos to Adults: A DOHaD Perspective on In Vitro Fertilization and Other Assisted Reproductive Technologies

Human in vitro fertilization (IVF) as a treatment for infertility is regarded as one of the most outstanding accomplishments of the 20th century, and its use has grown dramatically since the late 1970s. Although IVF is considered safe and the majority of children appear healthy, reproductive technologies have been viewed with some skepticism since the in vitro environment deviates substantially from that in vivo. This is increasingly significant because the Developmental Origins of Health and Disease (DOHaD) hypothesis has illuminated the sensitivity of an organism to its environment at critical stages during development, including how suboptimal exposures restricted specifically to gamete maturation or the preimplantation period can affect postnatal growth, glucose metabolism, fat deposition, and vascular function. Today, some of the physiological metabolic phenotypes present in animal models of IVF have begun to emerge in human IVF children, but it remains unclear whether or not in vitro embryo manipulation will have lasting health consequences in the offspring. Our expanding knowledge of the DOHaD field is fueling a paradigm shift in how disease susceptibility is viewed across the life course, with particular emphasis on the importance of collecting detailed exposure information, identifying biomarkers of health, and performing longitudinal studies for any medical treatment occurring during a developmentally vulnerable period. As IVF use continues to rise, it will be highly valuable to incorporate DOHaD concepts into the clinical arena and future approaches to public health policy.

Effects of Two Types of Melatonin-Loaded Nanocapsules with Distinct Supramolecular Structures: Polymeric (NC) and Lipid-Core Nanocapsules (LNC) on Bovine Embryo Culture Model

Melatonin has been used as a supplement in culture medium to improve the efficiency of in vitro produced mammalian embryos. Through its ability to scavenge toxic oxygen derivatives and regulate cellular mRNA levels for antioxidant enzymes, this molecule has been shown to play a protective role against damage by free radicals, to which in vitro cultured embryos are exposed during early development. In vivo and in vitro studies have been performed showing that the use of nanocapsules as active substances carriers increases stability, bioavailability and biodistribution of drugs, such as melatonin, to the cells and tissues, improving their antioxidant properties. These properties can be modulated through the manipulation of formula composition, especially in relation to the supramolecular structures of the nanocapsule core and the surface area that greatly influences drug release mechanisms in biological environments. This study aimed to evaluate the effects of two types of melatonin-loaded nanocapsules with distinct supramolecular structures, polymeric (NC) and lipid-core (LNC) nanocapsules, on in vitro cultured bovine embryos. Embryonic development, apoptosis, reactive oxygen species (ROS) production, and mRNA levels of genes involved in cell apoptosis, ROS and cell pluripotency were evaluated after supplementation of culture medium with non-encapsulated melatonin (Mel), melatonin-loaded polymeric nanocapsules (Mel-NC) and melatonin-loaded lipid-core nanocapsules (Mel-LNC) at 10⁻⁶, 10⁻⁹, and 10⁻¹² M drug concentrations. The highest hatching rate was observed in embryos treated with 10⁻⁹ M Mel-LNC. When compared to Mel and Mel-NC treatments at the same concentration (10⁻⁹ M), Mel-LNC increased embryo cell number, decreased cell apoptosis and ROS levels, down-regulated mRNA levels of BAX, CASP3, and SHC1 genes, and up-regulated mRNA levels of CAT and SOD2 genes. These findings indicate that nanoencapsulation with LNC increases the protective effects of melatonin against oxidative stress and cell apoptosis during in vitro embryo culture in bovine species.

Antioxidants improve mouse preimplantation embryo development and viability

STUDY QUESTION

What is the effect of three antioxidants (acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid), when used individually and in combination, on mouse embryo development in culture, and subsequent fetal development post-transfer?

SUMMARY ANSWER

A combination of antioxidants resulted in significant increases in blastocyst cell number, maintained intracellular glutathione (GSH) levels, supported earlier cleavage times from 5-cell stage to expanded blastocyst, and improved fetal developmental irrespective of incubator oxygen concentration.

WHAT IS KNOWN ALREADY

Acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid have been shown to have beneficial effects individually in several tissues, and most recently on developing embryos, in the presence of oxidative stress.

STUDY DESIGN, SIZE, DURATION

Morphokinetics of mouse embryos were quantitated using time-lapse imaging. GSH levels in pronucleate oocytes were measured. Blastocysts underwent differential nuclear staining for inner cell mass and trophectoderm cells or were transferred to recipient females to assess implantation and fetal development.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Pronucleate oocytes from F1 mice were cultured in 5 or 20% oxygen either individually or in groups of 10, in media G1/G2, in the presence or absence of 10 µM acetyl-L-carnitine /10 µM N-acetyl-L-cysteine /5 µM α-lipoic acid, either individually or in combination. Controls were embryos cultured without antioxidants. Intracellular levels of reduced glutathione were quantitated in pronucleate oocytes. Embryo development and viability were analysed through time-lapse microscopy and embryo transfers.

MAIN RESULTS AND THE ROLE OF CHANCE

Antioxidants significantly increased mouse blastocyst cell numbers compared with control when used individually (P< 0.05) and to a greater effect when all three were used in combination (P< 0.01) in 20% oxygen. The combination of antioxidants resulted in faster development rates to 5-cell cleavage stage, which continued until the expanded blastocyst stage when cultured in 20% oxygen. The beneficial effects of combining the antioxidants were greater for embryos cultured individually as opposed to in groups of 10 and for those embryos cultured in 20% compared to 5% oxygen. Levels of GSH were significantly decreased in control embryos that were incubated in the absence of antioxidants in 20% oxygen (P< 0.01), compared with in vivo flushed embryos. However, when embryos were cultured with antioxidants the level of GSH was not different to that of in vivo developed embryos. Embryos cultured in the presence of antioxidants in 20% oxygen and transferred resulted in significantly longer crown-rump length (11.6 ± 0.1 mm versus 11.3 ± 0.1 mm; P< 0.01), heavier fetuses (209.8 ± 11.8 mg versus 183.9 ± 5.9 mg; P< 0.05) and heavier placentas (103.5 ± 3.1 mg versus 93.6 ± 2.7 mg; P< 0.01) compared with controls (all data are mean ± SEM). Further, a post-implantation benefit of the antioxidant combination was also evident after culture in 5% oxygen.

LIMITATIONS, REASONS FOR CAUTION

Embryo development and implantation was only examined in the mouse.

WIDER IMPLICATIONS OF THE FINDINGS

These findings show that a combination of antioxidants in the culture media has a highly beneficial effect on mouse preimplantation embryo development in vitro and on subsequent fetal development post-transfer. These data indicate a potential role for the inclusion of specific antioxidant combinations in human embryo culture media irrespective of oxygen concentration. However, before application to human embryos, a proper evaluation of this approach in prospective, preferably randomized, trials will be required.

STUDY FUNDING/COMPETING INTERESTS

This work was funded by a research grant from Vitrolife AB (Sweden). The authors have no conflict of interest to declare.

Male obesity and subfertility, is it really about increased adiposity?

The prevalence of overweight and obesity in reproductive-aged men is increasing worldwide, with >70% of men >18 years classified as overweight or obese in some western nations. Male obesity is associated with male subfertility, impairing sex hormones, reducing sperm counts, increasing oxidative sperm DNA damage and changing the epigenetic status of sperm. These changes to sperm function as a result of obesity, are further associated with impaired embryo development, reduced live birth rates and increased miscarriage rates in humans. Animal models have suggested that these adverse reproductive effects can be transmitted to the offspring; suggesting that men's health at conception may affect the health of their children. In addition to higher adiposity, male obesity is associated with comorbidities, including metabolic syndrome, hypercholesterolemia, hyperleptinemia and a pro-inflammatory state, all which have independently been linked with male subfertility. Taken together, these findings suggest that the effects of male obesity on fertility are likely multifactorial, with associated comorbidities also influencing sperm, pregnancy and subsequent child health.

Oxygen modulates human embryonic stem cell metabolism in the absence of changes in self-renewal

Human embryonic stem (ES) cells are routinely cultured under atmospheric oxygen (~20%), a concentration that is known to impair embryo development in vitro and is likely to be suboptimal for maintaining human ES cells compared with physiological (~5%) oxygen conditions. Conflicting reports exist on the effect of oxygen during human ES cell culture and studies have been largely limited to characterisation of typical stem cell markers or analysis of global expression changes. This study aimed to identify physiological markers that could be used to evaluate the metabolic impact of oxygen on the MEL-2 human ES cell line after adaptation to either 5% or 20% oxygen in extended culture. ES cells cultured under atmospheric oxygen displayed decreased glucose consumption and lactate production when compared with those cultured under 5% oxygen, indicating an overall higher flux of glucose through glycolysis under physiological conditions. Higher glucose utilisation at 5% oxygen was accompanied by significantly increased expression of all glycolytic genes analysed. Analysis of amino acid turnover highlighted differences in the consumption of glutamine and threonine and in the production of proline. The expression of pluripotency and differentiation markers was, however, unaltered by oxygen and no observable difference in proliferation between cells cultured in 5% and 20% oxygen was seen. Apoptosis was elevated under 5% oxygen conditions. Collectively these data suggest that culture conditions, including oxygen concentration, can significantly alter human ES cell physiology with coordinated changes in gene expression, in the absence of detectable alterations in undifferentiated marker expression.

Metaboloepigenetic Regulation of Pluripotent Stem Cells

The differentiation of pluripotent stem cells is associated with extensive changes in metabolism, as well as widespread remodeling of the epigenetic landscape. Epigenetic regulation is essential for the modulation of differentiation, being responsible for cell type specific gene expression patterns through the modification of DNA and histones, thereby establishing cell identity. Each cell type has its own idiosyncratic pattern regarding the use of specific metabolic pathways. Rather than simply being perceived as a means of generating ATP and building blocks for cell growth and division, cellular metabolism can directly influence cellular regulation and the epigenome. Consequently, the significance of nutrients and metabolites as regulators of differentiation is central to understanding how cells interact with their immediate environment. This review serves to integrate studies on pluripotent stem cell metabolism, and the regulation of DNA methylation and acetylation and identifies areas in which current knowledge is limited.