Discrepancies between the effects of glutamine in cultures of preimplantation mouse embryos

Culture medium and protein supplementation affect sensitivity of the mouse embryo assay in detecting Triton X-100

RESEARCH QUESTION

To what extent does the type and concentration of protein and the type of culture medium affect the sensitivity of the mouse embryo assay (MEA) to detect Triton X-100 (TX-100) in culture media?

DESIGN

The effect of the concentration of bovine serum albumin (BSA) and human serum albumin (HSA) was assessed by supplementing media with 0.5 or 5 mg/ml. Potassium-supplemented simplex optimized medium (KSOM) and human tubal fluid (HTF) were used as complex and simple formulation media, respectively. Variables were combined, forming study groups where embryos were cultured in test media spiked with a sublethal TX-100 concentration. The conditions of greatest sensitivity were determined by statistical comparison of blastocyst formation rates and total cell counts between groups.

RESULTS

Although all of the study groups showed equal capacity for sustaining proper embryo development, the reported sensitivity of the MEA differed between groups when subjected to TX-100. HTF conferred significantly greater sensitivity than KSOM regardless of the type and concentration of protein used, and medium supplementation with 5 mg/ml BSA rather than 0.5 mg/ml BSA resulted in significantly higher sensitivity regardless of the type of medium used. This increase in concentration also resulted in higher sensitivity when supplementing HTF with HSA. The BSA groups provided more sensitivity than their HSA counterparts, except for the KSOM + 0.5 mg/ml BSA group. Cell count analysis did not provide further significant conclusions.

CONCLUSIONS

For TX-100 detection within culture medium, the type and concentration of protein and the type of culture medium have a direct effect on MEA sensitivity. These results could help to standardize the MEA protocol, and increase its ability to detect sublethal concentrations of embryotoxic substances, especially TX-100, thus avoiding possible clinical harmful effects.

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.

Ammonium accumulation in commercially available embryo culture media and protein supplements during storage at 2-8°C and during incubation at 37°C

STUDY QUESTION

Does ammonium accumulate in commercially available culture media and protein supplements used for in vitro development of human pre-implantation embryos during storage and incubation?

SUMMARY ANSWER

Ammonium accumulates in ready-to-use in vitro fertilization (IVF) culture media during storage at 2-8°C and in ready-to-use IVF culture media and protein supplements during incubation at 37°C.

WHAT IS KNOWN ALREADY

Both animal and human studies have shown that the presence of ammonium in culture medium has detrimental effects on embryonic development and pregnancy rate. It is, therefore, important to assess the amount of ammonium accumulation in ready-to-use IVF culture media under conditions that are common in daily practice.

STUDY DESIGN, SIZE, DURATION

Ammonium accumulation was investigated in 15 ready-to-use media, 11 protein-free media and 8 protein supplements.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ammonium was measured by the use of an enzymatic method with glutamate dehydrogenase. To simulate the storage and incubation conditions during IVF treatments, ammonium concentrations were measured at different time-points during storage at 2-8°C for 6 weeks and during incubation at 37°C for 4 days.

MAIN RESULTS AND THE ROLE OF CHANCE

All ready-to-use, i.e. protein supplemented, culture media showed ammonium accumulation during storage for 6 weeks (ranging from 9.2 to 99.8 µM) and during incubation for 4 days (ranging from 8.4 to 138.6 µM), resulting in levels that might affect embryo development. The protein supplements also showed ammonium accumulation, while the culture media without protein supplementation did not. The main sources of ammonium buildup in ready-to-use culture media were unstable glutamine and the protein supplements. No additional ammonium buildup was found during incubation when using an oil overlay or with the presence of an embryo in the culture droplet.

LIMITATIONS, REASONS FOR CAUTION

In addition to the unstable glutamine and the protein supplements, other free amino acids might contribute to the ammonium buildup. We did not investigate the deterioration of other components in the media.

WIDER IMPLICATIONS OF THE FINDINGS

Break-down of components into ammonium is more pronounced during incubation at 37°C, however, it is not negligible during storage at 2-8°C. This results in increasing ammonium levels in culture media over time that may affect embryo development. Therefore, it is important that the use of free l-glutamine in human embryo culture media is stopped and that the use of protein supplements is thoroughly evaluated.

STUDY FUNDING/COMPETING INTERESTS

No funding or no competing interests declared.

TRIAL REGISTRATION NUMBER

Not applicable.

Optimizing the culture environment and embryo manipulation to help maintain embryo developmental potential

With increased use of comprehensive chromosome screening (CCS), the question remains as to why some practices do not experience the same high levels of clinical success after implementation of the approach. Indeed, the debate surrounding the efficacy and usefulness of blastocyst biopsy and CCS continues. Importantly, several variables impact the success of an assisted reproductive technology cycle. Transfer of a euploid embryo is but one factor in an intricate system that requires numerous steps to occur successfully. Certainly, the culture environment and the manipulations of the embryo during its time in the laboratory can impact its reproductive potential. Environmental stressors ranging from culture media to culture conditions and even culture platform can impact biochemical, metabolic, and epigenetic patterns that can affect the developing cell independent of chromosome number. Furthermore, accompanying procedures, such as biopsy and vitrification, are complex and, when performed improperly, can negatively impact embryo quality. These are areas that likely still carry room for improvement within the IVF laboratory.

Human and mouse embryonic development, metabolism and gene expression are altered by an ammonium gradient in vitro

Ammonium is generated in culture media by the spontaneous deamination of amino acids at 37 °C and through the metabolism of amino acids by human embryos. The appearance of ammonium is a time-dependent phenomenon and can compromise embryo physiology, development and viability. In this study, the effects of a gradient of ammonium on the development, metabolism and transcriptome of human and mouse embryos were investigated. Pronucleate oocytes were cultured in the presence of an ammonium gradient that mimicked the spontaneous deamination of Eagle's amino acids together with 1 mM glutamine. All embryos were cultured in sequential media G1/G2 at 5% O2, 6% CO2 and 89% N2. Human embryo metabolism was assessed through a non-invasive fluorometric analysis of pyruvate consumption. Transcriptome analysis was performed on the resultant blastocysts from both species using a microarray technology. Embryo development prior to compaction was negatively affected by the presence of low levels of ammonium in both species. Human embryo metabolism was significantly inhibited after just 24 and 48 h of culture. Transcriptome analysis of blastocysts from both species revealed significantly altered gene expression profiles, both decreased and increased. Functional annotation of the altered genes revealed the following over represented biological processes: metabolism, cell growth and/or maintenance, transcription, cell communication, transport, development and transcription regulation. These data emphasize the enhanced sensitivity of the cleavage-stage embryo to its environment and highlight the requirement to renew culture media at frequent intervals in order to alleviate the in vitro induced effects of ammonium build-up in the environment surrounding the embryo.

Rethinking in vitro embryo culture: new developments in culture platforms and potential to improve assisted reproductive technologies

The preponderance of research toward improving embryo development in vitro has focused on manipulation of the chemical soluble environment, including altering basic salt composition, energy substrate concentration, amino acid makeup, and the effect of various growth factors or addition or subtraction of other supplements. In contrast, relatively little work has been done examining the physical requirements of preimplantation embryos and the role culture platforms or devices can play in influencing embryo development within the laboratory. The goal of this review is not to reevaluate the soluble composition of past and current embryo culture media, but rather to consider how other controlled and precise factors such as time, space, mechanical interactions, gradient diffusions, cell movement, and surface interactions might influence embryo development. Novel culture platforms are being developed as a result of interdisciplinary collaborations between biologists and biomedical, material, chemical, and mechanical engineers. These approaches are looking beyond the soluble media composition and examining issues such as media volume and embryo spacing. Furthermore, methods that permit precise and regulated dynamic embryo culture with fluid flow and embryo movement are now available, and novel culture surfaces are being developed and tested. While several factors remain to be investigated to optimize the efficiency of embryo production, manipulation of the embryo culture microenvironment through novel devices and platforms may offer a pathway toward improving embryo development within the laboratory of the future.

Dipeptide forms of glycine support mouse preimplantation embryo development in vitro and provide protection against high media osmolality

PURPOSE

To examine potential benefits of dipeptide forms of amino acids for embryo culture by determining ability of dipeptide glycine forms to support embryo development, act as osmolytes, and reduce ammonia production.

METHODS

Frozen thawed 1-cell mouse embryos were cultured in media with varying osmolality with glycine and dipeptide forms of glycine and development assessed. Ammonia levels were measured in various media.

RESULTS

Dipeptide forms of glycine, alanyl- and glycyl-glycine, can support mouse embryo development in vitro. Additionally, dipeptide glycine can act as an organic osmolyte in developing embryos, permitting blastocyst formation in high osmolality media. Interestingly, as evidenced by decreased embryo development, dipeptides are not as efficient as osmolytes as their constituent individual amino acids. Dipeptide glycine produced less ammonia than glycine.

CONCLUSION

Though dipeptides can provide osmoregulation in preimplantation embryos, efficacy may be lower than individual amino acids. The mechanism by which embryos transport and utilize dipeptide amino acids remains to be identified.

Advances in embryo culture platforms: novel approaches to improve preimplantation embryo development through modifications of the microenvironment

BACKGROUND

The majority of research aimed at improving embryo development in vitro has focused on manipulation of the chemical environment, examining details such as energy substrate composition and impact of various growth factors or other supplements. In comparison, relatively little work has been done examining the physical requirements of preimplantation embryos and the role culture platforms or devices can play in influencing embryo development.

METHODS

Electronic searches were performed using keywords centered on embryo culture techniques using PUBMED through June 2010 and references were searched for additional research articles.

RESULTS

Various approaches to in vitro embryo culture that involve manipulations of the physical culture environment are emerging. Novel culture platforms being developed examine issues such as media volume and embryo spacing. Furthermore, methods to permit dynamic embryo culture with fluid flow and embryo movement are now available, and novel culture surfaces are being tested.

CONCLUSIONS

Although several factors remain to be studied to optimize efficiency, manipulations of the embryo culture microenvironment through novel culture devices may offer a means to improve embryo development in vitro. Reduced volume systems that reduce embryo spacing, such as the well-of-the-well approach, appear beneficial, although more work is needed to verify the source of their true benefit in human embryos. Emerging microfluidic technology appears to be a promising approach. However, along with the work on specialized culture surfaces, more information is required to determine the impact on human embryo development.

Dynamic microfunnel culture enhances mouse embryo development and pregnancy rates

BACKGROUND

Despite advances in in vitro manipulation of preimplantation embryos, there is still a reduction in the quality of embryos produced leading to lower pregnancy rates compared with embryos produced in vivo. We hypothesized that a dynamic microfunnel embryo culture system would enhance outcomes by better mimicking the fluid-mechanical and biochemical stimulation embryos experience in vivo from ciliary currents and oviductal contractions.

METHODS AND RESULTS

Mouse embryos were cultured in microdrop-static control, microfunnel-static control or microfunnel-dynamic conditions with microfluidics. All groups tested had greater than 90% total blastocyst development from zygotes after 96 h culture. Blastocyst developmental stage was significantly enhanced (P < 0.01) under dynamic microfunnel culture conditions as evidenced by an increased percentage of hatching or hatched blastocysts (Microdrop-control 31%; Microfunnel-control 23%; Microfunnel-pulsatile 71%) and significantly higher (P < 0.01) average number of cells per blastocyst (Microdrop-control 67 +/- 3; Microfunnel-control 60 +/- 3; Microfunnel-pulsatile 109 +/- 5). Blastocyst cell numbers in dynamic microfunnel cultures (109 +/- 5) more closely matched numbers obtained from in vivo grown blastocysts (144 +/- 9). Importantly, dynamic microfunnel culture significantly improved embryo implantation and ongoing pregnancy rates over static culture to levels approaching that of in utero derived preimplantation embryos.

CONCLUSIONS

The improved pregnancy outcomes along with the simple and user-friendly design of the microfluidic/microfunnel system has potential to alleviate many inefficiencies in embryo production for biomedical research, genetic gain in domestic species and assisted reproductive technologies in humans.

Embryo culture: can we perform better than nature?

Culture of preimplantation-stage embryos has always been a key element of laboratory embryology and has contributed substantially to the success of many assisted reproduction procedures. During the past decade, its importance has increased as extended in-vitro embryo culture and single blastocyst transfer have become indispensable parts of the approach to decreasing the chance of multiple pregnancy while preserving the overall efficiency of the treatment. However, in spite of the scientific and commercial challenge stimulating research worldwide to optimize embryo culture conditions, a consensus is missing even in the basic principles, including composition and exchange of media, the required physical and biological environment and even the temperature of incubation. This review attempts to summarize the controversies, demonstrate the fragility of some widely accepted dogmas and generate an open-minded debate towards rapid and efficient optimization. New approaches expanding the traditional frames of mammalian embryo culture are also discussed. Although some researchers suppose that the efficiency of the presently applied in-vitro culture systems have already approached the biological limits, authors are confident that substantial improvement may be achieved that may expand considerably the possibilities of future assisted reproduction in humans.

Choosing a culture medium: making informed choices

OBJECTIVE

To analyze critically the reasons justifying the choice of two-step protocols requiring two media for the culture of human preimplantation embryos from the zygote to the blastocyst.

DESIGN

Literature review.

RESULT(S)

Two types of protocol are used for the culture of human preimplantation embryos from the zygote to the blastocyst, using either one medium (one-step protocol) or two media of different composition (two-step protocol). Two-step protocols are the most widely used, largely because all but one of the commercially available protocols are of this type. The reasons for the adoption of two-step protocols are described and critically analyzed. They are based on considerations of the functions of glucose, ethylenediaminetetraacetic acid (EDTA), glutamine, and amino acids that are included in the media. A reappraisal of the reasons for selecting two-step protocols is important because recent animal experiments and clinical observations have raised doubts as to whether the more complex, two-step protocols have any advantage over one-step protocols. The analyses show that all of conclusions reached should be considered equivocal.

CONCLUSION(S)

Clinical embryologists should evaluate the justification for selecting two-step protocols for the culture of human preimplantation embryos from the zygote to the blastocyst.

Dissection of culture media for embryos: the most important and less important components and characteristics

Improvements in culture media formulations have led to an increase in the ability to maintain the mammalian embryo in culture throughout the preimplantation and pre-attachment period. Amino acids and specific macromolecules have been identified as being key medium components, whereas temporal dynamics have been recognised as important media characteristics. Furthermore, other laboratory factors that directly impact embryo development and viability have been identified. Such factors include the use of a reduced oxygen tension, an appropriate incubation system and an adequate prescreening of all contact supplies. With rigourous quality systems in place, it is possible to obtain in vivo rates of embryo development in vitro using new media formulations while maintaining high levels of embryo viability. The future of embryo culture will likely be based on novel culture chips capable of providing temporal dynamics while facilitating real-time analysis of embryo physiology.

Virtues and limitations of the preimplantation mouse embryo as a model system

The mouse is the most widely used model of preimplantation embryo development, but is it a good model? Its small size, prolificacy and ease of handling make the mouse a relatively low cost, readily available and attractive alternative when embryos from other species are difficult or expensive to obtain. However, the real power of the mouse as a model lies in mouse genetics. The development of inbred mouse strains facilitated gene discovery as well as our understanding of gene function and regulation while the development of tools to introduce precise genetic modifications uniquely positioned the mouse as a powerful model system for uncovering gene function. However, all models have limitations; the small size of the mouse limits tissue availability and manipulations that can be performed and differences in physiology among species may make it inappropriate to extrapolate from the mouse to other species. Thus, rather than extrapolating directly from the mouse to other species, it may be more useful to use the mouse as a model system for developing and refining hypotheses to be tested directly in species of interest. In this brief review, the value of the preimplantation mouse embryo as a model is considered, both as a model for other species and as a model for the mouse, as understanding the virtues and limitations of the mouse as a model system is essential to its appropriate use.

One-step versus two-step culture of mouse preimplantation embryos: is there a difference?

BACKGROUND

A comparison has been made of the development of mouse zygotes in either one-step or two-step culture systems.

METHODS

Embryo culture, blastocyst cell counts and embryo transfer were done.

RESULTS

No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the inner cell mass (ICM) and trophectoderm (TE) that developed in protocols: one-step culture in potassium-enriched simplex optimized medium supplemented with glucose and amino acids (KSOMg(AA)), two-step culture in KSOMg(AA)/KSOMg(AA), and two-step culture in G1.2/G2.2. No gross abnormalities were observed in the fetuses that developed from zygotes in the one-step protocol using KSOMg(AA) and a two-step protocol using G1.2/G2.2. The body weights of these two groups of fetuses were not significantly different and no developmental abnormalities were observed. No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the ICM and TE that developed in protocols: one-step culture in KSOMg(AA), two-step culture in KSOMg(AA)/KSOMg(AA), and two-step culture in DM2/DM1. EDTA is not toxic to the initial cleavage stages of development at a concentration of 0.01 mmol/l in KSOMg(AA).

CONCLUSIONS

Two-step culture protocols are sufficient for the support of preimplantation mouse development in vitro but they are not necessary.

The problematic in-vitro embryo in the age of epigenetics

During use of many assisted reproductive technologies, the embryo spends time in vitro. The immediate and long-term epigenetic impacts of this exposure to an in-vitro environment are discussed in the context of the health of the offspring. Three exemplary types of possible epigenetic impact are discussed: embryonic cell numbers, mitochondria, and genomic imprints. There is evidence that all of these can be affected in the short term and that these short-term impacts can have heritable consequences across developmental cell generations into maturity. There is also evidence of association between the observed impact and pathology, but as yet no unequivocal evidence of causality for humans and mice. The problematic in-vitro embryo is considered paradigmatic for a central question facing biology: how does the environment interact epigenetically with the genome to produce variable phenotypic outcomes?

Mouse embryo development following IVF in media containing either l-glutamine or glycyl-l-glutamine

BACKGROUND

The development of the mouse zygote following fertilization in vitro in a KSOM-type medium containing either L-glutamine or glycyl-L-glutamine has been examined, and compared with the development of mouse zygotes produced by natural fertilization.

METHODS

Mouse IVF, embryo culture and embryo transfer.

RESULTS

Fertilization rates, development to the blastocyst stage, implantation rate, gross fetal development and fetal body weight are not different in a KSOM-type medium containing either L-glutamine or glycyl-L-glutamine. No evidence of abnormal fetal development, such as exencephaly, was observed. The replacement of L-glutamine with glycyl-L-glutamine favoured the development of relatively more inner cell mass cells than trophectoderm cells, and reduced the numbers of pyknotic and fragmented nuclei in the blastocysts that developed in vitro.

CONCLUSIONS

There is no evidence that the presence of glutamine in the medium used for IVF influences significantly the subsequent development of the zygote. Replacing glutamine with glycyl-L-glutamine may be advantageous.

Comparison of two sequential media for culturing cleavage-stage embryos and blastocysts: embryo characteristics and clinical outcome

This study was undertaken to compare the outcome of day 3, day 5, and frozen-thawed embryo transfer cycles where embryo culture was undertaken using the G1.2-G2.2 versus GIII series sequential media. A total of 400 day 3, 73 day 5 and 126 frozen-thawed embryo transfer cycles were analysed. Treatment cycles were quasi-randomized on the day of oocyte retrieval to embryo culture in G1.2-G2.2 versus GIII series sequential media. Randomization was undertaken according to alternating weekdays. Significantly more embryos were of grade 1 or 2 quality on day 3 in the GIII group (P < 0.05). Likewise, more embryos in the GIII group had eight blastomeres on day 3 (P < 0.05) and were able to hatch spontaneously (P < 0.05). For day 3 embryo transfer cycles, implantation and clinical pregnancy rates were 14.4 and 25.7% versus 37.8 and 50.3% in G1.2-G2.2 and GIII groups respectively (P < 0.05). For day 5 embryo transfer cycles, implantation rates were significantly higher (29 versus 45%; P < 0.05) in the GIII group. There was a trend towards higher pregnancy rates; however, this did not reach statistical significance due to fewer cycles analysed in this group. In-vitro culture in GIII series sequential media yields better quality embryos that implant more efficiently, compared with culture in G1.2-G2.2 media.

Enhanced effect of glycyl-L-glutamine on mouse preimplantation embryos in vitro

A comparison of the effects of replacing L -glutamine with either glycyl-L-glutamine or alanyl-L-glutamine in a KSOM-type medium on the development of mouse preimplantation embryos in vitro has been made. Alanyl-L-glutamine has no significant effect on the rates of blastocyst formation, onset or completion of hatching, and on the numbers of inner cell mass and trophectoderm cells that develop. Glycyl-L-glutamine has no effect on the rate of blastocyst formation; it stimulates slightly the onset of hatching, but significantly increases the numbers of inner cell mass and trophectoderm cells that develop. Embryo transfer experiments comparing media containing either glutamine or glycyl-L-glutamine have not produced any gross abnormal fetal development. Recently, alanyl-L-glutamine has been used to replace glutamine in media for the culture of human preimplantation embryos. The results in this paper suggest that glycyl-L-glutamine may be a better choice of dipeptide.