Oxidative stress is involved in the aetiology of defective embryo development. Reactive oxygen species (ROS) may originate from embryo metabolism and/or embryo surroundings. Embryo metabolism generates ROS via several enzymatic mechanisms. The relative contribution of each source seems different depending on the species, the stage of development, and the culture conditions. Several exogenous factors and culture conditions can enhance the production of ROS by embryos. ROS can alter most types of cellular molecules, and also induce development block and retardation. Multiple mechanisms of embryo protection against ROS exist, and these have complementary actions. External protection, present in follicular and tubal fluids, mainly comprises non-enzymatic antioxidants such as hypotaurine, taurine and ascorbic acid. Internal protection mainly comprises antioxidant enzymes: superoxide dismutase, glutathione peroxidase and gamma-glutamylcysteine synthetase. Transcripts encoding for these enzymes are present in the oocyte, embryo and oviduct. It may be important that these transcripts are stored during oocyte maturation in order to allow the embryo to acquire the aptitude to develop. It is now common to add antioxidant compounds to culture media. Nevertheless, maintaining the pro-oxidant-antioxidant equilibrium in embryos through such supplementation is a complex problem. Further studies are necessary to limit oxidative stress during embryo culture.

Oxidative stress and protection against reactive oxygen species in the pre-implantation embryo and its surroundings

There are only a handful of concepts concerning cancer and carcinogenesis that are currently beyond dispute. One such dogma is the adenoma-carcinoma sequence and that a multistep accumulation of genetic alterations is required for transformation from a benign to a neoplastic tissue. The inevitable derivative of this dogma is that every invasive carcinoma is in fact a missed intraepithelial tumor, and furthermore, a late evolutionary stage in the sequence of development from a precursor lesion. Until fairly recently, high-grade serous ovarian carcinoma seemed to be one of the only known deviants of these concepts. In this article, we discuss the emergence of the fallopian tube fimbria as a field of origin for high-grade serous carcinomas and present a binary model of ovarian cancer pathogenesis that takes into consideration prior epidemiologic, morphologic, and genetic data. With the rise of the fallopian tube secretory epithelial cell as a cell of origin for high-grade pelvic serous carcinomas, the need to develop tools and model systems to characterize the biology and physiology of this cell is recognized.

New Insights Into the Pathogenesis of Serous Ovarian Cancer and Its Clinical Impact

In human in vitro fertilization (I.V.F.), it was first assumed that all the embryos obtained had the same developmental potential whatever the quality of sperm. However, this has not been confirmed. We have used the coculture technique and determined the blastocyst formation rate in three groups of patients: group 1: patients with normal sperm count (> 20 x 10(6)/ml), motility (> 30%), and morphology (> 50%); group 2: patients treated by I.V.F. with frozen donor sperm; group 3: patients with severely impaired sperm quality (< 3 x 10(6) forward motile and morphologically normal spermatozoa per ml). In group 1, we found a strong correlation between cleavage rate and blastocyst formation rate (P < 0.0001) with a blastocyst formation rate comprised between 40% and 50%. This was not true for the two other groups for which the overall number of blastocysts obtained and the number of patients having at least one blastocyst were severely reduced (P < 0.0001). These data are discussed in terms of DNA quality, timing of formation of the pronuclei, and delays in cell cycles at the time of genomic activation. These observations lead to a new approach to the study of fertilizing ability of poor quality sperm. It may help in the decision as to whether couples treated for male infertility should be excluded from I.V.F. protocols.

Evidence for a strong paternal effect on human preimplantation embryo development and blastocyst formation.

Human "spare" embryos, judged unsuitable for freezing because of their poor quality, were cocultured for 5 days on a "Vero" cell layer. These epithelial cells were selected because kidney and genital tract have a common embryologic origin and "Vero" cells are a safe and highly controlled cellular support used for vaccine production. In the control group, the embryos were cultured in culture medium alone (B2 + 15% serum). At the end of the culture, the number of blastocysts was significantly higher in the coculture group: 61% vs. 3%. Moreover, at least half of the blastocysts were expanding and hatching (13/25), with a chronologically normal development. These observations suggest that (1) the coculture system improves human embryonic development; (2) it can rescue early degenerating embryos; (3) beneficial effects of coculture are not strictly genital-tract specific, but rather epithelium dependent. This coculture system could be used for in vitro fertilization to prolong in vitro culture and thus make it possible to transfer embryos at a more appropriate time, to eliminate early-blocked eggs, and to freeze embryos at the blastocyst stage, when freezing procedures are most successful.

/pdf/improvement-of-human-early-embryo-development-in-vitro-by-1vuok4g1da.pdf

Improvement of human early embryo development in vitro by coculture on monolayers of Vero cells.

Culture of in vitro produced bovine zygotes in vitro vs in vivo: Implications for early embryo development and quality

The development of 1-cell mouse embryos in explanted oviducts, on mouse and bovine oviduct epithelial cells and on two established cell line supports is compared. The best rates of blastocyst formation were obtained using explanted oviducts; mouse and to a lesser extent, bovine oviduct epithelial cells allow good embryonic development, associated with high viability after transfer of the blastocysts obtained in co-culture. MDBK (from bovine kidney) and Vero (from Green monkey kidney) have been tested. MDBK allows high rates of blastocyst formation (67%) and the blastocysts obtained are viable. Vero does not allow the 2-cell block to be overcome. Maintenance of cell polarity for all the feeder layers did not improve embryo development. A preliminary study on the metabolic modifications induced by the feeder layers showed no modifications at all related to a decrease in glucose, an increase in lactate and early embryonic development. On the other hand, for the free amino acids, cellular supports with high embryotrophic activity seem to mimic tubal secretions, especially with a high level of glycine. Neither a genital tract origin, nor a hormonal contribution are strictly necessary for embryo co-culture, as already demonstrated by co-culture with trophoblastic tissue. Established cell lines, which are easy to handle and control, could be useful tools in embryo biotechnology.

Co-culture of 1-cell mouse embryos on different cell supports

This study proposes a procedure for the isolation and culture of oviduct epithelial cells of several species. In-vitro culture on such a feeder seems to allow full embryonic development and viability. The inner linings of Fallopian tubes from mouse, rabbit, cow and human were trypsinized and the epithelial cells were enriched with Percoll gradient. Isolated cells, obtained in high yield with good viability, were maintained in monolayer culture in B2-Menezo medium supplemented with serum, which also supports early embryonic development in vitro. The plated primary cultures reached confluence within 8 days, producing a monolayer of cohesive polygonal cells. Associated with this large epithelial cell population, ciliated cells as well as polykaryotic cells and few fibroblastic nests were observed. After the first sub-culture, the ciliated cells disappeared and the epithelial cell monolayer grew rapidly to confluence within 3 days and displayed contact inhibition. No epithelial cell growth could be obtained in culture in the absence of serum. The addition of oestrogens had no effect on any of the cultured oviductal epithelial cells. A spontaneous alteration was observed in morphology and growth after several passages, the number of which depends mainly upon the species.

Culture of epithelial cells derived from the oviduct of different species

Studies of sperm movement characteristics concern mainly sperm swimming between two glass surfaces (as in the Makler chamber). Using automated videomicrography, (CellSoft, Cryo Resources, New York, USA), we have analysed the movements of human sperm swimming on monolayers of different origins: monkey kidney (Vero) cells, bovine oviduct cells, and human endometrial cells. About 10(5) sperm were deposited upon preparations consisting of monocellular layers adhering to a coverglass, and placed in a deep slide-coverglass system. Experiments were first performed at room temperature then at 37 degrees C. At room temperature, motion characteristics on Vero cell layers (six samples) were not different from those measured in either the conditioned or corresponding non-conditioned media, except for the amplitude of lateral head displacement (ALH) which was significantly lower. Comparison of the three different cell monolayers showed no difference between them for the corresponding motion parameters. The data were dramatically different at 37 degrees C: sperm swimming on cell monolayers of genital origin (oviduct or endometrium) exhibited high rates of hyperactivation (HA: 36.7% and 38.6% respectively), which was significantly more than on either Vero cells (10.9%) or in a control medium (12.6%). Moreover, HA rates were significantly higher on genital cell monolayers than in the corresponding conditioned medium. Hyperactivated sperm exhibited lasting 'star-spin' trajectories rather than 'transitional phases'. It is concluded that passage of sperm on either oviduct or endometrial epithelial cell monolayers can induce sperm hyperactivation and improve their fertilizing capacity.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2605.1991.tb01269.x

Movement characteristics and hyperactivation of human sperm on different epithelial cell monolayers.

Bovine epithelial cell monolayers were obtained for culture from fetal oviduct after in situ trypsinization. Isolated ciliated and secretory cells obtained in high yield with good viability were suspended in B2-MENEZO'S medium supplemented with 7.5% fetal bovine serum FBS. The plated primary cultures reached confluency 2 days after initial seeding, producing a monolayer of cohesive polygonal cells with viability of 85 to 95%. Associated with this large epithelial cell population, ciliated cells as well as a few elongated spindle cells were observed. After the first subculture the ciliated cells disappeared and the epithelial cells in the monolayer grew more rapidly to confluence than adult-derived cultures. In addition, frozen-thawed oviduct epithelial cells also maintained a level of 75 to 85% viability during postthaw subculture. The epithelial cells maintained their secretory activity in culture as indicated by electron microscopy and immunocytochemistry. The cell culture monolayers contained keratin, a specific cytoskeletal component of epithelial cells. This culture system may offer benefits for in vitro culture of mammalian embryos.

Fetal bovine oviduct epithelial cell monolayers: Method of culture and identification

Oocyte cryopreservation (OC) has increased in recent years; however, there is a paucity of published data on the use of cryopreserved oocytes and associated outcomes.A retrospective review of 748 OC cycles between 2013 and 2022 at a private fertility centre was performed. Outcome parameters for oocyte retrieval cycles were reviewed. For patients who returned for oocyte disposition, outcomes subsequent to oocyte re-warming, fertilization, and transfer were analyzed.There were 748 OC cycles (653 elective and 95 non-elective) in 646 patients (556 elective and 90 non-elective). Patients were older at the time of freezing in the elective oocyte group compared with the non-elective group (36.5 vs. 28.8 y; P < 0.001). Sixty-five patients returned to warm and fertilize their oocytes (50 in the elective group and 15 in the non-elective group). The survival rate for warmed oocytes was 76.1% (541/711), and 66.2% of surviving oocytes were successfully fertilized, and 39.1% reached blastulation. Twenty-three patients underwent embryo transfers (10 after preimplantation genetic testing for aneuploidy), with 15 patients having at least 1 delivery or ongoing pregnancy.To date, this is the largest published experience with OC in Canada. OC can lead to successful live births but does not guarantee a viable outcome for all patients. In this study, most patients with vitrified oocytes had not returned for disposition, so long-term follow-up is still required to verify the efficacy of OC. 

Nadia Ouhibi

Papers

Co-culture of 1-cell mouse embryos on different cell supports

Culture of epithelial cells derived from the oviduct of different species

Movement characteristics and hyperactivation of human sperm on different epithelial cell monolayers.

Fetal bovine oviduct epithelial cell monolayers: Method of culture and identification

Oocyte cryopreservation: A nine year single-centre experience.