Biomedical subjects

Y Menezo

Publications and source records attributed to Y Menezo.

At least 19 recordsLinked to original sources

PubMed2004

Cryopreservation of IVF embryos: which stage?

Embryo freezing is a mandatory tool in IVF technology as controlled ovarian hyperstimulation usually leads to extra embryos which are not transferred. One dilemma is the embryonic stage at which the embryos are to be frozen. Early stage freezing (PNs or cleavage stage) leads to a two step selection: at the time of thawing and a few hours or a day after. Then the recovering embryos are submitted to the classical in vitro developmental arrests in relation with maternal, paternal and cytogenetic factors. The "take home baby rate" per frozen embryo is low, rarely over 5%. Blastocyst have overcome the blocks in vitro: a first selection has already been made. The quality of freezing at this stage depends greatly on the culture conditions. It allows freezing of fewer embryos, but with higher yields: a >10% take home baby rate can be expected. It is clear to us that vitrification, beside the technical problems, has to be handled with care, especially if ethylene glycol (EG) is used. Metabolic products of EG might have negative effects on organogenesis.

Animals↗

PubMed2001

A physiological replacement for polyvinylpyrrolidone (PVP) in assisted reproductive technology.

The technique of intracytoplasmic sperm injection (ICSI) requires mechanical immobilization of the sperm that are to be injected; damage thus caused to the sperm membrane is considered to be necessary to activate the sperm for fertilization. Mechanical immobilization and the injection procedure are facilitated by introducing the sperm into a viscous medium that will hinder motility: a solution of polyvinylpyrrolidone (PVP) has been used successfully for this purpose. PVP is an artificial polymer, which has been regarded as chemically inert, although adverse effects have been reported as a result of its use both in vivo and in vitro. Therefore, the use of hyaluronate, the natural component of the extracellular matrix of the cumulus-oocyte complex, was investigated as a replacement for PVP during ICSI. A solution of hyaluronate was found to be as effective as PVP in facilitating the injection procedure, its effect on sperm motility was readily reversible, and its use did not affect the outcome of the treatment cycles in terms of fertilization, pregnancy and live birth rates. Every attempt should be made to eliminate artificial factors in assisted reproductive procedures. Hyaluronate, a natural and readily degradable glycosaminoglycan can be used as a substitute for the artificial PVP polymer without jeopardising the outcome of the treatment cycle.

Adult↗

PubMed1999

Glucose metabolism during the final stage of human oocyte maturation: genetic expression of hexokinase, glucose phosphate isomerase and phosphofructokinase.

The low involvement of glucose metabolism in early preimplantation embryos has suggested the presence of metabolic blocks in the glycolytic pathway. Genetic expression of hexokinase (HK), glucose-6-phosphate isomerase (GPI) or phosphofructokinase (PFK) were qualitatively analysed using the reverse transcription nested polymerase chain reaction (RT-nested PCR) in individual human immature oocytes at the germinal vesicle (GV) stage and in single non-fertilised human metaphase II (MII) oocytes, after IVF or ICSI failures. Transcripts encoding for HK, GPI and PFK were detectable in the majority of the oocytes analysed, and with different expression patterns. GPI transcripts were consistently present and appear to be constitutively expressed during GV and MII stages. In contrast, low quantities of transcripts encoding for HK and PFK were observed in all oocytes analysed. Our data revealed that the metabolic block previously reported at GPI or PFK levels underwent post-transcriptional regulation. The expression profiles of HK and PFK transcripts in GV and MII reflect a low level of transcription or active translation of maternal transcripts during oocyte maturation. Nevertheless, enzymatic activities of HK and PFK have previously been determined in human oocytes. This suggests that HK and PFK may be accumulated in protein (enzyme) form instead of maternal mRNA during human oocyte maturation. The expression pathway of glycolytic metabolism reflects the presence of different mechanisms involved in gene expression/regulation at the transcriptional and translational level and their accumulation during human oocyte maturation.

DNA Primers↗

PubMed1998

Human pregnancies after transfer of fresh (four- to eight-cell) versus frozen-thawed blastocysts resulting from intracytoplasmic sperm injection.

PURPOSE: The objective of this study was to obtain expanded blastocysts following intracytoplasmic sperm injection (ICSI) and Vero-cell co-culture, cryopreserve them at this stage, and transfer the frozen-thawed blastocysts to obtain pregnancies. METHODS: Twenty-two couples with severe male-factor infertility or failed fertilization in a previous in vitro fertilization cycle were included in this study. ICSI was performed for all of them, and sperm-injected oocytes were immediately subjected to Vero-cell co-culture for varying intervals. Then 14 couples were treated by embryo transfer at the four- to eight-cell stage (Group I), whereas 8 couples were treated by transfer of frozen-thawed blastocysts (Group II). RESULTS: Percentages of cleaved embryos and term survival rates were 57.1 and 73.3% for Group I and 50.0 and 37.5% for Group II, respectively. CONCLUSIONS: Blastocysts obtained after ICSI and Vero-cell co-culture can retain developmental competence after cryopreservation and thawing. Transfer of frozen-thawed blastocysts derived by these means holds promise for establishment of viable pregnancies.

Adult↗

PubMed1998

Intracellular pH regulation in the human oocyte.

We have used fluorescence techniques to study the regulation of intracellular pH during fertilization and preimplantation embryo development in human oocytes. The intracellular pH of human oocytes during maturation and fertilization was always 7.4, suggesting that these processes do not involve long-term changes in intracellular pH. The recovery of intracellular pH of human oocytes and embryos after extracellular acid or alkaline shock was investigated. Fresh metaphase II oocytes and preimplantation embryos showed similar rates of recovery following alkaline shock. However, aged and immature oocytes had a significantly slower rate of recovery to physiological pH. Early embryos up to the morula stage were unable to recover following acidosis, whereas blastocysts could control both acidosis and alkalosis. We assessed the sensitivity of fertilization and early development in the human to extracellular pH. Our results show that insemination in the human is pH-sensitive, whereas intracytoplasmic injection (ICSI) activated oocytes at all pH tested. We suggest that this is due to the pH-sensitivity of the sperm-zona pellucida interaction, which is bypassed during the ICSI procedure. Further development in human embryos is more sensitive to alkalinity than acidity. We discuss these results in terms of the extracellular pH in vivo in the female reproductive tract.

Blastocyst↗

PubMed1997

The mammalian oviduct: biochemistry and physiology.

Oviduct fluid and oviduct epithelium seem able to modulate in-time maturation and transport of gametes and embryos. They probably allow selection of spermatozoa through too early activation. Subtle changes in the composition of tubal secretion permit fertilization and embryo development in the best conditions. The mechanisms of these changes of oviduct fluid composition (induced by endocrine stimuli and/or by embryo) are under investigation. Numerous compounds isolated in oviduct fluid are now added to the synthetic media for in vitro maturation/in vitro fertilization/embryo culture (IVM/IVF/EC). The rationale is now to mimic more and more, the biochemical composition of tubal and uterine fluids even if interactions with embryo metabolism is still far from being understood.

Animals↗

PubMed1996

Cytogenetics of uncleaved oocytes and arrested zygotes in IVF programs.

PURPOSE: Cytogenetic studies of arrested oocytes and zygotes were used to understand in vitro fertilization (IVF) failures. METHODS: We investigated the cytogenetics (Giemsa banding and FISH) of 710 uncleaved oocytes and 94 arrested zygotes from 208 patients undergoing IVF procedures. RESULTS AND CONCLUSIONS: Of uncleaved oocytes without a polar body, 39% were judged cytogenetically abnormal (17% unbalanced predivision and 21.5% diploid). Of 575 oocytes with a polar body, 124 (21.5%) showed numerical or structural chromosome aberrations. In arrested zygotes, approximately equal cases were found with separate condensed haploid complements (no syngamy), nuclear asynchrony and pulverized DNA, and apparently cytogenetically normal zygotes arrested at mitosis. These data on chromosome abnormalities were also analyzed with respect to two ovarian stimulation protocols and to maternal age. Both ovarian stimulation protocols and to maternal age. Both ovarian stimulation protocols showed the same levels of chromosome abnormalities. Overall chromosome abnormalities and premature chromosome condensation were also unchanged with maternal age. These data illustrate the significance of chromosome aberrations in IVF failures.

Adult↗

PubMed1996

[Embryonal implantation. Fundamental and practical aspects].

The precise mechanisms of embryo implantation remain unclear: the uterus is a "hostile environment" which should become "neutral" at the time of implantation. Advances have been made both in terms of embryo quality and in implantation techniques, making better knowledge of the uterus-embryo dialogue essential. To meet this challenge, the Pharmaceutical firms Serono France and ARCEFAR have organized a symposium entitled "Embryo implantation: basic principles and practical aspects". The symposium, presided by André Hazout and Yves Menezo, will first focus on the fundamental role of the ovum then will explore the complex immunological processes involved in the uterus-embryo dialogue.

Cytokines↗

PubMed1995

Expression of complement regulatory proteins on human eggs and preimplantation embryos.

PROBLEM: To investigate the relation between the complement system and reproduction, expression of complement regulatory proteins (C3b receptors and inhibitor of the membrane attack complex) were screened on unfixed human eggs and preimplantation embryos. METHODS: Unfixed unfertilized oocytes and preimplantation embryos obtained from an in vitro fertilization program were stained by indirect immunofluorescence using monoclonal antibodies raised against membrane cofactor protein, (MCP or CD46), decay accelerating factor (DAF or CD55), protectin (CD59), human C3b/C4b receptor (CR1 or CD35), and major histocompatibility complex class I antigen (MHC class I). RESULTS: CD55 and CD59 were both expressed by the plasma membrane of unfertilized oocytes and pre-implantation embryos. CD46 was not expressed by unfertilized oocytes but appeared at the 6-to-8 cell stage embryo when human gene expression first occurs. CD35 and MHC class I antigens were not expressed at all on oocytes and preimplantation embryos. CONCLUSIONS: Selective expression of complement regulatory proteins (DAF and protectin) associated with the lack of MHC class I antigens may represent an immune protective mechanism by which human oocytes and preimplantation embryos escape complement-mediated damage during their travel through the female genital tract. Furthermore, participation of these complement regulatory proteins including MCP in cell to cell interaction during fertilization and/or implantation cannot be excluded.

Antibodies, Monoclonal↗

PubMed1995

Cocultured blastocyst cryopreservation: experience of more than 500 transfer cycles.

OBJECTIVE: To present our experience using cocultured cryopreserved and transferred blastocysts. DESIGN: Retrospective study of patients undergoing transfer of cryopreserved blastocysts. SETTING: Three different IVF centers. PATIENTS: Four hundred sixty-seven thawed cycles from January 1991 to June 1994. MAIN OUTCOME MEASURE: Pregnancy rate per cycle after transfer of pre-embryos developed from thawed blastocysts. RESULTS: One thousand two hundred thirty-nine blastocysts were thawed. Of these, 1,033 (83%) survived thawing and were transferred. Five hundred sixty-three thawed cycles resulted in 516 (92%) receiving intrauterine transfer. One hundred twelve clinical pregnancies were established, resulting in a 21.7% pregnancy per transfer with a 19% ongoing rate. The implantation rate of 13.4% results from 138 implanted pre-embryos. There was a higher PR in the programmed cycle (79/302; 26.2%) compared with the natural cycle (6/47;13%). CONCLUSIONS: Freezing at the blastocyst stage is a proven and reliable method in IVF technology. Although there may be fewer pre-embryos, their ability to implant appears to approach the potential of a fresh transfer.

Blastocyst↗

PubMed1995

[Demonstration of cysteine sulfinate decarboxylase (EC 4.1.1.29) in cultured oviduct epithelial cells in cows and goats].

Tubal fluid contains high amounts of hypotaurine and taurine. These amino-acids are important for gametes and embryo survival. They are synthesized and secreted by oviduct epithelial cells in vitro. Cysteine sulfinate decarboxylase (EC 4.1.1.29) activity was identified by selective immuno-trapping using a specific antiserum in cow and goat oviduct epithelial monolayers. This result suggests that cysteine is converted to hypotaurine and taurine via cysteine sulfinic acid in these cells.

Animals↗

PubMed1994

[Insulin-like growth factors I and II in follicular and oocyte maturation].

Insulin-like growth factors I and II are synthesized from animal and human follicles. Their reproduction is FSH-, LH- and oestrogen-dependent. Growth hormone is also involved. IGF-I receptor numbers increase in the presence of FSH, while estradiol has a synergic effect. IGF-I and IGF-II stimulate growth of different follicular cell elements. TGF-alpha has the same activity but seems to be mediated by an increase in IGFs. Conversely, TGF beta and activin inhibit follicular growth accompanied by a reduction in IGFs. In contrast to TGF alpha, IGFs do not cause acquisition of meiotic competence. Injection of IGF-I into cultures of prepuberal splenic primary follicles reduced IGF-II production.

Animals↗

PubMed1994

Methylation in fertilised and parthenogenetic preimplantation mouse embryos.

DNA methylation is one of the proposed biochemical mechanisms involved in cell differentiation and in genomic imprinting, and DNA methyltransferase (DMT) is a key enzyme in the embryo since mutation of its gene is lethal early in development. In order to verify that non-viability of uniparental embryos was not due to a defect in the regulation of DMT activity, we compared the metabolism of methylation in parthenogenetic embryos (maternal genome) and in fertilised embryos (maternal and paternal genomes). As regards total methylation, estimated by a measure of S-adenosyl methionine (SAM) and S-adenosyl homocysteine (SAH) formation, no significant difference was found between the two kinds of embryos during preimplantation development. Mean values were 4.5 +/- 0.6 fmol (SAM+SAH)/h per 2-cell embryo and 0.40 +/- 0.05 fmol SAH/h per 2-cell embryo, i.e. a SAH/(SAM+SAH) ratio of 9%; there was no detectable SAH formation in blastocysts. The same observation can be made for DMT activity, with mean values of: 7.8 fmol/h per oocyte, 8.5 fmol/h per 2-cell embryo, 6.1 fmol/h per 4-cell embryo, 4.1 fmol/h per morula, and no detectable activity in blastocysts. Total methylation as well as DNA methylation is characterised by a progressive drop in activity during preimplantation development.

Animals↗

PubMed1994

Interactions in glycine and methionine uptake, conversion and incorporation into proteins in the preimplantation mouse embryo.

Glycine is the most concentrated amino acid in the female genital tract. In this study, we report its conversion and incorporation into proteins in the presence or absence of methionine, in both 1-cell and blastocyst mouse embryos. The uptake, incorporation and conversion of radiolabelled glycine were studied in the presence or absence of unlabelled methionine. For control purposes, the reciprocal experiment was performed with labelled methionine in the presence or absence of unlabelled glycine. At the 1-cell stage neither glycine uptake nor its incorporation into proteins is inhibited by methionine. Glycine is, however, highly used as an oxidisable energy substrate, via glycolate. At the blastocyst stage, glycine conversion into other amino acids is high and mainly utilised in the formation of glutamic acid. Glycine is highly incorporated into proteins, resulting in a poor exchange of glycine from the preloaded embryos. Methionine competes for glycine uptake and consequently reduces its overall incorporation into proteins. For methionine, neither its uptake nor its incorporation into proteins is reduced in the presence of glycine for the two embryonic stages tested here. The embryo has different mechanisms for incorporation and utilisation of methionine and glycine. Glycine, which has an important function in the embryo, has an inefficient transport system compared with methionine. We were unable to demonstrate the presence of methylglycine since SAM-glycine-methyltransferase (EC 2.1.1.20) was not detected. The same results were obtained when exogenous methionine was added. We therefore concluded that glycine does not compete in transmethylation within the embryo.

Amino Acids↗

PubMed1994

Established cell lines and their conditioned media support bovine embryo development during in-vitro culture.

These experiments were conducted to evaluate the ability of different somatic-cell monolayers or conditioned medium from somatic cells for supporting bovine embryo development in vitro. In the first experiment, bovine embryos (2- to 4-cells) were allocated randomly to a control (medium 199 with 10% fetal bovine serum and antibiotics) group or co-cultured with bovine oviduct epithelial (BOEC), buffalo rat liver (BRL), Madin Darby bovine kidney (MDBK) or African green monkey kidney (Vero) cells. In the second experiment, bovine embryos (1-cell) were allocated randomly to the following groups: control medium or conditioned medium from BOEC, BRL, MDBK and Vero monolayers. In both experiments, development to the blastocyst stage was assessed after 8 days of incubation at 39 degrees C and 5% CO2. In Experiment 1, coculture improved development to the blastocyst stage compared with control medium alone, and the highest development was observed after co-culture with BOEC. In Experiment 2, conditioned medium enhanced development to morulae and blastocysts compared with the control medium; however, no differences were detected among different cell supports. These results indicate that both co-culture and conditioned medium from different cell monolayers supported development to the blastocyst stage at a higher efficiency than control medium alone.

Animals↗

PubMed1994

Use of lasers in assisted fertilization and hatching.

The erbium-yttrium-aluminium-garnet (Er:YAG) laser has been applied to micromanipulation in humans. It was used in the fertilization process for both subzonal insemination (SUZI) and for partial zona dissection (PZD). Laser-assisted micromanipulation achieved significantly higher fertilization rates (34.8%) when compared to mechanical SUZI (16.1%), but use of the laser did not improve the PZD results (laser 14.8% versus mechanical 14%). The Er:YAG laser was used to assist hatching. In the mouse it significantly improved the hatching rate (80 versus 29.3%) 110 h after administration of human chorionic gonadotrophin. This technique was applied in two different centres to patients with previous in vitro fertilization (IVF) failures. the implantation rate per embryo (14.4% laser-assisted hatching versus 6% control group) and the pregnancy rate per transfer (40 versus 16.2%) were improved.

Adult↗

PubMed1994

[Growth factors: from oocyte maturation to blastocyst].

Developmental arrests and losses of viability are observed in vitro, when embryos are cultured. A harmonious oocyte maturation is essential to obtain a balanced development. Factors that control this maturation are still unknown but growth factors seem to be involved: they are present in ovary and some of them (EGF, TGF-alpha, TGF-beta, PDGF) improve in vitro maturation. These factors are also involved in preimplantation development, either in an autocrine way (ligand and receptor genes expression in the embryo) or in a paracrine way (receptor gene expression in the embryo and ligand gene expression in the tractus). However, the precise role of each one and their interrelations are still speculative.

Blastocyst↗

PubMed1994

[Assisted hatching and micro-fertilization].

Erbium-YAG laser has been applied for micromanipulation in human beings. In a first series of attempts it was used in the fertilization process for subzonal insemination (SUZI): laser assisted micromanipulation achieved significant higher fertilization rates (34.8%) when compared to mechanical SUZI (16.1%), and for partial zona dissection (PZD): in this case laser did not improve the results (laser 14.8% vs mechanical 14%). Erbium-YAG laser was used to assist hatching. In the mouse it significantly improved the hatching rate (80% vs 29.3%) 110 hours post hCG. This technique was applied in two different centres to patients with previous IVF failures. The implantation rate per embryo (14.4% laser assisted hatching vs 6% control group) and the pregnancy rate per transfer (40% vs 16.2%) were improved.

Animals↗