beta-mercaptoethanol enhances blastocyst formation rate of bovine in vitro-matured/in vitro-fertilized embryos

An Overview of Reactive Oxygen Species Damage Occurring during In Vitro Bovine Oocyte and Embryo Development and the Efficacy of Antioxidant Use to Limit These Adverse Effects

The in vitro production (IVP) of bovine embryos has gained popularity worldwide and in recent years and its use for producing embryos from genetically elite heifers and cows has surpassed the use of conventional superovulation-based embryo production schemes. There are, however, several issues with the IVP of embryos that remain unresolved. One limitation of special concern is the low efficiency of the IVP of embryos. Exposure to reactive oxygen species (ROS) is one reason why the production of embryos with IVP is diminished. These highly reactive molecules are generated in small amounts through normal cellular metabolism, but their abundances increase in embryo culture because of oocyte and embryo exposure to temperature fluctuations, light exposure, pH changes, atmospheric oxygen tension, suboptimal culture media formulations, and cryopreservation. When uncontrolled, ROS produce detrimental effects on the structure and function of genomic and mitochondrial DNA, alter DNA methylation, increase lipid membrane damage, and modify protein activity. Several intrinsic enzymatic pathways control ROS abundance and damage, and antioxidants react with and reduce the reactive potential of ROS. This review will focus on exploring the efficiency of supplementing several of these antioxidant molecules on oocyte maturation, sperm viability, fertilization, and embryo culture.

Role of N-acetylcysteine treatment in women with advanced age undergoing IVF/ICSI cycles: A prospective study

Objective

The main objective of this study was to explore the efficacy of a new antioxidant N-acetylcysteine (NAC) supplementation in reproductive outcomes of advanced age women undergoing in vitro fertilization/intracytoplasmic sperm injection-embryo transfer (IVF/ICSI-ET), and the effect on the expression of L-glutathione (GSH) in follicular fluid (FF) and mitochondrial DNA (mtDNA) copy number of granulosa cells.

Methods

The present prospective randomized controlled study was conducted in 200 patients with advanced age women undergoing GnRH antagonist protocol. The treatment group (group A) consisted of 100 women who received N-acetylcysteine treatment from the menstrual phase of the previous cycle for about 45 days using the GnRH antagonist protocol. The control group (group B) consisted of 100 women who received the same protocol without N-acetylcysteine. Total gonadotrophin dosage the number of oocyte received, high-quality blastocysts, and pregnancy outcomes were compared between two groups. Pregnancy outcomes included biochemical pregnancy rate, clinical pregnancy rate, embryo implantation rate, ectopic pregnancy rate, multiple pregnancy rate, and ongoing pregnancy rate. Follicular fluid (FF) was collected after oocytes were gathered. The GSH content in the FF was tested with enzyme linked immunosorbent assay (ELISA). The mtDNA copy number of the granulosa cells was measured using real-time PCR techniques.

Results

Total doses of Gn in the NAC treatment group were less than those in the control group (2385.50 ± 879.19 vs. 2527.63 ± 1170.33, P = 0.047). Compared with the control, the number of high-quality blastocysts in NAC treatment increased significantly (1.82 ± 2.12 vs. 1.43 ± 1.58, p = 0.014). Clinical pregnancy rates did not differ in both groups (all P > 0.05). At the same time, the GSH content in the FF differed significantly between the two groups (1.88 ± 1.23 vs. 1.07 ± 0.70, p = 0.001). There was no significant difference in the mtDNA copy number between the two groups (P = 0.157).

Conclusion

A combination of NAC and Gn treatment is capable of improving the ovarian response to superovulation drugs in assisted reproductive technologies (ARTs) and also in aged populations. The addition of NAC during IVF can improve the quality of blastocysts in advanced age female subjects. However, more clinical trials are required to be designed to confirm this conclusion in future.

Ethics and dissemination

The experiment solicited approval from the Institutional ethics committee of the Affiliated Reproductive Hospital of Shandong University. All the participants provided written informed consent. This survey was conducted as per the Declaration of Helsinki and relevant amendments.

Trial registration number

www.chictr.org.cn, identifier ChiCTR2100048297.

N-acetyl-L-cysteine Improves the Developmental Competence of Bovine Oocytes and Embryos Cultured In Vitro by Attenuating Oxidative Damage and Apoptosis

Oxidative stress has been suggested to negatively affect oocyte and embryo quality and developmental competence, resulting in failure to reach full term. In this study, we investigated the effect of N-acetyl-L-cysteine (NAC), a cell-permeating antioxidant, on developmental competence and the quality of oocytes and embryos upon supplementation (0.1–10 mM) in maturation and culture medium in vitro using slaughterhouse-derived oocytes and embryos. The results show that treating oocytes with 1.0 mM NAC for 8 h during in vitro maturation attenuated the intracellular reactive oxygen species (ROS) (p < 0.05) and upregulated intracellular glutathione levels (p < 0.01) in oocytes. Interestingly, we found that NAC affects early embryonic development, not only in a dose-dependent, but also in a stage-specific, manner. Significantly (p < 0.05) decreased cleavage rates (90.25% vs. 81.46%) were observed during the early stage (days 0–2), while significantly (p < 0.05) increased developmental rates (38.20% vs. 44.46%) were observed during the later stage (from day 3) of embryonic development. In particular, NAC supplementation decreased the proportion of apoptotic blastomeres significantly (p < 0.05), resulting in enhanced hatching capability and developmental rates during the in vitro culture of embryos. Taken together, our results suggest that NAC supplementation has beneficial effects on bovine oocytes and embryos through the prevention of apoptosis and the elimination of oxygen free radicals during maturation and culture in vitro.

CRIOTOLERÂNCIA DE OÓCITOS E EMBRIÕES BOVINOS MATURADOS COM LÍQUIDO FOLICULAR E/OU β-MERCAPTOETANOL

Foi avaliada a criotolerância de oócitos e embriões bovinos maturados com adição de líquido folicular (LF) e/ou β-mercaptoetanol (BM). Após vitrificação, os oócitos foram maturados em: TCM-199 (controle); BM (24h TCM-199+100µM BM); LF (6h em LF+18h TCM-199) e LF+BM (6h LF+18h TCM-199+100µM BM). Não houve diferença (p>0,05) nas taxas de blastocistos dos tratamentos TCM (6,4%), BM (4,0%) e LF (3,4%). A eclosão e densidade celular dos embriões eclodidos não diferiram (p>0,05) nos tratamentos. No Experimento 2 blastocistos expandidos (Bx) obtidos em D7 ou D8 foram vitrificados, avaliando-se sua reexpansão e eclosão. A reexpansão foi semelhante (p>0,05), sendo observado comportamento distinto na eclosão entre Bx D7 e D8. Nos Bx D7 houve maior eclosão no controle (TCM–54,2%) em relação ao BM (40,32%) e LF+BM (33,89%). Os Bx D8 apresentaram menor eclosão no controle (TCM) em relação aos Bx D7. Nos tratamentos BM, LF e LF+BM a eclosão foi semelhante para Bx D7 ou D8. A maturação com adição de LF e/ou BM não melhora a criotolerância de oócitos imaturos e embriões PIV. Blastocistos expandidos precoces (D7) são mais criotolerantes e apresentam um comportamento distinto à adição de LF e BM, em relação aos tardios (D8).

Survival of vitrified in vitro-produced bovine embryos after a one-step warming in-straw cryoprotectant dilution procedure

Vitrification is an alternative to slow-rate freezing for cryopreserving bovine embryos. However, this technology requires simplification if it is to be used under field conditions. The main objective of this work was to develop a new system for the direct transfer of vitrified embryos to be used under farm conditions. For this, three objectives were set: (1) to compare the effect of vitrification, using the cryologic vitrification method (CVM), and slow-rate freezing on bovine embryo development and quality; (2) to develop a one-step warming procedure for bovine in vitro-produced (IVP) vitrified (by CVM) embryos; and (3) to assess the effects on embryo survival of a new method for the direct transfer of vitrified IVP bovine blastocysts. In vitro-produced blastocysts were initially either vitrified by CVM or subjected to slow freezing to compare embryo survival and quality (experiment 1). No differences were detected between these cryopreservation techniques in terms of the survival and quality variables at 24 hours or in terms of the proteins expressed. However, at 48 hours the vitrified embryos showed higher hatching rates, greater total cell numbers, and lower apoptotic indices (P < 0.05). In experiment 2, CVM-vitrified IVP blastocysts were warmed by the conventional two-step or one-step warming procedure by incubating them at 41 °C in 0.25 M sucrose for 10 minutes, 0.15 M sucrose for 10 minutes, or 0.25 M sucrose for 5 minutes. In addition, embryo transfer (ET) was performed using vitrified embryos warmed by the one-step procedure in 0.25 M sucrose solution for 5 minutes. As a control group, IVP fresh embryos were transferred to recipient females. No differences were observed in embryo survival or total cell number between any of the warming procedures. Moreover, no significant differences for pregnancy at 60 days were found between the ET groups. In experiment 3, expanded IVP blastocysts were then either vitrified using a conventional or a modified fiber plug designed to allow direct ET after in-straw cryoprotectant (CP) dilution. They were warmed using the one-step process (0.25 M sucrose, 5 minutes) in a 0.25 mL French straw. Embryo recovery associated with the modified fibreplug system was less reliable than with the conventional system. However, no differences were seen between the systems in terms of in vitro embryo survival among those finally recovered. Finally, IVP blastocysts were vitrified using conventional fibreplugs to maintain a high embryo recovery rate, and then warmed using the one-step warming in-straw CP dilution procedure, but using an adapter with a wider opening coupled to the French straw and a heated metal chamber to protect and keep the straw at 41 °C (experiment 4). No differences were seen in embryo survival rates between the two groups. The CVM combined with this new one-step warming in-straw CP dilution procedure could be used for direct ET under field conditions.

A review: alteration of in vitro reproduction processes by thiols -emphasis on 2-mercaptoethanol

Descriptions of organosulfurs altering biologically relevant cellular functions began some 40 years ago when murine in vitro cell mediated and humoral immune responses were shown to be dramatically enhanced by any of four xenobiotic, sulfhydryl compounds-2-mercaptoethanol (2ME), dithiothreitol (DTT), glutathione, and L-cysteine; the most effective were 2ME and DTT. These findings triggered a plethora of reports defining 2ME benefits for a multitude of immunological processes. This in turn led to investigations on 2ME alterations of (a) immune functions in other species, (b) activities of other cell-types, and (c) in vivo diseases. In addition, these early findings preceded the identification of previously undefined anticarcinogenic chemicals in specific foods as organosulfurs. Taken all together, there is little doubt that organosulfur compounds have enormous benefits for cellular functions and for a multitude of diseases. Issues of importance still to be resolved are (a) clarification of mechanisms that underlie alteration of in vitro and in vivo processes and perhaps more importantly, (b) which if any in vitro alterations are relevant for (i) alteration of in vivo diseases and (ii) identification of other diseases that might therapeutically benefit from organosulfurs. As one means to address these questions, reviews of different processes impacted by thiols could be informative. Therefore, the present review on alterations of in vitro fertilization processes by thiols (mainly 2ME, since cysteamine alterations have been reviewed) was undertaken. Alterations found to occur in medium supplemented with 2ME were enhancement, no effect, or inhibition. Parameters associated with which are discussed as they relate to postulated thiol mechanisms.

Media composition: antioxidants/chelators and cellular function

Protection of embryos against oxidative insults during culture is necessary to maintain viability. Generation of excessive levels of reactive oxygen species (ROS) is triggered by various components of the in vitro environment, most of which embryos do not normally encounter in vivo. To compensate for these deficiencies in the culture environment, antioxidants and chelators are often used to control or suppress ROS levels as embryos develop. However, there is no consensus regarding dosage, time of exposure, or appropriate combinations of antioxidants and chelators in embryo culture. In order to elucidate this aspect of an embryo's chemical surroundings in vitro, we present the current knowledge on the function and effect of each antioxidant or chelator that is often included in an embryo culture medium.

Antioxidants rescue stressed embryos at a rate comparable with co-culturing of embryos with human umbilical cord mesenchymal cells

PURPOSE

During laboratory manipulations, oocytes and embryos are inevitably exposed to suboptimal conditions that interfere with the normal development of embryos.

MATERIALS AND METHODS

In this study, we examined the effects of antioxidants, feeder cells and a conditioned medium on embryo development and cleavage rate following exposure of the embryos to suboptimal conditions. We exposed mouse two-cell embryos to visible light and divided them into four groups: control (E-ctr), co-culture (Co-c), conditioned medium (Cndm) and antioxidant-plus medium (Aopm). We used human umbilical cord matrix-derived mesenchymal cells for co-culture. A group of embryos was not exposed to visible light and served as the non-exposed control (NE-ctr) group.

RESULTS

The developmental rate was higher in NE-ctr embryos than in the E-ctr group. Exposed embryos in the various groups showed a comparable developmental rate at different stages. Blastomere number significantly increased (P < 0.05) in the Co-c and Aopm groups compared with the E-ctr and Cndm groups. No significant difference was observed between the Co-c and Aopm groups.

CONCLUSIONS

Our data indicate that in suboptimal conditions, antioxidants could improve the embryo cleavage rate in the same way as feeder cells. Antioxidants probably improve embryo quality through their ability to scavenge reactive oxygen species.

Synergistic effects of glutathione and β-mercaptoethanol treatment during in vitro maturation of porcine oocytes on early embryonic development in a culture system supplemented with L-cysteine

Various methods have been used to remove reactive oxygen species (ROS) generated from in vitro culture (IVC) conditions that can cause cell injury or death, including the application of low oxygen (O(2)) tension and the addition of antioxidants. The beneficial effects of antioxidants and O(2) tension on IVC of porcine embryos, however, are controversial among researchers. In this study, we sought to determine the effects and optimal concentrations of antioxidants for the development of porcine embryos in an IVC system. Specifically, we examined the synergistic effects of antioxidants on development to the blastocyst stage in a culture system supplemented with L-cysteine during IVM. Of the antioxidants tested (melatonin, glutathione (GSH), β-mercaptoethanol (β-ME), N-acetylcysteine (NAC) and dithiothreitol (DTT)), addition of GSH (1 mM) or β-ME (25 µM) significantly increased development to the blastocyst stage compared with the controls without antioxidant treatment (22.2 ± 4.2% for 1 mM GSH, 25.9 ± 2.2% for 25 µM β-ME and 12-13% for the control, P<0.05). In addition, the mean cell number per blastocyst was increased by approximately 1.7-fold in the presence of GSH or β -ME. These GSH- and β-ME-induced increases in development to the blastocyst stage and total cell number, however, were not mimicked by melatonin, NAC or DTT, all of which are ROS scavengers. The combination of GSH or β-ME with L-cysteine significantly reduced high O(2) tension-induced ROS production (P<0.05). These results suggest that a combination of 1 mM GSH or 25 µM β-ME with 1 mM L-cysteine could be used for production of high quality porcine blastocysts in IVC systems.

Antioxidant supplementation of culture medium during embryo development and/or after vitrification-warming; which is the most important?

PURPOSE

To determine the most optimal stage for antioxidant supplementation of culture medium to improve developmental competence, cryotolerance and DNA-fragmentation of bovine embryos.

METHODS

Presumptive zygotes were first cultured in presence or absence of beta-mercaptoethanol (beta-ME), for 8 days. Subsequently, half of the expanded blastocysts developed in both groups were vitrified, warmed within 30 min and post-warming embryos along with their corresponding non-vitrified embryos were cultured for two further days in presence or absence of (100 microM) betaME.

RESULTS

For vitrified and non-vitrified embryos, the best effect was found when betaME was added from day 1 of in vitro culture in continuation with post-warming culture period. Day 1-8 supplementation significantly increased the rates of cleavage, day 7 and day 8 blastocyst production. For non-vitrified embryos, betaME addition during day 1-8 and/or 9-10 of embryo culture improved both hatching rate and quality of hatched embryos. For vitrified embryos, however, the percentage of DNA-fragmentation (18.5%) was significantly higher (p < or = 0.05) than that of embryos developed in absence of betaME but supplemented with betaME during post-warming period (13.5%).

CONCLUSIONS

Exogenous antioxidant increases the chance of embryos, even those of fair-quality, to develop to blastocyst. However, antioxidant inclusion during in vitro embryo development is not sufficient to maintain the redox state of these embryos during the critical period of post-warming embryo culture, and therefore, there should be a surplus source of exogenous antioxidant during post-warming embryo culture.

Melatonin effect on bovine embryo development in vitro in relation to oxygen concentration

Melatonin promotes mouse embryo development in vitro. An effect of melatonin on bovine embryo development is described here. Slaughterhouse derived oocytes were subjected to standard in vitro maturation and fertilization procedures. Presumptive zygotes were cultured for 2 days in CR1aaLA medium supplemented with melatonin (10(-4) m) or without melatonin (control). Culture was performed under two different gas atmospheres containing physiological (7%) or atmospheric (20%) oxygen concentrations (2x2 factorial analysis). After day 2, embryos from each treatment group developed to at least four-cell stage, were cultured without melatonin until day 10 at optimum 7% O2 atmosphere. Blastocyst formation rates of presumptive zygotes and of four-cell embryos were calculated for each group. Significant interactions between oxygen tension and the melatonin treatment were found. Out of four-cell embryos put into in vitro culture after initial incubation in medium containing melatonin, decreased blastocyst rate was observed in melatonin group (47.7%) compared with control (67.7%; P=0.0327) when lower oxygen concentration was applied. A beneficial effect of melatonin was observed in 20% O2: out of 61 embryos, 42 (68.9%) developed to the blastocyst stage after treatment in melatonin versus 32 of 63 (50.8%; P=0.0458) blastocysts that developed in control group. In conclusion, beneficial or harmful effects of melatonin on bovine embryo development in vitro were observed, depending on the oxygen tension during the treatment.

Improved fertilization and embryo development resulting in birth of live piglets after intracytoplasmic sperm injection and in vitro culture in a cysteine-supplemented medium

The effects of cysteine treatment on fertilization rate, intracellular concentration of glutathione, and embryo development in vitro and after embryo transfer were examined following intracytoplasmic sperm injection (ICSI) of in vitro-matured porcine oocytes using a piezo drive unit. Culture of presumed zygotes after ICSI with 1.71-3.71 mM cysteine for 3-12h improved (P<0.05) fertilization rates as compared to treatment with 0.57 mM cysteine or to controls (0mM) (56 to 68%, 48%, 35%, respectively). Extension of treatment time with cysteine beyond 3h did not further increase fertilization rates, suggesting that cysteine promoted early developmental events after ICSI (e.g. decondensation of sperm chromatin). There was no effect of cysteine supplementation on oocyte glutathione levels after ICSI. Pretreatment of spermatozoa for 3h with 1.71 mM cysteine did not improve fertilization rates. The incidence of blastocysts formation when cultured in 1.71 mM cysteine for 3h after ICSI was 31%, which was higher (P<0.05) than controls (18%). Transfer of 20-38 embryos cultured with 1.71 mM cysteine for 3h after ICSI to each of seven recipients yielded three deliveries with an average litter size of 4.0. We concluded that cysteine supplementation for the first 3h after ICSI improved fertilization and embryo development rates, with no influence on glutathione levels in oocytes, and that the cysteine-treated ICSI embryos developed to full term. The study also showed that porcine oocytes matured in a chemically defined medium had the ability for full-term development after piezo-ICSI without additional treatments for oocyte activation.

Freezing of in vitro produced bovine embryos in animal protein-free medium containing vegetal peptones

Successful cryopreservation is essential for a large-scale dispersal of bovine in vitro produced (IVP) embryos that have been shown to be more sensitive to cryopreservation than their in vivo counterparts. On the other hand, the use of animal proteins in freezing media increases sanitary risks. We first replaced animal proteins, such as bovine serum albumin (BSA) in the freezing medium by plant-derived peptides (vegetal peptones). A batch of wheat peptones was selected after a preliminary experiment showing the absence of toxicity of concentrations<18 mg/mL on in vitro bovine blastocysts. Increasing concentrations of peptones were then added in the freezing medium. The surviving and hatching rates were not affected by comparison with those observed with BSA. No significant difference was observed between groups either for the total number of cells or for the ratio ICM/Total cell, nor for the rate of apoptosis in surviving embryos. When embryos were cryopreserved in 1.8 mg/mL peptone, the hatching rate and embryo quality as assessed at 48 h post-thawing were not significantly different from those of unfrozen embryos. In a second experiment two additives were added in this animal protein-free freezing medium containing 1.8 mg/mL peptones. No beneficial effect of adding 1 mg/mL sodium hyaluronate or 100 microM beta-mercaptoethanol was observed on embryo survival or quality. In conclusion, we have demonstrated that vegetal peptones can replace BSA in freezing media without affecting blastocyst survival and quality.

Effect of beta-mercaptoethanol during in vitro fertilization procedures on sperm penetration into porcine oocytes and the early development in vitro

This study was carried out to determine the effects of beta-mercaptoethanol (bME) during a transient co-culture of gametes for 10 min, and/or the following culture until 6–9 h after insemination, on sperm penetration of porcine in vitro maturation (IVM) oocytes and the early development in vitro. When fresh spermatozoa were cultured in various concentrations of bME for 2 h, bME neutralized the stimulatory effect of caffeine-benzoate on sperm capacitation and the spontaneous acrosome reaction at 50–250 μmol/l. When 50 μmol/l bME were added during a transient co-culture of gametes for 10 min, the sperm penetration rate was reduced 9 h after insemination (70.5–82.0% vs 90.5–94.0% in the absence of bME), but the incidence of monospermic penetration was not affected. When 50 μmol/l bME were supplemented during culture after a transient co-culture, the sperm penetration rate was not affected, but the incidence of monospermy oocytes was increased (43.9–45.8% vs 31.7–34.3% in the absence of bME). The presence of bME following a transient co-culture minimized a decrease of oocyte glutathione content at 6 h after insemination (7.9 pmol/oocyte before in vitro fertilization (IVF), 6.7 pmol/oocyte in the presence of bME vs 5.5 pmol/oocyte in the absence of bME). When the distribution of cortical granules was evaluated 1 h after activation with calcium ionophore, mean pixel intensity of fluorescein isothiocyanate-labeled peanut agglutinin (FITC-PNA) at the cortex region was lower in the oocytes activated and cultured in the presence of 50 μmol/l bME. Although the presence of 50 μmol/l bME during a transient co-culture for 10 min and the following culture did not increased blastocyst formation (29.6–37.7%), 50 μmol/l bME during the following culture significantly increased the mean cell numbers per blastocyst (73.3–76.4 vs 51.2 in the presence and absence of bME respectively). These results demonstrate that supplementation with bME during IVF procedures, except during a transient co-culture period of gametes in the presence of caffeine, has a beneficial effect in maintaining the function of gametes, the incidence of normal fertilization and, consequently, the quality of IVF embryos.

Effects of beta-mercaptoethanol and cycloheximide on survival and DNA damage of bovine embryos stored at 4 degrees C for 72 h

The objectives of this study were to determine the effects of cycloheximide (CHX) and beta-mercaptoethanol (beta-ME) during storage of in vitro-produced (IVP) bovine blastocysts for 72 h at 4 degrees C on their survival, hatching capacity and DNA damage. In Experiment 1, when blastocysts were stored in a medium supplemented with 25, 50 or 100 microg/mL of CHX, or 25, 50 or 100 microM of beta-ME, the blastocysts stored with 25 microg/mL of CHX had a significantly higher survival rate than that of the blastocysts stored without CHX (79.5% versus 54.2%). In contrast, beta-ME had no apparent effects on the survival and hatching capacity of stored embryos. In Experiment 2, to investigate synergistic effects of CHX and beta-ME during storage of blastocysts on their developmental parameters and DNA damage, they were stored in the medium with CHX (25 microg/mL) and beta-ME (50 microM). The combination of CHX and beta-ME had no significant effects on the survival of blastocysts. The proportion (6.8%) of DNA-fragmented cells in the blastocysts stored with CHX was similar to that (5.4%) in the non-stored blastocysts (positive control) and significantly lower than that (9.7%) in the blastocysts stored without CHX and beta-ME (negative control). However, there were no significant differences among the proportions of dead cells of blastocysts in the storage groups. Therefore, the supplementation of CHX in the storage medium had a beneficial effect on the proportions of survival and DNA-fragmented cells in the stored embryos, whereas the beta-ME alone or in combination with CHX had no positive effects on either of these proportions.

Effects of oxygen concentration and antioxidants on the in vitro developmental ability, production of reactive oxygen species (ROS), and DNA fragmentation in porcine embryos

After in vitro maturation and fertilization of porcine oocytes, the fertilized embryos were cultured under 5 or 20% oxygen (O2) for 7 days. In embryos cultured under 5% O2 versus 20% O2, development to the blastocyst stage was higher (36.3% versus 22.5%, P < 0.05); the hydrogen peroxide (H2O2) content as a reactive oxygen species was lower (92 pixels versus 111 pixels, P < 0.05); and fragmentation of DNA in 8- to 16-cell stage embryos (estimated by the comet assay) resulted in a shorter (P < 0.05) DNA tail (36 microm versus 141 microm). Antioxidants such as beta-mercaptoethanol (beta-ME) and Vitamin-E (Vit-E) suppressed oxidative damage in the embryos and improved their developmental ability. For embryos cultured under 20% O2, there were the following differences (P < 0.05) between embryos exposed to 0 microM versus 50 microM beta-ME: 28% versus 57% developed to the blastocyst stage; 125 pixels versus 98 pixels per embryo in H2O2 content; and a DNA tail of 209 microm versus 105 microm. In addition, for embryos cultured under 20% O2, there were also differences (P < 0.05) between those exposed to 0 microM versus 50 microM of Vit-E: 28% versus 40% rate of development to the blastocyst stage; 28.9 cells versus 35.9 cells in the expanded blastocyst; 122 pixels versus 95 pixels per embryo (H2O2 content); and 215 microm versus 97 microm length of the DNA tail. Therefore, a low O2 concentration during in vitro culture of porcine embryos decreased the H2O2 content and, as a consequence, reduced DNA fragmentation, and, thereby, improved developmental ability.

Protein Supplementation and the Incidence of Apoptosis and Oxidative Stress in Mouse Embryos

OBJECTIVE

To estimate the effect of protein supplementation of culture media on reactive oxygen species production and incidence of apoptosis in preimplantation mouse embryos.

METHODS

A total of 72 two-cell mouse embryos were cultured in human tubal fluid (HTF) alone (HTF-alone, control) and 71 embryos in HTF with protein supplementation (10% serum substitute supplement; HTF-SSS) for 72 hours. Total cell number per embryo was determined by staining with Hoechst 33258. Allocation of inner cell mass and trophectoderm in blastocysts and incidence of apoptosis were determined by confocal microscopy. Levels of reactive oxygen species in culture media were measured by chemiluminescence assay using luminol as probe.

RESULTS

Blastocyst development, total cell number, and the inner cell mass/trophectoderm ratio were similar between the 2 groups. The blastocyst hatching rate was significantly higher in the HTF-SSS group than in the HTF-alone group (20% compared with 4%, P = .007). Level of reactive oxygen species was significantly higher in HTF-alone compared with HTF-SSS at 24 hours (median and interquartile range 28 [13, 43] compared with 0 [0, 1], P = .02), 48 hours (24 [21, 26] compared with 2 [1, 2], P = .02), and 72 hours (26 [9, 32] compared with 2 [2, 3], P = .03). The incidence of apoptosis in blastocysts cultured in HTF-SSS was significantly lower than those in HTF-alone group (mean +/- standard deviation 2.38 +/- 0.68 and 5.81 +/- 1.11, respectively, P = .001).

CONCLUSION

Protein supplementation of culture media improves the hatching rate and reduces reactive oxygen species levels and the incidence of apoptosis in mouse preimplantation embryos.

Addition of β-mercaptoethanol or Trolox® at the morula/blastocyst stage improves the quality of bovine blastocysts and prevents induction of apoptosis and degeneration by prooxidant agents

This study was conducted to evaluate the effect of beta-mercaptoethanol (a stimulator of glutathione synthesis) and Trolox (an hydrosoluble analogue of Vitamin E) on bovine embryos cultured from the morula stage (Day 5 post-insemination; pi) under oxidative stress conditions. Culture of embryos with increased doses of Trolox showed a dose-dependent embryotoxicity on Day 8 pi. The use of 400 microM Trolox as well as beta-mercaptoethanol at 100 microM prevented at least partly (P < 0.05) the prooxidant-induced blastocyst degeneration on Day 8. Hatching rates of surviving blastocysts were significantly increased by both antioxidants and beta-mercaptoethanol alone improved their mean cell numbers, which was significant in the ICM (P < 0.05). Analysis of their effect on Day 7 pi showed that both the antioxidants significantly reduced the prooxidant-induced apoptosis and beta-mercaptoethanol diminished the physiological level of apoptosis as well as it stimulated the glutathione synthesis (P < 0.05). In addition, a comparison between in vitro- and in vivo-produced embryos showed that the levels of apoptosis were similar at the same age post-insemination (morulae and blastocysts) but increased steadily with the embryonic age in in vitro ones. In conclusion, beta-mercaptoethanol and Trolox added separately from the morula stage protected embryos against oxidative stress and improved the quality of the resulting blastocysts.

Effects of thioredoxin on the preimplantation development of bovine embryos

Thioredoxin (TRX) is an ubiquitous protein disulfide reductase, which is known to be involved in the implantation development of mouse embryos. In the present study, recombinant human TRX was used to evaluate its effect on the promotion of preimplantation development of bovine embryos derived from in vitro maturation and fertilization. Supplementation of the medium 24h post insemination with TRX significantly (P<0.05) enhanced the frequency of development to the blastocyst stage in 5% O(2) concentration. The optimal concentration was 0.5 microg/ml (P<0.05, compared with 0, 0.1 and 1.0 microg/ml). This effect of TRX was evident only when added around the time of the first cleavage stage (24 h post insemination); no promotion was found with treatment at 6h (one-cell) or 44 h (six- to eight-cell) after insemination. Moreover, it is of interest that even with the best combination of the dose and timing of TRX treatment (0.5 microg/ml, at 24 h post insemination), no promotion of development was observed when embryos were cultured under 20% O(2). However, a preincubation of TRX in the culture medium under 20% oxygen for 24h did not diminish the promoting effect in the subsequent TRX treatment under optimal conditions, thus suggesting that the possible oxidation of TRX alone may not be the reason for the disappearance of the effect under a high oxygen concentration. These results indicate that TRX does improve the development of bovine embryos in vitro, though unlike the general reducing reagents such as beta-mercaptoethanol or cysteamine, TRX may have to exert its effect at specific times and in more physiologic oxygen environments.

Antioxidant requirements for bovine oocytes varies during in vitro maturation, fertilization and development

Antioxidants may be beneficial additives to synthetic culture media because these well defined media lack serum or other macromolecules that serve as reactive oxygen species scavengers. In this study, three separate experiments were performed to determine the effects of antioxidants on the development of oocytes to the morula and blastocyst stage when added during in vitro maturation (IVM) of bovine oocytes, during in vitro fertilization (IVF), and during embryo culture for the first 72 h of the development period. Bovine oocytes were matured, fertilized (under 20% O(2)), and embryos were cultured (under 7% O(2)) in defined conditioned medium in vitro with or without supplementation with the antioxidant cysteine, N-acetyl-L-cysteine (NAC), catalase and superoxide dismutase (SOD). Significant improvements in the proportion of oocytes undergoing morula and blastocyst development (33.3% versus 20.3%, P<0.05) were achieved when cysteine (0.6 mM) was added to the maturation medium as compared to control medium without antioxidant supplementation. However, the addition of NAC (0.6mM), catalase (5 or 127 U/ml) or SOD (10 or 1000 U/ml) to the maturation medium did not improve the proportion of oocytes undergoing morula and blastocyst development. During the IVF period, addition of antioxidants (cysteine or NAC 0.6mM, catalase 127U/ml, SOD 100U/ml) significantly reduced the subsequent rate of bovine embryo development to the morula and blastocyst stage (P<0.05). In a defined medium for embryo culture (7% O(2)), the addition of cysteine improved the development of bovine embryos while NAC, catalase and SOD had no positive effect on embryonic development. Our study showed that medium supplementation with cysteine during IVM and in vitro culture (IVC) improved the rate of bovine embryo development, in contrast to extracellular antioxidants like catalase and SOD that caused no improvement.

Cysteamine supplementation during in vitro maturation and embryo culture: a useful tool for increasing the efficiency of bovine in vitro embryo production

Cysteamine when added during in vitro maturation (IVM) or in vitro embryo culture (IVC) stimulates glutathione (GSH) synthesis and improves embryo developmental rates. This suggests that GSH synthesis is decreased in the in vitro produced embryo. The present study was carried out to evaluate if addition of cysteamine to culture medium at the same time, during IVM and IVC of bovine oocytes, may promote an overall improvement on the developmental rate and embryo quality. Oocytes were matured in TCM 199 supplemented with 10% (v/v) fetal calf serum, hormones, and 0 or 100 microM of cysteamine for 24 hr. After IVM, the oocytes were fertilized (day 0). Day 2 embryos (2-8 cell) were washed and transferred to fresh IVC medium supplemented with 0, 25, 50, or 100 microM of cysteamine and cultured for 48 hr. After this, embryos were cultured in IVC medium without cysteamine until day 8 of IVC. In the present study, we confirmed our previous results by demonstrating that the percentage of embryos that developed to the blastocyst stage was significantly higher (P < 0.05) when 100 microM of cysteamine was added during IVM, and this was further improved when 100 and 50 microM of cysteamine where present during IVM and IVC, respectively (P < 0.05). After cryopreservation, no differences were observed on embryo development, but a significant increase on embryo hatching was found between unsupplemented and supplemented oocytes with 100 and 50 microM of cysteamine during IVM and IVC, respectively (P < 0.05). We can conclude that GSH synthesis stimulation during bovine IVM with cysteamine, concomitant with GSH stimulation during IVC, will be a useful and simple tool for increasing the efficiency of in vitro bovine embryo production.

Prevalence of apoptosis and inner cell allocation in bovine embryos cultured under different oxygen tensions with or without cysteine addition

Supraphysiological oxygen tension during embryo culture can generate reactive oxygen species (ROS), which can induce apoptosis. Antioxidants such as thiol compounds (cysteine, cysteamine) can be used to prevent ROS damage to the embryo. The purpose of this study was to evaluate the prevalence of apoptosis during bovine embryo development and to evaluate the effect of the presence or absence of cysteine 0.6 mM in modified synthetic oviduct fluid (mSOF) on in vitro produced cattle embryos cultured under two different oxygen tensions (5% O2 versus 20% O2). Effects were assessed by checking embryo development at Days 7, 8 and 9 and by evaluating Day 9 hatched blastocysts for differentiation by means of differential staining and for apoptosis by means of TUNEL-assay. Apoptotic cells were present in 94% of Day 7 blastocysts and in 100% of Days 8 and 9 blastocysts. Cysteine addition affected Day 8 blastocyst rates in a negative way (P < 0.05) regardless of the oxygen tension. In fact, cysteine addition to the mSOF culture medium had a negative effect upon embryo development in terms of blastocyst rates, hatching rates and apoptotic cell ratio. Embryos cultured under 5% O2 in the presence of cysteine, however, possessed significantly higher numbers of ICM cells. This finding corroborates the theoretical assumption that antioxidants are beneficial for ICM development.

Promoting effect of beta-mercaptoethanol on in vitro development under oxidative stress and cystine uptake of bovine embryos

The effects of beta-mercaptoethanol (beta-ME) on in vitro development under oxidative stress and cystine uptake of bovine embryos were investigated. Bovine 1-cell embryos obtained by in vitro fertilization were cultured in TCM-199 or synthetic oviductal fluid (SOF) in 20% O(2) supplemented with beta-ME. Addition of beta-ME significantly (P < 0.01) promoted embryo development when cultured in both TCM-199 and SOF under high levels of O(2), to almost the same rates when they were cultured in 5% O(2). To investigate whether the growth-promoting effect of beta-ME was related to cystine uptake, which is an important amino acid for intracellular glutathione (GSH) synthesis, 1-cell, 8-cell, morula, and blastocyst stage embryos were incubated in cystine, cysteine-free TCM-199 containing radioisotope-labeled cystine supplemented with or without beta-ME. It was found that cystine uptake was consistently low in each embryo stage incubated without beta-ME. In contrast, addition of beta-ME significantly (P < 0.05 to 0.0001) promoted cystine uptake in each stage of embryo development. This increase of cystine uptake by beta-ME was significantly inhibited by supplementation of buthionine sulfoximine, a specific inhibitor of GSH biosynthesis (P < 0.0001). High-performance liquid chromatography (HPLC) analysis clearly revealed a decrease of cystine in culture medium after supplementation by beta-ME, thereby forming another peak. HPLC analysis also showed the incorporated cystine by supplementation of beta-ME was possibly metabolized for GSH synthesis in the embryos. These results indicate that beta-ME has a protective effect in embryo development against oxidative stress and that the effect of beta-ME is associated with the promotion of cystine uptake of low availability in embryos.

Fertilizability and developmental capacity of bovine oocytes cultured individually in a chemically defined maturation medium

This study investigated effects of adding hypotaurine (HT), beta-merocaptoethanol (beta-ME), or both into a chemically defined maturation medium (TCM-199 containing 0.1% polyvinyl alcohol: PVA) on maturation, fertilization and development of individually (single) cultured bovine oocytes. Mean GSH concentration in the oocytes cultured in the medium supplemented with either beta-ME (1.11 +/- 0.05 nM) or HT plus beta-ME (0.97 +/- 0.03 nM) was significantly (P < 0.05) higher than that in the medium containing PVA alone (0.75 +/- 0.03 nM). Adding beta-ME showed a significantly (P < 0.05) higher rate of the second metaphase stage (93.6 +/- 3.3%) than in the medium containing PVA alone (single-control) (65.2 +/- 7.9%). Adding both HT and beta-ME showed significantly (P < 0.05) higher rates (92.6 +/- 2.7%) of normal fertilization than did adding HT alone (63.5 +/- 4.6%). Also, adding both HT and beta-ME significantly (P < 0.05) lowered the polyspermy rate than did adding HT alone. Adding either beta-ME or both HT and beta-ME showed no significant difference in cleavage. Blastocyst development did not improve significantly adding either HT, beta-ME or both, although beta-ME alone or HT plus beta-ME tended to result in a higher rate of blastocysts (6.4 and 6.8%, respectively) than resulted without additives (1.6%). Our results show that adding beta-ME to a chemically defined maturation medium increased the intracellular GSH level of bovine oocytes cultured individually, and can improve the maturation rate leading to the blastocyst stage throughout in vitro production.

Exogeneous substances affecting development of in vitro-derived bovine embryos before and after embryonic genome activation

Three experiments were conducted to evaluate how exogenous substances [fetal bovine serum (FBS), arachidonic acid (AA), glutathione (GSH), platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF), fibroblast growth factor (FGF), insulin, transferrin and selenium (ITS)] affect preimplantation bovine embryo development. Cumulus-oocyte complexes (COC) were matured and fertilized in vitro, and their development was monitored up to 192 h post insemination in a two-step culture system. In Experiment 1, inseminated oocytes were cultured in modified bovine embryo culture medium (mBECM) supplemented with FBS or BSA for up to 60 h post insemination, and the resultant 8-cell embryos were then cultured singly in mBECM supplemented with AA+GSH+PDGF+TGF. More (P<0.005) blastocysts were derived from 8-cell embryos produced in media containing FBS than BSA. In Experiment 2, the 8-cell embryos produced in mBECM supplemented with FBS were cultured singly in mBECM as follows: 1) no supplementation; 2) AA and GSH or 3) AA, GSH, PDGF and TGF. Compared with no supplementation, a significant (P<0.05) increase in the proportion of 16-cell embryos and morulae was obtained after the addition of either AA+GSH or AA+GSH+PDGF+TGF. In Experiment 3, oocytes were cultured singly in mBECM as follows: 1) no supplementation; 2) AA+GSH+PDGF+TGF; 3) AA+GSH+PDGF+TGF and FGF; 4) AA+GSH+PDGF+TGF and ITS; 5) AA+GSH+PDGF+TGF, FGF and ITS or 6) FBS. Eight-cell embryos grown in each system were subsequently cultured singly in mBECM with AA+GSH+PDGF+TGF. More (P<0.05) 16-cell embryos were obtained in medium supplemented with either AA+GSH+PDGF+TGF and ITS or FBS than in unsupplemented medium. Fewer (P<0.05) oocytes developed to the 8-cell stage with the addition of AA+GSH+PDGF+TGF and FGF than without. In conclusion, embryo development to the blastocyst stage is regulated by exogenous AA, GSH, PDGF, FGF and ITS in a stage-specific manner.

The importance of having high glutathione (GSH) level after bovine in vitro maturation on embryo development effect of beta-mercaptoethanol, cysteine and cystine

Supplementation of IVM medium with cysteamine, beta-mercaptoethanol, cysteine and cystine induced bovine oocyte glutathione (GSH) synthesis, but only the effect of cysteamine on the developmental competence of these oocytes was tested. During IVM of sheep oocytes, cysteamine but not beta-mercaptoethanol increased embryo development. However, it is not known how long the high intracellular oocyte GSH levels obtained after IVM with thiol compounds, can be maintained. Thus, the present study was carried out to evaluate the effects of supplementing maturation medium with 100 microM beta-mercaptoethanol, 0.6 mM cysteine and 0.6 mM cystine on 1) intracellular GSH level after IVM, 2) after IVF, 3) in 6 to 8-cell embryos and 4) on embryo development. In oocytes after IVM and in presumptive zygotes after IVF, intracellular GSH levels were significantly higher in the treated groups (P < 0.05). While, GSH content in 6 to 8-cell embryos was similar among treatment groups (P > 0.05). Differences in cleavage rates and the percentage of embryos that developed to morula and blastocyst stages were significantly higher (P < 0.05) for treated oocytes than for those matured in the control medium. We conclude from the results that the high intracellular GSH levels after induction of GSH synthesis in bovine IVM by thiol compounds remain during IVF and are still present at the beginning of IVC, improving developmental rates. Moreover, the results indicate that this metabolic pathway is an important component of the cytoplasmic maturation process that affects the subsequent steps of in vitro embryo production.

Coenzyme Q(10) in submicron-sized dispersion improves development, hatching, cell proliferation, and adenosine triphosphate content of in vitro-produced bovine embryos

Coenzyme Q(10) (CoQ(10)) is an essential component of the plasma membrane ion transporter (PMIT) system and of the electron transport chain in the inner mitochondrial membrane. Because of its intrinsic functions in cell growth and energy metabolism (ATP synthesis), and its protective effects against oxidative stress, CoQ(10) is a good candidate for supporting growth of cells in culture. However, because of its quinone structure, CoQ(10) is extremely lipophilic and practically insoluble in water. We used a specific technology to prepare a submicron-sized dispersion of CoQ(10), inhibiting re-crystallization by a stabilizer. This dispersion, which exhibits a very large specific surface area for drug dissolution, was tested as a supplement for the in vitro culture of bovine embryos in a chemically defined system. The rate of early cleavage of embryos (5- to 8-cell stages) was evaluated 66 h postinsemination (hpi) and was highest in medium supplemented with 30 or 100 microM CoQ(10) (66.5 +/- 0.8% and 68.7 +/- 1.1%, respectively) and lowest in 10 microM CoQ(10) (55.3 +/- 0.8%). The proportions of oocytes developing to blastocysts by 186 hpi were 19.0 +/- 0.6% and 25.2 +/- 0.3% in medium supplemented with 10 microM and 30 microM CoQ(10), respectively, and were significantly (p < 0.001) higher than those obtained with the equivalent amounts of stabilizer (9.9 +/- 0.4% and 11.3 +/- 0.4%). In the presence of 30 microM CoQ(10), significantly (p < 0.001) more blastocysts hatched by 210 hpi than in the equivalent amount of stabilizer (31.8 +/- 1.3 vs. 8.4 +/- 2.2). Expanded blastocysts produced in the presence of 30 microM CoQ(10) had significantly (p < 0.01) more inner cell mass cells and trophectoderm cells, and a significantly (p < 0.001) increased ATP content as compared to expanded blastocysts produced in the presence of the corresponding amount of stabilizer. Our results show that noncrystalline CoQ(10) in submicron-sized dispersion supports the development and viability of bovine embryos produced in a chemically defined culture system.

Effect of protein supplementation and presence of an antioxidant on the development of bovine zygotes in synthetic oviduct fluid medium under high or low oxygen tension

The aim of this study was to investigate the effect of protein supplementation of culture medium and the presence of a putative antioxidant on bovine zygote development under 5% (low) and 20% (high) O2. In Experiment 1, presumptive zygotes (n=992) were cultured in synthetic oviduct fluid (SOF) alone or supplemented with 3 mg/mL PVP, 3 mg/mL BSA (SOFB), and/or 10% FCS (SOFBF) in 5% CO2, 5% O2, 90% N2. In Experiment 2, zygotes (n=1916) were cultured in SOF, SOFB or SOFBF with or without taurine under high and low O2. In Experiment 1, presence of BSA or BSA plus FCS significantly increased the speed of development compared to SOF or SOF+PVP. Blastocyst quality was also improved, as evidenced by increased hatching rate and cell numbers. In Experiments 2, taurine had no effect on development irrespective of oxygen concentration or protein supplementation. In conclusion, the presence of protein in the culture medium and culture under reduced O2 significantly improved embryo development. Taurine had no effect on development.

Improvement of in vitro co-culture systems for bovine embryos using a low concentration of carbon dioxide and medium supplemented with beta-mercaptoethanol

Two experiments were conducted to investigate the effect of carbon dioxide (CO2) gas atmosphere and beta-mercaptoethanol on the development of bovine embryos in an in vitro co-culture system. In Experiment 1, in vitro-matured bovine oocytes were inseminated and then co-cultured with cumulus cells in culture medium (CM; 25 mM HEPES buffered TCM-199 supplemented with 5% superovulated cow serum and 0.5 mM sodium pyruvate). Oocytes matured and fertilized in 2 or 5% CO2 in air exhibited similar cleavage rates, but the proportion of embryos that developed to the blastocyst stage was higher for embryos co-cultured in 2 versus 5% CO2 in air. In Experiment two, 4- to 8-cell embryos produced under the condition of 2% CO2 in air were co-cultured with cumulus cells in CM supplemented with various levels of beta-mercaptoethanol (0, 5, 10, 50 microM). The percentage of embryos that developed to the blastocyst stage in CM with 10 microM beta-mercaptoethanol was higher (P<0.05) than that of embryos co-cultured with 0 or 50 microM beta-mercaptoethanol. These results indicate that cumulus cell co-culture in an atmosphere of 2% CO2 in air has a marked stimulatory effect on in vitro development of bovine embryos and that addition of beta-mercaptoethanol to the co-culture medium 2 d after insemination improved the in vitro development of bovine 4- to 8-cell embryos to the blastocyst stage.

Cryopreservation of bovine pre-morula-stage in vitro matured/in vitro fertilized embryos after delipidation and before use in nucleus transfer

We have determined that the tolerance of in vitro matured/in vitro fertilized (IVM/IVF) bovine embryos to cryopreservation at the pre-morula stage can be improved by removal of cytoplasmic lipid droplets by centrifugation. Nucleus transfer was also performed using cryopreserved, delipated (lipid droplets removed) 8- to 16-cell-stage blastomeres of IVM/IVF embryos as donor nuclei. In vitro developmental ability of the delipated embryos to the blastocyst stage (20 of 126) was found to be equal to that of undelipated embryos (35 of 176); and of 53 delipated embryos cryopreserved at the 8- to 16-cell stage, 12 developed into blastocysts in vitro after thawing. On the other hand, only 2 of 43 undelipated embryos and 5 of 59 sham-operated embryos survived (p < 0.05). When blastomeres isolated from cryopreserved, delipated 8- to 16-cell-stage embryos were used for nucleus transfer, 57 of 80 successfully fused with enucleated oocytes, which was significantly lower than the fusion rate obtained with blastomeres of unfrozen, undelipated embryos (93 of 104, p < 0.01). However, the developmental rate to the blastocyst stage for nucleus transfer embryos reconstituted with frozen, delipated blastomeres (9 of 57) was not different from that of the nucleus transfer embryos with unfrozen, undelipated embryos (23 of 93). These results confirm that removal of cytoplasmic lipid droplets from bovine IVM/IVF zygotes allows for successful cryopreservation at the 8- to 16-cell stage and that blastomeres from these embryos can be used as donors of karyoplasts for nucleus transfer.

Development of in-vitro-derived bovine embryos cultured in 5% CO2 in air or in 5% O2, 5% CO2 and 90% N2

To evaluate the effects of a three gas mixture of 5% O2, 5% CO2 and 90% N2 (OCN) on preimplantation embryo development, bovine in-vitro fertilization (IVF) oocytes were cultured in a defined medium (mBECM) with various supplements either under 5% CO2 in air or under OCN. When cultured in mBECM alone, embryo development was significantly stimulated in OCN compared to 5% CO2 in air (experiment 1). In the OCN atmosphere, blastocyst formation was further increased after addition of fetal bovine serum (FBS; 10%) or FBS + cumulus granulosa cells (CGC) to mBECM. The ratio of blastocysts to 8-cell embryos, number of hatched blastocysts and embryo diameter were markedly increased, and zona thickness was decreased after FBS addition. However, development up to the morula stage was fully supported by mBECM alone. There was no significant effect of beta-mercaptoethanol (ME; 10 microM) in OCN. In the 5% CO2 atmosphere, embryo development was significantly (P < 0.05) enhanced after addition of FBS + CGC + ME. In experiment 2, in OCN, FBS added at 60 h post-insemination was effective in stimulating blastocyst formation, but changes in medium volume per oocyte from 13.6 to 1.36 microliters had only a marginal effect. In conclusion, OCN gas mixture provides a suitable atmosphere for early embryo growth in vitro and mBECM + FBS in the optimal culture medium under this atmosphere.

Presence of beta-mercaptoethanol can increase the glutathione content of pig oocytes matured in vitro and the rate of blastocyst development after in vitro fertilization

The present study examined the effect of beta-mercaptoethanol (BME) during in vitro maturation (IVM) of pig oocytes on in vitro fertilization (IVF) parameters, intracellular glutathione (GSH) concentration, subsequent embryo development and blastocyst cell numbers. Cumulus-oocyte complexes were cultured in North Carolina State University (NCSU)-23 medium containing porcine follicular fluid, cysteine, hormonal supplements and 0 to 50 microM BME for 20 to 22 h. They were then cultured in the same medium but without hormonal supplements for an additional 20 to 22 h. After culture, cumulus-free oocytes were coincubated with frozen-thawed spermatozoa for 5 to 6 h. Putative embryos were transferred to NCSU-23 containing 0.4% BSA and cultured for 144 h (Experiment 1). In comparisons between the presence or absence of BME, no differences were observed in fertilization parameters. At 48 h, no mean differences were found in cleavage rates. However, at 144 h, compared with no addition (26%), the presence of 12.5 and 25 microM BME increased (P < 0.05) the proportion of blastocysts in a dose-dependent manner (34 and 41%). Further increase from 25 to 50 microM BME reduced (P < 0.05) the blastocyst development rate. Blastocysts derived from oocytes matured with 25 microM BME had the highest (P < 0.05) trophectoderm (TE) and total cell numbers. No difference was found in inner cell mass (ICM) cells among treatments. In Experiment 2, after IVM, oocytes were fixed to analyze the GSH concentration. Compared to no addition, a higher (P < 0.01) level of GSH was found in oocytes matured with 25 microM BME. Compared with 25 microM BME, GSH was low (P < 0.05) at 50 microM BME. The results show that at certain concentrations BME in IVM medium has beneficial effects on subsequent embryo development, and is correlated with intracellular GSH level in pig oocytes.

Improved development of in vitro-derived bovine embryos by use of a nitric oxide scavenger in a cumulus-granulosa cell coculture system

This study was conducted to examine the hypothesis that nitric oxide (NO) affects prehatching development of bovine oocytes fertilized in vitro. In experiment 1, inseminated oocytes were cultured in a cumulus-granulosa cell (CG) coculture system to which 0.008 or 0.04 mM of sodium nitroprusside (SNP), a spontaneous NO releaser, was added at 18 or 60 hr postinsemination. Embryo development was greatly (P < 0.001) inhibited by the addition of SNP, regardless of time of addition or SNP concentration. In experiment 2, eight-cell embryos were cultured singly in a defined medium, to which 0.0016, 0.008, or 0.04 mM of SNP was added. Development to the blastocyst stage was greatly (P < 0.001) decreased after addition of SNP compared with no addition. Higher (P < 0.02) concentration of NO metabolites was found in developmentally arrested embryos than in developing embryos at 144 hr postinsemination (experiment 3). In experiment 4, blastocyst formation of oocytes cocultured with CGs was significantly (P < 0.02) increased after addition of hemoglobin (Hb, 1 microgram/ml), an NO scavenger. Prehatching development of oocytes was significantly (P < 0.05) increased after addition of Hb at different time intervals (18, 60, or 144 hr postinsemination) in experiment 5. Embryo development was not enhanced by Hb addition to the culture medium in the absence of CGs (experiment 6). Prehatching development of eight-cell embryos derived from a Hb-containing culture system was not promoted by the further addition of Hb after transfer of the embryos to a defined and CG-free single-embryo culture system (experiment 7). In conclusion, NO, which may be secreted from CGs, has an inhibitory role in prehatching development of bovine oocytes fertilized in vitro, and use of an NO scavenger, Hb, in a coculture system enhances blastocyst formation.

Promotion of development of bovine embryos produced in vitro by addition of cysteine and beta-mercaptoethanol to a chemically defined culture system

The aim of this research was to determine the effects of L-cysteine and beta-mercaptoethanol on the in vitro development of bovine embryos that had been produced in vitro. A 2 x 3 factorial arrangement of treatments was used to evaluate the effect of 0.63 or 6.9 microM L-cysteine and 0, 10, or 100 microM beta-mercaptoethanol on the development of bovine embryos in a chemically defined medium. Embryos containing 6 to 8 cells were randomly allocated to one of the six treatment combinations and were cultured for 7 d. Both beta-mercaptoethanol and L-cysteine increased the number of embryos that reached the blastocyst stage of development, although no interaction was observed between the compounds. Embryos that were cultured in the presence of beta-mercaptoethanol had more cells at the blastocyst stage than did embryos cultured in medium without beta-mercaptoethanol. These findings provide evidence that beta-mercaptoethanol and L-cysteine promote increased embryonic development and that beta-mercaptoethanol increases the number of cells in bovine embryos produced in vitro and cultured in a cell-free, protein-free culture system.