Transporting bovine oocytes in a medium supplemented with different macromolecules and antioxidants: Effects on nuclear and cytoplasmic maturation and embryonic development in vitro

Melatonin protects oogenesis from hypobaric hypoxia-induced fertility damage in mice

Environmental hypoxia adversely affects reproductive health in humans and animals at high altitudes. Therefore, how to alleviate the follicle development disorder caused by hypoxia exposure and to improve the competence of fertility in plateau non-habituated female animals are important problems to be solved urgently. In this study, a hypobaric hypoxic chamber was used for 4 weeks to simulate hypoxic conditions in female mice, and the effects of hypoxia on follicle development, proliferation and apoptosis of granulosa cells, reactive oxygen species (ROS) levels in MII oocyte and 2-cell rate were evaluated. At the same time, the alleviating effect of melatonin on hypoxic exposure-induced oogenesis damage was evaluated by feeding appropriate amounts of melatonin daily under hypoxia for 4 weeks. The results showed that hypoxia exposure significantly increased the proportion of antral follicles in the ovary, the number of proliferation and apoptosis granulosa cells in the follicle, and the level of ROS in MII oocytes, eventually led to the decline of oocyte quality. However, these defects were alleviated when melatonin was fed under hypoxia conditions. Together, these findings suggest that hypoxia exposure impaired follicular development and reduced oocyte quality, and that melatonin supplementation alleviated the fertility reduction induced by hypoxia exposure.

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.

Supplementation of media with gamma-oryzanol as a novel antioxidant to overcome redox imbalance during bovine oocyte maturation in vitro

This study evaluated the effect of supplementing IVM media with γ-oryzanol (ORY), a nutraceutical derived from rice bran oil, on the development of bovine oocytes and hindering the compromising effect of redox imbalance. An in vitro model of the bovine cumulus-oocyte complex was used for the evaluation of nuclear maturation and development. Antioxidant activity was investigated by assessing the level of ROS (Reactive Oxygen Species) and GSH (glutathione) in oocytes and quantitative changes in gene expression in matured oocytes and their respective cumulus cells. ORY supplementation increased the proportion of MII oocytes, cleaved embryos, and total blastocysts (p < .05) and was linked to higher and lower levels of intracellular GSH and ROS, respectively (p < .05). The treated oocytes and their respective cumulus-granulosa cells showed a modulation in the expression of genes related to apoptosis (downregulation of BAX and CHOP) and oxidative stress (upregulation of NRF2, CAT, and SOD). Also, relative upregulation of OCT-4 and IGF2R in treated oocytes was concomitant with higher subsequent development in terms of cleavage and total blastocyst rates (p < .05). Based on our findings, it appears that ORY supplementation can improve the nuclear maturation and development of bovine oocytes into blastocysts and augment their enzymatic and non-enzymatic antioxidant systems, maintaining the Redox balance and high enzymatic activity against ROS generation.

Effects of cyclic adenosine monophosphate modulating agents during oocyte pre-maturation and the role of melatonin on in vitro maturation of bovine cumulus-oocyte complexes

This study investigated the effects of cyclic adenosine monophosphate modulating during cumulus-oocyte complexes (COCs) pre-maturation and the role of melatonin on in vitro maturation (IVM) of bovine COCs. In experiment one, COCs were pre-matured for 8 h in control medium or with 3-isobutyl-1-methylxanthine (IBMX) and forskolin, IBMX and C-type natriuretic peptide, c-type natriuretic peptide and forskolin or IBMX, forskolin and c-type natriuretic peptide. Then, meiotic progression was evaluated. In experiment two, COCs were pre-matured, followed by IVM in control medium alone or with 10-6, 10-7 or 10-8 M melatonin. After IVM, chromatin configuration, transzonal projections (TZPs), reactive oxygen species, mitochondrial distribution, ultrastructure and mRNA expression for antioxidant enzymes were evaluated. In experiment 1, COCs pre-matured with both C-type natriuretic peptide and forskolin or C-type natriuretic peptide, forskolin and IBMX had lower meiotic resumption rate when compared to control. Considering that IBMX had not an additional effect to potentiate inhibition of meiotic resumption, a combination of C-type natriuretic peptide and forskolin was chosen. In experiment 2, COCs matured with 10-8 M melatonin had greater rates of meiotic resumption when compared to the other treatments (P < 0.05). The COCs matured with 10-7 or 10-8 M melatonin had greater mitochondrial activity (P < 0.05), while those matured with 10-6 or 10-8 M of melatonin had greater levels of TZPs. Ultrastructure of oocyte and cumulus cells after IVM with melatonin was relatively well preserved. COCs matured with 10-8 M melatonin increased mRNA expression for superoxide dismutase (SOD) and catalase (CAT) (P < 0.05), when compared to non-cultured and pre-matured COCs, respectively. In conclusion, bovine COC pre-maturation with C-type natriuretic peptide and forskolin, followed by IVM with 10-8 M melatonin improves meiotic resumption rates, TZPs, mitochondrial distribution and mRNA expression for SOD and CAT.

ROS-CCL5 axis recruits CD8+ T lymphocytes promoting the apoptosis of granulosa cells in diminished ovary reserve

Follicular atresia was initiated with the apoptosis of granulosa cells (GCs) mostly mediated by oxidative stress (OS). Our previous studies found that the number of CD8⁺ T cells and proportion of CD8⁺/CD4⁺ T cells increased in the follicles of diminished ovary reserve (DOR). However, the mechanism was still poorly explored. Herein, our results showed that the level of H₂O₂ in follicular fluid (FF) and reactive oxygen species (ROS) in GCs were increased, while the expression of SOD1, SOD2 and GPX1 was down-regulated in GCs with DOR. In addition, we found that OS within a certain range promoted the expression of CCL5 in GCs, which facilitated the infiltration of CD8⁺ T cells to the follicles. In vitro co-culture experiment showed that CD8⁺ T cells inhibited GCs proliferation and promoted their apoptosis through intrinsic apoptosis pathway. Maraviroc, the CCR5 antagonist, alleviated CCL5-induced immune attack of CD8⁺ T cells. Our results indicated that ROS-CCL5 axis recruited CD8⁺ T cells into FF resulting in the apoptosis of GCs in DOR. This has further implications for the understanding of the pathology of DOR and searching for the therapeutic management of this disease.

Mechanisms of action of non-enzymatic antioxidants to control oxidative stress during in vitro follicle growth, oocyte maturation, and embryo development

In vitro follicle growth and oocyte maturation still has a series of limitations, since not all oocytes matured in vitro have the potential to develop in viable embryos. One of the factors associated with low oocyte quality is the generation of reactive oxygen species (ROS) during in vitro culture. Therefore, this review aims to discuss the role of non-enzymatic antioxidants in the control of oxidative stress during in vitro follicular growth, oocyte maturation and embryonic development. A wide variety of non-enzymatic antioxidants (melatonin, resveratrol, L-ascorbic acid, L-carnitine, N-acetyl-cysteine, cysteamine, quercetin, nobiletin, lycopene, acteoside, mogroside V, phycocyanin and laminarin) have been used to supplement culture media. Some of them, like N-acetyl-cysteine, cysteamine, nobiletin and quercetin act by increasing the levels of glutathione (GSH), while melatonin and resveratrol increase the expression of antioxidant enzymes and minimize oocyte oxidative stress. L-ascorbic acid reduces free radicals and reactive oxygen species. Lycopene positively regulates the expression of many antioxidant genes. Additionally, L-carnitine protects DNA against ROS-induced damage, while acteoside and laminarin reduces the expression of proapoptotic genes. Mogrosides increases mitochondrial function and reduces intracellular ROS levels, phycocyanin reduces lipid peroxidation, and lycopene neutralizes the adverse effects of ROS. Thus, it is very important to know their mechanisms of actions, because the combination of two or more antioxidants with different activities has great potential to improve in vitro culture systems.

Effects of different concentrations of eugenol in maturation medium on bovine oocytes, oxidative status and preimplantation embryos

ContextEugenol is a bioactive compound with defined attributes, including a role in reducing oxidative stress. Therefore, it is an interesting candidate for in vitro embryo production that has an environment that favours the formation of reactive oxygen species.AimThe objective of the study was to evaluate different concentrations of eugenol in bovine oocytes during in vitro maturation to observe the oxidative status and embryonic development.MethodsOocytes were allocated into five groups: control (without antioxidant), 100μM cysteamine, 83μM eugenol (E83), 100μM eugenol and 120μM eugenol. Three experiments were performed with 23 replicates. Oocytes were evaluated for metaphase II, first polar body, cytoplasmic maturation, cumulus cell expansion and viability. Oxidative status was measured by mitochondrial membrane potential, reactive oxygen species and glutathione. Oocytes were artificially activated and cultured in vitro.Key resultsThe presence of eugenol at 83μM improved the metaphase II rate compared with all treatments (P&lt;0.05). E83 and 100μM cysteamine improved first polar body extrusion, cumulus cell expansion, viability and mitochondrial aggregation rates (P&lt;0.05). All antioxidant treatments resulted in increased cytoplasmic maturation and decreased mitochondrial membrane potential (P&lt;0.05). Reactive oxygen species levels decreased, and glutathione levels increased with E83 and 100μM cysteamine treatments (P&lt;0.05). Finally, the E83 group increased the cleavage rates, embryo development, number of expanded blastocysts and number of blastomeres (P&lt;0.05).ConclusionsA low concentration of eugenol (83μM) is sufficient to generate a significant effect, attenuating the oxidative status and optimising in vitro maturation and embryo development.ImplicationsThis study provides information of a new natural antioxidant with defined concentration, 83μM eugenol, representing a lower cost alternative capable of improving the efficiency of in vitro embryo production in cattle.

Coenzyme Q10 ameliorates the quality of mouse oocytes during in vitro culture

Oxidative stress causes several diseases and dysfunctions in cells, including oocytes. Clearly, oxidative stress influences oocyte quality during in vitro maturation and fertilization. Here we tested the ability of coenzyme Q10 (CoQ10) to reduce reactive oxygen species (ROS) and improve mouse oocyte quality during in vitro culture. Treatment with 50 μM CoQ10 efficiently reduced ROS levels in oocytes cultured in vitro. The fertilizable form of an oocyte usually contains a cortical granule-free domain (CGFD). CoQ10 enhanced the ratio of CGFD-oocytes from 35% to 45%. However, the hardening of the zona pellucida in oocytes was not affected by CoQ10 treatment. The in vitro maturation capacity of oocytes, which was determined by the first polar body extrusion, was enhanced from 48.9% to 75.7% by the addition of CoQ10 to the culture medium. During the parthenogenesis process, the number of two-cell embryos was increased by CoQ10 from 43.5% to 67.3%. Additionally, treatment with CoQ10 increased the expression of Bcl2 and Sirt1 in cumulus cells. These results suggested that CoQ10 had a positive effect on ROS reduction, maturation rate and two-cell embryo formation in mouse oocyte culture.

Antioxidant Nobiletin Enhances Oocyte Maturation and Subsequent Embryo Development and Quality

Nobiletin is a polymethoxylated flavonoid isolated from citrus fruits with wide biological effects, including inhibition of reactive oxygen species (ROS) production and cell cycle regulation, important factors for oocyte in vitro maturation (IVM). Therefore, the objective of the present study was to evaluate the antioxidant activity of nobiletin during IVM on matured bovine oocyte quality (nuclear and cytoplasmic maturation; oocyte mitochondrial activity; intracellular ROS and glutathione (GSH) levels) and their developmental competence, steroidogenesis of granulosa cells after maturation, as well as quantitative changes of gene expression in matured oocytes, their cumulus cells, and resulting blastocysts. Bovine cumulus-oocyte complexes were in vitro matured in TCM-199 +10% fetal calf serum (FCS) and 10 ng/mL epidermal growth factor (EGF) (Control) supplemented with 10, 25, 50, or 100 μM of nobiletin (Nob10, Nob25, Nob50, and Nob100, respectively) or 0.1% dimethyl sulfoxide (CDMSO: vehicle for nobiletin dilution). A significantly higher percentage of matured oocytes in metaphase II was observed in Nob25 and Nob50 compared to other groups. Similarly, cleavage rate and cumulative blastocyst yield on Days 7 and 8 were significantly higher for Nob25 and Nob50 groups. Oocytes matured with 25 and 50 μM nobiletin showed a higher rate of migration of cortical granules and mitochondrial activity and a reduction in the ROS and GSH content in comparison with all other groups. This was linked to a modulation in the expression of genes related to metabolism (CYP51A1), communication (GJA1), apoptosis (BCL2), maturation (BMP15 and MAPK1), and oxidative stress (SOD2 and CLIC1). In conclusion, nobiletin offers a novel alternative for counteracting the effects of the increase in the production of ROS during IVM, improves oocyte nuclear and cytoplasmic maturation, and subsequent embryo development and quality in cattle.

Efficiency of different incubation systems for the in vitro production of bovine embryos

This study aimed to compare the efficiency of different incubation systems for in vitro embryo production in bovine. Oocytes/embryos were cultured in three incubators: conventional – CONV, mini bench – MINI and portable – PORT. After in vitro maturation (IVM), oocytes were verified for maturation rate. The remaining structures were submitted to in vitro fertilization and culture to verify cleavage (day 2) and blastocyst (day 7) rates. Reactive oxygen species (ROS) were evaluated in post-IVM oocytes and embryos (days 2 and 7) using arbitrary fluorescence units (AFUs). No significant difference (P>0.05) was observed for maturation rate. The CONV system (74.0%) produced the highest cleavage rate (P<0.05) when compared with PORT (59.5%), but similar (P>0.05) to MINI (65.0%). The same pattern and differences were observed for blastocyst rate: CONV (33.3%), MINI (32.3%) and PORT (21.9%). ROS levels were not different (P>0.05) in post-IVM oocytes: CONV (35.6±4.5), MINI (29.4±4.0) and PORT (35.6±4.5). For day-2 embryos, ROS levels were higher (P<0.05) in MINI (44.2±3.1) in comparison with CONV (27.7±3.7) and PORT (33.3±3.2). No significant difference (P>0.05) was observed in blastocysts. In conclusion, although it produced high ROS levels at day 2 of culture, the MINI system was as efficient as the CONV system for blastocyst production. This option may be an interesting and economical for the in vitro embryo industry.

Delaying meiotic resumption during transportation of bovine cumulus–oocyte complexes: effects on development, apoptosis and caspases activity of in vitro-produced embryos

This study examined the effects of meiosis inhibition during bovine oocyte transportation on developmental competence and quality of produced embryos. The transportation medium was supplemented with: 100 μM butyrolactone I (BL), 500 μM IBMX + 100 μM forskolin (mSPOM), 100 μM milrinone (MR) or follicular fluid (bFF), and was carried out in a portable incubator for 6 h. Next, oocytes were in vitro matured (IVM) for 18 h, without the meiotic inhibitors, with the exception of mSPOM group, in which was added 20 μM cilostamide. The three control groups were IVM with 10% fetal calf serum (FCS) (Control Lab FCS) or 0.6% bovine serum albumin (BSA) (Control Lab BSA) in a CO2 in air incubator or in the portable incubator with 0.6% BSA (Control Transp BSA). Higher cleavage rates (P < 0.05) were obtained in the Control Lab FCS group (84.5 ± 5.3%) compared with the other groups (59.6 ± 3.4% to 70.9 ± 2.3%). Embryonic development was higher (P < 0.05) in the Control Lab FCS group (39.8 ± 4.7%) than in the Control Transp BSA (22.7 ± 3.4%) and MR (21.6 ± 2.3%) groups. However, they were similar (P > 0.05) to the other groups (23.6 ± 3.3% to 28.8 ± 2.7%). The total number of blastomeres was higher (P < 0.05) in the Control Lab FCS group (85.2 ± 5.6) than in Control Lab BSA (53.6 ± 2.9), Control Transp BSA (55.5 ± 4.4), BL (58.2 ± 3.0), mSPOM (57.9 ± 4.9) and MR (59.2 ± 3.9), but all these treatments did not differ (P > 0.05) from bFF (67.7 ± 4.2). No differences (P > 0.05) were found in apoptosis by the activity of caspases (139.0 ± 3.2 to 152.4 ± 6.5, expressed in fluorescence intensity) as well as the percentage of TUNEL-positive cells (12.3 ± 2.0% to 15.7 ± 1.7%). In conclusion, the transportation of oocytes over 6 h with BL, mSPOM or bFF enabled the acquisition of developmental competence at similar rates to the Control Lab FCS group.