Effect of antioxidants on preimplantation embryo development in vitro: a review

Nobiletin as a novel agent to enhance porcine in vitro embryo development and quality

In vitro embryo production (IVP) is of great importance to the porcine industry, as well as for basic research and biomedical applications. Despite the large efforts made in laboratories worldwide to address suboptimal culture conditions, porcine IVP remains inefficient. Nobiletin (Nob, 5,6,7,8,3',4' hexamethoxyflavone) supplementation to in vitro culture (IVC) medium, enhances in vitro embryo development in various species. However, its impact on the quality and developmental capacity of in vitro-produced pig embryos is yet to be established. This study evaluated the effects of different concentrations (2.5 and 5 μM) of Nob during the early culture of in vitro-produced pig embryos on embryo developmental competence, mitochondrial activity, lipid content, intracellular Reactive Oxygen Species (ROS) and Glutathione (GSH) content, Total Cell Number (TCN) per blastocyst, and expression of genes related to embryo development, quality and oxidative stress. Embryos cultured in medium without Nob supplementation and in medium supplemented with 0.01 % dimethyl sulfoxide (DMSO-vehicle for Nob) constituted the Control and DMSO groups, respectively. Embryo development rates were evaluated on Days 2, 6 and 7 of IVC. Additionally, a representative group of embryos was selected to assess mitochondrial activity, lipid, ROS and GSH content (on Days 2 and 6 of IVC), TCN assessment and gene expression analyses (on Day 6 of IVC). No significant differences were observed in any of the parameters evaluated on Day 2 of IVC. In contrast, embryos cultured under the presence of Nob 2.5 showed higher developmental rates on Days 6 and 7 of IVC. In addition, Day 6 embryos showed increased mitochondrial activity, with decreased levels of ROS and GSH in the Nob 2.5 group compared to the other groups. Both Nob 2.5 and Nob 5 embryos showed higher TCN compared to the Control and DMSO groups. Furthermore, Nob 2.5 and Nob 5 upregulated the expression of Superoxide dismutase type 1 (SOD1) and Glucose-6-phosphate dehydrogenase (G6PDH) genes, which could help to counteract oxidative stress during IVC. In conclusion, the addition of Nob during the first 48 h of IVC increased porcine embryo development rates and enhanced their quality, including the upregulation of relevant genes that potentially improved the overall efficiency of the IVP system.

Embryos from Prepubertal Hyperglycemic Female Mice Respond Differentially to Oxygen Tension In Vitro

Reduced oxygen during embryo culture in human ART prevents embryo oxidative stress. Oxidative stress is also the major mechanism by which maternal diabetes impairs embryonic development. This study employed induced hyperglycemia prepubertal mice to mimic childhood diabetes to understand the effects of varying oxygen tension during in vitro embryonic development. The oocytes were fertilized and cultured at low (≈5%) oxygen (LOT) or atmospheric (≈20%) oxygen tension (HOT) for up to 96 h. Embryo development, apoptosis in blastocysts, inner cell mass (ICM) outgrowth proliferation, and Hif1α expression were assessed. Though the oocyte quality and meiotic spindle were not affected, the fertilization rate (94.86 ± 1.18 vs. 85.17 ± 2.81), blastocyst rate (80.92 ± 2.92 vs. 69.32 ± 2.54), and ICM proliferation ability (51.04 ± 9.22 vs. 17.08 ± 3.05) of the hyperglycemic embryos were significantly higher in the LOT compared to the HOT group. On the other hand, blastocysts from the hyperglycemic group, cultured at HOT, had a 1.5-fold increase in apoptotic cells compared to the control and lower Hif1α transcripts in ICM outgrowths compared to the LOT. Increased susceptibility of embryos from hyperglycemic mice to higher oxygen tension warrants the need to individualize the conditions for embryo culture systems in ART clinics, particularly when an endogenous maternal pathology affects the ovarian environment.

Astaxanthin Added during Post-Warm Recovery Mitigated Oxidative Stress in Bovine Vitrified Oocytes and Improved Quality of Resulting Blastocysts

Various antioxidants are tested to improve the viability and development of cryopreserved oocytes, due to their known positive health effects. The aim of this study was to find whether astaxanthin (AX), a xanthophyll carotenoid, could mitigate deteriorations that occurred during the vitrification/warming process in bovine oocytes. Astaxanthin (2.5 µM) was added to the maturation medium during the post-warm recovery period of vitrified oocytes for 3 h. Afterward, the oocytes were fertilized in vitro using frozen bull semen and presumptive zygotes were cultured in the B2 Menezo medium in a co-culture with BRL-1 cells at 38.5 °C and 5% CO2 until the blastocyst stage. AX addition significantly reduced ROS formation, lipid peroxidation, and lysosomal activity, while increasing mitochondrial activity in vitrified oocytes. Although the effect of AX on embryo development was not observed, it stimulated cell proliferation in the blastocysts derived from vitrified oocytes and improved their quality by upregulation or downregulation of some genes related to apoptosis (BCL2, CAS9), oxidative stress (GPX4, CDX2), and development (GJB5) compared to the vitrified group without AX. Therefore, the antioxidant properties of astaxanthin even during short exposure to bovine vitrified/warmed oocytes resulted in improved blastocyst quality comparable to those from fresh oocytes.

Epigen enhances the developmental potential of in vitro fertilized embryos by improving cytoplasmic maturation

Numerous growth factors contribute to oocyte maturation and embryonic development in vivo; however, only a few are understood. One such factor is epigen, a new member of the epidermal growth factor (EGF) family that is secreted by the granulosa cells of immature oocytes. We hypothesized that epigen may play a role in oocyte maturation, specifically in the nuclear and cytoplasmic aspects. This study aimed to investigate the effects of epigen on porcine oocyte maturation and embryo development in vitro. In this study, three different concentrations of epigen (3, 6, and 30 ng/mL) were added to tissue culture medium-199 (TCM-199) during in vitro maturation of porcine oocytes. A control group that did not receive epigen supplementation was also included. Mature porcine oocytes were fertilized, and the resulting zygotes were cultured until day 7. The levels of intracellular glutathione (GSH) and reactive oxygen species (ROS) were measured in the in vitro matured oocytes. At the same time, the expression patterns of genes related to apoptosis were detected in day 7 blastocysts (BLs) using real-time quantitative PCR Apoptosis was detected by annexin-V assays in mature oocytes. Data were analyzed using ANOVA and Duncan's test on SPSS, and results are presented as mean ± SEM. The group that received 6 ng/mL epigen had a significantly lower rate of germinal vesicle breakdown (GVBD) than the control group without affecting the nuclear maturation among the experimental groups. Among the treatment groups, the 6 ng/mL epigen group showed significantly higher levels of intracellular GSH and lower ROS production. Supplementation with 6 ng/mL epigen significantly improved blastocyst (BL) formation rates compared to those in the control and 3 ng/mL groups. Additionally, the blastocyst expansion rate was significantly higher with epigen supplementation (6 ng/mL). In the fertilization experiment, the group supplemented with 6 ng/mL epigen exhibited significantly higher levels of monospermy and fertilization efficiency and lower levels of polyspermy than the control group. This study indicated that adding epigen at a concentration of 6 ng/mL can significantly enhance the developmental potential of porcine oocytes fertilized in vitro. Specifically, the study found that epigen improves cytoplasmic maturation, which helps prevent polyspermy and emulates monospermic penetration.

Uterine Fluid Extracellular Vesicles Proteome Is Altered During the Estrous Cycle

Uterine environment is tightly and finely regulated via various signaling pathways mediated through endocrine, exocrine, autocrine, juxtacrine, and paracrine mechanisms. In utero signaling processes are paramount for normal and abnormal physiology which involves cell to cell, cells to gametes, cells to embryo, and even interkingdom communications due to presence of uterine microbiota. Extracellular vesicles (EVs) in the uterine fluid (UF) and their cargo components are known to be mediators of in utero signaling and communications. Interestingly, the changes in UF-EV proteome during the bovine estrous cycle and the effects of these differentially enriched proteins on embryo development are yet to be fully discovered. In this study, shotgun quantitative proteomics-based mass spectrometry was employed to compare UF-EV proteomes at day 0, 7, and 16 of the estrous cycle to understand the estrous cycle-dependent dynamics. Furthermore, different phase UF-EVs were supplemented in embryo cultures to evaluate their impact on embryo development. One hundred fifty-nine UF-EV proteins were differentially enriched at different time points indicating the UF-EV proteome is cycle-dependent. Overall, many identified pathways are important for normal uterine functions, early embryo development, and its nutritional needs, such as antioxidant activity, cell morphology and cycle, cellular homeostasis, cell adhesion, and carbohydrate metabolic process. Furthermore, the luteal phase UF-EVs supplementation increased in vitro blastocyst rates from 25.0 ± 5.9% to 41.0 ± 4.0% (p ≤ 0.05). Our findings highlight the importance of bovine UF-EV in uterine communications throughout the estrous cycle. Interestingly, comparison of hormone-synchronized EV proteomes to natural cycle UF-EVs indicated shift of signaling. Finally, UF-EVs can be used to improve embryo production in vitro.

Effect of Micronutrients and L-Carnitine as Antioxidant on Sperm Parameters, Genome Integrity, and ICSI Outcomes: Randomized, Double-Blind, and Placebo-Controlled Clinical Trial

The evaluation of sperm DNA integrity is recommended in the sixth edition of the 2021 World Health Organization guidelines. Oxidative stress has been identified as a crucial factor leading to genome decay, lipid peroxidation, and nucleoprotein oxidation. This double-blind, placebo-controlled clinical trial aimed to assess the effect of oral antioxidant treatment (Fertilis), which contains L-carnitine and some micronutrients, in the improvement of conventional sperm parameters, sperm DNA integrity and in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) outcomes. A total of 263 participants were enrolled and randomly divided into two groups: 131 participants received the antioxidant treatment, while 132 participants received a placebo. The male partners in both groups underwent the antioxidant treatment or the placebo for a duration of three months. For each participant, we performed a hormonal test, an infectious test, a spermogram, a TUNEL assay for sperm DNA fragmentation, a toluidine blue staining for sperm DNA decondensation, and an IVF/ICSI procedure. Sperm characteristics analysis (volume, count, motility, and vitality), sperm DNA fragmentation, and sperm DNA decondensation were assessed and compared to the results preceding the antioxidant treatment. The study outcome revealed a significant decrease in the DNA fragmentation index and a significant increase in sperm motility after 3 months of treatment (p = 0.01 and p = 0.02, respectively). Additionally, a significant improvement in clinical pregnancy rate (p = 0.01) and life birth rate (p = 0.031) was observed. No significant changes were observed in conventional sperm parameters (volume, count, and vitality) or sperm DNA decondensation (SDI). Antioxidant therapy has a beneficial impact on achieving pregnancy, whether through spontaneous conception or assisted reproductive procedures (ART).

Secretory Proteomic Responses of Endometrial Epithelial Cells to Trophoblast-Derived Extracellular Vesicles

Synchronized crosstalk between the embryo and endometrium during the periconception period is integral to pregnancy establishment. Increasing evidence suggests that the exchange of extracellular vesicles (EVs) of both embryonic and endometrial origin is a critical component of embryo-maternal communication during peri-implantation. Here, we investigated whether embryonic signals in the form of EVs can modulate the endometrial epithelial cell secretome. Receptive endometrial analog RL95-2 cells were supplemented with trophoblast analog JAr cell-derived EVs, and the secretory protein changes occurring in the RL95-2 cells were analyzed using mass spectrometry. EVs of non-trophoblastic origin (HEK 293 cells) were used as the control EV source to supplement endometrial cells. Trophoblast cell-derived EVs enriched endometrial epithelial cell secretions with proteins that support embryo development, attachment, or implantation, whereas control EVs were unable to induce the same effect. The present study suggests that embryonic signals in the form of EVs may prime receptive endometrial epithelial cells to enrich their secretory proteome with critical proteomic molecules with functional importance for periconception milieu formation.

Oxidative stress and mitochondrial dysfunction of granulosa cells in polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is one of the leading causes of anovulatory infertility in women, affecting 5%-15% of women of reproductive age worldwide. The clinical manifestations of patients include ovulation disorders, amenorrhea, hirsutism, and obesity. Life-threatening diseases, such as endometrial cancer, type 2 diabetes, hyperlipidaemia, hypertension, and cardiovascular disease, can be distant complications of PCOS. PCOS has diverse etiologies and oxidative stress (OS) plays an important role. Mitochondria, as the core organelles of energy production, are the main source of reactive oxygen species (ROS). The process of follicular growth and development is extremely complex, and the granulosa cells (GCs) are inextricably linked to follicular development. The abnormal function of GCs may directly affect follicular development and alter many symptoms of PCOS. Significantly higher levels of OS markers and abnormal mitochondrial function in GCs have been found in patients with PCOS compared to healthy subjects, suggesting that increased OS is associated with PCOS progression. Therefore, the aim of this review was to summarize and discuss the findings suggesting that OS and mitochondrial dysfunction in GCs impair ovarian function and induce PCOS.

Maternal zinc alleviates tert-butyl hydroperoxide-induced mitochondrial oxidative stress on embryonic development involving the activation of Nrf2/PGC-1α pathway

BACKGROUND

Mitochondrial dysfunction induced by excessive mitochondrial reactive oxygen species (ROS) damages embryonic development and leads to growth arrest.

OBJECTIVE

The purpose of this study is to elucidate whether maternal zinc (Zn) exert protective effect on oxidative stress targeting mitochondrial function using an avian model.

RESULT

In ovo injected tert-butyl hydroperoxide (BHP) increases (P < 0.05) hepatic mitochondrial ROS, malondialdehyde (MDA) and 8-hydroxy-2-deoxyguanosine (8-OHdG), and decreases (P < 0.05) mitochondrial membrane potential (MMP), mitochondrial DNA (mtDNA) copy number and adenosine triphosphate (ATP) content, contributing to mitochondrial dysfunction. In vivo and in vitro studies revealed that Zn addition enhances (P < 0.05) ATP synthesis and metallothionein 4 (MT4) content and expression as well as alleviates (P < 0.05) the BHP-induced mitochondrial ROS generation, oxidative damage and dysfunction, exerting a protective effect on mitochondrial function by enhancing antioxidant capacity and upregulating the mRNA and protein expressions of Nrf2 and PGC-1α.

CONCLUSIONS

The present study provides a new way to protect offspring against oxidative damage by maternal Zn supplementation through the process of targeting mitochondria involving the activation of Nrf2/PGC-1α signaling.

Oxidative Stress in Assisted Reproductive Techniques, with a Focus on an Underestimated Risk Factor

Based on current findings, the presence of oxidative stress has a significant impact on the quality of gametes and embryos when performing assisted reproductive techniques (ART). Unfortunately, in vitro manipulation of these cells exposes them to a higher level of reactive oxygen species (ROS). The primary goal of this review is to provide a comprehensive overview of the development of oxidative stress in female and male reproductive systems, as well as in the case of the pre-implantation embryo and its environment. This review also focuses on the origins of ROS and the mechanisms of oxidative stress-induced damage during ART procedures. A well-known but underestimated hazard, light exposure-related photo-oxidation, is particularly concerning. The effect of oxidative stress on ART outcomes, as well as the various strategies for preventing it, are also discussed. We emphasize the role and significance of antioxidants and light protection including forms, functions, and mechanisms in the development of gametes and embryos in vivo and in vitro.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: Reactive oxygen species in the mammalian pre-implantation embryo

In brief

Reactive oxygen species are generated throughout the pre-implantation period and are necessary for normal embryo formation. However, at pathological levels, they result in reduced embryo viability which can be mediated through factors delivered by sperm and eggs at conception or from the external environment.

Abstract

Reactive oxygen species (ROS) occur naturally in pre-implantation embryos as a by-product of ATP generation through oxidative phosphorylation and enzymes such as NADPH oxidase and xanthine oxidase. Biological concentrations of ROS are required for crucial embryonic events such as pronuclear formation, first cleavage and cell proliferation. However, high concentrations of ROS are detrimental to embryo development, resulting in embryo arrest, increased DNA damage and modification of gene expression leading to aberrant fetal growth and health. In vivo embryos are protected against oxidative stress by oxygen scavengers present in follicular and oviductal fluids, while in vitro, embryos rely on their own antioxidant defence mechanisms to protect against oxidative damage, including superoxide dismutase, catalase, glutathione and glutamylcysteine synthestase. Pre-implantation embryonic ROS originate from eggs, sperm and embryos themselves or from the external environment (i.e. in vitro culture system, obesity and ageing). This review examines the biological and pathological roles of ROS in the pre-implantation embryo, maternal and paternal origins of embryonic ROS, and from a clinical perspective, we comment on the growing interest in combating increased oxidative damage in the pre-implantation embryo through the addition of antioxidants.

Maternal metabolic health and fertility: we should not only care about but also for the oocyte!

Metabolic disorders due to obesity and unhealthy lifestyle directly alter the oocyte's microenvironment and impact oocyte quality. Oxidative stress and mitochondrial dysfunction play key roles in the pathogenesis. Acute effects on the fully grown oocytes are evident, but early follicular stages are also sensitive to metabolic stress leading to a long-term impact on follicular cells and oocytes. Improving the preconception health is therefore of capital importance but research in animal models has demonstrated that oocyte quality is not fully recovered. In the in vitro fertilisation clinic, maternal metabolic disorders are linked with disappointing assisted reproductive technology results. Embryos derived from metabolically compromised oocytes exhibit persistently high intracellular stress levels due to weak cellular homeostatic mechanisms. The assisted reproductive technology procedures themselves form an extra burden for these defective embryos. Minimising cellular stress during culture using mitochondrial-targeted therapy could rescue compromised embryos in a bovine model. However, translating such applications to human in vitro fertilisation clinics is not simple. It is crucial to consider the sensitive epigenetic programming during early development. Research in humans and relevant animal models should result in preconception care interventions and in vitro strategies not only aiming at improving fertility but also safeguarding offspring health.

Exogenous L-Glutathione Improves Vitrification Outcomes in Murine Preimplantation Embryos

Vitrification is an important tool to store surplus embryos in assisted reproductive technology (ART). However, vitrification increases oxidative damage and results in decreased viability. Studies have reported that L-glutathione (GSH) supplementation improves the preimplantation development of murine embryos. Glutathione constitutes the major non-protein sulphydryl compound in mammalian cells, which confers protection against oxidative damage. However, the effect of GSH supplementation on embryonic vitrification outcomes has yet to be reported. This study aims to determine whether GSH supplementation in culture media improves in vitro culture and vitrification outcomes, as observed through embryo morphology and preimplantation development. Female BALB/c mice aged 6−8 weeks were superovulated through an intraperitoneal injection of 10 IU of pregnant mare serum gonadotrophin (PMSG), followed by 10 IU of human chorionic gonadotrophin (hCG) 48 h later. The mated mice were euthanized by cervical dislocation 48 h after hCG to harvest embryos. Two-cell embryos were randomly assigned to be cultured in either Group 1 (GSH-free medium), Group 2 (GSH-free medium with vitrification), Group 3 (0.01 mM GSH-supplemented medium), or Group 4 (0.01 mM GSH-supplemented medium with vitrification). Non-vitrified (Groups 1 and 3) and vitrified (Groups 2 and 4) embryos were observed for morphological quality and preimplantation development at 24, 48, 72, and 96 h. In the non-vitrified groups, there were significant increases in the number of Grade-1 blastocysts in GSH cultures (p < 0.05). Similarly, in the vitrified groups, GSH supplementation was also seen to significantly increase blastocyst formation. Exogenous GSH supplementation resulted in a significant increase in intracellular GSH, a release of cytochrome c from mitochondria, and a parallel decrease in intracellular reactive oxygen species (ROS) levels in vitrified eight-cell embryos (p < 0.05). GSH supplementation was shown to upregulate Bcl2 expression and downregulate Bax expression in the vitrified preimplantation embryo group. The action of exogenous GSH was concomitant with an increase in the relative abundance of Gpx1 and Sod1. In conclusion, our study demonstrated the novel use and practical applicability of GSH supplementation for improving embryonic cryotolerance via a decrease in ROS levels and the inhibition of apoptotic events by improvement in oxidative status.

Sesamol protects the function and structure of rat ovaries against side effects of cyclophosphamide by decreasing oxidative stress and apoptosis

AIM

Chemotherapy with cyclophosphamide can damage ovaries and cause infertility in girls and women. Sesamol is a phenolic antioxidant that can protect various organs from damage. The purpose of this study was to evaluate the effects of sesamol on protecting the function and structure of rat ovaries against the side effects of a chemotherapy model with cyclophosphamide.

METHODS

Twenty-four adult female Wistar rats were randomly divided into three groups: (1) normal group, without any treatment, (2) control group, immediately after receiving cyclophosphamide, 0.5% dimethyl sulfoxide (DMSO) as the solvent of sesamol was intraperitoneally injected for 14 consecutive days, (3) sesamol group, immediately after receiving cyclophosphamide, 50 mg/kg sesamol was intraperitoneally injected for 14 consecutive days. Four weeks after the last injection, superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels in the ovary, anti-Mullerian hormone (AMH) levels in the serum, number of ovarian follicles in different stages, and expression of proteins growth differentiation factor-9 (GDF-9), Bcl-2, and Bax in the ovary were evaluated.

RESULTS

The results of SOD activity and MDA levels in the ovary, AMH levels in the serum, number of ovarian follicles in different stages, and expression of proteins GDF9, Bcl-2, and Bax in the ovary were significantly more favorable in the sesamol group than the control group.

CONCLUSIONS

The results suggest that sesamol may protect function and structure in the rat ovaries against side effects of the chemotherapy model with cyclophosphamide by decreasing oxidative stress and apoptosis in the ovary.

Effect of a Novel Hydroxybenzoic Acid Based Mitochondria Directed Antioxidant Molecule on Bovine Sperm Function and Embryo Production

Sperm cells are particularly vulnerable to reactive oxygen species (ROS), impairing their fertilizing ability. Our objective was to study the effect of a novel mitochondrial-directed antioxidant, AntiOxBEN2, on bovine sperm function. This antioxidant was added to the semen capacitation medium (CAP), during the swim-up process, and to the fertilization medium (FERT) during the co-incubation of matured oocytes and capacitated spermatozoa, in concentrations of 0 (control), 1, and 10 µM. After the swim-up, sperm motility (CASA and visual analysis), vitality (eosin-nigrosin), mitochondrial membrane potential (JC1), intracellular ROS, adenosine triphosphate (ATP) levels, and basal metabolism (Seahorse Xfe96) were evaluated. Embryo development and quality were also assessed. Higher cleavage rates were obtained when 1 µM AntiOxBEN2 were added to CAP and FERT media (compared to control, p < 0.04). A positive effect of AntiOxBEN2 on intracellular ROS reduction (p = 0.01), on the increment of mitochondrial membrane potential (p ≤ 0.003) and, consequently, on the sperm quality was identified. However, the highest dose impaired progressive motility, ATP production, and the number of produced embryos. The results demonstrate a beneficial effect of AntiOxBEN2 (1 µM) on sperm capacitation and fertilization processes, thus improving embryonic development. This may constitute a putative novel therapeutic strategy to improve the outcomes of assisted reproductive techniques (ART).

Oxidative Stress and Assisted Reproduction: A Comprehensive Review of Its Pathophysiological Role and Strategies for Optimizing Embryo Culture Environment

Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO2 incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.