Antioxidant supplementation during in vitro culture improves mitochondrial function and development of embryos from aged female mice

Mitochondrial dysfunction in pregnancy loss: a review

A receptive endometrium, a healthy embryo, and harmonious communication between the mother and the embryo/fetus are necessary for a healthy and successful pregnancy. Pregnancy loss (PL) can be the outcome if there is a flaw in any of these critical developmental processes. Multiple risk factors contribute to PL, including genetic predispositions, uterine abnormalities, immune imbalances, endocrine dysfunctions, and environmental exposures, among others. Despite extensive investigations, more than half of women with recurrent pregnancy loss (RPL) lack identifiable risk factors, and causes of RPL remain elusive. To date, an accumulating body of evidence indicates that mitochondrial dysfunction in reproductive organs or cells is a potential underlying factor that may trigger PL. In this comprehensive review, we delve into the intricate relationship between mitochondrial dysfunction and PL, examining studies that focus on this connection in the context of diverse reproductive organs and cells, to unravel the interwoven links between these factors and gain a deeper understanding of their interconnectedness.

The Effect of L-Carnitine Supplementation in Culture Medium on the Development and Cryopreservation of in Vitro Produced Bovine Embryos

BACKGROUND

In vitro culture media play a crucial role in supporting the growth and development of bovine embryos. Despite advancements in media formulations, there is ongoing interest in optimising these media by supplementing them with compounds like L-carnitine to improve embryo development and cryopreservation outcomes. However, the effects of L-carnitine supplementation in commercial culture media remain unclear. The aim of this study was to investigate the effects of adding 0.75 mM L-carnitine to commercial in vitro culture (IVC) media on bovine in vitro embryo production (IVP). The first phase of the study evaluated the effects of L-carnitine on embryo development, while the second phase evaluated the effects of L-carnitine on embryo cryopreservation.

METHODS

A total of 508 bovine ovaries used in the study were harvested from slaughterhouses. Only morphologically healthy ovaries were included in the study, while ovaries with cysts or any pathological findings were excluded. Oocytes were collected by aspiration method. The collected oocytes were fertilised in vitro using prepared spermatozoa under standard conditions. Following fertilisation, embryos were morphologically evaluated, and only those exhibiting uniform blastomeres and minimal cytoplasmic fragmentation were included in subsequent steps. The embryos were then randomly divided into two groups: one supplemented with 0.75 mM L-carnitine in the IVC medium and the other without supplementation. Cleavage rates on Day 4 and embryo development rates on 7 days after fertilisation were evaluated with the supplementation of L-carnitine. In addition, the survival effects of embryos collected on Day 7 after direct culture, slow freezing and vitrification were investigated.

RESULTS

It was determined that L-carnitine supplementation to IVC medium did not affect the cleavage rates on Day 4 and blastocyst development rates on Day 7 (p > 0.05). Moreover, it did not affect the survival and development rates of embryos collected on Day 7 following both slow freezing and thawing, as well as vitrification and warming processes (p > 0.05).

CONCLUSIONS

Supplementation of L-carnitine to commercially available in vitro culture medium did not enhance embryo development rates or survival rates after cryopreservation. This is likely due to the presence of antioxidant compounds in commercial embryo culture media.

Impact of Flavonoid-Enriched Antioxidant Nanoformulation Supplementation on In Vitro Maturation and Gene Expression of Buffalo Oocytes

Oocytes are exposed to various stressors during in vitro maturation (IVM). Antioxidant supplementation during IVM can mitigate oxidative stress. We investigated the effects of supplementing IVM medium with novel flavonoid-enriched antioxidant nanoformulations, namely, EMD-300® and EMP3-H200®, on oocyte IVM and analyzed the expression of oxidative stress, apoptosis, and pluripotency genes in buffalo. Cumulus oocyte complexes (COCs) obtained from buffalo ovaries were matured in IVM medium supplemented with either EMD-300® or EMP3-H200® at 0.5% and 1.0% for 22 h. Following IVM, nuclear maturation, gene expression, and the levels of total antioxidant capacity (TAC) and malondialdehyde (MDA) were analyzed. Nuclear maturation was lower (p < 0.001) for the 1.0% EMD-300® group than other groups. The expressions of the GPX4, SOD, CAT, and ATF6 genes were lower (p < 0.05) in the 0.5% EMD-300® and EMP3-H200® groups than in the control. OCT4 gene expression was higher (p < 0.05) for the treated groups than control group. The level of TAC in spent IVM medium was higher for the 0.5% EMD-300® and EMP3-H200® groups than for the control. However, the MDA concentrations were lower. In conclusion, supplementing IVM medium with EMD-300® or EMP3-H200® at 0.5% improved nuclear maturation of buffalo oocytes better than 1.0%. Our findings suggest that these compounds had antioxidant effects, which assures their ability in protecting oocytes against oxidative stress.

Culture media with antioxidants improved preimplantation embryo development and clinical outcomes of patients of advanced age

RESEARCH QUESTION

What are the clinical effects of using culture media supplemented with antioxidants (AOX) throughout the IVF process?

DESIGN

Prospective randomized single-centre study. Cumulus-oocyte complexes and semen samples collected from 127 treatment cycles were divided evenly between the study arm (culture media with AOX) and the control arm (culture media without AOX). The primary endpoint was the good-quality blastocyst (GQB) rate on day 5-6 per metaphase II (MII) oocyte.

RESULTS

Fertilization rate and day 5-6 blastocyst rate per MII oocyte differed significantly in favour of the study arm, whereas GQB rate did not. A subgroup analysis, stratified by maternal age, revealed significant improvements in the study arm for day 3 embryo development rate, day 5-6 blastocyst rate, GQB rate and blastocyst utilization rate for patients aged 35-40 years, while the impacts on these endpoints were much smaller in patients aged <35 years. Ninety-four single vitrified blastocyst transfers (SVBT) were performed in each arm. The blastocysts derived from the study arm showed better results of SVBT for patients aged 35-40 years, defined by embryo implantation rate, fetal heartbeat rate and live birth rate, whereas these variables did not differ significantly between the two arms when assessing the results for patients of all ages and patients aged <35 years.

CONCLUSIONS

Embryo development and SVBT outcomes of treatment cycles of patients aged 35-40 years improved significantly when using AOX-supplemented culture media throughout the IVF process.

Mating modifies the expression of crucial oxidative-reductive transcripts in the pig oviductal sperm reservoir: is the female ensuring sperm survival?

Background

Mating induces large changes in the female genital tract, warranting female homeostasis and immune preparation for pregnancy, including the preservation of crucial oxidative status among its pathways. Being highly susceptible to oxidative stress, sperm survival and preserved function depend on the seminal plasma, a protection that is removed during sperm handling but also after mating when spermatozoa enter the oviduct. Therefore, it is pertinent to consider that the female sperm reservoir takes up this protection, providing a suitable environment for sperm viability. These aspects have not been explored despite the increasing strategies in modulating the female status through diet control and nutritional supplementation.

Aims

To test the hypothesis that mating modifies the expression of crucial oxidative-reductive transcripts across the entire pig female genital tract (cervix to infundibulum) and, particularly in the sperm reservoir at the utero-tubal junction, before ovulation, a period dominated by estrogen stimulation of ovarian as well as of seminal origin.

Methods

The differential expression of estrogen (ER) and progesterone (PR) receptors and of 59 oxidative-reductive transcripts were studied using a species-specific microarray platform, in specific segments of the peri-ovulatory sow reproductive tract in response to mating.

Results

Mating induced changes along the entire tract, with a conspicuous downregulation of both ER and PR and an upregulation of superoxide dismutase 1 (SOD1), glutaredoxin (GLRX3), and peroxiredoxin 1 and 3 (PRDX1, PRDX3), among other NADH Dehydrogenase Ubiquinone Flavoproteins, in the distal uterus segment. These changes perhaps helped prevent oxidative stress in the area adjacent to the sperm reservoir at the utero-tubal junction. Concomitantly, there were a downregulation of catalase (CAT) and NADH dehydrogenase (ubiquinone) oxidoreductases 1 beta subcomplex, subunit 1 (NDUFB1) in the utero-tubal junction alongside an overall downregulation of CAT, SOD1, and PRDX3 in the ampullar and infundibulum segments.

Conclusions

Natural mating is an inducer of changes in the expression of female genes commanding antioxidant enzymes relevant for sperm survival during sperm transport, under predominant estrogen influence through the bloodstream and semen. The findings could contribute to the design of new therapeutics for the female to improve oxidative-reductive balance.

Antioxidants supplementation improves the quality of in vitro produced ovine embryos with amendments in key development gene expressions

The present study assessed the effects of supplementation of different antioxidants on oocyte maturation, embryo production, reactive oxygen species (ROS) production and expression of key developmental genes. In this study, using ovine as an animal model, we tested the hypothesis that antioxidant supplementation enhanced the developmental competence of oocytes. Ovine oocytes aspirated from local abattoir-derived ovaries were subjected to IVM with different concentrations of antioxidants [(Melatonin, Ascorbic acid (Vit C), alpha-tocopherol (Vit E), Sodium selenite (SS)]. Oocytes matured without any antioxidant supplementation were used as controls. The oocytes were assessed for maturation rates and ROS levels. Further, embryo production rates in terms of cleavage, blastocysts and total cell numbers were evaluated after performing in vitro fertilization. Real-Time PCR analysis was used to evaluate the expression of stress related gene (SOD-1), growth related (GDF-9, BMP-15), and apoptosis-related genes (BCL-2 and BAX). We observed that maturation rates were significantly higher in alpha-tocopherol (100 μM; 92.4%) groups followed by melatonin (30 μM; 89.1%) group. However, blastocyst rates in ascorbic acid (100 μM; 19.5%), melatonin (30 μM; 18.4%), alpha-tocopherol (100 μM; 18.2%), and sodium selenite (20 μM; 16.9%) groups were significantly higher (P 0.05) than that observed in the control groups. Total cell numbers in blastocysts in the melatonin, ascorbic acid and alpha-tocopherol groups were significantly higher than those observed in sodium selenite and control groups. ROS production was reduced in groups treated with melatonin (30 μM), vitamin C (100 μM), sodium selenite (20 μM) and α-tocopherol (200 μM) compared with that observed in the control group. Supplementation of antioxidants caused the alterations in mRNA expression of growth, stress, and apoptosis related gene expression in matured oocytes. The results recommend that antioxidants alpha-tocopherol (200 μM), sodium selenite (40 μM), melatonin (30 μM) and ascorbic acid (100 μM) during IVM reduced the oxidative stress by decreasing ROS levels in oocytes, thus improving embryo quantity and quality.

Granulosa cell-derived extracellular vesicles mitigate the detrimental impact of thermal stress on bovine oocytes and embryos

Climate change-induced global warming results in rises in body temperatures above normal physiological levels (hyperthermia) with negative impacts on reproductive function in dairy and beef animals. Extracellular vesicles (EVs), commonly described as nano-sized, lipid-enclosed complexes, harnessed with a plethora of bioactive cargoes (RNAs, proteins, and lipids), are crucial to regulating processes like folliculogenesis and the initiation of different signaling pathways. The beneficial role of follicular fluid-derived EVs in inducing thermotolerance to oocytes during in vitro maturation (IVM) has been evidenced. Here we aimed to determine the capacity of in vitro cultured granulosa cell-derived EVs (GC-EVs) to modulate bovine oocytes’ thermotolerance to heat stress (HS) during IVM. Moreover, this study tested the hypothesis that EVs released from thermally stressed GCs (S-EVs) shuttle protective messages to provide protection against subsequent HS in bovine oocytes. For this, sub-populations of GC-EVs were generated from GCs subjected to 38.5°C (N-EVs) or 42°C (S-EVs) and supplemented to cumulus-oocyte complexes (COCs) matured in vitro at the normal physiological body temperature of the cow (38.5°C) or HS (41°C) conditions. Results indicate that S-EVs improve the survival of oocytes by reducing ROS accumulation, improving mitochondrial function, and suppressing the expression of stress-associated genes thereby reducing the severity of HS on oocytes. Moreover, our findings indicate a carryover impact from the addition of GC-EVs during oocyte maturation in the development to the blastocyst stage with enhanced viability.

Ovarian inflammation mediated by Toll-like receptor 4 increased transcripts of maternal effect genes and decreased embryo development†

Obese women are subfertile and have reduced assisted reproduction success, which may be due to reduced oocyte competence. We hypothesize that consumption of a high-fat/high-sugar diet induces ovarian inflammation, which is a primary contributor to decreased oocyte quality and pre-implantation embryo development. To test this hypothesis, C57BL/6 (B6) mice with a normal inflammatory response and C3H/HeJ (C3H) mice with a dampened inflammatory response due to dysfunctional Toll-like receptor 4 were fed either normal chow or high-fat/high-sugar diet. In both B6 and C3H females, high-fat/high-sugar diet induced excessive adiposity and hyperglycemia compared to normal chow-fed counterparts. Conversely, ovarian CD68 levels and oocyte expression of oxidative stress markers were increased when collected from B6 high-fat/high-sugar but not C3H high-fat/high-sugar mice. Following in vitro fertilization of in vivo matured oocytes, blastocyst development was decreased in B6-high-fat/high-sugar but not C3H high-fat/high-sugar mice. Expression of cumulus cell markers of oocyte quality were altered in both B6 high-fat/high-sugar and C3H high-fat/high-sugar. However, there were no diet-dependent differences in spindle abnormalities in either B6 or C3H mice, suggesting potential defects in cytoplasmic maturation. Indeed, there were significant increases in the abundance of maternal effect gene mRNAs in oocytes from only B6 high-fat/high-sugar mice. These differentially expressed genes encode proteins of the subcortical maternal complex and associated with mRNA metabolism and epigenetic modifications. These genes regulate maternal mRNA degradation at oocyte maturation, mRNA clearance at the zygotic genome activation, and methylation of imprinted genes suggesting a mechanism by which inflammation induced oxidative stress impairs embryo development.

Effects of alpha lipoic acid treatment during in vitro maturation on the development of porcine somatic cell nuclear transfer embryos

Oxidative stress influences the embryo production efficiency in vitro. We investigated the effects of alpha lipoic acid (ALA) treatment during the in vitro maturation (IVM) period on the porcine somatic cell nuclear transfer (SCNT) embryo production. After IVM, maturation rates of the 12.5- and 25-μM ALA-treated groups were not significantly different from those of the 0-μM ALA-treated group. Compared to those in the 0-μM ALA-treated group, the reactive oxygen species and glutathione levels were significantly decreased and increased, respectively, in the cytoplasm of matured oocytes in the 12.5-50-μM ALA-treated groups. Apoptosis rate in cumulus cells after IVM was significantly lower in the 12.5-50-μM ALA-treated groups than in the 0-μM ALA-treated group. Blastocyst formation rate was significantly higher in parthenogenetic oocytes treated with 12.5-μM ALA than in the 0-, 25-, and 50-μM ALA-treated groups. Similarly, in SCNT embryos, the 12.5-μM ALA-treated group showed a significantly higher blastocyst formation rate than the 0-μM ALA-treated group. Apoptosis rate in SCNT blastocysts was significantly decreased by 12.5-μM ALA treatment. The results showed that treatment with 12.5-μM ALA during IVM improves porcine SCNT embryo development and partial quality.

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.

Effects of N-acetylcysteine on Growth, Viability, and Ultrastructure of In Vitro Cultured Bovine Secondary Follicles

This study aimed to investigate the effects of different concentrations of N-acetylcysteine (NAC) on the growth, antrum formation, viability, and ultrastructure of bovine secondary follicles cultured in vitro for 18 days. To this end, the follicles were cultured in TCM-199+ medium alone or supplemented with 1.0, 5.0, or 25.0 mM NAC. Follicular growth, antrum formation, viability (calcein-AM and ethidium homodimer-1) and ultrastructure were evaluated at the end of culture period. The results showed that 1.0 mM NAC increased the percentage of growing follicles and the fluorescence intensity for calcein-AM when compared to other treatments (p < 0.05). On the other hand, follicles cultured with 25.0 mM NAC had higher fluorescence intensity for ethidium homodimer-1, which is a sign of degeneration. Ultrastructural analysis showed that oocytes from follicles cultured in control medium alone or with 1 mM NAC had intact zonae pellucidae in close association with oolemmae, but the ooplasm showed mitochondria with a reduced number of cristae. On the other hand, oocytes from follicles cultured with 5 or 25 mM NAC had extremely vacuolated cytoplasm and no recognizable organelles. In conclusion, 1 mM NAC increases cytoplasmic calcein staining and the growth rate in bovine secondary follicles cultured in vitro, but the presence of 5 or 25 mM NAC causes damage in cellular membranes and organelles, as well as reducing the percentages of growing follicles.

Inverse Lansing Effect: Maternal Age and Provisioning Affecting Daughters' Longevity and Male Offspring Production

AbstractMaternal age effects on offspring life history are known in a variety of organisms, with offspring of older mothers typically having lower life expectancy (the Lansing effect). However, there is no consensus on the generality and mechanisms of this pattern. We tested predictions of the Lansing effect in several Daphnia magna clones and observed clone-specific magnitude and direction of the maternal age effect on offspring longevity. We also report ambidirectional, genotype-specific effects of maternal age on the propensity of daughters to produce male offspring. Focusing on two clones with contrasting life histories, we demonstrate that maternal age effects can be explained by lipid provisioning of embryos by mothers of different ages. Individuals from a single-generation maternal age reversal treatment showed intermediate life span and intermediate lipid content at birth. In the clone characterized by the "inverse Lansing effect," neonates produced by older mothers showed higher mitochondrial membrane potential in neural tissues than their counterparts born to younger mothers. We conclude that an inverse Lansing effect is possible and hypothesize that it may be caused by age-specific maternal lipid provisioning creating a calorically restricted environment during embryonic development, which in turn reduces fecundity and increases life span in offspring.

Importance of Antioxidant Supplementation during In Vitro Maturation of Mammalian Oocytes

The in vitro embryo production (IVEP) technique is widely used in the field of reproductive biology. In vitro maturation (IVM) is the first and most critical step of IVEP, during which, the oocyte is matured in an artificial maturation medium under strict laboratory conditions. Despite all of the progress in the field of IVEP, the quality of in vitro matured oocytes remains inferior to that of those matured in vivo. The accumulation of substantial amounts of reactive oxygen species (ROS) within oocytes during IVM has been regarded as one of the main factors altering oocyte quality. One of the most promising approaches to overcome ROS accumulation within oocytes is the supplementation of oocyte IVM medium with antioxidants. In this article, we discuss recent advancements depicting the adverse effects of ROS on mammalian oocytes. We also discuss the potential use of antioxidants and their effect on both oocyte quality and IVM rate.

Oxidative stress induces meiotic defects of oocytes in a mouse psoriasis model

Psoriasis, an immune-mediated inflammatory disease, is associated with poor pregnancy outcomes. Emerging evidence indicates that these defects are likely attributed to compromised oocyte competence. Nevertheless, little is known about the underlying associated mechanisms between psoriasis and poor oocyte quality. In this study, we construct an imiquimod-induced chronic psoriasis-like mouse model to review the effects of psoriasis on oocyte quality. We discover that oocytes from psoriasis-like mice display spindle/chromosome disorganization, kinetochore-microtubule mis-attachment, and aneuploidy. Importantly, our results show that melatonin supplement in vitro and in vivo not only increases the rate of matured oocytes but also significantly attenuates oxidative stress and meiotic defects by restoring mitochondrial function in oocytes from psoriasis-like mice. Altogether, our data uncover the adverse effects of psoriasis symptoms on oocytes, and melatonin supplement ameliorates oxidative stress and meiotic defects of oocytes from psoriatic mice.

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.

Protective Effect of Minocycline Hydrochloride on the Mouse Embryonic Development Against Suboptimal Environment

Numerous studies have reported how inner cell mass (ICM) and trophectoderm (TE) was determined during the process of early mouse embryonic development from zygotes into organized blastocysts, however, multiple mysteries still remain. It is noteworthy that pluripotent stem cells (PSCs), which are derived from embryos at different developmental stages, have identical developmental potential and molecular characteristics to their counterpart embryos. Advances of PSCs research may provide us a distinctive perspective of deciphering embryonic development mechanism. Minocycline hydrochloride (MiH), a critical component for maintaining medium of novel type of extended pluripotent stem cells, which possesses developmental potential similar to both ICM and TE, can be substituted with genetic disruption of Parp1 in our previous study. Though Parp1-deficient mouse ESCs are more susceptible to differentiate into trophoblast derivatives, what role of MiH plays in mouse preimplantation embryonic development is still a subject of concern. Here, by incubating mouse zygotes in a medium containing MiH till 100 h after fertilization, we found that MiH could slow down embryonic developmental kinetics during cleavage stage without impairing blastocyst formation potential. Olaparib and Talazoparib, two FDA approved PARP1 inhibitors, exhibited similar effects on mouse embryos, indicating the aforementioned effects of MiH were through inhibiting of PARP1. Besides, we showed an embryonic protective role of MiH against suboptimal environment including long term exposure to external environment and H2O2 treatment, which could mimic inevitable manipulation during embryo culture procedures in clinical IVF laboratory. To our knowledge, it is not only for the first time to study MiH in the field of embryo development, but also for the first time to propose MiH as a protective supplement for embryo culture, giving the way to more studies on exploring the multiple molecular mechanisms on embryonic development that might be useful in assisted reproductive technology.

Interplay of Oxidants and Antioxidants in Mammalian Embryo Culture System

One principal purpose of assisted reproductive technology (ART) is to produce viable and good quality embryos. However, a variety of environmental factors may induce epigenetic changes in the embryo. Moreover, laboratory conditions including the culture media may also affect embryo development. Therefore, media change is an important factor in maintaining proper oxidant/antioxidant balance during embryo culture. Alterations in the oxidant/antioxidant balance are related to various cellular responses such as an increase in the level of reactive oxygen species (ROS) and consequent lipid peroxidation (LPO), DNA damage, and apoptosis. The current study focuses on the role of external factors on embryo culture and the ability of antioxidants to enhance in vitro fertilization (IVF) outcomes. Indeed, an optimization of media culture by the addition of enzymatic and nonenzymatic antioxidants in animal models and human embryos in ART has been updated in this study, with an emphasis on comparing the available results and their possible reasons.

Resveratrol enhanced mitochondrial recovery from cryopreservation-induced damages in oocytes and embryos

BACKGROUND

Mitochondria play a crucial role in nuclear maturation, fertilization, and subsequent embryo development. Cryopreservation is an important assisted reproductive technology that is used worldwide for humans and domestic animals. Although mitochondrial quantity and quality are decisive factors for successful development of oocytes and embryos, cryopreservation induces mitochondrial dysfunction. Upon thawing, the damaged mitochondria are removed, and de novo synthesis occurs to restore the function of mitochondria. Resveratrol, 3,5,4'-trihydroxystilbene, is a polyphenolic antioxidant that has versatile target proteins, among which sirtuin-1 (SIRT1) is a key regulator of in mitochondrial biogenesis and degradation.

METHODS

The present study is a literature review focusing on experiments involving the hypothesis that the activation of mitochondrial biogenesis and degradation following cryopreservation and warming by resveratrol may help mitochondrial recovery and improve oocyte and embryo development.

MAIN FINDINGS AND CONCLUSION

Resveratrol improves oocyte maturation and development and upregulates mitochondrial biogenesis and degradation. When vitrified-warmed embryos are treated with resveratrol, it helps in mitochondrial regulation and recovery of embryos from cryopreservation-induced damage.

CONCLUSION

Resveratrol treatment is a possible countermeasure against cryopreservation-induced mitochondrial damage.

Advanced maternal age perturbs mouse embryo development and alters the phenotype of derived embryonic stem cells

Advanced maternal age (AMA) is known to reduce fertility, increases aneuploidy in oocytes and early embryos and leads to adverse developmental consequences which may associate with offspring lifetime health risks. However, investigating underlying effects of AMA on embryo developmental potential is confounded by the inherent senescence present in maternal body systems further affecting reproductive success. Here, we describe a new model for the analysis of early developmental mechanisms underlying AMA by the derivation and characterisation of mouse embryonic stem cell (mESC-like) lines from naturally conceived embryos. Young (7-8 weeks) and Old (7-8 months) C57BL/6 female mice were mated with young males. Preimplantation embryos from Old dams displayed developmental retardation in blastocyst morphogenesis. mESC lines established from these blastocysts using conventional techniques revealed differences in genetic, cellular and molecular criteria conserved over several passages in the standardised medium. mESCs from embryos from AMA dams displayed increased incidence of aneuploidy following Giemsa karyotyping compared with those from Young dams. Moreover, AMA caused an altered pattern of expression of pluripotency markers (Sox2, OCT4) in mESCs. AMA further diminished mESC survival and proliferation and reduced the expression of cell proliferation marker, Ki-67. These changes coincided with altered expression of the epigenetic marker, Dnmt3a and other developmental regulators in a sex-dependent manner. Collectively, our data demonstrate the feasibility to utilise mESCs to reveal developmental mechanisms underlying AMA in the absence of maternal senescence and with reduced animal use.

Mitochondria: emerging therapeutic strategies for oocyte rescue

As the vital organelles for cell energy metabolism, mitochondria are essential for oocyte maturation, fertilization, and embryo development. Abnormalities in quantity, quality, and function of mitochondria are closely related to poor fertility and disorders, such as decreased ovarian reserve (DOR), premature ovarian aging (POA), and ovarian aging, as well as maternal mitochondrial genetic disease caused by mitochondrial DNA (mtDNA) mutations or deletions. Mitochondria have begun to become a therapeutic target for infertility caused by factors such as poor oocyte quality, oocyte aging, and maternal mitochondrial genetic diseases. Mitochondrial replacement therapy (MRT) has attempted to use heterologous or autologous mitochondria to rebuild healthy state of oocyte by increasing the amount of mitochondria (e.g., partial ooplasm transfer, autologous mitochondrial transfer), or to stop the transmission of mtDNA diseases by replacing abnormal maternal mitochondria (e.g., pronuclei transfer, spindle transfer, polar body transfer). Among them, autologous mitochondrial transfer is the most promising therapeutic technology as of today which does not involve using a third party, but its clinical efficacy is controversial due to many factors such as the aging phenomenon of germ line cells, the authenticity of the existence of ovarian stem cells (OSC), and secondary damage caused by invasive surgery to patients with poor ovarian function. Therefore, the research of optimal autologous cell type that can be applied in autologous mitochondrial transfer is an area worthy of further exploration. Besides, the quality of germ cells can also be probably improved by the use of compounds that enhance mitochondrial activity (e.g., coenzyme Q10, resveratrol, melatonin), or by innovative gene editing technologies which have shown capability in reducing the risk of mtDNA diseases (e.g., CRISPR/Cas9, TALENTs). Though the current evidences from animal and clinical trials are not sufficient, and some solutions of technical problems are still needed, we believe this review will guide a new direction in the possible clinical applied mitochondrial-related therapeutic strategies in reproductive medicine.

Comparison of Embryo and Clinical Outcomes in Different Types of Incubator Between Two Different Embryo Culture Systems

This study aimed to compare the clinical outcomes of an oxidative stress-reducing embryo culture system (ORES) containing compounds that minimize intercellular oxidative stress, with those of a standard embryo culture system (StES). Furthermore, we investigated the efficiency of the ORES regarding the type of incubator used (time-lapse incubator [TLI] or non-time-lapse dry incubator [non-TLI]) and maternal age. In this retrospective study, we analyzed 3610 oocyte retrieval cycles (in 2537 patients) and 1726 single vitrified-warmed blastocyst transfer (SVBT) cycles (in 1726 patients) performed in a single center between April 2018 and July 2019. Transfers of single vitrified-warmed blastocysts, confirmed by fetal heartbeat, were used to assess clinical outcomes. The clinical outcomes of ORES and StES were compared in both TLI and non-TLI. Groups were stratified according to maternal age (≤39 years old, young age group; ≥40 years old, advanced age group). A significant difference in ongoing pregnancy rates was observed between the ORES and StES groups when non-TLI was used (34.9 vs. 27.0%, respectively; p < 0.05), unlike when TLI was used. Furthermore, ongoing pregnancy rates were significantly higher in the ORES group (24.8%) than in the StES group (14.9%) in the advanced age group, unlike in the young age group when non-TLI was used. In conclusion, compared to StEs, the ORES during all in vitro fertilization procedures improved ongoing pregnancy rates in the advanced age group using the non-TLI.

Alpha-lipoic acid improves the maturation and the developmental potential of goat oocytes in vitro

Oxidative stress inevitably occurs during oocyte maturation in vitro. α-lipoic acid (α-LA) has a strong antioxidant capacity, but the effect of α-LA on parthenogenetic activation of oocytes was rarely reported. This study aims to investigate the effect of supplementing α-LA to in vitro maturation medium on the subsequent developmental ability of goat parthenogenetic embryos during oocytes maturation. In the study, the goat cumulus-oocyte complex was divided into the experimental (with 25 μmol/L α-LA) and the control (without α-LA) groups. Oxidase expression was measured using RT-qPCR. After 18-22 hr of maturation, the oocytes were then parthenogenetic activated. The total antioxidant capacity of embryos was measured after 0, 24, 48, 72 and 96 hr of culture. Rates of oocyte maturation and the rates of development for parthenogenetic embryos in the α-LA group were significantly improved by 7.88% (p < .05) and 5.41% (p < .05) compared with those in the control group, respectively. After 24 hr, the difference in total antioxidant capacity was extremely significant in both groups. An evident decrease in the control group and a minor decrease in the α-LA group were observed (p < .01). The ratio of inner cell mass cells to the total cell number of blastocysts in the α-LA group increased compared with that in the control group (p < .05) on day 8. α-LA significantly promoted the expression of SOD and GPX4 of parthenogenetic blastocysts and maturated oocytes. α-LA (25 μmol/L) improved the maturation rate and the developmental competence of the parthenogenetic activation of oocytes, which might be mediated by maintaining the total antioxidant ability of oocytes during the culture period.

Clinical Application of Antioxidants to Improve Human Oocyte Mitochondrial Function: A Review

Mitochondria produce adenosine triphosphate (ATP) while also generating high amounts of reactive oxygen species (ROS) derived from oxygen metabolism. ROS are small but highly reactive molecules that can be detrimental if unregulated. While normally functioning mitochondria produce molecules that counteract ROS production, an imbalance between the amount of ROS produced in the mitochondria and the capacity of the cell to counteract them leads to oxidative stress and ultimately to mitochondrial dysfunction. This dysfunction impairs cellular functions through reduced ATP output and/or increased oxidative stress. Mitochondrial dysfunction may also lead to poor oocyte quality and embryo development, ultimately affecting pregnancy outcomes. Improving mitochondrial function through antioxidant supplementation may enhance reproductive performance. Recent studies suggest that antioxidants may treat infertility by restoring mitochondrial function and promoting mitochondrial biogenesis. However, further randomized, controlled trials are needed to determine their clinical efficacy. In this review, we discuss the use of resveratrol, coenzyme-Q10, melatonin, folic acid, and several vitamins as antioxidant treatments to improve human oocyte and embryo quality, focusing on the mitochondria as their main hypothetical target. However, this mechanism of action has not yet been demonstrated in the human oocyte, which highlights the need for further studies in this field.

The Role of Resveratrol in Mammalian Reproduction

Resveratrol is one of the most investigated natural polyphenolic compounds and is contained in more than 70 types of plants and in red wine. The widespread interest in this polyphenol derives from its antioxidant, anti-inflammatory and anti-aging properties. Several studies have established that resveratrol regulates animal reproduction. However, the mechanisms of action and the potential therapeutic effects are still unclear. This review aims to clarify the role of resveratrol in male and female reproductive functions, with a focus on animals of veterinary interest. In females, resveratrol has been considered as a phytoestrogen due to its capacity to modulate ovarian function and steroidogenesis via sirtuins, SIRT1 in particular. Resveratrol has also been used to enhance aged oocyte quality and as a gametes cryo-protectant with mainly antioxidant and anti-apoptotic effects. In males, resveratrol enhances testes function and spermatogenesis through activation of the AMPK pathway. Furthermore, resveratrol has been supplemented to semen extenders, improving the preservation of sperm quality. In conclusion, resveratrol has potentially beneficial effects for ameliorating ovarian and testes function.

Oxygen concentration alters mitochondrial structure and function in in vitro fertilized preimplantation mouse embryos

STUDY QUESTION

Does the oxygen concentration in the culture medium [either physiologic (5%) or atmospheric (20%)] affect mitochondrial ultrastructure and function in preimplantation mouse embryos generated by IVF?

SUMMARY ANSWER

Embryos cultured in 20% oxygen show increased mitochondrial abnormalities compared to embryos cultured in 5% oxygen.

WHAT IS KNOWN ALREADY

ART are widely used and have resulted in the birth of more than 8 million children. A variety of media and oxygen concentrations are used to culture embryos. Embryos cultured under physiological O2 tension (5%) reach the blastocyst stage faster and have fewer alterations in gene expression when compared with embryos cultured under atmospheric oxygen conditions (20%). The mechanisms by which oxygen tension affects preimplantation development remain unclear, but mitochondria are believed to play an important role. The aim of this study was to evaluate how mitochondrial ultrastructure and function in IVF embryos were affected by culture under physiologic (5%) or atmospheric (20%) oxygen concentrations.

STUDY DESIGN, SIZE, DURATION

Zygotes, 2-cell, 4-cell, morula and blastocyst were flushed out of the uterus after natural fertilization and used as controls. IVF was performed in CF1 x B6D2F1 mice and embryos were cultured in Potassium simplex optimized medium (KSOM) with amino acids (KAA) under 5% and 20% O2 until the blastocyst stage. Embryo development with the addition of antioxidants was also tested.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Mitochondrial function was assessed by measuring mitochondrial membrane potential, reactive oxygen species (ROS) production, ATP levels, and the expression of selected genes involved in mitochondrial function. Mitochondria ultrastructure was evaluated by transmission electron microscopy (TEM).

MAIN RESULTS AND THE ROLE OF CHANCE

Embryos cultured under 20% O2 had fewer mitochondria and more vacuoles and hooded (abnormal) mitochondria compared to the other groups (P < 0.05). At the blastocyst stage the mitochondria of IVF embryos cultured in 20% O2 had lower mtDNA copy number, a denser matrix and more lamellar cristae than controls. Overall IVF-generated blastocysts had lower mitochondrial membrane potential, higher ROS levels, together with changes in the expression of selected mitochondrial genes (P < 0.05). ATP levels were significantly lower than controls only under 5% O2, with the 20% O2 IVF group having intermediate levels. Unexpectedly, adding antioxidant to the culture medium did not improve development.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Findings in mice embryos might be different from human embryos.

WIDER IMPLICATIONS OF THE FINDINGS

This study suggests that changes in the mitochondria may be part of the mechanism by which lower oxygen concentration leads to better embryo development and further emphasize the importance of mitochondria as a locus of reprogramming.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by R01 HD 082039 to PFR, the Department of Life, Health and Environmental Sciences, University of L'Aquila, Italy (RIA 2016-2018) and the Department of Anatomy, Histology, Forensic Medicine and Orthopaedics, La Sapienza University of Rome, Italy (University grants 2016-2017). The authors declare no competing interests.

Mechanisms of oocyte aneuploidy associated with advanced maternal age

It is well established that maternal age is associated with a rapid decline in the production of healthy and high-quality oocytes resulting in reduced fertility in women older than 35 years of age. In particular, chromosome segregation errors during meiotic divisions are increasingly common and lead to the production of oocytes with an incorrect number of chromosomes, a condition known as aneuploidy. When an aneuploid oocyte is fertilized by a sperm it gives rise to an aneuploid embryo that, except in rare situations, will result in a spontaneous abortion. As females advance in age, they are at higher risk of infertility, miscarriage, or having a pregnancy affected by congenital birth defects such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Turner syndrome (monosomy X). Here, we review the potential molecular mechanisms associated with increased chromosome segregation errors during meiosis as a function of maternal age. Our review shows that multiple exogenous and endogenous factors contribute to the age-related increase in oocyte aneuploidy. Specifically, the weight of evidence indicates that recombination failure, cohesin deterioration, spindle assembly checkpoint (SAC) disregulation, abnormalities in post-translational modification of histones and tubulin, and mitochondrial dysfunction are the leading causes of oocyte aneuploidy associated with maternal aging. There is also growing evidence that dietary and other bioactive interventions may mitigate the effect of maternal aging on oocyte quality and oocyte aneuploidy, thereby improving fertility outcomes. Maternal age is a major concern for aneuploidy and genetic disorders in the offspring in the context of an increasing proportion of mothers having children at increasingly older ages. A better understanding of the mechanisms associated with maternal aging leading to aneuploidy and of intervention strategies that may mitigate these detrimental effects and reduce its occurrence are essential for preventing abnormal reproductive outcomes in the human population.

A novel culture medium with reduced nutrient concentrations supports the development and viability of mouse embryos

Further refinement of culture media is needed to improve the quality of embryos generated in vitro. Previous results from our laboratory demonstrated that uptake of nutrients by the embryo is significantly less than what is supplied in traditional culture media. Our objective was to determine the impact of reduced nutrient concentrations in culture medium on mouse embryo development, metabolism, and quality as a possible platform for next generation medium formulation. Concentrations of carbohydrates, amino acids, and vitamins could be reduced by 50% with no detrimental effects, but blastocyst development was impaired at 25% of standard nutrient provision (reduced nutrient medium; RN). Addition of pyruvate and L-lactate (+PL) to RN at 50% of standard concentrations restored blastocyst development, hatching, and cell number. In addition, blastocysts produced in RN + PL contained more ICM cells and ATP than blastocysts cultured in our control (100% nutrient) medium; however, metabolic activity was altered. Similarly, embryos produced in the RN medium with elevated (50% control) concentrations of pyruvate and lactate in the first step medium and EAA and Glu in the second step medium were competent to implant and develop into fetuses at a similar rate as embryos produced in the control medium. This novel approach to culture medium formulation could help define the optimal nutrient requirements of embryos in culture and provide a means of shifting metabolic activity towards the utilization of specific metabolic pathways that may be beneficial for embryo viability.

Effects of resveratrol, granulocyte-macrophage colony-stimulating factor or dichloroacetic acid in the culture media on embryonic development and pregnancy rates in aged mice

The success rate of assisted reproductive technology is closely correlated with maternal age. Reproductive aging pathologies are frequently caused by impaired DNA repair, genomic instability, and mitochondrial dysfunction. Several reports have shown that resveratrol can prevent age-related diseases by improving mitochondrial function. Improved blastocyst development and mitochondrial output by dichloroacetic acid (DCA) supplementation were reported in aged mice. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has significant effects on implantation rates in women with previous miscarriages. Therefore, this study was conducted to observe how those compounds influence the developmental and the reproductive potential of aged oocytes. BDF1 female mice at 58-62 weeks old were used for this study. MII oocytes were fertilized and cultured in MRC media supplemented with or without resveratrol (0.5 μM), GM-CSF (2 ng/ml) or DCA (1.0 mM). The addition of resveratrol, GM-CSF or DCA tended to increase blastocyst development and pregnancy rates. Supplementation with resveratrol significantly increased the pregnancy and implantation rates (p < 0.05). Moreover, resveratrol decreased reactive oxygen species production and increased mitochondrial membrane potential. These results suggest that the addition of resveratrol can increase pregnancy outcomes in women of advanced maternal age.

l-carnitine supplementation during in vitro culture regulates oxidative stress in embryos from bovine aged oocytes

Aging oocytes undergo various molecular, cellular, and biochemical changes. Aging of oocytes results in reduced embryo developmental capacity and blastocyst quality, which is thought to be caused partly by the accumulation of reactive oxygen species (ROS). This study aimed to determine the effect of l-carnitine (LC) on the development of embryos formed from aged oocytes in vitro. The development and quality of the blastocysts in the LC-treated group were significantly higher than those in the untreated aged group after in vitro fertilization (IVF). In addition, after LC treatment, the level of intracellular ROS in aged group significantly decreased, and glutathione (GSH) levels significantly increased compared with those in the untreated aged group. There was no significant difference in the mitochondrial membrane potential among the three groups. Moreover, ROS could induce autophagy and LC3 antibody was widely used as a marker for detecting autophagy. The fluorescence intensity of LC3 in the aged group was significantly higher than that of LC3 in the LC-treated group. Furthermore, Real-time reverse transcriptase-polymerase chain reaction showed that the mRNA levels of antioxidation genes GPX4 and SOD1 were significantly higher in embryos from LC-treated group than in those from the untreated aged group. In summary, our results indicated that LC can improve the developmental capacity of embryos from aging oocytes in vitro by reducing oxidative stress.

Mitochondria as a tool for oocyte rejuvenation

Ovarian aging leads to a decrease in the quantity and quality of oocytes. Aged oocytes have significantly reduced amounts of mitochondria, the energy factories of cells, leading to lower fertilization rates and poor embryonic development. Various techniques have tried to use heterologous or autologous sources of mitochondria to reestablish oocyte health by providing more energy. However, heterologous sources are no longer used owing to the known risk of heteroplasmy. Although autologous methods have recently been tested in humans, they have not shown a clear improvement in embryo quality. In this review, we describe the techniques that have been tested in recent years to provide a state of the art on oocyte rejuvenation through extra injection of mitochondria.

N-acetylcysteine addition after vitrification improves oocyte mitochondrial polarization status and the quality of embryos derived from vitrified murine oocytes

Background

Vitrification is the safest method to cryopreserve oocytes, however the process alters mitochondrial function resulting from increased reactive oxygen species (ROS) production. Our aim was to alleviate ROS stress in vitrified mice oocytes using N-acetylcysteine (NAC at 1 mM), to improve the oocyte’s developmental competence.

Results

Hence, four experimental groups were compared: fresh oocytes (F-C), vitrified oocytes (V-C), NAC addition prior to oocyte vitrification (V-NAC-Pre) and NAC addition after vitrification (V-NAC-Post). V-NAC-Pre and V-NAC-Post exhibited higher levels of mitochondrial polarization compared to vitrified oocytes (36.5 ± 3.1, 37.7 ± 1.3 and 27.2 ± 2.4 measured as the spatial coefficient of variation/oocyte respectively, mean ± SEM; p < 0.05). However, ROS production increased in vitrified oocytes added with NAC compared to the vitrified control (1124.7 ± 102.1 [V-NAC-Pre] and 1063.2 ± 82.1 [V-NAC-Post] vs. 794.6 ± 164.9 [V-C]; arbitrary fluorescence units/oocyte, mean ± SEM; p < 0.05). ATP significantly decreased in V-NAC-Pre compared to V-NAC-Post oocytes (18.5 ± 6.9 vs. 54.2 ± 4.6 fmol/oocyte respectively, mean ± SEM; p < 0.05), and no differences were observed between V-NAC-Post, F-C and V-C groups. Blastocyst rates derived from F-C oocytes was higher than those derived from V-NAC-Pre (90.7 ± 1.8 vs. 79.1 ± 1.8, respectively, mean % ± SEM,; p < 0.05) but similar to those derived from V-NAC-Post (90.7 ± 1.8, mean % ± SEM, p > 0.05). Total blastomere count of blastocysts derived from V-NAC-Post after in vitro fertilization (IVF) was higher than embryos produced from V-C.

Conclusions

The addition of NAC after vitrification improves the quality of vitrified mature murine oocytes while its addition prior to vitrification is advised against.

Antioxidant defense capacity of ovarian tissue after vitrification in a metal closed system

OBJECTIVE

The present study analyzed the quality of bovine ovarian tissue after vitrification in a metal closed chamber, in terms of putative changes in tissue viability (lactate dehydrogenase -LDH- release), anti-oxidant defenses, and redox parameters caused by cryopreservation.

METHODS

Small and large fragmented bovine ovarian tissue specimens were vitrified in a metal chamber. After rewarming, tissue samples were fixed or cultured for 48 hours. Glutathione (GSH), protein sulfhydryl content, Total Radical Trapping Antioxidant Potential (TRAP), and lactate dehydrogenase were analyzed immediately after rewarming and after tissue culture.

RESULTS

No changes in antioxidant parameters or viability of rewarmed tissue samples were found immediately or 48h after vitrification. The method of vitrification in a metal closed chamber used in this study preserved the quality of bovine ovarian tissue. Furthermore, our data showed that the size of the tissue specimens did not affect post-vitrification biochemical viability parameters.

CONCLUSIONS

We believe that the vitrification methodology employed in the present study is safe and effective, and should be evaluated for use in humans.

A pre-in vitro maturation medium containing cumulus oocyte complex ligand-receptor signaling molecules maintains meiotic arrest, supports the cumulus oocyte complex and improves oocyte developmental competence

STUDY QUESTION

Can a pre-in vitro maturation (pre-IVM) medium containing signaling molecules rather than chemical/pharmaceutical agents, sustain meiotic arrest and improve developmental competence of in vitro matured oocytes in CF1 outbred mice?

SUMMARY ANSWER

A short 2 h period of pre-IVM prevents spontaneous meiotic resumption, improves mitochondria activity in subsequently matured oocytes, and increases developmental competence, pregnancy rate and implantation of resulting embryos.

WHAT IS KNOWN ALREADY

Spontaneous resumption of meiosis in vitro is detrimental for oocyte developmental competence. Pre-IVM systems that prevent spontaneous meiotic resumption with chemical/pharmaceutical agents are a promising approach to improving IVM oocyte competence; however, the success of these methods has proven to be inconsistent.

STUDY DESIGN, SIZE, DURATION

This study consisted of a series of experiments using cumulus oocyte complexes (COC) derived from outbred mice following ovarian stimulation. The study was designed to examine if a novel, ligand/receptor-based pre-IVM treatment could sustain meiotic arrest in vitro and improve oocyte developmental competence, compared to control IVM. Two pre-IVM durations (2 h and 24 h) were evaluated, and the effect of the mitochondrial stimulator PQQ during 24 h pre-IVM was studied.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Murine (outbred CF1) immature COC were cultured in vitro in the presence of C-type natriuretic peptide (CNP) (30 nM), estradiol (100 nM), FSH (1 × 10-4 IU/ml) and bone morphogenic protein 15 (BMP15) (100 ng/ml) for 2 h or 24 h prior to IVM. Meiotic status during pre-IVM and IVM was analyzed using orcein staining, and functionality of gap junction communication was confirmed using the functional gap junction inhibitor carbenoxolone (CBX). Oocytes exposed to pre-IVM treatment were compared to control oocytes collected on the same day from the same females and undergoing standard IVM. Developmental competence and embryo viability was assessed by oocyte mitochondrial activity and ATP concentration, in vitro embryo development following IVF and in vitro culture, blastocyst cell number and allocation, embryo morphokinetics, and embryo transfer. Differences were determined to be significant when P < 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

Both a short (2 h) and long (24 h) pre-IVM period successfully prevented spontaneous resumption of meiosis. Moreover, gap junctions remained open during the pre-IVM period, as shown by the resumption of meiosis (95.9 ± 2.1%) in the presence of CBX during pre-IVM. A 2 h pre-IVM treatment improved blastocyst development after 96 h of culture per cleaved embryo compared to control (71.9 ± 7.4% versus 53.3 ± 6.2%, respectively), whereas a longer 24 h pre-IVM had no effect on development. A short 2 h period of pre-IVM increased mitochondrial activity in mature oocytes. On the contrary, mitochondrial activity was reduced in mature oocytes following 24 h of arrest and IVM. Treatment of arrested COC with pyrroloquinoline quinone (PQQ) during the 24 h pre-IVM period successfully maintained mitochondrial activity equal to control. However, PQQ was not able to improve blastocyst development compared to pre-IVM 24 h without PQQ. Moreover, ATP concentration in mature oocytes following pre-IVM and/or IVM, did not differ between treatments. A 2 h pre-IVM period prior to IVM improved pregnancy rate following transfer to recipient females. Implantation was also improved after transfer of embryos derived from oocytes arrested for either 2 h or 24 h prior to IVM, compared to control IVM derived embryos (41.9 ± 9%, 37.2 ± 9.5% and 17.2 ± 8.3%, respectively), although fetal development did not differ.

LIMITATIONS, REASONS FOR CAUTION

Slower meiotic resumption and enhanced mitochondrial activity likely contribute to improved developmental competence of oocytes exposed to pre-IVM for 2 h, but further experiments are required to identify specific mechanisms. Maintaining oocytes in meiotic arrest for 24 h with this approach could be a potential window to improve oocyte quality. However, an initial attempt to utilize this period of arrest to manipulate quality with PQQ, a mitochondrial stimulator, did not improve oocyte competence.

WIDER IMPLICATIONS OF THE FINDINGS

IVM could be an attractive clinical alternative to conventional IVF, with reduced time, cost and reliance on high doses of exogenous hormones to stimulate follicle growth, thus eliminating ovarian hyperstimulation syndrome (OHSS). Currently IVM is not widely used as it results in reduced embryo development and lower pregnancy outcomes compared to embryos produced from in vivo matured oocytes. Our approach to IVM, incorporating a ligand/receptor pre-IVM period, could improve human oocyte quality following IVM leading to routine adoption of this patient friendly technology. In addition, our methodology of pre-IVM containing signaling molecules rather than chemical/pharmaceutical agents may prove to be more consistent at improving oocyte quality than those focusing only on cAMP modulation with pharmacological agents. Finally, a reliable method of maintaining oocytes in meiotic arrest in vitro provides a novel window of opportunity in which the oocyte may be manipulated to address specific physiological deficiencies prior to meiotic resumption.

LARGE SCALE DATA

N/A.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Colorado Center for Reproductive Medicine (CCRM, Lone Tree, Colorado USA). We declare no conflict of interest.

Endometriosis Is a Cause of Infertility. Does Reactive Oxygen Damage to Gametes and Embryos Play a Key Role in the Pathogenesis of Infertility Caused by Endometriosis?

Approximately, 10-15% of women of reproductive age are affected by endometriosis, which often leads to infertility. Endometriosis often has an inherited component, and several causative predisposing factors are hypothesized to underlie the pathogenesis of endometriosis. One working hypothesis is the theory of retrograde menstruation. According to the theory of retrograde menstruation, components of refluxed blood, including apoptotic endometrial tissue, desquamated menstrual cells, lysed erythrocytes, and released iron, induce inflammation in the peritoneal cavity. This in turn activates macrophage release of reactive oxygen species (ROS), leading to oxidative stress via the respiratory burst. Refluxed blood promotes the Fenton reaction, terminating in the production of hydroxyl radical, the most potently destructive ROS. In this article, we review the papers that demonstrate decreased quantity and quality of oocytes and embryos retrieved from IVF/ICSI patients with endometriosis. We discuss literature data demonstrating that ROS are generated in endometriotic tissues that have physical proximity to gametes and embryos, and demonstrating adverse impacts on oocyte, sperm and embryo microtubule apparatus, chromosomes, and DNA. Data that addresses the notions that endometriosis causes oocyte and fetal aneuploidy and that these events are mediated by ROS species are also discussed. Literature data are also discussed that employ use of anti-oxidant molecules to evaluate the importance of ROS-mediated oxidative damage in the pathogenesis of endometriosis. Studies are discussed that have employed anti-oxidants compounds as therapeutics to improve oocyte and embryo quality in infertile subjects, and improve fertility in patients with endometriosis.

Mitochondrial DNA content is associated with ploidy status, maternal age, and oocyte maturation methods in mouse blastocysts

PURPOSE

It was reported that mitochondrial DNA (mtDNA) was significantly increased in aneuploid human embryos compared to euploid embryos and was also associated with maternal age. In this study, we further established the mouse model of mtDNA quantitation in reproductive samples based on whole-genome amplification (WGA) and next-generation sequencing (NGS).

METHODS

WGA followed by NGS-based mtDNA quantitation was first performed on 6 single- and 100-cell samples from a tumor-derived mouse cell line, which was exposed to ethidium bromide to reduce mtDNA content. The relative mtDNA content was normalized to nuclear DNA. This method was then applied to mouse reproductive samples, including 40 pairs of oocytes and polar bodies from 8 CD-1 female mice of advanced reproductive age and 171 blastocysts derived via in vitro maturation (IVM) or in vivo maturation (IVO) from young (6-9 weeks) and reproductively aged (13.5 months) female CF-1 mice.

RESULTS

Exposure to ethidium bromide for 3 and 6 days decreased mtDNA levels in both the single- and 100-cell samples as expected. Results demonstrated that the first polar body contained an average of 0.9% of mtDNA relative to oocytes. Compared to the cells in blastocysts, oocytes contained about 180 times as much mtDNA per cell. mtDNA levels were compared among blastocysts from reproductively young and old female mice that had either been produced by IVM or IVO. Cells in blastocysts from younger mice contained significantly lower amounts of mtDNA compared to aged mice (P < 0.0001). Cells in blastocysts produced via IVO had higher mtDNA content than IVM-derived blastocysts (P = 0.0001). Cells in aneuploid blastocysts were found to have significantly higher (1.74-fold) levels of mtDNA compared to euploid blastocysts (P = 0.0006).

CONCLUSION

A reliable method for assessing mtDNA content in mouse gametes and embryos was established. Relative mtDNA levels were elevated in aneuploid embryos relative to euploid embryos, were higher in blastocysts from reproductively old mice relative to young mice, and were lower in embryos derived from IVM compared to IVO.

The lipid peroxidation product 4-hydroxynonenal contributes to oxidative stress-mediated deterioration of the ageing oocyte

An increase in intraovarian reactive oxygen species (ROS) has long been implicated in the decline in oocyte quality associated with maternal ageing. Oxidative stress (OS)-induced lipid peroxidation and the consequent generation of highly electrophilic aldehydes, such as 4-hydroxynonenal (4-HNE), represents a potential mechanism by which ROS can inflict damage in the ageing oocyte. In this study, we have established that aged oocytes are vulnerable to damage by 4-HNE resulting from increased cytosolic ROS production within the oocyte itself. Further, we demonstrated that the age-related induction of OS can be recapitulated by exposure of germinal vesicle (GV) oocytes to exogenous H₂O₂. Such treatments stimulated an increase in 4-HNE generation, which remained elevated during in vitro oocyte maturation to metaphase II. Additionally, exposure of GV oocytes to either H₂O₂ or 4-HNE resulted in decreased meiotic completion, increased spindle abnormalities, chromosome misalignments and aneuploidy. In seeking to account for these data, we revealed that proteins essential for oocyte health and meiotic development, namely α-, β-, and γ-tubulin are vulnerable to adduction via 4-HNE. Importantly, 4-HNE-tubulin adduction, as well as increased aneuploidy rates, were resolved by co-treatment with the antioxidant penicillamine, demonstrating a possible therapeutic mechanism to improve oocyte quality in older females.

Protective effect of antioxidants on the pre-maturation aging of mouse oocytes

Pre-maturation aging of immature oocytes may adversely affect the fate of an oocyte. Oxidative stress is one of the most detrimental factors affecting oocyte developmental competence and maturation during aging. In this study, experiments were designed to examine whether supplementation of antioxidants in a culture medium could protect immature mouse oocytes from damages caused by oxidative stress. Mouse oocytes at germinal vesicle stage were prevented from meiosis resumption and cultured in a medium with or without antioxidants for 12–36 h to allow oocytes to undergo aging. After aging, oocytes were cultured for maturation. Nuclear maturation, mitochondria activity, spindle morphology and DNA integrity were examined after maturation. It was found that antioxidants had protective effects on the oocytes in terms of nuclear maturation, functional mitochondria, spindle morphology and DNA integrity. As aging time was prolonged from 12 to 36 h, the protective effect of antioxidants became more obvious. However, as compared with oocytes without aging, it was found that aging significantly inhibited nuclear maturation, impaired mitochondria function, and damaged the spindle and DNA. These results indicate that pre-maturation aging is detrimental to oocytes’ competence to undergo maturation and other cellular activities, and antioxidants can protect oocytes from damages caused by aging.

Cerium oxide nanoparticles (CeO2 NPs) improve the developmental competence of in vitro-matured prepubertal ovine oocytes

The present study investigated whether supplementation with different doses of cerium dioxide nanoparticles (CeO2 NPs) during in vitro maturation (IVM) of prepubertal ovine oocytes influenced their embryonic development in vitro. Cumulus–oocyte complexes derived from the ovaries of slaughtered prepubertal sheep underwent IVM with CeO2NPs (0, 44, 88 or 220 µg mL–1). Matured oocytes were fertilised in vitro and zygotes were cultured for 7 days. The results demonstrated that CeO2NPs were internalised in the cumulus cells and not in the oocyte. The treatment with CeO2NPs did not affect nuclear maturation or intracellular levels of reactive oxygen species of the oocytes. The percentage of oocytes with regular chromatin configuration and cytoskeleton structures when treated with 44 µg mL–1 CeO2NPs was similar to oocytes matured in the absence of CeO2NPs and significantly higher than those treated with 88 or 220 µg mL–1 CeO2NPs. The relative quantification of transcripts in the cumulus cells of oocytes matured with 44 µg mL–1 CeO2NPs showed a statistically lower mRNA abundance of BCL2-associated X protein (BAX), B-cell CLL/lymphoma 2 (BCL2) and superoxide dismutase 1 (SOD1) compared with the 0 µg mL–1 CeO2 NPs group. A concentration of 44 µg mL–1 CeO2NPs significantly increased the blastocyst yield and their total, inner cell mass and trophectoderm cell numbers, compared with the 0 and 220 µg mL–1 groups. A low concentration of CeO2NPs in the maturation medium enhanced in vitro embryo production of prepubertal ovine oocytes.

Bu Shen Tiao Chong recipe restores diminished ovary reserve through the BDNF pathway

PURPOSE

The purpose of this study was to explore the molecular pathway of BSTCR (Bu Shen Tiao Chong recipe) in retrieving diminished ovary reserve (DOR).

METHODS

The DOR model was established through injecting cyclophosphamide and the effect of BSTCR was examined under this background.

RESULTS

BSTCR was shown to restore depleted brain-derived neurotrophic factor (BDNF), CDC2, cyclin B, GSH1, and P38 levels as well as impaired oocyte maturation and the higher apoptosis induced in DOR. BSTCR also enhances the response of oocytes to in vitro fertilization, with higher implantation rate, birth rate, and placenta weight.

CONCLUSION

BSTCR might exert its beneficial role in oocyte maturation and restore DOR through regulating the BDNF pathway. And this pathway itself is probably through the consequence on several serum hormones such as FSH, E2, Inhibin B, etc.

Antioxidants improve mouse preimplantation embryo development and viability

STUDY QUESTION

What is the effect of three antioxidants (acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid), when used individually and in combination, on mouse embryo development in culture, and subsequent fetal development post-transfer?

SUMMARY ANSWER

A combination of antioxidants resulted in significant increases in blastocyst cell number, maintained intracellular glutathione (GSH) levels, supported earlier cleavage times from 5-cell stage to expanded blastocyst, and improved fetal developmental irrespective of incubator oxygen concentration.

WHAT IS KNOWN ALREADY

Acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid have been shown to have beneficial effects individually in several tissues, and most recently on developing embryos, in the presence of oxidative stress.

STUDY DESIGN, SIZE, DURATION

Morphokinetics of mouse embryos were quantitated using time-lapse imaging. GSH levels in pronucleate oocytes were measured. Blastocysts underwent differential nuclear staining for inner cell mass and trophectoderm cells or were transferred to recipient females to assess implantation and fetal development.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Pronucleate oocytes from F1 mice were cultured in 5 or 20% oxygen either individually or in groups of 10, in media G1/G2, in the presence or absence of 10 µM acetyl-L-carnitine /10 µM N-acetyl-L-cysteine /5 µM α-lipoic acid, either individually or in combination. Controls were embryos cultured without antioxidants. Intracellular levels of reduced glutathione were quantitated in pronucleate oocytes. Embryo development and viability were analysed through time-lapse microscopy and embryo transfers.

MAIN RESULTS AND THE ROLE OF CHANCE

Antioxidants significantly increased mouse blastocyst cell numbers compared with control when used individually (P< 0.05) and to a greater effect when all three were used in combination (P< 0.01) in 20% oxygen. The combination of antioxidants resulted in faster development rates to 5-cell cleavage stage, which continued until the expanded blastocyst stage when cultured in 20% oxygen. The beneficial effects of combining the antioxidants were greater for embryos cultured individually as opposed to in groups of 10 and for those embryos cultured in 20% compared to 5% oxygen. Levels of GSH were significantly decreased in control embryos that were incubated in the absence of antioxidants in 20% oxygen (P< 0.01), compared with in vivo flushed embryos. However, when embryos were cultured with antioxidants the level of GSH was not different to that of in vivo developed embryos. Embryos cultured in the presence of antioxidants in 20% oxygen and transferred resulted in significantly longer crown-rump length (11.6 ± 0.1 mm versus 11.3 ± 0.1 mm; P< 0.01), heavier fetuses (209.8 ± 11.8 mg versus 183.9 ± 5.9 mg; P< 0.05) and heavier placentas (103.5 ± 3.1 mg versus 93.6 ± 2.7 mg; P< 0.01) compared with controls (all data are mean ± SEM). Further, a post-implantation benefit of the antioxidant combination was also evident after culture in 5% oxygen.

LIMITATIONS, REASONS FOR CAUTION

Embryo development and implantation was only examined in the mouse.

WIDER IMPLICATIONS OF THE FINDINGS

These findings show that a combination of antioxidants in the culture media has a highly beneficial effect on mouse preimplantation embryo development in vitro and on subsequent fetal development post-transfer. These data indicate a potential role for the inclusion of specific antioxidant combinations in human embryo culture media irrespective of oxygen concentration. However, before application to human embryos, a proper evaluation of this approach in prospective, preferably randomized, trials will be required.

STUDY FUNDING/COMPETING INTERESTS

This work was funded by a research grant from Vitrolife AB (Sweden). The authors have no conflict of interest to declare.

Next Generation Sequencing-Based Comprehensive Chromosome Screening in Mouse Polar Bodies, Oocytes, and Embryos

Advanced reproductive age is unequivocally associated with increased aneuploidy in human oocytes, which contributes to infertility, miscarriages, and birth defects. The frequency of meiotic chromosome segregation errors in oocytes derived from reproductively aged mice appears to be similar to that observed in humans, but a limitation of this important model system is our inability to accurately identify chromosome-specific aneuploidy. Here we report the validation and application of a new low-pass whole-genome sequencing approach to comprehensively screen chromosome aneuploidy in individual mouse oocytes and blastocysts. First, we validated this approach by using single mouse embryonic fibroblasts engineered to have stable trisomy 16. We further validated this method by identifying reciprocal chromosome segregation errors in the products of meiosis I (gamete and polar body) in oocytes from reproductively aged mice. Finally, we applied this technology to investigate the incidence of aneuploidy in blastocysts derived from in vitro- and in vivo-matured oocytes in both young and reproductively aged mice. Using this next generation sequencing approach, we quantitatively assessed meiotic and mitotic segregation errors at the single chromosome level, distinguished between errors due to premature separation of sister chromatids and classical nondisjunction of homologous chromosomes, and quantified mitochondrial DNA (mtDNA) segregation in individual cells. This whole-genome sequencing technique, therefore, greatly improves the utility of the mouse model system for the study of aneuploidy and is a powerful quantitative tool with which to examine the molecular underpinnings of mammalian gamete and early embryo chromosome segregation in the context of reproductive aging and beyond.

Building a better mouse embryo assay: effects of mouse strain and in vitro maturation on sensitivity to contaminants of the culture environment

PURPOSE

The aim of this study is to compare the sensitivity of the standard one-cell mouse embryo assay (MEA) to that using in vitro-matured oocytes from hybrid and outbred mice.

METHODS

The study was done by culturing embryos in the presence or absence of two concentrations (0.0005 or 0.001 % v/v) of Triton X-100 (TX100). Embryonic development, blastocyst cell numbers (total and allocation to the trophectoderm [TE] and inner cell mass [ICM]), and blastocyst gene expression were evaluated.

RESULTS

Neither concentration of TX100 affected (P > 0.05) cleavage, blastocyst development, or hatching in one-cell embryos from BDF1 mice. However, all cell number endpoints were reduced (P < 0.05) by the high concentration of TX100 and the number of ICM cells was reduced (P < 0.05) by the low concentration of TX100. Inhibitory (P < 0.05) effects of the high concentration of TX100 were observed in in vitro maturation (IVM) embryos from BDF1, CF1, and SW, but not ICR, mice. Cell number and allocation were negatively affected by the high concentration of TX100 in CF1 and SW embryos, but not in BDF1 or ICR embryos. The only developmental endpoints affected by the low concentration of TX100 were cleavage of BDF1 oocytes, blastocyst development of SW embryos, and cell numbers (total and inner cell mass (ICM)) of SW blastocysts.

CONCLUSIONS

The sensitivity of the MEA to TX100 is improved by using embryos from in vitro-matured oocytes, using oocytes from some outbred (SW or CF1, not ICR) strains of mice, and evaluating blastocyst cell number and allocation.

The impact of the protein stabilizer octanoic acid on embryonic development and fetal growth in a murine model

PURPOSE

The purpose of this study was to determine the effect of the protein stabilizer octanoic acid on blastocyst development, implantation, and fetal growth in a murine model.

METHODS

One-cell mouse embryos were collected and individually cultured in medium supplemented with recombinant human serum albumin for 96 h at 5 % oxygen in an EmbryoScope. Embryos were randomly allocated to four octanoic acid groups (0, 400, 800, or 1200 μM). Blastocyst development and cell cycle timings were calculated at 96 h of culture, and experiments were repeated in triplicate. Blastocysts were stained and fixed at 96 h for differential cell counts. Following 96 h of culture, blastocysts were transferred to recipients to determine implantation rates and fetal and placental weights.

RESULTS

Blastocyst development, hatching rates, developmental kinetics, and total number of cells were negatively affected by octanoic acid at concentrations commonly used in human IVF. Implantation was not affected by octanoic acid but fetal and placental weights at 800 μM octanoic acid were increased relative to control.

CONCLUSIONS

Octanoic acid, a standard additive to human protein supplements used in IVF, can have long-term negative effects on embryonic and fetal development. The use of octanoic acid for human embryo culture should be monitored and reduced.