Impact of Oxidative Stress on Age-Associated Decline in Oocyte Developmental Competence

Ovarian Aging: Role of Pituitary-Ovarian Axis Hormones and ncRNAs in Regulating Ovarian Mitochondrial Activity

The number of mitochondria in the oocyte along with their functions (e.g., energy production, scavenger activity) decline with age progression. Such multifaceted functions support several processes during oocyte maturation, ranging from energy supply to synthesis of the steroid hormones. Hence, it is hardly surprising that their impairment has been reported in both physiological and premature ovarian aging, wherein they are crucial players in the apoptotic processes that arise in aged ovaries. In any form, ovarian aging implies the progressive damage of the mitochondrial structure and activities as regards to ovarian germ and somatic cells. The imbalance in the circulating hormones and peptides (e.g., gonadotropins, estrogens, AMH, activins, and inhibins), active along the pituitary-ovarian axis, represents the biochemical sign of ovarian aging. Despite the progress accomplished in determining the key role of the mitochondria in preserving ovarian follicular number and health, their modulation by the hormonal signalling pathways involved in ovarian aging has been poorly and randomly explored. Yet characterizing this mechanism is pivotal to molecularly define the implication of mitochondrial dysfunction in physiological and premature ovarian aging, respectively. However, it is fairly difficult considering that the pathways associated with ovarian aging might affect mitochondria directly or by altering the activity, stability and localization of proteins controlling mitochondrial dynamics and functions, either unbalancing other cellular mediators, released by the mitochondria, such as non-coding RNAs (ncRNAs). We will focus on the mitochondrial ncRNAs (i.e., mitomiRs and mtlncRNAs), that retranslocate from the mitochondria to the nucleus, as active players in aging and describe their role in the nuclear-mitochondrial crosstalk and its modulation by the pituitary-ovarian hormone dependent pathways. In this review, we will illustrate mitochondria as targets of the signaling pathways dependent on hormones and peptides active along the pituitary/ovarian axis and as transducers, with a particular focus on the molecules retrieved in the mitochondria, mainly ncRNAs. Given their regulatory function in cellular activities we propose them as potential diagnostic markers and/or therapeutic targets.

Prolonged Cryopreservation Negatively Affects Embryo Transfer Outcomes Following the Elective Freeze-All Strategy: A Multicenter Retrospective Study

BACKGROUND

With the development of embryo freezing and warming technology, frozen-thawed embryo transfer (FET) has been widely utilized. However, studies investigating the association between cryopreservation duration and FET outcomes are limited and controversial, and previous studies did not conduct stratification analyses based on demographic or clinical characteristics.

METHODS

This multicenter retrospective study included 17,826 women who underwent their first FET following the freeze-all strategy during the period from January 2014 to December 2018. Duration of cryopreservation was categorized into five groups: 3-8 weeks, 8-12 weeks, 12-26 weeks, 26-52 weeks, and >52 weeks. Modified Poisson regression and multivariate logistic regression were used to assess the association between cryostorage time of vitrified embryos and transfer outcomes. Moreover, further stratification analyses were performed according to variables with p <0.05 in multivariate models.

RESULTS

In this large multicenter study, we observed that storage duration was inversely associated with the possibility of pregnancy and live birth (p <0.001), but not with the risk of ectopic pregnancy and miscarriage. Stratification analyses based on maternal age, the number of oocytes retrieved, and condition of embryo transferred indicated that the inverse correlation was significant in the subpopulation with characteristics: (1) less than 40 years old, (2) more than 3 oocytes retrieved, and (3) only high-quality blastocysts transferred.

CONCLUSION

The results of this large, multicenter, retrospective study suggested that prolonged cryopreservation was inversely associated with the probability of pregnancy and live birth. Therefore, for patients who adopt a freeze-all strategy, early FET might achieve a better outcome.

Imperatorin Ameliorates the Aging-Associated Porcine Oocyte Meiotic Spindle Defects by Reducing Oxidative Stress and Protecting Mitochondrial Function

Imperatorin (IMP) exhibits a variety of pharmacological properties, including antioxidant, anti-inflammatory, antibacterial, anti-cancer, and anti-hypertension activities. However, its effects on animal reproduction systems, especially oocyte development, maturation, and aging are not yet clear. In this study, the effects of IMP on oocyte development and aging as well as the underlying molecular mechanisms were explored. Oocytes were cultured for an additional 24 h for aging. Results revealed that the blastocyst formation and hatching rates of embryos, which were parthenogenetically activated aged oocytes, were significantly increased with IMP treatment (40 μM). Simultaneously, well-distributed cortical granules but no significant difference in zona pellucida hardness were observed after IMP treatment. During this stage, intracellular reactive oxygen species, apoptosis, and autophagy levels were decreased, while mitochondrial membrane potential, glutathione level, and activity of superoxide dismutase and catalase were increased. IMP-treated aged oocytes also showed significantly higher expression of MOS, CCNB1, BMP15, and GDF9 than non-IMP-treated aged oocytes although their levels were still lower than those in the fresh oocytes. These results suggest that IMP can effectively ameliorate the quality of aged porcine oocytes by reducing oxidative stress and protecting mitochondrial function.

Attenuation of the mutual elevation of iron accumulation and oxidative stress may contribute to the neuroprotective and anti-seizure effects of xenon in neonatal hypoxia-induced seizures

Previous studies have suggested that xenon inhalation has neuroprotective and antiepileptic effects; however, the underlying mechanisms involved remain unclear. This study aimed to investigate the possible xenon inhalation mechanisms involved in the neuroprotection and antiepileptic effects. A neonatal hypoxic C57BL/6J mouse model was used for the experiments. Immediately after hypoxia treatment, the treatment group inhaled a xenon mixture (70% xenon/21% oxygen/9% nitrogen) for 60 min, while the hypoxia group inhaled a non-xenon mixture (21% oxygen/79% nitrogen) for 60 min. Seizure activity was recorded at designated time points using electroencephalography. Oxidative stress levels, iron levels, neuronal injury, and learning and memory functions were also studied. The results showed that hypoxia increased the levels of iron, oxidative stress, mitophagy, and neurodegeneration, which were accompanied by seizures and learning and memory disorders. In addition, our results confirmed that xenon treatment significantly attenuated the hypoxia-induced seizures and cognitive defects in neonatal C57 mice. Moreover, the increased levels of iron, oxidative stress, mitophagy, and neuronal injury were reduced in xenon-treated mice. This study confirms the significant protective effects of a xenon mixture on hypoxia-induced damage in neonatal mice. Furthermore, our results suggest that reducing oxidative stress levels and iron accumulation may be the underlying mechanisms of xenon activity. Studying the protective mechanisms of xenon will advance its applications in potential therapeutic strategies.

Prenatal exposure to an environmentally relevant phthalate mixture accelerates biomarkers of reproductive aging in a multiple and transgenerational manner in female mice

Phthalates are known endocrine-disrupting chemicals that are found in many consumer products. Our laboratory previously developed a relevant phthalate mixture consisting of six phthalates and found that it disrupted female fertility in mice. However, it is unknown if prenatal exposure to phthalate mixtures can accelerate reproductive aging and if this occurs in multiple generations. Thus, we tested the hypothesis that prenatal exposure to a mixture of phthalates accelerates biomarkers of reproductive aging in multiple generations of female mice. Pregnant CD-1 mice were orally dosed with vehicle control or a phthalate mixture (20 μg/kg/day-500 mg/kg/day) daily from gestational day 10 to birth. Adult F1 females born to these dams were used to create the F2 and F3 generations by mating them with unexposed males. At 13 months, estrous cyclicity was monitored and ovaries and sera were collected for analysis. In the F1 generation, the mixture decreased testosterone and inhibin B levels, but increased follicle-stimulating hormone and luteinizing hormone levels compared to control. In the F2 generation, the phthalate mixture decreased the percent of antral follicles and testosterone hormone levels compared to control. In the F3 generation, prenatal exposure to the phthalate mixture increased ovarian weight, increased the time in metestrus/diestrus, altered follicle numbers, and decreased the levels of luteinizing hormone compared to control. Collectively, these data suggest that prenatal exposure to a phthalate mixture may accelerate several biomarkers of reproductive aging in a multi- and transgenerational manner in female mice.

EZH2 is essential for spindle assembly regulation and chromosomal integrity during porcine oocyte meiotic maturation†

Enhancer of zeste homolog 2 (EZH2) has been extensively investigated to participate in diverse biological processes, including carcinogenesis, the cell cycle, X-chromosome inactivation, and early embryonic development. However, the functions of this protein during mammalian oocyte meiotic maturation remain largely unexplored. Here, combined with RNA-Seq, we provided evidence that EZH2 is essential for oocyte meiotic maturation in pigs. First, EZH2 protein expression increased with oocyte progression from GV to MII stage. Second, the siRNA-mediated depletion of EZH2 led to accelerated GVBD and early occurrence of the first polar body extrusion. Third, EZH2 knockdown resulted in defective spindle assembly, abnormal SAC activity, and unstable K-MT attachment, which was concomitant with the increased rate of aneuploidy. Finally, EZH2 silencing exacerbated oxidative stress by increasing ROS levels and disrupting the distribution of active mitochondria in porcine oocytes. Furthermore, parthenogenetic embryonic development was impaired following the depletion of EZH2 at GV stage. Taken together, we concluded that EZH2 is necessary for porcine oocyte meiotic progression through regulating spindle organization, maintaining chromosomal integrity, and mitochondrial function.

Neurophysiology of cognitive behavioural therapy, deep breathing and progressive muscle relaxation used in conjunction with ART treatments: a narrative review

BACKGROUND

Infertility is defined as the failure to achieve clinical pregnancy after 12 months of regular unprotected intercourse. It could be due to male or female factors, each requiring different treatment options. ART treatment exposes couples to numerous psychological stressors. Therefore, it has been recommended by the ESHRE Psychology and Counselling Guideline Development Group recently that psychosocial support should be offered as a complementary therapy during infertility treatments. In this context, the efficiency of different psychological interventions, such as cognitive behaviour therapy (CBT), deep breathing (DB), and progressive muscle relaxation (PMR), was evaluated in several clinical trials in terms of couples' mental health and pregnancy outcomes.

OBJECTIVE AND RATIONALE

The neurophysiology of CBT, DB and PMR, which are used in interventional studies, in both men and women undergoing ART, has not yet been fully elucidated. This review represents a comprehensive report, aiming to collate novel insights into the neurobiological processes and physiological mechanisms that occur during the practice of CBT, DB and PMR.

SEARCH METHODS

PubMed, Google Scholar and Cochrane Library were interrogated to conduct this comprehensive literature review. The search was carried out using combinations of MeSH terms and keywords: infertility, assisted reproductive techniques, IVF, ICSI, emotions, psychological stress, cognitive behavioural therapy, mind-body therapies and relaxation. Relevant information related to the mechanism of action of stress management techniques were obtained from original articles and reviews published in English without taking into consideration the time of publication. Moreover, as it was not the major focus of the review, only recent systematic reviews (2015-2019) pinpointing the effects of psychological interventions on infertility treatment outcomes were also retrieved from the above-mentioned databases.

OUTCOMES

CBT, DB and PMR may modify the activity of stress-related brain regions such as the prefrontal cortex, amygdala, hypothalamus and hippocampus, as demonstrated by functional MRI and electroencephalogram studies. Furthermore, applying these techniques was associated with mood improvements and a decline in stress biomarkers, and, hypothetically, reducing stress biomarkers attenuates the stress-induced effects on ART outcomes.

WIDER IMPLICATIONS

Increasing the knowledge of fertility staff, researchers and physicians regarding the mechanisms of action of these stress management techniques has several advantages. For instance, understanding the underlying neurophysiological pathways would assist practitioners to engage ART couples in the practice of these techniques. Also, it may enhance the quality of the support programmes and psychological research. Accordingly, this will ensure that these interventions reach their full potential and therefore improve clinical outcomes.

Nonylphenol exposure affects mouse oocyte quality by inducing spindle defects and mitochondria dysfunction

Nonylphenol (NP) is a chemical raw material and intermediate which is mainly used in the production of surfactants, lubricating oil additives and pesticide emulsifiers. NP is reported to be toxic on the immune system, nervous system and reproductive system due to its binding to estrogen receptors. However, the toxicity of NP on mammalian oocyte quality remains unclear. In present study, we explored the effects of NP exposure on mouse oocyte maturation. Our results showed that 4 weeks of NP exposure increased the number of atresia follicles and decreased oocyte developmental competence. Transcriptomic analysis indicated that NP exposure altered the expression of more than 800 genes in oocytes, including multiple biological pathways. Subcellular structure examination indicated that NP exposure disrupted meiotic spindle organization and caused chromosome misalignment. Moreover, aberrant mitochondrial distribution and decreased membrane potential were also observed, indicating that NP exposure caused mitochondria dysfunction. Further analysis showed that NP exposure resulted in the accumulation of reactive oxygen species (ROS), which causes oxidative stress; and the NP-exposed oocytes showed positive Annexin-V signal, indicating the occurrence of early apoptosis. In summary, our results indicated that NP exposure reduced oocyte quality by affecting cytoskeletal dynamics and mitochondrial function, which further induced oxidative stress and apoptosis in mice.

Does coenzyme Q10 supplementation improve fertility outcomes in women undergoing assisted reproductive technology procedures? A systematic review and meta-analysis of randomized-controlled trials

OBJECTIVE

Increased oxidative stress has been identified as a pathogenetic mechanism in female infertility. However, the effect of specific antioxidants, such as coenzyme Q10 (CoQ10), on the outcomes after assisted reproductive technologies (ART) has not been clarified. The aim of this study was to systematically review and meta-analyze the best available evidence regarding the effect of CoQ10 supplementation on clinical pregnancy (CPR), live birth (LBR), and miscarriage rates (MR) compared with placebo or no-treatment in women with infertility undergoing ART.

METHODS

A comprehensive literature search was conducted in PubMed (MEDLINE), Cochrane, and Scopus, from inception to March 2020. Data were expressed as odds ratio (OR) with 95% confidence intervals (CI). The I2 index was employed for heterogeneity.

RESULTS

Five randomized-controlled trials fulfilled eligibility criteria (449 infertile women; 215 in CoQ10 group and 234 in placebo/no treatment group). Oral supplementation of CoQ10 resulted in an increase of CPR when compared with placebo or no-treatment (28.8% vs. 14.1%, respectively; OR 2.44, 95% CI 1.30-4.59, p = 0.006; I2 32%). This effect remained significant when women with poor ovarian response and polycystic ovarian syndrome were analyzed separately. No difference between groups was observed regarding LBR (OR 1.67, 95% CI 0.66-4.25, p = 0.28; I2 34%) and MR (OR 0.61, 95% CI 0.13-2.81, p = 0.52; I2 0%).

CONCLUSIONS

Oral supplementation of CoQ10 may increase CPR when compared with placebo or no-treatment, in women with infertility undergoing ART procedures, without an effect on LBR or MR.

Characterization of the Age-Dependent Changes in Antioxidant Defenses and Protein's Sulfhydryl/Carbonyl Stress in Human Follicular Fluid

The oxidative stress, characterized by the imbalance between pro-oxidants and antioxidants molecules, seems to be involved in the pathogenesis of female subfertility. In particular, the presence of different markers of oxidative stress has been reported in human follicular fluid (FF) surrounding oocytes. Based on its distinctive composition and on the close proximity to the oocyte, FF creates a unique microenvironment having a direct impact on oocyte quality, implantation, and early embryo development. An imbalance in reactive oxygen species (ROS) production in ovarian follicular fluid may have a negative effect on these processes and, as a consequence, on female fertility. Therefore, the aim of this study was to evaluate the redox state of the FF through various methodological approaches. By means of 2D-electrophoresis we demonstrated that the main structural changes occurring in the proteins of the follicular fluid of normovulatory women were correlated to the age of the patients and to the antioxidant defenses present in the FF. Measurement of these parameters could have clinical relevance, since the assessment of the oxidative stress rate may be helpful in evaluating in vitro fertilization potential.

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.

Platelet rich plasma efficiently substitutes the beneficial effects of serum during in vitro oocyte maturation and helps maintain the mitochondrial activity of maturing oocytes

Platelets contain most of the potent mitogenic factors present in serum and follicular fluid and intraovarian injection of autologous platelet rich plasma (PRP) was shown to improve ovarian function and development of preantral follicles. This study evaluated the effect of PRP on caprine oocyte maturation in vitro and subsequent fertilization and embryonic development. Cumulus oocyte complexes were cultured in a maturation medium supplemented with (1) fetal bovine serum (FBS, control), (2) PRP, extracted from healthy female goats, (3) polyvinyl alcohol (PVA), and (4) PVA plus PRP (PVA-PRP). The degree of cumulus expansion was scored, and denuded oocytes were used for assessment of nuclear maturation, mitochondrial activity, lipid content, redox status, yield and quality of in vitro embryo development, and cryosurvival of the resulting blastocysts. PRP supported the same beneficial effects of FBS on cumulus expansion, nuclear maturation, in vitro developmental competence of oocytes, and survival of vitrified-warmed blastocysts. Moreover, PRP protected oocytes from undesirable effects FBS exerted on the mitochondrial activity and intracytoplasmic lipid content of maturing oocyte. Although PVA could support the same beneficial effects of neither FBS nor PRP on oocyte maturation, its combined addition with PRP improved the yield and quality of oocyte maturation at rates closely similar to PRP. PRP efficiently substitutes beneficial effects of serum during in vitro oocyte maturation and helps maintain the mitochondrial activity of maturing oocytes.

Reactive oxygen species in reproduction: harmful, essential or both?

The process of embryonic development is crucial and radically influences preimplantation embryo competence. It involves oocyte maturation, fertilization, cell division and blastulation and is characterized by different key phases that have major influences on embryo quality. Each stage of the process of preimplantation embryonic development is led by important signalling pathways that include very many regulatory molecules, such as primary and secondary messengers. Many studies, both in vivo and in vitro, have shown the importance of the contribution of reactive oxygen species (ROS) as important second messengers in embryo development. ROS may originate from embryo metabolism and/or oocyte/embryo surroundings, and their effect on embryonic development is highly variable, depending on the needs of the embryo at each stage of development and on their environment (in vivo or under in vitro culture conditions). Other studies have also shown the deleterious effects of ROS in embryo development, when cellular tissue production overwhelms antioxidant production, leading to oxidative stress. This stress is known to be the cause of many cellular alterations, such as protein, lipid, and DNA damage. Considering that the same ROS level can have a deleterious effect on the fertilizing oocyte or embryo at certain stages, and a positive effect at another stage of the development process, further studies need to be carried out to determine the rate of ROS that benefits the embryo and from what rate it starts to be harmful, this measured at each key phase of embryonic development.

Equine Aging and the Oocyte: A Potential Model for Reproductive Aging in Women

Numerous similarities in reproductive aging have been documented between the mare and woman. Aging is associated with a decline in fertility. In mares and women, oocyte transfer procedures were initially used to establish that oocyte donor age is associated with oocyte quality. Age-associated differences in oocytes include altered morphology, gene expression, and developmental potential. Reactive oxygen species and mitochondrial dysfunction are thought to be important contributors to loss of oocyte quality. In the woman, aneuploidy is a primary consideration with maternal aging. Although misalignment of chromosomes during meiosis has been observed in the mare, less is known in this area. Reproductive aging will be reviewed in the mare and compared with the woman with emphasis on factors that affect oocyte quality and developmental potential. Areas in which the mare could be used as a research model to study reproductive aging in women will be highlighted.

Prospective randomized multicentre comparison on sibling oocytes comparing G-Series media system with antioxidants versus standard G-Series media system

RESEARCH QUESTION

Does the inclusion of three antioxidants (A3), acetyl-l-carnitine (ALC), N-acetyl-l-cysteine (NAC) and alpha-lipoic acid (ALA) improve human embryo development and pregnancy potential?

DESIGN

Prospective randomized multicentre comparison of sibling oocytes. A total of 1563 metaphase II oocytes from 133 patients in two IVF centres. Day 3 embryo and day 5/6 blastocyst quality were assessed. Good embryo quality on day 3 was defined as 8 to 10 cells with even cells and low fragmentation; good quality blastocysts as 3BB or greater. Clinical outcome was assessed on transfers of fresh or vitrified-warmed blastocyst on day 5.

RESULTS

Of the two-pronuclei, 40.7% (G-Series) and 50.2% (G-Series with A3 group) resulted in good quality embryos on day 3 (P < 0.05). The implantation rate by fetal sac was 39.2% and 50.6%, and by fetal heartbeat was 37.8% and 47.1% for the G-Series and G-Series with A3 group, respectively. When stratified by female patient age, patients 35-40 years had an implantation rate by fetal sac and heart of 23.5% in the G-Series compared with 57.5% (P < 0.05) and 50.0% (P < 0.05) in the A3 group. The ongoing pregnancies in patients 35-40 years were significantly higher in the A3 group (50%) compared with the control (25.8%) (P < 0.05).

CONCLUSIONS

The presence of antioxidants during IVF and embryo culture for patients 35-40 years resulted in a significant increase in implantation and pregnancy rate. Supplementation of antioxidants to IVF and culture media may therefore improve the viability of human embryos in assisted reproductive technologies, plausibly through the reduction of oxidative stress.