Cumulus Cell DNA Damage as an Index of Human Oocyte Competence

In Vitro Toxicity of a DEHP and Cadmium Mixture on Sheep Cumulus-Oocyte Complexes

Di-(2-ethylhexyl) phthalate (DEHP) and Cadmium (Cd) affect female reproduction. To date, toxicological research has focused on the effects of individual contaminants, whereas living beings are exposed to mixtures. This study analyzed the effects of a DEHP/Cd mixture on nuclear and cytoplasmic maturation of sheep cumulus-oocyte complexes (COCs) compared with single compounds. COCs recovered from slaughterhouses-derived sheep ovaries were in vitro exposed to 0.5 μM DEHP, 0.1 μM Cd, or DEHP/Cd mixture at the same concentrations during 24 h of in vitro maturation (IVM). After IVM, oocyte nuclear chromatin configuration was evaluated, and bioenergetic/oxidative parameters were assessed on expanded cumulus cells (CCs) and matured oocytes (chi-square test and one-way ANOVA; p < 0.05). Under examined conditions, oocyte nuclear maturation was never impaired. However, COC bioenergetics was affected with stronger effects for the mixture than single compounds. Indeed, the percentages of matured oocytes with healthy mitochondrial distribution patterns were reduced (p < 0.001 and p < 0.05 for mixture and single compounds, respectively). Oocyte mitochondrial membrane potential, intracellular ROS levels, and mitochondria/ROS co-localization were reduced, with the same significance level, in all contaminated conditions. CCs displayed increased ROS levels only upon mixture exposure (p < 0.001). In conclusion, in vitro exposure to the DEHP/Cd mixture affected COC quality in the sheep to a greater extent than separate compounds.

Cumulus cell DNA damage linked to fertilization success in females with an ovulatory dysfunction phenotype

Intracytoplasmic sperm injection (ICSI) is a widely used technique in fertility centers. ICSI success depends on both nuclear and cytoplasmic oocyte maturation. Cumulus cells, which surround the oocytes, play a pivotal role in oocyte competence. However, the significance of DNA damage in cumulus cells as a marker of fertilization success remains largely unexplored. This study aims to investigate the relationship between DNA damage in cumulus cells of females undergoing ICSI, and oocyte competence, with a focus on in vitro fertilization (IVF) outcomes. We employed the alkaline comet assay to assess DNA damage levels (%TDNA) in cumulus cells and whole blood from 22 potentially fertile females and 35 infertile females, including 20 with an ovulatory disfunction phenotype. Our results revealed significant differences between the levels of %TDNA in cumulus cells and blood. Females with an ovulatory dysfunction phenotype exhibited higher levels of %TDNA in cumulus cells compared to potentially fertile females. Additionally, within the group of females with ovulatory dysfunction, a significant correlation was observed between %TDNA levels and the number of oocytes with two pronuclei. Our findings suggest that blood does not accurately reflect DNA damage in cumulus cells, which was correlated with the fertilization success in females with ovulatory dysfunction. High levels of %TDNA in cumulus cells were associated with a higher likelihood of successful fertilization. Moreover, our results imply that low levels of %TDNA may be linked to oocytes that fail to complete maturation and, consequently, do not fertilize (oocytes with zero pronuclei). Further research with larger cohorts is necessary to validate these findings and to explore potential applications in female fertility. However, our study provides evidence that DNA damage in cumulus cells may serve as a valuable biomarker for predicting fertilization success and oocyte competence.

New Approach to the Cryopreservation of GV Oocytes and Cumulus Cells through the Lens of Preserving the Intercellular Gap Junctions Based on the Bovine Model

Differences in structural and functional properties between oocytes and cumulus cells (CCs) may cause low vitrification efficiency for cumulus-oocyte complexes (COCs). We have suggested that the disconnection of CCs and oocytes in order to further cryopreservation in various ways will positively affect the viability after thawing, while further co-culture in vitro will contribute to the restoration of lost intercellular gap junctions. This study aimed to determine the optimal method of cryopreservation of the suspension of CCs to mature GV oocytes in vitro and to determine the level of mRNA expression of the genes (GJA1, GJA4; BCL2, BAX) and gene-specific epigenetic marks (DNMT3A) after cryopreservation and in vitro maturation (IVM) in various culture systems. We have shown that the slow freezing of CCs in microstraws preserved the largest number of viable cells with intact DNA compared with the methods of vitrification and slow freezing in microdroplets. Cryopreservation caused the upregulation of the genes Cx37 and Cx43 in the oocytes to restore gap junctions between cells. In conclusion, the presence of CCs in the co-culture system during IVM of oocytes played an important role in the regulation of the expression of the intercellular proteins Cx37 and Cx43, apoptotic changes, and oocyte methylation. Slow freezing in microstraws was considered to be an optimal method for cryopreservation of CCs.

Comparison of DNA damage in granulosa cells of women undergoing controlled ovarian stimulation in in vitro fertilization protocols with the recombinant human follicle-stimulating hormones Corneumon®, Gonal-F®, Pergoveris® and Puregon®: a randomized trial

PURPOSE

To compare the DNA damage in granulosa cells (GCs) of women undergoing ovarian-stimulated cycles with four widely used recombinant human follicle-stimulating hormones (rhFSH) in in vitro fertilization (IVF) protocols (Corneumon®, Gonal-F®, Pergoveris® and Puregon®).

METHODS

A randomized trial was carried out at a Mexican hospital. GCs were isolated from 18 women with infertility undergoing assisted reproductive techniques (ART). Four controlled ovarian stimulation (COS) protocols including Corneumon®, Gonal-F®, Pergoveris® or Puregon® were used. GCs DNA damage was assessed by the Comet assay. Two parameters were measured: comet tail length (CTL), and Olive tail moment (OTM, the percentage of DNA in the tail multiplied by the distance between the center of the tail and head).

RESULTS

Use of the different hrFSH in COS caused variable and statistically significant levels of DNA damage in GCs of infertile women. CTL was similar in the Corneumon® and Pergoveris® groups (mean values of 48.73 and 55.18, respectively) and Corneumon® CTL was significantly lower compared to the Gonal-F® and Puregon® groups (mean values of 61.98 and 91.17, respectively). Mean OTM values were significantly lower in Corneumon® and Pergoveris® groups, compared to Gonal-F® and Puregon® groups (25.59, 27.35, 34.76, and 47.27, respectively).

CONCLUSION

Use of Corneumon® and Pergoveris® in COS caused statistically significantly lower levels of DNA damage in GCs of infertile women undergoing ART, which could potentially correlate with better reproductive outcomes.

Biomarkers Assessing the Role of Cumulus Cells on IVF Outcomes: A Systematic Review

PURPOSE

Although significant improvements in assisted reproductive technology (ART) outcomes have been accomplished, a critical question remains: which embryo is most likely to result in a pregnancy? Embryo selection is currently based on morphological and genetic criteria; however, these criteria do not fully predict good-quality embryos and additional objective criteria are needed. The cumulus cells are critical for oocyte and embryo development. This systematic review assessed biomarkers in cumulus-oocyte complexes and their association with successful IVF outcomes.

METHODS

A comprehensive search was conducted using PubMed, Embase, Scopus, and Web of Science from inception until November 2022. Only English-language publications were included. Inclusion criteria consisted of papers that evaluated genetic biomarkers associated with the cumulus cells (CCs) in humans and the following three outcomes of interest: oocyte quality, embryo quality, and clinical outcomes, including fertilization, implantation, pregnancy, and live birth rates.

RESULTS

The search revealed 446 studies of which 42 met eligibility criteria. Nineteen studies correlated genetic and biochemical biomarkers in CCs with oocyte quality. A positive correlation was reported between oocyte quality and increased mRNA expression in CCs of genes encoding for calcium homeostasis (CAMK1D), glucose metabolism (PFKP), extracellular matrix (HAS2, VCAN), TGF-β family (GDF9, BMP15), and prostaglandin synthesis (PTGS2). Nineteen studies correlated genetic and biochemical biomarkers in CCs with embryo quality. A positive correlation was reported between embryo quality and increased mRNA expression in CCs of genes encoding for extracellular matrix (HAS2), prostaglandin synthesis (PTGS2), steroidogenesis (GREM1), and decreased expression of gene encoding for hormone receptor (AMHR2). Twenty-two studies assessed genetic and biochemical biomarkers in CCs with clinical outcomes. Increased expression of genes encoding for extracellular matrix (VCAN), and TGF-β family (GDF9, BMP15) were positively correlated with pregnancy rate.

CONCLUSION

Genetic biomarkers from cumulus cells were associated with oocyte quality (CAMK1D, PFKP, HAS2, VCAN, GDF-9, BMP-15, PTGS2), embryo quality (GREM1, PTGS2, HAS2), and pregnancy rate (GDF9, BMP15, VCAN). These results might help guide future studies directed at tests of cumulus cells to devise objective criteria to predict IVF outcomes.

Chronic stress decreases fertility parameters in female rats

Multiple effects of stress on health have been reported; however, reproductive alterations in oocytes and cumulus cells have not been fully described. In females, chronic stress has been shown to produce alterations in the estrous cycle, to decrease oocyte in vivo maturation, and to increase the percentage of abnormal oocytes. The aim of this study was to evaluate whether the oocytes from chronically stressed female rats could recover and mature in vitro by providing them with all the necessary culture conditions, as well as to evaluate the functionality of the GAP junctions, and the viability and DNA integrity of the cumulus cells, which are crucial for the complete maturation and development of the oocyte. For this, rats were stressed daily by cold water immersion (15 °C) during 15 min for 30 consecutive days. Corticosterone serum levels in rats increased as an indicator of stress. Chronic stress decreased the percentage of in vitro matured oocytes because the cumulus cells presented irreparable damage to their DNA that led to their death, being unable to establish bidirectional communication with the oocyte for its meiotic resumption through the GAP junctions, which were also damaged. These findings could partially explain an association between stress and infertility.