Alteration of the Intrafollicular Thiol-Redox System in Infertile Women with Endometriosis: Relationship with Oocyte and Embryo Quality

Abstract

INTRODUCTION: Oxidative stress and chronic inflammation play important roles in the pathophysiology of endometriosis. However, their roles in female infertility remain unclear. The thiol-redox system participates in a variety of diseases related to oxidative stress. Oxidative stress induces the expression of inflammatory cytokines, which further promote oxidative stress. The role of these systems in the intrafollicular microenvironment of infertile patients with endometriosis is unknown. The aim of this study was to compare biomarkers of the thiol-redox system and chronic inflammation in infertile patients with and without endometriosis who were receiving in vitro fertilization (IVF). We also examined correlations between biomarker concentrations and IVF outcome.

METHODS: Sixty-five patients receiving IVF were included in this prospective observational study. Patients were divided into two groups: 31 patients with endometriosis (endometriosis group) vs. 34 patients with unexplained infertility or infertility due to male or tubal factors (controls). Follicular fluid (FF) was obtained from a single dominant follicle during oocyte retrieval and stored at -70°C. Malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GPX)-3, thioredoxin (TRX), TRX-binding protein (TBP)-2, and peroxiredoxin (PRX)-4 levels were measured in the FF samples with enzyme-linked immunosorbent assays (ELISAs) as biomarkers of oxidative stress. The inflammatory cytokines interleukin (IL)-1β, IL-6, IL-8, and tumor-necrosis factor (TNF)-α were also measured by ELISAs. Expression levels were compared between groups and statistically analyzed with a Students t-test or Mann-Whitney U test. Linear regression analysis was performed to correlate expression levels and IVF outcomes. Logistic regression analysis was performed to identify predictive factors for clinical pregnancy.

RESULTS: GSH levels were significantly lower in the FF samples from the endometriosis group compared to those from the control group (12.73±5.67 vs. 16.19±6.94 µg/mL, P=0.033). TBP-2 levels were significantly higher in the FF samples from the endometriosis group compared to those from the control group (219.97±507.23 vs. 3.27±6.14 ng/mL, P=0.042). MDA, SOD, GPX-3, TRX, and PRX-4 levels were not significantly different between the two groups. MDA levels negatively correlated with TRX levels in FF (r=-0.264, P=0.047) and positively correlated with TBP-2 levels (r=0.354, P=0.009). SOD levels negatively correlated with PRX-4 levels in FF (r=-0.247, P=0.035). IL-6, IL-8, and TNF-α levels were significantly higher in the endometriosis group compared to those in the control (16.97±29.62 vs. 4.11±2.89 pg/mL, P=0.022

216.26±95.73 vs. 171.50±72.06 pg/mL, P=0.037

0.93±1.01 vs. 0.43±0.33 pg/mL, P=0.036, respectively). IL-1β levels were higher in the endometriosis group compared to those in the control, but differences were not significant. There were significant positive correlations among the four inflammatory cytokines. The levels of all of the inflammatory cytokines positively correlated with the levels of TRX in the FF samples. GSH levels were positively correlated with the number of high-quality embryos (r=0.299, P=0.024). GPX-3 and TRX levels were negatively correlated with the percentage of mature oocytes (r=0.275, P=0.046

r=0.398, P=0.004, respectively). TNF-α levels were negatively correlated with the cumulative embryo score per embryo (r=0.278, P=0.025). Logistic regression analysis revealed that the number of high-quality embryos was an independent factor predicting clinical pregnancy (OR 0.975, P=0.024).

CONCLUSIONS: These findings suggest that there may be an imbalance of the thiol-redox system and increased levels of inflammatory cytokines in the intrafollicular microenvironment of infertile patients with endometriosis who are receiving IVF. These factors may affect the qualities of the oocyte and embryo.