As the human ovarian follicle enlarges in the course of a regular cycle or following controlled ovarian stimulation, the changes in its structure reveal the oocyte environment composed of cumulus oophorus cells and the follicular fluid (FF). In contrast to the dynamic nature of cells, the fluid compartment appears as a reservoir rich in biomolecules. In some aspects, it is similar to the plasma, but it also exhibits differences that likely relate to its specific localization around the oocyte. The chemical composition indicates that the follicular fluid is able to detect and buffer excessive amounts of reactive oxygen species, employing a variety of antioxidants, some of them components of the intracellular milieu. An important part is played by albumin through specific cysteine residues. But the fluid contains other molecules whose cysteine residues may be involved in sensing and buffering the local oxidative conditions. How these molecules are recruited and regulated to intervene such process is unknown but it is a critical issue in reproduction. In fact, important proteins in the FF, that regulate follicle growth and oocyte quality, exhibit cysteine residues at specific points, whose untoward oxidation would result in functional loss. Therefore, preservation of controlled oxidative conditions in the FF is a requirement for the fine-tuned oocyte maturation process. In contrast, its disturbance enhances the susceptibility to the establishment of reproductive disorders that would require the intervention of reproductive medicine technology.

This study aims to identify molecular markers with prognostic value for biochemical pregnancy in follicular fluid (FF) samples from women with endometriosis after assisted reproductive technology (ART) intervention. Levels of growth differentiation factor-9 (GDF-9), bone morphogenetic protein-15 (BMP-15), and anti-Mullerian hormone (AMH) proteins were semi-quantified by Western blotting and microRNAs 20a_1, 145_1, 320a_1, 125-b-5p, 212-3p, and 199_a by qPCR in FF samples from women submitted to ART with a previous diagnosis of endometriosis (n = 20) or male factor infertility (controls) (n = 44). An increase in GDF-9 and BMP-15 and a decrease in AMH mature protein were observed, as well as an increase in miR20a_1 (p = 0.04), miR145_1 (p = 0.003), and miR320a_1 (p = 0.006) in FF samples collected from women with endometriosis compared with controls. A reduction was observed in miR125b-5p (p = 0.004) and 212-3p (p = 0.02) in endometriosis. Receiver operating characteristic (ROC) curve analysis indicated that miR125b-5p, miR212-3p, and miR-145_1 are potential predictors of endometriosis, and miR145_1 and miR320a_1 of biochemical pregnancy in controls. Although limited by a small sample size, the current study demonstrated alterations in AMH, BMP-15, GDF-9, and specific miRNA levels in FF samples harvested from women with endometriosis, emphasizing their potential roles in endometriosis-related infertility. These microRNAs, dysregulated in women with endometriosis, unveil their biomarker properties and their predictive value for ART success.