Biochemical alterations in the follicular fluid of bovine peri-ovulatory follicles and their association with final oocyte maturation

Abstract

Follicular fluid (FF), a product of vascular transudate and granulosa and thecal cell secretions, is the milieu that has evolved to support oocyte growth and maturation which plays a central role in oocyte quality determination. Therefore, a suboptimal FF composition may be reflected in compromised oocyte progression through maturation, fertilization or embryo development. To date, the composition of bovine FF remains understudied. To address this, we comprehensively characterized the metabolomic constituency of bovine FF in the period during which the oocyte undergoes meiotic maturation. More specifically, FF from pre (-24 h) and peri (-2 h) -ovulatory follicles was profiled by high-throughput untargeted ultra-high-performance liquid chromatography tandem mass spectroscopy. A total of 634 metabolites were identified, comprising: lipids (37.1%), amino acids (30.0%), xenobiotics (11.5%), nucleotides (6.8%), carbohydrates (4.4%), cofactors and vitamins (4.4%), peptides (3.6%) and energy substrates (2.1%). The concentrations of 67 metabolites were significantly affected by stage of follicle development, 33.3% (n=21) were reduced (P≤0.05) by a mean of 9.0-fold, whereas 46 were elevated (P≤0.05) by a mean of 1.7-fold in peri vs. pre -ovulatory FF. The most pronounced individual metabolite concentration decreases were hypoxanthine (98.9-fold), xanthine (65.7-fold), 17β-oestradiol (12.4-fold), and inosine (4.6-fold). In contrast, the greatest increases were in retinal (4.9-fold), 1-methyl-5-imidazoleacetate (2.7-fold), and isovalerylcarnitine (2.7-fold). This global metabolomic analysis of bovine FF temporal dynamics provides new information for understanding the environment supporting oocyte maturation and facilitating ovulation, that has the potential for improving oocyte quality both in vivo and in vitro.

Fertilization with follicular fluid reduces HSP70 and BAX expression on bovine in vitro embryos

“…However, it is established that many of these compounds are more concentrated in smaller ovarian follicles, such as the pre-ovulatory follicles utilized in this study (8 mm to 10 mm in diameter) (Alrabiah et al, 2023).…”

“…A study conducted by Alrabiah et al. (2023) described the identification of 634 metabolites in BFF extracted from pre‐ovulatory follicles, consisting of lipids (37.1%), amino acids (30.0%), xenobiotics (11.5%), nucleotides (6.8%), carbohydrates (4.4%), cofactors and vitamins (4.4%), peptides (3.6%) and energy substrates (2.1%). The wide spectrum of compounds in BFF makes it challenging to attribute the observed gene expression results to a singular factor.…”

“…The composition of BFF encompasses a diverse array of metabolites. A study conducted by Alrabiah et al (2023) described the identification of 634 metabolites in BFF extracted from pre-ovulatory follicles, consisting of lipids (37.1%), amino acids (30.0%), xenobiotics (11.5%), nucleotides (6.8%), carbohydrates (4.4%), cofactors and vitamins (4.4%), peptides (3.6%) and energy substrates (2.1%).…”

“…SOD2, being a mitochondrial enzyme, constitutes a part of the antioxidant defence mechanisms that deal with reactive oxygen species (ROS) produced as a consequence of aerobic respiration and substrate oxidation (Fukai & Ushio‐Fukai, 2011). The activity of SOD2 might have been influenced by factors such as the carbohydrate ratio (Orsi et al., 2005) and the high amount of fatty acids in BFF (Alrabiah et al., 2023). Additionally, follicular fluid contains various antioxidants (Revelli et al., 2009) that could potentially impact SOD2 activity in IVP embryos (Cajas et al., 2020).…”

Sperm activate TLR2/TLR1 heterodimerization to induce a weak proinflammatory response in the bovine uterus

“…However, sperm attachment to bovine oviduct epithelial cells is mediated also by TLR2 but leads to an anti-inflammatory response. The ovum releasing from the ovary lead to a tightly regulated sterile inflammatory response in bovine oviduct which is rapidly resolved during early corpus luteum formation ( 9 ). Meanwhile, TLR2 is also expressed in cumulus cells of cumulus-oocyte complexes (COCs) and plays immune protective functions critical for cell survival during ovulation and fertilization ( 10 , 11 ).…”