Lipopolysaccharide reduces progesterone and cytokines in equine follicular fluid without affecting oocyte development in vitro.

Overview

• This study investigated the presence of lipopolysaccharide (LPS) in the follicular fluid of horses and its association with hormone and cytokine levels, as well as the impact of LPS exposure on oocyte development during in vitro maturation.
• The research found that while LPS was present and associated with reduced progesterone and cytokine levels, it did not adversely affect the developmental competence of equine oocytes in vitro.

Background

• Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria and can act as an endotoxin.
• In other species like cows and mice, LPS in the follicular fluid negatively affects steroid hormone production and the developmental competence of oocytes.
• The developmental competence of oocytes is crucial for successful fertilization and embryo development.
• This study aimed to investigate if similar effects occur in horses by examining follicular fluid LPS levels, hormone and cytokine concentrations, and the impact of LPS on equine oocyte maturation and development in vitro.

Experiment 1: LPS and Biochemical Analysis in Follicular Fluid

• Follicular fluid was collected from large follicles (>30 mm in diameter) of 16 slaughterhouse mares, representing clinically healthy animals.
• Concentrations of LPS, estradiol (an estrogen steroid hormone), progesterone (a steroid hormone essential for reproduction), and cytokines TNF-α and IL-6 (inflammatory mediators) were measured.
• LPS concentrations ranged from 5.21 to 12.08 endotoxin units per milliliter (EU/mL), with 10 EU equating to 1 ng.
• A negative correlation was found between LPS levels and progesterone, TNF-α, and IL-6, indicating that higher LPS was associated with lower concentrations of these substances.
• No specific correlation between LPS and estradiol was mentioned, suggesting estradiol might not be affected similarly.

Experiment 2: Effect of LPS on Oocyte Maturation and Development

• Cumulus-oocyte complexes (COCs) were collected and held overnight before undergoing in vitro maturation (IVM).
• The COCs were divided into two groups: one matured with LPS exposure (1 ng/mL) and one without LPS (control group).
• Following maturation, oocytes were fertilized via intracytoplasmic sperm injection (ICSI).
• Measured endpoints included maturation rate (percentage of oocytes reaching metaphase II), cleavage rate (early embryo division), and blastocyst rate (embryo reaching blastocyst stage).
• Results showed no significant differences between LPS-treated and control groups in maturation (56% vs. 61%), cleavage (71% vs. 65%), or blastocyst rates (21% vs. 19%).

Conclusions and Implications

• This study is the first to detect LPS in equine follicular fluid from healthy mares.
• LPS presence correlates negatively with progesterone and inflammatory cytokines (TNF-α, IL-6), indicating possible modulation of the follicular environment by LPS.
• Despite these changes in hormone and cytokine levels, LPS exposure during in vitro maturation at the dose tested did not impair oocyte developmental competence as measured by embryo development up to blastocyst stage.
• The absence of immediate detrimental effects on embryo development suggests equine oocytes may tolerate low levels of LPS during maturation better than those of other species.
• The study points out the need for further research, especially to determine whether embryos derived from LPS-exposed oocytes can result in successful pregnancies following embryo transfer.

Significance and Future Directions

• Understanding the impact of bacterial endotoxins like LPS on reproduction is important for improving fertility management in horses, especially in clinical or agricultural contexts.
• The findings suggest that while LPS can alter the follicular microenvironment, it may not necessarily compromise the developmental potential of equine oocytes under in vitro conditions.
• Future studies should assess long-term developmental outcomes post-transfer, including pregnancy establishment and offspring health.
• Exploring the mechanisms behind the apparent resilience of equine oocytes to LPS exposure could reveal protective factors or species differences valuable for reproductive biology.