Effect of N-acetyl cysteine treatment on uterine cytokine and chemokine profiles in mares with persistent breeding-induced endometritis.

Overview

• This study investigated whether treating mares affected by persistent breeding-induced endometritis (PBIE) with the antioxidant N-acetyl cysteine (NAC) alters inflammatory molecules in the uterus.
• The researchers aimed to understand why previous NAC treatments did not improve clinical signs by examining uterine cytokine and chemokine profiles after treatment.

Background

• Persistent breeding-induced endometritis (PBIE) is a significant cause of infertility in mares because it causes lasting uterine inflammation after breeding.
• Previous findings showed that administering NAC, an antioxidant, directly into the uterus before breeding did not improve observable clinical symptoms of PBIE at 12 and 60 hours post-breeding.
• Cytokines and chemokines are molecules involved in regulating inflammation and immune responses in tissues, including the uterus.
• Understanding how NAC affects these inflammatory molecules could reveal why NAC fails to improve PBIE symptoms and help guide more effective treatments.

Study Objective

• To determine the effects of intrauterine NAC treatment on the profile of inflammatory cytokines and chemokines in the uterus of mares with PBIE.
• To evaluate both the protein levels in uterine fluid and gene expression in uterine tissue biopsies at critical times after breeding.

Methods

• A randomized, blinded, cross-over study design was used involving nine mares susceptible to PBIE.
• Each mare underwent two treatment cycles: one with NAC (treatment) and one with sterile saline (control), with at least one estrous cycle washout period between treatments to eliminate carryover effects.
• Treatment consisted of an intrauterine infusion of 180 mL of 3.3% NAC solution or sterile saline administered 12 hours before insemination.
• Uterine fluid samples were collected 12 and 60 hours after insemination to measure inflammatory cytokines and chemokines at the protein level.
• Endometrial biopsy samples were also taken at these time points to analyze gene expression levels of selected inflammatory cytokines: interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α).

Results

• There were no statistically significant differences (p > 0.05) in the concentrations of inflammatory cytokines and chemokines in uterine fluid between NAC-treated and control cycles at either 12 or 60 hours post-insemination.
• Gene expression analysis from endometrial biopsies showed that the levels of IL-6, IL-10, IL-1β, and TNF-α were also not significantly different (p > 0.05) between NAC and control treatments.
• Essentially, NAC treatment did not modulate the uterine inflammatory profile either at the protein or gene expression level in mares with PBIE.

Conclusions and Implications

• The lack of effect of NAC on inflammatory cytokines and chemokines suggests that this treatment does not alter the uterine inflammatory environment in PBIE-affected mares.
• This provides a mechanistic explanation for why NAC infusion before breeding did not improve clinical signs of PBIE in previous studies.
• These findings indicate that NAC, as administered in this protocol, is unlikely to be effective for managing or preventing PBIE-related infertility.
• Future research may need to explore alternative therapeutic agents or different administration protocols to effectively modulate uterine inflammation and improve fertility outcomes in mares with PBIE.