N-acetyl cysteine as a potential treatment for persistent breeding-induced endometritis in the mare
Persistent breeding-induced endometritis (PBIE) is a major cause of infertility in mares. PBIE susceptible mares do not clear inflammation post-breeding in a timely fashion, ultimately resulting in early embryonic death. N-acetyl cysteine (NAC), a mucolytic, has anti-inflammatory properties, affects inflammatory cytokines and is a mild inhibitor of nitric oxide synthase. Increased nitric oxide (NO) levels and alterations in inflammatory cytokines have been documented in PBIE mares. The objective of this study was to determine if NAC treatment of PBIE-susceptible mares would lower NO and inflammatory cytokine levels, thereby resulting in the resolution of clinical signs associated with PBIE. The effects of NAC histologically on the endometrium were also determined. A randomized, blinded, cross-over design clinical trial was performed utilizing PBIE susceptible mares (n=9). Intrauterine infusion of 180mls of 3.3% NAC was performed 12 hours prior to insemination. Mares were sampled for endometrial cytology and intra-uterine fluid to determine interleukin-6 concentration (ELISA) and nitric oxide (Colorimetric assay) levels at 12 and 60 hours post-insemination. Endometrial biopsies were taken at the same time points post-insemination for scoring based on the degree of inflammation present and to determine gene expression of inflammatory cytokines by qPCR. Clinical signs of endometrial edema and intra-uterine fluid volumes were assessed at 12 and then every 24 hours post breeding. Statistical analysis was performed using a repeated measures ANOVA and a Mann Whitney Wilcoxon Test. Pre-breeding intrauterine treatment with NAC did not improve clinical signs in PBIE-affected mares, nor did it affect NO levels, IL-6 concentration or cytokine gene expression. Differences across time points post-AI were noted for IL-6 gene expression, which was highest at 12 hours post-AI (p=0.003). Expression of other cytokines evaluated did not change over time. Treatment with NAC did have a significant effect on the degree of endometrial inflammation noted histologically, with treated cycles displaying more diffuse and severe neutrophil infiltration compared to control cycles. The effects of NAC on the endometrium of PBIE- susceptible mares seen in this study is concerning. Further research is required to evaluate the safety of NAC in the treatment of PBIE-susceptible mares.