Effect of in vitro maturation medium supplementation with N-acetylcysteine on the developmental competence of sheep oocytes

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Abstract
The present study aimed to evaluate the effect of N-acetylcysteine (NAC) on in vitro maturation (IVM) and in vitro embryo production in sheep. Cumulus–oocyte complexes (COCs) were collected and matured in vitro in a control medium or supplemented with different concentrations of NAC (1, 1.5 and 2.0 mM). After maturation, a subset of oocytes was used for morphological assessment and chromatin configuration analysis, as well as for evaluating intracellular levels of reactive oxygen species (ROS), glutathione (GSH), mitochondrial activity and DNA fragmentation using the TUNEL assay. Another subgroup of oocytes was subjected to in vitro fertilization (IVF), and the presumed zygotes were cultured in in vitro culture (IVC) medium to assess cleavage rates. Data were statistically analysed, considering significance at P < 0.05. The concentration of 1 mM NAC resulted in lower ROS levels compared to the control and 1.5 mM groups, in addition to reducing DNA fragmentation. No significant differences ( P > 0.05) were observed in GSH levels or mitochondrial activity between treated and control groups. Furthermore, oocytes treated with 1 mM NAC showed higher cleavage rates compared to the other experimental groups. In conclusion, supplementation with 1 mM NAC improves oocyte quality and early embryonic development, as demonstrated by reduced oxidative stress and DNA fragmentation, resulting in increased cleavage rates.

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