Impact of N‐acetyl‐L‐cysteine on spindle morphology and reactive oxygen species in vitrified/warmed in vitro matured bovine oocytes

Low developmental potential of vitrified in vitro matured (IVM) bovine oocytes is frequently attributed to high levels of reactive oxygen species (ROS) and abnormal spindle assembly. This study aimed to evaluate the efficacy of N-acetyl-L-cysteine (NAC), a cell-permeating antioxidant, added to IVM medium in reducing ROS and preserving spindle configuration of vitrified/warmed IVM bovine oocytes. Oocytes collected from abattoir ovaries were either cultured in IVM medium or in IVM medium supplemented with 1 mM NAC for the initial 8 h of IVM. Half of the oocytes of each group were vitrified/warmed, and spindle morphology and ROS production were assessed at 24 h of IVM. Results indicated that fresh oocytes IVM with NAC improved spindle configuration, with significantly lower ROS levels compared to the control group. Vitrification resulted in lower percentages of bovine oocytes reaching the metaphase II stage but similar ROS levels to non-vitrified oocytes, regardless of NAC supplementation. However, the supplementation of NAC during maturation had no effect on spindle or chromosome configuration of vitrified oocytes. These findings emphasize NAC's potential in enhancing the quality of IVM bovine oocytes but its addition at 1 mM for 8 h to IVM medium did not decrease levels of ROS nor improve spindle assembly after vitrification.