LAUSR

Vitrification is the best method for embryo cryopreservation although it increases endogenous reactive oxygen species (ROS) production. As N-acetylcysteine (NAC) is a free radical scavenger, the aim of this study was to investigate if its addition to fresh or vitrified and warmed 2-cell embryos at different time points or during the entire culture improves their developmental competence or the cell number at the blastocyst stage. Thus, 2-cell embryos were obtained in vivo or by in vitro fertilization (IVF), and were vitrified or cultured fresh in presence or absence of 1 mM of NAC during: a) the entire embryo culture, b) for 24 hours with NAC at days 1.5 (G1) or 2.5 (G2) and returned to basal embryo culture (KSOM) or c) cultured in the presence of NAC for 12 hours at day 3.5 (G3). Despite NAC addition to fresh or vitrified embryos produced in vivo or by IVF, blastocyst rates remained unchanged. In vitrified-warmed IU or IVF-derived embryos, total cell number varied when NAC was added at day 1.5 although differences were not significant (60.1 ± 1.9 vs. 59.4 ± 1.3 for IU G1 and control respectively; and 59.3 ± 1.6 and 52.6 ± 3.0 IVF G1 and control respectively; mean cell number ± SEM, p > 0.05). It seems that the embryo culture medium supplementation with 1 mM of NAC in the first day of development improves blastocyst quality of murine embryos and before that moment does not exert any beneficial effect.