Concentration-dependent effects of 2-oxothiazolidine-4-carboxylate during bovine oocyte in vitro maturation on oxidative status and embryo quality.

This study evaluated the effects of supplementing bovine in vitro maturation medium with 2-oxothiazolidine-4-carboxylate (OTC), a cysteine precursor, on oocyte quality, intracellular oxidative status, embryo development, and gene expression in oocytes and derived blastocysts. Oocytes were matured in TCM-199 maturation medium supplemented with 0 (control), 1, 2, or 4 mM OTC, followed by in vitro fertilization and embryo culture. Nuclear maturation, intracellular reactive oxygen species (ROS), glutathione (GSH) levels, embryo development, blastocyst quality, and expression of genes associated with developmental competence were evaluated. OTC supplementation significantly reduced intracellular ROS levels in all treated groups compared with the control. Intracellular GSH concentrations remained unchanged. OTC supplementation reduced the proportion of oocytes reaching the MII stage, whereas cleavage and blastocyst formation rates were not significantly affected in the separate set of oocytes subjected to IVF. Blastocysts derived from oocytes matured with 1 and 2 mM OTC contained significantly higher total cell numbers than controls. Gene expression analyses demonstrated concentration-dependent changes in selected oocyte and blastocyst transcripts. In conclusion, OTC exerted concentration-dependent effects on bovine oocyte maturation and subsequent embryo characteristics. OTC reduced intracellular ROS without altering total intracellular GSH, while 1-2 mM OTC increased blastocyst total cell number without increasing blastocyst yield. However, OTC supplementation reduced MII-stage maturation, and its effects on selected oocyte and blastocyst transcripts varied with concentration. These findings demonstrate endpoint-specific responses to OTC supplementation and support further investigation of its effects during bovine IVM.