5-oxoproline supplementation enhances maturation and developmental competence of low-quality porcine cumulus-oocyte complexes during in vitro maturation.

Abstract

This study investigated whether 5-oxoproline, a key metabolic intermediate in the gamma-glutamyl cycle, improves the maturation and developmental competence of low-quality porcine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM). High-quality grade A COCs were used as the positive control (PC), whereas low-quality grade B COCs served as the negative control (NC) or were cultured for 44 h in IVM medium supplemented with 5-oxoproline. Among the concentrations tested, 500 μM 5-oxoproline most effectively restored nuclear maturation in grade B oocytes to a level comparable with that of the PC group. This treatment significantly reduced intracellular reactive oxygen species, increased intracellular glutathione (GSH) levels, and rescued cumulus cell expansion. Quantitative real-time PCR analysis demonstrated that 5-oxoproline upregulated the antioxidant-related gene TXN and cumulus expansion-associated genes, including HAS2, PTGS2, and VCAN, while reducing the sustained overexpression of the hyaluronan receptor CD44 toward PC baseline levels. Functionally, 5-oxoproline supplementation enhanced the developmental competence of grade B oocytes as demonstrated by increased blastocyst formation after both parthenogenetic activation and in vitro fertilization. These findings suggest that 5-oxoproline improves the quality of compromised porcine oocytes by restoring redox homeostasis, supporting cumulus matrix remodeling, and enhancing subsequent embryo development. 5-Oxoproline may therefore represent a useful metabolic supplement for improving the efficacy of porcine in vitro embryo production.