Epigallocatechin-3-gallate enhances in vitro maturation and developmental competence of sheep oocytes

In vitro maturation (IVM) is essential for sheep oocyte competence in embryo production, yet oxidative stress during culture impairs both nuclear and cytoplasmic maturation. To address this, we investigated the effects of supplementing IVM medium with epigallocatechin-3-gallate (EGCG)-a green tea catechin with antioxidant and mitochondrial-protective properties-at concentrations ranging from 0 to 30 μmol/L. Supplementation with 10 μmol/L EGCG significantly improved IVM outcomes. Specifically, it increased first polar body extrusion and cumulus expansion, reduced ROS, and elevated glutathione (GSH) levels. EGCG also enhanced mitochondrial activity, membrane potential, and relative ATP levels, while attenuating Ca²⁺ overload. Furthermore, it reduced spindle-chromosome abnormalities and promoted cytoplasmic maturation, reflected in improved cortical granule distribution, enhanced endoplasmic reticulum activity, and elevated lysosomal function. Following parthenogenetic activation, EGCG-treated oocytes exhibited higher blastocyst rates. After IVF, these oocytes also showed higher cleavage and blastocyst rates. Blastocysts derived from these oocytes contained a higher total cell number, including both trophectoderm and inner cell mass (ICM), whereas the ICM:trophectoderm ratio remained unchanged. In summary, 10 μmol/L EGCG improved ovine IVM by supporting redox homeostasis, mitochondrial function, spindle-chromosome integrity, and cytoplasmic maturation.