Effect of Sericin on In Vitro Maturation of Bovine Oocytes Under Oxidative Stress Induced by Hydrogen Peroxide

This study investigated the protective effects of sericin during both pre-IVM and IVM phases in bovine oocytes. All oocytes were cultured in tissue culture medium (TCM-199) at 38.5 °C under 5% CO₂ and allocated into three groups: (1) the control group, without H₂O₂ induction and without sericin (control); (2) the oxidative stress group, exposed to 100 µM H₂O₂ for 1 h in collecting media and subsequently cultured in standard medium, (-SC); and (3) the sericin-supplemented group, exposed to H₂O₂ under the same condition as –SC group but supplemented with 0.1% sericin in the collecting medium and 0.05% sericin in the maturation medium (+SC). After culture, two parameters were assessed: nuclear maturation to the metaphase II (MII) stage, evaluated by aceto-orcein staining, and malondialdehyde (MDA) levels, as an indicator of lipid peroxidation. The maturation rates were 70.36 ± 3.94%, 32.62 ± 5.89%, and 74.56 ± 6.05% for the control, -SC, and +SC groups, respectively, with significant differences observed between the -SC group and the control and +SC groups (p < 0.001). The corresponding MDA levels were 1.97 ± 0.14, 2.94 ± 0.28, and 1.09 ± 0.32 µM, with the +SC group showing significantly lower MDA levels than both the control (p < 0.05) and the -SC groups (p < 0.001). These findings demonstrated that sericin supplementation effectively reduced oxidative damage and improved nuclear maturation rates to levels comparable to or exceeding those of the control group, suggesting its potential as a valuable additive for enhancing in vitro culture systems in animal reproductive biotechnology.