Antioxidant effect of bioactive compounds isolated from Syzygium aromaticum essential oil on the in vitro developmental potential of bovine oocytes

Abstract

Syzygium aromaticum essential oil (EOSA) is an interesting antioxidant supplement for improving bovine in vitro embryo production (IVEP). Therefore, identifying the bioactives in EOSA is essential for increasing embryonic development. In this study, we compared the effect of EOSA to that of its bioactive compounds on nuclear and cytoplasmic maturation, bioenergetic/oxidative stress parameters, and preimplantation embryonic development of bovine oocytes. Viable oocytes (n = 2,272) were matured under six conditions: control (without antioxidant), cysteamine (100 μM CYS), EOSA20 (20 μg/mL EOSA), eugenol (83 μM EUG), β-caryophyllene (19 μM β-CA), and acetyl eugenol (12 μM ACT). In the first experiment, oocytes were evaluated to determine their in vitro maturation (IVM) according to the expansion and viability of cumulus cell layer, presence of the first polar body (1 PB), metaphase II (MII), and mitochondrial distribution. In the second experiment, oocytes were evaluated to determine their bioenergetic/oxidative status based on the levels of reactive oxygen species (ROS), glutathione (GSH), and mitochondrial membrane potential (ΔΨm). In the third experiment, mature oocytes were parthenogenetically activated (PA), and the embryos were cultured. In the first experiment, no difference was observed in the percentage of MII among groups containing antioxidants (P > 0.05). However, EOSA20, EUG, and CYS improved the percentage of 1 PB oocytes (P < 0.05). Moreover, EUG improved the viability and expansion of cumulus cell layers (P < 0.05). Additionally, cytoplasmic maturation was higher in the EUG and ACT, and mitochondrial aggregation patterns were higher in the EUG, CYS, and ACT than in the other groups (P < 0.05). In the second experiment, ROS levels were reduced in oocytes matured with EUG and CYS (P < 0.05) and GSH levels increased in the same groups (P < 0.05). Oocytes treated with EOSA20, EUG, ACT, and CYS had lower ΔΨm than control. In the third experiment, EUG, EOSA20, and CYS resulted in higher cleavage rates, and EUG and β-CA resulted in more structures with ≥ 8 cells than the other components (P < 0.05). EUG caused a higher percentage of blastocysts than the other components (P < 0.05). EUG, EOSA20, and CYS improved embryo quality (P < 0.05). In conclusion, EUG is the EOSA bioactive compound with the greatest potential for application as an antioxidant and can be commercially applied for IVM of bovine oocytes to result in higher reproducibility and efficiency for IVEP.