Melatonin supplementation during prolonged in vitro maturation improves the quality and development of poor-quality porcine oocytes via anti-oxidative and anti-apoptotic effects.

Poor-quality oocytes (those with 1-2 layers of cumulus cells) typically possess low meiotic competence and development. Prolonging the duration of in vitro maturation (IVM; 52 hr) can enhance the maturation rate of poor-quality oocytes, but it does not improve subsequent embryonic development. This likely reflects the increased reactive oxygen species (ROS) production and apoptosis seen in these oocytes compared with the non-prolonged IVM (44 hr) group. Melatonin is a free radical scavenger, anti-oxidant and anti-apoptotic agent that reported to enhance the quality of embryos by inhibiting ROS generation and apoptosis. Therefore, we herein investigated whether melatonin combined with prolonged IVM (52 hr) could improve the quality and development of poor-quality oocytes. We supplemented IVM and/or in vitro culture (IVC) media with various concentrations (0, 10-7 , 10-6 , 10-5  M) of melatonin, and estimated parameters related to oocyte quality and development. The addition of melatonin (10-6  M) to a prolonged IVM system improved the oocyte quality and development compared with those of the melatonin-free poor-quality oocytes group, and that this was due to decreases in ROS generation, apoptosis, and DNA damage. When melatonin was added during both IVM (10-6  M) and IVC (10-6  M), we observed a cumulative positive influence on the embryonic development and quality; this treatment enhanced the expression level of Oct4 and decreased the levels of ROS, DNA damage, and apoptosis. Together, these findings suggest that the combination of melatonin plus prolonged IVM can improve the quality and development of poor-quality porcine oocytes via anti-oxidative and anti-apoptotic effects.