Melatonin rescues the development and quality of oocytes and cumulus cells after prolonged ovary preservation: An ovine in vitro model.

The preservation of ovaries beyond 7 h dramatically decreases the developmental potential of oocytes to reach the blastocyst stage during in vitro embryo production. Here we investigated the protective effects of melatonin in the ovarian preservation solution after prolonged storage (7 h) in ovine as an animal model. Slaughterhouse adult sheep ovaries were preserved in saline solution for 2 h (Control) and 7 h (Control stress), and with melatonin for 7 h and at different concentrations (Melatonin 10, 10, 10, 10, and 10 M). First, the fertilizing ability, embryo development rates, and blastocyst quality were investigated. Notably, a concentration of 10 M melatonin showed the greatest number (p < 0.05) of blastocysts produced after 7 h of ovary storage (24.75 ± 1.57%) and was comparable (p > 0.05) to that obtained after just 2 h of storage in the untreated Control (30.77 ± 1.57%). Then, oocyte quality parameters showed that, compared to Control stress, Melatonin actively reduced intracellular ROS content, caspase-3 activity, DNA fragmentation, and the abundance of pro-apoptotic transcripts BAX and CASP3, while increasing that of GDF9 and GPX1. In cumulus cells, flow cytometry results showed that melatonin decreased apoptosis and increased mitochondrial activity (p < 0.05). In addition, there was a greater (p < 0.05) abundance of HAS2, STAR, and PTGS mRNA transcripts in Melatonin compared to Control stress. These findings reveal a melatonin-mediated developmental rescue of oocytes against ischemic damage during ovary preservation which represents a promising strategy for successfully producing embryos when prolonged ovarian transport times are required.