Effects of Mechanical Delipation in Porcine Oocytes on Mitochondrial Distribution, Ros Activity and Viability After Vitrification

BACKGROUND: Porcine oocytes were sensitive to cooling because of the presence of excessive lipids. OBJECTIVE: To evaluate the effect of lipid removal on the mitochondrial distribution, the formation of reactive oxygen species (ROS) and the viability of porcine oocytes after vitrification. MATERIALS AND METHODS: Porcine oocytes were cultured in vitro, and lipid droplets were removed at the MII stage by mechanical delipation via micromanipulation. Mitochondrial distribution, ROS activity and oocyte viability were assessed after delipation and vitrification. RESULTS: Vitrification disrupted mitochondrial distribution in oocytes. The vitrified groups had a significantly lower rate of oocytes with normal mitrochondrial distribution than the fresh control group (39.6% and 58.5% versus 88.9%). The percentage of oocytes with normal mitochondrial distribution was significantly lower in the delipated group than that in the undelipated group after vitrification (39.6% vs 58.5%, p < 0.05). Vitrification also increased the ROS activity (p < 0.05); but there was no significant difference between the delipated and the undelipated groups (p > 0.05). Delipated oocytes developed into blastocysts via parthenogenetic activation without vitrification. Delipation significantly decreased the rate of blastocyst formation. Vitrification also decreased the rates of cleavage and blastocyst formation (p < 0.05). The delipated group had a significantly higher cleavage rate than the undelipated group after vitrification (21.4% versus 10.4%). CONCLUSION: Lipid removal at the MII stage via micromanipulation impaired their subsequent development of porcine oocytes. Although vitrification causes an abnormal distribution of mitochondria and an increase in ROS production in porcine oocytes, the removal of lipid droplets improves subsequent development after vitrification.