The effect of preincubation time on oxidative stress and mitochondrial alteration of mouse MII oocytes in the simple and myo-inositol supplemented media

Background: Preincubation is the temporary cultivation of oocytes at 37oC and 5-6% of CO2 before ART procedures. There is not any explanation regarding a standard preincubation time in ART laboratory guidelines and it is dependent completely on the laboratory workload. Myo-inositol as the most important form of inositol, is involved in several systemic processes and its antioxidant action has been suggested recently.Objective: The study aimed to evaluate the effect of preincubation time of mouse MII oocytes in the simple and myo-inositol supplemented medium on the oxidative stress and mitochondrial alterations.Materials and Methods: Cumulus Oocyte Complexes which were retrieved from superovulated NMRI mices were divided randomly in five experimental groups: (1) control (2) 4 hours preincubation in simple medium (3) 4 hours preincubation in 20 mmol/l of myo-inositol supplemented medium (4) 8 hours preincubation in simple medium (5) 8 hours preincubation in 20 mmol/l of myo-inositol supplemented medium. COCs were denuded and intracellular Reactive Oxygen Species (ROS), glutathione (GSH), Mitochondrial Membrane Potential (MMP) and mitochondrial distribution were measured by a fluorometric assay. ATP content of oocytes also was measured using the ELISA method.Results: The ROS and GSH levels, mitochondrial distribution, MMP as well as ATP content were significantly different between groups. Levels of ROS, GSH and mitochondrial distribution were improved in oocytes preincubated in MYO supplemented medium compared to simple medium. The groups with 4 hours preincubation in simple media and 8 hours preincubation in supplemented media were at the same level in terms of the ROS, GSH and mitochondrial distribution. MMP of oocytes was not reduced after 4 hr of preincubation, but 8 hr of preincubation time could decrease it significantly. ATP content did not decline in oocytes preincubated for 4 and 8 hr, while supplementation of MYO could increase it in groups with 4 and 8 hr of preincubation.Conclusion: Short preincubation time can influence the oocyte quality related to alternation in ROS, GSH, MMP and mitochondrial integrity. Supplementation of MYO in mediums improves the quality drop significantly in addition to groups with preincubation in the simple media but does not prevent quality drop compared to the control group.

Keywords:

Oocyte preincubation time 1 , Oocyte quality 2 , Myo-inositol supplement 3 , Oxidative stress 4 , Mitochondrial alteration 5