Effects of different activation intensities on mitochondrial adenosine triphosphate and reactive oxygen species production in mouse oocytes during fertilization

Abstract

Objective To observe the effect of different levels of activation intensity on mitochondrial metabolism in mouse oocyte during fertilization by detecting adenosine triphosphate (ATP) content and reactive oxygen species (ROS) level. Methods After intracytoplasmic sperm injection (ICSI) with weak sperm, different concentrations of ionomycin (0 μmol/L, 2.5 μmol/L, 10 μmol/L) were applied for 10 min to assist the oocyte activation, and ICSI with normal mouse sperm was used as the control. According to the treatment methods, they were divided into four groups: normal sperm group (normal, N group), weak sperm group (W group), weak sperm + moderate AOA group (M group), weak sperm + excessive assisted oocyte activation (AOA) group (E group). ATP and ROS levels in oocyte were measured within 1.5-2 h after ICSI. In addition, ATP level of oocyte groups (O group) without ICSI was detected. Results 1) With the increase of activation power, the average ATP content in oocyte of O group [(2.005±0.053) pmol], W group [(2.485±0.064) pmol], M group [(3.763±0.075) pmol] gradually increased, with a significant difference (P 0.05). In addition, the average ATP content of eggs in E group [(3.204±0.070) pmol] was significantly lower than that in N group (P<0.001), although it was higher than that in O group. 2) The level of ROS showed that with the increase of activation power, the levels of ROS in W group (0.420±0.028, n=9), M group (1.097±0.037, n=9), E group (1.361±0.033, n=10) increased gradually (P<0.001), and the level of ROS in M group only showed slight difference with that of N group (1.000±0.026, n=10) (P=0.044). Conclusion This study preliminarily found that the level of activation power during fertilization will have a significant impact on mitochondrial metabolism of oocyte. In mouse, when oocyte was moderately activated after ICSI with weak acitivtion ability sperm, ATP production will increase, while ROS production will be less; however, excessive activation intensity will lead to the decrease of ATP production and the increase of ROS production. Key words: Fertilization; Intracytoplasmic sperm injection; Reactive oxygen species; Adenosine triphosphate; Assisted oocyte activation