Repeated Ovarian Stimulations Induce Oxidative Damage and Mitochondrial DNA Mutations in Mouse Ovaries

Abstract

Superovulation by injection of exogenous gonadotropin is the elementary method to produce in vivo-derived embryos for embryo transfer in women. Increased oocyte aneuploidy, embryo mortality, fetal growth retardation, and congenital abnormalities have been studied at higher-dose stimulations. Ovarian and oocyte biological aging possibly may have adverse implications for human oocyte competence with repeated hyperstimulation. In this study, we found that reduced competence for the human oocyte has been associated with degenerative embryo upsurge during embryo culture and failure to develop into the blastocyst stage in the three, four, five, and six stimulation cycles. On the other hand, the numbers of ovulated oocytes were decreased in the groups with more ovarian stimulation. More aggregated mitochondria were found in the cytoplasm of the repetitively stimulated embryos. Higher amounts of oxidative damage including 8-OH-dG, lipoperoxides, and carbonyl proteins were also revealed in the ovaries with more cycle numbers of ovarian stimulation. Higher proportions of mtDNA mutations were also found. The detected molecular size of the mutated band was approximately 675 bp. Increased amounts of carbonyl proteins were also revealed after repeated stimulation. An understanding of the relationship between oocyte competence and ovarian responses to stimulation in the mouse may provide insights into the origin of oocyte defects and the biology of ooplasmic aging that could be of clinical relevance in the diagnosis and treatment of human infertility.

Age-related Accumulation of Non-heme Ferric and Ferrous Iron in Mouse Ovarian Stroma Visualized by Sensitive Non-heme Iron Histochemistry

“…Under these conditions, increased redox-active iron in aged ovaries would be a pro-oxidant for the generation of toxic ROS such as hydroxyl radicals, resulting in a loss of the balance between ROS and antioxidants. To prove this hypothesis, oxidative stress level in aged or iron-overloaded ovarian tissue can be further investigated using reliable markers such as protein carbonyls and 8-hydroxydeoxyguanosine in mitochondrial DNA (Chao et al 2005;Miyamoto et al 2010;Tarin et al 2004). Moreover, the levels of antioxidants, including superoxide dismutases, catalase, and glutathione, also can be investigated to assess the pro-oxidative condition.…”

Deficit of mitochondria-derived ATP during oxidative stress impairs mouse MII oocyte spindles

“…Metabolic inhibitors such as FCCP and oligmycin A, and Th+2. 5 . However, Th+2.5 mM Ca 2+ alone did not significantly alter the ATP level and the spindle structure within oocytes.…”

“…The rate of meiotic division errors increases corresponding to maternal aging, which leads to non-extrusion of the first polar body, shrunken size of spindles, irregular distribution of chromosomes and occurrence of aneuploidies. Recent studies indicate that maternal aging is accompanied by the generation of oxidative stress in oocytes [4][5][6][7], suggesting that oxidation may contribute to the age-related increase in the rate of meiotic division errors and aneuploidies. Tarin has proposed a mechanism based on 'the oxygen radical-mitochondrial injury hypothesis of aging' to explain the effects of aging on mammalian oocytes [7,8].…”

Molecular alterations during female reproductive aging: Can aged oocytes remind youth?

“…However, the levels of free radical scavengers, including SOD1, SOD2, and catalase, were significantly decreased in the granulosa cells from older women compared with those in the granulosa cells from younger women (Tatone et al 2006). In addition, oxidative damages measured by the expression of 8-hydroxydeoxyguanosine were observed in oocytes after ovulation (Chao et al 2005;Miyamoto et al 2010). Although the ovarian levels of oxidative stress during aging remain unclear, excess ROS induced by ovulation may affect the quality of oocytes that are stored in the ovaries (Fig.…”

“…3). In fact, ovulation induced ROS generation in the ovaries, resulting in oxidative damage of genomic DNA and mitochondrial DNA mutations (Agarwal et al 2005;Chao et al 2005).…”