Abstract
The open carrier system (OC) is used for vitrification due to its high efficiency in preserving female fertility, but concerns remain that it bears possible risks of cross-contamination. Closed carrier systems (CC) could be an alternative to the OC to increase safety. However, the viability and developmental competence of vitrified/warmed (VW) oocytes using the CC were significantly lower than with OC. We aimed to improve the efficiency of the CC. Metaphase II oocytes were collected from mice after superovulation and subjected to in vitro fertilization after vitrification/warming. Increasing the cooling/warming rate and exposure time to cryoprotectants as key parameters for the CC effectively improved the survival rate and developmental competence of VW oocytes. When all the conditions that improved the outcomes were applied to the conventional CC, hereafter named the modified vitrification/warming procedure using CC (mVW-CC), the viability and developmental competence of VW oocytes were significantly improved as compared to those of VW oocytes in the CC. Furthermore, mVW-CC increased the spindle normality of VW oocytes, as well as the cell number of blastocysts developed from VW oocytes. Collectively, our mVW-CC optimized for mouse oocytes can be utilized for humans without concerns regarding possible cross-contamination during vitrification in the future.
Highlights
Considering an increase in cancer survival rates, especially in young patients, the preservation of fertility is critical [1]
The survival rate of VW mouse oocytes using the Closed carrier systems (CC) was significantly lower than that using the open carrier system (OC) (96.8% vs. 76.1%, p < 0.05) (Figure 2B)
These results clearly demonstrated that CC lowers the survival and developmental rates of VW oocytes, suggesting that CC procedures need to be modified to be more efficient
Summary
Considering an increase in cancer survival rates, especially in young patients, the preservation of fertility is critical [1]. Fertility preservation among these patients is preferred [2,3], resulting in successful childbirth [4,5]. The risk of damage is relatively high during freezing and thawing as the chromosomes and meiotic spindles are exposed in the cytoplasm [11,12] These physical and morphological characteristics make oocytes extremely sensitive to various insults during freezing and thawing [13]. The use of a high concentration of cryoprotectant during vitrification allows the dehydration of cells and prevents the formation of ice crystals [16,17]. Vitrification is currently the recommended technique to cryopreserve embryos [18] and oocytes [19]
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