Effects of vitrification solutions and equilibration times on the morphology of cynomolgus ovarian tissues

This study assessed the effects of vitrification solutions and equilibration times on morphology of cynomolgus ovarian tissues. Ovarian cortical sections (0.1–0.2 cm thickness) of seven cynomolgus monkeys were randomly allocated to either a control group or one of six vitrification groups. Ovarian tissue sections were vitrified ultra-rapidly by placing them directly into liquid nitrogen using two different vitrification solutions (VSEGP: 5.64 mol/l ethylene glycol + 5% (w/v) polyvinylpyrrolidone + 0.5 mol/l sucrose; and VSED: 3.22 mol/l ethylene glycol + 2.56 mol/l dimethylsulphoxide + 0.5 mol/l sucrose) after three different exposure times (5–20 min). After warming, follicle morphology was analysed using light and transmission electron microscopy. The proportion of morphologically normal follicles vitrified using VSED after a 5-min exposure was lower (P < 0.05) than those vitrified by other conditions. The proportion of normally structured mitochondria in oocytes of preantral follicles vitrified after a 5-min exposure to VSED (56%) was lower (P < 0.01) than those vitrified by other conditions (78–88%). Following tissue vitrification with VSED, the surface ratio of lysosome was increased compared with non-vitrified oocytes (1.64% versus 1.11%; P < 0.05). These results indicate that VSEGP can support the morphology of vitrified preantral follicles and oocytes.Cryopreservation of preantral follicles in ovarian tissues has been expected to be an effective measure for preserving fertility in young women who need to undergo cytotoxic therapy. However, a cryopreservation protocol has not yet been well established. This paper revealed that only 5-min exposure time to a cryoprotectant containing a combination of ethylene glycol and polyvinylpyrrolidone yields better follicle and oocyte morphology at an ultra-structural level in mammalian ovarian tissues after ultra-rapid vitrification using a new ultra-rapid vitrification device compared with a cryoprotectant containing a combination of ethylene glycol and dimethylsulphoxide. Survival rates of cancer patients are increasing. However, patients requiring chemotherapy and/or radiotherapy for cancer, leukaemia or other benign pathologies are likely to experience premature ovarian failure and loss of fertility as a consequence of these potentially gonadotoxic treatments. Use of the procedure reported in this study may increase the chance of fertility preservation.