Influence of stage of maturation of bovine oocytes at time of vitrification on the incidence of diploid metaphase II at completion of maturation

Effects of melatonin and human follicular fluid supplementation of in vitro maturation medium on mouse vitrified germinal vesicle oocytes: A laboratory study

Background

Vitrification as the most efficient method of cryopreservation, enables successful storage of oocytes for couples who undergo specific procedures including surgery and chemotherapy. However, the efficacy of in vitro maturation (IVM) methods with vitrified germinal vesicle (GV) oocytes could be improved.

Objective

As melatonin and follicular fluid (FF) might enhance IVM conditions, we used these supplements to assess the maturation rate of vitrified GV oocytes and their artificial fertilization rate.

Materials and Methods

Four hundred mouse GV oocytes were harvested, vitrified, and assigned into control (C-Vit-GV) and treatment groups of melatonin (M-Vit-GV), human follicular fluid (HFF-Vit-GV), and a combination (M + HFF-Vit-GV). A non-vitrified group of GV oocytes (non-Vit-GV) and a group of in vivo matured metaphase II (Vivo-MII) oocytes served as control groups to evaluate the vitrification and IVM conditions, respectively. Maturation of GV oocytes to MII and further development to two-cell-stage embryos were determined in the different groups.

Results

Development to two-cell embryos was comparable between the Vivo-MII and non-Vit-GV groups. IVM and in vitro fertilization (IVF) results in the non-Vit-GV group were also comparable with the C-Vit-GV oocytes. In addition, the IVM and IVF outcomes were similar across the different treatment groups including the M-Vit-GV, HFF-Vit-GV, M + HFF-Vit-GV, and C-Vit-GV oocytes.

Conclusion

Employing an appropriate technique of vitrification followed by suitable IVM conditions can lead to reasonable IVF outcomes which may not benefit from extra supplementations. However, whether utilizing other supplementation formulas could improve the outcome requires further investigation.

Morphological, biochemical and functional studies to evaluate bovine oocyte vitrification

The aim of the present study was to evaluate the effect of vitrification on morphological, biochemical and functional parameters of matured bovine oocytes at different recovery times. To this end, matured bovine oocytes were vitrified using the Cryotech® kit (a minimum-volume system) and then incubated in maturation medium for different post-warming durations (0 h, 3 h or 21 h). Morphology, viability and biochemical parameters were assessed at each time point mentioned above and the recovery of the metaphase plate was analyzed at 2 h, 3 h and 4 h post-warming. The vitrification-warming process did not affect the viability or morphology of oocytes at any time point. However, the recovery of the metaphase plate occurred mostly between 3 and 4 h rather than at 2 h after warming (P < 0.05). Both control and vitrified-warmed oocytes showed changes in cytosolic oxidative activity, quantification of active mitochondria, reactive oxygen species (ROS) levels and redox status at the different time points studied (P < 0.05). However, differences between control and vitrified-warmed oocytes were found only in the quantification of active mitochondria and ROS production (P < 0.05). Finally, in vitro fertilization and embryo culture were carried out as functional studies to establish whether vitrification-warming affected oocyte competence, and a significant decrease was found both in the cleavage rate and embryo development (P < 0.05). We concluded that major improvements in oocyte vitrification, at list with Cryotech® kit, are still needed to avoid variations in oocyte metabolism which could contribute to the reduction in the developmental competence of bovine oocytes.

Closed system for bovine oocyte vitrification

The aim of our study was to develop a vitrification carrier for bovine oocyte cryopreservation. The carrier was to be cheap enough, elementary in its construction and meet contemporary requirements for a safe closed system. In a closed system, a cell is prevented from direct exposure to liquid nitrogen, thus minimizing the risk of cross-contamination. Furthermore, two questions regarding the proper vitrification technique were resolved: if it is necessary to partially denude the oocytes before the vitrification process or whether intact cumulus oocyte complexes should be frozen; and if it is more advantageous to preheat the vitrification solutions to female body temperature (39 °C) or to keep them at room temperature. Our results show that it is better to partially denude the oocytes prior to vitrification because cryopreserved intact cumulus oocyte complexes often proved dark, non-homogeneous or fragmented cytoplasm after warming, with many of them having visibly widened perivitelline spaces or fractured zonae pellucidae as a result of extensive damage during vitrification. Consequently, intact cumulus oocyte complexes showed significantly lower numbers of cleavage stage embryos on Day 3 compared to partially denuded oocytes (7.4% and 26%, respectively). On the other hand, the survival rate and following development of fertilized oocytes in preheated vitrification solution were equal to results reached at room temperature conditions. In conclusion, results achieved with the newly developed carrier were comparable to previously published studies and therefore they could be recommended for common use.

Vitrification of bovine oocytes: implications of follicular size and sire on the rates of embryonic development

PURPOSE

The objectives were to test how the source of oocytes and semen impacted vitrification of large numbers of bovine oocytes and subsequent IVF and early embryo development to test procedures that may assist with assisted reproductive technologies in humans.

METHODS

Bovine oocytes were vitrified from follicles of different diameters, small (< or =4 mm) and medium (4 to 10 mm), using nylon mesh. Oocytes were exposed to the cryoprotectant composed of 40% (v/v) ethylene glycol, 18% (w/v) Ficoll-70, and 0.3 M sucrose in three stepwise dilutions. Thawing was conducted with a series of 0.5, 0.25 and 0.125 M sucrose dilutions in 20% fetal bovine serum.

RESULTS

The cleavage (39.1% vs. 58.5%) and blastocyst rates (5.1% vs. 22.9%) were significantly lower for the vitrified oocytes. Follicle size had a significant impact on the development of embryos. Sires had significant effects on embryonic developmental rates.

CONCLUSIONS

We conclude that differences in development exist due to follicle source and sire used for IVF after vitrification.

OPS vitrification of mouse immature oocytes before or after meiosis: the effect on cumulus cells maintenance and subsequent development

Cryopreservation can cause cumulus cell damage around the immature oocytes, which may result in poor subsequent development. To evaluate the effect of the meiosis stage on the cumulus cell cryoinjury and determine the suitable stage for cryopreservation in immature oocytes, mouse oocytes at germinal vesicle (GV) and germinal vesicle breakdown (GVBD) stages were vitrified using open pulled straw (OPS) method. Cumulus cells damage was scored immediately after thawing by double-fluorescent staining. The survival rate of the oocytes was evaluated and the subsequent development of oocytes was assessed through in vitro culture (IVC) and in vitro fertilization (IVF) separately. After vitrification, a higher proportion of cumulus cells of GV oocytes were damaged than those of GVBD and untreated control groups. The survival rate of vitrified GVBD oocytes (94.1%) was significantly higher (p < 0.05) than that of GV oocytes (85.4%). Oocytes vitrified at GVBD stage (55.7%) showed similar cleavage rate compared to those at GV stage (49.2%), but significantly higher (p < 0.05) blastocyst rate (40.9% vs. 27.4%). These results demonstrate that oocytes at GVBD stage remain better cumulus membrane integrity and developmental ability during vitrification than those at GV stage, indicating they are more suitable for immature oocytes cryopreservation in mice.

Effect of Meiotic Stages During In Vitro Maturation on the Survival of Vitrified-Warmed Buffalo Oocytes

The present study was conducted to investigate the effect of meiotic stages during in vitro maturation (IVM) on the survival of vitrified-warmed buffalo oocytes, vitrified at different stages of IVM. Cumulus oocyte complexes obtained from slaughterhouse ovaries were randomly divided into 6 groups: control (non-vitrified, matured for 24 h at 38 +/- 1 degrees C, 5% CO2 in humidified air), and those matured for 0 h (vitrified before IVM) or 6, 12, 18 and 24 h before vitrification. Cumulus oocyte complexes were vitrified in solution consisting of 40% w/v propylene glycol and 0.25 mol/L trehalose in phosphate-buffered saline supplemented with 4% w/v bovine serum albumin. Vitrified cumulus oocyte complexes were stored at -196 degrees C (liquid nitrogen) for at least 7 days and then thawed at 37 degrees C; cryoprotectant was removed with 1 mol/L sucrose solution. Cumulus oocyte complexes in the 0, 6, 12, 18 and 24 h groups were then matured for an additional 24, 18, 12, 6 and 0 h, respectively, to complete 24 h of IVM. Among the five vitrification groups, 89-92% of cumulus oocyte complexes were recovered, after warming, of which 84-91% were morphologically normal. Overall survivability of vitrified cumulus oocyte complexes was lower (p < 0.05) than that of non-vitrified cumulus oocyte complexes (94.5%). Survival rates of cumulus oocyte complexes matured 24 h prior to vitrification (61.3%) were higher (p < 0.05) than those matured for 12 h (46.7%), 6 h (40.6%) and 0 h (37.6%). Nuclear status following 24 h IVM was assessed. A higher proportion of non-vitrified (control) oocytes (72.7%) reached metaphase II (M-II) stage in control than oocytes vitrified for 24 h (60.0%), 18 h (54.4), 12 h (42.3%), 6 h (33.3%) and 0 h (31.6%) (p < 0.05). The results suggest that length of time in maturation medium prior to vitrification influences post-thaw survivability of buffalo oocytes; longer intervals resulted in higher survival rates.