Bovine oocyte vitrification: Effect of ethylene glycol concentrations and meiotic stages

Cryodevices developed for minimum volume cooling vitrification of bovine oocytes

Unfertilized bovine oocytes can be efficiently cryopreserved only when an extremely rapid cooling rate (>20,000°C/min) is applied to oocytes with a very limited amount of surrounding vitrification solution. This protocol is defined as minimum volume cooling (MVC) vitrification. Various types of cryodevices, such as open pulled straw, Cryoloop, and Cryotop, have been developed to accelerate the cooling efficacy. Furthermore, hollow fibers with nano-scale pores, triangle nylon mesh sheets, and multilayer silk fibroin sheets have been optimized for the loading of large quantities of oocytes and/or the subsequent removal of excess vitrification solution, without requiring skillful operation to transfer individual oocytes using fine capillaries. This article provides an up-to-date review of cryodevices suitable for the MVC vitrification of bovine oocytes at the immature (germinal vesicle-) and mature (metaphase II-) stages.

Vitrification protocol for immature Brycon orbignyanus ovarian tissue as an extinction escape strategy

Piracanjunba (Brycon orbignyanus) is an endangered South American fish, and ovarian tissue cryopreservation is an alternative method for preserving maternal germplasm and genetic diversity. Therefore, our aim was to test a vitrification protocol for ovarian tissue containing primary growth (PG) oocytes of B. orbignyanus as a strategy to avoid the threat of extinction. Two vitrification solutions were evaluated (VS1: 1.5 M methanol + 4.5 M propylene glycol and VS2: 1.5 M methanol + 5.5 M Me₂SO) and compared using control/fresh ovarian tissue. After vitrification, the following factors were analyzed: membrane integrity using trypan blue, morphology using a histological assessment, oxidative stress (total reactive antioxidant potential (TRAP) and reduced thiol [-SH]), mitochondrial activity using MTT, and DNA damage using a comet assay. The vitrified oocytes (VS1= 24.3 ± 0.49% and VS2= 24.8 ± 0.69%) showed higher DNA damage than the control group (control= 20.7 ± 1.03%) (P = 0.004). In contrast, in most evaluations (membrane integrity, membrane damage, oxidative stress, and mitochondrial activity), there were no discernible differences between the control group and the vitrified samples. In addition, oocyte (P = 0.883) and nuclear diameter (P = 0.118) did not change after vitrification. VS2 treatment resulted in higher nuclear damage (15.7 ± 1.45%) than in the control treatment (3.5 ± 1.19%); however, VS1 treatment did not result in significantly more damage (9.5 ± 3.01%) than in the control (P = 0.015). Therefore, the protocol for ovarian tissue vitrification tested in this study resulted in high maintenance of PG oocyte cell integrity, making it a promising alternative for B. orbignyanus maternal genome preservation.

Vitrification of immature bovine oocytes in protein-free media: The impact of the cryoprotectant treatment protocol, base medium, and ovary storage

Protein-free media are essential for the sanitary cryopreservation of bovine genetic resources. Our aim was to set up an optimized protocol for the vitrification of immature bovine oocytes using protein free media which can provide the highest embryo development rates and embryo quality after subsequent in vitro maturation and fertilization. First, using a protein free NCSU-37 as base medium we compared the efficacy of vitrification on Cryotop device with two different CPA protocols. "Protocol A″ employed a combination of ethylene glycol and propylene glycol as permeating cryoprotectants (pCPA) and equilibration in 4% total pCPA (2% ethylene glycol + 2% propylene glycol). "Protocol B″ employed a combination of ethylene glycol and DMSO and equilibration in 15% total pCPA (7.5% ethylene glycol + 7.5% DMSO). The 2 protocols were equally effective in terms of oocyte survival and subsequent development to the blastocyst stage. However, blastocyst cell numbers were significantly higher with "Protocol A". TCM-199 and NCSU-37 were equally effective as base media for vitrification. Vitrification with "Protocol A″ reduced the percentage of live oocytes and subsequent development to blastocyst stage but did not affect the hatching and cell numbers of blastocysts when compared to the non-treated group. CPA treatment of "Protocol A″ without cooling did not affect embryo development. Storage of ovaries in PBS at 15 °C for overnight reduced the percentage of surviving oocytes after vitrification but not their subsequent development to the blastocyst stage. In conclusion we established a vitrification protocol for the cryopreservation of immature bovine oocytes employing protein-free media which provided high blastocyst quality without noticeable toxic effects.

Development and ultrastructure of bovine matured oocytes vitrified using electron microscopy grids

The aim of this study was to establish a methodology of cryopreservation of cattle oocytes and the quality assessment of oocytes and subsequent embryos produced in vitro under our laboratory conditions. Previously in vitro matured (IVM) oocytes were vitrified in minimum volume by ultra-rapid cooling technique. The oocytes were put into the equilibration solution (3% ethylene glycol in M199-HEPES + 10% foetal bovine serum) for 12 min, transferred to vitrification solution (30% ethylene glycol + 1 M sucrose in M199-HEPES + 10% foetal bovine serum) at room temperature for 25 s, then placed onto nickel electron microscopy grids and plunged into liquid nitrogen. After warming 75% of the oocytes were assessed as viable. Part of viable oocytes was taken for electron microscopy, the remaining oocytes were fertilized in vitro, and the presumptive zygotes were cultured until the blastocyst stage. Embryo cleavage and blastocyst rates in vitrified group after warming were 64.98% and 17.3%, resp. versus 70.72% and 25.54% in the control group (P < 0.05). No significant differences were found in the blastocyst total cell number, TUNEL and dead cell indexes between both groups. Ultrastructure of vitrified oocytes showed damages in smooth endoplasmic reticulum (SER) vesicles and lipid droplets as well as irregular arrangement of solitary cortical granules. Several mitochondria were damaged and the microtubules around the chromosomes were less occurred compared to the control group. However, the extent of injuries was lower than reported by other authors studying the ultrastructure of vitrified bovine oocytes, what is also supported by the better development of our oocytes after IVF. In conclusion, the designed oocyte vitrification technique ensures obtaining the blastocysts of the quality comparable to the fresh oocytes.

Methodological approaches for vitrification of bovine oocytes

Numerous factors affect vitrification success and post-thaw development of oocytes after in vitro fertilization. Therefore, elaboration of an optimal methodology ensuring higher cryotolerance of oocytes and subsequent blastocyst yield is still of great interest. This paper describes and evaluates critical factors affecting the success of oocyte vitrification. In particular, an appropriate oocyte stage such as maturation status (germinal vesicle stage, metaphase II stage), presence/absence of cumulus cells before vitrification, and the effect of follicle size, as well as different culture systems and media for in vitro production of embryos, the types and concentrations of cryoprotectants, and cooling and warming rates at vitrification are considered. Special attention is paid to various cryocarriers used for low-volume vitrification, which ensures safe storage of oocytes/embryos in liquid nitrogen and their successful post-thaw recovery. At the end, we focussed on how age of oocyte donors (heifers, cows) influences post-thaw development. This review summarizes results of recently published studies describing different methodologies of cryopreservation and post-thaw oocyte development with the main focus on vitrification of bovine oocytes.

Meiotic Status Does Not Affect the Vitrification Effectiveness of Domestic Cat Oocytes

Simple Summary

Assisted reproduction techniques (ART) are crucial for preserving endangered animal species. Cryopreservation by vitrification can maintain gamete viability for a long time. Efforts to preserve endangered species within the Felidae family are focused on developing appropriate ART procedures. The domestic cat is a good biomedical model. Unfortunately, the current state of knowledge on vitrification of cat oocytes is inconclusive and the efficiency of ART procedures is low. A key example concerns how the meiotic status of the oocyte influences suitability for vitrification. This is the main question of this study. First, we conducted a toxicity test to make sure that the vitrification solution (VS) we proposed does not have a toxic effect on cat oocytes. Next, we performed vitrification on cat oocytes before (nonmature) and after in vitro maturation (IVM) and checked their developmental potential. There was no negative impact of the applied VS on oocyte maturation and fertilization, demonstrating a possibility to obtain embryos in vitro regardless of the meiotic status. There is a need for more research on vitrification of the domestic cat oocytes as a model species for wild cats.

Abstract

Cryopreservation is important for animal fertility and biodiversity. Unfortunately, cryopreservation of feline oocytes is still an experimental technique. The aims of this study were to analyze the potential toxicity of the cryoprotectants in the vitrification solution (VS) on cat oocytes and to investigate whether the meiotic status of oocytes influences their developmental potential after vitrification. Two experiments were conducted with the VS composed of 20% ethylene glycol, 20% dimethyl sulfoxide, 20% fetal calf serum, 1.5 M trehalose, and 10% Ficoll PM-70: (1) toxicity assessment of the VS on immature cumulus oocyte complexes (COCs), and subsequently in vitro maturation (IVM) and in vitro fertilization; (2) assessment of the influence of the meiotic status on vitrification effectiveness, where immature and in vitro matured COCs were vitrified on the Cryotop. After rewarming, vitrified oocytes were subjected to IVM (immature) and intracytoplasmic sperm injection (ICSI) with fresh epididymal sperm. The toxicity test revealed no negative effect of oocyte exposure to the applied VS on their developmental potential (p > 0.05). Although the vitrification procedure itself significantly reduced the meiotic competence of oocytes, their meiotic status before vitrification (immature vs. in vitro matured) did not influence fertilization and morula rates. The only parameter affected by vitrification was the rate of oocytes suitable for ICSI, which was significantly lower for immature oocytes. Regardless of the meiotic status of vitrified oocytes, morphologically normal morulae were obtained. Moreover, the two meiotic stages examined are suitable for vitrification, with mature oocytes being a better choice when a well-equipped laboratory is available.

Aging-related mitochondrial alterations in bovine oocytes

Advanced maternal age is an emerging health problem which involves many functional and structural alterations in oocytes, and its study is relevant to design better approaches to improve the reproductive function in women of advanced age. A constraint to this type of studies is the limited amount of samples and the ethical problems of working with human gametes. This study aims to characterize the in vitro-induced age-related modifications in a bovine model, as well as to determine if this model is a reliable approach to study human aging. For this purpose, we have focused on aging-related alterations related to oocyte mitochondrial dysfunction, a key hallmark in aging. Morphological and bioenergetic in vitro-induced alterations in bovine oocytes were compared to an in vivo aged group and to the already reported information regarding humans and other animal models. Parameters monitored included ooplasmic volume; mitochondrial mass, distribution and aggregation, assessed by MitoTracker Green; mitochondrial activity, monitored by JC-1; and the mitochondrial levels of hydrogen peroxide (H₂O₂), quantified using MitoPY. Results show a significant decrease in oocyte cytoplasmic volume after both in vitro and in vivo aging (p < 0.001). Additionally, the levels of H₂O₂ increased significantly after in vitro and in vivo aging (p < 0.001) and mitochondrial aggregation patterns were significantly different after 30 h of in vitro maturation, with MII oocytes presenting small aggregates inside the cytoplasm, whereas aged oocytes had a lack of granularity (p < 0.001). In contrast, there were no differences between the different aging groups in terms of mitochondrial mass, distribution and activity. In conclusion, this in vitro approach of inducing aging-related alterations may be considered as a reliable approach to study the aging process in human female gametes, since it causes the same types of alterations in both species.

In vitro supplementation of trans-10, cis-12 conjugated linoleic acid ameliorated deleterious effect of heat stress on bovine oocyte developmental competence

Environmental stresses, such as heat stress (HS), have been shown to have diverse effects on the developmental competence of oocytes. The aim of this study was to determine the effect of exogenous conjugated linoleic acid (CLA) supplementation in maturation medium on bovine oocyte maturation and developmental competence under HS condition. Accordingly, cumulus-oocyte complexes (COCs) were cultured at 41 °C and 38.5 °C for the first and second 12 h of maturation in the presence of 0 (PC), 50 (CLA50-HS) and 100 (CLA100-HS) μM CLA. Also, a group of COCs were cultured at 38.5 °C for 24 h of maturation without CLA supplementation as negative control (NC). Nuclear maturation, level of intracellular glutathione (GSH), reactive oxygen species (ROS) content, cleavage and blastocyst rates as well as relative expression of BAX, and BCL2 genes in blastocysts were investigated. Our finding for the PC and NC groups revealed that HS decreased the percentage of MII oocytes, cleavage and blastocyst rates (P < 0.05). Moreover, HS lead to an increase in ROS levels and relative expression of BAX gene, decreased the intracellular content of GSH and relative expression of BCL2 gene (P < 0.05). However, the cleavage and blastocyst rates tended to increase in the CLA-supplemented groups compared to PC group (p < 0.10). Also, ROS and GSH levels in the matured oocytes decreased and increased in the CLA50-HS group compared to the PC group (P < 0.05), respectively. The ratio of expression levels of BAX to BCL2 genes was not different between the PC and CLA50-HS groups (P > 0.05). These findings suggest that HS has undesirable effects on the maturation competence of bovine oocyte and subsequent embryo development while administration of CLA can ameliorate some of adverse effects of HS.

Vitrifying immature equine oocytes impairs their ability to correctly align the chromosomes on the MII spindle

Vitrified-warmed immature equine oocytes are able to complete the first meiotic division, but their subsequent developmental competence is compromised. Therefore, the present study investigated the effects of vitrifying immature horse oocytes on the chromosome and spindle configuration after IVM. Cumulus-oocytes complexes (COCs) were collected and divided into two groups based on mare age (young ≤14 years; old ≥16 years). COCs were then either directly matured invitro or vitrified and warmed before IVM. Spindle morphology and chromosome alignment within MII stage oocytes were assessed using immunofluorescent staining, confocal microscopy and three-dimensional image analysis. Vitrification reduced the ability of oocytes to reach MII and resulted in ultrastructural changes to the meiotic spindle, including shortening of its long axis, and an increased incidence of chromosomes failing to align properly at the metaphase plate. We hypothesise that aberrant chromosome alignment is an important contributor to the reduced developmental competence of vitrified equine oocytes. Contrary to expectation, oocytes from young mares were more severely affected than oocytes from older mares; we propose that the reduced effect of vitrification on oocytes from older mares is related to pre-existing compromise of spindle assembly checkpoint control mechanisms in these mares.

Effects of laser-assisted hatching and exposure time to vitrification solution on mouse embryo development

Objective

This study was conducted to investigate the efficacy of laser-assisted hatching (LAH) and various vitrification times for embryonic development and blastocyst cell numbers.

Methods

First, 2-cell and 8-cell embryos were collected by flushing out the oviducts. In the control groups, they were vitrified for 8 or 10 minutes without LAH. The LAH groups underwent quarter laser zona thinning-assisted hatching before vitrification (4, 6, and 8 minutes or 4, 7, and 10 minutes, respectively). After incubation, double-immunofluorescence staining was performed.

Results

The hatched blastocyst rate 72 hours after the 2-cell embryos were thawed was significantly higher in the 2LAH-ES8 group (33.3%) than in the other groups (p<0.05). In the control-8 group (22.1±4.6), the cell number of the inner cell mass was higher than in the LAH groups (p<0.05). The number of trophectoderm cells was higher in the 2LAH-ES6 group (92.8±8.9) than in the others (p<0.05). The hatched blastocyst rate 48 hours after the 8-cell embryos were thawed was higher in the 8LAH-ES4 group (45.5%) than in the other groups, but not significantly. The inner cell mass cell number was highest in the 8LAH-ES7 group (19.5±5.1, p<0.05). The number of trophectoderm cells was higher in the 8LAH-ES10 group (73.2±12.1) than in the other groups, but without statistical significance.

Conclusion

When LAH was performed, 2-cell embryos with large blastomeres had a lower hatched blastocyst rate when the exposure to vitrification solution was shorter. Conversely, 8-cell embryos with small blastomere had a higher hatched blastocyst rate when the exposure to vitrification solution was shorter.

Effect of vitrification on the zona pellucida hardening and follistatin and cathepsin B genes expression and developmental competence of in vitro matured bovine oocytes

The purpose of our study was to assess the effect of vitrification with or without the presence of calcium in the vitrification solution on the: 1) diameter of oocytes and thickness of the zona pellucida, 2) zona pellucida hardening, 3) expression of mRNA follistatin (FST) and cathepsin B (CTSB) in oocytes and 4) developmental competence of embryos derived from in vitro matured and vitrified oocytes. The results of our study demonstrate, that vitrification did not alter thickness of the zona pellucida and diameter of the oocytes, however it triggered hardening of the zona pellucida. The presence of calcium in the vitrification solutions intensified hardening of zona in immature and mature oocytes (P < 0.04, P < 0.001, respectively) and provoked increased mRNA FST expression in oocytes matured in vitro compared to immature oocytes (P < 0.01) and those vitrified without calcium (P < 0.004). CTSB mRNA expression was increased in immature oocytes and oocytes vitrified with calcium compare to mature oocytes (P < 0.02). The developmental potential of vitrified oocytes was impaired compared to non-vitrified oocytes, being more evident in oocytes vitrified with calcium. In summary, vitrification did not change the oocyte diameter and thickness of the zona pellucida and expression of FST and CTSB mRNA. It diminished developmental potential of the vitrified oocytes. The presence of calcium in the vitrification solutions increased hardening of zona pellucida as well as affected the level of FST and CTSB mRNA in oocytes and developmental potential of these oocytes.

L-proline: a highly effective cryoprotectant for mouse oocyte vitrification

Recent studies have shown that L-proline is a natural osmoprotectant and an antioxidant to protect cells from injuries such as that caused by freezing and thawing in many species including plant, ram sperm and human endothelial cells. Nevertheless, this nontoxic cryoprotectant has not yet been applied to mammalian oocyte vitrification. In this study we evaluated the efficiency and safety of the new cryoprotectant in oocyte vitrification. The results indicated that L-proline improves the survival rate of vitrified oocytes, protects mitochondrial functions and could be applied as a new cryoprotectant in mouse oocyte vitrification.

Spindle configuration and developmental competence of in vitro-matured bovine oocytes exposed to NaCl or sucrose prior to Cryotop vitrification

In the present study we examined whether exposure to high concentrations of NaCl or sucrose before vitrification improves the cryotolerance of in vitro-matured bovine oocytes. In Experiment 1, oocytes were exposed to different concentrations of NaCl (375-1517 mOsm) or sucrose (375-812 mOsm) for 1h. On the basis of the results of this experiment, in Experiment 2 oocytes were exposed to 0.25% NaCl (375 mOsmol) or 2.77% sucrose (375 mOsmol) solution, vitrified and warmed. Microtubule and chromosome configurations were examined by immunocytochemistry. In Experiment 3, in vitro embryo development was assessed after vitrification of oocytes with or without 2.77% sucrose (375 mOsmol) pretreatment. There was a similar percentage of oocytes showing normal spindle configurations in the sucrose-pretreated and control groups. Higher rates of abnormal spindles were found in groups treated with NaCl or sucrose solutions with >375 mOsmol. After vitrification and warming, a significantly higher percentage of oocytes with normal chromosome configurations was recorded for oocytes exposed to 375 mOsmol sucrose solution before vitrification compared with the control vitrified oocytes. However, these percentages were significantly lower than those recorded in untreated controls. Cleavage and blastocyst rates were higher in non-vitrified than vitrified oocytes. In conclusion, pretreatment with 375 mOsmol NaCl or sucrose solution had no adverse effects on the spindle status of vitrified-warmed cow oocytes. However, sucrose pretreatment offered no benefits for embryo development.

Vitrification of mouse preantral follicles versus slow freezing: Morphological and apoptosis evaluation

The aim of this study was evaluation of survivability, maturation rate and apoptotic gene expression of preantral follicles after vitrification and slow freezing technique. Normal mouse preantral follicles were randomly divided into three experimental groups. In the control group, follicles were cultured immediately; in the vitrification and slow freezing groups, follicles were cultured after vitrification-warming and slow freezing-thawing procedures. Follicular viability was assessed by using 0.4% trypan blue, and molecular evaluation of messenger RNA levels of apoptosis-related genes was performed by the semi-quantitative RT-PCR method after 3 h of culture. Oocyte maturation rates were also evaluated on day 14 of culture. Survival and maturation rate in the slow freezing group were significantly lower than those in control and vitrification groups (P ≤ 0.05). Although there was no difference in Survivin expression among the three experimental groups, Bcl-2 expression was significantly lower in the slow freezing group compared to the other groups (P ≤ 0.05). The expression of Bax, P53, Fas and Bax/Bcl-2 ratio in the slow freezing group was significantly higher than control and vitrification groups (P ≤ 0.05). Preantral follicle vitrification seems to be better than slow freezing as seen in the survival, maturation and expression rates of apoptotic gene variants.

Oocytes recovered after ovarian tissue slow freezing have impaired H2AX phosphorylation and functional competence

It has been shown that oocytes isolated from ovarian tissue cryopreservation acquire DNA damage during the process of freeze-thawing. Using a mouse model, here we have investigated the functional competence and phosphorylation of H2AX (γ-H2AX) in germinal vesicle (GV) and parthenogenetically activated oocytes derived from conventional ovarian tissue slow freezing and vitrification techniques. The number of GV-stage oocytes with γ-H2AX foci was not significantly different between the slow-freezing and vitrification groups. Although the in vitro maturation (IVM) potential of GV oocytes in the slow-freezing group showed a significant delay (P<0.0001) in the process of germinal vesicle breakdown, no difference in the maturation rate was observed between the two protocols. Nevertheless, parthenogenetic activation of IVM oocytes using strontium chloride showed a significantly lower activation rate in the slow-freezing group compared with the vitrification (P<0.05) and control (P<0.01) groups. Importantly, H2AX phosphorylation was significantly perturbed in the slow-freezing group in comparison to the control (P<0.05). Therefore, we conclude that impaired sensing of DNA strand breaks and repair processes are associated with the reduced functional competence of the oocytes recovered from the slow-freezing group, which may have a significant impact on the reproductive outcome.

Ovarian tissue vitrification is more efficient than slow freezing in protecting oocyte and granulosa cell DNA integrity

Ovarian tissue cryopreservation is the primary treatment modality currently available to women at risk of losing their ovarian function due to cytotoxic therapy. However, the impact of these techniques on the oocyte DNA integrity is not elucidated. Here we have investigated the effect of vitrification and conventional slow freezing of eight week old Swiss albino mouse ovarian tissues on the oocyte and granulosa cell DNA integrity using the comet assay. The intracellular levels of reactive oxygen species in oocytes was measured by 2',7'-dichlorodihydrofluorescein diacetate fluorescence. The cryopreservation of ovarian tissue by the slow freezing technique resulted in a significantly higher level of DNA fragmentation in oocytes in comparison to vitrification (p < 0.05) whereas DNA fragmentation in granulosa cells was significantly higher than the control (p < 0.01). Further, reactive oxygen species were significantly elevated in oocytes derived from slow freezing when compared to vitrification (p < 0.05). Therefore, we conclude that the ovarian tissue slow freeze-thawing makes the oocyte and granulosa cells more vulnerable to DNA damage whereas vitrification appears to be a safer method than slow freezing for ovarian tissue cryopreservation.

In vitro growth and maturation of vitrified-warmed bovine oocytes collected from early antral follicles

Cryopreservation of growing oocytes enriches the choice of timing and location of artificial embryo production. However, completion of oocyte growth after warming is crucial when using such cryopreserved oocytes. Our research objective was to develop a sequential system that incorporates cryopreservation of growing bovine oocytes and their subsequent in vitro growth. Oocyte-granulosa cell complexes with a mean oocyte diameter of approximately 100 µm were vitrified-warmed and then cultured for 14 days. The percentage of surviving oocytes following cryopreservation and 14-day culture was approximately 80%. More than half of the surviving oocytes were capable of maturing to metaphase II after in vitro maturation; the rate was comparable to that of control oocytes grown in vitro without cryopreservation. Taken together, the combined protocols for vitrification-warming of growing oocytes and subsequent in vitro growth can produce oocytes capable of undergoing meiotic maturation.

Nuclear maturation and embryo development of porcine oocytes vitrified by cryotop: effect of different stages of in vitro maturation

The present study was designed to evaluate the viability, meiotic competence and subsequent development of porcine oocytes vitrified using the cryotop method at different stages of in vitro maturation (IVM). Cumulus-oocyte complexes (COCs) were cultured in IVM medium supplemented with 1mM dibutyryl cAMP (dbcAMP) for 22 h and then for an additional 22 h without dbcAMP in the medium. Germinal vesicle (GV), germinal vesicle breakdown (GVBD), metaphase I (MI), anaphase I/telophase I (AI/TI) and metaphase II (MII) were found to occur predominantly at 0-22, 26, 32, 38 and 44 h of IVM, respectively. Oocytes were exposed to cryoprotectant (CPA) or vitrified after different durations of IVM (0, 22, 26, 32, 38 and 44 h). After CPA exposure and vitrification, surviving oocytes that were treated before completion of the 44 h maturation period were placed back into IVM medium for the remaining maturation period, and matured oocytes were incubated for 2h. CPA treatment did not affect the viability of oocytes matured for 26, 32, 38 or 44 h, but significantly decreased survival rate of oocytes matured for 0 or 22 h. CPA treatment had no effect on the ability of surviving oocytes to develop to the MII stage regardless of the stage during IVM; however, blastocyst formation following PA was severely lower (P<0.05) than that in the control. At 2h post-warming, the survival rates of oocytes vitrified at 26, 32, 38 and 44 h of IVM were similar but were higher (P<0.05) than those of oocytes vitrified at 0 or 22 h of IVM. The MII rates of surviving oocytes vitrified at 0 and 38 h of IVM did not differ from the control and were higher (P<0.05) than those of oocytes vitrified at 22, 26 or 32 h of IVM. After parthenogenetic activation (PA), both cleavage and blastocyst rates of vitrified oocytes matured for 22, 26, 32, 38 and 44 h did not differ, but all were lower (P<0.05) than those matured 0 h. In conclusion, our data indicate that survival, nuclear maturation and subsequent development of porcine oocytes may be affected by their stage of maturation at the time of vitrification; a higher percentage of blastocyst formation can be obtained from GV oocytes vitrified before the onset of maturation.

Optimized protocol for cryopreservation of human eggs improves developmental competence and implantation of resulting embryos

Background

Successful egg cryopreservation has many potential benefits to a variety of patients. However, a superior standard protocol describing all aspects of oocyte cryopreservation has not yet been identified. Oocyte cryopreservation is still a technical challenge for many infertility clinics. To maintain satisfactory clinical outcomes, there is a need to develop an easy to use, yet efficient laboratory protocol. The present study was designed to examine if human embryos resulting from eggs frozen with an optimized vitrification protocol have similar developmental competence as those from fresh eggs.

Methods

Twenty recipients received donated eggs vitrified with a protocol in which short exposure time to the vitrification solution was used and 23 recipients received donated eggs and 6 patients had their own eggs vitrified with a modified protocol in which long exposure time to the vitrification solution was used. After warming, egg survival, fertilization, cleavage, blastocyst formation, clinical pregnancy and implantation rates were compared. The developmental competence of eggs vitrified with the optimized protocol was further compared with fresh eggs donated from the same donors.

Results

There was no difference in the oocyte survival, fertilization, cleavage, clinical pregnancy or implantation rates between the short and long protocol groups. However, blastocyst formation rate was significantly (P < 0.001) higher in the long protocol group (50.8%) than that in short protocol group (26.5%), resulting in more blastocysts being transferred and frozen. When frozen eggs vitrified with long protocol and fresh eggs from the same donors (12) were compared in 39 recipients, no differences were observed in terms of fertilization (86.4 vs 80.1%), blastocyst formation (50.0 vs 59.2%), clinical pregnancy (63.2 vs 60.0%) and implantation (41.7 vs 44.7%) rates. Four out of 6 patients had ongoing pregnancy after transfer of embryos from their own frozen eggs with a 46.2% implantation rate.

Conclusions

These results indicate that blastocyst development is an appropriate measure for egg survival after cryopreservation and frozen eggs have similar developmental potential as fresh eggs if they are frozen with an optimized method.

Vitrification of immature bovine cumulus-oocyte complexes: effects of cryoprotectants, the vitrification procedure and warming time on cleavage and embryo development

BACKGROUND

The present studies evaluated the effects of cryoprotectants, the vitrification procedure and time in the warming solution containing sucrose on cleavage and embryo development of immature (GV stage) bovine cumulus-oocyte complexes (COCs).

METHODS

Two experiments were conducted. In Experiment 1, COCs (n = 420) were randomly assigned to four groups: 1) CONTROL GROUP: no treatment; 2) VS1 group: COCs were exposed to vitrification solution 1 (VS1) containing 7.5% ethylene glycol [EG] + 7.5% dimethyl sulfoxide [DMSO] + 20% calf serum [CS] in TCM-199 at 37 C for 5 min; 3) VS1 + VS2 group: COCs were exposed to VS1 for 5 min followed by VS2 (15% EG + 15% DMSO + 17.1% sucrose + 20% CS) at 37 C for 45-60 sec; and 4) Vitrified group: COCs were exposed to VS1 and VS2, loaded on cryotops, vitrified in liquid nitrogen and then warmed in TCM-199 + 17.1% sucrose + 20% CS at 37 C for 1 min. In Experiment 2, COCs (n = 581) were assigned to the same groups, but those in VS1, VS1 + VS2 and Vitrified groups were sub-divided and exposed to the warming solution for either 1 or 5 min. After treatment and/or warming, all COCs in both experiments underwent in vitro maturation, in vitro fertilization and in vitro culture.

RESULTS

Cleavage and blastocyst rates did not differ among Control, VS1 and VS1 + VS2 groups in either experiment. In Experiment 2, there was no effect of time in the warming solution.However, both cleavage and blastocyst rates were lower (P < 0.001) in the Vitrified group than in the Control, VS1 and VS1 + VS2 groups (40.9 and 1.6% vs 92.2 and 34.4%, 79.4 and 25.2%, and 80.2 and 20.8%, respectively in Experiment 1, and 25.0 and 1.7% vs 75.3 and 27.2%, 67.9 and 19.5%, and 62.7 and 22.5%, respectively in Experiment 2).

CONCLUSIONS

The permeating cryoprotectants (EG and DMSO) present in VS1 and VS2 solutions and the time in the warming solution containing sucrose had no adverse effects on cleavage and blastocyst rates of immature bovine COCs. However, cleavage rate and early embryo development were reduced following the vitrification and warming.

Cryotop and development of vitrified immature bovine oocytes

The effectiveness of different cryodevices (open-pulled straw (OPS), electron microscopy grid (EMG), and Cryotop was evaluated for vitrification of immature bovine oocytes. Polar body, metaphase II stage (MII), survivability, and subsequent developmental rates were determined. Only oocytes with four or five layers of cumulus cells were used. Oocytes were equilibrated in two vitrification solutions - 1: 10% DMSO + 10% ethylene glycol (EG) for 30-45sec and 2: 20% DMSO + 20% EG +0.5M sucrose for 25sec -, mounted on one of the cryodevices and directly plunged into liquid nitrogen for 10 days. Immature vitrified oocytes using Cryotop showed the highest rates of polar body extrusion (PB) and nuclear maturity (MII); 41 and 58% respectively. Vitrified oocytes using OPS and EMG showed 26 and 32%; and 35 and 46% of PB and MII rates, respectively. The highest survivability resulted from Cryotop and EMG groups and no significant difference was found between them. Vitrified oocytes using Cryotop had the highest cleavage and blastocyst rates. All of the mean rates for vitrified immature oocytes were significantly lower than that of control group (P<0.05). The results of this study showed the superiority of Cryotop device for vitrification of immature bovine oocytes

Effect of bovine cumulus-oocyte complexes-conditioned medium on in-vitro maturation of canine oocytes

Purpose

To investigate the ability of medium conditioned with bovine cumulus-oocyte complexes (COCs) to support nuclear maturation of canine oocytes recovered from domestic dog ovaries.

Methods

Cumulus-oocyte complexes were obtained from ovaries of domestic bitches (8 months old to 7 years old), and in-vitro maturation was evaluated in TCM-199 supplemented with different concentrations (0, 20, 30 or 50%) of bovine COCs-conditioned medium (BCM). The canine COCs were cultured for 72 or 96 h at 38.5°C in 5% CO₂, 5% O₂ and 90% N₂. The bovine COCs-conditioned medium was obtained from culture of bovine COCs with TCM-199 supplemented with 5% FCS for 22 h at 38.5°C in 2% CO₂, 98% air.

Results

The proportion of germinal vesicle breakdown (GVBD) after 72 h was significantly higher (P < 0.05) in medium supplemented with 30% BCM (20.7%) compared with the control group (13.4%). The rates of GVBD-MII stage were significantly higher (P < 0.05) when oocytes were matured with BCM at concentration of 30% (41.5%) compared with control (26.6%) after 72 h in-vitro culture. After 96 h in-vitro culture, the oocytes matured in medium supplemented with 30% BCM (5.5%) showed a significant increase (P < 0.05) in the proportion of MII compared with control (0.7%). However, increasing the cultivation time from 72 to 96 h resulted in an increase in oocyte degeneration rate.

Conclusions

The results suggested that bovine COCs-conditioned medium supplementation significantly increased nuclear maturation of canine oocytes.

Cryopreservation of Mammalian oocyte for conservation of animal genetics

The preservation of the female portion of livestock genetics has become an international priority; however, in situ conservation strategies are extremely expensive. Therefore, efforts are increasingly focusing on the development of a reliable cryopreservation method for oocytes, in order to establish ova banks. Slow freezing, a common method for cryopreservation of oocytes, causes osmotic shock (solution effect) and intracellular ice crystallization leading to cell damage. Vitrification is an alternative method for cryopreservation in which cells are exposed to a higher concentration of cryoprotectants and frozen with an ultra rapid freezing velocity, resulting in an ice crystal free, solid glass-like structure. Presently, vitrification is a popular method for cryopreservation of embryos. However, vitrification of oocytes is still challenging due to their complex structure and sensitivity to chilling.

Membrane permeability characteristics of bovine oocytes and development of a step-wise cryoprotectant adding and diluting protocol

Membrane permeability is very helpful for the optimization of effective cryopreservation protocols. In this study, experiments were performed to determine these characteristics for immature (germinal vesicle (GV)) and in vitro matured (metaphase II (MII)) bovine oocytes within 4-37 degrees C, and a new step-wise adding and diluting protocol for ethylene glycol (EG) was developed and verified. Osmotically inactive volumes (V(b)) of GV and MII oocytes were calculated to be 16.1% and 26.1%. The membrane permeability of the oocytes to water (L(p)) in the presence of EG were between 0.08-0.18 and 0.14-0.28 microm/min/atm, and the membrane permeability of the oocytes to solutes (Ps) were between 0.0011-0.0038 and 0.0029-0.0061 cm/min for GV and MII oocytes, respectively. The activation energies (E(a)) for L(p) and P(s) in the presence of EG were 3.68 and 6.84 kcal/mol for GV oocyte, while 3.62 and 0.83-9.08 kcal/mol for MII oocyte. The data indicated that L(p) and P(s) varied significantly between developmental stages and among temperatures evaluated. Based on these results, different protocols for EG adding and diluting from oocytes were developed and tested. The assessment of cleavage rate and embryonic development in vitro confirmed that the designed 4-step adding 2-step diluting protocol indicated a better outcome. The present study is helpful for better understanding of cryobiological properties and the design of cryopreservation protocols for bovine oocytes.

Mouse oocyte vitrification: the effects of two methods on maturing germinal vesicle breakdown oocytes

PURPOSE

Evaluation of viability and subsequent developmental ability of mouse germinal vesicle breakdown oocytes vitrified in conventional straws.

METHODS

Oocytes with compact cumulus cells were cultured for 3 h in TCM199 medium GVBD and vitrified by two methods: the step-wise and single-step. After vitrification, the oocytes were thawed, and subjected to in vitro maturation and in vitro fertilization. Oocyte survival (post-thaw) was assessed by morphological appearance and staining, using propidium iodide (PI)/Hoechst 33342. The oocyte maturation and fertilization rates were examined in vitro.

RESULTS

In the single-step method the rates of post thaw survival, maturation to metaphase II and cleavage (2-cell embryos) were 58.68%, 56.41% and 38.63%, respectively. In the step-wise method, the corresponding rates were 81.75%, 68.59% and 51.80%, respectively.

CONCLUSION

Vitrification of mouse germinal vesicle breakdown oocytes by the step-wise method had the advantage of maintaining the viability and subsequent production of 2-cell embryos. In comparison with that in unvitrified control oocytes, the development of MII oocytes to 2-cell embryos was impaired following vitrification.

Optimization of cryopreservation condition for hematopoietic stem cells from umbilical cord blood

The conditions for cryopreservation of CD34(+) hematopoietic stem cells (HSC) from umbilical cord blood (UCB) were optimized with a new cryo-medium containing 10% ethylene glycol (EG) and 2% dimethyl sulfoxide (Me(2)SO) using a controlled-rate freezing (CRF) method. After the cryopreservation of mononuclear cells (MNC) from UCB, recoveries of MNC, CD34(+) cells, and total colony-forming units (CFU) were significantly improved compared to those in the control cryo-medium containing 10% Me(2)SO and 2% Dextran-40 (P<0.05). This study shows that the new cryo-medium and CRF method provide better recoveries of MNC, HSC and total CFU than the control cryo-medium and isopropylalcohol freezing (IPA) method. Therefore, this cryo-medium, combined with the CRF method, is valuable for optimizing cryopreservation conditions for HSC from UCB to obtain satisfactory HSC recovery.

Vitrification of immature mouse oocyte using stepwise equilibration before or after in vitro maturation

Immature mouse oocytes before or after in vitro maturation (IVM) were vitrified by the use of either conventional one-step or three-step equilibration. Although vitrification after IVM using the stepwise method does not affect the cleavage rate, the early embryonic development was profoundly impaired in both protocols.

Cryopreservation of immature bovine oocytes to reconstruct artificial gametes by germinal vesicle transplantation

Joining immature gamete cryopreservation and germinal vesicle transplantation (GVT) technique could greatly improve assisted reproductive technologies in animal breeding and human medicine. The present work was aimed to assess the most suitable cryopreservation protocol between slow freezing and vitrification for immature denuded bovine oocytes, able to preserve both nuclear and cytoplasmic competence after thawing. In addition, the outcome of germinal vesicle transfer procedure and gamete reconstruction was tested on the most effective cryopreservation system. Oocytes, isolated from slaughterhouse ovaries, were stored after cumulus cells removal either by slow freezing or by vitrification in open pulled straws. After thawing, oocytes were matured for 24 h in co-culture with an equal number of just isolated intact cumulus enclosed oocytes, and fixed in order to evaluate the stage of meiotic progression and cytoskeleton organization. Our results showed that after warming, vitrified oocytes reached metaphase II (MII) in a percentage significantly higher than oocytes cryopreserved by slow freezing (76.2% and 36.5% respectively, p < 0.05). Moreover, vitrification process preserved the organization of cytoskeleton elements in a higher proportion of oocytes than slow freezing procedure. Therefore vitrification has been identified as the elective method for denuded immature oocytes banking and it has been applied in the second part of the study. Our results showed that 38.3% of oocytes reconstructed from vitrified gametes reached the MII of meiotic division, with efficiency not different from oocytes reconstructed with fresh gametes. We conclude that vitrification represents a suitable method of GV stage denuded oocyte banking since both nuclear and cytoplasmic components derived from cryopreserved immature oocytes can be utilized for GVT.