Effect of chilling bovine oocytes on their developmental competence

A recently developed minimum volume, absorbent, vitrification device, the Kitasato Vitrification System gives excellent outcomes for in vitro produced bovine blastocysts

Cryopreservation of embryos is a crucial component of current assisted reproductive technologies (ART). While the ART outcomes for many species have been greatly improved by the introduction of minimum volume vitrification devices, these devices can be difficult to handle and load. To reduce this problem, we recently developed a vitrification carrier which has a highly absorbent surface so that it simply and rapidly removes excess free vitrification solution from the specimen before the cooling step. This Kitasato Vitrification System (KVS) gives excellent results for human and mouse embryo vitrification. This study aimed to determine whether the KVS would also be effective for bovine blastocyst vitrification by comparing outcomes for the control device that was the KVS without excess vitrification solution absorber. The effect of varying the length of time spent in the first equilibration solution (0-10 min) was also evaluated. Vitrification with the KVS resulted in significantly higher survival and hatching rates than with the control device loaded with the same volume of vitrification solution (survival: 98.6% vs 87.6%, hatching at 72 h post warming: 87.3% vs 66.7%, respectively). The best outcomes were obtained with a 10 min equilibration step prior to exposure to the vitrification solution for 30 s. We also evaluated the effect of embryo quality on blastocyst viability when using the KVS. Survival rates of high- and low-quality embryos were comparable but low quality embryos had significantly lower hatching rates. Overall, the results indicate that the KVS vitrification device is effective for bovine blastocyst vitrification.

Trehalose delivered by cold-responsive nanoparticles improves tolerance of cumulus-oocyte complexes to microwave drying

PURPOSE

Trehalose is a non-permeable protectant that is the key to preserve live cells in a dry state for potential storage at ambient temperatures. After intracellular trehalose delivery via cold-responsive nanoparticles (CRNPs), the objective was to characterize the tolerance of cat cumulus-oocyte complexes (COCs) to different levels of microwave-assisted dehydration.

METHODS

Trehalose was first encapsulated in CRNPs. After exposure to trehalose-laden CRNPs, different water amounts were removed from cat COCs by microwave drying. After each dehydration level, meiotic and developmental competences were evaluated via in vitro maturation, fertilization, and embryo culture. In addition, expressions of critical genes were assessed by quantitative RT-PCR.

RESULTS

CRNPs effectively transported trehalose into COCs within 4 h of co-incubation at 38.5 °C followed by a cold-triggered release at 4 °C for 15 min. Intracellular presence of trehalose enabled the maintenance of developmental competence (formation of blastocysts) as well as normal gene expression levels of HSP70 and DNMT1 at dehydration levels reaching up to 63% of water loss.

CONCLUSION

Intracellular trehalose delivery through CRNPs improves dehydration tolerance of COCs, which opens new options for oocyte storage and fertility preservation at ambient temperatures.

Microenvironment factors promoting the quality of vitrified cat oocytes

In oocyte cryopreservation programs, vitrification has overthrown conventional slow freezing both in veterinary and human medicine. In animals, its feasibility in field conditions makes it the preferred technique for the safeguard of genetic resources from zoo or wild animals, including threatened felids, for which the domestic cat is an excellent model. However, many cellular injuries, such as cytoskeleton, mitochondria and meiotic spindle alterations, DNA damage, zona pellucida hardening and cumulus cell loss, might occur following vitrification. After warming, although the exact mechanisms are still unclear, degeneration is a frequent outcome for cat vitrified oocytes. For immature (germinal vesicle) gametes, in vitro maturation after warming is a challenge, and cleavage after fertilization barely reaches 15-30%, while for mature (metaphase II) cryopreserved gametes it can get to 30-50%. Anyway, the progression to late embryos stages is often impaired, and improvements are needed. Standard cryopreservation protocol and the use of conventional in vitro culture systems after warming may not be enough for vitrified oocytes to recover and demonstrate their full developmental potential. Physical or chemical factors applied to oocytes undergoing vitrification, as an enrichment to the vitrification step, or to the culture microenvironment, could create more favorable conditions and promote vitrified oocyte survival and development. From the use of three-dimensional culture systems to the regulation of metabolic activities and cellular pathways, this review aims to explore all the possibilities employed so far, including the studies performed by our own lab, and the future perspectives, to present the most effective strategies for cat oocyte vitrification and the best time for their application (i.e., before, during, or after vitrification-warming).

The Open Cryotop System Is Effective for the Simultaneous Vitrification of a Large Number of Porcine Embryos at Different Developmental Stages

The Superfine Open Pulled Straw (SOPS) system is the most commonly used method for vitrification of pig embryos. However, this system only allows the vitrification of four to seven embryos per straw. In this study, we investigated the effectiveness of the open (OC) and closed (CC) Cryotop^® systems to simultaneously vitrify a larger number of porcine embryos. Morulae, early blastocysts and full blastocysts were vitrified with the open Cryotop^® (n = 250; 20 embryos per device) system, the closed Cryotop^® (n = 158; 20 embryos per device) system and the traditional superfine open pulled straw (SOPS; n = 241; 4–7 embryos per straw) method. Fresh embryos from each developmental stage constituted the control group (n = 132). Data expressed as percentages were compared with the Fisher's exact test. The Kruskal-Wallis test was used to analyze the effect of the different vitrification systems on the embryo quality parameters and two-by-two comparisons were accomplished with the Mann-Whitney U test. Differences were considered statistically significant when p < 0.05. Vitrified and control embryos were incubated for 24 h and examined for viability and quality. At the warming step, the embryo recovery rate for the CC system was 51%, while all embryos were recovered when using OC and SOPS. There were no differences between the vitrification and control groups in the postwarming viability of full blastocysts. In contrast, morulae and early blastocysts that were vitrified-warmed with the SOPS system had lower viability (p < 0.01) compared to those from the OC, CC and control groups. The embryonic viability was similar between the OC and control groups, regardless of the developmental stage considered. Moreover, the embryos from the OC group had comparable total cell number and cells from the inner cell mass and apoptotic index than the controls. In conclusion, the OC system is suitable for the simultaneous vitrification of 20 porcine embryos at different developmental stages and provides comparable viability and quality results to fresh embryos subjected to 24 h of in vitro culture.

Oocyte Cryopreservation in Domestic Animals and Humans: Principles, Techniques and Updated Outcomes

Oocyte cryopreservation plays important roles in basic research and the application of models for genetic preservation and in clinical situations. This technology provides long-term storage of gametes for genetic banking and subsequent use with other assisted reproductive technologies. Until recently, oocytes have remained the most difficult cell type to freeze, as the oocytes per se are large with limited surface area to cytoplasm ratio. They are also highly sensitive to damage during cryopreservation, and therefore the success rate of oocyte cryopreservation is generally poor when compared to noncryopreserved oocytes. Although advancement in oocyte cryopreservation has progressed rapidly for decades, the improvement of cryosurvival and clinical outcomes is still required. This review focuses on the principles, techniques, outcomes and prospects of oocyte cryopreservation in domestic animals and humans.

Effect of cryoprotectant concentration on bovine oocyte permeability and comparison of two membrane permeability modelling approaches

The plasma membrane permeability to water and cryoprotectant (CPA) significantly impacts vitrification efficiency of bovine oocytes. Our study was designed to determine the concentration-dependent permeability characteristics for immature (GV) and mature (MII) bovine oocytes in the presence of ethylene glycol (EG) and dimethyl sulphoxide (Me₂SO), and to compare two different modeling approaches: the two parameter (2P) model and a nondilute transport model. Membrane permeability parameters were determined by consecutively exposing oocytes to increasing concentrations of Me₂SO or EG. Higher water permeability was observed for MII oocytes than GV oocytes in the presence of both Me₂SO and EG, and in all cases the water permeability was observed to decrease as CPA concentration increased. At high CPA concentrations, the CPA permeability was similar for Me₂SO and EG, for both MII and GV oocytes, but at low concentrations the EG permeability of GV oocytes was substantially higher. Predictions of cell volume changes during CPA addition and removal indicate that accounting for the concentration dependence of permeability only has a modest effect, but there were substantial differences between the 2P model and the nondilute model during CPA removal, which may have implications for design of improved methods for bovine oocyte vitrification.

Cryopreservation of equine oocytes: looking into the crystal ball

Invitro embryo production has evolved rapidly in the horse over the past decade, but blastocyst rates from vitrified equine oocytes remain quite poor and further research is needed to warrant application. Oocyte vitrification is affected by several technical and biological factors. In the horse, short exposure of immature oocytes to the combination of permeating and non-permeating cryoprotective agents has been associated with the best results so far. High cooling and warming rates are also crucial and can be obtained by using minimal volumes and open cryodevices. Vitrification of invivo-matured oocytes has yielded better results, but is less practical. The presence of the corona radiata seems to partially protect those factors that are necessary for the construction of the normal spindle and for chromosome alignment, but multiple layers of cumulus cells may impair permeation of cryoprotective agents. In addition to the spindle, the oolemma and mitochondria are also particularly sensitive to vitrification damage, which should be minimised in future vitrification procedures. This review presents promising protocols and novel strategies in equine oocyte vitrification, with a focus on blastocyst development and foal production as most reliable outcome parameters.

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.

An efficiency comparison of different in vitro fertilization methods: IVF, ICSI, and PICSI for embryo development to the blastocyst stage from vitrified porcine immature oocytes

Background

Most studies carried out to evaluate recovery and development after porcine oocyte vitrification, reported better rates when cryopreserved in embryonic development stages or zygotes, but not in immature oocytes. For this reason, many studies are performed to improve immature oocyte vitrification protocols testing the use of different cryoprotectant concentrations, cooling devices, incubation times; but only a few of them have evaluated which fertilization procedure enhances blastocyst rates in vitrified oocytes. Therefore, this study was aimed to evaluate: 1) if the sperm selection with hyaluronic acid (HA) or polyvinylpyrrolidone (PVP) before injection could play a key role in increasing fertilization and blastocyst formation and 2) the embryo developmental ability and blastocyst production of porcine immature oocytes retrieved after vitrification-warming and co-cultured with granulosa cells during IVM, using different fertilization techniques: in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI) and conventional ICSI with hyaluronic acid (HA) sperm selection, known as physiological intracytoplasmic sperm injection (PICSI) and.

Results

Sperm selected with HA-PICSI displayed a higher percentage of live/acrosome reacted status compared to those in control and exposed to PVP. Higher dead/acrosome reacted rates were obtained after PVP exposure compared to control and HA. In oocytes, viability significantly decreased after IVM in vitrified oocytes. Besides, IVM rates were not different between control denuded oocytes cultured with granulosa cells (DO-GC) and vitrified oocytes. Regarding fertilization parameters, IVF showed higher percentages of total fertilization rate than those obtained by ICSI and PICSI. However, results demonstrate that PICSI fertilization increased the blastocysts formation rate in control DO-GC and vitrified oocytes compared to IVF and ICSI.

Conclusions

To achieve high blastocyst formation rates from vitrified GV oocytes, it is recommended that sperm should be selected with HA instead of PVP before injection since high viability and acrosome reaction rates were obtained. Also, PICSI fertilization was the best method to produce higher blastocyst rates compared to the IVF and ICSI procedures.

A new, simple, automatic vitrification device: preliminary results with murine and bovine oocytes and embryos

PURPOSE

This paper reports the use of a novel automatic vitrification device (Sarah, Fertilesafe, Israel) for cryopreservation of oocytes and embryos.

METHODS

Mice oocytes (n = 40) and embryos (8 cells, n = 35 and blastocysts, n = 165), bovine embryos (2PN, n = 35), and MII oocytes (n = 84) were vitrified using this automated device. A total of 42 (2 cells) mice embryos, 20 (2PN) bovine embryos, and 150 MII bovine oocytes were used as fresh controls and grown to blastocysts. Upon rewarming, all were assessed for viability, cleavage, blastocyst, and hatching rates.

RESULTS

Ninety-five % (38/40) of the mice MII oocytes regained isotonic volumes and all (100%) the surviving were viable. Rewarmed 8-cell mice embryos had 95% (33/35) blastulation rate and 80% (28/35) hatched. Rewarmed mice blastocysts had 97% survival rate (160/165) and 81% (135/165) hatched. Fresh control mice embryos had 100% (42/42) blastulation and 73% (21/42) hatching rates. Bovine embryos' survival was 100% with 54% (19/35) cleavage and 9% (3/35) blastulation rate. Fresh control bovine embryos had 65% (13/20) cleavage and 20% (4/20) blastulation rate. Vitrified bovine oocytes had 100% survival (84/84), 73% (61/84) cleavage, and 7% (6/84) blastocysts' rates; fresh control had 83% (125/150) cleavage and 11% (17/150) blastocysts' rates.

CONCLUSION

This novel automatic vitrification device is capable to produce high survival rates of oocytes and embryos. We anticipate that as the demand for vitrification of gametes, embryos, and reproductive tissues increases worldwide, the availability of an automated vitrification device will become indispensable for standardization, simplification, and reproducibility of the entire process.

Vitreous Cryopreservation of Human Umbilical Vein Endothelial Cells with Low Concentration of Cryoprotective Agents for Vascular Tissue Engineering

Cryopreservation of human umbilical vein endothelial cells (HUVECs) is important to tissue engineering applications and the study of the role of endothelial cells in cardiovascular and cerebrovascular diseases. The traditional methods for cryopreservation by vitrification (cooling samples to a cryogenic temperature without apparent freezing) using high concentration of cryoprotective agents (CPAs) and slow freezing are suboptimal due to the severe toxicity of high concentration of CPAs and ice formation-induced cryoinjuries, respectively. In this study, we developed a method to cryopreserve HUVECs by vitrification with low concentration of CPAs. This is achieved by optimizing the CPAs and using highly thermally conductive quartz capillary (QC) to contain samples for vitrification. The latter minimizes the thermal mass to create ultra-fast cooling/warming rates. Our data demonstrate that HUVECs can be vitrified in the QC using 1.4 mol/L ethylene glycol and 1.1 mol/L dimethyl sulfoxide with more than 90% viability. Moreover, this method significantly improves the attachment efficiency of the cryopreserved HUVECs. The attached cells post-cryopreservation proliferate similarly to fresh cells. Therefore, this study may provide an effective vitrification technique to bank HUVECs for vascular tissue engineering and other applications.

The effect of temperature during liquid storage of in vitro-matured bovine oocytes on subsequent embryo development

The aim of the present study was to optimize the temperature for the temporal storage of matured bovine oocytes. In vitro-matured bovine oocytes were preserved in HEPES-buffered TCM199 medium supplemented with 10% newborn calf serum at different temperatures (4 °C, 15 °C, 25 °C, and 38.5 °C) for 20 hours. Embryo development and blastocyst quality after in vitro fertilization, cytoplasmic ATP and glutathione levels in oocytes, and the frequency of apoptotic oocytes were compared among storage groups and a control group without storage. Among the storage groups, those at 25 °C and 38.5 °C showed the highest rates of blastocyst development (19.3% and 24.5%, respectively) compared with those stored at 4 °C and 15 °C (8.5% and 14.9%, respectively); however, blastocyst formation rates in all storage groups were lower than that in the control group (39.8%; P < 0.05). Storage at 38.5 °C and 15 °C was associated with reduced cell numbers in resultant blastocysts compared with the control and the 25 °C storage groups. Storage at 4 °C reduced metabolic activity of oocytes characterized by their lower ATP levels compared with the other groups. Storage for 20 hours significantly reduced the glutathione content in oocytes in all groups in a similar manner, irrespective of the temperature. Storage at 4 °C or 15 °C but not at 25 °C and 38.5 °C significantly increased the percentage of apoptotic oocytes compared with the control group. In conclusion, 25 °C was found to be the most suitable temperature for the temporal storage of matured bovine oocytes regarding both the developmental competence of oocytes and the quality of resultant blastocysts.

Combined inhibitory effects of low temperature and N-acetyl-l-cysteine on the postovulatory aging of mouse oocytes

The postovulatory aging of oocytes eventually affects the development of oocytes and embryos. Oxidative stress is known to accelerate the onset of apoptosis in oocytes and influence their capacity for fertilisation. This study aimed to reveal the roles of temperature and the antioxidant N-acetyl-l-cysteine in preventing the aging of postovulatory mouse oocytes. First, newly ovulated mouse oocytes were cultured at various temperature and time combinations in HCZB medium with varying concentrations of N-acetyl-l-cysteine to assess signs of aging and developmental potential. When cultured in HCZB with 300 μM N-acetyl-l-cysteine at different temperature and incubation time combinations (namely 25°C for 12 h, 15°C for 24 h and 5°C for 12 h), the increase in the susceptibility of oocytes to activating stimuli was efficiently prevented, and the developmental potential was maintained following Sr2+ activation or in vitro fertilisation. After incubation at either 15°C for 36 h or 5°C for 24 h, oocytes that had decreased blastocyst rates displayed unrecoverable abnormal cortical granule distribution together with decreased BCL2 levels, total glutathione concentrations and glutathione/glutathione disulphide (GSH/GSSG) ratios. In conclusion, postovulatory oocyte aging could be effectively inhibited by appropriate N-acetyl-l-cysteine addition at low temperatures. In addition, a simple method for the temporary culture of mature oocytes was established.

cAMP modulation during sheep in vitro oocyte maturation delays progression of meiosis without affecting oocyte parthenogenetic developmental competence

Removal of oocytes from their natural inhibitory follicular environment results in spontaneous resumption of meiosis independent of normal signaling events that occur in vivo. Controlling the onset of meiotic resumption via maintenance of elevated oocyte cAMP levels with adenylyl cyclase (AC) activation and phosphodiesterase (PDE) inhibition, and subsequent hormone stimulation with follicle FSH has been shown to dramatically improve developmental competence of bovine and murine IVM oocytes. This study evaluated the effect of cAMP modulation during IVM of sheep oocytes on meiotic progression and development to blastocyst after parthenogenetic activation. Changes in oocyte cAMP levels were quantified during the first 2h of in vitro maturation in control or cAMP-modulating medium. No significant changes in intra-oocyte cAMP were observed under control conditions, though a slight and transient drop was noticed at 15 min of maturation. Addition of the AC stimulator Forskolin and the PDE inhibitors IBMX altered the cAMP profile, resulting in 10-fold elevation of cAMP by 15 min and sustained >3-fold elevated levels from 30 to 120 min. The effect of cAMP elevation on meiotic resumption was measured by completion of germinal vesicle breakdown. Modulated oocytes were significantly delayed when compared to control media oocytes. Also, progression to MII was significantly delayed in modulated versus control oocytes at 20 and 24h, though no differences persisted to 28 h. Lastly, when control and modulated oocytes were parthenogenetically activated, no differences in blastocyst formation were observed. Thus, while cAMP modulation delayed meiotic progression, it did not improve developmental competence of sheep IVM oocytes.

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.

Recent progress in cryopreservation of bovine oocytes

Principle of oocyte cryoinjury is first overviewed and then research history of cryopreservation using bovine oocytes is summarized for the last two decades with a few special references to recent progresses. Various types of cryodevices have been developed to accelerate the cooling rate and applied to the oocytes from large domestic species enriched with cytoplasmic lipid droplets. Two recent approaches include the qualitative improvement of IVM oocytes prior to the vitrification and the short-term recovery culture of vitrified-warmed oocytes prior to the subsequent IVF. Supplementation of L-carnitine to IVM medium of bovine oocytes has been reported to reduce the amount of cytoplasmic lipid droplets and improve the cryotolerance of the oocytes, but it is still controversial whether the positive effect of L-carnitine is reproducible. Incidence of multiple aster formation, a possible cause for low developmental potential of vitrified-warmed bovine oocytes, was inhibited by a short-term culture of the postwarm oocytes in the presence of Rho-associated coiled-coil kinase (ROCK) inhibitor. Use of an antioxidant α-tocopherol, instead of the ROCK inhibitor, also supported the revivability of the postwarm bovine oocytes. Further improvements of the vitrification procedure, combined with pre- and postvitrification chemical treatment, would overcome the high sensitivity of bovine oocytes to cryopreservation.

Effect of different culture systems on adipocyte differentiation-related protein (ADRP) in bovine embryos

Bovine embryos cultured in serum-containing media abnormally accumulate lipid droplets, compared to their in vivo counterparts. The objective of this study was to investigate the effect of different culture systems on the mRNA expression and on the quantification and localisation of adipocyte differentiation-related protein (ADRP), a protein associated with lipid accumulation in bovine blastocysts. Two experiments were independently performed for ADRP mRNA expression analysis. In experiment A, blastocysts were produced in modified synthetic oviduct fluid (mSOF)+10% foetal calf serum (FCS), in coculture (bovine oviduct epithelial cells, Boec) and in ewe oviducts, whereas in experiment B, they were produced in mSOF+10μM docosahexaenoic acid (DHA) and in vivo. Control groups were also performed. ADRP mRNA expression was downregulated in the Boec, ewe oviduct and in vivo groups compared to the 10% FCS or DHA groups, respectively. Moreover, the expression of this protein was downregulated in the Boec group compared to the control group (P<0.05). A third experiment (experiment C) was performed to quantify and localise ADRP protein. Boec, in vivo and control groups were tested. After immunofluorescence staining followed by confocal microscopy analysis, embryonic ADRP was clearly localised around lipid droplets, indicating that ADRP is also a lipid droplet coat protein in bovine embryos. In conclusion, our results demonstrate that bovine embryos at the blastocyst stage expressed ADRP mRNA and protein, and that the embryonic culture system modified this expression.

Vitrification in human and domestic animal embryology: work in progress

According to the analysis of papers published in major international journals, rapidly increasing application of vitrification is one of the greatest achievements in domestic animal and especially human embryology during the first decade of our century. This review highlights factors supporting or hampering this progress, summarises results achieved with vitrification and outlines future tasks to fully exploit the benefits of this amazing approach that has changed or will change many aspects of laboratory (and also clinical) embryology. Supporting factors include the simplicity, cost efficiency and convincing success of vitrification compared with other approaches in all species and developmental stages in mammalian embryology, while causes that slow down the progress are mostly of human origin: inadequate tools and solutions, superficial teaching, improper application and unjustified concerns resulting in legal restrictions. Elimination of these hindrances seems to be a slower process and more demanding task than meeting the biological challenge. A key element of future progress will be to pass the pioneer age, establish a consensus regarding biosafety requirements, outline the indispensable features of a standard approach and design fully-automated vitrification machines executing all phases of the procedure, including equilibration, cooling, warming and dilution steps.

Efficient production of live offspring from mouse oocytes vitrified with a novel cryoprotective agent, carboxylated ε-poly-L-lysine

In cryopreservation of mammalian germ cells, unfertilized oocytes are one of the most available stages because these cryopreserved oocytes can be used for assisted reproductive technologies, including in vitro fertilization (IVF) and intracytoplasmic sperm injection. However, it has been generally reported that the fertility and developmental ability of the oocytes are reduced by cryopreservation. Therefore further improvement will be required. Very recently, a new cryoprotective agent (CPA), called as carboxylated ε-poly-L-lysine (COOH-PLL), has been developed to reduce physical and physiological damage by cryopreservation in mammalian stem cells. However, it is unclear the effect of COOH-PLL on fertility and developmental ability of vitrified oocytes. In this study, we used COOH-PLL as a CPA with ethylene glycol (EG) for vitrification of mouse oocytes. Cumulus-oocyte complexes (COCs) were collected from ICR mice and then vitrified with Cryotop using different concentration of COOH-PLL and EG. A combined treatment with COOH-PLL and EG showed high survival rate (more than 90%) of vitrified-warmed COCs after in vitro fertilization. In addition, the fertility and developmental ability of COCs vitrified with E20P10 [EG 20% (v/v) and COOH-PLL 10% (w/v)] or E15P15 group (EG 15% and COOH-PLL 15%) were significantly higher than those with E10P20 (EG10% and COOH-PLL 20%) or P30 group (PLL30%). The vitrified COCs in E20P10 group developed to term at a high success rate (46.2%) and it was significantly higher than that in control (E30) group (34.8%). Our present study demonstrated for the first time that COOH-PLL is effective for vitrification of mouse oocytes.

Yusoff NJ, Jusof WHW, Rajikin MH, Froemming GRA, Khan NAMN. Cytoskeletal alterations in different developmental stages of in vivo cryopreserved preimplantation murine embryos

BACKGROUND

This study aimed to investigate the effects of vitrification and slow freezing on actin, tubulin, and nuclei of in vivo preimplantation murine embryos at various developmental stages using a Confocal Laser Scanning Microscope (CLSM).

MATERIAL/METHODS

Fifty female mice, aged 4-6 weeks, were used in this study. Animals were superovulated, cohabitated overnight, and sacrificed. Fallopian tubes were excised and flushed. Embryos at the 2-cell stage were collected and cultured to obtain 4- and 8-cell stages before being cryopreserved using vitrification and slow freezing. Fixed embryos were stained with fluorescence-labelled antibodies against actin and tubulin, as well as DAPI for staining the nucleus. Labelled embryos were scanned using CLSM and images were analyzed with Q-Win software V3.

RESULTS

The fluorescence intensity of both vitrified and slow-frozen embryos was significantly lower for tubulin, actin, and nucleus as compared to non-cryopreserved embryos (p<0.001). Intensities of tubulin, actin, and nucleus in each stage were also decreased in vitrified and slow-frozen groups as compared to non-cryopreserved embryos.

CONCLUSIONS

Cryopreservation of mouse embryos by slow freezing had a more detrimental effect on the actin, tubulin, and nucleus structure of the embryos compared to vitrification. Vitrification is therefore superior to slow freezing in terms of embryonic cryotolerance.

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.

Lipid content and composition during the oocyte development of two gorgonian coral species in relation to low temperature preservation

Our previous studies have suggested that chilling sensitivity of coral oocytes may relate to their relatively high lipid intracellular content and lipid composition. The distribution of lipids during the oocyte development was determined here for the first time in two gorgonian species (Junceella juncea and Junceella fragilis). The main lipid classes in the two gorgonian oocytes were total lipid, wax ester, triacylglycerol, total fatty acid, phosphatidylethanolamine and phosphatidylcholine. The results indicated that early stage oocytes of J. juncea and J. fragilis were found to have increased lipid content than late stage oocytes. The content of wax ester was significantly higher in the early stage oocytes of two gorgonian corals (51.0±2.5 and 41.7±2.9 µg/mm(3)/oocyte) than those of late stage oocytes (24.0±1.4 and 30.4±1.2 µg/mm(3)/oocyte, respectively). A substantial amount of phosphatidylethanolamine and total fatty acid was detected at each stage of oocyte development in two gorgonian ranges from 107 to 42 µg/mm(3)/oocyte and 106 to 48 µg/mm(3)/oocyte, whilst low levels of phosphatidylcholine were found in two gorgonian oocytes. The levels of total lipid in the late stage oocytes of J. juncea were significantly higher than those of J. fragilis. The observed differences may partially be related to different habitat preferences as higher lipid levels in J. juncea, a deeper-water coral species exposed to lower temperature seawater, might relate to adjustments of cell membranes in order to increase membrane fluidity.

The effect of chilling and cryoprotectants on hard coral (Echinopora spp.) oocytes during short-term low temperature preservation

Understanding chilling sensitivity and chilling injury of coral oocytes, in the presence and absence of a cryoprotectant, is important in developing cryopreservation protocols, as well as for short-term storage and transport (e.g., for species conservation). The objective of this study was to investigate the chilling sensitivity of hard coral (Echinopora spp.) oocytes and the effectiveness of methanol (as a cryoprotectant) in protecting these oocytes during short-term, low temperature preservation. Oocytes were exposed to 0.5, 1, or 2 m methanol at 5, 0, or -5 °C for 1, 2, 4, 6, 8, 16, or 32 h, and their quality determined based on adenosine triphosphate (ATP) content. Methanol at 0.5 m was the most effective means to reduce chilling-induced reduction in ATP concentrations. Coral oocytes can be stored at room temperature for 4 h in filtered nature seawater with no detrimental effect on oocyte quality; however, in the present study, oocyte survival was extended for 8 h by addition of methanol in low concentrations (0.5 or 1 m) at low temperatures (5 and 0 °C). These findings should enhance conservation efforts and facilitate low-temperature transport of endangered and threatened coral species.

Novel Approaches to the Cryopreservation of Human Spermatozoa: History and Development of the Spermatozoa Vitrification Technology

Cryobiology is very intensively applied in reproductive and veterinary medicine for preservation of gametes, embryos and reproductive tissues. Sub-zero temperatures combined with appropriate cryoprotective agents preserve the physiological and reproductive functions of the cells making long-term storage possible without loss of viability. With the use of cryoprotective agents it has become possible to develop cryopreservation techniques, such as the slow conventional freezing and vitrification that are in use in the present times. In slow controlled-rate conventional freezing extracellular ice crystals are formed whereas in vitrification no ice crystals are formed. Glass formation is compatible with the survival of the cell and the preservation of its intracellular structures provided the type(s) and concentrations of cryoprotectant used are not chemo- or osmotoxic. However, irrespective of the type of cooling method employed the cryosurvival of cells and tissues is influenced by the size and maturity of cells, amounts of intracellular water, quality and quantity of intracellular lipids, type of cells, their function and morphology. The intracellular milieu of cryopreserved cells and tissues remain less understood. The application of nanotechnology may help reveal and help advance our knowledge of the cryobiological principles involved in cryosurvival. At this moment the methods of cryopreservation that merit further investigation are vitrification and lyophilization. Vitrification is cheap if reagents are prepared in-house and the procedure can be performed rapidly. It has been successfully applied for gametes and embryos (of different stages of development), and reproductive cells/tissues, somatic cells and stem cells. However, vitrification is more demanding technically and requires operation and storage at sub-zero temperatures. On the other hand lyophilization deserves further investigation because it is a cheaper form of cryopreservation that may enable cryostorage at less demanding temperatures of 4°C and may even allow transport at ambient temperature. These possibilities are explored in this review.

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.

Closed-system solid surface vitrification versus slow programmable freezing of mouse 2-cell embryos

PURPOSE

To compare closed-system solid surface vitrification with slow freezing.

METHODS

Mouse 2-cell embryos (n = 348) were divided into vitrification, slow freezing and non-frozen groups. For vitrification, embryos were exposed to 10% ethylene glycol (EG), 10% dimethylsulfoxide (DMSO) and 10% fetal bovine serum (FBS) in phosphate-buffered saline (PBS) for 10 min, then transferred into 17.5% EG, 17.5% DMSO, 0.25 M trehalose and 10% FBS in PBS. They were placed on hemi-straws and inserted into 0.5 ml straws inside a previously cooled aluminum cylinder. Slow freezing was done in straws by the conventional method.

RESULTS

Vitrified embryos had significantly higher survival, further cleavage and blastocyst formation rates than those in the slow freezing group (p < 0.001) and were comparable to controls. Blastocysts in the vitrification and control groups had significantly more cells than those in the slow freezing group (p < 0.05).

CONCLUSIONS

Closed-system vitrification was more effective than conventional slow freezing.

A critical evaluation of ovarian tissue cryopreservation and grafting as a strategy for preserving the human female germline

Ovarian tissue freezing has been used successfully in animals and it has recently begun to be offered clinically to young women who have medical conditions with a high risk of sterility. Although no frozen human ovarian grafts have yet been returned to the donor and resulted in a pregnancy, there are many indications that this procedure should be feasible. Although live young have been derived from frozen grafts in several species, research should aim to make further improvements to the cryopreservation and grafting procedures to optimize follicle survival, and hence minimize the amount of tissue that needs to be collected, stored and returned. Ovarian tissue freezing, particular if used in combination with egg and embryo freezing, should allow a patient to safeguard their chance of becoming a parent later (Table 1). In cases where the patient has a systemic cancer or infection and malignant cells or viruses may be present in the systemic circulation and the gonadal tissue, ovarian tissue could be collected and frozen, but grafting is not currently recommended (Table 3).