Effect of freezing rate and exposure time to cryoprotectant on the development of mouse pronuclear stage embryos

Proteomic profiling of cryopreserved Trichormus variabilis using various cryoprotectants

Algae, which may be unicellular or multicellular, can carry out photosynthesis just like plants as they effectively utilize light energy. They contain various physiologically active substances and are, therefore, widely used commercially to produce healthy food and feed additives, cosmetics, and energy supplements. For useful applications, the cryopreservation technique has been used in various fields. Recently, to develop suitable cryopreservation methods for algal applications, various studies have been performed. However, adequate investigations have not been conducted to understand the mechanism underlying algal cryopreservation at the molecular level. Therefore, this study examined the profile alteration of the proteome using cryopreservation with various cryoprotectants (CPAs). Trichormus variabilis was cultured and then cryopreserved with 10% dimethyl sulfoxide, methanol, and glycerol, after which, proteome profiling was done. Finally, signaling pathway search was performed, and a new signaling pathway was established based on differentially expressed proteins. As a result, the expression levels of 17 proteins were observed. Additionally, it was confirmed that the differentially expressed proteins were related to 16 signaling pathways and that they were capable of interacting with each other. The findings suggest that the differentially expressed proteins may be applied as biomarkers for algal cryopreservation and to understand the mechanism underlying T. variabilis cryopreservation. Moreover, it is anticipated that the results from this study would be useful in selecting suitable CPAs and in upgrading the cryopreservation techniques.

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.

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.

Comparative study between slow freezing and vitrification of mouse embryos using different cryoprotectants

The objective of this study was to evaluate the effects of different cryoprotectants and different cryopreservation protocols on the development of mouse eight-cell embryos. Mouse eight-cell embryos were cryopreserved by using propylene glycerol (PROH), ethylene glycerol (EG), dimethyl sulfoxide (DMSO) or glycerol (G) as cryoprotectant with slow-freezing or Vit-Master vitrification protocol. After thawing, the survival rate, blastocyst formation rate and blastocyst hatching rate of the embryos were compared. When the mouse eight-cell embryos were cryopreserved by the slow-freezing, the survival rate, the blastocyst formation rate and the blastocyst hatching rate of the embryos with PROH were significantly higher than those of DMSO and G (p < 0.05, respectively), but not significantly different among those of DMSO, G and EG (p > 0.05, respectively), and not significantly different between those of PROH and EG (p > 0.05, respectively). When the mouse eight-cell embryos were cryopreserved by Vit-Master vitrification, the survival rate, the blastocyst formation rate and the blastocyst hatching rate of the embryos with EG were significantly higher than those of PROH, DMSO and G (p < 0.05, respectively). Yet, there were no significant differences among those of PROH, DMSO and G (p > 0.05, respectively). In conclusion, PROH was the optimal cryoprotectant for the cryopreservation of mouse eight-cell embryos by slow-freezing protocol. EG was the optimal cryoprotectant for the cryopresevation of mouse eight-cell embryos by Vit-Master vitrification protocol, which may be commonly used in clinical and laboratory practice.

Effect of the polyvinylpyrrolidone concentration of cryoprotectant on mouse embryo development and production of pups: 7.5% of PVP is beneficial for in vitro and in vivo development of frozen-thawed mouse embryos

In this study, we investigated the effect of polyvinylpyrrolidone (PVP) concentration on in vitro and in vivo development of 2 cell stage, vitrified ICR mouse embryos using a cryoprotectant consisting of ethylene glycol (EG) and sucrose. M2 was selected as the basic medium for vitrification and thawing. After equilibration with 4% (v/v) EG at 37 C for 15 min, the embryos were vitrified with 35% EG, 5, 6 or 7.5% (w/v) PVP and 0.4 M sucrose at 37 C for 30 sec. One week later, the cryotubes of cryopreserved embryos in liquid nitrogen were directly immersed into a 37 C water bath for 1 min and transferred serially into 300 microl of 0.5 or 0.3 M sucrose at room temperature for 5 min and M2 medium at 37 C for 10 min. The surviving embryos were cultured in KSOM (potassium simplex optimized medium) for 96-120 h in an atmosphere of 5% CO(2) in humidified air. Survival was evaluated by morphological appearance, including membrane integrity and presence of apoptotic blastomeres after thawing. For in vivo evaluation, blastocysts were transferred to the uteri of pseudopregnant mice. The survival rates of the 5 and 7.5% PVP concentration groups showed a significantly higher difference compared with that of the 6% PVP group (85.5 and 86.5 vs. 71.2%), respectively. Each pup in the of 5 and 6% groups was cannibalized immediately after parturition. A litter of live pups was obtained from only the 7.5% PVP groups. Our study indicated that supplementation of EG and sucrose cryoprotectant solution with 7.5% PVP is optimal for successful vitrification of 2-cell stage ICR mouse embryos.

Survival rate of human oocytes and pregnancy outcome after vitrification using slush nitrogen in assisted reproductive technologies

OBJECTIVE

To report the survival rate of oocytes and the rate of successful pregnancies obtained from super-rapid cooling of oocytes using slush nitrogen (SN(2)).

DESIGN

Prospective clinical research.

SETTING

A university-affiliated hospital.

PATIENT(S)

Twenty-eight infertile women who underwent 30 cycles of IVF-ET using previously vitrified oocytes.

INTERVENTION(S)

Oocytes were vitrified by super-rapid cooling using SN(2).

MAIN OUTCOME MEASURE(S)

Morphological normality of thawed oocytes and clinical outcome.

RESULT(S)

In 30 cycles of ovarian stimulation for IVF, 364 surplus oocytes from 28 patients were vitrified using SN(2). Three hundred two (85.1% +/- 2.9%) of the oocytes survived after warming. Fertilization and cleavage rates were 77.4% +/- 3.5% (168/218) and 94.3% +/- 2.1% (158/168), respectively. Thirteen pregnancies (43.3%) resulted from 30 uterine transfers of 120 embryos with an implantation rate of 14.2% (17/120). There were no differences between the pregnancy rate after vitrification/warming and that obtained from routine noncryopreserved oocytes.

CONCLUSION(S)

The present report suggests that super-rapid cooling may improve the clinical efficacy of human oocyte vitrification and may be a valuable tool for human assisted reproductive technologies.

Comparing ethylene glycol with glycerol for cryopreservation of canine semen in egg-yolk TRIS extenders

The objective of this work was to evaluate the possibility of substituting glycerol (G) for ethylene glycol (EG) when cryopreserving dog semen. A total of 15 ejaculates from 13 dogs was pooled into five samples and frozen in egg-yolk Tris extenders with variable ethylene glycol and glycerol concentrations, with or without Equex STM Paste. Two widely used glycerol extenders (Uppsala Equex II and Norwegian) were utilized as controls. Semen quality parameters assessed after thawing were total subjective motility (TSM), computer assisted sperm analysis (CASA), eosin-nigrosin staining, and flow cytometry (FC) after staining with the PI/Fitc-PSA (fluorescein isotiocianate conjugated with the agglutinin of Pisum sativum, PSA) fluorochromes. No advantages were seen in using EG to replace G when freezing dog semen or combining EG and G in the freezing medium. The Uppsala Equex II provided the best overall post-thaw parameters, followed by the egg-yolk Tris experimental extender with 5% EG and Equex STM Paste. The extender with 4% EG produced similar results to the Norwegian extender. High correlations (r>0.98) were obtained between eosin-nigrosin staining and FC, as well as between subjective and computerized motility assessment (r>0.90).

Cryosystem assessment by glucose uptake of murine blastocysts

Glucose uptake was used as a measure of metabolic activity and implantation potential to compare vitrification and slow freezing in a prospective randomized trial using murine blastocysts. Frozen 2-cell embryos (n = 132) thawed and cultured for 48 h to the blastocyst stage were randomly divided into four groups: (i) control - not refrozen; (ii) slow freezing using a programmed rate (PR); (iii) vitrification by super-cooled (VSC) liquid nitrogen; and (iv) vitrification in liquid nitrogen (VLN). Upon re-thawing, embryos were cultured individually for 24 h to determine glucose uptake non-invasively. Morphological assessments included total cell counts and inner cell mass (ICM) detection following immunosurgery. Mean glucose uptake was lower for each treatment (PR and VSC, 4.3 pmol/embryo per h; VLN, 4.9 pmol/embryo per h) versus controls (6.8 pmol/embryo per h). PR and VSC embryos had fewer cells (57.4 +/- 24.2 and 64.1 +/- 31.5) versus controls (85.7 +/- 26.2), and fewer embryos containing a detectable ICM (42.9 and 61.8%) compared with controls (88.2%). The only difference between control and VLN embryos was absolute glucose uptake, although in both treatments glucose uptake was increased from embryos with an ICM compared with those without. Glucose uptake appears to be a sensitive, non-invasive method to validate cryopreservation protocols.

Vitrification of mouse pronuclear embryos after polar body biopsy without direct contact with liquid nitrogen

OBJECTIVE

To evaluate the viability of vitrified mouse pronuclear embryos after polar body biopsy by cooling directly in liquid nitrogen in comparison with cooling in closed 0.5 mL straw (aseptic system).

DESIGN

In vitro culture after vitrification.

SETTING

Department of Gynecological Endocrinology and Reproductive Medicine, University of Bonn, Germany.

PATIENT(S)

Superovulated mice.

INTERVENTION(S)

Biopsied embryos were vitrified, warmed, and cultured in vitro.

MAIN OUTCOME MEASURE(S)

Development after warming.

RESULT(S)

Development rates up to expanded blastocyst stage after in vitro culture were 25% in group with "direct" vitrification and 23% in group with "straw in straw" vitrification.

CONCLUSION(S)

Cryopreservation of biopsied mouse pronuclear embryos in open-pulled straws, which are placed inside a hermetically closed container, guarantees a complete isolation of embryos from liquid nitrogen and avoids potential contamination by pathogenic microorganisms. The combination of plunging this container into liquid nitrogen and rapid warming makes this process as efficient as conventional vitrification.

Birth of offspring after transfer of Mongolian gerbil (Meriones unguiculatus) embryos cryopreserved by vitrification

The Mongolian gerbil (Meriones unguiculatus) has been used as a laboratory species in many fields of research, including neurology, oncology, and parasitology. Although the cryopreservation of embryos has become a useful means to protect valuable genetic resources, its application to the Mongolian gerbil has not yet been reported. In this study, we investigated the in vitro and in vivo developmental competence of Mongolian gerbil embryos cryopreserved by vitrification. In vivo-fertilized embryos were vitrified on the day of collection using the ethylene glycol (EG)-based solutions EFS20 and EFS40, which contained 20% and 40% EG, respectively, in PB1 containing 30% (w/v) Ficoll 70 and 0.5 M sucrose. First, we compared one-step and two-step vitrification protocols. In the one-step method, the embryos were directly transferred into the vitrification solution (EFS40), whereas in the two-step method, the embryos were exposed serially to EFS20 and EFS40 and then vitrified. After liquefying (thawing), late two-cell embryos (collected on day 3) vitrified by the two-step method showed significantly better rates of in vitro development to the morula stage compared to those vitrified by the one-step method (65% vs. 5%, P < 0.0001). We then examined whether the same two-step method could be applied to early two-cell embryos (collected on day 2), four-cell embryos (day 4), morulae (day 5), and blastocysts (day 6). After liquefying, 87%-100% of the embryos were morphologically normal in all groups, and 23% and 96% developed to the compacted morula stage from early two- and four-cell embryos, respectively. After transfer into recipient females, 3% (4/123), 1% (1/102), 5% (4/73), and 10% (15/155) developed to full-term offspring from vitrified and liquefied early two-cell embryos, late two-cell embryos, morulae, and blastocysts, respectively. This demonstrates that Mongolian gerbil embryos can be safely cryopreserved using EG-based vitrification solutions.

Offspring resulting from transfer of cryopreserved embryos in camel (Camelus dromedarius)

The dromedary embryos, collected at hatched blastocyst stage, survived freezing and thawing in the presence of a high concentration of ethylene glycol (7.0 mol/L) with sucrose (0.5 mol/L) and direct plunging in liquid nitrogen. The rate of survival, as judged by the morphological appearance of the embryos after thawing, was high (92%). The transfer of frozen-thawed embryos into the recipients during the breeding (n=20) and non-breeding season (n=25) resulted in two and one pregnancy, respectively. One of the two pregnant recipients, with embryos transferred during the breeding season, delivered a normal healthy male calf at term. To our knowledge, this offspring is the first camelid produced following transfer of a frozen-thawed embryo.

Comparison on in vitro fertilized bovine embryos cultured in KSOM or SOF and cryopreserved by slow freezing or vitrification

The objectives of this study were to identify an improved in vitro cell-free embryo culture system and to compare post-warming development of in vitro produced (IVP) bovine embryos following vitrification versus slow freezing. In Experiment 1, non-selected presumptive zygotes were randomly allocated to four medium treatments without co-culture: (1) SOF + 5% FCS for 9 days; (2) KSOM + 0.1% BSA for 4 days and then KSOM + 1% BSA to Day 9; (3) SOF + 5% FCS for 4 days and then KSOM + 1% BSA to Day 9; and (4) KSOM + 0.1% BSA for 4 days and then SOF + 5% FCS to Day 9. Treatment 4 (sequential KSOM-SOF culture system) improved (P > 0.05) morulae (47%), early blastocysts (26%), Day-7 blastocysts (36%), cell numbers, as well as total hatching rate (79%) compared to KSOM alone (Treatment 2). Embryos cultured in KSOM + BSA alone developed slowly and most of them hatched late on Day 9, compared to other treatments. In Experiment 2, the sequential KSOM-SOF culture system was used and Day-7 blastocysts were subjected to following cryopreservation comparison: (1) vitrification (VS3a, 6.5 M glycerol); or (2) slow freezing (1.36 M glycerol). Warmed embryos were cultured in SOF with 7.5% FCS. Higher embryo development and hatching rates (P < 0.05) were obtained by vitrification at 6h (71%), 24h (64%), and 48h (60%) post-warming compared to slow freezing (48, 40, and 31%, respectively). Following transfer of vitrified embryos to synchronized recipients, a 30% pregnancy rate was obtained. In conclusion, replacing KSOM with SOF after 4 days of culture produced better quality blastocysts. Vitrification using VS3a may be used more effectively to cryopreserve in vitro produced embryos than the conventional slow freezing method.

Vitrification versus programmable rate freezing of late stage murine embryos: a randomized comparison prior to application in clinical IVF

A prospective randomized trial was performed to compare post-thaw development of murine blastocysts following programmable rate freezing and two methods of vitrification. Frozen 2-cell murine embryos (n = 429) thawed and cultured for 48 h, were randomly allocated by stage of development into four groups: control (not refrozen), programmable rate freezing (PR) in 0.25 ml straws, vitrification in flexible micropipettes by immersion in super-cooled (VSC) liquid nitrogen (LN2), and vitrification in flexible micropipettes by immersion in LN2 (VLN). Survival, developmental stage progression, presence or absence of an inner cell mass (ICM), and cell counts were recorded 24 h post-thaw. All measured outcomes were different between embryos from the control group and all freezing methods. Controlled-rate freezing resulted in the lowest total cell counts and fewest embryos with a distinct ICM. A higher percentage of embryos survived 24 h post-thaw, progressed to more advanced developmental stages and had higher total cell counts after VLN compared with PR. Moreover, fewer embryos, frozen by either PR or VSC, contained a detectable ICM compared with VLN. These data demonstrate that vitrification may be a better method for freezing murine blastocysts than PR, and may prove to be a superior method for freezing human blastocysts.