Developmental rate and ultrastructure of vitrified human pronuclear oocytes after step-wise versus direct rehydration

Aseptic Cryoprotectant-Free Vitrification of Human Spermatozoa by Direct Dropping into a Cooling Agent

Spermatozoa cryopreservation is used for the management of infertility and some other medical conditions. Routinely applied cryopreservation techniques depend on permeating cryoprotectants and relatively slow freezing rates. Cryoprotectant-free vitrification is an alternative and cost-effective method that is based on rapid cooling of spermatozoa by direct plunging into a cooling agent to prevent lethal intracellular ice crystallization and the detrimental effects of high salt concentrations. One of the problems with this technique is that full sterilization of commercially produced liquid nitrogen, which could be contaminated with different pathogens, is not possible. Here we use a benchtop device for the production of sterile liquid air with the same temperature as liquid nitrogen (-195.7 °C). This has been used to develop aseptic technology for cryoprotectant-free vitrification of human spermatozoa.

Ultrastructural changes of sheep cumulus–oocyte complexes following different methods of vitrification

To determine the ultrastructural changes of sheep cumulus–oocyte complexes (COCs) following different methods of vitrification, good quality isolated COCs (GV stage) were randomly divided into the non-vitrified control, conventional straw, cryotop and solid surface vitrification groups. In both conventional and cryotop methods, vitrified COCs were respectively loaded by conventional straws and cryotops, and then plunged directly into liquid nitrogen (LN2); whereas in the solid surface group, vitrified COCs were first loaded by cryotops and then cooled before plunging into LN2. Post-warming survivability and ultrastructural changes of healthy COCs in the cryotop group especially in comparison with the conventional group revealed better viability rate and good preservation of the ooplasm organization. However in all vitrification groups except the cryotop group, mitochondria were clumped. Solely in the conventional straw group, the mitochondria showed different densities and were extremely distended. Moreover in the latter group, plenty of large irregular connected vesicles in the ooplasm were observed and in some parts their membrane ruptured. Also, in the conventional and solid surface vitrification groups, cumulus cells projections became retracted from the zona pellucida in some parts. In conclusion, the cryotop vitrification method as compared with other methods seems to have a good post-warming survivability and shows less deleterious effects on the ultrastructure of healthy vitrified–warmed sheep COCs.

Novel direct cover vitrification for cryopreservation of ovarian tissues increases follicle viability and pregnancy capability in mice

BACKGROUND

Cryopreservation of ovarian tissue is valuable for fertility preservation. We develop an innovative vitrification method using less concentrated cryoprotectants and direct application of liquid nitrogen to the ovarian tissue (direct cover vitrification, DCV) to improve its efficiency.

METHODS

Ovaries of 5- to 6-week-old C57BL/6J mice were randomly allocated to four groups: DCV, conventional vitrification, slow-freezing and non-frozen controls. Experiment 1: observing the follicle morphology. Experiment 2: assessing viability. Experiment 3: investigating the ultrastructure. Experiment 4: examining the follicle number after grafting. Experiment 5: ascertaining pregnancy potential by allogeneic orthotopic transplantation.

RESULTS

The percentages of morphologically normal or viable follicles from DCV were significantly greater than those achieved from conventional vitrification and slow freezing (P < 0.01). The ultrastructure of primordial follicles from DCV appeared better than that achieved from conventional vitrification and slow freezing. After grafting, the follicle number from DCV was greater than conventional vitrification (P = 0.001) and slow freezing (P = 0.021). The pregnancy rate of DCV was higher than conventional vitrification (P < 0.01). The litter size from DCV was comparable with that from non-frozen graft and was significantly greater than that achieved from conventional vitrification and slow freezing (P < 0.01).

CONCLUSIONS

DCV is highly efficient for cryopreservation of ovarian tissue. Using less concentrated cryoprotectants appears to reduce toxicity. Direct cover by liquid nitrogen maximizes cooling that could facilitate vitrification and prevent ice crystal injury.

Ultrastructure of preimplantation genetic diagnosis-derived human blastocysts grown in a coculture system after vitrification

OBJECTIVE

To evaluate ultrastructural features of preimplantation genetic diagnosis (PGD) blastocysts before and after vitrification.

DESIGN

Descriptive study of both vitrified and fresh hatching blastocysts.

SETTING

PGD program at the Instituto Universitario, Instituto Valenciano de Infertilidad.

PATIENT(S)

Patients undergoing PGD donated their abnormal embryos for research (n = 26).

INTERVENTION(S)

Biopsied embryos were cultured in the presence of human endometrial cells until day 6. Sixteen blastocysts were vitrified. A total of 11 high-scored hatching blastocysts, 6 warmed and 5 fresh, were fixed for ultrastructure.

MAIN OUTCOME MEASURE(S)

The cytoskeleton structure, type of intercellular junctions, and basic intracellular organelles in trophoectoderm cells and the inner cell mass were analyzed.

RESULT(S)

Ten of 16 blastocysts (62%) survived the warming process. Six of these showed no signs of cell degeneration and light microscopy revealed similar ultrastructural characteristics to those of controls. However, in trophoectoderm cells from both fresh and cryopreserved blastocysts, a reduced number of tight junctions and the presence of degradation bodies were detected.

CONCLUSION(S)

The particular ultrastructural features observed in PGD-derived blastocysts could be related to embryo manipulation and culture conditions. Vitrification does not seem to alter blastocysts, as those that survive hatching do not display detectable cellular alterations when observed through electron microscopy.

1,2-propanediol and the type of cryopreservation procedure adversely affect mouse oocyte physiology

BACKGROUND

The aim of this work was to examine the effect of 1,2-propanediol (PrOH) and type of cryopreservation procedure (slow freezing and vitrification) on oocyte physiology.

METHODS

Intracellular calcium of mouse metaphase II (MII) oocytes was quantified by fluorescence microscopy. The effect of PrOH on cell physiology was further assessed through analysis of zona pellucida hardening and cellular integrity. Protein profiles of cryopreserved oocytes were generated by time-of-flight mass spectrometry (TOF-MS).

RESULTS

PrOH caused a protracted increase in calcium, which was sufficient to induce zona pellucida hardening and cellular degeneration. Using 'nominally calcium free' media during PrOH exposure significantly reduced the detrimental effects. Proteomic analysis identified numerous up- and down-regulated proteins after slow freezing when compared with control and vitrified oocytes.

CONCLUSIONS

Using such approaches to assess effects on cellular physiology is fundamental to improving assisted reproduction techniques (ART). This study demonstrates that PrOH causes a significant rise in intracellular calcium. Using calcium-free media significantly reduced the increase in calcium and the associated detrimental physiological effects, suggesting that calcium-free media should be used with PrOH. In addition, analysis of the oocyte proteome following cryopreservation revealed that slow freezing has a significant effect on protein expression. In contrast, vitrification had a minimal impact, indicating that it has a fundamental advantage for the cryopreservation of oocytes.

Comparison of open and closed methods for vitrification of human embryos and the elimination of potential contamination

Survival and development of human embryos was compared following slow cooling versus vitrification involving more than 13,000 vitrified embryos. In addition, the efficacy of an open system, the Cryotop, and a closed vitrification system, the CryoTip(trade mark), were compared using human blastocysts. One hundred percent of vitrified human pronuclear stage embryos survived and 52% developed to blastocysts as compared with 89% survival and 41% blastocyst development after slow cooling. Similar survival rates were seen with vitrification of 4-cell embryos (98%) as compared with slow cooling (91%). Furthermore, 90% of vitrified blastocysts survived and resulted in a 53% pregnancy rate following transfer, as compared with 84% survival and 51% pregnancy rates following slow cooling. All corresponding values were significantly different. When the closed and open vitrification systems were compared, no difference was found with regard to supporting blastocyst survival (93 and 97% for CryoTip and Cryotop respectively), pregnancies (51 versus 59% respectively) and deliveries (48 versus 51% respectively). Vitrification is a simple, efficient and cost-effective way to improve cumulative pregnancy rates per cycle. The use of the closed CryoTip system eliminates the potential for embryo contamination during cryopreservation and storage without compromising survival and developmental rates in vitro and in vivo.

Optimization of a dilution method for human expanded blastocysts vitrified using EM grids after artificial shrinkage

PURPOSE

To verify a more effective dilution method that can be applied to human expanded blastocysts that are vitrified after artificial shrinkage.

METHODS

Surplus expanded blastocysts that remained after embryo transfer (ET) in in vitro fertilization (IVF) cycles, were cryopreserved. The blastocysts were vitrified on EM grids following artificial shrinkage. After thawing the blastocysts, cryoprotectants were diluted using either a 6- or 2-step method. We examined the survival rate and clinical outcome of blastocysts of 151 patients in our ET program after thawing.

RESULTS

The survival rate of blastocysts that were thawed using a 2-step method (91.6%, 239/261) was comparable with that of the 6-step method (89%, 186/209). The clinical pregnancy rate (45.9%, 39/85) and implantation rate (24.1%, 53/220) were slightly higher in the 2-step method than in the 6-step method (40.9%, 27/66; 19.4%, 33/170).

CONCLUSIONS

Our data indicate that the 2-step dilution method could be a simpler and more effective protocol for human expanded blastocysts that are vitrified using EM-grid following artificial shrinkage.

Effective method for in-vitro culture of cryopreserved human ovarian tissue

It is widely accepted that it is possible to successfully cryopreserve human ovarian tissue by direct plunging into liquid nitrogen using permeable cryoprotectants only, without disaccharides. This study aimed to search for and test a new method for in-vitro culture of vitrified tissue. Ovarian biopsies were obtained during operative laparoscopy. Pieces of ovarian tissue were vitrified and warmed. After warming, tissue pieces were randomly distributed into three groups for further culture: in 2 ml of culture medium which was regularly renewed (group 1), in 30 ml of culture medium without agitation (group 2) and in 30 ml of culture medium with agitation (group 3). During the 2-week and 6-week culture, the growth of follicles within the vitrified-warmed ovarian tissue pieces was investigated. After 2 weeks of culture, mean numbers of non-degenerated follicles per mm(2) of tissue were 1.5, 1.7 and 4.5 for groups 1, 2 and 3 respectively (groups 1 and 2 versus group 3, P < 0.05). Agitation during culture of ovarian tissue is beneficial, and can be used as a prognostic tool for future warming and autotransplantation of ovarian tissue.

Human oocyte cryopreservation: past, present and future

Despite inferior results in the past compared with embryo freezing, oocyte cryopreservation has made great strides in recent years. In fact, it has become a necessity in assisted reproduction technology, providing alternatives to legal, moral and religious problems originating from embryo freezing. Recent advances in freezing technology, modifications of conventional protocols used and continuing optimization of vitrification have efficiently improved the method. A historical description of the method's progression over time, and a comparison of principles, procedures and results as reported in the literature are presented in this review.

The effect of equilibration time on survival and development rates of mouse pronuclear-stage embryos vitrified in solid surface (SSV) and convential straws: In vitro and In vivo evaluations

The objective of this study was to improve the efficiency of cryopreservation of pronuclear-stage (PN) mouse embryos. A novel vitrification technique (solid surface vitrification, SSV) was compared with a convential one in straws both for cryosurvival and obtaining progeny from cryopreserved PN mouse embryos. In the SSV method, 15-20 PN embryos were exposed to vitrification solutions for approximately 20 sec after equilibration, and then they were dropped in 2 microl drops onto a pre-cooled (-150 to -180 degrees C) metal surface. In the straws method, groups of 5-10 PN embryos were loaded in a single straw after equilibration. In experiment I, it was compared the effect of the vitrification solutions alone, without vitrification. No reduction was detected in survival, cleavage and blastocysts rates and the lowest development rate was obtained from hatched blastocyst for 20 min equilibration (24.5%). In experiment II, SSV method resulted in significantly higher survival and cleavage rates than that of in-straw vitrified 15-20 min group (87% vs. 60%, 83% vs. 67%, respectively; P < 0.05). There were no statistical differences among any of the blastocyts groups. However, there was a statistical difference in hatched blastocysts between 15 to 5, 10, and 20 min (P < 0.05). In experiment III, it was found no major effect among equilibration time periods in toxicity groups according to the mean cell number of blastocysts developed from PN embryos. But, there was a significant differences between 15 min SSV and 10 min in straw vitrified according to the mean cell number of blastocysts developed from PN embryos following vitrification (P < 0.05). The good results were obtained from 15 min equilibration group for SSV and 10 min equilibration group for straw vitrification. In the last experiment, embryo transfer after vitrification and toxicity was investigated. There were significant differences between SSV and straw just on the rate of pups born (30% and 20.5% respectively; P < 0.05). In conclusion, vitrification of PN mouse embryos by SSV can result in high rates of in vitro development to expanded and hatched blastocyst stage and in vivo development to live pups.

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.

Aseptic technology of vitrification of human pronuclear oocytes using open-pulled straws

BACKGROUND

The aim of this study was to compare the viability of human pronuclear oocytes subjected to vitrification using cooling by direct submerging of open-pulled straws in liquid nitrogen versus vitrification by cooling of open-pulled straws located inside a closed 0.5 ml straw (aseptic system).

METHODS

Two- and three-pronuclei stage oocytes (n=114) were cryopreserved in super-open-pulled straws by vitrification in 20% ethylene glycol +20% dimethylsulphoxide (DMSO) + osmotic active and neutral non-permeable cryoprotectants with a four-step exposure in 20, 33, 50 and 100% vitrification solution for 2, 1 and 1 min, and 30-50 s, respectively at room temperature, and plunging into liquid nitrogen. Oocytes of group 1 (n=42) were rapidly cooled at a speed of 20,000 degrees C/min by direct plunging of open-pulled straws into liquid nitrogen. Oocytes of group 2 (n=44) were first located in 0.5 ml straws, which were closed at both sides by metal balls, and then plunged into liquid nitrogen. This method resulted in a cooling speed of 200 degrees C/min. For both groups, oocytes were thawed rapidly at a speed of 20 000 degrees C/min using an identical protocol. Oocytes subsequently were expelled into a graded series of sucrose solutions (1.0, 0.75, 0.5, 0.25 and 0.12 mol/l) at 2.5 min intervals.

RESULTS

Oocyte development up to expanded blastocyst stage after in vitro culture was 15% in group 1, 14% in group 2 and 29% in an untreated control group.

CONCLUSION

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