In vitro blastocyst formation of human oocytes obtained from unstimulated and stimulated cycles after vitrification at various maturational stages

C-phycocyanin improves the developmental potential of cryopreserved human oocytes by minimizing ROS production and cell apoptosis

PURPOSE

The cryopreservation process damages oocytes and impairs development potential. As a potent antioxidant, C-phycocyanin (PC) regulates reproductive performance. However, its beneficial effects on vitrified human oocytes remain unknown.

METHODS

In this study, human GV-stage oocytes obtained from controlled ovarian hyperstimulation (COH) cycles were randomly allocated to three groups: fresh oocyte without freezing (F group), vitrification in medium supplemented with PC (P group), and vitrification in medium without PC as control group (C group). After warming, viable oocytes underwent in vitro maturation.

RESULTS

Our results showed that 3 μg/mL PC treatment increased the oocyte maturation rate after cryopreservation. We also found that PC treatment maintains the regular morphological features of oocytes. After PC treatment, confocal fluorescence staining showed a significant increase in the mitochondrial membrane potential of the vitrified oocytes, along with a notable decrease in intracellular reactive oxygen species and the early apoptosis rate. Finally, after in vitro maturation and parthenogenetic activation, vitrified oocytes had a higher potential for cleavage and blastocyst formation after PC treatment.

CONCLUSION

Our results suggest that PC improves the developmental potential of cryopreserved human GV-stage oocytes by attenuating oxidative stress and early apoptosis and increasing the mitochondrial membrane potential.

Effects of meiotic stage-specific oocyte vitrification on mouse oocyte quality and developmental competence

Introduction

Acquisition of germinal vesicle (GV) stage oocytes for fertility preservation (FP) offers several benefits over in vivo matured oocyte cryopreservation following ovarian stimulation, particularly for cancer patients necessitating immediate treatment. Two FP approaches for GV oocytes are available: vitrification before in vitro maturation (IVM) at the GV stage (GV-VI) or post-IVM at the metaphase II (MII) stage (MII-VI). The optimal method remains to be determined.

Methods

In this study, mouse oocytes were collected without hormonal stimulation and vitrified either at the GV stage or the MII stage following IVM; non-vitrified in vitro matured MII oocytes served as the control (CON). The oocyte quality and developmental competence were assessed to obtain a better method for immediate FP.

Results

No significant differences in IVM and survival rates were observed among the three groups. Nevertheless, GV-VI oocytes exhibited inferior quality, including abnormal spindle arrangement, mitochondrial dysfunction, and early apoptosis, compared to MII-VI and CON oocytes. Oocyte vitrification at the GV stage impacted maternal mRNA degradation during IVM. In addition, the GV-VI group demonstrated significantly lower embryonic developmental competence relative to the MII-VI group. RNA sequencing of 2-cell stage embryos revealed abnormal minor zygotic genome activation in the GV-VI group.

Conclusion

Vitrification at the GV stage compromised oocyte quality and reduced developmental competence. Consequently, compared to the GV stage, oocyte vitrification at the MII stage after IVM is more suitable for patients who require immediate FP.

Effects of cyclic adenosine monophosphate modulators on maturation and quality of vitrified-warmed germinal vesicle stage mouse oocytes

BACKGROUND

It is still one of the unresolved issues if germinal vesicle stage (GV) oocytes can be successfully cryopreserved for fertility preservation and matured in vitro without damage after warming. Several studies have reported that the addition of cyclic adenosine monophosphate (cAMP) modulators to in vitro maturation (IVM) media improved the developmental potency of mature oocytes though vitrification itself provokes cAMP depletion. We evaluated whether the addition of cAMP modulators after GV oocytes retrieval before vitrification enhances maturation and developmental capability after warming of GV oocytes.

METHODS

Retrieved GV oocytes of mice were divided into cumulus-oocyte complexes (COCs) and denuded oocytes (DOs). Then, GV oocytes were cultured with or without dibutyryl-cAMP (dbcAMP, cAMP analog) and 3-isobutyl-l-methylxanthine (phosphodiesterase inhibitor) during the pre-vitrification period for 30 min.

RESULTS

One hour after warming, the ratio of oocytes that stayed in the intact GV stage was significantly higher in groups treated with cAMP modulators. After 18 h of IVM, the percentage of maturation was significantly higher in the COC group treated with dbcAMP. The expression of F-actin, which is involved in meiotic spindle migration and chromosomal translocation, is likewise increased in this group. However, there was no difference in chromosome and spindle organization integrity or developmental competence between the MII oocytes of all groups.

CONCLUSIONS

Increasing the intracellular cAMP level before vitrification of the GV oocytes maintained the cell cycle arrest, and this process may facilitate oocyte maturation after IVM by preventing cryodamage and synchronizing maturation between nuclear and cytoplasmic components. The role of cumulus cells seems to be essential for this mechanism.

Immature Oocyte for Fertility Preservation

In vitro maturation (IVM) of human immature oocytes has been offered to women who are at risk of developing ovarian hyperstimulation syndrome (OHSS) caused by gonadotropin stimulation, such as PCO(S) patients or who have poor ovarian reserve. Cryopreservation of oocytes matured in vivo obtained in IVF cycles has improved after implementing the vitrification method and many successful results have been reported. Now, this procedure can be successfully offered to fertility preservation programs for patients who are in danger of losing their ovarian function due to medical or social reasons, and to oocyte donation programs. This vitrification technique has also been applied to cryopreserve oocytes obtained from IVM program. Some advantages of oocytes vitrification related with IVM are: (1) eliminating costly drugs and frequent monitoring; (2) completing treatment within 2 to 10 days (3) avoiding the use of hormones in cancer patients with hormone-sensitive tumors; and (4) retrieving oocytes at any point in menstrual cycle, even in the luteal phase. In addition, immature oocytes can also be collected from extracorporeal ovarian biopsy specimens or ovaries during caesarian section. Theoretically, there are two possible approaches for preserving immature oocytes: oocyte cryopreservation at the mature stage (after IVM) and oocyte cryopreservation at the Germinal Vesicle (GV)-stage (before IVM). Both vitrification of immature oocyte before/after IVM is not currently satisfactory. Nevertheless, many IVF centers worldwide are doing IVM oocyte cryopreservation as one of the options to preserve fertility for female cancer. Therefore, more studies are urgently required to improve IVM- and vitrification method to successfully preserve oocytes collected from cancer patients. In this review, present oocyte maturation mechanisms and recent progress of human IVM cycles will be discussed first, followed by some studies of the vitrification of human IVM oocyte.

Evaluation of cryopreservation efficiency on embryo growth after exposing them in intracellular cryoprotectant ethylene glycol or glycerol and replacing them by trehalose

The present study was conducted to see whether toxicity could be reduced by replacing some of the penetrating cryoprotectant (intracellular cryoprotectant) with a disaccharide as well as finding out the optimum equilibration time in a vitrification solution before rapid cooling. Goat ovaries (1,685) were aspirated and 1,761 culturable oocytes (COC) were recovered. The recovered COCs were matured in maturation medium and evaluated on the basis of cumulus expansion. The matured oocytes were coincubated with fresh semen capacitated in TALP media, for 18 h. The inseminated oocytes were further cultured in mSOF for in vitro embryo development. The cleavage rate was 11.76% and the development rate of embryos to 4–8 and 8–16 cells morulae was 55.6% and 42.4%, respectively. In vitro produced goat embryos (132), 4–16 cell stages, were used for cryopreservation using different protocols. In protocol- 1, 2, 3 and 4, there was no survivability of embryos. In protocol- 5, 6, 7 and 8, the survivability of embryo after freezing was 10, 25, 35.7 and 72.2%, respectively. In protocol- 8, the percentage of live embryos was significantly higher than other protocols. Also it was found that the survivability rate of embryos in protocol 6 and 7 were significantly higher as compared to protocol 1, 2, 3, 4 and 5. However, non-significant differences were found among protocol 1, 2, 3, 4 and 5, and between 6 and 7. From our results, it can be concluded that cryopreservation using 20% ethylene glycol and 0.9 M trehalose for 30 min gives significantly higher post thaw (72.2%) survivability of embryos.

Mesenchymal Stem Cell-Conditioned Medium Modulates Apoptotic and Stress-Related Gene Expression, Ameliorates Maturation and Allows for the Development of Immature Human Oocytes after Artificial Activation

The aim of the present study was to determine whether mesenchymal stem cell-conditioned medium (MSC-CM) modulates apoptotic and stress-related gene expression, and ameliorates maturation and developmental potential of immature human oocytes after artificial activation. A total of 247 surplus immature germinal vesicle (GV) oocytes obtained from infertile women were allocated into two in vitro maturation (IVM) groups: 1: GV oocytes (n = 116) matured in vitro (fIVM), and 2: GV oocytes (n = 131) that were vitrified, then in vitro matured (vIVM). Also, two maturation media were used: Alpha-minimum essential medium (α-MEM) and human umbilical cord-derived MSCs (hUCM). After 36 h of incubation, the IVM oocytes were examined for nuclear maturation. In IVM-matured oocytes, cytoplasmic maturation was evaluated after artificial activation through Ionomycin. Moreover, the quantitative expressions of B-cell CLL/lymphoma 2 (BCL2), BCL2-associated X protein (BAX), superoxide dismutase (SOD), and Heat shock proteins (HSP70) in matured oocytes were assessed by quantitative Real-time polymerase chain reaction (qRT-PCR) and compared with fresh and vitrified in vivo matured oocytes, which were used as fIVM and vIVM controls, respectively. The highest maturation rate was found in hUCM in fIVM, and the lowest maturation rate was found using α-MEM in vIVM (85.18% and 71.42%, respectively). The cleavage rate in fIVM was higher than that in vIVM (83.4% vs. 72.0%). In addition, the cleavage rate in α-MEM was lower than that in the hUCM (66.0% vs. 89.4%). Furthermore, the difference between parthenote embryo arrested in 4-8 cells (p < 0.04) and the quality of embryo arrested in 8-cell (p < 0.007) were significant. The developmental stages of parthenote embryos in hUCM versus α-MEM were as follows: 2-4 cell (89.45% vs. 66.00%, respectively), 4-8 cell (44.31% vs. 29.11%, respectively), morula (12.27% vs. 2.63%, respectively), and blastocysts (2.5% vs. 0%, respectively). The messenger RNA (mRNA) expression levels of BCL2, BAX and SOD were significantly different (p < 0.05) between the matured IVM oocytes. Overall, hUCM showed potential efficacy in terms of ameliorating oocyte maturation and in promoting the development and mRNA expression of BAX, BCL2, and SOD.

Vitrification of Human Germinal Vesicle Oocytes: before or after In Vitro Maturation?

BACKGROUND

The use of immature oocytes derived from stimulated cycles could be of great importance, particularly for urgent fertility preservation cases. The current study aimed to determine whether in vitro maturation (IVM) was more successful before or after vitrification of these oocytes.

MATERIALS AND METHODS

This prospective study was performed in a private in vitro fertilization (IVF) center. We collected 318 germinal vesicle (GV) oocytes from 104 stimulated oocyte donation cycles. Oocytes were divided into two groups according to whether vitrification was applied at the GV stage (group 1) or in vitro matured to the metaphase II (MII) stage and then vitrified (group 2). In the control group (group 3), oocytes were in vitro matured without vitrification. In all three groups, we assessed survival rate after warming, maturation rate, and MII-spindle/chromosome configurations. The chi-square test was used to compare rates between the three groups. Statistical significance was defined at P<0.05 and we used Bonferroni criterion to assess statistical significance regarding the various pairs of groups. The Statistical Package for the Social Sciences version 17.0 was used to perform statistical analysis.

RESULTS

There was no significant difference in the survival rate after vitrification and warming of GV (93.5%) and MII oocytes (90.8%). A significantly higher maturation rate occurred when IVM was performed before vitrification (82.9%) compared to after vitrification (51%). There was no significant difference in the incidence of normal spindle/ chromosome configurations among warmed oocytes matured in vitro before (50.0%) or after (41.2%) vitrification. However, a higher incidence of normal spindle/chromosome configurations existed in the in vitro matured oocytes which were not subjected to vitrification (fresh oocytes, 77.9%).

CONCLUSION

In stimulated cycles, vitrification of in vitro matured MII oocytes rather than GV oocytes seems to be more efficient. This approach needs to be verified in nonstimulated fertility preservation cases.

Bio-inspired solute enables preservation of human oocytes using minimum volume vitrification

The ability to cryopreserve human oocytes has significant potential for fertility preservation. Current cryopreservation methods still suffer from the use of conventional cryoprotectants, such as dimethyl sulphoxide (DMSO), causing loss of viability and function. Such injuries result from the toxicity and high concentration of cryoprotectants, as well as mechanical damage of cells due to ice crystal formation during the cooling and rewarming processes. Here we report the preservation of human oocytes following vitrification using an innovative bio-inspired cryoprotectant integrated with a minimum volume vitrification approach. The results demonstrate that the recovered human oocytes maintained viability following vitrification and rewarming. Moreover, when this approach was used to vitrify mouse oocytes, the recovered oocytes preserved their viability and function following vitrification and rewarming. This bio-inspired approach substitutes DMSO, a well-known toxic cryoprotectant, with ectoine, a non-toxic naturally occurring solute. The bio-inspired vitrification approach has the potential to improve fertility preservation for women undergoing cancer treatment and endangered mammal species.

Chapter 1 Historical Background on Gamete and Embryo Cryopreservation

This chapter describes the development of the science of cryopreservation of gametes and embryos of various species including human. It attempts to record in brief the main contributions of workers in their attempts to cryopreserve gametes and embryos. The initial difficulties faced and subsequent developments and triumphs leading to present-day state of the art are given in a concise manner. The main players and their contributions are mentioned and the authors' aim is to do justice to them. This work also attempts to ensure that credit is correctly attributed for significant advances in gamete and embryo cryopreservation. In general this chapter has tried to describe the historical development of the science of cryopreservation of gametes and embryos as accurately as possible without bias or partiality.

Osmotic-shock produced by vitrification solutions improves immature human oocytes in vitro maturation

BACKGROUND

During cytoplasmic oocyte maturation, Ca(2+) currents are vital for regulating a broad range of physiological processes. Recent studies have demonstrated that DMSO and EG cause large transient increases in intracellular Ca(2+) in mouse oocytes. The CP used in vitrifying protocols also increases the intracellular calcium transient. The aim of this study is to evaluate the effects of vitrifying time (before and after IVM) and exposure to the vitrification solutions and ionomycin on oocyte quality and embryonic development.

METHODS

221 GV-oocytes unsuitable for IVF-ICSI cycles were randomly distributed into one of the following three groups. G1 (control group): 41 GV-oocytes IVM until MII; G2: 43 oocytes vitrified at GV stage and IVM until MII stage; and G3: 53 GV-oocytes IVM until MII and then vitrified. In order to clarify the effect of vitrification solutions (VS) on human oocyte IVM through the intracellular Ca(2+) oscillation, the following two groups were also included. G4: 43 GV-oocytes exposed to VS and IVM until MII; and G5: 41 GV-oocytes exposed to ionomycin and IVM until MII. All GV-oocytes that reached MII-stage were parthenogenetically activated to assess oocyte viability. IVM was performed in IVF-medium (24-48 h). Chemical treatment (ionomycin) and osmotic treatment (vitrification solutions) were performed without liquid-N2 immersion. The following rates were evaluated: survival (SR), in-vitro maturation (IVMR), activation (AR), development to 2-cell (DRC), development to morula (DRCM) and development to blastocyst (DRB). Ratios between the different treatment groups were compared using contingency tables analysis (chi-square test).

RESULTS

A high survival rate was obtained in G2 (95.5 %) and G4 (96.6 %). In-vitro maturation rate was significantly higher for G4 (86 %) and G2 (83.7 %) compared to G1 (63.4 %), G3 (56.6 %) and G5 (48.8 %). DRCM was significantly higher for G1 and G2 compared to G3 (G1: 15.8 %, G2: 20.7 % and G3: 0 %). DRB was only obtained for the oocytes vitrified before IVM (G2: 3.4 %). AR was also significantly higher for G2 and G4 compared to G5 (G2: 80.5 %, G4: 86.5 % and G5: 55 %). DRCM and DRB were only obtained in G2 and G4. DRCM was significantly higher for oocytes vitrified at GV stage (G2) and for oocytes exposed to the VS in G4 compared to the oocytes exposed to the ionomycin in G5 (G2: 20.7 %; G4: 37.5 % and G5: 0 %).

CONCLUSIONS

Vitrifying GV-oocytes improves their IVM. Further investigation could look to increase the oocyte pool and improve fertility preservation options.

Oocyte cryopreservation: searching for novel improvement strategies

PURPOSE

To highlight emerging techniques aimed at improving oocyte cryopreservation.

METHODS

Review of available and relevant literature through Pubmed and Medline searches.

RESULTS

Oocyte cryopreservation is an increasingly common procedure utilized for assisted reproduction and may benefit several patient populations. Therefore, improving efficiency is paramount in realizing the tremendous promise of this approach. However, in addition to numerous studies looking to improve oocyte cryopreservation efficacy via examination of variables involved with protocol methodology, such as type/concentration of cryoprotectant (CPA), type of storage device, or cooling/warming rates, there are more novel approaches for improvement. These alternate approaches include utilizing different the stages of oocytes, examining alteration of basal media and buffer composition, optimizing CPA exchange protocols and device loading through use of automated technology, as well as examination/manipulation of oocyte cellular composition to improve cryotolerance. Finally, elucidating more accurate or insightful indicators of "success" is crucial for continued improvement of oocyte cryopreservation.

CONCLUSION

Oocyte cryopreservation has improved dramatically in recent years and is receiving widespread clinical use. Novel approaches to further improve success, as well as improved methods to assess this success will aid in continued improvement.

New trends in female fertility preservation: in vitro maturation of oocytes

As antineoplastic treatments have become more successful, an increasing number of women with cancer survive to endure the long-term consequences of chemotherapy. One of the most important of these consequences in young females is premature ovarian failure and infertility. Owing to increasing survival rates, many of these young women are seeking methods to preserve their fertility. Currently, embryo/oocyte cryopreservation obtained after controlled ovarian stimulation appears to provide the best fertility preservation option. However, patients may not have enough time to undergo ovarian stimulation prior to chemotherapy and/or have contraindications to exogenous gonadotropin administration owing to estrogen-dependant tumors. In vitro maturation of oocytes is an attractive alternative for fertility preservation in cancer patients because it does not require ovarian stimulation and it can be performed at any time of the menstrual cycle. In addition, this technique can be combined with ovarian tissue cryobanking. In this review, we discuss the position of in vitro maturation of oocytes in the fertility preservation strategy in young women.

Maturation outcomes are improved following Cryoleaf vitrification of immature human oocytes when compared to choline-based slow-freezing

PURPOSE

The cryopreservation of immature oocytes permits oocyte banking for patients at risk of losing their fertility. However, the optimum protocol for such fertility preservation remains uncertain.

METHODS

The present study investigated the survival, maturation, cytoskeletal and chromosome organization of sibling immature oocytes leftover from controlled ovarian stimulation cycles, that were either slow-frozen (with choline-substitution) or vitrified. A comparison group included oocytes that were never cryopreserved.

RESULTS

Among the three groups, comparable rates were observed for both survival (67-70%) and polar body extrusion (59-79%). Significantly more oocytes underwent spontaneous activation after IVM following slow-freezing compared with either vitrification or no cryopreservation. Likewise, the incidence of spindle abnormalities was greatest in the slow-frozen group, with no differences in spindle morphometrics or chromosome organization.

CONCLUSIONS

While the overall incidence of mature oocytes with normal bipolar spindles from warmed immature oocytes was low, the yield using Cryoleaf vitrification was slightly superior to choline-based slow-freezing.

Successful live birth from vitrified oocytes after 5 years of cryopreservation

OBJECTIVE

To report a birth of a healthy boy after long-term cryopreservation of oocytes by vitrification.

DESIGN

Clinical application.

SETTING

IVF Center.

PATIENT

A 17 year-old female with secondary pulmonary hypertension caused by transposition of great vessels visited our center in 2002, and she wished oocytes cryopreservation to avoid possible sterility after the following category X medication treatment.

INTERVENTION(S)

Vitrified oocytes on Electron Microscope (EM) grids were warmed after 5 years of storage. Surviving MII oocytes were microinjected for fertilization and two embryos were transferred into a gestational carrier day 5 after microinjection.

MAIN OUTCOME MEASURE(S)

Survival, fertilization, cleavage, clinical pregnancy and delivery.

RESULT(S)

Eleven out of fourteen oocytes (78.6%) survived warming. Eight Metaphase II (MII) oocytes and 3 in vitro matured oocytes were microinjected; all 11 oocytes (100%) fertilized and 2 embryos were transferred on day 5. A healthy baby boy weighing 3,600 g was delivered at 38 weeks of gestation. Live-birth rates per warmed oocyte and per injected oocyte were 7.1% and 9.1% respectively.

CONCLUSION(S)

Cryopreservation after vitrification with EM grids maintained the developmental competence of oocytes after long-term storage and resulted in a successful live birth.

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.

Oocyte cryopreservation

Over the last few years, there has been renewed interest and scientific debate concerning human oocyte cryopreservation. The aim of this study was to analyse the clinical data coming from our long experience of slow-freezing oocytes. Between 2001 and 2007, 1280 thawing cycles were carried out using oocytes previously frozen by means of a slow 1,2 propaniedol+sucrose protocol. A total of 7585 oocytes were thawed, of which 4409 survived and 3622 were microinjected; 144 clinical pregnancies were obtained. The number of thawing cycles increased from 19 in 2001 to 268 in 2007, and the number of thawed oocytes from 197 to 1652. Although the survival rate was significantly lower in the period 2002-2005 than in the period 2006-2007, pregnancy and implantation rates steadily improved from respectively 6.7% and 2.4% in 2001 to 15% and 8.2% in 2007. Our data demonstrate a clinically important improvement in oocyte crypreservation over the years in a Centres with proved experience, and can be offered as a standard of care not only before cancer treatment but also for couples refusing embryo crypreservation or in countries with very restrictive limitations on embryo or zygote freezing.

A new safe, simple and successful vitrification method for bovine and human blastocysts

This study examined a new method for vitrification of blastocysts that is safe, simple and easy to learn and use. Current vitrification techniques have shortcomings that include the use of dimethyl sulphoxide, one of the more toxic cryoprotectants, and minute containers that are difficult to handle and are usually open to contamination. Cell handling and loading times are very short, which allows no room for user-associated errors and increases the difficulty of the procedure. This study describes a method of vitrification without these shortcomings. Human and bovine blastocysts were exposed to a series of three cryoprotectant solutions and loaded into a 0.25 ml sterile straw, heat sealed at both ends and vitrified. This technique allowed sufficient time for cryoprotectant exposure, loading, sealing and vitrification. Research blastocysts were thawed, cultured for 24 h, and stained for cell viability. The majority survived and on average had few lysed cells. In clinical studies from three different centres, 81.4% of vitrified blastocysts were intact after thawing. Out of 43 transfers with 76 blastocysts replaced, 44.7% implanted, 43.4% yielded a fetal heart beat, and a total of 32 babies have been delivered or are ongoing. The overall clinical pregnancy per transfer rate was 60.4%. The high survival rates and clinical pregnancy rates obtained with this new, safe and easy-to-use vitrification procedure are encouraging.

Osmotic tolerance and freezability of isolated caprine early-staged follicles

Isolated caprine early-staged follicles were submitted to osmotic tolerance tests in the presence of sucrose, ethylene glycol (EG), or NaCl solutions and were exposed to and cryopreserved (by slow or rapid cooling) in MEM alone or MEM supplemented with sucrose, EG (1.0 or 4.0 M), or both. When follicles were exposed to 1.5 M NaCl, only 2% of the follicles were viable, whereas 87% of the follicles were viable after exposure to 4.0 M EG. Regarding exposure time, the highest percentage of viable follicles was obtained when follicles were exposed for 10 min to 1.0 M EG + 0.5 M sucrose; exposure for 60 s to 4.0 M EG + 0.5 M sucrose also maintained high percentage viability in follicles. Slow cooling in the presence of 1.0 M EG + 0.5 M sucrose (75%) or rapid cooling in the presence of 4.0 M EG + 0.5 M sucrose (71%) resulted in a significantly higher proportion of viable follicles than all other treatments (P < 0.05). A 24-h culture of frozen-thawed follicles was used to assess survival; only slow-frozen follicles showed viability rates similar to control follicles (64% vs. 69% respectively; P > 0.05). Interestingly, the percentage of viable rapid-cooled follicles (59%) was similar to that obtained after in vitro culture of conventional slow-cooled follicles but was significantly lower than that in controls. Thus, in addition to determining improved procedures for the exposure of follicles to EG and sucrose before and after freezing of caprine early-staged follicles, we report the development of rapid- and slow-cooling protocols.

Cryopreservation of human embryos by vitrification or slow freezing: a systematic review and meta-analysis

OBJECTIVE

To examine the literature systematically in order to identify prospective comparative trials answering the following question: Is vitrification of human embryos associated with a higher postthawing survival rate as compared with slow freezing?

DESIGN

Systematic review and meta-analysis.

SETTING

University-based hospital.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Vitrification versus slow freezing for cryopreservation of human embryos.

MAIN OUTCOME MEASURE(S)

Postthawing survival rate.

RESULT(S)

Four eligible studies were identified, three of which were randomized controlled trials. Overall, the current review summarizes information from 8,824 cryopreserved human cleavage stage embryos/blastocysts (vitrification: n = 7,482; slow freezing: n = 1,342). Survival rate of cleavage stage embryos was significantly higher after vitrification as compared with slow freezing (odds ratio 15.57, 95% confidence interval 3.68-65.82; random effects model). Postthawing survival rate of vitrified blastocysts was significantly higher compared with that observed with slow freezing (odds ratio 2.20, 95% confidence interval 1.53-3.16; fixed effects model).

CONCLUSION(S)

Vitrification appears to be associated with a significantly higher postthawing survival rate than slow freezing. Further prospective trials are necessary to confirm the above results and, in addition, allow the evaluation of the two cryopreservation methods in terms of pregnancy achievement.

Human oocyte cryopreservation

The clinical role of oocyte cryopreservation in assisted reproduction, as an adjunct to sperm and embryo cryopreservation, has been comparatively slow to evolve as a consequence of theoretical concerns related to efficacy and safety. Basic biological studies in the 1990's alleviated many of these concerns leading to more widespread adoption of the technology. While a number of babies were born from the approach validated in the 1990's, its perceived clinical inefficiency led to the search for improved methods. Introduction of elevated dehydrating sucrose concentrations during cryopreservation increased survival and fertilization rates, but there is no well-controlled evidence of improved clinical outcome. Similarly, the use of sodium-depleted cryopreservation media has not been demonstrated to increase clinical efficiency. More recently, and in the absence of basic biological studies addressing safety issues, the application of vitrification techniques to human oocytes has resulted in reports of a number of live births. The small number of babies born from clinical oocyte cryopreservation and the paucity of well-controlled studies currently preclude valid comparisons between approaches. Legal restrictions on the ability to select embryos from cryopreserved oocytes in Italy, where many of the available reports originate, also obscure attempts to assess oocyte cryopreservation objectively.

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.

Cryotop vitrification of human oocytes results in high survival rate and healthy deliveries

Vitrification, an ultra-rapid cooling technique, offers a new perspective in attempts to develop an optimal cryopreservation procedure for human oocytes and embryos. To further evaluate this method for human oocytes, 796 mature oocytes (metaphase II) were collected from 120 volunteers. Since Italian legislation allows the fertilization of a maximum of only three oocytes per woman, there were 463 supernumerary oocytes; instead of being discarded, they were vitrified. When, in subsequent cycles, these oocytes were utilized, 328 out of 330 (99.4%) oocytes survived the warming procedure. The fertilization rate, pregnancy rate and implantation rate per embryo were 92.9, 32.5 and 13.2% respectively. Thus, as already reported in the literature, the vitrification procedure seems to be highly effective, safe (since healthy babies have been born) and easy to apply. In situations where embryo cryopreservation is not permitted (as in Italy), there is now good indication for routine application of the method, once further standardization is achieved.

Cryoloop vitrification of human day 3 cleavage-stage embryos: post-vitrification development, pregnancy outcomes and live births

Vitrification technology has shown great promise for cryopreservation of human embryos. The majority of this work has been with blastocyst-stage embryos. This report describes initial clinical results following vitrification of human embryos on day 3 of culture at the 6- to 8-cell stage. A total of 236 embryos were cryopreserved on cryoloops using a vitrification protocol. Warmed embryos were cultured until day 5 before transfer to the patient. The post-warming survival rate was 85%. The clinical pregnancy rate was 44% (34/77), and the implantation rate was 20% (40/201). In transfers where at least one warmed embryo reached the blastocyst stage by the day of transfer, the clinical pregnancy rate was 58% (28/48). The cryoloop was an excellent vessel for ultra-rapid cryopreservation of embryos. This study supports the effectiveness of a dimethylsulphoxide/ethylene glycol cryoprotectant combination for vitrification of human embryos at the 6- to 8-cell stage.

Novel gamete storage

The aim of this review is to outline recent advances in gamete storage that are beneficial for rescuing endangered species or for the breeding of companion animals. Much more information is available on the technical resolutions and practical applications of sperm cryopreservation in various species than of female gametes, reproductive tissues or organs. Mammalian sperm cryopreservation often works relatively efficiently; however, the ability of female gametes to be cryopreserved and still be viable for fertilisation is also essential for rescuing endangered species. For a proper evaluation of gamete cryopreservation possibilities in a given species, it is essential to understand the basic mechanism affecting the survival of cryopreserved cells, the technical and physical limitations, the available techniques and the new avenues to resolve the specific problems in that species. This paper is aimed to provide some help for this process. The limited length of this paper resulted in the omission of information on many important areas, including most data on teleosts, amphibian and insect cryopreservation.

Aseptic vitrification of human germinal vesicle oocytes using dimethyl sulfoxide as a cryoprotectant

OBJECTIVE

To evaluate the viability of vitrified human germinal vesicle (GV)-oocytes to mature to metaphase II (MII) stage after "rapid" cooling directly in liquid nitrogen in comparison with "slow" cooling in a closed 0.5-mL straw (aseptic system), with or without dimethyl sulfoxide (DMSO) in vitrification solution. The possibility of avoiding parthenogenesis of the oocytes after vitrification using DMSO was investigated.

DESIGN

In vitro maturation after vitrification.

SETTING

Assisted reproduction centers.

PATIENT(S)

Patients undergoing standard superovulation treatment and having GV-oocytes after follicular puncture.

INTERVENTION(S)

The GV-oocytes were vitrified with long/short exposure to DMSO using slow or rapid cooling, then warmed and matured in vitro.

MAIN OUTCOME MEASURE(S)

Maturation after warming.

RESULT(S)

Oocyte development up to MII stage after vitrification with DMSO was 71% in the group with "rapid" cooling, and in groups with "slow" cooling, 68% and 72% for long and short exposure to DMSO, respectively. The maturation rate of GV-oocytes after slow cooling without DMSO was 51%. In the vitrification with long-term contact of oocytes with DMSO group, a high rate of parthenogenesis was observed. When vitrification with short-term contact of oocytes with DMSO at room temperature was used, no parthenogenesis was observed.

CONCLUSION(S)

Cryopreservation of human GV-oocytes in open-pulled straws OPS) using an aseptic slow cooling method gives high maturation rates but only in combination with DMSO. To avoid spontaneous parthenogenesis, the exposure to DMSO must occur for a reduced time and at room temperature.

Birth after double cryopreservation of human oocytes at metaphase II and pronuclear stages

OBJECTIVE

To document the possibility to double-cryopreserve human metaphase II and pronuclear oocytes.

DESIGN

Case report.

SETTING

University-based IVF center.

PATIENT(S)

A couple with primary andrological infertility.

INTERVENTION(S)

Pronuclear stage oocytes derived after sperm injection into frozen-thawed metaphase II oocytes were cryopreserved again for later transfer.

MAIN OUTCOME MEASURE(S)

Post-thaw survival rates and pregnancy.

RESULT(S)

Five metaphase II oocytes survived the freeze-thaw procedure. Three of five oocytes presented with two pronuclei after sperm injection and were cryopreserved again. Post-thawing, all three oocytes developed into good quality embryos for transfer. A singleton pregnancy was achieved, resulting in the birth of a healthy girl.

CONCLUSION(S)

Double-cryopreservation of oocytes at metaphase II and at pronuclear stage is a treatment option in human-assisted reproduction.

Cryopreservation of unfertilized human oocytes

Previous investigations revealed that choline-based freezing media developed in our laboratory were superior to conventional sodium-based media for storing mouse oocytes. This paper examines the ability of the choline-based medium CJ2 and a modified form of this medium, CJ3, to cryopreserve unfertilized human oocytes. Oocytes that were consented for research and matured overnight, as well as freshly collected, donor, mature metaphase II (MII) oocytes, were cryopreserved using choline-based media and an optimized slow-cooling protocol. The results showed higher survival and fertilization rates when CJ3 supplemented with 0.2 mmol/l sucrose was used as compared with CJ2 supplemented with either 0.1 mmol/l or 0.2 mmol/l sucrose. Freshly collected oocytes were more difficult to cryopreserve than those matured in vitro. Modification of the base medium proved to be one of the key factors in obtaining survival rates over 90%. Fertilization rates, embryo development, and genetic analysis of embryos resulting from control and frozen-thawed oocytes are provided. There appears to be a high correlation between chromosomal anomalies and abnormal morphology in embryos from thawed oocytes.

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.

Cryoloop vitrification of rabbit oocytes

BACKGROUND

Vitrification is assumed to be a promising method to cryopreserve human oocytes but still needs optimization. In this study, rabbit oocytes (fertilized by ICSI) were vitrified with cryoloops, and the effect of three different cryopreservation protocols on spindle configuration and embryo quality was assessed.

METHODS

Metaphase II rabbit oocytes were randomly assigned to one of four groups: (i) control; (ii) E40 [40% ethylene glycol (EG)]; (iii) ED20 [20% EG + 20% dimethylsulphoxide (DMSO)]; and (iv) ED20 + M (20% EG + 20% DMSO + vitrification machine). After warming, one part of each group was fertilized by ICSI to examine the fertilization and embryo cleavage ability, and the others were immunostained for tubulin and chromatin before visualization using confocal microscopy.

RESULTS

The survival rates after warming were 79.1, 83.1 and 82.3%, respectively. In protocols E40 and ED20, the spindles were severely injured and the embryo quality not good compared with those in the ED20 + M group.

CONCLUSIONS

The fastest cooling rate in combination with EG and DMSO as cryoprotectants had the fewest adverse effects on the spindle configuration of rabbit oocytes and embryo development.

Highly efficient vitrification method for cryopreservation of human oocytes

Two experiments were performed to develop a method to cryopreserve MII human oocytes. In the first experiment, three vitrification methods were compared using bovine MII oocytes with regard to their developmental competence after cryopreservation: (i) vitrification within 0.25-ml plastic straws followed by in-straw dilution after warming (ISD method); (ii) vitrification in open-pulled straws (OPS method); and (iii) vitrification in <0.1 microl medium droplet on the surface of a specially constructed fine polypropylene strip attached to a plastic handle (Cryotop method). In the second experiment, the Cryotop method, which had yielded the best results, was used to vitrify human oocytes. Out of 64 vitrified oocytes, 58 (91%) exhibited normal morphology after warming. After intracytoplasmic sperm injection, 52 became fertilized, and 32 (50%) developed to the blastocyst stage in vitro. Analysis by fluorescence in-situ hybridization of five blastocysts showed that all were normal diploid embryos. Twenty-nine embryo transfers with a mean number of 2.2 embryos per transfer on days 2 and 5 resulted in 12 initial pregnancies, seven healthy babies and three ongoing pregnancies. The results suggest that vitrification using the Cryotop is the most efficient method for human oocyte cryopreservation.

Intracytoplasmic sperm injection of frozen-thawed bovine oocytes and subsequent embryo development

Oocyte cryopreservation and intracytoplasmic sperm injection (ICSI) are advantageous to expand their usefulness in genetic engineering. Oocytes matured for 22 hr were vitrified in droplets of cryoprotectants (3.2 M ethylene glycol (EG), 2.36 M dimethyl sulfoxide (DMSO), 0.6 M sucrose) on copper electron microscope (EM) grids. After being warmed, the oocytes were cultured in IVM medium for an additional 2 hr. Sperm treated with dithiothreitol were utilized for ICSI. Oocytes injected with sperm were activated by combination of ionomycin with cycloheximide (CHX). The ICSI oocytes were compared for the rates of pronuclear formation, development, cell number, and the ratio of ICM to those of fresh ICSI and IVF control. The proportion of 2PN formation was significantly higher in IVF control (Group 1) than those in other treated groups. Among the treated groups a significant lower 2PN formation was observed in IVF-frozen-thawed than in ICSI-fresh and frozen-thawed groups. Cleavage rates in IVF-frozen-thawed and ICSI-frozen-thawed groups were significantly lower than those of IVF control and ICSI-fresh groups. In ICSI groups, the rates of cleavage and blastocyst in fresh oocytes were significantly higher than in frozen-thawed. Development rates into blastocysts in the ICSI-fresh and frozen-thawed groups were significantly lower than that of IVF control. Total cell number was significantly lower in both frozen-thawed IVF and ICSI groups than those in IVF-control and ICSI-fresh groups. However, the rates of the remaining cells that were found in the ICM were significantly higher in both frozen-thawed IVF and ICSI than in the IVF-control and ICSI-fresh groups. The results indicated that frozen-thawed bovine oocytes were suitable for ICSI procedure.

An overview of oocyte cryopreservation

The ability to cryopreserve human oocytes and store them indefinitely would be beneficial for cancer patients at risk of becoming sterile after therapy, allow women to delay reproduction, and alleviate religious concerns associated with embryo storage. In 1986, Chen was the first to report a pregnancy originating from a frozen-thawed human oocyte. Although over 100 babies have been born from oocyte storage since then, pregnancy rates remain unacceptably low. Adapting embryo cryopreservation techniques to oocyte storage has had limited success and new reproducible methods are needed. Problem areas other than intracellular ice formation and osmotic effects need to be identified. A broad approach of critical analysis should be conducted regarding the entire cryopreservation process from pre-equilibration and cooling, to thawing and stepout. All established facets deserve reanalysis in order to assess which aspects can be optimized or changed so that cellular demise can be avoided and cellular viability enhanced. New methods, including the use of choline-based media and vitrification have proven useful in increasing survival and pregnancy rates in some clinics. Other methods yet untested, such as injection of complex carbohydrates into the oocyte, deserve further studies. Vitrification research has led to the formulation of new ideas and has demonstrated the flexibility of cells to survive cryopreservation. Although successful, vitrification protocols are potentially harmful and technically challenging, due to elevated cryoprotectant concentrations and rapid cooling rates. Bovine embryo vitrification methods have been used to store human oocytes and embryos, particularly blastocysts with some success. Vitrification solutions containing high molecular weight polymers have also proved beneficial by reducing solution toxicity. In general, further advances are needed to improve human oocyte storage before widespread routine clinical use.

High Survival Rate of Bovine Oocytes Matured In Vitro Following Vitrification

Improving pregnancy rates associated with the use of cryopreserved human oocytes would be an important advance in human assisted reproductive technology (ART). Vitrification allows glasslike solidification of a solution without ice crystal formation in the living cells. We have attempted to improve the survival rates of oocytes by a vitrification technique using bovine models. In vitro matured oocytes with or without cumulus cells were vitrified with either 15.0% (v/v) ethylene glycol (EG) + 15% (v/v) dimethylsulfoxide (DMSO) + 0.5 M sucrose or 15% (v/v) EG + 15% (v/v) 1,2-propanediol (PROH) + 0.5 M sucrose, using 'Cryotop' or 'thin plastic sticker', respectively. The oocyte survival rates after vitrifying-warming, and the capacity for fertilization and embryonic development were examined in vitro. The rate of embryonic development to blastocyst was significantly higher (P<0.05) in the oocytes vitrified with 15% (v/v) EG + 15% (v/v) PROH + 0.5 M sucrose than in the oocytes vitrified with 15% (v/v) EG + 15% (v/v) DMSO + 0.5 M sucrose (7.4% +/- 4.1 vs. 1.7% +/- 3.0, respectively). Oocytes vitrified without cumulus cells had a higher survival rate after thawing and a superior embryonic developmental capacity compared with oocytes vitrified with cumulus cells. Prolonged pre-incubation time after thawing adversely affected the rates of embryonic cleavage and development. These results indicate that in vitro matured bovine oocytes can be vitrified successfully with the mixture of the cryoprotectants, EG + PROH, the absence of cumulus cells for vitrification does not affect oocyte survival rate after warming, and vitrified and warmed oocytes do not require pre-incubation before in vitro fertilization.

Vitrificação de ovócitos imaturos de bovinos utilizando etilenoglicol associado à trehalose e polivinilpirrolidona

Avaliaram-se os efeitos da vitrificação de ovócitos imaturos de bovinos utilizando o etilenoglicol (EG) associado à trehalose e à polivinilpirrolidona (PVP). Utilizaram-se ovócitos provenientes de ovários de vacas abatidas em matadouro, distribuídos aleatoriamente em três tratamentos (T). TI - ovócitos não desnudados e não congelados, TII - ovócitos vitrificados com cumulus oophorus e TIII - ovócitos desnudados vitrificados. A percentagem de ovócitos recuperados e ovócitos com morfologia normal após a vitrificação foi diferente entre TII e TIII (92,2 e 72,6%; 79,0 e 63,6%, respectivamente). Os ovócitos normais foram cultivados à 38,5ºC em atmosfera de 5% de CO2 por 24 horas. Após o cultivo, os ovócitos foram fecundados e os embriões cultivados in vitro por sete dias. Foram encontradas diferenças entre tratamentos quanto às taxas de maturação nuclear, fecundação e clivagem (83,9, 70,0 e 44,0%; 17,5, 23,7 e 5,1%; 0,0, 0,0 e 0,0% para os tratamentos I, II e III, respectivamente). Apenas no TI foram obtidas mórulas e blastocistos (21,4%). Os procedimentos de vitrificação, segundo os protocolos utilizados, não são indicados para a criopreservação de ovócitos imaturos de bovinos.

Live births after vitrification of oocytes in a stimulated in vitro fertilization-embryo transfer program

OBJECTIVE

To assess the usefulness of the vitrification method in clinical practice.

DESIGN

Clinical study of vitrification of human oocytes.

SETTING

A university-affiliated hospital.

PATIENT(S)

Thirty-four patients who agreed to undergo additional IVF-ET after the failed fresh cycle using the previously vitrified/thawed oocytes.

INTERVENTION(S)

Surplus oocytes from the IVF-ET patients were vitrified for the next cycle.

MAIN OUTCOME MEASURES

Morphologic normality of post-thawed oocytes, fertilization, cleavage, pregnancy, and implantation rate.

RESULT(S)

Overall morphological survival and fertilization rates of vitrified/liquefied oocytes were 68.6% (325/474) and 71.7% (142/198), respectively. Pregnancy rate and implantation rate per embryo transfer were 21.4% (6/28) and 6.4% (8/125), respectively. All pregnancies resulted in the delivery of healthy babies (1 twin and 5 singletons/6 pregnancies).

CONCLUSION(S)

The feasibility of the vitrification method for human oocytes was confirmed by our clinical results. Subsequent studies on vitrification and thawing procedures should be undertaken for further optimizing the vitrification method.