Problems in the cryopreservation of unfertilized eggs by slow cooling in dimethyl sulfoxide

The Nuclear Maturation and Embryo Development of Mice Germinal Vesicle Oocytes with and without Cumulus Cell after Vitrification

BACKGROUND

Cryobiology is an essential tool in assisted reproductive technology. Research in this area focuses on the possibility of restoring fertility in women with reproductive problems or after cancer treatments.

AIM

The purpose of this study was to evaluate viability of oocytes, In vitro maturation and embryo development in vitrified germinal vesicle oocytes with and without cumulus cell after single and stepwise vitrification procedure.

MATERIALS AND METHODS

Germinal vesicle oocytes with or without cumulus cells were obtained from 4 weeks old female mice 48h after intraperitoneal injection of 7.5 IU pregnant mare serum gonadotropin (PMSG). For vitrification collected oocytes vitrification were exposed to cryoprotectant, which was composed of 30% (v/v) ethylene glycol, 18% (w/v) Ficoll-70, and 0.3 M sucrose, either by single step or in a step-wise way. After exposure to cryoprotectant and immerged in liquid nitrogen, the oocytes were thawed and washed in medium TCM199 two times. Then the oocytes transferred to IVM medium for maturation and embryo development to blastocyst.

RESULTS

The oocytes survival rates after vitrifying-warming, maturation rate, the capacity of fertilization and embryonic development to blastocyst were examined in vitro. The oocytes survival, maturation to MII, fertilization developmental rate in the step-wise exposure and with cumulus cell was significantly higher (p<0.05) as compared with corresponding rate in the single step procedure without cumulus cell.

CONCLUSION

The results of present study indicated that oocytes vitrified with cumulus cells and stepwise procedure had positive effect on maturation and developmental rate to blastocyst than oocytes without cumulus cell and single step procedure.

History of oocyte cryopreservation

The potential advantages of being able to cryopreserve oocytes have been apparent for many decades. Technical difficulties associated with the unique properties of the mammalian oocyte initially retarded rapid development in this area but recent advances have overcome many of the problems. A stage has now been reached where oocyte cryopreservation can be considered an important component of human assisted reproductive technology. The potential advantages of being able to cryopreserve oocytes have been apparent for many decades. Technical difficulties associated with the unique properties of the mammalian oocyte initially retarded rapid development in this area but recent advances have overcome many of the problems. A stage has now been reached where oocyte cryopreservation can be considered an important component of human assisted reproductive technology.

Comparison of the developmental potential of 2-week-old preantral follicles derived from vitrified ovarian tissue slices, vitrified whole ovaries and vitrified/transplanted newborn mouse ovaries using the metal surface method

Background

Cryopreservation of preantral follicles or ovarian tissues would enable the storage of large numbers of primordial follicles or preantral follicles and preserves the structural integrity of somatic and reproductive cells. In the present study, we compared the developmental potential of cryopreserved two-week-old mouse preantral follicles, ovarian tissue slices, two-week-old mouse ovaries and newborn mouse ovaries using a metal plate with a high cooling rate for cooling the droplet of vitrification solution.

Methods

Groups of 2 to 4 samples (including of 14-day old preantral follicles, ovarian tissue slices, whole ovaries, and whole newborn ovaries) were exposed to 4% ethylene glycol (EG) in DPBS + 10% FBS for 15 min and then rinsed in a vitrification solution composed of 6 M ethylene glycol and 0.4 M trehalose in DPBS + 10% FBS. Equilibration in room temperature was performed for 20–30 seconds for preantral follicle and 5 min equilibration was performed in an ice bath for ovaries. The samples were dropped onto the surface of metal plate around -180°C in the volume of 2 μl and 6 μl. After thawing, the ovarian tissue was mechanically isolated for collecting the preantral follicles. The thawed newborn ovaries were transplanted under the renal capsule of recipient male mice for 14 days. Preantral follicles collected from each groups were cultured individually in 20-μl droplets of α-MEM culture medium in culture dish for 12 days. On the day 12 of culture, the cumulus-oocyte complexes (COCs) were collected for IVM and IVF. Fertilization and embryo cleavage were scored.

Results

After the vitrification of 14-day-old preantral follicles using 2 μl or 6 μl droplet onto surface of metal plate, the results indicated that no significant difference in survival rate, antral-like cavity formation, COCs collected, 2 cell embryo cleavage and blastocyst development was found in vitrification of the 2 μl and 6 μl droplet groups. As comparing 14-day old ovarian tissue (ovarian tissue slices and whole ovaries) and whole newborn ovaries vitrified in 6 μl droplet, lower success rates of antral-like cavity formation and COCs collection were found in the whole ovaries group.

Conclusion

Our results suggest that the metal plate surface vitrification method is an appropriate and convenient method for cryopreservation of mouse ovaries and preantral follicles. The droplet volume of vitrification solution in 2 μl and 6 μl can be an option.

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.

[What are at present the real hopes of pregnancy after ovarian cryopreservation?]

Survival rates for cancers that occur in childhood and adolescence have improved over the last decades, and preservation of future fertility in these patients has become a relevant issue. Premature ovarian failure is a consequence of exposing women to chemotherapeutic drugs and ionizing radiation. Ovarian cryopreservation is an alternative to cryopreservation of embryos or oocytes for theses patients. Ovarian cryopreservation aims to reimplant ovarian tissue after complete remission into the pelvic cavity (orthotopique site) or a heterotopic site like the abdominal wall or the forearm. In vitro folliculogenesis, that aims at the maturation of ovarian cortex primordial follicles cryopreserved for a FIV, is still in an experimental research stage. In this review, the objective was to evaluate the real hopes of pregnancy after ovarian cryopreservation. Indeed, many teams offer ovarian cryopreservation at present time, although only two pregnancies have been achieved to date. In both cases, it can be discussed whether the fertilized oocyte originated from the transplant or from the native ovary. Furthermore, the potential for reintroduction of cancerous cells may limit this technique in cancers that are known to have a risk of ovarian dissemination. The hopes engendered by ovarian cryopreservation, but also its limits, must be explained to the patients before an ovarian surgery for cryopreservation.

Cryopreservation of immature and in vitro matured porcine oocytes by solid surface vitrification

Cryopreservation of normal, lipid-containing porcine oocytes has had limited practical success. This study used solid surface vitrification (SSV) of immature germinal vesicle (GV) and mature meiosis II (MII) porcine oocytes and evaluated the effects of pretreatment with cytochalasin B, cryoprotectant type (dimethylsulfoxide (DMSO), ethylene glycol (EG), or both), and warming method (two-step versus single-step). Oocyte survival (post-thaw) was assessed by morphological appearance, staining (3',6'-diacetyl fluorescein), nuclear maturation, and developmental capacity (after in vitro fertilization). Both GV and MII oocytes were successfully vitrified; following cryopreservation in EG, more than 60% of GV and MII stage porcine oocytes remained intact (no significant improvement with cytochalasin B pretreatment). Oocytes (GV stage) vitrified in DMSO had lower (P<0.05) nuclear maturation rates (31%) than those vitrified in EG (51%) or EG+DMSO (53%). Survival was better with two-step versus single-step dilution. Despite high survival rates, rates of cleavage (20-26%) and blastocyst formation (3-9%) were significantly lower than for non-vitrified controls (60 and 20%). In conclusion, SSV was a very simple, rapid, procedure that allowed normal, lipid-containing, GV or MII porcine oocytes to be fertilized and develop to the blastocyst stage in vitro.

Cryopreservation of Human Oocytes and Ovarian Tissue

Oocyte cryopreservation has the potential to be an important adjunct to assisted reproductive technologies and bypasses some ethical, moral, and religious dilemmas posed by human embryo cryopreservation. The success of human oocyte cryopreservation depends on morphological and biophysical factors that could influence oocyte survival after thawing. Among the morphological factors, the maturity, quality, size of the oocyte, the presence or the absence of the cumulus oophorus seems to play an important role in oocyte survival after thawing. The main biophysical factor of cellular disruption during cryopreservation process in the intracellular ice formation that can be avoided by an adequate cell dehydration; thus reducing the intracellular water by increasing the dehydration process we can limit the damages of the cryopreservation procedure. The dehydration process can be affected by the presence and concentration of the cryoprotectants in the freezing solutions (equilibration and loading solutions), and by the freezing and thawing rate. Two additional properties of cryoprotectants help to protect cells during slow cooling, when the cells are very dehydrated and are surrounded by concentrated salts. The cryoprotectants appear to reduce damage caused by high levels of salt, a property known as salt buffering. Some events occurring to the oocyte during cryopreservation procedure has been found to be a premature exocitosis of cortical granules, leading to an intempestive zona hardening and consequently to a reduction of fertilization rate, and the cryoinjury to the zona pellucida leading to a polispermic fertilization. ICSI is an efficient method to by pass these two events and to achieve a satisfactory outcome in terms of normal fertilization of cryopreserved oocytes. The application of the ICSI to cryopreserved oocytes did not seem to increase the degeneration rate after insemination with respect to fresh oocytes. The increased oocyte survival rate and the use of ICSI have facilitated the recent increase in the number of pregnancies and live birth.

Membrane integrity and development of immature murine cumulus–oocyte complexes following slow cooling to −60°C: The effect of immediate rewarming, plunging into LN2 and two-controlled-rate-stage cooling

Cryopreservation of murine germinal vesicle (GV) stage cumulus-oocyte complexes (COCs) has been shown to result in poor development and cumulus cell damage. In an attempt to determine the stage of the cryopreservation protocol at which damage occurs, three cooling profiles were compared: slow-cooling (0.3 degrees C/min) to -60 degrees C (protocol A); slow-cooling to -60 degrees C and plunging to -196 degrees C (protocol B); or slow-cooling to -60 degrees C followed by further cooling at 10 degrees C/min to -150 degrees C, then plunging to -196 degrees C (protocol C). GV-stage COCs were collected from hormone-primed mice by repeated puncturing of ovarian follicles. COCs were exposed to 1.5 M Me(2)SO prior to cooling to -60 or -196 degrees C. Membrane integrity was assessed immediately after thawing using carboxy fluorescein and propidium iodide. A greater proportion of cumulus cells were damaged following protocol B than protocol A. Damage was less extensive following protocol C than following protocol B. For assessment of development, COCs were matured and fertilised in vitro. Morphological normality was significantly reduced following cooling to -60 or -196 degrees C compared with non-cryopreserved controls. Fertilisation of oocytes assessed as normal post-treatment was not significantly different between any of the groups. Development to blastocyst was least from oocytes exposed to protocol B, being significantly worse than for oocytes exposed to protocol A, but not significantly different to protocol C. A protocol comprising two stages of controlled-rate cooling decreased damage to the membranes of cumulus cells but did not significantly improve embryo development.

Cryopreservation of immature bovine oocytes by vitrification in straws

The aim of this study was to cryopreserve by vitrification by ethylene glycol (EG) and dimethyl sulfoxide (DMSO) immature bovine oocytes in straws and to investigate the effects of vitrification on post-thaw oocyte maturation. A total of 575 cumulus oocyte complexes were obtained by follicle aspiration from 238 ovaries of cows slaughtered at a local abattoir. Following selection, oocytes with compacted cumulus cells and evenly granulated ooplasm were vitrified using one of the three different solutions with a non-vitrified group served as control. The first step vitrification solution contained 20% EG while the second step solution contained 40% EG+1M sucrose in a basic media used in group EG. Oocytes were matured in N-2-hidroxyethyl piperazine-N-2-ethanosulfonic acid (HEPES) buffered tissue culture medium (TCM) 199 for 24h at 39 degrees C in a humidified atmosphere of 5% CO2 in air. Oocytes were fixed following evaluation for polar body formation, stained with Giemsa solution and nuclear maturation was examined. The numbers of oocytes which were observed at Metaphase II (MII) stage were 41 (34.1%), 17 (14.9%), 29 (20.7%) and 78 (79.6%) in groups EG, DMSO, Mix and Control, respectively. Maturation rate distribution in group Mix was not statistically different when compared to maturation rate distributions in groups EG and DMSO (p>0.05). Differences between other groups were significant (p<0.001). However, better results were obtained in EG group compared to DMSO and mix groups. Maturation rates were lower in all treatment groups than the control group. The lowest maturation result was obtained in DMSO group. Maturation rate in group Mix was between maturation rates of EG and DMSO groups. Immature bovine oocytes can be vitrified in straws, but maturation success differs with the cryoprotectant and it seems that to obtain better maturation rates, new cryopreservation techniques specific for immature bovine oocytes are needed.

Strategies for preservation of ovarian and testicular function after immunosuppression

Gonadal toxicity as a side effect of cyclophosphamide therapy is a common long-term problem in the treatment of a variety of glomerular diseases. In both men and women treated with cyclophosphamide, the consequences of infertility can have great physical and emotional consequences; thus, this issue often has a critical role in the decision to decline treatment with cyclophosphamide. There exists a critical need for strategies for preservation of fertility in both men and women who require treatment with cyclophosphamide. This review explores emerging therapeutic options in this arena, which include sperm and oocyte cryopreservation, medical treatments such as testosterone therapy for men and gonadotropin-releasing hormone agonist therapy for both men and women, and, finally, the relatively new strategy of germ-cell transplantation for both ovarian and testicular tissue, which still remains in the experimental stages.

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.

The cryopreservation of ovarian tissue: uses and indications in veterinary medicine

Animal experiments have shown that cryopreservation of the ovarian cortex, containing primordial follicles, could be used to preserve gametes thereby restoring fertility in humans and animals. During the last 100 years, many hundreds of species have been lost, and a third of the breeding animals are threatened with extinction. To preserve genetic diversity, notably for the conservation of endangered species, it is essential to conserve female and male gametes. Today, biotechnologies such as artificial insemination and embryo transfer are used in breeding programs and are well developed. However, even using these advanced techniques, there are problems due to the limited number of individuals used as the source of gametes, so that the risk of inbreeding is high, even in large populations. To preserve genetic diversity, it is necessary to create gene banks of male and female gametes and embryos, using a very large number of individual donors. Cryopreservation of ovarian tissue could present a means for enlarging the gene pool. Cryopreserved ovarian tissue could be used in auto- or xenografts, or for in vitro maturation (IVM) of primordial follicles. In this review, we describe the processes for cryopreservation of ovarian tissue and the various possibilities for using it.

Vitrification of mouse oocytes using closed pulled straws (CPS) achieves a high survival and preserves good patterns of meiotic spindles, compared with conventional straws, open pulled straws (OPS) and grids

BACKGROUND

We modified the loading of pulled straws into a new closed system, called closed pulled straws (CPS) for holding oocytes for vitrification. The morphological survival, dynamics of meiotic spindles, and fertilization in vitro of vitrified oocytes using CPS were compared with conventional straws, open pulled straws (OPS), and grids.

METHODS

Surviving oocytes were stained for spindles and chromosomes after 1, 2 and 3 h incubations, and compared with controls. The capacity of fertilization and embryonic cleavage were examined in vitro.

RESULTS

The survival rates of the CPS (79%) and straw (77%) groups were significantly higher (P < 0.05) than the OPS (63%) and grid (39%) groups. At a 1h incubation, vitrified oocytes of four groups had significantly fewer normal spindles than controls (P < 0.05). The straw group was inferior to the others in spindle morphology (P < 0.05). After a 3 h incubation, recovery of vitrified oocytes with normal spindles was significantly improved in all groups (P < 0.05). The percentages of fertilization and blastocyst formation of vitrified oocytes after a 1 h incubation was significantly lower than controls (P < 0.05), but they were improved after 2 or 3 h incubations (P < 0.05).

CONCLUSIONS

Oocytes vitrified using CPS, OPS or grids could lessen spindle injuries and expedite recuperation. The survival using OPS or grids is lower. Sufficient culture time for recovery of meiotic spindle would be imperative for fertilization events of vitrified oocytes. CPS has the advantages of achieving a high survival and preserving good spindles.

Human oocyte cryopreservation

Despite early success with sperm and embryo cryopreservation, human oocyte cryopreservation has met with limited success both in terms of survival and subsequent fertilization. However, compared with embryo cryopreservation, oocyte freezing has great potential for eliminating the ethical and legal problems of embryo storage.

Open pulled straws for vitrification of mature mouse oocytes preserve patterns of meiotic spindles and chromosomes better than conventional straws

Vitrification of oocytes has been applied recently for humans, but remains elusive. The microtubules of oocytes are vulnerable to cryoprotectants and thermal changes. Using mouse oocytes, the effects of vitrification in open pulled straws (OPS) were investigated on survival, the meiotic spindle, and chromosomes and compared with conventional straws. Mature oocytes were allocated to four groups for exposure to cryoprotectants, vitrification in conventional straws, or vitrification in OPS. They were diluted in stepwise sucrose solutions. Oocytes without treatments were used as controls. The surviving oocytes were stained for meiotic spindles and chromosomes. After dilution, all of the oocytes exposed to cryoprotectants survived. Vitrification sometimes resulted in lysis so that survival using OPS (62%) was significantly (P < 0.05) smaller than that using conventional straws (81%). Oocytes exposed to cryoprotectants or vitrified exhibited serious disturbances of microtubules immediately post-dilution. After 1 h incubation, the microtubules could repolymerize so that the OPS group had significantly (P < 0.05) more normal spindles (78%) than did the conventional straw group (21%). The former also tended to have more compact chromosomes (87%) than did the latter (78%). OPS for vitrification of oocytes achieve more rapid cooling, warming, and dilution and so reduce spindle injury. However, the lower survival rate in OPS needs improvement.

Cryopreservation of immature human oocytes and ovarian tissue: an emerging technology?

OBJECTIVE

To review the potential for cryopreserving immature follicles either in situ or after isolation from ovarian stroma and to consider the options for fertility by transplantation or in vitro follicle growth.

DESIGN

The problems of storing embryos and mature (metaphase II) oocytes were considered in light of the needs of patients to protect fertility before undergoing potentially sterilizing therapy for cancer. The evidence from the experimental biology literature showing that immature oocytes (prophase I) in primordial follicles can be cryopreserved successfully and transplanted to produce fertile eggs was reviewed. The review, which was compiled from MEDLINE and other bibliographic databases, is intended to emphasize the practical opportunities for this technology and the need for future research rather than to be a comprehensive treatment of the subject.

CONCLUSION(S)

The disappointing results obtained with the cryopreservation of oocytes at metaphase II and ethical concerns about embryo storage are giving impetus to the banking of ovarian tissue for patients who require conservation of fertility. The numbers of needy patients are growing as long-term survivorship after high-dose chemotherapy and bone marrow transplantation rises. More speculatively, if ovarian tissue banking becomes a proven effective method, young, healthy women may request storage of ovarian biopsy samples to keep their reproductive options open in midlife when oocyte fertility is declining. Although the cryotechnology is not yet perfected, the major question now is how to use the tissue most effectively after thawing. For the present, ovarian tissue cryopreservation is still at the experimental stage, but it holds the promise of valuable applications.

Chromosome and spindle configurations of human oocytes matured in vitro after cryopreservation at the germinal vesicle stage

OBJECTIVE

To investigate effects of cryoprotectant and cryopreservation on the chromosome and microtubule configuration of human immature oocytes.

DESIGN

Intact cumulus-enclosed immature oocytes were collected from unstimulated ovaries and divided into three groups: group 1, no treatment (control); group 2, only 1,2-propanediol treatment, and group 3, cryopreserved oocytes. Oocytes in groups 1 and 2, and oocytes that survived after cryopreservation in group 3 were cultured for 48 hours.

SETTING

Infertility Medical Center at the CHA General Hospital, Seoul, Korea.

PATIENT(S)

Oocytes were obtained from patients undergoing gynecologic surgery.

MAIN OUTCOME MEASURE(S)

Maturation rate and abnormality in chromosomes by fluorescence in situ hybridization and in the spindle by immunostaining for tubulin.

RESULT(S)

There was no effect of propanediol-only treatment on the chromosomal (41.4%) and spindle abnormalities (35.3%) in group 2 compared with control oocytes (31.8% and 22.2%, respectively), whereas a statistically significant increase in abnormalities in chromosomes (77.8%) and spindles (70%) was found in group 3.

CONCLUSION(S)

Human oocytes matured in vitro after cryopreservation at the germinal vesicle stage showed increased incidence of chromosomal and spindle abnormalities. These abnormalities may impair the capacity for further development of the embryos derived from frozen-thawed oocytes.

Approaches for obtaining sperm in patients with male factor infertility

OBJECTIVE

To describe methods of sperm retrieval for intracytoplasmic sperm injection (ICSI) in patients with male factor infertility and to review the clinical results using sperm from the different sources.

DESIGN

The literature on sperm-obtaining methods and ICSI was reviewed. Studies related to this topic were identified through MEDLINE.

RESULTS(S)

This review describes the evolution of sperm retrieval methods. Sperm can be obtained by microepididymal sperm aspiration (MESA), percutaneous sperm aspiration (PESA), and testicular sperm extraction (TESE), from patients with congenital absence of the vas deferens or acquired vas obstruction. When ICSI is performed with ejaculated, epididymal, or testicular sperm, good fertilization and pregnancy rates are achieved without significant differences among the various sperm sources. The original percutaneous sperm aspiration method has been modified slightly and yields successful results.

CONCLUSION(S)

Viable pregnancies can be achieved with ICSI by using not only ejaculated sperm, but also epididymal and testicular sperm. Microepididymal sperm aspiration, percutaneous sperm aspiration, modified percutaneous sperm aspiration, and testicular sperm extraction can be considered standard procedures to treat male factor infertility.

Effect of chilling bovine oocytes on their developmental competence

Bovine oocytes are damaged when chilled to temperatures near 0 degree C. We have determined the temperatures at which this injury occurs, as well as its kinetics and the functional consequences for oocytes both at the germinal vesicle-stage (GV) and after in vitro maturation (IVM). Cooling GV oocytes had no effect on their nuclear maturation or fertilization. Compared to control oocytes held at 30 degrees C, the development of GV oocytes into blastocysts following maturation and fertilization was unaffected by cooling them to 20 degrees C for 30 min (blastocyst formation: 25% vs 26%, respectively), but development decreased after cooling them to 10 degrees C and 0 degree C (blastocyst: 6% and 1%, respectively). Cooling oocytes after maturation gave similar results, with no difference between controls and oocytes cooled to 20 degrees C (blastocyst: 25% and 26%, respectively). However, cooling them to 10 degrees C and 0 degree C did reduce development (blastocyst: 8% and 3%, respectively). Chilling oocytes to 0 degree C for 30 sec reduced their cleavage and blastocyst formation by > 40%; there was a high negative correlation between the length of exposure and subsequent survival, both for GV-stage and for IVM oocytes. The extreme sensitivity of both GV and IVM oocytes to chilling can explain the limited success obtained for cryopreservation of bovine oocytes by conventional slow-cooling procedures.

Effects of 1,2-propanediol and freezing-thawing on the in vitro developmental capacity of human immature oocytes

OBJECTIVE

To investigate effects of 1,2-propanediol and freezing-thawing treatment on the maturation and developmental capacity of the human immature oocytes obtained from unstimulated ovaries.

DESIGN

Intact cumulus-enclosed immature oocytes collected from unstimulated ovaries were divided into three groups, such as no treatment as control (group 1), only 1,2-propanediol-treated (group 2), and cryopreserved group (group 3). Oocytes in group 1, group 2, and survived oocytes from cryopreservation in group 3 were cultured for 48 hours. A random selection of matured oocytes was inseminated with normal donor sperm to evaluate the fertilization and developmental capacity.

SETTING

Infertility Medical Center at the CHA General Hospital, Seoul, Korea.

PATIENT(S)

Oocytes were obtained from patients undergoing gynecological surgery.

MAIN OUTCOME MEASURE(S)

Rates of survival, maturation to metaphase II, fertilization, and cleavage.

RESULT(S)

Survival rate after freezing-thawing in group 3 was 55.1% (54/98). Oocytes were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 20% fetal bovine serum, 10 IU/mL pregnant mare serum gonadotropin, and 10 IU/mL hCG. Maturation rates were 76.8% (63/82), 67.1% (47/70), and 59.3% (32/54) in the groups 1, 2, and 3, respectively. Maturation rate in group 3 was significantly lower than that of group 1. Fertilization rates were 90.5% (19/21), 81.0% (17/21), and 42.9% (6/14), and cleavage rates were 94.7% (18/19), 88.2% (15/17), and 16.7% (1/6) in groups 1, 2, and 3, respectively. Fertilization and cleavage rates of survived oocytes in group 3 also were significantly lower than those of groups 1 and 2.

CONCLUSION(S)

Results suggest that the pretreatment with 1.5 M 1,2-propanediol itself before the freezing has no inhibitory effect on the maturation, fertilization, and cleavage of human immature oocytes in vitro. However, the freezing-thawing procedure used had detrimental effects on the maturation and developmental capacity.

Extracorporeal development and ultrarapid freezing of human fetal ova

PURPOSE

The present study was performed to culture human fetal ova to determine whether they can be matured and cryopreserved using ultrarapid freezing.

METHODS

Thirty-three pairs of fetal ovaries were obtained from fetuses of 16-20 weeks' gestation following elective abortion. Ovarian tissues were minced into approximately 1-mm sizes and cultured in Waymouth media either before or after ultrarapid freezing. The Waymouth medium was supplemented with 15% (v/v) fetal bovine serum, 0.03 IU/ml FSH and 35 ng/ml insulin. The tissue was cultured at 37 degrees C in 5% CO2 in air for 5-25 days in Falcon dishes and 30-40 days in Costar Transwell-COL membranes prior to induction of final maturation in the presence of LH and human follicular fluid. Minced tissues were also frozen by ultrarapid freezing in M199 with 4.2 M dimethylsulfoxide (DMSO) and 0.35 M sucrose and plunged directly into liquid nitrogen. For thawing, the straws were plunged into a 37 degrees C water bath for 5 s. The contents were then expelled and diluted 1:5 with thawing medium containing 0.42 M sucrose. After washing the thawed tissues were cultured as described for the fresh tissues.

RESULTS

Patches of monolayer consisting of fibroblasts had formed within 2-3 days of culture of fresh tissues. After 1 week of culture, follicles separated out from the ovarian tissue but remained attached to the monolayer. The maximal number of follicles separating out from the tissue appeared about 1 week after initiating the culture (154 follicles per 10 fields at Day 5 and 61 and Day 25). After 40 days of culture in Costar dishes, 34% of the ova reached a diameter of more than 80 microns, which was significantly higher than at the beginning of culture (6%; P < 0.05). Among these ova, 34% were found to be surrounded by the zona pellucida, which was not observed at the beginning of culture. Following induction of final maturation, extrusion of the first polar body was noted in 25% of ova grown in Costar dishes for 40 days. Twelve percent of the oocytes showed the first polar body when they were grown in Costar dishes for less than 30 days. For frozen-thawed tissues, 14% of minced ovarian tissues displayed central necrosis immediately after thawing. Following digestion and Trypan blue staining, 75% of ova and 85% of somatic cells survived ultrapid freezing. Nineteen percent of the ova which have been cultured as described for fresh tissues displayed extrusion of the first polar body, comparing favorably with the 25% maturation rate observed with the fresh tissue (P > 0.05).

CONCLUSION

This study demonstrates that morphologically normal, mature human ova can be obtained from primordial follicles in vitro development. Using a simple, quick ultrarapid freezing method, human fetal ova can be cryopreserved in the form of minced tissue without significantly compromising their ability to grow in vitro.

Effects of cooling and equilibration in DMSO, and cryopreservation of mouse oocytes, on the rates of in vitro fertilization, development, and chromosomal abnormalities

In a previous study, we have shown that the cryopreservation of mouse oocytes caused increases in the rates of degeneration and of digynic polyploid embryos, while the fertility of frozen-thawed oocytes was decreased. In this study, we have attempted to determine the different stages in the complete freezing-thawing process which are deleterious for the oocytes and the subsequent zygotes. IVF assays showed that DMSO decreased the fertility of oocytes, whereas cooling to 0 degrees C had no effect. DMSO, used at 0 degrees C, was less deleterious for oocytes. Thus, the prefreezing manipulations seem to be important for the quality and fertility of oocytes. However, neither DMSO nor cooling increased the incidence of chromosomal abnormalities in embryos obtained from inseminated exposed oocytes. Therefore, the increased frequency of polyploidy observed in embryos after the cryopreservation of mouse oocytes must correspond to disruption occurring during the freezing-thawing process.

Fertilization and in vitro development of cryopreserved human prophase I oocytes

OBJECTIVE

To determine the potential for in vitro maturation, fertilization, and cleavage after cryopreservation of immature, prophase I human oocytes.

DESIGN

Immature oocytes obtained in excess of the number required by the patient were randomized and cryopreserved at the prophase I stage or cultured as control. After thawing and maturation in vitro, test and control oocytes were inseminated with husband's sperm and evaluated for fertilization and cleavage in vitro.

SETTING

In vitro fertilization program.

PATIENTS

Consenting patients undergoing controlled ovarian hyperstimulation for the purposes of IVF.

MAIN OUTCOME MEASURES

Rates of maturation to metaphase II, fertilization, and cleavage were compared between control and cryopreserved oocytes.

RESULTS

Upon thaw, 58.5% (72/123) of prophase I oocytes were viable. Control oocytes demonstrated a 74.8% (98/131) maturation rate to metaphase II, a 56.5% (52/92) fertilization rate, and an 11.5% (6/52) blastocyst rate. Cryopreserved oocytes showed a 83.3% (60/72) rate of maturation, a 57.7% (30/52) fertilization rate, and a 3.3% (1/30) blastocyst rate. No significant differences were noted between any of these parameters.

CONCLUSIONS

These results demonstrate that prophase I oocytes from stimulated IVF cycles are able to survive cryopreservation and resume meiosis to achieve full nuclear maturation post-thaw. In addition, cryopreserved oocytes retain the same capacity for fertilization and development as control oocytes.

Successful freezing of unfertilized mouse oocytes and effect of cocultures in oviducts on development of in vitro fertilized embryos after thawing

PURPOSE

To establish a freeze-thawing method for unfertilized oocytes with a high success rate, we examined several conditions for freeze-thawing. The effects of EDTA and cocultures in oviducts on the development of embryos fertilized in vitro after thawing were also studied.

RESULTS

In the first experiment, unfertilized oocytes that were frozen in 1.5 M dimethylsulfoxide (DMSO) supplemented with 0.2 M sucrose by a slow freeze-thawing method showed the best results (fertilization rate, 71.9%; blastocyst rate per frozen oocyte, 18.8%). The proportion of embryos that developed to blastocysts was significantly higher when DMSO was added at 4 degrees C than at room temperature (39.4 vs 19.4%; P < 0.01). The addition of EDTA (10 microM) to the culture medium did not promote embryo development after fertilization in vitro. However, the rate of development of in vitro fertilized embryos to blastocysts after thawing was significantly higher when the embryos were cultured in oviducts in vitro than the rates in control cultures and those cultured with EDTA (blastocyst rate from fertilized oocytes, 71.4 vs 51.0 and 52.8%, respectively; P < 0.01).

CONCLUSION

Unfertilized mouse oocytes can be cryopreserved successfully by a slow freeze-thawing method with the addition of 1.5 M DMSO and 0.2 M sucrose at low temperatures, and coculture with oviducts enhances the development of embryos that are fertilized in vitro after thawing.

Experimental study of cryopreserved allogeneic transfer of vessel: preliminary report

It has long been known that the antigenicity of tissues is depressed when they are kept at a very low temperature. In this study, Lewis rats and Brown Norway (B.N.) rats were used because these species are significantly dissimilar at the major histocompatibility complex (MHC) Femoral arteries were harvested from Lewis rats, frozen while lowering the temperature in a stepwise fashion to -70 degrees C. After three weeks of cryogenic storage, the arteries were transplanted into Lewis and B.N. rats. At various times from the first to the twelfth week after surgery, grafted vessels were observed, and pathological and electron microscopic studies were carried out. The vessels were found to be in good condition at the end of the 12 week observation period. These results strongly suggest that prolonged cryopreservation of vessels makes allotransplantation without immunosuppression possible.

Parthenogenetic activation pattern and microtubular organization of the mouse oocyte after exposure to 1,2-propanediol

We have studied the effect of 1,2-propanediol (PROH) on cumulus-oocyte complexes from the mouse. We determined the morphological survival rate, the pattern of parthenogenetic activation, and the microtubular and chromosomal organization. Cumulus-oocyte complexes were collected at 16 h post hCG from superovulated female hybrid mice. These cumulus-intact oocytes were exposed to 1.5 or 3 M PROH for 6, 12, or 18 min at 0, 22, or 37 degrees C. The cryoprotectant was diluted out in a 1 M sucrose solution at 22 degrees C. After 5-6 h at 37 degrees C, oocytes were denuded and examined under Nomarski optics. The results show that PROH can induce degeneration and parthenogenetic activation in the mouse oocyte in a concentration, temperature, and time-dependent way. As the activation stimulus was strengthened, an increasing proportion of oocytes shifted from parthenogenetic activation with polar body extrusion to parthenogenetic activation with polar body retention and even to immediate cleavage. Nontoxic and nonactivating conditions involved mainly exposure to 1.5 M PROH at 0 degrees C. Spindle integrity and chromosomal organization were analyzed for exposure to 1.5 and 3 M PROH for 12 min at 0 degrees C. The separate effect of cooling and exposure to 1 M sucrose were also evaluated. Microtubules were visualized by monoclonal anti-alpha-tubulin labeling followed by immunogold-silver staining. Cooling and exposure to 1 M sucrose or to 1.5 M PROH did not induce major abnormalities in the microtubular or chromosomal organization. On the other hand, a significant percentage of deformities such as spindle size reduction and loss of bipolarity were observed after exposure to 3 M PROH. The results of the present study demonstrate that the use of PROH as a single cryoprotectant for the freezing of mature unfertilized oocytes cannot be recommended in procedures involving ambient temperature or concentrations exceeding 1.5 M PROH. On the other hand, the potential beneficial effect of low temperatures may outweigh the effect of concentration at subzero temperatures and could be explored further in the tailoring of conditions for slow controlled freezing.

A freezing and thawing method of hamster oocytes designed for both the penetration test and chromosome assay of human spermatozoa

Superovulated hamster oocytes were cryopreserved and thawed according to our carefully designed procedures. More than 90% (92 +/- 4%) of oocytes survived freezing and thawing. They were proven to be well conserved, showing excellent performance comparable to freshly ovulated oocytes in the human sperm penetration test (proportion of penetrated ova: 94.7% vs. 93.6%) and human sperm chromosome analysis (proportion of metaphasic ova: 81.8% vs. 83.6%). There was no statistically significant difference in the incidences of sperm chromosome aberrations between assays using fresh and frozen-thawed oocytes. In addition, there was no statistically significant increase of aberrations in female pronuclear (hamster) chromosomes. This freezing-thawing method was found to be reliable, yielding viable hamster oocytes of high quality.

Survival of human oocytes cryopreserved with or without the cumulus in 1,2-propanediol

BACKGROUND

Although cryopreservation of human preembryos has been carried out with success, the cryostorage of oocytes, which pose fewer controversial moral, ethical, and legal problems has been much less successful. Various attempts to cryopreserve human oocytes have been mostly unsuccessful and the search for an optimal protocol for oocyte cryopreservation remains elusive. We therefore undertook this study to determine the effect of oocyte cryostorage in 1,2-propanediol.

METHOD

Mature human oocytes with or without their cumuli were cryopreserved in precooled 1,2-propanediol, then thawed and inseminated with sperms for in vitro fertilization. The outcome of insemination and subsequent embryonic development were also recorded and compared.

RESULTS

Postthaw cryosurvival rate was significantly better when cryostorage was carried out with the oocyte cumulus intact as compared to those oocytes denuded of their cumuli (54 versus 27%, respectively; P < 0.05). Eight (44%) of 18 surviving postthaw oocytes with intact cumuli were fertilized normally, with cleavage in six, as compared to two (25%) and one, respectively, of those denuded of their cumulus prior to cryostorage. Development to the blastocyst stage was achieved in three embryos derived from oocytes with an intact cumulus at cryostorage.

CONCLUSION

We conclude that 1,2-propanediol can be used with success in oocyte cryopreservation, although the issue of parthenogenecity is still to be resolved. Oocyte's with intact cumulus survive cryostorage better than those without it.

The effects of cooling mouse oocytes

The effects of cooling and warming on meiotic spindles of mouse oocytes have been assessed by transmission electron microscopy. Intact cumulus-oocyte complexes were immediately cooled from 37 to 15, 4, 0, and -7 degrees C (seeding temperature) for 15 min in a programmed biological freezer and fixed at these temperatures. Other complexes, cooled to these temperatures, were rapidly warmed to 37 degrees C and incubated for 2 hr before fixation at 37 degrees C. Of 334 oocytes assessed at various temperatures, at least 100 were examined for metaphase II spindles. Spindle microtubules completely disappear at 0 and -7 degrees C, while complete or partial depolymerization of microtubules was observed at 4 degrees C. Cooling to 15 degrees C did not cause major disruptions of spindle structure in most oocytes. Chromosomes tended to rotate or clump at lower temperatures but chromosome scatter outside the spindle zone was rarely observed. Centrosomal material was fragmented at 4 degrees C and occasionally at 15 degrees C and was not evident at the spindle poles at 0 and -7 degrees C. Kinetochores were seen at all temperatures. Spindle structure was evidently restored in the majority of oocytes on rewarming at 37 degrees C. Changes in the ooplasm induced by cooling were elongation and disruption of vesicular smooth endoplasmic reticulum, especially between lipid globules and disappearance of fibrillar inclusions. Cortical granule exocytosis was not observed on cooling, while microfilaments were intact. Swelling of membranous organelles was also observed in cumulus cells. Most of the cytoplasmic changes were also reversed on rewarming. The response of mouse oocytes to cooling is compared to that of human oocytes, reported previously.