Permeability characteristics of human oocytes in the presence of the cryoprotectant dimethylsulphoxide

Human oocyte and ovarian tissue cryopreservation and its application

PURPOSE

To review the recent progress in human oocyte and ovarian tissue cryopreservation, and in the application of these two technologies for preserving female fertility of patients who are undergoing cancer treatment.

DESIGN

The literature on human oocyte and ovarian tissue freezing was searched with PubMed. The scientific background, current developments and potential future applications of these two methods were reviewed.

RESULTS

Chemotherapy and/or radiotherapy can induce premature ovarian failure in most of female cancer patients. Consequently, there has been a greater need for options to preserve the reproductive potential of these individuals. However, options are somewhat limited currently, particularly following aggressive chemotherapy and/or radiotherapy treatment protocols. In recent years, there have been considerable advances in the cryopreservation of human oocytes and ovarian tissue. For women facing upcoming cancer therapies, cryopreservation of ovarian tissue and oocytes is a technology that holds promise for banking reproductive potential for the future. Recent laboratory modifications have resulted in improved oocyte survival, oocyte fertilization, and pregnancy rates from frozen-thawed oocytes in IVF. This suggests potential for clinical application.

CONCLUSIONS

In the case of patients who are facing infertility due to cancer therapy, oocyte cryopreservation may be one of the few options available. Ovarian tissue cryopreservation can only be recommended as an experimental protocol in carefully selected patients. In ovarian tissue transplantation, more research is needed in order to enhance the revascularization process with the goal of reducing the follicular loss that takes place after tissue grafting. These technologies are still investigational, although tremendous progress has been made. The availability of such treatment will potentially lead to its demand not only from patients with cancer but also from healthy women who chose to postpone childbearing until later in life and therefore wish to retain their fertility.

Human oocyte vitrification: the permeability of metaphase II oocytes to water and ethylene glycol and the appliance toward vitrification

OBJECTIVE

To determine the permeability of human metaphase II oocytes to ethylene glycol and water in the presence of ethylene glycol, and to use this information to develop a method to vitrify human oocytes.

DESIGN

An incomplete randomized block design.

SETTING

A university-affiliated assisted reproductive center.

PATIENT(S)

Women undergoing assisted reproduction in the Center for Reproductive Medicine at Shandong University.

INTERVENTION(S)

Oocytes were exposed to 1.0 molar ethylene glycol in a single step and photographed during subsequent volume excursions.

MAIN OUTCOME MEASURE(S)

A two-parameter model was employed to estimate the permeability to water and ethylene glycol.

RESULT(S)

Water permeability ranged from 0.15 to 1.17 microm/(min.atm), and ethylene glycol permeability ranged from 1.5 to 30 microm/min between 7 degrees C at 36 degrees C. The activation energies for water and ethylene glycol permeability were 14.42 Kcal/mol and 21.20 Kcal/mol, respectively.

CONCLUSION(S)

Despite the lower permeability of human metaphase II oocytes to ethylene glycol compared with previously published values for propylene glycol and dimethylsulfoxide, methods to add and remove human oocytes with a vitrifiable concentration of ethylene glycol can be designed that prevent excessive osmotic stress and minimize exposure to high concentrations of this compound.

Cell encapsulating droplet vitrification

The capability to encapsulate single cells in droplets while retaining high cell viability (>90%) has great impact on tissue engineering, high-throughput screening, as well as clinical diagnostics and therapeutics. We demonstrate a novel method to vitrify a small number of cells using cell-encapsulating droplets. The method allows vitrification at low cryoprotectant concentration (1.5 M propanediol and 0.5 M trehalose), similar to that used in slow freezing protocols. The method was successfully applied to five different mammalian cell types: AML-12 hepatocytes, NIH-3T3 fibroblasts, HL-1 cardiomyocytes, mouse embryonic stem cells, and RAJI cells.

Human oocyte cryopreservation and the fate of cortical granules

OBJECTIVE

To examine the effect of the commonly used oocyte cryopreservation protocol on the cortical granules (CGs) of human immature germinal vesicle (GV) and mature metaphase II (MII) oocytes.

DESIGN

Laboratory study.

SETTING

IVF unit.

INTERVENTION(S)

Unfertilized, intracytoplasmic sperm injected (ICSI) oocytes, and immature oocytes were cryopreserved using a slow freezing-rapid thawing program with 1,2-propanediol (PROH) as a cryoprotectant.

MAIN OUTCOME MEASURE(S)

Cortical granule exocytosis (CGE) was assessed by either confocal microscopy or transmission electron microscopy (TEM).

RESULT(S)

The survival rates of frozen-thawed oocytes (mature and immature) were significantly lower compared with zygotes. Both mature and immature oocytes exhibited increased fluorescence after cryopreservation, indicating the occurrence of CGE. Mere exposure of oocytes to cryoprotectants induced CGE of 70% the value of control zygotes. The TEM revealed a drastic reduction in the amount of CGs at the cortex of frozen-thawed GV and MII oocytes, as well as appearance of vesicles in the ooplasm.

CONCLUSION(S)

The commonly used PROH freezing protocol for human oocytes resulted in extensive CGE. This finding explains why ICSI is needed to achieve fertilization of frozen-thawed human oocytes.

Permeability of ovine primordial follicles to different cryoprotectants

OBJECTIVE

To determine the behavior of isolated primordial follicles that were exposed to different concentrations of dimethyl sulfoxide (DMSO), ethylene glycol (EG), propylene glycol (PROH), and glycerol (GLY).

DESIGN

Isolated primordial follicles were exposed to the cryoprotectant (CPA) solution and photographed to calculate their volume at different periods of exposure.

SETTING

Laboratorio Renzo Giuliani, University of Florence, Italy.

ANIMAL(S)

Lambs, 30-40 days old.

INTERVENTION(S)

Isolation of primordial follicles and subsequent exposure to CPA.

MAIN OUTCOME MEASURE(S)

Follicular volume.

RESULT(S)

At 2 minutes of CPA exposure, all follicles appeared to be shrunken. At approximately 5 minutes, shrinkage ceased, and follicles started to swell, absorbing the CPA and water to maintain osmotic equilibrium. When DMSO was tested, follicular dehydration in all concentrations did not exceed 17%; with PROH and EG, it reached 33% and 27%, respectively. The highest degree of dehydration (48%) was seen with GLY. In almost all tested concentrations, follicular shrinkage occurred up to 5 minutes.

CONCLUSION(S)

Volume changes in isolated primordial follicles can fluctuate according to the CPA used and its concentration.

Extracellular respiration of dimethyl sulfoxide by Shewanella oneidensis strain MR-1

Shewanella species are renowned for their respiratory versatility, including their ability to respire poorly soluble substrates by using enzymatic machinery that is localized to the outside of the cell. The ability to engage in "extracellular respiration" to date has focused primarily on respiration of minerals. Here, we identify two gene clusters in Shewanella oneidensis strain MR-1 that each contain homologs of genes required for metal reduction and genes that are predicted to encode dimethyl sulfoxide (DMSO) reductase subunits. Molecular and genetic analyses of these clusters indicate that one (SO1427-SO1432) is required for anaerobic respiration of DMSO. We show that DMSO respiration is an extracellular respiratory process through the analysis of mutants defective in type II secretion, which is required for transporting proteins to the outer membrane in Shewanella. Moreover, immunogold labeling of DMSO reductase subunits reveals that they reside on the outer leaflet of the outer membrane under anaerobic conditions. The extracellular localization of the DMSO reductase in S. oneidensis suggests these organisms may perceive DMSO in the environment as an insoluble compound.

Permeability of mouse oocytes and embryos at various developmental stages to five cryoprotectants

To assess the permeability of mouse oocytes and embryos, matured oocytes and embryos at various stages of development were placed in five cryoprotectant solutions at 25 C for 25 min. From the cross-sectional areas of the oocytes/embryos, the relative change in volume was analyzed. In oocytes, shrinkage was least extensive and recovery was quickest in the propylene glycol solution, showing that propylene glycol permeates the oocytes most rapidly. Dimethyl sulfoxide, acetamide, and ethylene glycol permeated the oocytes slightly more slowly than propylene glycol. The oocytes in glycerol shrunk extensively and then expanded marginally, indicating slow permeation. The volume changes of 1-cell and 2-cell embryos were similar to those of oocytes, showing little change in permeability. In 8-cell embryos, the volume recovered much faster than in the earlier stages especially in glycerol and acetamide. In morulae, the volume recovery was much faster in glycerol and in ethylene glycol; in ethylene glycol, the extent of shrinkage was small and the recovery was fast, indicating an extremely rapid permeation. Although the permeability of oocytes/embryos generally increased as embryo development proceeded, the degree of increase varied greatly among the cryoprotectants. Interestingly, the volume change in propylene glycol was virtually unaffected by the stage of development. Such information will be valuable for determining a suitable protocol for the cryopreservation of oocytes/embryos at different stages of development.

Oocyte cryopreservation: a biological perspective

Oocyte cryopreservation would amount to a major breakthrough in reproductive medicine. Diverse strategies have been tested to minimise cooling-induced cell injury. Nevertheless, oocytes from various species have shown a particular sensitivity to freezing, due to their unique biological characteristics. Storage of human mature oocytes with slow freezing has resulted in low survival rates, although recent studies based on modified methods have reported higher success. Survival after thawing is not necessarily a guarantee of unaltered viability. Developmental failure at pre- or postimplantation stages may originate from critical perturbations of various cell components, such as the chromosome segregation apparatus, the intracellular calcium signalling system, and the cytoskeleton. Germinal vesicle (GV)-stage oocytes have been suggested to be more amenable to freezing. But their use would require efficient in vitro maturation systems, which are not presently available. Oocyte cryopreservation remains a realistic objective, provided that more systematic approaches are applied, such as thorough analysis of the plasmalemma permeability to water and the diverse cryoprotectants.

Human oocyte cryopreservation: a valid alternative to embryo cryopreservation?

Embryo cryopreservation has become an ethical necessity due to the way human in vitro fertilization (IVF) infertility therapy has developed. Limited embryonic implantation has by necessity driven IVF therapy to adopt ways to maximize the harvest of oocytes following ovarian hyperstimulation with its attendant risks. Collection of more oocytes has allowed more embryos to be generated to compensate for poor embryonic viability, often leading to transfer of multiple embryos to increase per transfer pregnancy rates. In an era of improving embryonic viability and prevailing trend toward single embryo transfers, production of excessive numbers of surplus embryos appears increasingly inappropriate. At which stage embryo cryopreservation can be undertaken most effectively remains controversial. Embryo cryopreservation nevertheless represents the current solution to the problem of excessive embryo production, but inherently raises ethical concerns for certain couples uncomfortable with what they might perceive to be "experimental" cryostorage, who in extreme circumstances may even choose to limit the number of oocytes inseminated to obviate the production of spare embryos. On a more practical level, cryostored embryos are co-owned by two people who may separate, and as such the embryos then face an uncertain fate, commonly decided in courts of law. Oocyte cryopreservation, if consistent and successful, offers a way to avoid the above complications of routine IVF therapy. Oocytes may need to be cryostored in the event of unforeseen non-production of sperm during IVF therapy, allowing a more measured consideration of donor sperm use or other means of sperm retrieval. Beyond IVF for infertility therapy using a couple's own gametes, oocyte cryopreservation provides a wonderful opportunity to optimize donor oocyte cryo-banking, reducing costs and improving convenience. Meanwhile, frozen embryo donation is an approach that many couples are uncomfortable with, and allows only for retrospective donor screening, and less gametic choice. Advances in ovarian tissue cryopreservation will probably provide the best approach for long term storage of female gametes for women wishing to elect to prolong their reproductive potential, or prior to cancer therapy. However, improved consistency with vitrification technology through standardization of protocols and cell-carrying systems is bringing routine single oocyte cryostorage, at all stages of egg maturity, closer to reality. This, coupled with in vitro maturation, will aid development of oocyte collection protocols using minimal amounts of gonadotropins. All of which will help drive IVF programs to consider cryostorage of excess oocytes and not embryos, inseminating post-thaw/warming only a limited number of oocytes at any one time, in anticipation of the need for only one or two embryos at transfer. The question then is how close are we to being able to provide routine clinical application of human oocyte cryostorage, and when will it be appropriate?

Factors affecting the uptake of DMSO by the eggs and embryos of medaka, Oryzias latipes

High performance liquid chromatography (HPLC) was used to assess the uptake dynamics of the cryoprotectant DMSO by intact unfertilized eggs (stage 0), 8-cell (stage 5) and eyed embryos (stage 30) of medaka, Oryzias latipes, the relation of the internal concentration (Cin) of DMSO with fertilization and survival rates, and the effects of several factors on these processes. The factors examined were: cryoprotectant concentration (0.6, 1.2, 1.9 and 2.5 M), impregnation time (1, 3, 5, 10, 15 and 20 min), temperature (0, 5 and 20 degrees C), hydrostatic pressure (0 and 50 atm), and the osmotic conditions of the materials (normal or partially dehydrated). Cryoprotectant permeation, estimated from the initial rates of DMSO uptake, was higher in embryos than in eggs and increased with embryonic development; however, the DMSO Cin in eyed embryos reached a plateau at 1-5 min and could not be increased by prolonging impregnation. The highest fertilization and survival rates for any given DMSO Cin were obtained with high concentrations and short times of impregnation rather than low concentrations and long impregnation times. Application of hydrostatic pressure (50 atm) and exposure for 3 min to a 1 M trehalose solution prior to impregnation induced a substantial increase in the DMSO Cin of 8-cell embryos in comparison to untreated controls with no significant effect on survival. Hydrostatic pressure also promoted DMSO uptake in unfertilized eggs, but with rapid loss of viability, and was ineffective in eyed embryos. The uptake of DMSO and its toxicity to 8-cell embryos were directly proportional to the temperature of impregnation. The results of this study reveal important interactions between cryoprotectant concentration, impregnation time and the developmental stage (or type) of the materials and provide evidence that hydrostatic pressure, temperature of impregnation and the osmotic conditions of the materials can be manipulated to increase the uptake of cryoprotectant by fish eggs and embryos.

Permeability characteristics and osmotic sensitivity of rhesus monkey (Macaca mulatta) oocytes

BACKGROUND

Permeability characteristics and sensitivity to osmotic shock are principal parameters that are important to derive procedures for the successful cryopreservation of mammalian oocytes.

METHODS AND RESULTS

The osmotically inactive volume of rhesus monkey oocytes was determined by measuring their volumes in the presence of hypertonic solutions of sucrose from 0.2 to 1.5 mol/l, compared with their volume in isotonic TALP-HEPES solution. Boyle-van't Hoff plots at infinite osmolality indicated that the non-osmotic volumes of immature and mature oocytes were 20 and 17% respectively. Osmotic responses of oocytes exposed to 1.0 mol/l solutions of glycerol, dimethylsulphoxide (DMSO) and ethylene glycol (EG) were determined. Rhesus monkey oocytes appeared to be less permeable to glycerol than to DMSO or to EG. Sensitivity of oocytes to osmotic shock was determined by exposing them to various solutions of EG (0.1 to 5.0 mol/l) and then abruptly diluting them into isotonic medium. Morphological survival, as measured by membrane integrity, of oocytes diluted out of EG depended significantly on the concentration of EG (P < 0.01).

CONCLUSION

Determination of permeability characteristics and sensitivity to osmotic shock of rhesus oocytes will aid in the derivation of procedures for their cryopreservation.

Cryoloop vitrification yields superior survival of Rhesus monkey blastocysts

BACKGROUND

Vitrification using the cryoloop procedure was evaluated for preservation of non-human primate blastocysts by comparing survival results from two different cryoprotectant mixtures with prior results from controlled rate cooling.

METHODS

Rhesus monkey blastocysts were produced by intracytoplasmic sperm injection of mature oocytes from cycling females stimulated with recombinant human hormones. Morphologically well-formed blastocysts were divided between Procedure A (2.8 mol/l dimethylsulphoxide and 3.6 mol/l ethylene glycol with 0.65 mol/l sucrose and 25 micromol/l Ficoll in TALP-HEPES with 20% fetal bovine serum (TH20)) and Procedure B (3.4 mol/l glycerol and 4.5 mol/l ethylene glycol in TH20). After >48 h in liquid nitrogen, the removal of cryoprotectants was accomplished in the presence of a 3-step series of decreasing sucrose concentrations in TH20. Surviving embryos were co-cultured on buffalo rat liver cells.

RESULTS

Of 16 blastocysts vitrified via Procedure A, 38% survived with minimal lysis and only one hatched in culture; in contrast, of 33 blastocysts vitrified by Procedure B, 85% survived and 71% hatched. Of 22 blastocysts cryopreserved by conventional slow cooling, 36% survived and 6% hatched. Transfer into three recipients, each with two embryos vitrified with Procedure B, resulted in a successful twin-term pregnancy.

CONCLUSION

Modified cryoloop vitrification with a final solution of 3.4 mol/l glycerol and 4.5 mol/l ethylene glycol is a promising procedure for preserving Rhesus monkey blastocysts that is simple, rapid, and inexpensive.

Recent progress in oocyte and ovarian tissue cryopreservation and transplantation

Ovarian tissue cryopreservation and transplantation is an experimental technique that has been developed to sustain the reproductive function of women and children who are faced with sterilizing chemotherapy, radiotherapy, or radical reproductive surgery. Oocyte cryopreservation, on the other hand, is less feasible in the context of cancer because there is usually inadequate time to complete an ovarian stimulation cycle. The main promise of oocyte cryopreservation is that it offers an alternative when embryo freezing is not possible for technical, regulatory, or religious reasons. Oocyte freezing is more suitable for a single woman when the concern is age-related decline in fecundity. There have been significant scientific advances in the field of cryopreservation of ovarian tissue and oocytes, especially within the past few years. Ovarian function has been reported after the first cases of ovarian transplantation, and the number of pregnancies from cryopreserved oocytes has grown. Ovarian tissue and oocyte freezing can now be recommended in a carefully selected group of patients, provided that these options are offered under protocols that are approved by an institutional review board.

Oocyte cryopreservation and ovarian tissue banking

Oocyte cryopreservation, despite its impact on conservation of genetic resources, is not yet an established technology. Several problems need to be solved before this technology can be applied regularly. Chilling membrane susceptibility and formation of ice due to the large volume of the cell are the major problems observed. However, during the last years, several studies were done to obtain viable oocytes after cryopreservation. The addition of molecules known to stabilize membranes and the creation of freezing systems with rapid cooling throughout the transition phase have yielded a good percentage of viable immature and mature oocytes More recently, storage of female gametes was achieved by cryopreservation of cortical ovarian tissue. The possibility of restoring fertility by transplantation of frozen ovarian tissue or its long-term culture in vitro represents an important future means of preserving the fertility of patients and of storing the gametes of rare animals.

Membrane permeability of human oocytes in the presence of the cryoprotectant propane-1,2-diol

OBJECTIVE

To determine the permeability of unfertilized human oocytes to water and the cryoprotectant propane-1,2-diol over a range of temperatures and to use these data to predict osmotic responses under given conditions.

DESIGN

Laboratory-based study.

SETTING

Teaching hospital.

PATIENT(S)

Infertility patients donating unfertilized oocytes in excess of those required for treatment.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Water and cryoprotectant permeability were determined from measurements of oocyte volume excursions on exposure to 1.5 M propane-1,2-diol at 30 degrees C, 24 degrees C, and 10 degrees C.

RESULT(S)

Permeability of human oocytes to water and cryoprotectant increased as temperature increased. The predicted response of oocytes, based on these data, closely matched the measured response of an oocyte on exposure to a widely used method for addition of cryoprotectant before freezing.

CONCLUSION(S)

Commonly used cryopreservation protocols involving slow cooling in the presence of propane-1,2-diol cause potentially damaging excursions in cell volume on exposure to cryoprotectant. Modifications that can be expected to reduce cell volume excursions, based on oocyte permeability data, are suggested.

Osmotic behavior of in vitro produced bovine blastocysts in cryoprotectant solutions as a potential predictive test of survival

The osmotic behavior of bovine blastocysts produced in vitro was filmed during exposure to and dilution of cryoprotectant solutions used for vitrification. The relationship between the changes in the diameter of embryos and their subsequent survival was assessed. Embryos collected on Day 6 and Day 7 postinsemination were exposed to 10% glycerol (GLY) for 5 min, 10% GLY + 20% ethylene glycol (EG) for 5 min, and 25% Gly + 25% EG for 30 s, before dilution in 0.85 M galactose and finally in embryo transfer freezing medium (ETF). Embryos that had a higher probability of survival behaved as perfect osmometers, shrinking, reexpanding, or swelling according to an identical pattern, whereas embryos that deviated from this standard usually did not survive. The initial embryo diameter, duration of shrinkage and expansion in 10% glycerol, duration of reexpansion in ETF, and final embryo diameter were clearly predictive of the ability to hatch after culture in vitro. On a given day postinsemination, larger blastocysts were more likely than smaller blastocysts to survive and hatch after exposure to cryoprotectants with or without vitrification.

Temperature dependence of Kedem-Katchalsky membrane transport coefficients for mature mouse oocytes in the presence of ethylene glycol

Ethylene glycol (EG) is the emerging cryoprotectant of choice for preservation of mammalian embryos but has not been widely used for oocyte preservation. Techniques for oocyte cryopreservation need to be improved before they can be incorporated into routine clinical practice. Hence the permeability characteristics of oocytes in the presence of EG have been determined in order to facilitate the design of cryopreservation protocols using this cryoprotectant. Individual mouse oocytes were held using negative pressure applied to the zona pellucida by means of a micropipet. Each oocyte was perfused with 1 ml 1.5 mol L(-1) EG at 30, 19, or 10 degrees C, a total of 10 oocytes being perfused at each temperature. The osmotic response of each oocyte before, during and after perfusion was recorded on videotape. Measurements of mean cell diameter across three axes were used to calculate oocyte volume, assuming them to be spherical, and, using mathematical modeling, values for hydraulic conductivity (L(p)) were found to be 0.91 +/- 0.05, 0.51 +/- 0.02, and 0.18 +/- 0.01 microm min(-1) atm(-1); cryoprotectant permeability (P(EG)) was 0.24 +/- 0.01, 0.09 +/- 0.005, and 0.03 +/- 0.004 microm s(-1); and reflection coefficient (sigma) was 0.98 +/- 0.005, 0.96 +/- 0.01, and 0.97 +/- 0.01 at 30, 19, and 10 degrees C, respectively. The activation energy (E(a)) of L(p) was 14. 0 kCal mol(-1) and of P(EG) was 16.4 kCal mol(-1).