Viability of bovine blastocysts obtained after 7, 8 or 9 days of culture in vitro following vitrification and one-step rehydration

The Natural Cryoprotectant Honey for Fertility Cryopreservation

Honey is a mixture of 25 sugars with other bioactive substances (i.e., organic acids, enzymes, antioxidants, and vitamins) and has been known as a highly nutritious functional food. Traditionally, it has been widely used in medicinal applications to cure various diseases. The effectiveness of honey in different applications has been used for its antimicrobial activity, absorption of hydrops, cleansing, removing odor, assisting granulation, recovery of nutrition, and formation of tissue and epithelium, which proved that honey has dehydrating and preserving properties to make it ideal for the cryopreservation of cells and tissues. Cryopreservation is an advanced preservation technique for tissue, cells, organelles, or other biological specimen storage, performed by cooling the sample at a very low temperature. It is the most common approach to improved preserving fertility (sperm, embryos, and oocytes) in different species that may undergo various life-threatening illnesses and allows for the genetic screening of these cells to test the sample for diseases before use. However, with toxic cryoprotectant (CPA), cryopreservation of fertility has been challenging because of their particular structure and sensitivity to chilling. Honey’s unique composition, as well as its dehydrating and preserving properties, qualify it to be used as a natural cryoprotectant. The aim of this study is to emphasize the ability of honey as a natural cryoprotectant in cryopreservation. The articles for this review were searched from Google Scholar, PubMed, Science Direct, Web of Science, and Scopus, using the keywords, honey, cryopreservation, natural cryoprotectant/CPAs, extenders, and fertility. Honey, as a natural cryoprotectant in fertility cryopreservation, yielded satisfactory results, with respect to improved post-thaw quality and viability. It is now proved as a non-toxic and highly efficient natural cryoprotectant in fertility preservation because its increasing viscosity at low temperature can provide a protective barrier to cells by reducing ice formation. Furthermore, its antioxidant property plays a vital role in protecting the cells from thermal damage by reducing the reactive oxygen species (ROS). This review provides a road map for future studies to investigate the potential of honey in the cryopreservation of other cells and tissue and contribute to the scientific research, regarding this remarkable natural product.

The role of apoptosis in cryopreserved animal oocytes and embryos

Cryopreservation of both gametes and embryos, both for storage and for the preservation of their developmental capacity is a critical aspect of assisted reproductive technology. The survival of reproductive material following cryopreservation protocols is not only vital to clinical applications in the human in vitro fertilisation clinic, but is also important in the in vitro production of livestock embryos. The ability to routinely cryopreserve oocytes and embryos of livestock species has the potential to improve animal welfare, reduce environmental impact, and reduce the associated costs for breeding companies through the reduction of live animal transportation. Unfortunately, frozen oocytes and embryos are regularly documented to contain a higher proportion of apoptotic cells compared to their non-frozen counterparts, with freezing procedures thought to trigger apoptotic pathways of cell death. Comparisons between frozen and non-frozen samples also show changes in the gene expression of apoptotic factors such as Bcl-2 and Bax in response to cryopreservation. Apoptotic inhibition has the potential to improve cryosurvival, and how to achieve this is subject to debate. Here, we review how exposure to low temperatures during cryopreservation may be responsible for the abnormal activation of apoptotic pathways in mammalian oocytes and embryos, and discuss the ways in which they can be influenced to improve cryopreservation protocols, particularly in agriculturally important species.

A Shorter Equilibration Period Improves Post-Warming Outcomes after Vitrification and in Straw Dilution of In Vitro-Produced Bovine Embryos

This study was designed to the optimize vitrification and in-straw warming protocol of in vitro-produced bovine embryos by comparing two different equilibration periods, short equilibrium (SE: 3 min) and long equilibrium (LE: 12 min). Outcomes recorded in vitrified day seven (D7) and day eight (D8) expanded blastocysts were survival and hatching rates, cell counts, apoptosis rate, and gene expression. While survival rates at 3 and 24 h post-warming were reduced (p < 0.05) after vitrification, the hatching rates of D7 embryos vitrified after SE were similar to the rates recorded in fresh non-vitrified blastocysts. The hatching rates of vitrified D8 blastocysts were lower (p < 0.05) than of fresh controls regardless of treatment. Total cell count, and inner cell mass and trophectoderm cell counts were similar in hatched D7 blastocysts vitrified after SE and fresh blastocysts, while vitrified D8 blastocysts yielded lower values regardless of treatment. The apoptosis rate was significantly higher in both treatment groups compared to fresh controls, although rates were lower for SE than LE. No differences emerged in BAX, AQP3, CX43, and IFNτ gene expression between the treatments, whereas a significantly greater abundance of BCL2L1 and SOD1 transcripts was observed in blastocysts vitrified after SE. A shorter equilibration vitrification protocol was found to improve post-warming outcomes and time efficiency after in-straw warming/dilution.

Natural honey acts as a nonpermeating cryoprotectant for promoting bovine oocyte vitrification

Sugars are commonly supplemented into vitrification solution to dehydrate cells in order to reduce the formation of fatal intracellular ice crystals. Natural honey is a mixture of 25 sugars (mainly fructose and glucose) that have different biological and pharmacological benefits. The present study was designed to determine if honey can be used as a nonpermeating cryoprotectant in vitrification of bovine oocytes. In the first experiment, denuded-MII oocytes were exposed to 0.25, 0.5, 1.0, 1.5 or 2.0 M of honey or sucrose. Natural honey and sucrose caused similar ooplasm dehydration. A significant relationship existed between time and ooplasm volume change (P < 0.05), during dehydration and rehydration phases, in both honey and sucrose solutions. In the second experiment, the immature cumulus-oocyte complexes (COCs) were vitrified in an EG/DMSO-based vitrification solution containing honey (0.5, 1 or 1.5 M) or sucrose (0.5 M) as a gold standard. The vitrified-warmed COCs were matured in vitro and evaluated for nuclear maturation. The maturation (MII) rate was greater in nonvitrified control (81%) than vitrified groups (54%, P < 0.05). In the third experiment, COCs were either remained nonvitrified (control) or vitrified in 1.0 M honey or 0.5 M sucrose, followed by IVM, IVF and IVC (for 9 days). Cleavage rate was greater in control (74%) than in vitrified groups (47%, P < 0.05), without significant difference between sugars. Blastocyst rate was 34, 13 and 3% in control, honey and sucrose groups respectively (P < 0.05). In conclusion, natural honey acted as a nonpermeating cryoprotectant in vitrification solution and improved the embryonic development in vitrified bovine COCs.

Effect of sex on cryotolerance of bovine embryos produced in vitro

Male and female embryos are known to be different in developmental kinetics, metabolism, gene expression, and epigenetic patterns. Therefore, the objective of this study was to clarify whether the morphological criteria used to select embryos for cryopreservation lead to a deviation in the male:female ratio, and whether vitrification effects vary according to embryo sex. Initially, five sires were tested to evaluate the effect of the bull on embryo development, sex ratio, speed of development, and response to cryopreservation. Results showed that bulls affected (P < 0.05) embryo production, response to cryopreservation, and sex ratio. Then, one bull was selected, and used to produce embryos in vitro to characterize the responses of male and female embryos to vitrification. Results suggested that male and female embryos have the same morphological responses to vitrification, as no differences (P > 0.05) were observed between the two sexes in post-warming survival and re-expansion rates. However, their molecular responses as evaluated by gene expression (FOSL1, HSPB1, CASP3, CASP8, HSPA5, HSPA1A, G6PD, and PGK1) analysis indicated an effect of sex on vitrification; vitrified female embryos exhibited higher mRNA levels of HSPA1A, CASP3, and G6PD compared to their male counterparts. In conclusion, bulls affected embryo production, speed of development, sex ratio, and response to cryopreservation. Male and female embryos differed in their molecular responses to vitrification; and also, deviations in the male:female ratio when selecting embryos for cryopreservation were confirmed.

Cryotolerance of porcine in vitro-produced blastocysts relies on blastocyst stage and length of in vitro culture prior to vitrification

The aim of our study was to assess whether the cryotolerance of in vitro-produced embryos could be influenced by the length of in vitro culture and size of blastocoel cavity before vitrification, using the pig as a model. For this purpose we analysed the cryoresistance and apoptosis rate of blastocysts at different stages of development as derived on Day 5 and 6 of in vitro culture. Blastocysts were subsequently vitrified, warmed and cultured for 24 h. Re-expansion rates were recorded at 3 and 24 h and total cell number and apoptotic cells were determined at 24 h. Day-6 blastocysts showed the highest rates of survival after warming, which indicates higher quality compared with Day-5 blastocysts. Higher re-expansion rates were observed for expanded blastocysts and those in the process of hatching when compared with early blastocysts. Total cell number and apoptotic cells were affected by blastocyst stage, vitrification–warming procedures and length of in vitro culture, as expanding and hatching–hatched blastocysts from Day 6 presented higher percentages of apoptotic cells than fresh blastocysts and blastocysts vitrified at Day 5. Our findings suggest that the cryotop vitrification method is useful for the cryopreservation of porcine blastocysts presenting a high degree of expansion, particularly when vitrification is performed after 6 days of in vitro culture. Furthermore, these results show that faster embryo development underlies higher blastocyst cryotolerance and provide evidence that blastocoel cavity expansion before vitrification is a reliable index of in vitro-produced embryo quality and developmental potential.

Developmental kinetics of in vitro-produced bovine embryos: An aid for making decisions

Embryo developmental kinetics and embryo survival after cryopreservation have been correlated with embryo quality and viability. The main objectives of this work were to analyze developmental ability and quality of in vitro-produced bovine embryos in relation to their kinetics and to establish a criterion of quality to predict further viability. Embryos were classified and grouped by their specific stage of development (2, 3-4, or ≥ 5 cells) at 44 hours post insemination (hpi) and cultured separately up to Day 8. On Days 7 and 8, good quality expanded blastocysts were vitrified or frozen. Cryopreserved surviving hatched embryos were stained for cell counts. Embryos at a more advanced stage (3-4 cells, and ≥5 cells) developed to morulae (P < 0.001) and blastocysts (P < 0.01) at higher rates than those embryos that had cleaved once by 44 hpi. Vitrification improved the hatching rates of blastocysts at 48 hours (P < 0.001) when compared with slow-rate freezing within each group of embryos (3-4 cells and ≥5 cells). After vitrification/warming, blastocysts coming from 3- to 4-cell embryos had higher hatching rates at 48 hours than those that came from ≥5-cell embryos. With regard to differential cell counts, no effect of the initial developmental stage was observed after warming/thawing. However, trophectoderm and total cells were higher in vitrified/warmed than in the frozen/thawed embryos (P < 0.001). These data show that selecting IVF embryos at 44 hpi, after the evaluation of their in vitro embryo development, could be used as noninvasive markers of embryo developmental competence and may help to select IVF embryos that would be more suitable for cryopreservation.

Survival and apoptosis rates after vitrification in cryotop devices of in vitro-produced calf and cow blastocysts at different developmental stages

Two experiments were designed to determine the ability of in vitro-cultured blastocysts at different stages of development to survive the vitrification procedure using cryotop devices. Day 7 and Day 8 embryos were classified as non-expanded, expanded or hatching and/or hatched blastocysts. In the first experiment, we examined the survival rate of vitrified-warmed blastocysts after 3 h incubation in synthetic oviducal fluid (SOF) medium. In the second experiment, vitrified-warmed blastocysts were evaluated using the terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL) technique to detect nuclei with damaged DNA. In both experiments, results for cow and calf blastocysts were compared. No differences in survival rates were observed after vitrification of Day 8 expanded (52.4%) and hatched (50%) cow blastocysts or Day 8 expanded (54.5%) and hatched (59.4%) calf blastocysts. When embryos were vitrified on Day 7, survival rates of 78.4% and 66.7% were observed after warming expanded and hatched cow blastocysts, respectively, compared with rates of 80% and 76.9%, respectively, for calf blastocysts. Lowest survival rates were recorded for non-expanded blastocysts (26%-54%) compared with the other developmental stages, particularly those vitrified at Day 8 (</=40%). The DNA integrity index obtained after vitrification-warming was comparable to that for control fresh blastocysts, regardless of the length of embryo culture, the developmental stage of the embryo or the source of the oocytes. Our findings suggest that the cryotop vitrification method is particularly useful for the cryopreservation of blastocysts presenting with a high degree of expansion (expanded or hatched blastocysts), particularly when vitrification is performed after 7 days of in vitro embryo culture.

Development and quality of bovine morulae cultured in serum-free medium with specific retinoid receptor agonists

Retinoids regulate development and differentiation of the bovine blastocyst in vitro, although the underlying mechanisms remain to be clarified. A challenge in reproductive biotechnology is the identification of pathways that regulate early embryonic development and their influence on blastocyst differentiation, apoptosis and survival to cryopreservation as traits of embryo quality. The present paper analyses the effects of short-term exposure (24 h) to retinoids on in vitro-produced bovine morulae. Immature cumulus oocyte complexes were in vitro matured and fertilised. Presumptive zygotes were subsequently cultured in modified synthetic oviduct fluid up to Day 6, in which morulae were randomly allocated to the different experimental groups. The treatments consisted of 0.1 microM LG100268 (LG; a retinoid X receptor agonist), 0.7 microM all-trans retinoic acid (ATRA; a retinoic acid receptor agonist) or no additives. Day 8 blastocyst development was increased in the ATRA-treated group compared with the LG and untreated embryos. In Day 7 embryos, the number of total cells and cells allocated to the trophectoderm were higher in the ATRA-treated group compared with untreated embryos. Apoptosis in the inner cell mass increased after LG treatment, whereas ATRA had no effect. After vitrification and warming, survival and hatching rates of Day 7 blastocysts did not change with retinoid treatment. Within the LG-treated and untreated blastocyst groups, survival and hatching rates were higher for Day 7 than Day 8 embryos; however, Day 8 blastocysts treated with ATRA showed improved hatching rates. In conclusion, treatment of morulae with ATRA in serum-free medium improves embryo development and quality without increasing the incidence of apoptosis and necrosis.

Vitrification of Immature Bovine Oocytes by the Microdrop Method

This study was conducted to determine the optimal vitrification conditions for immature bovine oocytes using the microdrop method. In experiment 1, the optimal pre-equilibration period for microdrop vitrification was examined. The maturation rate of vitrified oocytes with a 3 min first pre-equilibration period (41.1%) was higher than that of vitrified oocytes with a 0 min first pre-equilibration period (21.4%), and the values of those with a 1 (33.9%) or 5 min (27.4%) first pre-equilibration period were intermediate. The value for a 1 min second pre-equilibration period (44.4%) was significantly higher (P<0.05) than those for a 0.5 (28.6%) and 2 min (21.4%) second pre-equilibration period. In experiment 2, the distribution of microtubules in matured oocytes was investigated. There was no difference among the first pre-equilibration times in terms of the rates of normal spindles in vitrified oocytes. However, this value was significantly higher (P<0.05) in the 1 min group (52.8%) compared with the 0.5 (16.7%) and 2 min groups (12.3%). In experiment 3, we investigated the developmental capacity of immature bovine oocytes vitrified under optimal pre-equilibration conditions (3 min and 1 min for the first and second pre-equilibrations, respectively). Although the total fertilization rates were significantly lower (P<0.05) in the vitrified oocytes (65.6%) compared with the control oocytes (92.4%), there was no difference in the rate of normal fertilization (2PN) between the vitrified (78.6%) and control (82.0%) oocytes. Cleavage and blastocyst rates were significantly lower (P<0.05) in vitrified oocytes (55.7 and 2.3%) than in control oocytes (84.4 and 34.7%). Thus, these results indicated that immature bovine oocytes can survive after microdrop vitrification and subsequently can be cultured to mature oocytes capable of undergoing fertilization in vitro and developing into blastocysts.

Cryopreservation of pig granulosa cells: effect of FSH addition to freezing medium

We cryopreserved swine granulosa cells by a slow cooling rate system; FSH was added to the freezing medium to test its effectiveness in protecting the cells. After thawing, proliferative activity, viability, steroidogenesis and apoptosis were tested; moreover, we determined heat shock protein (HSP70) production, to investigate the recovery from stress and superoxide dismutase (SOD) and catalase activity to evaluate a possible impairment of the antioxidant pathway. E2 production was enhanced by cryopreservation in particular with FSH; on the contrary, P4 production was inhibited by the freezing process in particular without FSH. Only the higher FSH concentration (10 ng/ml) stimulated steroid secretion in freshly collected cells; P4 production by cells cryopreserved in the presence and in absence of FSH was increased by both 5 and 10 ng/ml while the lowest concentration was effective in stimulating E2 production only when FSH was added to freezing medium. Freezing did not modify proliferative activity, while apoptosis was higher in frozen than in fresh cells. HSP70 production was lower in cells cryopreserved in presence of FSH, whose antioxidant metabolism was also conserved: SOD and catalase activities were similar to control. In conclusion, cryopreservation does not seem to markedly affect granulosa cells, in particular if they are frozen in presence of FSH; the gonadotrophin somehow improves their performances after thawing, probably stimulating E2 production and the antioxidant metabolism.

Cryopreservation of Bovine Somatic Cell Nuclear-Transferred Blastocysts: Effect of Developmental Stage

The effect of developmental stage on the survival of bovine somatic cell nuclear-transferred blastocysts after freezing and thawing was evaluated. We also investigated how freezing affects nuclear-transferred (NT) embryos and in vitro fertilized (IVF) bovine embryos. Advanced-stage bovine NT blastocysts survived freezing better than early-stage NT blastocysts (86 vs 14%). The trend was similar with IVF embryos (87 vs 30%). At the stages tested, there was no significant difference in the survivability of NT and IVF embryos from advanced (86 vs 87%) or early-stage blastocysts (14 vs 30%). The average survival rate did not differ between NT and IVF bovine embryos (50 vs 51%). The higher survival rate of advanced-stage blastocysts compared to early-stage blastocysts in NT and IVF bovine embryos might be due to their higher cell number. In NT (128 +/- 25 vs 53 +/- 20) and IVF (128 +/- 29 vs 75 +/- 22) groups, advanced-stage blastocysts contained a significantly higher total cell number than early-stage blastocysts. There was no difference in total cell number between advanced-stage NT and IVF blastocysts (128 +/- 25 vs 128 +/- 29), however, early-stage NT and IVF blastocysts (53 +/- 20 vs 75 +/- 22) differed significantly.

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.

Trehalose: a review of properties, history of use and human tolerance, and results of multiple safety studies

This paper contains a review of the history, natural occurrence, human consumption, metabolism, manufacture, and the results of eight standardized animal safety studies using trehalose. Trehalose (alpha,alpha-trehalose) is a naturally occurring sugar containing two D-glucose units in an alpha,alpha-1,1 linkage. Trehalose functions in many organisms as an energy source or a protectant against the effects of freezing or dehydration. It also possesses physical and/or chemical properties that are different than other sugars, which may make trehalose an attractive ingredient in food, health and beauty and pharmaceutical products. Data are presented supporting safe human consumption of trehalose in doses up to 50 g, and the physiologic ability of humans to digest it. No consistent treatment-related, dose-dependent adverse effects were observed in any of the eight safety studies performed at doses up to 10% of the diets. On the basis of these toxicity studies, human studies in which doses of trehalose were administered to various populations, and consumption of trehalose in commercial products in Japan, it is concluded that trehalose is safe for use as an ingredient in consumer products when used in accordance with current Good Manufacturing Practices.

The effect of prefreezing the diluent portion of the straw in a step-wise vitrification process using ethylene glycol and polyvinylpyrrolidone to preserve bovine blastocysts

A total of 678 bovine blastocysts, which had been produced by in vitro maturation, fertilization, and culture, were placed into plastic straws and were vitrified in various solutions of ethylene glycol (EG) + polyvinylpyrrolidone (PVP). Part of the straw was loaded with TCM199 medium + 0.3 M trehalose as a diluent; the diluent portions of the straw were prefrozen to either -30 or -196 degrees C. Then, the embryos suspended in the vitrification solution were pipetted into the balance of the straw and vitrified by direct immersion into liquid nitrogen. For thawing, the straws were warmed for 3 s in air and 20 s in a water bath at 39 degrees C and then agitated to mix the diluent and cryoprotectant solution for 5 min followed by culture in TCM199 + 10% FCS + 5 + microg/ml insulin + 50 microg/ml gentamycin sulfate for 72 h. Variables that were examined were the time of exposure to EG prior to vitrification, the PVP concentration, and the temperature of exposure to EG + PVP prior to vitrification. Survival and hatching rates of the blastocysts exposed to 40% EG in four steps at 4 degrees C were higher than those of embryos exposed in two steps (81.3 +/- 4.3% and 80.2 +/- 3.4% vs 67.6 +/- 4.5% and 71.5 +/- 4.7%, respectively; P < 0.05). The same indices were superior following vitrification-thawing of the blastocysts in 40% EG + 20% PVP than it was in 40% EG + 10% PVP (76.1 +/- 5.5% vs 63.7 +/- 1.8%; P < 0.05; and 61.6 +/- 6.0% vs 70.5 +/- 4.7%; P < 0.01, respectively). Exposure to the vitrification solution (40% EG + 20% PVP) at higher temperatures (37.5 degrees C vs 4 degrees C) reduced both survival and hatching rates (45.8 +/- 6.9% vs 83.9 +/- 4.4% and 41.5 +/- 1.8% vs 64.0 +/- 4.7%, respectively; P < 0.001). These results indicate that blastocysts vitrified after prefreezing the diluent portions of the straws do favor developmental competence of in vitro produced embryos.

Vitrification of the oocytes and embryos of domestic animals

After the first successful application of vitrification for embryo cryopreservation 15 years ago, a rapid application of the method in domestic animal embryology was presumed. However, although the advantages of vitrification (simplicity, cost efficiency, speed of the procedure) were widely acknowledged, its use has been mainly restricted to experimental studies. For commercial embryo transfer purposes, the traditional slow-rate or equilibrium freezing has been used. This review attempts to explain the reasons for this phenomenon and discusses the theoretical and practical differences between the two technologies as well as their commercial prospects. Recent developments that improve the efficiency of vitrification and applications to other reproductive technologies are also summarized. These advances may result in considerable advantage and could lead to widespread application of vitrification in certain areas of domestic animal embryology.

Effects of vitrification medium composition on the survival of bovine in vitro produced embryos, following in straw-dilution, in vitro and in vivo following transfer

This study examined the effects of adding a macromolecule, polyvinylpyrrolidone (10% PVP) and a sugar (0.3 M trehalose) to vitrification solutions (VS) containing either one (40% ethylene glycol [EG], two (25% EG+25% DMSO) or three (20% EG+20% DMSO+10% 1, 3-butanediol [BD]) permeable cryoprotectants on the survival and hatching of IVP bovine embryos, following vitrification, warming and in-straw cryoprotectant dilution. Grade 1 and 2 compact morulae and blastocysts were selected on Day 7 (Day 0=IVF) of culture in SOFaaBSA and equilibrated for 10 min at room temperature in 10% EG. Following exposure, for up to 1 min at 4 degrees C, to one of the above VS (with or without PVP+trehalose), the embryos were loaded into straws and immersed in liquid nitrogen. Following warming and in-straw cryoprotectant dilution, the embryos were cultured for 48 h to assess hatching. There was no effect of VS on the survival of embryos after 24 h, however fewer compact morulae than blastocysts survived after 24 h (24% vs. 75%; P<0.001) or hatched after 48 h (15% vs. 59%; P<0.001). When blastocysts only were considered, an interaction between VS and additional PVP+trehalose was also observed (P<0.01). Hatching was reduced when they were added to 25% EG+25% DMSO (70% vs. 45%) but was not affected for either 40% EG (44 and 49%) or to 20% EG+20% DMSO+10% BD (72 and 72%). Pregnancy rates (Day 90 ultrasound) of recipients that were transferred either two non-vitrified or two vitrified (20% EG+20% DMSO+10% BD) blastocysts, did not differ (3/6 [50%] and 11/20 [55%]). However, significantly (P<0.02) fewer recipients that received compact morulae maintained pregnancy to Day 90 although this was not affected by vitrification (fresh vs. vitrified; 1/5 [20%] vs. 3/18 [17]). These data demonstrate that a VS comprising three cryoprotectants, rather than one, enables more embryos to hatch during post-thaw culture and that the survival, following direct transfer of these vitrified embryos, is not different to non-vitrified embryos.

Cellular alteration after dilution of cryoprotective solutions used for the vitrification of in vitro-produced bovine embryos

Embryo quality of in vitro-produced bovine blastocysts was assessed at several steps of a vitrification procedure in which glycerol and ethylene glycol were used as cryoprotectants (3-step equilibration with cryoprotectants followed by vitrification, dilution of the cryoprotectants in 0.85 M galactose then in embryo transfer freezing medium [ETF], and finally co-culture for periods). To visualize cell membrane alterations, double staining was performed using a cell permeant fluorochrome (bisbenzimide--BIS) and a nonpermeant one (propidium iodide--PI). In Experiment 1, the effect of the vitrification procedure on the hatching rate and total cell number was assessed 72 h after treatment. Hatching rate and the number of stained nuclei were decreased in comparison with untreated embryos when blastocysts were exposed to the whole procedure with or without vitrification (respectively 42 and 53% vs 76% for hatching and 128 +/- 17 and 141 +/- 17 vs 226 +/- 13 for stained nuclei). In Experiment 2, the effect of cryoprotectants and their dilution was evaluated on membrane permeability and total cell numbers at various steps of the vitrification procedure. Blastocysts exposed only to cryoprotectant solutions and stained immediately after dilution in galactose showed no modification. After dilution in ETF, the total number of stained nuclei decreased, and the number of blastomeres showing membrane permeabilization (PI-stained) increased (respectively, 74 +/- 5 vs 110 +/- 5 and 32 +/- 2% vs 0.1 +/- 1.8%). In Experiment 3, we demonstrated that the total number of stained nuclei after ethanol fixation (membrane permeabilization) was higher when embryos treated up to dilution in ETF were stained with PI than when the same embryos were stained with BIS. This suggests that, for unknown reasons, some nuclei of the treated embryos were not stained with BIS. Membrane permeabilization and inability of BIS to stain some nuclei were the most obvious alterations probably induced by osmotic shock at dilution. This hypothesis is supported by the fact that the introduction of a further dilution step in 0.42 M galactose (Experiment 4) before dilution in ETF decreased the proportion of cells permeant to PI and increased the hatching rate after 72 h of co-culture. In conclusion, double staining with BIS and PI allowed for discrimination between different types of cellular injuries after the various steps of our vitrification protocol. It represents a useful tool for adjusting equilibration and dilution conditions during a cryopreservation procedure.

Timing of the first cleavage post-insemination affects cryosurvival of in vitro-produced bovine blastocysts

The time of the first cleavage of bovine zygotes during in vitro culture can affect the rate of development and cell number of the blastocysts. The aim of this work was to study the effect of the timing of first cleavage on the cryosurvival of the resulting blastocysts. Following standard IVM and IVF, zygotes were cultured in modified synthetic oviduct fluid (SOF), with 10% fetal calf serum (FCS) added 48 hr post insemination, in a humidified atmosphere of 5% CO2, 5% O2 and 90% N2. Embryos which cleaved by 24, 27, 30, 33, or 36 hr after insemination (IVF) were harvested and further cultured to the blastocyst stage (day 7 or day 8 post IVF). All developing blastocysts on days 7 and 8 were classified into three groups and were cryopreserved by vitrification. Group A consisted of blastocysts (<150 microm, small blastocysts); group B consisted of expanded or hatching blastocysts (>150 microm, large blastocysts); and group C consisted of morphologically poor quality blastocysts. The vitrification solution consisted of 6.5 M glycerol and 6% bovine serum albumin in PBS (VS3a). Thawed embryos were cultured further and survival was defined as the re-expansion and maintenance of the blastocoel over 24, 48, and 72 hr, respectively. Overall survival and hatching at 72 hr post-thawing was higher in blastocysts formed by day 7 than those formed by day 8 (60% vs. 40% survival; 63% vs. 45% hatching). Large blastocysts from day-7 and day-8 groups survived significantly better than small or poor quality blastocysts (76% vs. 63% and 31%; 72% vs. 30% and 26%, respectively; P < 0.05). Day-7 blastocysts from the 27- and 30-hr cleavage groups survived significantly better than those from the 36-hr group (63% and 66% vs. 25%, P < 0.05). Day-8 blastocysts from later cleaved (30 hr) zygotes had a higher survival than the 27-hr cleavage groups (52% vs. 26%, P < 0.05). These results indicate that the day of blastocyst appearance, developmental stage, and timing of the first cleavage post-insemination can influence the cryosurvival of bovine blastocysts following vitrification.