Detailed Morphological Analysis of Cryoinjury in Human Ovarian Tissue Following Vitrification or Slow Freezing

Cryopreservation of human ovarian tissue represents a key procedure for fertility preservation. The two most widely used cryopreservation methods for human ovarian cortex samples are slow freezing\thawing (SF\T) and vitrification\warming (V\W). The aim of the present study was to analyze the effects of SF\T and V\W using a metal chamber, on specific follicle and oocyte structures and on the stromal organization post-cryopreservation. We did histology analysis of SF\T and V\W ovarian fragments from nine healthy subjects. Overall results showed that cryopreserved tissues presented significant rates of damage in primordial and primary follicles. Altered nuclear structure of primordial follicles and cell detachment from primordial and primary follicles were the main injuries observed after V/W and SF/T. The stromal components were similarly well preserved after cryopreservation. We conclude that both cryopreservation methods may be used for fertility preservation purposes with similar outcomes in terms of follicular and stromal integrity. Detachment of follicle cells from basal membrane represents an important cryoinjury that deserves further investigation.

132 VITRIFICATION SYSTEM (OPEN AND CLOSED) IN NEW INCUBATOR WITH REDUCED OXYGEN

Most IVF laboratories uses high oxygen tension (20%) during embryonic culture. However, it is known that under physiological conditions, oxygen tension in the female reproductive tract ranges between 2 and 8%. Therefore, the aim of this study was to evaluate survival and hatching rate after in vitro culture of vitrified/thawed bovine in vitro-produced blastocysts cultured under different oxygen concentrations. The experiment consisted of comparing 2 culture systems using different concentrations of oxygen: conventional incubator (20% O2, Thermo Scientific, model 3130) and a new incubator (5% O2, WTA Watanabe Tecnologia Aplicada, model Eve). Only Day 7 expanded blastocysts grade 1 were used. Embryos were produced according to conventional IVF protocols. Briefly, cumulus-oocyte complexes were aspirated from postmortem ovarian follicles, matured in TCM199 + 10% FCS + 0.5 mg FSH mL–1 + 50 mg LH mL–1 + 1 mg oestradiol mL–1, for 24 h at 38.5°C, 5% CO2 in air. Live spermatozoa from Nellore bull were obtained by centrifugation in Percoll gradients (45 and 90%) and cultured with cumulus-oocyte complexes at 1 million of sperm mL–1 in TALP medium + 10 mg of heparin mL–1. After 20 h incubation, zygotes were transferred to CR2 + 2.5% FCS + 4 mg of BSA mL–1 and granulosa monolayer for 7 days. Expanded blastocysts were randomly allocated to 2 treatments for vitrification (open system – cryotop and closed system – HSV Kit, IMV-Technologies) using the same vitrification media and protocol (VS1: 10% ethylene glycol + 10% dimethyl sulfoxide and VS2: 20% ethylene glycol + 20% dimethyl sulfoxide for 8 min and 50 s, respectively). After exposure to the vitrification solutions, 2 embryos were loaded/straw, and the straws were plunged into LN. The warming procedure consisted of, immediately after removal from LN2, transferring the embryos in 2 successive warming solutions with decreased concentrations of sucrose (1 M and 0.50 M for 5 min each). The vitrified/rewarmed embryos were transferred to in vitro culture. There were no differences in survival rates (P < 0.05) between the open and closed vitrification system for blastocysts produced in reduced oxygen in the Eve incubator – 5% O2 (96% – 109/114 and 98% – 158/161, respectively) compared with embryos produced in the high oxygen environment in the Thermo incubator – 20% O2 (93% – 214/230 and 92% – 94/102, respectively). Hatching rates were increased for blastocysts cultured in the lower oxygen environment (EVE treatment: 95 and 98%, respectively, for open and closed vitrification protocols) when compared with the high oxygen environment (Thermo treatment: 86 and 87%, respectively, for open and closed systems); P < 0.05. In vitro culture in a reduced-oxygen environment improves blastocysts competence after vitrification. Financial support was received from CNPq-RHAE.

360 EMBRYONIC DEVELOPMENT AND STEROIDOGENESIS OF BOVINE CUMULUS - OOCYTE COMPLEXES MATURED IN α-MEM MEDIUM SUPPLEMENTED WITH PVA OR PVP-40

The influence of the culture medium and its supplements on IVM and steroid secretion by bovine COCs was examined. Immature COCs were matured for 24 h in a-MEM supplemented with IGF-1 (10 ng mL-1), insulin (100 ng mL-1) and 0.1% polyvinyl alcohol (PVA; Sigma Chemical Co., St. Louis, MO, USA) or 0.1% polyvinylpyrrolidone-40 (PVP; molecular weight of 40 000; Sigma). Neither FSH nor LH was used in either treatment. The control group consisted of COCs matured in TCM supplemented with FSH (20 μg mL-1) and 10% estrous cow serum. After fertilization, presumptive zygotes were co-cultured with cumulus cells until 224 h post-insemination. Steroid production was measured in culture medium after IVM and cumulus cells (CC) aromatase activity was estimated by estradiol (E2) production and by the determination of the ratio of E2 to testosterone (T). Cleavage, blastocyst, and hatching rates were evaluated 168-224 h post-insemination. Hormone determination data were analyzed using the GraphPad 5.0 for Windows software (GraphPad Software, San Diego, CA, USA). The means and standard deviations were first calculated for all variables, followed by the Kolmogorov-Smirnov normality test. Since the values were not normally distributed, the treatments were compared by the Kruskal-Wallis test. Blastocyst formation, cleavage, and hatching rates were analyzed by the chi-square test. The level of significance was set at P < 0.05 in all analyses. High aromatase activity (E2:T ratio > 1.0) was detected in the culture medium of both chemically defined IVM systems. E2 concentrations were 22.86 ng mL-1 and 22.46 ng mL-1 for PVA and PVP-40, respectively, and 0.27 ng mL-1 (P < 0.001) for the control group. Progesterone secretion was lower in a-MEM + PVP-40 medium. Testosterone was not secreted by COCs matured in control medium. There was a significantly higher cleavage rate in the control group, but no differences (P > 0.05) in blastocyst (48.92%, 49.56%, and 44.21%) or hatching (38.46%, 41.96%, and 40.78%) rates between the PVA, PVP, and control groups, respectively. Our results show that CC of COCs cultured in serum-supplemented medium show decreased aromatase activity. Also, the addition of IGF-I/insulin and PVA or PVP-40 to IVM medium had no significant effect on the rates of oocyte maturation and embryonic development when compared with results obtained in medium supplemented with estrous cow serum and FSH. Supported by FAPESP/FAEPA-HCFMRP/USP.

Early cleavage of human embryos: an effective method for predicting successful IVF/ICSI outcome

BACKGROUND

The need for effective parameters for selecting the best embryos is paramount when a large number of them are available for transfer. Other studies have reported that transfer of pre-selected embryos, based on cleavage to the 2-cell stage at 25 h and 27 h post-insemination/intracytoplasmic sperm injection (ICSI), increases implantation and pregnancy rates. We investigated whether extending the time for selection of cleaved embryos to 29 h post-insemination/ICSI had a similar effect on pregnancy and implantation rates.

METHODS

Cleavage to the 2-cell stage was assessed at 25, 27 and 29 h post-insemination/ICSI. Embryos that had cleaved at any of these time points were designated as 'early cleavage' (EC), while others were designated as 'non-early cleavage' (NEC). EC embryos were selected and preferentially transferred.

RESULTS

EC occurred in 57% of the cycles (61% IVF; 51% ICSI). Significantly (P = 0.02) more clinical pregnancies occurred in the EC group (23/42, 55%) compared with the group that had no embryo undergoing first cleavage up to 29 h post-insemination/ICSI (8/32, 25%). The EC group of patients was significantly younger than the NEC.

CONCLUSION

Transfer of selected embryos that reached the 2-cell stage between 25 and 29 h post-insemination/ICSI is a reliable prognostic tool for patients undergoing assisted reproduction techniques.

Meiotic and mitotic Ca2+ oscillations affect cell composition in resulting blastocysts

At fertilization periodic Ca2+ oscillations release oocytes from meiotic arrest. The present study examined whether these oscillations have a long-term role in pre- and postimplantation development, independent of their immediate effect. Sr(2+)-containing medium was used to induce oscillations during exit from meiosis and first embryonic mitosis and Sr(2+)-activated parthenotes were compared to ethanol-activated parthenotes and embryos generated by in vitro fertilization. After embryo culture, blastocysts were differentially stained for the inner cell mass and trophectoderm. It was found that oscillations both during exit from meiosis and during mitosis acted to increase the number of inner cell mass cells. In contrast, the trophectoderm cell number was largest in ethanol-activated parthenotes and smallest in fertilized embryos. Postimplantation development was also modestly improved by extending the time of exposure to Sr(2+)-containing medium. Together these data suggest that Ca2+ oscillations have a role in long-term embryonic events and that they provide more than merely a stimulus for meiotic resumption.

A cell cycle-associated change in Ca2+ releasing activity leads to the generation of Ca2+ transients in mouse embryos during the first mitotic division

We have used Ca2+-sensitive fluorescent dyes to monitor intracellular Ca2+ during mitosis in one-cell mouse embryos. We find that fertilized embryos generate Ca2+ transients at nuclear envelope breakdown (NEBD) and during mitosis. In addition, fertilized embryos arrested in metaphase using colcemid continue to generate Ca2+ transients. In contrast, parthenogenetic embryos produced by a 2-h exposure to strontium containing medium do not generate detectable Ca2+ transients at NEBD or in mitosis. However, when parthenogenetic embryos are cultured continuously in strontium containing medium Ca2+ transients are detected in mitosis but not in interphase. This suggests that mitotic Ca2+ transients are detected in the presence of an appropriate stimulus such as fertilization or strontium. The Ca2+ transient detected in fertilized embryos is not necessary for inducing NEBD since parthenogenetic embryos undergo nuclear envelope breakdown (NEBD). Also the first sign that NEBD is imminent occurs several minutes before the Ca2+ transient. The Ca2+ transient at NEBD appears to be associated with the nucleus since nuclear transfer experiments show that the presence of a karyoplast from a fertilized embryo is essential. Finally, we show that the intracellular Ca2+ chelator Bapta inhibits NEBD in fertilized and parthenogenetic embryos in a dose-dependent manner. These studies show that during mitosis there is an endogenous increase in Ca2+ releasing activity that leads to the generation of Ca2+ transients specifically during mitosis. The ability of Ca2+ buffers to inhibit NEBD regardless of the presence of global Ca2+ transients suggests that the underlying cell cycle-associated Ca2+ releasing activity may take the form of localized Ca2+ transients.

Analysis of the chromosome complement of frozen-thawed mouse oocytes after parthenogenetic activation

Frozen-thawed mouse oocytes were artificially activated with Sr2+ and analyzed cytogenetically at the first cleavage division to examine the behavior of the maternal chromosomes independently of the paternal complement. There was no significant difference in the rate of activation between frozen-thawed and freshly collected oocytes and the majority of oocytes (> 90%) had a normal haploid chromosome constitution. The incidence of second polar body retention in frozen-thawed oocytes was low and did not differ significantly from that observed in fresh oocytes and oocytes exposed to dimethylsulfoxide (DMSO) at 0 degree C or 37 degrees C for extended periods beyond those required for protection. The frequency of aneuploidy was similar for frozen-thawed and fresh oocytes but oocytes held at 0 degree C without DMSO or held at 37 degrees C with DMSO for 1 hr showed a 2.5 and 12-fold increase in the frequency of aneuploidy compared with oocytes subjected to a conventional oocyte/embryo freezing regime. It is concluded that the procedures used in successful oocyte cryopreservation do not increase the incidence of chromosomal abnormalities of maternal origin in the resulting embryos.

Cytogenetical analysis and developmental potential of vitrified mouse oocytes

Mature mouse oocytes were cryopreserved by vitrification in 6 M dimethyl sulfoxide (VS). After warming they were either artificially activated with strontium (Sr2+), and the incidence of chromosome non-disjunction was assessed at first cleavage metaphase; or they were fertilized in vitro, and postimplantation survival was examined at Day 15 of gestation. Similar proportions of vitrified and freshly collected oocytes were activated with Sr2+ (75% and 82%, respectively). The majority of activated oocytes extruded the second polar body and formed a single pronucleus ( > 90%). When the exposure time to VS was increased from 90 to 110 sec without cooling, a significant proportion of activated oocytes arrested at the pronuclear stage (30%), and chromosome condensation did not occur. The frequency of aneuploidy in vitrified and control oocytes was similar, but when exposure to VS without cooling was extended, aneuploidy and second polar body retention were significantly higher than those of controls (p < 0.05). The rates of fertilization of vitrified (85%) and control oocytes (92%) did not differ. After transfer, similar proportions of vitrified and control embryos implanted (68-80%) and formed normal fetuses (38-49%). We conclude that vitrification in 6 M dimethyl sulfoxide is a simple and safe procedure for the preservation of mouse oocytes provided that the time of exposure to the cryoprotectant is carefully controlled.

Calcium oscillations and protein synthesis inhibition synergistically activate mouse oocytes

We have examined the ability of the two parthenogenetic agents, strontium (Sr2+) and cycloheximide, to activate mouse oocytes. We demonstrate that Sr2+ and cycloheximide act synergistically to promote parthenogenetic activation up to the pronuclear stage in oocytes collected immediately after ovulation. These two agents appeared to act independently, since incubation in Sr2+ media triggered a series of intracellular Ca2+ rises without affecting protein synthesis and cycloheximide inhibited protein synthesis without causing any intracellular Ca2+ changes. In addition, cycloheximide did not alter the pattern of Ca2+ oscillations induced by Sr2+. In contrast, we show that another commonly used parthenogenetic activation treatment, the Ca2+ ionophore A23187, has dual effects. Exposure of oocytes to the Ca2+ ionophore, A 23187, in Ca(2+)- and Mg(2+)-free medium leads to the activation of young oocytes. However, as well as generating a Ca2+ increase, the treatment of mouse oocytes with A23187 and Ca(2+)- and Mg(2+)-free media led to a marked inhibition of protein synthesis. Our data show that parthenogenetic agents may have two important loci for activating mammalian oocytes and that the combined effect on Ca2+ release and protein synthesis is most effective.