Fresh and vitrified bovine preantral follicles have different nutritional requirements during in vitro culture

Influence of TCM 199B, α-MEM, Waymouth MB 752/1 culture media, VEGF, Estradiol-17β, GDF-9 and FGF on in vitro development of preantral follicles in sheep

A total of 2792 preantral follicles (PFs') isolated from 750 ovaries of sheep were cultured in four different experiments. The efficacy of three commercially available culture media viz., TCM 199B, α-MEM and Waymouth MB 752/1 on the growth of sheep PFs' was tested in experiment I. Among the three media TCM 199B supported better development of PFs' in culture. The remaining experiments established the best concentrations of vascular endothelial growth factor (VEGF), Estradiol-17β (E2), GDF-9, Fibroblast growth factor (FGF) and their best combinations for the in-vitro development of PFs'. Inclusion of VEGF at 10 ng/mL, Estradiol-17β at 5 ng/mL, GDF-9 at 10 ng/mL or FGF at 10 ng/mL individually in a standard medium (SM) (containing FSH, IGF-I, GH and T4) supported better nuclear maturation of the oocytes to MII stage. Different combinations of VEGF, Estradiol-17β, GDF-9 and FGF supplemented in the SM promoted similar overall follicular growth. However, (a) SM + VEGF(10 ng/mL) + E2(5 ng/mL) supported higher increase in the diameter, (b) SM without any supplements induced antrum formation in greater proportion of follicles, and (c) SM + VEGF(10 ng/mL) + GDF 9(10 ng/mL) or SM + E2 (5 ng/mL) + FGF(10 ng/mL) supported high proportion of oocytes to reach MII stage. To conclude, TCM 199B appeared to be a better medium for development of sheep PFs'. VEGF, Estradiol-17 β, GDF-9 and FGF have beneficial influence on the development of sheep PFs' when supplemented in TCM 199B.

Supportive techniques to investigate in vitro culture and cryopreservation efficiencies of equine ovarian tissue: A review

During the reproductive lifespan of a female, only a limited quantity of oocytes are naturally ovulated; therefore, the mammalian ovary possesses a substantial population of preantral follicles available to be handled and explored in vitro. Hence, the manipulation of preantral follicles enclosed in ovarian tissue aims to recover a considerable population of oocytes of high-value animals for potential application in profitable assisted reproductive technologies (ARTs). For this purpose, the technique of preantral follicle in vitro culture (IVC) has been the most common research tool, achieving extraordinary results with offspring production in the mouse model. Although promising outcomes have been generated in livestock animals after IVC of preantral follicles, the quantity and quality of embryo production with those oocytes are still poor. In recent years, the mare has become an additional model for IVC studies due to remarkable similarities with women and livestock animals regarding in vivo and in vitro ovarian folliculogenesis. For a successful IVC system, several factors should be carefully considered to provide an optimum culture environment able to support the viability and growth of preantral follicles enclosed in ovarian tissue. The cryopreservation of the ovarian tissue is another important in vitro manipulation technique that has been used to preserve the reproductive potential in humans and, in the future, may be used in highly valuable domestic animals or endangered species. Several improvements in cryopreservation protocols are necessary to support the utilization of ovarian tissue of different species in follow-up ARTs (e.g., ovarian fragment transplantation). This review aims to provide an update on the most current advances regarding supportive in vitro techniques used in equids to evaluate and manipulate preantral follicles and ovarian tissue, as well as methodological approaches used during IVC and cryopreservation techniques.

Advances in in vitro folliculogenesis in domestic ruminants

The in vitro follicle culture (IVFC) represents an outstanding tool to enhance our understanding of the control of folliculogenesis and to allow the future use of a large number of immature oocytes enclosed in preantral follicles (PFs) in assisted reproductive techniques in humans as well as in others mammalian species including the ruminants. So far, the best results of IVFC were reported from mice with the production of live offspring from primordial follicles cultured in vitro. Live birth has been obtained after the in vitro culture of bovine early antral follicles. However, in other ruminant species, these results have been limited to the production of a variable number of mature oocytes and low percentages of embryos after in vitro culture of goat, buffalo and sheep isolated secondary preantral follicles. The present review presents and discusses the main findings, limitations, and prospects of in vitro folliculogenesis in ruminants focusing on bovine, caprine, and ovine species.

Impacts of different synthetic polymers on vitrification of ovarian tissue

Type and concentration of cryoprotective agents (CPAs) are important factors which influence the likelihood of a successful ovarian tissue vitrification outcome. In an attempt to address this factor, the present study was conducted to evaluate the impacts of different synthetic polymers (Supercool X-1000, Supercool Z-1000 and PVP K-12) on vitrification of bovine ovarian tissue. From each ovarian pair, fragments were recovered and immediately fixed for analysis (fresh control) or submitted to vitrification, either or not followed by in vitro culture for one or five days. Vitrification was performed using the ovarian tissue cryosystem (OTC) system. The ovarian tissues were intended for histological and viability analysis [Reactive oxygen species (ROS) production and degenerate cells assay (Ethidium homodimer-1)], as well as immunolocalization of AQP3 and AQP9 were measured. The results showed that during almost all the periods after warming, in treatment groups which contain polymer (X-1000, Z-1000 and PVP), the percentage of morphologically normal follicles was the highest in the X-1000 samples. Furthermore, post-thawed X-1000 group revealed stronger labeling for AQP9 in primordial and transitional follicles, when compared with others. However, morphology after cryopreservation did not correlate with follicle viability and function where the levels of degeneration and tissue damage of PVP K-12 group were lower in comparison with X-1000 group and only in PVP K-12 group, ROS level was similar to that of the fresh control group. We believe that in addition to permeating CPAs, the addition of one (Supercool X-1000) or maybe a combination (Supercool X-1000 and PVP K-12) of non-permeating polymers could be useful to improve the outcome for vitrified bovine ovarian tissue.

Early ovine preantral follicles have a potential to grow until antral stage in two-step culture system in the presence of aqueous extract of Justicia insularis

The objective of this study was to determine whether preantral follicles cultured in vitro for 7 days within ovine ovarian cortical strips could be isolated at the secondary follicles (SF) and grown until antral stage during an additional 6 days period of in vitro culture in the presence of aqueous extract of Justicia insularis. Fresh ovarian fragments from 16 adult sheep were fixed for histological analysis (Control 1) or in vitro cultured individually in α-MEM⁺ supplemented with 0.3 mg/ml J. insularis (Step 1) for 7 days. Part of the fragments then were fixed for histological analysis (in vitro culture group). Remaining fragments were exposed stepwise to increasing trehalose concentrations before immediate isolation of SF and viability assessment (Control 2) or after 6 days of culture in α-MEM⁺⁺ supplemented with 0.3 mg/ml J. insularis (Step 2). In Step 1, percentage of follicular activation was 80%. In Step 2, a significant increase (p < 0.05) in follicular diameter and antrum formation within 6 days in vitro culture of isolated follicles was achieved. The total antioxidant capacity from both steps significantly increase (p < 0.05) from day 2 to day 6. Confocal analysis of oocytes showed 57.14% oocytes with homogeneous distribution and 42.86% with peri-cortical distribution. In conclusion, SF can be successfully isolated from sheep ovarian cortex after 7 days of culture and are capable of surviving and forming an antral cavity if cultured in vitro for an additional 6 days in the presence of 0.3 mg/ml J. insularis.

Effects of new synthetic cryoprotectant agents on histological characteristics of various classes of vitrified bovine pre-antral follicles

Previous studies have reported many discrepancies about the best type and concentration of cryoprotective agents (CPAs) and biological variability among various pre-antral follicle classes after cryopreservation of ovarian tissue. The aim of this study was to investigate the impacts of some synthetic polymers on histological characteristics of different types of pre-antral follicles after bovine ovarian tissue vitrification. From each bovine ovarian pair, fragments were recovered and immediately fixed for analysis (fresh control group) or submitted to vitrification (sucrose, X-1000, Z-1000 and polyvinylpyrrolidone groups), either followed by in vitro culture for 1 or 5 days. In this case, although, the addition of X-1000 resulted in greater percentages of normal follicles for almost all pre-antral follicle classes compared to those of other groups, there are some exceptions. These results indicate that the inclusion of polyvinylpyrrolidone in the freezing media can improve the morphology of the post-warmed transitional follicles and cultured primordial follicles on day five more than other CPAs. According to the results of this study, it can be concluded that although ovarian tissue cryopreservation is often performed to preserve the primordial follicles, by choosing the best combination of permeating and non-permeating CPAs (synthetic polymers), more advanced stages of bovine pre-antral follicles, transitional, primary and secondary follicles, may also survive the cryopreservation process.

Comparison of vitrification and conventional slow freezing for cryopreservation of ovarian tissue with respect to the number of intact primordial follicles: A meta-analysis

BACKGROUND

Vitrification is the standard method for cryopreserving human oocytes and embryos, but its effects on ovarian tissue are uncertain. The purpose of this meta-analysis was to compare the proportion of intact primordial follicles in ovarian tissue cryopreserved with vitrification versus slow freezing.

METHODS

Medline, Cochrane, EMBASE, and Google Scholar databases were searched until November 11, 2014 using combinations of the search terms: ovarian tissue, cryopreservation, vitrification, follicle, follicles. Inclusion criteria were randomized controlled trails, two-arm prospective studies, and retrospective studies in which ovarian tissues were preserved by vitrification or conventional slow freezing. The primary outcome was the proportion of intact primordial follicles.

RESULTS

Six studies were included in the meta-analysis. The number of patients ranged from 3 to 20, and age ranged from 20 to 43 years. Total number of morphologically intact follicles ranged from 14 to 2058, among which 6 to 724 were primordial. The pooled odds ratio (OR) showed no significant difference in the proportion of intact primordial follicles after slow freezing or vitrification (OR = 1.228, 95% confidence interval [CI]: 0.769-1.961, P = 0.390). Sensitivity analysis using the leave-one-out approach indicated no considerable changes in the direction and magnitude of the pooled estimates when individual studies were excluded one at a time, indicating good reliability of the current analysis.

CONCLUSIONS

Vitrification and slow freezing produce equivalent results with respect to intact primordial follicles for the cryopreservation of human ovarian tissue. However, the included studies varied in the cryopreservation protocols used.

The preservation of vital functions in cat ovarian tissues during vitrification depends more on the temperature of the cryoprotectant exposure than on the sucrose supplementation

The objective of this study was to better characterize the impact of cryoprotectant exposure (temperature and sucrose supplementation) on the health and function of preantral follicles in ovarian tissues during vitrification using the domestic cat model. Ovarian cortical pieces from peri-pubertal individuals were exposed to cryoprotectants at 4 °C or room temperature and supplemented with 0 or 0.5 M of sucrose, followed by vitrification. After rapid warming, cortical pieces were cultured in vitro and assessed for normal follicular morphology, viability and resumption of transcriptional activities for up to 7 days. Throughout the culture period, follicular morphology (up to 67.5% normal follicles) and global RNA transcription (up to 50.9% follicles with transcriptional activity) in warmed tissues were improved by cryoprotectant exposure at 4 °C compared to room temperature, but viability (up to 84.6% viable follicles) did not seem to be affected by exposure temperature. Sucrose supplementation did not have a consistent effect as it increased RNA transcription but decreased normal follicular morphology. For the first time, the study demonstrated that the preservation of critical tissue functions, such as the transcriptional activities, highly depends on the temperature of the cryoprotectant exposure and not necessarily on the presence of sucrose.

Damage to fetal bovine ovarian tissue caused by cryoprotectant exposure and vitrification is mitigated during tissue culture

PURPOSE

The objective of this study is to characterize the impact of exposure to cryoprotectants followed by vitrification on primordial follicle survival and activation using a fetal bovine model.

METHODS

In the first study, fetal bovine cortical pieces were exposed to cryoprotectants with or without sucrose and cultured up to 7 days in the presence or absence of insulin. In the second study, cortical pieces were exposed to cryoprotectants with or without sucrose, vitrified, and cultured up to 7 days after warming in the presence or absence of insulin. Viability and morphology of follicles, as well as proliferation and/or DNA repair in ovarian tissue were analyzed.

RESULTS

When compared to non-exposed controls, normal follicular morphology was affected in groups exposed to cryoprotectants only immediately post-exposure and after 1 day of culture, but improved by day 3 and did not significantly differ by day 7. Similarly, normal follicular morphology was compromised in vitrified groups after warming and on day 1 compared to controls, but improved by days 3 and 7. Proliferation and/or DNA repair in ovarian tissue was not affected by vitrification in this model. Cryoprotectant exposure and vitrification of ovarian tissue did not impair the activation of primordial follicles in response to insulin, although activation was delayed relative to non-exposed controls. Interestingly, sucrose had no noticeable protective effect.

CONCLUSION

Vitrified fetal bovine ovarian tissue has the intrinsic capacity to mitigate the immediate damage to primordial follicles' morphology and retains the capacity to activate. These findings provide a basis for a successful cryopreservation protocol for ovarian cortical tissue in other species including humans.