Evaluation of sheep ovarian tissue cryopreservation with slow freezing or vitrification after chick embryo chorioallantoic membrane transplantation

Human ovarian cryopreservation: vitrification versus slow freezing from histology to gene expression

Cryopreservation of ovarian tissue is one of the strategies offered to girls and women needing gonadotoxic treatment to preserve their fertility. The reference method to cryopreserve is slow freezing; vitrification is an alternative method. The aim was to evaluate which of the two is the best method for human ovarian tissue cryopreservation. Each ovary was divided into three groups: (i) fresh; (ii) slow freezing; and (iii) vitrification. An evaluation of the follicular density, quality and the expression six genes (CYP11A, STAR, GDF9, ZP3, CDK2, CDKN1A) were performed. We observed no significant difference in follicular density within these three groups. Slow freezing altered the primordial follicles compared to the fresh tissue (31.8% vs 55.9%, p = 0.046). The expression of genes involved in steroidogenesis varied after cryopreservation compared to the fresh group; CYP11A was under-expressed in slow freezing group (p = 0.01), STAR was under-expressed in the vitrification group (p = 0.01). Regarding the expression of genes involved in cell cycle regulation, CDKN1A was significantly under-expressed in both freezing groups (slow freezing: p = 0.0008; vitrification: p = 0.03). Vitrification had no effect on the histological quality of the follicles at any stage of development compared to fresh tissue. There was no significant difference in gene expression between the two techniques.

Ischemia and vasculogenesis after transplantation of frozen and vitrified human ovarian tissue onto Chick Embryo Chorioallantoic Membrane (CAM)

OBJECTIVES

The first days of post-ovarian transplantation are critical periods, as the ischemic injury can diminish the success rate. In this study, the first day's events of ovarian transplantation in two dimensions of structure and ultrastructure following slow freezing and vitrification were assessed.

STUDY DESIGN

Ovarian tissues (OTs) from 10 cancerous patients were frozen in two methods of slow freezing and vitrification. Tissues were transplanted onto the CAM and then retrieved at 5 and 10 days of culture. Nine groups were assigned as follows; I-III; fresh, 5 and 10 days culture, IV-VI; vitrification, 5 and 10 days culture, and VII-IX; slow freezing, 5 and 10 days culture. Structural and ultra-structural studies were done to assess the tissue viability and integrity following CAM transplantation. Image J software was used to measure the amounts of fibrosis and necrosis.

RESULTS

The first sign of successful transplantation was found on day 3 post-transplantation. Vitrified tissues showed higher viability and transplantation rate compared to the slow frozen group (65% vs 57.5%) (p = 0.7). Tissue fibrosis and areas didn't increase significantly after cryopreservation using two methods (p > 0.05). The areas of fibrosis and necrosis and avian vessels increased significantly after 5 and 10 days of culture (p < 0.05). Large ultra-structural follicular deformities were noticed after 10 days of CAM transplantation. Better stromal ultrastructure features can be found after vitrified tissue culture. Also, the CAM transplantation technique had negative effects on the integrity of follicles, independent of the freezing procedure.

CONCLUSION

Evaluation of early events of the ovarian post-transplantation is of amount importance, since the hypoxia during this period may accelerate follicular pool depletion, before the tissue stability. Vitrification can be considered a reliable alternative for slow freezing. CAM transplantation is a good technique for confirmation of tissue viability after warming but damaged the follicle ultrastructure in a short period.

Ultrastructure of human ovarian tissues and risk of cancer cells re-implantation after transplantation to chick embryo chorioallantois membrane (CAM) following vitrification or slow freezing

Ovarian follicle depletion and premature ovarian failure are significant challenges in cancer patients subjected to radio- or chemotherapy. Ovarian tissue (OT) cryopreservation would be an option when other fertility preservation methods are not accessible. This study aimed to analyze the structure and ultrastructure of human OTs transplanted onto chick embryo chorioallantois membrane (CAM) after cryopreservation by vitrification or slow freezing. OTs from 10 cancer patients underwent cryopreservation. CAM transplantation was done on fresh and cryopreserved OTs, to assign samples to nine study groups as follows: 1) FI-FIII = fresh, 5- and 10-days post-CAM transplantation groups; 2) VI-VIII = vitrified, 5- and 10-days post-transplantation vitrified groups; 3) SFI-SFIII: slow frozen, 5- and 10-days post-transplantation slow freezing groups. Proliferation ability, folliculogenesis, and structural and ultrastructure were analyzed. The density of primordial follicles did not change after both freezing methods, but reduced after 5 (P ≥ 0.05) and 10 days (P ≤ 0.05) post-CAM transplantation. The follicular grade significantly decreased in all transplanted tissues (P ≤ 0.0). The proliferation marker increased after cryopreservation, but reduced after transplantation (P ≤ 0.05). TEM evaluation showed better follicular ultrastructure in the fresh group, after transplantation. Stromal ultrastructure appeared more preserved after vitrification compared with slow freezing. There was no sign of malignant cell contamination after transplantation. Some follicular TEM abnormalities were found in both methods of freezing, with a better transplantation rate after vitrification. Also, enhanced follicular activation resulted in faster follicular depletion in this method. The information regarding post grafting events would improve our knowledge for longer OTs' lifespans.

Proliferating cell nuclear antigen presentation, as a marker of folliculogenesis, in the transplanted ovarian tissue

AIM

One of the most important ways to understand the ovarian biology is studding the initiation of primordial follicle development and subsequent folliculogenesis control. In this study, proliferating cell nuclear antigen (PCNA) presentation was used as a marker of follicular development in the thawed ovarian tissue (OT) following transplantation onto chick embryo chorioallantoic membrane (CAM) using two methods of freezing of slow freezing and vitrification.

METHODS

Samples of OT from 10 patients were subjected to slow freezing and vitrification. After warming, CAM transplantation was done and PCNA proliferation index (PI; percent of PCNA-positive granulosa cells) was calculated for each follicle stage. Image J software was used to determine the mean staining intensity.

RESULTS

PCNA was positive for granulosa cells and oocytes nuclei, but negative for ooplasm. There were no remarkable PCNA staining in the granulosa cells of primordial follicles, but increased significantly as follicle progression (p < 0.05). Proliferation rate was also insignificantly higher in the vitrified than slow freezing group, before and after transplantation (p < 0.05). Lower PCNA presentation index was observed after CAM transplantation (p < 0.05). The earliest stage of follicular recruitment took place in the transitional follicles, before squamous cells transform to cuboidal cells.

CONCLUSION

PCNA showed that follicles had proliferation power after cryopreservation. Higher presentation after vitrification may indicate accelerated folliculogenesis in the thawed OT.

Cellular and Molecular Impact of Vitrification Versus Slow Freezing on Ovarian Tissue

Objective: To evaluate a vitrification protocol from histology to gene expression to slow freezing. Methods: Ovaries from 12 prepubertal ewes. The same ovary was cut into fragments, studied fresh, frozen, and vitrified. Follicle morphology by hematoxylin-eosin-safran staining, vitality by Trypan Blue, and apoptosis by marking cleaved caspase-3 were studied. The expression of gene: anti-Müllerian hormone (AMH), cytochrome p450 family 11 subfamily A member 1 (CYP11A), and steroidogenic acute regulatory protein (STAR; granulosa cells); growth differentiation factor 9 (GDF9) and zona pellucida glycoprotein 3 (ZP3; oocytes); and cyclin D2 (CCND2) and cyclin-dependent kinase inhibitor 1A (CDKN1A; cell cycle regulation), was evaluated by reverse transcription quantitative polymerase chain reaction. Results: The slow freezing protocol had a significant negative impact on intact primordial follicles compared with fresh tissue (37.6% vs. 62.5%, p = 0.003). More intact follicles after vitrification were observed compared with slow freezing (p = 0.037). The apoptotic primordial follicles were similar after slow freezing and vitrification (12.6% vs. 13.9%). Concerning granulosa cell genes, slow freezing led to a trend toward overexpression of AMH messenger RNA (mRNA; p = 0.07); while vitrification led to a significant overexpression of CYP11A mRNA (p = 0.003), and a trend toward an overexpression of STAR mRNA (p = 0.06). Concerning oocyte genes, both techniques did not lead to a difference of GDF9 and ZP3 mRNA. Concerning cell cycle genes, slow freezing led to a significant underexpression of CCND2 (p = 0.04); while vitrification did not lead to a difference for CCND2 and CDKN1A mRNA. Conclusion: Vitrification preserved follicular morphology better than slow freezing and led to gene overexpressed, while slow freezing led to gene underexpressed. Impact statement The preservation of female fertility and in particular the cryopreservation of ovarian tissue (OT) is a major public health issue aimed at improving the quality of life of patients after gonadotoxic treatments. The use of slow freezing of this OT, which is the reference technique, is not optimal due to tissue alteration. The alternative would be vitrification. This study compares these two techniques. We have highlighted that vitrification preserved follicular morphology better than slow freezing and led to gene overexpressed, while slow freezing led to gene underexpressed.

Antifreeze Protein Supplementation During the Warming of Vitrified Bovine Ovarian Tissue Can Improve the Ovarian Tissue Quality After Xenotransplantation

The occurrence of ice crystallization during ovarian tissue (OT) cryopreservation causes unavoidable cryodamage, and ice recrystallization during the warming is more detrimental than ice crystallization. Here, we investigated that antifreeze protein (AFP) treatment during the warming procedure can improve the bovine OT quality after xenotransplantation (XT). Bovine OTs (n=120) were evenly assigned to four groups: fresh, vitrified-warmed, vitrified-warmed with 10 mg/mL Leucosporidium ice-binding protein (LeIBP, a type of AFP) (LeIBP-10), and vitrified-warmed with 20 mg/mL LeIBP (LeiBP-20). LeIBPs were added to the first warming solution. Twenty pieces of OTs were assigned to each category. The remaining 10 OTs from each category were assigned to the XT-Fresh control, XT-Vitrified-warmed control, XT-LeIBP-10, and XT-LeIBP-20 groups, respectively, and xenotransplanted to 9-week-old ovariectomized nude mice for one week. LeIBP treatment during the warming step increased morphological follicle normality and decreased apoptotic follicle ratios after vitrification-warming and XT. The XT-vitrified-warmed control group showed significantly reduced microvessel density and increased fibrosis when compared to that of the XT-fresh group. Microvessel density and fibrosis were recovered in both LeIBP treated groups. There was no significant difference between the LeIBP-10 and LeIBP-20 groups in all outcomes. AFP treatment during the warming procedure can prevent OT damage, and improve ovarian follicle morphology and apoptosis in both the vitrified-warmed bovine OT and its graft. After confirmation in a human study, AFPs can potentially be applied to human OT cryopreservation to reduce cryodamage and improve the OT quality.

Construction and cryopreservation of an artificial ovary in cancer patients as an element of cancer therapy and a promising approach to fertility restoration

The proportion of cancer patients that survive is increasing because of improvements in cancer therapy. However, some cancer treatments, such as chemo- and radio-therapies, can cause considerable damage to reproductive function. The issue of fertility is paramount for women of childbearing age once they are cured from cancer. For those patients with prepubertal or haematogenous cancer, the possibilities of conventional fertility treatments, such as oocyte or embryo cryopreservation and transplantation, are limited. Moreover, ovarian tissue cryopreservation as an alternative to fertility preservation has limitations, with a risk of re-implanting malignant cells in patients who have recovered from potentially fatal malignant disease. One possible way to restore fertility in these patients is to mimic artificially the function of the natural organ, the ovary, by grafting isolated follicles embedded in a biological scaffold to their native environment. Construction and cryopreservation of an artificial ovary might offer a safer alternative option to restore fertility for those who cannot benefit from traditional fertility preservation techniques. This review considers the protocols for constructing an artificial ovary, summarises advances in the field with potential clinical application, and discusses future trends for cryopreservation of these artificial constructions.

In vitro survival of follicles in prepubertal ewe ovarian cortex cryopreserved by slow freezing or non-equilibrium vitrification

PURPOSE

Vitrification is a well-accepted fertility preservation procedure for cryopreservation of oocytes and embryos but little is known regarding ovarian tissue, for which slow freezing is the current convention. The aim of the present study was to assess the efficiency of non-equilibrium vitrification compared to conventional slow freezing for ovarian cortex cryopreservation.

METHODS

Using prepubertal sheep ovaries, the capacity of the tissue to sustain folliculogenesis following cryopreservation and in vitro culture was evaluated. Ovarian cortex fragments were cultured in wells for 9 days, immediately or after cryopreservation by conventional slow freezing or non-equilibrium vitrification in straws. During culture, follicular populations within cortex were evaluated by histology and immunohistochemistry for PCNA and TUNEL. Steroidogenic activity of the tissue was monitored by assay for progesterone and estradiol in spent media.

RESULTS

No significant differences in follicle morphology, PCNA, or TUNEL labeling were observed between cryopreservation methods at the initiation of culture. Similar decreases in the proportion of primordial follicle population, and increases in the proportion of growing follicles, were observed following culture of fresh or cryopreserved ovarian tissue regardless of cryopreservation method. At the end of culture, PCNA and TUNEL-positive follicles were not statistically altered by slow freezing or vitrification in comparison to fresh cultured fragments.

CONCLUSIONS

Overall, for both cryopreservation methods, the cryopreserved tissue showed equal capacity to fresh tissue for supporting basal folliculogenesis in vitro. Taken together, these data confirm that both non-equilibrium vitrification and slow-freezing methods are both efficient for the cryopreservation of sheep ovarian cortex fragments.

Histological evaluation of sheep ovarian tissue after laparoscopic partial ovariectomy

In the present study, there was assessment of the damage to tissue caused by partial laparoscopic ovariectomy using bipolar forceps in sheep. Fragments of ovaries of six sheep were removed using bipolar forceps by making a transverse section in the middle third of the organ via three-portals that were made using laparoscopy. The fragments were subjected to standard histological examinations and the lesions attributed to the procedure were investigated using an optical microscope and Image J software. The results were assessed using an analysis of variance and the Tukey test. All the laminae had minimal tissue damage. The mean amount of highly damaged tissue was 1.8%, and of partially damaged tissue was 5.6%. The mean total area of healthy tissue in the fragments was 94.4%. The results of the study indicate this procedure can be conducted withvery little tissue damage occurring. The use of this procedure, therefore, can be incorporated in future reproductive studies without altering the functions of the in situ ovarian tissues.