Successful vitrification of bovine immature oocyte using liquid helium instead of liquid nitrogen as cryogenic liquid

Three live births after human embryo vitrification with the use of aluminum oxide as an intermediate cooling agent: a case report

Objective

To study the possibility of increasing the cooling rates of the vitrification procedure in a closed system with the use of aluminum oxide as an intermediate coolant.

Design

Case report.

Subjects

Six patients undergoing procedures for assisted reproduction.

Intervention

Comparative studies of cryopreservation of donor embryos with aluminum oxide as an intermediate cooling agent (experimental group) and without it (control group) have been performed. After thawing, the embryo morphology and its potential to develop to the blastocyst stage have been assessed. The methodology was then applied to clinical practice.

Main Outcome Measures

Twenty embryos of 6 patients have been vitrified on day 4 after fertilization with the use of aluminum oxide as an intermediate coolant. Fourteen of them have been thawed. All have displayed normal morphology and 10 have formed blastocysts after 24 hours of culture. Four of the patients received embryo transfer with 2 embryos and the other 2 with single embryos.

Results

After preliminary comparative studies of embryos frozen with aluminum oxide and a control group, the results showed no statistically significant difference between their quality and potential to reach to blastocyst stage. That gave us ground to apply the methodology in clinical practice. After the embryo transfer, 3 clinical pregnancies with successful live births have been obtained.

Conclusions

Our experience shows that preimplantation embryos can be cryopreserved aseptically, in closed systems, with the help of aluminum oxide as an intermediate coolant.

Cryodevices developed for minimum volume cooling vitrification of bovine oocytes

Unfertilized bovine oocytes can be efficiently cryopreserved only when an extremely rapid cooling rate (>20,000°C/min) is applied to oocytes with a very limited amount of surrounding vitrification solution. This protocol is defined as minimum volume cooling (MVC) vitrification. Various types of cryodevices, such as open pulled straw, Cryoloop, and Cryotop, have been developed to accelerate the cooling efficacy. Furthermore, hollow fibers with nano-scale pores, triangle nylon mesh sheets, and multilayer silk fibroin sheets have been optimized for the loading of large quantities of oocytes and/or the subsequent removal of excess vitrification solution, without requiring skillful operation to transfer individual oocytes using fine capillaries. This article provides an up-to-date review of cryodevices suitable for the MVC vitrification of bovine oocytes at the immature (germinal vesicle-) and mature (metaphase II-) stages.

Vitrification of immature bovine oocytes in protein-free media: The impact of the cryoprotectant treatment protocol, base medium, and ovary storage

Protein-free media are essential for the sanitary cryopreservation of bovine genetic resources. Our aim was to set up an optimized protocol for the vitrification of immature bovine oocytes using protein free media which can provide the highest embryo development rates and embryo quality after subsequent in vitro maturation and fertilization. First, using a protein free NCSU-37 as base medium we compared the efficacy of vitrification on Cryotop device with two different CPA protocols. "Protocol A″ employed a combination of ethylene glycol and propylene glycol as permeating cryoprotectants (pCPA) and equilibration in 4% total pCPA (2% ethylene glycol + 2% propylene glycol). "Protocol B″ employed a combination of ethylene glycol and DMSO and equilibration in 15% total pCPA (7.5% ethylene glycol + 7.5% DMSO). The 2 protocols were equally effective in terms of oocyte survival and subsequent development to the blastocyst stage. However, blastocyst cell numbers were significantly higher with "Protocol A". TCM-199 and NCSU-37 were equally effective as base media for vitrification. Vitrification with "Protocol A″ reduced the percentage of live oocytes and subsequent development to blastocyst stage but did not affect the hatching and cell numbers of blastocysts when compared to the non-treated group. CPA treatment of "Protocol A″ without cooling did not affect embryo development. Storage of ovaries in PBS at 15 °C for overnight reduced the percentage of surviving oocytes after vitrification but not their subsequent development to the blastocyst stage. In conclusion we established a vitrification protocol for the cryopreservation of immature bovine oocytes employing protein-free media which provided high blastocyst quality without noticeable toxic effects.

Cryopreservation of equine oocytes: looking into the crystal ball

Invitro embryo production has evolved rapidly in the horse over the past decade, but blastocyst rates from vitrified equine oocytes remain quite poor and further research is needed to warrant application. Oocyte vitrification is affected by several technical and biological factors. In the horse, short exposure of immature oocytes to the combination of permeating and non-permeating cryoprotective agents has been associated with the best results so far. High cooling and warming rates are also crucial and can be obtained by using minimal volumes and open cryodevices. Vitrification of invivo-matured oocytes has yielded better results, but is less practical. The presence of the corona radiata seems to partially protect those factors that are necessary for the construction of the normal spindle and for chromosome alignment, but multiple layers of cumulus cells may impair permeation of cryoprotective agents. In addition to the spindle, the oolemma and mitochondria are also particularly sensitive to vitrification damage, which should be minimised in future vitrification procedures. This review presents promising protocols and novel strategies in equine oocyte vitrification, with a focus on blastocyst development and foal production as most reliable outcome parameters.

Relationship between bovine oocytes developmental competence and mRNA expression of apoptotic and mitochondrial genes following the change of vitrification temperatures and cryoprotectant concentrations

The present study analyzed the relationship between bovine oocytes developmental competence and mRNA expression of apoptotic and mitochondrial genes following the change of vitrification temperatures (VTs) and cryoprotectant agent concentrations (CPAs). Cumulus oocyte complexes were randomly divided into five groups: control, vitrified in liquid nitrogen (LN; -196 °C) with 5.6 M CPAs (LN 5.6 M), LN with 6.6 M CPAs (LN 6.6 M), liquid helium (LHe; -269 °C) with 5.6 M CPAs (LHe 5.6 M), and LHe with 6.6 M CPAs (LHe 6.6 M). After vitrification and warming, oocytes of vitrified and control groups were subjected to in vitro maturation (IVM), in vitro fertilization and in vitro culture. The blastocyst rate in LHe 5.6 M group was the highest among the four vitrified groups (13.7% vs. 9.4%, 1.3%, and 8.4%; P < 0.05). The mRNA expression level of 8 apoptotic- and 12 mitochondria-related genes were detected through qRT-PCR after IVM. Lower VT (LHe, -269 °C) positively affected the mRNA expression levels of apoptotic genes (BAD, BID, BTK, TP53, and TP53I3) and mitochondrial genes (COX6B1, DERA, FIS1, NDUFA1, NDUFA4, PRDX2, SLC25A5, TFB1M, and UQCRB), and reduced oxidative stress from freezing. Decreased CPAs (5.6 M) positively affected mRNA expression levels of apoptotic genes (BAD, BCL2A1, BID, and CASP3) in LHe vitrification but negatively affected apoptotic genes (BAD, BAX, BID, BTK, and BCL2A1) in LN vitrification. In conclusion, decreased VTs and CPAs in LHe vitrification may increase the blastocyst rate by changing the mRNA expression levels of these apoptotic and mitochondrial genes for the vitrified oocytes.

Effect of vitrification temperature and cryoprotectant concentrations on the mRNA transcriptome of bovine mature oocytes after vitrifying at immature stage

The present study aimed to investigate the effect of vitrification temperature (VT) and cryoprotective agent concentrations (CPAs) on the mRNA transcriptome of bovine mature oocytes after vitrifying at immature stage. Cumulus oocyte complexes (COCs) were randomly divided into the following five groups: fresh oocytes (control), oocytes vitrified in liquid helium (LHe; -269 °C) with 5.6 M CPAs (LHe 5.6 M), oocytes vitrified in LHe with 6.6 M CPAs (LHe 6.6 M), oocytes vitrified in liquid nitrogen (LN; -196 °C) with 5.6 M CPAs (LN 5.6 M), and oocytes vitrified in LN with 6.6 M CPAs (LN 6.6 M). We performed two experiments in this study. In experiment 1, after vitrification and thawing, oocytes of vitrified and control groups were subjected to in vitro maturation (IVM), in vitro fertilization (IVF) and in vitro culture (IVC). The rates of normal morphology, maturation, cleavage, and blastocyst formation in LHe 5.6 M were higher than those in LN 5.6 M (P < 0.05). The rates of normal morphology and cleavage in LHe 6.6 M were higher than those in LN 6.6 M (P < 0.05). However, the maturation and blastocyst rates were similar (P > 0.05) between LHe 6.6 M and LN 6.6 M. The blastocyst rate of 13.31% in LHe 5.6 M was the highest among all vitrified groups (P < 0.05). In experiment 2, the mRNA transcriptome of each sample was analyzed by Smart-Seq4, and the differentially expressed genes (DEGs) were detected by edgeR (P ≤ 0.05; fold-change ≥ 2). A total of 505 DEGs (342 upregulated and 163 downregulated genes) were detected in LHe 5.6 M; 609 DEGs (493 upregulated and 116 downregulated genes) were detected in LHe 6.6 M; 218 DEGs (101 upregulated and 117 downregulated genes) were determined in LN 5.6 M; and 221 DEGs (104 upregulated and 117 downregulated genes) were detected in LN 6.6 M. LHe vitrification affected the mRNA transcriptome of bovine mature oocytes after vitrifying at immature stage mainly by upregulating gene expression. Decreased CPAs (5.6 M) reduced the effect of vitrification on mRNA transcriptome when LHe vitrification was used. Among the DEGs closely related to bovine oocytes, the genes possibly related to VT were ND2, MPV17L2, PIF1, LPIN1, IMP3, BRD1, DCTN3, DERA, ATP7B, NEK5, HVCN1, and MARK2. The gene that may be associated with CPAs is CC2D2A. Genes that may be affected by VT and CPAs included PGK1, SLC7A3, FITM2, NPM3, ISCU, CWC15, and PSAP.