Application of hollow fiber vitrification for cryopreservation of bovine early cleavage stage embryos and porcine morula-blastomeres

Specifics of vitrification of in vitro-produced cattle embyos at various development stages

Producing embryos in vitro is an important technology used to improve the genetic potential of cattle and perfect the programs of their breeding. Regardless of the way they are produced, all embryos that had not been used for transplantation to recipients must be conserved. Because of significantly increased interest in the problem of cryoconservation of embryos, both coming from scientists and businesses, there are emerging new commercial environments that allow the facilitation of cryoconservation and the increase in the embryo survival. Oocyte-cumulus complexes obtained from the ovaries of slaughtered clinically healthy cows matured in 22–24 h in in vitro conditions. The oocytes were co-cultured with spermatozoids in Fertilization medium, and the obtained zygotes were cultured in Culture medium with Sodium-Pyruvate for 4 or 7 days up to the stage of morula or blastocyste, respectively. For the vitrification of cow embryos, we used a commercial kit for the vitrification of human embryos, having compared the duration of equilibration. According to the results of the studies, we observed high efficiency of cryoconservation of cow embryos using the commercial kit for vitrification of human embryos. The results revealed the significant effect of equilibration on survival and further development of embryos. In addition, we described the dependence of development stage of cattle embryo on the duration of the contact of embryo with equilibration solution. Therefore, optimal time of contact of cattle embryos at the morula stage with equilibration solution was 12 minutes. On the 24th h after thawing, 46.7 ± 3.3% of the embryos were observed to undergo blastulation, and on 48th h, this parameter increased to 96.7 ± 3.3%, which corresponded to the parameters in the group of embryos that had not been subjected to cryoconservation. In the conditions of further cultivation, the percentage of blastocystes that hatched in the experimental group was no different from that of the control. At the same time, the highest efficiency of vitrification of blastocystes of cows was seen after the contact with the equilibration solution for 15 min, since the percentage of hatched blastocystes was the same as in the control group. Therefore, using the commercial kit for vitrification of human embryos is beneficial, for it promotes the parameters of cow embryos after vitrification/thawing that are similar to such of intact embryos (without freezing). The data we analyzed and presented in the paper could help to increase the efficiency of cryoconservation of cattle embryos for both scientific and commercial purposes.

Vitrification of mouse two-cell and blastocyst stage embryos in simplified closed system using either a hemi-straw or a hollow fiber device

Two-cell stage and blastocyst stage mouse embryos were equilibrated in a medium containing 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO) for 8-15 min. Vitrification was performed in a medium containing 0.5 M sucrose and either 15% EG + 15% DMSO, 17.5% EG + 17.5% DMSO, or 20% EG + 20% DMSO for 30 s. They were then placed either on a hemi-straw (HS) or a hollow fiber vitrification (HFV) device and vitrified by cooled air inside a 0.5-ml straw. In two-cell embryos, a 100% survival rate was obtained from all groups except the 20% HS group (P > .05). All vitrified two-cell groups showed similar rates of blastocyst development to that of fresh control group (P > .05), except 17.5% and 20% HFV groups, which were significantly lower than the other groups (P < .05). In the blastocyst embryos, the HFV groups were divided into two subgroups (non-collapsed; HFV-NC and collapsed; HFV-C blastocyst). Re-expansion rate in 15% HFV-NC, 17.5% HFV-NC, and 15% HFV-C groups was reduced (P < .05), whereas the rest were similar to control. In conclusion, we established a simplified, reliable, and closed system for HFV vitrification applying hemi-straw, which does not require skilled practitioners.

Cryopreservation of Porcine Embryos: Recent Updates and Progress

Cryopreservation of embryos is important for long-distance embryo transfer and conservation of genetic resources. Porcine research is important for animal husbandry and biomedical research. However, porcine embryos are difficult to cryopreserve because of their high cytoplasmic lipid content and sensitivity to chilling stress. Vitrification is more efficient than slow freezing, and vitrification is mostly used in embryo cryopreservation. So far, the vitrification process of porcine embryos has been continuously improved, resulting in improved survival rates of warmed embryos and farrowing rates after the transplant procedure. It is worth noting that automatic vitrification has made great progress, which is expected to promote the standardization and application of vitrification. In this article, the vitrification process of porcine embryos at the blastula stage and early development stages is reviewed in detail. In addition, the efficiency of different vitrification systems was compared. In addition, we summarize technology that can improve the survival rate of cryopreserved porcine embryos, such as delipidation methods (including physical delipidation and chemical delipidation) and medium improvements (including chemically defined media and adding antioxidants). Meanwhile, gene expression changes during cryopreservation are also elaborated.

Hollow fiber vitrification allows cryopreservation of embryos with compromised cryotolerance

PURPOSE

This study aims to demonstrate vitrification methods that provide reliable cryopreservation for embryos with compromised cryotolerance.

METHODS

Two-cell stage mouse embryos and in vitro produced porcine embryos were vitrified using the hollow fiber vitrification (HFV) and Cryotop (CT) methods. The performance of these two methods was compared by the viability of the vitrified-rewarmed embryos.

RESULTS

Regardless of the method used, 100% of the mouse 2-cell embryos developed successfully after vitrification-rewarming into the blastocyst stage, whereas vitrification tests using porcine morulae with the HFV method produced significantly better results. The developmental rates of vitrified porcine morula into the blastocyst stage, as well as blastocyst cell number, were 90.3% and 112.3 ± 6.9 in the HFV group compared with 63.4% and 89.5 ± 8.1 in the CT group (P < .05). Vitrification tests using 4- to 8-cell porcine embryos resulted in development into the blastocyst stage (45.5%) in the HFV group alone, demonstrating its better efficacy. The HFV method did not impair embryo viability, even after spontaneous rewarming at room temperature for vitrified embryos, which is generally considered a contraindication.

CONCLUSION

Vitrification test using embryos with compromised cryotolerance allows for more precise determining of effective cryopreservation methods and devices.

Nylon Mesh Device for Vitrification of Large Quantities of Rat Pancreatic Islets

The practical requirements of islet transplantation necessitate that a large quantity of pancreatic islets be cryopreserved for a long period of time in a simple and convenient manner. We cryopreserved rat islets (size range 101-150 μm in mean diameter) by vitrification with either a Cryotop^® device or a ø = 57-μm nylon mesh device in units of 10 islets, or by conventional freezing with a Bicell^® vessel in units of 50 islets. Postwarm/thaw survival rates of the islets were 68.1% ± 5.9%, 64.1% ± 3.5%, and 47.7 ± 1.2% following Cryotop vitrification, nylon mesh vitrification, and Bicell freezing, respectively (p < 0.05). Glucose-stimulated insulin secretion in the two vitrification groups (stimulus index [SI] = 3.1-3.9) was superior to that in the freezing group (SI = 0.8). Additional experiments involved scaling-up the cryopreservation process using the nylon mesh device in units of 10, 50, or 100 islets. Increased numbers of islets per device had no adverse effects on cryosurvival (58.6%-68.5%) or insulin secretion potential (SI = 2.8-4.2). As the nylon mesh device does not require the handling of individual islets with glass pipettes, pre- and postvitrification islet treatment is less complicated. Therefore, nylon mesh can serve as a simple cryodevice for the vitrification of large quantities of rat pancreatic islets.

Survival and developmental competence of bovine embryos at different developmental stages and separated blastomeres after vitrification in different solutions

Generating techniques to enhance the success of blastomere separation is important for bovine economy, because it increases the number of transferable embryos. This study aimed to identify the optimum cryoprotectants for the vitrification of bovine embryos and the separation of blastomeres at different stages. In experiment 1, expanded blastocysts were vitrified in two different vitrification solutions, either (1) ethylene glycol (EG) + propylene glycol (PG) or (2) EG. The survival rate of blastocysts in the EG + PG was higher than that of the EG. In experiment 2, intact two-cell and eight-cell stage embryos were vitrified in the same solutions used in experiment 1. The EG + PG produced more dead embryos than the EG (P < 0.05). In the EG, the rate of blastocyst formation was similar for the vitrified two- and eight-cell embryos and the non-vitrified ywo-cell embryos. In experiment 3, separated blastomeres of two- and eight-cell embryos were vitrified in EG. There was no difference in the rate of blastocyst formation and total number of cells between the two vitrified groups. In summary, at the blastocyst stage, EG + PG was superior, based on both survival rates and cell numbers; however, at the 2-8 cell stage, the use of EG alone was better than the other groups.