Cellular damage suffered by equine embryos after exposure to cryoprotectants or cryopreservation by slow-freezing or vitrification.

The research article investigates the damage done to horse embryos during cryopreservation, a process of freezing biological material for future use. The study compares two methods, slow-freezing and vitrification, and finds that large embryos have a higher incidence of cell death using the vitrification method, suggesting it may not be the best choice for freezing larger embryos.

Objective and Methods

• The research had a clear objective, to compare the damage done by two common embryo freezing techniques, slow-freezing and vitrification on small and large horse embryos.
• A total of sixty-three Day 6.5-7 embryos were used for the experiments. They were divided based on their size and assigned to either a control group or one of four treatment groups: exposure to slow-freezing cryoprotectants, exposure to vitrification cryoprotectants, cryopreservation by slow-freezing, or cryopreservation by vitrification.
• After undergoing the assigned treatments, embryos were stained with fluorescent stains which indicate various aspects of cellular integrity. Following staining, the embryos were examined under a multiphoton microscope.

Results and Conclusions

• The results pointed out a clear difference in outcomes between the two methods of cryopreservation for the larger embryos. Large embryos exposed to vitrification cryoprotectants showed a significantly higher percentage of cell death compared to those exposed to slow-freezing media.
• Both forms of cryopreservation were found to cause cell death and disruptions in the cytoskeleton, the structure giving a cell its shape and mechanical resistance.
• However, when it came to small embryos, vitrification resulted in a higher proportion of cells with fragmented or condensed (apoptotic) nuclei than slow-freezing.
• Interestingly, slow-freezing led to a higher rate of entire embryos disintegrating, unlike vitrification.
• Another interesting revelation was that while vitrification changed mitochondrial distribution in the embryos, it didn’t considerably affect their overall mitochondrial activity.
• The final conclusion drawn from the study is that cryopreservation caused more damage to large embryos than smaller ones. But the researchers do not unconditionally recommend slow-freezing as vitrification, despite causing occasionally very high percentages of dead or damaged cells, led to a lower incidence of entire embryos disintegrating. They suggest that improvements to reduce the level of cellular damage caused by vitrification are required before it can be considered the preferred method for cryopreserving horse embryos.