Permeability of the equine embryonic capsule to ethylene glycol and glycerol in vitro.

The research looked to understand the poor survival rates of horse embryos during cryopreservation by investigating how efficiently cryoprotective agents (CPAs) like ethylene glycol and glycerol permeate the embryonic capsule. This was investigated using a lab tool named Valia-Chien permeation apparatus. The findings indicate that the penetration of CPAs through the capsule is more complex than just simple diffusion and thus, the use of alternative CPAs or methods to ensure entry into the cells may be needed.

Objectives and Methodology

• The main objective of the research was to understand the reason behind low survival rates of equine expanded blastocysts during cryopreservation.
• The researchers theorized that this issue could arise from the low penetration of the embryonic capsule by CPAs like ethylene glycol (EG) and glycerol (GLY).
• To verify this hypothesis, the researchers used pieces of embryonic capsules from day 14 to 18 and placed them in a Valia-Chien permeation apparatus. This setup had a “donor” and a “recipient” chamber separated by the embryonic capsule.
• The donor chamber contained various concentrations of either ethylene glycol or glycerol, or saline (as a control). The movement of these substances through the embryonic capsule was then measured via gas chromatography.

Findings

• The permeation of the embryonic capsule by 1.5M EG was found to be significantly faster than that of 0.87M GLY or 0.74M EG.
• However, despite this differential permeation rate, both CPAs permeated significantly slower than saline solution.
• The study also found that the accumulation of these molecules in the recipient chamber depended more on the initial concentration in the donor chamber than on the type of CPA.
• Interestingly, the accumulation rates for the CPAs and saline were found to be linear only when the capsule was present, pointing to the complexity of their penetration through the embryonic capsule.

Conclusions

• These findings suggest that the permeation of CPAs is not a simple process of diffusion but a more complex interaction requiring contextual factors such as the embryonic capsule.
• Oppositely, improving the cryopreservation success rate of equine expanded blastocysts may require alternative CPAs that can more efficiently permeate the embryonic capsule, or unique methods to ensure optimal CPA entry into the cells.