Honey is an efficient natural cryoprotectant in fertility preservation

To date, encouraging studies on fertility preservation (sperm, embryos, and oocytes) have confirmed the beneficial effect of honey as a cryoprotectant on the viability of cryopreserved sperm and embryos. [1]  

 

The role of cryoprotectants 

 

Cryopreservation uses low temperature (−196 °C) to preserve living cells and tissue. Successful cryopreservation relies on more than simply freezing cells, which exposes them to numerous stresses, including dehydration and mechanical pressures. Fertility cryopreservation is challenging because of gametes and embryos morphological, functional, and genetic changes in the cells after freeze-thawing. Usually, a cryoprotective agent or cryoprotectant (CPA) is added to minimise freezing damage by inhibiting ice formation, preserving cellular membranes and promoting vitrification. Unfortunately, review articles indicate that the most commonly used CPAs have some toxicity, making them unsuitable or inefficient for many clinical applications. [2] 

 

CPAs are classified into two broad categories: penetrating and non-penetrating. Non-penetrating CPAs include small molecules (such as sugars) that cannot penetrate membranes as well as large, long chain polymers, added to aqueous cryoprotective solutions (commonly called vitrification solutions). These molecules inhibit ice growth, but do not permeate cells. Non-penetrating cryoprotectants are generally less toxic than penetrating ones at the same concentration. Therefore, they reduce the amount of penetrating cryoprotectants needed. 

 

The benefits of honey as a cryoprotectant 

 

According to a recent review article, honey is an effective natural non-penetrating cryoprotectant. It can inhibit ice crystal growth and provide a protective barrier by allowing slow perfusion and permeation into cells, due to its higher viscosity at low temperatures. Additionally, its antioxidant property protects the cells from thermal damage. [1] 

 

Studies have proved that cells’ survival rate is improved more effectively by adding a mixture of two sugars (sucrose and glucose) to the vitrification medium, rather than by adding sucrose alone. Natural honey contains 25 sugars, mainly fructose and glucose, which make up about 95% of its dry weight.  

 

Combining honey with penetrating CPAs in vitrification solution could improve mammalian tissues viability and functionalities after thawing, compared to vitrification media containing only penetrating CPAs. When honey is added to contribute to the vitrification medium viscosity and tonicity, it supports penetrating CPAs in vitrification, thereby reducing the concentrations of penetrating CPAs required and  decreasing cytotoxicity risks and osmotic shock effects of the penetrating CPAs. 

 

Concerning the freezing-thawing process, however, studies have revealed that different animal species have different tolerance ranges. These variations might be due to the honey concentration used in the different species; therefore, the effect of various honey concentrations should be reassessed. 

 

 

Sources 

[1] Cheepa, F. F., Liu, H., & Zhao, G. (2022). The Natural Cryoprotectant Honey for Fertility Cryopreservation. Bioengineering, 9(3), 88. https://doi.org/10.3390/bioengineering9030088 
[2] Raju, R., Bryant, S. J., Wilkinson, B. L., & Bryant, G. (2021). The need for novel cryoprotectants and cryopreservation protocols: Insights into the importance of biophysical investigation and cell permeability. Biochimica et Biophysica Acta (BBA)-General Subjects, 1865(1), 129749. https://doi.org/10.1016/j.bbagen.2020.129749