Possible Protective Mechanisms of Coenzyme Q10 Action on Spermatozoa During Cryopreservation or Cooled-Stored Condition

Artificial insemination (AI) with frozen or cooled-stored semen plays a key role in the widespread distribution of germplasm of elite livestock resources and the protection of endangered species. Cryopreservation provides long-term preservation of sperm and also encourages a greater exchange of genetic material between distant populations. However, freezing has some detrimental effects on sperm, including premature induction of acrosome response, reduced sperm motility, reduced viability, and impaired sperm DNA integrity and fertility. The transition of the membrane phase occurs when the sperm cools down, and lipid accumulation damages the micro-domain, thereby impairing membrane functions, leaving a gap between the gel and the liquid membrane region. Coenzyme Q10 (CoQ10) is a vital lipophilic molecule found in all respiratory eukaryotic cells, including spermatozoa. When such a lipophilic antioxidant is added to the sperm, it can directly diffuse into the polyunsaturated lipid chain present in the plasma membrane, thereby affecting the structure and function of the sperm by generating energy and preventing reactive oxygen. Coenzyme Q10 treatment of sperm from various species improves sperm quality during cryopreservation and cooled-stored condition. It is, however, unclear how this antioxidant affects sperm to improve survival during freezing or cooled-stored condition. Thus, this review highlights the potential protective mechanisms of coenzyme Q10 action during the sperm freezing process.