Compounds with antioxidant activity as a supplement of media used for human semen cryopreservation: a narrative review

Sperm cryopreservation is an important technique in preserving male fertility. Several methods for semen and sperm cryopreservation are available; however, the quality of thawed spermatozoa is poor and this is due to different mechanisms during the freezing-thawing process, including temperature changes, crystal ice formation, osmotic stress and oxidative stress (OS). OS is the result of an overproduction of reactive oxygen species (ROS) that, if present in high concentration, can damage the cellular structures and impair sperm function. Modulation of OS is an important issue in human sperm freezing. A large group of antioxidant molecules is used in cryopreservation processes as a pharmacological strategy to counteract the oxidizing effects of preservation procedures and thus protect sperm quality. The main body of the review comprises the analysis of different studies, starting from 2000 up to the present, dealing with the effects of different antioxidant compounds, including natural extract, used as supplement of cryopreservation media. Many studies have reported several beneficial effects of antioxidants that are added during freezing-thawing protocols on sperm cryo-damages; however, these improvements are not always evident. Over the past decade, the attention has been mainly focused on the phytoextracts and natural extracts. Phytoextracts can be obtained by waste products, which are a rich source of compounds with strong antioxidant activity. Because these by-products can be used in the industrial, cosmetic, nutraceutical, and human and animal reproductive fields, this topic of research is worthwhile implementing. The freezing and thawing protocols still have many pitfalls and the quality of thawed spermatozoa is not satisfactory. For this reason, new strategies to minimize cyodamages and to increase sperm cryostability are advisable to guarantee better sperm function and survival, permitting successful future clinical application.