Mechanisms underlying human sperm cryodamage: the role of reactive oxygen species (ROS) and antioxidants

Sperm cryopreservation is an efficient procedure for male fertility preservation, although the freeze-thaw procedure causes irreversible structural and functional changes in human spermatozoa. Indeed, the procedure is responsible for harmful changes that may affect sperm biology. In mammalian cells, cryopreservation induces a shift of redox homeostasis towards increasing generation of reactive oxygen species (ROS). The characteristics of ROS and the cellular outcomes depend on the cell type. Supra-physiological ROS levels during cryopreservation severely impact sperm survival, reproductive potential and DNA integrity, the latter a fundamental factor for fertilisation and transmission of paternal genetic information to offspring. The aim of this review is to summarise current knowledge of the main molecular mechanisms underlying ROS generation during sperm cryopreservation and its subsequent effects. In addition, we report current experimental approaches based on the supplementation of cryopreservation media with enzymatic and non-enzymatic antioxidants with the aim of minimising the harmful effects of ROS, and thus improving post-thaw sperm quality. Current data indicate that the potential use of antioxidants as constituents of the sperm freezing solution in clinical settings would require considerable attention. KEY WORDS: Spermatozoa, cryopreservation, ROS, oxidative stress, antioxidants.