Impacts of oxidative stress on bovine sperm function and subsequent in vitro embryo development

Low levels of reactive oxygen species (ROS) in sperm are essential for various sperm functions such as capacitation, hyperactivation and acrosome reaction. However, increased synthesis of ROS or a disruption of antioxidative status (e.g. in cryopreserved sperm) can induce oxidative stress (OS). Sperm are particularly vulnerable to OS, as their plasma membrane contains large amounts of polyunsaturated fatty acids and they have limited antioxidative capacity (due to low cytoplasmic volume). Oxidative stress disturbs sperm function by damaging sperm proteins, lipids and DNA. Under relatively low OS sperm may retain their fertilizing ability, which might result in transfer of impaired paternal molecules (e.g. damaged DNA) to the fertilized oozyte. Oocytes can repair damaged paternal DNA, but only to a certain extent. Most embryos are either repaired (based on limited DNA damage in blastocysts) or eliminated (based on low percentage of blastocyst formation when sperm with damaged DNA is used for fertilization). However, some blastocysts had increases in both DNA damage and apoptosis, which could have important implications for subsequent development. In several studies, exogenous antioxidants improved quality of sperm exposed to oxidative stress and subsequent embryo development. However, there is still a knowledge gap regarding whether these alterations affect embryonic survival and further development to a live fetus and healthy offspring.