Induced sperm oxidative stress in dogs: Susceptibility against different reactive oxygen species and protective role of seminal plasma

Oxidative stress (OS) is characterized by an unbalance between increased levels of reactive oxygen species (ROS) and/or impaired antioxidant protection. In this context, the composition of seminal plasma (SP) plays a key role in protecting sperm against OS. However, reproductive biotechnologies applied to dogs recommend the removal of SP. Thus, antioxidant therapy may be an important alternative when applying biotechniques such as semen cryopreservation in this specie. However, in order to be efficient, the choice of the ideal antioxidant in each condition is essential since each ROS is preferably neutralized by different antioxidant systems. Therefore, this study aims to evaluate the susceptibility of canine spermatozoa to different oxidative challenges (superoxide anion [O2−], hydrogen peroxide [H2O2], hydroxyl radical [OH−] and malondialdehyde [MDA]) in the present or absence of SP. We used ejaculates of eight dogs and submitted to induce oxidative challenges (with or without SP). After incubations, samples were evaluated for the susceptibility to lipid peroxidation, motility, mitochondrial activity and function, DNA integrity, plasma membrane and acrosome integrity. Sperm with SP had mitochondrial function preserved against ROS. However, in the absence of SP, H2O2 reduced mitochondrial membrane potential. In addition, regardless on SP, H2O2 was deleterious to sperm kinetics and plasma/acrosomal membranes. Incubation with OH− reduced mitochondrial activity and increased DNA fragmentation also independent on the absence of presence of SP. Furthermore, samples with SP were more resistant to lipid peroxidation (i.e., decreased concentration of TBARS). In conclusion, H2O2 and OH− appears to be the most deleterious ROS to dog sperm and SP protects the spermatozoa against mitochondrial injuries and lipid peroxidation.