The protective effects of antioxidants against endogenous and exogenous oxidative stress on bull sperm

Oxidative stress, caused by both endogenous and exogenous factors, affects sperm function by damaging morphology and reducing metabolic activity, leading to reduced fertilization ability. The purpose of this study was to investigate the effects of oxidative stress on bull sperm and to evaluate the efficacy of targeted antioxidants in mitigating these detrimental effects. Fresh bull semen samples were subjected to hydrogen peroxide (H₂O₂) and antimycin treatments to induce oxidative stress, and the antioxidants PQQ, ergothioneine, and vitamin C were applied to counteract the induced stress. Sperm motility, viability, and reactive oxygen species (ROS) levels in the cytoplasm and mitochondria of sperm were assessed using computer-assisted sperm analysis (CASA) and flow cytometry. The treatment with H₂O₂ rapidly decreased sperm viability, and antimycin-induced mitochondrial ROS mainly decreased sperm motility; PQQ and vitamin C effectively reduced mitochondrial ROS, while ergothioneine and vitamin C reduced cytosolic ROS. In frozen-thawed sperm, oxidative stress was elevated in both cytoplasm and mitochondria, and all three antioxidants improved sperm motility by inhibiting ROS production. Furthermore, the localization of oxidized lipids (4-hydroxynonenal) in sperm was detected using immunofluorescence, indicating that oxidative stress affects the head and midpiece of sperm. These findings highlight the potential of targeted antioxidants to mitigate the detrimental effects of oxidative stress on bull sperm and provide valuable insights to improve semen quality and optimize the use of antioxidants in artificial insemination.