Spermatozoa Have Decreased Antioxidant Enzymatic Capacity and Increased Reactive Oxygen Species Production During Aging in the Brown Norway Rat

ABSTRACT: As the proportion of aged males attempting to reproduce continues to rise, so does the concern regarding the quality of spermatozoa from aged men. An imbalance between the generation of reactive oxygen species (ROS) and cellular antioxidant defenses, as occurs in aging, ultimately leads to decreased protein, lipid, and DNA quality. Spermatozoa are highly susceptible to oxidative damage, and thus an age-related shift in redox status may have serious implications for fertility. Therefore, we examined the effect of age on antioxidant enzymatic activity, ROS production, and extent of lipid peroxidation in both caput and cauda epididymal spermatozoa from young (4-month-old) and old (21-month-old) Brown Norway rats. Glutathione peroxidase (Gpx1, Gpx4) and superoxide dismutase (SOD) enzymes had decreased activity in aging spermatozoa. Immunofluorescence studies indicated that Gpx4 expression was decreased in both the head and midpiece regions of spermatozoa in aged animals. The decrease in nuclear Gpx4 points to a novel potential mechanism that may explain the previously noted decreased levels of protamine disulfide bonds in aged sperm nuclei. Further, hydrogen peroxide (H₂O₂) and superoxide (O₂•–) production were increased significantly in aging spermatozoa. Finally, lipid peroxidation was found to be drastically increased in aged spermatozoa. Taken together, these results suggest a decreased capacity for aged spermatozoa to handle oxidative stress and provide a potential basis for understanding the underlying cause of decreased quality of spermatozoa during aging.