Induced sub-lethal oxidative damage affects osmotic tolerance and cryosurvival of spermatozoa.

This research investigates the effect of sub-lethal oxidative damage on the osmotic tolerance and survival rates of frozen spermatozoa. The findings reveal that such damage, produced artificially in the lab, can adversely impact sperm viability, with little benefit from processing or mitigation techniques.

Research Method

• The researchers induced oxidative damage in stallion spermatozoa via incubation with xanthine and xanthine oxidase (X-XO). This treatment produced specific quantities of superoxide and hydrogen peroxide, leading to sub-lethal oxidative harm.
• The study focused on understanding the impact of this treatment on various sperm characteristics, with a particular emphasis on sperm osmotic tolerance prior to freezing and the relationship with cryopreservation survival. The latter is crucial as the freezing process exposes cells to osmotic stress.

Key Findings

• Reactive oxygen species (ROS) accumulation primarily occurred in the sperm midpiece, where the mitochondria are located.
• Increasing concentrations of X-XO led to a dose-dependent decrease in sperm motility, but the percentages of sperm with intact plasma membranes weren’t affected.
• Sperm membrane stability under hypotonic stress conditions diminished as levels of induced oxidative stress increased.
• Infrared spectroscopic studies revealed that X-XO treatment did not change sperm membrane phase behavior.
• Pre-freeze exposure to amplified levels of oxidative stress reduced the survival rates of sperm post-cryopreservation.
• Processing techniques, such as centrifugation and the use of catalase, had minimal beneficial effects.

Implications

• The research findings underscore the detrimental effects of excessive ROS, leading to decreased sperm osmotic tolerance and cryosurvival. This could have serious implications for assisted reproductive technologies, particularly those using cryopreserved spermatozoa.
• The study also raises questions about the effectiveness of currently used sperm processing methods and suggests the need for improved techniques to guard against oxidative damage.