75 INFLUENCE OF CRYOPRESERVATION ON THE SUSCEPTIBILITY OF GOAT SPERM AGAINST DIFFERENT REACTIVE OXYGEN SPECIES

Abstract

Semen quality after cryopreservation is one of the main limiting factors for the success of artificial insemination in goats. Previous studies indicate that cryo-injuries may be related to the oxidative stress which is caused by the reactive oxygen species (ROS) and leads to structural and functional damages to the sperm. The understanding of sperm oxidative mechanisms in goats may provide information on possible treatments to improve semen quality post cryopreservation. The aim of the present study was to verify the resistance of cryopreserved goat spermatozoa to different reactive oxygen species. Semen samples from 5 adult goats were collected and cryopreserved (Botubov^®, Biotech Ltda.). After thawing, samples were washed twice with PBS and incubated (1 h, 37°C) with 4 ROS inducer mechanisms: xanthine/xanthine oxidase (produces superoxide anion), hydrogen peroxide (4 mM), ascorbate and ferrous sulfate (4 mM; produces hydroxyl radical) with and without the addition of seminal plasma. Samples were analysed for motility using computer-assisted sperm analysis (CASA); the 3–3′ diaminobenzidine stain, as an index of mitochondrial activity; the eosin nigrosin stain, as an index of membrane integrity; the simple stain (Fast green/Bengal rose), as an index of acrosome integrity; sperm chromatin structure assay as an index of DNA fragmentation; and the measurement of thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation. Statistical analysis was performed using the SAS System for Windows (SAS Institute Inc., Cary, NC, USA; least significant differences test and Spearman correlation; P < 0.05). Results showed that cryopreserved goat sperm after thawing is highly susceptible to the hydroxyl radical. No differences were found on CASA variables between the different ROS. On the other hand, lipid peroxidation and DNA fragmentation were higher for samples treated with hydroxyl radical when compared to samples treated with the other ROS. Furthermore, sperm showing low mitochondrial activity were lower also for samples treated with hydroxyl radical. Negative correlations were found between lipid peroxidation, and most of the variables evaluated by the CASA. A positive correlation was found between the percentage of sperm showing low mitochondrial potential and DNA fragmentation, indicating that impaired mitochondrial activity may be related to an increase on DNA fragmentation. Previous studies indicate that fresh goat semen is highly susceptible to the attack of hydrogen peroxide. We observed that after thawing there is a shift towards a higher susceptibility to the hydroxyl radical. This may indicate that seminal plasma in goats may be an important source of hydroxyl radical scavengers and that, due to the dilution of the seminal plasma with the extender, such antioxidant protection may be impaired. Therefore, an alternative to improve semen quality in cryopreserved goat semen would be the treatment with hydroxyl radical scavengers such as vitamins E and C, reduced glutathione, and other non-enzymatic antioxidants.