235 MANGALARGA STALLION SPERM IS HIGHLY SUSCEPTIBLE TO THE HYDROXYL RADICAL

Abstract

Mangalarga, due to its marching abilities, is the mostly widespread and numerous equine breed in Brazil. Furthermore, previous studies indicate that the semen of these horses is particularly susceptible to cryo-injuries. Therefore, the use of chilled semen is crucial when employing reproductive biotechnologies. However, previous studies indicate that chilled semen is highly impaired by the oxidative stress, which is caused by reactive oxygen species (ROS). An alternative to overcome the injuries caused by oxidative stress is antioxidant treatment, which requires the identification of those ROS that are the most deleterious. The aim of this study was to identify the most harmful ROS to Mangalarga sperm. Semen samples from 4 horses were collected, mixed with chilling media (Equimix^®, Nutricell) and transported to the laboratory at 15°C. Samples were then incubated (1 h, 37°C) with 4 ROS inducing mechanisms: xanthine/xanthine oxidase (produces superoxide anion), hydrogen peroxide (4 mM), ascorbate and ferrous sulfate (4 mM; produces hydroxyl radical). Samples were analysed for motility using computer assisted sperm analysis (CASA). The 3-3′ diaminobenzidine stain was used 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 (SCSA) 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 Mangalarga sperm is highly susceptible to the hydroxyl radical. Samples treated with this ROS showed a lower percentage of sperm with high mitochondrial activity then samples treated with hydrogen peroxide (24.6 ± 5.9 v. 43.7 ± 6.8%, respectively). Similarly, lipid peroxidation (TBARS) was higher in samples treated with hydroxyl radical when compared with those treated with both superoxide anion and hydrogen peroxide (2037.7 ± 154.8, 681.2 ± 170.1, and 789.4 ± 124.5 ng/10⁶ sperm). In addition, for all variables analysed using CASA except for ALH and BCF, samples treated with hydroxyl radical showed decreased quality when compared with the other samples. A positive correlation was found between TBARS and mitochondrial activity, indicating that the higher the sperm susceptibility of sperm against oxidative stress, the lower the mitochondrial activity. Level of TBARS also correlated negatively with most of the variables evaluated by CASA. The present results suggest that Mangalarga sperm is highly susceptible to the hydroxyl radical, a mechanism apparently related to the mitochondrial activity. Therefore, an alternative to overcome the deleterious influence of oxidative stress in semen of Mangalarga stallions would be the treatment with hydroxyl radical scavengers such as vitamins C and E, reduced glutathione, and other nonenzymatic antioxidants.