Superoxide production, oxidative damage and enzymatic antioxidant defenses in shark skeletal muscle

Pelagic sharks, unlike teleost fish, require constant active swimming to obtain a suitable oxygen (O₂) supply. An increase in O₂ consumption during exercise enhances production of reactive oxygen species (ROS). We hypothesized that shark species that display vigorous exercise, such as Isurus oxyrinchus and Carcharhinus falciformis, have higher ROS production and, in consequence, higher antioxidant enzyme activities in muscle in comparison with species with less active swimming, like Sphyrna zygaena. Superoxide radical (O₂^•-) production, lipid peroxidation levels (TBARS) and the activity of antioxidant enzymes: superoxide dismutase (total, t-SOD; manganese-dependent, Mn-SOD, and copper and zinc-dependent, Cu, Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR), were measured by spectrophotometric assays in skeletal muscle extracts of three shark species (C. falciformis, I. oxyrinchus and S. zygaena). Higher O₂^•- production and GPx and GST activities (p < 0.05) were found in C. falciformis and I. oxyrinchus than in S. zygaena. These results suggest that in antioxidant enzymes (GPx, GST) activity suffices to balance the production of ROS and to maintain lower TBARS levels (p < 0.05) than in C. falciformis or S. zygaena, contributing to the capacity of I. oxyrinchus to maintain high muscular activity.