Oxyradical scavenging capacity by the S9 fraction of Hexagenia spp. nymphs from the Western Basin of Lake Erie: neutralisation of three potent oxidants

Abstract

Oxidative stress is a general response of aquatic organisms to environmental contamination. Metals and organic compounds capable of redox cycling cause proliferation of reactive oxygen species (ROS) within organisms. Harm results from ROS-mediated DNA damage, lipid peroxidation, enzyme degradation and compromised intermediary metabolism. Variations in concentrations or activities of antioxidants have been proposed as biomarkers of toxicant-mediated oxidative stress in aquatic organisms. The total oxyradical scavenging capacity (TOSC) assay provides an index of biological resistance to ROS. Burrowing mayflies (Hexagenia spp.) are key indicator species of the health of numerous water bodies, including Lake Erie. TOSC has been used to evaluate the ROS scavenging capacity of tissues from a number of marine and freshwater invertebrates. This is the first study to evaluate ROS scavenging capacity in Hexagenia nymphs. Hexagenia nymphal tissue was homogenised in TRIS buffer containing a protease inhibitor cocktail and then differentially centrifuged to obtain a 9000 g supernatant (S9). The specific TOSC values (±SD, n=3) per μg protein are 2.08±0.43 for peroxyl radicals, 3.06±0.19 for hydroxyl radicals and 0.36±0.02 for peroxynitrite (n=3 to 4 determinations). These values for peroxyl radical scavenging capacity were equivalent to 11.9% and 77.0% that of Trolox (a water soluble analogue of vitamin E) and reduced glutathione TOSC equivalents, respectively, on a per μg basis. These results show that Hexagenia nymphal S9 is capable of neutralising peroxyl radicals and hydroxyl radicals effectively, but neutralises peroxynitrite considerably more weakly. The efficacy of this parameter as a biomarker of exposure to or effect of environmental contaminants will require controlled exposure analysis.