Total oxyradical scavenging capacity of Antarctic, Arctic, and Mediterranean scallops

The Total Oxyradical Scavenging Capacity (TOSC) assay was used in three species of scallops for quantifying their ability to neutralise peroxyl (ROO*) and hydroxyl (*OH) radicals and peroxynitrite (HOONO). Adamussium colbecki and Chlamys islandicus represent key organisms for monitoring Antarctic and Arctic regions while Pecten jacobaeus was chosen for comparison with a related temperate species. TOSC values for ROO* were significantly higher in A. colbecki, indicating that this species is the most efficient ROO* scavenger. Mediterranean scallops had the lowest TOSC for ROO*. Adamussium colbecki also exhibited the highest scavenging capacity for *OH with values more than two-fold greater than for C. islandicus and P. jacobaeus. TOSC values for HOONO were lower for all scallops as compared to those for ROO* or *OH; for microsomes they were not significantly different among the species for any reactive oxygen species studied, and the percentage contribution to the specific TOSC for the various oxidants of microsomes of all scallops accounted for 1-3% of the total TOSC of the post-mitochondrial fraction. The specific TOSC of scallop microsomes for *OH was -10 times lower than that for ROO* or HOONO. The higher basal capability of the Antarctic scallop to neutralise different reactive oxygen species is discussed in terms of a possible adaptation to this extreme environment, and TOSC is validated as a quantifiable measure of susceptibility to oxidative stress in marine organisms. In a second part of this study, the seasonal fluctuations of susceptibility to oxidative stress were analysed in the Antarctic scallop Adamussium colbecki by the TOSC Assay. A marked increase in the capability to neutralise peroxyl radicals and hydroxyl radicals was demonstrated at the end of December, while resistance towards peroxynitrite did not show significant variations during the Antarctic summer. The increased resistance to these specific oxyradicals was almost contemporary with the period of highest feeding activity and the development of gonadic tissues. Sensitivity to hydroxyl radicals and peroxyl radicals toxicity was also influenced by UV-B and UV-Á wavelengths, as indicated by the lower TOSC values in scallops exposed under laboratory conditions. Toxicity of UV radiation seems partly mediated by formation of reactive oxygen species caused by the direct exposure of mantle edges and/or the photochemical production of hydrogen peroxide in sea water.