Defenses against oxidative stress in the Antarctic scallop Adamussium colbecki and effects of acute exposure to metals

Since a general pathway of toxicity induced by pollutants is the enhancement of reactive oxygen species, biochemical responses associated with variations in the antioxidant cellular system have been often proposed as biomarkers of pollutantmediated toxicity associated with oxidative stress. Antarctic organisms live in an extreme environment characterized by low water temperature, high level of dissolved oxygen, presence of ice and strong seasonal changes in light intensity and availability of food, conditions which could influence both the formation of reactive oxygen species and the mechanisms for their removal. In this respect and considering the utility of this as a key species for monitoring marine Antarctic environment it was of interest to investigate the antioxidant defense system of the scallop Adamussium colbecki. The parameters examined in the digestive gland of the scallop were the concentration of glutathione and the activity of several glutathione dependent and antioxidant enzymes (glyoxalase I and II, glutathione S-transferases, glutathione peroxidases, glutathione reductase, catalase, superoxide dismutase). Very high levels of catalase suggest a possible adaptation to Antarctic extreme conditions, while the high activities of glutathione S-transferases are more probably related to the feeding behavior of Pectinids. Enzymes from Adamussium colbecki generally appeared to be active at low temperatures but, with a few exceptions, their activities increased with rising temperature. Exposure of A. colbecki to sublethal concentrations of Cu or Hg resulted in a significant reduction in the levels of total glutathione and in the activity of catalase and glutathione S-transferases. Antioxidant responses of A. colbecki could represent a useful tool in assessing the biological impact of environmental pollutants in the Antarctic ecosystems.