GLUTATHIONE, GLUTATHIONE-DEPENDENT AND ANTIOXIDANT ENZYMES IN MUSSEL, MYTILUS-GALLOPROVINCIALIS, EXPOSED TO METALS UNDER FIELD AND LABORATORY CONDITIONS - IMPLICATIONS FOR THE USE OF BIOCHEMICAL BIOMARKERS

The effects of exposure to metals under and laboratory conditions were investigated in the Mediterranean mussel Mytilus galloprovincialis. The examined biological responses included the concentrations of heavy metals, the level of glutathione, and the activity of several enzymes selected among glutathione-dependent oxidoreductases and hydrolases: glutathione reductase, EC1.6.4.2; glyoxalase I, EC4.4.1.5; glyoxalase II, EC3.1.2.6; glutathione S-transferases, EC2.5.1.18; Se-dependent, EC1.11.1.9 and Se-independent, EC2.5.1.18 glutathione peroxidases; catalase, EC1.11.1.6; superoxide dismutase, EC1.15.1.1; alkaline phosphatase, EC3.1.3.1; cholinesterase, EC3.1.1.8; arylesterases, EC3.1.1.2. The analyses were carried out on digestive gland and gills of mussels from two populations, respectively from a polluted and a clean site. The same parameters were measured in control mussels transplanted to the polluted environment, and in molluscs exposed to copper under laboratory conditions. The comparison between different field and laboratory exposures was expected to give useful indications for a proper use of biochemical responses as biomarkers in monitoring trace metal pollution. Compared to control mussels, the polluted ones (native, transplanted and copper-exposed) showed significantly lower levels of glutathione and higher activities of the glyoxalases (which detoxify reactive alpha-ketoaldehydes formed in cellular oxidative processes). On the other hand, native mussels from both the polluted and control populations exhibited similar enzymatic activities of glutathione reductase, glutathione peroxidases, catalase, superoxide dismutase and alkaline phosphatase, whereas, in both transplanted and copper-exposed mussels, these enzymes showed significant variations. This finding could suggest the occurrence of some adaptation or compensatory mechanism in chronically polluted organisms. No clear results were obtained with glutathione S-transferases, whereas arylesterases and cholinesterases appeared not to be affected by metal pollution. From the results, three different kind of biological responses were identified and the implications for ecotoxicological studies discussed.