Antioxidant enzymes, glutathione and lipid peroxidation as relevant biomarkers of experimental or field exposure in the gills and the digestive gland of the freshwater bivalve Unio tumidus

Abstract

The aim of this work was to evaluate the potential utility of antioxidant parameters as indicators of exposure to toxicants and of toxic effects in the freshwater mussel Unio tumidus. Antioxidant enzymes (glutathione peroxidase (EC 1.11.1.9), glutathione reductase (EC 1.6.4.2), Superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6)), redox status of glutathione and lipid peroxidation were measured at first in the gills and the digestive glands of mussels after exposure to copper (30 μg l −1) or/and thiram (100 μg l −1) for 3 days. The effects of a complex industrial effluent on the antioxidant system were investigated afterwards in a field study: encaged mussels were placed in a river upstream and downstream from a pollution source consisting of the effluent of a cokery for 1 week. These studies demonstrated that in both experimental exposures, the most sensitive parameters were selenium-dependent glutathione peroxidase activity (SeGPx), reduced glutathione levels (GSH) and especially glutathione reductase activity (GRd) which significantly decreased. Decreases in SeGPX and GRd activities were more pronounced in the gills under coexposure to copper and thiram, with 74% and 78% of reduced activity, respectively ( P < 0.01); reduction of GSH levels was 50% in this case. In the field study, the activities could be reduced by 35% and 72% in the gills for SeGPx and GRd, respectively; reduction of GSH levels could reach 45%. In contrast, superoxide dismutase and catalase activities remained generally constant in all the treatment groups compared with controls. Lipid peroxidation, as expressed by malonaldehyde content measured by HPLC, was slightly enhanced in experiment with copper+thiram and this increase (from 1.8 to 2.8 fold) was concomitant with a depletion of antioxidant defences. The responses of antioxidant parameters were overall greater in the gills than in the digestive glands of exposed mussels. These results suggest that among antioxidant defence systems, SeGPx, GSH levels and particularly GRd, could represent biomarkers of interest for the estimation of the effects of environmental contamination on freshwater invertebrates.