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Immunological and antioxidant enzyme responses in the pearl oyster Pinctada imbricate (Mollusca: Pteridae) exposed to sublethal levels of fuel oil n°6

Abstract:

The immune and antioxidant enzyme defenses in pearl oyster Pinctada imbricata were evaluated after shot-term (7d) exposure to 25 and 100% water-soluble fraction (WSF) of Fuel Oil N°6, a source of polyaromatic hydrocarbon and heavy metal contamination of marine ecosystems. Lysozyme activity in the digestive gland and the phagocytic activity of hemocytes were measured as humoral and cellular immunological responses, respectively, using heat killed yeast cells as antigen for the phagocytosis assay. The viability and total number of hemocytes were recorded. The detoxifying enzymes Glutathione-S-transferase (GST), glutathione peroxidase (GPx), glutathione reductase (GR) and catalase (CAT) were evaluated from the digestive gland and mantle extracts. In the digestive gland the exposure to WSF treatments resulted in significant increases of GST and CAT. In the mantle, both experimental treatments increased GPx and decreased GST activity, while CAT was not affected. Immunological indicators were not affected by the treatments, excepting cellular viability which decreased under exposure to 100% WSF. The results suggest that the antioxidant enzymes in the digestive gland and mantle of P. imbricate are sensitive to short-term exposure to Fuel Oil N°6, suggesting an increased oxiradical flux and biochemical manifestations of oxidative injury in both tissues. These parameters should be considered as potential tools for the biomonitoring of marine environmental contamination.