Influence of tributyltin on activity of detoxifying enzymes from haemocytes of a colonial ascidian

Filter-feeding invertebrates are used as bioindicators of organotins in coastal areas, because they are known to concentrate these xenobiotics and suffer many toxic effects, the most important of which is severe immunosuppression. As antioxidant enzymes have often been proposed as biomarkers of oxidative stress following exposure to contaminants, it was of interest to investigate whether the activities of glutathione S-transferase (GST) and glutathione peroxidase (GPX) in cultured haemocytes of the colonial ascidian Botryllus schlosseri are influenced by exposure to tributyltin (TBT). Results suggest the presence, in ascidian haemocytes, of the above enzymes involved in detoxification processes since positivity to both GST and Se-dependent GPX antibodies was observed. The immunocytochemical location of GST and GPX disappeared by incubation in the presence of 0.1 and 1 μM TBT, respectively, as a possible consequence of conformational changes due to direct interaction of TBT with the antioxidant enzymes. Moreover, spectrophotometric assays on haemolysate showed that TBT can inhibit the activities of both GST and Se-independent GPX, the latter in a more effective manner than Se-dependent GPX, suggesting that ascidians possess a detoxifying defence system similar to that reported by other authors for bivalve molluscs.