Effect of hydrogen peroxide on antioxidant systems and metallothionein level in the digestive gland of Mytilus galloprovincialis

The pro-oxidant effect of H₂O₂ at a concentration of 20 μM was examined in the digestive gland of Mytilus galloprovincialis, a bivalve mollusc frequently used in biomonitoring programs. The oxidative stress caused by H₂O₂ has been evaluated in terms of lipid peroxidation and lysosomal system alteration. Complex cellular antioxidant defence mechanisms of the mussel were investigated at the enzymatic and non-enzymatic level in order to explain their relative role in reducing the risk of oxidative injury. Metallothionein, glutathione, superoxide dismutase, catalase and glutathione peroxidase were assayed after 1, 4 and 7 days of exposure to H₂O₂. The metallothionein content showed an increase by 43% after 4 days of exposure, followed by a decrease back to control values at 7 days. Antioxidant enzyme activities followed a similar pattern with a moderate increase after 1 or 4 days of treatment and a return to control values at 7 days. All data indicate a 'transient' oxidative stress response, after which mussel cells restore the redox balance.