Role of metallothionein against oxidative stress in the mussel Mytilus galloprovincialis

Metallothionein (MT) is a sulfhydryl-rich protein involved mainly in heavy metal homeostasis and detoxification. In this study, the use of the mussel as an experimental model allowed us to test MT antioxidant properties at th e molecular, cellular, and organism level. MT induction was achieved by mus sel exposure to Cd (200 mu g/l) in aquaria for 7 days followed by detoxific ation in the sea for 28 days. Cd-preexposed and nonexposed mussels were the n treated with Fe (300-600 mu g/l) in aquaria for 3 days. Biochemical assay s on digestive gland tissue showed that treatment with Fe led to a signific ant increase in oxyradical production and malondialdehyde level only in mus sels not preexposed to Cd. The Cd-dependent resistance to oxidative stress was ascribed to MT induction, as Cd produced no significant variation of re duced glutathione and major antioxidant enzymes. Digital imaging of isolate d digestive gland cells showed lower oxyradical rise and higher viability i n cells from Cd-preexposed mussels after treatments with 0.5-5 mM H2O2. Ana lyses on whole organisms showed that anoxic survival was lowered in mussels that had been treated with Fe, but such an effect was less pronounced in C d-preexposed mussels compared with nonpreexposed ones. In conclusion, data suggest an antioxidant role for MT, which seems to occur through oxyradical scavenging and is able to protect both isolated cells and the entire organ ism from oxidative stress.