Response of antioxidant and biotransformation systems of selected freshwater mussels (Dreissena polymorpha, Anadonta cygnea, Unio tumidus, and Corbicula java']javanicus) to the cyanobacterial neurotoxin β-N-methylamino-L-alanine

Response of selected biotransformation and antioxidant enzymes (glutathione S-transferase (GST), catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GPx)) of four different freshwater mussel species (Dreissena polymorpha, Corbicula javanicus, Anadonta cygnea, and Unio tumidus) was compared after a static exposure to 100 mu g L-1 beta-N-methylamino-L-alanine (BMAA) for 24 or 48hours. Whereas D. polymorpha and A. cygnea did not show significant alteration in the activity of the selected enzymes, C. javanicus reacted with increased GST and GR activity after 24hours and decreased CAT and GPx activity after 48hours. U. tumidus displayed increased CAT and GR activity after 24hours. Comparison between the concentration-dependent reaction of invasive D. polymorpha and native U. tumidus (exposure to 10, 100, and 500 mu g L-1 BMAA) suggested a greater susceptibility of U. tumidus to BMAA. A further experiment on the time-dependent response to BMAA in U. tumidus gave an insight into the progression of the enzymatic response(s). An increase in CAT activity occurred after merely four hours, while a decrease of GPx activity was in turn only considerable after a longer exposure, for four or seven days. The data suggest that the BMAA exposure in freshwater mussels provokes changes in selected oxidative stress enzymes, which could result in the enhancement or inhibition of antioxidant systems.