Trophic transfer of the neurotoxin BMAA from the bivalve Dreissena polymorpha to the fish Rutilus rutilus and impact on the fish

Due to eutrophication of freshwaters, the frequency of cyanobacteria proliferations is increasing worldwide and the presence of associated cyanotoxins represent a threat for ecosystems and for human health. Most cyanobacteria produce a neurotoxic amino acid β-methylamino-L-alanine (BMAA) linked to serious neurodegenerative diseases (amyotrophic lateral sclerosis (ALS), Alzheimer and Parkinsonism). Knowledge should be extended about the scale of BMAA accumulation in the foodweb and also about its impact on aquatic organisms. We previously demonstrated that the bivalve Dreissena polymorpha accumulated free and bound BMAA in tissues during an exposure to dissolved BMAA. Therefore D. polymorpha is potentially a BMAA-vector through the food web. This study focus on the trophic transfer of BMAA between D.polymorpha and the fish Rutilus rutilus and the consequences on this latter in terms of : 1) BMAA accumulation and elimination in the liver, brain and muscle, 2) acetylcholinesterase (AchE) activity in the brain and muscle, 3) oxidative stress response in the liver via activities of enzymes catalase (CAT), superoxide dismutase (SOD), Ethoxyresorufin-O-deethylase (EROD), glutathione peroxydase (GPx), glutathione (GSH), and glutathione-S-transferase (GST), and 4) activity of digestive enzymes (amylase and trypsin) in the gut. Fish were fed with BMAA-intoxicated mussels during a 2-weeks intoxication period followed by 1 week of depuration. Results show a BMAA trophic transfer from the bivalve to the fish with an accumulation of BMAA in the brain, liver and muscle of fish after 4 days of ingestion of BMAA-intoxicated mussels. BMAA content in fish organs increased from day 4 to day 14 of exposure with a maximum of 3.16 +- 2.07 ug BMAA g-1 protein in muscle. BMAA content decreased during the depuration period in the fish liver and in the brain but increased in muscle up to 5.7 +- 4.53 ug BMAA g-1 protein at the day 7 of depuration. No significant alteration in the activity of amylase, trypsin, SOD, GSH and GST enzymes was reported. In the liver GPx and EROD activity were respectively decreased and increased after 4 days of exposure, whereas CAT activity was decreased after 14 days. The neurotransmetor AchE showed a decreased activity in the brain at the end of the depuration period