Detection, transfer and role of an environmentally spread neurotoxin (BMAA) with focus on cyanobacteria and the Baltic Sea region

Abstract: ?-N-methylamino-L-alanine (BMAA) is one of the more recently discovered bioactive compounds produced by cyanobacteria. BMAA is a non-protein amino acid reported present in human brain tissues of patients deceased from a neurodegenerative disease, such as Alzheimer´s disease or amyotrophic lateral sclerosis (ALS). This observation in combination with its neurotoxic effects in eukaryotes (in vivo and in vitro) and its potential to incorporate into (human) proteins, causing protein aggregation, suggests BMAA as a possible causative environmental agent for neurodegenerative diseases. Due to the ubiquitous nature of cyanobacteria with a wide occurrence in both aquatic and terrestrial environments, BMAA could be globally spread. Hence, investigations of a possible coupling between BMAA and neurodegeneration are urgently needed as well as to identify sources of BMAA in Nature.The aim of this thesis was to examine the potential occurrence of BMAA in bloom forming cyanobacteria of the Baltic Sea and its possible transfer to other organisms of this ecosystem. Of importance was also to reveal any likely routes for human BMAA exposure in the Baltic Sea region and to further investigate BMAA as a triggering agent for neurodegenerative diseases. Acknowledged difficulties of analysing BMAA in biological samples also inferred method development as part of the experimental studies. Investigating the role of BMAA in its producers was another purpose of the thesis, which may be crucial for future management of BMAA-producing cyanobacteria.By screening natural populations of the major filamentous bloom forming cyanobacteria of the Baltic Sea, we discovered the presence of BMAA throughout the entire summer season of two consecutive years, using a highly specific analytical method (liquid chromatography-tandem mass spectrometry; LC-MS/MS). BMAA was found to bioaccumulate in zooplankton and fish, as well as in mussels and oysters from the Swedish west coast. To improve the understanding of BMAA analyses in natural samples, the formation of carbamate adducts in the presence of bicarbonate was examined. Using two derivatization techniques in combination with LC-MS/MS, we could show that BMAA detection was not hindered by carbamate formation. Exogenously added BMAA inhibited nitrogen fixation in the model cyanobacterium Nostoc sp. PCC 7120, which was also hampered in growth and displayed signs of nitrogen starvation. Finally, BMAA was detected in cerebrospinal fluid in three of 25 Swedish test individuals, and represents the first confirmation of BMAA in the human central nervous system using LC-MS/MS as the primary analytical method. However, the association of BMAA to neurodegenerative diseases could not be verified as BMAA was present in both control individuals (two) and in one ALS-patient. Nevertheless, the finding of a known neurotoxic compound in the human central nervous system is alarming and potential consequences should be investigated.The discovery of the neurotoxic compound BMAA in Baltic Sea organisms, and in the central nervous system of humans potentially consuming fish from this ecosystem is concerning and warrants continued investigations of BMAA occurrence and human exposure. Further knowledge on the function and regulation of BMAA may help in developing strategies aiming to minimise human exposure.