Bacteria do not incorporate β-N-methylamino-l-alanine into their proteins

A systematic review on analytical methods of the neurotoxin β-N-methylamino-L-alanine (BMAA), and its causative microalgae and distribution in the environment

β-N-Methylamino-L-alanine (BMAA), a neurotoxin produced by various microalgal groups, is associated with neurodegenerative diseases and is considered a major environmental factor potentially linked to sporadic amyotrophic lateral sclerosis. This study systematically reviews the analytical methods used to study BMAA in publications from 2019 to the present. It also investigates the causative microalgae of BMAA and its geographical distributions in aquatic ecosystems based on studies conducted since 2003. A comprehensive search using the Web of Science database revealed that hydrolysis for extraction (67%), followed by quantification using LC-MS/MS (LC: 84%; MS/MS: 88%), is the most commonly employed method in BMAA analysis. Among analytical methods, RPLC-MS/MS had the highest percentage (88%) of BMAA-positive results and included a high number of quality control (QC) assessments. Various genera of cyanobacteria and diatoms have been reported to produce BMAA. The widespread geographical distribution of BMAA across diverse ecosystems highlights significant environmental and public health concerns. Notably, BMAA accumulation and biomagnification are likely more potent in marine or brackish water ecosystems than in freshwater ecosystems, potentially amplifying its ecological impacts. Future research should prioritize advanced, sensitive methods, particularly LC-MS/MS with as many QC assessments as possible, and should expand investigations to identify novel microalgal producers and previously uncharted geographical areas, with a special focus on marine or brackish water ecosystems. This effort will enhance our understanding of the environmental distribution and impacts of BMAA.

How does the neurotoxin β-N-methylamino-L-alanine exist in biological matrices and cause toxicity?

The neurotoxin β-N-methylamino-L-alanine (BMAA) has been deemed as a risk factor for some neurodegenerative diseases such as amyotrophic lateral sclerosis/parkinsonism dementia complex (ALS/PDC). This possible link has been proved in some primate models and cell cultures with the appearance that BMAA exposure can cause excitotoxicity, formation of protein aggregates, and/or oxidative stress. The neurotoxin BMAA extensively exists in the environment and can be transferred through the food web to human beings. In this review, the occurrence, toxicological mechanisms, and characteristics of BMAA were comprehensively summarized, and proteins and peptides were speculated as its possible binding substances in biological matrices. It is difficult to compare the published data from previous studies due to the inconsistent analytical methods and components of BMAA. The binding characteristics of BMAA should be focused on to improve our understanding of its health risk to human health in the future.

Protection against β-N-methylamino-l-alanineꟷinduced vesicular monoamine transporter 2 inhibition by hydroxyl-containing proteinogenic amino acids

β-N-methylamino-l-alanine (BMAA) has been shown to inhibit vesicular monoamine transporter 2 (VMAT2), thereby preventing the uptake of monoaminergic neurotransmitters into platelet dense granules and synaptic vesicles. The inhibition is hypothesized to be through direct association of BMAA with hydroxyl groupꟷcontaining amino acid residues in VMAT2. This study evaluated whether BMAA-induced inhibition of VMAT2 could be prevented directly by co-incubation of BMAA with amino acids, and if this protection was specific for BMAA inhibition of VMAT2. l-tyrosine, and to a lesser extent l-serine, was able to prevent BMAA-induced VMAT2 inhibition in a concentration-dependent manner, whereas neither l-threonine nor amino acids without side chain hydroxyl groups could reduce this inhibition. Reserpine-induced VMAT2 inhibition was unaffected by any of the amino acids. These data support the hypothesized interaction between BMAA and hydroxyl groupꟷcontaining amino acids and suggests that this interaction might be leveraged to protect against the toxicity of BMAA.

Harmful and beneficial properties of cyanotoxins: Two sides of the same coin

Cyanotoxins are by definition "harmful agents" produced by cyanobacteria. Their toxicity has been extensively studied and reviewed over the years. Cyanotoxins have been commonly classified, based on their poisonous effects on mammals, into three main classes, neurotoxins, hepatotoxins and dermatotoxins, and, considering their chemical features, mainly identified as peptides, alkaloids and lipopolysaccharides. Here we propose a broader subdivision of cyanotoxins into eight distinct classes, taking into account their molecular structures, biosynthesis and modes of action: alkaloids, non-ribosomal peptides, polyketides, non-protein amino acids, indole alkaloids, organophosphates, lipopeptides and lipoglycans. For each class, the structures and primary mechanisms of toxicity of the main representative cyanotoxins are reported. Despite their powerful biological activities, only recently scientists have considered the biotechnological potential of cyanotoxins, and their applications both in medical and in industrial settings, even if only a few of these have reached the biotech market. In this perspective, we discuss the potential uses of cyanotoxins as anticancer, antimicrobial, and biocidal agents, as common applications for cytotoxic compounds. Furthermore, taking into account their mechanisms of action, we describe peculiar potential bioactivities for several cyanotoxin classes, such as local anaesthetics, antithrombotics, neuroplasticity promoters, immunomodulating and antifouling agents. In this review, we aim to stimulate research on the potential beneficial roles of cyanotoxins, which require interdisciplinary cooperation to facilitate the discovery of innovative biotechnologies.

Non-Proteinogenic Amino Acid β-N-Methylamino-L-Alanine (BMAA): Bioactivity and Ecological Significance

Research interest in a non-protein amino acid β-N-methylamino-L-alanine (BMAA) arose due to the discovery of a connection between exposure to BMAA and the occurrence of neurodegenerative diseases. Previous reviews on this topic either considered BMAA as a risk factor for neurodegenerative diseases or focused on the problems of detecting BMAA in various environmental samples. Our review is devoted to a wide range of fundamental biological problems related to BMAA, including the molecular mechanisms of biological activity of BMAA and the complex relationships between producers of BMAA and the environment in various natural ecosystems. At the beginning, we briefly recall the most important facts about the producers of BMAA (cyanobacteria, microalgae, and bacteria), the pathways of BMAA biosynthesis, and reliable methods of identification of BMAA. The main distinctive feature of our review is a detailed examination of the molecular mechanisms underlying the toxicity of BMAA to living cells. A brand new aspect, not previously discussed in any reviews, is the effect of BMAA on cyanobacterial cells. These recent studies, conducted using transcriptomics and proteomics, revealed potent regulatory effects of BMAA on the basic metabolism and cell development of these ancient photoautotrophic prokaryotes. Exogenous BMAA strongly influences cell differentiation and primary metabolic processes in cyanobacteria, such as nitrogen fixation, photosynthesis, carbon fixation, and various biosynthetic processes involving 2-oxoglutarate and glutamate. Cyanobacteria were found to be more sensitive to exogenous BMAA under nitrogen-limited growth conditions. We suggest a hypothesis that this toxic diaminoacid can be used by phytoplankton organisms as a possible allelopathic tool for controlling the population of cyanobacterial cells during a period of intense competition for nitrogen and other resources in various ecosystems.

Cysteine biosynthesis contributes to β-methylamino-l-alanine tolerance in Escherichia coli

In contrast to mammalian cells, bacteria such as Escherichia coli have been shown to display tolerance towards the neurotoxin β-methylamino-l-alanine (BMAA) suggesting that these prokaryotes possess a way to metabolise BMAA or its products, resulting in their export, degradation, or detoxification. Single gene deletion mutants of E. coli K-12 with inactivated amino acid biosynthesis pathways were treated with 500 μg/ml BMAA and the resulting growth was monitored. Wild type E. coli and most of the gene deletion mutants displayed unaltered growth in the presence of BMAA over 12 h. Conversely, deletion of genes in the cysteine biosynthesis pathway, cysE, cysK or cysM resulted in a BMAA dose-dependent growth delay in minimal medium. Through further studies of the ΔcysE strain, we observed increased susceptibility to oxidative stress from H2O2 in minimal medium, and disruptions in glutathione levels and oxidation state. The cysteine biosynthesis pathway is therefore linked to the tolerance of BMAA and oxidative stress in E. coli, which potentially represents a mechanism of BMAA detoxification.

Reviewing Interspecies Interactions as a Driving Force Affecting the Community Structure in Lakes via Cyanotoxins

The escalating occurrence of toxic cyanobacterial blooms worldwide is a matter of concern. Global warming and eutrophication play a major role in the regularity of cyanobacterial blooms, which has noticeably shifted towards the predomination of toxic populations. Therefore, understanding the effects of cyanobacterial toxins in aquatic ecosystems and their advantages to the producers are of growing interest. In this paper, the current literature is critically reviewed to provide further insights into the ecological contribution of cyanotoxins in the variation of the lake community diversity and structure through interspecies interplay. The most commonly detected and studied cyanobacterial toxins, namely the microcystins, anatoxins, saxitoxins, cylindrospermopsins and β-N-methylamino-L-alanine, and their ecotoxicity on various trophic levels are discussed. This work addresses the environmental characterization of pure toxins, toxin-containing crude extracts and filtrates of single and mixed cultures in interspecies interactions by inducing different physiological and metabolic responses. More data on these interactions under natural conditions and laboratory-based studies using direct co-cultivation approaches will provide more substantial information on the consequences of cyanotoxins in the natural ecosystem. This review is beneficial for understanding cyanotoxin-mediated interspecies interactions, developing bloom mitigation technologies and robustly assessing the hazards posed by toxin-producing cyanobacteria to humans and other organisms.

Misincorporation Proteomics Technologies: A Review

Proteinopathies are diseases caused by factors that affect proteoform conformation. As such, a prevalent hypothesis is that the misincorporation of noncanonical amino acids into a proteoform results in detrimental structures. However, this hypothesis is missing proteomic evidence, specifically the detection of a noncanonical amino acid in a peptide sequence. This review aims to outline the current state of technology that can be used to investigate mistranslations and misincorporations whilst framing the pursuit as Misincorporation Proteomics (MiP). The current availability of technologies explored herein is mass spectrometry, sample enrichment/preparation, data analysis techniques, and the hyphenation of approaches. While many of these technologies show potential, our review reveals a need for further development and refinement of approaches is still required.

Toxicity and bioaccumulation of two non-protein amino acids synthesised by cyanobacteria, β-N-Methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB), on a crop plant

In order to study the toxicity of the cyanobacterial non-protein amino acids (NPAAs) L-β-N-methylamino-L-alanine (BMAA) and its structural isomer L-2,4-diaminobutyric acid (DAB) in the forage crop plant alfalfa (Medicago sativa), seedlings were exposed to NPAA-containing media for four days. Root growth was significantly inhibited by both treatments. The content of derivatised free and protein-bound BMAA and DAB in seedlings was then analysed by LC-MS/MS. Both NPAAs were detected in free and protein-bound fractions with higher levels detected in free fractions. Compared to shoots, there was approximately tenfold more BMAA and DAB in alfalfa roots. These results suggest that NPAAs might be taken up into crop plants from contaminated irrigation water and enter the food chain. This may present an exposure pathway for NPAAs in humans.

Evaluating amino acids as protectants against β-N-methylamino-l-alanine-induced developmental neurotoxicity in a rat model

With accumulating evidence that supports the role of β-N-methylamino-l-alanine (BMAA) in neurodegeneration, it is necessary to elucidate the mechanisms and modes of BMAA toxicity so as to facilitate the search for potential preventative/therapeutic strategies. Daily supplementation with l-serine was suggested as a possible therapy to treat BMAA-induced neurotoxicity, based on the hypothesized mechanism of BMAA misincorporation into proteins for l-serine. As an alternative to misincorporation, it was hypothesized that BMAA toxicity may, in part, be due to its high affinity for associating with hydroxyl group-containing amino acids, and that a dietary excess of the hydroxyl-containing l-serine might offer protection by binding to BMAA and reducing its toxicity. Additionally, l-serine can also reduce the uptake of BMAA into human cells by competitive uptake at ASCT2, and l-phenylalanine, by competitive uptake at LAT1, and l-alanine, by competitive uptake at SNAT2, can also reduce BMAA uptake into human cells. The aim of this study was therefore to determine the protective value of l-serine, l-phenylalanine and l-alanine in reducing the effects of neonatal exposure to BMAA in a Sprague Dawley rat model. Pre-treatment with l-phenylalanine reduced the observed behavioral abnormalities and neuropathologies by 60-70% in most cases. l-serine was also effective in reducing some of the behavioral abnormalities and neuropathologies, most markedly spinal cord neuronal loss. However, the protective effect of l-serine was obfuscated by neuropathies that were observed in l-serine-treated control male rats. l-alanine had no effect in protecting against BMAA-induced neurotoxicity, suggesting that competitive amino acid uptake plays a minor role in protecting against BMAA-induced neurotoxicity.

Metabolism of the neurotoxic amino acid β-N-methylamino-L-alanine in human cell culture models

Human dietary exposure to the environmental neurotoxin β-N-methylamino-L-alanine (BMAA) has been implicated in an increased risk of developing sporadic neurodegenerative diseases like Alzheimer's and amyotrophic lateral sclerosis. Evidence suggests that humans are exposed to BMAA globally, but very little is known about BMAA metabolism in mammalian systems, let alone in humans. The most plausible, evidence-based mechanisms of BMAA toxicity rely on the metabolic stability of the amino acid and that, following ingestion, it enters the circulatory system unmodified. BMAA crosses from the intestinal lumen into the circulatory system, and the small intestine and liver are the first sites for dietary amino acid metabolism. Both tissues have substantial amino acid metabolic needs, which are largely fulfilled by dietary amino acids. Metabolism of BMAA in these tissues has been largely overlooked, yet is important in gauging the true human exposure risk. Here we investigate the potential for BMAA metabolism by the human liver and small intestine, using in vitro cell systems. Data show that BMAA metabolism via common proteinogenic amino acid metabolic pathways is negligible, and that in the presence of other amino acids cellular uptake of BMAA is substantially reduced. These data suggest that the majority of ingested BMAA remains unmodified following passage through the small intestine and liver. This not only supports oral BMAA exposure as a plausible exposure route to toxic doses of BMAA, but also supports previous notions that protein deficient diets or malnutrition may increase an individual's susceptibility to BMAA absorption and subsequent toxicity.

Vegetables cultivated with exposure to pure and naturally occurring β-N-methylamino-L-alanine (BMAA) via irrigation

Bioaccumulation and biomagnification of β-N-methylamino-L-alanine (BMAA), a potent neurotoxin, has been demonstrated in various food webs. It is alarming as this intensification of BMAA will result in exposure to higher concentrations from a direct cyanobacterial source. As more food items are being identified as a source of BMAA and with the large variations in BMAA content, the aim of the present study was to evaluate BMAA uptake by, and accumulation in, two commonly consumed vegetables, Lactuca sativa and Allium fistulosum. Plants exposed to pure BMAA in controlled laboratory experiments, as well as vegetables naturally irrigated with water containing a BMAA producing cyanobacterial bloom were evaluated during growth and ripening. In the laboratory exposures, free BMAA was detected in both the edible ripe parts of L. sativa and A. fistulosum after 60 days of exposure to a total of 4.5 µg BMAA. However, in the bloom exposure samples no BMAA could be detected in the ripe vegetables of A. fistulosum, Cucurbita pepo, or Brassica rapa chinensis. The study emphasises the need to further screen items for BMAA to understand the human exposure risk as well as the difference between BMAA uptake patterns with free BMAA and that contained in cyanobacterial cells.

β- N-methylamino-L-alanine Inhibits Human Catalase Activity: Possible Implications for Neurodegenerative Disease Development

The naturally produced, nonprotein amino acid β- N-methylamino-l-alanine (BMAA) has been proposed as a significant contributor to sporadic neurodegenerative disease development worldwide. However, the existing hypothesized mechanisms of toxicity do not adequately explain the role of BMAA in neurodegenerative disease development. There is evidence for BMAA-induced enzyme inhibition, but the effect of BMAA on human stress response enzymes has received little attention, despite the well-described role of oxidative stress in neurodegenerative disease development. The aim of this study was therefore to investigate the effect of BMAA on human catalase activity and compare it to the known inhibitor 3-amino-1,2,4-triazole. BMAA inhibited human erythrocyte catalase in a cell-free exposure to the same extent as the known inhibitor. Based on enzyme kinetics, the inhibition appears to be noncompetitive, possibly as a result of BMAA binding in the nicotinamide adenine dinucleotide phosphate (NADPH) binding site. BMAA-induced catalase inhibition was also observed in a human cell line culture. We therefore propose that BMAA-induced enzyme inhibition, specifically catalase inhibition, is a mechanism of toxicity that may contribute to the neurotoxicity of BMAA, further supporting the role of BMAA in neurodegenerative disease development.

β- N-Methylamino-l-alanine (BMAA) Not Involved in Alzheimer's Disease

β- N-Methylamino-l-alanine (BMAA) is a neurotoxic agent implicated in ALS as well as Parkinson's and Alzheimer's diseases. It is produced by blue-green algae and could find its way via fish and seafood into the human food supply. Isolation from biological samples yields the compound in monomeric and protein-bound form. It has been suggested that the protein-bound fraction may result from genetic misincorporation into proteins in place of serine. Concomitant misfolding of the mutated proteins may be responsible for the neurological diseases. Recent reports that contradict the misincorporation theory leave unresolved the nature of the protein-bound form of BMAA. We have found from quantum mechanical calculations on model systems that it is possible to bind BMAA with high affinity in a noncovalent fashion to proteins. Because of our interest in Alzheimer's disease, molecular dynamics simulations were applied to search for such binding between BMAA and the β-amyloid peptide and to discover whether replacement of either of its two serine residues could affect its aggregation into neurotoxic oligomers. No stable noncovalently bound complex was found, and it was concluded that incorporation of BMAA in place of serine would not alter the conformational dynamics of the β-amyloid peptide.

Occurrence of β-N-methylamino-l-alanine (BMAA) and Isomers in Aquatic Environments and Aquatic Food Sources for Humans

The neurotoxin β-N-methylamino-l-alanine (BMAA), a non-protein amino acid produced by terrestrial and aquatic cyanobacteria and by micro-algae, has been suggested to play a role as an environmental factor in the neurodegenerative disease Amyotrophic Lateral Sclerosis-Parkinsonism-Dementia complex (ALS-PDC). The ubiquitous presence of BMAA in aquatic environments and organisms along the food chain potentially makes it public health concerns. However, the BMAA-associated human health risk remains difficult to rigorously assess due to analytical challenges associated with the detection and quantification of BMAA and its natural isomers, 2,4-diamino butyric acid (DAB), β-amino-N-methyl-alanine (BAMA) and N-(2-aminoethyl) glycine (AEG). This systematic review, reporting the current knowledge on the presence of BMAA and isomers in aquatic environments and human food sources, was based on a selection and a score numbering of the scientific literature according to various qualitative and quantitative criteria concerning the chemical analytical methods used. Results from the best-graded studies show that marine bivalves are to date the matrix containing the higher amount of BMAA, far more than most fish muscles, but with an exception for shark cartilage. This review discusses the available data in terms of their use for human health risk assessment and identifies knowledge gaps requiring further investigations.

Investigating β-N-Methylamino-l-alanine Misincorporation in Human Cell Cultures: A Comparative Study with Known Amino Acid Analogues

Misincorporation of β-N-methylamino-l-alanine (BMAA) into proteins has been proposed to be a mechanism of toxicity to explain the role of BMAA in neurodegenerative disease development. However, studies have shown that all detectable BMAA can be removed from proteins by SDS-PAGE purification and that the toxicity of l-canavanine cannot be reproduced in prokaryotes or in a rat pheochromocytoma cell line, strongly indicating that the misincorporation hypothesis of BMAA should be re-investigated. The aim of this study was therefore to determine if BMAA misincorporates into proteins in cells of human origin with subsequent misincorporation-type toxicity. Almost complete loss of viability in response to exposure to l-4-fluorophenylalanine and l-m-tyrosine was observed in all of the cell lines, corresponding to a concentration-dependent increase of the analogues in protein extracts from exposed cells. In contrast, BMAA exposure resulted in slight toxicity in one of the cell lines but the observed toxicity was not the result of misincorporation of BMAA into proteins, as no BMAA was detected in any of the SDS-PAGE purified protein extracts that were obtained from the cells following BMAA exposure. The results show that BMAA is not misincorporated into human proteins and that misincorporation is not a valid mechanism of toxicity.

Investigation of the interaction of β-methylamino-L-alanine with eukaryotic and prokaryotic proteins

There is a strong body of evidence linking the non-protein amino acid (NPAA) β-methylamino-L-alanine (BMAA) to the development of a number of neurodegenerative diseases. BMAA has been found globally, is produced by a number of organisms including cyanobacteria, diatoms, and dinoflagellates; and has been shown to biomagnify through trophic levels. The role of BMAA in neurodegenerative disease is highlighted by its presence in the brains of a number of neurodegenerative disease patients, where it was found in a protein-bound form. We have previously shown that BMAA is bound to cell proteins, and results in the upregulation of the unfolded protein response, an endoplasmic reticulum stress response activated by the presence of misfolded proteins within the cell. Structurally aberrant proteins are features of a number of neurodegenerative diseases, and further investigation of how BMAA interacts with proteins is crucial to our understanding of its toxicity. Here we use radiolabelled BMAA to investigate the interaction and binding of BMAA to eukaryotic and prokaryotic proteins. We found differences in the presence and distribution of protein-bound BMAA between E. coli and neuroblastoma cells, with an increase in binding over time only seen in the eukaryotic cells. We also found that BMAA was unable to bind to pure proteins, or cell lysate in native or denaturing conditions, indicating that biological processing is required for BMAA to bind to proteins.

Metabolic solutions to the biosynthesis of some diaminomonocarboxylic acids in nature: Formation in cyanobacteria of the neurotoxins 3-N-methyl-2,3-diaminopropanoic acid (BMAA) and 2,4-diaminobutanoic acid (2,4-DAB)

The non-encoded diaminomonocarboxylic acids, 3-N-methyl-2,3-diaminopropanoic acid (syn: α-amino-β-methylaminopropionic acid, MeDAP; β-N-methylaminoalanine, BMAA) and 2,4-diaminobutanoic acid (2,4-DAB), are distributed widely in cyanobacterial species in free and bound forms. Both amino acids are neurotoxic in whole animal and cell-based bioassays. The biosynthetic pathway to 2,4-DAB is well documented in bacteria and in one higher plant species, but has not been confirmed in cyanobacteria. The biosynthetic pathway to BMAA is unknown. This review considers possible metabolic routes, by analogy with reactions used in other species, by which these amino acids might be biosynthesised by cyanobacteria, which are a widespread potential environmental source of these neurotoxins. Where possible, the gene expression that might be implicated in these biosyntheses is discussed.

L-Serine: a Naturally-Occurring Amino Acid with Therapeutic Potential

In human neuroblastoma cell cultures, non-human primates and human beings, L-serine is neuroprotective, acting through a variety of biochemical and molecular mechanisms. Although L-serine is generally classified as a non-essential amino acid, it is probably more appropriate to term it as a "conditional non-essential amino acid" since, under certain circumstances, vertebrates cannot synthesize it in sufficient quantities to meet necessary cellular demands. L-serine is biosynthesized in the mammalian central nervous system from 3-phosphoglycerate and serves as a precursor for the synthesis of the amino acids glycine and cysteine. Physiologically, it has a variety of roles, perhaps most importantly as a phosphorylation site in proteins. Mutations in the metabolic enzymes that synthesize L-serine have been implicated in various human diseases. Dosing of animals with L-serine and human clinical trials investigating the therapeutic effects of L-serine support the FDA's determination that L-serine is generally regarded as safe (GRAS); it also appears to be neuroprotective. We here consider the role of L-serine in neurological disorders and its potential as a therapeutic agent.

A critical review of the postulated role of the non-essential amino acid, β-N-methylamino-L-alanine, in neurodegenerative disease in humans

The compound BMAA (β-N-methylamino-L-alanine) has been postulated to play a significant role in four serious neurological human diseases: Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC) found on Guam, and ALS, Parkinsonism, and dementia that occur globally. ALS/PDC with symptoms of all three diseases first came to the attention of the scientific community during and after World War II. It was initially associated with cycad flour used for food because BMAA is a product of symbiotic cycad root-dwelling cyanobacteria. Human consumption of flying foxes that fed on cycad seeds was later suggested as a source of BMAA on Guam and a cause of ALS/PDC. Subsequently, the hypothesis was expanded to include a causative role for BMAA in other neurodegenerative diseases including Alzheimer's disease (AD) through exposures attributed to proximity to freshwaters and/or consumption of seafood due to its purported production by most species of cyanobacteria. The hypothesis that BMAA is the critical factor in the genesis of these neurodegenerative diseases received considerable attention in the medical, scientific, and public arenas. This review examines the history of ALS/PDC and the BMAA-human disease hypotheses; similarities and differences between ALS/PDC and the other diseases with similar symptomologies; the relationship of ALS/PDC to other similar diseases, studies of BMAA-mediated effects in lab animals, inconsistencies and data gaps in the hypothesis; and other compounds and agents that were suggested as the cause of ALS/PDC on Guam. The review concludes that the hypothesis of a causal BMAA neurodegenerative disease relationship is not supported by existing data.

Methods for the Chemical Analysis of β-N-Methylamino-L-A lanine: What Is Known and What Remains to Be Determined

β-N-Methylamino-L-alanine (BMAA) is a non-canonical amino acid implicated as a cause for amyotrophic lateral sclerosis/parkinsonism dementia complex and potentially other neurodegenerative diseases. As interest in this molecule has increased, there has been a proliferation of methods along with a plethora of opinions as to the superiority of some methods over others. We analyzed the literature with reference to BMAA and its naturally occurring isomers, N-(2-aminoethyl) glycine (AEG) and 2,4 diaminobutyric acid (DAB). A comparison of methods, results, and critiques reveal that a single method has been approved by the AOAC but several different methods provide comparable BMAA quantification concentrations in similar tissues. We also describe a productive way to move forward as technology improves and changes.

β-N-Methylamino-L-alanine (BMAA) perturbs alanine, aspartate and glutamate metabolism pathways in human neuroblastoma cells as determined by metabolic profiling

β-Methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid that induces long-term cognitive deficits, as well as an increased neurodegeneration and intracellular fibril formation in the hippocampus of adult rodents following short-time neonatal exposure and in vervet monkey brain following long-term exposure. It has also been proposed to be involved in the etiology of neurodegenerative disease in humans. The aim of this study was to identify metabolic effects not related to excitotoxicity or oxidative stress in human neuroblastoma SH-SY5Y cells. The effects of BMAA (50, 250, 1000 µM) for 24 h on cells differentiated with retinoic acid were studied. Samples were analyzed using LC-MS and NMR spectroscopy to detect altered intracellular polar metabolites. The analysis performed, followed by multivariate pattern recognition techniques, revealed significant perturbations in protein biosynthesis, amino acid metabolism pathways and citrate cycle. Of specific interest were the BMAA-induced alterations in alanine, aspartate and glutamate metabolism and as well as alterations in various neurotransmitters/neuromodulators such as GABA and taurine. The results indicate that BMAA can interfere with metabolic pathways involved in neurotransmission in human neuroblastoma cells.

L-β-N-methylamino-l-alanine (BMAA) nitrosation generates a cytotoxic DNA damaging alkylating agent: An unexplored mechanism for neurodegenerative disease

BACKGROUND

L-β-N-methylamino-l-alanine (BMAA) is a non-proteinic amino acid, that is neurotoxic in vitro and in animals, and is implicated in the causation of amyotrophic lateral sclerosis and parkinsonism-dementia complex (ALS-PDC) on Guam. Given that natural amino acids can be N-nitrosated to form toxic alkylating agents and the structural similarity of BMAA to other amino acids, our hypothesis was that N-nitrosation of BMAA might result in a toxic alkylating agent, providing a novel mechanistic hypothesis for BMAA action.

FINDINGS

We have chemically nitrosated BMAA with sodium nitrite to produce nitrosated BMAA (N-BMAA) which was shown to react with the alkyl-trapping agent, 4-(p-nitrobenzyl)pyridine, cause DNA strand breaks in vitro and was toxic to the human neuroblastoma cell line SH-SY5Y under conditions in which BMAA itself was minimally toxic.

CONCLUSIONS

Our results indicate that N-BMAA is an alkylating agent and toxin suggesting a plausible and previously unrecognised mechanism for the neurotoxic effects of BMAA.

Neurotoxic Non-proteinogenic Amino Acid β-N-Methylamino-L-alanine and Its Role in Biological Systems

Secondary metabolites of photoautotrophic organisms have attracted considerable interest in recent years. In particular, molecules of non-proteinogenic amino acids participating in various physiological processes and capable of producing adverse ecological effects have been actively investigated. For example, the non-proteinogenic amino acid β-N-methylamino-L-alanine (BMAA) is neurotoxic to animals including humans. It is known that BMAA accumulation via the food chain can lead to development of neurodegenerative diseases in humans such as Alzheimer's and Parkinson's diseases as well as amyotrophic lateral sclerosis. Moreover, BMAA can be mistakenly incorporated into a protein molecule instead of serine. Natural sources of BMAA and methods for its detection are discussed in this review, as well as the role of BMAA in metabolism of its producers and possible mechanisms of toxicity of this amino acid in different living organisms.

A Collaborative Evaluation of LC-MS/MS Based Methods for BMAA Analysis: Soluble Bound BMAA Found to Be an Important Fraction

Exposure to β-N-methylamino-l-alanine (BMAA) might be linked to the incidence of amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. Analytical chemistry plays a crucial role in determining human BMAA exposure and the associated health risk, but the performance of various analytical methods currently employed is rarely compared. A CYANOCOST initiated workshop was organized aimed at training scientists in BMAA analysis, creating mutual understanding and paving the way towards interlaboratory comparison exercises. During this workshop, we tested different methods (extraction followed by derivatization and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis, or directly followed by LC-MS/MS analysis) for trueness and intermediate precision. We adapted three workup methods for the underivatized analysis of animal, brain and cyanobacterial samples. Based on recovery of the internal standard D₃BMAA, the underivatized methods were accurate (mean recovery 80%) and precise (mean relative standard deviation 10%), except for the cyanobacterium Leptolyngbya. However, total BMAA concentrations in the positive controls (cycad seeds) showed higher variation (relative standard deviation 21%–32%), implying that D₃BMAA was not a good indicator for the release of BMAA from bound forms. Significant losses occurred during workup for the derivatized method, resulting in low recovery (<10%). Most BMAA was found in a trichloroacetic acid soluble, bound form and we recommend including this fraction during analysis.

Trans generational effects of the neurotoxin BMAA on the aquatic grazer Daphnia magna

β-N-Methylamino-l-alanine (BMAA) is a neurotoxin that is suspected to play a role in the neurological diseases amyotrophic lateral sclerosis, Alzheimer's disease and Parkinson's disease. BMAA has been detected in phytoplankton and globally, the main exposure routes for humans to BMAA are through direct contact with phytoplankton-infested waters and consumption of BMAA-contaminated fish and invertebrates. As BMAA can be transferred from mothers to offspring in mammals, BMAA exposure is expected to have transgenerational effects. The aim of our study was to determine whether maternal exposure to BMAA affects offspring fitness in zooplankton. We performed a multigenerational life history experiment and a multigenerational uptake experiment with the water flea Daphnia magna as a model species. In both experiments, offspring from nonexposed and exposed mothers were raised in clean and BMAA-containing medium. Direct exposure to 110μg/l BMAA reduced survival, somatic growth, reproduction and population growth. Maternal exposure did not affect D. magna fitness: animals from exposed mothers that were raised in clean medium had a higher mortality and produced lighter neonates than the controls, but this did not result in lower population growth rates. No evidence of adaptation was found. Instead, multigeneration exposure to BMAA had a negative effect: animals that were exposed during two generations had a lower brood viability and neonate weight than animals born from unexposed mothers, but raised in BMAA-containing medium. Maternal transfer of BMAA was observed, but BMAA concentrations in neonates raised in BMAA containing medium were similar for animals born from exposed and unexposed mothers. Our results indicate that zooplankton might be an important vector for the transfer of BMAA along the pelagic food chain, but whether BMAA plays a role in preventing zooplankton from controlling cyanobacterial blooms needs further investigation.

Environmental neurotoxin interaction with proteins: Dose-dependent increase of free and protein-associated BMAA (β-N-methylamino-L-alanine) in neonatal rat brain

β-Methylamino-L-alanine (BMAA) is implicated in the aetiology of neurodegenerative disorders. Neonatal exposure to BMAA induces cognitive impairments and progressive neurodegenerative changes including intracellular fibril formation in the hippocampus of adult rats. It is unclear why the neonatal hippocampus is especially vulnerable and the critical cellular perturbations preceding BMAA-induced toxicity remains to be elucidated. The aim of this study was to compare the level of free and protein-associated BMAA in neonatal rat brain and peripheral tissues after different exposures to BMAA. Ultra-high performance liquid chromatography-tandem mass spectrometry analysis revealed that BMAA passed the neonatal blood-brain barrier and was distributed to all studied brain areas. BMAA was also associated to proteins in the brain, especially in the hippocampus. The level in the brain was, however, considerably lower compared to the liver that is not a target organ for BMAA. In contrast to the liver there was a significantly increased level of protein-association of BMAA in the hippocampus and other brain areas following repeated administration suggesting that the degradation of BMAA-associated proteins may be lower in neonatal brain than in the liver. Additional evidence is needed in support of a role for protein misincorporation in the neonatal hippocampus for long-term effects of BMAA.