Neurotoxin BMAA and its isomeric amino acids in cyanobacteria and cyanobacteria-based food supplements

Nodding syndrome: A role for environmental biotoxins that dysregulate MECP2 expression?

Nodding syndrome is an epileptic encephalopathy associated with neuroinflammation and tauopathy. This initially pediatric brain disease, which has some clinical overlap with Methyl-CpG-binding protein 2 (MECP2) Duplication Syndrome, has impacted certain impoverished East African communities coincident with local civil conflict and internal displacement, conditions that forced dependence on contaminated food and water. A potential role in Nodding syndrome for certain biotoxins (freshwater cyanotoxins plus/minus mycotoxins) with neuroinflammatory, excitotoxic, tauopathic, and MECP2-dysregulating properties, is considered here for the first time.

The chemical and microbiological safety of emerging alternative protein sources and derived analogues: A review

Climate change and changing consumer demand are the main factors driving the protein transition. This shift toward more sustainable protein sources as alternatives to animal proteins is also reflected in the rapid upscaling of meat and dairy food analogues. Such changes could challenge food safety, as new food sources could result in new and unexpected food safety risks for consumers. This review analyzed the current knowledge on chemical and microbiological contamination of emerging alternative protein sources of plant origin, including soil-based (faba bean, mung bean, lentils, black gram, cowpea, quinoa, hemp, and leaf proteins) and aquatic-based (microalgae and duckweeds) proteins. Moreover, findings on commercial analogues from known alternative protein sources were included. Overall, the main focus of the investigations is on the European context. The review aimed to enable foresight approaches to food safety concerning the protein transition. The results indicated the occurrence of multiple chemical and microbiological hazards either in the raw materials that are the protein sources and eventually in the analogues. Moreover, current European legislation on maximum limits does not address most of the "contaminant-food" pairs identified, and no legislative framework has been developed for analogues. Results of this study provide stakeholders with a more comprehensive understanding of the chemical and microbiological safety of alternative protein sources and derived analogues to enable a holistic and safe approach to the protein transition.

Cyanotoxins in food: Exposure assessment and health impact

The intricate nature of cyanotoxin exposure through food reveals a complex web of risks and uncertainties in our dietary choices. With the aim of starting to unravel this intricate nexus, a comprehensive review of 111 papers from the past two decades investigating cyanotoxin contamination in food was undertaken. It revealed a widespread occurrence of cyanotoxins in diverse food sources across 31 countries. Notably, 68% of the studies reported microcystin concentrations exceeding established Tolerable Daily Intake levels. Cyanotoxins were detected in muscles of many fish species, and while herbivorous fish exhibited the highest recorded concentration, omnivorous species displayed a higher propensity for cyanotoxin accumulation, exemplified by Oreochromis niloticus. Beyond fish, crustaceans and bivalves emerged as potent cyanotoxin accumulators. Gaps persist regarding contamination of terrestrial and exotic animals and their products, necessitating further exploration. Plant contamination under natural conditions remains underreported, yet evidence underscores irrigation-driven cyanotoxin accumulation, particularly affecting leafy vegetables. Finally, cyanobacterial-based food supplements often harbored cyanotoxins (57 % of samples were positive) warranting heightened scrutiny, especially for Aphanizomenon flos-aquae-based products. Uncertainties surround precise concentrations due to methodological variations (chemical and biochemical) and extraction limitations, along with the enigmatic fate of toxins during storage, processing, and digestion. Nonetheless, potential health consequences of cyanotoxin exposure via contaminated food include gastrointestinal and neurological disorders, organ damage (e.g. liver, kidneys, muscles), and even elevated cancer risks. While microcystins received significant attention, knowledge gaps persist regarding other cyanotoxins' accumulation, exposure, and effects, as well as combined exposure via multiple pathways. Intriguing and complex, cyanotoxin exposure through food beckons further research for our safer and healthier diets.

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.

Simultaneous Analysis of Cyanotoxins β-N-methylamino-L-alanine (BMAA) and Microcystins-RR, -LR, and -YR Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

β-N-methylamino-L-alanine (BMAA) and its isomers, 2,4-diaminobutyric acid (2,4-DAB) and N-(2-aminoethyl)-glycine (AEG), along with microcystins (MCs)-RR, -LR, and -YR (the major MC congeners), are cyanotoxins that can cause detrimental health and environmental impacts during toxic blooms. Currently, there are no reverse-phase (RP) LC-MS/MS methods for the simultaneous detection and quantification of BMAA, its isomers, and the major MCs in a single analysis; therefore, multiple analyses are required to assess the toxic load of a sample. Here, we present a newly developed and validated method for the detection and quantification of BMAA, 2,4-DAB, AEG, MC-LR, MC-RR, and MC-YR using RP LC-MS/MS. Method validation was performed, assessing linearity (r2 > 0.996), accuracy (>90% recovery for spiked samples), precision (7% relative standard deviation), and limits of detection (LODs) and quantification (LOQs) (ranging from 0.13 to 1.38 ng mL-1). The application of this combined cyanotoxin analysis on a culture of Microcystis aeruginosa resulted in the simultaneous detection of 2,4-DAB (0.249 ng mg-1 dry weight (DW)) and MC-YR (4828 ng mg-1 DW). This study provides a unified method for the quantitative analysis of BMAA, its isomers, and three MC congeners in natural environmental samples.

Non-Canonical Amino Acids in Analyses of Protease Structure and Function

All known organisms encode 20 canonical amino acids by base triplets in the genetic code. The cellular translational machinery produces proteins consisting mainly of these amino acids. Several hundred natural amino acids serve important functions in metabolism, as scaffold molecules, and in signal transduction. New side chains are generated mainly by post-translational modifications, while others have altered backbones, such as the β- or γ-amino acids, or they undergo stereochemical inversion, e.g., in the case of D-amino acids. In addition, the number of non-canonical amino acids has further increased by chemical syntheses. Since many of these non-canonical amino acids confer resistance to proteolytic degradation, they are potential protease inhibitors and tools for specificity profiling studies in substrate optimization and enzyme inhibition. Other applications include in vitro and in vivo studies of enzyme kinetics, molecular interactions and bioimaging, to name a few. Amino acids with bio-orthogonal labels are particularly attractive, enabling various cross-link and click reactions for structure-functional studies. Here, we cover the latest developments in protease research with non-canonical amino acids, which opens up a great potential, e.g., for novel prodrugs activated by proteases or for other pharmaceutical compounds, some of which have already reached the clinical trial stage.

Determination of Multiclass Cyanotoxins in Blue-Green Algae (BGA) Dietary Supplements Using Hydrophilic Interaction Liquid Chromatography-Tandem Mass Spectrometry

In recent years, the consumption of blue-green algae (BGA) dietary supplements is increasing because of their health benefits. However, cyanobacteria can produce cyanotoxins, which present serious health risks. In this work we propose hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry (HILIC-MS/MS) to determine cyanotoxins in BGA dietary supplements. Target toxins, including microcystin-leucine-arginine (MC-LR) and microcystin-arginine-arginine (MC-RR), nodularin, anatoxin-a and three non-protein amino acids, β-N-methylamino-L-alanine (BMAA), 2,4-diaminobutyric acid (DAB) and N-(2-aminoethyl)glycine (AEG), were separated using a SeQuant ZIC-HILIC column. Cyanotoxin extraction was based on solid-liquid extraction (SLE) followed by a tandem-solid phase extraction (SPE) procedure using Strata-X and mixed-mode cation-exchange (MCX) cartridges. The method was validated for BGA dietary supplements obtaining quantification limits from 60 to 300 µg·kg^-1. Nine different commercial supplements were analyzed, and DAB, AEG, and MCs were found in some samples, highlighting the relevance of monitoring these substances as precaution measures for the safe consumption of these products.

Degradation mechanisms of cyanobacteria neurotoxin β-N-methylamino-l-alanine (BMAA) during UV254/H2O2 process: Kinetics and pathways

In this work, the UV₂₅₄/H₂O₂ process was utilized to remove β-N-methylamino-l-alanine (BMAA), a kind of cyanobacteria neurotoxin, and the influence of reaction parameters and environmental factors on the degradation of BMAA has been systematically investigated. The results showed that BMAA could be effectively removed in the UV₂₅₄/H₂O₂ system compared to UV or H₂O₂ alone and OH was confirmed as the main ROS to degrade BMAA. The degradation rate of BMAA increased first and then decreased with the increase of pH and the maximum k_obs was 0.1545 min^-1 obtained at pH 9. The removal of BMAA in the UV₂₅₄/H₂O₂ system was inhibited in actual water, while the degradation rate of BMAA in actual water could still exceed 90% by appropriately extending the reaction time. The decrease in the degradation efficiency of BMAA in actual water was primarily due to the ultraviolet light absorption and competition effects of NOM, and anions (Cl^- and HCO₃^-) would also inhibit the degradation of BMAA. Five by-products ([M - H]^- = 118, 103, 88, 87 and 59) were identified in this study and the degradation pathways of BMAA were proposed. The production of by-products was attributed to the fracture of the C-N bond and hydroxylation reaction. This study is worthwhile to deepen the understanding of the degradation mechanism of BMAA in the UV₂₅₄/H₂O₂ system.

Occurrence of BMAA Isomers in Bloom-Impacted Lakes and Reservoirs of Brazil, Canada, France, Mexico, and the United Kingdom

The neurotoxic alkaloid β-N-methyl-amino-l-alanine (BMAA) and related isomers, including N-(2-aminoethyl glycine) (AEG), β-amino-N-methyl alanine (BAMA), and 2,4-diaminobutyric acid (DAB), have been reported previously in cyanobacterial samples. However, there are conflicting reports regarding their occurrence in surface waters. In this study, we evaluated the impact of amending lake water samples with trichloroacetic acid (0.1 M TCA) on the detection of BMAA isomers, compared with pre-existing protocols. A sensitive instrumental method was enlisted for the survey, with limits of detection in the range of 5−10 ng L−1. Higher detection rates and significantly greater levels (paired Wilcoxon’s signed-rank tests, p < 0.001) of BMAA isomers were observed in TCA-amended samples (method B) compared to samples without TCA (method A). The overall range of B/A ratios was 0.67−8.25 for AEG (up to +725%) and 0.69−15.5 for DAB (up to +1450%), with absolute concentration increases in TCA-amended samples of up to +15,000 ng L−1 for AEG and +650 ng L−1 for DAB. We also documented the trends in the occurrence of BMAA isomers for a large breadth of field-collected lakes from Brazil, Canada, France, Mexico, and the United Kingdom. Data gathered during this overarching campaign (overall, n = 390 within 45 lake sampling sites) indicated frequent detections of AEG and DAB isomers, with detection rates of 30% and 43% and maximum levels of 19,000 ng L−1 and 1100 ng L−1, respectively. In contrast, BAMA was found in less than 8% of the water samples, and BMAA was not found in any sample. These results support the analyses of free-living cyanobacteria, wherein BMAA was often reported at concentrations of 2−4 orders of magnitude lower than AEG and DAB. Seasonal measurements conducted at two bloom-impacted lakes indicated limited correlations of BMAA isomers with total microcystins or chlorophyll-a, which deserves further investigation.

Effect of chewing betel nut on the gut microbiota of Hainanese

Betel nut chewing (BNC) is prevalent in South Asia and Southeast Asia. BNC can affect host health by modulating the gut microbiota. The aim of this study is to evaluate the effect of BNC on the gut microbiota of the host. Feces samples were obtained from 34 BNC individuals from Ledong and Lingshui, Hainan, China. The microbiota was analyzed by 16S rRNA gene sequencing. BNC decreased the microbial α-diversity. Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria were the predominant phyla, accounting for 99.35% of the BNC group. The Firmicutes-to-Bacteroidetes ratio was significantly increased in the BNC group compared to a control group. The abundances of the families Aerococcaceae, Neisseriaceae, Moraxellaceae, Porphyromonadaceae, and Planococcaceae were decreased in the BNC/BNC_Male/BNC_Female groups compared to the control group, whereas the abundances of Coriobacteriaceae, Streptococcaceae, Micrococcaceae, Xanthomonadaceae, Coxiellaceae, Nocardioidaceae, Rhodobacteraceae, and Succinivibrionaceae were increased. In general, the gut microbiome profiles suggest that BNC may have positive effects, such as an increase in the abundance of beneficial microbes and a reduction in the abundance of disease-related microbes. However, BNC may also produce an increase in the abundance of disease-related microbes. Therefore, extraction of prebiotic components could increase the beneficial value of betel nut.

Food web biomagnification of the neurotoxin β-N-methylamino-L-alanine in a diatom-dominated marine ecosystem in China

The neurotoxin β-N-methylamino-L-alanine (BMAA) reported in some cyanobacteria and eukaryote microalgae is a cause of concern due to its potential risk of human neurodegenerative diseases. Here, BMAA distribution in phytoplankton, zooplankton, and other marine organisms was investigated in Jiaozhou Bay, China, a diatom-dominated marine ecosystem, during four seasons in 2019. Results showed that BMAA was biomagnified in the food web from phytoplankton to higher trophic levels. Trophic magnification factors (TMFs) for zooplankton, bivalve mollusks, carnivorous crustaceans and carnivorous gastropod mollusks were ca. 4.58, 30.1, 42.5, and 74.4, respectively. Putative identification of β-amino-N-methylalanine (BAMA), an isomer of BMAA, was frequently detected in phytoplankton samples. A total of 56 diatom strains of the genera Pseudo-nitzschia, Thalassiosira, Chaetoceros, Planktoniella, and Minidiscus isolated from the Chinese coast were cultured in the laboratory, among which 21 strains contained BMAA mainly in precipitated bound form at toxin concentrations ranging from 0.11 to 3.95 µg/g dry weight. Only 2,4-diaminobutyric acid (DAB) but not BMAA or BAMA was detected in seven species of bacteria isolated from the gut of gastropod Neverita didyma, suggesting that this benthic vector of BMAA may have accumulated this compound via trophic transfer.

Interaction of the neutral amino acid transporter ASCT2 with basic amino acids

Glutamine transport across cell membranes is performed by a variety of transporters, including the alanine serine cysteine transporter 2 (ASCT2). The substrate-binding site of ASCT2 was proposed to be specific for small amino acids with neutral side chains, excluding basic substrates such as lysine. A series of competitive inhibitors of ASCT2 with low µM affinity were developed previously, on the basis of the 2,4-diaminobutyric acid (DAB) scaffold with a potential positive charge in the side chain. Therefore, we tested whether basic amino acids with side chains shorter than lysine can interact with the ASCT2 binding site. Molecular docking of L-1,3-diaminopropionic acid (L-DAP) and L-DAB suggested that these compounds bind to ASCT2. Consistent with this prediction, L-DAP and L-DAB, but not ornithine, lysine or D-DAP, elicited currents when applied to ASCT2-expressing cells. The currents were carried by anions and showed the hallmark properties of ASCT2 currents induced by transported substrates. The L-DAP response could be eliminated by a competitive ASCT2 inhibitor, suggesting that binding occurs at the substrate binding site. The KM for L-DAP was weakly voltage dependent. Furthermore, the pH dependence of the L-DAP response showed that the compound can bind in several protonation states. Together, these results suggest that the ASCT2 binding site is able to recognize L-amino acids with short, basic side chains, such as the L-DAP derivative β-N-methylamino-l-Alanine (BMAA), a well-studied neurotoxin. Our results expand the substrate specificity of ASCT2 to include amino acid substrates with positively charged side chains.

The Proposed Neurotoxin β-N-Methylamino-l-Alanine (BMAA) Is Taken up through Amino-Acid Transport Systems in the Cyanobacterium Anabaena PCC 7120

Produced by cyanobacteria and some plants, BMAA is considered as an important environmental factor in the occurrence of some neurodegenerative diseases. Neither the underlying mechanism of its toxicity, nor its biosynthetic or metabolic pathway in cyanobacteria is understood. Interestingly, BMAA is found to be toxic to some cyanobacteria, making it possible to dissect the mechanism of BMAA metabolism by genetic approaches using these organisms. In this study, we used the cyanobacterium Anabaena PCC 7120 to isolate BMAA-resistant mutants. Following genomic sequencing, several mutations were mapped to two genes involved in amino acids transport, suggesting that BMAA was taken up through amino acid transporters. This conclusion was supported by the protective effect of several amino acids against BMAA toxicity. Furthermore, targeted inactivation of genes encoding different amino acid transport pathways conferred various levels of resistance to BMAA. One mutant inactivating all three major amino acid transport systems could no longer take up BMAA and gained full resistance to BMAA toxicity. Therefore, BMAA is a substrate of amino acid transporters, and cyanobacteria are interesting models for genetic analysis of BMAA transport and metabolism.

β-Ν-Methylamino-L-alanine interferes with nitrogen assimilation in the cyanobacterium, non-BMAA producer, Synechococcus sp. TAU-MAC 0499

The production of β-Ν-methylamino-L-alanine (BMAA) in cyanobacteria is triggered by nitrogen-starvation conditions and its biological role, albeit unknown, is associated with nitrogen assimilation. In the present study, the effect of BMAA (773 μg L^-1) on nitrogen metabolism and physiology of the non-diazotrophic cyanobacterium and non-BMAA producer, Synechococcus sp. TAU-MAC 0499, was investigated. In order to study the combined effect of nitrogen availability and BMAA, nitrogen-starvation conditions were induced by transferring cells in nitrogen-free medium and subsequently exposing the cultures to BMAA. After short-term treatment (180 min) and in the presence of nitrogen, BMAA inhibited glutamine synthetase, which resulted in low concentration of glutamine. In the absence of nitrogen, although there was no effect on glutamine synthetase, a possible perturbation in nitrogen assimilation is reflected on the significant decrease in glutamate levels. During the long-term exposure (24-96 h), growth, photosynthetic pigments and total protein were not affected by BMAA exposure, except for an increase in protein and phycocyanin levels at 48 h in nitrogen replete conditions. Results suggest that BMAA interferes with nitrogen assimilation, in a different way, depending on the presence or absence of combined nitrogen, providing novel data on the potential biological role of BMAA.

A systematic review of analytical methods for the detection and quantification of β-N-methylamino-l-alanine (BMAA)

Neurodegenerative diseases are influenced by environmental factors such as exposure to toxins including the cyanotoxin β-N-methylamino-l-alanine (BMAA) that can bioaccumulate in common food sources such as fish, mussels and crabs. Accurate and precise analytical methods are needed to detect and quantify BMAA to minimize human health risks. The objective of this review is to provide a comprehensive overview of the methods used for BMAA analysis from 2003 to 2019 and to evaluate the reported performance characteristics for each method to determine the consensus data for each analytical approach and different sample matrices. Detailed searches of the database Web of Science™ (WoS) were performed between August 21st, 2018 and April 5th, 2019. Eligible studies included analytical methods for the detection and quantification of BMAA in cyanobacteria and bioaccumulated BMAA in higher trophic levels, in phytoplankton and zooplankton and in human tissues and fluids. This systematic review has limitations in that only the English language literature is included and it did not include standard operating protocols nor any method validation data that have not been made public. We identified 148 eligible studies, of which a positive result for BMAA in one or more samples analyzed was reported in 84% (125 out of 148) of total studies, 57% of HILIC studies, 92% of RPLC studies and 71% of other studies. The largest discrepancy between different methods arose from the analysis of cyanobacteria samples, where BMAA was detected in 95% of RPLC studies but only in 25% of HILIC studies. Without sufficient published validation of each method's performance characteristics, it is difficult to establish each method as fit for purpose for each sample matrix. The importance of establishing methods as appropriate for their intended use is evidenced by the inconsistent reporting of BMAA across environmental samples, despite its prevalence in diverse ecosystems and food webs.

Harmful algal blooms under changing climate and constantly increasing anthropogenic actions: the review of management implications

The present review reports all management approaches (physical, chemical, and biological) traditionally adopted in mitigating the global impact of harmful cyanobacterial blooms (cyanoHABs). It recognizes that each mitigation strategy shows characteristic associated limitations and notes that no remedial step has provided a sustainable solution to HABs on a global scale. It emphasizes that the putative anthropogenic N&P inputs reduction through improved wastewater treatment and regulation of point and non-point sources-agricultural fertilizers only offer a short term solution. These approaches are rather preventive than curative hence, do not address concerns relating to the recovery of already-eutrophic and hypereutrophic systems. It raises new concerns on the implications of non-agricultural pollutants such as hydrocarbon fractions in bloom accretions often neglected while addressing HAB triggers. It also accesses the global impacts of HABs as it pertains to socio-economic implications in the geographically diverse world. It, therefore, proposes that Integrated Management Intervention involving the merging of two or more mitigation steps be administered across the aquatic continua as a prudent management solution to complement the current N&P dual management paradigm. It stresses that the contemporaneous adoption of management options with both preventive and curative measures is a key to sustainable HAB management. This review provides sufficient advances and current scenarios for approaching cyanoHABs. Further, it advocates that future research perspectives tackle the mitigation design beyond the short-term nutrient regulations and the parochial attention to the point and non-point N&P input sources.

The Diversity of Cyanobacterial Toxins on Structural Characterization, Distribution and Identification: A Systematic Review

The widespread distribution of cyanobacteria in the aquatic environment is increasing the risk of water pollution caused by cyanotoxins, which poses a serious threat to human health. However, the structural characterization, distribution and identification techniques of cyanotoxins have not been comprehensively reviewed in previous studies. This paper aims to elaborate the existing information systematically on the diversity of cyanotoxins to identify valuable research avenues. According to the chemical structure, cyanotoxins are mainly classified into cyclic peptides, alkaloids, lipopeptides, nonprotein amino acids and lipoglycans. In terms of global distribution, the amount of cyanotoxins are unbalanced in different areas. The diversity of cyanotoxins is more obviously found in many developed countries than that in undeveloped countries. Moreover, the threat of cyanotoxins has promoted the development of identification and detection technology. Many emerging methods have been developed to detect cyanotoxins in the environment. This communication provides a comprehensive review of the diversity of cyanotoxins, and the detection and identification technology was discussed. This detailed information will be a valuable resource for identifying the various types of cyanotoxins which threaten the environment of different areas. The ability to accurately identify specific cyanotoxins is an obvious and essential aspect of cyanobacterial research.