Liquid chromatographic determination of the cyanobacterial toxin beta-n-methylamino-L-alanine in algae food supplements, freshwater fish, and bottled water

The maternal hair metabolome is capable of discriminating intrahepatic cholestasis of pregnancy from uncomplicated pregnancy

Introduction

Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy-specific liver disease associated with elevated bile acids in the blood. Diagnosis typically only occurs after the manifestation of clinical symptoms and the metabolic mechanisms underlying its development remain unclear. The aim of this study was to investigate potential specific metabolites and the underlying metabolic changes occurring during the development of ICP in the maternal plasma and hair metabolomes of women diagnosed with either ICP or having a healthy pregnancy.

Methods

A total of 35 Chinese women with ICP and 42 healthy pregnancies were enrolled in our study. Plasma and hair samples, total bile acid levels (TBA), alanine transaminase levels (ALT), aspartate aminotransferase levels (AST), and additional clinical information were collected during the third trimester. Metabolites from maternal plasma and hair segments collected pre-conception and analyzed using gas chromatography-mass spectrometry (GC-MS).

Results

Three plasma metabolites (p < 0.05, q < 0.38) and 21 hair metabolites (p < 0.05, q < 0.05) were significantly different between ICP and healthy pregnancies. A combination of the eight most significant hair metabolites in a multivariate receiver operating characteristic curve model showed the best area under the curve (AUC) was 0.885, whereas the highest AUC using metabolites from plasma samples was only 0.74. Metabolic pathway analysis revealed 32 pathways were significantly (p and q values < 0.05) affected in the hair samples of patients with ICP. Pathways associated with glutathione metabolism and ABC transporters were affected. No metabolic pathways were significantly affected in plasma.

Discussion

Overall, this study showed that the hair metabolome could be more useful than the plasma metabolome for distinguishing ICP from normal pregnancy.

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.

Insufficient evidence for BMAA transfer in the pelagic and benthic food webs in the Baltic Sea

The evidence regarding BMAA occurrence in the Baltic Sea is contradictory, with benthic sources appearing to be more important than pelagic ones. The latter is counterintuitive considering that the identified sources of this compound in the food webs are pelagic primary producers, such as diatoms, dinoflagellates, and cyanobacteria. To elucidate BMAA distribution, we analyzed BMAA in the pelagic and benthic food webs in the Northern Baltic Proper. As potential sources, phytoplankton communities were used. Pelagic food chain was represented by zooplankton, mysids and zooplanktivorous fish, whereas benthic invertebrates and benthivorous fish comprised the benthic chain. The trophic structure of the system was confirmed by stable isotope analysis. Contrary to the reported ubiquitous occurrence of BMAA in the Baltic food webs, only phytoplankton, zooplankton and mysids tested positive, whereas no measurable levels of this compound occurred in the benthic invertebrates and any of the tested fish species. These findings do not support the widely assumed occurrence and transfer of BMAA to the top consumers in the Baltic food webs. More controlled experiments and field observations are needed to understand the transfer and possible transformation of BMAA in the food web under various environmental settings.

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

Cyanobacteria are photosynthetic microorganisms distributed globally in aquatic and terrestrial environments. They are also industrially cultivated to be used as dietary supplements, as they have a high nutritional value; however, they are also known to produce a wide range of toxic secondary metabolites, called cyanotoxins. BMAA (β-methylamino-l-alanine) and its most common structural isomers, DAB (2,4-diaminobutyric acid) and AEG (N-2-aminoethylglycine) produced by cyanobacteria, are non-proteinogenic amino acids that have been associated with neurodegenerative diseases. A possible route of exposure to those amino acids is through consumption of food supplements based on cyanobacteria. The review critically discusses existing reports regarding the occurrence of BMAA, DAB and AEG in cyanobacteria and cyanobacteria-based food supplements. It is shown that inconsistencies in reported results could be attributed to performance of different methods of extraction and analysis applied and in ambiguities regarding determination of soluble and bound fractions of the compounds. The critical aspect of this review aims to grow awareness of human intake of neurotoxic amino acids, while results presented in literature concerning dietary supplements aim to promote further research, quality control as well as development of guidelines for cyanotoxins in food products.

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.

Detection of Cyanotoxins in Algae Dietary Supplements

Algae dietary supplements are marketed worldwide as natural health products. Although their proprieties have been claimed as beneficial to improve overall health, there have been several previous reports of contamination by cyanotoxins. These products generally contain non-toxic cyanobacteria, but the methods of cultivation in natural waters without appropriate quality controls allow contamination by toxin producer species present in the natural environment. In this study, we investigated the presence of total microcystins, seven individual microcystins (RR, YR, LR, LA, LY, LW, LF), anatoxin-a, dihydroanatoxin-a, epoxyanatoxin-a, cylindrospermopsin, saxitoxin, and β-methylamino-l-alanine in 18 different commercially available products containing Spirulina or Aphanizomenon flos-aquae. Total microcystins analysis was accomplished using a Lemieux oxidation and a chemical derivatization using dansyl chloride was needed for the simultaneous analysis of cylindrospermopsin, saxitoxin, and β-methylamino-l-alanine. Moreover, the use of laser diode thermal desorption (LDTD) and ultra-high performance liquid chromatography (UHPLC) both coupled to high resolution mass spectrometry (HRMS) enabled high performance detection and quantitation. Out of the 18 products analyzed, 8 contained some cyanotoxins at levels exceeding the tolerable daily intake values. The presence of cyanotoxins in these algal dietary supplements reinforces the need for a better quality control as well as consumer's awareness on the potential risks associated with the consumption of these supplements.

Beta-N-methylamino-L-alanine: LC-MS/MS optimization, screening of cyanobacterial strains and occurrence in shellfish from Thau, a French Mediterranean lagoon

β-N-methylamino-l-alanine (BMAA) is a neurotoxic non-protein amino acid suggested to be involved in neurodegenerative diseases. It was reported to be produced by cyanobacteria, but also found in edible aquatic organisms, thus raising concern of a widespread human exposure. However, the chemical analysis of BMAA and its isomers are controversial, mainly due to the lack of selectivity of the analytical methods. Using factorial design, we have optimized the chromatographic separation of underivatized analogues by a hydrophilic interaction chromatography coupled to tandem mass spectrometry (HILIC-MS/MS) method. A combination of an effective solid phase extraction (SPE) clean-up, appropriate chromatographic resolution and the use of specific mass spectral transitions allowed for the development of a highly selective and sensitive analytical procedure to identify and quantify BMAA and its isomers (in both free and total form) in cyanobacteria and mollusk matrices (LOQ of 0.225 and 0.15 µg/g dry weight, respectively). Ten species of cyanobacteria (six are reported to be BMAA producers) were screened with this method, and neither free nor bound BMAA could be found, while both free and bound DAB were present in almost all samples. Mussels and oysters collected in 2009 in the Thau Lagoon, France, were also screened, and bound BMAA and its two isomers, DAB and AEG, were observed in all samples (from 0.6 to 14.4 µg/g DW), while only several samples contained quantifiable free BMAA.

Presence of the neurotoxin BMAA in aquatic ecosystems: what do we really know?

The neurotoxin β-N-methylamino-l-alanine (BMAA) is suspected to play a role in the neurological diseases amyotrophic lateral sclerosis, Alzheimer’s disease, and Parkinson’s disease. BMAA production by cyanobacteria has been reported and contact with cyanobacteria infested waters or consumption of aquatic organisms are possible pathways to human exposure. However, there is little consensus regarding whether BMAA is present in cyanobacteria or not, and if so, at what concentrations. The aim of this review is to indicate the current state of knowledge on the presence of BMAA in aquatic ecosystems. Some studies have convincingly shown that BMAA can be present in aquatic samples at the µg/g dry weight level, which is around the detection limit of some equally credible studies in which no BMAA was detected. However, for the majority of the reviewed articles, it was unclear whether BMAA was correctly identified, either because inadequate analytical methods were used, or because poor reporting of analyses made it impossible to verify the results. Poor analysis, reporting and prolific errors have shaken the foundations of BMAA research. First steps towards estimation of human BMAA exposure are to develop and use selective, inter-laboratory validated methods and to correctly report the analytical work.

Co-occurrence of the cyanotoxins BMAA, DABA and anatoxin-a in Nebraska reservoirs, fish, and aquatic plants

Several groups of microorganisms are capable of producing toxins in aquatic environments. Cyanobacteria are prevalent blue green algae in freshwater systems, and many species produce cyanotoxins which include a variety of chemical irritants, hepatotoxins and neurotoxins. Production and occurrence of potent neurotoxic cyanotoxins β-N-methylamino-l-alanine (BMAA), 2,4-diaminobutyric acid dihydrochloride (DABA), and anatoxin-a are especially critical with environmental implications to public and animal health. Biomagnification, though not well understood in aquatic systems, is potentially relevant to both human and animal health effects. Because little is known regarding their presence in fresh water, we investigated the occurrence and potential for bioaccumulation of cyanotoxins in several Nebraska reservoirs. Collection and analysis of 387 environmental and biological samples (water, fish, and aquatic plant) provided a snapshot of their occurrence. A sensitive detection method was developed using solid phase extraction (SPE) in combination with high pressure liquid chromatography-fluorescence detection (HPLC/FD) with confirmation by liquid chromatography-tandem mass spectrometry (LC/MS/MS). HPLC/FD detection limits ranged from 5 to 7 µg/L and LC/MS/MS detection limits were <0.5 µg/L, while detection limits for biological samples were in the range of 0.8–3.2 ng/g depending on the matrix. Based on these methods, measurable levels of these neurotoxic compounds were detected in approximately 25% of the samples, with detections of BMAA in about 18.1%, DABA in 17.1%, and anatoxin-a in 11.9%.

Analysis of β-N-methylamino-L-alanine (BMAA) in spirulina-containing supplements by liquid chromatography-tandem mass spectrometry

Over the last decade the amino acid beta-N-methylamino-L-alanine (BMAA) has come under intense scrutiny. International laboratory and epidemiological research continues to support the hypothesis that environmental exposure to BMAA (e.g., through dietary practices, water supply) can promote the risk of various neurodegenerative diseases. A wide variety of cyanobacteria spp. have previously been reported to produce BMAA, with production levels dependent upon species, strain and environmental conditions. Since spirulina (Arthrospira spp.) is a member of the cyanobacteria phylum frequently consumed via dietary supplements, the presence of BMAA in such products may have public health implications. In the current work, we have analyzed ten spirulina-containing samples for the presence of BMAA; six pure spirulina samples from two separate raw materials suppliers, and four commercially-available multi-ingredient products containing 1.45 g of spirulina per 8.5 g serving. Because of controversy surrounding the measurement of BMAA, we have used two complementary liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods: one based on reversed phase LC (RPLC) with derivatization and the other based on hydrophilic interaction LC (HILIC). Potential matrix effects were corrected for by internal standardization using a stable isotope labeled BMAA standard. BMAA was not detected at low limits of detection (80 ng/g dry weight) in any of these product samples. Although these results are reassuring, BMAA analyses should be conducted on a wider sample selection and, perhaps, as part of ongoing spirulina production quality control testing and specifications.

Good mass spectrometry and its place in good science

The mass spectrometry community has expanded as instruments became more powerful, user-friendly, affordable and readily available. This opens up opportunities for novice users to perform high impact research, using highly advanced instrumentation. This introductory tutorial is targeted at the novice user working in a research setting. It aims to offer the benefit of other people's experiences and to help newcomers avoid known pitfalls and problematic issues. It discusses some of the essential features of sound analytical chemistry and highlights the need to use validated analytical methods that provide high quality results along with a measure of their uncertainty. Examples are used to illustrate potential pitfalls and their consequences.

Elucidation of matrix effects and performance of solid-phase extraction for LC-MS/MS analysis of β-N-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB) neurotoxins in cyanobacteria

A liquid chromatography-mass spectrometry (LC-MS/MS) method using hydrophilic interaction liquid chromatography (HILIC) was developed for the analysis of neurotoxins β-N-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB), using multiple reaction monitoring (MRM) scan mode. Oasis-MCX and Strata-X-C polymeric cation-exchange cartridges were used to clean extracts of cyanobacterial cultures, including two strains of Microcystis aeruginosa and one strain of Nostoc sp. The performance of the solid-phase extraction (SPE) cartridges for BMAA and DAB were evaluated using mixed standards and spiked cyanobacterial extracts, which demonstrated recoveries of BMAA and DAB ranging from 66% to 91%. Matrix effects in LC-MS/MS were evaluated, and while there was no effect on BMAA quantitation, suppression of DAB was found. Full scan (Q1) and enhanced product ion (EPI) monitoring showed that the DAB suppression may be due to closely eluting compounds, including lysine, histidine, arginine and three other compounds with [M + H](+) m/z of 88, 164 and 191. The procedures developed allow the sensitive and effective analysis of trace BMAA and DAB levels in cyanobacteria. While DAB was confirmed to be present, no BMAA was found in the cyanobacterial samples tested in the present study.

Distinguishing the cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) from other diamino acids

β-N-methylamino-L-alanine (BMAA) is produced by diverse taxa of cyanobacteria, and has been detected by many investigators who have searched for it in cyanobacterial blooms, cultures and collections. Although BMAA is distinguishable from proteinogenic amino acids and its isomer 2,4-DAB using standard chromatographic and mass spectroscopy techniques routinely used for the analysis of amino acids, we studied whether BMAA could be reliably distinguished from other diamino acids, particularly 2,6-diaminopimelic acid which has been isolated from the cell walls of many bacterial species. We used HPLC-FD, UHPLC-UV, UHPLC-MS, and triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) to differentiate BMAA from the diamino acids 2,6-diaminopimelic acid, N-2(amino)ethylglycine, lysine, ornithine, 2,4-diaminosuccinic acid, homocystine, cystine, tryptophan, as well as other amino acids including asparagine, glutamine, and methionine methylsulfonium.

Prominent human health impacts from several marine microbes: history, ecology, and public health implications

This paper overviews several examples of important public health impacts by marine microbes and directs readers to the extensive literature germane to these maladies. These examples include three types of dinoflagellates (Gambierdiscus spp., Karenia brevis, and Alexandrium fundyense), BMAA-producing cyanobacteria, and infectious microbes. The dinoflagellates are responsible for ciguatera fish poisoning, neurotoxic shellfish poisoning, and paralytic shellfish poisoning, respectively, that have plagued coastal populations over time. Research interest on the potential for marine cyanobacteria to contribute BMAA into human food supplies has been derived by BMAA's discovery in cycad seeds and subsequent implication as the putative cause of amyotrophic lateral sclerosis/parkinsonism dementia complex among the Chamorro people of Guam. Recent UPLC/MS analyses indicate that recent reports that BMAA is prolifically distributed among marine cyanobacteria at high concentrations may be due to analyte misidentification in the analytical protocols being applied for BMAA. Common infectious microbes (including enterovirus, norovirus, Salmonella, Campylobacter, Shigella, Staphylococcus aureus, Cryptosporidium, and Giardia) cause gastrointestinal and skin-related illness. These microbes can be introduced from external human and animal sources, or they can be indigenous to the marine environment.