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

β-N-methylamino-L-alanine production, photosynthesis and transcriptional expression in a possible mutation strain and a wild strain of Thalassiosira minima

The neurotoxin β-N-methylamino-L-alanine (BMAA) produced by marine diatoms has been implicated as an important environmental trigger of neurodegenerative diseases in humans. However, the biosynthesis mechanism of BMAA in marine diatoms is still unknown. In the present study, the strain of diatom Thalassiosira minima almost lost the biosynthesis ability for BMAA after a long-term subculture in our laboratory. The production of BMAA-containing proteins in the mutant strain of T. minima reduced to 18.2 % of that in the wild strain, meanwhile the cell size decreased but pigment content increased in the mutant strain. Take consideration of our previous transcriptional data on the mixed diatom and cyanobacterium cultures, the current transcriptome analysis showed four identical and highly correlated KEGG pathways associated with the accumulation of misfolded proteins in diatom, including ribosome, proteasome, SNARE interactions in vesicle transport, and protein processing in the endoplasmic reticulum. Analysis of amino acids and transcriptional information suggested that amino acid synthesis and degradation are associated with the biosynthesis of BMAA-containing proteins. In addition, a reduction in the precision of ubiquitination-mediated protein hydrolysis and vesicular transport by the COPII system will exacerbate the accumulation of BMAA-containing proteins in diatoms.

Impact of the neurotoxin β-N-methylamino-L-alanine on the diatom Thalassiosira pseudonana using metabolomics

The neurotoxin β-N-methylamino-L-alanine (BMAA) has emerged as an environmental factor related to neurodegenerative diseases. BMAA is produced by various microorganisms including cyanobacteria and diatoms, in diverse ecosystems. In the diatom Phaeodactylum tricornutum, BMAA is known to inhibit growth. The present study investigated the impact of BMAA on the diatom Thalassiosira pseudonana by exposing it to different concentrations of exogenous BMAA. Metabolomics was predominantly employed to investigate the effect of BMAA on T. pseudonana, and MetaboAnalyst (https://www.metabo-analyst.ca/) was used to identify BMAA-associated metabolisms/pathways in T. pseudonana. Furthermore, to explore the unique response, specific metabolites were compared between treatments. When the growth was obstructed by BMAA, 17 metabolisms/pathways including nitrogen and glutathione (i.e. oxidative stress) metabolisms, were influenced in T. pseudonana. This study has further determined that 11 out of 17 metabolisms/pathways could be essentially affected by BMAA, leading to the inhibition of diatom growth.

Presence of the neurotoxin β-N-methylamino-L-alanine in irrigation water and accumulation in cereal grains with human exposure risk

The present study demonstrates the presence of the neurotoxin β-N-methylamino-L-alanine and its cyanobacterial producers in irrigation water and grains of some cereal plants from farmlands irrigated with Nile River water in Egypt. BMAA detected by LC-MS/MS in phytoplankton samples was found at higher concentrations of free form (0.84-11.4 μg L-1) than of protein-bound form (0.16-1.6 μg L-1), in association with the dominance of cyanobacteria in irrigation water canals. Dominant cyanobacterial species isolated from these irrigation waters including Aphanocapsa planctonica, Chroococcus minutus, Dolichospermum lemmermanni, Nostoc commune, and Oscillatoria tenuis were found to produce different concentrations of free (4.8-71.1 µg g-1 dry weight) and protein-bound (0.1-11.4 µg g-1 dry weight) BMAA. In the meantime, BMAA was also detected in a protein-bound form only in grains of corn (3.87-4.51 µg g-1 fresh weight) and sorghum (5.1-7.1 µg g-1 fresh weight) plants, but not in wheat grains. The amounts of BMAA accumulated in these grains correlated with BMAA concentrations detected in relevant irrigation water canals. The presence of BMAA in cereal grains would constitute a risk to human and animal health upon consumption of contaminated grains. The study, therefore, suggests continuous monitoring of BMAA and other cyanotoxins in irrigation waters and edible plants to protect the public against exposure to such potent toxins.

Evaluation of cyanotoxin L-BMAA effect on α-synuclein and TDP43 proteinopathy

The complex interplay between genetic and environmental factors is considered the cause of neurodegenerative diseases including Parkinson's disease (PD) and Amyotrophic Lateral Sclerosis (ALS). Among the environmental factors, toxins produced by cyanobacteria have received much attention due to the significant increase in cyanobacteria growth worldwide. In particular, L-BMAA toxin, produced by diverse taxa of cyanobacteria, dinoflagellates and diatoms, has been extensively correlated to neurodegeneration. The molecular mechanism of L-BMAA neurotoxicity is still cryptic and far from being understood. In this research article, we have investigated the molecular pathways altered by L-BMAA exposure in cell systems, highlighting a significant increase in specific stress pathways and an impairment in autophagic processes. Interestingly, these changes lead to the accumulation of both α-synuclein and TDP43, which are correlated with PD and ALS proteinopathy, respectively. Finally, we were able to demonstrate specific alterations of TDP43 WT or pathological mutants with respect to protein accumulation, aggregation and cytoplasmic translocation, some of the typical features of both sporadic and familial ALS.

Cell cycle of microalga Isochrysis galbana arrested by neurotoxin β-N-methylamino-l-alanine and corresponding molecular mechanisms

The phycotoxin β-N-methylamino-l-alanine (BMAA) has attracted attention due to its risks to marine organisms and human health. In this study, approximately 85 % of synchronized cells of the marine microalga Isochrysis galbana were arrested at the cell cycle G1 phase by BMAA at 6.5 μM for a 24-h exposure. The concentration of chlorophyll a (Chl a) gradually decreased, while the maximum quantum yield of PSII (F_v/F_m), the maximum relative electron transport rate (rETR_max), light utilization efficiency (α) and half-saturated light irradiance (I_k) reduced early and recovered gradually in I. galbana exposed to BMAA in 96-h batch cultures. Transcriptional expression of I. galbana analyzed at 10, 12, and 16 h disclosed multiple mechanisms of BMAA to suppress the microalgal growth. Production of ammonia and glutamate was limited by the down-regulation of nitrate transporters, glutamate synthase, glutamine synthetase, cyanate hydrolase, and formamidase. Diverse extrinsic proteins related to PSII, PSI, cytochrome b6f complex, and ATPase were influenced by BMAA at transcriptional level. Suppression of the DNA replication and mismatch repair pathways increased the accumulation of misfolded proteins, which was reflected by the up-regulated expression of proteasome to accelerate proteolysis. This study improves our understanding of the chemical ecology impacts of BMAA in marine ecosystems.

Marine natural products

Covering: January to December 2021This review covers the literature published in 2021 for marine natural products (MNPs), with 736 citations (724 for the period January to December 2021) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1425 in 416 papers for 2021), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. An analysis of the number of authors, their affiliations, domestic and international collection locations, focus of MNP studies, citation metrics and journal choices is discussed.

β-N-Methylamino-L-Alanine (BMAA) Modulates the Sympathetic Regulation and Homeostasis of Polyamines

The neurotoxin β-N-methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid produced by cyanobacteria. Non-neuronal toxicity of BMAA is poorly studied with a reported increase in reactive oxygen species and a decrease in the antioxidant capacity of liver, kidney, and colorectal adenocarcinoma cells. The aim of this research is to study the toxicity of BMAA (0.1-1 mM) on mitochondria and submitochondrial particles with ATPase activity, on the semicarbazide-sensitive amino oxidases (SSAOs) activity of rat liver, and on an in vitro model containing functionally active excitable tissues-regularly contracting heart muscle preparation with a preserved autonomic innervation. For the first time the BMAA-dependent inhibition of SSAO activity, the elimination of the positive inotropic effect of adrenergic innervation, and the direct and reversible inhibition of adrenaline signaling in ventricular myocytes with 1 mM BMAA were observed. Additionally, it is confirmed that 1 mM BMAA can activate mitochondrial ATPase indirectly. It is concluded that a higher dose of BMAA may influence multiple physiological and pathological processes as it slows down the degradation of biogenic amines, downregulates the sympathetic neuromediation, and embarrasses the cell signaling of adrenergic receptors.

Degradation of cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) using ozone process: influencing factors and mechanism

β-N-methylamino-L-alanine (BMAA), which has been considered as an environmental factor that caused amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) or Alzheimer's disease, could be produced by a variety of genera cyanobacteria. BMAA is widely present in water sources contaminated by cyanobacteria and may threaten human health through drinking water. Although oxidants commonly used in drinking water plants such as chlorine, ozone, hydrogen peroxide, and hydroxyl radicals have been shown to effectively degrade BMAA, there are limited studies on the mechanism of BMAA degradation by different oxidants, especially ozone. This work systematically explored the effectiveness of BMAA ozonation degradation, investigated the effect of the operating parameters on the effectiveness of degradation, and speculated on the pathways of BMAA decomposition. The results showed that BMAA could be quickly eliminated by ozone, and the removal rates of BMAA were nearly 100% in pure water, but the removal rates were reduced in actual water. BMAA was primarily degraded by direct oxidation of ozone molecules in acidic and near-neutral conditions, and indirect oxidation of •OH accounted for the main part under strong alkaline conditions. The pH value had a significant effect on the decomposition of BMAA, and the degradation rate of BMAA was fastest at near-neutral pH value. The degradation rates of TOC were significantly lower than that of BMAA, indicating that by-products were generated during the degradation process. Three by-products ([M-H]⁺  = 105, 90, and 88) were identified by UPLC-MS/MS, and the degradation pathways of BMAA were proposed. The production of by-products was attributed to the fracture of the C-N bonds. This work is helpful for the in-depth understanding on the mechanism and demonstration of the feasibility of the oxidation of BMAA by the ozone process. HIGHLIGHTS: • The reaction of ozonation BMAA was easy to occur. • The degradation rate was fast under near-neutral conditions. • Direct oxidation under neural conditions was the main pathway for ozone degradation of BMAA. • Three products were detected, and the reaction path was inferred.

Occurrence and spatial distribution of paralytic shellfish toxins in seawater and marine organisms in the coastal waters of Qinhuangdao, China

In recent years, paralytic shellfish toxins (PSTs) have been prevalent in the coastal waters of Qinhuangdao, the west coast of the Bohai Sea, China. The content of PSTs in shellfish often exceeded the regulatory limit of 800 μg STX equivalent (eq.) kg^-1, which poses a serious threat to human health. In this study, two surveys were conducted in May 2021 and May 2022 to investigate the distribution of PSTs in the coastal waters of Qinhuangdao. Seawater, surface sediment, phytoplankton, zooplankton, and other marine organism samples were collected, and the composition and concentration of PSTs were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results showed that multiple PST components were detected in all seawater samples collected at different depths, mainly including GTX1/4, GTX2/3, dcGTX2, STX and C1/2, and the highest concentration of PSTs reached 244 ng STX eq. L^-1. The sediment samples also contained low levels of C1/2 and GTX2/3. Trace amounts of C1/2 and GTX1-4 were detected in phytoplankton and zooplankton. Moreover, all bivalve shellfish samples were found to contain PSTs, and the scallop Azumapecten farreri and the ark clam Anadara kagoshimensis showed relatively high concentrations of 607 and 497 μg STX eq. kg^-1, respectively. In addition, low levels of PSTs were also found in some non-traditional PST vectors, including whelk Rapana venosa, octopus Amphioctopus ovulum, goby Ctenotrypauchen chinensis, and greenling Hexagrammos agrammus. Results of this study improve the understanding of the distribution of PSTs in seawater and marine organisms and the potential risk of persistent PSTs in seawater to marine ecosystems and human health.

Putative biosynthesis mechanism of the neurotoxin β-N-methylamino-L-alanine in marine diatoms based on a transcriptomics approach

The neurotoxin β-N-methylamino-L-alanine (BMAA) has been presumed as an environmental cause of human neurodegenerative disorders, such as Alzheimer's disease. Marine diatoms Thalassiosira minima are demonstrated here to produce BMAA-containing proteins in axenic culture while the isomer diaminobutyric acid was bacterially produced. In the co-culture with Cyanobacterium aponinum, diatom growth was inhibited but the biosynthesis of BMAA-containing proteins was stimulated up to seven times higher than that of the control group by cell-cell interactions. The stimulation effect was not caused by the cyanobacterial filtrate. Nitrogen deprivation also doubled the BMAA content of T. minima cells. Transcriptome analysis of the diatom in mixed culture revealed that pathways involved in T. minima metabolism and cellular functions were mainly influenced, including KEGG pathways valine and leucine/isoleucine degradation, endocytosis, pantothenate and CoA biosynthesis, and SNARE interactions in vesicular transport. Based on the expression changes of genes related to protein biosynthesis, it was hypothesized that ubiquitination and autophagy suppression, and limited COPII vesicles transport accuracy and efficiency were responsible for biosynthesis of BMAA-containing proteins in T. minima. This study represents a first application of transcriptomics to investigate the biological processes associated with BMAA biosynthesis in diatoms.

Evidence of 2,4-diaminobutyric acid (DAB) production as a defense mechanism in diatom Thalassiosira pseudonana

The neurotoxic secondary metabolite β-N-methylamino-L-alanine (BMAA) and its structural isomer 2,4-diaminobutyric acid (DAB) are known to be produced by various phytoplankton groups. Despite the worldwide spread of these toxin producers, no obvious role and function of BMAA and DAB in diatoms have been identified. Here, we investigated the effects of biotic factors, i.e., predators and competitors, as possible causes of BMAA and/or DAB regulation in the two diatom species Phaeodactylum tricornutum and Thalassiosira pseudonana. DAB was specifically regulated in T. pseudonana by the presence of predators and competitors. The effects of DAB on both diatoms as competitors and on the copepod Tigriopus sp. as predator at individual and at population levels were examined. The toxic effects of DAB on the growth of T. pseudonana and the population of Tigriopus sp. were significant. The effect of DAB as a defensive secondary metabolite is assumed to be environmentally relevant depending on the number of the copepods. The results show a potential function of DAB that can play an important role in defense mechanisms of T. pseudonana.

Effect and function of β-N-methylamino-L-alanine in the diatom Phaeodactylum tricornutum

The neurotoxin β-N-methylamino-L-alanine (BMAA) is an environmental factor connected to neurodegenerative diseases. BMAA can be produced by various microorganisms (e.g. bacteria, cyanobacteria, dinoflagellates and diatoms) present in diverse ecosystems. No previous study has revealed the function of BMAA in diatoms. In the present study, we combined physiological data with metabolomic and transcriptional data in order to investigate the effect and function of BMAA in the diatom Phaeodactylum tricornutum. P. tricornutum, exposed to different concentrations of exogenous BMAA, showed concentration dependent responses. When the concentration of supplemented BMAA was sufficient to arrest the growth of P. tricornutum, oxidative stress and obstructed carbon fixation were obtained from the specific metabolite and transcriptional data. Results also indicated increased concentration of intracellular chlorophyll a and alterations in the GS-GOGAT cycle, whereas the urea cycle was suppressed. We therefore conclude that BMAA represents a toxic metabolite able to control the growth of P. tricornutum by triggering oxidative stress, and further influencing photosynthesis and nitrogen metabolisms.

Matrix Effect of Diverse Biological Samples Extracted with Different Extraction Ratios on the Detection of β-N-Methylamino-L-Alanine by Two Common LC-MS/MS Analysis Methods

Neurotoxin β-N-methylamino-L-alanine (BMAA) is hypothesized as an important pathogenic factor for neurodegenerative diseases such as amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS-PDC). Comparative study on the accuracy of BMAA analyzed by the regular LC-MS/MS methods is still limited for different biological matrices. In this study, a free-BMAA sample of cyanobacterium and BMAA-containing positive samples of diatom, mussel, scallop, and oyster were extracted with varied extraction ratios (ER) ranging from 1:20 to 1:2000. These extracts were then purified by MCX cartridges. After SPE purification, these different biological samples were analyzed by two common LC-MS/MS analysis methods, a direct analysis without derivatization by a hydrophilic interaction liquid chromatography (HILIC)-MS/MS and pre-column 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) derivatization combined with a C18 column. The results suggested that the recoveries of BMAA spiked in the cyanobacterial sample were close to 100% in the total soluble form extracts with the ER of 1:100 (g/mL) and the precipitated bound form extracts with the ER of 1:500. The recommended ER for the precipitated bound form of BMAA in diatoms and the total soluble form of BMAA in mollusks are 1:500 and 1:50, respectively. The quantitative results determined by the AQC derivatization method were lower than those determined by the direct analysis of the HILIC method in diatom and mollusk samples. The results of the HILIC method without the derivatization process were closer to the true value of BMAA in cyanobacteria. This work contributes to the performance of the solid-phase extraction (SPE) purification protocol and the accuracy of BMAA analysis by LC-MS/MS in diverse biological samples.

Neuropathological Mechanisms of β-N-Methylamino-L-Alanine (BMAA) with a Focus on Iron Overload and Ferroptosis

The incidence of neurodegenerative diseases and cyanobacterial blooms is concomitantly increasing worldwide. The cyanotoxin β-N-methylamino-L-alanine (BMAA) is produced by most of the Cyanobacteria spp. This cyanotoxin is described as a potential environmental etiology factor for some sporadic neurodegenerative diseases. Climate change and eutrophication significantly increase the frequency and intensity of cyanobacterial bloom in water bodies. This review evaluates different neuropathological mechanisms of BMAA at molecular and cellular levels and compares the related studies to provide some useful recommendations. Additionally, the structure and properties of BMAA as well as its microbial origin, especially by gut bacteria, are also briefly covered. Unlike previous reviews, we hypothesize the possible neurotoxic mechanism of BMAA through iron overload. We also discuss the involvement of BMAA in excitotoxicity, TAR DNA-binding protein 43 (TDP-43) translocation and accumulation, tauopathy, and other protein misincorporation and misfolding.

No β-N-Methylamino-L-alanine (BMAA) Was Detected in Stranded Cetaceans from Galicia (North-West Spain)

The neurotoxin β-N-methylamino-L-alanine (BMAA), a non-proteinogenic amino acid produced by several species of both prokaryotic (cyanobacteria) and eukaryotic (diatoms) microorganisms, has been proposed to be associated with the development of neurodegenerative diseases. At first, BMAA appeared to be ubiquitously present worldwide in various organisms, from aquatic and terrestrial food webs. However, recent studies, using detection methods based on mass spectrometry, instead of fluorescence detection, suggest that the trophic transfer of BMAA is debatable. This study evaluated BMAA in 22 cetaceans of three different species (Phocoena phocoena, n = 8, Delphinus delphis, n = 8, and Tursiops truncatus, n = 6), found stranded in North-West Spain. BMAA analysis of the liver, kidney, or muscle tissues via sensitive liquid chromatography with tandem mass spectrometry did not reveal the presence of this compound or its isomers. The absence recorded in this study highlights the need to better understand the trophic transfer of BMAA and its anatomical distribution in marine mammals.

Progress on the investigation and monitoring of marine phycotoxins in China

Marine phycotoxins associated with paralytic shellfish poisoning (PSP), diarrhetic shellfish poisoning (DSP), amnesic shellfish poisoning (ASP), neurotoxic shellfish poisoning (NSP), ciguatera fish poisoning (CFP), tetrodotoxin (TTX), palytoxin (PLTX) and neurotoxin β-N-methylamino-L-alanine (BMAA) have been investigated and routinely monitored along the coast of China. The mouse bioassay for monitoring of marine toxins has been progressively replaced by the enzyme-linked immunosorbent assay (ELISA) and liquid chromatography tandem mass spectrometry (LC-MS/MS), which led to the discovery of many new hydrophilic and lipophilic marine toxins. PSP toxins have been detected in the whole of coastal waters of China, where they are the most serious marine toxins. PSP events in the Northern Yellow Sea, the Bohai Sea and the East China Sea are a cause of severe public health concern. Okadaic acid (OA) and dinophysistoxin-1 (DTX1), which are major toxin components associated with DSP, were mainly found in coastal waters of Zhejiang and Fujian provinces, and other lipophilic toxins, such as pectenotoxins, yessotoxins, azaspiracids, cyclic imines, and dinophysistoxin-2(DTX2) were detected in bivalves, seawater, sediment, as well as phytoplankton. CFP events mainly occurred in the South China Sea, while TTX events mainly occurred in Jiangsu, Zhejiang and Fujian provinces. Microalgae that produce PLTX and BMAA were found in the phytoplankton community along the coastal waters of China.