Fate of Planktothrix-derived toxins in aquatic food webs: A case study in Lake Mindelsee (Germany).

Blooms of the red, filamentous cyanobacterium Planktothrix rubescens occur frequently in pre-alpine lakes in Europe, often with concomitant toxic microcystin (MC) production. Trophic transfer of MCs has been observed in bivalves, fish, and zooplankton species, while uptake of MCs into Diptera species could facilitate distribution of MCs into terrestrial food webs and habitats. In this study, we characterized a Planktothrix bloom in summer 2019 in Lake Mindelsee and tracked possible trophic transfer and/or bioaccumulation of MCs via analysis of phytoplankton, zooplankton (Daphnia) and emergent aquatic insects (Chaoborus, Chironomidae and Trichoptera). Using 16 S rRNA gene amplicon sequencing, we found that five sequence variants of Planktothrix spp. were responsible for bloom formation in September and October of 2019, and these MC-producing variants, provisionally identified as P. isothrix and/or P. serta, occurred exclusively in Lake Mindelsee (Germany), while other variants were also detected in nearby Lake Constance. The remaining cyanobacterial community was dominated by Cyanobiaceae species with high species overlap with Lake Constance, suggesting a well-established exchange of cyanobacteria species between the adjacent lakes. With targeted LC-HRMS/MS we identified two MC-congeners, MC-LR and [Asp3]MC-RR with maximum concentrations of 45 ng [Asp3]MC-RR/L in lake water in September. Both MC congeners displayed different predominance patterns, suggesting that two different MC-producing species occurred in a time-dependent manner, whereby [Asp3]MC-RR was clearly associated with the Planktothrix spp. bloom. We demonstrate an exclusive transfer of MC-LR, but not [Asp3]MC-RR, from phytoplankton into zooplankton reaching a 10-fold bioconcentration, yet complete absence of these MC congeners or their conjugates in aquatic insects. The latter demonstrated a limited trophic transfer of MCs from zooplankton to zooplanktivorous insect larvae (e.g., Chaoborus), or direct transfer into other aquatic insects (e.g. Chironomidae and Trichoptera), whether due to avoidance or limited uptake and/or rapid excretion of MCs by higher trophic emergent aquatic insects.

Proliferation and anatoxin production of benthic cyanobacteria associated with canine mortalities along a stream-lake continuum.

Proliferations of benthic cyanobacteria are increasingly in the public eye, with rising animal deaths associated with benthic rather than planktonic blooms. In early June 2021, two dogs died after consuming material on the shore of Shubenacadie Grand Lake, Nova Scotia. Preliminary investigations indicated anatoxins produced by benthic cyanobacterial mats were responsible for the deaths. In this study, we monitored the growth of a toxic benthic cyanobacterial species (Microcoleus sp.) along a stream-lake continuum where the canine poisonings occurred. We found that the species was able to proliferate in both lentic and lotic environments, but temporal growth dynamics and the predominant sub-species were influenced by habitat type, and differed with hydrodynamic setting, nutrient and sunlight availability. Toxin concentration was greatest in cyanobacterial mats growing in the oligotrophic lakeshore environment (maximum measured total anatoxins (ATXs) >20 mg·kg-1 wet weight). This corresponded with a shift in the profile of ATX analogues, which also indicated changing sub-species dominance along the stream-lake transition.

Liquid chromatography-high-resolution tandem mass spectrometry of anatoxins, including new conjugates and reduction products.

Anatoxins (ATXs) are a potent class of cyanobacterial neurotoxins for which only a handful of structural analogues have been well characterized. Here, we report the development of an LC-HRMS/MS method for the comprehensive detection of ATXs. Application of this method to samples of benthic cyanobacterial mats and laboratory cultures showed detection of several new ATXs. Many of these result from nucleophilic addition to the olefinic bond of the α,ß-unsaturated ketone functional group of anatoxin-a (ATX) and homoanatoxin-a (hATX), analogous to the conjugation chemistry of microcystins, which contain similar α,ß-unsaturated amide functionality. Conjugates with glutathione, γ-glutamylcysteine, methanethiol, ammonia, methanol and water were detected, as well as putative C-10 alcohol derivatives. Structural confirmation was obtained by simple and selective analytical-scale semisynthetic reactions starting from available ATX standards. Methanol, water and ammonia conjugates were found to result primarily from sample preparation. Reduction products were found to result from enzymatic reactions occurring primarily after cell lysis in laboratory cultures of Kamptonema formosum and Cuspidothrix issatschenkoi. The relative contributions of the identified analogues to the anatoxin profiles in a set of 22 benthic-cyanobacterial-mat field samples were estimated, showing conjugates to account for up to 15% of total ATX peak area and 10-hydroxyanatoxins up to 38%. The developed methodology, new analogues and insight into the chemical and enzymatic reactivity of ATXs will enable a more comprehensive study of the class than possible previously.

Genomic characterization of coexisting anatoxin-producing and non-toxigenic Microcoleus subspecies in benthic mats from the Wolastoq, New Brunswick, Canada.

The presence of toxigenic benthic cyanobacteria in riverine ecosystems is an increasing concern around the world. In 2018, the death of three dogs along the Wolastoq (also known as the Saint John River) in New Brunswick, Canada, was attributed to anatoxin exposure after they ingested benthic microbial mats found along the shore. Here, we shotgun sequenced the DNA of 15 non-axenic cyanobacterial isolates derived from four anatoxin-containing benthic mat samples associated with the dog deaths. Anatoxins were produced by some of the isolates, but not all. We retrieved near-complete Microcoleus metagenome-assembled genomes (MAGs) from the isolates that are closely related to anatoxin-producing Microcoleus from the Cardrona River (New Zealand), although the Microcoleus MAGs from the Wolastoq varied in the presence/absence of the anatoxin-a biosynthesis cluster. Sequence similarity at the genomic level suggests that toxigenic and non-toxigenic Microcoleus MAGs from the Wolastoq belong to the same species but are separate subspecies. The toxigenic and nontoxic Wolastoq Microcoleus subspecies coexisted in the mat samples in similar relative abundance. Overall genomic comparisons revealed that toxigenic Microcoleus MAGs are longer and code for more accessory genes than their non-toxigenic relatives, suggesting a differential responsiveness to changing environments, stress conditions and nutrient availability.

Anatoxins from benthic cyanobacteria responsible for dog mortalities in New Brunswick, Canada.

In July 2018 three dogs died after visiting the Wolastoq (Saint John River) near Fredericton, New Brunswick, in Atlantic Canada. All showed signs of toxicosis, and necropsies revealed non-specific pulmonary edema and multiple microscopic brain hemorrhages. Liquid chromatography-high-resolution mass spectrometry (LC-HRMS) analysis of vomitus and stomach contents as well as water and biota from the mortality sites confirmed the presence of anatoxins (ATXs), a class of potent neurotoxic alkaloids. The highest levels were measured in a dried benthic cyanobacterial mat that two of the dogs had been eating before falling ill and in a vomitus sample collected from one of the dogs. Concentrations of 357 and 785 mg/kg for anatoxin-a and dihydroanatoxin-a, respectively, were measured in the vomitus. Known anatoxin-producing species of Microcoleus were tentatively identified using microscopy and confirmed by 16S rRNA gene sequencing. The ATX synthetase gene, anaC, was detected in the samples and isolates. The pathology and experimental results confirmed the role of ATXs in these dog mortalities. Further research is required to understand drivers for toxic cyanobacteria in the Wolastoq and to develop methodology for assessing occurrence.

Rapid Quantitation of Anatoxins in Benthic Cyanobacterial Mats Using Direct Analysis in Real-Time-High-Resolution Tandem Mass Spectrometry.

Toxic benthic cyanobacterial mats are increasingly reported worldwide as being responsible for animal mortalities due to their production of the potent neurotoxin anatoxin-a (ATX) and its analogues. Improved analytical methods for anatoxins are needed to address public health and watershed management challenges arising from extremely high spatial and temporal variability within impacted systems. We present the development, validation, and application of a direct analysis in real-time-high-resolution tandem mass spectrometry (DART-HRMS/MS) method for analysis of anatoxins in cyanobacterial field samples, including a simplified sample preparation approach. The method showed excellent sensitivity and selectivity for ATX, homoanatoxin-a, and dihydroanatoxin-a. Isotopically labeled ATX was used as an internal standard for all three analogues and successfully corrected for the matrix effects observed (86 ± 16% suppression). The limit of detection and recovery for ATX was estimated as 5 ng/g and 88%, respectively, using spiked samples. The total analysis time was ∼2 min, and excellent agreement was observed with results from a liquid chromatography-HRMS reference method. Finally, the DART-HRMS/MS method was applied to a set of 45 Microcoleus-dominated benthic cyanobacterial mat samples from the Wolastoq near Fredericton, Canada, demonstrating its power and applicability in enabling broad-scale field studies of ATX distribution.

Non-target analysis and stability assessment of reference materials using liquid chromatography‒high-resolution mass spectrometry.

Development and characterization of biological and environmental matrix certified reference materials (CRMs) for organic analytes typically relies heavily on targeted analytical methods, such as liquid chromatography (LC) with triple-quadrupole mass spectrometry detection. LC with high-resolution mass spectrometry (LC‒HRMS) can also provide high quality data for both targeted and non-targeted analytes, with the potential for retrospective data analysis. Here, we demonstrate the utility of non-target analysis (NTA) using LC‒HRMS for profiling and stability assessment of a mussel tissue matrix CRM certified for several classes of marine algal toxins (CRM-FDMT1). First, the NTA method was developed using data-dependent MS/MS acquisition and commercial metabolomics software for data processing. Of 128 toxin analogues previously reported in CRM-FDMT1, 125 were detected by LC-HRMS, with 97 triggered for MS/MS by data dependant acquisition. Automated data processing detected 119 of these compounds and 109 were retained after automated filtering of results for putative toxin analogues. Those analogues not detected were low abundance ions, or poorly resolved isomers. The method was then used to demonstrate new strategies for CRM stability assessment considering the stability of certified analytes, related toxin analogues, and unrelated matrix compounds. Several analogues from each toxin class in CRM-FDMT1 as well as other unrelated matrix compounds were observed to be significantly less stable than the certified toxins. Using this method, no instability was measured for any compounds at conditions ≤4 °C, providing a greater degree of confidence in CRM stability than could be achieved using conventional approaches to stability assessment targeting only the certified analytes. The NTA method and stability assessment approach presented are applicable to future CRM development with other matrices and organic analyte classes.

A Feasibility Study into the Production of a Mussel Matrix Reference Material for the Cyanobacterial Toxins Microcystins and Nodularins.

Microcystins and nodularins, produced naturally by certain species of cyanobacteria, have been found to accumulate in aquatic foodstuffs such as fish and shellfish, resulting in a risk to the health of the seafood consumer. Monitoring of toxins in such organisms for risk management purposes requires the availability of certified matrix reference materials to aid method development, validation and routine quality assurance. This study consequently targeted the preparation of a mussel tissue reference material incurred with a range of microcystin analogues and nodularins. Nine targeted analogues were incorporated into the material as confirmed through liquid chromatography with tandem mass spectrometry (LC-MS/MS), with an additional 15 analogues detected using LC coupled to non-targeted high resolution mass spectrometry (LC-HRMS). Toxins in the reference material and additional source tissues were quantified using LC-MS/MS, two different enzyme-linked immunosorbent assay (ELISA) methods and with an oxidative-cleavage method quantifying 3-methoxy-2-methyl-4-phenylbutyric acid (MMPB). Correlations between the concentrations quantified using the different methods were variable, likely relating to differences in assay cross-reactivities and differences in the abilities of each method to detect bound toxins. A consensus concentration of total soluble toxins determined from the four independent test methods was 2425 ± 575 µg/kg wet weight. A mean 43 ± 9% of bound toxins were present in addition to the freely extractable soluble form (57 ± 9%). The reference material produced was homogenous and stable when stored in the freezer for six months without any post-production stabilization applied. Consequently, a cyanotoxin shellfish reference material has been produced which demonstrates the feasibility of developing certified seafood matrix reference materials for a large range of cyanotoxins and could provide a valuable future resource for cyanotoxin risk monitoring, management and mitigation.

CyanoMetDB, a comprehensive public database of secondary metabolites from cyanobacteria.

Harmful cyanobacterial blooms, which frequently contain toxic secondary metabolites, are reported in aquatic environments around the world. More than two thousand cyanobacterial secondary metabolites have been reported from diverse sources over the past fifty years. A comprehensive, publically-accessible database detailing these secondary metabolites would facilitate research into their occurrence, functions and toxicological risks. To address this need we created CyanoMetDB, a highly curated, flat-file, openly-accessible database of cyanobacterial secondary metabolites collated from 850 peer-reviewed articles published between 1967 and 2020. CyanoMetDB contains 2010 cyanobacterial metabolites and 99 structurally related compounds. This has nearly doubled the number of entries with complete literature metadata and structural composition information compared to previously available open access databases. The dataset includes microcytsins, cyanopeptolins, other depsipeptides, anabaenopeptins, microginins, aeruginosins, cyclamides, cryptophycins, saxitoxins, spumigins, microviridins, and anatoxins among other metabolite classes. A comprehensive database dedicated to cyanobacterial secondary metabolites facilitates: (1) the detection and dereplication of known cyanobacterial toxins and secondary metabolites; (2) the identification of novel natural products from cyanobacteria; (3) research on biosynthesis of cyanobacterial secondary metabolites, including substructure searches; and (4) the investigation of their abundance, persistence, and toxicity in natural environments.

Rapid quantitative screening of cyanobacteria for production of anatoxins using direct analysis in real time high-resolution mass spectrometry.

RATIONALE: Anatoxins (ATXs) are a potent class of cyanobacterial neurotoxins that are increasingly problematic in drinking water reservoirs and recreational water bodies worldwide. Because of their high polarity and low molecular weight, analysis of ATXs is challenging and they can be considered underreported compared with other classes of cyanobacterial toxins. Improved screening methods are therefore needed to effectively assess their occurrence and concentrations in the environment. METHODS: A rapid screening method was developed for ATXs in cyanobacteria using direct analysis in real time combined with high-resolution mass spectrometry (DART-HRMS), requiring less than 2 min per sample for triplicate analysis. The developed method was evaluated for its quantitative capabilities, applied to the screening of 30 cyanobacterial culture samples for the presence of anatoxin-a, homoanatoxin-a and dihydroanatoxin-a, and compared with a more typical liquid chromatography (LC)/HRMS method. RESULTS: Excellent linearity was observed in the analysis of a matrix-matched calibration curve using DART-HRMS, with ionization suppression of about 50% and relative standard deviations between replicate analyses of approximately 30%. Limits of detection for both anatoxin-a and homoanatoxin-a were estimated as 1 ng/mL. Excellent agreement was observed between DART-HRMS and LC/HRMS with all ATX-producing cultures correctly identified and only one false positive culture by DART-HRMS. CONCLUSIONS: DART-HRMS shows excellent promise for the rapid, quantitative screening of ATXs in cyanobacteria and could be expanded in the future to include the analysis of field samples and drinking water, as well as additional ATX analogues.

Semiquantitation of Paralytic Shellfish Toxins by Hydrophilic Interaction Liquid Chromatography-Mass Spectrometry Using Relative Molar Response Factors.

Paralytic shellfish toxins (PSTs) are a complex class of analogs of the potent neurotoxin saxitoxin (STX). Since calibration standards are not available for many PSTs, including C-11 hydroxyl analogs called M-toxins, accurate quantitation by liquid chromatography-mass spectrometry (LC-MS) can be challenging. In the absence of standards, PSTs are often semiquantitated using standards of a different analog (e.g., STX), an approach with a high degree of uncertainty due to the highly variable sensitivity between analytes in electrospray ionization. Here, relative molar response factors (RMRs) were investigated for a broad range of PSTs using common LC-MS approaches in order to improve the quantitation of PSTs for which standards are unavailable. First, several M-toxins (M1-M6, M9 and dcM6) were semipurified from shellfish using preparative gel filtration chromatography and quantitated using LC-charged aerosol detection (LC-CAD). The RMRs of PST certified reference materials (CRMs) and M-toxins were then determined using selective reaction monitoring LC-MS/MS and full scan LC-high-resolution MS (LC-HRMS) methods in positive and negative electrospray ionization. In general, RMRs for PSTs with similar chemical structures were comparable, but varied significantly between subclasses, with M-toxins showing the lowest sensitivity. For example, STX showed a greater than 50-fold higher RMR than M4 and M6 by LC-HRMS. The MS instrument, scan mode and polarity also had significant impacts on RMRs and should be carefully considered when semiquantitating PSTs by LC-MS. As a demonstration of their utility, the RMRs determined were applied to the semiquantitation of PSTs in contaminated mussels, showing good agreement with results from calibration with CRMs.

Structural Diversity, Characterization and Toxicology of Microcystins.

Hepatotoxic microcystins (MCs) are the most widespread class of cyanotoxins and the one that has most often been implicated in cyanobacterial toxicosis. One of the main challenges in studying and monitoring MCs is the great structural diversity within the class. The full chemical structure of the first MC was elucidated in the early 1980s and since then, the number of reported structural analogues has grown steadily and continues to do so, thanks largely to advances in analytical methodology. The structures of some of these analogues have been definitively elucidated after chemical isolation using a combination of techniques including nuclear magnetic resonance, amino acid analysis, and tandem mass spectrometry (MS/MS). Others have only been tentatively identified using liquid chromatography-MS/MS without chemical isolation. An understanding of the structural diversity of MCs, the genetic and environmental controls for this diversity and the impact of structure on toxicity are all essential to the ongoing study of MCs across several scientific disciplines. However, because of the diversity of MCs and the range of approaches that have been taken for characterizing them, comprehensive information on the state of knowledge in each of these areas can be challenging to gather. We have conducted an in-depth review of the literature surrounding the identification and toxicity of known MCs and present here a concise review of these topics. At present, at least 279 MCs have been reported and are tabulated here. Among these, about 20% (55 of 279) appear to be the result of chemical or biochemical transformations of MCs that can occur in the environment or during sample handling and extraction of cyanobacteria, including oxidation products, methyl esters, or post-biosynthetic metabolites. The toxicity of many MCs has also been studied using a range of different approaches and a great deal of variability can be observed between reported toxicities, even for the same congener. This review will help clarify the current state of knowledge on the structural diversity of MCs as a class and the impacts of structure on toxicity, as well as to identify gaps in knowledge that should be addressed in future research.

Comprehensive multi-technique approach reveals the high diversity of microcystins in field collections and an associated isolate of Microcystis aeruginosa from a Turkish lake.

Microcystins (MCs) are hepatotoxic and potentially carcinogenic cyanotoxins. They exhibit high structural variability, with nearly 250 variants described to date. This variability can result in incomplete detection of MC variants during lake surveys due to the frequent use of targeted analytical methods and a lack of standards available for identification and quantitation. In this study, Lake Uluabat in Turkey was sampled during the summer of 2015. Phylogenetic analysis of the environmental mcyA sequences suggested Microcystis spp. were the major MC contributors. A combination of liquid chromatography-tandem mass spectrometry (LC-MS/MS), liquid chromatography with UV detection and mass spectrometry (LC-UV-MS), and a novel liquid chromatography-high resolution mass spectrometry (LC-HRMS) method, together with thiol and periodate reactivity, revealed more than 36 MC variants in the lake samples and a strain of M. aeruginosa (AQUAMEB-24) isolated from Lake Uluabat. Only MCs containing arginine at position-4 were detected in the culture, while MC-LA, -LY, -LW and -LF were also detected in the lake samples, suggesting the presence of other MC producers in the lake. The previously unreported MCs MC-(H2)YR (dihydrotyrosine at position-2) (17), [epoxyAdda5]MC-LR, [DMAdda5]MC-RR (1) and [Mser7]MC-RR (8) were detected in the culture and/or field samples. This study is a good example of how commonly used targeted LC-MS methods can underestimate the diversity of MCs in freshwater lakes and cyanobacteria cultures and how untargeted LC-MS methods can be used to comprehensively assess MC diversity present in a new system.

Screening of cyclic imine and paralytic shellfish toxins in isolates of the genus Alexandrium (Dinophyceae) from Atlantic Canada.

The dinoflagellate genus Alexandrium Halim has frequently been associated with harmful algal blooms. Although a number of species from this genus are known to produce paralytic shellfish toxins (PST) and/or cyclic imines (CI), studies on comprehensive toxin profiling using techniques capable of detecting the full range of PST and CI analogues are limited. Isolates of Alexandrium spp. from Atlantic Canada were analyzed by targeted and untargeted liquid chromatography-tandem mass spectrometry (LC-MS). Results showed a number of distinct profiles and wide ranging cell quotas of PST and spirolides (SPX) in both A. catenella (Whedon & Kofoid) Balech and A. ostenfedii (Paulsen) Balech & Tangen. The concentration of PST in A. catenella ranged from 0.0029 to 54 fmol cell-1 with the major components being C2 and GTX4. In addition, putative PST metabolites were confirmed for the first time in A. catenella by high resolution MS/MS. By comparison, A. ostenfeldii isolates showed much lower concentrations of PST (

Dynamics of paralytic shellfish toxins and their metabolites during timecourse exposure of scallops Chlamys farreri and mussels Mytilus galloprovincialis to Alexandrium pacificum.

New C-11 hydroxyl metabolites of paralytic shellfish toxins (PSTs) have been reported in shellfish. To gain further information on these metabolites, as well as the potential for formation of phase-II metabolites and acyl esters of PSTs, bivalves were fed with the PSTs-producing dinoflagellate Alexandrium pacificum (strain ATHK). Through independent experiments, scallops (Chlamys farreri) were fed for 9 days and mussels (Mytilus galloprovincialis) for 5 days plus an additional 5 days of depuration, with representative samples taken throughout. Several common PSTs (C1-4, GTX1-6 and NEO) and metabolites including M1, M3, M5, M7, M9, M2 and M8 were detected in the hepatopancreas of scallops during toxin accumulation and in the hepatopancreas of mussels during both toxin accumulation and elimination periods. The relative molar ratio of metabolites to precursor molecules was used to estimate relative metabolic conversion rates. Conversion rates of C1/2 and GTX2/3 were higher than those of C3/4 and GTX1/4, in scallops and mussels. The first metabolites observed in both bivalve species investigated were M1/3, which are formed from C1/2. However, the conversion of GTX2/3 to M2 was more complete than other biotransformation reactions in both mussels and scallops. In general, metabolic conversion of PSTs was observed after a shorter time and to a greater extent in mussels than in scallops in the exposure period. No acyl esters or conjugation products of PSTs with glucuronic acid, glutathione, cysteine and taurine were detected by liquid chromatography with high resolution tandem mass spectrometry in the samples investigated. Additionally, only GTX1/4 and GTX2/3 were detected in the kidney of scallops, which demonstrates that PSTs are mainly metabolized through the hepatic metabolism pathway in bivalves. This work improves the understanding of PST metabolism during toxin accumulation and depuration in commercially harvested shellfish.

Capillary electrophoresis-tandem mass spectrometry for multiclass analysis of polar marine toxins.

Polar marine toxins are more challenging to analyze by mass spectrometry-based methods than lipophilic marine toxins, which are now routinely measured in shellfish by multiclass reversed-phase liquid chromatography-tandem mass spectrometry (MS/MS) methods. Capillary electrophoresis (CE)-MS/MS is a technique that is well suited for the analysis of polar marine toxins, and has the potential of providing very high resolution separation. Here, we present a CE-MS/MS method developed, with use of a custom-built interface, for the sensitive multiclass analysis of paralytic shellfish toxins, tetrodotoxins, and domoic acid in seafood. A novel, highly acidic background electrolyte (5 M formic acid) was designed to maximize protonation of analytes and to allow a high degree of sample stacking to improve the limits of detection. The method was applied to a wide range of regulated and less common toxin analogues, and exhibited a high degree of selectivity between toxin isomers and matrix interference. The limits of detection in mussel tissue were 0.0052 mg/kg for tetrodotoxins, 0.160 mg/kg for domoic acid, and between 0.0018 and 0.120 mg/kg for paralytic shellfish toxins, all of which showed good linearity. Minimal ionization suppression was observed when the response from neat and mussel-matrix-matched standards was corrected with multiple internal standards. Analysis of shellfish matrix reference materials and spiked samples demonstrated good accuracy and precision. Finally, the method was transferred to a commercial CE-MS/MS system to demonstrate its widespread applicability for use in both R & D and routine regulatory settings. The approach of using a highly acidic background electrolyte is of broad interest, and can be considered generally applicable to simultaneous analysis of other classes of small, polar molecules with differing pKa values. Graphical abstract ᅟ.

Differential Mobility-Mass Spectrometry Double Spike Isotope Dilution Study of Release of ß-Methylaminoalanine and Proteinogenic Amino Acids during Biological Sample Hydrolysis.

The non-protein amino acid ß-methylamino-L-alanine (BMAA) has been linked to neurodegenerative disease and reported throughout the environment. Proposed mechanisms of bioaccumulation, trophic transfer and chronic toxicity of BMAA rely on the hypothesis of protein misincorporation. Poorly selective methods for BMAA analysis have led to controversy. Here, a recently reported highly selective method for BMAA quantitation using hydrophilic interaction liquid chromatography-differential mobility spectrometry-tandem mass spectrometry (HILIC-DMS-MS/MS) is expanded to include proteinogenic amino acids from hydrolyzed biological samples. For BMAA quantitation, we present a double spiking isotope dilution approach using D3-BMAA and 13C15N2-BMAA. These methods were applied to study release of BMAA during acid hydrolysis under a variety of conditions, revealing that the majority of BMAA can be extracted along with only a small proportion of protein. A time course hydrolysis of BMAA from mussel tissue was carried out to assess the recovery of BMAA during sample preparation. The majority of BMAA measured by typical methods was released before a significant proportion of protein was hydrolyzed. Little change was observed in protein hydrolysis beyond typical hydrolysis times but the concentration of BMAA increased linearly. These findings demonstrate protein misincorporation is not the predominant form of BMAA in cycad and shellfish.

Hydrophilic interaction liquid chromatography-tandem mass spectrometry for quantitation of paralytic shellfish toxins: validation and application to reference materials.

Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by marine dinoflagellates that are responsible for paralytic shellfish poisoning (PSP) in humans. This work highlights our ongoing efforts to develop quantitative methods for PSTs using hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS). Compared with the commonly used method of liquid chromatography with post-column oxidation and fluorescence detection (LC-ox-FLD), HILIC-MS/MS has the potential of being more robust, sensitive and straightforward to operate, and provides unequivocal confirmation of toxin identity. The main driving force for the present work was the need for a complementary method to LC-ox-FLD to assign values to shellfish tissue matrix reference materials for PSTs. Method parameters that were optimized included LC mobile and stationary phases, electrospray ionization (ESI) conditions, and MS/MS detection parameters. The developed method has been used in the detection and identification of a wide range of PSTs including less common analogues and metabolites in a range of shellfish and algal samples. We have assessed the matrix effects of shellfish samples and have evaluated dilution, standard addition and matrix matched calibration as means of mitigating them. Validation on one LC-MS/MS system for nine common PST analogues (GTX1-4, dcGTX2&3, STX, NEO, and dcSTX) was completed using standard addition. The method was then transferred to a more sensitive LC-MS/MS system, expanded to include five more PSTs (C1&2, dcNEO and GTX5&6) and validated using matrix matched calibration. Limits of detection of the validated method ranged between 6 and 280 nmol/kg tissue using standard addition in extracts of blue mussels, with recoveries between 92 and 108%. Finally, this method was used in combination with the AOAC Official Method based on LC-ox-FLD to measure PSTs in a new mussel tissue matrix reference material.