Effects of Heating on Proportions of Azaspiracids 1-10 in Mussels (Mytilus edulis) and Identification of Carboxylated Precursors for Azaspiracids 5, 10, 13, and 15

Co-localisation of Azaspiracid Analogs with the Dinoflagellate Species Azadinium spinosum and Amphidoma languida in the Southwest of Ireland

Phytoplankton and biotoxin monitoring programmes have been implemented in many countries to protect human health and to mitigate the impacts of harmful algal blooms (HABs) on the aquaculture industry. Several amphidomatacean species have been confirmed in Irish coastal waters, including the azaspiracid-producing species Azadinium spinosum and Amphidoma languida. Biogeographic distribution studies have been hampered by the fact that these small, armoured dinoflagellates share remarkably similar morphologies when observed by light microscopy. The recent releases of species-specific molecular detection assays have, in this context, been welcome developments. A survey of the south west and west coasts of Ireland was carried out in August 2017 to investigate the late summer distribution of toxic amphidomataceans and azaspiracid toxins. Azadinium spinosum and Am. languida were detected in 83% of samples in the southwest along the Crease Line and Bantry Bay transects between 20 and 70 m depth, with maximal cell concentrations of 7000 and 470,000 cells/L, respectively. Azaspiracid concentrations were well aligned with the distributions of Az. spinosum and Am. languida, up to 1.1 ng/L and 4.9 ng/L for combined AZA-1, -2, -33, and combined AZA-38, -39, respectively. Although a snapshot in time, this survey provides new insights in the late summer prominence of AZAs and AZA-producing species in the southwest of Ireland, where major shellfish aquaculture operations are located. Results showed a substantial overlap in the distribution of amphidomatacean species in the area and provide valuable baseline information in the context of ongoing monitoring efforts of toxigenic amphidomataceans in the region.

In Vitro Metabolism of Azaspiracids 1-3 with a Hepatopancreatic Fraction from Blue Mussels (Mytilus edulis)

Azaspiracids (AZAs) are a group of biotoxins produced by the marine dinoflagellates Azadinium and Amphidoma spp. that can accumulate in shellfish and cause food poisoning in humans. Of the 60 AZAs identified, levels of AZA1, AZA2, and AZA3 are regulated in shellfish as a food safety measure based on occurrence and toxicity. Information about the metabolism of AZAs in shellfish is limited. Therefore, a fraction of blue mussel hepatopancreas was made to study the metabolism of AZA1-3 in vitro. A range of AZA metabolites were detected by liquid chromatography-high-resolution tandem mass spectrometry analysis, most notably the novel 22α-hydroxymethylAZAs AZA65 and AZA66, which were also detected in naturally contaminated mussels. These appear to be the first intermediates in the metabolic conversion of AZA1 and AZA2 to their corresponding 22α-carboxyAZAs (AZA17 and AZA19). α-Hydroxylation at C-23 was also a prominent metabolic pathway, producing AZA8, AZA12, and AZA5 as major metabolites of AZA1-3, respectively, and AZA67 and AZA68 as minor metabolites via double-hydroxylation of AZA1 and AZA2, but only low levels of 3β-hydroxylation were observed in this study. In vitro generation of algal toxin metabolites, such as AZA3, AZA5, AZA6, AZA8, AZA12, AZA17, AZA19, AZA65, and AZA66 that would otherwise have to be laboriously purified from shellfish, has the potential to be used for the production of standards for analytical and toxicological studies.

Complex profiles of azaspiracid analogues in two culture strains of Azadinium poporum (Amphidomataceae, Dinophyceae) isolated from Japanese coastal waters determined by LC-MS/MS

Lipophilic marine biotoxins azaspiracids (AZAs) are produced by dinoflagellates Azadinium and Amphidoma. Recently, several strains of Azadinium poporum were isolated from Japanese coastal waters. In our present study, AZA analogues in two strains (mdd421 and HM536) of A. poporum were analyzed by several detection techniques on the liquid chromatography-tandem mass spectrometry (LC-MS/MS) and liquid chromatography-quadrupole time of flight mass spectrometry (LC-QTOFMS). The dominant AZA analogue in the Japanese A. poporum strains was AZA2. Other known AZA analogues were AZA11, AZA35, AZA2 methyl ester and AZA2 phosphate ester. Besides these AZAs, thirteen new AZA analogues were discovered in the two strains. A putative AZA analogue (Compound 1) with the smallest molecular weight ever found in nature was also discovered in the two strains. This is the first report describing detailed AZA profiles in Japanese isolates of A. poporum.

A mussel tissue certified reference material for multiple phycotoxins. Part 5: profiling by liquid chromatography-high-resolution mass spectrometry

A freeze-dried mussel tissue-certified reference material (CRM-FDMT1) was prepared containing the marine algal toxin classes azaspiracids, okadaic acid and dinophysistoxins, yessotoxins, pectenotoxins, cyclic imines, and domoic acid. Thus far, only a limited number of analogues in CRM-FDMT1 have been assigned certified values; however, the complete toxin profile is significantly more complex. Liquid chromatography-high-resolution mass spectrometry was used to profile CRM-FDMT1. Full-scan data was searched against a list of previously reported toxin analogues, and characteristic product ions extracted from all-ion-fragmentation data were used to guide the extent of toxin profiling. A series of targeted and untargeted acquisition MS/MS experiments were then used to collect spectra for analogues. A number of toxins previously reported in the literature but not readily available as standards were tentatively identified including dihydroxy and carboxyhydroxyyessotoxin, azaspiracids-33 and -39, sulfonated pectenotoxin analogues, spirolide variants, and fatty acid acyl esters of okadaic acid and pectenotoxins. Previously unreported toxins were also observed including compounds from the pectenotoxin, azaspiracid, yessotoxin, and spirolide classes. More than one hundred toxin analogues present in CRM-FDMT1 are summarized along with a demonstration of the major acyl ester conjugates of several toxins. Retention index values were assigned for all confirmed or tentatively identified analogues to help with qualitative identification of the broad range of lipophilic toxins present in the material.

Evaluation of the shucking of certain species of scallops contaminated with lipophilic toxins with a view to the production of edible parts meeting the safety requirements foreseen in the Union legislation

EFSA was asked by the European Commission to provide information on levels of lipophilic shellfish toxins in whole scallops that would ensure levels in edible parts below the regulatory limits after shucking, i.e. removal of non-edible parts. This should include the okadaic acid (OA), the azaspiracid (AZA) and the yessotoxin (YTX) groups, and five species of scallops. In addition, EFSA was asked to recommend the number of scallops in an analytical sample. To address these questions, EFSA received suitable data on the three toxin groups in two scallop species, Aequipecten opercularis and Pecten maximus, i.e. data on individual and pooled samples of edible and non-edible parts from contamination incidents. The majority of the concentration levels were below limit of quantification (LOQ)/limit of detection (LOD), especially in adductor muscle but also in gonads. Shucking in most cases resulted in a strong decrease in the toxin levels. For Pecten maximus, statistical analysis showed that levels in whole scallops should not exceed 256 μg OA eq/kg or 217 μg AZA1 eq/kg to ensure that levels in gonads are below the regulatory limits of 160 μg OA or AZA1 eq/kg with 99% certainty. Such an analysis was not possible for yessotoxins or any toxin in Aequipecten opercularis and an assessment could only be based on upper bound levels. To ensure a 95% correct prediction on whether the level in scallops in an area or lot is correctly predicted to be compliant/non-compliant, it was shown that 10 scallops per sample would be sufficient to predict with 95% certainty if levels of OA-group toxins in the area/lot were 25% below or above the regulatory limit. However, to predict with a 95% certainty for levels between 140 and 180 μg OA eq/kg, a pooled sample of more than 30 scallops would have to be tested.

Fatty acid esters of azaspiracids identified in mussels (Mytilus edulis) using liquid chromatography-high resolution mass spectrometry

Azaspiracids (AZAs) are lipophilic polyether toxins produced by Azadinium and Amphidoma species of marine microalgae. The main dinoflagellate precursors AZA1 and AZA2 are metabolized by shellfish to produce an array of AZA analogues. Many marine toxins undergo fatty acid esterification in shellfish, therefore mussel tissues contaminated with AZAs were screened for intact fatty acid esters of AZAs using liquid chromatography-high resolution mass spectrometry. Acyl esters were primarily observed for AZAs containing hydroxy groups at C-3 with 3-O-palmitoylAZA4 identified as the most abundant acyl ester, while other fatty acid esters including 18:1, 16:1, 17:0, 20:2 and 18:0 acyl esters were detected. The structures of these acyl derivatives were determined through LC-MS/MS experiments, and supported by periodate cleavage reactions and semi-synthesis of palmitate esters of the AZAs. Esters of the hydroxy groups at C-20 or C-21 were not observed in mussel tissue. The relative proportion of the most abundant AZA ester was less than 3% of the sum of the major free AZA analogues. These findings reveal an additional metabolic pathway for AZAs in shellfish.

•

Fatty acid esters of azaspiracids were identified in mussels (Mytilus edulis).

•

Fatty acid esters of azaspiracids with hydroxy groups at C-3 were primarily observed.

•

Fatty acid esters of regulated azaspiracids (AZA1, 2, −3) were absent.

•

Structures were determined with LC-HRMS and confirmed by semi-synthesis of palmitate esters and periodate cleavage.

•

This work reveals an additional metabolic pathway for azaspiracids in shellfish.

Variability and profiles of lipophilic toxins in bivalves from Great Britain during five and a half years of monitoring: azaspiracids and yessotoxins

Cefas has been responsible for the delivery of official control biotoxin testing of bivalve molluscs from Great Britain for just over a decade. Liquid chromatography tandem mass spectrometric (LC-MS/MS) methodology has been used for the quantitation of lipophilic toxins (LTs) since 2011. The temporal and spatial distribution of okadaic acid group toxins and profiles in bivalves between 2011 and 2016 have been recently reported. Here we present data on the two other groups of regulated lipophilic toxins, azaspiracids (AZAs) and yessotoxins (YTXs), over the same period. The latter group has also been investigated for a potential link with Protoceratium reticulatum and Lingulodinium polyedra, both previously recognised as YTXs producing phytoplankton. On average, AZAs were quantified in 3.2% of all tested samples but notable inter-annual variation in abundance was observed. The majority of all AZA contaminated samples were found between July 2011 and August 2013 in Scotland, while only two, three-month long, AZA events were observed in 2015 and 2016 in the south-west of England. Maximum concentrations were generally reached in late summer or early autumn. Reasons for AZAs persistence during the 2011/2012 and 2012/2013 winters are discussed. Only one toxin profile was identified, represented by both AZA1 and AZA2 toxins at an approximate ratio of 2 : 1, suggesting a single microalgal species was the source of AZAs in British bivalves. Although AZA1 was always the most dominant toxin, its proportion varied between mussels, Pacific oysters and surf clams. The YTXs were the least represented group among regulated LTs. YTXs were found almost exclusively on the south-west coast of Scotland, with the exception of 2013, when the majority of contaminated samples originated from the Shetland Islands. The highest levels were recorded in the summer months and followed a spike in Protoceratium reticulatum cell densities. YTX was the most dominant toxin in shellfish, further strengthening the link to P. reticulatum as the YTX source. Neither homo-YTX, nor 45-OH homo-YTX were detected throughout the monitored period. 45-OH YTX, thought to be a shellfish metabolite associated with YTX elimination, contributed on average 26% in mussels. Although the correlation between 45-OH YTX abundance and the speed of YTX depuration could not be confirmed, we noted the half-life of YTX was more than two-times longer in queen scallops, which contained 100% YTX, than in mussels. No other bivalve species were affected by YTXs. This is the first detailed evaluation of AZAs and YTXs occurrences and their profiles in shellfish from Great Britain over a period of multiple years.

A Practical ELISA for Azaspiracids in Shellfish via Development of a New Plate-Coating Antigen

Azaspiracids (AZAs) are a group of biotoxins that appear periodically in shellfish and can cause food poisoning in humans. Current methods for quantifying the regulated AZAs are restricted to LC-MS but are not well suited to detecting novel and unregulated AZAs. An ELISA method for total AZAs in shellfish was reported recently, but unfortunately, it used relatively large amounts of the AZA-1-containing plate-coating conjugate, consuming significant amounts of pure AZA-1 per assay. Therefore, a new plate-coater, OVA-cdiAZA1 was produced, resulting in an ELISA with a working range of 0.30-4.1 ng/mL and a limit of quantification of 37 μg/kg for AZA-1 in shellfish. This ELISA was nearly twice as sensitive as the previous ELISA while using 5-fold less plate-coater. The new ELISA displayed broad cross-reactivity toward AZAs, detecting all available quantitative AZA reference materials as well as the precursors to AZA-3 and AZA-6, and results from shellfish analyzed with the new ELISA showed excellent correlation ( R² = 0.99) with total AZA-1-10 by LC-MS. The results suggest that the new ELISA is suitable for screening samples for total AZAs, even in cases where novel AZAs are present and regulated AZAs are absent, such as was reported recently from Puget Sound and the Bay of Naples.

Diversity, distribution, and azaspiracids of Amphidomataceae (Dinophyceae) along the Norwegian coast

Azaspiracids (AZA) are a group of lipophilic polyether compounds which have been implicated in shellfish poisoning incidents around Europe. They are produced by a few species of the dinophycean genera Azadinium and Amphidoma (Amphidomataceae). The presence of AZA toxins in Norway is well documented, but knowledge of the distribution and diversity of Azadinium and other Amphidomataceae along the Norwegian coast is rather limited and poorly documented. On a research survey along the Norwegian coast in 2015 from the Skagerrak in the South to Trondheimsfjorden in the North, plankton samples from 67 stations were analysed for the presence of Azadinium and Amphidoma and their respective AZA by on-board live microscopy, real-time PCR assays specific for Amphidomataceae, and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Microscopy using live samples and positive real-time PCR assays using a general family probe and two species specific probes revealed the presence of Amphidomataceae distributed throughout the sampling area. Overall abundance was low, however, and was in agreement with a lack of detectable AZA in plankton samples. Single cell isolation and morphological and molecular characterisation of established strains revealed the presence of 7 amphidomatacean species (Azadiniun spinosum, Az. poporum, Az. obesum, Az. dalianense, Az. trinitatum, Az. polongum, Amphidoma languida) in the area. Azaspiracids were produced by the known AZA producing species Az. spinosum, Az. poporum and Am. languida only. LC-MS/MS analysis further revealed that Norwegian strains produce previously unreported AZA for Norway (AZA-11 by Az. spinosum, AZA-37 by Az. poporum, AZA-38 and AZA-39 by Am. languida), and also four novel compounds (AZA-50, -51 by Az. spinosum, AZA-52, -53 by Am. languida), whose structural properties are described and which now can be included in existing analytical protocols. A maximum likelihood analysis of concatenated rDNA regions (SSU, ITS1-ITS2, partial LSU) showed that the strains of Az. spinosum fell in two well supported clades, where most but not all new Norwegian strains formed the new Ribotype B. Ribotype differentiation was supported by a minor morphological difference with respect to the presence/absence of a rim around the pore plate, and was consistently reflected by different AZA profiles. Strains of Az. spinosum from ribotype A produce AZA-1, -2 and -33, whereas the new strains of ribotype B produce mainly AZA-11 and AZA-51. Significant sequence differences between both Az. spinosum ribotypes underline the need to redesign the currently used qPCR probes in order to detect all AZA producing Az. spinosum. The results generally underline the conclusion that for the Norwegian coast area it is important that amphidomatacean species are taken into account in future studies and monitoring programs.

Identification of 21,22-Dehydroazaspiracids in Mussels ( Mytilus edulis) and in Vitro Toxicity of Azaspiracid-26

Azaspiracids (AZAs) are marine biotoxins produced by the genera Azadinium and Amphidoma, pelagic marine dinoflagellates that may accumulate in shellfish resulting in human illness following consumption. The complexity of these toxins has been well documented, with more than 40 structural variants reported that are produced by dinoflagellates, result from metabolism in shellfish, or are extraction artifacts. Approximately 34 μg of a new AZA with MW 823 Da (AZA26 (3)) was isolated from blue mussels ( Mytilus edulis), and its structure determined by MS and NMR spectroscopy. AZA26, possibly a bioconversion product of AZA5, lacked the C-20-C-21 diol present in all AZAs reported thus far and had a 21,22-olefin and a keto group at C-23. Toxicological assessment of 3 using an in vitro model system based on Jurkat T lymphocyte cells showed the potency to be ∼30-fold lower than that of AZA1. The corresponding 21,22-dehydro-23-oxo-analogue of AZA10 (AZA28) and 21,22-dehydro analogues of AZA3, -4, -5, -6, -9, and -10 (AZA25, -48 (4), -60, -27, -49, and -61, respectively) were also identified by HRMS/MS, periodate cleavage reactivity, conversion from known analogues, and NMR (for 4 that was present in a partially purified sample of AZA7).

Accumulation and transformation of azaspiracids in scallops (Chlamys farreri) and mussels (Mytilus galloprovincialis) fed with Azadinium poporum, and response of antioxidant enzymes

Azaspiracid (AZA) producing microalgae have been reported internationally and could potentially impact a variety of seafood. Scallops (Chlamys farreri) and mussels (Mytilus galloprovincialis) from China were fed with the AZA2 producer, Azadinium poporum, to study uptake, metabolism and oxidative stress in the shellfish. LC-MS/MS showed significant accumulation and differential metabolism of AZA2 in the scallops and mussels. In mussels AZA2 was metabolized to AZA19, with subsequent decarboxylation to AZA6. In scallops no AZA19 or AZA6 was observed, however, a novel AZA metabolite was formed that is isobaric with AZA19 ([M+H]⁺, m/z 886), but elutes at a different retention time. In addition it was noted that the scallop metabolite was stable during heating, while AZA19 has been shown to decarboxylate. Concentrations of reactive oxygen species (ROS) and activities of antioxidant enzymes were monitored. ROS levels increased slightly in the meat of scallops and mussels due to starvation in the acclimation and depuration periods, but reduced in the feeding periods with non-toxic Isochrysis galbana or toxic A. poporum. No obvious variations were found in activities for a range of antioxidant enzymes. These results provide new insights on the potential for accumulation and metabolism of AZAs in bivalve species relevant to this area of China, which is of importance considering the recent finding of AZA producing microalgae in the region.