Ubiquitous 'benign' alga emerges as the cause of shellfish contamination responsible for the human toxic syndrome, azaspiracid poisoning

Effects of Azaspiracid-1, A Potent Cytotoxic Agent, on Primary Neuronal Cultures. A Structure−Activity Relationship Study

Azaspiracids (AZAs) are marine phycotoxins with an unknown mechanism of action, implicated in human intoxications. We investigated the effect of azaspiracid-1 (AZA-1) on the cytosolic calcium concentration ([Ca2+]c), intracellular pH (pHi), and neuron viability in neuronal cultures. AZA-1 increased [Ca2+]c and decreased neuronal viability. The effects of several fragments of the AZA-1 molecule (13 different chemical structures) were examined. The ent-ABCD-azaspiracid-1 (2) showed similar potency to AZA-1 (1) in increasing [Ca2+]c but higher cytotoxity than AZA-1. The chemical structures containing only the ABCD or the ABCDE ring domains (3-8) caused a [Ca2+]c increase but did not alter cell viability. The compounds containing only the FGHI ring domain of AZA-1 (9-14) did not modify the [Ca2+]c or the cell viability. Therefore, the effect of AZA-1 on [Ca2+]c depends on the presence of the ABCD or the ABCDE-ring structure, but the complete chemical structure is needed to produce neurotoxic effects.

Biotechnological significance of toxic marine dinoflagellates

Dinoflagellates are microalgae that are associated with the production of many marine toxins. These toxins poison fish, other wildlife and humans. Dinoflagellate-associated human poisonings include paralytic shellfish poisoning, diarrhetic shellfish poisoning, neurotoxic shellfish poisoning, and ciguatera fish poisoning. Dinoflagellate toxins and bioactives are of increasing interest because of their commercial impact, influence on safety of seafood, and potential medical and other applications. This review discusses biotechnological methods of identifying toxic dinoflagellates and detecting their toxins. Potential applications of the toxins are discussed. A lack of sufficient quantities of toxins for investigational purposes remains a significant limitation. Producing quantities of dinoflagellate bioactives requires an ability to mass culture them. Considerations relating to bioreactor culture of generally fragile and slow-growing dinoflagellates are discussed. Production and processing of dinoflagellates to extract bioactives, require attention to biosafety considerations as outlined in this review.

Illnesses caused by marine toxins

Marine toxins are produced by algae or bacteria and are concentrated in contaminated seafood. Substantial increases in seafood consumption in recent years, together with globalization of the seafood trade, have increased potential exposure to these agents. Marine toxins produce neurological, gastrointestinal, and cardiovascular syndromes, some of which result in high mortality and long-term morbidity. Routine clinical diagnostic tests are not available for these toxins; diagnosis is based on clinical presentation and a history of eating seafood in the preceding 24 h. There is no antidote for any of the marine toxins, and supportive care is the mainstay of treatment. In particular, paralytic shellfish poisoning and puffer fish poisoning can cause death within hours after consuming the toxins and may require immediate intensive care. Rapid notification of public health authorities is essential, because timely investigation may identify the source of contaminated seafood and prevent additional illnesses. Extensive environmental monitoring and sometimes seasonal quarantine of a harvest are employed to reduce the risk of exposure.

Tissue distribution, effects of cooking and parameters affecting the extraction of azaspiracids from mussels, Mytilus edulis, prior to analysis by liquid chromatography coupled to mass spectrometry

This study used liquid chromatography coupled to mass spectrometry to identify some parameters important in the analysis of azaspiracids. The first aspect was the distribution of azaspiracids within mussels, in particular the content in the digestive gland as compared to the remaining tissues. In our study, azaspiracids accumulated in the digestive gland, similar to other lipophilic toxins. The ratio of toxin in the digestive gland compared to the whole mussel was on average circa 5, both for a bulk sample collected in Norway in 2004 and for 28 samples from Ireland collected over 3 years (2001-2003). These results may justify the practise to only analyse the digestive gland, a step considered necessary to achieve adequate detection limits for azaspiracids both in the mouse bioassay and other analytical techniques. Steaming of mussels as a sample pre-treatment was found to be another parameter affecting the result. Azaspiracids concentrated indirectly, i.e. through the loss of water or juice from the matrix. The cooked shellfish tissues had a concentration of azaspiracids 2-fold higher than the uncooked shellfish, both for whole flesh and for digestive gland tissue. This finding is of particular importance since it may affect the maximum guidance level at which shellfish may be allowed for human consumption. Finally, parameters affecting the extraction efficiency were studied, including the nature of the extraction solvent, the sample-to-solvent ratio and replicate extraction. The largest differences were observed between different solvents and between different sample-to-solvent ratios, while the effect of replicate extraction was minimal if large sample-to-solvent ratios were used. Duplicate extraction using 100% methanol was found to be the best combination of parameters.

Azaspiracid-4 inhibits Ca2+ entry by stored operated channels in human T lymphocytes

Azaspiracids (AZs) are a new group of phycotoxins discovered in the Ireland coast that includes the isolated analogues: AZ-1, AZ-2, AZ-3, AZ-4 and AZ-5 and the recently described AZ-6-11. Azaspiracid toxic episodes show gastrointestinal illness, but neurotoxic symptoms are also observed in mouse bioassay. Despite their great importance in human health, so far its mechanism of action is largely unknown. In this report, we present the first data about the effect of AZ-4 on cytosolic calcium concentration [Ca2+]i in freshly human lymphocytes. Cytosolic Ca2+ variations were determined by fluorescence digital imaging microscopy using Fura2 acetoxymethyl ester (Fura2-AM). AZ-4 did not modify cytosolic Ca2+ in resting cells. However, the toxin dose-dependent inhibited the increase in cytosolic Ca2+ levels induced by thapsigargin (Tg). AZ-4 decreased Ca2+-influx induced by Tg but did not affect the Ca2+-release from internal stores induced by this drug. The effects of AZ-4 on Ca2+-influx induced by Tg were reversible and not regulated by adenosine 3',5'-cyclic monophosphate (cAMP) pathway. When AZ-4 was added before, after or together with nickel, an unspecific blocker of Ca2+ channels, the effects were indistinguishable and additive. AZ-4 also inhibited maitotoxin (MTX)-stimulated Ca2+-influx by 5-10%. Thus, AZ-4 appeared to be a novel inhibitor of plasma membrane Ca2+ channels, affecting at least to store operated channels, showing an effect clearly different from other azaspiracid analogues.

Teratogenic effects of azaspiracid-1 identified by microinjection of Japanese medaka (Oryzias latipes) embryos

Azaspiracid-1 (AZA-1) is a newly identified phycotoxin that accumulates in commercially important bivalve molluscs harvested in several European countries and causes severe human intoxications. Molluscan shellfish are known vectors for accumulation and subsequent transfer of phycotoxins such as brevetoxin and domoic acid through various trophic levels within food webs. Finfish can also accumulate phycotoxins, both directly from toxic algae or from consumption of contaminated shellfish and smaller intoxicated fish. To evaluate the teratogenic potential of AZA-1 and its relevancy to toxin accumulation in finfish, we have utilized a microinjection technique to mimic the maternal-egg toxin transfer of an AZA-1 reference standard and a shellfish extract containing azaspiracids in an embryonic Japanese medaka (Oryzias latipes) fish model. Microinjection of purified AZA-1 caused dose-dependent effects on heart rate, developmental rate, hatching success, and viability in medaka embryos. Within 4 days of exposure to doses > or = 40 pg AZA-1/egg, substantial retardation in development was observed as reduced somatic growth and yolk absorption, and delayed onset of blood circulation and pigmentation. Embryos treated to > or =40 pg AZA-1/egg had slower heart rates (bradycardia) for the 9 days in ovo period, followed by reduced hatching success. Microinjection of a contaminated mussel (Mytilus edulis) extract containing AZAs (AZA-1, -2, and -3), okadaic acid, and dinophysistoxin-2 resulted in similar responses from the fish embryos at equivalent doses. These studies demonstrate that AZA-1 is a potent teratogen to finfish. This work will complement future investigations on AZA-1 accumulation in marine food webs and provide a basis for understanding its toxicity at different trophic levels.

Cytotoxic and cytoskeletal effects of azaspiracid-1 on mammalian cell lines

Azaspiracid-1 (AZA-1) is a newly identified phycotoxin reported to accumulate in molluscs from several northern European countries and documented to have caused severe human intoxications. The mechanism of action of AZA-1 is unknown. Our initial investigations have shown that AZA-1 is cytotoxic to a range of cell types. Cytotoxicity was evident in all seven cell types tested, suggesting a broad-spectrum mode of action, and was both time- and concentration-dependent. However, AZA-1 took an unusually long time (>24 h) to cause complete cytotoxicity in most cell types, with the exception of the rat pituitary GH(4)C(1). Extended exposure times did not always lower the EC(50) value for a given cell line, but always resulted in more complete cytotoxicity over a very narrow concentration range. The Jurkat cell line (human lymphocyte T) appeared to be very sensitive to AZA-1, although the EC(50) values (24-72 h) for all the cell types were in the low nanomolar range (0.9-16.8 nM). The effect of AZA-1 on membrane integrity was tested on Jurkat cells and these data confirm our visual observations of cytotoxicity and necrotic cell lysis following exposure of Jurkat cells to AZA-1 and suggest that AZA-1 has some properties unique among marine algal toxins. Additionally, there were dramatic effects of AZA-1 on the arrangement of F-actin with the concurrent loss of pseudopodia, cytoplasmic extensions that function in mobility and chemotaxis. Although these phycotoxin-specific effects of AZA-1 suggest a possible site of action, further work using cell-based approaches is needed to determine the precise mode of action of AZA-1.

Overview of key phytoplankton toxins and their recent occurrence in the North and Baltic Seas

The frequency and intensity of harmful algal blooms (HABs) appear to be on the rise globally. There is also evidence of the geographic spreading of toxic strains of these algae. Consequently, methods had to be established and new ones are still needed for the evaluation of possible hazards caused by increased algal toxin production in the marine food chain. Different clinical effects of algae-related poisoning have attracted scientific attention; paralytic shellfish poisoning, diarrhetic shellfish poisoning, and amnesic shellfish poisoning are among the most common. Additionally, cyanobacteria (blue-green algae) in brackish waters often produce neurotoxic and hepatotoxic substances. Bioassays with mice or rats are common methods to determine algal and cyanobacterial toxins. However, biological tests are not really satisfactory because of their low sensitivity. In addition, there is growing public opposition to animal testing. Therefore, there has been increasing effort to determine algal toxins by chemical methods. Plankton samples from different European marine and brackish waters were taken during research cruises and analyzed on board directly. The ship routes covered marine areas in the northwest Atlantic, Orkney Islands, east coast of Scotland, and the North and Baltic seas. The first results on the occurrence and frequency of harmful algal species were obtained in 1997 and 1998. During the 2000 cruise an HPLC/MS coupling was established on board, and algal toxins were measured directly after extraction of the plankton samples. In contrast to earlier cruises, the sampling areas were changed in 2000 to focusing on coastal zones. The occurrence of toxic algae in these areas was compared to toxin formation during HABs in the open sea. It was found that the toxicity of the algal blooms depended on the prevailing local conditions. This observation was also confirmed by monitoring cyanobacterial blooms in the Baltic Sea. Optimal weather conditions, for example, during the summers of 1997 and 2003, favored blooms of cyanobacteria in all regions of the Baltic. The dominant species regarding the HABs in the Baltic was Nodularia spumigena. However, in addition to high concentrations of Nodularia spumigena in coastal zones, other blue-green algae are involved in bloom formation, with changes in plankton communities influencing both toxin profiles and toxicity.

Is there a risk of human poisoning by azaspiracids from shellfish harvested at the Portuguese coast?

Azaspiracid poisoning (AZP), the most recently discovered human gastrointestinal illness resulting from consumption of contaminated shellfish, so far has been found in coastal areas of northern Europe. This is the first report of a survey carried out for contamination of shellfish harvested in costal areas of Portugal for the presence of azaspiracids. The study design covered the commercial species usually more contaminated by toxins from dinoflagellates (blue mussel, common cockle, donax clam) in coastal areas representative of the NW, SW and south coasts. A method based on liquid chromatography-mass spectrometry was setup for the first time for this purpose. No azaspiracids were found on 300 samples tested between 2002 and 2003. On at least three samples a peak with a retention time matching that of AZA2 was found, never surpassing one tenth of the current EU limit. Unambiguous identification of any known AZA did not occur yet. The risk for human outbreaks of AZP seems to be very low, comparatively with amnesic shellfish poisoning (ASP), where levels close to the allowance level are found sparsely, or to diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP), where high levels and registered human outbreaks have been found in recent years.

Dinoflagellates: a remarkable evolutionary experiment

In this paper, we focus on dinoflagellate ecology, toxin production, fossil record, and a molecular phylogenetic analysis of hosts and plastids. Of ecological interest are the swimming and feeding behavior, bioluminescence, and symbioses of dinoflagellates with corals. The many varieties of dinoflagellate toxins, their biological effects, and current knowledge of their origin are discussed. Knowledge of dinoflagellate evolution is aided by a rich fossil record that can be used to document their emergence and diversification. However, recent biogeochemical studies indicate that dinoflagellates may be much older than previously believed. A remarkable feature of dinoflagellates is their unique genome structure and gene regulation. The nuclear genomes of these algae are of enormous size, lack nucleosomes, and have permanently condensed chromosomes. This chapter reviews the current knowledge of gene regulation and transcription in dinoflagellates with regard to the unique aspects of the nuclear genome. Previous work shows the plastid genome of typical dinoflagellates to have been reduced to single-gene minicircles that encode only a small number of proteins. Recent studies have demonstrated that the majority of the plastid genome has been transferred to the nucleus, which makes the dinoflagellates the only eukaryotes to encode the majority of typical plastid genes in the nucleus. The evolution of the dinoflagellate plastid and the implications of these results for understanding organellar genome evolution are discussed.

Synthesis of the ABCD and ABCDE ring systems of azaspiracid-1

The efficient syntheses of the ABCD ring system of the originally proposed structure of azaspiracid-1 and the ABCDE ring system of the revised structure of azaspiracid-1 containing the correct stereochemistry at C(6), C(10), C(13), C(14), C(16), C(17), C(19), C(21), C(22), C(24) and C(25) have been achieved.

Liquid chromatography--multiple tandem mass spectrometry for the determination of ten azaspiracids, including hydroxyl analogues in shellfish

Azaspiracids (AZAs) are a group of polyether toxins that cause food poisoning in humans. These toxins, produced by marine dinoflagellates, accumulate in filter-feeding shellfish, especially mussels. Sensitive liquid chromatography-electrospray ionisation mass spectrometry (LC-ESI-MS(n)) methods have been developed for the determination of the major AZAs and their hydroxyl analogues. These methods, utilising both chromatographic and mass resolution, were applied for the determination of 10 AZAs in mussels (Mytilus edulis). An optimised isocratic reversed phase method (3 microm Luna-2 C18 column) separated 10 azaspiracids using acetonitrile/water (46:54, v/v) containing 0.05% trifluoroacetic acid (TFA) and 0.004% ammonium acetate in 55 min. Analyte determination using MS3 involved trapping and fragmentation of the [M + H]+ and [M + H - H2O]+ ions with detection of the [M + H - 2H2O]+ ion for each AZA. Linear calibrations were obtained for AZA1, using spiked shellfish extracts, in the range 0.05-1.00 microg/ml (r2 = 0.997) with a detection limit of 5 pg (signal : noise = 3). The major fragmentation pathways in hydroxylated azaspiracids were elucidated using hydrogen/deuterium (H/D) exchange experiments. An LC-MS3 method was developed using unique parent ions and product ions, [M + H - H2O - CgH10O2R1R3]+, that involved fragmentation of the A-ring. This facilitated the discrimination between 10 azapiracids, AZA1-10. Thus, this rapid LC-MS3 method did not require complete chromatographic resolution and the run-time of 7 min had detection limits better than 20 pg for each toxin.

Azaspiracid poisoning, the food-borne illness associated with shellfish consumption

Azaspiracid poisoning (AZP) is a recently discovered toxic syndrome that was identified following severe gastrointestinal illness from the consumption of contaminated mussels (Mytilus edulis). The implicated toxins, azaspiracids, are polyethers with unprecedented structural features. Studies toward total toxin synthesis revealed that the initial published structures were incorrect and they have now been revised. These toxins accumulate in bivalve molluscs that feed on toxic microalgae of the genus Protoperidinium, previously considered to be toxicologically benign. Although first identified in shellfish from Ireland, azaspiracid contamination of several types of bivalve shellfish species has now been confirmed throughout the western coastline of Europe. Toxicological studies have indicated that azaspiracids can induce widespread organ damage in mice and that they are probably more dangerous than previously known classes of shellfish toxins. The exclusive reliance on live animal bioassays to monitor azaspiracids in shellfish failed to prevent human intoxications. This was a consequence of poor sensitivity of the assay and the fact that azaspiracids are not exclusively found in the shellfish digestive glands used for toxin testing. The strict regulatory control of azaspiracids in shellfish now requires frequent testing of shellfish using highly specific and sensitive methods involving liquid chromatography-mass spectrometry.

Most cited papers in Toxicon

Citation of a published work is one of the parameters considered in the analysis of relevance and importance of scientific contributions. In 2002, for the first time the Impact Factor of Toxicon has risen above 2.0, placing it at the 17th position among 76 journals in the 'toxicology' field. The aim of this article was to identify the most cited articles in Toxicon, that have contributed to the steady increase of its Impact Factor. The number of citations, complete reference and type of all documents appearing in Toxicon in the period 1963-2003 were retrieved from the ISI Web-of-Science homepage. The documents retrieved were sorted by the number of citations received. A 'citation index', defined as the number of citations divided by the number of years since publication, was calculated for each document. It was clearly seen that reviews in Toxicon received 4.4-fold more citations than articles. Unexpectedly, it was found that recent papers were proportionally more cited than old ones. A decrease in the proportion of papers dealing on 'snake*' through out the period and the broadened range of subjects of the most cited papers recently published in Toxicon reflects an increased 'visibility' in other fields of toxinology. Research on plant toxins gained its own space in Toxicon with newer publications showing high citation indexes. It can be postulated that these facts helped to increase Toxicon's Impact Factor from 1.248 in 1999 to 2.003 in 2002. With the increased number of issues in Toxicon as well as publications of subject-dedicated volumes containing mostly reviews, the Impact Factor of Toxicon is expected to keep rising in the near future.

Food poisoning associated with biotoxins in fish and shellfish

PURPOSE OF REVIEW

In recent times the number of blooms of algae that produce toxins has increased in frequency, intensity and geographical distribution. This review describes some of the illnesses caused by fish and shellfish contaminated with toxins produced by marine algae and by bacteria.

RECENT FINDINGS

The increase in toxic algal blooms may be a result of increased awareness, aquaculture, eutrophication, or transport of cysts in ship ballast. Improved chemical methods for the detection of algal toxins are now being developed, and so the number of toxins recognized is increasing. Toxicological data on some of these algal toxins are lacking. Despite the increase in occurrence of algal toxins, scombrotoxic poisoning remains the most common cause of food poisoning associated with the consumption of fish and shellfish. This may be real or it may be a reflection of lack of suitable tests for algal toxins or under-recognition by workers in health care.

SUMMARY

The major problem worldwide in this field is the lack of pure toxins for use in developing and standardizing chemical methods for toxin detection. Such methods would permit increased testing of both food and clinical specimens, and hence would prevent the entry of toxic food into the food chain and increase laboratory confirmation of incidents of illness.

Elucidation of the fragmentation pathways of azaspiracids, using electrospray ionisation, hydrogen/deuterium exchange, and multiple-stage mass spectrometry

Collision-induced dissociation (CID) mass spectra were generated for azaspiracids using electrospray ionisation (ESI), and hydrogen/deuterium (H/D) exchange was used to ascertain the number and type of replaceable hydrogens in the three predominant azaspiracid toxins. H/D exchange was conveniently achieved using deuterated solvents for liquid chromatography (LC). Using ion-trap mass spectrometry, multiple-stage CID experiments (MS(n)) on the protonated and fully exchanged ions were performed to decipher characteristic fragmentation pathways. The precursor and product ions from azaspiracids lost up to five water molecules from different regions during MS(n) experiments and it was possible to distinguish between the water losses from different molecular regions. These studies confirmed that the first water-loss ion in the spectra of azaspiracids resulted from dehydration at the vicinal diol at C20-C21. Five MS dissociation pathways were identified that resulted from fragmentation of the carbon skeleton of azaspiracids producing nitrogen-containing ions. Two pathways, involving cleavage of the E-ring and C27-C28, gave ions that were found in all azaspiracids. Three pathways, A-ring, C-ring and C19-C20 cleavages, were useful for distinguishing between azaspiracid analogues. The same product ions from backbone fragmentation were also observed using hybrid quadrupole time-of-flight mass spectrometry (QqTOFMS). The fragmentation of the A-ring was the most facile and was exploited in the development of LC/MS(n) methods for the analysis of azaspiracids.

The first identification of azaspiracids in shellfish from France and Spain

Incidents of human intoxications throughout Europe, following the consumption of mussels have been attributed to Azaspiracid Poisoning (AZP). Although first discovered in Ireland, the search for the causative toxins, named azaspiracids, in other European countries has now led to the first discovery of these toxins in shellfish from France and Spain. Separation of the toxins, azaspiracid (AZA1) and analogues, AZA2 and AZA3, was achieved using isocratic reversed-phase liquid chromatography coupled, via an electrospray ionisation source, to an ion-trap mass spectrometer. Azaspiracids were identified in mussels (Mytilus galloprovincialis), 0.24 microg/g, from Galicia, Spain, and scallops (Pecten maximus), 0.32 microg/g, from Brittany, France. Toxin profiles were similar to those found in the equivalent shellfish in Ireland in which AZA1 was the predominant toxin.

Studies on azaspiracid biotoxins. III. Instrumental validation for rapid quantification of AZA 1 in complex biological matrices

Azaspiracids are neurotoxins produced by marine algae that have been detected in harvested mussels since 1995. They pose a significant threat to human health through the consumption of contaminated shellfish, and negatively impact the economy of areas where shellfish are harvested and processed. Regulatory agencies are beginning to advocate instrumental assays over traditional mouse bioassay methods. The development and validation of an assay method for AZA 1, the predominant azaspiracid toxin, and the production of a calibration standard and reference material will therefore be vital for quality control in monitoring laboratories worldwide. This report demonstrates a rapid and reproducible liquid chromatography/mass spectrometry (LC/MS) method for separation of all twelve known azaspiracids. Using a triple-quadrupole mass spectrometer, ultra-high sensitivity was obtained at the low-femtogram level injected on-column. At the same time, a linear response of three orders of magnitude was observed. We compared the results with those measured on an ion-trap mass spectrometer. The triple-quadrupole instrument was more sensitive, reliable and reproducible than the ion-trap instrument. The detection limit obtained on the ion-trap mass spectrometer was ten times higher than that obtained on the triple quadrupole. During the study, a new azaspiracid analog (AZA 7c) was discovered.