Comparison of ELISA and LC-MS analyses for yessotoxins in blue mussels (Mytilus edulis)

Yessotoxins in Mollusks of the Galician Coast from 2014 to 2022: Variability, Biotransformation, and Resistance to Alkaline Hydrolysis

The presence of yessotoxins (YTXs) was analyzed in 10,757 samples of Galician bivalves from 2014 to 2022. Only YTX and 45-OH YTX were found. YTX was detected in 31% of the samples, while 45-OH YTX was found in 11.6% of them. Among the samples containing YTX, 45-OH YTX was detected in 37.3% of cases. The maximum recorded levels were 1.4 and 0.16 mg of YTX-equivalentsg-1, for YTX and 45-OH YTX, respectively, which are well below the regulatory limit of the European Union. The YTX and 45-OH YTX toxicities in the raw extracts and extracts subjected to alkaline hydrolysis were strongly and linearly related. Due to the lack of homo-YTX in Galician samples, the effect of alkaline hydrolysis on homo-YTX and 45OH-Homo-YTX was only checked in 23 additional samples, observing no negative effect but a high correlation between raw and hydrolyzed extracts. Hydrolyzed samples can be used instead of raw ones to carry out YTXs determinations in monitoring systems, which may increase the efficiency of those systems where okadaic acid episodes are very frequent and therefore a higher number of hydrolyzed samples are routinely analyzed. The presence of YTX in the studied bivalves varied with the species, with mussels and cockles having the highest percentages of YTX-detected samples. The presence of 45-OH YTX was clearly related to YTX and was detected only in mussels and cockles. Wild populations of mussels contained proportionally more 45-OH YTX than those that were raft-cultured. Spatially, toxin toxicities varied across the sampling area, with higher levels in raft-cultured mussels except those of Ría de Arousa. Ría de Ares (ARE) was the most affected geographical area, although in other northern locations, lower toxin levels were detected. Seasonally, YTX and 45-OH YTX toxicities showed similar patterns, with higher levels in late summer and autumn but lower toxicities of the 45-OH toxin in August. The relationship between the two toxins also varied seasonally, in general with a minimum proportion of 45-OH YTX in July-August but with different maximum levels for raft-cultured and wild mussel populations. Interannually, the average toxicities of YTX decreased from 2014 to 2017 and newly increased from 2018 to 2021, but decreased slightly in 2022. The relationship between 45-OH YTX and YTX also varied over the years, but neither a clear trend nor a similar trend for wild and raft mussels was observed.

Bioactives from microalgal dinoflagellates

Dinoflagellate microalgae are an important source of marine biotoxins. Bioactives from dinoflagellates are attracting increasing attention because of their impact on the safety of seafood and potential uses in biomedical, toxicological and pharmacological research. Here we review the potential applications of dinoflagellate toxins and the methods for producing them. Only sparing quantities of dinoflagellate toxins are generally available and this hinders bioactivity characterization and evaluation in possible applications. Approaches to production of increased quantities of dinoflagellate bioactives are discussed. Although many dinoflagellates are fragile and grow slowly, controlled culture in bioreactors appears to be generally suitable for producing many of the metabolites of interest.

Combined oral toxicity of azaspiracid-1 and yessotoxin in female NMRI mice

For many years, the presence of yessotoxins (YTXs) in shellfish has contributed to the outcome of the traditional mouse bioassay and has on many occasions caused closure of shellfisheries. Since YTXs do not appear to cause diarrhoea in man and exert low oral toxicity in animal experiments, it has been suggested that they should be removed from regulation. Before doing so, it is important to determine whether the oral toxicity of YTXs is enhanced when present together with shellfish toxins known to cause damage to the gastrointestinal tract. Consequently, mice were given high doses of YTX, at 1 or 5 mg/kg body weight, either alone or together with azaspiracid-1 (AZA1) at 200 μg/kg. The latter has been shown to induce damage to the small intestine at this level. The combined exposure caused no clinical effects, and no pathological changes were observed in internal organs. These results correspond well with the very low levels of YTX detected in internal organs by means of LC-MS/MS and ELISA after dosing. Indeed, the very low absorption of YTX when given alone remained largely unchanged when YTX was administered in combination with AZA1. Thus, the oral toxicity of YTX is not enhanced in the presence of sub-lethal levels of AZA1.

Marine toxins: chemistry, toxicity, occurrence and detection, with special reference to the Dutch situation

Various species of algae can produce marine toxins under certain circumstances. These toxins can then accumulate in shellfish such as mussels, oysters and scallops. When these contaminated shellfish species are consumed severe intoxication can occur. The different types of syndromes that can occur after consumption of contaminated shellfish, the corresponding toxins and relevant legislation are discussed in this review. Amnesic Shellfish Poisoning (ASP), Paralytic Shellfish Poisoning (PSP), Diarrheic Shellfish Poisoning (DSP) and Azaspiracid Shellfish Poisoning (AZP) occur worldwide, Neurologic Shellfish Poisoning (NSP) is mainly limited to the USA and New Zealand while the toxins causing DSP and AZP occur most frequently in Europe. The latter two toxin groups are fat-soluble and can therefore also be classified as lipophilic marine toxins. A detailed overview of the official analytical methods used in the EU (mouse or rat bioassay) and the recently developed alternative methods for the lipophilic marine toxins is given. These alternative methods are based on functional assays, biochemical assays and chemical methods. From the literature it is clear that chemical methods offer the best potential to replace the animal tests that are still legislated worldwide. Finally, an overview is given of the situation of marine toxins in The Netherlands. The rat bioassay has been used for monitoring DSP and AZP toxins in The Netherlands since the 1970s. Nowadays, a combination of a chemical method and the rat bioassay is often used. In The Netherlands toxic events are mainly caused by DSP toxins, which have been found in Dutch shellfish for the first time in 1961, and have reoccurred at irregular intervals and in varying concentrations. From this review it is clear that considerable effort is being undertaken by various research groups to phase out the animal tests that are still used for the official routine monitoring programs.

Is yessotoxin the main phycotoxin in Croatian waters?

With the aim of investigating whether yessotoxin (YTX) is responsible for diarrhetic shellfish poisoning (DSP) events in Croatian waters, three different methods were combined: a modified mouse bioassay (MBA) that discriminates YTX from other DSP toxins, the enzyme-linked immunosorbent assay method (ELISA) and liquid chromatography-mass spectrometry (LC-MS/MS). Among 453 samples of mussels and seawater analyzed in 2007, 10 samples were DSP positive. Results obtained by the modified MBA method revealed that most of the samples were positive for YTX, with the exception of samples from Lim Bay (LB 1) The ELISA method also identified the presence of YTX in these samples. DSP toxin profiles showed the presence of okadaic acid (OA) in three, and YTX in four out of nine samples that were analyzed by LC-MS/MS. The phytoplankton community structure pattern revealed Lingulodinium polyedrum (Stein) Dodge, which was present in the water prior to and/or during toxicity events at low concentrations (80 to 1440 cells L⁻¹), as a potential YTX producing species. It is proposed that L. polyedrum cells accumulated in mussels and the subsequently observed toxicity may be related to metabolism after ingestion, resulting in carboxy YTX as the major analog in the mussel.

Sensitive method for the determination of lipophilic marine biotoxins in extracts of mussels and processed shellfish by high-performance liquid chromatography-tandem mass spectrometry based on enrichment by solid-phase extraction

A solid-phase extraction (SPE) method for the enrichment and clean-up of lipophilic marine biotoxins from extracts of different species of bivalve molluscs and processed shellfish products was developed. Okadaic acid (OA), pectenotoxin2 (PTX2), azaspiracid1 (AZA1) and yessotoxin (YTX) were determined by LC-MS/MS in hydrolyzed and non-hydrolyzed extracts. Applying a concentration factor of 10 the limit of quantification for the four toxins was determined to be 1 microg/kg. An organized in-house ring trial proved transferability of the method protocol and satisfactory results for all four toxins with a relative standard deviation (RSD) of 5-12%. The precision of the whole method including LC-MS detection was determined by processing seven independent extractions analyzed in independent sequences. RSD ranged between 12% and 24%. This SPE method was tested within a concentration range corresponding to the range of the current European Union regulatory limits (up to 160 microg/kg for the OA group), but it would also be applicable to a lower microg/kg range which is important in view of a possible decrease of regulatory limits as proposed by a working group of the European Food Safety Authority. The potential of SPE as a cleaning tool to cope with matrix effects in LC-MS/MS was studied and compared to liquid-liquid portioning.

Yessotoxins, a group of marine polyether toxins: an overview

Yessotoxin (YTX) is a marine polyether toxin that was first isolated in 1986 from the scallop Patinopecten yessoensis. Subsequently, it was reported that YTX is produced by the dinoflagellates Protoceratium reticulatum, Lingulodinium polyedrum and Gonyaulax spinifera. YTXs have been associated with diarrhetic shellfish poisoning (DSP) because they are often simultaneously extracted with DSP toxins, and give positive results when tested in the conventional mouse bioassay for DSP toxins. However, recent evidence suggests that YTXs should be excluded from the DSP toxins group, because unlike okadaic acid (OA) and dinophyisistoxin-1 (DTX-1), YTXs do not cause either diarrhea or inhibition of protein phosphatases. In spite of the increasing number of molecular studies focused on the toxicity of YTX, the precise mechanism of action is currently unknown. Since the discovery of YTX, almost forty new analogues isolated from both mussels and dinoflagellates have been characterized by NMR or LC-MS/MS techniques. These studies indicate a wide variability in the profile and the relative abundance of YTXs in both, bivalves and dinoflagellates. This review covers current knowledge on the origin, producer organisms and vectors, chemical structures, metabolism, biosynthetic origin, toxicological properties, potential risks to human health and advances in detection methods of YTXs.

Convenient large-scale purification of yessotoxin from Protoceratium reticulatum culture and isolation of a novel furanoyessotoxin

Yessotoxins from a large-scale culture (226 L) of Protoceratium reticulatum strain CAWD129 were harvested by filtration followed by solid-phase extraction. The extract was purified by column chromatography over basic alumina and reverse-phase flash chromatography to afford pure yessotoxin (193 mg). Isolation of yessotoxin was greatly facilitated by selection of a strain which did not produce analogues that interfered with yessotoxin isolation. In addition to yessotoxin, numerous minor yessotoxins were detected by LC-MS in other fractions. From one of these, an early eluting minor analogue with the same molecular weight as yessotoxin and a similar mass spectrometric fragmentation pattern was isolated. This analogue was identified by NMR and mass spectrometry as a novel yessotoxin analogue containing a furan ring in the side chain. This finding reveals biosynthetic flexibility of the yessotoxin pathway in P. reticulatum and confirms earlier findings of production of many minor yessotoxin analogues by this alga. Production of these analogues appeared to be a constitutive trait of P. reticulatum CAWD129.

Yessotoxins profile in strains of Protoceratium reticulatum from Spain and USA

Seven strains of Protoceratium reticulatum isolated from Spain and the USA were cultured in the laboratory. Yessotoxins (YTXs) quantification and toxin profile determination were performed by LC-FLD and LC-MS/MS. The four Spanish strains were found to produce YTX and known YTX analogs, however, YTX was not detected in any of the three USA strains. Among the strains that produced YTXs, toxin production ranged between 2.9 and 28.6pg/cell. The YTX profile was substantially different between strains, in three out of the four Spanish strains YTX was the main toxin and in the fourth homoYTX was the prominent toxin. This work demonstrates that YTX is not always the main toxin in P. reticulatum and a high variability in YTX amounts and profile found in other locations is confirmed.

Extraction and cleaning methods to detect yessotoxins in contaminated mussels

Yessotoxin (YTX) and its analogues are a newly recognized group of toxins with increased presence in shellfish in recent years. They can be quantified by various functional assays due to their interaction with phosphodiesterases (PDEs). One of these assays detects the binding between the YTX and the fluorescently labeled PDE I using fluorescence polarization, a spectroscopic technique based on exciting a fluorescent molecule with plane-polarized light and measuring the polarization degree of the emitted light. The aim of this study was to develop a YTX extraction procedure from mussels that does not interfere with this detection method. YTX concentrations were measured in spiked mussel extracts obtained through use of different extraction methods and cleaning procedures. The percentages of toxin recovery in various steps of the processes were calculated using these concentrations. Six extraction methods and two cleaning steps were used and no matrix effects and high toxin recoveries were obtained in two cases. One case used acetone as extraction solvent followed by three dichloromethane partitions and the other case used methanol. The cleaning procedure includes a silica cartridge and a 10,000 NMWL filter. Finally these two extraction-cleaning-detection methods were applied to a naturally contaminated mussel sample and results showed that not only YTX but also homoYTX and hydroxyYTX can be quantified with a 85-90% recovery.

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.

Identification of 45-hydroxy-46,47-dinoryessotoxin, 44-oxo-45,46,47-trinoryessotoxin, and 9-methyl-42,43,44,45,46,47,55-heptanor-38-en-41-oxoyessotoxin, and partial characterization of some minor yessotoxins, from Protoceratium reticulatum

Preparative HPLC purification of a side-fraction obtained during purification of 44,55-dihydroxyyessotoxin (6) afforded fractions containing previously unidentified yessotoxin analogues. Careful analysis of these fractions by HPLC-UV, LC-MS3, and NMR spectroscopy, revealed the identities of some of these analogues as 45-hydroxy-46,47-dinoryessotoxin (1), 44-oxo-45,46,47-trinoryessotoxin (2) and 9-methyl-42,43,44,45,46,47,55-heptanor-38-en-41-oxoyessotoxin (5). Numerous other analogues were present but could only be characterized by HPLC-UV and LC-MS3 due to their low abundance. The HPLC-UV and LC-MS3 data confirm the presence of large numbers of yessotoxin analogues, some of which may be oxidative degradation products, in extracts of Protoceratium reticulatum. Compound-1 is the first 46,47-dinoryessotoxin to be identified.

Isolation and identification of (44-R,S)-44,55-dihydroxyyessotoxin from Protoceratium reticulatum, and its occurrence in extracts of shellfish from New Zealand, Norway and Canada

44,55-Dihydroxyyessotoxin (1) was isolated from extracts of Protoceratium reticulatum and identified by analysis of its one- and two-dimensional NMR and mass spectra. In addition, LC-MS methods revealed the presence of compounds tentatively identified as (44-R,S)-44,55-dihydroxy-41a-homoyessotoxin (2) and (44-R,S)-44,55-dihydroxy-9-methyl-41a-homoyessotoxin (3). LC-MS analyses indicate that 1 is a constituent of P. reticulatum in New Zealand and Norway, and it was present in three species of mussels from New Zealand, Norway, and Canada.