LC-MS of palytoxin and its analogues: State of the art and future perspectives

Investigating the etiology of Haff disease: Optimization and validation of a sensitive LC-MS/MS method for palytoxins analysis in directly associated freshwater and marine food samples from Brazil

Haff disease typically develops after eating contaminated marine or freshwater species, especially fish. Despite still having an unknown etiology, recent reports have suggested its possible correlation with palytoxins. Therefore, the present work aimed to optimize and perform a validation of a sensitive method using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for the analysis of palytoxin and some of its analogs, with the main purpose of investigating their presence in marine and freshwater food samples associated with Haff disease in Brazil. The method optimization was performed using a central composite rotatable design and fish samples fortified with the palytoxin standard. Then, the optimized method was validated for different food matrices, including freshwater and marine fish, mollusks, and crustaceans. The sample preparation involved a solid-liquid extraction using methanol and water, solid-phase extraction using Strata-X cartridges, and on-column palytoxin oxidation. The detection of the main oxidized fragments (amino and amide aldehydes) was achieved by LC-MS/MS with electrospray ionization in positive mode, using a C18 column, as well as acetonitrile and water as mobile phases, both acidified with 0.1 % of formic acid. After optimization and validation, the etiological investigation involved the analysis of 16 Brazilian Haff disease-related food samples (in natura and leftover meals) from 2022. The method was demonstrated to be appropriate for quantitative analysis of freshwater and marine species. So far, it has proven to be one of the most sensitive methods related to palytoxin detection (LOD 10 μg/kg), being able to work in a range that includes the provisional ingestion limit (30 μg/kg). Regarding the Haff disease-related samples analysis, there is a strong indication of palytoxin contamination since the amino aldehyde (common fragment for all palytoxins) was detected in 15 of the 16 samples. Selected results were confirmed using liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS).

Ecophysiological responses of Ostreopsis towards temperature: A case study of benthic HAB facing ocean warming

Reports of the benthic dinoflagellate Ostreopsis spp. have been increasing in the last decades, especially in temperate areas. In a context of global warming, evidences of the effects of increasing sea temperatures on its physiology and its distribution are still lacking and need to be investigated. In this study, the influence of temperature on growth, ecophysiology and toxicity was assessed for several strains of O. cf. siamensis from the Bay of Biscay (NE Atlantic) and O. cf. ovata from NW Mediterranean Sea. Cultures were acclimated to temperatures ranging from 14.5 °C to 32 °C in order to study the whole range of each strain-specific thermal niche. Acclimation was successful for temperatures ranging from 14.5 °C to 25 °C for O. cf. siamensis and from 19 °C to 32 °C for O. cf. ovata, with the highest growth rates measured at 22 °C (0.54-1.06 d-1) and 28 °C (0.52-0.75 d-1), respectively. The analysis of cellular content of pigments and lipids revealed some aspects of thermal acclimation processes in Ostreopsis cells. Specific capacities of O. cf. siamensis to cope with stress of cold temperatures were linked with the activation of a xanthophyll cycle based on diadinoxanthin. Lipids (neutral reserve lipids and polar ones) also revealed species-specific variations, with increases in cellular content noted under extreme temperature conditions. Variations in toxicity were assessed through the Artemia franciscana bioassay. For both species, a decrease in toxicity was observed when temperature dropped under the optimal temperature for growth. No PLTX-like compounds were detected in O. cf. siamensis strains. Thus, the main part of the lethal effect observed on A. franciscana was dependent on currently unknown compounds. From a multiclonal approach, this work allowed for defining specificities in the thermal niche and acclimation strategies of O. cf. siamensis and O. cf. ovata towards temperature. Potential impacts of climate change on the toxic risk associated with Ostreopsis blooms in both NW Mediterranean Sea and NE Atlantic coast is further discussed, taking into account variations in the geographic distribution, growth abilities and toxicity of each species.

The application and sustainable development of coral in traditional medicine and its chemical composition, pharmacology, toxicology, and clinical research

This review discusses the variety, chemical composition, pharmacological effects, toxicology, and clinical research of corals used in traditional medicine in the past two decades. At present, several types of medicinal coral resources are identified, which are used in 56 formulas such as traditional Chinese medicine, Tibetan medicine, Mongolian medicine, and Uyghur medicine. A total of 34 families and 99 genera of corals are involved in medical research, with the Alcyoniidae family and Sarcophyton genus being the main research objects. Based on the structural types of compounds and the families and genera of corals, this review summarizes the compounds primarily reported during the period, including terpenoids, steroids, nitrogen-containing compounds, and other terpenoids dominated by sesquiterpene and diterpenes. The biological activities of coral include cytotoxicity (antitumor and anticancer), anti-inflammatory, analgesic, antibacterial, antiviral, immunosuppressive, antioxidant, and neurological properties, and a detailed summary of the mechanisms underlying these activities or related targets is provided. Coral toxicity mostly occurs in the marine ornamental soft coral Zoanthidae family, with palytoxin as the main toxic compound. In addition, nonpeptide neurotoxins are extracted from aquatic corals. The compatibility of coral-related preparations did not show significant acute toxicity, but if used for a long time, it will still cause toxicity to the liver, kidneys, lungs, and other internal organs in a dose-dependent manner. In clinical applications, individual application of coral is often used as a substitute for orthopedic materials to treat diseases such as bone defects and bone hyperplasia. Second, coral is primarily available in the form of compound preparations, such as Ershiwuwei Shanhu pills and Shanhu Qishiwei pills, which are widely used in the treatment of neurological diseases such as migraine, primary headache, epilepsy, cerebral infarction, hypertension, and other cardiovascular and cerebrovascular diseases. It is undeniable that the effectiveness of coral research has exacerbated the endangered status of corals. Therefore, there should be no distinction between the advantages and disadvantages of listed endangered species, and it is imperative to completely prohibit their use and provide equal protection to help them recover to their normal numbers. This article can provide some reference for research on coral chemical composition, biological activity, chemical ecology, and the discovery of marine drug lead compounds. At the same time, it calls for people to protect endangered corals from the perspectives of prohibition, substitution, and synthesis.

Occurrence of potentially toxic microalgae and diarrhetic shellfish toxins in the digestive tracts of green sea turtles (Chelonia mydas) from southern Brazil

Algal toxins are involved in the mortality and/or illness of marine organisms via consumption of contaminated prey, or upon direct exposure to toxic cells. In this study, the presence of potentially toxic microalgal cells was investigated within the digestive tract contents of a threatened species of green turtle (Chelonia mydas). Additionally, lipophilic toxins were determined by LC-MS/MS in tissue samples (liver, stomach and/or intestine) of selected animals (n = 39 individuals) found dead-stranded in southern Brazil, from winter/2015 to autumn/2016. Thirteen potentially toxic species of microalgae (both benthic and planktonic), including seven dinoflagellates, six cyanobacteria and one diatom, were found in the digestive tract contents of green turtles. Among them, dinoflagellates belonging to the Dinophysis acuminata species complex were the most frequent (36%) and abundant (maximum average abundance of 566 cells g-1 in spring/2015). Moreover, 23% of the examined sea turtles exhibited detectable levels of the diarrhetic shellfish toxin okadaic acid (OA) in washed digestive tissues. Seven individuals accumulated OA in their intestines (max. 24.1 ng g-1) and two in the stomachs (max. 7.4 ng g-1). Toxin levels in the tissues were directly and significantly (r = 0.70, p < 0.025) associated with the cell abundance of OA-producing D. acuminata and Prorocentrum lima species complexes within the digestive contents of green turtles. Although OA concentrations were relatively low, possible chronic exposure might deteriorate general health conditions of exposed sea turtles, increasing the risk for diseases. Okadaic acid has been regarded as a tumor-promoting compound and an environmental co-factor in the incidence of fibropapillomatosis, a frequent disease in juvenile green turtles inhabiting this geographic region. Even though, only one green turtle containing OA in the digestive tissues (out of six examined) also presented fibropapillomatosis in this study. Notwithstanding, sea turtles are sentinels of ocean health. Monitoring the accumulation of algal toxins and their negative effects on these organisms contributes to conserving biodiversity and marine habitats.

Multiply charged ion profiles in the UHPLC-HRMS analysis of palytoxin analogues from Ostreopsis cf. ovata blooms

Analogues of palytoxin (PLTX), one of the most potent marine biotoxins, are produced by some species of the marine dinoflagellates of the genus Ostreopsis. The proliferation of these species in different coastal zones represents a potential threat of seafood poisoning in humans because the produced toxins can be transferred through marine food webs. Thus, the determination of the concentration of PLTX analogues (ovatoxins-OVTXs, ostreocins-OSTs and isobaric PLTX) in different matrices (seawater, marine fauna, etc.) is necessary to protect human health. This study is addressed to overcome some of the challenges that the chemical complexity of these molecules poses to their quantification by ultra-high-performance liquid chromatography high-resolution mass spectrometry-based techniques (UHPLC-HRMS). In particular, the mass spectra of the palytoxin analogues show the presence of a large number of ions (including mono- and multiply charged ions) whose nature, relative abundances and behavior can lead to quantitation errors if the correct ions are not selected. In this work, the variability of the PLTX and OVTX profiles under different instrument conditions, including the use of diverse electrospray generation sources and different quantitation methods, is studied. Moreover, the extraction protocol in seawater containing Ostreopsis sp. ovata cells is also evaluated. The use of a heated electrospray operating at 350 °C and a quantitative method including ions from different multiply charged species provides a more robust and reliable method for overcoming the problems due to the variability in the toxin's mass spectrum profile. A single MeOH : H2O (80 : 20, v/v) extraction is proposed as the best and reliable procedure. The overall method proposed was applied to quantify OVTXs (-a to -g) and iso-PLTX along the 2019 Ostreopsis cf. ovata bloom. The cells contained a total toxin concentration of up to 20.39 pg per cell.

Recent advancements in LC-MS based analysis of biotoxins: Present and future challenges

There has been a rising concern regarding the harmful impact of biotoxins, source of origin, and the determination of the specific type of toxin. With numerous reports on their extensive spread, biotoxins pose a critical challenge to figure out their parent groups, metabolites, and concentration. In that aspect, liquid chromatography-mass spectrometry (LC-MS) based analysis paves the way for its accurate identification and quantification. The biotoxins are ideally categorized as phytotoxins, mycotoxins, shellfish-toxins, ciguatoxins, cyanotoxins, and bacterial toxins such as tetrodotoxins. Considering the diverse nature of biotoxins, both low-resolution mass spectrometry (LRMS) and high-resolution mass spectrometry (HRMS) methods have been implemented for their detection. The sample preparation strategy for complex matrix usually includes "QuEChERS" extraction or solid-phase extraction coupled with homogenization and centrifugation. For targeted analysis of biotoxins, the LRMS consisting of a tandem mass spectrometer operating in multiple reaction monitoring mode has been widely implemented. With the help of the reference standard, most of the toxins were accurately quantified. At the same time, the suspect screening and nontarget screening approach are facilitated by the HRMS platforms during the absence of reference standards. Significant progress has also been made in sampling device employment, utilizing novel sample preparation strategies, synthesizing toxin standards, employing hybrid MS platforms, and the associated data interpretation. This critical review attempts to elucidate the progress in LC-MS based analysis in the determination of biotoxins while pointing out major challenges and suggestions for future development.

Functional and Structural Biological Methods for Palytoxin Detection

Palytoxin (PLTX) and its analogues are marine polyethers identified in Palythoa and Zoanthus corals, Ostreopsis dinoflagellates, and Trichodesmium cyanobacteria. Humans can be exposed to these toxins by different routes with a series of adverse effects but the most severe risk is associated with poisonings by the consumption of edible marine organisms accumulating these toxins, as occurs in (sub)-tropical areas. In temperate areas, adverse effects ascribed to PLTXs have been recorded after inhalation of marine aerosols and/or cutaneous contact with seawater during Ostreopsis blooms, as well as during cleaning procedures of Palythoa-containing home aquaria. Besides instrumental analytical methods, in the last years a series of alternative or complementary methods based on biological/biochemical tools have been developed for the rapid and specific PLTX detection required for risk assessment. These methods are usually sensitive, cost- and time-effective, and do not require highly specialized operators. Among them, structural immunoassays and functional cell-based assays are reviewed. The availability of specific anti-PLTX antibodies allowed the development of different sensitive structural assays, suitable for its detection also in complex matrices, such as mussels. In addition, knowing the mechanism of PLTX action, a series of functional identification methods has been developed. Despite some of them being limited by matrix effects and specificity issues, biological methods for PLTX detection represent a feasible tool, suitable for rapid screening.

A Generic LC-HRMS Screening Method for Marine and Freshwater Phycotoxins in Fish, Shellfish, Water, and Supplements

Phycotoxins occur in various marine and freshwater environments, and can accumulate in edible species such as fish, crabs, and shellfish. Human exposure to these toxins can take place, for instance, through consumption of contaminated species or supplements and through the ingestion of contaminated water. Symptoms of phycotoxin intoxication include paralysis, diarrhea, and amnesia. When the cause of an intoxication cannot directly be found, a screening method is required to identify the causative toxin. In this work, such a screening method was developed and validated for marine and freshwater phycotoxins in different matrices: fish, shellfish, water, and food supplements. Two LC methods were developed: one for hydrophilic and one for lipophilic phycotoxins. Sample extracts were measured in full scan mode with an Orbitrap high resolution mass spectrometer. Additionally, a database was created to process the data. The method was successfully validated for most matrices, and in addition, regulated lipophilic phycotoxins, domoic acid, and some paralytic shellfish poisoning toxins could be quantified in shellfish. The method showed limitations for hydrophilic phycotoxins in sea water and for lipophilic phycotoxins in food supplements. The developed method is a screening method; in order to confirm suspected compounds, comparison with a standard or an additional analysis such as NMR is required.

Rapid and simultaneous purification of aflatoxin B1, zearalenone and deoxynivalenol using their monoclonal antibodies and magnetic nanoparticles

To develop a new simple and simultaneous purification method for mycotoxins in feeds and grains, magnetic nanoparticles (MNPs) conjugated with monoclonal antibodies (mAbs) against mycotoxins were used to separate aflatoxin B1 (AFB₁), zearalenone (ZEA) and deoxynivalenol (DON). For a single spike of each mycotoxin into the buffer solution (16% MeOH in PBS), mean recoveries were 93.1-95.0% for AFB₁ (5-20 ng/mL spiked), 87.2-96.0% for ZEA (125-500 ng/mL spiked) and 75.2-96.9% for DON (250-1,000 ng/mL spiked) by HPLC and ELISA. Recoveries of AFB₁ (20 ng/mL) and ZEA (500 ng/mL) simultaneously spiked into the buffer solution were 87.0 and 99.8%, respectively. Recovery rates of AFB₁/DON and DON/ZEA spiked simultaneously were 86.2%/76.6% and 92.0%/86.7%, respectively, at concentrations of 20 ng/mL AFB₁, 500 ng/mL ZEA, and 1,000 ng/mL DON. Recoveries using the novel mAb-MNP conjugated system in a buffer solution simultaneously spiked with AFB₁, ZEA and DON were 82.5, 94.6 and 73.4%, respectively. Recoveries of DON in animal feed were 107.7-132.5% at concentrations of 250-1,000 ng/g spiked in feed. The immunoaffinity chromatography (IAC) clean-up method was compared with the purification method using novel mAb-MNP. After fortification of animal feed with AFB₁ (5, 10 and 20 ng/g feed) and ZEA (125, 250 and 500 ng/g feed), AFB₁ and ZEA were purified using both the methods. In the case of the novel mAb-MNP conjugated system, mean recoveries for AFB₁ were 89.4, 73.1 and 88.3% at concentrations of 5, 10 and 20 ng/g feed, respectively. For ZEA, mean recoveries were 86.7, 85.9 and 79.1% at concentrations of 125, 250 and 500 ng/g, respectively. For IAC purification, recoveries were 42.9-45.1% for AFB₁ and 96.8-103.2% for ZEA. In conclusion, the present purification method using monoclonal antibodies conjugated to MNPs can be used for simple and simultaneous purification of mycotoxins from feed and maize.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-020-00083-w.

Current Trends and Challenges for Rapid SMART Diagnostics at Point-of-Site Testing for Marine Toxins

In the past twenty years marine biotoxin analysis in routine regulatory monitoring has advanced significantly in Europe (EU) and other regions from the use of the mouse bioassay (MBA) towards the high-end analytical techniques such as high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS). Previously, acceptance of these advanced methods, in progressing away from the MBA, was hindered by a lack of commercial certified analytical standards for method development and validation. This has now been addressed whereby the availability of a wide range of analytical standards from several companies in the EU, North America and Asia has enhanced the development and validation of methods to the required regulatory standards. However, the cost of the high-end analytical equipment, lengthy procedures and the need for qualified personnel to perform analysis can still be a challenge for routine monitoring laboratories. In developing regions, aquaculture production is increasing and alternative inexpensive Sensitive, Measurable, Accurate and Real-Time (SMART) rapid point-of-site testing (POST) methods suitable for novice end users that can be validated and internationally accepted remain an objective for both regulators and the industry. The range of commercial testing kits on the market for marine toxin analysis remains limited and even more so those meeting the requirements for use in regulatory control. Individual assays include enzyme-linked immunosorbent assays (ELISA) and lateral flow membrane-based immunoassays (LFIA) for EU-regulated toxins, such as okadaic acid (OA) and dinophysistoxins (DTXs), saxitoxin (STX) and its analogues and domoic acid (DA) in the form of three separate tests offering varying costs and benefits for the industry. It can be observed from the literature that not only are developments and improvements ongoing for these assays, but there are also novel assays being developed using upcoming state-of-the-art biosensor technology. This review focuses on both currently available methods and recent advances in innovative methods for marine biotoxin testing and the end-user practicalities that need to be observed. Furthermore, it highlights trends that are influencing assay developments such as multiplexing capabilities and rapid POST, indicating potential detection methods that will shape the future market.

Recent progress in micro/nano biosensors for shellfish toxin detection

Shellfish toxins, as one kind of marine toxin, have attracted worldwide attention due to their severe threat to food safety and human health. Therefore, it is highly essential and urgent to develop a low-cost and convenient method to detect these toxins. With the rapid advance in microfabrication processes, micro/nano biosensors provide novel approaches to address this issue. In addition to their features of low cost, portability, easy operation, high efficiency and high bioactivity, micro/nano biosensors have great potential to realize on-the-spot, rapid detection of shellfish toxins. This review focuses on the most recent advances in the development of micro/nano biosensors for shellfish toxin detection. These biosensors are mainly classified into five categories according to their transducer detection principles, which include optical devices, electrochemical sensors, electrochemiluminescence, field-effect transistors, and acoustic devices. Sensor strategies, toxin analytes, biosensitive elements, coupling methods and field detection performance are highlighted to discuss the applications of shellfish toxin detection. With advances in sensor technology, biomaterials, microfabrication and miniaturized electronics, micro/nano biosensors applied to in-field fast detection of shellfish toxins are expected to play a critical role in food safety, environmental monitoring, and foreign trade in the foreseeable future. Finally, the current challenges and future development trends of micro/nano biosensors for shellfish toxin detection are discussed.

Efficient, fast and inexpensive bioassay to monitor benthic microalgae toxicity: Application to Ostreopsis species

Even though HPLC-MS is commonly used to quantify the toxin content of Ostreopsis spp. cells, there is a need to develop easy-to-use toxicological tests to set thresholds during Ostreopsis spp. blooms. The crustacean Artemia has been widely used to evaluate the presence and toxicity of chemicals and biological contaminants and we anticipated that it could also be useful to test Ostreopsis spp. toxicity. Its relevance was first assessed by investigating the variability of the toxic effects among Ostreopsis spp. strains and throughout the dinoflagellate life cycle in combination with chemical analyses of the toxinic content by UHPLC-HRMS. After testing the toxicity of fractions prepared from Ostreopsis spp. cells, the known ova- and paly-toxins were not the only toxic metabolites to Artemia franciscana, indicating that other toxic compounds synthesized by Ostreopsis spp. still remain to be identified. To extend the bioassay to in situ monitoring, the toxicity of the benthic microalgal consortium was tested during a natural bloom of Ostreopsis cf. ovata in the NW Mediterranean Sea. The results highlight the accuracy and sensitivity of the ecotoxicological assay with Artemia franciscana to assess the toxicity of Ostreopsis spp. blooms.

Study of the binding mechanism of aptamer to palytoxin by docking and molecular simulation

This paper provides a feasible model for molecular structure analysis and interaction mechanism of aptamer and micromolecule. In this study, modeling and dynamic simulation of ssDNA aptamer (P-18S2) and target (Palytoxin, PTX) were performed separately. Then, the complex structure between DNA and PTX was predicted, and docking results showed that PTX could combine steadily at the groove’s top of DNA model by strong hydrogen-bonds and electrostatic interaction. Thus, we truncated and optimized P-18S2 by simulating. At the same time, we also confirmed the reliability of simulation results by experiments. With the experimental and computational results, the study provided a more reasonable interpretation for the high affinity and specific binding of P-18S2 and PTX, which laid the foundation for further optimization and development of aptamers in molecular diagnostics and therapeutic applications.

Structure elucidation of ostreocin-A and ostreocin-E1, novel palytoxin analogs produced by the dinoflagellate Ostreopsis siamensis, using LC/Q-TOF MS

Palytoxin analogs are marine toxins with large complex polyol structures. A benthic dinoflagellate Ostreopsis siamensis produces more than ten palytoxins (ostreocins, OSTs). The limited sample availability of minor OSTs restricts the definition of their chemical structures. The present investigation characterizes structures of two minor OSTs, i.e., ostreocin-A (OSTA) and ostreocin-E1 (OSTE1), using ostreocin-D (OSTD) as a reference compound, by liquid chromatography/quadrupole-time-of-flight mass spectrometry. The molecular formulas of OSTA and OSTE1 were C127H219N3O54 and C127H217N3O52, respectively. Compared to OSTD, OSTA has an extra oxygen atom whereas OSTE1 lacks one oxygen atom and two hydrogen atoms. The MS/MS experiments (precursor ions: [M + H]+ and [M-H]−) suggested a hydroxyl substitution at C82 in OSTA and alteration(s) between C53 and C100 in OSTE1. Further analysis of structural details in OSTE1 was performed through a pseudo-MS3 experiment (precursor ion: m/z 1432.748). Accordingly, the planar structures of OSTA and OSTE1 were assigned to 42,82-dihydroxy-3,26-didemethyl-19,44-dideoxypalytoxin and 42-hydroxy-3,26-didemethyl-19,44,73-trideoxypalytoxin-72-ene, respectively.

Abbreviations:CID: collision induced dissociation; HR-LC/MS/MS: high-resolution liquid chromatography/tandem mass spectrometry; LC/ESI/Q-TOF MS: liquid chromatography/quadrupole time-of-flight mass spectrometry equipped with an electrospray ionization source; NMR: nuclear magnetic resonance; OSTs: ostreocins; OSTA: ostreocin-A; OSTB: ostreocin-B; OSTD: ostreocin-D; OSTE1: ostreocin-E1; OVTX-a: ovatoxin-a; OVTXs: ovatoxins; PLTX: palytoxin

Extended Targeted and Non-Targeted Strategies for the Analysis of Marine Toxins in Mussels and Oysters by (LC-HRMS)

When considering the geographical expansion of marine toxins, the emergence of new toxins and the associated risk for human health, there is urgent need for versatile and efficient analytical methods that are able to detect a range, as wide as possible, of known or emerging toxins. Current detection methods for marine toxins rely on a priori defined target lists of toxins and are generally inappropriate for the detection and identification of emerging compounds. The authors describe the implementation of a recent approach for the non-targeted analysis of marine toxins in shellfish with a focus on a comprehensive workflow for the acquisition and treatment of the data generated after liquid chromatography coupled with high resolution mass spectrometry (LC-HRMS) analysis. First, the study was carried out in targeted mode to assess the performance of the method for known toxins with an extended range of polarities, including lipophilic toxins (okadaic acid, dinophysistoxins, azaspiracids, pectenotoxins, yessotoxins, cyclic imines, brevetoxins) and domoic acid. The targeted method, assessed for 14 toxins, shows good performance both in mussel and oyster extracts. The non-target potential of the method was then challenged via suspects and without a priori screening by blind analyzing mussel and oyster samples spiked with marine toxins. The data processing was optimized and successfully identified the toxins that were spiked in the blind samples.

Simple structural elucidation of ostreocin-B, a new palytoxin congener isolated from the marine dinoflagellate Ostreopsis siamensis, using complementary positive and negative ion liquid chromatography/quadrupole time-of-flight mass spectrometry

RATIONALE

Ostreocin-B is a new palytoxin congener of comparable complexity. Elucidation of the chemical structure by nuclear magnetic resonance has been hampered due to limited sample availability. More importantly, the dihedral angles of protons at the base of the hydroxyl groups on the ring structures are predicted to produce little couplings and thus disrupt connectivity. The present investigation solved the problem through mass spectrometry.

METHODS

Structural elucidation was performed by high-performance liquid chromatograph coupled to a quadrupole time-of-flight mass spectrometer equipped with an electrospray ionization source operated in positive and negative ion mode. Measurement parameters were optimized to achieve high sensitivity and a high ratio of singly charged ions. Ostreocin-D (C₁₂₇ H₂₁₉ N₃ O₅₃ ), another palytoxin congener possessing an unambiguously determined structure, was used as a template.

RESULTS

The molecular formula of ostreocin-B, C₁₂₇ H₂₁₉ N₃ O₅₄ , indicates that it has one more oxygen atom than ostreocin-D. Comparison of the product ion spectra in negative ion mode indicates the occurrence of hydroxyl substitution at C44 in ostreocin-B, unlike in ostreocin-D. Positive ion spectra also support the 44-OH substructure by producing conjugated polyenes ascribable to the sequential loss of hydroxyls on the cyclic hemiacetal.

CONCLUSIONS

The planar structure of ostreocin-B is assigned to 42-hydroxy-3,26-didemethyl-19-deoxypalytoxin (=44-hydroxyostreocin-D). The method used in this study is an excellent tool to obtain structural information on interspecies and intrastrain variation of palytoxin congeners in marine organisms.

Variability in Toxin Profiles of the Mediterranean Ostreopsis cf. ovata and in Structural Features of the Produced Ovatoxins

Fifty-five strains of Ostreopsis were collected in the Mediterranean Sea and analyzed to characterize their toxin profiles. All the strains were grown in culture under the same experimental conditions and identified by molecular PCR assay based on the ITS-5.8S rDNA. A liquid chromatography-high resolution multiple stage mass spectrometry (LC-HRMSⁿ) approach was used to analyze toxin profiles and to structurally characterize the detected toxins. Despite morphological and molecular characterization being consistent within the species O. cf. ovata, a certain degree of toxin variability was observed. All the strains produced ovatoxins (OVTXs), with the exception of only one strain. Toxin profiles were quite different from both qualitative and quantitative standpoints: 67% of the strains contained OVTX-a to -e, OVTX-g, and isobaric PLTX, in 25% of them only OVTX-a, -d, -e and isobaric PLTX were present, while 4% produced only OVTX-b and -c. None of the strains showed a previously identified profile, featuring OVTX-f as dominant toxin, whereas OVTX-f was a minor component of very few strains. Toxin content was mostly in the range 4-70 pg/cell with higher levels (up to 238 pg/cell) being found in strains from the Ligurian and South Adriatic Sea. Structural insights into OVTX-b, -c, -d, and -e were gained, and the new OVTX-l was detected in 36 strains.

First Identification of Palytoxin-Like Molecules in the Atlantic Coral Species Palythoa canariensis

Palytoxin (PLTX) is a complex marine toxin produced by Zoanthids (Palyhtoa), dinoflagellates (Ostreopsis), and cyanobacteria (Trichodesmium). Contact with PLTX-like compounds present in aerosols or marine organisms has been associated with adverse effects on humans. The worldwide distribution of producer species and seafood contaminated with PLTX-like molecules illustrates the global threat to human health. The identification of species capable of palytoxin production is critical for human safety. We studied the presence of PLTX analogues in Palythoa canariensis, a coral species collected in the Atlantic Ocean never described as a PLTX-producer before. Two methodologies were used for the detection of these toxins: a microsphere-based immunoassay that offered an estimation of the content of PLTX-like molecules in a Palythoa canariensis extract and an ultrahigh-pressure liquid chromatography coupled to an ion trap with a time-of-flight mass spectrometer (UPLC-IT-TOF-MS) that allowed the characterization of the toxin profile. The results demonstrated the presence of PLTX, hydroxy-PLTX and, at least, two additional compounds with PLTX-like profile in the Palythoa canariensis sample. The PLTX content was estimated in 0.27 mg/g of lyophilized coral using UPLC-IT-TOF-MS. Therefore, this work demonstrates that Palythoa canariensis produces a mixture of PLTX-like molecules. This is of special relevance to safeguard human health considering Palythoa species are commonly used for decoration by aquarium hobbyists.

A novel application of an adaptable modeling approach to the management of toxic microalgal bloom events in coastal areas

Harmful algal blooms have been increasing in frequency in recent years, and attention has shifted from describing to modeling and trying to predict these phenomena, since in many cases they pose a risk to human health and coastal activities. Predicting ecological phenomena is often time and resource consuming, since a large number of field collected data are required. We propose a novel approach that involves the use of modeled meteorological data as input features to predict the concentration of the toxic benthic dinoflagellate Ostreopsis cf. ovata in seawater. Ten meteorological features were used to train a Quantile Random Forests model, which was then validated using field collected concentration data over the course of a summer sampling season. The proposed model was able to accurately describe Ostreopsis abundance in the water column in response to meteorological variables. Furthermore, the predictive power of this model appears good, as indicated by the validation results, especially when the quantile for predictions is tuned to match management requirements. The Quantile Random Forests method was selected, as it allows for greater flexibility in the generated predictions, thus making this model suitable as a tool for coastal management. The application of this approach is novel, as no other models or tools that are adaptable to this degree are currently available. The model presented here was developed for a single species over a limited geographical extension, but its methodological basis appears flexible enough to be applied to the prediction of HABs in general and it could also be extended to the case of other ecological phenomena that are strongly dependent on meteorological drivers, that can be independently modeled and potentially globally available.

Recent Trends in Marine Phycotoxins from Australian Coastal Waters

Phycotoxins, which are produced by harmful microalgae and bioaccumulate in the  marine food web, are of growing concern for Australia. These harmful algae pose a threat to  ecosystem and human health, as well as constraining the progress of aquaculture, one of the fastest  growing food sectors in the world. With better monitoring, advanced analytical skills and an  increase in microalgal expertise, many phycotoxins have been identified in Australian coastal  waters in recent years. The most concerning of these toxins are ciguatoxin, paralytic shellfish  toxins, okadaic acid and domoic acid, with palytoxin and karlotoxin increasing in significance. The  potential for tetrodotoxin, maitotoxin and palytoxin to contaminate seafood is also of concern,  warranting future investigation. The largest and most significant toxic bloom in Tasmania in 2012  resulted in an estimated total economic loss of~AUD$23M, indicating that there is an imperative to  improve  toxin  and  organism  detection  methods,  clarify  the  toxin  profiles  of  species  of  phytoplankton and carry out both intra- and inter-species toxicity comparisons. Future work also  includes the application of rapid, real-time molecular assays for the detection of harmful species  and toxin genes. This information, in conjunction with a better understanding of the life histories  and  ecology  of  harmful  bloom  species,  may  lead  to  more  appropriate  management  of  environmental, health and economic resources.

Genetic and toxinological characterization of North Atlantic strains of the dinoflagellate Ostreopsis and allelopathic interactions with toxic and non-toxic species from the genera Prorocentrum, Coolia and Gambierdiscus

The genus Ostreopsis includes several toxic species that can develop blooms in benthic ecosystems, with potential harmful consequences for human health and marine invertebrates. Despite of this, little is known about the allelopathic interactions between these organisms and other co-occurring microalgae that exploit similar spatial and nutrient resources in benthic ecosystems. The aim of this study was to follow these interactions in cultures of two Ostreopsis ribotypes with different toxin profiles (O. cf. ovata contained ovatoxins-a, b, c and e, while only ovatoxin-d was found in O .sp. "Lanzarote-type"), mixed with species of three benthic dinoflagellate genera (Coolia, Prorocentrum and Gambierdiscus), isolated from the same area (North East Atlantic, Canary Islands). In a first experiment, the potential allelopathic effects on growth rates were followed, in mixed cultures of Coolia monotis (a non toxic species) exposed to the clarified medium and to cells of O. sp."Lanzarote-type" and O. cf. ovata. Growth delayed in C. monotis was observed specially in clarified medium, while the O. sp. "Lanzarote-type" strain attained much lower densities in mixed cultures. In a second experiment, we examined the potential effects of clarified media from O. sp."Lanzarote-type" and O. cf. ovata on the adherence capacity in two toxic species (Prorocentrum hoffmannianum and Gambierdiscus excentricus). Contrasting effects were found: a significant increase of adherence capacity in P. hoffmannianum vs attachment decline in G. excentricus, that experienced also severe deleterious effects (cell lysis). Our results suggest the existence of weak to moderate allelopathic interactions between the studied organisms, although the outcome is dependent on the species involved.

Enzyme-linked, aptamer-based, competitive biolayer interferometry biosensor for palytoxin

In this study, we coupled biolayer interferometry (BLI) with competitive binding assay through an enzyme-linked aptamer and developed a real-time, ultra-sensitive, rapid quantitative method for detection of the marine biotoxin palytoxin. Horseradish peroxidase-labeled aptamers were used as biorecognition receptors to competitively bind with palytoxin, which was immobilized on the biosensor surface. The palytoxin: horseradish peroxidase-aptamer complex was then submerged in a 3,3'-diaminobenzidine solution, which resulted in formation of a precipitated polymeric product directly on the biosensor surface and a large change in the optical thickness of the biosensor layer. This change could obviously shift the interference pattern and generate a response profile on the BLI biosensor. The biosensor showed a broad linear range for palytoxin (200-700pg/mL) with a low detection limit (0.04pg/mL). Moreover, the biosensor was applied to the detection of palytoxin in spiked extracts and showed a high degree of selectivity for palytoxin, good reproducibility, and stability. This enzyme-linked, aptamer-based, competitive BLI biosensor offers a promising method for rapid and sensitive detection of palytoxin and other analytes.

Effects of the harmful dinoflagellate Ostreopsis cf. ovata on different life cycle stages of the common moon jellyfish Aurelia sp

The frequency and geographic extension of microalgae and gelatinous zooplankton blooms seem to have been increasing worldwide over recent decades. In particular, the harmful dinoflagellate Ostreopsis cf. ovata and the Schyphozoan jellyfish Aurelia sp. are two of the most frequent and long lasting species forming blooms in the Mediterranean Sea. A kind of interaction among any of their life cycle stages (i.e. planula-polyp-ephyrae vs Ostreopsis cells) can likely occur, although in this area there are no data available on the co-occurrence of these species. The aim of this study was to investigate, for the first time, the potential noxious effect of O. cf. ovata on different life stages of Aurelia sp. (polyps and ephyrae), testing several concentrations of whole algal culture. Rsults of toxicity bioassay highlighted that ephyrae, but not polyps, are affected by this harmful dinoflagellate and comparisons among other model organisms show that Aurelia sp. ephyrae are the most sensitive model organism tested so far (EC_50-24h=10.5cells/mL). These findings suggest an interesting scenario on the interaction of these two bloom forming species in the natural marine environment.

Phylogenetic structure of bacterial assemblages co-occurring with Ostreopsis cf. ovata bloom

Extensive blooms of the toxic epiphytic/benthic dinoflagellate Ostreopsis cf. ovata are being reported with increasing frequency and spatial distribution in temperate coastal regions including the Mediterranean. These blooms are of human and environmental health concern due to the production of isobaric palytoxin and a wide range of ovatoxins by Ostreopsis cf. ovata. Bacterial-microalgal interactions are important regulators in algal bloom dynamics and potentially toxin dynamics. This study investigated the bacterial assemblages co-occurring with O. cf. ovata (OA) and from ambient seawaters (SW) during the early and peak phases of bloom development in NW Adriatic Sea. Fractions of the bacterial assemblages co-occurring with O. cf. ovata (OA) and more closely associated to the mucilage layer (LA) embedding O. cf. ovata cells were also reported. In total, 14 bacterial phyla were detected by targeted 454 pyrosequencing of the 16S rRNA gene. The dominant bacterial phyla in the OA assemblages were Proteobacteria and Bacteroidetes; while at the class level, Alphaproteobacteria were the most abundant (83 and 66%, relative abundance, early and peak bloom phases), followed by Flavobacteria (7 and 19%, early and peak phases). Actinobacteria and Cyanobacteria were of minor importance (<5% of the relative bacterial abundance each). Gammaproteobacteria showed a notably presence in OA assemblage only at the early phase of the bloom (genus Haliea, 13%). The Alphaproteobacteria were predominately composed by the genera Ruegeria, Jannaschia and Erythrobacter which represented about half of the total phylotypes' contribution of OA at both early and peak phases of the O. cf. ovata bloom, suggesting interactions between this consortium and the microalga. Moreover, the highest contribution of Ruegeria (30% of the total phylotypes) was observed at the early phase of the bloom in LA assemblage. Microbial assemblages associated with the ambient seawaters while being also dominated by Alphaproteobacteria and Flavobacteria were partially distinct from those associated with O. cf. ovata due to the presence of genera almost not retrieved in the latter assemblages.

Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21st century

Microalgal blooms are a natural part of the seasonal cycle of photosynthetic organisms in marine ecosystems. They are key components of the structure and dynamics of the oceans and thus sustain the benefits that humans obtain from these aquatic environments. However, some microalgal blooms can cause harm to humans and other organisms. These harmful algal blooms (HABs) have direct impacts on human health and negative influences on human wellbeing, mainly through their consequences to coastal ecosystem services (fisheries, tourism and recreation) and other marine organisms and environments. HABs are natural phenomena, but these events can be favoured by anthropogenic pressures in coastal areas. Global warming and associated changes in the oceans could affect HAB occurrences and toxicity as well, although forecasting the possible trends is still speculative and requires intensive multidisciplinary research. At the beginning of the 21st century, with expanding human populations, particularly in coastal and developing countries, mitigating HABs impacts on human health and wellbeing is becoming a more pressing public health need. The available tools to address this global challenge include maintaining intensive, multidisciplinary and collaborative scientific research, and strengthening the coordination with stakeholders, policymakers and the general public. Here we provide an overview of different aspects of the HABs phenomena, an important element of the intrinsic links between oceans and human health and wellbeing.

Detection of palytoxin-like compounds by a flow cytometry-based immunoassay supported by functional and analytical methods

Palytoxin (PLTX) is a complex marine toxin produced by zoanthids (i.e. Palythoa), dinoflagellates (Ostreopsis) and cyanobacteria (Trichodesmium). PLTX outbreaks are usually associated with Indo-Pacific waters, however their recent repeated occurrence in Mediterranean-European Atlantic coasts demonstrate their current worldwide distribution. Human sickness and fatalities have been associated with toxic algal blooms and ingestion of seafood contaminated with PLTX-like molecules. These toxins represent a serious threat to human health. There is an immediate need to develop easy-to-use, rapid detection methods due to the lack of validated protocols for their detection and quantification. We have developed an immuno-detection method for PLTX-like molecules based on the use of microspheres coupled to flow-cytometry detection (Luminex 200™). The assay consisted of the competition between free PLTX-like compounds in solution and PLTX immobilized on the surface of microspheres for binding to a specific monoclonal anti-PLTX antibody. This method displays an IC50 of 1.83 ± 0.21 nM and a dynamic range of 0.47-6.54 nM for PLTX. An easy-to-perform extraction protocol, based on a mixture of methanol and acetate buffer, was applied to spiked mussel samples providing a recovery rate of 104 ± 8% and a range of detection from 374 ± 81 to 4430 ± 150 μg kg(-1) when assayed with this method. Extracts of Ostreopsis cf. siamensis and Palythoa tuberculosa were tested and yielded positive results for PLTX-like molecules. However, the data obtained for the coral sample suggested that this antibody did not detect 42-OH-PLTX efficiently. The same samples were further analyzed using a neuroblastoma cytotoxicity assay and UPLC-IT-TOF spectrometry, which also pointed to the presence of PLTX-like compounds. Therefore, this single detection method for PLTX provides a semi-quantitative tool useful for the screening of PLTX-like molecules in different matrixes.

Modelling the Stoichiometric Regulation of C-Rich Toxins in Marine Dinoflagellates

Toxin production in marine microalgae was previously shown to be tightly coupled with cellular stoichiometry. The highest values of cellular toxin are in fact mainly associated with a high carbon to nutrient cellular ratio. In particular, the cellular accumulation of C-rich toxins (i.e., with C:N > 6.6) can be stimulated by both N and P deficiency. Dinoflagellates are the main producers of C-rich toxins and may represent a serious threat for human health and the marine ecosystem. As such, the development of a numerical model able to predict how toxin production is stimulated by nutrient supply/deficiency is of primary utility for both scientific and management purposes. In this work we have developed a mechanistic model describing the stoichiometric regulation of C-rich toxins in marine dinoflagellates. To this purpose, a new formulation describing toxin production and fate was embedded in the European Regional Seas Ecosystem Model (ERSEM), here simplified to describe a monospecific batch culture. Toxin production was assumed to be composed by two distinct additive terms; the first is a constant fraction of algal production and is assumed to take place at any physiological conditions. The second term is assumed to be dependent on algal biomass and to be stimulated by internal nutrient deficiency. By using these assumptions, the model reproduced the concentrations and temporal evolution of toxins observed in cultures of Ostreopsis cf. ovata, a benthic/epiphytic dinoflagellate producing C-rich toxins named ovatoxins. The analysis of simulations and their comparison with experimental data provided a conceptual model linking toxin production and nutritional status in this species. The model was also qualitatively validated by using independent literature data, and the results indicate that our formulation can be also used to simulate toxin dynamics in other dinoflagellates. Our model represents an important step towards the simulation and prediction of marine algal toxicity.

First finding of Ostreopsis cf. ovata toxins in marine aerosols

Since the late 1990s, a respiratory syndrome has been repetitively observed in humans concomitant with Ostreopsis spp. blooms (mainly O. cf. ovata) in the Mediterranean area. Previous studies have demonstrated that O. cf. ovata produces analogues of palytoxin (ovatoxins and a putative palytoxin), one of the most potent marine toxins. On the basis of the observed association between O. cf. ovata blooms, respiratory illness in people, and detection of palytoxin complex in algal samples, toxic aerosols, containing Ostreopsis cells and/or the toxins they produce, were postulated to be the cause of human illness. A small scale monitoring study of marine aerosol carried out along the Tuscan coasts (Italy) in 2009 and 2010 is reported. Aerosols were collected concomitantly with O. cf. ovata blooms, and they were analyzed by both PCR assays and LC-HRMS. The results, besides confirming the presence of O. cf. ovata cells, demonstrated for the first time the occurrence of ovatoxins in the aerosol at levels of 2.4 pg of ovatoxins per liter of air. Given the lack of toxicological data on palytoxins by inhalation exposure, our results are only a first step toward a more comprehensive understanding of the Ostreopsis-related respiratory syndrome.

Surface plasmon resonance biosensor method for palytoxin detection based on Na+,K+-ATPase affinity

Palytoxin (PLTX), produced by dinoflagellates from the genus Ostreopsis was first discovered, isolated, and purified from zoanthids belonging to the genus Palythoa. The detection of this toxin in contaminated shellfish is essential for human health preservation. A broad range of studies indicate that mammalian Na⁺,K⁺-ATPase is a high affinity cellular receptor for PLTX. The toxin converts the pump into an open channel that stimulates sodium influx and potassium efflux. In this work we develop a detection method for PLTX based on its binding to the Na⁺,K⁺-ATPase. The method was developed by using the phenomenon of surface plasmon resonance (SPR) to monitor biomolecular reactions. This technique does not require any labeling of components. The interaction of PLTX over immobilized Na⁺,K⁺-ATPase is quantified by injecting different concentrations of toxin in the biosensor and checking the binding rate constant (k_obs). From the representation of k_obs versus PLTX concentration, the kinetic equilibrium dissociation constant (K_D) for the PLTX-Na⁺,K⁺-ATPase association can be calculated. The value of this constant is K_D = 6.38 × 10⁻⁷ ± 6.67 × 10⁻⁸ M PLTX. In this way the PLTX-Na⁺,K⁺-ATPase association was used as a suitable method for determination of the toxin concentration in a sample. This method represents a new and useful approach to easily detect the presence of PLTX-like compounds in marine products using the mechanism of action of these toxins and in this way reduce the use of other more expensive and animal based methods.

Innovative detection methods for aquatic algal toxins and their presence in the food chain

Detection of aquatic algal toxins has become critical for the protection of human health. During the last 5 years, techniques such as optical, electrochemical, and piezoelectric biosensors or fluorescent-microsphere-based assays have been developed for the detection of aquatic algal toxins, in addition to optimization of existing techniques, to achieve higher sensitivities, specificity, and speed or multidetection. New toxins have also been incorporated in the array of analytical and biological methods. The impact of the former innovation on this field is highlighted by recent changes in legal regulations, with liquid chromatography-mass spectrometry becoming the official reference method for marine lipophilic toxins and replacing the mouse bioassay in many countries. This review summarizes the large international effort to provide routine testing laboratories with fast, sensitive, high-throughput, multitoxin, validated methods for the screening of seafood, algae, and water samples.

Toxicity of palytoxin after repeated oral exposure in mice and in vitro effects on cardiomyocytes

Palytoxin (PLTX) is a highly toxic hydrophilic polyether detected in several edible marine organisms from intra-tropical areas, where seafood poisoning were reported. Symptoms usually start with gastro-intestinal malaise, often accompanied by myalgia, muscular cramps, dyspnea and, sometimes, arrhythmias. Monitoring programs in the Mediterranean Sea have detected PLTX-like molecules in edible mollusks and echinoderms. Despite the potential exposure of the human population and its high toxic potential, the toxicological profile of the molecule is still an issue. Thus, the effects of repeated oral administration of PLTX in mice were investigated. Seven days of PLTX administration caused lethality and toxic effects at doses ≥ 30 μg/kg/day. A NOAEL was estimated equal to 3 μg/kg/day, indicating a quite steep dose-response curve. This value, due to the limited number of animal tested, is provisional, although represents a sound basis for further testing. Macroscopic alterations at gastrointestinal level (gastric ulcers and intestinal fluid accumulation) were observed in mice dead during the treatment period. Histological analysis highlighted severe inflammation, locally associated with necrosis, at pulmonary level, as well as hyper-eosinophilia and fiber separation in myocardium. A cardiac damage was supported by the in vitro effect of the toxin on cardiomyocytes, indicating a severe and irreversible impairment of their electrical properties: electrophysiological recordings detected a progressive cell depolarization, arrest of action potentials and beating.

New insights on cytological and metabolic features of Ostreopsis cf. ovata Fukuyo (Dinophyceae): a multidisciplinary approach

The harmful dinoflagellate Ostreopsis cf. ovata has been causing toxic events along the Mediterranean coasts and other temperate and tropical areas, with increasing frequency during the last decade. Despite many studies, important biological features of this species are still poorly known. An integrated study, using different microscopy and molecular techniques, Raman microspectroscopy and high resolution liquid chromatography-mass spectrometry (HR LC-MS), was undertaken to elucidate cytological aspects, and identify main metabolites including toxins. The species was genetically identified as O. cf. ovata, Atlantic-Mediterranean clade. The ultrastructural results show unique features of the mucilage network abundantly produced by this species to colonize benthic substrates, with a new role of trichocysts, never described before. The amorphous polysaccharidic component of mucilage appears to derive from pusule fibrous material and mucocysts. In all stages of growth, the cells show an abundant production of lipids. Different developmental stages of chloroplasts are found in the peripheral cytoplasm and in the centre of cell. In vivo Raman microspectroscopy confirms the presence of the carotenoid peridinin in O. cf. ovata, and detects in several specimen the abundant presence of unsaturated lipids structurally related to docosahexaenoic acid. The HR LC-MS analysis reveals that ovatoxin-a is the predominant toxin, together with decreasing amounts of ovatoxin-b, -d/e, -c and putative palytoxin. Toxins concentration on a per cell basis increases from exponential to senescent phase. The results suggest that benthic blooms of this species are probably related to features such as the ability to create a unique mucilaginous sheath covering the sea bottom, associated with the production of potent toxins as palytoxin-like compounds. In this way, O. cf. ovata may be able to rapidly colonize benthic substrates outcompeting other species.

Sandwich ELISA assay for the quantitation of palytoxin and its analogs in natural samples

Palytoxins are potent marine biotoxins that have recently become endemic to the Mediterranean Sea, and are becoming more frequently associated with seafood. Due to their high toxicity, suitable methods to quantify palytoxins are needed. Thus, we developed an indirect sandwich ELISA for palytoxin and 42-hydroxy-palytoxin. An intralaboratory study demonstrated sensitivity (limit of detection, LOD = 1.1 ng/mL; limit of quantitation, LOQ = 2.2 ng/mL), accuracy (bias of 2.1%), repeatability (RSDr = 6% and 9% for intra- and interassay variability, respectively) and specificity: other common marine toxins (okadaic acid, domoic acid, saxitoxin, brevetoxin-3, and yessotoxin) do not cross-react in this assay. It performed well in three different matrices: observed LOQs were 11.0, 9.6, and 2.4 ng/mL for mussel extracts, algal net samples and seawater, respectively, with good accuracy and precision. The LOQ in seafood is 11 μg palytoxin/kg mussel meat, lower than that of the most common detection technique, LC-MS/MS.

Highly sensitive electrochemiluminescent nanobiosensor for the detection of palytoxin

Marine toxins appear to be increasing in many areas of the world. An emerging problem in the Mediterranean Sea is represented by palytoxin (PlTX), one of the most potent marine toxins, frequently detected in seafood. Due to the high potential for human toxicity of PlTX, there is a strong and urgent need for sensitive methods toward its detection and quantification. We have developed an ultrasensitive electrochemiluminescence-based sensor for the detection of PlTX, taking advantage of the specificity provided by anti-PlTX antibodies, the good conductive properties of carbon nanotubes, and the excellent sensitivity achieved by a luminescence-based transducer. The sensor was able to produce a concentration-dependent light signal, allowing PlTX quantification in mussels, with a limit of quantification (LOQ = 2.2 μg/kg of mussel meat) more than 2 orders of magnitude more sensitive than that of the commonly used detection techniques, such as LC-MS/MS.

A sensitive assay for palytoxins, ovatoxins and ostreocins using LC-MS/MS analysis of cleavage fragments from micro-scale oxidation

Palytoxin is a highly toxic non-proteinaceous marine natural product that can pass through the food chain and result in human illnesses. A recent review by the European Food Safety Authority concluded that palytoxin requires regulation in seafood and a limit of 30 μg kg⁻¹ for shellfish flesh was suggested. Current methods based on LC-MS detection of intact palytoxins do not have sufficient sensitivity to enforce this limit for palytoxin. To improve sensitivity for trace analysis, a novel screen approach has been developed that uses LC-MS/MS analysis of substructures generated by oxidative cleavage of vicinal diol groups present in the intact toxin. Oxidation of palytoxins, ovatoxins or ostreocins using periodic acid generates two nitrogen-containing aldehyde fragments; an amino aldehyde common to these toxins, and an amide aldehyde that may vary depending on toxin type. Conditions for micro-scale oxidation of palytoxin were optimised, which include a novel SPE cleanup and on-column oxidation step. Rapid analysis of cleavage fragments was established using LC-MS/MS. Linear calibrations were established for the amino aldehyde from a palytoxin reference standard, which is suitable for all known palytoxin-like compounds, and for the confirmatory amide aldehydes of palytoxin and ostreocin-D. Palytoxin recoveries (at 10 μg kg⁻¹) from shellfish and fish tissues were 114-119% (as amine aldehyde) and 90-115% (as amide aldehyde) with RSDs for both of ≤ 18% (all tissues, n = 12). The method LOD was determined to be approximately 1 ng mL⁻¹ and the LOQ 4 ng mL⁻¹, which corresponds to 10 μg kg⁻¹ in tissue (flesh of shellfish or fish). The method has potential for use in research and is sufficiently sensitive for regulatory testing, should it be required.

Toxin-producing Ostreopsis cf. ovata are likely to bloom undetected along coastal areas

Mass appearances of the toxic dinoflagellate genus Ostreopsis are known to cause dangerous respiratory symptoms in humans exposed to aerosols. The outbreaks can appear in shallow marine waters of temperate regions around the globe. We followed a massive bloom event on a public beach on the northern Adriatic coast near Rovinj, Croatia. We identified the responsible species and the produced toxins as well as the dynamics of the event with respect to environmental conditions. Ostreopsis cf. ovata appeared in masses from September through October 2010 on a public beach near Rovinj, Croatia but stayed undetected by public health organizations. Respiratory symptoms were observed whenever humans were exposed to substrate samples containing large numbers of Ostreopsis cells. During the mass abundance of O. cf. ovata also exposure to the aerosols on the beach evoked respiratory symptoms in humans. Our measurements showed high cell abundances and high toxin contents with a stable relative contribution of putative Palytoxin and Ovatoxins a-e. Artificial beach structures proved to dramatically reduce settling of the observed Ostreopsis biofilm. Blooms like those reported herein have a high potential to happen undetected with a high potential of affecting the health of coastal human populations. Increased monitoring efforts are therefore required to understand the ecology and toxicology of those bloom events and reduce their negative impact on coastal populations.

High resolution LC-MS(n) fragmentation pattern of palytoxin as template to gain new insights into ovatoxin-a structure. The key role of calcium in MS behavior of palytoxins

Palytoxin is a potent marine toxin and one of the most complex natural compounds ever described. A number of compounds identified as palytoxin congeners (e.g., ovatoxins, mascarenotoxins, ostreocins, etc.) have not been yet structurally elucidated due to lack of pure material in quantities sufficient to an NMR-based structural investigation. In this study, the complex fragmentation pattern of palytoxin in its positive high resolution liquid chromatography tandem mass spectra (HR LC-MS(n)) was interpreted. Under the used conditions, the molecule underwent fragmentation at many sites of its backbone, and a large number of diagnostic fragment ions were identified. The natural product itself was used with no need for derivatization. Interestingly, most of the fragments contained calcium in their elemental formula. Evidence for palytoxin tendency to form adduct ions with calcium and other divalent cations in its mass spectra was obtained. Fragmentation pattern of palytoxin was used as template to gain detailed structural information on ovatoxin-a, the main toxin produced by Ostreopsis ovata, (observe correct font) a benthic dinoflagellate that currently represents the major harmful algal bloom threat in the Mediterranean area. Either the regions or the specific sites where ovatoxin-a and palytoxin structurally differ have been identified.

Preliminary study for rapid determination of phycotoxins in microalgae whole cells using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Rapid and sensitive methods for identification of several phycotoxins produced by microalgae species such as yessotoxins (YTXs) for Protoceratium reticulatum, okadaic acid (OA) and pectenotoxins (PTXs) for Prorocentrum spp. and Dinophysis spp., Palytoxins (PLTXs) for Ostreopsis spp., ciguatoxins (CTXs) for Gambierdiscus spp. or domoic acid (DA) for Pseudo-nitzschia spp. are of great importance to the shellfish and fish industry. In this study, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to detect several phycotoxins in whole cells of some microalgae which are known as toxin producers. To achieve an appropriate MALDI matrix and a sample preparation method, several matrices and solvent mixtures were tested. The most appropriate matrix system for toxin detection was obtained with 10 µg μL(-1) of DHB in 0.1% TFA/ACN (3:7, v/v) by mixing the intact cells with the matrix solution directly on the MALDI target (dried-droplet technique). Toxin detection by this procedure is much faster than current procedures based on solvent extraction and chromatographic separation. This method allowed the rapid detection of main phycotoxins in some dinoflagellate cells of genus Ostreopsis, Prorocentrum, Protoceratium, Gambierdiscus, Dinophysis and diatoms from Pseudo-nitzschia genus.

Ostreopsis cf. ovata bloom in the northern Adriatic Sea during summer 2009: ecology, molecular characterization and toxin profile

Intense blooms of the benthic dinoflagellate Ostreopsis cf. ovata have occurred in the northern Adriatic Sea since 2006. These blooms are associated with noxious effects on human health and with the mortality of benthic organisms because of the production of palytoxin-like compounds. The O. cf. ovata bloom and its relationships with nutrient concentrations at two stations on the Conero Riviera (northern Adriatic Sea) were investigated in the summer of 2009. O. cf. ovata developed from August to November, with the highest abundances in September (1.3×10(6) cells g(-1) fw corresponding to 63.8×10(3) cells cm(-2)). The presence of the single O. cf. ovata genotype was confirmed by a PCR assay. Bloom developed when the seawater temperature was decreasing. Nutrient concentrations did not seem to affect bloom dynamics. Toxin analysis performed by high resolution liquid chromatography-mass spectrometry revealed a high total toxin content (up to 75 pg cell(-1)), including putative palytoxin and all the ovatoxins known so far.