Tetrazolium-based cell bioassay for neurotoxins active on voltage-sensitive sodium channels: semiautomated assay for saxitoxins, brevetoxins, and ciguatoxins

A Reliable Multifaceted Solution against Foodborne Viral Infections: The Case of RiLK1 Decapeptide

Food-borne transmission is a recognized route for many viruses associated with gastrointestinal, hepatic, or neurological diseases. Therefore, it is essential to identify new bioactive compounds with broad-spectrum antiviral activity to exploit innovative solutions against these hazards. Recently, antimicrobial peptides (AMPs) have been recognized as promising antiviral agents. Indeed, while the antibacterial and antifungal effects of these molecules have been widely reported, their use as potential antiviral agents has not yet been fully investigated. Herein, the antiviral activity of previously identified or newly designed AMPs was evaluated against the non-enveloped RNA viruses, hepatitis A virus (HAV) and murine norovirus (MNV), a surrogate for human norovirus. Moreover, specific assays were performed to recognize at which stage of the viral infection cycle the peptides could function. The results showed that almost all peptides displayed virucidal effects, with about 90% of infectivity reduction in HAV or MNV. However, the decapeptide RiLK1 demonstrated, together with its antibacterial and antifungal properties, a notable reduction in viral infection for both HAV and MNV, possibly through direct interaction with viral particles causing their damage or hindering the recognition of cellular receptors. Hence, RiLK1 could represent a versatile antimicrobial agent effective against various foodborne pathogens including viruses, bacteria, and fungi.

Automated Patch Clamp for the Detection of Tetrodotoxin in Pufferfish Samples

Tetrodotoxin (TTX) is a marine toxin responsible for many intoxications around the world. Its presence in some pufferfish species and, as recently reported, in shellfish, poses a serious health concern. Although TTX is not routinely monitored, there is a need for fast, sensitive, reliable, and simple methods for its detection and quantification. In this work, we describe the use of an automated patch clamp (APC) system with Neuro-2a cells for the determination of TTX contents in pufferfish samples. The cells showed an IC50 of 6.4 nM for TTX and were not affected by the presence of muscle, skin, liver, and gonad tissues of a Sphoeroides pachygaster specimen (TTX-free) when analysed at 10 mg/mL. The LOD achieved with this technique was 0.05 mg TTX equiv./kg, which is far below the Japanese regulatory limit of 2 mg TTX equiv./kg. The APC system was applied to the analysis of extracts of a Lagocephalus sceleratus specimen, showing TTX contents that followed the trend of gonads > liver > skin > muscle. The APC system, providing an in vitro toxicological approach, offers the advantages of being sensitive, rapid, and reliable for the detection of TTX-like compounds in seafood.

Detection of Extremely Low Level Ciguatoxins through Monitoring of Lithium Adduct Ions by Liquid Chromatography-Triple Quadrupole Tandem Mass Spectrometry

Ciguatera poisoning (CP) is the most common type of marine biotoxin food poisoning worldwide, and it is caused by ciguatoxins (CTXs), thermostable polyether toxins produced by dinoflagellate Gambierdiscus and Fukuyoa spp. It is typically caused by the consumption of large fish high on the food chain that have accumulated CTXs in their flesh. CTXs in trace amounts are found in natural samples, and they mainly induce neurotoxic effects in consumers at concentrations as low as 0.2 µg/kg. The U.S. Food and Drug Administration has established CTX maximum permitted levels of 0.01 µg/kg for CTX1B and 0.1 µg/kg for C-CTX1 based on toxicological data. More than 20 variants of the CTX1B and CTX3C series have been identified, and the simultaneous detection of trace amounts of CTX analogs has recently been required. Previously published works using LC-MS/MS achieved the safety levels by monitoring the sodium adduct ions of CTXs ([M+Na]+ > [M+Na]+). In this study, we optimized a highly sensitive method for the detection of CTXs using the sodium or lithium adducts, [M+Na]+ or [M+Li]+, by adding alkali metals such as Na+ or Li+ to the mobile phase. This work demonstrates that CTXs can be successfully detected at the low concentrations recommended by the FDA with good chromatographic separation using LC-MS/MS. It also reports on the method's new analytical conditions and accuracy using [M+Li]+.

Tissue Distribution and Metabolization of Ciguatoxins in an Herbivorous Fish following Experimental Dietary Exposure to Gambierdiscus polynesiensis

Ciguatoxins (CTXs), potent neurotoxins produced by dinoflagellates of the genera Gambierdiscus and Fukuyoa, accumulate in commonly consumed fish species, causing human ciguatera poisoning. Field collections of Pacific reef fish reveal that consumed CTXs undergo oxidative biotransformations, resulting in numerous, often toxified analogs. Following our study showing rapid CTX accumulation in flesh of an herbivorous fish, we used the same laboratory model to examine the tissue distribution and metabolization of Pacific CTXs following long-term dietary exposure. Naso brevirostris consumed cells of Gambierdiscus polynesiensis in a gel food matrix over 16 weeks at a constant dose rate of 0.36 ng CTX3C equiv g-1 fish d-1. CTX toxicity determination of fish tissues showed CTX activity in all tissues of exposed fish (eight tissues plus the carcass), with the highest concentrations in the spleen. Muscle tissue retained the largest proportion of CTXs, with 44% of the total tissue burden. Moreover, relative to our previous study, we found that larger fish with slower growth rates assimilated a higher proportion of ingested toxin in their flesh (13% vs. 2%). Analysis of muscle extracts revealed the presence of CTX3C and CTX3B as well as a biotransformed product showing the m/z transitions of 2,3-dihydroxyCTX3C. This is the first experimental evidence of oxidative transformation of an algal CTX in a model consumer and known vector of CTX into the fish food web. These findings that the flesh intended for human consumption carries the majority of the toxin load, and that growth rates can influence the relationship between exposure and accumulation, have significant implications in risk assessment and the development of regulatory measures aimed at ensuring seafood safety.

Ciguatera poisoning in French Polynesia: A review of the distribution and toxicity of Gambierdiscus spp., and related impacts on food web components and human health

Ciguatera Poisoning (CP) is a seafood poisoning highly prevalent in French Polynesia. This illness results from the consumption of seafood contaminated with ciguatoxins (CTXs) produced by Gambierdiscus, a benthic dinoflagellate. Ciguatera significantly degrades the health and economic well-being of local communities largely dependent on reef fisheries for their subsistence. French Polynesia has been the site of rich and active CP research since the 1960's. The environmental, toxicological, and epidemiological data obtained in the frame of large-scale field surveys and a country-wide CP case reporting program conducted over the past three decades in the five island groups of French Polynesia are reviewed. Results show toxin production in Gambierdiscus in the natural environment may vary considerably at a temporal and spatial scale, and that several locales clearly represent Gambierdiscus spp. "biodiversity hotspots". Current data also suggest the "hot" species G. polynesiensis could be the primary source of CTXs in local ciguateric biotopes, pending formal confirmation. The prevalence of ciguatoxic fish and the CTX levels observed in several locales were remarkably high, with herbivores and omnivores often as toxic as carnivores. Results also confirm the strong local influence of Gambierdiscus spp. on the CTX toxin profiles characterized across multiple food web components including in CP-prone marine invertebrates. The statistics, obtained in the frame of a long-term epidemiological surveillance program established in 2007, point towards an apparent decline in the number of CP cases in French Polynesia as a whole; however, incidence rates remain dangerously high in some islands. Several of the challenges and opportunities, most notably those linked to the strong cultural ramifications of CP among local communities, that need to be considered to define effective risk management strategies are addressed.

Determination of neurotoxic shellfish poisoning toxins in shellfish by liquid chromatography-tandem mass spectrometry coupled with dispersive solid phase extraction

An innovative method based on dispersive solid phase extraction (d-SPE) in conjunction with LC-MS/MS had been developed for the simultaneous quantitative determination of three brevetoxins (BTXs), which can result in neurotoxic shellfish poisoning (NSP), in shellfish. The toxins were extracted with a 50 % acetonitrile (v/v) and cleaned by alumina-neutral sorbent. After chromatographic separation on a C18 column, the analytes were qualitatively and quantitatively detected using multiple reaction monitoring (MRM) in positive ionization mode. The created approach was validated by SANTE 11312/2021. The LOQs were 5 μg/kg for each toxin, below the advised regulatory limit of 800 μg BTX-2/kg. The mean recoveries of brevetoxins were in the range of 75.9 %-114.1 %, and the ranges of their intra- and inter-day precisions were 0.9-9.7 % and 0.6-7.2 %, respectively. The matrix effects for three BTXs in four shellfish matrices were in the range of 85.6 %-114.8 %. The method demonstrated great consistency and high sensitivity, and it can meet the requirements of daily monitoring.

Antimicrobial activity, membrane interaction and structural features of short arginine-rich antimicrobial peptides

Antimicrobial activity of many AMPs can be improved by lysine-to-arginine substitution due to a more favourable interaction of arginine guanidinium moiety with bacterial membranes. In a previous work, the structural and functional characterization of an amphipathic antimicrobial peptide named RiLK1, including lysine and arginine as the positively charged amino acids in its sequence, was reported. Specifically, RiLK1 retained its β-sheet structure under a wide range of environmental conditions (temperature, pH, and ionic strength), and exhibited bactericidal activity against Gram-positive and Gram-negative bacteria and fungal pathogens with no evidence of toxicity on mammalian cells. To further elucidate the influence of a lysine-to-arginine replacement on RiLK1 conformational properties, antimicrobial activity and peptide-liposome interaction, a new RiLK1-derivative, named RiLK3, in which the lysine is replaced with an arginine residue, was projected and characterised in comparison with its parental compound. The results evidenced that lysine-to-arginine mutation not only did not assure an improvement in the antimicrobial potency of RiLK1 in terms of bactericidal, virucidal and fungicidal activities, but rather it was completely abolished against the hepatitis A virus. Therefore, RiLK1 exhibited a wide range of antimicrobial activity like other cationic peptides, although the exact mechanisms of action are not completely understood. Moreover, tryptophan fluorescence measurements confirmed that RiLK3 bound to negatively charged lipid vesicles with an affinity lower than that of RiLK1, although no substantial differences from the structural and self-assembled point of view were evidenced. Therefore, our findings imply that antimicrobial efficacy and selectivity are affected by several complex and interrelated factors related to substitution of lysine with arginine, such as their relative proportion and position. In this context, this study could provide a better rationalisation for the optimization of antimicrobial peptide sequences, paving the way for the development of novel AMPs with broad applications.

Evaluation of Toxicity Equivalency Factors of Tetrodotoxin Analogues with a Neuro-2a Cell-Based Assay and Application to Puffer Fish from Greece

Tetrodotoxin (TTX) is a potent marine neurotoxin involved in poisoning cases, especially through the consumption of puffer fish. Knowledge of the toxicity equivalency factors (TEFs) of TTX analogues is crucial in monitoring programs to estimate the toxicity of samples analyzed with instrumental analysis methods. In this work, TTX analogues were isolated from the liver of a Lagocephalus sceleratus individual caught on South Crete coasts. A cell-based assay (CBA) for TTXs was optimized and applied to the establishment of the TEFs of 5,11-dideoxyTTX, 11-norTTX-6(S)-ol, 11-deoxyTTX and 5,6,11-trideoxyTTX. Results showed that all TTX analogues were less toxic than the parent TTX, their TEFs being in the range of 0.75-0.011. Then, different tissues of three Lagocephalus sceleratus individuals were analyzed with CBA and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The obtained TEFs were applied to the TTX analogues' concentrations obtained by LC-MS/MS analysis, providing an indication of the overall toxicity of the sample. Information about the TEFs of TTX analogues is valuable for food safety control, allowing the estimation of the risk of fish products to consumers.

Ciguatera Fish Poisoning in the Caribbean Sea and Atlantic Ocean: Reconciling the Multiplicity of Ciguatoxins and Analytical Chemistry Approach for Public Health Safety

Ciguatera is a major circumtropical poisoning caused by the consumption of marine fish and invertebrates contaminated with ciguatoxins (CTXs): neurotoxins produced by endemic and benthic dinoflagellates which are biotransformed in the fish food-web. We provide a history of ciguatera research conducted over the past 70 years on ciguatoxins from the Pacific Ocean (P-CTXs) and Caribbean Sea (C-CTXs) and describe their main chemical, biochemical, and toxicological properties. Currently, there is no official method for the extraction and quantification of ciguatoxins, regardless their origin, mainly due to limited CTX-certified reference materials. In this review, the extraction and purification procedures of C-CTXs are investigated, considering specific objectives such as isolating reference materials, analysing fish toxin profiles, or ensuring food safety control. Certain in vitro assays may provide sufficient sensitivity to detect C-CTXs at sub-ppb levels in fish, but they do not allow for individual identification of CTXs. Recent advances in analysis using liquid chromatography coupled with low- or high-resolution mass spectrometry provide new opportunities to identify known C-CTXs, to gain structural insights into new analogues, and to quantify C-CTXs. Together, these methods reveal that ciguatera arises from a multiplicity of CTXs, although one major form (C-CTX-1) seems to dominate. However, questions arise regarding the abundance and instability of certain C-CTXs, which are further complicated by the wide array of CTX-producing dinoflagellates and fish vectors. Further research is needed to assess the toxic potential of the new C-CTX and their role in ciguatera fish poisoning. With the identification of C-CTXs in the coastal USA and Eastern Atlantic Ocean, the investigation of ciguatera fish poisoning is now a truly global effort.

Approaches to Construction of the Medium-Sized Ring Structure in Zetekitoxin AB by Ring-Closing Metathesis

Zetekitoxin AB (ZTX), a member of the saxitoxin (STX) family isolated from the Panamanian golden frog Atelopus zeteki, shows extremely potent Na_V-inhibitory activity. Here, we investigate the synthesis of 12-membered ring structure with the C11 tertiary hydroxyl group in ZTX by means of the Mislow-Evans rearrangement reaction and subsequent ring-closing metathesis reaction. Although this approach did not provide access to the 12-membered macrocycle, we obtained a new STX analog with an 18-membered macrolactam structure as a synthetic mimic of ZTX.

Detection of Ciguatoxins and Tetrodotoxins in Seafood with Biosensors and Other Smart Bioanalytical Systems

The emergence of marine toxins such as ciguatoxins (CTXs) and tetrodotoxins (TTXs) in non-endemic regions may pose a serious food safety threat and public health concern if proper control measures are not applied. This article provides an overview of the main biorecognition molecules used for the detection of CTXs and TTXs and the different assay configurations and transduction strategies explored in the development of biosensors and other biotechnological tools for these marine toxins. The advantages and limitations of the systems based on cells, receptors, antibodies, and aptamers are described, and new challenges in marine toxin detection are identified. The validation of these smart bioanalytical systems through analysis of samples and comparison with other techniques is also rationally discussed. These tools have already been demonstrated to be useful in the detection and quantification of CTXs and TTXs, and are, therefore, highly promising for their implementation in research activities and monitoring programs.

Evaluation of relative potency of calibrated ciguatoxin congeners by near-infrared fluorescent receptor binding and neuroblastoma cell-based assays

Ciguatera fish poisoning (CFP) is a foodborne illness affecting > 50,000 people worldwide annually. It is caused by eating marine invertebrates and fish that have accumulated ciguatoxins (CTXs). Recently, the risk of CFP to human health, the local economy, and fishery resources have increased; therefore, detection methods are urgently needed. Functional assays for detecting ciguatoxins in fish include receptor binding (RBA) and neuroblastoma cell-based assay (N2a assay), which can detect all CTX congeners. In this study, we made these assays easier to use. For RBA, an assay was developed using a novel near-infrared fluorescent ligand, PREX710-BTX, to save valuable CTXs. In the N2a assay, a 1-day assay was developed with the same detection performance as the conventional 2-day assay. Additionally, in these assays, we used calibrated CTX standards from the Pacific determined by quantitative NMR for the first time to compare the relative potency of congeners, which differed significantly among previous studies. In the RBA, there was almost no difference in the binding affinity among congeners, showing that the differences in side chains, stereochemistry, and backbone structure of CTXs did not affect the binding affinity. However, this result did not correlate with the toxic equivalency factors (TEFs) based on acute toxicity in mice. In contrast, the N2a assay showed a good correlation with TEFs based on acute toxicity in mice, except for CTX3C. These findings, obtained with calibrated toxin standards, provide important insights into evaluating the total toxicity of CTXs using functional assays.

Cyclodextrin polymer clean-up method for the detection of ciguatoxins in fish with cell-based assays

Ciguatoxins (CTXs) are marine toxins produced by microalgae of the genera Gambierdiscus and Fukuyoa, which are transferred through the food webs, reaching humans and causing a poisoning known as ciguatera. The cell-based assay (CBA) is commonly used for their detection because of its high sensitivity and the provided toxicological information. However, matrix effects may interfere in the CBA. In this work, γ-cyclodextrin-hexamethylene diisocyanate (γ-CD-HDI), γ-cyclodextrin-epichlorohydrin (γ-CD-EPI) and γ-CD-EPI conjugated to magnetic beads (γ-CD-EPI-MB) have been evaluated as clean-up materials for fish flesh extracts containing CTXs. The best results were achieved with γ-CD-HDI in column format, which showed a CTX1B recovery of 42% and 32% for Variola louti and Seriola dumerili, respectively, and allowed exposing cells to at least 400 mg/mL of fish flesh. This clean-up strategy provides at least 4.6 and 3.0-fold higher sensitivities to the assay for V.louti and S.dumerili, respectively, improving the reliability of CTX quantification.

Reductive Amination for LC-MS Signal Enhancement and Confirmation of the Presence of Caribbean Ciguatoxin-1 in Fish

Ciguatera poisoning is a global health concern caused by the consumption of seafood containing ciguatoxins (CTXs). Detection of CTXs poses significant analytical challenges due to their low abundance even in highly toxic fish, the diverse and in-part unclarified structures of many CTX congeners, and the lack of reference standards. Selective detection of CTXs requires methods such as liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) or high-resolution MS (LC-HRMS). While HRMS data can provide greatly improved resolution, it is typically less sensitive than targeted LC-MS/MS and does not reliably comply with the FDA guidance level of 0.1 µg/kg CTXs in fish tissue that was established for Caribbean CTX-1 (C-CTX-1). In this study, we provide a new chemical derivatization approach employing a fast and simple one-pot derivatization with Girard's reagent T (GRT) that tags the C-56-ketone intermediate of the two equilibrating C-56 epimers of C-CTX-1 with a quaternary ammonium moiety. This derivatization improved the LC-MS/MS and LC-HRMS responses to C-CTX-1 by approximately 40- and 17-fold on average, respectively. These improvements in sensitivity to the GRT-derivative of C-CTX-1 are attributable to: the improved ionization efficiency caused by insertion of a quaternary ammonium ion; the absence of adduct-ions and water-loss peaks for the GRT derivative in the mass spectrometer, and; the prevention of on-column epimerization (at C-56 of C-CTX-1) by GRT derivatization, leading to much better chromatographic peak shapes. This C-CTX-1-GRT derivatization strategy mitigates many of the shortcomings of current LC-MS analyses for C-CTX-1 by improving instrument sensitivity, while at the same time adding selectivity due to the reactivity of GRT with ketones and aldehydes.

Identification of New CTX Analogues in Fish from the Madeira and Selvagens Archipelagos by Neuro-2a CBA and LC-HRMS

Ciguatera Poisoning (CP) is caused by consumption of fish or invertebrates contaminated with ciguatoxins (CTXs). Presently CP is a public concern in some temperate regions, such as Macaronesia (North-Eastern Atlantic Ocean). Toxicity analysis was performed to characterize the fish species that can accumulate CTXs and improve understanding of the ciguatera risk in this area. For that, seventeen fish specimens comprising nine species were captured from coastal waters inMadeira and Selvagens Archipelagos. Toxicity was analysed by screening CTX-like toxicity with the neuroblastoma cell-based assay (neuro-2a CBA). Afterwards, the four most toxic samples were analysed with liquid chromatography-high resolution mass spectrometry (LC-HRMS). Thirteen fish specimens presented CTX-like toxicity in their liver, but only four of these in their muscle. The liver of one specimen of Muraena augusti presented the highest CTX-like toxicity (0.270 ± 0.121 µg of CTX1B equiv·kg−1). Moreover, CTX analogues were detected with LC-HRMS, for M. augusti and Gymnothorax unicolor. The presence of three CTX analogues was identified: C-CTX1, which had been previously described in the area; dihydro-CTX2, which is reported in the area for the first time; a putative new CTX m/z 1127.6023 ([M+NH4]+) named as putative C-CTX-1109, and gambieric acid A.

Supramolecular Complexes of Plant Neurotoxin Veratridine with Cyclodextrins and Their Antidote-like Effect on Neuro-2a Cell Viability

Veratridine (VTD) is a plant neurotoxin that acts by blocking the voltage-gated sodium channels (VGSC) of cell membranes. Symptoms of VTD intoxication include intense nausea, hypotension, arrhythmia, and loss of consciousness. The treatment for the intoxication is mainly focused on treating the symptoms, meaning there is no specific antidote against VTD. In this pursuit, we were interested in studying the molecular interactions of VTD with cyclodextrins (CDs). CDs are supramolecular macrocycles with the ability to form host–guest inclusion complexes (ICs) inside their hydrophobic cavity. Since VTD is a lipid-soluble alkaloid, we hypothesized that it could form stable inclusion complexes with different types of CDs, resulting in changes to its physicochemical properties. In this investigation, we studied the interaction of VTD with β-CD, γ-CD and sulfobutyl ether β-CD (SBCD) by isothermal titration calorimetry (ITC) and nuclear magnetic resonance (NMR) spectroscopy. Docking and molecular dynamics studies confirmed the most stable configuration for the inclusion complexes. Finally, with an interest in understanding the effects of the VTD/CD molecular interactions, we performed cell-based assays (CBAs) on Neuro-2a cells. Our findings reveal that the use of different amounts of CDs has an antidote-like concentration-dependent effect on the cells, significantly increasing cell viability and thus opening opportunities for novel research on applications of CDs and VTD.

Current Trends and New Challenges in Marine Phycotoxins

Marine phycotoxins are a multiplicity of bioactive compounds which are produced by microalgae and bioaccumulate in the marine food web. Phycotoxins affect the ecosystem, pose a threat to human health, and have important economic effects on aquaculture and tourism worldwide. However, human health and food safety have been the primary concerns when considering the impacts of phycotoxins. Phycotoxins toxicity information, often used to set regulatory limits for these toxins in shellfish, lacks traceability of toxicity values highlighting the need for predefined toxicological criteria. Toxicity data together with adequate detection methods for monitoring procedures are crucial to protect human health. However, despite technological advances, there are still methodological uncertainties and high demand for universal phycotoxin detectors. This review focuses on these topics, including uncertainties of climate change, providing an overview of the current information as well as future perspectives.

A smartphone-controlled amperometric immunosensor for the detection of Pacific ciguatoxins in fish

Ciguatoxins (CTXs) are marine neurotoxins produced by microalgae of the genera Gambierdiscus and Fukuyoa. CTXs may reach humans through food webs and cause ciguatera fish poisoning (CFP). An immunosensor for the detection of Pacific CTXs in fish was developed using multiwalled carbon nanotube (MWCNT)-modified carbon electrodes and a smartphone-controlled potentiostat. The biosensor attained a limit of detection (LOD) and a limit of quantification (LOQ) of 6 and 27 pg/mL of CTX1B, respectively, which were 0.001 and 0.005 μg/kg in fish flesh. In the analysis of fish samples from Japan and Fiji, excellent correlations were found with sandwich enzyme-linked immunosorbent assays (ELISAs), a cell-based assay (CBA) and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Stability of at least 3 months at -20 °C was predicted. In just over 2 h, the biosensor provides reliable, accurate and precise Pacific CTX contents in fish extracts, being suitable for monitoring and research programs.

Yeast Cell as a Bio-Model for Measuring the Toxicity of Fish-Killing Flagellates

Harmful algal blooms are a significant environmental problem. Cells that bloom are often associated with intercellular or dissolved toxins that are a grave concern to humans. However, cells may also excrete compounds that are beneficial to their competition, allowing the cells to establish or maintain cells in bloom conditions. Here, we develop a yeast cell assay to assess whether the bloom-forming species can change the toxicity of the water environment. The current methods of assessing toxicity involve whole organisms. Here, yeast cells are used as a bioassay model to evaluate eukaryotic cell toxicity. Yeast is a commonly used, easy to maintain bioassay species that is free from ethical concerns, yet is sensitive to a wide array of metabolic and membrane-modulating agents. Compared to methods in which the whole organism is used, this method offers rapid and convenient cytotoxicity measurements using a lower volume of samples. The flow cytometer was employed in this toxicology assessment to measure the number of dead cells using alive/dead stain analysis. The results show that yeast cells were metabolically damaged after 1 h of exposure to our model toxin-producing euryhaline flagellates (Heterosigma akashiwo and Prymnesium parvum) cells or extracts. This amount was increased by extending the incubation time.

Guidance Level for Brevetoxins in French Shellfish

Brevetoxins (BTXs) are marine biotoxins responsible for neurotoxic shellfish poisoning (NSP) after ingestion of contaminated shellfish. NSP is characterized by neurological, gastrointestinal and/or cardiovascular symptoms. The main known producer of BTXs is the dinoflagellate Karenia brevis, but other microalgae are also suspected to synthesize BTX-like compounds. BTXs are currently not regulated in France and in Europe. In November 2018, they have been detected for the first time in France in mussels from a lagoon in the Corsica Island (Mediterranean Sea), as part of the network for monitoring the emergence of marine biotoxins in shellfish. To prevent health risks associated with the consumption of shellfish contaminated with BTXs in France, a working group was set up by the French Agency for Food, Environmental and Occupational Health & Safety (Anses). One of the aims of this working group was to propose a guidance level for the presence of BTXs in shellfish. Toxicological data were too limited to derive an acute oral reference dose (ARfD). Based on human case reports, we identified two lowest-observed-adverse-effect levels (LOAELs). A guidance level of 180 µg BTX-3 eq./kg shellfish meat is proposed, considering a protective default portion size of 400 g shellfish meat.

Extraction and LC-MS/MS Analysis of Ciguatoxins: A Semi-Targeted Approach Designed for Fish of Unknown Origin

Ciguatoxins (CTXs) are polyether marine biotoxins that can cause ciguatera poisoning (CP) after the consumption of fish or invertebrates containing sub ppb levels; concentrations that present a challenge for current extraction and analysis methods. Here, a newly developed and (partly) validated single-day extraction protocol is presented. First, the fish sample is broken-down by enzymatic digestion, followed by extraction and extract clean-up by defatting and two solid-phase extractions. Final extracts were investigated using two different CTX-analysis methods; an in vitro cytotoxicity assay (N2a-assay) and by LC-MS/MS. Validation was performed for both fillet and freeze-dried samples of snapper, parrotfish, and grouper spiked with CTX1B, 52-epi-54-deoxyCTX1B, 54-deoxyCTX1B, and CTX3C. Based on recovery rates (35–88%) and matrix effects (66–116%) determined by LC-MS/MS, the enzyme protocol is applicable to various matrices. The protocol was applied to naturally contaminated fish tissue (Lutjanus bohar) obtained during a CP incident in Germany. Several potential CTX congeners were identified by a two-tier LC-MS/MS approach (screening of sodium adducts, high-resolution or low-resolution confirmation via ammonium adducts). Inclusion of >30 known CTX congeners into the LC-MS/MS methods and single-day sample preparation make the method suitable for analysis of ciguatera suspect samples at sub ppb levels also with undisclosed CTX profiles.

An Update on Ciguatoxins and CTX-like Toxicity in Fish from Different Trophic Levels of the Selvagens Islands (NE Atlantic, Madeira, Portugal)

The Selvagens Islands, which are a marine protected area located at the southernmost point of the Portuguese maritime zone, have been associated with fish harboring ciguatoxins (CTX) and linked to ciguatera fish poisonings. This study reports the results of a field sampling campaign carried out in September 2018 in these remote and rarely surveyed islands. Fifty-six fish specimens from different trophic levels were caught for CTX-like toxicity determination by cell-based assay (CBA) and toxin content analysis by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Notably, high toxicity levels were found in fish with an intermediate position in the food web, such as zebra seabream (Diplodus cervinus) and barred hogfish (Bodianus scrofa), reaching levels up to 0.75 µg CTX1B equivalent kg⁻¹. The LC-MS/MS analysis confirmed that C-CTX1 was the main toxin, but discrepancies between CBA and LC-MS/MS in D. cervinus and top predator species, such as the yellowmouth barracuda (Sphyraena viridis) and amberjacks (Seriola spp.), suggest the presence of fish metabolic products, which need to be further elucidated. This study confirms that fish from coastal food webs of the Selvagens Islands represent a high risk of ciguatera, raising important issues for fisheries and environmental management of the Selvagens Islands.

Toxicity Screening of a Gambierdiscus australes Strain from the Western Mediterranean Sea and Identification of a Novel Maitotoxin Analogue

Dinoflagellate species of the genera Gambierdiscus and Fukuyoa are known to produce ciguatera poisoning-associated toxic compounds, such as ciguatoxins, or other toxins, such as maitotoxins. However, many species and strains remain poorly characterized in areas where they were recently identified, such as the western Mediterranean Sea. In previous studies carried out by our research group, a G. australes strain from the Balearic Islands (Mediterranean Sea) presenting MTX-like activity was characterized by LC-MS/MS and LC-HRMS detecting 44-methyl gambierone and gambieric acids C and D. However, MTX1, which is typically found in some G. australes strains from the Pacific Ocean, was not detected. Therefore, this study focuses on the identification of the compound responsible for the MTX-like toxicity in this strain. The G. australes strain was characterized not only using LC-MS instruments but also N2a-guided HPLC fractionation. Following this approach, several toxic compounds were identified in three fractions by LC-MS/MS and HRMS. A novel MTX analogue, named MTX5, was identified in the most toxic fraction, and 44-methyl gambierone and gambieric acids C and D contributed to the toxicity observed in other fractions of this strain. Thus, G. australes from the Mediterranean Sea produces MTX5 instead of MTX1 in contrast to some strains of the same species from the Pacific Ocean. No CTX precursors were detected, reinforcing the complexity of the identification of CTXs precursors in these regions.

Naphthalimide-gold-based nanocomposite for the ratiometric detection of okadaic acid in shellfish

Okadaic acid (OA) is one of the known marine biotoxins produced by various dinoflagellates and exists in seafood such as shellfish. The consumption of contaminated shellfish with OA leads to diarrheic shellfish poisoning (DSP), which results in the inhibition of protein phosphatase enzymes in humans. This poisoning can cause immunotoxicity and tumor promotion due to the accumulation of okadaic acid in more than the allowed limit in bivalve molluscs. The reported methods for the detection of okadaic acid include mouse bioassays, immunoassays, chromatography coupled with spectroscopic techniques, electrochemical sensors and immunosensors. We have developed a naphthalimide-gold-based nanocomposite for the detection of okadaic acid. Individually, the organic nanoparticles (ONPs) of synthesized naphthalimide-based receptors and gold-coated ONPs are less sensitive for detection. However, fabrication of the composite of Au@ONPs and ONPs enhance the sensing properties and selectivity. The composite shows a ratiometric response in the UV-Vis absorption spectrum and quenching in the fluorescence profile with a detection limit of 20 nM for OA in aqueous medium. In cyclic voltammetry, a shift was observed in the cathodic peak (-0.532 V to -0.618 V) as well as in the anodic peak (-0.815 V to -0.847 V) with the addition of okadaic acid. To study the quick binding of the composite with OA, a time response experiment was performed. Also, the developed sensor retains its sensing ability in the pH range of 5-9 and in high salt conditions. Our developed composite can be used for the detection of OA in real applications.

High Levels of Tetrodotoxin (TTX) in Trumpet Shell Charonia lampas from the Portuguese Coast

Tetrodotoxin (TTX) is a potent neurotoxin, considered an emerging toxin in Europe where recently a safety limit of 44 µg TTX kg⁻¹ was recommended by authorities. In this study, three specimens of the large gastropod trumpet shell Charonia lampas bought in a market in south Portugal were analyzed using a neuroblastoma cell (N2a) based assay and by LC-MS/MS. N2a toxicity was observed in the viscera of two individuals analyzed and LC-MS/MS showed very high concentrations of TTX (42.1 mg kg⁻¹) and 4,9-anhydroTTX (56.3 mg kg⁻¹). A third compound with m/z 318 and structurally related with TTX was observed. In the edible portion, i.e., the muscle, toxin levels were below the EFSA recommended limit. This study shows that trumpet shell marine snails are seafood species that may reach the markets containing low TTX levels in the edible portion but containing very high levels of TTX in non-edible portion raising concerns regarding food safety if a proper evisceration is not carried out by consumers. These results highlight the need for better understanding TTX variability in this gastropod species, which is critical to developing a proper legal framework for resources management ensuring seafood safety, and the introduction of these gastropods in the markets.

Improving in vitro ciguatoxin and brevetoxin detection: selecting neuroblastoma (Neuro-2a) cells with lower sensitivity to ouabain and veratridine (OV-LS)

Marine biotoxins accumulating in seafood products pose a risk to human health. These toxins are often potent in minute amounts and contained within complex matrices; requiring sensitive, reliable, and robust methods for their detection. The mouse neuroblastoma (Neuro-2a) cytotoxicity assay (N2a-assay) is a sensitive, high-throughput, in vitro method effective for detecting sodium channel-specific marine biotoxins. The N2a-assay can be conducted to distinguish between specific effects on voltage-gated sodium (Na_V) channels, caused by toxins that activate (e.g., ciguatoxins (CTXs), brevetoxins (PbTxs)) or block (e.g., tetrodotoxins, saxitoxins) the target Na_V. The sensitivity and specificity of the assay to compounds activating the Na_V are achieved through the addition of the pharmaceuticals ouabain (O) and veratridine (V). However, these compounds can be toxic to Neuro-2a cells and their application at insufficient or excessive concentrations can reduce the effectiveness of this assay for marine toxin detection. Therefore, during growth incubation, Neuro-2a cells were exposed to O and V, and surviving cells exhibiting a lower sensitivity to O and V (OV-LS) were propagated. OV-LS Neuro-2a cells were selected for 60-80% survival when exposed to 0.22/0.022 mM O/V during the cytotoxicity assay. At these conditions, OV-LS N2a cells demonstrated a 3.5-fold higher survival rate 71% ± 7.9 SD (n = 232), and lower sensitivity to O/V, compared to the original Neuro-2a cells 20% ± 9.0 SD (n = 16). Additionally, OV-LS N2a cells were 1.3-2.6-fold more sensitive for detecting CTX3C 1.35 pg/ml, CTX1B 2.06 pg/ml, and PbTx-3 3.04 ng/ml compared to Neuro-2a cells using 0.1/0.01 mM O/V. Detection of CTX3C in a complex fish matrix using OV-LS cells was 0.0048 pg CTX3C/mg fish tissue equivalent. This work shows the potential for a significant improvement in sensitivity for CTX3C, CTX1B, and PbTx-3 using the OV-LS N2a-assay.

Search for potential biomarkers for saxitoxin detection

The Neuro-2a cell assay has been a promising in vitro alternative for the detection of saxitoxin (STX)-like toxins. However, its application is problematic in samples with complex matrices containing different toxins, whose mechanisms of action could be antagonistic. In the search of alternative procedures that reduce or avoid this interference, we evaluated the transcriptional modulation produced by a 24-h exposure to STX in Neuro-2a cells under three conditions: exposure to STX (33 nM), a mussel meat matrix (12.5 mg meat/mL) and a fortified sample (STX-fortified matrix). Differential gene expression was evaluated by RNA-seq after Illumina high-throughput sequencing, and data were analyzed to identify genes differentially expressed regardless of the matrix. From the 9487 identified genes, 213 were differentially expressed of these, 10 genes were identified as candidate markers for STX detection due to their regulation by STX regardless of the matrix interference. Expression dynamics of 7 of these candidate genes (Fgf-1, Adgrb2, Tfpt, Zfr2, Nup 35, Fam195a, and Dusp7) was further evaluated by qRT-PCR analysis of cells exposed to different concentrations of STX for up to 24 h. A downregulation of some markers expression was observed, namely Nup35 (involved in nucleo-cytoplasmic transporter activity) and Zfr-2 (involved in nucleic acids binding), whereas Fgf-1 (apoptosis signaling) was significantly upregulated. Markers' expression was not influenced by the matrix, suggesting that gene expression variations are directly related to STX response. These results support the potential of these genes as biomarkers for the development of an alternative STX-like toxins screening method.

Identification of Emerging Hazards in Mussels by the Galician Emerging Food Safety Risks Network (RISEGAL). A First Approach

Emerging risk identification is a priority for the European Food Safety Authority (EFSA). The goal of the Galician Emerging Food Safety Risks Network (RISEGAL) is the identification of emerging risks in foods produced and commercialized in Galicia (northwest Spain) in order to propose prevention plans and mitigation strategies. In this work, RISEGAL applied a systematic approach for the identification of emerging food safety risks potentially affecting bivalve shellfish. First, a comprehensive review of scientific databases was carried out to identify hazards most quoted as emerging in bivalves in the period 2016–2018. Then, identified hazards were semiquantitatively assessed by a panel of food safety experts, who scored them accordingly with the five evaluation criteria proposed by EFSA: novelty, soundness, imminence, scale, and severity. Scores determined that perfluorinated compounds, antimicrobial resistance, Vibrio parahaemolyticus, hepatitis E virus (HEV), and antimicrobial residues are the emerging hazards that are considered most imminent and severe and that could cause safety problems of the highest scale in the bivalve value chain by the majority of the experts consulted (75%). Finally, in a preliminary way, an exploratory study carried out in the Galician Rías highlighted the presence of HEV in mussels cultivated in class B production areas.

Rapid detection of ciguatoxins in Gambierdiscus and Fukuyoa with immunosensing tools

Consumption of seafood contaminated with ciguatoxins (CTXs) leads to a foodborne disease known as ciguatera. Primary producers of CTXs are epibenthic dinoflagellates of the genera Gambierdiscus and Fukuyoa. In this study, thirteen Gambierdiscus and Fukuyoa strains were cultured, harvested at exponential phase, and CTXs were extracted with an implemented rapid protocol. Microalgal extracts were obtained from pellets with a low cell abundance (20,000 cell/mL) and were then analyzed with magnetic bead (MB)-based immunosensing tools (colorimetric immunoassay and electrochemical immunosensor). It is the first time that these approaches are used to screen Gambierdiscus and Fukuyoa strains, providing not only a global indication of the presence of CTXs, but also the ability to discriminate between two series of congeners (CTX1B and CTX3C). Analysis of the microalgal extracts revealed the presence of CTXs in 11 out of 13 strains and provided new information about Gambierdiscus and Fukuyoa toxin profiles. The use of immunosensing tools in the analysis of microalgal extracts facilitates the elucidation of further knowledge regarding these dinoflagellate genera and can contribute to improved ciguatera risk assessment and management.

Gambierdiscus and Fukuyoa as potential indicators of ciguatera risk in the Balearic Islands

Gambierdiscus and Fukuyoa are genera of toxic dinoflagellates which were mainly considered as endemic to marine intertropical areas, and that are well known as producers of ciguatoxins (CTXs) and maitotoxins (MTXs). Ciguatera poisoning (CP) is a human poisoning occurring after the consumption of fish or more rarely, shellfish containing CTXs. The presence of these microalgae in a coastal area is an indication of potential risk of CP. This study assesses the risk of CP in the Balearic Islands (Western Mediterranean Sea) according to the distribution of both microalgae genera, and the presence of CTX-like and MTX-like toxicity in microalgal cultures as determined by neuro-2a cell based-assay (neuro-2a CBA). Genetic identification of forty-three cultured microalgal strains isolated from 2016 to 2019 revealed that all of them belong to the species G. australes and F. paulensis. Both species were widely distributed in Formentera, Majorca and Minorca. Additionally, all strains of G. australes and two of F. paulensis exhibited signals of CTX-like toxicity ranging respectively between 1 and 380 and 8-16 fg CTX1B equivalents (equiv.) • cell^-1. Four extracts of F. paulensis exhibited a novel toxicity response in neuro-2a cells consisting of the recovery of the cell viability in the presence of ouabain and veratridine. In addition, G. australes showed MTX-like toxicity while F. paulensis strains did not. Overall, the low CTX-like toxicities detected indicate that the potential risk of CP in the Balearic Islands is low, although, the presence of CTX-like and MTX-like toxicity in those strains reveal the necessity to monitor these genera in the Mediterranean Sea.

Further advance of Gambierdiscus Species in the Canary Islands, with the First Report of Gambierdiscus belizeanus

Ciguatera Poisoning (CP) is a human food-borne poisoning that has been known since ancient times to be found mainly in tropical and subtropical areas, which occurs when fish or very rarely invertebrates contaminated with ciguatoxins (CTXs) are consumed. The genus of marine benthic dinoflagellates Gambierdiscus produces CTX precursors. The presence of Gambierdiscus species in a region is one indicator of CP risk. The Canary Islands (North Eastern Atlantic Ocean) is an area where CP cases have been reported since 2004. In the present study, samplings for Gambierdiscus cells were conducted in this area during 2016 and 2017. Gambierdiscus cells were isolated and identified as G. australes, G. excentricus, G. caribaeus, and G. belizeanus by molecular analysis. In this study, G. belizeanus is reported for the first time in the Canary Islands. Gambierdiscus isolates were cultured, and the CTX-like toxicity of forty-one strains was evaluated with the neuroblastoma cell-based assay (neuro-2a CBA). G. excentricus exhibited the highest CTX-like toxicity (9.5-2566.7 fg CTX1B equiv. cell^-1) followed by G. australes (1.7-452.6.2 fg CTX1B equiv. cell^-1). By contrast, the toxicity of G. belizeanus was low (5.6 fg CTX1B equiv. cell^-1), and G. caribaeus did not exhibit CTX-like toxicity. In addition, for the G. belizeanus strain, the production of CTXs was evaluated with a colorimetric immunoassay and an electrochemical immunosensor resulting in G. belizeanus producing two types of CTX congeners (CTX1B and CTX3C series congeners) and can contribute to CP in the Canary Islands.

Advances in Detecting Ciguatoxins in Fish

Ciguatera fish poisoning (CFP) is currently the most common marine biotoxin food poisoning worldwide, associated with human consumption of circumtropical fish and marine invertebrates that are contaminated with ciguatoxins. Ciguatoxins are very potent sodium-channel activator neurotoxins, that pose risks to human health at very low concentrations (>0.01 ng per g of fish flesh in the case of the most potent Pacific ciguatoxin). Symptoms of CFP are nonspecific and intoxication in humans is often misdiagnosed. Presently, there is no medically approved treatment of ciguatera. Therefore, to mitigate the risks of CFP, reliable detection of ciguatoxins prior to consumption of fish tissue is acutely needed, which requires application of highly sensitive and quantitative analytical tests. During the last century a number of methods have been developed to identify and quantify the concentration of ciguatoxins, including in vivo animal assays, cell-based assays, receptor binding assays, antibody-based immunoassays, electrochemical methods, and analytical techniques based on coupling of liquid chromatography with mass spectrometry. Development of these methods, their various advantages and limitations, as well as future challenges are discussed in this review.

Evaluation of Matrix Issues in the Applicability of the Neuro-2a Cell Based Assay on the Detection of CTX in Fish Samples

Ciguatoxins (CTXs) are a group of neurotoxins responsible for the syndrome ciguatera fish poisoning (CFP) as a result of the consumption of contaminated fish. The presence of these toxins has been detected around the Pacific, Caribbean and Indian coasts. Recent reports indicate the emergence of CFP in other geographic areas, in particular in European coasts, of the Canary Islands (Spain) and Madeira (Portugal). A neuroblastoma cell line of murine origin (N2a) has been applied to assay different groups of neurotoxins, acting on voltage-gated sodium channel (VGSC) of excitable cells, N2a-MTT. The great potential of N2a-MTT as a sensitive tool for the CTXs screening is clearly recognized, notably because it allows the detection of these toxins at levels below recommended as security levels. However, the complexity of the matrix is a critical point on the application of N2a-MTT, which needs to be evaluated. The aim of this work is to provide recommendations for an implemented N2a-MTT method for CTXs determination in fish that avoids matrix effects, particularly those related to high lipid content.

Revisiting the Neuroblastoma Cell-Based Assay (CBA-N2a) for the Improved Detection of Marine Toxins Active on Voltage Gated Sodium Channels (VGSCs)

The neuroblastoma cell-based assay (CBA-N2a) is widely used for the detection of marine biotoxins in seafood products, yet a consensus protocol is still lacking. In this study, six key parameters of CBA-N2a were revisited: cell seeding densities, cell layer viability after 26 h growth, MTT incubation time, Ouabain and Veratridine treatment and solvent and matrix effects. A step-by-step protocol was defined identifying five viability controls for the validation of CBA-N2a results. Specific detection of two voltage gated sodium channel activators, pacific ciguatoxin (P-CTX3C) and brevetoxin (PbTx3) and two inhibitors, saxitoxin (STX) and decarbamoylsaxitoxin (dc-STX) was achieved, with EC50 values of 1.7 ± 0.35 pg/mL, 5.8 ± 0.9 ng/mL, 3 ± 0.5 ng/mL and 15.8 ± 3 ng/mL, respectively. When applied to the detection of ciguatoxin (CTX)-like toxicity in fish samples, limit of detection (LOD) and limit of quantification (LOQ) values were 0.031 ± 0.008 and 0.064 ± 0.016 ng P-CTX3C eq/g of flesh, respectively. Intra and inter-assays comparisons of viability controls, LOD, LOQ and toxicity in fish samples gave coefficients of variation (CVs) ranging from 3% to 29%. This improved test adaptable to either high throughput screening or composite toxicity estimation is a useful starting point for a standardization of the CBA-N2a in the field of marine toxin detection.

Addressing the Analytical Challenges for the Detection of Ciguatoxins Using an Electrochemical Biosensor

The importance of ciguatoxins (CTXs) in seafood safety and their emerging occurrence in locations far away from tropical areas highlight the need for simple and low-cost methods for the sensitive and rapid detection of these potent marine toxins to protect seafood consumers. Herein, an electrochemical immunosensor for the detection of CTXs is presented. A sandwich configuration is proposed, using magnetic beads (MBs) as immobilization supports for two capture antibodies, with their combination facilitating the detection of CTX1B, CTX3C, 54-deoxyCTX1B, and 51-hydroxyCTX3C. PolyHRP-streptavidin is used for the detection of the biotinylated detector antibody. Experimental conditions are first optimized using colorimetry, and these conditions are subsequently used for electrochemical detection on electrode arrays. Limits of detection at the pg/mL level are achieved for CTX1B and 51-hydroxyCTX3C. The applicability of the immunosensor to the analysis of fish samples is demonstrated, attaining detection of CTX1B at contents as low as 0.01 μg/kg and providing results in correlation with those obtained using mouse bioassay (MBA) and cell-based assay (CBA), and confirmed by liquid chromatography coupled to high-resolution mass spectrometry (LC-ESI-HRMS). This user-friendly bioanalytical tool for the rapid detection of CTXs can be used to mitigate ciguatera risk and contribute to the protection of consumer health.

Toxicity Characterisation of Gambierdiscus Species from the Canary Islands

In the last decade, several outbreaks of ciguatera fish poisoning (CFP) have been reported in the Canary Islands (central northeast Atlantic Ocean), confirming ciguatera as an emerging alimentary risk in this region. Five Gambierdiscus species, G. australes, G. excentricus, G. silvae, G. carolinianus and G. caribaeus, have been detected in macrophytes from this area and are known to produce the ciguatoxins (CTXs) that cause CFP. A characterization of the toxicity of these species is the first step in identifying locations in the Canary Islands at risk of CFP. Therefore, in this study the toxicity of 63 strains of these five Gambierdiscus species were analysed using the erythrocyte lysis assay to evaluate their maitotoxin (MTX) content. In addition, 20 of the strains were also analysed in a neuroblastoma Neuro-2a (N2a) cytotoxicity assay to determine their CTX-like toxicity. The results allowed the different species to be grouped according to their ratios of CTX-like and MTX-like toxicity. MTX-like toxicity was especially high in G. excentricus and G. australes but much lower in the other species and lowest in G. silvae. CTX-like toxicity was highest in G. excentricus, which produced the toxin in amounts ranging between 128.2 ± 25.68 and 510.6 ± 134.2 fg CTX1B equivalents (eq) cell⁻¹ (mean ± SD). In the other species, CTX concentrations were as follows: G. carolinianus (100.84 ± 18.05 fg CTX1B eq cell⁻¹), G. australes (31.1 ± 0.56 to 107.16 ± 21.88 fg CTX1B eq cell⁻¹), G. silvae (12.19 ± 0.62 to 76.79 ± 4.97 fg CTX1B eq cell⁻¹) and G. caribaeus (<LOD to 90.37 ± 15.89 fg CTX1B eq cell⁻¹). Unlike the similar CTX-like toxicity of G. australes and G. silvae strains from different locations, G. excentricus and G. caribaeus differed considerably according to the origin of the strain. These differences emphasise the importance of species identification to assess the regional risk of CFP.

Ciguatera Fish Poisoning: The Risk from an Aotearoa/New Zealand Perspective

Gambierdiscus and Fukuyoa species have been identified in Aotearoa/New Zealand's coastal waters and G. polynesiensis, a known producer of ciguatoxins, has been isolated from Rangitāhua/Kermadec Islands (a New Zealand territory). The warming of the Tasman Sea and the waters around New Zealand's northern subtropical coastline heighten the risk of Gambierdiscus proliferating in New Zealand. If this occurs, the risk of ciguatera fish poisoning due to consumption of locally caught fish will increase. Research, including the development and testing of sampling methods, molecular assays, and chemical and toxicity tests, will continue. Reliable monitoring strategies are important to manage and mitigate the risk posed by this emerging threat. The research approaches that have been made, many of which will continue, are summarised in this review.

Ciguatoxin Occurrence in Food-Web Components of a Cuban Coral Reef Ecosystem: Risk-Assessment Implications

In Cuba, ciguatera poisoning associated with fish consumption is the most commonly occurring non-bacterial seafood-borne illness. Risk management through fish market regulation has existed in Cuba for decades and consists of bans on selected species above a certain weight; however, the actual occurrence of ciguatoxins (CTXs) in seafood has never been verified. From this food safety risk management perspective, a study site locally known to be at risk for ciguatera was selected. Analysis of the epiphytic dinoflagellate community identified the microalga Gambierdiscus. Gambierdiscus species included six of the seven species known to be present in Cuba (G. caribaeus, G. belizeanus, G. carpenteri, G. carolinianus, G. silvae, and F. ruetzleri). CTX-like activity in invertebrates, herbivorous and carnivorous fishes were analyzed with a radioligand receptor-binding assay and, for selected samples, with the N2A cell cytotoxicity assay. CTX activity was found in 80% of the organisms sampled, with toxin values ranging from 2 to 8 ng CTX3C equivalents g⁻¹ tissue. Data analysis further confirmed CTXs trophic magnification. This study constitutes the first finding of CTX-like activity in marine organisms in Cuba and in herbivorous fish in the Caribbean. Elucidating the structure–activity relationship and toxicology of CTX from the Caribbean is needed before conclusions may be drawn about risk exposure in Cuba and the wider Caribbean.

Emerging Lyngbya wollei toxins: A new high resolution mass spectrometry method to elucidate a potential environmental threat

Mass spectrometric methods for the quantitative and qualitative analyses of algal biotoxins are often complicated by co-eluting compounds that present analytically as interferences. This issue is particularly critical for organic polyamines, where co-eluting materials can suppress the formation of cations during electrospray ionization. Here we present an extraction procedure designed specifically to overcome matrix-derived ion suppression of algal toxins in samples of Lyngbya wollei, a filamentous benthic algae known to produce several saxitoxin analogues. Lyngbya wollei samples were collected from a large, persistent harmful algal bloom in Lake Wateree, SC. Six known Lyngbya wollei-specific toxins (LWT1-6) were successfully resolved and quantified against saxitoxin using hydrophilic interaction liquid chromatography coupled with triple quadrupole and quadrupole time-of-flight mass spectrometry. The parent ions [M²⁺ - H⁺]⁺ were observed for LWTs 1-6 and the [M]²⁺ ion was observed for LWT5. High resolution mass spectra and unique fragmentation ions were obtained for LWTs 1-6. A dilution factor of 50 resulted in a linear calibration of saxitoxin in the algae matrix. Ion suppression was resolved by sample dilution, which led to linear, positive correlations between peak area and mass of the extracted sample (R² > 0.96). Optimized sample extraction method and instrument parameters are presented.

Emerging Marine Biotoxins in Seafood from European Coasts: Incidence and Analytical Challenges

The presence of emerging contaminants in food and the sources of the contamination are relevant issues in food safety. The impact of climate change on these contaminations is a topic widely debated; however, the consequences of climate change for the food system is not as deeply studied as other human and animal health and welfare issues. Projections of climate change in Europe have been evaluated through the EU Commission, and the impact on the marine environment is considered a priority issue. Marine biotoxins are produced by toxic microalgae and are natural contaminants of the marine environment. They are considered to be an important contaminant that needs to be evaluated. Their source is affected by oceanographic and environmental conditions; water temperature, sunlight, salinity, competing microorganisms, nutrients, and wind and current directions affect the growth and proliferation of microalgae. Although climate change should not be the only reason for this increase and other factors such as eutrophication, tourism, fishery activities, etc. could be considered, the influence of climate change has been observed through increased growth of dinoflagellates in areas where they have not been previously detected. An example of this is the recent emergence of ciguatera fish poisoning toxins, typically found in tropical or subtropical areas from the Pacific and Caribbean and in certain areas of the Atlantic Sea such as the Canary Islands (Spain) and Madeira (Portugal). In addition, the recent findings of the presence of tetrodotoxins, typically found in certain areas of the Pacific, are emerging in the EU and contaminating not only the fish species where these toxins had been found before but also bivalve mollusks. The emergence of these marine biotoxins in the EU is a reason for concern in the EU, and for this reason, the risk evaluation and characterization of these toxins are considered a priority for the European Food Safety Authorities (EFSA), which also emphasize the search for occurrence data using reliable and efficient analytical methods.

An Attempt to Characterize the Ciguatoxin Profile in Seriola fasciata Causing Ciguatera Fish Poisoning in Macaronesia

Ciguatera Fish Poisoning is a worldwide concern caused by the consumption of fish contaminated with ciguatoxins not only in endemic regions in the Pacific Ocean or the Caribbean Sea but also in emerging areas of Macaronesia on the eastern Atlantic. The recent emergence of these toxins in other coastal areas worldwide, prompted the need for the characterization of the risk in these areas. This Ciguatera Fish Poisoning risk has been recently identified as a potential threat in subtropical areas of the Atlantic coast and scientific efforts are being focused in the identification and confirmation of the toxins involved in this potential risk. Neuroblastoma cell assay has been widely used for the evaluation of the toxicity in several marine biotoxin groups, and found to be a very useful tool for toxicity screening. LC-MS/MS has been also used for confirmatory purposes although the main limitation of the advances on LC-MS/MS development is due to commercial unavailability of reference materials and hampers method implementation and validation or even confirmation of the ciguatoxins (CTXs) responsible for the toxic profiles. While neuroblastoma cell assay (N2a) is typically used for toxicity screening as mentioned above, being necessary to confirm this N2a toxicity by LC-MS/MS, this study is designed using N2a as a tool to confirm the toxicity of the fractions obtained corresponding to potential CTXs analogues according to the analysis by LC-MS/MS. With this aim, an amberjack sample (Seriola fasciata) from Selvagen Islads (Portugal) and implicated in Ciguatera Fish Poisoning was analyzed by LC-MS/MS and Caribbean Ciguatoxins were found to be mainly responsible for the toxicity. N2a was used in this work as a tool to help in the confirmation of the toxicity of fractions obtained by HPLC. Caribbean Ciguatoxin-1 was found as the main analogue responsible for the N2a toxicity while three Caribbean Ciguatoxin-1 (C-CTX1) metabolites which contribute to the total toxicity were also identified.

The Incidence of Marine Toxins and the Associated Seafood Poisoning Episodes in the African Countries of the Indian Ocean and the Red Sea

The occurrence of Harmful Algal Blooms (HABs) and bacteria can be one of the great threats to public health due to their ability to produce marine toxins (MTs). The most reported MTs include paralytic shellfish toxins (PSTs), amnesic shellfish toxins (ASTs), diarrheic shellfish toxins (DSTs), cyclic imines (CIs), ciguatoxins (CTXs), azaspiracids (AZTs), palytoxin (PlTXs), tetrodotoxins (TTXs) and their analogs, some of them leading to fatal outcomes. MTs have been reported in several marine organisms causing human poisoning incidents since these organisms constitute the food basis of coastal human populations. In African countries of the Indian Ocean and the Red Sea, to date, only South Africa has a specific monitoring program for MTs and some other countries count only with respect to centers of seafood poisoning control. Therefore, the aim of this review is to evaluate the occurrence of MTs and associated poisoning episodes as a contribution to public health and monitoring programs as an MT risk assessment tool for this geographic region.

Detection of pacific ciguatoxins using liquid chromatography coupled to either low or high resolution mass spectrometry (LC-MS/MS)

Ciguatera Fish Poisoning (CFP) is primarily caused by consumption of tropical and sub-tropical fish contaminated by Ciguatoxins (CTXs). These lipid-soluble, polyether neurotoxins are produced by dinoflagellates in the genera Gambierdiscus and Fukuyoa. While there is no regulatory level in Europe for CTXs, the European Food Safety Authority (EFSA) adopted the United States guidance level of 0.01 μg P-CTX1B eq.kg^-1 of fish. This limit is extremely low and requires significant improvement in the detection of CTXs. In this study, we compared analytical protocols based on liquid chromatography coupled to tandem low or high resolution mass spectrometry (LC-LRMS or HRMS) to find the best conditions for sensitivity and/or selectivity. Different approaches such as LC conditions, ion choice and acquisition modes, were evaluated to detect the Pacific-ciguatoxins (P-CTXs) on a triple quadrupole (API4000 Qtrap, Sciex) or a quadrupole time of flight (QTOF 6550, Agilent Technologies) spectrometer. Moreover, matrix effects were calculated using matrix-matched calibration solutions of P-CTX1B and P-CTX3C prepared in purified fish extract. Subsequently, the method performance was assessed on naturally contaminated samples of seafood and phytoplankton. With LRMS, the ammoniated adduct ion used as a precursor ion showed an advantage for selectivity through confirmatory transitions, without affecting signal-to-noise ratios, and hence limits of detection (LODs). As also reported by some studies in the literature, methanol-based mobile phase gave better selectivity and sensitivity for the detection of P-CTXs. While the LOD for P-CTX1B and P-CTX3C met the EFSA recommendation level when using LRMS, the findings suggested careful evaluation of instrumental parameters for determination of CTXs. LODs were significantly higher for HRMS, which currently results in the need for a significantly higher sample intake. Nevertheless, HRMS allowed for the identification of artefacts and may allow for improved confirmation of the identity of P-CTXs analogues. Consequently, LRMS and HRMS are considered complementary to ensure adequate quantitation and identification of P-CTXs.

Experimental evidence of dietary ciguatoxin accumulation in an herbivorous coral reef fish

Ciguatoxins (CTXs) are potent algal toxins that cause widespread ciguatera poisoning and are found ubiquitously in coral reef food webs. Here we developed an environmentally-relevant, experimental model of CTX trophic transfer involving dietary exposure of herbivorous fish to the CTX-producing microalgae Gambierdiscus polynesiensis. Juvenile Naso brevirostris were fed a gel-food embedded with microalgae for 16 weeks (89 cells g^-1 fish daily, 0.4 μg CTX3C equiv kg^-1 fish). CTXs in muscle tissue were detectable after 2 weeks at levels above the threshold for human intoxication (1.2 ± 0.2 μg CTX3C equiv kg^-1). Although tissue CTX concentrations stabilized after 8 weeks (∼3 ± 0.5 μg CTX3C equiv kg^-1), muscle toxin burden (total μg CTX in muscle tissue) continued to increase linearly through the end of the experiment (16 weeks). Toxin accumulation was therefore continuous, yet masked by somatic growth dilution. The observed CTX concentrations, accumulation rates, and general absence of behavioural signs of intoxication are consistent with field observations and indicate that this method of dietary exposure may be used to develop predictive models of tissue-specific CTX uptake, metabolism and depuration. Results also imply that slow-growing fish may accumulate higher CTX flesh concentrations than fast-growing fish, which has important implications for global seafood safety.

Tissue Distribution and Elimination of Ciguatoxins in Tridacna maxima (Tridacnidae, Bivalvia) Fed Gambierdiscus polynesiensis

Ciguatera is a foodborne disease caused by the consumption of seafood contaminated with ciguatoxins (CTXs). Ciguatera-like poisoning events involving giant clams (Tridacna maxima) are reported occasionally from Pacific islands communities. The present study aimed at providing insights into CTXs tissue distribution and detoxification rate in giant clams exposed to toxic cells of Gambierdiscus polynesiensis, in the framework of seafood safety assessment. In a first experiment, three groups of tissue (viscera, flesh and mantle) were dissected from exposed individuals, and analyzed for their toxicity using the neuroblastoma cell-based assay (CBA-N2a) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. The viscera, flesh, and mantle were shown to retain 65%, 25%, and 10% of the total toxin burden, respectively. All tissues reached levels above the safety limit recommended for human consumption, suggesting that evisceration alone, a practice widely used among local populations, is not enough to ensure seafood safety. In a second experiment, the toxin content in contaminated giant clams was followed at different time points (0, 2, 4, and 6 days post-exposure). Observations suggest that no toxin elimination is visible in T. maxima throughout 6 days of detoxification.

Ciguatoxins activate the Calcineurin signalling pathway in Yeasts: Potential for development of an alternative detection tool?

Ciguatoxins (CTXs) are lipid-soluble polyether compounds produced by dinoflagellates from the genus Gambierdiscus spp. typically found in tropical and subtropical zones. This endemic area is however rapidly expanding due to environmental perturbations, and both toxic Gambierdiscus spp. and ciguatoxic fishes have been recently identified in the North Atlantic Ocean (Madeira and Canary islands) and Mediterranean Sea. Ciguatoxins bind to Voltage Gated Sodium Channels on the membranes of sensory neurons, causing Ciguatera Fish Poisoning (CFP) in humans, a disease characterized by a complex array of gastrointestinal, neurological, neuropsychological, and cardiovascular symptoms. Although CFP is the most frequently reported non bacterial food-borne poisoning worldwide, there is still no simple and quick way of detecting CTXs in contaminated samples. In the prospect to engineer rapid and easy-to-use CTXs live cells-based tests, we have studied the effects of CTXs on the yeast Saccharomyces cerevisiae, a unicellular model which displays a remarkable conservation of cellular signalling pathways with higher eukaryotes. Taking advantage of this high level of conservation, yeast strains have been genetically modified to encode specific transcriptional reporters responding to CTXs exposure. These yeast strains were further exposed to different concentrations of either purified CTX or micro-algal extracts containing CTXs. Our data establish that CTXs are not cytotoxic to yeast cells even at concentrations as high as 1μM, and cause an increase in the level of free intracellular calcium in yeast cells. Concomitantly, a dose-dependent activation of the calcineurin signalling pathway is observed, as assessed by measuring the activity of specific transcriptional reporters in the engineered yeast strains. These findings offer promising prospects regarding the potential development of a yeast cells-based test that could supplement or, in some instances, replace current methods for the routine detection of CTXs in seafood products.