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

Metabolic Profiling of SH-SY5Y and Neuro2A Cells in Relation to Fetal Calf Serum (FCS) Concentration in Culture Media

The neuroblastoma cell lines SH-SY5Y and Neuro2A are commonly utilized models in neurobiological research. DMEM supplemented with different nutrients and 5-10% Fetal Calf Serum (FCS) is typically used for culturing these cell lines. During special treatments, a reduced FCS content is often deployed to reduce cellular proliferation or the content of bioactive compounds. The impact of the reduction of FCS in culture media on the metabolic profile of SH-SY5Y and Neuro2A cells is currently unknown. Using an Amplex Red Assay, this study showed that the consumption of L-glutamine decreased after FCS reduction. Glucose and pyruvate consumption increased in both cell lines after the reduction of FCS. Thus, lactate production also increased with reduced FCS concentration. The reduction of FCS in the cell culture medium resulted in a reduced aerobic ATP production for SH-SY5Y cells and a complete shut down of aerobic ATP production for Neuro2A cells, measured using the Seahorse XF Real-Time ATP Rate Assay. Utilizing the Seahorse XF Glutamine Oxidation Stress Test, Neuro2A cells showed an increased utilization of L-glutamine oxidation after reduction of FCS. These results indicate that changes in FCS concentration in culture media have an impact on the different energy production strategies of SH-SY5Y and Neuro2A cells which must be considered when planning special treatments.

Establishing a Receptor Binding Assay for Ciguatoxins: Challenges, Assay Performance and Application

Ciguatera, a global issue, lacks adequate capacity for ciguatoxin analysis in most affected countries. The Caribbean region, known for its endemic ciguatera and being home to a majority of the global small island developing states, particularly needs established methods for ciguatoxin detection in seafood and the environment. The radioligand receptor binding assay (r-RBA) is among the in vitro bioassays currently used for ciguatoxin analysis; however, similarly to the other chemical-based or bioassays that have been developed, it faces challenges due to limited standards and interlaboratory comparisons. This work presents a single laboratory validation of an r-RBA developed in a Cuban laboratory while characterizing the performance of the liquid scintillation counter instrument as a key external parameter. The results obtained show the assay is precise, accurate and robust, confirming its potential as a routine screening method for the detection and quantification of ciguatoxins. The new method will aid in identifying high-risk ciguatoxic fish in Cuba and the Caribbean region, supporting monitoring and scientific management of ciguatera and the development of early warning systems to enhance food safety and food security, and promote fair trade fisheries.

Synergistic Effect of Brevetoxin BTX-3 and Ciguatoxin CTX3C in Human Voltage-Gated Nav1.6 Sodium Channels

Emerging marine biotoxins such as ciguatoxins and brevetoxins have been widely and independently studied as food pollutants. Their maximum levels in food components were set without considering their possible synergistic effects as consequence of their coexistence in seafood and their action at the same cellular target. The absolute lack of data and regulations of the possible combined effects that both marine biotoxins may have raised the need to analyze their direct in vitro effects using electrophysiology techniques. The results presented in this study indicate that ciguatoxins and brevetoxins had a synergistic effect on human Nav1.6 voltage-gated sodium channels by hyperpolarizing their activation and inactivation states. The results presented here indicate that brevetoxin 3 (BTX-3) acts as partial agonist of human sodium channels, while ciguatoxin 3C (CTX3C) was a full agonist, explaining the differences in the effect of each toxin in the channel. Therefore, this work sets the cellular basis to further apply this type of studies to other food toxicants that may act synergistically and thus implement the corresponding regulatory limits considering their coexistence and the risks to human and animal health derived from it.

Mouse N2a Neuroblastoma Assay: Uncertainties and Comparison with Alternative Cell-Based Assays for Ciguatoxin Detection

The growing concern about ciguatera fish poisoning (CF) due to the expansion of the microorganisms producing ciguatoxins (CTXs) increased the need to develop a reliable and fast method for ciguatoxin detection to guarantee food safety. Cytotoxicity assay on the N2a cells sensitized with ouabain (O) and veratridine (V) is routinely used in ciguatoxin detection; however, this method has not been standardized yet. This study demonstrated the low availability of sodium channels in the N2a cells, the great O/V damage to the cells and the cell detachment when the cell viability is evaluated by the classical cytotoxicity assay and confirmed the absence of toxic effects caused by CTXs alone when using the methods that do not require medium removal such as lactate dehydrogenase (LDH) and Alamar blue assays. Different cell lines were evaluated as alternatives, such as human neuroblastoma, which was not suitable for the CTX detection due to the greater sensitivity to O/V and low availability of sodium channels. However, the HEK293 Nav cell line expressing the α1.6 subunit of sodium channels was sensitive to the ciguatoxin without the sensitization with O/V due to its expression of sodium channels. In the case of sensitizing the cells with O/V, it was possible to detect the presence of the ciguatoxin by the classical cytotoxicity MTT method at concentrations as low as 0.0001 nM CTX3C, providing an alternative cell line for the detection of compounds that act on the sodium channels.

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.

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.

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.

Gambierone and Sodium Channel Specific Bioactivity Are Associated with the Extracellular Metabolite Pool of the Marine Dinoflagellate Coolia palmyrensis

Tropical epibenthic dinoflagellate communities produce a plethora of bioactive secondary metabolites, including the toxins ciguatoxins (CTXs) and potentially gambierones, that can contaminate fishes, leading to ciguatera poisoning (CP) when consumed by humans. Many studies have assessed the cellular toxicity of causative dinoflagellate species to better understand the dynamics of CP outbreaks. However, few studies have explored extracellular toxin pools which may also enter the food web, including through alternative and unanticipated routes of exposure. Additionally, the extracellular exhibition of toxins would suggest an ecological function and may prove important to the ecology of the CP-associated dinoflagellate species. In this study, semi-purified extracts obtained from the media of a Coolia palmyrensis strain (DISL57) isolated from the U.S. Virgin Islands were assessed for bioactivity via a sodium channel specific mouse neuroblastoma cell viability assay and associated metabolites evaluated by targeted and non-targeted liquid chromatography tandem and high-resolution mass spectrometry. We found that extracts of C. palmyrensis media exhibit both veratrine enhancing bioactivity and non-specific bioactivity. LC-HR-MS analysis of the same extract fractions identified gambierone and multiple undescribed peaks with mass spectral characteristics suggestive of structural similarities to polyether compounds. These findings implicate C. palmyrensis as a potential contributor to CP and highlight extracellular toxin pools as a potentially significant source of toxins that may enter the food web through multiple exposure pathways.

Methodological advances in the detection of biotoxins and pathogens affecting production and consumption of bivalve molluscs in a changing environment

The production, harvesting and safe consumption of bivalve molluscs can be disrupted by biological hazards that can be divided into three categories: (1) biotoxins produced by naturally occurring phytoplankton that are bioaccumulated by bivalves during filter-feeding, (2) human pathogens also bioaccumulated by bivalves and (3) bivalve pathogens responsible for disease outbreaks. Environmental changes caused by human activities, such as climate change, can further aggravate these challenges. Early detection and accurate quantification of these hazards are key to implementing measures to mitigate their impact on production and safeguard consumers. This review summarises the methods currently used and the technological advances in the detection of biological hazards affecting bivalves, for the screening of known hazards and discovery of new ones.

Facile Synthesis of Molecularly Imprinted Ratiometric Fluorescence Sensor for Ciguatoxin P-CTX-3C Detection in Fish

Ciguatoxin (CTX) detection methods are essential due to the serious hazard that bioaccumulation in fish and transmission along the food chain poses to human health. We report the rapid and simple development of a dual-emitting, molecularly imprinted, ratiometric fluorescence sensor (MIPs@BCDs/RCDs@SiO₂) to detect ciguatoxin P-CTX-3C with high sensitivity and selectivity. The sensor was fabricated via sol–gel polymerization using monensin as the fragmentary dummy template molecule, blue carbon dots (BCDs) as the response signal, and red carbon dots (RCDs) as the reference signal. The fluorescence emission of BCDs was selectively quenched in the presence of P-CTX-3C, leading to a favorable linear correlation between the fluorescence intensity ratio (I₄₄₀/I₆₇₅) and the P-CTX-3C concentration in the range of 0.001–1 ng/mL with a lower detection limit of 3.3 × 10⁻⁴ ng/mL. According to LC-MS measurement results, the proposed sensor can rapidly detect ciguatoxin P-CTX-3C in coral reef fish samples with satisfactory recoveries and standard deviations. This study provides a promising strategy for rapid trace analysis of marine toxins and other macromolecular pollutants in complex matrices.

Anti-cancer activity of sustained release capsaicin formulations

Capsaicin (trans-8-methyl-N-vanillyl-6-noneamide) is a hydrophobic, lipophilic vanilloid phytochemical abundantly found in chili peppers and pepper extracts. Several convergent studies show that capsaicin displays robust cancer activity, suppressing the growth, angiogenesis and metastasis of several human cancers. Despite its potent cancer-suppressing activity, the clinical applications of capsaicin as a viable anti-cancer drug have remained problematic due to its poor bioavailability and aqueous solubility properties. In addition, the administration of capsaicin is associated with adverse side effects like gastrointestinal cramps, stomach pain, nausea and diarrhea and vomiting. All these hurdles may be circumvented by encapsulation of capsaicin in sustained release drug delivery systems. Most of the capsaicin-based the sustained release drugs have been tested for their pain-relieving activity. Only a few of these formulations have been investigated as anti-cancer agents. The present review describes the physicochemical properties, bioavailability, and anti-cancer activity of capsaicin-sustained release agents. The asset of such continuous release capsaicin formulations is that they display better solubility, stability, bioavailability, and growth-suppressive activity than the free drug. The encapsulation of capsaicin in sustained release carriers minimizes the adverse side effects of capsaicin. In summary, these capsaicin-based sustained release drug delivery systems have the potential to function as novel chemotherapies, unique diagnostic imaging probes and innovative chemosensitization agents in human cancers.

Geographical distribution, molecular and toxin diversity of the dinoflagellate species Gambierdiscus honu in the Pacific region

An increase in cases of ciguatera poisoning (CP) and expansion of the causative species in the South Pacific region highlight the need for baseline data on toxic microalgal species to help identify new areas of risk and manage known hot spots. Gambierdiscus honu is a toxin producing and potential CP causing dinoflagellate species, first described in 2017. Currently no high-resolution geographical distribution, intraspecific genetic variation or toxin production diversity data is available for G. honu. This research aimed to further characterize G. honu by investigating its distribution using species-specific real-time polymerase chain reaction assays at 25 sites in an area spanning ∼8000 km of the Coral Sea/Pacific Ocean, and assessing intraspecific genetic variation, toxicity and toxin production of isolated strains. Assessment of genetic variation of the partial rRNA operon of isolates demonstrated no significant intraspecific population structure, in addition to a lack of adherence to isolation by distance (IBD) model of evolution. The detected distribution of G. honu in the Pacific region was within the expected tropical to temperate latitudinal ranges of 10° to -30° and extended from Australia to French Polynesia. In the lipophilic fractions, the neuroblastoma cell-based assay (CBA-N2a) showed no ciguatoxin (CTX)-like activity for nine of the 10 isolates, and an atypical pattern for CAWD233 isolate which showed cytotoxic activity in OV- and OV+ conditions. In the same way, liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis confirmed no Pacific-CTXs (CTX-3B, CTX-3C, CTX-4A, CTX-4B) were produced by the ten strains. The CBA-N2a assessment of the hydrophilic fractions showed moderate to high cytotoxicity in both OV- and OV+ condition for all the strains showing a cytotoxic profile similar to that of gambierone. Indeed, this study is the first to show the cytotoxic activity of gambierone on mouse neuroblastoma cells while no cytotoxicity was observed when 44-MG was analysed at the same concentrations using the CBA-N2a. Analysis of the hydrophilic via LC-MS/MS confirmed production of gambierone in all isolates, ranging from 2.1 to 38.1 pg/cell, with 44-methylgambierone (44-MG) also produced by eight of the isolates, ranging from 0.3 to 42.9 pg/cell. No maitotoxin-1 was detected in any of the isolates. Classification of the G. honu strains according to the quantities of gambierone produced aligned with the classification of their cytotoxicity using the CBA-N2a. Finally, no maitotoxin-1 (MTX) was detected in any of the isolates. This study shows G. honu is widely distributed within the Pacific region with no significant intraspecific population structure present. This aligns with the view of microalgal populations as global metapopulations, however more in-depth assessment with other genetic markers could detect further structure. Toxicity diversity across 10 isolates assessed did not display any geographical patterns.

Cytotoxic and Hemolytic Activities of Extracts of the Fish Parasite Dinoflagellate Amyloodinium ocellatum

The dinoflagellate Amyloodinium ocellatum is the etiological agent of a parasitic disease named amyloodiniosis. Mortalities of diseased fish are usually attributed to anoxia, osmoregulatory impairment, or opportunistic bacterial infections. Nevertheless, the phylogenetic proximity of A. ocellatum to a group of toxin-producing dinoflagellates from Pfiesteria, Parvodinium and Paulsenella genera suggests that it may produce toxin-like compounds, adding a new dimension to the possible cause of mortalities in A. ocellatum outbreaks. To address this question, extracts prepared from different life stages of the parasite were tested in vitro for cytotoxic effects using two cell lines derived from branchial arches (ABSa15) and the caudal fin (CFSa1) of the gilthead seabream (Sparus aurata), and for hemolytic effects using erythrocytes purified from the blood of gilthead seabream juveniles. Cytotoxicity and a strong hemolytic effect, similar to those observed for Karlodinium toxins, were observed for the less polar extracts of the parasitic stage (trophont). A similar trend was observed for the less polar extracts of the infective stage (dinospores), although cell viability was only affected in the ABSa15 line. These results suggest that A. ocellatum produces tissue-specific toxic compounds that may have a role in the attachment of the dinospores’ and trophonts’ feeding process.

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.

Comparative Study on the Performance of Three Detection Methods for the Quantification of Pacific Ciguatoxins in French Polynesian Strains of Gambierdiscus polynesiensis

Gambierdiscus and Fukuyoa dinoflagellates produce a suite of secondary metabolites, including ciguatoxins (CTXs), which bioaccumulate and are further biotransformed in fish and marine invertebrates, causing ciguatera poisoning when consumed by humans. This study is the first to compare the performance of the fluorescent receptor binding assay (fRBA), neuroblastoma cell-based assay (CBA-N2a), and liquid chromatography tandem mass spectrometry (LC-MS/MS) for the quantitative estimation of CTX contents in 30 samples, obtained from four French Polynesian strains of Gambierdiscus polynesiensis. fRBA was applied to Gambierdiscus matrix for the first time, and several parameters of the fRBA protocol were refined. Following liquid/liquid partitioning to separate CTXs from other algal compounds, the variability of CTX contents was estimated using these three methods in three independent experiments. All three assays were significantly correlated with each other, with the highest correlation coefficient (r2 = 0.841) found between fRBA and LC-MS/MS. The CBA-N2a was more sensitive than LC-MS/MS and fRBA, with all assays showing good repeatability. The combined use of fRBA and/or CBA-N2a for screening purposes and LC-MS/MS for confirmation purposes allows for efficient CTX evaluation in Gambierdiscus. These findings, which support future collaborative studies for the inter-laboratory validation of CTX detection methods, will help improve ciguatera risk assessment and management.

Evaluating Age and Growth Relationship to Ciguatoxicity in Five Coral Reef Fish Species from French Polynesia

Ciguatera poisoning (CP) results from the consumption of coral reef fish or marine invertebrates contaminated with potent marine polyether compounds, namely ciguatoxins. In French Polynesia, 220 fish specimens belonging to parrotfish (Chlorurus microrhinos, Scarus forsteni, and Scarus ghobban), surgeonfish (Naso lituratus), and groupers (Epinephelus polyphekadion) were collected from two sites with contrasted risk of CP, i.e., Kaukura Atoll versus Mangareva Island. Fish age and growth were assessed from otoliths’ yearly increments and their ciguatoxic status (negative, suspect, or positive) was evaluated by neuroblastoma cell-based assay. Using permutational multivariate analyses of variance, no significant differences in size and weight were found between negative and suspect specimens while positive specimens showed significantly greater size and weight particularly for E. polyphekadion and S. ghobban. However, eating small or low-weight specimens remains risky due to the high variability in size and weight of positive fish. Overall, no relationship could be evidenced between fish ciguatoxicity and age and growth characteristics. In conclusion, size, weight, age, and growth are not reliable determinants of fish ciguatoxicity which appears to be rather species and/or site-specific, although larger fish pose an increased risk of poisoning. Such findings have important implications in current CP risk management programs.

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.

Deep-Water Fish Are Potential Vectors of Ciguatera Poisoning in the Gambier Islands, French Polynesia

Ciguatera poisoning (CP) cases linked to the consumption of deep-water fish occurred in 2003 in the Gambier Islands (French Polynesia). In 2004, on the request of two local fishermen, the presence of ciguatoxins (CTXs) was examined in part of their fish catches, i.e., 22 specimens representing five deep-water fish species. Using the radioactive receptor binding assay (rRBA) and mouse bioassay (MBA), significant CTX levels were detected in seven deep-water specimens in Lutjanidae, Serranidae, and Bramidae families. Following additional purification steps on the remaining liposoluble fractions for 13 of these samples (kept at -20 °C), these latter were reanalyzed in 2018 with improved protocols of the neuroblastoma cell-based assay (CBA-N2a) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Using the CBA-N2a, the highest CTX-like content found in a specimen of Eumegistus illustris (Bramidae) was 2.94 ± 0.27 µg CTX1B eq. kg^-1. Its toxin profile consisted of 52-epi-54-deoxyCTX1B, CTX1B, and 54-deoxyCTX1B, as assessed by LC-MS/MS. This is the first study demonstrating that deep-water fish are potential ciguatera vectors and highlighting the importance of a systematic monitoring of CTXs in all exploited fish species, especially in ciguatera hotspots, including deep-water fish, which constitute a significant portion of the commercial deep-sea fisheries in many Asian-Pacific countries.

Depuration Kinetics and Growth Dilution of Caribbean Ciguatoxin in the Omnivore Lagodon rhomboides: Implications for Trophic Transfer and Ciguatera Risk

Modeling ciguatoxin (CTX) trophic transfer in marine food webs has significant implications for the management of ciguatera poisoning, a circumtropical disease caused by human consumption of CTX-contaminated seafood. Current models associated with CP risk rely on modeling abundance/presence of CTX-producing epi-benthic dinoflagellates, e.g., Gambierdiscus spp., and are based on studies showing that toxin production is site specific and occurs in pulses driven by environmental factors. However, food web models are not yet developed and require parameterizing the CTX exposure cascade in fish which has been traditionally approached through top-down assessment of CTX loads in wild-caught fish. The primary goal of this study was to provide critical knowledge on the kinetics of C-CTX-1 bioaccumulation and depuration in the marine omnivore Lagodon rhomboides. We performed a two-phase, 17 week CTX feeding trial in L. rhomboides where fish were given either a formulated C-CTX-1 (n = 40) or control feed (n = 37) for 20 days, and then switched to a non-toxic diet for up to 14 weeks. Fish were randomly sampled through time with whole muscle, liver, and other pooled viscera dissected for toxin analysis by a sodium channel-dependent MTT-based mouse neuroblastoma (N2a) assay. The CTX levels measured in all tissues increased with time during the exposure period (days 1 to 20), but a decrease in CTX-specific toxicity with depuration time only occurred in viscera extracts. By the end of the depuration, muscle, liver, and viscera samples had mean toxin concentrations of 189%, 128%, and 42%, respectively, compared to fish sampled at the start of the depuration phase. However, a one-compartment model analysis of combined tissues showed total concentration declined to 56%, resulting in an approximate half-life of 97 d (R² = 0.43). Further, applying growth dilution correction models to the overall concentration found that growth was a major factor reducing C-CTX concentrations, and that the body burden was largely unchanged, causing pseudo-elimination and a half-life of 143-148 days (R² = 0.36). These data have important implications for food web CTX models and management of ciguatera poisoning in endemic regions where the frequency of environmental algal toxin pulses may be greater than the growth-corrected half-life of C-CTX in intermediate-trophic-level fish with high site fidelity.

Experimental Evidence of Ciguatoxin Accumulation and Depuration in Carnivorous Lionfish

Ciguatera poisoning is a food intoxication associated with the consumption of fish or shellfish contaminated, through trophic transfer, with ciguatoxins (CTXs). In this study, we developed an experimental model to assess the trophic transfer of CTXs from herbivorous parrotfish, Chlorurus microrhinos, to carnivorous lionfish, Pterois volitans. During a 6-week period, juvenile lionfish were fed naturally contaminated parrotfish fillets at a daily dose of 0.11 or 0.035 ng CTX3C equiv. g⁻¹, as measured by the radioligand-receptor binding assay (r-RBA) or neuroblastoma cell-based assay (CBA-N2a), respectively. During an additional 6-week depuration period, the remaining fish were fed a CTX-free diet. Using r-RBA, no CTXs were detectable in muscular tissues, whereas CTXs were measured in the livers of two out of nine fish sampled during exposure, and in four out of eight fish sampled during depuration. Timepoint pooled liver samples, as analyzed by CBA-N2a, confirmed the accumulation of CTXs in liver tissues, reaching 0.89 ng CTX3C equiv. g⁻¹ after 41 days of exposure, followed by slow toxin elimination, with 0.37 ng CTX3C equiv. g⁻¹ measured after the 6-week depuration. These preliminary results, which need to be pursued in adult lionfish, strengthen our knowledge on CTX transfer and kinetics along the food web.

Ciguatera Mini Review: 21st Century Environmental Challenges and the Interdisciplinary Research Efforts Rising to Meet Them

Globally, the livelihoods of over a billion people are affected by changes to marine ecosystems, both structurally and systematically. Resources and ecosystem services, provided by the marine environment, contribute nutrition, income, and health benefits for communities. One threat to these securities is ciguatera poisoning; worldwide, the most commonly reported non-bacterial seafood-related illness. Ciguatera is caused by the consumption of (primarily) finfish contaminated with ciguatoxins, potent neurotoxins produced by benthic single-cell microalgae. When consumed, ciguatoxins are biotransformed and can bioaccumulate throughout the food-web via complex pathways. Ciguatera-derived food insecurity is particularly extreme for small island-nations, where fear of intoxication can lead to fishing restrictions by region, species, or size. Exacerbating these complexities are anthropogenic or natural changes occurring in global marine habitats, e.g., climate change, greenhouse-gas induced physical oceanic changes, overfishing, invasive species, and even the international seafood trade. Here we provide an overview of the challenges and opportunities of the 21st century regarding the many facets of ciguatera, including the complex nature of this illness, the biological/environmental factors affecting the causative organisms, their toxins, vectors, detection methods, human-health oriented responses, and ultimately an outlook towards the future. Ciguatera research efforts face many social and environmental challenges this century. However, several future-oriented goals are within reach, including digital solutions for seafood supply chains, identifying novel compounds and methods with the potential for advanced diagnostics, treatments, and prediction capabilities. The advances described herein provide confidence that the tools are now available to answer many of the remaining questions surrounding ciguatera and therefore protection measures can become more accurate and routine.

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.

Marine invertebrate interactions with Harmful Algal Blooms - Implications for One Health

Harmful Algal Blooms (HAB) are natural atypical proliferations of micro or macro algae in either marine or freshwater environments which have significant impacts on human, animal and ecosystem health. The causative HAB organisms are primarily dinoflagellates and diatoms in marine and cyanobacteria within freshwater ecosystems. Several hundred species of HABs, most commonly marine dinoflagellates affect animal and ecosystem health either directly through physical, chemical or biological impacts on surrounding organisms or indirectly through production of algal toxins which transfer through lower-level trophic organisms to higher level predators. Traditionally, a major focus of HABs has concerned their natural production of toxins which bioaccumulate in filter-feeding invertebrates, which with subsequent trophic transfer and biomagnification cause issues throughout the food web, including the human health of seafood consumers. Whilst in many regions of the world, regulations, monitoring and risk management strategies help mitigate against the impacts from HAB/invertebrate toxins upon human health, there is ever-expanding evidence describing enormous impacts upon invertebrate health, as well as the health of higher trophic level organisms and marine ecosystems. This paper provides an overview of HABs and their relationships with aquatic invertebrates, together with a review of their combined impacts on animal, human and ecosystem health. With HAB/invertebrate outbreaks expected in some regions at higher frequency and intensity in the coming decades, we discuss the needs for new science, multi-disciplinary assessment and communication which will be essential for ensuring a continued increasing supply of aquaculture foodstuffs for further generations.

Evidence for the Range Expansion of Ciguatera in French Polynesia: A Revisit of the 2009 Mass-Poisoning Outbreak in Rapa Island (Australes Archipelago)

Ciguatera poisoning (CP) results from the consumption of seafood contaminated with ciguatoxins (CTXs). This disease is highly prevalent in French Polynesia with several well-identified hotspots. Rapa Island, the southernmost inhabited island in the country, was reportedly free of CP until 2007. This study describes the integrated approach used to investigate the etiology of a fatal mass-poisoning outbreak that occurred in Rapa in 2009. Symptoms reported in patients were evocative of ciguatera. Several Gambierdiscus field samples collected from benthic assemblages tested positive by the receptor binding assay (RBA). Additionally, the toxicity screening of ≈250 fish by RBA indicated ≈78% of fish could contain CTXs. The presence of CTXs in fish was confirmed by liquid chromatography tandem mass spectrometry (LC-MS/MS). The potential link between climate change and this range expansion of ciguatera to a subtropical locale of French Polynesia was also examined based on the analysis of temperature time-series data. Results are indicative of a global warming trend in Rapa area. A five-fold reduction in incidence rates was observed between 2009 and 2012, which was due in part to self-regulating behavior among individuals (avoidance of particular fish species and areas). Such observations underscore the prominent role played by community outreach in ciguatera risk management.

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.

Assessment of the Chemical Diversity and Potential Toxicity of Benthic Cyanobacterial Blooms in the Lagoon of Moorea Island (French Polynesia)

In the last decades, an apparent increase in the frequency of benthic cyanobacterial blooms has occurred in coral reefs and tropical lagoons, possibly in part because of global change and anthropogenic activities. In the frame of the survey of marine benthic cyanobacteria proliferating in the lagoon of Moorea Island (French Polynesia), 15 blooms were collected, mainly involving three species—Anabaena sp.1, Lyngbya majuscula and Hydrocoleum majus-B. Their chemical fingerprints, obtained through high performance liquid chromatography combined with UV detection and mass spectrometry (HPLC-UV-MS) analyses, revealed a high extent of species-specificity. The chemical profile of Anabaena sp.1 was characterized by three major cyclic lipopeptides of the laxaphycin family, whereas the one of L. majuscula was characterized by a complex mixture including tiahuramides, trungapeptins and serinol-derived malyngamides. Toxicity screening analyses conducted on these cyanobacterial samples using Artemia salina and mouse neuroblastoma cell-based (CBA-N2a) cytotoxic assays failed to show any toxicity to a degree that would merit risk assessment with regard to public health. However, the apparently increasing presence of blooms of Lyngbya, Hydrocoleum, Anabaena or other benthic cyanobacteria on coral reefs in French Polynesia encourages the implementation of ad hoc monitoring programs for the surveillance of their proliferation and potential assessment of associated hazards.