Suitability of the Neuro-2a cell line for the detection of palytoxin and analogues (neurotoxic phycotoxins)

A genetically engineered neuronal membrane-based nanotoxoid elicits protective immunity against neurotoxins

Given their dangerous effects on the nervous system, neurotoxins represent a significant threat to public health. Various therapeutic approaches, including chelating agents, receptor decoys, and toxin-neutralizing antibodies, have been explored. While prophylactic vaccines are desirable, it is oftentimes difficult to effectively balance their safety and efficacy given the highly dangerous nature of neurotoxins. To address this, we report here on a nanovaccine against neurotoxins that leverages the detoxifying properties of cell membrane-coated nanoparticles. A genetically modified cell line with constitutive overexpression of the α7 nicotinic acetylcholine receptor is developed as a membrane source to generate biomimetic nanoparticles that can effectively and irreversibly bind to α-bungarotoxin, a model neurotoxin. This abrogates the biological activity of the toxin, enabling the resulting nanotoxoid to be safely delivered into the body and processed by the immune system. When co-administered with an immunological adjuvant, a strong humoral response against α-bungarotoxin is generated that protects vaccinated mice against a lethal dose of the toxin. Overall, this work highlights the potential of using genetic modification strategies to develop nanotoxoid formulations against various biological threats.

Toxic responses of metabolites produced by Ostreopsis cf. ovata on a panel of cell types

Blooms of the dinoflagellate Ostreopsis cf. ovata are regularly associated with human intoxications that are attributed to ovatoxins (OVTXs), the main toxic compounds produced by this organism and close analogs to palytoxin (PlTX). Unlike for PlTX, information on OVTXs'toxicity are scarce due to the absence of commercial standards. Extracts from two cultures of Mediterranean strains of O. cf. ovata (MCCV54 and MCCV55), two fractions containing or not OVTXs (prepared from the MCCV54 extract) and OVTX-a and -d (isolated from the MCCV55 extract) were generated. These chemical samples and PlTX were tested on a panel of cell types from several organs and tissues (skin, intestine, lung, liver and nervous system). The MCCV55 extract, containing a 2-fold higher amount of OVTXs than MCCV54 extract, was shown to be more cytotoxic on all the cell lines and more prone to increase interleukin-8 (IL-8) release in keratinocytes. The fraction containing OVTXs was also cytotoxic on the cell lines tested but induced IL-8 release only in liver cells. Unexpectedly, the cell lines tested showed the same sensitivity to the fraction that does not contain OVTXs. With this fraction, a pro-inflammatory effect was shown both in lung and liver cells. The level of cytotoxicity was similar for OVTX-a and -d, except on intestinal and skin cells where a weak difference of toxicity was observed. Among the 3 toxins, only PlTX induced a pro-inflammatory effect mostly on keratinocytes. These results suggest that the ubiquitous Na+/K+ ATPase target of PlTX is likely shared with OVTX-a and -d, although the differences in pro-inflammatory effect must be explained by other mechanisms.

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.

Functional and Structural Biological Methods for Palytoxin Detection

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

On the Hunt for New Toxin Families Produced by a Mediterranean Strain of the Benthic Dinoflagellate Ostreopsis cf. ovata

Ostreopsis cf. ovata is a benthic dinoflagellate known to produce palytoxin (PLTX) and its analogues. Recent investigations suggested the production of unknown toxins by a Mediterranean strain. In the present work, two new families of toxins, potentially novel in their structures, were purified from this same Mediterranean strain of Ostreopsis cf. ovata. The low amount of material isolated only allowed for acquisition of high-resolution mass spectrometry data and the evaluation of their cytotoxicity to human lung cancer cells. Based on their HRMS data, none of these new compounds appear to be close PLTX analogues, although their mass spectra suggest poly-hydroxylated long chain compounds of high molecular weight (1370–2143 Da). The cell cytotoxicity concentrations (CC₅₀) of these new purified toxins ranged between 0.68 and 3.12 µg/mL, and this was enhanced when they were tested as mixtures, suggesting synergistic effects of Ostreopsis toxins. The two families of compounds were named the liguriatoxins (LGTX) and rivieratoxins (RVTX), with each family containing three members. Additional work on purification is needed to fully characterize the structures of these six new dinoflagellate toxins.

Taxonomy and toxicity of a bloom-forming Ostreopsis species (Dinophyceae, Gonyaulacales) in Tahiti island (South Pacific Ocean): one step further towards resolving the identity of O. siamensis

Among dinoflagellates responsible for benthic harmful algal blooms, the genus Ostreopsis primarily described from tropical areas has been increasingly reported from subtropical and temperate areas worldwide. Several species of this toxigenic genus produce analogs of palytoxin, thus representing a major threat to human and environmental health. The taxonomy of several species needs to be clarified as it was based mostly on morphological descriptions leading in some cases to ambiguous interpretations and misidentifications. The present study aims at reporting a benthic bloom that occurred in April 2019 in Tahiti island, French Polynesia. A complete taxonomic investigation of the blooming Ostreopsis species was realized using light, epifluorescence and field emission electron microscopy and phylogenetic analyses inferred from LSU rDNA and ITS-5.8S rDNA regions. Toxicity of a natural sample and strains isolated from the bloom was assessed using both neuroblastoma cell-based assay and LC-MS/MS analyses. Morphological observations showed that cells were round to oval, large, 58.0-82.5 µm deep (dorso-ventral length) and 45.7-61.2 µm wide. The cingulum was conspicuously undulated, forming a 'V' in ventral view. Thecal plates possessed large pores in depressions, with a collar rim. Detailed observation also revealed the presence of small thecal pores invisible in LM. Phylogenetic analyses were congruent and all sequences clustered within the genotype Ostreopsis sp. 6, in a subclade closely related to sequences from the Gulf of Thailand and Malaysia. No toxicity was found on the field sample but all the strains isolated from the bloom were found to be cytotoxic and produced ostreocin D, a lower amount of ostreocins A and B and putatively other compounds. Phylogenetic data demonstrate the presence of this species in the Gulf of Thailand, at the type locality of O. siamensis, and morphological data are congruent with the original description and support this identification.

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.

Ostreopsis lenticularis Y. Fukuyo (Dinophyceae, Gonyaulacales) from French Polynesia (South Pacific Ocean): A revisit of its morphology, molecular phylogeny and toxicity

To date, the genus Ostreopsis comprises eleven described species, of which seven are toxigenic and produce various compounds presenting a major threat to human and environmental health. The taxonomy of several of these species however remains controversial, as it was based mostly on morphological descriptions leading, in some cases, to ambiguous interpretations and even possible misidentifications. The species Ostreopsis lenticularis was first described by Y. Fukuyo from French Polynesia using light microscopy observations, but without genetic information associated. The present study aims at revisiting the morphology, molecular phylogeny and toxicity of O. lenticularis based on the analysis of 47 strains isolated from 4 distinct locales of French Polynesia, namely the Society, Australes, Marquesas and Gambier archipelagos. Observations in light, epifluorescence and field emission scanning electron microscopy of several of these strains analyzed revealed morphological features in perfect agreement with the original description of O. lenticularis. Cells were oval, not undulated, 60.5-94.4 μm in dorso-ventral length, 56.1-78.2 μm in width, and possessed a typical plate pattern with thecal plates showing two sizes of pores. Phylogenetic analyses inferred from the LSU rDNA and ITS-5.8S sequences revealed that the 47 strains correspond to a single genotype, clustering with a strong support with sequences previously ascribed to Ostreopsis sp. 5. Clonal cultures of O. lenticularis were also established and further tested for their toxicity using the neuroblastoma cell-based assay and LCMS/MS analyses. None of the 19 strains tested showed toxic activity on neuroblastoma cells, while LCMS/MS analyses performed on the strains from Tahiti Island (i.e. type locality) confirmed that palytoxin and related structural analogs were below the detection limit. These findings allow to clarify unambiguously the genetic identity of O. lenticularis while confirming previous results from the Western Pacific which indicate that this species shows no toxicity, thus stressing the need to reconsider its current classification within the group of toxic species.

Rapid Extraction and Identification of Maitotoxin and Ciguatoxin-Like Toxins from Caribbean and Pacific Gambierdiscus Using a New Functional Bioassay

Background

Ciguatera is a circumtropical disease produced by polyether sodium channel toxins (ciguatoxins) that enter the marine food chain and accumulate in otherwise edible fish. Ciguatoxins, as well as potent water-soluble polyethers known as maitotoxins, are produced by certain dinoflagellate species in the genus Gambierdiscus and Fukuyoa spp. in the Pacific but little is known of the potential of related Caribbean species to produce these toxins.

Methods

We established a simplified procedure for extracting polyether toxins from Gambierdiscus and Fukuyoa spp. based on the ciguatoxin rapid extraction method (CREM). Fractionated extracts from identified Pacific and Caribbean isolates were analysed using a functional bioassay that recorded intracellular calcium changes (Ca²⁺) in response to sample addition in SH-SY5Y cells. Maitotoxin directly elevated Ca²⁺_i, while low levels of ciguatoxin-like toxins were detected using veratridine to enhance responses.

Results

We identified significant maitotoxin production in 11 of 12 isolates analysed, with 6 of 12 producing at least two forms of maitotoxin. In contrast, only 2 Caribbean isolates produced detectable levels of ciguatoxin-like activity despite a detection limit of >30 pM. Significant strain-dependent differences in the levels and types of ciguatoxins and maitotoxins produced by the same Gambierdiscus spp. were also identified.

Conclusions

The ability to rapidly identify polyether toxins produced by Gambierdiscus spp. in culture has the potential to distinguish ciguatoxin-producing species prior to large-scale culture and in naturally occurring blooms of Gambierdiscus and Fukuyoa spp. Our results have implications for the evaluation of ciguatera risk associated with Gambierdiscus and related species.

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

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

Emergent toxins in North Atlantic temperate waters: a challenge for monitoring programs and legislation

Harmful Algal Blooms (HAB) are complex to manage due to their intermittent nature and their severe impact on the economy and human health. The conditions which promote HAB have not yet been fully explained, though climate change and anthropogenic intervention are pointed as significant factors. The rise of water temperature, the opening of new sea canals and the introduction of ship ballast waters all contribute to the dispersion and establishment of toxin-producing invasive species that promote the settling of emergent toxins in the food-chain. Tetrodotoxin, ciguatoxin, palytoxin and cyclic imines are commonly reported in warm waters but have also caused poisoning incidents in temperate zones. There is evidence that monitoring for these toxins exclusively in bivalves is simplistic and underestimates the risk to public health, since new vectors have been reported for these toxins and as well for regulated toxins such as PSTs and DSTs. In order to avoid public health impacts, there is a need for adequate monitoring programs, a need for establishing appropriate legislation, and a need for optimizing effective methods of analysis. In this review, we will compile evidence concerning emergent marine toxins and provide data that may indicate the need to restructure the current monitoring programs of HAB.

Alternative methods for the detection of emerging marine toxins: biosensors, biochemical assays and cell-based assays

The emergence of marine toxins in water and seafood may have a considerable impact on public health. Although the tendency in Europe is to consolidate, when possible, official reference methods based on instrumental analysis, the development of alternative or complementary methods providing functional or toxicological information may provide advantages in terms of risk identification, but also low cost, simplicity, ease of use and high-throughput analysis. This article gives an overview of the immunoassays, cell-based assays, receptor-binding assays and biosensors that have been developed for the screening and quantification of emerging marine toxins: palytoxins, ciguatoxins, cyclic imines and tetrodotoxins. Their advantages and limitations are discussed, as well as their possible integration in research and monitoring programs.

Development of a haemolytic-enzymatic assay with mediated amperometric detection for palytoxin analysis: application to mussels

An electrochemical sensor for palytoxin (PlTX) detection, based on a strip of eight screen-printed electrodes connected to a cost-effective and portable apparatus, is reported. Sheep erythrocytes were used to test the palytoxin detector and degree of haemolysis was evaluated by measuring release of the cytosolic lactate dehydrogenase (LDH). Percentage haemolysis and, therefore, the amount of LDH measured, by use of NADH/pyruvate and appropriate electrochemical mediators, was correlated with the concentration of the toxin. Two different electrochemical approaches were investigated for evaluation of LDH release, but only one based on the use of a binary redox mediator sequence (phenazine methosulfate in conjugation with hexacyanoferrate(III)) proved useful for our purpose. After analytical and biochemical characterization, the sensor strip was used to measure palytoxin. Sheep blood and standard solutions of PlTX were left to react for two different incubation times (24 h or 4 h), resulting in working ranges of 7 × 10(-3)-0.02 ng mL(-1) and 0.16-1.3 ng mL(-1), respectively. The specificity of the test for palytoxin was evaluated by use of ouabain, which acts in the same way as PlTX on the Na(+)/K(+)-ATPase pump. A cross-reactivity study, using high concentrations of other marine biotoxins was also conducted. Experiments to evaluate the matrix effect and recovery from mussels are discussed.

Characterization of palytoxin binding to HaCaT cells using a monoclonal anti-palytoxin antibody

Palytoxin (PLTX) is the reference compound for a group of potent marine biotoxins, for which the molecular target is Na+/K+-ATPase. Indeed, ouabain (OUA), a potent blocker of the pump, is used to inhibit some PLTX effects in vitro. However, in an effort to explain incomplete inhibition of PLTX cytotoxicity, some studies suggest the possibility of two different binding sites on Na+/K+-ATPase. Hence, this study was performed to characterize PLTX binding to intact HaCaT keratinocytes and to investigate the ability of OUA to compete for this binding. PLTX binding to HaCaT cells was demonstrated by immunocytochemical analysis after 10 min exposure. An anti-PLTX monoclonal antibody-based ELISA showed that the binding was saturable and reversible, with a K(d) of 3 × 10-10 M. However, kinetic experiments revealed that PLTX binding dissociation was incomplete, suggesting an additional, OUA-insensitive, PLTX binding site. Competitive experiments suggested that OUA acts as a negative allosteric modulator against high PLTX concentrations (0.3-1.0 × 10-7 M) and possibly as a non-competitive antagonist against low PLTX concentrations (0.1-3.0 × 10-9 M). Antagonism was supported by PLTX cytotoxicity inhibition at OUA concentrations that displaced PLTX binding (1 × 10-5 M). However, this inhibition was incomplete, supporting the existence of both OUA-sensitive and -insensitive PLTX binding sites.

Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay

Ciguatera fish poisoning (CFP), a disease caused by consuming fish that have accumulated ciguatoxins (CTXs) in their tissue, is regarded as the most prevalent form of intoxication in French Polynesia. Recently, the Australes, one of the least affected archipelago until the early 1980s, has shown a dramatic increase in its incidence rates in 2009 with unusual CFP cases. In the present work, potential health hazards associated with the proliferation of various marine phytoplankton species and the consumption of fish and marine invertebrates highly popular among local population were assessed in three Australes islands: Raivavae, Rurutu and Rapa. Extracts from the marine dinoflagellates Gambierdiscus, Ostreospis and mat-forming cyanobacteria as well as fish, giant clams and sea urchin samples were examined for the presence of CTXs and palytoxin (PLTX) by using the neuroblastoma cell-based assay (CBA-N2a). Cytotoxic responses observed with both standards (Pacific CTX-3C and PLTX) and targeted marine products indicate that CBA-N2a is a robust screening tool, with high sensitivity and good repeatability and reproducibility. In Rurutu and Raivavae islands, our main findings concern the presence of CTX-like compounds in giant clams and sea urchins, suggesting a second bio-accumulation route for CFP toxins in the ciguatera food chain. In Rapa, the potential CFP risk from Gambierdiscus bloom and fish was confirmed for the first time, with levels of CTXs found above the consumer advisory level of 0.01 ng Pacific CTX-1B g(-1) of flesh in three fish samples. However, despite the presence of trace level of PLTX in Ostreopsis natural assemblages of Rapa, no sign of PLTX accumulation is yet observed in tested fish samples. Because this multi-toxinic context is likely to emerge in most French Polynesian islands, CBA-N2a shows great potential for future applications in the algal- and toxin-based field monitoring programmes currently on hand locally.

Induction to oxidative stress by saxitoxin investigated through lipid peroxidation in Neuro 2A cells and Chlamydomonas reinhardtii alga

Saxitoxin (STX) is a cyanotoxin, which can cause neurotoxic effects and induce ecological changes in aquatic environments, a potential risk to public and environmental health. Many studies of cytotoxicity on animal cells and algae have been performed, although few compare the toxic effects between the two models. In this sense, we investigated the oxidative stress induced by STX (0.4-3.0 nM) in two different cellular models: Neuro-2A (N2A) cells and Chlamydomonas reinhardtii alga by quantification of malondialdehyde (MDA) levels as indicative of lipid peroxidation (LPO). Also was evaluated the antioxidant defense of these cells systems after exposure to STX by the addition of antioxidants in N2A cells culture, and by the measure of antioxidants enzymes activity in C. reinhardtii cells. The MDA levels of N2A cells increased from 15% to 113% for 0.4 and 3.0 nM of STX, respectively, as compared to control. Superoxide-dismutase and catalase did not appear to protect the cell from STX effect while, in cells treated with vitamin E, the rates of MDA production decreased significantly, except for higher concentrations of STX. No MDA productions were observed in algal cells however some effects on antioxidant enzymes activity were observed when algae were exposed to 3.0 nM STX. Our results indicate that the concentrations of STX that may induce oxidative stress through LPO are different in animal and phytoplankton communities. A combination of algal and animal bioassays should be conducted for reliable assessment of oxidative stress induced by STX.

The cytotoxic effect of palytoxin on Caco-2 cells hinders their use for in vitro absorption studies

Palytoxin (PLTX), found in Palythoa zoanthids and Ostreopsis dinoflagellates, has also been detected in crabs and fish, through which it can enter into the food chain. Indeed, PLTX is considered the causative agent of several cases of human seafood poisoning resulting in systemic symptoms. Available epidemiological data on PLTX human toxicity suggest that the intestinal tract may be one of its in vivo targets and its potential site of access into the bloodstream. Hence, the purpose of this study was to investigate the suitability of the human intestinal Caco-2 cell line for evaluating PLTX oral absorption. A detailed analysis of PLTX cytotoxicity revealed a high sensitivity of Caco-2 cells: 4h toxin exposure reduced mitochondrial activity (MTT assay, EC(50) of 8.9±3.7×10(-12)M), cell density (SRB assay, EC(50) of 2.0±0.6×10(-11)M) and membrane integrity (LDH release, EC(50) of 4.5±1.4×10(-9)M and PI uptake, EC(50) of 1.0±0.8×10(-8)M). After low PLTX concentration (1.0×10(-11)M) exposure for 1-8h, followed by 24h recovery time in toxin-free medium, cell density reduction was only partially reversible. These results indicate that, due to the high susceptibility to PLTX cytotoxic effects, Caco-2 cells do not represent an appropriate and reliable model for investigating intestinal barrier permeation by this toxin.

Palytoxin induces cell lysis by priming a two-step process in mcf-7 cells

The cytolytic action of palytoxin (PlTX) was recognized long ago, but its features have remained largely undetermined. We used biochemical, morphological, physiological, and physical tools, to study the cytolytic response in MCF-7 cells, as our model system. Cytolysis represented a stereotyped response induced by the addition of isotonic phosphate buffer (PBS) to cells that had been exposed to PlTX, after toxin removal and under optimal and suboptimal experimental conditions. Cytolysis was sensitive to osmolytes present during cell exposure to PlTX but not in the course of the lytic phase. Fluorescence microscopy showed that PlTX caused cell rounding and rearrangement of the actin cytoskeleton. Atomic force microscopy (AFM) was used to monitor PlTX effects in real time, and we found that morphological and mechanical properties of MCF-7 cells did not change during toxin exposure, but increased cell height and decreased stiffness at its surface were observed when PBS was added to PlTX-treated cells. The presence of an osmolyte during PlTX treatment prevented the detection of changes in morphological and mechanical properties caused by PBS addition to toxin-treated cells, as detected by AFM. By patch-clamp technique, we confirmed that PlTX action involved the transformation of the Na(+),K(+)-ATPase into a channel and found that cell membrane capacitance was not changed by PlTX, indicating that the membrane surface area was not greatly affected in our model system. Overall, our findings show that the cytolytic response triggered by PlTX in MCF-7 cells includes a first phase, which is toxin-dependent and osmolyte-sensitive, priming cells to lytic events taking place in a separate phase, which does not require the presence of the toxin and is osmolyte-insensitive but is accompanied by marked reorganization of actin-based cytoskeleton and altered mechanical properties at the cell's surface. A model of the two-step process of PlTX-induced cytolysis is presented.

Spatial distribution of ciguateric fish in the Republic of Kiribati

Ciguatera is food poisoning caused by human consumption of reef fish contaminated with ciguatoxins (CTXs). The expanding international trade of tropical fish species from ciguatera-endemic regions has resulted in increased global incidence of ciguatera, and more than 50000 people are estimated to suffer from ciguatera each year worldwide. The Republic of Kiribati is located in the Pacific Ocean; two of its islands, Marakei and Tarawa, have been suggested as high-risk areas for ciguatera. The toxicities of coral reef fish collected from these islands, including herbivorous, omnivorous and carnivorous fish (24% [n=41], 8% [n=13] and 68% [n=117], respectively), were analyzed using the mouse neuroblastoma assay (MNA) after CTX extraction. The MNA results indicated that 156 fish specimens, or 91% of the fish samples, were ciguatoxic (CTX levels >0.01 ng g(-1)). Groupers and moray eels were generally more toxic by an order of magnitude than other fish species. All of the collected individuals of eight species (n=3-19) were toxic. Toxicity varied within species and among locations by up to 10000-fold. Cephalapholis argus and Gymnothorax spp. collected from Tarawa Island were significantly less toxic than those from Marakei Island, although all individuals were toxic based on the 0.01 ng g(-1) threshold. CTX concentrations in the livers of individuals of two moray eel species (Gymnothorax spp., n=6) were nine times greater than those in muscle, and toxicity in liver and muscle showed a strong positive correlation with body weight. The present study provides quantitative information on the ciguatoxicity and distribution of toxicity in fish for use in fisheries management and public health.

First evidence of palytoxin and 42-hydroxy-palytoxin in the marine cyanobacterium Trichodesmium

Marine pelagic diazotrophic cyanobacteria of the genus Trichodesmium (Oscillatoriales) are widespread throughout the tropics and subtropics, and are particularly common in the waters of New Caledonia. Blooms of Trichodesmium are suspected to be a potential source of toxins in the ciguatera food chain and were previously reported to contain several types of paralyzing toxins. The toxicity of water-soluble extracts of Trichodesmium spp. were analyzed by mouse bioassay and Neuroblastoma assay and their toxic compounds characterized using liquid chromatography coupled with tandem mass spectrometry techniques. Here, we report the first identification of palytoxin and one of its derivatives, 42-hydroxy-palytoxin, in field samples of Trichodesmium collected in the New Caledonian lagoon. The possible role played by Trichodesmium blooms in the development of clupeotoxism, this human intoxication following the ingestion of plankton-eating fish and classically associated with Ostreopsis blooms, is also discussed.

Occurrence of palytoxin-group toxins in seafood and future strategies to complement the present state of the art

Palytoxin (PlTX) and palytoxin-like (PlTX-like) compounds in seafood have been raising scientific concern in the last years. The constant increase in record numbers of the causative dinoflagellates of the genus Ostreopsis together with the large spatial expansion of this genus has led to intensification of research towards optimization of methods for determination of PlTX presence and toxicity. In this context, identification of seafood species which could possibly contain PlTXs constitutes an important issue for public health protection. In the present paper, worldwide occurrence of PlTX-like compounds in seafood is reviewed, while potential future strategies are discussed. PlTX has been reported to be present in several species of fish, crustaceans, molluscs and echinoderms. In one occasion, PlTX has been identified in freshwater puffer fish whereas all other records of PlTXs refer to marine species and have been recorded in latitudes approximately between 43°N and 15°S. PlTX determination in seafood has relied on different methodologies (mainly LC-MS, mouse bioassay and hemolysis neutralization assay) that have evolved over time. Future recommendations include systematic screening of PlTX in those species and areas where PlTX has already been recorded implementing updated methodologies.

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

The state of the art of LC-MS of palytoxin and its analogues is reported in the present review. MS data for palytoxin, 42-hydroxy-palytoxin, ostreocin-D, mascarenotoxins, and ovatoxins, obtained using different ionization techniques, namely fast-atom bombardment (FAB), matrix assisted laser desorption ionization (MALDI), and electrospray ionization (ESI), are summarized together with the LC-MS methods used for their detection. Application of the developed LC-MS methods to both plankton and seafood analysis is also reported, paying attention to the extraction procedures used and to limits of detection (LOD) and quantitation (LOQ) achieved. In a research setting, LC-MS has shown a good potential in determination of palytoxin and its analogues from various sources, but, in a regulatory setting, routine LC-MS analysis of palytoxins is still at a preliminary stage. The LOQ currently achieved in seafood analysis appears insufficient to detect palytoxins in shellfish extract at levels close to the tolerance limit for palytoxins (30 μg/kg) proposed by the European Food Safety Authority (EFSA, 2009). In addition, lacking of certified reference standard of palytoxins as well as of validation studies for the proposed LC-MS methods represent important issues that should be faced for future perspectives of LC-MS technique.

Update on methodologies available for ciguatoxin determination: perspectives to confront the onset of ciguatera fish poisoning in Europe

Ciguatera fish poisoning (CFP) occurs mainly when humans ingest finfish contaminated with ciguatoxins (CTXs). The complexity and variability of such toxins have made it difficult to develop reliable methods to routinely monitor CFP with specificity and sensitivity. This review aims to describe the methodologies available for CTX detection, including those based on the toxicological, biochemical, chemical, and pharmaceutical properties of CTXs. Selecting any of these methodological approaches for routine monitoring of ciguatera may be dependent upon the applicability of the method. However, identifying a reference validation method for CTXs is a critical and urgent issue, and is dependent upon the availability of certified CTX standards and the coordinated action of laboratories. Reports of CFP cases in European hospitals have been described in several countries, and are mostly due to travel to CFP endemic areas. Additionally, the recent detection of the CTX-producing tropical genus Gambierdiscus in the eastern Atlantic Ocean of the northern hemisphere and in the Mediterranean Sea, as well as the confirmation of CFP in the Canary Islands and possibly in Madeira, constitute other reasons to study the onset of CFP in Europe [1]. The question of the possible contribution of climate change to the distribution of toxin-producing microalgae and ciguateric fish is raised. The impact of ciguatera onset on European Union (EU) policies will be discussed with respect to EU regulations on marine toxins in seafood. Critical analysis and availability of methodologies for CTX determination is required for a rapid response to suspected CFP cases and to conduct sound CFP risk analysis.

Rapid isolation of single-chain antibodies by phage display technology directed against one of the most potent marine toxins: Palytoxin

Several recombinant antibodies against one of the most potent marine toxins, Palytoxin (PlTX), were obtained using two naive human semi-synthetic phage display libraries (Tomlinson I and J) as an effective method for generating specific anti-toxin single-chain variable fragment (scFv) antibodies. After four rounds of panning and selection on free palytoxin adsorbed immunotubes, individual clones were isolated, sequenced and characterized by Enzyme-Linked Immunosorbent Assay (ELISA). Four phage-antibody clones specifically recognized the toxin. A competitive ELISA assay was optimized with one of these phage antibodies giving a very reproducible standard curve with a linear regression (R(2)=0.9945), showing a working range of 0.0005-500ngmL(-1). Several spiked shellfish samples were analysed by competitive ELISA to determine the accuracy of the assay, with a mean recovery rate of 90%. This study demonstrates that phage display libraries provide a valuable system for the easy and rapid generation of specific antibody fragments directed against difficult antigenic targets, such as free small molecules. Large-scale, low-cost production of anti-palytoxin scFv antibodies in Escherichia coli (E. coli) is an exciting prospect for the development of rapid and simple detection methods. Our results suggest that anti-palytoxin phage antibodies could be a valuable tool with competitive ELISA to detect palytoxin in natural shellfish samples.

Cytotoxic effect of palytoxin on mussel

Palytoxin is a large and complex polyhydroxylated molecule with potent neurotoxic activity. Dinoflagellates from the Ostreopsis genera were demonstrated to be producers of this compound and analogues. Even though initially palytoxin appearance was restricted to tropical areas, the recent occurrence of Ostreopsis outbreaks in Mediterranean Sea point to a worldwide dissemination probably related to climatic change. Those dinoflagellates can bioaccumulate in shellfish, especially in filter-feeding mollusks and have been involved in damaging effects in seafood or human toxic outbreaks. The present study describes palytoxins effect on metabolic activity of mantle and hepatopancreas cells from the mussel Mytilus galloprovincialis Lmk. Our results indicate that palytoxin is highly cytotoxic to mussel cells; unlike it happens with other toxins more common in European coasts such as okadaic acid and azaspiracid. These findings have a special significance for the marine environment and aquiculture since they are evidence for the ability of palytoxin to affect the integrity of bivalve mollusks that are not adapted to the presence of this toxin.