Ciguatera: Australian perspectives on a global problem

Precautions for seafood consumers: An updated review of toxicity, bioaccumulation, and rapid detection methods of marine biotoxins

Seafood products are globally consumed, and there is an increasing demand for the quality and safety of these products among consumers. Some seafoods are easily contaminated by marine biotoxins in natural environments or cultured farming processes. When humans ingest different toxins accumulated in seafood, they may exhibit different poisoning symptoms. According to the investigations, marine toxins produced by harmful algal blooms and various other marine organisms mainly accumulate in the body organs such as liver and digestive tract of seafood animals. Several regions around the world have reported incidents of seafood poisoning by biotoxins, posing a threat to human health. Thus, most countries have legislated to specify the permissible levels of these biotoxins in seafood. Therefore, it is necessary for seafood producers and suppliers to conduct necessary testing of toxins in seafood before and after harvesting to prohibit excessive toxins containing seafood from entering the market, which therefore can reduce the occurrence of seafood poisoning incidents. In recent years, some technologies which can quickly, conveniently, and sensitively detect biological toxins in seafood, have been developed and validated, these technologies have the potential to help seafood producers, suppliers and regulatory authorities. This article reviews the seafood toxins sources and types, mechanism of action and bioaccumulation of marine toxins, as well as legislation and rapid detection technologies for biotoxins in seafood for official and fishermen supervision.

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.

Model of the Origin of a Ciguatoxic Grouper (Plectropomus leopardus)

Published data were used to model the transfer of ciguatoxins (CTX) across three trophic levels of a marine food chain on the Great Barrier Reef (GBR), Australia, to produce a mildly toxic common coral trout (Plectropomus leopardus), one of the most targeted food fishes on the GBR. Our model generated a 1.6 kg grouper with a flesh concentration of 0.1 µg/kg of Pacific-ciguatoxin-1 (P-CTX-1 = CTX1B) from 1.1 to 4.3 µg of P-CTX-1 equivalents (eq.) entering the food chain from 0.7 to 2.7 million benthic dinoflagellates (Gambierdiscus sp.) producing 1.6 pg/cell of the P-CTX-1 precursor, P-CTX-4B (CTX4B). We simulated the food chain transfer of ciguatoxins via surgeonfishes by modelling Ctenochaetus striatus feeding on turf algae. A C. striatus feeding on ≥1000 Gambierdiscus/cm² of turf algae accumulates sufficient toxin in <2 days that when preyed on, produces a 1.6 kg common coral trout with a flesh concentration of 0.1 µg/kg P-CTX-1. Our model shows that even transient blooms of highly ciguatoxic Gambierdiscus can generate ciguateric fishes. In contrast, sparse cell densities of ≤10 Gambierdiscus/cm² are unlikely to pose a significant risk, at least in areas where the P-CTX-1 family of ciguatoxins predominate. The ciguatera risk from intermediate Gambierdiscus densities (~100 cells/cm²) is more difficult to assess, as it requires feeding times for surgeonfish (~4-14 days) that overlap with turnover rates of turf algae that are grazed by herbivorous fishes, at least in regions such as the GBR, where stocks of herbivorous fishes are not impacted by fishing. We use our model to explore how the duration of ciguatoxic Gambierdiscus blooms, the type of ciguatoxins they produce, and fish feeding behaviours can produce differences in relative toxicities between trophic levels. Our simple model indicates thresholds for the design of risk and mitigation strategies for ciguatera and the variables that can be manipulated to explore alternate scenarios for the accumulation and transfer of P-CTX-1 analogues through marine food chains and, potentially, for other ciguatoxins in other regions, as more data become available.

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.

Critical Review and Conceptual and Quantitative Models for the Transfer and Depuration of Ciguatoxins in Fishes

We review and develop conceptual models for the bio-transfer of ciguatoxins in food chains for Platypus Bay and the Great Barrier Reef on the east coast of Australia. Platypus Bay is unique in repeatedly producing ciguateric fishes in Australia, with ciguatoxins produced by benthic dinoflagellates (Gambierdiscus spp.) growing epiphytically on free-living, benthic macroalgae. The Gambierdiscus are consumed by invertebrates living within the macroalgae, which are preyed upon by small carnivorous fishes, which are then preyed upon by Spanish mackerel (Scomberomorus commerson). We hypothesise that Gambierdiscus and/or Fukuyoa species growing on turf algae are the main source of ciguatoxins entering marine food chains to cause ciguatera on the Great Barrier Reef. The abundance of surgeonfish that feed on turf algae may act as a feedback mechanism controlling the flow of ciguatoxins through this marine food chain. If this hypothesis is broadly applicable, then a reduction in herbivory from overharvesting of herbivores could lead to increases in ciguatera by concentrating ciguatoxins through the remaining, smaller population of herbivores. Modelling the dilution of ciguatoxins by somatic growth in Spanish mackerel and coral trout (Plectropomus leopardus) revealed that growth could not significantly reduce the toxicity of fish flesh, except in young fast-growing fishes or legal-sized fishes contaminated with low levels of ciguatoxins. If Spanish mackerel along the east coast of Australia can depurate ciguatoxins, it is most likely with a half-life of ≤1-year. Our review and conceptual models can aid management and research of ciguatera in Australia, and globally.

Animal toxins - Nature's evolutionary-refined toolkit for basic research and drug discovery

Venomous animals have evolved toxins that interfere with specific components of their victim's core physiological systems, thereby causing biological dysfunction that aids in prey capture, defense against predators, or other roles such as intraspecific competition. Many animal lineages evolved venom systems independently, highlighting the success of this strategy. Over the course of evolution, toxins with exceptional specificity and high potency for their intended molecular targets have prevailed, making venoms an invaluable and almost inexhaustible source of bioactive molecules, some of which have found use as pharmacological tools, human therapeutics, and bioinsecticides. Current biomedically-focused research on venoms is directed towards their use in delineating the physiological role of toxin molecular targets such as ion channels and receptors, studying or treating human diseases, targeting vectors of human diseases, and treating microbial and parasitic infections. We provide examples of each of these areas of venom research, highlighting the potential that venom molecules hold for basic research and drug development.

High sensitivity of rat cardiomyoblast H9c2(2-1) cells to Gambierdiscus toxic compounds

Ciguatera fish poisoning is a frequently reported non-bacterial food-borne illness related to the consumption of seafood contaminated with ciguatoxins, and possibly maitotoxins. These toxins are synthesized by marine dinoflagellate species of Gambierdiscus and Fukuyoa genera, and their abundance is a matter of great concern due to their adverse effects to aquatic life and human health. The present study aims to assess the sensitivity of rat cardiomyoblast H9c2(2-1) cells to Gambierdiscus toxic compounds using concentration- and time-dependent sulforhodamine B (SRB) colorimetric assays. Low concentrations of Gambierdiscus extracts (corresponding to 1.3-2.3 cells mL^-1) induced a concentration-dependent response. Specificity in time-dependent response of H9c2(2-1) cells was demonstrated for G. excentricus after a 180 min exposure compared to both G. cf. belizeanus and G. silvae species, with EC_50s obtained after 720 and 360 min, respectively. The sensitivity of H9c2(2-1) cells to dinoflagellate toxic compounds was also tested with other genera from benthic (Coolia malayensis, Ostreopsis cf. ovata, Prorocentrum hoffmannianum and P. lima) and planktonic (Amphidinium carterae and Lingulodinium polyedrum) habitats. Amphidinium, Coolia and Lingulodinium data did not present any concentration-response relationships, and EC₅₀ values could only be obtained after 720 and 1440 min of exposure to both Prorocentrum species and O. cf. ovata, respectively. This study demonstrated that the H9c2(2-1) SRB assay represents a promising and sensitive tool for the detection of Gambierdiscus toxic compounds present in water samples, particularly of G. excentricus at very low cell abundances.

Possible food safety hazards of ready-to-eat raw fish containing product (sushi, sashimi)

It is undeniable that with the popularity of sushi and sashimi over the last decade the consumption of raw fish has extremely increased. Raw fish is very appreciated worldwide and has become a major component of human diet because of its fine taste and nutritional properties. Possible hazards concerning fish safety and quality are classified as biological and chemical hazards. They are contaminants that often accumulate in edible tissue of fish and transmit to humans via the food chain affecting the consumer's health. Although their concentration in fish and fishery products are found at non-alarming level of a daily basis period, they induce hazardous outcome on human health due to long and continuous consumption of raw fish. Regular sushi and sashimi eaters have to be aware of the contaminants found in the other components of their dish that often add up to acceptable residue limits found in fish. Hence, there is the urge for effective analytical methods to be developed as well as stricter regulations to be put in force between countries to monitor the safety and quality of fish for the interest of public health.

Uptake and Depuration Kinetics of Pacific Ciguatoxins in Orange-Spotted Grouper (Epinephelus coioides)

Ciguatoxins (CTXs), produced by toxic benthic dinoflagellates, can bioaccumulate in marine organisms at higher trophic levels. The current study evaluated the uptake and depuration kinetics of some of the most potent CTXs, Pacific CTX-1, -2, and -3 (P-CTX-1, -2, and -3), in orange-spotted grouper (Epinephelus coioides) exposed to 1 ng P-CTXs g^-1 fish daily. Over a 30 d exposure, P-CTX-1, -2, and -3 were consistently detected in various tissues of exposed fish, and the concentrations of the total P-CTXs in tissues generally ranked following the order of liver, intestine, gill, skin, brain, and muscle. Relatively higher uptake rates of P-CTX-1 in the groupers were observed compared with those of P-CTX-2 and -3. The depuration rate constants of P-CTX-1, -2, and -3 in different tissues were (0.996-16.5) × 10^-2, (1.51-16.1) × 10^-2, and (0.557-10.6) × 10^-2 d^-1, respectively. The accumulation efficiencies of P-CTX-1, -2, and -3 in whole groupers were 6.13%, 2.61%, and 1.15%, respectively. The increasing proportion of P-CTX-1 and the decreasing proportion of P-CTX-2 and -3 over the exposure phase suggest a likely biotransformation of P-CTX-2 and -3 to P-CTX-1, leading to higher levels of P-CTX-1 in fish and possibly a higher risk of CTXs in long-term exposed fish.

Presence of CTXs in moray eels and dusky groupers in the marine environment of the Canary Islands

Local population frequently consumes moray eels and dusky groupers from the Canary Islands. These species are top predators and the interactions between them include predation but also, in some cases, collaborative hunting. These fish are well known to cause ciguatera (CFP) outbreaks in several marine areas such as Japan, Hawaii, French Polynesia and Caribe. Groupers have been involved in CFP events in the Canary Islands, however, moray eels have not yet been well studied in this regard. The present research seeks to describe the finding of a black moray in the stomach of a positive dusky grouper during its necropsy, and to clarify the implication of groupers and moray eels in the food webs, accumulating CTXs in the Canarian environment. The study also updates statistics on the presence of toxic groupers in this archipelago. For these purposes, 248 grouper samples from the CFP official control in the Canary Islands (2018-2019) were analysed and 36 moray eels (5 species) were collected under the EuroCigua project and one was obtained during a dusky grouper necropsy. All samples were analysed with the Neuro-2a cell-based assay (CBA) to evidence CTX-like toxicity. Regarding the necropsied grouper and the moray eel found in its stomach content, the LCMS/MS method allowed the identification and quantification of CCTX1 in both fish at similar levels while none of the P-CTXs for which standards were available were detected. Among groupers, 25.4 % displayed CTX-like toxicity with differences between islands. For moray eels 38.9 % showed toxicity, involving 4 species. Black moray exhibited a high proportion of positives (9/12) and a positive correlation was found between CTX-like toxicity quantification and the black moray weight. Regarding the grouper, and the moray eel found in its stomach, the LCMS/MS method allowed the identification and quantification of C-CTX1 in both fish at similar levels. This found suggests a trophic interaction between these species and their role in maintaining CTXs in the Canary waters where local population commonly demand those species for consumption. The island of El Hierro stands out above all the other Canary Islands with the concerning percentage of positive grouper samples and the high CTX toxicity levels obtained in moray eel specimens analysed in this marine area. This is the first report of CTX-like toxicity in flesh of moray eels fished in the Canary archipelago and the confirmation of the presence of C-CTX1 by LCMS/MS in a black moray from this marine area.

Marine Toxins Targeting Kv1 Channels: Pharmacological Tools and Therapeutic Scaffolds

Toxins from marine animals provide molecular tools for the study of many ion channels, including mammalian voltage-gated potassium channels of the Kv1 family. Selectivity profiling and molecular investigation of these toxins have contributed to the development of novel drug leads with therapeutic potential for the treatment of ion channel-related diseases or channelopathies. Here, we review specific peptide and small-molecule marine toxins modulating Kv1 channels and thus cover recent findings of bioactives found in the venoms of marine Gastropod (cone snails), Cnidarian (sea anemones), and small compounds from cyanobacteria. Furthermore, we discuss pivotal advancements at exploiting the interaction of κM-conotoxin RIIIJ and heteromeric Kv1.1/1.2 channels as prevalent neuronal Kv complex. RIIIJ's exquisite Kv1 subtype selectivity underpins a novel and facile functional classification of large-diameter dorsal root ganglion neurons. The vast potential of marine toxins warrants further collaborative efforts and high-throughput approaches aimed at the discovery and profiling of Kv1-targeted bioactives, which will greatly accelerate the development of a thorough molecular toolbox and much-needed therapeutics.

Effects of dietary exposure to ciguatoxin P-CTX-1 on the reproductive performance in marine medaka (Oryzias melastigma)

Ciguatoxins are natural compounds produced by benthic dinoflagellates Gambierdiscus and Fukuyoa spp., which cause fish intoxication by ciguatera fish poisoning. This study aimed to assess the dietary exposure effects of ciguatoxin P-CTX-1 on the reproductive performance in marine medaka (Oryzias melastigma). Fish which ingested >1.16 pg·day^-1 for 21 days exhibited abnormal behaviors including diarrhea, abnormal swimming, loss of appetite and decreased egg production. After 7-day exposure to P-CTX-1 at a dose of 1.93 pg·day^-1, significant gender-specific differences in reproductive performance and decreased hatching rate of the offspring were observed. Chemical analysis of P-CTX-1 showed that the P-CTX-1 accumulation rates were 24.1 ± 1.4% in female fish and 9.9 ± 0.4% in male fish, and 0.05 pg·egg^-1 was detected. The results illustrate that dietary exposure to P-CTX-1 affected the reproductive performance and survival of offspring, and caused bioaccumulation and maternal transfer of P-CTX-1 in marine medaka.

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.

Intraspecific Variability in the Toxin Production and Toxin Profiles of In Vitro Cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia

Ciguatera poisoning (CP) is a foodborne disease caused by the consumption of seafood contaminated with ciguatoxins (CTXs) produced by dinoflagellates in the genera Gambierdiscus and Fukuyoa. The toxin production and toxin profiles were explored in four clones of G. polynesiensis originating from different islands in French Polynesia with contrasted CP risk: RIK7 (Mangareva, Gambier), NHA4 (Nuku Hiva, Marquesas), RAI-1 (Raivavae, Australes), and RG92 (Rangiroa, Tuamotu). Productions of CTXs, maitotoxins (MTXs), and gambierone group analogs were examined at exponential and stationary growth phases using the neuroblastoma cell-based assay and liquid chromatography–tandem mass spectrometry. While none of the strains was found to produce known MTX compounds, all strains showed high overall P-CTX production ranging from 1.1 ± 0.1 to 4.6 ± 0.7 pg cell⁻¹. In total, nine P-CTX analogs were detected, depending on strain and growth phase. The production of gambierone, as well as 44-methylgamberione, was also confirmed in G. polynesiensis. This study highlighted: (i) intraspecific variations in toxin production and profiles between clones from distinct geographic origins and (ii) the noticeable increase in toxin production of both CTXs, in particular CTX4A/B, and gambierone group analogs from the exponential to the stationary phase.

Development of a quantitative PCR assay for the detection and enumeration of a potentially ciguatoxin-producing dinoflagellate, Gambierdiscus lapillus (Gonyaulacales, Dinophyceae)

Ciguatera fish poisoning (CFP) is an illness contracted through the ingestion of seafood containing ciguatoxins. It is prevalent in tropical regions worldwide, including in Australia. Ciguatoxins are produced by some species of Gambierdiscus. Therefore, screening of Gambierdiscus species identification through quantitative PCR (qPCR), along with the determination of species toxicity, can be useful in monitoring potential ciguatera risk in these regions. In Australia, CFP is prevalent in tropical Queensland and increasingly in sub-tropical regions of Australia, but has a report rate of approximately 10%. Yet the identity, distribution and abundance of ciguatoxin producing Gambierdiscus spp. is largely unknown. In this study, we developed a rapid qPCR assay to quantify the presence and abundance of Gambierdiscus lapillus, a likely ciguatoxic species first described from Australia. We assessed the specificity and efficiency of the qPCR assay. The assay was tested on 25 environmental samples from the Heron Island reef in the southern Great Barrier Reef, a ciguatera endemic region, to determine the presence and patchiness of this species across samples from Chnoospora sp., Padina sp. and Sargassum sp. macroalgal hosts.

Characterisation of Two Toxic Gambierdiscus spp. (Gonyaulacales, Dinophyceae) from the Great Barrier Reef (Australia): G. lewisii sp. nov. and G. holmesii sp. nov

Ciguatera fish poisoning (CFP) is a human illness caused via consumption of seafood contaminated with neurotoxins produced by some species from the epiphytic dinoflagellate genus Gambierdiscus. In this study, we describe two new species of Gambierdiscus isolated from Heron Island in the Southern Great Barrier Reef, Queensland, Australia. These new species were analysed using light microscopy, scanning electron microscopy, and phylogenetic analyses of nuclear encoded ribosomal ITS, SSU as well as D1-D3 and D8-D10 of the LSU gene regions. Gambierdiscus lewisii sp. nov. (Po, 3', 0a, 7″, 6c,? s, 5‴, 0p, 2'‴) is distinguished by its strong reticulate-foveate ornamentation and is genetically distinct from its sister species, G. pacificus. Gambierdiscus holmesii sp. nov. (Po, 3', 0a, 7″, 6c, 6s?, 5‴, 0p, 2'‴) is morphologically distinct from the genetically similar species G. silvae because of a strongly ventrally displaced apical pore complex and a characteristic fold at the anterior edge of the sulcus. Both G. lewisii and G. holmesii produce putative Maitotoxin-(44-Methylgambierone) and compounds which show ciguatoxin and maitotoxin-like activities. Identification of two new Gambierdiscus species will enable us to more accurately assess the risk of CFP in Australia and internationally.

Predictive score and probability of CTX-like toxicity in fish samples from the official control of ciguatera in the Canary Islands

This research identifies factors associated with the contamination by ciguatoxins (CTXs) in a population of fish and proposes a predictive score of the presence of CTX-like toxicity in amberjack samples from the official control program of ciguatera in the Canary Islands of the Directorate-General (DG) Fisheries (Canary Government). Out of the 970 samples of fish studied, 177 (18.2%) samples showed CTX-like toxicity. The fish were classified according to the species, amberjack (Seriola dumerili and S. rivoliana) (n = 793), dusky grouper (Epinephelus marginatus) (n = 145) and wahoo (Acanthocybium solandri) (n = 32). The data were separated by species category and statistically examined, resulting in 137 (17.3%) amberjack and 39 (26.9%) grouper samples showing CTX-like toxicity; regarding wahoo species, only 1 toxic sample (3.1%) was found. According to fishing location the contamination rates suggested grouping the islands in four clusters; namely: {El Hierro: HI; La Gomera: LG; La Palma: LP}, {Gran Canaria: GC; Tenerife: TF}, {Fuerteventura: FU} and {Lanzarote: LZ}. For the amberjack species, the multivariate logistic regression showed the factors that maintained independent association with the outcome, which were the warm season (OR = 3.617; 95% CI = 1.249-10.474), the weight (per kg, 1.102; 95% CI = 1.069-1.136) and the island of fish catching. A prediction score was obtained for the probability of contamination by CTX in amberjack fish samples. The area under de curve (AUC) obtained using the validation data was 0.747 (95% CI = 0.662-0.833). Regarding grouper species, the island of fishing was the only factor that showed significant differences associated with the presence of CTX-like toxicity. We provide herein data for a better management and prediction of ciguatera in the Canary Islands, suggesting a review of the minimum limits of fish weight established by the Canary Government for the control program.

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.

Growth and Toxin Production of Gambierdiscus spp. Can Be Regulated by Quorum-Sensing Bacteria

Gambierdiscus spp. are the major culprit responsible for global ciguatera fish poisoning (CFP). At present, the effects of microbiological factors on algal proliferation and toxin production are poorly understood. To evaluate the regulatory roles of quorum-sensing (QS) bacteria in the physiology of Gambierdiscus, co-culture experiments with screened QS strains were conducted in this study. Except for the growth-inhibiting effect from the strain Marinobacter hydrocarbonoclasticus, the algal host generally displayed much higher growth potential and toxin production ability with the existence of QS strains. In addition, Bacillus anthracis particularly exhibited a broad-spectrum growth enhancement effect on various Gambierdiscus types, as well as a remarkable influence on algal toxicity. The variations of algal physiological status, including growth rate, chlorophyll content, and responsive behaviors, are potential reasons for the observed positive or negative affection. This study suggests that QS bacteria regulate the algal growth and toxin production. Based on the evidence, we further speculate that QS bacteria may contribute to the site-specific distribution of CFP risk through regulating the algal host biomass and toxicity.

Investigation of ciguatoxins in invasive lionfish from the greater caribbean region: Implications for fishery development

Lionfish, native to reef ecosystems of the tropical and sub-tropical Indo-Pacific, were introduced to Florida waters in the 1980s, and have spread rapidly throughout the northwestern Atlantic, Caribbean Sea and the Gulf of Mexico. These invasive, carnivorous fish significantly reduce other fish and benthic invertebrate biomass, fish recruitment, and species richness in reef ecosystems. Fisheries resource managers have proposed the establishment of a commercial fishery to reduce lionfish populations and mitigate adverse effects on reef communities. The potential for a commercial fishery for lionfish is the primary reason to identify locations where lionfish accumulate sufficient amounts of ciguatoxin (CTX) to cause ciguatera fish poisoning (CFP), the leading cause of non-bacterial seafood poisoning associated with fish consumption. To address this issue, an initial geographic assessment of CTX toxicity in lionfish from the Caribbean and Gulf of Mexico was conducted. Lionfish samples (n = 293) were collected by spearfishing from 13 locations (74 sampling sites) around the Caribbean and Gulf of Mexico between 2012 and 2015. The highest frequencies of lionfish containing measurable CTX occurred in areas known to be high-risk regions for CFP in the central to eastern Caribbean (e.g., 53% British Virgin Islands and 5% Florida Keys). Though measurable CTX was found in some locations, the majority of the samples (99.3%) contained CTX concentrations below the United States Food and Drug Administration guidance level of 0.1 ppb Caribbean ciguatoxin-1 (C-CTX-1) equivalents (eq.). Only 0.7% of lionfish tested contained more than 0.1 ppb C-CTX-1 eq. As of 2018, there has been one suspected case of CFP from eating lionfish. Given this finding, current risk reduction techniques used to manage CTX accumulating fish are discussed.

Ciguatoxins Evoke Potent CGRP Release by Activation of Voltage-Gated Sodium Channel Subtypes NaV1.9, NaV1.7 and NaV1.1

Ciguatoxins (CTXs) are marine toxins that cause ciguatera fish poisoning, a debilitating disease dominated by sensory and neurological disturbances that include cold allodynia and various painful symptoms as well as long-lasting pruritus. Although CTXs are known as the most potent mammalian sodium channel activator toxins, the etiology of many of its neurosensory symptoms remains unresolved. We recently described that local application of 1 nM Pacific Ciguatoxin-1 (P-CTX-1) into the skin of human subjects induces a long-lasting, painful axon reflex flare and that CTXs are particularly effective in releasing calcitonin-gene related peptide (CGRP) from nerve terminals. In this study, we used mouse and rat skin preparations and enzyme-linked immunosorbent assays (ELISA) to study the molecular mechanism by which P-CTX-1 induces CGRP release. We show that P-CTX-1 induces CGRP release more effectively in mouse as compared to rat skin, exhibiting EC₅₀ concentrations in the low nanomolar range. P-CTX-1-induced CGRP release from skin is dependent on extracellular calcium and sodium, but independent from the activation of various thermosensory transient receptor potential (TRP) ion channels. In contrast, lidocaine and tetrodotoxin (TTX) reduce CGRP release by 53–75%, with the remaining fraction involving L-type and T-type voltage-gated calcium channels (VGCC). Using transgenic mice, we revealed that the TTX-resistant voltage-gated sodium channel (VGSC) Na_V1.9, but not Na_V1.8 or Na_V1.7 alone and the combined activation of the TTX-sensitive VGSC subtypes Na_V1.7 and Na_V1.1 carry the largest part of the P-CTX-1-caused CGRP release of 42% and 34%, respectively. Given the contribution of CGRP to nociceptive and itch sensing pathways, our findings contribute to a better understanding of sensory symptoms of acute and chronic ciguatera that may help in the identification of potential therapeutics.

Ladder-Shaped Ion Channel Ligands: Current State of Knowledge

Ciguatoxins (CTX) and brevetoxins (BTX) are polycyclic ethereal compounds biosynthesized by the worldwide distributed planktonic and epibenthic dinoflagellates of Gambierdiscus and Karenia genera, correspondingly. Ciguatera, evoked by CTXs, is a type of ichthyosarcotoxism, which involves a variety of gastrointestinal and neurological symptoms, while BTXs cause so-called neurotoxic shellfish poisoning. Both types of toxins are reviewed together because of similar mechanisms of their action. These are the only molecules known to activate voltage-sensitive Na⁺-channels in mammals through a specific interaction with site 5 of its α-subunit and may compete for it, which results in an increase in neuronal excitability, neurotransmitter release and impairment of synaptic vesicle recycling. Most marine ciguatoxins potentiate Nav channels, but a considerable number of them, such as gambierol and maitotoxin, have been shown to affect another ion channel. Although the extrinsic function of these toxins is probably associated with the function of a feeding deterrent, it was suggested that their intrinsic function is coupled with the regulation of photosynthesis via light-harvesting complex II and thioredoxin. Antagonistic effects of BTXs and brevenal may provide evidence of their participation as positive and negative regulators of this mechanism.

Taxonomic assignment of the benthic toxigenic dinoflagellate Gambierdiscus sp. type 6 as Gambierdiscus balechii (Dinophyceae), including its distribution and ciguatoxicity

Recent molecular phylogenetic studies of Gambierdiscus species flagged several new species and genotypes, thus leading to revitalizing its systematics. The inter-relationships of clades revealed by the primary sequence information of nuclear ribosomal genes (rDNA), however, can sometimes be equivocal, and therefore, in this study, the taxonomic status of a ribotype, Gambierdiscus sp. type 6, was evaluated using specimens collected from the original locality, Marakei Island, Republic of Kiribati; and specimens found in Rawa Island, Peninsular Malaysia, were further used for comparison. Morphologically, the ribotype cells resembled G. scabrosus, G. belizeanus, G. balechii, G. cheloniae and G. lapillus in thecal ornamentation, where the thecal surfaces are reticulate-foveated, but differed from G. scabrosus by its hatchet-shaped Plate 2', and G. belizeanus by the asymmetrical Plate 3'. To identify the phylogenetic relationship of this ribotype, a large dataset of the large subunit (LSU) and small subunit (SSU) rDNAs were compiled, and performed comprehensive analyses, using Bayesian-inference, maximum-parsimony, and maximum-likelihood, for the latter two incorporating the sequence-structure information of the SSU rDNA. Both the LSU and SSU rDNA phylogenetic trees displayed an identical topology and supported the hypothesis that the relationship between Gambierdiscus sp. type 6 and G. balechii was monophyletic. As a result, the taxonomic status of Gambierdiscus sp. type 6 was revised, and assigned as Gambierdiscus balechii. Toxicity analysis using neuroblastoma N2A assay confirmed that the Central Pacific strains were toxic, ranging from 1.1 to 19.9 fg P-CTX-1 eq cell^-1, but no toxicity was detected in a Western Pacific strain. This suggested that the species might be one of the species contributing to the high incidence rate of ciguatera fish poisoning in Marakei Island.

Biooxidation of Ciguatoxins Leads to Species-Specific Toxin Profiles

Ciguatoxins (CTXs) contaminate fish worldwide and cause the foodborne illness ciguatera. In the Pacific, these toxins are produced by the dinoflagellate Gambierdiscus toxicus, which accumulates in fish through the food chain and undergoes oxidative modification, giving rise to numerous analogs. In this study, we examined the oxidation of CTXs in vitro with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis using reference toxins, and found that CTX4A, CTX4B, and CTX3C, which are produced by the alga, are oxidized to the analogs found in fish, namely CTX1B, 52-epi-54-deoxyCTX1B, 54-deoxyCTX1B, 2-hydroxyCTX3C, and 2,3-dihydroxyCTX3C. This oxidation was catalyzed by human CYP3A4, fish liver S9 fractions, and microsomal fractions prepared from representative ciguateric fishes (Lutjanus bohar, L. monostigumus, and Oplegnathus punctatus). In addition, fish liver S9 fractions prepared from non-ciguateric fishes (L. gibbus and L. fulviflamma) in Okinawa also converted CTX4A and CTX4B to CTX1B, 54-deoxyCTX1B, and 52-epi-54-deoxyCTX1B in vitro. This is the first study to demonstrate the enzymatic oxidation of these toxins, and provides insight into the mechanism underlying the development of species-specific toxin profiles and the fate of these toxins in humans and fish.

Regional Variations in the Risk and Severity of Ciguatera Caused by Eating Moray Eels

Moray eels (Gymnothorax species) from tropical waters have long been known to be high-risk species, and the consumption of particularly the viscera or ungutted eels can result in severe ciguatera (known as Gymnothorax or moray eel poisoning), characterized by prominent neurological features. In this review, the main objective was to describe the risk and severity of ciguatera caused by eating moray eels in different parts of the world. Moray eels can accumulate very high ciguatoxin (CTX) levels in the flesh and particularly the liver. Therefore, even the smaller ones can be toxic and the consumption of an average portion (particularly liver) can result in severe or fatal ciguatera. Moray eels (particularly when ungutted) must never be served in gatherings since they can cause mass poisoning because of their large sizes and high CTX levels. Apart from regulatory measures restricting or excluding access, the public should be repeatedly warned to avoid eating moray eels.

LSU rDNA based RFLP assays for the routine identification of Gambierdiscus species

The Gambierdiscus genus is a group of benthic dinoflagellates commonly associated with ciguatera fish poisoning (CFP), which is generally found in tropical or sub-tropical regions around the world. Morphologically similar species within the genus can vary in toxicity; however, species identifications are difficult or sometimes impossible using light microscopy. DNA sequencing of ribosomal RNA genes (rDNA) is thus often used to identify and describe Gambierdiscus species and ribotypes, but the expense and time can be prohibitive for routine culture screening and/or large-scale monitoring programs. This study describes a restriction fragment length polymorphism (RFLP) typing method based on analysis of the large subunit rDNA that can successfully identify at least nine of the described Gambierdiscus species and two Fukuyoa species. The software programs DNAMAN 6.0 and Restriction Enzyme Picker were used to identify a set of restriction enzymes (SpeI, HpyCH4IV, and TaqαI) capable of distinguishing most of the known Gambierdiscus species for which DNA sequences were available. This assay was tested using in silico analysis and cultured isolates, and species identifications of isolates assigned by RFLP typing were confirmed by DNA sequencing. To verify the assay and assess intra-specific heterogeneity in RFLP patterns, identifications of 63 Gambierdiscus isolates comprising ten Gambierdiscus species, one ribotype, and two Fukuyoa species were confirmed using RFLP typing, and this method was subsequently employed in the routine identification of isolates collected from the Caribbean Sea. The RFLP assay presented here reduces the time and cost associated with morphological identification via scanning electron microscopy and/or DNA sequencing, and provides a phylogenetically sensitive method for routine Gambierdiscus species assignment.

Effects of temperature, salinity and composition of the dinoflagellate assemblage on the growth of Gambierdiscus carpenteri isolated from the Great Barrier Reef

Increases in reported incidence of ciguatera fish poisoning (hereafter ciguatera) have been linked to warmer sea temperatures that are known to trigger coral bleaching events. The drivers that trigger blooms of ciguatera-causing dinoflagellates on the Great Barrier Reef (GBR) are poorly understood. This study investigated the effects of increased temperatures and lowered salinities, often associated with environmental disturbance events, on the population growth of two strains of the potentially ciguatera-causing dinoflagellate, Gambierdiscus carpenteri (NQAIF116 and NQAIF380). Both strains were isolated from the central GBR with NQAIF116 being an inshore strain and NQAIF380 an isolate from a stable environment of a large coral reef aquarium exhibit in ReefHQ, Townsville, Australia. Species of Gambierdiscus are often found as part of a mixed assemblage of benthic toxic dinoflagellates on macroalgal substrates. The effect of assemblage structure of dinoflagellates on the growth of Gambierdiscus populations has, however, not been explored. The study, therefore investigated the growth of G. carpenteri within mixed assemblages of benthic dinoflagellates. Population growth was monitored over a period of 28days under three salinities (16, 26 and 36) and three temperature (24, 28 and 34°C) conditions in a fully crossed experimental design. Temperature and salinity had a significant effect on population growth. Strain NQAIF380 exhibited significantly higher growth at 28°C compared to strain NQAIF116, which had highest growth at 24°C. When strain NQAIF116 was co-cultured with the benthic dinoflagellates, Prorocentrum lima and Ostreopsis sp., inhibitory effects on population growth were observed at a salinity of 36. In contrast, growth stimulation of G. carpenteri (strain NQAIF116) was observed at a salinity of 26 and particularly at 16 when co-cultured with Ostreopsis-dominated assemblages. Range expansion of ciguatera-causing dinoflagellates could lead to higher frequency of reported ciguatera illness in populated temperate Australian regions, outside the tropical range of the GBR. Therefore, the findings on salinity and temperature tolerance of two strains of G. carpenteri indicates potential adaptability to different local environmental conditions. These are baseline data for future investigations into the potential southward range expansion of ciguatera-causing dinoflagellates originating from the GBR.

The pharmacology of voltage-gated sodium channel activators

Toxins and venom components that target voltage-gated sodium (Na_V) channels have evolved numerous times due to the importance of this class of ion channels in the normal physiological function of peripheral and central neurons as well as cardiac and skeletal muscle. Na_V channel activators in particular have been isolated from the venom of spiders, wasps, snakes, scorpions, cone snails and sea anemone and are also produced by plants, bacteria and algae. These compounds have provided key insight into the molecular structure, function and pathophysiological roles of Na_V channels and are important tools due to their at times exquisite subtype-selectivity. We review the pharmacology of Na_V channel activators with particular emphasis on mammalian isoforms and discuss putative applications for these compounds. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Characterization of Gambierdiscus lapillus sp. nov. (Gonyaulacales, Dinophyceae): a new toxic dinoflagellate from the Great Barrier Reef (Australia)

Gambierdiscus is a genus of benthic dinoflagellates found worldwide. Some species produce neurotoxins (maitotoxins and ciguatoxins) that bioaccumulate and cause ciguatera fish poisoning (CFP), a potentially fatal food-borne illness that is common worldwide in tropical regions. The investigation of toxigenic species of Gambierdiscus in CFP endemic regions in Australia is necessary as a first step to determine which species of Gambierdiscus are related to CFP cases occurring in this region. In this study, we characterized five strains of Gambierdiscus collected from Heron Island, Australia, a region in which ciguatera is endemic. Clonal cultures were assessed using (i) light microscopy; (ii) scanning electron microscopy; (iii) DNA sequencing based on the nuclear encoded ribosomal 18S and D8-D10 28S regions; (iv) toxicity via mouse bioassay; and (v) toxin profile as determined by Liquid Chromatography-Mass Spectrometry. Both the morphological and phylogenetic data indicated that these strains represent a new species of Gambierdiscus, G. lapillus sp. nov. (plate formula Po, 3', 0a, 7″, 6c, 7-8s, 5‴, 0p, 2″″ and distinctive by size and hatchet-shaped 2' plate). Culture extracts were found to be toxic using the mouse bioassay. Using chemical analysis, it was determined that they did not contain maitotoxin (MTX1) or known algal-derived ciguatoxin analogs (CTX3B, 3C, CTX4A, 4B), but that they contained putative MTX3, and likely other unknown compounds.

Developmental toxicity and molecular responses of marine medaka (Oryzias melastigma) embryos to ciguatoxin P-CTX-1 exposure

Ciguatoxins are produced by toxic benthic dinoflagellates and cause ciguatera fish poisoning worldwide, but the toxic effects on developing marine fish have not been well investigated. The Pacific ciguatoxin (P-CTX-1), is a potent sodium channel agonist, which is one of the most toxic members among all CTXs. This study evaluated the toxic effects of microinjecting purified Pacific ciguatoxin-1 (P-CTX-1) on embryonic development of marine medaka Oryzias melastigma. A lower 96h-LD₅₀ value was estimated for eleuthero-embryos (1.32ngg^-1) than that for embryos (1.71ngg^-1), indicating that P-CTX-1 is more lethal to newly hatched medaka larvae. P-CTX-1 induced detrimental effects during embryonic development, including hatching failure, abnormalities in physical development (caudal fin malformation and spinal deformities), internal damage (green coloration of the gall bladder and hemorrhaging), immune dysfunction, and altered muscle physiology (bradycardia and hyperkinetic twitching). The results of a transcriptional expression analysis of genes related to the stress/immune responses, cardiac and bone development, and apoptosis supported the observed developmental abnormalities. This study advanced the understanding of P-CTX-1 mediated toxic mechanisms in the development of early life stages of a fish, and thus contributed to the toxicity assessment of CTXs in marine ecosystems.

Gambierdiscus balechii sp. nov (Dinophyceae), a new benthic toxic dinoflagellate from the Celebes Sea (SW Pacific Ocean)

A new benthic toxic dinoflagellate is described from the Celebes Sea. Gambierdiscus balechii sp. nov. was isolated from seaweeds growing in tidal ponds. Its morphology was studied by means of LM and SEM; G. balechii has a very ornamented theca, a hatchet shaped second apical plate, a narrow second antapical plate and an asymmetrical third precigular plate, a unique combination of characters among Gambierdiscus species. It has a very wide size range with widths from 36 to 88μm. Phylogenetic analyses of two G. balechii strains, based on LSU rRNA (D8-D10) and partial SSUrRNA sequences confirmed that these clustererd in its' own group, separated from the rest of Gambierdiscus species and with G. pacificus, G. belizeanus and G. scabrosus as its closest relatives. Thecate cysts are described from culture as non motile vegetative-like cells which germinated after being isolated and transferred to fresh medium. Mouse tests showed that this species is toxic and hence it is a potential cause of ciguatera in the Celebes Sea.

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.

Gambierol and n-alkanols inhibit Shaker Kv channel via distinct binding sites outside the K(+) pore

The marine polycyclic-ether toxin gambierol and 1-butanol (n-alkanol) inhibit Shaker-type Kv channels by interfering with the gating machinery. Competition experiments indicated that both compounds do not share an overlapping binding site but gambierol is able to affect 1-butanol affinity for Shaker through an allosteric effect. Furthermore, the Shaker-P475A mutant, which inverses 1-butanol effect, is inhibited by gambierol with nM affinity. Thus, gambierol and 1-butanol inhibit Shaker-type Kv channels via distinct parts of the gating machinery.

How Safe Is Safe for Marine Toxins Monitoring?

Current regulation for marine toxins requires a monitoring method based on mass spectrometric analysis. This method is pre-targeted, hence after searching for pre-assigned masses, it identifies those compounds that were pre-defined with available calibrants. Therefore, the scope for detecting novel toxins which are not included in the monitoring protocol are very limited. In addition to this, there is a poor comprehension of the toxicity of some marine toxin groups. Also, the validity of the current approach is questioned by the lack of sufficient calibrants, and by the insufficient coverage by current legislation of the toxins reported to be present in shellfish. As an example, tetrodotoxin, palytoxin analogs, or cyclic imines are mentioned as indicators of gaps in the system that require a solid comprehension to assure consumers are protected.

Characteristic Features and Contributory Factors in Fatal Ciguatera Fish Poisoning--Implications for Prevention and Public Education

In this review, the main objective was to describe the characteristic features of fatal ciguatera fish poisoning and identify contributory factors, with a view to promote prevention and public education. Ciguatera-related deaths, although rare, have been reported from the Pacific, Caribbean, and Indian Ocean regions. The clinical features were generally dominated by convulsions and coma, with various focal neurological signs. Several contributory factors could be identified, including consumption of ciguatoxin (CTX)-rich fish parts (viscera and head) in larger amounts, the most ciguatoxic fish species (e.g.,Gymnothorax flavimarginatus) and reef fish collected after storms and individuals' susceptibility. Mass ciguatera fish poisoning with mortalities also occurred when G. flavimarginatus and other ciguatoxic fish species were shared in gatherings and parties. The characteristic features of fatal ciguatera fish poisoning must be recognized early. The public should be repeatedly reminded to avoid eating the most ciguatoxic fish species and the CTX-rich parts of reef fish. To prevent mass poisoning in gatherings and parties, the most ciguatoxic fish species and potentially toxic fish species must be avoided. Particularly after hits by disastrous storms, it is important to monitor the toxicity of reef fish and the incidence rates of ciguatera.

Ionic mechanisms of spinal neuronal cold hypersensitivity in ciguatera

Cold hypersensitivity is evident in a range of neuropathies and can evoke sensations of paradoxical burning cold pain. Ciguatoxin poisoning is known to induce a pain syndrome caused by consumption of contaminated tropical fish that can persist for months and include pruritus and cold allodynia; at present no suitable treatment is available. This study examined, for the first time, the neural substrates and molecular components of Pacific ciguatoxin-2-induced cold hypersensitivity. Electrophysiological recordings of dorsal horn lamina V/VI wide dynamic range neurones were made in non-sentient rats. Subcutaneous injection of 10 nm ciguatoxin-2 into the receptive field increased neuronal responses to innocuous and noxious cooling. In addition, neuronal responses to low-threshold but not noxious punctate mechanical stimuli were also elevated. The resultant cold hypersensitivity was not reversed by 6-({2-[2-fluoro-6-(trifluoromethyl)phenoxy]-2-methylpropyl}carbamoyl)pyridine-3-carboxylic acid, an antagonist of transient receptor potential melastatin 8 (TRPM8). Both mechanical and cold hypersensitivity were completely prevented by co-injection with the Nav 1.8 antagonist A803467, whereas the transient receptor potential ankyrin 1 (TRPA1) antagonist A967079 only prevented hypersensitivity to innocuous cooling and partially prevented hypersensitivity to noxious cooling. In naive rats, neither innocuous nor noxious cold-evoked neuronal responses were inhibited by antagonists of Nav 1.8, TRPA1 or TRPM8 alone. Ciguatoxins may confer cold sensitivity to a subpopulation of cold-insensitive Nav 1.8/TRPA1-positive primary afferents, which could underlie the cold allodynia reported in ciguatera. These data expand the understanding of central spinal cold sensitivity under normal conditions and the role of these ion channels in this translational rat model of ciguatoxin-induced hypersensitivity.

Ciguatoxic Potential of Brown-Marbled Grouper in Relation to Fish Size and Geographical Origin

To determine the ciguatoxic potential of brown-marbled grouper (Epinephelus fuscoguttatus) in relation to fish size and geographical origin, this review systematically analyzed: 1) reports of large ciguatera outbreaks and outbreaks with description of the fish size; 2) Pacific ciguatoxin (P-CTX) profiles and levels and mouse bioassay results in fish samples from ciguatera incidents; 3) P-CTX profiles and levels and risk of toxicity in relation to fish size and origin; 4) regulatory measures restricting fish trade and fish size preference of the consumers. P-CTX levels in flesh and size dependency of toxicity indicate that the risk of ciguatera after eating E. fuscoguttatus varies with its geographical origin. For a large-sized grouper, it is necessary to establish legal size limits and control measures to protect public health and prevent overfishing. More risk assessment studies are required for E. fuscoguttatus to determine the size threshold above which the risk of ciguatera significantly increases.

Ciguatera fish poisoning in East Asia and southeast Asia

In the coastal countries of East Asia and Southeast Asia, ciguatera should be common because of the extensive tropical and subtropical coral reefs along the coasts and in the neighboring seas with ciguatoxic fishes. An extensive search of journal databases, the Internet and the government websites was performed to identify all reports of ciguatera from the regions. Based on the official data and large published case series, the incidence of ciguatera was higher in the coastal cities (Hong Kong, Foshan, Zhongshan) of southern China than in Japan (Okinawa Prefecture). In Singapore, ciguatera appeared to be almost unknown. In other countries, only isolated cases or small case series were reported, but under-reporting was assumed to be common. Ciguatera may cause severe acute illness and prolonged neurological symptoms. Ciguatera represents an important public health issue for endemic regions, with significant socio-economic impact. Coordinated strategies to improve risk assessment, risk management and risk communication are required. The systematic collection of accurate data on the incidence and epidemiology of ciguatera should enable better assessment and management of its risk. Much more work needs to be done to define the size threshold for important coral reef fish species from different regions, above which the risk of ciguatera significantly increases.

Emergence and epidemiology of ciguatera in the coastal cities of southern China

In the present review of 23 published case studies, the main objective is to report the emergence and epidemiology of ciguatera in the coastal cities of southern China. There was a sudden surge in ciguatera outbreaks in 2004. Ciguatera mostly occurred in the Guangdong Province. In Shenzhen, the incidence of ciguatera in 2004 was estimated to be over 7.5 per million people. In Foshan and Zhongshan, three large outbreaks each affecting over 100–200 subjects (caused by tiger grouper served at banquets) accounted for the much higher incidence of ciguatera in 2004 (>48.7 and >129.9 per million people). Humphead wrasse and areolated coral grouper were the other important ciguatoxic fish. In some subjects, risk factors for increased likelihood of (severe) ciguatera were present, namely concomitant alcohol consumption and ingestion of large reef fishes and CTX-rich fish parts. To prevent large outbreaks and severe illness, large apex predators from coral reefs should never be served at banquets and the public should realize the increased risk of severe symptoms due to ingestion of CTX-rich fish parts with alcohol. The systematic collection of accurate details, implementation of risk assessment process and continuing education for the public on prevention are of obvious importance.

Epidemiology and clinical features of ciguatera fish poisoning in Hong Kong

In the present review, the main objective was to describe the epidemiology and clinical features of ciguatera fish poisoning in Hong Kong. From 1989 to 2008, the annual incidence of ciguatera varied between 3.3 and 64.9 (median 10.2) per million people. The groupers have replaced the snappers as the most important cause of ciguatera. Pacific-ciguatoxins (CTX) are most commonly present in reef fish samples implicated in ciguatera outbreaks. In affected subjects, the gastrointestinal symptoms often subside within days, whereas the neurological symptoms can persist for weeks or even months. Bradycardia and hypotension, which can be life-threatening, are common. Treatment of ciguatera is primarily supportive and symptomatic. Intravenous mannitol (1 g/kg) has also been suggested. To prevent ciguatera outbreaks, the public should be educated to avoid eating large coral reef fishes, especially the CTX-rich parts. A Code of Practice on Import and Sale of Live Marine Fish for Human Consumption for Prevention and Control of Ciguatera Fish Poisoning was introduced from 2004 to 2013. The Food Safety Ordinance with a tracing mechanism came into full effect in February 2012. The Government would be able to trace the sources of the fishes more effectively and take prompt action when dealing with ciguatera incidents.

A phylogenetic re-analysis of groupers with applications for ciguatera fish poisoning

BACKGROUND

Ciguatera fish poisoning (CFP) is a significant public health problem due to dinoflagellates. It is responsible for one of the highest reported incidence of seafood-borne illness and Groupers are commonly reported as a source of CFP due to their position in the food chain. With the role of recent climate change on harmful algal blooms, CFP cases might become more frequent and more geographically widespread. Since there is no appropriate treatment for CFP, the most efficient solution is to regulate fish consumption. Such a strategy can only work if the fish sold are correctly identified, and it has been repeatedly shown that misidentifications and species substitutions occur in fish markets.

METHODS

We provide here both a DNA-barcoding reference for groupers, and a new phylogenetic reconstruction based on five genes and a comprehensive taxonomical sampling. We analyse the correlation between geographic range of species and their susceptibility to ciguatera accumulation, and the co-occurrence of ciguatoxins in closely related species, using both character mapping and statistical methods.

RESULTS

Misidentifications were encountered in public databases, precluding accurate species identifications. Epinephelinae now includes only twelve genera (vs. 15 previously). Comparisons with the ciguatera incidences show that in some genera most species are ciguateric, but statistical tests display only a moderate correlation with the phylogeny. Atlantic species were rarely contaminated, with ciguatera occurrences being restricted to the South Pacific.

CONCLUSIONS

The recent changes in classification based on the reanalyses of the relationships within Epinephelidae have an impact on the interpretation of the ciguatera distribution in the genera. In this context and to improve the monitoring of fish trade and safety, we need to obtain extensive data on contamination at the species level. Accurate species identifications through DNA barcoding are thus an essential tool in controlling CFP since meal remnants in CFP cases can be easily identified with molecular tools.

Large outbreaks of ciguatera after consumption of brown marbled grouper

Brown marbled grouper (Epinephelus fuscoguttatus) is an apex predator from coral reefs of the Indo-Pacific region. All five published case series of ciguatera after consumption of brown marbled grouper were reviewed to characterize the types, severity and chronicity of ciguatera symptoms associated with its consumption. Three of these case series were from large outbreaks affecting over 100–200 subjects who had eaten this reef fish served at banquets. Affected subjects generally developed a combination of gastrointestinal, neurological and, less commonly, cardiovascular symptoms. Gastrointestinal symptoms occurred early and generally subsided in 1–2 days. Some neurological symptoms (e.g., paresthesia of four limbs) could last for weeks or months. Sinus bradycardia and hypotension occurred early, but could be severe and prolonged, necessitating the timely use of intravenous fluids, atropine and dopamine. Other cardiovascular and neurological features included atrial ectopics, ventricular ectopics, dyspnea, chest tightness, PR interval >0.2 s, ST segment changes, polymyositis and coma. Concomitant alcohol consumption was associated with a much higher risk of developing bradycardia, hypotension and altered skin sensation. The public should realize that consumption of the high-risk fish (especially the ciguatoxin-rich parts and together with alcohol use) and repeated ciguatoxin exposures will result in more severe and chronic illness.

Ciguatera fish poisoning in Hong Kong--a 10-year perspective on the class of ciguatoxins

The present study used liquid chromatography-tandem mass spectrometry (LC-MS/MS) to investigate retrospectively ciguatoxin (CTX)-positive samples as determined by mouse bioassay (MBA) in the past 10 years in Hong Kong. The results showed that Pacific CTXs (P-CTX-1, -2 and -3) were the most commonly observed toxins found in the samples, indicating Pacific Ocean areas as the most important origin of ciguatera fish poisoning. Clinical diagnosis from ciguatera patients also revealed the predominance of neurological illnesses in most cases, supporting intoxication of Pacific origin. This study demonstrated the ability of laboratory analysis to identify and quantify Pacific CTXs in suspected fish samples, so as to support the clinical diagnosis of ciguatera. Comparative analysis (Student's t-test and Spearman's rank correlation analysis) on the two CTX detection methods showed approximate linearity for overall P-CTXs (P-CTX-1, -2 and -3)/P-CTX-1 alone as derived by LC-MS/MS and total toxicity levels (P-CTX-1 equivalent) as determined by MBA. The LC-MS/MS method coupled with the rapid extraction method could allow the detection of trace amount of CTXs at levels below the clinically relevant limit, 0.1 ppb P-CTX-1 in fish flesh. For practical application, the adoption of a two-tiered approach for testing, chemical analysis by LC-MS/MS for toxic fish screening, coupled with biological assay by MBA for final toxicity confirmation, was proposed for first-line screening of CTX in potentially contaminated fish samples in the market, with an aim to minimizing the use of laboratory mice and at the same time providing reasonably effective means for routine analysis.

Neuroprotective effects of rosmarinic acid on ciguatoxin in primary human neurons

Ciguatoxin (CTX), is a toxic compound produced by microalgae (dinoflagellate) Gambierdiscus spp., and is bio-accumulated and bio-transformed through the marine food chain causing neurological deficits. To determine the mechanism of CTX-mediated cytotoxicity in human neurons, we measured extracellular lactate dehydrogenase (LDH) activity, intracellular levels of nicotinamide adenine dinucleotide (NAD(+)) and H2AX phosphorylation at serine 139 as a measure for DNA damage in primary cultures of human neurons treated with Pacific (P)-CTX-1B and P-CTX-3C. We found these marine toxins can induce a time and dose-dependent increase in extracellular LDH activity, with a concomitant decline in intracellular NAD(+) levels and increased DNA damage at the concentration range of 5-200 nM. We also showed that pre- and post-treatment with rosmarinic acid (RA), the active constituent of the Heliotropium foertherianum (Boraginaceae) can attenuate CTX-mediated neurotoxicity. These results further highlight the potential of RA in the treatment of CTX-induced neurological deficits.

Recent progress in neuroactive marine natural products

This review covers the isolation, chemical structure, biological activity, structure activity relationships including synthesis of chemical probes, and pharmacological characterization of neuroactive marine natural products; 302 references are cited.

Modulation of TRP ion channels by venomous toxins

Venoms are evolutionarily fine-tuned mixtures of small molecules, peptides, and proteins-referred to as toxins-that have evolved to specifically modulate and interfere with the function of diverse molecular targets within the envenomated animal. Many of the identified toxin targets are membrane receptors and ion channels. Due to their high specificity, toxins have emerged as an invaluable tool set for the molecular characterization of ion channels, and a selected group of toxins even have been developed into therapeutics. More recently, TRP ion channels have been included as targets for venomous toxins. In particular, a number of apparently unrelated peptide toxins target the capsaicin receptor TRPV1 to produce inflammatory pain. These toxins have turned out to be invaluable for structural and functional characterizations of the capsaicin receptor. If toxins will serve similar roles for other TRP ion channels, only future will tell.

Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati

Ciguatera fish poisoning (CFP) is a foodborne illness caused by consumption of coral reef fishes contaminated by ciguatoxins (CTXs); of the known CTX congeners, the Pacific ciguatoxins (P-CTXs) are the most toxic. Little is known about the trophodynamics of P-CTXs in coral reef systems. The present study explores the distribution, transfer, and trophic magnification of P-CTX-1, -2, and -3 in coral reef systems with high (ciguatoxic) and low (reference) ciguatoxicity in a CFP-endemic nation by use of liquid chromatography-tandem mass spectrometry (LC-MS/MS). In ciguatoxic coral reef systems, P-CTXs were detected in 54% of herbivorous fishes [total P-CTXs <0.500-1670 pg/g wet weight (ww)], 72% of omnivorous fishes (<0.500-1810 pg/g ww), and 76% of carnivorous fishes (<0.500-69 500 pg/g ww), as well as a lobster ( Panulirus penicillatus ; 2.36 pg/g ww) and an octopus (Octopodidae; 2.56 pg/g ww). The dominant P-CTXs in grazers and piscivorous fishes were P-CTX-2 and -1, respectively. No significant correlation between P-CTX levels and lipid content in three target predatory fishes indicated that accumulation of P-CTXs does not depend on fat content. A weak but significant positive relationship was observed between δ(15)N and P-CTX-1 levels, but further investigation is required to confirm its biomagnification potential.