Diversity and distribution of benthic dinoflagellates in Tonga include the potentially harmful genera Gambierdiscus and Fukuyoa

Benthic dinoflagellates that can cause illness, such as ciguatera poisoning (CP), are prevalent around the Pacific but are poorly described in many locations. This study represents the first ecological assessment of benthic harmful algae species in the Kingdom of Tonga, a country where CP occurs regularly. Surveys were conducted in June 2016 in the Tongatapu island group, and in June 2017 across three island groups: Ha'apai, Vava'u, and Tongatapu. Shallow subtidal coastal habitats were investigated by measuring water quality parameters and conducting quadrat surveys. Microalgae samples were collected using either macrophyte collection or the artificial substrate method. Benthic dinoflagellates (Gambierdiscus and/or Fukuyoa, Ostreopsis, and Prorocentrum) were counted using light microscopy, followed by molecular analyses (real-time PCR in 2016 and high throughput sequencing (metabarcoding) in 2017) to identify Gambierdiscus and Fukuyoa to species level. Six species were detected from the Tongatapu island group in 2016 (G. australes, G. carpenteri, G. honu, G. pacificus, F. paulensis, and F. ruetzleri) using real-time PCR. Using the metabarcoding approach in 2017, a total of eight species (G. australes, G. carpenteri, G. honu, G. pacificus, G. cheloniae, G. lewisii, G. polynesiensis, and F. yasumotoi) were detected. Species were detected in mixed assemblages of up to six species, with G. pacificus and G. carpenteri being the most frequently observed. Ha'apai had the highest diversity with eight species detected, which identifies this area as a Gambierdiscus diversity 'hotspot'. Vava'u and Tongatapu had three and six species found respectively. Gambierdiscus polynesiensis, a described ciguatoxin producer and proposed causative agent of CP was found only in Ha'apai and Vava'u in 2017, but not in Tongatapu in either year. Ostreopsis spp. and Prorocentrum spp. were also frequently observed, with Prorocentrum most abundant at the majority of sites. In 2016, the highest number of Gambierdiscus and/or Fukuyoa cells were observed on seagrass (Halodule uninervis) from Sopu, Tongatapu. In 2017, the highest numbers of Gambierdiscus and/or Fukuyoa from artificial substrate samples were recorded in the Halimeda dominant habitat at Neiafu Tahi, Vava'u, a low energy site. This raised the question of the effect of wave motion or currents on abundance measurements from artificial substrates. Differences in detection were noticed between macrophytes and artificial substrates, with higher numbers of species found on artificial substrates. This study provides a baseline of benthic dinoflagellate distributions and diversity for Tonga that may be used for future studies and the development of monitoring programmes.

Outbreak of ciguatera poisoning in a commercial vessel: lessons learnt and prospects of early diagnosis, management, and prophylaxis

An outbreak of food poisoning of unknown origin was notified to Central Queensland Public Health Unit on 9 December 2021. The bulk carrier sailing from Higashiharima, Japan to Gladstone, Australia reported an incident of sudden illness, with 19 out of 20 sailors on board reporting a combination of gastrointestinal and neurological symptoms. Central Queensland Public Health Unit started the outbreak investigation as per Queensland Health public health management guidelines. All 20 of the sailors consumed a self-caught barracuda and squid, prepared by the ship's cook, the day before. Unconsumed samples of the fish and squid were sent for testing. The affected sailors were triaged on arrival and were provided with medical care as required. The barracuda sample contained ciguatoxins (CTXs; P-CTX-1, P-CTX-2, P-CTX-3) with a total count of 3.40 ug/kg confirming the diagnosis. We propose the usage of the combination of gastrointestinal symptoms and paraesthesia in the light of a recent intoxication event for early detection of ciguatera poisoning (CP) in the eastern seaboard of Australia.

Phycotoxins and marine annelids - A global review

Several species of microalgae can produce potent phycotoxins that negatively affect aquatic organisms and their consumers following different exposure routes, as well as toxicokinetic (TK) and toxicodynamic (TD) processes. Benthic organisms are especially vulnerable as they are exposed to both benthic and planktonic species causative of harmful algal blooms (HABs). While benthic algae can come into direct contact with annelids during substrate remobilization, planktonic cells can settle to the bottom mostly during senescence and/or encystment stages, and in shallow and calm waters. We performed a systematic, qualitative review of the literature on the phycotoxin TK and TD processes in marine annelids, summarizing the most relevant findings and general trends. Besides, by using innovative analytical/statistical approaches, we were able to detect patterns and gaps in the current literature, thus pointing to future research directions. We retrieved and analyzed studies involving diarrhetic shellfish toxins (DSTs), paralytic shellfish toxins (PSTs), brevetoxins (PbTXs), domoic acid (DA), as well as palytoxin and its congeners, the ovatoxins (treated together as PLTXs). It is worth mentioning that studies evaluating other phycotoxins (e.g., ciguatoxins, yessotoxins) were not found in the literature. The absence of data on PbTXs, PSTs and DA is the largest gap hampering TK assessment in annelids, although some relevant information on TD is already available. Whereas lethal effects from DSTs have not been reported, more potent toxins like PbTXs, PSTs, DA and those grouped as PLTX-like compounds can cause mortality and/or marked decrease in annelid abundance. In addition, phycotoxins have been linked to sublethal effects on annelid cells. Although very sparse, field and laboratory studies offer strong evidence that annelids may be reliable indicators of toxin exposure and their negative effects during both early and later stages of HABs in marine environments. Besides quickly responding to these compounds at both organismic and suborganismic levels, annelids are easily found in areas affected by HABs. The use of annelids in future investigations evaluating the action mechanisms of toxic microalgae on marine invertebrates should be thus encouraged. In this case, the choice for widely dispersed and numerically dominant species of annelids would strengthen the validation and extrapolation of results from risk assessments in areas affected by HABs worldwide.

Cell immunolocalization of ciguatoxin-like compounds in the benthic dinoflagellate Gambierdiscus australes M. Chinain & M.A. Faust by confocal microscopy

Dinoflagellates of the genera Gambierdiscus and Fukuyoa are able to produce potent neurotoxins like ciguatoxins (CTXs), which, after biooxidation in fish, are responsible for ciguatera intoxication. An isolate of G. australes from the Canary Islands, that revealed the presence of CTX-like compounds by immunosensing tools, was studied by immunocytochemistry to localize intracellular CTX-like compounds, using 8H4 monoclonal antibody that specifically recognizes the right wing of CTX1B and CTX3C analogues. Confocal microscopy observations of immunostained whole cells revealed a strong positive reaction on cell surface and all along the cell outline, while no reaction was detected inside the cells, probably because the antibody was not able to pass through thecal plates. Cell sections showed a positive antibody staining not only on thecal plates, but also inside cytoplasm, with numerous small dots and larger tubule-like reticulate structures. Small fluorescent dots were detected also on the nuclear surface. These observations indicate that CTX-like compounds are present in G. australes cytoplasm, and then are, at least in part, released to cover the cell surface.

Structural Characterization of Maitotoxins Produced by Toxic Gambierdiscus Species

Identifying compounds responsible for the observed toxicity of the Gambierdiscus species is a critical step to ascertaining whether they contribute to ciguatera poisoning. Macroalgae samples were collected during research expeditions to Rarotonga (Cook Islands) and North Meyer Island (Kermadec Islands), from which two new Gambierdiscus species were characterized, G. cheloniae CAWD232 and G. honu CAWD242. Previous chemical and toxicological investigations of these species demonstrated that they did not produce the routinely monitored Pacific ciguatoxins nor maitotoxin-1 (MTX-1), yet were highly toxic to mice via intraperitoneal (i.p.) injection. Bioassay-guided fractionation of methanolic extracts, incorporating wet chemistry and chromatographic techniques, was used to isolate two new MTX analogs; MTX-6 from G. cheloniae CAWD232 and MTX-7 from G. honu CAWD242. Structural characterization of the new MTX analogs used a combination of analytical chemistry techniques, including LC–MS, LC–MS/MS, HR–MS, oxidative cleavage and reduction, and NMR spectroscopy. A substantial portion of the MTX-7 structure was elucidated, and (to a lesser extent) that of MTX-6. Key differences from MTX-1 included monosulfation, additional hydroxyl groups, an extra double bond, and in the case of MTX-7, an additional methyl group. To date, this is the most extensive structural characterization performed on an MTX analog since the complete structure of MTX-1 was published in 1993. MTX-7 was extremely toxic to mice via i.p. injection (LD₅₀ of 0.235 µg/kg), although no toxicity was observed at the highest dose rate via oral administration (155.8 µg/kg). Future research is required to investigate the bioaccumulation and likely biotransformation of the MTX analogs in the marine food web.

Electrochemical biosensor for the dual detection of Gambierdiscus australes and Gambierdiscus excentricus in field samples. First report of G. excentricus in the Balearic Islands

Several genera of marine dinoflagellates are known to produce bioactive compounds that affect human health. Among them, Gambierdiscus and Fukuyoa stand out for their ability to produce several toxins, including the potent neurotoxic ciguatoxins (CTXs), which accumulate through the food web. Once fishes contaminated with CTXs are ingested by humans, it can result in an intoxication named ciguatera. Within the two genera, only some species are able to produce toxins, and G. australes and G. excentricus have been highlighted to be the most abundant and toxic. Although the genera Gambierdiscus and Fukuyoa are endemic to tropical areas, their presence in subtropical and temperate regions has been recently recorded. In this work, the combined use of species-specific PCR primers for G. australes and G. excentricus modified with short oligonucleotide tails allowed the development of a multiplex detection system for these two toxin-producing species. Simultaneous detection was achieved using capture probes specific for G. australes and G. excentricus immobilized on maleimide-coated magnetic beads (MBs), separately placed on the working electrodes of a dual electrode array. Additionally, a rapid DNA extraction technique based on a portable bead beater system and MBs was developed, significantly reducing the extraction time (from several hours to 30 min). The developed technique was able to detect as low as 10 cells of both Gambierdiscus species and allowed the first detection of G. excentricus in the Balearic Islands in 8 out of the 12 samples analyzed. Finally, field samples were screened for CTXs with an immunosensor, successfully reporting 13.35 ± 0.5 pg CTX1B equiv. cell^-1 in one sample and traces of toxins in 3 out of the 9 samples analyzed. These developments provide rapid and cost-effective strategies for ciguatera risk assessment, with the aim of guaranteeing seafood safety.

Characterizing ciguatoxin (CTX)- and Non-CTX-producing strains of Gambierdiscus balechii using comparative transcriptomics

Gambierdiscus spp. can produce the polyketide compound, ciguatoxin (CTX), and are hence responsible for ciguatera fish poisoning (CFP). Studying the molecular mechanism that regulates CTX production is crucial for understanding the environmental trigger of CTX as well as for better informing fishery management. Commonly, polyketide synthases are important for polyketide synthesis; however, no gene has been confirmatively assigned to CTX production. Here, suppression subtractive hybridization (SSH) and transcriptome sequencing (RNA-Seq) were used to compare a CTX-producing strain with a non-CTX-producing strain. Using both methods, a total of 52 polyketide synthase (PKS) genes were identified to be up-regulated in the CTX-producing G. balechii, including transcripts encoding single-domain PKSs as well as transcripts encoding multi-domain PKSs. Using reverse transcription quantitative PCR, the expression of these genes in the CTX-producing strain and in nitrogen-limited cultures of the strain was further documented. These data suggest that PKSs are likely involved in polyketide synthesis and potentially in CTX synthesis in this dinoflagellate species. Our study provides the candidate biomarkers for the detection of CTXs or CFP in waters or any other organisms as well as a valuable genomic resource for the research on Gambierdiscus and other dinoflagellates.

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.

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.

Global impact of ciguatoxins and ciguatera fish poisoning on fish, fisheries and consumers

Ciguatera fish poisoning (CFP) is one of the most devastating food-borne illnesses caused by fish consumption. Ciguatoxins (CTXs) are potent neurotoxins synthesized by the benthic microalgae Gambierdiscus spp. and Fukuyoa spp. that are transmitted to fish by grazing and predation. Despite the high incidence of CFP, affecting an estimated number of 50,000 persons per year in tropical and subtropical latitudes, the factors underlying CTXs occurrence are still not well understood. Toxin transfer and dynamics in fish and food-webs are complex. Feeding habits and metabolic pathways determine the toxin profile and toxicity of fish, and migratory species may transport and spread the hazard. Furthermore, CTX effect on fish may be a limiting factor for fish recruitment and toxin prevalence. Recently, new occurrences of Gambierdiscus spp. in temperate areas have been concomitant with the detection of toxic fish and CFP incidents in non-endemic areas. CFP cases in Europe have led to implementation of monitoring programs and fisheries restrictions with considerable impact on local economies. More than 400 species of fish can be vectors of CTXs, and most of them are high-valued commercial species. Thus, the risk uncertainty and the spread of Gambierdiscus have serious consequences for fisheries and food safety. Here, we present a critical review of CTXs impacts on fish, fisheries, and humans, based on the current knowledge on CFP incidence and CTXs prevalence in microalgae and fish.

Distribution and potential toxicity of benthic harmful dinoflagellates in waters of Florida Bay and the Florida Keys

Few studies have been carried out on benthic dinoflagellates along the Florida Keys, and little is known about their distribution or toxicity in Florida Bay. Here, the distribution and abundance of benthic dinoflagellates was explored in northern and eastern Florida Bay and along the bay and ocean sides of the Florida Keys. Isolates were brought into culture and their toxicity was tested with oyster larvae bioassays. Seven genera were detected, including Prorocentrum, Coolia, Ostreopsis, Amphidinium, Gambierdiscus, Fukuyoa (all included potentially toxic species) and Sinophysis. In general, distribution increased with water temperature and nutrient availability, especially that of phosphate. This study documented the first record of Coolia santacroce in the Florida Keys. Potential toxic effects of Gambierdiscus caribaeus, the abundance of which exceeded 1000 cells g^-1 fw at some sites, were established using oyster larvae as a bioassay organism. These findings suggest a potential risk of ciguatera fish poisoning in this area.

Ciguatera-Causing Dinoflagellate Gambierdiscus spp. (Dinophyceae) in a Subtropical Region of North Atlantic Ocean (Canary Islands): Morphological Characterization and Biogeography

Dinoflagellates belonging to the genus Gambierdiscus produce ciguatoxins (CTXs), which are metabolized in fish to more toxic forms and subsequently cause ciguatera fish poisoning (CFP) in humans. Five species of Gambierdiscus have been described from the Canary Islands, where CTXs in fish have been reported since 2004. Here we present new data on the distribution of Gambierdiscus species in the Canary archipelago and specifically from two islands, La Palma and La Gomera, where the genus had not been previously reported. Gambierdiscus spp. concentrations were low, with maxima of 88 and 29 cells·g⁻¹ wet weight in samples from La Gomera and La Palma, respectively. Molecular analysis (LSUrRNA gene sequences) revealed differences in the species distribution between the two islands: only G. excentricus was detected at La Palma whereas four species, G. australes, G. caribaeus, G. carolinianus, and G. excentricus, were identified from La Gomera. Morphometric analyses of cultured cells of the five Canary Islands species and of field specimens from La Gomera included cell size and a characterization of three thecal arrangement traits: (1) the shape of the 2′ plate, (2) the position of Po in the anterior suture of the 2′ plate, and (3) the length–width relationship of the 2″″ plate. Despite the wide morphological variability within the culture and field samples, the use of two or more variables allowed the discrimination of two species in the La Gomera samples: G. cf. excentricus and G. cf. silvae. A comparison of the molecular data with the morphologically based classification demonstrated important coincidences, such as the dominance of G. excentricus, but also differences in the species composition of Gambierdiscus, as G. caribaeus was detected in the study area only by using molecular methods.

Species-specific PCR assays for Gambierdiscus excentricus and Gambierdiscus silvae (Gonyaulacales, Dinophyceae)

The two most toxic Gambierdiscus species identified from the Caribbean are G. excentricus and G. silvae. These species are the primary causes of ciguatera fish poisoning and likely contribute disproportionately to the toxicity of marine food webs. While Gambierdiscus species are difficult to distinguish using light or scanning electron microscopy, reliable species-specific molecular identification methods have been developed and used successfully to identify a number of other Gambierdiscus species. Corresponding species-specific assays are not yet available for G. excentricus and G. silvae, which imposes limitations on species identification and related ecological studies. The following note describes species-specific polymerase chain reaction assays for G. excentricus and G. silvae that can be used for these purposes.

Psammodinium inclinatum gen. nov. et comb. nov. (=Thecadinium inclinatum Balech) is the closest relative to the toxic dinoflagellate genera Gambierdiscus and Fukuyoa

The heterotrophic sand-dwelling dinoflagellate Thecadinium inclinatum has been re-examined by light and scanning electron microscopy in order to resolve the discrepancies on its plate pattern from the literature, and to obtain its phylogenetic information single-cell PCR technique has been used. The comparison of morphological and molecular information available for other Thecadinium species confirms the genus is polyphyletic and T. inclinatum seems not related to other representatives of the genus sensu lato. Thus, a new genus and combination for the species, Psammodinium inclinatum gen. nov., comb. nov. is proposed. Cells are heterotrophic and strongly laterally flattened, with sulcal pocket. The revised tabulation is: APC 3' 7" 7c 7s? 5"' 1p 2"" with a long-shank fishhook-shaped apical pore and descending cingulum. The cingulum inclines ventrally and declines on the right lateral side producing an asymmetrical epitheca. The epitheca is much smaller than the hypotheca. The phylogenetic results showed a strong relationship with the autotrophic epiphytic genera Gambierdiscus and Fukuyoa, being closely related with the latter. The Gambierdiscus species typically have a tropical and sub-tropical distribution and produce ciguatoxins, causing thousands of intoxications every year by consumption of contaminated fish. Fukuyoa representatives have a wider distribution including warm and temperate waters, and it has been demonstrated that they are also able to produce ciguatoxins, even though at lower amounts. P. inclinatum, which potential toxicity remains to be determined, represents an interesting independent evolutionary branch that resulted in the loss of chloroplasts, the strong lateral compression and the adaptation to sandy habitats in temperate and cold waters.

Gambierdiscus jejuensis sp. nov., an epiphytic dinoflagellate from the waters of Jeju Island, Korea, effect of temperature on the growth, and its global distribution

The genus Gambierdiscus produces ciguatera toxins, which has led to extensive studies of this genus. Epiphytic dinoflagellate cells were isolated from coralline macroalgae collected from the coastal waters of Jeju Island, Korea, and two clonal cultures were established. The morphology of these cells was examined using light and scanning electron microscopy, and the sequences of the small subunit (SSU), large subunit (LSU), and internal transcribed spacer (ITS) region of rDNA were determined. The phylogenetic trees based on SSU, LSU (D1-D3), and LSU (D8-D10) rDNA showed the two Korean isolates forming a clade with unidentified strains named Gambierdiscus sp. type 2. This clade showed a clear divergence from the two closest clades containing of the G. caribaeus and G. carpenteri strains. Morphologically, the Korean isolates had an anteroposteriorly compressed cell shape having a smooth theca ornamentation. Growth of the Korean isolates ceased when water temperatures were <20 °C or >30 °C with an optimum at 26 °C. This temperature preference may account for why Gambierdiscus sp. type 2 has only been isolated from the temperate waters of Korea and Japan. However, the two most closely related species G. caribaeus and G. carpenteri have broader temperature ranges tolerating as high as 34-36 °C and are globally distributed. Based on these results, the Korean isolates are proposed as a new species in the genus Gambierdiscus and named Gambierdiscus jejuensis sp. nov. Furthermore, it is suggested that the unidentified strains belonging to the Gambierdiscus sp. type 2 be transferred to the new species, G. jejuensis.

Ciguatera fish poisoning: Incidence, health costs and risk perception on Moorea Island (Society archipelago, French Polynesia)

Ciguatera Fish Poisoning (CFP) is a non-bacterial seafood poisoning well characterized in the remote archipelagos of French Polynesia, yet poorly documented in the Society archipelago, most notably on Moorea, the second most populated island in French Polynesia, which counts a high proportion of fishermen fishing on a regular basis. To address this knowledge gap, a holistic study of the ciguatera issue was conducted on Moorea. First, ciguatera risk was analysed in terms of incidence rate, fish species most commonly involved and risk stratification in Moorea lagoon based on 2007-2013 epidemiological data. A mean incidence rate of 8 cases per 10,000 inhabitants for the study period and an average under-reporting rate of 54% were found. Taking into account hospitalization and medication fees, and loss of productive days, the health-related costs due to CFP were estimated to be USD $1613 and $749 for each reported and unreported case, respectively, with an overall cost of USD $241,847 for the study period. Comparison of the present status of CFP on Moorea with a risk map established in the late 1970's showed that the spatial distribution of the risk has stayed relatively stable in time, with the north shore of the island remaining the most prone to ciguatera. Evaluation of the current knowledge on CFP among different populations groups, i.e. fishermen, residents and visitors, was also conducted through direct and indirect interviews. About half of the fishermen interviewed were actually able to identify risky fishing areas. While, overall, the CFP risk perception in the fishing community of Moorea seemed accurate, although not scientifically complete, it was sufficient for the safe practice of their fishing activities. This may be due in part to adaptive responses adopted by 36% of the fishermen interviewed, such as the avoidance of either high-risk fishing sites or toxic species. At the residents and visitors' level, the study points out a striking lack of awareness of the CFP issue among visitors, as compared to local residents. Indeed, less than 25% of Moorea visitors vs. an average of 98% in residents were aware of CFP or of its presence on the island. Interestingly, evaluation of the fish consumption preferences showed that 70% of visitors do not consume lagoon fish during their stay, not for fear of CFP, but mainly due to the lack of availability of these species in recreational facilities or because they have nutritional preference for pelagic fish. This lack of awareness, along with the report by several CFP patients of the consumption of fish species yet banned for sale, stress the need for improved communication efforts on this critical issue among both residents and visitors on Moorea. The implementation of a public outreach strategy is proposed, based on both existing information networks and low-cost communication actions through information displays at various strategic locations, e.g. Tahiti-Faa'a international airport, the ferry boat station, recreational facilities, as well as the major trading points on Moorea Island.

Chemical Diversity, Origin, and Analysis of Phycotoxins

Microalgae, particularly those from the lineage Dinoflagellata, are very well-known for their ability to produce phycotoxins that may accumulate in the marine food chain and eventually cause poisoning in humans. This includes toxins accumulating in shellfish, such as saxitoxin, okadaic acid, yessotoxins, azaspiracids, brevetoxins, and pinnatoxins. Other toxins, such as ciguatoxins and maitotoxins, accumulate in fish, where, as is the case for the latter compounds, they can be metabolized to even more toxic metabolites. On the other hand, much less is known about the chemical nature of compounds that are toxic to fish, the so-called ichthyotoxins. Despite numerous reports of algal blooms causing massive fish kills worldwide, only a few types of compounds, such as the karlotoxins, have been proven to be true ichthyotoxins. This review will highlight marine microalgae as the source of some of the most complex natural compounds known to mankind, with chemical structures that show no resemblance to what has been characterized from plants, fungi, or bacteria. In addition, it will summarize algal species known to be related to fish-killing blooms, but from which ichthyotoxins are yet to be characterized.

Ciguatera fish poisoning: treatment, prevention and management

Ciguatera Fish Poisoning (CFP) is the most frequently reported seafood-toxin illness in the world, and it causes substantial physical and functional impact. It produces a myriad of gastrointestinal, neurologic and/or cardiovascular symptoms which last days to weeks, or even months. Although there are reports of symptom amelioration with some interventions (e.g. IV mannitol), the appropriate treatment for CFP remains unclear to many physicians. We review the literature on the treatments for CFP, including randomized controlled studies and anecdotal reports. The article is intended to clarify treatment options, and provide information about management and prevention of CFP, for emergency room physicians, poison control information providers, other health care providers, and patients.

Transcriptional profiling of whole blood and serum protein analysis of mice exposed to the neurotoxin Pacific Ciguatoxin-1

Ciguatoxins (CTX) are a suite of cyclic polyether toxins produced by the marine dinoflagellate Gambierdiscus sp., are potent activators of voltage-gated sodium channels and a leading cause of human poisoning from food fish. This report characterizes the genomic and proteomic response in whole blood of adult male mice exposed i.p. to 264 ng/kg of the Pacific congener of CTX (P-CTX-1) at 1, 4 and 24h. Whole genome microarray expression data were filtered by tightness of fit between replicates, fold change (1.8) and p-value (10(-5)), resulting in 183 annotated genes used for trending analysis, K-means clustering and ontology classification. Genes involved with cytokine signaling, proteasome complex and ribosomal function were dominant. qPCR performed on 19 genes of interest had a correlation of 0.95 to array results by Pearson's correlation coefficient. Serum protein analysis showed small but significant changes in 6 of 60 proteins assayed: Ccl2, Ccl12, CD40, IL-10, leptin and M-CSF. In large part, the gene expression was consistent with a Th2 immune response with interesting similarities to expression seen in asthmatic models.

Synthesis of an F-H gambierol subunit using a C-glycoside-centered strategy

[structure: see text] This manuscript describes our synthesis of the F-H subunit of gambierol. In addition to the synthesis of the tricycle, of note is an interesting protecting group influence on the generation of a C(23) C-glycoside as well as the use of ring-closing metathesis to generate a tetrasubstituted enol ether.

Total synthesis of gambierol

The convergent total synthesis of gambierol (1) is described. The octacyclic ether framework of 1 was constructed via the intramolecular allylation of alpha-chloroacetoxy ether followed by ring-closing metathesis. A modified Stille coupling was successfully applied to the synthesis of the triene side chain.

Total synthesis of (-)-gambierol

The first total synthesis of (-)-gambierol (1), a marine polycyclic ether toxin, has been achieved. Key features of the successful synthesis include (1) a convergent union of the ABC and EFGH ring fragments (5 and 6, respectively) via our developed B-alkyl Suzuki-Miyaura cross-coupling strategy leading to the octacyclic polyether core 4 and (2) a late-stage introduction of the sensitive triene side chain by use of Pd(PPh(3))(4)/CuCl/LiCl-promoted Stille coupling. The ABC ring fragment 5 was synthesized in a linear manner (B --> AB --> ABC), wherein the A ring was formed by intramolecular hetero-Michael reaction and the C ring was constructed via 6-endo cyclization of hydroxy epoxide 7. An improved synthetic entry to the EFGH ring fragment 6 is also described, in which SmI(2)-induced reductive cyclization methodology was applied to the stereoselective construction of the F and H rings, leading to 6 with remarkable overall efficiency. Stereoselective hydroboration of 5 and subsequent Suzuki-Miyaura coupling with 6 provided endocyclic enol ether 45 in high yield, which was then converted to octacyclic polyether core 4. Careful choice of the global deprotection stage was a key element for the successful total synthesis. Functionalization of the H ring and global desilylation gave (Z)-vinyl bromide 2. Finally, cross-coupling of 2 with (Z)-vinyl stannane 3 under Corey's Pd(PPh(3))(4)/CuCl/LiCl-promoted Stille conditions completed the total synthesis of (-)-gambierol (1).

Pacific ciguatoxin-1b effect over Na+ and K+ currents, inositol 1,4,5-triphosphate content and intracellular Ca2+ signals in cultured rat myotubes

1. The action of the main ciguatoxin involved in ciguatera fish poisoning in the Pacific region (P-CTX-1b) was studied in myotubes originated from rat skeletal muscle cells kept in primary culture. 2. The effect of P-CTX-1b on sodium currents at short times of exposure (up to 1 min) showed a moderate increase in peak Na+ current. During prolonged exposures, P-CTX-1b decreased the peak Na+ current. This action was always accompanied by an increase of leakage currents, tail currents and outward Na+ currents, resulting in an intracellular Na+ accumulation. This effect is blocked by prior exposure to tetrodotoxin (TTX) and becomes evident only after washout of TTX. 3. Low to moderate concentrations of P-CTX-1b (2-5 nM) partially blocked potassium currents in a manner that was dependent on the membrane potential. 4. P-CTX-1b (2-12 nM) caused a small membrane depolarization (3-5 mV) and an increase in the frequency of spontaneous action potential discharges that reached in general low frequencies (0.1-0.5 Hz). 5. P-CTX-1b (10 nM) caused a transient increase of intracellular inositol 1,4,5-trisphosphate (IP(3)) mass levels, which was blocked by TTX. 6. In the presence of P-CTX-1b (10 nM) and in the absence of external Ca2+, the intracellular Ca2+ levels show a transient increase in the cytoplasm as well as in the nuclei. The time course of this effect may reflect the action of IP(3) over internal stores activated by P-CTX-1b-induced membrane depolarization.

Total synthesis of gambierol

[structure: see text] The first total synthesis of gambierol, a marine polycyclic ether toxin, has been achieved. The synthesis features the Pd(PPh3)4/CuCl/LiCl-promoted Stille coupling for the stereoselective construction of the sensitive triene side chain that includes a conjugated (Z,Z)-diene moiety.

The chemistry and biological function of natural marine toxins

Studies on ciguatera fish poisoning led to clarification of the absolute stereochemistry of ciguatoxin, gambierol, gambieric acids, and maitotoxin. Anisotropic NMR reagents and fluorometric chiral HPLC reagents were effectively used together with synthesis of partial structures. Structures of 16 ciguatoxin congeners were successfully elucidated by FAB/MS/MS using samples of 5 microg or less. Stereochemical assignments were also achieved on dinophysistoxin-1, pectenotoxins, yessotoxins, polycavernoside-A, azaspiracid, and prymnesins. The toxins possessed poly-cyclic-ether structures and originated from unicellular algae. Biological functions are briefly described.

Convergent synthesis of polycyclic ethers via the intramolecular allylation of alpha-acetoxy ethers and subsequent ring-closing metathesis

The Lewis acid mediated reaction of alpha-acetoxy ethers 15-22 gave the corresponding cyclized products 23, 25, 27, 29, 31, 32, 34, and 36 in good yields with high stereoselectivities. Those cyclized products were subjected to ring-closing metathesis to afford the polycyclic ethers 38-42, 44, and 45 in good yields. The usefulness of the present methodology was demonstrated by the convergent synthesis of the CDEF ring system of brevetoxin B (1) and the CDEFG ring system of gambierol (2).

Convergent synthesis of the E'FGH' ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

[reaction: see text] A convergent synthesis of the E'FGH' ring fragment of ciguatoxin has been accomplished through (i) coupling between the E' ring-acetylide and the H' ring-aldehyde, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function, and (iv) reductive hydroxy-ketone cyclization to construct the G ring.

Synthetic studies toward gambierol. Convergent synthesis of the octacyclic polyether core

[structure: see text]. A convergent synthetic route to the octacyclic polyether core of gambierol, a marine polycyclic ether toxin, has been developed. The synthesis involves construction of two fragments representing the ABC and EFGH ring systems followed by their coupling via a B-alkyl Suzuki reaction.

C-glycosides to fused polycyclic ethers. An efficient entry into the A-D ring system of gambierol

[reaction: see text]. This Letter describes our use of C-glycosides to synthesize the A-D ring system of the marine ladder toxin gambierol in 20 steps.

Stereoselective syntheses of the C'D'E'F'-ring system of maitotoxin and the FG-ring system of gambierol

[structure: see text]. The stereoselective syntheses of the C'D'E'F'-ring system of maitotoxin and the FG-ring system of gambierol were accomplished. The key steps involve 6-endo-cyclization of methylepoxide, SmI2-induced reductive cyclization, 6-endo-cyclization of vinylepoxide, and formation of the lactone ring.

[Neurological features after consumption of a variety of neo-caledonian shellfish]

A few days after a seafood meal a patient suffered ataxia and stupor. His examination revealed a confused patient with cerebellar signs and ocular disturbances (hypotropia). Blood results, cerebrospinal fluid and brain CT scan were unremarkable. The patient developed a septic shock and died 4 weeks after admission. No necropsy was performed. Questioning his family confirmed that he had eaten a shellfish meal a few hours before onset of the digestive signs. Trocas (Tectus pyramis) were definitely identified. The clinical picture strongly suggested a seafood poisoning, namely ciguatera. However, no toxicologic assay was performed. To our knowledge, this poisoning has never been reported with trocas. Nevertheless, the feeding habits of trocas would suggest similarity with ciguatera poisoning.

Gambiertoxin (CTX-4B), purified from wild Gambierdiscus toxicus dinoflagellates, induces Na(+)-dependent swelling of single frog myelinated axons and motor nerve terminals in situ

The effects of gambiertoxin (CTX-4B), purified from the dinoflagellate Gambierdiscus toxicus, were assessed on the morphology of both frog myelinated axons and motor nerve terminals, using confocal laser scanning microscopy. During the action of the toxin (24 and 30 nM), a marked swelling of nodes of Ranvier and motor nerve terminals was observed. The CTX-4B-induced swelling could be prevented by blocking voltage-dependent Na+ channels with tetrodotoxin, and could be partly reversed by an external hyperosmotic solution containing 100 mM D-mannitol. The results suggest that CTX-4B, by modifying voltage-dependent Na+ channels, increases internal Na+ concentration of axons and nerve terminals and consequently induces water influx to compensate such an increase. It is suggested that stimulated transmitter release by CTX-4B, as well as by hyperosmotic dmannitol, contribute also to the swelling of the terminals through an increase in their surface area.

Evolution of Gambierdiscus toxicus populations in the coral reef complex of Mayotte Island (SW Indian Ocean) during the 1985-1991 period

Evolution of the Gambierdiscus toxicus populations during the 1979/1985-1991 period shows an increase of the average densities until 1988-Sept. that seems linked with climatic parameters (insolation, rainfalls) but mainly with anthropogenetic disturbances. After a bloom the populations are now stabilized at a level higher than at the beginning of the monitoring. Without clear correlation, Gtx densities seems associated to physical and chemical features of the lagoonal and reefal waters.

Clinical features of ciguatera fish poisoning: a study of the disease in the US Virgin Islands

Clinical data were obtained on 33 patients involved in 27 episodes of ciguatera fish poisoning occurring during a 14-week period on St Thomas in the US Virgin Islands. All patients had gastrointestinal tract symptoms, with 30 patients (91%) complaining of diarrhea and 23 patients (70%) complaining of vomiting; these symptoms occurred early in the disease and were of short duration. Twenty-three patients (70%) complained of malaise, and 19 patients (58%) had pain and weakness in the lower extremities. Dysesthesias were noted by 19 patients (58%); the median duration of dysesthesias was two weeks or more, with symptoms present is some cases for more than two months. Cardiovascular signs and symptoms, including both hypotension and bradycardia were noted in some acute cases. Therapy included antidiarrheal and antiemetic agents, intravenous fluids, atropine, and pralidoxime chloride. Efficacy of pralidoxime therapy could not be established on the basis of our data.

[Significance of the various toxins present on dead coral substrata in the origin of ciguatera]

The authors look directly on the coral reefs the toxins carried by poisonous fish. Pointing out two major toxic substances, they discuss their respective role in ciguatera physiopathology and suggest a new hypothesis for the origin of the phenomenon.