The Gastropods Possessing TTX and/or PSP

Automated Patch Clamp for the Detection of Tetrodotoxin in Pufferfish Samples

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

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

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

Tetrodotoxin in marine bivalves and edible gastropods: A mini-review

Tetrodotoxin (TTX) is a potent neurotoxin responsible for countless human intoxications and deaths around the world. The distribution of TTX and its analogues is diverse and the toxin has been detected in organisms from both marine and terrestrial environments. Increasing detections seafood species, such as bivalves and gastropods, has drawn attention to the toxin, reinvigorating scientific interest and regulatory concerns. There have been reports of TTX in 21 species of bivalves and edible gastropods from ten countries since the 1980's. While TTX is structurally dissimilar to saxitoxin (STX), another neurotoxin detected in seafood, it has similar sodium channel blocking action and potency and both neurotoxins have been shown to have additive toxicities. The global regulatory level for the STX group toxins applied to shellfish is 800 μg/kg. The presence of TTX in shellfish is only regulated in one country; The Netherlands, with a regulatory level of 44 μg/kg. Due to the recent interest surrounding TTX in bivalves, the European Food Safety Authority established a panel to assess the risk and regulation of TTX in bivalves, and their final opinion was that a concentration below 44 μg of TTX per kg of shellfish would not result in adverse human effects. In this article, we review current knowledge on worldwide TTX levels in edible gastropods and bivalves over the last four decades, the different methods of detection used, and the current regulatory status. We suggest research needs that will assist with knowledge gaps and ultimately allow development of robust monitoring and management protocols.

New Invasive Nemertean Species (Cephalothrix Simula) in England with High Levels of Tetrodotoxin and a Microbiome Linked to Toxin Metabolism

The marine nemertean Cephalothrix simula originates from the Pacific Ocean but in recent years has been discovered in northern Europe. The species has been associated with high levels of the marine neurotoxin Tetrodotoxin, traditionally associated with Pufferfish Poisoning. This study reports the first discovery of two organisms of C. simula in the UK, showing the geographical extent of this species is wider than originally described. Species identification was initially conducted morphologically, with confirmation by Cox 1 DNA sequencing. 16S gene sequencing enabled the taxonomic assignment of the microbiome, showing the prevalence of a large number of bacterial genera previously associated with TTX production including Alteromonas, Vibrio and Pseudomonas. LC-MS/MS analysis of the nemertean tissue revealed the presence of multiple analogues of TTX, dominated by the parent TTX, with a total toxin concentration quantified at 54 µg TTX per g of tissue. Pseudomonas luteola isolated from C. simula, together with Vibrio alginolyticus from the native nemertean Tubulanus annulatus, were cultured at low temperature and both found to contain TTX. Overall, this paper confirms the high toxicity of a newly discovered invasive nemertean species with links to toxin-producing marine bacteria and the potential risk to human safety. Further work is required to assess the geographical extent and toxicity range of C. simula along the UK coast in order to properly gauge the potential impacts on the environment and human safety.

The Acute Toxicity of Tetrodotoxin and Tetrodotoxin⁻Saxitoxin Mixtures to Mice by Various Routes of Administration

Tetrodotoxin (TTX) is a potent neurotoxin associated with human poisonings through the consumption of pufferfish. More recently, TTX has been identified in bivalve molluscs from diverse geographical environments, including Europe, and is therefore recognised as an emerging threat to food safety. A recent scientific opinion of the EFSA Panel on Contaminants in the Food Chain recognised the need for further data on the acute oral toxicity of TTX and suggested that, since saxitoxin (STX) and TTX had similar modes of action, it was possible that their toxicities were additive so could perhaps be combined to yield one health-based guideline value. The present study determined the toxicity of TTX by various routes of administration. The testing of three different mixtures of STX and TTX and comparing the experimentally determined values to those predicted on the basis of additive toxicity demonstrated that the toxicities of STX and TTX are additive. This illustrates that it is appropriate to treat TTX as a member of the paralytic shellfish group of toxins. Since the toxicity of TTX was found to be the same as STX by feeding, a molar toxicity equivalence factor of 1.0 for TTX can be applied.

Bacterial diversity and tetrodotoxin analysis in the viscera of the gastropods from Portuguese coast

To trace the pathway of tetrodotoxin (TTX) producing microorganism in the Atlantic coast of Portugal, culture-dependent evaluation of the bacterial isolates from the viscera of the gastropods Monodonta lineata, Gibbula umbilicalis, Nucella lapillus and Patella intermedia, and from the environmental samples (biofilm and surrounding sea water) was carried out. Samples were collected from eight different coastal locations of Northern Portugal. A total of 311 isolates were identified. The observed bacterial diversity was distributed over five different classes (Gammaproteobacteria, Alphaproteobacteria, Flavobacteria, Bacilli and Actinobacteria) with the greatest number of 16S rRNA gene sequence derived from the Gammaproteobacteria (75%). Phylogenetic analysis based on the 16S rRNA gene showed that bacterial isolates were highly diverse and most of which were found in other marine environment. Among the different species isolated, Vibrio was found abundant. Eventhough TTX was not detected (UPLC-MS/MS) in the isolates from this study, PCR screening identified some natural product biosynthesis genes (PKS and NRPS) involved in its assembly. Further PCR screening of the TTX producing two ATCC Vibrio sp. reveals that NRPS might be involved in the biosynthesis of TTX through the incorporation of arginine.

Potential Threats Posed by Tetrodotoxins in UK Waters: Examination of Detection Methodology Used in Their Control

Tetrodotoxin is a neurotoxin responsible for many human fatalities, most commonly following the consumption of pufferfish. Whilst the source of the toxin has not been conclusively proven, it is thought to be associated with various species of marine bacteria. Whilst the toxins are well studied in fish and gastropods, in recent years, there have been a number of reports of tetrodotoxin occurring in bivalve shellfish, including those harvested from the UK and other parts of Europe. This paper reviews evidence concerning the prevalence of tetrodotoxins in the UK together with methodologies currently available for testing. Biological, biomolecular and chemical methods are reviewed, including recommendations for further work. With the recent development of quantitative chromatographic methods for these and other hydrophilic toxins, as well as the commercial availability of rapid testing kits, there are a number of options available to ensure consumers are protected against this threat.

[Accumulation of tetrodotoxin from diet in two species of scavenging marine snails]

A feeding experiment of TTX-containing diet was conducted using the small scavenging marine snails Pliarcularia globosa and Reticunassa festiva. Seventy-five specimens of each species were divided into 15 groups of 5 individuals, of which 3 groups were directly submitted, without feeding, to toxin quantification as described below. TTX was not detected. Each of the remaining 12 groups was accommodated in a plastic case (80×70×40 mm) filled with seawater, and fed for 24 hours with ovary tissue (0.1 g) of the pufferfish Takifugu vermicularis, whose TTX content had previously been determined. Then the seawater was exchanged for fresh seawater, the snails were reared for 4 days without feeding, and then the seawater was changed again. This feeding/rearing cycle (5 days) was repeated 8 times, and 3 groups were sampled every 2 cycles. The combined viscera and combined muscle of each group were each extracted with 0.1% aqueous acetic acid, and then TTX was quantified by liquid chromatography-mass spectrometry. The estimated amount of ingested TTX was calculated by multiplying the difference between the amounts of ovary tissue supplied and remaining by the toxin content (122-126 MU/g). Similar mean values of 5.1 MU/group/cycle in P. globosa and 5.3 MU/group/cycle in R. festiva were obtained. Toxin content (TTX amount per gram of tissue) and toxin amount (TTX amount per group) during the experimental period were 0.23-2.85 MU/g and 0.05-0.96 MU/group, respectively, in P. globosa viscera. Both values increased markedly from the 2nd cycle to the 6th cycle. In contrast, no such increase in toxin content/amount was observed throughout the experimental period in P. globosa muscle (<0.05-0.86 MU/g, <0.02-0.27 MU/group), R. festiva viscera (<0.05-0.8 MU/g, <0.02-0.33 MU/group), and R. festiva muscle (<0.05-0.81 MU/g, <0.02-0.23 MU/group). The remaining ratio of TTX (percentage of total toxin amount [sum of the toxin amount of viscera and muscle] to estimated TTX ingestion amount) was less than 4% in P. globosa, and less than 2% in R. festiva after the 4th cycle, suggesting that the possibility that these two species would accumulate TTX at levels high enough to raise food hygiene issues is low.

Tetrodotoxin and paralytic shellfish poisons in gastropod species from Vietnam analyzed by high-performance liquid chromatography and liquid chromatography–tandem mass spectrometry

Among marine toxins, tetrodotoxin (TTX) and paralytic shellfish poisons (PSPs) are known as notorious neurotoxins that induce serious food poisoning incidents in the Southeast Asia region. The aim of this study was to investigate whether TTX and PSP toxins are important issues of seafood safety. Paralytic toxicity was observed in mice exposed to 34 specimens from five species of gastropods using a PSP bioassay. Five species of gastropods, Natica vitellus, Natica tumidus, Oliva hirasei, Oliva lignaria, and Oliva annulata, were collected from the coastal seawaters in Nha Trang City, Vietnam, between August 2007 and October 2007. The average lethal potency of gastropod specimens was 90 ± 40 (mean ± standard deviation) mouse units (MU) for N. vitellus, 64 ± 19 MU for N. tumidus, 42 ± 28 MU for O. hirasei, 51 ± 17 MU for O. lignaria, and 39 ± 18 MU for O. annulata. All toxic extracts from the sample species were clarified using a C18 Sep-Pak solid-phase extraction column and a microcentrifuge filter prior to analysis. High-performance liquid chromatography coupled with fluorescence detection indicated that the toxins of the olive shell (O. hirasei, O. lignaria, and O. annulata) were mainly composed of saxitoxin (STX) (73–82%), gonyautoxin (GTX) 2, 3 (12–22%), and minor levels of TTX (5–6%). The toxins of N. vitellus and N. tumidus were mainly composed of STX (76–81%) and GTX 1, 4 (19–24%). Furthermore, liquid chromatography–tandem mass spectrometry analysis was used to verify the identity of the PSPs and TTX. Our evidence shows that these gastropods have novel toxin profiles.

Microbial diversity associated with tetrodotoxin production in marine organisms

Tetrodotoxin (TTX), is a potent neurotoxin found in genetically diversed organisms. Many TTX producing microorganism have also been isolated from TTX bearing animals. The TTX producing microbes found in four different phylum (Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes), the Proteobacteria are the dominating one. In most of the cases, TTX producing microbes are found in the intestine of the TTX producing vector indicating the origin of TTX through food chain. This paper reviews the TTX and its analogs and the geographic distribution of TTX in symbiotic microorganism and its production.

The molecular mystique of tetrodotoxin

In many respects tetrodotoxin (TTX) is the quintessential natural toxin. It is unequivocally toxic to mammals with LD(50) values for mice in the range of 10 μg/kg (intraperitoneal), 16 μg/kg (subcutaneous), and 332 μg/kg (oral) (Kao, 1966). Its biothreat status is recognized by its listing as a "Select Agent" by the US Department of Health and Human Services which includes regulated agents "determined to have the potential to pose a severe threat to both human and animal health" (http://www.selectagents.gov/). It has a well-defined cellular target (i.e., NaV channels) and pharmacological mode of action (i.e., block of nerve and muscle action potentials), and it is an indispensable chemical tool in neuroscience. It is widely distributed in marine and terrestrial ecosystems where it plays a role in the chemical ecology of predator-prey relationships and drives evolutionary selection of TTX-resistance (Hanifin, 2010; Williams, 2010; Zimmer and Ferrer, 2007). Lastly, TTX has acquired a certain mystique in scientific lore attributable to many fascinating aspects of its natural history and molecular interactions as presented in selected summary below. Additional information may be found in other excellent reviews (Fozzard and Lipkind, 2010; Kao, 1966; Lee and Ruben, 2008; Narahashi, 2001, 2008).

Bioactives from microalgal dinoflagellates

Dinoflagellate microalgae are an important source of marine biotoxins. Bioactives from dinoflagellates are attracting increasing attention because of their impact on the safety of seafood and potential uses in biomedical, toxicological and pharmacological research. Here we review the potential applications of dinoflagellate toxins and the methods for producing them. Only sparing quantities of dinoflagellate toxins are generally available and this hinders bioactivity characterization and evaluation in possible applications. Approaches to production of increased quantities of dinoflagellate bioactives are discussed. Although many dinoflagellates are fragile and grow slowly, controlled culture in bioreactors appears to be generally suitable for producing many of the metabolites of interest.

Tetrodotoxin poisoning due to pufferfish and gastropods, and their intoxication mechanism

Marine pufferfish generally contain a large amount of tetrodotoxin (TTX) in their skin and viscera, and have caused many incidences of food poisoning, especially in Japan. Edible species and body tissues of pufferfish, as well as their allowable fishing areas, are therefore clearly stipulated in Japan, but still 2 to 3 people die every year due to pufferfish poisoning. TTX is originally produced by marine bacteria, and pufferfish are intoxicated through the food chain that starts with the bacteria. Pufferfish become nontoxic when fed TTX-free diets in a closed environment in which there is no possible invasion of TTX-bearing organisms. On the other hand, TTX poisoning due to marine snails has recently spread through Japan, China, Taiwan, and Europe. In addition, TTX poisoning of dogs due to the ingestion of sea slugs was recently reported in New Zealand. TTX in these gastropods also seems to be exogenous; carnivorous large snails are intoxicated by eating toxic starfish, and necrophagous small-to-medium snails, the viscera of dead pufferfish after spawning. Close attention must be paid to the geographic expansion and/or diversification of TTX-bearing organisms, and to the sudden occurrence of other forms of TTX poisoning due to their ingestion.

Behavioral and chemical ecology of marine organisms with respect to tetrodotoxin

The behavioral and chemical ecology of marine organisms that possess tetrodotoxin (TTX) has not been comprehensively reviewed in one work to date. The evidence for TTX as an antipredator defense, as venom, as a sex pheromone, and as an attractant for TTX-sequestering organisms is discussed. Little is known about the adaptive value of TTX in microbial producers; thus, I focus on what is known about metazoans that are purported to accumulate TTX through diet or symbioses. Much of what has been proposed is inferred based on the anatomical distribution of TTX. Direct empirical tests of these hypotheses are absent in most cases.

[Toxicity and toxin profile of tetrodotoxin detected in the scavenging gastropod Nassarius (Alectrion) glans "Kinshibai"]

From September 2007 to January 2008, a total of 66 specimens of 7 gastropod species, Nassarius (Alectrion) glans (n=22), Bufonaria rana (n=11), Ficus subintermedia (n=10), Stellaria (Onustus) exutus (n=8), Tonna luteostoma (n=7), Hemifusus tuba (n=4) and Semicassis bisulcata persimilis (n=4), were collected from Tachibana Bay, Nagasaki Prefecture, Japan, and their toxicity was determined by mouse bioassay. Among the gastropods tested, all N. glans specimens were toxic, whereas no other species showed toxicity of more than 5 MU/g. The toxicity scores of N. glans were very high; 48-2,730 MU/g(775+/-615 MU/g)in the muscle, and 16-10,200 MU/g(1,490+/-2,530 MU/g)in the viscera, including digestive gland. Interestingly, toxin was localized in the muscle in 13 of 22 specimens, where the total toxicity of the muscle (725-9,860 MU/individual) was 5.9-110 times higher than that of the viscera. LC/MS analysis demonstrated that the toxin of N. glans consisted mainly of TTX, which accounting for about 60-65% of the total toxicity. As for the remaining toxicity, participation of 11-oxoTTX was suggested. No paralytic shellfish poison was detected in HPLC-FLD analysis.