Involvement of carrier-mediated transport system in uptake of tetrodotoxin into liver tissue slices of puffer fish Takifugu rubripes

Comparative biochemical characterization of pufferfish saxitoxin and tetrodotoxin-binding protein (PSTBP) homologs in the plasma from four Takifugu species: Conservation of heat-stable PSTBP orthologs having three and two tandemly repeated lipocalin domains in genus Takifugu

To study the relationship between domain characteristics of pufferfish saxitoxin and tetrodotoxin binding protein (PSTBP) proteoforms and their thermal stability, a comparative biochemical characterization of PSTBPs from the plasma of four Takifugu species (T. flavipterus, T. pardalis, T. alboplumbeus and T. rubripes) was conducted by Western blot analysis. The heat-tolerance tetrodotoxin (TTX)-binding ability of PSTBP proteoforms in T. rubripes plasma was verified by ultrafiltration and liquid chromatography tandem mass spectrometry (LC-MS/MS). These results suggest that the heat-stable PSTBP proteoforms, composed of three and two tandemly repeated lipocalin domains, are genetically conserved and ubiquitous in the genus Takifugu. This study builds on our knowledge of the structural and functional properties of PSTBP proteoforms, which is vital for understanding how toxins are transmitted and accumulate in organisms and is essential for evaluating the potential risks of toxins in seafood.

Epidermal distribution of tetrodotoxin-rich cells in newly hatched larvae of Takifugu spp

Pufferfish of the genus Takifugu possess tetrodotoxin (TTX), known as "pufferfish toxin" and it is believed that pufferfish eggs and newly hatched larvae utilize TTX as a defensive substance against predators. However, the mechanism for the placement of TTX to specific cells on the larval body surface during the developmental process remains unknown. In this study, we clarify the distribution and characteristics of TTX-rich cells. We performed whole-mount immunohistochemistry (IHC) using anti-TTX monoclonal antibody on larvae of two pufferfish species, Takifugu rubripes and Takifugu alboplumbeus, just after hatching. This allowed observation of the TTX location and compared it with those of wheat germ agglutinin (WGA)-positive (periodic acid-Schiff (PAS)-positive) cells for mucous cells and IHC using anti-Na+/K+-ATPase (NKA) monoclonal antibody for ionocytes. As a result, uniformly scattered localization of TTX-rich cells was commonly observed in the epidermis of the larvae of the two Takifugu species. TTX-rich cells were WGA-negative (PAS-negative) and structurally distinct from NKA-positive cells, suggesting that TTX-rich cells are unreported small cells unique to pufferfish skin, but not mucous cells nor ionocytes.

Tetrodotoxin and Its Analogues (TTXs) in the Food-Capture and Defense Organs of the Palaeonemertean Cephalothrix cf. simula

Tetrodotoxin (TTX), an extremely potent low-molecular-weight neurotoxin, is widespread among marine animals including ribbon worms (Nemertea). Previously, studies on the highly toxic palaeonemertean Cephalothrix cf. simula showed that toxin-positive structures are present all over its body and are mainly associated with glandular cells and epithelial tissues. The highest TTXs concentrations were detected in a total extract from the intestine of the anterior part of the body and also in a total extract from the proboscis. However, many questions as to the TTXs distribution in the organs of the anterior part of the worm's body and the functions of the toxins in these organs are still unanswered. In the present report, we provide additional results of a detailed and comprehensive analysis of TTXs distribution in the nemertean's proboscis, buccal cavity, and cephalic gland using an integrated approach including high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), confocal laser scanning microscopy with anti-TTX antibodies, light and electron microscopies, and observations of feeding behavior. For the proboscis, we have found a TTXs profile different from that characteristic of other organs and tissues. We have also shown for the first time that the major amount of TTXs is localized in the anterior part of the proboscis that is mainly involved in hunting. TTX-containing glandular cells, which can be involved in the prey immobilization, have been found in the buccal cavities of the nemerteans. A significant contribution of the cephalic gland to the toxicity of this animal has been shown for the first time, and the role of the gland is hypothesized to be involved not only in protection against potential enemies but also in immobilizing prey. The data obtained have made it possible to extend the understanding of the role and features of the use of TTXs in the organs of the anterior part of nemertean's body.

Wheat germ agglutinin affinity chromatography enrichment and glyco-proteomic characterization of tetrodotoxin-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes)

Efficient enrichment of tetrodotoxin (TTX)-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes) was achieved by ammonium sulfate fractionation and wheat germ agglutinin (WGA) affinity chromatography. The enrichment efficiency was validated by ultrafiltration-LC/MS-based TTX-binding assay and proteomics. Major proteins in the WGA-bound fraction were identified as isoform X1 (125 kDa) and X2 variants (88 and 79 kDa) derived from pufferfish saxitoxin and tetrodotoxin-binding protein (PSTBP) 1-like gene (LOC101075943). The 125-kDa X1 protein was found to be a novel member of the lipocalin family, having three tandemly repeated domains. X2 variants, X2α and X2β, were estimated to have two domains, and X2β is structurally related to Takifugu pardalis PSTBP2 in their domain type and arrangement. Among 11 potential N-glycosylation sites in the X2 precursor, 5 N-glycosylated Asn residues (N55, N89, N244, N308, and N449) were empirically determined. Structural relationships among PSTBP homologs and complexity of their proteoforms are discussed.

[Tetrodotoxin Content of the Small Gastropod Nassarius sufflatus]

Severe tetrodotoxin (TTX) poisoning due to small gastropods has been documented in Japan. In this study, we investigated the TTX content of the muscles and viscera of Nassarius sufflatus collected off the coast of Futaoi Island, Shimonoseki, Yamaguchi Prefecture, Japan, to prevent the occurrence of TTX poisoning caused by this small gastropod. Live specimens were obtained, and their muscles and viscera were collected. Test solutions were prepared from tissues of specimens and analyzed for TTX by HPLC-fluorescence detection. TTX was detected in both tissues at concentrations ranging from <0.1 to 18.2 μg/g for muscle and <0.1 to 130.7 μg/g for viscera. These results suggested that N. sufflatus accumulates TTX not only in its viscera but also in its muscles, and that precautions should be taken to prevent food poisoning due to this gastropod.

An Overview of the Anatomical Distribution of Tetrodotoxin in Animals

Tetrodotoxin (TTX), a potent paralytic sodium channel blocker, is an intriguing marine toxin. Widely distributed in nature, TTX has attracted attention in various scientific fields, from biomedical studies to environmental safety concerns. Despite a long history of studies, many issues concerning the biosynthesis, origin, and spread of TTX in animals and ecosystems remain. This review aims to summarize the current knowledge on TTX circulation inside TTX-bearing animal bodies. We focus on the advances in TTX detection at the cellular and subcellular levels, providing an expanded picture of intra-organismal TTX migration mechanisms. We believe that this review will help address the gaps in the understanding of the biological function of TTX and facilitate the development of further studies involving TTX-bearing animals.

Local Differences in the Toxin Amount and Composition of Tetrodotoxin and Related Compounds in Pufferfish (Chelonodon patoca) and Toxic Goby (Yongeichthys criniger) Juveniles

Tetrodotoxin (TTX)-bearing fish ingest TTX from their preys through the food chain and accumulate TTX in their bodies. Although a wide variety of TTX-bearing organisms have been reported, the missing link in the TTX supply chain has not been elucidated completely. Here, we investigated the composition of TTX and 5,6,11-trideoxyTTX in juveniles of the pufferfish, Chelonodon patoca, and toxic goby, Yongeichthys criniger, using LC-MS/MS, to resolve the missing link in the TTX supply chain. The TTX concentration varied among samples from different localities, sampling periods and fish species. In the samples from the same locality, the TTX concentration was significantly higher in the toxic goby juveniles than in the pufferfish juveniles. The concentration of TTX in all the pufferfish juveniles was significantly higher than that of 5,6,11-trideoxyTTX, whereas the compositional ratio of TTX and 5,6,11-trideoxyTTX in the goby was different among sampling localities. However, the TTX/5,6,11-trideoxyTTX ratio in the goby was not different among samples collected from the same locality at different periods. Based on a species-specific PCR, the detection rate of the toxic flatworm (Planocera multitentaculata)-specific sequence (cytochrome c oxidase subunit I) also varied between the intestinal contents of the pufferfish and toxic goby collected at different localities and periods. These results suggest that although the larvae of the toxic flatworm are likely to be responsible for the toxification of the pufferfish and toxic goby juveniles by TTX, these fish juveniles are also likely to feed on other TTX-bearing organisms depending on their habitat, and they also possess different accumulation mechanisms of TTX and 5,6,11-trideoxyTTX.

Tetrodotoxin in live bivalve mollusks from Europe: Is it to be considered an emerging concern for food safety?

Tetrodotoxins (TTXs) are a group of potent neurotoxins named after the Tetraodontidae fish family (pufferfish). TTXs have been reported in several animal taxa, both terrestrial and marine. The ingestion of TTX-contaminated flesh can cause serious neurotoxic symptomatology and can eventually lead to death. Traditionally, TTXs have been associated with Asian countries, in particular with pufferfish consumption. However, they have also been reported in bivalve mollusks farmed in the Pacific area and, recently, in European seas. In Europe, different countries have reported TTXs, especially those bordering the Mediterranean Sea. As a consequence, in 2017 the European Food Safety Authority (EFSA) released an opinion with reference to TTX present in marine gastropods and bivalves, proposing a safety limit of 44 µg/kg TTXs in shellfish meat, below which no adverse effects should be observed in humans. Nevertheless, this limit has been exceeded on many occasions in European shellfish and, while for bivalves there have been no registered human intoxications, that is not the case for marine gastropods. However, TTXs have not yet been included in the list of marine biotoxins officially monitored in live bivalve mollusks within the European Union (EU). Thus, the aims of this manuscript are to discuss the increasing occurrence of TTXs in live bivalve mollusks from European sea waters, to acknowledge the still ongoing knowledge gaps that should be covered and to stimulate constructive debate on the eventuality of adopting a shared regulatory context, at least in the EU, for monitoring and managing this potential threat to food safety.

Evidence of accumulation of tetrodotoxin (TTX) in tissues and body parts of ectoparasitic copepods via their feeding on mucus of TTX-bearing pufferfish

Adults of the ectoparasitic copepod Caligus fugu found on tetrodotoxin (TTX)-bearing pufferfish such as Takifugu alboplumbeus and Takifugu flavipterus are known to accumulate TTX in body tissues and parts other than the ovaries, oviducts, eggs, and cuticles. This study aimed to demonstrate, using immunoenzymatic staining techniques, that the TTX-free planktonic/infective copepodid stage of C. fugu could accumulate TTX in the tissues after molting into the parasitic stage (chalimus I) and then fed on mucus of host puffers. All the tissues of the planktonic copepodids were completely TTX-free, whereas chalimus I copepods accumulated TTX in parts other than the cuticles, guts, and some muscles. Chalimus IV and adult copepods retained TTX in these body parts but not in the reproductive organs, which were TTX-resistant, indicating that TTX was not vertically transmitted via eggs. Non-cellular TTX-positive contents found in the guts of some chalimi and adults indicated that the copepods potentially accumulated TTX by feeding on host mucus rather than skin tissues and blood. This study revealed that the presence or absence of TTX in some body parts differed among individuals of the parasite.

Tetrodotoxin/Saxitoxins Selectivity of the Euryhaline Freshwater Pufferfish Dichotomyctere fluviatilis

The present study evaluated differences in the tetrodotoxin (TTX)/saxitoxins (STXs) selectivity between marine and freshwater pufferfish by performing in vivo and in vitro experiments. In the in vivo experiment, artificially reared nontoxic euryhaline freshwater pufferfish Dichotomyctere fluviatilis were intrarectally administered a mixture of TTX (24 nmol/fish) and STX (20 nmol/fish). The amount of toxin in the intestine, liver, muscle, gonads, and skin was quantified at 24, 48, and 72 h. STX was detected in the intestine over a long period of time, with some (2.7-6.1% of the given dose) being absorbed into the body and temporarily located in the liver. Very little TTX was retained in the body. In the in vitro experiments, slices of intestine, liver, and skin tissue prepared from artificially reared nontoxic D. fluviatilis and the marine pufferfish Takifugu rubripes were incubated in buffer containing TTX and STXs (20 nmol/mL each) for up to 24 or 72 h, and the amount of toxin taken up in the tissue was quantified over time. In contrast to T. rubripes, the intestine, liver, and skin tissues of D. fluviatilis selectively took up only STXs. These findings indicate that the TTX/STXs selectivity differs between freshwater and marine pufferfish.

Tetrodotoxin and Its Analogues in Cephalothrix cf. simula (Nemertea: Palaeonemertea) from the Sea of Japan (Peter the Great Gulf): Intrabody Distribution and Secretions

Some nemertean species from the genus Cephalothrix accumulate tetrodotoxin (TTX) in extremely high concentrations. The current study is the first to provide high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) data on tetrodotoxin and its analogues (TTXs) profile and concentration in different regions and organs of Cephalothrix cf. simula, and its secretions produced in response to stimulation. Different specimens of C. cf. simula possessed 7-11 analogues, including nine previously found in this species and two new for nemerteans-4,9-anhydro-8-epi-5,6,11-trideoxyTTX and 1-hydroxy-8-epi-5,6,11-trideoxyTTX. The study of the toxins' distribution in different regions and organs of nemerteans revealed the same qualitative composition of TTXs throughout the body but differences in the total concentration of the toxins. The total concentration of TTXs was highest in the anterior region of the body and decreased towards the posterior; the ratio of the analogues also differed between regions. The data obtained suggest a pathway of TTXs uptake in C. cf. simula and the role of toxins in the life activity of nemerteans.

Evaluation of the tetrodotoxin uptake ability of pufferfish Takifugu rubripes tissues according to age using an in vitro tissue slice incubation method

The tetrodotoxin (TTX) uptake ability of pufferfish Takifugu rubripes tissues and its growth-associated changes were investigated using an in vitro tissue slice incubation method. Tissue slices prepared from the liver, skin, and intestine of a non-toxic cultured adult T. rubripes (20 months old) and incubated with incubation buffer containing 25 μg/mL TTX for 1-48 h showed a time-dependent increase in the TTX content in all tissues. The TTX contents of the skin and intestine slices were comparable to or slightly higher than that of the liver slices, with a similar transition pattern, suggesting similar TTX uptake ability among the skin, intestine, and liver. The TTX uptake ability of the liver and intestine did not differ significantly between young (8 months old) and adult (20 months old) fish, but the skin slices of young fish took up approximately twice as much TTX as that of adult fish, suggesting that the TTX uptake ability of the skin is involved in the growth-dependent changes in the toxin distribution inside the body in T. rubripes. To estimate the TTX uptake pathway in each tissue, an immunohistochemical technique was used to observe temporal changes in the intra-tissue microdistribution of TTX during incubation. The findings suggested that TTX is transferred and accumulates from pancreatic exocrine cells to hepatic parenchymal cells in the liver, from connective tissues to basal cells in the skin, and from villi epithelial cells via the lamina propria to the muscle layer in the intestine.

Chromosomal-level assembly of Takifugu obscurus (Abe, 1949) genome using third-generation DNA sequencing and Hi-C analysis

The Tetraodontidae family are known to have relatively small and compact genomes compared to other vertebrates. The obscure puffer fish Takifugu obscurus is an anadromous species that migrates to freshwater from the sea for spawning. Thus the euryhaline characteristics of T. obscurus have been investigated to gain understanding of their survival ability, osmoregulation, and other homeostatic mechanisms in both freshwater and seawater. In this study, a high quality chromosome-level reference genome for T. obscurus was constructed using long-read Pacific Biosciences (PacBio) Sequel sequencing and a Hi-C-based chromatin contact map platform. The final genome assembly of T. obscurus is 381 Mb, with a contig N50 length of 3,296 kb and longest length of 10.7 Mb, from a total of 62 Gb of raw reads generated using single-molecule real-time sequencing technology from a PacBio Sequel platform. The PacBio data were further clustered into chromosome-scale scaffolds using a Hi-C approach, resulting in a 373 Mb genome assembly with a contig N50 length of 15.2 Mb and and longest length of 28 Mb. When we directly compared the 22 longest scaffolds of T. obscurus to the 22 chromosomes of the tiger puffer Takifugu rubripes, a clear one-to-one orthologous relationship was observed between the two species, supporting the chromosome-level assembly of T. obscurus. This genome assembly can serve as a valuable genetic resource for exploring fugu-specific compact genome characteristics, and will provide essential genomic information for understanding molecular adaptations to salinity fluctuations and the evolution of osmoregulatory mechanisms.

The evolution and origin of tetrodotoxin acquisition in the blue-ringed octopus (genus Hapalochlaena)

Tetrodotoxin is a potent non-proteinaceous neurotoxin, which is commonly found in the marine environment. Synthesised by bacteria, tetrodotoxin has been isolated from the tissues of several genera including pufferfish, salamanders and octopus. Believed to provide a defensive function, the independent evolution of tetrodotoxin sequestration is poorly understood in most species. Two mechanisms of tetrodotoxin resistance have been identified to date, tetrodotoxin binding proteins in the circulatory system and mutations to voltage gated sodium channels, the binding target of tetrodotoxin with the former potentially succeeding the latter in evolutionary time. This review focuses on the evolution of tetrodotoxin acquisition, in particular how it may have occurred within the blue-ringed octopus genus (Hapalochlaena) and the subsequent impact on venom evolution.

Difference in Uptake of Tetrodotoxin and Saxitoxins into Liver Tissue Slices among Pufferfish, Boxfish and Porcupinefish

Although pufferfish of the family Tetraodontidae contain high levels of tetrodotoxin (TTX) mainly in the liver, some species of pufferfish, boxfish of the family Ostraciidae, and porcupinefish of the family Diodontidae do not. To clarify the mechanisms, uptake of TTX and saxitoxins (STXs) into liver tissue slices of pufferfish, boxfish and porcupinefish was examined. Liver tissue slices of the pufferfish (toxic species Takifugu rubripes and non-toxic species Lagocephalus spadiceus, L. cheesemanii and Sphoeroides pachygaster) incubated with 50 µM TTX accumulated TTX (0.99-1.55 µg TTX/mg protein) after 8 h, regardless of the toxicity of the species. In contrast, in liver tissue slices of boxfish (Ostracion immaculatus) and porcupinefish (Diodon holocanthus, D. liturosus, D. hystrix and Chilomycterus reticulatus), TTX content did not increase with incubation time, and was about 0.1 µg TTX/mg protein. When liver tissue slices were incubated with 50 µM STXs for 8 h, the STXs content was <0.1 µg STXs/mg protein, irrespective of the fish species. These findings indicate that, like the toxic species of pufferfish T. rubripes, non-toxic species such as L. spadiceus, L. cheesemanii and S. pachygaster, potentially take up TTX into the liver, while non-toxic boxfish and porcupinefish do not take up either TTX or STXs.

A novel function of vitellogenin subdomain, vWF type D, as a toxin-binding protein in the pufferfish Takifugu pardalis ovary

Marine pufferfish of the Tetraodontidae family contain high levels of tetrodotoxin (TTX) in the liver and ovary. TTX is suggested to transfer from the liver to the ovary in female pufferfish during maturation. TTX in pufferfish eggs may act as a repellent against predators and as a sexual pheromone to attract male pufferfish. The toxification mechanism of the pufferfish ovary is poorly understood. Here we evaluated the chemical form of TTX and its related substances in the ovary of the panther pufferfish Takifugu pardalis by LC-ESI/MS. TTX and its analogs 4-epi-TTX, 4, 9-anhydroTTX, deoxyTTX, dideoxyTTX, and trideoxyTTX were detected in a low molecular weight fraction by Sephacryl S-400 column chromatography. The finding of an unknown TTX-related substance in a high molecular weight fraction from the Sephacryl S-400 column suggested the occurrence of toxin-binding protein in the ovary. The toxin-binding protein in the ovary was purified by ion-exchange HPLC, gel filtration HPLC, and SDS-PAGE. Amino acid sequencing and cDNA cloning revealed that the toxin-binding protein, TPOBP-10 (Takifugu pardalis ovary toxin-binding protein with a molecular mass of 10 kDa) was homologous with the predicted vitellogenin-1-like protein [Takifugu rubripes] subdomain, a von Willebrand factor type D domain. TPOBP-10 mRNA was highly expressed in the ovary and liver and less in other organs of female individuals based on RT-PCR. These findings reveal a novel function of the vitellogenin subdomain as binding with TTX-related substances, and its involvement in the toxification of the pufferfish ovary.

Different effects of growth hormone and fasting on the induction patterns of two hormone-sensitive lipase genes in red seabream Pagrus major

Growth hormone (GH) increases phosphorylation and mRNA levels of hormone-sensitive lipase (HSL) in the livers of some marine teleosts. The hepatic GH-HSL axis appears to play important roles in fasting-induced lipolysis. However, it is not known whether GH exerts similar effects on HSL in fish adipose tissues. Functional differentiation of two fish-specific HSL isoforms (HSL1 and HSL2) also remains unclear. The present study seeks to address two unanswered questions about fish lipolysis using red seabream (Pagrus major): (1) Does GH increase phosphorylation and mRNA levels of HSL in adipose tissue? (2) How do GH and fasting affect mRNA levels of two HSL isoform genes in the liver and adipose tissue? To this end, we first cloned HSL1 and HSL2 cDNAs and investigated their tissue distribution. Transcripts of both HSLs and HSL1 proteins were abundant in the visceral adipose tissue, gonads, and liver, suggesting the important role of HSL in adipose tissue lipolysis. HSL2 transcript levels were 20-65% those of HSL1 except in the skin, and HSL2 proteins were not detected by our in-house antisera. Ex vivo administration of GH increased HSL1 phosphorylation, non-esterified fatty acid (NEFA) release, and levels of HSL1 and HSL2 mRNA in both the liver and visceral adipose tissue. Hepatic HSL2 mRNA was particularly sensitive to GH administration and sometimes exceeded HSL1 mRNA levels with up to 13-fold induction. In contrast, fasting for 4 and 7d increased HSL1 mRNA levels, but had only marginal effects on HSL2 mRNA levels in both adipose tissue or liver. We concluded that GH would increase HSL mRNAs during adipose tissue lipolysis in red seabream; however, GH and fasting result in different induction ratio of two HSL isoform genes, suggesting that other hormone(s) also contributes to fasting-induced lipolysis.

Tetrodotoxin, an Extremely Potent Marine Neurotoxin: Distribution, Toxicity, Origin and Therapeutical Uses

Tetrodotoxin (TTX) is a potent neurotoxin responsible for many human intoxications and fatalities each year. The origin of TTX is unknown, but in the pufferfish, it seems to be produced by endosymbiotic bacteria that often seem to be passed down the food chain. The ingestion of contaminated pufferfish, considered the most delicious fish in Japan, is the usual route of toxicity. This neurotoxin, reported as a threat to human health in Asian countries, has spread to the Pacific and Mediterranean, due to the increase of temperature waters worldwide. TTX, for which there is no known antidote, inhibits sodium channel producing heart failure in many cases and consequently death. In Japan, a regulatory limit of 2 mg eq TTX/kg was established, although the restaurant preparation of “fugu” is strictly controlled by law and only chefs qualified are allowed to prepare the fish. Due to its paralysis effect, this neurotoxin could be used in the medical field as an analgesic to treat some cancer pains.

First Report of Ciguatoxins in Two Starfish Species: Ophidiaster ophidianus and Marthasterias glacialis

Ciguatera fish poisoning (CFP) is a syndrome caused by the ingestion of fish contaminated with Ciguatoxins (CTXs). These phycotoxins are produced mainly by dinoflagellates that belong to the genus Gambierdiscus that are transformed in more toxic forms in predatory fish guts, and are more present in the Indo-Pacific and Caribbean areas. It is estimated that CFP causes per year more than 10,000 intoxications worldwide. With the rise of water temperature and anthropogenic intervention, it is important to study the prevalence of CFP in more temperate waters. Through inter- and subtidal sampling, 22 species of organisms were collected, in Madeira and Azores archipelagos and in the northwestern Moroccan coast, during September of 2012 and June and July of 2013. A total of 94 samples of 22 different species of bivalves, gastropods, echinoderms and crustaceans where analyzed by Ultra Performance Liquid Chromatography-Mass Spectometry-Ion Trap-Time of Flight (UPLC-MS-IT-TOF) and Ultra Performance Chromatography- Mass Spectrometry (UPLC-MS). Our main aim was to detect new vectors and ascertain if there were some geographical differences. We detected for the first time putative CTXs in echinoderms, in two starfish species-M. glacialis and O. ophidianus. We detected differences regarding uptake values by organisms and geographical location. Toxin amounts were significant, showing the importance and the need for continuity of these studies to gain more knowledge about the prevalence of these toxins, in order to better access human health risk. In addition, we suggest monitoring of these toxins should be extended to other vectors, starfish being a good alternative for protecting and accessing human health risk.

DNA Microarray Analysis on the Genes Differentially Expressed in the Liver of the Pufferfish, Takifugu rubripes, Following an Intramuscular Administration of Tetrodotoxin

Pufferfish accumulate tetrodotoxin (TTX) mainly in the liver and ovary. This study aims at investigating the effect of TTX accumulation in the liver of cultured specimens of torafugu Takifugu rubripes on the hepatic gene expression by microarray analysis on Day 5 after the intramuscular administration of 0.25 mg TTX/kg body weight into the caudal muscle. TTX was detected in the liver, skin and ovary in the TTX-administered individuals. The total amount of TTX accumulated in the body was 67 ± 8% of the administered dose on Day 5. Compared with the buffer-administered control group, a total of 59 genes were significantly upregulated more than two-fold in the TTX-administered group, including those encoding chymotrypsin-like elastase family member 2A, transmembrane protein 168 and Rho GTP-activating protein 29. In contrast, a total of 427 genes were downregulated by TTX administration, including those encoding elongation factor G2, R-spondin-3, nuclear receptor activator 2 and fatty acyl-CoA hydrolase precursor. In conclusion, our results demonstrate that the intramuscular administration of TTX changes the expression of hepatic genes involved in various signaling pathways.

Comparison of the localization of tetrodotoxin between wild pufferfish Takifugu rubripes juveniles and hatchery-reared juveniles with tetrodotoxin administration

To reveal the accumulation profile of tetrodotoxin (TTX) in pufferfish Takifugu rubripes juveniles, we compared the localization of TTX in various tissues among wild juveniles and hatchery-reared juveniles with or without TTX administration using immunohistochemical technique with anti-TTX monoclonal antibody. Immuno-positive reaction was observed in hepatic tissue, basal cell of skin and olfactory, olfactory epithelium, optic nerve and brain (optic tectum, cerebellum, medulla oblongata) of wild juveniles (body length: BL, 4.7-9.4 cm). TTX was detected in the same tissues as wild juveniles and epithelial cell layer of intestine of hatchery-reared juveniles (BL, 5.0-5.3 cm) to which TTX was orally administrated. No positive reaction was observed from the tissues of hatchery-reared juveniles without TTX administration. These results suggest that orally administrated TTX to the non-toxic cultured juveniles is accumulated in the same manner of wild juveniles. In addition, our study revealed that pufferfish accumulates TTX in the central nervous system.

Change in the transfer profile of orally administered tetrodotoxin to non-toxic cultured pufferfish Takifugu rubripes depending of its development stage

To investigate the effects of growth (organ development) on tetrodotoxin (TTX) dynamics in the pufferfish body, TTX-containing feed homogenate was administered to 6- and 15-month old non-toxic cultured specimens of the pufferfish Takifugu rubripes at a dose of 40 mouse units (MU) (8.8 μg)/20 g body weight by oral gavage. After 24 h, the specimens were killed and the skin tissues (dorsal and ventral), muscle, liver, digestive tract, and gonads were separated. TTX content (μg/g) in each tissue, determined by liquid chromatography/mass spectrometry, revealed that the TTX distribution profile, particularly the TTX content of the liver, greatly differed between the two ages; the TTX score of 15-month old fish (3.3 μg/g) was nearly 5-fold that of 6-month old fish (0.68 μg/g). The total remaining TTX amount per individual (relative amount to the given dose) was 31% in 6-month old fish, of which 71% was in the skin, and 84% in 15-month old fish, of which 83% was in the liver. The gonadosomatic index (GSI) and hepatosomatic index (HSI) scores, and histologic observations of the gonads and liver suggest that although there is little difference in maturation stage between these two ages, there are clear distinctions in the developmental stage of the liver. The results suggest that the TTX dynamics in T. rubripes are linked to the development of the liver, i.e., the TTX taken up into the pufferfish body via food organisms is eliminated or transferred mainly to the skin in young fish with an undeveloped liver, but as the fish grow and the liver continues to develop, most of the TTX is transferred to and accumulated in the liver.

Alterations in activity and mRNA expression of acetylcholinesterase in the liver, kidney and gill of common carp exposed to atrazine and chlorpyrifos

Insecticides and herbicides are widely used in modern agricultural production. The intensive use of insecticide chlorpyrifos (CPF) and herbicide atrazine (ATR) has resulted in serious environmental problems. Herein, we investigated alteration in activity and mRNA levels of AChE in the liver, kidney and gill from common carp after 40d exposure to CPF and ATR alone or in combination and 20d recovery treatment. Results indicated that activity and mRNA levels of AChE at all high-dose groups have been significantly decreased after CPF and ATR alone or ATR/CPF mixture exposure, and the changes were improved in the end of recovery tests in varying degrees, the activity and gene expression of AChE in the joint toxicity of ATR and CPF groups were significantly lower than that in the single toxicant group. Our study suggests that the decrease of AChE activity observed at all high-dose groups (CPF and ATR alone or in combination) may be directly related to a lower AChE expression, and the joint toxicity of ATR and CPF is higher than ATR and CPF alone.

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).

Transfer profile of orally and intramuscularly administered tetrodotoxin to artificial hybrid specimens of the pufferfish Takifugu rubripes and Takifugu porphyreus

Tetrodotoxin (TTX) was administered to artificially hybridized specimens of the pufferfish Takifugu rubripes and Takifugu porphyreus to investigate toxin accumulation in hybrids and TTX transfer/accumulation profiles in the pufferfish body. In test fish administered TTX-containing feed homogenate at a dose of ∼400 MU/fish by oral gavage using a syringe (OGA group), the toxin content (MU/g tissue) of the digestive tract rapidly decreased and that of the liver increased from 1 to 24 h after administration. From 24 to 120 h, the toxin content of the liver decreased gradually, and the toxin appeared in the skin. On the other hand, intramuscularly administered TTX (400 MU/fish) was rapidly transferred to the liver and skin via the blood, and only a little toxin remained in the muscle even at 1 h (IMA group). The total amount of toxin remaining in the whole body (% of administered toxin) was 31-45% in the OGA group, and 42-74% in the IMA group; the scores in the OGA group were generally lower than those in the IMA group. In both OGA and IMA groups, the greatest amount of toxin accumulated in the liver (23-52%) after 8 h, followed by the skin (11-21%) after 72 h. The TTX administration experiment, especially using the oral gavage administration method, revealed that skins and livers of 'torama' pufferfish hybrid are endowed with TTX-accumulating ability, but the muscles are not, and that TTX taken up from toxic feed to the pufferfish body is transferred first to the liver and then to the skin via the blood.

New gastropod vectors and tetrodotoxin potential expansion in temperate waters of the Atlantic Ocean

Tetrodotoxin is a potent low weight marine toxin found in warm waters, especially of the Indian and Pacific Oceans. Intoxications are usually linked to the consumption of the puffer fish, although TTX was already detected in several different edible taxa. Benthic organisms such as mollusks and echinoderms, with different feeding habits, were collected monthly along the Portuguese coast from the summer of 2009 until the end of 2010. The extraction and analysis techniques were optimized and TTX and some analogues were detected for the first time in two intertidal gastropod species-Gibbula umbilicalis and Monodonta lineata by LC-MS/MS and UPLC-MS/MS. Although the levels are low, these findings suggest that monitoring of TTX and analogues in North Atlantic species should be implemented so as to detect potentially new toxin vectors and seasonal and/or geographical patterns.

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.

Transfer profile of intramuscularly administered tetrodotoxin to artificial hybrid specimens of pufferfish, Takifugu rubripes and Takifugu niphobles

Tetrodotoxin (TTX) was intramuscularly administered to artificially hybridized specimens of the pufferfish Takifugu rubripes and Takifugu niphobles to investigate toxin accumulation in hybrids, and TTX transfer/accumulation profiles in the pufferfish body. In the test fish administered 146 MU TTX in physiologic saline, TTX rapidly transferred from the muscle via the blood to other organs. Toxin transfer to the ovary rapidly increased to 53.5 MU/g tissue at the end of the 72-h test period. The TTX content in the liver and skin was, at most, around 4-6 MU/g tissue, and in the testis it was less than 0.01 MU/g tissue. On the other hand, based on the total amount of toxin per individual (% of the administered toxin), the skin and the liver contained higher amounts (20-54% and 2-24%, respectively), but the amount in the liver rapidly decreased after 8-12 h, and fell below the level in the ovary after 48 h. These findings suggest that part of the TTX is first taken up in the liver and then transferred/accumulated in the skin in male specimens and in the ovary in female specimens.

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

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

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.

Plasma protein binding of tetrodotoxin in the marine puffer fish Takifugu rubripes

To elucidate the involvement of plasma protein binding in the disposition of tetrodotoxin (TTX) in puffer fish, we used equilibrium dialysis to measure protein binding of TTX in the plasma of the marine puffer fish Takifugu rubripes and the non-toxic greenling Hexagrammos otakii, and in solutions of bovine serum albumin (BSA) and bovine alpha-1-acid glycoprotein (AGP). TTX (100-1000 microg/mL) bound to protein in T. rubripes plasma with low affinity in a non-saturable manner. The amount of bound TTX increased linearly with the TTX concentration, reaching 3.92+/-0.42 microg TTX/mg protein at 1000 microg TTX/mL. Approximately 80% of the TTX in the plasma of T. rubripes was unbound in the concentration range of TTX examined, indicating that TTX exists predominantly in the unbound form in the circulating blood of T. rubripes at a wide range of TTX concentrations. TTX also bound non-specifically to H. otakii plasma proteins, BSA, and bovine AGP. The amount of the bound TTX in the plasma of H. otakii and BSA, respectively, was 1.86+/-0.36 and 4.65+/-0.70 microg TTX/mg protein at 1000 microg TTX/mL, and that in the bovine AGP was 8.78+/-0.25 microg TTX/mg protein at 200 microg TTX/mL.

Revisiting the association between sea surface temperature and the epidemiology of fish poisoning in the South Pacific: reassessing the link between ciguatera and climate change

The most detailed dataset of ciguatera intensity is that produced by the South Pacific Epidemiological and Health Information Service (SPEHIS) of the Secretariat of the Pacific Community. The SPEHIS fish poisoning database has been previously analysed yielding statistically significant correlations between the Southern Oscillation Index (SOI) and ciguatera case numbers in several countries raising concerns this affliction will increase as oceans warm. Mapping of the SPEHIS records and other data hints at ciguatera not only being restricted to warm waters but that the Indo-Pacific Warm Pool, a body of water that remains hot throughout much of the year, may inhibit ciguatera prevalence. A qualitative assessment of ciguatera intensity and sea surface temperature (SST) behaviour within the EEZ of selected South Pacific nations supported the notion that ciguatera intensity was highest when SST was between an upper and lower limit. Many more climate and SST indices beyond the SOI are now available, including some that measure the abovementioned phenomenon of oceanic warm pools. Statistically significant, positive and negative cross-correlations were obtained between time series of annual ciguatera case rates from the SPEHIS dataset and the Pacific Warm Pool Index and several ENSO related indices which had been lagged for up to 2 years before the ciguatera time series. This further supports the possibility that when considering the impact of climate change on ciguatera, one has to consider two thresholds, namely waters that remain warm enough for a long enough period can lead to ciguatera and that extended periods where the water remains too hot may depress ciguatera case rates. Such a model would complicate projections of the effects of climate change upon ciguatera beyond that of a simple relationship where increased SST may cause more ciguatera.

Maturation-associated changes in toxicity of the pufferfish Takifugu poecilonotus

From October 2006 to December 2007, wild specimens of the pufferfish Takifugu poecilonotus (93 females, 45 males) were collected from the Ariake Sea. Tissue toxicity was examined by mouse bioassay, and tetrodotoxin (TTX) content in the blood plasma by enzyme-linked immunosorbent assay. The relationship between toxicity and maturation was investigated based on changes in the gonadosomatic index: December-March in females and November-March in males, the 'maturation period'; April, 'just after spawning'; and the other months, the 'ordinary period'. Toxicity of both sexes was high throughout the year, but sharply declined in April. In all tissues examined (skin, liver, and ovary) other than testis, toxicity exceeded 1000 MU/g or 10,000 MU/individual in many individuals. Seasonal profiles of tissue toxicity differed markedly between sexes. In females, liver toxicity was high during the ordinary period, and ovary toxicity was high during the maturation period. In males, little maturation-associated change in the toxin distribution was observed. Plasma TTX levels were similar between the sexes (1.59-15.1 MU/ml), and fluctuated largely throughout the year without corresponding changes in tissue toxicity. The percentage of TTX binding to high molecular-weight substances in the plasma varied in association with maturation; the binding ratio fluctuated at relatively low levels during the ordinary period, and stabilized at a high level during the maturation period.

Transfer profile of intramuscularly administered tetrodotoxin to non-toxic cultured specimens of the pufferfish Takifugu rubripes

Tetrodotoxin (TTX) was intramuscularly administered to non-toxic cultured specimens of the pufferfish Takifugu rubripes to investigate TTX transfer/accumulation profiles in the pufferfish body. In two groups of test fish administered either 50MU/individual of TTX standard (purified TTX; PTTX) or crude extract of toxic pufferfish ovary (crude TTX; CTTX), TTX rapidly transferred from the muscle via the blood to other organs. The toxin transfer profiles differed between groups, however, from 4 to 72h. In the PTTX group, little TTX was retained in the liver, and most (>96%) of the toxin remaining in the body transferred/accumulated in the skin after 12h, whereas in the CTTX group, a considerable amount of toxin (15%-23% of the administered toxin or 28%-58% of the remaining toxin) was transferred/retained in the liver for up to 24h, despite the fact that 89% of the remaining toxin transferred/accumulated in the skin at the end of rearing period (168h). The total amount of toxin remaining in the entire body at 1-4h was approximately 60% of the administered toxin in both groups, which decreased at 8-12h, and then increased again to approximately 60%-80% at 24-168h. Immunohistochemical observation revealed that the toxin accumulated in the skin was localized at the basal cells of the epidermal layer.

Tetrodotoxin--distribution and accumulation in aquatic organisms, and cases of human intoxication

Many pufferfish of the family Tetraodontidae possess a potent neurotoxin, tetrodotoxin (TTX). In marine pufferfish species, toxicity is generally high in the liver and ovary, whereas in brackish water and freshwater species, toxicity is higher in the skin. In 1964, the toxin of the California newt was identified as TTX as well, and since then TTX has been detected in a variety of other organisms. TTX is produced primarily by marine bacteria, and pufferfish accumulate TTX via the food chain that begins with these bacteria. Consequently, pufferfish become non-toxic when they are fed TTX-free diets in an environment in which the invasion of TTX-bearing organisms is completely shut off. Although some researchers claim that the TTX of amphibians is endogenous, we believe that it also has an exogenous origin, i.e., from organisms consumed as food. TTX-bearing animals are equipped with a high tolerance to TTX, and thus retain or accumulate TTX possibly as a biologic defense substance. There have been many cases of human intoxication due to the ingestion of TTX-bearing pufferfish, mainly in Japan, China, and Taiwan, and several victims have died. Several cases of TTX intoxication due to the ingestion of small gastropods, including some lethal cases, were recently reported in China and Taiwan, revealing a serious public health issue.