Tetrodotoxin and Its Analogues in the Pufferfish Arothron hispidus and A. nigropunctatus from the Solomon Islands: A Comparison of Their Toxin Profiles with the Same Species from Okinawa, Japan

Tetrodotoxins in Tissues and Cells of Different Body Regions of Ribbon Worms Kulikovia alborostrata and K. manchenkoi from Spokoynaya Bay, Sea of Japan

Nemerteans, or ribbon worms, possess tetrodotoxin and its analogues (TTXs), neurotoxins of bacterial origin, which they presumably use for capturing prey and self-defense. Most TTXs-containing nemertean species have low levels of these toxins and, therefore, have usually been neglected in studies of TTXs functions and accumulation. In the present study, Kulikovia alborostrata and K. manchenkoi, two closely related species, were analyzed for TTXs distribution in the body using the HPLC-MS/MS and fluorescence microscopy methods. The abundance of TTXs-positive cells was determined in the proboscis, integument, and digestive system epithelium. As a result, six TTXs-positive cell types were identified in each species; however, only four were common. Moreover, the proportions of the toxins in different body parts were estimated. According to the HPLC-MS/MS analysis, the TTXs concentrations in K. alborostrata varied from 0.91 ng/g in the proboscis to 5.52 ng/g in the precerebral region; in K. manchenkoi, the concentrations ranged from 7.47 ng/g in the proboscis to 72.32 ng/g in the posterior body region. The differences observed between the two nemerteans in the distribution of the TTXs were consistent with the differences in the localization of TTXs-positive cells. In addition, TTXs-positive glandular cell types were found in the intestine and characterized for the first time. TTXs in the new cell types were assumed to play a unique physiological role for nemerteans.

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.

The quite low cross-reactivity of Kawatsu's anti-tetrodotoxin monoclonal antibody to 5,6,11-trideoxytetrodotoxin, 11-nortetrodotoxin-6(S)-ol, and 11-oxotetrodotoxin, the major tetrodotoxin analogues in pufferfish

The monoclonal antibody against tetrodotoxin (TTX), prepared by Kawatsu et al. (1997), has been used in several TTX-related studies. Herein, we confirmed the quite low cross-reactivity of this antibody to three major TTX analogues in pufferfish using competitive ELISA: 5,6,11-trideoxyTTX (<2.2%), 11-norTTX-6(S)-ol (<0.3%), and 11-oxoTTX (<1.5%), with reactivity against TTX being 100%. We further confirmed that the presence of these analogues did not cause a marked overestimation of TTX in pufferfish extracts using competitive ELISA.

Tetrodotoxin Profiles in Xanthid Crab Atergatis floridus and Blue-Lined Octopus Hapalochlaena cf. fasciata from the Same Site in Nagasaki, Japan

The xanhid crab Atergatis floridus and the blue-lined octopus Hapalochlaena cf. fasciata have long been known as TTX-bearing organisms. It has been speculated that the TTX possessed by both organisms is exogenously toxic through the food chain, since they are reported to have geographic and individual differences. The source and supply chain of TTX for both of these organisms, however, remain unclear. On the other hand, since crabs are one of the preferred prey of octopuses, we focused our attention on the relationship between the two species living in the same site. The aim of this study was to determine TTX concentrations and TTX profiles of A. floridus and H. cf. fasciata, collected simultaneously in the same site, and examine the relationship between them. Although there were individual differences in the TTX concentration in both A. floridus and H. cf. fasciata, the toxin components commonly contained 11-norTTX-6(S)-ol in addition to TTX as the major components, with 4-epiTTX, 11-deoxyTTX, and 4,9-anhydroTTX as the minor components. The results suggest that octopuses and crabs in this site acquire TTX from common prey, including TTX-producing bacteria and/or may have a predator–prey relationship.

Tetrodotoxins in Ribbon Worms Cephalothrix cf. simula and Kulikovia alborostrata from Peter the Great Bay, Sea of Japan

Tetrodotoxin, an extremely potent low-molecular-weight neurotoxin, and its analogues (TTXs) are widely distributed in aquatic and terrestrial ecosystems. Most investigations concerning TTXs have been conducted mainly on puffer fish, octopus, and mollusks, without paying due attention to various non-edible animals including nemerteans, a small group of marine worms, several species of which have been shown to possess high amounts of TTXs. In this study, for the first time, variations in TTX and its analogues, in 32 specimens of Cephalothrix cf. simula and 36 specimens of Kulikovia alborostrata, from Peter the Great Bay Sea of Japan were investigated, which may contribute to elucidation of TTXs migration pathways in ecosystems. Using high performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS), it was found that the total TTXs concentrations within both species vary by one to several orders of magnitude, 85.75-7108.26 µg/g and 0.35-8.11 ng/g in C. cf. simula and K. alborostrata, respectively. The intra- and interspecies similarities in proportions of TTXs in both species were observed; based on the results, a possible way of their toxification was discussed.

An almost nontoxic tetrodotoxin analog, 5,6,11-trideoxytetrodotoxin, as an odorant for the grass puffer

Toxic puffers contain the potent neurotoxin, tetrodotoxin (TTX). Although TTX is considered to serve as a defense substance, previous behavioral studies have demonstrated that TTX acts as an attractive pheromone for some toxic puffers. To elucidate the physiological mechanism of putative pheromonal action of TTX, we examined whether grass puffers Takifugu alboplumbeus can detect TTX. Electroolfactogram (EOG) results suggest that the olfactory epithelium (OE) of grass puffers responded to a type of TTX analog (5,6,11-trideoxyTTX), although it did not respond to TTX. We also examined the attractive action of 5,6,11-trideoxyTTX on grass puffers by recording their swimming behavior under dark conditions. Grass puffers preferred to stay on the side of the aquarium where 5,6,11-trideoxyTTX was administered, and their swimming speed decreased. Additionally, odorant-induced labeling of olfactory sensory neurons by immunohistochemistry against neural activity marker (phosphorylated extracellular signal regulated kinase; pERK) revealed that labeled olfactory sensory neurons were localized in the region surrounding "islets" where there was considered as nonsensory epithelium. 5,6,11-trideoxyTTX has been known to accumulate in grass puffers, but its toxicity is much lower (almost nontoxic) than TTX. Our results suggest that toxic puffers may positively use this TTX analog, which has been present in their body with TTX but whose function was unknown, as an odorant for chemical communication or effective TTX accumulation.

Tetrodotoxin and analogues in two local pufferfish species from Inhaca Island - South of Mozambique: First report in the Mozambican coast

Tetrodotoxins (TTXs) were investigated in two local pufferfish species, Diodon hystrix and Arothron hispidus, from Mozambican coast. TTX and analogues 4-epiTTX, 4,9-anhydroTTX, 11-deoxyTTX, and 11-norTTX-6-(R/S)-ol were found in both species and high level of TTX was found in A. hispidus (9522.0 μg TTX kg^-1) than in D. hystrix (350.9 μg TTX kg^-1). The distribution of TTX and their analogues in A. hispidus was intestine > liver > skin ≫ muscle > gonads. This is the first report of TTXs in Mozambican coast.

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.

Development of a polyclonal antibody-based indirect competitive ELISA for the determination of tetrodotoxins in marine ribbon worms (NEMERTEA) and its comparison with high performance liquid chromatography-tandem mass spectrometry

Tetrodotoxin (TTX) is a potent neurotoxin frequently occurring in marine organisms along with its numerous analogues. To determine the total TTX content, we developed an enzyme-linked immunosorbent assay (ELISA) technique utilizing polyclonal antibodies against TTX. The technique was tested using extracts of marine worms of the phylum Nemertea and confirmed by HPLC-MS/MS. It proved to be suitable for a preliminary assessment of the toxicity of marine organisms.

Temporal Variation of the Profile and Concentrations of Paralytic Shellfish Toxins and Tetrodotoxin in the Scallop, Patinopecten yessoensis, Cultured in a Bay of East Japan

Paralytic shellfish toxins (PSTs) are the major neurotoxic contaminants of edible bivalves in Japan. Tetrodotoxin (TTX) was recently detected in bivalve shellfish around the world, drawing widespread attention. In Japan, high levels of TTX were reported in the digestive gland of the scallop, Patinopecten yessoensis, in 1993; however, no new data have emerged since then. In this study, we simultaneously analyzed PSTs and TTX in scallops cultured in a bay of east Japan using hydrophilic interaction chromatography (HILIC)-MS/MS. These scallops were temporally collected from April to December 2017. The highest concentration of PSTs (182 µmol/kg, total congeners) in the hepatopancreas was detected in samples collected on May 23, lined to the cell density of the dinoflagellate, Alexandrium tamarense, in seawater around the scallops, whereas the highest concentration of TTX (421 nmol/kg) was detected in samples collected on August 22. Contrary to the previous report, temporal variation of the PSTs and TTX concentrations did not coincide. The highest concentration of TTX in the entire edible tissues was 7.3 µg/kg (23 nmol/kg) in samples obtained on August 22, which was lower than the European Food Safety Authority (EFSA)-proposed threshold, 44 µg TTX equivalents/kg shellfish meat. In addition, 12β-deoxygonyautoxin 3 was firstly identified in scallops.

Quantitation of Tetrodotoxin and Its Analogues with a Combination of Liquid Chromatography-Tandem Mass Spectrometry and Quantitative 1H-NMR Spectroscopy

Tetrodotoxin and its analogues are the causative toxins of pufferfish poisoning. Tetrodotoxin has been recently detected in bivalve mollusks collected in New Zealand and Europe, highlighting the need to include tetrodotoxin in monitoring programs for bivalves by instrumental methods. In the present study, tetrodotoxin and its analogues in commercially available tetrodotoxin reagents were quantitated accurately by quantitative ¹H-nuclear magnetic resonance (qNMR) spectroscopy. The results were applied to estimate relative molar responses of tetrodotoxin and its analogues in hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC/MS/MS). All four components (tetrodotoxin hemilactal form (1), tetrodotoxin 10,7-lactone form (2), 4-epitetrodotoxin (3), and 4,9-anhydrotetrodotoxin (4)) generated by equilibrating tetrodotoxin in aqueous solution were prepared as a mixture. From the HSQC spectrum of the mixture, the separated signals derived from three components, excluding 1, were selected and used for the quantitation. In addition, the relative molar responses of 3 and 4 on HILIC/MS/MS were calculated to be 0.73 and 0.46, respectively. These values could be useful for quantitation of 3 and 4 using the tetrodotoxin standard by HILIC/MS/MS. Our results also indicate that qNMR is useful for preparation of tetrodotoxin certified reference material.

Novel Polyclonal Antibody Raised against Tetrodotoxin Using Its Haptenic Antigen Prepared from 4,9-anhydrotetrodotoxin Reacted with 1,2-Ethaneditiol and Further Reacted with Keyhole Limpet Hemocyanin

A novel polyclonal antibody against tetrodotoxin (TTX) was raised using its haptenic antigen, where 4,9-anhydroTTX was reacted with 1,2-ethanedithiol and this derivative was further reacted with keyhole limpet hemocyanin (KLH). This newly designed antigen (KLH-TTX) was inoculated into rabbits, resulting in the production of the specific polyclonal antibody, which reacted well with TTX and its analogs, 4-epiTTX, 11-oxoTTX and 5,6,11-trideoxyTTX, except for 4,9-anhydroTTX. The enzyme-linked immunosorbent assay (ELISA) system using this specific antibody was also developed in the present study. This newly developed polyclonal antibody with analytical procedures using direct one-step ELISA is useful to detect TTX and its analogs in toxic organisms and also disclose the mechanisms involved in their metabolic pathways and accumulation of TTX.

Contrasting Toxin Selectivity between the Marine Pufferfish Takifugu pardalis and the Freshwater Pufferfish Pao suvattii

To clarify the differences in toxin selectivity between marine and freshwater pufferfish, we conducted experiments in artificially reared nontoxic specimens of Takifugu pardalis (marine) and Pao suvattii (freshwater) using tetrodotoxin (TTX) and paralytic shellfish poison (PSP; decarbamoylsaxitoxin (dcSTX) or saxitoxin (STX)). T. pardalis specimens were administered feed homogenate containing TTX or dcSTX (dose of toxin, 55.2 nmol/fish) and P. suvattii specimens were administered feed homogenate containing TTX + STX (dose of each toxin, 19.2 nmol/fish) by oral gavage. The toxin content in the intestine, muscle, skin, liver, and gonads was quantified after 24 and 48 or 72 h. In T. pardalis, TTX administered into the intestine was absorbed into the body and transferred and retained mainly in the skin and liver, while dcSTX was hardly retained in the body, although it partly remained in the intestine. In strong contrast, in P. suvattii, little TTX remained in the body, whereas STX was absorbed into the body and was transferred and retained in the ovary and skin. The findings revealed that TTX/PSP selectivity differs between the marine species T. pardalis and the freshwater species P. suvattii. T. pardalis, which naturally harbors TTX, selectively accumulates TTX, and P. suvattii, which naturally harbors PSP, selectively accumulates PSP.

Pufferfish Saxitoxin and Tetrodotoxin Binding Protein (PSTBP) Analogues in the Blood Plasma of the Pufferfish Arothron nigropunctatus, A. hispidus, A. manilensis, and Chelonodon patoca

Pufferfish saxitoxin and tetrodotoxin (TTX) binding protein (PSTBP) is a glycoprotein that we previously isolated from the blood plasma of the pufferfish Takifugu pardalis; this protein was also detected in seven species of the genus Takifugu. We proposed that PSTBP is a carrier protein for TTX in pufferfish; however, PSTBP had not yet been found in genera other than Takifugu. In this study, we investigated the presence of PSTBP-like proteins in the toxic pufferfish Arothron nigropunctatus, A. hispidus, A. manilensis, and Chelonodon patoca. On the basis of ultrafiltration experiments, TTX was found to be present and partially bound to proteins in the plasma of these pufferfish, and Western blot analyses with anti-PSTBP antibody revealed one or two bands per species. The observed decreases in molecular mass following deglycosylation with glycopeptidase F suggest that these positive proteins are glycoproteins. The molecular masses of the deglycosylated proteins detected in the three Arothron species were larger than that of PSTBP in the genus Takifugu, whereas the two bands detected in C. patoca had molecular masses similar to that of tributyltin-binding protein-2 (TBT-bp2). The N-terminal amino acid sequences of 23–29 residues of these detected proteins were all homologous with those of PSTBP and TBT-bp2.

Evaluation of tetrodotoxins in puffer fish caught along the Mediterranean coast of Spain. Toxin profile of Lagocephalus sceleratus

Although consumption of Tetraodontidae species is prohibited in the EU, intoxications are still reported. The evaluation of tetrodotoxins (TTXs) by mass spectrometry (LC-MS/MS and LC-HRMS) and a screening immunoassay (mELISA) in tetraodontid fishes caught along the Western Mediterranean Sea revealed high concentrations of TTXs in Lagocephalus sceleratus while no TTXs were identified in L. lagocephalus and Sphoeroides pachygaster individuals. The high TTXs content found in the L. sceleratus analysed herein demonstrate the occurrence of highly toxic puffer fish in the Western Mediterranean Sea. Being L. sceleratus a recent invasive species in the Mediterranean, surveillance, risk assessment and risk management measures are necessary. The strategy used within this research work could be a valuable tool for future food safety monitoring.

Risks for public health related to the presence of tetrodotoxin (TTX) and TTX analogues in marine bivalves and gastropods

Tetrodotoxin (TTX) and its analogues are produced by marine bacteria and have been detected in marine bivalves and gastropods from European waters. The European Commission asked EFSA for a scientific opinion on the risks to public health related to the presence of TTX and TTX analogues in marine bivalves and gastropods. The Panel on Contaminants in the Food Chain reviewed the available literature but did not find support for the minimum lethal dose for humans of 2 mg, mentioned in various reviews. Some human case reports describe serious effects at a dose of 0.2 mg, corresponding to 4 μg/kg body weight (bw). However, the uncertainties on the actual exposure in the studies preclude their use for derivation of an acute reference dose (ARfD). Instead, a group ARfD of 0.25 μg/kg bw, applying to TTX and its analogues, was derived based on a TTX dose of 25 μg/kg bw at which no apathy was observed in an acute oral study with mice, applying a standard uncertainty factor of 100. Estimated relative potencies for analogues are lower than that of TTX but are associated with a high degree of uncertainty. Based on the occurrence data submitted to EFSA and reported consumption days only, average and P95 exposures of 0.00-0.09 and 0.00-0.03 μg/kg bw, respectively, were calculated. Using a large portion size of 400 g bivalves and P95 occurrence levels of TTX, with exception of oysters, the exposure was below the group ARfD in all consumer groups. A concentration below 44 μg TTX equivalents/kg shellfish meat, based on a large portion size of 400 g, was considered not to result in adverse effects in humans. Liquid chromatography with tandem mass spectroscopy (LC-MS/MS) methods are the most suitable for identification and quantification of TTX and its analogues, with LOQs between 1 and 25 μg/kg.

LC-MS/MS method for the determination of tetrodotoxin (TTX) on a triple quadruple mass spectrometer

Tetrodotoxin (TTX), often referred to as the 'puffer fish' poison, is a marine toxin and it has been identified as the agent responsible for many food poisoning incidents around the world. It is a neurotoxin that blocks voltage-gated sodium channels, resulting in respiratory paralysis and even death in severe cases. It is known to occur in many different species of fish and other organisms. The toxin is mainly found in the Southeast Asia region. Worryingly, TTX is starting to appear in European waters. It is suspected that this is a consequence of Lessepsian migration, also known as the Erythrean invasion. Therefore, straightforward and reliable extraction and analytical methods are now urgently required to monitor seafood of European origin for TTX. This paper provides a versatile, dependable and robust method for the analysis of TTX in puffer fish and trumpet shellfish using LC-MS/MS. A three-stage approach was implemented involving: (1) the screening of samples using fast multiple reaction monitoring (MRM) mass spectral analysis to identify quickly positive samples on a triple quadrupole mass spectrometer (QqQMS/MS), the API 3000; (2) a Fourier-transform (FT)-MS full-scan analysis of positive samples to collect qualitative data; and (3) a method with a longer chromatography run to identify and quantitate the positive samples using the QqQMS. The quantitative LC-QqQMS method delivered excellent linearity for solvent-based standards (0.01-7.5 µg ml^-1; R² ≥ 0.9968) as well as for matrix-matched standards (0.05-37.50 µg g^-1; R² ≥ 0.9869). Good inter-day repeatability was achieved for all the relevant analytes with %RSD values (n = 9) ranging from 1.11% to 4.97% over a concentration range of 0.01-7.5 µg ml^-1. A sample clean-up procedure for the puffer fish and trumpet shellfish was developed to ensure acceptable and reproducible recoveries to enable accurate and precise determination of TTX in a myriad of tissues types. Blank mackerel matrix was used for the TTX standard spiking studies in order to calculate the recoveries of the toxin during the extraction procedure. The recovery was 61.17% ± 5.42% for the extraction protocol. MS/MS studies were performed on a linear-trap quadruple-Orbitrap mass spectrometer (LTQ-Orbitrap) to obtain high-mass-accuracy data of the target analytes and their characteristic fragment ions in the puffer fish and trumpet shellfish samples. This facilitated identification of TTX and its associated analogues. These high-mass-accuracy studies facilitated the development of a rapid MRM-based quantitative method for TTX determination on the LC-QqQMS.