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

Tetrodotoxin and the state-of-the-art progress of its associated analytical methods

Tetrodotoxin (TTX), which is found in various marine organisms, including pufferfish, shellfish, shrimp, crab, marine gastropods, and gobies, is an effective marine toxin and the cause of many seafood poisoning incidents. Owing to its toxicity and threat to public health, the development of simple, rapid, and efficient analytical methods to detect TTX in various food matrices has garnered increasing interest worldwide. Herein, we reviewed the structure and properties, origin and sources, toxicity and poisoning, and relevant legislative measures of TTX. Additionally, we have mainly reviewed the state-of-the-art progress of analytical methods for TTX detection in the past five years, such as bioassays, immunoassays, instrumental analysis, and biosensors, and summarized their advantages and limitations. Furthermore, this review provides an in-depth discussion of the most advanced biosensors, including cell-based biosensors, immunosensors, and aptasensors. Overall, this study provides useful insights into the future development and wide application of biosensors for TTX detection.

Tissue Localization of Tetrodotoxin in the Flatworm Planocera multitentaculata (Platyhelminthes: Polycladida)

Tetrodotoxin (TTX), a pufferfish toxin, is a highly potent neurotoxin that has been found in a wide variety of animals. The TTX-bearing flatworm Planocera multitentaculata possesses a large amount of TTX and is considered responsible for the toxification of TTX-bearing animals such as pufferfish (Takifugu and Chelonodon) and the toxic goby Yongeichthys criniger. However, the mechanism underlying TTX accumulation in flatworms remains unclear. Previous studies have been limited to identifying the distribution of TTX in multiple organs, such as the digestive organs, genital parts, and the remaining tissues of flatworms. Here, we performed liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis and immunohistochemical staining using a monoclonal anti-TTX antibody to elucidate the detailed localization of TTX in the tissues and organs of the flatworm P. multitentaculata. Immunohistochemical staining for P. multitentaculata showed that TTX-specific signals were detected not only in the ovaries and pharynx but also in many other tissues and organs, whereas no signal was detected in the brain, Lang's vesicle, and genitalia. In addition, combined with LC-MS/MS analysis, it was revealed for the first time that TTX accumulates in high concentrations in the basement membrane and epidermis. These findings robustly support the hypotheses of "TTX utilization protection from predators."

The impact of tetrodotoxin (TTX) on the gut microbiome in juvenile tiger pufferfish, Takifugu rubripes

Tetrodotoxin (TTX) is a potent neurotoxin that accumulates in Takifugu rubripes, commonly known as pufferfish, through the ingestion of TTX-bearing organisms as part of their food chain. Although researchers believe that pufferfish use TTX to relieve stress, data are not currently available on how TTX affects the gut microbiota of pufferfish. To address this gap, our study aimed to investigate whether administering TTX to fish could alter their gut microbiota and overall health under various salinity conditions, including 30.0 ppt, 8.5 ppt, and 1.7 ppt salinity, which represent full-strength, isosmotic, and low-salinity stress, respectively. We analyzed the effect of TTX ingestion on the community structure, core microbiome, and metabolic capabilities of the gut microbiome using high-throughput sequencing technologies. The predominant bacterial taxa within the gut microbiome were Firmicutes (21-85%), Campilobacterota (2.8-67%), Spirochaetota (0.5-14%), and Proteobacteria (0.7-9.8%), with Mycoplasma, uncultured Arcobacteraceae, Brevinema, Vibrio, Rubritalea, and uncultured Pirellulaceae as core genera. Our findings indicated that the impact of TTX on high-abundance genera at 30.0 ppt and 8.5 ppt salinity levels was negligible, indicating their stability and resilience to TTX ingestion. However, at 1.7 ppt, TTX-fed fish showed a significant increase in uncultured Arcobacteraceae. Furthermore, our analysis of TTX-fed fish revealed taxonomic alterations in low-abundance taxa, which altered the predicted functions of the gut microbiota at all salinity levels. These results suggest that TTX administration could cause subtle effects on the metabolic functions of gut microbial communities. Overall, our study provides insights into the complex relationship between a TTX-accumulating animal, T. rubripes, and its gut microbiota.

Japanese Planocerid Flatworms: Difference in Composition of Tetrodotoxin and Its Analogs and the Effects of Ingestion by Toxin-Bearing Fishes in the Ryukyu Islands, Japan

Tetrodotoxin (TTX), known as pufferfish toxin, is a potent neurotoxin blocking sodium channels in muscle and nerve tissues. TTX has been detected in various taxa other than pufferfish, including marine polyclad flatworms, suggesting that pufferfish toxin accumulates in fish bodies via food webs. The composition of TTX and its analogs in the flatworm Planocera multitentaculata was identical to those in wild grass puffer Takifugu alboplumbeus. Previously, Planocera sp. from Okinawa Island, Japan, were reported to possess high level of TTX, but no information was available on TTX analogs in this species. Here we identified TTX and analogs in the planocerid flatworm using high-resolution liquid chromatography-mass spectrometry, and compared the composition of TTX and analogs with those of another toxic and non-toxic planocerid species. We show that the composition of TTX and several analogs, such as 5,6,11-trideoxyTTX, dideoxyTTXs, deoxyTTXs, and 11-norTTX-6(S)-ol, of Planocera sp. was identical to those of toxic species, but not to its non-toxic counterpart. The difference in the toxin composition was reflected in the phylogenetic relationship based on the mitochondrial genome sequence. A toxification experiment using predatory fish and egg plates of P. multitentaculata demonstrated that the composition of TTX and analogs in wild T. alboplumbeus juveniles was reproduced in artificially toxified pufferfish. Additionally, feeding on the flatworm egg plates enhanced the signal intensities of all TTX compounds in Chelonodon patoca and that of deoxyTTXs in Yongeichthys criniger.

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

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

Tetrodotoxin Detection in Japanese Bivalves: Toxification Status of Scallops

Tetrodotoxin (TTX), or pufferfish toxin, has been frequently detected in edible bivalves around the world during the last decade and is problematic in food hygiene and safety. It was reported recently that highly concentrated TTX was detected in the midgut gland of the akazara scallop Chlamys (Azumapecten) farreri subsp. akazara collected in coastal areas of the northern Japanese archipelago. The toxification of the bivalve was likely to involve the larvae of the flatworm, Planocera multitentaculata. However, the overall status of bivalve TTX toxification has not been elucidated. In this study, 14 species/subspecies of bivalves from various Japanese waters were subjected to LC-MS/MS analysis to reveal TTX toxification state, demonstrating that the Pectinidae, including C. farreri akazara, Chlamys farreri nipponensis, Chlamys (Mimachlamys) nobilis, and Mizuhopecten yessoensis, accumulated TTX in their midgut gland. Many individuals of C. farreri akazara and C. farreri nipponensis were found with high concentrations of TTX, while C. nobilis and M. yessoensis exhibited low concentrations. The extent of TTX accumulation in C. farreri akazara and C. farreri nipponensis varied widely by region and season. Curiously, no other bivalve species investigated in this study showed evidence of TTX. These results suggest that monitoring for TTX, like other shellfish toxins, is necessary to ensure that pectinid bivalves are a safe food resource.

Geographical differences in the composition of tetrodotoxin and 5,6,11-trideoxytetrodotoxin in Japanese pufferfishes and their origins

Tetrodotoxin (TTX)-bearing fish are thought to accumulate TTXs in their bodies through a food chain that begins with marine bacteria. However, the mechanism of TTXs transfer between prey and predators in the food chain remains unclear and the reasons for regional differences in pufferfish toxicity are also unknown. To investigate these matters, we collected juveniles of four species of pufferfish, Takifugu alboplumbeus, Takifugu flavipterus, Takifugu stictonotus, and Chelonodon patoca, from various locations in the Japanese Islands, and subjected them to liquid chromatography-tandem mass spectrometry analysis for TTX and its analog 5,6,11-trideoxyTTX (TDT). Concentrations of these substances tended to be higher in pufferfish juveniles collected from the Sanriku coastal area (Pacific coast of northern Japan) than in those from other locations. Juveniles had higher concentrations of TTX at all locations than of TDT. Mitochondrial cytochrome c oxidase subunit I (COI) sequences specific to the TTX-bearing flatworm, Planocera multitentaculata, were detected in the intestinal contents of up to 100% of pufferfish juveniles from various sampling sites, suggesting that P. multitentaculata was widely involved in the toxification of the juveniles in the coastal waters of Japan. A toxification experiment was conducted on three species of pufferfish juveniles (T. alboplumbeus, Takifugu rubripes and C. patoca) using TTX-bearing flatworm eggs harboring equal amounts of TTX and TDT. The TTX content of juveniles fed on flatworm eggs was found to be more than twice that of TDT, suggesting that pufferfish preferentially incorporate TTX compared to TDT.

Levels of Tetrodotoxins in Spawning Pufferfish, Takifugu alboplumbeus

Tetrodotoxin (TTX), also known as pufferfish toxin, is an extremely potent neurotoxin thought to be used as a biological defense compound in organisms bearing it. Although TTX was thought to function as a chemical agent for defense and anti-predation and an attractant for TTX-bearing animals including pufferfish, it has recently been demonstrated that pufferfish were also attracted to 5,6,11-trideoxyTTX, a related compound, rather than TTX alone. In this study, we attempted to estimate the roles of TTXs (TTX and 5,6,11-trideoxyTTX) in the pufferfish, Takifugu alboplumbeus, through examining the location of TTXs in various tissues of spawning pufferfish from Enoshima and Kamogawa, Japan. TTXs levels in the Kamogawa population were higher than those in the Enoshima population, and there was no significant difference in the amount of TTXs between the sexes in either population. Individual differences were greater in females than in males. However, the location of both substances in tissues differed significantly between sexes: male pufferfish accumulated most of their TTX in the skin and liver and most of their 5,6,11-trideoxyTTX in the skin, whereas females accumulated most of their TTX and 5,6,11-trideoxyTTX in the ovaries and skin.

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.

Changes in Tissue Distribution of Tetrodotoxin and Its Analogues in Association with Maturation in the Toxic Flatworm, Planocera multitentaculata

The toxic flatworm, Planocera multitentaculata, possesses highly concentrated tetrodotoxin (TTX), also known as pufferfish toxin, throughout its life cycle, including the egg and larval stages. Additionally, TTX analogues, 5,6,11-trideoxyTTX and 11-norTTX-6(S)-ol, have also been detected in the flatworm. The high concentration of TTX in the eggs and larvae appears to be for protection against predation, and 11-norTTX-6(S)-ol in the pharyngeal tissue in the adults is likely used to sedate or kill prey during predation. However, information on the role of 5,6,11-trideoxyTTX, a potential important biosynthetic intermediate of TTX, in the toxic flatworm is lacking. Here, we aimed to determine the region of localization of TTX and its analogues in the flatworm body, understand their pharmacokinetics during maturation, and speculate on their function. Flatworm specimens in four stages of maturity, namely juvenile, mating, spawning, and late spawning, were subjected to LC-MS/MS analysis, using the pharyngeal tissue, oocytes in seminal receptacle, sperm, and tissue from 12 other sites. Although TTX was consistently high in the pharyngeal tissue throughout maturation, it was extremely high in the oocytes during the spawning period. Meanwhile, 5,6,11-trideoxyTTX was almost undetectable in the pharyngeal part throughout the maturation but was very abundant in the oocytes during spawning. 11-norTTX-6(S)-ol consistently localized in the pharyngeal tissue. Although the localization of TTX and its analogues was approximately consistent with the MS imaging data, TTX and 11-norTTX-6(S)-ol were found to be highly localized in the parenchyma surrounding the pharynx, which suggests the parenchyma is involved in the accumulation and production of TTXs.

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.

Tetrodotoxins in the flatworm Planocera multitentaculata

The marine polyclad flatworm Planocera multitentaculata is known to possess high levels of tetrodotoxin (TTX), but the presence of TTX analogues in the species has been unexplored. In this study, TTX and several analogues such as 5,6,11-trideoxyTTX, monodeoxyTTXs, dideoxyTTXs, and 11-norTTX-6(S)-ol were identified in three adults and egg plates of P. multitentaculata using high resolution liquid chromatography-mass spectrometry (HR-LC/MS) for the first time.