Biliary excretion of tetrodotoxin in the cultured pufferfish Takifugu rubripes juvenile after intramuscular administration

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.

Transcriptome analysis revealed gene expression feminization of testis after exogenous tetrodotoxin administration in pufferfish Takifugu flavidus

Tetrodotoxin (TTX) is a deadly neurotoxin and usually accumulates in large amounts in the ovaries but is non-toxic or low toxic in the testis of pufferfish. The molecular mechanism underlying sexual dimorphism accumulation of TTX in ovary and testis, and the relationship between TTX accumulation with sex related genes expression remain largely unknown. The present study investigated the effects of exogenous TTX treatment on Takifugu flavidus. The results demonstrated that exogenous TTX administration significantly incresed level of TTX concentration in kidney, cholecyst, skin, liver, heart, muscle, ovary and testis of the treatment group (TG) than that of the control group (CG). Transcriptome sequencing and analysis were performed to study differential expression profiles of mRNA and piRNA after TTX administration of the ovary and testis. The results showed that compared with female control group (FCG) and male control group (MCG), TTX administration resulted in 80 and 23 piRNAs, 126 and 223 genes up and down regulated expression in female TTX-treated group (FTG), meanwhile, 286 and 223 piRNAs, 2 and 443 genes up and down regulated expression in male TTX-treated group (MTG). The female dominant genes cyp19a1, gdf9 and foxl2 were found to be up-regulated in MTG. The cyp19a1, whose corresponding target piRNA uniq_554482 was identified as down-regulated in the MTG, indicating the gene expression feminization in testis after exogenous TTX administration. The KEGG enrichment analysis revealed that differentially expressed genes (DEGs) and piRNAs (DEpiRNAs) in MTG vs MCG group were more enriched in metabolism pathways, indicating that the testis produced more metabolic pathways in response to exogenous TTX, which might be a reason for the sexual dimorphism of TTX distribution in gonads. In addition, TdT-mediated dUTP-biotin nick end labeling staining showed that significant apoptosis was detected in the MTG testis, and the role of the cell apoptotic pathways was further confirmed. Overall, our research revealed that the response of the ovary and testis to TTX administration was largely different, the ovary is more tolerant whereas the testis is more sensitive to TTX. These data will deepen our understanding on the accumulation of TTX sexual dimorphism in Takifugu.

Chronic In Vivo Effects of Repeated Exposure to Low Oral Doses of Tetrodotoxin: Preliminary Evidence of Nephrotoxicity and Cardiotoxicity

Tetrodotoxin (TTX) is one of the most potent naturally occurring neurotoxins. InitiallyTTX was associated with human food intoxications in Japan, but nowadays, concerns about thehuman health risks posed by TTX have increased in Europe after the identification of the toxin infish, marine gastropods, and bivalves captured in European waters. Even when TTX monitoring isnot currently performed in Europe, an acute oral no observable effect level (NOAEL) of 75 μg/kghas been recently established but, to date, no studies evaluating the chronic oral toxicity of TTXhave been released, even when EFSA has highlighted the need for them. Thus, in this work, thechronic effects of low oral TTX doses (below the acute lethal dose 50) were evaluated followinginternationally adopted guidelines. The results presented here demonstrate that low oral doses ofTTX have deleterious effects on renal and cardiac tissues. Moreover, alterations in bloodbiochemistry parameters, urine production, and urinalysis data were already detected at the oraldose of 75 μg/kg after the 28 days exposure. Thus, the data presented here constitute an initialapproach for the chronic evaluation of the in vivo toxicity of tetrodotoxin after its ingestion throughcontaminated fishery products.

Urinary Excretion of Tetrodotoxin Modeled in a Porcine Renal Proximal Tubule Epithelial Cell Line, LLC-PK₁

This study examined the urinary excretion of tetrodotoxin (TTX) modeled in a porcine renal proximal tubule epithelial cell line, LLC-PK₁. Time course profiles of TTX excretion and reabsorption across the cell monolayers at 37 °C showed that the amount of TTX transported increased linearly for 60 min. However, at 4 °C, the amount of TTX transported was approximately 20% of the value at 37 °C. These results indicate that TTX transport is both a transcellular and carrier-mediated process. Using a transport inhibition assay in which cell monolayers were incubated with 50 µM TTX and 5 mM of a transport inhibitor at 37 °C for 30 min, urinary excretion was significantly reduced by probenecid, tetraethylammonium (TEA), l-carnitine, and cimetidine, slightly reduced by p-aminohippuric acid (PAH), and unaffected by 1-methyl-4-phenylpyridinium (MPP+), oxaliplatin, and cefalexin. Renal reabsorption was significantly reduced by PAH, but was unaffected by probenecid, TEA and l-carnitine. These findings indicate that TTX is primarily excreted by organic cation transporters (OCTs) and organic cation/carnitine transporters (OCTNs), partially transported by organic anion transporters (OATs) and multidrug resistance-associated proteins (MRPs), and negligibly transported by multidrug and toxic compound extrusion transporters (MATEs).

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.