Detection of Tetrodotoxins in Puffer Fish by a Self-Assembled Monolayer-Based Immunoassay and Comparison with Surface Plasmon Resonance, LC-MS/MS, and Mouse Bioassay

Marine toxins in seafood: Recent updates on sample pretreatment and determination techniques

Marine toxins can lead to varying degrees of human poisoning, often resulting in fatal symptoms and causing significant economic losses in seafood-producing regions. To gain a deeper comprehension of the role of marine toxins in seafood and their impact on the environment, it is imperative to develop rapid, cost-effective, environmentally friendly, and efficient methods for sample pretreatment and determination to mitigate adverse impacts of marine toxins. This review presents a comprehensive overview of advancements made in sample pretreatment and determination techniques for marine toxins since 2017. The advantages and disadvantages of various technologies were critically examined. Additionally, the current challenges and future development strategies for the analysis of marine toxins are provided.

Automated Patch Clamp for the Detection of Tetrodotoxin in Pufferfish Samples

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

Assessment of Human Health Impacts from Invasive Pufferfish (Attacks, Poisonings and Fatalities) across the Eastern Mediterranean

The silver-cheeked toadfish Lagocephalus sceleratus (Gmelin 1789), and to a lesser degree the orange spotted toadfish Torquigener hypselogeneion (Bleeker, 1852), pose threats to human health from physical attacks and poisonings in the Eastern Mediterranean Sea. This study reviewed human health-related impacts resulting from these pufferfish, compiling and assessing records from online sources, the peer-reviewed literature, medical records, personal interviews, and observations across the Eastern Mediterranean in the years 2004 to 2023. A total of 198 events impacting human health were documented: 28 records of physical attacks, at least 144 non-lethal poisoning episodes, and 27 human fatalities resulting from consumption. The majority of the reported incidences occurred in Syria, Türkiye, and Lebanon. Most physical attacks occurred in summer, while most poisoning events occurred during winter. The number of recorded incidents greatly increased after 2019, especially with regard to poisonings, yet whether this is related to greater media attention, or to increased fish abundance is unclear. This is the first comprehensive study to collate findings on attacks, poisonings and fatalities caused by these pufferfish in the Mediterranean Sea, and may help in improving national health policies. We urge the continuation of national campaigns to caution residents and tourists of these species' high toxicities and potential aggressiveness.

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.

Monthly Variation of Tetrodotoxin Levels in Pufferfish (Lagocephalus sceleratus) Caught from Antalya Bay, Mediterranean Sea

The silver-cheeked toadfish (Lagocephalus sceleratus), an invasive alien pufferfish species that has rapidly settled throughout the Mediterranean region, poses significant threats not only to native marine species and fisheries but also to public health due to the tetrodotoxin (TTX) they harbor. In this study, TTX concentrations in L. sceleratus from Antalya Bay in the Northeastern Mediterranean Sea were investigated using Q-TOF-LC-MS on a monthly basis over a one-year period. Pufferfish were caught by angling from May 2018 to April 2019. The TTX levels in three different tissues (gonads, liver, and muscle) of 110 pufferfish in total were determined in both male and female individuals caught for 11 months. The highest TTX mean levels generally occurred in the gonads and the lowest in the muscle samples. As regards the maximum TTX contents, the highest concentrations determined were 68.2, 34.2, and 7.8 µg/g in the gonad, liver, and muscle tissues, respectively. The highest levels were generally observed in late autumn to winter (especially in November and December) in all tissues from both genders. Female individuals were generally found to be more toxic than male individuals. The TTX levels found confirm that the consumption of L. sceleratus from Antalya Bay remains dangerous throughout the year, and thus L. sceleratus constantly constitutes an important risk source for public health.

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

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

First Toxicological Analysis of the Pufferfish Sphoeroides pachygaster Collected in Italian Waters (Strait of Sicily): Role of Citizens Science in Monitoring Toxic Marine Species

Pufferfish (Tetraodontidae) inhabiting the Mediterranean Sea may represent an emerging public health risk due to the possible accumulation of marine neurotoxins such as tetrodotoxin (TTXs) and saxitoxin (STXs) in their tissues. In this study, the presence of pufferfish species in the Strait of Sicily (Lampedusa Island, Italy) was investigated using a citizen science (CS) approach, involving local fishermen. Samples (liver, intestine, gonads, muscle, skin) from 20 specimens were sent to the National Reference Laboratory on Marine Biotoxins for TTXs detection using a validated HILIC-MS/MS method on fish tissue. The presence of STXs was also screened in part of the specimens. Overall, 56 specimens identified as Sphoeroides pachygaster (Müller &Troschel, 1848) were collected. Data on their total length, body weight, fishing method and catch area (with relative depth temperature and salinity) were analyzed and compared with the S. pachygaster records reported in literature which were updated to 2022. All the analysed tissues were found to be negative for both TTXs and STXs. CS played an essential role in monitoring potentially toxic marine species in this investigation. Outcomes from this study, which is the first investigating S. pachygaster toxicity in Italian waters, may provide useful data for the proper assessment of this emerging risk.

Detection of Ciguatoxins and Tetrodotoxins in Seafood with Biosensors and Other Smart Bioanalytical Systems

The emergence of marine toxins such as ciguatoxins (CTXs) and tetrodotoxins (TTXs) in non-endemic regions may pose a serious food safety threat and public health concern if proper control measures are not applied. This article provides an overview of the main biorecognition molecules used for the detection of CTXs and TTXs and the different assay configurations and transduction strategies explored in the development of biosensors and other biotechnological tools for these marine toxins. The advantages and limitations of the systems based on cells, receptors, antibodies, and aptamers are described, and new challenges in marine toxin detection are identified. The validation of these smart bioanalytical systems through analysis of samples and comparison with other techniques is also rationally discussed. These tools have already been demonstrated to be useful in the detection and quantification of CTXs and TTXs, and are, therefore, highly promising for their implementation in research activities and monitoring programs.

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 and Its Analogues in Food: Recent Updates on Sample Preparation and Analytical Methods Since 2012

Tetrodotoxin (TTX), found in various organisms including pufferfish, is an extremely potent marine toxin responsible for numerous food poisoning accidents. Due to its serious toxicity and public health threat, detecting TTX and its analogues in diverse food matrices with a simple, fast, efficient method has become a worldwide concern. This review summarizes the advances in sample preparation and analytical methods for the determination of TTX and its analogues, focusing on the latest development over the past five years. Current state-of-the-art technologies, such as solid-phase microextraction, online technology, novel injection technology, two-dimensional liquid chromatography, high-resolution mass spectrometry, newly developed lateral flow immunochromatographic strips, immunosensors, dual-mode aptasensors, and nanomaterials-based approaches, are thoroughly discussed. The advantages and limitations of different techniques, critical comments, and future perspectives are also proposed. This review is expected to provide rewarding insights to the future development and broad application of pretreatment and detection methods for TTX and its analogues.

Emerging Marine Biotoxins in European Waters: Potential Risks and Analytical Challenges

Harmful algal blooms pose a challenge regarding food safety due to their erratic nature and forming circumstances which are yet to be disclosed. The best strategy to protect human consumers is through legislation and monitoring strategies. Global warming and anthropological intervention aided the migration and establishment of emerging toxin producers into Europe's temperate waters, creating a new threat to human public health. The lack of information, standards, and reference materials delay effective solutions, being a matter of urgent resolution. In this work, the recent findings of the presence of emerging azaspiracids, spirolildes, pinnatoxins, gymnodimines, palitoxins, ciguatoxins, brevetoxins, and tetrodotoxins on European Coasts are addressed. The information concerning emerging toxins such as new matrices, locations, and toxicity assays is paramount to set the risk assessment guidelines, regulatory levels, and analytical methodology that would protect the consumers.

An Updated Review of Tetrodotoxin and Its Peculiarities

Tetrodotoxin (TTX) is a crystalline, weakly basic, colorless organic substance and is one of the most potent marine toxins known. Although TTX was first isolated from pufferfish, it has been found in numerous other marine organisms and a few terrestrial species. Moreover, tetrodotoxication is still an important health problem today, as TTX has no known antidote. TTX poisonings were most commonly reported from Japan, Thailand, and China, but today the risk of TTX poisoning is spreading around the world. Recent studies have shown that TTX-containing fish are being found in other regions of the Pacific and in the Indian Ocean, as well as the Mediterranean Sea. This review aims to summarize pertinent information available to date on the structure, origin, distribution, mechanism of action of TTX and analytical methods used for the detection of TTX, as well as on TTX-containing organisms, symptoms of TTX poisoning, and incidence worldwide.

Keeping Lagocephalus sceleratus off the Table: Sources of Variation in the Quantity of TTX, TTX Analogues, and Risk of Tetrodotoxication

The invasion of the tetrodotoxin (TTX)-bearing silver-cheeked toadfish and potential poisoning due to its consumption (tetrodotoxication) threatens public safety in the Mediterranean Sea. In this study, TTX and TTX analogues of Lagocephalus sceleratus (Gmelin, 1789) were measured using liquid chromatography tandem mass spectrometry (LC-MS/MS) in fish collected off the island of Crete (Southern Mediterranean). We tested the synergistic effect of a suite of factors potentially affecting toxins' levels and tetrodotoxication risk using general and generalized linear models, respectively. The type of tissue, geographic origin (Cretan Sea, Libyan Sea), sex, and fish maturity stage were significant predictors of toxin concentrations. Mean TTX was higher in gonads and lower in muscles, higher in the Libyan Sea and in female fish, and lower in juvenile (virgin) fish. The concentration of TTX was also significantly and positively correlated with the concentration of several TTX analogues (4-epiTTX, 4,9-anhydroTTX, 11-deoxyTTX, 5,11/6,11-dideoxyTTX, 5,6,11-trideoxyTTX, 11-norTTX-6-ol). The analysis showed that fish originating from the Libyan Sea had significantly higher probability to cause tetrodotoxication in case of consumption. The variability explained by the models developed in this study was relatively low, indicating that toxin levels are hard to predict and the consumption of L. sceleratus should therefore be avoided.

Hybrid Antibody-Aptamer Assay for Detection of Tetrodotoxin in Pufferfish

The marine toxin tetrodotoxin (TTX) poses a great risk to public health safety due to its severe paralytic effects after ingestion. Seafood poisoning caused by the consumption of contaminated marine species like pufferfish due to its expansion to nonendemic areas has increased the need for fast and reliable detection of the toxin to effectively implement prevention strategies. Liquid chromatography-mass spectrometry is considered the most accurate method, although competitive immunoassays have also been reported. In this work, we sought to develop an aptamer-based assay for the rapid, sensitive, and cost-effective detection of TTX in pufferfish. Using capture-SELEX combined with next-generation sequencing, aptamers were identified, and their binding properties were evaluated. Finally, a highly sensitive and user-friendly hybrid antibody–aptamer sandwich assay was developed with superior performance compared to several assays reported in the literature and commercial immunoassay kits. The assay was successfully applied to the quantification of TTX in pufferfish extracts, and the results obtained correlated very well with a competitive magnetic bead-based immunoassay performed in parallel for comparison. This is one of the very few works reported in the literature of such hybrid assays for small-molecule analytes whose compatibility with field samples is also demonstrated.

Current Trends and Challenges for Rapid SMART Diagnostics at Point-of-Site Testing for Marine Toxins

In the past twenty years marine biotoxin analysis in routine regulatory monitoring has advanced significantly in Europe (EU) and other regions from the use of the mouse bioassay (MBA) towards the high-end analytical techniques such as high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS). Previously, acceptance of these advanced methods, in progressing away from the MBA, was hindered by a lack of commercial certified analytical standards for method development and validation. This has now been addressed whereby the availability of a wide range of analytical standards from several companies in the EU, North America and Asia has enhanced the development and validation of methods to the required regulatory standards. However, the cost of the high-end analytical equipment, lengthy procedures and the need for qualified personnel to perform analysis can still be a challenge for routine monitoring laboratories. In developing regions, aquaculture production is increasing and alternative inexpensive Sensitive, Measurable, Accurate and Real-Time (SMART) rapid point-of-site testing (POST) methods suitable for novice end users that can be validated and internationally accepted remain an objective for both regulators and the industry. The range of commercial testing kits on the market for marine toxin analysis remains limited and even more so those meeting the requirements for use in regulatory control. Individual assays include enzyme-linked immunosorbent assays (ELISA) and lateral flow membrane-based immunoassays (LFIA) for EU-regulated toxins, such as okadaic acid (OA) and dinophysistoxins (DTXs), saxitoxin (STX) and its analogues and domoic acid (DA) in the form of three separate tests offering varying costs and benefits for the industry. It can be observed from the literature that not only are developments and improvements ongoing for these assays, but there are also novel assays being developed using upcoming state-of-the-art biosensor technology. This review focuses on both currently available methods and recent advances in innovative methods for marine biotoxin testing and the end-user practicalities that need to be observed. Furthermore, it highlights trends that are influencing assay developments such as multiplexing capabilities and rapid POST, indicating potential detection methods that will shape the future market.

Puffer Fish Gut Microbiota Studies Revealed Unique Bacterial Co-Occurrence Patterns and New Insights on Tetrodotoxin Producers

Tetrodotoxin (TTX) is a potent neurotoxin isolated mainly from toxic puffer fish. To date, the TTX biosynthetic mechanism inside its hosts remains unresolved. Here, we hypothesize the TTX synthesis relies on the host gut microbiota, including the neglected non-culturable bacteria. In these studies, we collected the gut contents from 5 puffer fish species of the genus Takifugu including one suspected hybrid species for gut microbiota study by 16S rRNA amplicon metagenomics approach. Their gut samples were divided into toxic and non-toxic groups based on the TTX concentrations in the livers detected by LC-MS/MS. Bacterial diversity studies showed that gut microbiota structures were significantly different between toxic and non-toxic species. Vibrio and Cyanobacteria centered at the gut bacterial co-occurrence network, suggesting their importance in TTX biosynthesis. The results of PICRUSt2 metagenomic prediction and gene set enrichment analysis provided new support of arginine-precursor required in TTX biosynthesis. This is the first study to profile the gut microbiota in toxic and non-toxic puffer fish species by 16S rRNA amplicon metagenomic approach, defining significant microbial co-occurrence patterns in their gut environment. Our data supported the proposed biosynthesis of TTX inside the hosts by their gut bacterial symbionts using arginine as a precursor.

A gold nanoparticle-based lateral flow immunosensor for ultrasensitive detection of tetrodotoxin

Tetrodotoxin (TTX) is a potent marine neurotoxin. Its frequent detection and widespread distribution pose a substantial health risk to consumers. The work presented herein describes the development of a lateral flow immunosensor based on a gold nanoparticle-labeled monoclonal antibody probe, which allows the affinity reaction of antigen-antibody and amplifies the reaction signal. The immunosensor assay was found to provide a visible limit of detection (vLOD) of 10 μg kg^-1 in crucian and clam matrices without time-consuming pretreatment. Spiked samples were analyzed using the immunosensor and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The immunosensor gave average intra-assay recoveries of 84.0-103.9%, inter-assay recoveries of 76.1-105% for the crucian matrix and intra-assay recoveries of 78.5-93.0%, inter-assay recoveries of 74.8-85.7% for the clam matrix. The results obtained using the immunosensor and LC-MS/MS were in good agreement. The immunosensor test could be completed within 10 min, offering a convenient option or complementarity to the traditional methods of TTX detection.

Voltammetric Detection of Tetrodotoxin Real-Time In Vivo of Mouse Organs using DNA-Immobilized Carbon Nanotube Sensors

Background:

Tetrodotoxin (TTX) is a biosynthesized neurotoxin that exhibits powerful anticancer and analgesic abilities by inhibiting voltage-gated sodium channels that are crucial for cancer metastasis and pain delivery. However, for the toxin’s future medical applications to come true, accurate, inexpensive, and real-time in vivo detection of TTX remains as a fundamental step.

Methods:

In this study, highly purified TTX extracted from organs of Takifugu rubripes was injected and detected in vivo of mouse organs (liver, heart, and intestines) using Cyclic Voltammetry (CV) and Square Wave Anodic Stripping Voltammetry (SWASV) for the first time. In vivo detection of TTX was performed with auxiliary, reference, and working herring sperm DNA-immobilized carbon nanotube sensor systems.

Results:

DNA-immobilization and optimization of amplitude (V), stripping time (sec), increment (mV), and frequency (Hz) parameters for utilized sensors amplified detected peak currents, while highly sensitive in vivo detection limits, 3.43 µg L-1 for CV and 1.21 µg L-1 for SWASV, were attained. Developed sensors herein were confirmed to be more sensitive and selective than conventional graphite rodelectrodes modified likewise. A linear relationship was observed between injected TTX concentration and anodic spike peak height. Microscopic examination displayed coagulation and abnormalities in mouse organs, confirming the powerful neurotoxicity of extracted TTX.

Conclusion:

These results established the diagnostic measures for TTX detection regarding in vivo application of neurotoxin-deviated anticancer agents and analgesics, as well as TTX from food poisoning and environmental contamination.

Public Health Risks Associated with Tetrodotoxin and Its Analogues in European Waters: Recent Advances after The EFSA Scientific Opinion

Tetrodotoxin (TTX) and its analogues are naturally occurring toxins responsible worldwide for human intoxication cases and fatalities, mainly associated with pufferfish consumption. In the last decade, TTXs were detected in marine bivalves and gastropods from European waters. As TTXs are not regulated or monitored at EU level, their unexpected occurrence in shellfish raised concerns as a food safety hazard and revealed the necessity of a thorough assessment on the public health risks associated with their presence. For this reason, the European Food Safety Authority (EFSA) was requested by the European Commission to provide a scientific opinion, finally adopted in March 2017, according to which a provisional 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. The EFSA expert panel, however, recognized a number of shortcomings and uncertainties related to the unavailability of sufficient scientific data and provided relevant recommendations for future research to overcome these data gaps identified in order to further refine the risk assessment on TTXs. The present review aims to summarize the knowledge obtained towards addressing these recommendations in the two years following publication of the EFSA opinion, at the same time highlighting the points requiring further investigation.

Detection of tetrodotoxins in juvenile pufferfish Lagocephalus sceleratus (Gmelin, 1789) from the North Aegean Sea (Greece) by an electrochemical magnetic bead-based immunosensing tool

Two small Lagocephalus sceleratus juveniles were captured in picarel targeting catches from North Aegean Sea (Greece) in the autumn of 2017. An electrochemical immunosensing tool using magnetic beads as immobilisation support was developed and applied to the rapid screening of tetrodotoxins (TTXs), potent neurotoxins that constitute a food safety hazard when present in seafood. This tool revealed the presence of TTXs in both individuals. Results were compared with those provided by mELISA and LC-HRMS, the latter confirming the presence of TTX. Some of the tissues contained TTX contents close to or above 2 mg/kg. L. sceleratus juveniles had been considered as non-toxic and, to our knowledge, this is the first report of high TTX levels in small L. sceleratus individuals. Such specimens can be mistaken with other edible species, posing a threat to consumers. The availability of low-cost and user-friendly tools for TTXs detection will contribute to guarantee seafood safety.

Pull-down Assay on Streptavidin Beads and Surface Plasmon Resonance Chips for SWATH-MS-based Interactomics

BACKGROUND/AIM

Pul-down assay is a popular in vitro method for identification of physical interactors of selected proteins. Here, for the first time, we compared three conventional variants of pull-down assay with the streptavidin-modified surface plasmon resonance (SPR) chips for the detection of PDZ and LIM domain protein 2 (PDLIM2) interaction partners.

MATERIALS AND METHODS

PDLIM2 protein-protein interactions were analysed by three variants of pull-down assay on streptavidin beads using LC-MS/MS in "Sequential Window Acquisition of all Theoretical fragment ion spectra (SWATH)" mode and compared with LC-SWATH-MS/MS data from SPR chips.

RESULTS

The results showed that (i) the use of SPR chip led to comparable data compared to on-column streptavidin beads, (ii) gravity flow and microflow in wash and elution steps provided better results than centrifugation, and (iii) type and concentration of detergent did not significantly affect the interactome data of cancer-associated PDLIM2.

CONCLUSION

Our study supports further application of SPR-based affinity purification with SWATH mass spectrometry for reproducible and controlled characterization of cancer-associated interactomes.

Self-assembled monolayer-based immunoassays for okadaic acid detection in seawater as monitoring tools

Rapid and cost-effective methods to monitor the presence of diarrhetic shellfish poisoning (DSP) toxins in seawater samples in an easy and reliable manner are required to protect human health and avoid economic losses to shellfish industry. Immunoassays for the detection of okadaic acid (OA) and dinophysistoxin-1 and dinophysistoxin-2 are developed by immobilising OA on self-assembled monothiols or dithiols in an ordered and oriented way, providing an effective limit of detection of ∼1 ng OA equiv./mL seawater. The immunoassays are applied to the analysis of the particulate fraction of seawater samples from two Catalan harbours (NW Mediterranean) and samples collected periodically from the Galician Rias (E Atlantic), as well as a reference mussel sample. Results are in agreement with LC-MS/MS and the certified values. OA concentration in seawater correlates with Dinophysis cell abundance, with a 1-2 weeks lag. The immunoassays provide powerful high-throughput analytical methods potentially applicable as alternative monitoring tools.

Rapid screening and multi-toxin profile confirmation of tetrodotoxins and analogues in human body fluids derived from a puffer fish poisoning incident in New Caledonia

In August 2014, a puffer fish poisoning incidence resulting in one fatality was reported in New Caledonia. Although tetrodotoxin (TTX) intoxication was established from the patients' signs and symptoms, the determination of TTX in the patient's urine, serum or plasma is essential to confirm the clinical diagnosis. To provide a simple cost-effective rapid screening tool for clinical analysis, a maleimide-based enzyme-linked immunosorbent assay (mELISA) adapted for the determination of TTX contents in human body fluids was assessed. The mELISA was applied to the analysis of urine samples from two patients and a response for the presence of TTX and/or structurally similar analogues was detected in all samples. The analysis by LC-MS/MS confirmed the presence of TTX but also TTX analogues (4-epiTTX, 4,9-anhydroTTX and 5,6,11-trideoxyTTX) in the urine. A change in the multi-toxin profile in the urine based on time following consumption was observed. LC-MS/MS analysis of serum and plasma samples also revealed the presence of TTX (32.9 ng/mL) and 5,6,11-trideoxyTTX (374.6 ng/mL) in the post-mortem plasma. The results provide for the first time the TTX multi-toxin profile of human samples from a puffer fish intoxication and clearly demonstrate the implication of TTX as the causative agent of the reported intoxication case.

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.

Development and validation of a maleimide-based enzyme-linked immunosorbent assay for the detection of tetrodotoxin in oysters and mussels

The recent detection of tetrodotoxins (TTXs) in puffer fish and shellfish in Europe highlights the necessity to monitor the levels of TTXs in seafood by rapid, specific, sensitive and reliable methods in order to protect human consumers. A previous immunoassay for TTX detection in puffer fish, based on the use of self-assembled monolayers (SAMs) for the immobilization of TTX on maleimide plates (mELISA), has been modified and adapted to the analysis of oyster and mussel samples. Changing dithiol for cysteamine-based SAMs enabled reductions in the assay time and cost, while maintaining the sensitivity of the assay. The mELISA showed high selectivity for TTX since the antibody did not cross-react with co-occurring paralytic shellfish poisoning (PSP) toxins and no interferences were observed from arginine (Arg). Moreover, TTX-coated maleimide plates stored for 3 months at -20°C and 4°C were stable, thus when pre-prepared, the time to perform the assay is reduced. When analyzing shellfish samples, matrix effects and toxin recovery values strongly depended on the shellfish type and the sample treatment. Blank oyster extracts could be directly analyzed without solid-phase extraction (SPE) clean-up, whereas blank mussel extracts showed strong matrix effects and SPE and subsequent solvent evaporation were required for removal. However, the SPE clean-up and evaporation resulted in toxin loss. Toxin recovery values were taken as correction factors (CFs) and were applied to the quantification of TTX contents in the analysis of naturally-contaminated shellfish samples by mELISA. The lowest effective limits of detection (eLODs) were about 20 and 50µg/kg for oyster extracts without and with SPE clean-up, respectively, and about 30µg/kg for mussel extracts with both protocols, all of them substantially below the eLOD attained in the previous mELISA for puffer fish (230µg/kg). Analysis of naturally-contaminated samples by mELISA and comparison with LC-MS/MS quantifications demonstrated the viability of the approach. This mELISA is a selective and sensitive tool for the rapid detection of TTX in oyster and mussel samples showing promise to be implemented in routine monitoring programs to protect human health.

Surface plasmon resonance biosensing: Approaches for screening and characterising antibodies for food diagnostics

Research in biosensing approaches as alternative techniques for food diagnostics for the detection of chemical contaminants and foodborne pathogens has increased over the last twenty years. The key component of such tests is the biorecognition element whereby polyclonal or monoclonal antibodies still dominate the market. Traditionally the screening of sera or cell culture media for the selection of polyclonal or monoclonal candidate antibodies respectively has been performed by enzyme immunoassays. For niche toxin compounds, enzyme immunoassays can be expensive and/or prohibitive methodologies for antibody production due to limitations in toxin supply for conjugate production. Automated, self-regenerating, chip-based biosensors proven in food diagnostics may be utilised as rapid screening tools for antibody candidate selection. This work describes the use of both single channel and multi-channel surface plasmon resonance (SPR) biosensors for the selection and characterisation of antibodies, and their evaluation in shellfish tissue as standard techniques for the detection of domoic acid, as a model toxin compound. The key advantages in the use of these biosensor techniques for screening hybridomas in monoclonal antibody production were the real time observation of molecular interaction and rapid turnaround time in analysis compared to enzyme immunoassays. The multichannel prototype instrument was superior with 96 analyses completed in 2h compared to 12h for the single channel and over 24h for the ELISA immunoassay. Antibodies of high sensitivity, IC50's ranging from 4.8 to 6.9ng/mL for monoclonal and 2.3-6.0ng/mL for polyclonal, for the detection of domoic acid in a 1min analysis time were selected. Although there is a progression for biosensor technology towards low cost, multiplexed portable diagnostics for the food industry, there remains a place for laboratory-based SPR instrumentation for antibody development for food diagnostics as shown herein.

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

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