Chemiluminescent Receptor Binding Assay for Ciguatoxins and Brevetoxins Using Acridinium Brevetoxin-B2

Ciguatera Fish Poisoning in the Caribbean Sea and Atlantic Ocean: Reconciling the Multiplicity of Ciguatoxins and Analytical Chemistry Approach for Public Health Safety

Ciguatera is a major circumtropical poisoning caused by the consumption of marine fish and invertebrates contaminated with ciguatoxins (CTXs): neurotoxins produced by endemic and benthic dinoflagellates which are biotransformed in the fish food-web. We provide a history of ciguatera research conducted over the past 70 years on ciguatoxins from the Pacific Ocean (P-CTXs) and Caribbean Sea (C-CTXs) and describe their main chemical, biochemical, and toxicological properties. Currently, there is no official method for the extraction and quantification of ciguatoxins, regardless their origin, mainly due to limited CTX-certified reference materials. In this review, the extraction and purification procedures of C-CTXs are investigated, considering specific objectives such as isolating reference materials, analysing fish toxin profiles, or ensuring food safety control. Certain in vitro assays may provide sufficient sensitivity to detect C-CTXs at sub-ppb levels in fish, but they do not allow for individual identification of CTXs. Recent advances in analysis using liquid chromatography coupled with low- or high-resolution mass spectrometry provide new opportunities to identify known C-CTXs, to gain structural insights into new analogues, and to quantify C-CTXs. Together, these methods reveal that ciguatera arises from a multiplicity of CTXs, although one major form (C-CTX-1) seems to dominate. However, questions arise regarding the abundance and instability of certain C-CTXs, which are further complicated by the wide array of CTX-producing dinoflagellates and fish vectors. Further research is needed to assess the toxic potential of the new C-CTX and their role in ciguatera fish poisoning. With the identification of C-CTXs in the coastal USA and Eastern Atlantic Ocean, the investigation of ciguatera fish poisoning is now a truly global effort.

Evaluation of relative potency of calibrated ciguatoxin congeners by near-infrared fluorescent receptor binding and neuroblastoma cell-based assays

Ciguatera fish poisoning (CFP) is a foodborne illness affecting > 50,000 people worldwide annually. It is caused by eating marine invertebrates and fish that have accumulated ciguatoxins (CTXs). Recently, the risk of CFP to human health, the local economy, and fishery resources have increased; therefore, detection methods are urgently needed. Functional assays for detecting ciguatoxins in fish include receptor binding (RBA) and neuroblastoma cell-based assay (N2a assay), which can detect all CTX congeners. In this study, we made these assays easier to use. For RBA, an assay was developed using a novel near-infrared fluorescent ligand, PREX710-BTX, to save valuable CTXs. In the N2a assay, a 1-day assay was developed with the same detection performance as the conventional 2-day assay. Additionally, in these assays, we used calibrated CTX standards from the Pacific determined by quantitative NMR for the first time to compare the relative potency of congeners, which differed significantly among previous studies. In the RBA, there was almost no difference in the binding affinity among congeners, showing that the differences in side chains, stereochemistry, and backbone structure of CTXs did not affect the binding affinity. However, this result did not correlate with the toxic equivalency factors (TEFs) based on acute toxicity in mice. In contrast, the N2a assay showed a good correlation with TEFs based on acute toxicity in mice, except for CTX3C. These findings, obtained with calibrated toxin standards, provide important insights into evaluating the total toxicity of CTXs using functional assays.

Characterization of the Ciguatoxin Profile in Fish Samples from the Eastern Atlantic Ocean using Capillary Liquid Chromatography-High Resolution Mass Spectrometry

Ciguatera Poisoning is an emerging risk in the east Atlantic Ocean. Despite characterization efforts, the complete profile of ciguatoxin chemical species in these waters is still unknown. These efforts have been complicated by a lack of reference materials and scarcity of fish contaminated with high levels of ciguatoxins. Development and application of analytical methods with enhanced selectivity and sensitivity is essential for ciguatoxin characterization. Here, we developed an analytical characterization approach using capillary liquid chromatography coupled to high resolution mass spectrometry applied to reference materials obtained from ciguatoxin contaminated fish. Capillary LC coupled mass spectrometry resulted in increased sensitivity leading to the confirmation of C-CTX1 as the principal ciguatoxin present in these samples. We also detected and structurally characterized minor C-CTXs analogues consisting of C-CTX3/4, hydroxy-, didehydro-, and methoxy- metabolites.

Development of a New Monoclonal Antibody against Brevetoxins in Oyster Samples Based on the Indirect Competitive Enzyme-Linked Immunosorbent Assay

The consumption of shellfish contaminated with brevetoxins, a family of ladder-frame polyether toxins formed during blooms of the marine dinoflagellate Karenia brevis, can cause neurotoxic poisoning, leading to gastroenteritis and neurotoxic effects. To rapidly monitor brevetoxin levels in oysters, we generated a broad-spectrum antibody against brevetoxin 2 (PbTx-2), 1 (PbTx-1), and 3 (PbTx-3) and developed a rapid indirect competitive enzyme-linked immunosorbent assay (icELISA). PbTx-2 was reacted with carboxymethoxylamine hemihydrochloride (CMO) to generate a PbTx-2-CMO hapten and reacted with succinic anhydride (HS) to generate the PbTx-2-HS hapten. These haptens were conjugated to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) to prepare immunogen and coating antigen reagents, respectively, using the active ester method. After immunization and cell fusion, a broad-spectrum monoclonal antibody (mAb) termed mAb 1D3 was prepared. The 50% inhibitory concentration (IC₅₀) values of the icELISA for PbTx-2, PbTx-1, and PbTx-3 were 60.71, 52.61, and 51.83 μg/kg, respectively. Based on the broad-spectrum mAb 1D3, an icELISA was developed to determine brevetoxin levels. Using this approach, the limit of detection (LOD) for brevetoxin was 124.22 μg/kg and recoveries ranged between 89.08% and 115.00%, with a coefficient of variation below 4.25% in oyster samples. These results suggest that our icELISA is a useful tool for the rapid monitoring of brevetoxins in oyster samples.