A competitive enzyme-linked immunoassay for domoic acid determination in human body fluids

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.

Applying molecular modelling and experimental studies to develop molecularly imprinted polymer for domoic acid enrichment from both seawater and shellfish

A highly selective sample cleanup method using molecularly imprinted polymers (MIP) was developed for the enrichment of domoic acid (DA, an amnesic shellfish toxin) from both seawater and shellfish samples. Molecular modelling was firstly applied to screening a suitable functional monomer and optimize the polymer preparation. Theoretical results were in a good agreement with those of the experimental studies. MIP was prepared by precipitation polymerization using 1, 3, 5-pentanetricarboxylic acid and 2-(Trifluoromethyl)acrylic acid as the template molecule and functional monomer, respectively. The morphology and molecular structure of MIP were revealed by scanning electron microscope (SEM) and fourier transform infrared spectroscopy (FTIR), respectively. The obtained MIP showed high affinity and selectivity for DA with binding site numbers of 0.875 mg g^-1 and an average association constant of 0.219 L mg^-1 evaluated by adsorption experiments. The developed molecularly imprinted solid-phase extraction (MISPE) column achieved satisfied adsorption rate (99.2%) and recovery (71.2%) with relative standard deviation (RSD) less than 1.0%, which is more stable and precise than the C₁₈, SAX, and HLB columns. Finally, the determination method for DA in both seawater and shellfish samples was then successfully established and validated using MISPE coupled with high-performance liquid chromatography-ultraviolet detection (HPLC-UV). The method limit of detection was 20 μg L^-1 and 50 μg kg^-1 for seawater and shellfish, respectively. This study demonstrates that molecular modelling is a useful tool to screening functional monomer and optimize polymer preparation. It provides an innovative polymer for trace DA monitoring in both seawater and shellfish.

Analytical approaches for an important shellfish poisoning agent: domoic Acid

Domoic acid (DA), a neurotoxic amino acid produced by some strains of phytoplankton, is responsible for the human toxic syndrome amnesic shellfish poisoning. This exocitotoxin results in neuronal degeneration and necrosis in specific regions of the hippocampus. Because DA accumulates mostly in shellfish, causing outbreaks in different countries, screening for DA has been carried out with various assays. Although bioassays and immunoassays have been developed, several liquid chromatographic methods for the determination of DA in different matrices such as shellfish, algae, or seawater have been reported. Additionally, other alternative methods such as capillary electrophoresis and capillary electrochromatography have been described. This paper summaries the toxicology, the chemistry, and the developed determination methods of DA.

Development of ELISAs for detecting domoic acid, okadaic acid, and saxitoxin and their applicability for the detection of marine toxins in samples collected in Belgium

Okadaic acid, a diarrhetic shellfish poison, domoic acid, an amnesic shellfish poison, and saxitoxin, a paralytic shellfish poison, are three of the best-known marine biotoxins. The mouse bioassay is the method most widely used to detect many of these toxins in shellfish samples, but animal welfare concerns have prompted researchers to seek alternative methods of detection. In this study, three direct competitive enzyme-linked immunosorbent assays (ELISAs), each based on antibodies raised in rabbits against a conjugate of the analyte of interest, were developed for marine biotoxin detection in mussel, oyster, and scallop. One assay was for okadaic acid, one for saxitoxin, and one for domoic acid usually detected and quantified by high-performance liquid chromatography-ultraviolet light (HPLC-UV). All three compounds and a number of related toxins were extracted quickly and simply from the shellfish matrices with a 9 : 1 mixture of ethanol and water before analysis. The detection capabilities (CCbeta values) of the developed ELISAs were 150 microg kg(-1) for okadaic acid, 50 microg kg(-1) for domoic acid, and 5 microg kg(-1) or less for saxitoxin. The assays proved satisfactory when used over a 4-month period for the analysis of 110 real samples collected in Belgium.

Chromatographic separation for domoic acid using a fragment imprinted polymer

We prepared molecularly imprinted polymers for an amnesic shellfish poison, domoic acid. To prepare the polymer, we tested several commercial aromatic dicarboxylic compounds such as isomers of phthalic acid for templates of molecularly imprinted polymers. The highest selective recognition ability of the polymer for domoic acid in the tested compounds was found when o-phthalic acid was used as the template. The ability was due to the acidity of the carboxylic acids in the domoic acid and the similarity of the shape around the carboxylic acids of domoic acid and the templates. The effective chromatographic separation of domoic acid in the extract from blue mussels was achieved with a LC column packed with the fragment imprinted polymer using o-phthalic acid as the template. This polymer can be utilized for a clean up procedure of domoic acid in toxic shellfish.

Toxins: Bacterial and Marine Toxins

The term toxin refers in a specific way to a toxic substance of biologic origin; that is, a true toxin is a poison produced by a living organism. The purpose of this article is to review some of the most potentially dangerous toxins of concern today. Mechanisms of action, routes of exposure, diagnostic tools, and treatment recommendations are addressed. In addition, current therapeutic uses for certain toxins are discussed.

Detection of domoic acid in rat serum and brain by direct competitive enzyme-linked immunosorbent assay (cELISA)

In 1987 a large-scale incident of human poisoning in Canada was traced to commercial mussels contaminated with domoic acid (DOM). Since then, routine screening of shellfish domoic acid content has been carried out using a variety of assays, with liquid chromatography using ultraviolet absorbance detection (LC-UV) or mass spectrometric detection (LC-MS) being the currently accepted standard methodologies. Recently, a highly specific competitive enzyme-linked immunosorbent assay (cELISA) has been developed for the detection and analysis of DOM in commercial shellfish, but its accuracy relative to LC methods has not been independently verified in mammalian tissues. In this study we demonstrate that measurement of rat serum DOM concentration by cELISA gives a good correlation (r2 = 0.993) across a broad range of concentrations when compared to LC-MS analysis, with only a small (15%) overestimation of sample DOM content. In addition, we have developed an extraction method for analysis of DOM in rat brain by cELISA which yields complete recovery across a range of sample dilutions.

Surface plasmon resonance sensor for domoic acid based on grafted imprinted polymer

A molecularly imprinted polymer (MIP) film for domoic acid (DA) was synthesised by direct photo-grafting onto a gold chip suitable for a surface plasmon resonance (SPR) based bioanalytical instrument system, the BIAcore 3000. The gold surface was first functionalised with a self-assembled monolayer of 2-mercaptoethylamine and subsequent carbodiimide chemistry was performed for covalent attachment of the photoinitiator, 4,4'-azobis(cyanovaleric acid). This ensured that the formation of the MIP thin film, comprising 2-(diethylamino) ethyl methacrylate as functional monomer and ethylene glycol dimethacrylate as cross-linker, occurred only at the surface level. Optimisation and control over the grafting procedure were achieved using contact angle measurements and atomic force microscope (AFM) imaging. The surface grafting resulted in the formation of thin and homogeneous MIP film with thickness of 40 nm. A competitive binding assay was performed with free DA and its conjugate with horseradish peroxidase, which was used as a refractive label. The sensor was evaluated for its sensitivity, cross-reactivity, and robustness by using a BIAcore 3000. Likewise, monoclonal antibodies acting as natural receptors for the toxin were studied with the same BIAcore system. Results of a comparison between the artificial and natural receptors are reported. In contrast to monoclonal antibodies, the regeneration of MIP chip did not affect its recognition properties and continuous measurement was possible over a period of at least 2 months.

Development of a sensitive enzyme-linked immunosorbent assay for the determination of domoic Acid in shellfish

Polyclonal antibodies for domoic acid were generated from rabbits after the animals had been immunized with either domoic acid-keyhole limpet hemocyanin (KLH) or domoic acid-bovine serum albumin (BSA). A competitive direct enzyme-linked immunosorbent assay (cdELISA) and a competitive indirect ELISA (ciELISA) were used for the characterization of the antibodies and for analysis of domoic acid in blue mussels and clams. The antibody titers in the serum of rabbits immunized with domoic acid-KLH were considerably higher than those in rabbits immunized with domoic acid-BSA. The antibodies from the rabbits immunized with domoic acid-KLH were further characterized. In the cdELISA, the concentrations causing 50% inhibition (IC(50)) of binding of domoic acid-horseradish peroxidase to the antibodies by domoic acid and a domoic acid analogue, kainic acid, were found to be 0.75 and 200 ng/mL, respectively. In the presence of blue mussel matrix, the detection limit of domoic acid was <25 ng/g. The overall analytical recovery of domoic acid (25-500 ng/g) added to the blue mussels and then extracted with 50% aqueous methanol in the cdELISA was found to be 81.1%. The efficacy of cdELISA was also confirmed by the high-performance liquid chromatography method. Analysis of domoic acid in shellfish samples showed that 10 of the 15 shellfish examined were contaminated with domoic acid at levels of <50 ng/g.

Amnesic shellfish poison

Amnesic shellfish poisoning (ASP) is caused by consumption of shellfish that have accumulated domoic acid, a neurotoxin produced by some strains of phytoplankton. The neurotoxic properties of domoic acid result in neuronal degeneration and necrosis in specific regions of the hippocampus. A serious outbreak of ASP occurred in Canada in 1987 and involved 150 reported cases, 19 hospitalisations and 4 deaths after consumption of contaminated mussels. Symptoms ranged from gastrointestinal disturbances, to neurotoxic effects such as hallucinations, memory loss and coma. Monitoring programmes are in place in numerous countries worldwide and closures of shellfish harvesting areas occur when domoic acid concentrations exceed regulatory limits. This paper reviews the chemistry, sources, metabolism and toxicology of domoic acid as well as human case reports of ASP and discusses a possible mechanism of toxicity.