Characterisation of okadaic acid related toxins by liquid chromatography coupled with mass spectrometry

Oriented-aptamer encoded magnetic nanosensor with laser-induced fluorescence for ultrasensitive test of okadaic acid

Okadaic acid (OA) biotoxin acts a well-established inhibitor of protein phosphatase even a tumor promoter of human being, arouse great attention in safety monitoring. However, the powerful and convenient nanosensing technologies for addressing the demands such as rapidity, high sensitivity, and stability in the in-field test of OA shellfish toxin is still scarce. Herein, a high-performance magnetic biometric nanosensor (MBNS) integrating oriented aptamers and ultrasensitive laser-induced fluorescence (LIF) was firstly proposed for the in-field detection of trace OA in seafoods. High-density aptamers hybridized with FAM-labeled cDNA were tethered to the surface of AuNPs on magnetic MIL-101@Fe3O4, and then finely regulated by mercaptohexyl alcohol (MCH) to be orderly assembled, as was successfully utilized to engineer an active biological nanosensor for highly specific recognition of OA. Aptamers anchored on magnetic Fe3O4@MOF@AuNPs activate a biometric microreactor of OA, in which the superior LIF properties, conformation regulation of aptamer, and the specific recognition using aptamer genes were adopted. The magnetic nanosensor with an excellent specificity and super sensitivity for OA analysis was achieved within 20 min. Moreover, the content of captured OA could facilely be recorded by measuring the fluorescence intensity, and the limit of detection (LOD) and limit of quantitation of OA (LOQ) reached 0.015 and 0.050 ng/mL respectively, which was far better than most aptamer-based biometric sensing methods. The feasibility for accurate test of trace OA toxin in the fortified shellfish samples was validated with the recovery yields of 88.2-107.5% and RSD of 0.5-7.6%, respectively. The result demonstrated that the oriented-aptamer encoded MNS had significant practical values in rapid and ultrasensitive detection of OA biotoxin and the related safety applications.

Cyclodextrin polymers as passive sampling materials for lipophilic marine toxins in Prorocentrum lima cultures and a Dinophysis sacculus bloom in the NW Mediterranean Sea

Cyclodextrins, cyclic oligomers that form a conical structure with an internal cavity, are proposed as new and sustainable materials for passive sampling of lipophilic marine toxins. Two applicability scenarios have been tested. First, disks containing β-cyclodextrin-hexamethylene diisocyanate (β-CD-HDI) and β-cyclodextrin-epichlorohydrin (β-CD-EPI) polymers were immersed in Prorocentrum lima cultures for different days (2, 12 and 40). LC-MS/MS analysis showed capture of free okadaic acid (OA) and dinophysistoxin-1 (DTX1) by cyclodextrins at contents that increased with immersion time. Cyclodextrins resulted more efficient in capturing DTX1 than OA. In a second experiment, disks containing β-CD-HDI, β-CD-EPI, γ-CD-HDI and γ-CD-EPI were deployed in harbor waters of El Masnou (NW Mediterranean Sea) during a Dinophysis sacculus bloom in February 2020. Free OA and pectenotoxin-2 (PTX2) were captured by cyclodextrins. Toxin contents were higher at sampling points and sampling weeks with higher D. sacculus cell abundance. In this case, PTX2 capture with cyclodextrins was more efficient than OA capture. Therefore, cyclodextrins have provided information regarding the toxin profile of a P. lima strain and the spatial and temporal dynamics of a D. sacculus bloom, proven efficient as passive sampling materials for environmental monitoring.

Degradation of okadaic acid in seawater by UV/TiO2 photocatalysis - Proof of concept

The consumption of contaminated shellfish with marine toxins causes adverse socioeconomical, environmental and health impacts. The marine toxin okadaic acid (OA) provokes diarrhetic shellfish poisoning (DSP) syndrome characterized by severe gastrointestinal symptoms. Therefore, there is increasing interest in removing these toxins from the marine environment to protect shellfish harvesting sites. Photocatalysis is proposed as an efficient method to detoxify the marine environment. In this study, Prorocentrum lima was used to produce high purity DSP toxins, in particular OA, for degradation studies. The profiling, characterization and quantification of DSP toxins in the culture of P. lima were achieved by ultrahigh performance liquid chromatography coupled to quadrupole-time of flight mass spectrometry (UPLC-QTOF-MSE) for accurate-mass full spectrum acquisition data. The effectiveness of UV/TiO2 system to degrade OA in seawater was assessed in lab-scale experiments and identification of transformation products was proposed based on the data obtained during analysis by UPLC-QTOF-MSE. The detoxification potential of the UV/TiO2 system was investigated using the phosphatase inhibition assay. Sufficient amount of high-purity OA (25 mg, >90% purity) was produced in-house for use in photocatalysis experiments by simple reversed-phase flash chromatography. Complete degradation of OA was observed in seawater after 30 min and 7.5 min in deionized water. The rate constants fitted with the pseudo-first order kinetic model (R2 > 0.96). High-resolution mass spectrometry analysis of the photocatalyzed OA allowed tentative identification of four transformation products. Detoxification was achieved in parallel with the degradation of OA in deionized water and artificial ocean water (≤20 min) but not for seawater. Overall, results suggest that UV/TiO2 photocatalysis can be an effective approach for degrading OA and their TPs in the marine environment. To the best of our knowledge, this is the first report on the use of photocatalysis to degrade marine toxins and its promising potential to protect shellfish harvesting sites.

Simple Diffusion as the Mechanism of Okadaic Acid Uptake by the Mussel Digestive Gland

Okadaic acid (OA) and other toxins of the diarrheic shellfish poisoning (DSP) group are accumulated and transformed mainly in many bivalves, inside the digestive gland cells. In this work the absorption of okadaic acid by those cells has been studied by supplying the toxin dissolved in water and including it in oil droplets given to primary cell cultures, and by checking if the uptake is saturable and/or energy-dependent. Okadaic acid was found to be absorbed preferentially from the dissolved phase, and the uptake from oil droplets was substantially lower. The process did not require energy and was non-saturable, indicating that it involved a simple diffusion across the cellular membrane. Some apparent saturation was found due to the quick biotransformation of OA to 7-O-acyl esters.

The toxic benthic dinoflagellate Prorocentrum maculosum Faust is a synonym of Prorocentrum hoffmannianum Faust

Three strains of the toxic benthic dinoflagellate Prorocentrum hoffmannianum were isolated in the Canary Islands (north-east Atlantic Ocean, Spain). The identity of the strains was determined by phylogenetic analyses of partial LSU rDNA (D1-D2 regions) but their morphology based on SEM images corresponded to P. maculosum. Their toxin profiles were analyzed by liquid chromatography and high resolution mass spectrometry analysis (LC-HRMS) on cell extracts and culture media. Okadaic acid and three analogs were detected in all strains. Rather, in culture media the detected compounds were variable among strains, two of them being okadaic acid analogs not found on cell extracts. As a result, the taxonomy of the species was revised and P. maculosum is proposed as a junior synonym of P. hoffmannianum whose description is emended.

Morphology and phylogeny of Prorocentrum caipirignum sp. nov. (Dinophyceae), a new tropical toxic benthic dinoflagellate

A new species of toxic benthic dinoflagellate is described based on laboratory cultures isolated from two locations from Brazil, Rio de Janeiro and Bahia. The morphology was studied with SEM and LM. Cells are elliptical in right thecal view and flat. They are 37-44μm long and 29-36μm wide. The right thecal plate has a V shaped indentation where six platelets can be identified. The thecal surface of both thecal plates is smooth and has round or kidney shaped and uniformly distributed pores except in the central area of the cell, and a line of marginal pores. Some cells present an elongated depression on the central area of the apical part of the right thecal plate. Prorocentrum caipirignum is similar to Prorocentrum lima in its morphology, but can be differentiated by the general cell shape, being elliptical while P. lima is ovoid. In the phylogenetic trees based on ITS and LSU rDNA sequences, the P. caipirignum clade appears close to the clades of P. lima and Prorocentrum hoffmannianum. The Brazilian strains of P. caipirignum formed a clade with strains from Cuba, Hainan Island and Malaysia and it is therefore likely that this new species has a broad tropical distribution. Prorocentrum caipirignum is a toxic species that produces okadaic acid and the fast acting toxin prorocentrolide.

Profiling of Extracellular Toxins Associated with Diarrhetic Shellfish Poison in Prorocentrum lima Culture Medium by High-Performance Liquid Chromatography Coupled with Mass Spectrometry

Extracellular toxins released by marine toxigenic algae into the marine environment have attracted increasing attention in recent years. In this study, profiling, characterization and quantification of extracellular toxin compounds associated with diarrhetic shellfish poison (DSP) in the culture medium of toxin-producing dinoflagellates were performed using high-performance liquid chromatography–high-resolution mass spectrometry/tandem mass spectrometry for the first time. Results showed that solid-phase extraction can effectively enrich and clean the DSP compounds in the culture medium of Prorocentrum lima (P. lima), and the proposed method achieved satisfactory recoveries (94.80%–100.58%) and repeatability (relative standard deviation ≤9.27%). Commercial software associated with the accurate mass information of known DSP toxins and their derivatives was used to screen and identify DSP compounds. Nine extracellular DSP compounds were identified, of which seven toxins (including OA-D7b, OA-D9b, OA-D10a/b, and so on) were found in the culture medium of P. lima for the first time. The results of quantitative analysis showed that the contents of extracellular DSP compounds in P. lima culture medium were relatively high, and the types and contents of intracellular and extracellular toxins apparently varied in the different growth stages of P. lima. The concentrations of extracellular okadaic acid and dinophysistoxin-1 were within 19.9–34.0 and 15.2–27.9 μg/L, respectively. The total concentration of the DSP compounds was within the range of 57.70–79.63 μg/L. The results showed that the proposed method is an effective tool for profiling the extracellular DSP compounds in the culture medium of marine toxigenic algae.

Characterization of Prorocentrum elegans and Prorocentrum levis (Dinophyceae) from the southeastern Bay of Biscay by morphology and molecular phylogeny

Benthic Prorocentrum species can produce toxins that adversely affect animals and human health. They are known to co-occur with other bloom-forming, potentially toxic, benthic dinoflagellates of the genera Ostreopsis, Coolia, and Gambierdiscus. In this study, we report on the presence of P. elegans M.Faust and P. levis M.A.Faust, Kibler, Vandersea, P.A. Tester & Litaker from the southeastern Bay of Biscay. Sampling was carried out in the Summer-Autumn 2010-2012 along the Atlantic coast of the Iberian Peninsula, but these two species were only found in the northeastern part of the Peninsula. Strains were isolated from macroalgae collected from rocky-shore areas bordering accessible beaches. Morphological traits of isolated strains were analyzed by LM and SEM, whereas molecular analyses were performed using the LSU and internal transcribed spacer (ITS)1-5.8S-ITS2 regions of the rDNA. A bioassay with Artemia fransciscana and liquid chromatography-high-resolution mass spectrometry analyses were used to check the toxicity of the species, whose results were negative. The strains mostly corresponded to their species original morphological characterization, which is supported by the phylogenetic analyses in the case of P. levis, whereas for P. elegans, this is the first known molecular characterization. This is also the second known report of P. elegans.

Dinophysis toxins: causative organisms, distribution and fate in shellfish

Several Dinophysis species produce diarrhoetic toxins (okadaic acid and dinophysistoxins) and pectenotoxins, and cause gastointestinal illness, Diarrhetic Shellfish Poisoning (DSP), even at low cell densities (<103 cells·L⁻¹). They are the main threat, in terms of days of harvesting bans, to aquaculture in Northern Japan, Chile, and Europe. Toxicity and toxin profiles are very variable, more between strains than species. The distribution of DSP events mirrors that of shellfish production areas that have implemented toxin regulations, otherwise misinterpreted as bacterial or viral contamination. Field observations and laboratory experiments have shown that most of the toxins produced by Dinophysis are released into the medium, raising questions about the ecological role of extracelular toxins and their potential uptake by shellfish. Shellfish contamination results from a complex balance between food selection, adsorption, species-specific enzymatic transformations, and allometric processes. Highest risk areas are those combining Dinophysis strains with high cell content of okadaates, aquaculture with predominance of mytilids (good accumulators of toxins), and consumers who frequently include mussels in their diet. Regions including pectenotoxins in their regulated phycotoxins will suffer from much longer harvesting bans and from disloyal competition with production areas where these toxins have been deregulated.

Marine toxins: chemistry, toxicity, occurrence and detection, with special reference to the Dutch situation

Various species of algae can produce marine toxins under certain circumstances. These toxins can then accumulate in shellfish such as mussels, oysters and scallops. When these contaminated shellfish species are consumed severe intoxication can occur. The different types of syndromes that can occur after consumption of contaminated shellfish, the corresponding toxins and relevant legislation are discussed in this review. Amnesic Shellfish Poisoning (ASP), Paralytic Shellfish Poisoning (PSP), Diarrheic Shellfish Poisoning (DSP) and Azaspiracid Shellfish Poisoning (AZP) occur worldwide, Neurologic Shellfish Poisoning (NSP) is mainly limited to the USA and New Zealand while the toxins causing DSP and AZP occur most frequently in Europe. The latter two toxin groups are fat-soluble and can therefore also be classified as lipophilic marine toxins. A detailed overview of the official analytical methods used in the EU (mouse or rat bioassay) and the recently developed alternative methods for the lipophilic marine toxins is given. These alternative methods are based on functional assays, biochemical assays and chemical methods. From the literature it is clear that chemical methods offer the best potential to replace the animal tests that are still legislated worldwide. Finally, an overview is given of the situation of marine toxins in The Netherlands. The rat bioassay has been used for monitoring DSP and AZP toxins in The Netherlands since the 1970s. Nowadays, a combination of a chemical method and the rat bioassay is often used. In The Netherlands toxic events are mainly caused by DSP toxins, which have been found in Dutch shellfish for the first time in 1961, and have reoccurred at irregular intervals and in varying concentrations. From this review it is clear that considerable effort is being undertaken by various research groups to phase out the animal tests that are still used for the official routine monitoring programs.

Identification of 19-epi-okadaic acid, a new diarrhetic shellfish poisoning toxin, by liquid chromatography with mass spectrometry detection

Okadaic acid (1) (OA) and its congeners are mainly responsible for diarrhetic shellfish poisoning (DSP) syndrome. The presence of several OA derivatives have already been confirmed in Prorocentrum and Dinophysis spp. In this paper, we report on the detection and identification of a new DSP toxin, the OA isomer 19-epi-okadaic acid (2) (19-epi-OA), isolated from cultures of Prorocentrum belizeanum, by determining its retention time (RT) and fragmentation pattern using liquid chromatography coupled with mass spectrometry (LC–MS/MS).

Characterization of fatty acid esters of okadaic acid and related toxins in blue mussels (Mytilus edulis) from Norway

Marine algal toxins of the okadaic acid group can occur as fatty acid esters in blue mussels, and are commonly determined indirectly by transformation to their parent toxins by alkaline hydrolysis. Some data are available regarding the identity of the fatty acid esters, mainly of palmitic acid (16:0) derivatives of okadaic acid (OA), dinophysistoxin-1 (DTX1) and dinophysistoxin-2 (DTX2). Other fatty acid derivatives have been described, but with limited mass spectral data. In this paper, the mass spectral characterization of the [M-H](-) and [M+Na](+) ions of 16 fatty acid derivatives of each of OA, DTX1 and DTX2 is presented. The characteristic fragmentation of [M+Na](+) ions of OA analogues provided a useful tool for identifying these, and has not been described previously. In addition, a set of negative ion multiple reaction monitoring (MRM) methods was developed for direct determination of 16 fatty acid esters of OA, 16 fatty acid esters of DTX1 and 16 fatty acid esters of DTX2 in shellfish extracts. The MRM methods were employed to study the profiles of fatty acid esters of OA analogues in blue mussels and to compare these with fatty acid ester profiles reported for other groups of marine algal toxins.