A comparison of the mouse bioassay with liquid chromatography-mass spectrometry for the detection of lipophilic toxins in shellfish from Scottish waters

Simultaneous determination of trace marine lipophilic and hydrophilic phycotoxins in various environmental and biota matrices

An efficient and sensitivity approach, which combines solid-phase extraction or ultrasonic extraction for pretreatment, followed by ultra-performance liquid chromatography-tandem mass spectrometry, has been established to simultaneously determine eight lipophilic phycotoxins and one hydrophilic phycotoxin in seawater, sediment and biota samples. The recoveries and matrix effects of target analytes were in the range of 61.6-117.3 %, 55.7-121.3 %, 57.5-139.9 % and 82.6 %-95.0 %, 85.8-106.8 %, 80.7 %-103.3 % in seawater, sediment, and biota samples, respectively. This established method revealed that seven, six and six phycotoxins were respectively detected in the Beibu Gulf, with concentrations ranging from 0.14 ng/L (okadaic acid, OA) to 26.83 ng/L (domoic acid, DA) in seawater, 0.04 ng/g (gymnodimine-A, GYM-A) to 2.75 ng/g (DA) in sediment and 0.01 ng/g (GYM-A) to 2.64 ng/g (domoic acid) in biota samples. These results suggest that the presented method is applicable for the simultaneous determination of trace marine lipophilic and hydrophilic phycotoxins in real samples.

A 2D carbon nitride-based electrochemical aptasensor with reverse amplification for highly sensitive detection of okadaic acid in shellfish

Okadaic acid (OA) is one of the main virulence factors of diarrheal shellfish toxins (DSP). It is of great significance to detect OA with an accurate, specific and cost-effective technique in the fields of seafood safety and water quality control. In this work, an electrochemical aptasensor with reverse amplification was developed for the sensitive detection of OA. A two-dimensional graphite-phase nanomaterial (carbon nitride) modified with an anti-OA aptamer and thionine (Th) was immobilized onto the surface of the electrochemical electrode as the sensitive element to capture target OA molecules. ssDNA-modified carbon nitride was used as the reverse amplification element by hybridizing with non-OA linked aptamers. The preparation of the electrochemical aptasensor was well characterized by Scanning Electron Microscopy (SEM), zeta potential detection, UV-Vis absorption, Brunner-Emmet-Teller (BET) measurements, and electrochemical measurements. The quantitative assessment of OA was achieved by differential pulse voltammetry (DPV). Experimental results indicated that this aptasensor showed a concentration-dependent response to OA with a good detection performance including in terms of selectivity, repeatability, reproducibility, and stability. It exhibited 100-fold selectivity between OA and other toxins including dinophysistoxins (DTX), pectenotoxins (PTX), and yessotoxins (YTX). In addition, it showed a much wider quantification range, which is 10-13 M-10-10 M (0.080-80.50 pg mL-1). The detection limit was as low as 10-13 M (0.080 pg mL-1). The aptasensor also successfully achieved significant practicality on real shellfish samples contaminated by OA. All these results demonstrated that the reverse amplification strategy for marine toxin detection may provide a label-free and rapid detection approach for portable applications in the fields of environmental monitoring and food security.

Upregulation of Peridinin-Chlorophyll A-Binding Protein in a Toxic Strain of Prorocentrum hoffmannianum under Normal and Phosphate-Depleted Conditions

Some strains of the dinoflagellate species Prorocentrum hoffmannianum show contrasting ability to produce diarrhetic shellfish poisoning (DSP) toxins. We previously compared the okadaic acid (OA) production level between a highly toxic strain (CCMP2804) and a non-toxic strain (CCMP683) of P. hoffmannianum and revealed that the cellular concentration of OA in CCMP2804 would increase significantly under the depletion of phosphate. To understand the molecular mechanisms, here, we compared and analyzed the proteome changes of both strains growing under normal condition and at phosphate depletion using two-dimensional gel electrophoresis (2-DE). There were 41 and 33 differential protein spots observed under normal condition and phosphate depletion, respectively, of which most were upregulated in CCMP2804 and 22 were common to both conditions. Due to the lack of matched peptide mass fingerprints in the database, de novo peptide sequencing was applied to identify the differentially expressed proteins. Of those upregulated spots in CCMP2804, nearly 60% were identified as peridinin-chlorophyll a-binding protein (PCP), an important light-harvesting protein for photosynthesis in dinoflagellates. We postulated that the high expression of PCP encourages the production of DSP toxins by enhancing the yields of raw materials such as acetate, glycolate and glycine. Other possible mechanisms of toxicity related to PCP might be through triggering the transcription of non-ribosomal peptide synthetase/polyketide synthase genes and the transportation of dinophysistoxin-4 from chloroplast to vacuoles.

A Review of In Situ Methods-Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the Collection and Concentration of Marine Biotoxins and Pharmaceuticals in Environmental Waters

Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) are in situ methods that have been applied to pre-concentrate a range of marine toxins, pesticides and pharmaceutical compounds that occur at low levels in marine and environmental waters. Recent research has identified the widespread distribution of biotoxins and pharmaceuticals in environmental waters (marine, brackish and freshwater) highlighting the need for the development of effective techniques to generate accurate quantitative water system profiles. In this manuscript, we reviewed in situ methods known as Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the collection and concentration of marine biotoxins, freshwater cyanotoxins and pharmaceuticals in environmental waters since the 1980s to present. Twelve different adsorption substrates in SPATT and 18 different sorbents in POCIS were reviewed for their ability to absorb a range of lipophilic and hydrophilic marine biotoxins, pharmaceuticals, pesticides, antibiotics and microcystins in marine water, freshwater and wastewater. This review suggests the gaps in reported studies, outlines future research possibilities and guides researchers who wish to work on water contaminates using Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) technologies.

A smartphone-assisted microarray immunosensor coupled with GO-based multi-stage signal amplification strategy for high-sensitivity detection of okadaic acid

Okadaic acid (OA) is one of the main virulence factors of diarrheal shellfish toxins (DSP), which can cause acute carcinogenic or teratogenic effects after ingestion of contaminated shellfish. Therefore, high-sensitivity and fast detection of OA is a key to preventing the occurrence of safety accidents. In this paper, we effectively established a smartphone-assisted microarray immunosensor combined with an indirect competitive ELISA (iELISA) for quantitative colorimetric detection of OA. To further improve the detection sensitivity and match the smartphone imaging, a novel graphene oxide (GO) composite probe was developed to realize the multi-stage signal amplification. The system exhibited a wide linear range for the detection of OA (0.02-33.6 ng ·mL^-1) with low detection limit of 0.02 ng ·mL^-1. The recovery of OA in spiked shellfish samples was in the range of 80%-103.5%, which indicates the good applicability of this biosensor. The whole detection system has advantages of simplicity, low cost, high sensitivity and portability, which is expected to be a powerful alternative tool for on-site detecting and early warning of the pollution of marine products.

Aptamers and Aptasensors for Highly Specific Recognition and Sensitive Detection of Marine Biotoxins: Recent Advances and Perspectives

Marine biotoxins distribute widely, have high toxicity, and can be easily accumulated in water or seafood, exposing a serious threat to consumer health. Achieving specific and sensitive detection is the most effective way to prevent emergent issues caused by marine biotoxins; however, the previous detection methods cannot meet the requirements because of ethical or technical drawbacks. Aptamers, a kind of novel recognition element with high affinity and specificity, can be used to fabricate various aptasensors (aptamer-based biosensors) for sensitive and rapid detection. In recent years, an increasing number of aptamers and aptasensors have greatly promoted the development of marine biotoxins detection. In this review, we summarized the recent aptamer-related advances for marine biotoxins detection and discussed their perspectives. Firstly, we summarized the sequences, selection methods, affinity, secondary structures, and the ion conditions of all aptamers to provide a database-like information; secondly, we summarized the reported aptasensors for marine biotoxins, including principles, detection sensitivity, linear detection range, etc.; thirdly, on the basis of the existing reports and our own research experience, we forecast the development prospects of aptamers and aptasensors for marine biotoxins detection. We hope this review not only provides a comprehensive summary of aptamer selection and aptasensor development for marine biotoxins, but also arouses a broad readership amongst academic researchers and industrial chemists.

Variability and profiles of lipophilic toxins in bivalves from Great Britain during five and a half years of monitoring: Okadaic acid, dinophysis toxins and pectenotoxins

Official control biotoxin testing of bivalve molluscs from Great Britain has been conducted by Cefas for over a decade. Reflecting the changes in legislation, bioassays were gradually replaced by analytical methods, firstly for analysis of Paralytic shellfish toxins, followed by introduction of liquid chromatography tandem mass spectrometric (LCMS/MS) method for lipophilic toxins (LTs) in 2011. Twelve compounds, representing three main groups of regulated lipophilic toxins, as well as two non-regulated cyclic imines were examined in over 20,500 samples collected between July 2011 and December 2016. The toxins belonging to Okadaic acid (OA) group toxins were the most prevalent and were quantified in 23% of samples, predominantly from Scotland. The temporal pattern of OA group occurrences remained similar each year, peaking in summer months and tailing off during autumn and winter, however their abundance and magnitude varied between years significantly, with concentrations reaching up to 4993 μg OA eq./kg. Three toxin profiles were identified, reflecting the relative contribution of the two main toxins, OA and dinophysis toxin-2 (DTX2). Dinophysis toxin-1 (DTX1) was less common and was never detected in samples with high proportions of DTX2. Inter-annual changes in profiles were observed within certain regions, with the most notable being an increase of DTX2 occurrences in north-west Scotland and England in the last three years of monitoring. In addition, seasonal changes of profiles were identified when OA, the dominant toxin in early summer, was replaced by higher proportions of DTX2 in late summer and autumn. The profile distribution possibly reflected the availability of individual Dinophysis species as a food source for shellfish, however persistence of DTX2 during autumn and winter in mussels might have also been attributed to their physiology. Mussels were the only species with higher average proportions of non-esterified toxins, while Pacific oysters, cockles, surf clams, razors and queen scallops contained almost exclusively ester forms. In addition, a temporal change in proportion of OA and DTX2 free form was observed in mussels. Pectenotoxin-2 (PTX2) was quantified only on rare occasions.

Interannual variability in Dinophysis spp. abundance and toxin accumulation in farmed mussels (Perna perna) in a subtropical estuary

This study evaluated an 8-year dataset (2007 to 2015, except 2008) in the attempt to identify the most susceptible periods for the occurrence of diarrheic shellfish poisoning (DSP) episodes associated with the presence of toxigenic dinoflagellates, Dinophysis spp., in the mussel farming area of Babitonga Bay (southern Brazil). Dinophysis acuminata complex was the most frequent (present in 66% of the samples) and abundant (max. 4100 cells L^-1) taxon, followed by D. caudata (14%; max. 640 cells L^-1) and D. tripos (0.9%; max. 50 cells L^-1). There was a marked onset of the annual rise in Dinophysis spp. abundance during weeks 21-25 (early winter) of each year, followed by a second peak on week 35 (spring). Mussel (Perna perna) samples usually started testing positive in DSP mouse bioassays (MBA) in late winter. Positive results were more frequent in 2007 and 2011 when the mean D. acuminata complex abundance was ~ 500 cells L^-1. Although positive DSP-MBA results were observed in only 11% of the samples during the studied period, the toxin okadaic acid (OA) was present in 90% of the analyzed mussels (max. 264 μg kg^-1). MBA results were positive when D. acuminata complex cell densities exceed 1200 ± 300 cells L^-1, while trace toxin amounts could be detected at cell densities as low as 150 ± 50 cells L^-1 (free OA) to 200 ± 100 cells L^-1 (conjugated OA). Low salinity and the meteorological conditions triggered by La Niña events were the main factors associated with both Dinophysis abundance and OA accumulation in mussels.

Lipophilic toxins in cultivated mussels (Mytilus galloprovincialis) from Baja California, Mexico

Here, we report different lipophilic toxins (LTs) detected by LC-MS/MS in Mediterranean mussels (Mytilus galloprovincialis) collected through 2012 in Todos Santos Bay, northwest Baja California, Mexico. The concentration of okadaic acid (OA), dinophysistoxin 2 (DTX2), and pectenotoxin 2 (PTX2) reached 500 μg kg(-1) during July and increased to 1647 μg kg(-1) in October. These toxins were associated with the presence of Dinophysis fortii and Dinophysis acuminata and a strong stratification of the water column. Other LTs present were yessotoxins, with a maximum concentration of 1080 μg kg(-1) in June. Cyclic imines (13-desmethyl spirolide and gymnodimine) and azaspiracid 1 were also detected in the mussels but at low concentrations. Diarrhetic toxins concentrations evaluated by LC-MS/MS were compared with the results of two mouse bioassay protocols. Positive results were obtained with both MBA protocols in several samples that presented toxicities below 160 μg OA-eq kg(-1), as estimated by LC-MS/MS results whereas other samples returned negative MBA results in samples with concentrations above this level. Therefore, analytical methods need to be applied to confirm the presence of regulated LTs. This is the first report of LTs in mussels cultivated in Mexico. The occurrence of these toxins represents an emerging problem in the region.

Okadaic acid meet and greet: an insight into detection methods, response strategies and genotoxic effects in marine invertebrates

Harmful Algal Blooms (HABs) constitute one of the most important sources of contamination in the oceans, producing high concentrations of potentially harmful biotoxins that are accumulated across the food chains. One such biotoxin, Okadaic Acid (OA), is produced by marine dinoflagellates and subsequently accumulated within the tissues of filtering marine organisms feeding on HABs, rapidly spreading to their predators in the food chain and eventually reaching human consumers causing Diarrhetic Shellfish Poisoning (DSP) syndrome. While numerous studies have thoroughly evaluated the effects of OA in mammals, the attention drawn to marine organisms in this regard has been scarce, even though they constitute primary targets for this biotoxin. With this in mind, the present work aimed to provide a timely and comprehensive insight into the current literature on the effect of OA in marine invertebrates, along with the strategies developed by these organisms to respond to its toxic effect together with the most important methods and techniques used for OA detection and evaluation.

[Determination of azaspiracid-1 in shellfishes by liquid chromatography with tandem mass spectrometry]

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of azaspiracid-1 (AZA1) in shellfishes was described. After being extracted using methanol and water (80:20, v/v), the extract was cleaned-up by solid phase extraction (SPE) of MAX column, then determined by using a reversed-phase high performance liquid chromatography (HPLC) isocratic program coupled with tandem mass spectrometry in selected reaction monitoring mode (SRM). And the extract was eluted with acetonitrile-water (80:20, v/v) on an Atlantis dC18 column (150 mm x 4.6 mm, 5.0 microm) with mobile phase containing 50 mmol/L formic acid and 2 mmol/L ammonium formate. The detection limit was 11.00 pg/g. The calibration curve was linear (R2 = 0.998 1) in the range of 48.85-2 442 ng/L. The average recoveries of the shellfish tissue extract at three spiked levels (36.64, 73.27, 146.54 pg/g) were from 75.8% to 82.5% (n = 6). The relative standard derivations (RSDs) were less than 10%. The 112 shellfish samples from the local markets of Dalian, Qingdao, Guangzhou were detected by the method, and AZA1 was detected in some samples from Dalian and Guangzhou. The results showed that the method is simple, rapid, sensitive and suitable for the detection of AZA1 in shellfishes.

Implementing scientifically-robust and humane shellfish toxicity testing: we're still waiting

The response to a Parliamentary Question put to the then-Home Office Minister on 8 March 2006, was that "All protocols for the detection of toxins in shellfish intended for human consumption were assigned a substantial severity limit", and that "A total of 6,468 animals were used in the relevant procedures [for the testing of shellfish toxins in the UK] during 2004". The official European Union (EU) method for shellfish toxin testing is the Mouse Bioassay (MBA). The MBA is the primary method, although the Rat Bioassay (RBA) is permitted for some toxins. Six years later, following the completion of ten reports from the European Food Safety Authority (EFSA) stating that current reliance on the MBA is scientifically inappropriate, the regulatory climate for testing is almost unchanged, despite the availability of alternatives. The reliance on such a scientifically questionable method, and the welfare concerns for the animals used, highlight the extent of the clash between policy and science. The ongoing struggle to persuade the European Commission to formally adopt non-animal testing methods for all of the relevant toxins has been fruitless, and evidence remains that thousands of mice are used every year in lethal tests that could be replaced. There is an absolute requirement for advanced scientific methods to replace questionable methods which rely on outdated, inaccurate animal tests; in this case, marine biotoxin testing has surely been waiting in line for far too long.

Quantitative determination of gymnodimine-A by high performance liquid chromatography in contaminated clams from Tunisia coastline

Quantitative determination by high performance liquid chromatography (HPLC) was performed for gymnodimine-A (GYM-A), a phycotoxin responsible for the contamination of Tunisian clams. This study demonstrates a rapid and reproducible HPLC-ultraviolet (UV) method for extraction, detection and quantification of GYM-A in toxic clams. The extraction of GYM-A from the digestive gland of clams in acetone, subsequent clean-up with diethyl ether and extraction with dichloromethane is the more valid protocol. Chromatography analyses were performed using a gradient of acetonitrile-water (10:90 to 90:10), containing trifluoroacetic acid (0.1%) for 20 min at 1 mL/min rate with a C18 column. Recovery rates exceeded 96%, and limits of detection and quantification were 5 ng/mL and 8 ng/g digestive gland, respectively. Repeatability and reproducibility were tested for various samples containing different levels of GYM-A. A significant correlation was observed between toxicity level of samples and the determined amount of GYM-A. Also, the persistence of GYM-A in contaminated clams from Boughrara lagoon was demonstrated. The kinetics discharge study of GYM-A in controlled medium, during 1 month, showed that the process of depuration was biphasic with an exponential discharge of 75% of the total amount of sequestered GYM-A during the first 12 days followed by a slow discharge (>10%) for the subsequent days up to the seventeenth day. This is the first time that a quantitative study of GYM-A in clams from Tunisian coasts is performed through the development of a new method for detection and quantify of this phycotoxin. We found HPLC-UV a reliable and suitable alternative to the mouse bioassay.

Determination of okadaic acid, dinophysistoxin-1 and related esters in Greek mussels using HPLC with fluorometric detection, LC-MS/MS and mouse bioassay

An approach involving both chemical and biological methods was undertaken for the detection and quantification of the marine toxins okadaic acid (OA), dinophysistoxin-1 (DTX-1) and their respective esters in mussels from different sampling sites in Greece during the period 2006-2007. Samples were analyzed by means of a) high performance liquid chromatography with fluorometric detection (HPLC-FLD), using 9-athryldiazomethane (ADAM), as a pre-column derivatization reagent, b) liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and c) the mouse bioassay. Free OA and DTX-1 were determined by both HPLC-FLD and LC-MS/MS, while their respective esters were determined only by LC-MS/MS after alkaline hydrolysis of the samples. The detection limit (L.O.D.) and quantification limit (L.O.Q.) of the HPLC-FLD method were 0.015 microg/g HP and 0.050 microg/g HP, respectively, for OA. The detection limit (L.O.D.) and quantification limit (L.O.Q.) of the LC-MS/MS method were 0.045 microg/g HP and 0.135 microg/g HP, respectively, for OA. Comparison of results between the two analytical methods showed excellent agreement (100%), while both HPLC-FLD and LC-MS/MS methods showed an agreement of 97.1% compared to the mouse bioassay.

Lipophilic toxins analyzed by liquid chromatography-mass spectrometry and comparison with mouse bioassay in fresh, frozen, and processed molluscs

The search for alternative methods to the mouse bioassay (MBA) has intensified over recent years. The present work analyzes seven different species of shellfish (clams, small scallops, small clams, mussels, oysters, cockles, and edible whelks) in fresh, frozen boiled, and canned presentations using liquid chromatography-mass spectrometry (LC-MS/MS), and the results are compared with the same samples analyzed through MBA. The toxins studied were OA, DTX1, DTX2, YTX, PTX2, and AZA1, which are legislated in the EU, and SPX1, which is not regulated yet. Consistent results between LC-MS/MS and MBA were found in 69% of the samples, whereas 26% of MBA showed "false-positive" results with respect to the toxins analyzed. No "false negatives" were observed. The possibility of LC-MS/MS as an alternative or complementary technique to MBA is discussed.