Detection of okadaic acid esters in the hexane extracts of Spanish mussels

Esterification of okadaic acid in the mussel Mytilus galloprovincialis

Okadaic acid and other toxins of the diarrheic shellfish poisoning (DSP) group are transformed mainly to their acyl-derivatives in bivalves. Some recent studies suggest that bacteria present in the bivalve gut could contribute substantially to the acylation of the toxins. By feeding microcapsules containing okadaic acid to mussels we have shown unequivocally that the ingested okadaic acid is nearly completely transformed to its fatty acid esters (acyl-derivatives). Treating mussels with antibiotics did not have any significant effect on the acylation of the supplied okadaic acid, suggesting that bacteria do not play any significant role in this process. The microsomal and mitochondrial subcellular fractions of the cells of the digestive gland have been shown to have contain enzymes that are able to transfer a fatty acid molecule from Coenzyme A to okadaic acid (so, that have Acyl-CoA:OA acyltransferase activity). This activity was related to that of the enzyme Cytochrome C reductase (NADPH), a marker of endoplasmic reticulum, suggesting that this organelle is the main responsible for the acylation process. Acylation of DSP toxins seems to be a key step in the depuration of these toxins from mussels, as these compounds are found in feces as acyl-derivatives. This is probably true for most bivalves. The proportion of acyl-derivatives accumulated can point to the key process of the depuration: acylation or excretion of acylated derivatives. In the mussels Mytilus galloprovincialis, Mytilus edulis and in Donax trunculus, the first process seems to be the most important, but in most bivalve species it seems to be the second one. Other aspects of the relationship between depuration and acylation are also discussed.

Detection of diarrheic shellfish poisoning and azaspiracid toxins in Moroccan mussels: comparison of the LC-MS method with the commercial immunoassay kit

Diarrheic shellfish poisoning (DSP) is a recurrent gastrointestinal illness in Morocco, resulting from consumption of contaminated shellfish. In order to develop a rapid and reliable technique for toxins detection, we have compared the results obtained by a commercial immunoassay-“DSP-Check” kit” with those obtained by LC-MS. Both techniques are capable of detecting the toxins in the whole flesh extract which was subjected to prior alkaline hydrolysis in order to detect simultaneously the esterified and non esterified toxin forms. The LC-MS method was found to be able to detect a high level of okadaic acid (OA), low level of dinophysistoxin-2 (DTX2), and surprisingly, traces of azaspiracids 2 (AZA2) in mussels. This is the first report of a survey carried out for azaspiracid (AZP) contamination of shellfish harvested in the coastal areas of Morocco. The “DSP-Check” kit was found to detect quantitatively DSP toxins in all contaminated samples containing only OA, provided that the parent toxins were within the range of detection and was not in an ester form. A good correlation was observed between the two methods when appropriate dilutions were performed. The immunoassay kit appeared to be more sensitive, specific and faster than LC-MS for determination of DSP in total shellfish extract.

Profiles and levels of fatty acid esters of okadaic acid group toxins and pectenotoxins during toxin depuration. Part I: brown crab (Cancer pagurus)

In 2002, two outbreaks of diarrhetic shellfish poisoning (DSP) occurred in Norway, which was later confirmed to be caused by the consumption of brown crab (Cancer pagurus) contaminated predominantly by esters of okadaic acid (OA) after feeding on toxic blue mussels (Mytilus edulis). In addition to OA-group toxins, pectenotoxins (PTXs) are commonly detected in the toxin-producing algae (i.e. Dinophysis). In this paper, an experiment was set up to study the fatty acid ester profiles and depuration rates of OA-group toxins and PTXs from C. pagurus after feeding on M. edulis containing these toxin groups. OA, DTX1, DTX2 and PTX2 SA were all detected primarily in the form of fatty acid esters in the crab hepatopancreas (HP). Crabs preferentially assimilated toxins of the OA group after feeding on the mussels for 1 week. Detailed analysis of the fatty acid ester profile in crabs and mussels showed that the ester profiles in the crabs differed slightly from profiles of the fatty acid esters in M. edulis, but neither ester profile nor ester to free toxin ratio appeared to change in the crabs during the first 2 weeks of depuration. Calculations of depuration rates of the free forms of toxins resulted in similar reduction rates for OA and DTX2, whereas the depuration rate of DTX1, PTX2 and PTX2 SA was considerably faster. From the industrial perspective, the PTX-compounds are of minor importance compared to the OA group toxins in crabs, considering (1) the uncertainty regarding the oral toxicity of the PTXs, (2) the preferential ingestion of OA-group toxins compared to PTXs and (3) the faster depuration of PTXs.

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.

Enzymatic hydrolysis of esterified diarrhetic shellfish poisoning toxins and pectenotoxins

Okadaic acid (OA) and dinophysistoxins-1 and -2 (DTX1, DTX2), the toxins responsible for incidents of diarrhetic shellfish poisoning (DSP), can occur as complex mixtures of ester derivatives in both plankton and shellfish. Alkaline hydrolysis is usually employed to release parent OA/DTX toxins, and analyses are conducted before and after hydrolysis to determine the concentrations of nonesterified and esterified toxins. Recent research has shown that other toxins, including pectenotoxins and spirolides, can also exist as esters in shellfish, but these toxins cannot survive alkaline hydrolysis. A promising alternative approach is enzymatic hydrolysis. In this study, two enzymatic methods were developed for the hydrolysis of 7-O-acyl esters, "DTX3," and the carboxylate esters of OA, "diol-esters." Porcine pancreatic lipase induced complete conversion of DTX3 to OA and DTXs within one hour for reference solutions. The presence of mussel tissue matrix reduced the rate of hydrolysis, but an optimized lipase concentration resulted in greater than 95% conversion within four hours. OA-diol-ester was hydrolyzed by porcine liver esterase and was completely converted to OA in less than 30 min, even in the presence of mussel tissue matrix. Esters and OA/DTX toxins were all monitored by LC-MS. Further experiments with pectenotoxin esters indicated that enzymatic hydrolysis could also be applied to esters of other toxins. Enzymatic hydrolysis has excellent potential as an alternative to the conventional alkaline hydrolysis procedure used in the preparation of shellfish samples for the analysis of toxins.

Diarrheic shellfish poisoning due to toxic mussel consumption: The first recorded outbreak in Greece

During the week of 14-20 January 2000, 120 people visited the Emergency Departments of hospitals in Thessaloniki, northern Greece, complaining of acute gastrointestinal illness after eating mussels (Mytilus galloprovincialis). The symptoms indicated diarrhoeic shellfish poisoning, and the toxicity of mussels harvested from Thermaikos Gulf in Thessaloniki during the outbreak was investigated using mouse bioassays. The bioassays revealed toxicity to mice by the mussel samples; while high numbers of toxic algae Dinophysis acuminata were identified in water samples from Thermaikos Gulf. The harvesting of mussels was immediately suspended and a monitoring programme for algal blooms was established from then onwards. During a follow-up of the mussels' toxicity from January 2000 to January 2005, two more mussel samples were found positive for diarrheic shellfish poisoning: one harvested in March 2001 from the area of the outbreak (Thermaikos Gulf) and the other harvested in January 2001 from Amvrakikos Gulf in north-western Greece. However, no sporadic cases or outbreaks were reported during this period.

Identification of fatty acid esters of pectenotoxin-2 seco acid in blue mussels (Mytilus edulis) from Ireland

Pectenotoxins from marine dinoflagellates of the genus Dinophysis are rapidly hydrolyzed by many shellfish to give pectenotoxin-2 seco acid, which isomerizes to 7-epi-pectenotoxin-2 seco acid. Three series of fatty acid esters of pectenotoxin-2 seco acid (PTX-2 seco acid) and 7-epi-PTX-2 seco acid were detected by LC-MS analysis of extracts from blue mussels (Mytilus edulis) from Ireland. The locations of the fatty acid ester linkages were identified by a combination of LC-MSn in positive- and negative-ion modes, LC-MS analysis of the products from reaction of the esters with sodium periodate, and NMR analysis of purified samples of the two most abundant ester derivatives. The 37-O-acyl esters of PTX-2 seco acid were the most abundant, followed by the corresponding 11-O-acyl esters, accompanied by low levels of the 33-O-acyl esters. The most abundant fatty acid esters in the fractionated sample were, in order, the 16:0, 22:6, 14:0, 16:1, 18:4, and 20:5 fatty acids, although a wide array of other PTX-2 seco acid fatty acid esters were also present at low levels.

Investigation of the toxin profile of Greek mussels Mytilus galloprovincialis by liquid chromatography—mass spectrometry

Samples of Mytilus galloprovincialis were harvested from five different locations in Thermaikos gulf, Greece after harmful algae bloom. All of the mussel samples were found positive by mouse bioassay for diarrhetic shellfish poisoning (DSP) toxins. Liquid chromatography (LC) coupled with mass spectrometry (MS) was used to search for the following lipophilic toxins: okadaic acid (OA), dinophysistoxins (DTXs), pectenotoxins (PTXs), azaspiracids (AZAs) and yessotoxins (YTXs). In order to investigate the presence of okadaic acid esters, alkaline hydrolysis was performed for all the samples, and LC-MS analyses were carried out on the samples before and after hydrolysis. Hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS) analyses were also carried out to investigate the presence of domoic acid and paralytic shellfish poisoning (PSP) toxins at trace levels. All of the samples were found to be contaminated only with okadaic acid at levels 0.10-0.20 microg/g.

Diarrhetic shellfish poisoning toxin esters in Danish blue mussels and surf clams

Until recently, little focus was given to the presence of diarrhetic shellfish poisoning (DSP) toxin esters in seafood products. However, during the last few years, the occurrence of a high percentage of esters of the total amount of DSP toxins present in some seafood products has been observed. Samples of Danish surf clams (Spisola spp.) and blue mussels (Mytilus edulis) from 1999-2004 were analysed by liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) for the presence of DSP toxin esters. The samples contained only okadaic acid and esters of okadaic acid. The level of total okadaic acid equivalents ranged from 224 to 2516 microg kg-1 in surf clams. The percentage of okadaic acid esters of the total okadaic acid equivalents ranged from 83 to 98%, mean 95%. The level of total okadaic acid equivalents ranged from 43 to 1631 microg kg-1 in blue mussels. The percentage of okadaic acid esters of the total okadaic acid equivalents ranged from 21 to 86%, mean 59%. The probability of a high percentage of okadaic acid esters seems to increase with higher amounts of total okadaic acid equivalents in the bivalves. The large prevalence of DSP toxin esters are of particular importance because of the increased use of chemical methods instead of mouse bioassay for the detection of DSP toxicity.

METABOLIC TRANSFORMATION OF DINOPHYSISTOXIN-3 INTO DINOPHYSISTOXIN-1 CAUSES HUMAN INTOXICATION BY CONSUMPTION OF O-ACYL-DERIVATIVES DINOPHYSISTOXINS CONTAMINATED SHELLFISH

This paper describes for the first time a massive intoxication episode due to consumption of shellfish contaminated with 7-O-acyl-derivative dinophysistoxin-1, named Dinophysistoxin-3 (DTX-3). 7-O-acyl-derivative dinophysistoxin-1, a compound recently described in the literature, was found in shellfish samples collected in the Chilean Patagonia fjords. This compound does not inhibit Protein Phosphatases and also does not elicit the symptoms described for Diarrheic Shellfish Poisoning (DSP). The data showed here, give evidence of metabolic transformation of 7-O-acyl-derivative dinophysistoxin-1 (DTX-3) into Dinophysistoxin-1 (DTX-1, Methyl-Okadaic acid) in intoxicated patients. This metabolic transformation is responsible for the diarrheic symptoms and the intoxication syndrome showed by patients that consumed contaminated shellfish, which showed only the presence of 7-O-acyl-derivative dinophysistoxin-1. Patients fecal bacterial analysis for the presence of enteropathogens was negative and the mouse bioassay for DSP, performed as described for regulatory testing, was also negative. The HPLC-FLD and HPLC-MS analysis showed only the presence of DTX-3 as the only compound associated to DSP toxins in the contaminated shellfish samples. No other DSP toxins were found in the shellfish sample extracts. However, the patient fecal samples showed DTX-1 as the only DSP toxins detected in fecal. Moreover, the patient fecal samples did not show DTX-3. Since 7-O-acyl-derivative dinophysistoxin-1 (DTX-3) was the only compound associated to DSP toxins detected in the shellfish samples, an explanation for the diarrheic symptoms in the intoxicated patients would be the metabolic transformation of DTX-3 into DTX-1. This transformation should occur in the stomach of the poisoned patients after consuming 7-O-acyl-derivatives dinophysistoxin-1 (DTX-3) contaminated bivalves.

Analysis of the importance of lipid breakdown for elimination of okadaic acid (diarrhetic shellfish toxin) in mussels, Mytilus edulis: results from a field study and a laboratory experiment

Okadaic acid (OA) is a lipophilic phycotoxin, which accumulates in the digestive organs of mussels and may cause diarrhetic shellfish poisoning (DSP) in humans. Depuration of toxic mussels is a potential option for the shellfish industry to increase the availability of marketable mussels. To develop cost-effective depuration methods for DSP toxins, knowledge about the environmental conditions and physiological processes regulating the rate of depuration is essential. In this paper, the importance of lipid breakdown for elimination of OA in mussels was investigated by performing a field study and a manipulative laboratory experiment. First, total lipid content and concurrent concentration of OA in the digestive glands of farmed blue mussels, Mytilus edulis, was analysed on a monthly basis from January to June 2000. A significant positive correlation between levels of OA and lipid content was observed between January and March, when lipid levels were showing a decreasing trend. This supported a previously proposed model that breakdown of lipid stores may affect the release and elimination of this lipophilic toxin. To test this causal model, a laboratory experiment was performed. Mussels containing OA were exposed to experimental treatments (increased seawater temperature and/or food limitation) for 24 days in order to increase the energy requirements and need to use lipids as an energy source. It was predicted that mussels exposed to these treatments would have a faster elimination rate of OA compared to feeding mussels kept in ambient seawater temperature. The results showed that lipid content was significantly reduced in mussels exposed to an increased water temperature (24 degrees C) compared to ambient temperature (18 degrees C). The amount of lipids was not affected by food limitation. Although lipid content was reduced in 24 degrees C, the rate of depuration of OA was not faster for mussels in this treatment and no correlation was detected between lipid content and OA. Depuration rates were very similar for all treatments and followed an exponential decrease relationship (t(1/2) = 8 days). Thus, the proposed model that lipid breakdown affects the mechanism of elimination of OA was not supported. Nevertheless, the observed rates of depuration provide useful information and a potential predictive tool for large-scale depuration methods of mussels. The difficulties to influence the rate of depuration of this toxin by changing the environmental conditions suggest that processes, insensitive to short-term manipulation of the external environment, regulate depuration of OA.

Accumulation and transformation of DSP toxins in mussels Mytilus galloprovincialis during a toxic episode caused by Dinophysis acuminata

The time course of several outbreaks of the diarrhetic shellfish poisoning (DSP) producer Dinophysis acuminata and the consequent kinetic of accumulation and loss of toxins in mussels Mytilus galloprovincialis feeding on them was studied. Samples of mussels and seawater were frequently (2-3 times a week) collected from a raft in the Ri;a de Vigo. DSP toxins content of mussels and water was analyzed by HPLC-FD and phytoplankton was quantified in an inverted light microscope. Only okadaic acid (OA) and some of its conjugated forms (OA CF), estimated by enzymatic hydrolysis, were found in the plankton samples obtained, comprised mainly of D. acuminata cells. The main accumulated form in mussels was OA reaching a maximum of 10.1 microg OA g(-1) in the digestive gland (d.g.) in 16 days, falling below the quarantine level (ca. 2 microg OA g(-1) d.g.) by 45 days. The low polarity conjugated forms (LPCF), estimated by hexane extraction, accounted for 6.2% of the total toxin burden of the mussels. To quantify the rates of the processes involved in the accumulation, transformation and loss of the toxins, two dynamic models, a one-compartment and a two-compartment, including OA and its conjugated forms as variables were designed and implemented. The one-compartment model provided a good fit to the OA and LPCF actual data (r(2)=0.92 and r(2)=0.94, respectively). The two-compartment model did not fit the data markedly better than its one-compartment counterpart (r(2)=0.93 and r(2)=0.95, for OA and LPCF, respectively). High hydrolysis rates were estimated for most of the OA CF, which means that these forms came largely from the ingested plankton. The low estimated acylation rates support the previous point and suggest that the formation of LPCF by direct acylation of the OA is of little importance in M. galloprovincialis. Only in cases where the intoxication period is very long, can the formed acyl-derivatives be important, because they seem to accumulate for a long time in the mussels, as suggested by the low hydrolysis and depuration rates estimated from model fitting.

Basis for a new procedure to eliminate diarrheic shellfish toxins from a contaminated matrix

The natural contamination of shellfish with diarrheic shellfish toxins (DSP) has important public health implications. To avoid the economic effects of toxic episodes on shellfish farmers and the related industry, research on artificial methods alternative to the natural detoxification of shellfish is needed. Because the usual thermal processes are not efficient, alternative technologies have to be studied. Here preliminary results are presented about the lability of the DSP toxin okadaic acid in a supercritical atmosphere of carbon dioxide with acetic acid. Most of the toxin is eliminated (up to 90%), and the biological activity against its target enzyme is also severely affected (up to 70% reduction). Detoxification of contaminated shellfish requires a partial dehydration, and the detoxification yield is lower than that obtained with free toxin. Mass spectrometry experiments suggest that acetylation of the toxin molecule is not the basis of the inactivating mechanism, but a conformational change is suggested. This is the first report of the use of supercritical fluids to inactivate toxins.

Esterification of DSP toxins by Portuguese bivalves from the Northwest coast determined by LC-MS--a widespread phenomenon

Okadaic acid (OA) and dinophysistoxin-2 (DTX2) were confirmed by liquid chromatography with mass spectrometry detection both in extracts of digestive glands and edible parts of Portuguese shellfish. No dinophysistoxin-1 was found even in highly contaminated samples examined. However, only in blue mussel (Mytilus edulis) were these two parent toxins commonly found in a free form. Usually they were found largely esterified in all remaining shellfish species-common cockle (Cerastoderma edule), peppery furrow shell (Scrobicularia plana), carpet shell (Venerupis pullastra), oyster (Crassostrea japonica), razor clam (Ensisspp.), and clam (Ruditapes decussata). Oysters were the least toxic. In mussels esterified OA did not surpass 50% of the total OA found in edible parts, while DTX2 esterification rates were usually much lower. In remaining shellfish species usually more than 95% of the total OA was found esterified, while free DTX2 was rarely found. Also ratios of total DTX2/total OA were higher in mussels than in the remaining species examined. From all these species commercially exploited at the northern coast, mussels and cockles contained the highest levels of DSP toxins, thus representing the highest theoretical health risk. The previous association of DTX2 with the dinoflagellate Dinophysis acuta was confirmed with selective MS detection; while OA was the only parent diarrhoeic toxin found associated with Dinophysis acuminata.

Toxin composition of the toxic dinoflagellate Prorocentrum lima isolated from different locations along the Galician coast (NW Spain)

The DSP toxin composition of 19 Prorocentrum lima isolates from different locations of the Galician rias (Vigo and Pontevedra) was investigated by high performance liquid chromatography coupled with fluorimetric detection. Boiling and freeze/thaw/hydrolyse methodology were applied during extraction to detect OA, DTX1, DTX2 and their esterified derivatives. OA and DTX2 were detected in both free and esterified form, the latter always in very low amounts, whilst DTX1 was always present in the free form. This indicate that the hypothesized self-protection mechanism of toxin storage in the less active esterified forms does not seem to apply to DTX1. A slight increase in the toxin concentration per cell was found during growth, although toxin composition did not vary appreciably. Toxin production and toxin profile varied significantly depending on the isolate. Four groups of P. lima were differentiated by cluster analysis according to their toxin composition. It is noteworthy that one of the clusters comprised all the strains collected from one location characterised by its geographical isolation, whereas the other clusters consisted of isolates from different locations. The differences in the toxin profile from P. lima strains and from the DSP contaminated shellfish, together with the very good correlation between Dinophysis spp occurrence and DSP toxicity in shellfish, support that these planktonic species are the main agents responsible for DSP events in Galicia.

Isolation and structural determination of DTX-6, a new okadaic acid derivative

Diarrhetic shellfish poisoning is an illness caused by toxins accumulated in shellfish and produced by dinoflagellates, mainly of the Dinophysis and Prorocentrum genera. This paper reports the isolation and spectroscopic structural elucidation of a new compound, DTX-6 (2), an ester derivative of okadaic acid (OA) (1), isolated from an artificial culture of strain PLV2 of Prorocentrum lima.

Comparison of dinophysistoxin-1 and esterified dinophysistoxin-1 (dinophysistoxin-3) contents in the scallop Patinopecten yessoensis and the mussel Mytilus galloprovincialis

Okadaic acid (OA) homologues in toxic dinoflagellate Dinophysis fortii, scallops Patinopecten yessoensis and mussels Mytilus galloprovincialis collected at the same site in Mutsu Bay, Japan were determined by high-performance liquid chromatography fluorescence detection (HPLC-FLD) as their 9-anthryldiazomethane (ADAM) derivatives. Prominent toxin in the scallops and the mussels was esterified dinophysistoxin-1 (DTX3) and dinophysistoxin-1 (DTX1), respectively, although only DTX1 was detected in D. fortii. Toxin contents in the mussels were significantly higher than those in the scallops, indicating that mussels have higher potential to accumulate OA homologues than scallops.

Influence of amino acids on okadaic acid production

Okadaic acid (OA) (1)) was the first example of a group of polyether toxins known to be produced by marine microalgae, which are responsible for the natural phenomena known as Diarrhetic Shellfish Poisoning (DSP) red tides. It is also a highly selective inhibitor of protein phosphatases type 1 (PP1) and 2A (PP2A), as well as being a potent tumour promoter. For these reasons, OA is an extremely useful tool for studying cellular processes and an important standard for polluted shellfish control. In this paper, we report on a double objective: to improve the production of toxins and verify the apparent participation of amino acids in the formation of these polyethers by monitoring their influence on the promotion of growth, total cell yield and increased in toxicity in Prorocentrum lima of the PL2V strain in batch cultures, in a modified K medium.

Protein phosphatase inhibition assay adapted for determination of total DSP in contaminated mussels

The fluorescence protein phosphatase (PP-2A) inhibition assay detects okadaic acid (OA) and DTX-1 in mussels down to 1 microg/100 g of mussel tissue. It is more sensitive than the mouse bioassay (detection limit, 20 microg/100 g) or ELISA using the SCETI DSP check kit (detection limit, 10 microg/100 g). A drawback of the PP-2A assay method has been its lack of sensitivity towards the ester derivatives of OA and DTX-1. This has been addressed by including a hydrolysis step in the pretreatment of extracts which allows these derivatives to be converted to either okadaic acid or DTX-1 prior to the DSP assay. The method has been applied to the analysis of DSP in 19 samples of naturally contaminated mussels and the results from the PP-2A inhibition assay compared to those for HPLC. A good correlation was obtained for OA determined by the two methods in both unhydrolysed and hydrolysed samples. The new procedure will substantially reduce the incidence of false negatives in the DSP assay.

Liquid chromatography-electrospray ionization mass spectrometry of the diarrhetic shellfish-poisoning toxins okadaic acid, dinophysistoxin-1 and pectenotoxin-6 in bivalves

Determination of diarrhetic shellfish-poisoning (DSP) toxins, okadaic acid (OA), dinophysistoxin-1 (DTX1) and pectenotoxin-6 (PTX6) was carried out by liquid chromatography (LC) followed by on-line atmospheric pressure electrospray ionization-mass spectrometric (ESI-MS) detection with a heated capillary interface. Mass spectra of authentic OA, DTXI and PTX6 standards exhibited abundant [M-H] at m/z 803, 817 and 887, respectively. Linearity of peak area obtained by selected-ion monitoring (SIM) for [M-H]- of each toxin was confirmed over a wide range of concentrations from 10 pg to 30 ng. LC-ESI-MS analysis of OA, DTX1 and PTX6 in scallops and mussels, collected at the same site (Mutsu Bay, Japan), was carried out. Scallops and mussels collected at the same site showed different toxin profiles. Although PTX6 was detected from scallops, it was not detected from mussels.

Comparison between HPLC and a commercial immunoassay kit for detection of okadaic acid and esters in Portuguese bivalves

Liquid chromatography (HPLC), used to identify diarrhoeic shellfish poisoning (DSP) toxins in Portuguese shellfish, has detected okadaic acid (OA), dinophysistoxin-2 (DTX2) and esters of both of these. In Donax clams, a surprisingly high level of esters has been recently associated with some outbreaks of diarrhoea in shellfish consumers. In view of these events, we have proposed that screening for esters must be included in monitoring programmes for DSP toxins. HPLC is laborious, time-consuming and suffers from some interferences at low detection levels in total meat extracts. An enzyme-linked immunosorbent assay (ELISA) based on the procedure of Usagawa et al. ('DSP-Check' kit) was tested against HPLC. The 'DSP-Check' kit was capable of quantitatively detecting DSP toxins in all the tested contaminated samples containing only okadaic acid, provided that the parent toxins were within the range of detection and were not in the ester form. A high correlation was observed between the two methods when appropriate dilutions were performed. The immunoassay kit tested appeared to be more sensitive, specific and faster than HPLC for determination of DSP in total shellfish meat extracts. No problems were found when using hydrolysed semi-purified extracts in order to detect esters of okadaic acid. In view of the results obtained so far, Donax clams appeared to be an excellent indicator of shellfish contamination with diarrhoeic toxins. On sandy beaches of the Portuguese southern coast, were rock mussels are not so abundant, they should be screened more often than other species in order to prevent diarrhoea in humans.

Esters of okadaic acid and dinophysistoxin-2 in Portuguese bivalves related to human poisonings

Liquid chromatography (HPLC) was used to search for esters of DSP toxins in Portuguese bivalves. Hexane-soluble derivatives of okadaic acid (OA) and dinophysistoxin-2 (DTX-2) were found. Presumably they are acyl derivatives, globally known as 'dinophysistoxin-3' (DTX-3). In certain instances DTX-3 content surpassed 50% of the total amount of DSP toxins. A human diarrhetic poisoning (DSP) incident with Donax clams (Donax trunculus) harvested at Fuzeta (Algarve coast) was confirmed where the apolar (DTX-3 type) and other esters remaining in the polar aqueous methanol layer were implicated. The percentage of acyl esters of OA was always higher than those of DTX-2. An enzymic mechanism for the conversion of OA and DTX-2 seems to be implicated in some kind of detoxification process because the percentage of esters increases with the toxin amount ingested by the bivalve and there is some degree of selectivity as DTX-2 seems more difficult to acylate. These findings pose a problem for the current assay methods used to detect DSP because mainly they are able to detect the parent toxins but not their esters. The current bioassay method [Le Baut, C., Bardin, B., Bardouil, M., Bohec, M., Masselin, P., Truquet, P., 1990. Etude de la decontamination de moules toxiques. Rapport IFREMER DERO-90-02 MR. 21 pp.] used in Portugal includes a hexane washing step that prevents interference from free fatty acids. However, it cannot detect the presence of acyl derivatives because they are highly soluble in hexane.

Further studies on the analysis of DSP toxin profiles in galician mussels

Further studies on mussel samples from Galicia, Spain, have revealed the presence of okadaic acid (OA), dinophysistoxin 2 (DTX2), and the fatty acid acyl esters of both of these toxins as the "DTX3" complex. Measurements were performed with an improved in situ method for the formation of 9-anthryldiazomethane (ADAM) derivatives followed by liquid chromatography with fluorescence detection. Base hydrolysis of DTX3 toxins gave free OA and DTX2, which were determined following ADAM derivatization. Results were confirmed by liquid chromatography/mass spectrometry analyses, and in most of the samples, free DTX2 was the most abundant toxin. However, the OA/DTX2 ratio in the DTX3 conjugated form was different, with OA being the most abundant in all cases. This difference could be due to different rates of metabolism of OA and DTX2 to the acyl esters or due to contamination of the shellfish by the two toxins at different points in time, resulting in less acyl ester formation for one toxin versus the other. The second possibility would be reasonable if two different source organisms were producing the toxins.

Direct evidence of transformation of dinophysistoxin-1 to 7-O-acyl-dinophysistoxin-1 (dinophysistoxin-3) in the scallop Patinopecten yessoensis

Non-toxic scallops Patinopecten yessoensis were reared for 5 days with the toxic dinoflagellate Dinophysis fortii sampled from the sea. The total cell number ingested by five scallops during the feeding experiment was approximately 682 x 10(3). Okadaic acid (OA), dinophysistoxin-1 (DTX1) and esterified toxins of OA and DTX1 in D. fortii and scallop extracts were determined by liquid chromatography fluorescence detection (LC-FLD) as their 9-anthryldiazomethane (ADAM) derivatives. Only DTX1 was detected in D. fortii extracts used for the feeding experiment. The content of esterified DTXI in scallops fed on D. fortii was significantly higher than that of DTX1. Identification of esterified DTX1, 7-O-palmitoyl DTX1 (7-O-16:0 DTX1), in D. fortii and scallop extracts was carried out by LC equipped with an atmospheric pressure electrospray ionization-mass spectrometry (ESI-MS). Only extracts of scallops fed on D. fortii yielded a mass spectrum exhibiting abundant [M-H]- at m/z 1055 corresponding to 7-O-16:0 DTX1. These findings are the first direct evidence of the transformation of DTX1 to 7-O-acyl DTX1 in scallop tissues.