Immediate and delayed effects of a heatwave and Prorocentrum lima ((Ehrenberg) Stein 1878) bloom on the toxin accumulation, physiology, and survival of the oyster Magallana gigas (Thunberg, 1793)

Warming could facilitate the intensification of toxic algal blooms, two important stressors for marine organisms that are predicted to co-occur more frequently in the future. We investigated the immediate and delayed effects of a heatwave and a simulated bloom (3 × 106 cells L-1) of the diarrhetic shellfish toxin (DST)-producing benthic dinoflagellate Prorocentrum lima on the survival, physiology (oxygen consumption rate, condition index, immune parameters), and toxin accumulation in the Pacific rock oyster Magallana (Crassostrea) gigas. Oysters exposed to both stressors contained higher mean DST concentrations (mean ± 1 SE: 173.3 ± 19.78 μg kg-1 soft tissue) than those exposed to P. lima bloom alone (120.4 ± 20.90 μg kg-1) and exceeded the maximum permitted levels for human consumption. Exposure to individual stressors and their combination modified the physiology of M. gigas. Oysters exposed to heatwave alone had significantly higher oxygen consumption rates (0.7 ± 0.06 mg O2 h-1 g-1) than the control (0.3 ± 0.06 mg O2 h-1 g-1). However, this was not observed in oysters exposed to both heatwave and P. lima (0.5 ± 0.06 mg O2 h-1 g-1). This alteration of the metabolic response to warming in the presence of P. lima may affect the ability of rock oysters to adapt to environmental stressors (i.e., a heatwave) to ensure survival. Immunomodulation, through changes in total hemocyte count, was observed in oysters exposed to P. lima alone and in combination with warming. Individual stressors and their combination did not influence the condition index, but one mortality was recorded in oysters exposed to both stressors. The findings of this study highlight the vulnerability of rock oysters to the predicted increased frequency of heatwaves and toxic algal blooms, and the increased likelihood of shellfish containing higher than regulatory levels of DST in warming coasts.

New Trends in the Occurrence of Yessotoxins in the Northwestern Adriatic Sea

Yessotoxins (YTXs) are polycyclic toxic ether compounds produced by phytoplanktonic dinoflagellates which accumulate in filter-feeding organisms. We know that the water temperature in our areas Northwestern Adriatic Sea is optimal for the growth of potentially toxic algae (around 20 °C). In recent years, these temperatures have remained at these levels for longer and longer periods, probably due to global warming, which has led to an excessive increase in toxin levels. The interruption of mussel harvesting caused by algae negatively affects farmers’ revenues and the availability of local fish, causing a major economic loss in Italy’s main shellfish sector. Methods: In the nine years considered, 3359 samples were examined: 1715 marine waters, 73 common clams; 732 mussels; 66 oysters; and 773 veracious clams. Bivalve molluscs were examined for the presence of marine biotoxins, including YTXs, while potentially toxic algae, including those producing YTXs, were searched for and counted in marine waters. The method adopted for the quantification of lipophilic toxins involves the use of an LC-MS/MS system. The enumeration of phytoplankton cells was performed according to the Utermhöl method. Results: Between 2012 and 2020, 706 molluscs were tested for YTXs. In total, 246 samples tested positive, i.e., 34.84%. Of the positive samples, 30 exceeded the legal limit. Conclusion: In this regard, it is essential to develop and activate, as soon as possible, an “early warning” system that allows a better control of the production areas of live bivalve molluscs, thus allowing an optimal management of the plants in these critical situations.

Occurrence of lipophilic marine toxins in shellfish from Galicia (NW of Spain) and synergies among them

Lipophilic marine toxins pose a serious threat for consumers and an enormous economic problem for shellfish producers. Synergistic interaction among toxins may play an important role in the toxicity of shellfish and consequently in human intoxications. In order to study the toxic profile of molluscs, sampled during toxic episodes occurring in different locations in Galicia in 2014, shellfish were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS), the official method for the detection of lipophilic toxins. The performance of this procedure was demonstrated to be fit for purpose and was validated in house following European guidelines. The vast majority of toxins present in shellfish belonged to the okadaic acid (OA) group and some samples from a particular area contained yessotoxin (YTX). Since these toxins occur very often with other lipophilic toxins, we evaluated the potential interactions among them. A human neuroblastoma cell line was used to study the possible synergies of OA with other lipophilic toxins. Results show that combination of OA with dinophysistoxin 2 (DTX2) or YTX enhances the toxicity triggered by OA, decreasing cell viability and cell proliferation, depending on the toxin concentration and incubation time. The effects of other lipophilic toxins as 13-desmethyl Spirolide C were also evaluated in vitro.

Detection of yessotoxin by three different methods in Mytilus galloprovincialis of Adriatic Sea, Italy

Samples of Mytilus galloprovincialis collected from shellfish aquaculture plans located in the Adriatic Sea were analysed for yessotoxin (YTX) by three methods, in vivo (Mouse Bioassay, MBA), in vitro (functional assay) and chemical test (Liquid Chromatography-Mass Spectrometry, LC-MS/MS). As YTX coexists with other phycotoxins in shellfish, namely the diarrhoetic shellfish poisoning, okadaic acid, dinophysistoxins, pectenotoxins, and azaspirazids, the MBA is not completely satisfactory because it is difficult to identify which toxin causes the death of the mice. So, the two other techniques were proposed to detect and quantify YTX and its analogues in order to avoid this problem. The global results showed no difference among the three methods and the correlation between the functional assay and LC-MS/MS was positive (Spearman r=0.72). Both analytical methods demonstrated advantages; the functional assay is specific, very sensitive and correlates well with real toxicity, whereas LC-MS/MS is convenient because it allows the detection of YTX and some analogues which are currently included in the EU regulation. For this reason LC-MS/MS will become the official method starting 1st January 2015 (Regulation 15/2011/EU). Only four samples exceeded the current EU regulation limit of 1mg of YTX equivalent kg(-1). However, all samples belonged to a monitoring program and they were not suitable for consumers.

[Rapid biochemical method for the detection of paralytical shellfish poisoning toxins in shellfish from seafood market]

A rapid biochemical method was discussed in order to detect low concentration of paralytic shellfish poisoning (PSP) in sea food. The mice were injected with PSP extract of bivalves (1 and 0.2 microg/kg respectively, as STX equivalents) purchased from seafood market. ACh, AChE, NO and NOS in blood were studied at 15, 60, 120 min respectively. The results showed that at low dose (0.2 microg/kg) and 15 min, only the contents of ACh changed significantly compared with control group (p < 0.05), which was (141.2 +/- 14.8) microg/mg, while the contents of NO and the activities of NOS changed until 120 min, compared to control group (p < 0.05) ,which were (68.7 +/- 3.8) micromol/g and (40.1 +/- 4.9) U/mg respectively. At high dose the contents of ACh changed at all three time point. It can be suggested that the contents of ACh is the only one of four indexes which can response to PSP at low dose in an early stage (15 min) and may be selected as a biochemical index for rapid detection of PSP.

Advanced studies for the application of high-performance capillary electrophoresis for the analysis of yessotoxin and 45-hydroxyyessotoxin

Yessotoxins (YTXs) are a group of polyether toxins which have been previously reported as responsible for seafood contamination in several places worldwide. Despite their toxicity, which is not yet fully discussed, YTXs have been reported as an interference in the success of mouse bioassay for the determination of diarrhetic shellfish poisoning (DSP) toxins, and therefore, efficient and reliable analytical methodologies are required to evaluate their presence, avoiding false positives for DSP. High-performance capillary electrophoresis (HPCE) is presented in this work as an alternative to HPLC technique widely used for the analysis of YTXs. Improvements in the applicability of HPCE have been carried out through the development of different CE modes as well as different detection modes. With this aim, micellar electrokinetic chromatography (MEKC) has been considered for an increased selectivity while an increased sensitivity was achieved by using sample stacking. Moreover, the coupling of CE with mass spectrometry allowed the confirmation of YTXs present in the contaminated samples evaluated in this work. The results obtained showed the potential of CE as an alternative to HPLC for the analysis of YTXs present in naturally contaminated samples.

Distribution of tetrodotoxin in the body of the blue-ringed octopus (Hapalochlaena maculosa)

Tetrodotoxin (TTX) was quantitatively assayed in six specimens of semi-adult blue-ringed octopus, Hapalochlaena maculosa, by a post-column fluorescent-HPLC system. TTX was found to be present in all body parts, e.g. in high concentrations in the arms followed by the abdomen and cephalothorax. The toxin is not associated exclusively with the posterior salivary gland.

[Phycotoxins of ASP, PSP and DSP groups in aquaris organisms]

In this article the results of analysis of ASP, PSP and DSP phycotoxins content in aquatic organisms are presented. Methods of determination of toxins were ELISA and HPLS.

Isolation and Structure-Activity of μ-Conotoxin TIIIA, A Potent Inhibitor of Tetrodotoxin-Sensitive Voltage-Gated Sodium Channels

Mu-conotoxins are three-loop peptides produced by cone snails to inhibit voltage-gated sodium channels during prey capture. Using polymerase chain reaction techniques, we identified a gene sequence from the venom duct of Conus tulipa encoding a new mu-conotoxin-TIIIA (TIIIA). A 125I-TIIIA binding assay was established to isolate native TIIIA from the crude venom of Conus striatus. The isolated peptide had three post-translational modifications, including two hydroxyproline residues and C-terminal amidation, and <35% homology to other mu-conotoxins. TIIIA potently displaced [3H]saxitoxin and 125I-TIIIA from rat brain (Nav1.2) and skeletal muscle (Nav1.4) membranes. Alanine and glutamine scans of TIIIA revealed several residues, including Arg14, that were critical for high-affinity binding to tetrodotoxin (TTX)-sensitive Na+ channels. We were surprised to find that [E15A]TIIIA had a 10-fold higher affinity than TIIIA for TTX-sensitive sodium channels (IC50, 15 vs. 148 pM at rat brain membrane). TIIIA was selective for Nav1.2 and -1.4 over Nav1.3, -1.5, -1.7, and -1.8 expressed in Xenopus laevis oocytes and had no effect on rat dorsal root ganglion neuron Na+ current. 1H NMR studies revealed that TIIIA adopted a single conformation in solution that was similar to the major conformation described previously for mu-conotoxin PIIIA. TIIIA and analogs provide new biochemical probes as well as insights into the structure-activity of mu-conotoxins.

[Lipophilic toxin profiles associated with diarrhetic shellfish poisoning in scallops, Patinopecten yessoensis, collected in Hokkaido and comparison of the quantitative results between LC/MS and mouse bioassay]

Lipophilic toxins associated with diarrhetic shellfish poisoning (DSP) in scallops, Patinopecten yessoensis, collected in Hokkaido, Japan were quantified by liquid chromatography-mass spectrometry (LC/MS). Pectenotoxin-6 (PTX6) and yessotoxin (YTX) were the dominant toxins in the scallops, although the percentages of these toxins were different depending on the production area or the sampling period. The quantitative results obtained for the scallops in LC/MS and in mouse bioassay (MBA) were compared. Fifty of the 55 samples found to be exceeding the local quarantine level (0.025 MU/g whole meat) in Hokkaido by LC/MS were quantified by MBA as being below the quarantine level. It is suggested that this discrepancy is due to poor detection of YTX by MBA. These results indicate that LC/MS is a better method than MBA in terms of sensitivity and accuracy to quantify known lipophilic toxins, including YTX.

Screening for post-translational modifications in conotoxins using liquid chromatography/mass spectrometry: an important component of conotoxin discovery

Mass spectrometry has emerged as an important technique for conotoxin analysis due to its capacity for selective, sensitive, information-rich analyses. Using liquid chromatography/mass spectrometry, Conus venom can be fractionated and the peptides surveyed for specific post-translational modifications, indicating those toxin components likely to have an important biological function. With Conus striatus and Conus victoriae venom as models, bromination, carboxylation and glycosylation modifications are identified through characteristics such as isotopic distribution and labile losses observed during mass spectrometric analysis. This modification screening approach enables the identification of a C. victoriae bromo-carboxy-conotoxin, designated vc5c, as a candidate for detailed mass spectrometric analysis. Using a cDNA sequence coupled with liquid chromatography/mass spectrometry and nanoelectrospray ionization-ion trap-mass spectrometry, the sequence of vc5c is determined to be ICCYPNXWCCD, where W is 6-bromotryptophan, X is gamma-carboxy glutamate and C is disulfide-linked cysteine. This represents the ninth T-superfamily (-CC-CC- scaffold) toxin that has been isolated from venom and characterized.

Quantification of yessotoxin using the fluorescence polarization technique and study of the adequate extraction procedure

Yessotoxin (YTX) is a polycyclic ether toxin produced by phytoplanktonic microalgae from the group of dinoflagellates. It has been shown that YTX increases the 3',5'-cyclic nucleotide phosphodiesterases (PDEs) activity and that there is a binding between these proteins and the toxin. Fluorescence polarization (FP) is a spectroscopic technique that can be used to study the interactions between molecules. It is based on exciting a fluorescent molecule with plane-polarized light and measuring the polarization degree of the emitted light. In this study, the FP is applied to the study of the interaction between YTX and phosphodiesterases I and II (PDE I and II). The phosphodiesterases are labeled with a reactive succinimidyl esther of carboxyfluorescein, and the FP of the protein-dye conjugate is measured when the YTX concentration in the medium increases. The results show that in both cases the fluorescence polarization of the conjugates decreases when they bind to YTX. For the PDE I, it is possible to draw a Gaussian curve or a straight line that relates the two variables (FP and YTX concentration). The concentration of this toxin in a spiked mussel extract (which contains the conjugate) can be quantified measuring its FP and using the equations of those lines. Different extraction methods are tried in this study, and those that can be used to obtain an appropriate mussel extract to be quantified with this technique are determined.

Comparison of ELISA and LC-MS analyses for yessotoxins in blue mussels (Mytilus edulis)

Blue mussels (Mytilus edulis) collected from Flødevigen Bay, Norway, in 2001 and 2002 were analysed for yessotoxins (YTXs) by ELISA and yessotoxin (YTX), 45-hydroxyYTX, and carboxyYTX by LC-MS. Results from the two methods were compared to evaluate the ELISA. The response in the ELISA was 3-13 times higher than LC-MS, probably due to the antibodies binding to other YTX analogues not included in the LC-MS analysis. Nevertheless, the correlation between ELISA and LC-MS was good, with r2 values> or =0.8. The results indicate that the ELISA is a reliable method for estimating the total level of YTXs in mussels, and are consistent with extensive metabolism of algal YTXs in mussels. YTX was a minor component in the blue mussels at all times compared to 45-hydroxyYTX and especially carboxyYTX, except when the P. reticulatum bloom occurred. The results also indicate the presence of significant amounts of YTX analogues in addition to those measured by LC-MS. All samples below 4 mg/kg by ELISA were below the current EU regulatory limit of 1 mg/kg by LC-MS. Therefore, we propose using ELISA as a screening tool with a cut-off limit at 4 mg/kg for negative samples, whereas samples above this limit would be reanalyzed by LC-MS.

Stable isotopically labeled internal standards in quantitative bioanalysis using liquid chromatography/mass spectrometry: necessity or not?

It appears to be a general belief that stable isotopically labeled (SIL) internal standards yield better assay performance results for quantitative bioanalytical liquid chromatography/mass spectrometry (LC/MS) assays than does any other internal standard. In this article we describe our experiences with structural analogues and SIL internal standards and their merits and demerits. SIL internal standards are the first choice, but deuterium-labeled compounds may demonstrate unexpected behavior, such as different retention times or recoveries, than the analyte. In addition, a SIL internal standard with identical chemical properties as the analyte may cover up assay problems with stability, recovery, and ion suppression. Since SIL internal standards are not always available or are very expensive, structural analogues can be used, however, with consideration of several issues, which are usually displayed during method validation.

Resonant mirror biosensor detection method based on yessotoxin–phosphodiesterase interactions

Yessotoxin (YTX) is a generic name for a group of lipophilic compounds recently discovered and chemically characterized. Association measurements were done in a resonant mirror biosensor. The instrument detects changes in the refractive index and/or thickness occurring within a few hundred nanometers form the sensor surface where a molecule is attached. We used aminosilane surfaces where phosphodiesterase 3',5'-cyclic-nucleotide-specific from bovine brain (PDEs) was immobilized. Over this immobilized ligand different amounts of YTX were added and typical association curve profiles were observed. These association curves fit a pseudo-first-order kinetic equation where the apparent association rate constant (k(on)) can be calculated. The value of this constant increases with YTX concentration. From the representation of k(on) versus YTX concentration we obtained the association rate constant (k(ass)) 248+/-40 M(-1)s(-1) and the dissociation rate constant (k(diss)) 9.36 x 10(-4)+/-1.72 x 10(-4)s(-1). From these values the kinetic equilibrium dissociation constant (K(D)) for YTX-PDEs association can be calculated. The value of this last constant is 3.74 x 10(-6)+/-8.25 x 10(-8)M YTX. The PDE-YTX association was used as a method suitable for determination of the toxin concentration in a shellfish sample. The assay had sufficient sensitivity and can be used on simple shellfish extracts.

The red tide event in El Salvador, August 2001-January 2002

A red tide event occurred in El Salvador from August 2001 to January 2002. National health authorities usually measured toxin levels in Ostrea iridescens, however other species were analyzed during this microalgae bloom: Anadara similis, Anadara tuberculosa and Modiolus sp. El Salvador authorities consider 400 mouse units/100 g the highest value that is safe for human health. During this period toxin levels in 0. iridescens and Modiolus sp. increased from values under 400 to 3977 and 15,468 mouse units/100 g, respectively. Persistent and higher levels were recorded in oyster and mussel banks on the west part of the country. The Ministry of Health and Social Assistance treated 41 slight to moderate intoxications associated to bivalve mollusks consumption.

Simultaneous presence of Paralytic and Diarrheic Shellfish Poisoning toxins in Mytilus chilensis samples collected in the Chiloe Island, Austral Chilean Fjords

The study shown here provides the first indisputable evidence that shellfish can be contaminated with Paralytic Shellfish Poisoning (PSP) and Diarrheic Shellfish Poisoning (DSP) toxins during the summer season in the Southern Chilean fjords. Quantitative analysis of the simultaneous presence of PSP and DSP toxins in Mytilus chilensis samples collected in the Chiloe Island are shown. The High Performance Liquid Chromatography (HPLC) analysis with pre-column derivatization method for DSP toxins and the post-column derivatization methods for PSP toxins, both with fluorescent on-line detections, showed that both type of toxins were concentrated by the filter bivalve Mytilus chilensis in amounts above the international safe limits. The phytoplankton analysis showed the presence of both Alexandrium catenella and Dinophysis acuta in the water column. The data shows stratification of the toxic dinoflagellates in the water column, since the lowest amount of both DSP and PSP toxins were measured in the superficial and deeper levels of the water column. Moreover, the highest toxicities of both types of toxins were shown by the shellfish samples collected at a depth of 6 meters with 190 nanograms of DTX-1 / gram of digestive gland and 709.8 microg of PSP toxins / 100 grams of mussel meat.

Cloning of Octopus cephalotocin receptor, a member of the oxytocin/vasopressin superfamily

We reported that the common octopus, Octopus vulgaris, in common with vertebrates, possesses two members of the oxytocin/vasopressin superfamily: octopressin (OP) and cephalotocin (CT). This was the first observation of its kind in invertebrates. As OP and CT have different biological activities, the presence of specific receptors has been proposed. We cloned the cDNA of an orphan receptor from Octopus brain and found it to encode a polypeptide of 397 amino acids that displays sequences characteristic of G-protein coupled receptors. The orphan receptor showed high homology to receptors of the oxytocin/vasopressin superfamily and seemed to conserve the agonist-binding pocket common to the oxytocin and vasopressin receptors. Xenopus oocytes that express the orphan receptor responded to the application of CT by an induction of membrane Cl(-) currents coupled to the inositol phosphate/Ca(2+) pathway. OP and the other members of the oxytocin/vasopressin superfamily did not activate this receptor. HPLC fractionation of the Octopus brain extract combined with an oocyte assay yielded a single substance that was identical to CT. On the basis of these results, we conclude that the cloned receptor is the CT receptor (CTR). Expression of CTR mRNA in Octopus was detected in the central and the peripheral nervous systems, the pancreas, the oviduct and the ovary. This receptor may mediate physiological functions of CT in Octopus such as neurotransmission, reproduction and metabolism.

Complex yessotoxins profile in Protoceratium reticulatum from north-western Adriatic sea revealed by LC-MS analysis

While the occurrence of yessotoxin (YTX) has been reported worldwide from Protoceratium reticulatum, the biogenetic origin of some YTX analogues is still unknown, thus raising an issue whether they are metabolites of YTX formed in mussels or true products of different dinoflagellate species. Findings reported herein suggest that P. reticulatum from the north-western Adriatic sea is responsible for production, together with YTX (1), of homoYTX (2), 45-OHYTX (3), carboxyYTX (5), and noroxoYTX (7). YTX and its analogues have been determined by high performance liquid chromatography coupled with electrospray ion trap mass spectrometry (HPLC-MS and HPLC-MSn experiments). The result is the first to confirm production of these YTX analogues from this species and indicate it as a producing organism of homoYTX, 45-OHYTX, carboxyYTX, and noroxoYTX found in shellfish.

The seasonality and role of the neurotoxin tetramine in the salivary glands of the red whelk Neptunea antiqua (L.)

The red whelk Neptunea antiqua (family Buccinidae) is a sublittoral species of marine prosobranch mollusc that occurs in the cold temperate waters of the Eastern Atlantic Boreal Region. A clearly defined seasonal cycle was revealed in the concentration of the whelk's salivary gland neurotoxin, tetramine, ranging from undetectable levels to 6530 microg/g over the course of an annual sampling period in the central western Irish Sea. Concentrations of this amine were indirectly related to feeding activity through the use of digestive gland indices. Additionally, laboratory observations confirmed the suspected ability of these whelks to actively predate on bivalves, supporting the use of this toxin in food procurement.

Repeatability and validity of a fluorimetric HPLC method in the quantification of yessotoxin in blue mussels (Mytilus edulis) related to the mouse bioassay

Repeatability and validity of a fluorimetric HPLC method in quantification of yessotoxin (YTX) in mussels related to the mouse bioassay was studied. Blue mussels (Mytilus edulis) from the Sognefjord, Norway were sampled from March to November, 1997, and October to December, 1998. A total of 75 samples were analysed for YTX by HPLC using 4-[2-(6,7-dimethoxy-4-methyl-3-oxo-3, 4-dihydroquinoxalinyl) ethyl]-1,2,4-triazoline-3, 5-dione (DMEQ-TAD) as a fluorimetric derivatization agent. Among these, 28 of the samples were analysed by HPLC in duplicate. All samples were analysed by the mouse bioassay using both chloroform and ether in the final step of extraction. The duplicate measurements using HPLC was found equal and the method repeatable (p<0.05). The absolute difference between the two measurements was found to increase with increasing level of measurements. This significant positive correlation (p<0.05) was mainly due to concentrations of YTX higher than 200 microg/100g mussel meat. However the precision of the results obtained was not found to be less in the upper level than in the lower level. Based on the internal correlation analysis including the mouse bioassay and the HPLC method a cut-off value of < or =10 microg YTX/5 g digestive gland was found preferable. The mouse bioassay of ether extracts often failed to detect high levels of YTX, and as demonstrated by the low kappa-values, the agreement between the mouse bioassay of ether extracts and the HPLC method was very weak. The HPLC method was found to give repeatable results and thereby found to be reliable. Consequently, the HPLC method seems to the method of choice for detection and quantification of YTX in mussels when compared with the mouse bioassay.

Integrated enzyme-linked immunosorbent assay screening system for amnesic, neurotoxic, diarrhetic, and paralytic shellfish poisoning toxins found in New Zealand

Enzyme-linked immunosorbent assays (ELISAs) were developed for amnesic, neurotoxic, and diarrhetic shellfish poisoning (ASP, NSP, and DSP) toxins and for yessotoxin. These assays, along with a commercially available paralytic shellfish poisoning (PSP) ELISA, were used to test the feasibility of an ELISA-based screening system. It was concluded that such a system to identify suspect shellfish samples, for subsequent analysis by methods approved by international regulatory authorities, is feasible. The assays had sufficient sensitivity and can be used on simple shellfish extracts. Alcohol extraction gave good recovery of all toxin groups. The ease of ELISAs permits the ready expansion of the system to screen for other toxins, as new ELISAs become available.

Determination of paralytic shellfish toxins in Portuguese shellfish by automated pre-column oxidation

Automated pre-column oxidation (the method of Lawrence) was implemented on a routine basis since the end of 1996 to study paralytic shellfish poisoning (PSP) toxins in Portuguese shellfish. Liquid chromatography confirmed the presence of PSP toxins when the known toxic algae were present: Gymnodinium catenatum and/or Alexandrium cf. lusitanicum. On the other side, it has eliminated PSP toxins as a possible recurrent contaminant in oysters from Sado estuary. These oysters were already known to contain high levels of some metals (mainly zinc, copper and cadmium) due to their location in a contaminated area and their particular physiology prone to accumulate metals. The presence of PSP toxins in Scrobicularia plana from Mondego estuary and Tellina crassa from the northern coast, during the absence of the above toxic microalgae in the water column, was confirmed. Unlike other shellfish, these two genera have the feeding habit of aspirating more sediment than organisms in suspension, and probably ingest from the sediment resting cysts of PSP producing microalgae. This is another route of contamination that may help to explain why after a bloom certain shellfish species maintain toxicity for long periods. The method revealed to have a fast implementation on a daily basis, short analysis time (around 20 min between samples), high sensitivity and robustness, and therefore, it is one of the best HPLC methods for screening a large number of shellfish samples for monitoring purposes.

The repeatability of two HPLC methods and the PP2A assay in the quantification of diarrhetic toxins in blue mussels (Mytilus edulis)

Repeatability in the quantification of diarrhetic shellfish toxins was investigated for two fluorometric HPLC methods and a colorimetric PP2A assay, using agreement analysis. Blue mussels (Mytilus edulis) from the Sognefjord on the southwest coast of Norway were sampled during the periods of July to October, 1996, March to November, 1997, and October to December, 1998. The results from the first and the duplicate measurement were found to be very similar for both HPLC methods using two fluorogenic reagents, 4-bromomethyl,7-methoxycoumarin and 9-anthryl diazomethane, and the colorimetric PP2A inhibition assay in detection of diarrhetic shellfish toxins. The levels of agreement between the measurements were satisfactory for all three methods. Significant correlations were found between the level of observation and the absolute difference between the two measurements and were mainly due to concentrations of OA/DTX-1 higher than 100 microg/100 g mussel meat. However, the precision of quantifying DSP toxins in the upper level was not found to be less than in the lower level. Both the HPLC methods and the PP2A assay were found to give repeatable results and thereby found to be reliable.

Confirmation of yessotoxin and 45,46,47-trinoryessotoxin production by Protoceratium reticulatum collected in Japan

Two different strains of the dinoflagellate Protoceratium reticulatum collected at Harima Nada and Yamada Bay in Japan were cultured and analyzed by fluorometric HPLC for yessotoxin production. Only the Yamada Bay strain produced yessotoxin. The toxin together with its analog, 45,46,47-trinoryessotoxin, were isolated from larger scale culture and unambiguously confirmed by (1)H NMR and MS measurements. This is the first confirmation of the biogenetic origin of yessotoxin in Japan, where the toxin was first reported. The results also indicate that the production of yessotoxins by P. reticulatum differs from strain to strain, in a similar way to that observed in many other toxigenic dinoflagellates such as Dinophysis spp. and Alexandrium spp.

The strategy used by some piscivorous cone snails to capture their prey: the effects of their venoms on vertebrates and on isolated neuromuscular preparations

Three piscivorous Conus species, C. ermineus, C. consor and C. catus were acclimatized in aquaria. The study of their strategy to capture the prey and details of their radula's morphology revealed that all of them used a 'hook and line' strategy which consists of immobilizing the prey rapidly before engulfing it. The venoms from these piscivorous species clearly elicit, when injected into fish, an excitotoxic shock characterized by a sudden tetanus of the prey. In mammals, the venoms induce both flaccid paralysis via i.p. injection and seizures via i.c.v. injection. Intracellular recordings from frog nerve-muscle preparations revealed that the venoms from these Conus species first caused spontaneous synaptic potentials which in turn triggered muscle action potentials. Such spontaneous activity is due to an increased nerve terminal excitability. In addition, the venoms suppressed neuromuscular transmission probably by blocking postsynaptic nicotinic acetylcholine receptors. No direct effect of these Conus venoms was observed on the membrane of skeletal muscle fibres. In conclusion, C. ermineus, C. consor and C. catus, which have not securely tethered their prey used a mixture of toxins which target both pre-and postsynaptic elements of the neuromuscular junction and which produce rapid immobilization of their prey.

Fluorometric measurement of yessotoxins in shellfish by high-pressure liquid chromatography

A rapid HPLC method with fluorescence detection of yessotoxin (YTX) and its two analogs (45-OHYTX and norYTX) in mussels and scallops is presented. A dienophile reagent, DMEQ-TAD, was used for fluorescence labeling. YTX was measured in the range 1-100 ng. The method confirmed the occurrence of YTX and 45-OHYTX for the first time in mussels from Chile and New Zealand.

Presence of serotonin in the venom of Conus imperialis

The bioactive components in the venoms of cone snails are largely small peptides which target to a diverse set of ion channels and neuronal receptors. We report here the presence of substantial levels of serotonin in the venom of the imperial cone snail, Conus imperialis. This venom also contains many small bioactive peptides. The identification of serotonin has been confirmed by mass spectroscopy, NMR, HPLC mobility and UV spectroscopy. Although serotonin has been reported in arthropod venoms, it was previously reported to be absent in Conus venoms. We examined a total of fourteen different Conus species, and found detectable serotonin only in the venom of C. imperialis. Conus imperialis specializes in feeding upon the amphinomid polychaete Eurythoe complanata. We speculate that serotonin may play a role in the capture of this prey.

Presence of paralytic shellfish poisoning toxins and soluble proteins in toxic butter clams (Saxidomus giganteus)

Butter clams obtained from a variety of locations along the northern British Columbia coast were assayed for the presence of individual paralytic shellfish poisoning toxins (PSPT) by HPLC and total PSPT toxicity using the mouse bioassay. Specific organs, namely the siphon, adductor muscle, foot and mantle were examined for soluble antigens that crossreacted with crab Saxitoxin-Induced Protein (SIP) using immunochemical (Western blotting) techniques. Butter clams containing high concentrations of PSPT also had several proteins that crossreacted with crab anti-SIP serum. In particular, soluble proteins with distinctly different molecular weights were found in the siphon and foot, respectively, in toxic shellfish. These proteins were absent in nontoxic butter clams. The concept of using PSPT-induced proteins in the butter clam as a screen for identifying toxic shellfish is introduced.

Occurrence of a new toxin and tetrodotoxin in two species of the gastropod mollusk Nassariidae

The lethalities of 102 specimens of three species of the gastropod mollusk Nassariidae, collected from fish markets in Taiwan, were examined. The frequency of toxicity in Zeuxis scalaris and Z. castus-like specimens was 94 and 41%, respectively. The range of lethal potency in toxic specimens of Zeuxis scalaris and Z. castus-like was 2-140 and 2-13 mouse units, respectively, while all tissues of Z. castus were non-toxic. The toxins were partially purified from the toxic specimens of Z. scalaris and Z. castus-like. Two toxin fractions were obtained from the extract of each species of Nassariidae by using Bio-Gel P-2 column chromatography. Analyses by thin layer chromatography, electrophoresis, high performance liquid chromatography and ultraviolet spectroscopy, showed that toxin fraction I contained tetrodotoxin while toxin fraction II contained a new neurotoxin.

Toxicity of adductor muscles from the purple hinge rock scallop (Crassadoma gigantea) along the Pacific coast of North America

Mouse bioassay results of rock scallops occasionally monitored by official agencies of British Columbia, Washington and California before and/or after algal blooms from 1980-1990 revealed that 24%, 38% and 87% of adductor muscles, whole body and viscera, respectively, were unsafe (greater than or equal to 80 micrograms saxitoxin equivalents/100 g tissue) for human consumption. The safety of adductor muscles could not be predicted from corresponding toxicity levels of the viscera but the absence of detectable toxin could.

Monoclonal antibodies against the presynaptic calcium channel antagonist omega-conotoxin GVI A from cone snail poison

Monoclonal antibodies have been prepared against omega-conotoxin GVI A, a peptide isolated from marine snails of the genus Conus (Conus geographus and Conus magus). This toxin is a blocker of select presynaptic Ca2+ channels in the central nervous system. Antigenic omega-conotoxin GVI A was synthesized as a covalent conjugate with bovine serum albumin and injected s.c. An ELISA assay combined with a competitive inhibition assay was used to select and characterize monoclonal antibodies able to recognize and bind the free toxin. Several of the antibodies were found to block omega-conotoxin GVI A inhibition of 45Ca transport into rat brain synaptosomes and to block omega-conotoxin GVI A binding to membranes from the same preparation. The antibodies recognize native, synthetic toxin, and are useful for analysis of toxin in biological fluids.

Onchidal: a naturally occurring irreversible inhibitor of acetylcholinesterase with a novel mechanism of action

Onchidal has been identified as the major lipid-soluble component of the defensive secretion of the mollusc Onchidella binneyi, and it has been proposed as the compound responsible for the chemical protection of Onchidella [Bioorg. Chem. 7:125-131 (1978)]. In support of this hypothesis, we now report that onchidal can be found in several different species of Onchidella and that it is toxic to fish. Because onchidal is an acetate ester similar to acetylcholine, its ability to interact with nicotinic acetylcholine receptors and acetylcholinesterase was investigated. Although onchidal did not prevent the binding of 125I-alpha-bungarotoxin to nicotinic acetylcholine receptors, it inhibited acetylcholinesterase in a progressive, apparently irreversible, manner. The apparent affinity of onchidal for the initial reversible binding to acetylcholinesterase (Kd) was approximately 300 microM, and the apparent rate constant for the subsequent irreversible inhibition of enzyme activity (kintact) was approximately 0.1 min-1. Onchidal was a substrate for acetylcholinesterase, and approximately 3250 mol of onchidal were hydrolyzed/mol of enzyme irreversibly inhibited. The calculated kcat for onchidal was 325 min-1. Irreversible inhibition resulted from either onchidal itself or a reactive intermediate in the enzyme-catalyzed hydrolysis of onchidal, rather than from the hydrolysis products of onchidal. Irreversible inhibition of enzyme activity was prevented by coincubation with reversible agents that either sterically block (edrophonium and decamethonium) or allosterically modify (propidium) the acetylcholine binding site. Enzyme activity was not regenerated by incubation with oxime reactivators; therefore, the mechanism of irreversible inhibition does not appear to involve acylation of the active site serine. Because onchidal contains a potentially reactive alpha,beta-unsaturated aldehyde, irreversible inhibition of acetylcholinesterase may result from formation of a novel covalent bond between the toxin and the enzyme. Thus, this novel toxin could potentially be exploited in the design of a new class of anticholinesterase insecticides and in the identification of amino acids that contribute to the binding and hydrolysis of acetylcholine.

Solution conformation of conotoxin GI determined by 1H nuclear magnetic resonance spectroscopy and distance geometry calculations

Conformational analysis of conotoxin GI, one of the neurotoxic peptides produced by a marine snail, genus Conus, was performed by a combination of nuclear magnetic resonance spectroscopy (NMR) and distance geometry calculations. The resulting conformers on minimization of the target function were classified into two groups. The difference in the structures of the conformers is mainly due to the difference in the orientation of the side chain of the tyrosyl residue. The results show that the solution structure of conotoxin GI satisfies the conformational requirements for the biological activity of an antagonist toward nicotinic cholinergic receptors elucidated in a series of studies on alkaloids. The structure is discussed on the basis of the results of comparison of the atomic arrangements of the active sites of snake venom peptides and molecular models based on the results of secondary structure prediction.

Autoradiographic visualization in rat brain of receptors for omega-conotoxin GVIA, a newly discovered calcium antagonist

Putative N-type voltage-sensitive calcium channels were localized autoradiographically in thaw-mounted rat brain slices using [125I]omega-conotoxin GVIA as a ligand. Density of the toxin binding sites were highly heterogeneous throughout the brain. The highest density of the binding sites was observed in the glomerular layer of the olfactory bulb, cerebral cortex, molecular layer of the hippocampus, amygdaloid complex, reticular part of the substantia nigra, molecular layer of the cerebellar cortex, and nucleus of the solitary tract. White matter tract regions such as the internal capsule, corpus callosum, fimbria of the hippocampus, fornix, and fasciculus retroflexus showed an extremely low density.

Invertebrate vasopressin/oxytocin homologs. Characterization of peptides from Conus geographus and Conus straitus venoms

The vasopressin-oxytocin family of peptides is of very ancient lineage, found in organisms as diverse as hydra and man. Although these peptides have been intensively studied in vertebrates, the presumably more extensive invertebrate series was defined primarily by immunological methods. In this report, we describe the purification and structures of two peptides of the vasopressin-oxytocin family from molluscs ("Conopressins"), which were found in the venom of fish-hunting marine snails of the genus Conus. The biological activity observed when the two snail peptides are injected intracerebrally into mice is very similar to that elicited by the vertebrate neurohypophyseal hormones and presumably reflects their actions upon a common receptor in the brain. The sequences of the purified peptides reveal unique features not found in the vertebrate peptide series, most notably an additional positive charge. These are the first members of the invertebrate series of the vasopressin-oxytocin family to be characterized biochemically. The sequences of these peptides are: from Conus geographus venom, Lys-conopressin-G, Cys-Phe-Ile-Arg-Asn-Cys-Pro-Lys-Gly-NH2; and from Conus striatus venom, Arg-conopressin-S, Cys-Ile-Ile-Arg-Asn-Cys-Pro-Arg-Gly-NH2.

Potent excitatory effects of a cardiotonic protein from the venom of the marine snail Conus magus on the guinea-pig left atria, vas deferens and ileum

An active component (MAC) of Conus magus venom has been purified by gel filtration and ion exchange chromatographies, monitored by cardiotonic activity in the guinea-pig isolated left atria. MAC was estimated to be a protein of mol. wt between 45,000 and 65,000 by gel filtration and protease experiments. The purified protein at concentrations above 10(-7) g/ml elicited powerful rhythmic contractions of the guinea-pig vas deferens, rhythmic transient contractions of the ileum followed by relaxations, and a marked increase in the contractile force of the left atria. These responses to the toxin were abolished by tetrodotoxin. These results suggest that the action of MAC on the ileum and vas deferens may be mediated via nerves. It is also suggested that the major mechanism of action is due to activation of Na channels on the cell membrane.

Purification and sequence of a presynaptic peptide toxin from Conus geographus venom

A novel toxin, omega-conotoxin (omega-CgTX), from the venom of the fish-eating marine mollusc Conus geographus has been purified and biochemically characterized. Recently, this omega-conotoxin has been shown to inhibit the voltage-activated entry of Ca2+, thus providing a potentially powerful probe for exploring the vertebrate presynaptic terminal [Kerr, L. M., & Yoshikami, D. (1984) Nature (London) 308, 282-284]. The toxin is a basic 27 amino acid peptide amide with three disulfide bridges. An unusual feature is a remarkable preponderance of hydroxylated amino acids. The sequence of omega-CgTx GVIA is Cys-Lys-Ser- Hyp-Gly5-Ser-Ser-Cys-Ser-Hyp10-Thr-Ser-Tyr-Asn-Cys15-C ys-Arg-Ser- Cys-Asn20-Hyp-Tyr-Thr-Lys-Arg25-Cys-Tyr-NH2.

A common antigenic determinant found in two functionally unrelated toxins

The heat-stable enterotoxin ST Ib produced by enterotoxigenic E. coli strains shares a sequence homology with the sea snail neurotoxin, conotoxin GI. Rabbit antisera were raised against synthetic analogs of these toxins and to a six-residue peptide representing the region common to both toxins. Results from enzyme-linked immunosorbent assays indicate that the homologous region of both toxins represents part of their antigenic site. The lack of cross-reactivity exhibited by the six-residue common domain with serum directed against either toxin suggests that this region probably retains a similar conformation in the intact toxins but not in the isolated fragment.