Brevetoxin B4 isolated from greenshell mussels Perna canaliculus, the major toxin involved in neurotoxic shellfish poisoning in New Zealand

Identification and cross-species comparison of in vitro phase I brevetoxin (BTX-2) metabolites in northern Gulf of Mexico fish and human liver microsomes by UHPLC-HRMS(/MS)

Brevetoxins (BTX) are a group of marine neurotoxins produced by the harmful alga Karenia brevis. Numerous studies have shown that BTX are rapidly accumulated and metabolized in shellfish and mammals. However, there are only limited data on BTX metabolism in fish, despite growing evidence that fish serve as vectors for BTX transfer in marine food webs. In this study, we aimed to investigate the in vitro biotransformation of BTX-2, the major constituent of BTX profiles in K. brevis, in several species of northern Gulf of Mexico fish. Metabolism assays were performed using hepatic microsomes prepared in-house as well as commercially available human microsomes for comparison, focusing on phase I reactions mediated by cytochrome P450 monooxygenase (CYP) enzymes. Samples were analyzed by UHPLC-HRMS(/MS) to monitor BTX-2 depletion and characterize BTX metabolites based on MS/MS fragmentation pathways. Our results showed that both fish and human liver microsomes rapidly depleted BTX-2, resulting in a 72-99% reduction within 1 h of incubation. We observed the simultaneous production of 22 metabolites functionalized by reductions, oxidations, and other phase I reactions. We were able to identify the previously described congeners BTX-3 and BTX-B5, and tentatively identified BTX-9, 41,43-dihydro-BTX-2, several A-ring hydrolysis products, as well as several novel metabolites. Our results confirmed that fish are capable of similar BTX biotransformation reactions as reported for shellfish and mammals, but comparison of metabolite formation across the tested species suggested considerable interspecific variation in BTX-2 metabolism potentially leading to divergent BTX profiles. We additionally observed non-enzymatic formation of BTX-2 and BTX-3 glutathione conjugates. Collectively, these findings have important implications for determining the ecotoxicological fate of BTX in marine food webs.

Chemodiversity of Brevetoxins and Other Potentially Toxic Metabolites Produced by Karenia spp. and Their Metabolic Products in Marine Organisms

In recent decades, more than 130 potentially toxic metabolites originating from dinoflagellate species belonging to the genus Karenia or metabolized by marine organisms have been described. These metabolites include the well-known and large group of brevetoxins (BTXs), responsible for foodborne neurotoxic shellfish poisoning (NSP) and airborne respiratory symptoms in humans. Karenia spp. also produce brevenal, brevisamide and metabolites belonging to the hemi-brevetoxin, brevisin, tamulamide, gymnocin, gymnodimine, brevisulcenal and brevisulcatic acid groups. In this review, we summarize the available knowledge in the literature since 1977 on these various identified metabolites, whether they are produced directly by the producer organisms or biotransformed in marine organisms. Their structures and physicochemical properties are presented and discussed. Among future avenues of research, we highlight the need for more toxin occurrence data with analytical techniques, which can specifically determine the analogs present in samples. New metabolites have yet to be fully described, especially the groups of metabolites discovered in the last two decades (e.g tamulamides). Lastly, this work clarifies the different nomenclatures used in the literature and should help to harmonize practices in the future.

Guidance Level for Brevetoxins in French Shellfish

Brevetoxins (BTXs) are marine biotoxins responsible for neurotoxic shellfish poisoning (NSP) after ingestion of contaminated shellfish. NSP is characterized by neurological, gastrointestinal and/or cardiovascular symptoms. The main known producer of BTXs is the dinoflagellate Karenia brevis, but other microalgae are also suspected to synthesize BTX-like compounds. BTXs are currently not regulated in France and in Europe. In November 2018, they have been detected for the first time in France in mussels from a lagoon in the Corsica Island (Mediterranean Sea), as part of the network for monitoring the emergence of marine biotoxins in shellfish. To prevent health risks associated with the consumption of shellfish contaminated with BTXs in France, a working group was set up by the French Agency for Food, Environmental and Occupational Health & Safety (Anses). One of the aims of this working group was to propose a guidance level for the presence of BTXs in shellfish. Toxicological data were too limited to derive an acute oral reference dose (ARfD). Based on human case reports, we identified two lowest-observed-adverse-effect levels (LOAELs). A guidance level of 180 µg BTX-3 eq./kg shellfish meat is proposed, considering a protective default portion size of 400 g shellfish meat.

Industrial Applications of Dinoflagellate Phycotoxins Based on Their Modes of Action: A Review

Dinoflagellates are an important group of phytoplanktons, characterized by two dissimilar flagella and distinctive features of both plants and animals. Dinoflagellate-generated harmful algal blooms (HABs) and associated damage frequently occur in coastal areas, which are concomitant with increasing eutrophication and climate change derived from anthropogenic waste and atmospheric carbon dioxide, respectively. The severe damage and harmful effects of dinoflagellate phycotoxins in the fishing industry have been recognized over the past few decades, and the management and monitoring of HABs have attracted much attention, leaving aside the industrial application of their valuable toxins. Specific modes of action of the organisms' toxins can effectively be utilized for producing beneficial materials, such as Botox and other therapeutic agents. This review aims to explore the potential industrial applications of marine dinoflagellate phycotoxins; furthermore, this review focuses on their modes of action and summarizes the available knowledge on them.

Chemiluminescent Receptor Binding Assay for Ciguatoxins and Brevetoxins Using Acridinium Brevetoxin-B2

Ciguatera is the term for poisoning resulting from eating fish from tropical or subtropical regions. The causative toxins collectively named ciguatoxins (CTXs) widely differ in structures depending on their geographic origins, which range from the Pacific Ocean and the Indian Ocean to the Caribbean Sea. Neurotoxic shellfish poisoning (NSP) is caused by the ingestion of bivalve shellfish contaminated with brevetoxins (BTXs). Structurally, both CTXs and BTXs consist of fused ether rings aligned in a ladder shape. Pharmacologically, they bind at the same site (site-5) of voltage-gated sodium channels. However, the great structural diversity and the rare availability of reference toxins hinder LC-MS and ELISA methods, which operate on structure-based recognition. In this study, we prepared a chemiluminescent ligand, acridinium BTXB2 (ABTX), and tested its suitability for use in competitive binding assays to detect CTXs and BTXs. The affinity of ABTX to the rat brain synaptosome estimated by K_i (1.66 pM) was approximately two-fold higher than that of PbTx-3 (BTX3). In addition, the equilibrium dissociation constant (K_D) was 0.84 nM, the maximum number of binding was 6.76 pmol toxin/mg protein, and the detection limit was 1.4 amol. The assays performed on samples spiked with CTX3C or BTXB4 (N-palmitoylBTXB2) at 0.2–1.0 ng CTX/g fish flesh, and 200–800 ng BTXB4/g shellfish showed a linear relationship between the theoretical and observed toxin amounts.

Molecular Determinants of Brevetoxin Binding to Voltage-Gated Sodium Channels

Brevetoxins are produced by dinoflagellates such as Karenia brevis in warm-water red tides and cause neurotoxic shellfish poisoning. They bind to voltage-gated sodium channels at neurotoxin receptor 5, making the channels more active by shifting the voltage-dependence of activation to more negative potentials and by slowing the inactivation process. Previous work using photoaffinity labeling identified binding to the IS6 and IVS5 transmembrane segments of the channel α subunit. We used alanine-scanning mutagenesis to identify molecular determinants for brevetoxin binding in these regions as well as adjacent regions IVS5-SS1 and IVS6. Most of the mutant channels containing single alanine substitutions expressed functional protein in tsA-201 cells and bound to the radioligand [42-³H]-PbTx3. Binding affinity for the great majority of mutant channels was indistinguishable from wild type. However, transmembrane segments IS6, IVS5 and IVS6 each contained 2 to 4 amino acid positions where alanine substitution resulted in a 2–3-fold reduction in brevetoxin affinity, and additional mutations caused a similar increase in brevetoxin affinity. These findings are consistent with a model in which brevetoxin binds to a protein cleft comprising transmembrane segments IS6, IVS5 and IVS6 and makes multiple distributed interactions with these α helices. Determination of brevetoxin affinity for Na_v1.2, Na_v1.4 and Na_v1.5 channels showed that Na_v1.5 channels had a characteristic 5-fold reduction in affinity for brevetoxin relative to the other channel isoforms, suggesting the interaction with sodium channels is specific despite the distributed binding determinants.

Human Poisoning from Marine Toxins: Unknowns for Optimal Consumer Protection

Marine biotoxins are produced by aquatic microorganisms and accumulate in shellfish or finfish following the food web. These toxins usually reach human consumers by ingestion of contaminated seafood, although other exposure routes like inhalation or contact have also been reported and may cause serious illness. This review shows the current data regarding the symptoms of acute intoxication for several toxin classes, including paralytic toxins, amnesic toxins, ciguatoxins, brevetoxins, tetrodotoxins, diarrheic toxins, azaspiracids and palytoxins. The information available about chronic toxicity and relative potency of different analogs within a toxin class are also reported. The gaps of toxicological knowledge that should be studied to improve human health protection are discussed. In general, gathering of epidemiological data in humans, chronic toxicity studies and exploring relative potency by oral administration are critical to minimize human health risks related to these toxin classes in the near future.

Role of Biomarkers in Monitoring Brevetoxins in Karenia brevis Exposed Shellfish

Monitoring and management programs for marine toxins in seafood depend on efficient detection tools for their success in protecting public health. Here we review current methods of detection for neurotoxic shellfish poisoning (NSP) toxins, and current knowledge in brevetoxin metabolism in shellfish. In addition, we discuss a novel approach to developing monitoring tools for NSP toxins in molluscan shellfish. NSP is a seafood-borne disease caused by the consumption of brevetoxin-contaminated shellfish. Brevetoxins are a suite of cyclic polyether compounds found in blooms of the marine dinoflagellate Karenia brevis (K. brevis) and are potent neurotoxins. Preventive controls for NSP in the U.S. currently rely upon environmental monitoring of K. brevis blooms and assessment of their shellfish toxicity by mouse bioassay. The mouse bioassay for NSP approved by National Shellfish Sanitation Program was developed in the 1960s when very little information on the structural and toxicological properties of brevetoxins in algae and shellfish was available. Alternative methods to mouse bioassay based on current scientific knowledge in the area are needed for monitoring NSP toxins. It is now established that brevetoxins are metabolized extensively in shellfish. Algal brevetoxins undergo oxidation and reduction, as well as conjugation with fatty acids and amino acids in shellfish. Recently, three metabolites have been identified as biomarkers of brevetoxin exposure and toxicity in Eastern oyster (Crassostrea virginica) and hard clam (Mercenaria sp.). The role of these biomarkers in monitoring NSP toxins in K. brevis exposed molluscan shellfish is reviewed. Comparisons of biomarker levels by liquid chromatography-mass spectrometry (LC-MS) with composite toxin as measured by enzyme linked immunosorbent assay (ELISA), and shellfish toxicity by mouse bioassay, support the application of these biomarkers as a dynamic and powerful approach for monitoring brevetoxins in shellfish and prevention of NSP.

Uptake and elimination of brevetoxin in the invasive green mussel, Perna viridis, during natural Karenia brevis blooms in southwest Florida

Perna viridis is a recently introduced species to US coastal waters and have vigorously spread throughout the southeastern seaboard since their invasion. Little information regarding their response to local environmental factors has been reported including responses to the local HAB species, Karenia brevis. This study monitored the tissue toxin concentration of brevetoxins in P. viridis from existing populations throughout two consecutive natural K. brevis blooms. The results showed P. viridis to rapidly accumulate PbTx upon exposure to the bloom, far exceeding the peak tissue concentrations of oysters, Crassostrea virginica, sampled during the same period, 57,653 ± 15,937 and 33,462 ± 10,391 ng g(-1) PbTx-3 equivalent, respectively. Further, P. viridis retained high PbTx concentrations in their tissues post bloom remaining above the regulatory limit for human consumption for 4-5 months, significantly longer than the depuration time of 2-8 weeks for native oyster and clam species. In the second year, the bloom persisted at high cell concentrations resulting in prolonged exposure and higher PbTx tissue concentrations indicating increased bioaccumulation in green mussels. While this species is not currently harvested for human consumption, the threat for post bloom trophic transfer could pose negative impacts on other important fisheries and higher food web implications.

Tissue distribution of amino acid- and lipid-brevetoxins after intravenous administration to C57BL/6 mice

Brevetoxins produced during algal blooms of the dinoflagellate Karenia are metabolized by shellfish into reduction, oxidation, and conjugation products. Brevetoxin metabolites comprising amino acid- and lipid conjugates account for a large proportion of the toxicity associated with the consumption of toxic shellfish. However, the disposition of these brevetoxin metabolites has not been established. Using intravenous exposure to C57BL/6 mice, we investigated the disposition in the body of three radiolabeled brevetoxin metabolites. Amino acid-brevetoxin conjugates represented by S-desoxy-BTX-B2 (cysteine-BTX-B) and lipid-brevetoxin conjugates represented by N-palmitoyl-S-desoxy-BTX-B2 were compared to dihydro-BTX-B. Tissue concentration profiles were unique to each of the brevetoxin metabolites tested, with dihydro-BTX-B being widely distributed to all tissues, S-desoxy-BTX-B2 concentrated in kidney, and N-palmitoyl-S-desoxy-BTX-B2 having the highest concentrations in spleen, liver, and lung. Elimination patterns were also unique: dihydro-BTX-B had a greater fecal versus urinary elimination, whereas urine was a more important elimination route for S-desoxy-BTX-B2, and N-palmitoyl-S-desoxy-BTX-B2 persisted in tissues and was eliminated equally in both urine and feces. The structures particular to each brevetoxin metabolite resulting from the reduction, amino acid conjugation, or fatty acid addition of BTX-B were likely responsible for these tissue-specific distributions and unique elimination patterns. These observed differences provide further insight into the contribution each brevetoxin metabolite class has to the observed potencies.

Semisynthesis of radiolabeled amino acid and lipid brevetoxin metabolites and their blood elimination kinetics in C57BL/6 mice

Brevetoxin B (BTX-B), produced by dinoflagellates of the species Karenia, is a highly reactive molecule, due in part to an α,β-unsaturated aldehyde group at the terminal side chain, leading to the production of metabolites in shellfish by reduction, oxidation, and conjugation. We have investigated in mice the blood elimination of three common bioactive brevetoxin metabolites found in shellfish, which have been semisynthesized from BTX-B in radioactive forms. BTX-B was reduced at C42 to yield [(3)H] dihydro-BTX-B. [(3)H] S-desoxy-BTX-B2 (cysteine brevetoxin B) was semisynthesized from BTX-B by the conjugation of cysteine at the C50 olefinic group then [(3)H] radiolabeled by C42 aldehyde reduction. [(14)C] N-Palmitoyl-S-desoxy-BTX-B2 was prepared using S-desoxy-BTX-B2 as the starting material with addition of the [(14)C] radiolabeled fatty acid via cysteine-amide linkage. The elimination of intravenously administered [(3)H] S-desoxy-BTX-B2, [(14)C] N-palmitoyl-S-desoxy-BTX-B2, or [(3)H] dihydro-BTX-B was measured in blood collected from C57BL/6 mice over a 48 h period. Each brevetoxin metabolite tested exhibited biexponential elimination kinetics and fit a two-compartment model of elimination that was applied to generate toxicokinetic parameters. The rate of transfer between the central compartment (i.e., blood) and the peripheral compartment (e.g., tissue) for each brevetoxin differed substantially, with dihydro-BTX-B exchanging rapidly with the peripheral compartment, S-desoxy-BTX-B2 eliminating rapidly from the central compartment, and N-palmitoyl-S-desoxy-BTX-B2 eliminating slowly from the central compartment. Toxicokinetic parameters were analyzed in the context of the unique structure of each brevetoxin metabolite resulting from a reduction, amino acid conjugation, or fatty acid addition to BTX-B.

Characterization of brevetoxin metabolism in Karenia brevis bloom-exposed clams (Mercenaria sp.) by LC-MS/MS

Brevetoxin metabolites were identified and characterized in the hard clam (Mercenaria sp.) after natural exposure to Karenia brevis blooms by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Principal brevetoxins BTX-1 and BTX-2 produced by K. brevis were not detectable in clams. Metabolites of these brevetoxins found in clams included products of oxidation, reduction, hydrolysis and amino acid/fatty acid conjugation. Of highest abundance were cysteine and taurine conjugates. We also found glutathione, glycine-cysteine, and γ-glutamyl-cysteine conjugates. A series of fatty acid derivatives of cysteine-brevetoxin conjugates were also identified.

Shellfish toxicity: human health implications of marine algal toxins

Five major human toxic syndromes caused by the consumption of shellfish contaminated by algal toxins are presented. The increased risks to humans of shellfish toxicity from the prevalence of harmful algal blooms (HABs) may be a consequence of large-scale ecological changes from anthropogenic activities, especially increased eutrophication, marine transport and aquaculture, and global climate change. Improvements in toxin detection methods and increased toxin surveillance programmes are positive developments in limiting human exposure to shellfish toxins.

Advances in monitoring and toxicity assessment of brevetoxins in molluscan shellfish

Herein, we describe advancements in monitoring of brevetoxins in molluscan shellfish, with respect to exposure management and control of neurotoxic shellfish poisoning (NSP). Current knowledge of the fate of brevetoxins in molluscan shellfish, and the toxic potency of brevetoxin metabolites, is presented. We review rapid assays for measuring composite brevetoxins, and methodology for measuring constituent brevetoxins, in contaminated shellfish. The applicability of in vitro methods for estimating brevetoxin burden and composite toxicity in shellfish is assessed. Specific and measurable biomarkers of brevetoxin exposure and toxicity in shellfish, and of human intoxication, are described. Their utility in regulatory monitoring of toxic shellfish and in clinical diagnosis of NSP is evaluated.

Bibliographical investigation of complementary alternative medicines for osteoarthritis and rheumatoid arthritis

BACKGROUND

A variety of complementary and alternative medicine (CAM) treatments are provided to the elderly. We investigated the efficacy and safety of CAM substances that are available to patients with osteoarthritis (OA) and rheumatoid arthritis (RA), both in Japan and overseas.

METHODS

Information on CAM products was collected from the World Wide Web, using the keywords "arthritis" and "supplement" in five languages (Japanese, English, French, Italian and German) using a popular search engine for each of the languages. References to published work on the products were researched using PubMed with the keywords of "arthritis", "anti-inflammatory" and "analgesics". Such published work was classified according to the evidence levels established by the Cochrane Library.

RESULTS

Two-hundred and sixty CAM products for OA or RA were available in Japan, of which 41 CAM products had been tested in randomized controlled trials (RCT); there was no scientific evidence for the remaining 219 CAM products. Most of the previous RCT suggested that CAM was effective in OA or RA. Herein, we confirmed the significant OA relieving effects of chondroitin sulfate through a meta-analysis. Effectiveness was assessed using subjective scores, not disease-specific immunological or serological markers for assessment. Toxicological investigations had only been performed for a few CAM products.

CONCLUSION

Some CAM products that are effective against RA may be used together with biological therapy. However, some of the CAM products available in Japan should be tested using objective markers. Some CAM products for OA could be used for the relief of pain.

Neurotoxic shellfish poisoning

Neurotoxic shellfish poisoning (NSP) is caused by consumption of molluscan shellfish contaminated with brevetoxins primarily produced by the dinoflagellate, Karenia brevis. Blooms of K. brevis, called Florida red tide, occur frequently along the Gulf of Mexico. Many shellfish beds in the US (and other nations) are routinely monitored for presence of K. brevis and other brevetoxin-producing organisms. As a result, few NSP cases are reported annually from the US. However, infrequent larger outbreaks do occur. Cases are usually associated with recreationally-harvested shellfish collected during or post red tide blooms. Brevetoxins are neurotoxins which activate voltage-sensitive sodium channels causing sodium influx and nerve membrane depolarization. No fatalities have been reported, but hospitalizations occur. NSP involves a cluster of gastrointestinal and neurological symptoms: nausea and vomiting, paresthesias of the mouth, lips and tongue as well as distal paresthesias, ataxia, slurred speech and dizziness. Neurological symptoms can progress to partial paralysis; respiratory distress has been recorded. Recent research has implicated new species of harmful algal bloom organisms which produce brevetoxins, identified additional marine species which accumulate brevetoxins, and has provided additional information on the toxicity and analysis of brevetoxins. A review of the known epidemiology and recommendations for improved NSP prevention are presented.

Semisynthesis of S-desoxybrevetoxin-B2 and brevetoxin-B2, and assessment of their acute toxicities

Brevetoxins are neurotoxins associated with blooms of marine algae such as Karenia brevis and can accumulate in the marine food chain, causing intoxication of marine animals and people consuming seafood. Brevetoxin-B2 ( 5) is a toxic metabolite produced in shellfish exposed to algae that contain brevetoxin-B ( 1). S-Desoxybrevetoxin-B2 ( 4) has been proposed as a cometabolite produced during this transformation, and while LC-MS analyses suggest its presence in shellfish, it has not yet been isolated and characterized. Studies on these materials are severely constrained by the difficulty of obtaining and purifying them from natural sources. We have developed a convenient one-pot conversion of commercially available brevetoxin-B ( 1) into S-desoxybrevetoxin-B2 ( 4), and a simple method for converting 4 into brevetoxin-B2 ( 5). Full NMR and mass-spectral characterization of 4 and 5 confirmed their structures and showed that the ratio of diastereoisomers in the synthetic 4 and 5 was similar to that observed in naturally contaminated shellfish. The LD 50 values for 4, 5, and dihydrobrevetoxin-B ( 6) by ip injection in mice were 211, 400, and 250 microg/kg, respectively. The methodology for synthesis of brevetoxin metabolites should greatly facilitate toxicological, biochemical and immunochemical studies of these substances, as well as the production of analytical standards.

Chemical defenses: from compounds to communities

Marine natural products play critical roles in the chemical defense of many marine organisms and in some cases can influence the community structure of entire ecosystems. Although many marine natural products have been studied for biomedical activity, yielding important information about their biochemical effects and mechanisms of action, much less is known about ecological functions. The way in which marine consumers perceive chemical defenses can influence their health and survival and determine whether some natural products persist through a food chain. This article focuses on selected marine natural products, including okadaic acid, brevetoxins, lyngbyatoxin A, caulerpenyne, bryostatins, and isocyano terpenes, and examines their biosynthesis (sometimes by symbiotic microorganisms), mechanisms of action, and biological and ecological activity. We selected these compounds because their impacts on marine organisms and communities are some of the best-studied among marine natural products. We discuss the effects of these compounds on consumer behavior and physiology, with an emphasis on neuroecology. In addition to mediating a variety of trophic interactions, these compounds may be responsible for community-scale ecological impacts of chemically defended organisms, such as shifts in benthic and pelagic community composition. Our examples include harmful algal blooms; the invasion of the Mediterranean by Caulerpa taxifolia; overgrowth of coral reefs by chemically rich macroalgae and cyanobacteria; and invertebrate chemical defenses, including the role of microbial symbionts in compound production.

Brevetoxins, like ciguatoxins, are potent ichthyotoxic neurotoxins that accumulate in fish

Brevetoxins and ciguatoxins are closely related potent marine neurotoxins. Although ciguatoxins accumulate in fish to levels that are dangerous for human consumption, live fish have not been considered as potential sources of brevetoxin exposure in humans. Here we show that, analogous to ciguatoxins, brevetoxins can accumulate in live fish by dietary transfer. We experimentally identify two pathways leading to brevetoxin-contaminated omnivorous and planktivorous fish. Fish fed with toxic shellfish and Karenia brevis cultures remained healthy and accumulated high brevetoxin levels in their tissues (up to 2675 ng g(-1) in viscera and 1540 ng g(-1) in muscle). Repeated collections of fish from St. Joseph Bay in the Florida panhandle reveal that accumulation of brevetoxins in healthy fish occurs in the wild. We observed that levels of brevetoxins in the muscle of fish at all trophic levels rise significantly, but not to dangerous levels, during a K. brevis bloom. Concentrations were highest in fish liver and stomach contents, and increased during and immediately following the bloom. The persistence of brevetoxins in the fish food web was followed for 1 year after the K. brevis bloom.

Intrinsic potency of synthetically prepared brevetoxin cysteine metabolites BTX-B2 and desoxyBTX-B2

In mammals and shellfish, brevetoxins produced by the dinoflagellate Karenia brevis are rapidly metabolized to cysteine conjugates. These metabolites identified by mass spectrometry are produced in abundance in mammals and are potentially major bioactive products for intoxication. They are also abundant metabolites in shellfish where they are, in contrast to mammals, retained for prolonged periods, posing a potential threat to shellfish consumers. In this work, we analyze the intrinsic potency of the semi-synthetic cysteine brevetoxin sulfoxide (BTX-B2) and the cysteine brevetoxin (desoxyBTX-B2), each confirmed for purity by LC-MS and NMR techniques, on receptor site 5 of the voltage-gated sodium channels (VGSCs) in brain, heart and skeletal muscle. We show that both brevetoxin conjugates compete with the tritiated reduced parent brevetoxin ([(3)H]PbTx-3) in rat brain membrane preparations and in HEK cells expressing skeletal muscle or cardiac VGSC, albeit, with 8-16-fold lower affinity than the PbTx-3. On neuroblastoma cell assays we show a 3-fold reduction in cytotoxic potency for BTX-B2 relative to PbTx-3, and an 8-fold reduction for desoxyBTX-B2. In conclusion, the major transformation product of brevetoxin observed in diverse species through cysteine adduction and oxidation leads to metabolites with reduced potency on brain, skeletal muscle and heart cells.

Overview of aerosolized Florida red tide toxins: exposures and effects

Florida red tide is caused by Karenia brevis, a dinoflagellate that periodically blooms, releasing its potent neurotoxin, brevetoxin, into the surrounding waters and air along the coast of the Gulf of Mexico. Exposure to Florida red tide toxins has been associated with adverse human health effects and massive fish and marine mammal deaths. The articles in this mini-monograph describe the ongoing interdisciplinary and interagency research program that characterizes the exposures and health effects of aerosolized Florida red tide toxins (brevetoxins). The interdisciplinary research program uses animal models and laboratory studies to develop hypotheses and apply these findings to in situ human exposures. Our ultimate goal is to develop appropriate prevention measures and medical interventions to mitigate or prevent adverse health effects from exposure to complex mixtures of aerosolized red tide toxins.

Identification of a Rapid Detoxification Mechanism for Brevetoxin in Rats

We examined detoxification of brevetoxin in rats through metabolic activities and key elimination routes by analyzing samples from individual rats exposed to two brevetoxin congeners (PbTx-2 and PbTx-3). Brevetoxins were detected by radioimmunoassay in methanolic extracts of blood within 1 h post intraperitoneal (ip) administration. The toxin assay response was about three times higher in PbTx-2-treated rats versus the same dose (180 microg/kg) of PbTx-3. This difference persisted for up to 8 h postexposure. When the blood samples were reextracted with 20% methanol to enhance recovery of potential polar brevetoxin metabolites, 25-fold higher assay activity was present in the PbTx-2-treated rats. Analysis of urine from the same animals identified 7-fold more activity in the PbTx-2-treated rats that accumulated over the course of 24 h. Radioimmunoassay-guided high performance liquid chromatographic analysis of urine from PbTx-2-treated rats yielded three major peaks of activity. The first peak was attributed to the two cysteine adducts, cysteine-PbTx sulfoxide and cysteine-PbTx (MH(+): m/z 1034 and 1018). The second peak was attributed to the oxidized form of PbTx-2 (MH(+): m/z 911) and its reduction product PbTx-3. The third peak remains unidentified. Brevetoxin cysteine conjugate and its sulfoxide product contributed nearly three-quarters of the brevetoxin immunoactivity. Our findings indicate the most commonly occurring PbTx-2 is rapidly transformed to a polar metabolite of a reduced biological activity that appears in blood and remains for up to 8 h, yet is cleared mostly to the urine within 24 h.

Effects of environmental stressors on lymphocyte proliferation in Florida manatees, Trichechus manatus latirostris

The health of many Florida manatees (Trichechus manatus latirostris) is adversely affected each year by exposure to cold weather or harmful algal blooms (red tide; Karenia brevis). Exposures can be sublethal, resulting in stressed animals that are rescued and taken to authorized facilities for rehabilitation, or lethal if exposures are prolonged or unusually severe. To investigate whether sublethal environmental exposures can impair immune function in manatees, rendering animals vulnerable to disease or death, mitogen-induced proliferation was assessed in lymphocytes from manatees exposed to cold temperatures (N=20) or red tide (N=19) in the wild, and compared to lymphocyte responses from healthy free-ranging manatees (N=32). All animals sampled for this study were adults. Lymphocytes were stimulated in vitro with either concanavalin A (ConA) or phytohemagglutinin (PHA) and proliferation was assessed after 96 h using incorporation of the thymidine analog, bromodeoxyuridine (BrdU), into newly synthesized DNA. Proliferation of lymphocytes from manatees rescued from exposure to red tide or cold-stress was approximately one-third that of lymphocytes from healthy free-ranging manatees. To examine the direct effects of red tide toxins on lymphocyte function, mitogen-induced proliferation was assessed following co-culture of lymphocytes with K. brevis toxin extracts. Stimulation indices decreased with increasing toxin concentration, with a significant decrease in proliferation occurring in the presence of 400 ng red tide toxins/ml. When lymphocytes from cold-stressed manatees were co-cultured with red tide toxin extracts, proliferative responses were reduced even further, suggesting multiple stressors may have synergistic effects on immune function in manatees.

Brevetoxin metabolism and elimination in the Eastern oyster (Crassostrea virginica) after controlled exposures to Karenia brevis

The metabolism and elimination of brevetoxins were examined in the Eastern oyster (Crassostrea virginica) following controlled exposures to Karenia brevis cultures in the laboratory. After a 2-day exposure period ( approximately 62 million cells/oyster), elimination of brevetoxins and their metabolites was monitored by using liquid chromatography/mass spectrometry (LC/MS). Composite toxin in oyster extracts was measured by in vitro assay (i.e. cytotoxicity, receptor binding, and ELISA). Of the parent algal toxins, PbTx-1 and PbTx-2 were not detectable by LC/MS in K. brevis-exposed oysters. PbTx-3 and PbTx-9, which are accumulated directly from K. brevis and through metabolic reduction of PbTx-2 in the oyster, were at levels initially (after exposure) of 0.74 and 0.49 microg equiv./g, respectively, and were eliminated largely within 2 weeks after dosing. PbTx-7 and PbTx-10, the reduced forms of PbTx-1, were non-detectable. Conjugative brevetoxin metabolites identified previously in field-exposed oysters were confirmed in the laboratory-exposed oysters. Cysteine conjugates of PbTx-1 and PbTx-2, and their sulfoxides, were in the highest abundance, as apparent in LC/MS ion traces, and were detectable for up to 6 months after dosing. Composite toxin measurements by in vitro assay also reflected persistence (up to 6 months) of brevetoxin residues in the oyster. Levels of cysteine conjugates, as determined by LC/MS, were well correlated with those of composite toxin, as measured by ELISA, throughout depuration. Composite toxin levels by cytotoxicity assay were well correlated with those by receptor binding assay. Cysteine-PbTx conjugates are useful LC/MS determinants of brevetoxin exposure and potential markers for composite toxin in the Eastern oyster.

Comparative concentrations of brevetoxins PbTx-2, PbTx-3, BTX-B1 and BTX-B5 in cockle, Austrovenus stutchburyi, greenshell mussel, Perna canaliculus, and Pacific oyster, Crassostrea gigas, involved neurotoxic shellfish poisoning in New Zealand

Previously, we found brevetoxins PbTx-3, BTX-B5 and BTX-B1 in cockle, Austrovenus (A.) stutchburyi, PbTx-2, PbTx-3 and BTX-B1 in Pacific oyster, Crassostrea (C.) gigas and PbTx-3 and BTX-B1 in greenshell mussel, Perna (P.) canaliculus following outbreak of neurotoxic shellfish poisoning (NSP) in New Zealand by isolation and/or liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). In this study, procedures for quantitative determination of PbTx-2 and BTX-B5 were developed and those for PbTx-3 and BTX-B1 were further examined by LC-MS/MS. In mass spectrometry with an electrospray ionization interface operating in the positive or negative ion mode, the protonated ions [M+H]+ of PbTx-2 (m/z 895), [M+H]+ of PbTx-3 (m/z 897), [M-H]- of BTX-B5 (m/z 909), and [M-Na]- of BTX-B1 (m/z 1016) were generated abundantly, when 0.1% formic acid-acetonitrile was used as the mobile phase for column chromatography. The product ions of m/z 877, 725, 111 and 80 from PbTx-2, PbTx-3, BTX-B5 and BTX-B1 were identified, respectively, allowing unambiguous confirmation of these toxins by selective reaction monitoring LC-MS/MS analysis. High levels of PbTx-3 and BTX-B5 were detected in C. gigas, of PbTx-3, BTX-B1 and BTX-B5 in A. stutchburyi, and of PbTx-2, PbTx-3 and BTX-B5 in P. canaliculus by this LC-MS/MS method.

Confirmation of brevetoxin metabolism in cockle, Austrovenus stutchburyi, and greenshell mussel, Perna canaliculus, associated with New Zealand neurotoxic shellfish poisoning, by controlled exposure to Karenia brevis culture

We examined metabolism of PbTxs in New Zealand cockle, Austrovenus (A.) stutchburyi, and greenshell mussel, Perna (P.) canaliculus, by means of liquid chromatography coupled with tandem mass spectrometry. PbTx-2, PbTx-3 and BTX-B5 were detected in Karenia (K.) brevis culture medium in the ratio of ca. 50:2:5. The amounts of PbTx-3 and BTX-B5 were greatly increased in both seawater and shellfish exposed to K. brevis cultures or supernatant prepared by disruption of K. brevis under appropriate condition, while those of PbTx-2 were decreased. Some PbTx-2 was present in P. canaliculus, but not in A. stutchburyi. Low levels of BTX-B1 were detected in A. stutchburyi, but not P. canaliculus. Levels of PbTx-3 and BTX-B5 were highest immediately after exposure and then declined rapidly in both shellfish. BTX-B1 increased in concentration after exposure, and was then gradually eliminated from A. stutchburyi. Three successive exposures of A. stutchburyi to K. brevis cultures resulted in similar initial levels of PbTx-3 and BTX-B5, while BTX-B1 accumulated after each dose. In P. canaliculus, initial levels of PbTx-3 were similar, while PbTx-2 and BTX-B5 accumulated after each dose. PbTx-3 and BTX-B5 are proposed to be suitable markers for monitoring shellfish toxicity after a red tide event.

Literature Review of Florida Red Tide: Implications for Human Health Effects

Florida red tides are a natural phenomenon caused by dense aggregations of single cell or several species of unicellular organisms. Patches of discolored water, dead or dying fish, and respiratory irritants in the air often characterize these algal blooms. In humans, two distinct clinical entities, depending on the route of exposure, are associated with exposure to the Florida red tide toxins (particularly the brevetoxins). With the ingestion of brevetoxin-contaminated shellfish, neurotoxic shellfish poisoning (NSP) presents as a milder gastroenteritis with neurologic symptoms compared with other marine toxin diseases such as paralytic shellfish poisoning (PSP) or ciguatera fish poisoning. With the inhalation of the aerosolized red tide toxins (especially the brevetoxins) from the sea spray, respiratory irritation and possibly other health effects are reported in both humans and other mammals (Baden 1995, Fleming 1998a, Fleming 1998b, Fleming 1999a, Bossart 1998, Asai 1982, Eastaugh 1989, Pierce 1986, Music 1973, Temple 1995, Anderson 1994).This paper reviews the literature on the known and possible human health effects of exposure to the Florida red tides and their toxins. The review includes discussion of the red tide organisms and their toxins, as well as the effects of these toxins on both wild and laboratory animals as they relate to possible human health effects and exposures.

Detection of Sodium Channel Activators by a Rapid Fluorimetric Microplate Assay

Marine toxins such as brevetoxins and ciguatoxins are produced by dinoflagellates and can accumulate in seafood. These toxins affect humans through seafood consumption. Intoxication is mainly characterized by gastrointestinal and neurological disorders and, in most severe cases, by cardiovascular problems. To prevent the consumption of food contaminated with these toxins, shellfish have been tested by mouse bioassay. However, this method is expensive, time-consuming, and ethically questionable. The objective of this study was to use a recently developed fluorimetric microplate assay to rapidly detect brevetoxins and ciguatoxins. The method is based on the pharmacological effect of brevetoxins and ciguatoxins known to activate sodium channels and involves (i). the incubation of excitable cells in 96 well microtiter plates with the fluorescent dye bis-oxonol, whose distribution across the membrane is potential-dependent, and (ii). dose-dependent cell depolarization by the toxins. Our findings demonstrate that measuring changes in membrane potential induced by brevetoxins and ciguatoxins allowed their quantitation. Active toxins could be reliably detected at concentrations in the nanomolar range. The simplicity, sensitivity, and possibility of being automated provide the basis for development of a practical alternative to conventional testing for brevetoxins and ciguatoxins.

LC/MS analysis of brevetoxin metabolites in the Eastern oyster (Crassostrea virginica)

Brevetoxin (PbTx) metabolism was examined in the Eastern oyster (Crassostrea virginica) following exposure to a Karenia brevis red tide, by using LC/MS(/MS) and cytotoxicity assay. Metabolites observed in field-exposed oysters were confirmed in oysters exposed to K. brevis cultures in the laboratory. Previously, we identified a cysteine conjugate and its sulfoxide (MH(+): m/z 1018 and 1034) as metabolites of the brevetoxin congener PbTx-2. In the present study, we found a cysteine conjugate and its sulfoxide with A-type brevetoxin backbone structure (MH(+): m/z 990 and 1006), as probable derivatives of PbTx-1. We also found glycine-cysteine-PbTx (m/z 1047 and 1075), gamma-glutamyl-cysteine-PbTx (m/z 1147), and glutathione-PbTx (m/z 1176 and 1204) conjugates with A- and B-type backbone structures. Amino acid-PbTx conjugates react with fatty acids through amide linkage to form a series of fatty acid-amino acid-PbTx conjugates. These fatty acid conjugates are major contributors to the composite cytototoxic responses obtained in extracts of brevetoxin-contaminated oysters. Other brevetoxin derivatives found in oysters are consistent with hydrolytic ring-opening and oxidation/reduction reactions.

Food poisoning associated with biotoxins in fish and shellfish

PURPOSE OF REVIEW

In recent times the number of blooms of algae that produce toxins has increased in frequency, intensity and geographical distribution. This review describes some of the illnesses caused by fish and shellfish contaminated with toxins produced by marine algae and by bacteria.

RECENT FINDINGS

The increase in toxic algal blooms may be a result of increased awareness, aquaculture, eutrophication, or transport of cysts in ship ballast. Improved chemical methods for the detection of algal toxins are now being developed, and so the number of toxins recognized is increasing. Toxicological data on some of these algal toxins are lacking. Despite the increase in occurrence of algal toxins, scombrotoxic poisoning remains the most common cause of food poisoning associated with the consumption of fish and shellfish. This may be real or it may be a reflection of lack of suitable tests for algal toxins or under-recognition by workers in health care.

SUMMARY

The major problem worldwide in this field is the lack of pure toxins for use in developing and standardizing chemical methods for toxin detection. Such methods would permit increased testing of both food and clinical specimens, and hence would prevent the entry of toxic food into the food chain and increase laboratory confirmation of incidents of illness.

Measurement of brevetoxin levels by radioimmunoassay of blood collection cards after acute, long-term, and low-dose exposure in mice

We developed a radioimmunoassay (RIA) using a sheep anti-brevetoxin antiserum to evaluate detection of brevetoxin on blood collection cards from mice treated with the brevetoxin congener PbTx-3. The RIA has high affinity for PbTx-3 [half-maximal effective concentration (EC(50)) +/- SE = 1.2 +/- 0.2 nM; n = 10] and recognizes both type 1 and type 2 brevetoxins, but not ciguatoxin. Direct comparison of the RIA with a radiolabeled [(3)H]-PbTx-3 receptor-binding assay (RBA) revealed excellent sensitivity, congener selectivity, and minimal interference from blood matrix. We first analyzed blood samples from an acute time course exposure, using a maximal nonlethal dose [180 microg/kg body weight (bw)] for 0.5, 1, 2, 4, and 24 hr. Mean blood brevetoxin levels were 36 nM at 30 min and stayed above 20 nM during the 1-4 hr time points. We next analyzed blood brevetoxin levels after longer exposure (0.5, 1, 2, 3, 4, or 7 days). Mean blood brevetoxin levels were 26.0 nM at 0.5 days, decreased to 8.2 nM at 1.0 day, and maintained a significant level (p < 0.05) of 1.3 nM at day 2. We next determined the lowest measurable dose using increasing concentrations of PbTx-3 (10-300 micro g/kg bw). Analysis of the blood samples at 60 min revealed a linear relationship between administered and internal doses (r(2) = 0.993). All doses of brevetoxin administered were detectable at 1 hr, with significant levels found for the lowest administered dose of 10 micro g/kg bw--a dose that was 10-fold lower than the lowest observable effect level. This RIA provides an optimal first-tier detection of brevetoxin from blood collection cards and, used in combination with the RBA and liquid chromatography-mass spectrometry, should provide a complete panel of methods to biomonitor brevetoxin exposure.

Implication of brevetoxin B1 and PbTx-3 in neurotoxic shellfish poisoning in New Zealand by isolation and quantitative determination with liquid chromatography-tandem mass spectrometry

Brevetoxin B1 (BTX-B1) was isolated from Austrovenus stutchburyi following the 1992-1993 outbreak of neurotoxic shellfish poisoning (NSP) in New Zealand. We report here the first isolation of PbTx-3 from the same shellfish and the development of a procedure for quantitative determination of PbTx-3 and BTX-B1. PbTx-3 was isolated by chromatography on columns of SiO2, ODS, and LH-20, followed by reverse-phase HPLCs. In mass spectrometry (MS) with an electrospray ionization (ESI) interface operating in the positive or negative ion mode, the abundant protonated ion [M+H]+ of PbTx-3 (m/z 897) and the de-sodiated ion [M-Na]- of BTX-B1 (m/z 1016) were generated, respectively. These served as precursor ions for collision-induced dissociation, and the product ions of m/z 725 from PbTx-3 and m/z 80 from BTX-B1 were identified, allowing unambiguous confirmation of these toxins by selected reaction monitoring liquid chromatography-tandem mass spectrometry (SRM LC-MS/MS) analysis. The determination limits were 0.4 and 2 ng/g for BTX-B1 and PbTx-3 at a signal-to-noise ratio of five, respectively. This LC-MS/MS method was successfully applied to determine BTX-B1 and PbTx-3 in the NSP-associated toxic shellfish. BTX-B1 was found in both A. stutchburyi and Perna canaliculus, but not in Crassostrea gigas, while PbTx-3 was found in all three.

Confirmation of brevetoxin metabolism in the Eastern oyster (Crassostrea virginica) by controlled exposures to pure toxins and to Karenia brevis cultures

Previously, we analyzed Eastern oysters (Crassostrea virginica) naturally exposed to a Karenia brevis red tide and found that brevetoxins (PbTx) are rapidly accumulated and metabolized. Several metabolites were isolated and later identified, including a cysteine-PbTx conjugate (MH(+): m/z 1018) and its sulfoxide product (m/z 1034). In the present study, we confirm and extend those findings by examining PbTx metabolism and elimination in oysters exposed to pure toxins (PbTx-2 and -3) under controlled conditions. Waterborne PbTx-3 was rapidly accumulated, but not metabolized, in the oyster and was largely eliminated within 2 weeks after exposure. In contrast, PbTx-2 was accumulated and rapidly metabolized. Metabolites of PbTx-2 included the reduction product PbTx-3 (m/z 897), and the cysteine conjugates (m/z 1018 and 1034) isolated previously from the field samples. Levels of the metabolite PbTx-3 in PbTx-2-exposed oysters were highest immediately after exposure and declined at a rate similar to parent PbTx-3 in PbTx-3-exposed oysters. Cysteine-PbTx persisted for 8 weeks after exposure. The same metabolites were confirmed in oysters exposed to laboratory cultures of K. brevis. PbTx metabolites contribute to neurotoxic shellfish poisoning (NSP) and should be included in analytical protocols for monitoring shellfish toxicity after a K. brevis red tide event.

The chemistry and biological function of natural marine toxins

Studies on ciguatera fish poisoning led to clarification of the absolute stereochemistry of ciguatoxin, gambierol, gambieric acids, and maitotoxin. Anisotropic NMR reagents and fluorometric chiral HPLC reagents were effectively used together with synthesis of partial structures. Structures of 16 ciguatoxin congeners were successfully elucidated by FAB/MS/MS using samples of 5 microg or less. Stereochemical assignments were also achieved on dinophysistoxin-1, pectenotoxins, yessotoxins, polycavernoside-A, azaspiracid, and prymnesins. The toxins possessed poly-cyclic-ether structures and originated from unicellular algae. Biological functions are briefly described.