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PubMed2005

Illnesses caused by marine toxins.

Marine toxins are produced by algae or bacteria and are concentrated in contaminated seafood. Substantial increases in seafood consumption in recent years, together with globalization of the seafood trade, have increased potential exposure to these agents. Marine toxins produce neurological, gastrointestinal, and cardiovascular syndromes, some of which result in high mortality and long-term morbidity. Routine clinical diagnostic tests are not available for these toxins; diagnosis is based on clinical presentation and a history of eating seafood in the preceding 24 h. There is no antidote for any of the marine toxins, and supportive care is the mainstay of treatment. In particular, paralytic shellfish poisoning and puffer fish poisoning can cause death within hours after consuming the toxins and may require immediate intensive care. Rapid notification of public health authorities is essential, because timely investigation may identify the source of contaminated seafood and prevent additional illnesses. Extensive environmental monitoring and sometimes seasonal quarantine of a harvest are employed to reduce the risk of exposure.

Animals↗
PubMed2006

Toxins: bacterial and marine toxins.

The term toxin refers in a specific way to a toxic substance of biologic origin; that is, a true toxin is a poison produced by a living organism. The purpose of this article is to review some of the most potentially dangerous toxins of concern today. Mechanisms of action, routes of exposure, diagnostic tools, and treatment recommendations are addressed. In addition, current therapeutic uses for certain toxins are discussed.

Bacterial Toxins↗
PubMed1996

A family of novel actin-inhibiting marine toxins.

1. We have examined the effects of marine toxins with a macrolide structure on actin. These toxins include mycalolide B, aplyronine A and bistheonellide A. 2. Measuring actin polymerization by monitoring fluorescent intensity of pyrenyl-actin, mycalolide B did not accelerate the actin polymerization but quickly depolymerized F-actin. In contrast, cytochalasin D, which inhibits actin polymerization by binding to the barbed end of F-actin, accelerated actin nucleation and depolymerized F-actin at a slower rate. 3. Analysing the kinetics of depolymerization by monitoring the rate of spontaneous depolymerization of F-actin under the unpolymerizable state or the rate of polymerization where F-actin was seeded as a nucleus, mycalolide B was suggested to sever F-actin. 4. The relationship between the concentration of total actin and F-actin at different concentrations of mycalolide B suggests that mycalolide B forms a 1:1 complex with G-actin. Viscometry and electron microscopic observations further suggest that the actin filament was depolymerized by mycalolide B. Furthermore, mycalolide B suppressed actin-activated myosin Mg(2+)-ATPase activity, although cytochalasin D did not. Aplyronine A has similar effects on actin. 5. Bistheonellide A also depolymerized F-actin and sequestered G-actin by forming a 1:2 complex with G-actins, but, its severing effect was not detected. We conclude that mycalolide B, aplyronine A and bistheonellide A are novel types of actin-depolymerizing agents, the mechanism of action of which is different from that of cytochalasin D. These structurally related marine toxins may be categorized as 'actin depolymerizing macrolides' and may serve as novel pharmacological tools for analysing actin-mediated cell functions.

Actins↗
PubMed1997

Mechanism of cardiotoxicity induced by a marine toxin isolated from Ptychodiscus brevis.

An organophosphate toxin of marine origin isolated from red tide dinoflagellate P. brevis produced a dose-dependent dual effect on rat atria, i.e. positive inotropic effect at low concentrations (2.8 x 10(-8) to 8.4 x 10(-7) M) and negative inotropic and chronotropic responses at an elevated dose (4.8 x 10(-6) to 7.2 x 10(-4) M). The negative chronotropic and inotropic responses of the toxin were potentiated with physostigmine and ouabain whereas antagonized by atropine and hemicholinium-3 pretreatments and those effects remained unaltered by isoproterenol, phenylephrine and ouabain pretreatments. The results indicate that the toxin induced negative inotropic and chronotropic effects are mediated through release of acetylcholine from the nerve endings and consequent activation of muscarinic receptor. In atria exposed to guanethidine, bretylium, propranolol and tyramine tachyphylaxis, the positive inotropic response of the toxin was not modified. However, the response was antagonized by EGTA, nifedipine, ryanodine, calcium-free ringer and potentiated with caffeine and amiloride pretreatments. The results suggest that the positive inotropic effect of the toxin is mediated through Ca2+ influx and impairment of Na+/Ca2+ exchange process.

Animals↗
PubMed1983

Contractile response of the rabbit aorta to maitotoxin, the most potent marine toxin.

Maitotoxin (MTX), the most potent marine toxin, caused a dose-dependent contraction of the rabbit isolated aorta at concentrations of 10(-10)-3 X 10(-8) g/ml. The dose-contractile response curve for MTX was shifted to the right in a parallel manner by verapamil (10(-6) M), was slightly shifted to the right by phentolamine (10(-6) M) and was not or little affected by tetrodotoxin, methysergide, chlorpheniramine or indomethacin. The MTX-induced contraction was abolished by incubation in Ca2+-free medium and was increased in a linear fashion with Ca2+ concentrations between 0.03 and 1.2 mM. In Ca2+-free solution, the contractile responses produced by re-introduction of Ca2+, Sr2+ or Ba2+ were potentiated after treatment with MTX (10(-8) g/ml.) and a high concentration of KCl (4 X 10(-2) M). After treatment with verapamil (10(-7)-10(-6) M), the dose-contractile response curve for Ca2+, Sr2+ or Ba2+ in the presence of MTX or KCl was shifted to the right in a parallel manner, indicating competitive antagonism. But the dose-response curve for Ca2+ in the presence of A23187 (3 X 10(-5) M), a Ca ionophore, was not affected at all by verapamil (10(-6) M). The tissue Ca content of the aorta was increased 31% by treatment with MTX (10(-8) g/ml.). This effect of MTX was markedly inhibited in the presence of verapamil. On the basis of these results, it is suggested that the MTX-induced contraction of the aorta is caused mainly by a direct action on smooth muscle, possibly due to an increase in Ca2+ permeability which occurred through voltage-sensitive Ca2+ channels in the smooth muscle cell membrane.

Animals↗
PubMed1999

Synergistic effects of some metals contaminating mussels on the cytotoxicity of the marine toxin okadaic acid.

Okadaic acid (OA), a marine toxin is cytotoxic and promotes tumours in mouse skin. It is a specific and potent inhibitor of protein synthesis and also inhibits phosphatases A1 and A2 in vitro. In the present study, we investigated the influence of metals found at acceptable levels in mussels as environmental pollutants on the cytotoxicity of OA in Vero cells. Among the metals found in mussels (Mytilus edulis), the most represented, in terms of molar quantities per gram of dried weight are aluminium (230 nmol/g), copper (58 nmol/g), lead (16 nmol/g), mercury (14 nmol/g) and cadmium (7.4 nmol/g). A solution containing these five metals Al(3+), Cu(2+), Pb(2+), Hg(2+) and Cd(2+) combined at the concentrations detected in mussels, stimulated protein synthesis (+25%, P < 0.01), whereas different dilutions of this solution in the presence of okadaic acid (15 ng/ml, i.e. 18.7 x 10(-9) M) increased the percentage of protein synthesis inhibition from 35 to 79%. The metals also increased the lactate dehydrogenase (LDH) release into the medium and the lipid peroxidation induced by this algal toxin. In addition, these metals reduced the cell viability for an incubation period of 24 h especially at the two higher concentrations. These results indicate that metals (Al(3+), Cu(2+), Pb(2+), Hg(2+), Cd(2+)) in concentration ranges largely below the acceptable levels, synergistically increase the cytotoxicity of low concentrations of OA in cultured cells.

Animals↗
PubMed2004

Pharmacological effects of the marine toxins, brevetoxin and saxitoxin, on murine frontal cortex neuronal networks.

Brevetoxins and saxitoxins (STXs), which are produced by marine dinoflagellates, are very potent neurotoxins targeting separate sites of the alpha subunit of voltage-dependent sodium channels (VDSCs). An attractive approach for marine toxin detection relies on pharmacological modulation of VDSCs expressed in cells or tissues. While these function-based cellular assays exhibit the required sensitivity, they are typically slow and have limited potential use for field applications. Cultured neuronal networks grown on substrate integrated microelectrode arrays (MEAs) have emerged as a robust and sensitive approach for environmental threat detection. The present work describes the rapid effects of brevetoxin-2 (PbTx-2) and STX on embryonic murine frontal cortex neuronal networks on MEAs. Network recording parameters such as mean spike rate, burst rate, burst duration, number of spikes per burst and spike amplitude were analyzed before and after exposure to the toxins. STX produced fast and reversible inhibition of all electrophysiological parameters with IC(50)s ranging between 1.2 and 2.2nM. Although PbTx-2 also caused inhibition of most of the network electrophysiological parameters, it produced an increase in burst duration at lower concentrations (EC(50)=15+/-2 nM, n=4) followed by inhibition at higher ones (IC(50)=63+/-4 nM, n=4). Exposure of frontal cortex networks to PbTx-2 and STX also caused differential effects on spike amplitude. This work demonstrates that cultured neuronal networks not only could be used for pharmacological characterization of marine toxins but they also provide a tool with unique properties for their detection.

Action Potentials↗
PubMedDate not supplied

Detection of marine toxins using reconstituted sodium channels.

Specific binding of the marine toxins saxitoxin, tetrodotoxin, and brevetoxin to the rat brain sodium channel is demonstrated using purified sodium channels reconstituted into phospholipid vesicles. Restoration of sodium channel function and binding activity by incorporation into phospholipid vesicles provides the only rigorous proof that the purified protein contains the neurotoxin receptor sites. In addition, reconstitution provides a valuable experimental preparation for biochemical analysis of neurotoxin binding sites and may facilitate the development of a specific toxin detection system.

Animals↗
PubMedDate not supplied

Determinations of marine toxins in foods.

Prospects of new analytical methods for determining marine toxins in foods are described. The methods discussed include fluorometric liquid chromatography, cytotoxicity assays, channel binding assays, and enzyme-immunoassays. Emphasis was laid on assay methods for ciguatoxins and diarrhetric shellfish toxins.

Animals↗
PubMed2001

Characterization of spirolides a, c, and 13-desmethyl c, new marine toxins isolated from toxic plankton and contaminated shellfish.

Three additional marine toxins, spirolides A (1), C (3), and 13-desmethyl-C (7), were isolated from contaminated scallops and phytoplankton collections obtained from a Nova Scotian aquaculture site, as well as from batch cultures of the dinoflagellate Alexandrium ostenfeldii obtained as a single-cell isolate from these phytoplankton assemblages. The structures of these new spirolide derivatives, characterized by mass spectrometry and NMR, indicate a close relationship with spirolides B (2) and D (4) isolated previously from contaminated shellfish in the same area. All of these compounds display "fast-acting" toxicity in the traditional bioassay used for monitoring shellfish, and this is related to the presence of a cyclic imine function in all these compounds. Those spirolides containing a vicinal dimethyl group in the seven-membered ring are resistant to oxalic acid hydrolysis, whereas those that do not are readily hydrolyzed. These observations suggest that the extra methyl group on the seven-membered imine ring of 3, 4, and 7 appears to block the process of imine hydrolysis perhaps by stereochemical interference.

Animals↗
PubMed1983

Contraction and increase in tissue calcium content induced by maitotoxin, the most potent known marine toxin, in intestinal smooth muscle.

Maitotoxin (MTX), the most potent known marine toxin, isolated from toxic dinoflagellates and poisonous fish, caused a dose-dependent contraction of the guinea-pig isolated ileum and taenia caeci at concentrations of 100 pg to 30 ng/ml. These contractile responses to MTX (3 ng/ml) in both tissues were abolished by incubation in Ca2+-free solution and were markedly inhibited by treatment with methoxyverapamil (D600), but were not affected by tetrodotoxin and atropine. Furthermore, MTX markedly elevated tissue Ca2+ content of the taenia caeci. These results suggest that MTX activates Ca2+ channels in the smooth muscle membrane of both tissues to increase Ca2+ influx and thus induces contractions.

Animals↗
PubMed1983

Excitatory effect of the most potent marine toxin, maitotoxin, on the guinea-pig vas deferens.

The most potent marine toxin, maitotoxin (MTX) (10(-9) to 3 X 10(-8) g/ml) caused a slower contraction of the isolated guinea-pig vas deferens (second component) in a dose-dependent manner after the first rapid phasic contraction (first component). The second component of the MTX-induced contraction was markedly inhibited by phentolamine and reserpine, whereas the first component remained unaffected. Both components were inhibited or abolished by verapamil or a Ca-free medium, but were not affected by atropine, chlorpheniramine or tetrodotoxin. The tissue Ca content of the vas deferens was increased by MTX 10(-9) to 3 X 10(-8) g/ml) in a dose-dependent manner. Furthermore, MTX (10(-9) to 3 X 10(-8) g/ml) caused a dose-dependent release of norepinephrine from the tissue, which was inhibited or abolished by verapamil or a Ca-free medium. In Na+-free medium, MTX still caused a profound increase in the tissue Ca content and a marked release of norepinephrine from the vas deferens. These results suggest that the major part of the first component is the result of a direct action of MTX on smooth muscle membrane, whereas the second component is primarily the result of indirect action mediated through the norepinephrine release from the adrenergic nerve terminals. It is also suggested that both components are possibly due to an increased Ca++ permeability of the voltage sensitive Ca++ channels in smooth muscle and nerve membrane.

Animals↗
PubMed1983

Ca2+ channel activating function of maitotoxin, the most potent marine toxin known, in clonal rat pheochromocytoma cells.

Actions of maitotoxin, the most potent marine toxin known obtained from toxic dinoflagellate, Gambier-discus toxicus, were studied using clonal rat pheochromocytoma cells (PC12), rat liver mitochondria and liposomes. Maitotoxin induced a profound release of norepinephrine and dopamine from PC12 cells and the molar ratio of norepinephrine to dopamine was almost the same as that stored in the cells. This releasing action was apparent at a concentration of 5 X 10(-10) g/ml or more, the releasing rate increased with an increase in the concentration of applied maitotoxin and attained maximum at about 10(-6) g/ml. The [3H]norepinephrine release induced by maitotoxin was abolished in the absence of external Ca2+ and increased with increasing concentration of external Ca2+ up to 10 mM. The release gradually decreased as the external Na+ concentrations were reduced from 130 to 20 mM, but maitotoxin is still able to induce a profound release in the absence of external Na+. The releasing action of maitotoxin was markedly suppressed by various Ca2+ channel blockers, such as Mn2+, verapamil, and nicardipine, and by a local anesthetic, tetracaine. The inhibitory actions of Ca2+ channel blockers were antagonized by external Ca2+ and became less obvious in the higher Ca2+ concentration range. Maitotoxin did not exhibit any ionophoretic activities on rat mitochondrial and liposomal membranes. These results suggest that maitotoxin has the ability to activate voltage-dependent Ca2+ channels of PC12 cells.

Adrenal Gland Neoplasms↗
PubMed2000

A rapid hemolysis assay for the detection of sodium channel-specific marine toxins.

Current methods of detection for fish and shellfish biotoxins in monitoring and research purposes are either labor intensive, expensive, require specialized techniques or all of the above. This paper reports on the development of a fairly sensitive, rapid, and inexpensive assay which detects the presence of compounds that affect the sodium channel. It is based on the principles of the mouse neuroblastoma tissue culture assay for sodium channel specific-biotoxins using red blood cells (RBCs) from the red tilapia (Sarotherodon mossambicus). This assay has the potential to complement the use of live animal bioassay testing for marine toxins. Veratridine, a sodium channel activator and ouabain, an inhibitor of Na(+)/K(+) ATPase, both react with the tilapia RBCs by affecting the permeability of the cell's membrane. Saxitoxin (STX), its analogs, and tetrodotoxin (TTX) can inhibit the action of veratridine and ouabain leaving the cell morphologically normal. By sequencing the addition of veratridine and ouabain, with either the extracted samples, saxitoxin, tetrodotoxin, or ciguatoxin (CTX-a sodium channel activator) to the RBCs a sodium channel antagonist or activator can be detected. Results using pure concentrations of a sodium channel-specific toxin could be detected to inhibit hemolysis at a concentration of 0.3 microg/ml STX, 3.5 microg/ml for neo-STX, 3.0 microg/ml for GTX, and 5.0 microgl for TTX in the presence of ouabain and veratridine. CTX was detected at a concentration of 50 microg/ml. The RBCs from the red tilapia was used due to the fish's ability to osmoregulate its internal environment to survive in both fresh and saltwater. In addition, with growing opposition to live animal testing, this assay has been designed as a non-lethal means of testing for sodium channel affecting marine toxins. No test animals are sacrificed and blood may be drawn from the same fish for continued sample testing.

Animals↗
PubMed1997

A molecular basis for different interactions of marine toxins with protein phosphatase-1. Molecular models for bound motuporin, microcystins, okadaic acid, and calyculin A.

The hepatotoxic cyclic heptapeptide microcystins and cyclic pentapeptide nodularins are powerful liver tumor promoters and potent inhibitors of the catalytic subunits of protein phosphatase-1 and -2A (PP-1c and PP-2Ac). In marked contrast to microcystins, which interact covalently with PP-1 and PP-2A, the nodularins do not bind covalently to PP-1 and PP-2A and may additionally possess unique carcinogenic properties. The conformation of microcystin-LR has been determined in solution and bound to PP-1c. We show here that the free NMR solution structures of two distinct microcystin structural congeners (microcystin-LR and -LL) are remarkably similar to the bound crystal structure of microcystin-LR. We have exploited this finding by using Metropolis Monte Carlo modeling to dock the solution structures of microcystin-LL and the marine toxin motuporin (nodularin-V) onto the crystal structure of PP-1c. Both of these toxins occupy a position similar to that of microcystin-LR when bound to PP-1c. However, although there are relatively minor differences in the structural orientation of microcystin-LL compared with microcystin-LR, there is a striking difference in the position of the N-methyldehydrobutyrine residue in motuporin relative to the comparable N-methyldehydroalanine residue in microcystin-LR. We propose that this difference in orientation provides a molecular explanation for why nodularins are incapable of forming a covalent linkage with PP-1c. Furthermore, the predicted position of N-methyldehydrobutyrine in motuporin is at the surface of the PP-1c-toxin complex, which may thus facilitate chemical interaction with a further macromolecule(s) possibly relating to its carcinogenic properties. PP-1c and PP-2Ac are also targets for other marine toxins such as okadaic acid and calyculin A. It was therefore of interest to use Metropolis Monte Carlo modeling to dock the known free crystal structures of okadaic acid and calyculin A to the crystal structure of PP-1c. These experiments predict that both okadaic acid and calyculin A are strikingly similar to microcystins and motuporin in their tertiary structure and relative PP-1c binding position.

Animals↗
PubMed2004

Lack of DNA damage induction by okadaic acid, a marine toxin, in the CHO-Hprt and the in vitro UDS assays.

Okadaic acid (OA) is a marine toxin produced by dinoflagellates and responsible for human intoxications. OA is a specific inhibitor of serine/threonine protein phosphatases PP1 and PP2A and a potent tumor promoter in mouse skin and rat glandular stomach. In a previous study, we demonstrated that OA induced aneuploidy in CHO-K1 cells using the cytokinesis-block micronucleus (CBMN) assay coupled to FISH and concluded that OA was not a direct mutagen. As some previous in vitro mutagenicity studies had given positive results with OA, we decided to perform two additional in vitro mutagenicity assays in accordance with the OECD guidelines: (i) the CHO/Hprt test, which provides end points about locus-specific gene mutation; (ii) the in vitro unscheduled DNA synthesis (UDS) assay in rat hepatocytes, which measures [(3)H]thymidine incorporation into DNA undergoing excision repair. In the CHO/Hprt assay, there was no significant increase in the number of mutants for doses ranging from 5 to 5000 nM in the presence or absence of rat liver S9 fraction. In the in vitro UDS assay, OA did not induce primary DNA damages in rat hepatocytes following 18 h exposure at concentrations between 1.32 and 100 nM. As OA could affect the DNA repair systems via the inhibition of protein phosphatases, its effects on the repair kinetic of 2AAF-induced DNA damage were also investigated with the UDS assay. The results showed that OA did not interact with the DNA-repair process involved in in vitro UDS in rat hepatocytes. We concluded that OA failed to induce direct DNA damage but acted principally by altering the chromosome number, which could contribute to its carcinogenic effect.

Animals↗
PubMed2006

Comparative analysis of purified Pacific and Caribbean ciguatoxin congeners and related marine toxins using a modified ELISA technique.

The monoclonal antibody to ciguatoxin (CTX) produced from a hybridoma cell line was assayed for the detection of four congeners of CTX: Pacific ciguatoxin-1 (P-CTX-1), Pacific ciguatoxin-2 (P-CTX-2), Pacific ciguatoxin-3 (P-CTX-3), and Caribbean ciguatoxin-1 (C-CTX-1) and related marine toxins, including domoic acid, palytoxin, and okadaic acid, using a modified enzyme-linked immunosorbent assay (ELISA). Lower detection limits were assessed and linearity was statistically established (P<0.05) for P-CTX-1, P-CTX-2, and P-CTX-3 and C-CTX-1 at concentrations ranging from 0 to 5.00 ng, while the other marine toxins showed statistically insignificant cross-reactivities at similar concentrations. Thus, the monoclonal antibody to CTX is able to specifically detect various CTX congeners at levels comparable to those naturally occurring in ciguatoxic fish.

Acrylamides↗
PubMed2004

Rapid determination of polyether marine toxins using liquid chromatography-multiple tandem mass spectrometry.

The diarrhetic shellfish poisoning (DSP) toxins, okadaic acid (OA), dinophysistoxins (DTX); pectenotoxin-2 (PTX2) and pectenotoxin-2 seco acids, were determined in marine phytoplankton, Dinophysis acuta, and mussels (Mytilus edulis) collected along the southwest coast of Ireland. Liquid chromatography-multiple tandem mass spectrometry (LC-MS/MS) was employed for the simultaneous determination of a series of marine toxins with large polarity differences. Separation of five DSP toxins was achieved on a C18 column (Luna-2, 150 mm x 2.1 mm, 5 microm) using an acetonitrile-water gradient with ammonium acetate as an eluent modifier. Electrospray ionisation (ESI) in negative mode, was used to generate the molecule related ion, [M-H]-, for each toxin. To develop a multiple reaction monitoring (MRM) method, fragmentation studies were performed to determine the optimum precursor-product ion combinations: OA (803/255), DTX2 (803/255), DTX1 (817/255), PTX2SAs (875/137) and PTX2 (857/137). This highly sensitive method had detection limits better than 1 pg (on-column). Linear calibrations were obtained for shellfish extracts that were spiked with toxins, OA, 0.007-1.00 microg/ml (r2 = 0.9993, N = 3) and DTX2, 0.054-8.5 microg/ml (r2 = 0.9992, N = 3). Good reproducibility data were also achieved with %RSD values (N = 3) ranging from 3.15% (0.56 microg DTX2/ml) to 5.71% (0.14 microg DTX2/ml), for shellfish extracts. The method was sufficiently sensitive to permit the determination of DSP toxins in small numbers of picked phytoplankton cells (N = 12-40). In one sample of D. acuta the average toxin composition per cell was: OA (7.0 pg), DTX2 (11 pg) and PTX2 (7.2 pg).

Chromatography, High Pressure Liquid↗