Relationship between domoic acid levels in the blue mussel (Mytilus edulis) and toxicity in mice

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

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

Public health risks associated with chronic, low-level domoic acid exposure: A review of the evidence

Domoic acid (DA), the causative agent for the human syndrome Amnesic Shellfish Poisoning (ASP), is a potent, naturally occurring neurotoxin produced by common marine algae. DA accumulates in seafood, and humans and wildlife alike can subsequently be exposed when consuming DA-contaminated shellfish or finfish. While strong regulatory limits protect people from the acute effects associated with ASP, DA is an increasingly significant public health concern, particularly for coastal dwelling populations, and there is a growing body of evidence suggesting that there are significant health consequences following repeated exposures to levels of the toxin below current safety guidelines. However, gaps in scientific knowledge make it difficult to precisely determine the risks of contemporary low-level exposure scenarios. The present review characterizes the toxicokinetics and neurotoxicology of DA, discussing results from clinical and preclinical studies after both adult and developmental DA exposure. The review also highlights crucial areas for future DA research and makes the case that DA safety limits need to be reassessed to best protect public health from deleterious effects of this widespread marine toxin.

What California sea lions exposed to domoic acid might teach us about autism: lessons for predictive and preventive medicine

Autism spectrum disorder (ASD) shares many biological and behavioral similarities with the deleterious effects of domoic acid (DA) exposure. DA is produced by marine algae and most commonly by species of Pseudo-nitzschia. Humans and marine mammals can be exposed to DA when they consume whole fish or shellfish. The mammalian fetus is highly sensitive to the deleterious effects of DA exposure. Both ASD and exposures to toxic levels of DA feature repetitive behaviors, challenges with social interaction, and seizures. They can also share a commonality in brain anatomy and function, particularly the balance between excitatory and inhibitory mechanisms. The current article is relevant to predictive, preventive, and personalized medicine for three reasons. First, shellfish consumption may be a risk factor for ASD and the regulatory limit for DA should be adjusted to prevent this possibility. Human contributions to increased algal production of DA in coastal waters should be identified and reduced. Second, evaluations of sentinel species wild and free-roaming in the environment, though typically outside the purview of biomedical research, should be much more fully employed to gain insights to risk factors for human disease. To better identify and prevent disease, biomedical researchers should study wild populations. Third, studies of DA exposure highlight the possibility that glutamate additives to processed foods may also have deleterious impacts on human brain development and behavior.

The Molecular Basis of Toxins' Interactions with Intracellular Signaling via Discrete Portals

An understanding of the molecular mechanisms by which microbial, plant or animal-secreted toxins exert their action provides the most important element for assessment of human health risks and opens new insights into therapies addressing a plethora of pathologies, ranging from neurological disorders to cancer, using toxinomimetic agents. Recently, molecular and cellular biology dissecting tools have provided a wealth of information on the action of these diverse toxins, yet, an integrated framework to explain their selective toxicity is still lacking. In this review, specific examples of different toxins are emphasized to illustrate the fundamental mechanisms of toxicity at different biochemical, molecular and cellular- levels with particular consideration for the nervous system. The target of primary action has been highlighted and operationally classified into 13 sub-categories. Selected examples of toxins were assigned to each target category, denominated as portal, and the modulation of the different portal’s signaling was featured. The first portal encompasses the plasma membrane lipid domains, which give rise to pores when challenged for example with pardaxin, a fish toxin, or is subject to degradation when enzymes of lipid metabolism such as phospholipases A₂ (PLA₂) or phospholipase C (PLC) act upon it. Several major portals consist of ion channels, pumps, transporters and ligand gated ionotropic receptors which many toxins act on, disturbing the intracellular ion homeostasis. Another group of portals consists of G-protein-coupled and tyrosine kinase receptors that, upon interaction with discrete toxins, alter second messengers towards pathological levels. Lastly, subcellular organelles such as mitochondria, nucleus, protein- and RNA-synthesis machineries, cytoskeletal networks and exocytic vesicles are also portals targeted and deregulated by other diverse group of toxins. A fundamental concept can be drawn from these seemingly different toxins with respect to the site of action and the secondary messengers and signaling cascades they trigger in the host. While the interaction with the initial portal is largely determined by the chemical nature of the toxin, once inside the cell, several ubiquitous second messengers and protein kinases/ phosphatases pathways are impaired, to attain toxicity. Therefore, toxins represent one of the most promising natural molecules for developing novel therapeutics that selectively target the major cellular portals involved in human physiology and diseases.

Fetal domoic acid exposure affects lateral amygdala neurons, diminishes social investigation and alters sensory-motor gating

Domoic acid (DA) is an algal neurotoxin that accumulates in marine fish and shellfish. DA can move across the placenta and concentrate in amniotic fluid, which can be swallowed during late gestation. DA also transfers to infants via milk. Preclinical studies to determine effects of developmental DA expose have primarily involved DA exposure during the postnatal period and little is known about late CNS effects following prenatal DA. In the present study, we tested the hypothesis that prenatal exposure of FVB mice to low levels of DA would result in diminished social interaction and sensory motor gating associated with alterations in parvalbumin immunoreactivity in relevant brain regions undergoing development during and following DA exposure. In addition to parvalbumin, we stained with NeuN for a neuronal specific nuclear protein to determine if neuronal loss followed prenatal DA exposure. A single moderate dose of DA administered during gestation produces diminishes social investigation and alters sensorimotor gating, behavioral effects more pronounced in males than females. These behavioral changes were associated with discrete alterations in the parvalbumin-positive subtype of GABAergic neurons in the dentate gyrus and lateral amygdala.

Domoic acid uptake and elimination kinetics in oysters and mussels in relation to body size and anatomical distribution of toxin

Toxin accumulation by suspension-feeding qualifier depends on a balance between processes regulating toxin uptake (i.e. ingestion and absorption of toxic cells) and elimination (i.e. egestion, exchange among tissues, excretion, degradation and/or biotransformation) during exposure to toxic blooms. This laboratory study compares the size-specific uptake and elimination kinetics of domoic acid (DA) from Pseudo-nitzschia multiseries in two co-occurring bivalves, the oyster Crassostrea virginica and the mussel Mytilus edulis. Domoic acid concentrations were measured in visceral and non-visceral tissues of different-sized oysters and mussels during simultaneous long-term exposure to toxic P. multiseries cells in the laboratory, followed by depuration on a non-toxic algal diet. Mussels attained 7-17-fold higher DA concentrations than oysters, depending on the body size and exposure time, and also detoxified DA at higher rates (1.4-1.6 d(-1)) than oysters (0.25-0.88 d(-1)) of a comparable size. Small oysters attained markedly higher weight-specific DA concentrations (maximum=78.6 μg g(-1)) than large, market-sized individuals (≤ 13 μg g(-1)), but no clear relationship was found between body size and DA concentration in mussels (maximum=460 μg g(-1)). Therefore, differential DA accumulation by the two species was, on average, approximately 3-fold more pronounced for large bivalves. An inverse relationship between DA elimination rate and body size was established for oysters but not mussels. Elimination of DA was faster in viscera than in other tissues of both bivalves; DA exchange rate from the former to the latter was higher in oysters. The contribution of viscera to the total DA burden of mussels was consistently greater than that of other tissues during both uptake (>80%) and depuration (>65%) phases, whereas it rapidly decreased from 70-80% to 30-40% in oysters, and this occurred faster in smaller individuals. Residual DA concentrations (≤ 0.25 μg g(-1)) were detected at later depuration stages (up to 14 d), mainly in viscera of oysters and non-visceral tissues of mussels, suggesting that a second, slower-detoxifying toxin compartment exists in both species. However, a simple exponential decay model was found to adequately describe DA elimination kinetics in these bivalves. The lower capacity for DA accumulation in oysters compared to mussels can thus only be explained by the former's comparatively low toxin intake rather than faster toxin elimination.

Domoic acid as a developmental neurotoxin

Domoic acid (DomA) is an excitatory amino acid which can accumulate in shellfish and finfish under certain environmental conditions. DomA is a potent neurotoxin. In humans and in non-human primates, oral exposure to a few mg/kg DomA elicits gastrointestinal effects, while slightly higher doses cause neurological symptoms, seizures, memory impairment, and limbic system degeneration. In rodents, which appear to be less sensitive than humans or non-human primates, oral doses cause behavioral abnormalities (e.g. hindlimb scratching), followed by seizures and hippocampal degeneration. Similar effects are also seen in other species (from sea lions to zebrafish), indicating that DomA exerts similar neurotoxic effects across species. The neurotoxicity of DomA is ascribed to its ability to interact and activate the AMPA/KA receptors, a subfamily of receptors for the neuroexcitatory neurotransmitter glutamate. Studies exploring the neurotoxic effects of DomA on the developing nervous system indicate that DomA elicits similar behavioral, biochemical and morphological effects as in adult animals. However, most importantly, developmental neurotoxicity is seen at doses of DomA that are one to two orders of magnitude lower than those exerting neurotoxicity in adults. This difference may be due to toxicokinetic and/or toxicodynamic differences. Estimated safe doses may be exceeded in adults by high consumption of shellfish contaminated with DomA at the current limit of 20 microg/g. Given the potential higher susceptibility of the young to DomA neurotoxicity, additional studies investigating exposure to, and effects of this neurotoxin during brain development are warranted.

Enhancement of domoic acid neurotoxicity on Diptera larvae bioassay by marine fungal metabolites

Peptaibols are small linear fungal peptides which are produced in the marine environment. They exhibit neurotoxicity by forming pores in neuronal membranes. This work describes their combine effect with domoic acid, a neurotoxic phycotoxin, on Diptera larvae. The Acute toxicity bioassay on this biological model was tested with a panel of different toxins (microbial, algal or fungal). It allowed the discrimination of neurotoxins and non-neurotoxic toxins, and an evaluation of the toxicity level (MED and ED(50)) which were correlated with published LD(50) in mice for neurotoxins tested. The highest activities on this test were found for Na(+) channel blockers tetrodotoxin (ED(50) = 0.026 mg/kg) and saxitoxin (ED(50) = 0.18 mg/kg). Domoic acid was less active with an ED(50) = 7.6 mg/kg. For synergism study, longibrachin-A-I, a 20-mer peptaibol isolated from cultures of a marine-derived strain of Trichoderma longibrachiatum Rifai was chosen. Bioassay results confirmed its neuroactivity. Its level of toxicity (ED(50) = 270 mg/kg) was lower than those of phycotoxins tested but higher than mycotoxin ones. Injected together, longibrachin-A-I and domoic acid exhibited an increase of their activities. With doses of longibrachin-A-I below its Minimal Effective Dose (MED), the synergism factor which expresses the enhancement of domoic acid toxicity could reach 34.5. Both domoic acid and longibrachin-A-I are acting on ion channels and pores in neuronal membranes which contribute to the intake of Ca(2+) into cells.

Gene expression profiles in zebrafish brain after acute exposure to domoic acid at symptomatic and asymptomatic doses

Domoic acid (DA) is a neuroexcitatory amino acid that is naturally produced by some marine diatom species of the genus Pseudo-nitzschia. Ingestion of DA-contaminated seafood by humans results in a severe neurotoxic disease known as amnesic shellfish poisoning (ASP). Clinical signs of ASP include seizures and neuronal damage from activation of ionotropic glutamate receptors. However, the impacts of DA exposure at levels below those known to induce outward signs of neurobehavioral exicitotoxicity have not been well characterized. To further understand the mechanisms of neurotoxic injury associated with DA exposure, we examined the transcriptome of whole brains from zebrafish (Danio rerio) receiving intracoelomic (IC) injection of DA at both symptomatic and asymptomatic doses. A majority of zebrafish exposed to high-dose DA (1.2 microg DA/g) exhibited clinical signs of neuroexcitotoxicity (EC(50) of 0.86 microg DA/g) within 5-20 min of IC injection. All zebrafish receiving low-dose DA (0.47 microg DA/g) or vehicle only maintained normal behavior. Microarray analysis of symptomatic and asymptomatic exposures collectively yielded 306 differentially expressed genes (1.5-fold, p </= 0.05) predominately represented by signal transduction, ion transport, and transcription factor functional categories. Transcriptional profiles were suggestive of neuronal apoptosis following an overwhelming of protective adaptive pathways. Further, potential molecular biomarkers of neuropathic injury, including the zebrafish homolog of human NDRG4, were identified and may be relevant to DA exposure levels below that causing neurobehavioral injury. In general, DA-modulated gene expression was consistent with other model species thereby validating zebrafish as an appropriate vertebrate model to study mechanisms of DA neurotoxicity. These data provide a basis for identifying pathways of DA-induced injury as well as biomarkers of asymptomatic and symptomatic DA exposure levels.

Domoic acid toxicologic pathology: a review

Domoic acid was identified as the toxin responsible for an outbreak of human poisoning that occurred in Canada in 1987 following consumption of contaminated blue mussels [Mytilus edulis]. The poisoning was characterized by a constellation of clinical symptoms and signs. Among the most prominent features described was memory impairment which led to the name Amnesic Shellfish Poisoning [ASP]. Domoic acid is produced by certain marine organisms, such as the red alga Chondria armata and planktonic diatom of the genus Pseudo-nitzschia. Since 1987, monitoring programs have been successful in preventing other human incidents of ASP. However, there are documented cases of domoic acid intoxication in wild animals and outbreaks of coastal water contamination in many regions world-wide. Hence domoic acid continues to pose a global risk to the health and safety of humans and wildlife. Several mechanisms have been implicated as mediators for the effects of domoic acid. Of particular importance is the role played by glutamate receptors as mediators of excitatory neurotransmission and the demonstration of a wide distribution of these receptors outside the central nervous system, prompting the attention to other tissues as potential target sites. The aim of this document is to provide a comprehensive review of ASP, DOM induced pathology including ultrastructural changes associated to subchronic oral exposure, and discussion of key proposed mechanisms of cell/tissue injury involved in DOM induced brain pathology and considerations relevant to food safety and human health.

Absence of neurotoxic effects in leopard sharks, Triakis semifasciata, following domoic acid exposure

Domoic acid (DA), a potent neurotoxin produced by select species of algae and diatoms, kills neurons bearing kainic acid-type glutamate receptors. Studies have shown that DA bioaccumulates in invertebrates and fish that consume the diatoms. In every vertebrate species tested or observed in the wild, dietary or systemic DA causes neuronal damage or clinical signs of neurotoxicity. Sharks, like marine birds and mammals, are exposed to DA through their diet; however, no research has demonstrated the effect of DA on shark behavior or physiology. In this study, juvenile leopard sharks (Triakis semifasciata) were given DA by intracoelomic injection at doses of 0, 1, 3, 9, and 27 mg/kg and observed for 7 days. The sharks failed to demonstrate behavioral or histological changes in response to the toxin. We identified putative brain glutamate receptors by probing western blots with an antibody specific for kainic acid-type glutamate receptors and demonstrated receptor localization in the cerebellum with immunohistochemistry. Blood levels of DA in three sharks dosed at 9 mg/kg fell rapidly within 1.5h of injection. We show that leopard sharks possess the molecular target for DA but are resistant to doses of DA known to be toxic to other vertebrates.

Amnesic shellfish poison

Amnesic shellfish poisoning (ASP) is caused by consumption of shellfish that have accumulated domoic acid, a neurotoxin produced by some strains of phytoplankton. The neurotoxic properties of domoic acid result in neuronal degeneration and necrosis in specific regions of the hippocampus. A serious outbreak of ASP occurred in Canada in 1987 and involved 150 reported cases, 19 hospitalisations and 4 deaths after consumption of contaminated mussels. Symptoms ranged from gastrointestinal disturbances, to neurotoxic effects such as hallucinations, memory loss and coma. Monitoring programmes are in place in numerous countries worldwide and closures of shellfish harvesting areas occur when domoic acid concentrations exceed regulatory limits. This paper reviews the chemistry, sources, metabolism and toxicology of domoic acid as well as human case reports of ASP and discusses a possible mechanism of toxicity.

Electroencephalographic, behavioral, and c-fos responses to acute domoic acid exposure

Domoic acid, a potent excitotoxic analogue of glutamate and kainate, may cause seizures, amnesia, and sometimes death in humans consuming contaminated shellfish. Continuous behavioral observations and recordings of the electrocorticogram (ECoG, via bipolar, epidural electrodes) were obtained from nonanesthetized rats for 2 h after intraperitoneal injection with either saline, 2.2, or 4.4 mg/kg of domoic acid. Rats were then sacrificed for c-fos immunohistochemistry. Fast Fourier transformation (FFT) of the ECoG data to obtain the voltage as a function of frequency indicated that the lower frequency bands (theta, 4.75-6.75 Hz and delta, 1.25-4.50 Hz) were the first to respond, with a significant elevation by 30 min after the high dose of domoic acid. The lower dose of domoic acid also caused a significant elevation of ECoG voltage, but not until later in the session. Sixty minutes after dosing, the behavioral biomarkers of "ear scratching" and "rearing, praying" (RP) seizures became significantly elevated in the high-dose rats. The low-dose rats showed no significant alterations in behavior at any time during the session. In postmortem brains obtained immediately after the sessions, c-fos was activated in the anterior olfactory nucleus by both the low and high doses of domoic acid. However, only the high dose increased c-fos immunoreactivity in the hippocampus, affecting both the granule and pyramidal neurons. These data indicate that electroencephalographic and c-fos responses can be obtained at a dose of domoic acid that fails to activate the behavioral response most commonly used as a bioassay for this marine toxin: ear scratching with the ipsilateral foot.

Glutamate uptake

Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.

Analysis of domoic acid in shellfish by thin-layer chromatography

A thin-layer chromatography (TLC) method has been developed for the semi-quantitative analysis of domoic acid (DA) in shellfish tissues. Tissues were extracted in a single-step homogenization of tissue with 50 % aqueous methanol and then taken through a selective strong anion exchange cleanup. Cleaned extracts were applied directly to silica gel TLC plates and developed with a butanol-acetic acid-water mixture (3:1:1, Rf = 0.45 for DA). As little as 10 microg DA per gram of tissue could be detected after chromatography using a hand-held short-wave UV lamp to detect fluorescence quenching. Confirmation was provided by spraying the plate with ninhydrin, which reacts with the secondary amine of DA to give a distinctive yellow colored product. The extraction, cleanup and TLC procedures are fast and simple, and do not require the use of expensive equipment. This method should prove useful for the routine screening of shellfish tissues in those laboratories not equipped with an LC system. It should also be useful as a chemical confirmation method for DA in samples tested positive by assay methods such as immunoassay.

Detection of domoic acid in northern anchovies and California sea lions associated with an unusual mortality event

The occurrence of an unusual mortality event involving California sea lions (Zalophus californianus) along the central California coast in May 1998 was recently reported. The potent neurotoxin domoic acid (DA), produced naturally by the diatom Pseudo-nitzschia australis and transmitted to the sea lions via planktivorous northern anchovies (Engraulis mordax), was identified as the probable causative agent. Details of DA analyses for anchovy tissues and sea lion feces are described. Domoic acid levels were estimated in anchovy samples by HPLC-UV, and in sea lion feces using the same method as well as a microplate receptor binding assay, with absolute confirmation by tandem mass spectrometry. The highest DA concentrations in anchovies occurred in the viscera (223 +/- 5 microg DA g(-1)), exceeding values in the body tissues by seven-fold and suggesting minimal bioaccumulation of DA in anchovy tissue. HPLC values for DA in sea lion fecal material (ranging from 152 to 136.5 microg DA g(-1)) required correction for interference from an unidentified compound. Inter-laboratory comparisons of HPLC data showed close quantitative agreement. Fecal DA activity determined using the receptor binding assay corresponded with HPLC values to within a factor of two. Finally, our detection of P. australis frustules, via scanning electron microscopy, in both anchovy viscera and fecal material from sea lions exhibiting seizures provides corroborating evidence that this toxic algal species was involved in this unusual sea lion mortality event.

Domoic Acid Attenuates the Adenosine-5'-Triphosphate-Induced Increase in

BACKGROUND: Although domoic acid (DA), a shellfish neurotoxin, carries a negative surface charge at physiological pH like that of adenosine-5'-triphosphate (ATP), very little is known about its cellular effects. In view of the potentially significant role of extracellular ATP as a signaling molecule for increasing the intracellular concentration of Ca(2+) ([Ca(2+)](i)), we examined the possibility that DA may interfere with this signal transduction mechanism in the myocardium. METHODS AND RESULTS: Cardiomyocytes were isolated from rat heart and loaded with Fura-2 to measure the [Ca(2+)](i). ATP produced a gradual rise in [Ca(2+)](i), reaching a peak level in 25-30 seconds and declining thereafter. DA did not affect the [Ca(2+)](i) in cardiomyocytes; however, it diminished the ATP-induced elevation in [Ca(2+)](i) in the concentration-dependent manner. Kainic acid, an analogue of DA, had a similar effect but at a 25-fold higher concentration, whereas glutamate and aspartate did not modify the action of ATP. Well-known inhibitors of L-type voltage-sensitive Ca(2+) channels, nifedipine and nicardipine, depressed the ATP-induced increase in [Ca(2+)](i), but DA did not produce additive effects with either of these agents. On the other hand, DA potentiated the KCl-induced increase in [Ca(2+)](i) in quiescent cardiomyocytes and augmented the nicardipine-sensitive Ca(2+) transients in electrically stimulated cardiomyocytes. CONCLUSIONS: These results suggest that DA may diminish the ATP-induced increase in [Ca(2+)](i) by inhibiting the ATP interaction with cardiomyocytes in a specific manner.

Aquatic biotoxins: design and implementation of seafood safety monitoring programs

Naturally occurring toxicants are usually odorless, tasteless, and generally undetectable by any simple chemical test. Various programs have been established that are effective in reducing risks associated with these toxicants in food. These programs include setting regulatory limits, monitoring susceptible commodities for toxin levels, and using decontamination procedures. Bioassays have been used traditionally to monitor suspect products. All traditional bioassays, however, have one common disadvantage, i.e., the lack of specificity for individual toxins. The lack of available reference standards for specific toxins has also hampered implementation of monitoring programs. Utilizing the knowledge gained with regulatory monitoring and decontamination programs for other toxins, e.g., aflatoxin, similar seafood safety programs can be developed for aquatic biotoxins that will reduce risks and hazards associated with the contaminant to practicable levels and help to preserve an adequate food supply. Research is needed in several areas identified in this article. International cooperation has an important role in achieving these essential elements. Global programs will help in the adequate management of risks associated with aquatic biotoxins. To have an effective monitoring program, it is necessary to define precisely the local needs for information in a short or long time range. It is necessary to have basic knowledge about the biological, chemical, and physical conditions as well as temporal and geographic variations within the region of interest (2). Regardless of the overall success of fish/shellfish toxin monitoring plans, emergencies will occur. Therefore, contingency plans should be developed so there will be no misunderstanding of what actions to take (148). In general, however, the structure of the program must be kept as simple as possible to facilitate fast and uncomplicated flow of information among the various organizations and individuals involved (2). Public health and safety requires the removal of any toxic shellfish from the market, within practicability, and closure of any suspect harvest area. It should be important to remember that economic value of the fish or shellfish resource is always secondary to public health and safety (148).

Effect of pH on domoic acid toxicity in mice

Domoic acid is a shellfish toxin which produces gastrointestinal distress, followed by neurological symptoms such as headache, confusion, disorientation and severe deficits in short-term memory. Domoic acid is an amino acid which contains three carboxylic groups, and one imino group, and its solubility, rate of absorption, and elimination would vary depending on the protonation of these groups at different pH's. We propose that domoic acid toxicity varies with pH of administered domoic acid solution. Domoic acid toxicity was measured in mice as the onset times for scratching behaviour, seizure activity, and death, after the intraperitoneal administration of domoic acid at different pH's. Results of the present study show that the scratching behaviour, seizure activity, and death, occurred at 12, 40, and 55 min, after intraperitoneal administration of domoic acid at pH 3.7. Apparently, the onset times for three types of behaviours were relatively long, and well separated from each other. Domoic acid toxicity was lowest at pH 3.7, and highest at pH 7.4, with intermediate toxicity at other pH's. The onset time of scratching behaviour was not influenced by pH of domoic acid solution at three different doses. In contrast, the onset times for seizure activity, and death were significantly affected by pH of domoic acid, toxicity being higher at pH 7.4 than at pH 3.7. The pH effect on domoic acid toxicity diminished as the dose of domoic acid was increased. In fact, at 14.5 mg/kg domoic acid toxicity was similar at both pH's of 3.7 and 7.4. It is concluded that in vivo toxicity of domoic acid varies depending on pH of the administered solution. The differential toxicity of domoic acid at different pH may be related to its solubility, rate of absorption, and elimination, depending on the degree of protonation of domoic acid molecule. Domoic acid toxicity would also vary depending on the age of animal, receptor sensitivity and density in different regions of brain.

Subchronic toxicity study of domoic acid in the rat

Male and female Sprague-Dawley rats were dosed by gavage for 64 days with 0, 0.1 or 5 mg/kg/day domoic acid. Treated animals showed no clinical abnormalities. Terminal values in haematology and clinical chemistry did not reveal differences between treated and control groups. Findings in histopathology and immunohistochemistry were unremarkable. The 24-hr urinary excretion rate for domoic acid determined at three time points was approximately 1.8% of the dose and remained unchanged during the study.

Salt clean-up procedure for the determination of domoic acid by HPLC

Domoic acid (DA) was first reported in mussels from Prince Edward Island, Canada, in 1987. It reappeared in anchovies and pelicans from Monterey Bay, California, in 1991. Later that year, domoic acid was found in razor clams and Dungeness crabs along the Washington and Oregon coasts. Since the initial outbreak, a variety of analytical methods for the detection of this neurotoxin have been developed. Here, we describe a modification to the solid phase extraction (SPE) clean-up step in Quilliam's HPLC-UV method (1991: NRCC No. 33001). The standard 10% acetonitrile (MeCN) wash and 0.5M ammonium citrate buffer (ACB) in 10% MeCN (pH = 4.5) eluting solution have been replaced with a 0.1M sodium chloride (NaCl) in 10% MeCN wash and a 0.5M NaCl in 10% MeCN eluting solution. This modification allows the analysis to work equally well on both clam and crab viscera and meat. Chromatograms of visceral samples no longer contain interfering or late eluting peaks; and all chromatograms are free of the large solvent peak tailing associated with the ACB eluent. The newly modified method allows for an improved and more versatile domoic acid analysis.

Renal clearance of domoic acid in the rat

The renal clearance (Clr) of the seafood toxin domoic acid (DA) was investigated in the rat. Following cannulation of the right femoral artery, the left femoral vein and the bladder of anaesthetized rats, a single bolus injection of either [3H]DA, [14C]p-aminohippuric acid (PAH) or [3H]inulin was administered through the venous cannula. Blood samples were taken from the arterial cannula at 1, 2, 10, 30, 50, 70, 90, 110 and 130 min following injection, and urine samples were collected at 20-min intervals starting from the time of bolus injection. Based on plasma concentration-time profiles, the total clearances (Clt) for DA, PAH and inulin were 9.12, 33.17 and 7.50 ml/min/kg body weight, respectively. The Clr calculated from urinary excretion rates were not significantly different from the Clt. Probenecid significantly reduced the Clr of PAH but did not affect that of DA. When DA was given at doses of 0.5 ng, 0.5 mg and 2.0 mg/kg body weight, the pharmacokinetic parameters Clt, Clr, elimination-rate constant and apparent volume of distribution at steady state were not statistically different between doses. The entire dose of 3H was recovered in the urine by 160 min after dosing, and analysis of urine samples by HPLC confirmed that the radiolabel (3H) was associated predominantly with the parent form of DA. The results of the present study demonstrate that DA is cleared from plasma primarily through the kidneys. DA clearance occurs primarily by renal glomerular filtration since its Clt is comparable with that of inulin, is less than that of PAH and is not affected by probenecid.

Purification of domoic acid from toxic blue mussels (Mytilus edulis) and phytoplankton

Domoic acid was the primary neurotoxin in blue mussel (Mytilus edulis) that caused poisoning in humans. Further research showed that the algae, Nitzschia pungens, was the source of this toxin. In this study, a method for the extraction and purification of domoic acid from contaminated mussels and phytoplankton was developed. Domoic acid was extracted from these sources by treatment with a mixture of chloroform and methanol (1:2, v/v). The resulting extract was subjected to ultrafiltration through a PM1 Millipore filter, followed by repeated high-performance liquid chromatography on a reversed-phase column. The purity and yield of domoic acid prepared by this method are compared with two previously described methods of extraction. The current method is relatively simple, rapid, and results in improved recovery with comparable purity of domoic acid.

Hippocampal damage produced by systemic injections of domoic acid in mice

The effect of systemic administration of domoic acid, a potent structural analogue of kainic acid, on the mouse hippocampus has been studied using light and electron microscopic techniques. Intraperitoneal injections of either domoic acid (4 mg/kg) or kainic acid (32 mg/kg) produced a series of behavioural changes including sedation, rigidity, stereotypy (scratching, head nodding), balance loss, and discrete or generalized convulsions. Both qualitative and quantitative histological analysis revealed similar but not identical patterns of neuronal damage in the hippocampal formation of domoic acid- and kainic acid-treated mice. With both toxins the most extensive damage was always observed in the CA3 region of the hippocampus, with lesser degrees of damage observed in other hippocampal regions (CA4 greater than CA1 greater than CA2 greater than dentate granule cells). In general, neuronal damage was more widespread following administration of kainic acid than domoic acid. In the CA3 region, however, the percentage of cells exhibiting damage was greater following domoic acid (82.1%) than kainic acid (58.8%) following systemic administration. No damage was found in the hippocampi of vehicle control-treated mice. Electron microscopy of the CA3 region following domoic acid revealed two subpopulations of damaged neurons: (1) swollen cells that exhibited vacuolization of their cytoplasm and (2) shrunken irregularly shaped electron-dense cells. Swollen processes of astroglial origin were observed surrounding electron-dense cells, and electron-dense processes were often found extending into the neuropil. These results suggest that although domoic acid and kainic acid produce similar changes in both open field behaviour and hippocampal neuropathology, responses to these toxins are not identical at equitoxic doses. Lesions in the domoic acid-treated mice are more selective for the CA3 hippocampal region than are those produced by kainic acid following systemic administration. Domoic acid may, therefore, be a better tool for studying certain aspects of excitatory amino acid neurotoxicity.