Red tide (Ptychodiscus brevis) toxin aerosols: a review

Method performance verification for the combined detection and quantitation of the marine neurotoxins cyclic imines and brevetoxin shellfish metabolites in mussels (Mytilus edulis) and oysters (Crassostrea gigas) by UHPLC-MS/MS

A single laboratory method performance verification is reported for a rapid sensitive UHPLC-MS/MS method for the quantification of eight cyclic imine and two brevetoxin analogues in two bivalve shellfish matrices: mussel (Mytilus edulis) and Pacific oyster (Crassostrea gigas). Targeted cyclic imine analogues were from the spirolide, gymnodimine and pinnatoxin groups, namely 20-Me-SPX-C, 13-desMe-SPX-C, 13,19-didesMe-SPX-C, GYM-A, 12-Me-GYM, PnTx-E, PnTx-F and PnTx-G. Brevetoxin analogues consisted of the shellfish metabolites BTX-B5 and S-desoxy-BTX-B2. A rapid dispersive extraction was used as well as a fast six-minute UHPLC-MS/MS analysis. Mobile phase prepared using ammonium fluoride and methanol was optimised for both chromatographic separation and MS/MS response to suit all analytes. Method performance verification checks for both matrices were carried out. Matrix influence was acceptable for the majority of analogues with the MS response for all analogues being linear across an appropriate range of concentrations. In terms of limits of detection and quantitation the method was shown to be highly sensitive when compared with other methods. Acceptable recoveries were found with most analogues, with laboratory precision in terms of intra- and inter-batch precision deemed appropriate. The method was applied to environmental shellfish samples with results showing low concentrations of cyclic imines to be present. The method is fast and highly sensitive for the detection and quantification of all targeted analogues, in both mussel and oyster matrices. Consequently, the method has been shown to provide a useful tool for simultaneous monitoring for the presence or future emergence of these two toxin groups in shellfish.

Harmful Algal Bloom Toxins in Aerosol Generated from Inland Lake Water

Harmful algal blooms (HABs) caused by cyanobacteria in freshwater environments produce toxins (e.g., microcystin) that are harmful to human and animal health. HAB frequency and intensity are increasing with greater nutrient runoff and a warming climate. Lake spray aerosol (LSA) released from freshwater lakes has been identified on lakeshores and after transport inland, including from lakes with HABs, but little is known about the potential for HAB toxins to be incorporated into LSA. In this study, freshwater samples were collected from two lakes in Michigan: Mona Lake during a severe HAB with microcystin concentrations (>200 μg/L) well above the Environmental Protection Agency (EPA) recommended "do not drink" level (1.6 μg/L) and Muskegon Lake without a HAB (<1 μg/L microcystin). Microcystin toxins were identified in freshwater, as well as aerosol particles generated in the laboratory from Mona Lake water by liquid chromatography-tandem mass spectrometry (LC-MS/MS) at atmospheric concentrations up to 50 ± 20 ng/m³. Enrichment of hydrophobic microcystin congeners (e.g., microcystin-LR) was observed in aerosol particles relative to bulk freshwater, while enrichment of hydrophilic microcystin (e.g., microcystin-RR) was lower. As HABs increase in a warming climate, understanding and quantifying the emissions of toxins into the atmosphere is crucial for evaluating the health consequences of HABs.

Explosive exhalations by common bottlenose dolphins during Karenia brevis red tides

Harmful algal blooms (HABs) such as those produced by Karenia brevis have acute negative impacts on common bottlenose dolphins (Tursiops truncatus) in Florida coastal waters, frequently causing illness and death. However, much less is known about chronic, sub-acute effects on these important sentinel species. This study investigates whether bottlenose dolphin behavior in Sarasota Bay, Florida is influenced by the presence of severe red tide events, focusing on respiratory and other behaviors likely affected by abundant toxin aerosols produced during these blooms. Through focal animal behavioral follows, we observed free-ranging dolphin respiratory behavior, activity budgets, and movement patterns relative to K. brevis abundance in the study area. We compared behavior from dolphins observed during a 2005 K. brevis bloom to those observed during inter-bloom conditions where K. brevis was present at background concentrations. We found that the rate of “chuffing”, an explosive type of exhalation, was significantly greater in dolphins observed during the bloom. No apparent effect on respiratory rate, heading change rate or activity budgets was observed. We propose that this chuffing behavior is analogous to symptoms of respiratory irritation observed in humans exposed to such red tide events, and suggest that this may be a type of disturbance response. With an observed increase in both the frequency and severity of HABs, such disturbance responses may have large-scale chronic impacts to the health and fitness of bottlenose dolphins in regions where such HABs are common.

Occurrence of Karenia papilionacea (Dinophyceae) and its novel sister phylotype in Japanese coastal waters

Several species of the genus Karenia (Dinophyceae) form blooms and often cause the mortality of cultured and wild fish. In Japan, blooms caused by two species - namely Karenia mikimotoi and Karenia brevis - have been reported so far. On the basis of morphological and molecular-phylogenic examinations, the present investigation found Karenia papilionacea and its novel sister phylotype for the first time in the coastal waters of the various regions of Japan. Of 34 strains isolated from the coastal waters, 27 strains displayed the typical morphological characteristics of K. papilionacea and further showed consensus DNA sequences corresponding to those of the originally described K. papilionacea. The other 7 strains displayed the same morphological characteristics of K. papilionacea, but showed divergent DNA sequences, at a genetic distance of over 0.04 (Internal Transcribed Spacer regions) from those of the original phylotype of K. papilionacea. These divergent strains were characterized as a novel sister phylotype (phylotype-I) of K. papilionacea. In the coastal waters of Japan, K. papilionacea-like (K. papilionacea and/or its phylotype-I) formed blooms at 20.3-30.4°C and salinity 30.1-33.9. No K. brevis was identified in Japanese coastal waters during this study. These findings demonstrated that K. papilionacea occurs along the coasts of western Japan and possibly shares several coastal regions with K. mikimotoi and K. papilionacea phylotype-I. In order to assess the risks of Karenia blooms to aquaculture, it is essential that the growth physiology and ichthyotoxicity of K. papilionacea and its novel phylotype should be characterized.

Do airborne biogenic chemicals interact with the PI3K/Akt/mTOR cell signalling pathway to benefit human health and wellbeing in rural and coastal environments?

Living and taking recreation in rural and coastal environments promote health and wellbeing, although the causal factors involved are unclear. It has been proposed that such environments provide a counter to the stresses of everyday living, leading to enhanced mental and physical health. Living in natural environments will result in airborne exposure to a wide range of biogenic chemicals through inhalation and ingestion of airborne microbiota and particles. The "biogenics" hypothesis formulated here is that regular exposure to low concentrations of mixtures of natural compounds and toxins in natural environments confers pleiotropic health benefits by inhibiting the activities of interconnected cell signalling systems, particularly PI3K/Akt/mTORC1. When overactive, Akt and mTOR (mTORC1) can lead to many pathological processes including cancers, diabetes, inflammation, immunosuppression, and neurodegenerative diseases. There is a substantial body of evidence that many natural products (i.e., from bacteria, algae, fungi and higher plants) inhibit the activities of these protein kinases. Other mTOR-related interconnected metabolic control "switches" (e.g., PTEN & NF-κB), autophagy and other cytoprotective processes are also affected by natural products. The "biogenics" hypothesis formulated here is that regular intermittent exposure to a mixture of airborne biogenic compounds in natural environments confers pleiotropic health benefits by inhibiting activities of the highly interconnected PI3K/Akt/mTORC1 system. It is proposed that future experimental exposures to biogenic aerosols in animal models coupled with epidemiology, should target the activities of the various kinases in the PI3K/Akt/mTORC1 systems and related physiological processes for selected urban, rural and coastal populations in order to test this hypothesis.

Marine aerosol as a possible source for endotoxins in coastal areas

Marine aerosols, that are very common in the highly populated coastal cities and communities, may contain biological constituents. Some of this biological fraction of marine aerosols, such as cyanobacteria and plankton debris, may influence human health by inflammation and allergic reactions when inhaled. In this study we identify and compare sources for endotoxins sampled on filters in an on-shore and more-inland site. Filter analysis included endotoxin content, total bacteria, gram-negative bacteria and cyanobacteria genome concentrations as well as ion content in order to identify possible sources for the endotoxins. Satellite images of chlorophyll-a levels and back trajectory analysis were used to further study the cyanobacteria blooms in the sea, close to the trajectory of the sampled air. The highest endotoxin concentrations found in the shoreline site were during winter (3.23±0.17 EU/m(3)), together with the highest cyanobacteria genome (1065.5 genome/m(3)). The elevated endotoxin concentrations were significantly correlated with cyanobacterial levels scaled to the presence of marine aerosol (r=0.90), as well as to chlorophyll-a (r=0.96). Filters sampled further inland showed lower and non-significant correlation between endotoxin and cyanobacteria (r=0.70, P value=0.19), suggesting decrease in marine-originated endotoxin, with possible contributions from other sources of gram-negative non-cyanobacteria. We conclude that marine cyanobacteria may be a dominant contributor to elevated endotoxin levels in coastal areas.

Synthesis, modeling, and biological evaluation of analogues of the semisynthetic brevetoxin antagonist beta-naphthoyl-brevetoxin

Brevetoxins are neurotoxic compounds produced by the dinoflagellate Karenia brevis. Extensive blooms induce neurotoxic shellfish poisoning (NSP) and asthma-like symptoms in humans. beta-naphthoyl-brevetoxin, the first semisynthetic brevetoxin antagonist, has been defined as the lead compound in the investigation of the mechanisms of bronchoconstriction induced by inhaled brevetoxins and relaxation or reversal of those effects by selected derivatives. In pursuit of more potent and effective brevetoxin antagonists, a series of beta-naphthoyl-brevetoxin analogues have been synthesized. Activities were determined by competitive displacement of tritiated brevetoxin-3 from rat brain synaptosomes and by lung resistance measurements in sheep. Additionally, preliminary computational structural studies have been performed. All analogues bound to rat brain synaptosomes with affinities similar to beta-naphthoyl-brevetoxin but exhibited very different responses in sheep. The biological evaluations along with computational studies suggest that the brevetoxin binding site in rat brain synaptosome might be different from the ones in lung tissue and both steric and electrostatic factors contribute to the efficacy of brevetoxin antagonism.

Brevetoxin-induced phosphorylation of Pyk2 and Src in murine neocortical neurons involves distinct signaling pathways

Brevetoxins (PbTx-1 to PbTx-10) are potent lipid soluble polyether neurotoxins produced by the marine dinoflagellate Karenia brevis. Brevetoxins bind to site 5 of the alpha-subunit of voltage-gated sodium channels (VGSCs) and augment Na(+) influx. In neocortical neurons brevetoxins elevate intracellular Ca(2+) and augment NMDA receptor signaling. In this study, we explored the effects of PbTx-2 on Pyk2 and Src activation in neocortical neurons. We found that both Pyk2 and Src were activated following PbTx-2 exposure. PbTx-2-induced Pyk2 Tyr402 phosphorylation was dependent on elevation of Ca(2+) influx through NMDA receptors. Moreover, Pyk2 Tyr402 phosphorylation was also found to require PKC activation inasmuch as RO-31-8425 and GF 109203x both attenuated the response. In contrast, PbTx-2-induced Src Tyr416 phosphorylation involved a Gq-coupled receptor inasmuch as U73122, a specific PLC inhibitor, abolished the response. This Gq-coupled receptor appears to be mGluR 5. The PKCdelta inhibitor rottlerin abolished PbTx-2-induced Src activation demonstrating that this isoform of PKC is involved in the activation of Src by PbTx-2. Considered together these data suggest that although activation of neuronal Pyk2 and Src result from PbTx-2 stimulation of VGSC, engagement of these two non-receptor tyrosine kinases involves distinct signaling pathways.

Exacerbation of asthma by Florida "red tide" during an ocean sailing trip

A 36-year-old man with adult-onset nonallergic triad asthma developed acute bronchospasm and copious sputum production during an offshore sailing excursion on the Gulf Coast of Florida. Symptoms were linked to proximity to blooms of the marine dinoflagellate Karenia brevis (red tide) and heavy aerosolized brevetoxin exposure, and symptoms recurred during rechallenge. Patients with respiratory disease who are planning a visit to red tide-prone seaside areas should be cautioned to bring their pulmonary medications, and clinicians should be aware that reactive airway symptoms may be triggered by exposure to red tide.

Characterization of in vitro oxidative and conjugative metabolic pathways for brevetoxin (PbTx-2)

Brevetoxins are potent marine toxins produced by the dinoflagellate Karenia brevis, the causative organism of Florida red tides. An in vitro metabolism of PbTx-2 was performed using purified cDNA-expressed rat liver cytochrome P-450 (CYP) enzymes and freshly isolated rat hepatocytes. The metabolic activities of six CYP enzymes, CYP1A2, CYP2A2, CYP2C11, CYP2D1, CYP2E1, and CYP3A1, were examined by incubation with PbTx-2 for up to 4 h in the presence of a NADPH-generating system. Further identification of the metabolites produced by CYP1A2 and CYP3A1 was preformed using high performance liquid chromatography-mass spectrometry (LC/MS). Both CYP1A2 and CYP3A1 metabolized PbTx-2 to PbTx-3 (MH+: m/z 897), PbTx-9 (MH+: m/z 899), and a newly recorded diol brevetoxin-2 metabolite (MH+: m/z 929). CYP3A1 also produced a considerably higher amount of BTX-B5 (MH+: m/z 911). Subsequent incubation of PbTx-2 with rat hepatocytes produced additional phase 1 metabolites of MH+: m/z 911, 913, 915, 917, and 931, indicating a CYP-catalyzed epoxidation at H-ring (C27,C28-double bond) and a subsequent A-ring hydrolysis of PbTx-2 metabolic products. A conjugation metabolism was identified by the production of a glutathione-brevetoxin conjugate (MH+: m/z 1222) and a cysteine-brevetoxin conjugate (MH+: m/z 1018). Structures of the new metabolites are postulated, and a likely CYP-catalyzed metabolism pathway of PbTx-2 metabolism are discussed.

Characterization of rat liver microsomal and hepatocytal metabolites of brevetoxins by liquid chromatography–electrospray tandem mass spectrometry

Brevetoxins are natural neurotoxins that are produced by "red tide" algae. This class of compounds can cause neurotoxic shellfish poisoning and other health problems. Brevetoxin-2 is the most abundant among the nine brevetoxins that have been characterized, whereas brevetoxin-1 is the most toxic. In this study, brevetoxin-1 and brevetoxin-2 were incubated with rat liver hepatocytes and rat liver microsomes, respectively. After clean-up steps were taken to remove the proteins, samples were analyzed by liquid chromatography (LC) coupled with electrospray mass spectrometry (LC-MS). After incubation of brevetoxin-1, two metabolites were found: brevetoxin-1-M1 (molecular weight = 900 Da), and brevetoxin-1-M2 (molecular weight = 884 Da). The increase in molecular weight combined with evidence from tandem mass spectrometry showing an increased tendency for loss of water molecules, along with considerations of established precedents for chemical transformations led to the conclusion that brevetoxin-1-M1 was formed by converting one double bond in the E or F ring of brevetoxin-1 into a diol. The second metabolite (brevetoxin-1-M2) is proposed to be a hydrolysis product of brevetoxin-1 involving opening of the lactone ring with the addition of a water molecule. The incubation study of the other starting compound, brevetoxin-2, found two metabolites in the LC-ES-MS selected ion chromatogram. Brevetoxin-2-M1 (molecular weight = 912 Da) gave a large [M-H]- peak at m/z 911, and its product ion mass spectrum allowed the deduction that this metabolite was the hydrolysis product of brevetoxin-2 involving conversion of the lactone to a carboxylic acid and an alcohol. The second metabolite (brevetoxin-2-M2, molecular weight = 896 Da) was deduced to have the same structure as that of brevetoxin-3 based on identical chromatographic retention times and similar mass spectra as those obtained for a brevetoxin-3 standard.

Uptake and elimination of brevetoxin in blood of striped mullet (Mugil cephalus) after aqueous exposure to Karenia brevis

There is a critical need to simply and reliably monitor brevetoxins routinely in the blood of humans and aquatic animals. We used striped mullet as laboratory test animals to better define the uptake and elimination kinetics of brevetoxin during an aqueous exposure to the brevetoxin-producing dinoflagellate Karenia brevis. Striped mullet were first exposed to sublethal densities of K. brevis (approximately 250,000 cells/L) for 1, 4, 8, 12, and 24 hr. No mortality was observed in the aquaria, and at each time point blood samples were taken and applied to blood collection cards for brevetoxin analysis using radioimmunoassay (RIA). The RIA indicated that blood levels of brevetoxin (PbTx-3) increased to values significantly different from that of the controls at all five time points during exposure (p < 0.05). Striped mullet were then exposed to a K. brevis culture with a known brevetoxin concentration of 0.5 ng/mL. Even after exposures at a low brevetoxin concentration, RIA was able to detect 2.25 +/- 0.62 ng/mL PbTx-3 equivalents in the blood of the mullet at 8 hr of exposure. When exposed to higher brevetoxin concentrations (3.5 and 5.4 ng/mL), blood brevetoxin increased to peak levels at 12 hr and then reached equilibrium after 24 hr in the continued presence of K. brevis. During this time of equilibrium, the mullet maintained brevetoxins with a blood:water coefficient of 2.2. To define the elimination of brevetoxin, striped mullet were next exposed for 8-10 hr and then transferred to fresh seawater containing no K. brevis for up to 116 hr. Blood brevetoxin levels remained elevated and decreased only by 50% 116 hr after transfer. The rate of elimination fit best to a two-phase exponential decay with a biologic half-life of 12 and 266 hr. This study, using RIA in conjunction with blood collection cards, demonstrates an effective means to monitor blood brevetoxin levels in finfish and provides a foundation to characterize biologically relevant levels of brevetoxin in other species impacted by red tide events.

Brevetoxin augments NMDA receptor signaling in murine neocortical neurons

Brevetoxins (PbTx) are potent allosteric enhancers of voltage-gated sodium channel (VGSC) function and are associated with periodic "red tide" blooms. These neurotoxins produce neuronal injury and death in cerebellar granule cells (CGC) following acute exposure. In murine neocortical neurons, brevetoxin induces Ca(2+) influx that is mediated through both glutamatergic and non-glutamatergic pathways. Inasmuch as Src kinase is capable of upregulating the NMDA subtype of glutamate receptors, we determined whether Src kinase participated in PbTx-2-induced Ca(2+) influx. Inhibition of Src kinase blocked PbTx-2-induced Ca(2+) influx. PbTx-2 treatment moreover increased tyrosine phosphorylation of the NR2B subunit. A rise in intracellular [Na(+)] and phosphorylation of NMDA receptors by Src kinase is known to increase NMDA receptor activity. We therefore explored the influence of brevetoxin on NMDA receptor function. We found that PbTx-2 augments NMDA receptor-mediated Ca(2+) influx in both spontaneously oscillating mature neurons and in non-oscillatory immature neurons. PbTx-2 also enhanced the effect of bath-applied NMDA on extracellular signal-regulated kinase 2 (ERK2) activation. These results suggest that brevetoxin augments NMDA receptor signaling in neocortical neurons, and this upregulation may be mediated by coincidence of an elevation in intracellular [Na(+)] and Src kinase activation.

Brevenal is a natural inhibitor of brevetoxin action in sodium channel receptor binding assays

1. Florida red tides produce profound neurotoxicity that is evidenced by massive fish kills, neurotoxic shellfish poisoning, and respiratory distress. Red tides vary in potency, potency that is not totally governed by toxin concentration. The purpose of the study was to understand the variable potency of red tides by evaluating the potential for other natural pharmacological agents which could modulate or otherwise reduce the potency of these lethal environmental events. 2. A synaptosome binding preparation with 3-fold higher specific brevetoxin binding was developed to detect small changes in toxin binding in the presence of potential antagonists. Rodent brain labeled in vitro with tritiated brevetoxin shows high specific binding in the cerebellum as evidenced by autoradiography. Synaptosome binding assays employing cerebellum-derived synaptosomes illustrate 3-fold increased specific binding. 3. A new polyether natural product from Florida's red tide dinoflagellate Karenia brevis, has been isolated and characterized. Brevenal, as the nontoxic natural product is known, competes with tritiated brevetoxin for site 5 associated with the voltage-sensitive sodium channel (VSSC). Brevenal displacement of specific brevetoxin binding is purely competitive in nature. 4. Brevenal, obtained from either laboratory cultures or field collections during a red tide, protects fish from the neurotoxic effects of brevetoxin exposure. 5. Brevenal may serve as a model compound for the development of therapeutics to prevent or reverse intoxication in red tide exposures.

Brevetoxin activation of voltage-gated sodium channels regulates Ca dynamics and ERK1/2 phosphorylation in murine neocortical neurons

Voltage-gated sodium channels (VGSC) are involved in the generation of action potentials in neurons. Brevetoxins (PbTx) are potent allosteric enhancers of VGSC function and are associated with the periodic 'red tide' blooms. Using PbTx-2 as a probe, we have characterized the effects of activation of VGSC on Ca(2+) dynamics and extracellular signal-regulated kinases 1/2 (ERK1/2) signaling in neocortical neurons. Neocortical neurons exhibit synchronized spontaneous Ca(2+) oscillations, which are mediated by glutamatergic signaling. PbTx-2 (100 nm) increased the amplitude and reduced the frequency of basal Ca(2+) oscillations. This modulatory effect on Ca(2+) oscillations produced a sustained rise in ERK1/2 activation. At 300 nm, PbTx-2 disrupted oscillatory activity leading to a sustained increase in intracellular Ca(2+) ([Ca(2+)](i)) and induced a biphasic, activation followed by dephosphorylation, regulation of ERK1/2. PbTx-2-induced ERK1/2 activation was Ca(2+) dependent and was mediated by Ca(2+) entry through manifold routes. PbTx-2 treatment also increased cAMP responsive element binding protein (CREB) phosphorylation and increased gene expression of brain-derived neurotrophic factor (BDNF). These findings indicate that brevetoxins, by influencing the activation of key signaling proteins, can alter physiologic events involved in survival in neocortical neurons, as well as forms of synaptic plasticity associated with development and learning.

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.

A rapid assay for the brevetoxin group of sodium channel activators based on fluorescence monitoring of synaptoneurosomal membrane potential

A functional pharmacologically-based assay for the brevetoxin group of sodium channel activators was developed using synaptoneurosomes isolated from the brains of CD1 mice. The assay can detect the depolarizing effect of brevetoxin congeners PbTx-2 and PbTx-3 as enhancements of the veratridine-dependent increase in fluorescence of the voltage-sensitive fluorescent probe rhodamine 6G. The assay is relatively rapid and can detect brevetoxin activity in the nanomolar range. The synaptoneurosomal assay has been used to analyse mussel tissue extracts spiked with PbTx-2, and composite toxicity, expressed as PbTx-3 equivalents in extracts of oysters naturally exposed to brevetoxins. In this latter context, the synaptoneurosomal technique was shown to compare favorably with the cytotoxicity assay, the receptor binding assay and HPLC/MS. Our results support the concept that this membrane potential assay detects brevetoxins based on their interaction with sodium channels.

Therapy and prophylaxis of inhaled biological toxins

This review highlights the current lack of therapeutic and prophylactic treatments for use against inhaled biological toxins, especially those considered as potential biological warfare (BW) or terrorist threats. Although vaccine development remains a priority, the use of rapidly deployable adjunctive therapeutic or prophylactic drugs could be life-saving in severe cases of intoxication or where vaccination has not been possible or immunity not established. The current lack of such drugs is due to many factors. Thus, methods involving molecular modelling are limited by the extent to which the cellular receptor sites and mode of action and structure of a toxin need to be known. There is also our general lack of knowledge of what effect individual toxins will have when inhaled into the lungs - whether and to what extent the action will be cell specific and cytotoxic or rather an acute inflammatory response requiring the use of immunomodulators. Possible sources of specific high-affinity toxin antagonists being investigated include monoclonal antibodies, selected oligonucleotides (aptamers) and derivatized dendritic polymers (dendrimers). The initial selection of suitable agents of these kinds can be made using cytotoxicity assays involving cultured normal human lung cells and a range of suitable indicators. The possibility that a mixture of selected antibody, aptamer or dendrimer-based materials for one or more toxins could be delivered simultaneously as injections or as inhaled aerosol sprays should be investigated.

Brevetoxin derivatives act as partial agonists at neurotoxin site 5 on the voltage-gated Na+ channel

Brevetoxins (PbTx-1 to PbTx-10) are potent lipid-soluble polyether neurotoxins produced by the marine dinoflagellate Karina brevis, an organism associated with 'red tide' blooms in the Gulf of Mexico. Ingestion of shellfish contaminated with K. brevis produces neurotoxic shellfish poisoning (NSP) in humans. NSP symptoms emanate from brevetoxin activation of neurotoxin site 5 on voltage-gated sodium channels (VGSC) [Toxicon 20 (1982) 457]. In primary cultures of rat cerebellar granule neurons (CGN), brevetoxins produce acute neuronal injury and death. The ability of a series of naturally occurring and synthetic brevetoxins to trigger Ca(2+) influx in CGN was explored in the present study. Intracellular Ca(2+) concentration was monitored in fluo-3-loaded CGN using a fluorescent laser imaging plate reader. The naturally occurring derivatives PbTx-1, PbTx-2 and PbTx-3 all produced a rapid and concentration-dependent increase in cytosolic [Ca(2+)]. The maximum response to PbTx-1 was approximately two-fold greater than that of either PbTx-2 or PbTx-3. Two synthetic derivatives of PbTx-3, alpha-naphthoyl-PbTx-3 and beta-naphthoyl-PbTx-3, were also tested. Both alpha- and beta-naphthoyl-PbTx-3 stimulated a rapid and concentration-dependent Ca(2+) influx that was, however, less efficacious than that of PbTx-3. These data indicate that, analogous to neurotoxin site 2 ligands, activators of neurotoxin site 5 display a range of efficacies, with PbTx-1 being a full agonist and other derivatives acting as partial agonists.

Monitoring brevetoxins during a Gymnodinium breve red tide: comparison of sodium channel specific cytotoxicity assay and mouse bioassay for determination of neurotoxic shellfish toxins in shellfish extracts

In October of 1996, a Gymnodinium breve bloom occurred in shellfish harvesting waters of Alabama, Mississippi and Louisiana, Gulf of Mexico, USA. Bloom densities reached 5.6x10(5) cells liter(-1) and bloom residence at shellfish sampling stations ranged from 3 to 28 days. Brevetoxin-2 dominated G. breve toxin profiles in bloom seawater extracts. Shellfish toxicity, assessed by mouse bioassay, exceeded the guidance level for up to 75 days after the bloom had dissipated. Cytotoxicity assays and mouse bioassays showed similar temporal patterns of shellfish toxicity, but the two methods differed in estimations of brevetoxin-3 equivalent toxicity by a factor of 93 to 1. LC-ESI-MS showed the temporal patterns in shellfish toxicity reflected metabolism of G. breve toxins. The molecular ions m/z 1004, 1017 and 1033 dominated LC-ESI-MS spectra of toxic chromatographic fractions from the extracts and were identified as brevetoxin metabolites on the basis of LC-APCI-MS-MS. The discrepancy between cytotoxicity and mouse bioassay estimates of brevetoxin-3 equivalent toxicity resulted from the difference in extraction efficiency of solvents used in the respective methods and the relative sensitivity of the assays to toxin metabolite mixtures present in the extracts. The normalized cytotoxicity assay showed 75% agreement with mouse bioassay positive test samples and 64% agreement with mouse bioassay negative test samples. Published in 1999 by John Wiley & Sons, Ltd.

Brevetoxin-induced autocrine excitotoxicity is associated with manifold routes of Ca2+ influx

Real-time alterations in intracellular Ca2+ ([Ca2+]i) were monitored in fluo-3-loaded cerebellar granule neurons (CGNs) exposed to the brevetoxin PbTx-1. [Ca2+]i was measured using a fluorescent plate reader (FLIPR), which measures simultaneously the mean intracellular Ca2+ change in a population of cultured cells in each well of a 96-well plate. PbTx-1 produced rapid and concentration-dependent increases in neuronal [Ca2+]i with a potency nearly identical to that determined previously for PbTx-1-induced neurotoxicity. The NMDA receptor antagonists MK-801, dextrorphan, and D(-)-2-amino-5-phosphonopentanoic acid, and tetanus toxin, an inhibitor of Ca2+-dependent exocytotic neurotransmitter release, effected significant reductions in both the integrated fluo-3 fluorescence response and excitatory amino acid release and protected CGNs against PbTx-1 neurotoxicity. The L-type Ca2+ channel antagonist nifedipine produced a modest reduction in the fluo-3 response but reduced substantially the plateau phase of the PbTx-1 increment in [Ca2+]i when combined with MK-801. When nifedipine and MK-801 were combined with the Na+/Ca2+ exchanger (reversed mode) inhibitor KB-R7943, the PbTx-1 increment in [Ca2+]i was nearly completely attenuated. These data show that Ca2+ entry into PbTx-1-exposed CGNs occurs through three primary routes: NMDA receptor ion channels, L-type Ca2+ channels, and reversal of the Na+/Ca2+ exchanger. There was a close correlation between reduction of the integrated fluo-3 fluorescence response and the level of neuroprotection afforded by blockers of each Ca2+ entry pathway; however, simultaneous blockade of L-type Ca2+ channels and the Na+/Ca2+ exchanger, although reducing the integrated [Ca2+]i response to a level below that provided by NMDA receptor blockade alone, failed to completely attenuate PbTx-1 neurotoxicity. This finding suggests that in addition to total [Ca2+]i load, neuronal vulnerability is governed principally by the NMDA receptor Ca2+ influx pathway.

Solution reactivity of brevetoxins as monitored by electrospray ionization mass spectrometry and implications for detoxification

The reactivities of brevetoxin compounds in acid and base and under oxidizing conditions were studied using electrospray ionization mass spectrometry (ESI-MS) to monitor reaction products. Brevetoxins are determined to be unstable in acidic and basic solutions. Under acidic conditions, brevetoxins containing an aldehyde functional group in the terminal "tail" side chain are easily converted to acetal structures, while "head" side lactone ring opening proceeds more slowly. Measurement of reaction rate constants indicates the following order of reactivity under acidic conditions: Btx-1 > Btx-2 > Btx-9. Under basic conditions, hydroxide ion attack at the head portion leads to lactone ring opening. Base hydrolysis (0.01 N NaOH in 50:50 methanol/water) goes to completion in 120 min for Btx-2 and Btx-9, but Btx-1 did not react to completion. Both acid and base hydrolyses can lead to reversible lactone ring opening, but base hydrolysis proceeds faster than acid hydrolysis under comparable conditions. Acid treatment is not an effective method for detoxifying brevetoxins. Base treatment can open the lactone ring (type B brevetoxins proceed faster than type A brevetoxins), leading to a product that is reportedly nontoxic, but the reaction is reversible. Brevetoxins are shown to be readily oxidized by permanganate in an irreversible and relatively fast reaction, likely through addition to double bonds followed by bond cleavage, suggesting that it is a viable method for detoxification.

Methods for in vitro skin absorption studies of a lipophilic toxin produced by red tide

The penetration and distribution of [3H]PbTx-3 into pig skin was determined using in vivo and in vitro methods. The dose used in each topical study was 0.3-0.4 micrograms/cm2 skin, with dimethylsulfoxide as the vehicle. In the in vivo study, mean cutaneous absorption after 48 h (expressed as percentage of the dose) was 11.5% (n = 3). In the in vitro study, mean cutaneous absorption after 48 h was 1.6% (n = 12), when based on accumulation of radioactivity in receptor fluid, or 9.9% when based on receptor fluid and dermis. [3H]PbTx-3 readily penetrated through the epidermis into the dermis, reaching maximal dermal accumulation at 4 h (9.1% in vivo and 18% in vitro). At 24 h, the amount in the dermis decreased to 2.3% and 15% in vivo and in vitro, respectively and at 48 h the amount in the dermis decreased to 8.2% in vitro. These results demonstrate the important role of the dermis as a reservoir for a lipophilic compound in both in vivo and in vitro percutaneous absorption studies.

Respiratory effects of brevetoxin and saxitoxin in awake guinea pigs

Ptychodiscus brevis toxin (brevetoxin) is associated with 'Florida red tide' and cause neurotoxic shellfish poisoning. Saxitoxin is the agent of paralytic shellfish poisoning. Clinical reports of human intoxication suggest that both toxins affect the respiratory system. The toxins were administered by slow intravenous infusion. The effects of the toxins on respiratory function of awake guinea pigs in a pressure plethysmograph were studied. Both toxins caused lactic acidosis of unknown etiology, which was compensated for by increased minute volume with brevetoxin (PbTx-3)- but not with saxitoxin-intoxicated animals. In general, brevetoxin increased ventilation, before respiratory failure, while saxitoxin had a depressive effect on ventilation. Airways resistance was not increased, nor was dynamic compliance decreased during intoxication, although the data suggest that respiratory system failure was the primary cause of death. The responses seen in these experiments are consistent with the dissimilar molecular actions of these toxins.