Search Results (29)

Exposure to toxigenic harmful algal blooms (HABs) can result in widely recognized acute poisoning in humans. The five most commonly recognized HAB-related illnesses are diarrhetic shellfish poisoning (DSP), paralytic shellfish poisoning (PSP), amnesic shellfish poisoning (ASP), neurotoxic shellfish poisoning (NSP), and ciguatera poisoning (CP). Despite being caused by exposure to various toxins or toxin analogs, these clinical syndromes share numerous similarities. Humans are exposed to these toxins mainly through the consumption of fish and shellfish, which serve as the main biological vectors. However, the risk of human diseases linked to toxigenic HABs is on the rise, corresponding to a dramatic increase in the occurrence, frequency, and intensity of toxigenic HABs in coastal regions worldwide. Although a growing body of studies have focused on the toxicological assessment of HAB-related species and their toxins on aquatic organisms, the organization of this information is lacking. Consequently, a comprehensive review of the adverse effects of HAB-associated species and their toxins on those organisms could deepen our understanding of the mechanisms behind their toxic effects, which is crucial to minimizing the risks of toxigenic HABs to human and public health. To this end, this paper summarizes the effects of the five most common HAB toxins on fish, shellfish, and humans and discusses the possible mechanisms. Full article

Harmful cyanobacterial blooms (HCBs) are of growing global concern due to their production of toxic compounds, which threaten ecosystems and human health. Saxitoxins (STXs), commonly known as paralytic shellfish poison, are a neurotoxic alkaloid produced by some cyanobacteria. Although many field studies indicate a widespread distribution of STX, it is understudied relative to other cyanotoxins such as microcystins (MCs). In this study, we assessed eleven U.S. urban lakes using qPCR, sxtA gene-targeting sequencing, and 16S rRNA gene sequencing to understand the spatio-temporal variations in cyanobacteria and their potential role in STX production. During the blooms, qPCR analysis confirmed the presence of the STX-encoding gene sxtA at all lakes. In particular, the abundance of the sxtA gene had a strong positive correlation with STX concentrations in Big 11 Lake in Kansas City, which was also the site with the highest quantified STX concentration. Sequencing analysis revealed that potential STX producers, such as Aphanizomenon, Dolichospermum, and Raphidiopsis, were present. Further analysis targeting amplicons of the sxtA gene identified that Aphanizomenon and/or Dolichospermum are the primary STX producer, showing a significant correlation with sxtA gene abundances and STX concentrations. In addition, Aphanizomenon was associated with environmental factors, such as conductivity, sulfate, and orthophosphate, whereas Dolichospermum was correlated with temperature and pH. Overall, the results herein enhance our understanding of the STX-producing cyanobacteria and aid in developing strategies to control HCBs. Full article

Brevetoxins (BTXs) constitute a family of lipid-soluble toxic cyclic polyethers mainly produced by Karenia brevis, which is the main vector for a foodborne syndrome known as neurotoxic shellfish poisoning (NSP) in humans. To prevent health risks associated with the consumption of contaminated shellfish in France, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) recommended assessing the effects of BTXs via an acute oral toxicity study in rodents. Here, we investigated the effect of a single oral administration in both male and female mice with several doses of BTX-3 (100 to 1,500 µg kg⁻¹ bw) during a 48 h observation period in order to provide toxicity data to be used as a starting point for establishing an acute oral reference dose (ARfD). We monitored biological parameters and observed symptomatology, revealing different effects of this toxin depending on the sex. Females were more sensitive than males to the impact of BTX-3 at the lowest doses on weight loss. For both males and females, BTX-3 induced a rapid, transient and dose-dependent decrease in body temperature, and a transient dose-dependent reduced muscle activity. Males were more sensitive to BTX-3 than females with more frequent observations of failures in the grip test, convulsive jaw movements, and tremors. BTX-3’s impacts on symptomatology were rapid, appearing during the 2 h after administration, and were transient, disappearing 24 h after administration. The highest dose of BTX-3 administered in this study, 1,500 µg kg⁻¹ bw, was more toxic to males, leading to the euthanasia of three out of five males only 4 h after administration. BTX-3 had no effect on water intake, and affected neither the plasma chemistry parameters nor the organs’ weight. We identified potential points of departure that could be used to establish an ARfD (decrease in body weight, body temperature, and muscle activity). Full article

The excitatory neurotoxin domoic acid (DA) consistently contaminates food webs in coastal regions around the world. Acute exposure to the toxin causes Amnesic Shellfish Poisoning, a potentially lethal syndrome of gastrointestinal- and seizure-related outcomes. Both advanced age and male sex have been suggested to contribute to interindividual DA susceptibility. To test this, we administered DA doses between 0.5 and 2.5 mg/kg body weight to female and male C57Bl/6 mice at adult (7–9-month-old) and aged (25–28-month-old) life stages and observed seizure-related activity for 90 min, at which point we euthanized the mice and collected serum, cortical, and kidney samples. We observed severe clonic–tonic convulsions in some aged individuals, but not in younger adults. We also saw an association between advanced age and the incidence of a moderately severe seizure-related outcome, hindlimb tremors, and between advanced age and overall symptom severity and persistence. Surprisingly, we additionally report that female mice, particularly aged female mice, demonstrated more severe neurotoxic symptoms following acute exposure to DA than males. Both age and sex patterns were reflected in tissue DA concentrations as well: aged mice and females had generally higher concentrations of DA in their tissues at 90 min post-exposure. This study contributes to the body of work that can inform intelligent, evidence-based public health protections for communities threatened by more frequent and extensive DA-producing algal blooms. Full article

Phytoplankton are photosynthetic microorganisms in aquatic environments that produce many bioactive substances. However, some of them are toxic to aquatic organisms via filter-feeding and are even poisonous to humans through the food chain. Human poisoning from these substances and their serious long-term consequences have resulted in several health threats, including cancer, skin disorders, and other diseases, which have been frequently documented. Seafood poisoning disorders triggered by phytoplankton toxins include paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), diarrheic shellfish poisoning (DSP), ciguatera fish poisoning (CFP), and azaspiracid shellfish poisoning (AZP). Accordingly, identifying harmful shellfish poisoning and toxin-producing species and their detrimental effects is urgently required. Although the harmful effects of these toxins are well documented, their possible modes of action are insufficiently understood in terms of clinical symptoms. In this review, we summarize the current state of knowledge regarding phytoplankton toxins and their detrimental consequences, including tumor-promoting activity. The structure, source, and clinical symptoms caused by these toxins, as well as their molecular mechanisms of action on voltage-gated ion channels, are briefly discussed. Moreover, the possible stress-associated reactive oxygen species (ROS)-related modes of action are summarized. Finally, we describe the toxic effects of phytoplankton toxins and discuss future research in the field of stress-associated ROS-related toxicity. Moreover, these toxins can also be used in different pharmacological prospects and can be established as a potent pharmacophore in the near future. Full article

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

The consumption of shellfish contaminated with brevetoxins, a family of ladder-frame polyether toxins formed during blooms of the marine dinoflagellate Karenia brevis, can cause neurotoxic poisoning, leading to gastroenteritis and neurotoxic effects. To rapidly monitor brevetoxin levels in oysters, we generated a broad-spectrum antibody against brevetoxin 2 (PbTx-2), 1 (PbTx-1), and 3 (PbTx-3) and developed a rapid indirect competitive enzyme-linked immunosorbent assay (icELISA). PbTx-2 was reacted with carboxymethoxylamine hemihydrochloride (CMO) to generate a PbTx-2-CMO hapten and reacted with succinic anhydride (HS) to generate the PbTx-2-HS hapten. These haptens were conjugated to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) to prepare immunogen and coating antigen reagents, respectively, using the active ester method. After immunization and cell fusion, a broad-spectrum monoclonal antibody (mAb) termed mAb 1D3 was prepared. The 50% inhibitory concentration (IC₅₀) values of the icELISA for PbTx-2, PbTx-1, and PbTx-3 were 60.71, 52.61, and 51.83 μg/kg, respectively. Based on the broad-spectrum mAb 1D3, an icELISA was developed to determine brevetoxin levels. Using this approach, the limit of detection (LOD) for brevetoxin was 124.22 μg/kg and recoveries ranged between 89.08% and 115.00%, with a coefficient of variation below 4.25% in oyster samples. These results suggest that our icELISA is a useful tool for the rapid monitoring of brevetoxins in oyster samples. Full article

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

Ciguatera fish poisoning (CFP) and neurotoxic shellfish poisoning syndromes are induced by the consumption of seafood contaminated by ciguatoxins and brevetoxins. Both toxins cause sensory symptoms such as paresthesia, cold dysesthesia and painful disorders. An intense pruritus, which may become chronic, occurs also in CFP. No curative treatment is available and the pathophysiology is not fully elucidated. Here we conducted single-cell calcium video-imaging experiments in sensory neurons from newborn rats to study in vitro the ability of Pacific-ciguatoxin-2 (P-CTX-2) and brevetoxin-1 (PbTx-1) to sensitize receptors and ion channels, (i.e., to increase the percentage of responding cells and/or the response amplitude to their pharmacological agonists). In addition, we studied the neurotrophin release in sensory neurons co-cultured with keratinocytes after exposure to P-CTX-2. Our results show that P-CTX-2 induced the sensitization of TRPA1, TRPV4, PAR2, MrgprC, MrgprA and TTX-r NaV channels in sensory neurons. P-CTX-2 increased the release of nerve growth factor and brain-derived neurotrophic factor in the co-culture supernatant, suggesting that those neurotrophins could contribute to the sensitization of the aforementioned receptors and channels. Our results suggest the potential role of sensitization of sensory receptors/ion channels in the induction or persistence of sensory disturbances in CFP syndrome. Full article

Okadaic acid (OA) is an important liposoluble shellfish toxin distributed worldwide, and is mainly responsible for diarrheic shellfish poisoning in human beings. It has a variety of toxicities, including cytotoxicity, embryonic toxicity, neurotoxicity, and even genotoxicity. However, there is no direct evidence of its developmental toxicity in human offspring. In this study, using the chicken (Gallus gallus) embryo as the animal model, we investigated the effects of OA exposure on neurogenesis and the incidence of neural tube defects (NTDs). We found that OA exposure could cause NTDs and inhibit the neuronal differentiation. Immunofluorescent staining of pHI3 and c-Caspase3 demonstrated that OA exposure could promote cell proliferation and inhibit cell apoptosis on the developing neural tube. Besides, the down-regulation of Nrf2 and increase in reactive oxygen species (ROS) content and superoxide dismutase (SOD) activity in the OA-exposed chicken embryos indicated that OA could result in oxidative stress in early chick embryos, which might enhance the risk of the subsequent NTDs. The inhibition of bone morphogenetic protein 4 (BMP4) and Sonic hedgehog (Shh) expression in the dorsal neural tube suggested that OA could also affect the formation of dorsolateral hinge points, which might ultimately hinder the closure of the neural tube. Transcriptome and qPCR analysis showed the expression of lipopolysaccharide-binding protein (LBP), transcription factor AP-1 (JUN), proto-oncogene protein c-fos (FOS), and C-C motif chemokine 4 (CCL4) in the Toll-like receptor signaling pathway was significantly increased in the OA-exposed embryos, suggesting that the NTDs induced by OA might be associated with the Toll-like receptor signaling pathway. Taken together, our findings could advance the understanding of the embryo–fetal developmental toxicity of OA on human gestation. Full article

Red tides involving Karenia brevis expose humans to brevetoxins (PbTxs). Oral exposition triggers neurotoxic shellfish poisoning, whereas inhalation induces a respiratory syndrome and sensory disturbances. No curative treatment is available and the pathophysiology is not fully elucidated. Protease-activated receptor 2 (PAR2), cathepsin S (Cat-S) and substance P (SP) release are crucial mediators of the sensory effects of ciguatoxins (CTXs) which are PbTx analogs. This work explored the role of PAR2 and Cat-S in PbTx-1-induced sensory effects and deciphered the signaling pathway involved. We performed calcium imaging, PAR2 immunolocalization and SP release experiments in monocultured sensory neurons or co-cultured with keratinocytes treated with PbTx-1 or P-CTX-2. We demonstrated that PbTx-1-induced calcium increase and SP release involved Cat-S, PAR2 and transient receptor potential vanilloid 4 (TRPV4). The PbTx-1-induced signaling pathway included protein kinase A (PKA) and TRPV4, which are compatible with the PAR2 biased signaling induced by Cat-S. Internalization of PAR2 and protein kinase C (PKC), inositol triphosphate receptor and TRPV4 activation evoked by PbTx-1 are compatible with the PAR2 canonical signaling. Our results suggest that PbTx-1-induced sensory disturbances involve the PAR2-TRPV4 pathway. We identified PAR2, Cat-S, PKA, and PKC that are involved in TRPV4 sensitization induced by PbTx-1 in sensory neurons. Full article

Chautauqua Lake, New York, is a two-basin lake with a deeper, cooler, and less nutrient-rich Northern Basin, and a warmer, shallower, nutrient-replete Southern Basin. The lake is populated by a complex mixture of cyanobacteria, with toxigenic strains that produce microcystins, anatoxins, and paralytic shellfish poisoning toxins (PSTs). Samples collected from 24 sites were analyzed for these three toxin classes over four years spanning 2014–2017. Concentrations of the three toxin groups varied widely both within and between years. During the study, the mean and median concentrations of microcystins, anatoxin-a, and PSTs were 91 and 4.0 μg/L, 0.62 and 0.33 μg/L, and 32 and 16 μg/L, respectively. Dihydro-anatoxin was only detected once in Chautauqua Lake, while homo-anatoxin was never detected. The Northern Basin had larger basin-wide higher biomass blooms with higher concentrations of toxins relative to the more eutrophied Southern Basin, however blooms in the North Basin were infrequent. Chlorophyll concentrations and toxins in the two basins were correlated with different sets of environmental and physical parameters, suggesting that implementing controls to reduce toxin loads may require applications focused on more than reductions in cyanobacterial bloom density (e.g., reduction of phosphorus inputs), and that lake limnological factors and morphology are important determinants in the selection of an appropriate management strategy. Chautauqua Lake is a drinking water source and is also heavily used for recreation. Drinking water from Chautauqua Lake is unlikely to be a significant source of exposure to cyanotoxins due to the location of the intakes in the deeper North Basin, where there were generally low concentrations of toxins in open water; however, toxin levels in many blooms exceeded the US Environmental Protection Agency’s recreational guidelines for exposure to cyanotoxins. Current cyanotoxin monitoring in Chautauqua Lake is focused on microcystins. However, the occurrence of blooms containing neurotoxic cyanotoxins in the absence of the microcystins indicates this restricted monitoring may not be sufficient when aiming to protect against exposure to cyanotoxins. The lake has a large number of tourist visitors; thus, special care should be taken to prevent recreational exposure within this group. Full article

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

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

Domoic acid (DA)-producing harmful algal blooms (HABs) have been present at unprecedented geographic extent and duration in recent years causing an increase in contamination of seafood by this common environmental neurotoxin. The toxin is responsible for the neurotoxic illness, amnesic shellfish poisoning (ASP), that is characterized by gastro-intestinal distress, seizures, memory loss, and death. Established seafood safety regulatory limits of 20 μg DA/g shellfish have been relatively successful at protecting human seafood consumers from short-term high-level exposures and episodes of acute ASP. Significant concerns, however, remain regarding the potential impact of repetitive low-level or chronic DA exposure for which there are no protections. Here, we report the novel discovery of a DA-specific antibody in the serum of chronically-exposed tribal shellfish harvesters from a region where DA is commonly detected at low levels in razor clams year-round. The toxin was also detected in tribal shellfish consumers’ urine samples confirming systemic DA exposure via consumption of legally-harvested razor clams. The presence of a DA-specific antibody in the serum of human shellfish consumers confirms long-term chronic DA exposure and may be useful as a diagnostic biomarker in a clinical setting. Adverse effects of chronic low-level DA exposure have been previously documented in laboratory animal studies and tribal razor clam consumers, underscoring the potential clinical impact of such a diagnostic biomarker for protecting human health. The discovery of this type of antibody response to chronic DA exposure has broader implications for other environmental neurotoxins of concern. Full article