Repeated Dietary Exposure to Low Levels of Domoic Acid and Problems with Everyday Memory: Research to Public Health Outreach

The health risks of marine biotoxins associated with high seafood consumption: Looking beyond the single dose, single outcome paradigm with a view towards addressing the needs of coastal Indigenous populations in British Columbia

People who consume high quantities of seafood are at a heightened risk for marine biotoxin exposure. Coastal Indigenous peoples may experience higher levels of risk than the general population due to their reliance on traditional marine foods. Most evidence on the health risks associated with biotoxins focus on a single exposure at one point in time. There is limited research on other types of exposures that may occur among those who regularly consume large quantities of seafood. The objective of this review is to assess what is known about the unique biotoxin exposure risks associated with the consumption patterns of many coastal Indigenous populations. These risks include [1]: repeated exposure to low doses of a single or multiple biotoxins [2]; repeated exposures to high doses of a single or multiple biotoxins; and [3] exposure to multiple biotoxins at a single point in time. We performed a literature search and collected 23 recent review articles on the human health effects of different biotoxins. Using a narrative framework synthesis approach, we collated what is known about the health effects of the exposure risks associated with the putative consumption patterns of coastal Indigenous populations. We found that the health effects of repeated low- or high-dose exposures and the chronic health effects of marine biotoxins are rarely studied or documented. There are gaps in our understanding of how risks differ by seafood species and preparation, cooking, and consumption practices. Together, these gaps contribute to a relatively poor understanding of how biotoxins impact the health of those who regularly consume large quantities of seafood. In the context of this uncertainty, we explore how known and potential risks associated with biotoxins can be mitigated, with special attention to coastal Indigenous populations routinely consuming seafood. Overall, we conclude that there is a need to move beyond the single-dose single-outcome model of exposure to better serve Indigenous communities and others who consume high quantities of seafood.

Precautions for seafood consumers: An updated review of toxicity, bioaccumulation, and rapid detection methods of marine biotoxins

Seafood products are globally consumed, and there is an increasing demand for the quality and safety of these products among consumers. Some seafoods are easily contaminated by marine biotoxins in natural environments or cultured farming processes. When humans ingest different toxins accumulated in seafood, they may exhibit different poisoning symptoms. According to the investigations, marine toxins produced by harmful algal blooms and various other marine organisms mainly accumulate in the body organs such as liver and digestive tract of seafood animals. Several regions around the world have reported incidents of seafood poisoning by biotoxins, posing a threat to human health. Thus, most countries have legislated to specify the permissible levels of these biotoxins in seafood. Therefore, it is necessary for seafood producers and suppliers to conduct necessary testing of toxins in seafood before and after harvesting to prohibit excessive toxins containing seafood from entering the market, which therefore can reduce the occurrence of seafood poisoning incidents. In recent years, some technologies which can quickly, conveniently, and sensitively detect biological toxins in seafood, have been developed and validated, these technologies have the potential to help seafood producers, suppliers and regulatory authorities. This article reviews the seafood toxins sources and types, mechanism of action and bioaccumulation of marine toxins, as well as legislation and rapid detection technologies for biotoxins in seafood for official and fishermen supervision.

What happens in the shadows - Influence of seasonal and non-seasonal dynamics on domoic acid monitoring in the Monterey Bay upwelling shadow

Domoic acid produced by toxigenic Pseudo-nitzschia species is the main toxin threat from harmful algal blooms in Monterey Bay and the larger California Current region on the West Coast of the United States. Toxin monitoring in Monterey Bay includes a long-running time series of weekly measurements of domoic acid from water samples, sentinel mussels, and solid phase adsorption toxin tracking (SPATT) at the Santa Cruz Municipal Wharf (SCW). The SCW sampling site is unusual because of its position in the Monterey Bay upwelling shadow in the north bay. The upwelling shadow circulation pattern has been previously characterized as a bloom incubator for dinoflagellates, but it has not yet been analyzed in the context of long-term monitoring methods. In data collected from the SCW from 2012 - 2020, domoic acid from water samples and sentinel mussels had a different temporal distribution than domoic acid from SPATT. Here we explore the discrepancy through a seasonal and non-seasonal analysis including physical oceanography of the region. Results show that domoic acid from water samples and sentinel mussels are related to seasonal upwelling and Pseudo-nitzschia blooms. Domoic acid monitored by SPATT, on the other hand, is correlated to anomalous upwelling and warmer than usual temperatures during the relaxation season. This work builds on previous analyses of the SCW time series and contributes to understanding of the circulation of dissolved toxin in the environment. Results lend rationale for the continuation of rigorous domoic acid monitoring in Monterey Bay and encourage stakeholders to consider local physical dynamics when interpreting toxin monitoring data.

Exploring marine toxins: comparative analysis of chemical reactivity properties and potential for drug discovery

Marine toxins, produced by various marine microorganisms, pose significant risks to both marine ecosystems and human health. Understanding their diverse structures and properties is crucial for effective mitigation and exploration of their potential as therapeutic agents. This study presents a comparative analysis of two hydrophilic and two lipophilic marine toxins, examining their reactivity properties and bioavailability scores. By investigating similarities among these structurally diverse toxins, valuable insights into their potential as precursors for novel drug development can be gained. The exploration of lipophilic and hydrophilic properties in drug design is essential due to their distinct implications on drug distribution, elimination, and target interaction. By elucidating shared molecular properties among toxins, this research aims to identify patterns and trends that may guide future drug discovery efforts and contribute to the field of molecular toxinology. The findings from this study have the potential to expand knowledge on toxins, facilitate a deeper understanding of their bioactivities, and unlock new therapeutic possibilities to address unmet biomedical needs. The results showcased similarities among the studied systems, while also highlighting the exceptional attributes of Domoic Acid (DA) in terms of its interaction capabilities and stability.

The Role of Nonhuman Primates in Neurotoxicology Research: Preclinical Models and Experimental Methods

Although noteworthy progress has been made in developing alternatives to animal testing, nonhuman primates still play a critical role in advancing biomedical research and will likely do so for many years. Core similarities between monkeys and humans in genetics, physiology, reproduction, development, and behavior make them excellent models for translational studies relevant to human health. This unit is designed to specifically address the role of nonhuman primates in neurotoxicology research and outlines the specialized assessments that can be used to measure exposure-related changes at the structural, chemical, cellular, molecular, and functional levels. © 2023 Wiley Periodicals LLC.

Progresses of the Influencing Factors and Detection Methods of Domoic Acid

Domoic acid (DA) is a neurotoxin mainly produced by Pseudo-nitzschia diatom, which belongs to the genera Rhomboida. It can combine with the receptors of glutamate of neurotransmitters, then affecting the normal nerve signal transmission of the organism and causing nervous system disorders. However, as a natural marine drug, DA can also be used for pest prevention and control. Although the distribution of DA in the world has already been reported in the previous reviews, the time and location of its first discovery and the specific information are not complete. Therefore, the review systematically summarizes the first reported situation of DA in various countries (including species, discovery time, and collection location). Furthermore, we update and analyze the factors affecting DA production, including phytoplankton species, growth stages, bacteria, nutrient availability, trace metals, and so on. These factors may indirectly affect the growth environment or directly affect the physiological activities of the cells, then affect the production of DA. Given that DA is widely distributed in the environment, we summarize the main technical methods for the determination of DA, such as bioassay, high-performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA), biosensor, and so on, as well as the advantages and disadvantages of each method used so far, which adds more new knowledge in the literature about DA until now. Finally, the DA research forecast and its industrial applications were prospected to prevent its harm and fully explore its potential value.

Residue Analysis and Assessment of the Risk of Dietary Exposure to Domoic Acid in Shellfish from the Coastal Areas of China

Harmful algal blooms in Chinese waters have caused serious domoic acid (DA) contamination in shellfish. Although shellfish are at particular risk of dietary exposure to DA, there have been no systematic DA risk assessments in Chinese coastal waters. A total of 451 shellfish samples were collected from March to November 2020. The presence of DA and four of its isomers were detected using liquid chromatography-tandem mass spectrometry. The spatial-temporal distribution of DA occurrence and its potential health risks were examined. DA was detected in 198 shellfish samples (43.90%), with a maximum level of 942.86 μg/kg. DA was recorded in all 14 shellfish species tested and Pacific oysters (Crassostrea gigas) showed the highest average DA concentration (82.36 μg/kg). The DA concentrations in shellfish showed distinct spatial-temporal variations, with significantly higher levels of occurrence in autumn than in summer and spring (p < 0.01), and particularly high occurrence in Guangdong and Fujian Provinces. The detection rates and maximum concentrations of the four DA isomers were low. While C. gigas from Guangdong Province in September showed the highest levels of DA contamination, the risk to human consumers was low. This study improves our understanding of the potential risk of shellfish exposure to DA-residues.

Emerging harmful algal blooms caused by distinct seasonal assemblages of a toxic diatom

Diatoms in the Pseudo-nitzschia genus produce the neurotoxin domoic acid. Domoic acid bioaccumulates in shellfish, causing illness in humans and marine animals upon ingestion. In 2017, high domoic acid levels in shellfish meat closed shellfish harvest in Narragansett Bay, Rhode Island for the first and only time in history, although abundant Pseudo-nitzschia have been observed for over 60 years. To investigate whether an environmental factor altered endemic Pseudo-nitzschia physiology or new domoic acid-producing strain(s) were introduced to Narragansett Bay, we conducted weekly sampling from 2017 to 2019 and compared closure samples. Plankton-associated domoic acid was quantified by LC-MS/MS and Pseudo-nitzschia spp. were identified using a taxonomically improved high-throughput rDNA sequencing approach. Comparison with environmental data revealed a detailed understanding of domoic acid dynamics and seasonal multi-species assemblages. Plankton-associated domoic acid was low throughout 2017-2019, but recurred in fall and early summer maxima. Fall domoic acid maxima contained known toxic species as well as a novel Pseudo-nitzschia genotype. Summer domoic acid maxima included fewer species but also known toxin producers. Most 2017 closure samples contained the particularly concerning toxic species, P. australis, which also appeared infrequently during 2017-2019. Recurring Pseudo-nitzschia assemblages were driven by seasonal temperature changes, and plankton-associated domoic acid correlated with low dissolved inorganic nitrogen. Thus, the Narragansett Bay closures were likely caused by both resident assemblages that become toxic depending on nutrient status as well as the episodic introductions of toxic species from oceanographic and climatic shifts.

Symptomatic and asymptomatic domoic acid exposure in zebrafish (Danio rerio) revealed distinct non-overlapping gene expression patterns in the brain

Domoic acid (DA) is a naturally produced neurotoxin synthesized by marine diatoms in the genus Pseudo-nitzschia. DA accumulates in filter-feeders such as shellfish, and can cause severe neurotoxicity when contaminated seafood is ingested, resulting in Amnesic Shellfish Poisoning (ASP) in humans. Overt clinical signs of neurotoxicity include seizures and disorientation. ASP is a significant public health concern, and though seafood regulations have effectively minimized the human risk of severe acute DA poisoning, the effects of exposure at asymptomatic levels are poorly understood. The objective of this study was to determine the effects of exposure to symptomatic and asymptomatic doses of DA on gene expression patterns in the zebrafish brain. We exposed adult zebrafish to either a symptomatic (1.1 ± 0.2 μg DA/g fish) or an asymptomatic (0.31 ± 0.03 µg DA/g fish) dose of DA by intracelomic injection and sampled at 24, 48 and 168 h post-injection. Transcriptional profiling was done using Agilent and Affymetrix microarrays. Our analysis revealed distinct, non-overlapping changes in gene expression between the two doses. We found that the majority of transcriptional changes were observed at 24 h post-injection with both doses. Interestingly, asymptomatic exposure produced more persistent transcriptional effects - in response to symptomatic dose exposure, we observed only one differentially expressed gene one week after exposure, compared to 26 in the asymptomatic dose at the same time (FDR <0.05). GO term analysis revealed that symptomatic DA exposure affected genes associated with peptidyl proline modification and retinoic acid metabolism. Asymptomatic exposure caused differential expression of genes that were associated with GO terms including circadian rhythms and visual system, and also the neuroactive ligand-receptor signaling KEGG pathway. Overall, these results suggest that transcriptional responses are specific to the DA dose and that asymptomatic exposure can cause long-term changes. Further studies are needed to characterize the potential downstream neurobehavioral impacts of DA exposure.

Prolonged, Low-Level Exposure to the Marine Toxin, Domoic Acid, and Measures of Neurotoxicity in Nonhuman Primates

BACKGROUND

The excitotoxic molecule, domoic acid (DA), is a marine algal toxin known to induce overt hippocampal neurotoxicity. Recent experimental and epidemiological studies suggest adverse neurological effects at exposure levels near the current regulatory limit (20 ppm, ∼0.075-0.1mg/kg). At these levels, cognitive effects occur in the absence of acute symptoms or evidence of neuronal death.

OBJECTIVES

This study aimed to identify adverse effects on the nervous system from prolonged, dietary DA exposure in adult, female Macaca fascicularis monkeys.

METHODS

Monkeys were orally exposed to 0, 0.075, and 0.15mg/kg per day for an average of 14 months. Clinical blood counts, chemistry, and cytokine levels were analyzed in the blood. In-life magnetic resonance (MR) imaging assessed volumetric and tractography differences in and between the hippocampus and thalamus. Histology of neurons and glia in the fornix, fimbria, internal capsule, thalamus, and hippocampus was evaluated. Hippocampal RNA sequencing was used to identify differentially expressed genes. Enrichment of gene networks for neuronal health, excitotoxicity, inflammation/glia, and myelin were assessed with Gene Set Enrichment Analysis.

RESULTS

Clinical blood counts, chemistry, and cytokine levels were not altered with DA exposure in nonhuman primates. Transcriptome analysis of the hippocampus yielded 748 differentially expressed genes (fold change≥1.5; p≤0.05), reflecting differences in a broad molecular profile of intermediate early genes (e.g., FOS, EGR) and genes related to myelin networks in DA animals. Between exposed and control animals, MR imaging showed comparable connectivity of the hippocampus and thalamus and histology showed no evidence of hypomyelination. Histological examination of the thalamus showed a larger microglia soma size and an extension of cell processes, but suggestions of a GFAP+astrocyte response showed no indication of astrocyte hypertrophy.

DISCUSSION

In the absence of overt hippocampal excitotoxicity, chronic exposure of Macaca fascicularis monkeys to environmentally relevant levels of DA suggested a subtle shift in the molecular profile of the hippocampus and the microglia phenotype in the thalamus that was possibly reflective of an adaptive response due to prolonged DA exposure. https://doi.org/10.1289/EHP10923.

Prevalence and distribution of domoic acid and cyclic imines in bivalve mollusks from Beibu Gulf, China

Beibu Gulf is an important shellfish aquaculture area in the northwest of the South China Sea, China. In this study, the toxin profile and spatial-temporal distribution of domoic acid (DA) and 10 lipophilic phycotoxins were systematically analyzed in the bivalve mollusks collected in Beibu Gulf from October 2018 to October 2020. Neurotoxin DA was first detected in the mollusks from the investigative regions with a prevalence of 17.7%, peaking at 401 µg kg^-1. Cyclic imines (CIs) including gymnodimine-A (GYM-A, 46.6%) and 13-desmethyl-spirolide-C (SPX1, 15.8%) predominated the lipophilic phycotoxins in shellfish, peaking at 10.1 µg kg^-1 and 19.6 µg kg^-1, respectively. Gymnodimine-A partially accompanied by SPX1 was detected in all batches of shellfish samples, suggesting that Alexandrium ostenfeldii and Karenia selliformis were possible sources of CIs-group toxins in Beibu Gulf. During the investigative period, relatively higher levels of DA occurred in shellfishes from March to August, while slightly higher contents of CIs in mollusks appeared in October and December. Spatial distribution of the targeted phycotoxins demonstrated that shellfishes tended to accumulate relatively higher contents of toxins in Lianzhou, Qinzhou and Tieshan bays.

Adaptogenic potential of ginsenosides against domoic acid-induced toxicity by regulating neuronal stress and kinate receptors: Ex vivo and in silico studies

This study is focused on potential effects of ginsenosides from Panax ginseng (PG) against amnesic shell fish poison, that is, domoic acid-induced excitotoxicity. Mice received PG at two different dosages by oral feeding for a period of 28 days (50 and 100 mg kg^-1 bwt.^-1 ). Domoic acid was injected to the mice to induce excitotoxicity (DA; 3 mg kg^-1  bwt.^-1 ) and piracetam-injected animals (PIR; 100 mg kg^-1  bwt.^-1 ) were treated as positive control. DA-induced cognitive impairment was reverted by PG supplementation, which was observed in Morris water maze and novel object task. Moreover, PG supplementation restored levels of GABA and antioxidant enzymes. Our results further elucidated ameliorative effects of PG supplementation on DA-induced changes in the expression of synaptic plasticity (BDNF), inflammation (NFkB), and apoptotic (Bcl2, Bax, and Caspase 3) markers. Hence, this study elucidates potential nootropic effects of ginsenosides from P. ginseng extract against DA-induced neuronal impairments via, modulation of behavioral and biochemical mechanisms involved in excitotoxicity, oxidative stress, neuro-inflammation, and apoptosis. PRACTICAL APPLICATIONS: This study highlights potential effects of ginsenosides from Panax ginseng against amnesic shell fish poison, that is, domoic acid-induced excitotoxicity for the first time. This study confirms that ginsenosides have the beneficial effects against amelioration of DA-induced toxicity. This study elucidates the potential nootropic effects of P. ginseng extract against DA-induced neuronal impairments via, modulation of synaptic plasticity markers and oxido-inflammatory responses leading to apoptosis. This study will be helpful in offering various mechanisms involved in pharmacological applications of P. ginseng in the management of DA-induced excitotoxicity.

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.

Long Term Memory Outcome of Repetitive, Low-Level Dietary Exposure to Domoic Acid in Native Americans

Domoic acid (DA) is a marine-based neurotoxin that, if ingested via tainted shellfish, is associated with Amnesic Shellfish Poisoning (ASP). These acute effects of elevated DA exposure in humans have been well described. In contrast, the long-term impacts of lower level, repetitive, presumably safe doses of DA (less than 20 ppm) are minimally known. Since Native Americans (NA) residing in coastal communities of the Pacific NW United States are particularly vulnerable to DA exposure, this study focuses on the long-term, 8-year memory outcome associated with their repeated dietary consumption of the neurotoxin. Measures of razor clam consumption, memory, clerical speed and accuracy, and depression were administered over eight years to 500 randomly selected adult NA men and women ages 18–64. Data were analyzed using GEE analyses taking into consideration the year of study, demographic factors, and instrumentation in examining the association between dietary exposure and outcomes. Findings indicated a significant but small decline in total recall memory within the context of otherwise stable clerical speed and accuracy and depression scores. There is reason to believe that a continuum of memory difficulties may be associated with DA exposure, rather than a unitary ASP syndrome.

Occurrence of domoic acid and cyclic imines in marine biota from Lebanon-Eastern Mediterranean Sea

Marine biotoxins are naturally existing chemicals produced by toxic algae and can accumulate in marine biota. When consumed with seafood, these phycotoxins can cause human intoxication with symptoms varying from barely-noticed illness to death depending on the type of toxin and its concentration. Recently, the occurrence of marine biotoxins has been given special attention in the Mediterranean as it increased in frequency and severity due to anthropogenic pressures and climate change. Up to our knowledge, no previous study reported the presence of lipophilic toxins (LTs) and cyclic imines (CIs) in marine biota in Lebanon. Hence, this study reports LTs and CIs in marine organisms: one gastropod (Phorcus turbinatus), two bivalves (Spondylus spinosus and Patella rustica complex) and one fish species (Siganus rivulatus), collected from various Lebanese coastal areas. The results show values below the limit of detection (LOD) for okadaic acid, dinophysistoxin-1 and 2, pectenotoxin-1 and 2, yessotoxins, azaspiracids and saxitoxins. The spiny oyster (S. spinosus) showed the highest levels of domoic acid (DA; 3.88 mg kg^-1), gymnodimine (GYM-B) and spirolide (SPX) (102.9 and 15.07 μg kg^-1, respectively) in congruence with the occurrence of high abundance of Pseudo-nitzchia spp., Gymnodinium spp., and Alexandrium spp. DA levels were below the European Union (EU) regulatory limit, but higher than the Lowest Observed Adverse Effect Level (0.9 μg g^-1) for neurotoxicity in humans and lower than the Acute Reference Dose (30 μg kg^-1 bw) both set by the European Food Safety Authority (EFSA, 2009). Based on these findings, it is unlikely that a health risk exists due to the exposure to these toxins through seafood consumption in Lebanon. Despite this fact, the chronic toxicity of DA, GYMs and SPXs remains unclear and the effect of the repetitive consumption of contaminated seafood needs to be more investigated.

Developmental Neurotoxicity of the Harmful Algal Bloom Toxin Domoic Acid: Cellular and Molecular Mechanisms Underlying Altered Behavior in the Zebrafish Model

BACKGROUND

Harmful algal blooms (HABs) produce potent neurotoxins that threaten human health, but current regulations may not be protective of sensitive populations. Early life exposure to low levels of the HAB toxin domoic acid (DomA) produces long-lasting behavioral deficits in rodent and primate models; however, the mechanisms involved are unknown. The zebrafish is a powerful in vivo vertebrate model system for exploring cellular processes during development and thus may help to elucidate mechanisms of DomA developmental neurotoxicity.

OBJECTIVES

We used the zebrafish model to investigate how low doses of DomA affect the developing nervous system, including windows of susceptibility to DomA exposure, structural and molecular changes in the nervous system, and the link to behavioral alterations.

METHODS

To identify potential windows of susceptibility, DomA (0.09-0.18 ng) was delivered to zebrafish through caudal vein microinjection during distinct periods in early neurodevelopment. Following exposure, structural and molecular targets were identified using live imaging of transgenic fish and RNA sequencing. To assess the functional consequences of exposures, we quantified startle behavior in response to acoustic/vibrational stimuli.

RESULTS

Larvae exposed to DomA at 2 d postfertilization (dpf), but not at 1 or 4 dpf, showed consistent deficits in startle behavior at 7 dpf, including lower responsiveness and altered kinematics. Similarly, myelination in the spinal cord was disorganized after exposure at 2 dpf but not 1 or 4 dpf. Time-lapse imaging revealed disruption of the initial stages of myelination. DomA exposure at 2 dpf down-regulated genes required for maintaining myelin structure and the axonal cytoskeleton.

DISCUSSION

These results in zebrafish reveal a developmental window of susceptibility to DomA-induced behavioral deficits and identify altered gene expression and disrupted myelin structure as possible mechanisms. The results establish a zebrafish model for investigating the mechanisms of developmental DomA toxicity, including effects with potential relevance to exposed sensitive human populations. https://doi.org/10.1289/EHP6652.

Power spectrum analysis of EEG in a translational nonhuman primate model after chronic exposure to low levels of the common marine neurotoxin, domoic acid

Domoic acid (DA), the focus of this research, is a marine algal neurotoxin and epileptogen produced by species in the genus Pseudo-nitzschia. DA is found in finfish and shellfish across the globe. The current regulatory limit for DA consumption (20 ppm in shellfish) was set to protect humans from acute toxic effects, but there is a growing body of evidence suggesting that regular consumption of DA contaminated seafood at or below the regulatory limit may lead to subtle neurological effects in adults. The present research uses a translational nonhuman primate model to assess neurophysiological changes after chronic exposure to DA near the regulatory limit. Sedated electroencephalography (EEG) was used in 20 healthy adult female Macaca fascicularis, orally administered 0.075 and 0.15 mg DA/kg/day for at least 10 months. Paired video and EEG recordings were cleaned and a Fast Fourier Transformation was applied to EEG recordings to assess power differences in frequency bands from 1-20 Hz. When DA exposed animals were compared to controls, power was significantly decreased in the delta band (1-4 Hz, p < 0.005) and significantly increased in the alpha band (5-8 Hz, p < 0.005), theta band (9-12 Hz, p < 0.01), and beta band (13-20 Hz, p < 0.05). The power differences were not dose dependent or related to the duration of DA exposure, or subtle clinical symptoms of DA exposure (intentional tremors). Alterations of power in these bands have been associated with a host of clinical symptoms, such as deficits in memory and neurodegenerative diseases, and ultimately provide new insight into the subclinical toxicity of chronic, low-dose DA exposure on the adult primate brain.

Dose-response assessment for impaired memory from chronic exposure to domoic acid among native American consumers of razor clams

Domoic acid (DA) is a marine neurotoxin that accumulates in filtering shellfish during harmful algal blooms. A health protection limit of 20 ppm DA in razor clams (RC) has been set based principally upon an episode of acute DA toxicity in humans that included Amnesic Shellfish Poisoning among survivors. The objective of this study was to determine the dose-response relationship between estimated DA exposure through RC consumption and memory loss in Washington state Native Americans from 2005 to 2015. Results from total learning recall (TLR) memory scores were compared before and after the highest DA exposures. A decrease in TLR was related to DA dose (p < 0.01) regardless whether the effect was assumed to be transient or lasting, and whether the dose was expressed as an average daily dose or an average dose per meal. Benchmark dose modeling identified BMDL₁₀ values of 167 ng/kg-day and 2740 ng/kg-meal assuming a transient effect, and 196 ng/kg-day and 2980 ng/kg-meal assuming no recovery of function occurs. These DA dose thresholds for a measurable memory function reduction observed in this study of clam consumers are well below the safe acute dose underpinning the current regulatory DA limit of 20 ppm (ca. 60 μg/kg).

Maternal-fetal disposition of domoic acid following repeated oral dosing during pregnancy in nonhuman primate

Domoic acid (DA) is a marine algal toxin that causes acute and chronic neurotoxicity in animals and humans. Prenatal exposure to DA has been associated with neuronal damage and cognitive and behavioral deficits in juvenile California sea lions, cynomolgus monkeys and rodents. Yet, the toxicokinetics (TK) of DA during pregnancy and the maternal-fetal disposition of DA have not been fully elucidated. In this study, we investigated the TK before, during, and after pregnancy and the maternal-fetal disposition of DA in 22 cynomolgus monkeys following daily oral doses of 0.075 or 0.15 mg/kg/day of DA. The AUC0-τ of DA was not changed while the renal clearance of DA was increased by 30-90% during and after pregnancy when compared to the pre-pregnancy values. DA was detected in the infant plasma and in the amniotic fluid at delivery. The infant plasma concentrations correlated positively with both the maternal plasma and the amniotic fluid concentrations. The paired infant-to-maternal plasma DA concentration ratios ranged from 0.3 to 0.6 and increased as a function of time which suggests placental efflux and longer apparent fetal half-life than the maternal half-life. The paired amniotic fluid-to-infant plasma DA concentration ratios ranged from 4.5 to 7.5 which indicates significant accumulation of DA in the amniotic fluid. A maternal-fetal TK model was developed to explore the processes that give the observed maternal-fetal disposition of DA. The final model suggests that placental transport and recirculation of DA between the fetus and amniotic fluid are major determining factors of the maternal-fetal TK of DA.

Discovery of a Potential Human Serum Biomarker for Chronic Seafood Toxin Exposure Using an SPR Biosensor

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.

Chronic, low-level oral exposure to marine toxin, domoic acid, alters whole brain morphometry in nonhuman primates

Domoic acid (DA) is an excitatory neurotoxin produced by marine algae and responsible for Amnesiac Shellfish Poisoning in humans. Current regulatory limits (˜0.075-0.1 mg/kg/day) protect against acute toxicity, but recent studies suggest that the chronic consumption of DA below the regulatory limit may produce subtle neurotoxicity in adults, including decrements in memory. As DA-algal blooms are increasing in both severity and frequency, we sought to better understand the effects of chronic DA exposure on reproductive and neurobehavioral endpoints in a preclinical nonhuman primate model. To this end, we initiated a long-term study using adult, female Macaca fascicularis monkeys exposed to daily, oral doses of 0.075 or 0.15 mg/kg of DA for a range of 321-381, and 346-554 days, respectively. This time period included a pre-pregnancy, pregnancy, and postpartum period. Throughout these times, trained data collectors observed intentional tremors in some exposed animals during biweekly clinical examinations. The present study explores the basis of this neurobehavioral finding with in vivo imaging techniques, including diffusion tensor magnetic resonance imaging and spectroscopy. Diffusion tensor analyses revealed that, while DA exposed macaques did not significantly differ from controls, increases in DA-related tremors were negatively correlated with fractional anisotropy, a measure of structural integrity, in the internal capsule, fornix, pons, and corpus callosum. Brain concentrations of lactate, a neurochemical closely linked with astrocytes, were also weakly, but positively associated with tremors. These findings are the first documented results suggesting that chronic oral exposure to DA at concentrations near the current human regulatory limit are related to structural and chemical changes in the adult primate brain.

Preclinical modeling of exposure to a global marine bio-contaminant: Effects of in utero Domoic acid exposure on neonatal behavior and infant memory

Domoic Acid (DA) is a naturally-occurring marine neurotoxin that is increasingly recognized as an important public health issue. Prenatal DA exposure occurs through the maternal consumption of contaminated shellfish/finfish. To better understand the fetal risks associated with DA, we initiated a longitudinal, preclinical study focused on the reproductive and developmental effects of chronic, low-dose oral DA exposure. To this end, 32 adult female Macaca fascicularis monkeys were orally dosed with 0, 0.075 or 0.15 mg/kg/day DA on a daily basis prior to breeding and throughout breeding and pregnancy. The doses included the proposed human Tolerable Daily Intake (TDI) (0.075 mg/kg/day) for DA. Adult females were bred to nonexposed males. To evaluate development during early infancy, offspring were administered a Neonatal Assessment modeled after the human Neonatal Behavior Assessment Scale and a series of Visual Recognition Memory problems using the novelty paradigm. Results indicated that prenatal DA exposure did not impact early survival reflexes or responsivity to the environment. Findings from the recognition memory assessment, given between 1 and 2 months of age, showed that exposed and control infants demonstrated robust novelty scores when test problems were relatively easy to solve. Performance was not diminished by the introduction of delay periods. However, when more difficult recognition problems were introduced, the looking behavior of the 0.15 mg/kg DA group was random and infants failed to show differential visual attention to novel test stimuli. This finding suggests subtle but significant impairment in recognition memory and demonstrates that chronic fetal exposure to DA may impact developing cognitive processes.

Are pelagic seabirds exposed to amnesic shellfish poisoning toxins?

Marine birds have been hypothesized to be underreported victims of harmful algal blooms (HABs). Toxic blooms of Pseudo-nitzschia spp., the primary amnesic toxin producer microalgae, domoic acid (DA) are known to cause massive mortalities of coastal seabirds and marine mammals around the world. However, these fatalities are only detected when birds die nearby the coastline and little is known about possible outbreaks of pelagic seabirds in oceanic areas. Here we aim to understand whether pelagic seabirds are exposed to amnesic shellfish poisoning (ASP) toxins. For this purpose, we tracked pelagic seabirds feeding on small epipelagic fish and squid, reported to be vectors of DA, which are obtained in high productivity zones where intense Pseudo-nitzschia blooms regularly occur. In particular, we tracked Cory's (Calonectris borealis) and Scopoli's (C. diomedea) shearwaters breeding in Gran Canaria (Canary Is.) and in Menorca (Balearic Is.) and feeding on the Canary Current region and the Catalonian coast, respectively. We sampled birds for blood at the recovery of the GPS (Global Positioning System) and analyzed it for DA determination by Liquid Chromatography coupled with Tandem Mass Spectrometry (LC-MS/MS). Among the 61 samples analyzed from Gran Canaria, and 87 from Menorca, 31 (50.8%) and 28 (32.2%) from each location presented detectable levels of DA ranging 1.0-10.6 ng mL^-1. This work reveals that DA can be detected at variable levels in the blood of ASP-asymptomatic shearwaters and suggests a chronic exposure of shearwaters to DA, highlighting the need for further studies on DA effects. These results are of high relevance due to the vulnerability of these marine birds, which populations are in continuous decline. Since global warming is expected to alter and increase the occurrence of HABs, marine toxins might become an additional stressor for seabirds and exacerbate the already precarious conservation status of many species.

Effects of oral domoic acid exposure on maternal reproduction and infant birth characteristics in a preclinical nonhuman primate model

Domoic Acid (DA) is a naturally-occurring excitotoxin, produced by marine algae, which can bioaccumulate in shellfish and finfish. The consumption of seafood contaminated with DA is associated with gastrointestinal illness that, in the case of high DA exposure, can evolve into a spectrum of responses ranging from agitation to hallucinations, memory loss, seizures and coma. Because algal blooms that produce DA are becoming more widespread and very little is known about the dangers of chronic, low-dose exposure, we initiated a preclinical study focused on the reproductive and developmental effects of DA in a nonhuman primate model. To this end, 32 adult female Macaca fascicularis monkeys were orally exposed to 0, 0.075 or 0.15 mg/kg/day DA on a daily basis, prior to and during pregnancy. Females were bred to non-exposed males and infants were evaluated at birth. Results from this study provided no evidence of changes in DA plasma concentrations with chronic exposure. DA exposure was not associated with reproductive toxicity or adverse changes in the physical characteristics of newborns. However, in an unanticipated finding, our clinical observations revealed the presence of subtle neurological effects in the form of intentional tremors in the exposed adult females. While females in both dose groups displayed increased tremoring, the effect was dose-dependent and observed at a higher rate in females exposed to 0.15 mg/kg/day. These results demonstrate that chronic, low-level exposure to DA is associated with injury to the adult CNS and suggest that current regulatory guidelines designed to protect human health may not be adequate for high-frequency shellfish consumers.

Biosynthesis of the neurotoxin domoic acid in a bloom-forming diatom

Oceanic harmful algal blooms of Pseudo-nitzschia diatoms produce the potent mammalian neurotoxin domoic acid (DA). Despite decades of research, the molecular basis for its biosynthesis is not known. By using growth conditions known to induce DA production in Pseudo-nitzschia multiseries, we implemented transcriptome sequencing in order to identify DA biosynthesis genes that colocalize in a genomic four-gene cluster. We biochemically investigated the recombinant DA biosynthetic enzymes and linked their mechanisms to the construction of DA's diagnostic pyrrolidine skeleton, establishing a model for DA biosynthesis. Knowledge of the genetic basis for toxin production provides an orthogonal approach to bloom monitoring and enables study of environmental factors that drive oceanic DA production.

Human Poisoning from Marine Toxins: Unknowns for Optimal Consumer Protection

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