Targets and effects of yessotoxin, okadaic acid and palytoxin: a differential review

Effects of the toxic dinoflagellate Protoceratium reticulatum and its yessotoxins on the survival and feed ingestion of Argopecten purpuratus veliger larvae

The effects of yessotoxins (YTXs) produced by the dinoflagellate Protoceratium reticulatum in the early stages of bivalves have not been studied in detail. The present study evaluates the effects of P. reticulatum and YTXs on the survival and feed ingestion of veliger larvae of Argopecten purpuratus. Larvae were 96 h-exposed to 500, 1000 and 2000 P. reticulatum cells mL-1, and their equivalent YTX extract was prepared in methanol. Results show a survival mean of 82 % at the highest density of dinoflagellate, and 38 % for larvae with the highest amount of YTX extract. Feed ingestion is reduced in the dinoflagellate exposure treatments as a function of cell density. Therefore, the effect of YTXs on A. purpuratus represents a new and important area of study for investigations into the deleterious effects of these toxins in the early stages of the life cycle of this and, potentially, other bivalves.

Cascade-Enhanced Lateral Flow Immunoassay for Sensitive Detection of Okadaic Acid in Seawater, Fish, and Seafood

In this investigation, a new approach for developing a sensitive lateral flow immunoassay (LFIA) was proposed for the detection of the hazardous marine toxin okadaic acid (OA). It is based on the indirect format with anti-species antibodies labeled by gold nanoparticles (AuNPs) and cascade signal amplification. The latter is performed by first passing a mixture of anti-OA antibodies and a tested sample along the immunochromatographic test strip and then performing several cycles of the interaction of anti-species antibodies conjugated with AuNPs with free antibodies, which bind to anti-species antibodies but are not specific to the target analyte. As a result, branched aggregates are formed, due to which the colorimetric signal intensification occurs. The developed test system enabled the detection of OA with an instrumental detection limit of 30 pg/mL and a cutoff of 1 ng/mL, which exceeds these characteristics in the LFIA without amplification by 7 and 2 times, respectively. The OA recoveries from seawater, fish, and seafood varied from 76.9% to 126%. The test system may be required for point-of-care monitoring of samples for phycotoxin contamination; the developed principle of signal amplification can be used in cases where highly sensitive detection of trace amounts of a contaminant is required.

Phytoplankton Toxins and Their Potential Therapeutic Applications: A Journey toward the Quest for Potent Pharmaceuticals

Phytoplankton are prominent organisms that contain numerous bioactive substances and secondary metabolites, including toxins, which can be valuable to pharmaceutical, nutraceutical, and biotechnological industries. Studies on toxins produced by phytoplankton such as cyanobacteria, diatoms, and dinoflagellates have become more prevalent in recent years and have sparked much interest in this field of research. Because of their richness and complexity, they have great potential as medicinal remedies and biological exploratory probes. Unfortunately, such toxins are still at the preclinical and clinical stages of development. Phytoplankton toxins are harmful to other organisms and are hazardous to animals and human health. However, they may be effective as therapeutic pharmacological agents for numerous disorders, including dyslipidemia, obesity, cancer, diabetes, and hypertension. In this review, we have focused on the properties of different toxins produced by phytoplankton, as well as their beneficial effects and potential biomedical applications. The anticancer properties exhibited by phytoplankton toxins are mainly attributed to their apoptotic effects. As a result, phytoplankton toxins are a promising strategy for avoiding postponement or cancer treatment. Moreover, they also displayed promising applications in other ailments and diseases such as Alzheimer’s disease, diabetes, AIDS, fungal, bacterial, schizophrenia, inflammation, allergy, osteoporosis, asthma, and pain. Preclinical and clinical applications of phytoplankton toxins, as well as future directions of their enhanced nano-formulations for improved clinical efficacy, have also been reviewed.

Current Trends and New Challenges in Marine Phycotoxins

Marine phycotoxins are a multiplicity of bioactive compounds which are produced by microalgae and bioaccumulate in the marine food web. Phycotoxins affect the ecosystem, pose a threat to human health, and have important economic effects on aquaculture and tourism worldwide. However, human health and food safety have been the primary concerns when considering the impacts of phycotoxins. Phycotoxins toxicity information, often used to set regulatory limits for these toxins in shellfish, lacks traceability of toxicity values highlighting the need for predefined toxicological criteria. Toxicity data together with adequate detection methods for monitoring procedures are crucial to protect human health. However, despite technological advances, there are still methodological uncertainties and high demand for universal phycotoxin detectors. This review focuses on these topics, including uncertainties of climate change, providing an overview of the current information as well as future perspectives.

Hiding in plain sight: Shellfish-killing phytoplankton in Washington State

Summer bivalve shellfish mortalities have been observed in Puget Sound for nearly a century and attempts to understand and mitigate these losses have been only partially successful. Likewise, the understanding of the environmental conditions triggering shellfish mortalities and successful strategies for their mitigation are incomplete. In the literature, phytoplankton have played only a cursory role in summer shellfish mortalities in Washington State because spawning stress and bacteria were thought to be the primary causes. In recent years, the occurrence of Protoceratium reticulatum (Claparede & Lachmann) Buetschli and Akashiwo sanguinea (Hirasaka) Hansen & Moestrup, have been documented by the SoundToxins research and monitoring partnership in increasing numbers and duration and have been associated with declining shellfish health or mortality at various sites in Puget Sound. Blooms of these species occur primarily in summer months and have been shown to cause mass mortalities of shellfish in the U.S. and other parts of the world. In 2016-2017, yessotoxins (YTX) were measured in several species of Puget Sound bivalve shellfish, with a maximum concentration of 2.20 mg/kg in blue mussels, a value below the regulatory limit of 3.75 mg/kg established by the European Union for human health protection but documented to cause shellfish mortalities in other locations around the world. In July 2019, a bloom of P. reticulatum coincided with a summer shellfish mortality event, involving a dramatic surfacing of stressed, gaping Manila clams, suggesting that YTX could be the cause. YTX concentrations in their tissues were measured at a maximum of 0.28 mg/kg and histology of these clams demonstrated damage to digestive glands. A culture of P. reticulatum, isolated from North Bay during this massive bloom and shellfish mortality event, showed YTX reaching 26.6 pg/cell, the highest recorded toxin quota measured in the U.S. to date. Concentrations of YTX in phytoplankton samples reached a maximum of 920 ng/L during a P. reticulatum bloom in Mystery Bay on 13 August 2019 when cell abundance reached 1.82 million cells/L. The highest cellular YTX quota during that bloom that lasted into September was 10.8 pg/cell on 3 Sept 2019. Shellfish producers in Washington State have also noted shellfish larvae mortalities due to A. sanguinea passing through filtration intake systems into hatchery facilities. Early warning of shellfish-killing harmful algal bloom (HAB) presence in Puget Sound, through partnerships such as SoundToxins, provides options for shellfish growers to mitigate their effects through early harvest, movement of shellstock to upland facilities, or enhanced filtration at aquaculture facilities.

A novel microfluidic system for the sensitive and cost-effective detection of okadaic acid in mussels

Okadaic acid (OA) is produced by marine dinoflagellates and it can be easily accumulated in shellfish, causing intoxications when consumed by humans. Consequently, there is a need for sensitive, reliable and cost-effective methods to detect OA in real samples. In this work, we developed a novel and affordable microfluidic system to detect OA based on the protein phosphatase 1 inhibition colorimetric assay. This enzyme was immobilized in a microfluidic chamber by physisorption in an alumina sol-gel. The results show good enzyme stability over time when maintained at 4 °C. The developed system was sensitive for OA standard solutions, presenting a limit of detection (LOD) of 11.6 nM over a large linear range (43.4 to 3095.8 nM). Our method revealed an LOD as low as 0.2 μg kg-1 and a linear range between 1.47 and 506 μg kg-1 for extracted mussel matrix, detecting OA concentrations in contaminated mussels much lower than the regulated limit (160 μg kg-1). The enzyme stability and reusability along with the simplicity and low cost associated with microfluidics systems make this method very interesting from a commercial point of view.

Co-culture model of Caco-2/HT29-MTX cells: A promising tool for investigation of phycotoxins toxicity on the intestinal barrier

Most lipophilic phycotoxins have been involved in human intoxications but some of these toxins have never been proven to induce human gastro-intestinal symptoms, although intestinal damage in rodents has been documented. For investigating the in vitro toxicological profile of lipophilic phycotoxins on intestine, the epithelial Caco-2 cell line has been the most commonly used model. Nevertheless, considering the complexity of the intestinal epithelium, in vitro co-cultures integrating enterocyte-like and mucus-secreting cell types are expected to provide more relevant data. In this study, the toxic effects (viability, inflammation, cellular monolayer integrity, modulation of cell type proportion and production of mucus) of four lipophilic phycotoxins (PTX2, YTX, AZA1 and OA) were evaluated in Caco-2/HT29-MTX co-cultured cells. The four toxins induced a reduction of viability from 20% to 50% and affected the monolayer integrity. Our results showed that the HT29-MTX cells population were more sensitive to OA and PTX2 than Caco-2 cells. Among the four phycotoxins, OA induced inflammation (28-fold increase of IL-8 release) and also a slight increase of both mucus production (up-regulation of mucins mRNA expression) and mucus secretion (mucus area and density). For PTX2 we observed an increase of IL-8 release but weaker than OA. Intestinal cell models integrating several cell types can contribute to improve hazard characterization and to describe more accurately the modes of action of phycotoxins.

Novel Insights on the Toxicity of Phycotoxins on the Gut through the Targeting of Enteric Glial Cells

In vitro and in vivo studies have shown that phycotoxins can impact intestinal epithelial cells and can cross the intestinal barrier to some extent. Therefore, phycotoxins can reach cells underlying the epithelium, such as enteric glial cells (EGCs), which are involved in gut homeostasis, motility, and barrier integrity. This study compared the toxicological effects of pectenotoxin-2 (PTX2), yessotoxin (YTX), okadaic acid (OA), azaspiracid-1 (AZA1), 13-desmethyl-spirolide C (SPX), and palytoxin (PlTX) on the rat EGC cell line CRL2690. Cell viability, morphology, oxidative stress, inflammation, cell cycle, and specific glial markers were evaluated using RT-qPCR and high content analysis (HCA) approaches. PTX2, YTX, OA, AZA1, and PlTX induced neurite alterations, oxidative stress, cell cycle disturbance, and increase of specific EGC markers. An inflammatory response for YTX, OA, and AZA1 was suggested by the nuclear translocation of NF-κB. Caspase-3-dependent apoptosis and induction of DNA double strand breaks (γH2AX) were also observed with PTX2, YTX, OA, and AZA1. These findings suggest that PTX2, YTX, OA, AZA1, and PlTX may affect intestinal barrier integrity through alterations of the human enteric glial system. Our results provide novel insight into the toxicological effects of phycotoxins on the gut.

Devastating farmed abalone mortalities attributed to yessotoxin-producing dinoflagellates

A large dinoflagellate bloom in Walker Bay (South Africa) in January 2017 impacted 3 land-based abalone farms resulting in the death of several million animals. Satellite-derived images of Chl-a from the Ocean and Land Colour Imager (OLCI) on board the European Space Agency Sentinel-3 A showed bloom initiation in late December 2016 and dispersal in mid-February 2017. The bloom was dominated by two dinoflagellate species identified by light microscopy as Gonyaulax spinifera (Claparède & Lachmann) Diesing, 1866 and Lingulodinium polyedrum (Stein) Dodge, 1989. These morphologically based identifications were confirmed by phylogenetic analysis using partial sequences of the large subunit rDNA of both dinoflagellates. The appearance of yessotoxins (YTX) in abalone clearly coincided with increases in dinoflagellate concentrations. Yessotoxins in both the plankton and abalone were dominated by the two analogues homo-YTX and 45-hydroxy-YTX. The absence of toxins in a clonal culture of L. polyedrum implicated G. spinifera as the likely source of YTX. Toxin concentrations were found to be highest in the gills which showed the most significant pathology, including severe, generalized disruption of the gill epithelium characterized by degeneration and necrosis of epithelial cells accompanied by a modest inflammatory response. Some farms undertook pre-emptive or emergency harvesting to reduce financial losses.

Biotechnological and Pharmacological Applications of Biotoxins and Other Bioactive Molecules from Dinoflagellates

The long-lasting interest in bioactive molecules (namely toxins) produced by (microalga) dinoflagellates has risen in recent years. Exhibiting wide diversity and complexity, said compounds are well-recognized for their biological features, with great potential for use as pharmaceutical therapies and biological research probes. Unfortunately, provision of those compounds is still far from sufficient, especially in view of an increasing demand for preclinical testing. Despite the difficulties to establish dinoflagellate cultures and obtain reasonable productivities of such compounds, intensive research has permitted a number of advances in the field. This paper accordingly reviews the characteristics of some of the most important biotoxins (and other bioactive substances) produced by dinoflagellates. It also presents and discusses (to some length) the main advances pertaining to dinoflagellate production, from bench to large scale-with an emphasis on material published since the latest review available on the subject. Such advances encompass improvements in nutrient formulation and light supply as major operational conditions; they have permitted adaptation of classical designs, and aided the development of novel configurations for dinoflagellate growth-even though shearing-related issues remain a major challenge.

Exposure of okadaic acid alters the angiogenesis in developing chick embryos

Okadaic acid (OA) is a common phycotoxin, which concerns diarrheic shellfish poisoning (DSP) in human being. It has been known that OA can induce disorganization in cytoskeletal architecture and cell-cell contact, cause chromosome loss, apoptosis, DNA damage and inhibit phosphatases, suggesting its potential embryotoxicity. In this paper, we found that low concentration of OA (50 nM, 100 nM and 200 nM) significantly reduced the density of vascular plexus in yolk-sac membrane (YSM) of chick embryo, while high concentration of OA (500 nM) distinctly depressed the blood vessel density in chorioallantoic membrane (CAM). After exposed to OA, MDA level and SOD activity increased significantly in CAM tissues. However, addition of vitamin C could rescue OA-suppressed angiogenesis in CAM of chick embryo. After exposure of OA, Ang-2 expression was down-regulated in CAM tissues. Taking together, we proposed that OA interfered with angiogenesis in developing chick embryo, through, at least partly, the induction of excessive ROS generation.

High resolution mass spectrometry-based screening reveals lipophilic toxins in multiple trophic levels from the North Sea

Lipophilic marine biotoxins, which are mainly produced by small dinoflagellates, are increasingly detected in coastal waters across the globe. As these producers are consumed by zooplankton and shellfish, the toxins are introduced, bioaccumulated and possibly biomagnified throughout marine food chains. Recent research has demonstrated that ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) is an excellent tool to detect marine toxins in algae and seafood. In this study, UHPLC-HRMS was used to screen lipophilic marine biotoxins in organisms from different trophic levels of the Belgian coastal zone ecosystem. A total of 20 tentatively identified lipophilic compounds was detected. Hereby, the trophic transfer of lipophilic marine biotoxins to the upper trophic level was considered to be rather limited. Furthermore, 36% of the compounds was clearly transferred between different organisms. A significant biotransformation of compounds from the okadaic acid and spirolide toxin groups was observed (64%), mainly in filter feeders. Through a multi-targeted approach, this study showed that marine organisms in the Belgian coastal zone are exposed to a multi-toxin mixture. Further research on both single compound and interactive toxic effects of the frequently detected lipophilic marine toxin ester metabolites throughout the food chain is therefore needed. As a future perspective, confirmatory identification of potential toxins by studying their fragmentation spectra (using new tools such as hybrid quadrupole Q-Exactive™ Orbitrap-MS) is designated.

Protein phosphatase 2A regulatory subunit B56β modulates erythroid differentiation

Anemia due to attenuated erythroid terminal differentiation is one of the most common hematological disorders occurring at all stages of life. We previously demonstrated that catalytic subunit α of protein phosphatase 2A (PP2Acα) modulates fetal liver erythropoiesis. However the corresponding PP2A regulatory subunit in this process remains unknown. In this study, we report that chemical inhibition of PP2A activity with okadaic acid impairs hemin-induced erythroid differentiation. Interestingly, B56 family member B56β is the only regulatory subunit whose expression is induced by both erythropoietin in fetal liver cells and hemin in erythroleukemia K562 cells. Finally, knockdown of B56β attenuates hemin-induced K562 erythroid differentiation. Collectively, our data identify B56β as the potential functional regulatory subunit of PP2A in erythroid differentiation, shedding light on new target for precise modulation of PP2A activity for treatment of anemia and related diseases.

Yessotoxin, a Promising Therapeutic Tool

Yessotoxin (YTX) is a polyether compound produced by dinoflagellates and accumulated in filter feeding shellfish. No records about human intoxications induced by this compound have been published, however it is considered a toxin. Modifications in second messenger levels, protein levels, immune cells, cytoskeleton or activation of different cellular death types have been published as consequence of YTX exposure. This review summarizes the main intracellular pathways modulated by YTX and their pharmacological and therapeutic implications.

Forensic genomics as a novel tool for identifying the causes of mass mortality events

Toxic spills, hypoxia, disease outbreaks and toxin-producing algal blooms are all possible causes of mass mortality events, but in many cases it can be difficult to pinpoint the cause of death. Here we present a new approach that we name 'forensic genomics', combining field surveys, toxin testing and genomic scans. Forensic genomics queries allele frequencies of surviving animals for signatures of agents causing mass mortality and, where genetic diversity is high, is uniquely suited to identify natural selection in action. As a proof of concept, we use this approach to investigate the causes of an invertebrate mass mortality event, and its genetic effects on an abalone population. Our results support that a harmful algal bloom producing a yessotoxin was a major causative agent to the event.

Gene expression profiles in zebrafish (Danio rerio) liver after acute exposure to okadaic acid

Okadaic acid (OA), a main component of diarrheic shellfish poisoning (DSP) toxins, is a strong and specific inhibitor of the serine/threonine protein phosphatases PP1 and PP2A. However, not all of the OA-induced effects can be explained by this phosphatase inhibition, and controversial results on OA are increasing. To provide clues on potential mechanisms of OA other than phosphatase inhibition, here, acute toxicity of OA was evaluated in zebrafish, and changes in gene expression in zebrafish liver tissues upon exposure to OA were observed by microarray. The i.p. ED50 (6 h) of OA on zebrafish was 1.54 μg OA/g body weight (bw). Among the genes analyzed on the zebrafish array, 55 genes were significantly up-regulated and 36 down-regulated in the fish liver tissue upon exposure to 0.176 μg OA/g bw (low-dose group, LD) compared with the low ethanol control (LE). However, there were no obvious functional clusters for them. On the contrary, fish exposure to 1.760 μg OA/g bw (high-dose group, HD) yielded a great number of differential expressed genes (700 up and 285 down) compared with high ethanol control (HE), which clustered in several functional terms such as p53 signaling pathway, Wnt signaling pathway, glutathione metabolism and protein processing in endoplasmic reticulum, etc. These genes were involved in protein phosphatase activity, translation factor activity, heat shock protein binding, as well as transmembrane transporter activity. Our findings may give some useful information on the pathways of OA-induced injury in fish.

Okadaic acid: more than a diarrheic toxin

Okadaic acid (OA) is one of the most frequent and worldwide distributed marine toxins. It is easily accumulated by shellfish, mainly bivalve mollusks and fish, and, subsequently, can be consumed by humans causing alimentary intoxications. OA is the main representative diarrheic shellfish poisoning (DSP) toxin and its ingestion induces gastrointestinal symptoms, although it is not considered lethal. At the molecular level, OA is a specific inhibitor of several types of serine/threonine protein phosphatases and a tumor promoter in animal carcinogenesis experiments. In the last few decades, the potential toxic effects of OA, beyond its role as a DSP toxin, have been investigated in a number of studies. Alterations in DNA and cellular components, as well as effects on immune and nervous system, and even on embryonic development, have been increasingly reported. In this manuscript, results from all these studies are compiled and reviewed to clarify the role of this toxin not only as a DSP inductor but also as cause of alterations at the cellular and molecular levels, and to highlight the relevance of biomonitoring its effects on human health. Despite further investigations are required to elucidate OA mechanisms of action, toxicokinetics, and harmful effects, there are enough evidences illustrating its toxicity, not related to DSP induction, and, consequently, supporting a revision of the current regulation on OA levels in food.

Female hormone release of microencapsulated Xenopus laevis ovarian cells

Cell microencapsulation has potential for the treatment of endocrine diseases. This study aims to probe the feasibility of Xenopus laevis as an animal model for cell microencapsulation and transplantation and to evaluate the female hormone release of microencapsulated X. laevis ovarian cells. The cells were harvested, cultured and microencapsulated into alginate-chitosan-alginate microcapsules with an electrostatic generator. The estradiol and progesterone releases of the microencapsulated X. laevis ovarian cells were investigated both in vitro and in vivo. The results showed that the microencapsulated cells kept secreting estradiol and progesterone in vitro for 60 days. After transplantation, serum estradiol and progesterone levels in ovariectomized X. laevis remained elevated for 60 days. X. laevis has been proved to be a suitable animal model for cell microencapsulation and transplantation. Microencapsulated ovarian cells may be considered as a promising endogenous drug delivery system for the treatment of deficiency of female hormones.

Self-association of okadaic acid: structural and pharmacological significance

Okadaic acid (OA) has been an invaluable pharmacological tool in the study of cellular signaling. The great affinity of this polyether for its targets together with its high specificity to inhibit certain protein phosphatases enables the differential study of these proteins. Crystallographic structures of protein phosphatases in complex with OA show a 1:1 protein to toxin ratio. Nevertheless, it has been found that OA is able to self-associate under certain conditions although very little is known about the importance of this phenomenon. Here we review the available knowledge on the latter topic and we report on the existence of an unusual self-associated tetrameric form. The structure of these oligomers is proposed based on spectroscopic data and molecular modeling calculations.

Use of okadaic acid to identify relevant phosphoepitopes in pathology: a focus on neurodegeneration

Protein phosphorylation is involved in the regulation of a wide variety of physiological processes and is the result of a balance between protein kinase and phosphatase activities. Biologically active marine derived compounds have been shown to represent an interesting source of novel compounds that could modify that balance. Among them, the marine toxin and tumor promoter, okadaic acid (OA), has been shown as an inhibitor of two of the main cytosolic, broad-specificity protein phosphatases, PP1 and PP2A, thus providing an excellent cell-permeable probe for examining the role of protein phosphorylation, and PP1 and PP2A in particular, in any physiological or pathological process. In the present work, we review the use of okadaic acid to identify specific phosphoepitopes mainly in proteins relevant for neurodegeneration. We will specifically highlight those cases of highly dynamic phosphorylation-dephosphorylation events and the ability of OA to block the high turnover phosphorylation, thus allowing the detection of modified residues that could be otherwise difficult to identify. Finally, its effect on tau hyperhosphorylation and its relevance in neurodegenerative pathologies such as Alzheimer’s disease and related dementia will be discussed.

Detection of yessotoxin by three different methods in Mytilus galloprovincialis of Adriatic Sea, Italy

Samples of Mytilus galloprovincialis collected from shellfish aquaculture plans located in the Adriatic Sea were analysed for yessotoxin (YTX) by three methods, in vivo (Mouse Bioassay, MBA), in vitro (functional assay) and chemical test (Liquid Chromatography-Mass Spectrometry, LC-MS/MS). As YTX coexists with other phycotoxins in shellfish, namely the diarrhoetic shellfish poisoning, okadaic acid, dinophysistoxins, pectenotoxins, and azaspirazids, the MBA is not completely satisfactory because it is difficult to identify which toxin causes the death of the mice. So, the two other techniques were proposed to detect and quantify YTX and its analogues in order to avoid this problem. The global results showed no difference among the three methods and the correlation between the functional assay and LC-MS/MS was positive (Spearman r=0.72). Both analytical methods demonstrated advantages; the functional assay is specific, very sensitive and correlates well with real toxicity, whereas LC-MS/MS is convenient because it allows the detection of YTX and some analogues which are currently included in the EU regulation. For this reason LC-MS/MS will become the official method starting 1st January 2015 (Regulation 15/2011/EU). Only four samples exceeded the current EU regulation limit of 1mg of YTX equivalent kg(-1). However, all samples belonged to a monitoring program and they were not suitable for consumers.

Evaluation of genotoxicity in gills and hemolymph of clam Ruditapes decussatus fed with the toxic dinoflagellate Prorocentrum lima

Diarrheic shellfish poisoning (DSP) is a gastrointestinal (GIT) disease that appears a few hours after ingesting okadaic acid (OA)-contaminated mollusks; okadaic acid is present in dinoflagellates of the genera Dinophysis and Prorocentrum. Toxic manifestations occur all year round at a higher or lesser intensity, and as a consequence, extractive production factories need to be closed during these periods which affects the economy of aquaculture industries. Although the concentration of harmful algae is usually found at high levels in clam digestive gland, bivalve mortality was not increased. In this study, the genotoxic effects produced by OA in clam Ruditapes decussatus were determined using the comet assay. In vitro (exposing hemocytes to different concentrations of OA) and in vivo (feeding clams with toxic dinoflagellate Prorocentrum lima) experiments were conducted in order to determine the genotoxic effects of OA on bivalve cells. Hemocytes and gill cells were analyzed by in vivo and in vitro approaches. While the in vitro study showed a rapid effect of OA on hemocytes, data obtained in the in vivo experiment reflected contradictory results dependent upon the concentration of OA and cell type evaluated. An increase in DNA damage was observed at the lower concentration and only in gill tissue. The results obtained may contribute to a better understanding of the mechanisms underlying genotoxic effects induced by OA on bivalves.

Evaluation of okadaic acid-induced genotoxicity in human cells using the micronucleus test and γH2AX analysis

Marine algal blooms have become a public health concern due to increasing frequency in the environment and severity of exposure consequences. Human intoxications produced by phycotoxins occur globally through consumption of marine fish products containing bioaccumulated toxins. Okadaic acid (OA) is the main representative of diarrheic shellfish poisoning (DSP) toxin. OA was found to inhibit protein phosphatases and to produce oxidative damage, as well as to disturb different cellular functions including cell cycle, gene expression, and DNA repair mechanisms. The aim of this study was to determine whether OA induced genotoxicity by using a micronucleus (MN) test and γH2AX analysis, and to elucidate the underlying mechanisms. Human peripheral blood leukocytes, neuroblastoma cells (SHSY5Y), and hepatoma cells (HepG2) were treated with a range of OA concentrations in the presence and absence of S9 fraction. MN induction was observed in leukocytes at all concentrations tested, and in SHSY5Y and HepG2 cells only at the highest concentration (1000 nM). In contrast, γH2AX analysis was only positive for HepG2 cells. Taking together these data, in addition to the comet assay results obtained in a previous study in this issue, OA was found to exert a either a clastogenic or aneugenic effect dependent upon the cell types examined.