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

Multiparametric in vitro genotoxicity assessment of different variants of amorphous silica nanomaterials in rat alveolar epithelial cells

The hazard posed to human health by inhaled amorphous silica nanomaterials (aSiO2 NM) remains uncertain. Herein, we assessed the cyto- and genotoxicity of aSiO2 NM variants covering different sizes (7, 15, and 40 nm) and surface modifications (unmodified, phosphonate-, amino- and trimethylsilyl-modified) on rat alveolar epithelial (RLE-6TN) cells. Cytotoxicity was evaluated at 24 h after exposure to the aSiO2 NM variants by the lactate dehydrogenase (LDH) release and WST-1 reduction assays, while genotoxicity was assessed using different endpoints: DNA damage (single- and double-strand breaks [SSB and DSB]) by the comet assay for all aSiO2 NM variants; cell cycle progression and γ-H2AX levels (DSB) by flow cytometry for those variants that presented higher cytotoxic and DNA damaging potential. The variants with higher surface area demonstrated a higher cytotoxic potential (SiO2_7, SiO2_15_Unmod, SiO2_15_Amino, and SiO2_15_Phospho). SiO2_40 was the only variant that induced significant DNA damage on RLE-6TN cells. On the other hand, all tested variants (SiO2_7, SiO2_15_Unmod, SiO2_15_Amino, and SiO2_40) significantly increased total γ-H2AX levels. At high concentrations (28 µg/cm2), a decrease in G0/G1 subpopulation was accompanied by a significant increase in S and G2/M sub-populations after exposure to all tested materials except for SiO2_40 which did not affect cell cycle progression. Based on the obtained data, the tested variants can be ranked for its genotoxic DNA damage potential as follows: SiO2_7 = SiO2_40 = SiO2_15_Unmod > SiO2_15_Amino. Our study supports the usefulness of multiparametric approaches to improve the understanding on NM mechanisms of action and hazard prediction.

Toxic Effects and Tumor Promotion Activity of Marine Phytoplankton Toxins: A Review

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.

Unveiling the Toxicity of Fine and Nano-Sized Airborne Particles Generated from Industrial Thermal Spraying Processes in Human Alveolar Epithelial Cells

High-energy industrial processes have been associated with particle release into workplace air that can adversely affect workers’ health. The present study assessed the toxicity of incidental fine (PGFP) and nanoparticles (PGNP) emitted from atmospheric plasma (APS) and high-velocity oxy-fuel (HVOF) thermal spraying. Lactate dehydrogenase (LDH) release, 2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) metabolisation, intracellular reactive oxygen species (ROS) levels, cell cycle changes, histone H2AX phosphorylation (γ-H2AX) and DNA damage were evaluated in human alveolar epithelial cells at 24 h after exposure. Overall, HVOF particles were the most cytotoxic to human alveolar cells, with cell viability half-maximal inhibitory concentration (IC₅₀) values of 20.18 µg/cm² and 1.79 µg/cm² for PGFP and PGNP, respectively. Only the highest tested concentration of APS-PGFP caused a slight decrease in cell viability. Particle uptake, cell cycle arrest at S + G₂/M and γ-H2AX augmentation were observed after exposure to all tested particles. However, higher levels of γ-H2AX were found in cells exposed to APS-derived particles (~16%), while cells exposed to HVOF particles exhibited increased levels of oxidative damage (~17% tail intensity) and ROS (~184%). Accordingly, APS and HVOF particles seem to exert their genotoxic effects by different mechanisms, highlighting that the health risks of these process-generated particles at industrial settings should not be underestimated.

Histopathological alterations induced by marine environmental pollutants on the bivalve Cerastoderma glaucum (Bruguière 1789) from Temsah Lake, Suez Canal, Egypt

Bivalves are considered a main consumed matrix for coastal communities worldwide and classified as hyperaccumulators of pollutants. The present study aims to determine some micro-organisms, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and okadaic acid (OA) levels in Cerastoderma glaucum collected from Temsah Lake, Egypt, and their induction through histopathological damage and caspase-3 protein expression. During the autumn, it was found different types of biological and chemical pollutants, especially benzo[a]pyrene (BaP) that accumulated in C. glaucum soft tissues and exceeded the safety limit for shellfish consumption. Dioxin-like PCB3 was predominant in C. glaucum soft tissues during autumn, but the total levels of PCBs in these tissues have not exceeded the permissible limit. Chlorophyll-a (Chl. a), nutrient concentrations, and Prorocentrum lima dinoflagellates in the water significantly increased during autumn. High P. lima abundance was confirmed by high OA in the soft tissues during this season compared to the other seasons. The measured contaminants may render C. glaucum more susceptible to bacterial and fungal infections. The autumn season showed a significant increase in the colony-forming units (CFU). C. glaucum showed calcification abnormalities and adhering of abnormal brown organic material to the inner surface of the shell valves, which was related to poor water conditions and Vibrio infection. Damages or injuries on gills and digestive gland tissues indicated an impact of the pollutants on C. glaucum. Also, high expressions of caspase-3 were recorded in these tissues during all the seasons. So, C. glaucum cockles, collected from Temsah Lake, may induce serious diseases to consumers, especially when eaten raw or insufficient cooking.

Responses of JNK signaling pathway to the toxic dinoflagellate Prorocentrum lima in the mussel Perna viridis

Diarrheic shellfish poisoning (DSP) toxins are widely distributed over the world, causing diarrhea, vomiting, and even tumor in human. However, bivalves, the main carrier of the DSP toxins, have some tolerant mechanisms to DSP toxins, though it remains unclear. In this study, we scrutinized the role of Jun N-terminal kinases (JNK) in tolerance of DSP toxins and the relationship between JNK, apoptosis and nuclear factor E2-related factor/antioxidant response element (Nrf2/ARE) pathways. We found that the phosphorylated level of JNK protein was significantly increased both in hemocytes (6 h) and gills (3 h) of the mussel Perna viridis after short-term exposure to DSP toxins-producing dinoflagellate Prorocentrum lima. Exposure of P. lima induced oxidative stress in mussels. Hemocytes and gills displayed different sensitivities to the cytotoxicity of DSP toxins. Exposure of P. lima activated caspase-3 and induced apoptosis in gills but did not induce caspase-3 and apoptosis in hemocytes. The short-term exposure of P. lima could activate Nrf2/ARE signaling pathway in hemocytes (6 h), while longer-term exposure could induce glutathione reductase (GR) expression in hemocytes (96 h) and glutathione-S-transferases (GST) in gills (96 h). Based on the phylogenetic tree of Nrf2, Nrf2 in P. viridis was closely related to that in other mussels, especially Mytilus coruscus, but far from that in Mus musculus. The most likely phosphorylated site of Nrf2 in the mussels P. viridis is threonine 504 for JNK, which is different from that in M. musculus. Taken all together, the tolerant mechanism of P. viridis to DSP toxins might be involved in JNK and Nrf2/ARE signaling pathways, and JNK play a key role in the mechanism. Our findings provide a new clue to further understand tolerant mechanisms of bivalves to DSP toxins.

Applicability of flow cytometry γH2AX assay in population studies: suitability of fresh and frozen whole blood samples

Phosphorylation of H2AX histone (γH2AX) represents an early event in the DNA damage response against double-strand breaks (DSB); hence, its measurement provides a surrogate biomarker of DSB. Recently, we reported initial steps in the standardization of γH2AX assay in peripheral blood leukocytes (PBL), addressing the possibility of using cryopreserved samples, and the need of phytohaemagglutinin (PHA) stimulation prior analysis (Toxicol Sci 2015, 144:406-13). Validating the use of whole blood samples as cell specimen for this assay would be particularly useful for human population studies. Hence, in the current study we determined for the first time the feasibility of whole blood samples, both fresh and frozen, to be used in the γH2AX assay, evaluated by flow cytometry, and the convenience of PHA stimulation. Freshly collected and cryopreserved whole blood samples were treated with bleomycin (BLM), actinomycin-D (Act-D) and mitomycin C (MMC); half of the samples were previously incubated with PHA. Results were compared with those from PBL. Negative responses in MMC treatments were probably due to the quiescence of unstimulated cells, or to the short treatment time in PHA stimulated cells. Fresh whole blood samples exhibited a more intense response to BLM and Act-D treatments in stimulated cells, probably due to DSB indirectly produced from other less relevant types of DNA damage. Results obtained in frozen whole blood samples indicate that PHA stimulation is not advisable. In conclusion, this study demonstrates that whole blood samples can be used to assess DSB-related genotoxicity by the flow cytometry γH2AX assay.

Toxicity and differential oxidative stress effects on zebrafish larvae following exposure to toxins from the okadaic acid group

Okadaic acid-group (OA-group) is a set of lipophilic toxins produced only in seawater by species of the Dinophysis and Prorocentrum genera, and characterized globally by being associated with harmful algal blooms (HABs). The diarrhetic shellfish poisoning toxins okadaic acid (OA) and dinophysistoxin-1 (DTX-1) are the most prevalent toxic analogues making up the OA-group, which jeopardize environmental safety and human health through consumption of hydrobiological organisms contaminated with these toxins that produce diarrhetic shellfish poisoning (DSP) syndrome in humans. Consequently, a regulatory limit of 160 μg of OA-group/kg was established for marine resources (bivalves). The aim of this study was to investigate effects varying concentrations of 1-15 μg/ml OA or DTX-1 on toxicity, development, and oxidative damage in zebrafish larvae (Danio rerio). After determining the lethal concentration 50 (LC₅₀) in zebrafish larvae of 10 and 7 μg/ml (24 h) and effective concentration 50 (EC₅₀) of 8 and 6 μg/ml (24 h), different concentrations (5, 6.5, or 8 μg/ml of OA and 4, 4.5, or 6 μg/ml of DTX-1) were used to examine the effects of these toxins on oxidative damage to larvae at different time points between 24 and 120 hpf. Macroscopic evaluation during the exposure period showed alterations in zebrafish including pericardial edema, cyclopia, shortening in the anteroposterior axis, and developmental delay. The activity levels of biochemical biomarkers superoxide dismutase (SOD) and catalase (CAT) demonstrated a concentration-dependent decrease while glutathione peroxidase (GPx) and glutathione reductase (GR) were markedly elevated. In addition, increased levels of oxidative damage (malondialdehyde and carbonyl content) were detected following toxin exposure. Data demonstrate that high concentrations of OA and DTX-1produced pathological damage in the early stages of development <48 h post-fertilization (hpf) associated with oxidative damage.

Cytotoxic and genotoxic effects of the flame retardants (PBDE-47, PBDE-99 and PBDE-209) in human bronchial epithelial cells

Polybrominated diphenyl ethers (PBDEs) are widespread as flame-retardants in different types of consumer products. PBDEs present in the air or dust and their inhalation can damage human health by influencing the respiratory system. We evaluated the effects of environment relevant concentrations (0.01-1  μM) of PBDE-47, PBDE-99 and PBDE-209 on the mechanism of oxidative stress, dysregulation of cell proliferation, apoptosis, and DNA damage and repair (in term of H2AX phosphorylation ser139) in an in-vitro/ex-vivo model of bronchial epithelial cells. PBDEs (-47, -99 and -209) at the environment relevant concentrations (0.01 and 1  μM) induce oxidative stress (in term of NOX-4 expression as well as ROS and JC-1 production), activate the mechanism of DNA-damage and repair affecting Olive Tail length (comet assay) production and H2AX phosphorylation (ser139) in normal human bronchial epithelial cells. Furthermore PBDEs, although do not affect cell viability, induce cell apoptosis and single cell capacity to grow into a colony (like a cancer phenotype) in bronchial epithelial cells. Finally, PBDE-47 had a greater effect than -99 and -209. PBDE-47, -99 and -209 congeners exert cytotoxic and genotoxic effects, and play a critical role in the dysregulation of oxidative stress, damaging DNA and the related gene expression in bronchial epithelial cells. Our findings might suggest that PBDEs inhalation might have adverse effect on human health regarding pulmonary diseases in the areas of environmental pollution.

Benchmark dose analyses of γH2AX and pH3 endpoints for quantitative comparison of in vitro genotoxicity potential of lipophilic phycotoxins

The phycotoxins, okadaic acid (OA) and dinophysistoxins 1 and 2 (DTX-1 and -2), are protein phosphatase PP2A and PP1 inhibitors involved in diarrhetic shellfish poisoning (DSP) in humans. Data on the in vivo acute toxicity of the OA-group toxins show some differences and the European Food Safety Authority (EFSA) has determined toxicity equivalent factors (TEFs) of one for the reference toxin, OA, as well as for DTX-1 and 0.6 for DTX-2. However, recent in vitro studies indicated that DTX-1 seems to be more toxic than OA. As OA was described as apoptotic and aneugenic compound, we analyzed the DNA damage responses induced by the 3 toxins through γH2AX and pH3 biomarkers on proliferative HepaRG cells using High Content Analysis. We quantitatively examined the responses for γH2AX and pH3 by benchmark dose analyzing (BMD) using PROAST software. We found that the three toxins increased both γH2AX- and pH3-positive cells populations in a concentration-dependent manner. The 3 toxins induced mitotic arrest, characteristic of aneugenic compounds, as well as DNA strand-breaks concomitantly to cytotoxicity. BMD analysis showed that DTX-1 is the most potent inducer of DNA damage, followed by OA and DTX-2. The quantitative genotoxic data provided in this study are additional findings for reconsidering the estimated TEFs of this group of phycotoxins.

Genotoxicity of TiO2 Nanoparticles in Four Different Human Cell Lines (A549, HEPG2, A172 and SH-SY5Y)

Titanium dioxide nanoparticles (TiO2 NPs) have a wide variety of applications in many consumer products, including as food additives, increasing the concern about the possible hazards that TiO2 NPs may pose to human health. Although most previous studies have focused on the respiratory system, ingestion must also be considered as an important exposure route. Furthermore, after inhalation or ingestion, TiO2 NPs can reach several organs, such as the liver, brain or lungs. Taking this into consideration, the present study focuses on the uptake and potential genotoxicity (micronuclei induction) of TiO2 NPs on four human cell lines of diverse origin: lung cells (A549), liver cells (HepG2), glial cells (A172) and neurons (SH-SY5Y), using flow cytometry methods. Results showed a concentration-, time- and cell-type- dependent increase in TiO2 NPs uptake but no significant induction of micronuclei in any of the tested conditions. Data obtained reinforce the importance of cell model and testing protocols choice for toxicity assessment. However, some questions remain to be answered, namely on the role of cell culture media components on the agglomeration state and mitigation of TiO2 NPs toxic effects.

UNCERTAINTY ON RADIATION DOSES ESTIMATED BY BIOLOGICAL AND RETROSPECTIVE PHYSICAL METHODS

Biological and physical retrospective dosimetry are recognised as key techniques to provide individual estimates of dose following unplanned exposures to ionising radiation. Whilst there has been a relatively large amount of recent development in the biological and physical procedures, development of statistical analysis techniques has failed to keep pace. The aim of this paper is to review the current state of the art in uncertainty analysis techniques across the 'EURADOS Working Group 10-Retrospective dosimetry' members, to give concrete examples of implementation of the techniques recommended in the international standards, and to further promote the use of Monte Carlo techniques to support characterisation of uncertainties. It is concluded that sufficient techniques are available and in use by most laboratories for acute, whole body exposures to highly penetrating radiation, but further work will be required to ensure that statistical analysis is always wholly sufficient for the more complex exposure scenarios.

Cytotoxicity and genotoxicity effects of arsenic trioxide on SQ20B human laryngeal carcinoma cells

This study investigates the cytotoxicity and the genotoxicity induced by arsenic trioxide As₂O₃in human laryngeal SQ20B carcinoma cell line. SQ20B cells were exposed to graded concentrations of arsenic trioxide (2 and 5μM) for 48h. Comet assay and γ-H2AX foci formation were used for measuring DNA damages, flow cytometry was used to identify cell cycle alterations and apoptosis, while cell morphology was visualized using transmission electron microscopy. The results show a dose-dependent induction of DNA damages and double strand breaks, alterations in cell cycle and morphologic alterations of cells. These results prove that As₂O₃ is highly cytotoxic and genotoxic at the micromolar range ina human laryngeal carcinoma cell line.

Comparative study of human neuronal and glial cell sensitivity for in vitro neurogenotoxicity testing

Cell cultures from neuronal and glial origin have proven to be powerful tools for elucidating cellular and molecular mechanisms of nervous system development and physiology, and as neurotoxicity models to evaluate in vitro the possible effects of chemicals. But cellular heterogeneity of nervous system is considerable and these cells have been shown to respond diversely to neurotoxic insults, leading to disparate results from different studies. To shed more light on suitability of cellular models of nervous origin for neurotoxicity screening, the objective of this study was to compare the sensitivity to genetic damage induction of two nervous cell lines. To this aim, neurons (SH-SY5Y) and glial (A172) cells were treated with differently-acting genotoxic agents (bleomycin, actinomycin-D, methyl methanesulfonate, mitomycin C, and griseofulvin). After discarding cytotoxicity, genotoxicity was evaluated by a battery of assays encompassing detection of different genetic lesions. Results obtained showed that glial cells are generally more resistant to genotoxic damage induced by clastogenic agents, but more sensitive to aneugenic effects. These results highlight the need of proper design of in vitro neurotoxicology studies, especially for neurogenotoxicity screening, emphasizing the importance of employing more than one nervous cell type for testing the potential toxicity of a particular exposure.

Genotoxic effects of cadmium in human head and neck cell line SQ20B

As cadmium may be involved in the etiology of head and neck cancers, we investigated in the present work, the cytotoxic and genotoxic effects of Cd on human larynx cells. SQ20B cells were exposed to 25 and 50 μM Cd for 48 and 72 h. Results showed a dose-dependent decrease in cell viability, especially after 48 h, associated with mitochondria alterations as showed by transmission electronic microscopy. Surprisingly, the flow cytometry shows that the cells treated with Cd have a normal proliferative cycle like the untreated cell especially in G1 or G2 phase of cell cycle. DNA damages were investigated by comet assay and immunofluorescence for gamma layer of the H2AX (g-H2AX) foci formation. Results show a strong induction of DNA double-strand breaks after Cd exposure. Overall, our results demonstrate the cytotoxicity and genotoxicity of Cd in human larynx cells and support the view that Cd could be an etiologic factor of head and neck cancers.

In vitro toxicity evaluation of silica-coated iron oxide nanoparticles in human SHSY5Y neuronal cells

Iron oxide nanoparticles (ION) have been widely used in biomedical applications, for both diagnosis and therapy, due to their unique magnetic properties. They are intensively explored in neuromedicine mostly because of their ability to cross the blood brain barrier. Hence, their potential harmful effects on neuronal cells need to be carefully assessed. The objective of this study was to evaluate the toxicity of silica-coated ION (S-ION) (10-200 μg ml-1) on human neuronal SHSY5Y cells. Alterations in the cell cycle, cell death by apoptosis or necrosis, and membrane integrity were assessed as cytotoxicity parameters. Genotoxicity was determined by a γH2AX assay, a micronucleus (MN) test, and a comet assay. Complementarily, possible effects on DNA damage repair were also analysed by means of a DNA repair competence assay. All analyses were performed in complete and serum-free cell culture media. Iron ion release from the nanoparticles was notable only in complete medium. Despite being effectively internalized by the neuronal cells, S-ION presented in general low cytotoxicity; positive results were only obtained in some assays at the highest concentrations and/or the longest exposure time tested (24 h). Genotoxicity evaluations in serum-free medium were negative for all conditions assayed; in complete medium, dose and time-dependent increase in DNA damage not related to the production of double strand breaks or chromosome loss (according to the results of the γH2AX assay and MN test), was obtained. The presence of serum slightly influenced the behaviour of S-ION; further studies to investigate the formation of a protein corona and its role in nanoparticle toxicity are necessary.

Evaluation of in vitro cytotoxicity and genotoxicity of copper-zinc alloy nanoparticles in human lung epithelial cells

In the present study, in vitro cytotoxic and genotoxic effect of copper-zinc alloy nanoparticles (Cu-Zn ANPs) on human lung epithelial cells (BEAS-2B) were investigated. XTT test and clonogenic assay were used to determine cytotoxic effects. Cell death mode and intracellular reactive oxygen species formations were analyzed using M30, M65 and ROS Elisa assays. Genotoxic effects were evaluated using micronucleus, comet and γ-H2AX foci assays. Cu-Zn ANPs were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential measurements. Characterization of Cu-Zn ANPs showed an average size of 200nm and zeta potential of -22mV. TEM analyses further revealed the intracellular localization of Cu-Zn ANPs in cytoplasm within 24h. Analysis of micronucleus, comet and γ-H2AX foci counts showed that exposure to Cu-Zn ANPs significantly induced chromosomal damage as well as single and double stranded DNA damage in BEAS-2B cells. Our results further indicated that exposure to Cu-Zn ANPs significantly induced intracellular ROS formation. Evaluation of M30:M65 ratios suggested that cell death was predominantly due to necrosis.

Follow-up study of genotoxic effects in individuals exposed to oil from the tanker Prestige, seven years after the accident

The accident with the oil tanker Prestige in November 2002 resulted in a major spill of about 63,000 tons of heavy fuel oil. More than 300,000 people participated in the clean-up activities, which lasted for up to 10 months. Previous studies reported increases in genotoxicity endpoints in individuals exposed to Prestige oil, both at the moment of exposure [DNA breakage, micronuclei (MN), sister chromatid exchange] and two years later (chromosomal aberrations). In this work we carried out for the first time the follow-up of genotoxic effects in subjects exposed to an oil spill seven years after the exposure. The main objective was to determine the possible persistence of genotoxic damage in individuals exposed to Prestige oil seven years after the accident. The exposed group was composed of 54 residents of Galician villages in Spain that were heavily affected by the spill. This group was involved in clean-up labor for at least two months in the period November 2002-September 2003. They were compared with 50 matched controls. Primary DNA damage was evaluated by the comet assay, mutagenicity by the T-cell receptor (TCR) mutation assay, and MN frequency was determined both by the cytokinesis-block test and by flow cytometry. The results obtained showed no significant differences between the exposed and the controls in the comet assay, the TCR mutation assay and the cytokinesis-block MN test. An unexpected and significant decrease was observed in the exposed group for the results of the MN test evaluated by flow cytometry, probably influenced by modifying factors - other than age, sex and smoking - not considered in this study. Our results show no evidence of the persistence of genotoxic damage in individuals exposed to Prestige oil seven years later. Nevertheless, the need to plan biomonitoring studies on people participating in clean-up activities in case a new oil spill occurs should be established.

Risk assessment of shellfish toxins

Complex secondary metabolites, some of which are highly toxic to mammals, are produced by many marine organisms. Some of these organisms are important food sources for marine animals and, when ingested, the toxins that they produce may be absorbed and stored in the tissues of the predators, which then become toxic to animals higher up the food chain. This is a particular problem with shellfish, and many cases of poisoning are reported in shellfish consumers each year. At present, there is no practicable means of preventing uptake of the toxins by shellfish or of removing them after harvesting. Assessment of the risk posed by such toxins is therefore required in order to determine levels that are unlikely to cause adverse effects in humans and to permit the establishment of regulatory limits in shellfish for human consumption. In the present review, the basic principles of risk assessment are described, and the progress made toward robust risk assessment of seafood toxins is discussed. While good progress has been made, it is clear that further toxicological studies are required before this goal is fully achieved.

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.

Okadaic acid meet and greet: an insight into detection methods, response strategies and genotoxic effects in marine invertebrates

Harmful Algal Blooms (HABs) constitute one of the most important sources of contamination in the oceans, producing high concentrations of potentially harmful biotoxins that are accumulated across the food chains. One such biotoxin, Okadaic Acid (OA), is produced by marine dinoflagellates and subsequently accumulated within the tissues of filtering marine organisms feeding on HABs, rapidly spreading to their predators in the food chain and eventually reaching human consumers causing Diarrhetic Shellfish Poisoning (DSP) syndrome. While numerous studies have thoroughly evaluated the effects of OA in mammals, the attention drawn to marine organisms in this regard has been scarce, even though they constitute primary targets for this biotoxin. With this in mind, the present work aimed to provide a timely and comprehensive insight into the current literature on the effect of OA in marine invertebrates, along with the strategies developed by these organisms to respond to its toxic effect together with the most important methods and techniques used for OA detection and evaluation.

The marine toxin okadaic acid induces alterations in the expression level of cancer-related genes in human neuronal cells

Okadaic acid (OA) is one of the most common and highly distributed marine toxins. It can be accumulated in several molluscs and other marine organisms and cause acute gastrointestinal symptoms after oral consumption by humans, called diarrheic shellfish poisoning. However other toxic effects beyond these gastrointestinal symptoms were also reported. Thus, OA was found to induce important chromosomal abnormalities and other genetic injuries that can lead to severe pathologies, including cancer. Furthermore, the relationship between OA and carcinogenic processes has been previously demonstrated in in vivo studies with rodents, and also suggested in human epidemiological studies. In this context, further research is required to better understand the underlying mechanisms of OA-related tumourigenesis. In a previous study, we identified 247 genes differentially expressed in SHSY5Y neuroblastoma cells exposed to 100nM OA at different times (3, 24 and 48h) by means of suppression subtractive hybridization. These genes were involved in relevant cell functions such as signal transduction, cell cycle, metabolism, and transcription and translation processes. However, due to the high potential percentage of false positives that may be obtained by this approach, results from SSH are recommended to be analyzed by an independent method. In the present study, we selected ten genes related to cancer initiation or progression, directly or indirectly, for further quantitative PCR analysis (ANAPC13, PTTG1, CALM2, CLU, HN1, MALAT1, MAPRE2, MLLT11, SGA-81M and TAX1BP1). Results obtained showed important alterations in the expression patterns of all the genes evaluated at one or more treatment times, providing, for the first time, a possible explanation at the molecular level of the potential relationship between the consumption of OA-contaminated shellfish and the incidence of different cancers in humans. Nevertheless, given the complexity of this process, more exhaustive studies are required before drawing any final conclusion.

Identification of dynamic changes in proteins associated with the cellular cytoskeleton after exposure to okadaic acid

Exposure of cells to the diarrhetic shellfish poison, okadaic acid, leads to a dramatic reorganization of cytoskeletal architecture and loss of cell-cell contact. When cells are exposed to high concentrations of okadaic acid (100–500 nM), the morphological rearrangement is followed by apoptotic cell death. Okadaic acid inhibits the broad acting Ser/Thr protein phosphatases 1 and 2A, which results in hyperphosphorylation of a large number of proteins. Some of these hyperphosphorylated proteins are most likely key players in the reorganization of the cell morphology induced by okadaic acid. We wanted to identify these phosphoproteins and searched for them in the cellular lipid rafts, which have been found to contain proteins that regulate cytoskeletal dynamics and cell adhesion. By using stable isotope labeling by amino acids in cell culture cells treated with okadaic acid (400 nM) could be combined with control cells before the isolation of lipid rafts. Protein phosphorylation events and translocations induced by okadaic acid were identified by mass spectrometry. Okadaic acid was shown to regulate the phosphorylation status and location of proteins associated with the actin cytoskeleton, microtubules and cell adhesion structures. A large number of these okadaic acid-regulated proteins have previously also been shown to be similarly regulated prior to cell proliferation and migration. Our results suggest that okadaic acid activates general cell signaling pathways that induce breakdown of the cortical actin cytoskeleton and cell detachment.

Neuronal cytotoxicity and genotoxicity induced by zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO NPs) are one of the most abundantly used nanomaterials in consumer products and biomedical applications. As a result, human exposure to these NPs is highly frequent and they have become an issue of concern to public health. Although toxicity of ZnO NPs has been extensively studied and they have been shown to affect many different cell types and animal systems, there is a significant lack of toxicological data for ZnO NPs on the nervous system, especially for human neuronal cells and tissues. In this study, the cytotoxic and genotoxic effects of ZnO NPs on human SHSY5Y neuronal cells were investigated under different exposure conditions. Results obtained by flow cytometry showed that ZnO NPs do not enter the neuronal cells, but their presence in the medium induced cytotoxicity, including viability decrease, apoptosis and cell cycle alterations, and genotoxicity, including micronuclei production, H2AX phosphorylation and DNA damage, both primary and oxidative, on human neuronal cells in a dose- and time-dependent manner. Free Zn(2+) ions released from the ZnO NPs were not responsible for the viability decrease, but their role on other types of cell damage cannot be ruled out. The results obtained in this work contribute to increase the knowledge on the genotoxic and cytotoxic potential of ZnO NPs in general, and specifically on human neuronal cells, but further investigations are required to understand the action mechanism underlying the cytotoxic and genotoxic effects observed.

Comparative study on effects of two different types of titanium dioxide nanoparticles on human neuronal cells

Titanium dioxide (TiO2) are among most frequently used nanoparticles (NPs). They are present in a variety of consumer products, including food industry in which they are employed as an additive. The potential toxic effects of these NPs on mammal cells have been extensively studied. However, studies regarding neurotoxicity and specific effects on neuronal systems are very scarce and, to our knowledge, no studies on human neuronal cells have been reported so far. Therefore, the main objective of this work was to investigate the effects of two types of TiO₂ NPs, with different crystalline structure, on human SHSY5Y neuronal cells. After NPs characterization, a battery of assays was performed to evaluate the viability, cytotoxicity, genotoxicity and oxidative damage in TiO₂ NP-exposed SHSY5Y cells. Results obtained showed that the behaviour of both types of NPs resulted quite comparable. They did not reduce the viability of neuronal cells but were effectively internalized by the cells and induced dose-dependent cell cycle alterations, apoptosis by intrinsic pathway, and genotoxicity not related with double strand break production. Furthermore, all these effects were not associated with oxidative damage production and, consequently, further investigations on the specific mechanisms underlying the effects observed in this study are required.

The CHROMEVALOA database: a resource for the evaluation of Okadaic Acid contamination in the marine environment based on the chromatin-associated transcriptome of the mussel Mytilus galloprovincialis

Okadaic Acid (OA) constitutes the main active principle in Diarrhetic Shellfish Poisoning (DSP) toxins produced during Harmful Algal Blooms (HABs), representing a serious threat for human consumers of edible shellfish. Furthermore, OA conveys critical deleterious effects for marine organisms due to its genotoxic potential. Many efforts have been dedicated to OA biomonitoring during the last three decades. However, it is only now with the current availability of detailed molecular information on DNA organization and the mechanisms involved in the maintenance of genome integrity, that a new arena starts opening up for the study of OA contamination. In the present work we address the links between OA genotoxicity and chromatin by combining Next Generation Sequencing (NGS) technologies and bioinformatics. To this end, we introduce CHROMEVALOAdb, a public database containing the chromatin-associated transcriptome of the mussel Mytilus galloprovincialis (a sentinel model organism) in response to OA exposure. This resource constitutes a leap forward for the development of chromatin-based biomarkers, paving the road towards the generation of powerful and sensitive tests for the detection and evaluation of the genotoxic effects of OA in coastal areas.

Genotoxic effects of occupational exposure to lead and influence of polymorphisms in genes involved in lead toxicokinetics and in DNA repair

Lead is still widely used in many industrial processes and is very persistent in the environment. Although toxic effects caused by occupational exposure to lead have been extensively studied, there are still conflicting results regarding its genotoxicity. In a previous pilot study we observed some genotoxic effects in a population of lead exposed workers. Thus, we extended our study analysing a larger population, increasing the number of genotoxicity endpoints, and including a set of 20 genetic polymorphisms related to lead toxicokinetics and DNA repair as susceptibility biomarkers. Our population comprised 148 workers from two Portuguese factories and 107 controls. The parameters analysed were: blood lead levels (BLL) and δ-aminolevulinic acid dehydratase (ALAD) activity as exposure biomarkers, and T-cell receptor (TCR) mutation assay, micronucleus (MN) test, comet assay and OGG1-modified comet assay as genotoxicity biomarkers. Lead exposed workers showed markedly higher BLL and lower ALAD activity than the controls, and significant increases of TCR mutation frequency (TCR-Mf), MN rate and DNA damage. Oxidative damage did not experience any significant alteration in the exposed population. Besides, significant influence was observed for VDR rs1544410 polymorphism on BLL; APE1 rs1130409 and LIG4 rs1805388 polymorphisms on TCR-Mf; MUTYH rs3219489, XRCC4 rs28360135 and LIG4 rs1805388 polymorphisms on comet assay parameter; and OGG1 rs1052133 and XRCC4 rs28360135 polymorphisms on oxidative damage. Our results showed genotoxic effects related to occupational lead exposure to levels under the Portuguese regulation limit of 70 μg/dl. Moreover, a significant influence of polymorphisms in genes involved in DNA repair on genotoxicity biomarkers was observed.

Chromatin specialization in bivalve molluscs: a leap forward for the evaluation of Okadaic Acid genotoxicity in the marine environment

Marine biotoxins synthesized by Harmful Algal Blooms (HABs) represent one of the most important sources of contamination in marine environments as well as a serious threat to fisheries and aquaculture-based industries in coastal areas. Among these biotoxins Okadaic Acid (OA) is of critical interest as it represents the most predominant Diarrhetic Shellfish Poisoning biotoxin in the European coasts. Furthermore, OA is a potent tumor promoter with aneugenic and clastogenic effects on the hereditary material, most notably DNA breaks and alterations in DNA repair mechanisms. Therefore, a great effort has been devoted to the biomonitoring of OA in the marine environment during the last two decades, mainly based on physicochemical and physiological parameters using mussels as sentinel organisms. However, the molecular genotoxic effects of this biotoxin make chromatin structure a good candidate for an alternative strategy for toxicity assessment with faster and more sensitive evaluation. To date, the development of chromatin-based studies to this purpose has been hampered by the complete lack of information on chromatin of invertebrate marine organisms, especially in bivalve molluscs. Our preliminary results have revealed the presence of histone variants involved in DNA repair and chromatin specialization in mussels and clams. In this work we use this information to put forward a proposal focused on the development of chromatin-based tests for OA genotoxicity in the marine environment. The implementation of such tests in natural populations has the potential to provide an important leap in the biomonitoring of this biotoxin. The outcome of such monitoring may have critical implications for the evaluation of DNA damage in these marine organisms. They will provide as well important tools for the optimization of their harvesting and for the elaboration of additional tests designed to evaluate the safety of their consumption and potential implications for consumer's health.

Identification of differentially expressed genes in SHSY5Y cells exposed to okadaic acid by suppression subtractive hybridization

Background

Okadaic acid (OA), a toxin produced by several dinoflagellate species is responsible for frequent food poisonings associated to shellfish consumption. Although several studies have documented the OA effects on different processes such as cell transformation, apoptosis, DNA repair or embryogenesis, the molecular mechanistic basis for these and other effects is not completely understood and the number of controversial data on OA is increasing in the literature.

Results

In this study, we used suppression subtractive hybridization in SHSY5Y cells to identify genes that are differentially expressed after OA exposure for different times (3, 24 and 48 h). A total of 247 subtracted clones which shared high homology with known genes were isolated. Among these, 5 specific genes associated with cytoskeleton and neurotransmission processes (NEFM, TUBB, SEPT7, SYT4 and NPY) were selected to confirm their expression levels by real-time PCR. Significant down-regulation of these genes was obtained at the short term (3 and 24 h OA exposure), excepting for NEFM, but their expression was similar to the controls at 48 h.

Conclusions

From all the obtained genes, 114 genes were up-regulated and 133 were down-regulated. Based on the NCBI GenBank and Gene Ontology databases, most of these genes are involved in relevant cell functions such as metabolism, transport, translation, signal transduction and cell cycle. After quantitative PCR analysis, the observed underexpression of the selected genes could underlie the previously reported OA-induced cytoskeleton disruption, neurotransmission alterations and in vivo neurotoxic effects. The basal expression levels obtained at 48 h suggested that surviving cells were able to recover from OA-caused gene expression alterations.

In vivo genotoxicity assessment in rats exposed to Prestige-like oil by inhalation

One of the largest oil spill disasters in recent times was the accident of the oil tanker Prestige in front of the Galician coast in 2002. Thousands of people participated in the cleanup of the contaminated areas, being exposed to a complex mixture of toxic substances. Acute and prolonged respiratory symptoms and genotoxic effects were reported, although environmental exposure measurements were restricted to current determinations, such that attribution of effects observed to oil exposure is difficult to establish. The aim of this study was to analyze peripheral blood leukocytes (PBL) harvested from a rat model of subchronic exposure to a fuel oil with similar characteristics to that spilled by the Prestige tanker, in order to determine potential genotoxic effects under strictly controlled, in vivo exposure. Wistar Han and Brown Norway rats were exposed to the oil for 3 wk, and micronucleus test (MN) and comet assay, standard and modified with 8-oxoguanine DNA glycosylase (OGG1) enzyme, were employed to assess genotoxicity 72 h and 15 d after the last exposure. In addition, the potential effects of oil exposure on DNA repair capacity were determined by means of mutagen sensitivity assay. Results obtained from this study showed that inhalation oil exposure induced DNA damage in both Brown Norway and Wistar Han rats, especially in those animals evaluated 15 d after exposure. Although alterations in the DNA repair responses were noted, the sensitivity to oil substances varied depending on rat strain. Data support previous positive genotoxicity results reported in humans exposed to Prestige oil during cleanup tasks.

GENE EXPRESSION PROFILING OF HUMAN LIVER CARCINOMA (HepG2) CELLS EXPOSED TO THE MARINE TOXIN OKADAIC ACID

The marine toxin, okadaic acid (OA) is produced by dinoflagellates of the genera Prorocentrum and Dinophysis and is the causative agent of the syndrome known as diarrheic shellfish poisoning (DSP). In addition, OA acts as both a tumor promoter, attributed to OA-induced inhibition of protein phosphatases as well as an inducer of apoptosis. To better understand the potentially divergent toxicological profile of OA, the concentration dependent cytotoxicity and alterations in gene expression on the human liver tumor cell line HepG2 upon OA exposure were determined using RNA microarrays, DNA fragmentation, and cell proliferation assays as well as determinations of cell detachment and cell death in different concentrations of OA. mRNA expression was quantified for approximately 15,000 genes. Cell attachment and proliferation were both negatively correlated with OA concentration. Detached cells displayed necrotic DNA signatures but apoptosis also was broadly observed. Data suggest that OA has a concentration dependent effect on cell cycle, which might explain the divergent effects that at low concentration OA stimulates genes involved in the cell cycle and at high concentrations it stimulates apoptosis.

Alterations in metabolism-related genes induced in SHSY5Y cells by okadaic acid exposure

Okadaic acid (OA) is a widely distributed marine toxin produced by several phytoplanktonic species and responsible for diarrheic shellfish poisoning in humans. At the molecular level OA is a specific inhibitor of several types of serine/threonine protein phosphatases. Due to this enzymic inhibition, OA was reported to induce numerous alterations in relevant cellular physiological processes, including several metabolic pathways such as glucose uptake, lipolysis and glycolysis, heme metabolism, and glycogen and protein synthesis. In order to further understand the underlying mechanisms involved in OA-induced effects on cellular metabolism, the expression levels of six genes related to different catabolic and anabolic metabolism-related processes were analyzed by real-time polymerase chain reaction. Specifically, the expression patterns of GAPDH, TOMM5, SLC25A4, COII, QARS, and RGS5 genes were determined in SHSY5Y human neuroblastoma cells exposed to OA for 3, 24, or 48 h. All these genes showed alterations in their expression levels after at least one of the OA treatments tested. These alterations provide a basis to understand the mechanisms underlying the previously described OA-induced effects on different metabolic processes, mainly regarding glucose and mitochondrial metabolism. However, other OA-induced affected genes can not be ruled out, and further studies are required to more comprehensively characterize in the mechanisms of OA-induced interaction on cell metabolism.