Collapse of mitochondrial membrane potential and caspases activation are early events in okadaic acid-treated Caco-2 cells

Phosphorus rather than nitrogen driving biosynthesis of diarrhetic shellfish toxins in Prorocentrum caipirignum via ATP

Okadaic acid and its analogues such as dinophysisitoxins-1, -2 (DTX-1, -2) are potent inhibitors of protein phosphatase and causative toxins of diarrhetic shellfish poisoning (DSP). These toxins are produced by dinoflagellate genera Dinophysis and Prorocentrum. Numerous studies have reported that the cellular content of these toxins increased under macronutrient limitation or other stress conditions in genus Prorocentrum. However, our recent study demonstrated positive linear or exponential relationships between toxin production rate (Rtox) and phosphate consumption rate in five strains of P. lima complex/P. caipirignum. To further clarify macronutrients roles in OA production, P. caipirignum SE10 selected for its extremely low DTX-1 content due to potential competitive relationship with OA, was exposed to nitrogen (N) or phosphorus (P) limitation via batch or semi-batch cultures, after which the depleted nutrients were replenished to assess OA production dynamics. The Rtox of OA peaked initially before declining under both N and P-limited treatments. Notably, Rtox increased only upon P replenishment rather than N replenishment, confirming phosphorus's critical role in OA production. In P-addition experiments, Rtox stagnated in the P-deficient condition but rose proportionally with increasing P concentration. Meanwhile, ATP and NADPH levels surged 7.5-fold and 1.5-fold, respectively, within 1 h of P-addition compared to P-deficient treatment. To probe how P affects OA production, inhibitors targeting ATP and NADPH synthesis were applied. OA production was specifically suppressed by ATP inhibitors, such as N, N-dicyclohexylcarbodiimid (DCCD), rotenone (ROT), and 2,4-dintrophenol (DNP). The highest inhibition occurred with 20 μM DCCD, reducing OA cellular content by 90 % after 48 h. Moreover, increasing ATP inhibitor concentration shift Rtox from positive to negative values. These finding demonstrated that phosphorus drives OA production primarily by modulating ATP levels, which directly regulate toxin synthesis.

Spatiotemporal distribution of lipophilic shellfish toxins in plankton and shellfish in the offshore regions of Shandong province, China

Lipophilic shellfish toxins (LSTs) threaten the ecosystem health and seafood safety. To comprehensively investigate the spatiotemporal distribution of common LSTs in phytoplankton, zooplankton and economic shellfish, three cruises were conducted in five typical offshore aquaculture regions of Shandong province, China, including Haizhou Bay, Jiaozhou Bay, Sanggou Bay, Sishili Bay and Laizhou Bay, in spring (March-April), summer (July-August) and autumn (November-December). This study revealed significant variability in the composition and content of LSTs in phytoplankton samples collected from different regions. Pectenotoxin-2 (PTX2), dinophysistoxin-1 (DTX1) and okadaic acid (OA) were mainly detected in the ranges of not detected (nd)-5045 pmol g-1 dry weight (dw), nd-159 pmol g-1 dw, and nd-154 pmol g-1 dw, respectively. In zooplankton, DTX1 and OA were the predominant components of LSTs, with the highest levels of ∑LSTs in spring ranging from nd to 406 pmol g-1 dw. Spearman's correlation analysis between LSTs and environmental factors indicated significant correlations for the contents of homo-yessotoxin (hYTX), gymnodimine-A (GYM-A), and spirolide-1 (SPX1) with these factors. Totally relatively low levels of LSTs with dominative DTX1 were detected in economic shellfish, which showed a low risk to seafood safety for human health.

Apoptosis and oxidative stress of mouse breast carcinoma 4T1 and human intestinal epithelial Caco-2 cell lines caused by the phycotoxin gymnodimine-A

Gymnodimine-A (GYM-A) is a cyclic imine phycotoxin produced by some marine dinoflagellates. It can cause rapid death of mice via intraperitoneal administration and frequently accumulate in shellfish potentially threatening human health. In this study, four different cell lines were exposed to GYM-A for the viability assessment. Results showed that GYM-A was cytotoxic with concentration-dependent pattern to each cell type, with mean IC50 values ranging from 1.39 to 2.79 μmol L-1. Results suggested that the loss of cell viability of 4T1 and Caco-2 cells was attributed to apoptosis. Furthermore, the collapse of mitochondrial membrane potential and caspases activation were observed in the GYM-A-treated cells. Reactive oxygen species (ROS) and lipid peroxides (LPO) levels were markedly increased in 4T1 and Caco-2 cells exposed to GYM-A at 2 μmol L-1, and the oxidative stress in 4T1 cells was more obvious than that in Caco-2 cells. Additionally, unusual ultrastructure impairment on mitochondria and mitophagosomes occurred in the GYM-A-treated cells. These results suggested that an ROS-mediated mitochondrial pathway for apoptosis and mitophagy was implicated in the cytotoxic effects induced by GYM-A. This is the first report to explore the cytotoxic mechanisms of GYM-A through apoptosis and oxidative stress, and it will provide theoretical foundations for the potential therapeutic applications of GYM-A.

Exposure to okadaic acid could disrupt the colonic microenvironment in rats

Okadaic acid (OA) is one of the most prevalent marine phycotoxin with complex toxicity, which can lead to toxic symptoms such as diarrhea, vomiting, nausea, abdominal pain, and gastrointestinal discomfort. Studies have shown that the main affected tissue of OA is digestive tract. However, its toxic mechanism is not yet fully understood. In this study, we investigated the changes that occurred in the epithelial microenvironment following OA exposure, including the epithelial barrier and gut bacteria. We found that impaired epithelial cell junctions, mucus layer destruction, cytoskeletal remodeling, and increased bacterial invasion occurred in colon of rats after OA exposure. At the same time, the gut bacteria decreased in the abundance of beneficial bacteria and increased in the abundance of pathogenic bacteria, and there was a significant negative correlation between the abundance of pathogenic bacteria represented by Escherichia/Shigella and animal body weight. Metagenomic analysis inferred that Escherichia coli and Shigella spp. in Escherichia/Shigella may be involved in the process of cytoskeletal remodeling and mucosal layer damage caused by OA. Although more evidence is needed, our results suggest that opportunistic pathogens may be involved in the complex toxicity of OA during OA-induced epithelial barrier damage.

Cytotoxicity and intestinal permeability of phycotoxins assessed by the human Caco-2 cell model

Phycotoxins are a class of multiple natural metabolites produced by microalgae in marine and freshwater ecosystems that bioaccumulate in food webs, particularly in shellfish, having a great impact on human health. Phycotoxins are mainly leached and absorbed in the small intestine when human consumers accidentally ingest toxic aquatic products contaminated by them. To assess the intestinal uptake and damage of phycotoxins, a typical in vitro model was developed and widely applied using the human colorectal adenocarcinoma Caco-2 cell line. In this review, the application cases were summarized for multiple phycotoxins, including microcystins (MCs), cylindrospermopsins (CYNs), domoic acids (DAs), saxitoxins (STXs), palytoxins (PLTXs), okadaic acids (OAs), pectenotoxins (PTXs) and azaspiracids (AZAs). The results of the previous studies showed that each group of phycotoxins presented different cytotoxicity and mechanisms to Caco-2 cells, and significant discrepancies in the transport of phycotoxin across the Caco-2 cell monolayers. Therefore, this review describes the evaluation assays of the Caco-2 cell monolayer model, illustrates the principles of several primary cytotoxicity evaluation assays, and summarizes the cytotoxicity of each group of phycotoxins to Caco-2 cells line and their cellular transport, and finally proposes the development of multicellular intestinal models for future comprehensive studies on the toxicity and absorption of phycotoxins in the intestine. It will improve the understanding of Caco-2 cell monolayer models in the toxicology studies on phycotoxins and the potentially detrimental effects of microalgal toxins on the human intestine.

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.

Okadaic Acid Exposure Induced Neural Tube Defects in Chicken (Gallus gallus) Embryos

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

In vitro Evaluation of Programmed Cell Death in the Immune System of Pacific Oyster Crassostrea gigas by the Effect of Marine Toxins

Programmed cell death (PCD) is an essential process for the immune system's development and homeostasis, enabling the remotion of infected or unnecessary cells. There are several PCD's types, depending on the molecular mechanisms, such as non-inflammatory or pro-inflammatory. Hemocytes are the main component of cellular immunity in bivalve mollusks. Numerous infectious microorganisms produce toxins that impair hemocytes functions, but there is little knowledge on the role of PCD in these cells. This study aims to evaluate in vitro whether marine toxins induce a particular type of PCD in hemocytes of the bivalve mollusk Crassostrea gigas during 4 h at 25°C. Hemocytes were incubated with two types of marine toxins: non-proteinaceous toxins from microalgae (saxitoxin, STX; gonyautoxins 2 and 3, GTX2/3; okadaic acid/dynophysistoxin-1, OA/DTX-1; brevetoxins 2 and 3, PbTx-2,-3; brevetoxin 2, PbTx-2), and proteinaceous extracts from bacteria (Vibrio parahaemolyticus, Vp; V. campbellii, Vc). Also, we used the apoptosis inducers, staurosporine (STP), and camptothecin (CPT). STP, CPT, STX, and GTX 2/3, provoked high hemocyte mortality characterized by apoptosis hallmarks such as phosphatidylserine translocation into the outer leaflet of the cell membrane, exacerbated chromatin condensation, DNA oligonucleosomal fragments, and variation in gene expression levels of apoptotic caspases 2, 3, 7, and 8. The mixture of PbTx-2,-3 also showed many apoptosis features; however, they did not show apoptotic DNA oligonucleosomal fragments. Likewise, PbTx-2, OA/DTX-1, and proteinaceous extracts from bacteria Vp, and Vc, induced a minor degree of cell death with high gene expression of the pro-inflammatory initiator caspase-1, which could indicate a process of pyroptosis-like PCD. Hemocytes could carry out both PCD types simultaneously. Therefore, marine toxins trigger PCD's signaling pathways in C. gigas hemocytes, depending on the toxin's nature, which appears to be highly conserved both structurally and functionally.

Exposure to marine benthic dinoflagellate toxins may lead to mitochondrial dysfunction

Even though marine dinoflagellates are important primary producers, many toxic species may alter the natural equilibrium of aquatic ecosystems and even generate human intoxication incidents, as they are the major causative agents of harmful algal blooms. In order to deepen the knowledge regarding benthic dinoflagellate adverse effects, the present study aims to clarify the influence of Gambierdiscus excentricus strain UNR-08, Ostreopsis cf. ovata strain UNR-03 and Prorocentrum lima strain UNR-01 crude extracts on rat mitochondrial energetic function and permeability transition pore (mPTP) induction. Our results, expressed in number of dinoflagellate cell toxic compounds tested in a milligram of mitochondrial protein, revealed that 934 cells mg prot-1 of G. excentricus, and 7143 cells mg prot-1 of both O. cf. ovata and P. lima negatively affect mitochondrial function, including by decreasing ATP synthesis-related membrane potential variations. Moreover, considerably much lower concentrations of dinoflagellate extracts (117 cells mg prot-1 of G. excentricus, 1429 cells mg prot-1 of O. cf. ovata and 714 cells mg prot-1 of P. lima) produced mPTP-induced swelling in Ca2+-loaded isolated mitochondria. The present study clearly demonstrates the toxicity of G. excentricus, O. cf. ovata and P. lima extracts at the mitochondrial level, which may lead to mitochondrial failure and consequent cell toxicity, and that G. excentricus always provide much more severe effects than O. cf. ovata and P. lima.

Cultures of Dinophysis sacculus, D. acuminata and pectenotoxin 2 affect gametes and fertilization success of the Pacific oyster, Crassostrea gigas

Harmful algal blooms (HABs) of toxic species of the dinoflagellate genus Dinophysis are a threat to human health as they are mainly responsible for diarrheic shellfish poisoning (DSP) in the consumers of contaminated shellfish. Such contamination leads to shellfish farm closures causing major economic and social issues. The direct effects of numerous HAB species have been demonstrated on adult bivalves, whereas the effects on critical early life stages remain relatively unexplored. The present study aimed to determine the in vitro effects of either cultivated strains of D. sacculus and D. acuminata isolated from France or their associated toxins (i.e. okadaic acid (OA) and pectenotoxin 2 (PTX2)) on the quality of the gametes of the Pacific oyster Crassostrea gigas. This was performed by assessing the ROS production and viability of the gametes using flow cytometry, and fertilization success using microscopic counts. Oocytes were more affected than spermatozoa and their mortality and ROS production increased in the presence of D. sacculus and PTX2, respectively. A decrease in fertilization success was observed at concentrations as low as 0.5 cell mL^-1 of Dinophysis spp. and 5 nM of PTX2, whereas no effect of OA could be observed. The effect on fertilization success was higher when both gamete types were concomitantly exposed compared to separate exposures, suggesting a synergistic effect. Our results also suggest that the effects could be due to cell-to-cell contact. These results highlight a potential effect of Dinophysis spp. and PTX2 on reproduction and recruitment of the Pacific oyster.

EMT is the major target for okadaic acid-suppressed the development of neural crest cells in chick embryo

As a main marine phycotoxin, okadaic acid (OA) is mainly responsible for diarrheic shellfish poisoning (DSP), through specifically inhibiting phosphatase (PP1 and PP2A). It has been shown that isotope labelled-OA could cross the placental barrier in mice. However, it remains obscure how OA exposure could affect the formation of neural crest cells (NCCs), especially cranial NCCs in early embryo development. Here, we explored the effects of OA exposure on the generation of neural crest cells during embryonic development using the classic chick embryo model. We found that OA exposure at 100 nM (80.5 μg/L) could cause craniofacial bone defects in the developing chick embryo and delay the development of early chick embryos. Immunofluorescent staining of HNK-1, Pax7, and Ap-2α demonstrated that cranial NCC generation was inhibited by OA exposure. Double immunofluorescent staining with Ap-2α/PHIS3 or Pax7/c-Caspase3 manifested that both NCC proliferation and apoptosis were restrained by OA exposure. Furthermore, the expression of Msx1 and BMP4 were down-regulated in the developing chick embryonic neural tubes, which could contribute the inhibitive production of NCCs. We also discovered that expression of EMT-related adhesion molecules, such as Cadherin 6B (Cad6B) and E-cadherin, was altered following OA exposure. In sum, OA exposure negatively affected the development of embryonic neural crest cells, which in turn might result in cranial bone malformation.

Effects of algal toxin okadaic acid on the non-specific immune and antioxidant response of bay scallop (Argopecten irradians)

Okadaic acid (OA) is produced by dinoflagellates during harmful algal blooms and is a diarrhetic shellfish-poisoning (DSP) toxin. This toxin is particularly problematic for bivalves that are cultured for human consumption. This study aimed to reveal the effects of exposure to OA on the non-specific immune responses of bay scallop, Argopecten irradians. Various immunological parameters (superoxide dismutase (SOD), acid phosphatase (ACP), alkaline phosphatase (ALP), lysozyme activities, and total protein level) were assessed in the hemolymph of bay scallops at 3, 6, 12, 24, and 48 h post-exposure (hpe) to different concentrations (50, 100, and 500 nM) of OA. Moreover, the expression of immune system-related genes (MnSOD, PrxV, PGRP, and BD) was also measured. Results showed that SOD and ACP activities were decreased between 12 and 48 hpe. The ALP, lysozyme activities, and total protein levels were also modulated after exposure to different concentrations of OA. The expression of immune-system-related genes was also assessed at different time points during the exposure period. Overall, our results suggest that the exposure to OA had negative effects on the antioxidant and non-specific immune responses, and even disrupted the metabolism of bay scallops, making them more vulnerable to environmental stress-inducing agents; they provide a better understanding of the response status of bivalves against DSP toxins.

Individual and combined use of ginsenoside F2 and cyanidin-3-O-glucoside attenuates H2O2-induced apoptosis in HEK-293 cells via the NF-κB pathway

Ginsenoside F2 and cyanidin-3-O-glucoside synergistically inhibited H₂O₂-induced apoptosis in HEK-293 cells through mitochondria-mediated apoptotic and NF-κB pathways.

Neolignans from Nectandra megapotamica (Lauraceae) Display in vitro Cytotoxic Activity and Induce Apoptosis in Leukemia Cells

Nectandra megapotamica (Spreng.) Mez. (Lauraceae) is a well-known Brazilian medicinal plant that has been used in folk medicine to treat several diseases. In continuation of our ongoing efforts to discover new bioactive natural products from the Brazilian flora, this study describes the identification of cytotoxic compounds from the MeOH extract of N. megapotamica (Lauraceae) leaves using bioactivity-guided fractionation. This approach resulted in the isolation and characterization of eight tetrahydrofuran neolignans: calopeptin (1), machilin-G (2), machilin-I (3), aristolignin (4), nectandrin A (5), veraguensin (6), ganschisandrin (7), and galgravin (8). Different assays were conducted to evaluate their cytotoxic activities and to determine the possible mechanism(s) related to the activity displayed against human leukemia cells. The most active compounds 4, 5 and 8 gave IC₅₀ values of 14.2 ± 0.7, 16.9 ± 0.8 and 16.5 ± 0.8 µg/mL, respectively, against human leukemia (HL-60) tumor cells. Moreover, these compounds induced specific apoptotic hallmarks, such as plasma membrane bleb formation, nuclear DNA condensation, specific chromatin fragmentation, phosphatidyl-serine exposure on the external leaflet of the plasma membrane, cleavage of PARP as well as mitochondrial damage, which as a whole could be related to the intrinsic apoptotic pathway.

Apoptosis of hemocytes from lions-paw scallop Nodipecten subnodosus induced with paralyzing shellfish poison from Gymnodinium catenatum

The toxic dinoflagellate Gymnodinium catenatum produces paralyzing shellfish poisons (PSPs) that are consumed and accumulated by bivalves. Previously, we recorded a decrease in hemocytes 24h after injection of PSPs (gonyautoxin 2/3 epimers, GTX2/3) in the adductor muscle in the lions-paw scallop Nodipecten subnodosus. In this work, qualitative and quantitative analyses, in in vivo and in vitro experiments, revealed that the lower count of hemocytes results from cells undergoing typical apoptosis when exposed to GTX 2/3 epimers. This includes visible morphological alterations of the cytoplasmic membrane, damage to the nuclear membrane, condensation of chromatin, DNA fragmentation, and release of DNA fragments into the cytoplasm. Induction of apoptosis was accompanied by phosphatidylserine exposure to the outer cell membrane and activation of cysteine-aspartic proteases, caspase 3 and caspase 8. Addition of an inhibitor of caspase to the medium suppressed activation in hemocytes exposed to the toxins, suggesting that cell death was induced by a caspase-dependent apoptotic pathway. The results are important for future investigation of the scallop's immune system and should provide new insights into apoptotic processes in immune cells of scallops exposed to PSPs.

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.

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.

In vitro approaches to evaluate toxicity induced by organotin compounds tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) in neuroblastoma cells

The toxic effects of the organotin compounds (OTCs) monobutyltin (MBT), dibutyltin (DBT), and tributyltin (TBT) were evaluated in vitro in a neuroblastoma human cell line. Mechanisms of cell death, apoptosis versus necrosis, were studied by using several markers: inhibition of cell viability and proliferation, F-actin, and mitochondrial membrane potential changes as well as reactive oxygen species (ROS) production and DNA fragmentation. The most toxic effects were detected with DBT and TBT even at very low concentrations (0.1-1 μM). In contrast, MBT induced lighter cytotoxic changes at the higher doses tested. None of the studied compounds stimulated propidium iodide uptake, although the most toxic chemical, TBT, caused lactate dehydrogenase release at the higher concentrations tested. These findings suggest that in neuroblastoma, OTC-induced cytotoxicity involves different pathways depending on the compound, concentration, and incubation time. A screening method for DBT and TBT quantification based on cell viability loss was developed, allowing a fast detection alternative to complex methodology.

Effects of okadaic acid on haemocytes from Mytilus galloprovincialis: a comparison between field and laboratory studies

Individuals of Mytilus galloprovincialis, contaminated with Diarrheic Shellfish Poisoning (DSP) toxins, were studied with the aim to correlate the okadaic acid (OA) body burden and the percentage of damaged haemocytes by quantifying annexin V positive cells by flow cytometry. Results showed less percentage of damaged haemocytes in high OA contaminated samples. These data were compared with results of in vitro assays of mussel haemocytes exposed to increased concentrations of OA. Similarly, haemocytes exposed to the most concentrated OA solution were less damaged.

Effect of okadaic acid on cultured clam heart cells: involvement of MAPkinase pathways

Okadaic acid (OA) is one of the main diarrhetic shellfish poisoning toxins and a potent inhibitor of protein phosphatases 1 and 2A. The downstream signal transduction pathways following the protein phosphatase inhibition are still unknown and the results of most of the previous studies are often conflicting. The aim of the present study was to evaluate the effects of OA on heart clam cells and to analyse its possible mechanisms of action by investigating the signal transduction pathways involved in OA cytotoxicity. We showed that OA at 1 µM after 24 h of treatment induces disorganization of the actin cytoskeleton, rounding and detachment of fibroblastic cells. Moreover, treatment of heart cells revealed a sequential activation of MAPK proteins depending on the OA concentration. We suggest that the duration of p38 and JNK activation is a critical factor in determining cell apoptosis in clam cardiomyocytes. In the opposite, ERK activation could be involved in cell survival. The cell death induced by OA is a MAPK modulated pathway, mediated by caspase 3-dependent mechanism. OA was found to induce no significant effect on spontaneous beating rate or inward L-type calcium current in clam cardiomyocytes, suggesting that PP1 was not inhibited even by the highest dose of OA.

Laminarin induces apoptosis of human colon cancer LOVO cells through a mitochondrial pathway

Many scientific studies have shown that laminarin has anti-tumor effects, but the anti-tumor mechanism was unclear. The purpose of this study was to investigate the effect of laminarin on the induction of apoptosis in human colon cancer LOVO cells and the molecular mechanism involved. LOVO cells were treated with different concentrations of laminarin at different times. Morphology observations were performed to determine the effects of laminarin on apoptosis of LOVO cells. Flow cytometry (FCM) was used to detect the level of intracellular reactive oxygen species (ROS) and pH. Laser scanning confocal microscope (LSCM) was used to analyze intracellular calcium ion concentration, mitochondrion permeability transition pore (MPTP) and mitochondrial membrane potential (MMP). Western blotd were performed to analyze the expressions of Cyt-C, Caspase-9 and -3. The results showed the apoptosis morphology, which showed cell protuberance, concentrated cytoplasm and apoptotic bodies, was obvious after 72 h treatment. Laminarin treatment for 24 h increased the intracellular level of ROS and Ca²⁺; decreased pH value; activated intracellular MPTP and decreased MMP in dose-dependent manners. It also induced the release of Cyt-C and the activation of Caspase-9 and -3. In conclusion, laminarin induces LOVO cell apoptosis through a mitochondrial pathway, suggesting that it could be a potent agent for cancer prevention and treatment.

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.

Okadaic acid inhibits cell growth and photosynthetic electron transport in the alga Dunaliella tertiolecta

Okadaic acid (OA), which is produced by several dinoflagellate species, is a phycotoxin known to induce a decrease of biomass production in phytoplankton. However, the mechanisms of OA cytotoxicity are still unknown in microalgae. In this study, we exposed the green microalga Dunaliella tertiolecta to OA concentrations of 0.05 to 0.5 μM in order to evaluate its effects on cell division, reactive oxygen species production and photosynthetic electron transport. After 72 h of treatment under continuous illumination, OA concentrations higher than 0.10 μM decreased culture cell density, induced oxidative stress and inhibited photosystem II electron transport capacity. OA effect in D. tertiolecta was strongly light dependent since no oxidative stress was observed when D. tertiolecta was exposed to OA in the dark. In the absence of light, the effect of OA on culture cell density and photosystem II activity was also significantly reduced. Therefore, light appears to have a significant role in the toxicity of OA in microalgae. Our results indicate that the site of OA interaction on photosynthetic electron transport is likely to be at the level of the plastoquinone pool, which can lead to photo-oxidative stress when light absorbed by the light-harvesting complex of photosystem II cannot be dissipated via photochemical pathways. These findings allowed for a better understanding of the mechanisms of OA toxicity in microalgae.

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.

Cytotoxic activity of extracts of marine sponges from NW Spain on a neuroblastoma cell line

Six species of marine sponges collected at intertidal and sublittoral sites of the coast of Galicia (NW Spain) were screened for potential cytotoxic properties on Neuroblastoma BE(2)-M17 cell line. Exposure to Halichondria panicea, Pachymatisma johnstonia, Ophlitaspongia seriata and Haliclona sp. aqueous extracts strongly affected cell appearance, inducing loss of neuron-like morphology and the formation of clumps. Extracts from these species also caused significant rates of cell detachment and decrease of mitochondrial membrane potential. Incubation with P. johnstonia, O. seriata and Suberites massa extracts also decreased the rate of cell proliferation. The increase of incubation time enhanced propidium iodide uptake by neuroblastoma cells. Toxic responses triggered by sponge extracts are compatible with apoptotic phenomena in neuroblastoma cells, even though increasing propidium uptake at long periods of exposure might indicate the induction of secondary necrosis. The cytotoxic properties of the tested extracts suggest the presence of compounds with potential pharmacological or biotechnological applications in the screened sponge species.

Modulation of ROS/MAPK signaling pathways by okadaic acid leads to cell death via, mitochondrial mediated caspase-dependent mechanism

Okadaic acid (OA) is a specific and potent protein phosphatase inhibitor and tumor promoter. The present study establishes the role of reactive oxygen species (ROS) and mitogen activated protein kinases in cell death induced by okadaic acid. The study showed that okadaic acid is cytotoxic at 10 nM with an IC50 of 100 nM in U-937 cells. The CVDE assay and mitochondrial dehydrogenase assay showed a time dependent cytotoxicity. The phase contrast visualization of the OA treated cells showed the apoptotic morphology and was confirmed with esterase staining for plasma membrane integrity. OA activated caspases-7, 9 and 3, PARP cleavage and induced nuclear damage in a time and dose dependent manner. Compromised mitochondrial membrane potential, release of cytochrome-c and apoptosis inducing factor confirms the involvement of mitochondria. A time dependent decrease in glutathione levels and a dose dependent increase in ROS with maximum at 30 min were observed. ROS scavenger-N-acetyl cysteine, mitochondrial stabilizer-cyclosporin-A, and broad spectrum caspase inhibitor Z-VAD-FMK inhibited the OA induced caspase-3 activation, DNA damage and cell death but caspase-8 inhibitor had no effect. OA activated p38 MAPK and JNK in a time dependent manner, but not ERK½. MAP kinase inhibitors SB203580, SP600125 and PD98059 confirm the role of p38 MAPK and JNK in OA induced caspase-3 activation and cell death. Over all, our results indicate that OA induces cell death by generation of ROS, and activation of p38 MAPK and JNK, and executed through mitochondrial mediated caspase pathway.

Okadaic acid induces morphological changes, apoptosis and cell cycle alterations in different human cell types

Okadaic acid (OA) is a marine toxin produced by dinoflagellate species which is frequently accumulated in molluscs usual in the human diet. The exact action mechanism of OA has not been described yet and the results of most reported studies are often conflicting. The aim of this work was to evaluate the OA effects on morphology, cell cycle and apoptosis induction by means of light microscopy and flow cytometry, in three different types of human cells (leukocytes, HepG2 cells and SHSY5Y cells). Cells were treated with a range of OA concentrations in the presence and absence of S9 fraction. OA induced morphological changes in all the cell types studied, and cell cycle disruption only in leukocytes and neuronal cells. SHSY5Y cells were the most sensitive to OA assault. Results obtained in the presence and absence of metabolic activation were similar, suggesting that OA acts both directly and indirectly. Furthermore, OA was found to increase the subG(1) region in the flow cytometry cell cycle analysis, suggesting induction of apoptosis. These results were confirmed by the employment of specific methodologies for studying apoptosis such as caspase 3 activation and annexin V staining. Increases in the apoptosis rate were obtained in all the cells treated in the absence of S9 fraction, accompanied by increases in caspase 3 activation, suggesting that apoptosis induced by OA is a caspase 3-dependent process. Nevertheless, in the presence of S9 fraction no apoptosis was detected, indicating a metabolic detoxifying activity, although necrosis was observed in neuroblastoma cells.

Disruption of the F-actin cytoskeleton and monolayer barrier integrity induced by PAF and the protective effect of ITF on intestinal epithelium

To explore whether platelet-activating factor (PAF) can disrupt the intestinal epithelial barrier directly and is associated with structural alterations of the F-actin-based cytoskeleton, and to observe the protective effect of intestinal trefoil factor (ITF), we establish an intestinal epithelia barrier model using Caco-2 cells in vitro. Transepithelial electrical resistance and unidirectional flux of lucifer yellow were measured to evaluate barrier permeability; immunofluorescent staining and flow cytometry were applied to observe morphological alterations and to quantify proteins of the F-actin cytoskeleton: the tight junction marker ZO-1 and Claudin-1 were observed using immunofluorescent staining. PAF significantly increased paracellular permeability, at the same time, F-actin and tight junction proteins were disrupted. It was thought that ITF could reverse the high permeability by restoring normal F-actin, ZO-1 and Claudin-1 structures. These results collectively demonstrated that PAF plays an important role in the regulation of mucosal permeability and the effects of PAF are correlated with structural alterations of the F-actin-based cytoskeleton and of tight junctions. ITF can protect intestinal epithelium against PAF-induced disruption by restricting the rearrangement of the F-actin cytoskeleton and of tight junctions.

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.

Morphological and biochemical changes associated with apoptosis induced by okadaic acid in human amniotic FL cells

The marine toxin okadaic acid (OA) is an apoptosis inducer and a tumor promoter. During recent years, extensive studies have demonstrated that OA can induce apoptosis in a wide variety of cell types. In contrast to the relatively longer incubation time or higher treatment concentrations of OA in apoptosis shown previously, relatively lower concentrations (<or=100 nM) and shorter time (4 h) were designed in the current study to observe the toxic effects of OA in human amniotic cells (FL cells). The present study was undertaken to determine the morphological and biochemical changes of FL cells induced by OA. Results indicated that externalization of phosphatidylserine, cytoskeletal disruption, DNA strand breaks and decrease of Bcl-2 protein expression levels as well as increase of PP2A-A subunit protein were all involved in the apoptosis of FL cells induced by OA. This work not only provided further evidence of apoptosis induced by OA but also suggested that PP2A might play a pivotal role in apoptosis induced by protein phosphatases inhibitors.

Titanium dioxide nanoparticles induce apoptosis through the JNK/p38-caspase-8-Bid pathway in phytohemagglutinin-stimulated human lymphocytes

We investigated the signaling pathways underlying nano-TiO(2)-induced apoptosis in cultured human lymphocytes. Nano-TiO(2) increased the proportion of sub-G1 cells, activated caspase-9 and caspase-3, and induced caspase-3-mediated PARP cleavage. Nano-TiO(2) also induced loss of mitochondrial membrane potential, which suggests that nano-TiO(2) induces apoptosis via a mitochondrial pathway. A time-sequence analysis of the induction of apoptosis by nano-TiO(2) revealed that nano-TiO(2) triggered apoptosis through caspase-8/Bid activation. We also observed that inhibition of caspase-8 by z-IETD-fmk suppressed the caspase-8/Bid activation, caspase-3-mediated PARP cleavage, and apoptosis. Nano-TiO(2) activated two MAPKs, p38 and JNK. In addition, the selective p38 inhibitor SB203580 and selective JNK inhibitor SP600125 suppressed nano-TiO(2)-induced apoptosis and caspase-8 activation to moderate and significant extents, respectively. Knockdown of protein levels of JNK1 and p38 using an RNA interference technique also suppressed caspase-8 activation. Our results suggest that nano-TiO(2)-induced apoptosis is mediated by the p38/JNK pathway and the caspase-8-dependent Bid pathway in human lymphocytes.

Multiple signal transduction pathways in okadaic acid induced apoptosis in HeLa cells

Okadaic acid (OA) is the major component of diarrhetic shell fish poisoning toxins and a potent inhibitor of protein phosphatase 1 and 2A. We investigated the signal transduction pathways involved in OA induced cell death in HeLa cells. OA induced cytotoxicity and apoptosis at IC50 of 100nM. OA treatment resulted in time dependent increase in reactive oxygen species and depleted intracellular glutathione levels. Loss of mitochondrial membrane permeability led to translocation of bax, cytochrome-c and AIF from mitochondria to cytosol. The cells under fluorescence microscope showed typical apoptotic morphology with condensed chromatin, and nuclear fragmentation. We investigated the mitochondrial-mediated caspase cascade. The time dependent activation and cleavage of of bax, caspases-8, 10, 9, 3 and 7 was observed in Western blot analysis. In addition to caspase-dependent pathway AIF mediated caspase-independent pathway was involved in OA mediated cell death. OA also caused time dependent inhibition of protein phosphatase 2A activity and phosphorylation of p38 and p42/44 MAP kinases. Inhibitor studies with Ac-DEVO-CHO and Z-VAD-FMK could not prevent the phosphorylation of p38 and p42/44 MAP kinases. Our experiments with caspase inhibitors Ac-DEVD-CHO, Z-IETD-FMK and Z-VAD-FMK inhibited capsase-3, 8 cleavages but did not prevent OA-induced apoptosis and DNA fragmentation. Similarly, pretreatment with cyclosporin-A and N-acetylcysteine could not prevent the DNA fragmentation. In summary, the results of our study show that OA induces multiple signal transduction pathways acting either independently or simultaneously leading to apoptosis.

In vitro approaches to evaluate palytoxin-induced toxicity and cell death in intestinal cells

Palytoxin isolated from the genus Palythoa is the most potent marine toxin known. The aim of the present study was to quantify palytoxin-induced cellular injury in the human intestinal cell line Caco-2. Cellular damage was measured by evaluating cell proliferation, cell membrane permeability, cell morphology and apoptotic markers. Furthermore, changes in F-actin were studied after exposure of cells to increasing amounts of palytoxin. The results show that cell proliferation decreased in a concentration-dependent manner with a mean IC(50) value of about 0.1 nM. A noticeable increase of cell detachment correlated with cell rounding and F-actin depolymerization was observed in palytoxin-treated cells. Moreover LDH was released from the cells in a dose and time dependent manner, although under these conditions there was no propidium iodide uptake. On the other hand, palytoxin impaired mitochondrial activity but other apoptotic markers, such as DNA fragmentation or caspases activation, were not observed. The results obtained in this paper suggest that the effects of palytoxin in Caco-2 cells were very potent and unspecific, since a primary necrosis and a secondary apoptosis seem to occur under these conditions.

Characteristics of palytoxin-induced cytotoxicity in neuroblastoma cells

Cation fluxes appear to play a key role in palytoxin-induced signal. There are other cellular targets that have not been described as well as the biochemical signaling cascades that transmit palytoxin-stimulated signals remain to be clarified. Since modifications of cations, mainly calcium, are generally associated to cell death or apoptosis, we wanted to further evaluate the effect of palytoxin on cell death. Then, in vitro cytotoxic effects of palytoxin were characterized on human neuroblastoma cells. By using several techniques, we studied markers of cell death and apoptosis, such as cell detachment, mitochondrial membrane potential, caspases, DNA damage, LDH leakage, propidium iodide uptake, F-actin depolymerization and inhibition of cellular proliferation. Results show that palytoxin triggers a series of toxic responses; it inhibits cell proliferation, induces cell rounding, detachment from the substratum and F-actin disruption. Among the apoptotic markers studied we only detected fall in mitochondrial membrane potential. Neither caspases activation nor chromatin condensation or DNA fragmentation were observed in palytoxin-treated cells.

Cytotoxic effects of BADGE (bisphenol A diglycidyl ether) and BFDGE (bisphenol F diglycidyl ether) on Caco-2 cells in vitro

Bisphenol A diglycidyl ether (BADGE) and bisphenol F diglycidyl ether (BFDGE) are used as starting substances for the manufacturing of epoxy resins used in internal can coatings. They are obtained by a condensation reaction between epichlorohydrin with bisphenol A and bisphenol F, respectively. These potential endocrine disrupting chemicals are able to enter the food chain and to reach the intestinal epithelium, causing structural and functional damages. The human colorectal adenocarcinoma cell line Caco-2 is a widely used in vitro model of the intestinal cells. The aim of this study was to characterize BADGE and BFDGE toxicity in Caco-2 cells, in particular, at the cellular and molecular level. Using several approaches, we characterized BADGE- and BFDGE-induced cell toxicity in Caco-2 cells. The treatment was done using different concentrations up to cytotoxic doses and different times of exposure to the agents. We evaluated the effect of these compounds on cell morphology, cell detachment, cell proliferation, F-actin disruption and plasma membrane integrity. Both compounds are able to induce morphological changes, cell detachment from the substratum and to inhibit cell proliferation, being these effects time and dose-dependent. Moreover, BADGE and BFDGE induce F-actin depolymerization, this effect is very potent at 24 h of incubation with the agents and a complete F-actin disruption can be observed at 200 microM BADGE or BFDGE. In addition, cell integrity is not damaged, since neither propidium iodide uptake nor LDH release takes place in Caco-2 cells exposed to high doses of these agents for 24 h.