Caspase activation and death induced by yessotoxin in HeLa cells

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

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

Single-Cell Tracking of A549 Lung Cancer Cells Exposed to a Marine Toxin Reveals Correlations in Pedigree Tree Profiles

Long-term video-based tracking of single A549 lung cancer cells exposed to three different concentrations of the marine toxin yessotoxin (YTX) reveals significant variation in cytotoxicity, and it confirms the potential genotoxic effects of this toxin. Tracking of single cells subject to various toxic exposure, constitutes a conceptually simple approach to elucidate lineage correlations and sub-populations which are masked in cell bulk analyses. The toxic exposure can here be considered as probing a cell population for properties and change which may include long-term adaptation to treatments. Ranking of pedigree trees according to a measure of "size," provides definition of sub-populations. Following single cells through generations indicates that signaling cascades and experience of mother cells can pass to their descendants. Epigenetic factors and signaling downstream lineages may enhance differences between cells and partly explain observed heterogeneity in a population. Signaling downstream lineages can potentially link a variety of observations of cells making resulting data more suitable for computerized treatment. YTX exposure of A549 cells tends to cause two main visually distinguishable classes of cell death modalities ("apoptotic-like" and "necrotic-like") with approximately equal frequency. This special property of YTX enables estimation of correlation between cell death modalities for sister cells indicating impact downstream lineages. Hence, cellular responses and adaptation to treatments might be better described in terms of effects on pedigree trees rather than considering cells as independent entities.

Mitotic Catastrophe in BC3H1 Cells following Yessotoxin Exposure

The marine toxin yessotoxin (YTX) can cause various cytotoxic effects depending on cell type and cell line. It is well known to trigger distinct mechanisms for programmed cell death which may overlap or cross-talk. The present contribution provides the first evidence that YTX can cause genotoxicity and induce mitotic catastrophe which can lead to different types of cell death. This work also demonstrates potential information gain from non-intrusive computer-based tracking of many individual cells during long time. Treatment of BC3H1 cells at their exponential growth phase causes atypical nuclear alterations and formation of giant cells with multiple nuclei. These are the most prominent morphological features of mitotic catastrophe. Giant cells undergo slow cell death in a necrosis-like manner. However, apoptotic-like cell death is also observed in these cells. Electron microscopy of treated BC3H1 cells reveal uncondensed chromatin and cells with double nuclei. Activation of p-p53, p-H2AX, p-Chk1, p-ATM, and p-ATR and down-regulation of p-Chk2 indicate DNA damage response and cell cycle deregulation. Micronuclei formation further support this evidence. Data from tracking single cells reveal that YTX treatment suppresses a second round of cell division in BC3H1 cells. These findings suggest that YTX can induce genomic alterations or imperfections in chromosomal segregation leading to permanent mitotic failure. This understanding extends the list of effects from YTX and which are of interest to control cancer and tumor progression.

Yessotoxin, a Promising Therapeutic Tool

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

Lifetime Distributions from Tracking Individual BC3H1 Cells Subjected to Yessotoxin

This work shows examples of lifetime distributions for individual BC3H1 cells after start of exposure to the marine toxin yessotoxin (YTX) in an experimental dish. The present tracking of many single cells from time-lapse microscopy data demonstrates the complexity in individual cell fate and which can be masked in aggregate properties. This contribution also demonstrates the general practicality of cell tracking. It can serve as a conceptually simple and non-intrusive method for high throughput early analysis of cytotoxic effects to assess early and late time points relevant for further analyzes or to assess for variability and sub-populations of interest. The present examples of lifetime distributions seem partly to reflect different cell death modalities. Differences between cell lifetime distributions derived from populations in different experimental dishes can potentially provide measures of inter-cellular influence. Such outcomes may help to understand tumor-cell resistance to drug therapy and to predict the probability of metastasis.

Palytoxin induces dissociation of HSP 27 oligomers through a p38 protein kinase pathway

Palytoxin (PlTX) induces a stress response in MCF-7 cells that involves the phosphorylation of HSP 27 at serines 15, 78, and 82 by an as yet undetermined mechanism. We have studied the involvement of major groups of the mitogen-activated protein kinase (MAPK) family in this molecular response and focused our analyses on the ERK1/2, JNK, p38 protein kinase (p38K), and ERK5 pathways. The results show that PlTX induces the activation of JNK and p38 kinase but not ERK1/2 and 5 in MCF-7 cells. Through the use of protein kinase inhibitors, we established that blocking p38K, but not JNK, prevents the phosphorylation of HSP 27 induced by PlTX and that MAPKAPK2 participates in the response induced by the toxin under our experimental conditions. The cell death response induced by PlTX was inhibited by preventing JNK phosphorylation but not by blocking p38K/MAPKAPK2 and HSP 27 phosphorylation. Sucrose density gradient centrifugation revealed that MCF-7 cell extracts contain a heterodisperse population of HSP 27, including oligomers and smaller forms. Treating MCF-7 cells with PlTX caused the dissociation of HSP 27 oligomers, and using inhibitors of the JNK and p38K pathways showed that the dissociation of HSP 27 oligomers induced by PlTX involves a p38K-dependent process. We conclude that the changes induced by PlTX in the HSP 27 stress response protein system proceed through a molecular mechanism involving the activation of the p38 kinase pathway and its substrate, MAPKAK2, leading to dissociation of HSP 27 oligomers and the stabilization of a cellular pool of monomers phosphorylated at serines 15, 78 and 82, which could play a protective role against the death response induced by PlTX.

Role of AKAP 149-PKA-PDE4A complex in cell survival and cell differentiation processes

The cellular localization of A-kinase anchoring proteins (AKAPs), protein kinase A (PKAs) and phosphodiesterases (PDEs) is a key step to the spatiotemporal regulation of the second messenger adenosine 3',5'-cyclic monophosphate (cAMP). In this paper the cellular distribution of the mitochondrial AKAP 149-PKA-PDE4A complex and its implications in the cell death induced by YTX treatment, a known PDE modulator, was studied. K-562 cell line was incubated with YTX for 24 or 48 h. Under these conditions AKAP 149, PKA and type-4A PDE (PDE4A) levels were measured in the cytosol, in the plasma membrane and in the nucleus. Apoptotic hallmarks were also measured after the same conditions. In addition, YTX effect on cell viability was checked after AKAP 149 and PDE4A silencing. The results obtained show a decrease in AKAP 149-PKA-PDE4A levels in cytosol after YTX exposure. 24h after the toxin addition, the complex expression increased in the plasma membrane and after 48 h in the nucleus domain. Furthermore Bcl-2 levels were decreased and the expression of caspase 3 together with caspase 8 activity were increased after 24h of toxin incubation but not after 48 h. These results suggest apoptotic cell death at 24h and a non-apoptotic cell death after 48 h. When AKAP 149 and PDE4A were silenced YTX did not induce cellular death. In summary, AKAP 149-PKA-PDE4A complex localization is related with YTX effect in K-562 cell line. When this complex is mainly located in the plasma membrane apoptosis is activated while when the complex is in the nuclear domain non-apoptotic cellular death or cellular differentiation is activated. Therefore AKAP 149-PKA-PDE4A distribution and integrity have a key role in cellular survival.

Yessotoxin triggers ribotoxic stress

This work tests the hypothesis that the marine algal toxin yessotoxin (YTX) can trigger ribotoxic stress response in L6 and BC3H1 myoblast cells. YTX exposure at a concentration of 100 nM displays the characteristics of a ribotoxic stress response in such cells. The exposure leads to activation of the p38 mitogen-activated protein kinase, the stress-activated protein kinase c-jun, and the double-stranded RNA-activated protein kinase (PKR). YTX treatment also causes ribosomal RNA cleavage and inhibits protein synthesis. These observations support the idea that YTX can act as a ribotoxin.

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

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

Effect of yessotoxin on cytosolic calcium levels in human hepatocellular carcinoma cells in vitro

Yessotoxin (YTX) and its analogs are a type of marine toxins found in marine environments in numerous coastal countries. These toxins tend to accumulate in filter-feeding molluscs and may threaten the shellfish industry and public health. Several previous studies indicated that YTX may induce apoptosis in different types of cell lines, although the exact underlying mechanisms have not yet been elucidated. The aim of this study was to mainly focus on the effect of YTX on cytosolic Ca²⁺ levels in human hepatocellular carcinoma cells. In order to investigate the exact mechanism of YTX-evoked Ca²⁺ increase, laser scanning confocal microscopy was used, with the addition of the chelator ethylene glycol tetraacetic acid (EGTA) and nifedipine, an L-type Ca²⁺ channel blocker, to the reaction system. The results demonstrated that YTX caused cytosolic Ca²⁺ level increase in Bel7402 cells and the YTX-evoked Ca²⁺ increase was successfully blocked by EGTA and nifedipine. Therefore, our results indicated that YTX may cause apoptosis via inducing Ca²⁺ entry in Bel7402 cells.

Role of yessotoxin in calcium and cAMP-crosstalks in primary and K-562 human lymphocytes: the effect is mediated by anchor kinase A mitochondrial proteins

Yessotoxin (YTX) is a marine polyether toxin previously described as a phosphodiesterase (PDE) activator in fresh human lymphocytes. This toxin induces a decrease of adenosine 3',5'-cyclic monophosphate (cAMP) levels in fresh human lymphocytes in a medium with calcium (Ca(2+) ), whereas the contrary effect has been observed in a Ca(2+) -free medium. In the present article, the effect of YTX in K-562 lymphocytes cell line has been analysed. Surprisingly, results obtained in K-562 cell line are completely opposite than in fresh human lymphocytes, since in K-562 cells YTX induces an increase of cAMP levels. YTX cytotoxicity was also studied in both K-562 cell line and fresh human lymphocytes. Results demonstrate that YTX does not modify fresh human lymphocytes viability, whereas in K-562 cells, YTX has a highly cytotoxic effect. It has been described in a previous study that YTX induces a small cytosolic Ca(2+) increase in fresh human lymphocytes but no effect was observed on Ca(2+) pools depletion in these cells. However, our results show that, in K-562 cells, YTX has no effect on cytosolic Ca(2+) levels in a medium with Ca(2+) and induces an increase on Ca(2+) pools depletion followed by a Ca(2+) influx. As far as Ca(2+) modulation is concerned these results demonstrate that YTX has a clear opposite effect in tumoural and fresh human lymphocytes. In addition, intracellular Ca(2+) reservoirs affected by YTX are different than thapsigargin-sensible pools. Furthermore, YTX-dependent Ca(2+) pools depletion was abolished by cAMP analogue (dibutyryl cAMP), phosphodiesterase-4 (PDE4) inhibitor (rolipram), protein kinase A inhibitor (H89) and oxidative phosphorylation uncoupler carbonyl cyanide p-(trifluoromethoxy) (FCCP) treatments. This evidences the crosstalks between Ca(2+) , YTX and cAMP pathways. Also, results obtain demonstrate that YTX-dependent Ca(2+) influx was only abolished by FCCP pre-treatment, which indicates a link between YTX and mitochondria in K-562 cell line. Cytosolic expression of A-kinase anchor proteins (AKAPs), the proteins which integrates phosphodiesterases (PDEs) and PKA to the mitochondria, was determined in both cell models. On the one hand, in human fresh lymphocytes, YTX increases AKAP149 cytosolic expression. This fact is accompanied with a decrease in cAMP levels, and therefore PDEs activation, which finally leads to cell survival. On the other hand, in tumoural lymphocytes, YTX has an opposite effect since decreases AKAP149 cytosolic expression and increase cAMP levels which leads to cell death. This is the first time that YTX and mitochondrial AKAPs proteins relationship is characterised.

Yessotoxin affects fMLP-induced cell shape changes inMytilus galloprovincialisimmunocytes

Using computer-assisted microscopic image analysis, we have found that algal yessotoxin (YTX) affects the immune response of Mytilus galloprovincialis. Indeed, YTX increases immunocyte cell motility through the involvement of both extracellular Ca2+ and cAMP, but not through protein kinase A, protein kinase C or phosphoinositide 3-kinase. Alone, however, the toxin does not induce any effect, as its action on cell motility is observed only after addition of the chemotactic substance N-formyl-Meth-Leu-Phe (fMLP). fMLP is known to induce cellular changes via both the phosphatidylinositol and cAMP pathways and, from this scenario, we can surmise that Ca2+ and cAMP concentrations rise sufficiently in fMLP-activated immunocytes to reveal YTX action. One possible explanation is that the toxin increases fMLP-mediated cell activation by intervening in L-type Ca2+-channel opening through a cAMP-dependent/PKA-independent pathway.

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

In this review, we focus on processes, organs and systems targeted by the marine toxins yessotoxin (YTX), okadaic acid (OA) and palytoxin (PTX). The effects of YTX and their basis are analyzed from data collected in the mollusc Mytilus galloprovincialis, the annelid Enchytraeus crypticus, Swiss CD1 mice and invertebrate and vertebrate cell cultures. OA and PTX, two toxins with a better established mode of action, are analyzed with regard to their effects on development. The amphibian Xenopus laevis is used as a model, and the Frog Embryo Teratogenesis Assay-Xenopus (FETAX) as the experimental protocol.

Yessotoxin inhibits phagocytic activity of macrophages

Yessotoxin (YTX) is a sulphated polyether compound produced by some species of dinoflagellate algae, that can be accumulated in bivalve mollusks and ingested by humans upon eating contaminated shellfish. Experiments in mice have demonstrated the lethal effect of YTX after intraperitoneal injection, whereas its oral administration has only limited acute toxicity, coupled with an alteration of plasma membrane protein turnover in the colon of the animals. In vitro studies have shown that this effect is due to the inhibition of endocytosis induced by the toxin. In this work, we investigated the effects of YTX on phagocytosis by using the J774 macrophage cell line. We found that macrophages exposed to 10 or 1 nM YTX display a reduced phagocytic activity against Candida albicans; moreover, phagosome maturation is also inhibited in these cells. Such results were confirmed with resident peritoneal macrophages from normal mice. The inhibition of both phagocytosis and phagosome maturation likely involves cytoskeletal alterations, since a striking rearrangement of the F-actin organization occurs in YTX-treated J774 macrophages. Surprisingly, YTX also enhances cytokine production (TNF-alpha, MIP-1alpha and MIP-2) by J774 macrophages. Overall, our results show that low doses of YTX significantly affect both effector and secretory functions of macrophages.

In vitro effects of yessotoxin on a primary culture of rat cardiomyocytes

Oral administration of yessotoxin (YTX) has been reported to induce ultrastructural alterations in rodent cardiac muscle. To study its effects on various fundamental aspects of cardiac muscle cells activity, that is, cell beating, Ca(2+) and cyclic adenosine 3',5'-monophosphate (cAMP) levels, as well as cell vitality, a primary culture of rat cardiomyocytes was used. Patch-clamp recordings, Ca(2+) imaging, and cAMP assays were performed on cultured cardiomyocytes to characterize YTX effects on the cell beating frequency. 3-(4,5-Dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) and sulforhodamine B (SRB) tests were carried out to determine its effect on cardiomyocytes viability. Videoimaging techniques showed a time- and concentration-dependent reduction in the beating frequency after 1, 5, and 24 h incubation with YTX (0.1-1 microM). This effect was neither associated to the uncoupling between the membrane electrical activity and Ca(2+) release from intracellular stores nor to the impairment of the mechanisms controlling the Ca(2+) homeostasis. In addition, 1 microM YTX did not modify basal cAMP levels in cardiomyocytes. MTT and SRB assays revealed that incubation of cardiomyocytes with YTX (0.01-1 microM; 24, 48, and 72 h) caused a decrease in cell viability in a concentration- and time-dependent way. This effect was still evident in cardiomyocytes exposed to YTX for 1, 5, and 24 h and cultured up to 72 h in YTX-free medium. Our results demonstrate that, at nanomolar concentrations, a short incubation with YTX causes an inhibition of the beating activity and an irreversible reduction of viability of cardiac cells in vitro.

Yessotoxins, a group of marine polyether toxins: an overview

Yessotoxin (YTX) is a marine polyether toxin that was first isolated in 1986 from the scallop Patinopecten yessoensis. Subsequently, it was reported that YTX is produced by the dinoflagellates Protoceratium reticulatum, Lingulodinium polyedrum and Gonyaulax spinifera. YTXs have been associated with diarrhetic shellfish poisoning (DSP) because they are often simultaneously extracted with DSP toxins, and give positive results when tested in the conventional mouse bioassay for DSP toxins. However, recent evidence suggests that YTXs should be excluded from the DSP toxins group, because unlike okadaic acid (OA) and dinophyisistoxin-1 (DTX-1), YTXs do not cause either diarrhea or inhibition of protein phosphatases. In spite of the increasing number of molecular studies focused on the toxicity of YTX, the precise mechanism of action is currently unknown. Since the discovery of YTX, almost forty new analogues isolated from both mussels and dinoflagellates have been characterized by NMR or LC-MS/MS techniques. These studies indicate a wide variability in the profile and the relative abundance of YTXs in both, bivalves and dinoflagellates. This review covers current knowledge on the origin, producer organisms and vectors, chemical structures, metabolism, biosynthetic origin, toxicological properties, potential risks to human health and advances in detection methods of YTXs.

Induction of apoptosis by YTX in myoblast cell lines via mitochondrial signalling transduction pathway

Yessotoxin (YTX) can induce apoptotic events in myoblast L6 and BC3H1 cell lines from rat and mouse, respectively. The present study indicates that apoptosis induced by YTX in these cell lines can occur through activation of the mitochondrial pathway indicating an intracellular response. Terminal events during mitochondrial-mediated apoptosis involve perturbations to mitochondria resulting in loss of mitochondrial membrane potential (DeltaPsi(m)), permeability transition pore (PTP) opening and the release of proapoptotic factors cytochrome c, smac/DIABLO into the cytosol. Results from western blotting, electron and fluorescent microscopy of YTX-treated myoblast cells provided experimental data for evaluation of cytochrome c, smac/DIABLO release and caspase-9 activation. Loss of mitochondrial membrane potential and swelling of mitochondria indicated an active role of mitochondria during the early phase of apoptosis in L6 and BC3H1 cells after YTX exposure. These observations show that YTX targets mitochondria and involve activation of a cascade of events through mitochondrial regulation.

Apoptotic events induced by yessotoxin in myoblast cell lines from rat and mouse

This study reports apoptotic events after yessotoxin (YTX) exposure in L6 (rat) and BC3H1 (mouse) skeletal muscle myoblast cell lines. These cell lines are relevant targets to study the cytotoxic effect since this toxin has been reported as cardiotoxic. Mechanisms of action of YTX in multicellular organisms are not fully elucidated. Cell culture studies can contribute to find some of these mechanisms and trace the molecular pathways involved. The present work shows results from exposing cells to 100 nM purified YTX for 72 h. Morphological and biochemical changes characteristic of apoptotic cell death were evaluated in the two cell lines. Immunofluorescence and western blot techniques showed caspase-3 and caspase-9 activation. Western blot analysis of poly(ADP-ribose)-polymerase (PARP) confirmed caspase-3 activation in both cell lines. DNA fragmentation was not detected in these cell lines. This evidence reflect that oligonucleosomal DNA fragmentation is not a biochemical event that can be used as a definitive apoptotic marker in L6 and BC3H1 myoblast cell lines. The results indicate that the time-course and degree of apoptotic events induced by YTX depend on cell line sensitivity.

Oral administration of yessotoxin stabilizes E-cadherin in mouse colon

YTX has been shown to disrupt the E-cadherin-catenin system in cultured epithelial cells, raising some concern that ingestion of seafood contaminated by YTX might favour tumour spreading and metastasis formation in vivo. In order to probe whether YTX might affect cadherin systems in vivo, we have set up a study involving repeated oral dosing of the toxin in mice (1mg/kg/day, for 7 days) and analysis of E-cadherin and N-cadherin in tissue extracts obtained at the end of the dosing scheme, as well as 1 and 3 months after YTX administration. We found that the E-cadherin pools obtained from lung and kidney were not altered by YTX in any of our experimental conditions. Extracts from mouse colon contained intact E-cadherin and an E-cadherin fragment of about 90 kDa (ECRA(90)), displaying a molecular alteration resembling that caused by YTX in cultured cells. We found that the relative proportion of ECRA(90), as compared to intact E-cadherin, was higher in colon extracts from control mice than from YTX-treated animals, indicating that oral administration of YTX to mice stabilizes E-cadherin of mouse colon. No significant difference could be detected in samples prepared from colons obtained 30 or 90 days after termination of YTX treatment. Oral administration of YTX to mice did not lead to a significant increase in the fragments of E-cadherin detectable in serum, neither it altered the N-cadherin pool of mouse heart. Electron microscopy analysis showed no substantial ultrastructural differences between controls and YTX-treated mice. Our findings show that ingestion of food contaminated by YTX poses a low risk of disruption of the E-cadherin system in vivo.

Lysosomes as the target of yessotoxin in invertebrate and vertebrate cell lines

The toxic effects of the algal polyether phycotoxin yessotoxin (YTX) are studied in the insect fat body IPLB-LdFB and the mouse fibroblast NIH3T3 cell lines. Our experiments confirm the cytotoxic action exerted by the toxin in both insect and mammalian cells, but morphological observations, TUNEL experiments and electrophoretic evalution of DNA integrity failed to evidence a clear pro-apoptotic role for YTX. In both IPLB-LdFB and NIH3T3 cell lines, neutral red and acridine orange stainings, together with evaluation of acid phosphatase activity demonstrate that YTX first damages lysosomal vesicles. This is then followed by a progressive depolymerization of actin microfilaments, as shown by phalloidin fluorescent immunostaining. Overall, our data identify in early lysosomal damage and the subsequent cytoskeletal disruption two common steps related to YTX toxicity towards metazoan cells.

Cleavage of tensin during cytoskeleton disruption in YTX-induced apoptosis

Yessotoxin (YTX) is a marine algal toxin previously shown to induce apoptosis in L6 and BC3H1 myoblast cell lines. Disassembly of the F-actin cytoskeleton and cleavage of tensin, a cytoskeletal protein localised at the focal adhesion contacts, appear during this apoptotic process. Tensin binds to actin filaments at the focal adhesion contacts and it links the actin cytoskeleton to the extracellular matrix (ECM). This binding occurs via integrin receptors and it makes tensin a potential link between the actin cytoskeleton and signal transduction. This study evaluates disruption in the F-actin cytoskeleton and change of tensin in myoblast cell lines exposed to 100 nM YTX up to 72 h. YTX treatment cleaves tensin and makes it translocate to the cell centre. Tensin has normally a role in the maintenance of cell shape and YTX-treatment may therefore alter the shape of the cells. YTX exposure also induces formation of lamellas associated with pseudopodia. Alternative linkages and cytoskeletal proteins anchoring the actin filaments to focal contacts remain to be identified.

Potent Neurotoxic Action of the Shellfish Biotoxin Yessotoxin on Cultured Cerebellar Neurons

Yessotoxin (YTX) and its analogues are disulphated polyether compounds of increasing occurrence in seafood. The biological effects of these algal toxins on mammals and the risk associated to their ingestion have not been clearly established. We have used primary cultures of rat cerebellar neurons to investigate whether YTX affected survival and functioning of central nervous system neurons. Exposure to YTX (> or =25 nM) caused first (approximately 8 h) weakening, granulation, and fragmentation of neuronal network, and later (approximately 48 h) complete disintegration of neurites and extensive neuronal death, with a significant decrease in the amount of filamentous actin. The concentration of YTX that reduced by 50% the maximum neuronal survival (EC50(48)) was approximately 20 nM. Lower toxin concentrations (approximately 15 nM) also caused visible signs of toxicity affecting neuronal network primarily. Removal of YTX after 5 h exposure delayed the onset of neurotoxicity but did not prevent neuronal degeneration and death. YTX induced a two-fold increase in cytosolic calcium that was prevented by the voltage-sensitive calcium channel antagonists nifedipine and verapamil. These antagonists were, however, completely ineffective in reducing neurotoxicity. Voltage-sensitive sodium channel antagonists saxitoxin and nefopam, and the NMDA receptor antagonist MK-801 also failed to prevent YTX neurotoxicity. Neuronal death by YTX involved typical hallmarks of apoptosis and required the synthesis of new proteins. Our data suggest neuronal tissue to be a vulnerable biological target for YTX. The potent neurotoxicity of YTX we report raises reasonable concern about the potential risk that exposure to YTX may represent for neuronal survival in vivo.

Resonant mirror biosensor detection method based on yessotoxin–phosphodiesterase interactions

Yessotoxin (YTX) is a generic name for a group of lipophilic compounds recently discovered and chemically characterized. Association measurements were done in a resonant mirror biosensor. The instrument detects changes in the refractive index and/or thickness occurring within a few hundred nanometers form the sensor surface where a molecule is attached. We used aminosilane surfaces where phosphodiesterase 3',5'-cyclic-nucleotide-specific from bovine brain (PDEs) was immobilized. Over this immobilized ligand different amounts of YTX were added and typical association curve profiles were observed. These association curves fit a pseudo-first-order kinetic equation where the apparent association rate constant (k(on)) can be calculated. The value of this constant increases with YTX concentration. From the representation of k(on) versus YTX concentration we obtained the association rate constant (k(ass)) 248+/-40 M(-1)s(-1) and the dissociation rate constant (k(diss)) 9.36 x 10(-4)+/-1.72 x 10(-4)s(-1). From these values the kinetic equilibrium dissociation constant (K(D)) for YTX-PDEs association can be calculated. The value of this last constant is 3.74 x 10(-6)+/-8.25 x 10(-8)M YTX. The PDE-YTX association was used as a method suitable for determination of the toxin concentration in a shellfish sample. The assay had sufficient sensitivity and can be used on simple shellfish extracts.

Lethal and sub-lethal yessotoxin dose-induced morpho-functional alterations in intraperitoneal injected Swiss CD1 mice

Histological and immunocytochemical investigations were performed on different organs (brain, duodenum and thymus) of mice following lethal (420 microg/kg) or sublethal (10 microg/kg) intraperitoneal injection of yessotoxin (YTX). No morpho-functional modifications were observed in large neurons of the cerebral and cerebellar cortex with the sub-lethal dose, nor in the cerebral cortex with the lethal dose. The duodenum also did not show significant alterations. However, there was an inflammation response to the toxin, in which blood cells and cytokines were involved. This was more evident with the lethal YTX dose. The thymus and, in general, the immune system are the main targets of YTX at both the concentrations used. Furthermore, the alterations present in the thymus may support tumorigenic implications.

Yessotoxin, a shellfish biotoxin, is a potent inducer of the permeability transition in isolated mitochondria and intact cells

The diarrhetic poisoning by bivalve molluscs, diarrhetic shellfish poisoning, is due to consumption of mussels containing biotoxins produced by some Dinoflagellate species. Toxic effects of yessotoxin (YTX) include morphological alterations of mitochondria from heart and liver but the biochemical basis for these alterations is completely unknown. This paper demonstrates that YTX is a very powerful compound that opens the permeability transition pore (PTP) of the inner mitochondrial membrane of rat liver mitochondria at nanomolar concentrations. The effect requires the presence of a permissive level of calcium, by itself incapable of opening the pore. The direct effect of YTX on PTP is further confirmed by the inhibition exerted by cyclosporin A (CsA) that is known as a powerful inhibitor of PTP opening. Moreover, YTX induces membrane depolarization as shown by the quenching of tetramethylrhodamine methyl ester (TMRM), also prevented by the addition of CsA. YTX caused PTP opening in Morris Hepatoma 1C1 cells, as shown by the occurrence of CsA-sensitive depolarization within minutes of the addition of submicromolar concentrations of the toxin. These results provide a biochemical basis for the mitochondrial alterations observed in the course of intoxication with YTX, offering the first clue into the pathogenesis of diseases caused by YTX, and providing a novel tool to study the PTP in situ.

Short-term oral toxicity of homoyessotoxins, yessotoxin and okadaic acid in mice

A short-term toxicity study after 7 days oral daily administration of yessotoxin (YTX; 2 mg/kg/day), homoYTX (1 mg/kg/day), 45-hydroxy-homoYTX (1 mg/kg/day) and of the main diarrhoetic shellfish toxin okadaic acid (OA; 1 mg/kg/day) was carried out in mice. Symptoms, lethality, food consumption, body and organ weights, gross pathology and histopathology of the main organs and tissues, leukocytes formula as well as plasmatic levels of transaminases, lactate dehydrogenase and creatinine phosphokinase were evaluated. Heart tissue was studied also hystochemically for the presence of apoptotic nuclei and by transmission electron microscopy. No mortality, signs of toxicity or cumulative effects were induced by the repeated oral exposure to YTXs. Only ultrastructural changes in the cardiac muscle cells near the capillaries, such as package of rounded mitochondria and alteration of the cells boundary were observed, without any increase of lactate dehydrogenase, an index of cardiac damage. OA induced diarrhoea, body weight loss, reduced food consumption, and the death of 2/5 mice after 5 days. Necroscopy and/or light microscopy analysis revealed toxic effects mainly at forestomach (ulceration and hyperplasia), liver and, indirectly to body weight loss of mice, atrophic signs in the lymphoid organs and exocrine pancreas. Electron microscopy of heart tissue showed alterations of mitochondria and fibers in myocardiocytes, although no apoptotic change was recorded.

Acute toxic effect of the algal yessotoxin on Purkinje cells from the cerebellum of Swiss CD1 mice

Swiss CD1 mice died less than 2 h after intraperitoneal injection of 420 microg/kg of algal yessotoxin (YTX). The morphological, histochemical and immunocytochemical studies performed on the cerebellar cortex revealed damage to the Purkinje cells. The main cytological alterations were observed in the cytoplasm, while less sufferance was detected in the nucleus. The immunocytochemical experiments showed an increased positivity to S100 protein while there was a decreased response to calbindin D-28K, beta-tubulin and neurofilaments. These changes in intracellular Ca(2+)-binding proteins and the modifications in the cytoskeletal components of Purkinje cells suggest that YTX may be involved in neurological disorders.

Microcystin-LR and okadaic acid-induced cellular effects: a dualistic response

Microcystins, potent heptapeptide hepatotoxins produced by certain bloom-forming cyanobacteria, are strong protein phosphatase inhibitors. They covalently bind the serine/threonine protein phosphatases 1 and 2A (PP1 and PP2A), thereby influencing regulation of cellular protein phosphorylation. The paralytic shellfish poison, okadaic acid, is also a potent inhibitor of these PPs. Inhibition of PP1 and PP2A has a dualistic effect on cells exposed to okadaic acid or microcystin-LR, with both apoptosis and increased cellular proliferation being reported. This review summarises the existing data on the molecular effects of microcystin-LR inhibition of PP1 and PP2A both in vivo and in vitro, and where possible, compares this to the action of okadaic acid.