Evaluation of the effects of the marine toxin okadaic acid by using FETAX assay

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.

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.

Exposure of okadaic acid alters the angiogenesis in developing chick embryos

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

Assessing differences in toxicity and teratogenicity of three phthalates, Diethyl phthalate, Di-n-propyl phthalate, and Di-n-butyl phthalate, using Xenopus laevis embryos

Phthalates, compounds used to add flexibility to plastics, are ubiquitous in the environment. In particular, the diethyl (DEP), di-n-propyl (DnPP), and di-n-butyl (DBP) phthalates were found to exert detrimental effects in both mammalian and non-mammalian studies, with toxic effects varying according to alkyl chain length. Embryos of Xenopus laevis, the African clawed frog, have been used to assess toxicity and teratogenicity of several compounds and serves as a model for assessing adverse and teratogenic effects of ortho-phthalate esters. The purpose of this study was to develop a model for comparison of developmentally toxic effects of ortho-phthalate esters using Xenopus embryos. In this study developing Xenopus laevis embryos were exposed to increasing concentrations of DEP, DnPP, and DBP using the 96-h Frog Embryo Teratogenesis Assay-Xenopus (FETAX), with 96-h lethal concentrations, effective concentrations to induce malformations, teratogenic indices, and concentrations to inhibit growth determined. DEP, DnPP, and DBP showed enhanced toxicity with increasing ester length. Developing Xenopus laevis exposed to DEP, DnPP, and DBP showed similar malformations that also occurred at lower concentrations with increasing alkyl chain length. Teratogenic risk did not change markedly with alkyl chain length, with data showing only DBP to be teratogenic.

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.

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.

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.

Effects of marine toxins on the reproduction and early stages development of aquatic organisms

Marine organisms, and specially phytoplankton species, are able to produce a diverse array of toxic compounds that are not yet fully understood in terms of their main targets and biological function. Toxins such as saxitoxins, tetrodotoxin, palytoxin, nodularin, okadaic acid, domoic acid, may be produced in large amounts by dinoflagellates, cyanobacteria, bacteria and diatoms and accumulate in vectors that transfer the toxin along food chains. These may affect top predator organisms, including human populations, leading in some cases to death. Nevertheless, these toxins may also affect the reproduction of aquatic organisms that may be in contact with the toxins, either by decreasing the amount or quality of gametes or by affecting embryonic development. Adults of some species may be insensitive to toxins but early stages are more prone to intoxication because they lack effective enzymatic systems to detoxify the toxins and are more exposed to the toxins due to a higher metabolic growth rate. In this paper we review the current knowledge on the effects of some of the most common marine toxins on the reproduction and development of early stages of some organisms.

Embryotoxic effects of the marine biotoxin okadaic acid on murine embryonic stem cells

Okadaic acid (OA), a marine toxin produced by dinoflagellates, can accumulate in various bivalve molluscs. In humans, consumption of OA induces acute toxic effects like diarrhoea, nausea, vomiting and abdominal pain. OA is a potent inhibitor of protein phosphatase 1 (PP1) and 2A (PP2A), enzymes that are known to be critical regulators of embryonic development. To determine the embryotoxic potential of OA, we performed two independent cellular in-vitro assays, both of which are applicable for the detection of teratogenic compounds: (i) the validated embryonic stem cell test (EST) based on the morphological analysis of beating cardiomyocytes in embryoid bodies and (ii) the F9 cell assay quantifying the induction of cell differentiation by measuring the emitted luminescence of a reporter gene. In the presence of OA, beating cardiomyocytes in the EST were inhibited and the reporter gene in transiently transfected F9 cells was activated. Furthermore, OA treatment led to rapid morphological changes including cell rounding, the loss of cell-cell contacts and changed electrical impedance as monitored in real time by the xCELLigence system. The two independent bioassays (EST and F9 cell test) detected OA as a potential embryotoxic compound, since OA influences the differentiation process of cultured murine embryonic cells.

Expression of the genes siamois, engrailed-2, bmp4 and myf5 during Xenopus development in presence of the marine toxins okadaic acid and palytoxin

The present investigation examines the effects of the marine toxins, okadaic acid (OA) and palytoxin (PTX), on some genes involved in the neural and muscular specification and patterning of Xenopus laevis. The RT-PCR analyses performed at different stages of embryonic and larval development (stages 11-47) demonstrated that both toxins induce an over-expression of the genes siamois and engrailed-2 and a different behaviour in bmp4 and myf5. Indeed, OA provoked a significant increase in bmp4 in the earliest stage (11) examined, a down-regulation from stages 12 to 17, and a renewed increase from the beginning of hatching onwards (stages 35-47). In contrast, myf5 was up-regulated in all stages up to 35. PTX induced an over-expression of both bmp4 and myf5 during the embryonic and early larval development stages. The results show that PTX induces an increase in expression levels in all tested genes, while the response to OA seems to be more stage-dependent, with the embryonic development stage more sensitive to the toxin than the larval stages.

Toxicological effects of marine palytoxin evaluated by FETAX assay

The FETAX (frog embryo teratogenesis assay Xenopus) is considered a useful bioassay to detect health hazard substances. In the study of the marine toxin palytoxin (PTX), FETAX has revealed evident impacts on embryo mortality, teratogenesis and growth at the two highest (370 and 37nM) concentrations used. Significant mortality rates, peaks in the number of malformed embryos and delays in growth were found, while the total sample number fell by about 80% at the end of the assay with the concentrated dose. The histological analysis to evaluate the morpho-functional induced modifications demonstrated damage to the nervous and muscle tissue, a general reduction in the size of the main inner visceral organs and severe injury to the heart structure in some specimens. No inflammatory response was observed.

Age-related toxic effects and recovery from okadaic acid treatment in Enchytraeus crypticus (Annelida: Oligochaeta)

The effects of 48 h okadaic acid (OA) treatment and the ability to recover the induced toxicological injuries were examined in Enchytraeus crypticus of different ages (25 days and 3 months). The results demonstrated that the older worms are more sensitive to the toxin and show less capacity to recover. After 48 h OA treatment, the structural organization of the chloragogenous tissue appeared modified and associated with an immune response involving a higher number of circulating coelomocytes immunoreactive to anti-IL-6 antibody. The toxin effects were more evident in 3-month-old animals compared to specimens aged 25 days. Regarding the morpho-functional recovery from the induced modifications, first signs of recuperation were observed in younger worms at 48 h, and recovery was almost complete within 1 week. In older animals, the morphology of the chloragogenous tissue had not been restored, while a reduction in coelomocyte number was found after 1 week.