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Marine Drugs Oct 2015Okadaic acid (OA) and microcystin (MC) as well as several other microbial toxins like nodularin and calyculinA are known as tumor promoters as well as inducers of... (Review)
Review
Okadaic acid (OA) and microcystin (MC) as well as several other microbial toxins like nodularin and calyculinA are known as tumor promoters as well as inducers of apoptotic cell death. Their intracellular targets are the major serine/threonine protein phosphatases. This review summarizes mechanisms believed to be responsible for the death induction and tumor promotion with focus on the interdependent production of reactive oxygen species (ROS) and activation of Ca(2+)/calmodulin kinase II (CaM-KII). New data are presented using inhibitors of specific ROS producing enzymes to curb nodularin/MC-induced liver cell (hepatocyte) death. They indicate that enzymes of the arachidonic acid pathway, notably phospholipase A2, 5-lipoxygenase, and cyclooxygenases, may be required for nodularin/MC-induced (and presumably OA-induced) cell death, suggesting new ways to overcome at least some aspects of OA and MC toxicity.
Topics: Animals; Apoptosis; Carcinogens; Cell Death; Enzyme Inhibitors; Humans; Marine Toxins; Microcystins; Okadaic Acid; Oxazoles; Peptides, Cyclic; Phosphoprotein Phosphatases; Reactive Oxygen Species
PubMed: 26506362
DOI: 10.3390/md13106505 -
Marine Drugs Mar 2013Mammalian Ste20-like kinases 1 and 2 (MST1 and MST2) are activated in NIH3T3 cells exposed to okadaic acid. The Hippo pathway is a newly emerging signaling that... (Review)
Review
Mammalian Ste20-like kinases 1 and 2 (MST1 and MST2) are activated in NIH3T3 cells exposed to okadaic acid. The Hippo pathway is a newly emerging signaling that functions as a tumor suppressor. MST1 and MST2 work as core kinases of the Hippo pathway and their activities depend on the autophosphorylation, which is negatively regulated by protein phosphatase 2A (PP2A). Okadaic acid has been frequently used to enhance the phosphorylation of MST1 and MST2 and to trigger the activation of the Hippo pathway. However other components of the Hippo pathway could also be targets of okadaic acid. In this review we first briefly summarize the molecular architecture of the Hippo pathway for the reference of researchers outside the field. We explain how MST kinases are regulated by PP2A and how okadaic acid activates MST2. Thereafter we discuss which components of the Hippo pathway are candidate substrates of protein phosphatases and which points we need to consider in the usage of okadaic acid to study the Hippo pathway.
Topics: Animals; Hippo Signaling Pathway; Humans; Mice; NIH 3T3 Cells; Okadaic Acid; Phosphoprotein Phosphatases; Phosphorylation; Protein Phosphatase 2; Protein Serine-Threonine Kinases; Serine-Threonine Kinase 3; Signal Transduction
PubMed: 23493077
DOI: 10.3390/md11030896 -
Marine Drugs Nov 2016Okadaic acid (OA) and the closely related dinophysistoxins (DTXs) are algal toxins that accumulate in shellfish and are known serine/threonine protein phosphatase...
Okadaic acid (OA) and the closely related dinophysistoxins (DTXs) are algal toxins that accumulate in shellfish and are known serine/threonine protein phosphatase (ser/thr PP) inhibitors. Phosphatases are important modulators of enzyme activity and cell signaling pathways. However, the interactions between the OA/DTX toxins and phosphatases are not fully understood. This study sought to identify phosphatase targets and characterize their structure-activity relationships (SAR) with these algal toxins using a combination of phosphatase activity and cytotoxicity assays. Preliminary screening of 21 human and yeast phosphatases indicated that only three ser/thr PPs (PP2a, PP1, PP5) were inhibited by physiologically saturating concentrations of DTX2 (200 nM). SAR studies employed naturally-isolated OA, DTX1, and DTX2, which vary in degree and/or position of methylation, in addition to synthetic 2--DTX2. OA/DTX analogs induced cytotoxicity and inhibited PP activity with a relatively conserved order of potency: OA = DTX1 ≥ DTX2 >> 2--DTX. The PPs were also differentially inhibited with sensitivities of PP2a > PP5 > PP1. These findings demonstrate that small variations in OA/DTX toxin structures, particularly at the head region (i.e., C1/C2), result in significant changes in toxicological potency, whereas changes in methylation at C31 and C35 (tail region) only mildly affect potency. In addition to this being the first study to extensively test OA/DTX analogs' activities towards PP5, these data will be helpful for accurately determining toxic equivalence factors (TEFs), facilitating molecular modeling efforts, and developing highly selective phosphatase inhibitors.
Topics: Antineoplastic Agents; Cell Survival; Enzyme Inhibitors; Eutrophication; Humans; Jurkat Cells; Marine Toxins; Okadaic Acid; Phosphoprotein Phosphatases; Pyrans; Shellfish Poisoning; Structure-Activity Relationship
PubMed: 27827901
DOI: 10.3390/md14110207 -
Archives of Toxicology Oct 2021Diarrhetic shellfish-poisoning (DSP) toxins such as okadaic acid and dinophysistoxins harm the human gastrointestinal tract, and therefore, their levels are regulated to...
The diarrhetic shellfish-poisoning toxin, okadaic acid, provokes gastropathy, dysbiosis and susceptibility to bacterial infection in a non-rodent bioassay, Galleria mellonella.
Diarrhetic shellfish-poisoning (DSP) toxins such as okadaic acid and dinophysistoxins harm the human gastrointestinal tract, and therefore, their levels are regulated to an upper limit of 160 μg per kg tissue to protect consumers. Rodents are used routinely for risk assessment and studies concerning mechanisms of toxicity, but there is a general move toward reducing and replacing vertebrates for these bioassays. We have adopted insect larvae of the wax moth Galleria mellonella as a surrogate toxicology model. We treated larvae with environmentally relevant doses of okadaic acid (80-400 μg/kg) via intrahaemocoelic injection or gavage to determine marine toxin-related health decline: (1) whether pre-exposure to a sub-lethal dose of toxin (80 μg/kg) enhances susceptibility to bacterial infection, or (2) alters tissue pathology and bacterial community (microbiome) composition of the midgut. A sub-lethal dose of okadaic acid (80 μg/kg) followed 24 h later by bacterial inoculation (2 × 10 Escherichia coli) reduced larval survival levels to 47%, when compared to toxin (90%) or microbial challenge (73%) alone. Histological analysis of the midgut depicted varying levels of tissue disruption, including nuclear aberrations associated with cell death (karyorrhexis, pyknosis), loss of organ architecture, and gross epithelial displacement into the lumen. Moreover, okadaic acid presence in the midgut coincided with a shift in the resident bacterial population over time in that substantial reductions in diversity (Shannon) and richness (Chao-1) indices were observed at 240 μg toxin per kg. Okadaic acid-induced deterioration of the insect alimentary canal resembles those changes reported for rodent bioassays.
Topics: Animals; Biological Assay; Disease Susceptibility; Dose-Response Relationship, Drug; Dysbiosis; Escherichia coli; Escherichia coli Infections; Larva; Moths; Okadaic Acid; Toxicity Tests
PubMed: 34374792
DOI: 10.1007/s00204-021-03132-x -
Marine Drugs Oct 2013Okadaic 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,... (Review)
Review
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.
Topics: Animals; Environmental Monitoring; Humans; Marine Toxins; Okadaic Acid; Shellfish Poisoning
PubMed: 24184795
DOI: 10.3390/md11114328 -
Food and Chemical Toxicology : An... Nov 2022Okadaic acid (OA) is an important marine lipophilic phycotoxin responsible for diarrhetic shellfish poisoning (DSP). This toxin inhibits protein phosphatases (PPs) like...
Okadaic acid (OA) is an important marine lipophilic phycotoxin responsible for diarrhetic shellfish poisoning (DSP). This toxin inhibits protein phosphatases (PPs) like PP2A and PP1, though, this action does not explain OA-induced toxicity and symptoms. Intestinal epithelia comprise the defence barrier against external agents where transport of fluid and electrolytes from and to the lumen is a tightly regulated process. In some intoxications this balance becomes dysregulated appearing diarrhoea. Therefore, we evaluated diarrhoea in orally OA-treated mice as well as in mice pre-treated with several doses of cyproheptadine (CPH) and then treated with OA at different times. We assessed stools electrolytes and ultrastructural alteration of the intestine, particularly evaluating tight and adherens junctions. We detected increased chloride and sodium faecal concentrations in the OA-exposed group, suggesting a secretory diarrhoea. Pre-treatment with CPH maintains chloride concentration in values similar to control mice. Intestinal cytomorphological alterations were observed for OA mice, whereas CPH pre-treatment attenuated OA-induced damage in proximal colon and jejunum at 2 h. Conversely, tight junctions' distance was only affected by OA in jejunum at the moment diarrhoea occurred. In this study we found cellular mechanisms by which OA induced diarrhoea revealing the complex toxicity of this compound.
Topics: Animals; Mice; Chlorides; Cyproheptadine; Diarrhea; Okadaic Acid; Phosphoprotein Phosphatases; Sodium; Tight Junctions; Jejunum
PubMed: 36206954
DOI: 10.1016/j.fct.2022.113449 -
Marine Drugs Mar 2010In 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... (Review)
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.
Topics: Acrylamides; Animals; Annelida; Cell Line; Cnidarian Venoms; Embryo, Nonmammalian; Immune System; Mice; Mollusk Venoms; Mytilus; Okadaic Acid; Oxocins; Xenopus laevis
PubMed: 20411120
DOI: 10.3390/md8030658 -
Toxins Dec 2018Mycotoxins are emerging toxins in the marine environment, which can co-occur with algal toxins to exert synergistic or antagonistic effects for human seafood...
Mycotoxins are emerging toxins in the marine environment, which can co-occur with algal toxins to exert synergistic or antagonistic effects for human seafood consumption. The current study assesses the cytotoxicity of the algal toxin okadaic acid, shellfish, and dust storm-associated mycotoxins alone or in combination on human intestinal (HT-29) and neuroblastoma (SH-SY5Y) cell lines. Based on calculated IC (inhibitory concentration 50%) values, mycotoxins and the algal toxin on their own exhibited increased cytotoxicity in the order of sydowinin A < sydowinin B << patulin < alamethicin < sydowinol << gliotoxin ≈ okadaic acid against the HT-29 cell line, and sydowinin B < sydowinin A << alamethicin ≈ sydowinol < patulin, << gliotoxin < okadaic acid against the SH-SY5Y cell line. Combinations of okadaic acid⁻sydowinin A, ⁻alamethicin, ⁻patulin, and ⁻gliotoxin exhibited antagonistic effects at low-moderate cytotoxicity, but became synergistic at high cytotoxicity, while okadaic acid⁻sydowinol displayed an antagonistic relationship against HT-29 cells. Furthermore, only okadaic acid⁻sydowinin A showed synergism, while okadaic acid⁻sydowinol, ⁻alamethicin, ⁻patulin, and ⁻gliotoxin combinations demonstrated antagonism against SH-SY5Y. While diarrhetic shellfish poisoning (DSP) from okadaic acid and analogues in many parts of the world is considered to be a comparatively minor seafood toxin syndrome, our human cell model studies suggest that synergisms with certain mycotoxins may aggravate human health impacts, depending on the concentrations. These findings highlight the issues of the shortcomings of current regulatory approaches, which do not regulate for mycotoxins in shellfish and treat seafood toxins as if they occur as single toxins.
Topics: Cell Line, Tumor; Cell Survival; Drug Interactions; Humans; Intestines; Mycotoxins; Neuroblastoma; Okadaic Acid
PubMed: 30544794
DOI: 10.3390/toxins10120526 -
Toxins Jul 2021Two high-mass polar compounds were observed in aqueous side-fractions from the purification of okadaic acid () and dinophysistoxin-2 () from blooms in Spain and Norway....
Identification of 24--β-d-Glycosides and 7-Deoxy-Analogues of Okadaic Acid and Dinophysistoxin-1 and -2 in Extracts from Blooms, and Cultures, and Shellfish in Europe, North America and Australasia.
Two high-mass polar compounds were observed in aqueous side-fractions from the purification of okadaic acid () and dinophysistoxin-2 () from blooms in Spain and Norway. These were isolated and shown to be 24--β-d-glucosides of and ( and , respectively) by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and enzymatic hydrolysis. These, together with standards of , , dinophysistoxin-1 (), and a synthetic specimen of 7-deoxy- (), combined with an understanding of their mass spectrometric fragmentation patterns, were then used to identify -, the 24--β-d-glucoside of dinophysistoxin-1 (), , 7-deoxy- (), and 7-deoxy- () in a range of extracts from blooms, cultures, and contaminated shellfish from Spain, Norway, Ireland, Canada, and New Zealand. A range of cultures was also examined by liquid chromatography-high resolution tandem mass spectrometry (LC-HRMS/MS) and was found to contain , , , and . However, although - were not detected in these cultures, low levels of putative glycosides with the same exact masses as and were present. The potential implications of these findings for the toxicology, metabolism, and biosynthesis of the okadaic acid group of marine biotoxins are briefly discussed.
Topics: Animals; Australasia; Biological Monitoring; Bivalvia; Dinoflagellida; Europe; Food Contamination; Glycosides; North America; Okadaic Acid; Shellfish
PubMed: 34437381
DOI: 10.3390/toxins13080510 -
Cellular Physiology and Biochemistry :... 2018Okadaic acid (OA) and the structurally related compounds dinophysistoxin-1 (DTX1) and dinophysistoxin-2 (DTX2) are marine phycotoxins that cause diarrheic shellfish...
BACKGROUND/AIMS
Okadaic acid (OA) and the structurally related compounds dinophysistoxin-1 (DTX1) and dinophysistoxin-2 (DTX2) are marine phycotoxins that cause diarrheic shellfish poisoning (DSP) in humans due to ingestion of contaminated shellfish. In order to guarantee consumer protection, the regulatory authorities have defined the maximum level of DSP toxins as 160 µg OA equivalent kg-1 shellfish meat. For risk assessment and overall toxicity determination, knowledge of the relative toxicities of each analogue is required. In absence of enough information from human intoxications, oral toxicity in mice is the most reliable data for establishing Toxicity Equivalence Factors (TEFs).
METHODS
Toxins were administered to mice by gavage, after that the symptomatology and mice mortality was registered over a period of 24 h. Organ damage data were collected at necropsy and transmission electron microscopy (TEM) was used for ultrastructural studies. Toxins in urine, feces and blood were analyzed by HPLC-MS/MS. The evaluation of in vitro potencies of OA, DTX1 and DTX2 was performed by the protein phosphatase 2A (PP2A) inhibition assay.
RESULTS
Mice that received DSP toxins by gavage showed diarrhea as the main symptom. Those toxins caused similar gastrointestinal alterations as well as intestine ultrastructural changes. However, DSP toxins did not modify tight junctions to trigger diarrhea. They had different toxicokinetics and toxic potency. The lethal dose 50 (LD50) was 487 µg kg-1 bw for DTX1, 760 µg kg-1 bw for OA and 2262 µg kg-1 bw for DTX2. Therefore, the oral TEF values are: OA = 1, DTX1 = 1.5 and DTX2 = 0.3.
CONCLUSION
This is the first comparative study of DSP toxins performed with accurate well-characterized standards and based on acute toxicity data. Results confirmed that DTX1 is more toxic than OA by oral route while DTX2 is less toxic. Hence, the current TEFs based on intraperitoneal toxicity should be modified. Also, the generally accepted toxic mode of action of this group of toxins needs to be reevaluated.
Topics: Administration, Oral; Animals; Body Weight; Chromatography, High Pressure Liquid; Female; Heart; Intestine, Small; Liver; Mice; Myocardium; Okadaic Acid; Protein Phosphatase 2; Pyrans; Stomach; Tandem Mass Spectrometry; Toxicity Tests
PubMed: 30176657
DOI: 10.1159/000493039