Sensitive detection of apoptogenic toxins in suspension cultures of rat and salmon hepatocytes

Cytotoxic and immunological responses of fish leukocytes to nodularin exposure in vitro

Nodularin (NOD) is a cyclic peptide released by bloom-forming toxic cyanobacteria Nodularia spumigena commonly occurring in brackish waters throughout the world. Although its hepatotoxic effects are well known, other negative effects of NOD have not yet been completely elucidated. The present study aims were to evaluate and compare the cytotoxic and immunotoxic effects of the toxin on primary leukocytes (from head kidney [HK]) and stable fish leukocytes (carp leucocyte cell line [CLC] cells). The cells were incubated with the cyanotoxin at concentrations of 0.001, 0.01, 0.05, or 0.1 μg/ml. After 24 h of exposure, the concentrations ≥0.05 μg/ml of toxin resulted in cytotoxicity in the primary cells, while in CLC cells, the toxic effect was obtained only with the highest concentration. Similarly, depending on the concentration, exposure to NOD causes a significant inhibition of chemotaxis of the phagocytic abilities of primary leukocytes and a significant reduction in the proliferation of lymphocytes isolated from the HKs. Moreover, CLC cells and HK leukocytes incubated with this toxin at all the mentioned concentrations showed an increased production of reactive oxygen and nitrogen species. NOD also evidently influenced the expression of genes of cytokine TNF-α and IL-10 and, to a minor extent, IL-1β and TGF-β. Notably, the observed changes in the mRNA levels of cytokines in NOD-exposed cells were evident, but not clearly dose-dependent. Interestingly, NOD did not affect the production and release of IL-1β of the CLC cells. This study provides evidence that NOD may exert cytotoxicity and immune-toxicity effects depending on cell type and toxin concentration.

Comprehensive insights into the occurrence and toxicological issues of nodularins

The occurrence of cyanobacterial toxins is being increasingly reported. Nodularins (NODs) are one of the cyanotoxins group mainly produced by Nodularia spumigena throughout the world. NODs may exert adverse effects on animal and human health, and NOD-R variant is the most widely investigated. However, research focused on them is still limited. In order to understand the realistic risk well, the aim of this review is to compile the available information in the scientific literature regarding NODs, including their sources, distribution, structural characteristics, physicochemical properties, biosynthesis and degradation, adverse effects in vitro and vivo, and toxicokinetics. More data is urgently needed to integrate the cumulative or synergistic effects of NODs on different species and various cells to better understand, anticipate and aggressively manage their potential toxicity after both short- and long-term exposure in ecosystem, and to minimize or prevent the adverse effects on human health, environment and the economy.

Risk Assessment of Pectenotoxins in New Zealand Bivalve Molluscan Shellfish, 2009-2019

Pectenotoxins (PTXs) are produced by Dinophysis spp., along with okadaic acid, dinophysistoxin 1, and dinophysistoxin 2. The okadaic acid group toxins cause diarrhetic shellfish poisoning (DSP), so are therefore regulated. New Zealand currently includes pectenotoxins within the DSP regulations. To determine the impact of this decision, shellfish biotoxin data collected between 2009 and 2019 were examined. They showed that 85 samples exceeded the DSP regulatory limit (0.45%) and that excluding pectenotoxins would have reduced this by 10% to 76 samples. The incidence (1.3%) and maximum concentrations of pectenotoxins (0.079 mg/kg) were also found to be low, well below the current European Food Safety Authority (EFSA) safe limit of 0.12 mg/kg. Inclusion within the DSP regulations is scientifically flawed, as pectenotoxins and okadaic acid have a different mechanism of action, meaning that their toxicities are not additive, which is the fundamental principle of grouping toxins. Furthermore, evaluation of the available toxicity data suggests that pectenotoxins have very low oral toxicity, with recent studies showing no oral toxicity in mice dosed with the PTX analogue PTX2 at 5000 µg/kg. No known human illnesses have been reported due to exposure to pectenotoxins in shellfish, a fact which combined with the toxicity data indicates that they pose negligible risk to humans. Regulatory policies should be commensurate with the level of risk, thus deregulation of PTXs ought to be considered, a stance already adopted by some countries.

Cell Death Inducing Microbial Protein Phosphatase Inhibitors--Mechanisms of Action

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 Ca²⁺/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.

Does the marine biotoxin okadaic acid cause DNA fragmentation in the blue mussel and the pacific oyster?

Two bivalve species of global economic importance: the blue mussel, Mytilus edulis and the pacific oyster, Crassostrea gigas were exposed in vivo, to the diarrhoetic shellfish toxin okadaic acid (OA), and impacts on DNA fragmentation were measured. Shellfish were exposed using two different regimes, the first was a single (24 h) exposure of 2.5 nM OA (∼0.1 μg/shellfish) and algal feed at the beginning of the trial (T0), after which shellfish were only fed algae. The second was daily exposure of shellfish to two different concentrations of OA mixed with the algal feed over 7 days; 1.2 nM OA (∼0.05 μg OA/shellfish/day) and 50 nM OA (∼2 μg OA/shellfish/day). Haemolymph and hepatopancreas cells were extracted following 1, 3 and 7 days exposure. Cell viability was measured using the trypan blue exclusion assay and remained above 85% for both cell types. DNA fragmentation was examined using the single-cell gel electrophoresis (comet) assay. A significant increase in DNA fragmentation was observed in the two cell types from both species relative to the controls. This increase was greater in the pacific oyster at the higher toxin concentration. However, there was no difference in the proportion of damage measured between the two cell types, and a classic dose response was not observed, increasing toxin concentration did not correspond to increased DNA fragmentation.

Microcystin-LR and cylindrospermopsin induced alterations in chromatin organization of plant cells

Cyanobacteria produce metabolites with diverse bioactivities, structures and pharmacological properties. The effects of microcystins (MCYs), a family of peptide type protein-phosphatase inhibitors and cylindrospermopsin (CYN), an alkaloid type of protein synthesis blocker will be discussed in this review. We are focusing mainly on cyanotoxin-induced changes of chromatin organization and their possible cellular mechanisms. The particularities of plant cells explain the importance of such studies. Preprophase bands (PPBs) are premitotic cytoskeletal structures important in the determination of plant cell division plane. Phragmoplasts are cytoskeletal structures involved in plant cytokinesis. Both cyanotoxins induce the formation of multipolar spindles and disrupted phragmoplasts, leading to abnormal sister chromatid segregation during mitosis. Thus, MCY and CYN are probably inducing alterations of chromosome number. MCY induces programmed cell death: chromatin condensation, nucleus fragmentation, necrosis, alterations of nuclease and protease enzyme activities and patterns. The above effects may be related to elevated reactive oxygen species (ROS) and/or disfunctioning of microtubule associated proteins. Specific effects: MCY-LR induces histone H3 hyperphosphorylation leading to incomplete chromatid segregation and the formation of micronuclei. CYN induces the formation of split or double PPB directly related to protein synthesis inhibition. Cyanotoxins are powerful tools in the study of plant cell organization.

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

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

Innovative detection methods for aquatic algal toxins and their presence in the food chain

Detection of aquatic algal toxins has become critical for the protection of human health. During the last 5 years, techniques such as optical, electrochemical, and piezoelectric biosensors or fluorescent-microsphere-based assays have been developed for the detection of aquatic algal toxins, in addition to optimization of existing techniques, to achieve higher sensitivities, specificity, and speed or multidetection. New toxins have also been incorporated in the array of analytical and biological methods. The impact of the former innovation on this field is highlighted by recent changes in legal regulations, with liquid chromatography-mass spectrometry becoming the official reference method for marine lipophilic toxins and replacing the mouse bioassay in many countries. This review summarizes the large international effort to provide routine testing laboratories with fast, sensitive, high-throughput, multitoxin, validated methods for the screening of seafood, algae, and water samples.

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

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

Apoptotic responses of Carassius auratus lymphocytes to nodularin exposure in vitro

Nodularin, a metabolite of Nodularin spumigena, is widely detected in water blooms worldwide and causes serious negative effects on fish. The apoptosis-related cytotoxic effects and mechanisms of nodularin on Carassius auratus lymphocytes were investigated. Transmission electron microscopy results showed that nodularin-treated lymphocytes display a series of morphological changes, including condensed cytoplasm, nuclear chromatin agglutination and marginalization. DNA fragmentation was verified by the DNA-ladder and formation of sub-G1 DNA peaks. These cell characteristics confirmed the occurrence of apoptosis in lymphocytes. Flow cytometric results showed that the percentages of apoptotic cells incubated with 1, 5, 10, and 100 μg/L nodularin for 12 h reached 15.76%, 17.36%, 20.34% and 44.21%, respectively; controls showed low rates of apoptosis (2.4%). The mechanism of apoptosis induced by nodularin was determined, and results showed that nodularin exposure caused a significant increase in intracellular reactive oxygen species (ROS), loss of mitochondrial transmembrane potential in a dose-dependent manner, upregulation of intracellular Ca²⁺, downregulation of Bcl-2 and upregulation of Bax expression at the mRNA and protein levels, and activation of caspase-3 and caspase-9 without caspase-8. In summary, all the results suggest that nodularin induces lymphocyte apoptosis via the mitochondrial apoptotic pathway and destroys the immune response of fish.

Exploring marine cyanobacteria for lead compounds of pharmaceutical importance

The Ocean, which is called the "mother of origin of life," is also the source of structurally unique natural products that are mainly accumulated in living organisms. Cyanobacteria are photosynthetic prokaryotes used as food by humans. They are excellent source of vitamins and proteins vital for life. Several of these compounds show pharmacological activities and are helpful for the invention and discovery of bioactive compounds, primarily for deadly diseases like cancer, acquired immunodeficiency syndrome (AIDS), arthritis, and so forth, while other compounds have been developed as analgesics or to treat inflammation, and so forth. They produce a large variety of bioactive compounds, including substances with anticancer and antiviral activity, UV protectants, specific inhibitors of enzymes, and potent hepatotoxins and neurotoxins. Many cyanobacteria produce compounds with potent biological activities. This paper aims to showcase the structural diversity of marine cyanobacterial secondary metabolites with a comprehensive coverage of alkaloids and other applications of cyanobacteria.

A novel cyanobacterial nostocyclopeptide is a potent antitoxin against microcystins

Cyanobacterial hepatotoxins (microcystins and nodularins) cause numerous animal poisonings worldwide each year and are threats to human health. However, we found that extracts from several cyanobacteria isolates failed to induce hepatotoxicity even if they contained high concentrations of the liver toxin microcystin. The antitoxic activity abolishes all morphological hallmarks of microcystin-induced apoptosis, and therefore invalidates cell-based assays of the microcystin content of bloom-forming cyanobacteria. The antitoxin was purified from a cyanobacterial isolate (Nostoc sp. XSPORK 13A) from the Baltic Sea, and the activity was shown to reside in a novel cyclic peptide of the nostocyclopeptide family (nostocyclopeptide M1, Ncp-M1) that consists of seven amino acids (Tyr1-Tyr2-D-HSe3-L-Pro4-L-Val5-(2S,4S)-4-MPr6-Tyr7; MW=881) with an imino linkage between Tyr1 and Tyr7. Ncp-M1 did not compete with labelled microcystin for binding to protein phosphatase 2A; this explains why the antitoxin did not interfere with phosphatase-based microcystin assays. Currently used agents that interfere with microcystin action, such as inhibitors of ROS formation, microcystin uptake and Cam-kinase activity, are themselves inherently toxic. Since Ncp-M1 is potent and nontoxic it promises to become a useful mechanistic tool as soon as its exact cellular target is elucidated.

The apoptosis-inducing activity towards leukemia and lymphoma cells in a cyanobacterial culture collection is not associated with mouse bioassay toxicity

Cyanobacteria (83 strains and seven natural populations) were screened for content of apoptosis (cell death)-inducing activity towards neoplastic cells of the immune (jurkat acute T-cell lymphoma) and hematopoetic (acute myelogenic leukemia) lineage. Apoptogenic activity was frequent, even in strains cultured for decades, and was unrelated to whether the cyanobacteria had been collected from polar, temperate, or tropic environments. The activity was more abundant in the genera Anabaena and Microcystis compared to Nostoc, Phormidium, Planktothrix, and Pseudanabaena. Whereas the T-cell lymphoma apoptogens were frequent in organic extracts, the cell death-inducing activity towards leukemia cells resided mainly in aqueous extracts. The cyanobacteria were from a culture collection established for public health purposes to detect toxic cyanobacterial blooms, and 54 of them were tested for toxicity by the mouse bioassay. We found no correlation between the apoptogenic activity in the cyanobacterial isolates with their content of microcystin, nor with their ability to elicit a positive standard mouse bioassay. Several strains produced more than one apoptogen, differing in biophysical or biological activity. In fact, two strains contained microcystin in addition to one apoptogen specific for the AML cells, and one apoptogen specific for the T-cell lymphoma. This study shows the potential of cyanobacterial culture collections as libraries for bioactive compounds, since strains kept in cultures for decades produced apoptogens unrelated to the mouse bioassay detectable bloom-associated toxins.

Biological methods for marine toxin detection

The presence of marine toxins in seafood poses a health risk to human consumers which has prompted the regulation of the maximum content of marine toxins in seafood in the legislations of many countries. Most marine toxin groups are detected by animal bioassays worldwide. Although this method has well known ethical and technical drawbacks, it is the official detection method for all regulated phycotoxins except domoic acid. Much effort by the scientific and regulatory communities has been focused on the development of alternative techniques that enable the substitution or reduction of bioassays; some of these have recently been included in the official detection method list. During the last two decades several biological methods including use of biosensors have been adapted for detection of marine toxins. The main advances in marine toxin detection using this kind of technique are reviewed. Biological methods offer interesting possibilities for reduction of the number of biosassays and a very promising future of new developments.

Use of biosensors as alternatives to current regulatory methods for marine biotoxins

Marine toxins are currently monitored by means of a bioassay that requires the use of many mice, which poses a technical and ethical problem in many countries. With the exception of domoic acid, there is a legal requirement for the presence of other toxins (yessotoxin, saxitoxin and analogs, okadaic acid and analogs, pectenotoxins and azaspiracids) in seafood to be controlled by bioassay, but other toxins, such as palytoxin, cyclic imines, ciguatera and tetrodotoxin are potentially present in European food and there are no legal requirements or technical approaches available to identify their presence. The need for alternative methods to the bioassay is clearly important, and biosensors have become in recent years a feasible alternative to animal sacrifice. This review will discuss the advantages and disadvantages of using biosensors as alternatives to animal assays for marine toxins, with particular focus on surface plasmon resonance (SPR) technology.

Oxidative stress induced by microcystin-LR on PLHC-1 fish cell line

Increasing evidences suggest that oxidative stress may play a significant role in microcystins (MCs) toxicity not only in mammals, but also in fish. In this regard, many in vivo studies have been performed but little is still known about the alteration of oxidative stress biomarkers on fish cell lines so far. In this study, the toxic effects of MC-LR were investigated in the fish cell line PLHC-1, derived from a hepatocellular carninoma of the topminnow Poeciliosis lucida, after 48 h of exposure. The different response of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST), as well as lipid peroxidation (LPO) as a biomarker of oxygen-mediated toxicity, were assessed in PLHC-1 cells. The increases in the antioxidant enzymatic activities (SOD, GPx, and GST) as well as in LPO values observed evidenced the oxidative stress induced by MC-LR exposure. Moreover, the enhancements of these enzymes could suggest an adaptative response to combat oxidative injure induced by MC-LR, confirming that this mechanism is involved in the damage induced by MCs on fish cells.

Accumulation and effects of nodularin from a single and repeated oral doses of cyanobacterium Nodularia spumigena on flounder (Platichthys flesus L.)

Nodularin (NODLN) is a cyclic pentapeptide hepatotoxin produced by the cyanobacterium Nodularia spumigena, which occurs regularly in the Baltic Sea during the summer season. In this study flounder (Platichthys flesus L.) was orally exposed to NODLN either as a single dose or as three repeated doses 3 days apart. Liver and bile samples of the fish were taken 4 days after the last dose. Liver glutathione-S-transferase (GST) activity was also measured and the histopathology of the liver was investigated. The liver of the exposed fish was analyzed by liquid chromatography-mass spectrometry for NODLN concentration. The content of NODLN-like compounds in the bile was analyzed by enzyme-linked immunosorbent assay. NODLN exposure caused slightly incoherent liver architecture and degenerative cell changes in both groups. The mean liver GST activity was significantly higher in the repeatedly dosed flounders than in the singly dosed flounders or in the control. In conclusion, the significantly lower NODLN concentration and the increased GST activity in the liver of the repeatedly dosed flounders compared to the singly dosed flounders suggest that NODLN is rapidly detoxificated. The absence of NODLN glutathione conjugates and the low concentrations of NODLN-like compounds in the bile indicate that detoxification products disintegrate or they are rapidly excreted.

Cytoskeletal toxicity of pectenotoxins in hepatic cells

BACKGROUND AND PURPOSE

Pectenotoxins are macrocyclic lactones found in dinoflagellates of the genus Dinophysis, which induce severe liver damage in mice after i.p. injection. Here, we have looked for the mechanism(s) underlying this hepatotoxicity.

EXPERIMENTAL APPROACH

Effects of pectenotoxin (PTX)-1, PTX-2, PTX-2 seco acid (PTX-2SA) and PTX-11 were measured in a hepatocyte cell line with cancer cell characteristics (Clone 9) and in primary cultures of rat hepatocytes. Cell morphology was assessed by confocal microscopy; F- and G-actin were selectively stained and cell viability measured by Alamar Blue fluorescence.

KEY RESULTS

Clone 9 cells and primary hepatocytes showed a marked depolymerization of F-actin with PTX-1, PTX-2 and PTX-11 (1-1000 nM) associated with an increase in G-actin level. However, morphology was only clearly altered in Clone 9 cells. PTX-2SA had no effect on the actin cytoskeleton. Despite the potent F-actin depolymerizing effect, PTX-1, PTX-2 or PTX-11 did not decrease the viability of Clone 9 cells after 24-h treatment. Only prolonged incubation (> 48 h) with PTXs induced a fall in viability, and under these conditions, morphology of both Clone 9 and primary hepatocytes was drastically changed.

CONCLUSIONS AND IMPLICATIONS

Although the actin cytoskeleton was clearly altered by PTX-1, PTX-2 and PTX-11 in the hepatocyte cell line and primary hepatocytes, morphological assessments indicated a higher sensitivity of the cancer-like cell line to these toxins. However, viability of both cell types was not altered.

Gene expression profiles in liver of zebrafish treated with microcystin-LR

Microcystin-LR (MC-LR) is the most frequently studied cyclic heptatoxin produced by cyanobacteria, which has tremendous negative impacts on fish, while its molecular mechanism behind remained unclear at present. Here, Affymetrix Zebrafish GeneChip was used to identify alterations in gene expression of zebrafish (Danio rerio) after MC-LR exposure. Among the 14,900 transcripts in the microarray, 273 genes were differentially expressed, in which 243 genes were elevated and 30 were decreased. According to GOstat analysis, MC-LR mainly influenced the cell cycle and mitogen-activated protein kinases (MAPK) signaling pathways. In addition, many immune-related genes were also influenced. These data suggest that MC-LR could promote tumorigenesis and cause immunotoxicity in fish.

Nucleotide excision repair impairment by nodularin in CHO cell lines due to ERCC1/XPF inactivation

The problem of toxicity of cyanobacterial toxins is of increasing concern, as the incidence of such blooms grows. Among the toxins, the most abundant in the environment are hepatotoxins known as nodularins and microcystins. These toxins are responsible for almost all known cases of fresh and brackish water intoxication and are responsible for recurrent episodes of human and animal illness and death. Moreover, they are believed to be potent tumor promoters and initiators. However, the mechanisms by which these toxins induce liver cancer are not well understood. The aim of the present study was to determine the effect of nodularin on the kinetics of nucleotide excision repair (NER) in Chinese hamster ovary (CHO) cells exposed to UV radiation. The first set of experiments was performed to define the optimal treatment conditions for nodularin to avoid the possibility of encountering false positive signals in the comet assay due to the apoptogenic activity of nodularin. Based on the analysis of apoptosis, the 6-h treatment time of cells with nodularin (1mug/ml, 10mug/ml and 20mug/ml) was chosen for the alkaline comet assay. The kinetics of NER was determined in CHO cell lines: AA8 (wild-type) and mutant cell lines: UV135 (XPG(-)), UV41 (XPF(-)) and UV20 (ERCC1(-)) exposed to 20J/m(2) UV radiation. The micronucleus assay was performed to determine a residual DNA damage in four cell lines treated with nodularin (10mug/ml) and exposed to equitoxic doses UV radiation. Radiation doses of UV producing 50% of survival for AA8, UV135, UV20 and UV41 cell lines were calculated from UV survival curves. The results show that nodularin impairs the incision/excision step of NER in CHO cells by the ERCC1/XPF inactivation and leads to an increased level of UV-induced cytogenetic DNA damage.

Antimicrobial and cytotoxic assessment of marine cyanobacteria - Synechocystis and Synechococcus

Aqueous extracts and organic solvent extracts of isolated marine cyanobacteria strains were tested for antimicrobial activity against a fungus, Gram-positive and Gram-negative bacteria and for cytotoxic activity against primary rat hepatocytes and HL-60 cells. Antimicrobial activity was based on the agar diffusion assay. Cytotoxic activity was measured by apoptotic cell death scored by cell surface evaluation and nuclear morphology. A high percentage of apoptotic cells were observed for HL-60 cells when treated with cyanobacterial organic extracts. Slight apoptotic effects were observed in primary rat hepatocytes when exposed to aqueous cyanobacterial extracts. Nine cyanobacteria strains were found to have antibiotic activity against two Gram-positive bacteria, Clavibacter michiganensis subsp. insidiosum and Cellulomonas uda. No inhibitory effects were found against the fungus Candida albicans and Gram-negative bacteria. Marine Synechocystis and Synechococcus extracts induce apoptosis in eukaryotic cells and cause inhibition of Gram-positive bacteria. The different activity in different extracts suggests different compounds with different polarities.

A structural basis for regulation of actin polymerization by pectenotoxins

(PTXs) are polyether macrolides found in certain dinoflagellates, sponges and shellfish, and have been associated with diarrhetic shellfish poisoning. In addition to their in vivo toxicity, some PTXs are potently cytotoxic in human cancer cell lines. Recent studies have demonstrated that disruption of the actin cytoskeleton may be a key function of these compounds, although no clarification of their mechanism of action at a molecular level was available. We have obtained an X-ray crystal structure of PTX-2 bound to actin, which, in combination with analyses of the effect of PTX-2 on purified actin filament dynamics, provides a molecular explanation for its effects on actin. PTX-2 formed a 1:1 complex with actin and engaged a novel site between subdomains 1 and 3. Based on models of the actin filament, PTX binding would disrupt key lateral contacts between the PTX-bound actin monomer and the lower lateral actin monomer within the filament, thereby capping the barbed-end. The location of this binding position within the interior of the filament indicates that it may not be accessible once polymerization has occurred, a hypothesis supported by our observation that PTX-2 caused filament capping without inducing filament severing. This mode of action is unique, as other actin filament destabilizing toxins appear to exclusively disrupt longitudinal monomer contacts, allowing many of them to sever filaments in addition to capping them. Examination of the PTX-binding site on actin provides a rationalization for the structure-activity relationships observed in vivo and in vitro, and may provide a basis for predicting toxicity of PTX analogues.

Acute and subacute toxic effects produced by microcystin-YR on the fish cell lines RTG-2 and PLHC-1

Approximately 80 microcystins (MCs) variants have been isolated in surface water worldwide. The toxicity of the most frequently MCs are encountered, MC-LR and MC-RR, has been extensively studied in humans and animals. However, studies dealing with MC-YR toxicity are still scarce. In this work, the toxic effects of MC-YR were investigated in the fish cell line PLHC-1, derived from a hepatocellular carcinoma of the topminnow Poeciliopsis lucida, and RTG-2 fibroblast-like cells derived from the gonads of rainbow trout Oncorhynchus mykiss. After 48 h, morphological and biochemical changes (total protein content, neutral red uptake and methylthiazol tetrazolium salt metabolization) were determined. The most sensitive endpoint for both cell lines was the reduction of total protein content, with EC(50) values of 35 microM for PLHC-1 cells and 67 microM for the RTG-2 cell line. Lysosomal function and methylthiazol tetrazolium salt metabolization were stimulated at low concentrations, while they decreased at high doses. Increase of piknotic cells, rounding effects, reduction in cell number and cell size, hydropic degeneration, and death mainly by necrosis but also by apoptosis were observed in the morphological study. Furthermore, PLHC-1 cells are more sensitive than RTG-2 cells to MC-YR exposure. These results were similar to those obtained when both cell lines were exposed for 24h to a Microcystis aeruginosa isolated strain extract containing MC-LR.

Synthetic studies towards the pectenotoxins: a review

In this article we provide an overview of synthetic studies towards pectenotoxins (PTXs) that have been reported by several research groups. The difficulties encountered in the synthesis of these series of polyketides are highlighted by the fact that only one total synthesis of PTX4 and PTX8 has been completed to date. The strategies used in the critical bond forming steps and the introduction of key stereogenic centres are compared and contrasted.

Accumulation of nodularin in sediments, mussels, and fish from the Gulf of Gdańsk, southern Baltic Sea

In the Gulf of Gdańsk, as in other parts of the Baltic Sea, toxic blooms of Nodularia spumigena are an annual phenomenon. In the present work, the accumulation of nodularin (NOD), a cyanobacterial pentapeptide hepatotoxin, in sediments, blue mussels, and flounders from the Gulf of Gdańsk was studied by enzyme-linked immunosorbent assay (ELISA). In the surface layers of the sediments NOD concentration ranged from 2.3 ng/g dry weight (dw) several months after cyanobacterial bloom to 75 ng/g dw during the bloom. The highest toxin content in mussels was 139 ng/g dw. In two sampling stations situated in the coastal waters of the Gulf of Gdańsk the concentrations of NOD in sediments and mussels were significantly lower than those measured in the Gulf of Finland. In sediments and mussels collected in the Gulf of Gdańsk, the toxin was also detected in March when N. spumigena did not occur. In flounder, NOD accumulated in the liver (489 ng/g dw), guts (21 ng/g dw), and gonads (21 ng/g dw). Hybride quadrupole-time-of-flight liquid chromatography/mass spectrometry/mass spectrometry (TOF-LC/MS/MS) confirmed the presence of NOD in sediment, mussel, and fish samples. Additionally, other NOD analogues, ([DMAdda(3)]NOD and [dhb(5)]NOD), were detected in sediments and mussel tissue. No NOD conjugates with reduced glutathione or cysteine were found in fish and mussels.

Toxic effects produced by microcystins from a natural cyanobacterial bloom and a Microcystis aeruginosa isolated strain on the fish cell lines RTG-2 and PLHC-1

Toxic cyanobacterial blooms are a worldwide problem, causing serious water pollution and public health hazard to humans and livestock. The intact cells as well as the toxins released after cellular lysis can be responsible for toxic effects in both animals and humans and are actually associated with fish kills. Two fish cell lines-PLHC-1 derived from a hepatocellular carcinoma of the topminnow Poeciliopsis lucida and RTG-2 fibroblast-like cells derived from the gonads of rainbow trout Oncorhynchus mykiss were exposed to several concentrations of extracts from a natural cyanobacterial bloom and a Microcystis aeruginosa-isolated strain. After 24 hours, morphologic and biochemical changes (total protein content, lactate dehydrogenase leakage, neutral red uptake, methathiazole tetrazolium salt metabolization, lysosomal function, and succinate dehydrogenase [SDH] activity) were investigated. The most sensitive end point for both cyanobacterial extracts in PLHC-1 cells was SDH activity, with similar EC(50) values (6 microM for the cyanobacterial bloom and 7 microM for the isolated strain). RTG-2 cells were less susceptible according to SDH activity, with their most sensitive end point lysosomal function with an EC(50) of 4 microM for the M. aeruginosa-isolated strain and 72 microM for the cyanobacterial bloom. The lysosomal function was stimulated at low concentrations, although SDH activity increased at high doses, indicating lysosomal and energetic alterations. Increased secretion vesicles, rounding effects, decreased cell numbers and size, hydropic degeneration, esteatosis, and apoptosis were observed in the morphologic study. Similar sensitivity to the M. aeruginosa-isolated strain was observed in both cell lines, whereas the cyanobacterial bloom was more toxic to the PLHC-1 cell line.

Nodularin-induced genotoxicity following oxidative DNA damage and aneuploidy in HepG2 cells

The problem of toxicity of Nodularia spumigena to animals and people is of increasing concern, as the incidence of such blooms grows. It was shown that nodularin is a liver carcinogen possessing both initiating and tumor-promoting activities. However, the mechanisms by which this toxin damages the DNA and induces liver cancer are not well understood. The aim of the present study was to investigate the DNA damaging properties of nodularin. The effect of different doses of nodularin (1-10 microg/ml) on DNA damage was determined in HepG2 cells after 6, 12, 24 and 48 h of the treatment. The modified comet assay in conjunction with Fpg (ROS-induced DNA damage) and FISH-micronucleus assay (clastogenic and/or aneugenic activities of nodularin) were applied. In addition the occurrence of apoptosis was estimated by the morphological analysis of chromatin condensation and the annexin method using flow cytometry. We found that nodularin induces oxidative DNA damage by oxidation of purines and increases the formation of centromere positive micronuclei due to aneugenic activity. In addition to genotoxic properties, nodularin exerts a cytotoxic activity by inducing apoptosis in HepG2 cells. These results suggest a causative role for nodularin in the process leading to the accumulation of genetic alterations which may be implicated in carcinogenesis.

Toxic potential of microcystin-containing cyanobacterial extracts from three Romanian freshwaters

The aim of this study was to characterise for the first time the toxin profile and in vivo/in vitro toxicological effects of cyanobacteria obtained from three Romanian freshwater blooms. Two strains of Microcystis aeruginosa were isolated from blooms occurring in different fish ponds. As well, a complex bloom sample obtained from a recreational lake area and dominated by Microcystis aeruginosa and Microcystis viridis was explored. The morphological identity of the cyanobacterial species could be confirmed by sequence analysis of the intergenic spacer region of the phycocyanin operon, PC-IGS. As well, both the strains and the field sample were confirmed to possess mcyA and mcyB genes, which correlated with the formation of several microcystins (MCYSTs). A number of cyanopeptolins and a new aeruginosin were also found. Despite these mixtures of compounds, in vivo as well as in vitro toxicological responses resembled those previously found for MCYST-LR. These include strong hepatotoxicity in mice with parenchymal disintegration and the emergence of haemorrhagic centres, a lack of responsiveness of human and fish cell lines most likely due to a lack of active transport systems, and a significant subcellular damage most prominent on the level of the lysosomes in primary hepatocytes of mice and rainbow trout. We thus conclude that the formation of blooms in the Romanian fish ponds and the recreational area may impact on animal and human health. A broader survey of cyanotoxin occurrence and related toxicity is necessary in Romania in order to assess the extent of this animal and human health hazard.

Degeneration and regeneration of ultraviolet cone photoreceptors during development in rainbow trout

Ultraviolet-sensitive (UVS) cones disappear from the retina of salmonid fishes during a metamorphosis that prepares them for deeper/marine waters. UVS cones subsequently reappear in the retina near sexual maturation and the return migration to natal streams. Cellular mechanisms of this UVS cone ontogeny were investigated using electroretinograms, in situ hybridization, and immunohistochemistry against opsins during and after thyroid hormone (TH) treatments of rainbow trout (Oncorhynchus mykiss). Increasing TH levels led to UVS cone degeneration. Labeling demonstrated that UVS cone degeneration occurs via programmed cell death and caspase inhibitors can inhibit this death. After the cessation of TH treatment, UVS cones regenerated in the retina. Bromodeoxyuridine (BrdU) was applied after the termination of TH treatment and was detected in the nuclei of cells expressing UVS opsin. BrdU was found in UVS cones but not other cone types. The most parsimonious explanation for the data is that UVS cones degenerated and UVS cones were regenerated from intrinsic retinal progenitor cells. Regenerating UVS cones were functionally integrated such that they were able to elicit electrical responses from second-order neurons. This is the first report of cones regenerating during natural development. Both the death and regeneration of cones in retinae represent novel mechanisms for tuning visual systems to new visual tasks or environments.

Sensitive apoptosis induced by microcystins in the crucian carp (Carassius auratus) lymphocytes in vitro

Microcystins including leucine-arginine l-amino acid (MCLR) and arginine-arginine l-amino acid (MCRR) can inhibit several serine/threonine protein phosphatases. In this study, we focused on the efficient biomarker for analyzing toxic cyanobacteria blooms using in vitro apoptosis bioassay. We explored the existence of sensitive apoptosis induced by MCLR and MCRR on isolated lymphocytes of the crucian carp (Carassius auratus) at a low exposure level. Apoptosis was detected in vitro and was clearly distinguished by condensation of nuclear chromatin and formation of apoptotic bodies, after 2 h exposure at 1, 5, 10 nM MCLR and MCRR, respectively. Agarose gel electrophoresis further revealed DNA fragmentation (DNA ladder) caused by apoptosis. We found that MCLR and MCRR can induce lymphocyte apoptosis in a dose- and time-dependent manner with flow cytometry analysis. Our study provides the first evidence that microcystins can induce fish lymphocytes apoptosis and may impair fish immune function.

A high proportion of Baltic Sea benthic cyanobacterial isolates contain apoptogens able to induce rapid death of isolated rat hepatocytes

To assess the potential hepatotoxicity of benthic cyanobacteria, we isolated 41 strains from the Baltic Sea. The bacteria were differentially extracted with solvents of decreasing polarity. The extracts were tested for ability to induce death of primary rat hepatocytes in suspension culture. Mainly morphological criteria were used to discriminate between cell death with apoptotic features (shrinkage, chromatin hypercondensation, budding) or necrotic features (swelling, loss of plasma membrane integrity). The 24 isolates containing hepatotoxic compounds were of the genus Anabaena. The non-toxic isolates were mainly Nostoc and Calothrix. The toxicity was not due to the known hepatotoxic cyanobacterial protein phosphatase inhibitors microcystin or nodularin, as demonstrated by lacking competition with microcystin for PP2A binding. Apoptotic cell death was rapid, being evident from 10 to 60 min after the addition of extract. Sometimes the initial apoptosis was followed by secondary necrosis. Three cyanobacterial extracts produced apoptosis with unusual cell morphology including actin rearrangements. It will be of interest to know if they contain substance(s) acting through novel death pathways. We conclude that benthic Anabaena cyanobacteria represent a rich source of apoptogenic toxins, presumably directed against competitors or predators in the aquatic environment, but obviously able also to induce cell death in mammalian parenchymal liver cells.

The use of the fish cell lines RTG-2 and PLHC-1 to compare the toxic effects produced by microcystins LR and RR

Cyanobacterial toxins, especially microcystins (MC), are found in eutrophied waters through the world. Acute poisonings of animals and humans has been reported following MC exposure. In the present study, two fish cell lines, PLHC-1 and RTG-2, were evaluated after exposure to the cyanobacterial toxins MC-LR and MC-RR. The effects of different concentrations of the toxins were investigated in both cell lines at morphological and biochemical levels (total protein content, lactate dehydrogenase leakage, lysosomal activity and succinate dehydrogenase activity). The results obtained showed a decrease in protein content and no relevant increase in cell disruption, except for MC-LR in PLHC-1 cells. Morphological changes produced by microcystins were cellular swelling, blebbling, rounding, reduction in the cell number and increase in the number and size of lysosomal bodies. In addition, steatosis was produced in hepatoma PLHC-1 cells, particularly with MC-RR. Furthermore, the fish PLHC-1 cell line was more sensitive than RTG-2 cells to the cyanobacterial toxins compared, being the stimulation of the lysosomal function and the induction of steatosis the most specific changes detected.

Neuro-apoptogenic and blood platelet targeting toxins in benthic marine cyanobacteria from the Portuguese coast

Six strains of marine cyanobacteria, of which five benthic, were isolated from an area of the Portuguese coast with no known apparent toxic microbial bloom. Five strains were lethal for mice. Four of them produced lethargy and four lead to bleeding. One of the toxic strains was from a genus (Aphanothece) not previously associated with toxin production. Extracts from four isolates induced SH-SY5Y-neuroblastoma cell apoptosis without affecting the viability of hepatocytes, NRK kidney cells, or fibroblasts. Aqueous extract from four isolates inhibited thrombin-induced blood platelet activation, with decreased P-selectin expression, platelet aggregation and shedding of platelet-derived micro-vesicles. Curiously, platelets treated with organic extracts from two of the cyanobacterial strains formed platelet micro-vesicles, expressed P-selectin on the surface and showed a distinct phosphotyrosine protein pattern, but failed to aggregate. We conclude that low-abundance marine cyanobacteria growing at low rates may be an important source for novel toxins that may be useful to dissect mammalian signalling pathways of apoptosis and platelet function.

Protective effect of a 50% hydroalcoholic fruit extract of Emblica officinalis against anti-tuberculosis drugs induced liver toxicity

The present report showed the hepatoprotective property of a 50% hydroalcoholic extract of the fruits of Emblica officinalis (fruit) (EO-50) against antituberculosis (anti-TB) drugs-induced hepatic injury. The biochemical manifestations of hepatotoxicity induced by rifampicin (RIF), isoniazid (INH) and pyrazinamide (PZA), either given alone or in combination were evaluated. In vitro studies were done on suspension cultures of rat hepatocytes while sub-acute studies were carried out in rats. The hepatoprotective activity of EO-50 was found to be due to its membrane stabilizing, antioxidative and CYP 2E1 inhibitory effects.

Functional assays in marine biotoxin detection

The contamination of seafood by algal toxins regularly affects animals living in several areas of the world, and the number of toxic phycotoxins which are being characterized is steadily increasing. The extreme dynamics characterizing the field of algal toxins has stimulated the development of tools to be implemented in the monitoring of contamination of seafood by individual toxin classes. Under these circumstances, functional assays which can encompass the analytical potential of chemical methods and the predictive features of biological tests are sought. A variety of functional assays for the detection of phycotoxins has been developed in the last 20 years, and the analysis of their features reveals that their specificity is related to the hierarchical level of the biological response to the toxin that has been exploited for its detection. Ideally, analytical methods which could allow accurate estimates of the overall toxicity of multiple classes of toxins in a single procedure would provide the best means for the highest standards in consumer protection and the most rational and economical tools in the management of risks posed by phycotoxins in a wider scale. The achievement of a "systemic functional assay for marine biotoxins" does not appear to be at hand, but its inclusion among the foreseeable events is fully justified by the new research tools and approaches which have become available for the high throughput analysis of entire molecular domains at the cellular level.

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.