An ultrasensitive competitive binding assay for the detection of toxins affecting protein phosphatases

The Mouse Bioassay for Diarrhetic Shellfish Poisoning: A Gross Misuse of Laboratory Animals and of Scientific Methodology

The UK shellfish industry has recently been affected by the statutory closure of several cockle beds, following the detection of samples causing rapid and severe reactions in the regulatory approved test for diarrhetic shellfish poisoning (DSP) toxins, the mouse bioassay (MBA). It is contended that these so-called atypical results are due to procedural artefacts of the MBA; so far, several studies have failed to identify their cause. This paper critically assesses the development, regulatory use and methodological deficiencies of the MBA. It also discusses how testing for DSP toxins could and should have been improved and made more humane by applying the Three Rs concept of Reduction, Refinement and Replacement, and by the proper validation of the test method used. It is concluded that the MBA should not have been developed for the routine screening of shellfish samples, as it has a substantially severe endpoint and is not used as part of a tiered-testing strategy with non-animal methods. Moreover, during the UK monitoring programme for DSP toxins, the assay has been used without an optimised and universal protocol, and apparently without due regard to the principles of basic scientific methodology. In view of this, the atypical results obtained for cockle samples cannot be relied on as evidence of a human health hazard. It is recommended that the use of the MBA should be discontinued as soon as possible, in favour of other methods, especially those involving non-animal techniques. In the short-term, these methods should be based on analytical chemical detection systems and the essential availability of the relevant pure toxin standards. The lack of any known toxins in samples should be taken as evidence of lack of contamination. The suitability of the existing non-animal methods needs to be assessed as a matter of urgency. It is crucial that all new methods should be properly validated, and that their acceptability for their stated purposes should be endorsed by recognised criteria and validation centres, before being recommended to, or required by, regulatory agencies. In this way, the possibility that scientifically unsuitable methods will once again be used for monitoring for the contamination of shellfish with toxins can be avoided. This gross misuse of laboratory animals and ill-judged application of science should never be allowed to occur again.

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.

Effect of cyanobacteria on immune function of crucian carp (Carassius auratus) via chronic exposure in diet

Cyanobacterial blooms caused by water eutrophication have become a worldwide problem. Microcystins (MCs) released during cyanobacterial blooms exert toxicity on fish. Up to now, immunotoxicity of MCs on fish has been rarely reported. The present study investigated immune response of crucian carp (Carassius auratus) to cyanobacteria via chronic exposure in diet. Fish were fed with diets containing 20% (low dose group) and 40% (high dose group) of cyanobacteria lyophilized powder. After exposure of 30 d, a batch of assays was determined for assessing immunotoxicity of MCs. The head kidney and spleen indexes significantly increased in high dose group. Blood nitroblue tetrazolium activity in high dose group was nearly twice as much as that in control group with no cyanobacteria additive. Marked haemorrhage and hyperemia were observed in kidney and spleen in high dose group. The edematous mitochondria, deformation of the nucleus and compaction of chromatin occurred in lymphocytes of head kidney and spleen in both cyanobacteria groups. Lysozyme activity showed an obvious increase in low dose group but a sharp decrease in high dose group. Significant increase of macrophage bactericidal activity was detected in low dose group. The present findings indicate that via chronic diet exposure of different cyanobacteria levels, fish exhibit various immune responses. Fish immunity tends to proceed toward the direction of immunostimulative response at low MCs concentrations but toward the trend of immunosuppressive answer at high MCs concentrations.

Preliminary study for rapid determination of phycotoxins in microalgae whole cells using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Rapid and sensitive methods for identification of several phycotoxins produced by microalgae species such as yessotoxins (YTXs) for Protoceratium reticulatum, okadaic acid (OA) and pectenotoxins (PTXs) for Prorocentrum spp. and Dinophysis spp., Palytoxins (PLTXs) for Ostreopsis spp., ciguatoxins (CTXs) for Gambierdiscus spp. or domoic acid (DA) for Pseudo-nitzschia spp. are of great importance to the shellfish and fish industry. In this study, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to detect several phycotoxins in whole cells of some microalgae which are known as toxin producers. To achieve an appropriate MALDI matrix and a sample preparation method, several matrices and solvent mixtures were tested. The most appropriate matrix system for toxin detection was obtained with 10 µg μL(-1) of DHB in 0.1% TFA/ACN (3:7, v/v) by mixing the intact cells with the matrix solution directly on the MALDI target (dried-droplet technique). Toxin detection by this procedure is much faster than current procedures based on solvent extraction and chromatographic separation. This method allowed the rapid detection of main phycotoxins in some dinoflagellate cells of genus Ostreopsis, Prorocentrum, Protoceratium, Gambierdiscus, Dinophysis and diatoms from Pseudo-nitzschia genus.

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.

Marine benthic diatoms contain compounds able to induce leukemia cell death and modulate blood platelet activity

In spite of the high abundance and species diversity of diatoms, only a few bioactive compounds from them have been described. The present study reveals a high number of mammalian cell death inducing substances in biofilm-associated diatoms sampled from the intertidal zone. Extracts from the genera Melosira, Amphora, Phaeodactylum and Nitzschia were all found to induce leukemia cell death, with either classical apoptotic or autophagic features. Several extracts also contained inhibitors of thrombin-induced blood platelet activation. Some of this activity was caused by a high content of adenosine in the diatoms, ranging from 0.07 to 0.31 μg/mg dry weight. However, most of the bioactivity was adenosine deaminase-resistant. An adenosine deaminase-resistant active fraction from one of the extracts was partially purified and shown to induce apoptosis with a distinct phenotype. The results show that benthic diatoms typically found in the intertidal zone may represent a richer source of interesting bioactive compounds than hitherto recognized.

Acyloxymethyl esterification of nodularin-R and microcystin-LA produces inactive protoxins that become reactivated and produce apoptosis inside intact cells

We report the esterification of the carboxyl groups of the cyclic peptide toxins nodularin-R and microcystin-LA to produce stable diacetoxymethyl and dipropionyloxymethyl ester derivatives. The derivatives had no activity but were reactivated upon esterase treatment. When injected into cells, the acyloxymethyl moieties were cleaved off and apoptosis induced. Linking the acyloxymethyl-ester moiety of these potent toxins to carriers destined for endocytosis paves the way for selective apoptosis induction in target (e.g., cancer) cells.

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.

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.

Effect of microcystin-LR on protein phosphatase activity and glycogen content in isolated hepatocytes of fed and fasted juvenile goldfish Carassius auratus L

Toxic effects of microcystin-LR were studied in hepatocytes isolated from fed and fasted juvenile goldfish Carassius auratus (30 g body weight). The hepatocytes were incubated with 10 microgMC-LR l(-1) during 4 h. MC-LR induces no effect in terms of cell number and viability. The toxin accumulation pattern was different in fed and fasted treatments. MC-LR accumulated more rapidly in 'fasted' cells where the highest concentration was observed by 1 h of exposure. It was delayed to 4 h in the 'fed' cells. MC-LR accumulation induced a severe decrease in hepatic protein phosphatase activity in both treatments. It was almost totally inhibited in both treatments during the first hour of exposure. The glycogen content was significantly reduced after 2 h of exposure in the fasting treatments, but not in the feeding one.

Microcystin-producing blooms--a serious global public health issue

The investigation on microcystin topics is increasing due to the related ecological and public health risks. Recent investigation confirms a gap in establishing global patterns relating a particular environment to the bloom occurrence of a species and the production of certain microcystin variants. All the results concerning the environmental effects on the microcystin synthesis of one species must be checked in the light of genome diversity. Thus, the poisoning risks of a bloom depend on the strain causing toxicity. To be more effective, specific water treatment methods are required for blooms of different microcystin producing species (such as colonial and filamentous cyanobacteria found in stratified and unstratified water bodies, respectively). With the increasing number of new microcystin variants discovered, the development of new rapid, inexpensive and sensitive enough monitoring methods to promptly screen simultaneously a great diversity of toxins and also check their toxic effects is becoming necessary.

Fluoride and organic weak acids as modulators of microbial physiology

Fluoride is widely used as an anticaries agent in drinking water and a variety of other vehicles. This use has resulted in major health benefits. However, there are still open questions regarding the mechanisms of anticaries action and the importance of antimicrobial effects in caries reduction. Fluoride acts in multiple ways to affect the metabolism of cariogenic and other bacteria in the mouth. F(-)/HF can bind directly to many enzymes, for example, heme-containing enzymes or other metalloenzymes, to modulate metabolism. Fluoride is able also to form complexes with metals such as aluminum or beryllium, and the complexes, notably AlF(4)(-) and BeF(3)(-).H(2)O, can mimic phosphate with either positive or negative effects on a variety of enzymes and regulatory phosphatases. The fluoride action that appears to be most important for glycolytic inhibition at low pH in dental plaque bacteria derives from its weak-acid properties (pK(a)=3.15) and the capacity of HF to act as a transmembrane proton conductor. Since many of the actions of fluoride are related to its weak-acid character, it is reasonable to compare fluoride action to those of organic weak acids, including metabolic acids, food preservatives, non-steroidal anti-inflammatory agents and fatty acids, all of which act to de-energize the cell membrane by discharging DeltapH. Moreover, with the realization that the biofilm state is the common lifestyle for most microorganisms in nature, there is need to consider interactions of fluoride and organic weak acids with biofilm communities. Hopefully, this review will stimulate interest in the antimicrobial effects of fluoride or other weak acids and lead to more effective use of the agents for disease control and other applications.

Cloud-point extraction and preconcentration of cyanobacterial toxins (microcystins) from natural waters using a cationic surfactant

A new cloud-point extraction and preconcentration method using a cationic surfactant, Aliquat-336 (tricaprylylmethylammonium chloride), has been developed for the determination of cyanobacterial toxins, microcystins, in natural waters. Sodium sulfate was used to induce phase separation at 25 degrees C. The phase behavior of Aliquat-336 with respect to concentration of Na2SO4 was studied. The cloud-point system revealed a very high phase volume ratio compared to other established systems of nonionic, anionic, and cationic surfactants. At pH 6-7, it showed an outstanding selectivity in analyte extraction for anionic species. Only MC-LR and MC-YR, which are known to be predominantly anionic, were extracted (with averaged recoveries of 113.9 +/- 9% and 87.1 +/- 7%, respectively). MC-RR, which is likely to be amphoteric at the above pH range, was not detectable in the extract. Coupled to HPLC/UV separation and detection, the cloud-point extraction method (with 2.5 mM Aliquat-336 and 75 mM Na2SO4 at 25 degrees C) offered detection limits of 150 +/- 7 and 470 +/- 72 pg/mL for MC-LR and MC-YR, respectively, in 25 mL of deionized water. Repeatability of the method was 7.6% for MC-LR and 7.3% for MC-YR. The cloud-point extraction process can be completed within 10-15 min with no cleanup steps required. Applicability of the new method to the determination of microcystins in real samples was demonstrated using natural surface waters collected from a local river and a local duck pond spiked with realistic concentrations of microcystins. Effects of salinity and organic matter (TOC) content in the water sample on the extraction efficiency were also studied.

Using an enzyme linked immunosorbent assay (ELISA) and a protein phosphatase inhibition assay (PPIA) for the detection of microcystins and nodularins

Cyanotoxins produced by cyanobacteria (blue-green algae) include potent neurotoxins and hepatotoxins. The hepatotoxins include cyclic peptide microcystins and nodularins plus the alkaloid cylindrospermopsins. Among the cyanotoxins the microcystins have proven to be the most widespread, and are most often implicated in animal and human poisonings. This paper presents a practical guide to two widely used methods for detecting and quantifying microcystins and nodularins in environmental samples-the enzyme linked immunosorbant assay (ELISA) and the protein phosphatase inhibition assay (PPIA).

Production and specificity of monoclonal antibodies against nodularin conjugated through N-methyldehydrobutyrine

Nodularin (Nod) is a cyclic pentapeptide hepatotoxin produced by the cyanobacterial genus Nodularia living in brackish waters and coastal lagoons. The toxicity of Nod is due to specific inhibition of the type-1 and type-2A intracellular protein phosphatases (PP1 and PP2A, respectively). We have developed a monoclonal antibody against Nod using chemical modification (aminoethylation) of one of its core amino acids, N-methyldehydrobutyrine. The developed antibody is highly specific for Nod, with negligible reactivity to the closely related cyanobacterial toxin microcystin (MC). The monoclonal antibody was employed for quantitative competitive ELISA assay. The analytical sensitivity of the assay was up to 0.2 ng/ml. Comparison of the developed ELISA test with HPLC-based measurements of Nod, with both laboratory and field samples, showed a good correspondence between the results yielded by these two methods. The antibodies developed by this technique provide means for developing extremely sensitive and specific analytical assays for direct measurement of nodularin and related toxins in cyanobacterial or water samples.

Different methods for toxin analysis in the cyanobacterium Nodularia spumigena (Cyanophyceae)

The brackish water cyanobacterium Nodularia spumigena produce the hepatotoxic cyclic pentapeptide nodularin. Intoxications for both human as well as animal may arise when water reservoirs are contaminated with potentially toxic Nodularia species. Here, results of three independent methods for the determination of nodularin in different strains of N. spumigena are presented. The results obtained with a protein phosphatase assay and a HPLC/UV/MS method are compared with the results obtained with a bioluminescence assay, which is successfully introduced here for nodularin determination. Statistical evaluation of the three applied methods revealed a good comparability towards the detected toxin content. The methods were evaluated taking into consideration the parameters: handling, efficiency, sensitivity and selectivity. The detection limit in the protein phosphatase assay is highest (0.05ng nodularin) and lowest (250ng nodularin) in the bioluminescence assay- it was determined with 5ng (MS) and 25ng (UV) for the HPLC/UV/MS methods. The different selectivities and sensitivities are critically discussed and an analytical pathway for the determination of the biotoxin nodularin from Nodularia samples is proposed.

Establishment of okadaic acid resistant cell clones using a cDNA expression library

The mechanism whereby the universal apoptogen and serine/threonine phosphatase inhibitor okadaic acid (OA) kills cells, is still unclear. To create a novel tool for probing of OA action, fibroblasts were selected for OA-resistance after infection with a retroviral Jurkat T-cell cDNA expression library. Twenty-one clones were selected. Two of these (OAR1, OAR2) were studied in detail. OAR1 and 2 had each a retrovirally introduced short cDNA, corresponding to a human gene (oar1 and oar2, respectively) with unknown function. Reintroduction of oar1 or oar2 cDNA into wild-type cells reproduced the OA-resistant phenotype. OAR1 and 2 were cross-resistant to other phosphatase inhibitors (calyculin A, cantharidin), but not to staurosporine or microinjected Cytochrome c, thus, indicating a disturbance in a limited number of death pathways, upstream or independent of apaf-1/caspases-3/9. The action of OA involved caspase-dependent and caspase-independent components. Both components were less efficient in OAR1 and 2, than in wild-type cells. Subtle differences existed between OA-induced phosphoprotein patterns in wild-type cells, OAR1, and OAR2, indicating that a narrow selection of protein phosphorylation events had been targeted. We propose that the clones have defects in a hitherto non-elucidated signal pathway linking OA-induced protein phosphorylation to initiation of a death execution pathway provided with a caspase-dependent amplification loop. The novel OA-resistant cell clones will be used to elucidate the significance for apoptosis of oar1 and 2, their link to altered protein phosphorylation, and the potential link of the latter to initiation of apoptosis.

Apoptotic effect of cyanobacterial extract on rat hepatocytes and human lymphocytes

Toxic cyanobacterial blooms are an increasing problem in Poland. The production of cyanobacterial toxins and their presence in drinking and recreational waters represent a growing danger to human and animal health. This is connected with the increase of cyanobacterial biomass caused by excessive eutrophication of the water ecosystem. There is evidence that cyanobacterial hepatotoxins can act as a potent promoter of primary liver cancer. The apoptotic effect of microcystins in Polish cyanobacterial bloom samples on rat hepatocytes and human lymphocytes was observed using light and fluorescence microscopy, flow cytometry, and electrophoretic analysis. The incubation time needed to observe the first morphological apoptotic changes in hepatocytes was approximately 30 min; however, the characteristic biochemical changes in DNA were not observed even after 120 min. In lymphocyte cultures the morphological changes characteristic for apoptosis were observed after 24 h of incubation and a 48-h incubation was found to be optimal for analysis of internucleosomal DNA fragmentation, which is one of the main biochemical hallmarks of programmed cell death. These cells are an easily isolated and inexpensive material for medical diagnostics. Therefore the apoptotic changes, together with the clastogenic effect seen in lymphocyte cultures, are proposed as a future analytical method for these toxins.