Toxicity of microcystins in the isolated hepatocytes of common carp (Cyprinus carpio L.)

Possibility for Water Quality Biocontrol: Observation of Microcystin Transfer in the “Cyanobacteria–Cladohorn–Fish” Food Chain

Microcystins appear to be considered one of the most dangerous cyanobacterial toxins in the world. The accumulation and change of microcystins MC-LR and MC-RR in the “cyanobacteria–cladocera–fish” food chain were studied. Microcystis aeruginosa was fed to Moina macrocopa at three densities, 5.0 × 103, 5.0 × 105, and 5.0 × 106 cells/mL, and then passed to Cyprinus flammans. The total amount of MCs in the cyanobacteria cell extract increased with increasing density. The content of MCs in M. macrocopa increased with the feeding density of M. aeruginosa. In the final stage of experiments, MC-RR was the only MC that could be transmitted by M. macrocopa and persisted in red carp. In this study, changes in the concentrations of MC-LR and MC-RR in the liver of red carp seem to indicate some kind of transformation or degradation mechanism. It shows the possibility of MCs concentration-controlled biodefense in eutrophic waters.

Effect of microcystin-LR on human placental villous trophoblast differentiation in vitro

Microcystin-LR is a cyanobacterial toxin found in surface and recreational waters that inhibits protein phosphatases and may disrupt the cytoskeleton. Microcystins induce apoptosis in hepatocytes at ≤ 2.0 µM. Nothing is known about the effects of microcystins on human placental trophoblast differentiation and function. The differentiation of villous trophoblasts to form syncytiotrophoblast occurs throughout pregnancy and is essential for normal placental and fetal development. To investigate the effects of microcystin, villous cytotrophoblasts were isolated from term placentas using an established method and exposed to microcystin-LR. Microcystin-LR below the cytotoxic dose of 25 µM did not cause cell rounding or detachment, had no effect on apoptosis, and no effect on the morphological differentiation of mononucleated cytotrophoblasts to multinucleated syncytiotrophoblast. However, secretion of human chorionic gonadotropin (hCG) increased in a microcystin-LR dose-dependent manner. When incubated with l-buthionine sulphoximine (BSO) to deplete glutathione levels, trophoblast morphological differentiation proceeded normally in the presence of microcystin-LR. Microcystin-LR did not disrupt the trophoblast microtubule cytoskeleton, which is known to play a role in trophoblast differentiation. Immunofluorescence studies showed that trophoblasts express organic anion transport protein 1B3 (OATP1B3), a known microcystin transport protein. In comparison to hepatocytes, trophoblasts appear to be more resistant to the toxic effects of microcystin-LR. The physiological implications of increased hCG secretion in response to microcystin-LR exposure remain to be determined.

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.

WITHDRAWN: Cyanobacterial bioactive molecules - Biosynthesis and genetic regulation

This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Cytotoxicity of the venom from the nematocysts of jellyfish Cyanea nozakii Kishinouye

In this article, the cytotoxicity of the venom from the nematocysts of jellyfish Cyanea nozakii Kishinouye on human hepatoma cells (Bel-7402, SMMC-7721) and human colon cancer cells (H630) was investigated first. Of the three kinds of cells, the venom had the strongest cytotoxicity on H630 cells with the 50% lethal concentration (IC50) of 5.1 μg/ml. However, the IC50 on Bel-7402 and SMMC-7721 was approximate 17.9 and 24.3 μg/ml, respectively. The cytotoxicity of the venom was affected by pH, temperature and storage conditions. At the pH 4.5–8.5, the venom displayed obvious cytotoxicity and the percentage of survival was about 50%. When pre-incubated at temperatures over 60°C for as short as 10 min, the percentage of survival sharply improved from 4.6% up to 80%. The venom was stored in a more stable condition at −80°C and in lyophilized state compared to other storage conditions used in this study. Lactate dehydrogenase release assay performed on H630 cells indicated that exposure to the venom could result in damage to the cell membrane.

Highly sensitive and rapid detection of microcystin-LR in source and finished water samples using cantilever sensors

Microcystin-leucine-arginine (MCLR) is one of the toxic microcystin congeners produced by the common cyanobacteria, blue-green algae. A piezoelectric-excited millimeter-sized cantilever (PEMC) sensor was developed for the sensitive detection of MCLR in a flow format using both monoclonal and polyclonal antibodies that bind specifically to MCLR. PEMC is a resonant cantilever sensor whose resonant frequency decreases as target analyte binds to its surface. Monoclonal antibody against MCLR was immobilized on the sensor surface via amine coupling. As the toxin in the sample water bound to the antibody, resonant frequency decreased proportional to toxin concentration. Three water matrices, namely buffer, tap water, and river water, were spiked with MCLR standards and were successfully detected in the dynamic range of 1 pg/mL to 100 ng/mL (effective concentration -250 fg/mL to 25 ng/mL). The sensor response was characterized by a log-linear relationship between resonant frequency change and MCLR concentration. Positive verification of MCLR detection was confirmed by a sandwich binding on the sensor with a second antibody binding to MCLR on the sensor (attached in first detection step) which caused a further resonant frequency decrease. We show for the first time that MCLR in various water samples can be detected at 1 pg/mL.

The toxic effects of microcystin-LR on the reproductive system of male rats in vivo and in vitro

The aim of this study was to investigate whether microcystin-LR, one of the most common cyanobacterial toxins has toxic effects on reproductive system in vivo or Leydig cells in vitro. Male rats were treated with MC-LR (i.p.) at a dose of 0, 5, 10 or15 microg/(kgday) for 28 days. Leydig cells were cultured with a culture medium including 0, 0.5, 5, 50 or 500 nM MC-LR. In vivo study, we observed exposure to 5 microg/(kgday) of MC-LR decreased the sperm motility, increasing the sperm abnormality rate, 15 microg/(kgday) of MC-LR led to the decrease of testis weight and sperm concentration, decreased the levels of serum testosterone, FSH and LH. The histological findings showed that the seminiferous tubules atrophied and obstructed. In vitro study evaluated MC-LR-induced toxicity and oxidative stress in Leydig cells. It was observed 50 and 500 nM MC-LR significantly decreased the cell viability, increasing the apoptotic DNA fragmentation, and increasing the ratio of necrotic cells. The Leydig cells exposed to MC-LR decreased testosterone production. 500 nM MC-LR increased ROS production, 50 or 500 nM MC-LR enhanced the lipid peroxidation. All Leydig cells exposed to MC-LR showed decreased SOD activity. The results of this study showed that the oxidative stress of MC-LR might lead to cytotoxicity, which may play an important role in cell apoptosis. Then could reduce the production of testosterone in Leydig cells and result in reproductive toxicity.

Cyanobacterial toxins as allelochemicals with potential applications as algaecides, herbicides and insecticides

Cyanobacteria ("blue-green algae") from marine and freshwater habitats are known to produce a diverse array of toxic or otherwise bioactive metabolites. However, the functional role of the vast majority of these compounds, particularly in terms of the physiology and ecology of the cyanobacteria that produce them, remains largely unknown. A limited number of studies have suggested that some of the compounds may have ecological roles as allelochemicals, specifically including compounds that may inhibit competing sympatric macrophytes, algae and microbes. These allelochemicals may also play a role in defense against potential predators and grazers, particularly aquatic invertebrates and their larvae. This review will discuss the existing evidence for the allelochemical roles of cyanobacterial toxins, as well as the potential for development and application of these compounds as algaecides, herbicides and insecticides, and specifically present relevant results from investigations into toxins of cyanobacteria from the Florida Everglades and associated waterways.