Adverse effect of cylindrospermopsin on embryonic development in zebrafish (Danio rerio).

Eutrophication of freshwater bodies increases the occurrence of toxic cyanobacterial blooms. The cyanobacterial toxin cylindrospermopsin (CYN) is receiving great interest due to its increasing presence in waterbodies. However, the toxic effects of CYN on zebrafish development are poorly understood, especially the toxicological mechanism, which is still unclear. In this study, we examined the adverse effects of CYN on embryonic development in zebrafish. CYN (2-2000 nM) exposure decreased embryos survival rate, hatching rate, body length and eye size in a concentration-dependent manner and caused abnormalities in embryo morphology, including pericardial edema, spinal curvature, tail deformity, uninflated swim bladder, cardiac and vascular defects. CYN at concentrations of 20 nM or higher significantly increased ROS level and promoted cell apoptosis in zebrafish embryos. To preliminarily elucidate the potential mechanism of zebrafish developmental toxicity caused by CYN, we examined the expression of oxidative stress- and apoptotic-related genes. CYN could promote the expression of oxidative stress-related genes (SOD1, CAT and GPx1) and induce changes in transcriptional levels of apoptotic-related genes (p53, Bax and Bcl-2). Taken together, CYN induced adverse effects on zebrafish embryos development, which may associate with oxidative stress and apoptosis. These outcomes will advance our understanding of CYN toxicity, environmental problems and health hazards caused by climate changes and eutrophication.

Interactions between Microcystis aeruginosa and coexisting bisphenol A at different phosphorus levels.

Microcystis aeruginosa is known as the main contributor to cyanobacterial bloom, which is prevalent globally and degrades freshwater systems worldwide. The argument that the introduction of anthropogenic contaminants in fresh water stimulates cyanobacterial growth and microcystin production has attracted widespread attention. Bisphenol A (BPA), one of the most abundant endocrine-disrupting compounds, is often detected in various water bodies due to its notably high annual levels of production and use. Research on the combined effects of endocrine-disrupting compounds and environmental factors on cyanobacteria remains limited. To investigate the mechanism of interactions between contaminants and cyanobacteria at the cellular and proteomic levels, the growth rate, chlorophyll-a content, photosynthetic activities, microcystin-LR (MC-LR) production and release, reactive oxygen species (ROS) content, superoxide dismutase (SOD) activities, malondialdehyde (MDA) content, and proteome expression of M. aeruginosa under 1 µM BPA stress at a standard phosphorus level were investigated. The results showed that stress responses to BPA included increases in the growth rate, chlorophyll-a content, and Fv/Fm and rETRmax values under the low phosphorus condition. Responses involving ROS, SOD, and MDA indicated that phosphorus sufficiency and BPA caused oxidative stress in M. aeruginosa. Moreover, phosphorus sufficiency and BPA stimulated the production and release of MCs. Compared to levels in the non-BPA-treated group, exposure of M. aeruginosa to BPA caused 72 up-regulated proteins, which were primarily associated with photosynthesis, ribosome, fatty acid biosynthesis, glycolysis/glyconeogenesis, and carbon fixation in photosynthetic organisms. The 105 down-regulated proteins were related to quorum sensing, base excision repair, ABC transporters, longevity regulating and cell cycle-caulobacter, suggesting that the cytotoxicity of cyanobacterial cells induced by BPA was significantly increased. These findings provide insights into the molecular mechanism of the effects of BPA and phosphorus on M. aeruginosa, suggesting that coexisting pollutants may cause greater harm to and health risks in the environment.

Combined treatment of toxic cyanobacteria Microcystis aeruginosa with hydrogen peroxide and microcystin biodegradation agents results in quick toxin elimination.

Under some conditions the growth of toxic cyanobacteria must be controlled by treatment with algicidal compounds. Hydrogen peroxide has been proposed as an efficient and relatively safe chemical which can remove cyanobacteria from the environment selectively, without affecting other microorganisms. However, the uncontrolled release of secondary metabolites, including toxins may occur after such a treatment. Our proposal presented in this paper concerns fast biodegradation of microcystin released after cell lysis induced by hydrogen peroxide. The effectiveness of both, Sphingomonas sp. and heterologously expressed MlrA enzyme, in the removal of the toxin from Microcystis aeruginosa culture was investigated. The results indicate that neither Sphingomonas cells nor MlrA are affected by hydrogen peroxide at the concentrations which stop the growth of cyanobacteria. A several-fold reduction in microcystin levels was documented in the presence of these agents with biodegradation ability. Our results provide evidence that such a combined treatment of water reservoirs dominated by microcystin-producing cyanobacteria may be a promising alternative which allows fast elimination of both, the bloom forming species and toxins, from the environment.

Epigallocatechin-3-gallate attenuates microcystin-LR induced oxidative stress and inflammation in human umbilical vein endothelial cells.

Epigallocatechin-3-gallate (EGCG) has been shown to possess anti-inflammatory effects. Microcystin-LR (MC-LR) is a potent toxin and our past research suggested that it also mediated human umbilical vein endothelial cell (HUVEC) injury. The aim of this study was to investigate the effects of EGCG on MC-LR-induced oxidative stress and inflammatory responses in HUVECs. HUVECs were stimulated with MC-LR in the presence or absence of EGCG. MC-LR (40 µM) significantly increased cell death and decreased cell viability, migration, and tube formation, whereas EGCG (50 µM) inhibited these effects. Furthermore, the results indicated that EGCG inhibited the production of reactive oxygen species (ROS), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) in MC-LR-stimulated HUVECs. Compared with MC-LR, EGCG significantly increased superoxide dismutase (SOD) and glutathione (GSH) levels and decreased malondialdehyde (MDA) levels. Moreover, the analysis indicated that EGCG suppressed MC-LR-induced NF-κB activation. In conclusion, the effects of EGCG were associated with inhibition of the NF-κB signaling pathway, which resulted in decreased ROS and TNF-α, thereby attenuating MC-LR-mediated oxidative and inflammatory responses.

How do toxic metals affect harmful cyanobacteria? An integrative study with a toxigenic strain of Microcystis aeruginosa exposed to nickel stress.

Nickel (Ni) is an essential metal for some organisms, but also a common toxic pollutant released into the water. Toxicity of Ni has not been completely established for cyanobacteria; for this reason, we evaluated the effect of sub-inhibitory Ni concentrations on a toxigenic strain of Microcystis aeruginosa and on microcystins production. Population growth, photosynthetic pigments concentration, biomarkers, including antioxidant enzymes (catalase [CAT], glutathione peroxidase [GPx], and superoxide dismutase [SOD]), as well as macromolecules (proteins, carbohydrates and lipids) were quantified; SEM and TEM observations were also performed. Population growth was affected starting at 3µgL(-1), and at 24µgL(-1) growth was completely inhibited; the 96-h Ni(2+) IC50 was 3.7µgL(-1). Ni exposure increased pigments concentration, augmented all the macromolecules, and increased activities of CAT and GPx; alterations on the internal cell structure were also observed. The integrated biomarker response revealed that Ni(2+) augmented the antioxidant response and the macromolecules content. Ni stress also increased microcystins production. M. aeruginosa was affected by Ni at very low concentrations, even lower than those established as safe limit to protect aquatic biota. Aside from the toxic effects produced in this cyanobacterium, stimulation to produce toxins could potentiate the environmental risks associated with water pollution and eutrophication.

Mechanism and Reaction Pathways for Microcystin-LR Degradation through UV/H2O2 Treatment.

Microcystin-LR (MCLR) is the most common cyanotoxin in contaminated aquatic systems. MCLR inhibits protein phosphatases 1 and 2A, leading to liver damage and tumor formation. MCLR is relatively stable owing to its cyclic structures. The combined UV/H2O2 technology can degrade MCLR efficiently. The second-order rate constant of the reaction between MCLR and hydroxyl radical (·OH) is 2.79(±0.23)×1010 M-1 s-1 based on the competition kinetics model using nitrobenzene as reference compound. The probable degradation pathway was analyzed through liquid chromatography mass spectrometry. Results suggested that the major destruction pathways of MCLR were initiated by ·OH attack on the benzene ring and diene of the Adda side chain. The corresponding aldehyde or ketone peptide residues were formed through further oxidation. Another minor destruction pathway involved ·OH attack on the methoxy group of the Adda side chain, followed by complete removal of the methoxy group. The combined UV/H2O2 system is a promising technology for MCLR removal in contaminated aquatic systems.

Microcystin-LR altered mRNA and protein expression of endoplasmic reticulum stress signaling molecules related to hepatic lipid metabolism abnormalities in mice.

To explore the effects of microcystin-LR (MC-LR), a hepatotoxin, on the incidence of liver lipid metabolism abnormality, and the potential molecular mechanisms of action, healthy male Balb/c mice were intraperitoneally injected with MC-LR at doses of 0, 5, 10, and 20 µg/kg/d for 14 days. Hepatic histopathology and serum lipid parameters of mice were determined, and the changes of mRNA and protein expression of endoplasmic reticulum (ER) stress signaling molecules related to the lipid metabolism abnormalities in the livers of mice were investigated by quantitative real-time polymerase chain reaction (qPCR) and Western blotting, respectively. The results indicated that 5-20 µg/kg/d MC-LR altered serum lipid parameters and caused hepatic steatosis. MC-LR treatment at 10 or 20 µg/kg/d changed mRNA and protein expression of ER stress signaling molecules, including upregulation of mRNA and protein expression of activating transcription factor 6 (ATF6), pancreatic ER eukaryotic translation initiation factor 2α (eIF-2α) kinase (PERK), and eIF-2α. MC-LR exposure at 10 or 20 µg/kg/d also altered mRNA and protein expression of downstream factors and genes of ER stress signaling pathways, including the downregulation of sterol regulatory element binding protein 1c (SREBP-1c) and fatty acid synthase (FASn), and upregulation of acetyl-coenzyme A carboxylase α (ACACA) and glycogen synthase kinase 3ß (Gsk-3ß). Our results reveal that ER stress plays a significant role in hepatic lipid metabolism abnormalities in mice exposed to MC-LR.

Cellular and transcriptional responses in Microcystis aeruginosa exposed to two antibiotic contaminants.

The responses of Microcystis aeruginosa under exposure to spiramycin and amoxicillin were investigated on both cellular and genetic levels through a 7-day exposure test. Algal growth was inhibited by spiramycin while promoted by amoxicillin at test concentrations of 0.6-1.8 µg L(-1), indicating a higher toxicity of spiramycin than amoxicillin. During the whole exposure period, the chlorophyll a content and expression levels of psbA, psaB, and rbcL were significantly inhibited by spiramycin at test concentrations of 1.2 and 1.8 µg L(-1) (p < 0.05) and stimulated by 0.6-1.8 µg L(-1) of amoxicillin (p < 0.05), with respective decreases of up to 26, 75, 72, and 82% compared to the control and respective increases of 20, 70, 135, and 55%. During the 4 to 7 days of exposure, the microcystin-LR content and expression levels of mcyB and grpE were reduced by up to 66, 47, and 72% in spiramycin-treated algal cells, respectively, and stimulated by up to 1.3-, 1.4-, and 1.5-folds in amoxicillin-treated algal cells, respectively. Elevated recA expression was only observed in 1.2 and 1.8 µg L(-1) of spiramycin-treated algal cells, indicating severe DNA damage due to the high toxicity. Target antibiotics were suspected to regulate the growth and microcystin-production in M. aeruginosa via the photosynthesis system.

Oxidation by-products formation of microcystin-LR exposed to UV/H2O2: toward the generative mechanism and biological toxicity.

The presence of microcystins (MCs) in water sources is of concern due to their direct threats to human health and potential to form oxidation by-products (OBPs) in finished water. To control the environmental risk of MCs related OBPs, we evaluated their generative mechanisms and biological toxicity by mass spectrometry technology and molecular toxicity experiment. Exposed to UV/H2O2, model toxin microcystin-LR (MCLR) in clean water was quickly transformed but successively generated seven types of MCLR-OBPs with the chemical formulas of C49H74N10O13, C49H76N10O14, C49H78N10O16, C49H76N10O15, C37H58N10O12, C33H54N10O12, and C34H54N10O12. Probable isomers for each MCLR-OBP type were then separated and identified, indicating the aromatic ring and conjugated diene in Adda and the CC bond in Mdha were the major target sites of oxidation. Though subsequent toxicology data showed the toxicity of MCLR-OBPs on protein phosphatases 1 and 2A decreased with the extending of treatment by and large, they still possessed considerable biological toxicity (especially for product d). Influenced by MCLR-OBP distribution, concentration and residual toxicity, the secondary pollution of MCLR-OBPs in drinking water also deserved further attention even though MCLR was totally destroyed.