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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.

Microcystin-LR (MC-LR) is a widely known hepatotoxin which could induce the occurrence and metastasis of hepatocellular carcinoma. In recent years, with the frequent outbreak of cyanobacteria, the harm of MC-LR has gradually attracted more attention. Hence, this study focused on the effect of MC-LR on DNA damage in HepG2 cells, identifying the types and sources of free radicals that make an important function on this issue. Our data suggested that MC-LR induced concentration- and time-dependent increasement of DNA double-strand breaks (DSBs). After exposure to 1 μM MC-LR for 3 days, the protein expression and immunofluorescence staining of γ-H2AX was significantly increased. Using a scavenger of mitochondrial O2.- (4-hydroxy-tempo), a inhibitor of mitochondrial NOS (7-nitroindazole), and a scavenger of ONOO− (uric acid), it was revealed that ONOO− originated from mitochondria made a significant contribution to the genotoxicity of MC-LR. Moreover, a significant decreasement of mitochondrial membrane potential (MMP) was observed. These findings suggested that peroxynitrite targeting mitochondria plays a vital role in the MC-LR-induced genotoxic response in mammalian cells.

The use of short-term, fast-acting curative treatments to rapidly suppress the proliferation of upcoming cyanobacterial blooms without negative side effects on overall water quality is important for environmental regulatory agencies. A 15-day in situ mesocosm experiment was conducted to evaluate the effects of algal harvest at different intensities and the effect of hydrogen peroxide on the mitigation of cyanobacterial blooms, subsequent algal growth and phytoplankton community structure. The results indicate that filtration through a 30-μm-pore-size net could remove most of the Microcystis colonies, leading to a decline in algal biomass. However, algal harvest at 30% and 60% intensities tended to promote cyanobacterial growth under nutrient-replete conditions, and the mitigation effect only lasted a few days, since cyanobacteria biomass exhibited no significant difference between the control and those two treatments on Day 6. When the algal harvest intensity was 90%, the cyanobacterial biomass remained at a relatively low level for 15 days. The average Microcystis colony size rapidly returned to the initial level after an initial decline across all the algal harvest intensities, indicating that algal harvest should be repeatedly performed within a short time period to mitigate Microcystis blooms. Furthermore, removing Microcystis colonies by filtration led to increased diversity in the phytoplankton community, as the proportion of non-Microcystis cyanobacteria increased with harvest intensity. This result might pose a challenge for cyanobacterial bloom control over the long term if filamentous cyanobacteria become dominant. The 10.0 mg L−1 H2O2 treatment selectively suppressed cyanobacteria throughout the experimental period, leading to succession from a cyanobacteria-dominated to a Chlorophyta-dominated community after Day 9. Overall, using hydrogen peroxide is more effective than algal harvesting as a one-time quick curative measure.

The wide presence of polycyclic aromatic hydrocarbons (PAHs) in lakes necessitates a better understanding of cyanobacteria metabolites under the contamination of PAHs. The M. aeruginosa strain PCC7806 was selected to investigate the effects of naphthalene and pyrene on the physiological and biochemical reactions of cyanobacteria, including antioxidant defense system (superoxide dismutase, catalase), intracellular microcystin (MC) content, phycobiliprotein (phycocyanin, allophycocyanin) contents, and specific growth rate. Naphthalene and pyrene altered the growth of the M. aeruginosa strain, reduced the contents of phycocyanin and allophycocyanin, and stimulated the activities of antioxidant enzymes without lipid peroxidation. Remarkably, the intracellular MC content was significantly increased by 68.1% upon exposure of M. aeruginosa to 0.45 mg L−1 naphthalene, and increased by 51.5% and 77.9% upon exposure of M. aeruginosa to 0.45 mg L−1 pyrene and 1.35 mg L−1 pyrene, respectively (P＜0.05). Moreover, significant correlations were observed between these physiological reactions, referring that a series of physiological and biochemical reactions in M. aeruginosa worked together against the PAH contamination. Considering that MCs are the most studied cyanobacterial toxins, our results clarified that the promoting MC production by PAH contamination cannot be neglected when making related risk assessments of eutrophic waters.

Our previous study showed that the tea extract, epigallocatechin-3-gallate (EGCG), protects against microcystin-LR (MC-LR) -mediated apoptosis of human umbilical vein endothelial cells (HUVECs); however, the mechanism underlying MC-LR-induced HUVEC apoptosis remains incompletely understood. In this study, we investigated whether the nuclear factor erythroid-like 2 (NRF2)/heme oxygenase-1 (HO-1) pathway, which regulates antioxidant transcriptional regulation of oxidative stress and apoptosis, is involved in this process. Mitochondrial membrane potential (MMP) and caspase-3/-9 activities were evaluated in HUVECs by JC-1 staining and colorimetric activity assay, and a DCFH-DA fluorescent probe assay was used to quantitate reactive oxygen species (ROS) generation. The effects of MC-LR, EGCG, NF2, and HO-1 on HUVEC apoptosis were explored by western blotting and small interfering RNA (siRNA) analyses. MC-LR treatment downregulated HUVEC mitochondrial membrane potential, and decreased levels of cytochrome c release and activated caspase-3/-9, ROS generation, consequently inducing HUVEC apoptosis. EGCG treatment attenuated MC-LR-mediated HUVEC oxidative stress and mitochondria-related apoptosis. EGCG induced NRF2/HO-1 expression and activation in MC-LR treated HUVECs, while downregulation of NRF2/HO-1 by specific siRNAs revealed that NRF2/HO-1 signaling was involved in EGCG attenuation of MC-LR-induced HUVEC apoptosis. Our findings indicate that EGCG treatment protects against MC-LR-mediated HUVEC apoptosis via activation of NRF2/HO-1 signaling.

Microcystins (MCs) produced by toxic cyanobacteria cause serious water pollution and public health hazard to humans and animals. However, direct molecular mechanisms of MC-LR in vascular endothelial cells (ECs) have not been understood yet. In this study, we investigated whether MC-LR induces vascular inflammatory process in cultured human umbilical vein endothelial cells (HUVECs). Our data demonstrated that MC-LR decreased HUVECs proliferation and tube formation and enhanced apoptosis. MC-LR also induced intracellular reactive oxygen species formation (ROS) in HUVECs. The MC-LR directly stimulated phosphorylation of NF-κB. Furthermore, MC-LR also increased cell adhesion molecules (ICAM-1 and VCAM-1) expression in HUVECs. Taken together, the present data suggested that MC-LR induced vascular inflammatory process, which may be closely related to the oxidative stress, NF-κB activation, and cell adhesion molecules expression in HUVECs. Our findings may highlight that MC-LR causes potential damage to blood vessels.

Lake Chaohu is a eutrophic lake that experiences massive cyanobacterial blooms. The high concentrations of microcystin observed in this lake are the result of the bloom's high proportion of toxic cyanobacteria strains. Groundwater is the important source of water for drinking, washing, and irrigation in the watershed of Lake Chaohu. This study examines the space-time distribution of microcystins and related environmental factors in wells near Lake Chaohu. All collected groundwater samples from the Lake Chaohu region had detectable concentrations of microcystins. The highest concentration of microcystins, 1.07 μg L(-1), occurred in a well hundreds of meters from the western coast of the lake in September. The distance from the lake shore to the well was significantly and positively correlated with the microcystin concentration in the groundwater. Moreover, a correlation analysis shows that the microcystin concentration in the groundwater was positively correlated with the total dissolved phosphorus (TDP) and microcystin concentration of the nearby lake water. Therefore, the microcystin in the groundwater likely originates from penetration by nearby lake water. Our results suggest that the groundwater near Lake Chaohu poses a significant health risk for the local residents when used for drinking water.

Lake Chaohu, which is a large, shallow, hypertrophic freshwater lake in southeastern China, has been experiencing lake-wide toxic Microcystis blooms in recent decades. To illuminate the relationships between microcystin (MC) production, the genotypic composition of the Microcystis community and environmental factors, water samples and associated environmental data were collected from June to October 2012 within Lake Chaohu. The Microcystis genotypes and MC concentrations were quantified using quantitative real-time PCR (qPCR) and HPLC, respectively. The results showed that the abundances of Microcystis genotypes and MC concentrations varied on spatial and temporal scales. Microcystis exists as a mixed population of toxic and non-toxic genotypes, and the proportion of toxic Microcystis genotypes ranged from 9.43% to 87.98%. Both Pearson correlation and stepwise multiple regressions demonstrated that throughout the entire lake, the abundances of total and toxic Microcystis and MC concentrations showed significant positive correlation with the total phosphorus and water temperature, suggesting that increases in temperature together with the phosphorus concentrations may promote more frequent toxic Microcystis blooms and higher concentrations of MC. Whereas, dissolved inorganic carbon (DIC) was negatively correlated with the abundances of total and toxic Microcystis and MC concentrations, indicating that rising DIC concentrations may suppress toxic Microcystis abundance and reduce the MC concentrations in the future. Therefore, our results highlight the fact that future eutrophication and global climate change can affect the dynamics of toxic Microcystis blooms and hence change the MC levels in freshwater.

Microcystins (MCs) produced by toxic cyanobacteria pose a health hazard to humans and animals. Some environmental factors can alter the MC concentrations by affecting the abundance of toxin-producing strains in a cyanobacteria population and/or their toxin production. In this study, we designed a monoculture and competition experiment to investigate the impacts of UV-B radiation on MC production and the competition between toxin and non-toxin producing strains of Microcystis aeruginosa. UV-B radiation resulted in higher inhibition of the growth and photosynthetic activity of the non-toxin producing strain relative to that observed for the toxin-producing strain. Both intracellular and extracellular MC contents decreased markedly when the toxin-producing strain was exposed to UV-B radiation. In addition, a quantitative real-time PCR assay revealed that the ratio of toxin-producing M. aeruginosa under UV-B exposure was higher than that under PAR alone at an early stage of the experiment. However, its abundance under UV-B exposure was lower compared with the PAR alone treatment after day 12. Our study demonstrated that UV-B radiation has a great impact on the abundance of the toxin-producing strain in the Microcystis population and their toxin production, which suggests that the fluctuation of UV-B radiation affects the MC level of cyanobacteria blooms.

In an attempt to elucidate the effects of different CO2 concentrations (270, 380, and 750 μL/L) on the competition of microcystin-producing (MC-producing) and non-MC-producing Microcystis strains during dense cyanobacteria blooms, an in situ simulation experiment was conducted in the Meiliang Bay of Lake Taihu in the summer of 2012. The abundance of total Microcystis and MC-producing Microcystis genotypes was quantified based on the 16S rDNA and mcyD gene using real-time PCR. The results showed that atmospheric CO2 elevation would significantly decrease the pH value and increase the dissolved inorganic carbon (DIC) concentration. Changes in CO2 concentration did not show significant influence on the abundance of total Microcystis population. However, CO2 concentrations may be an important factor in determining the subpopulation structure of Microcystis. The enhancement of CO2 concentrations could largely increase the competitive ability of non-MC-producing over MC-producing Microcystis, resulting in a higher proportion of non-MC-producing subpopulation in treatments using high CO2 concentrations. Concurrently, MC concentration in water declined when CO2 concentrations were elevated. Therefore, we concluded that the increase of CO2 concentrations might decrease potential health risks of MC for human and animals in the future.