Mitochondrial toxicity of microcystin-LR on cultured cells: application to the analysis of contaminated water samples

The cytotoxicity of microcystin-LR: ultrastructural and functional damage of cells

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria, which is widely distributed in eutrophic water bodies and has multi-organ toxicity. Previous cytotoxicity studies have mostly elucidated the effects of MC-LR on intracellular-related factors, proteins, and DNA at the molecular level. However, there have been few studies on the adverse effects of MC-LR on cell ultrastructure and function. Therefore, research on the cytotoxicity of MC-LR in recent years was collected and summarized. It was found that MC-LR can induce a series of cytotoxic effects, including decreased cell viability, induced autophagy, apoptosis and necrosis, altered cell cycle, altered cell morphology, abnormal cell migration and invasion as well as leading to genetic damage. The above cytotoxic effects were related to the damage of various ultrastructure and functions such as cell membranes and mitochondria. Furthermore, MC-LR can disrupt cell ultrastructure and function by inducing oxidative stress and inhibiting protein phosphatase activity. In addition, the combined toxic effects of MC-LR and other environmental pollutants were investigated. This review explored the toxic targets of MC-LR at the subcellular level, which will provide new ideas for the prevention and treatment of multi-organ toxicity caused by MC-LR.

Hepatotoxicity of cyanotoxin microcystin-LR in human: Insights into mechanisms of action in the 3D culture model Hepoid-HepaRG

Microcystin-LR (MC-LR) is a potent hepatotoxin produced by harmful cyanobacterial blooms (CyanoHABs). MC-LR targets highly differentiated hepatocytes expressing organic anion transporting polypeptides OATP1B1 and OATP1B3 that are responsible for hepatocellular uptake of the toxin. The present study utilized an advanced 3D in vitro human liver model Hepoid-HepaRG based on the cultivation of collagen-matrix embedded multicellular spheroids composed of highly differentiated and polarized hepatocyte-like cells. 14-d-old Hepoid-HepaRG cultures showed increased expression of OATP1B1/1B3 and sensitivity to MC-LR cytotoxicity at concentrations >10 nM (48 h exposure, EC20 = 26 nM). MC-LR induced neither caspase 3/7 activity nor expression of the endoplasmic reticulum stress marker gene BiP/GRP78, but increased release of pro-inflammatory cytokine IL-8, indicating a necrotic type of cell death. Subcytotoxic (10 nM) and cytotoxic (≥100 nM) MC-LR concentrations disrupted hepatocyte functions, such as xenobiotic metabolism phase-I enzyme activities (cytochrome P450 1A/1B) and albumin secretion, along with reduced expression of CYP1A2 and ALB genes. MC-LR also decreased expression of HNF4A gene, a critical regulator of hepatocyte differentiation and function. Genes encoding hepatobiliary membrane transporters (OATP1B1, BSEP, NTCP), hepatocyte gap junctional gene connexin 32 and the epithelial cell marker E-cadherin were also downregulated. Simultaneous upregulation of connexin 43 gene, primarily expressed by liver progenitor and non-parenchymal cells, indicated a disruption of tissue homeostasis. This was associated with a shift in the expression ratio of E-cadherin to N-cadherin towards the mesenchymal cell marker, a process linked to epithelial-mesenchymal transition (EMT) and hepatocarcinogenesis. The effects observed in the human liver cell in vitro model revealed mechanisms that can potentially contribute to the MC-LR-induced promotion and progression of hepatocellular carcinoma (HCC). Hepoid-HepaRG cultures provide a robust, accessible and versatile in vitro model, capable of sensitively detecting hepatotoxic effects at toxicologically relevant concentrations, allowing for assessing hepatotoxicity mechanisms, human health hazards and impacts of environmental hepatotoxins, such as MC-LR.

Excluding interference and detecting Microcystin-LR in the natural lakes and cells based a unique fluorescence method

Cyanobacteria blooms that cause the death of aquatic and terrestrial organisms have attracted considerable attention since the 19th century. The most typical toxin in cyanobacteria blooms is cyanobacteria toxin, particularly microcystin-LR (MC-LR). Therefore, a simple and highly efficient method for detecting MC-LR plays a role in studying the ecological toxicology of MC-LR. However, as MC-LR itself is located in a complex environment, traditional techniques present complex and false-positive defects. To address the above issues, novel technologies should be explored and discovered. Herein, we describe the development of MC-BDKZ as the first paradigm of probes that can concurrently report MC-LR in natural lakes and cells. This novel material shows large Stokes Shift and possesses good photostability and high sensitivity. Considering the properties mentioned above, MC-BDKZ not only achieves the detection of MC-LR in the lake water samples, but also completes the imaging of exogenous MC-LR in cells. Moreover, the interference of many factors in the lake and cells is excluded completely in the process of MC-LR detection. We comprehensively analyzed the response principle and potential application of MC-BDKZ in the process of MC-LR detection. Compared with the conventional MC-LR detection technologies, fluorescence probe technology shows better convenience and greatly reduces distance from the practical application in vitro and in vivo. We envisioned that the development of this visual research tool could provide crucial clues for exploring the pathogenesis of MC-LR in body.

The monthly variation tendency of microcystin-LR levels in the Huangpu River (China) by applications of ELISA and HPLC

In this study, the contents of microcystin-LR (MC-LR) of Microcystis aeruginosa cultures in the laboratory and natural water samples from the Huangpu River in different seasons were detected through enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC), respectively. Excellent correlation between the two methods was obtained (R² > 0.99). ELISA was a reliable and simple method with high reproducibility (coefficient of variation < 25%) and satisfactory recovery for the monitoring of low levels of MC-LR. MC-LR concentrations in Huangpu River varied with the seasonal variation, which peaked in August with the temperature over 30 °C and then gradually declined with the decreasing temperature after August. The highest MC-LR concentration in the Huangpu River was below the WHO drinking water quality standard (1 µg/L). These results indicated that warm temperature accelerated the MC-LR synthesis and release, and it is necessary to regularly monitor the MC-LR levels, especially during the high algae period in summer. ELISA can be applied to detect the low levels of MC-LR in the field without complex treatment, avoiding the samples from denaturation and degradation during the transportation. Hence, ELISA is a better alternative of HPLC when HPLC is unavailable, especially when rapid testing is required in routine MC-LR analysis.

Cell density-dependent regulation of microcystin synthetase genes (mcy) expression and microcystin-LR production in Microcystis aeruginosa that mimics quorum sensing

As the secondary metabolites of cyanobacterial harmful algal blooms (Cyano-HABs), microcystins (MCs) were generated under various environmental and cellular conditions. The understanding of the causes of MCs generation is of great interest in the field of water treatment and environmental science. In this work, we studied how Microcystis aeruginosa (FACHB-905) cell densities affect the MCs synthetase genes (mcy) expression, microcystin-LR (MC-LR) and quorum sensing molecules (Acyl-homoserine lactones (AHLs)) production. An electrochemical sensor was developed here for sensitive and quantitative detection of MC-LR that cultured at different cell densities. The results showed that mcy expression and MC-LR concentration started to increase when the cell density reached ca. 22 × 10⁶ cells/mL, and was significantly increased with increasing cell densities. Moreover, the up-regulation of AHLs with increasing cell densities revealed that MC-LR is quorum sensing-mediated. Our results undoubtedly confirmed that MC-LR was produced in a cell density-dependent way that mimics quorum sensing, and the minimum cell density (ca. 22 × 10⁶ cells/mL) that was required to produce MC-LR was provided and offered a reference standard for the prevention and control of MCs pollution in the actual water environment.

An identified PfHMGB1 promotes microcystin-LR-induced liver injury of yellow catfish (Pelteobagrus fulvidraco)

Microcystin-LR (MC-LR) is a potent hepatotoxin that can cause liver inflammation and injury. However, the mode of action of related inflammatory factors is not fully understood. PfHMGB1 is an inflammatory factor induced at the mRNA level in the liver of juvenile yellow catfish (Pelteobagrus fulvidraco) that were intraperitoneally injected with 50 μg/kg MC-LR. The PfHMGB1 mRNA level was highest in the liver and muscle among 11 tissues examined. The full-length cDNA sequence of PfHMGB1 was cloned and overexpressed in E. coli, and the purified protein rPfHMGB1 demonstrated DNA binding affinity. Endotoxin-free rPfHMGB1 (6-150 μg/mL) also showed dose-dependent hepatotoxicity and induced inflammatory gene expression of primary hepatocytes. PfHMGB1 antibody (anti-PfHMGB1) in vitro reduced MC-LR (30 and 50 μmol/L)-induced hepatotoxicity, suggesting PfHMGB1 is important in the toxic effects of MC-LR. In vivo study showed that MC-LR upregulated PfHMGB1 protein in the liver. The anti-PfHMGB1 blocked its counterpart and reduced ALT/AST activities after MC-LR exposure. Anti-PfHMGB1 partly neutralized MC-LR-induced hepatocyte disorganization, nucleus shrinkage, mitochondria, and rough endoplasmic reticula destruction. These findings suggest that PfHMGB1 promotes MC-LR-induced liver damage in the yellow catfish. HMGB1 may help protect catfish against widespread microcystin pollution.

Synergistic Effect of MC-LR and C-Terminal Truncated HBx on HepG2 Cells and Their Effects on PP2A Mediated Downstream Target of MAPK Signaling Pathway

C-terminally truncated hepatitis B virus (HBV) X (ctHBx) infection and exposure to microcystins-LR (MC-LR) can lead to human hepatitis and liver cancer, but the mechanism associated with their synergistically effects not been fully elucidated. The ctHBx (HBxΔ4 and HBxΔ32) lentivirus were constructed and transfected into the HepG2 cells. Then we investigated the function of MC-LR and ctHBx using the molecular biology approaches, including enzyme-linked immunosorbent assay, clone formation assay, scratch wound testing, transwell assays, carried out flow cytometry respectively to examine cell cycle and apoptosis in each group, and detected the related proteins of HBx, MEK/ERK/JNK/p38 in mitogen-activated protein kinase (MAPK) pathway and the downstream proteins such as cdc2, cdc25C, and p53 by western blotting. We found that the protein phosphorylase 2A (PP2A) enzyme activity in MC-LR and HBxΔ32/HBxΔ4 groups decreased more than in MC-LR and HBx group at the same time point and MC-LR concentration (P < 0.05). Meanwhile the proliferation, migration, invasion and colony formation capability of HepG2 cells were significantly enhanced in MC-LR and ctHBx groups (P < 0.05). In addition the proportion of S stage cells in the MC-LR-treated HBxΔ32/HBxΔ4 groups was significantly greater than that in the untreated groups (P < 0.05). Furthermore, the protein expression of MAPK signaling pathway including phospho-MEK1/2, ERKl/2, p38, and JNK were up-regulated by MC-LR and HBxΔ32, and the expression of cyclin-related proteins, including p53, cdc25C, and cdc2 were also activated (P < 0.05). Taken together, our findings revealed the essential significance of the MC-LR and ctHBx on the PP2A/MAPK/p53, cdc25C and cdc2 axis in the formation and development of HCC and identified MC-LR and ctHBx as potential causal cofactors of hepatocarcinogenesis.

Microcystin-Leucine-Arginine Induces Tau Pathology Through Bα Degradation via Protein Phosphatase 2A Demethylation and Associated Glycogen Synthase Kinase-3β Phosphorylation

Microcystin-leucine-arginine (MC-LR) has been implicated as a potential environmental factor in Alzheimer's disease because of its potent inhibition of protein phosphatase 2A (PP2A) activity, but experimental evidence to support its detailed neurotoxic effects and their underlying mechanisms has been lacking. The present study investigated the role of PP2A catalytic subunit (PP2Ac) demethylation and its link with glycogen synthase kinase-3β (GSK)-3β in tau hyperphosphorylation induced by MC-LR. The results showed that MC-LR treatment significantly increased demethylation of PP2Ac, with a concomitant increase in GSK-3β phosphorylation at Ser9 resulting in elevated tau hyperphosphorylation at PP2A-favorable sites in SH-SY5Y cells and rat hippocampus. Coimmunoprecipitation experiments showed that MC-LR treatment dissociated PP2Ac from Bα, making it incompetent in binding tau, thus causing tau hyperphosphorylation. Moreover, we found that inhibition of PP2A resulted in an increase in phosphorylation of GSK-3β at Ser9 and a decrease in GSK-3β activity, which further promoted demethylation of PP2Ac induced by MC-LR. These findings suggest a scenario in which MC-LR-mediated demethylation of PP2Ac is associated with GSK-3β phosphorylation at Ser9 and contributes to dissociation of Bα from PP2Ac, which would result in Bα degradation and disruption of PP2A/Bα-tau interactions, thus promoting tau hyperphosphorylation and paired helical filaments-tau accumulation and, consequently, axonal degeneration and cell death.

Pharmacological inhibition of TLR4/NF-κB with TLR4-IN-C34 attenuated microcystin-leucine arginine toxicity in bovine Sertoli cells

This study investigated the pharmacological inhibition of the toll-like receptor 4 (TLR4) genes as a measure to attenuate microcystin-LR (MC-LR) reproductive toxicity. Bovine Sertoli cells were pretreated with TLR4-IN-C34 (C34) for 1 hour. Thereafter the pretreated and non-pretreated Sertoli cells were cultured in medium containing 10% heat-activated fetal bovine serum + 80 μg/L MC-LR for 24 hours to assess the ability of TLR4-IN-C34 to attenuate the toxic effects of MC-LR. The results showed that TLR4-IN-C34 inhibited MC-LR-induced mitochondria membrane damage, mitophagy and downregulation of blood-testis barrier constituent proteins via TLR4/nuclear factor-kappaB and mitochondria-mediated apoptosis signaling pathway blockage. The downregulation of the mitochondria electron transport chain, energy production and DNA replication related genes (mt-ND2, COX-1, COX-2, ACAT, mtTFA) and upregulation of inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor-α, IL-1β, interferon-γ, IL-4, IL-10, IL-13 and transforming growth factor β1) were modulated by TLR4-IN-C34. Taken together, we conclude that TLR4-IN-C34 inhibits MC-LR-related disruption of mitochondria membrane, mitophagy and downregulation of blood-testis barrier proteins of the bovine Sertoli cell via cytochrome c release and TLR4 signaling blockage.

Sodium Selenite inhibits mitophagy, downregulation and mislocalization of blood-testis barrier proteins of bovine Sertoli cell exposed to microcystin-leucine arginine (MC-LR) via TLR4/NF-kB and mitochondrial signaling pathways blockage

This study was conducted to investigate the ameliorative effect of selenium on microcystin-LR induced toxicity in bovine Sertoli cells. Bovine Sertoli cells were pretreated with selenium (Na₂SeO₃) for 24 h after which selenium pretreated and non-pretreated Sertoli cells were cultured in medium containing 10% heat activated fetal bovine serum FBS+ 80 µg/L MC-LR to assess its ameliorative effect on MC-LR toxicity. The results show that selenium pretreatment inhibited the MC-LR induced mitophagy, downregulation and mislocalization of blood-testis barrier constituent proteins in bovine Sertoli cells via NF-kB and cytochrome c release blockage. The observed downregulation of electron transport chain (ETC) related genes (mt-ND2, COX-1, COX-2) and upregulation of inflammatory cytokines (IL-6, TNF-α, IL-1β, IFN-γ, IL-4, IL-10, 1 L-13, TGFβ1) in non-pretreated cells exposed to MC-LR were ameliorated in selenium pretreated cells. There was no significant difference (P > 0.05) in the protein levels of blood-testis barrier constituent proteins (ZO-1, occludin, connexin-43, CTNNB1, N-cadherin) and mitochondria related genes (mt-ND2, COX-1, COX-2, ACAT1, mtTFA) of selenium pretreated Sertoli cell compared to the control. Taken together, we conclude that selenium inhibits MC-LR caused Mitophagy, downregulation and mislocalization of blood-testis barrier proteins of bovine Sertoli cell via mitochondrial and TLR4/NF-kB signaling pathways blockage.

Assessment of Hepatotoxic Potential of Cyanobacterial Toxins Using 3D In Vitro Model of Adult Human Liver Stem Cells

Cyanotoxins microcystin-LR (MC-LR) and cylindrospermopsin (CYN) represent hazardous waterborne contaminants and potent human hepatotoxins. However, in vitro monolayer cultures of hepatic cell lines were found to recapitulate, poorly, major hepatocyte-specific functions and inadequately predict hepatotoxic effects of MC-LR and CYN. We utilized 3-dimensional (3D), scaffold-free spheroid cultures of human telomerase-immortalized adult liver stem cells HL1-hT1 to evaluate hepatotoxic potential of MC-LR and CYN. In monolayer cultures of HL1-hT1 cells, MC-LR did not induce cytotoxic effects (EC₅₀ > 10 micromol/L), while CYN inhibited cell growth and viability (48h-96h EC₅₀ ≈ 5.5-0.6 micromol/L). Growth and viability of small growing spheroids were inhibited by both cyanotoxins (≥0.1 micromol/L) and were associated with blebbing and disintegration at the spheroid surface. Hepatospheroid damage and viability reduction were observed also in large mature spheroids, with viability 96h-EC₅₀ values being 0.04 micromol/L for MC-LR and 0.1 micromol/L for CYN, and No Observed Effect Concentrations <0.01 micromol/L. Spheroid cultures of adult human liver stem cells HL1-hT1 exhibit sensitivity comparable to cultures of primary hepatocytes and provide a simple, practical, and cost-effective tool, which can be effectively used in environmental and toxicological research, including assessment of hepatotoxic potential and effect-based monitoring of various samples contaminated with toxic cyanobacteria.

Phosphorescence based O2 sensors - Essential tools for monitoring cell and tissue oxygenation and its impact on metabolism

Oxygenation condition at the cellular level is a critical factor in tissue physiology and common pathophysiological states including cancer, metabolic disorders, ischemia-reperfusion injury and inflammation. O₂ and ROS signalling and hypoxia research are rapidly growing areas spanning life and biomedical sciences, but still many current cell and tissue models and experimental set ups lack physiological relevance, particularly precise control of cellular O₂. Quenched-phosphorescence O₂ sensing enables implementation of such in situ control of cellular O₂ and the creation of physiological conditions in respiring samples analysed in vitro. The advantages of optical O₂ sensing are the non-invasive, contactless, real-time, quantitative monitoring of O₂ concentration, which can be performed in the gas or liquid phase, macroscopically or microscopically, by point measurement or in imaging mode, with sub-cellular spatial resolution, in a flexible manner and with various cell and tissue models. Significantly, this same technology can also be used to probe the metabolism of cells and tissue under specific oxygenation conditions and their responses to changing conditions. Here we describe the range of available O₂ sensing systems and tools, their analytical capabilities, uses in cell/tissue physiology and hypoxia research, and strategies for integration in routine experimental procedures.

Chlorine/UV Process for Decomposition and Detoxification of Microcystin-LR

Microcystin-LR (MC-LR) is a potent hepatotoxin that is often associated with blooms of cyanobacteria. Experiments were conducted to evaluate the efficiency of the chlorine/UV process for MC-LR decomposition and detoxification. Chlorinated MC-LR was observed to be more photoactive than MC-LR. LC/MS analyses confirmed that the arginine moiety represented an important reaction site within the MC-LR molecule for conditions of chlorination below the chlorine demand of the molecule. Prechlorination activated MC-LR toward UV254 exposure by increasing the product of the molar absorption coefficient and the quantum yield of chloro-MC-LR, relative to the unchlorinated molecule. This mechanism of decay is fundamentally different than the conventional view of chlorine/UV as an advanced oxidation process. A toxicity assay based on human liver cells indicated MC-LR degradation byproducts in the chlorine/UV process possessed less cytotoxicity than those that resulted from chlorination or UV254 irradiation applied separately. MC-LR decomposition and detoxification in this combined process were more effective at pH 8.5 than at pH 7.5 or 6.5. These results suggest that the chlorine/UV process could represent an effective strategy for control of microcystins and their associated toxicity in drinking water supplies.

Separation of Microcystin-LR by Cyclodextrin-Functionalized Magnetic Composite of Colloidal Graphene and Porous Silica

Microcystin-LR belongs to the family of microcystins produced by cyanobacteria and known to be the most toxic of this family. Existence of cyanobacteria in water bodies leads to the contamination of drinking water with microcystin-LR and thus their separation is essential for an advanced water purification system. Here we report functional nanocomposite-based selective separation of microcystin-LR from contaminated water. We have synthesized cyclodextrin-functionalized magnetic composite of colloidal graphene and porous silica where the cyclodextrin component offers host-guest interaction with microcystin-LR and the magnetic component offers easier separation of microcystin-LR from water. High surface area and large extent of chemical functional groups offer high loading (up to 18 wt %) of cyclodextrin with these nanocomposites, and the dispersible form of the nanocomposite offers easier accessibility of cyclodextrin to microcystin-LR. We have shown that microcystin-LR separation efficiency is significantly enhanced after functionalization with cyclodextrin, and among all the tested cyclodextrins, γ-cyclodextrin offers the best performance. We have also found that graphene-based nanocomposite offers better performance over porous silica-based nanocomposite due to better accessibility of cyclodextrins for interaction with microcystin-LR. The proposed graphene-based functional nanocomposite is environment friendly, reusable, and applicable for advanced water purification.

Aggregate culture: A more accurate predictor of microcystin toxicity for risk assessment

Aggregate or spheroid culture has emerged as a more biologically relevant method for screening pharmaceutical compounds and understanding exact mechanism of action. Here in, the aggregate approach applied to the freshwater toxins, microcystins, further unearths exact mechanism(s) of toxicity and provides a markedly improved in vitro predictor of toxicity. Microcystins result in acute intoxication by binding covalently to protein phosphatase 1/2A, resulting in hepatocellular necrosis, hemorrhaging and death. Hepatocellular uptake by organic anion transporting polypeptides (OATPs), in addition to other intracellular sequelae, is considered essential for toxicity. In aggregate HepG2, expression of OAT1B1 and OATP1B3 significantly increased relative to monolayer culture. Uptake of two fluorescently labeled substrates significantly increased in aggregates compared with monolayer, confirmed by inhibition of uptake with known competitive substrates. Increased reaction oxygen species (ROS) production occurred following a three-hour exposure of microcystin LR at concentrations from 100 nM to 100 μM, with reversal by ROS scavengers, in contrast with no response in monolayers. These results suggest monolayer culture inadequately predict intracellular effects of microcystins and support evidence that aggregate culture more closely approximates in vivo form and function. The approach results in more reliable prediction of microcystin toxicity in vitro.

Availability of the key metabolic substrates dictates the respiratory response of cancer cells to the mitochondrial uncoupling

Active glycolysis and glutaminolysis provide bioenergetic stability of cancer cells in physiological conditions. Under hypoxia, metabolic and mitochondrial disorders, or pharmacological treatment, a deficit of key metabolic substrates may become life-threatening to cancer cells. We analysed the effects of mitochondrial uncoupling by FCCP on the respiration of cells fed by different combinations of Glc, Gal, Gln and Pyr. In cancer PC12 and HCT116 cells, a large increase in O2 consumption rate (OCR) upon uncoupling was only seen when Gln was combined with either Glc or Pyr. Inhibition of glutaminolysis with BPTES abolished this effect. Despite the key role of Gln, addition of FCCP inhibited respiration and induced apoptosis in cells supplied with Gln alone or Gal/Gln. For all substrate combinations, amplitude of respiratory responses to FCCP did not correlate with Akt, Erk and AMPK phosphorylation, cellular ATP, and resting OCR, mitochondrial Ca(2+) or membrane potential. However, we propose that proton motive force could modulate respiratory response to FCCP by regulating mitochondrial transport of Gln and Pyr, which decreases upon mitochondrial depolarisation. As a result, an increase in respiration upon uncoupling is abolished in cells, deprived of Gln or Pyr (Glc). Unlike PC12 or HCT116 cells, mouse embryonic fibroblasts were capable of generating pronounced response to FCCP when deprived of Gln, thus exhibiting lower dependence on glutaminolysis. Overall, the differential regulation of the respiratory response to FCCP by metabolic environment suggests that mitochondrial uncoupling has a potential for substrate-specific inhibition of cell function, and can be explored for selective cancer treatment.

Neurotoxicological evaluation of microcystin-LR exposure at environmental relevant concentrations on nematode Caenorhabditis elegans

Previous studies have not examined the adverse effects of microcystin-LR (MC-LR) at environmental relevant concentrations on the development and functions of nervous system. The neurotoxic effects of MC-LR exposure on neurotransmitter systems were investigated in Caenorhabditis elegans. After exposing L1 larvae to 0.1, 1, 10, and 100 μg l(-1) of MC-LR for 8 and 24 h, the adverse effects on GABAergic, cholinergic, serotonergic, dopaminergic, and glutamatergic neurons were examined. The expression levels of genes required for development and functions of GABAergic neurons were further investigated. Body bend frequency and head thrash frequency decreased significantly after MC-LR exposure for 8 h at concentrations more than 1 μg l(-1) and after MC-LR exposure for 24 h at concentrations more than 0.1 μg l(-1). Loss of GABAergic neurons increased significantly in a dose-dependent manner after MC-LR exposure at concentrations more than 0.1 μg l(-1). In contrast, no obvious neuronal losses or morphologic changes were observed in cholinergic, serotonergic, dopaminergic, and glutamatergic neurons in MC-LR-exposed nematodes. Quantitative real-time PCR assay further showed that expression levels of unc-30, unc-46, unc-47, and exp-1 genes required for development and function of GABAergic neurons decreased significantly in nematodes exposed to MC-LR at concentrations more than 0.1 or 1 μg l(-1). MC-LR at environmental relevant concentrations caused neurobehavioral defects, which may be largely due to the neuronal loss and the alterations of expression level of genes required for GABAergic neurotransmitter system in C. elegans.

Microcystin-LR promotes melanoma cell invasion and enhances matrix metalloproteinase-2/-9 expression mediated by NF-κB activation

This study aimed to explore the molecular mechanisms behind the stimulation effects of microcystin-LR (a well-known cyanobacterial toxin produced in eutrophic lakes or reservoirs) on cancer cell invasion and matrix metalloproteinases (MMPs) expression. Boyden chamber assay showed that microcystin-LR exposure (>12.5 nM) evidently enhanced the invasion ability of the melanoma cells (MDA-MB-435). Tumor Metastasis PCR Array demonstrated that 24 h microcystin-LR treatment (25 nM) caused overexpression of eight genes involved in tumor metastasis, including MMP-2, MMP-9, and MMP-13. Quantitative real-time PCR, Western blotting and gelatin zymography consistently demonstrated that mRNA and protein levels of MMP-2/-9 were increased in the cells after microcystin-LR exposure (P < 0.05 each). Immunofluorescence assay and electrophoretic mobility shift assay revealed that microcystin-LR could activate nuclear factor kappaB (NF-κB) by accelerating NF-κB translocation into the nucleus and enhancing NF-κB binding ability. Furthermore, addition of NF-κB inhibitor in culture medium could suppress the invasiveness enhancement and MMP-2/-9 overexpression. This study indicates that microcystin-LR can act as a NF-κB activator to promote MMP-2/-9 expression and melanoma cell invasion, which deserves more environmental health concerns.

Effects of microcystin-LR exposure on matrix metalloproteinase-2/-9 expression and cancer cell migration

This study assessed the effects of microcystin-LR (MC-LR) exposure on matrix metalloproteinases (MMPs) expression and cancer cell migration. After male mice were orally administered with different concentrations of MC-LR for 270 d, histopathologic observation revealed an obvious hepatic lymphocyte infiltration or fatty degeneration. Immunohistochemical staining and enzyme-linked immunosorbent assay demonstrated that MC-LR treatment (even at 1 nM) caused up-regulated expressions of hepatic MMP-2/-9. Quantitative reverse-transcriptase PCR showed that the exposure to 80 nM MC-LR induced an increase of MMP-2/-9 mRNA levels by 1.0 and 1.9 fold. Breast cancer cells (MDA-MB-435s) were also cultured with MC-LR solutions and a wound healing assay demonstrated that MC-LR posed a time/dose-dependent stimulation effect on migration of the cancer cells. Gelatin electrophoresis and quantitative PCR showed significant increases in cellular MMP-2/-9 expressions after MC-LR exposure. This study indicated that chronic exposure to MC-LR could alter MMP-2/-9 expressions and stimulate cancer cell migration.

Development of a colorimetric inhibition assay for microcystin-LR detection: comparison of the sensitivity of different protein phosphatases

A colorimetric protein phosphatase (PP) inhibition test for the detection of microcystin-LR (MC-LR) has been developed. Three PP2As, one recombinant and two natural versions, as well as one PP1 produced by molecular engineering, were tested. First, assays were performed using the enzymes in solution to compare their sensitivity to MC-LR. The PP2A purchased from ZEU Immunotec and PP1 appeared more sensitive to the toxin than the other enzymes. With PP2A from ZEU Immunotec, the colorimetric test showed a detection limit of 0.0039 μg L(-1) and an IC(50) value of 0.21 μg L(-1). With PP1, the assay gave a detection limit of 0.05 μg L(-1) and an IC(50) value of 0.56 μg L(-1). Therefore, this assay allowed the detection of lower microcystin-LR (MC-LR) concentrations than the maximum level (1 μg L(-1)) recommended by the World Health Organisation (WHO). The main drawback of this PP-based approach in solution is poor enzyme stabilisation. To overcome this problem, enzymes were entrapped within either a photopolymer or an agarose gel. PP2A from ZEU Immunotec and PP1 were immobilised at the bottom of microwells. The agarose-based tests performed better than the photopolymer-based assay for all of the enzymes. Therefore, the agarose gel is a good candidate to replace the photopolymer, which is generally used in PP-immobilising membranes. The assays based on enzyme-entrapping agarose gels showed detection limits equal to 0.17 μg L(-1) and 0.29 μg L(-1) with immobilised PP2A from ZEU and PP1, respectively. In view of these performances, these tests can potentially be used for monitoring water quality.

Microcystin-LR detection in water by the Fabry-Pérot interferometer using an optical fibre coated with a sol-gel imprinted sensing membrane

Cyanobacteria deteriorate the water quality and are responsible for emerging outbreaks and epidemics causing harmful diseases in Humans and animals because of their toxins. Microcystin-LR (MCT) is one of the most relevant cyanotoxin, being the most widely studied hepatotoxin. For safety purposes, the World Health Organization recommends a maximum value of 1 μg L(-1) of MCT in drinking water. Therefore, there is a great demand for remote and real-time sensing techniques to detect and quantify MCT. In this work a Fabry-Pérot sensing probe based on an optical fibre tip coated with a MCT selective thin film is presented. The membranes were developed by imprinting MCT in a sol-gel matrix that was applied over the tip of the fibre by dip coating. The imprinting effect was obtained by curing the sol-gel membrane, prepared with (3-aminopropyl) trimethoxysilane (APTMS), diphenyl-dimethoxysilane (DPDMS), tetraethoxysilane (TEOS), in the presence of MCT. The imprinting effect was tested by preparing a similar membrane without template. In general, the fibre Fabry-Pérot with a Molecular Imprinted Polymer (MIP) sensor showed low thermal effect, thus avoiding the need of temperature control in field applications. It presented a linear response to MCT concentration within 0.3-1.4 μg L(-1) with a sensitivity of -12.4±0.7 nm L μg(-1). The corresponding Non-Imprinted Polymer (NIP) displayed linear behaviour for the same MCT concentration range, but with much less sensitivity, of -5.9±0.2 nm L μg(-1). The method shows excellent selectivity for MCT against other species co-existing with the analyte in environmental waters. It was successfully applied to the determination of MCT in contaminated samples. The main advantages of the proposed optical sensor include high sensitivity and specificity, low-cost, robustness, easy preparation and preservation.