Dynamic cytotoxic response to microcystins using microelectronic sensor arrays

Toxic effects of a cyanobacterial strain on Chironomus riparius larvae in a multistress environment

Cyanobacteria and their toxic metabolites present a global threat to water habitats, but their impact on aquatic organisms in a multistress environment has been poorly investigated. Here we present the results of a survey on the effects of the toxic cyanobacterial strain Trichormus variabilis (heterotypic synonym Anabaena variabilis), and its toxic metabolite, cyanotoxin microcystin-LR, on Chironomus riparius larvae in a multistress environment. An environmentally relevant concentration of microcystin-LR (0.01 mg/L) caused an increase in larvae mortality in an acute toxicity test, which became greater in the presence of environmental stressors (NO₃^-, NH4⁺, PO₄^3- and Cd²⁺), pointing to an additive effect of these agents. Chronic exposure of C. riparius larvae to the microcystin-LR producing strain of T. variabilis in a multistress environment led to a reduction in the larval mass and hemoglobin concentration, and it induced DNA damage in larval somatic cells. The results revealed the additive effect of microcystin-LR in combination with all three tested stressors (NO₃^-, NH4⁺, PO₄^3-), and the deleterious effect of chronic exposure of C. riparius larvae to the microcystin-LR producing T. variabilis in a multistress environment. However, the present study further emphasizes the importance of investigating interactions between stressors and cyanotoxins, and their effect on aquatic organisms.

Permeability of the Cyanotoxin Microcystin-RR across a Caco-2 Cells Monolayer

Microcystins (MCs) are toxins produced by several cyanobacterial species found worldwide. While MCs have a common structure, the variation of two amino acids in their structure affects their toxicity. As toxicodynamics are very similar between the MC variants, their differential toxicity could rather be explained by toxicokinetic parameters. Microcystin-RR (MC-RR) is the second most abundant congener and induces toxicity through oral exposure. As intestinal permeability is a key parameter of oral toxicokinetics, the apparent permeability of MC-RR across a differentiated intestinal Caco-2 cell monolayer was investigated. We observed a rapid and large decrease of MC-RR levels in the donor compartment. However, irrespective of the loaded concentration and exposure time, the permeabilities were very low from apical to basolateral compartments (from 4 to 15 × 10⁻⁸ cm·s⁻¹) and from basolateral to apical compartments (from 2 to 37 × 10⁻⁸ cm·s⁻¹). Our results suggested that MC-RR would be poorly absorbed orally. As similar low permeability was reported for the most abundant congener microcystin-LR, and this variant presented a greater acute oral toxicity than MC-RR, we concluded that the intestinal permeability was probably not involved in the differential toxicity between them, in contrast to the hepatic uptake and metabolism.

Endocytosis in microcystis aeruginosa accelerates the synthesis of microcystins in the presence of lanthanum(III)

Microcystis aeruginosa bloom releases microcystins (MCs) into global aquatic environment, which other living organisms can ingest the released MCs. The toxic effects of MCs on organisms are amplified through the food chain, threatening human and animal health. Lanthanum(III) [La(III)], a pollutant in aquatic environments worldwide, has been confirmed to stimulate MC synthesis in M. aeruginosa. However, the involved cellular mechanism remains unclear. Here, using interdisciplinary approaches, it was first observed that La(III) activated the clathrin-mediated endocytosis in M. aeruginosa. This allowed the algal cells to rapidly absorb macro-elements (C, N and P) and micro-elements (K, Ca and Mg) through the clathrin-mediated endocytosis. These in turn stimulated chlorophyll production, photosynthesis, the growth of the algal cells, and the increases in the productions of MC-LW, MC-LR and MC-YR in M. aeruginosa. These results provide valuable insights for understanding the involved cellular mechanism on MC synthesis and managing MC pollution, which is important to protect global food chain and the ecosystem.

Fisetin induces autophagy in pancreatic cancer cells via endoplasmic reticulum stress- and mitochondrial stress-dependent pathways

Pancreatic cancer is one of the most aggressive tumors and patients have poor survival rates. Fisetin, a natural flavonoid, was recently reported to have antitumor effects in various cancer models. Autophagy is a conserved catabolic process that maintains cellular homoeostasis in response to stress, and together with apoptosis, determines cell fate. Herein, we examined the effect of fisetin on pancreatic cancer. We reveal that fisetin inhibits PANC-1 cell proliferation using a real-time cell analysis system. Moreover, the in vivo antitumor effect of fisetin was verified in pancreatic cancer using a luciferase-expressing murine xenograft pancreatic cancer model. We found that the AMPK/mTOR signaling pathway was enhanced after fisetin treatment; however, autophagy was not diminished by adding the AMPK inhibitor compound C. Thus, we hypothesized that an another autophagy regulating pathway existed. RNA-seq analysis revealed that the unfolded protein response pathway, which is activated by ER stress, was enriched. We also found that the stress-induced transcription factor p8 was increased in fisetin-treated PANC-1 cells, and that fisetin-induced autophagy was blocked by silencing p8. We revealed that p8-dependent autophagy was AMPK-independent, and that p8 regulated ATF6, ATF4, and PERK in response to ER stress via p53/PKC-α-mediated signaling. Furthermore, mitophagy was associated with Parkin and PINK1 in response to mitochondrial stress. Interestingly, ATF4 and ATF6 were increased in cells treated with fisetin and compound C. Moreover, inhibiting the AMPK/mTOR pathway with compound C may upregulate p8-dependent autophagy. Thus, there may be crosstalk between the AMPK/mTOR and p8-dependent pathways.

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.

Real-time cellular analysis for quantitative detection of functional Clostridium difficile toxin in stool

Rapid and accurate diagnosis and monitoring of Clostridium difficile infection (CDI) is critical for patient care and infection control. We will briefly review current laboratory techniques for the diagnosis of CDI and identify aspects needing improvement. We will also introduce a real-time cellular analysis (RTCA) assay developed for the diagnosis and monitoring of CDI using electronic impedance to assess the cell status. The RTCA assay uses impedance measurement to detect minute physiological changes in cells cultured on gold microelectrodes embedded in glass substrates in the bottom of microtiter wells. This assay has been adapted for quantitative detection of C. difficile functional toxin directly from stool specimens. Compared to conventional techniques and molecular assays, the RTCA assay provides a valuable tool for the diagnosis of CDI as well as for the assessment of clinical severity and for monitoring therapeutic efficacies.

Novel, real-time cell analysis for measuring viral cytopathogenesis and the efficacy of neutralizing antibodies to the 2009 influenza A (H1N1) virus

A novel electronic cell sensor array technology, the real-time cell analysis (RTCA) system, was developed to monitor cell events. Unlike the conventional methods labeling the target cells with fluorescence, luminescence, or light absorption, the RTCA system allows for label-free detection of cell processes directly without the incorporation of labels. Here, we used this new format to measure the cytopathic effect (CPE) of the 2009 influenza A (H1N1) virus and the efficacy of neutralizing antibodies in human sera to this virus. The real-time dynamic monitoring of CPE was performed on MDCK cell cultures infected with the H1N1 virus, ranging from 5.50×10² to 5.50×10⁷ copies/mL. The resulting CPE kinetic curves were automatically recorded and were both time and viral load dependent. The CPE kinetics were also distinguishable between different H1N1 stains, as the onset of CPE induced by the A/Shanghai/37T/2009 H1N1 virus was earlier than that of the A/Shanghai/143T/2009 H1N1 virus. Furthermore, inhibition of H1N1 virus-induced CPE in the presence of human specific anti-sera was detected and quantified using the RTCA system. Antibody titers determined using this new neutralization test correlated well with those obtained independently via the standard hemagglutination inhibition test. Taken together, this new CPE assay format provided label-free and high-throughput measurement of viral growth and the effect of neutralizing antibodies, illustrating its potential in influenza vaccine studies.

Use of chlorophyll a fluorescence to detect the effect of microcystins on photosynthesis and photosystem II energy fluxes of green algae

The phenomenon of cyanobacteria bloom occurs widely in lakes, reservoirs, ponds and slow flowing rivers. Those blooms can have important repercussions, at once on recreational and commercial activities but also on the health of animals and human beings. Indeed, many species are known to produce toxins which are released in water mainly at cellular death. The cyanotoxin most frequently encountered is the microcystin (MC), a hepatotoxin which counts more than 70 variants. The use of fast tests for the detection of this toxin is thus a necessity for the protection of the ecosystems and the human health. A promising method for their detection is a bioassay based on the chlorophyll a fluorescence of algae. Many studies have shown that algae are sensible to diverse pollutants, but were almost never used for cyanotoxins. Therefore, our goals were to evaluate the effect of microcystin on the fluorescence of different species of algae and how it can affect the flow of energy through photosystem II. To reach these objectives, we exposed four green algae (Scenedesmus obliquus CPCC5, Chlamydomonas reinhardtii CC125, Pseudokirchneriella subcapitata CPCC37 and Chlorella vulgaris CPCC111) to microcystin standards (variants MC-LF, LR, RR, YR) and to microcystin extracted from Microcystis aeruginosa (CPCC299), which is known to produce mainly MC-LR. Chlorophyll a fluorescence was measured by PEA (Plant Efficiency Analyzer) and LuminoTox. The results of our experiment showed that microcystins affect the photosynthetic efficiency and the flow of energy through photosystem II from 0.01 μg/mL, within only 15 min. From exposure to standard of microcystin, we showed that MC-LF was the most potent variant, followed by MC-YR, LR and RR. Moreover, green algae used in this study demonstrated different sensitivity to MCs, S. obliquus being the more sensitive. We finally demonstrated that LuminoTox was more sensitive to MCs than parameters measured with PEA, although the latter brings indication on the mode of action of MCs at the photosynthetic apparatus level. This is the first report showing a photosynthetic response within 15 min of exposure. Our results suggest that bioassay based on chlorophyll fluorescence can be used as a rapid and sensitive tool to detect microcystin.

Cell-based electrochemical biosensors for water quality assessment

During recent decades, extensive industrialisation and farming associated with improper waste management policies have led to the release of a wide range of toxic compounds into aquatic ecosystems, causing a rapid decrease of world freshwater resources and thus requiring urgent implementation of suitable legislation to define water remediation and protection strategies. In Europe, the Water Framework Directive aims to restore good qualitative and quantitative status to all water bodies by 2015. To achieve that, extensive monitoring programmes will be required, calling for rapid, reliable and cost-effective analytical methods for monitoring and toxicological impact assessment of water pollutants. In this context, whole cell biosensors appear as excellent alternatives to or techniques complementary to conventional chemical methods. Cells are easy to cultivate and manipulate, host many enzymes able to catalyse a wide range of biological reactions and can be coupled to various types of transducers. In addition, they are able to provide information about the bioavailability and the toxicity of the pollutants towards eukaryotic or prokaryotic cells. In this article, we present an overview of the use of whole cells, mainly bacteria, yeasts and algae, as sensing elements in electrochemical biosensors with respect to their practical applications in water quality monitoring, with particular emphasis on new trends and future perspectives. In contrast to optical detection, electrochemical transduction is not sensitive to light, can be used for analysis of turbid samples and does not require labelling. In some cases, it is also possible to achieve higher selectivities, even without cell modification, by operating at specific potentials where interferences are limited.

Noninvasive probing of inhibitory effects of cylindrospermopsin and microcystin-LR using cell-based impedance spectroscopy

In an effort to develop a noninvasive method for assessment of cyanobacterial toxins in drinking water, plausible cytotoxicity/inhibition of microcystin-LR and cylindrospermopsin was evaluated by cell-substrate impedance sensing (ECIS) using three different cell lines. Sf9 insect cells were attached to concanavalin A coated gold electrodes, whereas Chinese hamster ovary (CHO) and human embryo kidney (HEK) cells were attached to a fibronectin or laminin coated gold surface. Cytotoxic or inhibitory effects were dependent upon the cell line and the extracellular matrix (ECM) coating. Neither toxin exhibited any appreciable effect on the insect cells. In contrast, cytotoxicity of cylindrospermopsin on CHO cells was attested by both ECIS and viability tests. The half-inhibition concentration (ECIS50) of cylindrospermopsin for CHO cells was approximately 2 microg/mL (ppm) after 20 h of exposure and 4 microg/mL (ppm) after 30 h of exposure for a laminin or fibronectin coated surface. ECIS confirmed no significant effect of cylindrospermopsin on HEK cells. Microcystin-LR was also tested with CHO cells, resulting in an ECIS50 value of approximately 12 microg/mL (ppm) after 25 h of exposure for a laminin coated gold surface. The effect of microcystin-LR on CHO cells probed by ECIS was inhibitory rather than cytotoxic, as confirmed by cell viability assays.