Menadione metabolism to thiodione in hepatoblastoma by scanning electrochemical microscopy

Profiling H2O2 from single COS-7 cells by means of scanning electrochemical microscopy

We report quantitative determination of extracellular H₂O₂ released from single COS-7 cells with high spatial resolution, using scanning electrochemical microscopy (SECM). Our strategy of depth scan imaging in vertical x-z plane was conveniently utilized to a single cell for obtaining probe approach curves (PACs) to any positions on the membrane of a live cell by simply drawing a vertical line on one depth SECM image. This SECM mode provides an efficient way to record a batch of PACs, and visualize cell topography simultaneously. The H₂O₂ concentration at the membrane surface in the center of an intact COS-7 cell was deconvoluted from apparent O₂, and determined to be 0.020 mM by overlapping the experimental PAC with the simulated one having a known H₂O₂ release value. The H₂O₂ profile determined in this way gives insight into physiological activity of single live cells. In addition, intracellular H₂O₂ profile was demonstrated using confocal microscopy by labelling the cells with a luminomphore, 2',7'-dichlorodihydrofluorescein diacetate. The two methodologies have illustrated complementary experimental results of H₂O₂ detection, indicating that H₂O₂ generation is centered at endoplasmic reticula.

In Situ and Quantitatively Imaging of Heat-Induced Oxidative State and Oxidative Damage of Living Neurons Using Scanning Electrochemical Microscopy

Central nervous system is sensitive and vulnerable to heat. Oxidative state and oxidative damage of neurons under heat stress are vital for understanding early consequences and mechanisms of heat-related neuronal injury, which remains elusive partly due to the technical challenge of in situ and quantitative monitoring methods. Herein, a temperature-controlled scanning electrochemical microscopy (SECM) platform with programmable pulse potential and depth scan modes is developed for in situ and quantitatively monitoring of oxygen consumption, extracellular hydrogen peroxide level, and cell membrane permeability of neurons under thermal microenvironment of 37-42 °C. The SECM results show that neuronal oxygen consumption reaches a maximum at 40 °C and then decreases, extracellular H₂ O₂ level increases from 39 °C, and membrane permeability increases from 2.0 ± 0.6 × 10^-5 to 7.2 ± 0.8 × 10^-5 m s^-1 from 39 to 42 °C. The therapeutic effect on oxidative damage of neurons under hyperthermia conditions (40-42 °C) is further evaluated by SECM and fluorescence methods, which can be partially alleviated by the potent antioxidant edaravone. This work realizes in situ and quantitatively observing the heat-induced oxidative state and oxidative damage of living neurons using SECM for the first time, which results can contribute to a better understanding of the heat-related cellular injury mechanism.

A protocol for the cultivation and monitoring of ileal gut microbiota surrogates

AIMS

This research aimed to develop and validate a cultivation and monitoring protocol that is suitable for a surrogate microbial community that accounts for the gut microbiota of the ileum of the small intestine.

METHODS AND RESULTS

Five bacterial species have been selected as representatives of the ileal gut microbiota and a general anaerobic medium (MS-BHI, as minimally supplemented BHI) has been constructed and validated against BCCM/LGM recommended and commercial media. Moreover, appropriate selective/differential media have been investigated for monitoring each ileal gut microbiota surrogate. Results showed that MS-BHI was highly efficient in displaying individual and collective behavior of the ileal gut microbiota species, when compared with other types of media. Likewise, the selective/differential media managed to identify and describe the behavior of their targeted species.

CONCLUSIONS

MS-BHI renders a highly efficient, inexpensive and easy-to-prepare cultivation and enumeration alternative for the surrogate ileal microbiota species. Additionally, the selective/differential media can identify and quantify the bacteria of the surrogate ileal microbial community.

SIGNIFICANCE AND IMPACT OF STUDY

The selected gut microbiota species can represent an in vitro ileal community, forming the basis for future studies on small intestinal microbiota. MS-BHI and the proposed monitoring protocol can be used as a standard for gut microbiota studies that utilize conventional microbiological techniques.

Probing Cell Redox State and Glutathione-Modulating Factors Using a Monochlorobimane-Based Microplate Assay

Thiol compounds including predominantly glutathione (GSH) are key components of redox homeostasis, which are involved in the protection and regulation of mammalian cells. The assessment of cell redox status by means of in situ analysis of GSH in living cells is often preferable over established assays in cell lysates due to fluctuations of the GSH pool. For this purpose, we propose a microplate assay with monochlorobimane (MCB) as an available fluorescent probe for GSH, although poorly detected in the microplate format. In addition to the new procedure for improved MCB-assisted GSH detection in plate-grown cells and its verification with GSH modulators, this study provides a useful methodology for the evaluation of cell redox status probed through relative GSH content and responsiveness to both supplemented thiols and variation in oxygen pressure. The roles of extracellular interactions of thiols and natural variability of cellular glutathione on the assay performance were emphasized and discussed. The results are of broad interest in cell biology research and should be particularly useful for the characterization of pathological cells with decreased GSH status and increased oxidative status as well as redox-modulating factors.

Numerical Correction of In Situ AFM-SECM Measurements

Mass-transport-limited catalysis and membrane transport can be characterized by concentration profiles surrounding active surfaces. Scanning electrochemical microscopy (SECM) is a tool that has been used to measure concentration profiles; however, the presence and geometry of the tip can distort these profiles due to hindered diffusion, which in turn alters chemical behavior at the catalytic surface. To fully characterize the behavior of surface features such as catalytic sites, it is essential to account for and analytically remove the effect of tip presence. In this work, atomic force microscopy-based SECM (AFM-SECM) measurements over poly(tetrafluoroethylene) (PTFE) and gold electrode surfaces are used to measure negative and positive-feedback approach curves, respectively. By inversely fitting these approach curves with a finite element method (FEM) model, we derive kinetic and geometric tip parameters that characterize the effect of tip presence. Tip effects may be removed in the model to estimate concentration profiles and reaction properties for the case where no tip is present. A maximum 120% increase in the concentration at one tip radii above the surface is observed due to the presence of the tip, where the concentration field is compressed vertically, in proportion to surface feature size and tip separation. Conical AFM-SECM tips, with a higher ratio of tip height to the base size, introduce less concentration distortion than disk-shaped AFM-SECM tips.

Investigating the Effect of Substrate Stiffness on the Redox State of Cardiac Fibroblasts Using Scanning Electrochemical Microscopy

Cardiac fibrosis, in which cardiac fibroblasts differentiate into myofibroblasts, leads to oversecretion of the extracellular matrix, results in increased stiffness, and facilitates disequilibrium of cellular redox state, further leading to oxidative stress and various degrees of cell death. However, the relationship between the matrix stiffness and the redox status of cardiac fibroblasts remains unclear. In this work, we constructed an in vitro cardiac fibrosis model by culturing cardiac fibroblasts on polyacrylamide gels with tunable stiffness and characterized the differentiation of cardiac fibroblasts to myofibroblasts by immunofluorescence staining of α-smooth muscle actin. We then applied scanning electrochemical microscopy (SECM) with a depth scan mode to in situ and quantitatively assess the redox status by monitoring the glutathione (GSH) efflux rate (k) through the redox reaction between GSH (a typical indicator of cellular redox level) released from cardiac fibroblasts and SECM probe-oxidized ferrocenecarboxylic acid ([FcCOOH]⁺). The SECM results demonstrate that the GSH efflux from the cardiac fibroblasts decreased with increasing substrate stiffness (i.e., mimicking the increased fibrosis degree), indicating that a more oxidizing microenvironment facilitates the cell differentiation and GSH may serve as a biomarker to predict the degree of cardiac fibrosis. This work provides an SECM approach to quantify the redox state of cardiac fibroblasts by recording the GSH efflux rate. In addition, the newly established relationship between the redox balance and the substrate stiffness would help to better understand the redox state of cardiac fibroblasts during cardiac fibrosis.

Combination of Double-Mediator System with Large-Scale Integration-Based Amperometric Devices for Detecting NAD(P)H:quinone Oxidoreductase 1 Activity of Cancer Cell Aggregates

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a key enzyme providing cytoprotection from quinone species. In addition, it is expressed at high levels in many human tumors, such as breast cancer. Therefore, it is considered to be a potential target in cancer treatment. In order to detect intracellular NQO1 activity in MCF-7 aggregates as a cancer model, we present, in this study, a double-mediator system combined with large-scale integration (LSI)-based amperometric devices. This LSI device contained 20 × 20 Pt working electrodes with a 250 μm pitch for electrochemical imaging. In the detection system, menadione (MD) and [Fe(CN)₆]^3- were used. Since MD can diffuse into cells due to its hydrophobicity, it is reduced into menadiol by intracellular NQO1. The menadiol diffuses out of the cells and reduces [Fe(CN)₆]^3- of a hydrophilic mediator into [Fe(CN)₆]^4-. The accumulated [Fe(CN)₆]^4- outside the cells is electrochemically detected at 0.5 V in the LSI device. Using this strategy, the intracellular NQO1 activity of MCF-7 aggregates was successfully detected. The effect of rotenone, which is an inhibitor for Complex I, on NQO1 activity was also investigated. In addition, NQO1 and respiration activities were simultaneously imaged using the detection system that was further combined with electrochemicolor imaging. Thus, the double-mediator system was proven to be useful for evaluating intracellular redox activity of cell aggregates.

Characterization of lapachol cytotoxicity: contribution of glutathione depletion for oxidative stress in Saccharomyces cerevisiae

Over the years, quinones or its derivatives have been extensively studied due to their broad therapeutic spectrum. However, due to the significant structural differences between the individual naturally occurring quinones, investigation of the precise mechanism of their action is essential. In this context, we have analyzed the mechanism of lapachol [4-hydroxy-3-(3-methylbut-2-enyl)naphthalene-1,2-dione] toxicity using Saccharomyces cerevisiae as eukaryotic model organism. Analyzing yeast (wild type, sod1∆, and gsh1∆) cell growth, we observed a strong cytostatic effect caused by lapachol exposure. Moreover, survival of cells was affected by time- and dose-dependent manner. Interestingly, sod1∆ cells were more prone to lapachol toxicity. In this sense, mitochondrial functioning of sod1∆ cells were highly affected by exposure to this quinone. Lapachol also decreased glutathione (GSH) levels in wild type and sod1∆ cells even though glutathione disulfide (GSSG) remained unchanged. We believe that reduction of GSH contents has contributed to the enhancement of lipid peroxidation and intracellular oxidation, effect much more pronounced in sod1∆ cells. Overall, the collected data suggest that although lapachol can act as an oxidant, it seems that the main mechanism of its action initially consists in alkylation of intracellular targets such as GSH and then generating oxidative stress.

Advances in Electrochemistry for Monitoring Cellular Chemical Flux

The transport of organic and inorganic molecules, along with inorganic ions across the plasma membrane results in chemical fluxes that reflect the cellular function in healthy and diseased states. Measurement of these chemical fluxes enables the characterization of protein function and transporter stoichiometry, characterization of a single cell and embryo viability prior to implantation, and screening of pharmaceutical agents. Electrochemical sensors emerge as sensitive and non-invasive tools for measuring chemical fluxes immediately outside the cells in the boundary layer, that are capable of monitoring a diverse range of transported analytes including inorganic ions, gases, neurotransmitters, hormones, and pharmaceutical agents. Used on their own or in combination with other methods, these sensors continue to expand our understanding of the function of rare cells and small tissues. Advances in sensor construction and detection strategies continue to improve sensitivity under physiological conditions, diversify analyte detection, and increase throughput. These advances will be discussed in the context of addressing technical challenges to measuring chemical flux in the boundary layer of cells and measuring the resultant changes to the chemical concentration in the bulk media.

Recent Advances in Scanning Electrochemical Microscopy for Biological Applications

Scanning electrochemical microscopy (SECM) is a chemical microscopy technique with high spatial resolution for imaging sample topography and mapping specific chemical species in liquid environments. With the development of smaller, more sensitive ultramicroelectrodes (UMEs) and more precise computer-controlled measurements, SECM has been widely used to study biological systems over the past three decades. Recent methodological breakthroughs have popularized SECM as a tool for investigating molecular-level chemical reactions. The most common applications include monitoring and analyzing the biological processes associated with enzymatic activity and DNA, and the physiological activity of living cells and other microorganisms. The present article first introduces the basic principles of SECM, followed by an updated review of the applications of SECM in biological studies on enzymes, DNA, proteins, and living cells. Particularly, the potential of SECM for investigating bacterial and biofilm activities is discussed.

3D electrochemical and ion current imaging using scanning electrochemical-scanning ion conductance microscopy

Local cell-membrane permeability and ionic strength are important factors for maintaining the functions of cells. Here, we measured the spatial electrochemical and ion concentration profile near the sample surface with nanoscale resolution using scanning electrochemical microscopy (SECM) combined with scanning ion-conductance microscopy (SICM). The ion current feedback system is an effective way to control probe-sample distance without contact and monitor the kinetic effect of mediator regeneration and the chemical concentration profile. For demonstrating 3D electrochemical and ion concentration mapping, we evaluated the reaction rate of electrochemical mediator regeneration on an unbiased conductor and visualized inhomogeneous permeability and the ion concentration 3D profile on a single fixed adipocyte cell surface.

Core-shell self-assembly triggered via a thiol-disulfide exchange reaction for reduced glutathione detection and single cells monitoring

A novel core-shell DNA self-assembly catalyzed by thiol-disulfide exchange reactions was proposed, which could realize GSH-initiated hybridization chain reaction (HCR) for signal amplification and molecules gathering. Significantly, these self-assembled products via electrostatic interaction could accumulate into prominent and clustered fluorescence-bright spots in single cancer cells for reduced glutathione monitoring, which will effectively drive cell monitoring into a new era.

Scanning Electrochemical Microscopy (SECM): Fundamentals and Applications in Life Sciences

In recent years, scanning electrochemical microscopy (SECM) has made significant contributions to the life sciences. Innovative developments focusing on high-resolution imaging, developing novel operation modes, and combining SECM with complementary optical or scanning probe techniques renders SECM an attractive analytical approach. This chapter gives an introduction to the essential instrumentation and operation principles of SECM for studying biologically-relevant systems. Particular emphasis is given to applications aimed at imaging the activity of biochemical constituents such as enzymes, antibodies, and DNA, which play a pivotal role in biomedical diagnostics. Furthermore, the unique advantages of SECM and combined techniques for studying live cells is highlighted by discussion of selected examples.

Electrochemical push-pull probe: from scanning electrochemical microscopy to multimodal altering of cell microenvironment

To understand biological processes at the cellular level, a general approach is to alter the cells' environment and to study their chemical responses. Herein, we present the implementation of an electrochemical push-pull probe, which combines a microfluidic system with a microelectrode, as a tool for locally altering the microenvironment of few adherent living cells by working in two different perturbation modes, namely electrochemical (i.e., electrochemical generation of a chemical effector compound) and microfluidic (i.e., infusion of a chemical effector compound from the pushing microchannel, while simultaneously aspirating it through the pulling channel, thereby focusing the flow between the channels). The effect of several parameters such as flow rate, working distance, and probe inclination angle on the affected area of adherently growing cells was investigated both theoretically and experimentally. As a proof of concept, localized fluorescent labeling and pH changes were purposely introduced to validate the probe as a tool for studying adherent cancer cells through the control over the chemical composition of the extracellular space with high spatiotemporal resolution. A very good agreement between experimental and simulated results showed that the electrochemical perturbation mode enables to affect precisely only a few living cells localized in a high-density cell culture.

Electrochemical monitoring of intracellular enzyme activity of single living mammalian cells by using a double-mediator system

We evaluated the intracellular

NAD(P)H

quinone oxidoreductase (NQO) activity of single HeLa cells by using the menadione-ferrocyanide double-mediator system combined with scanning electrochemical microscopy (SECM). The double-mediator system was used to amplify the current response from the intracellular NQO activity and to reduce menadione-induced cell damage. The electron shuttle between the electrode and menadione was mediated by the ferrocyanide/ferricyanide redox couple. Generation of ferrocyanide was observed immediately after the addition of a lower concentration (10 μM) of menadione. The ferrocyanide generation rate was constant for 120 min. At a higher menadione concentration (100 μM), the ferrocyanide generation rate decreased within 30 min because of the cytotoxic effect of menadione. We also investigated the relationship between intracellular reactive oxygen species or glutathione levels and exposure to different menadione concentrations to determine the optimal condition for SECM with minimal invasiveness. The present study clearly demonstrates that SECM is useful for the analysis of intracellular enzymatic activities in single cells with a double-mediator system.

Electrochemical sensing of hepatocyte viability

We investigated the use of amperometric and chronoamperometric methods with a double mediator system and screen-printed electrodes (SPEs) for the electrochemical sensing of hepatocyte viability. Cell counts were determined based on measuring cellular respiration via interaction of electroactive redox mediators. The oxidation currents of chronoamperometric measurement were proportional to the concentrations of ferrocyanide which was produced via interaction of cellular respiration, succinate and ferricyanide. The integrated oxidation charges increased linearly with the density of the cultured primary rat hepatocytes over a range of 1 × 10(5) to 5 × 10(5) cells per well (slope = 1.98 (±0.08) μC per 10(5) cells; R(2) = 0.9969), and the detection limit was 7600 (±300) cells per well based on S/N = 3. Each density of cells was cultured in triple replicates and individual cell samples were evaluated. The results of the cytotoxic effect of the chronoamperometric method are comparable to those of the tetrazolium-based colorimetric assay. The chronoamperometric method with ferricyanide and succinate mediators is an efficient, alternative method for assessing the viability of primary hepatocytes which can be completed in 20 min. Succinate did not provide an efficient electron shuttle between cytosolic respiratory redox activity of cancer cells and extracellular ferricyanide, an effect that may be useful for distinguishing hepatocarcinoma cells from healthy hepatocytes.

Use of combined scanning electrochemical and fluorescence microscopy for detection of reactive oxygen species in prostate cancer cells

Release of ROS from prostate cancer (PC3) cells was studied using scanning electrochemical microscopy (SECM) and fluorescence microscopy. One-directional lateral scan SECM was used as a rapid and reproducible tool for simultaneous mapping of cell topography and reactive oxygen species (ROS) release. Fluorescence microscopy was used in tandem to monitor the tip position, in addition to providing information on intracellular ROS content via the use of ROS-reactive fluorescent dyes. A unique tip current (iT) vs lateral distance profile was observed when the tip potential (ET) was set at -0.65 V. This profile reflects the combined effects of topographical change and ROS release at the PC3 cell surfaces. Differentiation between topographical-related and ROS-induced current change was achieved by comparing the scans collected at -0.65 and -0.85 V. The effects of other parameters such as tip to cell distance, solvent oxygen content, and scan direction on the profile of the scan were systematically evaluated. Cells treated with tert-butyl hydroperoxide, a known ROS stimulus, were also evaluated using the lateral scanning approach. Overall, the SECM results correlate well with the fluorescence results. The extracellular ROS level detected at the SECM tip was found to be similar to the intracellular ROS level monitored using fluorescence microscopy. While the concentration of each contributing ROS species has not been determined and is thus part of the future study, here we have successfully demonstrated the use of a simple two-potential lateral scan approach for analysis of ROS released by living cells under real physiological conditions.

Single electron transistor in aqueous media

A gold nanoparticle necklace array spanning a ∼30-micrometer-wide channel shows a robust coulomb blockade effect at room temperature with a threshold of 1V in air. When this device is operated in the aqueous solution, a gain of ∼130 fold in conductance is obtained in electrochemical gating, significantly higher than other nanomaterial-based electrochemical transistors.

Assessment of multidrug resistance on cell coculture patterns using scanning electrochemical microscopy

The emergence of resistance to multiple unrelated chemotherapeutic drugs impedes the treatment of several cancers. Although the involvement of ATP-binding cassette transporters has long been known, there is no in situ method capable of tracking this transporter-related resistance at the single-cell level without interfering with the cell's environment or metabolism. Here, we demonstrate that scanning electrochemical microscopy (SECM) can quantitatively and noninvasively track multidrug resistance-related protein 1-dependent multidrug resistance in patterned adenocarcinoma cervical cancer cells. Nonresistant human cancer cells and their multidrug resistant variants are arranged in a side-by-side format using a stencil-based patterning scheme, allowing for precise positioning of target cells underneath the SECM sensor. SECM measurements of the patterned cells, performed with ferrocenemethanol and [Ru(NH3)6](3+) serving as electrochemical indicators, are used to establish a kinetic "map" of constant-height SECM scans, free of topography contributions. The concept underlying the work described herein may help evaluate the effectiveness of treatment administration strategies targeting reduced drug efflux.

Recent advances in high resolution scanning electrochemical microscopy of living cells--a review

This review discusses advances in the field of high resolution scanning electrochemical microscopy (HR-SECM) and scanning ion conductance microscopy (SICM) to study living cells. Relevant references from the advent of this technique in the late 1980s to most recent contributions in 2012 are presented with special discussion on high resolution images. A clear progress especially within the last 5 years can be seen in the field of HR-SECM. Furthermore, we also concentrate on the intrinsic properties of SECM imaging techniques e.g. different modes of image acquisition, their advantages and disadvantages in imaging living cells and strategies for further enhancement of image resolution, etc. Some of the recent advances of SECM in nanoimaging have also been discussed which may have potential applications in high resolution imaging of cellular processes.

Inhibition of the MRP1-mediated transport of the menadione-glutathione conjugate (thiodione) in HeLa cells as studied by SECM

Oxidative stress induced in live HeLa cells by menadione (2-methyl-1,4-napthaquinone) was studied in real time by scanning electrochemical microscopy (SECM). The hydrophobic molecule menadione diffuses through a living cell membrane where it is toxic to the cell. However, in the cell it is conjugated with glutathione to form thiodione. Thiodione is then recognized and transported across the cell membrane via the ATP-driven MRP1 pump. In the extracellular environment, thiodione was detected by the SECM tip at levels of 140, 70, and 35 µM upon exposure of the cells to menadione concentrations of 500, 250, and 125 µM, respectively. With the aid of finite element modeling, the kinetics of thiodione transport was determined to be 1.6 10(-7) m/s, about 10 times faster than menadione uptake. Selective inhibition of these MRP1 pumps inside live HeLa cells by MK571 produced a lower thiodione concentration of 50 µM in presence of 500 µM menadione and 50 µM MK571. A similar reduced (50% drop) thiodione efflux was observed in the presence of monoclonal antibody QCRL-4, a selective blocking agent of the MRP1 pumps. The reduced thiodione flux confirmed that thiodione was transported by MRP1, and that glutathione is an essential substrate for MRP1-mediated transport. This finding demonstrates the usefulness of SECM in quantitative studies of MRP1 inhibitors and suggests that monoclonal antibodies can be a useful tool in inhibiting the transport of these MDR pumps, and thereby aiding in overcoming multidrug resistance.

Metabolic recovery of Arabidopsis thaliana roots following cessation of oxidative stress

To cope with the various environmental stresses resulting in reactive oxygen species (ROS) production plant metabolism is known to be altered specifically under different stresses. After overcoming the stress the metabolism should be reconfigured to recover basal operation however knowledge concerning how this is achieved is cursory. To investigate the metabolic recovery of roots following oxidative stress, changes in metabolite abundance and carbon flow were analysed. Arabidopsis roots were treated by menadione to elicit oxidative stress. Roots were fed with (13)C labelled glucose and the redistribution of isotope was determined in order to study carbon flow. The label redistribution through many pathways such as glycolysis, the tricarboxylic acid (TCA) cycle and amino acid metabolism were reduced under oxidative stress. After menadione removal many of the stress-related changes reverted back to basal levels. Decreases in amounts of hexose phosphates, malate, 2-oxoglutarate, glutamate and aspartate were fully recovered or even increased to above the control level. However, some metabolites such as pentose phosphates and citrate did not recover but maintained their levels or even increased further. The alteration in label redistribution largely correlated with that in metabolite abundance. Glycolytic carbon flow reverted to the control level only 18 h after menadione removal although the TCA cycle and some amino acids such as aspartate and glutamate took longer to recover. Taken together, plant root metabolism was demonstrated to be able to overcome menadione-induced oxidative stress with the differential time period required by independent pathways suggestive of the involvement of pathway specific regulatory processes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-011-0296-1) contains supplementary material, which is available to authorized users.

Glyceraldehyde-3-phosphate dehydrogenase as a quinone reductase in the suppression of 1,2-naphthoquinone protein adduct formation

1,2-Naphthoquinone (1,2-NQ) is electrophilic, and forms covalent bonds with protein thiols, but its two-electron reduction product 1,2-dihydroxynaphthalene (1,2-NQH(2)) is not, so enzymes catalyzing the reduction with reduced pyridine nucleotides as cofactors could protect cells from electrophile-based chemical insults. To assess this possibility, we examined proteins isolated from the 9000g supernatant from mouse liver for 1,2-NQ reductase activity using an HPLC assay procedure for the hydroquinone of 1,2-NQ and Cibacron Blue 3GA column chromatography and Western blot analysis with specific antibody to determine 1,2-NQ-bound proteins. Among the proteins with high affinities for pyridine nucleotides that also inhibited 1,2-NQ-protein adduct formation in the presence of NADH, a 37-kDa protein was found and identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Using recombinant human GAPDH, we found that this glycolytic enzyme indeed catalyzes the two-electron reduction of 1,2-NQ accompanied by extensive NADH consumption under 20% oxygen conditions. When either 1,2-NQH(2) or 1,2-NQ was incubated with GAPDH in the presence of NADH, minimal covalent bonding to the enzyme occurred compared to that in its absence. These results indicate that GAPDH can inhibit 1,2-NQ-based electrophilic protein modification by conversion to the nonelectrophilic 1,2-NQH(2) via an NADH-dependent process.

GSH-mediated S-transarylation of a quinone glyceraldehyde-3-phosphate dehydrogenase conjugate

Many cellular proteins with reactive thiols form covalent bonds with electrophiles, thereby modifying their structures and activities. Here, we describe the recovery of a glycolytic protein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), from such an electrophilic attack by 1,2-napthoquinone (1,2-NQ). GAPDH readily formed a covalent bond with 1,2-NQ through Cys152 at a low concentration (0.2 μM) in a cell-free system, but when human epithelial A549 cells were exposed to this quinone at 20 μM, only minimal binding was observed although extensive binding to numerous other cellular proteins occurred. Depletion of cellular glutathione (GSH) with buthionine sulfoximine (BSO) resulted in some covalent modification of cellular GAPDH by 1,2-NQ and a significant reduction of GAPDH activity in the cells. Incubation of native, but not boiled, human GAPDH that had been modified by 1,2-NQ with GSH resulted in a concentration-dependent removal of 1,2-NQ from the GAPDH conjugate, accompanied by partial recovery of lost catalytic activity and formation of a 1,2-NQ-GSH adduct (1,2-NQ-SG). While GAPDH is recognized as a multifunctional protein, our results show that GAPDH also has a unique ability to recover from electrophilic modification by 1,2-NQ through a GSH-dependent S-transarylation reaction.

The disulfide proteome and other reactive cysteine proteomes: analysis and functional significance

Ten years ago, proteomics techniques designed for large-scale investigations of redox-sensitive proteins started to emerge. The proteomes, defined as sets of proteins containing reactive cysteines that undergo oxidative post-translational modifications, have had a particular impact on research concerning the redox regulation of cellular processes. These proteomes, which are hereafter termed "disulfide proteomes," have been studied in nearly all kingdoms of life, including animals, plants, fungi, and bacteria. Disulfide proteomics has been applied to the identification of proteins modified by reactive oxygen and nitrogen species under stress conditions. Other studies involving disulfide proteomics have addressed the functions of thioredoxins and glutaredoxins. Hence, there is a steadily growing number of proteins containing reactive cysteines, which are probable targets for redox regulation. The disulfide proteomes have provided evidence that entire pathways, such as glycolysis, the tricarboxylic acid cycle, and the Calvin-Benson cycle, are controlled by mechanisms involving changes in the cysteine redox state of each enzyme implicated. Synthesis and degradation of proteins are processes highly represented in disulfide proteomes and additional biochemical data have established some mechanisms for their redox regulation. Thus, combined with biochemistry and genetics, disulfide proteomics has a significant potential to contribute to new discoveries on redox regulation and signaling.

In situ electrochemical imaging of membrane glycan expression on micropatterned adherent single cells

A scanning electrochemical microscopic (SECM) method for in situ imaging of four types of membrane glycan motifs on single adherent cells was proposed using BGC-823 human gastric carcinoma (BGC) cells as the model. These adherent cells were first micropatterned in the microwell of poly(dimethylsiloxane) membrane for precisely controlling the localized surface interaction, and the membrane glycans were then specifically recognized with corresponding lectins labeled with horseradish peroxidase (HRP). On the basis of the enzymatic oxidization of ferrocenylmethanol (FMA) by H(2)O(2) to yield FMA(+), the glycan expression level was detected by the reduction current of FMA(+) at the SECM tip. The cell-surface glycans could, thus, be in situ imaged by SECM at a single-cell level without peeling the cells from culture dish. Under the optimized conditions, four types of membrane glycan motifs showed statistically distinguishable expression levels. The SECM results for different glycan motifs on adherent single cells were consistent with those estimated by flow cytometric assay. This work provides a reliable approach for in situ evaluation of the characteristic glycopattern of single living cells and can be applied in cell biologic study based on cell surface carbohydrate expression.

Electrochemistry in nanoscopic volumes

Exploration of electrochemical properties in ultrasmall volumes is still an emerging area. It is not only of great importance for the fundamental research, but also endowed with practical significance in the area of bioanalysis and medicine. Microelectrodes with superior electrochemical characteristics and versatile configurations are suitable tools for the investigation in confined geometries, and remarkable progress involving both preparation methods and theoretical interpretation has been made during the last few decades. Despite this success, electrochemical studies in nanoscopic volumes are still highly challenging due to the less predictable situations in very limited spatial and temporal domains, as well as difficulty in micromanipulation at the nanoscale. In this mini-review, we will summarize the main strategies for this topic, briefly look through the recent advances, and specifically introduce the design and application of a new kind of on-chip ultrasmall electrochemical cells based on micro- and nanogap electrodes, which are prepared by photolithographic method with volume ranging from femtolitre to attolitre. Finally, the limits of current systems and the future perspectives of this field are discussed.

Real-time monitoring of cell viability by its nanoscale height change with oxygen as endogenous indicator

A method for real-time evaluation of cell viability was developed by using oxygen as an endogenous indicator in scanning electrochemical microscopy to monitor the nanoscale height change of a single cell in a physiological environment with a novel Pt nanodisk electrode and a newly designed step-approaching strategy.

Imaging enzymes at work: metabolic mapping by enzyme histochemistry

For the understanding of functions of proteins in biological and pathological processes, reporter molecules such as fluorescent proteins have become indispensable tools for visualizing the location of these proteins in intact animals, tissues, and cells. For enzymes, imaging their activity also provides information on their function or functions, which does not necessarily correlate with their location. Metabolic mapping enables imaging of activity of enzymes. The enzyme under study forms a reaction product that is fluorescent or colored by conversion of either a fluorogenic or chromogenic substrate or a fluorescent substrate with different spectral characteristics. Most chromogenic staining methods were developed in the latter half of the twentieth century but still find new applications in modern cell biology and pathology. Fluorescence methods have rapidly evolved during the last decade. This review critically evaluates the methods that are available at present for metabolic mapping in living animals, unfixed cryostat sections of tissues, and living cells, and refers to protocols of the methods of choice.

Scanning electrochemical microscopy in neuroscience

This article reviews recent work involving the application of scanning electrochemical microscopy (SECM) to the study of individual cultured living cells, with an emphasis on topographical and functional imaging of neuronal and secretory cells of the nervous and endocrine system. The basic principles of biological SECM and associated negative amperometric-feedback and generator/collector-mode SECM imaging are discussed, and successful use of the methodology for screening soft and fragile membranous objects is outlined. The drawbacks of the constant-height mode of probe movement and the benefits of the constant-distance mode of SECM operation are described. Finally, representative examples of constant-height and constant-distance mode SECM on a variety of live cells are highlighted to demonstrate the current status of single-cell SECM in general and of SECM in neuroscience in particular.

In vitro and in vivo determination of antioxidant activity and mode of action of isoquercitrin and Hyptis fasciculata

Reactive oxygen species (ROS) are thought to underline the process of ageing and the pathogenicity of various diseases, such as neurodegenerative disorders and cancer. The use of traditional medicine is widespread and plants still present a large source of natural antioxidants that might serve as leads for the development of novel drugs. In this paper, the alcoholic extract from leaves of Hyptis fasciculata, a Brazilian medicinal plant, and isoquercitrin, a flavonoid identified in this species, showed to be active as 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavengers. The extract of Hyptis fasciculata and isoquercitrin were also able to increase tolerance of the eukaryotic microorganism Saccharomyces cerevisiae to both hydrogen peroxide and menadione, a source of superoxide. Cellular protection was correlated with a decrease in oxidative stress markers, such as levels of ROS, protein carbonylation and lipid peroxidation, confirming the antioxidant potential of Hyptis fasciculata and isoquercitrin.

Multidrug-resistance-associated protein plays a protective role in menadione-induced oxidative stress in endothelial cells

AIMS

Menadione, a redox-cycling quinone known to cause oxidative stress, binds to reduced glutathione (GSH) to form glutathione S-conjugate. Glutathione S-conjugates efflux is often mediated by multidrug-resistance-associated protein (MRP). We investigated the effect of a transporter inhibitor, MK571 (3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid), on menadione-induced oxidative stress in bovine aortic endothelial cells (BAECs).

MAIN METHODS

BAECs were treated with menadione and MK571, and cell viability was measured. Modulation of intracellular GSH levels was performed with buthionine sulfoximine and GSH ethyl ester treatments. Intracellular superoxide was estimated by dihydroethidium oxidation using fluorescence microscopy or flow cytometry. Expression of MRP was determined by flow cytometry using phycoerythrin-conjugated anti-MRP monoclonal antibody.

KEY FINDINGS

Intracellular GSH depletion by buthionine sulfoximine promoted the loss of viability of BAECs exposed to menadione. Exogenous GSH, which does not permeate the cell membrane, or GSH ethyl ester protected BAECs against the loss of viability induced by menadione. The results suggest that GSH binds to menadione outside the cells as well as inside. Pretreatment of BAECs with MK571 dramatically increased intracellular levels of superoxide generated from menadione, indicating that menadione may accumulate in the intracellular milieu. Finally, we found that MK571 aggravated menadione-induced toxicity in BAECs and that MRP levels were increased in menadione-treated cells.

SIGNIFICANCE

We conclude that MRP plays a vital role in protecting BAECs against menadione-induced oxidative stress, presumably due to its ability to transport glutathione S-conjugate.

The Kv channel blocker 4-aminopyridine enhances Ag+ uptake: a scanning electrochemical microscopy study of single living cells

We report that silver ion (Ag(+)) uptake is enhanced by 4-aminopyridine (4-AP), a well known voltage-sensitive potassium ion channel (K(v)) blocker. Both bacterial (Escherichia coli) and mammalian (3T3 fibroblast) cells were used as model systems. Ag(+) uptake was monitored with a scanning electrochemical microscope with an amperometric Ag(+) ion-selective electrode (Ag(+)-ISE) and the respiration rates of E. coli cells were measured by oxygen reduction at an ultramicroelectrode. The results showed that not only the amount but also the rate of silver uptake by the cells increased significantly when 4-AP was added to the solution. For fibroblasts, the Ag(+) uptake rate was 4.8 x 10(7) ions per cell per sec without 4-AP compared with 1.0 x 10(8) ions per cell per sec with 0.2 mM 4-AP. For E. coli cells, the uptake rate was 1.5 x 10(4) ions per cell per sec without 4-AP vs. 3.5 x 10(4) ions per cell per sec with 0.5 mM 4-AP and 5.9 x 10(4) ions per cell per sec with 1 mM 4-AP. Thus, 4-AP might be useful where silver is used as antimicrobial agent to speed its uptake.

Determination of physiological thiols by electrochemical detection with piazselenole and its application in rat breast cancer cells 4T-1

Glutathione (GSH), the most abundant cellular thiol, has been shown to play an important role in maintaining cellular redox equilibrium that is pivotal for cell growth and function. In the present paper a novel electrochemical probe of piazselenole containing a Se-N bond was well developed for the determination of GSH. The cyclic voltammogram of piazselenole scanned at 100 mV/s displayed an irreversible reduction peak at -0.106 V (vs Ag/AgCl electrode) and a significant peak current decrease could be further provoked with the addition of GSH into piazselenole solution. On the basis of the peak current decrease of piazselenole recorded by differential pulse voltammetry with the increase of GSH concentration, a working curve was constructed for GSH determination in the range of 5.0 x 10(-10) approximately 2.2 x 10(-8) M with the linear regression equation as DeltaiP (10(-6)A) = 0.0952 + 0.4287 x CGSH (10(-8) M) and the detection limit (3sigma) as 83 pM. The proposed method was satisfactorily applied to the extracts of rat breast cancer cells 4T-1 for intracellular thiols detection.