Rapid method for glutathione quantitation using high-performance liquid chromatography with coulometric electrochemical detection

Based on Fe and Ni prepared organic colloidal materials as efficient oxide nanozymes for chemiluminescence detection of GSH and Hg(II) ions

Metal-organic gels (MOGs) are a type of metal-organic colloid material with a large specific surface area, loose porous structure, and open metal active sites. In this work, FeNi-MOGs were synthesized by the simple one-step static method, using Fe(III) and Ni(II) as the central metal ions and terephthalic acid as the organic ligand. The prepared FeNi-MOGs could effectively catalyze the chemiluminescence of luminol without the involvement of H2O2, which exhibited good catalytic activity. Then, the multifunctional detected platform was constructed for the detection of GSH and Hg2+, based on the antioxidant capacity of GSH, and the strong affinity between mercury ion (Hg2+) and GSH which inactivated the antioxidant capacity of GSH. The experimental limits of detection (LOD) for GSH and Hg2+ were 76 nM and 210 nM, and the detection ranges were 2-100 μM and 8-4000 μM, respectively. The as-proposed sensor had good performance in both detection limit and detection range of GSH and Hg2+, which fully met the needs of daily life. Surprisingly, the sensor had low detection limits and an extremely wide detection range for Hg2+, spanning five orders of magnitude. Furthermore, the detection of mercury ions in actual lake water and GSH in human serum showed good results, with recovery rates ranging from 90.10 % to 105.37 %, which proved that the method was accurate and reliable. The as-proposed sensor had great potential as the platform for GSH and Hg2+ detection applications.

Multicolor detection of glutathione by manganese dioxide nanosheets and gold nanotetrapods based on an anti-etching mechanism

Glutathione (GSH) is a crucial non-protein thiol and an indispensable endogenous antioxidant. The aberrant expression of GSH in plasma and cytosol is closely related to numerous diseases, including cancer. Therefore, establishing a sensitive method for analyzing GSH has important application value for biomedical research and clinical medical detection. Herein, A method for the rapid and simple detection of GSH was proposed, which is based on an anti-etching mechanism by utilizing gold nanotetrapods (Au NTPs) and manganese dioxide nanosheets (MnO2 NSs). In the absence of GSH, Au NTPs solution can cause a distinct color change from gray-green to red through the etching effect of MnO2 NSs. However, in the presence of GSH, the redox reaction between GSH and MnO2 NSs inhibits the etching of Au NTPs by MnO2 NSs, and Au NTPs solution maintains persistent gray-green color. The colorimetric probe exhibited excellent selectivity for GSH. The limits of detection for GSH were 43.5 nM (UV-vis spectrum) and 0.25 μM (naked eyes). The sensing technique exhibited excellent linearity between wavelength shift and GSH concentration within the range of 0.25 μM-1.5 μM. The outcomes of GSH detection in actual biological samples demonstrate that this probe has the potential to be applied to GSH detection in intricate biological samples.

A High-Performance Liquid Chromatography with Electrochemical Detection Method Developed for the Sensitive Determination of Ascorbic Acid: Validation, Application, and Comparison with Titration, Spectrophotometric, and High-Performance Liquid Chromatography with Diode-Array Detection Methods

L-ascorbic acid (vitamin C, VC), an essential nutrient obtained from the diet to maintain various vital signs for the human body, is a crucial indicator of food quality and nutritional value. Herein, high-performance liquid chromatography with electrochemical detection (HPLC-ECD) was developed and validated with the advantages of higher sensitivity, simpler operation processes, and more rapid detection in measuring VC levels in honey samples when compared with the common methods (titration, spectrophotometric, and HPLC-DAD methods). The results of the HPLC-ECD methodological validation showed that the limit of detection (LOD) was 0.0043 µg mL-1; the relative standard deviations (RSDs) of the intra- and inter-day values were between 2.51% and 5.15%, and the regression coefficient was >0.999 in the linear range of 0.1 to 20 µg mL-1. The validated HPLC-ECD method was also successfully utilized to evaluate the VC levels in different varieties of honey samples with various storage durations as well as in fruit and biological samples. This study provided a perspective for the further accurate determination of VC content in food and biological samples.

Recent Advances in Electrochemical Sensors for Sulfur-Containing Antioxidants

Sulfur-containing antioxidants are an important part of the antioxidant defense systems in living organisms under the frame of a thiol-disulfide equilibrium. Among them, l-cysteine, l-homocysteine, l-methionine, glutathione, and α-lipoic acid are the most typical representatives. Their actions in living systems are briefly discussed. Being electroactive, sulfur-containing antioxidants are interesting analytes to be determined using various types of electrochemical sensors. Attention is paid to the chemically modified electrodes with various nanostructured coverages. The analytical capabilities of electrochemical sensors for sulfur-containing antioxidant quantification are summarized and discussed. The data are summarized and presented on the basis of the electrode surface modifier applied, i.e., carbon nanomaterials, metal and metal oxide nanoparticles (NPs) and nanostructures, organic mediators, polymeric coverage, and mixed modifiers. The combination of various types of nanomaterials provides a wider linear dynamic range, lower limits of detection, and higher selectivity in comparison to bare electrodes and sensors based on the one type of surface modifier. The perspective of the combination of chromatography with electrochemical detection providing the possibility for simultaneous determination of sulfur-containing antioxidants in a complex matrix has also been discussed.

Simultaneous quantitation of oxidized and reduced glutathione via LC-MS/MS to study the redox state and drug-mediated modulation in cells, worms and animal tissue

Alterations in reduced and oxidized glutathione (GSH/GSSG) levels represent an important marker for oxidative stress and potential disease progression in toxicological research. Since GSH can be oxidized rapidly, using a stable and reliable method for sample preparation and GSH/GSSG quantification is essential to obtain reproducible data. Here we describe an optimised sample processing combined with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, validated for different biological matrices (lysates from HepG2 cells, C. elegans, and mouse liver tissue). To avoid autoxidation of GSH, samples were treated with the thiol-masking agent N-ethylmaleimide (NEM) and sulfosalicylic acid (SSA) in a single step. With an analysis time of 5 min, the developed LC-MS/MS method offers simultaneous determination of GSH and GSSG at high sample throughput with high sensitivity. This is especially interesting with respect of screening for oxidative and protective properties of substances in in vitro and in vivo models, e.g. C. elegans. In addition to method validation parameters (linearity, limit of detection (LOD), limit of quantification (LOQ), recovery, interday, intraday), we verified the method by using menadione and L-buthionine-(S,R)-sulfoximine (BSO) as well established modulators of cellular GSH and GSSG concentrations. Thereby menadione proved to be a reliable positive control also in C. elegans.

A more accurate indicator to evaluate oxidative stress in rat plasma with osteoporosis

Background: oxidative stress is linked to various human diseases which developed into the idea of "disrupted redox signaling". Osteoporosis (OP) is a chronic skeletal disorder characterized by low bone mineral density and deterioration of bone microarchitecture among which estrogen deficiency is the main cause. Lack of estrogen leads to the imbalance between oxidation and anti-oxidation in patients, and oxidative stress is an important link in the pathogenesis of OP. The ratio of the reduced to the oxidized thiols can characterize the redox status. However, few methods have been reported for the simultaneous determination of reduced forms and their oxidized forms of thiols in plasma. Methods: we developed a hollow fiber centrifugal ultrafiltration (HFCF-UF) method for sample preparation and validated a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method to determine two reduced forms of thiols-homocysteine (Hcy), cysteine (Cys) levels and their respective oxidized compounds, homocystine (HHcy) and cystine (Cyss) in rat plasma simultaneously for the first time. Thirty-six female rats were randomly divided into three groups: normal control (NC), oxidative stress (ovariectomy, OVX) and ovariectomy with hydrogen-rich saline administration (OVX + HRS). Results: the validation parameters for the methodological results were within the acceptance criteria. There were both significant differences of Hcy/HHcy (Hcy reduced/oxidized) and Cys/Cyss (Cys reduced/oxidized) in rat plasma between three groups with both p < 0.05 and meanwhile, the p values of malondialdehyde, superoxide dismutase and glutathione peroxidase were all less than 0.01. The value of both Hcy/HHcy and Cys/Cyss were significantly decreased with the change of Micro-CT scan result of femoral neck in OVX group (both the trabecular thickness and trabecular number significantly decreased with a significant increase of trabecular separation) which demonstrate OP occurs. The change of Hcy/HHcy is more obvious and prominent than Cys/Cyss. Conclusions: the Hcy/HHcy and Cys/Cyss could be suitable biomarkers for oxidative stress and especially Hcy/HHcy is more sensitive. The developed method is simple and accurate. It can be easily applied in clinical research to further evaluate the oxidative stress indicator for disease risk factors.

Signal On-Off Electrochemical Sensor for Glutathione Based on a AuCu-Decorated Zr-Containing Metal-Organic Framework via Solid-State Electrochemistry of Cuprous Chloride

A novel signal on-off glutathione (GSH) electrochemical sensor was developed based on a AuCu bimetal-decorated Zr-containing metal-organic framework (Zr-MOF), in which a signal amplification strategy promoted by solid-state electrochemistry of cuprous chloride (CuCl) was used. The Zr-MOF with a large surface area can be effectively used as the substrate for the in situ growth of AuCu bimetals to obtain the Zr-MOF@AuCu nanocomposite. The interaction between Cu in Zr-MOF@AuCu and Cl^- in the solution accompanied with the formation of CuCl displays an enlarged stable oxidation current, which greatly declines with the addition of GSH owing to the specific Cu-GSH interaction. The conversion of CuCl into Cu-GSH triggered the "crowding-out effect" and resulted in a sharp drop in the peak current of CuCl, which can realize the ultrasensitive and selective detection of GSH. The detection mechanism was investigated, and the detection range was 10 pM-1 mM with the detection limit as low as 2.67 pM. The special response mechanism for the detection of GSH allows the highly selective detection of GSH in various real samples with reliable results, endowing the proposed electroanalysis sensor with broad application prospects in biological and food analysis.

A Yellow Fluorescence Probe for the Detection of Oxidized Glutathione and Biological Imaging

It is well-known that the ratio of reduced l-glutathione (GSH) to oxidized l-glutathione (GSSG) is a vital biomarker for monitoring overall cellular health, thus detecting the intracellular concentration of glutathione is of great significance. Recently, an increasing number of reports have published various methods for GSH detection, but studies on the detection of GSSG are still rare. Here, we report a kind of new yellow fluorescent carbon dots (CDs) for the detection of GSSG through a fluorescence "off-on" process. Because the surface is rich in amino groups, the CDs show a positive potential. When the concentration of GSSG was continuously increased, the CDs' fluorescence dropped sharply, while the fluorescence gradually recovered after the addition of sodium sulfide. The phenomenon of fluorescence quenching is linear with the concentration of the quencher (GSSG)(0-200 μM), and 0.18 μM is calculated as the detection limit. More interestingly, as a fluorescent probe, the CDs can be further used for fluorescence imaging in living cells and zebrafish.

Review of the Analytical Methods Based on HPLC-Electrochemical Detection Coupling for the Evaluation of Organic Compounds of Nutritional and Environmental Interest

This review would like to show the state of the art regarding the coupling of High-Performance Liquid Chromatography (HPLC) with Electrochemical Detection (ED). Since a universal detector for HPLC is not available, the electrochemical detection methods, thanks to their versatility and specificity, are competitive with respect to the detectors currently used. The papers present in literature on HPLC-ED technique are analyzed and discussed: for example, they regard the development of analytical determinations of resveratrol, rosmarinic acid, aromatic heterocyclic amines and glyphosate in food matrices such as meat, aromatic plants, vegetables, fruit and tomato juices. These papers show that electrochemical sensors used as detectors for HPLC can offer better sensitivity values than other detectors. Furthermore, the use of specific working potentials allows avoid matrix interferences to be avoided by almost exclusively determining the analytes of interest. It should be underlined that HPLC-ED methods have a selectivity that allows for limitation of the sample preparation and clean-up procedures to a minimum, making them quick and easy to apply. In addition, these methods offer advantages such as the possibility of direct analysis, that derivatization is often not necessary, the cost-effectiveness of the instrumentation and the possibility of regenerating the electrodes which allows numerous analyses in succession.

Comparison of three methods for in vivo quantification of glutathione in tissues of hypertensive rats

Glutathione (γ-L-glutamyl-L-cysteinyl-glycine, GSH) is a tripeptide that is part of the antioxidant defense system and contributes to numerous redox-regulatory processes. In vivo, reduced GSH and oxidized glutathione disulfide (GSSG) are present in redox equilibrium and their ratio provides important information on the cellular redox state. Here, we compared three different methods for in vivo quantification of glutathione in tissues of hypertensive rats, an accepted animal model of oxidative stress. In the present study, we used hypertensive rats (infusion of 1 mg/kg/d angiotensin-II for 7 days) to determine the levels of reduced GSH and/or GSH/GSSG ratios in different tissue samples. We used an HPLC-based method with direct electrochemical detection (HPLC/ECD) and compared it with Ellman's reagent (DTNB) dependent derivatization of reduced GSH to the GS-NTB adduct and free NTB (UV/Vis HPLC) as well as with a commercial GSH/GSSG assay (Oxiselect). Whereas all three methods indicated overall a decreased redox state in hypertensive rats, the assays based on HPLC/ECD and DTNB derivatization provided the most significant differences. We applied a direct, fast and sensitive method for electrochemical GSH detection in tissues from hypertensive animals, and confirmed its reliability for in vivo measurements by head-to-head comparison with two other established assays. The HPLC/ECD but not DTNB and Oxiselect assays yielded quantitative GSH data but all three assays reflected nicely the qualitative redox changes and functional impairment in hypertensive rats. However, especially our GSH/GSSG values are lower than reported by others pointing to problems in the work-up protocol.

Generation of a GLO-2 deficient mouse reveals its effects on liver carbonyl and glutathione levels

Objective

Hydroxyacylglutathione hydrolase (aka as GLO-2) is a component of the glyoxalase pathway involved in the detoxification of the reactive oxoaldehydes, glyoxal and methylglyoxal. These reactive metabolites have been linked to a variety of pathological conditions, including diabetes, cancer and heart disease and may be involved in the aging process. The objective of this study was to generate a mouse model deficient in GLO-2 to provide insight into the function of GLO-2 and to determine if it is potentially linked to endogenous oxalate synthesis which could influence urinary oxalate excretion.

Methods

A GLO-2 knock out mouse was generated using CRISPR/Cas 9 techniques. Tissue and 24-h urine samples were collected under baseline conditions from adult male and female animals for biochemical analyses, including chromatographic measurement of glycolate, oxalate, glyoxal, methylglyoxal, D-lactate, ascorbic acid and glutathione levels.

Results

The GLO-2 KO animals developed normally and there were no changes in 24-h urinary oxalate excretion, liver levels of methylglyoxal, glyoxal, ascorbic acid and glutathione, or plasma d-lactate levels. GLO-2 deficient males had lower plasma glycolate levels than wild type males while this relationship was not observed in females.

Conclusions

The lack of a unique phenotype in a GLO-2 KO mouse model under baseline conditions is consistent with recent evidence, suggesting a functional glyoxalase pathway is not required for optimal health. A lower plasma glycolate in male GLO-2 KO animals suggests glyoxal production may be a significant contributor to circulating glycolate levels, but not to endogenous oxalate synthesis.

Single run analysis of glutathione and its disulfide in food samples by liquid chromatography coupled to on-line post-column derivatization

Glutathione and its disulfide were determined in a single run using liquid chromatography with on-line post-column derivatization and fluorimetric detection (340 nm/425 nm). The analytes were separated using a reversed-phase column capable of operating at 100% aqueous mobile phase and detected following direct on-line reaction with o-phthalaldehyde (7.5 mmol L^-1) in highly basic medium (0.37 mol L^-1 NaOH). The instrumental and chemical variables were carefully investigated towards high sensitivity and throughput, while special attention was paid to validating potential matrix effects. Glutathione and its disulfide could be selectively determined with respective LODs of 0.10 and 0.30 μmol L^-1 in the absence of matrix effect (<6%). The endogenous content of the analytes was accurately determined in various food samples with recoveries ranging between 80 and 120% in all cases. The proposed method is reliable and promising as a generic analytical tool for the convenient estimation of the redox status of glutathione in various food matrices.

Analytical Capabilities of Coulometric Sensor Systems in the Antioxidants Analysis

The definition of antioxidants (AOs), their classification and properties as well as electrochemical sensor systems for AOs analysis are briefly discussed. The analytical capabilities of coulometric titration with electrogenerated titrants as sensor systems for AOs determination have been considered in detail. The attention focused on the individual AO quantification that was mainly used in the pharmaceutical analysis and estimation of total antioxidant parameters (total antioxidant capacity (TAC), ferric reducing power (FRP) and ceric reducing/antioxidant capacity (CRAC)) allowing the fast screening of the target samples including their quality control. The main advantages of coulometric sensor systems are pointed out. The selective quantification of individual AO in a complex matrix using a combination of chromatography with coulometric or coulometric array detection under potentiostatic mode is discussed. The future development of coulometric sensor systems for AOs analysis is focused on the application of novel coulometric titrants and the application of coulometric detection in flow injection analysis.

A simple and convenient dry-state SEIRS method for glutathione detection based on citrate functionalized silver nanoparticles in human biological fluids

Graphical representation for determination of glutathione using citrate functionalized AgNPs enriched dry-state SEIRS method.

Measurement of Glutathione as a Tool for Oxidative Stress Studies by High Performance Liquid Chromatography

Background: Maintenance of the ratio of glutathione in the reduced (GSH) and oxidised (GSSG) state in cells is important in redox control, signal transduction and gene regulation, factors that are altered in many diseases. The accurate and reliable determination of GSH and GSSG simultaneously is a useful tool for oxidative stress determination. Measurement is limited primarily to the underestimation of GSH and overestimation GSSG as a result of auto-oxidation of GSH. The aim of this study was to overcome this limitation and develop, optimise and validate a reverse-phase high performance liquid chromatographic (HPLC) assay of GSH and GSSG for the determination of oxidant status in cardiac and chronic kidney diseases. Methods: Fluorescence detection of the derivative, glutathione-O-pthaldialdehyde (OPA) adduct was used. The assay was validated by measuring the stability of glutathione and glutathione-OPA adduct under conditions that could affect the reproducibility including reaction time and temperature. Linearity, concentration range, limit of detection (LOD), limit of quantification (LOQ), recovery and extraction efficiency and selectivity of the method were assessed. Results: There was excellent linearity for GSH (r² = 0.998) and GSSG (r² = 0.996) over concentration ranges of 0.1 µM–4 mM and 0.2 µM–0.4 mM respectively. The extraction of GSH from tissues was consistent and precise. The limit of detection for GSH and GSSG were 0.34 µM and 0.26 µM respectively whilst their limits of quantification were 1.14 µM and 0.88 µM respectively. Conclusion: These data validate a method for the simultaneous measurement of GSH and GSSG in samples extracted from biological tissues and offer a simple determination of redox status in clinical samples.

Ferroptosis is involved in alcohol-induced cell death in vivo and in vitro

A critical pathogenic factor in the development of lethal liver failure is cell death induced by the accumulation of lipid reactive oxygen species. In this study, we discovered and illuminated a new mechanism that led to alcoholic liver disease via ferroptosis, an iron-dependent regulated cell death. Study in vitro showed that both necroptosis inhibitor and ferroptosis inhibitors performed significantly protective effect on alcohol-induced cell death, while apoptosis inhibitor and autophagy inhibitor had no such effect. Our data also indicated that alcohol caused the accumulation of lipid peroxides and the mRNA expression of prostaglandin-endoperoxide synthase 2, reduced the protein expression of the specific light-chain subunit of the cystine/glutamate antiporter and glutathione peroxidase 4. Importantly, ferrostatin-1 significantly ameliorated liver injury that was induced by overdosed alcohol both in vitro and in vivo. These findings highlight that targeting ferroptosis serves as a hepatoprotective strategy for alcoholic liver disease treatment.

Quantitative analysis of amino acid metabolism in liver cancer links glutamate excretion to nucleotide synthesis

We used a combination of experimental measurements and computer simulations to understand how liver cancer cells rewire their metabolism to grow faster. We observed that glutamate is excreted by the cells, and our simulations suggest that this occurs because glutamate is formed in excess in the cytoplasm, when cells rapidly synthesize nucleotides, which are required for growth. Meanwhile, glutamate that is formed in the mitochondria is, on the other hand, not excreted. Treating glutamate as two distinct pools, a cytosolic and a mitochondrial, is useful to better understand why many cancer cells rapidly consume glutamine, the precursor of glutamate. The results point toward potential drug targets that could be used to reduce growth of liver cancer cells.

Many cancer cells consume glutamine at high rates; counterintuitively, they simultaneously excrete glutamate, the first intermediate in glutamine metabolism. Glutamine consumption has been linked to replenishment of tricarboxylic acid cycle (TCA) intermediates and synthesis of adenosine triphosphate (ATP), but the reason for glutamate excretion is unclear. Here, we dynamically profile the uptake and excretion fluxes of a liver cancer cell line (HepG2) and use genome-scale metabolic modeling for in-depth analysis. We find that up to 30% of the glutamine is metabolized in the cytosol, primarily for nucleotide synthesis, producing cytosolic glutamate. We hypothesize that excreting glutamate helps the cell to increase the nucleotide synthesis rate to sustain growth. Indeed, we show experimentally that partial inhibition of glutamate excretion reduces cell growth. Our integrative approach thus links glutamine addiction to glutamate excretion in cancer and points toward potential drug targets.

A Solid-state Electrochemiluminescence Sensor for Detecting Glutathione with a Graphite-phase Carbon Nitride/Silica Modified Glassy Carbon Electrode

A solid-state electrochemiluminescence (ECL) sensor for the detection of reduced glutathione (GSH) based on a g-C₃N₄/SiO₂ modified glass carbon electrode (GCE) has been developed in this research. The g-C₃N₄, which is employed as a luminophore, is simply prepared and exhibits an excellent ECL response. Mesoporous silica hollow spheres (SiO₂) with a large specific surface area are introduced here to increase the loading amount of g-C₃N₄. Compared to a g-C₃N₄ modified GCE, the g-C₃N₄/SiO₂ modified GCE displays a much higher ECL intensity. A high enhancement effect on the ECL intensity of g-C₃N₄/SiO₂ modified GCE is obtained in the presence of GSH in the electrolyte. Moreover, the enhanced ECL intensity shows a good linear relationship to the GSH concentration in the range from 1.0 × 10^-7 to 5.0 × 10^-4 M, with a detection limit of 2.0 × 10^-8 M (6.1 ng/mL). Besides, the ECL sensor exhibits a good anti-interference ability and has been successfully applied in the detection of GSH in commercial samples. The proposed sensor provides a promising platform for life science.

Sensitively and Selectively Detect Biothiols by Using Fluorescence Method and Resonance Light Scattering Technique Simultaneously

In this paper, we designed a new quantitative and qualitive detection method for biothiols by using fluorescence method and resonance light scattering (RLS) technique. Nitrogen doped carbon quantum dots (C/N-dots) were obtained from tartaric acid and ethylenediamine by hydrothermal method, and then their morphology and optical properties were characterized by different techniques. A detection system consisting of C/N-dots and Ag⁺ complex was established. In this system, C/N-dots possessed the photoluminescent property and the Ag⁺ complex owned the RLS property, so, by combining the two luminescent properties to achieve complementary advantages, we could detect biothiols and solve the problem of distinguishing between Cys and GSH. Additionally, we optimized detecting conditions and investigated the detection mechanism of fluorescence quenching and RLS detecting. Results showed that the analytical response of fluorescence was linear in the range 0–140 μM and the detection limit (LOD) was calculated to be 6.6 μM for Cys, and the addition of GSH had no effect on fluorescence. RLS response ranges were 0–167 μM for Cys and 0–200 μM for GSH, with LOD down to 64 nM and 74 nM, respectively. Furthermore, the probe was successfully used for detecting Cys in fetal bovine serum (FBS) samples by fluorescence method, and also, by RLS technique, the content of GSH in FBS samples was detected.

Analysis of Food by High Performance Liquid Chromatography Coupled with Coulometric Detection and Related Techniques: A Review

The development of single coulometric cells in combination with high performance liquid chromatography to dual cells and to the coulometric electrode array detector is described. An overview is given about the application of these methods in food chemistry. Easily oxidizable compounds, such as phenolic substances, pesticides, or vitamins, can be determined, as well as substances with high oxidation potentials or electroinactive compounds. Substances exhibiting poor electrochemical activity can be transformed to electroactive compounds by precolumn derivatization, postcolumn photochemical reactions, postcolumn enzyme reactors, or by using the oxidative/reductive mode for coulometric electrode array detection. Furthermore, it is shown that the interesting combination of high performance liquid chromatography with electrochemistry and mass spectrometry has opened further possibilities with respect to interpretation of redox reactions, drug metabolism studies, metabolomics, and electrochemical derivatization.

Overview and recent advances in electrochemical sensing of glutathione - A review

The present paper is aimed at providing an overview of the recent advances in the electrochemical sensing of glutathione (GSH), an important electrochemically and biologically active molecule, for the period 2012-2018. Herein, the analytical performances of newly developed electrochemical methods, procedures and protocols for GSH sensing are comprehensively and critically discussed with respect to the type of method, electrodes used (new electrode modifications, advanced materials and formats), sample matrices, and basic validation parameters obtained (limit of detection, linear dynamic range, precision, selectivity/evaluation of interferences). This paper considers electrochemical methods used alone as well as the hyphenated methods with electrochemical detection (ECD), such as HPLC-ECD or CE-ECD. The practical applicability of the platforms developed for GSH detection and quantification is mostly focused on pharmaceutical and biomedical analysis. The most significant electrochemical approaches for GSH detection in multicomponent analyte samples and multicomponent matrices and for real-time in vivo GSH analysis are highlighted. The great variability in the electrochemical techniques, electrode approaches, and obtainable performance parameters, discussed in this review, brought new insights not only on current GSH and glutathione disulfide (GSSG) determinations, but, along with this, on the advances in electrochemical analysis from a more general point of view.

Dual role of BSA for synthesis of MnO2 nanoparticles and their mediated fluorescent turn-on probe for glutathione determination and cancer cell recognition

A MnO₂ nanoparticle (MnO₂ NP)-mediated fluorescent turn-on probe for sensitively and selectively detecting glutathione (GSH) and recognizing cancer cells was established in this work. MnO₂ NPs were synthesized simply and quickly through an in situ redox reaction by mixing bovine serum albumin (BSA) and KMnO₄, in which BSA served the dual roles of template and reductant. It was found that the MnO₂ NPs served as an effective energy acceptor and quenched the fluorescence intensity of carbon dots (CDs), owing to the fluorescence resonance energy transfer (FRET) process. Further, the addition of GSH triggered the decomposition of MnO₂, breaking the FRET between MnO₂ NPs and CDs and thus restoring the fluorescence intensity of CDs. Based on this mechanism, quantitative determination of GSH was performed. Under optimal conditions, a satisfactory linear range of 0.05-90 μM and limit of detection of 39 nM were obtained, and GSH content in human serum samples was detected. Moreover, taking advantage of the higher levels of GSH in cancer cells than in normal cells, the MnO₂ NP-CD probe was applied to distinguish SMMC-7721 cancer cells from L02 normal cells. The FRET was interrupted by GSH in cancer cells, and strong fluorescence was observed. This work provides a facile approach for synthesizing MnO₂ NPs, and this rapid, low-cost method with no need for reductants makes synthesis green and convenient. The MnO₂ NP-mediated fluorescent turn-on response to GSH could improve the MnO₂ nanomaterial-based biochemical analysis applications.

Metal coordination-functionalized Au–Ag bimetal SERS nanoprobe for sensitive detection of glutathione

Neocuproine-Cu functionalized Au–Ag nanoparticles as nanoprobe for detection of glutathione based on the SERS spectra changing from Neocuproine-Cu^II to Neocuproine-Cu^I.

Visual Assay of Glutathione in Vegetables and Fruits Using Quantum Dot Ratiometric Hybrid Probes

Future food safety monitoring with simple, fast, and visual methods has become increasingly important. Accordingly, this work was designed to construct a new-style dual-emission ratiometric fluorescent probe (CdSe@SiO₂@CdTe) for visual assay of glutathione (GSH) with a "turn on" strategy. After adding Hg²⁺, the red fluorescence of the outer CdTe quantum dots (QDs) was quenched through both electron transfer and ion-binding processes. Upon the addition of GSH, the red fluorescence occurred again owing to the strong affinity between GSH and Hg²⁺, whereas the inner green fluorescence of CdSe QDs was unchanged, leading to a clearly recognizable fluorescence color change (from green to orange-red). In the concentration range from 0.1 to 10 μM, the relative fluorescence intensity ratios ( I₆₁₉/ I₅₃₅) showed an excellent linear correlation with the concentration of GSH, and the detection limit was as low as 42 nM under optimal conditions. Meanwhile, the ratiometric hybrid probes were successfully applied for direct visual sensing GSH in real vegetable and fruit samples.

Quantification of cystine in human renal proximal tubule cells using liquid chromatography-tandem mass spectrometry

Nephropathic cystinosis is characterized by abnormal intralysosomal accumulation of cystine throughout the body, causing irreversible damage to various organs, particularly the kidneys. Cysteamine, the currently available treatment, can reduce lysosomal cystine and postpone disease progression. However, cysteamine poses serious side effects and does not address all of the symptoms of cystinosis. To screen for new treatment options, a rapid and reliable high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed to quantify cystine in conditionally immortalized human proximal tubular epithelial cells (ciPTEC). The ciPTEC were treated with N-ethylmaleimide, lysed and deproteinized with 15% (w/v) sulfosalicylic acid. Subsequently, cystine was measured using deuterium-labeled cystine-D4, as the internal standard. The assay developed demonstrated linearity to at least 20 μmol/L with a good precision. Accuracies were between 97.3 and 102.9% for both cell extracts and whole cell samples. Cystine was sufficiently stable under all relevant analytical conditions. The assay was successfully applied to determine cystine levels in both healthy and cystinotic ciPTEC. Control cells showed clearly distinguishable cystine levels compared with cystinotic cells treated with or without cysteamine. The method developed provides a fast and reliable quantification of cystine, and is applicable to screen for potential drugs that could reverse cystinotic symptoms in human kidney cells.

Potential role of the mitochondria as a target for the hepatotoxic effects of (-)-epigallocatechin-3-gallate in mice

Green tea and (-)-epigallocatechin-3-gallate (EGCG) have been studied for their obesity-related health effects. Many green tea extract (GTE)-based dietary supplements are commercially-available. Although green tea beverage has a long history of safe use, a growing number of case-reports have linked GTE-based supplements to incidents of hepatotoxicity. Animal studies support the hepatotoxic potential of GTE and EGCG, but the mechanisms remain unclear. Here, we examined the hepatotoxic effects of EGCG in C57BL/6J mice and evaluated changes in hepatic antioxidant response and mitochondria structure and function. Intragastric dosing with EGCG (500 - 750 mg/kg) once daily for 3 d caused hepatic inflammation, necrosis, and hemorrhage. Hepatotoxicity was associated with increased oxidative stress and decreased superoxide dismutase and glutathione peroxidase levels. Real-time PCR and transmission electron microscopy showed decreased hepatic mitochondria copy number in EGCG-treated mice. The mRNA levels of marker genes of respiratory complex I and III, sirtuin 3, forkhead box O3a, and peroxisome-EGCG-treated mice. Sirtuin 3 protein levels were also decreased by EGCG. Our data indicate the mitochondria may be a target for EGCG, and that inhibition of mitochondria function/antioxidant response may be important for the hepatotoxicity of bolus EGCG.

Effects of a six-week intraduodenal supplementation with quercetin on liver lipid metabolism and oxidative stress in peripartal dairy cows

The purpose of this study was to evaluate possible effects of quercetin (Q) on liver lipid metabolism and antioxidative status in periparturient dairy cows. The periparturient period is associated with enormous metabolic changes for dairy cows. Energy needs for incipient lactation are too high to be balanced by feed intake, leading to negative energy balance and body fat mobilization. It has been estimated that this leads to the development of fatty liver in about 50% of cows, which are at high risk for disease. Furthermore, the antioxidative status of these cows may be impaired. Quercetin is a plant flavonoid having hepatoprotective and antioxidative potential and the ability to reduce liver lipid accumulation in monogastric animals. Little information is available in regard to these effects in ruminants. To prevent microbial Q degradation in the rumen, Q was administered via a duodenal fistula to improve systemic availability. Five cows of the Q-treated group received, daily, 100 mg of quercetin dehydrate/kg BW in a 0.9% sodium chloride solution from d -20 until d 20 relative to calving, whereas 5 control (CTR) cows received only a sodium chloride solution. Blood samples were taken weekly and liver biopsies were performed in wk -4, -2, and 3 relative to calving. Cows treated with Q showed a tendency ( = 0.082) for lower liver fat content compared with CTR cows. Liver glycogen, glutathione concentrations, and relative mRNA abundance of genes related to hepatic lipid metabolism and antioxidative status as well as parameters of antioxidative status in plasma were not affected ( > 0.1) by Q supplementation. In conclusion, liver fat content in dairy cows tended to be reduced by Q supplementation, but potential underlying mechanisms remain unclear because analyzed parameters related to hepatic lipid metabolism and antioxidative defense were not altered by Q supplementation.

Elevation of GPRC5A expression in colorectal cancer promotes tumor progression through VNN-1 induced oxidative stress

The clearance of oxidative stress compounds is critical for the protection of the organism from malignancy, but how this key physiological process is regulated is not fully understood. Here, we found that the expression of GPRC5A, a well-characterized tumor suppressor in lung cancer, was elevated in colorectal cancer tissues in patients. In both cancer cell lines and a colitis-associated cancer model in mice, we found that GPRC5A deficiency reduced cell proliferation and increased cell apoptosis as well as inhibited tumorigenesis in vivo. Through RNA-Seq transcriptome analysis, we identified oxidative stress associated pathways were dysregulated. Moreover, in GPRC5A deficient cells and mouse tissues, the oxidative agents were reduced partially due to increased glutathione (GSH) level. Mechanistically, GPRC5A regulates NF-κB mediated Vanin-1 expression which is the predominant enzyme for cysteamine generation. Administration of cystamine (the disulfide form of cysteamine) in GPRC5A deficient cell lines inhibited γ-GCS activity, leading to reduction of GSH level and increase of cell growth. Taken together, our studies suggest that GPRC5a is a potential biomarker for colon cancer and promotes tumorigenesis through stimulation of Vanin-1 expression and oxidative stress in colitis associated cancer. This study revealed an unexpected oncogenic role of GPRC5A in colorectal cancer suggesting there are complicated functional and molecular mechanism differences of this gene in distinct tissues.

New Application of pH-Mediated Acid Stacking Technique for Amphoteric Compounds in Capillary Electrophoresis: Example Assay of Blood Glutathiones

Both reduced and oxidized forms of glutathiones were firstly stacked and detected using pH-mediated acid stacking method, in which glutathiones were stacked as cations and separated as anions. Factors, such as injection time, sweeping time, buffer pH, concentration of sodium chloride in sample matrix, that influenced stacking and separation were systematically studied and optimized. Under the optimum condition, the enhancement factors of ~20 times for both reduced and oxidized forms of glutathiones could be easily obtained within 20 min with satisfied sensitivities (limit of detections were 0.12 and 0.06 μmol/L for reduced and oxidized glutathione, respectively, at signal-to-noise ratio, S/N = 3), linearity range (0.3-300.0 and 0.6-300.0 μmol/L for reduced and oxidized glutathione, respectively), recoveries (>98%) and reproducibilities (relative standard deviation <5.1% for peak height). The proposed method provides an alternation way for assaying of glutathiones, as well as amphoteric compounds, in blood sample.

A dual-channel fluorescent chemosensor for discriminative detection of glutathione based on functionalized carbon quantum dots

A convenient, fluorescent dual-channel chemosensor on the basis of bis(3-pyridylmethyl)amine-functionalized carbon quantum dots (BPMA-CQDs) nanoprobe was constructed, and it can discriminatively detect glutathione from its analogues cysteine and homocysteine based on two distinctive strategies. Two distinct fluorescence responses of BPMA-CQDs probe to Cu(II) and Ag(I) were identified and further employed to achieve selective detection of Cu(II) and Ag(I) respectively. Based on the BPMA-CQDs/Cu(II) conjugate, discriminative detection of GSH was achieved in terms of correlation between the amounts of GSH and fluorescence recovery. The addition of GSH into BPMA-CQDs/Cu(II) system induces the reduction of Cu(II) to Cu(I), which could efficiently block PET process resulting in the following fluorescence recovery. Based on the BPMA-CQDs/Ag(I) conjugate, GSH assay could also be established on the basis of fluorescence response to GSH. The introduction of GSH into the preceding system triggers the competitive coordination to Ag(I) between BPMA and GSH, and silver ions are finally taken away by GSH from the probe, where the fluorescence is restored to its original weak state. Both of the detection strategies can achieve discriminative detection of GSH from Cys and Hcy. The assays showed good stability and repeatability, and covered a broad linear range of up to 13.3μM with a lowest detection limit of 42.0nM. Moreover, both of them were utilized to monitor GSH level in live cells.

A dopamine-modulated nitrogen-doped graphene quantum dot fluorescence sensor for the detection of glutathione in biological samples

A dopamine-modulated nitrogen-doped graphene quantum dot (N-GQD) system was explored to develop a fluorescent sensor based on a chemical redox mechanism for the facile, sensitive and selective detection of glutathione (GSH) in biological samples.

Switch-on fluorescence sensing of glutathione in food samples based on a graphitic carbon nitride quantum dot (g-CNQD)-Hg²⁺ chemosensor

Fluorescence sensing of specific biological molecules by artificial chemosensors is a versatile technique. In the present work, a switch-on fluorescence sensor for rapid, sensitive, and selective sensing of glutathione (GSH) in food samples was developed. This method was based on the g-CNQDs-Hg(2+) system, in which the initial fluorescence from g-CNQDs was quenched by Hg(2+) with an electron transfer process. In the presence of GSH, the fluorescence sensor was switched to the "on" state, which was attributed to a competitive affinity of Hg(2+) to GSH and the functional groups on the surface of g-CNQDs. Under the optimal conditions, the limit of detection (LOD) of 37 nM for GSH was achieved with a wide range of 0.16-16 μM. The repeatability was better than 5.3% for GSH in both standard and food samples (n = 3). Finally, this fluorescence sensor was successfully employed for the determination of GSH in various kinds of food samples with excellent recoveries. Furthermore, this application may pave a new way for fluorescence sensing of other substances in food samples.