Simultaneous determination of total homocysteine, cysteine, cysteinylglycine, and glutathione in human plasma by high-performance liquid chromatography: application to studies of oxidative stress

Fasting potentiates diclofenac-induced liver injury via inductions of oxidative/endoplasmic reticulum stresses and apoptosis, and inhibition of autophagy by depleting hepatic glutathione in mice

Diclofenac, a widely used non-steroidal anti-inflammatory drug, can cause liver damage via its metabolic activation by hepatic CYP450s and UGT2B7. Fasting can affect drug-induced liver injury by modulating the hepatic metabolism, but its influence on diclofenac hepatotoxicity is unknown. Thus, we investigated diclofenac-induced liver damage after fasting in mice, and the cellular events were examined. Male ICR mice fasted for 16 h showed the elevation of CYP3A11, but the decreases of UGT2B7, glutathione (GSH), and GSH S-transferase-μ/-π levels in the livers. Diclofenac (200 mg/kg) injection into the mice after 16-h fasting caused more significant liver damage compared to that in the diclofenac-treated fed mice, as shown by the higher serum ALT and AST activities. Diclofenac-promoted hepatic oxidative stress (oxidized proteins, 4-hydroxynonenal, and malondialdehyde), endoplasmic reticulum (ER) stress (BiP, ATF6, and CHOP), and apoptosis (cleaved caspase-3 and cleaved PARP) were enhanced by fasting. Autophagic degradation was inhibited in the diclofenac-treated fasting mice compared to that of the corresponding fed mice. The results suggest that fasting can make the liver more susceptible to diclofenac toxicity by lowering GSH-mediated detoxification; increased oxidative/ER stresses and apoptosis and suppressed autophagic degradation may be the cellular mechanisms of the aggravated diclofenac hepatotoxicity under fasting conditions.

Relative quantitation of chiral thiol compounds labeled based on isotope novel mass spectrometry probes: Monitoring of the dynamic changes of chiral thiol compounds in human urine during normal, exercise, and rest recovery states

Monitoring changes in the content of chiral thiol compounds in the human body is crucial for the early diagnosis of oxidative stress-related diseases and the exploration of their pathogenesis. To address this, we synthesized a novel isotope mass spectrometry (MS) probe, denoted as (R)-(5-(3-isothiocyanato (13C) pyrrolidin-1-yl)-5-oxopentyl) triphenylphosphonium (N13CS-OTPP), with triphenylphosphine as its parent structure. In this study, we established a new ultra-high-performance liquid chromatography high-resolution mass spectrometry (UHPLCHRMS) relative quantitative method to monitor chiral thiol compounds in human urine under varying oxidative stress conditions. This method relies on the ratio of 12C/13C isotope-labeled peak areas. To assess the chiral separation efficiency of N13CS-OTPP, we employed three types of thiol compounds (D/L-GSH, D/L-Cys, and D/L-Hcy) and observed separation degrees (Rs) ranging from 1.82 to 1.89. We further validated the accuracy and feasibility of our relative quantitative methods using D/L-Cys-as a model compound. N12C/13CS-OTPP-Cys-exhibited excellent linearity (R2 = 0.9993-0.9994) across different molar ratios (D/L-Cys = 10:1, 4:1, 2:1, 1:1, 1:2, 1:4, 1:10) and achieved a low limit of detection (LOD) of 2.5 fmol. Additionally, we monitored the dynamic changes in urine D/L-Cys-and D/L-Hcy ratios in 12 healthy volunteers (six males and six females) under various oxidative stress states. We generated fitting curves and investigated the trends in chiral thiol compounds in vivo. This study introduces a novel method for the relative quantitative monitoring of chiral thiol compounds in different oxidative stress states within the human body. It also presents a new strategy for understanding the pathogenesis of related diseases resulting from the abnormal metabolism of thiol compounds.

Oxidation Analysis of l-Cysteine with a Chiral Sensor Based on Quantum Weak Measurement

l-Cysteine, distinguished by its possession of reactive sulfhydryl groups within its molecular structure, plays a significant role in both biological systems and the pharmaceutical industry. It stands not only as a natural component integral to the constitution of glutathione but also as the principal precursor for the synthesis of l-cystine through an oxidation reaction. This study endeavors to introduce a novel approach to l-cysteine analysis, capitalizing on its optical activity, whereby an optical rotation detection system grounded in the principles of quantum weak measurement is proffered. The optical rotation angle corresponding to the concentration of chiral solutions can be accurately ascertained through spectral analysis. In practical implementation, a chiral sensing system, boasting a sensitivity of 372 nm/rad, was meticulously constructed, leveraging the concept of weak value amplification. Then, the real-time monitoring of chemical reactions involving l-cysteine and dimethyl sulfoxide was performed. Under the specific experimental conditions outlined in this investigation, it was observed that the oxidation process culminated within approximately 12 h. The application of weak measurement-based chiral sensors holds immense potential, providing robust technical support for real-time monitoring in fields such as chiral analysis and the synthesis of chiral pharmaceutical compounds.

Real-time monitoring of endogenous cysteine in LPS-induced oxidative stress process with a novel lysosome-targeted fluorescent probe

Cysteine (Cys), one of essential small-molecule-based biothiols in the human body, contributes to the regulation of redox reactions and is closely associated with many physiological and pathological metabolic processes. Herein, a novel fluorescent probe, hydroxyphenyl-conjugated benzothiazole (HBT-Cys) capable of detecting Cys was constructed, where acrylate served as the recognition group and hydroxyphenyl-linked benzothiazole acted as the fluorophore. The fluorescence of the probe was negligible in the absence of Cys, and an intense blue fluorescence was observed upon addition of Cys. The Cys-sensing mechanism could be ascribed to the Cys-involved hydrolysis reaction with acrylate, leading to light up the emission at 430 nm with about 80-fold enhancement. In addition, HBT-Cys exhibited a fast response time, remarkable selectivity and low detection limit. HBT-Cys also worked well in real-time monitoring of Cys in three different food samples (wolfberry, hawthorn, and red dates). Importantly, our probe had an excellent lysosomes-targeted ability, which was successfully employed to real-time visualize the fluctuation of both exogenous and endogenous Cys in living cells and zebrafish under lipopolysaccharide (LPS)-induced oxidative stress. Hopefully, the work shown here provides a potent candidate for the real-time tracking of Cys fluctuations in various biological samples.

A Clinically Relevant Dosage of Mitoxantrone Disrupts the Glutathione and Lipid Metabolic Pathways of the CD-1 Mice Brain: A Metabolomics Study

Long-term cognitive dysfunction, or "chemobrain", has been observed in cancer patients treated with chemotherapy. Mitoxantrone (MTX) is a topoisomerase II inhibitor that binds and intercalates with DNA, being used in the treatment of several cancers and multiple sclerosis. Although MTX can induce chemobrain, its neurotoxic mechanisms are poorly studied. This work aimed to identify the adverse outcome pathways (AOPs) activated in the brain upon the use of a clinically relevant cumulative dose of MTX. Three-month-old male CD-1 mice were given a biweekly intraperitoneal administration of MTX over the course of three weeks until reaching a total cumulative dose of 6 mg/kg. Controls were given sterile saline in the same schedule. Two weeks after the last administration, the mice were euthanized and their brains removed. The left brain hemisphere was used for targeted profiling of the metabolism of glutathione and the right hemisphere for an untargeted metabolomics approach. The obtained results revealed that MTX treatment reduced the availability of cysteine (Cys), cysteinylglycine (CysGly), and reduced glutathione (GSH) suggesting that MTX disrupts glutathione metabolism. The untargeted approach revealed metabolic circuits of phosphatidylethanolamine, catecholamines, unsaturated fatty acids biosynthesis, and glycerolipids as relevant players in AOPs of MTX in our in vivo model. As far as we know, our study was the first to perform such a broad profiling study on pathways that could put patients given MTX at risk of cognitive deficits.

Whole Body Distribution of Labile Coenzymes and Antioxidants in a Mouse Model as Visualized Using 1H NMR Spectroscopy

Coenzyme A, acetyl coenzyme A, coenzymes of cellular energy, coenzymes of redox reactions, and antioxidants mediate biochemical reactions fundamental to the functioning of all living cells. There is an immense interest in measuring them routinely in biological specimens to gain insights into their roles in cellular functions and to help characterize the biological status. However, it is challenging to measure them ex vivo as they are sensitive to specimen harvesting, extraction, and measurement conditions. This challenge is largely underappreciated and carries the risk of grossly inaccurate measurements that lead to incorrect inferences. To date, several efforts have been focused on alleviating this challenge using NMR spectroscopy. However, a comprehensive solution for the measurement of the compounds in a wide variety of biological specimens is still lacking. As a part of addressing this challenge, we demonstrate here that the total pool of each group of unstable metabolites offers a starting place for the representation of labile metabolites in biological specimens. Based on this approach, in this proof-of-concept study, we determine the distribution of the labile compounds in different organs including heart, kidney, liver, brain, and skeletal muscle of a mouse model. The results were independently validated using different specimens and a different metabolite extraction protocol. Further, we show that both stable and unstable metabolites were distributed differentially in different organs, which signifies their differential functional roles, the knowledge of which is currently lacking for many metabolites. Intriguingly, the concentration of taurine, an amino sulfonic acid, in skeletal muscle is >30 mM, which is the highest for any metabolite in a mammalian tissue known to date. To the best of our knowledge, this is the first study to profile the whole body distribution of the labile and other high-concentration metabolites using NMR spectroscopy. The results may pave ways for gaining new insights into cellular functions in health and diseases.

Effects of low-dose B vitamins plus betaine supplementation on lowering homocysteine concentrations among Chinese adults with hyperhomocysteinemia: a randomized, double-blind, controlled preliminary clinical trial

PURPOSE

To test the hypothesis that daily supplementation with low-dose B vitamins plus betaine could significantly reduce plasma homocysteine concentrations in Chinese adults with hyperhomocysteinemia and free from background mandatory folic acid fortification.

METHODS

One hundred apparently healthy adults aged 18-65 years with hyperhomocysteinemia were recruited in South China from July 2019 to June 2021. They were randomly assigned to either the supplement group (daily supplementation: 400 μg folic acid, 8 mg vitamin B₆, 6.4 μg vitamin B₁₂ and 1 g betaine) or the placebo group for 12 weeks. Fasting venous blood was collected at baseline, week 4 and week 12 to determine the concentrations of homocysteine, folate, vitamin B₁₂ and betaine. Generalized estimation equations were used for statistical analysis.

RESULTS

Statistically significant increments in blood concentrations of folate, vitamin B₁₂ and betaine after the intervention in the supplement group indicated good participant compliance. At baseline, there were no significant differences in plasma homocysteine concentration between the two groups (P = 0.265). After 12-week supplementation, compared with the placebo group, there was a significant reduction in plasma homocysteine concentrations in the supplement group (mean group difference - 3.87; covariate-adjusted P = 0.012; reduction rate 10.1%; covariate-adjusted P < 0.001). In the supplement group, the decreased concentration of plasma homocysteine was associated with increments of blood concentrations of both folate (β = -1.680, P = 0.004) and betaine (β = -1.421, P = 0.020) after 12 weeks of supplementation.

CONCLUSIONS

Daily supplementation with low-dose B vitamins plus betaine for 12 weeks effectively decreased plasma homocysteine concentrations in Chinese adults with hyperhomocysteinemia.

TRIAL REGISTRATION

This trial was registered at clinicaltrials.gov as NCT03720249 on October 25, 2018. Website: https://clinicaltrials.gov/ct2/show/NCT03720249 .

Hydrogen-Deuterium Addition and Exchange in N-Ethylmaleimide Reaction with Glutathione Detected by NMR Spectroscopy

Glutathione (GSH) is an important and ubiquitous thiol compound abundantly present in virtually every living cell. It is a powerful antioxidant critically required to protect cells from oxidative damage and free radical injury. Its quantification in ex vivo analysis remains a major challenge because it spontaneously oxidizes to form glutathione disulfide. N-Ethylmaleimide (NEM) is a well-known Michael acceptor, which reacts rapidly and irreversibly with thiol and prevents disulfide bond formation. Based on thiol conjugation to NEM, recently, the concentration of GSH was determined in human blood using NMR spectroscopy [Anal. Chem, 2021, 93(44): 14844-14850]. It was found that hydrogen-deuterium addition and exchange occur during the thiol-maleimide reaction as well as NMR analysis, generating a series of poorly explored diastereomers/isotopomers. Here, we establish a general NMR approach to identify the thiosuccinimide diastereomers/isotopomers derived from the thiol-maleimide reaction. The thiol-Michael addition reaction was conducted for GSH and another thiol compound, cysteine, separately, using D2O and H2O. The conjugates were characterized by 1H/13C 1D/2D NMR under different solvent, buffer, and pH conditions. The Michael addition combined with the H/D exchange formed twelve unique diastereomers/isotopomers. NMR measurements allowed the distinct assignment of all structures in solutions and quantification of H/D addition and exchange. Interestingly, the deuterium exchange rate was dependent on structure, pH, and buffer. The elucidation of the thiol-maleimide reaction and H/D exchange mechanism can potentially impact areas including metabolomics, small molecule synthesis, and bioconjugation chemistry.

Activation of the eIF2α-ATF4 Pathway by Chronic Paracetamol Treatment Is Prevented by Dietary Supplementation with Cysteine

Chronic treatment with acetaminophen (APAP) induces cysteine (Cys) and glutathione (GSH) deficiency which leads to adverse metabolic effects including muscle atrophy. Mammalian cells respond to essential amino acid deprivation through the phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α). Phosphorylated eIF2α leads to the recruitment of activating transcription factor 4 (ATF4) to specific CCAAT/enhancer-binding protein-ATF response element (CARE) located in the promoters of target genes. Our purpose was to study the activation of the eIF2α-ATF4 pathway in response to APAP-induced Cys deficiency, as well as the potential contribution of the eIF2α kinase GCN2 and the effect of dietary supplementation with Cys. Our results showed that chronic treatment with APAP activated both GCN2 and PERK eIF2α kinases and downstream target genes in the liver. Activation of the eIF2α-ATF4 pathway in skeletal muscle was accompanied by muscle atrophy even in the absence of GCN2. The dietary supplementation with cysteine reversed APAP-induced decreases in plasma-free Cys, liver GSH, muscle mass, and muscle GSH. Our new findings demonstrate that dietary Cys supplementation also reversed the APAP-induced activation of GCN2 and PERK and downstream ATF4-target genes in the liver.

Detection of glutathione, cysteine, and homocysteine by online derivatization-based electrospray mass spectrometry

RATIONALE

Electrospray ionization mass spectrometry (ESI-MS) is one of the most popular techniques for obtaining structural information, which is commonly used in bioanalysis and clinical diagnostics. However, for the detection of complicated samples with high reactivities (such as reactive sulfur species, RSS), traditional ESI-MS usually suffers from overlapped and inaccurate signals. In this study, based on the multiphase flow of extractive electrospray ionization (MF-EESI), an ambient MS technique of online derivatization was proposed to detect thiols without any other sample pretreatment.

METHODS

RSS molecules and the derivatization reagent of 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) were introduced into the internal and innermost capillary of the MF-EESI system, respectively. By a high-velocity nebulizing stream of N₂ gas through an external capillary, both flows of innermost biothiols and internal NBD-Cl were electrosprayed and mixed for online reactions. Therefore, the fast derivatization of thiols was used to generate stable ionized derivatives for MS detection.

RESULTS

By evaluating the changes in MS signals before and after the derivatization, the ions of RSS were identified simply and correctly. Without any sample pretreatment, the fast detection of cysteine, homocysteine, and glutathione has been achieved in the complicated samples.

CONCLUSIONS

The present online derivatization-based MF-EESI was successfully used for fast, simple, and accurate detection of biothiols. This presented a potential pathway for the fast identification of thiols in complicated samples.

Glutathione production by Saccharomyces cerevisiae: current state and perspectives

Glutathione (L-γ-glutamyl-cysteinyl-glycine, GSH) is a tripeptide synthesized through consecutive enzymatic reactions. Among its several metabolic functions in cells, the main one is the potential to act as an endogenous antioxidant agent. GSH has been the focus of numerous studies not only due to its role in the redox status of biological systems but also due to its biotechnological characteristics. GSH is usually obtained by fermentation and shows a variety of applications by the pharmaceutical and food industry. Therefore, the search for new strategies to improve the production of GSH during fermentation is crucial. This mini review brings together recent papers regarding the principal parameters of the biotechnological production of GSH by Saccharomyces cerevisiae. In this context, aspects, such as the medium composition (amino acids, alternative raw materials) and the use of technological approaches (control of osmotic and pressure conditions, magnetic field (MF) application, fed-batch process) were considered, along with genetic engineering knowledge, trends, and challenges in viable GSH production. KEY POINTS: • Saccharomyces cerevisiae has shown potential for glutathione production. • Improved technological approaches increases glutathione production. • Genetic engineering in Saccharomyces cerevisiae improves glutathione production.

Extending the Scope of 1H NMR-Based Blood Metabolomics for the Analysis of Labile Antioxidants: Reduced and Oxidized Glutathione

Glutathione is a ubiquitous cellular antioxidant, which is critically required to protect cells from oxidative damage and free radical injury. It is practically impossible to analyze glutathione in its native form after isolation from biological mixtures since the active form (reduced glutathione, GSH) spontaneously gets converted to the oxidized form (oxidized glutathione, GSSG). To address this challenge, numerous highly sensitive detection methods, including mass spectrometry, have been used in conjunction with derivatization to block the oxidation of GSH. Efforts so far to quantitate GSH and GSSG using the nuclear magnetic resonance (NMR) spectroscopy method have remained unsuccessful. With a focus on addressing this challenge, in this study, we describe an extension to our recent whole blood analysis method [ Anal. Chem. 2017, 89, 4620-4627] that includes the important antioxidants GSH and GSSG. Fresh and frozen human whole blood specimens as well as standard GSH and GSSG were comprehensively investigated using NMR without and with derivatization using N-ethylmaleimide (NEM). NMR experiments detect two diastereomers, distinctly, for the derivatized GSH and enable the analysis of both GSH and GSSG in human whole blood with an accuracy of >99%. Interestingly, the excess (unreacted) NEM used for blocking the GSH can be removed from the samples during a drying step after extraction, with no need for additional processing. This is an important characteristic that offers an added advantage for simultaneous analysis of the antioxidants (GSH and GSSG), redox coenzymes (oxidized nicotinamide adenine dinucleotide (NAD⁺), reduced nicotinamide adenine dinucleotide (NADH), oxidized nicotinamide adenine dinucleotide phosphate (NADP⁺), reduced nicotinamide adenine dinucleotide phosphate (NADPH)), energy coenzymes (adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP)), and a large number of other blood metabolites using the same one-dimensional (1D) NMR spectrum. The presented method broadens the scope of global metabolite profiling and adds a new dimension to NMR-based blood metabolomics. Further, the method demonstrated here for human blood can be extended to virtually any biological specimen.

Simultaneous Determination of Chiral Thiol Compounds and Monitoring of Dynamic Changes in Human Urine after Drinking Chinese Korean Ethnic Rice Wine

Chinese Korean ethnic rice wine, a traditional fermented wine made from rice or corn, has antioxidant and antihypertensive activities. Although the determination of amino acids and other nutrients in rice wine has been reported, the existence of chiral thiol compounds has not been published in the literature. Therefore, we established a highly sensitive and selective ultrahigh-performance liquid chromatography-high-resolution mass spectrometry method for simultaneous determination and chiral separation of dl-Cys-GSH, dl-Cys-Cys, and dl-Cys-Hcy based on (R)-(5-(3-isothiocyanatopyrrolidin-1-yl)-5-oxopentyl) triphenylphosphonium derivatization. Three thiol diastereomers were completely separated on a YMC Triart C18 (2.0 × 150 mm, 1.9 μm) column with a resolution value (Rs) ≥ 1.52. The correlation coefficients were ≥0.9996, limit of detection was 2.40-7.20 fmol, and mean recoveries were 83.33-98.59%. Furthermore, fitted curves for dynamic changes in three kinds of chiral thiols in 10 human urine samples after drinking rice wine were drawn. Meanwhile, the metabolic changes in d/l-thiol compounds in human urine were investigated.

A Mechanistic-Based and Non-invasive Approach to Quantify the Capability of Kidney to Detoxify Cysteine-Disulfides

Our general goal was to non-invasively evaluate kidney tubular dysfunction. We developed a strategy based on cysteine (Cys) disulfide stress mechanism that underlies kidney dysfunction. There is scarce information regarding the fate of Cys-disulfides (CysSSX), but evidence shows they might be detoxified in proximal tubular cells by the action of N-acetyltransferase 8 (NAT8). This enzyme promotes the addition of an N-acetyl moiety to cysteine-S-conjugates, forming mercapturates that are eliminated in urine. Therefore, we developed a strategy to quantify mercapturates of CysSSX in urine as surrogate of disulfide stress and NAT8 activity in kidney tubular cells. We use a reduction agent for the selective reduction of disulfide bonds. The obtained N-acetylcysteine moiety of the mercapturates from cysteine disulfides was monitored by fluorescence detection. The method was applied to urine from mice and rat as well as individuals with healthy kidney and kidney disease.

Metabolic Profiling Analysis Reveals the Potential Contribution of Barley Sprouts against Oxidative Stress and Related Liver Cell Damage in Habitual Alcohol Drinkers

Chronic excessive alcohol consumption is associated with multiple liver defects, such as steatosis and cirrhosis, mainly attributable to excessive reactive oxygen species (ROS) production. Barley sprouts (Hordeum vulgare L.) contain high levels of polyphenols that may serve as potential antioxidants. This study aimed to investigate whether barley sprouts extract powder (BSE) relieves alcohol-induced oxidative stress and related hepatic damages in habitual alcohol drinkers with fatty liver. In a 12-week randomized controlled trial with two arms (placebo or 480 mg/day BSE; n = 76), we measured clinical markers and metabolites at the baseline and endpoint to understand the complex molecular mechanisms. BSE supplementation reduced the magnitude of ROS generation and lipid peroxidation and improved the glutathione antioxidant system. Subsequent metabolomic analysis identified alterations in glutathione metabolism, amino acid metabolism, and fatty acid synthesis pathways, confirming the role of BSE in glutathione-related lipid metabolism. Finally, the unsupervised machine learning algorithm indicated that subjects with lower glutathione reductase at the baseline were responders for liver fat content, and those with higher fatigue and lipid oxidation were responders for γ-glutamyl transferase. These findings suggest that BSE administration may protect against hepatic injury by reducing oxidative stress and changing the metabolism in habitual alcohol drinkers with fatty liver.

Simultaneous determination of three endogenous chiral thiol compounds in serum from humans at normal and stress states using ultrahigh-performance liquid chromatography coupled to quadrupole-Orbitrap high resolution mass spectrometry

Measurement of chiral thiol compounds such as glutathione (GSH), cysteine (Cys), and homocysteine (Hcy) in human serum plays an important role in the early diagnosis and warning of cardiovascular disease, neurodegenerative disease, and cancer. We developed a novel chiral mass spectrometry derivatization reagent, (R)-(5-(3-isothiocyanatopyrrolidin-1-yl)-5-oxopentyl) triphenylphosphonium (NCS-OTPP), with triphenylphosphine (TPP) as a basic structure carrying a permanent positive charge for the diastereomeric separation of chiral thiol compounds by ultrahigh-performance liquid chromatography coupled to quadrupole-Orbitrap high resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS). A novel method was developed for simultaneous determination of three kinds of chiral thiol compounds based on the NCS-OTPP derivatization method. Three kinds of chiral thiol compounds on a YMC Triart C18 (2.0 × 150 mm, 1.9 μm) column with Rs were 1.56-1.68. The protonated precursor to product ion transitions monitored for GSH was m/z 780.16→747.24/473.18, Cys was m/z 594.20→561.18/473.18, and Hcy was m/z 608.21→575.19/473.18. An excellent linearity for all the analytes with correlation coefficients ≥ 0.9995 and suitable precision with inter-day and intra-day coefficients of variation RSDs was 0.83-4.06% and 0.95-3.11%. Satisfactory accuracy with recoveries between 83.73 and 103.35% was observed. The limit of detection (S/N = 3) was 2.4-7.2 fmol. Furthermore, the method was successfully applied to the simultaneous determination of three kinds of free and total thiol compounds in serum from 10 healthy volunteers at normal and stress states.

Long-term effect of parental selenium supplementation on the one-carbon metabolism in rainbow trout (Oncorhynchus mykiss) fry exposed to hypoxic stress

This study evaluated how different forms of selenium (Se) supplementation into rainbow trout broodstock diets modified the one-carbon metabolism of the progeny after the beginning of exogenous feeding and followed by hypoxia challenge. The progeny of three groups of rainbow trout broodstock fed either a control diet (Se level: 0·3 µg/g) or a diet supplemented with inorganic sodium selenite (Se level: 0·6 µg/g) or organic hydroxy-selenomethionine (Se level: 0·6 µg/g) was cross-fed with diets of similar Se composition for 11 weeks. Offspring were sampled either before or after being subjected to an acute hypoxic stress (1·7 mg/l dissolved oxygen) for 30 min. In normoxic fry, parental Se supplementation allowed higher glutathione levels compared with fry originating from parents fed the control diet. Parental hydroxy-selenomethionine treatment also increased cysteine and cysteinyl-glycine concentrations in fry. Dietary Se supplementation decreased glutamate-cysteine ligase (cgl) mRNA levels. Hydroxy-selenomethionine feeding also lowered the levels of some essential free amino acids in muscle tissue. Supplementation of organic Se to parents and fry reduced betaine-homocysteine S-methyltransferase (bhmt) expression in fry. The hypoxic stress decreased whole-body homocysteine, cysteine, cysteinyl-glycine and glutathione levels. Together with the higher mRNA levels of cystathionine beta-synthase (cbs), a transsulphuration enzyme, this suggests that under hypoxia, glutathione synthesis through transsulphuration might have been impaired by depletion of a glutathione precursor. In stressed fry, S-adenosylmethionine levels were significantly decreased, but S-adenosylhomocysteine remained stable. Decreased bhmt and adenosylmethionine decarboxylase 1a (amd1a) mRNA levels in stressed fry suggest a nutritional programming by parental Se also on methionine metabolism of rainbow trout.

Recent developments in voltammetric and amperometric sensors for cysteine detection

This review article aims to provide an overview of the recent advances in the voltammetric and amperometric sensing of cysteine (Cys). The introduction summarizes the important role of Cys as an essential amino acid, techniques for its sensing, and the utilization of electrochemical methods and chemically modified electrodes for its determination. The main section covers voltammetric and amperometric sensing of Cys based on glassy carbon electrodes, screen printed electrodes, and carbon paste electrodes, modified with various electrocatalytic materials. The conclusion section discusses the current challenges of Cys determination and the future perspectives.

Controlled "off-on" fluorescent probe for the specific detection of hyperhomocysteinemia

Hyperhomocysteinemia is an established risk factor for atherosclerosis and vascular disease. Therefore, designing a hyperhomocysteinemia specific probe is of great significance for the early warning of cardiovascular diseases. However, developing probes that can efficiently and specifically recognize homocysteine (Hcy) remains a tremendous challenge. Therefore, we designed an Hcy-specific fluorescent probe (HSFP) with excellent selectivity and anti-interference capability. Interestingly, this probe can automatically “off–on” in water solution, but the fluorescence of HSFP remains “off” when Hcy is present in the solution. The spectroscopic data demonstrated that the fluorescence of HSFP attenuated 13.8 folds toward Hcy in water without interference from other biothiols and amino acids. Furthermore, HSFP can sensitively reflect the change of Hcy content in cells. Therefore, HSFP was further applied to detect hyperhomocysteinemia in vivo with high efficiency. In summary, we have developed an Hcy-specific fluorescent probe to efficiently detect Hcy in vivo and in vitro, which may contribute to basic or clinical research.

An Hcy-specific fluorescent probe (HSFP) with excellent selectivity and anti-interference capability was developed for the detection of hyperhomocysteinemia.

Copolymer-Based Fluorescence Nanosensor for In Situ Imaging of Homocysteine in the Liver and Kidney of Diabetic Mice

Homocysteine (Hcy) is one of the important biomarkers of clinical diagnosis, which is closely related to the occurrence and development of many diseases. Current analysis methods have difficulties in detecting Hcy in cells and living organisms. As a powerful technique, fluorescence methods combined the laser confocal imaging technology can achieve real-time visual tracking in cells and in vivo. Herein, we establish a conjugated copolymer-based fluorescence nanosensor (DPA-PFNP-Cu(II)) using the connected 2,7-dibromofluorene and 4,7-bis (2-bromothiophen-5-yl)-2-1-3-benzothiadiazole as the main chain. The competitive coordination between Hcy and Cu(II) allows the fluorescence of the polymer off to on. Finally, the nanosensor is applied for in situ imaging of Hcy levels in the kidney and liver of diabetic mice and is found that Hcy levels were positively correlated with the degree of diabetes. Notably, the depth of tissue penetration of the nanosensor enables Hcy detection of the liver and kidney through in vivo imaging without damage. Two-photon imaging and in vivo imaging achieve consistent results, which correct each other, improving the accuracy of the test result. The present works provide a new imaging technique for studying the occurrence and development of diabetes and screening of new drugs for treatment at the living level.

Optimized Protocol for the In Situ Derivatization of Glutathione with N-Ethylmaleimide in Cultured Cells and the Simultaneous Determination of Glutathione/Glutathione Disulfide Ratio by HPLC-UV-QTOF-MS

Glutathione (GSH) and glutathione disulfide (GSSG) are commonly used to assess the oxidative status of a biological system. Various protocols are available for the analysis of GSH and GSSG in biomedical specimens. In this study, we present an optimized protocol for the in situ derivatization of GSH with N-ethylmaleimide (NEM) to prevent GSH autooxidation, and thus to preserve the GSH/GSSG ratio during sample preparation. The protocol comprises the incubation of cells in NEM containing phosphate buffered saline (PBS), followed by metabolite extraction with 80% methanol. Further, to preserve the use of QTOF-MS, which may lack the linear dynamic range required for the simultaneous quantification of GSH and GSSG in non-targeted metabolomics, we combined liquid chromatographic separation with the online monitoring of UV absorbance of GS-NEM at 210 nm and the detection of GSSG and its corresponding stable isotope-labeled internal standard by QTOF-MS operated with a 10 Da Q1 window. The limit of detection (LOD) for GS-NEM was 7.81 µM and the linear range extended from 15.63 µM to 1000 µM with a squared correlation coefficient R² of 0.9997. The LOD for GSSG was 0.001 µM, and the lower limit of quantification (LLOQ) was 0.01 µM, with the linear (R² = 0.9994) range extending up to 10 µM. The method showed high repeatability with intra-run and inter-run coefficients of variation of 3.48% and 2.51% for GS-NEM, and 3.11% and 3.66% for GSSG, respectively. Mean recoveries of three different spike-in levels (low, medium, high) of GSSG and GS-NEM were above 92%. Finally, the method was applied to the determination of changes in the GSH/GSSG ratio either in response to oxidative stress in cells lacking one or both monocarboxylate transporters MCT1 and MCT4, or in adaptation to the NADPH (nicotinamide adenine dinucleotide phosphate) consuming production of D-2-hydroxyglutarate in cells carrying mutations in the isocitrate dehydrogenase genes IDH1 and IDH2.

Colorimetric determination of cysteine by a paper-based assay system using aspartic acid modified gold nanoparticles

A method is described for cysteine (Cys) determination on paper-based analytical devices using aspartic acid modified gold nanoparticles (Asp-AuNPs). The Asp-AuNPs were characterized by their size, zeta potential, and UV-visible absorption spectrum. After the addition of Cys, it will interact with Asp-AuNPs selectively and leads to the aggregation of Asp-AuNPs. A color change from red to blue can be observed on the paper-based analytical devices. The results were recorded using a cell phone and subsequently analyzed using the Photoshop software. The ratiometric color intensity at red channel and blue channel (Red/Blue) increased linearly in the range 99.9-998.7 μM for Cys (R = 0.9984), and the limit of detection was 1.0 μM. The effects of assay conditions have been investigated and are discussed. The Cys concentration was determined as (0.27 ± 0.02 mM) in human plasma, and the recovery was from 99.2 to 101.1%. Graphical abstract Schematic representation of the paper-based assay system using aspartic acid modified gold nanoparticles (Asp-AuNPs). The ratiometric color intensity method was used for the cysteine (Cys) determination.

A paper-based colorimetric assay system for sensitive cysteine detection using a fluorescent probe

Sensitive analysis of Cys on a paper-based platform via colorimetric detection which abandons sophisticated instruments.

Diffusion-Based Recycling of Flavins Allows Shewanella oneidensis MR-1 To Yield Energy from Metal Reduction Across Physical Separations

We fabricated a microfluidic reactor with a nanoporous barrier to characterize electron transport between Shewanella oneidensis MR-1 and the metal oxide birnessite across a physical separation. Real-time quantification of electron flux across this barrier by strains with different electron transfer capabilities revealed that this bacterium exports flavins to its surroundings when faced with no direct physical access to an electron acceptor, allowing it to reduce metals at distances exceeding 60 μm. An energy balance indicates that flavins must be recycled for S. oneidensis MR-1 to yield energy from lactate oxidation coupled to flavin reduction. In our system, we find that flavins are recycled between 24 and 60 times depending on flow conditions. This energy saving strategy, which until now had not been systematically tested or captured in environmentally relevant systems, suggests that electron shuttling microorganisms have the capacity to access and reduce metals in physically distant or potentially toxic microenvironments (i.e., pores with soluble and transiently sorbed toxins) where direct contact is limited or unfavorable. Our results challenge the prediction that diffusion-based electron shuttling is only effective across short distances and may lead to improved bioremediation strategies or advance biogeochemical models of electron transfer in anaerobic sediments.

Insect Meal as Alternative Protein Source Exerts Pronounced Lipid-Lowering Effects in Hyperlipidemic Obese Zucker Rats

BACKGROUND

Specific dietary proteins exert strong health-related effects compared with casein.

OBJECTIVE

Herein, the hypothesis was tested using screening and conventional biochemical and molecular biological techniques that protein-rich insect meal compared with casein influences metabolic health in hyperlipidemic rats.

METHODS

A 4-wk feeding trial with male, 8-wk-old homozygous obese Zucker rats (n = 36) and male, 8-wk-old heterozygous lean Zucker rats (n = 12) was performed. Obese rats were randomly divided into 3 obese groups (OC, OI50, and OI100) of 12 rats each and lean rats served as a lean control group (LC). LC and OC were fed a control diet with 20% casein as protein source, whereas in OI50 and OI100 50% and 100% of the casein, respectively, was replaced isonitrogenously by insect meal from Tenebrio molitor L. All data were analyzed by 1-factor ANOVA, except transcriptomic data which were analyzed by groupwise comparisons with the OC group.

RESULTS

Transcript profiling revealed a coordinated inhibition by -17% to -521% and -37% to -859% of genes involved in fatty acid, triacylglycerol (TG), and cholesterol biosynthesis in the livers of OI100 and OI50, respectively, compared with OC (P < 0.05). Enzyme activities of fatty acid synthase, glucose-6 phosphate dehydrogenase, and 3-hydroxy-3-methylglutaryl-coenzyme-A reductase in the liver were 100-150% greater in OC compared with LC, but reduced by 50-60% in OI100 compared with OC (P < 0.05), to the same level as in LC. Liver and plasma concentrations of TG and cholesterol were 250-1000%, 30-800%, and 40-600% higher in OC, OI50, and OI100, respectively, than in LC (P < 0.05), but 40-60% and 20-60% lower in OI100 and OI50, respectively, than in group OC (P < 0.05). Plasma and liver concentrations of homocysteine were 20-30% lower in group OI100 than in group OC (P < 0.05).

CONCLUSION

Insect meal exerts pronounced lipid-lowering effects in hyperlipidemic rats and, thus, might be useful for hyperlipidemic individuals.

The Antisteatotic and Hypolipidemic Effect of Insect Meal in Obese Zucker Rats is Accompanied by Profound Changes in Hepatic Phospholipid and 1-Carbon Metabolism

SCOPE

The hypothesis is tested that insect meal, which has a low methionine content, reduces the hepatic phosphatidylcholine (PC):phosphatidylethanolamine (PE) ratio, which is a critical determinant of hepatic lipid synthesis, by decreasing availability of the methionine metabolite S-adenosylmethionine (SAM).

METHODS AND RESULTS

Obese rats (n = 24) are randomly divided into two groups (Obese Casein and Obese Insect) of 12 rats each. In addition, lean rats (n = 12) are used as control group (LC). Groups LC and OC receive a control diet with casein as protein source, whereas in the OI group, casein is replaced isonitrogenously by insect meal, which is found to be less digestible (-12% units). Plasma and liver concentrations of lipids and hepatic expression of lipid synthesizing genes are reduced in the OI group compared to the OC group. Plasma and liver concentration of PC and the PC:PE ratio are decreased in the OI group compared to the OC group, while hepatic concentration of SAM and the hepatic SAM:S-adenosylhomocysteine (SAH) ratio is lower in the OI group than in the OC group.

CONCLUSION

The decrease of the hepatic PC:PE ratio is probably a key mechanism explaining the pronounced antisteatotic and hypolipidemic action of insect meal in obese rats.

A ratiometric fluorescent BODIPY-based probe for rapid and highly sensitive detection of cysteine in human plasma

Biological thiols, especially low molecular weight thiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play a pivotal role in physiological and pathological systems. Thus, the detection of biothiols is highly important for early diagnosis of diseases and evaluation of disease progression. Herein, we developed a highly selective and sensitive ratiometric fluorescent 8-Cl BODIPY-based probe with high fluorescence quantum yields. The probe displayed a sensitive response to Cys and Hcy over other biothiols, which can be visualized colorimetrically and/or fluorescently. The probe was successfully applied to detect Cys in human plasma, demonstrating its great value for practical application in biological sample analysis.

In situ sulfur-doped graphitic carbon nitride nanosheets with enhanced electrogenerated chemiluminescence used for sensitive and selective sensing of l-cysteine

In this study, in situ sulfur-doped carbon nitride nanosheets (S-g-C₃N₄ NSs) are used for the sensitive and selective sensing of l-cysteine (l-Cys) based on the competitive coordination chemistry of Cu²⁺ between l-Cys and S-g-C₃N₄ NSs.

Constructing a far-red to near-infrared fluorescent probe for highly specific detection of cysteine and its bioimaging applications in living cells and zebrafish

A novel far-red to near-infrared fluorescent probe for highly specific detection of cysteine without interference.

Alleviation of paraquat-induced oxidative lung injury by betaineviaregulation of sulfur-containing amino acid metabolism despite the lack of betaine-homocysteine methyltransferase (BHMT) in the lung

Betaine regulates sulfur-containing amino acid metabolism in the lung despite the lack of BHMT and increases pulmonary antioxidant capacity.

A near-infrared Nile red fluorescent probe for the discrimination of biothiols by dual-channel response and its bioimaging applications in living cells and animals

Biothiols, including cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and H₂S, play important roles in human physiological processes.

A coumarin-based dual optical probe for homocysteine with rapid response time, high sensitivity and selectivity

In this study, a new coumarin-based fluorescent and chromogenic dual channel probe (DC) was used for the selective detection of homocysteine (Hcy) over other amino acids, especially for cysteine (Cys) and glutathione (GSH). When Hcy is present in the solution, the remarkable fluorescence enhancement and obvious blue shift in UV-vis spectra can be observed. In addition, the color change from purple to yellow can be observed clearly by unaided eyes. This probe DC has fast response time, excellent sensitivity and selectivity to Hcy. A linear relationship exists between the ratio of emissions at 486 and 625 nm, and Hcy can be detected in a wide concentration range (0-200 μM). The signal-to-background ratio of fluorescence at 486 nm can reach 8.4, and the detection limit is calculated to be 3.5 µM. The response mechanism is proved to be the Michael addition reaction by Hcy. Preliminary results on cell imaging enable the practical application of Hcy tracing in living cells.

Tunicamycin-Induced ER Stress is Accompanied with Oxidative Stress via Abrogation of Sulfur Amino Acids Metabolism in the Liver

Endoplasmic reticulum (ER) stress is involved in non-alcoholic fatty liver disease (NAFLD), but the relationship between oxidative stress, another well-known risk factor of NAFLD, and ER stress has yet to be elucidated. In this study, we treated mice with tunicamycin (TM) (2 mg/kg body weight) for 48 h to induce ER stress in the liver and examined the metabolic pathway that synthesizes the endogenous antioxidant, glutathione (GSH). Tunicamycin (TM) treatment significantly increased mRNA levels of CHOP and GRP78, and induced lipid accumulation in the liver. Lipid peroxidation in the liver tissue also increased from TM treatment (CON vs. TM; 3.0 ± 1.8 vs. 11.1 ± 0.8 nmol MDA/g liver, p < 0.001), which reflects an imbalance between the generation of reactive substances and antioxidant capacity. To examine the involvement of GSH synthetic pathway, we determined the metabolomic changes of sulfur amino acids in the liver. TM significantly decreased hepatic S-adenosylmethionine concentration in the methionine cycle. The levels of cysteine in the liver were increased, while taurine concentration was maintained and GSH levels profoundly decreased (CON vs. TM; 8.7 ± 1.5 vs. 5.4 ± 0.9 µmol GSH/g liver, p < 0.001). These results suggest that abnormal cysteine metabolism by TM treatment resulted in a decrease in GSH, followed by an increase in oxidative stress in the liver. In HepG2 cells, decreased GSH levels were examined by TM treatment in a dose dependent manner. Furthermore, pretreatment with TM in HepG2 cells potentiated oxidative cell death, by exacerbating the effects of tert-butyl hydroperoxide. In conclusion, TM-induced ER stress was accompanied by oxidative stress by reducing the GSH synthesis, which made the liver more susceptible to oxidative stress.

A Hybrid Coumarin-Semifluorescein-Based Fluorescent Probe for the Detection of Cysteine

A new type of turn-on fluorescent probe CF-AC for the detection of Cys was firstly reported. The probe exhibited an excellent response to Cys with high selectively and sensitivity. In the presence of Cys, two fluorescence emission peaks at 525 nm and 650 nm appeared accompanied by the fluorescence color change from blue to red. Morever, the probe had good biocompatibility and could be successfully used for fluorescence imaging of Cys in MCF-7 cells.

Improvement of neuronal differentiation by carbon monoxide: Role of pentose phosphate pathway

Over the last decades, the silent-killer carbon monoxide (CO) has been shown to also be an endogenous cytoprotective molecule able to inhibit cell death and modulate mitochondrial metabolism. Neuronal metabolism is mostly oxidative and neurons also use glucose for maintaining their anti-oxidant status by generation of reduced glutathione (GSH) via the pentose-phosphate pathway (PPP). It is established that neuronal differentiation depends on reactive oxygen species (ROS) generation and signalling, however there is a lack of information about modulation of the PPP during adult neurogenesis. Thus, the main goal of this study was to unravel the role of CO on cell metabolism during neuronal differentiation, particularly by targeting PPP flux and GSH levels as anti-oxidant system. A human neuroblastoma SH-S5Y5 cell line was used, which differentiates into post-mitotic neurons by treatment with retinoic acid (RA), supplemented or not with CO-releasing molecule-A1 (CORM-A1). SH-SY5Y cell differentiation supplemented with CORM-A1 prompted an increase in neuronal yield production. It did, however, not alter glycolytic metabolism, but increased the PPP. In fact, CORM-A1 treatment stimulated (i) mRNA expression of 6-phosphogluconate dehydrogenase (PGDH) and transketolase (TKT), which are enzymes for oxidative and non-oxidative phases of the PPP, respectively and (ii) protein expression and activity of glucose 6-phosphate dehydrogenase (G6PD) the rate-limiting enzyme of the PPP. Likewise, whenever G6PD was knocked-down CO-induced improvement on neuronal differentiation was reverted, while pharmacological inhibition of GSH synthesis did not change CO's effect on the improvement of neuronal differentiation. Both results indicate the key role of PPP in CO-modulation of neuronal differentiation. Furthermore, at the end of SH-SY5Y neuronal differentiation process, CORM-A1 supplementation increased the ratio of reduced and oxidized glutathione (GSH/GSSG) without alteration of GSH metabolism. These data corroborate with PPP stimulation. In conclusion, CO improves neuronal differentiation of SH-S5Y5 cells by stimulating the PPP and modulating the GSH system.