Determination of endogenous thiols and thiol drugs in urine by HPLC with ultraviolet detection

Using Agaricus bisporus crude extract in distance based 3D microfluidic paper-based analytical device and spectrophotometric analytical procedures for thiols determination

Novel and simple spectrophotometric and distance based procedures for thiols (L-cysteine, N-acetylcysteine, and glutathione) determination in biological fluids and pharmaceuticals have been proposed based on their inhibitory action on the oxidation of catechol in the presence of Agaricus bisporus crude extract (ABE). The influence of L-glycine, L-alanine, L-proline, L-methionine, L-cystine, ascorbic acid, uric acid, and bilirubin on the thiol determination has been investigated. Uric acid, bilirubin, L-cystine (oxidized thiol), and L-amino acids do not interfere with the determination. The interference of ascorbic acid up to 350 mg/L is eliminated by using Cucumis sativus crude extract (CSE) with ascorbate oxidase activity. Distance based microfluidic paper-based analytical device (DμPAD) has been developed using origami paper device approach and ABE-catechol-3-methyl-2-benzothiazolinone hydrazone (MBTH) system. DμPAD has the 3D structure of three layers: CSE microzone layer, ABE microzone layer, and chemometer layer (catechol + MBTH). This structure allows sequential sample treatment (ascorbic acid oxidation by CSE) and the following introduction of treated sample to ABE and its substrate to perform ABE inhibition. Separate loading of ABE and its substrate allows preventing their interaction prior to sample loading. DμPAD thiol determination is performed by measuring the length of uncolored flow channel, which allows very simple thiol determination and enables complete integration of analytical procedure steps: sample treatment and enzymatic determination with visual signal output. The analytical ranges are (0.3-2.5)∙10-4 M and (1.1-10.0)∙10-4 M, the recoveries are 80.5-126.7 % and 92.0-112.0 %, the RSD values are 1.6-19.0 % and 2.7-10.8 %, for spectrophotometric and DμPAD procedures, respectively. Both easy-to-use procedures have been successfully applied to the determination of total thiol content (all free sulfhydryl groups) in synthetic urine and N-acetylcysteine in a pharmaceutical sample. The values found with DμPAD and spectrophotometric procedures are in good agreement with values obtained using Ellman's reagent.

First HPLC-UV method for the determination of homocysteine thiolactone in human urine after derivatization with 1-benzyl-2-chloropyridinium bromide

The report presents first high performance liquid chromatography coupled with ultraviolet detection (HPLC-UV) based method for the determination of homocysteine thiolactone (HTL) in human urine. Sample preparation procedure chiefly involves chloroform liquid-liquid extraction of HTL and its re-extraction with hydrochloric acid, followed by evaporation to dryness and treatment of the residue with 1-benzyl-2-chloropyridinium bromide and perchloric acid. The chromatographic separation of obtained UV-absorbing 2-S-pyridinium derivative is achieved within 6 min at 25 °C on Zorbax SB-C18 (150 × 4.6 mm, 5 μm) column using gradient elution. The eluent consists of 0.1% acetic acid in a mixture with acetonitrile delivered at a flow rate of 1 mL/min. The analyte is quantified by monitoring at 316 nm. The assay linearity was observed within 0.1-1.0 µmol/L in urine. The limit of quantification was found to be 100 nmol/L. The accuracy ranged from 92.56 to 112.51% and 92.56-114.31%, while precision varied from 5.89 to 11.27% and 3.85-14.25% for intra- and inter-assay measurements, respectively. The method was successfully applied to urine samples delivered by apparently healthy donors. The presence of HTL was confirmed in twelve of eighteen study samples. The HTL concentration ranged from 36.67 to 693.12 nmol/L.

The Effectiveness of Curcumin in Treating Oral Mucositis Related to Radiation and Chemotherapy: A Systematic Review

Chemotherapy (CT) and radiation therapy (RT), while effective against cancer, often cause severe side effects, such as oral mucositis and other oral diseases. Oral mucositis, characterized by inflammation and ulceration of the oral mucosa, is one of the most painful side effects that can reduce quality of life and limit cancer treatment. Curcumin, a polyphenol from Curcuma longa, has garnered attention for its anti-inflammatory, antioxidant, and anti-carcinogenic properties, which protect the oral mucosa by reducing oxidative stress and modulating inflammation. This study reviews the therapeutic potential of curcumin in preventing and managing oral mucositis caused by CT and RT. Clinical trials show curcumin's effectiveness in reducing the incidence and severity of oral mucositis. Although curcumin supplementation appears to be a promising and cost-effective approach for mitigating oral complications in cancer patients, further clinical trials are needed to confirm its efficacy and optimize dosing strategies.

A New and Rapid LC-MS/MS Method for the Determination of Cysteamine Plasma Levels in Cystinosis Patients

Cystinosis is a rare lysosomal storage disorder caused by autosomal recessive mutations in the CTNS gene that encodes for the cystine transporter cystinosin, which is expressed on the lysosomal membrane mediating the efflux of cystine. Cysteamine bitartrate is a cystine-depleting aminothiol agent approved for the treatment of cystinosis in children and adults. In this study, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of cysteamine levels in plasma samples. This LC-MS/MS method was validated according to the European Medicines Agency (EMA)'s guidelines for bioanalytical method validation. An ultra-performance liquid chromatograph (UPLC) coupled with a 6470 mass spectrometry system was used for cysteamine determination. Our validated method was applied to plasma samples from n = 8 cystinosis patients (median, interquartile range (IQR) = 20.5, 8.5-26.0 years). The samples were collected before cysteamine oral administration (pre-dose) and 1 h after (post-dose). Our bioanalytical method fulfilled the regulatory guidelines for method validation. The cysteamine plasma levels in pre-dose samples were 2.57 and 1.50-3.31 μM (median and IQR, respectively), whereas the post-dose samples reported a cysteamine median concentration of 28.00 μM (IQR: 17.60-36.61). Our method allows the rapid determination of cysteamine plasma levels. This method was successfully used in cystinosis patients and, therefore, could be a useful tool for the evaluation of therapy adherence and for future pharmacokinetic (PK) studies involving a higher number of subjects.

The Role of Sulfhydryl (Thiols) Groups in Oral and Periodontal Diseases

AIM

The sulfhydryl (thiols) group of glutathione plays an important role in the neutralization of foreign organic compounds and the reduction in peroxides. The purpose of the study is to evaluate the concentration of sulfhydryl groups in the gingival tissue of healthy individuals and those with gingivitis or periodontitis, and to examine the differences between these groups.

MATERIAL AND METHODS

To assess the concentration of sulfhydryl groups (thiols) in the gingival tissue of healthy individuals and those with gingivitis or periodontitis, we used spectrophotometric analysis using dithionitrobenzoate (DTNB) as a reagent to measure the accessible sulfhydryl groups present in gingival tissue proteins. The sample was divided into three distinct groups: individuals with periodontal health, gingivitis, and periodontitis, and different indices were used to assess the periodontal status of the participants. Next, a statistical analysis was conducted to compare the concentrations of sulfhydryl groups among the different groups of patients.

CONCLUSIONS

The results of this study showed significantly decreased levels of sulfhydryl (thiols) groups in gingival tissue from patients with gingivitis and periodontitis, compared with healthy people (control group). These results confirm the role of sulfhydryl (thiols) groups in defense against free radicals. They share a significant role in detoxification, signal transduction, apoptosis, and various other functions at the molecular level.

Challenges and Opportunities of Using Fluorescent Metal Nanocluster-Based Colorimetric Assays in Medicine

Development of rapid colorimetric methods based on novel optical-active metal nanomaterials has provided methods for the detection of ions, biomarkers, cancers, etc. Fluorescent metal nanoclusters (FMNCs) have gained a lot of attention due to their unique physical, chemical, and optical properties providing numerous applications from rapid and sensitive detection to cellular imaging. However, because of very small color changes, their colorimetric applications for developing rapid tests based on the naked eye or simple UV-vis absorption spectrophotometry are still limited. FMNCs with peroxidase-like activity have significant potential in a wide variety of applications, especially for point-of-care diagnostics. In this review, the effect of using various capping agents and metals for the preparation of nanoclusters in their colorimetric sensing properties is explored, and the synthesis and detection mechanisms and the recent advances in their application for ultrasensitive chemical and biological analysis regarding human health are highlighted. Finally, the challenges that remain as well as the future perspectives are briefly discussed. Overcoming these limitations will allow us to expand the nanocluster's application for colorimetric diagnostic purposes in medical practice.

Sensitively detecting endogenous homocysteine in human serum and cardiomyocytes with a specific fluorescent probe

The elevated level of homocysteine (Hcy) in circulating blood is generally regarded as a risk factor for a variety of diseases including acute myocardial infarction (AMI), but there is no clear answer to whether circulating Hcy can be used for AMI diagnosis. To address it, here we have designed a tetraazacycle-based fluorescent probe for sensitive detection of endogenous Hcy in AMI patients' serum and cardiomyocytes, showing a perfect selectivity over other biothiols (e.g. Cys and GSH). It mainly relies on the formation of a stable six-membered ring structure when this probe responds to Hcy, which is accompanied by a weakening of photoinduced electron transfer (PET) that induces a sharp increase in the fluorescence emission. In this way, Hcy can be probed in biofluids with high sensitivity. We then employed this fluorescent sensor to statistically analyze the levels of Hcy in human circulating blood, indicating a big difference between AMI patients and the healthy participants. To tell whether such a difference is applicable to AMI diagnosis, we further compare the expression levels of Hcy in cardiomyocytes and other tissue cells. It reveals a lower level of endogenous Hcy in cardiomyocytes, implying no direct relationship between the elevated Hcy and cardiomyocyte damage. This observation suggests that Hcy in circulating blood cannot be utilized as a potential biomarker for AMI diagnosis, although it is proven as a risk factor for this disease.

Use of metal nanoparticles for preconcentration and analysis of biological thiols

Metal nanoparticles (NPs) exhibit several unique physicochemical properties, including redox activity, surface plasmon resonance, ability to quench fluorescence, biocompatibility, or a high surface-to-volume ratio. They are being increasingly used in analysis and preconcentration of thiol containing compounds, because they are able to spontaneously form a stable Au/Ag/Cu-S dative bond. They thus find wide application in environmental and particularly in medical science, especially in the analysis of biological thiols, the endogenous compounds that play a significant role in many biological systems. In this review article, we provide an overview of various types of NPs that have been applied in analysis and preconcentration of biological thiols, mainly in human biological fluids. We first discuss shortly the types of NPs and their synthesis, properties, and their ability to interact with thiol compounds. Then we outline the sample preconcentration and analysis methods that were used for this purpose with special emphasis on optical, electrochemical, and separation techniques.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Analysis of sodium 2-mercaptoethane sulfonate in rat plasma using high performance liquid chromatography tandem-mass spectrometry

Sodium 2-mercaptoethane sulfonate (MESNA) is a thiol-containing compound that has proven to be effective in inactivating acrolein, the toxic metabolite of some anti-cancer drugs (e.g., cyclophosphamide and ifosphamide). Also, it scavenges free radicals which cause numerous disorders by attacking biological molecules. Current methods available to analyze MESNA in biological matrices include colorimetry and high-performance liquid chromatography (HPLC) with ultraviolet, fluorescence, or electrochemical detection. These methods have several limitations including low sensitivity, poor selectivity, a high degree of difficulty, and long analysis times. Hence, a rapid, simple, and sensitive HPLC tandem mass spectrometry (MS/MS) method was developed and validated to quantify MESNA in rat plasma following IP administration. The analysis of MESNA was accomplished via plasma protein precipitation, centrifugation, supernatant evaporation, reconstitution, and HPLC-MS/MS analysis. The method showcases an outstanding limit of detection (20 nM), excellent linearity (R² = 0.999, and percent residual accuracy >90%) and a wide linear range (0.05-200 μM). The method also produced good accuracy and precision (100 ± 10% and <10% relative standard deviation, respectively). The validated method was successfully used to analyze MESNA from treated animals and will allow easier development of MESNA for therapeutic purposes.

Mass balance method for SI-traceable purity assignment of synthetic oxytocin

Oxytocin is not only a significant peptide drug for enhancing uterine contractions, but also an emerging biomarker and therapeutic target of mental disorders in clinical practice. There is a pressing need for the standardization of oxytocin assays because of its low pharmaceutical quality and large variations among measurement approaches. International System of Units (SI)-traceable analytical methods and well-characterized pure reference materials are urgently needed to set up standard reference measurement systems in laboratory medicine, ensuring the accuracy and comparability of test results. Herein, the purity assignment of a synthetic oxytocin containing a disulfide linkage was established based on a mass balance method, which had never been performed for a cross-linked peptide. An in-house validated liquid chromatography-high-resolution tandem mass spectrometry method was developed for the determination of structurally-related impurities in the study material. Twenty-one structurally-related impurities including deamidations, oxidations, and amino acid insertions, etc. ranging from 0.05 mg g^-1 to 15.65 mg g^-1 were identified and quantified by applying a hierarchy calibration concept. This study subsequently discusses a fit for purpose assessment for non-peptide related impurities including water, non-volatile counterions, inorganic elements, and volatile organic compounds that were determined using coulometric Karl Fischer titration, ion chromatography, inductively coupled plasma mass spectrometry, and headspace gas chromatography-mass spectrometry, respectively. The resulting assigned value (796.5 mg g^-1) is determined to be traceable to SI associated with a small measurement uncertainty of 6.5 mg g^-1 (k = 2). The method developed in this study has been verified through an international key comparison jointly coordinated by the Bureau International des Poids et Mesures and the National Institute of Metrology.

Thiol profiling in cancer cell lines by HPLC-mass spectrometry

We describe a protocol for identifying cellular thiol metabolites such as cysteine and cystine in adherent cells using high performance liquid chromatography (HPLC) tandem mass spectrometry-based metabolomics. We applied a modified extraction and sample derivatization protocol to accurately quantify the intracellular levels of labile thiol species and to inhibit oxidation prior to analysis.

For complete details on the use and execution of this protocol, please refer to Liu et al. (2020) and Koppula et al. (2021).

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LC-MS-based quantification of labile thiol species

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Modified extraction and derivatization procedure to prevent sample oxidation

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Protocol for quantification of reduced and oxidized thiol species

Surface Bonding Enhanced Self-Co-Reactant Electrogenerated Chemiluminescence for Sensitive and Selective Detection of Thioglycolic Acid in Cosmetics

Thioglycolic acid (TGA) is an organic compound widely used in cosmetics that cause a variety of health problems when overexposed to it. So far many attempts have been made to develop methods for TGA detection, but most of them need sophisticated instrumentations and are a little bit complicated. Therefore, a simple, cheap and sensitive detection method of TGA is highly desired. Herein, we demonstrated for the first time an Au-S bonding amplified, highly sensitive electrochemiluminescence (ECL) sensing method for TGA detection using tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+ ) as a luminophore and TGA as a self-co-reactant, via an anodic reaction at the Au electrode surface. Due to different molecular coordination environments of the TGA at the electrode surface, the ECL signal intensity of the developed ECL system gives much higher ECL signal in borate buffer than phosphate buffer of the same pH. Under the optimized experimental conditions, the ECL intensity has a direct relationship with the concentration of TGA in the range of 0.03 μM to 300 μM and a limit of detection of 0.013 µM (3σ/ m ). The reported ECL system has further been applied for the detection of TGA in cosmetics with acceptable recoveries.

The Influence of UV Varnishes on the Content of Cysteine and Methionine in Women Nail Plates-Chromatographic Studies

The main purpose of this work was to determine if the use of hybrid nail polishes causes changes in concentration of the most important sulfur amino acids that build nail plate structures, cysteine and methionine. We found that the average contents of cysteine and methionine in studied samples before the use of hybrid manicure were 1275.3 ± 145.9 nmol mg⁻¹ and 111.7 ± 23.8 nmol mg⁻¹, respectively. After six months of hybrid manicure use, the average amount of these sulfur amino acids in studied samples were 22.1% and 36.5% lower in the case of cysteine and methionine, respectively. The average amounts of cysteine and methionine in nail plate samples after the use of hybrid manicures were 992.4 ± 96.2 nmol mg⁻¹ and 70.9 ± 14.8 nmol mg⁻¹, respectively. We also confirmed that in studied women the application of UV light varnishes reduced the thickness of the nail plate, from 0.50 ± 0.12 mm before to 0.46 ± 0.12 mm after the use of the hybrid manicure.

A simple and accurate HFCF-UF method for the analysis of homocysteine, cysteine, cysteinyl-glycine, and glutathione in human blood

The presence of reduced aminothiols, including homocysteine (Hcy), cysteine (Cys), cysteinyl-glycine (CG), and glutathione (GSH), is significantly increased in the pathological state. However, there have been no reports on the relationship between reduced aminothiols (Hcy, Cys, CG, and GSH) and different genders, ages, and drug combinations in human blood. The accurate quantification of these reduced thiols in biological fluids is important for monitoring some special pathological conditions of humans. However, the published methods typically not only require cumbersome and technically challenging processing procedures to ensure reliable measurements, but are also laborious and time-consuming, which may disturb the initial physiological balance and lead to inaccurate results. We developed a hollow fiber centrifugal ultrafiltration (HFCF-UF) method for sample preparation coupled with a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method and used it to determine four reduced aminothiols (Hcy, Cys, CG, and GSH) in human blood for the first time. A total of 96 clinical patients were enrolled in our study. The influence of different genders, ages, and drug combinations on the levels of four reduced thiols in human blood was also discussed by SPSS 24.0. The sample preparation was simplified to a single 5 min centrifugation step in a sealed system that did not disturb the physiological environment. The validation parameters for the methodological results were excellent. The procedure was successfully applied to monitoring the concentrations of four reduced aminothiols (Hcy, Cys, CG, and GSH) in 96 clinical blood samples. There were no significant differences in Hcy, Cys, CG, or GSH for the different genders, ages, or combinations with methotrexate or vancomycin (P > 0.05). However, there was a significant increase in Hcy concentration in patients treated with valproic acid who were diagnosed with epilepsy (p=0.0007). It is advisable to measure reduced Hcy level in patients taking valproic acid. The developed HFCF-UF method was simple and accurate. It can be easily applied in clinical research to evaluate oxidative stress in further study.

Structures and kinetics of Thermotoga maritima MetY reveal new insights into the predominant sulfurylation enzyme of bacterial methionine biosynthesis

Bacterial methionine biosynthesis can take place by either the trans-sulfurylation route or direct sulfurylation. The enzymes responsible for trans-sulfurylation have been characterized extensively because they occur in model organisms such as Escherichia coli. However, direct sulfurylation is actually the predominant route for methionine biosynthesis across the phylogenetic tree. In this pathway, most bacteria use an O-acetylhomoserine aminocarboxypropyltransferase (MetY) to catalyze the formation of homocysteine from O-acetylhomoserine and bisulfide. Despite the widespread distribution of MetY, this pyridoxal 5'-phosphate-dependent enzyme remains comparatively understudied. To address this knowledge gap, we have characterized the MetY from Thermotoga maritima (TmMetY). At its optimal temperature of 70 °C, TmMetY has a turnover number (apparent k_cat = 900 s^-1) that is 10- to 700-fold higher than the three other MetY enzymes for which data are available. We also present crystal structures of TmMetY in the internal aldimine form and, fortuitously, with a β,γ-unsaturated ketimine reaction intermediate. This intermediate is identical to that found in the catalytic cycle of cystathionine γ-synthase (MetB), which is a homologous enzyme from the trans-sulfurylation pathway. By comparing the TmMetY and MetB structures, we have identified Arg270 as a critical determinant of specificity. It helps to wall off the active site of TmMetY, disfavoring the binding of the first MetB substrate, O-succinylhomoserine. It also ensures a strict specificity for bisulfide as the second substrate of MetY by occluding the larger MetB substrate, cysteine. Overall, this work illuminates the subtle structural mechanisms by which homologous pyridoxal 5'-phosphate-dependent enzymes can effect different catalytic, and therefore metabolic, outcomes.

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.

Gas Chromatography-Mass Spectrometry Based Approach for the Determination of Methionine-Related Sulfur-Containing Compounds in Human Saliva

Gas chromatography-mass spectrometry technique (GC-MS) is mainly recognized as a tool of first choice when volatile compounds are determined. Here, we provide the credible evidence that its application in analysis can be extended to non-volatile sulfur-containing compounds, to which methionine (Met), homocysteine (Hcy), homocysteine thiolactone (HTL), and cysteine (Cys) belong. To prove this point, the first method, based on GC-MS, for the identification and quantification of Met-related compounds in human saliva, has been elaborated. The assay involves simultaneous disulfides reduction with tris(2-carboxyethyl)phosphine (TCEP) and acetonitrile (MeCN) deproteinization, followed by preconcentration by drying under vacuum and treatment of the residue with a derivatizing mixture containing anhydrous pyridine, N-trimethylsilyl-N-methyl trifluoroacetamide (MSTFA), and trimethylchlorosilane (TMCS). The validity of the method was demonstrated based upon US FDA recommendations. The assay linearity was observed over the range of 0.5-20 µmol L^-1 for Met, Hcy, Cys, and 1-20 µmol L^-1 for HTL in saliva. The limit of quantification (LOQ) equals 0.1 µmol L^-1 for Met, Hcy, Cys, while its value for HTL was 0.05 µmol L^-1. The method was successfully applied to saliva samples donated by apparently healthy volunteers (n = 10).

Analysis of Total Thiols in the Urine of a Cystathionine β-Synthase-Deficient Mouse Model of Homocystinuria Using Hydrophilic Interaction Chromatography

Homocysteine and related thiols (cysteine, cysteinylglycine, and glutathione) in the urine of a cystathionine β-synthase (CBS)-deficient mouse model were quantified using hydrophilic interaction chromatography with fluorescence detection. Urine samples were incubated with tris(2-carboxyethyl) phosphine to reduce disulfide bonds into thiols. After deproteinization, thiols were fluorescently derivatized with ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F). Homocysteine, cysteine, cysteinylglycine, and glutathione in mouse urine were analyzed using an amide-type column with a mobile phase of acetonitrile/120 mM ammonium formate buffer (pH 3.0) (81:19). The developed method was well-validated. Thiol concentrations in the urine of CBS-wild type (-WT), -heterozygous (-Hetero), and -knockout (-KO) mice were quantified using the developed method. As expected, total homocysteine concentration in CBS-KO mice was significantly higher than that in CBS-WT and CBS-Hetero mice. The developed method shows promise for diagnoses in preclinical and clinical studies.

A Simplified Method for Simultaneous Determination of α-Lipoic Acid and Low-Molecular-Mass Thiols in Human Plasma

α-Lipoic acid, glutathione, cysteine, and cysteinylglycine can be applied as therapeutic agents in civilization diseases such as diabetes mellitus, cardiovascular diseases, and cancers. On the other hand, a higher concentration of homocysteine can result in health problems and has been indicated as an independent risk factor for cardiovascular disease and accelerated atherosclerosis. Here, the first simplified HPLC-UV assay that enables simultaneous determination of α-lipoic acid and low-molecular-mass thiols in plasma, reduces the number of steps, shortens the total time of sample preparation, and limits the amount of single-use polypropylene laboratory materials is described. The assay is based on reversed-phase high performance liquid chromatography with UV detection and simultaneous reduction of disulfide bound with tris(2-carboxyethyl)phosphine and the selective pre-column derivatization of the thiol group with 1-benzyl-2-chloropyridinium bromide. Linearity in the detector responses for plasma samples were observed in ranges: 0.12-5.0 nmol mL^-1 for α-lipoic acid; 2.0-20.0 nmol mL^-1 for glutathione, cysteinylglycine, and homocysteine; and 40.0-400.0 for cysteine. The LODs for α-lipoic acid and low-molecular-mass thiols were 0.08 and 0.12 nmol mL^-1, respectively, while LOQs were 0.12 and 0.16 nmol mL^-1, respectively. The usefulness of the proposed method has been proven by its application to real samples.

Application of Butylamine as a Conjugative Reagent to On-Column Derivatization for the Determination of Antioxidant Amino Acids in Brain Tissue, Plasma, and Urine Samples

(1) Antioxidants are involved in body protection mechanisms against reactive oxygen species. Amino acids such as glutathione (GSH) and N-acetylcysteine (NAC) are known to be involved in providing protection against oxidative lethality. A quick and simple method for the determination of NAC and GSH in various biological matrices such as urine, plasma, and homogenates of brain tissues has been developed and described in this work. (2) The assay is based on reversed phase high performance liquid chromatography with spectrofluorimetric detection and on-column derivatization. Butylamine and o-phthaldialdehyde have been used as derivatization reagents. Since o-phthaldialdehyde constitutes a part of the mobile phase, the derivatization reaction and chromatographic separation occur simultaneously. (3) Linearity in the detector response for NAC in human urine was observed in the range of 5–200 nmol mL⁻¹, and NAC and GSH in the brain tissue homogenates were observed in the range of 0.5–5 nmol mL⁻¹ and 0.5–15 nmol mL⁻¹, respectively. Human plasma linearity ranges covered 0.25–5.00 nmol mL⁻¹ and 0.5–15 nmol mL⁻¹ for NAC and GSH, respectively. The LODs for NAC and GSH were 0.01 and 0.02 nmol mL⁻¹ while the LOQs were 0.02 and 0.05 nmol mL⁻¹, respectively. The usefulness of the proposed method was proven through its application to real samples.

Optimization of tris(2-carboxyethyl) phosphine reduction conditions for fast analysis of total biothiols in mouse serum samples

In this study, we investigated suitable conditions for the reduction of disulfides in mouse serum samples by tris(2-carboxyethyl) phosphine (TCEP) for fast analysis of total biothiols. Disulfides were reduced with TCEP, and then, thiols were derivatized with the fluorogenic reagent, ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F). Interference peaks on chromatograms of mouse serum samples disappeared when the TCEP reaction was conducted on ice instead of at room temperature, which is used classically. Low-molecular-weight disulfides, such as cystine and glutathione disulfide, were nearly completely reduced by TCEP on ice. Six SBD-biothiols (homocysteine, cysteine, cysteinylglycine, glutathione, γ-glutamylcysteine, and N-acetylcysteine) were separated within 7.5 min on a sulfoalkylbetain-type column (ZIC-HILIC: 150 × 2.1 mm i.d., 3.5 μm), without interference peaks. The developed method showed good linearity and reproducibility, with inter- and intra-day precisions of less than 3%.

Application of simultaneous separation and derivatization for the determination of α-lipoic acid in urine samples by high-performance liquid chromatography with spectrofluorimetric detection

To help to clarify therapeutic functions of lipoic acid (LA) in biochemical and clinical practice we have elaborated a fast, simple and accurate HPLC method enabling determination of LA in human urine. The proposed analytical approach includes reduction of LA with tris(2-carboxyethyl)phosphine and simultaneous separation and derivatization of the analyte with butylamine and o-phthaldialdehyde followed by spectrofluorimetric detection at λ_ex  = 340 nm and λ_em  = 440 nm. The assay was performed using gradient elution and the mobile phase containing 0.0025 mol L^-1 o-phthaldialdehyde in 0.0025 mol L^-1 NaOH and acetonitrile. Linearity of the detector response for LA was observed in the range of 0.3-8 μmol L^-1 . Limits of detection and quantification for LA in urine samples were 0.02 and 0.03 μmol L^-1 , respectively. The total analysis time, including sample work-up, was <20 min. The analytical procedure was successfully applied to analysis of real urine samples delivered from six healthy volunteers who received a single 100 mg dose of LA.

Thiouracil: Comprehensive profile

Thiouracil, 2-sulfanylidene-1H-pyrimidin-4-one, has been used as anti-thyroid, coronary vasodilator, and in congestive heart failure. It was found to cause agranulocytosis and it is suspected to be teratogenic and carcinogenic. Owing to its high frequency of adverse reactions, especially agranulocytosis, its use was abandoned in favor of other, less toxic drugs, such as propylthiouracil and methimazole. Thiouracil refers both to a specific molecule consisting of a sulfated uracil and a family of molecules based upon the structure. An important member of this family is propylthiouracil, which is a thiourea antithyroid drug that acts by blocking the production of thyroid hormones; it also inhibits the peripheral deiodination of thyroxine to tri-iodothyronine. This profile is prepared to discuss and explain physical and chemical properties, proprietary and nonproprietary names of thiouracil and propylthiouracil. It also includes uses and applications, methods of preparation, thermal and spectral behavior and methods of analysis. In addition, metabolism, excretion and pharmacology of propylthiouracil are also discussed.

Simultaneous Determination of Cysteamine and Cystamine in Cosmetics by Ion-Pairing Reversed-Phase High-Performance Liquid Chromatography

Cysteamine has been used in cosmetics as an antioxidant, a hair straightening agent, and a hair waving agent. However, recent studies indicate that cysteamine can act as an allergen to hairdressers. The objective of this study was to develop and validate a simple and effective reversed-phase high-performance liquid chromatography (RP-HPLC) method for the measurement of cysteamine and its dimer, cystamine. Sodium 1-heptanesulfonate (NaHpSO) was used as an ion-pairing agent to improve chromatographic performance. Separation was performed on a Gemini C18 column (250 mm × 4.6 mm, 5 μm particle size) using a mobile phase composed of 85:15 (v/v) 4 mM NaHpSO in 0.1% phosphoric acid:acetonitrile. UV absorbance was monitored at 215 nm. The RP-HPLC method developed in this study was validated for specificity, linearity, limit of detection, limit of quantitation, precision, accuracy, and recovery. Cysteamine and cystamine were chromatographically resolved from other reducing agents such as thioglycolic acid and cysteine. Extraction using water and chloroform resulted in the recovery for cysteamine and cystamine ranging from 100.2-102.7% and 90.6-98.7%, respectively. This validated RP-HPLC method would be useful for quality control and monitoring of cysteamine and cystamine in cosmetics.

Electroanalytical Determination of Cysteine Using the Electrodes Based on Ternary Silver-Copper Sulfides

The amperometric determination of cysteine, using an electrode based on ternary silver-copper sulfide, is presented. Electrochemical characterizations (using cyclic voltammetry) of three electrode materials revealed that the electrode based on the material that consists of jalpaite (Ag₃CuS₂), doped with a small amount of metallic silver, has the best electrocatalytical performance for cysteine oxidation. For the amperometric determination, 0.142 V at pH 5 and 0.04 V at pH 7 vs. Ag/AgCl, related to the electrocatalytical oxidation of thiol group, were chosen. Electrochemical impedance spectroscopy together with Fourier transform infrared spectroscopy (FTIR) revealed that oxidation takes place on the electrode surface with fouling effect, which does not affect a wide linear working range between 1 μM and 100 μM. Sensitivities, at pH 5 and pH 7, are calculated to be 0.11 μA μM-1 and 0.10 μA μM-1, respectively. The detection limits were determined to be 0.036 μM and 0.024 μM for pH 5 and pH 7, respectively. In the presence of uric acid, folic acid, ascorbic acid, and glucose no interference was noticed. This electrode showed remarkable stability and excellent reproducibility. The electrode was exploited for the determination of cysteine in a dietary supplement with the excellent recoveries.

Simultaneous determination of tiopronin and its primary metabolite in plasma and ocular tissues by HPLC

Tiopronin, formally 2-mercaptopropionylglycine (MPG), is currently prescribed to treat cystinuria and rheumatoid arthritis, and its antioxidant properties have led to its investigation as a treatment for cataracts, a condition in which oxidative stress is strongly implicated. To study its accumulation in the eye, a reliable, isocratic HPLC method was developed for the determination of MPG and its primary metabolite 2-mercaptopropionic acid (MPA) in plasma and relevant ocular tissues. This method utilizes pre-column derivatization and fluorescence detection. The 3.5 min separation enables high-throughput analysis, and validation experiments demonstrated that this method is suitable for evaluating ocular accumulation of MPG and MPA at concentrations as low as 66 and 33 nm, respectively. Excellent linearity was achieved over the working concentration range with R²  > 0.997. Extraction recovery was reproducible within each matrix and exceeded 97%. Accuracy was within 13.3% relative error, and intra- and inter-day precisions were within 6% CV and 7% CV, respectively. Sample stability was demonstrated under various storage conditions, and the use of an internal standard conferred exceptional ruggedness. This method has been successfully applied for the determination of MPG and MPA in plasma, cornea, lens and retina following intraperitoneal administration of the drug in Wistar rats.

Capillary electrophoresis coupled with chloroform-acetonitrile extraction for rapid and highly selective determination of cysteine and homocysteine levels in human blood plasma and urine

A rapid and selective method has been developed for highly sensitive determination of total cysteine and homocysteine levels in human blood plasma and urine by capillary electrophoresis (CE) coupled with liquid-liquid extraction. Analytes were first derivatized with 1,1'-thiocarbonyldiimidazole and then samples were purified by chloroform-ACN extraction. Electrophoretic separation was performed using 0.1 M phosphate with 30 mM triethanolamine, pH 2, containing 25 μM CTAB, 2.5 μM SDS, and 2.5% polyethylene glycol 600. Samples were injected into the capillary (with total length 32 cm and 50 μm id) at 2250 mbar*s and subsequent injection was performed for 30 s with 0.5 M KОН. The total analysis time was less than 9 min, accuracy was 98%, and precision was <2.6%. The LOD was 0.2 μM for homocysteine and 0.5 μM for cysteine. The use of liquid-liquid extraction allowed the precision and sensitivity of the CE method to be significantly increased. The validated method was applied to determine total cysteine and homocysteine content in human blood plasma and urine samples obtained from healthy volunteers and patients with kidney disorders.

Synthesis of l-cysteine derivatives containing stable sulfur isotopes and application of this synthesis to reactive sulfur metabolome

Cysteine persulfide is an L-cysteine derivative having one additional sulfur atom bound to a cysteinyl thiol group, and it serves as a reactive sulfur species that regulates redox homeostasis in cells. Here, we describe a rapid and efficient method of synthesis of L-cysteine derivatives containing isotopic sulfur atoms and application of this method to a reactive sulfur metabolome. We used bacterial cysteine syntheses to incorporate isotopic sulfur atoms into the sulfhydryl moiety of L-cysteine. We cloned three cysteine synthases-CysE, CysK, and CysM-from the Gram-negative bacterium Salmonella enterica serovar Typhimurium LT2, and we generated their recombinant enzymes. We synthesized ³⁴S-labeled L-cysteine from O-acetyl-L-serine and ³⁴S-labeled sodium sulfide as substrates for the CysK or CysM reactions. Isotopic labeling of L-cysteine at both sulfur (³⁴S) and nitrogen (¹⁵N) atoms was also achieved by performing enzyme reactions with ¹⁵N-labeled L-serine, acetyl-CoA, and ³⁴S-labeled sodium sulfide in the presence of CysE and CysK. The present enzyme systems can be applied to syntheses of a series of L-cysteine derivatives including L-cystine, L-cystine persulfide, S-sulfo-L-cysteine, L-cysteine sulfonate, and L-selenocystine. We also prepared ³⁴S-labeled N-acetyl-L-cysteine (NAC) by incubating ³⁴S-labeled L-cysteine with acetyl coenzyme A in test tubes. Tandem mass spectrometric identification of low-molecular-weight thiols after monobromobimane derivatization revealed the endogenous occurrence of NAC in the cultured mammalian cells such as HeLa cells and J774.1 cells. Furthermore, we successfully demonstrated, by using ³⁴S-labeled NAC, metabolic conversion of NAC to glutathione and its persulfide, via intermediate formation of L-cysteine, in the cells. The approach using isotopic sulfur labeling combined with mass spectrometry may thus contribute to greater understanding of reactive sulfur metabolome and redox biology.

A novel near-infrared fluorescent probe with a large Stokes shift for biothiol detection and application in in vitro and in vivo fluorescence imaging

A novel near-infrared fluorescent probe with a large Stokes shift was developed for biothiol detection and application in in vitro and in vivo fluorescence imaging.

Characterization of the Cysteine Content in Proteins Utilizing Cysteine Selenylation with 266 nm Ultraviolet Photodissociation (UVPD)

Characterization of the cysteine content of proteins is a key aspect of proteomics. By defining both the total number of cysteines and their bound/unbound state, the number of candidate proteins considered in database searches is significantly constrained. Herein we present a methodology that utilizes 266 nm UVPD to count the number of free and bound cysteines in intact proteins. In order to attain this goal, proteins were derivatized with N-(phenylseleno)phthalimide (NPSP) to install a selectively cleavable Se-S bond upon 266 UVPD. The number of Se-S bonds cleaved upon UVPD, a process that releases SePh moieties, corresponds to the number of cysteine residues per protein. Graphical Abstract ᅟ.

A versatile method for analysis of saliva, plasma and urine for total thiols using HPLC with UV detection

A simple and rapid HPLC method using 2-chloro-1-methyllepidinium tetrafluoroborate (CMLT) as a derivatization reagent was developed for simultaneous determination of homocysteine (Hcy), glutathione (GSH), γ-glutamylcysteine (γ-GluCys), cysteinylglycine (CysGly), N-acetylcysteine (NACys) and cysteine (Cys) in human saliva, plasma and urine. Separation of the analytes was achieved in just 7min using an HPLC, followed by UV detection at 355nm. Chromatographic separation was accomplished on Aeris PEPTIDE XB-C18 (150mm×4.6mm, 3.6µm) column from Phenomenex with a gradient elution: 0-4.0min, 7-30% B; 4.0-5.5min, 30-7% B; 5.5-7.5min, 7% B; (A: B, v/v); (A) 0.5% CH3COOH and (B) EtOH. Mobile phase was delivered at a flow rate 1.0mLmin(-1). Linearity in detector response for total thiols was observed over the range of 0.1-20μmolL(-1) for Hcy, GSH and γ-GluCys, 0.25-50μmolL(-1) for NACys and CysGly and 5-300 for Cys. The LOQ values for Hcy, GSH, γ-GluCys, NACys, CysGly and Cys were 0.05, 0.05, 0.10, 0.06, 0.12 and 0.08μmolL(-1), respectively. The method was successfully implemented to analysis of the samples donated by 15 apparently healthy volunteers and 10 patients.

Determination of thiol metabolites in human urine by stable isotope labeling in combination with pseudo-targeted mass spectrometry analysis

Precursor ion scan and multiple reaction monitoring scan (MRM) are two typical scan modes in mass spectrometry analysis. Here, we developed a strategy by combining stable isotope labeling (IL) with liquid chromatography-mass spectrometry (LC-MS) under double precursor ion scan (DPI) and MRM for analysis of thiols in 5 types of human cancer urine. Firstly, the IL-LC-DPI-MS method was applied for non-targeted profiling of thiols from cancer samples. Compared to traditional full scan mode, the DPI method significantly improved identification selectivity and accuracy. 103 thiol candidates were discovered in all cancers and 6 thiols were identified by their standards. It is worth noting that pantetheine, for the first time, was identified in human urine. Secondly, the IL-LC-MRM-MS method was developed for relative quantification of thiols in cancers compared to healthy controls. All the MRM transitions of light and heavy labeled thiols were acquired from urines by using DPI method. Compared to DPI method, the sensitivity of MRM improved by 2.1-11.3 folds. In addition, the concentration of homocysteine, γ-glutamylcysteine and pantetheine enhanced more than two folds in cancer patients compared to healthy controls. Taken together, the method demonstrated to be a promising strategy for identification and comprehensive quantification of thiols in human urines.

Quantification of homocysteine and cysteine by derivatization with pyridoxal 5'-phosphate and hydrophilic interaction liquid chromatography

A simple and rapid assay using pyridoxal 5'-phosphate (PLP) as a derivatizing reagent was developed for the simultaneous determination of homocysteine (Hcy) and cysteine (Cys) in human plasma. Derivatization with PLP affords UV-absorbing tetrahydrothiazine and thiazolidine derivatives of Hcy and Cys, respectively. Separation of these derivatives was achieved in 5 min using a hydrophilic interaction liquid chromatography, followed by UV detection at 330 nm. Linearity in detector response was observed over the range of 0.25-20 μM for Hcy and 10-300 μM for Cys. The limit of quantification (LOQ) values for Hcy and Cys were 0.25 and 2.5 μM, respectively. The method was successfully applied to plasma samples donated by apparently healthy volunteers.

A colorimetric, ratiometric and water-soluble fluorescent probe for simultaneously sensing glutathione and cysteine/homocysteine

A chlorinated coumarin-aldehyde was developed as a colorimetric and ratiometric fluorescent probe for distinguishing glutathione (GSH), cystenine (Cys) and homocysteine (Hcy). The GSH-induced substitution-cyclization and Cys/Hcy-induced substitution-rearrangement cascades lead to the corresponding thiol-coumarin-iminium cation and amino-coumarin-aldehyde with distinct photophysical properties. The probe can be used to simultaneously detect GSH and Cys/Hcy by visual determination based on distinct different colors - red and pale-yellow in PBS buffer solution by two reaction sites. From the linear relationship of fluorescence intensity and biothiols concentrations, it was determined that the limits of detection for GSH, Hcy and Cys are 0.08, 0.09 and 0.18 μM, respectively. Furthermore, the probe was successfully used in living cell imaging with low cell toxicity.