High-performance liquid chromatographic determination of aliphatic thiols with aroylacrylic acids as fluorogenic precolumn derivatization reagents

High performance liquid chromatography analysis of MESNA (2-mercaptoethane sulfonate) in biological samples using ?uorescence detection

MESNA is the sodium salt of 2-mercaptoethane sulfonate, a thiol-containing drug. It is an antioxidant used particularly in renal protection. Several studies have proved that MESNA has beneficial effects in ischemic acute renal failure where it scavenges reactive oxygen species (ROS), due to the presence of the thiol group. It also reduces the size of urinary bladder cancer. MESNA was proved to be effective in preventing hemorrhagic cystitis induced by high doses of several chemotherapeutic regimens such as cyclophosphamide and ifosfamide. It has been shown that MESNA functions as an uroprotective substance in drug-induced experimental bladder cancer models. Moreover, recent studies have suggested that it is also effective in reducing intestinal inflammation in colitis. Because of the increased level of interest in using MESNA for treating various disorders, a new and sensitive method was needed to understand the pharmacokinetics of this drug. Accordingly, we developed a new method for determining free MESNA in biological samples by using ThioGlo-3 [3H-Naphto [2,1-b] pyran, 9-acetoxy-2-(4-(2,5-dihydro-2, 5-dioxo-1H-pyrrol-1-yl) phenyl-3-oxo)] as the derivatizing agent. MESNA was detected fluorimetrically by reverse-phase HPLC using acetonitrile:water (75:25) along with acetic acid and phosphoric acid (1 mL/L each) as the mobile phase. The detection limit was 1.64 nm per 20 microL injection volume, with a linearity (r = 0.999) in the calibration curve extending over a range 2.5-2500 nm. The coefficients of variation for within-run and between-run precision were 0.43 and 3.31%, respectively. The relative recoveries in the biological samples were in the range 87 +/- 6 to 93 +/- 2.4%. The concentrations of MESNA in the biological samples (lungs, liver, kidney and brain) were determined. The highest concentration of MESNA was found in plasma. Of all the tissues, the kidney was found to have the highest concentration while the liver had the lowest concentration.

Quantification of mesna and total mesna in kidney tissue by high-performance liquid chromatography with electrochemical detection

A sensitive and selective assay for the determination of mesna and total mesna in tissue was developed and validated. After a simple homogenization, extraction and deproteinization step, mesna could be measured immediately by HPLC with an electrochemical detector provided with a sensitive wall-jet gold electrode. Total mesna (i.e., free mesna and mesna present in mesna disulfides and mixed mesna disulfides) could be measured after pre-column reduction with sodium borohydride to free mesna. The lower limit of quantification of mesna and total mesna was for both compounds 10 nmol/g. The assays for mesna and total mesna in tissue were linear over the ranges of 10-3000 and 10-10000 nmol/g, respectively. The within-day and between-day precisions of both methods were better than 9%. The within-day and between-day accuracy of the mesna assay ranged from 103.7 to 113.6%, whereas the accuracies of the total mesna assay ranged from 97.8 to 106.7%. Mesna in an EDTA containing tissue homogenate or in deproteinized tissue homogenate stored at -80 degrees C was stable for at least 12 weeks. Total mesna was stable under all conditions measured. The developed assays will be applied for the determination of the distribution of mesna and total mesna in tissues of the rat after administration of mesna or BNP7787.

Development of hydrophilic fluorogenic derivatization reagents for thiols: 4-(N-acetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole and 4-(N-trichloroacetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole

Sensitive, reactive, and hydrophilic fluorogenic reagents for thiols with the benzofurazan skeleton, 4-(N-acetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (AcABD-F) and 4-(N-trichloroacetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (TCAcABD-F) have been developed. These reagents reacted with thiols within 10 min at 60 degrees C. AcABD-F and TCAcABD-F themselves do not fluoresce but are strongly fluorescent after the reaction with thiol compounds. The generated derivatives were highly water-soluble, since they dissociated a proton and ionized in the neutral pH region. The derivatives with four biologically important thiol compounds were separated on a reversed-phase HPLC column and detected fluorometrically at 504 nm with excitation at 388 nm. The detection limit attained for homocysteine with AcABD-F was 25 fmol on column (11 nM) (signal-to-noise ratio = 3), and that for glutathione with TCAcABD-F was 45 fmol on column (20 nM).

Facile and sensitive method for the determination of mesna in plasma by high-performance liquid chromatography with ultraviolet detection

The use of 2-chloro-1-methylquinolinium tetrafluoroborate, an ultraviolet tagging reagent, for the ion-pair, reversed-phase high-performance liquid chromatography of mesna in human plasma is reported. In order to achieve this objective optimization of the two-step procedure, derivatization and separation of mesna S-quinolinium derivative from that of other thiols present in plasma and internal standard, was investigated. The derivatization was optimized in terms of pH, reagent excess and time of the reaction, and the mobile phase in terms of ion-pairing reagent concentration, pH, organic modifier content and temperature. Baseline separation was achieved on an analytical Waters Nova-Pak C18 (150x3.9 mm, 5 microm) column with a mobile phase consisting of pH 2.3 0.05 M trichloroacetic acid-acetonitrile (89:11, v/v) pumped at 1.2 ml/min. The peak height ratios of the mesna derivative to that of the internal standard (thiomalic acid) varied linearly with the concentration of the analyte added to normal plasma with a correlation coefficient of 0.9997. The lower limits of detection and quantitation were 40 pmol/ml (0.8 pmol on-column) and 160 pmol/ml (3.2 pmol on-column), respectively. The intra-run imprecision and inaccuracy were from 1.3 to 2.4 and from 1.3 to 2.0%, respectively.

Quantification of BNP7787 (dimesna) and its metabolite mesna in human plasma and urine by high-performance liquid chromatography with electrochemical detection

A sensitive and accurate assay was developed and validated to determine BNP7787 (dimesna), a new protector against cisplatin-induced toxicities, and its metabolite mesna in plasma and urine of patients. Both analytes were measured as mesna in deproteinized plasma or in urine diluted with mobile phase using high-performance liquid chromatography with an electrochemical detector provided with a wall-jet gold electrode. The assays for BNP7787 and mesna in deproteinized plasma were linear over the range of 1.6-500 microM and 0.63-320 microM, respectively. In plasma, the mean recovery of BNP7787 over the whole concentration range was 100.6% and of mesna 94.6%. The lower limits of quantitation (LLQs) of BNP7787 and mesna in deproteinized plasma were 1.6 microM and 0.63 microM, respectively. For both compounds the within- and between-day accuracy and precision of the assay was better than 12%. The assays for BNP7787 and mesna in urine were linear over the range of 0.8-1200 microM and 0.63-250 microM, respectively. In urine, the mean recovery of BNP7787 over the whole concentration range was 94.1% and of mesna 93.1%. The LLQ of BNP7787 in urine was 0.8 microM and of mesna 1.6 microM. The within- and between-day accuracy and precision of the assay for BNP7787 and mesna was lower than 15%. The stability of mesna in urine increased with an increasing concentration of mesna, lower temperature and addition of EDTA (1 g/l) and hydrochloric acid (0.2 M). BNP7787 in urine was stable for at least 24 h at temperatures in the range of -20 degrees C up to 37 degrees C and independent of the concentration. The developed assays are currently applied for samples of patients with solid tumors participating in a phase I trial of BNP7787 in combination with cisplatin.

Estimation of methanogen biomass by quantitation of coenzyme M

Determination of the role of methanogenic bacteria in an anaerobic ecosystem often requires quantitation of the organisms. Because of the extreme oxygen sensitivity of these organisms and the inherent limitations of cultural techniques, an accurate biomass value is very difficult to obtain. We standardized a simple method for estimating methanogen biomass in a variety of environmental matrices. In this procedure we used the thiol biomarker coenzyme M (CoM) (2-mercaptoethanesulfonic acid), which is known to be present in all methanogenic bacteria. A high-performance liquid chromatography-based method for detecting thiols in pore water (A. Vairavamurthy and M. Mopper, Anal. Chim. Acta 78:363-370, 1990) was modified in order to quantify CoM in pure cultures, sediments, and sewage water samples. The identity of the CoM derivative was verified by using liquid chromatography-mass spectroscopy. The assay was linear for CoM amounts ranging from 2 to 2,000 pmol, and the detection limit was 2 pmol of CoM/ml of sample. CoM was not adsorbed to sediments. The methanogens tested contained an average of 19.5 nmol of CoM/mg of protein and 0.39 +/- 0.07 fmol of CoM/cell. Environmental samples contained an average of 0.41 +/- 0.17 fmol/cell based on most-probable-number estimates. CoM was extracted by using 1% tri-(N)-butylphosphine in isopropanol. More than 90% of the CoM was recovered from pure cultures and environmental samples. We observed no interference from sediments in the CoM recovery process, and the method could be completed aerobically within 3 h. Freezing sediment samples resulted in 46 to 83% decreases in the amounts of detectable CoM, whereas freezing had no effect on the amounts of CoM determined in pure cultures. The method described here provides a quick and relatively simple way to estimate methanogenic biomass.

2-(4-N-maleimidophenyl)-6-methoxybenzofuran: a superior derivatizing agent for fluorimetric determination of aliphatic thiols by high-performance liquid chromatography

The use of 2-(4-N-maleimidophenyl)-6-methoxybenzofuran as a fluorogenic pre-column derivatizing agent for sensitive high-performance liquid chromatographic (HPLC) determination of aliphatic thiols is described. The maleamic acid, its methyl ester and the N-maleimide derivatives of the common amine precursor were easily synthesized and characterized according to conventional methods. These derivatives lack fluorescent properties in their native form but display strong fluorescence upon reaction with aliphatic thiols. The reaction is rapid and highly selective for thiols over a wide pH range (7.1-8.8). Following derivatization, the thiol adducts were separated on a reversed-phase column (Ultrasphere-ODS) using 0.1% hexanesulfonic acid in 10 mM potassium hydrogen phosphate-acetonitrile (65:35, pH 4.5) and were detected fluorimetrically (excitation at 310 nm; emission at 390 nm). The method is highly sensitive (femtomole range) and is easily applied to the determination of SH-containing drugs and endogenous thiols in biological samples.

Determination of glutathione in biological samples by high performance liquid chromatography with fluorescence detection

A selective and sensitive high performance liquid chromatographic (HPLC) method has been developed for the determination of reduced glutathione (GSH) in biological samples (rat liver, spleen and plasma). The method involved a prechromatographic thiol derivatization with methyl 4-(6-methoxynaphthalen-2-yl)-4-oxo-2-butenoate; the reaction was rapid (5 min) under mild conditions (pH 7.5 and ambient temperature) and selective for the sulphydryl group. The thiol adducts were separated on a reversed-phase C-18 column using acetonitrile: 0.05 M triethylammonium (TEA) phosphate (pH 4) solution 32:68 (v/v) as the mobile phase. Fluorescence detection (lambda em = 450 nm; lambda exc = 310 nm) was used and the detection limit (S/N = 3) was about 0.5 pmole of the injected GSH adduct. The method was also applied to the determination of total glutathione in rat plasma after a preliminary reduction with dithiothreitol.

Derivatization of thiol-containing compounds

The determination of thiol-containing compounds in biological fluids is important in biochemistry and clinical chemistry. In this paper, derivatization reagents for thiols are reviewed with respect to their reactivity, selectivity, spectroscopic characteristics and their applicability especially to high-performance liquid chromatography. Derivatization used in ultraviolet and electrochemical detection. The derivatization reagents contain a functional group, e.g. an N-substituted maleimide, active halogen or aziridine, which react with the thiol group. Derivatization for use in flow injection analysis, thin-layer chromatography or gas chromatography-mass spectrometry is also described.

Derivatization reactions for neurotransmitters and their automation

Many reagents suitable for the derivatization of neurotransmitters are selective for the amino function. Others, however, are selective for the carboxyl-, thiol- and hydroxyl function, and recently, reagents selective for more than one function have been produced. Interest persists in the established reagents, with their well understood behaviour which assists automation of analysis as much as new technology. Workers appear reluctant to tackle the optimization of many novel reagents. Chiral reagents may become important if d-amino acids are shown to be significant from a physiological point of view. Solid-phase reagents offer better regulated chemistry and combined derivatization/solid-phase extraction, which make them an exciting prospect.

HPLC determination of glutathione and L-cysteine in pharmaceuticals after derivatization with ethacrynic acid

Ethacrynic acid and its methyl ester are proposed as useful pre-chromatographic derivatization reagents for the HPLC analysis (UV detection) of reduced glutathione (GSH) and L-cysteine. The optimum experimental conditions for the thiol derivatization, the removal of the excess reagent by liquid-liquid or solid-phase extraction and the reversed-phase chromatographic separations of the thiol adducts were investigated. The method was applied to the HPLC determination of GSH and L-cysteine in commercial formulations and proved to be suitable for the HPLC determination of oxidized glutathione (GSSG) after reduction to GSH using dithiothreitol (DTT).