5-(Pentafluorobenzoylamino)fluorescein: A selective substrate for the determination of glutathione concentration and glutathione S-transferase activity

Development of pathway-oriented screening to identify compounds to control 2-methylglyoxal metabolism in tumor cells

Controlling tumor-specific alterations in metabolic pathways is a useful strategy for treating tumors. The glyoxalase pathway, which metabolizes the toxic electrophile 2-methylglyoxal (MG), is thought to contribute to tumor pathology. We developed a live cell-based high-throughput screening system that monitors the metabolism of MG to generate D-lactate by glyoxalase I and II (GLO1 and GLO2). It utilizes an extracellular coupled assay that uses D-lactate to generate NAD(P)H, which is detected by a selective fluorogenic probe designed to respond exclusively to extracellular NAD(P)H. This metabolic pathway-oriented screening is able to identify compounds that control MG metabolism in live cells, and we have discovered compounds that can directly or indirectly inhibit glyoxalase activities in small cell lung carcinoma cells.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Evaluation of Glutathione S-Transferase Inhibition Effects on Idiopathic Pulmonary Fibrosis Therapy with a Near-Infrared Fluorescent Probe in Cell and Mice Models

Idiopathic pulmonary fibrosis (IPF) is a lung-limited and progressive fibrotic disease. The early diagnosis and therapies of IPF are still full of clinical challenges. Glutathione S-transferase (GSTs) plays significant roles in promoting the formation of pulmonary fibrosis. Herein, we report a fluorescent probe (Cy-GST) for the detection of GSTs concentration fluctuations in cells and in mice models. The probe can selectively and sensitively respond to GSTs with an "off-on" type fluorescence switch. Our results demonstrated that the level of intracellular GSTs increase in the pulmonary fibrosis cells and mice models. And the IPF patients hold high levels of GSTs concentrations. Thus, GSTs are likely to play important roles in pulmonary fibrosis. The inhibitor of GSTs TLK117 can reduce the severity of pulmonary fibrosis. The synergistic treatment of TLK117 and pirfenidone have better therapeutic effects than only using pirfenidone in pulmonary fibrosis mice models. The level of GSTs in IPF may be a new potential marker for IPF diagnosis. And the inhibition of GSTs may be a new therapeutic strategy for IPF treatment.

Fluorescence detection of glutathione S-transferases in a low GSH level environment

Glutathione S-transferases (GSTs) play crucial roles in the detoxification process and the development of drug-resistance and are proved to be important markers for various tumors.

Development of pyrethroid-like fluorescent substrates for glutathione S-transferase

The availability of highly sensitive substrates is critical for the development of precise and rapid assays for detecting changes in glutathione S-transferase (GST) activity that are associated with GST-mediated metabolism of insecticides. In this study, six pyrethroid-like compounds were synthesized and characterized as substrates for insect and mammalian GSTs. All of the substrates were esters composed of the same alcohol moiety, 7-hydroxy-4-methylcoumarin, and acid moieties that structurally mimic some commonly used pyrethroid insecticides, including cypermethrin and cyhalothrin. CpGSTD1, a recombinant Delta class GST from the mosquito Culex pipiens pipiens, metabolized our pyrethroid-like substrates with both chemical and geometric preference (i.e., the cis-isomers were metabolized at 2- to 5-fold higher rates than the corresponding trans-isomers). A GST preparation from mouse liver also metabolized most of our pyrethroid-like substrates with both chemical and geometric preference but at 10- to 170-fold lower rates. CpGSTD1 and mouse GSTs metabolized 1-chloro-2,4-dinitrobenezene (CDNB), a general GST substrate, at more than 200-fold higher rates than our novel pyrethroid-like substrates. There was a 10-fold difference in the specificity constant (k(cat)/K(M) ratio) of CpGSTD1 for CDNB and those of CpGSTD1 for cis-DCVC and cis-TFMCVC, suggesting that cis-DCVC and cis-TFMCVC may be useful for the detection of GST-based metabolism of pyrethroids in mosquitoes.

Identification and characterization of pharmacological chaperones to correct enzyme deficiencies in lysosomal storage disorders

Many human diseases result from mutations in specific genes. Once translated, the resulting aberrant proteins may be functionally competent and produced at near-normal levels. However, because of the mutations, the proteins are recognized by the quality control system of the endoplasmic reticulum and are not processed or trafficked correctly, ultimately leading to cellular dysfunction and disease. Pharmacological chaperones (PCs) are small molecules designed to mitigate this problem by selectively binding and stabilizing their target protein, thus reducing premature degradation, facilitating intracellular trafficking, and increasing cellular activity. Partial or complete restoration of normal function by PCs has been shown for numerous types of mutant proteins, including secreted proteins, transcription factors, ion channels, G protein-coupled receptors, and, importantly, lysosomal enzymes. Collectively, lysosomal storage disorders (LSDs) result from genetic mutations in the genes that encode specific lysosomal enzymes, leading to a deficiency in essential enzymatic activity and cellular accumulation of the respective substrate. To date, over 50 different LSDs have been identified, several of which are treated clinically with enzyme replacement therapy or substrate reduction therapy, although insufficiently in some cases. Importantly, a wide range of in vitro assays are now available to measure mutant lysosomal enzyme interaction with and stabilization by PCs, as well as subsequent increases in cellular enzyme levels and function. The application of these assays to the identification and characterization of candidate PCs for mutant lysosomal enzymes will be discussed in this review. In addition, considerations for the successful in vivo use and development of PCs to treat LSDs will be discussed.

Metabolic activation of a pentafluorophenylethylamine derivative: Formation of glutathione conjugatesin vitroin the rat

The aim was to investigate the metabolic activation potential of a pentafluorophenylethylamine derivative (compound I) in vitro in the rat and to identify the cytochrome P450 (CYP) enzymes that catalyse these metabolic activation processes. Reduced glutathione (GSH) was fortified in rat hepatocytes and liver microsomes to trap possible reactive intermediates. Four glutathione conjugates (M1-4) were identified by LC-MS(n) following incubation of compound I in GSH-enriched rat hepatocytes and liver microsomes. Three of these conjugates (M2-4) have not been reported previously for pentafluorophenyl derivatives. Elemental composition analysis of these conjugates was obtained using high-resolution quadrupole time-of-flight mass spectrometry. The formation of GSH conjugate M1 was rationalized as a direct nucleophilic replacement of fluoride by glutathione, whereas the formation of the GSH conjugates M2-4 was proposed to occur by NADPH-dependent metabolic activation of the pentafluorophenyl ring via arene oxide, quinone and/or quinoneimine reactive intermediates. Formation of these conjugates was enhanced three- to five-fold in liver microsomes obtained from phenobarbital- and dexamethasone-treated rats. In incubations with pooled rat liver microsomes and recombinant rat CYP3A1 and CYP3A2, troleandomycin (TAO) reduced the formation of GSH conjugates M2-4 by 80-90%, but it had no effect on the formation of M1. Incubation of compound I with rat supersomes indicated that only CYP3A1 and CYP3A2 were capable of mediating these metabolic activation processes.

Synthesis of chlorinated fluoresceins for labeling proteins

Two novel chlorinated fluoresceins 4,7,2',7'-tetrachloro-6-(5-carboxypentyl)fluorescein (8a) and 4,7,4',5'-tetra-chloro-6-(5-carboxypentyl)fluorescein (8b) were synthesized as fluorescent probes for labeling proteins. These two fluoresceins contain 6-aminohexanoic acid as spacer linker to minimize the fluorescence quenching of the fluorescein molecules by the proteins to be labeled.

A hydrophilic interaction chromatography coupled to a mass spectrometry for the determination of glutathione in plant somatic embryos

An electrospray ionization mass spectrometric (ESI-MS) determination of glutathione (GSH), a sulfur-containing tripeptide (gamma-Glu-Cys-Gly) with regulation and detoxication functions in metabolisms of most living organisms, from nanomolar to micromolar levels is described. A hydrophilic interaction chromatography (HILIC) with an isocratic elution using a mobile phase containing acetonitrile and an aqueous 0.00005% solution of trifluoroacetic acid (60/40%, v/v) was applied for the separation of GSH. The peptide detection was achieved in the presence of L-ascorbic acid which significantly enhanced the signal intensity of the molecular ion GSH [M+H]+ (m/z 308). The calibration curve was linear (R2=0.9995) in the concentration range from 2 nM to 10 microM with a detection limit (LOD, S/N=3) of 0.5 nM. The excellent detection limit, and the excellent selectivity and high reproducibility of this method enabled determination of GSH in a single plant somatic embryo of a Norway spruce (Picea abies). The average amount of GSH in the single somatic embryos (n=18) was 9 pmol per embryo. Owing to our results, it can be supposed that the proposed HILIC/ESI-MS analysis might be used for GSH determination in microscopic cell structures and in single cell analyses.

Electrophilic aromatic substituted luciferins as bioluminescent probes for glutathione S-transferase assays

New highly sensitive latent bioluminescent luciferin substrates were designed and synthesized for monitoring mammalian glutathione S-transferase (GST) and Schistosoma japonicum enzyme activities.

Differential multidrug resistance-associated protein 1 through 6 isoform expression and function in human intestinal epithelial Caco-2 cells

Multidrug resistance-associated protein (MRP) isoforms 1 through 6 mRNA are expressed in the human intestine and Caco-2 cells. In Caco-2 cells, the rank order for mRNA expression was MRP2 > or = MRP6 > MRP4 > or = MRP3 > MRP1 = MRP5. The functional expression of MRP-like activity was quantified as the efflux of the fluorescent probe calcein from confluent, polarized monolayers of Caco-2 cells. Calcein efflux was sensitive to temperature, energy depletion, and the MRP antagonist MK571 [3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid]. Calcein efflux across the apical membrane of Caco-2 cells exceeded that across the basolateral by approximately 2-fold, correlating with the apical localization of MRP2 visualized by immunocytochemical staining. T84 cells do not express MRP2 and show a predominance of basolateral calcein efflux over apical efflux. MRP3 was localized by immunocytochemical staining to the basolateral membrane. MRP1 staining was not localized to either membrane domain and MRP5 staining was not detected. Thus, basolateral calcein efflux may reflect a function of MRP3 or MRP4 and 6 inferred by their basolateral localization in other tissues. Basolateral, but not apical, calcein efflux was sensitive to glutathione depletion with buthioninesulfoximine, indicating that whereas MRP2-mediated apical efflux is independent of glutathione, basolateral efflux is glutathione-dependent. Benzbromarone, probenecid, pravastatin, and diclofenac were able to inhibit both apical and basolateral calcein efflux. The apical calcein efflux in Caco-2 cells was selectively sensitive to indomethacin and propranolol, but not verapamil or erythromycin, whereas the converse was observed for basal efflux. The differential pharmacological sensitivity of apical (MRP2) and basolateral calcein efflux provides tools for dissecting MRP isoform functional roles.

Frequency and significance of anti-glutathione S-transferase autoantibody (anti-GST A1-1) in autoimmune hepatitis

Several phase I and phase II multi-drug metabolizing enzymes, such as CYP2D6, 3A4, and UGTA1, were reported to act as immunotargets in a subset of autoimmune hepatitis and hepatic autoimmunity. However, it is uncertain whether glutathione S-transferase (GST) A1-1, one of the phase II multi-drug metabolizing enzymes, is also an immunotarget in autoimmune hepatitis. So, in the present study, we investigated the frequency and significance of anti-GST A1-1 in sera from patients with autoimmune hepatitis. A total of 74 serum samples from patients with autoimmune hepatitis were examined in the present study. As controls, 20 serum samples from patients with primary biliary cirrhosis, 10 serum samples from patients with primary sclerosing cholangitis, 40 serum samples from patients with liver cirrhosis type B and C, 32 serum samples from patients with systemic lupus erythematosus, and 20 serum samples from normal controls were used. Anti-GST A1-1 antibody was determined by immunoblotting using the recombinant full-length GST A1-1 protein as the antigen. The immunofluorescent staining pattern of anti-GST A1-1 was investigated using rat liver and kidney sections. We compared clinicopathologic findings between anti-GST A1-1-positive and -negative autoimmune hepatitis patients. Anti-GST A1-1 was detected in 12 (16%) of 74 patients with autoimmune hepatitis, however, it was not detected in any control serum samples except for two patients with primary biliary cirrhosis. The immunofluorescence staining pattern of anti-GST A1-1 was found to be unique and different from those of anti-mitochondrial antibody or anti-liver-kidney microsome type 1 antibody. Anti-GST A1-1 coexisted with other autoantibodies such as anti-nuclear or anti-smooth muscle antibodies, but did not coexist with anti-soluble liver antigen/liver pancreas. Anti-GST A1-1-positive autoimmune hepatitis patients had severe clinical features and a poor prognosis compared with anti-GST A1-1-negative patients. These findings suggested that despite the low frequency, anti-GST A1-1 might be the marker of an early progression in autoimmune hepatitis.

Thiol antioxidant reversal of pyrrolidine dithiocarbamate-induced reciprocal regulation of AP-1 and NF-kappaB

Pyrrolidine dithiocarbamate (PDTC) has been shown to have unique reciprocal activities in activating AP-1 and inhibiting NF-kappaB, two oxidative stress-sensitive transcription factors. The opposing effects of PDTC on these two transcription factors have been attributed to its thiol antioxidant properties. In the present study, PDTC activation of AP-1, like its inhibition of NF-kappaB, in bovine cerebral endothelial cells (BCECs) was zinc-dependent, consistent with the contention that PDTC acts as a zinc ionophore and the apparent reciprocal actions of PDTC are mediated by zinc. Unlike PDTC, other thiols and non-thiol antioxidants did not activate AP-1 on their own. Thiol, but not non-thiol, antioxidants reversed PDTC actions on AP-1 and NF-kappaB. PDTC reduced the intracellular glutathione content, and depletion of the cellular glutathione store by buthionine sulfoximine (BSO) further augmented PDTC actions on AP-1 and NF-kappaB. N-acetylcysteine (NAC), a thiol antioxidant, reversed PDTC actions even after irreversible depletion of the cellular glutathione store by BSO. These findings together suggest that thiol antioxidant reversal of PDTC actions on AP-1 and NF-kappaB is independent of their established roles in scavenging oxygen free radicals or repleting the cellular glutathione content. The results in the present and earlier studies suggest that thiol antioxidants are likely to act as metal chelators that buffer zinc mediation of the reciprocal actions of PDTC on AP-1 and NF-kappaB.

Synthesis and characterization of 6-chloroacetyl-2-dimethylaminonaphthalene as a fluorogenic substrate and a mechanistic probe for glutathione transferases

Here we demonstrate that the thiol-reactive, environmentally sensitive fluorogenic molecules 6-bromoacetyl-2-dimethylaminonaphthalene and 6-acryloyl-2-dimethylaminonaphthalene are substrates for glutathione transferases (GSTs). Product formation can be measured by strong increase in fluorescence of the glutathione conjugate. As these substances display a high nonenzymatic background reaction rate, we have synthesized and characterized 6-chloroacetyl-2-dimethylaminonaphthalene, which is less reactive, favoring the enzyme-catalyzed reaction. 6-Chloroacetyl-2-dimethylaminonaphthalene was found to be a substrate for all GSTs tested. Apparent k(cat)/K(m) values (ranging between 10 and 500 mM(-1)s(-1)) revealed a strong preference for soluble GSTP1-1, GSTA1-1, and activated MGST1. Thus, 6-chloroacetyl-2-dimethylaminonaphthalene can be used in a highly sensitive assay of these GSTs. 6-Acetyl-2-dimethylaminonaphthalene derivatives are very sensitive toward solvent polarity and potentially also toward properties of binding sites in proteins. Upon binding of the conjugate to GSTs the fluorescence intensity decreased and the emission maximum was blue-shifted. Therefore the interaction of the conjugate with GSTs can be characterized with regard to both binding affinity and kinetics by stopped-flow measurements, and 6-chloroacetyl-2-dimethylaminonaphthalene can be a valuable aid in mechanistic investigations of GSTs, especially those which possess low intrinsic fluorescence.

Analytical methods to investigate glutathione and related compounds in biological and pathological processes

Reduced glutathione (GSH, gamma-L-glutamyl-L-cysteinylglycine) is a fundamental low-molecular mass antioxidant that serves several biological functions. Upon enzymatic and non-enzymatic oxidation, GSH forms glutathione disulfide (GSSG) and, under particular conditions, may generate other oxidative products. The determination of GSH, its precursors, and metabolites in several bio-matrices is a useful tool in studying oxidative stress. Many separative and non-separative methods have been developed and improved for the assay of GSH and related compounds. At present, high-performance liquid chromatography and capillary electrophoresis are the most used separative techniques to determine GSH and congeners. The review will deal with analytical methods developed over the last few years for the determination of GSH and related compounds, and with the procedures performed in sample pre-treatment in order to minimize analytical errors. Since GSH, GSSG, and related compounds lack of strong chromophores or fluorophores, it is advantageous, in many assays, to derivatize the compounds in order to improve the detection limit with UV-Vis and to allow fluorescence, thus the most commonly used labeling agents are also described.

Redox-dependent trafficking of 2,3,4,5, 6-pentafluorodihydrotetramethylrosamine, a novel fluorogenic indicator of cellular oxidative activity

The trafficking of 2,3,4,5,6-pentafluorodihydrotetramethylrosamine (PF-H(2)TMRos, also known as RedoxSensor Red), a new fluorogenic indicator for oxidative activity, was evaluated in a contact-inhibited cell line, normal rat kidney fibroblast (NRK-49F), using quantitative fluorescence microscopy. After cells were incubated with 1-5 microM dye at 37 degrees C for 10 to 30 min, fluorescent staining of its oxidized product (PF-TMRos) distributed in mitochondria and/or lysosomes. This distribution pattern varied depending on the proliferation state of cells. In proliferating cells, PF-H(2)TMRos was internalized through a nonendocytic pathway, then oxidized in the cytosol, followed by immediate targeting to active mitochondria, resulting in fluorescent staining in this organelle. Photo-oxidation experiments demonstrated that PF-H(2)TMRos is not directly transported to mitochondria. On the contrary, in contact-inhibited cells whose proliferation is inhibited, PF-H(2)TMRos enters cells and is transported to lysosomes before it is oxidized. This results in lysosomal rather than mitochondrial staining. In both proliferating and quiescent cell states, subcellular distribution of the oxidized dye PF-TMRos can be altered by treatment with an oxidant (hydrogen peroxide) or an antioxidant (N-acetyl-L-cysteine), indicating a regulatory relationship between cell proliferation and oxidative activity. In solution assay, this probe can be oxidized by a broad spectrum of oxidizing species including horseradish peroxidase, hydrogen peroxide and horseradish peroxidase, cytochrome c, cytochrome c and hydrogen peroxide, superoxide and hydrogen peroxide, nitric oxide (or nitrite), peroxynitrite, and lipid hydroperoxide. Based on its subcellular distribution and its oxidation by a broad range of oxidizing species, PF-H(2)TMRos is demonstrated to be a novel indicator for cellular oxidative stresses.