Glutathione Conjugates Research Articles

In silico and in vitro investigations on the protein–protein interactions of glutathione S-transferases with mitogen-activated protein kinase 8 and apoptosis signal-regulating kinase 1

Cytosolic glutathione S-transferase (GST) enzymes participate in several cellular processes in addition to facilitating glutathione conjugation reactions that eliminate endogenous and exogenous toxic compounds, especially electrophiles. GSTs are thought to interact with various kinases, resulting in the modulation of apoptotic processes and cellular proliferation. The present research used a combination of in silico and in vitro studies to investigate protein–protein interactions between the seven most abundant cytosolic GSTs—GST alpha-1 (GST-A1), GST alpha-2 (GST-A2), GST mu-1 (GST-M1), GST mu-2 (GST-M2), GST mu-5 (GST-M5), GST theta-1 (GST-T1) and GST pi-1 (GST-P1)—and Mitogen-activated protein kinase 8 (MAPK8) and Apoptosis signal-regulating kinase 1 (ASK1). MAPK8 and ASK1 were chosen as this study’s protein interaction partners because of their predominant role in electrophile or cytokine-induced stress-mediated apoptosis, inflammation and fibrosis. The highest degree of sequence homology or sequence similarity was observed in two GST subgroups: the GST-A1, GST-A2 and GST-P1 isoforms constituted subgroup1; the GST-M1, GST-M2 and GST-M5 isoforms constituted subgroup 2. The GST-T1 isoform diverged from these isoforms. In silico investigations revealed that GST-M1 showed a significantly higher binding affinity to MAPK8, and its complex was more structurally stable than the other isoforms, in the order GST-M1 > GST-M5 > GST-P1 > GST-A2 > GST-A1 > GST-M2 > GST-T1. Similarly, GST-A1, GST-P1 and GST-T1 actively interacted with ASK1, and their structural stability was also better, in the order GST-T1 > GST-A1 > GST-P1 > GST-A2 > GST-M5 > GST-M1 > GST-M2. To validate in silico results, we performed in vitro crosslinking and mass spectroscopy experiments. Results indicated that GST-M1 interacted with GST-T1 to form heterodimers and confirmed the predicted interaction between GST-M1 and MAPK8. Communicated by Ramaswamy H. Sarma

Carbon-Dipyrromethenes: Bright Cationic Fluorescent Dyes and Potential Application in Revealing Cellular Trafficking of Mitochondrial Glutathione Conjugates.

Boron-dipyrromethenes (Bodipys), since first reported in 1968, have emerged as a fascinating class of dyes in the past few decades due to their excellent photophysical properties including bright fluorescence, narrow emission bandwidth, resistance to photobleaching, and environment insensitivity. However, typical Bodipys are highly lipophilic, which often results in nonfluorescent aggregates in aqueous solution and also severely limits their bioavailability to cells and tissues. In this work, based on a simple one-atom B → C replacement in the Bodipy scaffold, we present a new class of carbon-dipyrromethenes (Cardipys for short) fluorescent dyes with tunable emission wavelengths covering the visible and near-infrared regions. These Cardipys not only retain the excellent photophysical properties of conventional Bodipys but also show improved water solubility and photostability due to their cationic character. Moreover, the cationic character also makes them extremely easy to penetrate the cell membrane and specifically accumulate into mitochondria without resorting to any mitochondria-targeted groups. Interestingly, several Cardipys bearing active styryl groups could serve as fluorescent indicators to map cellular trafficking of the glutathione conjugates produced within mitochondria under the catalysis of glutathione S-transferase (GST), thus showing potential in either exploring the detoxification mechanism of the mitochondrial GST/GSH system or evaluating the drug resistance of cancer cells that is closely related with GST activity.

In vitro biotransformation of pyrrolizidine alkaloids in different species: part II\u2014identification and quantitative assessment of the metabolite profile of six structurally different pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PA) exert their toxic effects only after bioactivation. Although their toxicity has already been studied and metabolic pathways including important metabolites were described, the quantification of the latter revealed a large unknown portion of the metabolized PA. In this study, the qualitative and quantitative metabolite profiles of structurally different PAs in rat and human liver microsomes were investigated. Between five metabolites for europine and up to 48 metabolites for lasiocarpine were detected. Proposals for the chemical structure of each metabolite were derived based on fragmentation patterns using high-resolution mass spectrometry. The metabolite profiles of the diester PAs showed a relatively good agreement between both species. The metabolic reactions were summarized into three groups: dehydrogenation, oxygenation, and shortening of necic acid(s). While dehydrogenation of the necine base is considered as bioactivation, both other routes are considered as detoxification steps. The most abundant changes found for open chained diesters were dealkylations, while the major metabolic pathway for cyclic diesters was oxygenation especially at the nitrogen atom. In addition, all diester PAs formed several dehydrogenation products, via the insertion of a second double bond in the necine base, including the formation of glutathione conjugates. In rat liver microsomes, all investigated PAs formed dehydropyrrolizidine metabolites with the highest amount formed by lasiocarpine, whereas in human liver microsomes, these metabolites could only be detected for diesters. Our findings demonstrate that an extensive analysis of PA metabolism can provide the basis for a better understanding of PA toxicity and support future risk assessment.

Metabolic excretion associated with nutrient-growth dysregulation promotes the rapid evolution of an overt metabolic defect.

In eukaryotes, conserved mechanisms ensure that cell growth is coordinated with nutrient availability. Overactive growth during nutrient limitation (“nutrient–growth dysregulation”) can lead to rapid cell death. Here, we demonstrate that cells can adapt to nutrient–growth dysregulation by evolving major metabolic defects. Specifically, when yeast lysine-auxotrophic mutant lys− encountered lysine limitation, an evolutionarily novel stress, cells suffered nutrient–growth dysregulation. A subpopulation repeatedly evolved to lose the ability to synthesize organosulfurs (lys−orgS−). Organosulfurs, mainly reduced glutathione (GSH) and GSH conjugates, were released by lys− cells during lysine limitation when growth was dysregulated, but not during glucose limitation when growth was regulated. Limiting organosulfurs conferred a frequency-dependent fitness advantage to lys−orgS− by eliciting a proper slow growth program, including autophagy. Thus, nutrient–growth dysregulation is associated with rapid organosulfur release, which enables the selection of organosulfur auxotrophy to better tune cell growth to the metabolic environment. We speculate that evolutionarily novel stresses can trigger atypical release of certain metabolites, setting the stage for the evolution of new ecological interactions.

Interactions Between Odorants and Glutathione Transferases in the Human Olfactory Cleft.

Xenobiotic metabolizing enzymes and other proteins, including odorant-binding proteins located in the nasal epithelium and mucus, participate in a series of processes modulating the concentration of odorants in the environment of olfactory receptors (ORs) and finely impact odor perception. These enzymes and transporters are thought to participate in odorant degradation or transport. Odorant biotransformation results in 1) changes in the odorant quantity up to their clearance and the termination of signaling and 2) the formation of new odorant stimuli (metabolites). Enzymes, such as cytochrome P450 and glutathione transferases (GSTs), have been proposed to participate in odorant clearance in insects and mammals as odorant metabolizing enzymes. This study aims to explore the function of GSTs in human olfaction. Using immunohistochemical methods, GSTs were found to be localized in human tissues surrounding the olfactory epithelium. Then, the activity of 2 members of the GST family toward odorants was measured using heterologously expressed enzymes. The interactions/reactions with odorants were further characterized using a combination of enzymatic techniques. Furthermore, the structure of the complex between human GSTA1 and the glutathione conjugate of an odorant was determined by X-ray crystallography. Our results strongly suggest the role of human GSTs in the modulation of odorant availability to ORs in the peripheral olfactory process.

Glutathione Conjugation and Protein Adduction by Environmental Pollutant 2,4-Dichlorophenol In Vitro and In Vivo.

2,4-Dichlorophenol (2,4-DCP), an environmental pollutant, was reported to cause hepatotoxicity. The biochemical mechanisms of 2,4-DCP induced liver injury remain unknown. The present study showed that 2,4-DCP is chemically reactive and spontaneously reacts with GSH and bovine serum albumin to form GSH conjugates and BSA adducts. The observed conjugation/adduction apparently involved the addition of GSH and departure of chloride via the ipso substitution pathway. Two biliary GSH conjugates and one urinary N-acetyl cysteine conjugate were observed in rats given 2,4-DCP. The N-acetyl cysteine conjugate was chemically synthesized and characterized by mass spectrometry and NMR. As expected, 2,4-DCP was found to modify hepatic protein at cysteine residues in vivo by the same chemistry. The observed protein adduction reached its peak at 15 min and revealed dose dependency. The new findings allowed us to better understand the mechanisms of the toxic action of 2,4-DCP.

Analysis of carnosic acid metabolites in rats by UHPLC-Q-Exactive MS

A method of ultra-high performance liquid chromatography coupled with quadrupole/electrostatic field Obitrap high-resolution mass spectrometry(UHPLC-Q-Exactive MS) was established to comprehensively identify the metabolites of carnosic acid in rats. After oral gavage of carnosic acid CMC-Na suspension in rats, urine, plasma and feces samples were collected and pretreated by solid phase extraction(SPE). Acquity UPLC BEH C_(18 )column(2.1 mm×100 mm, 1.7 μm) was used with 0.1% formic acid solution(A)-acetonitrile(B) as the mobile phase for the gradient elution. Biological samples were analyzed by quadrupole/electrostatic field Obitrap high-resolution mass spectrometry in positive and negative ion mode. Based on the accurate molecular mass, fragment ion information, and related literature reports, a total of 28 compounds(including carnosic acid) were finally identified in rat samples. As a result, the main metabolic pathways of carnosic acid in rats are oxidation, hydroxylation, methylation, glucuronide conjugation, sulfate conjugation, S-cysteine conjugation, glutathione conjugation, demethylation, decarbonylation and their composite reactions. The study showed that the metabolism of carnosic acid in rats could be efficiently and comprehensively clarified by using UHPLC-Q-Exactive MS, providing a reference for clarifying the material basis and metabolic mechanism of carnosic acid.

Structural and biochemical characterization of a glutathione transferase from the citrus canker pathogen Xanthomonas.

The genus Xanthomonas comprises several cosmopolitan plant-pathogenic bacteria that affect more than 400 plant species, most of which are of economic interest. Citrus canker is a bacterial disease that affects citrus species, reducing fruit yield and quality, and is caused by the bacterium Xanthomonas citri subsp. citri (Xac). The Xac3819 gene, which has previously been reported to be important for citrus canker infection, encodes an uncharacterized glutathione S-transferase (GST) of 207 amino-acid residues in length (XacGST). Bacterial GSTs are implicated in a variety of metabolic processes such as protection against chemical and oxidative stresses. XacGST shares high sequence identity (45%) with the GstB dehalogenase from Escherichia coli O6:H1 strain CFT073 (EcGstB). Here, XacGST is reported to be able to conjugate glutathione (GSH) with bromoacetate with a Km of 6.67 ± 0.77 mM, a kcat of 42.69 ± 0.32 s-1 and akcat/Km of 6.40 ± 0.72 mM-1 s-1 under a saturated GSH concentration (3.6 mM). These values are comparable to those previously reported for EcGstB. In addition, crystal structures of XacGST were determined in the apo form (PDB entry 6nxv) and in a GSH-bound complex (PDB entry 6nv6). XacGST has a canonical GST-like fold with a conserved serine residue (Ser12) at the GSH-binding site near the N-terminus, indicating XacGST to be a serine-type GST that probably belongs to the theta-class GSTs. GSH binding stabilizes a loop of about 20 residues containing a helix that is disordered in the apo XacGST structure.

Extrahepatic metabolism of ibrutinib.

SummaryIbrutinib is a first-in-class Bruton’s kinase inhibitor used in the treatment of multiple lymphomas. In addition to CYP3A4-mediated metabolism, glutathione conjugation can be observed. Subsequently, metabolism of the conjugates and finally their excretion in feces and urine occurs. These metabolites, however, can reach substantial concentrations in human subjects, especially when CYP3A4 is inhibited. Ibrutinib has unexplained nephrotoxicity and high metabolite concentrations are also found in kidneys of Cyp3a knockout mice. Here, a mechanism is proposed where the intermediate cysteine metabolite is bioactivated. The metabolism of ibrutinib through this glutathione cycle was confirmed in cultured human renal proximal tubule cells. Ibrutinib-mediated toxicity was enhanced in-vitro by inhibitors of breast cancer resistance protein (BCRP), P-glycoprotein (P-gp) and multidrug resistance protein (MRP). This was a result of accumulating cysteine metabolite levels due to efflux inhibition. Finally, through inhibition of downstream metabolism, it was shown now that direct conjugation was responsible for cysteine metabolite toxicity.

GSTs polymorphisms are associated with epigenetic silencing of CDKN2A gene in esophageal squamous cell carcinoma.

Esophageal cancer is the eighth most common cancer and the sixth most frequent cause of cancer mortality worldwide. Exposure to polycyclic aromatic hydrocarbons formed by incomplete combustion of organic matter is an important risk factor. Genetic polymorphisms in genes encoding PAH-metabolizing enzymes like glutathione S-transferases (GSTM1, GSTP1, GSTT1) which conjugate glutathione to PAHs for reduction of oxidative stress may affect an individual's response to PAH exposure. Genomic DNA from 50 esophageal squamous cell carcinoma patients extracted from peripheral blood. PCR-RFLP technique was employed to determine GSTM1, GSTT1, and GSTP1 polymorphisms. Aberrant promoter methylation of CDKN2A was applied by methylation-specific PCR technique. Concentration of urinary 1-hydroxypyrene was determined using a HPLC system. About 38.7% showed the null GSTM1 genotype (54% cases and 13% controls), 23.7% showed GSTT1 null genotype (30% cases and 13% controls), and 62.5% were GSTP1 A/A genotype (66% cases and 56% controls). Polymorphic variants of GSTM1 and GSTT1 were significantly associated with aberrant methylation of CDKN2A gene. The null state of GSTT1 was significantly associated with high concentrations of 1-OHP in urea (p < 0.01). There was significant association between methylated states of CDKN2A and high concentrations of 1-OHP in urine (p < 0.01). We identified significant association between polymorphism of GSTs genes and epigenetic silencing of tumor suppressor gene CDKN2A in esophageal squamous cell carcinoma.

Biotransformation Capacity of Zebrafish (Danio rerio) Early Life Stages: Functionality of the Mercapturic Acid Pathway.

Zebrafish (Danio rerio) early life stages offer a versatile model system to study the efficacy and safety of drugs or other chemicals with regard to human and environmental health. This is because, aside from the well-characterized genome of zebrafish and the availability of a broad range of experimental and computational research tools, they are exceptionally well suited for high-throughput approaches. Yet, one important pharmacokinetic aspect is thus far only poorly understood in zebrafish embryo and early larvae: their biotransformation capacity. Especially, biotransformation of electrophilic compounds is a critical pathway because they easily react with nucleophile molecules, such as DNA or proteins, potentially inducing adverse health effects. To combat such adverse effects, conjugation reactions with glutathione and further processing within the mercapturic acid pathway have evolved. We here explore the functionality of this pathway in zebrafish early life stages using a reference substrate (1-chloro-2,4-dinitrobenzene, CDNB). With this work, we show that zebrafish embryos can biotransform CDNB to the respective glutathione conjugate as early as 4 h postfertilization. At all examined life stages, the glutathione conjugate is further biotransformed to the last metabolite of the mercapturic acid pathway, the mercapturate, which is slowly excreted. Being able to biotransform electrophiles within the mercapturic acid pathway shows that zebrafish early life stages possess the potential to process xenobiotic compounds through glutathione conjugation and the formation of mercapturates. The presence of this chemical biotransformation and clearance route in zebrafish early life stages supports the application of this model in toxicology and chemical hazard assessment.

Armillaria mellea (Vahl) P. Kumm’nın karaciğer glutatyon S-transferaz aktivitesi üzerine baskılayıcı etkileri

Armillaria mellea (Vahl) P. Kumm. commonly-known as the honey fungus is an edible mushroom and its antioxidant, antitumor, neuroprotective, and insulin resistance reductive effects have been well-characterized. Glutathione S-transferases (GST) are the group of detoxification enzymes has a function to conjugate glutathione to the variety of electrophile, making them more water-soluble for excretion. Their inhibition or activation could have profound toxicological or clinical implications. This study is conducted to investigate the inhibitory effects of A. mellea on GST enzymes. Total GST activities were measured using glutathione and 1 chloro-2,4-dinitrobenzene as substrates spectrophotometrically, and enzyme kinetic studies were conducted to determine Vmax and Km values. Additionally, aqueous and methanolic extracts of A. mellea were tested to see how they modulate the kinetic parameters. Vmax for liver GST enzyme was calculated as 443.90 ±11.52 U/mg, Km value for GSH, and CDNB were determined as 4.88± 0.53 mM and 10.43±1.07 mM, respectively. The decrease in Vmax and the increase in Km values with A. mellea extracts demonstrated a mixed-type inhibitory mechanism. Methanolic extract inhibits the GSH-dependent GST activity much more than the CDNB-dependent activity, but aqueous extract mainly affects CDNB-dependent GST activity. In conclusion, A. mellea could suppress the hepatic GST enzymes that might have toxicological consequences such as reduced cellular detoxification of electrophilic xenobiotics as well as alleviated drug resistance in the treatment of several diseases.

Is there a role for tau glutathione transferases in tetrapyrrole metabolism and retrograde signalling in plants?

In plants, tetrapyrrole biosynthesis occurs in chloroplasts, the reactions being catalysed by stromal and membrane-bound enzymes. The tetrapyrrole moiety is a backbone for chlorophylls and cofactors such as sirohaems, haems and phytochromobilins. Owing to this diversity, the potential cytotoxicity of some precursors and the associated synthesis costs, a tight control exists to adjust the demand and the fluxes for each molecule. After synthesis, haems and phytochromobilins are incorporated into proteins found in other subcellular compartments. However, there is only very limited information about the chaperones and membrane transporters involved in the trafficking of these molecules. After summarizing evidence indicating that glutathione transferases (GST) may be part of the transport and/or degradation processes of porphyrin derivatives, we provide experimental data indicating that tau glutathione transferases (GSTU) bind protoporphyrin IX and haem moieties and use structural modelling to identify possible residues responsible for their binding in the active site hydrophobic pocket. Finally, we discuss the possible roles associated with the binding, catalytic transformation (i.e. glutathione conjugation) and/or transport of tetrapyrroles by GSTUs, considering their subcellular localization and capacity to interact with ABC transporters. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.

The Mechanism of Zinc Sulfate in Improving Fertility in Obese Rats Analyzed by Sperm Proteomic Analysis.

This study investigates the mechanism underlying the improving effect of zinc on fertility in obese rats using proteomics. The effects of three different doses of ZnSO4 on spermatogenesis and hormone levels were studied. Testicular spermatogenesis was observed by HE staining. Serum estrogen and testosterone levels were measured by chemiluminescent microparticle immunoassay. Sperm proteomic analysis was performed by liquid chromatography-mass spectrometry. The DAVID database was used to perform the GO enrichment analysis and KEGG pathway analysis of the differentially expressed genes, and the STRING online database was used to construct a PPI network. The sperm count, sperm motility, and testosterone hormones of the ZnSO4-treated rats group were increased. ZnSO4 improved testicular structure and spermatogenesis abnormalities caused by obesity. Proteomic analysis showed that there were 401 differentially expressed proteins in a total of 6 sperm samples from the ZnSO4-treated group and the obesity groups. Differential proteins were input into the DAVID website. The 341 identified proteins were then classified according to their biological functions. The KEGG analysis showed that the enriched signal pathways included glycolysis/gluconeogenesis, carbon metabolism, citrate cycle, fatty acid metabolism, and pyruvate metabolism. Some proteins were shown to be associated with valine, leucine, and isoleucine degradation pathways. STRING analysis obtained 36 node proteins. Cytoscape analysis showed that these proteins mainly participated in nine networks including metabolic process, oxidation-reduction, aerobic respiration, RNA splicing, and glutathione conjugation. ZnSO4 may improve the fertility of obese male rats by regulating protein expression related to metabolism, inflammation, and sperm maturation.

The Disposal of Reactive Carbonyl Species through Carnosine Conjugation: What We Know Now.

Reactive Carbonyl Species are electrophiles generated by the oxidative cleavage of lipids and sugars. Such compounds have been described as important molecules for cellular signaling, whilst their accumulation has been found to be cytotoxic as they may trigger aberrant modifications of proteins (a process often referred to as carbonylation). A correlation between carbonylation of proteins and human disease progression has been shown in ageing, diabetes, obesity, chronic renal failure, neurodegeneration and cardiovascular disease. However, the fate of reactive carbonyl species is still far from being understood, especially concerning the mechanisms responsible for their disposal as well as the importance of this in disease progression. In this context, some data have been published on phase I and phase II deactivation of reactive carbonyl species. In the case of phase II mechanisms, the route involving glutathione conjugation and subsequent disposal of the adducts has been extensively studied both in vitro and in vivo for some of the more representative compounds, e.g. 4-hydroxynonenal. There is also emerging evidence of an involvement of carnosine as an endogenous alternative to glutathione for phase II conjugation. However, the fate of carnosine conjugates is still poorly investigated and, unlike glutathione, there is little evidence of the formation of carnosine adducts in vivo. The acquisition of such data could be of importance for the development of new drugs, since carnosine and its derivatives have been proposed as potential therapeutic agents for the mitigation of carbonylation associated with disease progression. Herein, we wish to review our current knowledge of the binding of reactive carbonyl species with carnosine together with the disposal of carnosine conjugates, emphasizing those aspects still requiring investigation such as conjugation reversibility and enzyme assisted catalysis of the reactions.

Metabolism and Pharmacokinetics of SP-8356, a Novel (1S)-(-)-Verbenone Derivative, in Rats and Dogs and Its Implications in Humans.

(1S,5R)-4-((E)-3,4-dihydroxy-5-methoxystryryl)-6,6-dimethylbicylco[3.1.1]hept-3-en-2-one (SP-8356) is a novel (1S)-(−)-verbenone derivative that is currently in preclinical development for the treatment of ischemic stroke and atherosclerosis. This report aimed at characterization of the metabolism and pharmacokinetic properties of SP-8356. Following intravenous dose in rats and dogs, plasma concentrations of SP-8356 declined rapidly with high clearance (CL) and short half-life; after oral administration in both species, its plasma levels were below the quantitation limit. Fourteen circulating metabolites, formed by mono-oxygenation, demethylation, glucuronidation, catechol O-methylation, sulfation and oxidation (bioactivation) followed by glutathione (GSH) conjugation, were tentatively identified in both species. Urinary excretion of SP-8356 appeared to be minimal in rats, compared to its metabolites. GSH conjugate of SP-8356 was also formed during incubation with rat liver S9 fraction consistent with oxidative bioactivation; this bioactivation was almost completely inhibited by the cofactors for glucuronidation, sulfation and methylation, indicating that it may be abolished by competing metabolic reactions in the body. The human pharmacokinetics of SP-8356 was predicted to be similar to that of the animals based on the current in vitro metabolic stability results. In summary, rapid phase II metabolism appears to be mainly responsible for its suboptimal pharmacokinetics, such as high CL and low oral absorption. Because of competing metabolic reactions, potential safety risks related to SP-8356 bioactivation may be low.

A systematic metabolic pathway identification of Common Gardenia Fruit (Gardeniae Fructus) in mouse bile, plasma, urine and feces by HPLC-Q-TOF-MS/MS

Gardeniae Fructus was a traditional Chinese medicine (TCM) containing various biological ingredients including iridoids and crocetins, monocyclic monoterpenes, organic acids, and flavonoids. However, few systematic identification studies of the bioactive components in vivo have been reported. Herein, the ingredients and metabolites of Gardeniae Fructus were investigated using high-performance liquid chromatography coupled with high-sensitivity Q-TOF mass spectrometry. A total of 45 prototype compounds in Gardeniae Fructus extract were tentatively identified. After oral administration, 69 of prototypes and metabolites were identified from mice bile, plasma, urine, and feces, in which, 31 compounds were prototypes, and 38 chemicals were metabolites. The in vivo biotransformation pathways of these metabolites were also proposed including phase I (hydrolysis, hydrogenation, oxidation, loss of O, and ketone formation, decarboxylation) and phase II reactions (glycine, cysteine, glutathione, and glutamine, and sulfate conjugation, and glucuronidation). For the first time, our results had revealed systematic metabolic profiles of ingredients in Gardeniae Fructus extract in vivo of mice and replenished novel knowledge into the explanation of effective material and/or toxicological basis of Gardeniae Fructus which deserves further investigation.

Interindividual Differences in DNA Adduct Formation and Detoxification of 1,3-Butadiene-Derived Epoxide in Human HapMap Cell Lines.

Smoking-induced lung cancer is a major cause of cancer mortality in the US and worldwide. While 11-24% of smokers will develop lung cancer, risk varies among individuals and ethnic/racial groups. Specifically, African American and Native Hawaiian cigarette smokers are more likely to get lung cancer as compared to Caucasians, Japanese Americans, and Latinos. It is important to identify smokers who are at the greatest risk of developing lung cancer as they should be candidates for smoking cessation and chemopreventive intervention programs. Among 60+ tobacco smoke carcinogens, 1,3-butadiene (BD) is one of the most potent and abundant (20-75 μg per cigarette in mainstream smoke and 205-361 μg per cigarette in side stream smoke). BD is metabolically activated to 3,4-epoxy-1-butene (EB), which can be detoxified by glutathione S-transferase theta 1 (GSTT1)-mediated conjugation with glutathione, or can react with DNA to form 7-(1-hydroxy-3-buten-2-yl)guanine (EB-GII) adducts. In the present study, we employed EBV-transformed human lymphoblastoid cell lines (HapMap cells) with known GSTT1 genotypes to examine the influence of the GSTT1 gene on interindividual variability in butadiene metabolism, DNA adduct formation/repair, and biological outcomes (apoptosis). We found that GSTT1- HapMap cells treated with EB in culture produced lower levels of glutathione conjugates and were more susceptible to apoptosis but had similar numbers of EB-GII adducts as GSTT1+ cells. Our results suggest that GSTT1 can influence an individual's susceptibility to butadiene-derived epoxides.

Cytosolic glutathione‐S‐transferase A1 (GSTA1) plays a primary role in the metabolic clearance of the aromatase inhibitor, Exemestane

Exemestane (EXE) is used to treat estrogen receptor positive (ER+) breast cancer in postmenopausal women by inhibiting the enzyme aromatase in the final step of estrogen biosynthesis. Variability exists in both overall patient response and adverse events, which may be attributed to inter‐individual variation in EXE metabolism. EXE is metabolized primarily to the active metabolite, 17β‐dihydro‐EXE (17β‐DHE), and preliminary studies have demonstrated that cysteine conjugates of EXE and 17β‐DHE comprise 77% of total EXE metabolites in the urine of patients. Cysteine conjugation is a multi‐step process, the first of which is glutathione (GSH) conjugation, catalyzed by the glutathione‐S‐transferase (GST) family of the enzymes. The goal of the present study was to identify the hepatic GSTs active in the metabolism of EXE and 17β‐DHE. In a screening of the Human Protein Atlas, 12 cytosolic GSTs were found to be hepatically expressed and were initially screened by incubating 0.5 μg of pure recombinant GST enzyme with EXE or 17β‐DHE (125 μM) and reduced glutathione (GSH). The resulting GS‐conjugates of EXE and 17β‐DHE were detected and quantified using UPLC‐MS/MS. Results from the conjugation assays indicated that the cytosolic enzyme GSTA1 is highly active against both EXE and 17β‐DHE, while GSTM3 and GSTM1 are only moderately active against EXE. No other recombinant cytosolic GST enzymes tested (GSTA2, GSTA4, GSTK1, GSTM2, GSTM4, GSTO1, GSTP1, GSTZ1 and GSTT1) exhibited activity against either EXE or 17β‐DHE. KM values for human liver cytosol (HLC) and purified recombinant GSTA1 were similar for both EXE (45 μM vs. 77 μM, respectively) and 17β‐DHE (54 μM and 30 μM, respectively) as substrate, suggesting that GSTA1 may be the main driver for EXE and 17β‐DHE glutathione conjugation in human liver cytosol. Using EXE as a substrate, Vmax value for GSTA1 was &gt;7‐fold higher than that observed for GSTM3 (9.8 nmol/min/mg vs. 1.3 nmol/min/mg, respectively). The EXE intrinsic clearance (ClINT) for GSTA1 (130 nl/min/mg) was &gt;10‐fold higher than that observed for GSTM3 (11 nl/min/mg). These data suggest that GSTA1 may be an important component in the metabolic pathway contributing to the elimination of EXE in breast cancer patients.Support or Funding InformationThis work is supported by grants from NIH, National Cancer Institute (grant R01‐CA164366; to P. Lazarus) and the Health Sciences and Services Authority of Spokane, Washington (grant WSU002292 to College of Pharmacy and Pharmaceutical Sciences, Washington State University)

Determining the role for Nuclear receptor SHP in liver and kidney metabolism

Nuclear receptors are a unique family of ligand‐activated transcription factors that can modulate gene expression across various cellular functions. Nuclear receptor SHP (Small Heterodimer Partner), is atypical such that it lacks the DNA binding domain and its endogenous ligand is currently unknown. SHP is well known for regulating hepatic bile acid synthesis as a downstream target of nuclear receptor FXR. But previously published reports suggest that SHP may control heart function, germ cell differentiation, and cellular transport. Therefore, we set to investigate SHP function in both liver and extra‐hepatic tissues using mouse models. Since SHP can regulate nuclear receptor Constitutive Androstane Receptor (CAR) that is primarily responsible for drug metabolism, we examined a role for SHP in coordinating detoxification pathways. In the liver, absence of SHP resulted in robust increases in cyclins in response to CAR activation despite no liver growth. Detoxification is largely controlled by a trifecta of organs consisting of the liver, gut, and kidney, where SHP expression is noticeable. In fact, some of the detoxifying phase I, II and III genes also control bile acid homeostasis. We have found under cholestatic conditions liver expression of phase I metabolic pathway genes (CYP1A2 and CYP2E10) were significantly repressed whereas phase II metabolic genes (GSTM1 and GSTA2) are upregulated in the absence of SHP. We also found that the deletion of FXR and SHP altered organic solute transporters and GSTA1/2 mRNA levels in kidneys. This data suggests that murine SHP may regulate phase I and II metabolic processes distinctly in the liver and potentially contribute towards glutathione conjugation in the kidney.Support or Funding InformationNIDDK(R01 DK113080 AE433)