Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.5.1.18 (glutathione S-transferase)
22,582 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The correlation between sequence diversity and enzymatic function was studied in a library of Theta class glutathione transferases (GSTs) obtained by stochastic recombination of fragments of cDNA encoding human GST T1-1 and rat GST T2-2. In all, 94 randomly picked clones were characterized with respect to sequence, expression level, and catalytic activity in the conjugation reactions between glutathione and six alternative electrophilic substrates. Out of these six different compounds, dichloromethane is a selective substrate for human GST T1-1, whereas 1-menaphthyl sulfate and 1-chloro-2,4-dinitrobenzene are substrates for rat GST T2-2. The other three substances serve as substrates for both enzymes. Through this broad characterization, we have identified enzyme variants that have acquired novel activity profiles that differ substantially from those of the original GSTs. In addition, the expression levels of many clones were improved in comparison to the parental enzyme. A library of mutants can thus display a distribution of properties from which highly divergent evolutionary pathways may emerge, resembling natural evolutionary processes. From the GST library, a clone was identified that, by the point mutation N49D in the rat GST T2-2 sequence, has a 1700% increased activity with 1-menaphthyl sulfate and a 60% decreased activity with 4-nitrophenethyl bromide. Through the N49D mutation, the ratio of these activities has thus been altered 40-fold. An extensive characterization of a population of stochastically mutated enzymes can accordingly be used to find variants with novel substrate-activity profiles and altered catalytic properties. Recursive recombination of selected sequences displaying optimized properties is a strategy for the engineering of proteins for medical and biochemical applications. Such sequential design is combinatorial protein chemistry based on remodeling of existing structural scaffolds and has similarities to evolutionary processes in nature.
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PMID:An ensemble of theta class glutathione transferases with novel catalytic properties generated by stochastic recombination of fragments of two mammalian enzymes. 1205 68

A biological monitoring method for urinary dichloromethane (DCM) has been developed by using head-space gas chromatography with FID detection. The calibration curve is linear in a wide range of DCM levels between 0.01 and 2 mg/l. The recovery rate is almost 100% and within-run coefficients of variation are 2.9-3.7%. A highly significant correlation is found between exposure levels and urinary concentrations of DCM. Determination of urine DCM by this method has many advantages such as sample storage, no need for correction of urine concentration, absence of gender difference and also no confounding effect of glutathione S-transferase T1 polymorphism.
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PMID:Biological monitoring of workers exposed to dichloromethane, using head-space gas chromatography. 1237 32

Recent data on the biology of aerobic methylotrophic bacteria capable of utilizing toxic halogenated methane derivatives as sources of carbon and energy are reviewed, with particular emphasis on the taxonomic, physiological, and biochemical diversity of mono- and dihalomethane-degrading methylobacteria and the enzymatic and genetic aspects of their primary metabolism. The initial steps of chloromethane dehalogenation to formate and HCl through a methylated corrinoid and methyletrahydrofolate are catalyzed by inducible cobalamin methyl transferase, made up of two proteins (CmuA and CmuB) encoded by the cmuA and cmuB genes. At the same time, the primary dehalogenation of dichloromethane to formaldehyde and HCl is catalyzed by cytosolic glutathione transferase with S-chloromethylglutathione as an intermediate. The latter enzyme is encoded by the structural dcmA gene and is under the negative control of the regulatory dcmR gene. In spite of considerable progress in the study of halomethane dehalogenation, some aspects concerning the structural and functional organization of this process and its regulation remain unknown, including the mechanisms of halomethane transport, the release of toxic dehalogenation products (S-chloromethylglutathione, CH2O, and HCl) from cells, and the maintenance of intracellular pH. Of particular interest is quantitative evaluation of the ecophysiological role of aerobic methylobacteria in the mineralization of halomethanes and protection of the biosphere from these toxic pollutants.
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PMID:[The biology of aerobic methylobacteria capable of degrading halomethanes]. 1275 Dec 36

Haloalkanes and haloalkenes constitute an important group of widely used chemicals that have the potential to induce toxicity and cancer. The toxicity of haloalkanes and haloalkenes may be associated with cytochromes P450- or glutathione transferase-dependent bioactivation. This review is concerned with the glutathione- and glutathione transferase-dependent bioactivation of dihalomethanes, 1,2-dihaloalkanes, and haloalkenes. Dihalomethanes, e.g., dichloromethane, and 1,2-dihaloethanes, e.g., 1,2-dichloroethane and 1,2-dibromoethane, undergo glutathione transferase-catalyzed bioactivation to give S-(halomethyl)glutathione or glutathione episulfonium ions, respectively, as reactive intermediates. Haloalkenes, e.g., trichloroethene, hexachlorobutadiene, chlorotrifluoroethene, and tetrafluoroethene, undergo cysteine conjugate beta-lyase-dependent bioactivation to thioacylating intermediates, including thioacyl halides, thioketenes, and 2,2,3-trihalothiiranes. With all of these compounds, the formation of reactive intermediates is associated with their observed toxicity.
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PMID:Glutathione-dependent bioactivation of haloalkanes and haloalkenes. 1555 37

GST (glutathione transferase) T1-1 plays an important role in the biotransformation of halogenated alkanes, which are used in large quantities as solvents and occur as environmental pollutants. Many reactions that are catalysed by GST T1-1 qualify as detoxification processes, but some reactions with dihalogenated alkanes lead to reactive products more toxic than the substrates. Murine GST T1-1 is particularly active with dichloromethane, which may explain the high carcinogenicity of dichloromethane in the mouse. Human GST T1-1 activity is considerably lower with halogenated hydrocarbons and some related substrates. Human GST T1-1 is polymorphic with a frequent null phenotype, suggesting that it is advantageous, under some circumstances, to lack the functional enzyme, which catalyses GSH conjugations that may cause bioactivation. The present study shows that amino acid residue 234 is a determinant of the differences in catalytic efficiency between the human and the rodent enzymes. The replacement of Trp234 in human GST T1-1 by arginine, found in the rodent enzyme, enhanced the alkyltransferase activity by an order of magnitude with a series of homologous iodoalkanes and some typical GST substrates. The specific activity of the alternative mutant Trp234-->Lys was lower than for the parental human GST T1-1 with many substrates, showing that a positive charge is not sufficient for increased activity. The enhanced activity of Trp234-->Arg with alkylating agents was dependent on the substrate tested, whereas no increase of the peroxidase activity with cumene hydroperoxide was noted. Residue 234 therefore is also involved in the control of the substrate selectivity of GST T1-1.
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PMID:Residue 234 in glutathione transferase T1-1 plays a pivotal role in the catalytic activity and the selectivity against alternative substrates. 1568 65

The current USEPA cancer risk assessment for dichloromethane (DCM) is based on deterministic physiologically based pharmacokinetic (PBPK) modeling involving comparative metabolism of DCM by the GST pathway in the lung and liver of humans and mice. Recent advances in PBPK modeling include probabilistic methods and, in particular, Bayesian inference to quantitatively address variability and uncertainty separately. Although Bayesian analysis of human PBPK models has been published, no such efforts have been reported specifically addressing the mouse, apart from results included in the OSHA final rule on DCM. Certain aspects of the OSHA model, however, are not consistent with current approaches or with the USEPA's current DCM cancer risk assessment. Therefore, Bayesian analysis of the mouse PBPK model and dose-response modeling was undertaken to support development of an improved cancer risk assessment for DCM. A hierarchical population model was developed and prior parameter distributions were selected to reflect parameter values that were considered the most appropriate and best available. Bayesian modeling was conducted using MCSim, a publicly available software program for Markov Chain Monte Carlo analysis. Mean posterior values from the calibrated model were used to develop internal dose metrics, i.e., mg DCM metabolized by the GST pathway/L tissue/day in the lung and liver using exposure concentrations and results from the NTP mouse bioassay, consistent with the approach used by the USEPA for its current DCM cancer risk assessment. Internal dose metrics were 3- to 4-fold higher than those that support the current USEPA IRIS assessment. A decrease of similar magnitude was also noted in dose-response modeling results. These results show that the Bayesian PBPK model in the mouse provides an improved basis for a cancer risk assessment of DCM.
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PMID:Revised assessment of cancer risk to dichloromethane: part I Bayesian PBPK and dose-response modeling in mice. 1644 84

Dichloromethane (DCM) is metabolically converted to carbon monoxide mostly by CYP2E1 in liver, resulting in elevation of blood carboxyhemoglobin (COHb) levels. We investigated the effects of a subtoxic dose of acetaminophen (APAP) on the metabolic elimination of DCM and COHb elevation in adult female rats. APAP, at 500 mg/kg i.p., was not hepatotoxic as measured by a lack of change in serum aspartate aminotransferase, alanine aminotransferase, and sorbitol dehydrogenase activities. In rats pretreated with APAP at this dose, the COHb elevation resulting from administration of DCM (3 mmol/kg i.p.) was enhanced significantly. Also blood DCM levels were reduced, and its disappearance from blood appeared to be increased. Hepatic CYP2E1-mediated activities measured with chlorzoxazone, p-nitrophenol, and p-nitroanisole as substrates were all induced markedly in microsomes of rats treated with APAP. Aminopyrine N-demethylase activity was also increased slightly, but significantly. Western blot analysis showed that APAP treatment induced the expression of CYP2E1 and CYP3A proteins. Neither hepatic glutathione contents nor glutathione S-transferase activity was changed by the dose of APAP used. The results indicate that, contrary to the well known hepatotoxic effects of this drug at large doses, a subtoxic dose of APAP may induce CYP2E1, and to a lesser degree, CYP3A expression. This is the first report that APAP can increase cytochrome P450 (P450)-mediated hepatic metabolism and the resulting toxicity of a xenobiotic in the whole animal. The pharmacological/toxicological significance of induction of P450s by a subtoxic dose of APAP is discussed.
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PMID:Induction of hepatic CYP2E1 by a subtoxic dose of acetaminophen in rats: increase in dichloromethane metabolism and carboxyhemoglobin elevation. 1762 Mar 48

Our previous study showed that the methanolic extract of Inula helenium (elecampane) had the potential to induce detoxifying enzymes such as quinine reductase (QR) and glutathione S-transferase. In this study we further fractionated the methanolic extract into hexane-, dichloromethane-, butanol-, and water-soluble fractions according to polarity. The hexane fraction showed the highest QR-inducing activity and also induced glutathione S-transferase in a dose-dependent manner. Its potential to induce the reporter activity suggested an antioxidant response element-mediated mechanism of action in the induction of phase II detoxifying enzymes. Intraperitoneal injection of the hexane fraction of I. helenium into ICR mice caused a significant increase of QR activity in liver, kidney, small intestine, and stomach. Sesquiterpenes, isolated from the hexane fraction, appeared to be major components responsible for QR induction. Among the seven compounds tested in this study, alantolactone, isoalantolactone, and 5alpha-epoxyalantolactone significantly induced QR activity in both Hepa1c1c7 and BPRc1 cells. In conclusion, sesquiterpenes, including alantolactone, isoalantolactone and 5-epoxyalantolactone, present in I. helenium merit further evaluation as chemopreventive agents.
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PMID:Induction of detoxifying enzyme by sesquiterpenes present in Inula helenium. 1788 45

A revised assessment of dichloromethane (DCM) has recently been reported that examines the influence of human genetic polymorphisms on cancer risks using deterministic PBPK and dose-response modeling in the mouse combined with probabilistic PBPK modeling in humans. This assessment utilized Bayesian techniques to optimize kinetic variables in mice and humans with mean values from posterior distributions used in the deterministic modeling in the mouse. To supplement this research, a case study was undertaken to examine the potential impact of probabilistic rather than deterministic PBPK and dose-response modeling in mice on subsequent unit risk factor (URF) determinations. Four separate PBPK cases were examined based on the exposure regimen of the NTP DCM bioassay. These were (a) Same Mouse (single draw of all PBPK inputs for both treatment groups); (b) Correlated BW-Same Inputs (single draw of all PBPK inputs for both treatment groups except for bodyweights (BWs), which were entered as correlated variables); (c) Correlated BW-Different Inputs (separate draws of all PBPK inputs for both treatment groups except that BWs were entered as correlated variables); and (d) Different Mouse (separate draws of all PBPK inputs for both treatment groups). Monte Carlo PBPK inputs reflect posterior distributions from Bayesian calibration in the mouse that had been previously reported. A minimum of 12,500 PBPK iterations were undertaken, in which dose metrics, i.e., mg DCM metabolized by the GST pathway/L tissue/day for lung and liver were determined. For dose-response modeling, these metrics were combined with NTP tumor incidence data that were randomly selected from binomial distributions. Resultant potency factors (0.1/ED(10)) were coupled with probabilistic PBPK modeling in humans that incorporated genetic polymorphisms to derive URFs. Results show that there was relatively little difference, i.e., <10% in central tendency and upper percentile URFs, regardless of the case evaluated. Independent draws of PBPK inputs resulted in the slightly higher URFs. Results were also comparable to corresponding values from the previously reported deterministic mouse PBPK and dose-response modeling approach that used LED(10)s to derive potency factors. This finding indicated that the adjustment from ED(10) to LED(10) in the deterministic approach for DCM compensated for variability resulting from probabilistic PBPK and dose-response modeling in the mouse. Finally, results show a similar degree of variability in DCM risk estimates from a number of different sources including the current effort even though these estimates were developed using very different techniques. Given the variety of different approaches involved, 95th percentile-to-mean risk estimate ratios of 2.1-4.1 represent reasonable bounds on variability estimates regarding probabilistic assessments of DCM.
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PMID:Probabilistic dose-response modeling: case study using dichloromethane PBPK model results. 1794 74

The radiosensitizing activity of dichloromethane extract of guduchi [Tinospora cordifolia (WILLD.) MIERS ex HOOK. F. & THOMS. Family: Menispermaceae (TCE)] in the mice transplanted with Ehrlich ascites carcinoma (EAC) was investigated. The EAC mice received 0, 25, 30, 40, 50 or 100 mg/kg b.wt. TCE 1 h before exposure to 6 Gy hemi-body gamma-radiation and then once daily for another eight consecutive days after irradiation. The EAC mice receiving TCE for the above regimen showed a dose-dependent elevation in tumor-free survival; the highest radiosensitizing activity was observed at 30 mg/kg b. wt. TCE. Treatment of animals with 30 mg/kg b. wt. TCE, 1 h before exposure to 6 Gy of hemi-body gamma irradiation and subsequently once daily for another six consecutive days post-irradiation increased the life span of EAC mice. This is evident by more number of long-term survivors (LTS) as well as survivors beyond 120 days when compared to the group of animals that received TCE after irradiation for six consecutive days. Treatment modality was also altered to assess the radiosensitizing effect of TCE before and after irradiation. Evaluation of glutathione (GSH), glutathione S-transferase (GST) and lipid peroxidation (LPx) in mice treated with TCE 1 h before irradiation and subsequently once daily for another six days showed a significant decline in GSH up to 14 h and GST up to 24 h accompanied by a significant elevation in LPx at 12 h post-irradiation. The radiosensitization of TCE may be due to depletion of glutathione and glutathione-S-transferase, accompanied by elevated levels of lipid peroxidation and DNA damage of tumor cells. Since Tinospora cordifolia is being used in India for treatment of various ailments, it may offer an alternative treatment strategy for cancer in combination with gamma radiation.
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PMID:Preliminary investigation of the radiosensitizing activity of guduchi (Tinospora cordifolia) in tumor-bearing mice. 1880 46


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