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)

It is well established that many types of tumor cells have reduced lipid peroxidation capacity compared to their normal counterparts. Changes in the activity of enzymes metabolizing aldehydes produced by lipid peroxidation have also been reported in a variety of tumor cells. We have investigated the relationship between changes in lipid peroxidation and changes in aldehyde-metabolizing enzymes in normal hepatocytes and two representative rat hepatoma cell lines, McA-RH-7777 and JM2. Compared to hepatocytes, both 7777 and JM2 cells have significantly lower basal and prooxidant-induced levels of lipid peroxidation than normal hepatocytes. Using 4-hydroxynonenal (4-HNE) as substrate, both cell lines also have significantly reduced activities of alcohol dehydrogenase (ADH) and glutathione S-transferase (GST) compared to hepatocytes. JM2 cells have significantly increased aldehyde dehydrogenase (ALDH) and aldehyde reductase (ALRD) activities with 4-HNE. In 7777 cells the ALDH and ALRD activities are not different from hepatocytes. The changes in enzyme activity are inversely correlated with the sensitivity of cells to 4-HNE. JM2 cells, with increased ALDH and ALRD and decreased ADH and GST, are much more resistant to the toxic effects of 4-HNE than 7777 cells. Normal hepatocytes and JM2 cells are approximately equally resistant to 4-HNE even though hepatocytes rely primarily on GST-mediated aldehyde conjugation to metabolize 4-HNE. Coupled with previous results from our laboratories, the overall increased sensitivity of certain hepatoma cells to lipid aldehydes appears due to decreased ability of these hepatoma cells to remove toxic products of lipid peroxidation. Moreover, hepatoma cells with increased levels of aldehyde dehydrogenase and aldehyde reductase appear most like hepatocytes in their ability to metabolize lipid aldehydes.
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PMID:Role of aldehyde metabolizing enzymes in mediating effects of aldehyde products of lipid peroxidation in liver cells. 803 12

Ingestion of aflatoxin B1 (AFB1) represents a major risk factor in the aetiology of human hepatocellular carcinoma. In the rat, the harmful effects of AFB1 can be prevented by the administration of certain drugs which induce hepatic detoxification enzymes. We have previously shown that treatment of rats with the chemoprotector ethoxyquin (EQ) results in a marked increase in expression of the Alpha-class glutathione S-transferase (GST) Yc2 subunit which has high activity towards AFB1-8,9-epoxide [Hayes, Judah, McLellan, Kerr, Peacock and Neal (1991) Biochem. J. 279, 385-398]. To allow an assessment of whether the increased expression of GST Yc2 represents a general adaptive resistance mechanism to chemical stress, that is invoked by both chemoprotectors and carcinogens, we have examined the effects of EQ, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), phenobarbital (PB), AFB1, 3-methylcholanthrene (3-MC) and clofibrate on the AFB1-glutathione-conjugating activity and the GST subunit levels in rat liver. In addition, the effect of these drugs on the hepatic levels of an aldehyde reductase (AFB1-AR) that metabolizes the cytotoxic dialdehydic form of AFB1 has been studied as this enzyme also appears to be important in chemoprotection. Administration of the antioxidants EQ, BHA or BHT, as well as PB, led to a marked increase in levels of the GST Yc2 subunit in rat liver, and this increase coincided with a substantial rise in the GST activity towards AFB1-8,9-epoxide; neither AFB1, 3-MC nor clofibrate caused induction of Yc2 or any of the GST subunits examined. Among the xenobiotics studied, EQ was found to be the most effective inducing agent for the Yc2 subunit as well as Yc1, Yb1 and Yf. However, PB was equally as effective as EQ in increasing levels of the Ya-type subunits, although it was not found to be as potent an inducer of the other GST subunits, including Yc2. In addition to induction of GST, EQ caused a substantial increase in the hepatic content of AFB1-AR. Both BHA and BHT were also able to induce this enzyme but, by contrast, PB was found to be a poor inducer of AFB1-AR. AFB1, 3-MC and clofibrate were unable to serve as inducers of this reductase. The presence of Alpha-class GST, including the Yc2 subunit, was examined in various rat tissues. Constitutive expression of Yc2 was found in the epididymis at levels comparable with that observed in the liver from EQ-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Regulation of aflatoxin B1-metabolizing aldehyde reductase and glutathione S-transferase by chemoprotectors. 819 22

A number of xenobiotics, including the synthetic antioxidant ethoxyquin, inhibit aflatoxin B1 (AFB1)-induced hepatocarcinogenesis in the rat. Two detoxification enzymes that mediate ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification: a glutathione S-transferase (GST) Yc2 subunit with at least 100-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases, and a unique aldehyde reductase with activity towards the dialdehydic form of AFB1-8,9-dihydrodiol. Molecular cloning has revealed that the Yc2 subunit is a class alpha GST and that the aflatoxin-metabolizing aldehyde reductase (AFAR) is a distant member of the aldo-keto reductase superfamily. Enzyme assay and western blotting have shown that many chemoprotectors, such as ethoxyquin, butylated hydroxyanisole, butylated hydroxytoluene, oltipraz and indole-3-carbinol, that inhibit AFB1-mediated hepatocarcinogenesis induce both GST Yc2 and AFAR. However, western blotting suggests that these enzymes are not always coordinately regulated, as treatment with phenobarbital and beta-naphthoflavone results in differences in the relative increase in hepatic GST Yc2 and AFAR. These findings indicate that GST Yc2 and AFAR represent important resistance mechanisms against AFB1 in the rat. This conclusion is supported by the observation that GST Yc2 and AFAR are overexpressed in rat liver preneoplastic nodules, which display pleiotropic drug resistance.
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PMID:Regulation of glutathione S-transferases and aldehyde reductase by chemoprotectors: studies of mechanisms responsible for inducible resistance to aflatoxin B1. 892 30

A range of potential chemoprotective agents, most of them natural dietary constituents, has been examined for ability to modulate both phase I (cytochrome P450 1A1, 1A2, 2B1/2, 2C11, 2E1, 3A, 4A) and phase II drug metabolizing enzymes (glutathione S-transferases, in particular subunits Yc2 and P, aflatoxin B1-aldehyde reductase and quinone reductase) in rat liver. In addition to assays of total enzyme activity and Western blots for individual isozymes, the ability of microsomes to metabolize aflatoxin B1, and of cytosols to conjugate aflatoxin B1 (AFB1)-epoxide to GSH and to produce AFB1-dialcohol, were measured. Induction of gamma-glutamyl transpeptidase activity was examined by histochemistry. Differing patterns of induction were observed, reflecting differences in the control of expression of the individual enzymes studied. Of the compounds examined, butylated hydroxytoluene, ethoxyquin, indole-3-carbinol and phenethyl isothiocyanate were the most potent bifunctional agents (inducing both phase I and II activities). Oltipraz, while only weakly inducing CYP1A2 and 2B1/2, was a potent inducer of phase II enzymes. Caffeic acid, garlic oil, sinigrin and propyl gallate all showed some ability to induce phase II enzymes. 4-Methyl catechol, alpha-tocopherol and red wine decreased certain phase I enzyme activities, while inducing total GST activity. Butylated hydroxytoluene, ethoxyquin, garlic oil and indole-3-carbinol induced gamma glutamyltranspeptidase in periportal hepatocytes. Particularly because of their ability to induce the detoxifying activities of glutathione S-transferase Yc2 and aldehyde reductase, butylated hydroxytoluene, ethoxyquin, indole-3-carbinol, oltipraz, phenethyl isothiocyanate and sinigrin will be effective blocking agents in rodents, if administered prior to AFB1. While these studies indicate the relative contributions of phase I and II metabolism in the overall protective effect in rat, care should be taken that a similar balance is achieved in man, and that relevant enzymes or iso forms are induced.
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PMID:Mechanism of action of dietary chemoprotective agents in rat liver: induction of phase I and II drug metabolizing enzymes and aflatoxin B1 metabolism. 932 68

Fischer 344 rats fed on a diet that is deficient in selenium are more resistant to the hepatocarcinogen aflatoxin B1 (AFB1) than those fed on a selenium-sufficient diet. Hepatic cytosol from either selenium-deficient Fischer 344 rats or Hooded Lister rats possesses a marked increase in both reductase activity toward AFB1-dialdehyde and glutathione S-transferase (GST) activity toward AFB(1)-8,9-epoxide than hepatic cytosol from selenium-sufficient rats. The elevation in hepatic AFB1-aldehyde reductase (AFAR) activity in selenium-deficient animals is accompanied by an increase of 11- and 15-fold in the levels of AFAR protein in liver cytosol from Fischer 344 and Hooded Lister rats, respectively. The amount of AFAR protein in selenium-sufficient and -deficient Fischer rats was modulated by treatment with N-acetylcysteine; this antioxidant reduced basal expression of AFAR but did not modulate the relative overexpression of AFAR during selenium deficiency. The enhanced capacity to conjugate glutathione with AFB(1)-8,9-epoxide in selenium-deficient livers from Fischer 344 and Hooded Lister rats is associated with a 5- and 7-fold increase, respectively, in the hepatic levels of the AFB1-metabolizing alpha-class GSTA5 subunit. The elevated levels of AFAR and GSTA5 protein in the selenium-deficient animals coincided with increases in the steady-state levels of their mRNAs. In selenium-deficient Fischer 344 rats, AFAR and GSTA5 were both found to be expressed throughout the centrilobular and midzonal areas of the liver lobule but were essentially absent from periportal hepatocytes. The effect of selenium insufficiency is pleiotropic, and it was also noted that the theta-class GSTT1 is overexpressed 3- and 10-fold in livers of selenium-deficient Hooded Lister and Fischer 344 rats. Inasmuch as GSTT1 is responsible for the metabolic activation of dihaloalkanes, selenium deficiency may increase the susceptibility of rats to mutagens such as dichloromethane.
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PMID:Protection conferred by selenium deficiency against aflatoxin B1 in the rat is associated with the hepatic expression of an aldo-keto reductase and a glutathione S-transferase subunit that metabolize the mycotoxin. 933 Oct 86

The rat can be protected against aflatoxin B1 (AFB1) hepatocarcinogenesis by being fed on a diet containing the synthetic antioxidant ethoxyquin. Evidence suggests that chemoprotection against AFB1 is due to increased detoxification of the mycotoxin by one or more inducible drug-metabolising enzymes. The glutathione S-transferase (GST) isoenzymes in rat liver that contribute to ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification. This approach resulted in the isolation of several heterodimeric class alpha GST, all of which contained the A5 subunit and possessed at least 50-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases. Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases. The A5 homodimer can also catalyse the conjugation of glutathione with other epoxides, such as trans-stilbene oxide and 1,2-epoxy-3-(4'-nitrophenoxy)propane, and possesses high catalytic activity for the reactive aldehyde 4-hydroxynonenal. Western blotting has shown that the A5 subunit is not only induced by ethoxyquin but that it is also induced by other cancer chemopreventive agents, such as butylated hydroxyanisole, oltipraz, benzyl isothiocyanate, indole-3-carbinol and coumarin. In addition to GSTA5, we have identified a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin. However, immunoblotting has shown that GSTA5 and AFAR are not always co-ordinately regulated by chemoprotectors. In order to gain a better understanding of the mechanisms responsible for the induction of GSTA5 protein, the GSTA5 gene has been cloned. It was isolated on two overlapping bacteriophage lambda clones and found to be approximately 12 kb in length. The transcriptional start site of GSTA5 has been identified 228 bp upstream from the ATG translational initiation codon. Computer-assisted analysis of the upstream sequence has indicated the presence of a putative antioxidant responsive element (located between -421 and -429 bp) which may be responsible for the induction of GSTA5 by chemopreventive agents.
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PMID:Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents: mechanisms of inducible resistance to aflatoxin B1. 967 43

Structurally diverse compounds can confer resistance to aflatoxin B1 (AFB1) hepatocarcinogenesis in the rat. Treatment with either phytochemicals [benzyl isothiocyanate, coumarin (CMRN), or indole-3-carbinol] or synthetic antioxidants and other drugs (butylated hydroxyanisole, diethyl maleate, ethoxyquin, beta-naphthoflavone, oltipraz, phenobarbital, or trans-stilbene oxide) has been found to increase hepatic aldo-keto reductase activity toward AFB1-dialdehyde and glutathione S-transferase (GST) activity toward AFB1-8,9-epoxide in both male and female rats. Under the conditions used, the natural benzopyrone CMRN was a major inducer of the AFB1 aldehyde reductase (AFAR) and the aflatoxin-conjugating class-alpha GST A5 subunit in rat liver, causing elevations of between 25- and 35-fold in hepatic levels of these proteins. Induction was not limited to AFAR and GSTA5: treatment with CMRN caused similar increases in the amount of the class-pi GST P1 subunit and NAD(P)H: quinone oxidoreductase in rat liver. Immunohistochemistry demonstrated that the overexpression of AFAR, GSTA5, GSTP1, and NAD(P)H:quinone oxidoreductase affected by CMRN is restricted to the centrilobular (periacinar) zone of the lobule, sometimes extending almost as far as the portal tract. This pattern of induction was also observed with ethoxyquin, oltipraz, and trans-stilbene oxide. By contrast, induction of these proteins by beta-naphthoflavone and diethyl maleate was predominantly periportal. Northern blotting showed that induction of these phase II drug-metabolizing enzymes by CMRN was accompanied by similar increases in the levels of their mRNAs. To assess the biological significance of enzyme induction by dietary CMRN, two intervention studies were performed in which the ability of the benzopyrone to inhibit either AFB1-initiated preneoplastic nodules (at 13 weeks) or AFB1-initiated liver tumors (at 50 weeks) was investigated. Animals pretreated with CMRN for 2 weeks prior to administration of AFB1, and with continued treatment during exposure to the carcinogen for a further 11 weeks, were protected completely from development of hepatic preneoplastic lesions by 13 weeks. In the longer-term dietary intervention, treatment with CMRN before and during exposure to AFB1 for a total of 24 weeks was found to significantly inhibit the number and size of tumors that subsequently developed by 50 weeks. These data suggest that consumption of a CMRN-containing diet provides substantial protection against the initiation of AFB1 hepatocarcinogenesis in the rat.
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PMID:Chemoprevention of aflatoxin B1 hepatocarcinogenesis by coumarin, a natural benzopyrone that is a potent inducer of aflatoxin B1-aldehyde reductase, the glutathione S-transferase A5 and P1 subunits, and NAD(P)H:quinone oxidoreductase in rat liver. 1070 11

Poultry are the most susceptible food animal species to the toxic effects of the mycotoxin aflatoxin B(1) (AFB(1)). Feed contaminated with even small amounts of AFB(1) results in significant adverse health effects in poultry. The purpose of this study was to explain the biochemical mechanism(s) for this extreme sensitivity. We measured microsomal activation of AFB(1) to the AFB(1)-8,9-epoxide (AFBO), the putative toxic intermediate, as well as cytosolic glutathione S-transferase (GST)-mediated detoxification of AFBO, in addition to other hepatic phase I and phase II enzyme activities, in 3-week-old male Oorlop strain turkeys. Liver microsomes prepared from these turkeys activated AFB(1) in vitro with an apparent K(m) of 109 microM and a V(max) of 1.25 nmol/mg/min. Preliminary evidence for the involvement of cytochromes P450 (CYP) 1A2 and, to a lesser extent, 3A4 for AFB(1) activation was assessed by the use of specific mammalian CYP inhibitors. The possible presence of avian orthologues of these CYPs was supported by activity toward ethoxyresorufin and nifedipine, as well as by Western immunoblotting using antibodies to human CYPs. Cytosol prepared from turkey livers exhibited GST-mediated conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) and 3,4-dichloronitrobenzene (DCNB), but at a much lower rate than that observed in other species. Western immunoblotting indicated the presence of alpha and sigma class GSTs and another AFB(1)-detoxifying enzyme, AFB(1)-aldehyde reductase (AFAR). Turkey liver cytosol also had quinone oxidoreductase (QOR) activity. Importantly, cytosol exhibited no measurable GST-mediated detoxification of microsomally activated AFB(1), indicating that turkeys are deficient in the most crucial AFB(1)-detoxification pathway. In total, our data indicate that the extreme sensitivity of turkeys to AFB(1) may be attributed to a combination of efficient AFB(1) activation and deficient detoxification by phase II enzymes, such as GSTs.
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PMID:Biochemical basis for the extreme sensitivity of turkeys to aflatoxin B(1). 1081 52

Poultry are some of the most sensitive species to the toxic effects of aflatoxin B(1) (AFB(1)), and younger poultry are more sensitive to this mycotoxin. To elucidate the mechanisms for this age-related susceptibility, various enzyme activities relevant to AFB(1) were measured in liver microsomes prepared from male turkeys 9, 41 and 65 days of age. Hepatic microsomal o-dealkylation of methoxy- and pentoxyresorufin significantly increased, while that of ethoxyresorufin decreased with age. Microsomal AFB(1) activation to the reactive AFB(1)-8,9-epoxide (AFBO) was most efficient in the youngest birds, with apparent K(m) and V(max) values of 168 and 19, 110 and 6, and 116 microM and 10 nmol/mg/min for 9, 41 and 65-day-old birds, respectively. The activity of hepatic cytosolic glutathione S-transferases (GSTs) was deficient in the youngest age group, but were higher in the older groups. There was also an age-related increase in the expression of GST isoforms Yc, Yc(2), as well as AFB(1)-aldehyde reductase (AFAR). However, livers from all ages lacked specific GST-mediated conjugation of AFBO, indicating that turkeys are deficient in this key AFB(1)-detoxification pathway. Our data indicate that efficient activation may underlie the extreme sensitivity of young turkeys to the toxic effects of AFB(1).
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PMID:Biochemical factors underlying the age-related sensitivity of turkeys to aflatoxin B(1). 1210 96

Oltipraz and related dithiolethiones constitute an important class of chemopreventive agents that enhance the expression of carcinogen detoxication and antioxidant genes. Dose-response studies were undertaken to characterize the cancer chemopreventive activities of several dithiolethiones that are at least as active as oltipraz as inducers. Inhibition of formation of pre-neoplastic lesions and formation of DNA adducts in livers of rats exposed to aflatoxin B1 (AFB1) was monitored. In the tumorigenesis experiment, the dithiolethiones were orally gavaged 3 days/week for 3 successive weeks and at four doses ranging from 0.03 to 0.3 mmol/kg body wt. AFB1 was gavaged beginning 1 week after the start of the dithiolethiones and for two successive weeks. The burden of AFB1-induced putative pre-neoplastic lesions (glutathione S-transferase-placental isoform positive foci) was quantified by light microscopy. Reduction in AFB-DNA adduct burden was assessed 24 h following the first dose of AFB1. Both the parent 1,2-dithiole-3-thione (D3T) and its 5-tert-butyl derivative were more potent inhibitors than oltipraz against these endpoints, while two of the seven tested analogs were slightly less inhibitory. D3T, the most potent dithiolethione of this series, was examined by microarray analysis for induction of hepatic genes at an intermediate chemopreventive dose (0.1 mmol/kg). Transcript levels of eight genes, including two known to detoxify aflatoxin, namely, glutathione S-transferase A5 (GSTA5) and AFB1 aldehyde reductase (AFAR) were elevated. Western analysis indicated that induction of hepatic GSTA5 and AFAR were directly related to the dose of D3T. At the highest dose of D3T (0.3 mmol/kg), protein levels of GSTA5 and AFAR were induced by 7- and 27-fold, respectively. While efficacy in humans has yet to be tested, D3T is clearly more potent than oltipraz and serves as a useful molecular probe for determining the key events associated with protection by this class of agents.
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PMID:Evaluation of the cancer chemopreventive potency of dithiolethione analogs of oltipraz. 1455 9


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