Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.2 (NQO1)
 6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of incubating young placental explants with HgCl2 on the activities of aryl hydrocarbon hydroxylase (AHH) (a phase I enzyme), quinone reductase (QR), catecholamine-O-methyltransferase (COMT) (both phase II enzymes), and glucose-6-phosphate dehydrogenase (G-6-PD) is described. Mercury (Hg) at low doses significantly elevated placental phase I and phase II enzyme activities, but decreased the activity of G-6-PD. The increase in activities, which was time- and dose-dependent, was higher in explants incubated for 24 hr than in those incubated for 6 hr. The decrease in placental G-6-PD activity was drastic at low Hg dose levels but at higher levels the inhibitory effect was milder for both incubation periods. Placental explants accumulated Hg in amounts proportional to its concentration in the incubation medium and this accumulation was greater in explants incubated for 24 hr. The data suggest that contamination with low Hg levels from the environment during pregnancy may affect placental enzymatic activity. The accumulation of Hg during short incubation indicates a strong placental cell affinity for Hg, which could affect its other metabolic functions. The system used in sensitive, as it shows alteration in enzyme activity even with relatively low concentrations of the metal and the response is dose-related.
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PMID:In vitro effect of mercury on enzyme activities and its accumulation in the first-trimester human placenta. 174 99

The effect of HgCl2 on human term placental aryl hydrocarbon hydroxylase (AHH), quinone reductase (QR), catecholamine-O-methyltransferase (COMT), and glucose-6-phosphate dehydrogenase (G-6-PD) enzyme activities was studied after incubation of placental explants with the salt for either a 6 or 24 hr period. Mercury (Hg) increased the activities of AHH, QR and COMT, but decreased that of G-6-PD. The increases in enzyme activities, as well as the decrease in G-6-PD activity observed were in all cases time- and dose-dependent. The data suggest that Hg exerts an enhancing effect on the activity of placental phase I enzyme (AHH) and phase II enzymes (QR and COMT). This enhancement may be due to increased de novo synthesis, elimination of some suppressing agent(s), or the decreased breakdown of enzyme protein. Also, the inhibitory effect of Hg on G-6-PD activity appears to indicate that this enzyme is appreciably more sensitive to Hg than the other three enzymes. These findings may imply increased cellular resistance to Hg toxicity. The altered state of activity may also be used as a tool for monitoring exposure to this metal.
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PMID:In vitro effect of mercury on aryl hydrocarbon hydroxylase, quinone reductase, catecholamine-O-methyltransferase and glucose-6-phosphate dehydrogenase activities in term human placenta. 194 76

The induction of NAD(P)H:quinone reductase (EC 1.6.99.2; QR) in Hepa 1c1c7 murine hepatoma cells provides a versatile quantitative model for measuring the potencies of inducers for Phase 2 detoxication enzymes. Since many inducers of these enzymes also protect animals and their cells against the toxic and neoplastic effects of carcinogens, understanding the mechanisms of induction of Phase 2 enzymes is important. Both HgCl2 and 2,3-dimercaptopropanol (BAL) are inducers of QR in these cells, and paradoxically BAL (which is about 30 times less potent than HgCl2) enhances the inducer potency of HgCl2 substantially. This synergism depends on the presence of two thiol groups on adjacent carbon atoms. Since nonchelated mercury(II)-thiol compounds did not show synergism, the formation of very high affinity bidentate chelates appears to be essential for such synergism. A major mechanism for the augmentation of the inducer potency of mercury(II) by BAL is the more rapid cellular uptake and the accumulation of higher intracellular concentrations of mercury. It is also possible that BAL-mercury chelates are intrinsically more potent as inducers. Although equimolar mixtures of BAL and HgCl2 and the synthetic chelate isolated from such mixtures were more potent inducers than HgCl2 alone, the presence of excess BAL increased this inducer synergism even further. By chromatography we showed the reversible formation of higher order complexes between BAL and mercury(II). Such complexes are transported into cells more efficiently and appear to be more potent than free HgCl2 or the chelate obtained from equimolar mixtures of BAL and HgCl2.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mercurials and dimercaptans: synergism in the induction of chemoprotective enzymes. 770 53

Exposure of rodents or their cells in culture to low doses of a wide variety of chemical agents, many of which are electrophiles, evokes a coordinated metabolic response that protects these systems against the toxicity (including mutagenicity and carcinogenicity) of higher doses of the same or other electrophiles. This response involves enhanced transcription of Phase 2 enzymes: glutathione transferases, NAD(P)H:quinone reductase, UDP-glucuronsyltransferases, and epoxide hydrolase, as well as the elevation of intracellular levels of reduced glutathione. We suggest that this cellular adaptation, which occurs in the liver and many peripheral tissues, be designated as the "Electrophile Counterattack" response. Seven families of highly diverse chemical agents that elicit this response include: oxidatively labile diphenols and quinones; Michael reaction acceptors (olefins conjugated to electron-withdrawing groups); isothiocyanates; organic hydroperoxides; vicinal dimercaptans; trivalent arsenicals; heavy metals (HgCl2, CdCl2) as well as mercury derivatives with high affinities for sulfhydryl groups; and 1,2-dithiole-3-thiones. An analysis of the molecular mechanisms of these enzyme inductions was carried out by transient expression in hepatoma cells of a plasmid containing a 41-bp enhancer element derived from the 5'-upstream region of the mouse glutathione transferase Ya gene, and the promoter region of this gene, linked to a human growth hormone reporter gene. The concentrations of 28 inducers (belonging to the seven chemical classes) required to double growth hormone production in this system spanned a range of four orders of magnitude and were closely and linearly correlated with the concentrations of the same compounds required to double the specific activity of quinone reductase in murine hepatoma cells. We therefore conclude that the regulation of these Phase 2 enzymes (and possibly also that of glutathione synthesis) by all of these inducers is mediated by the same enhancer element that contains AP-1-like sites. Similar enhancer sequences are present in the rat glutathione transferase Ya gene, and in the upstream regulatory regions of the quinone reductase genes of rat and human liver.
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PMID:The electrophile counterattack response: protection against neoplasia and toxicity. 835 13

Inductions of detoxication (phase 2) enzymes, such as glutathione transferases and NAD(P)H:(quinone-acceptor) oxidoreductase, are a major mechanism for protecting animals and their cells against the toxic and neoplastic effects of carcinogens. These inductions result from enhanced transcription, and they are evoked by diverse chemical agents: oxidizable diphenols and phenylenediamines; Michael reaction acceptors; organic isothiocyanates; other electrophiles--e.g., alkyl and aryl halides; metal ions--e.g., HgCl2 and CdCl2; trivalent arsenic derivatives; vicinal dimercaptans; organic hydroperoxides and hydrogen peroxide; and 1,2-dithiole-3-thiones. The molecular mechanisms of these inductions were analyzed with the help of a construct containing a 41-bp enhancer element derived from the 5' upstream region of the mouse liver glutathione transferase Ya subunit gene ligated to the 5' end of the isolated promoter region of this gene, and inserted into a plasmid containing a human growth hormone reporter gene. When this construct was transfected into Hep G2 human hepatoma cells, the concentrations of 28 compounds (from the above classes) required to double growth hormone production, and the concentrations required to double quinone reductase specific activities in Hepa 1c1c7 cells, spanned a range of four orders of magnitude but were closely linearly correlated. Six compounds tested were inactive in both systems. A 26-bp subregion of the above enhancer oligonucleotide (containing the two tandem "AP-1-like" sites but lacking the preceding ETS protein binding sequence) was considerably less responsive to the same inducers. We conclude that the 41-bp enhancer element mediates most, if not all, of the phase 2 enzyme inducer activity of all of these widely different classes of compounds.
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PMID:Chemical and molecular regulation of enzymes that detoxify carcinogens. 838 53

Mammalian cells have evolved elaborate mechanisms for protection against the toxic and neoplastic effects of electrophilic metabolites of carcinogens and reactive oxygen species. Phase 2 enzymes (e.g. glutathione transferase, NAD(P)H:quinone reductase, UDP-glucuronosyltransferases) and high intracellular levels of glutathione play a prominent role in providing such protection. Phase 2 enzymes are transcriptionally induced by low concentrations of a wide variety of chemical agents and such induction blocks chemical carcinogenesis. The inducers belong to many chemical classes including phenolic antioxidants. Michael reaction acceptors, isothiocyanates, 1,2-dithiole-3-thiones, trivalent arsenicals, HgCl2 and organomercurials, hydroperoxides, and vicinal dimercaptans. Induction by all classes of inducers involves the antioxidant/electrophile response element (ARE/EpRE). Inducers are widely, but unequally, distributed among edible plants. Search for such inducer activity in broccoli led to the isolation of sulforaphane, an isothiocyanate that is a very potent Phase 2 enzyme inducer and blocks mammary tumor formation in rats.
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PMID:Chemoprotection against cancer by phase 2 enzyme induction. 859 48