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

1. Treatment with N,N-bis (2-chloroethyl)-N-nitrosourea (BCNU) (80 microM) led to decreases in cell viability in both naive and sodium phenobarbital (PB) induced hepatocytes. 2. Dicumarol (30 microM) selectively increased the cytotoxicity of menadione in hepatocytes isolated from naive vs PB-pretreated rats. 3. Inclusion of both BCNU and dicumarol to the incubation medium abolished the characteristic concentration-response curves of the hepatocytes for menadione. 4. A greater proportion of menadione was metabolized by DT-diaphorase in the hepatocytes isolated from PB-pretreated rats. 5. The role of glutathione reductase vs DT-diaphorase in mitigating menadione-cytotoxicity in the naive vs PB-induced hepatocyte is discussed.
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PMID:Phenobarbital-induced cytoprotective mechanisms in menadione metabolism: the role of glutathione reductase and DT-diaphorase. 170 18

The interaction of N-(4-ethoxyphenyl)p-benzoquinone imine (NEPBQI), a metabolite formed during peroxidase catalyzed metabolism of p-phenetidine, with GSH and its effects in isolated rat hepatocytes were investigated. When reacted with GSH NEPBQI formed both a mono- and a diglutathione conjugate as well as GSSG. Formation of glutathione conjugates and GSSG also occurred when NEPBQI was added to isolated hepatocytes. The formation of GSSG was, however, only detectable if the hepatocytes had been pretreated with the GSSG reductase inhibitor BCNU (1,3-bis-(2-chloroethyl-1-nitrosourea). Similarly, NEPBQI caused a rapid decrease in cellular free protein thiols when added to hepatocytes, however this was expressed at higher concentrations than for effects on GSH. The protein thiol decrease was correlated with protein binding of NEPBQI. NEPBQI was also shown to be toxic to isolated hepatocytes. At a concentration of 400 microM extensive bleb formation was followed by loss of cell membrane integrity and cell death. To assess further the subcellular metabolism of NEPBQI microsomes and cytosol was used. NEPBQI was found to be preferentially reduced by cytochrome P-450 reductase in the microsomes whereas DT-diaphorase catalyzed its reduction in cytosol. NEPBQI did not undergo significant redox cycling since no formation of O2 was observed. Thus, the cytotoxic effect of NEPBQI appears to be due to protein arylation rather than redox cycling.
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PMID:Cellular effects of N(4-ethoxyphenyl)p-benzoquinone imine, a p-phenetidine metabolite formed during peroxidase reactions. 379 94

Aerobic sensitivity to indoloquinone EO9 has been shown to correlate with cellular levels of the two-electron reducing enzyme DT-diaphorase. However, little is known about the relative roles of one- and two-electron reducing enzymes in the hypoxic cytotoxicity of EO9. We have characterised a panel of 23 human tumour cell lines for both bioreductive enzyme activities and aerobic sensitivity to EO9. Eight cell lines were then selected for a comparison of aerobic and hypoxic sensitivities. Activities of DT-diaphorase showed a wide range (> 10,000-fold), while activities of the one-electron reducing cytochrome b5 and cytochrome P450 reductases were generally lower and showed only a 15- and 25-fold range respectively. The aerobic cytotoxicity of EO9 was clearly related to the cellular levels of DT-diaphorase (r = 0.87), with higher levels giving increased sensitivity, but not to the levels of one-electron reducing enzymes. In contrast, there was no relationship between sensitivity to BCNU, cisplatin or the bioreductive agent SR 4233 (tirapazamine) and activities of any of these reducing enzymes. Under hypoxic conditions sensitivity to EO9 was markedly increased in cell lines with low levels of DT-diaphorase activity, while cell lines with high levels show only a small increase in sensitivity. This is reflected by a clear correlation (r = 0.98) between cellular DT-diaphorase activity and the ratio of aerobic to hypoxic sensitivity to EO9. However, we have now for the first time demonstrated an inverse correlation (r = 0.93) between the cellular activity of DT-diaphorase and hypoxic sensitivity to EO9, that is sensitivity decreases with increasing DT-diaphorase activity. Moreover, this correlation was lost when cells were exposed to drug in the presence of dicoumarol, supporting an involvement of DT-diaphorase in this relationship. These observations question the previously straightforward role for DT-diaphorase in the metabolic activation of EO9. Whereas DT-diaphorase is associated with increased toxicity in air, it appears to reduce the cytotoxicity of EO9 in hypoxic conditions. This suggests either that the one-electron reduction product of EO9 metabolism, the semiquinone, is more toxic than the two-electron reduction product, the hydroquinone, or that the hydroquinone is not cytotoxic and aerobic toxicity is due to the transient appearance of the semiquinone upon back oxidation of the hydroquinone.
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PMID:DT-diaphorase protects cells from the hypoxic cytotoxicity of indoloquinone EO9. 752 85

This study describes characteristics of a human bladder cancer cell line, SCaBER/R, selected for resistance to a mitomycin C (MMC) analogue BMY 25067. The SCaBER/R cell line was isolated by repeated 24 h exposures of the parental cells to 0.09 microM BMY 25067 (IC90, 24 h drug exposure) over a period of about 180 days. Approximately 2.2-fold higher concentration of BMY 25067 was required to kill 50% of the SCaBER/R cell line compared with parental cells (p < 0.001). The IC20 and IC90 values for BMY 25067 were also significantly higher in the SCaBER/R cell line than in SCaBER. Unlike most MMC resistant cell lines, the SCaBER/R cell line displayed a marked cross-resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and lacked cross-resistance to cisplatin, doxorubicin or VP-16. The SCaBER/R cell line also displayed a marked cross-resistance to the parent drug (MMC) and BMY 25282, another analogue of MMC. NADPH cytochrome P450 reductase activity, an enzyme implicated in bio-reductive activation of MMC, did not differ significantly in these cells. DT-diaphorase activity, another MMC activation enzyme, was significantly lower in the SCaBER/R cell line when compared to the SCaBER cells. These results suggest that relatively lower sensitivity of SCaBER/R cell line to MMC and BMY 25067 may result from impaired drug activation. Cellular levels of glutathione (GSH) and GSH-transferase (GST), which have been suggested to affect the cytotoxicity of MMC, were comparable in SCaBER and SCaBER/R cell lines. BMY 25067 induced DNA interstrand cross-links (DNA-ISC) could not be detected in either of the cell lines even at drug concentrations which produced a significant cell kill. These findings suggest that (a) cellular resistance to BMY 25067 in the SCaBER/R cell line may be due to impaired drug activation, and (b) the nature of the cytotoxic produced by BMY 25067 may be different from that of MMC.
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PMID:Characterization of a human bladder cancer cell line selected for resistance to BMY 25067, a novel analogue of mitomycin C. 765 43

Chromium (VI) is an environmental and occupational carcinogen, and it is accepted that intracellular reduction is necessary for DNA damage and cytotoxicity. We have investigated the interaction of Cr(VI) with hepatocytes in vitro to determine the contribution of various hepatic enzymes to the reduction of Cr(VI). Cr(VI) caused a dose-dependent decrease in cell viability and intracellular reduced glutathione (GSH) levels between 100 and 500 microM within 3 h exposure of hepatocytes. Both DT-diaphorase and cytochrome P450 play only a minor role in detoxifying Cr(VI) and/or its metabolites. (GSH) appears to act as a non-enzymatic reductant, reducing Cr(VI) to a toxic form. The evidence for this is two-fold. Firstly, GSH was depleted during the metabolism of Cr(VI) and, secondly, pretreatment of the cells with diethylmaleate to deplete GSH levels, partially protected the cells from Cr(VI) toxicity. Glutathione reductase appears to play an important role in the enzymatic reduction of Cr(VI) as inhibition of this enzyme by carmustine (BCNU) markedly protected the cells from cytotoxicity.
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PMID:The role of glutathione reductase in the cytotoxicity of chromium (VI) in isolated rat hepatocytes. 1131 Dec 13

We compared the cytotoxicity of the bioreductive antitumor agents mitomycin C (MMC) and streptonigrin (SN) with or without the DT-diaphorase (DTD) inducer dimethyl fumarate (DMF) in four human glioblastoma cell lines with the conventional chemotherapeutic agent, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). We also examined four other types of cancer cells to compare with glioblastoma cells. Cytotoxicity was measured with the sulforhodamine B (SRB) assay and was represented by 50% inhibition concentration (IC50). Enzymatic activities of DTD, cytochrome b5 reductase and glutathione-S-transferase (GST) in cells were measured spectrophotometrically. IC50 for BCNU was in a range of 28-300 microM in the glioblastoma cell lines. Glioblastoma cells were more sensitive to MMC or SN than to BCNU. Pretreatment with DMF significantly increased cytotoxicity of MMC and SN in glioblastoma cell lines and the NCI-H1299 lung cancer cell line, but had no effect on BCNU cytotoxicity. DMF significantly increased DTD and cytochrome b5 reductase activity, and decreased GST in three of four glioblastoma cell lines. Addition of the DTD inhibitor, dicumarol, significantly inhibited cytotoxicity of MMC and SN, and reversed the increased cytotoxicity seen when DMF was combined with either MMC or SN in all glioblastoma cell lines. Combining inducers of DTD and cytochrome b5 reductase with bioreductive agents may be a potential therapeutic strategy for glioblastoma.
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PMID:Enhanced cytotoxicity of bioreductive antitumor agents with dimethyl fumarate in human glioblastoma cells. 1565 14

The geno- and cytotoxicity of chromate, an important environmental pollutant, is partly attributed to the flavoenzyme-catalyzed reduction with the concomitant formation of reactive oxygen species. The aim of this work was to characterize the role of NAD(P)H:quinone oxidoreductase (NQO1, DT-diaphorase, EC 1.6.99.2) and glutathione reductase (GR, EC 1.6.4.2) in the mammalian cell cytotoxicity of chromate, which was evidenced controversially so far. The chromate reductase activity of NQO1 was higher than that of GR, but lower than that of lipoamide dehydrogenase (EC 1.6.4.3), ferredoxin:NADP+ reductase (EC 1.18.1.2), and NADPH: cytochrome P-450 reductase (EC 1.6.2.4). The reduction of chromate by NQO1 was accompanied by the formation of reactive oxygen species. The concentration of chromate for 50% survival of bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) during a 24-h incubation was (22 +/- 4) microM. The cytotoxicity was partly prevented by desferrioxamine, the antioxidant N,N'-diphenyl-p-phenylene diamine and by an inhibitor of NQO1, dicumarol, and potentiated by 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU), which inactivates GR. The NADPH-dependent chromate reduction by digitonin-permeabilized FLK cells was partly inhibited by dicumarol and not affected by BCNU. Taken together, these data indicate that the oxidative stress-type cytotoxicity of chromate in FLK cells may be partly attributed to its reduction by NQO1, but not by GR. The effect of BCNU on the chromate cytotoxicity may indicate that the general antioxidant action of reduced glutathione is more important than its prooxidant activities arising from the reactions with chromate.
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PMID:Prooxidant cytotoxicity of chromate in mammalian cells: the opposite roles of DT-diaphorase and glutathione reductase. 1729 2

Strong radical-scavenging activity of Geranium macrorrhizum extracts isolated by using various solvent systems has been reported previously. This study aimed at expanding the knowledge on the bioactivities of antioxidatively active G. macrorrhizum butanol fraction, which was isolated from ethanolic extract (EB), and water fraction, which was isolated from water extract (WW) by measuring their singlet oxygen scavenging properties, as well as preliminary assessment of cytotoxicity and genotoxicity toward mammalian cells. The cytotoxicity (necrosis induction) of the extracts in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was partly prevented by antioxidants and stimulated by the prooxidant BCNU (N,N'-bis(2-chloroethyl)-N-nitrosourea). This indicates that the cytotoxicity of G. macrorrhizum extracts is at least partly attributed to their prooxidant action, presumably due to the formation of quinoidal products of their (auto)oxidation. The latter was evidenced by the nature of the peroxidase-catalyzed oxidation products, which supported DT-diaphorase-catalyzed oxidation of NADPH and participated in conjugation reactions with reduced glutathione. The genotoxic properties were studied using chromosome aberration (CA) and sister chromatid exchange (SCE) tests in human lymphocytes in vitro and Drosophila melanogaster somatic mutation and recombination test (SMART) in vivo. In the CA test, only the highest doses of both fractions significantly increased chromosome aberration frequency. In the SCE test, both fractions induced SCEs in a clear dose-dependent manner. G. macrorrhizum extracts were not genotoxic in the SMART test in vivo. Our data indicate that in spite of the possible beneficial (antioxidant) effects of Geranium extracts, the possibilities of their use as ingredients of functional foods and/or food supplements should be further examined due to their cyto- and genotoxic effects resulting mainly from the action of quercetin-derived components abundant in the extracts.
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PMID:A preliminary assessment of singlet oxygen scavenging, cytotoxic and genotoxic properties of Geranium macrorrhizum extracts. 2045 6