Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A novel pathway of polycyclic aromatic hydrocarbon (PAH) metabolism involves the oxidation of non-K-region trans-dihydrodiols by dihydrodiol dehydrogenase (DD) to yield PAH o-quinones whose cytotoxicity and genotoxicity are unknown. The cytotoxicity of several PAH o-quinones derived from this reaction [naphthalene-1,2-dione (NPQ), benzo[a]pyrene-7,8-dione (BPQ), and 7,12-dimethylbenz[a]anthracene-3,4-dione (DMBAQ)] was examined in rat (H-4IIe) and human (Hep-G2) hepatoma cells which are known to express DD. 2-Methylnaphthalene-1,4-dione (menadione), a known cytotoxic p-quinone, was used as a positive control. Hepatoma cells (1 x 10(6) cells/mL) were exposed to PAH o-quinones (1-100 microM) for 0-4 h, and cell viability and survival were measured and related to O2.- production and changes in redox potential [GSSG/GSH and NAD(P)+/NAD(P)H]. Three different modes of cytotoxicity were observed: (1) NPQ (no bay region) and DMBAQ (methylated bay region) were as cytotoxic as menadione in reducing cell survival but had less effect on cell viability. These o-quinones adversely affected GSH levels and the redox state of the cell and caused an increase in the production of O2.- in cell suspensions. This cytotoxicity was not enhanced by dicoumarol (10 microM), a DT-diaphorase inhibitor, implying that this enzyme is unable to prevent these PAH o-quinones from entering one-electron redox-cycles. (2) BPQ (bay region only) was the least cytotoxic of the PAH o-quinones studied. BPQ decreased cell viability (< 40% at 20 microM) but did not adversely affect cell survival or the redox state of the cell.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cytotoxicity of polycyclic aromatic hydrocarbon o-quinones in rat and human hepatoma cells. 768 7

Acetaminophen (APAP) when administered in excess can cause severe hepatic necrosis in vivo. To study the mechanism of APAP toxicity and the role of cytochrome P450, a previously established human hepatoma HepG2 subline, MVh2E1-9, that constitutively expresses human CYP2E1 was used as a model. At high concentrations (above 5 mM) and when intracellular reduced glutathione (GSH) was depleted, APAP caused severe cytotoxicity in MVh2E1-9, but not in MV-5 cells which lack CYP2E1. The APAP cytotoxicity was dependent on the concentration of APAP and time of exposure, and could be blocked by 4-methylpyrazole, ethanol, diallyl sulfide, N-acetylcysteine and N-t-butyl-alpha-phenylnitrone, but not by propylgallate, an inhibitor of lipid peroxidation. Significantly more 14C-labeled APAP protein adduct was detected in MVh2E1-9 cells than MV-5 cells, especially after depletion of GSH. The formation of the APAP adducts could be inhibited by the same agents which prevent APAP cytotoxicity. At a lower concentration (1-2 mM), APAP inhibited proliferation in both MVh2E1-9 and the control MV-5 cells to similar extents. This antiproliferative action of APAP did not require depletion of GSH as did the cytotoxic action of APAP. These data suggest that APAP has a dual toxic effect on MVh2E1-9 cells: a P450-independent antiproliferative effect and the CYP2E1-dependent cytotoxic effect. These results demonstrate the ability of human CYP2E1 to activate APAP to reactive metabolites which form covalent protein adducts and cause toxicity to a hepatoma cell line.
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PMID:Cytotoxicity of acetaminophen in human cytochrome P4502E1-transfected HepG2 cells. 779 Nov 25

Induction of glutathione S-transferase (GST) Ya gene expression by a variety of chemical agents is mediated by a regulatory element composed of two adjacent AP-1-like binding sites and activated by the Fos/Jun heterodimeric complex (AP-1). We have previously shown that the induction of GST Ya gene expression and of AP-1 binding activity is regulated by intracellular glutathione (GSH) levels. To study the role of reactive oxygen species in the induction of AP-1 activity and GST Ya gene expression and their effect on intracellular GSH levels, we have exposed hepatoma cells to adriamycin and two synthetic quinones, Qcb and Qn, with different capacities to generate oxygen radicals. The kinetics of quinone-mediated generation of hydroxyl radicals were monitored in intact cells by a spin trapping technique and EPR spectral measurements. We find that quinones which can chelate Fe(III) ions, adriamycin and Qcb, are more effective in hydroxyl radical production than the nonchelating quinone Qn. Furthermore, we show that the induction of AP-1 binding activity and GST Ya gene expression by these quinones correlates with their oxygen radical production, adriamycin and Qcb being stronger inducers that Qn. The present study indicates that the AP-1-mediated induction of GST Ya gene expression is part of the response to oxidative stress. A transient increase by 2.5-fold in the intracellular GSH level was observed 30 min after exposure of cells to quinone and was followed by a rapid depletion of GSH. This increase in the GSH level represents an induction of GSH synthesis since it was blocked by buthionine sulfoximine, an inhibitor of gamma-glutamylcysteine synthetase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Role of quinone-mediated generation of hydroxyl radicals in the induction of glutathione S-transferase gene expression. 781 27

Previous studies have suggested that both cAMP-dependent signal transduction pathway and Ca2+/protein kinase C-dependent pathway are involved in GSH efflux from hepatocytes. In the present study, GSH efflux from Hep G2 cells, a human-derived hepatoma cell line, was further characterized. Both epidermal growth factor (0.1-10 ng/ml) and insulin (1 microgram/ml) significantly increased GSH efflux from Hep G2 cells. A fall in the membrane potential produced by the replacement of Na+ with equivalent K+ did not affect GSH efflux significantly. Neither ouabain, a Na+/K+ ATPase inhibitor, vanadate, a Ca2+ ATPase inhibitor, nor BaCl2, a K+ channel blocker, significantly affected the GSH efflux. Methionine (1mM) decreased GSH efflux from the cells, although total GSH content in the cells was not affected during the incubation time of 60 min. Signal transductions through tyrosine kinase-coupled receptors may also be involved in GSH efflux from hepatocytes.
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PMID:Characterization of glutathione efflux from Hep G2 cells. 782 1

Yoshida rat ascites hepatoma (AH) has several cell lines with a characteristic sensitivity to antitumor drugs. AH66 cells overexpressed 160-170 kDa P-glycoprotein (P-gp) in the membrane and glutathione-S-transferase placental form (GST-P) in the cytosol. AH44 cells did not express P-gp but contained GST-P isozyme, while normal rat liver had GST-(1,2) and-(3,4) classes. AH44 and AH66 cells were more resistant to chlorambucil (CLB) than AH66F cells, which are a variant cell line derived from AH66 cells and lacked both proteins. CLB-resistant AH44 and AH66 cells contained a high amount of glutathione (GSH) and higher GST activity than AH66F cells. Ethacrynic acid, a GST-P inhibitor, and buthionine sulfoximine, a GSH biosynthesis inhibitor, significantly decreased the CBL resistance of AH44 and AH66 cells without influencing the sensitivity of AH66F cells. The CLB resistance of these cell lines were hardly influenced by verapamil, a calcium channel blocker with P-gp antagonistic action, which significantly decreased the vinblastine resistance of AH66 cells. This study indicates that AH66 cells showed multiple drug resistance dependent on P-gp and GST-P isozyme and that the AH44 cell line was CLB resistant through the GSH/GST-P detoxification system. These hepatomas are useful for investigation of the drug resistance of hepatic carcinomas and development of counteracting drugs.
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PMID:Glutathione-S-transferase P-form dependent chlorambucil resistance in Yoshida rat ascites hepatoma cell lines. 791 Jan 11

Effects of metallothionein (MT) synthesis inhibiting compounds (actinomycin D, cycloheximide), MT synthesis stimulating compounds (dexamethasone, dibu-cAMP) and interfering metals (Cd, Zn) on copper accumulation were investigated in rat hepatoma tissue culture cells. Copper-metallothionein (Cu-MT) and MT-associated copper levels were determined to find a possible correlation between cytosolic copper concentrations and MT as a Cu-detoxifying protein. Further, intracellular non-MT associated copper levels and levels of GSH and SOD were determined. Cell viability was tested under all experimental conditions by measuring LDH-release, K+ uptake and total cell protein. Administration of dexamethasone and dibu-cAMP showed no effect on MT levels (compared with controls), and only a marginal effect on 64Cu and total Cu accumulation. Administration of actinomycin D resulted in increased copper accumulation in the particulate fraction, possibly due to inhibition of copper secretion processes and/or protein synthesis. Presence of zinc had no effect on MT levels nor on total Cu and 64Cu levels, in contrast with cadmium which drastically enhanced copper accumulation and MT levels in the cells. Cu/MT ratios varied from 1.0 +/- 0.3 to 3.3 +/- 1.2, which is far below the assumed maximum molar ratio of 8-12 mol Cu per mol MT. SOD levels appeared to be enhanced up to 2- or 3-fold in the presence of Cd2+, relative to control values. The role of GSH as Cu-intermediate in intracellular Cu distribution plus its role in copper defence mechanism(s) was tested by application of BSO, an inhibitor of GSH synthesis. It was found that BSO had no effect on intracellular MT level; it was found however that MT-bound copper levels were markedly decreased. The results presented support a model for copper metabolism in hepatoma tissue culture (HTC) cells, where Cu(I) is complexed by GSH immediately after entering the cell. GSH is capable of transferring copper to MT where it is stored. Depletion of GSH (by administration of Cd2+, actinomycin D, cycloheximide) almost instantaneously results in enhanced cellular toxicity. When also MT is depleted (by actinomycin D) non-MT associated, 'free' cytosolic Cu2+ is elevated, and HTC cells rapidly loose their resistance to copper toxicity, as also reflected in loss of cell viability (LDH, K+ and total cell protein).
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PMID:Role of cytosolic copper, metallothionein and glutathione in copper toxicity in rat hepatoma tissue culture cells. 794 May 70

The murine aromatic hydrocarbon ([Ah]) gene battery consists of at least six genes that code for two functionalizing (Phase I) enzymes and four non-functionalizing (Phase II) enzymes. These enzymes are induced by compounds such as aromatic hydrocarbons and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) that bind to the cytosolic Ah receptor protein. Studies in rodents indicate that certain enzymes of this battery, namely cytochrome P4501A1 (CYP1A1), UDP-glucuronosyltransferase (UGT1*06) and NAD(P)H: quinone acceptor oxidoreductase (NMO1) are induced by the synthetic antioxidant 5,10-dihydroindeno[1,2-b]indole (DHII). The induction of [Ah] gene battery enzymes and the levels of reduced glutathione (GSH) were examined in mouse Hepa-1c1c7 hepatoma wild-type cells (wt), a CYP1A1 metabolism-deficient mutant (c37) and an Ah receptor nuclear translocation-defective mutant (c4). DHII and TCDD increased the activities of ethoxyresorufin O-deethylase, an indicator of CYP1A1 activity, as well as NMO1, UGT1*06, cytosolic aldehyde dehydrogenase class 3 and glutathione S-transferase form A1 in wt cells, but had little or no induction effect in c37 or c4 cells. DHII and TCDD differed in their effects on GSH levels; while DHII increased GSH levels 3-fold in wt, but not at all in c37 or c4 cells, TCDD had no effect on GSH levels in any cell type. However, GSH levels were enhanced in both wt and c4 cells by tert-butyl hydroquinone (TBHQ). L-Buthionine S,R-sulfoximine, an inhibitor of gamma-glutamylcysteine synthetase, prevented DHII-induced increases in wt cell GSH. The increase in GSH levels occurred after 8 h, while the induction of enzymes occurred within 4 h. The induction of the higher GSH levels in wt cells by DHII and TBHQ correlated with increases in intracellular levels of the GSH precursor thiol cysteine, as well as with increased activities of gamma-glutamylcysteine synthetase, the rate-limiting enzyme of GSH synthesis. However, TBHQ-mediated GSH increases in c4 cells were accompanied by increased gamma-glutamylcysteine synthetase activity with no change in intracellular cysteine concentration. The results suggest that DHII induction of [Ah] gene battery enzymes requires a functional Ah receptor, but not the functional gene product CYP1A1. Furthermore, metabolism, possibly via CYP1A1, appears to be required for DHII to enhance intracellular levels of cysteine and GCS activity that result in higher GSH levels.
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PMID:Regulation of [Ah] gene battery enzymes and glutathione levels by 5,10-dihydroindeno[1,2-b]indole in mouse hepatoma cell lines. 795 76

The addition of exogenous H2O2 inhibited hypoxia-induced erythropoietin (Epo) production in the human hepatoma cell line HepG2. Likewise, elevation of endogenous H2O2 levels by the addition of menadione or the catalase inhibitor, aminotriazole, dose-dependently lowered Epo production. The inhibitory effect of exogenous H2O2 on Epo formation could be completely overcome by co-incubation with catalase. When GSH levels in HepG2 cells were lowered, Epo production was more susceptible to H2O2-induced inhibition, indicating that H2O2 might affect thiol groups in regulatory proteins. Endogenous production of H2O2 in HepG2 cells was dependent on the pericellular O2 tension, being lowest under conditions of hypoxia. Our results support the hypothesis that an H2O2-generating haem protein might be part of the O2 sensor that controls Epo production. High H2O2 levels under conditions of normoxia suppress, whereas lower levels in hypoxic cells allow epo gene expression.
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PMID:Role of hydrogen peroxide in hypoxia-induced erythropoietin production. 798 Apr 10

Cellular responses to copper, applied in concentrations varying from 0.5 to 200 microM Cu2+, were investigated in two different cell types: rat hepatoma cells (HTC) and primary cultured rat hepatocytes. Accumulation of 64Cu, copper (AAS) levels, cellular viability parameters (cell growth and proliferation, LDH leakage, total cell protein, K+ uptake, and ATP levels), and cell toxicity parameters (metallothionein (MT), glutathione (GSH) and superoxide dismutase (SOD)) were examined over 24 hr incubation periods. Accumulation of radiolabeled copper (applied copper concentrations: 15-200 microM Cu2+) showed a four-fold increase in HTC cells (0.88-3.45 nmol Cu/mg cell protein) and a three-fold increase in hepatocytes (4.94-14.66 nmol Cu/mg cell protein), although quantitative uptake in HTC cells was five times lower. Most of the copper accumulated in the hepatoma cells and hepatocytes was found predominantly in the particulate fraction (i.e., cell membranes and organelles), while only a small quantity was present in the soluble fraction (cell cytosol). Metallothionein concentrations in HTC cells were increased from 43 pmol/mg cell protein (0.5 microM Cu2+ application) up to 223 pmol/mg cell protein (200 microM Cu2+ application), whereas MT in rat hepatocytes were elevated from 139 pmol/mg cell protein to 546 pmol/mg cell protein over the same range of administered Cu2+. Metallothionein synthesis rendered both cell types well equipped to deal with increasing intracellular copper levels. In hepatocytes however, MT synthesis resulted in decreasing non-MT-associated copper levels in the cytosol for Cu administrations up to 100 microM. Above that point however, MT failed to stay in line with increasing cytosolic Cu levels, resulting in cytotoxic effects shown by changes in cell viability and GSH/SOD levels. In HTC cells MT synthesis suppressed the free Cu levels in the cytosol to below 0.1 nmol Cu/mg cell protein over the total range of copper concentrations applied. The results presented indicate that hepatoma HTC cells are more capable of dealing with high accumulated Cu levels than the better established rat hepatocytes. Furthermore, it is clear that comparison of these two cell types regarding their ability to respond on (sub)toxic Cu should be discussed with full consideration for the copper applications involved.
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PMID:Effects of copper on rat hepatoma HTC cells and primary cultured rat hepatocytes. 813 49

7-N-((2-([2-(gamma-L-Glutamylamino)ethyl]dithio)ethyl))mitomycin C (KW-2149) is an analogue of mitomycin C (MMC) and has prominent activities against various tumors. We studied the antitumor effects of KW-2149 in MMC-resistant variants of human colon carcinoma HT-29 (HT-29/MMC) and mouse hepatoma Hepa-I (C4, B13NBii1) cells, which are deficient in DT-diaphorase and cytochrome P450 reductase, respectively. These enzymes mediate the reductive activation of MMC in the cells. Although HT-29/MMC and C4, B13NBii1 cells showed significant resistance to MMC, they showed sensitivity tl KW-2149 comparable to their parental tumors, indicating that DT-diaphorase and cytochrome P450 reductase could not be involved in the activation of KW-2149. In studying the activation mechanism of KW-2149, we found that glutathione (GSH) and cysteine significantly enhanced the cytotoxicity of KW-2149 in HT-29 cells. The DNA adduct of KW-2149 was increased when HT-29 cells or the isolated nuclei of the cells were incubated with KW-2149 in the presence of physiological concentrations of GSH and cysteine. KW-2149 alkylated calf thymus DNA in the presence of GSH and cysteine in vitro. These results indicate that activation of KW-2149 by thiol molecules, unlike MMC, could be an important activation mechanism of KW-2149 to form DNA adduct and to exert its cytotoxicity. This is the reason why KW-2149 is effective against MMC-resistant tumors with deficiencies in the MMC activation enzymes.
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PMID:Nonenzymatic reductive activation of 7-N-((2-([2-(gamma-L-glutamylamino)ethyl]dithio)ethyl))mitomycin C by thiol molecules: a novel mitomycin C derivative effective on mitomycin C-resistant tumor cells. 816 87


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