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

Phenobarbital is a potent inducer of several liver-specific genes such as those encoding detoxication enzymes, including cytochromes P450. However, the mechanisms of action of the barbiturate are poorly understood. Since both, phenobarbital and glucocorticoids, are capable of inducing the same cytochrome P450 species, we asked whether the glucocorticoid receptor could participate to the phenobarbital induced responses. The results presented here show that phenobarbital was able to induce a two-fold increase in the affinity of the glucocorticoid receptor for the binding of dexamethasone, as well as a 30% increase of the receptor number in Reuber rat hepatoma cells of the Fao line. These effects may have a biological significance since they were paralleled by an enhancement of the dexamethasone-induced tyrosine aminotransferase activity, a glucocorticoid inducible function in rat hepatoma cells and in rat liver. To our knowledge, phenobarbital is the first compound shown to be able to induce, in intact cells, an increase in the affinity of the glucocorticoid receptor for the binding of its ligand.
 ...
PMID:Effect of phenobarbital on the glucocorticoid receptor in rat hepatoma cells. 197 78

The present study was undertaken to investigate the mechanism by which dimethylsulfoxide (DMSO) exerts its protective action on cytochrome P450-dependent activities and differentiation in cultured rat hepatocytes. Loss of cytochrome P450 is associated with a shortage of heme and reduced activity of delta-aminolaevulinic acid dehydratase: the addition of DMSO, which induces this enzyme in human hepatoma cells, is not able to affect it in hepatocytes in primary culture. DMSO is a strong scavenger of hydroxyl radicals and may destroy the reactive oxygen species formed under conventional culture conditions (i.e., 95% air and 5% CO2). In fact other powerful scavengers of oxygen radicals like dimethylthiourea, desferal, and catalase itself maintain higher levels of cytochrome P450 and higher activities of 7-ethoxycoumarin O-deethylase during 3 days of culture. DMSO and the other scavengers are also able to retain features of the morphological and biochemical differentiation of hepatocytes such as the ability to induce tyrosine aminotransferase activity in response to glucocorticoids.
 ...
PMID:Mechanism of maintenance of liver-specific functions by DMSO in cultured rat hepatocytes. 201 49

The genotoxic potency of the hepatocarcinogen N-nitrosodiethylamine (NDEA) was tested in various Reuber hepatoma cell lines, which differ in their expression of differentiated liver specific functions including hepatic cytochrome P450 forms, and in rat hepatocytes, with the aim of characterizing the enzymes involved in activation. DNA single-strand breaks assessed by alkaline elution served as an indicator of genetic damage. Aldrin epoxidase activity was used as a marker for various hepatic cytochrome P450 forms. The poorly differentiated cell lines RH35 and H4IIEC3/T were apparently not affected by NDEA; moderate effects were observed in the well-differentiated lines H4IIEC3/G- and 2sFou, and major effects in two other well-differentiated lines, Fao and C2Rev7, and in hepatocytes. The degree of DNA damage in the cell lines correlated positively with the expression of aldrin epoxidase. Furthermore, DNA damage induced by N-nitrosodimethylamine (NDMA) was determined in C2Rev7 cells and in rat hepatocytes in order to assess a possible involvement of the NDMA-metabolizing cytochrome P45oIIE1 in the activation of NDEA by comparing the genotoxic potencies of the two compounds. NDMA was distinctly less effective than NDEA in C2Rev7 cells at all concentrations tested. In hepatocytes, NDMA induced more DNA damage than NDEA at low concentrations, but was slightly less active at high concentrations. The results suggest that NDEA is preferentially metabolized to genotoxic products by one or several cytochrome P450 forms different from P450IIE1.
 ...
PMID:Induction of DNA damage by N-nitrosodiethylamine in rat hepatoma cells: correlation with cytochrome P450-mediated aldrin epoxidase activity. 205 11

The cytochrome P450 in the transformable C3H/10T1/2 (10T1/2) cell line has been characterized and compared to the major polycyclic aromatic hydrocarbon (PAH)-inducible hepatic form, cytochrome P450IA1 (P450IA1). The mouse hepatoma cell line, Hepa-1, was used as an in vitro model for P450IA1 expression and regulation by PAH. Microsomes from uninduced and benz[a]anthracene (BA)-induced 10T1/2 cells provided PAH mono-oxygenated product profiles that were totally different from metabolite profiles produced by microsomes from uninduced and BA-induced Hepa-1 cells even though total activities were similar. The proximate carcinogen, 7,12-dimethylbenz[a]anthracene-3,4-diol (DMBA-3,4-diol) was a major product for the 10T1/2 microsomes, while Hepa-1 formed less than 2% of this metabolite. Hepa-1 converted benzo[a]pyrene (BP) to BP-4,5-diol and DMBA to 7-hydroxymethyl-12-methyl-BA, while 10T1/2 did not produce either product. Polyclonal antibody to rat hepatic P450IA1 did not inhibit metabolism of either PAH substrate by 10T1/2 microsomes, but totally inhibited such metabolism by Hepa-1 microsomes. Western immunoblot analysis of BA-induced 10T1/2 microsomes showed that less than 1% of total P450 was P450IA1. The PAH-metabolizing activity of 10T1/2 microsomes was highly inducible (14-fold) by pre-treatment of non-confluent intact cells with BA, but was only half as inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin. In contrast, the P450IA1 activity of Hepa-1 cells was highly inducible by both compounds. The distinct metabolite profiles, antibody inhibition data and lack of immunoreactivity all indicate that PAH metabolism in 10T1/2 cells is catalyzed by a form of P450 distinct from P450IA1. The anomalous induction patterns suggest that this novel isozyme is predominantly regulated by a mechanism other than the Ah receptor.
 ...
PMID:Characterization of a novel cytochrome P450 from the transformable cell line, C3H/10T1/2. 215 39

Twelve forms of human cytochrome P450 were synthesized in human hepatoma Hep G2 cells by means of cDNA-directed expression using vaccinia virus. The cDNA-expressed enzymes were tested for their ability to oxidize estradiol. Incubation of [14C]estradiol with cell lysates containing P450 IA2 resulted in the production of 2-hydroxy and 4-hydroxy metabolites with substrate turnovers of 2.74 and 0.27 min-1, respectively. P450s IIIA3 and IIIA4 yielded the same metabolites at about one third the rate of P450 IA2. Low levels of estradiol hydroxylation were also catalyzed by P450s IIC9, IIIA5, and IVB1. Six other P450 forms yielded no detectable metabolism. The roles of P450s IA2, IIA3, and IIIA4 were further established by immunoinhibition using antirat P450 antibodies. Antibody that specifically binds to P450 IIIA3 and IIIA4 inhibited 60-70% of estradiol hydroxylation, and antibody against P450 IA2 inhibited 20-40% of the estradiol hydroxylase activity in microsomes from two human liver specimens, suggesting that these enzymes constitute the major forms catalyzing estradiol oxidation in human liver. Immunoinhibition results also suggest that 2-hydroxy- and/or 4-hydroxycatechol estrogens are further metabolized to other yet uncharacterized metabolites by P450s IIIA3 and IIIA4.
 ...
PMID:Estradiol metabolism by complementary deoxyribonucleic acid-expressed human cytochrome P450s. 216 48

Twelve forms of human hepatic cytochrome P450 were expressed in hepatoma cells by means of recombinant vaccinia viruses. The expressed P450s were analyzed for their abilities to activate the potent hepatocarcinogen aflatoxin B1 to metabolites having mutagenic or DNA-binding properties. Five forms, P450s IA2, IIA3, IIB7, IIIA3, and IIIA4, activated aflatoxin B1 to mutagenic metabolites as assessed by the production of His revertants of Salmonella typhimurium in the Ames test. The same P450s catalyzed conversion of aflatoxin B1 to DNA-bound derivatives as judged by an in situ assay in which the radiolabeled carcinogen was incubated with cells expressing the individual P450 forms. Seven other human P450s, IIC8, IIC9, IID6, IIE1, IIF1, IIIA5, and IVB1, did not significantly activate aflatoxin B1 as measured by both the Ames test and the DNA-binding assay. Moreover, polyclonal anti-rat liver P450 antibodies that crossreact with individual human P450s IA2, IIA3, IIIA3, and IIIA4 each inhibited aflatoxin B1 activation catalyzed by human liver S-9 extracts. Inhibition ranged from as low as 10% with antibody against IIA3 to as high as 65% with antibody against IIIA3 and IIIA4. These results establish that metabolic activation of aflatoxin B1 in human liver involves the contribution of multiple forms of P450.
 ...
PMID:Five of 12 forms of vaccinia virus-expressed human hepatic cytochrome P450 metabolically activate aflatoxin B1. 216 57

Effects of agents affecting cytochrome P450 were studied on the production of erythropoietin (Epo) in cultures of the human hepatoma cell line HepG2. Epo was measured by radioimmunoassay of the culture media after 24 h of incubation. The addition of phenobarbital or 3-methylcholanthrene, which induce cytochrome P450, significantly enhanced the formation of Epo. Likewise, the thyroid hormones T3 and T4 stimulated the rate of the production of Epo. On the other hand, the formation of Epo was lowered following the addition of diethyldithiocarbamate or cysteamine chloride, which inhibit cytochrome P450. These findings support the idea that O2 sensitive hemoproteins of the microsomal mixed-functional oxidases play a role in the control of the synthesis of Epo.
 ...
PMID:Role of cytochrome P450 in the control of the production of erythropoietin. 216 16

Polycyclic aromatic hydrocarbon (PAH)-induced C3H/10-T1/2/CL8 mouse embryo fibroblasts (10T1/2) and mouse hepatoma-derived Hepa 1c1c7 cells (Hepa-1), exhibit comparable total cytochrome P450 levels and total PAH-metabolizing activities but very different distributions of PAH metabolites. Based on anti-P450IA1-IgG inhibition data, P450IA1 contributes essentially all PAH metabolism in Hepa-1 microsomes but is not involved in PAH metabolism by 10T1/2 cells. In addition, the microsomal epoxide hydratase (EHm) in Hepa-1 cells is far less effective in dihydrodiol (diol) formation compared to that in 10T1/2 microsomes [Pottenger, L.H. and Jefcoate, C.R. Carcinogenesis, 11, 321-327 (1990)]. In the present study, the levels of expression of P450IA1 and EHm proteins and the corresponding mRNAs, both prior to and following exposure to benz[a]anthracene (BA) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), have been correlated with microsomal PAH metabolism by each cell type. In 10T1/2 cells, P450IA1 protein (56 kd) and mRNA (2.6 kb) were detectable at extremely low levels in only two of five cell preparations and then only after maximum induction by TCDD and BA. Thus although 10T1/2 cells contain functional Ah receptors, their capacity to induce P450IA1 is highly suppressed, representing at most 2% of the total P450. TCDD (10 nM) was 4-fold more effective than BA (10 microM) in inducing P450IA1 mRNA, while the levels of immunodetectable protein were comparable. An even greater discrepancy between P450IA1 mRNA and protein levels was seen in BA-induced Hepa-1 cells, where a 4-fold increase in mRNA was paralleled by a 20-fold increase in protein. This difference is probably due to the greater effect of BA depletion on mRNA compared to protein levels. In 10T1/2 cells, BA and TCDD were equally effective at increasing expression of an unidentified 1.9 kb mRNA sequence that blotted very weakly with the P450IA1 cDNA probe. The expression of this mRNA was independent from that of P450IA1. A similar band was visible in Hepa-1 cells less than 1% of the P450IA1 mRNA. EHm mRNA was almost 3-fold higher in 10T1/2 compared to Hepa-1 cells and was unaffected by cell treatments. In Hepa-1 cells, BA and TCDD elevated EHm protein and hydrating activity to levels comparable to those expressed in 10T1/2 cells. It is, therefore, suggested that the relative ineffectiveness of Hepa-1, compared to 10T1/2 EHm, to hydrate low levels of PAH-epoxides is due to differences between the two proteins or their disposition in the microsomal membrane.
 ...
PMID:Differences in the modulation of P450IA1 and epoxide hydratase expression by benz[a]anthracene and 2,3,7,8-tetrachlorodibenzo-p-dioxin in mouse embryo versus mouse hepatoma-derived cell lines. 220 84

The metabolism of fluperlapine, a neuroleptic dibenzazepine derivative with a N-methyl-piperazinyl substituent, was investigated in continuous cultures of rat and human cells which express various cytochrome P450-dependent monooxygenase activities. The differentiated rat hepatoma cells H4IIEC3/G- and their variants 2sFou and FGC-5 metabolized fluperlapine predominantly by N-oxygenation and only to a minor degree by N-demethylation or glucuronidation of primary phenolic products. Total fluperlapine metabolism in dedifferentiated rat hepatoma cells H5 and partially differentiated human hepatoma cells HepG2 was much smaller than in the differentiated rat hepatoma lines. This was primarily attributable to their low capacity for N-oxygenation. Human lung adenocarcinoma lines NCI-H322 and NCI-H358 formed only trace amounts of fluperlapine N-oxide. Pretreatment of 2sFou cells with benz(a)anthracene, phenobarbital or dexamethasone markedly increased the formation of N-demethylated and glucuronidated products but did not affect the rate of N-oxide formation. Guanethidine and cysteamine, inhibitors of flavin-dependent monooxygenase activity, reduced fluperlapine N-oxidation more strongly than aldrin epoxidation, a marker for cytochrome P450 activity. In contrast, n-octylamine inhibited aldrin epoxidation but was without effect on fluperlapine N-oxygenation. The results suggest that certain cells in continuous culture are capable of expressing flavin-dependent monooxygenase(s) in addition to cytochrome P450-containing monooxygenases. Such cells may offer useful systems for studying the oxidative metabolism of a broad spectrum of xenobiotics and analysing the importance of the two oxygenation reactions for the biological effects of their substrates.
 ...
PMID:Metabolism of fluperlapine by cytochrome P450-dependent and flavin-dependent monooxygenases in continuous cultures of rat and human cells. 232 14

The metabolic pathways leading to genotoxicity of nitropropanes in mammalian cells were investigated by measuring the effects of 2-nitropropane (2-NP) and 1-nitropropane (1-NP) on various cell lines characterized for their expression of cytochrome P450-dependent mono-oxygenases. Cells used were the rat hepatoma cell lines 2sFou, H4IIEC3/G- and C2Rev7, which express various forms of cytochrome P450-dependent mono-oxygenases, and V79 Chinese hamster cells which lack these enzyme activities. Induction of DNA repair synthesis, micronuclei and, where assessable, mutations to 6-thioguanine (TG) resistance served as indicators of genotoxic effects. 2-NP elicited a positive response at all endpoints measured in the hepatoma lines after pretreatment of the cells with dexamethasone, an inducer of various liver-specific cytochrome P450 forms. Genotoxicity was much weaker or not detectable in cells not pretreated with the inducer. 1-NP was not genotoxic in the hepatoma cells irrespective of whether the cells were pretreated or not. Neither isomer elicited DNA repair synthesis in V79 cells, but both isomers caused mutations to TG resistance, and 1-NP increased the number of micronucleated and multinucleated cells. The findings show that there are different pathways in mammalian cells by which nitropropanes can be converted to genotoxic products. Presumably the induction of liver tumours by 2-NP is linked to the metabolic pathway which is characterized by the formation of genotoxic metabolites from 2-NP but not 1-NP. This pathway appears to depend on the presence of liver-specific, dexamethasone-inducible, cytochrome P450 forms. The relevance of the genotoxic effects of the nitropropanes observed in V79 cells for the situation in vivo is open to question.
 ...
PMID:Involvement of different pathways in the genotoxicity of nitropropanes in cultured mammalian cells. 239 19


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>