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)

Six alkyl ethers of 7-hydroxycoumarin, ranging from methoxy- to hexoxycoumarin, were studied for their NADPH-dependent metabolism by liver microsomes of male rats treated with phenobarbital (PB) or 3-methyl-cholanthrene (MC). The six alkyl ethers were metabolized by both types of microsomes, forming 7-hydroxycoumarin as the major product. Among the test compounds, 7-methoxycoumarin was unusual in that its dealkylation was inducible only by PB and not by MC. PB increased 7-methoxycoumarin-O-demethylase (MOCD) activity about four- to eightfold. Metyrapone strongly inhibited MOCD in PB-treated microsomes but not in MC-treated microsomes. Similarly, monoclonal antibodies directed toward PB-induced cytochrome P450s selectively suppressed MOCD in PB-treated microsomes. MOCD activity was observed in preparations of SD1 cells containing only cytochrome P450IIB1, while it was not found in preparations of XEM1 cells containing only cytochrome P450IA1. Demethylation of 7-methoxycoumarin was also mediated by the constitutive cytochrome P450 form(s) of liver, lung, small intestine, and kidney (in decreasing order). PB increased MOCD activity of small intestine by 40% but was without effect on the dealkylation activity of lung and kidney. MOCD activity was also detectable in differentiated rat hepatoma lines H4IIEC3 and 2sFou. The studies indicate that dealkylation of 7-methoxycoumarin is a highly sensitive, simple, and practical assay for estimating constitutive and PB-inducible cytochrome P450-dependent monooxygenase activities.
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PMID:Dealkylation of 7-methoxycoumarin as assay for measuring constitutive and phenobarbital-inducible cytochrome P450s. 186 30

Tamoxifen (TXF), a triphenylethylene antiestrogen, is the major therapeutic agent for breast cancer. In rare cases, TXF treatment appears to increase incidence of endometrial cancer. Also in rats, TXF was found to induce hepatocellular carcinoma. Previous studies suggested that metabolism of TXF may contribute to its antiestrogenic and anticancer activity. The current study demonstrates a novel route of TXF metabolism. TXF is metabolized by rat and human liver microsomes into a reactive intermediate (txf*) which binds irreversibly to microsomal proteins. The binding requires NADPH and O2 and is inhibited by CO, inhibitors of P-450, and antibodies to rat NADPH-P450 reductase, indicating catalysis by P450. Phenobarbital treatment of rats markedly increases binding, suggesting the involvement of induced P450s. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from incubation of [14C] TXF with phenobarbital-treated microsomes exhibits a major radiolabeled zone which corresponds to a molecular weight of approximately 54,000, suggesting binding to a P-450. Cysteine and glutathione inhibited the binding of TXF without significantly affecting P-450-mediated metabolism of TXF, possibly by reacting with txf* or by competing for the same binding sites. Exposure of phenobarbital-treated microsomes and control-microsomes to 50 degrees C for 90 s, which inactivates the flavin-containing monooxygenase (FMO), diminished binding and pH 8.6 enhanced binding. Also, alternate FMO substrates inhibited binding. These findings indicate that P-450 and possibly FMO catalyze the reactions leading to the formation of txf*. However, incubations with single-labeled and dual-radiolabeled tamoxifen or with [14C]TXF-N-oxide demonstrated that monodesmethyl-TXF and TXF-N-oxide, the principal P-450 and FMO-mediated metabolites, respectively, are not on the major route of txf* formation, indicating that txf* could not be an aldehyde derived from tamoxifen nitrone. Thus, though the structure of txf* was not characterized, certain possibilities were excluded. Speculations on the structure of txf* and on its possible pharmacological and toxicological activity are presented.
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PMID:Cytochrome P-450-mediated activation and irreversible binding of the antiestrogen tamoxifen to proteins in rat and human liver: possible involvement of flavin-containing monooxygenases in tamoxifen activation. 193 68

1. The activities of several drug-metabolizing enzymes change during the growth cycle (exponential growth to confluence) of Hep G2 cells in culture. As the rate of cell growth slowed down (days 7 to 10 after passage) the activities of ethoxy- and methoxy-resorufin O-dealkylase and of NADPH cytochrome c- and NADH cytochrome b5-reductase increased. In contrast, the O-dealkylations of pentoxy- and benzyloxy-resorufin did not change significantly during culture. 2. UDP-glucuronyltransferase activities also showed substrate-dependent alterations with time in culture. In contrast, glutathione-S-transferase activity remained constant despite a decline in the intracellular reduced glutathione content. 3. Epoxide hydrolase activity altered throughout time in culture, with an initial decrease in activity followed by a marked increase between days 7 and 10 after passage. 4. These results indicate the importance of standardizing the protocol with regard to the timing of experiments within the growth period of the cells when using hepatoma cell lines for assessing the metabolism and cytotoxicity of chemicals.
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PMID:Variation in drug-metabolizing enzyme activities during the growth of human Hep G2 hepatoma cells. 216 Nov 67

The tissues of hepatocellular carcinoma were operatively resected from six patients. All four components of the systems of microsomal cytochrome P-450-linked monooxygenase of the tissues were investigated and compared to those of normal liver tissue. The concentrations of cytochromes P-450, P-420 and b5 were measured optically and the concentrations of all components except cytochrome P-450 were measured by the Western blotting method followed by immunochemical staining. In microsomes of hepatocellular carcinoma tissues, there was as much cytochrome P-450 and other redox components as in the normal liver tissues, but cytochrome P-450 in liver cancer tissues was unstable and easily converted to cytochrome P-420. The specific activities of NADPH- and NADH-ferricyanide and cytochrome c reductase of each sample were also measured. In the microsomes of the cancer tissues, the specific activities were remarkably reduced compared with those of normal liver tissues. The lipid compositions of the microsomes and the phospholipid/cholesterol ratios (w/w) were 13.1 +/- 3.13 in the cancer tissues and 43.0 +/- 6.74 in normal liver tissues. This difference of the lipid composition elucidates the instability of cytochrome P-450 molecules and the inefficiency of the electron transport of cytochrome P-450-linked monooxygenase systems.
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PMID:Microsomal cytochrome P-450-linked monooxygenase systems and lipid composition of human hepatocellular carcinoma. 254 14

Glutamate dehydrogenase (GDH) was purified to homogeneity from cerebellar tissue of three normal subjects and seven patients with four distinct types of degenerative neurological disorders. Nonequilibrium pH gradient gel electrophoresis showed that the purified enzyme consists of four major isoproteins designated GDH 1, 2, 3, and 4. With one exception, the relative abundance and isoelectric points of the GDH isoproteins decrease and the molecular weights increase progressively going from isoprotein 1 to isoprotein 4. The enzyme isolated from the brain of one patient with a variant form of multiple system atrophy displayed marked reduction of GDH isoprotein 1. The Km values of the patients' GDH for alpha-ketoglutarate, glutamate, NADH, and NADPH were significantly increased as compared to GDH obtained from normal and neurologic control subjects. In addition, glutamate levels were reduced markedly in the patient's cerebellum. Pulse-chase studies have shown that both the human hepatoma HepG2 and the human glioma U373 cell lines synthesize exclusively GDH isoprotein 2. The different GDH isoproteins do not have a precursor-product relationship and may represent products of different GDH mRNA species.
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PMID:Characterization of glutamate dehydrogenase isoproteins purified from the cerebellum of normal subjects and patients with degenerative neurological disorders, and from human neoplastic cell lines. 257 5

The metabolism of chemical carcinogens was investigated in liver preparations from 28 captive woodchucks (Marmota monax). Of these, 23 were naturally infected with the woodchuck hepatitis virus (WHV), and eight also had primary hepatocellular carcinoma (PHC). Twenty-nine parameters were investigated in liver subcellular fractions, including cross-reactivity with HBsAg, and biochemical parameters, such as gamma-glutamyl transpeptidase, cytochrome P-450 and microsomal monooxygenases (aryl hydrocarbon hydroxylase, ethoxycoumarin and ethoxyresorufin deethylases, aminopyrine and dimethylnitrosamine demethylases, and testosterone 7 alpha-, 16 alpha- and 6 beta-hydroxylases), uridine 5'-diphosphoglucuronosyl transferase, GSH and related enzymes (peroxidase, reductase and S-transferase), as well as other cytosolic enzyme activities (glucose 6-phosphate and 6-phosphogluconate dehydrogenases, NADPH- and NADH-dependent diaphorases, and DT diaphorase). In addition, liver preparations were used in order to quantify the metabolic activation into bacterial mutagens of five procarcinogens (aflatoxin B1, the pyrolysis products Trp-P-2 and MeIQ, 2-aminofluorene and dimethylnitrosamine) and the decrease of potency of three direct-acting mutagens (sodium dichromate, ICR 191 and 4-nitroquinoline 1-oxide). WHV infection produced a significant stimulation of carcinogen metabolism, as shown by the simultaneous change in detoxification parameters (GSH depletion) and activation indices (enhancement of microsomal monooxygenases and of procarcinogen activation into mutagenic metabolites). There were no significant differences between WHV-positive samples from animals without PHC and the noncancerous tissue of PHC-bearing animals, whereas a decrease of both activation and detoxification indices was recorded in the tumorous tissue. There was a considerable interindividual variability among WHV carriers, which was tentatively ascribed to genetic factors. Pregnancy was the only known factor influencing the results in WHV carriers. However, even by excluding pregnant animals, the effects on carcinogen metabolism produced by WHV infection were still statistically significant. These results, together with previous data obtained in humans, revealed that metabolic factors may play a role in the synergism between viral hepatitis and chemical hepatocarcinogens in the etiopathogenesis of PHC.
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PMID:Enhanced metabolic activation of chemical hepatocarcinogens in woodchucks infected with hepatitis B virus. 272 Sep 3

Human fibroblasts and hepatoma (Hep G2) cells were grown in media containing 25% D2O. Cholesterol extracted from the cells and bile acids obtained from the media were analyzed by gas chromatography/mass spectrometry (GC/MS). Fibroblasts that were transferred serially in media containing D2O continued to grow and to synthesize cholesterol enriched in deuterium. The observed distribution of deuterium-enriched species of cholesterol corresponded to a distribution that was calculated based on C = 27, 13C = 1.107%, D2O/H2O = 0.25, hydrogen derived from water = 20, and is in agreement with the concept that deuterium incorporation occurs randomly and represents mostly the NADPD/NADPH ratio in the medium. The deuterium enrichment of cholesterol from hepatoma cells indicated a shift of the most abundant species from m/z 373 to m/z 375, which corresponds more closely to the derivation of 25 hydrogens from water and implies the formation of deuterated acetate in the medium. Analysis of chenodeoxycholic acid, the predominant bile acid synthesized by Hep G2 cells in vitro, indicates its derivation from both pre-formed and newly synthesized cholesterol and that A ring transformation from cholesterol utilizes deuterium derived from water. Analysis of the bile acids derived from hamster bile following the administration of D2O confirms that similar events occur in vivo.
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PMID:Cholesterol and bile acid synthesis: utilization of D2O for metabolic studies. 280 47

Nuclear membranes from many tumors contain an unusual redox chain discovered originally in the Hepatoma 22a nuclear membranes which catalyzes superoxide dismutase-sensitive adrenaline oxidation to adrenochrome in the presence of either NADPH or NADH as electron donor, the reaction being inhibited by cyanide and azide. This redox chain can reduce anthracycline antitumor antibiotics adriamycin and carminomycin to their free radical states under anaerobic conditions. Evidence has been obtained for a higher stability of the carminomycin radical as compared to that of adriamycin. Operation of the nuclear membrane-bound redox chain can be a source of oxygen radical-mediated single strand breaks in DNA. The role of the nuclear membrane-associated electron transfer chain in augmenting the anticancer action of the anthracycline antibiotics is discussed.
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PMID:An unusual NAD(P)H-dependent O2-.-enerating redox system in hepatoma 22a nuclei. 285 29

The existence of membrane-bound forms of glutathione reductase in rat liver and transplantable hepatoma G-27 was demonstrated, using differential centrifugation techniques. The activity of the sedimentable form of the liver enzyme was detected only in the presence of detergents. Conditions for the manifestation of the latent glutathione reductase activity in whole liver homogenates and in the 105000 g pellet were determined. Solubilization of the latent form of the enzyme in the presence of sodium deoxycholate increases 2-fold the glutathione reductase activity in liver homogenates (but not in hepatoma). Simultaneous determination of the disulfidereductase, nonspecific NADPH-oxidase and gamma-glutamyltransferase (membrane-bound enzyme of glutathione metabolism) activities was performed.
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PMID:[Latent form of glutathione reductase in the rat liver]. 287 72

The X-chromosome-linked glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP+ oxidoreductase, EC 1.1.1.49) of humans and other mammals consists of a subunit with a molecular weight of about 58,000. The enzyme plays a key role in the generation of NADPH, particularly in matured erythrocytes, and the genetic deficiency of the enzyme is associated with chronic and drug- or food-induced hemolytic anemia in humans. The enzyme was purified to homogeneity from human erythrocytes. The complete amino acid sequence of the subunit, consisting of 531 amino acid residues, was determined by automated and manual Edman degradation of tryptic, chymotryptic, thermolytic, and cyanogen bromide peptides obtained from the enzyme. Based on the amino acid sequence data thus obtained, a 41-mer oligonucleotide with unique sequence was prepared. Two cDNA libraries constructed in phage lambda gt11--i.e., a human liver cDNA library and a human hepatoma Li-7 cDNA library--were screened with the synthetic nucleotide probe. Two positive clones, lambda G6PD-19 and lambda G6PD-25, were obtained from the hepatoma library. lambda G6PD-19 contained an insertion of 2.0 kilobase pairs (kbp), and encoded 204 amino acid residues that were completely compatible with the COOH-terminal portion of the enzyme. The insertion of the clone had a 3' noncoding region of 1.36 kbp. The other clone, lambda G6PD-25, had an insertion of 1.8 kbp and encoded 362 amino acid residues of G6PD. Southern blot analysis of DNA samples obtained from cells with and without the human X chromosome indicated that the cDNA hybridizes with a sequence in the X chromosome.
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PMID:Human glucose-6-phosphate dehydrogenase: primary structure and cDNA cloning. 301 56


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