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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Uptake of cystine and factors affecting the transport were investigated in adult rat hepatocytes in primary monolayer culture. The cystine uptake was initially mediated by Na+-dependent route(s). However, the activity of Na+-dependent uptake decreased markedly during the culture, and Na+-independent uptake emerged with a lag period of 12 h in response to insulin and dexamethasone in the culture medium. After 48 h in culture, cystine was mainly transported into the cells through this Na+-independent route. The action of insulin and dexamethasone on the enhancement of the Na+-independent uptake was apparently additive, and the enhancement was completely blocked by cycloheximide or actinomycin D. Emergence of the Na+-independent uptake of cystine was also regulated by cell density; at lower density, the uptake tended to be elevated. The transport of cystine through the Na+-independent system was pH sensitive and was inhibited by some anionic amino acids, such as glutamate and homocysteate, but not by aspartate. These results suggest that the emerging system is similar to the ones reported in fibroblasts and in some hepatoma cell lines; the anionic form of cystine is transported through the system.
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PMID:Transport of cystine in isolated rat hepatocytes in primary culture. 614 43

9he synthesis and chemical characterization of the gamma-glutamyl adduct of phenylenediamine mustard is reported. The activity of this compound, gamma-[N,N-bis(2-chloroethyl)-p-phenylenediamine]-glutamate, as a substrate for gamma-glutamyl transferase is demonstrated and compared with the activity of glutathione. The possible use of this material as a directed anti-hepatoma agent is discussed.
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PMID:Synthesis and preliminary characterization of a novel substrate for gamma-glutamyl transferase. A potential anti-hepatoma drug. 614 15

The effects of folinic acid on a toxic pulse exposure of cultured hepatoma cells to methotrexate (4-amino-10-methylpteroylglutamic acid) is reported. Inclusion of folinic acid (5-formyl-5,6,7,8-tetrahydropteroylglutamic acid) (10 micro M) with the 2-hr pulse of methotrexate (10 micro M) nearly completely prevents the uptake and gamma-glutamylation of methotrexate and prevents toxicity. Addition of folinic acid after methotrexate results in a partial rescue that is time and concentration dependent. Restoration of cell growth in the presence of increasing amounts of folinic acid is accompanied by a concentration-dependent elevation in tritium release from [5-3H]deoxyuridine. In the absence of folinic acid, the release of tritium from [5-3H]deoxyuridine remains inhibited for three days after exposure to methotrexate, which can be related to the cellular formation and retention of methotrexate polyglutamates. Following the 2-hr pulse of methotrexate, the cellular pool consists of 70% polyglutamates of which the predominant species has three glutamate residues (4-NH2-10-CH3PteGlu3). When methotrexate is removed from medium, following the pulse, unmetabolized methotrexate rapidly leaves the cells, and 4-NH2-10-CH3PteGlu3 is converted to methotrexate polyglutamates containing four to six glutamate residues. Addition of folinic acid after the methotrexate pulse prevents the conversion of 4-NH2-10-CH3PteGlu3 to the higher-chain-length derivatives and causes a reduction in the total methotrexate cell pools over the next 48 hr. These results suggest that the effects of folinic acid on methotrexate polyglutamates may play a role in the rescue of cells containing these derivatives.
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PMID:Effects of folinic acid on hepatoma cells containing methotrexate polyglutamates. 618 49

Methotrexate polyglutamates are extensively synthesized when cultured hepatocytes and H35 hepatoma cells are exposed to micromolar concentrations of methotrexate. The predominant species found within the cell have from two to four additional gamma-linked glutamate residues. When either cell type containing a mixture of methotrexate and its polyglutamate derivatives is exposed to medium lacking methotrexate, there is a rapid release of methotrexate. This release has a T1/2 of 2 to 4 min and is apparently complete within 30 to 60 min. Methotrexate polyglutamates leave the cells much more slowly and appear to do so by two mechanisms. Although cleavage to methotrexate and subsequent efflux appears to be quantitatively the more important pathway, there is also a slow, finite loss of intact methotrexate polyglutamates from cells which exclude trypan blue. The T1/2 for the loss of methotrexate polyglutamates by both cell types, when placed in medium lacking methotrexate, is approximately 6 to 8 hr. These results, together with those of an earlier study (Galivan, J. (1980) Mol. Pharmacol. 17:105-110), suggest that the polyglutamate derivatives are forms of methotrexate which are as cytotoxic as methotrexate but which offer a potentially greater capacity for cellular destruction because they are retained longer in the tissue.
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PMID:Studies of formation and efflux of methotrexate polyglutamates with cultured hepatic cells. 619 87

The glutamylation of methotrexate has been evaluated in H35 hepatoma cells in vitro as a function of the conditions of culture. Glutamylation yields methotrexate polyglutamate with two to five additional glutamate residues and is a saturable process. The rate of glutamylation increases little above 10 microM extracellular methotrexate which corresponds to an intracellular concentration of approximately 4 microM. The rate of glutamylation measured over a 6-h period was stimulated by a reduction in cellular folates and prior incubation of the cells with insulin. Glutamylation was also more rapid in dividing cultures than in confluent cells. The combination of insulin inclusion and folate reduction, which was additive, caused approximately a fourfold increase in the rate of glutamylation over control cells under the conditions tested. The maximal rate of methotrexate glutamylation, which was 100 nmol/g/h, occurred in folate-depleted, insulin-supplemented cells. Supplementing folate-depleted cells with reduced folate coenzymes caused the glutamylation to be reduced by more than 90%. The turnover of methotrexate polyglutamates in cells saturated with these derivatives occurred at approximately one-half the rate of net synthesis and was stimulated to nearly the same extent by folate depletion and insulin. In addition to showing that folates can modify the rates of methotrexate polyglutamate formation, data are presented suggesting that methotrexate polyglutamates can regulate their own synthesis. The consequences of the formation of these retained forms of methotrexate in H35 hepatoma cells (M. Balinska, J. Galivan, and J.K. Coward (1981) Cancer Res. 41,2751-2756) and the effects of potential regulators of this process are discussed in terms of the glutamylation of folates in the cells and the chemotherapeutic effects of antifolates.
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PMID:Regulatory aspects of the glutamylation of methotrexate in cultured hepatoma cells. 619 70

1. The expression of twelve liver-specific enzymes was analysed in twenty-one independent rat hepatoma X human somatic cell hybrids, and in some cases up to forty-one subclones were also tested. 2. Seventeen hybrids continued to express most of the rat liver-specific enzymes and in some cases human isozymes of glutamate-pyruvate transaminase, alpha-glycerophosphate dehydrogenase, guanine deaminase, alcohol dehydrogenase and pyruvate kinase were clearly identified. 3. Analysis of the segregation of the human liver-specific enzymes in these hybrids led to the assignment of human GPT to chromosome 8 (previously reported, Kielty, Povey & Hopkinson, 1982) and suggests the assignment of human GPD1 to chromosome 12. 4. The expression of the various liver-specific enzymes in these hybrids appeared to be controlled by independent regulatory mechanisms. 5. Four unusual reverse segregant hybrids were also analysed, and in these no liver-specific enzyme activity was demonstrable.
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PMID:Regulation of expression of liver-specific enzymes. III. Further analysis of a series of rat hepatoma X human somatic cell hybrids. 629 71

Reuber hepatoma H-35 was found to retain the activity of carbamoyl-phosphate synthetase I. The content of this enzyme in H-35 grown in Eagle's minimal essential medium was about half that in rat liver. The enzyme from H-35 was the same as that from rat liver in molecular weight estimated by SDS-polyacrylamide gel electrophoresis, specific enzyme activity, kinetic parameters for ATP and N-acetyl-L-glutamate, and immunological crossreactivity. The enzyme in H-35 was induced by dexamethasone (1.4-fold) but not by glucagon or dibutyryl cAMP. Incorporation of [35S] methionine into the enzyme indicated that the effect of dexamethasone was due to increased synthesis of the enzyme protein (2.1-fold). By labeling with [35S]methionine, the precursor and the mature forms of carbamoyl-phosphate synthetase I were observed in the post-mitochondrial and mitochondrial fractions, respectively. By chasing the labeled cells with unlabeled methionine and cycloheximide, it was observed that the rate of translocation of the precursor into mitochondria is not affected by dexamethasone.
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PMID:Induction of carbamoyl-phosphate synthetase I in Reuber hepatoma H-35 by dexamethasone. 630 26

Mitochondria isolated from rapidly growing, poorly differentiated Morris hepatoma 3924A have been found to export the citrate they generate from pyruvate, at a rate greater than four times that of control liver preparations. These 3924A mitochondria fail to exhibit state 3 respiration when either pyruvate or citrate are supplied as respiratory fuels. Nevertheless, substrates that join the Krebs cycle beyond citrate (viz. isocitrate, glutamate, alpha-ketoglutarate, and succinate) are readily oxidized by tumor 3924A mitochondria. Blocking the tricarboxylate anion exchange carrier with the citrate transport inhibitor 1,2,3-benzenetricarboxylate restores the ability of tumor 3924A mitochondria to respire with pyruvate or citrate. Slowly growing, minimally deviated Morris hepatoma 16 possesses mitochondria that do not display discernably altered respiratory patterns with pyruvate or citrate, but they do exhibit a 30% increase in the rate of citrate export relative to control liver preparations. Paralleling the preferential citrate export from tumor mitochondria is a dramatic enrichment of the tumor mitochondrial membranes with cholesterol. Hepatoma 3924A mitochondria possess a more than 5-fold enrichment in cholesterol, and those from tumor 16 display a 2-fold enrichment. When normal mitochondria, isolated from ACI strain rat liver, were enriched with cholesterol in vitro via a solid-state molecule transfer method employing Sephadex G-10 beads coated with cholesterol, they exhibited altered patterns of Krebs cycle metabolism that were qualitatively identical to those obtained with isolated Morris hepatoma mitochondria (which become enriched in membrane cholesterol endogenously during tumorigenesis). The enrichment of mitochondrial membranes with cholesterol, either by experimental manipulation in vitro or during the proliferation of the tumor in the host animal, promotes these metabolic changes directly, apparently by effecting a functional alteration in the operation of the tricarboxylate (citrate) exchange carrier of the inner mitochondrial membrane. These results highlight two related but incompletely understood phenomena as follows: 1) a functionally truncated Krebs cycle in cholesterol-rich tumor mitochondria, and 2) a mechanism for providing higher cytoplasmic levels of precursor metabolite intermediates which help sustain deregulated cholesterogenesis in hepatomas and other malignant neoplasms.
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PMID:Enhanced rate of citrate export from cholesterol-rich hepatoma mitochondria. The truncated Krebs cycle and other metabolic ramifications of mitochondrial membrane cholesterol. 646 76

The purification and kinetic characterization of an NAD(P)+-malic enzyme from 22aH mouse hepatoma mitochondria are described. The enzyme was purified 328-fold with a final yield of 51% and specific activity of 38.1 units/mg of protein by employing DEAE-cellulose chromatography and an ATP affinity column. Sephadex G-200 chromatography yielded a native Mr = 240,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major subunit with Mr = 61,000, suggesting a tetrameric structure, and also showed that the preparation contained less than 10% polypeptide impurities. Use of the ATP affinity column required the presence of MnCl2 and fumarate (an allosteric activator) in the elution buffers. In the absence of fumarate, the Michaelis constants for malate, NAD+, and NADP+ were 3.6 mM, 55 microM, and 72 microM, respectively; in the presence of fumarate (2 mM), the constants were 0.34 mM, 9 microM, and 13 microM, respectively. ATP was shown to be an allosteric inhibitor, competitive with malate. However, the inhibition by ATP displayed hyperbolic competitive kinetics with a KI (ATP) of 80 microM (minus fumarate) and 0.5 mM (plus 2 mM fumarate). The allosteric properties of the enzyme are integrated into a rationale for its specific role in the pathways of malate and glutamate oxidation in tumor mitochondria.
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PMID:Purification, kinetic behavior, and regulation of NAD(P)+ malic enzyme of tumor mitochondria. 672 50

The antitumor drug acivicin, L-(alphaS,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid, in vivo irreversibly inactivated carbamoyl-phosphate synthetase II(glutamine-dependent)(EC 6.3.5.5), the first and rate-limiting enzyme of de novo pyrimidine nucleotide biosynthesis, in transplantable rat hepatoma and host liver. With two injections of 0.5 mg acivicin per 100 g body weight to one group and two injections of 5 mg to another group, enzyme activity decreased to 20 and 1% in hepatoma and to 99 and 31% in liver respectively. Aspartate carbamoyltransferase (EC 2.1.3.2) activity was not affected. Acivicin in vitro selectively inactivated glutamine-dependent activity of the synthetase II from the hepatoma and liver, with an inactivation constant (Kinact) of 90 microM and a minimum inactivation half-time (T) of 0.7 min. The inactivation velocity with 10 microM acivicin was 5.0-fold stimulated by 2 mM MgATP and 18.4-fold by 2 mM MgATP plus 16.7 mM bicarbonate. MgATP at 0.5 mM caused half-maximum stimulation of the inactivation velocity. Under in vitro conditions, L-glutamine (1 mM) protected the enzyme from inactivation by 10 microM acivicin. The synthetase activity was protected in vitro by 6 mM concentrations for glycine (84%), L-glutamate (59%) and L-aspartate (51%) and by 0.5 mM UTP (35%) from inactivation by 20 microM acivicin. The results are compatible with the suggestion that acivicin is an active site-directed affinity analog of L-glutamine.
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PMID:In vivo inactivation by acivicin of carbamoyl-phosphate synthetase II in rat hepatoma. 708 74


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