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)

We present evidence that normal hepatocytes can be specifically protected from galactosamine toxicity in vitro by targeting an antagonist to these cells via receptor-mediated endocytosis. The strategy is based upon the following principles: 1) galactosamine is a highly selective hepatotoxin that causes a dose-dependent depletion of uridine intermediates; 2) galactosamine toxicity can be antagonized by supplemental administration of uridine; 3) normal hepatocytes possess unique cell-surface receptors that can internalize galactose terminal (asialo-)glycoproteins with subsequent degradation of the glycoprotein ligand. Based on these facts, we hypothesized that chemical coupling of a galactosamine antagonist to an asialoglycoprotein could result in cell-specific delivery and protection of normal hepatocytes by targeting the antagonist via asialoglycoprotein receptors. Using a model system consisting of freshly isolated rat hepatocytes (receptor (+)) and Morris 7777 rat hepatoma (receptor (-)) cells, sensitivity to galactosamine in vitro was determined and found to be similar for both types of cells. A targetable antagonist was synthesized by coupling uridine monophosphate to asialoorosomucoid in a molar ratio of 5 to 1. Exposure of Morris 7777 cells to the targetable antagonist in the presence of a toxic concentration of galactosamine did not protect these cells as evidenced by a steady decline in the number of viable cells in a fashion identical to cells treated with galactosamine alone. However, normal hepatocytes that received the conjugate in the presence of galactosamine were protected as their viable cell number remained the same as control (untreated) cells. Competition by an excess of asialoglycoprotein inhibited the protective effect of the conjugate, supporting the concept that the asialoglycoprotein component of the conjugate was responsible for the specific delivery of the antagonist to the target cells.
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PMID:Targeted antagonism of galactosamine toxicity in normal rat hepatocytes in vitro. 335 Aug 10

Uridylate-trapping analogs of D-galactose or D-glucose divert the uridylate moiety of UDPglucose and/or UTP to UDP-sugar analogs that accumulate while the pools of UTP and of related pyrimidine nucleotides are depleted. The uridylate-trapping action of sugar analogs is determined by the enzyme pattern of the target tissue. D-Galactose analogs are preferentially metabolized by hepatoma cells and hepatocytes. TA3-mammary tumor cells are susceptible to the action of D-glucosamine and other D-glucose analogs. A high rate of de novo pyrimidine synthesis and/or an active salvage of extracellular uridine compensate for the uridylate-trapping action of sugar analogs and prevent depletion of UTP pools. Accordingly, synergistic actions are induced by combining sugar analogs, such as D-galactosamine or D-glucosamine, with inhibitors of de novo pyrimidine synthesis, such as lapachol or 6-azauridine. Uridylate-trapping by D-galactosamine, acting on hepatocytes, shifts the balance between uridine consumption and uridine release by the liver and results in a fall of uridine and cytidine concentrations in blood plasma (20). Cultured hepatocytes produce uridine and cytidine. Combination of 5-fluorouridine with sugar analogs results in the formation of fluorinated UDP-sugar analogs in hepatoma cells or in mammary tumor cells. Formation of FUDP-sugar analogs transiently removes intracellular FUTP, but FUDP can be released subsequently in glycosyltransferase reactions (22). Pretreatment of hepatoma cells or of TA3-mammary tumor cells with an uridylate-trapping sugar analog in combination with an inhibitor of de novo pyrimidine synthesis enhances the uptake of 5-fluorouridine, its incorporation into RNA, and its growth inhibitory effect. The chemotherapeutic action of 5-fluorouridine in rats and mice, carrying the AS-30D and the TA3 ascites tumor, respectively, is significantly improved by pretreatment with an amino sugar together with 6-azauridine.
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PMID:Potentiation of antimetabolite action by uridylate trapping. 383 24

The metabolism of acid mucopolysaccharides in Novikoff hepatoma and in hepatoma BW7756 was studied using the precursors -35S-sulfate, -H-glucosamine and -14C-galactosamine. There is an active formation of sulfated mucopolysaccharides at the mitochondria and cell membrane level. Hepatoma cells synthesize heparin to a lower rate than liver cells. In ascitic as well as in solid tumors there is a considerable accumulation of hyaluronic acid which does not seem to be elicited by the tumor cells but by the surrounding tissues. The possible implication of the low heparin production in the cell membrane characteristics is discussed.
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PMID:Metabolism of acid mucopolysaccharides in hepatoma and in normal liver. 437 92

Hepatoma tissue culture cells, grown in the presence of D-galactosamine and 6-azauridine, demonstrate a strong reduction of the intracellular UTP pool that can be replenished by formation of UTP from uridine and FUTP from 5-fluorouridine within 2 h. Concomitantly with the UTP deficiency, a decrease of dexamethasone-induced tyrosine aminotransferase activity occurs. 5-Fluorouridine, as compared to uridine, is even more efficient in restoring the activity of tyrosine aminotransferase. Treatment of the cells with D-galactosamine alone results in a minor lowering of UTP that is not followed by the inhibition of the enzyme induction. However, the administration of D-galactosamine, simultaneously or at any time up to 5 h before or after dexamethasone, leads to a 1.5- to 2-fold higher induction (superinduction) which appears 24 h later.
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PMID:Inhibition of tyrosine aminotransferase induction by UTP deficiency and its reversal by 5-fluorouridine in cultured hepatoma cells. 616 86

The cellular localization of alpha-fetoprotein (AFP) and albumin (ALB) in permissive states for AFP synthesis has been examined. The cells containing AFP associated with permissive states in the adult are similar in appearance to cells that are present during the development of fetal liver. In fetal liver, AFP is seen in most developing hepatocytes ranging from small 'oval' like cells to larger dividing hepatocytes and in cells organized in glandular structures. Following exposure to some chemical hepatocarcinogens, AFP can also be seen in small 'oval' cells, ductal-like cells, and larger atypical hepatocytes that form glandular-like structures. Following partial hepatectomy or galactosamine-induced live injury, AFP is seen in a few large parenchymal cells usually containing identifiable chromatin Cells which contain AFP almost always contain ALB as well, but for each cell type there are many more ALB containing cells than AFP containing cells. ALB and AFP containing hepatoma cells are more frequently located adjacent to tumor vessels and AFP production by hepatoma 777 in vitro is associated with the growth state of the tumor. The AFP containing cells that are seen during restitutive proliferation most likely arise from deregulation of proliferating adult hepatocytes. The non-hepatoma AFP containing cells that appear early during carcinogenesis may arise in the adult by retrodifferentiation of hepatocytes or by proliferation of stem cells. These morphologically different AFP containing cells may or may not be precursors of the hepatocellular carcinomas which develop later.
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PMID:Heterogeneity of alpha-fetoprotein(AFP) and albumin containing cells in normal and pathological permissive states for AFP production: AFP containing cells induced in adult rats recapitulate the appearance of AFP containing hepatocytes in fetal rats. 616 57

Of the RNA labelled after incubation of hepatoma cells with radioactive precursors for 20 and 150 min. 35% and 70%, respectively, can be isolated from nuclei by two consecutive extractions with 0.14 M NaCl at pH 8. The isolated RNA is complexed with nuclear proteins forming structures with sedimentation coefficients of less than 30 S to greater than 100 S. Similar complexes from rat liver isolated under the same experimental conditions show coefficients of 30-40 S. The RNA-associated proteins are similar, on the basis of sodium dodecyl sulphate/polyacrylamide gel electrophoresis, to the respective proteins of other cell types. The presence on these RNP complexes of six discrete small nuclear RNAs (snRNA) has been established. Experiments with a reversible inhibitor of RNA synthesis, D-galactosamine, demonstrated, differences in the turnover of hnRNA and snRNA. The half-lives of the six snRNA species has been determined, varying from 32 h for snRNA species a, b and d, to 22 h for snRNA species e and f and to 13 h for snRNA species c. Treatment of the nuclear extracts with 0.7 M and 1 M NaCl results in dissociation of hnRNA from the 'core' and other polypeptides, whereas snRNA remains complexed with polypeptides of Mr 54 000-59 000. Incubation of the nuclear extracts at 0 C with low doses of pancreatic R Nase (up to 1.5 micrograms/ml), which renders approximately 80% of the hnRNA acid-soluble and cleaves most of the snRNA, results in conversion of the high-molecular-weight hnRNPs to 30-S structures, without disrupting the 30-S RNP. Treatment of the nuclear extracts with higher doses of RNase (3 micrograms/ml) leads to disruption of the 30-S RNP and release of the hnRNA-associated proteins, underlining the importance of hnRNA-protein interaction for the retainment of the hnRNP structures.
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PMID:Isolation and characterization of hnRNA-snRNA-protein complexes from Morris hepatoma cells. 618 25

Purified membrane glycoproteins from liver or hepatoma tissue culture cells were incorporated in a right-side-out orientation into reconstituted phospholipid vesicles by a detergent dialysis method. The phospholipids were purified from membrane preparations of rat liver. The protein:phospholipid ratio of the reconstituted vesicles was optimized for efficient transfer of vesicle contents to the recipient cells, usually mouse L cells. Fluoresceinated albumin incorporated into the lumen of reconstituted vesicles was used as a marker for transfer after polyethylene glycol-mediated fusion. The redistribution and fate of both the lipids and the transferred membrane proteins were analysed by microscopic and biochemical methods. A hepatocyte-specific binding protein for galactose- or galactosamine-terminated serum glycoproteins and a set of hepatoma cell plasma membrane glycoproteins were successfully transferred to the plasma membrane of mouse fibroblasts by these methods. The biological function of the hepatic binding protein, namely delivery of the galactose-terminated glycoprotein ligand to the lysosome for degradation, was imparted to the mouse fibroblast after transfer. Further, both the polypeptide and the carbohydrate moieties of a set of membrane proteins were degraded at about the same relative rates as they had in the original donor cells, after transfer to the plasma membrane of recipient mouse fibroblasts. These studies show that the technique of inserting membrane constituents into the plasma membrane of another cell can help to elucidate the route and mechanism of membrane protein function and turnover.
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PMID:Transfer of plasma membrane proteins between cells using reconstituted membrane vesicles as shuttle vehicles. 656 Nov 33

Studies on Morris hepatomas demonstrate that the specific activity of the enzymes of the Leloir pathway are subject to a variation in tumor tissue. The key enzyme of the galactose pathway, uridine diphosphogalactose 4'-epimerase, is elevated 5- to 9-fold in the rapidly growing and poorly differentiated Tumors 3924A and 7777; in line 9618A2, an even 28-fold increase was found. The observed correlation between enzyme activity, growth rate, and degree of differentiation of the hepatoma suggests that the differences are not coincidental variations. Conversely, the activity of uridine diphosphoglucose: galactose-1-phosphate uridyltransferase was diminished by 40 to 70% as compared to host liver, and the level of galactokinase showed only minor changes. The uptake of galactose and galactosamine by the hepatoma is heavily impaired, whereas the transport of other hexoses and amino sugars (2-deoxyglucose, L-fucose, N-acetylglucosamine, N-acetylmannosamine) is hardly affected. It appears that part of the carrier-mediated diffusion for hexoses is altered without a decisive impact on the whole system. Moreover, autoradiographic analysis of [14C]galactose-labeled tumor plasma membranes revealed a shift of the incorporation pattern from high- to lower-molecular-weight galactopolypeptides. Our results indicate that specific alterations of the D-galactose metabolism are a characteristic feature of Morris hepatomas.
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PMID:Alterations of D-galactose metabolism in Morris hepatomas. 676 57

The glutamine antagonist acivicin, L-(alpha S, 5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid, strongly reduced CTP and GTP contents in AS-30D rat hepatoma cells in suspension. UTP only dropped to 63% of the respective control after 4 hr; however, by combining acivicin with the uridylate-trapping sugar analogue D-galactosamine, a synergistic decrease in UTP contents to 7% of control was induced. Incorporation of 14CO2 into purine and pyrimidine nucleotides followed by radio-high performance liquid chromatography showed marked inhibition of purine and pyrimidine biosynthesis de novo; the latter was reduced to 35% of control. The inhibitory potency of acivicin on glutamine-dependent carbamoyl-phosphate synthetase and consequently on de novo uracil nucleotide formation was also reflected by the complete suppression of the D-galactosamine-induced rise in total uridylate. Induction of UTP deficiency by interference with the first and rate-limiting step in pyrimidine biosynthesis de novo together with a trapping of uridylate by D-galactosamine may provide a promising approach to the chemotherapy of hepatocellular carcinoma.
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PMID:Combined action of acivicin and D-galactosamine on pyrimidine nucleotide metabolism in hepatoma cells. 688 63

The precise mechanism by which insulin elicits its effects remains to be fully determined. A glycophospholipid, isolated from H35 cells, has been proposed as a possible precursor for an insulin-generated second messenger that mediates the intracellular effects of insulin. This glycolipid contains a hexosamine moiety, inositol, galactose and palmitate. We have isolated a glycolipid from cultured rat hepatocytes that exhibits chromatographic and radiolabelling characteristics similar to this proposed precursor. The glycolipid can be radiolabelled with glucosamine, galactosamine, galactose and palmitate, but not myristate or myoinositol. Incorporation of radiolabel into this glycolipid was insensitive to the presence of either insulin (10(-7) M) or phosphatidylinositol-specific phospholipase C (PI-PLC) in the culture medium. The cultured hepatocytes used exhibited normal insulin responses with respect to glycogen turnover and gene expression. Treatment of partially purified glycolipid with either PI-PLC or nitrous acid did not result in the generation of an aqueous soluble phosphooligosaccharide indicating that the glycolipid was not cleaved by either agent. This is in contrast to the reported cleavage of the glycolipids found in H35 hepatoma and lymphocytes. These results question the role of the putative phosphooligosaccharide mediator in the intracellular transduction system activated by insulin.
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PMID:Glycolipids isolated from cultured rat hepatocytes: analysis of their role in insulin signal transduction. 838 92


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