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C A Toth

Publications and source records attributed to C A Toth.

65 records · Page 4Linked to original sources
PubMed1991

Evaluation of a commercial recombinant tissue-type plasminogen activator preparation in the subretinal space of the cat.

To explore the feasibility of using human recombinant tissue-type plasminogen activator in the management of subretinal hemorrhage, we examined the toxic effects of a commercial preparation of human recombinant tissue-type plasminogen activator in the subretinal space of the holangiotic retina of the cat. Various concentrations of human recombinant tissue-type plasminogen activator and controls were infused into the subretinal space with a glass micropipette (40- to 60-microns tip) to form a retinal bleb. Concentrations from 2.5 mg/L to 200 mg/L were well tolerated without ultrastructural toxic effects, while 1000 mg/L of human recombinant tissue-type plasminogen activator caused severe, irreversible toxic effects to the photoreceptor-retinal pigment epithelium complex. This toxic effect appeared to be due to the carrier vehicle rather than the human recombinant tissue-type plasminogen activator protein itself. Our results demonstrate that commercially prepared human recombinant tissue-type plasminogen activator can be safely used in the subretinal space of the cat with the range necessary for fibrinolysis.

Animals↗
PubMed1990

A carcinoembryonic antigen (CEA) binding protein from ascites influences CEA uptake by macrophages.

A variant of CEA which is less readily endocytosed by macrophages has been isolated from malignant ascites. In vivo, CEA is cleared more slowly by the liver (t1/2 = 15.1 minutes) than CEAs isolated from hepatic metastases (t1/2 = 3.1 minutes). In vitro, rat and human Kupffer cells and rat alveolar macrophages endocytose this CEA less effectively. This slow clearing form of CEA is associated with a smaller (45kD) acidic glycoprotein (CORA) with which it forms a stable complex. CORA can be visualized on reducing gels but not on non reducing gels or by HPLC run under non reducing conditions. This suggests a non-covalent complex between the two glycoproteins. Analysis of protein conformation by circular dichroism revealed changes in the ascites CEA consistent with binding of CORA to the molecule. Western blot showed that CORA crossreacts with antisera to alpha 1-acid glycoprotein and double immunodiffusion demonstrated cross-reactivity but not identify. Sequencing of CNBr peptides showed sequence homology with alpha 1-acid glycoprotein but areas of unique sequence were also found. It is suggested that binding of CORA to CEA blocks the macrophage receptor binding of CEA.

Amino Acid Sequence↗
PubMed1990

Carcinoembryonic antigen binding to Kupffer cells is via a peptide located at the junction of the N-terminal and first loop domains.

A 11kD glycopeptide has been isolated by pepsin digestion of carcinoembryonic antigen (CEA) that is rapidly endocytosed by isolated rat Kupffer cells and lung alveolar macrophages. Uptake of this glycopeptide by the isolated cells can be inhibited by excess unmodified CEA. Removal of the N-linked oligosaccharide chains by N-glycanase did not alter cellular uptake but reduced the MW to approximately 5500. A seventeen amino acid N-terminal sequence locates this peptide at the junction of the N-terminal and first loop domain of CEA. It is suggested that the recognition of a peptide sequence in this area of CEA is responsible for its clearance from the circulation.

Amino Acid Sequence↗
PubMed1990

The effect of interferon treatment on 14 human colorectal cancer cell lines: growth and carcinoembryonic antigen secretion in vitro.

The effect of interferons (IFNs) on growth inhibition and carcinoembryonic antigen (CEA) secretion by 14 established human colorectal carcinoma cell lines was studied in vitro. The cell lines were characterized by morphologic differentiation, level of CEA production, and rate of growth. All cell lines were treated in vitro with recombinant human IFN (alpha, beta, and gamma) and the effect of treatment on growth rate and CEA secretion determined. Each cell line exhibited an individual pattern of growth inhibition that was independent of degree of differentiation, level of CEA production, and rate of growth. IFN-beta treatment did not increase CEA secretion in any of the cell lines studied. IFN-alpha and IFN-gamma resulted in increased CEA production (2- to 81-fold increase) primarily in the moderately to well-differentiated cell lines. IFN-gamma was a more potent inducer of enhanced CEA secretion than IFN-alpha. The more poorly differentiated cell lines did not produce CEA and could not be induced to do so by any of the IFNs.

Carcinoembryonic Antigen↗
PubMed1989

Receptor-mediated endocytosis of carcinoembryonic antigen by rat alveolar macrophages in vitro.

Uptake of carcinoembryonic antigen (CEA) by isolated rat alveolar cells was time, temperature, and concentration dependent (Kuptake = 2.4 x 10(-7) M). Pretreatment of the alveolar cells with colchicine inhibited internalization of CEA. Uptake of 125I-labeled CEA by alveolar cells required divalent cations and was inhibited by cold CEA and nonspecific cross-reacting antigen (NCA). The carbohydrate portion of CEA was modified by neuraminidase treatment and Smith degradation. The modified glycoproteins inhibited endocytosis by the alveolar macrophages, thus excluding nonreducing terminal carbohydrate residues as the recognition site of the receptor. Endocytosis of CEA was independent of native protein conformation since performic acid oxidized CEA and glycopeptides produced by pepsin digestion were inhibitory. Rat alveolar macrophages bound CEA with similar specificity to that of rat Kupffer cells. Alveolar macrophages, unlike Kupffer cells, did not rapidly exocytose the internalized CEA. Neither P388D1, a macrophage-like murine cell line, nor murine peritoneal exudate cells were capable of endocytosing CEA in vitro.

Animals↗
PubMed1988

Hepatic clearance and metabolism in the rat of a human breast cancer associated glycoprotein (GCDFP-15).

Gross Cystic Disease Fluid Protein (GCDFP-15) is a 60,000 dalton glycoprotein isolated from human breast cyst fluid, composed of four 15,000 dalton monomers. Carbohydrate analysis indicates that each monomer has a single carbohydrate chain of the complex type. GCDFP-15 intravenously injected into rats showed a rapid circulatory clearance, the rate of clearance being faster in female animals [t1/2 = 12.8 (+/- 2.0) min. females, and 16.7 (+/- 2.6) min. males]. The major organs of clearance were the liver (70%) and kidneys (15%). Immunoperoxidase staining showed localization in Kupffer cells and the proximal convoluted tubules of the kidney. Removal of sialic acid from GCDFP-15 resulted in a more rapid clearance (t1/2 = 2.2 min) by the liver (85%). This clearance was inhibited by coinjection of asialo alpha 1 acid glycoprotein. About 3% of GCDFP-15 was excreted in bile with a transit time through the liver of 38 min. Examination of the uptake of GCDFP-15 by isolated rat Kupffer cells showed that yeast mannan, fucosylated BSA, and carcinoembryonic antigen (CEA) failed to inhibit uptake, though the binding of GCDFP-15 was clearly saturable. This suggests that a novel receptor system on the rat Kupffer cell may be responsible for GCDFP-15 clearance.

Animals↗
PubMed1985

Receptor-mediated endocytosis of carcinoembryonic antigen by rat liver Kupffer cells.

In vivo, carcinoembryonic antigen (CEA) is removed from the circulation by the liver Kupffer cells. Immunologically identifiable CEA is transferred from these macrophages to the hepatocytes, where degradation is completed. Circulatory clearance of CEA is specific, rapid [t1/2 = 3.7 +/- 0.9 (S.D.) min], and saturable. In vitro, Kupffer cells take up CEA by a saturable process which is time/temperature dependent and colchicine sensitive. Isolated Kupffer cells endocytose CEA with an apparent Km of 6 X 10(-8) M. There are approximately 16,000 CEA binding sites per cell. Nonspecific cross-reacting antigen (NCA), a glycoprotein structurally similar to CEA, is recognized with lower affinity by the same receptor. Endocytosis is independent of the nonreducing terminal sugars on the molecule: CEA modified by Smith degradation inhibits Kupffer cell recognition of native CEA. Since performic acid oxidized CEA also inhibits endocytosis, receptor binding is similarly independent of intact protein conformation. Isolated Kupffer cells have mannose and/or N-acetyl glucosamine receptor activity but do not internalize CEA by that mechanism. Galactose-terminated glycoproteins impede CEA and NCA clearance in vivo but not Kupffer cell endocytosis in vitro. Radiolabeled CEA released from isolated Kupffer cells following endocytosis shows no apparent molecular weight change. However, the released CEA contains species with higher isoelectric points, suggesting that perhaps the removal of sialic acid and the resulting exposure of galactose residues mediate the subsequent transfer to the hepatocyte.

Animals↗
PubMed1982

A new Kupffer cell receptor mediating plasma clearance of carcinoembryonic antigen by the rat.

Native human carcinoembryonic antigen is rapidly removed from the circulation by the rat liver Kupffer cell after intravenous injection. The molecule is subsequently transferred to the hepatocyte in an immunologically identifiable form. Carcinoembryonic antigen has a circulatory half-life of 3.7 (+/- 0.8) min, and cellular entry is by receptor-mediated endocytosis. Non-specific fluid pinocytosis and phagocytosis can be excluded as possible mechanisms by the kinetics of clearance and failure of colloidal carbon to inhibit uptake. Substances with known affinity for the hepatic receptors for mannose, N-acetylglucosamine, fucose and galactose all fail to inhibit carcinoembryonic antigen clearance. After two cycles of the Smith degradation, carcinoembryonic antigen is still able to inhibit clearance of the native molecule. Receptor specificity is apparently not dependent on those non-reducing terminal sugars of the native molecule. Performic acid-oxidized carcinoembryonic antigen also inhibits clearance of carcinoembryonic antigen in vivo. Receptor binding is not dependent on tertiary protein conformation. Non-specific cross-reacting antigen, a glycoprotein structurally similar to carcinoembryonic antigen, is cleared by the same mechanism.

Animals↗
PubMedDate not supplied

The mechanism of biliary excretion of alpha 1-acid glycoprotein in the rat: evidence for a molecular weight-dependent, nonreceptor-mediated pathway.

The transport of human alpha 1-acid glycoprotein from the circulation to the bile has been studied in the rat. Biliary excretion was proportional to the i.v. injected dose, and the percentage excreted remained constant. The amount excreted in the bile (over 4 hr) was inversely related to the rate of hepatic (hepatocyte) uptake and the galactose receptor which is specific for asialo glycoproteins was not involved. Reinjection of the glycoprotein excreted in bile resulted in a similar proportion of the dose being reexcreted, suggesting that a subset of the glycoprotein is not selected for excretion in bile. Transit times from blood to bile for glucagon, insulin, alpha 1-acid glycoprotein, fetuin, albumin, and carcinoembryonic antigen were directly related to their molecular weights. Removal of sialic acid from the asialo glycoproteins did not affect these transit times. Possible mechanisms for the biliary excretion of alpha 1-acid glycoprotein are discussed.

Animals↗