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At least 685 records · Page 38Linked to original sources
PubMed1995

Carbohydrate-binding proteins (plant/human lectins and autoantibodies from human serum) as mediators of release of lysozyme, elastase, and myeloperoxidase from human neutrophils.

Analysis of cell surface glycosylation not only provides information about cell properties such as their state of differentiation or histogenetic lineage. The carbohydrate chains also provide potentially functional binding sites to endogenous carbohydrate-binding proteins. This interaction can elicit consequent signalling processes. Because of the importance of neutrophils in the host defence system, we monitored the effect of the binding of such sugar receptors to their cell surface on the release of the enzymatic activities of lysozyme, elastase, and myeloperoxidase. Besides the mannose-binding lectin concanavalin A and the immunomodulatory alpha/beta-galactoside-binding lectin from Viscum album L., three preparations of human sugar receptors - beta-galactoside-binding lectin (M(r) 14 kDa) and two affinity-purified polyclonal IgG fractions from serum with the capacity to recognize alpha- or beta-galactosides, respectively - were used. Two animal lectins from chicken liver and intestine that bind beta-galactosides, as well as the lectin-like human serum amyloid P component, were included in order to assess the importance of slight differences in ligand recognition. Cytochalasin B-enhanced enzyme release was invariably seen with the two plant lectins and the chicken liver beta-galactoside-binding lectin, but the related intestinal lectin did not increase enzyme release. The mammalian homologue of these avian lectins triggered lysozyme secretion, and the lactoside-binding IgG fraction enhanced the amount of extracellular elastase activity slightly but significantly. Thus, the actual lectin, not the nominal specificity of sugar receptors, is crucial for elucidation of responses. Due to the highly stimulatory activity of the two plant lectins, neutrophils from patients with non-cancerous diseases and from patients with lung cancer were monitored for the extent of lectin-mediated enzyme release. Only the concanavalin A-mediated reactivity of the neutrophils was associated with the type of disease.

Adult↗
PubMedDate not supplied

Biochemical characterization of a component in extracts of Viscum album enhancing human NK cytotoxicity.

Enhancement of human NK cytotoxicity in the presence of fresh Viscum album extract and some commercial V. album extracts Iscador correlated strictly with an increased formation of lytic effector cell/K562 tumor cell conjugates in the single-cell assay. Both activities were completely destroyed by pretreatment of V. album extracts with pectinase, hemicellulase, amyloglucosidase and alpha-glucosidase, but not with proteases and RNase, i.e., the activities are linked to a polysaccharide. The active component in V. album extract was non-dialysable at a molecular weight cutoff of 10,000. Inhibition of both activities was observed with D-galacturonic acid, poly-galacturonic acid and pectins. The site of galacturonic acid-specific interaction could be identified on the effector cells. The rate of effector cell/tumor cell conjugate formation in the presence of V. album extracts, as well as the abrogation of both activities by pretreatment of V. album extracts with exoglycosidases specific for sugars other than galacturonic acid indicated an action of the NK cytotoxicity-enhancing component on the basis of a bridging mechanism. However, no conclusive results could be obtained for the structural specificity of the site interacting with the target cells.

Binding Sites↗
PubMedDate not supplied

Chemical specificity of effector cell/tumor cell bridging by a Viscum album rhamnogalacturonan enhancing cytotoxicity of human NK cells.

The component in Viscum album extract Iscador-M enhancing the NK cytotoxicity of human CD56+CD3- NK cells (87-95% enrichment) in cocultures with K562 tumor cells and increasing the formation of NK cell/tumor cell conjugates was identified as a rhamnogalacturonan. Both activities were abolished by treatment of V. album extract with poly-alpha-D-galacturonidase and alpha-rhamnosidase and both activities were inhibited in the presence of galacturonic acid and acetylated rhamnose (6-deoxymannose). Inhibition was also observed in the presence of structurally related derivatives such as acetylated mannose or acetylated mannonic acid gamma-lactone, the latter exhibiting a 5-10-fold higher inhibitory potential. The rapid formation of NK cell/tumor cell conjugates in the presence of V. album extract was based on the bridging of NK cells with tumor cells by rhamnogalacturonan. Using a specifically adapted agglutination assay, the saccharide residues of the rhamnogalacturonan interacting with NK cells and tumor cells could be identified by the formation of homologous cell conjugates induced by acetylated rhamnose or acetylated mannose conjugated to dextran and by polygalacturonic acid: terminal acetylated rhamnose or acetylated mannose bound only to NK cells in a dose-dependent manner but not to K562 tumor cells, and terminal galacturonic acid only to K562 tumor cells but not to NK cells. This type of bridging represents a novel mechanism of enhancement of NK cytotoxicity.

Agglutination Tests↗
PubMed1987

Mediation of human NK-activity by components in extracts of Viscum album.

Viscum album extracts (Iscador) were investigated for their potency to influence NK cytotoxicity in vitro. In vitro short term cytotoxicity assays (4 h) with human peripheral mononuclear cells (PMNC) and human K 562 tumor cells showed a drastic enhancement of NK cytotoxicity in the presence of V. album extracts. The presence of the V. album components during tumor cell lysis was essential since preincubation of PMNC with V. album extract followed by thorough washing did not lead to enhancement of NK cytotoxicity. One responding effector cell was identified as a member of the large granular lymphocyte (LGL) family carrying both Leu 7 and Leu 11 surface markers. Furthermore, monocytes depleted of LGL, but not differentiated macrophages, showed a weak enhancement of their cytolytic activity in the presence of V. album extract. Fractionation of V. album extracts revealed two active fractions one (C1) with about 3-4000 D and the other (C2) less than 1000 D. Both components enhanced NK cytotoxicity of LGL (Leu 7+, Leu 11+) as well as of monocytes showing enhancing effects also against moderately NK-sensitive tumor cell lines.

Adjuvants, Immunologic↗
PubMed1995

Effects of Viscum album L. on cyclophosphamide-treated peripheral blood mononuclear cells in vitro: sister chromatid exchanges and activation/proliferation marker expression.

Based on recently published data, Viscum album L. (VAL) extracts have been shown to provide a DNA stabilizing effect which seems to be restricted to the peripheral blood mononuclear cells (PBMC). We have now investigated whether VAL exerts effects of cellular protection for phytohemagglutinin-activated PBMC treated with cyclophosphamdie (CP) in vitro. The addition of VAL resulted in a slight reduction of CP-induced sister chromatid exchanges of cultured PBMC from healthy individuals. The incubation with CP significantly reduced the expression of the low affinity interleukin-2 receptor (IL-2R alpha chain) and of transferrin receptor (TfR) on PHA-stimulated T lymphocytes. The addition of 10 micrograms/ml VAL was protective against the CP-induced depression of IL-2R alpha chain and TfR expression on these cells. The simultaneous addition of CP and purified VAL components, such as ML I, ML II/III, and viscotoxins did not significantly change expression of IL-2R alpha chain and TfR on T cells. Thus, so far undefined VAL components might be responsible for the observed protection effects of the whole plant extract. The results presented here should encourage investigation of this drug, which might become an interesting adjuvant in cancer therapy.

Adult↗
PubMed1990

Effect of a preparation from Viscum album on tumor development in vitro and in mice.

The effect of Iscador, a commercial preparation made from Viscum album was studied on several cell lines using in vitro tissue culture as well as tumor-bearing animals. Iscador was found to be cytotoxic to animal tumor cells such as Dalton's lymphoma ascites cells (DLA cells) and Ehrlich ascites cells in vitro and inhibited the growth of lung fibroblasts (LB cells), Chinese hamster ovary cells (CHO cells) and human nasopharyngeal carcinoma cells (KB cells) at very low concentrations. Moreover, administration of Iscador was found to reduce ascites tumours and solid tumours produced by DLA cells and Ehrlich ascites cells. The effect of the drug could be seen when the drug was given either simultaneously, after tumour development or when given prophylactically, indicating a mechanism of action very different from other chemotherapeutic drugs. Iscador was not found to be cytotoxic to lymphocytes.

Animals↗
PubMed1994

Viscum album L. extracts reduce sister chromatid exchanges in cultured peripheral blood mononuclear cells.

Increasing concentrations of Viscum album L. extracts were shown to significantly reduce sister chromatid exchange (SCE) frequency of phytohaemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMC) of healthy individuals. This decrease of SCE could not be explained either by changes in lymphocyte subpopulations, by cytostatic effects of the drug or by accelerated proliferation of PHA-stimulated PBMC. Currently, no other cells tested have shown this effect. One therapeutic effect of these anti-mutagenic drugs could be a stabilisation of mononuclear blood cell DNA.

Adult↗
PubMed1998

Membrane fusion mediated by ricin and viscumin.

The ribosome inactivating plant proteins (RIPs) ricin and viscumin but not Ricinus communis agglutinin are able induce vesicle-vesicle fusion. A model is suggested in which the toxicity of the RIPs is partially determined by their fusogenicity. Herein, fusion is hypothesized to allow the RIPs to leak across endocytic vesicles to approve their access to cytoplasmic ribosomes.

Ricinus communis↗
PubMed1998

Dehydration of model membranes induced by lectins from Ricinus communis and Viscum album.

The effects of ribosome-inactivating proteins (RIPs) from Ricinus communis and from Viscum album on the water permeability, Pf, and the surface dielectric constant, epsilon, of model membranes were studied. Pf was calculated from microelectrode measurements of the ion concentration distribution in the immediate vicinity of a planar membrane, and epsilon was obtained from the fluorescence of dansyl phosphatidylethanolamine incorporated into unilamellar vesicles. Pf and epsilon of fully saturated phosphatidylcholine membranes were affected only in the presence of a lectin receptor (monosialoganglioside, GM1) in the bilayer. It is suggested that the membrane area occupied by clustered lectin-receptor complexes is markedly less permeable to water. Protein binding to the receptor was not a prelude for hydrophobic lipid-protein interactions when the membranes were formed from a mixture of natural phospholipids with a high content of unsaturated fatty acids. These membranes, characterized by a high initial water permeability, were found to interact with the RIPs unspecifically. From a decrease of both Pf and epsilon it was concluded that not only water partitioning but also protein adsorption correlates with looser packing of polyunsaturated lipids at the lipid-water interface.

Biophysical Phenomena↗
PubMed2000

Studies on the vascular effects of the fractions and phenolic compounds isolated from Viscum album ssp. album.

Viscum album L. has been used in the indigenous system of medicine for treatment of various diseases such as atherosclerosis and hypertension. In the literature, phenylpropan and flavonoid derivatives were suggested to play a role in the inhibition of cyclic adenosine monophosphate (cAMP)-phosphodiesterase (PDE) and a correlation was proposed between the in vitro inhibition of PDE and in vivo pharmacological activity. The vascular effects of the phenolic compounds and subfractions isolated from n-butanolic fraction of V. album ssp. album were studied on noradrenaline-contracted rat aortic rings. Isolated phenolic compounds (Syringin (VA-1), Coniferin (VA-9), 5, 7-dimethoxy-flavanone-4'-O-[beta-D-apiofuranosyl(1-->2)]-beta-D-gl uco pyranoside (VA-4)) produced concentration-dependent contractions in rat aortic rings. Only one compound (Kalopanaxin D (VA-15)) displayed very slight relaxant response. The weak concentration-dependent relaxing effect of the subfractions gave the idea that vasodilator activity were observed in the less polar subfractions. In addition, there was no clear correlation between the weak relaxant effects of subfractions and an inhibitory effect on cAMP-PDE.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

Antimicrobial and anticonvulsant activities of Viscum capense.

Dichloromethane, methanol and water extracts of Viscum sapense L.f., of the Loranthaceae family, were tested for antimicrobial activities against Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. Methanol extract was also tested for activity against seizures in albino mice induced by pentylenetetrazole (PTZ), bicuculline and N-methyl-DL-aspartic acid (NMDLA). Methanol extract of V. capense inhibited the growth of S. aureus. Methanol extract also protected the mice against PTZ- and bicuculline-induced tonic seizures but did not significantly alter NMDLA-induced tonic seizures. The data indicate that the extract of V. capense has antibacterial activity against S. aureus and also anticonvulsant activity.

Animals↗