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PubMed1987

Inhibition by monosaccharides of tumor associated macrophages mediated antibody dependent cell cytotoxicity to autologous tumor cells.

A number of mono- and oligosaccharides are known to inhibit direct contact mediated cytotoxicity of natural killer cells, cytotoxic T lymphocytes and macrophages. In antibody dependent cell mediated cytotoxicity (ADCC), where antibody molecules mediate target recognition, binding and lysis, the role of cell surface carbohydrates is not clearly defined. In the present paper the effects of D-mannose (D-man), N-acetylglucosamine (N-AcGlc), N-acetylgalactosamine (N-AcGal) and glucose on binding and lytic events of ADCC by the tumor associated macrophages (TAM) to autologous tumor cells (ATC) were studied. The TAM were isolated on day 3 of growth of a transplantable ascites tumor--S-180, in Swiss mice. D-man, N-AcGlc and N-AcGal when added to the assay partially inhibited ADCC at 15 mM but at 25 and 40 mM totally abrogated ADCC. Glucose marginally enhanced ADCC at 25 mM but at other concentrations partial inhibition of ADCC occurred. Preincubation of TAM with 25 mM of D-man, N--AcGlc and N-AcGal resulted in total abrogation of ADCC with significant reduction in their binding of ATC, whereas, pretreatment of ATC with the sugars produced 30-40% inhibition of lysis with marginal reduction in target binding. The inhibitory effects of D-man, N-AcGlc and N-AcGal were also observed on ADCC mediated by the peritoneal resident macrophages (RM) of Swiss mice. "Lectin-like" receptors were postulated to be present on the surface of TAM which were involved in ADCC and were inhibitable by sugars.

Acetylgalactosamine↗
PubMed1986

Effect of bisacodyl on the uptake of monosaccharides by isolated enterocytes.

Diphenolic laxatives are known to alter nutrient absorption and secretion in the small and large intestine. We have studied the effect of 0.75 mM bisacodyl on sugar transport in isolated chicken intestinal epithelial cells. Results show that (1) bisacodyl inhibits Na+-dependent alpha-methyl-glucoside (alpha-MG) accumulation by 45% after 40-minute incubation. (2) The drug reduces initial (1 minute) alpha-MG influx by 60%. This effect is much lower than that exerted by 0.15 mM phlorizin (90% inhibition). (3) Bisacodyl also reduces Na+-independent sugar flux through the basolateral membrane since initial 2-deoxy-glucose influx is reduced 67% by the drug. The effect of the drug on this pathway is lower than that exerted by theophylline (7.5 mM). The addition of bisacodyl or theophylline (plus 20 microM phlorizin to inhibit the apical sugar transport system) to cells preloaded with 3-oxy-methyl-glucose allowed calculation of the initial sugar efflux rate. This was found to be lower after theophylline addition than after the addition of bisacodyl, thus confirming that bisacodyl exerts an incomplete inhibition of the Na+-independent sugar transport system. It is concluded that the direct effects of bisacodyl on both apical and basolateral sugar transport pathways may explain in part the inhibitory effects of the drug on the intestinal absorption of sugars.

Animals↗
PubMed1985

Ultrastructural localization of monosaccharide residues on cerebral endothelium.

Biotinylated lectins were used to localize oligosaccharides on the luminal plasma membrane of endothelium of intracerebral cortical vessels. Binding of concanavalin A, wheat germ and Ricinus communis-I was observed on the endothelial luminal plasma membrane of cerebral arterioles and capillaries indicating the presence of alpha-D-mannosyl, alpha-D-glucosyl, beta-N-acetylglucosaminyl, sialyl, and beta-D-galactosyl residues. Lectin binding occurred on the plasma membrane of pinocytotic vesicles open to the vascular lumen and on membranes at the luminal end of interendothelial junctions but not on membranes within junctions. Higher concentrations of Ulex europaeus-I, soybean, and Dolichos biflorus agglutinins were required to demonstrate the alpha-L-fucosyl and alpha-N-acetyl-D-galactosaminyl residues. Pretreatment of brain slices with neuraminidase accentuated the staining produced by soybean agglutinin and resulted in exposure of peanut agglutinin-binding sites on endothelium of arterioles and capillaries. In this respect cerebral endothelium differs from noncerebral endothelium which binds peanut agglutinin without prior neuraminidase pretreatment. The role of these saccharide residues in endothelial permeability and charge remains to be determined.

Animals↗